Rheological and kinetic investigation into isothermal curing of a thermoset polythiourethane system

Abstract

ABSTRACTCuring of a thermoset polythiourethane system of a diisocyanate and a trithiol was studied by Fourier infrared (FTIR) spectroscopy, dynamic rheological measurements and scanning electron microscopy (SEM). The isocyanate conversion during the isothermal cure reaction from the FTIR spectroscopy results suggests that the rate of isocyanate conversion differs greatly in the temperature range of 100°C to 120°C. Time sweep at three constant temperatures was conducted to examine the isothermal curing process and determine the gel time of the polythiourethane system. The gel time can be determined by the crossover of storage modulus G′ and loss modulus G′′. The gel time is dramatically affected by the curing temperature. Frequency sweep was also performed to confirm the gel points obtained from the time sweep experiments. Scanning electron microscopy (SEM) observation indicates that polythiourethane polymers formed at different curing temperatures possess similar microstructures. Rheokinetics analysis shows the second-order kinetic characteristics of the cure reaction. The activation energy obtained based on the gel time was close to that obtained based on the rheokinetics analysis, indicative of the validness of the Kamal-Sourour model for the polythiourethane system.