Environmentally friendly processing of polyurethane foam for thermal insulation

An environmentally friendly processing method of polyurethane foam was proposed and evaluated for the application of thermal insulation. For the production of polyurethane foam, chlorofluorocarbon (CFC) gases were eliminated to minimize environmental destruction. Carbon dioxide gas was used as a blowing agent instead of the CFC gas. Ultrasonic excitation was also applied to the mixture of polyol and isocyanate,to increase the rate of nucleation and decrease the thermal conductivity. Nucleation and growth of bubbles were studied theoretically and experimentally. Water was used as a chemical blowing agent and carbon dioxide gas as the physical blowing agent. Experiments were carried out with different saturation pressures, and experimental results were evaluated to determine the best foaming conditions. Rate of bubble nucleation, final bubble sizes, conversion during polymerization reaction, and other parameters were predicted theoretically with the assumption that negative pressure is generated by the ultrasonic field and the bubble growth is controlled by diffusion of the gas from the resin into the bubble. The best results such as low thermal conductivity and small size of bubbles were obtained when the polyol which has been mixed with water was saturated with carbon dioxide gas and the ultrasonic excitation was applied to the mixture of polyol and isocyanate right after the impingement mixing.