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 g/cm 3

4 Plastics News December 29, 2003

5 Linear Low Density Polyethylene LLDPE Solution process and gas phase process Relative to LDPE, lower temperatures and pressures Organometallic catalysts ( Ziegler-Natta). For example TiCl 3 / triethylaluminum Hydrogen used to control molecular weight Butene, hexene, or octene used to control density g/cm 3

6 Plastics News December 29, 2003

7 High Density Polyethylene HDPE g/cm 3 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.

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18 Ethylene Copolymers EEA –Ethylene ethyl acrylate EVA –Ethylene vinyl acetate –Ethylene methacrylic acid

19 EEA

20 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

21 EVA

22 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

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24 Surlyn

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