Ameer Randolph
The type of plastic used for fuel tanks depends on the type of vehicle and the fuel tank size. For example, small gas tanks, like those used in lawnmowers and snowblowers, are typically made from high-density polyethylene (HDPE). In the 1990s, the North American industry favoured HDPE with a melt flow rate (MFR) of 4.0 g/10 min and a density of 0.946 g/cm3. However, automotive gas tanks are subject to stricter emission standards and often employ multilayer constructions with barrier materials to prevent gasoline diffusion. These tanks often combine HDPE with EVOH, specifically SoarnoL™, to prevent the rapid permeation of gasoline.
| Characteristics | Values |
|---|---|
| Type of Plastic | PA6 or PA66 with GF30, High-Density Polyethylene (HDPE) |
| Melt Flow Rate (MFR) | 4.0 g/10 min, 3.3 g/10 min |
| Density | 0.946 g/cm3, 0.945 g/cm3, 0.94 g/cm3 |
| Use Case | Small gas tanks for equipment like lawnmowers and snowblowers |
| Advantages | Good balance of load-bearing properties and ductility |
| Disadvantages | Cracking issues due to changes in density |
| Solution | Use of EVOH and SoarnoL™ to reduce VOC emissions and prevent gasoline permeation |
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What You'll Learn
Small gas tanks are made from high-density polyethylene (HDPE)
Small gas tanks, typically used for equipment like lawnmowers and snowblowers, are usually made from high-density polyethylene (HDPE). This plastic is produced by injection moulding, with the small tanks' two-piece design welded together before the plastic has cooled.
The use of HDPE in small gas tanks became popular in the 1990s, when it was the material of choice for the North American industry. This was due to its good balance of load-bearing properties and ductility, with an MFR of 4.0 g/10 min and a density of 0.946 g/cm3. This density is near the minimum for materials classified as HDPE.
However, a slight decrease in the density of the HDPE used for small gas tanks caused a widespread issue with cracked fuel tanks. This resulted in an industry-wide investigation, with many companies going out of business or choosing to stop supplying the tanks due to the risks. The problem was eventually solved by a material supplier who developed a grade with a lower density, solving the cracking issue.
Despite this issue, HDPE remains a popular choice for small gas tanks, although it is not suitable for automotive gas tanks due to its inability to prevent the rapid permeation of gasoline. For automotive applications, HDPE is often co-extruded with other materials to create multilayer plastic tanks that meet rigorous emission standards.
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HDPE combines load-bearing and ductility
High-density polyethylene (HDPE) is a type of plastic that is commonly used for fuel tanks. It is a versatile material with unique properties that make it suitable for a wide range of applications. One of its key advantages is its ability to combine load-bearing capacity and ductility.
HDPE pipes, for example, are known for their strength and durability. They can withstand both short-term and long-term pulls or impacts, making them highly resistant to corrosion, abrasion, and high impacts. This adaptability has made them a popular choice across various industries, including mining, agriculture, water distribution, and gas distribution.
The load-bearing capacity of HDPE is further enhanced when used in combination with other materials. For instance, a study on the improvement of bearing capacity in coastal sand found that HDPE woven fabric used as reinforcement in discrete layers significantly increased the load-bearing capacity of the sand. This discovery has important implications for infrastructure development, particularly in challenging soil conditions.
The ductility of HDPE is another critical factor in its structural integrity. Due to its relatively high strain rate, HDPE pipes are flexible and can deflect under soil weight, producing passive soil support. This ductility also ensures that HDPE exhibits a ductile fracture across all temperature ranges, allowing the material to deform under stress before breaking. As a result, HDPE pipes can maintain their structural integrity under different conditions and exhibit lesser temperature dependence than other materials such as PVC and CPVC pipes.
In conclusion, HDPE combines load-bearing capacity and ductility in a unique way that makes it a highly versatile and durable material. Its strength, flexibility, and resistance to corrosion and abrasion have revolutionized water infrastructure and expanded its applications across multiple industries. The ability of HDPE to maintain its structural integrity under various conditions makes it a reliable choice for pressure-rated applications.
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EVOH is used in multilayer plastic tanks to reduce VOC emissions
Stricter air pollution regulations have caused the automotive industry to seek alternatives to metal fuel tanks to reduce volatile organic compound (VOC) emissions. This has led to the development of multilayer plastic tanks using EVOH (ethylene vinyl alcohol copolymer) to reduce VOC emissions.
EVOH is an extrudable plastic barrier material with excellent barrier properties for oxygen and other gases. It is often used in food packaging and agricultural film sectors due to its ability to act as a gas and flavour barrier while preserving spices and aromas. When used in multilayer plastic tanks, EVOH provides a vapor barrier that effectively contains hydrocarbon emissions, specifically gasoline, a volatile organic compound.
The unique polar chemical composition of EVOH exhibits excellent resistance to hydrocarbons. When co-extruded with high-density polyethylene (HDPE), the primary material in plastic fuel tanks, EVOH creates an effective barrier to prevent the rapid permeation of gasoline to the outside air. This combination of EVOH and HDPE ensures compliance with stringent clean air standards and helps reduce VOC emissions from automobiles.
The six-layer construction of multilayer fuel tanks includes the EVOH layer, which reduces permeation to below 0.5 g/m2/day, meeting the EPA requirements. The HDPE layer provides durability, impact resistance, UV resistance, and chemical resistance. Additionally, multilayer fuel tanks can be moulded into complex shapes to maximise fuel capacity while remaining relatively lightweight.
The use of EVOH in multilayer plastic tanks is, therefore, a critical innovation in the automotive industry's efforts to reduce VOC emissions and meet increasingly strict environmental regulations.
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PA6 or PA66 with GF30 is used in plastic parts
PA6 or PA66 with GF30 is a type of plastic that is commonly used in the automotive industry and various other applications. The "GF30" in the name indicates that the material contains 30% glass fibres, which enhance its strength, stiffness, and impact resistance. This composition makes it ideal for manufacturing structural parts, housings, and connectors.
PA6 GF30 is a type of nylon-6 that offers superior tensile strength compared to standard PA6. It has a higher density, providing greater rigidity and stability. The glass fibres in PA6 GF30 improve its chemical resistance, making it suitable for resisting oils, greases, and solvents. Additionally, it exhibits ageing and wear resistance, maintaining its performance even in harsh environments.
On the other hand, PA66 GF30 is an engineering plastic with higher thermal properties and processing temperatures than PA6 GF30. It has a higher melting point, ranging from 260 to 265°C, compared to PA6's melting point of about 220°C. PA66 GF30 is commonly used in high-strength and heat-resistant applications, automotive components, and electronic equipment shells. It offers superior mechanical strength, chemical resistance, and heat resistance compared to pure PA66.
The choice between PA6 GF30 and PA66 GF30 depends on specific application requirements, including cost, chemical stability, heat resistance, and mechanical properties. PA6 GF30 is relatively low cost, while PA66 GF30 offers enhanced performance at a higher price point. Both materials are versatile and adaptable, making them suitable for a wide range of plastic parts, including those used in fuel tanks and other automotive applications.
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SoarnoL™ is coextruded with HDPE to prevent hydrocarbon permeation
Plastic fuel tanks (PFTs) are primarily made of high-density polyethylene (HDPE). However, HDPE alone cannot prevent the rapid permeation of gasoline (a volatile organic compound) from the tank to the outside air. This is where SoarnoL™ comes in.
SoarnoL™ is the trade name of ethylene-vinyl alcohol copolymer (EVOH), originally developed by Mitsubishi Chemical. It is composed primarily of carbon, oxygen, and hydrogen, and when burned, emits only carbon dioxide and water vapour. It does not contain harmful components that produce dioxins or other environmentally damaging substances. Its combustion heat is only half that of polyethylene, which helps reduce the burden on incinerators and provides increased service life.
SoarnoL™ exhibits excellent barrier properties to hydrocarbons such as gasoline due to its unique polar chemical composition. This means it can effectively prevent the permeation of gasoline through the fuel tank. By coextruding HDPE with SoarnoL™, the problem of gasoline permeation is resolved, and the automotive industry benefits from the design flexibility offered by SoarnoL™.
SoarnoL™ has found applications in various coextruded small engine tanks and portable fuel cans. It also offers innovative food packaging technology, preserving food flavour and freshness by shutting out oxygen to prevent spoilage. SoarnoL™’s excellent transparency helps ensure that food looks appealing, and its oxygen barrier properties can be adjusted according to ethylene content and humidity.
Overall, the coextrusion of HDPE with SoarnoL™ has revolutionised the design of plastic fuel tanks, improved fuel containment, and reduced VOC emissions, all while providing a safe and environmentally friendly solution.
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Frequently asked questions
High-density polyethylene (HDPE) is the primary material used for plastic fuel tanks (PFT).
HDPE offers a good balance of load-bearing properties and ductility.
HDPE alone cannot prevent the rapid permeation of gasoline from the tank to the outside air. A change of 0.006 g/cm3 in the density of the material used to produce the tanks can cause them to crack.
EVOH is used in multilayer plastic tanks to prevent the diffusion of gasoline through the tank wall. SoarnoL™ is co-extruded with HDPE to resolve the issue of gasoline permeation.
