A multi-component copolyester and its preparation method

Abstract

This invention provides a multi-component copolyester and its preparation method, belonging to the field of polyester technology. The multi-component copolyester of this invention comprises: component A, a dicarboxylic acid compound, based on the total molar amount of component A, including: a1, 35-65 mol% aliphatic dicarboxylic acid; a2, 35-65 mol% aromatic dicarboxylic acid or its derivatives; component B, 1,4-butanediol; and component C, a third monomer, based on the total molar amount of components B and C, wherein component C accounts for 5-30 mol%. The crystallinity of the multi-component copolyester is 5-22%, and the zinc content in the multi-component copolyester is ≤100 ppm, and the titanium content is ≤120 ppm. The multi-component copolyester of this invention uses waste polyester as raw material and, through primary alcoholysis, secondary alcoholysis, transesterification, and polycondensation steps, obtains a multi-component copolyester with low heavy metal content, suitable crystallinity, good printability, and good biodegradability.

Description

Technical Field

[0001] This invention relates to the field of recycled polyester technology, and in particular to a multi-component copolyester and its preparation method. Background Technology

[0002] Currently, globally, biodegradable plastics account for approximately 58% of plastic production, while non-biodegradable plastics account for 42%. The disposal of waste plastics is a pressing issue. In the future, my country will gradually address the environmental harm caused by traditional waste plastic treatment through methods such as source reduction, reuse, using bio-based or biodegradable plastics to replace fossil-derived materials, and recycling plastics through physical or chemical methods. Among these, the primary products of chemical recycling mainly include monomers and oligomers such as DMT, TPA, EG, BHET, and BHETA, while secondary products mainly include synthetic PET, UPR, ERD, VER, AR, PU, ​​UPP, NPS, PIF, OP, AD, and PBAT.

[0003] Polybutylene terephthalate (PBAT), a fully biodegradable polyester, is widely used in disposable packaging films and agricultural films due to its good toughness, film-forming properties, and easy blowing ability. Existing technologies have reported some methods for preparing recycled PBAT. For example, Chinese patent application CN112724388A discloses a production apparatus for recycling polyester into biodegradable PBAT. Dried recycled PET is alcoholyzed in an alcoholysis system to obtain crude BHET, which is then passed through a dealcoholization system to obtain BHET monomer. In a first esterification system, it reacts with BDO to obtain BHBT monomer, which then reacts with AA esterification in a second esterification system to obtain a copolyester. Finally, it undergoes pre-condensation and final condensation polymerization to increase the weight-average molecular weight, resulting in the PBAT product. However, PBAT has poor strength, especially low tensile strength. PBAT usually requires calcium addition or blending with PLA to achieve better physical properties. The mechanical properties of PBAT do not meet usage requirements, limiting its application range.

[0004] Existing technologies have reported methods for modifying PBAT to obtain multi-component copolyesters, thereby improving the mechanical properties of the materials. For example, CN 112080000 A discloses a method for synthesizing poly(terephthalic acid-adipate-m-epoxypentadecanylphenol butylene glycol) (PBATE material), which is synthesized from PBAT and m-epoxypentadecanylphenol, and its mechanical properties are superior to those of PBAT. CN 113861399 A discloses a biodegradable polyester poly(adipate-terephthalic acid-isosorbate-butylene glycol) (PBIAT) and its preparation method. The preparation method includes mixing 27-23% adipic acid, 31-26% terephthalic acid, 6-48% isosorbide, and 36-3% butanediol evenly, adding the mixture to a reactor for reaction, and then adding a catalyst to raise the temperature for polycondensation reaction to obtain PBIAT polyester. However, none of the aforementioned multi-component copolyesters reported in the prior art use waste polyester as raw material.

[0005] Furthermore, for recycled PBAT copolyester, existing technologies (Zhang Hongming, Zhao Junyu, Gao Fengxiang, et al. Study on the one-pot synthesis of biodegradable polymers by depolymerization-cocondensation of PET [J]. Acta Polymerica Sinica, 2022(009):053.) utilize diols with different structures to alcoholyze PET into low molecular weight prepolymers, and then add diacids for further esterification and condensation, so that the depolymerization and copolymerization reactions of PET are completed in a "one-pot" process. However, since recycled materials usually contain varying amounts of heavy metals, and heavy metal catalysts are also used in the depolymerization process, the residue of the catalyst will seriously affect the physical properties and aging resistance of the product. Currently, the production cost of petroleum-based biodegradable plastic PBAT is high, and its biodegradability is relatively slow. Moreover, since PBAT is mainly used for packaging bags, patterns, designs, or text are generally required to be printed on the packaging bags. If the printing performance is poor, the ink printing will easily fade, thus affecting the appearance and safety of the packaging bags.

[0006] Therefore, there is a need to provide a multi-component copolyester that has low residual heavy metal content, better degradation performance, better toughness and tensile strength, lower carbon emission value, and better printability. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies, such as high heavy metal content and poor printability, and to provide a multi-element copolyester.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned multi-component copolyester.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A multi-component copolyester, said multi-component copolyester comprising:

[0011] Component A, a dicarboxylic acid compound, comprises, based on the total molar amount of component A:

[0012] a1, at least one aliphatic dicarboxylic acid, 35-65 mol%;

[0013] a2, 35-65 mol% of at least one aromatic dicarboxylic acid or its derivative;

[0014] Component B, 1,4-Butanediol;

[0015] Component C, a third monomer, is based on the total molar amount of components B and C, wherein component C accounts for 5 to 30 mol%; and the third monomer is at least one of ethylene glycol, 1,4-cyclohexanediol, and isosorbide.

[0016] The crystallinity of the multi-component copolyester is 5-22%, including but not limited to 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, and 22%; the zinc content in the multi-component copolyester is ≤100ppm, and the titanium content is ≤120ppm.

[0017] The monomers of the multi-component copolyester of the present invention include aliphatic-aromatic dicarboxylic acid compounds, 1,4-butanediol, and a small amount of a third monomer. It has extremely low metal ion content, with zinc content ≤100ppm and titanium content ≤120ppm, and a crystallinity of 5~22%. The multi-component copolyester exhibits good biodegradability, tensile properties, and printability.

[0018] In this invention, the zinc and titanium residues in the multi-component copolyester are introduced from the catalysts used in the depolymerization and polycondensation processes, as well as from impurities in the waste polyester raw materials.

[0019] Preferably, the zinc content in the multi-component copolyester is 45-70 ppm, and the titanium content is 50-105 ppm.

[0020] Preferably, the calcium content in the multi-component copolyester is ≤71 ppm.

[0021] More preferably, the calcium content in the multi-component copolyester is 35-60 ppm.

[0022] Preferably, the silicon content in the multi-component copolyester is ≤85ppm.

[0023] More preferably, the silicon content in the multi-component copolyester is 35-50 ppm.

[0024] The residual calcium and silicon in multi-component copolyesters are mainly due to the introduction of impurities from the polyester raw materials.

[0025] In this invention, the crystallinity of the multi-component copolyester was analyzed using X-ray diffraction (XRD) according to standard JY / T 0587-2020. Specifically, a BRUKER D8 ADVANCE X-ray diffractometer was used at room temperature, with CuKa rays (λ = 0.154 nm) collected every 0.05°, and the scanning angle range was 6° to 60°.

[0026] In this invention, the zinc content and titanium content are tested according to the following method:

[0027] Inductively coupled plasma atomic emission spectrometry (ICP-OES) was used, and the determination method was performed according to the standard inductively coupled plasma atomic emission spectrometry method US EPA 6010C:2014.

[0028] Preferably, the melting point of the multi-component copolyester is 105~140℃, including but not limited to 105℃, 107℃, 109℃, 111℃, 113℃, 115℃, 117℃, 119℃, 121℃, 123℃, 125℃, 127℃, 129℃, 131℃, 133℃, 135℃, 137℃, 139℃, and 140℃.

[0029] The melting point of the multi-component copolyester was tested using a differential scanning calorimeter in accordance with standard ISO 11357-3:2018.

[0030] Preferably, the relative viscosity of the multi-component copolyester is 1.2 to 1.8, including but not limited to 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, and 1.8.

[0031] The relative viscosity of the multi-component copolyester was tested using the following method:

[0032] According to the standard method of GB / T 17931-1999, the concentration of the sample was determined in a phenol / chloroform solution with a weight ratio of 1:1 in a constant temperature water bath at 25±0.05 ℃, with a sample concentration of 5 mg / ml.

[0033] Preferably, the terminal carboxyl group content of the multi-component copolyester is 13~30 mmol / t, including but not limited to 13 mmol / t, 14 mmol / t, 15 mmol / t, 16 mmol / t, 17 mmol / t, 18 mmol / t, 19 mmol / t, 20 mmol / t, 21 mmol / t, 22 mmol / t, 23 mmol / t, 24 mmol / t, 25 mmol / t, 26 mmol / t, 27 mmol / t, 28 mmol / t, 29 mmol / t, and 30 mmol / t.

[0034] The content of terminal carboxyl groups was tested using the following method:

[0035] The content of terminal carboxyl groups was tested according to standard FZ / T 50012-2006 using an automatic potentiometric titration method.

[0036] Preferably, the weight-average molecular weight of the multi-component copolyester is 40,000 to 100,000, including but not limited to 40,000, 45,000, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, 85,000, 90,000, 95,000, and 100,000.

[0037] The weight-average molecular weight was tested using the following method:

[0038] According to the standard GB / T 21863-2008 Gel permeation chromatography (GPC), an ultra-high performance polymer chromatograph (APC) was used, tetrahydrofuran was used as the eluent, a differential detector was used, the column temperature was 40℃, and the flow rate was 0.5mL / min.

[0039] Preferably, the aliphatic dicarboxylic acid is selected from at least one of malonic acid, succinic acid, adipic acid, sebacic acid, pimelic acid, octanoic acid, and azelaic acid, and the aromatic dicarboxylic acid or its derivative is selected from at least one of terephthalic acid or its derivative, and isophthalic acid or its derivative.

[0040] This invention also protects a method for preparing the above-mentioned multi-component copolyester, comprising the following steps:

[0041] S1. Initial Deconstruction:

[0042] Waste terephthalic acid polyester was dissolved in an alcohol solvent containing a depolymerization catalyst, and a primary depolymerization reaction was carried out under normal pressure, an inert gas atmosphere, and microwave conditions to obtain the primary depolymerization product.

[0043] The initial depolymerization reaction is carried out at a temperature of 180~230℃ for 15~120 min.

[0044] S2. Re-disaggregation:

[0045] A portion of the diol is extracted from the initial depolymerization product obtained in step S1, and a chelating agent is added. The re-depolymerization reaction is carried out under normal pressure, inert gas atmosphere, and microwave conditions. The filtrate obtained after filtering the reactants is the re-depolymerization product.

[0046] The re-depolymerization reaction is carried out at a temperature of 160~190℃ for 10~20 min.

[0047] S3. Esterification reaction:

[0048] Based on the monomer content of the multi-component copolyester, at least one of aliphatic dicarboxylic acid, a third monomer, and 1,4-butanediol is added to the re-depolymerization product of step S2, along with a polymerization catalyst, a chain extender, and a stabilizer. The esterification reaction is carried out under an inert gas atmosphere until the theoretical water yield reaches 90%, thus obtaining the esterified product.

[0049] S4. Condensation polymerization:

[0050] After removing excess alcohol solvent from the esterification product of step S3, it is mixed with a polycondensation catalyst and subjected to a polycondensation reaction under vacuum to obtain the multi-component copolyester.

[0051] The method for preparing the multi-component copolyester of the present invention uses waste polyester as raw material and obtains a multi-component copolyester with low heavy metal content and suitable crystallinity through two alcoholysis, esterification reaction and polycondensation steps.

[0052] In the initial depolymerization step, waste polyester undergoes preliminary depolymerization under normal pressure, an inert gas atmosphere, and microwave conditions in the presence of a depolymerization catalyst. The initial depolymerization reaction temperature is relatively high, and most of the waste polyester is depolymerized into monomers or oligomers. Then, a portion of ethylene glycol is extracted from the initial depolymerization product, and a chelating agent is added for a second depolymerization, i.e., re-depolymerization. The re-depolymerization temperature is lower than that of the initial depolymerization, and the time is shorter. Under the action of the chelating agent, most of the heavy metal ions in the waste polyester are simultaneously removed during the re-depolymerization process, and the addition of the chelating agent does not negatively affect the printability or crystallinity of the polyester.

[0053] In the preparation method of this invention, a portion of the diol is extracted in step S2, the diol being a depolymerization byproduct. In step S3, an aliphatic dicarboxylic acid and a third monomer are added, both to obtain a multi-component copolyester with suitable monomer content. The monomer content of the finally obtained multi-component copolyester meets the following ranges: Component A, a dicarboxylic acid compound, based on the total molar amount of component A, includes: a1, 35-65 mol% of at least one aliphatic dicarboxylic acid; a2, 35-65 mol% of at least one aromatic dicarboxylic acid or its derivative; Component B, 1,4-butanediol; Component C, a third monomer, based on the total molar amount of components B and C, wherein component C accounts for 5-30 mol%.

[0054] The method for extracting a portion of ethylene glycol in step S2 can be vacuum distillation.

[0055] Preferably, the waste polyester includes one or more of recycled polyethylene terephthalate (PET), polybutylene terephthalate (PBT), PET / PBT alloy, and PBAT.

[0056] Optionally, the sources of the waste polyester include, but are not limited to, post-consumer recycled plastic (PCR), post-industry recycled plastic (PIR), ocean-bound plastic (OBP), and in-the-ocean plastics (IOP).

[0057] Preferably, the waste polyester further includes the steps of impurity removal, washing, and crushing before initial depolymerization.

[0058] Preferably, in step S2, the chelating agent is a biomass chelating agent.

[0059] Preferably, the chelating agent includes at least one of stearyl citrate, calcium citrate, tea polyphenols, and phytic acid.

[0060] More preferably, the chelating agent is tea polyphenols.

[0061] Tea polyphenols, as chelating agents, can not only efficiently complex residual metal ions in waste polyester, but also help stabilize the reaction system and reduce yellowing of products in multi-component copolyesters.

[0062] Preferably, in step S2, the amount of chelating agent added is 0.01~0.1 wt. of waste polyester.

[0063] Chelating agents can be added in small amounts to effectively remove metal ions from waste polyester.

[0064] Preferably, in step S1, the depolymerization catalyst includes at least one of zinc acetate, antimony acetate, sodium carbonate, titanate nanotubes, titanium phosphate, and tetrabutyl titanate.

[0065] Preferably, in step S1, the amount of the depolymerization catalyst added is 0.05~0.5 wt. of the waste polyester.

[0066] Preferably, the alcohol solvent includes at least one of 1,4-butanediol and ethylene glycol.

[0067] Preferably, the mass ratio of the waste polyester to the alcohol solvent is 1:0.8 to 1:2.

[0068] Preferably, the polymerization catalyst and the polycondensation catalyst are each independently selected from at least one of tetraisopropyl titanate, tetraisopropyl titanate, titanium phosphate compound, titanium silicon compound, titanium magnesium composite catalyst, ethylene glycol titanate, butanediol titanate, titanium dioxide, antimony dioxide, and monobutyltin oxide.

[0069] Preferably, in step S3, the aliphatic dicarboxylic acid is adipic acid and / or sebacic acid.

[0070] Since the waste polyester is depolymerized in steps S1 and S2, some aliphatic alcohols are already present in the depolymerization products. In step S3, a certain amount of aliphatic alcohols are added again, so that the alcohols in the entire reaction system are in excess.

[0071] The stabilizer is one or more of the following: organic phosphites, trimethyl phosphates, and hindered phenols.

[0072] Optionally, the organic phosphite stabilizer may be one or more of trimethyl phosphite, triethyl phosphite, or triphenyl phosphite.

[0073] Optionally, the phosphate ester stabilizer may be one or more of triphenyl phosphate, trimethyl phosphate, or triethyl phosphate.

[0074] Optionally, the hindered phenolic stabilizer may be 3,5-di-tert-butyl-4-hydroxybenzyl diethylphosphonate (antioxidant 1222) and / or antioxidant 1010.

[0075] The chain extender is at least one of pentaerythritol, trimethylolethane, trimethylolpropane (TMP), xylitol, sorbitol, HDI, MDI, TDI, isoflurone diisocyanate, ethylene-methyl methacrylate copolymer (EMA), and polyfunctional epoxy compound ADR.

[0076] Preferably, the amount of chain extender added is 0~0.1 wt. of waste polyester.

[0077] Preferably, in step S3, the esterification reaction is carried out at a temperature of 170~210℃ for 1~2 hours.

[0078] Preferably, in step S3, the amount of polymerization catalyst added is 0.01-0.1 wt. of waste polyester.

[0079] Preferably, in step S4, the amount of polycondensation catalyst added is 0.03~0.1 wt. of waste polyester.

[0080] Preferably, in step S4, the temperature of the polycondensation reaction is 240~250℃, the time is 2~5h, and the pressure is 20~100Pa.

[0081] Preferably, in step S1, the microwave reaction conditions are: frequency of 2450 Hz, temperature of 180-230 °C, and time of 15-120 min.

[0082] Preferably, in step S2, the microwave reaction conditions are: frequency of 2450 Hz, temperature of 160-190 °C, and time of 10-20 min.

[0083] Compared with the prior art, the beneficial effects of the present invention are:

[0084] This invention develops a multi-component copolyester and its preparation method. The multi-component copolyester of this invention uses waste polyester as raw material and undergoes primary alcoholysis, secondary alcoholysis, esterification reaction, and polycondensation steps to obtain a multi-component copolyester with low heavy metal content and suitable crystallinity.

[0085] The initial depolymerization and subsequent depolymerization are carried out under microwave conditions. The subsequent depolymerization includes the addition of a chelating agent. The addition of the chelating agent has a synergistic effect with the subsequent depolymerization reaction, removing most of the metal ion residues in the waste polyester. The resulting multi-component copolyester has extremely low heavy metal content, with zinc content ≤100ppm and titanium content ≤120ppm.

[0086] The multi-component copolyester of the present invention has extremely low heavy metal content and a good range of crystallinity. Therefore, the obtained multi-component copolyester has excellent printability and good biodegradability, and can be widely used in the fields of disposable packaging films and agricultural films. Attached Figure Description

[0087] Figure 1 The infrared spectrum of the multi-component copolyester of Example 1;

[0088] Figure 2 The 1H NMR spectrum of the multi-component copolyester of Example 1;

[0089] Figure 3 The XRD pattern of the multi-component copolyester of Example 1 is shown below.

[0090] Figure 4 The image shows the GPC diagram of the multi-component copolyester of Example 1. Detailed Implementation

[0091] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any way.

[0092] The raw materials used in the embodiments and comparative examples of this invention are all commercially available;

[0093] in:

[0094] Waste polyester-1, PET, recycled from electronic pallet material;

[0095] Waste polyester-2, rPET-pellet, recycled from Indonesian marine plastics;

[0096] Waste polyester-3, PET / PBT, recycled PET / PBT alloy;

[0097] Waste polyester-4, PBAT, recycled PBAT waste;

[0098] Condensation catalyst and polymerization catalyst: tetrabutyl titanate, purchased from Aladdin;

[0099] Depolymerization catalyst: Zinc acetate, purchased from Aladdin;

[0100] Chain extender: Trimethylolpropane;

[0101] Chelating agents: tea polyphenols, stearyl citrate, and phytic acid, all purchased from Maclean's;

[0102] Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0103] Examples 1-4

[0104] Examples 1-4 each provide a method for preparing a multi-component copolyester, comprising the following steps, with specific raw materials and reaction conditions shown in Table 1:

[0105] S1. Initial Deconstruction:

[0106] Waste polyester with an average particle size ≤2mm was dissolved in an alcohol solvent containing a depolymerization catalyst and placed in a microwave reactor (Yantai Haoming Microwave Company). Under a nitrogen atmosphere and microwave conditions, a primary depolymerization reaction was carried out to obtain the primary depolymerization product. The microwave conditions were: frequency 2450HZ.

[0107] S2. Re-disaggregation:

[0108] A portion of the diol was extracted from the initial depolymerization product obtained in step S1 by vacuum distillation, and a chelating agent was added. The mixture was then placed in a microwave reactor and subjected to a re-depolymerization reaction under normal pressure, an inert gas atmosphere, and microwave conditions. The filtrate obtained after filtration of the reactants was the re-depolymerization product. The microwave conditions were: a frequency of 2450 Hz.

[0109] S3. Esterification reaction:

[0110] Based on the monomer content of the target multi-component copolyester, at least one of aliphatic dicarboxylic acid, a third monomer, and 1,4-butanediol is added to the re-depolymerization product of step S2, along with a polymerization catalyst, chain extender, and stabilizer. The esterification reaction is carried out under an inert gas atmosphere until the theoretical water yield reaches 90%, thus obtaining the esterified product.

[0111] S4. Condensation polymerization:

[0112] After removing excess alcohol from the esterification product of step S3, it is mixed with a polycondensation catalyst and subjected to a polycondensation reaction under vacuum to obtain the multi-component copolyester.

[0113] Table 1. Raw materials and reaction conditions for Examples 1-4

[0114]

[0115] Examples 5-10

[0116] Examples 5-10 provide a method for preparing a multi-component copolyester. Except for step S2, the other steps are the same as in Example 1. Specifically, the preparation methods of Examples 5-10 differ from those of Example 1 in that:

[0117] In Example 5, the chelating agent was tea polyphenols;

[0118] In Example 6, the chelating agent was stearyl citrate;

[0119] In Example 7, the chelating agent accounted for 0.01 wt.% of the waste polyester.

[0120] In Example 8, the chelating agent accounted for 0.1 wt.% of the waste polyester.

[0121] In Example 9, the conditions for the re-depolymerization reaction were 190°C for 10 min;

[0122] The conditions for the re-depolymerization reaction in Example 10 were 160°C for 20 min.

[0123] The monomer ratios obtained in Examples 5-10 are shown in Table 2.

[0124] Table 2. Monomer Ratios in Multi-component Copolyesters Prepared in Examples 5-10

[0125]

[0126] Comparative Examples 1-5

[0127] Comparative Examples 1-5 provide a method for preparing a multi-component copolyester, comprising the following steps, with specific raw materials and reaction conditions shown in Table 3:

[0128] S1. Initial Deconstruction:

[0129] Waste polyester with an average particle size ≤2mm was dissolved in an alcohol solvent containing a depolymerization catalyst and placed in a microwave reactor (Yantai Haoming Microwave Company). Under a nitrogen atmosphere and microwave conditions, a primary depolymerization reaction was carried out to obtain the primary depolymerization product.

[0130] S2. Re-disaggregation:

[0131] By vacuum distillation, a portion of ethylene glycol is extracted from the initial depolymerization product obtained in step S1, and a chelating agent is added (or no chelating agent is added). The product is then placed in a microwave reactor and subjected to a re-depolymerization reaction under normal pressure, an inert gas atmosphere, and microwave conditions. The filtrate obtained after filtering the reactants is the re-depolymerization product.

[0132] S3. Esterification reaction:

[0133] Based on the monomer content of the target multi-component copolyester, at least one of aliphatic dicarboxylic acid, a third monomer, and 1,4-butanediol is added to the re-depolymerization product of step S2, along with a polymerization catalyst, chain extender, and stabilizer. The esterification reaction is carried out under an inert gas atmosphere until the theoretical water yield reaches 90%, thus obtaining the esterified product.

[0134] S4. Condensation polymerization:

[0135] After removing excess alcohol from the esterification product of step S3, it is mixed with a polycondensation catalyst and subjected to a polycondensation reaction under vacuum to obtain the multi-component copolyester.

[0136] Table 3. Raw materials and reaction conditions for Comparative Examples 1-5

[0137]

[0138] Performance testing

[0139] The performance of the multi-component copolyesters obtained in the above embodiments and comparative examples was tested, and the specific methods are as follows:

[0140] Melting point: ISO 11357-3:2018;

[0141] Relative viscosity: determined according to the standard method of GB / T 17931-1999 in a phenol / chloroform solution with a weight ratio of 1:1 in a constant temperature water bath at 25±0.05 ℃, with a sample concentration of 5 mg / ml;

[0142] Terminal carboxyl group content: FZ / T 50012-2006;

[0143] Metal ion residue: US EPA 6010C:2014;

[0144] Crystallinity: JY / T 0587-2020;

[0145] Weight-average molecular weight: determined by gel permeation chromatography (GPC);

[0146] 50-day biodegradation rate: Biodegradation performance was determined by composting in accordance with GB / T 19277-2003 "Determination of final aerobic biodegradation and disintegration capacity of materials under controlled composting conditions by measuring the released carbon dioxide".

[0147] Print retention rate: According to GB / T 38082-2019, Section 5.3.4 Print quality test for biodegradable plastic shopping bags.

[0148] The multi-component copolyester obtained in Example 1 was subjected to infrared spectroscopy, 1H NMR spectroscopy, and XRD, respectively, using the following methods:

[0149] Infrared spectroscopy: The sample preparation method was hot pressing to form a film, with a wavenumber range of 4000~400cm-1, 16 scans, a resolution of 4, and a sampling method of transmission.

[0150] 1H NMR: The 1H NMR spectrum was measured using deuterated trifluoroacetic acid as solvent and tetramethylsilane (TMS) as internal standard.

[0151] XRD: X-ray diffractometer (XRD) was used in accordance with standard JY / T 0587-2020.

[0152] Using XRD testing, the areas of crystalline peaks (sharp peaks) and non-crystalline peaks (diffuse peaks) are obtained. The crystallinity is then calculated using the following formula:

[0153]

[0154] In the formula:

[0155] Wc - Crystallinity

[0156] I C -Integral area of ​​diffraction peaks in crystalline form

[0157] I a -Integral area of ​​diffraction peaks in amorphous states

[0158] The infrared spectrum of the multi-component copolyester in Example 1 is shown in [reference needed]. Figure 1 The proton NMR spectrum is shown below. Figure 2 XRD pattern can be found Figure 3 GPC map see Figure 4 .

[0159] The test results of the examples are shown in Table 4, and the test results of the comparative examples are shown in Table 5.

[0160] Table 4

[0161]

[0162] Table 5

[0163]

[0164] According to the test results in Table 4, the crystallinity of the multi-component copolyester obtained using the technical solution of this invention is suitable, ranging from 10% to 19.5%, and the heavy metal ion content is extremely low. The resulting product exhibits excellent performance, with a 50-day biodegradability rate exceeding 35% and a printing peeling rate below 7%. Furthermore, the infrared spectrum and 1H NMR spectrum of the multi-component copolyester obtained in Example 1 show that this invention successfully prepared PBATE, and the proportions of different chain segments can be calculated. Infrared spectral analysis: as shown... Figure 1 The figure shown is 1731 cm. -1 The carbonyl (-C=O) stretching vibration peak appearing at 1104 cm⁻¹ belongs to the ester bond in the PBATE copolyester; -1 1271cm -1 This is the stretching vibration peak of the ether bond (COC). 731 cm⁻¹ -1 The peaks are the out-of-plane bending vibration peaks of CH on the para-disubstituted benzene ring, and the stretching and out-of-plane bending vibration absorption peaks of the (-CH) group at 3053 cm⁻¹ are attributed to the (-CH) group on the benzene ring. Figure 1 1577cm -1 The newly appearing absorption peak is the stretching vibration absorption peak of the benzene ring skeleton, at 1458 cm⁻¹. -1 The absorption peak at 2957 cm⁻¹ is the in-plane bending vibration absorption peak of -CH₂-CH₂- in PBATE copolyester; -1 and 1410cm -1 1360cm -1 These are the stretching vibration absorption peaks and in-plane bending vibration peaks of the methylene (-CH2-) group on the PBATE copolyester monomer and branch chain, respectively; located in the range of 3630–3400 cm⁻¹. -1 The peak at this point represents the stretching vibration of hydroxyl groups associated with intermolecular bonding, which is attributed to the terminal hydroxyl groups in the PBATE copolyester. This confirms that the obtained polyester is PBATE. Let T represent terephthalic acid. Structural unit, denoted by A for adipic acid Structural unit, denoted by B, for butanediol Structural unit, denoted by E for ethylene glycol Structural unit. From Figure 2As can be seen from the data, peak a at chemical shift δ 8.1 is the hydrogen atom peak on the benzene ring of structural unit T; peaks j, k, and l at δ 4.70-4.27 are the hydrogen atom peaks of the two methylene groups on structural unit E; peaks b, c, d, and e at δ 4.7-4.1 are the hydrogen atom peaks of the two methylene groups on structural unit B connected to oxygen atoms; peak f at δ 2.32 is the hydrogen atom peak of the two methylene groups on structural unit A connected to carbonyl groups; peaks g and h at δ 1.80-1.97 are the two middle methylene hydrogen atom peaks on structural unit B; and peak i at δ 1.54-1.66 is the two middle methylene hydrogen atom peaks on structural unit A. By studying the splitting peaks at δ = 4.70-4.27 and δ = 4.43-4.09, the composition ratio of chain segments in the copolyester can be calculated and the sequence distribution can be explored. The randomness R=1 indicates that it is a random copolymer, and the calculated molar ratio of ethylene glycol segments in the polyester is 5%.

[0165] According to Examples 1, 5, and 6, it can be seen that when tea polyphenols are used as chelating agents, compared with phytic acid or stearyl citrate, the metal ion content of the multi-component copolyester is relatively lower, the tensile strength is higher, the printability is better, and the biodegradability is better.

[0166] According to the test results of the comparative examples, in Comparative Examples 1 and 2, without the addition of chelating agents, the metal ions of the obtained multi-component copolyesters could not be effectively removed, the content of metal ions was very high, and the tensile strength of the multi-component copolyesters was poor.

[0167] Based on the test results of Comparative Examples 3 and 4, it can be seen that during the re-depolymerization process in step S2, if the re-depolymerization temperature is too high or too low, the chelating agent cannot effectively remove metal ions, and the metal ion content of the obtained multi-component copolyester is still too high; moreover, the crystallinity of the obtained multi-component copolyester is not within a suitable range, resulting in poor overall performance of the product.

[0168] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A multi-component copolyester, characterized in that, The multi-component copolyester comprises: Component A, a dicarboxylic acid compound, comprises, based on the total molar amount of component A: a1, at least one aliphatic dicarboxylic acid, 35-65 mol%; a2, 35-65 mol% of at least one aromatic dicarboxylic acid or its derivative; Component B, 1,4-Butanediol; Component C, a third monomer, is based on the total molar amount of components B and C, wherein component C accounts for 5 to 30 mol%; and the third monomer is at least one of ethylene glycol, 1,4-cyclohexanediol, and isosorbide. The crystallinity of the multi-component copolyester is 5-22%, and the zinc content in the multi-component copolyester is ≤100ppm, the titanium content is ≤120ppm, the calcium content is 35-60ppm, and the silicon content is 35-50ppm.

2. The multi-component copolyester according to claim 1, characterized in that, The melting point of the multi-component copolyester is 105~140℃.

3. The multi-component copolyester according to claim 1, characterized in that, The relative viscosity of the multi-component copolyester is 1.2~1.

8.

4. The multi-component copolyester according to claim 1, characterized in that, The end carboxyl group content of the multi-component copolyester is 13-30 mmol / t.

5. The multi-component copolyester according to claim 1, characterized in that, The zinc content in the multi-component copolyester is 45~70ppm, and the titanium content is 50~105ppm.

6. The multi-component copolyester according to claim 1, characterized in that, The aliphatic dicarboxylic acid is selected from at least one of malonic acid, succinic acid, adipic acid, sebacic acid, pimelic acid, octanoic acid, and azelaic acid, and the aromatic dicarboxylic acid or its derivative is selected from at least one of terephthalic acid or its derivative, and isophthalic acid or its derivative.

7. The method for preparing the multi-component copolyester according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Initial Deconstruction: Waste terephthalic acid polyester was dissolved in an alcohol solvent containing a depolymerization catalyst, and a primary depolymerization reaction was carried out under normal pressure, an inert gas atmosphere, and microwave conditions to obtain the primary depolymerization product. The initial depolymerization reaction is carried out at a temperature of 180~230℃ for 15~120 min. S2. Re-disaggregation: A portion of the diol is extracted from the initial depolymerization product obtained in step S1, and a chelating agent is added. The re-depolymerization reaction is carried out under normal pressure, inert gas atmosphere, and microwave conditions. The filtrate obtained after filtering the reactants is the re-depolymerization product. The re-depolymerization reaction is carried out at a temperature of 160~190℃ for 10~20 min. S3. Esterification reaction: Based on the monomer content of the multi-component copolyester, at least one of aliphatic dicarboxylic acid, a third monomer, and 1,4-butanediol is added to the re-depolymerization product of step S2, along with a polymerization catalyst, chain extender, and stabilizer. The esterification reaction is carried out under an inert gas atmosphere until the theoretical water yield reaches 85-95%, yielding the esterified product. S4. Condensation polymerization: After removing excess alcohol solvent from the esterification product of step S3, it is mixed with a polycondensation catalyst and subjected to a polycondensation reaction under vacuum until the relative viscosity of the system is 1.2~1.8, thus obtaining the multi-component copolyester.

8. The preparation method according to claim 7, characterized in that, The waste terephthalic acid polyester is one or more of the following: recycled PET, PBT, PET / PBT alloy, and PBAT.

9. The preparation method according to claim 7, characterized in that, At least one of the following (a)-(e): (a) In step S2, the chelating agent is at least one of stearyl citrate, calcium citrate, tea polyphenols, and phytic acid; (b) In step S1, the depolymerization catalyst is at least one of zinc acetate, antimony acetate, sodium carbonate, titanate nanotubes, titanium phosphate, and tetrabutyl titanate; (c) The polymerization catalyst and the polycondensation catalyst are each independently selected from at least one of tetraisopropyl titanate, tetraisopropyl titanate, titanium phosphorus compound, titanium silicon compound, titanium magnesium composite catalyst, ethylene glycol titanate, butanediol titanate, titanium dioxide, antimony dioxide, and monobutyltin oxide; (d) The stabilizer is one or more of the following: organic phosphites, trimethyl phosphates, and hindered phenols; (e) The chain extender is at least one of pentaerythritol, trimethylolethane, trimethylolpropane, xylitol, sorbitol, HDI, MDI, TDI, isoflurone diisocyanate, ethylene-methyl methacrylate copolymer, and polyfunctional epoxy compound ADR.

10. The preparation method according to claim 9, characterized in that, In step S2, the chelating agent is tea polyphenols.

11. The preparation method according to claim 7, characterized in that, At least one of the following (f)-(j): (f) In step S2, the amount of the chelating agent added is 0.01~0.1 wt.% of the waste polyester; (g) In step S1, the amount of the depolymerization catalyst added is 0.05~0.5 wt.% of the waste polyester. (h) The amount of chain extender added is 0~0.1 wt.% of the waste polyester; (i) In step S4, the amount of the polycondensation catalyst added is 0.03~0.1 wt.% of the waste polyester. (j) In step S3, the amount of the polymerization catalyst added is 0.01-0.1 wt. of the waste polyester.

Images