Develop a food grade HDPE recycling process - WRAP wrap_HDPE_Recycling_final... · 6.9 Summary of the literature review 28 ... 7.2 Sorting efficiency of the RTT pilot plant 31

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Creating markets for recycled resources

Develop a food grade HDPE recycling process

Written by: Dr. Frank Welle

Fraunhofer Institute for Process Engineering and Packaging (IVV)

Published by:

The Waste & Resources Action Programme The Old Academy, 21 Horse Fair, Banbury, Oxon OX16 0AH Tel: 01295 819900 Fax: 01295 819911 www.wrap.org.uk WRAP Business Helpline: Free phone: 0808 100 2040

Date June 4, 2005

ISBN: 1-84405-225-7

Scope

1 Executive Summery 4 2 Glossary 6 3 Introduction 8 4 Aim of the Project 9 5 Project Structure 10 6 Literature study 14

6.1 Research to develop guidelines for the safe use of recycled material 14 6.2 Factors that affect contaminant migration 15 6.3 Parameters which determine the recyclability of packaging plastics 16 6.4 Measuring the cleaning efficiency of recycling processes 20 6.5 Evaluating contaminant migration 22 6.6 Sensory testing 24 6.7 Mechanical properties 24 6.8 Studies of practical market applications 25 6.9 Summary of the literature review 28

7 Sorting efficiency for UK collected HDPE bottles 29 7.1 Sorting technology used 29 7.2 Sorting efficiency of the RTT pilot plant 31 7.3 Sorting efficiency at the industrial plant of Delleve Plastics 33

8 Washing the sorted HDPE bottle fraction 36 8.1 Washing post-consumer HDPE flakes 36 8.2 Challenge test of the washing process 42

9 Supercritical CO2 process for super-cleaning HDPE 44 9.1 Background 44 9.2 Patent review 45 9.3 Solubility data for melt phase super-critical CO2 extraction 45 9.4 Batch basis verification of the effect of CO2 pressure on extraction 49 9.5 Initial supercritical CO2 extrusion extraction trials to decontaminate HDPE 55 9.6 Optimisation of HDPE decontamination with supercritical CO2 60 9.7 Processing trials to optimise PP decontamination 62 9.8 Decontamination of post-consumer HDPE flakes 65 9.9 Conclusions 67

10 EREMA super-clean recycling process 68 10.1 Description of EREMA process for post-consumer HDPE Flakes 68

Development of food grade HDPE recycling process 2

10.2 Challenge test of the EREMA process 71 10.3 Specific migration of surrogates from test bottles using challenge test material 76

11 Analysis of HDPE materials 78 11.1 Analysis for post-consumer contaminants in raw materials 78 11.2 Analysis for post-consumer contaminants in milk containers made with recyclate 84 11.3 Statistical evaluation of the analytical data 87 11.4 Conclusions of the analytical work 91

12 Bottle filling trials and tests 92 12.1 Methodology 92 12.2 Results of the filling trials 92

13 Food law compliance tests 95 13.1 Migration tests 95 13.2 Sensory testing 96

14 Recyclate quality assurance 98 14.1 Quality assurance issues for post-consumer recyclate 98 14.2 Standard testing procedures 99 14.3 Correlation between migration into dairy product and choice of food simulant 99

15 Process validation (re-run) 100 16 Economic evaluation 102 17 Environmental impact assessment 104

17.1 System boundaries 104 17.2 Environmental impact assessment 107 17.3 LCA results 108 17.4 Limitations and Conclusions 111

18 Overall Project Conclusions 112 Appendix 1 – Project Consortium 114

Delleve Plastics 114 RTT Systemtechnik 114 Sorema/Previero 115 EREMA 115 RAPRA 115 Nampak 115 Dairy Crest 115 Fraunhofer IVV 115

Appendix 2 – Addresses of Participants 117 Appendix 3 - Literature 118

Publications within the Project 118 Cited Literature 118


1 Executive Summary

This project successfully developed an industrial scale process for sorting and recycling of post-consumer HDPE milk bottles from kerbside and bring scheme collections in the United Kingdom.

The process contains the following key steps:

• Sorting of natural HDPE milk bottles

• grinding and washing of the bottles by a conventional plastic bottle recycling process

• super-clean decontamination by the EREMA process using high temperatures and vacuum

The ability of this recycling process to produce material suitable for use in food contact applications was checked by means of a challenge test using artificial contaminants and by comparing the levels of contamination in the output material from the recycling process both with the input post-consumer HDPE milk bottles and with virgin polymer.

The analytical work demonstrated that the process is capable of producing high grade polymer suitable for use in food contact applications from post-consumer HDPE bottles. More surprisingly it demonstrated that the level of contaminants in bottles made from the recycled post-consumer material was lower than in bottles made from virgin polymer.

About 600 conventional recycled flake samples, from HDPE bottles collected and sorted in the United Kingdom were screened for post-consumer contaminants. Each sample consisted of 40 to 50 individual flakes so that the number of individual post-consumer milk bottles analysed was in the range of 24,000 to 30,000.

The analysis showed that the main contaminants in the recycled post-use HDPE flake samples were unsaturated oligomers. Unsaturated oligomers are short chain versions of the polymer molecule which still contain some carbon-carbon double bonds and are therefore potentially more reactive with foodstuffs. These same compounds were also found in the virgin HDPE pellet samples used for milk bottle production.

Compounds found in the recycled HDPE flake samples but rarely in the virgin polymer samples included:

• the flavour compound limonene

• a degradation product of the antioxidant additive di-tert-butylphenol

• small amounts of saturated oligomers

However, the total concentration of all contaminants in the post-consumer recycled samples was similar to or lower than found in virgin HDPE.

Contamination with other compounds that would not normally be found in virgin HDPE was rare and in most cases related to compounds originating from normal use of HDPE bottles in non-milk applications, for example shampoo. Non-milk containers comprised less than 2.1% of the input material to the recycling process. Contamination from unexpected re-use of containers was extremely rare. Levels measured were very low.

Migration tests, filling trials and sensory evaluations of 4 pint milk bottles made with recyclate contents of 30%, 70% and 100% also gave satisfactory results and confirmed their suitability for use in food contact applications.

The analytical and test work concluded that HDPE milk bottles containing up to 100% recyclate from the super-clean recycling process tested and validated during this project can be used safely for direct food contact applications


The commercial potential of the super-clean recycling process was assessed.

Costs per kg recycled HDPE (excluding the cost of baled input bottles to the sorting process) were estimated as follows:

Direct production cost €0.41/Kg

Overheads, personnel and infrastructure €0.20/Kg

Total €0.61/Kg

The overall production cost of €0.61/Kg compares to an average price for virgin HDPE of around €1.2 per Kg

An environmental impact comparison of the full super-clean recycling process including sorting, washing and EREMA super-clean treatment was conducted using a standard assessment methodology.

The environmental assessment demonstrated that the HDPE recycling process tested in this project has a lower environmental impact across all impact categories than the alternative of landfill.

In conclusion, this project demonstrates that HDPE milk bottles may be recycled in closed loop on a commercially viable and environmentally sound basis. The project demonstrates that the recycled product may be made comparable to or even indistinguishable from virgin polymer.

The project concluded that three main quality assurance elements are essential for safe and successful recycling of post-consumer HDPE milk bottles:

• careful source control

• tight production control

• regular analytical checks of input and output materials

The project also tested a supercritical carbon dioxide extraction process as an alternative to the EREMA process for the final recycling step to remove residual contaminants. Although some reduction in contaminants was demonstrated it was concluded after a series of trials that the supercritical CO2 extraction process is not yet sufficiently reliable for it to be usable at industrial scale.


2 Glossary

Adventitious contaminants:

Any unwanted substance that deliberately or inadvertently comes into contact with the packaging material before it is collected for recycling and that therefore may contaminate the plastic and negatively influence the quality of the product with which a recycled packaging material is brought into contact

Challenge test:

A test of the ability of a recycling process to remove chemical contamination from packaging materials or articles. The test involves introduction of exaggerated levels of surrogate compounds that simulate typical contaminants and includes an evaluation of the migration of these surrogates from a model food contact packaging article into a food or food simulant.

"Conventional" recycling processes:

A recycling procedure using process steps that include grinding, washing and surface drying of collected plastics. The output material of conventional recycling processes are flakes customarily used for non-food or for the core layer of multi-layer applications. Conventional recycled polymers are usually used as input material for super-clean recycling processes.

Consumption facto (CF): r

Generally, CFs are used to correct migration test results (measured concentration in food simulant) into an exposure value (average uptake by the consumer with the diet). The US Food and Drug Administration (FDA) standard CFs which are relevant to this project are: CF = 0.13 for HDPE and CF = 0.35 for other polyolefins1.

Extraction:

Dissolution of constituents from a plastic into a solvent.

Feedstock/feed stream:

Post consumer plastics used as raw materials for recycling.

Food grade HDPE:

In Europe: HDPE plastic of a suitable standard for food applications manufactured in compliance with EU Directive 2002/72/EEC (and future amendments).

In USA: the HDPE plastic must be compliant with 21 CFR 177.1520.

Migration:

Diffusion-controlled mass transfer from a packaging material or article into food or food simulant. Classically, migration is experimentally determined by standardised tests using food simulants. As a result of scientific progress in this field, migration can also be mathematically modelled and predicted.


Migration limits:

Limits set by food regulators for maximum concentrations of migrant compounds in food simulants or foodstuffs. For recycled food packaging material the legally prescribed overall migration limit for all compounds is of much lower relevance than specific migration limits as defined by a threshold of no concern in the US or the specific limits per substance laid down in EU legislation.

Post consumer HDPE:

HDPE resin that has been converted into bottles/containers, distributed and used by the consumer. Discarded post consumer HDPE material becomes the feedstock for recycling processes.

Post-industrial HDPE:

Industrial in house plant scrap generated during the manufacturing process, which may be reused in the production of new containers.

"Super-clean" recycling:

In most instances the process uses as a source the output material from conventional recycling, for example washed and surface-dried flakes, and includes one or more additional cleaning steps. The output of the "super-clean" process may be used for packaging applications in direct contact with the foodstuff, provided it meets the appropriate regulatory guidelines or legal requirements.

Surrogates:

Organic compounds (also known as "model contaminants"). Typically they are used at exaggerated contamination levels in tests to challenge the safety of recycled materials. They may be applied in tests individually or in mixtures.

Threshold of no concern:

The concentration of a migrant in a foodstuff, which, from a toxicological point of view, is considered to pose no health risk to the consumer.

Using the Threshold of Regulation concept as a basis (see US FDA 21 CFR 170.39), the US FDA has determined that exposure to contaminants from recycled food-contact articles of the order of 0.5 ppb dietary concentration or less generally is of negligible risk. In Europe, this concept is under discussion but a general threshold value has not yet been adopted.

A JECFA task force of FAO/WHO has adopted the concept of ‘threshold of toxicological concern for the evaluation of flavouring substances in food. The proposed no concern level is 1.5 µg per person per day[ , ]2 3 .


3 Introduction

Food packaging regulations in Europe prescribe that packaging materials must not cause mass transfer (migration) of harmful substances into food[ ]4 . This general requirement applies to food packaging made with both virgin and recycled material. It is set out in more detail in Commission Directive 2002/72/EC[ ]5 .

Until recently, the reuse of post-consumer packaging materials for new packaging applications was impossible due to a lack of suitable sorting and decontamination technologies and because of missing or incomplete information about typical contamination levels of post-consumer plastics. As a result most post-consumer packaging waste was sent to landfill or for incineration. Only uncontaminated in-house production waste was collected, granulated, pelletised and recycled back into packaging products without further decontamination.

In the last decade, considerable progress has been made in the development of collection and sorting technologies so that today an almost 100% single polymer stream may be supplied to the recycling process.

Most recently, decontamination processes based on sophisticated washing and thermal vacuum stripping methods have been developed. These processes enable removal of contaminants from post-consumer materials such as polyethylene terephthalate (PET) down to impurity levels similar to virgin materials.

Good progress has also been made in understanding and modelling the diffusion and migration of adventitious hazardous substances from recycled plastics into foodstuffs when in direct or indirect contact with food[ ]6 . Today, these migration models form the basis for compliance evaluation of food contact materials (FCM) and are being evaluated for consumer exposure and risk assessments from FCM[ ]7 .

Much of the knowledge about the reuse of packaging plastics has been gained within two EU projects, AIR-CT93-1014[ ] 8 and FAIR-CT98-4318[ ]9 . One of the major conclusions of these projects was that polyethylene terephthalate (PET), is the most promising polymer for reuse as a food packaging material due to its low diffusivity.

As a result of this evaluation several so-called "super-clean" recycling processes were developed for bottle-to-bottle recycling of post-consumer PET bottles. Some of these technologies are already established in the market. Others are now moving from pilot plant to industrial scale [ ]10 .

The low diffusivity of PET means that in most cases the container polymer picks up only low levels of contamination from the material it contains, even when the contact is from a non-food application. As a result it is not always essential to remove non-food contact containers in the sorting processes that feed into super-clean PET recycling processes. Several PET recycling processes have gained American Food and Drug Administration (US FDA) approval for recycling PET bottles which were filled in their first use with household or body care fluids.

In some cases recycled polymers with higher diffusion and sorption characteristics, including high density polyethylene (HDPE), have received ‘no objection’ letters from the US FDA for use in certain well defined conditions[ ]11 .

Increasing understanding of the level and nature of contamination in post-consumer plastics and further innovations in recycling and decontamination technologies mean that closed-loop recycling of packaging plastics with higher diffusivity than PET (e.g. HDPE) will soon become viable for a wider range of applications. The translation of this progress into practical industrial solutions is still awaited. One of the reasons for the slow progress in commercialising these processes is that the European legal requirements for food contact packaging made with recycled content are still under discussion and are not yet clearly or uniformly defined.


The legislators are concerned that there is still a lack of good quality and statistically meaningful information about the nature and amount of contaminants in recycled HDPE from post-use packaging. Data is needed for contaminants derived from the first use of the bottles and also from misuse.

This remains an important missing link in the chain of scientific knowledge on diffusion and migration into and out of HDPE. If the concentration of a contaminant in the recycled plastic can be correlated with the resulting time-dependent concentration in a foodstuff it will allow legislators to set meaningful limits for contaminant levels in recycled materials and make it easier to certify recycling processes for HDPE with confidence.

One of the aims of this project is to fill these gaps in scientific knowledge with statistically meaningful data on contaminant levels in HDPE from post-use packaging before and after recycling.

Linking this data with existing knowledge on HDPE diffusion behaviour and measurements of the cleaning efficiency of both conventional washing and "super-clean" recycling processes will enable scientifically convincing conclusions to be drawn about the safety of reusing HDPE in food contact applications.

It is expected that the knowledge developed in this project will also provide the basis for development of generally recognized standard test methods for HDPE recycling processes. These methods should be proportionate, practical and economical whilst safe-guarding the consumer at the same time. Current protocols are too cautious and challenging, although necessary at present as a precaution due to lack of data.

4 Aim of the Project

The overall aim of the project is to develop a cost-efficient recycling process to produce food-grade HDPE from post-consumer recyclate for new milk bottle applications.

To achieve this aim comprehensive analysis of the post-consumer HDPE feedstock is required in order to define the safety conditions for the process system as a basis for design of the individual process steps.


5 Project Structure

Table 1 provides an overview of the work packages and responsibilities of the partners within the project. The project structure and the interactions of the individual work packages are shown in Figure 1.

Table 1: Project work packages and responsibilities

Work Packages Content Responsibility

I. Planning phase Literature study Fraunhofer IVV

II. Collection, sorting

Provide HDPE scrap from different collection systems in the UK

Delleve Plastics

Optimise sorting efficiency RTT Systemtechnik

Measure sorting efficiency RTT Systemtechnik

III. Granulation, washing

Optimise label and glue removal Sorema/Previero

Optimise decontamination process Sorema/Previero

Analytical screening of flakes for post-consumer compounds

Fraunhofer IVV

Measure cleaning efficiency of the washing and granulation process

Fraunhofer IVV/ Sorema/Previero

IV: ‘Super-clean’ Re-extrusion and

Optimise decontamination by the EREMA process

EREMA

decontamination process options

Measure the cleaning efficiency of the EREMA process

Fraunhofer IVV/EREMA

Process development and optimisation of decontamination using the RAPRA supercritical CO2 extraction process

RAPRA

Measure the cleaning efficiency of the RAPRA supercritical CO2 extraction process

Fraunhofer IVV/RAPRA

Analytical screening of super-cleaned pellets for post-consumer compounds

Fraunhofer IVV

V: Quality assurance of recyclate

Develop suitable quality assurance system Fraunhofer IVV

VI: Bottle manufacture

Define the maximum acceptable amount of recycled HDPE

Nampak

Measure mechanical properties Nampak

Produce test containers Nampak


Continuation Table 1: Overview over the work packages and responsibilities

Work Packages Content Responsibility

VI: Bottle manufacture (cont.)

Compliance testing and evaluation of food law requirements of recyclate containing bottles

Fraunhofer IVV

VII. Filling of bottles

Fill test containers Dairy Crest

Product shelf life tests including sensory tests Dairy Crest

VIII: Report and assessment

Economic assessment of the recycling process Fraunhofer IVV

Environmental assessment of the recycling process

Fraunhofer IVV

Final project report Fraunhofer IVV


Figure 1: Project structure and interdependency of work packages

providing HDPE scrap Literature study

optimisation sorting efficiency

determination sorting efficiency

grinding and optimisationwashing efficiency- glues and labels- decontamination determination

washing efficiency

RAPRA process: optimisationextrusion and decontamination determination

cleaning efficiency

analytical screening flakes

analytical screening super - clean pellets

definition maximum amount recyclate production of test

containers determination of mechanical properties

food law compliance testing, migration modelling

economic and environmental assessment

filling test containers

sensory tests

EREMA process: optimisation extrusion and decontamination

development quality assurance system (SOPs)

Literature study provide HDPE scrap

measure optimise sorting efficiency sorting efficiency

shelf live tests

grinding and optimisation of- washing efficiency- glues and labels- decontamination measure

washing efficiency

RAPRA process: optimisationextrusion and decontamination measure

cleaning efficiency

analytical screening of flakes

analysis of super - clean pellets

definition maximum amount recyclate production of test

EREMA process: optimisation extrusion and decontamination

containers measure mechanical economic and properties environmental

assessment food law compliance testing, migration modelling development

filling test containers

sensory tests

quality assurance system (SOPs)

shelf life tests


Input: baled bottles3050 kg (20% HDPE milk bottles)

Input: hand-sorted HDPE milk bottles 9407 kg (Delleve)

Sorting PET bottles (RTT): approx. 548 kg

Washing (SOREMA)

Migration testing (IVV): 50 bottles each

Input: red HDPEflakes: 1500 kg

Super-cleaning (EREMA): approx. 5000 kg (without contamination), one-step process

Challenge test (SOREMA): 1500 kg red flakes plus 100 kg Challenge test (EREMA):

1500 kg without contamination plus 100 kg contaminated flakes,one-step process

Bottle manufacturing 30% (500 kg) recycled HDPE (1000 kg virgin)

Screening flakes and pellets (IVV): several kg each

Washing (SOREMA): approx. 8125 kg


Bottle manufacturing 100% (1500 kg) recycled HDPE

Bottle manufacturing 100% (1600 kg) recycled HDPE (contaminated)

Bottle manufacturing 100% (1600 kg) recycled HDPE(contaminated)

Challenge test (EREMA): 1500 kg without contamination plus 100 kg contaminated flakes, two-step process

Filling and shelf-life tests (Dairy Crest): 100 bottles

Challenge test (RAPRA): 300 kg

Input: virgin HDPE pellets

process development (RAPRA)


Bottle manufacturing 100% virgin HDPE (reference)

Input: baled bottles3050 kg (20% HDPE milk bottles)

Input: hand-sorted HDPE milk bottles 9407 kg (Delleve)

Sorting PET bottles (RTT): approx. 548 kg

Washing (SOREMA)

Migration testing (IVV): 50 bottles each

Input: red HDPEflakes: 1500 kg

Super-cleaning (EREMA): approx. 5000 kg (without contamination), one-step process

Challenge test (SOREMA): 1500 kg red flakes plus 100 kg Challenge test (EREMA):

1500 kg without contamination plus 100 kg contaminated flakes,one-step process


Screening flakes and pellets (IVV): several kg each

Washing (SOREMA): approx. 8125 kg


Bottle manufacturing 100% (1500 kg) recycled HDPE


Bottle manufacturing 100% (1600 kg) recycled HDPE(contaminated)

Challenge test (EREMA): 1500 kg without contamination plus 100 kg contaminated flakes, two-step process

Filling and shelf-life tests (Dairy Crest): 100 bottles

Challenge test (RAPRA): 300 kg

Input: virgin HDPE pellets

process development (RAPRA)


Bottle manufacturing 100% virgin HDPE (reference)

Figure 2: Material flows and test runs


6 Literature study

The project started with a literature review. Most of the literature data was already compiled by Fraunhofer IVV in a recently published review article[ ]12 . The literature review focused on:

• contamination levels of post-consumer plastics in general

• recycling techniques with their individual decontamination efficiencies

• mechanical properties and migration levels of containers made with recyclate

This section summarises the results of the literature review

6.1 Research to develop guidelines for the safe use of recycled material

European Projects "Recycle Re-use" and "Recyclability"

In the last decade the European Commission has supported two projects dealing with the question of recyclability and re-usability of post consumer plastics for new food packaging applications. The first project AIR2-CT93-1014[ ]13 dealt with plastics packaging materials collected from packaging waste. The second project FAIR CT98-4318[ ]14 focused on PET as the most favourable candidate plastic for direct food contact. Two other sections of the project are concerned with recycled paper, board and plastics protected by functional barriers to allow reuse in food contact applications. Both project reports provide in-depth information on analytical methods and their validation.

Based on the results of the European Project FAIR CT98-4318[ ]15 proposals for future legislation were written and filed with the European Commission. Two guidelines were published, based on contaminant migration estimates and the results of Europe-wide analysis of post-consumer PET flakes[ ]16 . The first document gives detailed recommendations for performing challenge tests and for quality assurance of recyclate containing PET articles. The second document gives guidance on the use of functional barriers[ ]17 .

I

US FDA Guidelines

In 1992 and 1995 the FDA published two guidelines for industry dealing with post-consumer plastics for direct food contact applications [ , ]18 19 . These guidelines provide recommendations for testing the cleaning efficiency of recycling processes, the maximum content of post-consumer substances in packaging materials that contain recyclate and threshold limits for migration.

Based on a review of submissions from third parties and its own research projects the FDA has recently issued an update of its guidelines [ ]20 . This update takes into account new data, mainly for PET, on the contamination of post-consumer material and the results of challenge tests. Recommendations are provided for selection of PET feedstock material from non-food applications, which is intended to be recycled into food packaging. The FDA also provides information on its internet homepage [11] about all "non objection letters" that it has issued for recycling processes.

European ILS Document

In 1997 an expert group led by the International Life Sciences Institute Europe (ILSI) proposed specific guidelines on the re-use of recycled plastics in food packaging [ ]21 . These guidelines, published in 1998, are based on the


results obtained from the European "Recycle Re-use" project. The intention of the document was to provide information for industry about the European view of closed-loop recycling of post-consumer plastics. The document gives recommendations for recycling and packaging companies, who want to use post-consumer plastics in food contact applications.

German BfR Recommendations

The German Bundesinstitut für Risikobewertung (BfR or formerly BgVV) published recommendations in 2000 on the mechanical recycling of post-consumer PET for direct food contact applications [ ]22 . This document is the result of a discussion of the German "Plastics Commission" on PET bottle-to-bottle recycling. The BfR document gives recommendations for source control, challenge testing and quality assurance of post-consumer PET intended for direct food contact.

6.2 Factors that affect contaminant migration

It is generally known that food contact packaging materials are not completely inert and can interact with the filled product[ ]23 . Interactions between packaging plastics and organic chemicals are of greatest interest. Such interactions start to occur at the point of filling and continue during the regular usage phase of a package. They may continue even longer, in the event that a consumer reuses the empty packaging for another application by filling it with an alternative material such as household cleaner, pesticide solution, mineral oil etc. The extent of these interactions depends on:

• the sorption properties of the polymer

• the diffusion behaviour of the materials contained by the packaging

• the time /temperature profile while the container and its contents are in contact.

These factors determine the potential risk of food contamination from recycled packaging plastics.

The sorption ability or ‘inertness’ of the polymer is the basic parameter which affects the ease of closed-loop recycling of packaging plastics. The inertness of common packaging polymers decreases in the following sequence:

Poly (ethylene naphthalate) (PEN) > poly (ethylene terephthalate) (PET) >rigid poly (vinyl chloride) (PVC) > polystyrene (PS) > high density polyethylene (HDPE), polypropylene (PP) > low density polyethylene (LDPE)

PEN, PET and rigid PVC are therefore easier to clean for reuse in packaging applications from a migration point of view than PS and HDPE. However polymers like PS and HDPE which are more prone to absorb contaminants may also be recycled in closed loop back into food contact packaging if the recycling process is able to remove the higher concentrations of post-consumer substances that are likely to be present in these materials.

In order to ensure consumer safety it is important to demonstrate that the chosen recycling process can reduce all post-consumer substances to concentrations similar to virgin materials. This requires that the recycler should be able to measure the composition and concentration of typical substances in post-consumer plastics before and after recycling and in the equivalent virgin polymer. .

The incoming concentration of post-consumer contaminants can be measured off-line with laboratory equipment such as gas chromatography or HPLC or online with detecting or sniffing devices. With the help of online devices it is possible to ensure an almost 100% check of the input materials.

If these analytical checks are performed at the feed to the recycling plant then ‘misused’ bottles and those with high concentrations of migratable substances can be rejected and the cleaning demand on the recycling process is lower. Source control is therefore an important factor.


The quality of the input material to the recycling process is also affected by the number of times it has been recycled already. The average number of cycles is a function of the blend ratio and the number of recycling steps carried out.

At present bottle to bottle recycling levels in the UK are very low so most bottles received by recycling plants contain a high proportion of virgin polymer. Even in parts of Europe where recycling levels are higher the average number of cycles range from one to three[8]. As a result the accumulation of polymer degradation products due to multiple recycling is in most cases of no concern.

An inherent problem in recycling, however, is the inhomogeneity of the input materials. Different polymer manufacturers and converters use different polymer additives, lubricants, etc. in order to provide the desired properties for their target applications. The recycled material will contain an average composition of these additives.

6.3 Parameters which determine the recyclability of packaging plastics

Source Control

Source control is the first and very important step in a closed loop recycling process for packaging plastics. Efficient collecting and sorting processes are required in order to ensure a high quality feed to the recycling process.

The feed stream material should have a minimum polymer type purity of about 99%. Other polymers, which may affect the final product properties must be removed from the recycling stream.

The first life of the packaging material is also important. Where possible, only packages previously filled with foodstuffs should be fed to a closed loop recycling process.

However there are exceptions. Two studies were undertaken [ , ]24 25 to assess whether PET materials previously used for non-food applications could be re-used for food contact. Both studies concluded that packages from non-food applications could be used as input material for a bottle-to-bottle recycling due to the low diffusivity of PET.

It was shown that deposit systems and collection systems such as kerbside packaging collections with efficient sorting processes are able to supply input materials for high value recycling. However, as mentioned above, the higher the diffusivity of the polymer the more important is source control in order to reduce contamination with post-consumer substances or misused packages. Modern detecting or sniffing devices are available which can reduce the intake of undesirable post-consumer substances in the recycling stream.

Contamination Levels and Frequency o Misuse of Recollected Plastics f

Most of the published data on typical contamination of post-consumer plastics is for PET bottles and corresponding recyclates. This section reviews several useful studies performed in this area.

Sadler et al[ , ]26 27 published two studies providing data on contaminants in recycled PET.

The first study identified that most compounds found in recycled PET come from the PET starting materials. These include oligomers, flavour bases, label materials and compounds originating from base cups. Contaminants which do not fall into one of these categories were rare.

In samples with high levels of contaminants the sum of all contaminant compounds was approximately 25 ppm. No single contaminant appeared to be present in post-consumer PET above 1 ppm. All unusual compounds (those not derived from the PET starting materials) in post-consumer PET were present below 0.1 ppm.


In the second study the identity and origin of contaminants in food grade virgin and commercially washed post-consumer PET flakes were analysed. A total of 18 samples of post-consumer recycled PET flakes were examined. In most cases, positive identification was possible, however, in a few cases ambiguity resulted from the similarities in mass spectra of closely related compounds. Compounds identified were classified into categories associated with their chemical nature or presumed origins e.g:

• small and ethylene glycol related compounds (methanol, formic acid, acetaldehyde, acetic acid)

• flavour compounds such as limonene

• benzoic acid or related benzene dicarboxylic acid substances (benzoic and terephthalic acid and corresponding esters, benzaldehyde, phthalates)

• aliphatic hydrocarbons and acids

• unexpected and miscellaneous compounds (Tinuvin, nicotine).

Bayer[24] has analysed samples from five different collection systems including PET containers from non-food applications. In these samples he identified 121 substances. The total concentration of all substances found in deposit material (returned PET food packaging where a deposit was reclaimed on the container) was 28.5 ppm. The corresponding total concentration of contaminants in PET flakes coming from non-food applications was found to be 39 ppm.

Key compounds identified included hexanal, benzaldehyde, limonene, methyl salicylate and 5-iso-propyl-2-methylphenol (the flavour compound carvacrol). In conventional washed flakes a maximum concentration of 18 ppm for limonene was determined. For PET flakes from non-food applications the major compound, methyl salicylate, was determined in a maximum concentration of 15.3 ppm.

Additionally the material was analysed after a super-clean recycling process. In this case no peak could be detected in concentrations above the FDA threshold of regulation limit for PET of 0.215 ppm.

All three published studies found no hints of misuse of post-consumer PET bottles e.g. for storage of household cleaners etc. This is most probably due to the fact that these studies are based on only very small flakes samples. Statistically flakes from misused bottles should be extremely rare due to the high dilution with non-misused containers. This is likely to be why the published studies did not detect any misuse.

Fraunhofer IVV co-ordinated a large EU project which was completed in 2002[ , , ]28 29 30 . 689 post-consumer PET flake samples from commercial washing plants were collected between 1997 and 2001. The samples were taken from conventionally recycled deposit and kerbside bottle fractions collected in twelve European countries. In addition, 38 reprocessed pellet samples and 142 samples from super-clean recycling processes were collected.

All samples were screened for post-consumer substances and for hints of possible misuse of the PET bottles by the consumer in order to obtain an overview of the quality of commercially recycled post-consumer PET.

For the 689 PET flake samples from conventional washing plants the average concentrations of the typical post-consumer compounds limonene and acetaldehyde were 2.9 ppm and 18.6 ppm, respectively. Maximum concentrations in a single sample were 20 ppm for limonene and 86 ppm for acetaldehyde. These results are in good agreement with the earlier studies.

The impact of the collection system and the country, where the post-consumer PET bottles were collected, on the nature and amount of contaminants was not significant. However in three bottle flakes hints of misuse of PET bottles e.g. for storage of household chemicals or fuels were found. A statistical evaluation of these results indicates that around 0.03 to 0.04% of the PET bottles might be misused.

Taking into account dilution of the PET flakes from misused bottles with non-misused PET bottles during washing and grinding it would be reasonable to predict average concentrations of 1.4 to 2.7 ppm of unusual substances


from misused PET bottles in bulk material from commercial washing plants. These concentration estimates can be used as the basis to set input concentrations for surrogate test compounds when designing challenge tests for PET recycling processes.

The frequency of misuse was also detected by two further studies:

Allen and Blakistone[ ]31 indicate that hydrocarbon "sniffers" for refillable PET bottles rejected between 0.3% and 1% of PET bottles as contaminated bottles. The majority of these rejections come from PET containers for "exotic" beverages and not from harmful contaminants. Therefore the proportion of genuine misused bottles is less than 0.3% to 1%.

Bayer et al[ ]32 reported the frequency of misuse of PET bottles is equivalent to one misused bottle in 10,000 uncontaminated bottles (0.01%). Both studies are in agreement with the results of the EU project led by Fraunhofer IVV.

Huber and Franz[ ]33 investigated 21 reprocessed HDPE pellet samples from the bottle fraction of household waste collections from five different sources. The aim of this study was to investigate the quality of the recycled HDPE samples, focusing on substances which are not present in virgin polymers. This study provides important background information for this project because it was the first published study to concentrate on HDPE rather than PET.

The samples were recycled by conventional washing and extrusion methods without a further super-clean recycling process. They found that the post-consumer related substances analysed in these different samples were similar for pellets from the 5 sources. They identified 74 substances which occured in concentrations above 0.5 ppm.

The predominant species were esters of saturated fatty acids, phthalates, hydrocarbons, preservatives, monoterpenes and sesquiterpenes including their derivatives. Most of the substances were identified as constituents of personal hygiene products, cosmetics and cleaning agents, which were absorbed by the polymer during storage.

The highest concentrations were found for limonene, diethylhexyl phthalate (DEHP) and the isopropyl esters of myristic and palmitic acid. These compounds were found in concentrations between 50 ppm to 200 ppm. Many odour compounds and preservatives were measured in concentrations of between 0.5 ppm and 10 ppm.

Huber and Franz concluded that,the nature and high concentration of contaminants found in the HDPE samples meant that the recycled material was only suitable for non-food packaging.

In a second study Huber and Franz[ ]34 investigated a total of 79 samples of different polymer types (HDPE, PP, PS and PET) from controlled collection sources. They found limonene in nearly all the polymer samples. Concentrations were up to 100 ppm for polyolefines (HDPE and PP) and 12 ppm and 3 ppm for PS and PET, respectively.

Limonene can be considered as a marker substance for post-consumer polymers. It is interesting to note that the differences in the limonene concentration follow the diffusion behaviour of the polymers.

In addition to limonene Huber and Franz found phthalates, esters, alkanes, 2,6-di-tert-butyl-4-hydroxytoluene and oligomers but no hints of misuse of the bottles for storage of toxic chemicals. They concluded that most of the conventionally recycled polymers that they investigated should be excluded from closed-loop recycling, because some of the contaminant substances detected are not permitted by the European positive list system for food contact materials35.


Ezrin and Lavigne[ , ]36 37 investigated four samples of post-consumer dairy grade HDPE that has been recycled by conventional processes. They assigned most of the 128 compounds that they detected to six major groups:

(i) aliphatic saturated hydrocarbons

(ii) aliphatic unsaturated hydrocarbons

(iii) aliphatic hydrocarbons with functional groups

(iv) aromatic hydrocarbons

(v) aromatic hydrocarbons with functional groups

(vi) fragrance and flavour compounds.

Most of the compounds were present at the ppb or low ppm levels in the recycled HDPE and below the levels of typical contaminants in virgin HDPE (e.g. oligomers). Benzene, toluene, xylene and di-tert-butylhydroxytoluene (BHT) were semi-quantified (average of four samples) at 232 ppb, 690 ppb, 388 ppb and 41 ppm, respectively.

In another study with dairy grade HDPE [ ]38 they compared two samples of recycled HDPE resin with two samples of virgin HDPE resin. Average concentrations of the major contaminants were schown in Table 2.

Table 2: Average concentrations from major contaminants in HDPE from Lit[38]

Contaminants Recycled HDPE [ppb] Virgin HDPE [ppb]

Benzene 283 57

Toluene 763 92

Xylene 529 63

di-tert-butylhydroxytoluene (BHT) 24 /

The major fragrance and flavour type compound found in the recycled HDPE samples was limonene.

Ezrin and Lavigne concluded that commercially recycled dairy grade resin does not appear to present significant contamination problems and that the material may be suitable for some direct food contact applications.

Recycling Technology

Today a wide range of recycling technologies are available for post-consumer plastics. Most of them use a water based washing step as their first step in order to reduce surface contamination and to separate dirt, labels and glue.

The material is also generally granulated to flakes as one of the first steps in the recycling process.

In most cases the washing step is combined with a wet separation step where different flakes of different polymer types such as polyolefines or PET are separated according to their density difference.

The cleaning efficiency of these washing processes can vary widely, depending on contact time, the use of hot or cold water based washing and the choice of detergents added to the washing solution. However, typical washing processes are only able to remove surface contaminants from the polymers [ , ]39 40 . They are unable to remove organic substances, which have migrated into the polymer. Therefore the purity of washed flakes is usually unsuitable for a closed loop recycling.

Simple remelting or re-extrusion of the washed flakes has an additional cleaning effect [ ]41 , however the purity is usually insufficient for reuse in the sensitive area of food packaging.


The so-called super-clean processes for closed loop recycling of packaging materials use further deep cleansing steps. Although there are many technologies commercially available, most deep cleansing processes use heat and either, surface treatment with chemicals or vacuum to decrease the concentration of unwanted substances in the polymers.

6.4 Measuring the cleaning efficiency of recycling processes

Challenge Test

The cleaning efficiency of recycling processes for food contact applications is usually determined by a challenge test. Challenge tests introduce artificial contamination to the material entering the recycling process and then measure the output results.

The aim of a challenge test is to simulate the worst possible scenario where the containers are misused for the storage of household or garden chemicals.

The first recommendation for such a challenge test came from the American Food and Drug Administration (US FDA)[18,19] in 1992. The US FDA originally suggested real contaminants such as chloroform, diazinon, gasoline, lindane, and disodium monomethyl arsenate as surrogate compounds for use in challenge tests. However it has been shown in the past that the stability of these surrogates during recycling is in some cases limited so that they may degrade during the recycling process. Also the analytical methods used to detect the surrogates are often difficult to develop and have high detection limits.

The surrogates used in a challenge test should not degrade during the recycling process. Otherwise the measured cleaning efficiency will be better than may be achieved in reality with other compounds and consumer safety may be compromised.

Over the past ten years alternative surrogates have been selected to ensure that challenge tests can be used to predict the behaviour of a wider range of other compounds.

This development was supported by evidence from more recent research that in practice the range of chemicals found in post-use plastic (especially known genotoxic carcinogens) is extremely limited.

The surrogates used today in challenge tests are selected to cover a range of physical properties such as polarity, volatility and different chemical types. Additionally, some compounds which are aggressive towards the polymer itself are selected. Care must be taken in selection because chemicals which are excessively aggressive may affect the physical properties of the polymer and its diffusion behaviour, reducing the validity of the challenge test.

Typical surrogates used in challenge tests today include volatile compounds such as toluene, chlorobenzene, chloroform or 1,1,1-trichloroethane and non-volatile substances like phenyl cyclohexane, methyl stearate, tetracosane, benzophenone, methyl salicylate and methyl stearate.

The aim of the challenge test is to present the recycling process with a worst-case scenario. If the recyclate that is produced still meets the food law requirements even under such worst case conditions it will provide confidence that the process is able to produce recyclate suitable for reuse in food contact applications under all foreseeable circumstances.

Over the last decade there has been controversy between scientists, industry and regulatory authorities regarding the choice of worst-case scenarios for such challenge tests. These debates have been hampered by a lack of good quality data on the average contamination in the input materials for recycling.


The choice of worst-case scenario depends on:

• the typical concentration of undesired substances found in misused post-consumer containers of the selected polymer type

• the frequency of misuse of plastic containers.

• Appropriate safety margins can be defined for each polymer type using this data.

Cleaning Efficiency of Conventional Recycling Processes

Post-consumer plastics for re-use in food packaging applications are usually recycled by super-clean recycling processes. However, these processes use conventional washing steps prior to the deep-cleansing steps.. The cleaning efficiency of conventional washing processes is therefore of interest because they set the input concentration of post-consumer substances in the feed material entering the deep-cleansing processes.

In the literature there are a few studies on the cleaning efficiency of conventional recycling processes. These processes contain washing and surface drying steps followed in some cases by remelting of the post-consumer material.

Komolprasert and Lawson[39] analysed the influence of NaOH concentration, mixer speed and temperature on removal of the surrogate tetracosane from spiked PET in a challenge test. The study measured residual tetracosane in PET flakes, which were washed in small-scale experiments using 13 different conditions.

Tetracosane concentration in the washed flakes was 1.4% to 3.3% of the initial spiked level. Only variations in mixer speed and temperature had a significant effect on removal of tetracosane from the PET flake. The effect of NaOH concentration was insignificant.

The percentage of non-volatile hydrocarbon residues in washed PET flakes varies with the initial concentration. The study determined a removal of 89% to 97% of each hydrocarbon by washing.

In a second study Komolprasert and Lawson[40] analysed the effect of washing and drying on the removal of surrogates in both spiked PET flakes and spiked PET bottles.

In the test on spiked PET bottles they concluded that the combination of washing and drying removed 97% to 99% of the organic surrogates. One of the surrogates used in this test was an organic copper compound. The copper concentration after washing and drying was found to be 21% of the input level (note: the low cleaning efficiency for the copper compound is probably due to the instability of this surrogate. It reacts during recycling to produce CuO, which cannot be removed. This behaviour shows that metal organic compounds are in general unsuitable as surrogates for challenge tests).

In the case of the spiked PET flakes, washing and drying removed more than 99% of the initial concentration of the organic surrogates. The high cleaning efficiencies of conventional washing and drying processes compared to washing alone are likely to be due to the high temperatures applied during the drying step and the fact that contaminants rarely penetrate more than a few µm into the polymer surface.

The initial concentrations of the surrogates in spiked bottles are much lower than in flakes, because the surface area of flakes is higher than for bottles.

A third study by Komolprasert et al[41] evaluates the decontamination effect of remelting in a laboratory extruder. This work shows that remelting can further reduce the contamination of spiked PET.

However the real reduction is difficult to evaluate, because some of the surrogates used (diazinon, malathion, metal organic copper compound) are not stable during extrusion. In addition volatile substances such as toluene are almost completely removed during washing, so that it is impossible to evaluate the additional cleaning effect during remelting for this surrogate.


In conclusion:

• conventional washing processes are able to reduce the input concentration of post-consumer substances in polymer flakes

• the washing process itself probably removes only surface contaminants

• thermal drying is able to remove substances, which are absorbed into the flakes.

• Remelting processes further reduce the contamination.

Due to the fact, that different conventional recycling processes use a wide range of parameters and equipment a general conclusion and a quantification of the cleaning effects for washing, drying and remelting processes is not possible on basis of the above mentioned literature results. Data for the cleaning efficiency of conventional recycling processes for HDPE are not published.

Cleaning Efficiency of Super-Clean Processes

In addition to challenge testing, quality assurance of processes for post-consumer (PCR) PET is based on careful feedstock control and regular analysis of the final product.

Three studies of the cleansing efficiency of super-clean recycling processes for PET have been published by Franz and Welle[ , , ]42 43 44 . The process investigated in the first two studies[42,43] contains three main steps; washing, re-extrusion and solid-state polycondensation (SSP).

The process was challenged with three different surrogate concentration levels. The cleaning efficiencies measured for the different surrogates and contamination levels were in the range 94% to 99%[42]. The results show no significant dependency on the input concentration of the surrogates going into the process.

In the first trial the process was tested without a washing process. When a conventional washing process was included in the second trial the cleaning efficiency increased to more than 99.3%, even for benzophenone, the most challenging substance[43].

In the third study[44] a recycling process without solid state polycondensation was investigated. Except for benzophenone, the recycling process reduced all surrogates by more than 95% for initial concentrations below 100 ppm and more than 90% for initial concentrations between 100 and 500 ppm. For the most challenging substance, benzophenone, the cleaning efficiency was approximately 77% at an initial contamination level of 294 ppm.

In this third trial the measured cleaning efficiencies were lower than for the super-clean recycling process with solid state polycondensation. However, even in this case the specific migrations of all surrogates from PET bottles made from contaminated and recycled PET were still far below the migration limit of 10 ppb given by the US FDA threshold of regulation concept for PET.

6.5 Evaluating contaminant migration

Migration from a food/plastic package system is influenced by both kinetic factors (diffusion in plastic and food) and thermodynamic factors (equilibrium partitioning between plastic and food).

It is useful to base migration evaluations on a worst-case assumption that estimates total mass transfer based on the starting concentration of each migrant in the plastic. If this calculation leads to a migration limit being exceeded, then it is necessary to refine the evaluation to take account of partitioning and diffusion as the critical parameters for migration. Scientific background and guidance on how to conduct such evaluations can be found in the literature[23].


The US FDA suggests that dietary exposures to contaminants from recycled food contact articles at a concentration of 0.5 ppb or less generally are of negligible risk[18,19, ]45 .

With the help of so-called consumption factors (CF) these dietary exposures can be converted into migration limits. According to this concept, the migration of unknown contaminants into food may be tolerated if a certain threshold value of concentration is not exceeded.

For an average daily food consumption the threshold concentration value is 0.5 ppb, irrespective of the packaging type and material. The application of CFs increases the actual maximum acceptable contaminant level for each type of polymer. For general polyolefins (CF = 0.35) the CF increases the maximum acceptable contaminant level to 1.5 ppb.

The migration limit can also be converted into a maximum bottle wall concentration for any substance occurring in post-consumer plastics (including substances from virgin polymers). For polyolefins the maximum concentration in the polymer which correlates with 1.5 ppb dietary intake level is 46 ppb for a typical polyolefin container at a thickness of 0.5 mm. This calculation is based on the very conservative assumption that all HDPE containers are contaminated and the contaminants are assumed to migrate completely from the container into the foodstuff. The contaminant limits calculated above also assume 100% recycled resin content in the finished article. For testing compliance with this threshold value, the US FDA recommends a challenge test, by which the efficiency of purification during the recycling process is determined using artificially incorporated model contaminants. For HDPE the US FDA defined a consumption factor of CF = 0.13[ ]46 .

It is generally accepted that in practice diffusion-controlled migration usually results in much less than complete transfer of substances into the foodstuffs.

Migration from virgin and post-consumer PET has been investigated in numerous projects where low diffusion and migration rates have been reported and confirmed[43,44, ]47 . In some cases the contamination levels measured are below the detection limits of the analytical methods used. Diffusion models therefore[6, , ]48 49 provide a useful scientific tool for more realistic correlation between the upper migration limit allowed in the packaged foodstuff and the corresponding maximum allowable contaminant concentration in the polymer.

A generally recognised migration model which relies on estimating the diffusion coefficients of organic chemical substances in polymers[23] has recently been completed within the European project SMT-CT98-7513 "Evaluation of Migration Models in Support of Directive 90/128/EEC"[ ]50 . This model correlates the migration of contaminants into food with the molecular weight of the bottle polymer and the corresponding maximum allowable concentrations of the surrogates in the bottle wall.

Klingelhofer et al[ ]51 determined the diffusion coefficients of two model contaminants in recycled HDPE. Methyl salicylate was used as a model compound for oil based household cleaners. Xylene was used as a model for the solvents used in paint thinner or gasoline. Xylene was found in typical post consumer recycled HDPE samples[36,37].

They found that the diffusion coefficients of xylene and methyl salicylate into (or out of) HDPE were 8.6 + 0.8 x108 cm2 s-1 and 1.4 + 0.06 x108 cm2 s-1, respectively.

Devlieghere et al[ ]52 investigated the migration behaviour of conventionally recycled post-consumer HDPE material, caustic washed material (5% NaOH, 60 min, 90 °C) and caustic washed/steam stripped (1 h, 1.7 kg steam per h and kg HDPE)/air dried (2 h, 90 °C) material which was re-used in HDPE bottles.

The migration characteristics of the different bottles were compared using various food simulants such as distilled water, 3% acetic acid, 15% ethanol, 95% ethanol and iso-octane. The bottles were filled and stored for 10days at 40 °C for distilled water, 3% acetic acid, 15% ethanol and 95% ethanol or 2 days at 20 °C in the case of iso-octane.


From the migration tests (and also from the sensory tests, see below) the conventionally washed and the caustic washed recycled materials were not safe for use as a food packaging. They found that a large numbers of contaminants were able to migrate. However the steam stripped recycled material seemed to perform almost as well as virgin polymer.

6.6 Sensory testing

Huber and Franz[34] investigated the sensory properties of conventionally recycled polymers (HDPE, PP, PS and PET) by means of odour testing.

In all the samples they detected the polymer specific odour found in virgin polymers. However they also found that all of the recycled polymers could be identified because they detected additional odour notes.

The lowest odour deviation was noticed for PET. Increasing off-odour was noted from PS to PP and HDPE. These results are not surprising because flavour compounds such as limonene can be found in significant concentrations in all the polymer samples. These flavour compounds absorbed from the first use of the packaging materials.

Deep cleansing of these polymers may be expected to improve the sensory properties of recycled polymers because the analytical work described earlier in 6.1 demonstrated that super-clean recycling processes can greatly reduce concentrations of flavour compounds in polymers.

The sensory properties of recycled polymers are a vital parameter for a closed loop recycling. They should be investigated in case-by-case studies for packaging materials containing the final recyclate from each recycling process . This is because the odour threshold limits of some flavour compounds are very low (in some cases below the analytical detection limits) so that the results of a challenge test cannot be used to predict the result of a sensory evaluation.

Devlieghere et al[52] noted the migration of numerous compounds which cause an easily recognized off-flavour in bottles manufactured from conventional recycled HDPE and also in bottles made from caustic washed recycled material (5% NaOH, 60 min, 90 °C). However steam stripped/air dried recycled material (1 h, 1.7 kg steam per h and kg HDPE followed by 2 h at 90 °C) seemed to perform almost as well as virgin material. In the sensory tests this material could not be distinguished from the equivalent virgin polymer.

6.7 Mechanical properties

Changes in the molecular structure of the polymer may occur during recycling.

Processes have been developed for polyester polymers such as PET which are able to increase the molecular weight by solid-state polycondensation (SSP). This process can improve the mechanical properties of the polymer.

In the case of polyolefins a decrease in molecular weight typically occurs due to oxidation and mechanical stress during bottle manufacturing, use and recycling. The sorption of compounds into the plastics material may also change the mechanical properties of post-consumer plastics. This is more likely in the case of polyolefins due to their higher sorption rates.

Spinks and Ayrton[ ]53 investigated the effects of multiple pass extrusion on the structure and properties of dairy-grade HDPE. In their tests they put the polymer through up to ten cycles. They found that repeated extrusion caused thermo-oxidative degradation.

During the first two cycles a cross-linking process was dominant. During further extrusion cycles chain scission was slightly more dominant.


Melt flow index and impact strength show a steady decline with multiple pass extrusion whereas the modulus increases. The most significant practical problem however, was a strong increase in colour (yellowing) during multiple pass extrusion.

El'darov et al[ ]54 also investigated multiple pass extrusion processing of HDPE. They found considerable changes in molecular weight. In the absence of an inhibitor additive the molecular weight of polyethylene either increases or decreases depending on the oxygen content of the processing environment.

They concluded that oxygen performs a double function. It increases the rate of radical initiation due to hydro peroxide decomposition and also affects the competition between degradation and cross-linking in the secondary reactions of the radicals. Peroxide radicals are incapable of attaching themselves to macromolecules, so the relative rate of degradation increases in the presence of oxygen.

In contrast a study from Boldizar et al[ ]55 found that post-consumer HDPE did not degrade to any significant degree during ten cycles of simulated recycling, where each cycle included one extrusion and one indoor aging step equivalent to 2-3 years.

Takahashi[ ]56 showed that melt temperature, heat of fusion, dynamic modulus of elasticity and tensile-impact energy of recycled HDPE material in the moulded form were within the range of variation of the equivalent virgin polymer.

Devlieghere et al[52] tested virgin and recycled HDPE and observed only minor and mostly non-significant differences for E-modulus, tensile strength and elongation.

The steam treated recycled material (1 h, 1.7 kg steam per h and kg HDPE followed by 2 h at 90 °C) was found to be an appropriate material for the production of HDPE bottles.

Pattanakul et al[ ]57 compared the physical properties of virgin HDPE with virgin/recycled HDPE blends containing up to 100% recycled material. The recycled HDPE was obtained from post-consumer milk bottles.

It was found that elongation at break was the mechanical property most affected by the content of recycled HDPE. Overall, however, the recycled HDPE from milk bottles was found to be a material with useful properties not very different from those of virgin resin and thus could be used, at an appropriate blend ratio with virgin HDPE.

6.8 Studies of practical market applications

Three-layer PP Cups for Dairy Products

Franz, Huber and Piringer presented a study in 1994[ ]58 which investigated the safety in food contact use of symmetrically coextruded three-layer polypropylene (PP) cups with recycled post-consumer PP in the core layer (mass fraction 50%) and virgin food grade PP in the adjacent layers.

The recycled PP contained about 95% PP and 5% PS. It was carefully source controlled and had been used for packaging of yoghurt in its first life. The intended application for the recycled material was again packaging of milk products such as yoghurt with short storage times under refrigerated conditions.

The strategy in this study was to compare the recycled plastic with new, food grade plastic material of the same type in three ways:

1. Analysis of the raw materials (virgin versus recycled PP pellets), 2. Analysis of the finished food contact articles (virgin versus recycled cups) 3. Migration testing of both types of cups (virgin and recycled) under both regular and more severe test

conditions


Post-consumer or recycling-related potential migrants were identified and quantified in the first two groups of tests. These compounds were then used as indicator substances to be monitored in migration measurements in the third set of tests..

The major post-consumer related compound was limonene, a flavour compound, which can be found in many foodstuffs and also in the non-food area.

It was found that none of the post-consumer or recycling-related substances could be detected analytically in the food simulants (at a detection limit of 13 ppb) under standard migration test conditions. However, from the results obtained under more severe test conditions, it could be concluded that even for limonene (the compound with the highest migration rate) migration into a milk product will be below 1 ppb and far below 1 ppb for other post-consumer substances.

In conclusion, based on the US FDA threshold of regulation concept[18] the use of co-extruded multi-layer material for the intended application was considered to be safe.

Multi-layer PET Bottles for Soft Drink Applications

Franz et al published a further study in 1996[ ]59 in which they investigated the effectiveness of a virgin PET layer in limiting chemical migration from recycled PET.

For this purpose three-layer bottles were prepared with an inner buried layer of PET, which was deliberately contaminated. The model contaminants used were toluene, 1,1,1-trichloroethane, chlorobenzene, phenyl decane, benzophenone, phenyl cyclohexane and copper(II) acetylacetonate.

No migration was detected through a barrier of virgin PET of 186 + 39 µm thickness into 3% acetic acid using general migration test conditions of 10 days at 40 °C and also after 6 months storage at room temperature.

Migration testing with 50% and 95% ethanol as severe contact media, which are relatively aggressive to PET also failed to produce measurable migration rates.

They used a diffusion model for limonene (a substance for which diffusion coefficients were available) to estimate that a breakthrough of a substance with comparable molecular weight would take place after 7.5 years or 0.8 years at room temperature or 40 °C, respectively for a 100 µm thick PET layer.

It was concluded that an intact PET bottle layer in contact with the food represents an efficient functional barrier against migration from any possible contaminant encapsulated in a recycled PET material under normal conditions of use for soft drinks.

Studies on Multi-layer PET and PET Films for Food Packaging

Piringer et al[ ]60 concluded a study in which,the migration behaviour under different test and contact medium conditions was systematically investigated for several co-extruded three-layer PET films.

These films were spiked in the core layer with toluene and chlorobenzene surrogates and had a PET barrier layer thickness either side of the core layer of between 20 µm to 60 µm. They observed that the migration measured through the different barrier layers was predictable and developed a diffusion model for predicting the functional barrier properties of layered films based on Fickian diffusion.

It was also found necessary to consider the effects of diffusion from the core layer to a virgin barrier layer during the co-extrusion process for reliable prediction of migration.

The mathematical model presented in this paper estimates the maximum allowable contaminant concentration in the core layer for a given barrier thickness and a given threshold or specific migration limit.

Similar studies[49] investigated the functional barrier behaviour of high impact polystyrene (HIPS) using symmetrical three-layer films, again spiked in the core layer with toluene and chlorobenzene.


The thickness of the HIPS barrier layer was greater than in the above PET example (50 µm, 100 µm and 200 µm). The contact medium was 50% ethanol, which is a recognised contact medium for fatty food products for this plastic. Testing was carried out at 40 °C for up to 76 days.

The research concluded that HIPS was an appropriate functional barrier, provided the barrier layer is optimised for the particular purpose. Generally, layer thicknesses from 100 µm to 200 µm were found to be very efficient, even under the exaggerated test conditions used in this study to simulate fatty contact.

For aqueous food products and ambient or refrigerated applications a HIPS barrier layer will be even more effective.

As in the PET study, this study investigated contamination of the virgin barrier layers by compounds from the core layer during the high temperatures of the co extrusion process. It was found that, for a 50 µm HIPS barrier layer, the same contamination of the food contact surface with the surrogate toluene was achieved within 1 second at the co-extrusion temperature of 200 °C as after one year of storage at room temperature.

Mono-layer PET Bottle for Sof Drink Applications t

Due to the higher cost of manufacturing multi-layer PET bottles, the bottle manufacturing and recycling companies started to develop high performance recycling processes, which allow bottles to be made without a functional barrier of virgin PET.

One decade later several super-clean recycling processes are now established at industrial scale[10]. By 2002, recycling companies in Europe had installed total recycling capacity of about 65.000 tons of super-clean post-consumer PET suitable for use in direct food contact applications. The cleaning efficiencies of all the industrial-scale deep-cleansing recycling processes for PET have been investigated by challenge tests and the results are well known.

Monolayer HDPE Bottles for Fresh Milk

In 2002 a milk bottle-recycling project was launched in Northern Ireland[ ]61 . Milk bottles were collected by a deposit system and were sent to a bottle-to-bottle recycling process. As a result of the deposit collection system the recycled HDPE was completely under source control and had been used in its prior application only for packaging of fresh milk.

The collected material was recycled first by a conventional washing based recycling process and then further deep-cleansed using a super-clean process. The recycled material was re-used in new milk bottles at 20% to 30% content without a functional barrier. The intended application was for fresh milk with short storage times under refrigerated conditions.

The project had several R&D phases. Firstly post-consumer HDPE milk bottles were analysed for compounds which could be potential migrants. Subsequently the deep-cleansing process was optimised and its cleaning efficiency was evaluated by a challenge test. Only HDPE related compounds such as oligomers could be detected in the recycled polymer after deep cleansing.

For quality control purposes an online sniffing device based on a so-called electronic nose was integrated into the recycling process. This sniffing device is able to detect potential migrants such as solvents or other volatile substances, which might be introduced into the recycling process.

Based on the challenge test results, upper limits for the concentration of volatile substances could be defined so that any HDPE batches with higher levels could be detected and separated for reuse in non-food packaging applications.

The sophisticated recycling techniques used in this project compensated for the greater difficulty of recycling HDPE in closed loop compared to PET.


Another point to note is that the project was started in Northern Ireland. This is a relatively small market scale which is easy to control. All of the HDPE milk bottles were provided by only two bottle manufacturers. These manufacturers were part of the project.

By reading the bar code the collection vendors are able to separate bottles from these two manufacturing companies and reject other milk bottles. As a result only milk bottles from bottle suppliers and filling companies which support the project are sent to the bottle-to-bottle recycling process. The recycling company was therefore able to influence the choice of glues, label and colours used by the bottle manufacturers. This helped to improve the recycling process further.

6.9 Summary of the literature review

The literature study indicates that there is no technical barrier to the use of recycled plastics in food applications. They can be applied in direct food contact applications provided super-clean recycling processes are used or they can be protected from direct food contact by a functional barrier.

From a legal point of view, there may be limitations on the use of recycled plastics in food contact applications, because different European countries still apply different regulations. The EU has not yet issued harmonised rules.

Whatever happens, the use of recycled plastic materials in packaging applications must not be at the expense of the public health, nor should it alter the quality of the food materials contained by the packaging.


7 Sorting efficiency for UK collected HDPE bottles

Delleve Plastics provided HDPE scrap for this project. This material was generally representative of post-consumer HDPE packaging material collected in the UK. This material was sourced from:

• A kerbside collection in the South East of the UK • A bring scheme collection in the North West of the UK

The input material for the project was the plastic bottle fraction from these sources with plastic films and other non-bottle material removed.

Table 3 gives an overview of the composition of the material that entered the sorting process.

Table 3: Composition of the input material (average value for 10 bales)

Bottle type Absolute amount [kg] Percentage

HDPE milk bottles 610 20%

Other HDPE bottles 610 20%

PET bottles 1525 50%

PS, PP, other plastic bottles 183 6%

Residue 122 4%

Total 3050 100%

7.1 Sorting technology used

The aim of the sorting trials was to collect natural HDPE milk bottles. The optical sorting technology of RTT Systemtechnik GmbH was used.


Figure 3: Schematic diagram showing separation of bottles by positive sorting

The newest technology from RTT, UniSort P, uses near infrared detection of the polymer types. The wavelengths of different polymer types are shown in Figure 4. Different polymer types such as PE, PP, PS, PA, PET, PVC and ABS can be separated with this technology.

Figure 4: NIR wavelength of different polymers (UniSort P)

The UniSort P technology from RTT is unable to separate natural and coloured HDPE bottles from each other. The HDPE fraction from the first sort was therefore sorted again using the UniSort C technology in order to separate the coloured HDPE bottles. See Figure 5.


Using this technology the separation of natural HDPE bottles was successful due to the fact that the natural HDPE milk bottles have characteristic wavelength between 1750 nm and 2100 nm in comparison to HDPE non-milk bottles.

Figure 5: NIR wavelength of HDPE milk bottles used for sorting from other HDPE bottles (UniSort C)

Both of the Unisort processes use principal components analysis (PCA or PLS methodology) for extraction of the characteristic wavelength for the different polymers and colours.

7.2 Sorting efficiency of the RTT pilot plant

In the first step of the project 12 tonnes of material provided by Delleve were shipped to RTT in Zittau. Part of this material was sorted by the pilot plant at RTT. The results were used to optimise the polymer database in order to increase the sorting efficiency. Table 3 shows the sorting results from the RTT pilot plant at Zittau.

Table 4: Results of the sorting trials from the pilot plant in Zittau (Unisort P)

Type Percentage

HDPE milk bottles 86.6%

HDPE milk bottles clumped with other bottles 10.1%

PET bottles 1.0%

Residue (mostly attached paper) 0.4%

HDPE non-milk bottles 1.9%

Total 100%


The following conclusions were drawn from the pilot plant sorting trials:

• The particle size of the bottle fraction is suitable for automatic separation

• The material contains a relatively small proportion of non-bottle materials

• The relatively small proportion of HDPE bottles in the input stream(20%) means that a positive sorting method, where HDPE items are positively identified and ejected, should give the best results

• Colour sorting should be done in a second step using the mixed HDPE fraction from the initial sort

• There was some clumping of HDPE bottles with PET (or other materials) which reduced the sorting efficiency

In conclusion the material provided by Delleve should be suitable for supply to a fully automated sorting process.

The small proportion of HDPE milk bottles in the mixed scrap made it necessary to sort large amounts of baled material in order to obtain the 8 te of natural HDPE milk bottles which were needed for the next stage of the project. In addition clumping of HDPE bottles with other materials during the baling process reduced the sorting efficiency. For full scale production the baling pressure of the input material should be optimised in order to minimise ‘clumping’ while maintaining an adequate bale volume.

It was interesting to note that wavelength differences of more than 1800 nm occurred in the near infra red wavelength spectra for non-milk and milk HDPE bottles. The question arose whether these differences are a special case for the UK market, since most of the virgin HDPE material for milk bottles in the UK originates from one virgin supplier.

Sorting tests were therefore performed on both milk bottles and non-milk containers from the US market. It was found that US milk containers are comparable with UK milk containers in that there is also a difference in the NIR spectra for milk and non-milk HDPE containers of about 1800 nm. It therefore appears that the technology applied in this study to remove non-milk containers may be viable for other regional markets as well.


1800 nm1800 nm

Figure 6: NIR wavelength of HDPE milk bottles from the US market used for sorting from other HDPE bottles (UniSort C)

7.3 Sorting efficiency at the industrial plant of Delleve Plastics

In the second stage of the trial the optimised database for bottle sorting that was generated in the pilot trials at Zittau was installed in the optical sorters used at the sorting plant of Delleve Plastics in St. Helens. The industrial scale plant was used to sort 3 tonnes of mixed baled bottles. A flow chart of the sorting steps and the mass flow through the sorting process is given in Figure 7.


UniSort Ppositive sorting

UniSort Cnegative sorting

material composition:(average value of 10 bales)HDPE milk bottels 20 % = 610 kgHDPE others 20 %= 610 kgPET 50 %= 1525 kgPS, PP, other plastic 6 %= 183 kgResidue 4 % = 122 kg

Total 100 % = 3050 kg

Input

flow path

material composition:

HDPE milk bottels 15 kgHDPE others 515 kgPET 1428 kgPS, PP, others 101 kgResidue 105 kg

Total 2164 kg

eject: PEmilk bottle

flow path

final producttwo bales

HDPE-milk bottels


HDPE milk bottels 8 kgHDPE others 83 kgPET 65 kgPS,PP, others 82 kgResidue 15 kg

Total 253 kg

eject 633 kg

Sorting Step 1positive by resin

Sorting Step 2positive by color

Input


HDPE milk bottelsclumped together 65 kgwith PET bottlesHDPE non milk 12 kgPET 6 kgResidue 2 kg

Total 85 kg

Handinspection

Bale 1 270 kgBale 2 278 kg

Total 548 kg

Shipped to Sorema, Italy

Sorting Step 3Manual inspection

eject 886 kg

UniSort Ppositive sorting

UniSort Cnegative sorting

material composition:(average value of 10 bales)HDPE milk bottels 20 % = 610 kgHDPE others 20 %= 610 kgPET 50 %= 1525 kgPS, PP, other plastic 6 %= 183 kgResidue 4 % = 122 kg

Total 100 % = 3050 kg

Inputmaterial composition:(average value of 10 bales)HDPE milk bottels 20 % = 610 kgHDPE others 20 %= 610 kgPET 50 %= 1525 kgPS, PP, other plastic 6 %= 183 kgResidue 4 % = 122 kg

Total 100 % = 3050 kg

Input

flow path


HDPE milk bottels 15 kgHDPE others 515 kgPET 1428 kgPS, PP, others 101 kgResidue 105 kg

Total 2164 kg

eject: PEmilk bottle

flow path

final producttwo bales

HDPE-milk bottels


HDPE milk bottels 8 kgHDPE others 83 kgPET 65 kgPS,PP, others 82 kgResidue 15 kg

Total 253 kg

eject 633 kg

Sorting Step 1positive by resin

Sorting Step 2positive by color

Input


HDPE milk bottelsclumped together 65 kgwith PET bottlesHDPE non milk 12 kgPET 6 kgResidue 2 kg

Total 85 kg

Handinspection

Bale 1 270 kgBale 2 278 kg

Total 548 kg

Shipped to Sorema, Italy

Sorting Step 3Manual inspection

eject 886 kg

Figure 7: Flowchart of the sorting steps at Delleve

The sorting efficiency of the process was tested for two scenarios (see Table 5):

(i) further sorting of the output stream of the RTT process by handpicking before automatic sorting

(ii) automatic sorting without further sorting.

In the first scenario the feed material was hand sorted on the conveyor belt before the automatic sorter in order to remove impurities such as HDPE milk bottles clumped with other bottles, PET bottles and non-bottle materials. In this scenario the output fraction contained more than 99% natural HDPE milk bottles.

For scenario (ii) no hand sorting was used on the basis that all other impurities apart from non-milk HDPE bottles should not be critical because the sink-swim process of the washing line that follows the automatic sorter should remove impurities such as PET. In scenario (ii) the HDPE milk bottle fraction contained about 12 kg of HDPE non-milk bottles. These could not be removed during the further recycling steps. In this scenario the output fraction of natural HDPE milk bottles is 97.9% (or slightly higher due to the fact that the HDPE bottles clumped with other bottle will increase the HDPE milk bottle fraction during grinding).


Table 5: Results of the sorting trials with two scenarios (i) further sorted by handpicking and (ii) without further sorting, but washing using a sink-swim step

Type Amount [kg]

Scenario 1 Scenario 2

HDPE milk bottles 548 548 548

HDPE milk bottles clumped with other bottles (mostly PET)

65 removed by handpicking

removed by downstream sink-swim process

PET bottles 6 removed by handpicking


Residue (mostly attached paper) 2 removed by handpicking


HDPE non-milk bottles 12 removed by handpicking

12

Total 633 548 560

Purity >99% >97.9%

In both scenarios the loss of HDPE milk bottles was 10.2% (610 kg in the input stream to 548 kg in the output).

In conclusion the sorting process is able to provide a good quality input material for the further cleaning steps, which is suitable for a closed loop recycling.

The ILSI document[21] recommends a minimum of 99% food grade polymer for the input material to closed loop recycling processes. This goal was achieved using scenario (i). For scenario (ii) the goal was also probably achieved, because most non-milk HDPE bottles are also manufactured from food grade HDPE.

However, some authorities define "food grade" polymers as a polymer which was in contact with foodstuff. The discussion as to whether the input material should be "food grade material" or "food grade material from bottles filled with foodstuffs" is not finalised.

The German BfR recommends a minimum fraction of 99% PET for the closed loop recycling of PET bottles[22]. This is defined such that PET bottles used for non-food applications are considered as a foreign polymer type.

The conclusion of this study is that non-milk bottles should be separated by handpicking until the EU discussion is finalised and the European Community has published its "Recycling Directive".


8 Washing the sorted HDPE bottle fraction

8.1 Washing post-consumer HDPE flakes

Post-consumer pre-sorted bottles from the sorting trials at Delleve were shipped to SOREMA, Italy. The aim of the washing trials was to remove glue, labels and other surface contaminants and to achieve some decontamination of post-consumer compounds. Target output of the washing trials was high quality HDPE flakes, suitable for further deep-cleansing processes.

SOREMA used the standard hot washing process that they manufacture for PET bottle-to-bottle recycling. Figure 8 below shows a flow chart of the SOREMA process.

Details of the procedure used at SOREMA are as follows:

Manual sorting

29 bales of input material with a total weight of 9407 kg were sorted manually.

Two separate fractions were processed:

First fraction: two bales from the initial pilot sorting trials at RTT with a total weight of 529 kg. 4 kg of PET, PVC, Fe and coloured HDPE were manually separated from this fraction prior to washing.

Second fraction: 23 bales from the bulk sorting trials at Delleve with a total weight of 7646 kg. 15 kg of PET, PVC, Fe and coloured HDPE were manually separated from this fraction prior to washing.

4 of the bales from Delleve (total weight of 1.232 kg) contained many bottles of coloured HDPE and contamination with a total weight of 220 kg.

Granulation and aerodynamic separation.

9168 kg of bottles were granulated and passed through a screen of 12 mm round holes followed by an aerodynamic separator. This step separated 438 kg of labels and fines.

Pre-washing

SOREMA’s patented hot pre-washing system takes the worst quality baled bottles and continuously removes large and abrasive contaminants, almost all glue, paper labels and dirt on the polymer surface. The machine used for this step is slow moving with very few moving parts.

The bottles are mixed with a hot caustic solution in a stainless steel cylindrical vessel. 30% caustic soda is added to the washing solution in order to give a caustic concentration in the vessel of 2% with approx. pH 12 and a temperature of about 93°C. The bottles were agitated in the solution long enough to remove any glue.

In this trial a total of 8730 kg HDPE flakes were processed. 150 kg of paper and HDPE fines were separated (estimated dry weight). The residence time was 4 to 10 min.


Grinding

After pre-washing the bottles were cut into smaller pieces in the grinding section. During grinding, water was sprayed into the cutting chamber. Any residual paper with the flakes was pulped and then separated in the washing centrifuge.

Chemical washing and separation

The final washing process was the chemical washing, separation, rinsing, drying and aerodynamic separation cycle. The washing temperature was approximately 93 °C. SOREMA added RP14 product (Mac Dermid), diluted at 2.5%, to the process water,

A total of 8580 kg HDPE flakes were processed.

The following residues were separated: 60 kg paper and fines from the chemical washing, 26 kg plastic from flotation and 119 kg labels from the aerodynamic separation. The residence time was 6 to 12 min.

Colour Sorting of Washed Flakes

The washed flakes still contained about 1% coloured flakes so a further colour-sorting step was necessary.

The flakes were optically sorted on an AF 0914 machine at the MikroSort testing laboratory in Wedel, Germany.

Before conducting the bulk separation the sorting process was optimised for maximum reduction of impurities and minimum loss of material in a pre-test.

The particle size distribution of the HDPE flakes was also measured. See Table 6

Table 6: Size distribution of the HDPE flakes

Particle size Amount [%]

>8.0 1.3

6.3 – 8.0 27.6

5.0 – 6.3 9.0

4.0 – 5.0 24.7

3.1 – 4.0 14.5

2.5 – 3.1 11.3

<2.5 11.6

4180 kg of dried flakes from the chemical washing process were sorted in the bulk trial without separation of the fine material (<2.5 mm). The product from the flake sorting process contained less than 100 ppm of coloured HDPE flakes. The loss of good material with the coloured flakes was approx. 3%. It was found that the optical sorter was able to distinguish between opaque and white flakes with an efficiency equivalent to the coloured flakes.

The mass balance of the washing trial is summarised in Table 7.


Table 7: Overall mass balance of the washing trials

Step Input [kg] Output [kg] Type of waste %

Bales 29 bales 9407 100.0

Manual sorting 9407 239 Containers 2.5

Granulation and aerodynamic separation

9168 438 Labels 4.8

Pre-washing 8730 150 Paper/fines/ contamination 1.7

Chemical washing and aerodynamic separation

8580 205 Paper/fines/ contamination 2.4

Flake sorting 8375 250 Coloured Flakes 3.0 (estimated)

Total 9407 8125 86.4


Figure 8: Flow chart of the SOREMA washing process


Figure 9: Flow chart of the colour sorting using the MikroSort technology

input 1,0t/h 0 12 mm -

Final productcoloured: <100ppm

0,25 t/h

1. sorting step

Mikrosort 1

0,2t/h 1,05t/h

3. sorting

step

MikroSort

1/3

2. sorting step

MikroSort 2/3

0,1t/h

Online return

0,15t/h

0,95t/h0,05t/h

Reject fraction

loss of transparent ≈ flakes: 3%


Input

coloured flakes 1.4%

coloured 9% coloured<500 ppm

coloured

Figure 10: Results of the colour sorting using the MikroSort technology

coloured 30% coloured<1% coloured<1%<100 ppm

Final productRejected Recirculated Recirculated625 kg 425 kg 4180 kg250 kg


8.2 Challenge test of the washing process

The cleaning efficiency of the washing process was measured by a challenge test. The test was carried out by deliberately introducing contaminated post-consumer HDPE material with the feed.

Natural HDPE flakes from the first washing trial were contaminated with surrogate contaminants. This contaminated material was then washed together with non-contaminated red HDPE flakes using SOREMA’s pilot plant washing line. Using the pilot plant with a throughput of about 1000 kg h-1 allowed the use of a small quantity (50 kg) of contaminated material for the challenge test. This reduced the amount of hazardous chemicals that had to be handled. After the washing step, samples were withdrawn and the contaminated natural flakes separated from the non-contaminated red flakes. The natural flakes were analysed for residual contamination levels.

The surrogates were chosen following FDA recommendations[18,19] and in agreement with EU-relevant criteria[16,21,22]. The surrogates chosen covered a spectrum of volatility and polarity and a broad range of migration-relevant molecular weights. They also contained a variety of functional groups inlcuding hydrocarbons, chlorinated hydrocarbons, a ketone and an ester functional group.

The following surrogates were used: toluene, chlorobenzene, phenyl cyclohexane, methyl stearate and benzophenone. Chloroform, a well-known very aggressive chemical to HDPE, was applied to ensure strong interactions with the HDPE matrix and therefore better transport of the surrogates into the polymer. All surrogates are commercially available and were used for the contamination experiments without further purification.

Contamination of the HDPE flakes was achieved by the following procedure: 50 g of each of the liquid and solid surrogates were mixed and stirred until a homogenous solution was obtained. This surrogate mixture was mixed with 5 kg of recycled post-consumer HDPE flakes to give a contaminated master-batch. The master-batch was blended with another portion of 50 kg of post-consumer HDPE material and then stored in a sealed steel container for 7 days at 50 °C with periodical agitation. During this time sorption of the chemical compounds into the contaminated HDPE flakes was achieved. Using this contamination procedure a total of 55 kg contaminated post-consumer HDPE flakes were produced for each contamination level.

The success of the contamination was verified by measurement of the concentration of the surrogates in the contaminated input material. The contaminated flakes were fed into the washing process as described above.

Contaminant concentrations were measured either by headspace screening of the contaminated flakes or solvent extraction followed by gas chromatography. The input surrogate concentrations were in the range 700 to 900 ppm.

The cleaning efficiency of the washing process was determined for each surrogate by comparison of the concentration in the HDPE samples after treatment with the initial concentration in flakes entering the washing process (Equation 1).

Eq. 1: 100%masssurrogateinitialrecyclingafter masssurrogate1(batch)efficiencycleaning •⎟⎟

⎠

⎞⎜⎜⎝

⎛−=

Unfortunately the analytical uncertainty was very high, especially for the non-volatile compounds. Therefore the estimated cleaning efficiencies also have a high degree of uncertainty. For this reason two independent analytical procedures were used for determination of the cleaning efficiencies. However, due to analytical interferences it was still not possible to estimate the cleaning efficiency of the washing process for some compounds.


For example the washed material appeared to contain higher levels of methyl stearate than the input material. It should be noted that the input contamination levels applied were extremely high in comparison to the concentrations typically found in post-consumer HDPE flakes (see Chapter 10.3).

Table 8 summarises the results of the washing process challenge test.

Table 8: Washing process challenge test results

Toluene Chlorobenzene Phenyl cyclohexane

Methyl stearate

Benzophenone

Initial concentration prior to washing and super-clean recycling

722 + 142 917 + 294 852 + 503 739 + 566 884 + 611

Estimated cleaning efficiency of washing process (measured by headspace GC)

60.1% 52.1% 8.9% n.d.[a] 26.3%

Concentration after washing process (measured by GC after solvent extraction)

405 + 25 583 + 34 973 + 113 1182 + 321 764 + 109

estimated cleaning efficiency 43.9% 36.4% n.d.[a] n.d.[a] 13.5%

[a]not determined due to analytical interferences (see text)


9 Supercritical CO2 process for super-cleaning HDPE

9.1 Background

Both the SOREMA washing process (see Chapter 8) and the EREMA super-clean recycling process (see Chapter 10) are commercially available processes, which have already been optimised for recycling of HDPE milk bottles. In contrast, the novel super-cleaning process based on supercritical CO2 that is described in this chapter is less developed.

It was decided to try to develop a process based on supercritical CO2 extraction because this process route should in principle offer a lower cost and more efficient method for extracting a wide range of contaminants than the EREMA process.

CO2 is a low cost extraction material. It can be made to enter the supercritical state relatively easily under typical extrusion conditions in standard vented extruders. Once in the supercritical state, it becomes a powerful solvent for a wide range of materials. It can be removed from the extruder by a simple venting process without the need for expensive vacuum extraction. It can then be recovered and separated from the contaminants that it has extracted, simply by reducing its pressure after the vent.

The trials and other investigations conducted are summarised in Table 9.

Table 9: Work Packages for Development of the supercritical CO2 process

Work done Feed material Investigators

Patent review / RAPRA Technology

Literature review of scCO2 solubility data / RAPRA Technology

Phenyl cyclohexane scCO2 solubility tests / Birmingham University

Batch contaminant extraction tests using scCO2

Virgin HDPE loaded with a mixture of surrogate compounds

Birmingham University

Initial decontamination trials for HDPE using scCO2 extrusion extraction

Virgin HDPE (Rigidex, BP Solvay) loaded with a mixture of surrogate compounds

RAPRA Technology

Optimisation of decontamination trials for HDPE using scCO2 extrusion extraction

Virgin HDPE (Stamylan HD9650, DSM) loaded with a mixture of surrogate compounds

RAPRA Technology

Further decontamination trials using scCO2

extrusion extraction with PP in place of HDPE

Virgin PP (BB125MO, Borealis) loaded with a mixture of surrogate compounds

RAPRA Technology

Decontamination of real HDPE bottle flake using scCO2 extrusion extraction

Post-consumer HDPE bottle flake from SOREMA washing trials loaded with a mixture of surrogate compounds

RAPRA Technology


Unfortunately it became obvious during the trials conducted for this project that the melt phase supercritical CO2 extraction process is not yet robust enough to allow routine super-cleaning of HDPE.

The results of the trials are still reported in detail in this section because super-cleaning of HDPE using supercritical CO2 may become a commercially viable alternative to the EREMA process with further process development work.

9.2 Patent review

A detailed review of the patent literature and intellectual property rights (IPR) relating to the use of super-critical carbon dioxide in extrusion processes was undertaken by Rapra Technology Ltd.

9.3 Solubility data for melt phase super-critical CO2 extraction

In order to confirm the viability of super-critical CO2 extraction in the melt and to help predict process temperature and pressure conditions the literature was reviewed for published data on the solubility and/or extraction of different chemicals from plastics using super-critical carbon dioxide at temperatures up to 145 °C.

Data on the ILSI surrogates[21] was particularly useful as these cover a range of polar and non-polar chemicals with differing volatilities and solubility parameters and can act as pointers to the likely behaviour of milk bottle contaminants. The applied surrogates were:

• 1,1,1-Trichloroethane (a polar, volatile penetrant)

• Benzophenone (polar, non-volatile penetrant)

• Toluene and chlorobenzene (non-polar, volatile penetrants)

• Phenyl cyclohexane (non-polar, non-volatile penetrant)

• Methyl stearate (substitute chemical for organometallic compounds, non-volatile penetrant)

• Heptane – Solvent for the above

9.3.1 Literature solubility data

Literature solubility data are shown in Figure 11. The reference temperatures shown for each of the chemicals were the recorded temperatures that were nearest to the likely maximum operating temperature of the process (approx. 145 °C).

Only liquid phase data were available for benzophenone. The data presented for this compound were predicted from the liquid phase data and should be treated with caution.

Solubility data for phenyl cyclohexane could not be found in the literature and were therefore determined experimentally.

The literature data show that, of the ILSI surrogates, the materials with the lowest solubility in super-critical CO2 were the polar non-volatile methyl stearate and the non- polar, non-volatile phenyl cyclohexane. A cross-over in their respective solubilities at approx. 200 bar was suggested from the data.


0

0.2

0.4

0.6

0.8

1

1.2

1.4

50 70 90 110 130 150 170 190 210 230 250 270 290

Pressure (bar)

Solu

bilit

y (g

Com

pone

nt/g

CO

2)

Heptane 121 C Heptane 204.1 CToluene 120.5 C Toluene 203.8 CMethyl Stearate 70 C Trichloroethane 80 CBenzophenone 50 C Chlorobenzene 80 CChlorobenzene 120 C Cyclohexylbenzene at 145 C

Figure 11: Solubility versus pressure [bar] for the compounds heptane[62], toluene[63], chloro-benzene[64], methyl stearate[65], trichloroethane[66], benzophenone[67]

The following observations may be made from the published data:

• Heptane, toluene, methyl stearate, trichloroethane, benzophenone and chlorobenzene all had some solubility in CO2.

• The critical mixture composition had been evaluated at the conditions reported for all the compounds with the exception of chlorobenzene. This means that an increase in pressure above the highest reported pressure would result in the component being totally miscible with CO2 (i.e. the existence of a single phase mixture). Extrapolating the data for chlorobenzene, the critical mixture pressure limit is approximately 160 bar at 80 °C and 230 bar at 120 °C. The latter is closer to the likely maximum operating temperature of the process.

• The data reported for methyl stearate, trichloroethane, benzophenone and chlorobenzene were at temperatures below the desired operating temperature. An increase in temperature will lead to an increase in the vapour pressure of the components and generally higher solubilities. However, an increase in temperature at constant pressure leads to a decrease in CO2 density, which would lead to a decrease in its solvent power toward the surrogate chemicals. There is always a trade-off between vapour pressure and CO2 density in a system. If the pressure is maintained at a high enough level then the decrease in density as a result of increased temperature will not be significant, and consequently, an increase in temperature will lead to increased solubility of the surrogate chemical in CO2.

• Methyl stearate requires the highest pressure to attain miscibility. The maximum temperature from available literature data was 70 °C. Again an increase in temperature will lead to increased solubility providing the CO2 density is not reduced significantly (see above).


• From the literature data, operating pressures close to or higher than 200 bar at the blow off stage of the extruder are proposed to give sufficient CO2 density (0.337 g cm-3 at 145 °C, 200 bar) for maximum extraction. (This is significantly higher than the pressures used in the initial extraction trials as discussed above).

• The solubilities reported in the literature were for pure component binary mixtures (i.e. CO2 + component). The apparent solubility of a component in the extrusion process will be affected by the presence of the polymer and the other surrogate components. The solubilities shown in Figure 11 are unlikely to be attained in practice as these are reported for systems at equilibrium. The extrusion process is dynamic and the solubility and hence the extractability of the components will depend on the flow rate of CO2 through the process.

• When CO2 is introduced into the feed it plasticizes the polymer. As a result an excess of CO2 must be used in order to ensure that contaminant chemicals are accessible and extractable from the polymer matrix.

9.3.2 Phenyl cyclohexane solubility tests

As solubility data for phenyl cyclohexane were not available in the literature they were measured at Birmingham University at 145 °C and pressures of 100 to 300 bar.

Materials: phenyl cyclohexane (98%) was supplied from Sigma-Aldrich UK, and was used without further purification. Liquid carbon dioxide was obtained from BOC, CP grade, and had a given purity of 99.995%.

Equipment: The apparatus used to determine the high-pressure vapour data is shown in Figure 12. The equilibrium cell (Parr Instruments, USA) had an internal volume of 25 cm3 and was fitted with in-line sapphire windows. It was maintained at 145 °C by a pair of thermostatically controlled band heaters. The pressure was recorded using a transducer (Druck PTX 1400) with dedicated display to within 0.1 bar and the temperature was recorded to within 0.1 °C using a Watlow 93 temperature controller and J type thermocouple.

5

Rotameter

P T P

1

2

3

4

6

Figure 12: Cloud point apparatus

1: Pressure Generator; 2: View Cell; 3: Cold Collector; 4: Stirrer; 5: Flow Totalyser; 6: Camera+Monitor

Procedure: A known mass of phenyl cyclohexane was charged into the cell and the vessel closed.

Liquid carbon dioxide was compressed by the use of a pressure generator (HIP, model 62-6-10) and supplied to the equilibrium cell. The temperature in the cell was increased to the desired isothermal condition and the pressure rose until dissolution of the compound occurred and a homogeneous phase existed.

The homogeneous condition was verified by a colour camera directed at the view cell. Dissolution was aided by the use of an impeller (Rushton turbine) coupled to an external magnetic drive.

Once the compound had been fully dissolved, the pressure was lowered to the onset of the cloud point by altering the volume of the cell. The pressure and temperature were then recorded.


The sample could then be re-dissolved by increasing the pressure and the above procedure was repeated to verify the cloud point pressure.

The pressures shown in Table 10 are the mean of up to three repeat determinations and the variance was no greater than +0.8 bar. The volume of CO2 present in the vessel at the cloud point was determined from the CO2 density and the internal volume of the cell. CO2 densities were taken from NIST.

Table 10 and Figure 13 show the solubility data obtained between nominal pressures of 100 and 300 bar. Due to the experimental technique used to measure the solubility, the determination of solubility at a particular pressure cannot be guaranteed (i.e. at 100, 150 or 200 bar etc.). The pressure depended on the amount of solute initially charged in the cell. The solubility data shown in Table 10 were therefore determined at the resulting cloud point pressures for the masses of phenyl cyclohexane charged into the pressure cell.

Table 10: Solubility data for phenyl cyclohexane in CO2

Pressure [bar] Solubility [g solute per g CO2]

102.8 0.017

171.7 0.065

223.9 0.139

240.7 0.258

280.3 0.640

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

100 150 200 250 300

P (bar)

Sol

ubilt

y g

com

pone

nt /

g C

O2

145 C

Figure 13: Solubility data for phenyl cyclohexane in CO2


9.4 Batch basis verification of the effect of CO2 pressure on extraction

Before commencing the extrusion trials batch extraction tests were conducted at Birmingham University to confirm the literature solubility data in the context of the HDPE extrusion process. Extruded material containing the ILSI surrogates was extracted using super-critical CO2 at 145 °C and at pressures of approx. 100 (actual 100.4) and 300 (actual 298.6) bar.

Contaminated HDPE material (sample 4) was extruded through the RAPRA extruder without the application of the addition of CO2.

Prior to extraction the HPDE sample was sheared into slivers using a plane type device. Photos of the prepared samples used for extraction at 100 and 300 bar are shown in Figure 14.

A B

Figure 14: Photographs of prepared HDPE samples prior to extraction, A: Sample for 100 bar, 145 °C, B Sample for 300 bar, 145 °C (Note the penny coin was used for scale and applies to both images).

The extraction involved passing a stream of CO2 continuously through the polymer bed. The experimental set up did not allow introduction of the high shear that is encountered in the extrusion process. However, the shear encountered in extrusion will enhance CO2 mixing and extraction of the surrogates.

Apparatus: A 100 ml stirred pressure vessel with two pairs of in-line sapphire windows (Parr Instrument Co., USA) was used for the extraction tests. Agitation was only applied during CO2 extraction. The windows enabled visual and photographic observation of the HDPE at the process conditions.

The once-through continuous supercritical extraction process involves compressing liquid carbon dioxide in a solvent delivery section to the process pressure P, which is beyond its critical pressure Pc (73.78 bar) and then heating this compressed liquid to the process temperature T, which is beyond its critical temperatureTc (31.04 °C).

The carbon dioxide, now in a supercritical fluid state, enters the extraction vessel and is contacted with the sample.

After passing through the material bed, the scCO2 stream containing any extracted compounds leaves the extraction vessel and is reduced to ambient pressure across a throttling valve. The volatile components that were present in the stream drop out of solution and the CO2 is vented to atmosphere.

A schematic of the process is shown in Figure 15.


D r y in gT u b e

P - 1L iq u id P u m p

P

P

B a c k - P r e s s u r eR e g u la to r

V e n t

E x t r a c to r

P u ls eD a m p e n e r

T

P

T

V - 1

M a s s F lo wM e te r

T

C O 2

H 1

T

PH 2

V e n t

Figure 15: Extraction apparatus

Solvent delivery: The solvent delivery section (shown in the highlighted box) was designed to supply CO2 to the extraction section at the desired temperature and pressure.

Carbon dioxide (BOC, liquid withdrawal CP grade) was withdrawn from the cylinder at bottle pressure (approx. 50 bar) through a shut off valve, a drying tube, an in-line 15 mm filter (Nupro SS-4TF-Filter), a non-return valve and a refrigerated heat exchanger, H1, maintained at approximately –5 °C by an external refrigeration unit (Grant). This ensured complete liquefaction of the CO2 prior to entry into the pneumatically driven liquid compressor pump P-1 (Haskell MCP-71).

The chiller unit was kept as close as possible to the pump and the feed pipe was lagged with insulating material in order to avoid vaporisation of the liquid CO2. The flow rate of CO2 was maintained slightly above the requirements of the system by adjusting the stroke rate of the pump and an air regulator valve (Wilkerson CB6-C4-F00).

An adjustable back pressure regulator control valve (BPR), (TESCOM 26-1720-22-099), maintained the desired system pressure downstream and recycled the excess CO2 through a recycle loop. This unit was accurate to within 1 bar throughout the pressure range used in these experiments.

After the pump the compressed liquid CO2 was fed through a non-return valve to H2, a thermostatically controlled jacket tube heat exchanger containing oil. The temperature of the liquid CO2 stream was raised to close to the extraction temperature, where the compressed liquid entered the super-critical fluid state.

A pressure gauge was sited at the entry to the heat exchanger and was coupled to an emergency depressurisation valve (Whitey SS-83-KS4).


The back pressure regulator allowed any CO2 leaving the pump at a higher pressure than desired to be re-circulated back into the low pressure feed side of the pump via the re-circulation loop situated after the non-return valve (Autoclave Engineers, TWO 4400). This valve was included to prevent high pressure CO2 from returning to the gas supply line. Adjustment of the back pressure regulator control valve loaded the spring closure thus allowing the compressed liquid CO2 into the extraction system. When the liquid pressure in the system reached the pressure limit on the spring closure it was forced open and the excess re-entered the CO2 feed line. This arrangement allowed the pump outlet pressure to be kept independent of the system pressure and CO2 flow rate.

Extraction: Prior to entering the extraction section, the CO2 stream first passed through a check valve (Autoclave, TWO 4400) and a mass flow meter (Rheonik RHE 08).

The stainless steel inlet tube was kept hot by a heating tape to avoid temperature fluctuations. A pair of thermostatically controlled band heaters heated the pressure vessel. A thermocouple probe connected to a digital readout was mounted in the solvent stream at the point of entry to the vessel. A further two thermocouples were situated in a port near the top of the pressure vessel and in the stream exiting the vessel.

System pressure was monitored by a pressure transducer (Druck, PTX-521-00 0-700 bar) that was coupled to a digital readout (Druck DEI 260).

Weighed quantities of the pre-treated polymer sample were charged into a glass sample holder, which was used to retain the polymer in the vessel. The extractor was raised to the desired pressure and temperature and held for 30 min to equilibrate the system. An inlet tube directed the CO2 stream into the polymer sample and mass transfer of the components into the CO2 occurred as the stream passed through the polymer bed. The stream left exited the base of the vessel, taking with it any solubilised surrogate chemicals.

Solute/solvent separation: Separation was achieved by pressure reduction directly to ambient conditions. This resulted in the deposition of the surrogate chemicals from the compressed gas stream.

The solute -laden solvent stream exited the pressure vessel and passed through a heated micro-metering valve (Hoke, 1335 G4Y). No extracted components were precipitated in the metering valve.

The CO2 stream was then directed to an external vent. A two-stage decompression was not necessary and there was no significant blocking of the vent valve due to the high process temperature. Any potential blockages were prevented by the use of a heat gun (Bosch PHG).

The flow of CO2 through the system was observed using an on-line mass flow meter. The CO2 flow was continually monitored and adjusted by the micro-metering valve to give a stable carbon dioxide flow rate. Further adjustments were made in order to maintain the temperature, pressure and flow rate constant as the extraction process proceeded for a duration of two hours. At 10 min intervals the mass flow of carbon dioxide, temperature and pressure were recorded. When the test finished, first the pressure and then the temperature were brought back to ambient conditions.

The mean mass flow rate was determined from the mass of carbon dioxide used and the duration of the extraction. A mean flow of 4.7 g min-1 was measured for the extraction at 100 bar and 3.8 g min-1 at 300 bar.

Once conditions had returned to ambient, the extraction vessel was opened and the polymer was removed from the sample holder, cut and placed in sample bottles.

During the extraction, photographs were taken of the polymer at the process conditions. Figure 16 A and B shows the polymer at 145 °C, 100 and 300 bar, respectively. The polymer can be seen in the top half of the window. The base of the glass sample holder can be seen in the bottom half. The window diameter is 15 mm.

It can be seen that the polymer became translucent during the test, presumably as it was plasticized by the CO2.

In comparison, Figure 17 A and B shows the system at 60 bar and 145 °C (at this condition the polymer has opacity) and at 200 bar in a preliminary extraction study. In Figure 17 A it appears that the polymer was less translucent. This was due to the modification of the CO2 contactor, which blocked the light source. The contactor tube can be just made out in the photograph.


A B

Figure 16: Photographs of HDPE extraction at process conditions, A at 100 bar, 145°C; B at 300 bar, 145°C

As a comparison, Figure 17 shows the system at 60 bar and 145°C (at this condition the polymer was opaque) and at 200 bar in a preliminary extraction study. In Figure 17A it appears that the polymer was less translucent. This was due to the modification of the CO2 contactor, which blocked the light source. The contactor tube can be just made out in the photograph.

A B

Figure 17: Photographs of HDPE at process conditions, A: at 60 bar, 145 °C, B at 200 bar, 145 °C

Analysis of samples: One gram portions of the samples (approx. 2 mm3) and non-extracted control material were allowed to stand in sealed 22 ml headspace vials with 5 ml of dichloromethane. The vials were sealed with PTFE lined septa and cap and stored at 40 °C for 6 d (144 h).

The resulting solutions were then examined by GC-FID together with standard mixed solutions of the surrogates of known concentration. The results are given in Table 11. The increased extraction of the non-volatile surrogates at 300 bar is in line with the theoretical predictions.


Table 11: Amounts of surrogate chemicals in flake samples (batch process)

Sample ID Concentration surrogates [µg g-1] (reduction due to CO2)

Trichloroethane Heptane Toluene Chlorobenzene Phenyl cyclohexane

Benzophenone

Methyl stearate

Sample 4 – 100 bar CO2

<5 (>84%) <1 (>99.6%) <1 (>90%) <1 (>50%) 19 (68%) 44 (10%) 82[a]

Sample 4 – 300 bar CO2

<5 (>84%) <1 (>99.6%) <1 (>90%) <1 (>50%) 0.6 (99%) 1.5 (97%) 3 (96%)

Control without CO2

32 238 10 2 60 49 67

[a] The higher level of the polar methyl stearate measured in the 100 bar extract compared to the control sample is assumed to be due to a non-uniform level of material contamination.

The molecular weight distributions of these samples, in particular the amount of residual material of molecular weight lower than 1000, was examined by gel permeation chromatography using the same experimental protocol as reported above.

The refractive index and differential pressure traces below (Figure 18 and Figure 19) show overlays of the computed molecular weight distributions for duplicate runs of the three materials. The plots were all normalised with respect to area, the y-axis being a function of weight fraction.

Note that the differential pressure chromatogram was reversed with respect to the molecular weight distribution. High molecular weight material was observed at low retention volume so appears on the left of the chromatograms but the right hand side of the molecular weight distributions.

Also the chromatograms were normalised with respect to maximum height. No effect on the shape of the distribution for the bulk of the HDPE resulting from the super-critical CO2 extraction was apparent from these traces.

An expanded "y" axis molecular weight distribution plot for duplicate runs of the three samples looking at the low molecular weight material is shown in Figure 20.

The amount of low molecular weight material (<1000 g mol-1) is in the range 0.2% to 0.3%.

These results show a small loss of low molecular weight HDPE material, particularly with the 300 bar CO2 extraction pressure. It is likely (but not proven) that such a small loss of low molecular weight HDPE will have no significant effect on the processing characteristics of the treated material.


Molecular Weight Distribution

Sample 1

Sample 4100 bar Sample 4300 bar

2.00 3.00 4.00 5.00 6.00 7.00 0.00

0.20

0.40

0.60

0.80

1.00

Log M

Wn(

logM

) Rapra Technology Limited

Figure 18: Molecular weight distributions of CO2 treated samples versus untreated reference sample

Differential Pressure ChromatogramsSample 1

Sample 4100 bar

Sample 4 300 bar

8.0 10.0 12.0 14.0 16.0 0

20

40

60

80

100

120

Retention Volume

Rel

ativ

e R

espo

nse

Rapra Technology Limited

Figure 19: Differential Pressure Chromatograms of CO2 treated samples versus untreated reference sample



Sample 1

Sample 4100 bar

Sample 4300 bar

2.00 3.00 4.00 5.00 6.00 7.00 0.00

0.20

0.40

0.60

0.80

1.00

Log M

Wn(

logM

) x10

-1


Figure 20: Molecular weight distributions of CO2 treated samples versus untreated reference sample (detail from Figure 19)

9.5 Initial supercritical CO2 extrusion extraction trials to decontaminate HDPE

Initial processing trials were undertaken using a vented, 50 mm single screw extruder at RAPRA.

The extruder screw had a L/D ratio of 34:1 and it was possible to inject super critical carbon dioxide at various barrel points upstream of the vented section.

Extrusion conditions were manipulated to ensure that the carbon dioxide was introduced into the process in the super-critical region (T = 31 °C: P = 73 bar). Initial trials were performed on a virgin HDPE material (Rigidex; BP Solvay) to establish appropriate conditions.

Extraction studies were performed at various scCO2 addition levels. From the results of these studies and from a theoretical assessment, subsequent work concentrated on refining the design of the extraction system.

It is suspected that the volatile stream exiting the extruder should to be kept at the super critical condition to maximise the efficiency of the extraction process. Work was undertaken to understand how these modifications could be implemented in practice.

Contaminated test material was first prepared by soaking 6 kg of virgin HDPE pellets (Rigidex BP Solvay received from Nampak) for 1 week at 40 °C with a solution of the following chemical surrogates in heptane:

• 2% methyl stearate

• 2% trichloroethane

• 2% benzophenone

• 10% toluene

• 2% chlorobenzene

• 2% phenyl cyclohexane


The heptane solution was then decanted and the granules dried in aluminium trays in the opening to a fume cupboard for approximately 72 h. The resulting granules were further dried in the open laboratory and subsequently mixed 20:1 with additional virgin material to obtain approximately 120 kg of contaminated material for trials.

Following installation, the extruder was run at various speed and temperature settings to determine those settings that would allow the injection of CO2 in the super critical phase. Out of these, four sets of settings were selected for detailed analytical evaluation.

For every set, the contaminated material was first run without introduction of carbon dioxide and then with low, moderate and high flows of supercritical CO2. Samples from each run (strips of extruded material 30 mm wide x 3 mm thick) were retained for analysis. Details of all zone temperatures, pressures, screw speeds, motor currents, output rates and pump settings were recorded.

Comparative analysis of levels of residual contaminants in strips extruded with and without the super critical CO2 was undertaken using headspace gas chromatography and dichloromethane extraction gas chromatography. The low volatility surrogates could not be measured using the headspace approach. The molecular weight distribution of material extruded with and without the CO2 extraction (Samples 2 and 4) was compared using gel permeation chromatography. Of particular interest was the effect of the CO2 on the amount of material of molecular weight less than 1000.

Extraction results obtained are provided in Table 12. (Similar data was obtained for the volatile species using headspace gas chromatography.)

Of the four settings examined in detail, three conditions generally gave significant reductions in surrogate concentrations in excess of those losses associated with processing. Some variations in the concentration of the absorbed surrogates in the feedstock were apparent. As expected, a greater loss of the volatile surrogates was observed with the CO2.


Table 12: Amounts of surrogate chemicals in original granules, control samples and 2160 cm3 h-1 of CO2 samples as determined by dichloromethane extraction (four specific process conditions)

Sample ID Concentration surrogates [µg g-1] (reduction due to CO2)

Trichloroethane Heptane Toluene Chlorobenzene Phenyl cyclohexane Benzophenone Methyl stearate

Sample 1 - Control without CO2 21 265 20 8 82 60 100

Sample 1 - with CO2 19 197 18 9 100 93 105


Sample 2 - with CO2 18 (46%) 177 (55%) 13 (66%) 5 (67%) 88 (24%) 53 (28%) 92 (32%)


Sample 3 - with CO2 16 (57%) 200 (48%) 18 (47%) 8 (39%) 102 (11%) 70 (7%) 113 (31%)


Sample 4 - with CO2 16 (52%) 205 (52%) 19 (51%) 10 (41%) 106 (19%) 76 (24%) 114 (0%)

Original Granules 1[a] 55 864 127 48 114 123 60[b]

Original Granules 2 57 905 132 51 120 119 59[b]

[a] corrected for 1/19 dilution with virgin HDPE, [b] Extraction variables?


For Samples 2 and 4 molecular weight distributions were measured in addition to the contaminant analysis. The results are presented in Table 13.

No significant changes in distribution were observed.

Table 13: Molecular weight distributions

Sample Mw Mn Polydispersity Peak area <1000 dalton

Sample 2 with CO2 104,000 104,000

19,300 19,200

5.4 5.4

0.27% 0.27%

Sample 2 no CO2 104,000 105,000

19,800 19,200

5.3 5.5

0.23% 0.25%

Sample 4 with CO2 104,000 103,000

18,400 18,200

5.7 5.6

0.27% 0.30%

Sample 4 no CO2 104,000 103,000

18,600 18,300

5.6 5.7

0.24% 0.25%

Figure 21 shows an overlay of the computed molecular weight distributions for duplicate runs of the four samples. The plots are all normalised with respect to area, the y-axis being a function of weight fraction. The minor differences in proportion of sample with molecular weights less than 1000 are not considered to be significant and this is confirmed by the overlay plot (Figure 22).

Molecular Weight DistributionSample 2

2160cc/hr with CO2 Sample 2No CO2Sample 4

2160cc/hr with CO2Sample 4No CO2

2.00 3.00 4.00 5.00 6.00 7.00 0.00

0.20

0.40

0.60

0.80

1.00

Log M

Wn(

logM

)


Figure 21: Molecular weight distributions for duplicate runs of the four samples

Development of a Food Grade HDPE Recycling Process

58


Sample 22160 cc/hr CO2

Sample 2No CO2Sample 4

2160 cc/hr CO2 Sample 4No CO2

2.00 3.00 4.00 5.00 6.00 7.00 0.00

0.25

0.50

0.75

1.00

Log M

-1

Wn(

logM

) x10

-1

Rapra Technology

Figure 22: Molecular weight distributions for duplicate runs of the four samples (detail from Figure 21)

In conclusion, initial studies of the possible use of super-critical CO2 for extraction of model contaminant compounds from HDPE established that a reduction in concentration of a range of surrogate chemicals can be achieved. These reductions are greater than those achieved by melt processing alone.

Under the conditions investigated, no detectable change was measured in the molecular weight distribution of material extruded with super-critical CO2.

The maximum observed reductions in surrogate concentrations compared to material extruded without CO2, are presented in Table 14.

Table 14: Average observed reductions (from Table 12) in surrogate concentrations compared to material extruded without CO2 and cleaning efficiencies in comparison to the input concentrations

Surrogate Input concentration [ppm]

Reduction during extrusion due to CO2

Overall cleaning efficiency

Trichloroethane 56 50% 69.6%

Heptane 885 51% 78.1%

Toluene 130 54% 86.9%

Chlorobenzene 50 47% 84.0%

Phenyl cyclohexane 117 11.6% 15.4%

Benzophenone 121 20.5% 45.5%

Methyl stearate 60 n.d.[a] n.d.[a]

[a] not determined due to analytical interferences

A theoretical assessment of the solubility and extractability of a range of chemicals (the ILSI proposed contaminant surrogates listed above) indicated that much higher levels of extraction should be possible if higher CO2 pressures are used and the CO2 is kept in the super-critical state until well after venting from the extruder. Modifications were made to the single screw extruder to investigate this.


59

9.6 Optimisation of HDPE decontamination with supercritical CO2

Whilst the initial work used Rigidex HD6007 XA HDPE material from BP Solvay, the work in this part of the project was undertaken on a different HDPE product, Stamylan HD9650 from DSM. These trials were also conducted at RAPRA.

Processing the Stamylan material proved difficult, the main problem being the propensity for vent flow. The material was prone to flow up, and freeze off in the vent port of the extruder. The Stamylan material appeared more prone to vent flow than the Rigidex material trialled earlier.

Considerable effort was directed at solving this problem through temperature profile manipulation, but ultimately it became necessary to run the extruder in a starve fed configuration. Feed material was metered into the throat of the extruder via a separate volumetric feeder, in this case a Brabender Flexi Wall 33 unit.

In a vented extruder the flow across the metering zones before and after the vent must be balanced to prevent accumulation in the vent area. The origin of the vent flow problem is unclear but it is likely that the problem is associated with incomplete melting of the material in the compression zone of the screw. The extruder screw used was probably incapable of dealing with high viscosity HDPE melts.

Material for these trials was contaminated according to the Fraunhofer protocol (see Chapter 8.2). The procedure was scaled such that a 25 l steel drum could be filled with 12.1 kg of contaminated feedstock. This allowed sufficient free space for mixing the contents during drum rolling.

Three extraction trials were run:

(i) without super-critical CO2,

(ii) with super-critical CO2 and atmospheric (non-pressurised) venting

(iii) with super-critical CO2 and pressurised venting.

The results are given in Table 15.

Even in the absence of CO2 the level of contaminant fell when the material was processed through the vented extruder, presumably as a result of heat and shear imparted by the process. Surprisingly, the effect was most pronounced for the non-volatile species methyl stearate and benzophenone.

Injecting super-critical CO2 to the extruder, with atmospheric extraction from the vent, promoted an increase in the extraction of the toluene and chlorobenzene species. These species are the most soluble in super-critical CO2 whilst phenyl cyclohexane and methyl stearate are the least soluble. The latter two show the least response to super-critical CO2, which may not be surprising.

The situation with pressurised extraction was more complex. The benefits anticipated were not observed. There was a decline in extraction level for all the species with the exception of benzophenone.

The melt extrudate from the pressurised extraction trial was heavily foamed, indicating the presence of dissolved carbon dioxide in the polymer. It is possible that the contaminants were carried through the process dissolved in the gas and therefore remained in the product at higher levels than expected.


60

Table 15: Results of the decontamination trials with Stamylan HD9650

Sample ID Concentration surrogates [ppm] (overall cleaning efficiency due to CO2)

Toluene Chlorobenzene Phenyl cyclohexane Benzophenone Methyl stearate

Input Concentration 458 613 702 800 815

Extraction in absence of super-critical CO2 384 (16.2%)

522 (14.8%)

652 (7.1%)

495 (38.1%)

632 (22.5%)

Extraction in the presence of super-critical CO2 with atmospheric (non pressurised) venting

198 (56.8%)

295 (51.9%)

571 (18.7%)

571 (28.6%)

661 (18.9%)

Extraction in the presence of super-critical CO2 with pressurised venting 280 (38.9%)

403 (34.3%)

638 (9.1%)

683 (14.6%)

638 (21.7%)

Development of a Food Grade HDPE Recycling Process 61

9.7 Processing trials to optimise PP decontamination

Initial trials (Section 9.5 and Section 9.6) concentrated on establishing the optimum conditions necessary to process HDPE resins. The aim was to establish a set of robust processing conditions under which it was likely that the CO2 would maintain supercritical conditions (31 °C and 73.1 bar) in the injection and mixing zones.

Because of problems with extruding HDPE on the RAPRA extruder it was subsequently decided to investigate the extraction process on a polypropylene (PP) material, using the same contamination procedure. Polypropylene would be easier to handle in the RAPRA extruder but should behave in a similar way to HDPE from a contamination extraction point of view. The polypropylene extraction trials were performed using a Borealis BB125MO copolymer resin.

The RAPRA extrusion system was modified to allow the extraction system to operate at supercritical pressures. This required the manufacture of a robust, certified, extraction housing which would be coupled to a down stream take-off system and which would allow pressure to be controlled and the contaminated species to be precipitated separately from the extrusion process.

The RAPRA trial rig used a 50 mm Bone Cravens Single screw extruder. The extruder screw had an L/D ratio of 34:1. The venting zone was located some 23D from the front of the feed zone.

The screw was derived from a 120 mm Falzoni extruder system, designed primarily for the recycling of soft PP scrap, where the vent was necessary for removal of volatiles. The overall compression ratio of the screw is 2.8:1.

To aid mixing of the super-critical CO2 the screw design incorporated two rows of mixing pins 2D downstream of the vent zone. The barrel of the extruder was tapped at several positions along its length to accommodate pressure transducers and poppet valve injectors for super-critical CO2 addition.

Gas was introduced into the process at a location 16D from the front of the feed zone, i.e. 7D upstream of the vent port.

A three strand-pelletising die was fitted to the extruder head and the output was cooled in a water bath prior to pelletisation.

A take-off pot was connected to the extruder vent zone by four M16 bolts. The pot was fitted with a flanged lid, which was secured by means of a "C" clamp arrangement. The take-off pot was fitted with both a calibrated pressure gauge and a pressure relief valve (100-150 bar range). Prior to use the apparatus was pressure tested and certified to 200 bar.

A flow diagram of the down stream extraction process after the extruder vent port is shown in Figure 23.

The volatile stream is directed from the extruder vent port along ¼ "Swagelock" tubing, to a knock-out vessel PV1. Valve V2 controls the flow rate in the system, whilst the regulating valve V3 allows the pressure within this vessel to be safely lowered to below supercritical pressures, typically around 10 bar.

Under these conditions volatiles should come out of the gas phase so they can be collected in the knock out vessel PV1.

The CO2 stream can exit the equipment by two routes. Route one passes the CO2 stream through a hydrocarbon trap and then to atmosphere. The second route vents the CO2 direct to atmosphere.

Carbon dioxide was drawn from a liquid take-off cylinder and pumped into the process via a ¼ "Williams piston pump" (model P250V250). The inlet of the pump was sub-cooled by attaching to a manifold block through which a refrigerant solution at ca. 4 °C was circulated. Sub-cooling was necessary to prevent the CO2 vaporising within the pump body. Pump output was controlled by the variables of piston stroke length and the stroke speed.

A poppet valve injector, flush fitting with the extruder barrel, was used to introduce the gas into the melt.


62

The carbon dioxide flow rate was measured by a Rheonik RHM015 mass flow meter situated in-line after the pumps. The device operates by the Coreolis principle and is capable of detecting flow rates in the range of 0.002-0.04 kg min-1. The mass flow meter was calibrated prior to experimentation.

to ambient

PRV1

V1

from extruder blow-off port

V2 V3

V4

V5

PV1 AT

V6

drain

to ambient

Figure 23: Flow diagram of the downstream extraction process after the extruder vent port

In order to measure the cleaning efficiencyof the process the material was contaminated according to the Fraunhofer protocol in a similar manner to the HDPE resin in the previous trials.

An experimental plan was drawn up to explore the relationship between super-critical CO2 flow rate, extruder output rate (screw speed) and extraction process (atmospheric pressure, vacuum and pressurised). This would give an insight on the effect that residence time and shear rate would have on the process; both factors having an influence on mass transfer and diffusion. The results of the decontamination trials are given in Table 16.

In the trials without super-critical CO2, best extraction was achieved using high screw speed and vacuum. As expected there was a decline in extraction with decreasing species volatility. Toluene offers the best result (39% removal) whilst benzophenone the least (14% removal). Methyl stearate did not seem to respond to any form of extraction. Indeed in most situations the concentration recorded in the extracted species was greater than the control.

In the trials using super-critical CO2 two trends were evident. The volatile substances (toluene and chlorobenzene) with greatest solubility in super-critical CO2 achieved the best extraction response when they were subjected to pressurised extraction (Runs 25/26; 31/32; 29/30; and 27/28).

The last run gave the best results for the more volatile species. In this case the material was simultaneously subjected to high levels of super-critical CO2 and a low throughput rate (long residence time). In this situation 70% of the toluene was extracted and 62% of the chlorobenzene.

For the non-volatile species (phenyl cyclohexane, benzophenone, and methyl stearate) the situation was reversed. In this instance pressurised extraction offered, on the whole, inferior extraction, when compared to atmospheric or vacuum venting. Phenyl cyclohexane and methyl stearate had the least solubility in CO2. It is likely that the poor uptake of the species in the CO2 limits extraction under pressure and these less volatile species are carried through to the outlet of the extruder.


63

Table 16: Results of the decontamination on Borealis BB125MO (best trial highlighted)

Contaminating level (ppm) Sample CO2 rate [a]

Output rate [b]

%CO2 Extraction mode

Toluene Chlorobenzene Phenyl cyclohexane Benzophenone Methyl stearate

Input - - - - 158 190 174 166 131

1/2 0 Low - Atmospheric 129 ±3 160 ±2 159 ±1 164 ±1 169 ±2

7/8 0 Low - Vacuum 115 ±10 144 ±13 137 ±1 147 ±3 166 ±1

3/4 0 High - Atmospheric 126 ±1 158 ±1 147 ±1 152 ±1 164 ±6

5/6 0 High - Vacuum 97 ±4 123 ±4 132 ±4 142 ±3 163 ±3

15/16 Low Low 30.6 Atmospheric 96±4 124 ±2 131 ±1 134 ±1 150 ±5

23/24 Low Low 20.1 Vacuum 90 ±0 116 ±1 131 ±1 138 ±2 155 ±1

25/26 Low Low 22.4 Pressurised 58 ±2 86 ±2 152 ±10 166 ±12 168 ±4

13/14 Low High 30.1 Atmospheric 67 ±2 91 ±2 123 ±1 132 ±1 155 ±2

21/22 Low High 16.8 Vacuum 72 ±1 96 ±3 129 ±1 137 ±3 147 ±1

31/32 Low High 15.8 Pressurised 62 ±2 89 ±3 130 ±4 139 ±3 155 ±3

9/10 High Low 47.7 Atmospheric 75 ±6 95 ±7 99 ±6 112 ±4 141 ±4

17/18 High Low 37.6 Vacuum 80 ±1 103 ±2 113 ±3 123 ±4 146 ±2

27/28 High Low 29.2 Pressurised 48 ±1 73 ±2 146 ±3 161 ±5 167 ±1

11/12 High High 29.2 Atmospheric 66 ±5 88 ±6 113 ±2 126 ±4 151 ±3

19/20 High High 24.3 Vacuum 65 ±5 88 ±6 118 ±5 128 ±8 145 ±1

29/30 High High 19.8 Pressurised 57 ±1 83 ±1 145 ±8 160 ±13 159 ±12 [a] high CO2 addition rate: approx. 4.8 kg h-1, low approx. 2.7 kg h-1, [b] high screw speed: 60rpm (approx. 17.5 kg h-1), low 35 rpm (approx. 12.8 kg h-1)


64

9.8 Decontamination of post-consumer HDPE flakes

The flake extraction trials were performed on sorted, recycled HDPE milk bottle flakes, which had previously gone through the SOREMA washing process.

The material was contaminated according the Fraunhofer contamination procedure (see Chapter 8.2).

The equipment arrangement was similar to that used for the polypropylene extraction (see above). The material proved difficult to process, and as with the Stamylan virgin grade, was prone to vent flow and erratic output rates. Because of the lack of reliability, it was decided to run the trial at a constant output rate of 50 rpm and vary the CO2 addition rate between two levels, in combination with the three extraction routes: atmospheric, vacuum and pressurised.

As with the earlier Stamylan HDPE trial it is clear that the process was not optimised for HDPE extrusion. The erratic extrusion output rate and the attendant effects on shear rate, residence time and CO2 addition rate made the results difficult to interpret with any degree of confidence.

There is a lot of variability in the data, particularly for pressurised extraction, which gave the least reliable process operation.

For the trial runs without CO2 extraction, the best extraction yields (approx. 20%) were obtained for the volatile species (toluene and chlorobenzene). As expected the non volatile species responded less favourably.

Extracting with super-critical CO2 improved the situation for all species but the variability of the results provided a less clear correlation between the benefits offered by the two alternative CO2 extraction routes.

Both the vacuum venting and pressurised extraction routes gave similar results. Approximately 60% of toluene and chlorobenzene were extracted by runs 11/12. This was the best result, and was achieved with vacuum venting.

The best extraction results for phenyl cyclohexane (37%), benzophenone (29%) and methyl stearate (16%) were all achieved under conditions of pressurised extraction in runs 13/14.


65

Table 17: Results of the decontamination of post-consumer HDPE flakes (best trial highlighted)

Contaminating level [ppm] Sample CO2 rate

Output rate [g min-1]

%CO2 Extraction mode


Benzophenone Methyl stearate

Input - - - - 123 ±5 165 ±9 143 ±6 152 ±8 134 ±5

1/2 0 279 - Atmospheric. 108 ±5 139 ±7 136 ±3 150 ±1 128 ±6

3/4 0 275 - Vacuum 99 ±1 130 ±2 132 ±5 147 ±4 115 ±10

5/6 NR (80%) 218 NR Atmospheric. 68 ±4 94 ±4 132 ±1 148 ±4 127 ±4

11/12 68 (80%) 136 50 Vacuum 47 ±0 67 ±1 119 ±2 139 ±3 116 ±1

13/14 60 (80%) 191 48 Pressurised 53 ±13 77 ±14 90 ±8 108 ±10 112 ±13

7/8 84 (100%) 188 45 Atmospheric. 57 ±3 80 ±5 125 ±6 142 ±6 119 ±5

9/10 96 (100%) 205 47 Vacuum 62 ±5 86 ±6 138 ±6 158 ±8 143 ±10

15/16/17 95 (100%) 143 66 Pressurised 51 ±7 73 ±10 110 ±8 136 ±14 127 ±20


66

9.9 Conclusions

The results of this Chapter show, that the supercritical CO2 extraction process developed during this project was able to remove contaminants.

Whilst trials with both PP and HDPE resulted in species extraction, PP was more successful, principally because the extrusion process was more reliable.

In the case of HDPE further work should be focused on the reproducibility of the decontamination results and reliability of the process in general.

It is likely that provision of a better melt seal in the process would allow for greater pressures to be developed, thus improving the extraction of the non volatile species by the pressurised route.

However as the earlier theoretical work showed, the pressures required to significantly improve the CO2 solubility of species such as methyl stearate are well beyond the super-critical point.

It will be difficult to establish a reliable melt seal - on either a twin or single screw extruder - without recourse to an isolating device such as a melt pump.

Of course it is still unclear if the high pressures necessary for more complete extraction would themselves cause issues with vent flow.

The extraction of polar components such as methyl stearate, which show limited interaction with CO2, could probably be enhanced by the use of a suitable co-solvent acting as a polar modifier. Such species could include methanol, ethanol or water and the modifier could be introduced into the process in combination with the CO2 stream. If high pressures prove unattainable, then this may become a viable route for improving the extraction performance of the process. However adding other co-solvents could complicate the solvent recovery part of the process.

The interesting feature of the process is that extraction of the volatile and non-volatile species are promoted by different regimes. The former respond to pressurised extraction with super-critical CO2, while the latter seemed to be hindered by this approach. The reason probably lies in the limited solubility of the species in carbon dioxide at the pressures encountered (30-50 bar, see Figure 11).

Another important point is the scaling up of the decontamination process. One has to bear in mind that ability to form an effective seal will vary with output rate and as such will also have an effect on scale up and economics.

Twin-screw extrusion invariably offers better mixing than a single screw process and hence the mass transfer of the system would be improved. If one accepts that a melt pump is necessary for a single screw process, then it can be safely assumed that it would be required for a twin-screw process, whose pressure generating capacity is reduced in comparison. The modular nature of a twin-screw extruder, equipped with a melt pump does potentially offer a greater applicability to the process than a single screw extruder.

In conclusion the results show that, in principle, the removal of post-consumer contaminants from HDPE is possible with a relatively simple, single step process and with a relatively short residence time.

However, the super-critical process investigated in this study was not sufficiently reliable for use as a commercial recycling process. Further investigations are necessary to make the process suitable for recycling applications.


10 EREMA super-clean recycling process

10.1 Description of EREMA process for post-consumer HDPE Flakes

The EREMA super-clean recycling process consists of two main process steps:

• pre-decontamination, where washed flakes are subjected to temperatures of about 90 °C and a vacuum of about 3-5 mbar (residence time about 30 min)

• decontamination, where the flakes are heated to about 120 °C with a vacuum of about 1-2 mbar (residence time about 45 min)

The decontamination step is followed immediately in the same unit by extrusion and melt filtration, where the material is re-extruded with degassing at 220-230 °C followed by melt filtration.

Both the SOREMA washing system and the EREMA super-clean recycling process are continuous operations. If these two processes are combined with downstream equipment for blending with virgin polymer and then production of bottles they can, in principle, be used for inline recycling of post-consumer HDPE bottles straight back into bottles.

In this study the EREMA super-clean process for HDPE flake was investigated at a throughput of 200-300 kg h-1.

The two step system described above was tested and also a single step system where the pre-decontamination step was eliminated.

The single step process was tried as a comparison to test the importance of the pre-decontamination step. If the pre-decontamination step could be eliminated it would reduce the capital and operating cost of the process.

Flow diagrams for the single-step and two-step systems are shown in Figure 24 and Figure 25.

The process operating conditions used in this study are given in Table 18.


Vacuum cutter

Rotating tools

Extruder

Double venting Screen changer

compactor/ drier

Extruder intake

conveyor screw

Vacuum slider

Figure 24: Process flow for the EREMA process for super-clean decontamination (one-step process)

3

Rotating tools

VACUREMA RGA T - VS

Crystallisation Drier KT

Vacuum pre - dryer

Rotating tools

Extruder

Screen changer

Conveying screw

Figure 25: Process flow for the EREMA process for super-clean decontamination (two-step process)


Table 18: Process parameters of the EREMA process used in this study for decontamination of post-consumer HDPE

Machine parameter Normal operation "one-step" (without artificial contamination)

Normal operation "two-step" (without artificial contamination)

Challenge Test "one-Step" (with artificial contamination)

Challenge Test "two-Step" (with artificial contamination)

Temperature KT [°C] / 87 / 85

Vacuum KT [mbar] / 3 - 6 / 3 - 5

Temperature reactor [°C]

130 120 120 120 – 125

Vacuum reactor [mbar]

0 - 3 1 - 2 0 - 2 0 - 3

Speed extruder [rpm] 160 140 160 160

Output [kg hr-1] 300 280 200 - 210 200

Melt temperature [°C] 255 226 251 249 – 252

Melt pressure [bar] 115 123 (123 – 151) 101 (85 – 130) 112 (82 – 128)

Screen [mesh] 150 150 150 150

Backflushing interval [min]

/ 20 / /


10.2 Challenge test of the EREMA process

The cleaning efficiency of the EREMA recycling process was measured by a challenge test.

The tests were carried out by purposely introducing 55 kg of contaminated post-consumer HDPE flake into the recycling process as a single ‘slug’ of material.

The contamination procedure is described in Chapter 8.2. This contaminated material was introduced into the super-clean recycling process without a washing step.

The process was challenged by introducing highly contaminated HDPE material as the full process feed over a period of about 15 min (55 kg of contaminated material added continuously at the full plant throughput of about 200 kg h-1 ).

The contamination procedure used represents a worst-case scenario in terms of both the amount of chemicals introduced and the contamination time. As a comparison, a single contaminated milk bottle will pass through the process in seconds.

Note that residence time, which is one of the major factors influencing the cleaning efficiency of the process, is the same if the process is running with contaminated material or not.

Because the process operates continuously, the cleaning efficiency had to be evaluated by taking timed samples. Therefore samples were drawn at regular periods through each trial. These samples were analysed for their residual contamination levels. The purification effect of the two processing steps was evaluated individually for each surrogate.

The EREMA super-clean recycling process can be operated in two modes:

(i) the discontinuous option where the extruded pellets are filled into big bags for re-use later to make bottles

(ii) the inline option where the recyclate is used immediately to make new HDPE bottles.

The cleaning efficiency of the super-clean recycling process in discontinuous mode was calculated using Equation 1 (Section 8.2).

The initial mass of surrogate compounds entering the recycling process was calculated using Equation 2:

Eq. 2: ionconcentratinputedcontaminatmasssurrogateinitial •= HDPEofmasstotal

Table 19: Initial surrogate concentrations in the contaminated material and cleaning efficiency after each recycling step

Concentration of surrogates in the contaminated input material and cleaning efficiencies compared to initial concentration


Methyl stearate

Benzophenone

Initial concentration for washing and super-clean recycling [ppm]

722 + 142 917 + 294 852 + 503 739 + 566 884 + 611

Super-clean process (1-step) 99.2% 99.1% 78.2% 33.7% 11.2%

Super-clean process (2-step) 99.8% 99.8% 94.5% 75.6% 38.1%

Washing and super-clean recycling (1-step) 99.7% 99.6% 71.0% >33.7% 34.5%

Washing and super-clean recycling (2-step) 99.9% 99.9% 95.0% >75.6% 54.3%


Cleaning efficiencies of more than 99% were measured for the highly volatile compounds such as toluene and chlorobenzene. Cleaning efficiencies were found to decrease with increasing molecular weight of the surrogates, due to their lower vapour pressure.

In the two-step process cleaning efficiencies of 93%, 76% and 38% were measured for phenyl cyclohexane, methyl stearate and benzophenone, respectively.

Note that these trials were conducted without washing the HDPE flake before super-clean recycling. The initial concentration of each surrogate in the feed material was in the range 700 ppm to 900 ppm.

In practice a washing step such as the SOREMA process described in Section 8 would normally be used to clean the flake before the super clean recycling process. This would increase the cleaning efficiency of the overall recycling process significantly, especially for the less volatile compounds.

The concentration/time relationships for the surrogates in Figure 26 show that the highest surrogate concentrations in the output material from the EREMA unit were measured between 30 and 60 min after first addition of the contaminated material.

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conc

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pm]

toluenechlorobenzenephenyl cyclohexanebenzophenonemethyl stearate

Figure 26: Concentrations in the output material from the EREMA two-step recycling process plotted against time after contamination (analysis of solvent extracts from the HDPE material)

For the most challenging surrogates (methyl stearate and benzophenone) concentrations of about 80 ppm were measured when 55 kg of homogeneously contaminated material at a concentration of 700 ppm to 900 ppm was introduced into the super-clean recycling process over a period of about 14 min.

It is extremely unlikely that such high concentrations would ever be encountered in the feed to the super-clean recycling process, especially when a hot washing process is used to clean the feed material. The scenario used in the tests may therefore be considered as a worst-case.


The individual contamination levels of each surrogate measured during the trials of the one-step and two-step processes are shown in Figure 27 to Figure 31.

In each case the concentration of the surrogate in output samples taken from the EREMA super-clean recycling unit is plotted against time after the start of addition of the 55Kg sample of contaminated material.

In each case the surrogate concentration was measured by headspace gas chromatography of the HDPE output material. Note that this analytical technique is different to the solvent extract gas chromatography method used for the results shown in Figure 26. However both techniques show similar concentration trends.

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Figure 27: Concentration of toluene in the output material after the one- and two-step processes

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Figure 28: Concentration of chlorobenzene in the output material after the one- and two-step processes


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Figure 29: Concentration of phenyl cyclohexane in the output material after the one- and two-step processes

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Figure 30: Concentration of benzophenone in the output material after the one and two-step processes


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Figure 31: Concentration of methyl stearate in the output material after one and two-step processes

The inline version of the super-clean recycling process allows the production of HDPE bottles that contain recyclate directly from washed post-consumer HDPE flakes.

For the inline process, the total amount of surrogates remaining after the recycling process was estimated by an integral equation, which takes account of time, surrogate concentration in the HDPE samples and HDPE mass flow. The procedure used is described in detail in the literature [44].

The maximum concentrations (cmax) of surrogate compounds measured in bottles made using the super-clean recycling process, when operated inline with a bottle blowing unit, are related not only to the cleaning efficiency of the recycling process but also to the dilution effect of the uncontaminated HDPE flakes which are mixed with the recycled material in the feed stream to the bottle extrusion and blowing unit.

Dilution with uncontaminated material means that the concentration of surrogate compounds measured in the bottles produced by the in-line process will be lower than in the product from the discontinuous super-clean recycling process, which is not diluted.

"Reducing factors" were therefore defined as described in Equation 3 in order to estimate the cleaning efficiency of the super clean recycling process when operated in inline mode:

Eq. 3: 100%ionconcentratinitial

ionconcentratmaximum1(inline)factorreducing •⎟⎟⎠

⎞⎜⎜⎝

⎛−=

Table 20 shows the estimated concentrations of the surrogates that could be achieved in HDPE bottles produced by the in-line option of the super-clean recycling process based on the results of the trials of the discontinuous process option.

For these estimates it was assumed that the finished bottles contained about 25% by weight of challenge test material. This is the same ratio as in the challenge test recorded in Table 19.


Table 20: Estimated maximum concentrations of the surrogates in the bottles that could be produced by the inline option of the super-clean recycling process and reduction factors (for initial concentrations see Table 19)

Maximum concentration of the surrogates in the HDPE material in [ppm] and reduction factors in comparison to the initial concentrations (Table 20)


Methyl stearate

Benzophenone

Super-clean process (1-step) 3 (99.6%) 4 (99.6%) 36 (95.8%) 78 (89.4%) 79 (91.1%)

Super-clean process (2-step) <1 (>99.9%) <1(>99.9%) 7 (99.2%) 44 (94.0%) 23 (97.4%)

10.3 Specific migration of surrogates from test bottles using challenge test material

Two batches of 4 Pint HDPE containers were manufactured by Nampak using samples of the challenge test material. See Section 10 for more detail. The following containers were shipped to Fraunhofer IVV for analysis:

• Test bottles manufactured from 100% one step super cleaned challenge test granules (contaminated material)

• Test bottles manufactured from 100% two step super cleaned challenge test granules (contaminated material)

The concentration of the surrogates measured in the bottle wall was below the analytical detection limit of about 0.02 ppm for the more volatile surrogate compounds and up to about 10 ppm for the less volatile surrogates.

The specific migration of the surrogate compounds into a food simulant (95% ethanol) was measured by immersing 1 dm2 of the bottle wall totally in 100ml of the the food simulant and storing for 10 days at 20 °C. The concentration of the surrogates in the migration solution was then measured.

The concentrations of the surrogates in the food simulant solution were found to be below 10 ppb.

Bottle manufacture and performance testing

After super-clean recycling with the EREMA process the material was used for bottle manufacturing by Nampak. The following material was shipped to Nampak:

• 1890 kg super cleaned granules (non-contaminated) processed by EREMA's one step process • 910 kg challenge test granules processed by EREMA's one step process • 1116 kg challenge test granules processed by EREMA's two step process

Test bottles of the super-clean recycled material were blow moulded at Nampak using a Uniloy 350 eight head unit. A 4 pint standard milk bottle (weight 42 g) was used as the test container.

In the first trial, bottles were blown from 100% super-cleaned granules without any adjustments to the operating parameters. The head temperature was 170 °C. However it was found necessary to increase the weight, as the bottles were 1.4 g below the weight of those produced with the virgin BP HDPE.

Unfortunately the granules delivered by EREMA had a slight green tinge and there was also a characteristic burnt odour, most probably coming from the PCR HDPE or from too high a temperature in the extruder during the super-clean recycling process.

Each of the three samples of super-clean recycled material was used to produce three batches of bottles containing 100%, 50% and 30% recyclate.


BP Rigidex 6007 XA HDPE was used as the virgin polymer for blending with the EREMA material. It was also used to produce a reference batch of 100% virgin bottles.

Bottles taken from the production trials were subjected to standard bottle testing procedures and successfully checked for:

• Weight • Neck and thread dimensions • Leak testing, bottles were filled and laid on their side.

Samples from each batch of bottles were analysed as described in section 11 below.


11 Analysis of HDPE materials

11.1 Analysis for post-consumer contaminants in raw materials

In order to conduct a risk assessment of closed loop recycling of HDPE milk bottles it is important to obtain good quality data on:

• the average concentration and nature of adventitious contaminants found in misused bottles

• the frequency of misuse of HDPE milk bottles

An important objective of this study was therefore to obtain statistically meaningful measurements of the nature and extent of post-consumer contaminants in post-consumer HDPE milk bottles recovered from the UK market.

In this study 600 conventionally recycled HDPE flakes from post-consumer milk bottles were screened for contaminants.

In addition, pellet samples were taken after super-clean recycling of the conventionally recycled HDPE material and analysed for residual contamination.

As a reference, 20 pellet samples of virgin HDPE were sampled by the bottle manufacturer over a period of several months and were also analysed.

A fast screening method for post-consumer compounds in HDPE samples was developed for the study in order to allow rapid analysis of the large number of samples required. The method chosen was headspace gas chromato-graphy. This reduces the sample preparation procedure to weighing and sealing the flakes into a headspace vial.

The following headspace GC/FID method was used:

• Sample preparation: 1.0 g of each HDPE sample was sealed into a 22 ml headspace vial

• Gas chromatograph: Perkin Elmer AutoSystem XL with flame ionising detector (FID)

• Column: DB 1 - 30 m - 0.25 mm i.d. - 0.25 µm film thickness,

• Temperature program: 50 °C (4 min), rate 20 °C min-1, 320 °C (15 min),

• Pressure: 50 kPa Helium, split: 10 ml min-1.

• Headspace autosampler: Perkin Elmer HS 40 XL,

• Oven temperature: 120 °C, needle temperature: 130 °C,

• Transfer line temperature: 140 °C,

• Equilibration time: 1 h, pressurisation time: 3 min,

• Injection time: 0.02 min,

• Withdrawal time: 3 min.

It was shown in earlier work[29,30] that the headspace GC method is able to measure substances up to molecular weights of approximately 350 g mol-1 with detection limits between about 0.02 ppm for highly volatile compounds and about 10 ppm for less volatile compounds.

The method developed for this study allows correlation of measured retention times of unknown analytes with their approximate molecular weights (Figure 32).


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rete

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Figure 32: Correlation between molecular weight and the retention of compounds using the headspace screening method

Molecular weight is a very important factor in risk assessment of potential contaminants because the migration rate into a food simulant depends on the initial concentration in the bottle wall and the molecular weight of the potential migrant[12,30].

105 standard substances were used for this correlation ranging from acetaldehyde as the smallest molecule (44 g mol-1) up to n-docosane (310 g mol-1). Using this correlation the molecular weight of unknown substances can be estimated from their retention times in the headspace screening test.

No change was made to the gas chromatographic system or the temperature program throughout the whole project duration of approximately three years. As a result the measured retention times vary by only approximately 0.1 min. This was proved with standard substances at regular intervals during the project.

An inherent characteristic of the post-consumer HDPE flake material was the high homogeneity of the 200 g samples taken for analysis. They may therefore be considered to be very representative of the bulk material.

Typically a 1.0 g aliquot taken from the 200g sample for analysis of post-consumer substances consists of 40 to 50 flakes. It is most unlikely that this analytical 1.0 g aliquot will contain two flakes from the same HDPE milk bottle. Consequently, there is high inhomogeneity between individual flakes in a small sample.

The advantage of this feature is that an overview of 40 to 50 bottles can be obtained by measurement of one analytical sample.

It is obvious that collected HDPE milk bottles are not homogeneously contaminated, therefore the amount of post-consumer substances and their concentrations in the recycled HDPE flakes will vary from sample to sample and from flake to flake.


The concentrations of suspicious compounds in the headspace gas chromatograms can be estimated by comparing the detector response of the headspace gas chromatograms to the concentrations found after solvent extraction in the same samples.

For this purpose the challenge test samples were analysed using both the headspace screening method and solvent extraction using dichloromethane as the extraction solvent.

The solvent extraction technique can be calibrated easily using standard solutions of the surrogates in dichloromethane.

There was a linear correlation between both sets of results.. The slope of the linear regression represents the sensitivity of the headspace screening method for compounds in the same retention time range. The results for phenyl cyclohexane and benzophenone are shown in Figure 33 and Figure 34.

y = 55,304xR2 = 0,8373

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Figure 33: Correlation between the detector response of headspace analysis and the concentration of phenyl cyclohexane in the HDPE samples when analysed by solvent extraction


y = 5,5027xR2 = 0,7804

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Figure 34: Correlation between the detector response of headspace analysis and the concentration of benzophenone in the HDPE samples when analysed by solvent extraction

Figure 35 shows a typical headspace gas chromatogram for virgin HDPE pellets. The major compounds detected are alkene oligomers of HDPE (e.g. decene (Rt = 7.5 min), dodecene (Rt = 9.6 min), tetradecene (Rt = 12.6 min)). The concentrations of decene and dodecene measured in the virgin samples were around 20 ppm.

Figure 36 shows a typical headspace gas chromatogram for washed post-consumer HDPE flake samples from the first washing trial The concentrations measured are similar to the those found in the virgin reference materials.

Figure 37 shows a typical headspace gas chromatogram of for a second sample of washed post-consumer HDPE flakes from a second washing trial that used a slightly different input material.

In this case the washed flake samples contain post-consumer compounds in a similar concentration range to the oligomers in the virgin samples. The following compounds were determined in nearly all of the flake samples tested from this batch: limonene (retention time Rt = 7.9 min), dodecane (Rt = 9.7 min), 2,4-di-tert-butylphenol (Rt = 12.0 min) and tetradecene (Rt = 12.7 min).

The flavour compound limonene probably comes from contamination of the material during collection of the HDPE bottles due to contact with soft drink bottles in the bale.

The saturated alkanes and 2,4-di-tert-butylphenol are generated by degradation during the recycling process. 2,4-di-tert-butylphenol is a degradation product of the additive Irgafos 168® (see below) which is commonly used as an antioxidant in polyolefins. The measured concentrations of these recycling-related compounds were similar to or lower than the oligomers found in virgin HDPE.

However additional substance peaks were found in some of the flake samples. Figure 38 and Figure 39 show chromatograms for washed HDPE flake samples which contain additional suspicious unknown compounds.in concentrations up to about 130 ppm.

For the HDPE flake material shown in Figure 39 the concentrations were estimated to be 130 ppm for the substance peak with retention time (Rt) of 7.5 min and 40 ppm for Rt = 9.4 min. Note that these concentrations are measured before super-clean recycling. If the cleaning efficiency of the super-clean recycling process is taken into account (e.g. 92.7% for the surrogate phenyl cyclohexane) then 130 ppm before super-clean recycling corresponds to about 10 ppm after super-clean recycling. 10ppm is similar to the concentration of oligomers detected in virgin HDPE.


When the analysis was repeated using a second sample from the same batch the additional substance peaks could not be detected. This is because the flake samples are not homogeneously contaminated. Only one or two individual flakes within the sample contain the unknown substance peaks. The origin of these substance peaks is likely to be either non-milk HDPE bottles or misused HDPE bottles.

Non-milk bottles collected from the handpicking process were investigated in order to investigate the origin of the unknown substance peaks. Most of the non-milk bottles contained higher concentrations of all the contaminant compounds and significantly higher concentrations of some individual compounds. The analyses show that in most cases the unknown compounds are fragrances that are typically used in shampoos or household cleaners.

In conclusion the unknown substance peaks identified during the screening of conventionally recycled HDPE flakes are most probably related to flakes from non-milk bottles.

Each sample of flakes analysed by headspace GC contains about 40 to 50 individual flakes. This means that during this project around 24,- 30,000 post-consumer milk bottles were screened for contamination. Only a small number of samples showed hints of additional compounds. Most of these are probably related to contamination with non-milk bottles rather than misuse.

retention time [min]

Figure 35: Typical headspace gas chromatogram of virgin pellets (reference sample)


Figure 36: Typical headspace gas chromatogram of post-consumer washed flake samples (washing trial 1)



Figure 37: Typical headspace gas chromatogram of post-consumer washed flake samples (washing trial 2)


Figure 38: Example of a headspace gas chromatogram for a washed flake sample with unknown compounds


Figure 39: Example of a headspace gas chromatogram for a washed flake sample with unknown compounds



Figure 40: Typical headspace gas chromatogram of super-clean recycled HDPE

11.2 Analysis for post-consumer contaminants in milk containers made with recyclate

A similar programme of analysis was conducted for the HDPE bottles containing recyclate that were produced for this project by Nampak.

The analytical method used was the same as for the flake and pellet materials (Chapter 11.1). This means that all gas chromatograms produced within this study are directly comparable.

Figure 41 shows a typical gas chromatogram for HDPE containers manufactured from 100% virgin material.

Figure 42 to Figure 44 show typical gas chromatograms for HDPE containers using 30%, 50% and 100% super-clean recyclate, respectively.

The gas chromatogram ‘fingerprints’ for all the test bottles are very similar. However, the concentrations of the compounds analysed decrease with increasing amount of recyclate.

This agrees with the results of the material analysis prior to bottle making where the super-clean recycled material was shown to contain smaller amounts of migration-relevant compounds than the virgin HDPE.

Note that the 1-step super-clean process of EREMA was used for production of the test containers.

From the results of the challenge tests it can be concluded that the amount of migration relevant compounds will decrease further for bottles manufactured from super-clean HDPE using the 2-step process.


Figure 41: Typical headspace gas chromatogram of milk container manufactured from 100% virgin HDPE (BP Rigidex 6000 XA)



Figure 42: Typical headspace gas chromatogram of milk container manufactured from 70% virgin HDPE (BP Rigidex 6000 XA) and 30% super-clean recycled HDPE (1-step process)


Figure 43: Typical headspace gas chromatogram of milk container manufactured from 50% virgin HDPE (BP Rigidex 6000 XA) and 50% super-clean recycled HDPE (1-step process)

Figure 44: Typical headspace gas chromatogram of milk container manufactured from 100% super-clean recycled HDPE (1-step process)

In order to compare the additive content and non-volatile compound contamination of the recycled HDPE material with virgin HDPE, the materials were also analysed by extraction with the solvent dichloromethane.

The extract samples were analysed by gas chromatography. The analytical method used is able to identify compounds with molecular weights between 150 g mol-1 and about 850 g mol-1.


The solvent extraction procedure is much more labour intensive than headspace screening so fewer samples could be analysed.

Two representative gas chromatograms of the dichloromethane extracts are shown in Figure 45 and Figure 46 for milk bottles containing 100% recyclate and milk bottles manufactured from virgin HDPE.

The signal pattern of HDPE oligomers in the solvent extracts was found to agree with the headspace screening results.

2,4-di-tert-butylphenol, a typical compound found in recyclates but not in virgin material was also identified in the solvent extraction samples from the recycled HDPE.

This shows that both analytical methods (headspace screening and extraction of compounds followed by GC) have overlapping detection areas so that no compounds could be missed from detection.

The concentrations of the compounds that were detected in both the virgin and recycled HDPE samples are in similar ranges. Two antioxidant additives were identified in the recycled HDPE samples: Tris(2,4-di-tert-butyl)phosphite (Irgafos 168® CAS-No. 31570-04-0) and Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Irganox 1076® , CAS-No. 2082-79-3). Both antioxidant additives were still present in their active form so that readditivation of the recyclate is probably unnecessary.

Figure 45: Typical gas chromatogram of the dichloromethane extracts of milk container manufactured from 100% super-clean recycled HDPE (1-step process)

Figure 46: Typical gas chromatogram of the dichloromethane extracts of milk container manufactured from virgin HDPE


11.3 Statistical evaluation of the analytical data

The principal component analysis (PCA) method was used to conduct a statistical evaluation of the analytical results.

This study used a software program that was developed at Fraunhofer IVV in cooperation with HKR Sensorsysteme, Munich, Germany. This program uses the raw data from the headspace gas chromatograms (ASCII output) as input for the PCA.

The quantitative information from headspace gas chromatograms is separated into 14 selected time slides on the retention time axis. These are integrated separately. Each headspace gas chromatogram is therefore reduced to 14 data points for analysis by PCA.

The software uses the Gaussian Decision Function for discrimination of the samples[68]. The ellipses around the different clusters are 95% borders with equal distance to the centre of the cluster (Mahalanobis Distance). As an artificial reference sample a virtual headspace gas chromatogram with no substance peaks was used.

The following retention time windows were defined (see faint cross-hatched areas in Figure 47):

#1: 0.00 to 6.00 min, #2. 6.00 to 7.40 min, #3: 7.40 to 7.80 min, #4: 7.8 to 8.10 min, #5: 8.10 to 9.75 min, #6: 9.75 to 11.20 min, #7: 11.20 to 11.40°min, #8: 11.40 to 11.80 min, #9: 11.80 to 12.20, #10: 12.20 to 12.60, #11: 12.60 to 13.00, #12: 13.00 to 13.80, #13: 13.80 to 14.20 and #14: 14.20 to 16.00.


Figure 47: Time slices used for evaluation of the HDPE samples (PCA approach):

red: typical headspace gas chromatogram of virgin HDPE

blue: typical headspace gas chromatogram of washed post-consumer HDPE flakes

The PCA results for the recyclate and virgin pellet samples analysed in this study are shown in Figure 48.


2. Dimension

1. Dimension

Figure 48: PCA analysis of post-consumer HDPE flakes and pellets samples in comparison to virgin HDPE:

• washed post-consumer HDPE flakes (First washing trial, 96 samples of 40 to 50 individual flakes)

washed post-consumer HDPE flakes (Second washing trial, 504 samples of 40 to 50 individual flakes)

super-clean recycled samples (17 pellet samples)

virgin HDPE (40 pellet samples)

"0" virtual gas chromatogram with no substance peaks.


The study analysed the headspace GC results from 600 conventionally washed flake samples, 17 super-clean recycled pellet samples and 20 virgin pellet samples. The washed samples came from two washing trials with two different input materials from 20 different lots of routine milk bottle production.

The analysis in Figure 48 shows that the virgin pellet samples were very similar. The PCA plot shows these samples clustered closely together which indicates similar concentrations of impurities within each pellet sample. The virgin material results are more closely clustered than any of the other groups of results which indicates the greatest homogeneity.

The super-clean recycled samples are closer to the zero point ("0" in Figure 48) than the virgin HDPE pellets. The zero point represents a virtual gas chromatogram with no substance peaks. The closer distance to the zero point indicates a lower concentration of polymer impurities in the super-clean pellets than in the virgin material.

The results for washed flakes are also quite closely clustered, which indicates that the washed flakes are also relatively homogenous in terms of their content of extractable compounds.

The flake samples from the two independent washing trials separated into two clusters. The reason is most probably not the washing efficiency itself but most likely the slightly different input quality used for both washing trials.

These results indicate the huge potential of Principle Component Analysis (PCA) for discriminating between polymer samples on the basis of their contamination level.

The sample, which shows the largest deviation from the cloud, is sample 34. The headspace chromatogram for this sample is shown in Figure 39. In this sample decene was measured in a significantly higher concentration (about 130 ppm) than in other flake samples. One other unknown substance peak was also found, in a concentration of about 40 ppm. Some of the flakes in this sample therefore possibly came from a bottle which had been misused.

The results of the PCA of the gas chromatogram results from HDPE test containers manufactured from different amounts of super-clean recycled HDPE are shown in Figure 49 below.


2. Dimension

1. Dimension

Figure 49: PCA analysis of bottles from post-consumer recycled HDPE (super-clean material) in comparison to HDPE pellets

For each bottle type 36 headspace gas chromatograms (from eight individual bottles each) were evaluated.

The results show that the clusters for 100% super-clean recycled pellets and the bottles manufactured from those pellets are closest to the zero point (virtual gas chromatogram without peaks). This indicates that super-clean recycled material contains the smallest amount of migration relevant compounds.

Results for bottles manufactured from 100% virgin pellets and the virgin pellets themselves are furthest from the zero point.

The cluster for the test bottles manufactured from 50% recyclate lies between the clusters for 100% virgin and 100% recyclate bottles.

The PCA method could therefore be used as a recognition test for bottles containing super-clean recyclate. It could also be used for semi-quantitative estimation of the recyclate amount used for bottle manufacturing.


11.4 Conclusions of the analytical work

600 conventionally recycled flake samples were analysed for post-consumer contamination levels within this study. Each sample contained 40 to 50 individual flakes so that the study effectively analysed 24-30,000 individual post-consumer milk bottles.

The most common contaminants in conventional recycled flake samples were unsaturated oligomers. These compounds were also found in virgin HDPE samples. In addition limonene, di-tert-butylphenol and saturated oligomers were found in the recycled material.

The concentrations of all the compounds found in the recycled material were similar to or lower than the ranges found in virgin HDPE.

Contamination with compounds not normally found in virgin HDPE compounds was rare and was in most cases related to non-milk bottles. Non-milk bottles were found to comprise less than 2.1% of the input material to the recycling process.

The maximum concentration found in one flake sample was 130 ppm, which corresponds to 5200 to 6500 ppm in the individual bottle on the assumption that the flake sample contained 40-50 flakes and that all the contamination came from a single flake within this sample.

The recycling process investigated in this study was based on an efficient sorting process, hot washing of the granulated bottles and in the case of the super-clean recycled samples, further deep cleaning of the flakes with high temperature and vacuum.

Although good results were obtained for bottles made by the single step EREMA process the two-step super-clean recycling process rather than the single step process should be used, due to its higher cleaning efficiency for less volatile compounds.

Handpicking after automatic sorting is recommended in order to decrease the amount of non-milk bottles in the feed to the recycling process.

The analytical results demonstrate clearly that the full super-clean recycling process including sorting, washing and two stage deep cleaning with vacuum and high temperature is suitable for the recycling of post-consumer HDPE bottles for direct food contact applications.

Future investigations should concentrate on migration testing of milk bottles containing up to 100% recyclate, shelf life testing and sensorial testing of the products.


12 Bottle filling trials and tests

12.1 Methodology

Filling trials are necessary to compare the mechanical strength, microbiological standard and sensory quality of milk bottles manufactured from the recycled polymer against bottles manufactured from virgin polymer and filled with fresh pasteurised milk.

For the filling trials 4-pint milk bottles were manufactured using different percentages of PCR polymer by Nampak Plastics in Newport Pagnell and supplied to Dairy Crest's Fenstanton site.

The following test bottles were used for the trials:

• A: Control, test bottles manufactured from 100% virgin HDPE (BP Rigidex 6007 XA)) • B: Test bottles manufactured from 30% super-cleaned granules (EREMA one-step process) / 70% virgin HDPE

(BP Rigidex 6007 XA) • C: Test bottles manufactured from 50% super-cleaned granules (EREMA one-step process) / 50% virgin HDPE

(BP Rigidex 6007 XA) • D: Test bottles manufactured from 100% super-cleaned granules (EREMA one-step process)

40 Bottles of each type, including the control samples were run through the complete system from de-bagging through conveying to bottle inversion (to remove any loose debris), filling (Fogg 24/9) and capping (induction heat seal). For this trial the labeller was not used because the bottles had to be left plain for the sensory analysis. Finally the bottles were hand packed into roll containers prior to sorting for analysis.

Microbiological assessment was carried out by Devan Laboratories Ltd., Shropshire.

Devan followed the standard Dairy Crest methodology for assessing new products, packaging or equipment. The method includes an aerobic plate count at 30 °C for Bacillus cereus, Enterobacteriaceae, Listeria, Staphylococcus aureus and Salmonella.

Testing was carried out in duplicate on day of production plus days 1, 5, 9, 10, 11, 12, 13 and 14. The milk was stored at 8 °C for the duration of the tests.

Sensory analysis was carried out by CCFRA in Chipping Campden to identify any burnt plastic characteristics in the milk.

A panel of eight trained assessors was asked to independently describe the odour of each sample as it was opened and when poured out and then to assess the taste of the milk. These assessments were carried out on two occasions – day 5 and day 7. The milk was stored at 2 °C to 5 °C. The samples were presented to the assessors under random three-digit codes.

12.2 Results of the filling trials

To be regarded as acceptable microbiologically results must show no detected pathogens (Listeria, S.aureus, Salmonella and B.cereus) at any time. The APC counts must be below 1.000.000 cfu per ml and Enterobacteriaceae must be below 10 cfu per ml.

The microbiological results gave no indication that there is any detrimental effect on the quality of the milk from the use of PCR material.


Samples labelled C did show very poor shelf life, this is most likely due to a "smash up" on the filler line, which occurred during the trial run. Therefore the microbiological data does not indicate any deterioration in the quality of the milk that is directly attributable to the use of PCR material.

Dairy Crest procedures require three satisfactory consecutive shelf life trials to be completed prior to accepting new packaging for use.

The results of the sensory tests are given in Table 21. The descriptors used by the panel were collated and inserted into Table 21, indicating the number of times each descriptor was used and the intensity found. To be regarded as acceptable organoleptically, results must show no off flavours or taints and no extraneous odours or taints.

The following scale was used to indicate the intensity of the attributes used: very slight, slight, moderate, strong, very strong.

Five days after packaging, the control sample was described on opening as having a moderate/strong milk and sour milk odour, with a very slight/slight plastic taint odour. Seven days after packaging, the milk odour intensity remained the same, the sour milk reduced to slight, and the plastic taint remained at the same intensity.

Regarding the odour in the cup, the intensity of fresh milk for the control sample decreased from strong to slight over the duration of the study. There was no presence of sour milk or plastic taint described.

Both samples B and C had similar intensity of fresh milk, whereas sample D appeared to decrease intensity. Sour milk was perceived as very slight in samples B and C at 5 days only; it was perceived as very slight in sample D at both 5 and 7 days after packaging.

Plastic taint was only perceived as slight in sample D at the 7th day assessment.

For the flavour all samples were described as being slightly sweet at 5 and 7 days after packaging and either slight or moderate for acid taste. Similarly, there was little change in intensity of fresh milk or sour milk flavour over the duration of the study. There was no mention of plastic taint in any of the samples.

Despite the strong burnt odour in the bottles (which dissipated with time) the sensory panel only detected a slight plastic taint in sample D. This suggests that test bottles made using PCR material, manufactured at correct processing temperatures would be indistinguishable from virgin bottles. However, the results showed that the plastic taint was detected in products during the odour assessments on opening. There was a slight increase in the intensity of plastic taint on all samples over time on opening. Sample D was the only sample that had a plastic taint perceived in the odour assessment in the cup at day 7. The increased concentration of plastic taint in the bottle may suggest that the taint was mainly in the headspace as the odour dissipated significantly on opening. Also, there were some slight changes in the intensity of the fresh milk and sour milk odour and flavour, which could be a natural change for milk over time. In general, there was very little change in the sensory characteristics of the milk over the duration of the study. Although these bottles had a strong distinctly burnt odour caused by reprocessing at incorrect temperatures it was agreed to go ahead with the filling trials.

The only concern was that the higher percentage of PCR added to the bottles gave them a distinct yellowish tint. This could affect consumer attitudes to the material. Further work would be needed to ensure there is no visible, mechanical or quality difference between bottles made using PCR and bottle made using virgin polymer.


Table 21: Free description sensory test on bottled milk

Criteria sample A (control) Sample B 30% recyclate Sample C 50% recyclate Sample D 100% recyclate

Odour on opening

5 d 7 d 5 d 7 d 5 d 7 d 5 d 7 d

Strength of fresh milk

3 (moderate) 3 (moderate) 2 (very slight/slight)

3 (slight) 2 (slight) 2 (slight) 2 (slight) 3 (moderate)

Sour milk 3 (moderate) 3 (slight) 3 (slight/moderate)

4 (moderate) 4 (very slight/slight)

3 (moderate) 3 (moderate) 3 (strong)

Plastic 4(very/slight/slight)

1 (slight) 2 (slight/moderate)

2 (moderate) 3 (slight) 1 (moderate) 2 (very slight) 2 (slight)

Odour in a cup

Strength of fresh milk

3 (strong) 5 (slight) 2 (very slight/slight)

5 (slight) 2 (slight) 5 (slight) 2 (slight) 5 (very slight)

Sour milk Nil Nil 1 (very slight) Nil 1 (very slight) Nil 1 (very slight) 1 (very slight)

Plastic Nil Nil Nil Nil Nil Nil Nil 1 (slight)

Flavour

Sweet 8 (slight) 8(slight/moderate)

7 (very slight/slight)

8 (slight) 8 (slight) 8 (slight) 7 (very slight/slight)

8 (slight/ moderate)

Acid 7 (slight) 5 (slight) 5 (slight) 5 (moderate) 7 (slight) 4 (moderate) 6 (slight) 4 (moderate)

Fresh Milk 7 (moderate/strong)

6 (moderate/ strong)

7 (slight/moderate)

6 (strong) 6 (slight/moderate)

6 (strong) 7 (moderate/strong)

6 (moderate/strong)

Sour Milk 1 (slight) Nil 2 (slight) Nil 1 (very slight) Nil 1 (very slight) 1 (slight)

Fatty /Creamy 5 (slight/moderate)

8 (moderate) 7 (very slight/slight)

7 (slight) 7 (slight/moderate)





13 Food law compliance tests

13.1 Migration tests

Food law compliance of the test bottles was evaluated by migration testing as part of this study.

Test bottles manufactured from the following materials were shipped to Fraunhofer for food law compliance testing:

• 100% virgin HDPE (BP Rigidex 6007 XA) • 100% super cleaned granules • 50% super cleaned granules / 50% virgin HDPE (BP Rigidex 6007 XA) • 30% super cleaned granules / 70% virgin HDPE (BP Rigidex 6007 XA)

Overall migration was tested on the bottles manufactured from recycled, but non-challenge test material.

The test conditions were 1 dm2 contact area with 100 ml 95% ethanol (total immersion) for 10 days at 20 °C.

The results of the overall migration tests are given in Table 22.

All containers show overall migration values far below the migration limit of 10 mg dm-2 and are therefore suitable for food contact.

Note that 95% ethanol was used in this study as the food stimulant. This can be considered as a worst-case food simulant for dairy products.

Table 22: Results of the overall migration tests on the tests bottles manufactured from different amounts of super-clean recycled HDPE

Bottle sample Overall migration into 95% ethanol [mg dm-2]

Individual values Mean value

100% virgin HDPE 00, 0.3, 0.2 0.2

100% super cleaned granules 0.1, 0.3, 0.4 0.3

50% super cleaned granules / 50% virgin HDPE 0.3, 0.3, 0.2 0.3

30% super cleaned granules / 70% virgin HDPE 0.0, 0.1, 0.0 0.0

The specific migration of the additives Irgafos 168®, Irganox 1076® and the degradation product 2,4-di-tert-butylphenol was also measured.

Test conditions were 1 dm2 contact area with 100 ml 95% ethanol (total immersion) for 10 days at 20 °C.

The test showed that specific migration into 95% ethanol for Irgafos 168®, Irganox 1076® and 2,4-di-tert-butylphenol was below the analytical detection limit of 10 µg dm-2 in each case.

Gas chromatographic screening of the migration solutions showed no other substance peaks at concentrations above 10 µg dm-2.


13.2 Sensory testing

Further sensory tests were carried out at Fraunhofer IVV in addition to those reported in Section 12.

For sensory testing the different bottles were filled with tap water and stored for 10 days at 8 °C.

The odour and taste of the water was evaluated by the sensory panel of the Fraunhofer IVV in comparison to the reference water stored in glass bottles. A panel of seven trained testers conducted the tests.

The rating scale used for the intensity of the odour or taste difference ranged from I = 0 (no perceptible change in smell or taste) to I = 4 (very noticeable change in smell or taste) as per DIN 10955.

Table 23: Results of the sensory tests (odour of water) on the test bottles manufactured from different amounts of super-clean recycled HDPE (Test conditions: bottle filled with tap water, 10 days at 8 °C)

Sample Description of odour Intensity

Bottles: 100% virgin HDPE No differences I = 0

Bottles: 100% super cleaned granules No differences I = 0

Bottles: 50% super cleaned granules / 50% virgin HDPE

No differences I = 0


No differences I = 0

Table 24: Results of the sensory tests (taste of water) on the test bottles manufactured from different amounts of super-clean recycled HDPE (Test conditions: bottle filled with tap water, 10 days at 8 °C)

Sample Description of taste Intensity

Bottles: 100% virgin HDPE Waxy, burnt, typical polyethylene I = 3.5

Bottles: 100% super cleaned granules Distinct polyethylene, sweet, dusty, bitter, post-taste slight waxy and polyethylene

I = 2.5


Slightly polyethylene, sweet, dusty I = 2.5


Waxy, burnt, distinct polyethylene I = 3.5

The odour test results show no differences in the odour of water stored in any of the HDPE bottles when compared to water stored in glass bottles.

The taste test results did note differences in the taste of water stored in HDPE bottles compared to water stored in glass bottles.

The taste panel recorded similar levels of off-taste for the bottles made from 100% virgin and recycled material. However the taste description of the bottle manufactured from 100% super-clean recycled HDPE had a more unpleasant character.


On the other hand, the intensity of the off-taste was lower for bottles made from 100% super-clean recycled material than for bottles made from 100% virgin polymer. This difference may correspond to the lower level of contaminant compounds found in the super-clean recycled HDPE pellets (see Chapter 11.2).

No differences were measured between bottles manufactured from 30% super-clean recycled HDPE and bottles made from 100% virgin polymer.

In conclusion, the HDPE bottles made from super-clean recycled polymer that were tested in this study seem to be suitable for milk storage. The sensorial impact appeared to be similar to HDPE containers manufactured from 100% virgin HDPE material.


14 Recyclate quality assurance

14.1 Quality assurance issues for post-consumer recyclate

Industrial production of Post Consumer Recycled (PCR) HDPE for food contact applications requires a quality assurance system in order to ensure consistent consumer safety.

Any super-clean recycling technology must be systematically checked and evaluated at least once by a challenge test.

Provided the process parameters are kept constant or are not changed so as to reduce cleaning performance, the same cleaning efficiency can be assumed for other equipment constructed in the same way.

A suitable analytical monitoring programme is recommended in order to ensure that the super-clean recycling process continues to operate correctly and that the input concentrations do not significantly exceed the contamination levels measured in the original challenge test study,.

The headspace analytical method developed in this study should be useful for such routine monitoring tests. Other analytical methods may also be suitable.

A data analysis methodology based on principal component analysis (PCA) was demonstrated in this study to be very useful for evaluation of the large amounts of raw data that are generated by routine analytical monitoring. PCA allows quick online and automated quality control.

As demonstrated in this report (Chapter 11.3) the PCA method may also be used as a recognition test for recyclates or for recyclate containing HDPE bottles.

Migration from a food/plastic package system is influenced by both kinetic (diffusion in plastic and food) and thermodynamic (equilibrium partitioning between plastic and food) factors.

It is useful to start migration evaluations using a worst case assumption where total mass transfer is estimated based on the concentration of a given migrant in the plastic (cP,0). If this calculation leads to a migration limit being exceeded, then the evaluation can be refined to take account of partitioning and diffusion as these are the crucial parameters for migration.

95% Ethanol seems to be a food simulant, which overestimates the migration in dairy product and can therefore be considered as the worst-case of migration.

The recyclate-containing bottles tested for this project had a burnt odour when unfilled. This was probably due to the high temperature conditions used during super-clean recycling. Water from stored in the bottles made from recyclate had no discernable odour.

The taste transfer into water from the bottles made with recyclate was in a similar range to that for bottles manufactured from 100% virgin HDPE.

To comply with food contact legislation sensory inertness of the recycle HDPE product for food contact articles must be assured. This can only be achieved by appropriate sensory testing at regular intervals.

Proposed worst case scenario test conditions for sensory testing are storage of the article in direct contact with an appropriate food simulant for 10 days at 20 °C. Water is suggested as the food contact medium. However, depending on the particular application, modified tests may be appropriate.


14.2 Standard testing procedures

Recycled HDPE will only be accepted for use in milk bottles if a suitable quality assurance system is in place to ensure compliance with food safety standards. One of the aims of this project was therefore to develop refined, optimised and simplified routine test methods.

A quality assurance system was established for post-consumer recycled HDPE based on the results from the material screening and the challenge tests.

Fraunhofer IVV developed Standard Testing Procedures (STPs) based on the lessons learned during the analytical work conducted for this project. These procedures are designed to be used by recycling companies, bottle manufacturers and dairy companies to ensure the quality of post-consumer recycled HDPE packaging material.

The results published in this report were measured using the same analytical methodology and parameters. Gas chromatographic fingerprints produced during routine testing can therefore be directly compared to the results of this study.

A list of the established Standard Testing Procedures during this project is given in Table 25. The complete Standard Testing Procedures are available from Fraunhofer IVV and WRAP.

Table 25: Standard Testing Procedures developed within this project (see Appendix)

STP 1.001 GC (FID) Method for Screening and Semi-quantification of Less Volatile Organic Compounds in PCR HDPE

STP 1.002 Headspace GC (FID) Method for Screening More Volatile Organic Compounds in PCR HDPE

STP 1.003 Multiple Headspace Extraction GC (FID) Method for Semi-quantification of More Volatile Organic Compounds in PCR HDPE

STP 2.001 Extraction of Polymer Additives or Impurities from PCR HDPE into Solvents and Sample Preparation for Gas Chromatographic Analysis

STP 3.001 Identification of Medium Volatile Compounds in PCR HDPE by GC/MS

STP 3.002 Identification of Volatile Compounds in PCR HDPE by Headspace GC/MS

14.3 Correlation between migration into dairy product and choice of food simulant

Current EU legislation still specifies that it is most appropriate to model milk products experimentally with water (simulant A or B) because the outer packaging contact phase of the emulsion is water. However milk has a heterogeneous liquid character. Large amounts of water (about 96%) are dispersed in small amounts (about 4%) of fatty substances.

The EU-Project "FOODMIGROSURE" (EU Contract NO. QLK1-CT2002-2390) investigated the migration into milk and milk products such as yoghurt or cream[ ]69 .

The results of this project indicate that the migration behaviour of 3.5% fat milk is more like olive oil.

The contact conditions used in this project (10 days at 40 °C using 95% ethanol, as food simulant for fatty foodstuff) are therefore more realistic than the water stimulant specified by the current legislation.

We understand that this issue will be considered in the next revision of the EU packaging legislation.


15 Process validation (re-run)

After the complete recycling process was developed, the full recycling process was re-run using about 2.5 tons of collected HDPE milk bottles in order to validate the results.

Apart from the EREMA technology, which used an optimised screw of the extruder and the two-step process, the same technology was used as for the first tests. The optimised parameters of the EREMA process are given in Table 18 (normal operation "two-step).

Nampak manufactured 4 pint standard milk bottles (42 g) with 30%, 70% and 100% recyclate From the re-run material.

This time there were no visual differences between bottles produced from 100% super-clean PCR HDPE when compared with bottles produced from 100% virgin material. The "burnt odour", which occurred in the first test run was significantly reduced and was barely detectable in any of the samples produced.

Samples from the re-run were also analysed using exactly the same headspace screening method that was used in the first process trials.

The results for the re-run show that the typical HDPE oligomeric pattern was significantly decreased with increasing amounts of super-clean recycled material in the product (Figure 50 to Figure 52).

These results indicate that HDPE milk bottles containing recyclate are likely to have better migration performance than HDPE containers made from 100% virgin material. In addition, di-tert-butylphenol was measured only in very small concentrations. These concentrations were close to the analytical detection limits.

The migration studies, sensory tests and filling trials were not repeated, because they gave successful results in the first run and the contaminant levels measured in the second run were lower.


Figure 50: Typical headspace gas chromatogram of milk containers produced from 100% super-clean recycled material from the validation re-run







16 Economic evaluation

An economic assessment was made of the full super-clean recycling process including the following steps:

• sorting (RTT technology)

• washing (Sorema technology)

• super-cleaning (EREMA technology, two step process)

The cost categories evaluated included:

• Investment costs

• Direct production costs: energy, operators, fresh water, waste water, cooling water etc.

• Overheads: overhead personnel costs (plant manager, secretary, analytical staff, etc), infra structure costs (power supply, water treatment, etc.)rental of floor space, depreciation, interest rate on finance (6% p.a. assumed)

The direct costs were calculated using the actual energy prices in UK from January 2005.

The economic evaluation does not include the cost of the baled input material to the sorting process because this cost can vary widely in response to supply and demand and external factors such as the price of oil.

The results are given in Table 26.

Costs per kg recycled HDPE were estimated as follows:

Direct production cost €0.41/Kg

Overheads, personnel and infrastructure €0.20/Kg

Total €0.61/Kg

The overall production cost of €0.61/Kg (excluding cost of baled input material) compares to an average price for virgin milk bottle grade HDPE of around €1.2 per Kg


Table 26: Economic assessment of the full super-clean recycling process for HDPE

Type Sorting (RTT technology) Washing (Sorema technology) Super-cleaning (EREMA)

Material Nominal output [kg h-1] 2200 1100 1000

Working time [h d-1] 24 24 24

Working time [d y-1] 350 350 225

Efficiency [%] 85 85 90

Investment Equipment [€] 1.000.000 3.000.000 2.000.000

Freight [€] 10.000 10.000 15.000

Commissioning [€] 50.000 50.000 50.000

Fixed Costs Depreciation time [y] 5 5 8

Depreciation/year [€] 200.000 600.000 250.000

Interests cost p.a. (rate 6%) [€] 63.600 183.600 123.900

Costs of floor space [€] 90.000 60.000 28.800

Variable Costs Operator costs, energy etc. [€ h-1] 62.26 166.82 38.79

Total production costs [€ kg-1] 0.05 0.26 0.10


17 Environmental impact assessment

An environmental impact assessment of the full super-clean recycling process was conducted using Life Cycle Assessment (LCA) methodology.

Possible environmental impacts of the system using this recycling process ("recycling system") were compared with the impacts of a "reference system".

The reference system was defined as the deposition of the post consumer waste in a landfill site ("standard" waste management system).

For each system an estimated LCA was conducted. The LCA took into account the principles of EN ISO 14040[ ]70 . However the study did not aim to conform fully to ISO14040, because impacts were estimated, not calculated precisely and because no critical review was conducted.

17.1 System boundaries

All relevant process steps were taken into account - from collection of post consumer waste up to the production of recycled HDPE for re-use or final disposal respectively.

For the recycling scenario the following relevant processes were examined:

• collection • sorting • washing • super clean recycling (EREMA 2-step process)

For the reference scenario "landfill disposal":

• collection • final disposal

Transportation and energy supply were considered in both cases.

In the case of the reference scenario the environmental impact of producing additional virgin HDPE to replace the material sent to landfill was taken into account (expanded reference scenario).

The processes upstream (production of virgin HDPE for first use, blow moulding of milk bottles, filling, distribution, use) and downstream (blow moulding from recyclate in the recycling system or from virgin material in the reference system) are identical for both scenarios.

An important fact in this context is that the high specification of the recycled HDPE material from the WRAP process enables the production of new milk bottles from 100% recycled material with the same weight as bottles from virgin material.

The upstream and downstream processes are excluded from the environmental impact assessment because they are the same for both scenarios. So only a part of the whole milk bottle life cycle, namely the waste management phase, is studied here. This is an important point, which must be taken into account when analysing and evaluating the results.


Life Cycle Inventory

For all processes including power supply and transportation detailed input/output descriptions were used including:

• amount and specification of input material, products and waste • amount of electrical power, water, emission into air and water • sorting and preparation losses, etc.

Input data was collated from the following sources:

• Interim WRAP Report on this project[ ]71 • Cost sheets[ ]72 • Charts / Data from SOREMA[ ]73 • Charts / Data from EREMA[ ]74

Not all of the data from these sources was fully compatible. Additional assumptions and estimates were made in order to complete the collection and recycling process descriptions for the purpose of the environmental impact evaluation.

The environmental impact parameters for landfill disposal, transportation, energy supply and HDPE production were estimated from published data[ , , , , , ]75 76 77 78 79 80 .

The flow chart for the full super-clean bottle-to-bottle recycling process is given in Figure 53.

The reference scenario "landfill" is described in Figure 54.


Collection/Transportation(truck 40 km)

Super Clean RecyclingEREMA

Washing Sorema

Sorting RTT

Recycling system

5000 kg Input material (bales)including 1000 kg milk bottles:20% Post consumer milk bottles20% other HDPE bottles50% kg PET bottles6% kg other plastic bottles4% kg residue

500 kg recycledHDPE for Re-use

19 kg diesel fuel emissions

4250 kg waste

emissions

emissions

1200 MJ from gas165 kWh electricity

2000 l water

50 kWh electricity

150 kWh electricity500 l water Landfill site

200 kg waste

5000 kg bales

750 kg milk bottles,sorted

550 kg milk bottles,washed

50 kg waste

2000 l waste water

Figure 53: Flow chart for the full super-clean HDPE recycling scenario (simplified)


Collection/Transportation(truck 40 km)

Landfill site

Reference system, expanded with HDPE production

emissions

emissions24,5 kg diesel fuel

5000 kg Input material(1000 kg milk bottles):20% Post consumer milk bottles20% other HDPE bottles50% kg PET bottles6% kg other plastic bottles4% kg residue

HDPE Production

500 kg primaryHDPE

emissions

resources

Figure 54: Flow chart for expanded landfill disposal reference scenario (simplified)

17.2 Environmental impact assessment

17.2.1 Impact categories

The results of the LCA study are presented in the following environmental impact categories:

• primary energy equivalent (in MJ/1000 kg used milk bottles) • global warming potential (in kg CO2-Equivalents/1000 kg used milk bottles) • acidification potential (in mol SO2/1000 kg used milk bottles) • eutrophication potential (in mol PO4/1000 kg used milk bottles) • amount of waste (in kg/1000 kg used milk bottles)

17.2.2 Classification and characterization

The environmental impacts in each category were calculated for both scenarios. The LCI results were converted into so-called indicator results for each impact category using standard characterization factors.

17.2.3 Sensitivity analysis

As a sensitivity check the more important process parameters were identified and additional calculations were carried out for each scenario using modified parameters in order to test the sensitivity of the results to variations in the parameters that were assumed.

The following additional scenarios were calculated with modified parameters:


Recycling system:

• Scenario "Recycling 75%" • Scenario "Recycling 75%+50 kWh": Need of electricity for sorting 100 kWh (instead of 50 kWh) per 750 kg

sorted milk bottle output • Scenario "Recycling 75%+100 km": Transport distance for recycled HDPE granulate to user: 100 km (instead of 0

km) • Scenario "Recycling 75%+200 km": Additional transport distance for collected waste: 100 km (instead of 0 km),

and transport distance for recycled HDPE granulate to user: 100 km (instead of 0 km) • Scenario "Recycling 60%": Recycling efficiency 60% (instead of 75%)

Reference system:

• "Landfill+HDPE 2003" • "Landfill+HDPE 1999": Data for virgin HDPE production in the reference system according APME 1999 (instead of

APME 2003)

17.3 LCA results

17.3.1 Primary energy equivalent PE

Figure 55 compares the environmental impacts estimated for each scenario in terms of primary energy equivalent.

In all cases the primary energy consumption of the recycling scenario is 25,000-30,000 MJ /1000 kg milk less than for the reference scenario. This difference is equivalent to approximately 300-400 kg virgin HDPE. The recycling efficiency (the amount of recycled HDPE used in each bottle) has the greatest influence on the result.

Primary Energy Equivalent, PE [MJ/1000 kg milk bottles]

05000

1000015000200002500030000350004000045000

Rec

yclin

g 75

%

Rec

yclin

g 75

%+5

0kW

h

Rec

yclin

g 75

%+1

00km

Rec

yclin

g 75

%+2

00km

Land

fill+

HD

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Figure 55: Primary energy Equivalent PE for the waste management scenarios

17.3.2 Global Warming Potential GWP

The difference in global warming potential between the recycling and reference scenarios is about 500 kg CO2 per 1000 kg milk bottles (Figure 56). This difference is equivalent to approximately 250-300 kg virgin HDPE.


Global Warming Potential, GWP [kg CO2/1000 kg milk bottles]

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Figure 56: Global Warming Potential GWP for the waste management scenarios

17.3.3 Eutrophication Potential EP

Transportation distances have a strong influence on the eutrophication potential environmental impact in the case of the recycling scenarios. This is because road transport is a major cause of eutrophication (smog formation) (Figure 57). The choice of APME data for virgin HDPE production have a strong influence on the result for the reference system.

The difference between the recycling and reference scenarios is about 1-6 mol PO4 per 1000 kg milk bottles. A similar impact is caused by the production of 250-400 kg virgin HDPE.

Eutrophication Potential, EP [Mol PO4/1000 kg milk bottles]

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Figure 57: Eutrophication Potential EP for the waste management scenarios


17.3.4 Acidification Potential AP

For AP, too, the most important effect on the difference between recycling and reference system comes from the choice of HDPE-data used in the reference system. The differences shown in Figure 58 (30-160 mol SO2 /1000 kg milk bottles) are equivalent to the impacts caused by the production of 350-450 kg virgin HDPE.

Acidification Potential, AP [Mol SO2/1000 kg milk bottles]

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Figure 58: Acidification Potential AP for the waste management scenarios

17.3.5 Municipal Solid Waste MSW

Dependent on recycling efficiency the amount of waste for disposal is 400-500 kg /1000 kg milk bottles less than in the reference system (Figure 59).

Municipal Solid Waste on landfill site, MSW, landfill [kg/1000 kg milk bottles]

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Figure 59: Municipal Solid Waste MSW for the waste management scenarios


17.3.6 Use of Water

In addition to the impact categories listed in section 17.2.1, the use of water by the different scenarios is compared in Figure 60 .

The two virgin HDPE production data sets used give very different figures for water consumption. The more recent APME data indicates no significant difference in water consumption between the two groups of disposal scenarios.

Use of Water [m³/1000 kg milk bottles]

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Figure 60: Use of water for the waste management scenarios

17.4 Limitations and Conclusions

This analysis assumes that the HDPE recyclate produced by the super-clean process can be used as a direct replacement for virgin HDPE polymer. If the recyclate can only be used in lower grade applications then the conclusions of the LCA will not be valid.

This analysis also assesses the environmental impact of the two scenarios in a limited range of impact categories and for a limited range of process conditions. No LCA can assess all possible impacts on the environment or all possible process conditions.

Taking these factors into account the following conclusions can be made:

• HDPE recycling via the developed bottle to bottle recycling process causes less impact on the environment than landfill disposal in the impact categories examined for this project.

• The impacts avoided by bottle to bottle recycling of 1000 kg milk bottles rather than landfill disposal are equivalent to the impacts caused by the production of about 300 kg virgin HDPE material.

• With the exception of the eutrophication potential category, transportation distance and energy consumption for the recycling processes are of minor importance for the results.

• Higher losses in the upstream sorting and preparation processes reduce the positive effects on the environment. For good positive a high recycling efficiency must be realized.

Within this study only the HDPE milk bottles were evaluated in comparison to the alternative scenario of "landfill disposal". However the bales, which are the input in the recycling process, contain approximately 50% PET bottles. For the 50% PET bottles it was assumed that these bottles are still going into landfill. If these PET bottles are also recycled (which in practice they would be because PET is easier to recycle) then the positive effect of the LCA would significantly increase. The reason for not taking PET bottles into account was that the LCA needs completely different boundaries.


18 Overall Project Conclusions

This project successfully developed an industrial scale process for sorting and recycling of post-consumer HDPE milk bottles from kerbside and bring scheme collections in the United Kingdom. The process contains the following key steps:

• Sorting of natural HDPE milk bottles from the feedstock material • Grinding and washing of the bottles • Super-clean decontamination

The sorting process was optimised within the project and its sorting efficiency was evaluated. A sorting efficiency of more than 99% of natural HDPE milk bottles was demonstrated, provided natural non-milk bottles were sorted out by hand-picking before the washing process.

If handpicking is not used the output fraction of natural HDPE milk bottles is 97.9%.

The ILSI recommended input specification (food grade polymer purity >99%) is achieved if handpicking is used. However the discussion about "food grade material" is still in progress.

The scenario without handpicking might be viable if the definition of polymer purity is in the range of 97%. For the time being manual post-sorting using handpicking is recommended until EU legislation is clarified.

The washing process was optimised and challenged at industrial scale using purposely contaminated HDPE flakes. The input concentrations of the surrogates were in the range 740 ppm to 920 ppm. Such input concentrations are very high and never reached in reality for the expected input materials. The cleaning efficiencies measured for the washing process alone were in the range 50% to 60% for volatile solvents. For non-volatile components the cleaning efficiencies were lower, for example, 9% and 27% for phenyl cyclohexane and benzophenone, respectively.

The EREMA super-clean recycling process, which is already used for PET decontamination, was successfully adapted to treat HDPE milk bottle flakes. The cleaning efficiency was also measured using a challenge test. Input concentrations were in the range 740 ppm to 920 ppm and the flakes were introduced in a worst-case scenario without step washing. The cleaning efficiencies measured for the super-clean recycling process were better than 99% for the solvents (toluene, chlorobenzene), approximately 95%, 76% and 38% for phenyl cyclohexane, methyl stearate and benzophenone, respectively.

Taking the washing process into account, the cleaning efficiencies for the overall process rise to 99.9% for toluene and chlorobenzene, 95%, 76% and 54% for phenyl cyclohexane, methyl stearate and benzophenone, respectively. As the cleaning efficiency most probably depends on the input concentration it can be assumed that the cleaning efficiency will be higher at real contamination levels, which will be much lower than the levels used in the challenge tests.

In order to measure actual contamination levels in post-consumer HDPE, about 600 conventional recycled flake samples, collected and sorted in the United Kingdom were analysed for post-consumer contaminants. Each sample consists of 40 to 50 individual flakes so that the number of individual containers tested was in the range 24000 to 30000 post-consumer milk bottles.

Predominant contaminants in hot-washed flake samples were unsaturated oligomers. These compounds were also found in virgin HDPE pellet samples used for milk bottle production.

The flavour compound limonene, the degradation product of antioxidant additives di-tert-butylphenol and small amounts of saturated oligomers were found in higher concentrations in the post-consumer samples than in the virgin HDPE. However, the overall concentrations of all contaminants in post-consumer recycled samples were similar to or lower than in virgin HDPE.


Contamination with other HDPE compounds not normally found associated with HDPE was rare and was in most cases related to the normal first use of HDPE bottles for non-milk applications such as shampoo. These type of bottles comprised <2.1% of the input to the recycling process.

The maximum concentration of an unknown compound found in one sample of 1 g (40-50 flakes) was estimated at 130 ppm, which corresponds to a contamination of 5200 to 6500 ppm in the individual bottle whioch contributed the contaminated flake to the sample.

Both the output material from the recycling process and HDPE milk bottles made with up to 100% recyclate were tested for their suitability for food contact.

Both the output material and the milk bottles made with recyclate were similar or better than virgin HDPE pellets from a migration point of view. This is because polymerisation side products like oligomers were also removed during the decontamination process.

In order to prove the performance of the bottles made with recyclate, migration tests, filling trials and sensory tests were successfully performed with 4 pint milk bottles with recyclate contents of 30%, 70% and 100%. All tests showed no significant differences between recyclate containing bottles (up to 100%) and reference bottles manufactured from virgin HDPE.

Research work was also done during the project on super-critical CO2 decontamination. The results show that in principle the decontamination of post-consumer contaminants is possible with a relatively simple, single step process and with a relatively short residence time. However the super-critical process investigated in this study was not sufficiently robust for use at industrial scale. Further investigations are necessary to make the process suitable for recycling applications.

An economic evaluation of the super-clean recycling process was conducted.

The direct production costs of the super-clean recycling process were calculated to be 0.41 € per kg recycled HDPE, excluding the cost of the baled input bottles.

Assuming overhead personal costs (plant manager, secretary, analytical staff, etc) and infra structure costs (power supply, water treatment, etc.) of 0.20 € kg-1 the overall production costs were calculated to be 0.61 € kg-1 excluding the cost of baled input bottles. This compares to a typical cost for virgin milk bottle grade HDPE of around €1.2/Kg.

The environmental impact assessment for the super-clean recycling process was positive. All impact categories analysed had a lower environmental impact than the alternative of landfill.

In conclusion the output material from the super-clean recycling process can be reused for direct food contact applications for HDPE milk bottles up to 100% recyclate content.

The process developed during this project has been demonstrated to work at tonnage scale and should be economically viable. It is a better environmental option for treatment of post-use HDPE bottles than landfill.


Appendix 1 – Project Consortium

Table 27 gives an overview of the project consortium and the role of the companies in the project. Detailed information about the companies is given below.

Table 27: Project consortium and the role of the participants in the project

Participant Role in the Project

Delleve Plastics, Stratford upon Avon, UK Source of baled bottles from several UK suppliers

RTT Systemtechnik, Zittau, Germany Sorting of bottles

Sorema/Previero, Alzate Brianza, Italy Granulation and washing of sorted bottles

EREMA, Linz, Austria Super-clean recycling

RAPRA Technology, Shawbury, UK Super-clean recycling, polymer characterisation

Nampak Plastics Limited, Milton Keynes, UK Bottle blow moulding , mechanical properties of the recyclate containing bottles

Dairy Crest Limited, Telford, UK Filling, product shelf life testing

Food Standards Agency, London, UK Member of the project Board providing advice on EU and UK legislative requirements and compliance

Fraunhofer Institute for Process Engineering and Packaging, IVV, Freising, Germany

Analytical screening of post-consumer HDPE, determination of process cleaning efficiency, challenge testing and compliance testing and evaluation

Delleve Plastics

Delleve Plastics, founded in 1964 and incorporated 1972, is UK’s only large user of domestic HDPE for bottle making, finished product, recycling and manufacturing. Source material is from a range of UK suppliers, such as local authorities and waste management companies. Delleve Plastics is involved in development of industry standards for recycled materials. Within the project Delleve Plastics supplied post-consumer HDPE bottles from a range of UK suppliers. Further information: http://delleve.co.uk.

RTT Systemtechnik

RTT Systemtechnik, founded in 1990 after the German Unification, is an equipment manufacturing company, which provides sorting solutions to the waste and recycling industry with a turnover of approx. 3.5 Mio. €. RTT also provides the European automotive industry with customised solutions in the field of special machinery and equipments. In 1995, RTT introduced the first UniSort® sorting module for post-consumer plastic bottles or other materials. Right from the start, RTT have invested substantial resources in developing sorting technology. Based on a high selective NIR UniSort® Sensor RTT is able to detect recyclable materials with 128 wavelengths per measure point (the standard NIR technology


uses a maximum of twelve wavelengths). The UniSort® was used in the project for optimising the sorting process. Further information: http://www.unisort.com.

Sorema/Previero

Sorema/Previero merged in 1992 from the two companies, which were founded 1976 and 1922, respectively. Sorema/Previero is the world leader in the supply of plastic washing equipment and bottle washing equipment with a turnover of approx. 20 Mio. €. Sorema/Previero has been involved in at least two PET bottle-to-bottle recycling projects and a food grade HDPE recycling project. Sorema / Previero has a permanent pilot scale test facility on site, which was used in the project for the optimisation of granulation and washing. Further information: http://www.sorema.it.

EREMA

EREMA, founded in 1983, is one of the world leaders in supply of plastics recycling equipment. EREMA has been involved in several of PET bottle to bottle recycling projects and also in HDPE recycling processes. In 2000 EREMA received their first no objection letter for their PET bottle-to-bottle recycling process from the American Food and Drug Administration (FDA)[ ]81 . Currently EREMA is supplying their “VacuREMA” super cleaning systems to a number of industrial use production companies in Europe and the Americas. EREMA has extensive testing facilities including their “VacuREMA” super cleaning systems, which was used in the project for decontamination. Further information: http://www.erema.at

RAPRA

RAPRA Technology Limited, formally known as the Rubber and Plastics Research Association of Great Britain, is the largest consultancy in the UK specialising in rubber and plastics materials, processes and products. It offers a comprehensive range of services to tackle both technical and commercial problems. In 2002 RAPRA had a turnover. Of £6.7 Mio. GBP. RAPRA has developed a decontamination process based on super-critical carbon dioxide (CO2), which will be further developed and optimised for the decontamination of post-consumer HDPE. Further information: http://www.rapra.net

Nampak

Nampak is one of the world leaders in supply of extrusion blow moulded plastic liquid containers. In UK Nampak is the leading supplier of HDPE milk containers with a turnover approx. £100 Mio. GBP (UK only). The global turnover is approx. 1.2 billion GBP. Nampak used a “production facility” Uniloy 4 head machine for manufacturing recyclate containing HDPE bottles. They also have test equipment for mechanical properties of test bottles. Further information: http://nampak.com.

Dairy Crest

Dairy Crest Group plc is the largest broadly based dairy food company in the UK, with leading brands Clover, Cathedral City, Davidstow, Frijj and, through a joint venture, the Yoplait brands. Dairy Crest operates in six business areas: spreads, cheese, liquid products, fresh dairy products (a JV with Yoplait), household and ingredients. Turnover in 2002 was £1.182 Mio. GBP. The company serves both the retail grocery trade and major food manufacturers and has leading positions in all sectors within the dairy market. Within the project Dairy Crest filled the recyclate containing bottles and conducted shelf life and sensory tests. Further information: http://www.dairycrest.co.uk

Fraunhofer IVV

The Fraunhofer-Institute for Process Engineering and Packaging (IVV) is one of 57 institutes of the Fraunhofer Association, which is the largest organisation for applied research and development in Europe. Fraunhofer IVV consists


of several scientific departments and groups one of them being the “Product Safety and Analysis” Department. Main research topic of this department is the interaction between foodstuffs and packaging materials. Further Information: http://www.ivv.fraunhofer.de.

The head of the migration group, Dr. Franz, is active as national or personal expert to the EU Commission (DG Sanco, DG Research) and the German BfR (former BgVV) as well as member of CEN TC 194/SC1 (General chemical methods of test for food contact materials) and its working groups (on overall migration, specific migration, plastics additives, migration modelling and other) as well as the German DIN mirror committee. He is also involved in topics of the Packaging Task Force Committee of the International Life Science Institute (ILSI). The group has successfully participated in and coordinated several European projects within the 3rd, 4th and 5th Framework programs of the European Commission.

The main areas of research and other activities, which are relevant to the project, have been for many years:

• Overall and specific migration testing of food contact materials (FCM) • Development of quick predictive and alternative evaluation methods for compliance testing of FCM • Theoretical approach to the diffusion-controlled migration of packaging components into foodstuffs • Development of highly selective and sensitive analytical methods for trace components in foods and packaging

materials including post-consumer recyclates • Membership in several national working groups dealing with legislative as well as analytical aspects of FCM


Appendix 2 – Addresses of Participants

Delleve Plastics Limited Unit 6, Goldicote Business Park Stratford upon Avon, CV37 7NB, UK Mr. Lee Clayton (general manager) Tel. 0044 (0) 1789 740 102 email: [email protected]

RTT Systemtechnik GmbH Hirschfelder Ring 9 02763 Zittau, Germany Mr. Ernie Beker (authorized representative) Tel. 0049 (0) 6104 665 761 email: [email protected]

Sorema/Previro Via dei Platani 11 22040 Alzate Brianza, Como, Italy Mr. Dario Previero (general manager) Tel. 0039 (0) 31 619 224 email: [email protected]

EREMA GmbH Freindorf Unterfeldstraße 3 4052 Ansfelden/Linz, Austria Mr. Manfred Hackl (management assistent) Tel. 0043 (0) 732 3190 144 email: [email protected]

RAPRA Technology Shawbury Shrewsbury, Shropshire SY4 4NR, UK Mr. John Sidwell (principal consultant polymer analysis)Tel 0044 (0) 193 9250 383 email: [email protected]

Nampak Plastic Europe Limited Woburn Sands Milton Keynes, Bucks, MK17 8SE, UK Mr. Jon Sweet (marketing director) Tel. 0044 (0) 1494 870 418 email: [email protected] Mr. Tony Hancock (consultant) Tel. 0044 (0) 208 952 960 20 email: [email protected]

Dairy Crest Limited Technical Development Centre Crudington Telfort, Shopshire, TF6 6HY, UK, Ms. Lesley Moody (senior packaging technologist) Tel. 0044 (0) 1952 653 069 email: [email protected]

Food Standards Agency Aviation House 125 Kingsway London WC2B 6NH Mr. Richard Sinclair Tel. 0044 (0) 2072 768 514 email: [email protected]

Fraunhofer-Institute for Process Engineering and Packaging (IVV) Giggenhauser Straße 35 85354 Freising, Germany Dr. Frank Welle (business field manager “Product Safety”) Tel. 0049 (0) 8161 491 724 email: [email protected] Dr. Roland Franz (head of migration group) Tel. 0049 (0) 8161 491 746 email: [email protected]


Appendix 3 - Literature

Publications within the Project

F. Welle, Post-consumer contamination in HDPE milk bottles and design of a bottle –to- bottle recycling process, oral presentation on 3rd International Symposium on Food Packaging - Ensuring the Safety and Quality of Foods, 18. November 2004, Barcelona, Spain

F. Welle, Post-consumer contamination in HDPE milk bottles and design of a bottle-to-bottle recycling process Food Additives and Contaminants, 2005, 22(10), 999-1011

Cited Literature [ ]1 Appendix IV at www.cfsan.fda.gov/~dms/opa2pmnc.html#aiv

[ ]2 WHO Food Additives Series 40: "Safety evaluation of certain food additives and contaminants", prepared by the 49th Meeting of JECFA, Annex 5: I.C. Munro and R. Kroes: Application of a threshold of toxicological concern in the safety evaluation of certain flavouring substances, pp. 499-532, WHO, Geneva 1998

[ ]3 WHO Technical Reports Series 884: "Evaluation of certain food additives and contaminants", prepared as 49th Report of JECFA, pp. 3-6, WHO, Geneva 1999

[ ]4 Commission of the European Communities: Council directive 89/109/EEC of 21 December 1988 on the approximation of the laws of the member states relating to materials and articles intended to come into food contact with foodstuffs, Official Journal o the European Communities, No. L 40/38, 1988 f

f

[ ]5 Commission of the European Communities: Commission directive 2002/72/EC of 6 August 2002 relating to plastic materials and articles intended to come into contact with foodstuffs, Official Journal o the European Communities, No. L 220/18-58. 2002

[ ]6 L. Baner, J. Brandsch, R. Franz, O. G. Piringer, The application of a predictive migration model for evaluation the compliance of plastic materials with European food regulations, Food Additives and Contaminants, 1996, 13, 587-601

[ ]7 EU Project QLK1-CT2002-2390 "Modelling migration from plastics into foodstuffs as a novel and cost efficient tool for estimation of consumer exposure from food contact material", coordinated by Fraunhofer IVV, internet: http://www.foodmigrosure.org

[ ]8 Final report of EU funded AIR project AIR2-CT93-1014, "Programme to establish criteria to ensure the quality and safety of recycled and re-used plastics for food packaging", Brussels, December 1997

[ ]9 Final report of EU project FAIR-CT98-4318, "Programme on the Recyclability of Food Packaging Materials with Respect to Food Safety Considerations - Polyethylene Terephthalate (PET), Paper & Board and Plastics Covered by Functional Barriers", Brussels, 2003

[ ]10 K. Fritsch, F. Welle, Polyethylene terephthalate (PET) for Packaging, Plast Europe, 2002, 92(10), 40-41

[ ]11 Recycled Plastics in Food Packaging, US Food and Drug Administration, Centre for Food Safety & Applied Nutrition, Office of Premarket Approval; internet: http://vm.cfsan.fda.gov/~dms/opa-recy.html

[ ]12 R. Franz, F. Welle, "Recycling Packaging Materials", in Novel Food Packaging Techniques, R. Ahvenainen (Editor), Chapter 23, Woodhead Publishing Cambridge, 2003, 497-518

[ ]13 Final report of EU funded AIR project AIR2-CT93-1014, Programme to establish criteria to ensure the quality and safety of recycled and re-used plastics for food packaging, Brussels, December 1997


t

[ ]14 Final report of EU project FAIR CT98-4318 "Programme on the Recyclability of Food Packaging Materials with Respect to Food Safety Considerations - Polyethylene Terephthalate (PET), Paper & Board and Plastics Covered by Functional Barriers", Brussels, 2003

[ ]15 Final Project workshop of EU project FAIR CT98-4318, organised by the European Commission Joint Research Centre, Food Products Unit, and held on 10.-11. February 2002 in Varese, Italy. A comprehensive download package of the presentations can be found at http://cpf.jrc.it/webpack/projects.htm

[ ]16 R. Franz, F. Bayer, F. Welle, Guidance and Criteria for Safe Recycling of Post consumer Polyethylene Terephthalate (PET) into new Food Packaging Applications, EU Report, 21155, ISBN 92-894-6776-2, Luxembourg, October 2004.

[ ]17 D. Dainelli, A. Feigenbaum, Guidelines for functional barrier applications, oral presentation at the workshop given under Lit. [15]. Internet download: http://cpf.jrc.it/webpack/projects.htm

[ ]18 Points to consider for the use of recycled plastics in food packaging: Chemistry considerations, US Food and Drug Administration, Centre for Food Safety and Applied Nutrition (HFF-410), Washington, May 1992

[ ]19 Guidelines for the safe use of recycled plastics for food packaging applications, Plastics Recycling Task Force document, National Food Processors Association, The Society of the Plastic Industry, Inc. March 1995

[ ]20 T.H. Begley, T. P. McNeal, J. E. Biles, K. E. Paquette, Evaluating the potential for recycling all PET bottles into new food packaging, Food Additives and Contaminants, 2002, 19, Supplement, 135-143

[ ]21 Recycling of Plastics for Food Contact Use, Guidelines prepared under the responsibility of the International Life Sciences Institute (ILSI), European Packaging Material Task Force, 83 Avenue E. Mounier, Brussels, Belgium, May 1998

[ ]22 Use of mechanical recycled plastic made from polyethylene terephthalate (PET) for the manufacture of articles coming in contact with food, Bundesinstitut für Risikobewertung BfR, Berlin, October 2000. Also implemented into BfR Recommendation XVII

[ ]23 O. -G. Piringer, A. L. Baner (Editors), Plastic Packaging Materials for Food - Barrier Function, Mass Transport, Quality Assurance and Legislation, 2000, WILEY-VCH, Weinheim, New York

[ ]24 F. L. Bayer, Polyethylene terephthalate (PET) recycling for food contact applications: Testing, safety and technologies -A global perspective, Food Additives and Con aminants, 2002, 19, Supplement, 111-134

[ ]25 T.H. Begley, T. P. McNeal, J. E. Biles, K. E. Paquette, Evaluating the potential for recycling all PET bottles into new food packaging, Food Additives and Contaminants, 2002, 19, Supplement, 135-143

[ ]26 D. Pierce, D. King, G. Sadler, Analysis of contaminants in recycled polyethylene terephthalate by thermal extraction gas chromatography - mass spectrometry, 208th American Chemical Society National Meeting. Washington DC, August 25, 1994, 458-471

[ ]27 G. D. Sadler, Recycled PET for food contact: Current status of research required for regulatory review, Proceedings: Society of Plastic Engineering Regional Technical Conference, Schaumburg, IL, USA, November 1995, 181-191

[ ]28 R. Franz, Programme on the recyclability of food-packaging materials with respect to food safety considerations - Polyethylene terephthalate (PET), paper & board and plastics covered by functional barriers, Food Additives and Contaminants, 2002, 19, Supplement, 93-100

[ ]29 F. Welle, R. Franz, Typical contamination levels and analytical recognition of post-consumer PET recyclates, Congress Proceedings: EU-Project Workshop "Recyclability", Varese, February 11, 2002

[ ]30 R. Franz, M. Mauer, F. Welle, European survey on post-consumer poly (ethylene terephthalate) materials to determine contamination levels and maximum consumer exposure from food packages made from recycled PET, Food Additives and Contaminants, 2004, 21(3), 265-286

[ ]31 B. H. Allen, B. A. Blakistone, Assessing reclamation processes for plastics recycling, 208th American Chemical Society National Meeting. Washington DC, August 25, 1994, 418-434

[ ]32 F. L. Bayer, D. V. Myers, M. J. Gage, Consideration of poly (ethylene terephthalate) recycling for food use, 208th American Chemical Society National Meeting. Washington DC, August 25, 1994, 152-160

[ ]33 M. Huber, R. Franz, Identification of migratable substances in recycled high density polyethylene collected from household waste, Journal of High Resolution Chromatography, 1997, 29, 427-430


[ ]34 M. Huber, R. Franz, Studies on contamination of post-consumer plastics from controlled resources for recycling into food packaging applications, Deutsche Lebensmittel-Rundschau, 1997, 93(10), 328-331

35 Euro positive list can be downloaded at: http://europa.eu.int/comm/food/fs/sfp/food_contact/synoptic_doc_en.pdf#search=’synoptic document’

[ ]36 M. Ezrin, G. Lavinge, Identification and semiquantificative analysis of organic compounds in recycled dairy grade HDPE, Congress Proceedings ANTEC'95, 1995, 3715-3719

[ ]37 M. Ezrin, G. Lavinge, Analysis of organic compounds in recycled dairy grade HDPE by thermal desorption gas chromatography/mass spectrometry, Congress Proceedings SPE Plastics Recycling Division Annual Recycling Conference, Akron, 1995, 1-7

[ ]38 M. Ezrin, E. D. Wyatt, G. Lavigne, A. Gardon, Quantification and control of contaminants in recycled HDPE, Congress Proceedings ANTEC'94, San Francisco, 1994, 2922-2926

[ ]39 V. Komolprasert, A. Lawson, Effects of aqueous-based washing on removal of hydrocarbons from recycled polyethylene terephthalate (PETE), Congress Proceedings ANTEC'94, San Francisco, 1994, 2906-2909

[ ]40 V. Komolprasert, A. Lawson, Residual contaminants in recycled poly (ethylene terephthalate) - Effects of washing and drying, 208th American Chemical Society National Meeting. Washington DC, 1994, 435-444

[ ]41 V. Komolprasert, A. R. Lawson, A. Gregor, Removal of contaminants from RPET by extrusion remelting, Packaging, Technology and Engineering, 1996, September, 25-31

[ ]42 R. Franz, M. Huber, F. Welle, Recycling of post-consumer poly (ethylene terephthalate) for direct food contact application - a feasibility study using a simplified challenge test, Deutsche Lebensmittel-Rundschau, 1998, 94(9), 303-308

[ ]43 R. Franz, F. Welle, Post-consumer poly (ethylene terephthalate) for direct food contact application - final proof of food law compliance, Deutsche Lebensmittel-Rundschau, 1999, 95(10), 424-427

[ ]44 R. Franz, F. Welle, Post-consumer poly (ethylene terephthalate) for direct food contact application - Challenge-test of an inline recycling process, Food Additives and Contaminants, 2002, 19(5), 502-511

[ ]45 F. L. Bayer, The threshold of regulation and its application to indirect food additive contaminants in recycled plastics, Food Additives and Contaminants, 1997, 14, 661-670

[ ]46 Preparation of Food Contact Notifications and Food Additive Petitions for Food Contact Substances: Chemistry Recommendations, US Food and Drug Administration, Centre for Food Safety and Applied Nutrition, Washington, April 2002

[ ]47 V. Komolprasert, A. R. Lawson, Considerations for the reuse of poly (ethylene terephthalate) bottles in food packaging: migration study, Journal o Agricultural and Food Chemistry, 1997, 45, 444-448 f[ ]48 T. H. Begley, H. C. Hollifield, Recycled polymers in food packaging: migration considerations, Food Technology, 1993, 109-112

[ ]49 R. Franz, M. Huber, O. G. Piringer, Presentation and experimental verification of a physico-mathematical model describing the migration across functional barrier layers into foodstuffs, Food Additives and Contaminants, 1997, 14(6-7), 627-640

[ ]50 O. Piringer, K. Hinrichs, Evaluation of Migration Models, Final Report of the EU-project contract SMT-CT98-7513, Brussels 2001

[ ]51 E. D. W. Klingelhofer, M. Ezrin, R. A. Weiss, Diffusion of hazardous contaminants in recycled high density polyethylene, Congress Proceedings ANTEC'95, 1995, 3710-3714

[ ]52 F. Devlieghere, B. De. Meuleanaer, J. Demyttenaere and A. Huygherbaert, Evaluation of recycled HDPE milk bottles for food applications, Food Additives and Contaminants, 1998, 15(3), 336-345

[ ]53 G. M. Spinks, S. Ayrton, Degradation of dairy-grade high density polyethylene during multiple pass extrusion, Materials Forum, 1992, 16, 137-140


l

f

f

r

[ ]54 E. G. El'darov, V. M. Gol'dberg and G. E. Zaikov, The kinetics of the chemical changes during extrusion of polyethylene, Polymer Degradation and Stabi ity, 1986, 16, 291-296.

[ ]55 A. Boldizar, A. Jansson, T. Gevert, K. Möller, Simulated recycling of post-consumer high density polyethylene material, Polymer Degradation and Stability, 2000, 68, 317-319

[ ]56 K. Takahashi, Performance of 25% recycled content HDPE blow moulded bottles, Congress Proceedings ANTEC'96, 1996, 3460-3463

[ ]57 C. Pattanakul, S. Selke, C. Lai, J. Miltz, Properties of recycled high desity polyethylene from milk bottles, Journal oApplied Polymer Science, 1991, 43(11), 2147-2150

[ ]58 R. Franz, M. Huber, O. -G. Piringer, Testing and evaluation of recycled plastics for food packaging use - possible migration through a functional barrier, Food Additives and Contaminants, 1994, 11(4), 479-496

[ ]59 R. Franz, M. Huber, O. -G. Piringer, A. P. Damant, S. M. Jickells, L. Castle, Study of functional barrier properties of multilayer recycled poly (ethylene terephthalate) bottles for soft drinks, Journal o Agricultural and Food Chemistry, 1996, 44(3), 892-897

[ ]60 O. Piringer, M. Huber, R. Franz, T. H. Begley, T. P. McNeal, Migration from food packaging containing a functional barrier: mathematical and experimental evaluation, Journal of Agricultu al and Food Chemistry, 1998, 46(4), 1532-1538

[ ]61 Personal Communication to Fraunhofer IVV from Green Cycle, Armagh, Northern Ireland, internet http://www.greencycle.info

[ ]62 Kalra et al., J. Chem. Eng. Data, 1978, 23(4), 317-321

[ ]63 Ng and Robinson, J. Chem. Eng. Data 1978, 23(4), 325-327

[ ]64 Walther and Maurer, Berichte Bunsenges. Phys. Chem. 1992, 8, 981-988

[ ]65 Inomata et al., Fluid Phase Equilibria 1989, 46, 41-52

[66] Fink and Hershey, Ind. Eng. Chem. Res. 1990, 29, 295-306

[ ]67 Tarantino et al., J. Chem. Eng. Data 1994, 39, 158-160

[ ]68 G. Niebling, Strategien der Signalverarbeitung in der Chemosensorik – Konventionelle Methoden und neuronale Netze, PhD Thesis, Technical University of Munich, 1996, page 14 ff.

[ ]69 R. Franz, Migration modelling from food contact plastics into foodstuffs as a new tool for consumer exposure estimation, Food Additives and Contaminants, in press

[ ]70 DIN EN ISO 14040, 14041, 14042 and 14043

[ ]71 Development of food grade HDPE recycling process (5. Interim Report), Fraunhofer IVV, published by WRAP

[ ]72 Process costs HDPE recycling process, email from Fraunhofer IVV from March 23, 2005

[ ]73 Emails from March 3 and 8, 2005 from Fraunhofer IVV and EREMA

[ ]74 Email from March 3, 2005 from Fraunhofer IVV

[ ]75 Actual data base for LCA calculation with the software "Heraklit"

[ ]76 Data from GEMIS 4.2, http://www.oeko.de/service/gemis/

[ ]77 Data from ProBas, http://www.probas.umweltbundesamt.de/php/index.php

[ ]78 Eco-Profile of High Density Polyethylene, APME 2003

[ ]79 WRAP: Plastic bottle recycling in the UK, March 2002

[ ]80 Heyde, M., Kremer, M.: Recycling and Recovery of Plastics from Packaging in Domestic Waste, LCA Documents Vol. 5, ecomed publishers 1999

[ ]81 No objection letter CTS 66652 for the EREMA process for PET bottle-to-bottle recycling with direct food contact from 17.11.2000 and amendments from 07.06.2001 and 10.02.2003


Appendix 4 - Standard Test Procedures for food grade HDPE

This section contains copies of the standard test procedures for food grade HDPE that were developed for this project by Fraunhofer IVV.


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