Plastic cars: light enough to take off

Press, 27 June 1983, Page 18

Plastic cars: light enough to take off

From the ‘Economist,’ London

Chemical manufacturers have long dreamed of the time when cars will be made completely of plastic. At present, some 200 pounds in weight of plastic is used in each car, as against 3000 pounds of metal. Reasons? Available plastics have been too weak to withstand collisions; when toughened, have been expensive and difficult to shape; and difficult to paint. Two American companies, General Electric and Du Pont, reckon these problems can now be overcome. General Motors has recently unveiled a car which gets its structural support from a steel chassis alone, on to which a plastic body, made of glass-reinforced plastic, can then be bolted. The two-seater sports car, the Fiero, will be launched in America this September and will cost about $lO,OOO. Also thanks to the development by paint manufacturers of polyurethane-based paints that can be applied at temperatures below 100 degrees centigrade, painting a plastic car is no longer a problem. (Older paints had to be baked on at temperatures that would melt plastic.) When suitable, plastics have two main advantages over metal. First, they are light, and less weight in a car means greater fuel economy. Volkswagen of America is planning to introduce an allK- "c fuel tank in its diesel it next year which will weigh eight pounds and replace a 121 b steel tank. Some plastic automotive parts can weigh as little as 20 per cent as much as their steel equivalents. Second, they are corrosion-re-sistant. In theory, they should also be easier and, in terms of energy, cheaper to make — if they can be moulded. So far, the Volkswagen tank will be the largest car component to be blow-moulded. Progress is being made in developing tougher plastics and in techniques for handling them. Consider, first, the new plastics. General Electric has developed a new plastic as tough as metal and easier to fabricate than glassreinforced plastics. Dubbed Xenoy, it is made from polycarbonates and polyesters. The Ford Sierra, aunched in Europe lashautumn, irries the first all-plasty bumper

— made of Xenoy. General Electric is playing around with Xenoy derivatives and mixtures to find a polymer suitable for use in car side and roof panels. It has prototypes which it hopes to commercialise by 1986. Xenoy is sensitive to petrol fumes. But General Electric thinks that it has solved this problem by producing a modified Xenoy. Du Pont has developed two collision-resistant plastics, Zytel 900 and Delrin ST, based on nylon and acetal. Zytel 900 is a chemically treated nylon blended with other plastics. Ordinary nylon fibre has a crystalline structure which absorbs moisture and loses its stiffness. Du Pont has modified the nylon in such a way that, although water is still taken up by the crystalline structure, it does not disrupt the shape of the molecule. In short, it will not become soft if left out in the rain. Du Pont hopes to launch its first all-plastic Zytel-900 bumper in 198 b. Delrin ST is even tougher. It has seven times the toughness and twice the impact resistance of untoughened acetal. Car manufacturers are thinking of using it in fuel-line parts and even as a fastener to stick on bits of chrome. Due Pont hopes that both its new plastics will be used in car bodies by the late 1980 s. It has already managed to mould a car side-panel out of Zytel 900. A challenge will be finding a plastic that can be used in car engines. Polimotor Research of New Jersey has made an engine which is 90 per cent made of a carbon-fibre-reinforced plastic called Torlon. The new engine is 50 per cent lighter than a metal engine and can manage 2% more miles a gallon. But it will cost $5OO more to make. Next year’s Formula-2 racing cars will carry the new engine, but a cheaper plastic is needed for ordinary cars. Two other hurdles remain. Injection moulding is suitable for most plastics, but the equipment is expensive. Du Pont reckons the answer is to find a way to mould large plastic parts by a technique called thermoforming. During thermoforming, a plastic sheet is gently heated over a mould and, as it cools, takes the mould’s shape. Using tWs, technique, car would

need only to retool — something they do anyway when introducing new models. Second, the all-plastic car would be so light that it would tend to take off. Getting good road-holding characteristics with much lighter cars may require a total redesign.