Recycling method for recycling bisphenol A epoxy resin organic components based on acidolysis method

Abstract

The invention provides a recycling method for recycling organic components of bisphenol A epoxy resin based on an acidolysis method, which comprises the following steps: selectively breaking a carbon-nitrogen bond (C-N bond) in a cross-linked network under mild conditions through a four-stage process of pretreatment, acidolysis, extraction and compounding, and treating a DDM cured bisphenol A epoxy resin material by using nitric acid as an acidolysis solution to obtain the organic components of the bisphenol A epoxy resin. And efficient recovery of organic components is realized. The influence rule of the low-temperature acidolysis condition on the resin decomposition rate is determined by optimizing the reaction temperature, the reaction time and the nitric acid concentration through an orthogonal experiment. A resin material is treated by a two-step chemical recovery method, and bisphenol A oligomer in a liquid product is extracted by an organic solvent. 5-15% of recycled organic components are used instead of original resin, the bending modulus of the regenerated composite material is greater than or equal to 2GPa, the bending strength is greater than or equal to 40MPa, the bending modulus is increased by 10-28%, and the bending strength is reduced by 5-27%; the material is suitable for automotive upholstery, electronic packaging materials or building non-bearing structural members.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material recycling, and particularly relates to a recycling method for recovering the organic components of bisphenol A epoxy resin based on acidolysis, realizing the controllable recovery of organic components by directionally breaking carbon-nitrogen bonds, and reusing them in the production of epoxy resin products. Background Art

[0002] Due to its excellent mechanical properties, thermal stability and interfacial adhesion, bisphenol A epoxy resin is widely used in fields such as aerospace, electronic packaging, automotive manufacturing and composite materials. The most widely used type of composite material in the industry is epoxy resin, especially bisphenol A epoxy resin. However, the three-dimensional cross-linked network structure formed after its curing (such as a system with diaminodiphenylmethane (DDM) as the curing agent) has high chemical inertness, resulting in the recycling of waste materials becoming a global challenge. At present, there are certain limitations in the recycling technologies for epoxy resin composites, and it is difficult to achieve the coordinated regeneration and high-value utilization of fibers and organic components.

[0003] The mechanical recycling method processes waste materials into short fibers or powders by means of physical crushing, grinding, etc. This method is simple to operate and has low costs, but the length of the recycled fibers is significantly shortened (usually <1 mm), and cracks or scratches are generated on the surface due to mechanical shearing, resulting in a decrease in tensile strength of more than 30%, making it difficult to meet the reuse requirements of high-performance composite materials. In addition, the resin matrix cannot be effectively separated, resulting in the mixing of organic components and fibers, and it can only be used as a low-value-added filler, with a resource utilization rate of less than 40%. The pyrolysis method cracks the resin in an inert atmosphere at high temperatures (400–600 °C) to generate gas, coke and low-molecular-weight liquid products. This method can achieve the preliminary recycling of fibers, but the energy consumption is extremely high (processing 1 ton of materials requires 2–3 tons of standard coal), and the pyrolysis products have complex compositions (such as containing phenol, dicyclopentadiene derivatives, etc.), and further rectification or catalytic reforming is required to be used as chemical raw materials. In addition, the high-temperature environment causes thermal oxidation or carbonization on the fiber surface, resulting in a strength loss of about 35% for glass fibers and a modulus decrease of 10%–15% for carbon fibers, and the performance of the recycled fibers deteriorates significantly. The sub / supercritical fluid method uses supercritical fluids (such as water, ethanol or acetone) to dissolve the resin matrix under high-temperature and high-pressure conditions (such as supercritical water requires 374 °C and 22.1 MPa). This method can recycle fibers with a clean surface, but the equipment needs to withstand extreme pressures (>30 MPa), the equipment investment and maintenance costs are high, and the solvent recovery rate is low (<75%), restricting industrial applications. For example, the supercritical ethanol method consumes 0.6 tons of solvent for processing each ton of materials, and the economy is poor.

[0004] In recent years, the chemical solvent decomposition method has gradually become a research hotspot. It realizes partial depolymerization of the crosslinked network through the chemical action between the solvent and the resin. However, there are problems such as solvent waste liquid treatment and high solvent recycling costs. Therefore, developing an efficient, low-temperature and highly selective depolymerization technology to achieve controllable fracture of the crosslinked network and efficient recovery of organic components under mild conditions while ensuring the integrity of fiber properties has become the key breakthrough for promoting the green recycling of epoxy-based composites. Summary of the Invention

[0005] In view of the above existing problems and deficiencies, the present invention proposes a recycling method for recovering organic components of amine-cured bisphenol A epoxy resin based on acidolysis. Through a four-stage process of "pretreatment - acidolysis - extraction - compounding", the carbon-nitrogen bond (C-N bond) in the crosslinked network is selectively broken under mild conditions to achieve controllable depolymerization of the resin matrix and efficient recovery and reuse of organic components, forming a closed-loop recycling process that conforms to the concept of circular economy. At the same time, it takes into account environmental protection and industrial feasibility, providing an innovative solution for the high-value regeneration of waste epoxy resin.

[0006] A recycling method for recovering organic components of bisphenol A epoxy resin based on acidolysis includes the following steps:

[0007] (1) Pretreatment: Using acetone as a solvent, the uncured components in the cured resin are removed by Soxhlet extraction. The extraction temperature is 58 - 60 °C, and the extraction time is 1 - 3 hours to obtain purified crosslinked resin.

[0008] (2) Nitric acid acidolysis: Mix the resin obtained in step (1) with glacial acetic acid and react at 80 - 120 °C for 30 - 60 min; then mix the resin with nitric acid solution and carry out directional acidolysis at a temperature of 90 - 100 °C, nitric acid concentration of 7 - 9 mol / L, and reaction time of 60 - 180 min to selectively break the carbon-nitrogen bond (C-N bond) and achieve controllable depolymerization of the resin matrix.

[0009] (3) Extraction and purification: After neutralizing the pH value of the acidolysis solution to neutral, carry out three extractions with ethyl acetate, and obtain the organic phase extract through dehydration filtration and evaporation of the ethyl acetate phase.

[0010] (4) Compounding and regeneration: Replace the original bisphenol A epoxy resin (73 - 79 wt%) with the organic phase extract in a mass ratio of 5 - 15%, and mix it with diaminodiphenylmethane (20 - 25 wt%) and phenol (1 - 2 wt%) by mass ratio. Pre-cure at 70 - 90 °C for 1.5 - 2 hours and secondarily cure at 110 - 150 °C for 1.5 - 2 hours to prepare a regenerated composite material.

[0011] (5) Nitric acid recovery: The NO2 generated by heating the nitric acid solution is collected and introduced into water synchronously with air to regenerate nitric acid, which is reused in the nitric acid acidolysis step of the resin, avoiding environmental pollution.

[0012] In the step (1), the thermal weight loss rate of the resin after Soxhlet extraction is ≤ 3%. The specific operation of Soxhlet extraction includes: crushing the cured resin into particles with a particle size of ≤ 5 mm and loading them into a filter paper sleeve; adding acetone at a liquid-solid ratio of 10:1 - 20:1 (mL / g), refluxing and extracting at 58 - 60 °C for 1.5 - 2 hours; after extraction, the resin is washed with distilled water and vacuum dried, and the residual amount of uncured components is ≤ 3%.

[0013] In the step (2), the reaction conditions of nitric acid acidolysis are optimized and determined through orthogonal experiments. The orthogonal experiment parameters are: the temperature level is 90 - 100 °C, the nitric acid concentration level is 7 - 9 mol / L; the reaction time level is 60 - 180 min; the optimal resin decomposition rate is ≥ 95%.

[0014] In the step (2), for the block resin material, a two-step acidolysis method is adopted: anhydrous acetic acid is used to swell at 80 - 120 °C for 30 - 60 min, accompanied by a condensing reflux device and a mechanical stirring device; a 7 - 9 mol / L nitric acid solution is used to react at 90 - 100 °C for 60 - 180 min, and the reaction vessel is a three-necked flask, accompanied by a condensing reflux device and a mechanical stirring device.

[0015] The specific steps of organic component extraction and purification in the step (3) include:

[0016] (a) Adding saturated sodium bicarbonate solution dropwise to the acidolysis solution to adjust the pH to 6 - 8;

[0017] (b) Adding ethyl acetate, oscillating and mixing, taking the organic phase after standing and separating, and repeating the extraction 3 - 4 times;

[0018] (c) Combining the organic phases, evaporating the ethyl acetate phase, and adding anhydrous sodium sulfate for dehydration for 30 - 60 min.

[0019] The preparation of the regenerated composite material in the step (4) includes:

[0020] (a) Replacing the original resin with the organic extract at a mass ratio of 5 - 15%;

[0021] (b) Mixing bisphenol A epoxy resin, DDM, and phenol to make a resin material. The mold is made of polytetrafluoroethylene material with dimensions of 100 × 10 × 4 mm 3 , and the surface is coated with silicone oil release agent;

[0022] (c) Pre-curing at 70 - 90 °C for 1.5 - 2 hours, secondary curing at 110 - 150 °C for 1.5 - 2 hours, and the heating rate is ≤ 5 °C / min.

[0023] The organic phase extract is a bisphenol A oligomer with a molecular weight of 500 - 1500 Da and nitroaniline compounds, which is verified by liquid chromatography - mass spectrometry; in the nitric acid acidolysis reaction, the carbon - nitrogen bond (C - N bond) is selectively broken, which is verified by infrared spectroscopy; the compound viscosity of the recovered organic components ≤ 500 mPa·s (measured at 25 °C), and the curing time ≤ 4 hours.

[0024] Using 5 - 15% of the recovered organic components to replace the original resin, the flexural modulus of the recycled composite material ≥ 2 GPa, and the flexural strength ≥ 40 MPa. The increase in flexural modulus is 10 - 28%, and the decrease in flexural strength is 5 - 27%; the flexural property test is based on GB / T9341 - 2008, with a span of 20 mm and a loading rate of 2 mm / min; the recycled composite material is applied to automotive interior parts, electronic packaging materials or building non - load - bearing structural parts.

[0025] The present invention discloses a recycling method for recovering organic components of bisphenol A epoxy resin based on acidolysis, belonging to the technical field of composite material recycling. This process adopts a four - stage process of "pretreatment - acidolysis - extraction - compounding", using nitric acid as the acidolysis solution to treat DDM - cured bisphenol A epoxy resin materials to achieve efficient recovery of organic components. Through orthogonal experiments, the reaction temperature, time and nitric acid concentration are optimized to determine the influence law of low - temperature acidolysis conditions on the resin decomposition rate. The resin material is treated by a two - step chemical recovery method, and the bisphenol A oligomer in the liquid product is extracted by an organic solvent. The recovered organic components are compounded and used to replace the original resin at a ratio of 5 - 15% to prepare a new composite material. This process has the characteristics of low temperature, high efficiency, low cost and environmental friendliness, providing a green solution for the recycling and remanufacturing of epoxy - based composite materials, and is suitable for the resource treatment of waste GFRP in fields such as automobiles and electronics. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings in the prior art description.

[0027] Figure 1 It is the technical roadmap provided by the present invention;

[0028] Figure 2 It is the schematic diagram of the Soxhlet extraction device provided by the present invention;

[0029] Figure 3 It is the swelling and decomposition reaction device diagram provided by the present invention;

[0030] Figure 4 It is the organic phase extraction technical roadmap provided by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the present invention.

[0032] S1. Pretreatment stage of Soxhlet extraction and swelling treatment: Acetone is used as the extraction solvent, and the cured resin is Soxhlet extracted at 58 - 60 °C to remove uncured components (mass loss rate 5 - 10%) to ensure that the subsequent acidolysis reaction targets the crosslinked network; the thermal stability of the resin after extraction is verified by thermogravimetric analysis (TGA), and it is confirmed that the residual amount of uncured components ≤ 3%; swelling reaction is carried out in glacial acetic acid (liquid-solid ratio 10:1 - 20:1) at 80 - 120 °C for 30 - 60 min, equipped with a condensing reflux device and a mechanical stirring device, and the stirring rate is 200 - 400 rpm.

[0033] The Soxhlet extraction equipment for the above method includes:

[0034] (a) A three-necked flask (250 mL), equipped with a condensing reflux device;

[0035] (b) A Soxhlet extraction container;

[0036] (c) A temperature controller, with an accuracy of ±1 °C;

[0037] (d) A heating device, connected to the temperature controller.

[0038] S2. Nitric acid acidolysis stage: Single-factor optimization is carried out by adjusting the reaction temperature, nitric acid concentration and time to determine the key influence law of the resin decomposition rate; Orthogonal experimental design: Based on a three-factor three-level orthogonal experiment (temperature 90 - 100 °C; concentration 7 - 9 mol / L; time 60 - 180 min), the acidolysis conditions are optimized to obtain a maximum decomposition rate ≥ 95%; for bulk materials, swelling pretreatment is first carried out (glacial acetic acid, swelling treatment at 80 - 120 °C for 30 min), and then acidolysis is carried out with 7 - 9 mol / L nitric acid at 90 - 100 °C for ≥ 180 min to achieve complete decomposition of the block.

[0039] The acidolysis equipment for the S2 nitric acid acidolysis stage includes:

[0040] (a) A three-necked flask (250 mL), equipped with a condensing reflux device and a mechanical stirring device;

[0041] (b) A mechanical stirrer, with a rotation speed range of 300 rpm;

[0042] (c) A temperature controller, with an accuracy of ±1 °C;

[0043] (d) A heating device, connected to the temperature controller;

[0044] (e) An exhaust gas absorption device, with an internal aeration device to provide air.

[0045] S3. Extraction and purification stage: Adjust the pH of the acidolysis solution to 6 - 8, extract three times with ethyl acetate, and combine with drying using anhydrous sodium sulfate to obtain a high-purity organic component (LC-MS detection and FTIR detection show that it is mainly bisphenol A oligomers and derivatives).

[0046] S4. Blending and recycling application: Replace the original resin with the recycled organic component at a ratio of 5 - 15%, mix epoxy resin (73 - 79 wt%), amine curing agent (20 - 25 wt%), and phenol (1 - 2 wt%), and pre-cure at 70 - 90 °C for 1.5 - 2 hours and secondarily cure at 110 - 150 °C for 1.5 - 2 hours to prepare a recycled composite material;

[0047] Performance characterization: For the recycled material, the flexural modulus improvement range is 1.9 - 2.1 GPa, with an increase of 10 - 28%, and the flexural strength range is 43 - 50 MPa, with a decrease of 5 - 27%. When the addition ratio is not higher than 10%, it can meet the general structural requirements, and when the addition ratio is 10 - 15%, it is applicable to non-load-bearing components with higher stiffness requirements. NO₂ generated by the decomposition of nitric acid during the reaction is collected and then introduced into water. There is an aeration device in the water, and NO₂ reacts with oxygen in the water to form nitric acid. After accumulating to a concentration of 7 - 9 mol / L, it is reused for the resin recovery step.

[0048] Figure 1 Among them, the method for recycling bisphenol A epoxy resin cured with DDM by nitric acid acidolysis is achieved in four steps, including:

[0049] S1. Pretreatment stage, including Soxhlet extraction treatment, effect verification, and swelling treatment;

[0050] S2. Nitric acid acidolysis stage, including acidolysis condition optimization, orthogonal experiment, product separation, and component analysis;

[0051] S3. Extraction and purification stage, including neutralization treatment and organic phase extraction;

[0052] S4. Blending and recycling application, including formulation design, curing process, performance testing, and recovery of the escaped gas.

[0053] Figure 2 is a schematic diagram of a Soxhlet extraction device. Explain the instruments in Figure 2 : 1 is an iron stand, 2 is an electric heating mantle, 3 is a round-bottom flask, 4 is a Soxhlet extractor, and 5 is a spherical condenser (connected to a hose leading to the absorbent solution). Load the resin particles into the filter paper sleeve (pore size 25 μm) of the Soxhlet extractor, and install the condensation device; add acetone to the flask (liquid-solid ratio 20:1); heat and reflux for extraction for 2 hours; wash the resin particles with ethanol 3 times and vacuum dry at 70 °C for 24 hours.

[0054] Figure 3 It is a diagram of the swelling and decomposition reaction device. The instruments of Figure 3 will be explained as follows: 1 is an iron stand, 2 is a mechanical stirrer, 3 is a spherical condenser, 4 is a three-necked flask, 5 is an electric heating mantle, and 6 is a temperature sensor. The swelling steps are as follows: Weigh the resin material and place it in the three-necked flask, and install the condensation device and the mechanical stirring device; Add glacial acetic acid to the flask, and the electric heating mantle heats the solution for the swelling reaction, and use the temperature sensor for temperature monitoring and control; After the swelling is completed, wash the resin material with distilled water and dry it. Weigh the resin material and place it in the three-necked flask, and install the condensation device and the mechanical stirring device; Add nitric acid solution to the flask, and the electric heating mantle heats the solution for the decomposition reaction, and use the temperature sensor for temperature monitoring and control.

[0055] Figure 4 It is the technical route diagram of the organic phase extraction provided by the present invention. The specific extraction steps are as follows: Prepare a saturated NaHCO3 solution, slowly drip the solution into the filtrate to neutralize the pH value; Add ethyl acetate solution, shake and mix, and then let it stand for layering, and take the upper ethyl acetate phase; Extract the filtrate three times repeatedly and combine the extracts; Add anhydrous sodium sulfate to the ethyl acetate phase to remove residual moisture; Evaporate the ethyl acetate to obtain the organic phase extract, and recycle the ethyl acetate for extraction; Repeat steps 2-4 once to obtain the final organic phase extract.

[0056] Example 1:

[0057] Before the treatment of the cured resin material, the content of bisphenol A epoxy resin is 73%, the content of amine curing agent is 25%, and the content of accelerator phenol is 2%.

[0058] In step 1, weigh 14.6 g of bisphenol A epoxy resin, 5 g of DDM and 0.4 g of phenol to make a fiberglass composite material. Place the curing agent in a round-bottomed flask and heat it to melt at a temperature of 80 °C with an electric heating mantle, then quickly stir and mix it with the epoxy resin and pour it into a mold. Place the mold in an oven and heat it for curing at a temperature of 70 °C for 2 hours, and then heat it for secondary curing at a temperature of 110 °C for 2 hours, with a heating rate of 5 °C / min. Take it out of the mold, cool it to room temperature, and break it into pieces with a size of 10 mm. The Soxhlet extraction device is as Figure 2As shown, 5 g of resin material was added to acetone at a liquid-solid ratio of 20:1 (mL / g), and reflux extraction was carried out at 58 °C for 2 hours; after extraction, the resin was washed with distilled water and dried in vacuo, and the mass loss was 5%. Thermogravimetric analysis (heating rate 10 °C / min, nitrogen atmosphere) results of the epoxy resin before and after extraction with acetone showed that there were very few unreacted bisphenol A epoxy resin monomers or low-molecular substances with low curing crosslinking degree in the material after acetone extraction. 2 g of the resin after acetone extraction was swollen and reacted in glacial acetic acid (liquid-solid ratio 10:1) at 80 °C for 30 min, equipped with a condensing reflux device and a mechanical stirring device, and the stirring rate was 200 rpm.

[0059] In step S2, through acidolysis condition optimization and orthogonal experiments, the reaction time was determined to be 180 min, the solution concentration was 8 mol / L, the reaction temperature was 95 °C, and the resin decomposition rate was 96%. 2 g of the swollen GFRP material was taken, and the solution volume was 75 mL. Figure 3 It is a diagram of the decomposition reaction device. LC-MS analysis combined with FTIR characterization analysis showed that most of the organic components were bisphenol A epoxy resin monomers and dimers.

[0060] In step S3, Figure 4 It is a technical route diagram for the extraction of organic components. The specific extraction steps are as follows: Prepare a saturated NaHCO3 solution, slowly drop the solution into the filtrate until the pH range is 7; add ethyl acetate solution (volume ratio 1:1), oscillate and mix (100 times / min), and then let it stand for stratification, and take the upper ethyl acetate phase. The filtrate was extracted repeatedly 3 times, and the extraction liquids were combined; anhydrous sodium sulfate was added to the ethyl acetate phase, and it was left standing for 30 min to remove residual moisture; the ethyl acetate was evaporated to obtain an organic phase extract, and the ethyl acetate was recovered and reused for extraction; the above steps were repeated once to obtain the final organic phase extract.

[0061] In step S4, the organic extract was used to replace the original resin at a mass ratio of 5%, and the cured resin material was prepared with the original material ratio and process conditions in step S1. Demoulding was carried out and cooled to room temperature. According to the determination of plastic flexural properties in GB / T 9341-2008, the three-point flexural strength of the prepared material was measured, the test span was 20 mm, and the loading rate was 2 mm / min. The flexural modulus of the material was 1.9 GPa, an increase of 10%, and the strength was 50 MPa, a decrease of 5%, meeting the requirements of the automotive lightweighting field. The NO2 gas collected through a hose in the decomposition device was introduced into the water absorption solution, with an aeration device inside, and reacted again to generate a nitric acid solution, which was then used for the resin decomposition step when the concentration reached 7 mol / L. The entire process not only recovered the glass fiber and organic resin components, but also recycled the ethyl acetate extractant. In addition, the NO2 decomposed from the nitric acid was converted into an internal circulation solvent for the acidolysis step, while preventing gas pollution to the environment.

[0062] Example 2:

[0063] Before the treatment of the cured resin material, the content of bisphenol A epoxy resin is 79%, the content of amine curing agent is 20%, and the content of accelerator phenol is 1%.

[0064] In Step 1, 15.8 g of bisphenol A epoxy resin, 4 g of DDM and 0.2 g of phenol were weighed to prepare a fiberglass composite material. The curing agent was placed in a round-bottom flask and melted by heating with an electric heating mantle at a temperature of 80 °C, and then quickly stirred and mixed with the epoxy resin and poured into a mold. The mold was placed in an oven and cured at a temperature of 80 °C for 2 hours, and then secondarily cured at a temperature of 130 °C for 2 hours with a heating rate of 4 °C / min. It was taken out of the mold, cooled to room temperature, and broken into pieces with a size of 8 mm. The Soxhlet extraction device is as Figure 2 shown. 5 g of resin material was added with acetone at a liquid-solid ratio of 15:1 (mL / g), and refluxed and extracted at 59 °C for 2 hours; after extraction, the resin was washed with distilled water and vacuum dried, and the mass loss was 8%. The thermogravimetric analysis (heating rate 10 °C / min, nitrogen atmosphere) results of the epoxy resin before and after the extraction treatment with acetone show that there are very few uncured bisphenol A epoxy resin monomers or low-molecular substances with low curing crosslinking degree in the material after acetone extraction. 2 g of the resin after acetone extraction was swollen in glacial acetic acid (liquid-solid ratio 15:1) at 100 °C for 50 min, equipped with a condenser reflux device and a mechanical stirring device, and the stirring rate was 300 rpm.

[0065] In Step S2, through the optimization of acidolysis conditions and orthogonal experiments, the reaction time was determined to be 240 min, the solution concentration was 7 mol / L, the reaction temperature was 90 °C, and the resin decomposition rate was 95%. 2 g of the swollen GFRP material was taken, and the solution volume was 75 mL. Figure 3 It is a diagram of the decomposition reaction device. LC-MS analysis combined with FTIR characterization analysis shows that most of the organic components are bisphenol A epoxy resin monomers and dimers.

[0066] In Step S3, Figure 4 It is a technical route diagram for the extraction of organic components. The specific extraction steps are as follows: Prepare a saturated NaHCO3 solution, slowly drip the solution into the filtrate until the pH range is 7; add an ethyl acetate solution (volume ratio 1:1.2), shake and mix (120 times / min) and then let it stand for stratification, and take the upper ethyl acetate phase. The filtrate was extracted repeatedly 4 times, and the extraction liquids were combined; anhydrous sodium sulfate was added to the ethyl acetate phase, and it was allowed to stand for 40 min to remove residual moisture; the ethyl acetate was evaporated to obtain an organic phase extract, and the ethyl acetate was recovered and reused for extraction; the above steps were repeated once to obtain the final organic phase extract.

[0067] In step S4, the organic extract is substituted for the original resin at a mass ratio of 10%, and the cured resin material is made with the original material ratio and process conditions in step S1. Demould and cool to room temperature. According to the determination of plastic flexural properties in GB / T 9341-2008, the three-point flexural strength of the made material is measured. The test span is 20 mm and the loading rate is 2 mm / min. The flexural modulus of the material is 2.0 GPa, an increase of 19.8%, and the strength is 45 MPa, a decrease of 14.8%, meeting the requirements of the automotive lightweighting field. The NO2 gas collected through the hose in the decomposition device is introduced into the water absorption solution, with an internal aeration device, and reacts again to generate nitric acid solution, which is reused in the resin decomposition step when the concentration reaches 7 mol / L. The entire process not only recovers the glass fiber and organic resin components, but also recycles the ethyl acetate extractant. In addition, the NO2 decomposed by heating nitric acid is converted into an internal circulation solvent for the acidolysis link, while preventing gas from polluting the environment.

[0068] Example 3:

[0069] Before the treatment of the cured resin material, the content of bisphenol A epoxy resin is 76%, the content of amine curing agent is 22.5%, and the content of promoter phenol is 1.5%.

[0070] In step 1, 15.2 g of bisphenol A epoxy resin, 4.5 g of DDM and 0.3 g of phenol are weighed to make a glass fiber reinforced plastic composite material. The curing agent is placed in a round bottom flask and heated and melted at a temperature of 80 °C with an electric heating mantle, and then quickly stirred and mixed with the epoxy resin and poured into a mold. The mold is placed in an oven and cured at a temperature of 90 °C for 1.5 hours, and then secondary heated and cured at a temperature of 150 °C for 1.5 hours, with a heating rate of 3 °C / min. Demould and cool to room temperature, and crush to a size of 5 mm. As shown in the Soxhlet extraction device Figure 2 shown, 5 g of resin material is added with acetone at a liquid-solid ratio of 10:1 (mL / g), and reflux extracted at 60 °C for 1.5 hours; after extraction, the resin is washed with distilled water and vacuum dried, with a mass loss of 10%. The thermogravimetric analysis (heating rate 10 °C / min, nitrogen atmosphere) results of the epoxy resin before and after acetone extraction treatment show that there are very few uncured bisphenol A epoxy resin monomers or low-molecular substances with low curing crosslinking degree in the material after acetone extraction. Take 2 g of the resin after acetone extraction and carry out a swelling reaction in glacial acetic acid (liquid-solid ratio 20:1) at 120 °C for 60 min, equipped with a condensing reflux device and a mechanical stirring device, and the stirring rate is 400 rpm.

[0071] In step S2, through acidolysis condition optimization and orthogonal experiments, the reaction time is determined to be 240 min, the solution concentration is 9 mol / L, the reaction temperature is 100 °C, and the resin decomposition rate is 99.8%. Take 2 g of the swollen GFRP material, and the solution volume is 75 mL.Figure 3 It is a diagram of the decomposition reaction device. Through LC-MS analysis combined with FTIR characterization analysis, it is known that most of the organic components are bisphenol A epoxy resin monomers and dimers.

[0072] In step S3, Figure 4 It is a technical route diagram for the extraction of organic components. The specific extraction steps are as follows: Prepare a saturated NaHCO3 solution, slowly drip the solution into the filtrate until the pH ranges from 7; add ethyl acetate solution (volume ratio 1:0.8), shake and mix (80 times / min), then let it stand for stratification, and take the upper ethyl acetate phase. Extract the filtrate three times repeatedly and combine the extracts; add anhydrous sodium sulfate to the ethyl acetate phase and let it stand for 60 min to remove residual moisture; evaporate the ethyl acetate to obtain the organic phase extract, and recycle the ethyl acetate for reuse in extraction; repeat the above steps once to obtain the final organic phase extract.

[0073] In step S4, replace the original resin with the organic extract at a mass ratio of 15%, and make the cured resin material with the original material ratio and process conditions in step S1. Take out the mold and cool it to room temperature. According to the determination of the flexural properties of plastics in GB / T 9341-2008, the three-point flexural strength of the made material is measured. The test span is 20 mm and the loading rate is 2 mm / min. The flexural modulus of the material is 2.1 GPa, an increase of 28%, and the strength is 43 MPa, a decrease of 27%, meeting the requirements of the automotive lightweighting field. Pass the NO2 gas collected through the hose in the decomposition device into the water absorption solution, with an internal aeration device, and react again to generate nitric acid solution, which is then used in the resin decomposition step when the concentration reaches 7 mol / L. The entire process not only recovers the glass fiber and organic resin components, but also recycles the ethyl acetate extractant. In addition, the NO2 decomposed from the heated nitric acid is converted into an internal circulation solvent for the acidolysis link, while preventing gas from polluting the environment.

Claims

1. A recycling method for recovering organic components of bisphenol A epoxy resin based on acidolysis method, characterized in that, It includes the following steps: (1) Pretreatment: Using acetone as a solvent, the uncured components in the cured resin are removed by Soxhlet extraction. The extraction temperature is 58 - 60 °C, and the extraction time is 1 - 3 hours to obtain purified crosslinked resin. (2) Nitric acid acidolysis: Mix the resin obtained in step (1) with glacial acetic acid and react at 80 - 120 °C for 30 - 60 min. Then mix the resin with nitric acid solution and carry out directional acidolysis at a temperature of 90 - 100 °C, nitric acid concentration of 7 - 9 mol / L, and reaction time of 60 - 180 min to selectively break the carbon-nitrogen bond (C-N bond) and achieve controllable depolymerization of the resin matrix. (3) Extraction and purification: After neutralizing the pH value of the acidolysis solution to neutral, perform three extractions with ethyl acetate, and obtain the organic phase extract through dehydration filtration and evaporation of the ethyl acetate phase. (4) Compound regeneration: Replace the original bisphenol A epoxy resin (73 - 79 wt%) with the organic phase extract at a mass ratio of 5 - 15%, and mix it with diaminodiphenylmethane (20 - 25 wt%) and phenol (1 - 2 wt%) by mass ratio. Pre-cure at 70 - 90 °C for 1.5 - 2 hours and secondarily cure at 110 - 150 °C for 1.5 - 2 hours to prepare the regenerated composite material. (5) Nitric acid recovery: Collect the NO₂ generated by heating the nitric acid solution, simultaneously introduce it into water with air, regenerate nitric acid, and reuse it for the nitric acid acidolysis step of the resin to avoid environmental pollution.

2. The method according to claim 1, characterized in that In step (1), the resin after Soxhlet extraction has a thermal weight loss rate ≤ 3%. The specific operation of Soxhlet extraction includes: crushing the cured resin into particles with a particle size ≤ 5 mm, loading them into a filter paper sleeve; adding acetone at a liquid-solid ratio of 10:1 - 20:1 (mL / g), and refluxing and extracting at 58 - 60 °C for 1.5 - 2 hours; after extraction, the resin is washed with distilled water and vacuum dried, and the residual amount of uncured components ≤ 3%.

3. The method according to claim 1, characterized in that, In step (2), the reaction conditions of nitric acid acidolysis are determined by optimizing through orthogonal experiments. The orthogonal experiment parameters are: the temperature level is 90 - 100 °C, the nitric acid concentration level is 7 - 9 mol / L; the reaction time level is 60 - 180 min; the optimal resin decomposition rate ≥ 95%.

4. The method according to claim 1, wherein In step (2), for the block resin material, a two-step acidolysis method is adopted: anhydrous acetic acid swells at 80 - 120 °C for 30 - 60 min, accompanied by a condensing reflux device and a mechanical stirring device; 7 - 9 mol / L nitric acid solution, reacts at 90 - 100 °C for 60 - 180 min, and the reaction vessel is a three-neck flask, accompanied by a condensing reflux device and a mechanical stirring device.

5. The method according to claim 1, characterized in that In step (3), the specific steps of extracting and purifying the organic components include: (a) Dropwise add saturated sodium bicarbonate solution to the acidolysis solution to adjust the pH to 6 - 8. (b) Add ethyl acetate, oscillate and mix, take the organic phase after standing and separating, and repeat the extraction 3 - 4 times. (c) Combine the organic phases, evaporate the ethyl acetate phase, and add anhydrous sodium sulfate for dehydration for 30 - 60 min.

6. The method according to claim 1, characterized in that, In step (4), the preparation of the regenerated composite material includes: (a) Replace the original resin with the organic extract at a mass ratio of 5 - 15%. (b) Mix bisphenol A epoxy resin, DDM, and phenol to produce a resin material. The mold is made of polytetrafluoroethylene material with dimensions of 100×10×4 mm 3 , and the surface is coated with silicone oil release agent; (c) Pre-cure at 70 - 90 °C for 1.5 - 2 hours, secondary cure at 110 - 150 °C for 1.5 - 2 hours, with a heating rate ≤ 5 °C / min.

7. The method according to claim 1, characterized in that The organic phase extract is a bisphenol A oligomer with a molecular weight of 500 - 1500 Da and nitroaniline compounds, verified by liquid chromatography - mass spectrometry; in the nitric acid hydrolysis reaction, the carbon - nitrogen bond (C - N bond) is selectively broken, verified by infrared spectroscopy; the compound viscosity of the recovered organic components ≤ 500 mPa·s (measured at 25 °C), and the curing time ≤ 4 hours.

8. The method according to claim 1, characterized in that Using 5 - 15% of the recovered organic components to replace the original resin, the flexural modulus of the recycled composite material ≥ 2 GPa, the flexural strength ≥ 40 MPa, the increase in flexural modulus is 10 - 28%, and the decrease in flexural strength is 5 - 27%; the flexural property test is based on GB / T9341 - 2008, span 20 mm, loading rate 2 mm / min; the recycled composite material is applied to automotive interior parts, electronic packaging materials or building non - load - bearing structural components.

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