Chemical and physical blowing agents in structural polyurethane foams: Simulation and characterization

Physical blowing agents such as n-pentane and methyl formate and, for compa rison, chemical blowing agents such as water were used to prepare structura l polyurethane rigid foams of different densities by reaction injection mol ding. Experimental runs were carried out with formulations based on oligome ric isocyanate and a mixture of polyether polyols. The constitutive equatio ns for the vaporization rate of the two blowing agents and the polymerizati on kinetics data are reported. Experimental results were compared with the prediction of a simplified theoretical model, and they showed a satisfactor y agreement in terms of temperatures and density profile. All the specimens were characterized by physical-mechanical properties such as hardness, imp act strength, flexural strength and elastic modulus and the results were re ported in function of the densities. The best mechanical performance were o btained with the physical blowing agents, due to a better density distribut ion profile and a thicker skin layer.