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Polyethylene,
the largest volume thermoplastic polymer used today, is available in a wide
variety of grades and formulations that have an equally wide range of
properties. Some polyethylenes are
flexible, others are rigid; some have poor impact strength, others are virtually
unbreakable; some have good clarity, others are opaque.
Service temperatures can range from –40 to +200o F.
In general, however, polyethylenes are characterized by toughness,
excellent chemical resistance and electrical properties, low coefficient of
friction, near-zero moisture absorption and ease of processing.
Polyethylenes
are classified into three categories, according to density:
Low
Medium
High
A
fourth type ultrahigh molecular weight polyethylene (UHMWPE) is in the medium to
high density range. Properties of this high-performance plastic are entirely
different from those of conventional polyethylenes. Also available is crosslinked polyethylene, a special grade
which, by chemical or irradiation treatment, becomes essentially a thermoset
material with outstanding hear resistance and strength.