Barrier and Mechanical Property Enhancement of High Density Polyethylene Through the Addition of Graphene Nanoplatelets

Abstract

Processing methods to disperse Graphene nanoplatelets (GnP) in high density polyethylene (HDPE) are being investigated in an attempt to manufacture a material with mechanical and barrier properties suitable for fabrication of vehicle fuel tanks. Previously reported results indicated that through a simple melt mixing process, the oxygen transmission through a 7.5% wt. GnP in HDPE composite was reduced by 55% compared to the neat composite, however there was also a 50% loss in impact resistance. Alternative methods to melt extrusion were investigated to improve the dispersion and alignment of GnP. Microlayer co-extrusion (MCE) of the GnP powder and HDPE, in which the melt nanocomposite is stretched into thin films, stacked and consolidated, resulted in higher relative improvements in barrier properties, however was still limited by dispersion issues. A 30% wt. GnP in HDPE masterbatch was produced and then processed through the MCE process. This actually resulted in a decrease in properties due to platelet curling and size reduction. A solution mixing approach was employed in which HDPE and GnP were mixed in heated xylene to improve the dispersion, but the advantage was lost when it was re-processed with melt extrusion. A low molecular weight hydrocarbon coating of the GnP platelets was applied prior to processing in melt extrusion to improve the dispersion but resulted in only a small improvement in the impact resistance, had a negative impact on the flexural properties, and did not improving the barrier properties. An elastomeric coating of the GnP resulted in recovering up to 34% of the lost impact resistance but the flexural modulus and strength were lowered and there was a negligible effect on barrier properties at a 5% wt. concentration. Alternative thin film methods are now currently being investigated