Evaluation of thermal endurance characteristics of thermosetting polyurethane elastomers and polyurethane foams by dynamic compression modulus

For evaluation of thermal endurance of elastomers and foamed plastics, the time dependences of compression dynamic modulus of thermosetting polyurethane elastomers, and of micro-cell, hard and flexible polyurethane foams were investigated by dynamic viscoelastic measurements. In the temperature range of interest, 140 similar to 290 degrees C, compression dynamic modulus of each elastomer and each foam lessened gradually with time, which is presumably due to thermal degradation of the elastomers and foams. The logarithm of the time t at which the compression dynamic modulus came to be 50% of its value at the beginning of the dynamic measurement was found to be a linear function of reciprocal temperature T-1. Therefore, thermal endurance characteristics of thermosetting polyurethane elastomers and polyurethane foams can be evaluated as well as closed-celled polyethylene foams from the linear relations between T-1 and the logarithm of time t at which the compression dynamic modulus came to be 50% of its initial value. The loss tangent of elastomer differs from that of foam. Thermal degradation is determined by compression deformation in elastomers that have no cells and by the bending deformation in foam that have closed or open cells.