Thermal Expansion Instability and Effect on Creep of Polyurethane

It was found that thermal expansion of polyurethane decreased markedly in several hundred hours. After heating the thermal expansion decreased gradually at constant temperature; after cooling the thermal contraction decreased with time but more slowly. The role of cross-linking as a cause of this effect is discussed. Creep during the expanded phase after heating is shown to be much greater than creep after thermal expansion has stabilized at the same temperature. Experiments are described which show that the effect of temperature on creep results primarily from thermal expansion rather than from thermal oscillation. (Author-PL)