Cardanol/triazine-based polyol and DOPO derivative for thermally insulating and flame retardancy rigid polyurethane foam composites

Researchers are increasingly focusing on the development of biobased polyol derived rigid polyurethane foams (RPUFs) as sustainable alternatives to traditional polyether polyol based RPUFs targeting improvements in flame resistance, mechanical strength and thermal insulation. In this context novel biobased cardanol/triazine based polyol was synthesized through co-condensation of cardanol, melamine and paraformaldehyde and its chemical structure and functional groups was confirmed by FT-IR and ¹H NMR analyses. Using this polyol cardanol/triazine based rigid polyurethane foam (C/N-RPUF) was fabricated via a one-pot reaction under –NCO/–OH ratio of 1.1. To enhance fire safety C/N-RPUF composites were produced by incorporating 1, 3 and 5 wt% of a reactive DOPO derived polyol (DOPOP). Structural characterizations of composites were performed using FTIR and SEM-EDS techniques. Remarkably C/N-RPUF with 5 wt% DOPOP demonstrated superior flame retardancy achieving a UL-94 V-0 classification, limiting oxygen index (LOI) of 26.5%. Compressive strength values of neat C/N-RPUF and C/N-RPUF/5wt% DOPOP were 0.081 and 0.127 MPa respectively with the improvement attributed to additional cross-linking interactions within the foam structure. Additionally, the 5 wt% DOPOP composites showed a thermal conductivity of 0.051 W/(m·K), which is lower than that of conventional RPUFs, suggested its superior thermal insulation performance. In terms of fire performance composite showed significant reductions compared to pristine C/N-RPUF with 39.6% decrease in peak heat release rate (PHRR) and a 64.2 % reduction in CO emission. Overall, this work introduces an eco-friendly and efficient strategy for producing high-performance biobased rigid polyurethane foams combining flame resistance, compressive strength and superior insulation properties.