Modified gas insulation film, preparation method thereof and liquid oxygen storage tank composite material

Abstract

The invention provides a modified gas barrier film, a preparation method thereof and a liquid oxygen storage tank composite material, and belongs to the technical field of aerospace materials. The method comprises the following steps: coating the surface of a fluorocarbon film with a calcium chloride solution, drying, and carrying out low-temperature plasma treatment on the hydrophilic modified film to obtain the modified gas barrier film. The fluorocarbon film can be compatible with liquid oxygen, low-temperature plasma is adopted for modification, the hydrophilicity can be improved, a calcium chloride solution is coated, polar groups are introduced into calcium chloride, chlorine free radicals can react with the fluorocarbon film to form C-Cl bonds or other oxygen-containing groups, attenuation of hydrophilic groups is delayed through the crosslinking effect of calcium ions, and the hydrophilicity of the fluorocarbon film is improved. The hydrophilic treatment effect is further improved, the prepared modified gas barrier film is good in hydrophilicity, the water contact angle reaches 20 degrees or below, the hydrophilicity is lasting, the problem that a fluorocarbon compound and a carbon fiber reinforced resin-based composite material cannot be bonded is solved, and then gas permeation of the composite material for the liquid oxygen storage tank is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of aerospace materials technology, and in particular to a modified gas-barrier membrane and its preparation method, and a liquid oxygen storage tank composite material. Background Technology

[0002] The shift from metal to composite materials for cryogenic propellant tanks in launch vehicles has become an inevitable trend in the global aerospace industry. Carbon fiber reinforced resin matrix composites possess advantages such as high specific strength and high specific stiffness, making them the preferred structural material for next-generation spacecraft. Liquid oxygen tanks, as essential structural components of spacecraft, account for over 60% of the spacecraft's dry weight. Compared to metal tanks, composite material tanks can achieve a 20%–40% weight reduction and a launch cost reduction of approximately 25%, significantly improving launch efficiency and economic benefits. Therefore, researching safe and reliable composite liquid oxygen tanks is of significant strategic importance for enhancing the equipment capabilities of various countries and developing the aerospace industry.

[0003] However, carbon fiber reinforced resin matrix composite liquid oxygen tanks suffer from leakage problems in cryogenic liquid oxygen environments (90K). Typical operating temperatures for liquid hydrogen and liquid oxygen fuel tanks range from -253℃ (20K) to -183℃ (90K). To prevent fuel vaporization, the operating pressure of cryogenic propellant tanks is typically maintained at 0.2–0.3 MPa. On one hand, due to the mismatch in thermal expansion coefficients between the resin matrix and carbon fiber, significant internal stress is generated within the resin matrix at cryogenic temperatures, leading to microcracks at the carbon fiber / resin interface. Furthermore, the poor toughness of the resin matrix makes it highly susceptible to microcrack formation at low temperatures, weakening the overall cryogenic mechanical properties. Ultimately, under the combined action of internal and mechanical stresses, the cracks propagate rapidly, causing tank leakage. On the other hand, carbon fiber composites often exhibit micropores or microcracks during winding and curing, allowing oxygen molecules to easily penetrate the composite layers and cause leakage. In summary, potential leakage pathways for liquid oxygen tanks include pores and defects within the matrix, the initiation and propagation of microcracks within the matrix under thermal and mechanical loads, and interlayer delamination damage and propagation. Flexible polymer toughening resins mainly include organosilicon oligomers, reactive liquid rubbers, reactive polyurethanes, flexible curing agents, rubber elastomers, and thermoplastic resins; nanomaterial toughening resins mainly include nano-silica, nano-titanium dioxide, carbon nanotubes, layered silicates, graphene, graphite nanosheets, and nanofibers. These methods reduce the generation of microcracks in the composite matrix to some extent and improve low-temperature leakage, but they cannot solve the problem of interlaminar leakage in composite materials. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a modified gas barrier membrane and its preparation method, as well as a liquid oxygen storage tank composite material. The modified gas barrier membrane obtained by this invention has good and durable hydrophilicity, solves the problem of the inability to bond fluorocarbon compounds to carbon fiber reinforced resin matrix composite materials, and thus effectively reduces gas permeation in the liquid oxygen storage tank composite material.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a modified gas-barrier membrane, which is obtained by a method comprising the following steps:

[0007] A hydrophilic modified film is obtained by coating the surface of a fluorocarbon film with a calcium chloride solution and then drying it.

[0008] The hydrophilic modified membrane was subjected to low-temperature plasma treatment to obtain the modified gas barrier membrane.

[0009] Preferably, the concentration of the calcium chloride solution is 0.1–5 wt%.

[0010] Preferably, the coating is applied by spraying, and the number of spraying operations is 2 to 3.

[0011] Preferably, the spraying conditions include: a nozzle diameter of 0.2 to 0.5 mm, a pressure of 0.2 to 0.5 MPa, and a spraying distance of 10 to 20 cm.

[0012] Preferably, the fluorocarbon film includes one or more of fluorinated ethylene propylene copolymer film (FEP film), perfluoroalkoxy polymer film (PFA film), and polyvinyl fluoride film (PVF film).

[0013] Preferably, the thickness of the fluorocarbon film is 200–300 μm.

[0014] Preferably, the conditions for the low-temperature plasma treatment include: oxygen plasma treatment time of 30–180 s, treatment power of 30–100 W, and gas flow rate of 100 sccm.

[0015] The present invention also provides a modified gas barrier membrane prepared by the preparation method described in the above technical solution.

[0016] The present invention also provides a liquid oxygen storage tank composite material, comprising a first carbon fiber reinforced resin matrix composite material, the modified gas barrier membrane described in the above technical solution, and a second carbon fiber reinforced resin matrix composite material stacked sequentially.

[0017] This invention also provides a method for preparing the liquid oxygen storage tank composite material described in the above technical solution, comprising the following steps:

[0018] The modified gas barrier membrane is placed between two layers of carbon fiber reinforced resin matrix composite prepreg, and then hot-pressed and cured to obtain the liquid oxygen storage tank composite material.

[0019] This invention provides a method for preparing a modified gas barrier membrane, which is obtained by a method including the following steps: coating the surface of a fluorocarbon thin film with a calcium chloride solution and then drying it to obtain a hydrophilic modified membrane; subjecting the hydrophilic modified membrane to low-temperature plasma treatment to obtain the modified gas barrier membrane.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] In this invention, the fluorocarbon film can pass the liquid oxygen impact sensitivity test and is compatible with liquid oxygen. Combined with a calcium chloride solution coating, calcium chloride introduces polar groups. The chlorine species in calcium chloride include chlorine free radicals and chloride ions. On the one hand, it bombards the polymer surface, increasing the surface roughness; on the other hand, it can react with the fluorocarbon film to form C-Cl bonds or other oxygen-containing groups. The role of calcium ions is to delay the decay of hydrophilic groups through cross-linking, improving the durability of the hydrophilic treatment effect. Modification by low-temperature plasma treatment can further improve hydrophilicity. The resulting modified gas barrier film has good hydrophilicity, with a water contact angle of less than 30°, and the hydrophilicity is long-lasting. This solves the problem that fluorocarbon compounds cannot bond with carbon fiber reinforced resin matrix composites, thereby effectively reducing gas permeation of the composite material in the liquid oxygen storage tank.

[0022] The present invention also provides a method for using the modified gas barrier membrane in liquid oxygen storage tank composite materials, which is prepared by hot pressing and curing the modified gas barrier membrane and two layers of carbon fiber reinforced resin matrix composite prepreg, providing a safer and more reliable approach for the development of next-generation aerospace vehicle composite liquid oxygen storage tanks. Attached Figure Description

[0023] Figure 1 This is a schematic diagram showing the positional relationship between the modified air-barrier membrane and the carbon fiber reinforced resin matrix composite material.

[0024] Figure 2 The contact angle of the original fluorocarbon film FEP and the contact angle change corresponding to the 2wt% calcium chloride treatment process in Example 1 were tracked.

[0025] Figure 3 The contact angle of the original fluorocarbon thin film FEP and the contact angle change corresponding to the 2wt% sodium chloride treatment process in Example 2 were tracked.

[0026] Figure 4 Tracking of contact angle changes corresponding to the 5wt% calcium chloride treatment process for fluorocarbon thin film FEP;

[0027] Figure 5This is a comparison of the low-temperature helium leakage performance of the composite material for liquid oxygen storage tank prepared with the modified gas barrier membrane in Example 3 and the composite material without the modified gas barrier membrane.

[0028] Figure 6 Contact angle changes were tracked for fluorocarbon thin film FEP treated with 0.1 wt% calcium chloride.

[0029] Figure 7 This is a comparison of the low-temperature helium leakage performance of the composite material for liquid oxygen storage tank prepared with the modified gas barrier membrane in Example 4 and the composite material without the modified gas barrier membrane.

[0030] Figure 8 Tracking of contact angle changes corresponding to the 3wt% calcium chloride treatment process for fluorocarbon thin film FEP;

[0031] Figure 9 This is a comparison of the low-temperature helium leakage performance of the composite material for liquid oxygen storage tank prepared with the modified gas barrier membrane in Example 5 and the composite material without the modified gas barrier membrane. Detailed Implementation

[0032] This invention provides a method for preparing a modified gas-barrier membrane, which is obtained by a method comprising the following steps:

[0033] A hydrophilic modified film is obtained by coating the surface of a fluorocarbon film with a calcium chloride solution and then drying it.

[0034] The hydrophilic modified membrane was subjected to low-temperature plasma treatment to obtain the modified gas barrier membrane.

[0035] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0036] The present invention involves coating the surface of a fluorocarbon thin film with a calcium chloride solution and then drying it to obtain a hydrophilic modified film.

[0037] In this invention, the fluorocarbon film preferably includes one or more of fluorinated ethylene propylene copolymer film (FEP film), perfluoroalkoxy polymer film (PFA film), and polyvinyl fluoride film (PVF film).

[0038] In this invention, the thickness of the fluorocarbon film is preferably 200-300 μm, specifically 200, 250 or 300 μm.

[0039] In this invention, the fluorocarbon film is preferably washed with ethanol, washed with water and dried in sequence before coating. The ethanol washing and water washing are preferably performed in an ultrasonic cleaner, and the washing time is preferably 15 minutes.

[0040] In this invention, the ethanol is preferably a 95 vol% ethanol solution.

[0041] In this invention, the drying is preferably carried out by baking, and the baking is preferably carried out in an oven. This invention does not have a special limitation on the specific method of drying, and any method known to those skilled in the art can be used.

[0042] In this invention, the concentration of the calcium chloride solution is preferably 0.1-5 wt%, specifically 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt%, or 5 wt%. In this invention, the calcium chloride introduces polar groups, and the chlorine species in the calcium chloride include chlorine free radicals and chloride ions. On the one hand, it bombards the polymer surface, increasing the surface roughness; on the other hand, it can react with fluorocarbon films to form C-Cl bonds or other oxygen-containing groups. The role of calcium ions is to delay the decay of hydrophilic groups through cross-linking, thereby improving the durability of the hydrophilic treatment effect.

[0043] In this invention, the coating is preferably applied by spraying, and the number of spraying operations is preferably 2 to 3.

[0044] In this invention, the preferred spraying conditions include: a nozzle diameter of 0.2 to 0.5 mm (specifically, 0.2, 0.3, 0.4, or 0.5 mm), a pressure of 0.2 to 0.5 MPa (specifically, 0.2, 0.3, 0.4, or 0.5 MPa), and a spraying distance of 10 to 20 cm (specifically, 10, 15, or 20 cm).

[0045] After the coating is completed, the present invention preferably requires the film to be left to stand for 15 minutes and then dried at room temperature to obtain the hydrophilic modified film.

[0046] After obtaining the hydrophilic modified membrane, the present invention performs low-temperature plasma treatment on the hydrophilic modified membrane to obtain the modified gas barrier membrane.

[0047] In this invention, the preferred conditions for the low-temperature plasma treatment include: an oxygen plasma treatment time of 30–180 s (specifically 30, 60, 90, 120, 150, or 180 s), a treatment power of 30–100 W (specifically 30, 40, 50, 60, 70, 80, 90, or 100 W), and a gas flow rate of 100 sccm. The low-temperature plasma treatment is used to modify the hydrophilic modified membrane, thereby solving the problem that the membrane cannot adhere to the surface of the composite material.

[0048] The present invention provides a modified gas barrier membrane prepared by the preparation method described in the above technical solution.

[0049] The present invention also provides a method for using the modified gas barrier membrane, wherein the modified gas barrier membrane is placed between layers of carbon fiber reinforced resin matrix composite material and heated and cured together to form an integral shape.

[0050] The present invention also provides a liquid oxygen storage tank composite material, comprising a first carbon fiber reinforced resin matrix composite material, the modified gas barrier membrane described in the above technical solution, and a second carbon fiber reinforced resin matrix composite material stacked sequentially.

[0051] Figure 1 This is a schematic diagram showing the positional relationship between the modified air-barrier membrane and the carbon fiber reinforced resin matrix composite material.

[0052] The present invention does not specifically limit the types of the first carbon fiber reinforced resin matrix composite material and the second carbon fiber reinforced resin matrix composite material, and any type known to those skilled in the art can be used, such as carbon fiber reinforced epoxy resin material.

[0053] This invention also provides a method for preparing the liquid oxygen storage tank composite material described in the above technical solution, comprising the following steps:

[0054] The modified gas barrier membrane is placed between two layers of carbon fiber reinforced resin matrix composite prepreg, and then hot-pressed and cured to obtain the composite material for the liquid oxygen storage tank.

[0055] The present invention does not have any special limitation on the composition of the carbon fiber reinforced resin matrix composite prepreg, and any composition known to those skilled in the art can be used, such as carbon fiber reinforced epoxy resin composite prepreg. The epoxy resin in the carbon fiber reinforced epoxy resin composite prepreg can tightly bond the modified gas barrier membrane and the carbon fiber reinforcing resin.

[0056] In this invention, the preferred conditions for hot-press curing include: a pressure of 0.3 MPa, curing at 100°C for 2 hours, and then raising the temperature to 155°C and maintaining the pressure for 4 hours.

[0057] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0058] The reference standards for the low-temperature helium leakage performance test of the integrated gas barrier composite material in this embodiment of the invention are GB / T 1038-2000, ASTM D1434 and ISO 2556.

[0059] Example 1

[0060] A 300 μm thick fluorocarbon film (FEP) was selected and first cleaned in an ultrasonic cleaner for 15 min in a 95 vol% ethanol solution, then cleaned in an ultrasonic cleaner in deionized water for 15 min, and finally dried in an oven. A 2 wt% calcium chloride solution was prepared using deionized water and uniformly sprayed onto the dried fluorocarbon film surface in two layers using a spraying method. The film was then allowed to stand for 15 min to dry at room temperature. The spraying device consisted of a 0.3 mm diameter nozzle, a pressure of 0.3 MPa, and a spraying distance of 15 cm. Finally, the film was treated with oxygen plasma for 60 s at a power of 50 W and a gas flow rate of 100 sccm.

[0061] Figure 2 The changes in the contact angle of the original fluorocarbon film FEP and the fluorocarbon film FEP modified by the 2wt% calcium chloride treatment process in Example 1 were tracked. It can be seen that the water contact angle of the unmodified gas barrier membrane was 115.1°. After treatment with calcium chloride solution and low-temperature plasma, the water contact angle decreased to 29.1°. After 70 days, the contact angle slowly increased to 46.0°.

[0062] The modified gas barrier membrane is placed between two layers of carbon fiber reinforced epoxy resin composite prepreg and integrally cured by hot pressing. The hot pressing curing conditions are: 0.3MPa pressure, first cured at 100℃ for 2 hours, then raised to 155℃ and kept at pressure for 4 hours, finally forming an integrated gas barrier carbon fiber composite material, namely the liquid oxygen storage tank composite material.

[0063] The cryogenic helium molecule leakage rate of the composite material in the liquid oxygen storage tank under pressurized and cryogenic conditions (-193℃) is 1.05×10⁻⁶. -8 Pa·m 3 / s.

[0064] Example 2

[0065] A 300 μm thick fluorocarbon film (FEP) was selected and first cleaned in an ultrasonic cleaner for 15 min in a 95 vol% ethanol solution, then cleaned in an ultrasonic cleaner in deionized water for 15 min, and finally dried in an oven. A 2 wt% sodium chloride solution was prepared using deionized water, and two layers of the calcium chloride solution were uniformly sprayed onto the dried fluorocarbon film surface using a spraying method. The film was then allowed to stand for 15 min to dry at room temperature. The spraying device consisted of a 0.3 mm diameter nozzle, a pressure of 0.3 MPa, and a spraying distance of 15 cm. Finally, the film was treated with oxygen plasma for 60 s at a power of 50 W and a gas flow rate of 100 sccm.

[0066] Figure 3The contact angle of the original fluorocarbon film FEP and the contact angle of the fluorocarbon film FEP modified by the 2wt% sodium chloride treatment process in Example 2 were tracked. It can be seen that the water contact angle of the unmodified gas barrier membrane is 104°. After treatment with sodium chloride and low-temperature plasma technology, the water contact angle is reduced to 40.4°. After 12 days and 70 days, the contact angle slowly increases to 43.4° and 60.2°, respectively. Both sodium chloride and calcium chloride contain chloride ions. It can be seen that chloride ions are the real factor that can reduce the contact angle. The role of calcium ions is to delay the decay of hydrophilic groups through cross-linking. After 70 days, the contact angle increases more with sodium chloride than with calcium chloride.

[0067] Example 3

[0068] A 300 μm thick fluorocarbon film (FEP) was selected and first cleaned in an ultrasonic cleaner for 15 min in a 95 vol% ethanol solution, then cleaned in an ultrasonic cleaner in deionized water for 15 min, and finally dried in an oven. A 5 wt% calcium chloride solution was prepared using deionized water and uniformly sprayed onto the dried fluorocarbon film surface in two layers using a spraying method. The film was then allowed to stand for 15 min to dry at room temperature. The spraying device used a nozzle with a diameter of 0.3 mm, a pressure of 0.3 MPa, and a spraying distance of 15 cm. Finally, the film was treated with oxygen plasma for 60 s, with a treatment power of 50 W and a gas flow rate of 100 sccm.

[0069] Figure 4 The changes in the contact angle of the original fluorocarbon film FEP and the contact angle of the fluorocarbon film FEP modified by the 5wt% calcium chloride treatment process in Example 3 were tracked. It can be seen that the water contact angle of the unmodified gas barrier membrane is 115.1°. After treatment with calcium chloride solution and low-temperature plasma, the water contact angle is reduced to 28.2°. After 70 days, the contact angle slowly increases to 47.4°.

[0070] The modified gas barrier membrane is placed between two layers of carbon fiber reinforced epoxy resin composite prepreg and integrally cured by hot pressing. The hot pressing curing conditions are: 0.3MPa pressure, first cured at 100℃ for 2 hours, then raised to 155℃ and kept at pressure for 4 hours, finally forming an integrated gas barrier carbon fiber composite material, namely the liquid oxygen storage tank composite material.

[0071] Figure 5 This comparison shows the cryogenic helium leakage performance of the composite material for liquid oxygen storage tank prepared with the modified gas-barrier membrane in Example 3, compared to the composite material without the modified gas-barrier membrane. It can be seen that under both pressurized and cryogenic conditions (-193℃), the helium molecule leakage rate is less than 10%. -6 Pa·m 3 / s, and after adding the modified gas barrier membrane, the helium molecule leakage rate was significantly reduced to 8.82×10 -9Pa·m 3 / s.

[0072] Example 4

[0073] Same as Example 3, except that the concentration of the calcium chloride solution is 0.1 wt%.

[0074] Figure 6 The contact angle change of the fluorocarbon thin film FEP treated with 0.1wt% calcium chloride was tracked, and it was found that the water contact angle of the modified gas barrier membrane decreased to 30°, and after 70 days, the contact angle was 48°.

[0075] Figure 7 A comparison of the cryogenic helium leakage performance of the liquid oxygen storage tank composite material prepared with the modified gas-barrier membrane in Example 4 and the composite material without the modified gas-barrier membrane shows that, under pressurized and cryogenic conditions (-193℃), the helium molecule leakage rate of the liquid oxygen storage tank composite material prepared with the modified gas-barrier membrane is 10% lower. -6 Pa·m 3 / s, which is 9.53×10 -9 Pa·m 3 / s.

[0076] Example 5

[0077] Same as Example 3, except that the concentration of the calcium chloride solution is 3 wt%.

[0078] Figure 8 The contact angle change of the fluorocarbon thin film FEP treated with 3wt% calcium chloride was tracked, and it was found that the water contact angle of the modified gas barrier membrane decreased to 27°, and after 70 days, the contact angle was 46°.

[0079] Figure 9 A comparison of the cryogenic helium leakage performance of the liquid oxygen storage tank composite material prepared with the modified gas-barrier membrane in Example 5 and the composite material without the modified gas-barrier membrane shows that, under pressurized and cryogenic conditions (-193℃), the helium molecule leakage rate of the liquid oxygen storage tank composite material prepared with the modified gas-barrier membrane is less than 10%. -6 Pa·m 3 / s, which is 7.01×10 -9 Pa·m 3 / s.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a modified gas-barrier membrane, characterized in that, Prepared by a method including the following steps: A hydrophilic modified film is obtained by coating the surface of a fluorocarbon film with a calcium chloride solution and then drying it. The hydrophilic modified membrane was subjected to low-temperature plasma treatment to obtain the modified gas barrier membrane.

2. The preparation method according to claim 1, characterized in that, The concentration of the calcium chloride solution is 0.1–5 wt%.

3. The preparation method according to claim 1 or 2, characterized in that, The coating is applied by spraying, and the number of spraying operations is 2 to 3.

4. The preparation method according to claim 3, characterized in that, The spraying conditions include: nozzle diameter of 0.2-0.5 mm, pressure of 0.2-0.5 MPa, and spraying distance of 10-20 cm.

5. The preparation method according to claim 1, characterized in that, The conditions for the low-temperature plasma treatment include: oxygen plasma treatment time of 30–180 s, treatment power of 30–100 W, and gas flow rate of 100 sccm.

6. The preparation method according to claim 1, characterized in that, The fluorocarbon films include one or more of fluorinated ethylene propylene copolymer films, perfluoroalkoxy polymer films, and polyvinyl fluoride films.

7. The preparation method according to claim 1 or 6, characterized in that, The thickness of the fluorocarbon film is 200–300 μm.

8. The modified air-barrier membrane prepared by the preparation method according to any one of claims 1 to 7.

9. A composite material for a liquid oxygen storage tank, characterized in that, It includes a first carbon fiber reinforced resin matrix composite material, the modified air barrier membrane as described in claim 8, and a second carbon fiber reinforced resin matrix composite material arranged in sequence.

10. The method for preparing the liquid oxygen storage tank composite material according to claim 9, characterized in that, Includes the following steps: The modified gas barrier membrane is placed between two layers of carbon fiber reinforced resin matrix composite prepreg, and then hot-pressed and cured to obtain the liquid oxygen storage tank composite material.

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