An efficient method for the pretreatment degradation and recycling of thermosetting epoxy resin based on mixed reactive solvothermal method

Abstract

The application provides an efficient method for pretreatment degradation and recovery of thermosetting epoxy resin based on a mixed reaction type solvothermal method, comprising the following steps: S1: providing cured epoxy resin; S2: adding the cured epoxy resin into double solvents for pre-soaking to provide a pretreated sample; the double solvents are selected from halogenated alkanes and aliphatic amines; S3: refluxing the pretreated sample in a low temperature range, cooling to room temperature, and obtaining a first filtrate after first suction filtration; mixing the first filtrate with water to precipitate or form a dispersion liquid, and recovering epoxy resin degradation small molecules or oligomers after second suction filtration of the precipitate and further separation of the dispersion liquid. The application can efficiently degrade thermosetting epoxy resin under the synergistic effect of the obtained mixture and the original solvent molecules through the mixed reaction type double solvents of halogenated alkanes-aliphatic amines in different proportions under pre-soaking and low temperature interval reflux, and is green, environmentally friendly and low in cost.

Description

Technical Field

[0001] This invention belongs to the field of epoxy resin recycling technology, specifically relating to an efficient method for the pretreatment, degradation, and recycling of thermosetting epoxy resin based on a mixed reaction solvothermal method. Background Technology

[0002] Epoxy resins possess excellent physical and mechanical properties, electrical insulation properties, chemical corrosion resistance, heat resistance, and adhesive properties, and are widely used in industries such as machinery and electronics, aerospace, transportation, construction, and chemical engineering. The superior properties of epoxy resins stem from the epoxy groups in their molecular structure and the insoluble, infusible, three-dimensional network molecular structure formed after curing and cross-linking. However, these material characteristics also mean that they are difficult to degrade, leading to significant challenges in the recycling and reuse of waste epoxy resins. The environmental pollution and resource waste caused by waste epoxy resins have become serious environmental, social, and economic problems in my country and globally. Therefore, breakthroughs are needed in key technologies for the high-value recycling of waste epoxy resins.

[0003] Currently, the technical pathways for the recycling and reuse of waste epoxy resin are as follows:

[0004] 1) Mechanical Method: Waste epoxy resin is mechanically pulverized and ground into powder of a certain particle size for low-value applications such as raw materials or fillers in the preparation of specific products. Although this technology is relatively mature, it is essentially just "solid waste transfer" and does not fundamentally achieve high-value recycling of waste epoxy resin. Furthermore, the pulverizing and grinding process generates a large amount of dust, causing severe wear and tear on processing equipment, which not only increases the cost of mechanical recycling but also creates new environmental problems. For example, Dow Global Technologies uses a mechanical method to convert waste resin into toughening fillers, achieving 100% efficient full conversion and utilization, but this method only applies to fiber-reinforced resin waste.

[0005] 2) Solution Method: Depending on the reaction solvent or medium, chemical solution methods for recycling mainly include alcoholysis, alkaline hydrolysis, hydrolysis, and hydrogenolysis. Under mild conditions, thermosetting epoxy resin matrices are decomposed into raw material monomers or their low-molecular-weight polymers through heating or chemical reactions, thereby achieving the separation and recycling of complex components. However, specific solvents or media can only handle a limited number of resin types, and the amount of solvent used is large. Furthermore, some solvents are only used as loosening agents and evaporate, resulting in high costs and new environmental pressures. Additionally, the dissolution rate is slow, the processing target is limited (i.e., only one type of epoxy resin can be processed), energy consumption is high, and the requirements for the materials of the processing equipment are high. Therefore, it is necessary to further improve the technical solutions for the recycling and reuse of waste epoxy resins to meet the needs of the circular economy. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an efficient method for the pretreatment, degradation and recycling of thermosetting epoxy resin based on a mixed reactive solvothermal method, and its preparation method. The method involves pre-soaking and refluxing of epoxy resin cured under various standard curing conditions with a mixed reactive dual solvent in a low-temperature range (e.g., ≤150°C) to break the major molecular bonds of most of the cured epoxy resin, achieving a degradation rate of approximately 100%. This method is used to solve the problems existing in the technical path of waste epoxy resin recycling and reuse in the prior art.

[0007] To achieve the above and other related objectives, the present invention is obtained through the following technical solution.

[0008] This invention provides an efficient method for the pretreatment, degradation, and recycling of thermosetting epoxy resins based on a mixed reactive solvothermal method, comprising the following steps:

[0009] S1: Provides cured epoxy resin;

[0010] S2: The cured epoxy resin is added to a dual solvent for pre-immersion to provide a pretreated sample; the dual solvent is selected from haloalkanes and aliphatic amines;

[0011] S3: The pretreated sample is refluxed in a low-temperature range and cooled to room temperature. After the first filtration, the first filtrate is obtained. The first filtrate is mixed with water to precipitate. The precipitate is then filtered a second time, and the dispersion is further separated to recover epoxy resin degradation small molecules or oligomers.

[0012] Compared with the prior art, the beneficial effects of the present invention are:

[0013] To achieve low-energy, environmentally friendly, and efficient recycling and degradation of cured epoxy resin raw materials, this invention aims to provide a highly efficient method for the pretreatment, degradation, and recycling of thermosetting epoxy resins based on a mixed-reaction solvothermal method. Compared to existing mechanical and solution methods for recycling and reusing waste epoxy resins, this invention employs a mixed-reaction dual-solvent method using different proportions of haloalkanes and aliphatic amines under pre-soaking and low-temperature reflux conditions (e.g., ≤150°C). The resulting mixture, along with the original solvent molecules, works synergistically to achieve highly efficient degradation, while also being environmentally friendly and cost-effective, greatly promoting the development of a circular economy for waste epoxy resins. Furthermore, this invention can process various types of low- and high-crosslinked epoxy resins, exhibiting wider applicability and overcoming the limitations of current epoxy resin degradation and recycling technologies. Attached Figure Description

[0014] Figure 1The images show the infrared spectra of dichloromethane, diethylenetriamine, and the reaction of dichloromethane and diethylenetriamine after heating.

[0015] Figure 2 The diagram shows the pretreatment and degradation results of the cured bisphenol A diglycidyl ether epoxy resin in Example 1 of this invention.

[0016] Figure 3 The images shown are infrared spectra of bisphenol A diglycidyl ether, cured bisphenol A diglycidyl ether epoxy resin, bisphenol A diglycidyl ether epoxy resin degradation residue, and recovered bisphenol A diglycidyl ether epoxy resin, as shown in Example 1 of this invention.

[0017] Figure 4 The graphs shown are thermogravimetric and heat flow curves of bisphenol A diglycidyl ether, cured bisphenol A diglycidyl ether epoxy resin, and recycled bisphenol A diglycidyl ether epoxy resin, as presented in Example 1 of this invention.

[0018] Figure 5 The graph shown is a differential scanning calorimetry (DSC) curve of bisphenol A diglycidyl ether, cured bisphenol A diglycidyl ether epoxy resin, and recycled bisphenol A diglycidyl ether epoxy resin, as shown in Example 1 of the present invention.

[0019] Figure 6 The images shown are of bisphenol A diglycidyl ether epoxy resin cured according to Example 1 of the present invention and recycled bisphenol A diglycidyl ether epoxy resin. 13 C-NMR spectrum.

[0020] Figure 7 The figures shown are the extracted ion chromatogram and the base peak ion chromatogram of the bisphenol A diglycidyl ether epoxy resin recovered in negative ion mode in Example 1 of the present invention at m / z 537.284.

[0021] Figure 8 The image shown is an infrared spectrum of diethylenetriamine and recovered diethylenetriamine as described in Example 1 of this invention.

[0022] Figure 9 The images shown are infrared spectra of bisphenol F diglycidyl ether, cured bisphenol F diglycidyl ether epoxy resin, bisphenol F diglycidyl ether epoxy resin degradation residue, and recovered bisphenol F diglycidyl ether epoxy resin, as shown in Example 2 of this invention.

[0023] Figure 10 The graph shown is a differential scanning calorimetry (DSC) curve of bisphenol F diglycidyl ether, cured bisphenol F diglycidyl ether epoxy resin, and recycled bisphenol F diglycidyl ether epoxy resin, as shown in Example 2 of the present invention.

[0024] Figure 11The images shown are of bisphenol F diglycidyl ether epoxy resin cured according to Example 2 of the present invention and recycled bisphenol A diglycidyl ether epoxy resin. 13 C-NMR spectrum.

[0025] Figure 12 The images shown are infrared spectra of tris(4-hydroxyphenyl)methane triglycidyl ether, cured tris(4-hydroxyphenyl)methane triglycidyl ether epoxy resin, degradation residue of tris(4-hydroxyphenyl)methane triglycidyl ether epoxy resin, and recovered tris(4-hydroxyphenyl)methane triglycidyl ether epoxy resin, as shown in Example 3 of the present invention.

[0026] Figure 13 The diagram shows the pretreatment and degradation results of the trimethylolpropane triglycidyl ether epoxy resin cured in Example 4.

[0027] Figure 14 The image shown is the infrared spectrum of the trimethylolpropane triglycidyl ether epoxy resin cured with acid anhydride as described in Example 4.

[0028] Figure 15 The image shown is the infrared spectrum of the tetrahydrophthalic acid diglycidyl ester epoxy resin cured with anhydride as described in Example 5.

[0029] Figure 16 The image shown is the infrared spectrum of the tetrahydrophthalic acid diglycidyl ester epoxy resin cured with tetrahydrophthalic acid diglycidyl ester and amines, as shown in Example 6.

[0030] Figure 17 The commercial E51 shown in Examples 7 and 8 is cured. Figure 17 a) and E44 Figure 17 b) Schematic diagram of epoxy resin pretreatment and degradation results.

[0031] Figure 18 Shown as Comparative Examples 1 and 2, the cured bisphenol A diglycidyl ether epoxy resin was used alone with diethylenetriamine ( Figure 18 a) and the use of dichloromethane alone ( Figure 18 b) Schematic diagram of pretreatment and degradation results. Detailed Implementation

[0032] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the efficient method for pretreatment, degradation, and recycling of thermosetting epoxy resins based on a mixed reactive solvothermal method, as per this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0033] This invention addresses the problems existing in current technologies for the recycling and reuse of waste epoxy resins by proposing a highly efficient method for the pretreatment, degradation, and recycling of thermosetting epoxy resins based on a mixed-reaction solvothermal process. Specifically, through the reaction of a mixed reactive dual solvent of haloalkanes and aliphatic amines in different proportions under pre-soaking and reflux at a low temperature (e.g., ≤150℃), the resulting mixture, along with the original solvent molecules, synergistically increases the selectivity of degradation or bond breaking and enhances nucleophilicity, achieving multi-selective and efficient degradation of the cured epoxy resin. Furthermore, both solvents are fully utilized in this degradation process, serving as degradation reactants and avoiding evaporation and waste. The main solvent components can also be recovered greenly through distillation, and the resulting small molecule or oligomer degradation products can be further recycled and reused. This method is applicable to a variety of low- and high-crosslinked cured epoxy resins. The epoxy resins studied are extensive and commonly used, including typical types such as bisphenol A epoxy resin, bisphenol F epoxy resin, polyphenol glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin, glycidyl ester epoxy resin, and glycidyl amine epoxy resin. This invention can achieve a degradation rate of up to approximately 100% for the cured products of these most common epoxy resins. Based on this, this application was completed.

[0034] This invention provides an efficient method for the pretreatment, degradation, and recycling of thermosetting epoxy resins based on a mixed reactive solvothermal method, comprising the following steps:

[0035] S1: Provides cured epoxy resin;

[0036] S2: The cured epoxy resin is added to a dual solvent for pre-immersion to provide a pretreated sample; the dual solvent is selected from haloalkanes and aliphatic amines;

[0037] S3: The pretreated sample is refluxed in a low-temperature range, and the thermosetting epoxy resin is efficiently degraded. After cooling to room temperature, the first filtrate is obtained by first filtration. The first filtrate is mixed with water to precipitate or form a dispersion. The precipitate is then filtered a second time, and the dispersion is further separated to recover the epoxy resin degraded small molecules or oligomers.

[0038] In the efficient method for pretreatment, degradation, and recycling of thermosetting epoxy resin provided by this invention, step S1 involves providing cured epoxy resin. In some embodiments, the method for preparing the cured epoxy resin includes: mixing and stirring epoxy resin monomers and a curing agent, and then curing at room temperature or by heating to obtain cured epoxy resin; wherein the curing agent is selected from anhydride curing agents and / or amine curing agents. In a specific embodiment, a certain amount of epoxy resin monomers and curing agent are weighed in a beaker, stirred for a period of time, poured into a mold, and the internal air is removed by vacuuming. Curing is then carried out under certain curing conditions to obtain cured epoxy resin.

[0039] In step S1 of the present invention, in some embodiments, the epoxy resin monomer may be one or more of the following: bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, tris(4-hydroxyphenyl)methane triglycidyl ether, trimethylolpropane triglycidyl ether, and tetrahydrophthalic acid diglycidyl ester.

[0040] In step S1 of the present invention, in some embodiments, the anhydride curing agent may be one or more of the following: phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, dodecenylsuccinic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, or trimellitic anhydride.

[0041] In step S1 of the present invention, in some embodiments, the amine curing agent is selected from one or more combinations of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylaminopropylamine, m-phenylenediamine, m-phenylenediamine, diaminodiphenylmethane, bis(4-amino-3-methylcyclohexyl)methane or bis(4-aminocyclohexyl)methane.

[0042] In step S1 of this invention, in some embodiments, a phenolic accelerator may also be included. The phenolic accelerator is also called a phenolic epoxy resin curing accelerator. In a specific embodiment, a certain amount of epoxy resin monomer, curing agent, and phenolic accelerator are weighed in a beaker, stirred for a period of time, poured into a mold, and the internal air is removed by vacuuming. Curing is then carried out under certain curing conditions to obtain cured epoxy resin.

[0043] In step S1 of the present invention, in some embodiments, the phenolic accelerator is selected from one or more combinations of phenol, o-cresol, m-cresol, resorcinol, tris(dimethylaminomethyl)phenol, or nonylphenol.

[0044] In step S1 of this invention, the amount of monomer used is for the step of providing the cured product, and the amount can be increased as needed. In some embodiments, the amount of epoxy resin monomer used is ≥20g. In specific embodiments, the amount of epoxy resin monomer used may also be, for example, 20-50g, 20-30g, 30-40g, or 40-50g, etc.

[0045] In step S1 of this invention, in some embodiments, the amount of curing agent is 10% to 70% of the amount of epoxy resin monomer. In specific embodiments, the amount of curing agent is 10% to 30%, 30% to 50%, or 50% to 70% of the amount of epoxy resin monomer, etc.

[0046] In step S1 of this invention, in some embodiments, the amount of the phenolic accelerator is 0% to 1.5% of the amount of epoxy resin monomer. In specific embodiments, the amount of the phenolic accelerator is 0% to 1.5%, 0% to 0.1%, 0.1% to 0.5%, 0.5% to 1%, 1% to 3%, or 3% to 5% of the amount of epoxy resin monomer, etc.

[0047] In step S1 of this invention, the stirring time is generally not limited. In some embodiments, the stirring time is, for example, ≥5 mins. In specific embodiments, the stirring time can be, for example, 5-10 mins, 10-15 mins, or 15-20 mins, etc.

[0048] In step S1 of this invention, the curing temperature can be, for example, room temperature, 100℃~150℃, 100℃~120℃, or 120℃~150℃. All room temperatures mentioned in this application are those known in the art. For example, it can be 20℃~25℃.

[0049] In step S1 of this invention, the curing time is ≥0.5h. For example, it can be 0.5~2h, 2~10h, 2~4h, 4~6h, 6~8h, or 8~10h, etc.

[0050] In the efficient method for pretreatment, degradation, and recycling of thermosetting epoxy resin provided by this invention, step S2 involves adding the cured epoxy resin to a dual solvent for pre-soaking to provide a pretreated sample. The dual solvent is selected from haloalkanes and aliphatic amines. In a specific embodiment, a certain amount of cured epoxy resin is weighed into a round-bottom flask, and then the dual solvent is added in a certain proportion. The flask is then sealed and stored in a cool, dry environment for a period of time for pre-soaking.

[0051] In step S2 of the present invention, in some embodiments, the haloalkane is selected from one or more combinations of dichloromethane, dichloroethane, dichloropropane, trichloromethane, and trichloroethane.

[0052] In step S2 of the present invention, in some embodiments, the aliphatic amine is selected from one or more combinations of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylaminopropylamine, bis(4-amino-3-methylcyclohexyl)methane or bis(4-aminocyclohexyl)methane.

[0053] In step S2 of this invention, the amount of cured epoxy resin can be increased as needed. In some embodiments, the amount of cured epoxy resin is ≥2g. Preferably, the amount of cured epoxy resin is 2g to 5g.

[0054] In step S2 of this invention, in some embodiments, the mass ratio of the cured epoxy resin to the dual solvents is 2-5:10-20. In specific embodiments, the mass ratio of the cured epoxy resin to the dual solvents can be, for example, 2-3:10-20, 3-5:10-20, etc.

[0055] In step S2 of this invention, the mass ratio of haloalkanes to aliphatic amines in the dual solvents is ≤1. Preferably, the mass ratio of haloalkanes to aliphatic amines is 0.05–1. Optionally, the mass ratio of haloalkanes to aliphatic amines can be, for example, 0.05–0.1, 0.1–0.3, 0.3–0.5, 0.5–0.8, or 0.8–1, etc. Figure 1 The images show the infrared spectra before and after the reaction in both solvents.

[0056] In step S2 of this invention, the pre-soaking time is generally not limited. In some embodiments, the pre-soaking time is, for example, ≥0.5h.

[0057] In the efficient method for pretreatment, degradation, and recycling of thermosetting epoxy resin provided by this invention, step S3 involves refluxing the pretreated sample in a low-temperature range, resulting in efficient degradation of the thermosetting epoxy resin. After cooling to room temperature and a first filtration, a first filtrate is obtained. This first filtrate is mixed with water to precipitate a precipitate or form a dispersion. The precipitate is then subjected to a second filtration, and the dispersion is further separated to recover the epoxy resin degradation molecules or oligomers. These epoxy resin degradation molecules or oligomers are recyclable.

[0058] In step S3 of this invention, the low-temperature range temperature is ≤150℃; preferably, the low-temperature range temperature is 100℃~150℃. Optionally, the low-temperature range temperature is, for example, 100℃~120℃, or 120℃~150℃, etc.

[0059] In step S3 of this invention, the reflux time is ≤70 mins. Preferably, the reflux time is 30 mins to 70 mins.

[0060] In step S3 of this invention, the second filtrate after filtration is distilled to recover the main solvent components. Specifically, the collected filtrate is distilled at atmospheric pressure at a certain temperature for a period of time to obtain the recovered main solvent components. The recovered main solvent components mainly include aliphatic amines, such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylaminopropylamine, bis(4-amino-3-methylcyclohexyl)methane, or bis(4-aminocyclohexyl)methane. The temperature is 100–150°C, and the distillation time is 2–8 hours.

[0061] In step S3 of this invention, epoxy resin degradation molecules or oligomers are recovered after filtration. The molecular weight of the epoxy resin degradation molecules is ≤500, and the molecular weight of the oligomers is ≤1500.

[0062] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0063] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0064] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0065] Example 1

[0066] In this embodiment, an efficient method for the pretreatment, degradation, and recycling of thermosetting epoxy resin based on a mixed reactive solvothermal method is described, comprising the following steps:

[0067] S1: Weigh 20g of bisphenol A diglycidyl ether, 70% of methyltetrahydrophthalic anhydride curing agent (by mass of bisphenol A diglycidyl ether), and 1% of tris(dimethylaminomethyl)phenol accelerator (by mass of bisphenol A diglycidyl ether) in a beaker. Stir for a period of time, pour into a mold, remove internal air by vacuuming, and cure at 120℃ for 2h and 150℃ for 4h to obtain cured bisphenol A diglycidyl ether epoxy resin.

[0068] S2: Weigh 2g of cured bisphenol A diglycidyl ether epoxy resin in a round-bottom flask, then add 1g of dichloromethane and 10g of diethylenetriamine in a 1:10 ratio, seal and store in a cool, dry environment for 48 hours for pre-soaking.

[0069] S3: The pretreated sample was refluxed at 130℃ for 50 min, then cooled to room temperature and filtered to obtain undegraded epoxy resin residue. After drying in a 60℃ oven, 0.0087 g of cured bisphenol A diglycidyl ether epoxy resin degradation filter residue was obtained, with a degradation rate as high as 99.56%. At the same time, the filtrate was added dropwise to water to mix with water and precipitate out. After filtration, the recovered epoxy resin was obtained. After drying in a 60℃ oven, 0.9551 g of recovered bisphenol A diglycidyl ether epoxy resin was obtained. The filtrate was collected and distilled at a certain temperature (130℃) under normal pressure for a period of time (6 h) to obtain recovered diethylenetriamine.

[0070] Depend on Figure 2 The schematic diagram shows that the bisphenol A diglycidyl ether epoxy resin produced less filter residue after degradation by a mixed reaction-type solvothermal method, and the spectrum of the recovered bisphenol A diglycidyl ether epoxy resin was obtained by infrared spectroscopy. Figure 3 As can be seen from the figure, the main chain skeleton of the bisphenol A diglycidyl ether epoxy resin was not destroyed after degradation, while at 1731 cm⁻¹... -1 The intensity of the C=O peak in the ester group at the ester group decreased significantly, indicating that the ester bond of the bisphenol A diglycidyl ether epoxy resin was broken. This was confirmed by thermogravimetric analysis (TGA). Figure 4 ) and the measured glass transition temperature ( Figure 5 It can be seen that the recovered bisphenol A diglycidyl ether epoxy resin is composed of small molecules or oligomers. The above conclusions are supported by elemental analysis (Table 1) and... 13 C-NMR ( Figure 6 This was further confirmed. After degradation, no ester groups were found at 173 ppm. This indicates that the degradation reaction of the mixed-reaction solvothermal method is mainly achieved through the cleavage of ester groups. The extraction ion chromatogram and base peak ion chromatogram of the recovered bisphenol A diglycidyl ether epoxy resin at m / z 537.284, as determined by liquid chromatography-mass spectrometry (LC-MS), are shown. Figure 7The significantly reduced molecular weight further demonstrates that the mixed-reaction solvothermal process effectively degrades the polymer into smaller molecules or oligomers. The infrared spectra of the recovered solvent were compared with those of the initially purchased diethylenetriamine. Figure 8 As can be seen from the figure, the peaks are basically the same, indicating that the recovered solvent is mainly composed of diethylenetriamine.

[0071] Table 1. Elemental analysis of bisphenol A diglycidyl ether, cured bisphenol A diglycidyl ether epoxy resin, and recycled bisphenol A diglycidyl ether epoxy resin in Example 1.

[0072]

[0073] Example 2

[0074] In this embodiment, an effective scheme for efficient solvent thermal degradation and recovery of various epoxy resins cured by thermosetting acid anhydrides and amines based on dual-solvent room temperature pretreatment is described, with the following steps:

[0075] S1: Weigh 20g of bisphenol F diglycidyl ether, 70% of methyltetrahydrophthalic anhydride curing agent (by mass of bisphenol F diglycidyl ether), and 1% of tris(dimethylaminomethyl)phenol accelerator (by mass of bisphenol F diglycidyl ether) in a beaker. Stir for a period of time, pour into a mold, remove internal air by vacuuming, and cure at 120℃ for 2h and at 150℃ for 4h to obtain cured bisphenol F diglycidyl ether epoxy resin.

[0076] S2: Weigh 2g of cured bisphenol F diglycidyl ether epoxy resin in a round-bottom flask, then add 1g of dichloromethane and 10g of diethylenetriamine in a 1:10 ratio, seal and store in a cool, dry environment for 48 hours for pre-soaking.

[0077] S3: The pretreated sample was refluxed at 130℃ for 50 min, then cooled to room temperature and filtered to obtain undegraded epoxy resin residue. After drying in a 60℃ oven, 0.0573 g of cured bisphenol F diglycidyl ether epoxy resin degradation filter residue was obtained, with a degradation rate as high as 97.14%. At the same time, the filtrate was added dropwise to water to mix with water and precipitate out. After filtration, the recovered epoxy resin was obtained. After drying in a 60℃ oven, 1.0643 g of recovered bisphenol F diglycidyl ether epoxy resin was obtained. The filtrate was collected and distilled at a certain temperature (130℃) under normal pressure for a period of time (6 h) to obtain recovered diethylenetriamine.

[0078] Similar to the characterization results of bisphenol A diglycidyl ether epoxy resin, the infrared spectrum of the recovered bisphenol F diglycidyl ether epoxy resin was analyzed. Figure 9Similarly, the main chain skeleton of bisphenol F diglycidyl ether epoxy resin was not destroyed after degradation, while at 1730cm -1 The C=O peak intensity in the ester group at the ester group decreased significantly, indicating that the ester bond of the bisphenol F diglycidyl ether epoxy resin was broken. This was determined by the measured glass transition temperature (…). Figure 10 It can be seen that the recovered bisphenol F diglycidyl ether epoxy resin is composed of small molecules or oligomers. The above conclusions are based on... 13 C-NMR ( Figure 11 This was further confirmed. After degradation, no ester groups were found at 173 ppm. This indicates that the degradation reaction in the mixed-reaction solvothermal method is mainly achieved through the cleavage of ester groups.

[0079] Example 3

[0080] In this embodiment, an effective scheme for efficient solvent thermal degradation and recovery of various epoxy resins cured by thermosetting acid anhydrides and amines based on dual-solvent room temperature pretreatment is described, with the following steps:

[0081] S1: Weigh 20g of tris(4-hydroxyphenyl)methane triglycidyl ether, 70% of the mass of tris(4-hydroxyphenyl)methane triglycidyl ether as a curing agent of methyltetrahydrophthalic anhydride, and 1% of the mass of tris(4-hydroxyphenyl)methane triglycidyl ether as a tri(dimethylaminomethyl)phenol accelerator in a beaker. Stir for a period of time, pour into a mold, remove the internal air by vacuuming, and cure at 120℃ for 2h and at 150℃ for 4h to obtain cured tris(4-hydroxyphenyl)methane triglycidyl ether epoxy resin.

[0082] S2: Weigh 2g of cured tri(4-hydroxyphenyl)methane triglycidyl ether epoxy resin in a round-bottom flask, then add 1g of dichloromethane and 10g of diethylenetriamine at a ratio of 1:10, and store in a cool, dry environment for 48 hours for pre-soaking.

[0083] S3: The pretreated sample was refluxed at 150℃ for 70 min, then cooled to room temperature and filtered to obtain undegraded epoxy resin residue. After drying in a 60℃ oven, 0.0888 g of cured tris(4-hydroxyphenyl)methane triglycidyl ether epoxy resin degradation filter residue was obtained, with a degradation rate as high as 95.56%. At the same time, the filtrate was added dropwise to water to mix with water and precipitate out. After filtration, the recovered epoxy resin was obtained. After drying in a 60℃ oven, 0.5276 g of recovered tris(4-hydroxyphenyl)methane triglycidyl ether epoxy resin was obtained. The filtrate was collected and distilled at a certain temperature (130℃) under normal pressure for a period of time (6 h) to obtain recovered diethylenetriamine.

[0084] The infrared spectrum of the recovered tris(4-hydroxyphenyl)methane triglycidyl ether epoxy resin shows that... Figure 12 After degradation, the main chain skeleton of tris(4-hydroxyphenyl)methane triglycidyl ether epoxy resin was not destroyed, while at 1728 cm⁻¹... -1 The significant decrease in the C=O peak intensity of the ester group indicates that the ester bonds of the tris(4-hydroxyphenyl)methane triglycidyl ether epoxy resin have been broken. This suggests that the mixed-reaction solvothermal method degrades the polymer into smaller molecules or oligomers.

[0085] Example 4

[0086] In this embodiment, an effective scheme for efficient solvent thermal degradation and recovery of various epoxy resins cured by thermosetting acid anhydrides and amines based on dual-solvent room temperature pretreatment is described, with the following steps:

[0087] S1: Weigh 20g of trimethylolpropane triglycidyl ether, 70% of the mass of trimethylolpropane triglycidyl ether as methyltetrahydrophthalic anhydride curing agent, and 1% of the mass of trimethylolpropane triglycidyl ether as tri(dimethylaminomethyl)phenol accelerator in a beaker, stir for a period of time, pour into a mold, evacuate to remove internal air, and cure at 120℃ for 2h and at 150℃ for 4h to obtain cured trimethylolpropane triglycidyl ether epoxy resin.

[0088] S2: Weigh 2g of cured trimethylolpropane triglycidyl ether epoxy resin in a round-bottom flask, then add 1g of dichloromethane and 10g of diethylenetriamine in a 1:10 ratio, seal and store in a cool, dry environment for 48 hours for pre-soaking.

[0089] S3: The pretreated sample was refluxed at 150°C for 70 minutes, then cooled to room temperature and filtered. The filter residue was very small, meaning that the undegraded epoxy resin was close to zero, and the degradation rate was as high as approximately 100%.

[0090] Depend on Figure 13 The schematic diagram shows that the cured trimethylolpropane triglycidyl ether epoxy resin exhibits virtually no residue after degradation via a mixed reactive solvothermal method. The infrared spectrum of the cured trimethylolpropane triglycidyl ether epoxy resin was obtained by infrared spectroscopy. Figure 14 As can be seen from the figure, the cured trimethylolpropane triglycidyl ether epoxy resin reaches a depth of 1729 cm⁻¹. -1 The high intensity of the C=O peak in the ester group indicates that the cured trimethylolpropane triglycidyl ether epoxy resin contains ester bonds.

[0091] Example 5

[0092] In this embodiment, an effective scheme for efficient solvent thermal degradation and recovery of various epoxy resins cured by thermosetting acid anhydrides and amines based on dual-solvent room temperature pretreatment is described, with the following steps:

[0093] S1: Weigh 20g of diglycidyl tetrahydrophthalate, 70% of the mass of diglycidyl tetrahydrophthalate, methyltetrahydrophthalic anhydride curing agent, and 1% of the mass of diglycidyl tetrahydrophthalate accelerator in a beaker. Stir for a period of time, pour into a mold, remove internal air by vacuum, and cure at 120℃ for 2h and 150℃ for 4h to obtain cured diglycidyl tetrahydrophthalate epoxy resin.

[0094] S2: Weigh 2g of cured tetrahydrophthalic acid diglycidyl ester epoxy resin in a round-bottom flask, then add 1g of dichloromethane and 10g of diethylenetriamine in a 1:10 ratio, and store in a cool, dry environment for 48 hours for pre-soaking.

[0095] S3: The pretreated sample was refluxed at 150℃ for 70 minutes, then cooled to room temperature and filtered. The filtration showed that there was basically no residue, meaning that the amount of undegraded epoxy resin was almost zero, and the degradation rate was as high as approximately 100%.

[0096] The spectrum of cured tetrahydrophthalic acid diglycidyl ester epoxy resin was obtained by infrared spectroscopy. Figure 15 As can be seen from the figure, the cured tetrahydrophthalic acid diglycidyl ester epoxy resin at 1726 cm⁻¹ -1 The high intensity of the C=O peak in the ester group indicates that the cured tetrahydrophthalic acid diglycidyl ester epoxy resin contains ester bonds.

[0097] Example 6

[0098] In this embodiment, an effective scheme for efficient solvent thermal degradation and recovery of various epoxy resins cured by thermosetting acid anhydrides and amines based on dual-solvent room temperature pretreatment is described, with the following steps:

[0099] S1: Weigh 20g of diglycidyl tetrahydrophthalate and 12% diethylenetriamine curing agent (by mass of diglycidyl tetrahydrophthalate) in a beaker, stir for a period of time, pour into a mold, remove internal air by vacuum, gel at 25℃ for 30min and cure at 120℃ for 2h to obtain cured diglycidyl tetrahydrophthalate epoxy resin.

[0100] S2: Weigh 2g of cured tetrahydrophthalic acid diglycidyl ester epoxy resin in a round-bottom flask, then add 1g of dichloromethane and 10g of diethylenetriamine in a 1:10 ratio, and store in a cool, dry environment for 48 hours for pre-soaking.

[0101] S3: The pretreated sample was refluxed at 130℃ for 50 minutes, then cooled to room temperature and filtered. The filtration showed almost no residue, meaning that the amount of undegraded epoxy resin was close to zero, and the degradation rate was as high as approximately 100%.

[0102] The spectrum of diethylenetriamine-cured tetrahydrophthalic acid diglycidyl ester epoxy resin was obtained by infrared spectroscopy. Figure 16 As can be seen from the figure, the cured tetrahydrophthalic acid diglycidyl ester epoxy resin at 1722 cm⁻¹ -1 The high intensity of the C=O peak in the ester group indicates that the diethylenetriamine-cured tetrahydrophthalic acid diglycidyl ester epoxy resin contains ester bonds.

[0103] Example 7

[0104] In this embodiment, an efficient method for the pretreatment, degradation, and recycling of thermosetting epoxy resin based on a mixed reactive solvothermal method is described, comprising the following steps:

[0105] S1: Weigh 20g of E51 resin (Phoenix brand) and 25g of commercially available modified methyltetrahydrophthalic anhydride in a beaker, stir for a period of time, pour into a mold, evacuate to remove internal air, and cure at 80℃ for 2 hours as recommended in the product instructions to obtain cured commercial E51 epoxy resin.

[0106] S2: Weigh 2g of cured commercial E51 epoxy resin in a round-bottom flask, then add 1g of dichloromethane and 10g of diethylenetriamine at a ratio of 1:10, and store in a cool, dry environment for 48 hours for pre-soaking.

[0107] S3: The pretreated sample was refluxed at 130℃ for 50 minutes, then cooled to room temperature and filtered. The residue obtained after filtration was undegraded epoxy resin. After drying in a 60℃ oven, only 0.0007g of undegraded cured commercial E51 epoxy resin was obtained, with a degradation rate as high as 99.97%. Figure 17 a).

[0108] Example 8

[0109] In this embodiment, an efficient method for the pretreatment, degradation, and recycling of thermosetting epoxy resin based on a mixed reactive solvothermal method is described, comprising the following steps:

[0110] S1: Weigh 20g of E44 resin (Phoenix brand) and 25g of commercially available modified methyltetrahydrophthalic anhydride in a beaker, stir for a period of time, pour into a mold, evacuate to remove internal air, and cure at 80℃ for 2 hours according to the product instructions to obtain cured commercial E44 epoxy resin.

[0111] S2: Weigh 2g of cured commercial E44 epoxy resin in a round-bottom flask, then add 1g of dichloromethane and 10g of diethylenetriamine in a 1:10 ratio, seal and store in a cool, dry environment for 48 hours for pre-soaking.

[0112] S3: The pretreated sample was refluxed at 130℃ for 50 minutes, then cooled to room temperature and filtered. The residue obtained after filtration was undegraded epoxy resin. After drying in a 60℃ oven, only 0.0002g of undegraded cured commercial E44 epoxy resin was obtained, with a degradation rate as high as 99.99%. Figure 17 b).

[0113] Comparative Example 1

[0114] In this embodiment, a comparative experiment was conducted with an efficient method for the pretreatment, degradation, and recycling of thermosetting epoxy resin based on a mixed reactive solvothermal method. The steps are as follows:

[0115] S1: Weigh 20g of bisphenol A diglycidyl ether, 70% of methyltetrahydrophthalic anhydride curing agent (by mass of bisphenol A diglycidyl ether), and 1% of tris(dimethylaminomethyl)phenol accelerator (by mass of bisphenol A diglycidyl ether) in a beaker. Stir for a period of time, pour into a mold, remove internal air by vacuuming, and cure at 120℃ for 2h and 150℃ for 4h to obtain cured bisphenol A diglycidyl ether epoxy resin.

[0116] S2: Weigh 2g of cured bisphenol A diglycidyl ether epoxy resin in a round-bottom flask, add 11g of dichloromethane separately, and store in a cool, dry environment for 48 hours for pre-soaking.

[0117] S3: The pretreated sample was refluxed at 130℃ for 50 min, then cooled to room temperature and filtered. The residue obtained after filtration was undegraded epoxy resin. After drying in a 60℃ oven, 2.3189 g of cured bisphenol A diglycidyl ether epoxy resin degradation residue was obtained, indicating no degradation effect. Figure 18 a).

[0118] Comparative Example 2

[0119] In this embodiment, a comparative experiment was conducted with an efficient method for the pretreatment, degradation, and recycling of thermosetting epoxy resin based on a mixed reactive solvothermal method. The steps are as follows:

[0120] S1: Weigh 20g of bisphenol A diglycidyl ether, 70% of methyltetrahydrophthalic anhydride curing agent (by mass of bisphenol A diglycidyl ether), and 1% of tris(dimethylaminomethyl)phenol accelerator (by mass of bisphenol A diglycidyl ether) in a beaker. Stir for a period of time, pour into a mold, remove internal air by vacuuming, and cure at 120℃ for 2h and 150℃ for 4h to obtain cured bisphenol A diglycidyl ether epoxy resin.

[0121] S2: Weigh 2g of cured bisphenol A diglycidyl ether epoxy resin in a round-bottom flask, add 11g of diethylenetriamine separately, and store in a cool, dry environment for 48 hours for pre-soaking.

[0122] S3: The pretreated sample was refluxed at 130℃ for 50 min, then cooled to room temperature and filtered. The residue obtained after filtration was undegraded epoxy resin. After drying in a 60℃ oven, 2.7575 g of cured bisphenol A diglycidyl ether epoxy resin degradation residue was obtained, indicating no degradation effect. Figure 18 b).

[0123] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A highly efficient method for the pre-treatment degradation recycling of thermoset epoxy resins based on a hybrid reactive solvothermal method, characterized in that, The method comprises the following steps: S1: providing a cured epoxy resin; S2: adding the cured epoxy resin into a double solvent for pre-soaking to provide a pretreated sample; the double solvent is selected from a halogenated alkane and an aliphatic amine; S3: refluxing the pretreated sample in a low temperature range, cooling to room temperature, and obtaining a first filtrate after first suction filtration; mixing the first filtrate with water to precipitate or form a dispersion liquid, and recovering the epoxy resin degradation small molecules or oligomers after second suction filtration of the precipitate and further separation of the dispersion liquid; In step S2, the mass ratio of the halogenated alkane and the aliphatic amine is ≤1; In step S3, the temperature of the low temperature range is ≤150℃, and the refluxing time is ≤70 min.

2. The efficient method for the pre-treatment degradation and recycling of thermoset epoxy resins based on hybrid reactive solvothermal method according to claim 1, characterized in that, In step S1, the preparation method of the cured epoxy resin comprises: mixing and stirring an epoxy resin monomer and a curing agent, and obtaining a cured epoxy resin after curing at room temperature or heating; wherein the curing agent is selected from an acid anhydride curing agent and / or an amine curing agent.

3. The efficient method for the pre-treatment degradation and recycling of thermoset epoxy resins based on hybrid reactive solvothermal method according to claim 2, characterized in that, The epoxy resin monomer is selected from a combination of one or more of bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, tris(4-hydroxyphenyl)methane triglycidyl ether, trimethylolpropane triglycidyl ether, and tetrahydrophthalic acid diglycidyl ester; and / or, the acid anhydride curing agent is selected from a combination of one or more of phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyl nadic anhydride, dodecenyl succinic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic dianhydride, or trimellitic anhydride; and / or, the amine curing agent is selected from a combination of one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylaminopropylamine, m-xylylenediamine, m-phenylenediamine, diaminodiphenylmethane, bis(4-amino-3-methylcyclohexyl)methane, or bis(4-aminocyclohexyl)methane; and / or, further comprising a phenolic accelerator, mixing and stirring the epoxy resin monomer, the curing agent, and the phenolic accelerator; and / or, the amount of the epoxy resin monomer is ≥20 g; and / or, the amount of the curing agent is 10% to 70% of the amount of the epoxy resin monomer.

4. The efficient method for the pre-treatment degradation and recycling of thermoset epoxy resins based on hybrid reactive solvothermal method according to claim 3, characterized in that, The phenolic accelerator is selected from a combination of one or more of phenol, o-cresol, m-cresol, m-dihydroxybenzene, tris(dimethylaminomethyl)phenol, or nonylphenol; and / or, the amount of the phenolic accelerator is 0% to 1.5% of the amount of the epoxy resin monomer.

5. The efficient method for the pre-treatment degradation and recycling of thermoset epoxy resins based on hybrid reactive solvothermal method according to claim 2, characterized in that, In step S1, the curing temperature is between room temperature and 200℃; and / or, in step S1, the curing time is ≥0.5 h.

6. The efficient method for the pre-treatment degradation and recycling of thermoset epoxy resins based on hybrid reactive solvothermal method according to claim 1, characterized in that, In step S2, the halogenated alkane is selected from a combination of one or more of dichloromethane, dichloroethane, dichloropropane, trichloromethane, and trichloroethane; and / or, in step S2, the aliphatic amine is selected from a combination of one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylaminopropylamine, bis(4-amino-3-methylcyclohexyl)methane, or bis(4-aminocyclohexyl)methane.

7. The efficient method for the pre-treatment degradation and recycling of thermoset epoxy resins based on hybrid reactive solvothermal method according to claim 1, characterized in that, In step S2, the amount of the cured epoxy resin is ≥2 g; And / or, in step S2, the mass ratio of the solidified epoxy resin to the double solvent is 2-5:10-20.

8. The efficient method for the pre-treatment degradation and recycling of thermoset epoxy resins based on hybrid reactive solvothermal method according to claim 1, characterized in that, In step S3, after the first time filtration, there is no filter residue or a certain amount of filter residue is obtained; when containing filter residue, the filter residue is the un-degraded solidified epoxy resin; And / or, after the second time filtration, a second filtrate is obtained, and the main solvent component is recovered by distillation.

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