Processing of highly elastomeric toughened cyanate esters through a modified resin transfer molding technique

Model cyanate ester resins containing different quantities of epoxy functio nal butadiene-acrylonitrile rubber (ETBN) to improve the fracture performan ce were developed as matrices for composites. With the elastomeric modifica tion, the resin systems exhibited rheological characteristics inappropriate for laminate fabrication by conventional resin transfer molding (RTM). To fabricate the carbon fiber based laminates in one liquid molding operation successfully, a process named bleed resin transfer molding (BRTM) was estab lished. The BRTM process combines features of RTM and resin film infusion p rocesses (RFI) and was therefore appropriate for processing high viscosity matrix resins. A novel catalyst was selected for the cyanate ester resin th at provided enough latency for the impregnation steps in the BRTM process. Through the use of thermal analytical tools, a high degree of phase separat ion and conversion was obtained. The conversion and the glass transition te mperature were found not to decrease with increasing elastomer content, whi ch is in contradiction to most toughening modifications. Mode I and Mode II interlaminar fracture toughness were found to increase significantly with increasing elastomer content. In Mode I, an increase of up to 140% was obse rved. Collectively, this work showed that through the use of the BRTM techn ique, matrices with toughness improvements usually only achieved by prepreg systems can be processed in an RTM-like manner.