Mixed solvent system, preparation method and application of mixed solvent system in degradation of epoxy resin

Abstract

The invention belongs to the technical field of waste high polymer material recovery, and particularly relates to a mixed solvent system, a preparation method and application of the mixed solvent system in degradation of epoxy resin. The invention provides a green reusable mixed solvent system, propylene carbonate has a hot pure characteristic, forms a homogeneous phase with an aqueous solution at a high temperature and is split in phase after cooling, water is easily separated from an organic phase at the end of a reaction, and carbon fibers, a depolymerization matrix and a catalyst are recovered through simple filtration and distillation, so that the carbon fibers are recycled. And the mixed system can be recycled and accords with circular economy. According to the mixed solvent system, the risks of explosion and fire caused by degradation are remarkably reduced, and the epoxy resin and the composite material thereof are degraded and recycled under green and mild conditions; damage of high temperature and high pressure to the recycled fibers in a traditional recycling method is avoided, the quality of the recycled fibers is improved, and cyclic recycling of epoxy resin and a degradation solvent system is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of waste polymer material recovery, and in particular relates to a mixed solvent system and a preparation method thereof, and application thereof in degrading epoxy resin. Background Art

[0002] Epoxy resin has excellent heat resistance, flow properties, and high cost-effectiveness. It is widely used in coatings, chemical corrosion protection, electronic appliances, vehicles and other fields, and is still rapidly expanding into new application areas. However, since epoxy resin forms a permanent three-dimensional cross-linked network after curing, a large number of electrical equipment cannot be efficiently degraded and recycled after retirement, resulting in serious waste of resources. This makes the recycling of epoxy resin a highly concerned issue.

[0003] Nowadays, it is crucial to have industrial processes that can sustainably treat the waste generated by epoxy composites. The existing technology generally uses acetic acid to degrade epoxy resins and hydrogen peroxide for oxidation. In this process, acetic acid not only acts as a solvent, but also as a reactant to form a very strong oxidant peracetic acid in situ in the degradation system, which has very effective degradation properties for epoxy resins, and the components used in this system are also renewable. However, since the peracetic acid formed by using hot concentrated acetic acid and hydrogen peroxide is toxic and prone to fire, the use of such oxidation systems in industrial environments will cause major safety issues and is incompatible with the circular economy.

[0004] Therefore, seeking a low-risk and recyclable mixed solvent to achieve the degradation of epoxy resin matrix and composite materials under mild conditions is of great significance for the recycling of epoxy resin matrix and fibers. Summary of the invention

[0005] In view of the above problems, the present application proposes a mixed solvent system and a preparation method thereof and its application in the degradation of epoxy resin and epoxy resin composite materials. The mixed solvent system can achieve the degradation of epoxy resin and its composite materials under green and mild conditions, improve the quality of recycled fibers after degradation of epoxy resin and its composite materials, realize the recycling of epoxy resin and mixed solvent system, and reduce recycling risk and recycling cost.

[0006] In order to achieve the above-mentioned object, the first technical solution of the present application provides a mixed solvent system, comprising

[0007] Propylene carbonate, hydrogen peroxide, citric acid.

[0008] Furthermore, the addition ratio of propylene carbonate, hydrogen peroxide and citric acid is: 8-20 mL: 3-10 mL: 0.2-1.0 g.

[0009] The second technical solution of the present application discloses a method for preparing the above-mentioned mixed solvent system, which is obtained by mixing and dissolving propylene carbonate, hydrogen peroxide and citric acid.

[0010] And, a mixed solvent system prepared according to the above preparation method.

[0011] The third technical solution of the present application discloses the application of the mixed solvent system in the degradation of epoxy resin and its composite materials.

[0012] Furthermore, the epoxy resin includes amine-cured epoxy resin, Schiff base epoxy resin, ester exchange epoxy resin, hemiacetal epoxy resin, disulfide bond epoxy resin, borate epoxy resin and composite materials thereof.

[0013] Furthermore, the application method is to mix the mixed solvent system with the epoxy resin or epoxy resin composite material and heat them until they are completely degraded.

[0014] Furthermore, the mass ratio of the epoxy resin or epoxy resin composite material to the mixed solvent system is 1:6-20.

[0015] Furthermore, the heating temperature is 60-120° C., and the heating time is 0.5-13 h.

[0016] The present invention has the following beneficial effects:

[0017] (1) The present invention proposes a green and reusable mixed solvent system, in which propylene carbonate has a thermally pure property and forms a homogeneous phase with an aqueous solution at high temperature, and separates into phases after cooling. At the end of the reaction, water can be easily separated from the organic phase. The carbon fiber in the epoxy resin composite material, the polyol matrix after epoxy resin depolymerization, and the catalyst citric acid can be recovered by simple filtration and distillation. The mixed system can be recycled in accordance with the circular economy.

[0018] (2) The mixed solvent system significantly reduces the risk of explosion and fire caused by degradation, and realizes the green and mild degradation and recycling of epoxy resin and its composite materials;

[0019] (3) It avoids the damage of the recycled fiber caused by high temperature and high pressure in the traditional recycling method, improves the quality of the recycled fiber, and realizes the recycling and utilization of epoxy resin and degradation solvent system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 These are photos before and after the epoxy resin recovery in Example 4;

[0021] Figure 2 These are photos of the composite material of Example 10 before and after recycling;

[0022] Figure 3These are SEM images of the composite material fibers of Example 10 before and after recovery. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so that once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0025] The first embodiment of the present application discloses a mixed solvent system, including propylene carbonate, hydrogen peroxide, and citric acid; the addition ratio of propylene carbonate, hydrogen peroxide, and citric acid is: 8-20 mL: 3-10 mL: 0.2-1.0 g.

[0026] In a specific embodiment, the mixed solvent system is prepared by mixing and dissolving propylene carbonate, hydrogen peroxide and citric acid.

[0027] The second embodiment of the present application discloses the use of the mixed solvent system in the degradation of epoxy resin and its composite materials.

[0028] It can be understood that the epoxy resin refers to a general term for a class of polymers containing more than two epoxy groups in the molecule, which is one of the three most widely used thermosetting resin matrices to date. Because different epoxy resins have different structures and epoxy equivalents, epoxy resins on the market are divided into various types. Among them, bisphenol A diglycidyl ether (DGEBA has a long service life and good physical and chemical properties, and has the characteristics of low cost and high return. Therefore, epoxy resins prepared based on bisphenol A occupy 90% of the global thermosetting material market. When curing epoxy, an amine curing agent containing (or not containing) dynamic bonds is required. The epoxy resins cured with different curing agents are respectively referred to as amine-cured epoxy resins (without dynamic bonds), Schiff base epoxy resins, ester exchange epoxy resins, hemiacetal epoxy resins, disulfide bond epoxy resins, and borate epoxy resins. Epoxy resin composites are composite materials composed of epoxy resins and fiber reinforcement materials, wherein the fibers include carbon fibers, glass fibers, etc.

[0029] In a specific embodiment, the application method is to mix the mixed solvent system with the epoxy resin or epoxy resin composite material and heat until it is completely degraded; the mass ratio of the epoxy resin or epoxy resin composite material to the mixed solvent system is 1:6-20; the heating temperature is 60-100°C, and the heating time is 0.5-13h. The ratio of the epoxy resin or epoxy resin composite material to the mixed solvent system is such that the solvent can completely immerse the material. Too much solvent system will cause waste of resources, and too little solvent system will result in poor degradation effect. The heating temperature is lower than the boiling point of water. After multiple experiments, it is concluded that the degradable temperature range is 60-100°C.

[0030] It should be noted that, in the specific degradation process, the hydrogen peroxide in the mixed solvent system is an oxidant, citric acid is used as a catalyst, and propylene carbonate has a thermally pure characteristic, and forms a homogeneous phase with the hydrogen peroxide solution containing citric acid during high-temperature degradation, and phase separation is performed after the degradation is completed and cooled to room temperature, at which time the hydrogen peroxide solution containing citric acid and propylene carbonate can be easily separated. The depolymerized matrix of the epoxy resin degraded into polyols is dispersed in the propylene carbonate layer, and the propylene carbonate and the depolymerized matrix can be further separated by reduced pressure distillation, wherein the propylene carbonate can be recycled by adding it again to the above-separated hydrogen peroxide solution containing citric acid, and the fiber reinforcement material in the epoxy resin composite material can also be fully recovered after the epoxy resin is degraded.

[0031] It can be understood that in order to improve the degradation efficiency, the epoxy resin or its composite material is crushed into blocks during the specific degradation process and degraded in the form of crushed materials.

[0032] The actual effects of this application will be disclosed below in conjunction with specific embodiments.

[0033] This embodiment takes amine-cured epoxy resin, Schiff base epoxy resin, transesterified epoxy resin, hemiacetal epoxy resin, disulfide bond epoxy resin, and borate epoxy resin as specific examples. The amine-cured epoxy resin, Schiff base epoxy resin, transesterified epoxy resin, hemiacetal epoxy resin, imine bond epoxy resin, disulfide bond epoxy resin, borate epoxy resin materials and composite materials used in the experiment are all prepared by ourselves. The specific preparation process is as follows:

[0034] (1) Amine-cured epoxy resin: obtained by curing commercial amine curing agent isophorone diamine with E51 epoxy resin at 80°C;

[0035] (2) Schiff base epoxy resin: Disperse terephthalaldehyde in a diluent, add isophorone diamine, stir at room temperature, add E51 epoxy resin after the reaction liquid becomes clear, and cure at 80°C to obtain

[0036] (3) Ester exchange epoxy resin: The acrylate monomer reacts with diamine at a certain temperature and is cured by adding E51.

[0037] (4) Hemiacetal epoxy resin: Hemiacetal acrylate monomer reacts with diamine at a certain temperature and E51 is added to cure it.

[0038] (5) Disulfide bond epoxy resin: obtained by curing 4,4'-disulfide diphenylamine with E51.

[0039] (6) Borate epoxy resin: obtained by reacting isophorone diamine with E51 and then adding trimethyl borate to cure.

[0040] Example

[0041] Prepare a mixed solvent system: measure 8-20 mL of propylene carbonate, 3-10 mL of hydrogen peroxide and 0.2-1.0 g of citric acid in a glass bottle, stir at room temperature to dissolve evenly to obtain a mixed solvent system, crush the epoxy resin or epoxy resin composite material into crushed materials, weigh 3 g of the crushed materials and add them to the mixed solvent, and heat at 90°C.

[0042] The epoxy resin or epoxy resin composite material and the degradation time are shown in Table 1.

[0043] Table 1

[0044]

[0045]

[0046] Result analysis: As shown in Table 1, the mixed solvent system of the present application can degrade common amine-cured epoxy resins, Schiff base epoxy resins, ester exchange epoxy resins, hemiacetal epoxy resins, disulfide bond epoxy resins, borate epoxy resins and composite materials. Figure 1These are photos before and after the epoxy resin recovery in Example 4. It can be seen that the epoxy resin is completely degraded, and the solvent system is clearly phase-separated after the degradation is completed. Figure 2 The photos of the composite material of Example 10 before and after recycling are shown in Figure 10. The epoxy resin in the composite material is completely degraded, and the carbon fiber therein is restored to its original loose state and can be directly recycled. The SEM images of the original and recycled carbon fiber are shown in Figure 10. Figure 3 , further demonstrating that the resin is completely degraded and the carbon fiber is completely recycled.

[0047] The above is a specific description of the degradation of amine-cured epoxy resins, Schiff base epoxy resins, ester exchange epoxy resins, hemiacetal epoxy resins, disulfide bond epoxy resins, and borate epoxy resins in combination with the embodiments of the present invention. In addition to the epoxy resin materials mentioned above, others including acid anhydrides, imidazoles, dicyandiamide, organic acid hydrazides, and boron trifluoride-amine complexes are within the scope of application of this invention.

Claims

1. A mixed solvent system, It is characterized in that include Propylene carbonate, hydrogen peroxide, citric acid.

2. The mixed solvent system according to claim 1, It is characterized in that The addition ratio of propylene carbonate, hydrogen peroxide and citric acid is: 8-20mL: 3-10mL: 0.2-1.0g.

3. A method for preparing the mixed solvent system as claimed in claim 1 or 2, It is characterized in that The method comprises the steps of mixing and dissolving propylene carbonate, hydrogen peroxide and citric acid.

4. The mixed solvent system prepared by the preparation method as shown in claim 3.

5. Use of the mixed solvent system as claimed in claim 1, 2 or 4 in the degradation of epoxy resin and its composite material.

6. The use according to claim 5, It is characterized in that The epoxy resin includes amine-cured epoxy resin, Schiff base epoxy resin, ester exchange epoxy resin, hemiacetal epoxy resin, disulfide bond epoxy resin, borate epoxy resin and composite materials thereof.

7. The use according to claim 5, It is characterized in that The application method comprises mixing the mixed solvent system with the epoxy resin or the epoxy resin composite material and heating them until they are completely degraded.

8. The use according to claim 6, It is characterized in that The mass ratio of the epoxy resin or epoxy resin composite material to the mixed solvent system is 1:6-20.

9. The use according to claim 6, It is characterized in that The heating temperature is 60-120° C., and the heating time is 0.5-13 h.

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