ABSTRACT
In general, material suppliers have concentrated on new polymers that, even in the unreinforced state, have higher melting points, greater stiffness, and higher heat-deflection properties than the high-volume resins discussed. Since PFA retains its electrical properties over a broad temperature range, it is used for insulators or sophisticated electronic equipment such as remote radar installations. To obtain the best properties from PFA moldings, it is necessary to minimize or, preferably, eliminate voids in the part because the effect of even microvoids can result in deleterious effects on fatigue life and gas permeability. Polyarylates are not particularly resistant to stress cracking in the presence of a number of organic solvents, and properties of the resins deteriorate with immersion in water over a fairly short period of time. Polyamide-imide is unaffected by aliphatic and aromatic hydrocarbons, halogenated solvents, and most acids and bases at normal ambient temperatures. At elevated temperatures, it is affected by steam, caustic, and some acids.
