Self-repairing anti-fatigue hydrogen-barrier coating and its application in type iv hydrogen storage cylinders

Abstract

The application belongs to the technical field of high-pressure hydrogen storage cylinders and interface engineering, and discloses a self-repairing anti-fatigue hydrogen barrier coating and application thereof in a type IV hydrogen storage cylinder. The self-repairing anti-fatigue hydrogen barrier coating is formed by curing a water-based polyurethane adhesive. The water-based polyurethane adhesive comprises water, a water-based polyurethane dispersion, a dihydrazine crosslinking agent, a flexible polyol, and a low-surface-energy filler. The application is as follows: first, the outer surface of a thermoplastic polymer liner is activated to introduce polar groups; then, the self-repairing anti-fatigue hydrogen barrier coating is formed on the activated surface by spraying; and finally, the outer surface of the self-repairing anti-fatigue hydrogen barrier coating is wrapped with a carbon fiber reinforced resin and cured to obtain the type IV hydrogen storage cylinder. The application improves the interface fatigue life from the structural level without significantly increasing the weight, wall thickness, and manufacturing complexity of the type IV high-pressure hydrogen storage cylinder, and avoids the problem that it is difficult to simultaneously consider hydrogen barrier, toughness, and self-healing.

Description

Self-healing, fatigue-resistant, and hydrogen-barrier bonding coating and its application in Type IV hydrogen storage cylinders Technical Field

[0001] This invention belongs to the field of high-pressure hydrogen storage cylinders and their interface engineering technology, specifically relating to a self-healing, fatigue-resistant, hydrogen-barrier composite coating and its application in Type IV hydrogen storage cylinders. Background Technology

[0002] Type IV high-pressure hydrogen storage cylinders are generally composed of a thermoplastic polymer inner liner (such as PA, HDPE, etc.) and an outer carbon fiber reinforced resin (CFRP) winding layer. They are characterized by lightweight, high hydrogen storage density, and good safety, making them an important carrier for vehicle-mounted and distributed hydrogen storage. In service scenarios with pressures of 70 MPa and above, the cylinders need to undergo a large number of pressure cycles (such as 70 MPa ↔ 5 MPa cycles). The periodic radial expansion and contraction will induce significant interlaminar shear strain and thermo-mechanical coupled residual stress between the inner liner and CFRP.

[0003] Existing research and engineering failure statistics show that the fatigue life of Type IV cylinders is usually not determined by the strength of the CFRP body, but rather by the initiation and propagation of microcracks at the "inner liner / wound layer interface". The interface fatigue damage process generally involves: interface crack initiation, the crack becoming a preferential diffusion channel for hydrogen, accelerated hydrogen permeation leading to debonding, and crack propagation along the interface causing delamination, ultimately resulting in a sharp drop in the cylinder's fatigue life. Therefore, the key to improving the fatigue life of Type IV hydrogen storage cylinders lies in simultaneously suppressing the initiation and propagation of interface cracks and blocking the crack-induced hydrogen permeation channels.

[0004] Regarding the reliability of the interface between type IV thermoplastic polymer liners and CFRP, existing technologies include liner surface activation to enhance adhesion, conventional high-strength adhesives / resin transition layers, and high-filler / multi-layer hydrogen-barrier coatings. However, none of these technologies have proposed "bonding coatings" as a fatigue-enhancing structural unit, and they suffer from the inherent contradiction of being difficult to balance hydrogen barrier properties, toughness, and self-healing.

[0005] Reference 1 (Development of Self-Healing Polyurethane and Applications in Flexible Electronic Devices: A Review[J].Polymers, 2025, 17(17):2274.) reports a self-healing polyurethane elastomer material based on the synergistic effect of dynamic disulfide bonds and hydrogen bonds. This material exhibits self-healing capability at room temperature for 24 hours or under heating (≤70°C), with a self-healing efficiency of up to 84% at room temperature for 24 hours. However, this material is primarily intended for flexible electronic skin applications, has low bulk mechanical strength (tensile strength typically <20 MPa), and does not address barrier design for hydrogen media, thus failing to meet the high-pressure shear resistance and high hydrogen barrier requirements of the interface layer in high-pressure hydrogen storage cylinders.

[0006] Reference 2 (A stretchable, mechanically robust polymer exhibiting shape-memory-assisted self-healing and clustering-triggered emission[J]. Nature Communications, 2023, 14: 4712) utilizes the shape memory effect to assist polymer chain diffusion, achieving crack closure and repair. However, this technology typically requires high temperatures (>70°C) to trigger shape memory recovery, while the thermoplastic liner of Type IV gas cylinders (especially HDPE or thin-walled PA) is temperature-sensitive, and excessively high repair temperatures can damage the thermal history and dimensional stability of the liner. Furthermore, it does not include fatigue strain energy dissipation design for the microstructure of the liner / CFRP interface.

[0007] Reference 3 (Preparation of Waterproof and Breathable Polyurethane FiberMembrane Modified by Fluorosilane-modified Silica[J]. Fibers and Polymers, 2020, 21(5):954-964.) utilizes fluorosilane-modified silica nanoparticles to improve the hydrophobicity and hydrostatic pressure resistance of polyurethane fiber membranes. However, this reference aims to improve waterproof and breathable properties, and the nanofiber membrane it prepares has a large number of microporous structures to ensure air permeability. This is completely contrary to the "high density and high barrier" requirements of the interface layer of hydrogen storage cylinders, and cannot be directly applied to hydrogen barrier.

[0008] Reference 4 (Solvent-free polyurethane adhesives with excellent adhesion performance at ultra-low temperature[J].Materials & Design, 2024, 244(000):11.) developed a solvent-free low-temperature resistant adhesive by adjusting the ratio of soft and hard segments and the molecular weight of polyurethane. However, this technology only focuses on improving static bond strength and lacks dynamic covalent bond network design. Under long-term cyclic loading, it cannot suppress the accumulation and propagation of interfacial microcracks, and the material itself does not have self-healing capabilities.

[0009] Therefore, there is an urgent need for an interface material and structural solution that aims to extend the fatigue life of the coating, and can achieve dynamic self-repair, flexible energy dissipation, and low-addition hydrogen barrier synergistic unity within the low-temperature processing window. Summary of the Invention

[0010] The purpose of this invention is to solve the problems existing in the prior art and to provide a self-healing, fatigue-resistant, hydrogen-barrier composite coating and its application in Type IV hydrogen storage cylinders.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A self-healing, fatigue-resistant, hydrogen-barrier bonding coating is formed by curing a water-based polyurethane adhesive.

[0013] By weight, the waterborne polyurethane adhesive includes water, a waterborne polyurethane dispersion (an adhesive matrix with waterborne polyurethane as the continuous phase and water as the dispersion medium), 6-10 parts of dihydrazine crosslinking agent, 4-8 parts of flexible polyol and 2-4 parts of low surface energy filler, wherein the waterborne polyurethane in the waterborne polyurethane dispersion is 100 parts by weight.

[0014] The main chain or side chain of the waterborne polyurethane dispersion contains structural units that form reversible acylhydrazone bonds by condensation with the hydrazine group of the dihydrazine crosslinking agent under curing conditions, such as β-dicarbonyl structural units and acetoacetate structural units, as well as structural units that undergo covalent reactions with flexible polyols under curing conditions.

[0015] The preparation method of the waterborne polyurethane dispersion is not limited, as long as the above conditions are met. For example, the preparation method is as follows: First, poly(1,4-butanediol adipate) oligomer (PBA) is dehydrated under vacuum at 110°C for 1 hour. Then, it is cooled to 65°C and IPDI and dimethylolpropionic acid (DMPA) are added and reacted for 2.5 hours to obtain a prepolymer. Then, the temperature is further lowered to 60°C and diacetone acrylamide (DAAM) or 2-hydroxyethyl acetoacetate is added and reacted for 1.5 hours to introduce ketone carbonyl groups. Then, the temperature is further lowered to 45°C and triethylamine is added to neutralize and form a salt. Finally, water is added and dispersed at high speed and acetone is removed by vacuum distillation to obtain the waterborne polyurethane dispersion.

[0016] Dihydrazine crosslinking agents are generated by the reaction of diisocyanates with dihydrazine compounds.

[0017] The self-healing, fatigue-resistant, and hydrogen-barrier bonding coating of this invention can achieve self-repair of cracks at low temperatures of ≤50°C, while also possessing strain dissipation and life-extending functions, and still significantly inhibiting hydrogen even at low addition levels. It can be used to improve the fatigue life and long-term interface reliability of Type IV hydrogen storage cylinders under high-pressure cyclic loading. Because the self-healing, fatigue-resistant, and hydrogen-barrier bonding coating of this invention is formed by curing with a water-based polyurethane adhesive, the formulation of the water-based polyurethane adhesive has been specially designed, as detailed below:

[0018] Waterborne polyurethane adhesives contain a certain amount of waterborne polyurethane dispersion and dihydrazine crosslinking agents. During the curing process, the hydrazine groups of the dihydrazine crosslinking agent can form a reversible acylhydrazone dynamic covalent network with specific structural units in the waterborne polyurethane chain. This allows the self-healing, fatigue-resistant, and hydrogen-barrier bonded coating to undergo fracture-rearrangement-regeneration at ≤50°C, achieving low-temperature self-repair and continuous passivation of fatigue microcracks. Appropriate addition of the dihydrazine crosslinking agent enables the acylhydrazone dynamic covalent network to possess both low-temperature rearrangement capability and sufficient initial crosslinking strength.

[0019] Waterborne polyurethane adhesives contain a certain amount of waterborne polyurethane dispersion and flexible polyol. During the curing process, the flexible polyol can undergo covalent block / grafting reactions with waterborne polyurethane segments to form flexible siloxane soft segments. This significantly improves the elongation at break, viscoelastic energy dissipation capacity, and interfacial strain mitigation capacity of the self-healing, fatigue-resistant, and hydrogen-barrier bonded coating, thereby buffering the elastic mismatch of the thermoplastic polymer liner / carbon fiber reinforced resin winding layer and reducing the peak value of cyclic strain. Appropriate addition of flexible polyol can improve the viscoelastic energy dissipation capacity of the self-healing, fatigue-resistant, and hydrogen-barrier bonded coating and inhibit interfacial cracking under cyclic strain.

[0020] Waterborne polyurethane adhesives contain a small amount of low surface energy filler, with 2-4 parts (2-4 phr) of low surface energy filler added per 100 parts of polyurethane. This dosage is significantly lower than the 5-30 phr filler loading levels commonly used in inorganic barrier filler / coating systems to achieve a significant barrier effect. The low surface energy filler can construct a low-polarity labyrinth diffusion hydrogen barrier pathway in the self-healing, fatigue-resistant, and hydrogen-barrier bonding coating, extending the hydrogen molecule diffusion path and reducing the diffusion coefficient. Under low addition conditions, it achieves a hydrogen permeation rate reduction of ≥25% without inducing embrittlement or self-healing loss. The low addition amount of low surface energy filler avoids the embrittlement, insufficient interfacial wetting, and restricted dynamic bond migration (which would reduce self-healing efficiency) caused by excessive filler in the self-healing, fatigue-resistant, and hydrogen-barrier bonding coating.

[0021] As a preferred technical solution:

[0022] The self-healing, fatigue-resistant, hydrogen-barrier bonded coating described above uses IPDI (isophorone diisocyanate) and H... 12 MDI (4,4'-dicyclohexylmethane diisocyanate) or HDI (hexamethylene diisocyanate);

[0023] Dihydrazine compounds are SDH (sedanoyl dihydrazine) or ADH (adiazine dihydrazine);

[0024] For example, the preparation process of dihydrazine crosslinking agent is as follows: IPDI and ADH are mixed in an anhydrous solvent (acetone / MEK) at a molar ratio of 1.8-2.2:1, stirred at 50-60°C for 1-3 hours under nitrogen or inert gas protection, and then post-treated (solvent removal and drying) to obtain the product;

[0025] The flexible polyol is hydroxyl-terminated PDMS (hydroxyl-terminated polydimethylsiloxane) or siloxane-polyether block polyol, and the number average molecular weight Mn of the flexible polyol is 2000-5000 g / mol.

[0026] The low surface energy filler is fluorosilane-modified nano-SiO2, fluorinated Al2O3, or alkylsilane-modified SiO2;

[0027] For example, the preparation method of low surface energy filler is as follows: disperse nano-SiO2 in ethanol / water, add fluorosilane and adjust the pH to about 4-5 with acetic acid, react at 60°C for 2-4 hours; filter, wash with ethanol, and dry at 60°C to obtain the filler.

[0028] The self-healing, fatigue-resistant, and hydrogen-barrier composite coating described above has a solid content of 30%-40% in the waterborne polyurethane adhesive and an average particle size of 10-100 nm for the low surface energy filler.

[0029] The self-healing, fatigue-resistant, and hydrogen-barrier bonding coating described above, by weight, the waterborne polyurethane adhesive further includes 1-3 parts of polycarbodiimide crosslinking agent, 3-8 parts of tackifier, 0.3-1.2 parts of rheology modifier, and 0.1-0.5 parts of defoamer;

[0030] Polycarbodiimide crosslinking agent refers to water-dispersible polycarbodiimide crosslinking agent containing -N=C=N- groups, which can react with carboxyl groups in the system to improve hydrolysis resistance and network stability;

[0031] The tackifier can be PBA or its equivalent, used to improve the initial wetting and bonding strength between the self-healing fatigue-resistant hydrogen-barrier bonding coating and the thermoplastic polymer liner / carbon fiber reinforced resin winding layer.

[0032] The rheology modifier can be a HEUR-type polyurethane thickener, used to maintain the viscosity of the adhesive at 1500-3000 mPa·s, which is suitable for spray coating.

[0033] As described above, the self-healing, fatigue-resistant, and hydrogen-barrier bonded coating requires high-speed shearing or ultrasonic dispersion before curing to ensure that the low surface energy filler does not agglomerate in the waterborne polyurethane adhesive. The curing process is divided into two stages: pre-curing and main curing. The pre-curing temperature is 35-45°C and the time is 2-6 hours. The main curing temperature is higher than the pre-curing temperature and is 45-55°C, with a time of 4-10 hours.

[0034] In this invention, curing involves three processes: (i) moisture evaporation / film formation, (ii) crosslinking reaction and network shaping with polycarbodiimide crosslinking agents, and (iii) reversible exchange of acylhydrazone dynamic bonds and interfacial segment rearrangement. In the prior art, the curing of self-healing, fatigue-resistant, and hydrogen-barrier composite coatings can typically be carried out at room temperature or higher. However, if high-temperature rapid curing is used directly, the following problems easily occur: first, stress will be generated inside the coating, forming microporous defects; second, the interface wetting is insufficient; and third, the migration of dynamic bonds is restricted, leading to a reduction in self-healing efficiency. Conversely, if curing is only carried out at room temperature for a long time, problems such as excessively long production cycles and insufficient early strength may arise. Therefore, this invention proposes a "two-stage curing window" of 35-45°C pre-curing (promoting gentle dehydration and interface wetting / penetration) + 45-55°C main curing (completing cross-linking and network stabilization, while maintaining the ability of dynamic bonds to rearrange within the range of ≤50°C), so as to take into account initial shear strength, resistance to damp heat and low temperature self-healing ability without damaging the thermal history of the inner liner or introducing excessive residual stress.

[0035] The present invention also provides a type IV hydrogen storage cylinder, comprising a thermoplastic polymer inner liner, a carbon fiber reinforced resin winding layer, and a self-healing, fatigue-resistant, hydrogen-barrier bonding coating as described above located between the two; the thickness of the self-healing, fatigue-resistant, hydrogen-barrier bonding coating is 50-120 μm. If the thickness is too small, the strain dissipation of the self-healing, fatigue-resistant, hydrogen-barrier bonding coating will be insufficient, which will lead to a decrease in fatigue retention rate. If the thickness is too large, the self-healing, fatigue-resistant, hydrogen-barrier bonding coating will be too soft, which will lead to a decrease in interfacial shear strength.

[0036] As a preferred technical solution:

[0037] The thickness of the self-healing, fatigue-resistant, hydrogen-barrier composite coating of the type IV hydrogen storage cylinder described above is 60-100 μm.

[0038] The thickness of the self-healing, fatigue-resistant, hydrogen-barrier composite coating of the type IV hydrogen storage cylinder described above is 70-90 μm.

[0039] As described above, the thermoplastic polymer inner liner of a type IV hydrogen storage cylinder is made of one or more of PA6, PA11, PA12, HDPE, modified PA6, modified PA11, modified PA12 and modified HDPE, where modification refers to blending, grafting or filling modification.

[0040] The outer surface of the thermoplastic polymer inner liner is treated with plasma, with a power of 80-150W and a duration of 60-180s.

[0041] The carbon fiber reinforced resin winding layer is a carbon fiber / epoxy resin composite winding layer.

[0042] As described above, a type IV hydrogen storage cylinder has a thermoplastic polymer inner liner with a thickness of 5-10 mm and a carbon fiber reinforced resin winding layer with a thickness of 10-70 mm.

[0043] As described above, the composite structure sample of a type IV hydrogen storage cylinder has an interfacial shear strength ≥5.5MPa at 25±2°C. The composite structure sample is obtained by sampling the product after the self-healing anti-fatigue hydrogen barrier coating is combined with the thermoplastic polymer liner and the carbon fiber reinforced resin winding layer.

[0044] The composite structure specimens exhibit self-healing capability at temperatures ≤50°C, with a self-healing efficiency (based on the recovery rate of interfacial shear strength before and after self-healing) ≥75%.

[0045] After undergoing 20,000 repeated pressure cycles with a lower limit of 5 MPa and an upper limit of 70 MPa, the composite structure specimen retains ≥85% of its interfacial shear strength.

[0046] After aging at 70-90°C and 85-95% relative humidity for 5-10 days, the composite structure specimens retain ≥80% of their interfacial shear strength.

[0047] The hydrogen permeability reduction rate of the composite structure sample was ≥25% compared to the control sample. The only difference between the control sample and the composite structure sample was that the control sample did not contain a self-healing, fatigue-resistant, hydrogen-blocking bonding coating.

[0048] Based on the above data, it can be seen that the self-healing fatigue-resistant hydrogen-blocking combined coating of the present invention can achieve both hydrogen blocking and self-healing without sacrificing toughness under low filler loading. Furthermore, during the service life of the Type IV hydrogen storage cylinder, the acylhydrazone dynamic bond rearrangement can be activated by heat preservation at 40-50°C for 2-8 hours to achieve self-healing of interface microcracks.

[0049] This invention also provides a method for preparing a Type IV hydrogen storage cylinder as described above. First, the outer surface of a thermoplastic polymer liner is activated to introduce polar groups. Then, a self-healing, fatigue-resistant, and hydrogen-barrier bonding coating is formed on the activated surface by spraying. Next, carbon fiber reinforced resin is wound and cured on the outer surface of the self-healing, fatigue-resistant, and hydrogen-barrier bonding coating to obtain the Type IV hydrogen storage cylinder. The activation treatment is at least one of plasma treatment, flame treatment, chemical etching, or solvent cleaning. The plasma treatment power is 80-150W, and the time is 60-180s. The activation treatment can improve the initial bonding strength between the thermoplastic polymer liner and the self-healing, fatigue-resistant, and hydrogen-barrier bonding coating. The spraying process requires optimization of the air pressure and spray gun speed.

[0050] Beneficial effects:

[0051] (1) Without significantly increasing the weight, wall thickness and manufacturing complexity of the Type IV high-pressure hydrogen storage cylinder, the present invention constructs a micron-level thin interface flexible energy-dissipating layer between the thermoplastic inner liner and the CFRP winding layer, thereby improving the interface fatigue life from a structural perspective. At the same time, by reducing the surface polarity of the filler and constructing a maze path under low load, the hydrogen permeability is reduced by ≥25% while taking into account toughness and self-healing.

[0052] (2) The present invention establishes a parameterized design window for thickness-ratio-low temperature curing regime, which enables the self-healing anti-fatigue hydrogen barrier combined coating to be stably reproduced and meet the multi-objective threshold requirements. At the same time, it also achieves the simultaneous improvement of the interface of the Type IV hydrogen storage cylinder in terms of hydrogen barrier, self-healing and fatigue life through "self-healing anti-fatigue hydrogen barrier combined coating + ternary synergistic material system + parameterized window". It has the advantages of mild process, environmental protection and easy industrialization.

[0053] (3) This invention achieves the coupling of cyclic strain peak passivation and crack self-repair through “hydroxyl-terminated PDMS flexible segments + dynamic acylhydrazone network + interface layer thickness (50-120μm)”, thereby advocating differentiated functional definitions and application scenarios. Attached Figure Description

[0054] Figure 1 is a schematic diagram of the structure of the Type IV hydrogen storage cylinder of the present invention;

[0055] In the figure, 1-thermoplastic polymer inner liner, 2-self-healing anti-fatigue hydrogen barrier coating, 3-carbon fiber reinforced resin winding layer. Detailed Implementation

[0056] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0057] The manufacturers and brands mentioned in the following embodiments are merely examples. The core of this invention lies in the technical solution itself, and it is not intended to limit specific manufacturers or brands. Products from other manufacturers and brands that meet the technical requirements and performance indicators specified in this invention can also meet the application requirements of this invention and are all feasible choices.

[0058] The test methods for the relevant performance indicators in the following embodiments and comparative examples are as follows:

[0059] Interfacial shear strength: In accordance with GB / T 7124-2008 "Determination of tensile shear strength of adhesives (rigid material to rigid material)", the composite structure specimen was tested using a universal testing machine at an ambient temperature of 25±2°C and a tensile speed of 5 mm / min.

[0060] Self-healing efficiency: The composite structure specimen was tested using the "cut-repair-tension method". The test process was as follows: First, the interfacial shear strength of the composite structure specimen was tested according to the above-mentioned interfacial shear strength test method. Then, the same composite structure specimen was completely cut with a blade. The cut surfaces were then joined together and repaired in a 50°C constant temperature oven for 6 hours. After being taken out and cooled to 25°C, the interfacial shear strength of the repaired composite structure specimen was tested according to the above-mentioned interfacial shear strength test method. Finally, the self-healing efficiency was calculated based on the measured data. The calculation formula is: Self-healing efficiency = (interfacial shear strength after repair / initial interfacial shear strength) × 100%.

[0061] Interfacial shear strength retention rate after 20,000 repeated pressure cycles: First, samples were taken from a Type IV hydrogen storage cylinder, and the interfacial shear strength of the composite structure sample was tested according to the above-mentioned interfacial shear strength test method. Then, according to the fatigue test method in GB / T35544-2017 "Automotive Compressed Hydrogen Aluminum Liner Carbon Fiber Fully Wound Cylinder", the same Type IV hydrogen storage cylinder as described above was subjected to a water pressure cycling test with a lower limit pressure of 5 MPa and an upper limit pressure of 70 MPa, a frequency of 6 times / min, and 20,000 cycles. After the cycle, the composite structure sample was cut from the cylinder section using a water jet, and the interfacial shear strength of the composite structure sample was tested according to the above-mentioned interfacial shear strength test method. Finally, the interfacial shear strength retention rate after 20,000 repeated pressure cycles was calculated based on the measured data. The calculation formula is: Interfacial shear strength retention rate after 20,000 repeated pressure cycles = (Interfacial shear strength of the composite structure sample after fatigue test / Interfacial shear strength of the composite structure sample before fatigue test) × 100%.

[0062] Interfacial shear strength retention rate after aging: First, test the interfacial shear strength of the composite structure sample according to the above interfacial shear strength test method. Then, according to GB / T 2423.50-2012 "Environmental Testing Part 2: Test Methods Test Cy: Constant Humidity and Heat Mainly Used for Accelerated Testing of Components", place the composite structure sample in a constant temperature and humidity chamber at 85°C and 85% relative humidity for 10 days (i.e., 240h) and then take it out. After adjusting it under standard environment (23°C, 50% RH) for 24h, test its interfacial shear strength according to the above interfacial shear strength test method. Finally, calculate the interfacial shear strength retention rate after aging based on the measured results. The calculation formula is: Interfacial shear strength retention rate after aging = (Interfacial shear strength after aging / Interfacial shear strength before aging) × 100%.

[0063] Hydrogen permeability: The hydrogen permeability of the sample was determined in accordance with ISO 15105-1:2007 "Determination of gas transmissibility of plastic films and sheets - Part 1: Differential pressure method"; the test gas was high-purity hydrogen (99.999%), the test temperature was 25°C, the pressure on the high-pressure side was set to the standard pressure, and the permeability coefficient was calculated by measuring the pressure change on the low-pressure side.

[0064] The tensile strength of the film prepared with waterborne polyurethane adhesive was tested using the same curing process as that used in the corresponding embodiment or comparative example for forming a hydrogen-barrier bonding coating on the inner liner of a type IV hydrogen storage cylinder. The specific steps were as follows: the prepared waterborne polyurethane adhesive was scraped onto a polytetrafluoroethylene mold, the wet film thickness was controlled to ensure a dry film thickness of 1.0 mm, and then the mold was placed in an oven for curing according to the curing procedure described in the corresponding embodiment or comparative example. After the film was completely cured and cooled, it was removed and cut into standard dumbbell-shaped specimens (Type 2) using a punching machine, referring to GB / T 528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber". Finally, a universal testing machine was used to test the specimen at a tensile speed of 200 mm / min at 25±2℃. The maximum load and elongation at break were recorded, and the tensile strength of the coating body was calculated.

[0065] Example 1

[0066] A method for preparing a Type IV hydrogen storage cylinder, comprising the following steps:

[0067] (1) PA6 (manufacturer: Ube Industries, Inc., Japan, grade: Nylon 1013B) was used to prepare PA6 thermoplastic inner liner by injection molding-welding process. After degreasing, dust removal and drying treatment of its outer surface, its thickness uniformity, concentricity and air tightness were pre-inspected to obtain a thermoplastic polymer inner liner with a thickness of 5mm; wherein, the mold temperature was 80℃;

[0068] (2) After clamping the thermoplastic polymer liner in the rotary station, the outer surface of the thermoplastic polymer liner is subjected to plasma treatment for 120s with a power of 100W.

[0069] (3) Preparation of waterborne polyurethane adhesive;

[0070] (3.1) Preparation of dihydrazine-based crosslinking agents;

[0071] IPDI and ADH were mixed in a molar ratio of 1:2 and added to an anhydrous solvent (a mixture of acetone and butanone in a volume ratio of 1:1). The mixture was stirred at 55°C for 2 hours under nitrogen atmosphere and then post-treated (removing solvent and drying) to obtain the dihydrazine crosslinking agent.

[0072] The mass ratio of IPDI to anhydrous solvent is 1:5;

[0073] (3.2) Preparation of fluorosilane-modified nano-SiO2;

[0074] Nano-SiO2 with an average particle size of 30 nm was dispersed in an ethanol-water solution (ethanol to water volume ratio of 9:1), perfluorooctyltriethoxysilane was added and the pH was adjusted to 4.5 with acetic acid. After reacting at 60°C for 3 h, the mixture was filtered, washed with ethanol, and dried at 60°C to obtain fluorosilane-modified nano-SiO2.

[0075] The mass ratio of nano-SiO2, aqueous ethanol solution, and perfluorooctyltriethoxysilane is 1:20:0.5;

[0076] (3.3) Preparation of aqueous polyurethane dispersion;

[0077] First, PBA (manufacturer: BASF (China) Co., Ltd., brand name: Lupraphen® 6601 / 3) was dehydrated under vacuum at 110°C for 1 hour. Then, it was cooled to 65°C and IPDI and DMPA were added and reacted for 2.5 hours to obtain a prepolymer. Next, the temperature was further lowered to 60°C and DAAM was added and reacted for 1.5 hours to introduce ketone carbonyl groups. Then, the temperature was further lowered to 45°C and triethylamine was added to neutralize and form a salt. Finally, water was added and dispersed at high speed, and acetone was removed by vacuum distillation to obtain an aqueous polyurethane dispersion. The molar ratio of PBA, IPDI, DMPA, and DAAM was 1:1.8:0.5:0.2.

[0078] The side chains of the obtained waterborne polyurethane dispersion contain β-dicarbonyl structural units that form reversible acylhydrazone bonds by condensation with the hydrazine group of the dihydrazine crosslinking agent under curing conditions, and the main chain of the waterborne polyurethane also contains -NCO structural units that undergo covalent reaction with flexible polyols under curing conditions.

[0079] (3.4) By mass, the aqueous polyurethane dispersion was first stirred at 45°C and 400 rpm. While maintaining continuous stirring, 8 parts of dihydrazine crosslinking agent were added and stirred for 1 hour to introduce acylhydrazone dynamic groups. Then, 6 parts of flexible polyol (hydroxyl-terminated PDMS, number average molecular weight Mn of 3000 g / mol) were added and reacted at 50°C for 40 minutes to form flexible siloxane segments. The temperature was then lowered to 40°C, and 0.2 parts of defoamer BYK-028 and 5 parts of poly(1,4-butanediol adipate) (manufacturer: BASF (China) Co., Ltd., brand name: Lupraphen® 6601 / 3) were added to adjust the viscosity to 2000 mPa·s. Then, 0.8 parts of hydrophobically modified polyurethane thickener (manufacturer: Dow Chemical, brand name: ACRYSOL) were added. RM-8W) and 3 parts of fluorosilane-modified nano-SiO2 were ultrasonically dispersed for 15 min to achieve uniform dispersion. Finally, 2 parts of polycarbodiimide crosslinking agent (manufacturer: Nisshinbo Holdings Co., Ltd., brand name: Carbodilite V-02) were added and stirred for 15 min. After aging at 25°C for 24 h, deionized water was added to obtain a waterborne polyurethane adhesive with a solid content of 35%. The waterborne polyurethane dispersion contained 100 parts by weight of waterborne polyurethane.

[0080] The tensile strength of the adhesive film made with water-based polyurethane adhesive is 18.5 MPa;

[0081] (4) Formation of a self-healing, fatigue-resistant, hydrogen-barrier bonding coating;

[0082] (4.1) The plasma-treated thermoplastic polymer inner liner is rotated at a constant speed of 10 rpm, and then water-based polyurethane adhesive is sprayed at a pressure of 0.3 MPa using a multi-pass cross-spraying process. After spraying, it is left to stand at 25°C for 1 hour to allow the surface to dry. The nozzle outlet diameter used for cross-spraying is 1.2 mm.

[0083] (4.2) The dried thermoplastic polymer inner liner is first pre-cured at 40°C for 4 hours, then cured at 50°C for 6 hours, and then cured at 25°C for 24 hours to obtain a self-healing anti-fatigue hydrogen barrier coating with a thickness of 80μm.

[0084] (5) After the carbon fiber reinforced resin (manufacturer: Toray Industries, Inc., Japan, brand name: T700S fiber) is wound and cured on the outer surface of the self-healing anti-fatigue hydrogen barrier coating to form a carbon fiber reinforced resin winding layer with a thickness of 25mm, the type IV hydrogen storage cylinder is obtained; wherein, the tension during winding is 20N, the curing temperature is 80℃, and the curing time is 4h.

[0085] The final type IV hydrogen storage cylinder, as shown in Figure 1, consists of a thermoplastic polymer inner liner 1, a carbon fiber reinforced resin winding layer 3, and a self-healing, fatigue-resistant, hydrogen-blocking bonding coating 2 located between the two.

[0086] Samples were taken from a Type IV hydrogen storage cylinder to obtain a composite structure sample consisting of a self-healing, fatigue-resistant, hydrogen-blocking combined coating 2, a thermoplastic polymer inner liner 1, and a carbon fiber reinforced resin winding layer 3.

[0087] The obtained composite structure specimen has an interfacial shear strength of 6.35 MPa at 25±2°C.

[0088] The composite structure specimens exhibit self-healing capability at temperatures ≤50°C, with a self-healing efficiency of 83.6%.

[0089] After undergoing 20,000 repeated pressure cycles with a lower limit of 5 MPa and an upper limit of 70 MPa, the composite structure specimen retained 90.4% of its interfacial shear strength.

[0090] After aging at 85°C and 85% relative humidity for 10 days, the composite structure specimen retained 88% of its interfacial shear strength.

[0091] The composite structure sample compared to the control sample (hydrogen permeability 3.5 × 10⁻⁶) -14 mol·m -1 ·s -1 ·Pa -1 The hydrogen permeability reduction rate of the sample was 31%. The only difference between the control sample and the composite structure sample was that the control sample did not have a self-healing, fatigue-resistant, hydrogen-blocking coating.

[0092] Comparative Example 1

[0093] A method for preparing a type IV hydrogen storage cylinder is basically the same as in Example 1, except that step (3.1) is omitted and the dihydrazine crosslinking agent in step (3.4) is replaced with an equal mass of ADH.

[0094] The tensile strength of the adhesive film prepared using the waterborne polyurethane adhesive in this comparative example is 11.5 MPa.

[0095] The final composite structure sample obtained from the prepared Type IV hydrogen storage cylinder had an interfacial shear strength of 4.85 MPa at 25±2°C.

[0096] The composite structure specimens exhibit self-healing capability at temperatures ≤50°C, with a self-healing efficiency of 35.4%.

[0097] After undergoing 20,000 repeated pressure cycles with a lower limit of 5 MPa and an upper limit of 70 MPa, the composite structure specimen retained 72.6% of its interfacial shear strength.

[0098] After aging at 85°C and 85% relative humidity for 10 days, the composite structure specimen retained 68.4% of its interfacial shear strength.

[0099] The hydrogen permeability of the composite structure sample decreased by 25.2% compared to the control sample. The only difference between the control sample and the composite structure sample is that the control sample does not have a self-healing, fatigue-resistant, hydrogen-blocking bonding coating.

[0100] Comparing Comparative Example 1 and Example 1, it can be seen that the fracture strength of the waterborne polyurethane adhesive prepared in this comparative example is significantly reduced. The interfacial shear strength, self-healing efficiency, and interfacial shear strength before and after aging of the Type IV hydrogen storage cylinder prepared with it are significantly reduced, while the hydrogen permeability increases. This is because pure ADH is a small molecule crystal, which has poor compatibility when directly added to the waterborne polyurethane dispersion, and is prone to agglomeration or migration precipitation, resulting in the inability to form a uniform acylhydrazone dynamic network in the polyurethane matrix. Moreover, ADH is a crystalline powder, and its dispersibility in the waterborne polyurethane dispersion is extremely poor, which is equivalent to introducing a large number of micro-defect points in the coating, resulting in stress concentration, which in turn leads to a significant decrease in the fracture strength of the self-healing, fatigue-resistant, and hydrogen-barrier composite coating. In contrast, Example 1 uses IPDI to semi-end-cap ADH, introducing an isophorone cyclic structure with good compatibility with the waterborne polyurethane dispersion, which ensures both dispersibility and retains the active hydrazine group, thereby constructing a highly efficient micro-self-healing network.

[0101] Comparative Example 2

[0102] A method for preparing a type IV hydrogen storage cylinder is basically the same as in Example 1, except that step (3.3) is omitted, and the waterborne polyurethane in step (3.4) is replaced with an equal mass of other waterborne polyurethane (manufacturer: Covestro Polymers (China) Co., Ltd., brand name: Dispercoll U54).

[0103] The tensile strength of the adhesive film prepared using the waterborne polyurethane adhesive in this comparative example is 24.0 MPa.

[0104] The final composite structure sample obtained from the prepared Type IV hydrogen storage cylinder had an interfacial shear strength of 4.18 MPa at 25±2°C.

[0105] Composite structure specimens do not have self-healing properties;

[0106] After undergoing 20,000 repeated pressure cycles with a lower limit of 5 MPa and an upper limit of 70 MPa, the composite structure specimen retained 62.8% of its interfacial shear strength.

[0107] After aging at 85°C and 85% relative humidity for 10 days, the composite structure specimen retained 63% of its interfacial shear strength.

[0108] The hydrogen permeability reduction rate of the composite structure sample was 0% compared to the control sample. The only difference between the control sample and the composite structure sample was that the control sample did not contain a self-healing, fatigue-resistant, hydrogen-blocking bonding coating.

[0109] Comparing Comparative Example 2 and Example 1, it can be seen that the Type IV hydrogen storage cylinder prepared in this comparative example does not have self-healing ability, and its strength retention rate and hydrogen barrier performance after fatigue are extremely poor. This is because ordinary waterborne polyurethane mainly relies on hydrogen bonds or physical entanglement to provide strength, lacks reversible covalent bonds (acylhydrazone bonds) to cope with crack repair, lacks flexible PDMS segment dissipation cyclic strain energy, and does not introduce a low surface energy labyrinth structure to block hydrogen permeation. Therefore, the interface fails rapidly under complex working conditions. In addition, the adhesive film prepared using the waterborne polyurethane adhesive of this comparative example has high fracture strength, but excessively high static strength is often accompanied by low toughness and no self-healing ability. Therefore, the Type IV hydrogen storage cylinder prepared with it does not have self-healing ability, and the interfacial shear strength retention rate is greatly reduced after repeated pressure cycles.

[0110] Example 2

[0111] A method for preparing a Type IV hydrogen storage cylinder, comprising the following steps:

[0112] (1) PA11 (manufacturer: Arkema AG, France, brand name: Rilsan BESNO TL) was used to prepare PA11 thermoplastic inner liner by blow molding process. After degreasing, dust removal and drying treatment of its outer surface, its thickness uniformity, concentricity and air tightness were pre-inspected to obtain a thermoplastic polymer inner liner with a thickness of 5 mm; wherein, the extrusion temperature was 230℃;

[0113] (2) After clamping the thermoplastic polymer liner in the rotary station, the outer surface of the thermoplastic polymer liner is subjected to plasma treatment at a power of 150W for 60s.

[0114] (3) Preparation of waterborne polyurethane adhesive;

[0115] (3.1) Preparation of dihydrazine-based crosslinking agents;

[0116] H 12 MDI and SDH are mixed in a molar ratio of 1:2.2 and added to anhydrous solvent (acetone). The mixture is stirred at 50°C for 3 hours under nitrogen atmosphere and then post-treated (solvent removal and drying) to obtain dihydrazine crosslinking agent.

[0117] H 12 The mass ratio of MDI to anhydrous solvent is 1:5;

[0118] (3.2) Preparation of fluorosilane-modified nano-SiO2;

[0119] Nano-SiO2 with an average particle size of 10 nm was dispersed in an ethanol-water solution (volume ratio of ethanol to water is 9:1), perfluorodecyltriethoxysilane was added and the pH was adjusted to 4 with acetic acid. After reacting at 60°C for 2 h, the mixture was filtered, washed with ethanol, and dried at 60°C to obtain fluorosilane-modified nano-SiO2.

[0120] The mass ratio of nano-SiO2, aqueous ethanol solution, and perfluorodecyltriethoxysilane is 1:20:0.5;

[0121] (3.3) Preparation of aqueous polyurethane dispersion;

[0122] First, PBA (manufacturer: BASF (China) Co., Ltd., brand name: Lupraphen® 6601 / 3) was dehydrated under vacuum at 110°C for 1 hour. Then, it was cooled to 65°C and IPDI and DMPA were added and reacted for 2.5 hours to obtain a prepolymer. Next, the temperature was further lowered to 60°C and DAAM was added and reacted for 1.5 hours to introduce ketone carbonyl groups. Then, the temperature was further lowered to 45°C and triethylamine was added to neutralize and form a salt. Finally, water was added and dispersed at high speed, and acetone was removed by vacuum distillation to obtain an aqueous polyurethane dispersion. The molar ratio of PBA, IPDI, DMPA, and DAAM was 1:1.8:0.5:0.2.

[0123] The side chains of the obtained waterborne polyurethane dispersion contain β-dicarbonyl structural units that form reversible acylhydrazone bonds by condensation with the hydrazine group of the dihydrazine crosslinking agent under curing conditions, and the main chain of the waterborne polyurethane also contains -NCO structural units that undergo covalent reaction with flexible polyols under curing conditions.

[0124] (3.4) By mass, the aqueous polyurethane dispersion was first stirred at 45°C and 400 rpm. While maintaining continuous stirring, 6 parts of dihydrazine crosslinking agent were added and stirred for 1 hour to introduce acylhydrazone dynamic groups. Then, 4 parts of flexible polyol (siloxane-polyether block polyol with a number average molecular weight Mn of 5000 g / mol) were added and reacted at 50°C for 40 minutes to form flexible siloxane segments. The temperature was then lowered to 40°C, and 0.1 parts of defoamer BYK-028 and 3 parts of poly(1,4-butanediol adipate) (manufacturer: BASF (China) Co., Ltd., brand name: Lupraphen® 6601 / 3) were added to adjust the viscosity to 1800 mPa·s. Then, 0.3 parts of hydrophobic modified polyurethane thickener (manufacturer: Dow Chemical, brand name: ACRYSOL) were added. RM-8W) and 2 parts of fluorosilane-modified nano-SiO2 were ultrasonically dispersed for 15 min to achieve uniform dispersion. Finally, 1 part of polycarbodiimide crosslinking agent (manufacturer: Nisshinbo Holdings Co., Ltd., brand name: Carbodilite V-02) was added and stirred for 15 min. After aging at 25°C for 24 h, deionized water was added to obtain a waterborne polyurethane adhesive with a solid content of 30%. The waterborne polyurethane dispersion contained 100 parts by weight of waterborne polyurethane.

[0125] The tensile strength of the adhesive film made with water-based polyurethane adhesive is 16.8 MPa;

[0126] (4) Formation of a self-healing, fatigue-resistant, hydrogen-barrier bonding coating;

[0127] (4.1) The plasma-treated thermoplastic polymer inner liner is rotated at a constant speed of 5 rpm, and then water-based polyurethane adhesive is sprayed at a pressure of 0.4 MPa using a multi-pass cross-spraying process. After spraying, it is left to stand at 27°C for 0.5 h to allow the surface to dry. The nozzle outlet diameter used for cross-spraying is 1.0 mm.

[0128] (4.2) The dried thermoplastic polymer inner liner is first pre-cured at 35°C for 6 hours, then cured at 45°C for 10 hours, and then cured at 23°C for 24 hours to obtain a self-healing anti-fatigue hydrogen barrier coating with a thickness of 50 μm.

[0129] (5) After the carbon fiber reinforced resin (manufacturer: Toray Industries, Inc., Japan, brand name: T700S fiber) is wound and cured on the outer surface of the self-healing anti-fatigue hydrogen barrier coating to form a carbon fiber reinforced resin winding layer with a thickness of 10 mm, the type IV hydrogen storage cylinder is obtained; wherein, the tension during winding is 25 N, the curing temperature is 85 °C, and the curing time is 3 h.

[0130] The final Type IV hydrogen storage cylinder consists of a thermoplastic polymer inner liner, a carbon fiber reinforced resin winding layer, and a self-healing, fatigue-resistant, hydrogen-blocking bonding coating located between the two.

[0131] Samples were taken from a Type IV hydrogen storage cylinder to obtain a composite structure sample consisting of a self-healing, fatigue-resistant, hydrogen-blocking combined coating, a thermoplastic polymer liner, and a carbon fiber reinforced resin winding layer.

[0132] The obtained composite structure specimen has an interfacial shear strength of 6.12 MPa at 25±2°C;

[0133] The composite structure specimens exhibit self-healing capability at temperatures ≤50°C, with a self-healing efficiency of 81.5%.

[0134] After undergoing 20,000 repeated pressure cycles with a lower limit of 5 MPa and an upper limit of 70 MPa, the composite structure specimen retained 88.5% of its interfacial shear strength.

[0135] After aging at 85°C and 85% relative humidity for 10 days, the composite structure specimen retained 86.5% of its interfacial shear strength.

[0136] The composite structure sample compared to the control sample (hydrogen permeability 3.6 × 10⁻⁶) -14 mol·m -1 ·s -1 ·Pa -1 The hydrogen permeability reduction rate of the sample was 30.5%. The only difference between the control sample and the composite structure sample was that the control sample did not have a self-healing, fatigue-resistant, hydrogen-blocking coating.

[0137] Example 3

[0138] A method for preparing a Type IV hydrogen storage cylinder, comprising the following steps:

[0139] (1) Modified PA6 (manufacturer: BASF AG, Germany, brand name: Ultramid B3L) was used to prepare modified PA6 thermoplastic inner liner by injection molding-welding process. After degreasing, dust removal and drying treatment of its outer surface, its thickness uniformity, concentricity and air tightness were pre-inspected to obtain a thermoplastic polymer inner liner with a thickness of 5 mm; wherein, the mold temperature was 85℃.

[0140] (2) After clamping the thermoplastic polymer liner in the rotary station, the outer surface of the thermoplastic polymer liner is subjected to plasma treatment at a power of 100W for 105s.

[0141] (3) Preparation of waterborne polyurethane adhesive;

[0142] (3.1) Preparation of dihydrazine-based crosslinking agents;

[0143] HDI and ADH were mixed in a molar ratio of 1:1.8 and added to anhydrous solvent (MEK). The mixture was stirred at 60°C for 1 hour under nitrogen atmosphere and then post-treated (solvent removal and drying) to obtain the dihydrazine crosslinking agent.

[0144] The mass ratio of HDI to anhydrous solvent is 1:5;

[0145] (3.2) Preparation of fluorosilane-modified nano-SiO2;

[0146] Nano-SiO2 with an average particle size of 50 nm was dispersed in an ethanol aqueous solution (volume ratio of ethanol to water is 9:1), perfluorooctyltrimethoxysilane was added and the pH was adjusted to 5 with acetic acid. After reacting at 60°C for 4 h, the mixture was filtered, washed with ethanol, and dried at 60°C to obtain fluorosilane-modified nano-SiO2.

[0147] The mass ratio of nano-SiO2, aqueous ethanol solution, and perfluorooctyltrimethoxysilane is 1:20:0.5;

[0148] (3.3) Preparation of aqueous polyurethane dispersion;

[0149] First, PBA (manufacturer: BASF (China) Co., Ltd., brand name: Lupraphen® 6601 / 3) was dehydrated under vacuum at 110℃ for 1 hour. Then, it was cooled to 65℃ and IPDI and DMPA were added and reacted for 2.5 hours to obtain a prepolymer. Next, it was cooled to 60℃ and 2-hydroxyethyl acetoacetate was added and reacted for 1.5 hours to end-cap and introduce acetoacetate structural units into the main chain. Then, it was cooled to 45℃ and triethylamine was added to neutralize and form a salt. Finally, water was added and dispersed at high speed, and acetone was removed by vacuum distillation to obtain an aqueous polyurethane dispersion. The molar ratio of PBA, IPDI, DMPA, and 2-hydroxyethyl acetoacetate was 1:1.8:0.5:0.2.

[0150] The obtained waterborne polyurethane dispersion contains acetoacetate structural units in the main chain of the waterborne polyurethane that form reversible acylhydrazone bonds by condensation with the hydrazine group of the dihydrazine crosslinking agent under curing conditions. The main chain of the waterborne polyurethane also contains -NCO structural units that undergo covalent reaction with flexible polyols under curing conditions.

[0151] (3.4) By mass, the aqueous polyurethane dispersion was first stirred at 45°C and 400 rpm. While maintaining continuous stirring, 10 parts of dihydrazine crosslinking agent were added and stirred for 1 hour to introduce acylhydrazone dynamic groups. Then, 8 parts of flexible polyol (hydroxyl-terminated PDMS, number average molecular weight Mn of 2000 g / mol) were added and reacted at 50°C for 40 minutes to form flexible siloxane segments. The temperature was then lowered to 40°C, and 0.5 parts of defoamer BYK-028 and 8 parts of poly(1,4-butanediol adipate) (BASF (China) Co., Ltd., brand name Lupraphen® 6601 / 3) were added to adjust the viscosity to 2200 mPa·s. Then, 1.2 parts of hydrophobic modified polyurethane thickener (manufacturer: Dow Chemical, brand name ACRYSOL) were added. RM-8W) and 4 parts of fluorosilane-modified nano-SiO2 were ultrasonically dispersed for 20 min to achieve uniform dispersion. Finally, 3 parts of polycarbodiimide crosslinking agent (manufacturer: Nisshinbo Holdings Co., Ltd., brand name: Carbodilite V-02) were added and stirred for 15 min. After aging at 25°C for 24 h, deionized water was added to obtain a waterborne polyurethane adhesive with a solid content of 40%. The waterborne polyurethane dispersion contained 100 parts by weight of waterborne polyurethane.

[0152] The tensile strength of the adhesive film made with water-based polyurethane adhesive is 15.2 MPa;

[0153] (4) Formation of a self-healing, fatigue-resistant, hydrogen-barrier bonding coating;

[0154] (4.1) The plasma-treated thermoplastic polymer inner liner is rotated at a constant speed of 20 rpm, and then water-based polyurethane adhesive is sprayed at a pressure of 0.2 MPa using a multi-pass cross-spraying process. After spraying, it is left to stand at 23°C for 2 hours to allow the surface to dry. The nozzle outlet diameter used for cross-spraying is 1.5 mm.

[0155] (4.2) The dried thermoplastic polymer inner liner is first pre-cured at 45°C for 2 hours, then cured at 55°C for 4 hours, and then cured at 27°C for 12 hours to obtain a self-healing anti-fatigue hydrogen barrier coating with a thickness of 120μm.

[0156] (5) After the carbon fiber reinforced resin (manufacturer: Toray Industries, Inc., Japan, brand name: T700S fiber) is wound and cured on the outer surface of the self-healing anti-fatigue hydrogen barrier coating to form a carbon fiber reinforced resin winding layer with a thickness of 30mm, the type IV hydrogen storage cylinder is obtained; wherein, the tension during winding is 15N, the curing temperature is 75℃, and the curing time is 5h.

[0157] The final Type IV hydrogen storage cylinder consists of a thermoplastic polymer inner liner, a carbon fiber reinforced resin winding layer, and a self-healing, fatigue-resistant, hydrogen-blocking bonding coating located between the two.

[0158] Samples were taken from a Type IV hydrogen storage cylinder to obtain a composite structure sample consisting of a self-healing, fatigue-resistant, hydrogen-blocking combined coating, a thermoplastic polymer liner, and a carbon fiber reinforced resin winding layer.

[0159] The obtained composite structure specimen has an interfacial shear strength of 5.95 MPa at 25±2°C.

[0160] The composite structure specimens exhibit self-healing capability at temperatures ≤50°C, with a self-healing efficiency of 85.2%.

[0161] After undergoing 20,000 repeated pressure cycles with a lower limit of 5 MPa and an upper limit of 70 MPa, the composite structure specimen retained 89.1% of its interfacial shear strength.

[0162] After aging at 85°C and 85% relative humidity for 10 days, the composite structure specimen retained 87.2% of its interfacial shear strength.

[0163] The composite structure sample compared to the control sample (hydrogen permeability 3.4 × 10⁻⁶) -14 mol·m -1 ·s -1 ·Pa -1 The hydrogen permeability reduction rate of the sample was 32.8%. The only difference between the control sample and the composite structure sample was that the control sample did not contain a self-healing, fatigue-resistant, hydrogen-blocking coating.

[0164] Example 4

[0165] A method for preparing a Type IV hydrogen storage cylinder, comprising the following steps:

[0166] (1) Modified PA12 (manufacturer: Evonik Industries Group, Germany, brand name: Vestamid L1901) was used to prepare modified PA12 thermoplastic inner liner by blow molding process. After degreasing, dust removal and drying treatment of its outer surface, its thickness uniformity, concentricity and air tightness were pre-inspected to obtain a thermoplastic polymer inner liner with a thickness of 8 mm; wherein, the extrusion temperature was 240℃.

[0167] (2) After clamping the thermoplastic polymer liner in the rotary station, the outer surface of the thermoplastic polymer liner is subjected to plasma treatment at a power of 80W for 180s.

[0168] (3) Preparation of waterborne polyurethane adhesive;

[0169] (3.1) Preparation of dihydrazine-based crosslinking agents;

[0170] IPDI and ADH were mixed in a molar ratio of 1:2 and added to an anhydrous solvent (a mixture of acetone and butanone in a volume ratio of 1:1). The mixture was stirred at 55°C for 2 hours under nitrogen atmosphere and then post-treated (removing solvent and drying) to obtain the dihydrazine crosslinking agent.

[0171] The mass ratio of IPDI to anhydrous solvent is 1:5;

[0172] (3.2) Preparation of fluorosilane-modified nano-SiO2;

[0173] Nano-SiO2 with an average particle size of 30 nm was dispersed in an ethanol-water solution (ethanol to water volume ratio of 9:1), perfluorooctyltriethoxysilane was added and the pH was adjusted to 4.5 with acetic acid. After reacting at 60°C for 3 h, the mixture was filtered, washed with ethanol, and dried at 60°C to obtain fluorosilane-modified nano-SiO2.

[0174] The mass ratio of nano-SiO2, aqueous ethanol solution, and perfluorooctyltriethoxysilane is 1:20:0.5;

[0175] (3.3) Preparation of aqueous polyurethane dispersion;

[0176] First, PBA (manufacturer: BASF (China) Co., Ltd., brand name: Lupraphen® 6601 / 3) was dehydrated under vacuum at 110°C for 1 hour. Then, it was cooled to 65°C and IPDI and DMPA were added and reacted for 2.5 hours to obtain a prepolymer. Next, the temperature was further lowered to 60°C and DAAM was added and reacted for 1.5 hours to introduce ketone carbonyl groups. Then, the temperature was further lowered to 45°C and triethylamine was added to neutralize and form a salt. Finally, water was added and dispersed at high speed, and acetone was removed by vacuum distillation to obtain an aqueous polyurethane dispersion. The molar ratio of PBA, IPDI, DMPA, and DAAM was 1:1.8:0.5:0.2.

[0177] The side chains of the obtained waterborne polyurethane dispersion contain β-dicarbonyl structural units that form reversible acylhydrazone bonds by condensation with the hydrazine group of the dihydrazine crosslinking agent under curing conditions, and the main chain of the waterborne polyurethane also contains -NCO structural units that undergo covalent reaction with flexible polyols under curing conditions.

[0178] (3.4) By mass, the aqueous polyurethane dispersion was first stirred at 45°C and 400 rpm. While maintaining continuous stirring, 8 parts of dihydrazine crosslinking agent were added and stirred for 1 hour to introduce acylhydrazone dynamic groups. Then, 6 parts of flexible polyol (hydroxyl-terminated PDMS, number average molecular weight Mn of 3000 g / mol) were added and reacted at 50°C for 40 minutes to form flexible siloxane segments. The temperature was then lowered to 40°C, and 0.2 parts of defoamer BYK-028 and 5 parts of poly(1,4-butanediol adipate) (BASF (China) Co., Ltd., brand name Lupraphen® 6601 / 3) were added to adjust the viscosity to 2000 mPa·s. Then, 0.8 parts of hydrophobically modified polyurethane thickener (manufacturer: Dow Chemical, brand name ACRYSOL) were added. RM-8W) and 3 parts of fluorosilane-modified nano-SiO2 were ultrasonically dispersed for 15 min to achieve uniform dispersion. Finally, 2 parts of polycarbodiimide crosslinking agent (manufacturer: Nisshinbo Holdings Co., Ltd., brand name: Carbodilite V-02) were added and stirred for 15 min. After aging at 25°C for 24 h, deionized water was added to obtain a waterborne polyurethane adhesive with a solid content of 35%. The waterborne polyurethane dispersion contained 100 parts by weight of waterborne polyurethane.

[0179] The tensile strength of the adhesive film made with water-based polyurethane adhesive is 18.0 MPa;

[0180] (4) Formation of a self-healing, fatigue-resistant, hydrogen-barrier bonding coating;

[0181] (4.1) The plasma-treated thermoplastic polymer inner liner is rotated at a constant speed of 10 rpm, and then water-based polyurethane adhesive is sprayed at a pressure of 0.3 MPa using a multi-pass cross-spraying process. After spraying, it is left to stand at 25°C for 1 hour to allow the surface to dry. The nozzle outlet diameter used for cross-spraying is 1.2 mm.

[0182] (4.2) The dried thermoplastic polymer inner liner is first pre-cured at 40°C for 4 hours, then cured at 50°C for 6 hours, and then cured at 25°C for 24 hours to obtain a self-healing anti-fatigue hydrogen barrier coating with a thickness of 100μm.

[0183] (5) After the carbon fiber reinforced resin (manufacturer: Toray Industries, Inc., Japan, brand name: T700S fiber) is wound and cured on the outer surface of the self-healing anti-fatigue hydrogen barrier coating to form a carbon fiber reinforced resin winding layer with a thickness of 35mm, the type IV hydrogen storage cylinder is obtained; wherein, the tension during winding is 20N, the curing temperature is 80℃, and the curing time is 4h.

[0184] The final Type IV hydrogen storage cylinder consists of a thermoplastic polymer inner liner, a carbon fiber reinforced resin winding layer, and a self-healing, fatigue-resistant, hydrogen-blocking bonding coating located between the two.

[0185] Samples were taken from a Type IV hydrogen storage cylinder to obtain a composite structure sample consisting of a self-healing, fatigue-resistant, hydrogen-blocking combined coating, a thermoplastic polymer liner, and a carbon fiber reinforced resin winding layer.

[0186] The obtained composite structure specimen has an interfacial shear strength of 6.28 MPa at 25±2°C;

[0187] The composite structure specimens exhibit self-healing capability at temperatures ≤50°C, with a self-healing efficiency of 82.8%.

[0188] After undergoing 20,000 repeated pressure cycles with a lower limit of 5 MPa and an upper limit of 70 MPa, the composite structure specimen retained 90.1% of its interfacial shear strength.

[0189] After aging at 85°C and 85% relative humidity for 10 days, the composite structure specimen retained 87.8% of its interfacial shear strength.

[0190] The composite structure sample compared to the control sample (hydrogen permeability 3.5 × 10⁻⁶) -14 mol·m -1 ·s -1 ·Pa -1 The hydrogen permeability reduction rate of the sample was 31.5%. The only difference between the control sample and the composite structure sample was that the control sample did not have a self-healing, fatigue-resistant, hydrogen-blocking coating.

[0191] Example 5

[0192] A method for preparing a Type IV hydrogen storage cylinder, comprising the following steps:

[0193] (1) HDPE (manufacturer: China National Petroleum Corporation, grade: HD5502GA) was blow-molded to prepare HDPE thermoplastic inner liner. After degreasing, dust removal and drying treatment of its outer surface, its thickness uniformity, concentricity and air tightness were pre-inspected to obtain a thermoplastic polymer inner liner with a thickness of 10 mm; wherein, the extrusion temperature was 200℃.

[0194] (2) After clamping the thermoplastic polymer liner in the rotary station, the outer surface of the thermoplastic polymer liner is subjected to plasma treatment at a power of 120W for 90s.

[0195] (3) Preparation of waterborne polyurethane adhesive;

[0196] (3.1) Preparation of dihydrazine-based crosslinking agents;

[0197] IPDI and ADH were mixed in a molar ratio of 1:2 and added to an anhydrous solvent (a mixture of acetone and butanone in a volume ratio of 1:1). The mixture was stirred at 55°C for 2 hours under nitrogen atmosphere and then post-treated (removing solvent and drying) to obtain the dihydrazine crosslinking agent.

[0198] The mass ratio of IPDI to anhydrous solvent is 1:5;

[0199] (3.2) Preparation of fluorosilane-modified nano-SiO2;

[0200] Nano-SiO2 with an average particle size of 30 nm was dispersed in an ethanol-water solution (ethanol to water volume ratio of 9:1), perfluorooctyltriethoxysilane was added and the pH was adjusted to 4.5 with acetic acid. After reacting at 60°C for 3 h, the mixture was filtered, washed with ethanol, and dried at 60°C to obtain fluorosilane-modified nano-SiO2.

[0201] The mass ratio of nano-SiO2, aqueous ethanol solution, and perfluorooctyltriethoxysilane is 1:20:0.5;

[0202] (3.3) Preparation of aqueous polyurethane dispersion;

[0203] First, PBA (manufacturer: BASF (China) Co., Ltd., brand name: Lupraphen® 6601 / 3) was dehydrated under vacuum at 110°C for 1 hour. Then, it was cooled to 65°C and IPDI and DMPA were added and reacted for 2.5 hours to obtain a prepolymer. Next, the temperature was further lowered to 60°C and DAAM was added and reacted for 1.5 hours to introduce ketone carbonyl groups. Then, the temperature was further lowered to 45°C and triethylamine was added to neutralize and form a salt. Finally, water was added and dispersed at high speed, and acetone was removed by vacuum distillation to obtain an aqueous polyurethane dispersion. The molar ratio of PBA, IPDI, DMPA, and DAAM was 1:1.8:0.5:0.2.

[0204] The side chains of the obtained waterborne polyurethane dispersion contain β-dicarbonyl structural units that form reversible acylhydrazone bonds by condensation with the hydrazine group of the dihydrazine crosslinking agent under curing conditions, and the main chain of the waterborne polyurethane also contains -NCO structural units that undergo covalent reaction with flexible polyols under curing conditions.

[0205] (3.4) By mass, the aqueous polyurethane dispersion was first stirred at 45°C and 400 rpm. While maintaining continuous stirring, 8 parts of dihydrazine crosslinking agent were added and stirred for 1 hour to introduce acylhydrazone dynamic groups. Then, 6 parts of flexible polyol (hydroxyl-terminated PDMS, number average molecular weight Mn of 3000 g / mol) were added and reacted at 50°C for 40 minutes to form flexible siloxane segments. The temperature was then lowered to 40°C, and 0.2 parts of defoamer BYK-028 and 5 parts of poly(1,4-butanediol adipate) (BASF (China) Co., Ltd., brand name Lupraphen® 6601 / 3) were added to adjust the viscosity to 2000 mPa·s. Then, 0.8 parts of hydrophobically modified polyurethane thickener (manufacturer: Dow Chemical, brand name ACRYSOL) were added. RM-8W) and 3 parts of fluorosilane-modified nano-SiO2 were ultrasonically dispersed for 15 min to achieve uniform dispersion. Finally, 2 parts of polycarbodiimide crosslinking agent (manufacturer: Nisshinbo Holdings Co., Ltd., brand name: Carbodilite V-02) were added and stirred for 15 min. After aging at 25°C for 24 h, deionized water was added to obtain a waterborne polyurethane adhesive with a solid content of 35%. The waterborne polyurethane dispersion contained 100 parts by weight of waterborne polyurethane.

[0206] The tensile strength of the adhesive film made with water-based polyurethane adhesive is 19.2 MPa;

[0207] (4) Formation of a self-healing, fatigue-resistant, hydrogen-barrier bonding coating;

[0208] (4.1) The plasma-treated thermoplastic polymer inner liner is rotated at a constant speed of 15 rpm, and then water-based polyurethane adhesive is sprayed at a pressure of 0.3 MPa using a multi-pass cross-spraying process. After spraying, it is left to stand at 25°C for 1 hour to allow the surface to dry. The nozzle outlet diameter used for cross-spraying is 1.2 mm.

[0209] (4.2) The dried thermoplastic polymer liner is first pre-cured at 40°C for 4 hours, then cured at 50°C for 6 hours, and then cured at 25°C for 24 hours to obtain a self-healing anti-fatigue hydrogen barrier coating with a thickness of 60μm.

[0210] (5) After the carbon fiber reinforced resin (manufacturer: Toray Industries, Inc., Japan, brand name: T700S fiber) is wound and cured on the outer surface of the self-healing anti-fatigue hydrogen barrier coating to form a carbon fiber reinforced resin winding layer with a thickness of 70 mm, the type IV hydrogen storage cylinder is obtained; wherein, the tension during winding is 20 N, the curing temperature is 80 °C, and the curing time is 4 h.

[0211] The final Type IV hydrogen storage cylinder consists of a thermoplastic polymer inner liner, a carbon fiber reinforced resin winding layer, and a self-healing, fatigue-resistant, hydrogen-blocking bonding coating located between the two.

[0212] Samples were taken from a Type IV hydrogen storage cylinder to obtain a composite structure sample consisting of a self-healing, fatigue-resistant, hydrogen-blocking combined coating, a thermoplastic polymer liner, and a carbon fiber reinforced resin winding layer.

[0213] The obtained composite structure specimen has an interfacial shear strength of 6.40 MPa at 25±2°C;

[0214] The composite structure specimens exhibit self-healing capability at temperatures ≤50°C, with a self-healing efficiency of 83.1%.

[0215] After undergoing 20,000 repeated pressure cycles with a lower limit of 5 MPa and an upper limit of 70 MPa, the composite structure specimen retained 89.5% of its interfacial shear strength.

[0216] After aging at 85°C and 85% relative humidity for 10 days, the composite structure specimen retained 88.2% of its interfacial shear strength.

[0217] The composite structure sample compared to the control sample (hydrogen permeability 5.5 × 10⁻⁶) -14 mol·m -1 ·s -1 ·Pa -1 The hydrogen permeability reduction rate of the sample was 30.8%. The only difference between the control sample and the composite structure sample was that the control sample did not contain a self-healing, fatigue-resistant, hydrogen-blocking bonding coating.

[0218] Example 6

[0219] A method for preparing a type IV hydrogen storage cylinder is basically the same as in Example 5, except that step-by-step curing is not used in step (4.2), and the dried thermoplastic polymer liner is cured at 50°C for 10 hours and then maintained.

[0220] The final Type IV hydrogen storage cylinder consists of a thermoplastic polymer inner liner, a carbon fiber reinforced resin winding layer, and a self-healing, fatigue-resistant, hydrogen-blocking bonding coating located between the two.

[0221] Samples were taken from a Type IV hydrogen storage cylinder to obtain a composite structure sample consisting of a self-healing, fatigue-resistant, hydrogen-blocking combined coating, a thermoplastic polymer liner, and a carbon fiber reinforced resin winding layer.

[0222] The obtained composite structure specimen has an interfacial shear strength of 5.82 MPa at 25±2°C;

[0223] The composite structure specimens exhibit self-healing capability at temperatures ≤50°C, with a self-healing efficiency of 78.5%.

[0224] After undergoing 20,000 repeated pressure cycles with a lower limit of 5 MPa and an upper limit of 70 MPa, the composite structure specimen retained 86.4% of its interfacial shear strength.

[0225] After aging at 85°C and 85% relative humidity for 10 days, the composite structure specimen retained 84.2% of its interfacial shear strength.

[0226] The hydrogen permeability of the composite structure sample decreased by 28.5% compared to the control sample. The only difference between the control sample and the composite structure sample is that the control sample does not have a self-healing, fatigue-resistant, hydrogen-blocking bonding coating.

Claims

1. A self-healing, fatigue-resistant, hydrogen-inhibiting bonding coating, characterized in that, It is formed by curing waterborne polyurethane adhesive; by weight, the waterborne polyurethane adhesive includes water, waterborne polyurethane dispersion, 6-10 parts of dihydrazine crosslinking agent, 4-8 parts of flexible polyol and 2-4 parts of low surface energy filler, wherein the waterborne polyurethane in the waterborne polyurethane dispersion has 100 parts by weight; the main chain or side chain of the waterborne polyurethane in the waterborne polyurethane dispersion contains structural units that condense with the hydrazine group of the dihydrazine crosslinking agent under curing conditions to form reversible acylhydrazone bonds, and also contains structural units that undergo covalent reaction with the flexible polyol under curing conditions; the flexible polyol is hydroxyl-terminated PDMS or siloxane-polyether block polyol, and the number average molecular weight Mn of the flexible polyol is 2000-5000 g / mol; the dihydrazine crosslinking agent is generated by reacting diisocyanate with dihydrazine compounds.

2. The self-healing, fatigue-resistant, hydrogen-barrier bonding coating according to claim 1, characterized in that, Diisocyanate is IPDI, H 12 MDI or HDI; dihydrazine compounds are SDH or ADH; low surface energy fillers are fluorosilane-modified nano-SiO2, fluorinated Al2O3, or alkylsilane-modified SiO2.

3. The self-healing, fatigue-resistant, hydrogen-barrier bonding coating according to claim 1, characterized in that, The solid content of the waterborne polyurethane adhesive is 30%-40%; the average particle size of the low surface energy filler is 10-100nm.

4. The self-healing, fatigue-resistant, hydrogen-barrier bonding coating according to any one of claims 1 to 3, characterized in that, By weight, waterborne polyurethane adhesives also include 1-3 parts of polycarbodiimide crosslinking agent, 3-8 parts of tackifier, 0.3-1.2 parts of rheology modifier and 0.1-0.5 parts of defoamer.

5. The self-healing, fatigue-resistant, hydrogen-barrier bonding coating according to claim 4, characterized in that, The curing process is divided into two stages: pre-curing and main curing. The pre-curing temperature is 35-45°C and the time is 2-6 hours. The main curing temperature is higher than the pre-curing temperature and is 45-55°C, with a time of 4-10 hours.

6. A type IV hydrogen storage cylinder, characterized in that, It includes a thermoplastic polymer inner liner, a carbon fiber reinforced resin winding layer, and a self-healing, fatigue-resistant, hydrogen-barrier bonding coating as described in any one of claims 1 to 5 located between the two; the thickness of the self-healing, fatigue-resistant, hydrogen-barrier bonding coating is 50-120 μm.

7. A type IV hydrogen storage cylinder according to claim 6, characterized in that, The thermoplastic polymer inner liner is made of one or more of PA6, PA11, PA12, HDPE, modified PA6, modified PA11, modified PA12, and modified HDPE; the outer surface of the thermoplastic polymer inner liner is plasma treated with a power of 80-150W for 60-180s; the carbon fiber reinforced resin winding layer is a carbon fiber / epoxy resin composite material winding layer.

8. A type IV hydrogen storage cylinder according to claim 6, characterized in that, The thickness of the thermoplastic polymer inner liner is 5-10mm, and the thickness of the carbon fiber reinforced resin winding layer is 10-70mm.

9. A type IV hydrogen storage cylinder according to claim 6, characterized in that, The composite structure specimen exhibits an interfacial shear strength ≥5.5 MPa at 25±2°C. The specimens were obtained by sampling the product after combining a self-healing, fatigue-resistant, hydrogen-barrier coating with a thermoplastic polymer liner and a carbon fiber reinforced resin winding layer. The composite structure specimen demonstrates self-healing capability at ≤50°C with a self-healing efficiency ≥75%. After undergoing 20,000 repeated pressure cycles with a lower limit of 5 MPa and an upper limit of 70 MPa, the composite structure specimen retains an interfacial shear strength ≥85%. After aging for 5-10 days at 70-90°C and 85-95% relative humidity, the composite structure specimen retains an interfacial shear strength ≥80%. The hydrogen permeability reduction rate of the composite structure specimen compared to the control sample is ≥25%. The only difference between the control sample and the composite structure specimen is that the control sample does not contain the self-healing, fatigue-resistant, hydrogen-barrier coating.

10. A method for preparing a Type IV hydrogen storage cylinder as described in any one of claims 6 to 9, characterized in that, First, the outer surface of the thermoplastic polymer inner liner is activated to introduce polar groups. Then, a self-healing, fatigue-resistant, and hydrogen-barrier bonding coating is formed on the activated surface by spraying. Finally, carbon fiber reinforced resin is wound and cured on the outer surface of the self-healing, fatigue-resistant, and hydrogen-barrier bonding coating to obtain the Type IV hydrogen storage cylinder.

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