Flame-retardant polyurethane and glass fiber-reinforced polymer composites enabled by aromatic heterocyclic liquid mixture flame retardants

Abstract

With the rapid development of the pultrusion molding process, glass fiber-reinforced polyurethane composites have become increasingly prominent in industrial applications due to their unique advantages. However, their high flammability significantly limits their potential uses. Here, hexaphenoxycyclotriphosphazene and hexakis(methoxymethyl)melamine resin were combined to create a novel liquid mixture flame retardant (LMFR) for polyurethane and its glass fiber-reinforced polymer composites. The resultant polyurethane exhibited excellent flame retardancy, achieving a V-0 rating in the UL-94 vertical burning test, and a 64.5 % reduction in the peak heat release rate. Similarly, its composite achieved a limiting oxygen index of 58.0 %, a UL-94 V-0 rating, and a 31.9 % reduction in total heat release. Notably, this flame retardant significantly reduced both the smoke production rate and total smoke production in polyurethane and its composite. Meanwhile, LMFR exhibited excellent heat resistance with minimal impact on the thermal stability of polyurethane resin. Mechanistic studies revealed that the LMFR achieved flame retardancy and smoke suppression through a synergistic interaction between the gas and condensed phases, providing an effective approach to improving the safety and performance of glass fiber-reinforced polyurethane composites.