Nitric acid acidolysis recovery method and regeneration application of glass fiber reinforced epoxy resin composite material

Abstract

The invention relates to a nitric acid acidolysis recovery method and regeneration application of a glass fiber reinforced epoxy resin composite material. The GFRP material is cut and crushed; glacial acetic acid is adopted as a swelling solvent; mixing the pretreated resin with a nitric acid solution for directional acidolysis, and separating out glass fibers; adjusting the pH value of the acidolysis solution to 6-8, performing extraction for three times by using ethyl acetate, dehydrating, filtering and evaporating an ethyl acetate phase to obtain an organic phase extract; the preparation method comprises the following steps: preparing a glass fiber reinforced plastic material from bisphenol A epoxy resin, diaminodiphenylmethane, phenol and glass fibers in a mold, pre-curing at 70-90 DEG C for 1.5-2 hours, and secondarily curing at 110-150 DEG C for 1.5-2 hours to prepare a regenerated glass fiber reinforced plastic composite material; when the regenerated epoxy resin composite material is applied to a bending performance test, according to GB / T 9341-2008, the span is 20 mm, the loading rate is 2 mm / min, the bending modulus is larger than or equal to 9 GPa, and the bending strength is larger than or equal to 80 MPa.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycling of polymer materials, and particularly relates to a method for depolymerizing glass fiber-reinforced amine-cured bisphenol A epoxy resin-based materials by using the strong oxidizing property of nitric acid. Particularly, it relates to a nitric acid acidolysis recovery method and a recycling application of glass fiber-reinforced epoxy resin composites. Background Art

[0002] Glass fiber-reinforced polymer (GFRP) composites are organic-inorganic composites with a fiber-reinforced polymer matrix, having advantages such as strong tensile and bending resistance, light weight, corrosion resistance, easy processing, and low thermal expansion. Specific application fields include fiberglass pipes, storage tanks and pressure vessels, fiberglass products for construction, various yachts and lifeboats, automotive molded parts, train car body covers, fiberglass fishplates for tracks, and wind turbine blades. Common polymer matrices include epoxy resins, vinyl esters, thermosetting polyesters, and phenolic resins, etc., among which fiberglass with a thermosetting polymer as the matrix accounts for more than 60%. The resin matrix material with the largest usage amount in fiberglass is epoxy resin, especially bisphenol A epoxy resin. However, there is a highly cross-linked structure between covalent molecules in the thermosetting matrix of glass fiber-reinforced epoxy resin, making such composites non-remeltable and non-re-moldable, and difficult to re-mold and depolymerize into the original monomers, with relatively high recycling difficulty. Currently, there are certain limitations in the recycling technologies for glass fiber-reinforced epoxy resin composites, and it is difficult to achieve the coordinated recycling and high-value utilization of fibers and organic components.

[0003] GFRP waste includes waste materials that have reached the end - of - life period, as well as the cured and uncured parts during production and processing. These materials are usually disposed of in landfills or incinerated when they reach the end of their service life in order to generate energy from combustion. The ultimate disposal method is landfilling. This traditional method does not recycle the materials for new industrial products according to the concept of circular economy. Currently, landfill and open - air burning in China account for more than 90% of the total. The recycling of fiber - reinforced materials mainly uses physical pulverization method, followed by simple cement incineration method and blast furnace iron - making reduction method. The mechanical recycling method is simple to operate and has low cost, but the length of the recycled fibers is significantly shortened (usually <1mm), and cracks or scratches are generated on the surface due to mechanical shearing, resulting in a significant decrease in mechanical strength and 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 filler with low added value, and the resource utilization rate is less than 40%. The pyrolysis method can achieve the preliminary recycling of fibers, but it has extremely high energy consumption, and the pyrolysis products have complex components (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, and the strength of glass fibers is lost by about 35%, and the performance of recycled fibers deteriorates significantly. The sub / supercritical fluid method can recycle fibers with a clean surface, but the equipment needs to withstand extreme pressures (>30MPa), the equipment investment and maintenance costs are high, and the solvent recovery rate is low (<75%), which limits its industrial application.

[0004] The recycling and reasonable disposal of FRP waste have become an urgent problem in China's current FRP industry, and it has great and far - reaching significance for the survival and development of the FRP industry. In recent years, the chemical solvent decomposition method has gradually become a research hotspot. It realizes the partial depolymerization of the cross - linked network through the chemical action between the solvent and the resin, but there are problems such as solvent waste liquid treatment and high solvent recycling cost. Therefore, developing a highly efficient, low - temperature and highly selective depolymerization technology for glass - fiber - reinforced DDM - cured bisphenol A epoxy resin materials to achieve the controllable fracture of the cross - linked network and the efficient recovery of organic components under mild conditions, while ensuring the integrity of fiber properties, and recycling the fibers and resin matrix for composite material production. Summary of the Invention

[0005] In view of the existing problems and deficiencies above, the present invention proposes a recycling method for glass - fiber - reinforced amine - cured bisphenol A epoxy resin composites based on acidolysis. Through a four - stage process of "pretreatment - acidolysis - extraction - compounding", the carbon - nitrogen bonds (C - N bonds) in the cross - linked network are selectively broken under mild conditions to achieve the depolymerization of the resin matrix and the efficient recovery and reuse of components, forming a closed - loop recycling process that conforms to the concept of circular economy, while taking into account environmental protection and industrial feasibility solutions.

[0006] The technical solution of the present invention is as follows:

[0007] A method for nitric acid acidolysis recovery of glass fiber reinforced epoxy resin composite material, comprising the following steps:

[0008] (1) Pretreatment: Cut and crush the GFRP material to a size less than 10 mm; Use glacial acetic acid as the swelling solvent, the swelling temperature is 80 - 120 °C, the swelling time is 30 - 60 min, and the GFRP swelling rate is 30 - 50%;

[0009] (2) Nitric acid acidolysis: Mix the pretreated resin with nitric acid solution, and carry out directional acidolysis at a temperature of 90 - 100 °C, a nitric acid concentration of 7 - 9 mol / L, and a reaction time of 60 - 180 min to separate the glass fiber;

[0010] (3) Extraction and purification: After adjusting the pH of the acidolysis solution to 6 - 8, carry out three extractions with ethyl acetate, and obtain the organic phase extract through dehydration filtration and evaporation of the ethyl acetate phase;

[0011] (4) Compound regeneration: Prepare a fiberglass material with bisphenol A epoxy resin, diaminodiphenylmethane (20 - 30 wt%) and phenol (1 - 2 wt%) and glass fiber (20 - 40 wt%) in a mold, and carry out pre-curing at 70 - 90 °C for 1.5 - 2 hours and secondary curing at 110 - 150 °C for 1.5 - 2 hours to prepare a regenerated fiberglass composite material;

[0012] (5) Nitric acid recovery: Collect NO2 generated during the heating of the nitric acid solution, introduce it into water with continuous aeration, regenerate nitric acid, and repeat it for the nitric acid acidolysis step of the resin to avoid environmental pollution.

[0013] The specific operation of the swelling operation in the step (1) includes:

[0014] (a) Add glacial acetic acid to a three-necked flask, heat it with an electric heating mantle at a temperature of 80 - 120 °C, equipped with a condensing reflux device and a mechanical stirring device;

[0015] (b) The liquid-solid ratio is 10 - 20 (mL / g), and carry out condensation reflux reaction swelling at 80 - 120 °C for 30 - 60 min;

[0016] (c) After swelling, the GFRP is washed with distilled water and vacuum dried, and the swelling degree is 30 - 50%.

[0017] The reaction conditions of the nitric acid acidolysis in the step (2) are determined by orthogonal experiment optimization. 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%.

[0018] In step (2), a two-step acid hydrolysis method is adopted for GFRP materials:

[0019] (a) Swelling pretreatment: Anhydrous acetic acid, swelling at 80 - 120 °C for 30 - 60 min, with a condensing reflux device and a mechanical stirring device;

[0020] (b) Acid hydrolysis reaction: 7 - 9 mol / L nitric acid solution, reacting at 90 - 100 °C for 60 - 180 min, the reaction vessel is a three-necked flask, the mechanical stirring rate is 200 - 400 rpm, with a condensing reflux device and a mechanical stirring device.

[0021] In step (3), the specific steps for organic component extraction include:

[0022] (a) Add saturated sodium bicarbonate solution dropwise to the acid hydrolysis solution to adjust the pH to 6 - 8;

[0023] (b) Add ethyl acetate and shake well, take the organic phase after standing and separating, repeat the extraction 3 - 4 times;

[0024] (c) Combine the organic phases, evaporate the ethyl acetate phase, and add anhydrous sodium sulfate for dehydration for 30 - 60 min.

[0025] In step (4), the preparation of the regenerated GFRP composite material includes:

[0026] (a) Replace the original resin with the organic extract at a mass ratio of 5 - 15%;

[0027] (b) Prepare a fiberglass reinforced plastic material with bisphenol A epoxy resin, amine curing agent and phenol and glass fiber, 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;

[0028] (c) The material is pre-cured at 70 - 90 °C for 1.5 - 2 hours, and then secondarily cured at 110 - 150 °C for 1.5 - 2 hours, with a heating rate ≤ 5 °C / min.

[0029] The components of the organic phase extract are bisphenol A oligomers with a molecular weight of 500 - 1500 Da and nitroaniline compounds, verified by liquid chromatography - mass spectrometry; the compound viscosity of the recovered organic components ≤ 500 mPa·s, and the curing time ≤ 4 hours; in the nitric acid acid hydrolysis reaction, the carbon-nitrogen bond is selectively broken, verified by infrared spectroscopy.

[0030] The minimum flexural strength of the regenerated composite material ≥ 85%, the tensile strength of the recovered fiber retains 90 - 93%, and the tensile modulus increases by 10 - 20%.

[0031] The nitric acid acidolysis recovery method of the glass fiber reinforced epoxy resin composite material of the present invention recovers glass fibers for use in the field of short fibers; the recovered resin is used for automotive interior parts, electronic packaging materials, or building non-load-bearing structural members.

[0032] For the application of the recycled epoxy resin composite material of the present invention, 5-15% of the recovered organic components are used instead of the original resin. The flexural property test is carried out according to GB / T 9341-2008, with a span of 20 mm and a loading rate of 2 mm / min. The flexural modulus is ≥9 GPa and the flexural strength is ≥80 MPa.

[0033] The nitric acid acidolysis recovery method of the glass fiber reinforced epoxy resin composite material of the present invention recovers glass fibers for use in the field of short fibers; the recovered resin is used for automotive interior parts, electronic packaging materials, or building non-load-bearing structural members.

[0034] The present invention discloses a nitric acid acidolysis recovery method and recycled application of a glass fiber reinforced epoxy resin composite material. A glass fiber reinforced plastic material is prepared from bisphenol A epoxy resin, an amine curing agent, phenol and glass fibers. After being pulverized, it is subjected to two-step acidolysis with a nitric acid solution. The reaction conditions are optimized through orthogonal experiments to obtain the best decomposition process. By extracting the epoxy resin oligomer in the liquid product with ethyl acetate, it is found that the recovered fibers have a clean surface and the mechanical property retention rate reaches 95%, which is suitable for short fiber products; the organic phase can meet the general structural requirements after being purified and compounded with a new resin in a proportion of 5-15%. The research reveals the mechanism by which nitric acid dissociates the composite material by destroying the resin crosslinking network. This method realizes the efficient recovery and resource utilization of fibers and resins, and provides a feasible solution for the green cycle of thermosetting composite materials. Description of the Drawings

[0035] Figure 1 is the technical roadmap provided by the present invention;

[0036] Figure 2 is the swelling and decomposition reaction device diagram provided by the present invention;

[0037] Figure 3 is the organic phase extraction step diagram provided by the present invention. Detailed Embodiments

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention.

[0039] S1. Use glacial acetic acid as the swelling solvent (liquid-solid ratio 10-20), and carry out swelling treatment on the GFRP material at 80-120 °C. After the composite material swells, the chemical solution can better penetrate into the laminated material, and the swelling rate of GFRP is 30-50%.

[0040] S2, GFRP decomposition process:

[0041] (1) By adjusting the reaction temperature, nitric acid concentration, and time, determine the key influencing laws of the resin decomposition rate of GFRP materials.

[0042] (2) Based on the three-factor three-level orthogonal experiment, optimize the acidolysis conditions to obtain a decomposition rate ≥ 95%.

[0043] (3) The pre-swollen GFRP material reacts with a 7 - 9 mol / L nitric acid solution at 90 - 100 °C for 60 - 180 min, achieving complete decomposition of the block, complete separation of the fiber and the resin, and obtaining an acidolysis solution and glass fiber.

[0044] S3. After neutralizing the pH value of the reaction solution to 6 - 8 using saturated sodium bicarbonate solution, extract it three times with ethyl acetate solvent, and combine with anhydrous sodium sulfate drying to obtain high-purity organic components (liquid chromatography - mass spectrometry detection and FTIR detection show that they are mainly bisphenol A oligomers and derivatives. The tensile strength of the recycled fiber decreases by 7 - 10%, and the tensile modulus increases by 10 - 20%.

[0045] S4. Recycling and application

[0046] (1) Component substitution: Prepare fiberglass materials with bisphenol A epoxy resin, amine curing agent (20 - 30 wt%), and phenol (1 - 2 wt%) and glass fiber (20 - 40 wt%). The GFRP material is pre-cured at 70 - 90 °C for 1.5 - 2 hours, and then secondarily cured at 110 - 150 °C for 1.5 - 2 hours, with a heating rate ≤ 5 °C / min.

[0047] (2) Performance characterization: The recycled organic components replace 5 - 15% of the original resin for GFRP preparation. While the modulus is significantly improved (≥ 20%), the strength loss is controllable (≤ 15%), which is suitable for application scenarios with high stiffness requirements and medium strength requirements, and has certain potential in the fields of automotive lightweight, electronic packaging, and building decoration.

[0048] (3) During the reaction process, NO2 generated by the decomposition of nitric acid is collected and then introduced into water. There is an aeration device in the water. NO2 reacts with oxygen in the water to form nitric acid, and after accumulating to a concentration of 6 - 9 mol / L, it is reused for the acidolysis step.

[0049] The swelling and acidolysis equipment of the present invention includes:

[0050] (a) A three-necked flask (250 mL), equipped with a condensation reflux device;

[0051] (b) A mechanical stirrer with a rotation speed range of 200 - 400 rpm;

[0052] (c) Temperature controller, with an accuracy of ±1 °C;

[0053] (d) Electric heating equipment, connected to the temperature controller;

[0054] (e) Gas absorption device, with an in-built aeration equipment.

[0055] Figure 1 In the method for recovering bisphenol A epoxy resin cured by DDM using nitric acid acidolysis, it is achieved in four steps, including:

[0056] S1. Swelling pretreatment;

[0057] S2. Nitric acid acidolysis stage, including optimization of acidolysis conditions, orthogonal experiment, product separation, and component analysis;

[0058] S3. Extraction and purification stage, including neutralization treatment and organic phase extraction;

[0059] S4. Compound and regeneration application, including formulation design, curing process, performance testing, and recovery of the escaped gas.

[0060] Figure 2 is a diagram of the acetic acid swelling and decomposition reaction device. The instruments in Figure 2 are explained as follows: 1 is an iron stand, 2 is a mechanical stirrer, 3 is a spherical condenser (the connecting hose leads to the gas absorption device), 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 GFRP 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 GFRP material with distilled water and dry it. Weigh the GFRP 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.

[0061] Figure 3 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 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 the residual moisture; Evaporate the ethyl acetate to obtain the organic phase extract, and recycle the ethyl acetate for reuse in extraction; Repeat steps 2 - 4 once to obtain the final organic phase extract.

[0062] Example 1:

[0063] The content of bisphenol A epoxy resin before the treatment of GFRP material is 58.4%, the content of amine curing agent is 20%, the content of promoter phenol is 1.6%, and the content of glass fiber is 20%.

[0064] In step 1, 11.68 g of bisphenol A epoxy resin, 4 g of DDM and 0.32 g of phenol were weighed to prepare the FRP 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 by heating at a temperature of 70 °C for 2 hours, and then cured by secondary heating at a temperature of 110 °C for 2 hours. It was taken out of the mold, cooled to room temperature, and broken into pieces with a size of 10 mm. 5 g of GFRP was mixed with glacial acetic acid (liquid-solid ratio 20:1) and placed in a flask. The solution was heated to 120 °C by an electric heating mantle for a swelling reaction for 30 min. A temperature sensor was used for temperature monitoring and control, and vacuum drying was carried out at 70 °C for 24 hours.

[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 2 It is a diagram of the decomposition reaction device. It is known from the LC-MS analysis combined with the FTIR characterization analysis that most of the organic components are bisphenol A epoxy resin monomers and dimers. It is known from the SEM analysis that the surface of the recovered glass fiber is clean and there is little residual fiber attachment. The elastic modulus of the recovered fiber increased by 10.8% compared with the original fiber, and the tensile strength decreased by 7.3%. The above results show that the mechanical strength of the recovered fiber has not been significantly damaged.

[0066] In step S3, Figure 3 It is a technical route diagram of 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 is 7; add ethyl acetate solution (volume ratio 1:2), shake and mix (120 times / min) and then let it stand for layering, 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 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.

[0067] In step S4, the organic extract is substituted for the original resin at a mass ratio of 5%, and the FRP composite material is made with the original material ratio and process conditions in step S1. According to the determination of the flexural properties of plastics in GB / T 9341-2008, the three-point flexural strength of the produced GFRP material is measured. The test span is 20 mm, and the loading rate is 2 mm / min. The flexural modulus of GFRP is increased by 20%, and the strength loss is 15%, 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, and an internal aeration device is installed to react again to generate a 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 and uses 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 2:

[0069] The content of bisphenol A epoxy resin in the GFRP material before treatment is 51.1%, the content of amine curing agent is 17.5%, the content of promoter phenol is 1.4%, and the content of glass fiber is 30%.

[0070] In step 1, 10.22 g of bisphenol A epoxy resin, 3.5 g of DDM, and 0.28 g of phenol are weighed to make the FRP composite material. The curing agent is placed in a round-bottom flask and melted by 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 is placed in an oven and cured at a temperature of 80 °C for 1.5 hours, and then cured again at a temperature of 130 °C for 1.5 hours. It is taken out of the mold, cooled to room temperature, and broken into pieces with a size of 10 mm. 5 g of GFRP is mixed with glacial acetic acid (liquid-solid ratio 15:1) and placed in a flask. The electric heating mantle heats the solution to 80 °C, and the swelling reaction lasts for 30 min. The swelling rate of GFRP is 30%, and a temperature sensor is used for temperature monitoring and control. After washing with distilled water, it is dried in vacuum at 70 °C for 24 hours.

[0071] In step S2, through the optimization of acidolysis conditions and orthogonal experiments, the reaction time is determined to be 180 min, the solution concentration is 8 mol / L, the reaction temperature is 100 °C, and the resin decomposition rate is 98%. 2 g of the swollen GFRP material is taken, and the solution volume is 75 mL. Figure 2 It is a diagram of the decomposition reaction device. Through LC-MS analysis and FTIR characterization analysis, it is known that most of the organic components are bisphenol A epoxy resin monomers and dimers. Through SEM analysis, it is known that the surface of the recovered glass fiber is clean and there is little residual fiber attachment. The elastic modulus of the recovered fiber has increased by 15.2% compared with the original fiber, and the tensile strength has decreased by 7.9%. The above results show that the mechanical strength of the recovered fiber has not been significantly damaged.

[0072] In step S3, Figure 3 It is the extraction technical roadmap 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 is 7; Add ethyl acetate solution (volume ratio 1:2), oscillate and mix (120 times / min), then let it stand for layering, and take the upper ethyl acetate phase. Extract the filtrate 4 times repeatedly, and combine the extracts; Add anhydrous sodium sulfate to the ethyl acetate phase, let it stand for 40 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 10%, and make the glass fiber reinforced plastic composite material with the original material ratio and process conditions in step S1. According to the determination of the flexural properties of plastics in GB / T 9341-2008, measure the three-point flexural strength of the made GFRP material. The test span is 20 mm, the loading rate is 2 mm / min, the flexural modulus of GFRP is increased by 25%, and the strength loss is 10%, meeting the requirements of the building decoration 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. When the concentration reaches 7 mol / L, it is used again in the resin decomposition step. The whole 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.

[0074] Example three:

[0075] The content of bisphenol A epoxy resin in the GFRP material before treatment is 43.8%, the content of amine curing agent is 15%, the content of accelerator phenol is 1.2%, and the content of glass fiber is 40%.

[0076] In step 1, weigh 8.76 g of bisphenol A epoxy resin, 3 g of DDM and 0.24 g of phenol to make the glass fiber reinforced plastic composite material. Place the curing agent in a round bottom flask, heat and melt it at 80 °C with an electric heating mantle, then quickly stir and mix it with the epoxy resin, and pour it into the mold. Place the mold in an oven and heat and cure it at 90 °C for 2 hours, and then heat and cure it at 150 °C for 2 hours for the second time. Take it out of the mold, cool it to room temperature, and break it into pieces with a size of 8 mm. Mix 5 g of GFRP with glacial acetic acid (liquid-solid ratio 10:1) and place it in a flask. Heat the solution to 120 °C with an electric heating mantle, and carry out a swelling reaction for 30 min. The swelling rate of GFRP is 50%, and a temperature sensor is used for temperature monitoring and control. After washing with distilled water, dry it in vacuum at 70 °C for 24 hours.

[0077] In step S2, through the optimization of acidolysis conditions and orthogonal experiments, the reaction time was determined to be 180 min, the solution concentration was 9 mol / L, the reaction temperature was 95 °C, and the resin decomposition rate was 99.8%. Take 2 g of the swollen GFRP material, and the solution volume is 75 mL. Figure 2 It is a diagram of the decomposition reaction device. From LC-MS analysis and FTIR characterization analysis, it is known that most of the organic components are bisphenol A epoxy resin monomers and dimers. From SEM analysis, it is known that the surface of the recycled glass fiber is clean and there is little residual fiber attachment. The elastic modulus of the recycled fiber has increased by 20% compared with the original fiber, and the tensile strength has decreased by 10%. The above results indicate that the mechanical strength of the recycled fiber has not been significantly damaged.

[0078] In step S3, Figure 3 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 is 7; add ethyl acetate solution (volume ratio 1:1), shake and mix (120 times / min), then let it stand for phase separation, and take the upper ethyl acetate phase. Extract the filtrate repeatedly 3 times, and combine the extracts; add anhydrous sodium sulfate to the ethyl acetate phase, 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.

[0079] In step S4, replace the original resin with the organic extract at a mass ratio of 10%, and make a glass fiber reinforced plastic composite material with the original material ratio and process conditions in step S1. According to the determination of the flexural properties of plastics in GB / T 9341-2008, the three-point flexural strength of the made GFRP material was measured. The test span was 20 mm, and the loading rate was 2 mm / min. The flexural modulus of GFRP increased by 30%, and the strength loss was 15%, meeting the requirements of the electronic packaging 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 a 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 by heating the nitric acid is converted into an internal circulation solvent for the acidolysis link, while preventing gas from polluting the environment.

Claims

1. A method for nitric acid acidolysis recovery of a glass fiber reinforced epoxy resin composite material, characterized in that, It includes the following steps: (1) Pretreatment: Cut and crush the GFRP material to a size less than 10 mm; use glacial acetic acid as the swelling solvent, with a swelling temperature of 80°C - 120°C, a swelling time of 30 - 60 min, and a GFRP swelling rate of 30 - 50%; (2) Nitric acid hydrolysis: Mix the pretreated resin with a nitric acid solution and carry out directional acid hydrolysis at a temperature of 90 - 100°C, a nitric acid concentration of 7 - 9 mol / L, and a reaction time of 60 - 180 min to separate the glass fiber; (3) Extraction and purification: After adjusting the pH of the acid hydrolysis solution to 6 - 8, carry out 3 - 4 extractions with ethyl acetate, and obtain the organic phase extract through dehydration filtration and evaporation of the ethyl acetate phase; (4) Compound regeneration: Prepare a fiberglass material with bisphenol A epoxy resin, diaminodiphenylmethane (20 - 30 wt%), phenol (1 - 2 wt%) and glass fiber (20 - 40 wt%) in a mold, and carry out pre - curing at 70 - 90°C for 1.5 - 2 hours and secondary curing at 110 - 150°C for 1.5 - 2 hours to prepare a regenerated fiberglass composite material; (5) Nitric acid recovery: Collect NO₂ generated during the heating of the nitric acid solution, introduce it into water with continuous aeration, regenerate nitric acid, and reuse it for the nitric acid hydrolysis step of the resin to avoid environmental pollution.

2. The method according to claim 1, characterized in that, The specific operation of the swelling operation in step (1) includes: (a) Add glacial acetic acid to a three - necked flask, heat it with an electric heating mantle at a temperature of 80 - 120°C, equipped with a condensing reflux device and a mechanical stirring device; (b) The liquid - solid ratio is 10 - 20 (mL / g), and carry out swelling reaction with condensing reflux at 80 - 120°C for 30 - 60 min; (c) After swelling, the GFRP is washed with distilled water and vacuum - dried, and the swelling degree is 30 - 50%.

3. The method according to claim 1, wherein The reaction conditions of nitric acid hydrolysis in step (2) 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, characterized in that, In step (2), a two - step acid hydrolysis method is adopted for the GFRP material: (a) Swelling pretreatment: Anhydrous acetic acid, swelling at 80 - 120°C for 30 - 60 min, equipped with a condensing reflux device and a mechanical stirring device; (b) Acid hydrolysis reaction: 7 - 9 mol / L nitric acid solution, react at 90 - 100°C for 60 - 180 min, the reaction vessel is a three - necked flask, the mechanical stirring rate is 200 - 400 rpm, equipped with a condensing reflux device and a mechanical stirring device.

5. The method according to claim 1, wherein The specific steps of organic component extraction in step (3) include: (a) Dropwise add saturated sodium bicarbonate solution to the acid hydrolysis solution to adjust the pH to 6 - 8; (b) Add ethyl acetate, oscillate and mix, take the organic phase after standing and separating layers, 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, The preparation of the regenerated GFRP composite material in step (4) includes: (a) Replace the original resin with the organic extract in a mass ratio of 5 - 15%; (b) Prepare a fiberglass reinforced plastic material using bisphenol A epoxy resin, amine curing agent, phenol, and glass fiber. The mold is made of polytetrafluoroethylene material with dimensions of 100×10×4 mm 3 , and a silicone oil release agent is coated on the surface; (c) The material is pre-cured at 70 - 90 °C for 1.5 - 2 hours, and then post-cured 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 components of the organic phase extract are bisphenol A oligomers with a molecular weight of 500 - 1500 Da and nitroaniline compounds, which are verified by liquid chromatography - mass spectrometry; the compound viscosity of the recovered organic components ≤ 500 mPa·s, and the curing time ≤ 4 hours; in the nitric acid acidolysis reaction, the carbon-nitrogen bond is selectively broken, which is verified by Fourier transform infrared spectroscopy (FTIR).

8. The method according to claim 1, wherein The minimum flexural strength of the recycled composite material ≥ 85%, the tensile strength of the recycled fibers is retained at 90 - 93%, and the tensile modulus increases by 10 - 20%.

9. The glass fiber recovered by the nitric acid acidolysis recovery method of the glass fiber-reinforced epoxy resin composite material according to claim 1 is applied to the field of short fiber applications; the recovered resin is applied to automotive interior parts, electronic packaging materials or non-load-bearing structural parts of buildings.

10. The application according to claim 9, characterized in that, For the application of recycled epoxy resin composite materials, 5 - 15% of the recovered organic components are used instead of the original resin. The flexural property test is carried out according to GB / T 9341-2008, with a span of 20 mm and a loading rate of 2 mm / min. The flexural modulus ≥ 9 GPa and the flexural strength ≥ 80 MPa.

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