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Polymers

Polymers. Classifications. Natural Sources. Plants Cellulose (table tennis balls) Cellulose accetate (film) Cellophane (wrapping) Bakelite (Used primarily from 40’s to 60’s) Trees Latex (rubber) Bitumen (roads) Resin (paint) Amber (operation) Gutta-percha (Musical strings) Animals

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Polymers

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  1. Polymers

  2. Classifications

  3. Natural Sources • Plants • Cellulose (table tennis balls) • Cellulose accetate (film) • Cellophane (wrapping) • Bakelite (Used primarily from 40’s to 60’s) • Trees • Latex (rubber) • Bitumen (roads) • Resin (paint) • Amber (operation) • Gutta-percha (Musical strings) • Animals • Horn (decoration) • Milk (glues) • Insects • Shellac (polish)

  4. Synthetic Sources • Crude Oil • Coal • Natural Gas

  5. Properties of Plastics • Compounds contain atoms which join together to form molecules. • When heat is applied molecules vibrate and separate • H2O exist as Ice (solid), Water (liquid), Steam (gas) – clear distinction between states. • Plastics change state far more gradually, and material becomes putty-like before melting.

  6. Micro-structure • Polymers – long chains of simple molecules (monomers) • Monomers joined together in polymerisation process to form giant molecules • Greek: Poly=many, mer=unit

  7. Example • Monomer – Ethylene C2H4 • Carbon links with hydrogen, but has spare electron so forms double bond with another carbon atom. • Polymer - Polyethylene (CH2)n • Heat and pressure used to break double bond. Allows units to link up

  8. Thermo Chains of polymers Connected by Van der Waals forces(mutual attraction) Weak links can be overcome by reheating Become soft and pliable, can be moulded Thermosetting Chains of polymers Connected by Covalent bonds(chemical cross links) Very strong links, cannot be reheated and changed Thermo v’s Thermosetting Covalent Bonds

  9. Thermoplastics • Acrylic • Polystyrene • PVC • PET • Polypropylene

  10. Thermosetting Plastics • Epoxy Resin • Urea Formaldehyde

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