The Effect of Graphene Nanoplatelets on the Mechanical Properties and Electrical Conductivity of Epoxy Resin Nanocomposites

Abstract

The aim of this investigation was to enhance the tensile strength and fracture toughness of epoxy resin matrices for carbon fibre epoxy composites in an effort to reduce a type of mechanical failure called inter-laminar cracking or delamination. The second objective was to increase the electrical conductivity of epoxy resin matrices for carbon fibre epoxy composites as a means of sensing structural damage if delamination occurred. The weak link of carbon fibre composites is the insulating and relatively brittle epoxy resin which is used to bind the carbon fibres together. In order to improve its performance the epoxy resin was reinforced using highly conductive and strong graphene nanoplatelets (GNPs). In the first instance un-functionalised (chemically unmodified) GNPs were shear mixed in epoxy resin at a range of different speeds and time durations at 0.1 wt% loading. There appeared to be no trend between the processing conditions and the mechanical properties of the epoxy resin. The addition of 5 wt% un-functionalised GNPs to epoxy resin reduced the tensile strength by up to 50%. The lack of bonding between the un-functionalised GNPs and the epoxy resin created a weak interface that was responsible for the deterioration of tensile properties. This was followed by adding functionalised (chemically modified) GNPs to epoxy resin. The results show that oxygen functionalised GNPs improved the tensile strength of epoxy resin due to better interfacial bonding between the GNPs and the polymer. An increase in tensile strength of up 7% was seen using a 0.1 wt% loading of oxygen functionalised GNPs. In terms of electrical conductivity the addition of GNPs to epoxy resin yielded barely any improvement. Adding 0.1 wt% GNPs to epoxy resin did not create a percolating network irrespective of the processing method used. The electrical conductivity was predicted using a model and AFM measurements of the dimensions of the GNPs. The model matched the experimental results reasonably. By contrast 0.1 wt% of multiwall carbon nanotubes (MWCNTs) did create a percolating network and was capable of enhancing the conductivity from ~10-12 S m-1 to 3.5x10-5 S m-1. The addition of 1 wt% MWCNTs to epoxy resin enhanced the electrical conductivity up 2.0x10-4 S m-1. Overall the results of this investigation have shown that chemical modification of GNPs is essential in order to increase the strength of the epoxy resin. Shear mixing as a technique appears to be too simplistic to control the distribution and dispersion of GNPs on the nanoscale. Carbon nanotubes are more efficient at creating a percolating network compared to GNPs but in order to significantly improve the conductivity of epoxy resin the distribution of MWCNTs need to be manipulated, for instance by an electromagnetic field, at the nanoscale to form a connected network of nanoparticles.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Constantinos Soutis (Supervisor) & Gresil (Supervisor)