HDPE
After its experimental preparation in the 1930s, the application in high frequency radar cables during World War II, gave impetus to its commercial production. This thermoplastic is available in a range of flexibilities depending on the production process. High density materials are the most rigid. The polymer can be formed by a wide variety of thermoplastic processing methods and is particularly useful where moisture resistance and low cost are required. Polyethylene is limited by a rather low temperature capability (200-250 F) but is manufactured in billions of pounds per year.
Vinyl acetate can be copolymerized with ethylene. The resulting product has improved transparency over homopolymerized polyethylene because of a reduction of crystallinity in the copolymer.
ADVANTAGES:
- Low cost
- Impact resistant from -40 C to 90 C
- Moisture resistance
- Good chemical resistance
- Food grades available
- Readily processed by all thermoplastic methods
- High thermal expansion
- Poor weathering resistance
- Subject to stress cracking
- Difficult to bond
- Flammable
- Poor temperature capability
NOTE:
In general, high density grades of polyethylene have densities up to 0.97 g/cm^. Low density grades are as low as 0.91 g/cm^. Typically, the high-density material is more linear and consequently more crystalline. As might be expected, this higher crystallinity permits use at temperatures up to 130 C degrees with somewhat better creep resistance below that temperature. Low density polyethylene has less stiffness than the high density type. Blends of the two types are common.
TYPICAL APPLICATIONS:
Toys, utensils, films, bottles, pipe and processing equipment. Wire and cable insulations.