Thermal-Diffusivity Measurements of Conductive Composites Based on EVA Copolymer Filled With Expanded and Unexpanded Graphite

Abstract

In this research, the thermal diffusivity of composites based on ethylenevinyl acetate (EVA) copolymer filled with two kinds of reinforcement graphite materials was investigated. The reinforcement graphite fillers were untreated natural graphite (UG) and expanded graphite (EG). Composite samples up to 29.3 % graphite particle volumetric concentrations (50 % mass concentration) were prepared by the meltmixing process in a Brabender Plasticorder. Upon mixing, the EG exfoliates in these films having nanosized thicknesses as evidenced by TEM micrographs. Thus, the thermal diffusivity and electrical conductivity of composites based on the ethylene-vinyl acetate matrix filled with nanostructuralized expanded graphite and standard, microsized graphite were investigated. From the experimental results it was deduced that the electrical conductivity was not only a function of filler concentration, but also strongly dependent on the graphite structure. The percolation concentration of the filler was found to be (15 to 17) vol% for micro-sized natural graphite, whereas the percolation concentration of the filler in nanocomposites filled with expanded graphite was much lower, about (5 to 6) vol%. The electrical conductivity of nanocomposites was also much higher than the electrical conductivity of composites filled with micro-sized filler at similar concentrations. Similarly, the values of the thermal diffusivity for the nanocomposites, EG-filled EVA, were significantly higher than the thermal diffusivity of the composites filled with micro-sized filler, UG-filled EVA, at similar concentrations. For 29.3 % graphite particle volumetric concentrations, the thermal diffusivity

Effect of surfactant and electron treatment on the electrical and thermal conductivity as well as thermal and mechanical properties of ethylene vinyl acetate/expanded graphite composites

“…[1][2][3][4][5][6][7][8][9] One way to improve the thermal and electrical conductivity, as well as the viscoelastic behavior and mechanical properties, of these materials is to combine polymer matrices with highly conductive fillers. However, there are many industrial applications such as circuit boards, heat exchangers, electromagnetic shielding devices, antistatic plastics, packaging, and others that require an improvement in both the thermal and electrical conductivity of polymers.…”

“…2,3 Tlili et al 2 reported on the thermal and electrical conductivities of EVA14 filled with EG and unexpanded graphite (UG). Some theoretical equations have been proposed to predict the electrical and thermal conductivities of polymeric materials.…”

“…Some theoretical equations have been proposed to predict the electrical and thermal conductivities of polymeric materials. Tavman et al 3 investigated the thermal diffusivity of conductive composites based on EVA14 filled with EG and UG. 2,3 Tlili et al 2 reported on the thermal and electrical conductivities of EVA14 filled with EG and unexpanded graphite (UG).…”

Effect of surfactant on EG dispersion in EVA and thermal and mechanical properties of the system

“…Their results show little change in thermal stability with increasing EG content and very little was reported on changes in the mechanical properties. Tavman et al and Tlili et al both compared the electrical properties of EVA (with 14 wt % vinyl acetate) containing respectively EG and unexpanded graphite. George et al reported a comprehensive study on reinforcement of EVA by differently treated naturally occurring graphites.…”

Preparation and Characterization of Conductive Polymer Nanocomposites Based on Ethylene–Vinylacetate Copolymer (EVA) Reinforced with Expanded and Unexpanded Graphite

“…The electrical conductivities of EVA/UG and EVA/EG composites were measured by four-point method [10], the results of the measurements are given in Fig. 7.…”