The Role of Isocyanate Index and Flame Retardant in Reducing CO(g) and Smoke Emissions of Soybased Rigid Polyisocyanurate Foams

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Abstract
Enhancing the flame retardancy of biobased rigid polyurethane foams is a crucial step towards improving the sustainability of the polyurethane industry. In this work, we systematically analyzed the effect of increasing the isocyanate index (NCOindex) and the flame retardant content using a polyol with high renewable content (>97 wt.%). We found outstanding results regarding the CO(g)/CO2(g) index, the most important safety parameter in terms of human safety, whereas a significant reduction of 78% and 69.6 % was observed as a function of increasing the NCOindex and flame retardant (FR) content, respectively. In addition, the FR did not cause an increase of the total smoke produced (TSP), on the contrary, it decreased up to 31.4% after increasing the FR concentration. The MAHRE parameter was also substantially improved, up to 40.6%, indicating the formation of a thicker char layer which protected the foam during burning. This was achieved simultaneously with outstanding improvements of the specific compressive strength of up to +155%. The studies were substantiated by a comprehensive physico-chemical characterization using TGA analysis, water absorption, initial thermal conductivity, FTIR analysis and cell geometry using SEM. These results are of paramount importance to promote the use of biobased rigid polyurethane foams with enhanced fire retardancy.

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