Pore Size Control Mechanism of a Rigid Polyurethane Foam

Rigid polyurethane foam is a widely used insulation material in various industrial fields. Enhancing its insulating performance often involves controlling pore size to reduce radiative conductivity and, in some cases, decrease gas thermal conductivity through the Knudsen effect. While numerous studies have addressed reducing the pore size of thermoplastic polymer foam to the nano-scale, limited research has focused on rigid polyurethane foam. Although some studies have shown that pore size changes with the addition of nucleating agents, a comprehensive understanding of the mechanisms governing pore size remains elusive. Therefore, this study investigates the factors determining the pore size of rigid polyurethane foam. Our findings confirm that the size of air bubbles formed during the blending of prepolymers has the most significant impact on pore size. Furthermore, we demonstrate that regulating the size of air bubbles before the urethane reaction allows for control over the final pore size. Experimental details substantiating these findings are presented.