carbon fibre cylinders with PET liners

PET replaces HDPE liners in “Type IV” pressure tanks

  • Patented technology for making the PET liner
  • Up to 100 times higher oxygen barrier
  • Application: oxygen breathing tanks

Italian SIPA has found a completely new PET application outside the beverage industry. The company cooperated with CTS (Composite Technical Systems), the manufacturer of ultralight compressed gas cylinders, to develop an all-new “Type IV” pressure tank.

Type IV pressure cylinders comprise a plastics liner inside a protective skin made from a continuous carbon fiber reinforced plastics composite. They differ from Type I, II and III pressure cylinders, which are either partly or completely made from metal and which have significant higher weight. Type IV pressure cylinders are already on the market, but virtually all of them feature blow moulded liners made from high density polyethylene. CTS wanted to use PET, which would be lighter and would give the liner a barrier to oxygen up to 100 times higher.

Five times ligther than an all-steel one

CTS asked SIPA for support to improve a process for making PET liners that CTS had begun to develop on its own, but without achieving the results it was looking for. It had developed its own basic injection moulding machine and equally simple blow moulding machine, which together were capable of producing containers. However, the tolerances were not acceptable, and machine operators were constantly adjusting the settings. This was the starting point for the two companies to cooperate on container development, prototyping, testing, and production.

Production is now underway on a range of the new pressure cylinders, with volumes ranging from two to nine liters. The smallest one weighs 0.9 kg, and the largest one just 4.0 kg, around 30% lighter than a cylinder with an aluminium liner, and five times lighter than an all-steel one. The new cylinders can all withstand a service pressure of 300 bar, and CTS gives them an unlimited service life. The company has patented worldwide its new technology for making the PET liner.

The pressure cylinders are used as oxygen breathing tanks for fire fighters

The pressure cylinders are used as oxygen breathing tanks for fire fighters

Collaboration provides SIPA with extra insight into the capabilities of PET

For its part, SIPA is very happy to be working with such an innovative customer. “The collaboration with CTS has provided us with extra insight into the capabilities of PET as a packaging material,” says Alberto Uliana. “This is the very first time that we have worked on an application where internal pressures is so high! We have all gained a lot from the experience.”

Initial target application for the pressure cylinders are oxygen breathing tanks for fire fighters. Other possible applications include scuba diving kits, fuel tanks for cars and devices in outer space. The two companies are now collaborating on the development of various types of plastics for the liners that could provide even higher performance in terms of oxygen barrier.

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