Modified polylactic acid materials, their preparation methods and applications

Abstract

This invention relates to polylactic acid (PLA) materials, and discloses a modified PLA material, its preparation method, and its applications. The modified PLA material comprises modified PLA, which contains PLA and a structural unit A attached to the PLA. Structural unit A has the structure shown in formula (I), wherein R1 is absent or is a C1-C6 alkylene group, R2 is absent or is a C1-C6 alkylene group, and R3 is a C1-C6 alkylene group. This modified PLA material exhibits high tensile strength, elongation at break, and Vicat softening temperature. Formula (I).

Description

Technical Field

[0001] This invention relates to polylactic acid (PLA) materials, specifically to a modified PLA material, its preparation method, and its applications. Background Technology

[0002] Driven by environmental protection needs, the global demand for biodegradable plastic products is gradually expanding. Polylactic acid (PLA) is generally divided into two optical isomers: L-polylactic acid (PLLA) and D-polylactic acid (PDLA). Due to its comprehensive properties being close to those of general-purpose plastic polypropylene, it has become one of the three major biodegradable materials for traditional Chinese medicine that are being developed globally, and its production capacity is rapidly increasing.

[0003] Although PLA's mechanical properties are comparable to some petroleum-based plastics, its impact resistance, temperature resistance, slow crystallization rate, susceptibility to deformation during processing, and high cost have become bottlenecks in expanding its applications. Excellent PLA properties can be obtained through copolymerization, grafting, blending, and plasticizing. Reactive blending is a simple and effective method for preparing modified PLA, but there is a lack of low-cost, high-efficiency, environmentally friendly, bio-based reactive copolyesters.

[0004] Moreover, the strength and heat resistance of existing modified polylactic acid still need to be improved. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem that the strength and heat resistance of modified polylactic acid in the prior art still need to be improved, and to provide a modified polylactic acid material, its preparation method and application. The modified polylactic acid material has high tensile strength, elongation at break and Vicat softening temperature.

[0006] To achieve the above objectives, a first aspect of the present invention provides a modified polylactic acid (PLA) material, the modified PLA material containing modified PLA, the modified PLA containing PLA and a structural unit A connected to the PLA, the structural unit A having the structure shown in formula (I). Formula (I); Wherein, R1 is absent or is a C1-C6 alkylene group, R2 is absent or is a C1-C6 alkylene group, and R3 is a C1-C6 alkylene group.

[0007] The second aspect of the present invention provides a method for preparing a modified polylactic acid material, comprising: reacting polylactic acid treated with mercapto-terminated groups with a polyester containing carbon-carbon double bonds in a contact reaction III.

[0008] The modified polylactic acid (PLA) material provided by this invention, through the above technical solution, contains modified PLA, which includes PLA and structural unit A connected to the PLA. Structural unit A has the structure shown in formula (I). Through the interaction between structural unit A and PLA, the tensile strength and elongation at break of the material can be further improved while simultaneously increasing the Vicat softening temperature, resulting in a material with high strength, toughness, and good heat resistance. It has good applications in packaging materials. Detailed Implementation

[0009] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0010] As previously stated, a first aspect of the present invention provides a modified polylactic acid (PLA) material, the modified PLA material containing modified PLA, the modified PLA containing PLA and a structural unit A connected to the PLA, the structural unit A having the structure shown in formula (I). Formula (I); Wherein, R1 is absent or is a C1-C6 alkylene group, R2 is absent or is a C1-C6 alkylene group, and R3 is a C1-C6 alkylene group.

[0011] According to the present invention, structural unit A can be detected by infrared radiation.

[0012] During their research, the inventors discovered that the modified polylactic acid (PLA) material contains modified PLA, which includes PLA and structural unit A connected to the PLA. Structural unit A has the structure shown in formula (I). Through the interaction between structural unit A and PLA, the tensile strength and elongation at break of the material can be further improved while simultaneously increasing the Vicat softening temperature, resulting in a material with high strength, toughness, and good heat resistance. It has promising applications in packaging materials.

[0013] According to the present invention, R1 may be absent or may be methylene, ethylene, propylene, butylene, pentylene, or hexylene; R2 may be absent or may be methylene, ethylene, propyleneene, butylene, pentylene, or hexylene; R3 may be methylene, ethylene, propyleneene, butylene, pentylene, or hexylene. Structural unit A is connected to polylactic acid through a chemical bond attached to R3. During the connection process, the hydroxyl groups in polylactic acid are dehydrogenated and then connected to the chemical bond attached to R3.

[0014] Preferably, R1 is a C1-C2 alkylene group, R2 is absent, and R3 is a C2-C4 alkylene group. These structural units have a good interaction effect with polylactic acid, which can further improve the tensile strength and elongation at break of the material while increasing its Vicat softening temperature. Further preferably, considering the ability to further improve the strength, toughness, and heat resistance of the material, R1 is methylene, R2 is absent, and R3 is ethylene.

[0015] Preferably, the structural unit A has the structure shown in formula (II). Formula (II); Wherein, R1 is absent or is a C1-C6 alkylene group, R2 is absent or is a C1-C6 alkylene group, R3 is a C1-C6 alkylene group, and R4 and R5 each independently contain at least one of a polyether structural unit, an ester structural unit, or hydrogen. The aforementioned structural unit A has a better interaction effect with polylactic acid, which can further improve the tensile strength and elongation at break of the material while increasing the Vicat softening temperature, resulting in a material with higher strength, toughness, and better heat resistance. Further preferably, considering the ability to further improve the strength, toughness, and heat resistance of the material, at least one of R4 and R5 contains a polyether structural unit, and at least one contains an ester structural unit.

[0016] Preferably, the polyether structural unit has the structure shown in formula (III), and the ester knot unit has the structure shown in formula (IV); Formula (III); Formula (IV); In this configuration, R7 is absent or is a C1-C4 alkylene group, R8 and R9 are each independently a C2-C6 alkylene group, and n is 200-250, where n is a natural number. Structural unit A, which contains the aforementioned polyether and ester structural units, exhibits better interaction with polylactic acid, thereby increasing the material's tensile strength and elongation at break while simultaneously raising its Vicat softening temperature, resulting in higher strength, toughness, and better heat resistance. Further preferably, considering the potential for further improvement in the material's strength, toughness, and heat resistance, R7, R8, and R9 are each independently a C2-C4 alkylene group.

[0017] Preferably, in the modified polylactic acid, the content of the polyether structural unit is 50-60 wt%, which can be 50 wt%, 51 wt%, 52 wt%, 53 wt%, 54 wt%, 55 wt%, 56 wt%, 57 wt%, 58 wt%, 59 wt%, 60 wt%, or any value between these values. Controlling the polyether structural unit within the above range can further improve the strength, toughness, and heat resistance of the material. From the perspective of further improving the strength, toughness, and heat resistance of the material, it is further preferred that the content of the polyether structural unit in the modified polylactic acid is 52-56 wt%.

[0018] Preferably, in the modified polylactic acid, the content of structural unit A is 89-97 wt%, which can be 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, or any value between these values. Controlling the content of structural unit A within the above range can further improve the interaction effect between structural unit A and polylactic acid, thereby further improving the strength, toughness, and heat resistance of the material. From the perspective of further improving the strength, toughness, and heat resistance of the material, it is further preferred that the content of structural unit A in the modified polylactic acid is 91.5-95 wt%.

[0019] Preferably, the modified polylactic acid material further contains unmodified polylactic acid, and the interaction between the unmodified and modified polylactic acid can further improve the strength, toughness, and heat resistance of the material. Considering the potential to further enhance the interaction effect between the modified and unmodified polylactic acid, it is further preferred that the mass ratio of the unmodified polylactic acid to the modified polylactic acid is 1:0.25-4. Even more preferably, the mass ratio of the unmodified polylactic acid to the modified polylactic acid is 1:0.67-1.34.

[0020] Preferably, the modified polylactic acid is dextrorotatory polylactic acid (DPL), and the unmodified polylactic acid is levorotatory polylactic acid (LPL). The interaction between the modified DPL and the unmodified LPL further enhances the material's strength, toughness, and heat resistance.

[0021] Preferably, the material has a tensile strength of 15-38 MPa, an elongation at break of 150-600%, and a Vicat softening temperature of 100-155°C. More preferably, the material has a tensile strength of 28-36.5 MPa, an elongation at break of 420-580%, and a Vicat softening temperature of 145-153.5°C.

[0022] According to the present invention, the tensile strength and elongation at break of the material are tested according to the method in GB / T 1040.2-2022, and the Vicat softening temperature is tested according to the method in GB / T 1633-2000.

[0023] The second aspect of the present invention provides a method for preparing a modified polylactic acid material, comprising: reacting polylactic acid treated with mercapto-terminated groups with a polyester containing carbon-carbon double bonds in a contact reaction III.

[0024] The preparation method provided by this invention allows the presence of carbon-carbon double bonds to vulcanize polyester into a cross-linked network structure, thereby improving its tensile strength, toughness, and heat resistance.

[0025] The method for preparing the polyester containing carbon-carbon double bonds may include: under esterification conditions, a diacid monomer, a diol monomer, a polyethylene glycol and a polymerization inhibitor are subjected to a contact reaction I to obtain reactant I; wherein the diacid monomer contains an unsaturated aliphatic diacid monomer. Under polymerization conditions, reactant I and catalyst I are subjected to contact reaction II.

[0026] Preferably, the method for preparing the polyester containing carbon-carbon double bonds includes: Under esterification conditions, saturated aliphatic diacid monomers, unsaturated aliphatic diacid monomers, diol monomers, polyethylene glycol and polymerization inhibitor are subjected to contact reaction I to obtain reactant I. Under polymerization conditions, reactant I and catalyst I are subjected to contact reaction II.

[0027] The unsaturated aliphatic diacid monomer is an aliphatic diacid monomer containing carbon-carbon double bonds. The ester formed by the saturated fatty acid diacid monomer can form a co-crystal with the ester formed by the unsaturated fatty acid diacid monomer to achieve the purpose of co-construction, and can also increase the crystallization rate of the crystal, thereby improving the tensile strength, toughness and heat resistance of polylactic acid material.

[0028] Preferably, the saturated aliphatic diacid monomer is a C2-C6 saturated aliphatic diacid monomer, and the unsaturated aliphatic diacid monomer is a C21-C6 unsaturated aliphatic diacid monomer; the diol monomer is a C2-C6 diol monomer, and the polyethylene glycol is a C2-C6 polyethylene glycol. More preferably, the saturated aliphatic diacid monomer is selected from at least one of ethylene glycol, malonic acid, and succinic acid. The unsaturated aliphatic diacid is selected from at least one of fumaric acid, penteneric acid, and oct-4-eneic acid. Fumaric acid is preferred. All raw materials used in this invention are of biological origin, and the resulting modified material is completely biodegradable.

[0029] Preferably, the molar ratio of the saturated aliphatic diacid monomer to the unsaturated aliphatic diacid monomer is 1-6:1, and can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, or any value between these values. Controlling the molar ratio of the saturated aliphatic diacid monomer to the unsaturated aliphatic diacid monomer within the above range can further improve the interaction effect between the saturated and unsaturated aliphatic diacids, thereby further improving the tensile strength, toughness, and heat resistance of the material. Further preferably, considering the ability to further improve the tensile strength, toughness, and heat resistance of the material, the molar ratio of the saturated aliphatic diacid monomer to the unsaturated fumaric acid monomer is 1.5-3.6:1.

[0030] Preferably, the amount of polydiol used is 200-300g relative to the total molar amount of 1 mol of the saturated aliphatic diacid monomer and the unsaturated aliphatic diacid monomer, and can be 200g, 220g, 240g, 260g, 280g, 300g, or any value between these values. Controlling the amount of polydiol within the above range can further improve the tensile strength, toughness, and heat resistance of the obtained material. Further preferably, considering the ability to further improve the tensile strength, toughness, and heat resistance of the material, the amount of polydiol used is 218-270g relative to the total molar amount of 1 mol of the saturated aliphatic diacid monomer and the unsaturated aliphatic diacid monomer.

[0031] The polymerization inhibitor can be any compound capable of achieving the polymerization inhibition effect; preferably, the polymerization inhibitor is p-hydroxyanisole. The amount of polymerization inhibitor added can be determined by the experimenter based on the actual situation; preferably, the amount of polymerization inhibitor relative to 1g of diol monomer is 0.04-0.06g.

[0032] Preferably, the esterification conditions include: a temperature of 180-200℃, which can be 180℃, 185℃, 190℃, 195℃, 200℃, or any value between these values; a time of 3-5h, which can be 3h, 3.5h, 4h, 4.5h, 5h, or any value between these values; and polymerization conditions including: a temperature of 195-215℃, which can be 195℃, 200℃, 205℃, 210℃, 215℃, or any value between these values; a vacuum degree less than or equal to 35Pa; and a time of 3-4h, which can be 3h, 3.2h, 3.4h, 3.6h, 3.8h, 4h, or any value between these values.

[0033] Preferably, catalyst I is an organotitanium catalyst. More preferably, it is a titanate catalyst. More preferably, catalyst I is tetrabutyl titanate. The amount of catalyst I can be determined by the experimenter according to the actual situation. Preferably, the amount of catalyst I is 2-2.6 g relative to 1 mol of dicarboxylic acid.

[0034] The mercapto-terminated polylactic acid can be prepared by any feasible method. Preferably, the preparation method of the mercapto-terminated polylactic acid includes: reacting lactide and mercaptoalkyl alcohol in a contact reaction IV in the presence of catalyst II. More preferably, the amount of mercaptoalkyl alcohol relative to 1g of lactide is 0.012-0.02mL, which can be 0.012mL, 0.014mL, 0.016mL, 0.018mL, 0.02mL, or any value between these values. Controlling the amount of lactide and mercaptoalkyl alcohol within the above range can further improve the reaction effect of lactide, mercaptoalkyl alcohol, and catalyst II, thereby further improving the tensile strength, toughness, and heat resistance of the obtained material. More preferably, the amount of mercaptoalkyl alcohol relative to 1g of lactide is 0.015-0.018mL.

[0035] Preferably, the mercaptoalkyl alcohol is a C2-C6 mercaptoalkyl alcohol. Using the aforementioned mercaptoalkyl alcohol results in a better reaction with lactide, thereby further improving the tensile strength, toughness, and heat resistance of the subsequently produced material. Further preferably, considering the ability to further improve the tensile strength, toughness, and heat resistance of the material, the mercaptoalkyl alcohol is 2-mercaptoethanol.

[0036] Preferably, catalyst II is a tin-based catalyst. This tin-based catalyst can be an organotin catalyst or an inorganic tin catalyst. More preferably, catalyst II is Sn(OTf)₂.

[0037] The amount of catalyst II can be determined by the experimenter based on the actual situation. Preferably, the amount of catalyst II is 0.04-0.06g relative to 1g of lactide.

[0038] Preferably, the molar ratio of polylactic acid (PLA) based on mercapto groups to the polyester containing carbon-carbon double bonds based on double bonds is 1:1-2; it can be 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, or any value between these values. Controlling the molar ratio of PLA to the polyester containing carbon-carbon double bonds within the above range can further enhance the interaction effect between the two materials, thereby further improving the tensile strength, toughness, and heat resistance of the resulting material. Further preferably, considering the ability to further improve the tensile strength, toughness, and heat resistance of the material, the molar ratio of PLA based on mercapto groups to the polyester containing carbon-carbon double bonds based on double bonds is 1:1.2-1.8.

[0039] Preferably, the method further includes mixing the product of contact reaction III with unmodified polylactic acid. Through the interaction between the product of contact reaction III and the unmodified polylactic acid, the tensile strength, toughness, and heat resistance of the resulting material can be further improved. More preferably, considering the ability to further improve the tensile strength, toughness, and heat resistance of the resulting material, the unmodified polylactic acid is L-polylactic acid.

[0040] Preferably, the mass ratio of the unmodified polylactic acid to the product of contact reaction III is 1:0.25-4, and can be 1:0.25, 1:0.75, 1:1.25, 1:1.75, 1:2.25, 1:2.75, 1:3.25, 1:3.75, 1:4, or any value between these values. Controlling the mass ratio of L-polylactic acid to reactant III within the above range can further improve the strength, toughness, and heat resistance of the material. Further preferably, considering the ability to further improve the strength, toughness, and heat resistance of the material, the mass ratio of the unmodified polylactic acid to the product of contact reaction III is 1:0.67-1.34.

[0041] Preferably, the contact reaction III is carried out under the conditions of an initiator, which can be a conventional photoinitiator, preferably photoinitiator 1173. The illumination conditions include at least: an ultraviolet lamp with an irradiance of 18-22 mW / cm². 2 It can reach 18mW / cm 2 19mW / cm 2 20mW / cm 2 21mW / cm 2 22mW / cm 2 , or any value between these values; the time is 1.5-2.5h, which can be 1.5h, 1.7h, 1.9h, 2.1h, 2.3h, 2.5h, or any value between these values.

[0042] Preferably, the conditions for the contact reaction IV include at least a reaction time of 10-14 hours. Prior to the contact reaction IV, the mixture of lactide and catalyst is subjected to a cooling-vacuuming-thawing process.

[0043] Preferably, in step S1, the diol unit is selected from at least one of ethylene glycol, propylene glycol, butanediol, pentanediol, and hexanediol.

[0044] Preferably, the mixing conditions include: a rotation speed of 20-100 rpm, a temperature of 160-200℃, and a time of 8-12 min.

[0045] A third aspect of this invention provides the application of modified polylactic acid (PLA) materials or methods for preparing modified PLA materials in packaging materials. The modified PLA exhibits high tensile strength, toughness, and heat resistance, making it well-suited for use in packaging materials.

[0046] According to a particularly preferred embodiment of the present invention, a method for preparing modified polylactic acid is provided, comprising the following steps: S1. In a reactor, add saturated aliphatic diacid monomers, unsaturated aliphatic diacid monomers, diol monomers, polyethylene glycol, and the polymerization inhibitor p-hydroxyanisole. Start the stirrer and purge with nitrogen for protection. Raise the temperature to 180-200℃ and maintain the temperature at 180-200℃ while stirring for 3-5 hours. Then add the catalyst, titanate ester. Raise the temperature to 195-215℃ and evacuate the apparatus, maintaining a vacuum of 25 Pa. Continue the reaction at this temperature for 3-4 hours. The final product exhibits a climbing effect. The resulting brown product is a multi-block copolyester of polyester and polyethylene glycol.

[0047] The molar ratio of the saturated aliphatic diacid monomer to the unsaturated aliphatic diacid monomer is 1-6:1. The amount of the polyethylene glycol used is 200-300g relative to 1 mol of the total molar amount of the saturated and unsaturated aliphatic diacid monomers. The amount of catalyst I used is 2-2.6g relative to 1 mol of diacid. The amount of polymerization inhibitor used is 0.04-0.06g relative to 1g of diol monomer.

[0048] S2. Dissolve lactide in chloroform and add Sn(OTf)2 as a catalyst. Stir at room temperature for 10-30 min until completely dissolved. Then add mercaptoalkyl alcohol, mix thoroughly, and perform three cycles of liquid nitrogen cooling-vacuuming-thawing. Seal the tube under vacuum and polymerize at room temperature for 10-14 h. After the reaction, open the polymerization tube, dilute the reaction solution with chloroform, precipitate in cold methanol, filter, and vacuum dry to obtain mercapto-terminated PDLA (T-PDLA). Dissolve T-PDLA and multi-block copolyester in chloroform (molar ratio of double bond to mercapto group is 1:1-2), use 1173 as a photoinitiator, and polymerize under ultraviolet light (light intensity 18-22 mW / cm²). 2 The reaction was carried out at room temperature for 1.5-2.5 h under irradiation. The product obtained was diluted with chloroform, precipitated in cold methanol, filtered, and dried under vacuum to obtain polymer I.

[0049] The amount of mercaptoalkyl alcohol used relative to 1 g of the lactide is 0.012-0.02 mL, and the amount of catalyst II used is 0.04-0.06 g.

[0050] S3 adds PLA and polymer to an internal mixer at a mass ratio of 1:0.25-4, mixes at a speed of 20-100 rpm and a temperature of 160-200℃ for 8-12 minutes, and then removes the mixture to obtain polymer II.

[0051] The modified polylactic acid prepared by the above method has high strength, toughness and heat resistance.

[0052] The present invention will be described in detail below through examples. In the following examples, the tensile strength and elongation at break of the materials were tested according to the method in GB / T 1040.2-2022, and the Vicat softening temperature was tested according to the method in GB / T 1633-2000. Polylactic acid was purchased from Nature Works, product number 4032D.

[0053] Example 1 In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 17.098 g of succinic acid, 6.990 g of fumaric acid, 18.925 g of 1,4-butanediol, and 51.600 g of polyethylene glycol (M) were added. w=10000) and 0.946g of polymerization inhibitor p-hydroxyanisole. After starting the stirrer and purging with nitrogen, the temperature was raised to 190℃ and maintained at 190℃ for stirring for 4 hours. Then, 0.473g of catalyst tetrabutyl titanate was added. The temperature was then raised to 205℃, and the apparatus was evacuated and maintained at a vacuum of 25Pa for 3.5 hours. Finally, the product exhibited a climbing effect. The resulting brown product was polybutylene succinate / fumarate (PBSF)-polyethylene glycol (PEG) multiblock copolyester (PBSF- b -PEG). The product was named PBSF30-PEG60 (10k).

[0054] 4.3239 g of lactide was dissolved in chloroform, and 0.02162 g of Sn(OTf)₂ was added as a catalyst. The mixture was stirred at room temperature for 20 min until completely dissolved. Then, 0.07 mL of 2-mercaptoethanol was added, and the mixture was stirred thoroughly. After three cycles of liquid nitrogen cooling-vacuuming-thawing, the tube was sealed under vacuum and polymerized at room temperature for 12 h. After the reaction was completed, the polymerization tube was opened, the reaction solution was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain thiol-terminated PDLA (T-PDLA). 5 g of T-PDLA and PBSF-b-PEG were dissolved in chloroform (molar ratio of double bond to thiol group was 1:1.5). Using 1173 as a photoinitiator, the mixture was heated under a UV lamp (light intensity 20 mW / cm²). 2 The product was reacted at room temperature for 2 hours under irradiation. The product was diluted with chloroform, precipitated in cold methanol, filtered, and dried under vacuum to obtain PBSF-b-PEG-PDLA.

[0055] The reaction equations for succinic acid, fumaric acid, 1,4-butanediol, and polyethylene glycol are as follows:

[0056] The reaction equation for lactide and 2-mercaptoethanol is as follows: .

[0057] The reaction equation between T-PDLA and PBSF-b-PEG is as follows: .

[0058] PLA and PBSF-b-PEG-PDLA were added to a mixer at a mass ratio of 8:2 and mixed at 50 rpm and 180°C for 10 minutes. The resulting product was PLA / PBSF-b-PEG-PDLA20.

[0059] Example 2 In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 17.098 g of succinic acid, 6.990 g of fumaric acid, 18.925 g of 1,4-butanediol, and 51.600 g of polyethylene glycol (M) were added. w =10000) and 0.946g of polymerization inhibitor p-hydroxyanisole. After starting the stirrer and purging with nitrogen, the temperature was raised to 190℃ and maintained at 190℃ for stirring for 4 hours. Then, 0.473g of catalyst tetrabutyl titanate was added. The temperature was then raised to 205℃, and the apparatus was evacuated and maintained at a vacuum of 25Pa for 3.5 hours. Finally, the product exhibited a climbing effect. The resulting brown product was polybutylene succinate / fumarate (PBSF)-polyethylene glycol (PEG) multiblock copolyester (PBSF- b -PEG). The product was named PBSF30-PEG60 (10k).

[0060] 4.3239 g of lactide was dissolved in chloroform, and 0.02162 g of Sn(OTf)₂ was added as a catalyst. The mixture was stirred at room temperature for 20 min until completely dissolved. Then, 0.07 mL of 2-mercaptoethanol was added, and the mixture was stirred thoroughly. After three cycles of liquid nitrogen cooling-vacuuming-thawing, the tube was sealed under vacuum and polymerized at room temperature for 12 h. After the reaction was completed, the polymerization tube was opened, the reaction solution was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain thiol-terminated PDLA (T-PDLA). 5 g of T-PDLA and PBSF-b-PEG were dissolved in chloroform (molar ratio of double bond to thiol group was 1:1.5). Using 1173 as a photoinitiator, the mixture was heated under a UV lamp (light intensity 20 mW / cm²). 2 The product was reacted at room temperature for 2 hours under irradiation. The product was diluted with chloroform, precipitated in cold methanol, filtered, and dried under vacuum to obtain PBSF-b-PEG-PDLA.

[0061] PLA and PBSF-b-PEG-PDLA were added to a mixer at a mass ratio of 7:3 and mixed at 50 rpm and 180°C for 10 minutes. The resulting product was PLA / PBSF-b-PEG-PDLA30.

[0062] Example 3 In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 17.098 g of succinic acid, 6.990 g of fumaric acid, 18.925 g of 1,4-butanediol, and 51.600 g of polyethylene glycol (M) were added. w=10000) and 0.946g of polymerization inhibitor p-hydroxyanisole. After starting the stirrer and purging with nitrogen, the temperature was raised to 190℃ and maintained at 190℃ for stirring for 4 hours. Then, 0.473g of catalyst tetrabutyl titanate was added. The temperature was then raised to 205℃, and the apparatus was evacuated and maintained at a vacuum of 25Pa for 3.5 hours. Finally, the product exhibited a climbing effect. The resulting brown product was polybutylene succinate / fumarate (PBSF)-polyethylene glycol (PEG) multiblock copolyester (PBSF- b -PEG). The product was named PBSF30-PEG60 (10k).

[0063] 4.3239 g of lactide was dissolved in chloroform, and 0.02162 g of Sn(OTf)₂ was added as a catalyst. The mixture was stirred at room temperature for 20 min until completely dissolved. Then, 0.07 mL of 2-mercaptoethanol was added, and the mixture was stirred thoroughly. After three cycles of liquid nitrogen cooling-vacuuming-thawing, the tube was sealed under vacuum and polymerized at room temperature for 12 h. After the reaction was completed, the polymerization tube was opened, the reaction solution was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain thiol-terminated PDLA (T-PDLA). 5 g of T-PDLA and PBSF-b-PEG were dissolved in chloroform (molar ratio of double bond to thiol group was 1:1.5). Using 1173 as a photoinitiator, the mixture was heated under a UV lamp (light intensity 20 mW / cm²). 2 The product was reacted at room temperature for 2 hours under irradiation. The product was diluted with chloroform, precipitated in cold methanol, filtered, and dried under vacuum to obtain PBSF-b-PEG-PDLA.

[0064] PLA and PBSF-b-PEG-PDLA were added to a mixer at a mass ratio of 6:4 and mixed at 50 rpm and 180°C for 10 minutes. The resulting product was PLA / PBSF-b-PEG-PDLA40.

[0065] Example 4 In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 17.098 g of succinic acid, 6.990 g of fumaric acid, 18.925 g of 1,4-butanediol, and 51.600 g of polyethylene glycol (M) were added. w=10000) and 0.946g of polymerization inhibitor p-hydroxyanisole. After starting the stirrer and purging with nitrogen, the temperature was raised to 190℃ and maintained at 190℃ for stirring for 4 hours. Then, 0.473g of catalyst tetrabutyl titanate was added. The temperature was then raised to 205℃, and the apparatus was evacuated and maintained at a vacuum of 25Pa for 3.5 hours. Finally, the product exhibited a climbing effect. The resulting brown product was polybutylene succinate / fumarate (PBSF)-polyethylene glycol (PEG) multiblock copolyester (PBSF- b -PEG). The product was named PBSF30-PEG60 (10k).

[0066] 4.3239 g of lactide was dissolved in chloroform, and 0.02162 g of Sn(OTf)₂ was added as a catalyst. The mixture was stirred at room temperature for 20 min until completely dissolved. Then, 0.07 mL of 2-mercaptoethanol was added, and the mixture was stirred thoroughly. After three cycles of liquid nitrogen cooling-vacuuming-thawing, the tube was sealed under vacuum and polymerized at room temperature for 12 h. After the reaction was completed, the polymerization tube was opened, the reaction solution was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain thiol-terminated PDLA (T-PDLA). 5 g of T-PDLA and PBSF-b-PEG were dissolved in chloroform (molar ratio of double bond to thiol group was 1:1.5). Using 1173 as a photoinitiator, the mixture was heated under a UV lamp (light intensity 20 mW / cm²). 2 The product was reacted at room temperature for 2 hours under irradiation. The product was diluted with chloroform, precipitated in cold methanol, filtered, and dried under vacuum to obtain PBSF-b-PEG-PDLA.

[0067] PLA and PBSF-b-PEG-PDLA were added to a mixer at a mass ratio of 5:5 and mixed at 50 rpm and 180°C for 10 minutes. The resulting product was PLA / PBSF-b-PEG-PDLA50.

[0068] Example 5 In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 17.098 g of succinic acid, 6.990 g of fumaric acid, 18.925 g of 1,4-butanediol, and 51.600 g of polyethylene glycol (M) were added. w=10000) and 0.946g of polymerization inhibitor p-hydroxyanisole. After starting the stirrer and purging with nitrogen, the temperature was raised to 190℃ and maintained at 190℃ for stirring for 4 hours. Then, 0.473g of catalyst tetrabutyl titanate was added. The temperature was then raised to 205℃, and the apparatus was evacuated and maintained at a vacuum of 25Pa for 3.5 hours. Finally, the product exhibited a climbing effect. The resulting brown product was polybutylene succinate / fumarate (PBSF)-polyethylene glycol (PEG) multiblock copolyester (PBSF- b -PEG). The product was named PBSF30-PEG60 (10k).

[0069] 4.3239 g of lactide was dissolved in chloroform, and 0.02162 g of Sn(OTf)₂ was added as a catalyst. The mixture was stirred at room temperature for 20 min until completely dissolved. Then, 0.07 mL of 2-mercaptoethanol was added, and the mixture was stirred thoroughly. After three cycles of liquid nitrogen cooling-vacuuming-thawing, the tube was sealed under vacuum and polymerized at room temperature for 12 h. After the reaction was completed, the polymerization tube was opened, the reaction solution was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain thiol-terminated PDLA (T-PDLA). 5 g of T-PDLA and PBSF-b-PEG were dissolved in chloroform (molar ratio of double bond to thiol group was 1:1.5). Using 1173 as a photoinitiator, the mixture was heated under a UV lamp (light intensity 20 mW / cm²). 2 The product was reacted at room temperature for 2 hours under irradiation. The product was diluted with chloroform, precipitated in cold methanol, filtered, and dried under vacuum to obtain PBSF-b-PEG-PDLA.

[0070] PLA and PBSF-b-PEG-PDLA were added to a mixer at a mass ratio of 4:6 and mixed at 50 rpm and 180°C for 10 minutes. The resulting product was PLA / PBSF-b-PEG-PDLA60.

[0071] Example 6 In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 17.098 g of succinic acid, 6.990 g of fumaric acid, 18.925 g of 1,4-butanediol, and 51.600 g of polyethylene glycol (M) were added. w=10000) and 0.946g of polymerization inhibitor p-hydroxyanisole. After starting the stirrer and purging with nitrogen, the temperature was raised to 190℃ and maintained at 190℃ for stirring for 4 hours. Then, 0.473g of catalyst tetrabutyl titanate was added. The temperature was then raised to 205℃, and the apparatus was evacuated and maintained at a vacuum of 25Pa for 3.5 hours. Finally, the product exhibited a climbing effect. The resulting brown product was polybutylene succinate / fumarate (PBSF)-polyethylene glycol (PEG) multiblock copolyester (PBSF- b -PEG). The product was named PBSF30-PEG60 (10k).

[0072] 4.3239 g of lactide was dissolved in chloroform, and 0.02162 g of Sn(OTf)₂ was added as a catalyst. The mixture was stirred at room temperature for 20 min until completely dissolved. Then, 0.07 mL of 2-mercaptoethanol was added, and the mixture was stirred thoroughly. After three cycles of liquid nitrogen cooling-vacuuming-thawing, the tube was sealed under vacuum and polymerized at room temperature for 12 h. After the reaction was completed, the polymerization tube was opened, the reaction solution was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain thiol-terminated PDLA (T-PDLA). 5 g of T-PDLA and PBSF-b-PEG were dissolved in chloroform (molar ratio of double bond to thiol group was 1:1.5). Using 1173 as a photoinitiator, the mixture was heated under a UV lamp (light intensity 20 mW / cm²). 2 The product was reacted at room temperature for 2 hours under irradiation. The product was diluted with chloroform, precipitated in cold methanol, filtered, and dried under vacuum to obtain PBSF-b-PEG-PDLA.

[0073] PLA and PBSF-b-PEG-PDLA were added to a mixer at a mass ratio of 3:7 and mixed at 50 rpm and 180°C for 10 minutes. The resulting product was PLA / PBSF-b-PEG-PDLA70.

[0074] Example 7 In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 17.098 g of succinic acid, 6.990 g of fumaric acid, 18.925 g of 1,4-butanediol, and 51.600 g of polyethylene glycol (M) were added. w=10000) and 0.946g of polymerization inhibitor p-hydroxyanisole. After starting the stirrer and purging with nitrogen, the temperature was raised to 190℃ and maintained at 190℃ for stirring for 4 hours. Then, 0.473g of catalyst tetrabutyl titanate was added. The temperature was then raised to 205℃, and the apparatus was evacuated and maintained at a vacuum of 25Pa for 3.5 hours. Finally, the product exhibited a climbing effect. The resulting brown product was polybutylene succinate / fumarate (PBSF)-polyethylene glycol (PEG) multiblock copolyester (PBSF- b -PEG). The product was named PBSF30-PEG60 (10k).

[0075] 4.3239 g of lactide was dissolved in chloroform, and 0.02162 g of Sn(OTf)₂ was added as a catalyst. The mixture was stirred at room temperature for 20 min until completely dissolved. Then, 0.07 mL of 2-mercaptoethanol was added, and the mixture was stirred thoroughly. After three cycles of liquid nitrogen cooling-vacuuming-thawing, the tube was sealed under vacuum and polymerized at room temperature for 12 h. After the reaction was completed, the polymerization tube was opened, the reaction solution was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain thiol-terminated PDLA (T-PDLA). 5 g of T-PDLA and PBSF-b-PEG were dissolved in chloroform (molar ratio of double bond to thiol group was 1:1.5). Using 1173 as a photoinitiator, the mixture was heated under a UV lamp (light intensity 20 mW / cm²). 2 The product was reacted at room temperature for 2 hours under irradiation. The product was diluted with chloroform, precipitated in cold methanol, filtered, and dried under vacuum to obtain PBSF-b-PEG-PDLA.

[0076] PLA and PBSF-b-PEG-PDLA were added to a mixer at a mass ratio of 2:8 and mixed at 50 rpm and 180°C for 10 minutes. The resulting product was PLA / PBSF-b-PEG-PDLA80.

[0077] Example 8 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method in Example 5, except that the molar ratio of double bonds to thiol groups was 1:1.

[0078] Example 9 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method in Example 5, except that the molar ratio of double bonds to thiol groups was 1:1.2.

[0079] Example 10 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method in Example 5, except that the molar ratio of double bonds to thiol groups was 1:1.8.

[0080] Example 11 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method in Example 5, except that the molar ratio of double bonds to thiol groups was 1:2.

[0081] Example 12 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method in Example 5, except that the mass of polyethylene glycol was 48g.

[0082] Example 13 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method in Example 5, except that the mass of polyethylene glycol was 55g.

[0083] Example 14 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method in Example 5, except that the mass of polyethylene glycol was 45g.

[0084] Example 15 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method in Example 5, except that the mass of polyethylene glycol was 58g.

[0085] Example 16 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method described in Example 5, except that the mass of succinic acid was 14.606 g and the mass of fumaric acid was 9.44 g.

[0086] Example 17 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method described in Example 5, except that the mass of succinic acid was 19.035 g and the mass of fumaric acid was 5.09 g.

[0087] Example 18 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method described in Example 5, except that the mass of succinic acid was 12.531 g and the mass of fumaric acid was 11.48 g.

[0088] Example 19 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method described in Example 5, except that the mass of succinic acid was 20.609 g and the mass of fumaric acid was 3.54 g.

[0089] Example 20 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method described in Example 5, except that 17.098 g of succinic acid was replaced with 15.058 g of malonic acid, and 18.925 g of butanediol was replaced with 15.959 g of propylene glycol.

[0090] Example 21 PLA / PBSF-b-PEG-PDLA60 was prepared according to the method described in Example 5, except that polyethylene glycol with a weight average molecular weight of 10,000 was replaced with polypropylene glycol with a weight average molecular weight of 9,000.

[0091] Example 22 In a reactor equipped with a heating device, a condensate separator, a mechanical stirrer, and a thermometer, add 23.800 g of fumaric acid, 18.925 g of 1,4-butanediol, and 51.600 g of polyethylene glycol (M). w =10000) and 0.946g of polymerization inhibitor p-hydroxyanisole. After starting the stirrer and purging with nitrogen, the temperature was raised to 190℃ and maintained at 190℃ for stirring for 4 hours. Then, 0.473g of catalyst tetrabutyl titanate was added. The temperature was then raised to 205℃, and the apparatus was evacuated to a vacuum of 25 Pa. The reaction was maintained at this temperature for 3.5 hours. Finally, the product exhibited a climbing effect. The resulting brown product was butylene fumarate-polyethylene glycol (PEG) multiblock copolyester.

[0092] 4.3239 g of lactide was dissolved in chloroform, and 0.02162 g of Sn(OTf)₂ was added as a catalyst. The mixture was stirred at room temperature for 20 min until completely dissolved. Then, 0.07 mL of 2-mercaptoethanol was added, and the mixture was stirred thoroughly. After three cycles of liquid nitrogen cooling-vacuuming-thawing, the tube was sealed under vacuum and polymerized at room temperature for 12 h. After the reaction was completed, the polymerization tube was opened, the reaction solution was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain mercapto-terminated PDLA (T-PDLA). 5 g of T-PDLA and 58.81 g of butylene fumarate-polyethylene glycol (PEG) multiblock copolyester were dissolved in chloroform (molar ratio of double bonds to mercapto groups of 1:1.5). Using 1173 as a photoinitiator, the mixture was heated under a UV lamp (light intensity 20 mW / cm²). 2 The reaction was carried out at room temperature for 2 hours under irradiation. The product was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain a copolymer of butylene fumarate-polyethylene glycol (PEG) multiblock copolyester and PDLA.

[0093] The copolymer of PLA and butylene fumarate-polyethylene glycol (PEG) multiblock copolyester and PDLA was added to a mixer at a mass ratio of 4:6 and mixed at 50 rpm and 180°C for 10 min to obtain the copolymer.

[0094] Example 23 The polymer was prepared according to the method described in Example 5, except that fumaric acid was replaced with pentenoic acid (CAS No.: 1724-02-3).

[0095] Comparative Example 1 In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 17.098 g of succinic acid, 6.990 g of fumaric acid, 18.925 g of 1,4-butanediol, and 51.600 g of polyethylene glycol (M) were added. w =10000) and 0.946g of polymerization inhibitor p-hydroxyanisole. After starting the stirrer and purging with nitrogen, the temperature was raised to 190℃ and maintained at 190℃ for stirring for 4 hours. Then, 0.473g of catalyst tetrabutyl titanate was added. The temperature was then raised to 205℃, and the apparatus was evacuated and maintained at a vacuum of 25Pa for 3.5 hours. Finally, the product exhibited a climbing effect. The resulting brown product was polybutylene succinate / fumarate (PBSF)-polyethylene glycol (PEG) multiblock copolyester (PBSF- b -PEG). The product was named PBSF30-PEG60 (10k).

[0096] PLA and PBSF30-PEG60 (10k) were added to a mixer at a mass ratio of 4:6 and mixed at 50 rpm and 180°C for 10 min. The resulting product was PLA / PBSF-PEG60.

[0097] Comparative Example 2 In a reactor equipped with a heating device, a condenser, a mechanical stirrer, and a thermometer, 24.210 g of succinic acid, 18.925 g of 1,4-butanediol, and 51.600 g of polyethylene glycol (M) were added. w =10000) and 0.946g of polymerization inhibitor p-hydroxyanisole. After starting the stirrer and purging with nitrogen, the temperature was raised to 190℃ and maintained at 190℃ for stirring for 4 hours. Then, 0.473g of catalyst tetrabutyl titanate was added. The temperature was then raised to 205℃, and the apparatus was evacuated and maintained at a vacuum of 25 Pa for 3.5 hours. The final product exhibited a climbing effect, yielding polybutylene succinate-polyethylene glycol multiblock copolyester.

[0098] 4.3239 g of lactide was dissolved in chloroform, and 0.02162 g of Sn(OTf)₂ was added as a catalyst. The mixture was stirred at room temperature for 20 min until completely dissolved. Then, 0.07 mL of 2-mercaptoethanol was added, and the mixture was stirred thoroughly. After three cycles of liquid nitrogen cooling-vacuuming-thawing, the tube was sealed under vacuum and polymerized at room temperature for 12 h. After the reaction was completed, the polymerization tube was opened, the reaction solution was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain mercapto-terminated PDLA (T-PDLA). 5 g of T-PDLA and 39.67 g of polybutylene succinate-polyethylene glycol multiblock copolyester were dissolved in chloroform. Using 1173 as a photoinitiator, the mixture was heated under a UV lamp (20 mW / cm²). 2 The reaction was carried out at room temperature for 2 hours under irradiation. The product was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain a copolymer of polybutylene succinate, polyethylene glycol multiblock copolyester and PDLA.

[0099] The copolymer of PLA and polybutylene succinate-polyethylene glycol multiblock copolyester and PDLA was added to a mixer at a mass ratio of 4:6 and mixed at 50 rpm and 180°C for 10 minutes. The copolymer was then removed.

[0100] Comparative Example 3 4.3239 g of lactide was dissolved in chloroform, and 0.02162 g of Sn(OTf)₂ was added as a catalyst. The mixture was stirred at room temperature for 20 min until completely dissolved. Then, 0.07 mL of 2-mercaptoethanol was added, and the mixture was thoroughly mixed. The mixture underwent three cycles of liquid nitrogen cooling-vacuuming-thawing. The tube was then sealed under vacuum, and polymerization was carried out at room temperature for 12 h. After the reaction was complete, the polymerization tube was opened, the reaction solution was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain mercapto-terminated PDLA (T-PDLA). 5 g of T-PDLA was then mixed with 39.67 g of polyethylene glycol (M... w =10000) dissolved in chloroform, using 1173 as a photoinitiator, under a UV lamp (light intensity 20mW / cm²). 2 The reaction was carried out at room temperature for 2 hours under irradiation. The product was diluted with chloroform, precipitated in cold methanol, filtered, and vacuum dried to obtain a copolymer of polyethylene glycol (PEG) multiblock copolyester and PDLA (PEG-PDLA).

[0101] The copolymer of PLA and PEG-PDLA was added to a mixer at a mass ratio of 4:6 and mixed at 50 rpm and 180°C for 10 min to obtain PLA / PEG-PDLA60.

[0102] The parameters of the polymers obtained in the examples and comparative examples are shown in Table 1.

[0103] Table 1

[0104] As can be seen from the results in Table 1, the tensile strength, elongation at break, and Vicat softening temperature of the modified polylactic acid material provided in the embodiments of the present invention are all higher than those of the polylactic acid composite material provided in the comparative example, indicating that the modified polylactic acid material provided in the present invention has higher tensile strength, toughness, and heat resistance.

[0105] 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 polylactic acid material, characterized by, The modified polylactic acid material contains modified polylactic acid, which in turn contains polylactic acid and structural unit A connected to the polylactic acid. Structural unit A has the structure shown in formula (I). Formula (I); Wherein, R1 is absent or is a C1-C6 alkylene group, R2 is absent or is a C1-C6 alkylene group, and R3 is a C1-C6 alkylene group.

2. The modified polylactic acid material according to claim 1, wherein The structural unit A has the structure shown in equation (II). Formula (II); R4 and R5 each contain at least one of polyether structural units, ester structural units, or hydrogen. Preferably, at least one of R4 and R5 contains a polyether structural unit and at least one contains an ester structural unit; Preferably, the polyether structural unit has the structure shown in formula (III), and the ester knot unit has the structure shown in formula (IV); Formula (III); Formula (IV); Wherein, R7 is absent or is a C1-C4 alkylene group, R8 and R9 are each independently a C2-C6 alkylene group, and are further preferably C2-C4 alkylene groups; n is 200-250, and n is a natural number; Preferably, in the modified polylactic acid, the content of the polyether structural unit is 50-60 wt%, more preferably 52-56 wt%.

3. The modified polylactic acid material according to claim 1 or 2, characterized in that, In the modified polylactic acid, the content of structural unit A is 89-97 wt%, preferably 91.5-95 wt%.

4. The modified polylactic acid material according to claim 1 or 2, characterized in that, The modified polylactic acid material also contains unmodified polylactic acid. Preferably, the mass ratio of the unmodified polylactic acid to the modified polylactic acid is 1:0.25-4, more preferably 1:0.67-1.34; Preferably, the modified polylactic acid is dextrorotatory polylactic acid, and the unmodified polylactic acid is levorotatory polylactic acid.

5. The modified polylactic acid material according to claim 1 or 2, characterized in that, The material has a tensile strength of 15-38 MPa, an elongation at break of 150-600%, and a Vicat softening temperature of 100-155℃. Preferably, the material has a tensile strength of 28-36.5 MPa, an elongation at break of 420-580%, and a Vicat softening temperature of 145-153.5 °C.

6. A method for preparing a modified polylactic acid material, characterized in that, include: III. Contact reaction of thiol-terminated polylactic acid with polyester containing carbon-carbon double bonds.

7. The preparation method according to claim 6, characterized in that, The method for preparing the polyester containing carbon-carbon double bonds includes: Under esterification conditions, saturated aliphatic diacid monomers, unsaturated aliphatic diacid monomers, diol monomers, polyethylene glycol and polymerization inhibitor are subjected to contact reaction I to obtain reactant I. Under polymerization conditions, reactant I and catalyst I are subjected to contact reaction II; Preferably, the saturated aliphatic diacid monomer is a C2-C6 saturated aliphatic diacid monomer, the unsaturated aliphatic diacid monomer is an aliphatic diacid monomer containing a carbon-carbon double bond, and further, a C2-C6 unsaturated aliphatic diacid monomer; the diol monomer is a C2-C6 diol monomer, and the polyethylene glycol is a C2-C6 polyethylene glycol; Preferably, the molar ratio of the saturated aliphatic dicarboxylic acid monomer to the unsaturated aliphatic dicarboxylic acid monomer is 1-6:1, more preferably 1.5-3.6:1; Preferably, the amount of the polyethylene glycol used is 200-300g relative to the total molar amount of 1 mol of the saturated aliphatic diacid monomer and the unsaturated aliphatic diacid monomer, and more preferably 218-270g. The polymerization inhibitor is p-hydroxyanisole; Preferably, catalyst I is an organotitanium catalyst, and more preferably a titanate ester.

8. The preparation method according to claim 6 or 7, characterized in that, The method for preparing the thiol-terminated polylactic acid includes: reacting lactide and mercaptoalkyl alcohol in a contact reaction IV in the presence of catalyst II; Preferably, the amount of the mercaptoalkyl alcohol used is 0.012-0.02 mL relative to 1 g of the lactide, more preferably 0.015-0.018 mL; Preferably, catalyst II is a tin-based catalyst, more preferably Sn(OTf)2; Preferably, the molar ratio of the polylactic acid, calculated as mercapto groups, to the polyester containing carbon-carbon double bonds, calculated as double bonds, is 1:1-2, more preferably 1:1.2-1.8; Preferably, the mercaptoalkyl alcohol is a C2-C6 mercaptoalkyl alcohol, and more preferably 2-mercaptoethanol.

9. The preparation method according to claim 6 or 7, characterized in that, The method further includes: mixing the product of contact reaction III with unmodified polylactic acid; Preferably, the unmodified polylactic acid is L-polylactic acid; Preferably, the mass ratio of the unmodified polylactic acid to the product of contact reaction III is 1:0.25-4, more preferably 1:0.67-1.

34.

10. The application of the modified polylactic acid material according to any one of claims 1 to 5 or the modified polylactic acid material prepared by the preparation method according to any one of claims 6 to 9 in packaging materials.

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