Development of fundamental understanding of the cure kinetics of benzoxazine epoxy blends

Abstract

This study attempts to bridge the gap between the current fundamental understanding of benzoxazines on the monomer level and their macro scale thermo-mechanical properties. Bisphenol-A based benzoxazine (Bz) was blended with di- and tri-functional epoxies to reduce viscosity for processing, and their resulting thermal and mechanical properties were characterized. Additionally, the formation of inter-molecular and intra-molecular hydrogen bonds was investigated within a Bz-epoxy two component system. Activation energy, heat of reaction, degradation temperature, hydrogen bonding characterization and thermo-mechanical characterization were studied using a differential scanning calorimeter, dynamic mechanical analyzer, thermogravimetric analysis, Fourier transform infrared spectroscopy and quasistatic tensile testing. Preliminary results show a synergistic increase in Tg of the blends, for both di- and tri-funcitonal epoxy blends. Surprisingly, while the two components exhibit Tg’s of ~ 150-170 oC, the blended systems consistently exhibited a Tg in the range of 210-250 oC. This work aims to expand upon thermal and mechanical characterization data generated by our collaborator Ehsan Barjasteh for the benzoxazine – di-functional epoxy system, as well as explore a new benzoxazine – tri-functional epoxy-based system. Our underlying motivations in this study are to identify the origins of the synergistic increase in Tg upon blending through various thermo-mechanical characterization methods and in-situ FT-IR analysis of cure kinetics, as well as identifying the compositions and functionality which exhibit the most desirable combination of thermal and mechanical properties.