Solid acid-reduced graphene oxide nanohybrid for enhancing thermal stability, mechanical property and flame retardancy of polypropylene

Reduced graphene oxide (RGO) is functionalized with a solid acid, phosphomolybdic acid (PMoA), via electrostatic interactions. RGO and PMoA in this nanohybrid (PMoA-RGO) exhibit strong interactions and the surface characteristic of the graphene nanosheets is modified. RGO and PMoA-RGO are blended with polypropylene (PP) and maleic anhydride grafted polypropylene via a master batch-based melt mixing method. Thermal stability, mechanical and flame retardancy properties of the nanocomposites are investigated. This nanohybrid greatly improves the stiffness and thermal-oxidative stability of PP. Compared to the neat sample, the onset decomposition temperature (T-onset) and the temperature at the maximum weight loss rate (T-max) of the nanocomposite increase by as much as 44 degrees C and 34 degrees C, respectively, at just 1 wt% loading of PMoA-RGO. Remarkable enhancements of the storage modulus in the glassy region and heat deflection temperature are obtained in PMoA-RGO/PP nanocomposites. The nanohybrid exhibits more marked reinforcing effects than the RGO. The heat release of the nanocomposites during the combustion is considerably reduced compared to neat PP. The improved thermal-oxidative stability and flame retardant properties of PP nanocomposites are mainly attributed to the barrier effect of graphene, in tandem with the enhanced radical trapping property of the nanohybrid.