Car makers will be able to increase the use of lightweight composites in vehicles without producing more landfill waste thanks to a recycling technique developed in the UK.
It is based on a combination of pyrolysis, which is currently used to recycle tyres by heating them in the absence of oxygen so they do not burn, and a separation system.
The technique, developed at Leeds University, allows composite plastics to be broken down into oil and fibre, which can then be reprocessed.
Composites are increasingly used to make car parts such as dashboards and bumpers as they are lightweight, aiding fuel efficiency. But unlike tyres, metal and glass, the material is difficult to recycle, said Prof Paul Williams at the university’s fuel and energy department. ‘Until now, fibre-reinforced polymer composites have been widely considered un-recyclable,’ he said.
Materials cannot simply be melted as they contain glass or other fibre, and a filler such as calcium carbonate. Burning off the plastic to recover the fibre requires temperatures of around 900oC, which damages the fibre.
As a result around 95 per cent of the material is dumped in landfill sites. ‘The Society of Motor Manufacturers and Traders was concerned that the increasing use of composites might mean car makers are unable to meet their targets under the European End-of-life Vehicle Directive,’ said Williams. The directive states that 85 per cent of plastics, rubber and glass must be recycled by 2006, and 95 per cent by 2015.
During pyrolysis, the composite plastic is heated without oxygen to around 500 degrees C, which is low enough to allow the glass fibre to retain much of its strength and to prevent it becoming brittle.
The composite is broken down into gas, oil, filler, a small amount of carbon and the glass fibre itself. The gas and oil can be separated off with the oil suitable for reuse as fuel.
The carbon, filler and glass fibre are separated using a process developed by the project’s leader, technology company Pera. ‘A mechanical system scrapes the material so you are left with clean glass fibre, which can be reused.’
New composites can be produced using around 25 per cent of the recycled fibre with 75 per cent virgin fibre without any deterioration in quality. The material can be used to make new car components and to build structures such as boat hulls.
The project, which was funded jointly by the EPSRC and the DTI, also involved the SMMT and the British Plastics Federation.