Plastics and Elastomers

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Plastics and Elastomers

• A plastic is a solid material composed primarily
  of a polymer of high molecular weight.
• An Elastomer is a solid polymeric material that
  can experience large and reversible elastic
  strains.

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Stiffness of Plastics and Elastomers
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Stress-Strain Behaviour of Typical Thermoplastic
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Effect of Temperature on Mechanical Properties -
Thermoplastics
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Physical States of Thermoplastics
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Creep Behaviour of Polycarbonate
Strain ()
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S-N curves for Various Plastics at Room
Temperature
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Visco-elastic Behaviour
Elastic Behaviour - Metals
Visco-Elastic Behaviour - Plastics
Viscous Behaviour - Fluids
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Mechanical Behaviour of Elastomers
X-linked elastomer
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Vulcanizing of Polyisoprene (Natural Rubber, NR)
Heat
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Silicone Rubbers

• Si-0 replaces C-C backbone in
• Chemically Inert
• Low conductivity
• Heat/cold resistant
• Relatively expensive
• X-linking increases stiffness and strength.

Polydimethylsiloxane
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Common Elastomers
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Injection Molding Extrusion of Plastics

• Most widely used process for thermoplastics
• Pellets fed to heating chamber where they are
  melted into a viscous liquid
• Molded under pressure - 10 to 30 s cycle time

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Compression Transfer Molding

• Thermoplastics and Thermosets