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CHM 585 / 490

CHM 585 / 490. Chapter 9 Polyolefins. Polyethylene #1 Volume plastic. About 30 billion pounds per year LDPE LLDPE HDPE Light weight, excellent chemical resistance, ease of processing and low cost Film, sheet, extrusion, injection molded, blow molded, rotomolded. Chapter 9.

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CHM 585 / 490

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  1. CHM 585 / 490 Chapter 9 Polyolefins

  2. Polyethylene#1 Volume plastic • About 30 billion pounds per year • LDPE • LLDPE • HDPE • Light weight, excellent chemical resistance, ease of processing and low cost • Film, sheet, extrusion, injection molded, blow molded, rotomolded Chapter 9

  3. Low Density Polyethylene (LDPE) • High temperature, high pressure autoclave • Radical process results in branched polymer • .910-.930 g/cm3

  4. Plastics News December 29, 2003

  5. Linear Low Density PolyethyleneLLDPE • Solution process and gas phase process • Relative to LDPE, lower temperatures and pressures • Organometallic catalysts ( Ziegler-Natta). For example TiCl3/ triethylaluminum • Hydrogen used to control molecular weight • Butene, hexene, or octene used to control density • .915-.940 g/cm3

  6. Plastics News December 29, 2003

  7. High Density PolyethyleneHDPE • .941-.965 g/cm3 • Slurry process, gas-phase process, solution process

  8. Plastics News December 29, 2003

  9. Crystallinity

  10. Crystallinity • HDPE about 95% crystallinity • LLDPE about 60-85% • LDPE about 60-75%

  11. Effect of Crystallinity and Density • As crystallinity and density increase • Heat-softening point increases • Gas and water permeation decreases • Stiffness increases • Stress crack resistance decreases • Low temperature toughness decreases

  12. Molecular Weight • As molecular weight increases: • Toughness increases • Tensile strength increases • Environmental stress crack resistance increases • Processing becomes more difficult

  13. Applications • Packaging film • Shrink wrap, grocery bags, laundry bags, salad packs • Injection molding • Ice cream, margarine tubs, garbage cans • Blow molding • Detergents, bleaches, milk bottles • Rotomolding • Toys, agricultural tanks

  14. Applications continued • Wire and cable • Gas pipes • Gasoline tanks • Storage drums

  15. Copolymers • When a polymer is made by linking only one type of small molecule, or monomer, together, it is called a homopolymer. • When two different types of monomers are joined in the same polymer chain, the polymer is called a copolymer.

  16. Ethylene Copolymers • EEA • Ethylene ethyl acrylate • EVA • Ethylene vinyl acetate • Ethylene methacrylic acid

  17. EEA

  18. EEA • 15-30% ethyl acrylate • Ethyl acrylate imparts flexibility and polarity • Polarity helps adhesion • With increasing ethyl acrylate, get increased toughness and resilience, but lower upper use temperature and reduced clarity • Used for flexible tubing, gasketing, diaper lining, disposable gloves

  19. EVA

  20. EVA • 5 – 50% vinyl acetate • Flexible and tough even at low temperatures • Low resistance to solvents and heat • Packaging, shoes, medial films, wire and cable insulation • As VA content increases, increase in clarity, flexibility, impact strength, but decrease in softening temperature and barrier properties

  21. Surlyn

  22. Additives • Antioxidants ( hindered phenols) • UV • Impact modifiers • Fillers • Clarifiers for transparency • Flame retardants • Nucleating agents

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