A method for preparing a variable stiffness flexible composite tube and its application

Abstract

A method for preparing a variable stiffness flexible composite material tube and its application belong to the field of engineering composite material preparation. The method involves mixing a UV curing agent, an imidazole derivative curing agent, acrylate resin, and epoxy resin, followed by vacuuming to remove air bubbles, then compounding with carbon fiber cloth. Using a polytetrafluoroethylene rod mold, the mixture is irradiated with ultraviolet light for 8-12 minutes, followed by pre-curing at 110-130℃ for 2.5-3.5 hours, and then curing at 140-160℃ for 2.5-3.5 hours to obtain a rigid material. This invention, through molecular synthesis design, prepares imidazole derivatives with higher molecular weights, improving the shelf life of the flexible material and thus significantly increasing the workability. The prepared imidazole derivatives are in a liquid state, greatly improving compatibility with the resin system. Through molecular synthesis design, the prepared imidazole derivatives can undergo a Michael reverse reaction at 120℃, releasing 2-ethyl-4-methylimidazolium, thereby achieving reaction polymerization at a lower temperature and improving application efficiency.

Description

Technical Field

[0001] This invention belongs to the field of engineering composite material preparation, specifically relating to a method for preparing a variable stiffness flexible composite material tube and its application. Background Technology

[0002] With the increasing demand for high-performance flexible materials in industry, especially in aerospace and automotive manufacturing, the application of flexible composite materials is becoming increasingly widespread. However, traditional flexible composite tubes, due to their non-adjustable stiffness, often cannot provide the required mechanical properties under dynamic conditions, especially in applications requiring variable stiffness or handling complex conditions. For example, in emergency rescue, high-pressure, high-temperature, or frequent bending environments, existing flexible composite tubes lack sufficient stiffness, severely impacting their performance and safety.

[0003] Currently, the use of curing agents in the preparation process of flexible composite materials still faces some technical bottlenecks. Traditional curing agents typically suffer from high activity and short shelf life, especially when high-precision stiffness adjustment is required, making the stability of the curing agent and the controllability of the reaction process particularly important. Conventional low-activity curing agents react slowly at low temperatures and have poor compatibility with resin systems, directly affecting material performance and production efficiency. These factors greatly limit the promotion and widespread adoption of variable stiffness flexible composite pipes in practical applications. Summary of the Invention

[0004] To address the problems of traditional flexible composite tubes having non-adjustable stiffness, failing to provide the required mechanical properties under dynamic conditions, and being unsuitable for emergency applications, this invention proposes a method for preparing variable stiffness flexible composite tubes and its application scheme. By optimizing the formula and process flow, efficient, stable, and low-cost preparation of variable stiffness functional tubes is achieved.

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

[0006] A method for preparing a variable stiffness flexible composite material tube, the method comprising:

[0007] Step 1: Weigh the imidazole derivative curing agent, add it to the epoxy resin, stir thoroughly and sonicate for 25-35 min, then heat in an oven at 50-70 ℃ for 4-8 min to obtain resin A;

[0008] Step 2: Take difunctional acrylate resin and pentafunctional acrylate resin, add photoinitiator, and sonicate for 8-12 minutes to dissolve the photoinitiator in the acrylate resin to obtain resin B;

[0009] Step 3: After mixing resin B and resin A, vacuum degas for 30 minutes. Then, using a hand lay-up method, 25-35 g of resin is combined with three pieces of carbon fiber cloth, each 15 cm long and 7.5 cm wide, and wrapped around a polytetrafluoroethylene rod-shaped mold. The mixture is then exposed to 365 nm ultraviolet light at an intensity of 40-60 mW / cm². 2 Irradiate for 8-12 minutes to obtain a flexible composite material tube. When needed, cure at 110-130℃ for 2.5-3.5 h and at 140-160℃ for 2.5-3.5 h to transform the flexible composite material tube into a rigid composite material tube.

[0010] Further, in step one, the preparation method of the imidazole derivative curing agent (PME) is as follows: maleic anhydride, polyethylene glycol-400 and p-toluenesulfonic acid are stirred and reacted at 55-65 °C for 3 h under a nitrogen atmosphere, and then heated to 100-120 °C for 4-5 h. After the reaction is completed, the water generated during esterification is removed in a vacuum oven. The obtained mixture is dissolved in dichloromethane and washed with saturated sodium chloride solution and saturated sodium carbonate solution to obtain the intermediate product PM. Subsequently, PM, 2-ethyl-4-methylimidazolium and 1,8-diazabicycloundec-7-ene are dissolved in acetonitrile and stirred and reacted at 40-50 °C for 10-12 h under a nitrogen atmosphere. After the reaction is completed, the acetonitrile is removed by vacuum distillation. The distilled product is then dissolved in anhydrous ethanol and washed 3-5 times with petroleum ether, and then vacuum dried at 35-45 °C for 24 h.

[0011] Furthermore, the molar ratio of maleic anhydride to polyethylene glycol-400 is 1:2~3, and the amount of p-toluenesulfonic acid added is 2~4% of the total mass of maleic anhydride and polyethylene glycol-400.

[0012] Furthermore, the molar ratio of PM to 2-ethyl-4-methylimidazole is 1:1~2, and the amount of 1,8-diazabicycloundec-7-ene added is 6~8% of the total mass of PM and 2-ethyl-4-methylimidazole.

[0013] Furthermore, in step one, the mass ratio of the imidazole derivative curing agent to the epoxy resin is 1:4~6.

[0014] Further, in step two, the photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0015] Further, in step two, the mass ratio of the difunctional acrylate resin to the pentafunctional acrylate resin is 17~19:1; the mass ratio of the pentafunctional acrylate resin to the photoinitiator is 2.2~2.5:1.

[0016] Furthermore, in step three, the total amount of resin A and resin B is 100%, of which resin A accounts for 50wt%~90wt%.

[0017] An application of the variable stiffness flexible composite material pipe prepared by the above-mentioned preparation method in emergency rescue is described. The application involves inserting a flexible pipe with a length greater than the damaged area into the pipeline system from the outermost damaged area. Then, the flexible pipe is passed through the damaged area inside the pipeline and flattened on the outside of the original pipeline to make it fit tightly against the outer wall of the original pipeline. Subsequently, in-situ stiffening is performed, which is like putting a coat on the damaged area of ​​the original pipeline, thus playing a role in sealing and protection. This repair method cannot be achieved by traditional rigid pipes because rigid pipes do not have sufficient flexibility and plasticity to adapt to such complex pipeline repair scenarios.

[0018] The advantages of this invention over the prior art are as follows:

[0019] 1. By designing a molecular synthesis scheme, imidazole derivatives with higher molecular weight were prepared, which improved the storage period of flexible materials and thus greatly increased the workability. The prepared imidazole derivatives were in a liquid physical state, which greatly improved their compatibility with the resin system.

[0020] 2. Through molecular synthesis design, the prepared imidazole derivative can undergo the Michael reverse reaction at 120℃ to release 2-ethyl-4-methylimidazolium, thereby achieving reaction polymerization at a lower temperature and improving application efficiency.

[0021] 3. Using variable stiffness flexible composite material pipes in pipeline emergency rescue can effectively improve the efficiency, reliability and stability of emergency rescue. Attached Figure Description

[0022] Figure 1 Design diagram for the synthesis of PME, an imidazole derivative curing agent;

[0023] Figure 2 The results of the 1H NMR spectrum of the synthesized product PME and the reactants EMI and PEG are shown.

[0024] Figure 3 Fourier transform infrared (FTIR) data of the synthesized product PME, reactants, and intermediates are shown in the figure.

[0025] Figure 4 The image shows a non-isothermal DSC diagram of the synthesized product PME, reactants, intermediates, and epoxy resin.

[0026] Figure 5 The molecular weight elution curve of the synthesized product PME is shown.

[0027] Figure 6 DSC diagram of 2-ethyl-4-methylimidazolium (EMI) and its product (PME) epoxy resin system;

[0028] Figure 7 The hydrogen nuclear magnetic resonance spectra of the synthesized product PME at different temperatures;

[0029] Figure 8 This is a strength comparison diagram between the flexible composite material tube and the rigid composite material tube in Example 1;

[0030] Figure 9 This is a comparison chart of the modulus of the flexible composite material tube and the rigid composite material tube in Example 1;

[0031] Figure 10 This is a comparison chart of the elongation at break of the flexible composite material tube and the rigid composite material tube in Example 1;

[0032] Figure 11 This is a comparison diagram of the glass transition temperatures of the flexible composite material tube and the rigid composite material tube in Example 1.

[0033] Figure 12 This is a strength comparison diagram between the flexible composite material tube and the rigid composite material tube in Example 2;

[0034] Figure 13 This is a comparison chart of the modulus of the flexible composite material tube and the rigid composite material tube in Example 2;

[0035] Figure 14 This is a comparison chart of the elongation at break of the flexible composite material tube and the rigid composite material tube in Example 2;

[0036] Figure 15 This is a comparison diagram of the glass transition temperatures of the flexible composite material tube and the rigid composite material tube in Example 2. Detailed Implementation

[0037] 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.

[0038] Example 1:

[0039] Reaction scheme: Maleic anhydride, polyethylene glycol, and p-toluenesulfonic acid were reacted under a nitrogen atmosphere at 60 °C with stirring for 3 h, followed by heating at 110 °C for 4.5 h. After the reaction, water generated during esterification was removed in a vacuum oven. The molar ratio of maleic anhydride to polyethylene glycol-400 was 1:2.5, and the amount of p-toluenesulfonic acid added was 3% of the total mass of maleic anhydride and polyethylene glycol-400. The resulting mixture was dissolved in dichloromethane and washed with saturated sodium chloride and sodium carbonate solutions to obtain intermediate product PM. Subsequently, PM, 2-ethyl-4-methylimidazolium, and 1,8-diazabicycloundec-7-ene were dissolved in acetonitrile and reacted under a nitrogen atmosphere at 45 °C with stirring for 12 h. After the reaction, acetonitrile was removed by vacuum distillation. The distillate was then dissolved in anhydrous ethanol, washed three times with petroleum ether, and vacuum dried at 40 °C for 24 hours. After h, an imidazole derivative (PME) was obtained; the molar ratio of PM to 2-ethyl-4-methylimidazolium was 1:1.5, and the amount of 1,8-diazabicycloundec-7-ene added was 7% of the total mass of PM and 2-ethyl-4-methylimidazolium.

[0040] Characterization tests: Hydrogen nuclear magnetic resonance (NMR) spectroscopy, such as... Figure 2 As shown, the peak at chemical shift 7.25 ppm is that of the solvent CDCl3. The figure shows that a hydroxyl peak exists at chemical shift 3.11 ppm in the 1H NMR spectrum of PEG, while its intensity decreases in the 1H NMR spectrum of PME, indicating that the anhydride group and hydroxyl group successfully undergo esterification to obtain the first-step product PM. In the 1H NMR spectrum of EMI, a characteristic peak (peak a) at chemical shift 10.53 ppm is observed, which is the NH peak at position 1 in EMI. However, no characteristic peak appears near 10 ppm in the 1H NMR spectrum of PM, indicating that EMI reacts completely with the double bond. Comparison of the NMR spectra of the synthesized product and the reaction substrate confirms the successful preparation of the imidazole derivative PME. Fourier transform infrared spectroscopy (FTIR) analysis shows... Figure 3 As shown, PM is at 1731 cm. -1 The characteristic peak of the carbonyl group is shown at 1639 cm⁻¹. -1 The presence of a characteristic peak for a double bond at [a specific location] indicates that, unlike PEG, no obvious hydroxyl region was observed in PM, suggesting that the first step of the esterification reaction proceeded smoothly and PM was successfully synthesized. A peak at 3000 cm⁻¹ was observed in the EMI spectrum. -1 Nearby and 1574 cm -1 The presence of an absorption peak at (NH) indicates that the absorption peaks at both locations disappear in PME, suggesting that EMI successfully reacted with PM to synthesize the final product PME.

[0041] To further analyze the obtained synthetic products and their thermal properties in reaction with epoxy resin, each reactant and intermediate product PM were mixed with epoxy resin in the same proportions as the PME / E51 system. Differential scanning calorimetry was used to observe whether an exothermic peak appeared. Figure 4 Analysis showed that the reactants maleic anhydride (MAH), polyethylene glycol (PEG), and the intermediate product (PM) did not exhibit exothermic peaks within the test temperature range of 50-250℃, while the final product (PME) showed a significant exothermic peak around 160℃. This further indicates that 2-ethyl-4-methylimidazole (EMI) successfully reacted with the intermediate product in the second step of the reaction. Gel chromatography analysis revealed... Figure 5 As shown in the figure, the analysis shows that the molecular weight of the synthesized product is 5886, which meets the requirement of a high molecular weight, can solve the problem of small molecule migration, extend the storage period, and improve the operation time.

[0042] like Figure 1 As shown, due to the design of the synthetic scheme, the final product PME undergoes a reverse Michael addition reaction with increasing temperature, causing 2-ethyl-4-methylimidazole (EMI) to detach from the molecular chain, as... Figure 7 As shown, when the temperature rises to 120℃, a peak appears at a chemical shift of 6 ppm, which is the absorption peak on the carbon-carbon double bond. This indicates that as the temperature increases, the product begins to undergo the reverse Michael addition reaction, and 2-ethyl-4-methylimidazole begins to be released, thereby catalyzing the epoxy resin to undergo a curing reaction, achieving reaction polymerization at a lower temperature and improving application efficiency.

[0043] Preparation of flexible composite tube: First, cut three pieces of carbon fiber cloth, each 15 cm long and 7.5 cm wide, and weigh 3.6 g of product PME. Then, add 18 g of epoxy resin, stir thoroughly, and sonicate for 30 min. Place in an oven and heat at 60℃ for 5 min. Weigh 27 g of difunctional acrylate resin and 1.5 g of pentafunctional acrylate resin, add 0.66 g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, and sonicate for 10 min to dissolve the photoinitiator in the acrylate resin. Mix the prepared acrylate resin and epoxy resin in a 2:8 ratio, and remove air bubbles by vacuum for 30 min. Then, use a hand lay-up method to composite 30 g of resin with three pieces of carbon fiber cloth, each 15 cm long and 7.5 cm wide, and wrap it around a polytetrafluoroethylene rod mold. Irradiate with 365 nm ultraviolet light at an intensity of 50 mW / cm². 2 After irradiation for 10 minutes, a flexible composite material tube is obtained. When needed, it can be cured at 120 ℃ for 3 h or at 150 ℃ for 3 h, and the flexible composite material tube can be transformed into a rigid composite material tube.

[0044] The application process of flexible composite material pipes: A flexible pipe with a length greater than the damaged part is inserted into the pipeline system from the outermost damaged part. Then, the flexible pipe is passed through the damaged pipeline area inside and flattened on the outside of the original pipeline so that it fits tightly against the outer wall of the original pipeline. Then, in-situ rigidification is performed.

[0045] Characterization testing: The mechanical properties of the manufactured composite material tubes are tested, such as... Figure 8 , 9 As shown in Figures 10 and 11, the tensile modulus, strength, and elongation at break of the flexible composite tube are 0.11 MPa, 0.05 MPa, and 44%, respectively; while the tensile modulus, strength, and elongation at break of the rigid composite tube are 1866 MPa, 50 MPa, and 6.7%, respectively. Furthermore, the glass transition temperature of the flexible composite tube increases from -6.4℃ to 117.6℃, which is higher than that of the rigid composite tube. Therefore, it can be concluded that the material successfully completed the transformation from a flexible composite tube to a rigid composite tube.

[0046] Example 2:

[0047] The difference between this embodiment and Embodiment 1 is that the mass ratio of acrylate to epoxy resin is adjusted to 5:5, and a flexible composite material tube is obtained by photoinitiation, followed by thermal initiation to obtain a rigid composite material tube.

[0048] Characterization testing: The mechanical properties of the manufactured composite material tubes are tested, such as... Figure 12 , 13 As shown in Figures 14 and 15, the tensile modulus, strength, and elongation at break of the flexible composite tube are 4.36 MPa, 1.36 MPa, and 33.5%, respectively. The tensile modulus, strength, and elongation at break of the rigid composite tube are 812.9 MPa, 29.6 MPa, and 13.5%, respectively, and the glass transition temperature of the flexible composite tube is increased from 10.1℃ to 60.6℃ of the rigid composite tube.

Claims

1. A method for preparing a variable stiffness flexible composite material tube, characterized in that: The method is as follows: Step 1: Weigh the imidazole derivative curing agent, add it to the epoxy resin, stir thoroughly and sonicate for 25-35 min, then heat in an oven at 50-70 ℃ for 4-8 min to obtain resin A; the preparation method of the imidazole derivative curing agent (PME) is as follows: maleic anhydride, polyethylene glycol-400 and p-toluenesulfonic acid are stirred and reacted at 55-65 ℃ for 3 h under a nitrogen atmosphere, then heated to 100-120 ℃ for 4-5 h. After the reaction is completed, the water generated during esterification is removed in a vacuum oven; the obtained mixture is dissolved in dichloromethane and washed with saturated sodium chloride solution and saturated sodium carbonate solution to obtain intermediate product PM; then PM, 2-ethyl-4-methylimidazolium and 1,8-diazabicycloundec-7-ene are dissolved in acetonitrile and stirred and reacted at 40-50 ℃ under a nitrogen atmosphere for 10-12 minutes. h, after the reaction is completed, acetonitrile is removed by vacuum distillation, then the distillation product is dissolved in anhydrous ethanol and washed 3 to 5 times with petroleum ether, and then vacuum dried at 35 to 45 °C for 24 h. Step 2: Take difunctional acrylate resin and pentafunctional acrylate resin, add photoinitiator, and sonicate for 8-12 minutes to dissolve the photoinitiator in the acrylate resin to obtain resin B; Step 3: After mixing resin B and resin A, vacuum the mixture to remove air bubbles. Then, using a hand lay-up method, combine 25-35 g of resin with three pieces of carbon fiber cloth, each 15 cm long and 7.5 cm wide, and wrap them around a polytetrafluoroethylene rod-shaped mold. Illuminate the mold with 365 nm ultraviolet light at an intensity of 40-60 mW / cm². 2 Irradiate for 8-12 minutes to obtain a flexible composite material tube. When needed, cure at 110-130℃ for 2.5-3.5 h and at 140-160℃ for 2.5-3.5 h to transform the flexible composite material tube into a rigid composite material tube.

2. The method for preparing a variable stiffness flexible composite material tube according to claim 1, characterized in that: The molar ratio of maleic anhydride to polyethylene glycol-400 is 1:2~3, and the amount of p-toluenesulfonic acid added is 2~4% of the total mass of maleic anhydride and polyethylene glycol-400.

3. The method for preparing a variable stiffness flexible composite material tube according to claim 1, characterized in that: The molar ratio of PM to 2-ethyl-4-methylimidazole is 1:1~2, and the amount of 1,8-diazabicycloundec-7-ene added is 6~8% of the total mass of PM and 2-ethyl-4-methylimidazole.

4. A method for preparing a variable stiffness flexible composite material tube according to any one of claims 1 to 3, characterized in that: In step one, the mass ratio of the imidazole derivative curing agent to the epoxy resin is 1:4~6.

5. The method for preparing a variable stiffness flexible composite material tube according to claim 1, characterized in that: In step two, the photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

6. The method for preparing a variable stiffness flexible composite material tube according to claim 1, characterized in that: In step two, the mass ratio of the difunctional acrylate resin to the pentafunctional acrylate resin is 17~19:1; the mass ratio of the pentafunctional acrylate resin to the photoinitiator is 2.2~2.5:

1.

7. The method for preparing a variable stiffness flexible composite material tube according to claim 1, characterized in that: In step three, the total amount of resin A and resin B is 100%, of which resin A accounts for 50wt%~90wt%.

8. The application of a variable stiffness flexible composite material pipe prepared by the preparation method according to any one of claims 1 to 7 in emergency rescue, characterized in that: The application involves inserting a flexible tube, longer than the damaged section, into the pipeline system from the outermost damaged area. The flexible tube is then passed through the damaged pipeline area inside and flattened on the outside of the original pipeline to fit tightly against the outer wall of the original pipeline. Subsequently, in-situ rigidification is performed.

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