Preparation method of high-strength regenerated polyester staple fiber

Abstract

The invention relates to the technical field of regenerated polyester, in particular to a preparation method of high-strength regenerated polyester staple fibers. Comprising the following steps: preparing a nanocellulose-nickel porphyrin complexing agent; performing N / S co-doping and melt extrusion granulation on the coffee grounds; and carrying out depolymerization, polycondensation and melt spinning on the polyester waste. The nanocellulose is dissolved and uniformly distributed in the cellulose solvent, so that the uniformity and efficiency of subsequent modification are improved, and then the nanocellulose-nickel porphyrin complexing agent is generated with the tetra-p-carboxyl phenyl nickel porphyrin through a photo-thermal synergistic effect, so that ester group oxygen atoms can be activated in the polycondensation process, the ester exchange activation energy is reduced, and the polymerization efficiency is improved. The regenerated polyester staple fibers can be more easily subjected to subsequent graft polymerization reaction, can be kept wet in a melt and promote the stability of crystal nucleuses, are beneficial to improving the crystallinity and crystallization property of the regenerated polyester staple fibers, and can endow the regenerated polyester staple fibers with more excellent mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of recycled polyester, and specifically relates to a method for preparing high-strength recycled polyester staple fibers. Background Art

[0002] Recycled polyester staple fibers are environmentally friendly fibers made from waste polyester (PET) materials (such as bottle chips and textile scraps) through processes such as melting, filtering, and spinning. Their production can reduce the consumption of petroleum resources and reduce landfill pollution of waste. Polyester staple fibers have been widely used in fields such as clothing, home textiles, and geotextiles, but their application in high-value-added industrial scenarios (such as automotive seat belts and tire cords) is still limited by insufficient mechanical properties. Therefore, developing high-strength recycled polyester staple fibers has important industrial value and environmental significance.

[0003] Existing polyester recycling technologies mainly include physical recycling and chemical recycling. Physical recycling refers to obtaining relatively pure PET chips by subjecting recycled waste PET to simple processes such as sorting, cleaning, crushing, separation, and drying, and then directly using the PET chips for melt spinning. Physical recycling has high requirements for the composition and purity of PET waste, and there are problems such as a decrease in molecular weight caused by thermal degradation and hydrolysis during the processing, as well as more impurities caused by a simple separation process, resulting in a more serious decline in the performance of the produced recycled polyester fibers. Chemical recycling involves depolymerizing waste PET into monomers and then polymerizing them to form recycled polyester materials. It has a high recovery rate and high product purity, but due to multiple processing steps, there are also problems with poor mechanical properties. In order to enhance the mechanical properties of recycled polyester fibers, existing technologies mostly use methods such as filling inorganic nanoparticles and adjusting mechanical stretching parameters. However, inorganic nanoparticles are prone to problems such as uneven dispersion and poor alignment orientation, while mechanical stretching is prone to generating a skin-core structure, with limited improvement in mechanical properties. Summary of the Invention

[0004] In order to solve the above technical defects, the present invention has developed a method for preparing high-strength recycled polyester staple fibers. By increasing the crystallinity inside the recycled fibers and the alignment orientation of nanocellulose, the prepared recycled polyester staple fibers have excellent mechanical properties.

[0005] A method for preparing high-strength recycled polyester staple fibers includes the following steps: S1: Preparation of nanocellulose-nickel porphyrin composite agent React N-methylimidazole and n-butyl chloride by heating under reflux to obtain a cellulose solvent. Dissolve nanocellulose in the cellulose solvent, add it to a photoreaction kettle, add nickel tetrakis(carboxyphenyl) porphyrin under a nitrogen atmosphere, and then carry out a heating and light reaction. After centrifugal elution and separation, freeze-dry to obtain the nanocellulose-nickel porphyrin composite agent; S2: N / S co-doping and melt extrusion granulation of coffee grounds The coffee grounds are ground and ultrasonically treated with ammonium thiocyanate in water, then transferred to a reaction kettle for heating reaction. The filtrate is taken by filtration and dialyzed, and then freeze-dried and melt extruded and granulated together with diethyl (3,5-di-tert-butyl-4-hydroxybenzyl) phosphate and pentaerythritol tetrakis(2-mercaptoacetate) to obtain a reinforced masterbatch, which is stored in a dry environment; S3: Depolymerization, polycondensation and melt spinning of polyester waste The waste polyester fabric is subjected to alkali treatment, depolymerization, decolorization, filtration, taking the filtrate, cooling crystallization, suction filtration, taking the filter cake and drying to obtain ethylene glycol terephthalate. The nanocellulose-nickel porphyrin composite agent, antimony glycolate and ethylene glycol terephthalate are mixed for polycondensation to obtain a dry polyester. The dry polyester and the reinforced masterbatch are melt-blended and then treated in an electromagnetic field, and then spun to obtain high-strength recycled polyester staple fibers.

[0006] Further, the preparation of the nanocellulose-nickel porphyrin composite agent in step S1 includes the following steps: S1.1: N-methylimidazole and n-butyl chloride are mixed in a volume ratio of 1:(1.6 - 1.8) and added to a flask equipped with a reflux device. Heating reflux is carried out at 105 - 110 °C and 200 - 250 rpm for 20 - 24 hours until the reflux liquid in the reflux device is significantly reduced. Then the reaction solution is rotary evaporated to remove the unreacted n-butyl chloride, and cooled to room temperature to obtain a cellulose solvent; S1.2: Nanocellulose is added to the cellulose solvent in a mass ratio of 1:(60 - 80), and microwave treatment is carried out while stirring. The microwave power is controlled at 400 - 450 W until the nanocellulose is completely dissolved in the cellulose solvent to obtain a cellulose homogeneous solution; S1.3: 45 - 50 parts of the cellulose homogeneous solution are added to a photoreaction kettle. After introducing dry nitrogen to drain the air, 0.2 - 0.3 part of tetrakis(4-carboxyphenyl) nickel porphyrin is added. After heating to 60 - 65 °C, the UV-LED light source irradiator is turned on for irradiation, and at the same time, stirring is carried out at a stirring speed of 120 - 150 rpm. After 3 - 4 hours, the pressure is released to atmospheric pressure. 8 - 10 times the mass of deionized water is added to the reaction product and stirred evenly, and then placed in a centrifuge and centrifuged at a speed of 15000 - 16000 rpm for 10 - 15 minutes. The supernatant is discarded and the precipitate is collected. The obtained precipitate is centrifuged and washed with water, and the process is repeated 2 - 3 times. Then the finally obtained precipitate is freeze-dried at -40 °C to -45 °C for 10 - 12 hours to obtain the nanocellulose-nickel porphyrin composite agent.

[0007] Further, the N / S co-doping and melt extrusion granulation of coffee grounds in step S2 includes the following steps: S2.1: After removing impurities from 2 - 3 parts of coffee grounds, grind them, sieve through a 100 - 120 mesh sieve to obtain coffee ground powder. Place the coffee ground powder and ammonium thiocyanate in a container at a mass ratio of 1:(1 - 1.2), then add 15 - 20 times the mass of deionized water, ultrasonically treat at a frequency of 25 - 30 kHz for 8 - 10 minutes, and then transfer to a reaction kettle lined with polytetrafluoroethylene. Heat to 180 - 200 °C, keep warm for 10 - 12 hours, then filter through a 0.2 - 0.25 μm ceramic membrane. Fill the obtained solution into a dialysis bag with a molecular weight cut-off of 1000 - 1500 Da, and then dialyze in deionized water for 24 - 30 hours, changing the deionized water every 6 - 8 hours. After freeze-drying, obtain N / S co-doped carbon powder; S2.2: Mix diethyl 3,5 - di-tert-butyl-4-hydroxybenzylphosphonate, N / S co-doped carbon powder, and pentaerythritol tetrakis(2-mercaptoacetate) in a mass ratio of 1:(2 - 3):(0.6 - 0.8), feed them into a twin-screw extruder, and perform extrusion granulation at 150 - 160 °C and 150 - 200 rpm to obtain a reinforced masterbatch, and store it in a dry environment.

[0008] Further, the depolymerization, polycondensation, and melt spinning of polyester waste in step S3 include the following steps: S3.1: Immerse waste polyester fabric in an aqueous sodium hydroxide solution with a mass concentration of 1.5 - 2 g / L and 15 - 20 times the mass. Stir for 25 - 30 minutes and then take it out. Rinse it clean with deionized water and then dry it to obtain polyester waste. Mix the polyester waste, zinc acetate, and ethylene glycol in a mass ratio of 1:(0.01 - 0.03):(3 - 4) and place them in a container for depolymerization. Then filter, take the filtrate, raise the temperature and add activated carbon for decolorization, filter again, take the filtrate, cool and crystallize, filter by suction, take the filter cake and dry it to obtain ethylene glycol terephthalate; S3.2: Mix the nanocellulose-nickel porphyrin composite agent, antimony glycolate, and ethylene glycol terephthalate in a mass ratio of (8 - 10):(0.4 - 0.5):100, and then carry out a polycondensation reaction at 220 - 240 °C and 35 - 40 Pa for 2 - 2.5 hours to obtain regenerated polyester. Place the regenerated polyester in a vacuum rotary drum drying oven and dry it until the water content < 0.1% to obtain dry polyester; S3.3: Put the dry polyester and the reinforcing masterbatch into a screw extruder at a mass ratio of 100:(6 - 8), blend and melt them at 220 - 225 °C to obtain a melt. Place the melt in a uniform electromagnetic field in the vertical direction for 2 - 3 minutes, with the electromagnetic field intensity of 1.2 - 1.5 T to obtain an electromagnetically treated melt. Place the electromagnetically treated melt in a spinning box, adjust the temperature to 225 - 230 °C, the spinning speed to 1000 - 1200 rpm, and the component pressure to 20 - 22 MPa for spinning. At the same time, air-cool the high-temperature short fibers spun out for solidification to obtain high-strength recycled polyester staple fibers.

[0009] Further, in step S1.3, the light wavelength of the light source irradiator is 400 - 450 nm, and the light intensity is 45 - 50 mW / cm 2 .

[0010] Further, the depolymerization conditions in step S3.1 are depolymerization for 5 - 6 hours at 195 - 215 °C in a nitrogen atmosphere.

[0011] Further, the mass ratio of the amount of activated carbon added to the polyester waste in step S3.1 is 1:(1 - 1.5).

[0012] Further, the air-cooling speed of air-cooling solidification in step S3.3 is 3 - 4 m / s, and the air-cooling temperature is 35 - 40 °C.

[0013] Beneficial effects are: 1. In the present invention, nanocellulose is dissolved in a cellulose solvent obtained by heating and refluxing N-methylimidazole and n-butyl chloride to obtain a cellulose homogeneous solution, enabling the nanocellulose to dissolve and be evenly distributed in the solvent, improving the uniformity and efficiency of subsequent modification. Tetrakis(carboxyphenyl)nickel porphyrin is added to the cellulose homogeneous solution, and a nanocellulose-nickel porphyrin composite agent is generated through the synergistic action of light and heat. It can not only activate the ester group oxygen atoms during the polycondensation process, reduce the activation energy of transesterification, making it easier to participate in the subsequent graft polymerization reaction, but also maintain wetting in the melt, promote the stability of crystal nuclei, contribute to improving the crystallinity and crystallization properties of the recycled polyester staple fibers, and endow the recycled polyester staple fibers with better mechanical properties.

[0014] 2. The present invention uses coffee grounds and ammonium thiocyanate to perform ultrasonic treatment in water and then transfers them to a reaction kettle for heating reaction to obtain N / S co-doped carbon powder. Then, it is melt-extruded and granulated together with diethyl (3,5-di-tert-butyl-4-hydroxybenzyl) phosphate and pentaerythritol tetra(2-mercaptoacetate) to prepare a reinforcing masterbatch. Among them, the N / S co-doped carbon powder can form a hydrogen bond network with polyester to improve the tensile strength of recycled polyester staple fiber. The carbon powder and diethyl (3,5-di-tert-butyl-4-hydroxybenzyl) phosphate can also enhance the thermal stability of the system and prevent the destruction of system groups at high temperatures. Moreover, pentaerythritol tetra(2-mercaptoacetate) has a multi-ester group structure, which can enhance the viscosity of the melt and improve the system compatibility. In summary, the overall mechanical properties of recycled polyester staple fiber are further improved.

[0015] 3. The present invention prepares a nanocellulose-nickel porphyrin composite agent to endow nanocellulose with certain magnetism. Then, the melt obtained by blending and melting dry polyester and the reinforcing masterbatch is treated with a vertical electromagnetic field. By adjusting the magnitude of the electromagnetic field to 2-3 T and the electromagnetic field treatment time to 2-3 minutes, it can not only ensure the full lateral arrangement of nanocellulose in the melt but also avoid the unidirectional aggregation of nanocellulose, unify the orientation degree of nanocellulose inside the recycled polyester staple fiber, and make it uniformly arranged, thereby enhancing the mechanical properties of the recycled polyester staple fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flowchart of the preparation method of the high-strength recycled polyester staple fiber adopted in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] Example 1 A preparation method of high-strength recycled polyester staple fiber, as Figure 1 shown, includes the following steps: S1: Preparation of nanocellulose-nickel porphyrin composite agent S1.1: Mix N-methylimidazole and n-butyl chloride in a volume ratio of 1:1.6 and add them to a flask equipped with a reflux device. Heat and reflux at 105 °C and 200 rpm for 20 hours until the reflux liquid in the reflux device significantly decreases. Then, perform rotary evaporation on the reaction solution to remove the unreacted n-butyl chloride, and cool to room temperature to obtain a cellulose solvent; S1.2: Add nanocellulose to the cellulose solvent at a mass ratio of 1:60, and perform microwave treatment while stirring. Control the microwave power at 400 W until the nanocellulose is completely dissolved in the cellulose solvent to obtain a cellulose homogeneous solution; S1.3: Add 45 parts of the cellulose homogeneous solution to a photoreactor. After purging the air with dry nitrogen, add 0.2 part of nickel porphyrin with four carboxyphenyl groups. After heating to 60 °C, turn on the UV-LED light source irradiator for irradiation. The light wavelength is 400 nm, and the light intensity is 45 mW / cm 2 , while stirring at a speed of 120 rpm. After 3 hours, release the pressure to atmospheric pressure. Add 8 times the mass of deionized water to the reaction product and stir evenly. Then place it in a centrifuge and centrifuge at 15,000 rpm for 10 minutes. Discard the supernatant and collect the precipitate. Add water to the obtained precipitate for centrifugal elution, repeat 2 times. Then freeze-dry the finally obtained precipitate at -40 °C for 10 hours to obtain a nanocellulose-nickel porphyrin composite agent.

[0019] S2: N / S co-doping and melt extrusion granulation of coffee grounds S2.1: Remove impurities from 2 parts of coffee grounds, then grind them and pass through a 100-mesh sieve to obtain coffee ground powder. Place the coffee ground powder and ammonium thiocyanate in a container at a mass ratio of 1:1, then add 15 times the mass of deionized water. After ultrasonic treatment at a frequency of 25 kHz for 8 minutes, transfer it to a reaction kettle with a polytetrafluoroethylene inner lining, heat to 180 °C, and keep warm for 10 hours. Then filter through a 0.2-μm ceramic membrane. Load the obtained solution into a dialysis bag with a molecular weight cut-off of 1000 Da, and then dialyze it in deionized water for 24 hours, changing the deionized water every 6 hours. After freeze-drying, obtain N / S co-doped carbon powder; S2.2: Mix diethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, N / S co-doped carbon powder, and pentaerythritol tetra(2-mercaptoacetate) in a mass ratio of 1:2:0.6 and feed them into a twin-screw extruder. Perform extrusion granulation at 150 °C and 150 rpm to obtain a reinforced masterbatch, and store it in a dry environment.

[0020] S3: Depolymerization, polycondensation, and melt spinning of polyester waste S3.1: Immerse the waste polyester fabric in an aqueous sodium hydroxide solution with a mass concentration of 1.5 g / L and 15 times the mass of the fabric. Stir for 25 minutes, then take it out, rinse it thoroughly with deionized water and dry it to obtain polyester waste. Mix the polyester waste, zinc acetate and ethylene glycol in a mass ratio of 1:0.01:3 and place them in a container. Depolymerize at 195 °C for 5 hours under a nitrogen atmosphere. Then filter, take the filtrate, raise the temperature and add activated carbon for decolorization. The addition amount of activated carbon is in a mass ratio of 1:1 to the polyester waste. Filter again, take the filtrate, cool and crystallize, filter by suction, take the filter cake and dry it to obtain ethylene glycol terephthalate; S3.2: Mix the nanocellulose-nickel porphyrin composite agent, antimony glycolate and ethylene glycol terephthalate in a mass ratio of 8:0.4:100, and then carry out a polycondensation reaction at 220 °C and 35 Pa for 2 hours to obtain regenerated polyester. Place the regenerated polyester in a vacuum rotary drum drying oven and dry it until the water content < 0.1% to obtain dry polyester; S3.3: Put the dry polyester and the reinforcing masterbatch into a screw extruder in a mass ratio of 100:6, melt and blend them at 220 °C to obtain a melt. Place the melt in a uniform electromagnetic field in the vertical direction and process it for 2 minutes. The electromagnetic field strength is 1.2 T to obtain an electromagnetically treated melt. Place the electromagnetically treated melt in a spinning box, adjust the temperature to 225 °C, the spinning speed to 1000 rpm, and the component pressure to 20 MPa for spinning. At the same time, air-cool and solidify the high-temperature short fibers spun out. The air-cooling speed is 3 m / s and the air-cooling temperature is 35 °C to obtain high-strength regenerated polyester short fibers.

[0021] Example 2 A method for preparing high-strength regenerated polyester short fibers, as Figure 1 shown, includes the following steps: S1: Preparation of nanocellulose-nickel porphyrin composite agent S1.1: Mix N-methylimidazole and n-butyl chloride in a volume ratio of 1:1.8 and add them to a flask equipped with a reflux device. Heat and reflux at 105 °C and 200 rpm for 20 hours until the reflux liquid in the reflux device is significantly reduced. Then carry out rotary evaporation on the reaction solution to remove the unreacted n-butyl chloride, and cool to room temperature to obtain a cellulose solvent; S1.2: Add nanocellulose to the cellulose solvent in a mass ratio of 1:80, and carry out microwave treatment while stirring. Control the microwave power at 400 W until the nanocellulose is completely dissolved in the cellulose solvent to obtain a cellulose homogeneous solution; S1.3: Add 50 parts of the cellulose homogeneous solution into the photoreactor. After purging the air with dry nitrogen, add 0.3 part of nickel porphyrin with four carboxyphenyl groups. After heating to 60 °C, turn on the UV-LED light source irradiator for irradiation. The light wavelength is 400 nm and the light intensity is 45 mW / cm 2 , and at the same time, stir at a stirring speed of 120 rpm. After 3 hours, release the pressure to atmospheric pressure. Add 8 times the mass of deionized water to the reaction product and stir evenly. Then place it in a centrifuge and centrifuge at 15000 rpm for 10 minutes. Discard the supernatant and collect the precipitate. Add water to the obtained precipitate for centrifugal elution, repeat 2 times. Then freeze-dry the finally obtained precipitate at -40 °C for 10 hours to obtain the nanocellulose-nickel porphyrin composite agent.

[0022] S2: N / S co-doping of coffee grounds and melt extrusion granulation S2.1: Remove impurities from 3 parts of coffee grounds and then grind them. Pass through a 100-mesh sieve to obtain coffee ground powder. Place the coffee ground powder and ammonium thiocyanate in a container at a mass ratio of 1:1.2, and then add 15 times the mass of deionized water. Ultrasonically treat for 8 minutes at a frequency of 25 kHz, then transfer to a reaction kettle with a polytetrafluoroethylene inner liner, heat to 180 °C, keep warm for 10 hours, and then filter through a 0.2-μm ceramic membrane. Fill the obtained solution into a dialysis bag with a molecular weight cut-off of 1000 Da, and then place it in deionized water for dialysis for 24 hours, changing the deionized water every 6 hours. After freeze-drying, obtain N / S co-doped carbon powder; S2.2: Mix 3,5-di-tert-butyl-4-hydroxybenzyl diethyl phosphate, N / S co-doped carbon powder, and pentaerythritol tetra(2-mercaptoacetate) in a mass ratio of 1:3:0.6 and feed them into a twin-screw extruder. Extrude and granulate at 150 °C and 150 rpm to obtain the reinforced masterbatch, and store it in a dry environment.

[0023] S3: Depolymerization, polycondensation, and melt spinning of polyester waste S3.1: Immerse the waste polyester fabric in an aqueous sodium hydroxide solution with a mass concentration of 1.5 g / L and 20 times the mass. After stirring for 25 minutes, take it out, rinse it with deionized water and then dry it to obtain polyester waste. Mix the polyester waste, zinc acetate, and ethylene glycol in a mass ratio of 1:0.03:4 and place them in a container. Depolymerize at 195 °C for 5 hours under a nitrogen atmosphere, then filter, take the filtrate, heat up and add activated carbon for decolorization. The addition amount of activated carbon is 1:1.5 with the mass of the polyester waste. Then filter again, take the filtrate, cool and crystallize, filter by suction, take the filter cake and dry it to obtain ethylene glycol terephthalate; S3.2: Mix the nanocellulose-nickel porphyrin composite agent, antimony glycolate, and ethylene terephthalate in a mass ratio of 10:0.5:100, and then carry out a polycondensation reaction at 220°C and 35 Pa for 2 hours to obtain regenerated polyester. Place the regenerated polyester in a vacuum drum drying oven and dry it until the water content is <0.1% to obtain dried polyester. S3.3: Feed the dried polyester and the reinforcing masterbatch into a screw extruder in a mass ratio of 100:8, and melt-blend them at 220°C to obtain a melt. Place the melt in a uniform electromagnetic field in the vertical direction and process it for 2 minutes. The electromagnetic field strength is 1.2 T to obtain an electromagnetically treated melt. Place the electromagnetically treated melt in a spinning box, adjust the temperature to 225°C, the spinning speed to 1000 rpm, and the assembly pressure to 20 MPa for spinning. At the same time, air-cool the high-temperature short fibers spun out. The air-cooling speed is 3 m / s, and the air-cooling temperature is 35°C to obtain high-strength regenerated polyester staple fibers.

[0024] Example 3 A method for preparing high-strength regenerated polyester staple fibers, as Figure 1 shown, includes the following steps: S1: Preparation of nanocellulose-nickel porphyrin composite agent S1.1: Mix N-methylimidazole and n-butyl chloride in a volume ratio of 1:1.6 and add them to a flask equipped with a reflux device. Heat and reflux at 110°C and 250 rpm for 24 hours until the reflux liquid in the reflux device significantly decreases. Then, rotary evaporate the reaction solution to remove the unreacted n-butyl chloride, and cool it to room temperature to obtain a cellulose solvent. S1.2: Add nanocellulose to the cellulose solvent in a mass ratio of 1:60, and carry out microwave treatment while stirring. Control the microwave power at 450 W until the nanocellulose is completely dissolved in the cellulose solvent to obtain a cellulose homogeneous solution. S1.3: Add 45 parts of the cellulose homogeneous solution to a photoreactor. After purging the air with dry nitrogen, add 0.2 part of tetrakis(4-carboxyphenyl) nickel porphyrin. After heating to 65°C, turn on the UV-LED light source irradiator for irradiation. The light wavelength is 450 nm, and the light intensity is 50 mW / cm 2 , and stir at a stirring speed of 150 rpm at the same time. After 4 hours, release the pressure to atmospheric pressure. Add 10 times the mass of deionized water to the reaction product and stir evenly. Then, centrifuge it at a speed of 16,000 rpm for 15 minutes in a centrifuge. Discard the supernatant and collect the precipitate. Add water to the obtained precipitate for centrifugal elution, repeat 3 times. Then, freeze-dry the finally obtained precipitate at -45°C for 12 hours to obtain the nanocellulose-nickel porphyrin composite agent.

[0025] S2: N / S co-doping of coffee grounds and melt extrusion granulation S2.1: After removing impurities from 2 parts of coffee grounds, grind them and pass through a 120-mesh sieve to obtain coffee ground powder. Place the coffee ground powder and ammonium thiocyanate in a container at a mass ratio of 1:1, then add 20 times the mass of deionized water, ultrasonically treat for 10 minutes at a frequency of 30 kHz, transfer to a reaction kettle with a polytetrafluoroethylene lining, heat to 200 °C, keep warm for 12 hours, then filter through a 0.25-μm ceramic membrane, put the obtained solution into a dialysis bag with a molecular weight cut-off of 1500 Da, then place it in deionized water for dialysis for 30 hours, change the deionized water every 8 hours, and obtain N / S co-doped carbon powder after freeze-drying; S2.2: Mix diethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, N / S co-doped carbon powder, and pentaerythritol tetra(2-mercaptoacetate) in a mass ratio of 1:2:0.8 and feed them into a twin-screw extruder, and carry out extrusion granulation at 160 °C and 200 rpm to obtain enhanced masterbatch, and store it in a dry environment.

[0026] S3: Depolymerization, polycondensation, and melt spinning of polyester waste S3.1: Immerse waste polyester fabric in an aqueous sodium hydroxide solution with a mass concentration of 2 g / L and 15 times the mass, stir for 30 minutes and then take it out, rinse it with deionized water and dry it to obtain polyester waste. Mix polyester waste, zinc acetate, and ethylene glycol in a mass ratio of 1:0.01:3 and place them in a container, depolymerize at 215 °C for 6 hours in a nitrogen atmosphere, then filter, take the filtrate, raise the temperature and add activated carbon for decolorization, the addition amount of activated carbon is in a mass ratio of 1:1 to the mass of polyester waste, then filter again, take the filtrate, cool and crystallize, filter by suction, take the filter cake and dry it to obtain ethylene glycol terephthalate; S3.2: Mix nanocellulose-nickel porphyrin composite agent, antimony glycolate, and ethylene glycol terephthalate in a mass ratio of 8:0.4:100, and then carry out a polycondensation reaction for 2.5 hours under the conditions of 240 °C and 40 Pa to obtain regenerated polyester. Place the regenerated polyester in a vacuum rotary drum drying oven and dry it until the water content < 0.1% to obtain dry polyester; S3.3: Put dry polyester and enhanced masterbatch into a screw extruder at a mass ratio of 100:6, melt and blend them at 225 °C to obtain a melt. Place the melt in a uniform electromagnetic field in the vertical direction and treat it for 3 minutes, the electromagnetic field strength is 1.5 T, to obtain an electromagnetically treated melt. Place the electromagnetically treated melt in a spinning box, adjust the temperature to 230 °C, the spinning speed to 1200 rpm, and the component pressure to 22 MPa for spinning. At the same time, air-cool and solidify the high-temperature short fibers spun out, the air-cooling speed is 4 m / s, and the air-cooling temperature is 40 °C, to obtain high-strength regenerated polyester short fibers.

[0027] Comparative Example 1 A preparation method of high-strength regenerated polyester staple fiber, which is different from Example 1 in that nano-cellulose nickel porphyrin composite agent is not added in step S3.2 to obtain dry polyester, and the rest of the steps are the same as those in Example 1 to obtain regenerated polyester staple fiber.

[0028] Comparative Example 2 A preparation method of high-strength regenerated polyester staple fiber, which is different from Example 1 in that the reinforcing masterbatch is not added in step S3.3 to obtain regenerated polyester staple fiber, and the rest of the steps are the same as those in Example 1.

[0029] Comparative Example 3 A preparation method of high-strength regenerated polyester staple fiber, which is different from Example 1 in that N / S co-doped carbon powder is not added in step S3.3 to obtain the reinforcing masterbatch, and the rest of the steps are the same as those in Example 1.

[0030] Comparative Example 4 A preparation method of high-strength regenerated polyester staple fiber, which is different from Example 1 in that pentaerythritol tetrakis(2-mercaptoacetate) is not added in step S2.2 to obtain the reinforcing masterbatch, and the rest of the steps are the same as those in Example 1.

[0031] Comparative Example 5 A preparation method of high-strength regenerated polyester staple fiber, which is different from Example 1 in that the melt is not subjected to electromagnetic field treatment in step S3.3, and the melt is directly placed in the spinning box for spinning to obtain regenerated polyester staple fiber, and the rest of the steps are the same as those in Example 1.

[0032] Experiment 1: Take the high-strength regenerated polyester staple fibers prepared in Examples 1-3 and the regenerated polyester staple fibers prepared in Comparative Examples 1-5 as samples, and test the mechanical properties of the regenerated polyester fibers according to the standard of GB / T14337-2008 "Determination of Single Fiber Breaking Strength and Elongation at Break of Chemical Fibers". Three samples are taken for each sample to test the tensile strength, and three samples are taken to test the elongation at break, and the test results are averaged, as shown in Table 1.

[0033] Table 1: Mechanical properties of high-strength regenerated polyester staple fiber

[0034] It can be seen from the data of Examples 1-3 in Table 1 that the high-strength regenerated polyester staple fibers prepared in the examples of the present application have high tensile strength and relatively high elongation at break, which can prove that they have good mechanical properties and high strength; It can be seen from Comparative Example 1 that when preparing dry polyester without adding the nanocellulose-nickel porphyrin composite agent, the mechanical properties of the finally prepared regenerated polyester staple fibers are significantly decreased. It can be proved that preparing the nanocellulose-nickel porphyrin composite agent and adding it into the polycondensation reaction to prepare polyester can endow the regenerated polyester staple fibers with better mechanical properties.

[0035] It can be seen from Comparative Examples 2-4 that without adding the reinforcing masterbatch, and without adding N / S co-doped carbon powder and pentaerythritol tetrakis(2-mercaptoacetate) during the preparation of the masterbatch will lead to a decrease in the mechanical properties of the regenerated fibers. It can be proved that preparing the reinforcing masterbatch can improve the mechanical properties of the regenerated polyester staple fibers, and the N / S co-doped carbon powder and pentaerythritol tetrakis(2-mercaptoacetate) in the reinforcing masterbatch play a key role in improving the mechanical properties; It can be seen from Comparative Example 5 that removing the electromagnetic field treatment of the melt will lead to a decrease in the mechanical properties of the regenerated polyester staple fibers, indicating that the uniform and vertical electromagnetic field treatment of the melt helps the nanocellulose to be fully arranged horizontally in the melt, thereby improving the mechanical properties of the regenerated polyester staple fibers.

[0036] The above embodiments are only illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A preparation method of high-strength regenerated polyester staple fiber, characterized in that, It includes the following steps: S1: Preparation of nanocellulose-nickel porphyrin composite N-methylimidazole and n-butyl chloride are subjected to heating reflux reaction to obtain a cellulose solvent. Nanocellulose is dissolved in the cellulose solvent and then added to a photoreaction kettle. Tetrakis(4-carboxyphenyl)nickel porphyrin is added under a nitrogen atmosphere, and then heating and light reaction are carried out. After centrifugation, elution and separation, freeze-drying is carried out to obtain the nanocellulose-nickel porphyrin composite; S2: N / S co-doping of coffee grounds and melt extrusion granulation Coffee grounds are ground and ultrasonically treated with ammonium thiocyanate in water, then transferred to a reaction kettle for heating reaction. The filtrate is taken by filtration and dialyzed. After freeze-drying, it is melt extruded and granulated together with diethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate and pentaerythritol tetrakis(2-mercaptoacetate) to obtain a reinforced masterbatch, which is stored in a dry environment; S3: Depolymerization, polycondensation and melt spinning of polyester waste Waste polyester fabric is subjected to alkali treatment, depolymerization, decolorization, filtration, taking the filtrate, cooling crystallization, suction filtration, taking the filter cake and drying to obtain ethylene glycol terephthalate. The nanocellulose-nickel porphyrin composite, antimony glycolate and ethylene glycol terephthalate are mixed for polycondensation to obtain dry polyester. The dry polyester and the reinforced masterbatch are melt blended and then treated in an electromagnetic field, and then spun to obtain high-strength regenerated polyester staple fibers.

2. The preparation method of a high-strength regenerated polyester staple fiber according to claim 1, characterized in that, The preparation of the nanocellulose-nickel porphyrin composite in step S1 includes the following steps: S1.1: N-methylimidazole and n-butyl chloride are mixed in a volume ratio of 1:(1.6-1.8) and added to a flask equipped with a reflux device. Heating reflux is carried out at 105-110 °C and 200-250 rpm for 20-24 hours until the reflux liquid in the reflux device is significantly reduced. Then the reaction solution is rotary evaporated to remove the unreacted n-butyl chloride, and cooled to room temperature to obtain a cellulose solvent; S1.2: Nanocellulose is added to the cellulose solvent in a mass ratio of 1:(60-80), and microwave treatment is carried out while stirring. The microwave power is controlled at 400-450 W until the nanocellulose is completely dissolved in the cellulose solvent to obtain a cellulose homogeneous solution; S1.3: 45-50 parts of the cellulose homogeneous solution are added to a photoreaction kettle. After purging the air with dry nitrogen, 0.2-0.3 parts of tetrakis(4-carboxyphenyl)nickel porphyrin are added. After heating to 60-65 °C, the UV-LED light source irradiator is turned on for irradiation, and at the same time, stirring is carried out at a stirring speed of 120-150 rpm. After 3-4 hours, the pressure is released to normal pressure. 8-10 times the mass of deionized water is added to the reaction product and stirred evenly, and then placed in a centrifuge and centrifuged at a speed of 15000-16000 rpm for 10-15 minutes. The supernatant is discarded and the precipitate is collected. The obtained precipitate is centrifuged and eluted with water, and the operation is repeated 2-3 times. Then the finally obtained precipitate is freeze-dried at -40 °C to -45 °C for 10-12 hours to obtain the nanocellulose-nickel porphyrin composite.

3. The preparation method of a high-strength regenerated polyester staple fiber according to claim 2, characterized in that, The N / S co-doping of coffee grounds and melt extrusion granulation in step S2 includes the following steps: S2.1: After removing impurities from 2 - 3 parts of coffee grounds, grind them, sieve through a 100 - 120 mesh sieve to obtain coffee ground powder. Place the coffee ground powder and ammonium thiocyanate in a container at a mass ratio of 1:(1 - 1.2), then add 15 - 20 times the mass of deionized water, perform ultrasonic treatment at a frequency of 25 - 30 kHz for 8 - 10 minutes, and then transfer it to a reaction kettle lined with polytetrafluoroethylene. Heat it to 180 - 200 °C, keep it warm for 10 - 12 hours, then filter through a 0.2 - 0.25 μm ceramic membrane. Load the obtained solution into a dialysis bag with a molecular weight cut-off of 1000 - 1500 Da, and then dialyze it in deionized water for 24 - 30 hours, changing the deionized water every 6 - 8 hours. After freeze-drying, obtain N / S co-doped carbon powder; S2.2: Mix diethyl 3,5 - di-tert-butyl-4-hydroxybenzylphosphonate, N / S co-doped carbon powder, and pentaerythritol tetra(2-mercaptoacetate) in a mass ratio of 1:(2 - 3):(0.6 - 0.8), and feed them into a twin-screw extruder. Perform extrusion granulation at 150 - 160 °C and 150 - 200 rpm to obtain the reinforced masterbatch, and store it in a dry environment.

4. The preparation method of a high-strength regenerated polyester staple fiber according to claim 3, wherein, Step S3 Depolymerization, polycondensation, and melt spinning of polyester waste, including the following steps: S3.1: Immerse the waste polyester fabric in an aqueous sodium hydroxide solution with a mass concentration of 1.5 - 2 g / L and 15 - 20 times the mass. Stir for 25 - 30 minutes and then take it out. Rinse it thoroughly with deionized water and then dry it to obtain polyester waste. Mix the polyester waste, zinc acetate, and ethylene glycol in a mass ratio of 1:(0.01 - 0.03):(3 - 4) in a container for depolymerization, then filter, take the filtrate, raise the temperature and add activated carbon for decolorization, then filter again, take the filtrate, cool and crystallize, perform suction filtration, take the filter cake and dry it to obtain ethylene glycol terephthalate; S3.2: Mix the nanocellulose-nickel porphyrin composite agent, antimony glycolate, and ethylene glycol terephthalate in a mass ratio of (8 - 10):(0.4 - 0.5):100, and then carry out a polycondensation reaction at 220 - 240 °C and 35 - 40 Pa for 2 - 2.5 hours to obtain the regenerated polyester. Place the regenerated polyester in a vacuum rotary drum drying oven and dry it until the water content < 0.1% to obtain the dried polyester; S3.3: Feed the dried polyester and the reinforced masterbatch into a screw extruder at a mass ratio of 100:(6 - 8), and carry out co-melting and blending at 220 - 225 °C to obtain a melt. Place the melt in a uniform electromagnetic field in the vertical direction for 2 - 3 minutes, with the electromagnetic field intensity of 1.2 - 1.5 T to obtain the electromagnetically treated melt. Place the electromagnetically treated melt in a spinning box, adjust the temperature to 225 - 230 °C, the spinning speed to 1000 - 1200 rpm, and the component pressure to 20 - 22 MPa for spinning. At the same time, perform air cooling and solidification on the spun high-temperature short fibers to obtain high-strength regenerated polyester short fibers.

5. The preparation method of a high-strength regenerated polyester staple fiber according to claim 2, characterized in that, In step S1.3, the illumination wavelength of the light source irradiator is 400 - 450 nm, and the illumination intensity is 45 - 50 mW / cm 2 .

6. The preparation method of a high-strength regenerated polyester staple fiber according to claim 4, characterized in that The conditions for depolymerization in step S3.1 are depolymerization for 5 - 6 hours in a nitrogen atmosphere at 195 - 215 °C.

7. The preparation method of a high-strength regenerated polyester staple fiber according to claim 4, characterized in that, In step S3.1, the mass ratio of the amount of activated carbon added to the mass of polyester waste is 1:(1 - 1.5).

8. The preparation method of a high-strength recycled polyester staple fiber according to claim 4, characterized in that, In step S3.3, the air cooling rate for air cooling and curing is 3 - 4 m / s, and the air cooling temperature is 35 - 40 °C.

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