|Lotus Elise with SrPP parts.|
British scientists working under the aegis of the Foresight Vehicle program have perfected a way of producing self-reinforced polypropylene (SrPP) vehicle parts. SrPP is up to six times stronger than conventional polypropylene (PP).
The breakthrough opens the door to a large array of lightweight car, truck and van parts that can be made more simply and cheaply than would be possible using conventional materials. The ultra-strong, ultra-light parts will help lower exhaust emission levels and decrease fuel consumption.
For manufacturers faced with a stringent End-of-Vehicle-Life Directive coming into force, the development also means 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, one of the research programs under the Society of Motor Manufacturers and Traders’s (SMMT) Foresight Vehicle initiative.
Polypropylene normally has to be reinforced with glass fiber, carbon fiber or natural materials (such as hemp, flax or sisal) to make it strong and stiff enough for application in autos. These traditional reinforcements, however, make recycling a complicated, time-consuming and expensive operation—ruling out all the other advantages of the 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 polypropylene, 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.
The RECYCLE team devised 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.
The scientists have already produced trial parts made from SrPP for the Lotus Elise sports car which are 57% 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.
The research has also found ways of bonding and joining SrPP products to other materials and to other parts made from SrPP.