Liquid molding of carbon fabric-reinforced nylon matrix composite laminates

The present work addresses the processing parameters, methodology, and limitations of vacuum assisted resin transfer molding (VARTM) of carbon fabric-reinforced thermoplastic polyamide 6 (PA6) matrix panels on the laboratory scale. VARTM is a mature technology for producing large-scale thermoset composite parts/structures but has not been used for thermoplastic composites, which are manufactured primarily by compression molding, extrusion, and/or injection molding. In general, liquid molding of thermoplastics has limitations, such as high resin viscosity, high temperature processing requirements, and a short processing window. The materials used in this study are casting grade PA6, epsilon-caprolactam with a sodium-based catalyst, and an initiator. This system allows the resin to maintain a very low viscosity (< 1 Pa s) for a reasonable period of time, at relatively low temperatures (100 degrees C). The carbon fabric preform is infused using VARTM after which the resin is fully polymerized in situ. The process developed for using VARTM to produce carbon fabric-reinforced PA6 matrix composites is explained in detail. Microscopic studies are presented to evaluate wet-out of the fibers at both the tow and the filament levels. The effects of infusion temperature and flow distance on the fiber weight fraction and crystallinity of the PA6 resin are investigated. The degree of monomer conversion to polymer is determined.