Structure/Property Relationships in Elastomers Filled with Graphite Nanoplatelets

Abstract

The microstructure and properties have been investigated in nanocomposites consisting of graphite nanoplatelets (GNPs) in natural rubber (NR) and nitrile butadiene rubber (NBR). Nanocomposites with four different loadings of three different sized GNPs (nominal lateral dimension of 5, 15 and 25 microns) were prepared that were bench-marked against nanocomposites loaded with N330 carbon black. The materials were processed using conventional melt-processing methods in a two-roll mill and the composition of the nanocomposites was confirmed by thermogravimetric analysis. The microstructure of the nanocomposites was characterised though a combination of scanning electron microscopy, polarised Raman spectroscopy and X-ray computer tomography (CT) scanning, where it was shown that the GNPs were well dispersed with a preferred orientation parallel to the surface of the nanocomposite sheets. The mechanical properties of the nanocomposites were evaluated through tensile testing, Shore A hardness testing and tear testing. It was shown that, for a given loading, there was a three times greater increase in stiffness for the GNPs than for the carbon black. The size effect of the particles is significant in the mechanical properties. Stress transfer from the NR and the NBR to the GNPs was evaluated from stress-induced Raman bands shifts indicating that the effective Young’s modulus of the GNPs in the NR was only of the order of 100 MPa, similar to the value evaluated using the rule of mixtures from the stress-strain data. A comprehensive theory was developed to explain the deficiency of the stress transfer in soft matrix systems. Transport properties including solvent diffusion and thermal conductivity were investigated. Anisotropic swelling was observed for all the GNPs composites due to the orientation of the GNP flakes. The diffusion coefficient decreases with the increasing loading of the fillers and the increasing particle size. Thermal conductivity was enhanced with the addition of the fillers and the largest particle gives rise to the highest enhancement.

Date of Award	1 Aug 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Robert Young (Supervisor) & Ian Kinloch (Supervisor)