Maya Ellison
The automotive industry has seen a shift from metal to plastic fuel tanks, with high-density polyethylene (HDPE) being the primary resin used for plastic tanks. This shift is due to stricter air pollution regulations, which HDPE tanks alone cannot meet. To address this, companies like Soarus LLC have developed multilayer plastic tanks using EVOH (ethylene-vinyl alcohol) barrier technology, which helps reduce VOC emissions. These tanks are designed to meet stringent emission standards and prevent the diffusion of gasoline through the tank wall. However, the transition to plastic fuel tanks has faced challenges, such as the need for specific technology to quickly collect and recycle various plastic types during the dismantling process.
| Characteristics | Values |
|---|---|
| Common materials | High-density polyethylene (HDPE), polypropylene (PP), regrind plastic (recycled polyethylene), plastic adhesive, ethyl vinyl alcohol (EVOH) |
| Recyclability | Recycled plastics are not cost-competitive with virgin plastics. HDPE tanks are easier to dismantle and avoid type mixing, but will not meet new evaporative emissions standards. |
| Durability | Plastic tanks are not susceptible to corrosion and will have longer useful lives. |
| Safety | Steel withstands high temperatures and is less likely to succumb in a fire. |
| Manufacturing | Plastic tanks are molded into a seamless one-piece construction that consists of at least six layers of a given material or several different materials. |
| Shape | Plastic fuel tanks can be rectangular, cone-bottomed, horizontal, cylindrical, or vertical. |
| Use cases | Plastic fuel tanks are used in cars, trucks, motorcycles, AGVs, boats, aerospace, construction, industrial, commercial, petroleum, marine, and military applications. |
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What You'll Learn
High-density polyethylene (HDPE) is the primary resin used
HDPE is a popular choice for plastic fuel tanks due to its resistance to corrosion and water damage. Water vapours can build up inside a tank when it is not completely full of fuel, and these vapours can cause a metal tank to rust from the inside out. Plastic tanks, however, are not susceptible to corrosion and will therefore last longer.
The use of HDPE in fuel tanks is also advantageous because it is a recyclable material. However, recycled plastics are not currently cost-competitive with virgin plastics. Additionally, multilayer tanks that meet new evaporative emissions standards are more challenging to recycle in a cost-effective manner.
Despite these challenges, manufacturers are increasing their production of HDPE fuel tanks due to their many benefits. For instance, HDPE can be moulded into a seamless one-piece construction that typically consists of at least six layers of different materials, providing various beneficial characteristics. However, it is important to note that the molding process for plastic fuel tanks results in roughly 30% of plastic material ending as industrial waste.
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Multilayer tanks use EVOH barrier technology
Plastic fuel tanks are typically made from high-density polyethylene (HDPE). However, multilayer tanks that use EVOH (ethylene-vinyl alcohol copolymer) barrier technology are also employed. EVOH is an excellent barrier to gases such as oxygen, nitrogen, carbon dioxide, and helium, making it ideal for fuel tanks.
EVOH is a flexible, crystal-clear, glossy thermoplastic copolymer with excellent flex-crack resistance and high resistance to hydrocarbons, oils, and organic solvents. It is often used as an internal layer in multilayer structures due to its superior gas barrier properties. The number of layers in a multilayer structure can dramatically improve the barrier properties of the material.
One example of a multilayer fuel tank that utilises EVOH is Ford's six-layer fuel tank. It consists of an inner layer of HDPE, an adhesive layer, a barrier layer of ethylene-vinyl alcohol copolymer, another adhesive layer, a layer of "regrind," and an outer layer of HDPE. This tank design meets California's strict evaporative fuel standards.
While multilayer EVOH tanks offer superior gas barrier properties, they pose a challenge in terms of cost-effective recycling. The recycling process for multilayer tanks is more complex and costly compared to single-layer tanks. Additionally, the absence of a robust plastics recycling infrastructure for automobiles further complicates the recycling process.
To address the recycling challenges, some companies have developed innovative solutions. For instance, Impact Plastics has incorporated EVOH into rollstock structures through extrusion lamination or multi-layer coextrusion processes. These processes allow for the creation of multilayer structures with distinct properties derived from each material used.
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$150.84
Kautex supplies Ford with six-layer HDPE tanks
Ford uses six-layer fuel tanks made of high-density polyethylene (HDPE). The automotive company had considered investing $110 million in machinery and equipment to produce the tanks, which would have been the first commercial use of coextruded tanks. However, Ford decided to increase its steel-tank stamping capacity at Dearborn, switching the Explorer and the new F-150 truck (PN96) gas tanks from plastic to zinc-nickel-coated steel.
Kautex is supplying Ford's facility in Milan, Michigan, with this six-layer technology. The tanks are designed to meet California's stricter evaporative fuel standards. They consist of an inner layer of HDPE, joined by an adhesive layer, and a barrier layer of polyamide or ethylene-vinyl alcohol copolymer. Another adhesive layer is joined by a layer of "regrind" and an outer layer of HDPE.
Kautex, a plastic fuel tank maker, has been doing well in the market. The company has kept up with the growing global requirements of plastic fuel systems by introducing "coextrusion", a multi-layer extrusion process that includes a series of virgin layers of HDPE extrusion, "regrind", and ethylene vinyl alcohol, the "barrier" layer that reduces hydrocarbon emissions.
Kautex offers light, reduced-noise conventional blow-moulding solutions with coextrusion. The company's plastic fuel systems are significantly lower in weight than traditional steel tanks, contributing to a reduction in the automobile's overall weight and emissions. In addition, Kautex's noise reduction technology addresses "slosh noise", the sound of the fuel moving through the tank when the car starts or stops moving.
Kautex's design teams work closely with customers to create flexible shapes and dimensions to meet required volumes. The company's lean thinking and solid manufacturing processes allow it to keep costs low, and it conducts significant testing to ensure its products are crash-test resistant and meet regulatory requirements.
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SoarnoL™ helps reduce VOC emissions
Stricter air pollution regulations have pushed the automotive industry to adopt multilayer plastic tanks using EVOH to reduce volatile organic compound (VOC) emissions from vehicles. While high-density polyethylene (HDPE) is the primary material in plastic fuel tanks, it cannot prevent the rapid permeation of gasoline (a volatile organic compound) from the tank to the outside air.
SoarnoL™, a unique polar chemical composition, acts as an excellent barrier to hydrocarbons such as gasoline. By co-extruding HDPE with SoarnoL™, the problem of VOC emissions is resolved. SoarnoL™ also provides design flexibility to automotive manufacturers. Its use has extended to various co-extruded small engine tanks and portable fuel cans.
SoarnoL™ has also been developed for use in food packaging, helping to maintain freshness and extend expiration dates. This contributes to the reduction of GHG emissions by reducing food loss. SoarnoL™ PB7104B, a newly developed product containing more than 25% biomass components, can reduce GHG emissions by up to 30% compared to general EVOH.
In addition to its sustainability benefits, SoarnoL™ has applications in the transportation industry. By replacing glass bottles and metal containers with multilayer plastic containers using SoarnoL™, weight can be reduced without compromising gas barrier properties. This can lead to a significant reduction in GHG emissions during transportation, contributing to carbon neutrality.
Overall, SoarnoL™ is a versatile material that helps reduce VOC and GHG emissions in various industries, including automotive, food packaging, and transportation. Its unique properties provide both environmental and functional benefits, making it a valuable solution for meeting stricter air pollution regulations.
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Cracked tanks can result from density changes
Plastic automotive fuel tanks are typically made from high-density polyethylene (HDPE). HDPE is a popular choice for fuel tanks due to its excellent chemical resistance, meaning it is not affected by strong acids or bases and is resistant to gentle oxidants and reducing agents. However, despite its durability, HDPE fuel tanks can still crack due to changes in density during the manufacturing process.
A case study detailed how a very small change in density—0.006 g/cm3—led to a significant decrease in PE stress-crack resistance, resulting in cracked fuel tanks. This change in density caused environmental stress cracking (ESC), a mechanically driven process accelerated by chemical influences. The interaction between material properties, part design, assembly methods, and the application environment all play a role in ESC.
In another instance, Ford considered investing $110 million in machinery to produce coextruded fuel tanks made of HDPE. However, they ultimately decided to switch back to zinc-nickel-coated steel tanks for their Explorer and F-150 truck models. This decision may have been influenced by the challenges of working with HDPE, including the potential for cracked tanks due to density changes.
To repair cracked plastic fuel tanks, several methods can be employed. One approach is to use a soldering iron to apply heat and melt a plastic stick of the same type as the tank (typically PE) to fill in the crack. This method ensures that the repair material behaves the same as the original tank material during contraction and expansion. Another technique involves welding the crack by melting the plastic and sealing it back together, effectively plastic welding. This method ensures that the crack is truly filled, rather than just covered over.
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Frequently asked questions
High-density polyethylene (HDPE) is the primary material used in automotive fuel tanks.
HDPE is used because it is a good barrier to hydrocarbons such as gasoline.
HDPE helps to reduce volatile organic compound (VOC) emissions from automobiles. It also offers more volume capacity than steel tanks.
Examples of vehicles that use HDPE fuel tanks include the Chrysler Jeep Cherokee, T300 trucks, and the LH series and Viper sports car.
Yes, there have been some concerns raised about the durability of HDPE fuel tanks, with some reports of cracked fuel tanks due to environmental stress cracking (ESC).
