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CHM 585 / 490

Chapter 9

Polyolefins

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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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Low Density Polyethylene (LDPE)

• High temperature, high pressure autoclave

• Radical process results in branched polymer

• .910-.930 g/cm3

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LDPE2004 North American Capacity

Equistar18%

Exxon Mobil16%

Dow15%

Westlake9%

Dupont8%

Eastman 7%

Others27%

Plastics News December 29, 2003

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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

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LLDPE2004 North American Capacity

Dow30%

Exxon Mobil18%Nova

17%

Equistar7%

Others28%

Dow

Exxon Mobil

Nova

Equistar

Others

Plastics News December 29, 2003

7

High Density PolyethyleneHDPE

• .941-.965 g/cm3

• Slurry process, gas-phase process, solution process

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HDPE2004 North American Capacity

Chevron Phillips

23%

Exxon Mobil21%

Equistar18%

Solvay11%

Formosa8%

Others19%

Plastics News December 29, 2003

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Crystallinity

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Crystallinity

• HDPE about 95% crystallinity

• LLDPE about 60-85%

• LDPE about 60-75%

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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

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Molecular Weight

• As molecular weight increases:– Toughness increases– Tensile strength increases– Environmental stress crack resistance increases– Processing becomes more difficult

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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

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Applications continued

• Wire and cable

• Gas pipes

• Gasoline tanks

• Storage drums

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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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17

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Ethylene Copolymers

• EEA– Ethylene ethyl acrylate

• EVA– Ethylene vinyl acetate– Ethylene methacrylic acid

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EEA

+O

OCH2CH3 CH2CH2( () )CH2CH

CO2CH2CH3x

y

random

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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

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EVA

+CH2CH2( () )CH2CH

Oxy

random

O

O O

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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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Surlyn

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Additives

• Antioxidants ( hindered phenols)

• UV

• Impact modifiers

• Fillers

• Clarifiers for transparency

• Flame retardants

• Nucleating agents

OH

O

OC18