A method of degrading an amine cured epoxy resin

Abstract

This invention discloses a method for degrading amine-cured epoxy resin. The method involves reacting an alkali metal or alkaline earth metal hydroxide with a high-boiling-point diol for dehydration until no more water vapor is released, yielding an alcohol-alkali solution. The high-boiling-point diol is selected from diethylene glycol, triethylene glycol, and tetraethylene glycol. The amine-cured epoxy resin is then added to the alcohol-alkali solution, and the temperature is raised to degrade the resin until it is completely dissolved. The degradation temperature is controlled at 200-280°C depending on the type and size of the amine-cured epoxy resin. The high-boiling-point diol is recovered by vacuum distillation, and the degradation product is precipitated, washed, and dried. This invention degrades amine-cured epoxy resin using an in-situ generated alcohol-alkali solution at temperatures above 200°C to obtain a soluble polyol. This method has the advantages of high degradation efficiency, degradation at atmospheric pressure, low reagent cost with no volatile corrosiveness, and environmentally friendly, low-toxicity, and easily recyclable solvents.

Description

Technical Field

[0001] This invention relates to the degradation of epoxy resins, and more particularly to a method for degrading amine-cured epoxy resins. Background Technology

[0002] Epoxy resins, as thermosetting polymers containing epoxy groups that react with curing agents to form a three-dimensional network structure, are widely used due to their extremely strong adhesion, low curing shrinkage, excellent mechanical strength, superior electrical insulation, and good chemical resistance. Their main applications include: 1) as adhesives for bonding critical structures in aerospace, machinery, and other fields; 2) as coatings for corrosion protection, flooring, and insulating varnishes; 3) in the electronics and electrical fields for manufacturing copper-clad laminates, encapsulating semiconductors, and preparing insulating castings; 4) as a matrix for composite materials, typically glass fiber reinforced epoxy resin (used in ship hulls, automotive parts, wind turbine blades, copper-clad laminates, etc.) and carbon fiber reinforced epoxy resin (used in aircraft parts, sporting goods, etc.), and also in building reinforcement materials. Statistics show that in 2024, China's annual epoxy resin production was approximately 2.45 million tons, accounting for 60% of global production.

[0003] Curing agents used in conjunction with epoxy resins mainly include amines, acid anhydrides, phenols, and imidazoles. The curing agent has a significant impact on the performance of epoxy resins; therefore, the curing agent must usually be specified in the product description. Among these, amine-cured epoxy resins are an important class due to their outstanding overall performance and are used in large quantities. They also have the most stable chemical structure, good weather resistance, and long service life. Acid anhydride-cured epoxy resins are easily degraded but have poorer performance and are used in smaller quantities.

[0004] The most representative amine-cured epoxy resins are those used in wind turbine blades and dicyandiamide-cured tetrabromobisphenol A epoxy resin, which is the most widely used in copper-clad laminates (CCLs). These resins combine high strength, high toughness, excellent adhesion, and chemical resistance. Specifically, wind turbine blades typically use polyetheramine-cured bisphenol A epoxy resin as the core matrix material to provide extremely high specific strength, fatigue resistance, and chemical stability. Most CCLs use dicyandiamide as a latent curing agent, combined with tetrabromobisphenol A epoxy resin to form a prepreg, which is rapidly cured during hot pressing, thus giving the board excellent heat resistance, dimensional stability, and electrical insulation. Although amine-cured epoxy resins have outstanding comprehensive performance, the stability of their chemical structure leads to difficulties in degradation. Currently, the degradation of most epoxy cured products refers to epoxy containing ester groups.

[0005] Given that wind turbine blades are a core material in the wind power industry, accounting for a significant portion of annual demand, and copper-clad laminates, as the basic carrier for all electronic devices, also have a massive consumption, it is estimated that these two sectors combined consume over 1 million tons of epoxy resin annually. This also means that over 1 million tons of solid waste, including retired wind turbine blades and discarded circuit boards, will be generated annually.

[0006] Currently, the common method for treating these waste epoxy resin composite materials is to physically crush them and use them as fillers to replace inorganic powder fillers such as sand or calcium carbonate. The price is less than 500 yuan / ton, which is difficult to cover the costs of dismantling, splitting, crushing, and transportation. If high-temperature pyrolysis is used, the environmental burden is heavy, especially for materials containing large amounts of toxic substances, such as tetrabromobisphenol A and dicyandiamide in circuit boards. The high-temperature decomposition process can easily cause serious air pollution, and the investment in pyrolysis equipment is large, the energy consumption is high, and the price of the recycled glass fiber is very low, making it difficult to cover the costs.

[0007] Currently, countries are vigorously developing biodegradable epoxy resins, but these new epoxy resins and curing agents are expensive. Most critically, they contain weak bonds to achieve degradation or reversible bond reconnection, leading to decreased heat resistance and mechanical properties, especially a significantly reduced service life. Therefore, their industrialization prospects are unclear. Chemical degradation of amine-cured epoxy resins remains the most promising method.

[0008] Research on the chemical degradation of amine-cured epoxy resin composites has been developing for many years. Amine-cured epoxy mainly contains CN bonds, CO ether bonds, and secondary alcohol groups formed by ring-opening of epoxy groups. Degradation primarily targets these three positions and can be mainly divided into three categories:

[0009] 1) Acid-catalyzed degradation

[0010] The mechanism of acid-catalyzed degradation mainly involves breaking the CO ether bonds in amine-cured epoxy. As early as 2005, a degradation system using N-methylpyrrolidone (NMP) as a solvent and nitric acid as a catalyst was proposed (Polymer, 2005, 46: 1905-1912). However, this method is impractical for industrialization due to the strong corrosiveness of nitric acid, high equipment requirements (requiring expensive materials such as Hastelloy), and limited economic value of the degradation products. Recently, a method using acetic acid at 270℃ for degradation was published in Nature (Nature 2025, 642 (8068)); this type of technology utilizes acid or Lewis acid for acidolysis, but still suffers from excessive corrosiveness. The potential dangers of acids include the generation of hydrogen gas, which can lead to explosions, and volatile acids can also cause metal corrosion and short circuits in the production environment.

[0011] 2) Oxidation method

[0012] The classic hydrogen peroxide and acetic acid system (ACS Sustainable Chem. Eng. 2018, 6, 1564−1571) essentially achieves degradation by breaking CN bonds through the generation of peracetic acid (for the reaction mechanism, please refer to: Fibers2022, 10, 55. https: / / doi.org / 10.3390 / fib10060055). However, due to the use of hydrogen peroxide, a controlled explosive chemical, and the generated, even more dangerous peracetic acid, industrialization is difficult. In 2024, there was also a report on using FeCl2 to generate highly oxidizing Feᴵⱽ=O free radicals that attack CN bonds to achieve degradation (Angew. Chem. Int. Ed. 2024, 63,e202405912). However, because it uses highly oxidizing and explosive reagents, the requirements for equipment and personnel are very high, making it unsuitable for the low-profit recycling industry.

[0013] In 2023, Nature published a ruthenium metal-catalyzed degradation method (Nature 2023), which mainly achieves degradation by oxidizing secondary alcohol groups to carbonyl groups and then further cleaving them. However, the paper used flammable and explosive isopropanol (boiling point of only 83°C and flash point of 11°C), which requires heating the isopropanol to 150°C for a long time for degradation. In addition, ruthenium catalysts are expensive and easily poisoned, making it difficult to promote industrialization.

[0014] 3) Alkali-catalyzed decomposition

[0015] Amine-cured epoxy mainly contains CN bonds, CO ether bonds, and secondary alcohol groups formed by ring opening of epoxy groups. The reaction between bases and secondary hydroxyl groups can only produce alcohol-base combinations, failing to achieve degradation. Furthermore, CN bonds and CO ether bonds are difficult to react; organic chemistry indicates that the positive charge of C in the CO ether bond is δ... +The drawback is that acid catalysis is required to enhance its positive charge in order to react with nucleophiles and ultimately break it. Existing technical literature claims to achieve rapid degradation of epoxy curing materials under mild conditions (normal pressure, below 200°C, even below 100°C), but most of these claims are for epoxy curing with acid anhydrides or carboxylic acids, and may even involve non-epoxy glass fiber reinforced composites. In reality, glass fiber reinforced composites, in addition to epoxy resin, also contain matrices such as unsaturated polyester and polyurethane. For example, the root baffles of wind turbine blades and nacelle covers use cheaper glass fiber reinforced unsaturated resins. These resins containing ester groups can be made with relatively weak corrosive acids such as sodium hydroxide (Polymer Degradation Stability 2012; 97(7): 1101–1106.), potassium phosphate (Journal of Xi'an Jiaotong University 2024, 58(7): 94-104), organic bases such as diethylenetriamine (Chemical Engineering Journal 2025, 509, 16117510.1016 / j.cej.2025.161175), and pyridine (Proceedings of the 13th International Conference on Advanced Materials and Engineering Materials, Springer Proceedings in Physics 2024, 324, 653-660). Essentially, this is a nucleophilic addition-elimination reaction of the ester group under alkaline conditions, i.e., a base-catalyzed hydrolysis reaction. The C atom in the ester group has a strong positive charge δ. ++ It is easily hydrolyzed, and can be accomplished even using a weak base with poor nucleophilicity.

[0016] Chinese invention patent application CN121021922A discloses a degradation solution for biodegradable amine-cured epoxy resin, a degradation and recycling method, and a regeneration method for amine-cured epoxy resin. The degradation solution comprises amine compounds, an inorganic alkaline solution, and water. The amine compounds constitute 15%-30%, the inorganic alkaline solution constitutes 6%-20%, and the remainder is water. The amine compounds include monoethanolamine, diethylenetriamine, and triethylenetetramine in a volume ratio of 1:(1-2):(1-2). In this degradation solution, monoethanolamine, promoted by diethylenetriamine and triethylenetetramine, achieves amidation of degradable weak bonds in the cured epoxy resin, thus degrading the amine-cured epoxy resin. This degradation solution can achieve rapid and complete degradation of the cured epoxy resin at a relatively low degradation temperature (around 100℃). The degradation products can be easily separated and purified to resynthesize the biodegradable epoxy resin. The degradation solution can be recycled through simple distillation. The technology is still in the public disclosure stage. Because it requires organic bases such as monoethanolamine, diethylenetriamine, and triethylenetetramine, which are highly toxic, irritating, volatile, and corrosive, it is not conducive to safe production and large-scale application.

[0017] Chinese invention patent CN 117143392 B discloses a method and apparatus for recycling carbon fiber; this technology mentions the ability to degrade bisphenol A type epoxy resin, unsaturated polyester resin, epoxy vinyl ester resin, and phenolic epoxy resin. However, this technology uses at least one of water (boiling point 100°C), methanol (boiling point 64°C), and ethanol (boiling point 78°C) as a proton pump additive. In its embodiments, for bisphenol A type epoxy resin, the degradation temperatures are 140°C, 160°C, and 180°C, far exceeding its boiling point. Therefore, this degradation process requires high pressure. High-pressure production lines not only involve huge equipment investments but also come with high safety risks and operating and maintenance costs, and impose stringent requirements on equipment, personnel, plant facilities, and security, resulting in low industrialization feasibility.

[0018] Despite the aforementioned chemical degradation methods, the main challenge facing amine-cured epoxy recycling technology is its high cost. The raw materials for amine-cured epoxy are bulk chemical commodities with relatively low prices. For example, the widely used bisphenol A epoxy resin (Whitberg LT-5088A) and polyetheramine (Whitberg LT-5088B) for wind turbine blades cost approximately 14,000 RMB / ton and 13,000 RMB / ton respectively, while tetrabromobisphenol A epoxy resin and dicyandiamide used in copper-clad laminates cost 22,000 RMB / ton and 9,000 RMB / ton respectively. Since the recycled degradation products can generally only be downgraded and cannot be used in high-end electronic products or durable goods, their price is limited to a few thousand RMB / ton, resulting in very limited profit margins. Considering the costs associated with dismantling, splitting, crushing, and transporting wind turbine blades, if the degradation method is too costly, especially given the high safety risks requiring specialized equipment such as high-pressure explosion-proof and corrosion-resistant equipment, the high investment and low production capacity will prevent profitability. Summary of the Invention

[0019] The purpose of this invention is to provide a method for degrading amine-cured epoxy resins that is carried out at atmospheric pressure, requires no high-pressure equipment, uses commercially available reagents that are inexpensive, produces no volatile or corrosive byproducts (such as hydrogen chloride) during the reaction process, is friendly to equipment and the environment, and uses solvents that are environmentally friendly, low in toxicity, and highly recyclable.

[0020] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0021] A method for degrading amine-cured epoxy resin specifically includes the following steps:

[0022] S1. A dehydration reaction is carried out between an alkali metal or alkaline earth metal hydroxide and a high-boiling-point diol until no more water vapor is distilled off, to obtain an alcohol-alkali solution; wherein the high-boiling-point diol is one of diethylene glycol, triethylene glycol, and tetraethylene glycol.

[0023] S2. Add the amine-cured epoxy resin to the alcohol-alkali solution. Depending on the type and size of the amine-cured epoxy resin, heat to 200~280℃ to degrade the amine-cured epoxy resin until it is completely dissolved. Control the temperature rise to not exceed the boiling point of the selected high-boiling-point diol.

[0024] S3. High-boiling-point diols are recovered by vacuum distillation, and the degradation products are precipitated, washed, and dried.

[0025] To further achieve the purpose of this invention, preferably, the alkali metal or alkaline earth metal hydroxide is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, and barium hydroxide.

[0026] Preferably, the mass ratio of the alkali metal or alkaline earth metal hydroxide to the high-boiling diol is 0.01~30:100.

[0027] Preferably, the solid content of the alcohol-alkali solution is 0.01~30%.

[0028] Preferably, the amine-cured epoxy resin is in block or powder form; the high-boiling-point diol is in excess relative to the hydroxide of alkali metal or alkaline earth metal.

[0029] Preferably, the time for the amine-cured epoxy resin to degrade to complete dissolution is 0.1 to 7 hours, depending on the type and size of the amine-cured epoxy resin and the heating temperature.

[0030] Preferably, the temperature of the dehydration reaction is 150~240℃, the time of the dehydration reaction is 10~120 minutes, and the degradation temperature is 230-280℃.

[0031] Preferably, the precipitation of degradation products is achieved by adding a precipitant.

[0032] Preferably, the precipitant is an acidic reagent or an aqueous solution of an acidic reagent; or the precipitant is an aqueous solution of magnesium chloride or calcium chloride.

[0033] Preferably, the washing is done with water; the drying is done under vacuum at 120-150°C for 0.5-6 hours; and the degradation product is a polyol oligomer containing phenolic and alcoholic hydroxyl groups.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] 1) The method of the present invention can control the degradation temperature to 200~280℃ according to the type and size of the amine-cured epoxy resin, so as to achieve rapid and efficient degradation. In particular, it can degrade block or cone-shaped amine-cured epoxy resin within 7 hours, which greatly improves the degradation efficiency and saves degradation costs.

[0036] 2) This invention discovers that, within a defined temperature range, the degradation rate can be roughly doubled by increasing the temperature by 10°C, thus solving the problem of the difficulty in quantitatively defining the degradation efficiency of existing technologies.

[0037] 3) The degradation method of amine-cured epoxy resin in this invention involves atmospheric pressure degradation, which does not require sophisticated equipment. Furthermore, the alkali metal hydroxides and alkaline earth metal hydroxides used in this invention are inexpensive and non-volatile / non-corrosive. This method offers advantages in terms of safety, environmental friendliness, and low cost.

[0038] 4) The solvent used in this invention has a high boiling point, is non-flammable, non-volatile, environmentally friendly, low in toxicity, recyclable, and conducive to large-scale production.

[0039] 5) This invention utilizes a high-boiling-point solvent, enabling degradation at higher temperatures and achieving a high degradation rate. The degradation rate increases with increasing temperature; therefore, degradation is proposed within the range of 200–280°C, preferably 230–280°C. This temperature range can still be achieved using conventional heating methods (such as heating wires or heat-conducting oil), making operation simple.

[0040] 6) The method of the present invention has high degradation efficiency and can degrade powders and even blocky materials, and does not have high requirements on the size of the raw materials.

[0041] 7) The method of the present invention does not require stirring, and the powder degradation rate can be as low as less than 10 minutes, which can reduce equipment requirements. For example, inexpensive stainless steel pipes can be used as reactors instead of reaction vessels, while achieving efficient degradation.

[0042] 8) Due to the low price of epoxy, the profit margin for degradation and recycling is very limited. Therefore, degradation and recycling methods with lower investment in plant equipment, easier scale-up, and higher degradation efficiency must be adopted. Compared to other methods that require high-pressure equipment above the boiling point, or use expensive catalysts (such as ruthenium catalysts), high-priced reagents (such as potassium tert-butoxide), volatile and corrosive acidic reagents (such as acetic acid and Lewis acids), or highly toxic, flammable, and explosive solvents (such as DMSO, NMP, and toluene), this method is highly efficient, safe, environmentally friendly, and low-cost, making it easier to achieve industrial-scale promotion. Attached Figure Description

[0043] Figure 1 The image shows the 1H NMR spectrum of the amine-cured epoxy model compound from Example 1.

[0044] Figure 2 The image shows the 1H NMR spectrum of the degradation product of the amine-cured epoxy model compound in Example 1.

[0045] Figure 3 This is the liquid chromatography-mass spectra of the amine-cured epoxy model compound from Example 1.

[0046] Figure 4 This is a diagram showing the external shape of the epoxy-cured casting of the copper-clad laminate obtained in Example 2.

[0047] Figure 5 The image shows the 1H NMR spectrum of the product obtained from the degradation of amine-cured epoxy resin in the copper-clad laminate of Example 2.

[0048] Figure 6 This is a molecular weight test diagram of the product after degradation of the amine-cured epoxy resin used in the copper-clad laminate obtained in Example 2.

[0049] Figure 7 The image shows the hydrogen spectrum of the epoxy curing degradation product used in Example 3 for copper-clad laminate.

[0050] Figure 8 This is a sample image of the epoxy-cured casting for wind turbine blades in Example 4.

[0051] Figure 9 Images of wind turbine blades after washing and drying with epoxy curing agent to degrade residues at different times and temperatures, as shown in Example 4.

[0052] Figure 10 This is a graph showing the effect of degradation temperature on degradation rate of the epoxy curing casting for wind turbine blades in Example 4.

[0053] Figure 11 The image shows the powder sample of the epoxy-cured casting used for wind turbine blades in Example 5, and its shape after degradation at 245°C for half an hour and at 270°C for 10 minutes.

[0054] Figure 12 This is a diagram showing the shape of the epoxy curing casting for wind turbine blades in Example 5 after degradation at 200°C for 12 hours.

[0055] Figure 13 Images of the residues of the epoxy curing compound for wind turbine blades in Example 6 at different degradation times at a temperature of 245°C.

[0056] Figure 14 The graph shows the effect of degradation time on the degradation rate of the epoxy-cured casting for wind turbine blades in Example 6 at 245°C.

[0057] Figure 15 The image shows the 1H NMR spectrum of the product after degradation of the epoxy curing casting for wind turbine blades in Example 6.

[0058] Figure 16 This is a molecular weight test diagram of the products after degradation of the epoxy cured casting for wind turbine blades in Example 6.

[0059] Figure 17 Images of the epoxy curing castings used for wind turbine blades in Comparative Example 2, showing degradation in tetrahydrofuran at 66°C for 12 hours (left) and in diethylene glycol at 190°C for 12 hours (right).

[0060] Figure 18 The degradation reaction equation for the amine-cured epoxy model compound in Example 1 is shown.

[0061] Figure 19 This is the reaction formula for the nucleophilic substitution of the CO ether bond by the nucleophile in Example 1 to generate phenolic anions and the amino anions generated after the CN bond is broken.

[0062] Figure 20 Example 4 shows the degradation reaction of the amine-cured epoxy model compound used in wind turbine blades. Detailed Implementation

[0063] To better understand this invention, the objectives, technical solutions, and effects of this invention are explained below, and further description is provided in conjunction with the accompanying drawings and specific embodiments. However, the implementation of this invention is not limited thereto. The described embodiments are some, but not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0064] Existing technologies for degrading amine-cured epoxy resins generally rely on high-pressure conditions, resulting in high equipment investment and operating costs. The use of catalysts (such as Lewis acids) that readily generate volatile strong acids (such as hydrochloric acid) not only corrodes equipment and poses a risk of electrical short circuits but also imposes stringent requirements on plant and process control. Furthermore, the use of highly toxic or difficult-to-recover solvents leads to high processing costs, making large-scale application difficult for the epoxy resin recycling industry, which has limited profit margins. The key feature of this invention is the discovery that an alcohol-alkali solution combined with a higher degradation temperature can achieve efficient and rapid degradation of amine-cured epoxy resins. Moreover, the degradation method is carried out under normal pressure, with relatively low temperature, eliminating the need for strong acids, and the treatment process is essentially non-toxic, ensuring safe and environmentally friendly production. It also offers significant cost advantages and clear advantages for large-scale processing. Specifically, this invention provides a method for degrading amine-cured epoxy resins, comprising the following steps:

[0065] An alkali metal or alkaline earth metal hydroxide is dehydrated with a high-boiling-point diol until no more water vapor is distilled off, yielding an alcohol-alkali solution; the high-boiling-point diol is one of diethylene glycol, triethylene glycol, and tetraethylene glycol.

[0066] Add the amine-cured epoxy resin to an alcohol-alkali solution and heat it to degrade the amine-cured epoxy resin until it is completely dissolved. Depending on the type and size of the amine-cured epoxy resin, control the degradation temperature to 200~280℃. For diethylene glycol as a solvent, the maximum degradation temperature is about 240℃. For triethylene glycol and tetraethylene glycol, the degradation temperature can be gradually increased to 280℃.

[0067] High-boiling-point diols are recovered by vacuum distillation, and the degradation products are precipitated, washed, and dried.

[0068] The alkali metal or alkaline earth metal hydroxides in this technology are one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, and barium hydroxide.

[0069] The key feature of this technology is the use of one of diethylene glycol, triethylene glycol, and tetraethylene glycol as a solvent. While existing technologies also employ diethylene glycol, triethylene glycol, and tetraethylene glycol as solvents, their use as solvents in resin recycling is unprecedented, let alone their application as a synthetic alcohol-alkali solution for epoxy resin degradation. The existing technologies regarding diethylene glycol, triethylene glycol, and tetraethylene glycol are described below:

[0070] Diethylene glycol, with the chemical formula C4H10O3, is a colorless, transparent, odorless, viscous liquid at room temperature. It is hygroscopic, non-corrosive, has a melting point of -10.5℃, a boiling point of 245℃, and is miscible with water, ethanol, and acetone, but insoluble in ether and carbon tetrachloride. This substance is mainly used as a gas dehydrating agent and an aromatic hydrocarbon extraction solvent, and is applied in the synthesis of unsaturated polyester resins, plasticizers, and the dissolving and treatment of nitrocellulose and oils. As a byproduct of the hydration of ethylene oxide to produce ethylene glycol, it can be purified by vacuum distillation.

[0071] Triethylene glycol, also known as triethylene glycol, has the molecular formula C6H. 14 O4, boiling point 278.3℃, freezing point -7.2℃, readily soluble in water, miscible with most fatty alcohols, ketones, esters, and low molecular weight halogenated hydrocarbons. Triethylene glycol is a weak acid and can react with active metals; it can undergo nucleophilic substitution reactions with hydrohalic acids; it can undergo intermolecular dehydration reactions with oxygen-containing inorganic acids; and it can undergo dehydration reactions upon heating under the catalysis of protic acids or Lewis acids. Triethylene glycol can be used in the production of polyethers and polyurethane foams; the synthesis of triethylene glycol esters, used as plasticizers and lubricants for PVC; the synthesis of triethylene glycol alkyl ethers, used as high-boiling-point solvents; the synthesis of triethylene glycol dichloride, used as a solvent for oils, fats, waxes, etc., and as an intermediate raw material for pharmaceutical bactericides, chemicals, and surfactants; the synthesis of crown ethers, used as catalysts in organic synthesis, for the chelation and separation of heavy metals, and for ion-selective electrodes; and the synthesis of tetraethylene glycol or higher glycols.

[0072] Tetraethylene glycol has the molecular formula C8H. 18 O5, with a boiling point of 314℃, can dissolve nitrocellulose, rubber, etc. Tetraethylene glycol is commonly used as a novel aromatic hydrocarbon extraction solvent, and as a solvent in cosmetics, lubricating oil for aircraft engines, and a blending agent for brake fluids.

[0073] This invention involves a dehydration reaction of alkali metal or alkaline earth metal hydroxides with high-boiling-point diols to obtain an alcohol-alkali solution. This solution is then used to degrade amine-cured epoxy resins. The degradation temperature can be controlled between 200 and 280°C, depending on the type and size of the amine-cured epoxy resin, achieving rapid and efficient degradation. In particular, the higher the degradation temperature, the faster the degradation rate. Furthermore, the smaller the particle size of the epoxy resin lumps, the faster the degradation. For example, epoxy resin pulverized to 1-5 mm can be completely degraded in 0.5-2 hours. Therefore, this invention can degrade blocky or conical amine-cured epoxy resins within 7 hours without the need for raw material pulverization, greatly improving degradation efficiency and saving degradation costs.

[0074] It should be emphasized that the present invention has found that the degradation time is related to the degradation temperature and the size of the epoxy resin block. Under normal pressure, the degradation method of the present invention can roughly double the degradation rate within the defined temperature range by increasing the temperature by 10°C, thus solving the problem that the degradation efficiency of the prior art is difficult to quantitatively define.

[0075] The present invention degrades soluble polyols, which can be reused as chemical raw materials.

[0076] It should be noted that the raw materials for amine-cured epoxy are themselves bulk chemical commodities with relatively low prices. For example, wind turbine blades currently widely use bisphenol A epoxy resin (Wheeber LT-5088A) and polyetheramine (Wheeber LT-5088B), priced at approximately 14,000 RMB / ton and 13,000 RMB / ton respectively. In contrast, the prices of tetrabromobisphenol A epoxy resin and dicyandiamide used in copper-clad laminates are 22,000 RMB / ton and 9,000 RMB / ton respectively. Since the degradation products after recycling can generally only be downgraded and cannot be used in high-end electronic products or durable goods, their price is unlikely to exceed 10,000 RMB / ton. Considering the costs of dismantling, splitting, crushing, and transporting wind turbine blades, if the degradation method is too costly, especially given the high safety risks, it will not be industrialized. Currently, the common treatment for these waste epoxy resin composite materials is to physically crush them and use them as fillers to replace inorganic powder fillers such as sand or calcium carbonate. The selling price is less than 500 RMB / ton, which is insufficient to cover the costs of dismantling, splitting, crushing, and transporting. High-temperature pyrolysis methods impose a heavy environmental burden, especially for circuit boards containing large amounts of toxic substances, such as tetrabromobisphenol A and dicyandiamide. The high-temperature decomposition process easily causes severe air pollution. Furthermore, pyrolysis equipment requires significant investment and consumes a lot of energy. The resulting glass fiber degrades due to the high temperature, and even new glass fiber only costs around 2000 yuan / ton, making it difficult to cover costs. The cost advantage of this invention provides a significant advantage for its implementation.

[0077] Example 1

[0078] 1. Synthesis of Amine-Cureable Epoxy Model Compounds

[0079] Base-catalyzed cleavage of CO ether bonds is very difficult, and there are few reports on existing techniques. To demonstrate the cleavage of CO ether bonds, this example designed a model compound with a specific structure (3,3'-[(4-methylphenyl)azanediyl]bis(1-phenoxyprop-2-ol)), an adduct of aniline and epoxide, to serve as a mechanism for study. Its advantages include fewer NMR peaks and less coupling, facilitating characterization and analysis.

[0080] 3.017 g of phenoxyglycidyl ether (colorless liquid) (M = 150 g·mol⁻¹, 0.0201 mol) was mixed with 1.078 g of p-toluidine (M = 107 g·mol⁻¹, 0.0101 mol). The mixture was stirred at 55 °C, and the reactants gradually dissolved, yielding a light reddish-brown solution. After 2 hours, the reaction system was heated to 150 °C and stirred overnight. The reaction solution gradually turned reddish-brown. Heating was stopped, and the system solidified into a gel upon cooling. Recrystallization was performed using approximately 30 mL of a petroleum ether / ethyl acetate (volume ratio 4:1), followed by dilution with petroleum ether. The solution was then filtered through a sintered glass funnel, and the solid was collected after 20 minutes and dried to give approximately 3.5 g of the product. The reaction formula is shown below. The calculated yield is approximately 85%. The melting point of the product is 100–102 °C. The 1H NMR spectrum of the amine-cured epoxy model compound is shown below. Figure 1 ¹H NMR (600 MHz, DMSO-d6) δ 7.27 (m, 4H), 6.92 (m, 8H), 6.67 (m, 2H), 5.38–5.20 (m, 1H, OH), 4.05 (m, 2H, CHOH), 3.90 (m, 4H, OCH₂), 3.70–3.30 (m, 2H, NCH₂), 2.14 (s, 3H, CH₃). This chemical shift and integral area are consistent with the hydrogen of the model compound (3,3'-[(4-methylphenyl)azanidinediyl]bis(1-phenoxyprop-2-ol)).

[0081]

[0082] 2. Degradation of amine-cured epoxy model compounds

[0083] 14 mg of potassium hydroxide and 2 mL of diethylene glycol were dissolved by heating to 180 °C to obtain the corresponding potassium alkoxide. After cooling, 72 mg of the above-mentioned amine-cured epoxy model compound was added, and the mixture was heated to 230 °C and stirred for 5 minutes. After cooling, 2 mL of 5% hydrochloric acid solution was added, and the color immediately changed from soy sauce to light yellow. Extraction was performed with 5 mL of dichloromethane. The dichloromethane layer was washed three times with deionized water, and dried for 2 hours with magnesium sulfate and a small amount of sodium bicarbonate. After filtration, the dichloromethane was evaporated to dryness, and the mixture was washed twice with methanol to obtain a white solid. The degradation equation of the amine-cured epoxy model compound is as follows:

[0084] Nuclear magnetic resonance (NMR) test, such as Figure 2 As shown, 1 ¹H NMR (600 MHz, DMSO-d6) δ 7.33 – 6.69 (m, 9H), 5.08 – 4.77 (m, 1H), 4.2 – 2.9 (m, 10H), 2.24 – 2.12 (m, 3H); There are nine chemical shifts of the H atoms on the benzene ring located between 7.33 and 6.69; the peaks at 5.08–4.77 are likely hydroxyl peaks, with a total integral of 1H; the peaks at 2.24–2.12 (m, 3H) are methyl peaks from the toluene group; and the peaks at 4.2–2.9 (m, 10H) are other alkyl peaks. These chemical shifts and integral areas conform to the following structural formula.

[0085]

[0086] Figure 3 This is the liquid chromatography-mass spectra (LC-MS) of the cyclic compound (2-phenoxymethyl-4-p-tolyl-1,4-oxaza-6-ol) obtained by base catalysis from the model compound in Example 1. It shows a large number of components, with the molecular ion peak at 314.1752. It is speculated that the secondary hydroxyl group undergoes a cyclization reaction, leading to the cleavage of the phenyl ether carbon and the formation of the cyclic compound (2-phenoxymethyl-4-p-tolyl-1,4-oxaza-6-ol). The theoretical value of the hydrogenated ion peak of this cyclic compound is 313.1678 + 1.0078 = 314.1756, which differs from the peak value of the strongest molecular ion peak (314.1752) in the LC-MS by less than 5 ppm, suggesting they are of the same molecular formula. Therefore, the model compound degrades into two parts: potassium phenolate and a cyclic compound.

[0087] From the perspective of organic chemistry and thermodynamics, the mechanism involves nucleophilic substitution of the CO ether bond by a nucleophile at high temperatures, where B... It is a secondary potassium alkoxide, a strong base that attacks the phenyl ether bond to form a stable phenolic anion, such as... Figure 19Because the phenol anion is a weak base, the process of obtaining a weak base from a strong base can occur at relatively high temperatures. From a thermodynamic perspective, although the carbon atom in the CN bond also exhibits positive charge, the resulting amino anion after breakage is also highly basic, such as... Figure 19 This leads to the reverse reaction, meaning the equilibrium constant of the cleavage reaction is very small. Therefore, the main process is the cleavage of CO bonds to generate phenolic molecules. Specifically, in amine-cured epoxy, cyclic compounds (2-phenoxymethyl-4-p-tolyl-1,4-oxaza-6-ol) are generated.

[0088] Example 2

[0089] Synthesis of amine-cured epoxy resin for copper clad laminates

[0090] To avoid the mixing of other acid anhydride-cured epoxy and impurities into the waste copper-clad laminate, the cured product is synthesized according to the general copper-clad laminate resin formulation, which facilitates molecular structure characterization.

[0091] Take approximately 15.8 grams of Nanya NPEB-400 tetrabromobisphenol A epoxy resin (epoxy equivalent approximately 380 / eq) and heat it to 90°C to reduce viscosity for easier subsequent mixing. While continuously stirring, slowly and evenly add 0.841 grams of dicyandiamide powder to the resin. Place the mixed adhesive in a vacuum drying oven and degas at 70°C for approximately 30 minutes. Pour the adhesive into a rubber mold and place it in an oven for programmed temperature curing. Typical curing conditions are: curing at 180°C for 60 minutes. See the sample of the epoxy cured casting for copper-clad laminate. Figure 4 .

[0092] Degradation of amine-cured epoxy resin for copper clad laminates

[0093] Dissolve 0.45 g of potassium hydroxide and 10 mL of triethylene glycol by heating to 180 °C, then cool to obtain a potassium alkoxide solution. Crush the copper-clad laminate with amine-cured epoxy resin using a hot press. Add 2 g of the crushed resin to the potassium alkoxide solution and gradually heat to above 270 °C. The solution gradually turns brownish-red and the viscosity increases. After 1 hour, cool and observe the degradation effect. After 2 hours, the epoxy curing material is completely dissolved. Distill off most of the solvent under reduced pressure. Add 7 mL of 3.5% hydrochloric acid solution dropwise while stirring, and then add 40 mL of water to precipitate the degradation product. Centrifuge, pour off the clear liquid, wash with 20 mL of water, centrifuge, and finally wash with 10 mL of water and centrifuge again. Dry the degradation product in a vacuum oven at 150 °C for two hours and perform NMR characterization. See [link to NMR diagram]. Figure 5 : 1¹H NMR (600 MHz, DMSO-d6) δ 9.1 (br, PhOH), 7.1 – 6.6 (m, Ar H), 5.3 – 4.5 (br, OH), 3.9 – 0.8 (m, alkylH). The NMR showed a weak phenolic hydroxyl group at 9.1; peaks at 7.1 – 6.6 representing the benzene ring H in bisphenol A; peaks at 5.3 – 4.5 representing secondary hydroxyl groups; and peaks at 3.9 – 0.8 representing alkyl hydrogens. The degradation product is soluble in DMSO. Molecular weight is shown in [reference needed]. Figure 6 The number-average molecular weight is 4900, and the weight-average molecular weight is approximately 6700. This indicates that the degradation products have only degraded to soluble oligomers with relatively high molecular weights.

[0094] Example 3

[0095] Degradation of amine-cured epoxy resin for copper clad laminates

[0096] Dissolve 0.2 g potassium hydroxide, 0.25 g calcium hydroxide, and 10 mL triethylene glycol by heating to 180°C, then cool to obtain an alcohol-alkali solution. Cut 2 g of the copper-clad laminate (CCL) cured with amine-cured epoxy resin and add it to the alcohol-alkali solution. Gradually heat to above 270°C; the solution gradually turns brownish-red and the viscosity increases. After 1 hour, cool and observe the degradation effect. After 4 hours, the CCL is completely dissolved in the epoxy curing agent. Distill off most of the solvent under reduced pressure, add 7 mL of 3.5% hydrochloric acid solution dropwise while stirring, and add 40 mL of water to precipitate the degradation product. Centrifuge, pour off the supernatant, wash with 20 mL of water, centrifuge, and finally wash with 10 mL of water and centrifuge again. Dry the degradation product in a vacuum oven at 150°C for two hours and perform NMR characterization (see attached figure). Figure 7 : 1 ¹H NMR (600MHz, DMSO-d6) δ 9.1 (br, PhOH), 7.1 – 6.6 (m, Ar H), 5.3 – 4.5 (br, OH), 3.9– 0.8 (m, alkyl H). The NMR spectrum is largely consistent with that of Example 2, indicating that the degradation mechanisms and degradation products are essentially the same, suggesting that the solvent did not participate in the reaction.

[0097] Example 4

[0098] Synthesis and degradation of amine-cured epoxy model compounds for wind turbine blades, investigating the effect of temperature on degradation rate.

[0099] Synthesis of amine-cured epoxy resin for wind turbine blades

[0100] Because the composition of retired wind turbine blades is complex, such as the root baffles and nacelle covers which use cheaper glass fiber reinforced unsaturated resin, this invention synthesizes a corresponding cured product using a commonly used epoxy resin formulation in wind turbine blades to avoid the introduction of other anhydride-cured epoxy and impurities into the retired wind turbine blades.

[0101] Take approximately 100 grams of Huibai epoxy resin LT-5088A and approximately 33 grams of Huibai curing agent LT-5088B, stir thoroughly for 10 minutes, pour into 3 ml plastic centrifuge tubes, heat at 75°C for 12 hours, cool, and cut open the centrifuge tubes to demold. The sample mass is approximately 1.08 grams. See [link to sample details]. Figure 8 The wind turbine blade shown is a sample of an epoxy-cured casting, which is conical in shape.

[0102] Degradation of wind turbine blades using amine-cured epoxy model compounds

[0103] Add 1.08 g of the cone sample to a headspace vial, add 0.110 g of potassium hydroxide, add 7.21 g of diethylene glycol, place the vial in a standard-mouth test tube and ventilate three times. Heat in a silicone oil bath at a set temperature without stirring, observe the degradation at regular intervals, cool and pour out, wash the undegraded solid with water, dry and weigh it, and calculate the degradation rate by the weight of the residue and the initial weight.

[0104] Test temperature has a decisive influence on the degradation rate. Test samples showed almost no degradation after 12 hours of degradation at 190℃, 200℃, 210℃, and 220℃, although the solution color gradually darkened. At 230℃, approximately 10.65% degradation occurred after 12 hours, while complete degradation was achieved at 245℃, reaching 98% degradation after 6 hours. The changes in the appearance of the residue after washing and drying with time and temperature are shown in the images. Figure 9 The relationship between the degradation temperature and degradation rate of the amine-cured epoxy model compound used in this embodiment of wind turbine blades is shown in the figure. Figure 10 As shown in the figure, for this embodiment, the degradation activation energy can only be significantly exceeded at temperatures above 230°C. Below 230°C, although the solution will also turn black, the degradation rate is very slow; the degradation mechanism is as follows. Figure 20 .

[0105] Example 5

[0106] Effect of sample size on the degradation of amine-cured epoxy model compounds for wind turbine blades

[0107] The synthesis of amine-cured epoxy resin for wind turbine blades is the same as in Example 4.

[0108] Scenario 1

[0109] The conical wind turbine blades were ground into powder using an amine-cured epoxy modeling compound on coarse abrasive paper. (See...) Figure 11On the far left, 1.0 g of the above powder sample was added to a headspace vial, along with 0.11 g of potassium hydroxide and 7.2 g of diethylene glycol. The vial was then placed in a standard-mouth test tube, and the mixture was vented three times. The vial was heated in a silicone oil bath at 245°C without stirring, and cooled every ten minutes. A sample was taken, diluted to a 5% concentration with dimethyl sulfoxide, and then centrifuged at 6000 rpm for 1 minute to confirm complete degradation. The results showed complete degradation within 30 minutes. Figure 11 No precipitate was observed during centrifugation. Compared to Example 4, where the cone required 12 hours for complete degradation at 245°C, reducing the size significantly improves degradation efficiency.

[0110] Scenario 2

[0111] The conical wind turbine blades were ground into powder using an amine-cured epoxy modeling compound on coarse abrasive paper. (See...) Figure 11 On the far left, 1.0 g of the above powder sample was added to a headspace vial, along with 0.10 g of potassium hydroxide and 7.2 g of diethylene glycol. The vial was then placed in a standard-mouth test tube, and the mixture was vented three times. The vial was heated in a sand bath at 270°C without stirring, and cooled every ten minutes. A sample was taken, diluted to a 5% concentration with dimethyl sulfoxide, and then centrifuged at 6000 rpm for 1 minute to confirm complete degradation. The results showed complete degradation within 10 minutes, and no precipitation was observed during centrifugation. Figure 11 On the far right. Compared to the cone in Example 4, which required 12 hours to completely degrade at 245°C, and the powder in Case 1 of Example 5, which required 30 minutes to completely degrade at 245°C, both reducing the size and increasing the temperature can greatly improve the degradation efficiency.

[0112] Example 6

[0113] The relationship between degradation time and degradation rate of amine-cured epoxy model compound for wind turbine blades at 245℃.

[0114] The synthesis of amine-cured epoxy resin for wind turbine blades was the same as in Example 4, yielding a conical sample. 1.08 g of the conical sample was added to a headspace vial, along with 0.110 g of potassium hydroxide and 7.21 g of diethylene glycol. The vial was then placed in a standard-mouth test tube, and the mixture was ventilated three times. Heating was performed in a silicone oil bath at 245°C without stirring, and the degradation was observed periodically. After cooling, the sample was poured out. The undegraded solid was washed with water, dried, and weighed. The degradation rate was calculated using the weight of the residue and the initial weight. The test results are as follows: Figure 13 As shown in Table 1 below, Figure 14 This embodiment shows a graph showing the relationship between the degradation rate and time of the amine-cured epoxy resin used in the wind turbine blades.

[0115] Table 1

[0116]

[0117] The images clearly show the physical morphological changes of the cone-shaped (a cone is also a block, as opposed to powder) epoxy cured sample over time under specific conditions. Initially to early stage (1–2 hours): degradation begins on the surface and the sample color gradually darkens.

[0118] 1.5 hours: The sample surface turned obviously black and broke into two pieces, one large and one small, indicating that the degradation reaction had triggered brittle fracture of the material structure.

[0119] 3.5 hours: Small pieces have completely disappeared, while large pieces continue to degrade, indicating that small-sized fragments reach complete degradation first.

[0120] 4–5 hours: Larger samples decompose further. By 5 hours, the residue has decomposed into several smaller fragments, at which point the degradation rate is approximately 63%. It is worth noting that the total volume of the residue after 5 hours appears to be larger than that after 4 hours. This phenomenon is mainly attributed to the swelling effect caused by the degradation agent penetrating into the material, while the material texture becomes noticeably softer.

[0121] 6 hours: The degradation process suddenly accelerated, with the degradation rate jumping to 98%. This indicates that when the sample is broken into small fragments, the contact area with the degradation agent increases dramatically, leading to a significant increase in the degradation rate.

[0122] 7 hours: The sample is completely degraded, and no solid residue is visible. The degradation products precipitate and are post-processed to obtain a solid soluble in DMSO.

[0123] The completely degraded solution was subjected to vacuum distillation to remove most of the solvent. A 3.5% hydrochloric acid solution was added dropwise until neutral, and then four times the volume of water was added to precipitate the degradation product. The precipitate was centrifuged, the supernatant was poured off, and the product was washed with water and centrifuged three times. Finally, the degradation product was dried in a 150°C vacuum oven for two hours and characterized by NMR. (See Appendix) Figure 15 . 1 ¹H NMR (600 MHz, DMSO-d6) δ 9.14 (br, PhOH), 7.3 – 6.7 (m, Ar H), 4.8 – 4.4 (br, OH), 3.9 – 3.4 (m, CH₂ and CH), 1.3 – 0.9 (m, CH₃). A weak phenolic hydroxyl group is observed at 9.14; 7.3–6.7 are peaks representing the benzene ring H in bisphenol A; 4.8–4.4 are secondary hydroxyl peaks; 3.9–3.4 are peaks representing the methylene and methine groups in the polyetheramine, which have higher chemical shifts due to their O atom atom attachment; and 1.3–0.9 (m, CH₃) are methyl peaks in the polyetheramine, indicating that the polyetheramine is an amino-terminated polyoxypropylene. The molecular weights of the degradation products are shown in [reference needed]. Figure 16 It can be seen that its number-average molecular weight is about 1500 and its weight-average molecular weight is about 2900.

[0124] The degradation process described in this embodiment demonstrates that the degradation of the cone-shaped sample is not a uniform linear process, but rather involves multiple stages: surface erosion → fracture → fragment swelling → accelerated degradation. This embodiment also reasonably proves that testing based solely on powder or small samples will severely underestimate the time required for the initial fracture and will fail to observe key phenomena such as swelling.

[0125] Comparative Example 1:

[0126] First, a sample of amine-cured epoxy resin for wind turbine blades was synthesized (same as in Example 4), resulting in a cone-shaped epoxy cured product.

[0127] Add 1.1 g of the cone-shaped sample to a headspace vial, add 0.11 g of potassium hydroxide, and drop in 10 mL of tetrahydrofuran. Place the vial in a standard-mouth test tube, purge three times, and heat in a silicone oil bath at 70 °C without stirring. After 12 hours, cool, take a sample, and observe the degradation (see appendix). Figure 17 (Left) The cone was removed, washed with water, and vacuum-dried at 80 degrees Celsius for 1 hour. It was then weighed, and no significant weight loss was observed. This indicates that the alkali-catalyzed degradation of amine-cured epoxy must be carried out at a relatively high temperature.

[0128] Comparative Example 2:

[0129] First, a sample of amine-cured epoxy resin for wind turbine blades was synthesized (same as in Example 4), resulting in a cone-shaped epoxy cured product.

[0130] Add 1.1 g of the cone-shaped sample to a headspace vial, add 0.11 g of potassium hydroxide, and drop in 7.22 g of diethylene glycol. Place the vial in a standard-mouth test tube, purge three times, and heat in a silicone oil bath at 190 °C without stirring. After 12 hours, cool, take a sample, and observe the degradation (see appendix). Figure 17 (Right) The cone was removed, washed with water, and vacuum-dried at 80 degrees Celsius for 1 hour. It was then weighed, and no significant weight loss was observed. This indicates that the alkali-catalyzed degradation of amine-cured epoxy must be carried out at a relatively high temperature.

[0131] As can be seen from the comparison of the above embodiments and comparative examples, it is important to control the degradation temperature of the present invention to 200~280℃. Although the method of the present invention can control the degradation temperature to achieve rapid and efficient degradation according to the type and size of the amine-cured epoxy resin, the degradation efficiency is significantly reduced below 200℃. At the same time, it can also be seen from Comparative Example 1 that the selection of high-boiling-point diols in the present invention is particularly important. Comparative Example 1 not only has high solvent costs, but also has a significantly lower degradation efficiency than the embodiments of the present invention.

[0132] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for degrading amine-cured epoxy resin, characterized in that, Includes the following steps: S1. A dehydration reaction is carried out between an alkali metal or alkaline earth metal hydroxide and a high-boiling-point diol until no more water vapor is distilled off, to obtain an alcohol-alkali solution; wherein the high-boiling-point diol is one of diethylene glycol, triethylene glycol, and tetraethylene glycol. S2. Add the amine-cured epoxy resin to the alcohol-alkali solution. Depending on the type and size of the amine-cured epoxy resin, heat to 200~280℃ to degrade the amine-cured epoxy resin until it is completely dissolved. Control the temperature rise to not exceed the boiling point of the selected high-boiling-point diol. S3. High-boiling-point diols are recovered by vacuum distillation, and the degradation products are precipitated, washed, and dried.

2. The degradation method of amine-cured epoxy resin according to claim 1, characterized in that, The alkali metal or alkaline earth metal hydroxide is one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, and barium hydroxide.

3. The degradation method of amine-cured epoxy resin according to claim 1, characterized in that, The mass ratio of the alkali metal or alkaline earth metal hydroxide to the high-boiling diol is 0.01~30:

100.

4. The degradation method of amine-cured epoxy resin according to claim 1, characterized in that, The alcohol-base solid content is 0.01~30%.

5. The degradation method of amine-cured epoxy resin according to claim 1, characterized in that, The amine-cured epoxy resin is in block or powder form; the high-boiling-point diol is in excess relative to the hydroxide of alkali metal or alkaline earth metal.

6. The degradation method of amine-cured epoxy resin according to claim 1, characterized in that, The time required for the degradation of the amine-cured epoxy resin to complete dissolution varies from 0.1 to 7 hours, depending on the type and size of the amine-cured epoxy resin and the heating temperature.

7. The degradation method of amine-cured epoxy resin according to claim 1, characterized in that, The dehydration reaction is carried out at a temperature of 150-240°C for 10-120 minutes; the degradation temperature is 230-280°C.

8. The degradation method of amine-cured epoxy resin according to claim 1, characterized in that, The precipitation of degradation products is achieved by adding a precipitant.

9. The degradation method of amine-cured epoxy resin according to claim 8, characterized in that, The precipitant is an acidic reagent or an aqueous solution of an acidic reagent; or the precipitant is an aqueous solution of magnesium chloride or calcium chloride.

10. The degradation method of amine-cured epoxy resin according to claim 1, characterized in that, The washing is done with water; the drying is done under vacuum at 120-150°C for 0.5-6 hours; the degradation product is a polyol oligomer containing phenolic and alcoholic hydroxyl groups.

Images