Evaluation of Thermal Endurance Characteristics by Time Dependence of Compression Dynamic Modulus of Flexible Polyurethane Foams

For evaluation of thermal endurance in foamed plastics, the temperature and time dependence of the compression dynamic modulus of seven flexible polyurethane foams were investigated by dynamic viscoclastic measurements. In a certain temperature range, the compression dynamic modulus of each polyurethane foam lessened gradually with time, presumably due to a relaxation phenomenon of foam skeletons accompanying deterioration in the bending stiffness of the skeleton. The logarithm of time t, by which the compression dynamic modulus fell to 50% of its initial value, has been found to be a linear function of reciprocal temperature T-1. The parameter A is the slope of this function and has been found to correlate negatively, with the porosity but with the hardness positively.