Effect of monomer temperature on foaming and properties of flexible polyurethane foams

Abstract

Polyurethane foam formation involves simultaneous polymerization and expansion. In an open cell foam, foam lamellae rupture at some stage of foam formation, resulting in a foam with continuous air channels. Experiments are carried out to study the effect of initial temperature of monomers on the open cell content of water-blown flexible polyurethane foams. The change in kinetics of the polymerization and blowing with initial monomer temperature is noted by measuring the gel and rise times during foaming. Both polymerization and blowing reactions are found to be faster with increasing monomer temperature. The cell size is found to increase with initial monomer temperature, and the height of the cured free rise foam is found to decrease. The open cell content of the foam increased considerably with initial monomer temperature, leading finally to the collapse of the foam at the highest temperatures studied. The mechanical properties of the foam at different monomer temperatures are determined by making molded foams. The indentation load deflection decreased with increasing monomer temperature indicating the formation of softer foams, but showed a slight increase near the temperature of collapse. Other mechanical properties showed a small degradation with increase in initial monomer temperatures.