Method for recycling waste aramid fibers and preparing high-valued composite particles

Abstract

The invention provides a waste aramid fiber recycling and regenerating and high-valued composite particle preparation method which comprises the steps of waste aramid fiber pretreatment, aramid fiber recycling and regenerating and high-valued composite particle preparation, specifically, in the pretreatment stage, waste aramid fibers are subjected to cleaning, impurity removal and drying treatment; impurities are removed, and the water content is reduced to 5% or below; in the recycling and regenerating stage, regenerated aramid fibers with excellent performance are obtained through chemical depolymerization, separation and purification, repolymerization and spinning processes; the preparation of the high-valued composite particles comprises the following steps: chopping the regenerated aramid fibers, mixing the chopped regenerated aramid fibers with thermoplastic resin and an additive, and carrying out melt blending and granulation molding to obtain the composite particles, so that efficient recovery and high-valued utilization of the waste aramid fibers are realized, and the method has the characteristics of remarkable environmental protection benefit, high resource utilization rate, low cost, excellent product performance and the like; the method is suitable for aerospace, automobile industry and other fields.

Description

Technical Field

[0001] This article belongs to the field of polymer material recycling and reprocessing technology, specifically involving a method for recycling and regenerating waste aramid fibers and preparing high-value composite particles. Background Technology

[0002] Aramid fibers are widely used in many fields such as aerospace, military defense, transportation, and electronics due to their excellent properties such as high strength, high modulus, high temperature resistance, and chemical corrosion resistance. However, with the continuous increase in the use of aramid fibers, the amount of waste aramid fibers is also growing rapidly.

[0003] Currently, the main methods for disposing of waste aramid fibers include landfill and incineration. Landfill not only occupies a large amount of land resources, but aramid fibers are also difficult to degrade and will remain in the soil for a long time, posing a potential threat to soil structure and the ecological environment. Incineration produces a large amount of harmful gases, such as dioxins, which seriously pollute the atmospheric environment and also cause a great waste of resources. In addition, a large amount of scrap material is generated during the production of aramid fiber reinforced composite materials, and these scrap materials also face the problem of being difficult to recycle effectively.

[0004] Existing recycling methods, such as thermal pyrolysis and inorganic strong acid decomposition, have problems such as high requirements for reaction equipment, harsh reaction conditions, difficulty in separating degradation products and post-treatment of degradation liquid, and high industrialization costs. Furthermore, the performance of recycled aramid fibers is often significantly affected, making it difficult to meet the demand for high-value reuse. Therefore, developing an efficient, environmentally friendly, and low-cost method for recycling and regenerating waste aramid fibers and preparing high-value composite particles is of great practical significance. Summary of the Invention

[0005] The present invention aims to provide a method for recycling and regenerating waste aramid fibers and preparing high-value composite particles, involving the pretreatment of waste aramid fibers, recycling and regenerating aramid fibers, and the preparation process of high-value composite particles.

[0006] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0007] A method for recycling and regenerating waste aramid fibers and preparing high-value composite particles includes the following steps: S1, pretreatment of waste aramid fibers.

[0008] Waste aramid fibers are placed in a stainless steel cleaning tank with a stirring function. A weak alkaline solution with a pH value controlled at 8-10 is used. The weak alkaline solution is a mixture of sodium carbonate and sodium bicarbonate with a mass ratio of 3:1-5:1 and a concentration of 2%-5%. The fibers are soaked and cleaned at a temperature of 40-60℃ for 1-2 hours to remove impurities such as oil, dust, and resin residue from the fiber surface. After cleaning, the impurities on the fiber surface are thoroughly removed by rinsing with a high-pressure water gun or centrifugal drying. The cleaned waste aramid fibers are then transferred to an oven and dried at a temperature of 80-100℃ for 2-4 hours to reduce the moisture content of the fibers to below 5%.

[0009] S2, Aramid fiber recycling

[0010] The dried waste aramid fibers are added to a reactor containing a specific depolymerization agent, a mixed solution of dimethyl sulfoxide and sodium hydroxide, with a mass ratio of dimethyl sulfoxide to sodium hydroxide of 10:1-15:1. The temperature inside the reactor is controlled at 180-200℃, the pressure is maintained at 0.5-1.0 MPa, and the reaction time is 3-5 hours. After the reaction, the mixture in the reactor is cooled to room temperature and then filtered through a filter cloth to separate unreacted solid impurities from the depolymerized solution. The solution is then purified by distillation under reduced pressure (0.08-0.09 MPa) at a temperature of 120-150℃. The organic solvent and small molecule byproducts in the solution are removed at a temperature of 250-280°C to obtain a high-purity aramid recycled raw material. The purified aramid recycled raw material is added to a polymerization reaction system containing phosphorus trichloride catalyst and polymerized at a certain temperature of 250-280°C and a pressure of 1.5-2.0 MPa for 2-3 hours. This allows the aramid molecular fragments to repolymerize and form a high molecular weight aramid polymer. The recycled aramid fiber is then prepared by wet spinning. During the wet spinning process, the concentration of the spinning solution is controlled at 15%-20%, the coagulation solution is a zinc sulfate solution with a concentration of 5%-8%, and the spinning speed is 50-80 m / min.

[0011] S3, Preparation of high-value composite particles

[0012] Regenerated aramid fibers are chopped to a length of 0.5-2 mm. Then, the chopped recycled aramid fibers are mixed uniformly with thermoplastic resins such as polypropylene, polyethylene, and polyamide, along with appropriate additives, in a specific ratio. The mass ratio of recycled aramid fibers to thermoplastic resins is 1:3-1:5, and the total mass of additives accounts for 1%-3% of the total mass of the mixture. The mixed raw materials are then added to a twin-screw extruder for melt blending. The screw diameter of the twin-screw extruder is 40-60 mm, and the length-to-diameter ratio is 30:1-40:1. The temperature settings for each section of the extruder are adjusted according to thermal conditions. The type of plastic resin is adjusted, the temperature of the feeding section is 180-200℃, the temperature of the melting section is 220-250℃, the temperature of the homogenization section is 230-260℃, and the screw speed is controlled at 200-400r / min to ensure that the raw materials are fully melted and mixed in the extruder. After melt blending, the material is extruded from the extruder head and cooled by water or air cooling. Then, the cooled material is cut into granules by a pelletizer to obtain high-value composite granules. The cutting speed of the pelletizer is 300-500r / min, and the length of the granules is controlled at 2-4mm and the diameter is controlled at 1-3mm.

[0013] Beneficial effects:

[0014] This process recycles and regenerates waste aramid fibers, avoiding the pollution caused by landfilling or incineration of large quantities of waste aramid fibers, reducing land occupation and harmful gas emissions, and conforming to the environmental protection concept of sustainable development.

[0015] This processing technology enables the recycled aramid fibers and the high-value composite particles prepared to have key properties such as tensile strength and modulus that are comparable to those of virgin aramid fibers and related products, thus meeting the application needs of many fields and expanding the application scope of waste aramid fibers. Attached Figure Description

[0016] Figure 1 This is a comparison table of pretreatment process parameters for waste aramid fibers;

[0017] Figure 2 This is a comparison table of aramid recycling and regeneration process parameters;

[0018] Figure 3 This is a comparison table of process parameters for preparing high-value composite particles;

[0019] Figure 4 This is a performance test data sheet for recycled aramid fibers. Detailed Implementation

[0020] To better understand the purpose, structure, and function of this invention, a method for recycling and regenerating waste aramid fibers and preparing high-value composite particles is described in further detail.

[0021] Example 1:

[0022] S1. Pretreatment of waste aramid fibers

[0023] Waste aramid fibers were placed in a cleaning tank containing a weak alkaline cleaning agent with a pH of 9 and soaked at 50°C for 1.5 hours. Then, they were rinsed with a high-pressure water gun to remove surface impurities. The cleaned fabric was then transferred to a hot air circulating oven and dried at 90°C for 3 hours to reduce its moisture content to 4%.

[0024] S2, Aramid fiber recycling

[0025] The dried fabric was cut into pieces and added to a reactor containing a 12:1 mass ratio of dimethyl sulfoxide to sodium hydroxide. The reactor temperature was controlled at 190℃ and the pressure at 0.8MPa. The reaction was carried out for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, and solid impurities were removed by filtration. Then, aramid recycled raw material with a purity of 95% was obtained by distillation. The aramid recycled raw material was added to a polymerization reaction system containing a catalyst. After the reaction, a wet spinning process was used with a spinning solution concentration of 18%, a zinc sulfate concentration of 6% in the coagulation solution, and a spinning speed of 60m / min to prepare recycled aramid fibers.

[0026] S3, Preparation of high-value composite particles

[0027] Regenerated aramid fibers were chopped into 1mm lengths and mixed with PP resin at a mass ratio of 1:4. Antioxidant and coupling agent, accounting for 2% of the total mass of the mixture, were added. The mixed raw materials were fed into a twin-screw extruder with a screw diameter of 50mm and an aspect ratio of 35:1. The feeding section temperature was 190℃, the melting section temperature was 230℃, the homogenization section temperature was 240℃, and the screw speed was 300r / min for melt blending. The blended material was extruded from the extruder die head, water-cooled, and then cut into granules using a pelletizer at a cutter speed of 400r / min, yielding high-value composite granules with a length of 3mm and a diameter of 2mm. Performance tests were conducted on the prepared recycled aramid fibers, showing a tensile strength of 2.81GPa and a modulus of 120GPa. Performance tests were conducted on the high-value composite granules, showing a tensile strength of 44MPa and a flexural strength of 60MPa.

[0028] Example 2

[0029] S1. Pretreatment of waste aramid fibers

[0030] The crushed waste aramid fibers are placed in a cleaning device and soaked in a weak alkaline solution with a pH of 8.5 at 45°C for 2 hours. Then, impurities and cleaning agents are removed by centrifugation, and the waste is dried in a hot air circulating oven at 85°C for 3.5 hours to reduce the moisture content of the waste to 3%.

[0031] S2, Aramid fiber recycling

[0032] The dried waste material was added to a reaction vessel containing a mixed solution of dimethyl sulfoxide and sodium hydroxide in a mass ratio of 13:1. The reaction temperature was 185℃, the pressure was 0.6MPa, and the reaction time was 3.5 hours. After cooling, filtration, and distillation, aramid recycled raw material with a purity of 96% was obtained. The aramid recycled raw material was added to a polymerization reaction system containing a catalyst. After the reaction, recycled aramid fibers were prepared using a wet spinning process with a spinning solution concentration of 15%, a coagulation solution zinc sulfide concentration of 8%, and a spinning speed of 75m / min.

[0033] S3, Preparation of high-value composite particles

[0034] Regenerated aramid fibers were chopped into 1.5mm lengths and mixed with PA resin at a mass ratio of 1:3.5. Antioxidant and coupling agent, accounting for 2.5% of the total mass of the mixture, were added. The mixture was melt-blended using a twin-screw extruder with a screw diameter of 45mm, an aspect ratio of 32:1, a feeding section temperature of 185℃, a melting section temperature of 225℃, a homogenization section temperature of 235℃, and a screw speed of 250r / min. After extrusion, the material was air-cooled and pelletized at a cutter speed of 350r / min. The pellets had a length of 2.5mm and a diameter of 1.5mm. The tensile strength of the recycled aramid fibers was 2.64GPa, and the modulus was 110GPa. The tensile strength of the high-value composite granules was 50MPa, and the flexural strength was 65MPa.

[0035] Example 3

[0036] S1. Pretreatment of waste aramid fibers

[0037] The crushed waste aramid fibers were placed in a cleaning device and soaked in a weak alkaline cleaning agent with a pH of 9.5 at 55°C for 1 hour. Then, they were rinsed with a high-pressure water gun and dried at 95°C for 2.5 hours until the moisture content dropped to 4.5%.

[0038] S2, Aramid fiber recycling

[0039] The dried fibers were added to a reactor containing a mixed solution of dimethyl sulfoxide and sodium hydroxide in a mass ratio of 14:1. The reaction was carried out at a temperature of 195℃ and a pressure of 0.9MPa for 4.5 hours. After filtration and distillation, aramid recycled raw material with a purity of 94% was obtained. Regenerated aramid fibers were prepared by wet spinning with a spinning solution concentration of 16%, a coagulation solution zinc sulfate concentration of 7%, and a spinning speed of 70m / min.

[0040] S3, Preparation of high-value composite particles

[0041] Regenerated aramid fibers were chopped to 0.8 mm and mixed with PE resin at a mass ratio of 1:4.5. Additives accounting for 1.5% of the total mass of the mixture were added. A twin-screw extruder with a screw diameter of 55 mm and an aspect ratio of 38:1 was used for melt blending. The feeding section temperature was 195℃, the melting section temperature was 240℃, the homogenization section temperature was 250℃, and the screw speed was 350 r / min. After water cooling, the mixture was pelletized at a cutter speed of 450 r / min to obtain particles with a length of 3.5 mm and a diameter of 2.5 mm. The tensile strength of the recycled aramid fibers was 2.71 GPa, and the modulus was 116 GPa. The tensile strength of the high-value composite particles was 48 MPa, and the flexural strength was 63 MPa.

[0042] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for preparing high-value composite particles from recycled and regenerated waste aramid fibers, characterized in that, Includes the following steps: S1. Pretreatment of waste aramid fibers: The waste aramid fibers are soaked in a cleaning tank containing a weak alkaline solution at 40-60℃ for 1-2 hours to clean them. They are then dried by a high-pressure water gun or centrifuge to remove impurities. Finally, they are placed in an oven to reduce the moisture content to below 5%. S2, Aramid fiber recycling and regeneration: The dried fibers are added to a reactor containing a mixture of dimethyl sulfoxide and sodium hydroxide at a mass ratio of 10:1-15:

1. The mixture is chemically depolymerized at 180-200℃ and 0.5-1.0MPa for 3-5 hours. After cooling and filtration, the fibers are purified by distillation. The purified raw material is then added to a polymerization system containing a catalyst and polymerized at 250-280℃ and 1.5-2.0MPa for 2-3 hours. Regenerated aramid fibers are then prepared by wet spinning. S3. Preparation of high-value composite particles: Regenerated aramid fibers are chopped into 0.5-2mm lengths using a rotary fiber cutter and mixed with thermoplastic resin at a mass ratio of 1:3-1:5 and 1%-3% of additives by mass, including antioxidant 1010, silane coupling agent KH550, and dioctyl phthalate plasticizer. The mixture is then fed into a twin-screw extruder at a feeding section temperature of 180-200℃, a melting section temperature of 220-250℃, a homogenization section temperature of 230-260℃, and a screw speed of 200-400 r / min for melt blending. After extrusion and cooling, the material is cut into granules with a length of 2-4mm and a diameter of 1-3mm using a pelletizer.

2. The method for preparing high-value composite particles from recycled and regenerated waste aramid fibers according to claim 1, characterized in that, The content of the waste aramid fiber is not less than 60%.

3. The method for preparing high-value composite particles from recycled and regenerated waste aramid fibers according to claim 1, characterized in that, The polymerization reaction system also includes a stabilizer with a mass fraction of 0.3%-0.5%, wherein the stabilizer is hydroquinone.

4. The method for preparing high-value composite particles from recycled and regenerated waste aramid fibers according to claim 1, characterized in that, The wet spinning process involves a spinning solution concentration of 15%-20%, a coagulation solution containing 5%-8% zinc sulfate, a temperature of 40-50℃, and a spinning speed of 50-80 m / min. The spinning solution is prepared by mixing aramid polymer and N-methylpyrrolidone (NMP) in a mass ratio of 1:4-1:

6.

5. The method for preparing high-value composite particles from recycled and regenerated waste aramid fibers according to claim 1, characterized in that, The thermoplastic resin is one or more of polypropylene, polyethylene, and polyamide 6, and the mass ratio of each component during mixing does not exceed ±5%.

6. The method for preparing high-value composite particles from recycled and regenerated waste aramid fibers according to claim 1, characterized in that, The screw assembly of the twin-screw extruder includes a conveying section, a melting section, a mixing section, and a metering section, wherein the mixing section is equipped with a reverse thread element, the length of which accounts for 15%-20% of the total screw length.

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