Hexaphenoxycyclotriphosphazene as FR for CFR anionic PA6 via T-RTM: A study of mechanical and thermal properties

The production of carbon fiber reinforced (CFR) anionic polyamide 6 (APA6) plates by thermoplastic resin transfer molding (T-RTM) processing is highly sensitive to the presence of polymer additives such as flame retardants (FRs). However, APA6 is flammable, and therefore, it is mandatory to protect the polymer matrix, especially if the produced materials are intended for aerospace applications. Typically used FR for PA6 cannot be incorporated in the T-RTM processes. With hexaphenoxycyclotriphosphazene, an incorporable and effective FR additive for CFR APA6 was discovered. Cone calorimetry measurements indicate a char formation-based mechanism, and the flame retardancy was further confirmed with limiting oxygen index tests, classification by UL94 (V-0), and FAR25 tests.