A degradable epoxy resin containing disulfide bonds for epoxy insulation parts

Abstract

The invention provides a disulfide bond-containing degradable resin for epoxy insulating parts, belonging to the technical field of resins. The disulfide bond-containing degradable resin is prepared from a raw material, a curing agent and a catalyst; the raw material is bisphenol A epoxy resin, the curing agent is a mixture of 3,3'-dithiodipropionate and 2-methylhexahydrophthalic anhydride, and the catalyst is 4-dimethylaminopyridine; the invention is based on disulfide bond metathesis, uses liquid disulfide ester compounds and adopts a simple method to synthesize a disulfide bond-containing degradable resin for epoxy insulating parts that is cured at medium and low temperatures and has good comprehensive performance.

Description

Technical Field

[0001] The invention belongs to the technical field of resins, and in particular relates to a degradable epoxy resin containing disulfide bonds for epoxy insulating parts. Background Art

[0002] Electric power resources are an indispensable part of modern society. In the process of electrical equipment serving society, insulating materials are undoubtedly an important part. Epoxy resin is widely used in insulating parts of electrical equipment such as transformers and insulating switch cabinets because of its excellent insulation effect and high strength, and it can play a certain degree of supporting role. Epoxy resin is generally formed by cross-linking epoxy compounds with amine or anhydride curing agents. The existence of its internal three-dimensional network structure, on the one hand, lays the foundation for the excellent application performance of epoxy resin, and on the other hand, hinders the recycling and reuse of epoxy materials, resulting in waste of resources and economy. Therefore, there is an urgent need for certain methods to solve the problems of epoxy resin reprocessing and recycling difficulties.

[0003] In order to reduce the impact of insulation aging on the service life of electrical equipment, reduce the impact of thermosetting polymer waste on the environment and resources, and achieve efficient and low-energy recycling of resources such as internal fibers and electronic components, it is an effective strategy to introduce chemical structures with dynamic characteristics into the cross-linked network of polymers. This network with dynamic cross-linking is called dynamic covalently adaptable network (CANs). Thermosetting materials containing covalently adaptable networks have the advantages of excellent mechanical and thermal properties, chemical stability of thermosetting materials and recyclability, reshaping and reprocessing of thermoplastic materials. Polymers with this feature are named glass-like polymers (vitrimer). More and more dynamic chemical bonds are introduced into the cross-linked network of polymers and applied to fields such as composite materials and insulation equipment. When preparing vitrimer resins, solid disulfide aromatic amine curing agents and disulfide carboxylic acid curing agents are commonly used on the market. The use of such curing agents requires high temperature curing and is difficult to process. Summary of the invention

[0004] Aiming at the characteristics of the traditional epoxy resin cross-linking network, the present invention is based on disulfide bond double decomposition and uses liquid disulfide ester compounds to synthesize a disulfide bond-containing biodegradable resin for epoxy insulation parts with medium and low temperature curing and good comprehensive performance in a simple way.

[0005] A disulfide bond-containing degradable resin for epoxy insulation is prepared from raw materials, a curing agent and a catalyst; the raw material is bisphenol A epoxy resin (DGEBA), the curing agent is a mixture of 3,3'-dithiodipropionate (DTDP) and 2-methylhexahydrophthalic anhydride (MHHPA), and the catalyst is 4-dimethylaminopyridine (DMAP).

[0006] Furthermore, the bisphenol A epoxy resin is E-51 bisphenol A epoxy resin (E-51 resin).

[0007] There are three main disadvantages of disulfide bonds that need to be overcome: First, most disulfides are solid, so it is necessary to evenly disperse the solid disulfide in the liquid epoxy resin at a temperature close to the melting point of the disulfide. If the uncured mixture is stirred at a higher temperature, the curing process may begin, resulting in a sharp increase in viscosity and difficulty in processing. Second, the compounds containing disulfide bonds reported at present are expensive, which limits their wide application. Third, the mechanical properties of disulfide-containing Vitrimer resins are poor and it is difficult to meet the needs of practical applications. Therefore, it is of great significance to develop an easy-to-process, high-performance, low-cost disulfide epoxy Vitrimer resin. In order to solve the problem that disulfide is difficult to evenly disperse in liquid epoxy resin, resulting in difficult processing, the present invention uses liquid DTDP as a curing agent. DTDP is a liquid and is easily dispersed in liquid epoxy resin. It is also very cheap, avoiding the problem of excessive viscosity caused by the melting of the curing agent, and DTDP can be hydrolyzed with moisture in the air to generate 3,3'-dithiodipropionic acid (DTDPA), and DTDPA further cures the epoxy resin to introduce disulfide bonds into the cross-linked network. In order to solve the problem of poor mechanical properties of disulfide bond-containing Vitrimer resin, the present invention blends and solidifies the curing agent DTDP and MHHPA, effectively improving the mechanical properties of the resin material and meeting its engineering application requirements. The catalyst DMAP is used to increase the reaction activity, reduce the curing temperature, and achieve low-temperature curing of the resin material. The prepared degradable resin containing disulfide bonds can be applied to the field of insulating parts of electrical equipment. The degradable resin containing disulfide bonds for insulating parts has excellent comprehensive performance, has the advantages of self-repair of damage, degradable recycling, etc., and is a new type of environmentally friendly resin with a wide range of applications.

[0008] The principle of preparing the disulfide bond-containing degradable resin of the present invention is: using the disulfide bond-containing DTDP to hydrolyze to generate 3,3'-dithiodipropionic acid (DTDPA) to introduce dynamic disulfide bonds into the cross-linked network. Since the reactivity of carboxylic acid curing agents with epoxy groups is low and the reaction is relatively complex, the mechanical properties of the cured resin are poor. To solve this problem, the present invention co-cures DTDP and MHHPA, uses DMAP as a catalyst to increase the reactivity of DTDP, accelerates the curing rate of epoxy groups and -COOH, and achieves medium and low temperature curing, thereby obtaining a new disulfide bond-containing degradable resin with better comprehensive performance that can be used for insulating parts.

[0009] Further, the molar ratio of the curing agent to the epoxy group in the bisphenol A epoxy resin is 1:1;

[0010] The molar ratio of the catalyst to the epoxy groups in the bisphenol A epoxy resin is 1:20.

[0011] Furthermore, the molar ratio of DTDP in the curing agent mixture (ie, the mixture of DTDP and MHHPA) is 20-60%, for example, the molar ratio of DTDP in the curing agent mixture is 20%, 30%, 40%, 50% or 60%.

[0012] Furthermore, the molar ratio of the DTDP in the curing agent mixture is 20-40%.

[0013] Furthermore, the molar ratio of the DTDP in the curing agent mixture is 40%.

[0014] The present invention utilizes DTDP and MHHPA for co-curing, that is, curing 1 mole of epoxy groups in the resin requires 1 mole of DTDP and MHHPA, and preparing disulfide-bond-containing degradable resins with different gradient disulfide bond contents by changing the mole ratio of DTDP in the total curing agent (20%, 30%, 40%, 50% and 60%). The catalyst is always 5% of the mole fraction of epoxy groups in the resin.

[0015] Compared with patent CN 116444768 A, the reaction principle of the catalyst of the present invention is different: patent CN 116444768 A uses triethanolamine as a catalyst to initiate anhydride ring opening and epoxy polymerization and promote the exchange reaction between ester bonds and hydroxyl groups at an appropriate temperature. However, triethanolamine has low activity as a catalyst. The present invention uses DMAP as a catalyst. In addition to improving the reaction activity and promoting the ester exchange reaction, it also promotes the reaction between the carboxyl group generated by the anhydride ring opening and the carboxyl group and epoxy of DTDPA. DTDP and MHHPA are blended as curing agents. By changing the ratio of the curing agent to adjust the cross-linked network structure, the comprehensive performance of the degradable resin containing disulfide bonds can be effectively improved. DTDP is hydrolyzed to generate DTDPA and methanol. The reaction between -COOH contained in DTDPA and epoxy is a nucleophilic addition reaction. DMAP reacts with -COOH as an organic base to generate -COO - , generating products with stronger nucleophilicity, effectively accelerating the curing rate of carboxylic acids and resins, and realizing medium and low temperature curing of degradable resins containing disulfide bonds.

[0016] The present invention also provides a method for preparing the above-mentioned degradable resin containing disulfide bonds for epoxy insulation, comprising the following steps:

[0017] Adding DTDP to bisphenol A epoxy resin and mixing them evenly to obtain a resin solution containing the DTDP;

[0018] Mixing MHHPA and DMAP so that the DMAP is completely dissolved in the MHHPA to obtain a MHHPA solution containing DMAP;

[0019] The resin solution containing the DTDP is mixed with the MHHPA solution containing DMAP, and heated and stirred to obtain a resin prepolymer glue solution;

[0020] The resin prepolymer glue solution is subjected to degassing treatment and heated for curing to obtain a degradable resin containing disulfide bonds for epoxy insulating parts.

[0021] Furthermore, the mixing temperature of the bisphenol A epoxy resin and the 3,3'-dithiodipropionate is 60°C.

[0022] Furthermore, the mixing temperature of the 2-methylhexahydrophthalic anhydride and the 4-dimethylaminopyridine is 110°C.

[0023] Furthermore, the heating curing is as follows: pouring the degassed resin prepolymer glue into a mold preheated at 70°C and coated with a release agent, first curing at 95°C for 2 hours, and then curing at 110°C for 4 hours.

[0024] Furthermore, the method for preparing the disulfide bond-containing degradable resin for epoxy insulation comprises the following steps:

[0025] E-51 resin is added to a container, and then curing agent DTDP is added to the above container, DTDP and E-51 resin are mixed and stirred at 60° C. (rotation speed is 700 rpm) for 5 hours to obtain a resin solution containing the DTDP; catalyst DMAP is added to the curing agent MHHPA (DMAP accounts for 5% of the molar fraction of epoxy groups in DGEBA), DMAP is completely dissolved in MHHPA at 110° C. to obtain an MHHPA solution containing DMAP. After cooling, the resin solution containing the DTDP and the MHHPA solution containing DMAP are mixed, stirred for 30 minutes at a constant temperature of 60°C in a water bath to obtain a resin prepolymer glue solution, and vacuum degassing is performed for 15 minutes in a vacuum drying oven at a temperature environment of 70°C. The degassed resin prepolymer glue solution is poured into a stainless steel mold preheated at 70°C and coated with a release agent, and then subjected to constant temperature vacuum degassing for 15 minutes. The mixture is first cured at a temperature of 95°C for 2 hours, and then cured at a temperature of 110°C for 4 hours. The mixture is naturally cooled and demolded to obtain a degradable resin containing disulfide bonds for epoxy insulating parts.

[0026] The present invention also provides application of the above-mentioned disulfide bond-containing degradable resin in the field of epoxy insulation parts.

[0027] The present invention uses a simple and easy method to introduce disulfide bonds into resins using a curing agent, prepares a degradable resin material containing disulfide bonds at medium and low temperatures, and applies it to the field of epoxy insulation parts. Its curing process does not affect the normal use of electrical equipment components and can be completely degraded in a DTT / DMF solution, thereby extending the service life of electrical equipment and recovering internal high-value materials.

[0028] Compared with the prior art, the present invention has the following advantages and technical effects:

[0029] 1. Excellent processing performance. DTDP is a liquid and can be evenly dispersed in epoxy resin at 60°C. At this time, the resin solution has good fluidity and is easy to carry out the next step of processing.

[0030] 2. Excellent comprehensive performance. When the DTDP content is 40%, the electrical properties of the resin material are excellent, and the glass transition temperature and mechanical properties meet the conditions for engineering applications. The degradable resin containing disulfide bonds has the ability to self-repair damage and can repair surface scratches at 150°C. Compared with patent CN 116444768 A, the comprehensive electrical performance of the resin of the present invention has been improved to a certain extent. The breakdown voltage of the resin in patent CN 116444768 A is 37.82kV, the leakage current is 38.04μA, and the dielectric loss tangent is 0.35%. The breakdown voltage of the resin in the present invention is 40.12kV, the leakage current is 32.57μA, and the dielectric loss tangent is 0.27%, and the performance is improved.

[0031] 3. Excellent recycling performance. When the DTDP content is 40%, the disulfide epoxy Vitrimer resin can be mechanically recycled and chemically degraded, while the resin in patent CN 116444768 A cannot be mechanically recycled. The resin material of the present invention is mechanically crushed and hot pressed for 6 hours at 180°C and 10MPa to be secondary molded, and the electrical performance retention rate is as high as 95%, and the mechanical performance retention rate is 80%. The resin material of the present invention is immersed in a 0.05g / mL dithiothreitol / dimethylformamide (DTT / DMF) solution and can be completely degraded in 2 hours at 90°C. The degradation mode of the resin in patent CN 116444768 A is that it can be completely degraded after 6 hours at 190°C in an ethylene glycol solution. Compared with the patent, the degradation conditions of the resin of the present invention are milder and the degradation rate is faster. The disulfide bonds in the resin of the present invention can be broken by reduction reaction with thiol, and the resin material of the present invention can be completely degraded at 90°C. Compared with patent CN 116444768 A, the present invention can realize the lossless recycling and reuse of high-value materials (such as fibers, non-ferrous metals, and electronic components) encapsulated inside the resin. The degradation temperature of the resin in patent CN116444768 A is 190°C, the degradation time is relatively long, and it is carried out in ethylene glycol, which may cause corrosion to the internal materials of the resin matrix, making it difficult to achieve lossless recycling. The resin of the present invention is carried out in a dimethylformamide solution containing dithiothreitol at a temperature of 90°C, and the degradation time is very short, which can achieve lossless recycling of high-value components.

[0032] 4. Wide application fields. The curing temperature and degradation temperature of most epoxy Vitrimers are relatively high, exceeding the maximum tolerance temperature of most electrical equipment parts, and cannot be used in the field of insulating parts. For example, compared with patent CN 116444768 A, the resin of the present invention can be used in the field of epoxy insulating parts. The curing process of the resin in patent CN 116444768 A is 110°C / 2h, 130°C / 2h and 150°C / 3h. The curing temperature exceeds the normal use temperature of some components in electrical equipment, which will cause damage to the components. The curing process of the resin of the present invention is 95°C / 2h and 110°C / 4h, which is within the normal use temperature range of the parts. The present invention uses DMAP as a catalyst to improve the reaction activity and reaction rate to achieve complete curing of the resin material at medium and low temperatures, and prepare a degradable epoxy resin for insulating parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0034] Figure 1The chemical reaction construction process of single MHHPA curing agent (a), single DTDP curing agent (b), DTDP and MHHPA curing agent blend (c), and schematic diagram of ester exchange and dynamic disulfide bond reversible cross-linking principle (d);

[0035] Figure 2 It is the catalytic principle of DMAP catalyst;

[0036] Figure 3 The present invention provides a process for preparing a degradable resin containing disulfide bonds;

[0037] Figure 4 The electrical properties of the disulfide-bonded degradable resins with different DTDP contents;

[0038] Figure 5 The self-repairing performance of resin damage with a DTDP molar ratio of 40% in the curing agent (a mixture of DTDP and MHHPA);

[0039] Figure 6 The resin hot pressing process is a process in which the molar ratio of DTDP in the curing agent (mixture of DTDP and MHHPA) is 40%;

[0040] Figure 7 The performance comparison of the resin before and after hot pressing with a DTDP molar ratio of 40% in the curing agent (a mixture of DTDP and MHHPA);

[0041] Figure 8 The degradation principle and morphological changes of the resin with a DTDP molar ratio of 40% in the curing agent (a mixture of DTDP and MHHPA) in dithiothreitol solution;

[0042] Fig. 9 The current change during encapsulation of LED lamps using a resin having a DTDP molar ratio of 40% in the curing agent (a mixture of DTDP and MHHPA);

[0043] Fig.10 This is a degradation experiment of a resin encapsulated LED lamp using a curing agent (a mixture of DTDP and MHHPA) with a DTDP molar ratio of 40%.

[0044] Fig.11 This is a degradation experiment of a resin basalt fiber composite material in which the molar ratio of DTDP in the curing agent (a mixture of DTDP and MHHPA) is 40%. DETAILED DESCRIPTION

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0047] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0048] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0049] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0050] All raw materials used in the examples of the present invention are commercially available.

[0051] The technical solution of the present invention is further illustrated by the following embodiments.

[0052] Comparative Example 1

[0053] Weigh 100g of E-51 resin and add it to a container; weigh 85% of the curing agent MHHPA by mass and add it to another container, add the catalyst DMAP accounting for 5% of the molar fraction of the epoxy group in the E-51 resin to the MHHPA, keep a constant temperature of 110°C in a water bath and stir until the DMAP is completely dissolved, cool to 60°C, pour the mixed solution of MHHPA and DMAP into the E51 resin to obtain a resin prepolymer glue, and perform vacuum degassing for 15 minutes in a vacuum drying oven at a temperature of 70°C. Pour the degassed resin prepolymer glue into a preheated stainless steel mold coated with a release agent, and then perform constant temperature vacuum degassing for 15 minutes. First, cure at 95°C for 2h, then cure at 110°C for 4h, cool naturally, and demold, to obtain a traditional resin cured product (Traditional) with a disulfide bond content of 0%.

[0054] In this comparative example, DTDP containing disulfide dynamic bonds was not added during the preparation of the resin.

[0055] Comparative Example 2

[0056] Weigh 100g of E-51 resin, 85% of curing agent MHHPA by mass, and 5% of the molar fraction of epoxy groups in E-51 resin in catalyst DMP-30, stir the resin prepolymer glue at a constant temperature of 80℃ for 10min in a water bath, and perform vacuum degassing for 5min in a vacuum drying oven at a temperature of 80℃. Pour the degassed resin prepolymer glue into a preheated stainless steel mold coated with a release agent, and then perform constant temperature vacuum degassing for 5min. First, cure at 120℃ for 2h, then cure at 150℃ for 5h, cool naturally, and demold, to obtain a resin cured product with a disulfide bond content of 0%.

[0057] In this comparative example, since the catalyst used is DMP-30, the curing temperature is relatively high and medium-low temperature curing cannot be achieved.

[0058] In the following examples, the molar ratio of curing agent (mixture of DTDP and MHHPA) to epoxy groups in E-51 resin is 1:1; the catalyst (DMAP) is always 5% of the molar fraction of epoxy groups in E-51 resin.

[0059] Example 1

[0060] Weigh 100 g of E-51 resin, add it to a container, weigh 20% of DTDP (the molar proportion of DTDP in the mixture of DTDP and MHHPA is 20%, the same below) as the curing agent, add it to the above container, and stir at 60°C for 5 hours to completely mix it; weigh 80% of MHHPA (the molar proportion of MHHPA in the mixture of DTDP and MHHPA is 80%, the same below) as the curing agent, add it to the container, add DMAP, a catalyst accounting for 5% of the molar fraction of epoxy groups in the E-51 resin, to MHHPA, completely dissolve DMAP at 110°C, cool to 60°C and set aside. The two solutions were mixed, stirred at a constant temperature of 60°C for 30 minutes in a water bath to obtain a resin prepolymer glue solution, vacuum degassing was performed in a vacuum drying oven at a temperature of 70°C for 15 minutes, and the degassing resin prepolymer glue solution was poured into a preheated stainless steel mold coated with a release agent, and then vacuum degassing was performed at a constant temperature for 15 minutes, first cured at a temperature of 95°C for 2 hours, and then cured at a temperature of 110°C for 4 hours. Natural cooling and demolding were performed to obtain a disulfide bond-containing degradable resin cured product (20% SS) with a disulfide bond content of 20%.

[0061] Example 2

[0062] Weigh 100g of E-51 resin and add it to a container, weigh 30% of DTDP, add it to the container, stir at 60°C for 5h to mix it completely; weigh 70% of MHHPA, add it to the container, add DMAP, a catalyst accounting for 5% of the molar fraction of epoxy groups in E-51 resin, to MHHPA, completely dissolve DMAP at 110°C, cool to 60°C and set aside. Mix the two solutions, stir at a constant temperature of 60°C in a water bath for 30min to obtain a resin prepolymer glue, vacuum degassing treatment for 15min in a vacuum drying oven at a temperature of 70°C, pour the degassed resin prepolymer glue into a preheated stainless steel mold coated with a release agent, and then vacuum degassing treatment for 15min at a constant temperature, first cure at 95°C for 2h, and then cure at 110°C for 4h. After natural cooling and demoulding, a disulfide bond-containing degradable resin cured product (30% SS) with a disulfide bond content of 30% is obtained.

[0063] Example 3

[0064] Weigh 100g of E-51 resin and add it to a container, weigh 40% of DTDP, add it to the container, stir at 60°C for 5h to mix it completely; weigh 60% of MHHPA, add it to the container, add DMAP, a catalyst that accounts for 5% of the molar fraction of epoxy groups in the E-51 resin, to MHHPA, dissolve DMAP completely at 110°C, and cool to 60°C for use. Mix the two solutions, stir at a constant temperature of 60°C in a water bath for 30min to obtain a resin prepolymer glue, vacuum degassing treatment for 15min in a vacuum drying oven at a temperature of 70°C, pour the degassed resin prepolymer glue into a preheated stainless steel mold coated with a release agent, and then vacuum degassing treatment for 15min at a constant temperature, first cure at 95°C for 2h, and then cure at 110°C for 4h. After natural cooling and demoulding, a disulfide bond-containing degradable resin cured product (40% SS) with a disulfide bond content of 40% is obtained.

[0065] Example 4

[0066] Weigh 100g of E-51 resin and add it to a container, weigh 50% of DTDP, add it to the container, stir it at 60℃ for 5h to make it completely mixed; weigh 50% of MHHPA, add it to the container, add DMAP, a catalyst that accounts for 5% of the molar fraction of epoxy groups in E-51 resin, to MHHPA, completely dissolve DMAP at 110℃, cool it to 60℃ and set it aside. Mix the two solutions, stir them at a constant temperature of 60℃ in a water bath for 30min to obtain a resin prepolymer glue, vacuum degassing treatment for 15min in a vacuum drying oven at a temperature of 70℃, pour the degassed resin prepolymer glue into a preheated stainless steel mold coated with a release agent, and then vacuum degassing treatment for 15min at a constant temperature, first cure it at 95℃ for 2h, and then cure it at 110℃ for 4h. After natural cooling and demoulding, a disulfide bond-containing degradable resin cured product (50% SS) with a disulfide bond content of 50% is obtained.

[0067] Example 5

[0068] Weigh 100g of E-51 resin and add it to a container, weigh 60% of DTDP as a curing agent, add it to the container, and stir it at 60°C for 5h to make it completely mixed; weigh 40% of MHHPA as a curing agent and add it to the container, add the catalyst DMAP accounting for 5% of the molar fraction of epoxy groups in the E-51 resin to MHHPA, completely dissolve DMAP at 110°C, and cool it to 60°C for use. Mix the two solutions, stir them at a constant temperature of 60°C in a water bath for 30min to obtain a resin prepolymer glue; then, vacuum degassing is carried out in a vacuum drying oven at a temperature of 70°C for 15min, and the degassed resin prepolymer glue is poured into a preheated stainless steel mold coated with a release agent, and then vacuum degassing is carried out at a constant temperature for 15min, first cured at 95°C for 2h, and then cured at 110°C for 4h. After natural cooling and demoulding, a disulfide bond-containing degradable resin cured product (60% SS) with a disulfide bond content of 60% is obtained.

[0069] The performance testing methods of the resin cured products prepared in the above comparative examples and embodiments are as follows:

[0070] 1. Electrical performance test:

[0071] 1) Power frequency breakdown voltage test: According to the requirements of standard IEC 60243-1-2013, a copper spherical electrode is used to test in dimethyl silicone oil. The voltage is increased at a constant rate of 2 kV / s until the sample breaks down. 15 valid data are recorded and the experimental results are statistically analyzed using Weibull distribution.

[0072] 2) Leakage current test: The test specimens are in accordance with the experimental requirements of standard DL / T 1580-2016. The test specimens are 300mm±0.5mm long and 50mm in diameter. There are 6 cylinders in total. They are placed in a 0.1% NaCl solution and boiled at 100℃ for 100h±10.5h. After the surface moisture is wiped off, the leakage current of the test specimens is measured. The power frequency voltage boost rate is 1kV / s, the test voltage is 12kV, and the withstand voltage time is 60s.

[0073] 3) Dielectric loss factor test: In accordance with the requirements of standard GB / T 1409-2006, the YG9100 fully automatic anti-interference precision dielectric loss tester is used for testing, and the test voltage is 2kV.

[0074] 2. Surface scratch damage repair test: Use a scalpel to scratch the surface of the solidified sample, observe the surface scratches with an optical microscope, and record the original appearance and width of the scratches. Place the sample in a 150℃ drying oven for 60 minutes, take it out and observe the relevant data after the surface scratch repair again with an optical microscope.

[0075] 3. Hot pressing performance test: The biodegradable resin solid containing disulfide bonds is mechanically crushed into small particles with a diameter of less than 2 mm and placed in a hot pressing mold. The mold is placed in a high-temperature vulcanizer and hot pressed for 5 hours at 180°C and 10MPa. After cooling, the mold is demolded to test its performance after hot pressing.

[0076] 4. Degradation and recycling experiment: 20mm×10mm×4mm 40% SS samples were immersed in 0.05g / mL dithiothreitol / dimethylformamide solution (DTT / DMF) at 90℃, and the morphological changes and mass changes were recorded every 30min. Scanning electron microscopy (SEM, JSM-IT500, JEOR) was used to observe the surface details of the winding before and after recycling.

[0077] 5. LED bulb packaging experiment: Pour the resin prepolymer glue into the container containing the LED bulb, degas at constant temperature for 15 minutes, and cure at 95℃ / 2h and 110℃ / 4h. Measure the change of the bulb current during the curing process. Soak the encapsulated components in the DMF solution of dithiothreitol to achieve the degradation of the encapsulated LED bulb, and measure the current of the LED bulb after degradation and recovery.

[0078] 6. Basalt fiber composite material degradation experiment: The basalt fiber composite material is immersed in a DMF solution of dithiothreitol to achieve the recovery of the basalt fiber and measure the tensile strength of the recycled fiber.

[0079] Figure 1 The chemical reaction construction process of single MHHPA curing agent (a), single DTDP curing agent (b), and blend of DTDP and MHHPA curing agents (c) and schematic diagram of the reversible cross-linking principle of ester exchange and dynamic disulfide bonds (d). It can be seen that after introducing two reversible dynamic structures, disulfide bonds and ester exchange dynamic bonds, into the resin cross-linking network, the reversible network topology can make the macro resin have excellent dynamic properties.

[0080] Figure 2 This is the catalytic principle of DMAP catalyst. It can be seen that DMAP, as an organic base, can react with -COOH to generate -COO, forming a product with stronger nucleophilicity, which promotes the nucleophilic addition reaction of -COOH and epoxy groups in the curing agent and greatly improves the reaction activity.

[0081] Figure 3 This is a preparation process of the disulfide bond-containing degradable resin of the present invention. Through the preparation process, the mold can be freely replaced to obtain a cured product sample of any desired shape.

[0082] Figure 4The electrical properties of the disulfide-containing degradable resin with different DTDP contents are shown in Figure 1. As the DTDP content in the curing agent increases, the electrical properties of the resin change. The power frequency breakdown voltage of the resin first gradually decreases, then increases, and finally decreases. The dielectric loss factor first decreases, then increases, and the leakage current gradually decreases. When the DTDP content is 40% (i.e., the disulfide bond content is 40%), the breakdown voltage increases to 40.12 kV / m, the leakage current is 32.57 μA, and the dielectric loss tangent is 0.27%. The comprehensive electrical properties are the best, meeting the basic requirements of electrical materials. At this time, the glass transition temperature of the resin is 106°C, which meets the conditions for engineering applications.

[0083] Figure 5 The present invention conducts self-repairing experiments on resins with different curing agent blending ratios at 150°C, and finds that the repair efficiency is significantly improved with the increase of DTDP content. When the DTDP molar ratio is 40%, due to the presence of disulfide dynamic bonds, it can be seen that the scratches on the damaged resin material become smaller after repairing it at 150°C for 30 minutes; after 60 minutes of repair, the surface scratches almost completely disappear. The disulfide dynamic bonds can be cross-linked at high temperature for secondary cross-linking, which gives the resin material a self-repairing property and can increase the service life of electrical equipment.

[0084] Figure 6 The resin hot pressing process is a process in which the molar ratio of DTDP in the curing agent (mixture of DTDP and MHHPA) is 40%; Figure 7 The performance comparison of the resin before and after hot pressing is shown in the figure with a DTDP molar ratio of 40% in the curing agent (a mixture of DTDP and MHHPA). When the DTDP molar ratio is 40%, the disulfide bonds in the cross-linked network can be re-cross-linked at high temperature and high pressure, so the crushed resin material can be hot-pressed for secondary molding at 180°C and 10MPa, and the mechanical property retention rate of the material after hot pressing is about 80%, and the insulation property retention rate is as high as 95%, which meets the requirements of industrial applications.

[0085] Figure 8 The degradation principle and morphological changes of the resin with a DTDP molar ratio of 40% in the curing agent (a mixture of DTDP and MHHPA) in a dithiothreitol solution are described. The degradable resin sample containing a disulfide bond is placed in a 0.05g / mL DTT / DMF solution for degradation treatment. The resin system first swells and then dissolves in the DTT / DMF solution. When the DTDP content is 40%, the resin can be completely degraded in 2 hours. The resin degradation conditions of the present invention are milder and the degradation rate is faster.

[0086] Fig. 9The current changes during the process of encapsulating an LED lamp using a resin in which the molar ratio of DTDP in the curing agent (a mixture of DTDP and MHHPA) is 40%. It can be seen that current always passes through the encapsulation process, the LED lamp maintains a normal working state, and the morphology of the lamp bead does not change significantly, proving that the resin material and curing conditions have no effect on its basic properties. The degradable resin containing disulfide bonds in the present invention can achieve the encapsulation of electronic components.

[0087] Fig.10 This figure records the degradation process of the encapsulated LED lamp using a resin encapsulated LED lamp with a DTDP molar ratio of 40% in the curing agent (a mixture of DTDP and MHHPA). To achieve the recycling of the LED lamp, the powered LED lamp was immersed in a 90°C 0.05g / mL DTT DMF solution. After 120 minutes of immersion, the encapsulation glue on the surface of the LED lamp was completely degraded and dissolved in the solution. The LED lamp was taken out, and the surface solvent was wiped off with a paper towel and dried. It can be seen that the surface paint of the recycled LED lamp partially fell off because the coating on the LED lamp was not resistant to DMF. The current before and after recycling did not change significantly, proving that the LED lamp can still be used normally, and the color of the degradation liquid changed significantly. The application of degradable resin containing disulfide bonds can achieve non-destructive recycling of high-value components inside the resin matrix. Compared with traditional incineration and landfilling, this recycling method greatly reduces solid waste pollution.

[0088] Fig.11 This figure records the degradation experiment of basalt reinforced composite materials using a resin with a DTDP molar ratio of 40% as the matrix in the curing agent (a mixture of DTDP and MHHPA). The degradation of the basalt reinforced composite material and the recovery of the internal basalt fibers are recorded. To achieve the recovery of the internal fibers, the composite material was immersed in a DMF solution of 0.05g / mL DTT at 90°C. After 120 minutes of immersion, the resin on the surface of the composite material was completely dissolved, exposing the scattered basalt fibers. The performance changes of the basalt fibers before and after recycling were tested by a single-filament tensile test. Compared with the original fibers, the tensile strength of the recycled basalt fibers decreased to 90.85% of the original strength, which shows that the recycled basalt fibers can still be used to prepare fiber-reinforced composite materials.

[0089] The present invention proposes a liquid curing agent DTDP containing dynamic disulfide bonds, which reacts with moisture in the air to generate DTDPA-cured E51 epoxy resin, and DTDP is mixed with a traditional anhydride curing agent MHHPA to prepare a disulfide-bond-containing degradable resin under the catalytic action of a catalyst DMAP. The disulfide bonds are introduced into the resin material by adjusting the ratio of the two curing agents DTDP and MHHPA to obtain a disulfide-bond-containing degradable resin, thereby ensuring that the resin material has excellent comprehensive performance. The presence of dynamic bonds gives the resin material excellent dynamic performance, realizes efficient repair of various damage forms and lossless recovery of high-value materials inside resin casting products or fiber-reinforced composite materials. The present invention can obtain disulfide-bond-containing degradable resins with different characteristics to prepare disulfide-bond-containing degradable resins with the best comprehensive performance, and is applicable to the fields of insulating parts of electrical equipment such as dry-type transformers and reactors in the power industry, packaging of power electronic devices, and research and development of environmentally friendly composite materials. Taking into account the curing agent cost and the comprehensive performance of the resin, when the molar ratio of DTDP in the curing agent mixture (i.e., the mixture of DTDP and MHHPA) is 40%, the performance is optimal.

[0090] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A disulfide bond-containing degradable resin for epoxy insulation, characterized in that: The method is prepared from raw materials, a curing agent and a catalyst; the raw material is bisphenol A epoxy resin, the curing agent is a mixture of 3,3'-dithiodipropionate and 2-methylhexahydrophthalic anhydride, and the catalyst is 4-dimethylaminopyridine; The molar ratio of the curing agent to the epoxy group in the bisphenol A epoxy resin is 1:1; The molar ratio of the catalyst to the epoxy groups in the bisphenol A epoxy resin is 1:20; The molar ratio of the 3,3'-dithiodipropionate in the curing agent mixture is 40%.

2. A method for preparing the disulfide bond-containing degradable resin for epoxy insulation according to claim 1, characterized in that: The following steps are involved: Adding 3,3'-dithiodipropionate to bisphenol A epoxy resin and mixing them evenly to obtain a resin solution containing the 3,3'-dithiodipropionate; Mixing 2-methylhexahydrophthalic anhydride and 4-dimethylaminopyridine, so that the 4-dimethylaminopyridine is completely dissolved in the 2-methylhexahydrophthalic anhydride, to obtain a 2-methylhexahydrophthalic anhydride solution containing 4-dimethylaminopyridine; Mixing the resin solution containing the 3,3'-dithiodipropionate with the 2-methylhexahydrophthalic anhydride solution containing 4-dimethylaminopyridine, heating and stirring, to obtain a resin prepolymer glue solution; The resin prepolymer glue solution is subjected to degassing treatment and heated for curing to obtain a degradable resin containing disulfide bonds for epoxy insulating parts.

3. The method for preparing a disulfide bond-containing degradable resin for epoxy insulation according to claim 2, characterized in that: The mixing temperature of the bisphenol A epoxy resin and the 3,3'-dithiodipropionate is 60°C.

4. The method for preparing a disulfide bond-containing degradable resin for epoxy insulation according to claim 2, characterized in that: The mixing temperature of the 2-methylhexahydrophthalic anhydride and the 4-dimethylaminopyridine is 110°C.

5. The method for preparing a disulfide bond-containing degradable resin for epoxy insulation according to claim 2, characterized in that: The heating curing is as follows: pouring the degassed resin prepolymer glue into a mold preheated at 70°C and coated with a release agent, first curing at 95°C for 2 hours, and then curing at 110°C for 4 hours.

6. Use of the disulfide bond-containing degradable resin according to claim 1 in the field of epoxy insulation parts.

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