No. PCT/EP2017/075339, filed Oct. 5, 2017, which designates the United States, and claims priority to European Patent Application No. 16192469.1, filed Oct. 5, 2016, and the entire contents of each of the above applications are hereby incorporated herein by reference in entirety.

The present invention relates to a liner for a composite pressure vessel. In particular, it relates to a non-metallic liner for the storage of hydrogen.

Some vehicles use compressed gas as fuel, in particular hydrogen. Generally, such vehicles are equipped with a composite pressure vessel. Generally, the composite pressure vessel comprises a liner for the storage of hydrogen. For example, an outer filament winding is applied around the liner. The filament winding can come in the form of a carbon fiber filament composite wound around the outside of the liner.

Both metallic and non-metallic liners are used, but non-metallic liners are preferred because of their lighter weight.

Non-metallic liners may be of the monolayer type or multilayer type.

Generally, liners of the monolayer type comprise a single layer of polyamide. PA-6 is generally used. A disadvantage of these known liners is that they have an important thickness (typically above 4 mm), in order to meet permeability standards in relation to the type of use for which they are designed and the environmental requirements that they have to satisfy. This increases the weight of the pressure vessel and thus increases the fuel consumption. This also increases the space occupied by the pressure vessel on the vehicle.

Generally, liners of the multilayer type comprise a structure of 6 layers: an inner thermoplastic-based layer, preferably HDPE; a first layer of adhesive; a layer comprising a barrier resin, preferably EVOH; a second layer of adhesive; a layer of regrind; and an outer thermoplastic-based layer. It is known that these known liners suffer from the relatively high diffusivity of hydrogen in the HDPE inner layer (which is in direct contact with the hydrogen). Hydrogen may concentrate in certain areas inside the HDPE inner layer. This accumulation generates bubbles at pressure release. This bubble formation is referred to herein as blistering. This blistering may cause damage in the form of cracking or mechanical degradation of the liner. One additional disadvantage of such structure is its low resistance to the high temperature variations that occur during a refuelling operation. Typically the liner is exposed to a fast temperature variation going from −40° C. up to +80° C. in a few minutes. This generates important amount of thermal stresses in the liner material which can lead to liner break.

WO2013108102 discloses a pressure vessel comprising a rounded container comprising a thermoplastic composition. The thermoplastic composition comprises a siloxane copolymer. The thermoplastic composition further comprises a blend of polyamide. This document does not, however, deal with providing a container having a liner with a low permeability to hydrogen and good blistering resistance. Further, WO2013108102 does not deal with liners being overwrapped with a reinforcing structure.

Other pressure vessels are described in US2009/0203845 and DE20201007414.

In view of the above-mentioned disadvantages, there exists a need for an improved pressure vessel for the storage of hydrogen.

It is, therefore, one aspect of the present invention to provide a composite pressure vessel comprising a monolayer liner, the liner being made by injection moulding, the liner comprising at least two shells weldable together. Advantageously, each shell is made of a polymer composition comprising at least 45% by weight of an aromatic polyamide relative to the total weight of said polymer composition, and at least 10% by weight of an aliphatic polyamide relative to the total weight of said polymer composition.

Thus, it is proposed a monolayer liner made of a polymer blend (i.e. polymer composition) composed of at least 45% by weight of an aromatic polyamide and at least 10% by weight of an aliphatic polyamide relative to the total weight of the polymer composition. The polymer blend of the invention provides for a monolayer liner having reduced thickness, while maintaining low permeability to hydrogen compared to known polyamide-based monolayer liner (i.e. pure PA-6 liner). Further, it provides for a monolayer liner having good mechanical strength for supporting, for example, a filament winding process and without jeopardizing the structure liner integrity after the filament winding process.

It is to note that the chemical proprieties of the polymer blend of the invention allow to slow down the migration (i.e. reduce the diffusion rate) of hydrogen inside the monolayer liner. The polymer blend of the invention provides a diffusion-delay function. Using such diffusion-delay function allows protection of the monolayer liner against the cracking effects due to blistering.

The composite pressure vessel of the invention is capable of storing gases at pressures above 700 bars.

The term “polymer composition” refers to a polymeric material having one or more monomer species, including homopolymers, copolymers, terpolymers, and the like.

The term “polymer composition” also refers to a blend of two or more polymers, and is interchangeable with the term “polymer blend”. It is another aspect of the present invention to provide a vehicle comprising a composite pressure vessel as described above.

