Automobile fuel and engine systems are characterized by extremes of heat, aggressive chemicals, fuel mixtures and sustained vibrations. The key components comprising the fuel systems include fuel seals, head and intake manifold gaskets, quick-connect O-rings, fuel injection seals, fuel fill hoses and vapor lines. The fuel systems not only demand long unimpeded life, resistance to fuels and aggressive lubricants, resistance to heat, low permeation rates but also compliance with stringent emission and clean air regulations. In this context, fluoropolymers, in particular fluoroelastomers, are pushing automotive fuel systems to the next level.
World's leading fluoropolymer producer Dyneon unveiled a fluoroelastomer; Dyneon THV X 815 G, which helps automotive parts manufacturers meet unique regulatory and design requirements of elastomeric fuel system barrier hose applications such as small diameter fuel and vapor lines and larger diameter fuel-fill hoses. Dyneon THV (a polymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride) offers a combination of performance advantages including low processing temperature, ability to bond to elastomers and hydrocarbon-based plastics, flexibility and optical clarity. It provides the low permeation performance that is critical in applications where the THV layer serves as the first line of defense against evaporative emissions, helping the entire fuel system to meet industry regulations such as CARB LEV II (California Air Resources Board-Low Emission Vehicle II) and EPA Tier 2 (Environmental protection Agency). Owing to these performance characteristics, the fluoroelastomer enables fuel fill hoses to be made in longer lengths without sacrificing durability or permeation resistance. It is also bondable to other substrates (for multi-layer constructions) and can be co-processed with many hydrocarbon elastomers. Additionally, in accordance with OEM material specifications, Dyneon fluoropolymers used in automotive applications do not contain extractables that can choke fuel systems.
Viton® fluoroelastomer from DuPont Performance Elastomers has long been known for its excellent (400°F/200°C) heat resistance. It offers excellent resistance to aggressive fuels and chemicals and has worldwide ISO 9000 and ISO/TS 16949 registration. It has been extensively used in making fuel seals, gaskets, connection O-rings, fuel injection seals of all descriptions, caulks, and advanced fuel hose components. They come in a number of grades to meet specific end-use and processing needs. There are differences between types of Viton® in terms of chemical resistance and mechanical properties. The general purpose types differ primarily from the specialty types in chemical resistance. The specialty family of Viton® comprise of four types that are tailored for superior fluid resistance, low-temperature performance or combinations of these properties. Viton® fluoroelastomer VTR-9039 veneered hose technology has replaced silicone or fluorosilicone in the inner critical layer of turbo hose, both of which delaminated through swelling in hot fuel vapor at +200oC, resulting in permeation and weeping. On contrary, Viton® has complied with intense flexibility and ageing requirements under high vibration. Also, a co-injection molded fuel filler neck hose has decreased the hydrocarbon emissions to below 0.01 gm/day, after using a 0.6 mm inner layer of Viton®. This is a dramatic improvement in emissions compared with a competitive NBR design that achieves approx. 1gm/day performance. Such filler fuel neck hose made of Viton® have already substituted the metal fuel filler pipes that require flexible filler neck hose connections.
Connector system technology has been developed using Viton® and other fluoroelastomers for the vital O-rings in its quick-connector systems. Quick connector systems are little components that join pipes and hoses to ensure fluid flows in automotive fuel, brake booster and particle filter lines. The fluoroelastomer-part in such connector systems is often used in combination with reinforced polyamide for the connector body. Apart from meeting tough LEV II (Low Emission Vehicle), PZEV (Partial Zero Emissions Vehicle) and Euro 5 automotive evaporative emissions control legislation requirements, Viton® provide fuel system sealing capability for the lifetime of the vehicle (15 years/150,000 miles) at operating temperatures well above 150°C, or as low as –40°C. They also resists fuel/alcohol/ether blends including methanol, “sour” gasoline, new biofuels and biodiesels. Typically, Viton® made with APA GLT-S and GF-S types are best suited to meet the requirements in specific applications.
BMW Sauber F1 team used Viton® fluoroelastomer for its critical fuel system, engine oil system, gearbox oil system, water systems and hydraulic system seals and driveshaft boots. The material provided solutions of seals that could withstand aggressive fuel at up to 60°C, engine and gearbox oil up to 160°C, and water and hydraulic fluids at 120°C.
Another fluoroelastomer, Aflas® developed by Asahi Glass Company is well known for its application including fabrication o-rings, gaskets, seals, and coatings. Aflas® is a copolymer of tetrafluoroethylene and propylene (TFE/P) exhibiting resistance to petroleum products, steam and phosphate-esters. In some respects it exhibits media compatibility properties similar to ethylene propylene and fluorocarbon. Service temperatures are -5°C (25°F) to 204°C (400°F). It provides improved chemical resistance to a wide spectrum of automotive fluids and additives. It is resistant to motor oils of all types, engine coolants with high level of rust inhibitors, extreme pressure (EP) gear lubricants, transmission and power steering fluids, and all types of brake fluids including DOT 3, mineral oil, and silicone oil. It is ideal for heat transfer media, amines, acids and bases, as well as hot water and steam up to 170°C (340°F). AFLAS® 100/150 fluoroelastomers are alternating copolymers of tetrafluoroethylene and propylene. They offer excellent heat resistance, exceptional chemical resistance especially to bases and amines, and high electrical resistivity. On the other hand, AFLAS® MZ is a terpolymer composed of tetrafluoroethylene, propylene and vinylidene fluoride. AFLAS® MZ offers a good balance of chemical resistance and improved low temperature performance.
Nevertheless, the fluoropolymer business has, since 2000, been haunted by the widespread use and environmental presence of ammonium salts of perfluorooctanoic acid (PFOA) owing to the use of PFOA as a polymerization surfactant in manufacture of fluoropolymers. Dyneon was the first company to come up with an emulsifier around early 2008, which would eliminate the use of ammonium perfluoroocatanoate (APFO), a salt derived from PFOA. Driven by the legal and regulatory actions over concerns of harmful salts of PFOA, Dyneon answered the same through this emulsifier turning its product manufacturing into a green approach. Following the lead, Asahi Glass Co achieved a remarkable feat, when it announced the introduction of its Fluon® PTFE E-SERIES, a new line of PTFE (Polytetrafluoroethylene) products to be used in applications such as, wire & cable insulation, cookware coatings, parts for electronics, hose and tubing, etc. Unlike conventional PTFE manufacturing, the new E-SERIES process will not use ammonium salts of perfluorooctanoic acid (PFOA). AGC is planning to completely convert not only Fluon® PTFE but also all other fluorinated products into PFOA free products (i.e., free of PFOA at or above detection limits) by 2012.
Asahi Glass Company is focusing research to develop the central part of fuel cells called Membrane Electrode Assembly (MEA) that converts the chemical energy of hydrogen and oxygen into electric energy (emitting only water which is clean). The higher performance a fuel cell is directly proportional to the properties of MEA. The MEA newly developed by the company is the first fluorinated-polymer based MEA that has successfully provided a continuous operation time of more than 4,000 hours and is the closest MEA ever to practical use for fuel cells. While conventional MEAs have the disadvantage that they operate only under low temperature and high humidity conditions, our new MEA can continuously operate even under high temperature and low humidity conditions which is cutting-edge breakthrough in MEAs in the world. The direction of such advancement invokes a thought that it is not too far when automobiles will employ such clean fuel cells which will not emit carbon but water albeit with some assistance from fluorinated-polymer based MEAs.
To sum up, the fuel and engine systems’ demanding requirements including longer warrantees, high temperature stability, chemical resistance, low permeation levels and environmental compliance have been met thanks to the wonders of fluoropolymers (fluoroelastomers in particular). Besides, the automotive community and more importantly, the global community expects some more milestones to come in area of clean fuel cells which generate electrical energy emitting clean water by the help of the fluorinated polymer-based Membrane Electrode Assembly