Low-vacuum-outgassing, self-reinforced composite materials for space deployable structures and methods of making the same

Abstract

A low-vacuum escaping, self-reinforced composite material for space deployment structure and a preparation method thereof belong to the field of materials for space environment. The method is as follows: vinyl imidazole is reacted with zinc chloride, and gradually a precipitate is generated in the solution system as the reaction proceeds, the precipitate is obtained after suction filtration, and the precipitate is dried to obtain a latent curing agent. After the photoinitiator, the latent curing agent, the acrylate resin and the epoxy resin are mixed, vacuum is applied to remove bubbles, the mixture is poured into a mold, and the mixture is irradiated by ultraviolet light for 10-40 minutes to obtain a one-stage flexible material; a two-stage epoxy resin curing agent is added to the one-stage acrylate network, and the flexible material is cured at a temperature of 170-250 DEG C for 2-6 h to prepare a rigid material. The synthesized latent curing agent contains a coordination bond Zn-N bond, which can passivate the reactivity with the epoxy resin, and therefore can be used as an epoxy resin latent curing agent.

Description

Technical Field

[0001] This invention belongs to the field of materials for space environment, specifically relating to a low-vacuum escape, self-reinforcing composite material for space deployment structures and its preparation method. Background Technology

[0002] Large space-deployable structures have significant application value in the aerospace field. To reduce the launch volume of such structures, sequential curing technology can be introduced. This technology mixes curing monomers with an initiator, first initiating the formation of a flexible material in the first stage, giving it excellent folding properties and thus significantly reducing the launch volume; subsequently, in the orbital environment, a second stage initiating the formation of a rigid material achieves structural rigidity and shape preservation.

[0003] Currently, the second-stage initiators in sequential curing technology are primarily additive initiators, meaning they exist in free form within the flexible material formed in the first stage. However, in aerospace applications, these free initiators may escape into space under negative pressure, causing vacuum leakage problems. Furthermore, due to the extraction of the initiator, the second-stage curing process is difficult to control precisely, thus affecting the final material's mechanical properties and structural stability. Especially after the flexible-to-rigid transition, the mechanical properties of the rigidified material do not improve significantly, failing to meet the high-strength requirements of aerospace structures. Therefore, improving the mechanical strength of rigidified materials has become an urgent problem to solve. To address the vacuum leakage problem of additive initiators and the challenges of insufficient rigidified material performance, it is necessary to further optimize the initiator design and curing mechanism to ensure the reliability and on-orbit stability of sequential curing technology, while simultaneously improving the mechanical properties of rigidified materials to meet the practical application needs of aerospace engineering. Summary of the Invention

[0004] The purpose of this invention is to solve the aforementioned problems in the prior art and to provide a low-vacuum escape, self-reinforcing composite material for space deployment structures and its preparation method.

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

[0006] A method for preparing a low-vacuum escape, self-reinforcing composite material for space deployment structures, the method comprising:

[0007] Step 1: React vinylimidazole with zinc chloride. Dissolve vinylimidazole in methanol or ethanol to obtain a vinylimidazole solution with a concentration of 0.5-4.0 mol / L (preferably 2.0 mol / L); dissolve zinc chloride in methanol or ethanol to obtain a zinc chloride solution with a concentration of 0.5-2.0 mol / L (preferably 1.0 mol / L); mix the vinylimidazole solution and zinc chloride solution at a molar ratio of 1-4:1 and react at 30-40℃ for 0.5-4 h. As the reaction proceeds, a precipitate gradually forms in the solution system. After filtration, the precipitate is obtained and dried in a vacuum oven at 50℃ for 12 h to obtain the latent curing agent VIM-Zn. As one of the reactants, the conjugation effect of vinylimidazole can reduce the nucleophilic activity of imidazole.

[0008] Step 2: Mix the photoinitiator, latent curing agent, acrylate resin and epoxy resin, then vacuum to remove air bubbles. Pour the mixture into a mold and irradiate it with ultraviolet light for 10-40 minutes to obtain a first-stage flexible material. Next, add the second-stage epoxy resin curing agent to the first-stage acrylate network and cure the flexible material at a temperature of 170℃-250℃ for 2-6 hours to prepare a rigid material.

[0009] Furthermore, in step two, the mass ratio of photoinitiator to acrylate is 1-5:100, the mass ratio of latent curing agent VIM-Zn to epoxy resin is 5-20:100, the total amount of resin is 100%, and the epoxy resin is 40%~90%.

[0010] Further, in step two, the photoinitiator 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.

[0011] A low-vacuum escape, self-reinforcing composite material for space deployment structures prepared by the above preparation method.

[0012] The advantages of this invention over the prior art are as follows:

[0013] (1) The synthesized latent curing agent contains coordinate bonds Zn-N bonds, which can passivate the reactivity with epoxy resin, and therefore can be used as a latent curing agent for epoxy resin.

[0014] (2) When the curing agent VIM-Zn is applied to the two-stage curing system of acrylate-epoxy resin, since there are double bonds in the synthesized curing agent, the curing agent is connected to the polyacrylate network during the first stage of acrylate free radical polymerization, and there is no problem of small molecule curing agent migration.

[0015] (3) When the flexible material is launched into orbit and successfully deployed, it triggers the reaction between VIM-Zn and epoxy resin to form Zn-O coordination bonds, which improves the mechanical strength of the rigid material. Attached Figure Description

[0016] Figure 1 The synthesis formula diagram for the curing agent VIM-Zn is shown below;

[0017] Figure 2 Infrared spectroscopy results for the reactant monomer vinylimidazolium (VIM) and the synthesized curing agent VIM-Zn.

[0018] Figure 3 The hydrogen nuclear magnetic resonance (NMR) spectra of the reactant monomer vinylimidazolium (VIM) and the synthesized curing agent VIM-Zn are shown.

[0019] Figure 4 Non-isothermal DSC test results of VIM-Zn cured epoxy resin at different heating rates;

[0020] Figure 5 A schematic diagram showing the extrapolated values ​​of the initial curing temperature Ti, peak curing temperature Tp, and post-curing temperature Tf for VIM-Zn cured epoxy resin.

[0021] Figure 6 This is a graph showing the oxygen element test results obtained after XPS testing of a rigid material.

[0022] Figure 7 This is a diagram showing the transformation of epoxy groups in the system after the flexible material of Example 4 has been stored at room temperature for four months;

[0023] Figure 8 This is a flexible material display diagram from Example 4;

[0024] Figure 9 This is a schematic diagram of the two-stage curing mechanism of acrylate-epoxy resin. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0026] Latent curing agent: Does not react with epoxy resin at room temperature, can be stored for a long time, and can cure epoxy resin at high temperature; Coordination bond reinforcement: Metal ions in the material form coordination bonds with some atoms in the polymer molecular network, which can enhance the mechanical properties of the material; Intermediate product: The material obtained by initiating the first-stage polymerization reaction of the liquid sequential curing resin system, also called the first-stage material; Final product: The material obtained by initiating the second-stage polymerization of the intermediate product, also called the second-stage material.

[0027] This invention has the following three main innovative features:

[0028] 1. Molecular design of epoxy resin curing agents: based on zinc ions (Zn 2+ Coordination was used to modify vinylimidazolium (VIM), a latent curing agent containing double bonds, to prepare a latent curing agent (VIM-Zn) with a double bond structure.

[0029] 2. Sequential Curing Resin Formulation Design: An acrylate-epoxy resin sequential curing system is selected. In the first stage, the free radical polymerization of double bonds is utilized. Under ultraviolet light excitation, the photoinitiator decomposes to generate photoradicals that initiate the polymerization of double bonds. The synthesized epoxy resin latent curing agent VIM-Zn is incorporated into the acrylate polymerization network to limit its migration. The intermediate material can undergo multiple folding and unfolding tests on the ground. Subsequently, after being launched into orbit, heating the flexible material causes the coordination bonds in VIM-Zn to break, exposing the highly active pyridine nitrogen atoms in the imidazole ring, which initiates the curing of the epoxy resin and completes the flexible-rigid transformation of the material.

[0030] 3. Coordination bonds exist in both flexible and rigid materials, and different types of coordination bonds play different roles. In the first-stage flexible material, there is a Zn-N coordination bond between zinc ions and the pyridine nitrogen atom on the imidazole ring, which inhibits the reactivity between the imidazole ring and the epoxy group. Therefore, at room temperature, this can extend the storage period of the flexible material, allowing it to maintain its flexibility for a longer period of time. When the second-stage curing is triggered by heating, the Zn-N coordination bond breaks, releasing highly reactive pyridine nitrogen atoms that react with the epoxy resin, completing the second-stage curing. At the same time, during the epoxy resin polymerization process, the epoxy group transforms into hydroxyl groups that coordinate with zinc ions to form Zn-OH bonds. These coordination bonds can enhance the mechanical strength of the rigid material.

[0031] Example 1:

[0032] Synthesis of VIM-Zn curing agent 1: 40 mmol of vinylimidazole was dissolved in 50 ml of ethanol. The solution was then transferred to a 250 ml single-necked flask. 20 mmol of ZnCl2 solid powder was weighed and dissolved in 30 ml of ethanol. This solution was transferred to a constant-pressure dropping funnel, and zinc chloride solution was gradually added dropwise to the vinylimidazole solution over 0.5 h at a reaction temperature of 40 ℃. After the reaction was complete, the resulting solid was filtered and dried in a vacuum oven at 50 ℃ for 12 h to obtain VIM-Zn. The synthesis formula is as follows: Figure 1 As shown.

[0033] Example 2:

[0034] Synthesis of VIM-Zn curing agent 2: 20 mmol of vinylimidazole was dissolved in 25 ml of methanol. The solution was then transferred to a 100 ml single-necked flask. 11 mmol of ZnCl2 solid powder was weighed and dissolved in 20 ml of methanol. This solution was transferred to a constant-pressure dropping funnel, and zinc chloride solution was gradually added dropwise to the vinylimidazole solution over 20 min at a reaction temperature of 40 °C. After the reaction was complete, the resulting solid was filtered and dried in a vacuum oven at 50 °C for 12 h to obtain VIM-Zn. The synthesis formula is as follows: Figure 1 As shown.

[0035] Coordination bond analysis of VIM-Zn curing agent and behavioral analysis of cured epoxy resin: Figure 2 This is an FTIR spectrum of vinylimidazole (VIM) and the synthesized product VIM-Zn. Figure 2 As can be seen, before coordination, the characteristic C=N absorption peak on the imidazole ring is located at 1588 cm⁻¹. -1 For VIM-Zn, the C=N absorption vibration peak is located at 1610 cm⁻¹. -1 At this point, the absorption vibration peak underwent a blue shift, indicating successful coordination. Figure 3 The 1H-NMR of VIM and VIM-Zn shows that the coordinated VIM-Zn... 1 The H-NMR chemical shift increases, shifting to a lower field—a deshielding effect. This is because during the coordination of vinylimidazole with zinc ions, the zinc ion coordinates with the pyridine nitrogen atom on the imidazole ring, reducing the electron density of the nitrogen atom and consequently decreasing the electron density around it. This makes the electron cloud around the hydrogen atoms on the imidazole ring more sparse, exhibiting a deshielding effect.

[0036] Figure 4 Non-isothermal DSC test charts of epoxy resin cured with VIM-Zn at heating rates of 5℃ / min, 10℃ / min, 15℃ / min, and 20℃ / min were generated. Figure 4The initial curing temperature T in i Peak curing temperature T p and post-curing temperature T f Extraction, plotting, and extrapolation to 0℃ / min yielded the following results: Figure 5 ,from Figure 5 The initial curing temperature T of the epoxy resin cured by the curing agent VIM-Zn was deduced. i The peak curing temperature is 132℃. p The post-curing temperature is 175℃. f The curing temperature is 215℃, which is relatively high. Therefore, the single-component epoxy resin system obtained at room temperature has latency.

[0037] Example 3:

[0038] Weigh 0.35 g of VIM-Zn, add an appropriate amount of methanol and ultrasonically disperse. Pour the dispersion into 7 g of epoxy resin and stir thoroughly. Remove the methanol under vacuum to obtain a pale yellow transparent epoxy resin system. Then, add 2.7 g of difunctional acrylate resin, 0.3 g of difunctional acrylate reactive diluent, and 0.06 g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone to the system. After ultrasonication for 10 min to dissolve the photoinitiator, vacuum the prepared two-stage curing resin system to remove air bubbles for 30 min. Pour the mixture into a silicone mold and irradiate with 365 nm ultraviolet light at an intensity of 50 mW / cm². 2 Irradiation for 10 minutes yielded a first-stage flexible material. This material was then cured at 170℃ for 2 hours and at 220℃ for 3 hours to obtain a second-stage rigid material. The tensile strength and modulus of the flexible material were 0.61±0.05 MPa and 1.97±0.05 MPa, respectively, while those of the rigid material were 60.66±1.96 MPa and 2205.24±96.36 MPa, respectively. This demonstrates that the material successfully transitioned from a flexible to a rigid state.

[0039] Example 4:

[0040] Weigh 0.35 g of VIM-Zn, add an appropriate amount of methanol, and ultrasonically disperse. Pour the dispersion into 7 g of epoxy resin and stir thoroughly. Remove the methanol under vacuum to obtain a pale yellow transparent epoxy resin system. Then, add 2.45 g of difunctional acrylate resin, 0.27 g of pentafunctional acrylate resin, 0.27 g of difunctional acrylate reactive diluent, and 0.06 g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone to this system. Sonicate for 10 min to dissolve the photoinitiator. Vacuum the prepared two-stage curing resin system to remove air bubbles for 30 min. Pour into a silicone mold and apply 365 nm ultraviolet light at an intensity of 50 mW / cm².2 Irradiation for 10 minutes yielded a first-stage flexible material. This material was then cured at 170℃ for 2 hours and at 220℃ for 3 hours to obtain a second-stage rigid material. The tensile strength and modulus of the flexible material were 1.13±0.11 MPa and 3.3±0.08 MPa, respectively, while those of the rigid material were 70.78±4.22 MPa and 2622.65±89.88 MPa, respectively. This demonstrates that the material successfully transitioned from a flexible to a rigid state. Figure 6 This is the result of oxygen element testing obtained after XPS testing of rigid materials. Figure 6 As can be seen from the data, 532.43 eV is the absorption peak of OH. This peak is due to the conversion of epoxy groups into hydroxyl groups during the anionic polymerization of epoxy resin. In addition, the value at 531.68 eV is the binding energy of the Zn-O coordination bond formed by zinc ions and hydroxyl groups. The coordination bond plays an enhancing role in the mechanical properties of rigid materials. Figure 7 This figure shows the transformation of epoxy groups in the system after the flexible material of this embodiment has been stored at room temperature for four months. The transformation rate is 27.56%, which is good. This is because the Zn-N coordination bond in the first-stage material inhibits the nucleophilic reactivity of the imidazole pyridine nitrogen atom on the epoxy resin. Figure 8 This is a demonstration of its flexibility; the flexible material retains good flexibility even after being stored for four months.

[0041] See the schematic diagram of the two-stage curing of acrylate-epoxy resin. Figure 9 As shown, during the first-stage free radical polymerization process, VIM is incorporated into the acrylate network. In the subsequent thermosetting process, the coordination bonds in VIM-Zn break, exposing the highly reactive pyridine nitrogen atoms in the imidazole ring, which initiates the curing of the epoxy resin and completes the flexible-rigid transition of the material.

Claims

1. A method for preparing a low-vacuum escape, self-reinforcing composite material for space deployment structures, characterized in that: The method is as follows: Step 1: React vinylimidazole with zinc chloride. Dissolve vinylimidazole in methanol or ethanol to obtain a vinylimidazole solution with a concentration of 0.5-4.0 mol / L; dissolve zinc chloride in methanol or ethanol to obtain a zinc chloride solution with a concentration of 0.5-2.0 mol / L; mix the vinylimidazole solution and the zinc chloride solution at a molar ratio of 1-4:1 and react at 30-40℃ for 0.5-4 hours. As the reaction proceeds, a precipitate gradually forms in the solution system. After filtration, the precipitate is obtained and dried in a vacuum oven at 50℃ for 12 hours to obtain a latent curing agent. Step 2: Mix the photoinitiator, latent curing agent, acrylate resin, and epoxy resin, then vacuum to remove air bubbles. Pour the mixture into a mold and irradiate with ultraviolet light for 10-40 minutes to obtain a first-stage flexible material. Cure the flexible material at 170℃-250℃ for 2-6 hours to prepare a rigid material. The mass ratio of photoinitiator to acrylate is 1-5:100, and the mass ratio of latent curing agent VIM-Zn to epoxy resin is 5-20:

100. The total resin content is 100%, and the epoxy resin content is 40%~90%.

2. The method for preparing a low-vacuum escape, self-reinforcing composite material for space deployment structures according to claim 1, characterized in that: In step two, the photoinitiator 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.

3. A low-vacuum escape, self-reinforcing composite material for space deployment structures prepared by the preparation method of claim 1 or 2.

Images