Materials for engineering, 3rd Edition - (Malestrom)

5
Organic polymeric materials
5.1 Introduction
In Chapter 1, we classified organic polymers as thermoplastics and thermosets
and we will now summarize the characteristics and typical applications of a
number of examples in each class of material.
5.1.1 Thermoplastics
Partially crystalline
Polyethylene (PE) is the commonest of the thermoplastics: it is of low
strength and has poor resistance to weathering, but is chemically resistant
and electrically insulating. Its uses include film wrapping material, tubing,
bottles, cups and battery parts.
Polypropylene (PP) is lighter and stiffer than PE and has similar uses,
including sterilizable bottles, TV cabinets and luggage.
Polyamides (nylons) have good mechanical strength and toughness and
are used for bearings, gears and bushings, as well as for textiles and rope.
Polyacetals (POMs) are highly crystalline and translucent, with good
stress relaxation resistance together with good rigid, tough, spring-like
qualities. Polyacetal uses include small pressure vessels, clock and watch
parts, plumbing systems and (because of its outstanding fatigue resistance)
shoe sole plates.
Thermoplastic polyester (PET) forms one of the toughest of plastic films,
with excellent fatigue and tear strength. Its uses include food packaging,
video tapes, clothing and automotive tyre cords.
Fluorocarbons (PTFEs). Teflon is chemically inert in almost all
environments, and may be used up to 260 °C. It exhibits a low coefficient
of friction and its uses include the coating of non-stick saucepans, as well
as for bearings, seals and chemical pipes and valves.
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