Rheology, Electrical Properties, and Percolation of TRGO‐Filled EVA‐Copolymers

Abstract

This paper describes the production of graphene nanocomposites via melt mixing of thermally reduced graphite oxide with ethylene vinyl‐acetate copolymers of different (0–70 wt%) vinyl acetate content, and their measured electrical and rheological properties. The aim of these studies was to investigate the influence of a continually changing polymer matrix polarity on the dispersion and percolating behavior of graphene fillers, an effect that can be expected to be most prominent with the high specific surfaces of the latter. Composites with graphite and multi‐walled carbon nanotubes were produced and examined for comparison. The effectivity of the dispersion process was checked by measuring the melt rheology and electrical conductivity of the samples. The percolation thresholds derived from these measurements show a minimum for VA contents around 20 wt%. The thresholds for electrical conductivity are by a factor around 1.5 lower than the rheological values, and both are distinctively higher than those observed from composites produced via solution mixing. The percolation behavior is compared to predictions made from the surface energy of the compounds.

Effect of Carbon-Based Particles on the Mechanical Behavior of Isotactic Poly(propylene)s

“…[ 25 ] Based on these properties, TrGO can be considered as a suitable fi ller for the development of functional polymeric nanocomposites, usually based on polar matrices. This is achieved by using frequently the solution- [ 26,[33][34][35] or melt-mixing methods [ 36 ] or combinations of both.…”

“…The dependence of viscoelastic parameters on the concentration of carbon-based fi ller has been widely studied in the literature for polymer composites with CNTs, [44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] but little has been addressed in composites with other fi llers such as graphite, [59][60][61] and/or TrGO. [ 36,45,60,62,63 ] Isotactic poly(propylene) nanocomposites with CNTs have a rheological percolation at concentrations between 0.3 and ≈ 3 wt%, [ 45,49,51,[56][57][58] while iPP/TrGO composites require concentration above 5 wt% to achieve rheological percolation, [ 45 ] showing that the size and aspect ratio of the carbon-based fi ller affect the melt rheology of the composite.…”

“…[ 62 ] This critical concentration of fi ller represents the rheological percolation threshold ( φ p ). Above the threshold, the plateau modulus G ′ is expected to increase with fi ller content following a simple power law [ 36,59,77 ] φ φ φ ( )…”

“…For a solid-like behavior δ drops toward zero. [ 36,46,47,81,82 ] This is based on the fact that the value of δ is 90° toward δ = 0° in the low | G* | region for a polymer melt, provided that the polymer chains are completely relaxed. [ 78 ] The deviation of δ from 90° in the low | G* | region indicates the elastic response of polymer chains by forming a network structure (or percolated network) in the melt sample.…”

“…Another method [ 36,49,81 ] to estimate the rheological percolation threshold is depicted in Figure 7 , showing a decrease in the loss tangent (tan δ ) with increasing fi ller concentration at different frequencies. The tan δ of a rheometrical measurement rises by decreasing the angular frequencies ω for liquids, and decreases toward zero for solids.…”