Lecture about PET bottles

1. Polymer processing
Michal Vonka
Institute of Chemical Technology in Prague
Department of Chemical Engineering
Group of Polymer Reactor Engineering

2. Outline
• Polymerization
• Polymer structure and properties
• Polyethylene terephthalate
• Polymer processing and blow molding
• Injection molding
• Recycling and further usage
• Health risks
• Conclusions and summary

3. Creation of polymer –
polymerization
Reaction mechanism :
reaction
Monomer + monomer Dimer
reaction
Dimer + something Active chain
n-times repeated
Loosing of chain activity
Dead polymer chain
(product?)
n is important

4. n is virtually EVERYTHING
Chain properties:
• Length
• Branching
Material properties:
• Crystallinity
• The Chain Length Distribution (CLD)
• Gloss
• Glass transition temperature
• Melting point
• Impact resistance
• Young modulus

5. Polymer chains and semi-crystallic
structure
Entanglement
semi-cystallic polymer
10 nm
spherulite
lamellae and
amorphous phase
curving and
branching of
10 µm lamella

6. Chain Length Distribution
Typical chain length distribution
Number
of species
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

7. • Synonym to POLYESTER
PET
• 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

8. Polycondensation of PET:
Dimethylphtalate
Ethanediol
Methanol
Polyethylene terephthalate

9. Injection molding – PET Mold?
Molding?
prefabricate & the lid
Molten Injector (230 – 250 °C)
polymer
Mold (5 – 20 MPa)
• Mass production vs. cooling rates of the mold
• More layers

10. Blow molding – the bottle
Furnace
High pressure injector
PET prefabricate
in the moving bed
• Mass production (100 000 pc / day)
• Attaching the lid

11. 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

12. Degradation and health risks
• Phthalates
– Teratogenes?
• Light degradation
• Thermal oxidation
Stoichiometric
Non-stoichiometric
Small particles of
carbon (2-7 microns) Ketones and aldehydes (irritants, carcinogens)
C

13. Summary and conclusions
• Polymer : chains & • Degradation
semi-crystalic • Health risks
structure • Usage
• The molding
conditions are
essential to the final
product
• Additives
• Difficult recycling
???