Polymer ProcessingPolymer Processing

Polymer materialsPolymer materials Primary Bond - Primary Bond -

Covalent BondingCovalent Bonding Secondary Bonds –Secondary Bonds –

van der Waalsvan der Waals Dipole BondsDipole Bonds Hydrogen BondsHydrogen Bonds

H

C

H

PE - mer

Polymer PropertiesPolymer Properties TTgg

Glass Transition Glass Transition TemperatureTemperature

MWMW Molecular WeightMolecular Weight

The combination of The combination of these two properties these two properties will be a great starting will be a great starting point for identifying point for identifying any polymer materialany polymer material

Reinforcing fibers 

Boron, carbon, fibrous minerals, glass, Kevlar 

  Increases tensile strength.   Increases flexural modulus.   Increases heat-deflection temperature (HDT).   Resists shrinkage and warpage.

Conductive fillers 

Aluminum powders, carbon fiber, graphite 

  Improves electrical and thermal conductivity.

Coupling agents 

Silanes, titanates 

  Improves interface bonding between polymer matrix and the fibers.

Flame retardants 

Chlorine, bromine, phosphorous, metallic salts 

  Reduces the occurrence and spread of combustion.

Extender fillers 

Calcium carbonate, silica, clay    Reduces material cost.

Plasticizers  Monomeric liquids, low-

molecular-weight materials 

  Improves melt flow properties.   Enhances flexibility.

Colorants (pigments and dyes) 

Metal oxides, chromates, carbon blacks  

  Provides colorfastness.   Protects from thermal and UV degradation (with carbon blacks).

Blowing agents 

Gas, azo compounds, hydrazine derivatives 

  Generates a cellular form to obtain a low-density material.

Major ProcessesMajor Processes

Extrusion Extrusion Injection MoldingInjection Molding Blow MoldingBlow Molding ThermoformingThermoforming RotomoldingRotomolding

Polymer ProcessesPolymer Processes

ExtrusionExtrusion

Extrusion Product Extrusion Product ExamplesExamples

ExtrusionExtrusion

The extrusion machine forms the The extrusion machine forms the basis of nearly all other polymer basis of nearly all other polymer processes.processes.

Basically involves melting polymer Basically involves melting polymer pellets and extruding them out pellets and extruding them out through a two dimensional die.through a two dimensional die.

Produces long, thin productsProduces long, thin products Coating for electrical wireCoating for electrical wire Fishing LineFishing Line Tubes, etc.Tubes, etc.

Injection MoldingInjection Molding

Injection Molding Product Injection Molding Product ExamplesExamples

Nylon sheaves

Injection Molding Machine Injection Molding Machine BasicsBasics

Injection Molding Machine Injection Molding Machine Operating SequenceOperating Sequence

The cavity fills as the The cavity fills as the screw moves forward as screw moves forward as a plungera plunger

The cavity is The cavity is packed as the screw packed as the screw continues to move continues to move forward as part forward as part solidifiessolidifies

Mold closes and Mold closes and screw begins moving screw begins moving forward for injectionforward for injection

Injection Molding Machine Injection Molding Machine Operating Sequence, ctdOperating Sequence, ctd

The cavity cools as the The cavity cools as the gate freezes off and gate freezes off and the screw begins to the screw begins to retract to plasticize retract to plasticize material for the next material for the next shotshot

The mold opens for The mold opens for part ejectionpart ejection

The mold closes and The mold closes and the next cycle begins the next cycle begins

Injection Molding Process Injection Molding Process ControlControl

Very similar to die Very similar to die castingcasting

Must control heat Must control heat transfer and fluid transfer and fluid flowflow

Do that by Do that by controlling controlling temperature and temperature and pressurepressure

Co-injection MoldingCo-injection Molding

1. 1. Inject Inject SkinSkin

2.a. Inject 2.a. Inject CoreCore

2.b. 2.b. Continue Continue injecting injecting core until core until cavity is cavity is

filledfilled

3. Inject 3. Inject Skin Skin

again to again to purge purge sprue.sprue.

Injecting hollow parts with Injecting hollow parts with complex interior geometrycomplex interior geometry

Gas Assist Injection Molding – Gas Assist Injection Molding – Hollow parts without interior Hollow parts without interior

controlcontrol

Injection – Compression Injection – Compression MoldingMolding

Very Very similar to similar to squeeze squeeze castingcasting

Injection Molding of Injection Molding of ThermosetsThermosets

Thermoplastics “set” when they coolThermoplastics “set” when they cool Mold temperature will be set to allow full cavity Mold temperature will be set to allow full cavity

fill, while increasing production ratefill, while increasing production rate Thermosets undergo a chemical Thermosets undergo a chemical

crosslinking that produces the solid crosslinking that produces the solid structurestructure Mold temperature will be hotter usually – set to Mold temperature will be hotter usually – set to

allow full cavity fill, while accelerating the allow full cavity fill, while accelerating the chemical reaction to cure.chemical reaction to cure.

Often called “Reaction Injection Molding” (RIM)Often called “Reaction Injection Molding” (RIM)

Blow MoldingBlow Molding

Blow MoldingBlow Molding

Injection Blow MoldingInjection Blow MoldingExtrusion Blow MoldingExtrusion Blow Molding

Stretch (Parasin) Blow Stretch (Parasin) Blow MoldingMolding

Blow Molding Cost AnalysisBlow Molding Cost Analysis

500 ml bottle – 500 ml bottle – using a preformusing a preform

Cost per bottleCost per bottle 500 ml bottle – 500 ml bottle – direct form mfgdirect form mfg

Cost per bottleCost per bottle

PreformPreform $0.040$0.040 BottleBottle $0.12$0.12

Shipping (500,000 Shipping (500,000 per container @ per container @ $3000 per 40') $3000 per 40')

$0.006$0.006 Shipping (50,000 Shipping (50,000 per container @ per container @ $3000 per 40’)$3000 per 40’)

$0.06$0.06

Labor ($12 per Labor ($12 per hour)hour)

$0.004$0.004

Waste (5%)Waste (5%) $0.002$0.002

Electricity ($0.20 Electricity ($0.20 per Kwh)per Kwh)

$0.004$0.004

TOTALTOTAL $0.056$0.056 TOTALTOTAL $0.18$0.18

ThermoformingThermoforming

Thermoforming ProductsThermoforming Products

ThermoformingThermoforming

Thermoforming VideoThermoforming Video

RotomoldingRotomolding

RotomoldingRotomolding Used for relatively Used for relatively

dimensionally inaccurate dimensionally inaccurate items, usually with a hollow items, usually with a hollow interiorinterior Can be very largeCan be very large Garbage CansGarbage Cans KayaksKayaks Interior dimensions can not Interior dimensions can not

be criticalbe critical Relatively primitive and Relatively primitive and

therefore inexpensive therefore inexpensive processprocess

Polymer RecyclingPolymer Recycling

1998 – Approximately 20% of plastic 1998 – Approximately 20% of plastic waste is recycled (optimistic waste is recycled (optimistic estimate)estimate)

1998 – Polymers account for 1998 – Polymers account for approximately 18% by volume of approximately 18% by volume of material to landfillsmaterial to landfills

Needs vs ChallengesNeeds vs Challenges Needs for a viable Needs for a viable

program:program: Stable supply of Stable supply of

materials with reliable materials with reliable collection and sortingcollection and sorting

Economical, proven Economical, proven and environmentally and environmentally sound recycling sound recycling processprocess

End use applications End use applications for the recycled for the recycled materialmaterial

ChallengesChallenges 10-12 main polymer 10-12 main polymer

typestypes Thousands of blendsThousands of blends AdditivesAdditives Impurities in supply Impurities in supply

(labels, glass, dirt, etc)(labels, glass, dirt, etc)

Recycling of PolymersRecycling of Polymers• PET (polyethylene terphthalate) beverage containers, boil-in food pouches, processed meat packages

• HDPE (high density polyethylene) milk bottles, detergent bottles, oil bottles, toys, plastic bags

• PVC (polyvinyl chloride) food wrap, vegetable oil bottles, blister packaging

• LDPE (low density polyethylene) shrink-wrap, plastic bags, garment bags

• PP (polypropylene) margarine and yogurt containers, caps for containers, wrapping to replace cellophane

• PS (polystyrene) egg cartons, fast food trays, disposable plastic silverware

• Other multi-resin containers

Basic recycling stepsBasic recycling steps

SortingSorting Size ReductionSize Reduction DensificationDensification PulverizationPulverization Melt FiltrationMelt Filtration

SortingSorting

Manual – very commonManual – very common Density based sorterDensity based sorter

CentrifugalCentrifugal Float/Sink methodsFloat/Sink methods

Optical – same as peas, Optical – same as peas, potato chips, etcpotato chips, etc

Spectroscopy – Infrared Spectroscopy – Infrared – automation possible– automation possible

Size ReductionSize Reduction

ShreddersShredders Rotary KnifeRotary Knife

DensificationDensification

Basic purpose is to reduce to volume Basic purpose is to reduce to volume taken up by bulk materialtaken up by bulk material Reduce from only 20 kg/mReduce from only 20 kg/m33 to almost 400 to almost 400

kg/mkg/m33

Agglomeration – heat it up and Agglomeration – heat it up and compact itcompact it

PulverizationPulverization

Convert clean Convert clean plastic waste into plastic waste into powderpowder

After this process, After this process, some of the product some of the product can actually be used can actually be used if low purity if low purity requirementsrequirements Recycled plastic Recycled plastic

lumber for examplelumber for example

Melt FiltrationMelt Filtration

Improve purity of Improve purity of pulverized polymerpulverized polymer Needed for extrusion, Needed for extrusion,

injection or blow molding injection or blow molding processesprocesses

Basic process concept:Basic process concept: Melt itMelt it Shove it through a Shove it through a

screenscreen Additional chemical Additional chemical

processing may be processing may be needed if additional needed if additional purity requirementpurity requirement