Preparation method of degradable polyethylene glycol terephthalate copolyester

Abstract

The invention discloses a preparation method of degradable polyethylene glycol terephthalate copolyester, and relates to the technical field of copolyester. The preparation method of the degradable polyethylene glycol terephthalate copolyester comprises the following specific steps: preparing bis (2-hydroxyethyl) terephthalate; copolyester is prepared through chain propagation and chain degradation bis (2-hydroxyethyl) terephthalate polycondensation, quaternary ammonium salt groups are introduced, antibacterial ions are introduced, the antibacterial ions are combined with the quaternary ammonium salt groups in the copolyester through ion exchange or coordination, and a metal-quaternary ammonium salt-polyester coordination structure is formed in the copolyester. According to the invention, through dual mechanisms, i.e., membrane damage auxiliary ion interference, antibacterial effect enhancement, no residual chlorinated organic compounds, avoidance of potential toxicity to soil microorganisms and lower environmental risk, and due to heat-resistant modification of quaternary ammonium salt, the finally obtained copolyester has higher processing stability.

Description

Technical Field

[0001] The invention relates to the technical field of copolyesters, in particular to a method for preparing degradable polyethylene terephthalate copolyester. Background Art

[0002] Polyethylene terephthalate copolyester (PET), chemical formula is (C 10 H8O4)n is produced by the transesterification of dimethyl terephthalate with ethylene glycol or the esterification of terephthalic acid with ethylene glycol to synthesize bis(hydroxyethyl terephthalate), followed by a polycondensation reaction. It is a crystalline saturated polyester, a milky white or light yellow, highly crystalline polymer with a smooth, glossy surface. It is a common resin in daily life and can be divided into APET, RPET, and PETG. It exhibits excellent physical and mechanical properties over a wide temperature range, with an operating temperature of up to 120°C. It also has excellent electrical insulation properties, maintaining good electrical properties even at high temperatures and high frequencies. However, it exhibits poor corona resistance, and exhibits excellent creep resistance, fatigue resistance, friction resistance, and dimensional stability.

[0003] At present, the demand for the antibacterial properties and degradability of PET has also become a hot topic in current materials. For example, a preparation method of degradable polyethylene terephthalate copolyester disclosed in Chinese Patent Publication No. CN111423569A, wherein glycolide is ring-opening polymerized to obtain low molecular weight polyglycolic acid, and then 5,5-dimethylhydantoin is modified to obtain 3-bis(hydroxymethyl)methyl-5,5-dimethylhydantoin diol monomer that can be used for polymerization, and then the monomers participating in the reaction, dimethyl terephthalate, ethylene glycol, 3-bis(hydroxymethyl)methyl-5,5-dimethylhydantoin and low molecular weight polyglycolic acid are placed in a reactor, and under the action of a catalyst, prepolymerized. and final polycondensation to prepare PET copolyester, and finally, dissolving the prepared PET copolyester in a sodium hypochlorite solution for chlorination; and a biodegradable antibacterial graphene in situ polymerization copolyester packaging film and its preparation process disclosed in Chinese Patent Publication No. CN112876710B, which uses graphene in situ polymerization biodegradable copolyester, introduces graphene components during the polymerization process of the biodegradable polyester material, and through the multi-level grid structure of the graphene, the macromolecules of the biodegradable polyester material are evenly distributed, the molecular weight distribution is narrower, and due to the regularity of the molecular structure, it exhibits many new properties that were not originally possessed, such as barrier properties, antibacterial properties, conductivity, etc. However, both of the above patent documents use a single approach to the antibacterial properties of PET, that is, 5,5-dimethylhydantoin is modified by hydroxymethylation and reacts with sodium hypochlorite to generate a structure containing an N-chloroamine group, which releases active chlorine through contact to destroy the microbial membrane. Graphene mainly inhibits the activity of bacteria by physical adsorption or wrapping. The antibacterial effect of graphene itself is poor, and due to its single nature, it is difficult to meet the antibacterial standards of new materials. The active chlorine of the N-chloroamine group is easily decomposed when encountering organic matter or light, and its single nature leads to insufficient antibacterial durability. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for preparing a degradable polyethylene terephthalate copolyester, which solves the problems raised in the above background technology.

[0005] To achieve the above objectives, the present invention is implemented by the following technical solution: a method for preparing a degradable polyethylene terephthalate copolyester, the method comprising the following specific steps:

[0006] S1, preparing copolyester; preparing copolyester by polycondensation of bis(hydroxyethyl) terephthalate through chain growth and chain degradation;

[0007] S2. Introducing quaternary ammonium salt groups; dimethylaminoethyl methacrylate is combined with the bis(hydroxyethyl) terephthalate copolyester obtained in S1 through free radical copolymerization or polycondensation reaction, and a quaternary ammonium salt group is generated through a quaternization reaction. The synthetic monomer of the copolyester is bis(hydroxyethyl) terephthalate, and the quaternary ammonium salt group is generated by combining dimethylaminoethyl methacrylate and bis(hydroxyethyl) terephthalate.

[0008] S3. Introduction of antibacterial ions; the antibacterial ions combine with the quaternary ammonium salt groups in the copolyester through ion exchange or coordination to form a metal-quaternary ammonium salt-polyester coordination structure in the copolyester.

[0009] A further improvement of the technical solution of the present invention is that S1 further includes the following specific preparation steps:

[0010] S1-1. PET bottles are subjected to alcoholysis with ethylene glycol to produce crude BHET, which is then purified by secondary thin-film evaporation at 140-180°C and 100-10,000 Pa and molecular distillation at 180-250°C and 1-100 Pa to remove oligomers and impurities.

[0011] S1-2, BHET and ethylene terephthalate react with tetrabutyl titanate at 190-220°C and 70-100 kPa for 20-60 minutes to produce ethylene terephthalate copolyester;

[0012] S1-3. Add ZnO:tetrabutyl titanate = 7:3, pre-condense at 250-265°C and 1-50 kPa for 40-100 minutes to form a low molecular weight prepolymer, heat to 270-280°C, reduce pressure to 50-500 Pa, and perform vacuum polycondensation to promote chain growth and remove small molecular by-products, such as EG, to finally obtain a high molecular weight copolyester.

[0013] A further improvement of the technical solution of the present invention is that S2 includes the following specific steps:

[0014] S2-1. An inert solvent is introduced into a reaction vessel, bis(hydroxyethyl) terephthalate is added to dissolve the bis(hydroxyethyl) terephthalate, dimethylaminoethyl methacrylate is added in a molar ratio, bis(hydroxyethyl) terephthalate and dimethylaminoethyl methacrylate are fully mixed, a free radical initiator is added, nitrogen is introduced, the temperature of the reaction vessel is raised to 120-140° C., free radical polymerization is initiated, and the reaction time is controlled to be 4-6 h. After the reaction is completed, the mixture is cooled and precipitated in methanol, filtered and dried to obtain PET copolyester grafted with dimethylaminoethyl methacrylate.

[0015] A further improvement of the technical solution of the present invention is that in S2-1, BHET and dimethylaminoethyl methacrylate are mixed in a molar ratio of (80-95):(5-20);

[0016] The inert solvent is selected from diphenyl ether or o-difluorobenzene having a high boiling point;

[0017] The free radical initiator is selected to be 0.5-1 wt% of azobisisobutyronitrile.

[0018] A further improvement of the technical solution of the present invention is that S3 further includes the following specific steps:

[0019] S3-1. Immerse the PET copolyester grafted with dimethylaminoethyl methacrylate obtained in S2-1 in AgNO3 solution, stir at a constant temperature of 60°C for 6-12 hours, use 1,2,7,8-diepoxyoctane vapor to crosslink the PET surface to fix the antibacterial ions, and wash and detect until no residue is left.

[0020] Beneficial effects

[0021] Compared with the prior art, the present invention has the following beneficial effects: the reaction of dimethylaminoethyl methacrylate and bis(hydroxyethyl) terephthalate generates quaternary ammonium groups through a quaternization reaction; the groups undergo heat-resistant modification, so that the material remains stable during high-temperature processing, reducing the risk of thermal decomposition, and is suitable for the preparation of thermal insulation materials. It can also be used as a building energy-saving and thermal insulation material; the generated quaternary ammonium groups destroy bacterial cell membranes through electrostatic adsorption, causing leakage of bacterial contents; and the copolyester main chain retains PET while the quaternary ammonium groups are incorporated from the side chains. The anions of the quaternary ammonium groups are replaced by metal ions in subsequent reactions, completing the remodeling of the coordination bond. This breaks through the limitation of the existing PET monomer that introduces a single antibacterial mechanism, and achieves a synergistic effect of interfering with enzyme activity and superimposing cell membrane destruction.

[0022] Through a dual mechanism, namely membrane destruction and auxiliary ion interference, the antibacterial effect is enhanced, and no chlorinated organic matter remains, avoiding potential toxicity to soil microorganisms, and the environmental risk is lower. In addition, because the quaternary ammonium salt has been heat-resistant modified, the processing stability of the final copolyester is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart for preparing the copolyester of the present invention. DETAILED DESCRIPTION

[0024] Various exemplary embodiments, features, and aspects of the present application will be described in detail below with reference to the accompanying drawings. The same reference numerals in the accompanying drawings represent elements with the same or similar functions. Although various aspects of the embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

[0025] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0026] In addition, numerous specific details are provided in the following specific examples to better illustrate the present application. Those skilled in the art will appreciate that the present application can be practiced without certain specific details. In some instances, methods, means, and components well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present application.

[0027] The present invention provides a method for preparing a degradable polyethylene terephthalate copolyester, the method comprising the following specific steps:

[0028] S1, preparing copolyester; preparing copolyester by polycondensation of bis(hydroxyethyl) terephthalate through chain growth and chain degradation;

[0029] S2. Introducing quaternary ammonium salt groups; dimethylaminoethyl methacrylate is combined with the bis(hydroxyethyl) terephthalate copolyester obtained in S1 through free radical copolymerization or polycondensation reaction, and a quaternary ammonium salt group is generated through a quaternization reaction. The synthetic monomer of the copolyester is bis(hydroxyethyl) terephthalate, and the quaternary ammonium salt group is generated by combining dimethylaminoethyl methacrylate and bis(hydroxyethyl) terephthalate.

[0030] S3. Introduction of antibacterial ions; the antibacterial ions combine with the quaternary ammonium salt groups in the copolyester through ion exchange or coordination to form a metal-quaternary ammonium salt-polyester coordination structure in the copolyester.

[0031] Example 1: This example further discloses the introduction of ammonium salt groups:

[0032] First, the BHET selected for the PET monomer needs to be prepared. Before preparation, it should be noted that the preparation of PET monomer is often achieved by mixing terephthalic acid (PTA) and ethylene glycol (EG) in a specific molar ratio and adding a titanium-based catalyst. However, its purity is low and it is highly dependent on primary resources. Therefore, the PET synthesized by BHET polycondensation has high purity and is suitable for closed-loop recycling. In the subsequent introduction of groups and ions, impurities are avoided, which would affect the biodegradability of the copolyester.

[0033] Said S1 also includes the following specific preparation steps:

[0034] S1-1. PET bottles are subjected to alcoholysis with ethylene glycol to produce crude BHET, which is then purified by secondary thin-film evaporation at 140-180°C and 100-10,000 Pa and molecular distillation at 180-250°C and 1-100 Pa to remove oligomers and impurities.

[0035] S1-2, BHET and ethylene terephthalate react with tetrabutyl titanate at 190-220°C and 70-100 kPa for 20-60 minutes to produce ethylene terephthalate copolyester;

[0036] S1-3. Add ZnO:tetrabutyl titanate = 7:3, pre-condense at 250-265°C and 1-50 kPa for 40-100 minutes to form a low molecular weight prepolymer, heat to 270-280°C, reduce pressure to 50-500 Pa, and perform vacuum polycondensation to promote chain growth and remove small molecular by-products, such as EG, to finally obtain a high molecular weight copolyester.

[0037] The PET monomer of the copolyester is selected as BHET, and the quaternary ammonium group is generated by combining dimethylaminoethyl methacrylate with BHET. Furthermore, dimethylaminoethyl methacrylate and bis(hydroxyethyl) terephthalate are then reacted through a quaternization reaction, such as a reaction with a halogenated hydrocarbon, to generate a quaternary ammonium group. Finally, the quaternary ammonium group destroys the bacterial cell membrane through electrostatic adsorption, causing leakage of the contents. This achieves the premise that the copolyester main chain retains PET and the quaternary ammonium group is incorporated from the side chain. The anion of the quaternary ammonium group is replaced by a metal ion in a subsequent reaction to complete the remodeling of the coordination bond, breaking through the limitation of the existing PET monomer introducing a single antibacterial mechanism and achieving a synergistic effect of interfering with enzyme activity and superimposing cell membrane destruction. Furthermore, the synthetic monomer of the copolyester is selected as bis(hydroxyethyl) terephthalate, and the quaternary ammonium group is generated by combining dimethylaminoethyl methacrylate with bis(hydroxyethyl) terephthalate.

[0038] The S2 includes the following specific steps:

[0039] S2-1. An inert solvent is introduced into a reaction vessel, bis(hydroxyethyl) terephthalate is added to dissolve the bis(hydroxyethyl) terephthalate, dimethylaminoethyl methacrylate is added in a molar ratio, bis(hydroxyethyl) terephthalate and dimethylaminoethyl methacrylate are fully mixed, a free radical initiator is added, nitrogen is introduced, the temperature of the reaction vessel is raised to 120-140° C., free radical polymerization is initiated, and the reaction time is controlled to be 4-6 h. After the reaction is completed, the mixture is cooled and precipitated in methanol, filtered and dried to obtain PET copolyester grafted with dimethylaminoethyl methacrylate.

[0040] In S2-1, BHET and dimethylaminoethyl methacrylate are mixed in a molar ratio of (80-95):(5-20);

[0041] The inert solvent is selected from diphenyl ether or o-difluorobenzene having a high boiling point;

[0042] The free radical initiator is selected to be 0.5-1 wt% of azobisisobutyronitrile.

[0043] After the introduction of the quaternary ammonium salt group, S3 and antibacterial ions are introduced; the antibacterial ions combine with the quaternary ammonium salt group in the copolyester through ion exchange or coordination to form a metal-quaternary ammonium salt-polyester coordination structure in the copolyester.

[0044] The S3 further includes the following specific steps:

[0045] S3-1. Immerse the PET copolyester grafted with dimethylaminoethyl methacrylate obtained in S2-1 in AgNO3 solution, stir at a constant temperature of 60°C for 6-12 hours, use 1,2,7,8-diepoxyoctane vapor to crosslink the PET surface to fix Ag+, and wash and detect until no residue is left.

[0046] Example 1: This example uses the following method to prepare a degradable polyethylene terephthalate copolyester, specifically:

[0047] S1, preparing copolyester; preparing copolyester by polycondensation of bis(hydroxyethyl) terephthalate through chain growth and chain degradation;

[0048] S2, introducing quaternary ammonium salt groups; dimethylaminoethyl methacrylate is combined with the bis(hydroxyethyl) terephthalate copolyester obtained in S1 through free radical copolymerization or polycondensation reaction, and quaternary ammonium salt groups are generated through quaternization reaction;

[0049] The synthetic monomer of the copolyester is bis(hydroxyethyl) terephthalate, and the quaternary ammonium salt group is formed by combining dimethylaminoethyl methacrylate and bis(hydroxyethyl) terephthalate.

[0050] S2-1. An inert solvent is introduced into a reaction vessel, bis(hydroxyethyl) terephthalate is added to dissolve the bis(hydroxyethyl) terephthalate, dimethylaminoethyl methacrylate is added in a molar ratio, bis(hydroxyethyl) terephthalate and dimethylaminoethyl methacrylate are fully mixed, a free radical initiator is added, nitrogen is introduced, the temperature of the reaction vessel is raised to 120-140° C., free radical polymerization is initiated, and the reaction time is controlled to be 4-6 h. After the reaction is completed, the mixture is cooled and precipitated in methanol, filtered and dried to obtain PET copolyester grafted with dimethylaminoethyl methacrylate.

[0051] S3, introduction of antibacterial ions; the antibacterial ions combine with the quaternary ammonium salt groups in the copolyester through ion exchange or coordination, forming a metal-quaternary ammonium salt-polyester coordination structure in the copolyester;

[0052] S3-1. Immerse the dimethylaminoethyl methacrylate-grafted PET copolyester obtained in S2-1 in an AgNO3 solution, stir at 60°C for 6-12 hours, crosslink the PET surface with 1,2,7,8-diepoxyoctane vapor to fix Ag+, and wash and inspect until no residue remains.

[0053] Finally, the degradable polyethylene terephthalate copolyester was obtained, which was recorded as experimental group 1.

[0054] Example 2: This example uses the following method to prepare a degradable polyethylene terephthalate copolyester, specifically:

[0055] Preparation of BHET; preparation of copolyesters by polycondensation of complete BHET through chain growth and chain degradation;

[0056] Introducing quaternary ammonium salt groups; dimethylaminoethyl methacrylate is combined with BHET obtained in S1 through free radical copolymerization or polycondensation reaction, and quaternary ammonium salt groups are generated through quaternization reaction;

[0057] An inert solvent is introduced into a reaction vessel, BHET is added to dissolve the BHET, dimethylaminoethyl methacrylate is added in a molar ratio, BHET and dimethylaminoethyl methacrylate are thoroughly mixed, a free radical initiator is added, nitrogen is introduced, and the reaction vessel is heated to 120-140° C. to initiate free radical polymerization. The reaction time is controlled to be 4-6 hours. After the reaction is completed, the mixture is cooled and precipitated in methanol, filtered and dried to obtain dimethylaminoethyl methacrylate-grafted PET copolyester (PET-co-DMAEMA);

[0058] Finally, the degradable polyethylene terephthalate copolyester was obtained, which was recorded as experimental group 2.

[0059] Example 3: This example uses the following method to prepare a degradable polyethylene terephthalate copolyester, specifically:

[0060] Dissolving hexamethylguanidine in water to obtain a hexamethylguanidine solution, adding a glycolic acid aqueous solution dropwise to the solution under stirring, and reacting at 60-90° C. for 5-10 hours, wherein the mass ratio of hexamethylguanidine to glycolic acid is 1:1.3; then adding an ethanol solution to the reacted solution at room temperature, removing unreacted glycolic acid solids, and then removing the solvent to obtain hexamethylguanidine glycolate;

[0061] Preparation of low molecular weight polyglycolic acid: glycolide and the ring-opening catalyst hexamethylguanidine glycolate are placed in a reactor and reacted at 80-180°C for 3-6 hours under inert gas protection to produce low molecular weight polyglycolic acid with a molecular weight of 6000-9000. The mass ratio of glycolide to the ring-opening catalyst hexamethylguanidine glycolate is 2000-3000:1.

[0062] Preparation of monomer 3-bis(hydroxymethyl)methyl-5,5-dimethylhydantoin: 5,5-dimethylhydantoin and 2-chloro-1,3-propylene glycol are placed in an 11 wt% potassium hydroxide ethanol solution, wherein the molar ratio of 5,5-dimethylhydantoin to 2-chloro-1,3-propylene glycol is 1:1.5-2, and reacted at 75-85° C. for 5-7 hours. The solvent is evaporated, and the organic layer is separated with ethyl acetate and water. The solvent is removed by rotary evaporation to obtain a crude product, and the crude product is then recrystallized in a toluene / propanol mixture to prepare 3-bis(hydroxymethyl)methyl-5,5-dimethylhydantoin;

[0063] Low molecular weight polyglycolic acid, dimethyl terephthalate, ethylene glycol, 3-bis(hydroxymethyl)methyl-5,5-dimethylhydantoin, and a catalyst are placed in a reactor, subjected to an ester exchange reaction at 170-230° C. and 0.2-0.3 MPa for 2-3 hours, and then subjected to a final polycondensation reaction at 240-260° C. for 4-5 hours to prepare a copolyester, wherein the molar ratio of ethylene glycol to 3-bis(hydroxymethyl)methyl-5,5-dimethylhydantoin is 1-4:1; the molar ratio of the sum of the molar amounts of dimethyl terephthalate and ethylene glycol to 3-bis(hydroxymethyl)methyl-5,5-dimethylhydantoin is 1:1.2-1.6; the amount of low molecular weight polyglycolic acid used is 10% to 50% of the total weight of each monomer; and the catalyst is antimony acetate used in an amount of 200-400 ppm of the total weight of the raw materials.

[0064] The obtained copolyester was dissolved in a 10 wt % sodium hypochlorite solution and chlorinated at 85-95° C. for 2-3 h to prepare a degradable polyethylene terephthalate copolyester, which was recorded as Experimental Group 3.

[0065] The samples of the above-mentioned test groups 1, 2 and 3 were hot pressed into films with a thickness of 20 mm ± 0.2 using a flat vulcanizing machine, washed several times with anhydrous ethanol and distilled water, and then dried. 0.1 mol / L citric acid solution and trisodium citrate solution were prepared, and the citric acid and sodium citrate solutions were added dropwise to the same container and diluted with deionized water to make the mixed solution pH = 4. The samples obtained from the test groups 1, 2 and 3 were placed in 3 ml of citric acid buffer solution with a pH of 4 and a mixture of Aspergillus niger enzyme. The enzyme citric acid buffer solution was replaced every 2 days. After degradation occurred, the degradation residues were taken out from the buffer solution, washed 3 times with anhydrous ethanol and deionized water respectively, and tested after vacuum drying. The degradation effect was characterized by changes in sample mass, molecular weight and appearance, as shown in the following table:

[0066]

[0067] It can be seen from the above table that the molecular weight distribution of test group 3 before and after degradation is wide. Even though the number of days for degradation of test groups 1 and 2 is close to that of test group 3, the degradation of the polyester film of test group 3 is difficult to advance internally and mostly occurs on the surface, that is, the molecular weight inside the film decreases slowly, resulting in a wider molecular weight distribution.

[0068] Furthermore, test groups 1, 2, and 3 were tested for their own performance characteristics, and the results are as follows:

[0069]

[0070]

[0071] As can be seen from the above table, the addition of quaternary ammonium salt groups and antibacterial ions to the copolyester does not significantly affect its performance.

[0072] Furthermore, experimental groups 1, 2, and 3 were made into 20 mm ± 0.2 films. Equal amounts of Helicobacter pylori were injected onto the films. After 1 day of inoculation, the films were rinsed with plasma water, and the plasma water was collected. 1 ml of the plasma water rinse solution was placed in the culture medium, and the reduction rate of the Helicobacter pylori colony was calculated, as shown in the following table:

[0073]

[0074] It can be seen that the experimental group 1 obtained in Example 1 has a synergistic effect of interfering enzyme activity and cell membrane destruction, which significantly improves the antibacterial effect.

[0075] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0076] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a degradable polyethylene terephthalate copolyester, characterized in that: The method comprises the following specific steps: S1, preparing copolyester; preparing copolyester by polycondensation of bis(hydroxyethyl) terephthalate through chain growth and chain degradation; S2, introducing quaternary ammonium salt groups; dimethylaminoethyl methacrylate is combined with the bis(hydroxyethyl) terephthalate copolyester obtained in S1 through free radical copolymerization or polycondensation reaction, and quaternary ammonium salt groups are generated through quaternization reaction, wherein the synthetic monomer of the copolyester is bis(hydroxyethyl) terephthalate, and the quaternary ammonium salt groups are generated by combining dimethylaminoethyl methacrylate and bis(hydroxyethyl) terephthalate; S3, introduction of antibacterial ions; The antibacterial ions combine with the quaternary ammonium salt groups in the copolyester through ion exchange or coordination, forming a metal-quaternary ammonium salt-polyester coordination structure in the copolyester.

2. The method for preparing a degradable polyethylene terephthalate copolyester according to claim 1, wherein: Said S1 also includes the following specific preparation steps: S1-1. Using PET bottles, alcoholyzing with ethylene glycol to produce crude bis(hydroxyethyl terephthalate), which is then purified by secondary thin-film evaporation at 140-180°C, 100-10,000 Pa, and molecular distillation at 180-250°C, 1-100 Pa, to remove oligomers and impurities. S1-2, bis(hydroxyethyl) terephthalate and ethylene terephthalate react with tetrabutyl titanate at 190-220° C. and 70-100 kPa for 20-60 minutes to produce ethylene terephthalate copolyester; S1-3. Add ZnO:tetrabutyl titanate in a ratio of 7:3, and pre-condense at 250-265°C and 1-50 kPa for 40-100 minutes to form a low molecular weight prepolymer. Raise the temperature to 270-280°C, reduce the pressure to 50-500 Pa, and perform vacuum polycondensation to promote chain growth and remove small molecular by-products, ultimately obtaining a high molecular weight copolyester.

3. The method for preparing a degradable polyethylene terephthalate copolyester according to claim 1, wherein: The S2 includes the following specific steps: S2-1. An inert solvent is introduced into a reaction vessel, bis(hydroxyethyl) terephthalate is added to dissolve the bis(hydroxyethyl) terephthalate, dimethylaminoethyl methacrylate is added in a molar ratio, bis(hydroxyethyl) terephthalate and dimethylaminoethyl methacrylate are fully mixed, a free radical initiator is added, nitrogen is introduced, the temperature of the reaction vessel is raised to 120-140° C., free radical polymerization is initiated, and the reaction time is controlled to be 4-6 h. After the reaction is completed, the mixture is cooled and precipitated in methanol, filtered and dried to obtain PET copolyester grafted with dimethylaminoethyl methacrylate.

4. The method for preparing a degradable polyethylene terephthalate copolyester according to claim 3, wherein: In S2-1, bis(hydroxyethyl) terephthalate and dimethylaminoethyl methacrylate are mixed in a molar ratio of (80-95):(5-20); The inert solvent is selected from diphenyl ether or o-difluorobenzene having a high boiling point; The free radical initiator is selected to be 0.5-1 wt% of azobisisobutyronitrile.

5. The method for preparing a degradable polyethylene terephthalate copolyester according to claim 4, wherein: The S3 further includes the following specific steps: S3-1. Immerse the PET copolyester grafted with dimethylaminoethyl methacrylate obtained in S2-1 in a silver nitrate solution, stir at a constant temperature of 60°C for 6-12 hours, use 1,2,7,8-diepoxyoctane vapor to crosslink the surface to fix the antibacterial ions, and wash and detect until no residue is left.

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