Thermo-mechanical properties of graphite-reinforced high-density polyethylene composites and its structure–property corelationship

Abstract

Composite prepared by mixing of different forms of carbon or other reinforcing fillers with polymer, is one of the possible ways to enhance the performance of polymeric materials. The present work focuses on the study of viscoelastic, thermal, electrical and mechanical properties of graphite flake-reinforced high-density polyethylene composites. The composites are processed by melt mixing using vertical twin-screw micro-compounder followed by final sample preparation via micro injection moulding. The reinforcing filler, graphite flake, is varied from 0 to 50 vol.% with respect to the polymer matrix. Dynamic mechanical thermal analysis reveals an increase in the storage modulus (E′) as well as loss modulus (E″) throughout the temperature range; however, damping (tan δ) shows a mixed behaviour. There is 550% and 479% increase of E′ and E″ in the rubbery region. Degree of entanglement, reinforcement efficiency and C factor are also calculated and correlated with the mechanical properties. On comparison, high-density polyethylene /graphite flake composite having 50 vol.% graphite flake with pure high-bcdensity polyethylene shows 52% increase in melt viscosity, whereas bulk density increases by 38%. This graphite flake is also responsible for the increase in the thermal stability (shift in the onset degradation temperature of ∼7℃ and the degradation temperature is more than 400℃), thermal conductivity (175% improvement) and electrical conductivity (∼6125% improvement, as the conductivity of pristine high-density polyethylene is ∼9.67 E-08 S/m). Mechanical properties determined by tensile and flexural tests show an initial increase and then a slight decrease in the tensile and flexural strength. Therefore, the graphite flake-reinforced high-density polyethylene composite with improved thermal conductivity, electrical conductivity, heat stability, viscoelastic behaviour and flexural modulus can be a promising as well as suitable composite material for making of various electronic and electrical accessories including bipolar plate for fuel cell applications.