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

Enhancing the flame retardancy of bio-based rigid polyurethane foams (RPUFs) is a crucial step toward improving the sustainability of the polyurethane industry. In this work, we systematically analyzed the effect of increasing the isocyanate index (NCO_index) and the flame retardant (FR) content using a polyol with high renewable content (> 97 wt.%). We found outstanding results regarding the CO_(g)/CO_2(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 NCO_index and FR content, respectively. In addition, the FR did not cause an increase in the total smoke production (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 that protected the foam during burning. This was achieved simultaneously with outstanding improvements in the specific compressive strength of up to +155%. The studies were substantiated by a comprehensive physicochemical 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 bio-based RPUFs with enhanced fire retardancy.