The growing use of bio-based fuels today has created new performance and design considerations for high-performance polyamides used in a range of automotive fuel components such as fuel rails, diesel fuel filter housings, fuel sender units, flanges, fuel connectors, and quick connectors. During the material selection process, engineers need to take into account not only the basic tenets of metal-to-plastic conversion, but also the type of fuel and its impact on the performance of the materials.
Conventional gasoline is being modified with aliphatic alcohols such as ethanol and methanol. In the U.S., the percentage of alcohol ranges up to 85% (E85) while in Brazil the usage of 100% ethanol (E100) is typical. Also, diesel fuel can be replaced by 100% of biodiesel sourced from sustainable resources such as soy, rape seed, sugar cane, and animal grease. In Brazil, B100 biodiesel (100% biodiesel content) isn't ready for commercial use. Currently, B5 (5% biodiesel content) is regulated for commercial use while in the U.S. and Europe auto makers are designing for components that use B20 (20% biodiesel) added to regular diesel and in some cases B30 (30% biodiesel).
These bio-based fuels can have an adverse effect on the long-term performance of aliphatic polyamides such as nylon 6, nylon 66, and nylon 12. However, semi-aromatic polyamides such as polyphthalamide (PPA) have demonstrated superior performance in these bio-fuel applications, retaining their properties over the long term.
Bio-based fuels can cause swelling in parts made of nylon 66, resulting in significant dimensional changes and weight gain. In addition, the alcohol's oxygen content can break down the carbon-carbon bond in the PA 66 backbone, resulting in a loss of mechanical properties such as tensile strength. Similarly, in biodiesel applications, parts made of aliphatic polyamides are significantly affected by the presence of corrosive water that can cause severe chemical attack to the polymers. Ultimately, this could lead to leaks and failures in certain applications.
Based on extensive testing and commercial use, higher performing semi-aromatic nylons such as PPA offer major advantages over aliphatic nylons, delivering superior chemical resistance, lower water absorption, and better dimensional stability. They offer the most favorable performance in critical fuel component applications, retaining mechanical performance after over 5000 hours of exposure.
This paper will present property comparisons and design recommendations for high-performance polyamides for bio-based fuel applications.