Light-weighting automotive electrical harnesses using nanomaterials

The many kilometres of electrical harnesses used in vehicles add significant weight to modern cars. The requirement for cables and wires to be bound in a non-flexing sleeve with cable ties and other forms of strapping adds weight and cost to the vehicle. This is also done to avoid shorting and such sleeves also provide fire retardant properties. Depending on the harness component, electrical insulation, electrical conductivity and flame retardency are all essential properties of the polymeric coatings and sleeves used in harnesses.

Nanoparticles (NPs) such as multi-walled carbon nanotubes (MWCNTs) and graphene have excellent electrical conductivity (up to 106 S/cm) and high current carrying densities. The incorporation of MWCNTs to polymers can increase the electrical conductivity of the polymer by many orders of magnitude (1015) at low loadings, and also enhance mechanical properties. Moreover, MWCNTs have been shown when added with nanoclay to polymers to have excellent fire retardant and intumescent properties. While nanoparticles of other electrical conductors are now available, e.g. nano-iron, they are much denser than MWCNT's. Other NP's, e.g. boron nitride (BN) are excellent electrical insulators and can be synthesised to have nanoscale dimensions, although most polymers are also electrical insulators.

The proposed project will focus initially on the incorporation of MWCNTs at low loadings (< 1 volume percent) into polymers used as sleeve materials in automotive electrical harnesses and the extrusion of the resultant composite material into thin layer tubing. Such materials would have much better electrical conductivity and be mechanically superior relative to the unfilled polymer. Thus, sleeve materials could be prepared from these composite materials but having thinner walls saving weight and having significantly enhanced electrical conductivity and perform similarly or better mechanically than the unfilled polymer. A similar approach will be adopted to enhance electrical insulation by addition of very low loadings (<0.1 volume percent) of an insulating inorganic nanoparticle to the polymer of interest. The combined addition of MWCNTs and nano-clays would also impart excellent fire retardant and electrical conductivity to the same polymer. This would avoid the use of environmentally contentious halogen based fire retardant packages used in many plastics.

A final, but much more speculative aspect of the project would be to explore the replacement of all copper wire in the harness with ropes of MWCNTs. Such ropes would, as described above, have outstanding electrical conductivity and high current carrying densities, but without generating heat. These ropes are much more flexible than copper wire and could also be readily covered with an electrical insulator by co-extrusion with a polymer. If this was achieved, it would represent an 80% plus reduction in the weight of the harness combined with significant space saving in the vehicle.

The project fits within the EPSRC remit and is directly linked to three EPSRC major research areas; 1) Graphene & Carbon Nanotechnology; 2) Materials Engineering - Composites and 3) Polymer Materials.