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ABSTRACT:The effects of temperature and moisture on thermal and mechanical properties of high-temperature cyanate ester composite materials were investigated. A resin transfer molding process was used to impregnate glass fiber fabrics with matrices that underwent thermoplastic or elastomeric toughness modifications. The elastomer-modified material obtained the highest mode I fracture toughness values primarily because the toughener did not phase separate. Extended exposure to 200°C, however, deteriorated initial toughness improvements regardless of the modifier utilized. Although the thermal stability was increased by using thermoplastic modifiers in comparison to the elastomer-modified material, the degradation was mainly governed by the cyanate ester network. Gaseous degradation products caused delaminations and therefore reduced strength when the materials were exposed to 200°C for 1000 h. Also, upon immersion in water at 95°C, the matrices absorbed up to 3.3 wt % more than previous values reported in the literature. Fiber/matrix interfacial phenomena were responsible for this behavior because fiber/matrix adhesion also was reduced drastically as shown by the strong reduction in flexural strength.

Model cyanate ester resins containing different quantities of epoxy functional butadiene‐acrylonitrile rubber (ETBN) to improve the fracture performance were developed as matrices for composites. With the elastomeric modification, 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 established. The BRTM process combines features of RTM and resin film infusion processes (RFI) and was therefore appropriate for processing high viscosity matrix resins. A novel catalyst was selected for the cyanate ester resin that provided enough latency for the impregnation steps in the BRTM process. Through the use of thermal analytical tools, a high degree of phase separation and conversion was obtained. The conversion and the glass transition temperature were found not to decrease with increasing elastomer content, which 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 observed. Collectively, this work showed that through the use of the BRTM technique, matrices with toughness improvements usually only achieved by prepreg systems can be processed in an RTM‐like manner.

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Composite materials have gained the attention of the automotive industry to substantially reduce vehicle weight, reduce CO 2 emissions and improve the fuel economy of next generation vehicles. Thermosetting matrix technology combined with glass or carbon fiber reinforcements are well suited for structural applications where mostly steel and aluminum are used today. However, the lack of fast production techniques and fast reacting matrix technologies have limited composites use to low volume production models. A new generation of epoxy resin systems has been developed that allows the rapid processing of structural composites for medium to high volume models. These advanced formulations maintain the excellent properties of traditional epoxy-based composites, yet the tested systems can process in a matter of minutes using modern manufacturing technologies such as the high pressure resin transfer molding (HP-RTM) process. The advanced formulations are unique in that they provide a long enough injection window for a robust impregnation of the reinforcing fibers while still enabling an extremely short cure cycle. The results from this development show that structural composite components can be produced economically and in high volume using today's innovative resin and process technology.