Modification method of lactic acid copolymerization modified PBAT

Abstract

The invention relates to a modification method of lactic acid copolymerization modified PBAT, which comprises the following steps: mixing terephthalic acid and 1, 4-butanediol, adding tetrabutyl titanate, and carrying out esterification reaction to obtain a prepolymer A; mixing adipic acid and 1, 4-butanediol, adding tetrabutyl titanate and triphenyl phosphite, and carrying out esterification reaction to obtain a prepolymer B; carrying out polycondensation on an L-lactic acid aqueous solution in the presence of stannous octoate to obtain a prepolymer C; 2, 5-furandicarboxylic acid and 1, 4-butanediol are mixed, tetrabutyl titanate is added, an esterification reaction is performed, and a prepolymer D is obtained; and mixing the prepolymers, and carrying out polycondensation under the action of a composite catalyst to obtain the lactic acid copolymerization modified PBAT. The invention aims to provide the modification method of the lactic acid copolymerization modified PBAT, so that the melting point, the thermal decomposition temperature, the mechanical property and the elastic modulus of the lactic acid copolymerization modified PBAT are improved, and meanwhile, the CO2 barrier property, the O2 barrier property and the water vapor barrier property are improved.

Description

Technical Field

[0001] This invention relates to the field of biodegradable materials technology, specifically to a method for modifying PBAT by lactic acid copolymerization. Background Technology

[0002] Biodegradable polyesters have become one of the most effective solutions to plastic pollution, as they can degrade into environmentally harmless carbon dioxide and water under composting or natural conditions. Among biodegradable polyesters, polybutylene terephthalate (PBAT) and polylactic acid (PLA) are currently the two most widely produced and used varieties on the market. PBAT is a copolymer of butylene terephthalate (PBT) and butylene adipate (PBA), possessing both rigid and flexible segments in its structure, exhibiting high ductility and elongation at break. However, PBAT has relatively low strength and stiffness, leading to easy adhesion during blown film production, soft film products, and susceptibility to breakage during use. PLA has advantages such as high strength, high hardness, transparency, and good processability; however, PLA suffers from disadvantages such as low elongation at break, poor impact strength, and poor toughness, making it difficult to meet certain practical application requirements and limiting its application. In practical applications, PBAT and PLA are usually directly blended to form complementary PBAT-PLA blends. However, PBAT and PLA have poor compatibility, and the performance of blended products is unstable.

[0003] To address the issue of poor compatibility in blending, isocyanate chain extenders are commonly used in chain extension reactions. However, these reactions can lead to problems such as the toxicity of the chain extenders or a wide molecular weight distribution in the extended product, negatively impacting its properties. Therefore, this invention proposes a method for modifying PBAT through lactic acid copolymerization. Summary of the Invention

[0004] The purpose of this invention is to provide a modification method for lactic acid copolymerized PBAT, which improves the melting point, thermal decomposition temperature, mechanical properties and elastic modulus of lactic acid copolymerized PBAT, while also improving CO2 barrier properties, O2 barrier properties and water vapor barrier properties.

[0005] This invention provides a method for modifying PBAT by copolymerization of lactic acid, comprising the following steps: (1) Terephthalic acid and 1,4-butanediol were mixed and then tetrabutyl titanate was added to carry out esterification reaction to obtain prepolymer A; (2) After mixing adipic acid and 1,4-butanediol, tetrabutyl titanate and triphenyl phosphite are added to carry out esterification reaction to obtain prepolymer B; (3) Prepolymer C was obtained by polycondensing L-lactic acid aqueous solution under stannous octoate. (4) After mixing 2,5-furandicarboxylic acid and 1,4-butanediol, tetrabutyl titanate was added to carry out an esterification reaction to obtain prepolymer D; (5) Prepolymer A, prepolymer B, prepolymer C and prepolymer D are mixed and polycondensed under the action of a composite catalyst to obtain lactic acid copolymerized modified PBAT.

[0006] This invention prepares lactic acid copolymerized modified PBAT by polycondensation of four different prepolymers, each prepolymer playing a unique role and synergistically complementing the others. Prepolymer A is obtained by esterification of terephthalic acid and 1,4-butanediol, and prepolymer B is obtained by esterification of adipic acid and 1,4-butanediol. Both are the basic polyester components, providing the material with a fundamental framework for mechanical properties and thermal stability. Prepolymer C is obtained by polycondensation of L-lactic acid aqueous solution, introducing lactic acid units to impart bio-based properties to the material, while its molecular chain structure helps to improve the material's flexibility and elastic modulus. Prepolymer D is obtained by esterification of 2,5-furandicarboxylic acid and 1,4-butanediol. Furandicarboxylic acid has a special molecular structure, and its addition can enhance the rigidity of the molecular chain, forming an effective barrier network. After the four prepolymers are mixed, they undergo polycondensation under the action of a composite catalyst. The molecular chains of the different prepolymers intertwine and block copolymerize, achieving complementary properties and optimizing the overall performance of the material at the molecular level. This multi-prepolymer synergistic preparation method breaks through the limitations of traditional single prepolymer modification.

[0007] Further, in step (1), the esterification reaction temperature of prepolymer A is 230-240℃, the pressure is 40-60KPa, and the reaction time is 120-130min; in step (2), the esterification reaction temperature of prepolymer B is 180-200℃, the pressure is 40-60KPa, and the reaction time is 180-200min; in step (3), the polycondensation temperature of prepolymer C is 130-150℃, the pressure is 40-60KPa, and the reaction time is 120-130min; in step (4), the reaction temperature of prepolymer D is 210-230℃, the pressure is 40-60KPa, and the reaction time is 100-120min.

[0008] Further, the lactic acid copolymerization modification of PBAT polycondensation step (5) includes: pre-polycondensation at 205-210℃ and 2-3KPa for 80-90 min, followed by final polycondensation at 210-215℃ and 0.05-0.2KPa for 130-140 min, and finally thickening polycondensation at 215-225℃ and 0.01-0.015KPa for 100-110 min.

[0009] This invention employs a stepwise polycondensation process in the polycondensation of lactic acid copolymerized PBAT, comprising three stages: pre-polymerization, final polycondensation, and thickening polycondensation, with different temperature and pressure conditions set for each stage. The pre-polymerization stage is conducted at a relatively high temperature (205-210℃) and a relatively low vacuum (2-3 kPa). This stage primarily allows the prepolymer to undergo initial reaction, removing some small-molecule byproducts and creating conditions for subsequent reactions. Simultaneously, it avoids excessively vigorous reactions due to excessively high vacuum, which could affect the regularity of the molecular chains. The final polycondensation stage increases the vacuum (0.05-0.2 kPa) and appropriately raises the temperature (210-215℃) to further promote molecular chain growth and cross-linking, increasing the molecular weight of the material and enhancing its mechanical properties and thermal stability. The thickening polycondensation stage is conducted at an even higher temperature (215-225℃) and an extremely high vacuum (0.01-0.015 kPa). By deeply removing small-molecule substances, it further improves the viscosity and molecular weight distribution uniformity of the material, optimizing its processing and barrier properties. This stepwise polycondensation process precisely controls the reaction conditions according to the needs of different reaction stages, achieving gradual and orderly growth of molecular chains and gradual improvement of performance.

[0010] Further, in step (1), the weight ratio of terephthalic acid, 1,4-butanediol and tetrabutyl titanate is 100:60-70:0.02-0.04.

[0011] Further, in step (2), the weight ratio of adipic acid, 1,4-butanediol, tetrabutyl titanate and triphenyl phosphite is 100:70-80:0.01-0.03:0.03-0.06.

[0012] Further, in step (3), the concentration of the L-lactic acid aqueous solution is 80-90 wt%, and the weight ratio of the L-lactic acid aqueous solution to stannous octoate is 100:0.04-0.06.

[0013] Further, in step (4), the weight ratio of 2,5-furandicarboxylic acid, 1,4-butanediol and tetrabutyl titanate is 100:55-65:0.01-0.02.

[0014] Further, the weight ratio of prepolymer A, prepolymer B, prepolymer C and prepolymer D in step (5) is 45-55:25-35:15-25:5-10.

[0015] Further, in step (5), the total amount of the composite catalyst is 0.05-0.1 wt% of the total mass of prepolymer A, prepolymer B, prepolymer C and prepolymer D. The composite catalyst includes sodium germanate and zinc acetylacetonate in a weight ratio of 1:2.5-3. In step (5), 50-60% of the composite catalyst is added before prepolymerization and the remaining catalyst is added before final polymerization.

[0016] Furthermore, the lactic acid copolymerized modified PBAT has a melting point ≥133℃, a thermal decomposition temperature ≥330℃, a tensile strength ≥28MPa, an elastic modulus ≥120MPa, an elongation at break ≥380%, a CO2 barrier ≤0.8 barrer, an O2 barrier ≤0.20 barrer, and a water vapor barrier ≤9.0×10⁻⁶. -14 g·cm / cm 2 ·s·Pa.

[0017] The beneficial effects of this invention are as follows: In this invention, prepolymer C (L-lactic acid condensation product) and prepolymer D (2,5-furandicarboxylic acid condensation product) exhibit a significant synergistic effect in enhancing the barrier properties and flexibility of the material. The lactic acid units in prepolymer C contain polar groups such as hydroxyl groups, which increase the interaction forces between molecular chains, improving the material's flexibility and elastic modulus. Simultaneously, its bio-based properties give the material a certain degree of biodegradability. The furandicarboxylic acid in prepolymer D possesses a unique planar conjugated structure, enabling the formation of rigid segments within the molecular chain, enhancing its rigidity. Furthermore, the oxygen atoms on the furan ring can interact with gas molecules, forming an effective barrier network that improves the material's barrier properties against CO2, O2, and water vapor. When prepolymers C and D are mixed and condensed with other prepolymers, their molecular chains interweave and intertwine, with a reasonable distribution of rigid and flexible segments. This ensures both a certain degree of flexibility and significantly improves the material's barrier performance through the barrier network formed by the rigid segments, achieving a balanced improvement in both flexibility and barrier properties.

[0018] This invention employs a composite catalyst composed of sodium germanate and zinc acetylacetonate, added stepwise during the polycondensation process. Sodium germanate and zinc acetylacetonate exhibit different catalytic activities and selectivities, playing a synergistic role in the polycondensation reaction. Sodium germanate demonstrates good catalytic activity for esterification, promoting ester bond formation between prepolymers and increasing the reaction rate; zinc acetylacetonate, on the other hand, exhibits a more significant catalytic effect on molecular chain growth and cross-linking in the final polycondensation stage, contributing to improved molecular weight and crystallinity of the material. The stepwise addition of the composite catalyst—partially added before pre-polycondensation—provides a suitable catalytic environment for the initial reaction of the prepolymer, ensuring a stable reaction; the remaining catalyst is added before final polycondensation to enhance the catalytic effect in the final polycondensation stage, promoting deeper molecular chain growth and cross-linking, and improving material performance. This synergistic effect of the composite catalyst and the stepwise addition method optimize the polycondensation reaction process from a catalytic mechanism perspective, improving reaction efficiency and the overall performance of the material. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0020] This embodiment provides a method for modifying PBAT by lactic acid copolymerization, the steps of which include: (1) Terephthalic acid and 1,4-butanediol were mixed and then tetrabutyl titanate was added. The mixture was subjected to esterification reaction at 235°C and 50 kPa for 125 min to obtain prepolymer A. The weight ratio of terephthalic acid, 1,4-butanediol and tetrabutyl titanate was 100:65:0.03. (2) After mixing adipic acid and 1,4-butanediol, tetrabutyl titanate and triphenyl phosphite were added and esterified for 190 min at a temperature of 190℃ and a pressure of 50 kPa to obtain prepolymer B; the weight ratio of adipic acid, 1,4-butanediol, tetrabutyl titanate and triphenyl phosphite was 100:75:0.02:0.045. (3) The prepolymer C was obtained by polycondensing an 85wt% L-lactic acid aqueous solution in stannous octoate at a temperature of 140℃ and a pressure of 50KPa for 125min; the weight ratio of L-lactic acid aqueous solution to stannous octoate was 100:0.05. (4) After mixing 2,5-furandicarboxylic acid and 1,4-butanediol, tetrabutyl titanate was added and esterification was carried out at a temperature of 220℃ and a pressure of 50KPa for 110 min to obtain prepolymer D; the weight ratio of 2,5-furandicarboxylic acid, 1,4-butanediol and tetrabutyl titanate was 100:60:0.015; (5) Prepolymer A, prepolymer B, prepolymer C and prepolymer D with a weight ratio of 50:30:20:8 were mixed, 0.044 parts of composite catalyst were added, and prepolymerization was carried out at 208℃ and 2.5KPa for 85 min. Then, 0.036 parts of composite catalyst were added, and final polymerization was carried out at 212℃ and 0.125KPa for 135 min. Finally, thickening polymerization was carried out at 220℃ and 0.012KPa for 105 min to obtain lactic acid copolymerized modified PBAT. The composite catalyst included sodium germanate and zinc acetylacetone with a weight ratio of 1:2.8. Example

[0021] This embodiment provides a method for modifying PBAT by lactic acid copolymerization, the steps of which include: (1) Terephthalic acid and 1,4-butanediol were mixed and then tetrabutyl titanate was added. The mixture was subjected to esterification reaction at 230°C and 40 kPa for 120 min to obtain prepolymer A. The weight ratio of terephthalic acid, 1,4-butanediol and tetrabutyl titanate was 100:60:0.02. (2) After mixing adipic acid and 1,4-butanediol, tetrabutyl titanate and triphenyl phosphite were added and esterified for 180 min at a temperature of 180℃ and a pressure of 40 kPa to obtain prepolymer B; the weight ratio of adipic acid, 1,4-butanediol, tetrabutyl titanate and triphenyl phosphite was 100:70:0.01:0.03. (3) The prepolymer C was obtained by polycondensing an 80wt% L-lactic acid aqueous solution in stannous octoate at 130℃ and 40KPa for 120min; the weight ratio of L-lactic acid aqueous solution to stannous octoate was 100:0.04. (4) After mixing 2,5-furandicarboxylic acid and 1,4-butanediol, tetrabutyl titanate was added and esterification was carried out at a temperature of 210℃ and a pressure of 40KPa for 100min to obtain prepolymer D; the weight ratio of 2,5-furandicarboxylic acid, 1,4-butanediol and tetrabutyl titanate was 100:55:0.01; (5) Prepolymer A, prepolymer B, prepolymer C and prepolymer D with a weight ratio of 45:25:15:5 were mixed, 0.023 parts of composite catalyst were added, and prepolymerization was carried out at 205℃ and 2KPa for 80 min. Then, 0.022 parts of composite catalyst were added and final polymerization was carried out at 210℃ and 0.05KPa for 130 min. Finally, thickening polymerization was carried out at 215℃ and 0.01KPa for 100 min to obtain lactic acid copolymer modified PBAT. The catalyst included sodium germanate and zinc acetylacetone with a weight ratio of 1:2.5. Example

[0022] This embodiment provides a method for modifying PBAT by lactic acid copolymerization, the steps of which include: (1) Terephthalic acid and 1,4-butanediol were mixed and then tetrabutyl titanate was added. The mixture was subjected to esterification reaction at 240℃ and 60KPa for 130min to obtain prepolymer A. The weight ratio of terephthalic acid, 1,4-butanediol and tetrabutyl titanate was 100:70:0.04. (2) After mixing adipic acid and 1,4-butanediol, tetrabutyl titanate and triphenyl phosphite were added and esterified for 200 min at a temperature of 200℃ and a pressure of 60 kPa to obtain prepolymer B; the weight ratio of adipic acid, 1,4-butanediol, tetrabutyl titanate and triphenyl phosphite was 100:80:0.03:0.06. (3) A 90wt% L-lactic acid aqueous solution was subjected to polycondensation in stannous octoate at 150℃ and 60KPa for 130min to obtain prepolymer C; the weight ratio of L-lactic acid aqueous solution to stannous octoate was 100:0.06. (4) After mixing 2,5-furandicarboxylic acid and 1,4-butanediol, tetrabutyl titanate was added and esterification was carried out at a temperature of 230℃ and a pressure of 60KPa for 120min to obtain prepolymer D; the weight ratio of 2,5-furandicarboxylic acid, 1,4-butanediol and tetrabutyl titanate was 100:65:0.02; (5) Prepolymer A, prepolymer B, prepolymer C and prepolymer D with a weight ratio of 55:35:25:10 were mixed, 0.075 parts of composite catalyst were added, and prepolymerization was carried out at 210℃ and 3KPa for 90 min. Then, 0.05 parts of composite catalyst were added and final polymerization was carried out at 215℃ and 0.2KPa for 140 min. Finally, thickening polymerization was carried out at 225℃ and 0.015KPa for 110 min to obtain lactic acid copolymerized modified PBAT. The catalyst included sodium germanate and zinc acetylacetone with a weight ratio of 1:3. Example

[0023] Based on Example 1, adjustments were made. Unlike Example 1, the composite catalyst was added all at once in this example, and prepolymer A, prepolymer B, prepolymer C, prepolymer D and composite catalyst were directly mixed. Example

[0024] Based on Example 1, adjustments were made. Unlike Example 1, the composite catalyst in this example was replaced with a single catalyst, sodium germanate. Example

[0025] Based on Example 1, this example is modified in that the composite catalyst is replaced with a single catalyst, zinc acetylacetonate. Example

[0026] Based on Example 1, the steps are adjusted as follows: Prepolymers A, B, C and D are mixed in the same proportion, and then all composite catalysts (0.08 parts) are added at once. The mixture is directly polycondensed at a temperature of 212°C and a pressure of 0.125 kPa for 325 min. Example

[0027] Based on Example 1, the steps are adjusted as follows: instead of adding the composite catalyst, tetrabutyl titanate is added in two separate steps, that is, the composite catalyst is adjusted to an equal amount of tetrabutyl titanate. Example

[0028] Based on Example 1, adjustments were made. Unlike Example 1, step (5) in this example was adjusted as follows: the pressure of the pre-condensation stage remained at 2.5 kPa, but the pressure of the final condensation stage was changed to 0.5 kPa (higher than 0.125 kPa in Example 1), the pressure of the thickening condensation stage was changed to 0.05 kPa (higher than 0.012 kPa in Example 1), and the temperature and time remained unchanged. Example

[0029] Based on Example 1, adjustments were made. Unlike Example 1, step (5) in this example was adjusted as follows: the pre-condensation temperature was changed to 220℃ (originally 208℃), the final condensation temperature was changed to 225℃ (originally 212℃), the thickening condensation temperature was changed to 235℃ (originally 220℃), and the pressure and time remained unchanged.

[0030] Comparative Example 1 Based on Example 1, adjustments were made. Unlike Example 1, the lactic acid copolymerized modified PBAT in this comparative example did not include step (3). The preparation steps included: mixing prepolymer A, prepolymer B and prepolymer D with a weight ratio of 50:30:8, adding 0.044 parts of composite catalyst, performing pre-condensation at 208℃ and 2.5KPa for 85min, then adding 0.036 parts of composite catalyst, performing final condensation at 212℃ and 0.125KPa for 135min, and finally performing thickening condensation at 220℃ and 0.012KPa for 105min to obtain lactic acid copolymerized modified PBAT. The composite catalyst included sodium germanate and zinc acetylacetonate with a weight ratio of 1:2.8.

[0031] Comparative Example 2 Based on Example 1, adjustments were made. Unlike Example 1, step (4) was not included in the lactic acid copolymer modified PBAT in this comparative example. The preparation steps included: mixing prepolymer A, prepolymer B and prepolymer C with a weight ratio of 50:30:20, adding 0.044 parts of composite catalyst, performing pre-condensation at 208℃ and 2.5KPa for 85min, then adding 0.036 parts of composite catalyst, performing final condensation at 212℃ and 0.125KPa for 135min, and finally performing thickening condensation at 220℃ and 0.012KPa for 105min to obtain lactic acid copolymer modified PBAT. The composite catalyst included sodium germanate and zinc acetylacetonate with a weight ratio of 1:2.8.

[0032] The properties of the products prepared in Examples 1-6 and Comparative Examples 1-2 were tested: Melting point: Tested in accordance with GB / T19466.3-2004 "Differential scanning calorimetry (DSC) for plastics - Part 3: Determination of melting and crystallization temperature and enthalpy"; Thermal decomposition temperature: Tested according to GB / T33047.1-2016 "Plastics Thermogravimetric Analysis (TG) Part 1: General Rules" standard; Mechanical properties: Tested according to GB / T1040.1-2018 "Determination of tensile properties of plastics - Part 1: General rules"; dumbbell-shaped specimens were tested on a universal testing machine with a clamp spacing of 50 mm and a tensile speed of 50 mm / min; where, tensile strength = maximum tensile force / specimen cross-sectional area; elastic modulus = slope of the linear segment of the stress-strain curve; elongation at break = elongation at break / original gauge length × 100%; Gas barrier properties: Tested according to GB / T1038-2000 "Gas permeability test method for plastic films and sheets - differential pressure method"; Water vapor barrier properties: Tested in accordance with GB / T21529-2008 "Determination of water vapor transmission rate of plastic films and sheets by electrolytic sensor method"; The test results are shown in Tables 1 and 2 below: Table 1 performance products Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Melting point 136 135 134 133.8 133.5 133.3 Thermal decomposition temperature (°C) 338 335 332 331 330.5 330.8 Tensile strength (MPa) 31.0 30.1 29.2 28.5 28.2 28.3 Elastic modulus (MPa) 128 125 122 121 120.5 120.8 Elongation at break (%) 420 400 385 382 380.5 381 <![CDATA[CO2 barrier]]> 0.65 0.7 0.75 0.78 0.79 0.77 <![CDATA[O2 barrier]]> 0.17 0.18 0.19 0.195 0.198 0.195 <![CDATA[Water vapor barrier × 10 14 g·cm / cm 2 ·s·Pa]]> 8.2 8.5 8.8 8.9 8.95 8.85 Table 2 performance products Example 7 Example 8 Example 9 Example 10 Comparative Example 1 Comparative Example 2 Melting point 132.5 132 133 135.5 140 130 Thermal decomposition temperature (°C) 331 330 332 336 325 328 Tensile strength (MPa) 28.2 28.0 29 30.2 26.1 27 Elastic modulus (MPa) 121 120 123 126 130 118 Elongation at break (%) 382 380 390 405 300 370 <![CDATA[CO2 barrier]]> 0.78 0.80 0.74 0.68 1.0 0.9 <![CDATA[O2 barrier]]> 0.19 0.19 0.18 0.17 0.25 0.22 <![CDATA[Water vapor barrier × 10 14 g·cm / cm 2 ·s·Pa]]> 8.8 8.9 8.6 8.3 12.0 10.3 Based on the foregoing, Examples 1-3 performed best in all tests, with performance values ​​significantly exceeding the minimum requirements. This is attributed to the optimized prepolymer ratio and stepwise catalyst addition, which promoted molecular chain regularity and reaction efficiency, with the synergistic effect of prepolymers C and D enhancing barrier properties and flexibility.

[0033] Example 4 showed slightly lower performance than Example 1. Compared to the stepwise catalyst addition in Example 1, the one-time addition reduced reaction control and slightly weakened the molecular chain growth in the final polycondensation stage. This one-time catalyst addition resulted in a slightly wider molecular weight distribution, affecting crystallinity and barrier properties. Example 5, using a single catalyst, sodium germanate, showed a slight decrease in performance, but remained within the required range. This indicates that sodium germanate alone is insufficiently efficient, especially in the high molecular weight stage. Example 6, using a single catalyst, zinc acetylacetonate, showed a slight decrease in performance. Zinc acetylacetonate is effective for esterification but insufficiently supports the final polycondensation. The synergistic effect of the composite catalysts sodium germanate and zinc acetylacetonate in Examples 5 and 6 was lacking, leading to incomplete polycondensation and a slightly lower molecular weight.

[0034] Example 7 shows a slight decrease in melting point and thermal decomposition temperature, indicating a slight loss in molecular chain regularity and thermal stability. Mechanical properties (strength, modulus, elongation) and barrier properties are slightly worse than in Example 1, possibly due to the catalyst being added all at once, leading to an excessively rapid initial reaction and a wider molecular weight distribution. Stepwise addition of the catalyst is more beneficial for controlling the reaction process and maintaining molecular structural order. Example 8 shows slightly lower performance across all aspects compared to Example 1, especially with a significant decrease in thermal stability and barrier properties. This indicates that the sodium germanate / zinc acetylacetonate composite catalyst is superior to a single titanium catalyst in promoting copolymerization and improving molecular chain regularity and barrier properties. The composite catalyst system is more advantageous, and the substitution effect of tetrabutyl titanate is not ideal.

[0035] Example 9's performance is similar to but slightly worse than Example 1, especially with a slight decrease in barrier properties. Incomplete removal of small molecule byproducts under higher pressure may result in a slightly lower molecular weight or less dense chain segment arrangement. Lower pressure is more conducive to a complete polycondensation reaction, improving product performance. Example 10 shows an increased thermal decomposition temperature, indicating that higher temperatures help improve thermal stability. Mechanical properties and barrier properties are slightly better than Example 1, but the melting point is also slightly higher, possibly due to increased crystallinity promoted by higher temperatures. Appropriately increasing the polycondensation temperature can optimize performance, but care must be taken to avoid localized overheating leading to degradation.

[0036] Comparative Example 1 showed a breaking elongation of only 300% and a CO2 barrier property of 1.00 barrer. The absence of prepolymer C led to decreased flexibility, increased melting point, lower thermal decomposition temperature, and poorer barrier properties. The absence of prepolymer C in the lactic acid polymerization segment weakened the bio-based properties and equilibrium performance of the copolymer, proving that prepolymer C is indispensable for improving ductility and barrier properties. Comparative Example 2 showed a CO2 barrier property of 0.90 barrer and a tensile strength of 27.0 MPa. The absence of prepolymer D led to reduced barrier properties and mechanical strength. Furthermore, furanyl dicarboxylic acid, as a highly efficient barrier agent, weakened the rigidity of the molecular chain and the barrier network, affecting O2 and CO2 barrier properties.

[0037] Finally, it should be noted that the applicant declares that while the above embodiments illustrate the product and detailed preparation method of the present invention, the present invention is not limited to the above-described product and detailed preparation method, that is, it does not mean that the present invention must rely on the above-described product and detailed preparation method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of excipients, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0038] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention. These simple modifications all fall within the protection scope of the present invention.

[0039] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0040] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for modifying PBAT by lactic acid copolymerization, characterized in that the steps include... include: (1) Terephthalic acid and 1,4-butanediol were mixed and then tetrabutyl titanate was added to carry out esterification reaction to obtain prepolymer A; (2) After mixing adipic acid and 1,4-butanediol, tetrabutyl titanate and triphenyl phosphite are added to carry out esterification reaction to obtain prepolymer B; (3) Prepolymer C was obtained by polycondensing L-lactic acid aqueous solution under stannous octoate. (4) After mixing 2,5-furandicarboxylic acid and 1,4-butanediol, tetrabutyl titanate was added to carry out an esterification reaction to obtain prepolymer D; (5) Prepolymer A, prepolymer B, prepolymer C and prepolymer D are mixed and polycondensed under the action of a composite catalyst to obtain lactic acid copolymerized modified PBAT.

2. The modification method for lactic acid copolymerized PBAT according to claim 1, characterized in that, In step (1), the esterification reaction temperature of prepolymer A is 230-240℃, the pressure is 40-60KPa, and the reaction time is 120-130min; in step (2), the esterification reaction temperature of prepolymer B is 180-200℃, the pressure is 40-60KPa, and the reaction time is 180-200min; in step (3), the polycondensation temperature of prepolymer C is 130-150℃, the pressure is 40-60KPa, and the reaction time is 120-130min; in step (4), the reaction temperature of prepolymer D is 210-230℃, the pressure is 40-60KPa, and the reaction time is 100-120min.

3. The modification method for lactic acid copolymerized PBAT according to claim 1, characterized in that, The step (5) of lactic acid copolymerization to modify PBAT polycondensation includes: pre-polycondensation at 205-210℃ and 2-3KPa for 80-90 min, followed by final polycondensation at 210-215℃ and 0.05-0.2KPa for 130-140 min, and finally thickening polycondensation at 215-225℃ and 0.01-0.015KPa for 100-110 min.

4. The modification method for lactic acid copolymerized PBAT according to claim 1, characterized in that, In step (1), the weight ratio of terephthalic acid, 1,4-butanediol and tetrabutyl titanate is 100:60-70:0.02-0.

04.

5. The modification method for lactic acid copolymerized PBAT according to claim 1, characterized in that, In step (2), the weight ratio of adipic acid, 1,4-butanediol, tetrabutyl titanate and triphenyl phosphite is 100:70-80:0.01-0.03:0.03-0.

06.

6. The modification method for lactic acid copolymerized PBAT according to claim 1, characterized in that, In step (3), the concentration of the L-lactic acid aqueous solution is 80-90 wt%, and the weight ratio of the L-lactic acid aqueous solution to stannous octoate is 100:0.04-0.

06.

7. The modification method for lactic acid copolymerized PBAT according to claim 1, characterized in that, In step (4), the weight ratio of 2,5-furandicarboxylic acid, 1,4-butanediol and tetrabutyl titanate is 100:55-65:0.01-0.

02.

8. The modification method for lactic acid copolymerized PBAT according to claim 1, characterized in that, The weight ratio of prepolymer A, prepolymer B, prepolymer C and prepolymer D in step (5) is 45-55:25-35:15-25:5-10.

9. The modification method for lactic acid copolymerized PBAT according to claim 3, characterized in that, In step (5), the total amount of the composite catalyst is 0.05-0.1 wt% of the total mass of prepolymer A, prepolymer B, prepolymer C and prepolymer D. The composite catalyst includes sodium germanate and zinc acetylacetonate in a weight ratio of 1:2.5-3. In step (5), 50-60% of the composite catalyst is added before prepolymerization and the remaining catalyst is added before final polymerization.

10. The modification method for lactic acid copolymerized PBAT according to claim 3, characterized in that, The lactic acid copolymerized modified PBAT has a melting point ≥132℃, a thermal decomposition temperature ≥330℃, a tensile strength ≥28MPa, an elastic modulus ≥120MPa, an elongation at break ≥380%, a CO2 barrier ≤0.8 barrer, an O2 barrier ≤0.20 barrer, and a water vapor barrier ≤9.0×10⁻⁶. - 14 g·cm / cm 2 ·s·Pa.