In contrast to crosslinking thermosets, whose cure reaction cannot be reversed, thermoplastics harden when cooled but retain their plasticity; that is, they will soften and can be reshaped repeatedly by reheating them above their processing temperature. Less-expensive thermoplastic matrices offer lower processing temperatures, but also have limited use temperatures. They draw from the menu of both engineered and commodity plastics, such as polyethylene (PE), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), polyamide (PA or nylon) and polypropylene (PP). High-volume commercial products, such as athletic footwear, orthotics and medical prostheses, benefit from the toughness and moisture resistance of these resins, as do automotive air intake manifolds and other underhood parts.
High-performance thermoplastic resins - polyetheretherketone (PEEK), polyetherketone (PEK), polyamide-imide (PAI), polyarylsufone (PAS), polyetherimide (PEI), polyethersulfone (PES), polyphenylene sulfide (PPS) and liquid crystal polymer (LCP) - function well in high-temperature environments and, when exposed to moisture, neither absorb water nor degrade. Reinforced with high-performance fibers, these resins exhibit lengthy prepreg shelf life without refrigeration and provide exceptional impact resistance and vibrational damping, although they present some processing challenges because of their high viscosity.