Styrene-free synthesis and curing behavior of vinyl ester resin films for hot-melt prepreg process

Abstract

Vinyl ester (VE) resin films were developed from epoxy resins via esterification with methacrylic acid without a reactive diluent to fabricate carbon fiber (CF) prepregs via a hot-melt impregnation process. The viscosity of VE resins suitable for the hot-melt prepreg method was optimized by mixing two different bisphenol-A epoxy precursors, with low and high molar masses. Unidirectional CF prepregs were fabricated via the hot-melt impregnation method using as-prepared VE films. Manual layup of as-prepared VE prepregs with subsequent curing in an autoclave led to the successful fabrication of CF-reinforced composites with good tensile and flexural strength. The kinetics and mechanism of the radical crosslinking of VE synthesized using various mixing ratios of two different epoxy precursors were studied using nonisothermal differential scanning calorimetry. Quantitative analyses with the autocatalytic model and model-free methods indicated that the higher viscosity of VE causes a higher energy barrier associated with molecular mobility and diffusion.