Resins for resin transfer molding (RTM) are typically formulated to release a minimal amount of volatiles during thermally-initiated polymerization in order to limit porosity in manufactured parts. However, new resins such as benzoxazines and benzoxazine blends, which are formulated for high service temperatures and mechanical performance, require solvent additives and may have higher levels of reaction-induced volatile release.  The structure and reaction product of a benzoxazine is shown below.  In the present study, we analyzed volatile release and the effects of residual solvent in a pre-commercial benzoxazine/epoxy system designed for liquid molding. Utilizing thermogravimetric analysis (TGA), nuclear magnetic resonance (NMR) spectroscopy, and dynamic mechanical analysis (DMA) we correlated the concentration of residual solvent remaining within the final manufactured part with its <i>T<sub>g</sub></i>, degradation temperature, and dynamic modulus. Afterwards, we demonstrated a resin synthesis method that eliminates residual solvent in order to produce carbon fiber reinforced polymer (CFRP) composite parts with optimal surface finish and thermomechanical properties. An investigation concerning the recycling and decomposition of benzoxazine species is forthcoming. These results demonstrate a methodology for optimizing resin chemistry for production of high-quality composite parts.

Eliminating porosity in benzoxazine thermosets

253rd National Meeting (2017)

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