Re-user friendly

A UK team claims to have perfected a new method of producing polypropylene vehicle components that are strong, lightweight and easy to recycle.

Researchers on the Recycle project, including Warwick University, Lotus Engineering and London Taxis International, have developed a technique for moulding, joining and finishing self-reinforced polypropylene (SrPP), which is claimed to be up to six times stronger than the standard form of the polymer.

The partners said the breakthrough could have major benefits for car manufacturers’ ability to meet tough new environmental regulations on materials recycling. The EU’s End of Life Vehicles Directive stipulates that by 2006, 80 per cent of a car’s bodyweight must be either reusable or recyclable, with that proportion rising further over the next decade.

Standard polypropylene is not strong enough for use in car manufacture, and normally has to be reinforced with glass fibre, carbon fibre or natural materials such as hemp or flax. But the reinforcing process renders polypropylene expensive and difficult to recycle.

To produce SrPP, engineers have to heat and stretch polypropylene to align its molecules, making it stronger but no heavier. As no extra materials need to be added, SrPP can be easily recycled.

The drawback is that during re-heating as part of the car production processes, the plastic’s reinforced properties can reverse and the SrPP can be weakened and lose its stiffness.

The Recycle project’s engineers have developed a way of precisely applying heat so that the SrPP sheets can be moulded, pressed and finished without losing their strength.

Dr Brendon Weager of Derbyshire firm NetComposites, and project manager on Recycle, said: ‘The key with this material is to control the heating accurately. The first step in the process is to heat it in an air oven or by infra-red. The second step is the forming-toshape in a mould. We have assessed what temperatures work best for the proper balance of chemical properties and get the final form on the moulding.’

Weager added that the team has also discovered how to bond and join SrPP to other materials, using SrPP as a ‘skin’ with other polypropylene-based products as the core, to develop recyclable products with a variety of distinct properties.

Trial car parts using SrPP have already been developed for the Lotus Elise which are 57 per cent lighter than conventional components. The Recycle team, which carried out the research as part of the automotive industry’s Foresight Vehicle initiative, said there was no reason it should not be applied to high-volume car production.

The development of a light, strong recyclable plastic could also have applications in other industries. Researchers have been looking into other uses for SrPP which include football shinpads, body armour, crash helmets and luggage.