Synergistic effect of exfoliated graphene nanoplatelets and non-halogen flame retardants on flame retardancy and thermal properties of kenaf flour-PP nanocomposites

A series of quaternary hybrid kenaf (K) flour-PP nanocomposites, such as PP/KF/MAPP/GNP/MgOH (K-GNP-MgOH), PP/KF/MAPP/GNP/APP (K-GNP-APP) and PP/KF/MAPP/GNP/MgO (K-GNP-MgO) filled with exfoliated graphene nanoplatelets (GNP)-3 phr acting as adjuvant in combination with mineral flame retardants, 20 mass/% magnesium hydroxide (Mg (OH)₂) and 20 mass/% magnesium oxide (MgO), and 20 mass/% intumescent ammonium polyphosphate (APP), respectively, were prepared through melt extrusion using co-rotating twin screw extruder. The resulting quaternary nanocomposites were characterized in terms of flame retardancy, thermomechanical, thermal conductivity, thermal behavior, heat deflection temperature (HDT), and mechanical, morphological and structural properties. Mass loss calorimeter data revealed a significant reduction of peak heat release rate, total heat release, effective heat of combustion, mass loss rate and delayed time to ignition due to GNP-MgOH, GNP-MgO and GNP-APP synergistic mechanism in hybrid nanocomposites, respectively. The effective thermal conductivities and HDT of quaternary nanocomposites were found to significantly increase. DSC results revealed enhanced crystallization temperatures with reduced degree of crystallinity, while melting points remained stable.