British scientists have perfected a way of producing reinforced polypropylene parts which will help vehicle manufacturers meet stringent new laws on recycling.
During a two-year research programme they have solved the problem of how to mould, join and finish self-reinforced polypropylene (SrPP), which is up to six times stronger than polypropylene (PP).
Until now, working with the revolutionary new material on an industrial scale, has proved difficult.
It opens the door to a vast range of lightweight car, truck and van parts that can be made more simply and cheaply than would be possible using conventional materials. And the ultra-strong, ultra-light parts will help lower exhaust emission levels and increase fuel economy.
But the biggest advantage of all, as the stringent End-of-Vehicle-Life Directive comes into force, is that all products made by the new technique can be recycled quickly, easily and cheaply.
The breakthrough was made by a consortium of engineers and scientists working on RECYCLE, a research programme under the Society of Motor Manufacturers and Traders Foresight Vehicle initiative.
Polypropylene already had many advantages, but on its own it was not strong enough for many automotive uses. Normally it has to be reinforced with glass fibre, carbon fibre or natural materials, such as hemp, flax or sisal to make it strong and stiff.
But adding in these traditional reinforcements makes recycling a complicated, time-consuming and expensive operation – ruling out all the other advantages of the useful plastic.
If panels made from polypropylene were simply made thicker, or strengthened with extra ribs, it would make the parts too heavy and again defeat the automotive industry’s quest to find strong and light alternatives to metal components.
SrPP takes normal PP and by heating and weaving treatments, stretches and aligns the molecules to make the end product much stronger, without any weight gain.
One of the main problems that RECYCLE engineers faced was that re-heating SrPP during production processes can reverse the process that gives the material its special properties.
So the RECYCLE team worked on ways of carefully applying heat so that SrPP sheets could be moulded, pressed, joined and finished without the risk of losing its high stiffness and strength.
There are many other advantages of the RECYCLE production techniques. Cutting and stamping tools benefit because SrPP contains no glass fibre. This reduces tooling costs. And SrPP can be moulded at low temperatures. However, finished surfaces are of A1 quality and other cosmetic finishes can be easily added to the final production process to make products that need high-grade finishes.
SrPP products also have high impact strengths, making them excellent for areas of pedestrian safety and passenger protection. And, because it is 100 per cent polypropylene, it is non-toxic and highly resistant to corrosion. It satisfies standard automotive manufacturing tests for hydraulic fluids and fuels.
The scientists have already produced trial parts made from SrPP for the Lotus Elise sports car, which are 57 per cent lighter than the conventional part. Lotus Engineering is one of the partners in the RECYCLE project.
Other partners in the SMMT Foresight Vehicle RECYCLE programme are NetComposites, Propex Fabrics, Warwick University, BI Composites, Trauma-Lite and London Taxis International.
Dr Brendon Weager, of Chesterfield-based firm NetComposites, was project manager on RECYCLE. He said: “Using this new material has a host of advantages. It will be easier and less expensive to mass-produce than other materials, because the tooling does not have to cope with high pressures or abrasive materials.
“The finish is much smoother than glass fibre reinforced plastics and it is safer to handle by human operators.”
The research has also found ways of bonding and joining SrPP products to other materials and to other parts made from SrPP.
Now the major technical hurdles have been overcome, the scientists are working towards full production and several vehicle manufacturers are taking a keen interest.
There has also been a spin-off to other industries. The RECYCLE scientists are now looking at other applications of the light, strong and totally recyclable plastics. They can be used to make shin pads for footballers, body armour, helmets and even suitcases – all products that need strong, lightweight plastics that do not harm the environment when they come to the end of their product lives.
More than 400 UK companies and universities have been participating in the industry-backed Foresight Vehicle initiative, which is led by the Society of Motor Manufacturers and Traders (SMMT).