Synergistic effect of expandable graphite and α-type zirconium phosphate on flame retardancy of polyurethane elastomer

Organically modified zirconium phosphate (OZrP) was prepared by cation exchange of natural counterions with hexadecyltri-n-butylphosphonium bromide. Subsequently, OZrP and expandable graphite (EG) were incorporated into polyurethane elastomer (PUE), and the thermal stability and flame retardancy of PUE composites were investigated. The thermogravimetric analysis indicated that partial substitution of EG with OZrP could improve both the thermal stability and char yield of PUE composites. The cone calorimetry and limiting oxygen index test showed that partial substitution of EG with OZrP could further enhance the flame retardancy of PUE composites and presented an excellent synergistic effect. Moreover, the char residue of PUE composites was analyzed by X-ray photoelectron spectroscopy and laser Raman spectroscopy. Their results indicated that the synergistic effect of the physical barrier to prevent transmission of heat and mass between condensed and gas phases. Therefore, the further combustion of the nether material could be inhibited, which created better flame retardancy.