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Rigid polyurethane foam (RPUF) is one of the most widely used construction materials, but it is flammable and releases toxic smoke during combustion. In this study, a novel, synergistic-effect flame retardant (FPASO-DOPO) was synthesized by the Atherton–Todd reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with fumaropimaric acid-based siloxane (FPASO). The obtained FPASO-DOPO was then introduced into the cross-linking network of an RPUF by chemical bonding. The flame retardancy was enhanced by the synergistic effect of phosphorus and silicon in the FPASO-DOPO, which captured the free radical in the gaseous phase and formed a compact silica-rich char layer in the condensed phase. More importantly, the incorporation of FPASO-DOPO not only increased the limiting oxygen index from 17.0% to 26.1% but also reduced the total smoke release by 17.5%. A cone-calorimeter test indicated that the peak heat-release rate of the modified foam was reduced by 33.7% compared with that of neat RPUF. Calculations determined that the flame retardancy index (FRI) value was 7.88 for a modified foam, which shows a “good” flame retardancy. Moreover, the modified foams exhibited improvements in both compressive and flexural strength owing to the introduction of the rosin. This study has important implications for the development of modified polymers with good flame and smoke suppression from renewable resources.
Wang et al. (Tue,) studied this question.