Page 75 - Handbook of Plastics Technologies

THERMOPLASTICS

THERMOPLASTICS 2.15

able is Barex (BP Chemicals). The copolymer has better barrier properties than both
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polypropylene and polyethylene terephthalate. Acrylonitrile is also used with butadiene
and styrene to form ABS polymers. Unlike the homopolymer, copolymers can be pro-
132
cessed by many methods, including extrusion, blow molding, and injection molding.
Acrylonitrile is often copolymerized with other monomers to form fibers. Copolymer-
ization with monomers such as vinyl acetate, vinyl pyrrolidone, and vinyl esters gives the
fibers the ability to be dyed using normal textile dyes. The copolymer generally contains at
least 85 percent acrylonitrile. 133 Acrylic fibers have good abrasion resistance, flex life, and
toughness, and high strength. They have good resistance to stains and moisture.
Modacrylic fibers contain between 35 and 85 percent acrylonitrile. 134
Most of the acrylonitrile consumed goes into the production of fibers. Copolymers also
consume large amounts of acrylonitrile. In addition to their use as fibers, polyacrylonitrile
polymers can be used as precursors to carbon fibers.

2.2.7 Polyamide-imide (PAI)
Polyamide-imide (PAI) is a high-temperature amorphous thermoplastic that has been
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available since the 1970s under the trade name of Torlon. PAI can be produced from the
reaction of trimellitic trichloride with methylenedianiline as shown in Fig. 2.11.

FIGURE 2.11 Preparation of polyamide-imide.

Polyamide-imides can be used from cryogenic temperatures to nearly 260°C. They
have the temperature resistance of the polyimides but better mechanical properties, includ-
ing good stiffness and creep resistance. PAI polymers are inherently flame retardant, with
little smoke produced when they are burned. The polymer has good chemical resistance,
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but at high temperatures it can be affected by strong acids, bases, and steam. PAI has a
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heat deflection temperature of 280°C, along with good wear and friction properties.
Polyamide-imides also have good radiation resistance and are more stable than standard
nylons under different humidity conditions. The polymer has one of the highest glass tran-
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sition temperatures, in the range of 270 to 285°C.

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