German firm Kautex Maschinenbau's blow-molding experts have successfully produced a large-volume polyamide liner for hydrogen pressure vessels by means of extrusion blow molding. The liner is more than two meters long (6.5 ft), with a diameter of approximately 500 mm (1.6 ft) and a volume of 320 liters (84.5 gal). This is reportedly the first time a liner for a hydrogen container has been produced in this size via blow molding.

Hydrogen presents considerable challenges in relation to the liner material’s permeability. Being the smallest molecule in the periodic table, hydrogen can diffuse through virtually every plastic. Special polyamides (PAs) have the best barrier properties. However, due to their low melt rigidity and complexity, these PA variants have been difficult to process on this scale by blow molding. Newly developed PAs and a special extrusion technique have now made this possible.

“Producing a liner of this size from polyamide has been a major challenge. The work we are doing here is truly pioneering,” said Abdellah El Bouchfrati, Head of Composite Business Development, where the new hydrogen liner was developed.

For some time now, Kautex has been devoting efforts into the development of composite pressure vessels for various applications such as hydrogen, CNG, and LPG tanks. Composite tanks consist of a thermoplastic liner; a boss part, to which the valve is connected; and a fiber winding that adds mechanical strength.

Containers and pressure vessels (CPVs) for hydrogen are generally designed for an operating pressure of 700 bar and a burst pressure of 1750 bar. The liner is a core component — it is the inner skin of the tank, surrounding the contents and sealing them off from the outside. The liner is subjected to high mechanical stresses and temperature ranges from –60° to 120°C (–140° to 248°F). The technology developed by Kautex in cooperation with a plastics manufacturer enables blow molding of hydrogen liners in sizes with industrial applications.

“The liner size we have now achieved is just the start. We are confident that, in the future, we will be able to use this method to produce considerably larger liners for hydrogen pressure vessels,” added El Bouchfrati.

The technology developed by Kautex Maschinenbau for producing large-volume liners for hydrogen containers means that a cost-effective solution for transport and infrastructure requirements is now within reach. Hydrogen is regarded as an alternative to fossil fuels and battery-powered electric propulsion systems in many areas today. China, Japan, and South Korea are leading the way. However, Europe is also making great strides in driving this technology forward. Experts have long considered that the sole reliance on battery technologies will not achieve the long-term goal of carbon-neutral mobility.

While fuel-cell technology in the passenger car sector does not yet appear to be economically viable because of production costs and a lack of infrastructure, hydrogen-powered drive and production technologies are already being successfully implemented in other areas. This technology currently appears to be of particular interest for heavy goods transport, local public transportation, shipbuilding, and in the aircraft industry. In those sectors, the primary demand is for safe, lightweight, and leak-proof tank systems.

Hydrogen is also a first-class energy storage medium, especially if it has been produced using renewable energies. Here, too, tank systems that can withstand the associated pressure and still store the extremely light gas safely are needed, said Kautex.