Study on the Cure Kinetic Behavior of Thermosetting Polyurethane Solids and Foams: Effect of Temperature, Density, and Carbon Nanofiber

Cure kinetic behavior was studied for both thermosetting polyurethane (PU) solids and foams. The effects of cure temperature, foam density, and carbon nanofiber (CNF) contents were examined. Cure studies were performed experimentally by measuring the evolution of complex shear modulus as a function of time using an advanced polymer analyzer operating in dynamic shear mode. Isothermal cure behavior of PU solid and foams was investigated at four different temperatures, namely, $25°C$⁠, $45°C$⁠, $60°C$⁠, and $80°C$ and at three different amounts of CNF, namely, 0.01%, 0.05%, and 0.1% by weight. The cure data were analyzed by using an autocatalytic cure kinetic model. The cure behavior of both solid and foam was found to be temperature dependent. Addition of CNF was also found to affect the cure behavior of the PU foam. It was observed that the PU foam with 0.1% CNF shows the highest polymerization reaction compared with the neat foam. It was also observed that the reaction rate constants follow an Arrhenius dependence on temperature, whereas the reaction orders remain fairly constant. A simple predictive model using the reaction orders indicated that the maximum cure reaction rate was occurred at 37.5% conversion.