Curing of epoxy-urethane copolymers in a heated mold: Effect of the curingconditions on the phase-separation process

The curing process of an epoxy-urethane copolymer in a heated mold was stud ied. The epoxy resin (DGEBA, Araldyt GY9527; Ciba Geigy), was coreacted wit h a urethane prepolymer (PU, Desmocap 12; Bayer) through an amine that acte d as crosslinking agent (mixture of cycloaliphatic amines; Distraltec). The study focused on the effect of the curing condition and PU concentration o n time-temperature profiles measured in the mold and the consequent final m orphologies obtained. As the PU concentration increases, the maximum temper ature reached in the mold decreases as a result of the dilution effect of t he elastomer on reaction heat, whereas the T, of the piece also decreases. Phase separation is a function of conversion and temperature reached in the curing part and was analyzed using experimental data and a mathematical mo del that predicts temperature and conversion throughout the thickness of th e mold. Scanning electron microscopy and atomic force microscopy were used to determine the characteristics of the dispersed phase for the different f ormulations and conditions of curing. It was shown that the size of the dis persed phase increased with the initial PU concentration, whereas there wer e practically no differences in the separated phase as a function of positi on or temperature of curing tin the range of 70 to 100 degreesC studied). T he superposition of the phase diagrams with the conversion-temperature traj ectories during cure provided an explanation of the morphologies generated. (C) 2001 John Wiley & Sons, Inc.