A method for solving vacuum degassing of soft-rigid conversion materials in space deployment structures

Abstract

A method for solving the vacuum degassing of flexible-rigid conversion materials in space deployment structures belongs to the field of space deployment material preparation. The method uses acrylate resin in the first stage, the mass ratio of photoradical initiator (or thermal radical initiator) to acrylate is 1-5:100, and epoxy resin is used in the second stage. The curing agent is an imidazole latent curing agent containing double bonds, and the mass ratio with epoxy resin is 7-20:100, and the epoxy resin accounts for 50% to 90% of the total resin. After the raw materials are mixed, vacuum is evacuated, bubbles are removed, and after pouring into the mold, a first-stage flexible material is prepared by ultraviolet irradiation for 10-20 minutes (or 60℃-70℃2-4h), and the flexible material is cured at 100℃-150℃ for 2-6h to obtain a rigid material. Since acrylate resin is selected in the first stage, after the first stage light initiation, the imidazole latent curing agent will be connected to the acrylate resin network, solving the problem that the second-stage curing agent in the material is extracted into the space due to the negative pressure in the space environment of the first-stage flexible material.

Description

Technical Field

[0001] The invention belongs to the field of preparation of space expansion materials, and in particular relates to a method for solving the vacuum degassing of soft-rigid conversion materials in a space expansion structure. Background Art

[0002] Large-scale space deployment structures have important application value in the aerospace field. In order to reduce the launch volume of such deployment structures, sequential curing technology is introduced: after mixing the curing monomer and the initiator, a flexible material is obtained through the first stage initiation, and a rigid material is obtained through the second stage initiation. Flexible materials prepared by sequential curing technology can be folded on the ground, which greatly reduces the launch volume of the deployment structure. After being launched into orbit, a rigid material is obtained through the second stage initiation, completing the on-orbit rigidification and shape preservation.

[0003] At present, the second-stage initiators in sequential curing technology are mostly added initiators, that is, the second type of initiator exists in the first-stage flexible material in a free form. When the flexible material is launched into orbit, this type of free initiator will be drawn into the space environment under the action of negative pressure, resulting in vacuum outgassing problems. At the same time, since the initiator is extracted, the second-stage curing becomes uncontrollable, which deteriorates the performance of the material. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of vacuum outgassing of the second-stage initiator in the flexible material and the short storage period of the flexible material, and to provide a method for solving the vacuum outgassing of the flexible-rigid conversion material in the space unfolding structure. The flexible-rigid conversion material system of the present invention is selected as an acrylate-epoxy resin system. After triggering the first-stage curing, a flexible polyacrylate material is obtained (at this time, the epoxy resin monomer has not been cured), and this material can be flexibly folded on the ground; after the flexible material is launched into orbit, the imidazole substances are triggered by heating to trigger the anionic curing of the epoxy resin, and the second-stage curing is completed to obtain a rigid material. An imidazole latent curing agent containing an acrylate group (or methacrylate group) is synthesized by molecular design. When the polymerization of the first-stage acrylate monomer is triggered, this type of imidazole curing agent can be connected to the acrylate resin network, that is, the initiator of the second-stage epoxy resin is connected to the first-stage acrylate resin network. At this time, after the flexible material is launched into orbit, under the action of vacuum, the second-stage curing agent in the material will not be drawn into the vacuum environment, and there is no problem of vacuum outgassing. Further, the imidazole curing epoxy resin is triggered by heating to complete the soft-rigid conversion of the material in the space environment. A solution is provided to solve the vacuum degassing problem of flexible-rigid conversion materials in space deployment structures.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for solving the vacuum degassing of a flexible-rigid conversion material in a space unfolding structure, the method comprising the following steps: a sequential curing system: an acrylate resin is used in the first stage, the mass ratio of a photoradical initiator (or a thermal free radical initiator) to the acrylate resin is 1-5:100, an epoxy resin is used in the second stage, the curing agent is a synthesized latent imidazole curing agent, the mass ratio of the curing agent to the epoxy resin is 7-20:100, the total amount of resin is 100%, and the epoxy resin is 50% to 90%, the photoradical initiator (or a thermal free radical initiator), the synthesized latent imidazole curing agent, the acrylate resin and the epoxy resin are mixed, vacuumized, bubbles are removed, poured into a mold, and then irradiated with ultraviolet light for 10-20 minutes (or maintained at 60°C-70°C for 2-4 hours) to prepare a first-stage flexible material, and the flexible material is post-cured at 100°C-150°C for 2-6 hours to obtain a rigid material.

[0007] Advantages: 1. The imidazole latent curing agent containing double bonds synthesized through molecular design is mixed with acrylate, epoxy resin and photoradical initiator. While triggering the acrylate radical curing, this type of latent curing agent containing double bonds is connected to the acrylate network. Therefore, this type of latent curing agent does not have migration phenomenon. In a vacuum environment, this type of curing agent will not be drawn from the first-stage flexible material into the vacuum environment, which can solve the vacuum outgassing problem of the first-stage material. Subsequently, heating triggers the imidazole to cure the epoxy resin, completing the soft-rigid transformation of the material in the space environment.

[0008] 2. The curing agent has the following notable characteristics: at room temperature, the curing activity for epoxy resin is low, but when heated to a specific temperature, the curing agent releases free imidazole through the reverse Michael reaction. At this time, the curing activity of imidazole for epoxy resin is significantly enhanced, and the curing process can be completed quickly. Therefore, the curing agent has the advantages of controllable activity, temperature-triggered curing, and efficient and rapid curing. These characteristics make it particularly suitable for use in space environments, helping to reduce the energy required for spacecraft to cure space-deployed structures.

[0009] Furthermore, the photo-radical initiator is one or more of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; the thermal-radical initiator is one of dibenzoyl peroxide BPO, azobisisoheptanenitrile ABVN, and azobisisobutyronitrile AIBN.

[0010] Furthermore, the synthesis method of the latent imidazole curing agent is as follows: 4.725g-7.56g of 4-maleimidophenol, 2.6g-4.16g of methacryloyl chloride (or acryloyl chloride), 250-350ml of solvent, and 2.5g-4.5g of acid binding agent are weighed and reacted under ice-water bath conditions for 4-48h, then poured into ice water, and after a large amount of yellow precipitate appears, filtered and dried the intermediate yellow product; 6.5g-10.28g of the intermediate yellow product is weighed, reacted with 1.7g-2.72g of imidazole, the reaction temperature is 40-80°C, after reacting for 3-8h, poured into cold petroleum ether, a large amount of red precipitate appears, filtered and dried to obtain the product; the synthesis equation of the latent imidazole curing agent is as follows: Fig. 9 shown.

[0011] Compared with imidazole substances, the synthesized product is a latent imidazole curing agent. Its reaction activity with epoxy resin at room temperature is lower than that of imidazole substances, and it can be used as a latent curing agent.

[0012] Furthermore, the solvent is one or more of tetrahydrofuran, ethyl acetate, dioxane, dichloromethane, dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide, and acetonitrile.

[0013] Furthermore, the acid binding agent is one of triethylamine, pyridine, anhydrous potassium carbonate and potassium hydroxide.

[0014] The beneficial effects of the present invention compared to the prior art are:

[0015] 1. The synthesized product is an imidazole curing agent containing methacrylate groups, and the H NMR spectrum is as follows: Figure 1 As shown. The flexible-rigid transition material system is selected as an acrylate-epoxy resin system. The flexible acrylate material is obtained after the first stage of light initiation or heat initiation. At this time, the synthetic product will be connected to the acrylate resin network, that is, the curing agent of the second stage epoxy resin is connected to the first stage acrylate network. When the flexible material is launched and deployed in orbit, under the action of vacuum, the second stage curing agent in the material will not be drawn into the vacuum environment. Subsequently, the imidazole is triggered by heating to cure the epoxy resin. At this time, the imidazole connected in the first stage will fall off, and the curing activity is strong, completing the flexible-rigid transition of the material in the space environment. The schematic diagram is shown as Figure 2 shown.

[0016] 2. Compared with imidazoles, latent imidazole curing agents are latent. For example, when 2wt% imidazole is mixed with epoxy resin at room temperature, the gel time of the system is 0.5d, and the non-isothermal DSC test shows that the peak exothermic temperature of the system is about 130℃. Figure 3As shown. When 5wt% of the synthetic latent imidazole curing agent is mixed with the epoxy resin at room temperature, the gel time of the system is about 13 days. The shorter the room temperature gel time, the stronger the reaction activity of the curing agent and the epoxy resin at room temperature. The longer the room temperature gel time, the weaker the reaction activity of the curing agent and the epoxy resin at room temperature, which can extend the storage period and processing time of the system. Further non-isothermal DSC testing shows that the peak exothermic temperature of the latent imidazole curing agent is around 160-170°C. Figure 4 As shown, it indicates that the latent imidazole curing agent needs to absorb more energy to cure the epoxy resin, that is, the synthetic product is latent and can extend the storage period of the first-stage flexible material. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the hydrogen nuclear magnetic data diagram of the synthetic product;

[0018] Figure 2 It is a schematic diagram of sequential curing;

[0019] Figure 3 This is the DSC graph of imidazole cured epoxy;

[0020] Figure 4 This is the DSC diagram of the designed and synthesized latent imidazole curing agent;

[0021] Figure 5 This is a comparison diagram of the stretching of the flexible material and the rigid material of Example 1;

[0022] Figure 6 is a comparison diagram of the modulus of the flexible material and the rigid material of Example 1;

[0023] Figure 7 This is a comparison diagram of the stretching of the flexible material and the rigid material of Example 2;

[0024] Figure 8 is a comparison diagram of the modulus of the flexible material and the rigid material of Example 2;

[0025] Fig. 9 Schematic diagram of the synthesis equation of latent imidazole curing agent. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0027] A latent curing agent is a special curing agent that does not react with epoxy resin at room temperature. Due to its inertness at room temperature, this curing agent can be stored for a long time in an unactivated state without affecting the stability of the epoxy resin. However, when exposed to high temperature conditions, this curing agent will be activated, prompting the epoxy resin to undergo a curing reaction.

[0028] Sequential curing technology is a process that utilizes two polymerizable monomers and their corresponding initiators present in the system. In this process, the first initiation reaction produces a flexible material that can be folded on the ground, significantly reducing its launch volume. Subsequently, after the material is launched and enters orbit, the flexible material is converted into a rigid material through a second initiation reaction, ensuring that it has sufficient rigidity and shape retention in orbit.

[0029] The vacuum outgassing problem is due to the free additives commonly used in the current sequential curing technology. Under low pressure, these free additives will gradually move from the polymer body to the surface and eventually escape into space. This process will not only reduce the initiator inside the material, making the second stage of curing uncontrollable, but also deteriorate the overall performance of the material, affecting its actual application effect in orbit.

[0030] Embodiment 1:

[0031] 4-Maleimidophenol 40mmol, methacryloyl chloride 50mmol, triethylamine 50mmol, 4-Maleimidophenol was dissolved in 200ml tetrahydrofuran, triethylamine was added to the solution, and methacryloyl chloride was added dropwise to the solution, reaction conditions: ice water bath, N2 atmosphere. After the reaction, 1L of water was poured to obtain a large amount of yellow precipitate, the precipitate was filtered, and dried at 60℃ for 12h to obtain 8.04g of intermediate product; 250ml of ethyl acetate and 250ml of petroleum ether were added to the flask, the dried intermediate product was poured in, stirred thoroughly, filtered to remove the insoluble matter, the filtrate was evaporated to remove the solvent, and the intermediate product was dried at 50℃ for 12h to obtain the purified intermediate product. Take 30mmol of the intermediate product and dissolve it in 200ml of dioxane solution. Dissolve 30mmol of imidazole in 30ml of dioxane. Add the imidazole solution drop by drop at 60℃ for 1h. Continue to react for 4h. After the reaction is completed, pour it into 1L of cold petroleum ether to obtain a large amount of red precipitate. After filtering and drying the red precipitate at room temperature, the synthetic product is obtained. Weigh 1g of the synthetic product and add it to 8g of epoxy resin. After fully stirring and ultrasonicating for 30min, the product slowly dissolves in the epoxy resin. Weigh 2g of difunctional acrylate resin, add 0.044g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, ultrasonicate for 10min to dissolve the photoinitiator in the acrylate resin. Mix the prepared epoxy resin and acrylate resin, vacuum and remove bubbles for 30min, pour it into a silicone mold, and use 365nm ultraviolet light with an illumination intensity of 50mW / cm 2 , irradiated for 10 minutes, and obtained the first stage flexible material. The material was cured at 100℃ for 2 hours and at 150℃ for 3 hours to obtain the second stage rigid material. Comparison of tensile strength and modulus of flexible material and rigid material Figure 5 , 6 As shown in Figure 2, the tensile strength and modulus of the flexible material are 0.2MPa and 0.2MPa respectively, and the tensile strength and modulus of the rigid material are 48.4MPa and 1935.9MPa respectively. It can be concluded that the material has completed the transition from the flexible state to the rigid state.

[0032] Embodiment 2:

[0033] 30mmol of 4-maleimidophenol, 40mmol of methacryloyl chloride, 50mmol of pyridine, 200ml of dichloromethane was used to dissolve 4-maleimidophenol, pyridine was added to the solution, and methacryloyl chloride was added dropwise to the solution, reaction conditions: ice water bath, N2 atmosphere. After the reaction, 1L of ice water was poured to obtain a large amount of yellow precipitate, the precipitate was filtered, and dried at 60℃ for 12h to obtain 6.2g of intermediate product; 250ml of ethyl acetate and 250ml of petroleum ether were added to the flask, the dried intermediate product was poured in, stirred thoroughly, filtered to remove the insoluble matter, the filtrate was evaporated to remove the solvent, and the intermediate product was dried at 50℃ for 12h to obtain the purified intermediate product. Take 30mmol of the intermediate product and dissolve it in 200ml of tetrahydrofuran solution. Dissolve 30mmol of imidazole in 30ml of tetrahydrofuran. Add the imidazole solution drop by drop at 60℃ for 1h. Continue to react for 4h after the addition is completed. After the reaction is completed, pour it into 1L of cold petroleum ether to obtain a large amount of red precipitate. After filtering and drying the red precipitate at room temperature, the synthetic product is obtained. Weigh 0.45g of the synthetic product and add it to 7g of epoxy resin. After fully stirring and ultrasonicating for 30min, the product slowly dissolves in the epoxy resin. Weigh 3g of difunctional acrylate resin, add 0.06g of thermal initiator ABVN, ultrasonicate for 10min to dissolve the thermal initiator in the acrylate resin. After mixing the prepared epoxy resin and acrylate resin, vacuumize and remove bubbles for 30min, pour it into an iron mold, and cure it at 70℃ for 2h to obtain a first-stage flexible material. The material is cured at 100℃ for 2h and 150℃ for 3h to obtain a second-stage rigid material. Comparison of tensile strength and modulus between flexible and rigid materials Figure 7 , 8 As shown in Figure 2, the tensile strength and modulus of the flexible material are 0.4 MPa and 1.7 MPa respectively, and the tensile strength and modulus of the rigid material are 25.4 MPa and 1198.9 MPa respectively. It can be concluded that the material has completed the transition from the flexible state to the rigid state.

Claims

1. A method for solving the vacuum degassing of soft-rigid conversion materials in a space expansion structure, characterized in that: The method comprises the following steps: a sequential curing system: an acrylate resin is used in the first stage, the mass ratio of a photoradical initiator or a thermal radical initiator to acrylate is 1-5:100, an epoxy resin is used in the second stage, a synthetic latent imidazole curing agent is used as a curing agent, and the mass ratio of the epoxy resin is 7-20:100, the total amount of resin is 100%, and the epoxy resin is 50% to 90%, after the photoradical initiator or the thermal radical initiator, the imidazole curing agent, the acrylate resin and the epoxy resin are mixed, vacuumized, bubbles are removed, poured into a mold, irradiated with ultraviolet light for 10-20 minutes or maintained at 60°C-70°C for 2-4 hours to prepare a first-stage flexible material, at which time, the second-stage epoxy resin curing agent is connected to the first-stage acrylate network, and the flexible material is post-cured at 100°C-150°C for 2-6 hours to obtain a rigid material; The synthesis method of the latent imidazole curing agent is as follows: weigh 4.725g-7.56g of 4-maleimidophenol, 2.6g-4.16g of methacryloyl chloride or acryloyl chloride, 250-350ml of solvent, and 2.5g-4.5g of acid binding agent, react under ice-water bath conditions for 4-48h, pour into ice water, and after a large amount of yellow precipitate appears, filter and dry the intermediate yellow product; weigh 6.5g-10.28g of the intermediate yellow product, react with 1.7g-2.72g of imidazole, the reaction temperature is 40-80°C, react for 3-8h, pour into cold petroleum ether, a large amount of red precipitate appears, filter and dry the final product.

2. A method for solving the vacuum degassing of soft-rigid conversion materials in a space expansion structure according to claim 1, characterized in that: The photo free radical initiator is one or more of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; the thermal free radical initiator is one or more of dibenzoyl peroxide BPO, azobisisoheptanenitrile ABVN, and azobisisobutyronitrile AIBN.

3. The method for solving the vacuum degassing of the soft-rigid conversion material in the space expansion structure according to claim 1, characterized in that: The solvent is one or more of tetrahydrofuran, ethyl acetate, dioxane, dichloromethane, dichloroethane, N,N-dimethylformamide, N,N-dimethylacetamide and acetonitrile.

4. The method for solving the vacuum degassing of the soft-rigid conversion material in the space expansion structure according to claim 1, characterized in that: The acid binding agent is one of triethylamine, pyridine, anhydrous potassium carbonate and potassium hydroxide.

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