In this study, we report effect of temperature on cure behavior and viscoelastic shear properties of rigid polyurethane foams. Both cure and viscoelastic studies were performed using an advanced polymer analyzer (APA) operating in shear mode. In the first phase, isothermal cure behavior of polyurethane foam was investigated at four different temperatures namely 25°C, 45°C, 60°C, and 80°C. The testing procedure consisted of measuring complex shear modulus, G* as a function of time. The data obtained was fit to a generalized cure kinetics model to evaluate various parameters such as rate constant, reaction order, and activation energy. In the second phase of the work, oven cured PU foam samples have been subjected to a temperature sweep in the range of 30°C - 150°C while monitoring the dynamic shear modulus (complex and loss). It is observed that the cure temperature has significant effect on reaction rate, vitrification time, and final shear modulus. The rate constants exhibit a straight line Arrhenius relationship. It is also observed that both 25°C and 60°C cure temperature show the highest shear modulus while 80°C cure temperature shows an order of magnitude higher reaction rate. The vitrification time decreases with increase in cure temperature. From the viscoelastic tests it is observed that 80°C cured sample shows the highest complex shear modulus at low temperature but the modulus decreases very sharply with temperature increase. Whereas the 60°C cured sample exhibits the lowest rate of modulus decrease. The corresponding glass transition temperatures are in the range between 130°C -140°C. Careful examination of the microstructure indicates that both APA and oven cured samples exhibit similar microstructure. The relatively smaller cell size of the APA cured foams is due to the lateral constraint by the APA die during curing. The general trend is the cell size decreases with increase in cure temperature.
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