Volatile Evolution in Thermoset Composites from Processing to Degradation

Using phenolic resin/carbon fiber composites as a model system, volatile evolution during thermoset composite processing was studied theoretically as well as experimentally. Water (and/or solvent) stabilization during the consolidation process could be described by combining gas-liquid phase equilibrium principles and the curing kinetics of the matrix system with a pseudo steady state approximation. Based on this consideration, voids from water (and/or solvents), which might vaporize during consolidation processing, could be suppressed by controlling the consolidation temperature and pressure with respect to time. Upon further heating the phenolic resin/carbon fiber composites up to 1000° C, composite degradation characteristics were investigated by using several thermal, mechanical, and chemical characterization techniques. Correlating these experimental results, characteristic features of each degradation stage were identified by weight loss, gas evolution, heat flow, dimensional stability, and modulus. Specifically, when the composite laminate was heated up to 300° C, where the matrix was expanding in the rubbery state, initially-generated microcracks were observed to close, resulting in a composite healing process.