Benzoxazines (Bz) are a class of thermoset resins that have been poised to replace traditional aerospace resins such as epoxy (Ep), bismaleimide, and phenolic due to their high glass transition temperature (Tg), excellent fire retardancy, small coefficient of thermal expansion (CTE), near zero cure shrinkage, low water absorption, and excellent solvent resistance. Unfortunately, they suffer from higher viscosities than resins used for additive manufacturing and vacuum-assisted resin transfer molding (VaRTM). In order to enhance the Tg of a traditional Bz resin without sacrificing its superior inherent qualities, we blended a Bz resin with epoxy resins of various functionality to alter the network formation during cure. The ratio of Bz and Ep were varied by weight to determine which yielded the highest Tg and lowest viscosity. Furthermore, fourier transform infrared spectroscopy (FTIR) was conducted during cure to identify the crosslinking reaction mechanisms that took place. Currently, there is no fundamental understanding of the crosslinking mechanism in the homopolymerization of Bz, let alone in the copolymerization of Bz/Ep hybrids. Previous studies by a collaborator showed that a significant increase in Tg (~100 °C) and decrease in viscosity (~102 Pa*s) can be obtained by mixing Bz and Ep at 50 wt. %/50 wt. %. To develop a better understanding of the mechanisms responsible for the aforementioned changes in the behavior of the Bz/Ep hybrid, IR spectra were obtained for the neat monomer resins. Next, Bz/Ep blends were fabricated by rotovaping predetermined amounts in a flask at 95 °C, and 60 RPM while under vacuum (50 mbar). The spectra were analyzed by running a Matlab script that identified peaks of particular interest and calculated the concentration of particular chemical bonds based on the Beer-Lambert law. The concentrations were plotted as a function of time and compared between systems.

Development of a fundamental understanding of the curing kinetics of benzoxazine/epoxy blends via in situ Fourier transform infrared spectroscopy

2019 Spring National Meeting

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