Phosphorization of exfoliated graphite for developing flame retardant ethylene vinyl acetate composites

Abstract

Ammonium polyphosphate (APP) was grafted onto the surface of exfoliated graphite nanoplatelet (GNP) to obtain a novel flame retardant, GNP-g-APP, and thereafter was incorporated into the ethylene vinyl acetate (EVA) to improve its flame retardancy. The chemical structures of the precursors and the target product were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and energy dispersive X-ray spectroscopy (EDS) techniques. FTIR spectra appeared at 1056 and 1103cm−1 were attributed to POC asymmetric stretching bond, that conformed formation of GNP-g-APP. Thermal stability behaviour and flame retardancy performance of the samples were evaluated by TGA, UL-94, micro-calorimetry, and cone calorimetry. TGA measurements revealed the superiority of GNP-g-APP over GNP. The micro-calorimetry analyses indicated a sharp fall in both the total heat release (THR) and the peak of heat release rate (pHRR) of EVA containing 30wt.% GNP-g-APP, evidenced by a thick char layer formed as barrier. Cone calorimetry confirmed flame-retardant effect of GNP-g-APP featured by a reduction in pHRR (−63 %) and THR (−31.6 %) due to the formation of a cohesive char layer. Although GNP addition sharply decreased the elongation at break of 70/30 (w/w) composites from 500% for neat EVA to 71%, a very promising value of 364% for EVA/GNP-g-APP sample preserved superior flexibility.