A polyester material based on rpet glycolysis products and a method for its preparation

Abstract

This invention discloses a polyester material based on rPET glycolysis products and its preparation method, belonging to the field of rPET recycling technology. The method includes the following steps: crushing rPET and subjecting it to a cooling thermal cycling pretreatment; glycolytic degradation of rPET; purification of crude glycolysis products through multi-stage filtration to obtain purified glycolysis products; sequential addition of functional comonomers and crosslinking aids for reaction; melting, extrusion, and granulation to obtain recycled polyester material. This invention uses a ternary metal salt-coordinated eutectic solvent and dopamine-grafted chitosan / polyvinyl alcohol-modified mica powder to prepare a composite catalyst, effectively improving the yield of the target product. The composite catalyst prepared by this invention can improve its cycle stability and significantly reduce catalyst consumption costs in the production process.

Description

Technical Field

[0001] This invention relates to the field of rPET recycling technology, specifically to a polyester material based on rPET glycolysis products and its preparation method. Background Technology

[0002] Glycolysis is one of the main chemical recycling pathways for improving the reuse value of recycled PET (rPET). In this process, post-consumer PET waste undergoes a controlled glycolysis reaction to produce a mixture mainly composed of bis(2-hydroxyethyl) terephthalate (BHET) monomers and containing low molecular weight oligomers (with a degree of polymerization mainly of 2-5).

[0003] The depolymerization mechanism of rPET is as follows: In the initial stage of the reaction, the PET macromolecular chain dissociates under the swelling effect of excess ethylene glycol, generating oligomers with terminal hydroxyl groups. Subsequently, the depolymerization process is gradually dominated by transesterification, and the oligomers are further degraded into BHET through a chain reaction.

[0004] It is important to note that when the residence time of BHET in the reaction system exceeds a critical threshold, the rate of the reverse reaction (repolymerization) accelerates significantly, affecting the yield of the target product. Furthermore, most existing catalysts have poor recyclability, increasing catalyst consumption costs during production. Therefore, developing a catalytic system that combines high selectivity with high recyclability to efficiently suppress the reverse reaction during depolymerization is of great practical significance for improving the product yield of PET glycolysis.

[0005] Furthermore, due to the poor compatibility between existing crosslinking auxiliaries and the recycled polyester reaction system, it is difficult to construct a stable and uniform molecular crosslinking structure in the system, which means that there is still room for improvement in the mechanical strength properties of recycled polyester materials, making it difficult to achieve high-value utilization.

[0006] Based on this, the present invention designs a polyester material based on rPET glycolysis products and its preparation method to solve the above problems. Summary of the Invention

[0007] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a polyester material based on rPET glycolysis products and its preparation method.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a polyester material based on rPET glycolysis products includes the following steps: Step 1: After crushing rPET, perform a cooling thermal circulation pretreatment; Step 2: Glycolytic degradation of rPET A composite catalyst was prepared by combining a ternary metal salt-coordinated eutectic solvent DMTHPM / Ace-Zn(OAc)2 with dopamine-grafted chitosan / polyvinyl alcohol-modified mica powder. The catalyst was used as a glycolytic agent to degrade pretreated rPET through glycolytic degradation. The method for preparing the dopamine-grafted chitosan / polyvinyl alcohol modified mica powder is as follows: (1) Preparation of dopamine-grafted chitosan: Dissolve 50-60 parts by weight of chitosan in a 1-3% dilute acetic acid aqueous solution and stir until completely dissolved to prepare a 2-5% chitosan acetic acid solution; add 16-25 parts by weight of dopamine hydrochloride to the chitosan acetic acid solution, adjust the pH to 8.0-8.5, stir at 30-40℃ in the dark for 4-6 hours to obtain a dopamine-grafted chitosan solution; (2) Add 40-70 parts by weight of polyvinyl alcohol (PVA) to the dopamine-grafted chitosan solution and stir at 60-70℃ for 20-30 min to obtain a dopamine-grafted chitosan / polyvinyl alcohol composite solution. (3) Add nano-sized mica powder to dopamine-grafted chitosan / polyvinyl alcohol composite liquid, control the solid-liquid ratio to 1:4-8, and stir at 50-60℃ for 2-4 hours; (4) Filtration: The solid material is washed with deionized water until neutral, and then dried to obtain dopamine-grafted chitosan / polyvinyl alcohol modified mica powder. Step 3: The crude sugar glycolysis product is purified by multi-stage filtration to obtain purified glycolysis product; Step 4: Add the functional comonomer and crosslinking agent sequentially, and proceed with the reaction; Step 5: Melt, extrude, and granulate to obtain recycled polyester material.

[0009] Furthermore, step one specifically involves: crushing the recycled rPET raw material and passing it through an 80-120 mesh sieve; then heating the rPET particles to 80-100℃ and holding them at that temperature for 12-18 minutes, followed by cooling them down to 10-15℃ using a combination of water and air cooling and holding them at that temperature for 20-25 minutes, repeating this cycle 3-5 times.

[0010] Furthermore, in step one, the cooling water temperature is 5-8℃, and the flow rate is 0.8-1.5m³ / h. 3 / h; air temperature 0-5℃, wind speed 1.2-2.0m / s, relative humidity ≤30%.

[0011] Furthermore, in step two, the glycolysis reaction conditions are: rPET 6.0-6.5g, composite catalyst 0.07-0.1g, glycolysis agent dosage 30-40g, reaction temperature 178-182℃, and reaction time 25-30min.

[0012] Furthermore, in step two, the glycolytic agent is one or more of ethylene glycol, diethylene glycol, and propylene glycol.

[0013] Furthermore, in step two, the preparation method of the composite catalyst is as follows: (1) Disperse 35-48 parts by weight of ternary metal salt coordination eutectic solvent DMTHPM / Ace-Zn(OAc)2 in anhydrous ethanol to prepare an active dispersion with a mass concentration of 15-22%; (2) Add 60-85 parts by weight of dopamine-grafted chitosan / polyvinyl alcohol modified mica powder to the above active dispersion and stir at 40-60℃ for 1-1.5h; (3) The resulting mixture was distilled under reduced pressure at 60-80℃, and then dried and granulated to obtain the composite catalyst.

[0014] Furthermore, step three specifically involves: purifying the crude sugar glycolysis product through multi-stage filtration: first, filtering through a 200-mesh filter cloth, and then filtering through an ultrafiltration membrane with a molecular weight cutoff of 500-1000 Da to obtain the purified glycolysis product.

[0015] Furthermore, in step four, the purified glycolysis products are transferred to a melting reactor, nitrogen gas is introduced, and the reactor is heated to 240-255°C to completely melt the glycolysis products. Then, functional comonomers are added, with the amount of functional comonomers being 5-15% of the mass of the purified glycolysis products. The stirring speed is adjusted to 300-350 r / min, and the reaction is carried out at a constant temperature of 240-255°C for 2-2.5 h to ensure that the functional comonomers react fully with the glycolysis products. In step four, the functional comonomer is one or more of adipic acid, polyethylene glycol, and 1,4-butanediol.

[0016] Furthermore, in step four, a grafting-modified crosslinking aid is added. The amount of grafting-modified crosslinking aid added is 2.5-5% of the mass of the purified glycolysis product. The reaction temperature is 220-225℃, the stirring rate is 250-350r / min, and the reaction is carried out at a constant temperature for 40-60min to construct a stable and uniform molecular crosslinking network. The preparation method of the graft-modified crosslinking aid is as follows: maleic anhydride, methyl acrylate and benzoyl peroxide (BPO) are added to toluene solvent at a mass ratio of 4-6:2-3:0.1-0.3 and stirred until completely dissolved; under nitrogen protection, the mixture is heated to 80-83℃ and refluxed for 5-7 hours; after the reaction, the toluene solvent is removed by vacuum distillation to obtain the graft copolymer; the graft copolymer is mixed with vinyltriethoxysilane at a mass ratio of 3-5:1, deionized water is added in an amount of 2-5% of the mass of vinyltriethoxysilane, and the mixture is stirred at 60-70℃ for 2-3 hours to obtain the graft-modified crosslinking aid.

[0017] To better achieve the objectives of this invention, this invention also provides a polyester material based on rPET glycolysis products prepared according to the method described above.

[0018] Compared with the prior art, the beneficial effects of this invention are as follows: 1. This invention uses a ternary metal salt coordination eutectic solvent and dopamine-grafted chitosan / polyvinyl alcohol modified mica powder to prepare a composite catalyst. The PET conversion rate can reach 100% and the BHET yield can reach 90.1%, which effectively improves the yield of the target product and solves the problem of product quality decline caused by the reverse reaction.

[0019] 2. The composite catalyst prepared by this invention can improve its cycle stability. After being recycled 10 times, the PET conversion rate can still reach 93.6% and the BHET yield can still reach 80.3%, which significantly reduces the catalyst consumption cost in the production process.

[0020] 3. This invention employs a graft-modified crosslinking agent, which can construct a stable and uniform molecular crosslinking network in the reaction system. Combined with a composite catalyst, this results in recycled polyester materials with excellent mechanical properties, achieving a tensile strength of up to 61.3 MPa and an impact strength of 12.2 kJ·m. 2 This effectively realizes the high-value utilization of recycled polyester materials. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Example 1: A method for preparing polyester material based on rPET glycolysis products, comprising the following steps: Step 1: After crushing rPET, perform a cooling thermal circulation pretreatment; Specifically, the recycled rPET raw material is crushed and passed through an 80-mesh sieve; then the rPET particles are first heated to 80°C and kept at that temperature for 18 minutes, and then cooled to 10°C by a combination of water cooling and air cooling and kept at that temperature for 25 minutes. This process is repeated 5 times. The cooling water temperature is 5℃ and the flow rate is 0.8m³ / h. 3 / h; air temperature 0℃, wind speed 1.2m / s, relative humidity 30%; Step 2: Glycolytic degradation of rPET A composite catalyst was prepared by combining a ternary metal salt-coordinated eutectic solvent DMTHPM / Ace-Zn(OAc)2 (1,2-dimethyl-1,4,5,6-tetrahydropyrimidine / acetamide-zinc acetate) with dopamine-grafted chitosan / polyvinyl alcohol-modified mica powder. The pretreated rPET was then subjected to glycolytic degradation using glycolytic agent (ethylene glycol) as the reaction medium. The glycolysis reaction conditions were: 6g rPET, 0.08g composite catalyst, 30g ethylene glycol, reaction temperature 178℃, reaction time 30min, PET conversion rate 100%, and BHET yield 96.7%. After 10 cycles of use, the composite catalyst achieved a PET conversion rate of 96.3% and a BHET yield of 88.9%.

[0023] Among them, the ternary metal salt coordination eutectic solvent DMTHPM / Ace-Zn(OAc)2 was prepared by Jiang Yuan et al. using the design of ternary metal salt coordination eutectic solvents and the study of their catalytic performance in PET glycolysis. The method for preparing the dopamine-grafted chitosan / polyvinyl alcohol modified mica powder is as follows: (1) Preparation of dopamine-grafted chitosan: Dissolve 50 parts by weight of chitosan in a 1% dilute acetic acid aqueous solution and stir until completely dissolved to prepare a 2% chitosan acetic acid solution; add 16 parts by weight of dopamine hydrochloride to the chitosan acetic acid solution, adjust the pH to 8.0, stir at 30°C in the dark for 6 hours to obtain a dopamine-grafted chitosan solution; (2) Add 40 parts by weight of polyvinyl alcohol (PVA) to the dopamine-grafted chitosan solution and stir at 60°C for 30 min to obtain a dopamine-grafted chitosan / polyvinyl alcohol composite solution. (3) Add nano-sized mica powder to dopamine-grafted chitosan / polyvinyl alcohol composite liquid, control the solid-liquid ratio to 1:4, and stir at 50℃ for 4 hours; (4) Filtration: The solid material is washed with deionized water until neutral, and then dried to obtain dopamine-grafted chitosan / polyvinyl alcohol modified mica powder. The preparation method of the composite catalyst is as follows: (1) 35 parts by weight of ternary metal salt coordination eutectic solvent DMTHPM / Ace-Zn(OAc)2 were dispersed in anhydrous ethanol to prepare an active dispersion with a mass concentration of 15%. (2) Add 60 parts by weight of dopamine-grafted chitosan / polyvinyl alcohol modified mica powder to the above active dispersion and stir at 40°C for 1.5 h; (3) The resulting mixture was distilled under reduced pressure at 60°C, and then dried and granulated to obtain the composite catalyst.

[0024] Step 3: Purification of crude sugar glycolysis products through multi-stage filtration: The crude sugar glycolysis products are purified through multi-stage filtration: first, they are filtered through a 200-mesh filter cloth, and then through an ultrafiltration membrane (molecular weight cutoff 500-1000 Da) to obtain purified glycolysis products. Step 4: Add functional comonomers; The purified glycolysis products were transferred to a melting reactor, nitrogen gas was introduced and the mixture was heated to 240°C to completely melt the glycolysis products. Then, a functional comonomer (adipic acid) was added, with the amount of functional comonomer added being 5% of the mass of the purified glycolysis products. The stirring speed was adjusted to 300 r / min, and the mixture was kept at 240°C for 2.5 h to allow the functional comonomer to fully react with the glycolysis products. Step 5: Add grafting modified crosslinking aid. The amount of grafting modified crosslinking aid added is 2.5% of the mass of the purified glycolysis product. The reaction temperature is 220℃, the stirring speed is 250r / min, and the reaction is carried out at a constant temperature for 60min to construct a stable and uniform molecular crosslinking network. The preparation method of the graft-modified crosslinking aid is as follows: maleic anhydride, methyl acrylate and benzoyl peroxide (BPO) are added to toluene solvent in a mass ratio of 4:2:0.1 and stirred until completely dissolved; under nitrogen protection, the mixture is heated to 80°C and stirred under reflux for 7 hours; after the reaction is completed, the toluene solvent is removed by vacuum distillation to obtain the graft copolymer; the graft copolymer is mixed with vinyltriethoxysilane in a mass ratio of 3:1, deionized water is added at 2% of the mass of vinyltriethoxysilane, and the mixture is stirred at 60°C for 3 hours to obtain the graft-modified crosslinking aid; Step 6: Melt, extrude, and granulate to obtain recycled polyester material.

[0025] The reaction system is heated to 250°C until it is completely melted, and then extruded through a twin-screw extruder. The extrusion temperature is controlled at 260-290°C and the screw speed is 100 r / min. Finally, the recycled polyester material is obtained by granulation.

[0026] Samples were prepared using the recycled polyester material obtained from the initial preparation, and the samples were subjected to performance tests. Tensile strength: 58.0 MPa; Elongation at break: 40.8%; Impact strength: 10.9 kJ·m 2 .

[0027] Example 2: A method for preparing polyester materials based on rPET glycolysis products, comprising the following steps: Step 1: After crushing rPET, perform a cooling thermal circulation pretreatment; Specifically, the recycled rPET raw material is crushed and passed through a 120-mesh sieve; then the rPET particles are first heated to 100°C and kept at that temperature for 12 minutes, and then cooled to 15°C by a combination of water cooling and air cooling and kept at that temperature for 20 minutes. This process is repeated 3 times. The cooling water temperature is 8°C and the flow rate is 1.5 m³ / h. 3 / h; air temperature 5℃, wind speed 2.0m / s, relative humidity 28%; Step 2: Glycolytic degradation of rPET A composite catalyst was prepared by combining a ternary metal salt-coordinated eutectic solvent DMTHPM / Ace-Zn(OAc)2 (1,2-dimethyl-1,4,5,6-tetrahydropyrimidine / acetamide-zinc acetate) and dopamine-grafted chitosan / polyvinyl alcohol-modified mica powder. The pretreated rPET was then subjected to glycolytic degradation using diethylene glycol as the reaction medium. The glycolysis reaction conditions were: 6.5g rPET, 0.1g composite catalyst, 40g diethylene glycol, reaction temperature 182℃, reaction time 28min, PET conversion rate 100%, and BHET yield 97.3%. After 10 cycles of use, the composite catalyst achieved a PET conversion rate of 97.1% and a BHET yield of 87.5%.

[0028] Among them, the ternary metal salt coordination eutectic solvent DMTHPM / Ace-Zn(OAc)2 was prepared by Jiang Yuan et al. using the design of ternary metal salt coordination eutectic solvents and the study of their catalytic performance in PET glycolysis. The method for preparing the dopamine-grafted chitosan / polyvinyl alcohol modified mica powder is as follows: (1) Preparation of dopamine-grafted chitosan: Dissolve 60 parts by weight of chitosan in a 3% dilute acetic acid aqueous solution and stir until completely dissolved to prepare a 5% chitosan acetic acid solution; add 25 parts by weight of dopamine hydrochloride to the chitosan acetic acid solution, adjust the pH to 8.5, stir at 40°C in the dark for 4 hours to obtain a dopamine-grafted chitosan solution; (2) Add 70 parts by weight of polyvinyl alcohol (PVA) to the dopamine-grafted chitosan solution and stir at 70°C for 20 min to obtain a dopamine-grafted chitosan / polyvinyl alcohol composite solution. (3) Add nano-sized mica powder to dopamine-grafted chitosan / polyvinyl alcohol composite liquid, control the solid-liquid ratio to 1:8, and stir at 60℃ for 2 hours; (4) Filtration: The solid material is washed with deionized water until neutral, and then dried to obtain dopamine-grafted chitosan / polyvinyl alcohol modified mica powder. The preparation method of the composite catalyst is as follows: (1) 48 parts by weight of ternary metal salt coordination eutectic solvent DMTHPM / Ace-Zn(OAc)2 were dispersed in anhydrous ethanol to prepare an active dispersion with a mass concentration of 22%. (2) Add 85 parts by weight of dopamine-grafted chitosan / polyvinyl alcohol modified mica powder to the above active dispersion and stir at 60°C for 1 hour; (3) The resulting mixture was distilled under reduced pressure at 80°C, and then dried and granulated to obtain the composite catalyst.

[0029] Step 3: Purification of crude sugar glycolysis products through multi-stage filtration: The crude sugar glycolysis products are purified through multi-stage filtration: first, they are filtered through a 200-mesh filter cloth, and then through an ultrafiltration membrane (molecular weight cutoff 500-1000 Da) to obtain purified glycolysis products. Step 4: Add functional comonomers; The purified glycolysis products were transferred to a melting reactor, nitrogen gas was introduced and the mixture was heated to 255°C to completely melt the glycolysis products. Then, a functional comonomer (polyethylene glycol) was added, with the amount of functional comonomer added being 15% of the mass of the purified glycolysis products. The stirring speed was adjusted to 350 r / min, and the mixture was kept at 255°C for 2 hours to allow the functional comonomer to fully react with the glycolysis products. Step 5: Add grafting modified crosslinking aid. The amount of grafting modified crosslinking aid added is 5% of the mass of the purified glycolysis product. The reaction temperature is 225℃, the stirring speed is 350r / min, and the reaction is carried out at a constant temperature for 40min to construct a stable and uniform molecular crosslinking network. The preparation method of the graft-modified crosslinking aid is as follows: maleic anhydride, methyl acrylate and benzoyl peroxide (BPO) are added to toluene solvent in a mass ratio of 6:3:0.3 and stirred until completely dissolved; under nitrogen protection, the mixture is heated to 83°C and stirred under reflux for 5 hours; after the reaction is completed, the toluene solvent is removed by vacuum distillation to obtain the graft copolymer; the graft copolymer is mixed with vinyltriethoxysilane in a mass ratio of 5:1, deionized water is added at 5% of the mass of vinyltriethoxysilane, and the mixture is stirred at 70°C for 2 hours to obtain the graft-modified crosslinking aid; Step 6: Melt, extrude, and granulate to obtain recycled polyester material.

[0030] The reaction system is heated to 280℃ until it is completely melted, and then extruded through a twin-screw extruder. The extrusion temperature is controlled at 260-290℃ and the screw speed is 150r / min. Finally, the recycled polyester material is obtained by granulation.

[0031] Samples were prepared using the recycled polyester material obtained from the initial preparation, and the samples were subjected to performance tests. Tensile strength: 56.5 MPa; Elongation at break: 42.7%; Impact strength: 11.4 kJ·m 2 .

[0032] Example 3: A method for preparing polyester materials based on rPET glycolysis products, comprising the following steps: Step 1: After crushing rPET, perform a cooling thermal circulation pretreatment; Specifically, the recycled rPET raw material is crushed and passed through a 100-mesh sieve; then the rPET particles are first heated to 90°C and kept at that temperature for 15 minutes, and then cooled to 12°C by a combination of water cooling and air cooling and kept at that temperature for 22 minutes. This process is repeated 4 times. The cooling water temperature is 6°C and the flow rate is 1.0 m³ / s. 3 / h; air temperature 3℃, wind speed 1.5m / s, relative humidity 25%; Step 2: Glycolytic degradation of rPET A composite catalyst was prepared by combining a ternary metal salt-coordinated eutectic solvent DMTHPM / Ace-Zn(OAc)2 (1,2-dimethyl-1,4,5,6-tetrahydropyrimidine / acetamide-zinc acetate) and dopamine-grafted chitosan / polyvinyl alcohol-modified mica powder. The pretreated rPET was then subjected to glycolytic degradation using propylene glycol as the reaction medium. The glycolysis reaction conditions were: 6.3g rPET, 0.07g composite catalyst, 35g propylene glycol, reaction temperature 180℃, reaction time 25min, PET conversion rate 100%, and BHET yield 97.1%. After 10 cycles of use, the composite catalyst achieved a PET conversion rate of 97.6% and a BHET yield of 89.3%.

[0033] Among them, the ternary metal salt coordination eutectic solvent DMTHPM / Ace-Zn(OAc)2 was prepared by Jiang Yuan et al. using the design of ternary metal salt coordination eutectic solvents and the study of their catalytic performance in PET glycolysis. The method for preparing the dopamine-grafted chitosan / polyvinyl alcohol modified mica powder is as follows: (1) Preparation of dopamine-grafted chitosan: Dissolve 55 parts by weight of chitosan in a 2% dilute acetic acid aqueous solution and stir until completely dissolved to prepare a 3% chitosan acetic acid solution; add 20 parts by weight of dopamine hydrochloride to the chitosan acetic acid solution, adjust the pH to 8.2, stir at 35°C in the dark for 5 hours to obtain a dopamine-grafted chitosan solution; (2) Add 55 parts by weight of polyvinyl alcohol (PVA) to the dopamine-grafted chitosan solution and stir at 66°C for 25 min to obtain a dopamine-grafted chitosan / polyvinyl alcohol composite solution. (3) Add nano-sized mica powder to dopamine-grafted chitosan / polyvinyl alcohol composite liquid, control the solid-liquid ratio to 1:5, and stir at 55℃ for 3 hours; (4) Filtration: The solid material is washed with deionized water until neutral, and then dried to obtain dopamine-grafted chitosan / polyvinyl alcohol modified mica powder. The preparation method of the composite catalyst is as follows: (1) 40 parts by weight of ternary metal salt coordination eutectic solvent DMTHPM / Ace-Zn(OAc)2 were dispersed in anhydrous ethanol to prepare an active dispersion with a mass concentration of 20%. (2) Add 65 parts by weight of dopamine-grafted chitosan / polyvinyl alcohol modified mica powder to the above active dispersion and stir at 50°C for 1.2 h; (3) The resulting mixture was distilled under reduced pressure at 70°C, and then dried and granulated to obtain the composite catalyst.

[0034] Step 3: Purification of crude sugar glycolysis products through multi-stage filtration: The crude sugar glycolysis products are purified through multi-stage filtration: first, they are filtered through a 200-mesh filter cloth, and then through an ultrafiltration membrane (molecular weight cutoff 500-1000 Da) to obtain purified glycolysis products. Step 4: Add functional comonomers; The purified glycolysis products were transferred to a melting reactor, nitrogen gas was introduced and the mixture was heated to 245°C to completely melt the glycolysis products. Then, a functional comonomer (1,4-butanediol) was added, with the amount of functional comonomer added being 10% of the mass of the purified glycolysis products. The stirring speed was adjusted to 330 r / min, and the mixture was kept at 250°C for 2.2 h to allow the functional comonomer to fully react with the glycolysis products. Step 5: Add grafting modified crosslinking aid. The amount of grafting modified crosslinking aid added is 3% of the mass of the purified glycolysis product. The reaction temperature is 222℃, the stirring speed is 280r / min, and the reaction is carried out at a constant temperature for 50min to construct a stable and uniform molecular crosslinking network. The preparation method of the graft-modified crosslinking aid is as follows: maleic anhydride, methyl acrylate and benzoyl peroxide (BPO) are added to toluene solvent in a mass ratio of 5:2.5:0.2 and stirred until completely dissolved; under nitrogen protection, the mixture is heated to 82°C and refluxed for 6 hours; after the reaction is completed, the toluene solvent is removed by vacuum distillation to obtain the graft copolymer; the graft copolymer is mixed with vinyltriethoxysilane in a mass ratio of 4:1, deionized water is added at a mass of 3.5% of the vinyltriethoxysilane mass, and the mixture is stirred at 65°C for 2.5 hours to obtain the graft-modified crosslinking aid; Step 6: Melt, extrude, and granulate to obtain recycled polyester material.

[0035] The reaction system is heated to 260℃ until it is completely melted, and then extruded through a twin-screw extruder. The extrusion temperature is controlled at 260-290℃ and the screw speed is 130r / min. Finally, the recycled polyester material is obtained by granulation.

[0036] Samples were prepared using the recycled polyester material obtained from the initial preparation, and the samples were subjected to performance tests. Tensile strength: 61.3 MPa; Elongation at break: 40.1%; Impact strength: 12.2 kJ·m 2 .

[0037] Comparative Example 1: Unlike Example 3, the composite catalyst was obtained by directly blending a ternary metal salt-coordinated eutectic solvent DMTHPM / Ace-Zn(OAc)2 (1,2-dimethyl-1,4,5,6-tetrahydropyrimidine / acetamide-zinc acetate) with dopamine-grafted chitosan / polyvinyl alcohol-modified mica powder. All other steps were the same.

[0038] The glycolysis reaction conditions were: 6.3g rPET, 0.07g composite catalyst, 35g propylene glycol, reaction temperature 180℃, reaction time 25min, PET conversion rate 96.8%, and BHET yield 85.6%. After 10 cycles of use, the composite catalyst achieved a PET conversion rate of 86.7% and a BHET yield of 71.0%.

[0039] Comparative Example 2: Unlike Example 3, the composite catalyst was replaced with a ternary metal salt-coordinated eutectic solvent DMTHPM / Ace-Zn(OAc)2 (1,2-dimethyl-1,4,5,6-tetrahydropyrimidine / acetamide-zinc acetate). All other steps were the same.

[0040] The glycolysis reaction conditions were: 6.3 g rPET, 0.07 g catalyst, 35 g propylene glycol, reaction temperature 180℃, reaction time 25 min, PET conversion rate 95.6%, and BHET yield 83.7%. After 10 cycles of use, the composite catalyst achieved a PET conversion rate of 83.0% and a BHET yield of 69.7%.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing polyester materials based on rPET glycolysis products, characterized in that, Includes the following steps: Step 1: After crushing rPET, perform a cooling thermal circulation pretreatment; Step 2: Glycolytic degradation of rPET A composite catalyst was prepared by combining a ternary metal salt-coordinated eutectic solvent DMTHPM / Ace-Zn(OAc)2 with dopamine-grafted chitosan / polyvinyl alcohol-modified mica powder. The catalyst was used as a glycolytic agent to degrade pretreated rPET through glycolytic degradation. The method for preparing the dopamine-grafted chitosan / polyvinyl alcohol modified mica powder is as follows: (1) Preparation of dopamine-grafted chitosan: Dissolve 50-60 parts by weight of chitosan in a 1-3% dilute acetic acid aqueous solution and stir until completely dissolved to prepare a 2-5% chitosan acetic acid solution; add 16-25 parts by weight of dopamine hydrochloride to the chitosan acetic acid solution, adjust the pH to 8.0-8.5, stir at 30-40℃ in the dark for 4-6 hours to obtain a dopamine-grafted chitosan solution; (2) Add 40-70 parts by weight of polyvinyl alcohol (PVA) to the dopamine-grafted chitosan solution and stir at 60-70℃ for 20-30 min to obtain a dopamine-grafted chitosan / polyvinyl alcohol composite solution. (3) Add nano-sized mica powder to dopamine-grafted chitosan / polyvinyl alcohol composite liquid, control the solid-liquid ratio to 1:4-8, and stir at 50-60℃ for 2-4 hours; (4) Filtration: The solid material is washed with deionized water until neutral, and then dried to obtain dopamine-grafted chitosan / polyvinyl alcohol modified mica powder. Step 3: The crude sugar glycolysis product is purified by multi-stage filtration to obtain purified glycolysis product; Step 4: Add the functional comonomer and crosslinking agent sequentially, and proceed with the reaction; Step 5: Melt, extrude, and granulate to obtain recycled polyester material.

2. The method for preparing polyester materials based on rPET glycolysis products according to claim 1, characterized in that, Step one is as follows: The recycled rPET raw material is crushed and passed through an 80-120 mesh sieve; then the rPET particles are heated to 80-100℃ and kept at a constant temperature for 12-18 minutes, and then cooled to 10-15℃ by water cooling combined with air cooling and kept at that temperature for 20-25 minutes. This cycle is repeated 3-5 times.

3. The method for preparing polyester materials based on rPET glycolysis products according to claim 2, characterized in that, In step one, the cooling water temperature is 5-8℃ and the flow rate is 0.8-1.5m³ / h. 3 / h; air temperature 0-5℃, wind speed 1.2-2.0m / s, relative humidity ≤30%.

4. The method for preparing polyester materials based on rPET glycolysis products according to claim 3, characterized in that, In step two, the glycolysis reaction conditions are: rPET 6.0-6.5g, composite catalyst 0.07-0.1g, glycolysis agent 30-40g, reaction temperature 178-182℃, and reaction time 25-30min.

5. The method for preparing polyester materials based on rPET glycolysis products according to claim 4, characterized in that, In step two, the glycolytic agent is one or more of ethylene glycol, diethylene glycol, and propylene glycol.

6. The method for preparing polyester materials based on rPET glycolysis products according to claim 5, characterized in that, In step two, the preparation method of the composite catalyst is as follows: (1) Disperse 35-48 parts by weight of ternary metal salt coordination eutectic solvent DMTHPM / Ace-Zn(OAc)2 in anhydrous ethanol to prepare an active dispersion with a mass concentration of 15-22%; (2) Add 60-85 parts by weight of dopamine-grafted chitosan / polyvinyl alcohol modified mica powder to the above active dispersion and stir at 40-60℃ for 1-1.5h; (3) The resulting mixture was distilled under reduced pressure at 60-80℃, and then dried and granulated to obtain the composite catalyst.

7. The method for preparing polyester materials based on rPET glycolysis products according to claim 6, characterized in that, Step 3 specifically involves: purifying the crude sugar glycolysis product through multi-stage filtration: first, filtering through a 200-mesh filter cloth, and then filtering through an ultrafiltration membrane with a molecular weight cutoff of 500-1000 Da to obtain the purified glycolysis product.

8. The method for preparing polyester materials based on rPET glycolysis products according to claim 7, characterized in that, In step four, the purified glycolysis products are transferred to a melting reactor, nitrogen gas is introduced and the mixture is heated to 240-255℃ to completely melt the glycolysis products. Then, functional comonomers are added, with the amount of functional comonomers being 5-15% of the mass of the purified glycolysis products. The stirring speed is adjusted to 300-350 r / min, and the mixture is kept at a constant temperature of 240-255℃ for 2-2.5 h to ensure that the functional comonomers react fully with the glycolysis products. In step four, the functional comonomer is one or more of adipic acid, polyethylene glycol, and 1,4-butanediol.

9. The method for preparing polyester materials based on rPET glycolysis products according to claim 8, characterized in that, In step four, a grafting-modified crosslinking aid is added. The amount of grafting-modified crosslinking aid added is 2.5-5% of the mass of the purified glycolysis product. The reaction temperature is 220-225℃, the stirring rate is 250-350r / min, and the reaction is carried out at a constant temperature for 40-60min to construct a stable and uniform molecular crosslinking network. The preparation method of the graft-modified crosslinking aid is as follows: maleic anhydride, methyl acrylate and benzoyl peroxide (BPO) are added to toluene solvent at a mass ratio of 4-6:2-3:0.1-0.3 and stirred until completely dissolved; under nitrogen protection, the mixture is heated to 80-83℃ and refluxed for 5-7 hours; after the reaction, the toluene solvent is removed by vacuum distillation to obtain the graft copolymer; the graft copolymer is mixed with vinyltriethoxysilane at a mass ratio of 3-5:1, deionized water is added in an amount of 2-5% of the mass of vinyltriethoxysilane, and the mixture is stirred at 60-70℃ for 2-3 hours to obtain the graft-modified crosslinking aid.

10. A polyester material based on rPET glycolysis products prepared by the method according to any one of claims 1 to 9.