WasteMINZ Plastics Webinar

Plastics 101Neil Edmonds, The University of Auckland

nr.edmonds@auckland.ac.nz

Introduction

Abbreviations for PlasticsABS Acrylonitrile-Butadiene-StyreneEVA Ethylene-Vinyl Acetate HDPE High-Density PolyethyleneLDPE Low-Density PolyethyleneLLDPE Linear Low-Density

PolyethylenePA Polyamide (nylon)PC PolycarbonatePE PolyethylenePET/PETE Polyethylene TerephthalatePETG Glycol Modified Polyester

TerephthalatePMMA Polymethyl methacrylate (acrylic)

PMP Polymethyl Pentene (TPX)POM Polyoxymethylene (acetal) PP PolypropylenePS PolystyrenePSU PolysulfonePTFE PolytetrafluoroethylenePU/PUR PolyurethanePVC Polyvinyl ChloridePVDF Polyvinylidene FluorideSAN Styrene AcrylonitrileTPE Thermoplastic ElastomerUHMW-PE Ultra High Molecular

Weight Polyethylene

Thermosetting polymers cannot be recycled

Classification of PolymersNatural Synthetic

Carbohydrates Thermoplasticseg. Cellulose, Starch Commodity Plastics (PE, PP, PS, PVC, PET)

Engineering Plastics (PA, POM, ABS,)Proteins Specialty Plastics (PTFE)eg. Wool, Silk

ElastomersThermoplastic (SBS, TPU)Thermosetting (NR, SI)

Thermosetting (3D, Network, Crosslinked)Epoxy Resins (EP)Unsaturated Polyester Resins (UP)

Thermoset polymers

resin + catalyst

Mix

CureReaction

Solidified thermosetThermoplastic polymers

Solid Stock or Granules Finished Product

Heat,Reshape,Mix, etc…

Elastomers (or rubbers) are flexible thermoplastic or thermoset polymers

Examples of simple polymers:

Ethylene Mer Polyethylene

Propylene PolypropyleneMer

ØDuring polymerization, monomers join together forming large molecules from multitudes (poly) of small repeating segments (mers).

ØThe behaviour of a plastic when molten depends on the monomers used. For example, nylons and polyesters have very low viscosity melts while HDPE and PS are high viscosity. This means they must be handled and processed differently.

Manufacture of Polymers

Thermoplastic polymers are typically received from the supplier in solid form, with the polymerisation reaction complete.

ØVery long polymer chains are already formed, these can be repeatedly melted, shaped and cooled with very little degradation of the polymer.

Ø Plastics manufacturers mould pellets, sheets or powder into products.

Properties of different polymers

Polyesters - PET Poly(ethylene terephthalate)

Key material properties:• high tensile strength and rigidity• very high heat resistance• excellent electrical insulation • chemical resistance• very good dimensional stability

Disadvantages:• high processing temperatures• careful drying required before processing

Applications:• packaging• electrical and electronic connectors and components• appliance components

Recyclability:• limited commercial recycling• main kerbside collection in NZ is of PET used for packaging which is largely

exported for reprocessing

Identification Code

High Density Polyethylene (HDPE)Key material properties:• translucent• high tensile strength• rigid• excellent chemical resistance

Disadvantages:• difficult to bond• stress cracking• poor weathering resistance

Applications:• household goods (basins, sieves, dishes, rubbish bins)• transport cases• pipes• electrical fittings• sports equipment• food and freezer containers

Recyclability:• highly recyclable• most common material for kerbside collection in NZ – milk bottles• also commercial recycling

Identification Code

Poly(vinyl chloride) – PVCKey material properties:• very good weathering resistance• resistant to a range of chemicals.• rigidity and strength properties • good electrical insulation• resistance to abrasion• clarity

Disadvantages:• contains chlorine• limited thermal capability• higher density than many other plastics

Applications:• pipes for external use • extruded profiles and frames• sheet for roofing or panelling• blown bottles for oil, wine

Recyclability:• limited commercial recycling of flexible PVC and PVC films in NZ• no household or kerbside PVC collection in NZ due to low volume & contamination risk

PVC

Identification Code

Polyethylene Low Density Polyethylene (LDPE), Linear Low Density Polyethylene (LLDPE)

Key material properties:• excellent chemical resistance• moisture transmission resistance• excellent electric insulation properties• low cost• excellent flexibility and toughness• low heat resistance, tensile strength and rigidity

Disadvantages:• difficulty in bonding• stress cracking• high gas transmission

Applications:• film for packaging• food containers, especially lids• pipes

Recyclability:• highly recyclable• high level of commercial LDPE film recycled in NZ – but little household

Identification Code

Polypropylene (PP)Key material properties:• greater hardness and stiffness than HDPE• excellent chemical resistance• electrical insulation properties• higher tensile strength and heat resistance than HDPE• good fatigue and abrasion resistance• high impact and flexural strength

Disadvantages:• poor weathering resistance• poor low temperature impact and flexural strength

Applications:• tool and travel cases• automotive parts - bumper bars, ducts, fuel tanks• food/packaging containers and boxes• sterilisable hospital items• appliance components• ropes and fibres

Recyclability:• commercial waste commonly recycled in NZ• very limited household/kerbside collection in NZ due to variety of applications & low volumes

Identification Code

Polystyrene - General Purpose Polystyrene (GPPS) Key material properties:• clarity• rigidity• low cost• high gloss• dimensionally stable

Disadvantages:• flammable• poor weatherability• poor solvent resistance• brittleness

Applications:• food containers - egg cartons, produce trays• disposable drinking cups and glasses

Recyclability:• limited commercial recycling in NZ• no NZ household/kerbside collection due to lower volumes and low material value

Identification Code

END USES Ø Thermoformed bowls, plates, dairy containers (HIPS)Ø Foamed packaging (HIPS)Ø Refrigerator liners (HIPS, ABS)Ø Automotive interiors (HIPS, ABS)Ø Injection moulded disposables (razors, pens) Ø Tools and computer housings (ABS)

STYRENE COPOLYMERSCopolymers are plastics containing more than one type of polymer (eg. ABS) Sometimes different polymers/copolymers are blended/alloyed eg. PC/ABS

Polyamides – NylonKey material properties:• excellent abrasion resistance• good chemical resistance• easy colouration• good impact strength after moisture saturation • good lubricity• high heat resistance• toughness, durability and very good fatigue resistance• properties frequently enhanced with additives

Disadvantages:• high moisture absorption• some dimensional instability• high shrinkage in moulded sections

Recyclability:• limited commercial recycling only

Identification Code

PA

18

Polymer AdditivesAdditives may limit recycling options:

Ø Pigments and Fillers - Increase Strength and StiffnessØ Impact Modifiers - Improve ToughnessØ Flame Retardants - Make Polymers More Difficult to BurnØ Stabilizer Systems:

• Oxidative Stabilizers - Reduce Oxidation• Ultraviolet Stabilizers - Improve Weathering• Thermal Stabilizers - Allow High Temperature

Processing

Plastics processing technologiesMany ways to convert plastics materials into products, most common methods are:

Ø extrusionØ thermoformingØ blow moulding Ø blown film Ø injection moulding Ø rotational moulding

Extrusion

Ø process used to make continuous shapesØ a wide range of different continuous shapes can be

produced

Injection MouldingØ a way to make solid, shaped, individual productsØ used to produce a very wide range of different shapes

and sizes

Thermoforming

Ø a way to make solid, shaped, individual productsØ suitable for very thin-walled products, very large or small

products or a small numbers of products

Blow MouldingØ a way to make enclosed, hollow shaped productsØ used to produce products like bottles and drums in a

wide range of sizes

Blown Film A process known as blown film extrusion uses an industrial blower to expand a hot plastic tube into a light, strong plastic bag. The air inflates the plastic tube like a balloon until a bag with the desired size and wall thickness is formed. The balloon moves slowly up a tower,the bubble being contained by rollersthat fold the film and roll it into a cylindrical shape. The final product can have multiple layers.

Rotational MouldingØ a way to make a wide range of enclosed, hollow shaped

productsØ large industry in New Zealand

Why are polymers selected for particular products?

Ref: SABIC Innovative Plastics

27

DimensionsGeometry, Weight,

Warpage (inner or outer part)Dimensional stability

Amorph/Semicrystallinefilled/unfilled

AestethicsTransparency (wavelength?), Opaque,

Color, Gloss, TextureFlow Lines, Scratch Resitance

Part visible?

MechanicalImpact, Stiffness, Abrasion, Fatigue

Additives, lifetime?

RegulatoryFood (FDA, FCEU), Water (KTW)Toys, Medical (ISO10993, EUP),

Flame retardancy (UL, ..), RoHS, WEEE,Forbidden Additives?

ElectricalUL, GWT, GWIT,

HAI, HWI, RTI, CTI Wall Thickness?EMI shielding?

AcousticsWhat Frequencies?Noise reduction?

FinancialsCost Expectation

(Material + Processing costs)System cost

Determination of Material Requirements

Enviroment Heat resistance, (HDT, BPT)

UV, Chemicals, WaterHow long, what temperature,

which chemicals?

ProcessingInjection Molding,Foaming, 2K

Extrusion, BlowmoldingThermoforming

Hot/Coldrunner, Cavities?

What requirements?What Application tests?

Second. Operation(Ultrasonic, Vibration, Laser Welding)

Glueing, Painting, Lasermarking, Powder coating, Metallisation,

28

Thermo-oxidativeThermal degradation

under influence of oxygen is significantly accelerated

(feee radical)s

ThermalThrough heat exposure

while drying(extended, too highTemp)

Use Temperature

MechanicalThrough granulation processes,

shear in melt flow.All lead to

material degradation

Mechanical StressInhomogeneous distribution of stresses

through tensile/torsion/bending forces

break molecules

PhotochemicalAbsorbtion of light

Influences stability of molecules- less energy to degrade

(Energy)

RadiationX- Rays, Gammas rays

Will lead to split of unsaturated bonds, build radicals

Chemicals Water, Acids/Basis/Organic media

Attack polymer through wetting, swelling.Dissolving of additives,

chemical reactions on surface

Anti AgeingLight protection (UV Ageing, Gamma),

Antioxidants, Heat stabilizerscan slow down ageing

Life Time TestingLife time of part?

Reasonable accelerated testingon parts necessary for evaluation

AgeingAccelerated and comparable

UV Ageing Hydrolytic and chemical testing

on test speciment(tensile bars, plaques)

Material Ageing:Irreversible chemical and

physical processesthrough degradation of the polymer chains,

crosslinking reactions and uncontrollable changes of the chemical structure

with loss of mechanical propeties, FR properties, color, gloss, brittleness,

chemical resistanceFactors amplify each other!

Material ageing: Example Plastics

Barriers to using recycled content in products

Ref: GH-SITA-Plastics-for-N.E.-Recycling-Forum-26-02-2015-v4

Barriers A:ØPlastics change when processed. Heating and forming of plastics results in changes to the chemical structure.

ØChanges include lowering of chain length and oxidation of polymers, both of which result in restricting recycling options.

ØDifferent types of plastics will not mix together,even different grades of the same plastic may not fully mix.

ØPlastics with additives such as pigments are more difficult to recycle.

Barriers B:Ø Not always a slot-in replacement. Reluctance to

change the specifications of the polymers that currently used.

Ø Variability/inconsistency of the recycled polymers from batch to batch and from different suppliers.

Ø Can be constraints on colour – often darkcolours such as grey, black.

Barriers C:Ø Client specifications not allowing moulder to use

recycled content.

Ø Cost and time implications in changing over from an existing material to a recycled one (e.g. optimising moulding parameters & machine settings).

Ø Security of supply.

Ø Potential damage to reputation.

Problematic Products

1. Black Plastics

Carbon black prevents near infrared sorters identifying polymer types.New pigments look black and enable NIR sorting.

2. Multi Layer/Laminates

Pouches, films, tubes and trays with sealing layers.

Laminates of different polymers or materials are beneficial because:Ø Reduce weight - savings in transport costs and emissionsØ Less material is used so less energyØ Lower weight to landfill.Ø Oxygen and light barriers prolong shelf life.

But..create low quality materials when recycled together

3. Multi Layer/Laminates: Tubes and Pouches

Plastic and Aluminium laminates: Pouches, tubes etc. Materials need to be separated to remain high value and be used again.

ØEnval process uses microwave-induced pyrolysis (no oxygen).

ØAluminium is recovered and oils & gases produced from plastics used for heat and electricity.

ØBeing commercialised.

Benefits of using recycled plasticsØ Some recycled polymers can be cheaper than the virgin

(in some cases by 10 to 20%)

Ø Marketing benefits –showing commitment to the environment -“walking the walk”

Ø Customers want products that reduce carbon impact

Ø Material security –It’s a resource we are producing lots of (>2Mt/yr plastic packaging)

Commercial challengesØ Reprocessing Infrastructure costs $Millions to set up

facilities Ø Access to funding not always easy-riskØ Enough collected to justify investment? Chicken and eggØ Volumes of some polymers too low to justify investment

(e.g. PS and PVC)Ø Recovery yields vs costs of disposal –QUALITY.Ø Low /volatile prices - squeezed margins. Ø ?????

uThank you for your attention

Questions?