A bio-based copolyester and methods of making and using the same

Abstract

This application relates to the field of bio-based copolyester technology, and discloses a bio-based copolyester, its preparation method, and its applications. The preparation method of the bio-based copolyester includes: prepolymerizing an aliphatic lactone under an inert atmosphere and at a temperature of 160–180°C in the presence of a catalyst to obtain a prepolymer; adding a cyclic butylene terephthalate oligomer to the prepolymer, and then prepolymerizing at 180–200°C; and finally, after vacuuming, heating to 220–250°C for further polymerization to obtain the bio-based copolyester. In this application, the aliphatic lactone is first prepolymerized at a lower temperature through ring-opening; the prepolymer and the cyclic butylene terephthalate oligomer are then mixed uniformly in a liquid state for prepolymerization, followed by final polymerization at a higher temperature; the prepolymerization, prepolymerization, and final polymerization are carried out stepwise at different temperatures to obtain a bio-based copolyester with controllable structure and high molecular weight. The copolyester of this application has a number-average molecular weight of 18,000 to 25,000, and the mechanical properties of the melt-spun fibers are ≥3.00 cN / dtex breaking strength and 20.0 to 50.0% breaking elongation.

Description

Technical Field

[0001] This application relates to the field of bio-based copolyester technology, specifically to a bio-based copolyester, its preparation method, and its application. Background Technology

[0002] Bio-based polyesters have attracted widespread attention due to their excellent biodegradability. Among them, aliphatic polyesters, represented by polylactic acid (PLA), have garnered significant attention for their highly flexible main chain structure. However, the single aliphatic molecular chain suffers from drawbacks such as low strength, low heat softening temperature, poor heat resistance, and poor weather resistance of fiber products, which limits their application range.

[0003] Currently, related technologies utilize the design of aliphatic-aromatic copolyesters to significantly improve the structural and mechanical properties of copolymers. For example, Xiang Hengxue et al. synthesized poly(ethylene terephthalate-2-hydroxypropionic acid) ester polymers from lactide, terephthalic acid, and ethylene glycol under the catalysis of stannous octoate. In this process, the monomers of polyethylene terephthalate are prepared by esterification polycondensation of terephthalic acid and ethylene glycol at a relatively high reaction temperature, approximately 275–290°C; while polylactic acid is obtained through ring-opening copolymerization of lactide at a lower reaction temperature, 160–200°C. The matching between the ring-opening copolymerization of polylactic acid and the esterification polycondensation of polyethylene terephthalate is poor.

[0004] When terephthalic acid, ethylene glycol, and lactide are copolymerized to prepare aliphatic-aromatic copolyesters, the temperature of the esterification polycondensation reaction is much higher than that of the ring-opening copolymerization. At the esterification polycondensation temperature, on the one hand, the molecular weight distribution of polylactic acid obtained from the ring-opening copolymerization of lactide is uneven; on the other hand, the polylactic acid obtained from the copolymerization decomposes. In addition, the low molecular weight polylactic acid generated by ring-opening copolymerization will react with ethylene glycol, terephthalic acid, and polyethylene terephthalate to generate byproducts and low molecular weight aliphatic-aromatic copolyesters. All of these factors lead to an uncontrollable reaction process, resulting in an uncontrollable copolyester structure, leading to low molecular weight copolyesters or even polymerization failure. Summary of the Invention

[0005] The purpose of this application is to provide a bio-based copolyester, its preparation method and application. It adopts a stepwise ring-opening prepolymerization-repolymerization method to solve the problem in the prior art that the reaction process is uncontrollable due to poor matching between polyethylene terephthalate and polylactic acid, which in turn leads to uncontrollable copolyester structure, low molecular weight of the obtained copolyester or even polymerization failure.

[0006] To achieve the above objectives, the present application adopts the following technical solution.

[0007] In a first aspect, this application provides a method for preparing a bio-based copolyester, comprising:

[0008] Aliphatic lactones were prepolymerized under an inert atmosphere and at a temperature of 160–180°C in the presence of a catalyst to obtain a prepolymer.

[0009] Cyclic butylene terephthalate oligomers are added to the prepolymer, and the temperature is raised to 180-200℃ for prepolymerization; after vacuuming, the temperature is raised to 220-250℃ for repolymerization to obtain the bio-based copolyester.

[0010] Preferably, the mass ratio of the aliphatic lactone to the cyclic butylene terephthalate oligomer is (1-10):1.

[0011] Preferably, the aliphatic lactone is any one or a mixture of two of glycolide and lactide in any ratio.

[0012] Preferably, the catalyst is a metal alkyl compound or a tin salt compound.

[0013] Preferably, the catalyst is stannous octoate;

[0014] The amount of stannous octoate used is 0.1-3% of the total mass of the aliphatic lactone and cyclic butylene terephthalate oligomers.

[0015] In a second aspect, this application provides a bio-based copolyester prepared by the above-described preparation method, wherein the bio-based copolyester has a random block structure and a number-average molecular weight of 18,000 to 25,000.

[0016] A third aspect of this application provides the application of the bio-based copolyester prepared by the above-described preparation method in the preparation of fibers.

[0017] This application also provides a bio-based copolyester fiber, which is a bio-based copolyester prepared by the above method or the above-mentioned bio-based copolyester, produced by melt spinning at a temperature of 220-240°C.

[0018] Preferably, the preparation method further includes:

[0019] The bio-based copolyester is pre-crystallized by heating it to 80-90°C under vacuum, then the temperature is raised to remove the water of crystallization, and then the temperature is lowered to 50°C for later use.

[0020] More preferably, the bio-based copolyester fiber has a breaking strength ≥3.00 cN / dtex and a breaking elongation of 25.0 to 50.0%.

[0021] Compared with the prior art, the beneficial effects of this application are as follows:

[0022] 1) This application involves prepolymerizing a single or composite aliphatic lactone at a lower temperature to obtain a prepolymer; then, the prepolymer is uniformly mixed with a cyclic butylene terephthalate oligomer in a liquid state for precondensation, followed by final condensation at a higher temperature. Prepolymerization, precondensation, and final condensation are carried out stepwise at different temperatures. During prepolymerization, the ring-opening and copolymerization reactions of the aliphatic lactone are controllable, resulting in a high molecular weight aliphatic lactone polymer with a uniform molecular weight distribution. During precondensation, the macrocyclic oligopolyester structure of the cyclic butylene terephthalate oligomer is opened, yielding a chain oligomer, which is then thoroughly mixed with lactic acid. Finally, final condensation yields a bio-based copolyester with a controllable structure and high molecular weight.

[0023] On the one hand, the aliphatic lactone polymer obtained by prepolymerization has a uniform molecular weight distribution, and under prepolymerization and precondensation conditions, the aliphatic lactone polymer is not easily decomposed, further increasing the molecular weight. On the other hand, precondensation after prepolymerization avoids the low molecular weight aliphatic lactone polymer generated during prepolymerization from condensing with the chain oligomers, thus generating a low molecular weight bio-based copolyester. After prepolymerization and precondensation, the weight / molar ratio of the aliphatic lactone polymer and the cyclic butylene terephthalate oligomer is stable; during the final condensation process, the low-boiling-point polymer is reduced by negative pressure, further increasing the molecular weight of the bio-based copolyester. The bio-based copolyester prepared by the prepolymerization-precondensation and final condensation method of this application has a controllable structure, high molecular weight, and high tensile strength.

[0024] The number-average molecular weight of the multi-component copolyester in this application reaches 18,000 to 25,000, and the mechanical properties of the melt-spun fibers reach a breaking strength ≥3.00 cN / dtex and a breaking elongation of 25.0 to 50.0%. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The NMR spectrum of the copolyester of Example 1 is shown below.

[0027] Figure 2 The NMR spectrum of the copolyester in Example 1 is a graph showing its glass transition temperature and melting point parameters.

[0028] Figure 3 This is a photograph of the copolyester fiber from Example 1. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0030] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0031] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0032] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0033] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0034] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0035] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] A first aspect of this application provides a method for preparing a bio-based copolyester, comprising:

[0038] Aliphatic lactones were prepolymerized under an inert atmosphere and at a temperature of 160–180°C in the presence of a catalyst to obtain a prepolymer.

[0039] Cyclic butylene terephthalate oligomers are added to the prepolymer, and the temperature is raised to 180-200℃ for prepolymerization; after vacuuming, the temperature is raised to 220-250℃ for repolymerization to obtain the bio-based copolyester.

[0040] The preparation method of this application involves first prepolymerizing aliphatic lactones at a lower temperature under the catalysis of a catalyst to obtain a prepolymer; then, the prepolymer and cyclic butylene terephthalate oligomers are mixed uniformly in a liquid state for precondensation, followed by final condensation at a higher temperature. Prepolymerization, precondensation, and final condensation are carried out stepwise at different temperatures, avoiding uneven molecular weight distribution of the aliphatic lactone polymer obtained from ring-opening copolymerization due to high temperatures, and preventing decomposition of the aliphatic lactone polymer obtained from ring-opening copolymerization; precondensation after prepolymerization avoids the condensation of low-molecular-weight aliphatic lactone polymers generated during prepolymerization with the chain oligomers, resulting in a low-molecular-weight bio-based copolyester. After prepolymerization and precondensation, the weight / molar ratio of the aliphatic lactone polymer and the cyclic butylene terephthalate oligomers is stable; during the final condensation process, negative pressure is used to reduce the low-boiling-point polymer, further increasing the molecular weight of the bio-based copolyester. The bio-based copolyester prepared by the prepolymerization-prepolymerization and final polymerization method of this application has a controllable structure, high molecular weight, and high tensile strength.

[0041] In the embodiments of this application, the mass ratio of the aliphatic lactone to the cyclic butylene terephthalate oligomer is (1-10):1, preferably (1-2):1, and more preferably (1.3-2):1. Within this ratio range, the prepared bio-based copolyester has high molecular weight and good mechanical properties.

[0042] In the embodiments of this application, the aliphatic lactide is any one or a mixture of two of glycolide and lactide in any ratio, which can prepare different bio-based copolyesters.

[0043] In the embodiments of this application, the catalyst is a metallic alkyl compound, such as 4-phenyltin or diethylcadmium; or a tin salt compound, such as stannous octoate or stannous isooctanoate. Stannous octoate is preferred as the catalyst, and the amount of stannous octoate used is 0.1-3% of the total mass of the lactide and cyclic butylene terephthalate oligomers, more preferably 1-2% of the total mass of the lactide and cyclic butylene terephthalate oligomers.

[0044] In the embodiments of this application, the pressure inside the reactor during the prepolymerization reaction is preferably atmospheric pressure, and the inert gas is either nitrogen or argon, preferably nitrogen. Nitrogen can reduce the occurrence of side reactions in the ring-opening reaction of aliphatic lactide and increase the molecular weight of the aliphatic lactide polymer.

[0045] In the embodiments of this application, before polycondensation, the reactor is evacuated to create a negative pressure, preferably 10–20 Pa. Within this pressure range, it helps to increase the yield of the polycondensation reaction, reduce low-boiling-point components in the polymer, and increase the molecular weight of the polymer.

[0046] Specifically, at 160–180°C, lactide and / or glycolide open their cyclic structures. Under the action of stannous octoate, the carbonyl oxygen on lactide coordinates with the tin element in stannous octoate, and the acyl oxygen bond of the lactide monomer enters the coordination bond to carry out chain growth and prepolymerization.

[0047] Cyclic butylene terephthalate oligomers are added to the prepolymer and heated to 180–200°C for prepolymerization. At this temperature, the cyclic butylene terephthalate oligomers undergo ring-opening to obtain a chain-like intermediate product with significantly reduced viscosity, making it easy to mix thoroughly with the prepolymer. After vacuuming, the temperature is raised to 220–250°C for final polymerization. The prepolymer and intermediate product undergo a polymerization reaction to produce a copolyester. As the reaction proceeds, the copolyester content continuously increases, and the viscosity in the reactor continues to rise. When the viscosity reaches the set value, it indicates that the molecular weight of the copolyester has reached the required molecular weight, and the copolyester is then discharged.

[0048] In the embodiments of this application, the viscosity of the product in the reactor is determined by the power value of the reactor agitator. As the reaction proceeds, the viscosity of the mixture in the reactor increases, and the agitation power gradually increases. According to experimental tests, when the agitation power reaches 55W, the viscosity of the product meets the requirements, and the prepared bio-based copolyester has a random block structure with a number-average molecular weight of 18,000–25,000. In the embodiments of this application, a agitation power of 55W is used as the set value for determining viscosity.

[0049] The bio-based copolyester of this application can be used to prepare bio-based copolyester fibers.

[0050] Another aspect of this application provides a bio-based copolyester fiber, which is a bio-based copolyester prepared by the above method or the above-mentioned bio-based copolyester, produced by melt spinning at a temperature of 220 to 240°C.

[0051] In the embodiments of this application, before melt spinning, the bio-based copolyester is pre-crystallized by heating it to 80-90°C under vacuum, then heated to remove the water of crystallization, and cooled to 50°C for later use. Pre-crystallization can increase the melting temperature of the bio-based copolyester and avoid polymer agglomeration during heating; if agglomeration exists in the polymer, it will reduce the strength of the fiber.

[0052] In the embodiments of this application, a melt spinning machine is used for melt spinning, wherein the metering pump speed is 26 r / min; the specifications of the melt spinning spinneret are: containing 24 spinneret holes, and the size of each spinneret hole is 0.25 × 0.63 mm.

[0053] The bio-based copolyester fiber prepared in this application has a breaking strength ≥3.30 cN / dtex and a breaking elongation of 20.0-50.0%.

[0054] The present application will be further illustrated by the following examples.

[0055] In the embodiments of this application, the cyclic butylene terephthalate oligomer was purchased from Cyclics, Inc., USA.

[0056] Example 1

[0057] 1) Preparation of polylactic acid-polybutylene terephthalate copolyester

[0058] In the polymerization reactor, 2 kg of lactide and 0.06 kg of stannous octoate were added, and nitrogen was used to purge the air from the reactor. Prepolymerization was carried out at 180°C and atmospheric pressure for 1 hour.

[0059] Add 2 kg of cyclic butylene terephthalate oligomer and continue the reaction at 180°C and atmospheric pressure for 1 hour. Evacuate the reactor to a pressure of 20 Pa, raise the temperature to 250°C, and react for 1 hour. When the mechanical stirring power reaches 55 W, discharge the product to obtain the polymerized product with a number average molecular weight of 21,000.

[0060] 2) Preparation of polylactic acid-polybutylene terephthalate copolyester fibers

[0061] Poly(lactic acid)-poly(lactic acid)-polybutylene terephthalate (PET) copolyester chips were vacuum dried at 90°C for 8 hours to ensure sufficient pre-crystallization, then heated to 120°C and vacuum dried for 24 hours to completely remove the water of crystallization; finally, the temperature was lowered to 50°C and maintained under vacuum for later use. The chips were then spun using a melt spinning machine at 220–240°C, with a spinneret containing 24 orifices of 0.25 × 0.63 mm and a metering pump speed of 26 r / min, yielding PET-PET-PET copolyester fibers with a breaking strength of 4.40 cN / dtex and an elongation at break of 25.0%.

[0062] The copolyester of Example 1 was subjected to structural and performance tests.

[0063] Figure 1 The NMR spectrum of the copolymer from Example 1 is shown. Peak a corresponds to the chemical shift peak of hydrogen atoms on the benzene ring of polybutylene terephthalate (PBT); peak c (2.2–2.3 ppm) and peak b1 (4.6–4.7 ppm) correspond to the chemical shift peaks of secondary hydrogen atoms on the butanediol structure in PBT; peak b2 is the chemical shift peak of the methylene groups at both ends of butanediol after the butanediol forms ester bonds with PTA and LA. This demonstrates that the copolyester material was synthesized in a controlled manner in Example 1.

[0064] Figure 2 This is a graph showing the thermal properties of polybutylene terephthalate (PET) and copolyester. From... Figure 2 It can be seen that as the PLA component increases, the melting point and crystallization temperature of the copolyester shift from the high-temperature direction to the low-temperature direction. This indicates that the increase of PLA molecular chain segments can increase the mobility of the copolyester molecular chains.

[0065] Example 2

[0066] 1) Preparation of polyglycolic acid-polylactide-polybutylene terephthalate copolyester

[0067] In the polymerization reactor, add 1 kg of lactide, 1 kg of glycolide and 0.04 kg of stannous octoate, and use nitrogen to purge the air from the reactor. Prepolymerize at 160°C and atmospheric pressure for 2 hours.

[0068] Add 0.2 kg of cyclic butylene terephthalate oligomer and continue the reaction at 180°C and atmospheric pressure for 1 hour. Evacuate the reactor to a pressure of 20 Pa, raise the temperature to 220°C, and react for 2 hours. When the mechanical stirring power reaches 55 W, discharge the product to obtain the polymerized product with a number average molecular weight of 27,000.

[0069] 2) Preparation of polyglycolic acid-polylactide-polybutylene terephthalate copolyester fibers

[0070] Poly(glycolic acid)-poly(lactic acid)-polybutylene terephthalate (PPT) copolyester chips were vacuum dried at 90°C for 8 hours to ensure sufficient pre-crystallization, then heated to 120°C and vacuum dried for 24 hours to completely remove the water of crystallization; finally, the temperature was lowered to 50°C and maintained under vacuum for later use. The chips were then spun using a melt spinning machine at 190–220°C, with a spinneret containing 24 orifices of 0.25 × 0.63 mm and a metering pump speed of 26 r / min, yielding PPT-poly(glycolic acid)-poly(lactic acid)-polybutylene terephthalate (PPT) copolyester fibers with a breaking strength of 3.30 cN / dtex and an elongation at break of 43.0%.

[0071] Example 3

[0072] 1) Preparation of polyglycolic acid-polylactide-polybutylene terephthalate copolyester

[0073] In the polymerization reactor, add 1.5 kg of lactide, 0.5 kg of glycolide and 0.035 kg of stannous octoate, and use nitrogen to purge the air from the reactor. Prepolymerize at 160°C and atmospheric pressure for 1.5 hours.

[0074] Add 1.5 kg of cyclic butylene terephthalate oligomer and continue the reaction at 180°C and atmospheric pressure for 1 hour. Evacuate the reactor to a pressure of 10 Pa, raise the temperature to 220°C, and react for 2 hours. When the mechanical stirring power reaches 55 W, discharge the product to obtain the polymerized product with a number average molecular weight of 22,000.

[0075] 2) Preparation of polyglycolic acid-polylactide-polybutylene terephthalate copolyester fibers

[0076] Poly(glycolic acid)-poly(lactic acid)-polybutylene terephthalate (PPT) copolyester chips were vacuum dried at 90°C for 8 hours to ensure sufficient pre-crystallization, then heated to 120°C and vacuum dried for 24 hours to completely remove the water of crystallization; finally, the temperature was lowered to 50°C and maintained under vacuum for later use. The chips were then spun using a melt spinning machine at 210–230°C, with a spinneret containing 24 orifices of 0.25 × 0.63 mm and a metering pump speed of 26 r / min, yielding PPT-poly(glycolic acid)-poly(lactic acid)-polybutylene terephthalate (PPT) copolyester fibers with a breaking strength of 4.80 cN / dtex and an elongation at break of 20.0%.

[0077] Example 4

[0078] 1) Preparation of polyglycolic acid-polylactide-polybutylene terephthalate copolyester

[0079] In the polymerization reactor, add 0.5 kg of lactide, 1.5 kg of glycolide and 0.06 kg of stannous octoate, and use nitrogen to purge the air from the reactor. Prepolymerize at 160°C and atmospheric pressure for 1 hour.

[0080] Add 1 kg of cyclic butylene terephthalate oligomer and continue the reaction at 180°C and atmospheric pressure for 2 hours. Evacuate the reactor to a pressure of 10 Pa, raise the temperature to 180°C, and react for 2 hours. When the mechanical stirring power reaches 55 W, discharge the product to obtain the polymerized product with a number average molecular weight of 23,000.

[0081] 2) Preparation of polyglycolic acid-polylactide-polybutylene terephthalate copolyester fibers

[0082] Poly(glycolic acid)-poly(lactic acid)-polybutylene terephthalate (PPT) copolyester chips were vacuum dried at 90°C for 8 hours to ensure sufficient pre-crystallization, then heated to 120°C and vacuum dried for 24 hours to completely remove the water of crystallization; finally, the temperature was lowered to 50°C and kept under vacuum for later use. The chips were then spun using a melt spinning machine at 200–220°C, with a spinneret containing 24 orifices of 0.25 × 0.63 mm and a metering pump speed of 26 r / min, yielding PPT-poly(glycolic acid)-poly(lactic acid)-polybutylene terephthalate (PPT) copolyester fibers with a breaking strength of 3.20 cN / dtex and an elongation at break of 47.0%.

[0083] Comparative Example 1

[0084] 1) Preparation of poly(2-hydroxypropionic acid-ethylene glycol) terephthalate polymer

[0085] Add 2 kg of lactide, 2.3 kg of terephthalic acid, 0.9 kg of ethylene glycol and 0.08 kg of stannous octoate to a reactor. Stir until homogeneous at room temperature. Purge the reactor with nitrogen four times to remove air. Heat to 180°C and react at atmospheric pressure for 2 hours, then heat to 220°C and react for 2 hours. Heat and evacuate to a pressure of 20 Pa in the reactor. React at 260°C for 2 hours. When the mechanical stirring power reaches 55 W, discharge the polymer, which has a molecular weight of approximately 9,000 and a melting point of 162°C.

[0086] 2) Preparation of poly(2-hydroxypropionic acid-ethylene glycol) polymer fibers:

[0087] Poly(2-hydroxypropionic acid) glycol terephthalate (PET) was pre-crystallized under vacuum at 90°C for 8 hours, then heated to 120°C and vacuum-dried for 24 hours to remove water of crystallization. The temperature was then lowered to 50°C and maintained under vacuum until use. The pretreated PET chips were then spun using a melt spinning machine at 220–240°C. The spinneret contained 24 orifices of 0.25 × 0.63 mm, and the metering pump rotated at 26 r / min to obtain polymer fibers.

[0088] The properties of the copolyesters and copolyester fibers of Examples 1-4 of this application, and the polymer and polymer fibers prepared in Comparative Example 1, were characterized as follows:

[0089] 1. The molecular weights of the bio-based copolyester and polymer were tested, and the test results are shown in Table 1.

[0090] Table 1 shows the molecular weights of the bio-based copolyesters in the examples and the polymers in the comparative examples.

[0091] Example 1 21000 Example 2 27000 Example 3 22000 Example 4 23000 Comparative Example 1 9000

[0092] As shown in Table 1, the number-average molecular weights of the bio-based copolyesters in Examples 1-4 range from 21,000 to 27,000, while the number-average molecular weight of the polymers in the comparative examples is 9,000. The molecular weights of the bio-based copolyesters in the examples of this application are significantly higher than those in the comparative examples. This indicates that high molecular weight bio-based copolyesters were obtained using the preparation method of this application.

[0093] 2. The physical properties of the copolyester fiber, including breaking strength and elongation at break, were tested. The test results are shown in Table 2.

[0094] Table 2 shows the performance test data of the copolyester fibers in the examples and the polymer fibers in the comparative examples.

[0095]

[0096]

[0097] As shown in Table 2, the bio-based copolyester fibers prepared in the examples all exhibited a breaking strength greater than 3.0 cN / dtex, with an average of 3.93 cN / dtex and a maximum of 4.8 cN / dtex. In contrast, the breaking strength of the polymer fibers in the comparative examples was 2.3 cN / dtex, significantly lower than that of the copolyester fibers in Examples 1-4. The bio-based copolyester fibers prepared in the examples of this application also exhibited an elongation at break greater than 25%, reaching a maximum of 47%, which is higher than that of the polymer fibers in the comparative examples.

[0098] Although this application has been described in detail in this specification with general description and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of this invention are within the scope of protection claimed by this invention.

Claims

1. A method for preparing a bio-based copolyester, characterized in that, include: Aliphatic lactones were prepolymerized under an inert atmosphere and at a temperature of 160~180 °C in the presence of a catalyst to obtain a prepolymer. The aliphatic lactone is any one or a mixture of two of glycolide and lactide in any ratio; Cyclic butylene terephthalate oligomers are added to the prepolymer, and the temperature is raised to 180~200 ℃ for prepolymerization; after vacuuming, the temperature is raised to 220~250 ℃ for repolymerization to obtain the bio-based copolyester.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the aliphatic lactone to the cyclic butylene terephthalate oligomer is (1-10):

1.

3. The preparation method according to claim 1, characterized in that, The catalyst is a metal alkyl compound or a tin salt compound.

4. The preparation method according to claim 3, characterized in that, The catalyst is stannous octoate; The amount of stannous octoate used is 0.1-3% of the total mass of the aliphatic lactone and cyclic butylene terephthalate oligomers.

5. The bio-based copolyester prepared by the preparation method according to any one of claims 1-4, characterized in that, The bio-based copolyester has a random block structure and a number-average molecular weight of 18,000 to 25,000.

6. The use of the bio-based copolyester prepared by the preparation method according to any one of claims 1-4 in the preparation of fibers.

7. A bio-based copolyester fiber, characterized in that, It is a bio-based copolyester prepared by the method according to any one of claims 1-4 or the bio-based copolyester according to claim 5, which is produced by melt spinning at a temperature of 220~240°C.

8. The bio-based copolyester fiber according to claim 7, characterized in that, Its preparation methods also include: The bio-based copolyester is pre-crystallized by heating it to 80-90°C under vacuum, then the temperature is raised to remove the water of crystallization, and then the temperature is lowered to 50°C for later use.

9. The bio-based copolyester fiber according to claim 8, characterized in that, The bio-based copolyester fiber has a breaking strength ≥3.00 cN / dtex and a breaking elongation of 25.0~50.0%.

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