Thermal expansion of polyurethane reinforced with continuous glass fibers

This paper is concerned with the study of the thermal expansion properties of polyurethanes which are reinforced with randomly oriented continuous glass fibers. The thermal expansion of reinforced polymers is of prime importance since it has a significiant effect on the overall dimensional stability of molded products. In this work the coefficient of linear thermal expansion (CLTE) is measured for both soft and rigid polyurethane containing various amounts of glass fibers. The experimental results show that: (1) there exists a maximum in the CLTE-temperature curves, the position of which depends on the type of resin and not on the glass content; (2) over the range of 0 to +70°C for rigid polyurethane, and –30 to +70°C for soft polyurethane, the CLTE decreases with temperature. The existence of a maximum in the above findings is confirmed with computations from a theoretical expression which was modified by the introduction of an efficiency factor. In applying this expression, parameters such as the Poison's ratios, elastic moduli, and the CLTe's of the resins had to be evaluated at various temperatures. Based on these results, the CLTE-temperature curves were obtained and found to be in agreement with the experimental observations.