Multilayer structure for transporting or storing hydrogen

Abstract

To provide a multilayer structure selected from a reservoir, a pipe or a tube, for transporting, distributing or storing hydrogen.SOLUTION: A multilayer structure comprises, from the inside to the outside, at least one sealing layer and at least one composite reinforcing layer, the innermost composite reinforcing layer being welded to the outermost adjacent sealing layer. The sealing layer is composed of a composition predominantly comprising at least one semi-crystalline thermoplastic polymer P1 having a Tm of less than 280°C, particularly less than 265°C. At least one thermoplastic polymer in each sealing layer may be the same or different. At least one of the composite reinforcing layers is composed of a fibrous material in the form of continuous fibers impregnated with a composition predominantly comprising at least one thermoplastic polymer P2, which is particularly semi-crystalline. The thermoplastic polymer P2 has a Tg higher than the maximum temperature of use (Tu) of the structure, and satisfies Tg≥Tu+20°C. Tu is higher than 50°C, particularly higher than 100°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This patent application relates to multilayer composite structures for the transport, distribution, or storage of hydrogen and methods of making them. [Background technology]

[0002] One of the goals being pursued in the automotive sector is to offer increasingly less polluting vehicles. Therefore, electric or hybrid vehicles equipped with batteries aim to gradually replace internal combustion engine vehicles, such as gasoline or diesel vehicles. Batteries have proven to be relatively complex vehicle components. Depending on the positioning of the battery in the vehicle, it may need to be protected from impacts and from an external environment that may have extreme temperatures and variable humidity. It is also necessary to avoid the risk of fire.

[0003] Furthermore, to maintain the life of the battery without damaging the cells, it is important that its operating temperature does not exceed 55°C. Conversely, in winter, for example, it may be necessary to increase the battery temperature to optimize its operation.

[0004] Moreover, electric vehicles still face several problems today, namely the range of their batteries, the use of rare earth elements in these batteries, whose resources are not inexhaustible, and the production of electricity in each country that can recharge the batteries.

[0005] Hydrogen can therefore be converted into electricity by fuel cells to power electric vehicles, thus providing an alternative to electric batteries.

[0006] However, storing hydrogen is technically difficult and expensive, especially when it comes to mobile storage, due to its very low molar mass and very low liquefaction temperature. To be effective, however, storage must be carried out in small volumes, which means that the hydrogen must be kept under high pressure at the temperatures at which the vehicle will be used. This is especially the case for fuel cell hybrid road vehicles, primarily for urban use, with a target range of around 600-700 km or less, in addition to battery-powered electric bases.

[0007] Hydrogen storage tanks are usually made with a metallic liner that must prevent hydrogen from leaking. This first liner itself must be protected by a second liner (usually made of composite materials) designed to withstand the internal pressure of the tank (e.g., 700 bar) and any impact or heat sources. The valve system must also be secure.

[0008] According to the Hydrogen Memento Sheet 4.2 of the French Association of Hydrogen and Fuel Cells (AFHYPAC), revised December 2016, pressurized hydrogen storage and distribution using cylindrical steel cylinders or cylinder assemblies inflated to 20 or 25 MPa (types I and II) has been standard practice for a very long time. The drawback of this storage method is that it is much slower than the 100 kg / m³ of methane. 3 compared to only 14 kg / m at 20 MPa and normal temperature (21°C). 3The main limitations of these tanks are their size and weight, which is due in particular to the use of low-stress steel to avoid problems with hydrogen embrittlement. This situation changed radically with the advent of composite tank technologies known as Type III or Type IV. Their basic principle is to separate the two essential functions of sealing and mechanical strength and manage them independently of each other. In this type of tank, a bladder made of resin (thermosetting or thermoplastic), also known as a liner (or sealing sheath), is combined with a reinforcing structure made of fibers (glass, aramid, carbon), also known as a reinforcing layer or sleeve, which allows the tank to operate at even higher pressures while reducing its mass and avoiding the risk of explosive rupture in the event of a severe external attack. Thus, 70 MPa (700 bar) has essentially become the current standard.

[0009] In Type IV tanks, the liner and reinforcing layer are made of different materials and have the drawback of presenting a lack of adhesion between the liner and the reinforcing layer, which leads to the problem of liner collapse when there is both gas accumulation at the interface between the liner and the composite and a drop in the internal pressure of the tank.

[0010] This problem led to the development of V-shaped reservoirs, which are based on using the same polymer for the liner and composite matrix to ensure good, durable adhesion between the liner and the composite.

[0011] When transporting or distributing hydrogen through rigid or flexible pipes, it is also preferable that the hydrogen be at low volume and therefore high pressure to ensure sufficient flow rates. Thus, for hydrogen storage, transport, or distribution, it is interesting to use composite pipes consisting of a hermetic sheath (ensuring gas tightness and chemical resistance) reinforced by an outer layer made of composite material produced by filament winding, made from unidirectional (UD) tapes deposited in successive layers on a liner. If it is desired to make this pipe flexible, one possibility is to wind the UD tapes at one or more orientation angles relative to the pipe axis, so that the composite reinforcement can support the deformation of the composite pipe during use. The composite reinforcement allows the pipe to withstand the internal pressure generated by the transported fluid.

[0012] For storage tanks, it is necessary for the sealing sheath to resist collapse, especially during production shutdowns that can lead to a sudden drop in pressure. This risk exists when the sheath is not bonded to the composite reinforcement and gas can be present between the sealing sheath and the composite reinforcement. To avoid this phenomenon, one solution is to add an internal reinforcement, called a carcass, to the pressure jacket. This reinforcement is often metallic and perforated to be flexible, and therefore not hermetic to the transported fluid. This adds weight, complexity, and expense to flexible pipes. Also, to reduce weight or eliminate the internal carcass of composite pipes, it is necessary to bond the composite reinforcement to the sealing sheath, as in the case of V-shaped storage tanks.

[0013] Furthermore, the sealing sheath must be capable of being continuously extruded onto the support of the inner carcass, as the case may be, as described above, and must be sufficiently chemically stable so that its mechanical and sealing properties do not deteriorate in a manner that would be detrimental during the life of the reservoir or flexible pipe.

[0014] In the case of flexible pipes with an internal metallic carcass, the sealing liner must be able to withstand the effects of creep of the material it is made of due to stresses induced in the sealing sheath by the internal pressure of the pipe. Creep occurs at the joints (gaps or clearances) between the metallic sheath on which the liner rests (e.g., self-clinching Zeta or T-shapes) when the pipe is pressurized by the transported fluid, creating protrusions of material, generating stress concentrations and therefore preferential failure zones of the sealing sheath, so the material that makes up the sealing sheath must also withstand these stresses.

[0015] For example, Airborne has developed a variety of flexible pipes that lack an internal carcass and instead feature a sealed sheath bonded to the composite reinforcement. These include PA11 liners with PA11 FC composites (JIP completed in 2011), PA12 liners with PA12 FC composites, and PVDF liners with PVDF FC composites. However, all of these structures suffer from the drawback that the matrix of the composite reinforcement has a glass transition temperature (Tg) lower than the pipe's operating temperature (Tu). For PA11- or PA12-based pipes, this is 50°C in dry conditions at operating temperatures (Tu) of 60–80°C, while for PVDF, it is -40°C at operating temperatures above 100°C and approaching 130°C in continuous operation. In the specific case of PVDF, the matrix stiffness (modulus) remains above its Tg until it reaches another transition, the alpha transition being approximately 100°C, above which its behavior becomes purely rubber-like. Therefore, in all the above industrial and commercial cases of TP matrix composite pipes, the matrix of the composite reinforcement is in a fully rubberized state at the service temperature Tu of the composite pipe.

[0016] To solve this problem and have a composite reinforcement with a Tg higher than the maximum use temperature so that the matrix does not become rubbery at a use temperature of 130°C in this case, Kutting&Total, then Vitrex and Magma, developed a solution consisting of a PEEK sealing sheath (or liner) reinforced with a composite material having a PEEK matrix. The Tg of PEEK is 140°C, and thus this Tg meets the requirement of high rigidity as it is higher than the maximum use temperature. The disadvantage is that as a result, the sealing sheath is also very rigid, which may limit the fatigue life and is a major disadvantage for the manufacture of flexible pipes. Furthermore, the processing temperature of this type of sealing sleeve is very high (typically 380 - 400°C), and in the case of the normal deformation process of tube extrusion, this presents great difficulties in terms of tooling and process control.

[0017] Furthermore, Ticona (Celanese) is collaborating with Airborne to provide composite pipes with PPS FC reinforcement and PPS sealing sheaths.

[0018] When Tu > 90°C, this structure presents the same problem of the composite material matrix as the PVDF - based solution (i.e., Tg < Tu), and furthermore shows a problem of the deformation temperature (in the case of PPS and PVDF, typically 350°C vs 250°C respectively).

[0019] When Tu < 90°C, PPS is suitable for the composite material matrix, but the problems of the extrusion temperature of the sealing liner and its high rigidity remain, limiting the flexibility of the composite pipe.

[0020] When hydrogen is rapidly filled, especially at about 110°C, since the compression of hydrogen causes a temperature rise in the storage tank, if the matrix of the composite material has a Tg lower than this temperature, it is necessary to make the composite material extremely large. Therefore, in the case of hydrogen storage tanks, similar technical problems are caused.

[0021] It remains therefore to be seen, on the one hand, that the composite matrix be optimized to optimize its mechanical strength at high temperatures, and, on the other hand, that the material constituting the sealing liner be optimized to optimize its application temperature without reducing the adhesion of the composite reinforcement to the sealing liner. Thus, possible modifications to the composition of the material constituting the sealing liner, to ensure at least partial miscibility with the composite matrix, must not lead to a significant increase in the temperature of the manufacture of this liner (extrusion blow, injection, rotational molding, etc.) compared to those currently practiced with polyamide and PVDF. Summary of the Invention

[0022] These problems are solved by providing the multilayer structure of the present invention, which is a fully bonded "two-material" composite pipe or tank, composed of a high strength composite reinforcement, i.e., a high Tg matrix, deposited by filament winding onto a previously extruded liner at a particularly relatively low temperature. The adhesion between the composite and the liner is very good.

[0023] Throughout this specification, the terms "liner," "sealing sheath," and "pressure jacket" have the same meaning.

[0024] The present invention therefore relates to a multilayer structure selected from a reservoir, a pipe or a tube intended for transporting or storing hydrogen, comprising, from the inside to the outside, at least one sealing layer and at least one composite reinforcing layer, the innermost composite reinforcing layer is welded to the outermost adjacent sealing layer; the sealing layer consists of a composition comprising mainly at least one semi-crystalline thermoplastic polymer P1i (i = 1 to n, n is the number of sealing layers) having a Tm of less than 280 ° C, in particular less than 265 ° C, measured according to ISO 11357-3:2013, the at least one thermoplastic polymer of each sealing layer may be the same or different, at least one of the composite reinforcing layers consists of a fibrous material in the form of continuous fibers impregnated with a composition mainly comprising at least one thermoplastic polymer P2j, in particular semi-crystalline, with j=1 to m, m being the number of reinforcing layers, the thermoplastic polymer P2j having a Tg, measured according to ISO 11357-3:2013, higher than the maximum use temperature (Tu) of the structure, Tg ≥ Tu + 20°C, in particular Tg ≥ Tu + 30°C, with Tu being higher than 50°C, in particular higher than 100°C; It relates to a multilayer structure.

[0025] Therefore, the inventors have proposed using different polymers for the composite matrix and liner, in particular: The matrix of the composite reinforcement is composed of a polymer having a Tg significantly higher than the maximum service temperature Tu of the tank or pipe (Tg>Tu+20°C, particularly typically Tg≥Tu+30°C) so as to remain in its glassy domain and have high stiffness, thereby allowing the composite to have high mechanical strength; It has been unexpectedly discovered that the semi-crystalline polymers constituting the liner have a low melting point Tm, which allows them to be processed by extrusion, extrusion blow molding, rotational molding, injection molding or pure resin film wrapping at moderate temperatures, as the case may be, relative to the Tm of this polymer, below 280°C, preferably below 265°C, as commonly used by those skilled in the art. The low Tm semi-crystalline polymers known to date also have a low Tg, which in most cases will be below the maximum use temperature. As a result, the polymers constituting the liner are very flexible and highly resistant to fatigue, since they operate in a rubberized region. Their semi-crystalline nature ensures good resistance to chemical attack, abrasion and creep, and The two polymers mentioned above (one constituting the composite matrix and one constituting the liner) are sufficiently miscible with each other to ensure weldability of the composite to the liner and, consequently, excellent adhesion between the liner and the composite. The durability of the adhesion is ensured by the durability of the materials constituting the mixture at the interface of the two materials, i.e., at the welded joint. The miscibility of the two polymers is preferably expressed by a single Tg or, if not, by a characteristic signature of a partially homogeneous mixture, for example, by the presence of two Tg values intermediate to those of the two pure polymers. DETAILED DESCRIPTION OF THE INVENTION

[0026] The immiscibility of the two polymers results in the presence of two Tg's in the mixture of the two polymers, which correspond to the Tg's of each of the pure polymers measured separately.

[0027] By "multilayer structure" is meant, for example, a reservoir, pipe or tube comprising or consisting of several layers, in particular two layers.

[0028] The sealing layer(s) are the innermost layer compared to the composite reinforcing layer, which is the outermost layer.

[0029] Even if there is an inner, and therefore innermost, non-sealing metal layer formed by a spirally wound metal strip, such as a staple strip, forming the carcass, onto which the sealing layer(s) are coated by extrusion, the sealing layer(s) will come into contact with hydrogen.

[0030] If several sealing layers are present, only the innermost sealing layer is in direct contact with hydrogen.

[0031] If there is only one sealing layer and one composite reinforcing layer, then there will be a two layer multi-layer structure, and these two layers will be welded together and in direct contact with each other to bond them together.

[0032] If several sealing layers and / or several composite reinforcing layers are present, the outermost layer of said sealing layer, and therefore the layer opposite the layer in contact with hydrogen, is welded to the innermost layer of said composite reinforcing layer and therefore in direct contact with and bonded to each other.

[0033] The other composite reinforcing layers are also welded together.

[0034] The other sealing layers are also welded together.

[0035] About the sealing layer and thermoplastic polymer P1i There may be one or more sealing layers.

[0036] Each of said layers consists of a composition mainly comprising at least one thermoplastic polymer P1i, where i corresponds to the number of layers present, i being 1 to 10, in particular 1 to 5, in particular 1 to 3, preferably i=1.

[0037] The term "predominantly" means that said at least one polymer is present in greater than 50% by weight relative to the total weight of the composition.

[0038] Advantageously, said at least one primary polymer is present in an amount of more than 60% by weight, in particular more than 70% by weight, in particular more than 80% by weight and more particularly 90% or more by weight relative to the total weight of the composition.

[0039] The composition may further comprise an impact modifier and / or additive.

[0040] The additives may be selected from antioxidants, heat stabilizers, UV absorbers, light stabilizers, lubricants, inorganic fillers, flame retardants, nucleating agents, plasticizers, dyes, carbon black, and carbonaceous nanofillers.

[0041] Advantageously, said composition consists mainly of said thermoplastic polymer P1i, 0-5% by weight of impact modifiers, 0-5% by weight of additives, the sum of the constituents of the composition being equal to 100% (for a maximum of 90% of P2i).

[0042] The at least one primary polymer in each layer may be the same or different.

[0043] In one embodiment, a single predominant polymer is present in at least the sealing layer welded to the composite reinforcing layer.

[0044] Thermoplastic polymer P1i A thermoplastic, or thermoplastic polymer, refers to a semi-crystalline material that is generally solid at room temperature and that may soften during an increase in temperature, particularly after passing its glass transition temperature (Tg), and may exhibit a sharp transition as it passes what is called its melting point (Tm), becoming solid again when the temperature drops below its crystallization temperature.

[0045] Tg, Tc, and Tm are determined by differential scanning calorimetry (DSC) according to standards 11357-2:2013 and 11357-3:2013, respectively.

[0046] The number average molecular weight Mn of said thermoplastic polymer is preferably in the range of 10 000 to 40 000, preferably in the range of 12 000 to 30 000. These Mn values may correspond to an intrinsic viscosity of 0.8 or greater, when determined with m-cresol according to standard ISO 307:2007, but by changing the solvent (using m-cresol instead of sulfuric acid, and the temperature being 20° C.).

[0047] Examples of suitable semi-crystalline thermoplastic polymers in the present invention include: Copolymers such as polyamide-polyether copolymers, polyesters, and polyamides including PVDF and PVDF / PEI blends where PVDF is predominant.

[0048] Particularly more preferred among the semi-crystalline polymers are polyamides and their semi-crystalline copolymers.

[0049] The nomenclature used to define polyamides is described in ISO standard 1874-1:2011 "Plastiques -- Materiaux polyamides (PA) pour moulage et extrusion - Partie 1: Designation", in particular page 3 (Tables 1 and 2), and is well known to those skilled in the art.

[0050] The polyamide may be a homopolyamide or a copolyamide or a mixture thereof.

[0051] Advantageously, said thermoplastic polymer is a long-chain aliphatic polyamide, ie a polyamide having an average number of carbon atoms per nitrogen atom greater than 8.5, preferably greater than 9.

[0052] In particular, the long-chain aliphatic polyamide is selected from polyamide 11 (PA11), polyamide 12 (PA12), polyamide 1010 (PA1010), polyamide 1012 (PA1012), polyamide 1212 (PA1012), or mixtures or copolyamides thereof, in particular PA11 and PA12.

[0053] Advantageously, said thermoplastic polymer is a long-chain semi-aromatic polyamide, i.e. a polyamide having an average number of carbon atoms per nitrogen atom greater than 8.5, preferably greater than 9, and having a melting point between 240°C and less than 280°C.

[0054] In particular, the long-chain semi-aromatic polyamide is chosen from polyamides 11 / 5T or 11 / 6T or 11 / 10T, where the ratio of 11 must obviously be chosen so that the Tm of the polymer is less than 280°C, preferably less than 265°C.

[0055] Advantageously, each sealing layer consists of a composition comprising the same type of polymer, in particular polyamide.

[0056] Advantageously, the composition comprising the polymer P1i is black and is able to absorb radiation suitable for welding.

[0057] There are various methods of welding thermoplastic polymer parts: thus, contact or non-contact heated blade, ultrasonic, infrared, vibration, rotary or even laser welding of one element to be welded to the other may be used.

[0058] The welding of thermoplastic polymer elements, particularly by laser welding, requires that the two elements to be welded have different properties with respect to radiation, particularly laser radiation: one element must be transparent to radiation, particularly laser radiation, while the other element must absorb radiation, particularly laser radiation. The radiation, particularly laser radiation, passes through the transparent part and then reaches the absorbing element, where it is converted into heat. This melts the contact area between the two elements, resulting in a weld.

[0059] In some applications, it is desirable that both the parts to be welded, including the part that is transparent to laser radiation, be black.

[0060] To make them absorbent, it is known to add various additives, including, for example, carbon black, to give the polymer a black color and the ability to absorb radiation suitable for welding.

[0061] In one embodiment, the welding is performed by a system selected from laser, infrared (IR) heating, LED heating, induction or microwave heating or radio frequency (HF) heating.

[0062] If the welding is carried out by laser welding, the composition P1i comprises a non-lumpy or non-agglomerated carbonaceous filler.

[0063] If the welding is carried out by induction, the composition P1i comprises metal particles.

[0064] Advantageously, the welding is carried out by a laser system.

[0065] Composite reinforcement layer and thermoplastic polymer P2j There may be one or more composite reinforcing layers.

[0066] Each of said layers consists of a composition mainly comprising at least one thermoplastic polymer P2j, where j corresponds to the number of layers present.

[0067] j is comprised between 1 and 10, in particular between 1 and 5, in particular between 1 and 3, with j=1 being preferred.

[0068] The term "predominantly" means that said at least one polymer is present in greater than 50% by weight relative to the total weight of the composition.

[0069] Advantageously, said at least one primary polymer is present in an amount of more than 60% by weight, in particular more than 70% by weight, in particular more than 80% by weight and more particularly 90% or more by weight relative to the total weight of the composition.

[0070] The composition may further comprise an impact modifier and / or additive.

[0071] The additives may be selected from antioxidants, heat stabilizers, UV absorbers, light stabilizers, lubricants, inorganic fillers, flame retardants, nucleating agents, plasticizers, and dyes.

[0072] Advantageously, said composition consists mainly of said thermoplastic polymer P2j, 0-5% by weight of impact modifiers, 0-5% by weight of additives, the sum of the components of the composition being equal to 100% (for a maximum of 90% of P2j).

[0073] The at least one primary polymer in each layer may be the same or different.

[0074] In one embodiment, a single predominant polymer is present in at least the composite reinforcing layer welded to the sealing layer.

[0075] In one embodiment, each reinforcing layer comprises the same type of polymer, in particular polyamide.

[0076] Thermoplastic polymer P2j Thermoplastics, or thermoplastic polymers, generally refer to materials that are solid at room temperature, may be semi-crystalline or amorphous, in particular semi-crystalline, and that soften during temperature increase, in particular after passing its glass transition temperature (Tg), and flow at higher temperatures if amorphous, or that may exhibit a sharp transition when passing the so-called melting temperature (Tm) if semi-crystalline, and become solid again when the temperature drops below its crystallization temperature Tc (in the case of semi-crystalline) and below its glass transition temperature (in the case of amorphous).

[0077] Tg, Tc, and Tm are determined by differential scanning calorimetry (DSC) according to standards 11357-2:2013 and 11357-3:2013, respectively.

[0078] The polymer P2j of at least one composition of said composite reinforcing layer is such that its Tg is higher than the maximum use temperature (Tu) of said structure, in particular Tg≧Tu+20°C, in particular Tg≧Tu+30°C.

[0079] In one embodiment, the polymer P2j has a Tg≧Tu+20° C., in particular a Tg≧Tu+30° C., regardless of the position of said reinforcing layer.

[0080] In another embodiment, said reinforcing layer consisting of a composition comprising a polymer P2j having a Tg≧Tu+20° C., in particular a Tg≧Tu+30° C., is the layer that is welded to said sealing layer.

[0081] In one embodiment, the polymer P2j of at least one composition of the composite reinforcing layer is such that its Tg is higher than the maximum use temperature (Tu) of the structure, Tg ≥ Tu + 20°C, and the reinforcing layer made of a composition comprising polymer P2j is the layer that is welded to the sealing layer.

[0082] In one embodiment, the polymer P2j of at least one composition of the composite reinforcing layer is such that its Tg is higher than the maximum use temperature (Tu) of the structure, Tg ≥ Tu + 30°C, and the reinforcing layer made of a composition comprising polymer P2j is the layer that is welded to the sealing layer.

[0083] In another embodiment, the reinforcing layer consisting of a composition comprising a polymer P2j having a Tg ≥ Tu + 20°C, in particular a Tg ≥ Tu + 30°C, is the outermost reinforcing layer of the structure. The number average molecular weight Mn of the thermoplastic polymer is preferably in the range of 10,000 to 40,000, preferably in the range of 12,000 to 30,000. These Mn values may correspond to an intrinsic viscosity of ≥ 0.8, when determined with m-cresol according to standard ISO 307:2007, but by changing the solvent (m-cresol instead of sulfuric acid, and at a temperature of 20°C).

[0084] Examples of suitable semi-crystalline thermoplastic polymers in the present invention include: Polyamides, in particular copolymers containing aromatic and / or alicyclic structures, such as polyamide-polyether copolymers; polyester, Polyaryletherketone (PAEK), Polyetheretherketone (PEEK), Polyetherketoneketone (PEKK), Polyetherketoneetherketoneketone (PEKEKK), polyimides, in particular polyetherimides (PEI) or polyamide-imides, Polysulfones (PSU), in particular polyarylsulfones such as polyphenylsulfone (PPSU), Polyethersulfone (PES) Examples include: Semi-crystalline polymers are particularly preferred, especially polyamides and their semi-crystalline copolymers.

[0085] The nomenclature used to define polyamides is described in ISO standard 1874-1:2011 "Plastiques - Materials polyamides (PA) pour moulage et extrusion - Partie 1: Designation", in particular page 3 (Tables 1 and 2), and is well known to those skilled in the art.

[0086] The polyamide may be a homopolyamide or a copolyamide or a mixture thereof.

[0087] Advantageously, the semicrystalline polyamide is a semi-aromatic polyamide, in particular a semi-aromatic polyamide of formula X / YAr as described in EP 1 505 099, in particular a semi-aromatic polyamide of formula A / XT, in which A is a unit derived from an amino acid, a unit derived from a lactam, and a represents the number of carbon atoms of the diamine, b represents the number of carbon atoms of the diacid, a and b each being between 4 and 36, advantageously between 9 and 18, and the units (Ca diamine) are chosen from linear or branched aliphatic diamines, cycloaliphatic diamines and alkylaromatic diamines, and the units (Cb diacid) are chosen from units corresponding to the formula (Ca diamine).(Cb diacid), which are chosen from linear or branched aliphatic diacids, cycloaliphatic diacids, aromatic diacids, XT, where x represents the number of carbon atoms in the Cx diamine, x being between 5 and 36, advantageously between 9 and 18, is in particular a polyamide having the formula A / 5T, A / 6T, A / 9T, A / 10T or A / 11T, where A is as defined above, in particular PA MPMDT / 6T, PA11 / 10T, PA5T / 10T, PA11 / BACT, PA11 / 6T / 10T, PA MXDT / 10T, PA MPMDT / 10T, PA BACT / 10T, PA BACT / 6T, PA denotes units obtained from the polycondensation of Cx diamine and terephthalic acid, a polyamide selected from BACT / 10T / 6T, PA11 / BACT / 6T, PA11 / MPMDT / 6T, PA11 / MPMDT / 10T, PA11 / BACT / 10T, PA11 / MXDT / 10T, 11 / 5T / 10T.

[0088] T corresponds to terephthalic acid, MXD corresponds to m-xylenediamine, MPMD corresponds to methylpentamethylenediamine and BAC corresponds to bis(aminomethyl)cyclohexane. The semi-aromatic polyamides defined above in particular have a Tg of greater than or equal to 80° C.

[0089] Advantageously, each composite reinforcing layer consists of a composition comprising the same type of polymer, in particular polyamide.

[0090] Advantageously, the composition comprising the polymer P2j is transparent to radiation suitable for welding.

[0091] Thermoplastic polymers are generally transparent for welding purposes, in particular laser welding. Carbonaceous nanofillers make it possible to impart a black color to a layer of a composition comprising a thermoplastic polymer while maintaining the layer's transparency to laser radiation.

[0092] Advantageously, the carbonaceous nanofillers are non-agglomerated or non-agglomerated.

[0093] Advantageously, the carbonaceous nanofiller is incorporated into the composition in an amount between 100 ppm and 500 ppm, preferably between 100 ppm and 250 ppm.

[0094] Advantageously, the carbonaceous nanofillers are chosen from carbon nanotubes (CNTs), carbon nanofibers, graphene, nanoscale carbon black and mixtures thereof.

[0095] Advantageously, the carbonaceous nanofiller does not include nanometric carbon black.

[0096] In one embodiment, the welding is performed by a system selected from laser, IR heating or induction heating.

[0097] Advantageously, the welding is carried out by a laser system.

[0098] Advantageously, the laser radiation is infrared laser radiation, preferably having a wavelength between 700 nm and 1200 nm, and preferably between 800 nm and 1100 nm.

[0099] About structures The multi-layer structure thus comprises at least one sealing layer and at least one composite reinforcing layer welded together.

[0100] In one embodiment, in said multilayer structure, each polymer P1i of each sealing layer is partially or fully miscible with each polymer P1i of an adjacent layer, each polymer P2j of each reinforcing layer is partially or fully miscible with each polymer P2j of an adjacent layer, and when adjacent, each polymer P2j is partially or fully miscible with each polymer P1i, and polymer P21 is partially or fully miscible with the polymer P11 adjacent to it; The complete or partial miscibility of the polymers is defined by the difference in the glass transition temperatures of the two resins in the mixture relative to the difference in the glass transition temperatures of the two resins before mixing; if said difference is equal to 0, the miscibility is complete, and if said difference is different from 0, the miscibility is partial, excluding immiscibility of polymer P2j with polymer P1i.

[0101] If the polymers are partially miscible, the difference is such that the greater the miscibility, the smaller the difference.

[0102] Advantageously, when the miscibility of said polymers is partial, said difference is less than 30%, preferably less than 20%, in absolute value.

[0103] In one embodiment, the glass transition temperature of the mixture, depending on whether miscibility is complete or partial, must be between the glass transition temperatures of the polymers prior to blending and differ therefrom by at least 5°C, preferably at least 10°C.

[0104] The expression "fully miscible" means that, for example, when two polymers P11 and P12 having Tg11 and Tg12 respectively are present in two adjacent sealing layers or two adjacent reinforcing layers, the mixture of the two polymers has only one Tg1112, the value of which is between Tg11 and Tg12.

[0105] This Tg1112 value is thus at least 5 °C, especially at least 10 °C higher than Tg11 and at least 5 °C, especially at least 10 °C lower than Tg12.

[0106] The expression "partially miscible" means that, for example, when two polymers P11 and P12 having Tg11 and Tg12 respectively are present in two adjacent sealing layers or two adjacent reinforcing layers, the mixture of the two polymers has two Tgs of Tg’11 and Tg’12 with Tg11 < Tg’11 < Tg’12 < Tg12.

[0107] These Tg’11 and Tg’12 values are at least 5 °C, especially at least 10 °C higher than Tg11 and at least 5 °C, especially at least 10 °C lower than Tg12.

[0108] The immiscibility of the two polymers results in the presence of two Tgs of Tg11 and Tg12 corresponding to the respective Tgs of the pure polymers measured separately in the mixture of the two polymers.

[0109] Advantageously, the welded sealing layer and the reinforcing layer are made of compositions each containing a different polymer.

[0110] Nevertheless, the different polymers may be of the same type.

[0111] Thus, if one of the two welded composite reinforcement and sealing layers is made from a composition comprising an aliphatic polyamide, the other layer is made from a composition comprising a polyamide that is not aliphatic, e.g., a semi-aromatic polyamide, so as to have a high Tg polymer as the matrix of the composite reinforcement.

[0112] The multi-layer structure may include up to 10 sealing layers and up to 10 composite reinforcing layers.

[0113] It will be appreciated that the multi-layer structure is not necessarily symmetrical and may therefore include more sealing layers than composite layers, or vice versa.

[0114] Advantageously, said multilayer structure comprises 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 sealing layers and 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 composite reinforcing layers.

[0115] Advantageously, said multilayer structure comprises 1, 2, 3, 4 or 5 sealing layers and 1, 2, 3, 4 or 5 composite reinforcing layers.

[0116] Advantageously, said multilayer structure comprises one, two or three sealing layers and one, two or three composite reinforcing layers.

[0117] Advantageously, they each consist of a composition comprising a different polymer.

[0118] Advantageously, they consist of compositions comprising polyamides corresponding to polyamides P1i and P2j, respectively.

[0119] Advantageously, they each consist of a composition comprising a different polyamide.

[0120] In one embodiment, the multi-layer structure comprises a single sealing layer and several reinforcing layers, the sealing layers being welded to the adjacent reinforcing layers.

[0121] In another embodiment, the multi-layer structure comprises a single reinforcing layer and several sealing layers, the reinforcing layers being welded to the adjacent sealing layers.

[0122] In one advantageous embodiment, the multi-layer structure includes a single sealing layer and a single composite reinforcing layer that are welded together.

[0123] Therefore, all combinations of these two layers are within the scope of the present invention, as long as at least the innermost composite reinforcing layer is welded to the outermost adjacent sealing layer, whether or not the other layers are welded together.

[0124] Advantageously, in said multilayer structure, each sealing layer consists of the same type of polymer P1i, in particular a composition comprising a polyamide.

[0125] The expression polymer of the same type means, for example, polyamides which may be the same or different depending on the layer.

[0126] Advantageously, said polymer P1i is a polyamide and said polymer P2j is a polyamide.

[0127] Advantageously, the polyamide P1i is the same for all sealing layers.

[0128] Advantageously, said polymer P1i is a long-chain aliphatic polyamide, in particular PA1010, PA1012, PA1212, PA11, PA12, in particular PA11 or PA12.

[0129] Advantageously, the polyamide P1i is a long-chain semi-aromatic polyamide, in particular PA11 / 5T, PA11 / 6T or PA11 / 10T, in which case the ratio of 11 must obviously be carefully selected so that the Tm of said polymer is less than 280°C, preferably less than 265°C.

[0130] Advantageously, in said multilayer structure, each reinforcing layer consists of a composition comprising the same type of polymer P2j, in particular polyamide.

[0131] Advantageously, the polyamide P2j is the same for all reinforcing layers.

[0132] Advantageously, said polymer P2j is a semi-aromatic polyamide chosen from PA MXDT / 6T, PA11 / 10T, PA11 / BACT, PA5T / 10T, PA11 / 6T / 10T, PA MXDT / 10T, PA MPMDT / 10T, PA BACT / 10T, PA BACT / 6T, PA BACT / 10T / 6T, PA11 / BACT / 6T, PA11 / MPMDT / 6T, PA11 / MPMDT / 10T, PA11 / BACT / 10T, PA11 / MXDT / 10T, PA5T / 10T.

[0133] Advantageously, in said multilayer structure, the polyamides P1i and P2j are different, i.e., each sealing layer consists of a composition comprising the same type of polymer P1i, in particular a polyamide, and each reinforcing layer consists of a composition comprising the same type of polymer P2j, in particular a polyamide, insofar as the sealing layer consists of a composition comprising a long-chain aliphatic polyamide, and the sealing layer consists of a composition comprising a semi-aromatic polyamide.

[0134] Advantageously, the polymer P1i is a long-chain aliphatic polyamide, in particular PA1010, PA1012, PA1212, PA11, PA12, in particular PA11 or PA12, and the polymer P2j is a semi-aromatic polyamide, in particular chosen from PA MPMDT / 6T, PA PA11 / 10T, PA11 / BACT, PA5T / 10T, PA11 / 6T / 10T, PA MXDT / 10T, PA MPMDT / 10T, PA BACT / 10T, PA BACT / 6T, PA BACT / 10T / 6T, PA11 / BACT / 6T, PA11 / MPMDT / 6T, PA11 / MPMDT / 10T, PA11 / BACT / 10T, PA11 / MXDT / 10T and PA5T / 10T.

[0135] Advantageously, the multilayer structure consists of a single reinforcing layer and a single sealing layer in which the polymer P1i is a long-chain aliphatic polyamide, in particular PA1010, PA1012, PA1212, PA11, PA12, in particular PA11 or PA12, and the polymer P2j is a semi-aromatic polyamide, in particular selected from PA MPMDT / 6T, PA PA11 / 10T, PA11 / BACT, PA11 / 6T / 10T, PA MXDT / 10T, PA MPMDT / 10T, PA BACT / 10T, PA BACT / 6T, PA BACT / 10T / 6T, PA11 / BACT / 6T, PA11 / MPMDT / 6T, PA11 / MPMDT / 10T, PA11 / BACT / 10T, PA11 / MXDT / 10T.

[0136] According to one embodiment, the multi-layer structure is a reservoir.

[0137] According to another embodiment, the multi-layer structure is a flexible pipe.

[0138] The maximum use temperature Tu of the multilayer structure is above 50°C, in particular above 100°C.

[0139] In one embodiment, said multilayer structure as defined above has vacuum resistance and drying capabilities.

[0140] In fact, when storing or transporting hydrogen, the permeability of the sealing layer to the transported or stored hydrogen can allow hydrogen to diffuse through the sealing layer from the inside of the tube or reservoir to the interface between the outermost sealing layer and the first composite reinforcement layer. The accumulation of hydrogen in this location can create pressures that lead to the collapse of the sealing layer if the internal pressure of the tube or reservoir is lower than the pressure at the interface with the composite reinforcement. This can occur especially during production shutdowns, when the pumping or transport of hydrogen stops, or when the storage reservoir is empty, during which the pressure drops by several hundred bar to atmospheric pressure. The same applies to internal hydrostatic testing of the reservoir: this water is likely to migrate by infiltration at the interface between the composite reinforcement and the outermost layer of the sealing layer, which will then be very difficult to remove, leading to lengthy and expensive drying cycles of the storage reservoir, especially under reduced pressure.

[0141] In another embodiment, said multi-layer structure as defined above further comprises a metal carcass located within the sealing layer.

[0142] This metal carcass is not leak-proof and is the innermost layer.

[0143] Advantageously, said multilayer structure further comprises at least one outer layer, in particular a metal layer, said layer being the outermost layer of said multilayer structure.

[0144] The outer layer is a second reinforcing layer, but is metallic and not composite.

[0145] There may also be a polymeric protective layer (outermost layer) on the structure, which serves as an abrasion protection or allows for inscriptions to be placed on the structure.

[0146] About fiber materials As regards the fibres that make up said fibrous material, these are in particular inorganic, organic or vegetable fibres.

[0147] Advantageously, said fibrous material may or may not be sized.

[0148] The fibrous material may therefore contain up to 0.1% by weight of organic material (thermosetting or thermoplastic type) called sizing agents.

[0149] Inorganic fibers include, for example, carbon fibers, glass fibers, basalt or basalt-based fibers, silica fibers, or silicon carbide fibers. Organic fibers include, for example, fibers based on thermoplastic or thermosetting polymers, such as semi-aromatic polyamide fibers, aramid fibers, or polyolefin fibers. Preferably, they are based on amorphous thermoplastic polymers, with a Tg higher than the glass transition temperature (Tg) of the polymer or thermoplastic polymer mixture that constitutes the pre-impregnated matrix if the polymer or thermoplastic polymer mixture is amorphous, or a Tg higher than the Tm of the polymer or thermoplastic polymer matrix that constitutes the pre-impregnated matrix if the polymer or thermoplastic polymer mixture is semi-crystalline. Advantageously, they are based on semi-crystalline thermoplastic polymers, with a melting temperature (Tm) higher than the Tg of the polymer or thermoplastic polymer mixture that constitutes the pre-impregnated matrix if the polymer or thermoplastic polymer mixture is amorphous, or a Tm higher than the Tm of the polymer or thermoplastic polymer matrix that constitutes the pre-impregnated matrix if the polymer or thermoplastic polymer mixture is semi-crystalline. Therefore, there is no risk of melting the organic fibers that constitute the fibrous material during impregnation with the thermoplastic matrix of the final composite. Plant fibers include natural linen, hemp, lignin, bamboo, silk, especially spider silk, sisal, and other cellulosic fibers, especially viscose, which can be used pure, treated, or coated with a coating layer to facilitate adhesion and impregnation of the thermoplastic polymer matrix.

[0150] The textile material may also be a woven fabric or braided cord.

[0151] It is also possible to accommodate fibers with supporting threads.

[0152] These constituent fibers may be used alone or as a mixture. Thus, the organic fibers may be mixed with the thermoplastic polymer powder to be pre-impregnated to form a pre-impregnated fibrous material.

[0153] The organic fiber strands can have any basis weight. Furthermore, they can have any geometric shape. The constituent fibers of the fiber material can also assume the form of a mixture of these reinforcing fibers with different geometric shapes. The fibers are continuous.

[0154] Preferably, the fibrous material consists of continuous carbon or glass fibres or a mixture thereof, in particular carbon fibres, which are used in the form of a roving or several rovings.

[0155] According to another aspect, the present invention relates to a method for manufacturing a multilayer structure as defined above, characterized in that it comprises a step of welding a reinforcing layer as defined above to a sealing layer as defined above.

[0156] Advantageously, the welding process is carried out by a system chosen from laser, infrared (IR) heating, LED heating, induction or microwave heating or radio frequency (HF) heating.

[0157] Advantageously, the method comprises the steps of extruding the sealing layer onto a metal carcass and welding a reinforcing layer to the sealing layer.

[0158] According to another aspect, the present invention relates to the use of a multilayer structure selected from a reservoir, a pipe or a tube, comprising, from the inside to the outside, at least one sealing layer as defined above and at least one composite reinforcing layer as defined above, the innermost composite reinforcing layer is welded to the outermost adjacent sealing layer to create a reservoir or pipe or tube for transporting, distributing or storing hydrogen; the sealing layer consists of a composition comprising mainly at least one semi-crystalline thermoplastic polymer P1i (i = 1 to n, n is the number of sealing layers) having a Tm of less than 280 ° C, in particular less than 265 ° C, measured according to ISO 11357-3:2013, the at least one thermoplastic polymer of each sealing layer may be the same or different, and at least one of the composite reinforcing layers consists of a fibrous material in the form of continuous fibers impregnated with a composition mainly comprising at least one thermoplastic polymer P2j, in particular semi-crystalline, where j=1 to m, m being the number of reinforcing layers, and the thermoplastic polymer P2j has a Tg, measured according to ISO 11357-3:2013, higher than the maximum use temperature (Tu) of the structure, Tg ≥ Tu + 20°C, in particular Tg ≥ Tu + 30°C, with Tu being higher than 50°C, in particular higher than 100°C; Regarding use. [Example]

[0159] In all cases the reservoir is obtained by rotational molding of the liner at a temperature compatible with the properties of the thermoplastic resin used, but in all cases below 280°C.

[0160] For epoxy, a wet filament winding method is used, which involves winding the fiber around a liner, pre-impregnating the fiber in a liquid epoxy bath, and then polymerizing it in an oven for two hours.

[0161] In all other cases, a fibrous material pre-impregnated with a thermoplastic resin (tape) is used, which is deposited by filament winding using a robot equipped with a 1500 W laser heater at a speed of 12 m / min, without a polymerization step.

[0162] Example 1 (counterexample) A type IV hydrogen storage tank consisting of T700SC31E (Toray Industries, Inc.) carbon fiber epoxy composite reinforcement (Tg 80°C) and a PA6 sealing layer. There is no miscibility between the two resins (see Table 1), which prevents welding between the fibrous reinforcement and the sealing layer.

[0163] Example 2 (counterexample) A type IV hydrogen storage tank consisting of T700SC31E (Toray Industries, Inc.) carbon fiber epoxy composite reinforcement (Tg 80°C) and an HDPE sealing layer. There is no miscibility between the two resins (see Table 1), which prevents welding between the fibrous reinforcement and the sealing layer.

[0164] Example 3 A type IV or V hydrogen storage tank constructed with T700SC31E (Toray Industries, Inc.) BACT / 10T carbon fiber composite reinforcement and a PA6 sealing layer. There is good partial compatibility between the two resins, allowing for good welding between the fibrous reinforcement and the sealing layer (see Table I).

[0165] The selected BACT / 10T composition has a melting temperature Tm of 283°C, a crystallization temperature Tc of 250°C, and a glass transition temperature of 164°C.

[0166] Tg, Tc, and Tm are determined by differential scanning calorimetry (DSC) according to standards 11357-2:2013 and 11357-3:2013, respectively.

[0167] Example 4 A type IV or V hydrogen storage tank constructed with T700SC31E (Toray Industries, Inc.) BACT / 10T carbon fiber composite reinforcement and a PA66 sealing layer. There is good partial miscibility between the two resins, allowing for good welding between the fibrous reinforcement and the sealing layer (see Table I). The selected BACT / 10T composition has a melting temperature (Tm) of 283°C, a crystallization temperature (Tc) of 250°C, and a glass transition temperature (Tg), Tc, and Tm are determined by differential scanning calorimetry (DSC) according to 11357-2:2013 and 11357-3:2013, respectively.

[0168] The higher melting point of the PA66 liner (268.8°C) compared to the PA6 liner of Example 3 (220°C) facilitates taping and manufacturing of the reservoir.

[0169] Example 5 CT24-5.0 / 270-T140 (manufactured by SGL Carbon) Type IV or V hydrogen storage tanks are constructed with 11 / BACT / 10T carbon fiber composite reinforcement and a PA11 sealing layer. There is good partial miscibility between the two resins (see Table 1), leading to good welding between the fibrous reinforcement and the sealing layer. The selected 11 / BACT / 10T composition has a melting temperature (Tm) of 280°C, a crystallization temperature (Tc) of 220°C, and a glass transition temperature (Tg), Tc, and Tm are determined by differential scanning calorimetry (DSC) according to 11357-2:2013 and 11357-3:2013, respectively.

[0170] Example 6 A type IV or V hydrogen storage tank made of CT24-5.0 / 270-T140 (manufactured by SGL Carbon) 11 / BACT / 10T carbon fiber composite reinforcement and a PA11 / 10T sealing layer. There is good partial compatibility between the two resins (see Table 1), leading to good welding between the fibrous reinforcement and the sealing layer.

[0171] The selected 11 / BACT / 10T composition has a melting temperature Tm of 280° C., a crystallization temperature Tc of 220° C., and a glass transition temperature Tg of 160° C. Tg, Tc, and Tm are determined by differential scanning calorimetry (DSC) according to 11357-2:2013 and 11357-3:2013, respectively.

[0172] The 11 / 10T composition used in the liner results in a Tm of 255°C.

[0173] The use of an 11 / 10T liner, which has a melting point of 255°C, close to that of the 11 / BACT / 10T resin used as the matrix for the composite, facilitates processing of the reservoir.

[0174] Example 7 A type IV or V hydrogen storage tank constructed with CT24-5.0 / 270-T140 (manufactured by SGL Carbon) 11 / BACT carbon fiber composite reinforcement and a PA11 sealing layer. There is good partial miscibility between the two resins (see Table 1), leading to good welding between the fibrous reinforcement and the sealing layer. The selected 11 / BACT composition has a melting temperature (Tm) of 278°C, a crystallization temperature (Tc) of 210°C, and a glass transition temperature (Tg), Tc, and Tm are determined by differential scanning calorimetry (DSC) according to 11357-2:2013 and 11357-3:2013, respectively.

[0175] The use of the slow crystallizing 11 / BACT polymer allows for lower taping temperatures than the previous example 11 / BACT / 10T, facilitating the use of a PA11 liner.

[0176] Example 8 A type IV or V hydrogen storage tank consisting of CT24-5.0 / 270-T140 (manufactured by SGL Carbon) 11 / BACT carbon fiber composite reinforcement and a PA11 / 10T sealing layer. There is good partial compatibility between the two resins (see Table 1), leading to good welding between the fibrous reinforcement and the sealing layer.

[0177] The selected 11 / BACT composition has a melting temperature Tm of 278° C., a crystallization temperature Tc of 210° C., and a glass transition temperature Tg of 157° C. Tg, Tc, and Tm are determined by differential scanning calorimetry (DSC) according to standards 11357-2:2013 and 11357-3:2013, respectively.

[0178] The 11 / 10T composition used in the liner results in a Tm of 255°C.

[0179] The use of the 11 / 10T liner, which has a melting point of 255°C, is similar to the 11 / BACT reinforcing resin of the composite, making the storage tank easier to implement.

[0180] In all examples in Table 1 below, to assess resin miscibility, blends were made from powders with particle size of approximately 150 μm in a Micro DSM with a 1 minute recirculation time after melting. All blends were made at 300°C, except for the epoxy-polyethylene blend, which was made at 220°C.

[0181] At the end of the mixing process, the mixture is poured into a mold to produce test specimens that are characterized by DMA. TIFF2025115988000001.tif148170 Compatibility test results - Column 4: Glass transition temperature of each resin before mixing - Column 5: Glass transition temperature of the resin in the mixture - Column 6: Ratio of the difference in glass transition temperature of the resins in the mixture to the difference in glass transition temperature of the resins before mixing. 100% indicates resin immiscibility; <80% indicates poor miscibility; <30% indicates good but partial miscibility; 0 indicates complete miscibility.

Claims

1. A multilayer structure selected from a reservoir, a pipe, or a tube intended for transporting, distributing, or storing hydrogen, said multilayer structure comprising, from the inside to the outside, at least one sealing layer and at least one composite reinforcing layer; The innermost composite reinforcement layer is welded to the adjacent outermost sealing layer; the sealing layer consists of a composition comprising mainly at least one semi-crystalline thermoplastic polymer P1i (i=1 to n, n is the number of sealing layers) having a Tm of less than 280°C, in particular less than 265°C, measured according to ISO 11357-3:2013, the at least one thermoplastic polymer of each sealing layer may be the same or different, at least one of the composite reinforcing layers consisting of a fibrous material in the form of continuous fibres impregnated with a composition comprising mainly at least one thermoplastic polymer P2j, in particular semi-crystalline, with j=1 to m, m being the number of reinforcing layers, said thermoplastic polymer P2j having a Tg, measured according to ISO 11357-3:2013, higher than the maximum use temperature (Tu) of the structure, Tg ≥ Tu + 20°C, in particular Tg ≥ Tu + 30°C, with Tu being higher than 50°C, in particular higher than 100°C; Multilayer structure.

2. Each polymer P1i of each sealing layer is partially or completely miscible with each polymer P1j of an adjacent layer, each polymer P2j of each reinforcing layer is partially or completely miscible with each polymer P2j of an adjacent layer, and polymer P21 is partially or completely miscible with the polymer P11 adjacent thereto; 10. The multilayer structure of claim 1, wherein the complete or partial miscibility of the polymers is defined by the difference in glass transition temperatures of the two resins in the blend relative to the difference in glass transition temperatures of the two resins prior to blending, where if said difference is equal to 0, miscibility is complete and if said difference is different from 0, miscibility is partial.

3. 3. A multilayer structure according to claim 1 or 2, characterized in that each sealing layer comprises the same type of polymer, in particular polyamide.

4. 3. A multilayer structure according to claim 1 or 2, characterized in that each reinforcing layer comprises the same type of polymer, in particular polyamide.

5. 5. A multilayer structure according to claim 3 or 4, characterized in that each sealing layer comprises the same type of polymer, in particular polyamide, and each reinforcing layer comprises the same type of polymer, in particular polyamide.

6. 6. A multilayer structure according to any one of claims 1 to 5, characterized in that it has a single sealing layer and a single reinforcing layer.

7. 7. A multilayer structure according to any one of claims 1 to 6, characterized in that the structure is a reservoir or a flexible pipe.

8. 8. A multilayer structure according to any one of claims 1 to 7, characterized in that the compositions comprising the polymers P1 and P2 also contain additives such as carbon black, carbon nanotubes (CNT) or graphene that enable them to absorb radiation suitable for welding.

9. 9. A multilayer structure according to claim 1, characterized in that the composition comprising the polymer P2j is transparent to radiation suitable for welding.

10. 10. Multilayer structure according to claim 8 or 9, characterized in that the welding is carried out by a system selected from laser, infrared (IR) heating, LED heating, induction or microwave heating or radio frequency (HF) heating.

11. 11. A multilayer structure according to any one of claims 1 to 10, characterized in that the polymer P1i is a polyamide.

12. 11. A multilayer structure according to any one of claims 1 to 10, characterized in that the polymer P2j is a polyamide.

13. 13. A multilayer structure according to claim 11 or 12, characterized in that the polymers P1i and P2j are polyamides.

14. 14. Multilayer structure according to claim 11 or 13, characterized in that the polymer P1i is a long-chain aliphatic polyamide, in particular PA1010, PA1012, PA1212, PA11, PA12, in particular PA11 or PA12, or semi-aromatic, in particular PA11 / 5T, PA11 / 6T and PA11 / 10T.

15. 14. Multilayer structure according to claim 12 or 13, characterized in that the polymer P2j is a semi-aromatic polyamide, in particular chosen from PA MPMDT / 6T, PA11 / 10T, PA11 / BACT, PA5T / 10T, PA11 / 6T / 10T, PA MXDT / 10T, PA MPMDT / 10T, PA BACT / 10T, PA BACT / 6T, PA BACT / 10T / 6T, PA11 / BACT / 6T, PA11 / MPMDT / 6T, PA11 / MPMDT / 10T, PA11 / BACT / 10T, PA11 / MXDT / 10T, PA11 / 5T / 10T.

16. The polymer P1i is a long-chain aliphatic polyamide, in particular PA1010, PA1012, PA1212, PA11, PA12, or is semi-aromatic, in particular PA11 / 5T, or PA11 / 6T or PA11 / 10T, in particular PA11 or PA12, and the polymer P2j is a semi-aromatic polyamide, in particular PA MPMDT / 6T, PA PA11 / 10T, PA11 / BACT, PA5T / 10T, PA11 / 6T / 10T, PA MXDT / 10T, PA MPMDT / 10T, PA BACT / 10T, PA BACT / 6T, PA 16. Multilayer structure according to any one of claims 13 to 15, characterized in that the multilayer structure is in particular selected from BACT / 10T / 6T, PA11 / BACT / 6T, PA11 / MPMDT / 6T, PA11 / MPMDT / 10T, PA11 / BACT / 10T, PA11 / MXDT / 10T, PA11 / 5T / 10T.

17. 17. A multilayer structure according to any one of claims 1 to 16, characterized in that it has resistance to reduced pressure and drying capacity.

18. 18. A multilayer structure according to any one of claims 1 to 17, characterized in that the structure further comprises a metallic carcass located within the sealing layer.

19. 19. A multilayer structure according to any one of claims 1 to 18, characterized in that the structure further comprises at least one outer layer, in particular a metallic layer, said layer being the outermost layer of the multilayer structure.

20. 20. A multilayer structure according to any one of the preceding claims, characterized in that the fibrous material is selected from glass fibres and carbon or basalt or basalt-based fibres.

21. 21. A method for manufacturing a multilayer structure as defined in any one of claims 1 to 20, characterized in that it comprises the step of welding a reinforcing layer as defined in claim 1 to a sealing layer as defined in claim 20.

22. 22. The method of claim 21, wherein the welding step is performed by a system selected from laser, infrared (IR) heating, LED heating, induction or microwave heating or radio frequency (HF) heating.

23. 23. A method according to claim 21 or 22, characterized in that it comprises the steps of extruding the sealing layer onto a metal carcass and welding a reinforcing layer to the sealing layer.

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