Cure Kinetics of Neat and Nanophased Polyurethane Foams

In this work, the isothermal cure behavior of a two part polyurethane foam system has been evaluated at temperatures between 25°C–80°C via a rheokinetic method. An ATD CSS 1000-Advanced Polymer Analyzer (APA) rheometer operating in torsion mode was used for this purpose. In the first phase of our work, neat polyurethane foams were investigated and the effects of cure temperature on the final cure modulus and density were documented. The testing procedure consisted of measuring G^* as a function of time. The data obtained was fit to a generalized cure kinetics model to evaluate various parameters such as rate constants, reaction orders and activation energies. The rate constants as a function of temperature exhibited a straight line Arrhenius relationship. In the second phase of the work, 1% by weight of cloisite-15A nanoclay was used to manufacture nanocomposite foams. Isothermal cure tests were performed on the nanocomposite foam sample at 25°C. A preliminary investigation of the effect of nanoclay infusion on the final cure properties revealed no significant change. However the nanoclay foam sample exhibited higher reaction rates than its neat counterpart at the same temperature. The cell structures of these foams were studied using a JEOL 960 Scanning Electron Microscope. The micrographs supported the observations that neat foam samples showed an increased density and modulus at lower temperatures than at higher temperatures. The nanoclay sample also showed a higher density relative to its neat counterpart.