Investigation On GNP Synergistic Flame Retardant EVA Nanocomposites

Ethylene-vinyl acetate copolymer (EVA), due to its flammability, isrestricted in some fields. Aluminum hydroxide (ATH) is a common inorganicflame retardant for EVA, however, high loading levels of ATH deteriorate theproperties of EVA. Because of large specific surface area and high thermalstability, graphite nanosheets (GNP) are widely used in improving the thermalstability and flame retardant properties of polymeric materials, which suggeststhat the combination of GNP and ATH would be helpful to achieve high flameretardancy.In the dissertation, GNP was prepared via wet ball milling method withexpanded graphite synthesized from natural graphite flakes and modified viadirect precipitation and mill-blending methods. The structure of GNP andmodified GNP were studied by X-ray diffraction (XRD), Raman spectroscopy,Scanning electron microscopy (SEM), Transmission electron microscopy (TEM).GNP/EVA and modified GNP/EVA nanocomposites were fabricated by meltblending method. The thermal degradation behaviors, tensile properties andelectrical properties of the composites were evaluated by thermal gravimetricanalysis (TGA), tensile strength and elongation at break, volume resistivity,respectively. GNP and modified GNP were compounded with ATH, which wereused to obtain flame retardant EVA. The synergistic flame retardant effectbetween GNP, modified GNP and ATH was investigated by limiting oxygenindex (LOI) and vertical burning test (UL-94).The results showed that the GNP was successfully prepared by wet millingmethod. GNP was also modified with Fe2O3, NiO, silane (KH560) and2-carboxyethyl phenyl phosphinic acid (CEPPA). Compared with EVA, GNP/EVAand modified GNP/EVA nanocomposites exhibit high thermal stability, lowmechanical properties and good insulation properties. GNP showed a synergistic flame retardant effect with ATH, which could increase the oxygen index and UL-94rating of the composite material. The synergistic flame retardant effectbetween modified GNP and ATH was also related to the loading modifiers. Thestudy showed that the GNP modified with CEPPA and KH560exhibited strongsynergistic flame retardant effect with ATH. After adding ATH, tensile propertiesof the composites significantly reduced, but the volume resistivity raised an orderof magnitude.