General Description : A semi-crystalline, white, semi-opaque commodity thermoplastic made in a very wide variety of grades and modifications. It is a linear polyolefin which can be compared in many ways to high density polyethylene (HDPE) and that is manufactured in a very similar way. The catalysts used control the polymer's stereoregularity quite well so that commercial polypropylenes are usually predominantly isotactic. Polypropylene homopolymer is harder and has a higher temperature resistance than HDPE but lower impact resistance and becomes brittle below ~0C. Hence copolymer grades are preferred for all applications exposed to cold/winter conditions. These copolymers have better impact strength, maintained down to lower temperatures, than homopolymer at the expense of quite small reductions in other properties. Like polyethylenes, polypropylene has good chemical but poor UV resistance (unless stabilized or protected).
Applications include (for homopolymers) appliance housings, housewares, packaging, cassette holders and fibers, monofilaments and slit-film tapes; for copolymers pipes, containers, boat hulls, seat shells and automotive parts e.g. battery cases and bumpers though the latter are often made from more heavily elastomer-modified polypropylenes.