Thermal conductivity, morphology and mechanical properties for thermally reduced graphite oxide-filled ethylene vinylacetate copolymers

Abstract

Systematic variation of copolymers (Poly (ethylene-covinylacetate)) composition provide an opportunity to change matrix polarities and thus explore their effects on the polymer/filler interactions and composite properties. The main objective of this work is to study the effect of vinyl acetate (VA) content on the extent of exfoliation and dispersion of thermally reduced graphite oxide (TrGO), as well as its impact on the thermal conductivity and mechanical properties of the resultant composites. The use of ethylene vinyl-acetate (EVA) copolymers of different (0–40 wt%) vinyl acetate content with similar melt viscosities allowed us to keep the processing conditions constant and quantitatively compare the thermal conductivity and mechanical properties of composites with different matrix polarities. Composites with conductive graphite (GT) and multiwalled carbon nanotubes (MWCNT) were also prepared and examined for comparison. Melt dispersion of TrGO in EVA copolymers was quantified using a range of characterization techniques: transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray scattering measurements. Electron microscopy and X-ray diffraction revealed highly exfoliated morphology of TrGO throughout the entire matrix, while GT remained multi-layer even after melt processing. Nanocomposites reinforced with TrGO showed significantly improved thermal conductivities and mechanical properties combined with low rheological percolation thresholds comparable to those achieved using MWCNT and GT. We propose a formalism to assess the thermal conductivity and mechanical properties of graphene nanocomposites based upon the interfacial excess energies of EVA copolymers.