STUDY OF GRAPHENE REINFORCED CROSS LINKABLE POYLETHYLENE (XLPE) COMPOSITES

Abstract

This project was to study composites of graphene with cross linkable polyethylene (XLPE). Traditionally, carbon black is used with cross linkable polyethylene for use as a semi conductive layer in high voltage cables. Composites with carbon black have a filler loading of upto 40% which possess many practical disadvantages to the industry. After the discovery of carbon nano tubes (CNT), CNT has been studied widely as a potential substitute for carbon. The filler loading required with CNTs drops significantly to achieve equivalent properties. But CNTs are extremely costly which makes it commercially unviable. This project aims to study graphene as a substitute for carbon black. Graphene is a single layer of graphite. The thickness of the graphene sheets is in the range of nano meters which makes is it an extremely good filler material. There has been growing interest among researchers to study graphene and graphene_ has been extensively studied in the recent past with various polymers but composites of graphene with cross linkable polyethylene have not yet been studied. Rheological measurements were used to follow the cross linking of the polymer. Rheological properties also have importance in this application because the semiconducting layer of XLPE is co extruded with the insulator layer and hence both must have similar flow behaviour for effective adhesion. XLPE was obtained commercially from Borealis and graphene was manufactured in the lab. FTIR was used to characterize the functional groups on graphene sheets. Composites were processed on a micro extruder which can compound 5 — 7 gm of the sample in one run. Samples containing 1%, 3% and 5% graphene were studied., DSC was used to determine the crystallinity of the pure as well as the composite samples. The samples were cross linked in a hot press at a temperature of 180°C for 20 minutes. Tensile Modulus and hardness tests were done on the cross linked and uncross linked samples. Tensile Modulus increased on addition of graphene but the reinforcing capability was diminished because graphene also reduced the crystallinity of the samples. Crystallinity also reduced after cross linking which led to a reduced tensile modulus after cross linking. Rheological data showed an increase in Molecular Weight after cross linking. SEM images revealed a smooth fractured surface for the pure XLPE and rough surface for composites.