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27.5.10, Pesaro, Italy

Andreas Zillessen, Harald Schwab

Quality Assesment

Fraunhofer Institute for Wood Research

Wilhelm-Klauditz-Institut WKI

Braunschweig

Limiting the Formaldehyde Emission of Wood Based Panels – Developments in Adhesives Technologies

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Content

Introduction

Process Engineering

Scavengers

Isocyanates

Biogenic Adhesives

Other Possibilities

Summary

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Introduction- Formaldehyde Emission-

Toxic

Respiratory Irritation

Carcinogenic (IARC Group 1)

Marutzky 2008

E1 : Blue Angle: CARB (Phase II):0.1 ppm 0.05 ppm (EN 717-1) 0.05-0.13 ppm (ASTM E 1333)

Formaldehyde:

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Introduction- Adhesives for Wood Based Panels - ~ 90% of the WBP are

produced using UF resins

+Availability of raw materials

+High reactivity

+Low Costs !

‒ Formaldehyde emission

‒ Moisture resistance

O

CNH2 NH2

CH2

O

+

Marutzky 2007

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Process Engineering

Raw materials

Flake drying

Hot press conditions

Density profile

Various parameters of the production process of wood based panels influence the formaldehyde emission

+Easy to implement

‒ May slow down production process or increase the costs

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Process Engineering

Process Parameter CH2O-

Emission

density of the top layer

moisture content before pressing

hot pressing temperature

hot pressing time

For some parameters the magnitude of the influence strongly depends on the F/U ratio.

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Scavengers

Scavengers can be added to the resin or the dried flakes

Formaldehyde scavengers react with the free formaldehyde in the panel

Amine containing chemicals or polyphenols like tannins can be used as scavengers

NH2 NH2

O

NN

N

N

N

N

N

NH2

NH2 NH2

NH

n

NH3

+Simple method to reduce formaldehyde emission

‒ Higher costs

‒ May influence other properties

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Isocyanates- as alternative adhesives - Adhesives based on MDI and its oligomers can be used as resins for

the production of flake and fibre boards.

During the curing process the MDI reacts with water to form a polymeric network.

PMDI reacts with several types of surfaces.

CO

NNC

O

NCO

n

n = 0-9

PMDI

+No formaldehyde

+Moisture resistance

+Improved mechanical properties

‒ Higher costs

‒ Poor processability

‒ Toxicity of monomers

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PMDI can also be used as an additive for UF resins

The addition of PMDI increases the mechanical properties

PMDI also act as an accelerator for UF resins

UF resins with lower F/U ratios can be used in combination with PMDI

Mixtures of PMDI and UF resins have to be processed quickly due to their low stability

Isocyanates- as additives -

+Lower cost compared to PMDI

+Improved mechanical properties

‒ Higher costs compared to UF resins

‒ Poor processability

‒ Toxicity of monomers

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Proteins

Tanins

Lignins

Starch and other Polysaccharides

Biogenic Adhesives- Overview -

Different bio-based adhesives can be used for the production of wood based panels

+Bio based raw materials

‒ Variations in the quality of the raw materials

‒ Limited availability

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Biogenic Adhesives- Proteins -

Proteins have been used as wood adhesives since historical times.

Proteins from animals (casein, albumin) or plants (wheat, soya, corn) can be used as source for raw materials.

Protein dispersion can be used as adhesives purely or in combination with crosslinking agents like formaldehyde.

Most promising are mixtures of proteins with PF resins.

+Good adhesion to wood

‒ Low moisture resistance

‒ High alkali content

‒ Competition with food production

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Tanins are polyphenolic compounds which can be extracted from wood (e.g. quebracho) or bark (e.g. mimosa).

Tanins can be used as formaldehyde based resins or with other reactants like hexamine.

Tanins also undergo an autocondensation reaction which can be catalyst by different hardeners.

Tanins also can be used as additive to conventional UF resins to reduce the formaldehyde emission.

Biogenic Adhesives- Tanins -

+Reactivity

+Versatility

‒ High costs

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Lignins are polyphenols and one of the major components of wood and accrue during the paper production process.

Lignins show a very low reactivity, e.g. towards formaldehyde, and cannot be used in industrial production processes so far

Lignins can be used in combination with other adhesives, e.g. UF,PMDI or PF.

Biogenic Adhesives- Lignins -

+Low Costs

+Availability

‒ Low reactivity

‒ Strong variations in quality

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Starch and other polysaccharides can directly be used as wood adhesives.

Mostly starch is used as modifier for other adhesives, eg. UF or PF.

Polysaccharide can also be used as raw material for the production of chemicals for other adhesives systems, eg. furanic resins.

Biogenic Adhesives- Starch -

+Availability

‒ Low moisture resistance

‒ Competition with food production

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Other Possibilities

Alternative adhesives

PF resins

MUF resins

PVAc

Substitution of Formaldehyde

Other aldehydes

Hexamine

Coatings

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Summary

There are several ways to further decrease the formaldehyde emission of wood based panels produced with UF resins.

Further decrease in the formaldehyde content

Use of scavengers

Combinations of UF resins with PMDI or other adhesives

If the requirements concerning the formaldehyde emission increase further other adhesives system become more interesting

PMDI

Combinations of biogenic adhesives and conventional resins

Thank you

For your

Attention