Polyimide Composites from 'Salt-Like' Solution Precursors

Four NASA Langley-developed polyimide matrix resins, LaRC™-IA, LaRC™-IAX, LaRC™-8515 and LaRC™-PETI-5, were produced via a ‘salt-like’ process developed by Unitika Ltd. The salt-like solutions (65% solids in NMP) were prepregged onto Hexcel IM7 carbon fibre using the NASA LaRC™ multipurpose tape machine. Process parameters were determined and composite panels fabricated. The temperature dependent volatile depletion rates, the thermal crystallization behaviour and the resin rheology were characterized. Composite moulding cycles were developed which consistently yielded well consolidated, void-free laminated parts. Composite mechanical properties such as the short beam shear strength; the longitudinal and transverse flexural strength and flexural modulus; the longitudinal compression strength and modulus; and the open hole compression strength and compression after impact strength were measured at room temperature and elevated temperatures. The processing characteristics and the composite mechanical properties of the four intermediate modulus carbon fibre/polyimide matrix composites were compared to existing data on the same polyimide resin systems and IM7 carbon fibre manufactured via poly(amide acid) solutions (30–35% solids in NMP). This work studies the effects of varying the synthetic route on the processing and mechanical properties of the polyimide composites.