Page 24 - Plastics Engineering

General Properties of Plastics 7

possibility of low production costs, this ease of processing permits imaginative
designs that often enable plastics to be used as a superior alternative to metals
rather than merely as a tolerated substitute.
Currently the materials generally regarded as making up the engineering
plastics group are Nylon, acetal, polycarbonate, modified polyphenylene oxide
(PPO), thermoplastic polyesters, polysulphone and polyphenylene sulphide.
The newer grades of polypropylene also possess good basic engineering
performance and this would add a further 0.5 m tonnes. And then there is
unplasticised polyvinyl chloride (uPVC) which is widely used in industrial
pipework and even polyethylene, when used as an artificial hip joint for
example, can come into the reckoning. Hence it is probably unwise to exclude
any plastic from consideration as an engineering material even though there is
a sub-group specifically entitled for this area of application.
In recent years a whole new generation of high performance engineering
plastics have become commercially available. These offer properties far supe-
rior to anything available so far, particularly in regard to high temperature
performance, and they open the door to completely new types of application
for plastics.
The main classes of these new materials are
(i) Polyarylethers and Polyarylthioethers

polyarylethersulphones (PES)
polyphenylene sulphide (PPS)
polyethernitrile (PEN)
polyetherketones (PEK and PEEK)
(ii) Polyimides and Polybenzimidazole
polyetherimide (PEI)
thermoplastic polyimide (PI)
polyamideimide (PAI)
(iii) Fluompolymers
fluorinated ethylene propylene (FEiP)
perfluoroalkoxy (PFA)
A number of these materials offer service temperatures in excess of 200°C and
fibre-filled grades can be used above 300°C.

1.3.2 Thermosets
In recent years there has been some concern in the thermosetting material
industry that usage of these materials is on the decline. Certainly the total
market for thermoset compounds has decreased in Western Europe. This has
happened for a number of reasons. One is the image that thermosets tend
to have as old-fashioned materials with outdated, slow production methods.
Other reasons include the arrival of high temperature engineering plastics