Preparation method and application of low-temperature-resistant anti-cracking epoxy resin composite material

Abstract

The invention discloses a preparation method and application of a low-temperature-resistant anti-cracking epoxy resin composite material, and belongs to the technical field of epoxy resin. According to the invention, the problems of poor impact resistance, cracking resistance, low-temperature toughness and low-temperature cracking resistance of the traditional epoxy resin as an insulator equipment material are solved. The preparation method of the composite material comprises the following steps: (1) taking 2, 5-furandicarboxylic acid and dipentaerythritol as raw materials to react to obtain a hydroxyl-terminated hyperbranched polymer; and (2) adding the hydroxyl-terminated hyperbranched polymer into a mixture of epoxy resin and a curing agent, dropwise adding an accelerant, carrying out ultrasonic treatment on the obtained epoxy resin mixed glue solution, pouring into a mold, heating and curing to obtain the epoxy resin composite material. The three-dimensional network structure of the hydroxyl-terminated hyperbranched polymer introduces a large number of cavities into epoxy resin, energy is absorbed when external force is applied, meanwhile, terminal hydroxyl participates in the curing process of the epoxy resin, the crosslinking density is improved, and improvement of the toughness of the epoxy resin is facilitated.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin technology, specifically to a method for preparing and applying a low-temperature resistant and crack-resistant epoxy resin composite material. Background Technology

[0002] Insulators, as core components in power systems providing electrical insulation and mechanical support, are crucial for ensuring safe power transmission and stable equipment operation. Their performance directly impacts the reliability and maintenance costs of the power grid. Throughout the development of the power industry, insulator materials have undergone multiple generations of iteration, initially primarily using inorganic materials such as ceramics and glass. Ceramic insulators offer advantages like high temperature resistance and high insulation strength, but suffer from drawbacks such as heavy weight, poor impact resistance, and susceptibility to breakage. Glass insulators offer stable insulation performance but are prone to cracking under extreme temperature variations, and both face the challenge of high maintenance costs in harsh environments. With the upgrading of global electricity demand, transmission systems are increasingly extending to harsh environments such as high altitudes, large temperature differences, and frequent sandstorms. Traditional materials are no longer adequate for the technical requirements of ultra-high voltage (UHV) and extra-high voltage (EHV) transmission lines and new energy power plants. Against this backdrop, epoxy resin-based composite materials have emerged as a core direction for insulator material upgrades due to their superior comprehensive performance. However, the high brittleness of epoxy resin after curing remains a major limitation to its application. Currently, the most widely studied methods for toughening epoxy resins include toughening with rubber elastomers, toughening with thermoplastic resins, toughening with nanoparticles, and toughening with hyperbranched polymers.

[0003] While the aforementioned methods can improve the room-temperature toughness of epoxy resin to some extent, existing toughening technologies offer limited improvement in the toughness of epoxy resin at low temperatures. The low-temperature crack resistance of epoxy resin materials remains insufficient, making it difficult to meet the requirements of insulators in high-altitude, cold regions with drastic temperature differences for long-term mechanical stability and fatigue resistance. Therefore, developing an epoxy resin material with good toughness and excellent low-temperature crack resistance has become a critical issue urgently needing to be addressed in the field of insulator technology. Summary of the Invention

[0004] To address the problems of poor impact resistance, crack resistance, low-temperature toughness, and low-temperature crack resistance of traditional epoxy resin as an insulator material, this invention provides a method for preparing and applying a low-temperature crack-resistant epoxy resin composite material.

[0005] The technical solution of the present invention is as follows: One objective of this invention is to provide a method for preparing a low-temperature resistant and crack-resistant epoxy resin composite material, the method comprising the following steps: Step 1: Preparation of hyperbranched polymers 2,5-furandicarboxylic acid and dipentaerythritol were dissolved in a solvent, and then a catalyst was added to carry out the reaction. The resulting solution was precipitated, filtered, washed and dried to obtain a hydroxyl-terminated hyperbranched polymer. Step 2: Preparation of low-temperature resistant and crack-resistant epoxy resin composite materials Epoxy resin and curing agent are mixed, and hydroxyl-terminated hyperbranched polymer is added. After mixing evenly, accelerator is added to obtain epoxy resin mixture. The epoxy resin mixture is ultrasonicated to remove air bubbles. After ultrasonication, the epoxy resin mixture is poured into a pretreated mold and cured by step temperature increase to obtain a low-temperature resistant and crack-resistant epoxy resin composite material.

[0006] To further specify, both 2,5-furandicarboxylic acid and dipentaerythritol in step one need to be dried in an oven at 60°C for 12 hours before use.

[0007] Further specifying, the organic solvent in step one is N-methylpyrrolidone, dimethyl sulfoxide, or dimethylacetamide.

[0008] Further specifying, the catalyst in step one is p-benzenesulfonic acid, methanesulfonic acid, or sulfuric acid.

[0009] Further specifying, the reaction temperature in step one is 160 ℃ and the time is 6 h.

[0010] Further specifying, in step one, the mass-volume ratio of 2,5-furandicarboxylic acid, dipentaerythritol, catalyst, and solvent is (1.5-1.8) g : (1.2-1.5) g : (0.03-0.04) g : (20-25) mL.

[0011] Further specifying, the curing agent in step two is methylhexahydrophthalic anhydride, and the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol.

[0012] Further specifying, the epoxy resin in step two is E51 type epoxy resin.

[0013] Further specifying, the amount of hyperbranched polymer used in step two is 1-7 wt% of epoxy resin.

[0014] Furthermore, the amount of hyperbranched polymer used is 1 wt%, 3 wt%, 5 wt%, or 7 wt% of the epoxy resin. Further specifying, the mass ratio of curing agent to epoxy resin in step two is (20-22):(22.5-25).

[0015] Further specifying, the mass ratio of accelerator to epoxy resin in step two is (0.22-0.25):(22.5-25).

[0016] Further specifying, the ultrasonic temperature in step two is 60 ℃, and the time is 0.5-1 h.

[0017] Further specifying, the step-by-step temperature curing regime in step two is as follows: hold at 80 ℃ for 2 h, then hold at 100 ℃ for 2 h, and finally hold at 120 ℃ for 2 h.

[0018] The second objective of this invention is to provide a low-temperature resistant and crack-resistant epoxy resin composite material prepared by the above method.

[0019] The third objective of this invention is to provide an application of the above-mentioned low-temperature resistant and crack-resistant epoxy resin composite material in insulator equipment materials.

[0020] The beneficial effects of this invention are as follows: (1) In this invention, a hyperbranched polymer is synthesized by mixing 2,5-furandicarboxylic acid and dipentaerythritol, while adding p-benzenesulfonic acid as a catalyst, and proceeding through steps such as reaction, precipitation, filtration, washing, and drying. Simultaneously, hydroxyl groups are capped by controlling the excess of dipentaerythritol relative to 2,5-furandicarboxylic acid. The hydroxyl-capped hyperbranched polymer is then added to the epoxy resin matrix as a toughening agent to modify the epoxy resin matrix and improve the low-temperature toughness of the epoxy resin composite material.

[0021] (2) The low-temperature resistant and crack-resistant epoxy resin composite material of the present invention exhibits excellent mechanical properties. The hydroxyl-terminated hyperbranched polymer has good compatibility with epoxy resin, and due to its unique three-dimensional network structure, it can introduce a large number of cavities into the epoxy resin, which can absorb energy when subjected to external force. At the same time, the presence of terminal hydroxyl groups can participate in the epoxy resin curing process, increasing the crosslinking points and improving the crosslinking density of the system. These characteristics all contribute to improving the toughness of epoxy resin and can effectively solve the problem of cracking of traditional epoxy resin. Therefore, it is very suitable as an insulator material. Furthermore, the hyperbranched polymer in the present invention is prepared by a one-step method, which is simple in preparation process, relatively low in cost, and conducive to large-scale production and application.

[0022] (3) The hyperbranched polymer of the present invention has a highly branched molecular structure. By combining with the epoxy resin matrix, it absorbs impact energy by means of the flexible deformation of the molecular chain and the internal cavity. At the same time, it can significantly improve the fracture toughness of the epoxy resin composite material while maintaining the key properties such as tensile strength. It can also simultaneously enhance the mechanical properties of the epoxy resin composite material under harsh environments such as low temperature. Attached Figure Description

[0023] Figure 1 Fourier transform infrared spectra of 2,5-furandicarboxylic acid, dipentaerythritol, and the hyperbranched polymer of Example 1, where curve a represents 2,5-furandicarboxylic acid, curve b represents dipentaerythritol, and curve c represents the hyperbranched polymer. Figure 2 The tensile and bending cross-sectional scanning electron microscope (SEM) images of the pure epoxy resin of Comparative Example 1 and the epoxy resin composite material of Example 3 with a hyperbranched polymer content of 5 wt% are shown below: (a) SEM image of the tensile cross-section of pure epoxy resin, (b) SEM image of the bending cross-section of pure epoxy resin, (c) SEM image of the tensile cross-section of epoxy resin composite material, and (d) SEM image of the bending cross-section of epoxy resin composite material. Figure 3 The X-ray diffraction patterns of the pure epoxy resin in Comparative Example 1 and the epoxy resin composites in Examples 1-4 with different amounts of hyperbranched polymers are shown below. Curve a represents the pure epoxy resin material without the addition of hyperbranched polymers, curve b represents the composite material with 1 wt% of epoxy resin and hyperbranched polymers, curve c represents the composite material with 3 wt% of epoxy resin and hyperbranched polymers, curve d represents the composite material with 5 wt% of epoxy resin and hyperbranched polymers, and curve e represents the composite material with 7 wt% of epoxy resin and hyperbranched polymers. Figure 4 The tensile strength test results of pure epoxy resin and epoxy resin composites doped with different amounts of hyperbranched polymers in Comparative Example 1 without high and low temperature cycling aging are shown. Curve a represents the pure epoxy resin material without the addition of hyperbranched polymers, curve b represents the composite material with 1 wt% of epoxy resin and hyperbranched polymers, curve c represents the composite material with 3 wt% of epoxy resin and hyperbranched polymers, curve d represents the composite material with 5 wt% of epoxy resin and hyperbranched polymers, and curve e represents the composite material with 7 wt% of epoxy resin and hyperbranched polymers. Figure 5 The tensile strength test graphs for pure epoxy resin of Comparative Example 1 and epoxy resin composites of Examples 1-4 with different amounts of hyperbranched polymers after one day of high and low temperature cycling are shown. Curve a represents pure epoxy resin material without hyperbranched polymer, curve b represents composite material with 1 wt% hyperbranched polymer, curve c represents composite material with 3 wt% hyperbranched polymer, curve d represents composite material with 5 wt% hyperbranched polymer, and curve e represents composite material with 7 wt% hyperbranched polymer. Figure 6The tensile strength test graphs for the pure epoxy resin of Comparative Example 1 and the epoxy resin composites of Examples 1-4 with different amounts of hyperbranched polymers after three days of high and low temperature cycling are shown. Curve a represents the pure epoxy resin material without the addition of hyperbranched polymers, curve b represents the composite material with 1 wt% of epoxy resin and hyperbranched polymers, curve c represents the composite material with 3 wt% of epoxy resin and hyperbranched polymers, curve d represents the composite material with 5 wt% of epoxy resin and hyperbranched polymers, and curve e represents the composite material with 7 wt% of epoxy resin and hyperbranched polymers. Figure 7 The graphs show the flexural strength of the pure epoxy resin in Comparative Example 1 and the epoxy resin composites in Examples 1-4 with different amounts of hyperbranched polymers without high and low temperature cycling aging. Curve a represents the pure epoxy resin material without hyperbranched polymers, curve b represents the composite material with 1 wt% hyperbranched polymer, curve c represents the composite material with 3 wt% hyperbranched polymer, curve d represents the composite material with 5 wt% hyperbranched polymer, and curve e represents the composite material with 7 wt% hyperbranched polymer. Figure 8 The graphs show the flexural strength of the pure epoxy resin of Comparative Example 1 and the epoxy resin composites of Examples 1-4 with different amounts of hyperbranched polymers after one day of high and low temperature cycling aging. Curve a represents the pure epoxy resin material without hyperbranched polymer, curve b represents the composite material with 1 wt% hyperbranched polymer, curve c represents the composite material with 3 wt% hyperbranched polymer, curve d represents the composite material with 5 wt% hyperbranched polymer, and curve e represents the composite material with 7 wt% hyperbranched polymer. Figure 9 The graphs show the flexural strength of the pure epoxy resin of Comparative Example 1 and the epoxy resin composites of Examples 1-4 with different amounts of hyperbranched polymers after three days of high and low temperature cycling aging. Curve a represents the pure epoxy resin material without hyperbranched polymer, curve b represents the composite material with 1 wt% hyperbranched polymer, curve c represents the composite material with 3 wt% hyperbranched polymer, curve d represents the composite material with 5 wt% hyperbranched polymer, and curve e represents the composite material with 7 wt% hyperbranched polymer. Figure 10The dielectric constant test graphs are for pure epoxy resin in Comparative Example 1 and epoxy resin composites doped with different amounts of hyperbranched polymers in Examples 1-4. ■ indicates pure epoxy resin material without hyperbranched polymer, ● indicates composite material with 1 wt% hyperbranched polymer, ▲ indicates composite material with 3 wt% hyperbranched polymer, ▼ indicates composite material with 5 wt% hyperbranched polymer, and ◆ indicates composite material with 7 wt% hyperbranched polymer. Figure 11 The dielectric loss test graphs are for pure epoxy resin in Comparative Example 1 and epoxy resin composites doped with different amounts of hyperbranched polymers in Examples 1-4; ■ represents pure epoxy resin material without hyperbranched polymer, ● represents composite material with 1 wt% hyperbranched polymer added to epoxy resin, ▲ represents composite material with 3 wt% hyperbranched polymer added to epoxy resin, ▼ represents composite material with 5 wt% hyperbranched polymer added to epoxy resin, and ◆ represents epoxy composite material with 7 wt% hyperbranched polymer added to epoxy resin. Detailed Implementation

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0025] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0026] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0027] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0028] Example 1 Step 1: Preparation of hyperbranched polymers 1.54 g of 2,5-furandicarboxylic acid and 1.27 g of dipentaerythritol were dissolved in 20 mL of N-methylpyrrolidone, followed by the addition of 0.03 g of p-benzenesulfonic acid. The reaction was carried out under magnetic stirring at 160 °C. The resulting solution was poured into 200 mL of deionized water and stirred to produce a precipitate. The precipitate was then filtered and washed with deionized water and alcohol. The solid was then dried in an oven at 60 °C for 12 h to obtain a hydroxyl-terminated hyperbranched polymer. 2,5-furandicarboxylic acid and dipentaerythritol need to be dried in an oven at 60 °C for 12 h before use. Step 2: Preparation of low-temperature resistant and crack-resistant epoxy resin composite materials Add 21.25 g of methylhexahydrophthalic anhydride to 25 g of epoxy resin and stir for 0.5 h until the two are uniformly mixed to obtain a mixture. Then add 0.25 g of hydroxyl-terminated hyperbranched polymer to the mixture and continue stirring for 0.5 h. The hyperbranched polymer is 1 wt% of the epoxy resin. Finally, add 0.25 g of 2,4,6-tris(dimethylaminomethyl)phenol and stir for 3-5 min. Place the stirred solution in an ultrasonic machine and sonicate at 60 ℃ for 0.5 h to remove air bubbles. Clean the mold surface with alcohol to remove impurities. Place the mold in an oven to dry and preheat at 80 ℃. Pour the ultrasonicated solution into the preheated mold for curing. During the curing process, the oven temperature is 80 ℃ for 2 h, then 100 ℃ for 2 h, and finally 120 ℃ for 2 h. After curing, remove the mold, cool it down, and then remove the sample. For subsequent cyclic aging tests, place the epoxy resin composite material in a high and low temperature oven for cyclic aging. The high and low temperature cyclic aging temperature is set to -30℃. The temperature was maintained at ℃ for 0.5 h, then at 130 ℃ for 0.5 h, and then dropped to -30 ℃ for 0.5 h, and this cycle was repeated.

[0029] Example 2 The difference between this embodiment and embodiment 1 is that: (2) the amount of hydroxyl-terminated hyperbranched polymer used is 3 wt% of epoxy resin, and the rest of the process operation and parameter settings are the same as in embodiment 1.

[0030] Example 3 The difference between this embodiment and embodiment 1 is that: (2) the amount of hydroxyl-terminated hyperbranched polymer used is 5 wt% of epoxy resin, and the rest of the process operation and parameter settings are the same as in embodiment 1.

[0031] Example 4 The difference between this embodiment and embodiment 1 is that: (2) the amount of hydroxyl-terminated hyperbranched polymer used is 7 wt% of epoxy resin, and the rest of the process operation and parameter settings are the same as in embodiment 1.

[0032] Comparative Example 1 The difference between this comparative example and Example 1 is that: no hydroxyl-terminated hyperbranched polymer is prepared; no hydroxyl-terminated hyperbranched polymer is added to the mixture; instead, 0.25 g of 2,4,6-tris(dimethylaminomethyl)phenol is added directly. The remaining process operations and parameter settings are the same as in Example 1. The resulting material is referred to as pure epoxy resin.

[0033] Figure 1 Curves a, b, and c in the figure are the Fourier transform infrared spectra of 2,5-furandicarboxylic acid, dipentaerythritol, and the hyperbranched polymer of Example 1, respectively. According to the infrared spectra, at a wavenumber of 3253 cm⁻¹... -1 The absorption peak corresponds to the characteristic peak of hydroxyl groups at a wavenumber of 1715 cm⁻¹. -1 The absorption peaks correspond to the characteristic peaks of ester bonds. The infrared spectrum shows that the hyperbranched polymer was successfully synthesized and hydroxyl end capping was achieved.

[0034] Figure 2 The images show scanning electron microscope (SEM) images of the tensile and flexural fracture surfaces of the pure epoxy resin in Comparative Example 1 and the epoxy resin composite material in Example 3. It can be seen that the tensile and flexural fracture surfaces of the pure epoxy resin are relatively smooth, with horizontal crack propagation paths and almost no deflection. However, after adding the hyperbranched polymer, the tensile and flexural fracture surfaces are significantly rougher, and no phase separation occurs. The tensile fracture surface shows the formation of numerous cavities after the addition of the hyperbranched polymer, and the flexural fracture surface shows the appearance of shear bands. These changes in microstructure are the reason for the improved mechanical properties of the epoxy resin.

[0035] Figure 3 The X-ray diffraction (XRD) spectra of pure epoxy resin and epoxy resin composites doped with different amounts of hyperbranched polymers are shown in Comparative Example 1. As can be seen from curve ae, since the hydroxyl-terminated hyperbranched polymers can participate in the epoxy resin curing process and have good compatibility with epoxy resin, no second phase will appear. Therefore, the XRD patterns of the epoxy resin composites before and after the addition of the hyperbranched polymers did not produce new diffraction peaks, and still showed a relatively broad diffuse peak.

[0036] Figure 4The figures show the tensile strength tests of pure epoxy resin and epoxy resin composites doped with different amounts of hyperbranched polymers in Comparative Example 1, without high and low temperature cycling aging. It can be seen that the tensile strength of the epoxy resin composites gradually increases with the increase of the hyperbranched polymer content. The maximum tensile strength of pure epoxy resin without hyperbranched polymer is 51.2 MPa, and the elongation at break reaches 4.3%. When the hyperbranched polymer content is 7 wt%, the tensile strength of the epoxy resin composite increases to 64.1 MPa, and the elongation at break reaches 5.0%, both properties are improved. This is because the unique three-dimensional spherical topology of the hyperbranched polymer can absorb some energy when stress occurs, and the hydroxyl end capping allows it to participate in the epoxy resin curing process, increasing the crosslinking density and thus improving the toughness of the epoxy resin.

[0037] Figure 5 The graph shows the tensile strength test results of pure epoxy resin and epoxy resin composites doped with different amounts of hyperbranched polymers after one day of high and low temperature cyclic aging, as shown in Comparative Example 1. It can be seen that after one day of cyclic aging, the maximum tensile strength of pure epoxy resin is 47.1 MPa, a decrease of approximately 8% compared to the unaged epoxy resin. The maximum tensile strength of the epoxy resin composite with 7 wt% hyperbranched polymer is 61.6 MPa, a decrease of approximately 4% compared to the unaged epoxy resin composite. Furthermore, regardless of the amount of hyperbranched polymer, its tensile strength is higher than that of pure epoxy resin after cyclic aging.

[0038] Figure 6 The graph shows the tensile strength test results of pure epoxy resin and epoxy resin composites doped with different amounts of hyperbranched polymers in Comparative Example 1 after three days of high and low temperature cyclic aging. It can be seen that after three days of cyclic aging, the maximum tensile strength of pure epoxy resin is 44.0 MPa, a decrease of approximately 14% compared to before aging. The maximum tensile strength of the epoxy resin composite with 7 wt% hyperbranched polymer is 57.6 MPa, a decrease of approximately 10% compared to before aging, but still higher than the maximum tensile strength of pure epoxy resin before aging.

[0039] Figure 7 The figures show the flexural strength tests of pure epoxy resin and epoxy resin composites doped with different amounts of hyperbranched polymers in Comparative Example 1, without high and low temperature cycling. It can be seen that the flexural strength of the epoxy resin composites gradually increases with the increase of the hyperbranched polymer content. The maximum flexural strength of pure epoxy resin without hyperbranched polymer is 107.3 MPa, and the elongation at break reaches 4.4%. When the hyperbranched polymer content is 7 wt%, the maximum flexural strength of the epoxy resin composite increases to 134.5 MPa, and the elongation at break reaches 5.2%, both properties are improved.

[0040] Figure 8 The graph shows the flexural strength test results of pure epoxy resin and epoxy resin composites doped with different amounts of hyperbranched polymers (Comparative Example 1) after one day of high and low temperature cyclic aging. It can be seen that after one day of cyclic aging, the maximum flexural strength of pure epoxy resin is 99.1 MPa, a decrease of approximately 7% compared to the unaged epoxy resin. The maximum flexural strength of the epoxy resin composite with 7 wt% hyperbranched polymer is 129.3 MPa, a decrease of approximately 4% compared to the unaged epoxy resin composite. Furthermore, regardless of the amount of hyperbranched polymer, the flexural strength of the composite after cyclic aging is higher than that of pure epoxy resin.

[0041] Figure 9 The figures show the flexural strength tests of pure epoxy resin and epoxy resin composites doped with different amounts of hyperbranched polymers in Comparative Example 1 after three days of high and low temperature cyclic aging. It can be seen that after three days of cyclic aging, the maximum tensile strength of the pure epoxy resin is 89.9 MPa, a decrease of approximately 16% compared to before aging. The maximum tensile strength of the epoxy resin composite with 7 wt% hyperbranched polymer is 121.8 MPa, a decrease of approximately 9% compared to the unaged epoxy resin composite. Even after aging, the epoxy resin composite still maintains a high level of flexural strength.

[0042] Figure 10 The graph shows the dielectric constant of pure epoxy resin and epoxy resin composites doped with different amounts of hyperbranched polymers, as compared to Example 1. It can be seen that the dielectric constant of the epoxy resin composites gradually decreases with increasing hyperbranched polymer content. This is because the terminal hydroxyl groups of the hyperbranched polymer react with the epoxy groups of the epoxy resin, consuming some of the strongly polar epoxy groups. Simultaneously, the branched structure hinders the directional arrangement of polar groups, weakening the polarization ability. As the amount of hyperbranched polymer increases, this polarity weakening effect becomes more significant, leading to a further decrease in the dielectric constant.

[0043] Figure 11 The graphs show the dielectric loss of pure epoxy resin and epoxy resin composites doped with different amounts of hyperbranched polymers in Comparative Example 1. It can be seen that the dielectric loss of the epoxy resin composites gradually decreases with increasing hyperbranched polymer content. This is because the hyperbranched polymer has a high degree of branching, restricting the movement of molecular chain segments. Furthermore, after the terminal hydroxyl groups react with the epoxy groups, the number of freely oriented polar groups in the system decreases, weakening the dipole polarization under an external electric field and reducing polarization loss.

[0044] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-temperature resistant and crack-resistant epoxy resin composite material, characterized in that, The method includes the following steps: Step 1: Preparation of hyperbranched polymers: 2,5-furandicarboxylic acid and dipentaerythritol were dissolved in a solvent, and then a catalyst was added to carry out the reaction. The resulting solution was precipitated, filtered, washed and dried to obtain a hydroxyl-terminated hyperbranched polymer. Step 2: Preparation of low-temperature resistant and crack-resistant epoxy resin composite material: Epoxy resin and curing agent are mixed, and hydroxyl-terminated hyperbranched polymer is added. After mixing evenly, accelerator is added to obtain epoxy resin mixture. The epoxy resin mixture is ultrasonicated to remove air bubbles. After ultrasonication, the epoxy resin mixture is poured into a pretreated mold and cured by gradient temperature increase to obtain a low-temperature resistant and crack-resistant epoxy resin composite material.

2. The preparation method according to claim 1, characterized in that, In step one, the solvent is N-methylpyrrolidone, dimethyl sulfoxide, or dimethylacetamide, and the catalyst is p-benzenesulfonic acid, methanesulfonic acid, or sulfuric acid.

3. The preparation method according to claim 1, characterized in that, In step one, the reaction temperature is 160 ℃ and the time is 6 h.

4. The preparation method according to claim 1, characterized in that, In step one, the mass-volume ratio of 2,5-furandicarboxylic acid, dipentaerythritol, catalyst, and solvent is (1.5-1.8) g : (1.2-1.5) g : (0.03-0.04) g : (20-25) mL.

5. The preparation method according to claim 1, characterized in that, In step two, the curing agent is methylhexahydrophthalic anhydride, the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol, and the epoxy resin is E51 type epoxy resin.

6. The preparation method according to claim 1, characterized in that, In step two, the amount of hyperbranched polymer used is 1-7 wt% of epoxy resin.

7. The preparation method according to claim 5, characterized in that, In step two, the mass ratio of curing agent to epoxy resin is (20-22):(22.5-25), and the mass ratio of accelerator to epoxy resin is (0.22-0.25):(22.5-25).

8. The preparation method according to claim 5, characterized in that, The gradient temperature curing regime in step two is as follows: hold at 80 ℃ for 2 h, then hold at 100 ℃ for 2 h, and finally hold at 120 ℃ for 2 h.

9. A low-temperature resistant and crack-resistant epoxy resin composite material, characterized in that, Prepared by the preparation method according to any one of claims 1-8.

10. The application of the low-temperature resistant and crack-resistant epoxy resin composite material according to claim 9 in insulator equipment materials.

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