New engineering resins take on automotive fluids.

New formulations of "extended-life" coolants and new fuel-emission standards are presenting performance challenges for semi-crystalline engineering thermoplastics in automotive under-the-hood applications and fuel systems. To meet those requirements, new grades of established engineering resins are being developed, and new families of materials are beginning to make commercial headway in these applications. Here is a look at what new materials are offering in terms of performance in automotive fluid and fuel applications.

NEW AGGRESSIVE COOLANTS

New coolant formulations that allow extended service intervals of 100,000 to 200,000 miles are replacing conventional coolant systems. The new generation of coolants use organic acid inhibitors that may have adverse effects on the chemical resistance of some plastics that are currently used on typical cooling systems.

One new material that is targeting engine coolant applications is Questra syndiotactic polystyrene (SPS) introduced earlier this year by Dow Plastics, Midland, Mich. According to Dow, Questra performed well compared to PPA, PPS, aliphatic aromatic polyamide, and nylon 66 when tested with long-life ethylene glycol and propylene glycol coolants at various temperatures. SPS was said to maintain its strength, elongation, flexural properties and dimension with improved hydrolytic stability. It also was less affected by changes in glycol composition and increased temperature than PPA, nylon 66, and aliphatic aromatic polyamide.

A new hydrolytic grade of Ryton PPS has been developed by Phillips Chemical Co., Bartlesville, Okla. In tests, Ryton BR4220 held 85% of its tensile strength after aging, compared with 60% for competitive materials, according to Greg Davis, Ryton automotive market development manager. One application of the new grade is the heater core of the ventilation system located in the passenger compartment, in which coolant flows through a small radiator.

LOWER FUEL EMISSIONS

Lower emissions requirements for fuel systems are prompting new resin developments. Carilon aliphatic polyketone, introduced late last year by Shell Chemical Co., Houston, is being targeted for several fuel applications. One of the most intriguing is as a barrier replacement for EVOH in multi-layer gas tanks, according to Paul Sykes, automotive market manager for Shell's Carilon. He says that because of Carilon's chemical resistance, it can come in direct contact with fuel, thus eliminating the need for inside PE and tie layers. The number of layers can be reduced from six to four (Carilon/tie/regrind/PE).

'FLEXIBLE' FUELS

Although the legislative effort to require alternative fuels has not been sustained, the use of "flexible" or alternative fuel formulations such as oxygenated fuel mixtures has increased to meet strict CAFE (corporate average fleet economy) ratings. Alternative fuels is one of several competing technologies for meeting CAFE requirements. Others include catalytic converters and secondary pumps that also allow for cleaner burning of exhaust gases, according to Kevin Cronin, senior product manager of Fortron PPS at Hoechst Technical Polymers, Summit, N.J.

According to Cronin, a move to oxygenated fuels would pose issues of permeability, swelling, and property degradation that would make linear PPS a good fit in applications such as fuel rails. Hoechst is presently working on toughening its linear PPS grades while maintaining the material's chemical resistance. The technology involves impact modification as well as reinforcement with long-glass fibers.

In addition, Hoechst has developed a new grade of acetal copolymer with improved resistance to alcohol-based fuels. A 25% glass-reinforced Celcon GC25T is said to resist wicking of the fuel along the glass-polymer interface, which can result in a subsequent loss of properties.

ANTI-STATIC MATERIALS

New non-conductive and static-dissipative grades of Delrin acetal are being developed by DuPont Engineering Polymers, Wilmington, Del., for fuel applications. Non-conductive resins, such as nylons, polyesters, and acetals including conventional Delrin grades, have surface resistivities of [10.sup.15] to [10.sup.16] ohms/cm, according to Jake Fenrick, Delrin product manager.

DuPont is developing carbon-filled acetal grades with a surface resistivity value in the [10.sup.6] ohms/cm range, allowing systems to be put together with a surface resistivity of [10.sup.8] ohms/cm or less, he says. DuPont is looking at two approaches: carbon-fiber and less expensive carbon-particle fillers, the latter of which will require additional toughening technology to bring the toughness to that of standard Delrin products. The company plans to offer two to four grades of conductive materials with varying levels of toughness. In Europe, DuPont has commercialized one carbon-fiber conductive grade, Delrin DE7018, which has a surface resistivity of [10.sup.6] ohms/cm.