Effect of surface curing temperature on depth-specific physical properties of poly(urethane-isocyanurate) foam panels in relation with local chemical composition and morphology

Abstract

Processing low density poly(urethane-isocyanurate) (PIR) rigid foam boards still remains challenging, especially for high thickness panels with the spontaneous formation of two-dimensional wrinkles. Increasing the double-belt conveyor temperature (mold temperature in this work) was regarded as a way to increase the rigidity of the foam base material and, ultimately to increase the stiffness of the PIR foam under the facing. For that purpose, PIR foam samples simulating real panels were prepared at different mold temperatures and were chemically analyzed using ATR-FTIR spectroscopy while a Shore durometer (type OO) was used to estimate the foam rigidity in various locations of the model panel. Obviously, the isocyanurate content of the foam under the facing was found to increase with the increase in mold temperature but surprisingly the Shore hardness demonstrated the reverse effect. This result was explained by the decrease in the density of the foam layer under the facing as the mold temperature increases, thereby counteracting the probable increase in stiffness of the foam base material itself. In addition, foam characterizations at different depths (rise direction) indicate that the chemical and mechanical gradients occurring in the first 20–30 mm tend to disappear as the mold temperature increases.