Low temperature environments affect the properties of polyurethane elastomers, but no degradation occurs and effect is completely revesible. The major effect is an increase in Young’ s modulus below 0 *C with a corresponding increase in hardness, tensile strength, tear strength and torsional stiffness and a decrease in resilience.
The two properties that can have an important bearing on the use of polyurethane at low temperature are the decrease in resilience which has already been mentioned and the increase in stiffness. In the use of polyesterurethane at low temperatures another phenomenon can sometimes be observed. This is that of crystallization of the polyurethane when held at moderately low temperature foe some period of time. When crystallized the polymers are considerably harder and their stiffness charecteristics are similar to those normally observed at much lower temperatures. The effect is reversible and can be removed by the application of heat or by the generation of internal heat by flexing. The use of mixed polyesters reduces this tendency to crystallization.