Electrical and mechanical properties of expanded graphite‐reinforced high‐density polyethylene

Abstract

High-density polyethylene (HDPE) was reinforced with expanded and untreated graphite in a meltcompounding process. Viscosity increased upon addition of graphite phase, with the expanded graphite (EG) showing more dramatic rise than the untreated graphite (UG) in viscosity. The increase in viscosity was attributed to the increased surface-to-volume ratio for the EG filler after acid treatment. Electrical conductivity also increased from that pertaining to an insulator to one characteristic of a semiconductor. The EG system showed a lower percolation threshold for transition in conductivity compared to that in the UG system. DSC results indicated that the fillers acted as a nucleating agent in inducing the crystallization of HDPE in the composites. However, the overall degree of crystallinity and melting temperature of HDPE decreased with the addition of EG and UG. Mechanical properties improved as a function of filler content but the overall enhancement was not impressive. It was conjectured that the filler-matrix interface was not optimized in the melt-mixing process. However, the role of EG as a reinforcement phase for both electrical and mechanical properties was unambiguously established. The EG composites demonstrated potentially useful attributes for antistatic, barrier, mechanical, electrical, and cost-effective applications.

Graphitic nanofillers in PMMA nanocomposites—An investigation of particle size and dispersion and their influence on nanocomposite properties

“…Zheng et al 16 showed that PMMA/EG composites prepared by solution-based processing yielded a 13% increase in modulus at 5 wt % loading. This same group 11 reported a large $75% increase in storage modulus (G 0 ) for a 3 wt % EG/polyethylene nanocomposite accompanied by a very small T g increase of 2%. Du et al 32 achieved the largest increase in flexural modulus (81% above the neat polymer) for a 15 wt % GNP-based composite with poly(4,4 0 -oxybis(benzene)disulfide).…”

“…In addition to recent demonstrations of significant enhancements in mechanical properties over those of the parent polymers, polymer nanocomposites also enable achievement of new multifunctional properties (e.g., electrical, thermal) that are not observed with micron-size fillers. [5][6][7][8][9][10][11][12][13][14] In particular, inclusion of nano-sized electrically conductive fillers such as carbon nanotubes and graphite particles can significantly increase the electrical conductivity of the polymer beyond a threshold level of loading. [15][16][17][18] Nanocomposites with highaspect-ratio, plate-like filler particles also exhibit dramatic changes in permeability, which has been attributed to the ''tortuous'' pathways required for migration of small molecules.…”

“…Several research groups 12,16,17,47,30,50,31,32 have claimed improvements in properties of polymer composites using graphite nanofillers (EG and GNP) with an emphasis on the electrical properties. Electrical percolation was quoted for a filler concentration of about 2 wt % for EG 11,16,22,31 or ''foliated graphite,'' 33,37 FG, (Foliated graphite, FG, is a term used in some papers to indicated EG in which the worm-like structure has been broken into separated platelets) but a loading of over 5 wt % is required for natural graphite 16,34 particles of larger dimension and thickness (as shown in Table 1). …”

Functionalized Graphenes and Thermoplastic Nanocomposites Based upon Expanded Graphite Oxide

“…They discovered that aspect ratio, concentration of the graphite nanoplatelets and poly(propylene) crystallization conditions can be tuned to control poly-(propylene) crystallization and electrical conductivity. [39] Several groups have employed expanded GO to prepare thermoplastic nanocomposites based upon polyethylene, [40] maleic-anhydride grafted poly(propylene), [41] polystyrene, [42] and ethylene/methyl acrylate/acrylic acid copolymers. [43] In comparison to conventional GO, the expanded GO with its much higher degree of exfoliation and high specific surface area gave improved stiffness and electrical properties at lower GO content.…”

Characterization of commercial expandable graphite fire retardants

“…Expandable graphite possess similar in-plane electrical conductivity to natural flake graphite [25]. This means that it could impart both antistatic and thermal conductivity [26] in addition to flame retardant properties to polymers [27].…”