A method for preparing an epoxy resin matrix for a composite material low-temperature storage tank

Abstract

The present invention discloses a method for preparing an epoxy resin matrix for composite low-temperature storage tanks, and relates to the technical field of polymer materials. The present invention introduces mesoporous silica material into the epoxy resin structure, and utilizes the mesoporous channels of the mesoporous silica to construct a cured molecular network structure of resin molecular chains and mesoporous silica interspersed segments, thereby reducing the thermal expansion coefficient of the resin, thereby significantly reducing the temperature stress generated in the carbon fiber composite material due to the ultra-low temperature environment, and effectively inhibiting the initiation of microcracks; the use of a three-roller rolling process can better remove the solvent and make the mesoporous silica more evenly dispersed, thereby increasing the strength of the resin matrix, and further inhibiting the initiation and expansion of microcracks. The epoxy resin matrix of the present invention is suitable for composite storage tanks for rocket propellants.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, in particular to a method for preparing an epoxy resin matrix for a composite material low-temperature storage tank. Background Art

[0002] The lightweighting of a rocket's structure directly determines its launch efficiency. As a key component of a rocket's structure, the propellant tank accounts for over 60% of the rocket's dry weight. Therefore, lightweighting the tank is crucial for improving launch efficiency. Currently, metal tanks are still used worldwide for launch vehicle propellant tanks. Compared to metal tanks, carbon fiber reinforced resin-based composite tanks can reduce structural weight by 20%-40%, lower overall costs by over 25%, and significantly shorten manufacturing cycles.

[0003] Composite tanks must withstand extremely low temperatures during service (liquid oxygen ≤ -183°C, liquid hydrogen ≤ -253°C, methane ≤ -161.5°C). However, due to the significant difference in thermal expansion coefficients between carbon fiber and the resin matrix, carbon fiber-reinforced epoxy resin-based composites are prone to severe temperature stress in ultra-low temperature media, which can lead to the initiation of microcracks within the composite material. The expansion and connection of microcracks can easily form leakage channels, which in turn poses a risk of propellant leakage during service in the composite tank, seriously threatening the tank's service safety. Currently, a common solution is to increase the toughness of the resin matrix, such as introducing flexible long-chain macromolecules to enhance the toughness of epoxy resin. The prior art CN113429747B mentions a method for preparing low-temperature resistant toughened epoxy resin by introducing macromolecules such as polyethersulfone, polyimide, and biscitraconimide into the resin. This method can change the cross-linked network structure of the epoxy resin, increase the free volume, and thus improve the low-temperature resistance of the epoxy resin; the prior art CN201611056182.X provides a method for synergistically toughening epoxy resin with graphene and poly(aryl ether sulfone) of naphthalene, wherein graphene regulates the degree of phase separation between poly(aryl ether sulfone) of naphthalene and epoxy resin during the curing process, so that the phase structure of the composite material remains in a "double continuous phase structure" during the curing process, thereby giving the epoxy resin composite material good ultra-low temperature toughness. The core idea of ​​the above two methods is to improve the low-temperature toughness of the resin by introducing flexible long-chain macromolecules. However, flexible macromolecules are more sensitive to changes in ambient temperature. When the ambient temperature drops from room temperature to ultra-low temperature, flexible macromolecules are prone to thermal shrinkage, thereby increasing the thermal expansion coefficient of the resin matrix, resulting in a significant increase in the temperature stress at the resin matrix / fiber interface, which has limited inhibitory effect on the initiation and expansion of microcracks in composite tanks. Summary of the Invention

[0004] To address one or more of the above-mentioned problems, the present invention introduces mesoporous silica into the epoxy resin structure, utilizing the mesoporous channels of the mesoporous silica to construct a cured molecular network structure of interlaced segments of resin molecular chains and mesoporous silica. This not only reduces the thermal expansion coefficient of the resin, thereby significantly reducing the temperature stress generated within the carbon fiber composite due to the ultra-low temperature environment, thereby effectively inhibiting the initiation of microcracks, but also effectively improves the strength of the resin matrix, further inhibiting the initiation and propagation of microcracks. The present invention prepares mesoporous SiO2 with a pore size of 2.61 nm through a sol-gel method, allowing epoxy resin molecules to intersperse into the mesoporous channels, thereby constructing a cured molecular network structure of interlaced segments, and preparing a low-temperature-resistant epoxy resin system suitable for composite low-temperature storage tanks.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for preparing an epoxy resin matrix for a composite material cryogenic storage tank comprises the following steps:

[0007] Step 1. After dissolving the template in water, add sodium hydroxide solution to adjust the pH, slowly stir in a water bath, add tetraethoxysilane (TEOS), and stir vigorously; after the reaction is complete, centrifuge the solution to a pH of 7, take the white precipitate at the bottom of the centrifuge tube, and place it in an oven to dry to obtain product A;

[0008] Step 2. Take out product A, grind it into white powder, and place it into a tubular furnace for calcination to obtain mesoporous SiO2.

[0009] Step 3. Disperse the mesoporous SiO2 in an ethanol solution to obtain a mesoporous SiO2 ethanol dispersion, add the mesoporous SiO2 ethanol dispersion to the epoxy resin and stir evenly at room temperature, and then remove the ethanol.

[0010] Step 4. Place the epoxy resin dispersed with mesoporous SiO2 in a three-roll mill, heat the rollers of the three-roll mill and circulate the rollers for multiple times to completely remove the ethanol and further improve the dispersibility of the mesoporous SiO2 in the epoxy resin to obtain the epoxy resin matrix.

[0011] In one embodiment, in step 1, the template is cetyltrimethylammonium bromide (CTAB), polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) or polyoxyethylene polyoxypropylene ether (F127).

[0012] In one embodiment, in step 1, the water bath stirring is carried out at 70-90° C. and 60-120 r / min for 30-60 min.

[0013] In one embodiment, in step 1, the vigorous stirring is at 70-90° C. and 800-1500 r / min for 1-3 hours.

[0014] In one embodiment, in step 1, the concentration of the NaOH solution is 1-3 M, and the pH is adjusted to 11-12.

[0015] In one embodiment, in step 1, the mass fractions of water, template and TEOS are 200-300 parts, 0.3-0.6 parts and 3-6 parts respectively; the centrifugal speed is 5000rpm-10000rpm, in order to obtain mesoporous SiO2 containing template.

[0016] In one embodiment, in step 2, the pore size of the mesoporous SiO2 is 2.2-2.7 nm.

[0017] In one embodiment, in step 2, the heating rate of the tubular furnace is set to 2-5°C / min; the calcination temperature is 500°C-650°C and the calcination time is 5-8h, the purpose of which is to remove the template in the mesoporous SiO2 and obtain hollow channels.

[0018] In one embodiment, in step 3, the content of the mesoporous SiO2 is 5 wt.%-20 wt.% of the epoxy resin mass.

[0019] In one embodiment, in step 3, the stirring is carried out using a mechanical stirrer.

[0020] In one embodiment, in step 3, the ethanol is removed by mechanical stirring at 65-90° C. or by reduced pressure distillation.

[0021] In one embodiment, in step 4, the temperature of the three-roller mill rollers is set to 60-80°C.

[0022] In one embodiment, in step 4, the number of cyclic rolling is 2 to 5 times. In one embodiment, in step 5, the content of the curing agent is 5 wt.% to 10 wt.% of the epoxy resin.

[0023] An epoxy resin matrix is ​​prepared by adopting the above method.

[0024] A composite material tank for rocket propellant is prepared by adopting the above-mentioned epoxy resin matrix.

[0025] A method for increasing the strength of an epoxy resin matrix and reducing the thermal expansion coefficient comprises the following steps:

[0026] Step 1. After dissolving the template in water, add sodium hydroxide solution, slowly stir in a water bath, add tetraethoxysilane (TEOS), and stir vigorously; after the reaction is complete, centrifuge the solution to a pH of 7, take the white precipitate at the bottom of the centrifuge tube, and dry it in an oven to obtain product A;

[0027] Step 2. Take out product A, grind it into white powder, and calcine it in a tube furnace to obtain mesoporous SiO2;

[0028] Step 3. Dispersing the mesoporous SiO2 in ethanol to obtain a mesoporous SiO2 ethanol dispersion, adding the mesoporous SiO2 ethanol dispersion to the epoxy resin and stirring at room temperature, and then removing the ethanol;

[0029] Step 4. Place the epoxy resin dispersed with mesoporous SiO2 in a three-roll mill, heat the rollers of the three-roll mill and circulate the rollers for multiple times to obtain an epoxy resin matrix.

[0030] A method for preparing an epoxy resin product comprises the following steps: using the epoxy resin matrix, adding a curing agent, and stirring to obtain a colloidal solution; and degassing the colloidal solution, molding, and curing the solution to obtain the epoxy resin product.

[0031] In one embodiment, the curing agent is an amine curing agent, an imidazole curing agent or an acid anhydride curing agent.

[0032] In one embodiment, the stirring is carried out at 80-95° C. and 60-120 r / min.

[0033] In one embodiment, the curing is performed according to a stepwise curing temperature of 90-110° C. for 1-3 hours, 120-140° C. for 1-3 hours, and 150-170° C. for 2-4 hours.

[0034] An epoxy resin product is prepared by the above method.

[0035] A method for increasing the strength of an epoxy resin matrix and reducing the thermal expansion coefficient comprises the following steps:

[0036] Step 1. After dissolving the template in water, add sodium hydroxide solution, slowly stir in a water bath, add tetraethoxysilane (TEOS), and stir vigorously; after the reaction is complete, centrifuge the solution to a pH of 7, take the white precipitate at the bottom of the centrifuge tube, and dry it in an oven to obtain product A;

[0037] Step 2. Take out product A, grind it into white powder, and place it into a tubular furnace for calcination to obtain mesoporous SiO2.

[0038] Step 3. Disperse the mesoporous SiO2 in ethanol to obtain a mesoporous SiO2 ethanol dispersion, add the mesoporous SiO2 ethanol dispersion to the epoxy resin and stir evenly at room temperature, and then remove the ethanol.

[0039] Step 4. Place the epoxy resin dispersed with mesoporous SiO2 in a three-roll mill, heat the rollers of the three-roll mill and circulate the rollers for multiple times to obtain an epoxy resin matrix.

[0040] Beneficial effects of the present invention:

[0041] The present invention introduces mesoporous silica material into the epoxy resin structure and utilizes the mesoporous channels of the mesoporous silica to construct a cured molecular network structure of resin molecular chains and mesoporous silica interlaced segments. The main effects of the present invention are: (1) reducing the thermal expansion coefficient of the resin and improving the synergy of the thermal expansion coefficient of the carbon fiber epoxy resin composite material, thereby greatly reducing the temperature stress generated in the carbon fiber composite material due to the ultra-low temperature environment and effectively inhibiting the initiation of microcracks; (2) improving the strength of the resin matrix, thereby further inhibiting the initiation and expansion of microcracks; (3) the present application adopts a three-roller rolling process, which can better remove the solvent and make the mesoporous silica more evenly dispersed. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a field emission scanning electron microscope image of mesoporous SiO2;

[0043] Figure 2 This is a transmission electron microscope image of mesoporous SiO2;

[0044] Figure 3 is the pore size distribution diagram of mesoporous SiO2;

[0045] Figure 4 Schematic diagram of epoxy resin / mesoporous SiO2 block curing

[0046] Figure 5 Transmission electron microscopy image of 10wt.% mesoporous SiO2 / epoxy resin

[0047] Figure 6 The epoxy resin products prepared by adding mesoporous SiO2 in different mass ratios;

[0048] Figure 7 Stress-strain curve of epoxy resin with added mesoporous SiO2 (0-20wt.%);

[0049] Figure 8 This is the trend graph of tensile strength of epoxy resin with added mesoporous SiO2 (0-20wt.%);

[0050] Figure 9 This is the trend graph of elastic modulus of epoxy resin with addition of mesoporous SiO2 (0-20wt.%);

[0051] Figure 10 This is the trend diagram of thermal expansion coefficient of epoxy resin with added mesoporous SiO2 (0-20wt.%);

[0052] Figure 11 Stress-strain curve of epoxy resin with added mesoporous SiO2 (0-20wt.%) of Comparative Example 1. DETAILED DESCRIPTION

[0053] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0054] Materials used in the examples:

[0055] Epoxy resin: Bisphenol F type 830 epoxy resin, purchased from Nantong Xingchen Synthetic Materials Co., Ltd.

[0056] The materials involved in the other embodiments can be obtained from commercial channels.

[0057] Example 1:

[0058] A method for preparing an epoxy resin matrix for a composite material cryogenic storage tank comprises the following steps:

[0059] Preparation of mesoporous silica:

[0060] Step 1. After dissolving the template agent CTAB in water, add 2M sodium hydroxide solution, adjust the pH to 11.22, and stir in a water bath at 80°C and 100 rpm for 30 minutes. Then add tetraethoxysilane TEOS with a mass ratio of water, CTAB, and TEOS of 240:0.5:4, and vigorously stir at 80°C and 1500 rpm for 2 hours. After the reaction is completed, the solution is centrifuged at 25,000 rpm to a pH of 7, and the white precipitate at the bottom of the centrifuge tube is obtained and dried at 80°C to obtain product A.

[0061] Step 2. Take out product A, grind it finely into white powder, put it into a tube furnace, set the heating rate to 2°C / min, and calcine it at 550°C for 6 hours to remove the template in the mesoporous silica and obtain mesoporous silica.

[0062] Preparation of mesoporous SiO2 / epoxy resin products:

[0063] Step 3. Disperse the mesoporous silica in anhydrous ethanol to obtain a mesoporous silica ethanol dispersion with a concentration of 10 wt.%, add the mesoporous silica ethanol dispersion to the liquid epoxy resin, the mass of the mesoporous silica being 5 wt.% of the epoxy resin mass, use mechanical stirring at 25°C to mix uniformly, and then stir in an 80°C oil bath to remove the ethanol.

[0064] Step 4. The epoxy resin glue is further placed in a three-roller mill, the roller temperature of the three-roller mill is set to 70°C, and the rollers are rolled 3 times in a cycle.

[0065] Step 5. Add 5 wt.% of the epoxy resin mass of the curing agent DETDA and stir evenly at 80°C.

[0066] Step 6. The resin mixture of step 5 is vacuum degassed, injected into the mold, and cured according to a step-by-step temperature curing process of curing at 110°C for 2h, 130°C for 2h, and 160°C for 2h to finally obtain a mesoporous SiO2 / epoxy resin product.

[0067] The structure of the epoxy resin product prepared above was analyzed, wherein the field emission scanning electron microscope image of the mesoporous silica was as follows: Figure 1 As shown in the transmission electron microscopy images Figure 2 As shown, the pore size distribution diagram is as follows Figure 3 The schematic diagram of epoxy resin molecular structure block curing is shown in Figure 4 As shown, Figure 4 Sequence number 1 represents the mesoporous silica pores, sequence number 2 represents the epoxy resin molecular chains, and sequence number 3 represents the epoxy resin molecular chains that have entered some of the mesoporous pores, forming a block-cured structure. The particle size of the mesoporous SiO2 ranges from 100nm to 160nm, with the largest pore size at 2.61nm. It can be well dispersed in ethanol and epoxy resin.

[0068] Example 2:

[0069] According to the method of Example 1, different mass ratios of mesoporous SiO2 were added to prepare epoxy resin products, such as Figure 6 As shown, from left to right, the addition ratios are 0 wt.%, 5 wt.% (sample prepared in Example 1), 10 wt.%, 15 wt.%, and 20 wt.%. The transmission electron microscope image of the mesoporous SiO2 / epoxy resin product prepared by adding 10 wt.% of mesoporous SiO2 is shown in FIG. Figure 5 shown.

[0070] Example 3:

[0071] The difference from Example 1 is that in step 1, the pH is adjusted to 11.30, the pore size of the prepared mesoporous SiO2 is 2.4 nm, and the particle size is between 100 nm and 160 nm. Other conditions are the same as in Example 1.

[0072] Example 4:

[0073] The difference from Example 1 is that in step 1, the pH is adjusted to 11.35, the pore size of the prepared mesoporous SiO2 is 2.2 nm, and the particle size is between 100 nm and 160 nm. Other conditions are the same as in Example 1.

[0074] Comparative Example 1:

[0075] Different from Example 1, the mesoporous SiO2 / / epoxy resin product was prepared without using a three-roller pressing process.

[0076] Comparative Example 2:

[0077] The difference from Example 1 is that the method for preparing nano-SiO2 is:

[0078] 80 ml of anhydrous ethanol and 7 ml of ammonia water were mixed and stirred at 500 r / min for 1 hour, which was recorded as solution A. At the same time, 40 ml of anhydrous ethanol and 10.4 g of TEOS were mixed and stirred at 500 r / min for 1 hour, which was recorded as solution B. After 1 hour, solution A and solution B were mixed at 25°C and stirred at 750 r / min for 24 hours to obtain a monodisperse nano-SiO2 suspension. A large-capacity high-speed refrigerated centrifuge was used for centrifugal separation at 14,000 r / min for 20 minutes. The precipitate after centrifugation was ultrasonically dispersed and centrifuged with ultrapure water for 4 times. The solution was centrifuged and washed until the pH was 7. The final centrifugal precipitate was ultrasonically dispersed in anhydrous ethanol using an ultrasonic cleaning machine, which was recorded as solution C. Solution C was placed in a 70°C oven and dried for 6 hours. Nano-SiO2 powder was obtained after grinding.

[0079] The particle size of the prepared nano-SiO2 is 40-80 nm, and the method for preparing the epoxy resin product is the same as that in Example 1.

[0080] Performance testing:

[0081] The mechanical properties of the epoxy resin products prepared in Examples 1-4 and Comparative Example 2 were tested according to the standard test for tensile properties of plastics in ASTM D638-10. The stress-strain curves, tensile strength variation trends, elastic modulus variation trends, and thermal expansion coefficient variation trends of the epoxy resin matrix products with different mass ratios of mesoporous SiO2 were tested. The test results are shown in FIG. Figure 7 is the stress-strain curve, Figure 8 This is the test result diagram of tensile strength change trend. Figure 9 is the trend diagram of elastic modulus change, Figure 10 Trend graph of the coefficient of thermal expansion of epoxy resin. Figure 11 This is a stress-strain curve obtained from the test of mesoporous silica / epoxy resin prepared in Comparative Example 1.

[0082] Table 1 Performance test results of epoxy resin products prepared in Example 1 and Example 2

[0083]

[0084] from Figure 7 As can be seen from the figure, it can be roughly observed that the mechanical properties of the epoxy resin matrix filled with mesoporous silica are improved to varying degrees compared to the epoxy resin matrix without fillers. Figure 8 It can be seen that the tensile strength of epoxy resin without mesoporous SiO2 reaches 79.26MPa, and the tensile strength of epoxy resin with 10wt.% mesoporous SiO2 reaches 101.16MPa, which is an increase of 21%. The tensile strength of epoxy resin with other additions also increases. Figure 9 It can be seen that the elastic modulus of epoxy resin without mesoporous SiO2 is about 2.8GPa, and the elastic modulus of epoxy resin with mesoporous SiO2 added (5-20wt.%) is improved, which is 3.8%, 6.4%, 13.8% and 17.6% higher than that of epoxy resin without mesoporous SiO2. It can be seen that the present invention can enhance the mechanical properties of epoxy resin matrix. Figure 10 It can be seen that with the increasing content of mesoporous silica, the thermal expansion coefficient of epoxy resin at -180℃ increases from 26.44×10 -6 ℃ -1 Continued to decrease to 14.87×10 -6 ℃ -1 (Adding 20wt.% mesoporous SiO2). Figure 7 and Figure 11 It can be seen that under the same silica addition amount, the tensile strength of the mesoporous silica / epoxy resin prepared without the three-roll pressing process is significantly lower than that of the silica / epoxy resin prepared using the three-roll pressing process.

Claims

1. A method for preparing an epoxy resin matrix for a composite low-temperature storage tank, comprising the following steps: Step 1. After dissolving the template in water, add sodium hydroxide solution to adjust the pH, stir, add tetraethoxysilane, and stir vigorously; after the reaction is completed, centrifuge the solution to clean it, take the white precipitate at the bottom of the centrifuge tube, and dry it to obtain product A; wherein the template is hexadecyltrimethylammonium bromide, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, or polyoxyethylene polyoxypropylene ether; Step 2. Take out product A, grind it into white powder, and calcine it to obtain mesoporous SiO2; the pore size of the mesoporous SiO2 is 2.2-2.7nm; Step 3. Disperse the mesoporous SiO2 in an ethanol solution to obtain a mesoporous SiO2 ethanol dispersion, add the mesoporous SiO2 ethanol dispersion to the epoxy resin, stir, and then remove the ethanol; wherein the content of the mesoporous SiO2 is 15wt.%-20wt.% of the epoxy resin mass; Step 4. Place the epoxy resin dispersed with mesoporous SiO2 in a three-roll mill, heat the rollers of the three-roll mill and circulate the rollers for multiple times to obtain an epoxy resin matrix; wherein the temperature of the three-roll mill rollers is set to 60-80°C.

2. The method according to claim 1, characterized in that In step 1, the concentration of NaOH is 1-3 M, and the pH is adjusted to 11-12.

3. The method according to claim 1, characterized in that In step 1, the weight proportions of water, template, and tetraethoxysilane are 200-300 parts, 0.3-0.6 parts, and 3-6 parts, respectively; and the centrifugal speed is 5000 rpm-10000 rpm.

4. The method according to claim 1, wherein In step 4, the three-roller machine rolls are cycled 2-5 times.

5. An epoxy resin matrix, characterized in that The method is prepared by any one of claims 1 to 4.

6. A method for preparing an epoxy resin product, characterized in that: The epoxy resin matrix according to claim 5 is used, a curing agent is added, and the mixture is stirred to obtain a colloidal solution; the colloidal solution is degassed, molded, and cured to obtain an epoxy resin product.

7. An epoxy resin product, characterized in that The method according to claim 6 is used for preparation.

8. A composite material tank for rocket propellant, characterized in that: It is prepared by using the epoxy resin matrix described in claim 5.

Images