Vessel for the storage of gas

Abstract

A vessel for the storage and transportation of gasses characterized by a good balance between low hydrogen permeability and ductility at cryogenic temperatures. The vessel is particularly adapted for the storage and transportation of compressed gasses in vehicles.

Description

VESSEL FOR THE STORAGE OF GASCross-reference to related patent applications

[0001] The present patent application claims priority filed on 25 June 2024 in Europe, with Nr. 24184464.6, the whole content of this application being incorporated herein for all purposes.Technical Field

[0002] The invention relates to a vessel for the storage and transport of gasses. The invention further relates to a gas stored in the vessel.Background Art

[0003] With the raising concerns regarding global warming and the strive to reduce CO2 emissions, the use of hydrogen, in particular the so-called “green hydrogen”, that is hydrogen produced using clean energy sources, will play an important role, in particular in decarbonizing sectors such as heavy-duty transport or certain industrial processes (e.g. steel manufacturing) where electrification is impossible or very expensive. The storage or transportation of large volumes of highly compressed hydrogen requires a shift from the use of metal containers or piping to lighter materials, such as polymeric materials.

[0004] Pressure vessels made of polymeric materials which are characterized by high gas barrier properties have been used for storing various gasses such as oxygen, carbon dioxide, nitrogen, argon, LPG (liquefied petroleum gas), methane, hydrogen, over a long period of time. Pressure vessels comprising a non-structural layer, or liner, surrounded with a structural fiber reinforced composite material for containing the fluid or gas under pressure are known. The liner acts as a barrier between the fluid or gas and the fiber reinforced composite material, thus preventing leaks and / or other degradations of the structure of the fiber reinforced composite material. The use of structural fiber reinforced composite materialscomprising a thermoplastic polymer matrix, rather than a thermoset one, is advantageous to facilitate recycling of the pressure vessel.

[0005] Pressure vessels comprising a polyamide-based liner and an outer layer which is a composite material that contains a continuous fiber and a polyamide resin impregnated into the continuous fiber are also disclosed, for instance in EP3225888, EP3390016, and WO21152254.

[0006] In addition, US 2025 / 0012406 (corresponding to WO23079823) discloses a liner which contains (i) a polyamide resin containing 50 mol% or more of a diamine-derived structural unit derived from xylylenediamine, (ii) a content of a toughness improver in a region up to 30% in a thickness direction from one surface of the liner from 5 to 10 mass % and a content of toughness improver in a region up to 30% in a thickness direction from the other surface of the lines of 0.5 mass% or less. This document discloses that a liner with two different regions is provided: a region containing a certain amount of the toughness improver and a region containing little or no toughness improver in a thickness direction of the liner.

[0007] However, the need still exists to develop pressure vessels, in particular pressure vessels for the transport and storage of hydrogen, which combine high performance qualities in terms of impermeability to hydrogen and mechanical properties. Incidentally, when the internal pressure of a hydrogen tank is set to a high pressure, such as 70 MPa, or even 100 MPa, with an aim toward lengthening travel distance, the hydrogen tank will be at a low temperature during high-speed depletion of the tank. Hence excellent mechanical resistance must be exhibited even at temperatures of -40°C or below.

[0008] Additionally, the liner must have a good resistance towards the so-called “blistering”. Static blistering occurs because hydrogen is absorbed by the liner material at high pressures and stresses are generated when the decompression rate exceeds the rate by which absorbed gas can escape by diffusion. Said stresses may lead to cracking or whitening of the liner material. Dynamic blistering occurs during successive hydrogen pressure and decompression cycles, between 0.5 to 87.5 MPa.

[0009] It is an object of the present invention to provide a hydrogen tank linermaterial with excellent gas barrier properties and with excellent ductility even at temperatures of -40°C, as well as reduced blistering.Summary of invention

[0010] The inventors have found that a good compromise between permeability to hydrogen, good mechanical properties over a broad temperature range, including excellent ductility at temperatures of -40°C, and reduced blistering can be obtained by a vessel comprising a barrier layer, or liner, as defined in the appended claims.

[0011] A first object of the invention is a vessel comprising at least one barrier layer, [Layer (BL)], which comprises a polyamide composition, [Composition (PC)], comprising:- 60.0 to 90.0 wt.% of a semi-aromatic polyamide comprising recurring units deriving from an aromatic diamine having 6 to 18 carbon atoms;- 10.0 to 40.0 wt.% of a maleic anhydride-grafted polyethylene polymer comprising from 0.2 to 3.0 wt.% of maleic anhydride with respect to the weight of the maleic anhydride-grafted polyethylene polymer;- 0 to 1 .0 wt.% of an antioxidant; and- 0 to 15.0 wt.% of a nucleating agent.

[0012] The vessel preferably comprises at least one barrier layer, [Layer (BL)] as above defined, and at least one composite layer, [Layer (CL)] in contact with the at least one barrier layer, wherein Layer (CL) comprises continuous reinforcing fibers and a polymer matrix. The polymer matrix may be either thermoplastic or thermoset. Layer (BL) represents the internal layer of the vessel, or liner, while Layer (CL) represents the external layer of the vessel.

[0013] The vessel is a pressure vessel, that is a vessel for the storage of a gas under pressure or a system for the transportation of a gas under pressure.

[0014] A second object of the invention is a compressed gas in the vessel of the first object, wherein Layer (BL) is in contact with the compressed gas. Further objects of the invention are the use of the vessel in vehicles or in gas transportation in general.Description of invention

[0015] In the present application:- any description, even though described in relation to a specific embodiment, is applicable to and interchangeable with other embodiments of the present disclosure;- where an element or component is said to be included in and / or selected from a list of recited elements or components, it should be understood that in related embodiments explicitly contemplated here, the element or component can also be any one of the individual recited elements or components, or can also be selected from a group consisting of any two or more of the explicitly listed elements or components; any element or component recited in a list of elements or components may be omitted from such list;- any recitation herein of numerical ranges by endpoints includes all numbers subsumed within the recited ranges as well as the endpoints of the range and equivalents;- the indeterminate article “a” in an expression like “a polyamide polymer”, is intended to mean “one or more”, or “at least one” unless indicated otherwise;- the expression “consist essentially” means in the context of the invention in relation to a composition, such as Composition (PC), that the composition comprises the indicated ingredients and may also comprise up to 2.0 wt.%, preferably up to 1 .0 wt.%, even more preferably up to 0.5 wt.%, of other ingredients other than the indicated ones that do not impact its targeted function and effect in the framework of the present invention; and- the use of brackets “( )” before and after names of compounds, symbols or numbers, e.g. “Layer (BL)”, has the mere purpose of better distinguishing that name, symbol or number from the rest of the text; thus, said parentheses could also be omitted.

[0016] Unless specifically expressed otherwise, the term “alkyl”, as well as derivative terms such as “alkoxy”, “acyl” and “alkylthio”, as used herein, include within their scope straight chain, branched chain and cyclicmoieties. Examples of alkyl groups are methyl, ethyl, 1 -methylethyl, propyl, 1 ,1 -dimethylethyl, and cyclo-propyl. Unless specifically stated otherwise, each alkyl and aryl group may be unsubstituted or substituted with one or more substituents selected from, but not limited to, halogen, hydroxy, C1- C6 alkoxy, C1-C6 alkylthio, C1-C6 acyl, formyl, cyano, C6-C15 aryloxy or C6-C15 aryl, provided that the substituents are sterically compatible and the rules of chemical bonding and strain energy are satisfied. The term “halogen” or “halo” includes fluorine, chlorine, bromine and iodine, with fluorine being preferred.

[0017] The term “aryl” refers to a phenyl, indanyl or naphthyl group. The aryl group may comprise one or more alkyl groups, and are called sometimes in this case “alkylaryl”; for example may be composed of a cyclo-aromatic group and two C1-C6 groups (e.g. methyl or ethyl). The aryl group may also comprise one or more heteroatoms, e.g. N, 0 or S, and are sometimes called “heteroaryl” groups; these heteroaromatic rings may be fused to other aromatic systems. The aryl or heteroaryl substituents may be unsubstituted or substituted with one or more substituents selected from but not limited to halogen, hydroxy, C1-C6 alkoxy, C1 -C6 alkylthio, C1-C6 acyl, formyl, cyano, C6-C15 aryloxy or C6-C15 aryl, provided that the substituents are sterically compatible and the rules of chemical bonding and strain energy are satisfied.

[0018] Laver (BL)

[0019] A first object of the invention is a vessel comprising at least one barrier layer, [Layer (BL)]. Layer (BL) is formulated to provide the barrier to permeation of gasses as well as high ductility at low temperature.

[0020] Layer (BL) does not contain any continuous reinforcing fiber; that is, Layer (BL) does not contain any fiber having a length, in the longest dimension, exceeding 5 mm.

[0021] Layer (BL) comprises a polyamide composition, [Composition (PC)], comprising:- 60.0 to 90.0 wt.% of a semi-aromatic polyamide comprising recurring units deriving from an aromatic diamine having 6 to 18 carbon atoms;- 10.0 to 40.0 wt.% of a maleic anhydride-grafted polyethylene polymer comprising from 0.2 to 3.0 wt.% of maleic anhydride with respect to the weight of the maleic anhydride-grafted polyethylene polymer;- 0 to 1 .0 wt.% of an antioxidant; and- 0 to 15.0 wt.% of a nucleating agent.

[0022] All percentages are calculated with respect to the total weight of Composition (PC).

[0023] Layer (BL) may essentially consist of or consist of Composition (PC).

[0024] The semi-aromatic polyamide

[0025] The semi-aromatic polyamide in Composition (PC) comprises at least 50 mol%, typically at least 70 mol% of recurring units deriving from the C6- C18 aromatic diamine with respect to the total amount of diamine units in the polyamide.

[0026] Examples of suitable C6-C18 aromatic diamines include, but are not limited to, m-phenylene diamine (MPD), p-phenylene diamine (PPD), 3,4’- diaminodiphenyl ether (3,4’ ODA), 4,4’-diaminodiphenyl ether (4,4’-ODA), p-xylylene diamine (PXD) and m-xylylenediamine (MXD).

[0027] Notable non-limiting examples of suitable polyamides comprising aromatic diamines are for instance polyamides comprising recurring units of formula MXDZ in which Z represents units deriving from a linear or branched, aliphatic, aromatic or cyclo-aliphatic diacid having z carbon atoms, wherein z is an integer equal to or greater than 6, and MXD is m-xylylenediamine. Z is preferably selected from the aliphatic diacids having 6 to 16 carbon atoms. Notable non-limiting examples are adipic acid, sebacic acid or dodecanedioic acid. More preferably, Z is adipic acid.

[0028] In some instances, more than one diacid may be used. For instance, Z may be a blend of a straight chain aliphatic dicarboxylic acid having 4 to 20 carbon atoms, preferably 6 to 10 carbon atoms, and isophthalic acid. The molar ratio of the constituent unit derived from the straight chain aliphatic dicarboxylic acid having 4 to 20 carbon atoms to the constituent unit derived from isophthalic acid is 30:70 to 100:0.

[0029] The semi-aromatic polyamide may additionally comprise recurring units of formula PXDZ wherein PXD represents units deriving from p-xylylene diamine and Z is as defined above.

[0030] In certain embodiments, the semi-aromatic polyamide is a polyamide of formula A / MXDZ in which A is a recurring unit derived from at least one of the following: an amino acid, that is a molecule containing a primary carboxylic acid and a primary amine, a lactam or a unit with the formula (Ca diamine). (Cb diacid), where “a” represents the number of carbon atoms of the diamine and “b” represents the number of carbon atoms of the diacid, and wherein “a” and “b” independently of each other are integers between 4 and 36, advantageously between 6 and 18. The component (Ca diamine) is preferably selected from the group consisting of the linear or branched aliphatic diamines, the cycloaliphatic diamines and the alkylaromatic diamines. Examples are, for instance, hexamethylenediamine, decanediamine, dodecanediamine and MXD.

[0031] The component (Cb diacid) is preferably selected from the group consisting of the linear or branched aliphatic diacids, the cycloaliphatic diacids and the aromatic diacids. Examples are for instance, adipic acid, sebacic acid or dodecanedioic acid or 3-(aminomethyl)benzoic acid (3- AMBa).

[0032] In an advantageous embodiment, the units A or Z can be derived from renewable materials. Non-limiting examples of suitable polyamides of this type are: PA MXD6, PA MXD10.

[0033] When the diamines other than xylylenediamine is used as the diamine component, the ratio of use is less than 50 mol% of the total structural unit derived from diamines, preferably 30 mol% or less, more preferably 1 to 25 mol %, and particularly 5 to 20 mol %.

[0034] The semi-aromatic polyamide conveniently has a glass transition temperature of at least 50°C, preferably at least 55°C. The glass transition temperature may be equal to or greater than 60°C. The glass transition temperature may be as high as 190°C, generally up to 180°C, in some instances as high as 170°C. The glass transition temperature of semiaromatic polyamide is conveniently from 50°C to 180°C, even from 55°C to 170°C, from 60°C to 160°C.

[0035] The semi-aromatic polyamide conveniently has a melting temperature of at most 320°C, even at most 315°C, in some instances at most 310°C. The melting temperature is generally at least 180°C, generally at least 185°C. The melting temperature of the thermoplastic polymer is conveniently from 180°C to 310°C, even from 180°C to 305°C, in some instances from 185°C to 280°C.

[0036] Glass transition temperature and melting temperature are measured using differential scanning calorimetry (DSC) according to ASTM D3418, on the second heat scan using a heating and cooling rate of 20 °C / min.

[0037] The maleic anhydride-grafted polyethylene polymer

[0038] The maleic anhydride grafted polyethylene polymer may be a maleic anhydride grafted high density polyethylene, a maleic anhydride grafted linear low density polyethylene, a maleic anhydride grafted linear very low density polyethylene or a maleic anhydride grafted polyethylene elastomer. Advantageously the maleic anhydride grafted polyethylene polymer is selected from the group consisting of maleic anhydride grafted linear low density polyethylene, maleic anhydride grafted linear very low density polyethylene and maleic anhydride grafted polyethylene elastomer.

[0039] The maleic anhydride grafted polyethylene typically comprises a copolymer of ethylene and at least one a-olefin, the a-olefin being propylene, but-1-ene, penta-1-ene, hexa-1-ene, hepta-1-ene and octa-1 - ene.

[0040] The amount of maleic anhydride grafted onto the polyethylene chain is from 0.2 to 3.0 wt% based on the weight of the polyethylene polymer. The amount of grafted maleic anhydride may be from 0.3 to 2.5 wt% based on the weight of the polyethylene, even 0.3 to 2.0 wt% based on the weight of the polyethylene. The amount of grafted maleic anhydride may be from 0.3 to 1 .5 wt% based on the weight of the polyethylene polymer.

[0041] The amount of maleic anhydride grafted on the polymer may be determined by titration analysis, FTIR analysis, or any other appropriate method.

[0042] The maleic anhydride grafted polyethylene polymer in Composition (PC) conveniently has a density of 0.930 g / cm3or less. To improve the ductilityat cryogenic temperatures it may be advantageous to employ a maleic anhydride grafted polyethylene polymer having a density which is less than 0.915 g / cm3, preferably less than 0.905 g / cm3. Good results were obtained with maleic anhydride grafted polyethylene polymers having a density from 0.850 g / cm3to 0.915 g / cm3, from 0.850 g / cm3to 0.905 g / cm3, even from 0.855 g / cm3to 0.900 g / cm3, from 0.855 g / cm3to 0.895 g / cm3. Density is measured according to ASTM D792.

[0043] The maleic anhydride grafted polyethylene in Composition (PC) conveniently has a melt index (measured at 230°C, 2.16 kg) of 0.2 g / 10 minutes to 5.0 g / 10 minutes. For example, the maleic anhydride grafted polyethylene can have a melt index from 0.3 to 5.0 g / 10 minutes, even from 0.3 to 4.0 g / 10 min, preferably from 0.4 to 2.0 g / 10 min. The melt index is measured according to ASTM D1238, at 230°C, 2.16 kg.

[0044] Furthermore, the maleic anhydride grafted polyethylene in Composition (PC) has a melting point in the range of 25 to 125° C, preferably 30 to 90° C.

[0045] Maleic anhydride grafted polyethylene polymers are known. Examples of maleic anhydride grafted polyethylene polymers that can be used in Composition (PC) include those commercially available from The Dow Chemical Company under the trade name Fusabond® or those commercially available from Mitsui Chemicals under the trade name Tafmer®.

[0046] Composition (PC)

[0047] The amount of the semi-aromatic polyamide in Composition (PC) may be 60.0 wt.% or more, even 65.0 wt.% or more. The amount of the semiaromatic polyamide may be less than 90.0 wt.%, even less than 88.0 wt.%. Advantageous amounts of the semi-aromatic polyamide were found to be from 65.0 wt.% to 88.0 wt.%, from 68.0 wt.% to 87.5 wt.%.

[0048] The amount of the maleic anhydride-grafted polyethylene polymer may be 10.0 wt.% or more, 12.0 wt.% or more, 12.5 wt.% or more, even 15.0 wt.% or more. The amount of the maleic anhydride-grafted polyethylene polymer may be less than 40.0 wt.%, even less than 35.0 wt.%, less than 32.0 wt.%, even less than 30.0 wt.% and even less than 28.0 wt.%.

[0049] Advantageous amounts of the maleic anhydride-grafted polyethylene polymer were found to be from 11 .0 to 35.0 wt.%, advantageously from 12.0 to 32.0 wt.%, more advantageously from 12.5 to 29.0 wt.% and even from 15.0 to 25.0 wt.%.

[0050] Composition (PC) may comprise one or more additives. Non limiting examples of suitable additives are antioxidants (e.g. ultraviolet light stabilizers and heat stabilizers), chain extenders, processing aids, nucleating agents, lubricants, flame retardants, smoke-suppressing agents, anti-static agents, anti-blocking agents, and pigments, such as carbon black.

[0051] In particular, Composition (PC) may comprise up to 1 .0 wt%, with respect to the weight of the composition, of an antioxidant. Typically the amount of antioxidant is from 0.1 to 0.7 wt.%, even from 0.1 to 0.5 wt.% with respect to the weight of the composition.

[0052] Antioxidants for use in Composition (PC) are generally selected from the group consisting of hindered amine compounds, hindered phenol compounds, and phosphorous compounds selected from the group consisting of phosphite esters, phosphonites and mixtures thereof. The antioxidant is preferably selected from the group consisting of hindered phenol compounds; and phosphite esters represented by the formula P(OR)3, wherein each of R, can be the same or different and is independently selected from the group consisting of a C1-20 alkyl, C3-22 alkenyl, C6-40 cycloalkyl, C7-40 cycloalkylene, aryl, alkaryl or arylalkyl moiety; as well as mixtures thereof.

[0053] Composition (PC) may comprise a nucleating agent. The nucleating agent can be present in an amount of up to 15.0 wt.%. Suitable nucleating agents are inorganic nucleating agents or polymeric nucleating agents. Among inorganic nucleating agents mention may be made of talc, silica, titanium dioxide. Among polymeric nucleating agents mention can be made of PA6 or PA66.

[0054] Composition (PC) may comprise a combination of inorganic and polymeric nucleating agents. In particular, Composition (PC) may comprise a combination of talc and PA6 or PA66. The weight ratio between talc andthe polymeric nucleating agent, PA6 or PA66, may be in the range 0.5:1 .0 to 1.0:0.5.

[0055] Composition (PC) may comprise other additives in addition to nucleating agents and antioxidants. The amount of other additives may be up to 10.0 wt% based on the weight of Composition (PC). Among such additional additives, mention may be made of pigments, in particular carbon black. The amount of carbon black may be from 0.1 to 10.0 wt.% based on the weight of Composition (PC).

[0056] Composition (PC) may advantageously comprise:65.0 to 88.0 wt.%, preferably 68.0 to 87.5 wt.%, of a semi-aromatic polyamide comprising at least 50 mol%, typically at least 70 mol% of recurring units deriving from m-xylylenediamine with respect to the total amount of diamine units in the polyamide;12.0 to 35.0 wt.%, preferably 12.5 to 32.0 wt.%, of a maleic anhydride- grafted polyethylene polymer comprising from 0.2 to 3.0 wt.%, preferably 0.3 to 2.0 wt.%, of maleic anhydride with respect to the weight of the polymer; and0 to 1 .0 wt.%, preferably 0.1 to 0.5 wt.%, of an antioxidant.

[0057] Composition (PC) may advantageously comprise, essentially consist of, consist of:- 65.0 to 88.0 wt.%, preferably 68.0 to 87.5 wt.%, of a semi-aromatic polyamide comprising at least 70 mol% of recurring units deriving from m-xylylenediamine with respect to the total amount of diamine units in the polyamide;- 12.0 to 35.0 wt.%, preferably 12.5 to 32.0 wt.%, of a maleic anhydride- grafted polyethylene polymer comprising from 0.2 to 3.0 wt.%, preferably 0.3 to 2.0 wt.%, of maleic anhydride with respect to the weight of the polymer;- 0 to 1 .0 wt.%, preferably 0.1 to 0.5 wt.%, of an antioxidant;- 0 to 10.0 wt.%, preferably 1 .0 to 5.0 wt.% of a nucleating agent; and- 0 to 10.0 wt.% of other additives, such as carbon black.

[0058] Composition (PC) may advantageously comprise, essentially consist of, or consist of:68.0 to 87.5 wt.% of a semi-aromatic polyamide comprising at least 70 mol% of recurring units deriving from m-xylylenediamine with respect to the total amount of diamine units in the polyamide;12.5 to 32.0 wt.% of a maleic anhydride-grafted polyethylene polymer comprising from 0.2 to 3.0 wt.%, preferably 0.3 to 2.0 wt.%, of maleic anhydride with respect to the weight of the polymer and having a melt flow index (230°C / 2.16 kg) of less than 0.915 g / cm3;0.1 to 0.5 wt.%, of an antioxidant;- 1 .0 to 5.0 wt.% of a nucleating agent; and- 0 to 10.0 wt.% of other additives.

[0059] Composition (PC) may advantageously comprise, essentially consist of, or consist of:68.0 to 87.5 wt.% of a semi-aromatic polyamide comprising at least 70 mol% of recurring units deriving from m-xylylenediamine with respect to the total amount of diamine units in the polyamide;12.5 to 32.0 wt.% of a maleic anhydride-grafted polyethylene polymer comprising from 0.2 to 3.0 wt.%, preferably 0.3 to 2.0 wt.%, of maleic anhydride with respect to the weight of the polymer and having a melt flow index (230°C / 2.16 kg) of less than 0.915 g / cm3;0.1 to 0.5 wt.%, of an antioxidant;- 1 .0 to 5.0 wt.% of a nucleating agent; and- 0.1 to 10.0 wt.% of carbon black.

[0060] The semi-aromatic polyamide is preferably selected from those of formula MXDZ in which MXD is m-xylylenediamine and Z represents units deriving from a linear or branched, aliphatic, aromatic or cyclo-aliphatic diacid having z carbon atoms, wherein z is an integer equal to or greater than 6. Preferably Z is selected from the aliphatic diacids having 6 to 16 carbon atoms, more preferably 6 to 12 carbon atoms. The semi-aromatic polyamide may conveniently be PA MXD6, preferably PA MXD6 having arelative viscosity in the range of 2.5 to 4.0 measured according to ISO 307, using 1 g / L solution in sulfuric acid 96 %.

[0061] The Applicant has found that Composition (PC) allows to obtain vessels characterized by good blistering resistance, in both static and dynamic conditions, combined with excellent mechanical properties over a broad range of temperatures, together with low permeation to hydrogen.

[0062] Barrier layers made of composition (PC) conveniently exhibit an elongation at break at -40°C of at least 10%. The elongation at break at -40°C may be at least 12%, even at least 15%.

[0063] Tensile properties, including elongation at break, are measured according to ISO 527-2 using test pieces according to ISO 1A.

[0064] Surprisingly, Composition (PC) exhibits a brittle transition at a temperature lower than - 50°C and at the same time a storage modulus exceeding 800 MPa up to a temperature of 80°C as measured using dynamic mechanical thermal analysis (tensile mode, from - 70°C to 150°C at 2 °C / min, 1 Hz frequency, 0.05 % amplitude). In other words, Composition (PC) remains ductile and has good mechanical properties over a very broad range of temperatures.

[0065] Composition (PC) exhibits a hydrogen permeation coefficient at 23°C that does not exceed 80 Ncm3.mm / m2.d.bar, preferably it does not exceed 60 Ncm3.mm / m2.d.bar.

[0066] When the semi-aromatic polyamide in Composition (PC) is PA MXD6 the hydrogen permeation coefficient at 23°C is conveniently less than 40 Ncm3.mm / m2.d.bar, even less than 30 Ncm3.mm / m2.d.bar.

[0067] The hydrogen permeation coefficient is determined by measuring the permeation of hydrogen through molded plaques of Composition (PC) which were annealed at a temperature of 35°C above their glass transition temperature for 2 hours. The detailed method for the determination is described in the experimental section of the present specification.

[0068] When more than one Layer (BL) is present in the vessel of the invention, each Layer (BL) may comprise the same or a different composition.

[0069] Laver (CL)

[0070] The vessel of the invention comprises at least one barrier layer, [Layer (BL)] as above defined, and it may comprise at least one composite layer,[Layer (CL)], in contact with the at least one barrier layer, wherein Layer (CL) comprises continuous reinforcing fibers and a polymer matrix.

[0071] Layer (BL) represents the internal layer of the vessel, or liner, while Layer (CL) represents the external layer of the vessel.

[0072] The polymer matrix in Layer (CL) may be either a thermoplastic or a thermoset polymer.

[0073] Among suitable thermoplastic polymers suitable as polymer matrix in Layer (CL) mention may be made of: polyamides, in particular comprising an aromatic and / or cycloaliphatic structure, polyesters, such as poly(butylene terephthalate), poly(aryl ether ketone) polymers as defined above, in particular poly(ether ether ketone) (PEEK), poly(ether ketone ketone ketone) (PEEKK), poly(ether ether ether ketone ketones) (PEKEKK), polyimides, in particular polyetherimides (PEI) or polyamide-imides, polysulfones, in particular polyarylsulfones such as polyphenylsulfones (PPSU), polyethersulfones (PES), poly(aryl sulfide) polymers; in particular polyphenylene sulfide (PPS).

[0074] Preferred thermoplastic polymers may be selected from the group consisting of polyamides, in particular semi-aromatic polyamides.

[0075] Among suitable thermoset materials for the polymer matrix in Layer (CL) mention may be made of epoxy-resins.

[0076] Layer (CL) comprises continuous reinforcing fibers. As used herein, the expression “continuous reinforcing fiber” refers to a fiber having a length, in the longest dimension, of at least 5 mm.

[0077] In some embodiments, the continuous reinforcing fiber has a length, in the longest dimension, of at least 1 cm, at least 25 cm or at least 50 cm. The length of the continuous reinforcing fiber is dependent on the shape and size of the finished part.

[0078] The continuous reinforcing fiber is selected from the group consisting of, glass fiber, carbon fibers, aluminum fiber, metallic fibers, ceramic fiber, titanium fiber, magnesium fiber, boron carbide fibers, rock wool fiber, steel fiber, aramid fiber and natural fiber (e.g. cotton, linen and wood). Preferably, the continuous reinforcing fiber is selected from the group consisting of glass fiber, carbon fiber, aramid fiber, and ceramic fiber. Advantageously, the continuous reinforcing fiber is carbon fiber.

[0079] In some embodiments, Layer (CL) may include one or more additional continuous reinforcing fibers, each distinct in compositions and as described above.

[0080] Overall, the continuous reinforcing fibers constitute at least 5.0% of the total volume of Layer (CL). Typically the continuous reinforcing fibers are at least 10.0%, at least 15.0%, even at least 20.0% of the total volume of Layer (CL). The continuous reinforcing fibers are no more than 80.0%, no more than 75.0%, even no more than 70.0% of the total volume of Layer (CL). The continuous reinforcing fibers may conveniently represent from 20.0% to 75.0%, from 25.0% to 70.0%, from 25.0% to 65.0% and even from 30.0% to 60.0% of the total volume of Layer (CL). The polymer matrix represents the remainder of the volume of Layer (CL).

[0081] The continuous reinforcing fibers in Layer (CL) are generally aligned along a single direction. Generally aligned fibers are oriented such that at least 70%, at least 80%, at least 90% or at least 95% of the fibers have a direction that is within 30 degrees, within 25 degrees, within 20 degrees, within 15 degrees, or within 10 degrees along the direction of the other fibers.

[0082] In certain embodiments the continuous reinforcing fibers in Layer (CL) may be arranged at an angle the ones with respect to the others. The continuous reinforcing fibers might be arranged as a woven fabric or a layered fabric or any combination of one or more.

[0083] Layer (CL) can be fabricated by methods well known in the art. In general, the method of fabrication includes a step of impregnation of the continuous reinforcing fibers with a polymer matrix or a precursor of the polymer matrix when the polymer is a thermosetting polymer, and subsequent cooling or drying to form a Layer (CL).

[0084] When more than one Layer (CL) is present, each Layer (CL) may be the same or different.

[0085] Layer (CL) has a thickness which is usually between 100 microns and 500 microns. The thickness is adapted to provide the required structural resistance to the vessel.

[0086] The vessel

[0087] The term “vessel” is used herein to refer to a hollow container or any system for the transportation of a fluid, in particular a pressurized gas. Thevessel of the invention can be a hollow container for containing a gas, preferably a pressurized gas. The vessel may be a pipe or a piping system for the transportation of a gas, in particular a pressurized gas.

[0088] Layer (BL) represents the sole or the internal layer of the vessel which is in contact with the gas to be transported or stored, hereinafter referred to as “liner”. Layer (CL), when present, represents the external layer of the vessel.

[0089] The vessel may comprise one Layer (BL) and one or more Layers (CL). In one aspect of this embodiment, when more Layers (CL) are present they have the same composition. Layers (CL) may be 2, 3, 5, 10, 50 and even up to 100 or more, such as 200 or 300. The layers (CL) may also vary in volume % of fibers and the nature of the fibers used.

[0090] The vessel is preferably a pressure vessel, that is a vessel suitable for the storage and transport of a gas under pressure.

[0091] The vessel, or preferably the pressure vessel, comprises a hollow body and at least one boss. A boss is known by a person skilled in the art and it refers to the opening in which a closure is attached which allows flow of gas or fluid in and out the vessel. A boss is usually made of metal. The boss could alternatively be made of a polymeric material, for instance a semi-aromatic polyamide as the one used in Composition (PC).

[0092] The hollow body may have any shape suitable for the storage of a gas, in particular of a gas under pressure.

[0093] In certain conventional embodiments, the vessel has a cylindrical shape and a boss is placed at the end. Often, a vessel has two bosses at each end of the cylindrical shape.

[0094] The shape of the hollow body is determined by the desired use. It is usually but not exclusively cylindrical; it typically has a diameter of between 10.0 cm and 1.00 m.

[0095] The length of a hollow body also depends on the end use and may for example be between 50.0 cm and up to lengths as large as 10.0 m. These higher lengths are usually employed for gas transport. As an example, for vessels in trucks the length is usually between 1 .0 m and 3.0 m.

[0096] The vessel of the invention may have an internal volume between 3.5 dm3and 10.0 m3, even from 5.0 dm3to 5.0 m3. The internal volume of thevessel may be at least 10.0 dm3, even at least 15.0 dm3. The internal volume may be up to 0.5 m3, even up to 1 .0 m3, up to 5.0 m3, even up to 10.0 m3.

[0097] The vessel comprises a hollow body which may consist solely of one or more Layer (BL). Alternatively the vessel may comprise, from the inside to the outside of the vessel: at least one Layer (BL), or liner, as defined above, and at least one structural composite layer, which is Layer (CL) as defined above, in contact with the at least one Layer (BL). Layer (BL) is in contact with the gas contained in the vessel.

[0098] The liner intends to provide a barrier between the fluid or gas and the Layer (CL), preventing leaks. In general, Layer (CL) is provided around the liner to provide mechanical properties, such as burst pressure resistance.

[0099] The vessel may be prepared according to any method known in the art.

[0100] For instance, the liner may be prepared by blow molding, tube extrusion, injection molding and welding and / or roto-molding. Layer (CL), when present, may then be applied on the outer surface of the liner by winding a tape or a towpreg comprising continuous reinforcing fibers and a polymer matrix around the hollow body made of the liner.

[0101] Other manufacturing processes as known in the art for the manufacture of pressure vessels can be used for making the inventive vessel.

[0102] The vessel of the invention is characterized by a good hydrogen barrier and mechanical properties.

[0103] The vessel according to the invention exhibits a nominal pressure of at least 2.5 MPa, typically at least 20.0 MPa, even at least 30.0 MPa. The nominal pressure may be up to 70.0 MPa, 100 MPa, even 150.00 MPa and more. Advantageously, the vessel of the invention has a nominal pressure of 20.0 to 70.0 MPa.

[0104] A burst pressure of at least 157.5 MPa may be reached for the storage of hydrogen gas with a vessel according to the invention. Vessels for the storage of compressed hydrogen typically require nominal pressures of 35.0 MPa or 70.0 MPa. Burst pressures, measured according to ECE R134, are typically up to 78.8 MPa and 157.5 MPa, respectively.

[0105] A further object of the invention is a compressed gas in a vessel of the first object, wherein Layer (BL) is in contact with the compressed gas. The gasis advantageously selected from the group consisting of hydrogen, oxygen, nitrogen, argon, helium, methane, propane, compressed natural gas, CO2 and ammonia.

[0106] The gas is typically at a pressure of at least 5.0 MPa, preferably at least 10.0 MPa. Depending on the gas, the pressure may be up to 150.0 MPa.

[0107] A further object of the invention is a vehicle comprising the vessel or the compressed gas contained in the vessel.

[0108] The vehicle may be a car, a truck, a train, a ship, an urban mobility vehicle, an airplane, a helicopter or any other vehicle that could be powered using the conversion of a gas into energy by any means.

[0109] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0110] The embodiments above are intended to be illustrative and not limiting. Additional embodiments are within the inventive concepts. In addition, although the present invention is described with reference to particular embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention.

[0111] Experimental section

[0112] MATERIALS- MXD6: MX 6121 a PA MXD6 with Tg= 85°C, Tm= 237°C supplied by Mitsubishi Gas Chemical- MA-g-PE(1 ) : Tafmer® MH5020C, maleic anhydride grafted polyethylene with 0.5-1.5 wt% grafted maleic anhydride, density 0.866 g / cm3supplied by Mitsui Chemicals- MA-g-PE(2) : Fusabond™ E226 , maleic anhydride grafted polyethylene with 0.5-1.0 wt% grafted maleic anhydride, density 0.930 g / cm3supplied by The Dow Chemical Company- AO : Irganox® B1171 supplied by BASF- Nu (1 ): Steamic® 00s talc supplied by Imerys Performance Additives- Nu (2): Radipol® A45 PA66; density 1.14 g / cm3, melting temperature 260°C, supplied by Radici Group

[0113] General procedure for the preparation of Compositions (PC)

[0114] Compositions shown in Table 1 were made on a twin-screw extruder by feeding all raw materials through the main hopper and setting temperature at 270°C and applying vacuum of 0.9 bar at the end of the extruder. Polymer exiting extruder is cooled in a water bath and pelletized.

[0115] The compositions and the testing results are detailed in Table 1

[0116] Tensile testing

[0117] Tensile properties were measured according to ISO 527-2 using samples meeting the requirements of ISO 1A at the indicated temperature. The samples were annealed at a temperature of 35°C above their glass transition temperatures for a period of 2 h to ensure full crystallinity prior to tensile testing.

[0118] H2 Permeation coefficient determination

[0119] Samples for hydrogen permeation testing were prepared as follows.Polymers were dried overnight at 107°C in a desiccant drying oven with a - 40°C dew point to ensure material was dry prior to injection molding into plates. Material was injection molded into 12.5 cm x 12.5 cm x 0.4 cm plates using a 180 ton Fanuc S-2000i molding machine, following the polymer suppliers recommended injection molding processing guidelines. The screw speed during dosing was 150 rpm. The molding machine was fitted with a 32 mm screw size. The temperature profile was 250°C in the feed zone up to 265 °C in the nozzle. Injection speed was 80 mm / s, commutation pressure approximately 140 MPa and maintained pressure was 50 MPa during 15 seconds. The plates were annealed at a temperature of 35°C above their glass transition temperatures for a period of 2 h to ensure full crystallinity prior to hydrogen permeation testing.

[0120] The sample in the form of a circular plate is mounted on a cell so as to form a barrier between two chambers. One chamber contains the test gas (H2) and the other chamber is purged with a sweep gas (synthetic air). The feed side is pressurized with H2 and during the measurement, the concentration of H2 in the sweep gas flow is measured, typically with anelectrochemical H2 sensor. Permeation coefficient (P) is calculated according to the equation 1 (Eq. 1 ):P = (C D d / A pp).(T° p / T p°) [Eq. 1] wherein:P = permeation coefficient (Ncm3 mm / m2 day bar)C = penetrant concentration (ppm)D = sweep gas flow rate (mL / min) d = sample thickness (mm)A = testing area in contact with the gas (m2) pp = penetrant partial pressure (bar)T = ambient temperature (K) p = ambient pressure (bar)T° = standard temperature (273.15 K) p° = standard pressure (1.013 bar)

[0121] Further normalization is done to standard temperature and pressure, i.e.273.15 K and 1.013 bar.

[0122] The results are shown in Table 1.

[0123] Static and Dynamic Blistering - Conditions for testing

[0124] The samples submitted to static and dynamic blistering testing were injection molded dog bone samples meeting the requirements of ISO37 1A standard. The samples were introduced in the testing apparatus and submitted to the following conditions.

[0125] DYNAMIC TESTING CONDITIONS: o Condition to 50 ± 2 °C o Perform 250 cycles o Pressurize to > 87.5 MPa o Hold at > 87.5 for 24.8 min o Depressurize to < 0.5 MPa at ca. 1000 MPa / hr o Hold at < 0.5 MPa for 24.8 min o Depressurize to ambient pressures o Remove samples from pressure vessel

[0113] At the end of the test’s samples were visually inspected to identify defects.The presence of blisters was noted. The wording “OK” indicates absence of blistering; the wording “not OK“ indicates presence of blistering.

[0114] STATIC TESTING CONDITIONS

[0115] Static blistering tests were performed under the following conditions: o Condition to 20 ± 2 °C o Pressurize to 87.5 MPa o Hold for 168 h (exposure) o Depressurize to ambient pressure as fast as possible (target: < 1s) o Remove samples from pressure vessel

[0116] At the end of the test’s samples were visually inspected to identify defects. The presence of blisters was noted. The wording “OK” indicates absence of blistering; the wording “not OK“ indicates presence of blistering.

[0117] The compositions and the results of the testing are reported in Table 1 .Table 1

[0126] The combination of the properties above show that the inventive composition allows the design of liners with excellent resistance toblistering, excellent ductility at -40°C and good hydrogen barrier properties.

Claims

Claims1 . A vessel comprising at least one barrier layer, [Layer (BL)], which comprises of a polyamide composition, [Composition (PC)], comprising:- 60.0 to 90.0 wt.% of a semi-aromatic polyamide comprising recurring units deriving from an aromatic diamine having 6 to 18 carbon atoms;- 10.0 to 40.0 wt.% of a maleic anhydride-grafted polyethylene polymer comprising from 0.2 to 3.0 wt.% of maleic anhydride with respect to the weight of the maleic anhydride-grafted polyethylene polymer;- 0 to 1 .0 wt.% of an antioxidant; and- 0 to 15.0 wt.% of a nucleating agent, all percentages being calculated with respect to the total weight of Composition (PC).

2. The vessel of claim 1 in which Composition (PC) comprises:- 65.0 to 88.0 wt.% of a semi-aromatic polyamide comprising at least 70 mol% of recurring units deriving from m-xylylenediamine with respect to the total amount of diamine units in the polyamide;- 12.0 to 35.0 wt.% of a maleic anhydride-grafted polyethylene polymer comprising from 0.2 to 3.0 wt.%, preferably 0.3 to 2.0 wt.%, of maleic anhydride with respect to the weight of the polymer;- 0 to 1 .0 wt.% of an antioxidant; and- 0 to 10.0 wt.% of a nucleating agent, all percentages being calculated with respect to the total weight of Composition (PC).

3. The vessel of claim 1 or 2 in which Composition (PC) comprises:- 68.0 to 87.5 wt.% of a semi-aromatic polyamide comprising at least 70 mol% of recurring units deriving from m-xylylenediamine with respect to the total amount of diamine units in the polyamide;- 12.5 to 32.0 wt.% of a maleic anhydride-grafted polyethylene polymer comprising from 0.2 to 3.0 wt.%, preferably 0.3 to 2.0 wt.%, of maleic anhydride with respect to the weight of the polymer;- 0.1 to 0.5 wt.%, of an antioxidant;- to 5.0 wt.% of a nucleating agent; and- 0.1 to 10.0 wt.% of carbon black, all percentages being calculated with respect to the total weight of Composition (PC).

4. The vessel of any one of the preceding claims in which the maleic anhydride- grafted polyethylene polymer has a density of less than 0.915 g / cm35. The vessel of any one of the preceding claims in which the nucleating agent is selected from the group of talc, PA6, PA66 and their blends.

6. The vessel of any one of the preceding claims in which the semi-aromatic polyamide is a polyamide of formula MXDZ in which MXD is m- xylylenediamine and Z represents units deriving from a linear or branched, aliphatic, aromatic or cyclo-aliphatic diacid having z carbon atoms, wherein z is an integer equal to or greater than 6, preferably Z is selected from the aliphatic diacids having 6 to 16 carbon atoms, more preferably from the aliphatic diacids having 6 to 12 carbon atoms.

7. The vessel of any one of the preceding claims wherein Composition (PC) is characterized by at least one of the following:- an elongation at break at -40°C which is at least 12%, even at least 15%, measured according to ISO 527-2 using test pieces according to ISO 1A;- a hydrogen permeation coefficient at 23°C that does not exceed 80 Ncm3.mm / m2.d.bar, preferably it does not exceed 60 Ncm3.mm / m2.d.bar.

8. The vessel of any one of the preceding claims which comprises at least one layer (BL) and at least one composite layer, [Layer (CL)], in contact with the at least one layer (BL), wherein Layer (CL) comprises continuous reinforcing fibers and a thermoplastic or thermoset polymer matrix.

9. The vessel of claim 8 in which the continuous reinforcing fibers are selected from the group consisting of glass fiber, carbon fiber, aramid fiber, and ceramic fiber, preferably in an amount of 20% to 75% with respect to the total volume of Layer (CL).

10. The vessel of any one of the preceding claims in which Layer (BL) represents the internal layer of the vessel and Layer (CL) represents the external layer of the vessel.11 . The vessel of any one of the preceding claims which is in the shape of a hollow body which has one or more of the following:- a diameter of 10.0 cm to 1 .0 m;- a length of 50.0 cm to 10.0 m; and- an internal volume of 3.5 dm3to 10.0 m312. A compressed gas contained in the vessel of any one of the preceding claims, wherein the compressed gas is in contact with Layer (BL).

13. The compressed gas of claim 12, which is selected from the group consisting of hydrogen, oxygen, nitrogen, argon, helium, methane, propane, compressed natural gas, CO2, ammonia.

14. The compressed gas of claim 12 or 13 which is at a pressure of at least 50 MPa.

15. Use of the vessel of any one of claims 1 to 11 for the storage or transportation of a compressed gas.

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