Plastics have revolutionized our society. The automotive industry, in particular, has benefited from the light weight and material characteristics of modern plastics. Although we may normally think of bumpers and interior materials, plastics are also revolutionizing an automotive part few people think about: fuel tanks.
Fuel tanks present unique design challenges to automakers. First, there is the fact that they are used to store highly volatile materials – meaning that any failure could have high consequences. Second, fuel products can be corrosive, necessitating a chemically inert tank material. Finally, fuels produce vapours that are regulated by environmental agencies in many countries. Fuel tanks in these countries must be largely impermeable to fuel vapours in order to meet the requirements of the regulations.
Traditionally, fuel tanks have been constructed of metal – specifically, terne-coated steel, which has an 8% tin-lead coating on both the interior and exterior. Despite the protective coating, metallic fuel tanks have many disadvantages, including susceptibility to exterior corrosion caused by road salt, chemicals, and dust, high weight, and conduction of electricity, which can cause sparks leading to explosions.
Enter plastic fuel tanks. Unlike metal tanks, lightweight plastic tanks can be seamlessly formed into one, solid part. This results in increased tank strength in crashes, resulting in higher crash-worthiness for the vehicle as a whole. In addition, plastic tanks do not conduct electricity, reducing the likelihood of electrostatic charges igniting fuel.
The biggest challenge facing auto manufacturers is making plastic fuel tanks impermeable to vapours. In the 1980s, fuel tanks were made of a single layer of polyethylene treated with fluorine, which prevented vapour diffusion. Unfortunately, the fluorine tended to dissipate over time, allowing vapours to escape. After environmental regulations were tightened in the ‘80s and ‘90s, producers developed a six-layer blow moulding process. A specially formulated vapour barrier layer is sandwiched between two adhesive layers. A structural layer made of recycled plastic is then layered on the outside of the tank. Finally, the inner and outer surfaces are layered with polyethylene. The six-layer technology has revolutionized the fuel storage industry by allowing plastics to come into their own.
Plastic tanks are most commonly used in small engine tools today, but as auto makers strive for safer, more efficient vehicles, they are likely to turn to the benefits provided by plastics and the industry that supports them.
If you’re interested in quantitative data on the benefits of plastic fuel tanks, you might want to take a look at this brief publication.