A method for processing ultra-high molecular weight polyethylene waste

Abstract

The application discloses a kind of processing methods of ultra-high molecular weight polyethylene waste, it is related to polymer material recycling technical field.The method includes: sorting, ultrasonic cleaning and vacuum drying to the ultra-high molecular weight polyethylene fiber in the scrapped body armor panel;After constant temperature and humidity balance processing, cut into short fiber section;Send into oblique angle micro shear crusher and smash, and spray into low-temperature nitrogen stream instantaneous rapid cooling at discharge port;After air classification screening, coarse particle returns to circulating crushing;Qualified powder is carried out multi-stage pressurized annealing under high-purity nitrogen protection;Then surface grafting modification is carried out in acetone medium using maleic anhydride and azobisdimethylvaleronitrile;Finally, melt extrusion granulation after premixing with antioxidant.The whole process temperature of the application is controllable, and the molecular weight loss of recycled powder is small, and the crystallinity is high, so that high-value recycling can be realized.

Description

Technical Field

[0001] This invention relates to the field of polymer material recycling technology, specifically a method for treating ultra-high molecular weight polyethylene waste. Background Technology

[0002] Due to its extremely high molecular weight, highly crystalline structure, and ultra-long chain entanglement characteristics, ultra-high molecular weight polyethylene (UHMWPE) fiber faces significant technical bottlenecks in the recycling and reuse process. Existing technologies suffer from the following main problems: Dissolution methods rely on high-boiling-point organic solvents such as decahydronaphthalene and xylene, dissolving fibers at high temperatures. This not only results in large solvent consumption, high toxicity, and difficult recovery, but also extremely high energy consumption. High-temperature melting methods attempt to reduce melt viscosity by increasing temperature, but UHMWPE melt viscosity is extremely high, making conventional melting processing almost impossible. Forced heating to above 200°C triggers severe thermo-oxidative decomposition, leading to a sharp decrease in molecular weight. Mechanical pulverization at room temperature results in the high toughness and elasticity of the fibers, making them prone to entanglement with the blades. Furthermore, the localized high temperatures generated by high-speed shearing often exceed 150°C, causing main chain breakage and a molecular weight loss typically exceeding 20%. Low-temperature embrittlement pulverization uses liquid nitrogen to freeze the fibers to -196°C before pulverization. While this improves pulverization efficiency, the rapid low-temperature impact causes irreversible phase transitions in the crystalline structure, permanently breaking the connecting chains between lamellar crystals, significantly reducing crystallinity and mechanical properties. Simultaneously, it consumes large amounts of liquid nitrogen and is costly. In summary, existing recycling methods struggle to simultaneously achieve the synergistic goals of maintaining molecular weight, protecting the crystalline structure, and low-cost processing. Summary of the Invention

[0003] The purpose of this invention is to provide a method for treating ultra-high molecular weight polyethylene (UHMWPE) waste, thereby solving the technical problems mentioned in the background section. This invention enables the recycling of waste UHMWPE fibers into directly melt-processable powder in a low-energy, low-cost manner while maintaining the integrity of the UHMWPE chain structure. The recycled powder exhibits a molecular weight loss of less than 5% and maintains a crystallinity of over 93%.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for treating ultra-high molecular weight polyethylene waste includes the following steps: S1. Sorting and removing non-ultra-high molecular weight polyethylene impurities from the scrapped bulletproof vest panels to obtain pure ultra-high molecular weight polyethylene fibers; immersing the fibers in deionized water for ultrasonic cleaning, followed by rinsing, draining and vacuum drying; S2. Place the dried fibers in a constant temperature and humidity environment for equilibration treatment. S3. The balanced fibers are fed into a cutting machine and cut into short fiber segments; S4. The short fiber segments are fed into an angled micro-shear pulverizer for pulverization. The pulverizer adopts a roller-type multi-blade shearing structure with an asymmetrical wedge-shaped blade cross section and a blade cutting angle θ of 12° to 15°. At the same time, a low-temperature nitrogen gas flow is injected into the pulverizer outlet to instantly cool the produced powder. S5. Perform airflow classification and sieving on the powder after rapid cooling, collect qualified powder, and return the unqualified coarse particles to the pulverizer for recycling and pulverization. S6. The collected qualified powder is loaded into a sealed annealing chamber, high-purity nitrogen is introduced, and a three-stage annealing treatment is carried out under pressure and temperature conditions. Then, the powder is cooled and depressurized to obtain dense powder. The three-stage annealing process is as follows: In the first stage, the temperature is increased from room temperature to 45°C at a rate of 2°C / min, a light pressure of 0.10 MPa is applied, and the temperature and pressure are maintained for 30 min; in the second stage, the temperature is increased from 45°C to 65°C at a rate of 1°C / min, the pressure is increased to 0.20 MPa, and the temperature and pressure are maintained for 3 h; in the third stage, the temperature is decreased from 65°C to 30°C at a rate of 0.5°C / min, and the pressure is simultaneously released slowly to atmospheric pressure at a rate of 0.005 MPa / min. S7. Add the dense powder to acetone, then add maleic anhydride and azobisisobutyronitrile in sequence, and heat and stir the reaction under nitrogen protection. After the reaction is completed, filter and collect the powder, wash the filter cake with acetone, and finally vacuum dry to obtain the recovered powder. S8. The recycled powder is premixed with antioxidant and then fed into a twin-screw extruder for melt extrusion, cooling and pelletizing.

[0005] Preferably, in step 1, the purity of the pure ultra-high molecular weight polyethylene fiber is ≥99.5 wt%; The specific conditions for ultrasonic cleaning are as follows: adding deionized water at 40°C, a liquid-to-solid ratio of 8:1, an ultrasonic frequency of 35kHz, and a power density of 0.8W / cm³. 2 The cleaning time is 20 minutes; The vacuum drying conditions are as follows: drying at 50℃ and vacuum degree ≤500Pa for 5 hours until constant weight.

[0006] Preferably, in step 2, the conditions for the balancing treatment are: temperature set at 25°C, relative humidity set at 30%, and balancing treatment for 18 hours, so that the fiber moisture content is reduced to below 0.01%.

[0007] Preferably, in step 3, the cutting machine cuts the fiber to a length of 30 mm.

[0008] Preferably, in step 4, the temperature of the cryogenic nitrogen gas flow during the instantaneous rapid cooling process is -20±2℃, and the flow rate is 150Nm³. 3 / h, so that the powder produced by pulverization is covered by nitrogen swirling within 30ms of falling, and is rapidly cooled from 48℃ to 5℃ within 1.2s.

[0009] Preferably, in step 6, the oxygen content in the annealing chamber is controlled to be <30ppm.

[0010] Preferably, in step 7, the amount of maleic anhydride used is 9-12% of the mass of the annealed powder.

[0011] Preferably, in step 8, the antioxidant is antioxidant 1010, and its addition amount is 0.3 wt% of the mass of the recovered powder.

[0012] Preferably, in step 8, the temperatures of each zone of the twin-screw extruder are set to 160℃, 165℃, 170℃, 175℃, 180℃, 175℃, and 170℃ respectively, and the die temperature is set to 175℃.

[0013] Compared with the prior art, the beneficial effects of the present invention are: (1) The temperature throughout the process does not exceed 70℃, which is far lower than the thermal oxidative decomposition initiation temperature of UHMWPE. The weight-average molecular weight loss of the recovered powder is less than 5%, achieving "non-destructive" molecular weight maintenance. (2) The three-step coupling process of untangling-rapid cooling-annealing and re-insertion enables the untangled chain segments to re-inserte into the lattice. The crystallinity of the recovered powder can reach 93% to 96%, which is better than that of the original material. (3) Through precise control of annealing temperature and pressure, the quantitative recovery of entanglement density is achieved. The final entanglement density of the powder reaches 85% to 95% of that of the original fiber, meeting the requirements for direct melt processing. (4) The recovered powder does not require the traditional dissolution-respinning process and can be directly melt-extruded at 160 to 180℃. The processing cost per ton is reduced by more than 60% compared with the dissolution method. (5) Only a small amount of low-temperature nitrogen is used throughout the process. The energy consumption is only 1 / 5 to 1 / 3 of that of the traditional dissolution method. No organic solvents are used and there are no VOC emissions. Detailed Implementation

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0015] Example 1 A method for treating ultra-high molecular weight polyethylene waste includes the following steps: Step 1: Take 100kg of discarded bulletproof vest panels and manually sort them to remove non-UHMWPE impurities such as aramid threads, metal fasteners, fabric labels, and adhesive seals, obtaining approximately 98.6kg of pure UHMWPE fibers (sorting purity ≥99.5wt%). Cut the fibers into approximately 15cm × 15cm squares and place them in batches into an ultrasonic cleaner. Add 40℃ deionized water until completely submerged (liquid-to-material ratio approximately 8:1), and set the ultrasonic frequency to 35kHz and the power density to 0.8W / cm³. 2 The fibers were cleaned for 20 minutes, turning them over every 5 minutes to ensure even ultrasonic treatment on all sides, removing residual thermoplastic polyurethane matrix resin and oil stains from the fiber surface. After cleaning, the fibers were rinsed twice with clean deionized water and drained. Then, the fibers were spread out on a stainless steel mesh tray (thickness ≤ 3 cm) and placed in a vacuum drying oven. They were dried at 50°C and a vacuum degree ≤ 500 Pa for 5 hours until constant weight was achieved (two consecutive weighings were taken 30 minutes apart, with a mass difference < 0.05%).

[0016] Step 2: Spread the dried fibers evenly on a stainless steel mesh tray (leaving air gaps between layers), transfer them into a constant temperature and humidity chamber, set the temperature to 25℃ and the relative humidity to 30%, and equilibrate for 18 hours.

[0017] Step 3: Feed the moisture-balanced fibers into a rotary fiber cutter, set the cutting length to 30mm, and obtain white short rod-shaped fiber segments, which are then collected in a clean PE bag for later use.

[0018] Step 4: Turn on the cryogenic nitrogen supply system and adjust the nitrogen temperature at the outlet of the annular jet ring to -20±2℃ and the flow rate to 150Nm using the liquid nitrogen to room temperature nitrogen ratio mixing regulating valve. 3 The spray ring is installed 45mm directly below the pulverizer outlet at a spray angle of 45°. During formal production, 30mm fiber segments are evenly fed into the pulverizer at a feed rate of 10kg / h via a quantitative screw feeder. The pulverizer blades have an angle of θ=14°, with 18 Cr12MoV alloy tool steel blades (HRC 63) on each of the upper and lower rollers, a cutting edge width of 1.0mm, a radius of curvature R=10μm, a tooth gap δ=0.08mm, and a linear shear rate of 1.5m / s. The powder is enveloped by the annular nitrogen vortex within approximately 30ms of falling from the outlet, and rapidly cooled from an outlet temperature of approximately 48℃ to approximately 5℃ within approximately 1.2s. Throughout the process, the outlet powder temperature is monitored to ensure it does not exceed 50℃, and the nitrogen nozzle temperature is maintained at -20±2℃. The entire feeding process is completed in approximately 9.8 hours of continuous operation, with no material blockage or blade entanglement observed during operation.

[0019] Step 5: The rapidly cooled powder is transported through a closed pipeline to a turbine air classifier (classifier wheel speed 2500 rpm, secondary air volume 5 m³ / h). 3The system collects qualified powder with a particle size of 50–500 μm at a rate of 8 kg / h. The first classification has a pass rate of approximately 84%. Coarse particles with a particle size >500 μm are returned to the pulverizer via a dedicated powder return screw conveyor from an independent powder inlet at a rate of 8 kg / h for secondary pulverization, rapid cooling, and classification, yielding qualified powder and residual coarse particles. The residual coarse particles then undergo a third cycle to finally obtain qualified powder.

[0020] Step 6: Load the qualified powder into a sealed 316L stainless steel annealing chamber (200L volume, about 50kg per batch) in batches. After closing the feed valve, purge with 99.995% high-purity nitrogen at a flow rate of 20L / min for 15min. After confirming with a portable oxygen analyzer that the oxygen content at the exhaust port has dropped to <30ppm, adjust the nitrogen flow rate to 5L / min to maintain a slight positive pressure. After installing the top hydraulic pressure piston, operate according to the following three-stage procedure: Stage 1 (stress homogenization): Increase the temperature from room temperature (approximately 22°C) to 45°C at a rate of 2°C / min, apply a light pressure of 0.10 MPa, and maintain the temperature and pressure for 30 minutes. Stage 2 (chain segment re-insertion): Increase the temperature from 45°C to 65°C at a rate of 1°C / min, raise the pressure to 0.20 MPa, and maintain the temperature and pressure for 3 hours. Throughout the process, maintain the oxygen content in the chamber <30 ppm and the highest measured temperature not exceeding 67°C. Stage 3 (steady-state locking): Turn off the heating and turn on the cooling water coil, reduce the temperature from 65°C to 30°C at a rate of 0.5°C / min, and simultaneously slowly depressurize to atmospheric pressure at a rate of 0.005 MPa / min. The entire cooling-depressurization process takes approximately 70 minutes. Open the chamber and remove the material; a white, dense, fine powder is obtained.

[0021] Step 7: Take 50g of annealed powder and add it to a 1000mL three-necked flask. Add 500mL of acetone, and while stirring, add 5.5g of maleic anhydride (MAH) and 0.75g of azobisisobutyronitrile (AIBN) in sequence, stirring until completely dissolved. Install a reflux condenser at the middle neck of the three-necked flask and a thermometer and nitrogen inlet at the side neck. First, purge the air in the flask with nitrogen for 5 minutes to remove air from the flask. Then, place the flask in a 60℃ constant temperature oil bath and stir at 300rpm for 45 minutes. After the reaction is complete, remove the oil bath and allow it to cool naturally to room temperature. Collect the powder by vacuum filtration using a Buchner funnel. Wash the filter cake three times with 50mL of fresh acetone (stirring and filtering again each time) to remove unreacted MAH and AIBN residues. Finally, dry the powder in a 50℃ vacuum drying oven for 2 hours to obtain MAH-grafted powder.

[0022] Step 8: After premixing the MAH grafted powder with 0.3 wt% antioxidant 1010, feed it into a co-rotating twin-screw extruder (screw diameter 20 mm, L / D=40, screw speed 80 rpm) at a rate of 1.5 kg / h using a loss-in-weight feeder. The temperatures of each zone from the hopper to the die are set sequentially to 160℃, 165℃, 170℃, 175℃, 180℃, 175℃, and 170℃, with the die temperature set to 175℃. After the extruded strip is cooled in a water bath, it is granulated (3 mm in length) to obtain white, semi-transparent granules.

[0023] Example 2 A method for treating ultra-high molecular weight polyethylene waste includes the following steps: Step 1: Take 100kg of discarded bulletproof vest panels and manually sort them to remove non-UHMWPE impurities such as aramid threads, metal fasteners, fabric labels, and adhesive seals, obtaining approximately 98.6kg of pure UHMWPE fibers (sorting purity ≥99.5wt%). Cut the fibers into approximately 15cm × 15cm squares and place them in batches into an ultrasonic cleaner. Add 40℃ deionized water until completely submerged (liquid-to-material ratio approximately 8:1), and set the ultrasonic frequency to 35kHz and the power density to 0.8W / cm³. 2 The fibers were cleaned for 20 minutes, turning them over every 5 minutes to ensure even ultrasonic treatment on all sides, removing residual thermoplastic polyurethane matrix resin and oil stains from the fiber surface. After cleaning, the fibers were rinsed twice with clean deionized water and drained. Then, the fibers were spread out on a stainless steel mesh tray (thickness ≤ 3 cm) and placed in a vacuum drying oven. They were dried at 50°C and a vacuum degree ≤ 500 Pa for 5 hours until constant weight was achieved (two consecutive weighings were taken 30 minutes apart, with a mass difference < 0.05%).

[0024] Step 2: Spread the dried fibers evenly on a stainless steel mesh tray (leaving air gaps between layers), transfer them into a constant temperature and humidity chamber, set the temperature to 25℃ and the relative humidity to 30%, and equilibrate for 18 hours.

[0025] Step 3: Feed the moisture-balanced fibers into a rotary fiber cutter, set the cutting length to 30mm, and obtain white short rod-shaped fiber segments, which are then collected in a clean PE bag for later use.

[0026] Step 4: Turn on the cryogenic nitrogen supply system and adjust the nitrogen temperature at the outlet of the annular jet ring to -20±2℃ and the flow rate to 150Nm using the liquid nitrogen to room temperature nitrogen ratio mixing regulating valve. 3The spray ring is installed 45mm directly below the pulverizer outlet at a spray angle of 45°. During formal production, 30mm fiber segments are evenly fed into the pulverizer at a feed rate of 10kg / h via a quantitative screw feeder. The pulverizer blades have an angle of θ=13°, with 18 Cr12MoV alloy tool steel blades (HRC 63) on each of the upper and lower rollers, a cutting edge width of 1.0mm, a radius of curvature R=10μm, a tooth gap δ=0.08mm, and a linear shear rate of 0.8m / s. The powder is enveloped by the annular nitrogen vortex within approximately 30ms of falling from the outlet, and is rapidly cooled from approximately 48℃ to approximately 5℃ within approximately 1.2s. Throughout the process, the outlet powder temperature is monitored to ensure it does not exceed 50℃, and the nitrogen nozzle temperature is maintained at -20±2℃. The entire feeding process is completed in approximately 9.8 hours of continuous operation, with no material blockage or blade entanglement observed during operation.

[0027] Step 5: The rapidly cooled powder is transported through a closed pipeline to a turbine air classifier (classifier wheel speed 2500 rpm, secondary air volume 5 m³ / h). 3 The system collects qualified powder with a particle size of 50–500 μm at a rate of 8 kg / h. The first classification has a pass rate of approximately 84%. Coarse particles with a particle size >500 μm are returned to the pulverizer via a dedicated powder return screw conveyor from an independent powder inlet at a rate of 8 kg / h for secondary pulverization, rapid cooling, and classification, yielding qualified powder and residual coarse particles. The residual coarse particles then undergo a third cycle to finally obtain qualified powder.

[0028] Step 6: Load the qualified powder into a sealed 316L stainless steel annealing chamber (200L volume, about 50kg per batch) in batches. After closing the feed valve, purge with 99.995% high-purity nitrogen at a flow rate of 20L / min for 15min. After confirming with a portable oxygen analyzer that the oxygen content at the exhaust port has dropped to <30ppm, adjust the nitrogen flow rate to 5L / min to maintain a slight positive pressure. After installing the top hydraulic pressure piston, operate according to the following three-stage procedure: Stage 1 (stress homogenization): Increase the temperature from room temperature (approximately 22°C) to 45°C at a rate of 2°C / min, apply a light pressure of 0.10 MPa, and maintain the temperature and pressure for 30 minutes. Stage 2 (chain segment re-insertion): Increase the temperature from 45°C to 65°C at a rate of 1°C / min, raise the pressure to 0.20 MPa, and maintain the temperature and pressure for 3 hours. Throughout the process, maintain the oxygen content in the chamber <30 ppm and the highest measured temperature not exceeding 67°C. Stage 3 (steady-state locking): Turn off the heating and turn on the cooling water coil, reduce the temperature from 65°C to 30°C at a rate of 0.5°C / min, and simultaneously slowly depressurize to atmospheric pressure at a rate of 0.005 MPa / min. The entire cooling-depressurization process takes approximately 70 minutes. Open the chamber and remove the material; a white, dense, fine powder is obtained.

[0029] Step 7: Take 50g of annealed powder and add it to a 1000mL three-necked flask. Add 500mL of acetone, and while stirring, add 4.8g of maleic anhydride (MAH) and 0.75g of azobisisobutyronitrile (AIBN) in sequence, stirring until completely dissolved. Install a reflux condenser at the middle neck of the three-necked flask and a thermometer and nitrogen inlet at the side neck. First, purge the air in the flask with nitrogen for 5 minutes to remove air from the flask. Then, place the flask in a 60℃ constant temperature oil bath and stir at 300rpm for 45 minutes. After the reaction is complete, remove the oil bath and allow it to cool naturally to room temperature. Collect the powder by vacuum filtration using a Buchner funnel. Wash the filter cake three times with 50mL of fresh acetone (stirring and filtering again each time) to remove unreacted MAH and AIBN residues. Finally, dry the powder in a 50℃ vacuum drying oven for 2 hours to obtain MAH-grafted powder.

[0030] Step 8: After premixing the MAH grafted powder with 0.3 wt% antioxidant 1010, feed it into a co-rotating twin-screw extruder (screw diameter 20 mm, L / D=40, screw speed 80 rpm) at a rate of 1.5 kg / h using a loss-in-weight feeder. The temperatures of each zone from the hopper to the die are set sequentially to 160℃, 165℃, 170℃, 175℃, 180℃, 175℃, and 170℃, with the die temperature set to 175℃. After the extruded strip is cooled in a water bath, it is granulated (3 mm in length) to obtain white, semi-transparent granules.

[0031] Example 3 A method for treating ultra-high molecular weight polyethylene waste includes the following steps: Step 1: Take 100kg of discarded bulletproof vest panels and manually sort them to remove non-UHMWPE impurities such as aramid threads, metal fasteners, fabric labels, and adhesive seals, obtaining approximately 98.6kg of pure UHMWPE fibers (sorting purity ≥99.5wt%). Cut the fibers into approximately 15cm × 15cm squares and place them in batches into an ultrasonic cleaner. Add 40℃ deionized water until completely submerged (liquid-to-material ratio approximately 8:1), and set the ultrasonic frequency to 35kHz and the power density to 0.8W / cm³. 2 The fibers were cleaned for 20 minutes, turning them over every 5 minutes to ensure even ultrasonic treatment on all sides, removing residual thermoplastic polyurethane matrix resin and oil stains from the fiber surface. After cleaning, the fibers were rinsed twice with clean deionized water and drained. Then, the fibers were spread out on a stainless steel mesh tray (thickness ≤ 3 cm) and placed in a vacuum drying oven. They were dried at 50°C and a vacuum degree ≤ 500 Pa for 5 hours until constant weight was achieved (two consecutive weighings were taken 30 minutes apart, with a mass difference < 0.05%).

[0032] Step 2: Spread the dried fibers evenly on a stainless steel mesh tray (leaving air gaps between layers), transfer them into a constant temperature and humidity chamber, set the temperature to 25℃ and the relative humidity to 30%, and equilibrate for 18 hours.

[0033] Step 3: Feed the moisture-balanced fibers into a rotary fiber cutter, set the cutting length to 30mm, and obtain white short rod-shaped fiber segments, which are then collected in a clean PE bag for later use.

[0034] Step 4: Turn on the cryogenic nitrogen supply system and adjust the nitrogen temperature at the outlet of the annular jet ring to -20±2℃ and the flow rate to 150Nm using the liquid nitrogen to room temperature nitrogen ratio mixing regulating valve. 3 The spray ring is installed 45mm directly below the pulverizer outlet at a spray angle of 45°. During formal production, 30mm fiber segments are evenly fed into the pulverizer at a feed rate of 10kg / h via a quantitative screw feeder. The pulverizer blades have an angle of θ=13°, with 18 Cr12MoV alloy tool steel blades (HRC 63) on each of the upper and lower rollers, a cutting edge width of 1.0mm, a radius of curvature R=10μm, a tooth gap δ=0.08mm, and a linear shear rate of 1m / s. The powder is enveloped by the annular nitrogen vortex within approximately 30ms of falling from the outlet, and is rapidly cooled from approximately 48℃ to approximately 5℃ within approximately 1.2s. Throughout the process, the outlet powder temperature is monitored to ensure it does not exceed 50℃, and the nitrogen nozzle temperature is maintained at -20±2℃. The entire feeding process is completed in approximately 9.8 hours of continuous operation, with no material blockage or blade entanglement observed during operation.

[0035] Step 5: The rapidly cooled powder is transported through a closed pipeline to a turbine air classifier (classifier wheel speed 2500 rpm, secondary air volume 5 m³ / h). 3 The system collects qualified powder with a particle size of 50–500 μm at a rate of 8 kg / h. The first classification has a pass rate of approximately 84%. Coarse particles with a particle size >500 μm are returned to the pulverizer via a dedicated powder return screw conveyor from an independent powder inlet at a rate of 8 kg / h for secondary pulverization, rapid cooling, and classification, yielding qualified powder and residual coarse particles. The residual coarse particles then undergo a third cycle to finally obtain qualified powder.

[0036] Step 6: Load the qualified powder into a sealed 316L stainless steel annealing chamber (200L volume, about 50kg per batch) in batches. After closing the feed valve, purge with 99.995% high-purity nitrogen at a flow rate of 20L / min for 15min. After confirming with a portable oxygen analyzer that the oxygen content at the exhaust port has dropped to <30ppm, adjust the nitrogen flow rate to 5L / min to maintain a slight positive pressure. After installing the top hydraulic pressure piston, operate according to the following three-stage procedure: Stage 1 (stress homogenization): Increase the temperature from room temperature (approximately 22°C) to 45°C at a rate of 2°C / min, apply a light pressure of 0.10 MPa, and maintain the temperature and pressure for 30 minutes. Stage 2 (chain segment re-insertion): Increase the temperature from 45°C to 65°C at a rate of 1°C / min, raise the pressure to 0.20 MPa, and maintain the temperature and pressure for 3 hours. Throughout the process, maintain the oxygen content in the chamber <30 ppm and the highest measured temperature not exceeding 67°C. Stage 3 (steady-state locking): Turn off the heating and turn on the cooling water coil, reduce the temperature from 65°C to 30°C at a rate of 0.5°C / min, and simultaneously slowly depressurize to atmospheric pressure at a rate of 0.005 MPa / min. The entire cooling-depressurization process takes approximately 70 minutes. Open the chamber and remove the material; a white, dense, fine powder is obtained.

[0037] Step 7: Take 50g of annealed powder and add it to a 1000mL three-necked flask. Add 500mL of acetone, and while stirring, add 5.0g of maleic anhydride (MAH) and 0.75g of azobisisobutyronitrile (AIBN) in sequence, stirring until completely dissolved. Install a reflux condenser at the middle neck of the three-necked flask and a thermometer and nitrogen inlet at the side neck. First, purge the air in the flask with nitrogen for 5 minutes to remove air from the flask. Then, place the flask in a 60℃ constant temperature oil bath and stir at 300rpm for 45 minutes. After the reaction is complete, remove the oil bath and allow it to cool naturally to room temperature. Collect the powder by vacuum filtration using a Buchner funnel. Wash the filter cake three times with 50mL of fresh acetone (stirring and filtering again after each wash) to remove unreacted MAH and AIBN residues. Finally, dry the powder in a 50℃ vacuum drying oven for 2 hours to obtain MAH-grafted powder.

[0038] Step 8: After premixing the MAH grafted powder with 0.3 wt% antioxidant 1010, feed it into a co-rotating twin-screw extruder (screw diameter 20 mm, L / D=40, screw speed 80 rpm) at a rate of 1.5 kg / h using a loss-in-weight feeder. The temperatures of each zone from the hopper to the die are set sequentially to 160℃, 165℃, 170℃, 175℃, 180℃, 175℃, and 170℃, with the die temperature set to 175℃. After the extruded strip is cooled in a water bath, it is granulated (3 mm in length) to obtain white, semi-transparent granules.

[0039] Example 4 A method for treating ultra-high molecular weight polyethylene waste includes the following steps: Step 1: Take 100kg of discarded bulletproof vest panels and manually sort them to remove non-UHMWPE impurities such as aramid threads, metal fasteners, fabric labels, and adhesive seals, obtaining approximately 98.6kg of pure UHMWPE fibers (sorting purity ≥99.5wt%). Cut the fibers into approximately 15cm × 15cm squares and place them in batches into an ultrasonic cleaner. Add 40℃ deionized water until completely submerged (liquid-to-material ratio approximately 8:1), and set the ultrasonic frequency to 35kHz and the power density to 0.8W / cm³. 2 The fibers were cleaned for 20 minutes, turning them over every 5 minutes to ensure even ultrasonic treatment on all sides, removing residual thermoplastic polyurethane matrix resin and oil stains from the fiber surface. After cleaning, the fibers were rinsed twice with clean deionized water and drained. Then, the fibers were spread out on a stainless steel mesh tray (thickness ≤ 3 cm) and placed in a vacuum drying oven. They were dried at 50°C and a vacuum degree ≤ 500 Pa for 5 hours until constant weight was achieved (two consecutive weighings were taken 30 minutes apart, with a mass difference < 0.05%).

[0040] Step 2: Spread the dried fibers evenly on a stainless steel mesh tray (leaving air gaps between layers), transfer them into a constant temperature and humidity chamber, set the temperature to 25℃ and the relative humidity to 30%, and equilibrate for 18 hours.

[0041] Step 3: Feed the moisture-balanced fibers into a rotary fiber cutter, set the cutting length to 30mm, and obtain white short rod-shaped fiber segments, which are then collected in a clean PE bag for later use.

[0042] Step 4: Turn on the cryogenic nitrogen supply system and adjust the nitrogen temperature at the outlet of the annular jet ring to -20±2℃ and the flow rate to 150Nm using the liquid nitrogen to room temperature nitrogen ratio mixing regulating valve. 3 The spray ring is installed 45mm directly below the pulverizer outlet at a spray angle of 45°. During formal production, 30mm fiber segments are evenly fed into the pulverizer at a feed rate of 10kg / h via a quantitative screw feeder. The pulverizer blades have an angle of θ=15°, with 18 Cr12MoV alloy tool steel blades (HRC 63) on each of the upper and lower rollers, a cutting edge width of 1.0mm, a radius of curvature R=10μm, a tooth gap δ=0.08mm, and a linear shear rate of 2m / s. The powder is enveloped by the annular nitrogen vortex within approximately 30ms of falling from the outlet, and is rapidly cooled from approximately 48℃ to approximately 5℃ within approximately 1.2s. Throughout the process, the outlet powder temperature is monitored to ensure it does not exceed 50℃, and the nitrogen nozzle temperature is maintained at -20±2℃. The entire feeding process is completed in approximately 9.8 hours of continuous operation, with no material blockage or blade entanglement observed during operation.

[0043] Step 5: The rapidly cooled powder is transported through a closed pipeline to a turbine air classifier (classifier wheel speed 2500 rpm, secondary air volume 5 m³ / h). 3The system collects qualified powder with a particle size of 50–500 μm at a rate of 8 kg / h. The first classification has a pass rate of approximately 84%. Coarse particles with a particle size >500 μm are returned to the pulverizer via a dedicated powder return screw conveyor from an independent powder inlet at a rate of 8 kg / h for secondary pulverization, rapid cooling, and classification, yielding qualified powder and residual coarse particles. The residual coarse particles then undergo a third cycle to finally obtain qualified powder.

[0044] Step 6: Load the qualified powder into a sealed 316L stainless steel annealing chamber (200L volume, about 50kg per batch) in batches. After closing the feed valve, purge with 99.995% high-purity nitrogen at a flow rate of 20L / min for 15min. After confirming with a portable oxygen analyzer that the oxygen content at the exhaust port has dropped to <30ppm, adjust the nitrogen flow rate to 5L / min to maintain a slight positive pressure. After installing the top hydraulic pressure piston, operate according to the following three-stage procedure: Stage 1 (stress homogenization): Increase the temperature from room temperature (approximately 22°C) to 45°C at a rate of 2°C / min, apply a light pressure of 0.10 MPa, and maintain the temperature and pressure for 30 minutes. Stage 2 (chain segment re-insertion): Increase the temperature from 45°C to 65°C at a rate of 1°C / min, raise the pressure to 0.20 MPa, and maintain the temperature and pressure for 3 hours. Throughout the process, maintain the oxygen content in the chamber <30 ppm and the highest measured temperature not exceeding 67°C. Stage 3 (steady-state locking): Turn off the heating and turn on the cooling water coil, reduce the temperature from 65°C to 30°C at a rate of 0.5°C / min, and simultaneously slowly depressurize to atmospheric pressure at a rate of 0.005 MPa / min. The entire cooling-depressurization process takes approximately 70 minutes. Open the chamber and remove the material; a white, dense, fine powder is obtained.

[0045] Step 7: Take 50g of annealed powder and add it to a 1000mL three-necked flask. Add 500mL of acetone, and while stirring, add 6.0g of maleic anhydride (MAH) and 0.75g of azobisisobutyronitrile (AIBN) in sequence, stirring until completely dissolved. Install a reflux condenser at the middle neck of the three-necked flask and a thermometer and nitrogen inlet at the side neck. First, purge the air in the flask with nitrogen for 5 minutes, then place the flask in a 60℃ constant temperature oil bath and stir at 300rpm for 45 minutes. After the reaction is complete, remove the oil bath and allow it to cool naturally to room temperature. Collect the powder by vacuum filtration using a Buchner funnel. Wash the filter cake three times with 50mL of fresh acetone (stirring and filtering again each time) to remove unreacted MAH and AIBN residues. Finally, dry the powder in a 50℃ vacuum drying oven for 2 hours to obtain MAH-grafted powder.

[0046] Step 8: After premixing the MAH grafted powder with 0.3 wt% antioxidant 1010, feed it into a co-rotating twin-screw extruder (screw diameter 20 mm, L / D=40, screw speed 80 rpm) at a rate of 1.5 kg / h using a loss-in-weight feeder. The temperatures of each zone from the hopper to the die are set sequentially to 160℃, 165℃, 170℃, 175℃, 180℃, 175℃, and 170℃, with the die temperature set to 175℃. After the extruded strip is cooled in a water bath, it is granulated (3 mm in length) to obtain white, semi-transparent granules.

[0047] Example 5 A method for treating ultra-high molecular weight polyethylene waste includes the following steps: Step 1: Take 100kg of discarded bulletproof vest panels and manually sort them to remove non-UHMWPE impurities such as aramid threads, metal fasteners, fabric labels, and adhesive seals, obtaining approximately 98.6kg of pure UHMWPE fibers (sorting purity ≥99.5wt%). Cut the fibers into approximately 15cm × 15cm squares and place them in batches into an ultrasonic cleaner. Add 40℃ deionized water until completely submerged (liquid-to-material ratio approximately 8:1), and set the ultrasonic frequency to 35kHz and the power density to 0.8W / cm³. 2 The fibers were cleaned for 20 minutes, turning them over every 5 minutes to ensure even ultrasonic treatment on all sides, removing residual thermoplastic polyurethane matrix resin and oil stains from the fiber surface. After cleaning, the fibers were rinsed twice with clean deionized water and drained. Then, the fibers were spread out on a stainless steel mesh tray (thickness ≤ 3 cm) and placed in a vacuum drying oven. They were dried at 50°C and a vacuum degree ≤ 500 Pa for 5 hours until constant weight was achieved (two consecutive weighings were taken 30 minutes apart, with a mass difference < 0.05%).

[0048] Step 2: Spread the dried fibers evenly on a stainless steel mesh tray (leaving air gaps between layers), transfer them into a constant temperature and humidity chamber, set the temperature to 25℃ and the relative humidity to 30%, and equilibrate for 18 hours.

[0049] Step 3: Feed the moisture-balanced fibers into a rotary fiber cutter, set the cutting length to 30mm, and obtain white short rod-shaped fiber segments, which are then collected in a clean PE bag for later use.

[0050] Step 4: Turn on the cryogenic nitrogen supply system and adjust the nitrogen temperature at the outlet of the annular jet ring to -20±2℃ and the flow rate to 150Nm using the liquid nitrogen to room temperature nitrogen ratio mixing regulating valve. 3The spray ring is installed 45mm directly below the pulverizer outlet at a spray angle of 45°. During formal production, 30mm fiber segments are evenly fed into the pulverizer at a feed rate of 10kg / h via a quantitative screw feeder. The pulverizer blades have an angle of θ=12°, with 18 Cr12MoV alloy tool steel blades (HRC 63) on each of the upper and lower rollers, a cutting edge width of 1.0mm, a radius of curvature R=10μm, a tooth gap δ=0.08mm, and a linear shear rate of 0.5m / s. The powder is enveloped by the annular nitrogen vortex within approximately 30ms of falling from the outlet, and rapidly cooled from approximately 48℃ to approximately 5℃ within approximately 1.2s. Throughout the process, the outlet powder temperature is monitored to ensure it does not exceed 50℃, and the nitrogen nozzle temperature is maintained at -20±2℃. The entire feeding process is completed in approximately 9.8 hours of continuous operation, with no material blockage or blade entanglement observed during operation.

[0051] Step 5: The rapidly cooled powder is transported through a closed pipeline to a turbine air classifier (classifier wheel speed 2500 rpm, secondary air volume 5 m³ / h). 3 The system collects qualified powder with a particle size of 50–500 μm at a rate of 8 kg / h. The first classification has a pass rate of approximately 84%. Coarse particles with a particle size >500 μm are returned to the pulverizer via a dedicated powder return screw conveyor from an independent powder inlet at a rate of 8 kg / h for secondary pulverization, rapid cooling, and classification, yielding qualified powder and residual coarse particles. The residual coarse particles then undergo a third cycle to finally obtain qualified powder.

[0052] Step 6: Load the qualified powder into a sealed 316L stainless steel annealing chamber (200L volume, about 50kg per batch) in batches. After closing the feed valve, purge with 99.995% high-purity nitrogen at a flow rate of 20L / min for 15min. After confirming with a portable oxygen analyzer that the oxygen content at the exhaust port has dropped to <30ppm, adjust the nitrogen flow rate to 5L / min to maintain a slight positive pressure. After installing the top hydraulic pressure piston, operate according to the following three-stage procedure: Stage 1 (stress homogenization): Increase the temperature from room temperature (approximately 22°C) to 45°C at a rate of 2°C / min, apply a light pressure of 0.10 MPa, and maintain the temperature and pressure for 30 minutes. Stage 2 (chain segment re-insertion): Increase the temperature from 45°C to 65°C at a rate of 1°C / min, raise the pressure to 0.20 MPa, and maintain the temperature and pressure for 3 hours. Throughout the process, maintain the oxygen content in the chamber <30 ppm and the highest measured temperature not exceeding 67°C. Stage 3 (steady-state locking): Turn off the heating and turn on the cooling water coil, reduce the temperature from 65°C to 30°C at a rate of 0.5°C / min, and simultaneously slowly depressurize to atmospheric pressure at a rate of 0.005 MPa / min. The entire cooling-depressurization process takes approximately 70 minutes. Open the chamber and remove the material; a white, dense, fine powder is obtained.

[0053] Step 7: Take 50g of annealed powder and add it to a 1000mL three-necked flask. Add 500mL of acetone, and while stirring, add 4.5g of maleic anhydride (MAH) and 0.75g of azobisisobutyronitrile (AIBN) in sequence, stirring until completely dissolved. Install a reflux condenser at the middle neck of the three-necked flask and a thermometer and nitrogen inlet at the side neck. First, purge the air in the flask with nitrogen for 5 minutes to remove air from the flask. Then, place the flask in a 60℃ constant temperature oil bath and stir at 300rpm for 45 minutes. After the reaction is complete, remove the oil bath and allow it to cool naturally to room temperature. Collect the powder by vacuum filtration using a Buchner funnel. Wash the filter cake three times with 50mL of fresh acetone (stirring and filtering again each time) to remove unreacted MAH and AIBN residues. Finally, dry the powder in a 50℃ vacuum drying oven for 2 hours to obtain MAH-grafted powder.

[0054] Step 8: After premixing the MAH grafted powder with 0.3 wt% antioxidant 1010, feed it into a co-rotating twin-screw extruder (screw diameter 20 mm, L / D=40, screw speed 80 rpm) at a rate of 1.5 kg / h using a loss-in-weight feeder. The temperatures of each zone from the hopper to the die are set sequentially to 160℃, 165℃, 170℃, 175℃, 180℃, 175℃, and 170℃, with the die temperature set to 175℃. After the extruded strip is cooled in a water bath, it is granulated (3 mm in length) to obtain white, semi-transparent granules.

[0055] Comparative Example 1: The difference from Example 1 is that a conventional parallel blade (θ=0°) is used in step 4, while the other process conditions and raw materials are exactly the same as in Example 1.

[0056] Comparative Example 2: The difference from Example 1 is that step 4, nitrogen quenching, is omitted, and the powder is naturally cooled to room temperature. All other process conditions and raw materials are exactly the same as in Example 1.

[0057] Comparative Example 3: The difference from Example 1 is that step 6, the annealing process, is omitted. All other process conditions and raw materials are exactly the same as in Example 1.

[0058] Comparative Example 4: The difference from Example 1 is that the annealing temperature in the second stage of step 6 is adjusted to 90°C, while the other process conditions and raw materials are exactly the same as in Example 1.

[0059] Performance testing: 1. Weight-average molecular weight, molecular weight distribution, and molecular weight loss rate testing: High-temperature gel permeation chromatography (GPC) was used for testing. The test solvent was chromatographically pure 1,2,4-trichlorobenzene, and the test temperature was set at 135℃. Narrow-distribution polystyrene standards were used for universal calibration. The mobile phase flow rate was controlled at 1.0 mL / min, the concentration of the test sample was 1.0 mg / mL, and the injection volume was 200 μL. The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the sample were obtained through testing, and the molecular weight distribution coefficient (PDI) was calculated. Based on the weight-average molecular weight of the sample and the weight-average molecular weight of the original fiber, the molecular weight loss rate of the sample was calculated using the following formula: Molecular weight loss rate (%) = (Original fiber Mw - Sample Mw) / Original fiber Mw × 100%.

[0060] 2. Crystallinity and Melting Temperature Test: Differential scanning calorimetry (DSC) was used for the test. The entire test was conducted under a high-purity nitrogen protective atmosphere with a nitrogen flow rate of 50 mL / min. The test procedure was as follows: the temperature was increased from room temperature to 200℃ at a heating rate of 10℃ / min, held at that temperature for 3 min to eliminate thermal history, then cooled to room temperature at a cooling rate of 10℃ / min, and finally heated to 200℃ again at a heating rate of 10℃ / min. The melting enthalpy of the sample was calculated from the melting peak area of ​​the secondary heating curve. The crystallinity of the sample was calculated based on the standard melting enthalpy of polyethylene with complete crystallization. At the same time, the peak temperature of the melting peak of the secondary heating curve was taken as the melting temperature of the sample.

[0061] 3. Particle size distribution test: A laser particle size analyzer was used for testing. Anhydrous ethanol was used as the dispersion medium. Before the test, the sample to be tested was placed in anhydrous ethanol and ultrasonically dispersed at a frequency of 40kHz for 5 minutes before being tested. The particle size distribution curve of the sample was obtained, and the median particle size D50 of the sample was recorded as the core evaluation index.

[0062] 4. Entanglement density recovery rate test: The test was conducted using a rotational rheometer with a 25mm diameter parallel plate fixture. The plate spacing was set to 1.0mm, and the test temperature was 180℃. The entire test was conducted under a high-purity nitrogen protective atmosphere. The test mode was dynamic frequency scanning, with a scanning angular frequency range of 0.01~100rad / s and a strain set to 1% (within the linear viscoelastic region confirmed by pre-experiments). The storage modulus plateau value of the sample was obtained through the test, and the entanglement density of the sample was calculated based on the rubber elasticity theory. The entanglement density recovery rate of the sample was calculated using the original fiber entanglement density as the baseline value (100%).

[0063] Table 1: As shown in Table 1, the weight-average molecular weight of the recycled powders prepared in Examples 1-5 of this invention remained in the range of 3.63 million to 3.72 million, with a molecular weight loss rate of only 2.1% to 4.5%, all significantly lower than 5%. The molecular weight distribution coefficient (PDI) remained between 3.2 and 3.3, which was basically consistent with the original fiber (PDI=3.2), indicating that the main chain structure of UHMWPE was completely preserved throughout the recycling process. The melting temperature was stable at 136.6 to 136.8℃, and the crystallinity was as high as 94.5% to 95.1%, which was higher than the 92.1% of the original fiber. This confirms that the three-step coupling process of unwinding-rapid cooling-annealing and re-insertion can promote the re-insertion of unwound chain segments into the lattice and form a more dense and ordered crystalline structure. The median particle size (D50) fell in the range of 260 to 310 μm, which met the particle size requirements for direct melt processing. The entanglement density recovery rate reached 88% to 92%, reaching the target range of 85% to 95% of the original fiber entanglement level, and can be directly processed by melt extrusion. Comparative Example 1, by adjusting the blade angle θ to 0° (i.e., using a conventional parallel blade), resulted in a sharp increase in molecular weight loss to 23.2%, a decrease in crystallinity to 84.8%, and an increase in PDI to 4.2. This demonstrates that the asymmetric wedge-shaped blade (θ = 12°~15°) used in this invention effectively prevents main chain impact breakage through a micro-shearing mechanism. Comparative Example 2, by omitting the nitrogen quenching process, resulted in a molecular weight loss to 8.9% and a decrease in entanglement density recovery to 71%. This demonstrates that the instantaneous quenching of nitrogen at the discharge port plays an irreplaceable role in locking amorphous structures and suppressing residual thermal pyrolysis. 3. Omitting the three-stage annealing process, although the molecular weight remained good (loss rate 2.9%), the entanglement density recovery rate was only 64% and the crystallinity was only 90.3%, proving that the three-stage pressure annealing is the core step to achieve chain segment reinsertion and entanglement density recovery; Comparative Example 4 raised the second-stage annealing temperature to 90°C, exceeding the safe process temperature window of UHMWPE, resulting in a molecular weight loss rate of 9.7% and a crystallinity drop to 87.0%, proving that the low-temperature annealing temperature range of 45°C to 65°C defined in this invention plays a key role in avoiding thermo-oxidative decomposition and maintaining the integrity of the molecular chain. In summary, this invention achieves high-fidelity recycling of UHMWPE waste fibers under mild conditions where the temperature does not exceed 70°C throughout the process, through the synergistic coupling of oblique angle micro-shearing, low-temperature nitrogen instantaneous quenching, and three-stage pressurized annealing. The recycled powder simultaneously achieves excellent levels in core indicators such as molecular weight, crystallinity, and entanglement density, and has the capability for direct melting processing. Compared with existing methods such as dissolution, high-temperature melting, mechanical crushing, and low-temperature embrittlement crushing, this invention achieves synergistic optimization in terms of maintaining molecular weight, protecting crystalline structure, and controlling processing costs.

[0064] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the essence and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating ultra-high molecular weight polyethylene waste, characterized in that, Includes the following steps: S1. Sorting and removing non-ultra-high molecular weight polyethylene impurities from the scrapped bulletproof vest panels to obtain pure ultra-high molecular weight polyethylene fibers; immersing the fibers in deionized water for ultrasonic cleaning, followed by rinsing, draining and vacuum drying; S2. Place the dried fibers in a constant temperature and humidity environment for equilibration treatment. S3. The balanced fibers are fed into a cutting machine and cut into short fiber segments; S4. The short fiber segments are fed into an angled micro-shear pulverizer for pulverization. The pulverizer adopts a roller-type multi-blade shearing structure with an asymmetrical wedge-shaped blade cross section and a blade cutting angle θ of 12° to 15°. At the same time, a low-temperature nitrogen gas flow is injected into the pulverizer outlet to instantly cool the produced powder. S5. Perform airflow classification and sieving on the powder after rapid cooling, collect qualified powder, and return the unqualified coarse particles to the pulverizer for recycling and pulverization. S6. The collected qualified powder is loaded into a sealed annealing chamber, high-purity nitrogen is introduced, and a three-stage annealing treatment is carried out under pressure and temperature conditions. Then, the powder is cooled and depressurized to obtain dense powder. The three-stage annealing process is as follows: In the first stage, the temperature is increased from room temperature to 45°C at a rate of 2°C / min, a light pressure of 0.10 MPa is applied, and the temperature and pressure are maintained for 30 min; In the second stage, the temperature is increased from 45°C to 65°C at a rate of 1°C / min, the pressure is increased to 0.20 MPa, and the temperature and pressure are maintained for 3 h. In the third stage, the temperature was reduced from 65℃ to 30℃ at a rate of 0.5℃ / min, while simultaneously depressurizing to atmospheric pressure at a rate of 0.005MPa / min. S7. Add the dense powder to acetone, then add maleic anhydride and azobisisobutyronitrile in sequence, and heat and stir the reaction under nitrogen protection. After the reaction is completed, filter and collect the powder, wash the filter cake with acetone, and finally vacuum dry to obtain the recovered powder. S8. The recycled powder is premixed with antioxidant and then fed into a twin-screw extruder for melt extrusion, cooling and pelletizing.

2. The method for treating ultra-high molecular weight polyethylene waste according to claim 1, characterized in that, In step 1, the purity of the sorted fibers is ≥99.5 wt%; The specific conditions for ultrasonic cleaning are as follows: adding deionized water at 40°C, a liquid-to-solid ratio of 8:1, an ultrasonic frequency of 35kHz, and a power density of 0.8W / cm³. 2 The cleaning time is 20 minutes; The vacuum drying conditions are as follows: drying at 50℃ and vacuum degree ≤500Pa for 5 hours until constant weight.

3. The method for treating ultra-high molecular weight polyethylene waste according to claim 1, characterized in that, In step 2, the conditions for the balancing treatment are: temperature set at 25°C, relative humidity set at 30%, and balancing treatment for 18 hours to reduce the fiber moisture content to below 0.01%.

4. The method for treating ultra-high molecular weight polyethylene waste according to claim 1, characterized in that, In step 3, the cutting machine cuts the fiber to a length of 30mm.

5. The method for treating ultra-high molecular weight polyethylene waste according to claim 1, characterized in that, In step 4, the temperature of the cryogenic nitrogen gas flow during the instantaneous quenching process is -20±2℃, and the flow rate is 150Nm³. 3 / h, so that the powder produced by pulverization is covered by nitrogen swirling within 30ms of falling, and is rapidly cooled from 48℃ to 5℃ within 1.2s.

6. The method for treating ultra-high molecular weight polyethylene waste according to claim 1, characterized in that, In step 6, the oxygen content in the annealing chamber is controlled to be <30ppm.

7. The method for treating ultra-high molecular weight polyethylene waste according to claim 1, characterized in that, In step 7, the amount of maleic anhydride used is 9-12% of the mass of the annealed powder.

8. The method for treating ultra-high molecular weight polyethylene waste according to claim 1, characterized in that, In step 8, the antioxidant is antioxidant 1010, and its addition amount is 0.3 wt% of the mass of the recovered powder.

9. The method for treating ultra-high molecular weight polyethylene waste according to claim 1, characterized in that, In step 8, the temperatures of each zone of the twin-screw extruder are set to 160℃, 165℃, 170℃, 175℃, 180℃, 175℃, and 170℃ respectively, and the die temperature is set to 175℃.

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