A high and low temperature resistant epoxy resin adhesive and its synthesis process

Abstract

The present invention provides a kind of high and low temperature resistant epoxy resin glue and its synthesis process, the epoxy resin glue includes the following parts by weight of raw materials: 60-80 parts of bisphenol A epoxy resin, 5-15 parts of polynorbornene, 10-20 parts of polysiloxane, 0.3-0.5 parts of tris(triphenylphosphine) rhodium chloride, 20-40 parts of solvent, 5-10 parts of bio-based cross-linking agent, 2-6 parts of nanofiller, 10-20 parts of diluent, 1-3 parts of coupling agent. By adding polynorbornene to epoxy resin, an interpenetrating network is formed, and this network structure can better resist deformation when stretched, thereby improving tensile strength. The rigidity and strength characteristics of polynorbornene can enhance the bending resistance of epoxy resin glue, so that it can better maintain shape and stability when subjected to bending stress. By adding polysiloxane to embed flexible chains in epoxy resin, epoxy resin toughness is improved, so that epoxy resin glue can better absorb and disperse energy when subjected to tensile stress, further improving tensile strength.

Description

Technical Field

[0001] The invention relates to the technical field of epoxy resins, and in particular to a high and low temperature resistant epoxy resin adhesive and a synthesis process thereof. Background Art

[0002] As a high-performance material, epoxy resin is widely used in coatings, adhesives, potting compounds and other fields due to its excellent bonding properties, outstanding corrosion resistance and good mechanical properties. Its unique properties enable epoxy resin to play an excellent role in a variety of application scenarios. In recent years, with the rapid development of national defense, aerospace and large-scale engineering fields, the requirements for material performance have been increasing, and epoxy resin glue has become increasingly popular in these fields due to its many advantages. However, the existing epoxy resin glue also has some shortcomings, such as greater brittleness, relatively poor toughness, and impact resistance needs to be improved. These problems have limited the application of epoxy resin glue in certain specific environments to a certain extent. Summary of the invention

[0003] In view of this, the present invention proposes an epoxy resin adhesive resistant to high and low temperatures and a synthesis process thereof to solve the above problems.

[0004] The technical solution of the present invention is achieved as follows: a high and low temperature resistant epoxy resin glue comprises the following raw materials in parts by weight: 60-80 parts of bisphenol A epoxy resin, 5-15 parts of polynorbornene, 10-20 parts of polysiloxane, 0.3-0.5 parts of tris(triphenylphosphine)rhodium chloride, 20-40 parts of solvent, 5-10 parts of bio-based cross-linking agent, 2-6 parts of nanofiller, 10-20 parts of diluent, and 1-3 parts of coupling agent.

[0005] Furthermore, the solvent is composed of cyclohexane and dichloromethane in a volume ratio of (7-9):(1.5-2.5).

[0006] Furthermore, the bio-based cross-linking agent is prepared by the following method: adding lignin to a 10wt% sodium hydroxide solution, heating to 55-65°C, maintaining heating for 1.5-2.5h, adding sodium chlorite, reacting for 3-5h, the mass volume ratio of lignin, sodium chlorite, and sodium hydroxide solution is (1.0-2.0):(0.5-1.5):(10-20) g / mL, adding dilute hydrochloric acid to adjust the pH to 7.0, filtering out the solids, and washing with deionized water to obtain modified lignin; adding chitosan to a 2wt% acetic acid solution, the mass volume ratio of chitosan and acetic acid solution is (1.0-2.0):(0.5-1.5):(10-20) g / mL, The ratio of g / mL is (1-2):(8-15), heated to 45-55°C, stirred until completely dissolved, and the insoluble matter is filtered out to obtain a chitosan solution; the modified lignin and chitosan solution are mixed at a mass volume ratio of g / mL (2.8-3.2):(1.9-2.1), 4-6% citric acid by volume of the above mixture is added, and the mixture is reacted at 60-80°C at 200-400r / min while being stirred for 5-7h; the solid is filtered out, washed with ethanol, and then placed in an oven and dried at 45-55°C for 20-25h to obtain a bio-based cross-linking agent.

[0007] Furthermore, the nano filler is one or a combination of nano silicon dioxide, nano aluminum oxide, nano boron nitride, nano zinc oxide, and nano carbon nitride, and the particle size of the nano filler is 40-100 nm.

[0008] Furthermore, the diluent is composed of butyl glycidyl ether and acetone in a volume ratio of (1-3):(2-4).

[0009] Furthermore, the coupling agent is one of γ-aminopropyltriethoxysilane, γ-glycidyloxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane.

[0010] Furthermore, a synthesis process of a high and low temperature resistant epoxy resin adhesive comprises the following steps:

[0011] S1. Weigh polynorbornene, tris(triphenylphosphine)rhodium chloride and solvent by weight, add polynorbornene to the solvent to dissolve, add tris(triphenylphosphine)rhodium chloride, and react under inert gas protection at 60-80° C. for 2-4 hours to obtain a pre-crosslinked polynorbornene network for standby use; the inert gas is one of nitrogen, argon and helium;

[0012] S2, weighing bisphenol A epoxy resin, polysiloxane, nanofiller, diluent, and coupling agent according to weight, stirring and mixing evenly to obtain a mixture I;

[0013] S3, swelling the pre-crosslinked polynorbornene network into the mixture I, stirring and mixing evenly to obtain a mixture II;

[0014] S4. Weigh the bio-based cross-linking agent by weight and add it to the mixture II. Then, place it in a microwave reaction device and react at 120-150°C for 0.5-1.5h. Raise the temperature to 160-180°C and continue to react for 1.0-2.0h. Then, raise the temperature to 200-220°C and react for 1.0-1.5h. Take out the reaction product and cool it to 25-30°C to obtain an epoxy resin adhesive.

[0015] Furthermore, the stirring speed in S1 is 200-400 r / min, the stirring speed in S2 is 300-600 r / min, and the stirring time is 10-20 min; the stirring speed in S3 is 200-400 r / min, and the stirring time is 30-40 min.

[0016] Furthermore, in S4, the ultrasonic power is 200-500 W, the ultrasonic frequency is 20-40 kHz, and the ultrasonic treatment time is 20-30 min; the microwave power is 300-600 W, and the microwave frequency is 2-3 GHz.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention forms an interpenetrating network by adding polynorbornene to epoxy resin, so that a tighter and more stable cross-linked network is formed between epoxy resin and polynorbornene, and this network structure can better resist deformation during stretching, thereby improving tensile strength. By adding polysiloxane to embed flexible chains in epoxy resin, the toughness of epoxy resin is improved, so that epoxy resin glue can better absorb and disperse energy when subjected to tensile stress, and further improves tensile strength. The rigidity and strength characteristics of polynorbornene can enhance the bending resistance of epoxy resin glue, so that it can better maintain shape and stability when subjected to bending stress. And the interpenetrating network structure helps to disperse stress during bending, prevent local damage caused by stress concentration, and thus improve overall bending strength. The embedded flexible chain can adapt to shape changes during bending, reduce internal stress caused by bending, and further improve bending strength.

[0018] The bio-based cross-linking agent of the present invention is prepared by reacting modified lignin and chitosan, and contains a large number of hydroxyl, carboxyl, and amino active groups in its molecular structure. These groups can react chemically with the epoxy groups of the epoxy resin during the curing process to form a dense cross-linking network, so that the epoxy resin glue can effectively disperse and transfer stress when subjected to tensile force, thereby improving the tensile strength and enhancing the overall rigidity and bending resistance of the material. During the modification process of the lignin in the bio-based cross-linking agent, the lignin is subjected to alkali treatment and oxidation treatment, and part of the structure is destroyed to form flexible segments, which are introduced into the epoxy resin glue, so that the epoxy resin glue can still maintain a certain elasticity at low temperatures, thereby improving its low temperature resistance. When the epoxy resin glue is subjected to external force, these flexible segments can undergo conformational changes, absorb and disperse energy, thereby preventing the material from brittle cracking.

[0019] The present invention improves the dispersibility and compatibility of various raw materials in the epoxy resin glue by ultrasonic treatment, so that various raw materials are more evenly distributed in the epoxy resin glue. This uniform dispersion helps to form a denser cross-linked network, thereby enhancing the tensile strength of the epoxy resin glue. In addition, the mechanical vibration and cavitation effect generated by the ultrasonic treatment help to break the weaker chemical bonds in the epoxy resin, so that the chemical bonds with stronger force are rearranged and formed, which helps to improve the bending strength of the epoxy resin glue.

[0020] The present invention heats the epoxy resin glue quickly and evenly by microwave treatment, so that it reaches a higher temperature in a short time, thereby accelerating the cross-linking reaction. This accelerated cross-linking reaction helps to form a more dense and uniform cross-linking network, thereby enhancing the tensile strength of the epoxy resin glue. At the same time, microwave treatment can also promote the movement and rearrangement of epoxy resin molecular chains, help eliminate internal stress, and further improve tensile strength. And the heat generated by microwave treatment can be evenly distributed in the epoxy resin glue, so that it can be evenly heated and cross-linked in all directions. This uniform heating and cross-linking helps to improve the overall uniformity of the epoxy resin glue, thereby enhancing its ability to resist bending stress. And microwave treatment can also promote the dispersion and anchoring of nano fillers in the epoxy resin glue, so that it can better play a reinforcing role and further improve bending strength. DETAILED DESCRIPTION

[0021] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0022] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0023] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0024] Example 1

[0025] A high and low temperature resistant epoxy resin adhesive comprises the following raw materials in parts by weight: 60 parts of bisphenol A epoxy resin, 5 parts of polynorbornene, 10 parts of polysiloxane, 0.3 parts of tri(triphenylphosphine)rhodium chloride, 20 parts of solvent, 5 parts of bio-based crosslinking agent, 2 parts of nanofiller, 10 parts of diluent, 1 part of coupling agent, and 0.5 parts of catalyst. Among them, the solvent is composed of cyclohexane and dichloromethane in a volume ratio of 7:1.5, the nanofiller is nanosilicon dioxide and the particle size of the nanofiller is 40nm, the diluent is composed of butyl glycidyl ether and acetone in a volume ratio of 1:2, and the coupling agent is γ-aminopropyltriethoxysilane.

[0026] The bio-based cross-linking agent is prepared by the following method: adding lignin to a 10wt% sodium hydroxide solution, heating to 55°C, keeping heating for 2.5h, adding sodium chlorite, reacting for 5h, the mass volume ratio of lignin, sodium chlorite and sodium hydroxide solution is 1.0:0.5:10 g / mL, adding dilute hydrochloric acid to adjust the pH to 7.0, filtering out the solids, washing with deionized water to obtain modified lignin; adding chitosan to a 2wt% acetic acid solution, chitosan, acetic acid The acid solution has a mass volume ratio of g / mL of 1:8, is heated to 45°C, stirred until completely dissolved, and insoluble matter is filtered out to obtain a chitosan solution; the modified lignin and chitosan solution are mixed at a mass volume ratio of g / mL2.8:1.9, 4% citric acid by volume of the above mixture is added, and the mixture is reacted at 60°C with stirring at 200r / min for 7h; the solid is filtered out, washed with ethanol, and then placed in an oven and dried at 45°C for 25h to obtain a bio-based cross-linking agent.

[0027] Example 2

[0028] A high and low temperature resistant epoxy resin adhesive comprises the following raw materials by weight: 80 parts of bisphenol A epoxy resin, 15 parts of polynorbornene, 20 parts of polysiloxane, 0.5 parts of tri(triphenylphosphine)rhodium chloride, 40 parts of solvent, 10 parts of bio-based crosslinking agent, 6 parts of nanofiller, 20 parts of diluent, 3 parts of coupling agent, and 2.0 parts of catalyst. Among them, the solvent is composed of cyclohexane and dichloromethane in a volume ratio of 9:2.5, the nanofiller is a combination of nanoalumina and nanoboron nitride in a ratio of 1:1 and the particle size of the nanofiller is 100nm, the diluent is composed of butyl glycidyl ether and acetone in a volume ratio of 3:4, and the coupling agent is γ-methacryloxypropyltrimethoxysilane.

[0029] The bio-based cross-linking agent is prepared by the following method: adding lignin to a 10wt% sodium hydroxide solution, heating to 65°C, keeping heating for 1.5h, adding sodium chlorite, reacting for 3h, the mass volume ratio of lignin, sodium chlorite, and sodium hydroxide solution is 2.0:1.5:20 g / mL, adding dilute hydrochloric acid to adjust the pH to 7.0, filtering out the solids, washing with deionized water to obtain modified lignin; adding chitosan to a 2wt% acetic acid solution, chitosan, acetic acid The solution has a mass volume ratio of g / mL of 2:15, is heated to 55°C, stirred until completely dissolved, and insoluble matter is filtered out to obtain a chitosan solution; the modified lignin and chitosan solution are mixed at a mass volume ratio of g / mL3.2:2.1, 6% citric acid by volume of the above mixture is added, and the mixture is reacted at 80°C with stirring at 400r / min for 5h; the solid is filtered out, washed with ethanol, and then placed in an oven and dried at 55°C for 20h to obtain a bio-based cross-linking agent.

[0030] Example 3

[0031] A high and low temperature resistant epoxy resin adhesive comprises the following raw materials by weight: 70 parts of bisphenol A epoxy resin, 10 parts of polynorbornene, 15 parts of polysiloxane, 0.4 parts of tri(triphenylphosphine)rhodium chloride, 30 parts of solvent, 8 parts of bio-based crosslinking agent, 4 parts of nanofiller, 15 parts of diluent, 2 parts of coupling agent, and 1.3 parts of catalyst. Among them, the solvent is composed of cyclohexane and dichloromethane in a volume ratio of 8:2, the nanofiller is a combination of nano silicon dioxide, nano zinc oxide, and nano carbon nitride in a ratio of 1:1:1, and the particle size of the nanofiller is 70nm, the diluent is composed of butyl glycidyl ether and acetone in a volume ratio of 2:3, and the coupling agent is γ-glycidyl ether oxypropyl trimethoxysilane.

[0032] The bio-based cross-linking agent is prepared by the following method: adding lignin to a 10wt% sodium hydroxide solution, heating to 60°C, keeping heating for 2.0h, adding sodium chlorite, reacting for 4h, the mass volume ratio of lignin, sodium chlorite, and sodium hydroxide solution is 1.5:1.0:15 g / mL, adding dilute hydrochloric acid to adjust the pH to 7.0, filtering out the solids, washing with deionized water, and obtaining modified lignin; adding chitosan to a 2wt% acetic acid solution, the mass volume ratio of chitosan and acetic acid solution is 1.5:1.0:15 g / mL, The mass volume ratio g / mL is 1.5:11.5, heated to 50°C, stirred until completely dissolved, and the insoluble matter was filtered out to obtain a chitosan solution; the modified lignin and chitosan solution were mixed at a mass volume ratio of g / mL3.0:2.0, 5% citric acid by volume of the above mixture was added, and the mixture was reacted at 70°C with stirring at 300r / min for 6h; the solid was filtered out, washed with ethanol, and then placed in an oven and dried at 50°C for 22.5h to obtain a bio-based cross-linking agent.

[0033] The high and low temperature resistant epoxy resin adhesive in Example 1-3 is synthesized according to the following process, including the following steps:

[0034] S1. Weigh polynorbornene, tris(triphenylphosphine)rhodium chloride and solvent by weight, add polynorbornene to the solvent to dissolve, add tris(triphenylphosphine)rhodium chloride, and react at 70° C. and 300 r / min under nitrogen protection for 3 hours to obtain a pre-crosslinked polynorbornene network for standby use;

[0035] S2, weighing bisphenol A epoxy resin, polysiloxane, nanofiller, diluent, and coupling agent by weight, stirring at 500 r / min for 15 min to mix them evenly, to obtain a mixture I;

[0036] S3, adding the pre-crosslinked polynorbornene network into the mixture I, stirring at 300 r / min for 35 min to mix them evenly, to obtain a mixture II;

[0037] S4. Weigh the bio-based cross-linking agent by weight and add it to the mixture II. Ultrasonic treatment is carried out for 250 minutes at an ultrasonic power of 400 W and an ultrasonic frequency of 30 kHz. Then, it is placed in a microwave reaction device and reacted at a microwave power of 5 W, a microwave frequency of 2.5 GHz and at 135°C for 1.0 hour. The temperature is increased to 170°C and the reaction is continued for 1.5 hours. The temperature is then increased to 210°C and the reaction is continued for 1.2 hours. The reaction product is taken out and cooled to 27°C to obtain an epoxy resin glue.

[0038] Example 4

[0039] Compared with Embodiment 3, the present embodiment is different in that the high and low temperature resistant epoxy resin adhesive of Embodiment 4 is synthesized according to the following process, including the following steps:

[0040] S1. Weigh polynorbornene, tris(triphenylphosphine)rhodium chloride and solvent by weight, add polynorbornene to the solvent to dissolve, add tris(triphenylphosphine)rhodium chloride, and react under argon protection at 60° C. at 200 r / min for 4 hours to obtain a pre-crosslinked polynorbornene network for standby use;

[0041] S2, weighing bisphenol A epoxy resin, polysiloxane, nanofiller, diluent, and coupling agent by weight, stirring at 300 r / min for 20 min to mix them evenly, to obtain a mixture I;

[0042] S3, adding the pre-crosslinked polynorbornene network into the mixture I, stirring at 2000 r / min for 40 min to mix them evenly, to obtain a mixture II;

[0043] S4. Weigh the bio-based cross-linking agent by weight and add it to the mixture II. Ultrasonic treatment is carried out for 30 minutes at an ultrasonic power of 200 W and an ultrasonic frequency of 20 kHz. Then, it is placed in a microwave reaction device and reacted at a microwave power of 300 W, a microwave frequency of 2 GHz and at 120°C for 1.5 hours. The temperature is increased to 160°C and the reaction is continued for 2.0 hours. The temperature is then increased to 200°C and the reaction is continued for 1.5 hours. The reaction product is taken out and cooled to 25°C to obtain an epoxy resin glue.

[0044] Example 5

[0045] Compared with Embodiment 3, the present embodiment is different in that the high and low temperature resistant epoxy resin adhesive of Embodiment 5 is synthesized according to the following process, including the following steps:

[0046] S1. Weigh polynorbornene, tris(triphenylphosphine)rhodium chloride, and solvent by weight, add polynorbornene to the solvent to dissolve, add tris(triphenylphosphine)rhodium chloride, and react under helium protection at 80° C. at 400 r / min for 2 h to obtain a pre-crosslinked polynorbornene network for standby use;

[0047] S2, weighing bisphenol A epoxy resin, polysiloxane, nanofiller, diluent, and coupling agent by weight, stirring at 600 r / min for 10 min to mix them evenly, to obtain a mixture I;

[0048] S3, adding the pre-crosslinked polynorbornene network into the mixture I, stirring at 400 r / min for 30 min to mix them evenly, to obtain a mixture II;

[0049] S4. Weigh the bio-based cross-linking agent by weight and add it to the mixture II. Ultrasonic treatment is carried out for 20 minutes at an ultrasonic power of 500 W and an ultrasonic frequency of 40 kHz. Then, it is placed in a microwave reaction device and reacted at a microwave power of 600 W, a microwave frequency of 3 GHz and at 150°C for 0.5 h. The temperature is increased to 180°C and the reaction is continued for 1.0 h. The temperature is then increased to 220°C and the reaction is continued for 1.0. The reaction product is taken out and cooled to 30°C to obtain an epoxy resin adhesive.

[0050] Comparative Example 1

[0051] Compared with Example 3, this comparative example is different in that the raw material does not contain polynorbornene, solvent, and tris(triphenylphosphine)rhodium chloride, and the steps related thereto are removed in the synthesis process, i.e., a high and low temperature resistant epoxy resin adhesive is synthesized according to the following process, comprising the following steps:

[0052] S1. Weigh bisphenol A epoxy resin, polysiloxane, nanofiller, diluent and coupling agent by weight, stir at 600 r / min for 10 min to mix them evenly, and obtain mixture I;

[0053] S2. Weigh the cross-linking agent and catalyst by weight and add them to the mixture I. Ultrasonic treatment is carried out for 20 minutes at an ultrasonic power of 500 W and an ultrasonic frequency of 40 kHz. Then, the mixture is placed in a microwave reaction device and reacted at a microwave power of 600 W, a microwave frequency of 3 GHz and at 135°C for 1.0 hour. The temperature is increased to 170°C and the reaction is continued for 1.5 hours. The temperature is then increased to 210°C and the reaction is continued for 1.2 hours. The reaction product is taken out and cooled to 30°C to obtain an epoxy resin adhesive.

[0054] Comparative Example 2

[0055] The difference between this comparative example and Example 3 is that the raw materials do not contain a bio-based cross-linking agent.

[0056] Comparative Example 3

[0057] This comparative example is compared with Example 3, except that the bio-based cross-linking agent consists only of modified lignin.

[0058] Comparative Example 4

[0059] The difference between this comparative example and Example 3 is that no ultrasonic treatment is performed in step S4 of the epoxy resin gluing process.

[0060] Comparative Example 5

[0061] The difference between this comparative example and Example 3 is that microwave treatment is not performed in step S4 of the epoxy resin gluing process.

[0062] 1. Performance testing

[0063] The epoxy resin adhesives prepared in Examples 1-5 and Comparative Examples 1-5 were respectively tested for performance according to the following method.

[0064] 1.1 Tensile strength test

[0065] The tensile strength test was carried out according to GB / T 1040-2006 standard. The epoxy resin adhesives synthesized in Examples 1-5 and Comparative Examples 1-5 were respectively made into 1BA type specimens. The specimens were made into the following specifications: width 5 mm, thickness 2 mm, length 75 mm, and the tensile rate was set to 10 mm / min. Each specimen was tested 5 times, and the average value was taken. The results are shown in Table 1.

[0066] 1.2 Bending strength test

[0067] The bending strength test was carried out according to GB / T 9341-2008 standard. The epoxy resin adhesives synthesized in Examples 1-5 and Comparative Examples 1-5 were respectively made into long strip specimens. The specimens were made into the following specifications: width 10 mm, thickness 4 mm, length 80 mm, and the bending rate was set to 2 mm / min. Each specimen was tested 5 times, and the average value was taken. The results are shown in Table 1.

[0068] 1.3 High and low temperature impact resistance test

[0069] The epoxy resin glue synthesized in Examples 1-5 and Comparative Examples 1-5 was made into samples of the following specifications: width 10mm, thickness 4mm, length 80mm, and 5 samples of each sample were made. The samples were placed in a test box, the temperature was set to 100°C for 3 hours, and then the temperature was set to -50°C for 3 hours, and the cycle was repeated 3 times. After the above operations were completed, an impact test was performed in accordance with GB / T 1843-2008 standard, and the pendulum energy was set to 3.0J. After the test, the sample was observed to see if there were cracks or cracks, and the observation results were recorded in Table 1.

[0070] Table 1

[0071] Tensile strength / MPa Bending strength / MPa High and low temperature impact resistance Example 1 72.7 135.5 No cracks or cracks Example 2 73.4 134.2 No cracks or cracks Example 3 75.3 138.7 No cracks or cracks Example 4 72.5 135.4 No cracks or cracks Example 5 71.9 134.1 No cracks or cracks Comparative Example 1 48.5 91.8 No cracks, small cracks Comparative Example 2 61.7 114.3 No cracks, small cracks Comparative Example 3 60.2 106.7 No cracks, small cracks Comparative Example 4 66.5 120.6 No cracks or cracks Comparative Example 5 63.1 113.8 No cracks or cracks

[0072] It can be seen from Table 1 that the epoxy resin adhesives prepared in Examples 1-5 have excellent high and low temperature impact resistance, high tensile strength and high bending strength, among which Example 3 has the best performance.

[0073] Compared with Comparative Example 1, Example 3 shows that the tensile strength is increased by 55.3%, the bending strength is increased by 51.1%, and the high and low temperature impact resistance is also improved. This is because by adding polynorbornene, the molecular chains of polynorbornene and the molecular chains of epoxy resin are interlaced and interwoven with each other, forming a close combination and forming an interpenetrating network structure. This network structure can better resist deformation during stretching, thereby improving the tensile strength. The rigidity and strength characteristics of polynorbornene can enhance the bending resistance of epoxy resin glue, so that it can better maintain its shape and stability when subjected to bending stress. And the interpenetrating network structure helps to disperse stress during bending and prevent local damage caused by stress concentration, thereby improving the overall bending strength. The molecular chain of polynorbornene can maintain its specific arrangement at high and low temperatures. The cyclic structure and strong interaction force in the molecular chain of polynorbornene make it difficult for the molecular chain to deform due to thermal motion at high temperatures and not easy to lose activity due to freezing at low temperatures. In high temperature environments, the molecular chain arrangement stability of polynorbornene helps prevent thermal deformation or softening of epoxy resin glue. Even if the temperature rises, the molecular chain of polynorbornene can maintain its rigidity, thereby supporting the structure of the entire epoxy resin glue. At the same time, the cross-linking points in the interpenetrating network structure can resist thermal degradation at high temperatures and maintain the cross-linking density and mechanical properties of the epoxy resin glue. In low temperature environments, the physical entanglement and chemical cross-linking between polynorbornene and epoxy resin molecular chains provide additional toughness, so that the interpenetrating network structure can still maintain a certain elasticity at low temperatures, preventing the epoxy resin glue from becoming brittle and hard. There are a large number of physical entanglements inside the polynorbornene molecular chain. These physical entanglement points act as a fixed phase, which can fix the shape of the material and allow the material to return to its original shape when subjected to external forces. During the impact process, the shape memory function of polynorbornene helps to disperse and redistribute stress, absorb and disperse impact energy through the rearrangement of molecular chains, prevent stress from concentrating in a certain area, reduce the risk of local damage, and thus reduce the tendency to crack and generate cracks. At the same time, the shape memory function of polynorbornene helps to maintain the stability of the cross-linking points after impact, preventing them from breaking or being damaged by impact. This further reduces the risk of permanent deformation and cracking.

[0074] Compared with Comparative Example 2, the tensile strength of Example 3 is increased by 21.0%, the bending strength is increased by 21.3%, and the high and low temperature impact resistance is also improved. This is because the bio-based cross-linking agent is prepared by the reaction of modified lignin and chitosan, and its molecular structure contains a large number of hydroxyl, carboxyl, and amino active groups. These groups can react chemically with the epoxy groups of the epoxy resin during the curing process to form a dense cross-linked network, so that the epoxy resin glue can effectively disperse and transfer stress when subjected to tensile force, thereby improving the tensile strength. The dense cross-linked network formed by the bio-based cross-linking agent and the epoxy resin enhances the overall rigidity and bending resistance of the material. When the material is subjected to bending force, this dense cross-linked structure can effectively resist deformation, thereby improving the bending strength. During the curing process of the epoxy resin glue, the hydroxyl, carboxyl, and amino active groups in the modified lignin and chitosan in the bio-based cross-linking agent are rearranged or cross-linked to form a dense structure, thereby blocking the transfer of heat. In addition, the organic components in modified lignin and chitosan may begin to carbonize at high temperatures to form carbonized precursors such as polycyclic aromatic hydrocarbons and carbon nanodots. These carbonized precursors have high thermal stability and thermal insulation properties, and can form a thin thermal insulation layer on the surface of epoxy resin glue, which acts as a thermal barrier to prevent heat from transferring into the interior of the material, reduce thermal stress, and improve the thermal stability of epoxy resin glue. In addition, during the modification process of lignin in the bio-based cross-linker, the lignin is treated with alkali and oxidation, and part of its structure is destroyed to form flexible segments. Flexible segments are introduced into the epoxy resin glue, so that the epoxy resin glue can still maintain a certain elasticity at low temperatures, improving its low temperature resistance. When the epoxy resin glue is subjected to external forces, these flexible segments can undergo conformational changes, absorb and disperse energy, thereby preventing brittle cracking of the material.

[0075] Compared with Comparative Example 3, the tensile strength of Example 3 is reduced by 20.1% and the bending strength is reduced by 23.1%. This is because the mixed reaction of modified lignin and chitosan can form a more complex network structure. This network structure can play a better role in strengthening and toughening the epoxy resin. When the epoxy resin is subjected to external force, this complex network structure can absorb and disperse energy, thereby preventing the material from brittle cracking.

[0076] Compared with Comparative Example 4, Example 3 shows an increase in tensile strength of 13.2% and flexural strength of 15.0%. This is because ultrasonic treatment can improve the dispersibility and compatibility of the raw materials in the epoxy resin glue, making the raw materials more evenly distributed in the epoxy resin glue. This uniform dispersion helps to form a denser cross-linked network, thereby enhancing the tensile strength of the epoxy resin glue. The mechanical vibration and cavitation effect generated by ultrasonic treatment help to break the weaker chemical bonds in the epoxy resin, rearrange them and form stronger chemical bonds, which helps to improve the flexural strength of the epoxy resin glue.

[0077] Compared with Comparative Example 5, Example 3 shows that the tensile strength is increased by 19.3% and the flexural strength is increased by 21.9%. This is because microwave treatment can quickly and evenly heat the epoxy resin glue, so that it reaches a higher temperature in a short time, thereby accelerating the cross-linking reaction. This accelerated cross-linking reaction helps to form a more dense and uniform cross-linked network, thereby enhancing the tensile strength of the epoxy resin glue. At the same time, microwave treatment can also promote the movement and rearrangement of the epoxy resin molecular chain, help eliminate internal stress, and further improve the tensile strength. The heat generated by microwave treatment can be evenly distributed in the epoxy resin glue, so that it can be evenly heated and cross-linked in all directions. This uniform heating and cross-linking helps to improve the overall uniformity of the epoxy resin glue, thereby enhancing its ability to resist bending stress. Microwave treatment can also promote the dispersion and anchoring of nanofillers in the epoxy resin glue, so that it can better play a reinforcing role and further improve the flexural strength.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high and low temperature resistant epoxy resin adhesive, characterized in that: The invention comprises the following raw materials in parts by weight: 60-80 parts of bisphenol A epoxy resin, 5-15 parts of polynorbornene, 10-20 parts of polysiloxane, 0.3-0.5 parts of tris(triphenylphosphine)rhodium chloride, 20-40 parts of solvent, 5-10 parts of bio-based cross-linking agent, 2-6 parts of nanofiller, 10-20 parts of diluent, and 1-3 parts of coupling agent; The bio-based cross-linking agent is prepared by the following method: adding lignin to a 10wt% sodium hydroxide solution, heating to 55-65°C, keeping heating for 1.5-2.5h, adding sodium chlorite, reacting for 3-5h, wherein the mass volume ratio of lignin, sodium chlorite and sodium hydroxide solution is (1.0-2.0):(0.5-1.5):(10-20) g / mL, adding dilute hydrochloric acid to adjust the pH to 7.0, filtering out solids, washing with deionized water to obtain modified lignin; adding chitosan to a 2wt% acetic acid solution, wherein the mass volume ratio of chitosan and acetic acid solution is (1.0-2.0):(0.5-1.5):(10-20) g / mL, The modified lignin and chitosan solution are mixed at a mass volume ratio of g / mL (2.8-3.2): (1.9-2.1), 4-6% citric acid by volume of the above mixture is added, and the mixture is reacted at 60-80°C at 200-400r / min while being stirred for 5-7h; the solid is filtered out, washed with ethanol, and then placed in an oven and dried at 45-55°C for 20-25h to obtain a bio-based cross-linking agent; The synthesis process of the high and low temperature resistant epoxy resin adhesive comprises the following steps: S1. Weigh polynorbornene, tris(triphenylphosphine)rhodium chloride and solvent by weight, add polynorbornene to the solvent to dissolve, add tris(triphenylphosphine)rhodium chloride, and react under inert gas protection at 60-80° C. for 2-4 hours to obtain a pre-crosslinked polynorbornene network for standby use; the inert gas is one of nitrogen, argon and helium; S2, weighing bisphenol A epoxy resin, polysiloxane, nanofiller, diluent, and coupling agent according to weight, stirring and mixing evenly to obtain a mixture I; S3, swelling the pre-crosslinked polynorbornene network into the mixture I, stirring and mixing evenly to obtain a mixture II; S4. Weigh the bio-based cross-linking agent by weight and add it to the mixture II. Then, place it in a microwave reaction device and react at 120-150°C for 0.5-1.5h. Raise the temperature to 160-180°C and continue to react for 1.0-2.0h. Then, raise the temperature to 200-220°C and react for 1.0-1.5h. Take out the reaction product and cool it to 25-30°C to obtain an epoxy resin adhesive.

2. The high and low temperature resistant epoxy resin adhesive according to claim 1, characterized in that: The solvent is composed of cyclohexane and dichloromethane in a volume ratio of (7-9):(1.5-2.5).

3. The high and low temperature resistant epoxy resin adhesive according to claim 1, characterized in that: The nano filler is one or a combination of nano silicon dioxide, nano aluminum oxide, nano boron nitride, nano zinc oxide, and nano carbon nitride, and the particle size of the nano filler is 40-100 nm.

4. The high and low temperature resistant epoxy resin adhesive according to claim 1, characterized in that: The diluent is composed of butyl glycidyl ether and acetone in a volume ratio of (1-3):(2-4).

5. The high and low temperature resistant epoxy resin adhesive according to claim 1, characterized in that: The coupling agent is one of γ-aminopropyltriethoxysilane, γ-glycidyloxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane.

6. The high and low temperature resistant epoxy resin adhesive according to claim 1, characterized in that: In the synthesis process S1, the stirring speed is 200-400 r / min, in the synthesis process S2, the stirring speed is 300-600 r / min, and the stirring time is 10-20 min; in the synthesis process S3, the stirring speed is 200-400 r / min, and the stirring time is 30-40 min.

7. The high and low temperature resistant epoxy resin adhesive according to claim 1, characterized in that: In S4 of the synthesis process, the ultrasonic power is 200-500W, the ultrasonic frequency is 20-40kHz, and the ultrasonic treatment time is 20-30min; the microwave power is 300-600W, and the microwave frequency is 2-3GHz.