The Influence of Heat Treatment on the Quality of Vehicle Component Parts Made of Rigid Polyurethane Foam

The paper provides the results of the investigation in the influence of heat treatment on the quality of vehicle component parts made of rigid polyurethane integral foam. The temperature of heat treatment was based on the exo-peak of the first heat cycle in DSC curve, and was equal to 135 °С. At that temperature, the samples were treated for 2-8 hours, and, as a result, they experienced an abnormal exo-effect in the glass transition region, which was indicative of thermal relaxation. The paper shows that the additional heat treatment stage for parts made of rigid polyurethane integral foam results in an increase in molecular mass of polymer, due to a smaller quantity of end groups, and, thus, in an increase in glass transition temperature from 169 °С to 176 °С. An increase in heat treatment time to 6 hours at 135 °С leads to a higher ultimate bending strength, which reaches its maximum, while further heat treatment (up to 8 hours) lowers this value. Therefore, with a higher degree of cross-linking the fracture toughness increases and passes its maximum, after that it starts to decrease, and the material becomes brittle.