Degradable polyester fiber and process for preparing the same

Abstract

The application provides a degradable polyester fiber and a preparation process thereof. The application generates a functional unit containing an imide structure by using a dibasic acid and an acid anhydride thereof to perform a thermal cyclization reaction on an amino alcohol, and introduces the functional unit into a PET main chain structure by using an esterification reaction to obtain a degradable polyester, and further obtains a fiber by using a spinning process. The polyester fiber provided by the application has the same performance as PET and has a biodegradable property.

Description

Technical Field

[0001] This invention belongs to the field of polymers, and specifically relates to a biodegradable polyester fiber and its preparation process. Background Technology

[0002] Polyester (PET, polyethylene terephthalate) is a synthetic fiber with high strength, excellent heat resistance, corrosion resistance, and sun resistance. It has a wide range of applications and low cost, making it the most in-demand and highest-producing synthetic fiber. However, because polyester is non-biodegradable, microplastic particles shed during washing or friction from textile products, or fabrics and fibers lost to the environment due to improper recycling, can pollute the environment and even pose a potential threat to biological health.

[0003] As a daily necessity, the "degradability" of polyester fiber is of great and positive significance for green living and environmental protection. CN113913965A describes achieving "degradability" by blending plastic starch, lignin, and other degradable masterbatches into PET chips using a twin-screw extruder. However, it's predictable that the basic chemical structure of the modified material is not optimized, and its degradability largely stems from the degradable masterbatch, not PET, thus not substantially achieving the degradability of polyester. CN115948817A describes an invention using a copolyester of polylactic acid and polyethylene terephthalate as a degradable masterbatch, which is then melt-blended and spun with polyester chips to obtain degradable polyester. This degradable polyester exhibits a 45-day degradation rate of approximately 7%, indicating poor degradation performance. The invention described in CN117966299A prepares biodegradable composite fibers by cross-linking polyethylene phthalate with biodegradable units polylactic acid and chitosan using reactive monomers. This process is not only lengthy, but also requires the use of solvents such as tetrachloroethane and chloroform, resulting in high costs and poor environmental performance. Furthermore, as polyester is a linear polymer, chemical cross-linking will inevitably affect the spinnability of the material, making it impractical. Summary of the Invention

[0004] This invention first provides a biodegradable fiber-forming polyester, the polyester having a main structural unit and a modified structural unit, the modified structural unit comprising the structure of Formula I:

[0005]

[0006] in:

[0007] R1 is a straight-chain or branched alkylene group with 2 or 3 carbon atoms, or a combination of both;

[0008] R2 is a straight-chain or branched alkyl group with 2 or 3 carbon atoms, or a combination of both;

[0009] The main structural unit includes C5-C for polymer synthesis.12 Carbocyclic or heterocyclic dicarboxylic acid residues and diol residues used in polymer synthesis;

[0010] The C5-C 12 The carbocyclic or heterocyclic dicarboxylic acid is selected from at least one of phthalic acid, hexahydrophthalic acid, norbornenic acid, tetrahydrophthalic acid, 2,3-furandicarboxylic acid, 3,4-furandicarboxylic acid, 2,3-pyridinedicarboxylic acid, 3,4-pyridinedicarboxylic acid, terephthalic acid, 2,5-furandicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid; more preferably, it is terephthalic acid, phthalic acid, 1,4-cyclohexanedicarboxylic acid, or 2,5-furandicarboxylic acid;

[0011] The C5-C 12 The carbocyclic or heterocyclic dicarboxylic acid may be optionally substituted with a substituent selected from halogen, alkyl or nitro groups;

[0012] The diol used for polymer synthesis is C2-C. 12 Aliphatic diols, including but not limited to ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol and 2,2-dimethyl-1,3-propanediol, or one or more of polyethylene glycol, polypropylene glycol and polytetrahydrofuran; preferably ethylene glycol, 1,3-propanediol or 1,4-butanediol.

[0013] In a specific embodiment of the present invention, the main structural unit includes the structure shown in Formula III: Wherein R3 is a straight-chain or branched alkylene group with 2-4 carbon atoms; more preferably, the main structural unit includes polyethylene terephthalate (PET) unit, polybutylene terephthalate (PBT) unit, or polypropylene terephthalate (PTT) unit or a combination thereof.

[0014] In a specific embodiment of the present invention, the modified structural unit is the following block structure (II):

[0015]

[0016] Where m is greater than or equal to 1;

[0017] Preferably, m is selected from any integer from 1 to 10; more preferably, m is selected from any integer from 1 to 5.

[0018] In a specific embodiment of the present invention, R2 is a residue of 2-amino-1,3-propanediol or 3-amino-1,2-propanediol, and R1 is a residue of 1,4-succinic acid or its anhydride.

[0019] In a specific embodiment of the present invention, the modified structural unit accounts for 0.01%-20% of the total structural units of the polyester.

[0020] In a specific embodiment of the present invention, the modified structural unit accounts for 0.01%-10% of the total structural units of the polyester; preferably, it is 0.01%-5%.

[0021] The present invention also provides a method for synthesizing the above-mentioned fiber-forming polyester, comprising the following steps 1) to 3):

[0022] 1) Under conditions of excess dicarboxylic acid, dicarboxylic acid HOOC-R1-COOH or its ester or its anhydride is cyclized with amino diol HO-R2(NH2)-OH and prepolymerized to obtain a polyester prepolymer with a modified structural unit and a carboxyl-terminated group;

[0023] 2) Obtain polyester prepolymers with terminal hydroxyl groups in the main polyester unit;

[0024] 3) The modified structural unit polyester prepolymer with terminal carboxyl groups and the polyester prepolymer with terminal hydroxyl groups are subjected to polycondensation to obtain the fiber-forming polyester.

[0025] Preferably, the molar ratio of the dicarboxylic acid HOOC-R1-COOH to the amino diol HO-R2(NH2)-OH is 1.01-10:1.

[0026] Preferably, the amount of modified structural unit polyester prepolymer with terminal carboxyl groups added in step 3) is controlled such that the molar ratio of the modified structural unit to the total polyester structural units is 0.01%-20%, preferably 0.01%-10%, and more preferably 0.01%-5%.

[0027] Preferably, the cyclization condition is a melt reaction.

[0028] Preferably, the cyclization in step 1) is carried out under melt heating conditions.

[0029] Preferably, the polyester prepolymer of step 1) or 2) is obtained by esterification, transesterification or polycondensation.

[0030] The present invention also provides a fiber or a chip or masterbatch for preparing the fiber, wherein the fiber or chip or masterbatch comprises the fiber-forming polyester described in any of the preceding claims.

[0031] Preferably, the fiber further comprises additives, including at least one of matting agents, heat stabilizers, viscosity promoters, optical brighteners, pigments, and antioxidants.

[0032] Preferably, the fiber has a density greater than 1 cN·dtex. -1 The fracture strength.

[0033] Preferably, the fiber has a breaking elongation greater than 10%.

[0034] Preferably, the fiber is FDY (fully drawn yarn) or POY (pre-oriented yarn).

[0035] In a specific embodiment of the present invention, the relative biodegradability of the fiber after 45 days is greater than 20%.

[0036] The present invention also provides fiber products, preferably multi-component fibers, yarns, multifilaments, fabrics or textiles.

[0037] The present invention also provides uses for the fiber products, such as in the manufacture of sportswear, outdoor products, padding, carpets, and industrial ropes and cables.

[0038] Beneficial technical effects

[0039] This invention provides a biodegradable polyester fiber and its preparation process. The invention involves a thermal cyclization reaction of a diacid and its anhydride with an amino alcohol to generate functional units containing an imide structure. These units are then introduced into the PET backbone structure via esterification to obtain a modified polyester, which is further used to prepare polyester fibers. The polyester fiber provided by this invention has properties comparable to PET and exhibits biodegradability. Attached Figure Description

[0040] Figure 1 This invention relates to biodegradable fully stretched polyester filament rolls.

[0041] Figure 2 This invention relates to biodegradable polyester pre-oriented yarn rolls. Detailed Implementation

[0042] Synthesis methods of fiber-forming polyester

[0043] This invention synthesizes polyester through a three-step method:

[0044] 1) Under conditions of excess dicarboxylic acid, dicarboxylic acid HOOC-R1-COOH or its ester or its anhydride is cyclized with aminodiol HO-R2(NH2)-OH and prepolymerized to obtain a modified prepolymer with terminal carboxyl group;

[0045] 2) Obtain the prepolymer of the polyester main unit;

[0046] 3) The prepolymer of the modified unit with the terminal carboxyl group and the prepolymer of the polyester host unit are subjected to polycondensation to obtain the polyester.

[0047] The cyclization reaction in step 1) can be carried out under conventional conditions in the art, such as under melt heating conditions.

[0048] Step 1) The reaction to synthesize the prepolymer can be carried out under conventional conditions in the art, such as under reduced pressure, heating and catalysis, preferably catalyzed by zinc acetate, for example.

[0049] The polyester prepolymer with terminal hydroxyl groups of the polyester host unit in step 2) can be obtained by conventional methods in the art, such as using an transesterification catalyst.

[0050] In step 3), the prepolymer is melt-polymerized under suitable polymer conditions, typically by polycondensation under reduced pressure, at elevated temperatures, and in the presence of a suitable catalyst. The temperature is preferably in the range of about the polymer's melting point to about 30°C above that melting point, but preferably not less than about 180°C. The pressure should preferably be gradually reduced, preferably reduced to as low as possible. The polycondensation catalyst can be a titanium(IV) alkoxide or titanium(IV) chelate, a zirconium(IV) chelate, or a zirconium(IV) salt (e.g., an alkoxide); a hafnium(IV) chelate; titanates, silicates, and metal acetates can also be used as catalysts.

[0051] Preparation of biodegradable fully stretched polyester fibers:

[0052] Polyester chips were obtained, pre-crystallized at 120°C, and then vacuum-dried in a rotary drum at 140°C, with a moisture content below 50 ppm. The experimental melt spinning machine (spinning assembly pressure: 5-10 MPa; number of spinnerets: 36) had five temperature zones from the feed port to the die head, ranging from 180°C to 265°C. The drawing hot roller settings were: GR1: 90°C, 1350 m / min; GR2: 135°C, 4050 m / min. Raw yarn, take-up, oiling, drawing, and winding were performed to obtain biodegradable FDY (fully drawn yarn).

[0053] The indicators in the examples and comparative examples were tested according to the following standards or methods:

[0054] Intrinsic viscosity (dL / g) test reference standard: GB / T 14190-2017;

[0055] The reference standard for fracture strength (cN / dtex) testing is GB / T 14344-2022.

[0056] Elongation at break (%) test reference standard: GB / T 14344-2022;

[0057] Standard moisture regain (%) test reference standard: GB / T 6503-2008, drying temperature 65℃;

[0058] The relative biodegradability was tested according to the standard GB / T 19277.1-2011. The dry weight ratio of compost and experimental / reference material (thin-layer chromatography grade cellulose) in the compost container was approximately 6:1. The test system was aerated with de-CO2 air to ensure that the oxygen concentration discharged from each compost container was not less than 6%, and the test was conducted at 58±2℃ in the dark. The carbon dioxide release was determined by titration.

[0059] Example

[0060] Example 1 (Molar addition of 3-amino-1,2-propanediol modified structural unit: 1%, fully drawn yarn)

[0061] Step 1: 236.93g of 3-amino-1,2-propanediol, dried at low temperature, and 921.45g of 1,4-succinic acid were added to reactor A. The mixture was stirred at room temperature, and nitrogen was used to completely replace the air in the reactor. Then, the mixture was slowly heated and melted in a nitrogen atmosphere at a nitrogen flow rate of 50mL / min. The mixture was stirred at a constant temperature for 3h to obtain an imide diol monomer.

[0062] In the second step, after the imidization reaction is completed, 200 ppm of zinc acetate (relative to the weight of the entire reaction system, the same below) is added, and the reaction is carried out at 160℃ and -0.08MPa for 2 hours to obtain the modified unit prepolymer with carboxyl-terminated groups.

[0063] The third step involves adding 42.33 kg of terephthalic acid, 22.12 kg of ethylene glycol, and 100 ppm of titanium-based chelating catalyst to a 150L polyester synthesis unit B. Simultaneously, 50 ppm of triphenyl phosphate is added. The mixture is stirred at 80°C, and nitrogen is used to fully replace the air inside the reactor. The temperature is then raised to 230°C and the pressure increased to 0.3 MPa. Once the temperature at the top of the process tower stabilizes, the pressure is slowly released while maintaining the temperature until the distillate reaches more than 95% of the theoretical amount, yielding polyethylene terephthalate oligomers.

[0064] Step 4: Using nitrogen gas, the terminal carboxyl diamine monomer obtained in step 2 is forced into the reactor through the constant pressure feeding port on device B for co-esterification reaction for 1 hour. Then, the temperature is raised to 260°C and polycondensation reaction is carried out under a negative pressure of 50 Pa. After that, the product is stretched, granulated, and dried to obtain biodegradable polyester chips 1 with an intrinsic viscosity of 0.68.

[0065] The fifth step is to prepare biodegradable FDY (fully drawn yarn).

[0066] Example 2 (3-Amino-1,2-propanediol modified unit molar addition: 2%, fully drawn yarn)

[0067] Step 1: 473.48g of 3-amino-1,2-propanediol and 1841.44g of 1,4-succinic acid, dried at low temperature, were added to reactor A. The mixture was stirred at room temperature, and nitrogen was used to completely replace the air in the reactor. Then, the mixture was slowly heated and melted in a nitrogen atmosphere at a nitrogen flow rate of 50mL / min. The mixture was stirred at a constant temperature for 3h to obtain an imide diol monomer.

[0068] In the second step, after the imidization reaction is completed, 200 ppm of zinc acetate (relative to the weight of the entire reaction system, the same below) is added, and the reaction is carried out at 160℃ and -0.08MPa for 2 hours to obtain the modified unit prepolymer with carboxyl-terminated groups.

[0069] The third step involves adding 41.44 kg of terephthalic acid, 21.65 kg of ethylene glycol, and 100 ppm of titanium-based chelating catalyst to a 150L polyester synthesis unit B. Simultaneously, 50 ppm of triphenyl phosphate is added. The mixture is stirred at 80°C, and the air inside the reactor is fully replaced with nitrogen. The temperature is then raised to 230°C and the pressure increased to 0.3 MPa. Once the temperature at the top of the process tower stabilizes, the reaction is slowly maintained at this temperature while releasing pressure until the distillate reaches more than 95% of the theoretical amount, yielding polyethylene terephthalate oligomers.

[0070] Step 4: Using nitrogen gas, the terminal carboxyl diamine monomer obtained in step 2 is forced into the reactor through the constant pressure feeding port on device B for co-esterification reaction for 1 hour. Then, the temperature is raised to 260°C and polycondensation reaction is carried out under a negative pressure of 50 Pa. After that, the product is stretched, granulated, and dried to obtain biodegradable polyester chips 2 with an intrinsic viscosity of 0.69.

[0071] The fifth step is to prepare biodegradable FDY (fully drawn yarn).

[0072] Example 3 (Molar addition of 3-amino-1,2-propanediol modified unit: 2.5%, fully drawn yarn)

[0073] Step 1: 591.62g of 3-amino-1,2-propanediol, dried at low temperature, and 2300.89g of 1,4-succinic acid were added to reactor A. The mixture was stirred at room temperature, and nitrogen was used to completely replace the air in the reactor. Then, the mixture was slowly heated and melted in a nitrogen atmosphere at a nitrogen flow rate of 50mL / min. The mixture was stirred at a constant temperature for 3h to obtain an imide diol monomer.

[0074] In the second step, after the imidization reaction is completed, 200 ppm of zinc acetate (relative to the weight of the entire reaction system, the same below) is added, and the reaction is carried out at 160℃ and -0.08MPa for 2 hours to obtain the modified unit prepolymer with carboxyl-terminated groups.

[0075] The third step involves adding 41.00 kg of terephthalic acid, 21.42 kg of ethylene glycol, and 100 ppm of titanium-based chelating catalyst to a 150L polyester synthesis unit B, along with 50 ppm of triphenyl phosphate. The mixture is stirred at 80°C, and nitrogen is used to fully replace the air inside the reactor. The temperature is then raised to 230°C and the pressure increased to 0.3 MPa. Once the temperature at the top of the process tower stabilizes, the reaction is slowly maintained at this temperature while releasing pressure until the distillate reaches more than 95% of the theoretical amount, yielding polyethylene terephthalate oligomers.

[0076] Step 4: Using nitrogen gas, the terminal carboxyl diamine monomer obtained in step 2 is forced into the reactor through the constant pressure feeding port on device B for co-esterification reaction for 1 hour. Then, the temperature is raised to 260°C and polycondensation reaction is carried out under a negative pressure of 50 Pa. After that, the product is stretched, granulated, and dried to obtain biodegradable polyester chips 3 with an intrinsic viscosity of 0.69.

[0077] The fifth step is to prepare biodegradable FDY (fully drawn yarn).

[0078] Example 4 (Molar addition of 2-amino-1,3-propanediol modified unit: 1%)

[0079] Step 1: 591.62g of 2-amino-1,3-propanediol, dried at low temperature, and 2300.89g of 1,4-succinic acid were added to reactor A. The mixture was stirred at room temperature, and nitrogen was used to completely replace the air in the reactor. Then, the mixture was slowly heated and melted in a nitrogen atmosphere at a nitrogen flow rate of 50mL / min. The mixture was stirred at a constant temperature for 3h to obtain an imide diol monomer.

[0080] In the second step, after the imidization reaction is completed, 200 ppm of zinc acetate (relative to the weight of the entire reaction system, the same below) is added, and the reaction is carried out at 160℃ and -0.08MPa for 2 hours to obtain the modified unit prepolymer with carboxyl-terminated groups.

[0081] The third step involves adding 41.00 kg of terephthalic acid, 21.42 kg of ethylene glycol, and 100 ppm of titanium-based chelating catalyst to a 150L polyester synthesis unit B, along with 50 ppm of triphenyl phosphate. The mixture is stirred at 80°C, and nitrogen is used to fully replace the air inside the reactor. The temperature is then raised to 230°C and the pressure increased to 0.3 MPa. Once the temperature at the top of the process tower stabilizes, the reaction is slowly maintained at this temperature while releasing pressure until the distillate reaches more than 95% of the theoretical amount, yielding polyethylene terephthalate oligomers.

[0082] Step 4: Using nitrogen gas, the terminal carboxyl diamine monomer obtained in step 2 is forced into the reactor through the constant pressure feeding port on device B for co-esterification reaction for 1 hour. Then, the temperature is raised to 260°C and polycondensation reaction is carried out under a negative pressure of 50 Pa. After that, the product is stretched, granulated, and dried to obtain biodegradable polyester chips 4 with an intrinsic viscosity of 0.67.

[0083] The fifth step is to prepare biodegradable FDY (fully drawn yarn).

[0084] Example 5 (Molar addition of 3-amino-1,2-propanediol modified unit: 1%, pre-oriented yarn)

[0085] Using the biodegradable polyester chips obtained in Example 1, biodegradable pre-oriented filaments can be obtained through the following single stretching process.

[0086] Based on the polyester chips obtained in Example 1, after pre-crystallization at 120°C, they were vacuum dried in a rotary drum at 140°C, and the moisture content was tested to be below 50 ppm. The experimental melt spinning machine (spinning assembly pressure: 5-10 MPa; number of spinnerets: 36) had five temperature zones from the feed port to the die head, ranging from 180°C to 265°C. The drawing hot roller settings were: GR2: 135°C, 3200 m / min. Raw yarn, take-up, oiling, drawing, and winding were performed to obtain biodegradable POY (pre-oriented yarn).

[0087] Comparative example (PET, fully drawn yarn)

[0088] In a 150L polyester synthesis unit, 48.65 kg of terephthalic acid, 25.43 kg of ethylene glycol, and 150 ppm of titanium-based chelating catalyst were added, along with 50 ppm of triphenyl phosphate. The mixture was stirred at 80°C, and nitrogen was used to fully replace the air in the reactor. The temperature was raised to 230°C and the pressure was increased to 0.3 MPa. After the temperature at the top of the process tower stabilized, the temperature was slowly maintained and the pressure was released until the distillate reached more than 95% of the theoretical amount, yielding polyethylene terephthalate oligomers. The temperature was then further raised to 270°C, and polycondensation was carried out under a negative pressure of 50 Pa. The resulting product was then drawn into strips, granulated, and dried to obtain polyester chips with an intrinsic viscosity of 0.65, which were then used to prepare FDY (fully drawn yarn).

[0089] Example of effect

[0090] Referring to the table below, with the addition of imide-modified monomers prepared from two amino alcohols, polyethylene terephthalate filaments, which were originally non-degradable, achieved a relative biodegradability of 23.7%–33.3% after 45 days under industrial composting conditions, while maintaining comparable fiber mechanical properties; this demonstrates the feasibility of this technical solution in achieving polyester degradation. For the same imide-modified monomer, within a certain range, as the monomer content increases, the mechanical properties decrease slightly, while the relative biodegradability increases accordingly, but still meets the weaving performance requirements for apparel textiles. This invention provides biodegradable polyester, applicable to both traditional two-stage stretching FDY and one-stage stretching POY melt spinning processes, exhibiting good compatibility with existing equipment and processes.

[0091] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Example 5 <![CDATA[Single fiber strength / cN·dtex -1 > 3.7 3.3 3.2 3.9 3.7 1.6 Elongation at break / % 25.2 27.4 28.4 26.1 26.8 197.5 Standard moisture regain / % 0.82 0.97 1.1 0.85 0.40 0.82 45-day relative biodegradation rate / % 23.7 27.9 33.2 24.5 0.04 23.7

[0092] The above embodiments are merely explanations of the technical solutions and do not constitute a limitation on the technical solutions of this invention. Those skilled in the art, based on existing knowledge of polyester synthesis, can obtain polyester chips with different viscosities and chain segment ratios by adjusting parameters such as raw material ratios, temperature, and pressure during the polymerization process.

[0093] Those skilled in the art should note that the embodiments described in this invention are merely illustrative, and various other substitutions, changes, and improvements can be made within the scope of this invention. Therefore, this invention is not limited to the above embodiments, but is defined only by the claims.

Claims

1. A biodegradable fiber-forming polyester, said polyester having a main structural unit and a modified structural unit, said modified structural unit comprising a structure of formula I: in: R1 is a straight-chain or branched alkylene group with 2 or 3 carbon atoms, or a combination of both; R2 is a straight-chain or branched alkyl group with 2 or 3 carbon atoms, or a combination of both; The main structural unit includes C5-C for polymer synthesis. 12 Carbocyclic or heterocyclic dicarboxylic acid residues and diol residues used in polymer synthesis; The C5-C 12 The carbocyclic or heterocyclic dicarboxylic acid is selected from at least one of phthalic acid, hexahydrophthalic acid, norbornenic acid, tetrahydrophthalic acid, 2,3-furandicarboxylic acid, 3,4-furandicarboxylic acid, 2,3-pyridinedicarboxylic acid, 3,4-pyridinedicarboxylic acid, terephthalic acid, 2,5-furandicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid; more preferably, it is terephthalic acid, phthalic acid, 1,4-cyclohexanedicarboxylic acid, or 2,5-furandicarboxylic acid; The C5-C 12 The carbocyclic or heterocyclic dicarboxylic acid may be optionally substituted with a substituent selected from halogen, alkyl or nitro groups; The diol used for polymer synthesis is C2-C. 12 Aliphatic diols, including but not limited to ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol and 2,2-dimethyl-1,3-propanediol, or one or more of polyethylene glycol, polypropylene glycol and polytetrahydrofuran; preferably ethylene glycol, 1,3-propanediol or 1,4-butanediol.

2. The fiber-forming polyester as described in claim 1, wherein the main structural unit comprises the structure shown in Formula III: Wherein R3 is a straight-chain or branched alkylene group with 2-4 carbon atoms; more preferably, the main structural unit includes polyethylene terephthalate (PET) unit, polybutylene terephthalate (PBT) unit, or polypropylene terephthalate (PTT) unit or a combination thereof.

3. The fiber-forming polyester according to any one of claims 1 or 2, wherein the modified structural unit is a block structure (II) as follows: Where m is greater than or equal to 1; Preferably, m is selected from any integer from 1 to 10; more preferably, m is selected from any integer from 1 to 5.

4. The fiber-forming polyester according to any one of claims 1-3, wherein, R2 is a residue of 2-amino-1,3-propanediol or 3-amino-1,2-propanediol, and R1 is a residue of 1,4-succinic acid or its anhydride.

5. The fiber-forming polyester according to any one of claims 1-4, wherein the modified structural unit accounts for 0.01%-20% of the total structural units of the polyester.

6. The fiber-forming polyester according to any one of claims 1-5, wherein the modified structural unit accounts for 0.01%-10% of the total structural units of the polyester; preferably, it is 0.01%-5%.

7. The method for synthesizing fiber-forming polyester according to any one of claims 1-6, comprising the following steps 1) to 3): 1) Under conditions of excess dicarboxylic acid, dicarboxylic acid HOOC-R1-COOH or its ester or its anhydride is cyclized with amino diol HO-R2(NH2)-OH and prepolymerized to obtain a polyester prepolymer with a modified structural unit and a carboxyl-terminated group; 2) Obtain polyester prepolymers with terminal hydroxyl groups in the main polyester unit; 3) The modified structural unit polyester prepolymer with terminal carboxyl groups and the polyester prepolymer with terminal hydroxyl groups are subjected to polycondensation to obtain the fiber-forming polyester. Preferably, the molar ratio of the dicarboxylic acid HOOC-R1-COOH to the amino diol HO-R2(NH2)-OH is 1.01-10:1; Preferably, the amount of modified structural unit polyester prepolymer with terminal carboxyl groups added in step 3) is controlled such that the molar ratio of the modified structural unit to the total polyester structural units is 0.01%-20%, preferably 0.01%-10%, and more preferably 0.01%-5%. Preferably, the cyclization condition is a melt reaction; Preferably, the cyclization in step 1) is carried out under molten heating conditions; Preferably, the polyester prepolymer of step 1) or 2) is obtained by esterification, transesterification or polycondensation.

8. A fiber or a chip or masterbatch for preparing a fiber, said fiber or chip or masterbatch comprising the fiber-forming polyester according to any one of claims 1-6; Preferably, the fiber further comprises additives, the additives including at least one of matting agents, heat stabilizers, viscosity promoters, optical brighteners, pigments and antioxidants; Preferably, the fiber has a density greater than 1 cN·dtex. -1 The fracture strength; Preferably, the fiber has a breaking elongation greater than 10%; Preferably, the fiber is FDY (fully drawn yarn) or POY (pre-oriented yarn).

9. The fiber or the chips or masterbatch for preparing the fiber as described in claim 8, wherein the fiber has a relative biodegradability of more than 20% after 45 days.

10. A fiber article made from the fiber of claim 8 or 9. Preferably, the fiber product is a multi-component fiber, yarn, multifilament, fabric, or textile.

11. Use of the fiber product of claim 10 for manufacturing sportswear, outdoor products, padding, carpets, and industrial ropes and cables.

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