The effect of post-mould curing on the mechanical properties of instant-setting poly(urethane-isocyanate) polymers

The effect of post-mould curing on selected properties of instant-setting poly(urethaneisocyanate) polymers was investigated. The changes in tensile, flexural and impact strength as a function of annealing, cooling rate and thickness were determined. Generally, the process of annealing was found to increase the tensile and structural strength by about 5%. The extent of this improvement depends on variables such as the thickness of the specimen, the heat treatment cycle and the composition of the polymer. It was found that annealing produces secondary cross-linking as a result of the reactions of isocyanate end groups with urethane groups and with themselves. It was also found that the relaxation of internal stresses as a result of annealing contributes to the measured mechanical properties.