Polyphthalamide

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Polyphthalamide (aka. PPA, High Performance Polyamide) is a thermoplastic synthetic resin of the nylon family that is used to replace metals in high temperature automotive applications, as the housing for high temperature electrical connectors and multiple other uses. It has found a degree of favour for use in cutlery, notably by Cold Steel in its Nightshade series of knives coming in a variety of shapes such as tanto, stiletto and punch daggers. This glass fibre reinforced series is advertised as being stealthy (due to them not being detected by metal detectors and having no metallic reflections) and, being made of "Grivory" (a trade name), stronger than previous models made of "Zytel".

As a member of the nylon family, it is a semi-crystalline material composed from a diacid and a diamine. However, the diacid portion contains at least 55% terephthalic acid (TPA) or isophthalic acid (IPA). TPA or IPA are aromatic components which serve to raise the melting point, glass transition temperature and generally improve chemical resistance vs. standard aliphatic nylon polymers.

PPA is manufactured under trade names Zytel(r) HTN, Amodel and Grivory.