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PACKAGING (VAI 226)Week-6: Plastic for Food Packaging

INTRODUCTION

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PLASTIC: BASIC POLYMER

1. Polyolefins

‣LDPE, LLDPE, HDPE, PP

2. Copolymers of ethylene

‣EVA, EVOH

3. Substituted olefins

‣PS, PVC, PVdC

4. Polyesters

‣PET

5. Polyamide (PA)

6. Regenerated cellulose film

PLASTICS: POLYOLEFINS

•Polyethylene (PE)

‣HDPE 940 kg/m3

‣LDPE < 915-939 kg/m3

•Polypropylene (PP)

‣900 kg/m3

•Permeability of polyolefins

‣High O2-permeability

‣Low H2O-permeability

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GAS BARRIER PROPERTIES

PLASTIC:POLYOLEFINS

•LDPE (Low Density PolyEthylene)

‣Excellent chemical resistance (e.g. acids)

‣Sensitive to oils and greases

‣Films and bottles (squeeze-bottles)

Suitable for deep-freezing applications

‣Excellent sealing properties: often used as outer layer of multi-layer films

‣50% cristallinity

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PLASTIC:POLYOLEFINS

• HDPE (High Density PolyEthylene)

‣90% cristallinity (more linear structure than LDPE)

=> higher density than LDPE

=> less transparant than LDPE

‣Better resistance to oils and greases than LDPE

‣Films and bottles

•LLDPE (Low Linear Density Polyethylene)

‣Similar molecular structure to HDPE

‣More crystalline than LDPE (more linear)

PLASTIC:POLYOLEFINS

•PP

‣Good resistance to greases and chemicals

‣High temperature stability

Suitable for heat processes (e.g. microwave applications, sterilisation)

Good gloss & high clarity => ideal for reverse printing

‣Trays, closures, films (cast –oriented form)

‣Seal layer in retortable pouches, hot filled bottles and microwaveable packaging

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PLASTICS: COPOLYMERS OF ETHYLENE

•Ethylene –Vinyl Acetate (EVA)

‣VA => crystallinity => permeability and clarity

‣Mostly used in multi-layer applications

‣Three advantage over LDPE

‧Heat sealing temperature is lower

‧Barrier properties are better

‧Excellent stretch properties

‣Applications

‧Stretch wrapping: replacing PVC

‧Heat sealing layer for PET and BOPP films

PLASTICS: COPOLYMERS OF ETHYLENE

• Ethylene –Vinyl Alcohol (EVOH)

• ‣Excellent processability on machines

• ‣Superior barriers to gasses, odors and solvents

• ‧Multi-layer applications (in many cases surrounded by polyolefins)!!!

• ‧Hydrophilic => moisture absorption => barrier properties

• ‣Ethylene => barrier properties and moisture barrier

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EVOH

• Gambar struktur

PLASTICS: SUBSTITUTED OLEFINS

• Polystyrene (PS)

‣Amorphous structure –different types

‣Examples

1. High Impact Polystyrene (HIPS)

–Adding synthetic rubbers during polymerization => brittleness of PS

–Thermoforming applications (cups for cream)

2. Expanded Polystyrene (EPS)

–PS foam

–Disposable packages (e.g. trays for meat and produce)

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PLASTICS: SUBSTITUTED OLEFINS

• PolyVinylChloride (PVC)

‣Largely amorphous polymer

‣Permeability properties

Water vapour barrier lower than polyolefins

Gas barrier higher than polyolefins

‣Applications

1. Film:

e.g. stretch wrapping (+ stabilizers and plasticizers)

Excellent gloss and transparency

2. Trays

Environmental issues!

PLASTICS: SUBSTITUTED OLEFINS

• PolyVinylidene Chloride (PVdC)

‣Unique combination of low permeability to water vapouránd gasses, odours, greases and alcohols

‣Suitable for hot filling applications and retorting

‣Component in multilayer barrier containers or films

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PLASTICS: POLYESTERSCarbon-oxygen-carbon links

1. Poly(Ethylene Terephtalate) (PET)

‣Bottles, films, trays

Largely amorphous => excellent transparency

‣Capacity to crystallize under certain controlled conditions (CPET)

Preventing deformation during cooking and serving

•PET bottles

‣Stretching: in biaxial orientation => good gas barrier => minimize bottle weights

PLASTICS: POLYAMIDE

Polyamide (PA)

‣Also called “nylons”

‣Mechanical strength (BOPA!)

‣Good gas barrier properties (when dry!)

‣Highly permeable to water vapor

‣Excellent thermal stability

‣Applications

‧In combination with LDPE or EVA

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PLASTICS:REGENERATED CELLULOSE FILMS

• Regenerated Cellulose Film (RCF)

‣Also called “cellophane”

Cellulose from wood, cotton, hemp

‣Good gas barrier properties (when dry!)

‣Often used in multi-layer film

‣Recently: replaced by BOPP in many cases

‣Twist wrapping of sweets

PLASTIC: MOST USED MATERIAL

• Rigid sheets for thermoforming

‣HIPS, HDPE, PP for bulk layers

•Flexible films

‣LDPE, LLDPE

•Bottles

‣PET, HDPE

•Barrier layers

‣EVOH, PVdC

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PLASTIC: PERMEABILITY OF PLASTICS

• Permeable to:

‣Gases

‣Water vapour

‣Organic vapors

‣Other low molecular weight compounds

•Permeability depends on:

‣Packaging material itself

‣Integrity of packages (including seals and closures!!!)

PLASTIC: MODIFICATION

• Adding additives in plastics

•Co-extrusion, lamination, coating

•Orientation

•Metallization

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PLASTIC:MODIFICATION

•Aim: improve different properties of the basic polymers to comply with the demands related to food packaging

•Example

‣Orientation / crystallization

Increase interaction between molecular strains => increase barrier properties

‣Filling agents

Decrease interaction between molecular strains => decrease barrier properties

Also when H2O is absorbed (e.g. in O2-barrier in EVOH decreases due to absorption of H2O)

PLASTICS: ADDING ADDITIVES

•Additive: an auxiliary ingredient enhancing the properties of the parent polymer without appreciably altering its chemical structure

•Food legislation: positive list!

•Types:

‣Processing additives

‣Flexibilizers

‣Antiaging additives: for ex: UV stabiliser

‣Surface property modifiers: antistatic and antifoaming agents

‣Optical property modifiers: give colour

‣Foaming agents:

‣Active packaging technology

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CO-EXTRUSION, LAMINATION, COATING

•Three methods to produce multilayer structures

‣Co-extrusion: simultaneously extrude two or more different polymers, which fuse into one film/sheet

‣Lamination: combining two or more different films/sheets (plastics or non-plastics) by means of adhesives and curing systems

‣Coating: applying one or more layers of a fluid or melt to the surface of a material