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The paper addresses the difference in electrical conductivities and rheological properties between two nanocomposites of reduced graphene oxide nanosheets (rGON) with commercial ultrahigh molecular weight polyethylene (C_PE) and a low-entanglement-density UHMWPE synthesized under controlled conditions (Dis_PE). It has been found that composites made with Dis_PE can reach conductivities at least 100 times higher than those made with C_PE on doing thermal treatment at lower temperatures. However, the difference in the electrical conductivity diminishes when both sets of samples are given a high temperature treatment. This phenomenon is attributed to the difference in morphology of the polymer matrices, for example, grain boundaries between the nascent particles. Furthermore, rheological analyses of the two sets of UHMWPE/rGON nanocomposites conclusively demonstrate differences in the interaction between polyethylene chain segments of the disentangled UHMWPE and rGON, compared to the entangled commercial UHMWPE. Both composites show minima in the storage modulus at a specific graphene composition. The strong interaction of polyethylene chains with the filler inhibits disentangled UHMWPE to achieve the thermodynamic equilibrium melt state, whereas in the commercial sample, having a broader molar mass distribution, the higher adhesion probability of the long chains to the graphene surface lowers the elastic modulus of the polymer melt. Correlation between the percolation threshold for electrical conductivity and rheological response of the composites has also been discussed.

In normal practice, ease in processing comes at the expense of a reduction in mechanical properties. Here we show that by controlled synthesis it is possible to synthesize a wide range of linear ultrahigh-molecular-weight polyethylenes that can be stretched uniaxially into tapes. In these uniaxially drawn tapes, the bundles of fibers align themselves in a preferred crystal plane orientation, accounting for an extraordinarily high tensile modulus. The stretching process is accomplished in the solid state with no need for any solvent. The ease of solid-state processing provides a unique opportunity to follow the influence of the molar mass on the tensile properties. The uniaxially drawn tapes, similar to the fibers spun from solvent, confirm the empirical relationship between tensile strength and tensile modulus proposed by van Krevelen in 1976 and subsequently supported by experimental findings on solution-spun fibers by Smith and Lemstra. However, the solid-state-processed tapes do not achieve the high values of tensile strength expected from this relationship, where a modulus of 200 GPa would correspond to a tensile strength of 5 GPa. The relatively lower tensile strength of 4 GPa for the extraordinarily high modulus of 200 GPa observed in the uniaxially stretched tapes is attributed to the presence of defects, as tapes can be considered composites of fibers. The high modulus in combination with the tensile strength in tapes has the potential to provide unique physical properties in composites.

ABSTRACT:It has been shown that, in suitable reaction conditions, it is possible to obtain ultra high molecular weight polyethylene with a reduced number of entanglements directly from the synthesis. This material shows interesting technological properties in terms of improved solid-state