Polymer processing

Institute of Chemical Technology in Prague

Department of Chemical Engineering

Group of Polymer Reactor Engineering

Michal Vonka

Outline

• Polymerization

• Polymer structure and properties

• Polyethylene terephthalate

• Polymer processing and blow molding

• Injection molding

• Recycling and further usage

• Health risks

• Conclusions and summary

Creation of polymer –polymerization

Monomer + monomer Dimer

Dimer + something

n-times repeated

Dead polymer chain (product?)

Active chain

Loosing of chain activity

reaction

reaction

Reaction mechanism :

n is important

n is virtually EVERYTHINGChain properties:• Length• Branching

Material properties: • Crystallinity • The Chain Length Distribution (CLD)• Gloss• Glass transition temperature• Melting point• Impact resistance• Young modulus

Polymer chains and semi-crystallic structure

semi-cystallic polymer

spherulite

10 µm

lamellae and

amorphous phase

curving and

branching of

lamella

10 nm

Entanglement

Chain Length Distribution

Number of species

Typical chain length distribution

Affected properties :

• Crystallinity • Glass transition temperature• Melting point• Gloss• Impact resistance• Young modulus• Etc…

PET example:particle size: 0.5 - 10 micron (gloss)Young modulus: 2800 – 3100 MPa

100 pm size of carbon atom

PET• Synonym to POLYESTER

• Many forms and industrially produced types (CLD, additives)

• Additives – color, gloss, conductivity, tensile strength,

impact resistance

• Usage: synthetic fibres (60%), beverage, food and other

liquid containers (30%), combination with glass fiber

• Year production 5 000 kt/year

• Price 0.5–1.25 !/kg

• Glass transition temperature ~ 75 °C

• Melting point 250 – 270 °C

Polycondensation of PET:

DimethylphtalateEthanediol

Methanol

Polyethylene terephthalate

Injection molding – PET prefabricate & the lid

Injector (230 – 250 °C)

Mold (5 – 20 MPa)

• Mass production vs. cooling rates of the mold

• More layers

Molten polymer

Mold? Molding?

Blow molding – the bottle

High pressure injectorFurnace

PET prefabricate

in the moving bed

• Mass production (100 000 pc / day)

• Attaching the lid

Recycling

• Sorting the types of polymers

• EXTREME costs vs. ECOLOGY

Two ways:

– Chemical way (decomposing to process intermediates and adding into the fresh production – lowering quality)

– Mechanical way (cleaning and new usage)

Mostly for more-layer PET

Degradation and health risks

• Phthalates– Teratogenes?

• Light degradation

• Thermal oxidationStoichiometric

Non-stoichiometric

Small particles of carbon (2-7 microns)

C

Ketones and aldehydes (irritants, carcinogens)

Summary and conclusions

• Polymer : chains & semi-crystalic structure

• The molding conditions are essential to the final product

• Additives

• Difficult recycling

• Degradation

• Health risks

• Usage

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