Modified aliphatic polyesters, processes for their preparation and use

Abstract

The application provides a modified aliphatic polyester and a preparation method and application thereof. The modified aliphatic polyester has structural unit 1 condensed by a dibasic acid and a dihydric alcohol, and structural unit 2 derived from citric acid; preferably, the structural unit 1 is shown as formula 1, and the structural unit 2 is shown as formula 2. The modified aliphatic polyester provided by the application has the characteristics of good heat resistance and toughness, and a wide processing temperature, which greatly improves the processing performance of the aliphatic polyester and is beneficial to the application of the aliphatic polyester material.

Description

Technical Field

[0001] This invention relates to the field of polyester materials technology, specifically to a modified aliphatic polyester, its preparation method, and its applications. Background Technology

[0002] Aliphatic polyesters are easily decomposed into non-toxic and harmless products such as water and carbon dioxide by lipolytic enzymes and microorganisms widely distributed in nature, making them fully biodegradable materials and ideal alternatives to petroleum-based plastics. They can also be used to manufacture agricultural mulch films, shopping bags, garbage bags, etc. However, linear aliphatic polyesters still have some shortcomings, such as high crystallinity and poor toughness, which limits their development in the field of biomaterials applications. Adding fillers and additives to biodegradable polyester research can optimize the properties of polyester materials and expand their application range. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a modified aliphatic polyester, its preparation method, and its application.

[0004] In a first aspect, the present invention provides a modified aliphatic polyester having a structural unit 1 formed by the condensation of a dicarboxylic acid and a diol, and a structural unit 2 derived from citric acid.

[0005] In some implementations, structural unit 1 is as shown in Equation 1 below:

[0006]

[0007] Structural unit 2 is shown in Equation 2 below:

[0008]

[0009] R1 and R2 are each independently a straight-chain or branched alkylene group of C2 to C20.

[0010] Structural unit 1 is capped with a hydroxyl group. The terminal hydroxyl group continues to react with the carboxyl group of citrate, and on this basis, it extends and forms a cross-linked network structure.

[0011] In some embodiments, R1 and R2 are each independently a C2-C10 straight-chain or branched alkylene group.

[0012] In some implementations, R1 and R2 are the same.

[0013] In some embodiments, R1 and R2 are ethylenes.

[0014] In some embodiments, structural unit 2 comprises 2-12 wt% of the modified aliphatic polyester. For example, it may be 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt%, 11 wt%, or 12 wt%.

[0015] In some embodiments, structural unit 2 accounts for 2-8 wt% of the modified aliphatic polyester.

[0016] In some embodiments, structural unit 2 accounts for 4-8 wt% of the modified aliphatic polyester.

[0017] In some embodiments, the modified aliphatic polyester has a weight-average molecular weight of 100,000 to 120,000 and a number-average molecular weight of 70,000 to 80,000.

[0018] In some embodiments, the glass transition temperature of the modified aliphatic polyester is 10-50°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, or 50°C.

[0019] In some embodiments, the modified aliphatic polyester has an elongation at break of 10-400%, for example, 10%, 50%, 100%, 150%, 200%, 250%, or 300%.

[0020] In some embodiments, the modified aliphatic polyester has a tensile strength of 30-55 MPa, for example 31 MPa, 33 MPa, 35 MPa, 38 MPa, 40 MPa, 43 MPa, 45 MPa, 48 MPa, 50 MPa, 52 MPa, and 54 MPa.

[0021] In a second aspect, the present invention provides a method for preparing a modified aliphatic polyester, comprising the following steps: prepolymerizing a diacid with a diol to obtain a first mixture; adding citric acid and a catalyst to the first mixture to carry out a polymerization reaction.

[0022] In some embodiments, the dicarboxylic acid and diol are heated and stirred under an inert gas atmosphere to form a mixture.

[0023] In some embodiments, the dicarboxylic acid is a C4-C22 dicarboxylic acid.

[0024] In some embodiments, the dicarboxylic acid is a C4-C12 dicarboxylic acid.

[0025] In some embodiments, the dicarboxylic acid is succinic acid and / or adipic acid.

[0026] In some embodiments, the diol is a C2 to C20 diol.

[0027] In some embodiments, the diol is a C2 to C10 diol.

[0028] In some embodiments, the diol is selected from one or more of ethylene glycol, butanediol, and hexanediol.

[0029] In some embodiments, the molar ratio of the dicarboxylic acid to the diol is 1:(1.1 to 1.3); for example, 1:1.1, 1:1.15, 1:1.2, 1:1.25, or 1:1.3.

[0030] In some embodiments, the molar ratio of the dicarboxylic acid to the diol is 1:(1.1 to 1.2).

[0031] In some embodiments, the prepolymerization temperature is 140–160°C; for example, 140°C, 145°C, 150°C, 155°C, or 160°C.

[0032] In some embodiments, the prepolymerization temperature is 145–150°C.

[0033] In some embodiments, the prepolymerization time is 3 to 5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours.

[0034] In some embodiments, the catalyst is a tin-based catalyst.

[0035] In some embodiments, the catalyst is stannous octoate and / or stannous chloride.

[0036] In some embodiments, the amount of catalyst added is 100 to 800 ppm of the total mass of the reactants; for example, 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, or 800 ppm.

[0037] In some embodiments, the amount of citric acid added is 2% to 12% of the total mass of the reactants; for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, or 12%.

[0038] In some embodiments, the amount of citric acid added is 2 to 8% of the total mass of the reactants.

[0039] In some embodiments, the amount of citric acid added is 4 to 8% of the total mass of the reactants.

[0040] If the proportion of citric acid is too high, the hardness of the modified aliphatic polyester will increase and the elongation at break will be low. By controlling the amount of citric acid added within the above range, a modified aliphatic polyester with both high toughness and high strength can be obtained.

[0041] The reactants mentioned above refer to dicarboxylic acid, diol, and citric acid.

[0042] In some embodiments, the temperature of the polycondensation dehydration reaction is 160–180°C, for example, 160°C, 165°C, 170°C, 175°C, or 180°C.

[0043] In some embodiments, the polymerization reaction is carried out using a gradient heating method.

[0044] In some embodiments, the heating rate of the gradient heating is 5 to 20 °C / h, for example, 8 °C / h, 10 °C / h, 12 °C / h, 14 °C / h, 16 °C / h, 18 °C / h, or 20 °C / h.

[0045] In some embodiments, the polycondensation dehydration reaction takes 3-5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours.

[0046] In some embodiments, the polycondensation and dehydration reaction is carried out under negative pressure conditions. Preferably, the negative pressure conditions are 40 to 260 mmHg, for example, 40 mmHg, 100 mmHg, 150 mmHg, 230 mmHg, or 255 mmHg.

[0047] In some embodiments, the polycondensation dehydration reaction is carried out until the output water reaches 90-95% of the theoretical output water (e.g., 90%, 91%, 92%, 93%, 94%, 95%), the temperature is raised to 180-250℃ (180℃, 190℃, 200℃, 210℃, 220℃, 230℃), the vacuum degree is adjusted to 50-500Pa (50Pa, 100Pa, 200Pa, 300Pa, 400Pa, 500Pa), and the polycondensation reaction continues for 1-5 hours (1h, 2h, 3h, 4h, 5h).

[0048] In some embodiments, the preparation method of the modified aliphatic polyester includes the following steps: heating and stirring a dicarboxylic acid and a diol under an inert gas atmosphere, pre-polymerizing at 140-160°C for 2-3 hours, adding citric acid and a catalyst, and performing dehydration polymerization at 160-180°C under negative pressure for 3-5 hours until the water output reaches 90%-95% of the theoretical water output. The temperature is then increased to 180-250°C, and polymerization is carried out at a vacuum of 50-500 Pa for 1-5 hours until the polymer exhibits a climbing phenomenon, thus obtaining a citric acid modified aliphatic polyester.

[0049] In some embodiments, the catalyst can be added simultaneously with the diacid and diol during the prepolymerization reaction, or it can be added after the prepolymerization reaction.

[0050] In some implementations, the catalyst is added after the prepolymerization reaction.

[0051] In a third aspect, the present invention provides a modified aliphatic polyester prepared by the preparation method described in the second aspect of the present invention, wherein the modified aliphatic polyester has a weight-average molecular weight of 100,000 to 120,000 and a number-average molecular weight of 70,000 to 80,000; and / or the modified aliphatic polyester has a glass transition temperature of 10 to 50°C; and / or the modified aliphatic polyester has an elongation at break of 10 to 400%; and / or the modified aliphatic polyester has a tensile strength of 30 to 55 MPa.

[0052] In a fourth aspect, the present invention provides the application of the modified aliphatic polyester described in the first or third aspect or the modified aliphatic polyester prepared by the preparation method described in the second aspect in the preparation of agricultural mulch films and / or biomaterials.

[0053] Citric acid (CA) is a tricarboxylic acid containing a tertiary hydroxyl group, with the molecular formula C6H8O7. It exhibits the chemical reactivity of general organic acids, and its low melting point allows the dehydration stage to be carried out at lower temperatures, effectively reducing the degree of etherification by side reactions. This invention synthesizes a modified polyester elastomer with a three-dimensional network structure using citric acid and linear aliphatic polyester. By changing the type of aliphatic polyester, modified polyester elastomers with different structures and lengths are synthesized. The modified aliphatic polyester prepared by this invention exhibits excellent biocompatibility and biodegradability, and its mechanical properties are improved by increasing the elongation at break of the aliphatic polyester. Furthermore, the modified aliphatic polyester of this invention leaves no solvent residue and is non-toxic and harmless. The modified aliphatic polyester provided by this invention possesses good heat resistance and toughness, and a wide processing temperature range, which greatly improves the processing performance of aliphatic polyesters and is beneficial for the application and promotion of aliphatic polyester materials. The preparation method of this invention leaves no solvent residue and is non-toxic and harmless. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and techniques have also been described in many publications.

[0055] Example 1

[0056] Succinic acid and butanediol were mixed at a molar ratio of 1:1.1 in a three-necked round-bottom flask equipped with a thermometer, water separator, nitrogen inlet tube, and mechanical stirrer. The mixture was heated to 150°C for 2 hours to remove water. Then, 2% citric acid and 400 ppm catalyst (stannous octoate) were added by mass of the total materials. Nitrogen gas was introduced, and the vacuum was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was raised to 180°C at a rate of 10°C / h. The dehydration reaction was maintained for 5 hours until the water output reached 90-95% of the theoretical output. The temperature was then raised to 230°C, and the vacuum was adjusted to 120 Pa to maintain the reaction for 5 hours. Under these conditions, modified polybutylene succinate was obtained. The glass transition temperature was 14°C, the elongation at break was 220%, and the tensile strength was 31 MPa. See Table 1 for details.

[0057] Example 2

[0058] Succinic acid and butanediol were mixed at a molar ratio of 1:1.1 and placed in a three-necked round-bottom flask equipped with a thermometer, water separator, nitrogen inlet tube, and mechanical stirrer. After heating to 150°C for 2 hours to remove water, 6% citric acid and 400 ppm catalyst (stannous octoate) were added by mass of the total materials. Nitrogen gas was introduced, and the vacuum was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was increased to 180°C at a rate of 10°C / h and maintained for 4 hours to remove water. The water output reached 90-95% of the theoretical output. The temperature was then increased to 230°C, and the vacuum was evacuated to 120 Pa to maintain the reaction for 3.5 hours. Under these conditions, modified polybutylene succinate was obtained.

[0059] Example 3

[0060] Succinic acid and butanediol were mixed at a molar ratio of 1:1.1 and placed in a three-necked round-bottom flask equipped with a thermometer, water separator, nitrogen inlet tube, and mechanical stirrer. After heating to 150°C for 2 hours to remove water, 8% citric acid and 400 ppm catalyst (stannous octoate) were added by mass of the total materials. Nitrogen gas was introduced, and the vacuum was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was increased to 180°C at a rate of 10°C / h and maintained for 4 hours to remove water. The water output reached 90-95% of the theoretical output. The temperature was then increased to 230°C, and the vacuum was evacuated to 120 Pa to maintain the reaction for 2.5 hours. Under these conditions, modified polybutylene succinate was obtained.

[0061] Example 4

[0062] Succinic acid and butanediol were placed in a three-necked round-bottom flask equipped with a thermometer, water separator, nitrogen inlet tube, and mechanical stirrer at a molar ratio of 1:1.1. After heating to 150°C for 2 hours to remove water, 10% citric acid and 400 ppm catalyst (stannous octoate) were added by mass of the total materials. Nitrogen gas was introduced, and the vacuum was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was increased to 180°C at a rate of 10°C / h. The dehydration reaction was maintained for 3 hours until the water output reached 90-95% of the theoretical output. The temperature was then increased to 230°C, and the vacuum was evacuated to 120 Pa to maintain the reaction for 2 hours. Under these conditions, modified polybutylene succinate was obtained.

[0063] Example 5

[0064] Succinic acid and butanediol were mixed at a molar ratio of 1:1.1 and placed in a three-necked round-bottom flask equipped with a thermometer, water separator, nitrogen inlet tube, and mechanical stirrer. After heating to 150°C for 2 hours to remove water, 8% citric acid and 200 ppm catalyst (stannous octoate) were added by mass of the total materials. Nitrogen gas was introduced, and the vacuum was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was increased to 180°C at a rate of 10°C / h. The dehydration reaction was maintained for 5 hours until the water output reached 90-95% of the theoretical output. The temperature was then increased to 230°C, and the vacuum was evacuated to 120 Pa to maintain the reaction for 3.5 hours. Under these conditions, modified polybutylene succinate was obtained.

[0065] Example 6

[0066] Succinic acid and butanediol were placed in a three-necked round-bottom flask equipped with a thermometer, water separator, nitrogen inlet tube, and mechanical stirrer at a molar ratio of 1:1.1. The mixture was heated to 150°C for 2 hours to remove water. Then, 8% citric acid and 400 ppm catalyst (by mass of the total material) were added. Nitrogen gas was introduced, and the vacuum was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was then raised to 180°C at a rate of 10°C / h, maintaining the dehydration reaction for 4 hours. The water output reached 90–95% of the theoretical output. The temperature was then raised to 230°C, and the vacuum was adjusted to 80 Pa, maintaining the reaction for 2 hours. The material exhibited a "climbing rod" phenomenon. Under these conditions, modified polybutylene succinate was obtained.

[0067] Example 7

[0068] Succinic acid and butanediol were placed in a three-necked round-bottom flask equipped with a thermometer, water separator, nitrogen inlet tube, and mechanical stirrer at a molar ratio of 1:1.1. The mixture was heated to 150°C for 2 hours to remove water. Then, 8% citric acid and 400 ppm catalyst (by mass of the total material) were added. Nitrogen gas was introduced, and the vacuum was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was then raised to 180°C at a rate of 10°C / h, maintaining the dehydration reaction for 4 hours. The water output reached 90-95% of the theoretical output. The temperature was then raised to 250°C, and the vacuum was adjusted to 120 Pa, maintaining the reaction for 3 hours. The material exhibited a "climbing rod" phenomenon. Under these conditions, modified polybutylene succinate was obtained.

[0069] Example 8

[0070] Succinic acid and butanediol were mixed at a molar ratio of 1:1.2 and placed in a three-necked round-bottom flask equipped with a thermometer, water separator, nitrogen inlet tube, and mechanical stirrer. The mixture was heated to 145°C for 3 hours to remove water. Then, 8% citric acid and 400 ppm catalyst (by mass of the total material) were added. Nitrogen gas was introduced, and the vacuum was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was then raised to 180°C at a rate of 20°C / h, maintaining the dehydration reaction for 4 hours. The water output reached 90–95% of the theoretical output. The temperature was then raised to 230°C, and the vacuum was adjusted to 80 Pa, maintaining the reaction for 2.5 hours. The material exhibited a "climbing rod" phenomenon. Under these conditions, modified polybutylene succinate was obtained.

[0071] Example 9

[0072] Adipic acid and hexanediol were placed in a molar ratio of 1:1.1 into a three-necked round-bottom flask equipped with a thermometer, water separator, nitrogen inlet tube, and mechanical stirrer. After heating to 155°C for 3 hours to remove water, 6% citric acid and 400 ppm catalyst (by mass of total material) were added. Nitrogen gas was introduced, and the vacuum was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was increased to 180°C at a rate of 10°C / h to maintain the dehydration reaction for 5 hours. The water output reached 90-95% of the theoretical output. The temperature was then increased to 250°C, and the vacuum was evacuated to 90 Pa to maintain the reaction for 4 hours. The material exhibited a rod-climbing phenomenon. Under these conditions, modified polyhexanediol adipate was obtained.

[0073] Example 10

[0074] Adipic acid and butylene glycol were placed in a molar ratio of 1:1.1 into a three-necked round-bottom flask equipped with a thermometer, a water separator, a nitrogen inlet tube, and a mechanical stirrer. The mixture was heated to 155°C for 3 hours to remove water. Then, 6% citric acid and 400 ppm catalyst (by mass of total materials) were added. Nitrogen gas was introduced, and the vacuum was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was increased to 180°C at a rate of 10°C / h. The dehydration reaction was maintained for 5 hours until the water output reached 90-95% of the theoretical output. The temperature was then increased to 250°C, and the vacuum was evacuated to 90 Pa to maintain the reaction for 5 hours. Under these conditions, modified polybutylene adipate was obtained.

[0075] Example 11

[0076] Succinic acid and hexanediol were placed in a three-necked round-bottom flask equipped with a thermometer, water separator, nitrogen inlet tube, and mechanical stirrer at a molar ratio of 1:1.1. After heating to 155°C for 3 hours to remove water, 6% citric acid and 400 ppm catalyst were added by mass of the total materials. Nitrogen gas was introduced, and the vacuum was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was increased to 180°C at a rate of 10°C / h to maintain the dehydration reaction for 5 hours. The water output reached 90-95% of the theoretical output. The temperature was then raised to 250°C, and the vacuum was evacuated to 90 Pa to maintain the reaction for 5 hours. Under these conditions, citric acid-modified polyhexanediol succinate was obtained.

[0077] The modified aliphatic polyesters prepared in the embodiments of the present invention have a weight-average molecular weight of 100,000 to 120,000 and a number-average molecular weight of 70,000 to 80,000.

[0078] Comparative Example 1

[0079] Succinic acid and butanediol were mixed at a molar ratio of 1:1.1 and placed in a three-necked round-bottom flask equipped with a thermometer, water separator, nitrogen inlet tube, and mechanical stirrer. The mixture was heated to 150°C for 3 hours to remove water. Then, 600 ppm of catalyst (by mass of total materials) was added, nitrogen was introduced, and the mixture was evacuated to 232 mmHg to continue dehydration. The vacuum was increased to 40 mmHg within 1 hour, and the temperature was then increased to 180°C at a rate of 10°C / h, maintaining the dehydration reaction for 5 hours. Finally, the temperature was increased to 230°C, and the vacuum was adjusted to 120 Pa, maintaining the reaction for 8 hours. Under these conditions, polybutylene succinate was obtained. The weight-average molecular weight of this polybutylene succinate was 45,000, and the number-average molecular weight was 28,000.

[0080] Table 1

[0081]

[0082]

[0083] As can be seen from the examples and comparative examples, the modified aliphatic polyester of the present invention has higher toughness and heat resistance.

[0084] As can be seen from Examples 2 and 9-11, the reactivity decreases relatively with the increase of carbon chain length. Compared with Example 2, the polymerization stage of Examples 9-11 requires higher temperature and pressure to promote the reaction.

[0085] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified aliphatic polyester having a structural unit 1 formed by the condensation of a diacid and a diol, and a structural unit 2 derived from citric acid; Structural unit 1 is shown in Equation 1 below: Formula 1 Structural unit 2 is shown in Equation 2 below: Formula 2 R1 and R2 are each independently a straight-chain or branched alkylene group of C2 to C20; in, The dicarboxylic acid is succinic acid and / or adipic acid; The diol is selected from one or more of ethylene glycol, butanediol, or hexanediol; Structural unit 2 accounts for 6-8 wt% of the modified aliphatic polyester; The modified aliphatic polyester has a weight-average molecular weight of 100,000 to 120,000 and a number-average molecular weight of 70,000 to 80,000; the modified aliphatic polyester has a glass transition temperature of 10 to 50°C; the modified aliphatic polyester has an elongation at break of 10 to 400%; and the modified aliphatic polyester has a tensile strength of 30 to 55 MPa.

2. The modified aliphatic polyester according to claim 1, characterized in that, R1 and R2 are the same.

3. The modified aliphatic polyester according to claim 1, characterized in that, R1 and R2 are ethylenes.

4. A method for preparing a modified aliphatic polyester according to any one of claims 1-3, comprising the following steps: A first mixture is obtained by prepolymerizing a dicarboxylic acid and a diol. Citric acid and a catalyst are added to the first mixture to carry out a polycondensation and dehydration reaction; The dicarboxylic acid is succinic acid and / or adipic acid; The diol is selected from one or more of ethylene glycol, butanediol, or hexanediol.

5. The preparation method according to claim 4, characterized in that, The molar ratio of the dicarboxylic acid to the diol is 1:(1.1~1.3).

6. The preparation method according to claim 4, characterized in that, The prepolymerization temperature is 140~160℃; and / or the prepolymerization time is 3~5h.

7. The preparation method according to claim 4, characterized in that, The catalyst is a tin-based catalyst.

8. The preparation method according to claim 4, characterized in that, The catalyst is stannous octoate and / or stannous chloride.

9. The preparation method according to claim 4, characterized in that, The catalyst is added in an amount of 100-800 ppm of the total mass of the reactants; and / or the citric acid is added in an amount of 2-12% of the total mass of the reactants.

10. The preparation method according to claim 4, characterized in that, The amount of citric acid added is 2-8% of the total mass of the reactants.

11. The preparation method according to claim 4, characterized in that, The temperature of the polycondensation dehydration reaction is 160~180℃; and / or the time of the polycondensation dehydration reaction is 3-5 hours.

12. The preparation method according to claim 4, characterized in that, The polycondensation and dehydration reaction is carried out using a gradient heating method.

13. The preparation method according to claim 12, characterized in that, The heating rate of the gradient heating is 5~20℃ / h.

14. The preparation method according to claim 4, characterized in that, The polycondensation and dehydration reaction is carried out under negative pressure; and / or The polycondensation and dehydration reaction proceeds until the output water reaches 90-95% of the theoretical output water. The temperature is then raised to 180-250℃, the vacuum is adjusted to 50-500Pa, and the polymerization reaction continues for 1-5 hours.

15. The preparation method according to claim 14, characterized in that, The negative pressure condition is 40~260 mmHg.

16. The use of a modified aliphatic polyester according to any one of claims 1-3 or a modified aliphatic polyester prepared by any one of claims 4-15 in the preparation of agricultural mulch films and / or biomaterials.

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