Auto industry fuels up with aliphatic polyketones

Paul Sykes believes he is witnessing a revolution of sorts. As automotive end-use manager for Shell Chemical, Sykes recently spent a week in Detroit visiting each of the Big Three to discuss material needs and design challenges for underhood parts. "We've come a long way from the days when plastics were a novelty in high-heat automotive environments," he confirms. "In fact, OEM designers are now focusing on polymer-to-polymer substitutions for better cost-performance based on their objective of a 10-year, 100,000-mile vehicle."

That's music to Sykes' ears, he tells IMM, because Shell's semicrystalline material-an aliphatic polyketone (Carilon)-may be one answer. Costs of substituting aliphatic polyketones for other automotive resins vary according to application, but during the life cycle of product development and manufacture, Sykes says, the material is cost competitive.

Sykes says Shell believes the material has potential use in underhood as well as fuel system applications. Traditionally, underhood automotive applications have been the domain of nylon 6 and 6/6. In the past, fuel systems applications have utilized acetal. "With nylon," Sykes says, "designers must still accommodate its hygroscopic tendency (a.k.a., moisture pickup). As for acetal, brittleness (in fuel systems) and dimensional stability seem to be the main constraints." Nylon picks up 6 to 8 percent moisture vs. Carilon's 2 percent, and the aliphatic polyketone also holds its properties better after moisture absorption, says Sykes. It also offers freedom from predrying and moisture conditioning steps in the manufacturing process.

Shell reports chemical resistance of Carilon to most automotive fuels is excellent, and its dimensional stability is better than that of acetal. Cycle times are also about 20 to 50 percent lower. A project now in progress for an outlet cover on a fuel pump with molded-in check valve shows Carilon can hold tolerances and reduce leakage rates better than acetal.

When it comes to the largest component in an automotive fuel system-the fuel tank-Sykes admits there are two approaches. "In the U.S., where tanks are still traditionally blowmolded, Carilon is being used as a barrier layer. However, in Europe, the interest leans toward injection molded fuel tanks because their new environmental legislation-Euro 2000 and 2005-exceeds the most stringent in the U.S. So we're working with European OEMs on a prototype, welded, injection molded tank. In addition to lower permeability, it can offer the ability to consolidate parts and, thus, reduce leak potentials."