A Rigid-Flexible Integrated Linear Polyurethane Simultaneously Flame Retardant and Toughened, Reinforced Epoxy Resin

In order to improve the inherent defects of epoxy resin (EP) and realize flame-retardant materials with high mechanical properties, a flame-retardant linear polyurethane (PPIT) containing rigid and flexible structures was designed and prepared in this paper. It was also successfully added to EP as a multifunctional flame retardant. The glass transition temperature (Tg) of the obtained EP/PPIT-15 thermosets reached 171 °C. Good compatibility was achieved between the EP system and PPIT, and the specific functional groups of PPIT facilitated the interactions between the two components, which effectively improved the mechanical properties of the thermosets. The flexural and tensile strengths of EP/PPIT-15 were improved by 28.9% and 46.1%, respectively, compared with those of EP, and the tensile fracture strength was improved by 142.9%. The incorporation of PPIT-20 into the EP matrix resulted in a 19.3% decrease in the total heat release (THR), a 30.3% reduction in the total smoke production (TSP), and a 21.5% drop in the peak smoke production rate (PSPR), compared to neat EP. The synergistic flame-retardant effect of PPIT in the gas and condensed phases significantly increased the ultimate oxygen index of EP/PPIT-20 composites to 36.0%, which significantly improved the flame-retardant performance of EP. The composite shows the characteristics of both stiffness and flexibility, realizing double improvement of the mechanical properties and flame retardancy, and as a multifunctional material, it shows great application potential in the field of high-performance EP monomer flame retardants to meet diversified needs.