The award in the Multifunctional Materials category of the Jec Awards ceremony went to a thermally conductive fibre reinforced composite material, developed by scientists at the RWTH Aachen University, Germany. It combines pitch-based carbon fibres and a thermoset resin to increase the thermal conductivity of fibre reinforced plastics. Potential application sectors include automotive and aircraft in particular.
Michael Glowania, Head of Division Composites, Institut für Textiltechnik (Ita)of RWTH Aachen University with the Jec Award
Plastics: Your thermally conductive fibre reinforced composite material has been given the Jec Award. What is it that makes this an innovation?
Glowania: We have explored the question of how we can process and align heat conductive but still very brittle fibres in such a way that they will convey heat within the component. By comparison with a standard fibre composite we have succeeded in improving heat conductivity by a factor of 40 upwards.
Plastics: What does that mean specifically?
Glowania: A value frequently aimed at by way of a benchmark fluctuates in the range of 10W/mK. We were keen to top this and are endeavouring to move towards 30W/mK. By way of comparison: on average, fibre reinforced plastics have a heat conductivity of 0.4 – 0.8W/mK. Our current combination brings that up to 26W/mK. The heat flow is guided from the in-plane direction through the honeycomb (out-of-plane) to the other face sheet where heat is dissipated. So the innovation can conduct heat away from heat sources or components in the desired directions.
Plastics: What about the structure of the material?
Glowania: We have combined pitch-based carbon fibres and a thermoset resin. First of all the fibres are gathered together in a bundle. This fibre bundle is encased to protect it against bending and coated with a thermoplastic polymer. This is then inserted into a shrink tube or wrapped in foil. There is no plastic inserted between the individual fibres. However, this does not have the effect of reducing the heat conductivity because it is canalised in the strand.
Thermally conductive fibre reinforced plastic (photo: Ita )
Plastics: The process is still taking place manually at the moment?
Glowania: That’s right. We work with commercially available honeycomb fabric and we stick the fibre bundle into it. However, there is potential for automating the encasement process and integrating the whole thing into the honeycomb production stage.
Pitch-based carbon fibres, honey-comb structures and thermally conductive prototype (photo: Ita)
Plastics: What fibres do you work with?
Glowania: We work exclusively with commercially available fibres and have given various suppliers a try, such as, for example, Mitsubishi, Nippon Graphite Fiber and Cytec.
Plastics: The innovation can be integrated in selected areas of the honeycomb, not necessarily in all cells. Besides the cost saving aspect, what are the applications where it could be useful to modify local properties?
Glowania: One possible area would be the electric car batteries sector. Here things get very hot and the heat needs to be dispersed. Another application area is the rear structure on helicopters. At the point of impact of the hot gases from the turbine (hot spot) there is an indication of a need for a reinforcement with greater heat conduction capability than is necessary in the remainder of the rear structure.
Thermally conductive fibre reinforced plastic prototype (photo: Ita)
Plastics: You have developed a prototype and the process is currently still operating manually. Are you nevertheless already in a position to be able to make a cost estimate?
Glowania: We have carried out a target costing analysis for the aerospace sector where we are moving within a good average segment. The additional fact that we also have a very lightweight material to contend with – we are talking here of a 70-80% reduction in weight by comparison with aluminium – is naturally an advantage that is likewise reflected in the balance sheet. Despite this, in the automotive sector there are difficulties in keeping up with the OEM specifications on the costs side. Here we tend to be premium price.
The innovation can be integrated in selected areas of the honeycomb, and not necessarily in all cells. (photo: Ita)
Plastics: Thank you very much, Mr Glowania.
www.ita.rwth-aachen.de
