thermoplastic gas tank

High pressure gas tanks in thermoplastic composites

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  • Thermoplastic composite for Compressed Natural Gas (CNG)
  • 70% weight reduction compared to steel
  • Extremely low gas permeation levels & fully recyclable

Royal DSM has introduced thermoplastic composite gas tanks for Compressed Natural Gas (CNG) that the company has developed with Covess, a specialist in advanced thermoplastic composite vessels. Thermoplastic tanks weigh around 70% less than steel tanks. For example, a traditional steel tank of 40L weighs around 60kg, while a composite ‘Type IV’ tank with polyamide Fuel Lock liner can weigh down to 20kg. In addition, the new tanks last longer than steel or even advanced thermoset gas tanks.

Natural gas as cost-effective fuel alternative

Hydrogen and natural gas are claiming their place in the field of cost-effective and low carbon-footprint fuels for use in automobiles. Countries with major natural gas reserves are looking at the advantages of using CNG as an alternative fuel which reduces the CO2 emission by 15% compared to current solutions in petrol or diesel.

Blow molded liner made from PA6-based engineering plastic

Type IV pressure vessels are based on plastics and continuous fiber reinforcements, unlike Type I, II and III pressure vessels, which contain metal components. At Fakuma, DSM demonstrated a tank with a liner blow molded in its Akulon Fuel Lock, a polyamide 6-based engineering plastic with very high barrier to hydrocarbons. The tank can be wrapped in a tape based on thermoset or thermoplastic resins, including its EcoPaXX polyamide 410.

Akulon Fuel Lock contains an additive formulation that further improves the already strong gas barrier of polyamide 6, and also provides it with extremely high impact resistance at low temperatures (down to -60°C). The permeation of HDPE liners is too high to allow the installation of composite Type IV tanks incorporating such liners inside a vehicle. However, Akulon Fuel Lock liner material reduces emissions by a factor of at least 150 compared to HDPE and therefore enables the use of Type IV tanks inside the car.

The Akulon Fuel Lock portfolio has been expanded with a grade that is suitable for blow molding of liners for large pressure vessels for heavy duty vehicles such as buses and trucks. It is normally difficult to make large blow moldings in polyamide 6 due to its relatively low melt strength, but this grade has sufficient melt strength to create a stable parison for tanks beyond a length of 2m, enabling high precision in control of the wall thickness.

Continuous fiber reinforced thermoplastic as tape material

In current Type IV pressure vessels, the tape reinforcement comprises either glass or carbon fibers in a thermosetting polymer, such as an epoxy or unsaturated polyester. DSM is cooperating in the development of next-generation Type V pressure vessels. These are made by winding a tape, developed by DSM, of continuous fiber reinforced with a thermoplastic, such as the company’s EcoPaXX polyamide 410, or another grade of Akulon.

Type V pressure vessels weigh around 70% less than steel tanks and can be lighter than Type IV pressure vessels too. They are more durable than steel, they have better chemical resistance (no corrosion), and they are also fully recyclable. EcoPaXX has the additional advantage that it has a zero carbon footprint from cradle to gate, owing to the fact that the polymer is made entirely from renewable resources.

Picture: Besides thermoplastic tape, DSM provides solutions for liners in Type IV composite pressure vessels with its Akulon Fuel Lock polyamide portfolio (Source: DSM Engineering Plastics)

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