Bio-based controllable degradation copolyester and continuous polymerization process

Abstract

The invention discloses a bio-based controllable degradation copolyester and a continuous polymerization process. Belongs to the technical field of biodegradable high polymer material synthesis. According to the copolyester, a polybutylene terephthalate prepolymer, L-lactic acid and bio-based adipic acid are taken as core comonomers, hydroxyl-terminated functionalized polyethylene glycol is introduced as a degradation kinetics regulator, and a'prepolymerization-chain extension-post-treatment 'three-section continuous polymerization system is constructed; by regulating and controlling the molar ratio of monomers, the temperature gradient of polymerization, the dosage of a chain extender and parameters of a catalytic system, the degradation period of the copolyester is precisely regulated and controlled within 3-12 months, and meanwhile, the copolyester is endowed with excellent mechanical properties. According to the method, the technical bottlenecks that the existing PBAT-based copolyester is poor in degradation rate controllability, wide in molecular weight distribution of continuous polymerization process products and insufficient in production stability are solved, a green catalytic system and a continuous production mode are adopted, and the products can be widely applied to the fields of controllable degradation agricultural mulching films, food contact-grade packaging materials and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis technology, specifically relating to a bio-based controllable degradable copolyester and a continuous polymerization process. Background Technology

[0002] Polybutylene terephthalate (PBAT), as a typical biodegradable polyester material, has broad application prospects in packaging, agricultural mulch films, and other fields due to its excellent flexibility and processability. However, pure PBAT has inherent defects such as low precision in degradation rate control and poor matching between mechanical strength and toughness, which limits its promotion in high-end applications. Currently, the industry mainly optimizes PBAT performance by copolymerizing it with monomers such as lactic acid and adipic acid, but existing technologies still have many bottlenecks: First, existing copolymerization processes mostly adopt batch production modes, resulting in low production efficiency, poor batch stability of products, and wide molecular weight distribution; second, continuous polymerization processes cannot simultaneously ensure the uniformity of product molecular weight and controllable degradation, and cannot achieve precise adaptation of degradation cycles; third, catalytic systems are mostly homogeneous catalysts, resulting in high catalytic residues and difficulties in subsequent separation, which do not meet the requirements of green production; fourth, the introduction of degradation regulators can easily lead to a decrease in the mechanical properties of the product, making it difficult to achieve balanced performance optimization. Therefore, developing a PBAT-based copolyester preparation technology that combines green and efficient continuous polymerization characteristics, precise and controllable degradation performance, and excellent mechanical properties is in line with the current cutting-edge development needs of biodegradable polymer materials and has significant industrialization value.

[0003] In the prior art, Chinese patent CN2020106005930 discloses a method for preparing biodegradable copolyester, which uses an intermittent polymerization process. Although this can improve the flexibility of the product to a certain extent, it suffers from problems such as a narrow range of degradation rate control (only 5-8 months), low production efficiency, and large batch-to-batch fluctuations. Chinese patent CN2020104285034 discloses a process and apparatus for continuous production of biodegradable polyester, but it uses a homogeneous catalytic system, resulting in high catalytic residue and lacking design for controllable degradation. The degradation performance of the product is limited and cannot adapt to the needs of different application scenarios. In summary, the prior art has not yet solved the problem of synergistic optimization of "continuous production - precise degradation control - green catalysis - excellent mechanical properties". This invention proposes a solution to address the above-mentioned technological gaps. Summary of the Invention

[0004] Purpose of the invention: This invention aims to overcome the technical defects in existing PBAT-based copolyester preparation technologies, such as poor continuous production stability, low precision in degradation rate control, insufficient greenness of the catalytic system, and poor mechanical property uniformity. It provides a bio-based controllable degradation copolyester and continuous polymerization process. By constructing an integrated technology system of "bio-based raw materials - heterogeneous green catalysis - three-stage continuous polymerization - online feedback control", the invention achieves green and efficient preparation of copolyester and precise control of degradation performance, while ensuring that the product has excellent mechanical property matching.

[0005] Technical solution: The continuous polymerization process for bio-based controllable degradable copolyester described in this invention includes the following steps: Step 1: Raw material pretreatment. Bio-based PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol are vacuum dried separately. The drying temperature is 85-105℃, the vacuum degree is ≤-0.097MPa, the drying time is 2.5-4h, and the moisture content of the raw materials after drying is ≤50ppm. Step 2, continuous prepolymerization: The pretreated raw materials are continuously fed into the first-stage prepolymerization reactor according to the set molar ratio. High-purity nitrogen is introduced for inert protection. The reaction temperature is controlled at 165-185℃, the absolute pressure at 0.35-0.55MPa, the stirring speed at 65-105r / min, and the reaction is maintained at this temperature for 1.5-2.5h to prepare a prepolymer product with a number average molecular weight of 20000-30000 g / mol. Step 3, continuous chain extension: The prepolymer product is continuously fed into the second chain extension reactor, and the chain extender and heterogeneous composite catalyst are added sequentially. The reaction temperature is controlled at 205-225℃, the absolute pressure at 0.06-0.12MPa, the stirring speed at 80-120r / min, and the reaction is maintained at this temperature for 1-1.8h to prepare a chain extension product with a number average molecular weight of 60000-100000 g / mol. Step 4, continuous post-processing: The chain-extended product is continuously fed into the third-stage devolatilization reactor. A gradient temperature vacuum devolatilization mode is adopted, and an online molecular weight monitoring and feedback control system is introduced to control the devolatilization temperature at 225-245℃, the vacuum degree at ≤-0.099MPa, and the devolatilization time at 0.6-1.2h. After devolatilization, the product is obtained by melt filtration, metering extrusion, and underwater pelletizing to prepare the bio-based controllable degradable modified copolyester product.

[0006] Preferably, the molar ratio of PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol in step 1 is 1:0.35-0.85:0.12-0.32:0.06-0.22; the number average molecular weight of the hydroxyl-terminated functionalized polyethylene glycol is 1000-4000 g / mol, and the hydroxyl-terminated content is ≥98%.

[0007] Preferably, the chain extender in step 3 is a bio-based isocyanate compound selected from bio-based 4,4'-diphenylmethane diisocyanate (MDI) or bio-based hexamethylene diisocyanate (HDI), and the amount of chain extender is 0.6-2.2% of the mass of the prepolymer product; the chain extender is prepared by transesterification reaction of aliphatic diamine with dimethyl carbonate, and the bio-based content is ≥75%.

[0008] Preferably, the heterogeneous composite catalyst in step 3 is a supported titanium-zinc composite catalyst, with modified mesoporous SiO2 as the support, a mass ratio of tetrabutyl titanate to zinc powder of 3:1, and an active component loading of 5-10% of the support mass; the catalyst dosage is 0.015-0.055% of the total raw material mass; the supported titanium-zinc composite catalyst is prepared by the sol-gel method and has a specific surface area ≥200 m². 2 / g.

[0009] Preferably, in step 2, the nitrogen gas introduction rate is 0.6-1.6 L / min, the first prepolymerization reactor adopts a jacketed heating and internal coil cooling temperature control mode with a temperature control accuracy of ±1℃; the molecular weight distribution index of the prepolymer product is 1.5-1.8.

[0010] Preferably, the gradient temperature vacuum devolatilization mode in step 4 is as follows: first, hold at 225℃ for 25 minutes, then raise the temperature to 235℃ and hold for 25 minutes, and finally raise the temperature to 245℃ and hold for 30 minutes; the online molecular weight monitoring and feedback control system monitors the molecular weight of the product online through gel permeation chromatography, and automatically adjusts the temperature and vacuum parameters of the third stage reactor when the molecular weight deviates from the set range of ±5%.

[0011] The second aspect of the present invention provides a controllable degradable copolyester prepared by the above process, wherein the copolyester has a number-average molecular weight of 85,000-160,000 g / mol, a molecular weight distribution index of 1.8-2.3, a glass transition temperature of -32 to -18°C, and a melting temperature of 110-130°C; the copolyester has a crystallinity of 25-35% and a thermal decomposition temperature ≥320°C.

[0012] Preferably, under the natural soil degradation conditions specified in GB / T 19277.1-2011, the weight loss rate is 22-38% after 3 months of degradation, 55-70% after 6 months of degradation, and 88-98% after 12 months of degradation; under the test conditions specified in GB / T 1040.3-2006, the tensile strength is 30-38 MPa, and the elongation at break is 480-600%.

[0013] The third aspect of this invention discloses the application of the above-mentioned controllable degradable copolyester in controllable degradable agricultural mulch films, food contact grade packaging materials, or disposable biodegradable tableware.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: This invention uses bio-based PBAT prepolymer, L-lactic acid, and bio-based adipic acid as core comonomers, introduces hydroxyl-terminated functionalized polyethylene glycol as a degradation kinetic regulator, and employs a supported titanium-zinc heterogeneous composite catalyst to construct a three-stage continuous polymerization system of "prepolymerization-chain extension-post-treatment." An online molecular weight monitoring and feedback control system is integrated, and by precisely controlling the monomer molar ratio, reaction temperature / pressure / speed at each stage, chain extender dosage, and devolatilization gradient parameters, the degradation cycle of the copolyester is precisely controlled, and its mechanical properties are optimized. The core technological innovations of this invention are: first, the use of bio-based raw materials and a heterogeneous green catalytic system reduces catalytic residue and environmental impact, aligning with the forefront of green chemistry; second, the synergy between three-stage continuous polymerization and online feedback control ensures the uniformity of product molecular weight and production stability; and third, the precise introduction of hydroxyl-terminated functionalized polyethylene glycol enables wide-range precise control of the degradation cycle (3-12 months), while simultaneously improving the matching of product mechanical properties through synergistic effects with the comonomers. Attached Figure Description

[0015] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0016] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0017] The supported titanium-zinc composite catalysts used in each embodiment were prepared by the sol-gel method: modified mesoporous SiO2 support was added to an ethanol solution of tetrabutyl titanate and zinc powder, stirred and dispersed evenly, and then dried and calcined (500℃, 2h) to obtain the catalyst, with an active component loading of 8%; the bio-based MDI and HDI used were prepared by transesterification reaction of aliphatic diamines and dimethyl carbonate, with a bio-based content ≥75%; the product performance tests were performed according to GB / T 1040.3-2006 (mechanical properties), GB / T19277.1-2011 (degradation performance), and GB / T 21866.2-2008 (molecular weight and distribution).

[0018] Example 1: A continuous polymerization method for bio-based controlled degradable copolyester is as follows: Step 1, raw material pretreatment: PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol (number average molecular weight 1000 g / mol) were vacuum dried in a molar ratio of 1:0.35:0.12:0.06. The drying temperature was 85℃, the vacuum degree was -0.097MPa, and the drying time was 4h. The moisture content of the raw materials after drying was ≤45ppm. Step 2, continuous prepolymerization: The pretreated raw materials are continuously fed into the first-stage prepolymerization reactor, and high-purity nitrogen gas (purity 99.99%, rate 0.6 L / min) is introduced. The reaction temperature is controlled at 165℃, the absolute pressure at 0.35 MPa, the stirring speed at 65 r / min, and the reaction is maintained at this temperature for 2.5 h to obtain a prepolymer product with a number average molecular weight of 22000 g / mol and a molecular weight distribution index of 1.6. Step 3, continuous chain extension: The prepolymer product is continuously fed into the second chain extension reactor. 0.6% by mass of bio-based MDI is added as a chain extender, and 0.015% by mass of the total raw materials is added. The reaction temperature is controlled at 205℃, the absolute pressure at 0.06MPa, the stirring speed at 80r / min, and the reaction is maintained at this temperature for 1.8h to prepare a chain-extended product with a number average molecular weight of 75000 g / mol. Step 4, continuous post-processing: The chain-extended product is continuously fed into the third-stage devolatilization reactor, where a gradient temperature devolatilization process is used (225℃ for 25 min → 235℃ for 25 min → 245℃ for 30 min). The vacuum degree is -0.099 MPa. Devolatilization parameters are adjusted via feedback from an online molecular weight monitoring system. After devolatilization, the product undergoes melt filtration, metered extrusion, and underwater pelletizing to obtain a controllable degradable copolyester product. Product properties: Number average molecular weight 92000 g / mol, molecular weight distribution index 2.0, glass transition temperature -32℃, tensile strength 30 MPa, elongation at break 480%; weight loss rate after 3 months of natural soil degradation is 22%, and after 12 months, it is 88%.

[0019] Example 2: A continuous polymerization method for bio-based controlled degradable copolyester is as follows: Step 1, raw material pretreatment: PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol (number average molecular weight 2000 g / mol) were vacuum dried in a molar ratio of 1:0.45:0.16:0.09. The drying temperature was 88℃, the vacuum degree was -0.097MPa, and the drying time was 3.5h. After drying, the moisture content of the raw materials was ≤42ppm. Step 2, continuous prepolymerization: The pretreated raw materials are continuously fed into the first-stage prepolymerization reactor, and high-purity nitrogen gas (purity 99.99%, rate 0.9 L / min) is introduced. The reaction temperature is controlled at 170℃, the absolute pressure at 0.4 MPa, the stirring speed at 75 r / min, and the reaction is maintained at this temperature for 2.2 h to obtain a prepolymer product with a number average molecular weight of 25000 g / mol and a molecular weight distribution index of 1.7. Step 3, continuous chain extension: The prepolymer product is continuously fed into the second chain extension reactor, and 0.9% by mass of bio-based MDI is added as a chain extender. 0.025% by mass of the total raw materials is added with a supported titanium-zinc composite catalyst. The reaction temperature is controlled at 210℃, the absolute pressure at 0.07MPa, the stirring speed at 90r / min, and the reaction is maintained at this temperature for 1.6h to prepare a chain extension product with a number average molecular weight of 82000 g / mol. Step 4, Continuous Post-processing: The chain-extended product is continuously fed into the third-stage devolatilization reactor, where a gradient temperature devolatilization process is used (225℃ for 25 min → 235℃ for 25 min → 245℃ for 30 min). The vacuum degree is -0.099 MPa. Devolatilization parameters are adjusted based on feedback from an online molecular weight monitoring system. After devolatilization, the product undergoes melt filtration, metered extrusion, and underwater pelletizing to obtain a controllable degradable copolyester product. Product properties: Number-average molecular weight 105,000 g / mol, molecular weight distribution index 2.1, glass transition temperature -30℃, tensile strength 32 MPa, elongation at break 520%; weight loss rate after 3 months of natural soil degradation is 25%, and after 12 months, it is 90%.

[0020] Example 3: A continuous polymerization method for bio-based controlled degradable copolyester is as follows: Step 1, Raw material pretreatment: PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol (number average molecular weight 3000 g / mol) were vacuum dried in a molar ratio of 1:0.55:0.2:0.12. The drying temperature was 92℃, the vacuum degree was -0.098MPa, and the drying time was 3h. The moisture content of the raw materials after drying was ≤40ppm. Step 2, continuous prepolymerization: The pretreated raw materials are continuously fed into the first-stage prepolymerization reactor, and high-purity nitrogen gas (purity 99.99%, rate 1.1L / min) is introduced. The reaction temperature is controlled at 175℃, the absolute pressure at 0.45MPa, the stirring speed at 85r / min, and the reaction is maintained at this temperature for 2h to obtain a prepolymer product with a number average molecular weight of 28000 g / mol and a molecular weight distribution index of 1.65. Step 3, continuous chain extension: The prepolymer product is continuously fed into the second chain extension reactor, and 1.3% of the prepolymer product mass of bio-based HDI is added as a chain extender. 0.035% of the total mass of the raw materials of the supported titanium-zinc composite catalyst is added. The reaction temperature is controlled at 215℃, the absolute pressure is 0.08MPa, the stirring speed is 100r / min, and the reaction is kept at this temperature for 1.4h to prepare a chain extension product with a number average molecular weight of 90000 g / mol. Step 4, Continuous Post-processing: The chain-extended product is continuously fed into the third-stage devolatilization reactor, where a gradient temperature devolatilization process is used (225℃ for 25 min → 235℃ for 25 min → 245℃ for 30 min). The vacuum degree is -0.099 MPa. Devolatilization parameters are adjusted based on feedback from an online molecular weight monitoring system. After devolatilization, the product undergoes melt filtration, metered extrusion, and underwater pelletizing to obtain a controllable degradable copolyester product. Product properties: Number-average molecular weight 125,000 g / mol, molecular weight distribution index 2.2, glass transition temperature -25℃, tensile strength 35 MPa, elongation at break 550%; weight loss rate after 3 months of natural soil degradation is 30%, and after 12 months, it is 93%.

[0021] Example 4: A continuous polymerization method for bio-based controlled degradable copolyester is as follows: Step 1, Raw material pretreatment: PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol (number average molecular weight 3000 g / mol) were vacuum dried in a molar ratio of 1:0.55:0.18:0.14. The drying temperature was 92℃, the vacuum degree was -0.098MPa, and the drying time was 3h. The moisture content of the raw materials after drying was ≤38ppm. Step 2, continuous prepolymerization: The pretreated raw materials are continuously fed into the first-stage prepolymerization reactor, and high-purity nitrogen gas (purity 99.99%, rate 1.3L / min) is introduced. The reaction temperature is controlled at 178℃, the absolute pressure at 0.46MPa, the stirring speed at 88r / min, and the reaction is kept at this temperature for 1.8h to prepare a prepolymer product with a number average molecular weight of 29000 g / mol and a molecular weight distribution index of 1.6. Step 3, continuous chain extension: The prepolymer product is continuously fed into the second chain extension reactor, and 1.1% by mass of bio-based MDI is added as a chain extender. 0.035% by mass of the total raw materials is added, and the reaction temperature is controlled at 218℃, the absolute pressure at 0.09MPa, the stirring speed at 105r / min, and the reaction is kept at this temperature for 1.3h to prepare a chain extension product with a number average molecular weight of 95000 g / mol. Step 4, Continuous Post-processing: The chain-extended product is continuously fed into the third-stage devolatilization reactor, where a gradient temperature devolatilization process is used (225℃ for 25 min → 235℃ for 25 min → 245℃ for 30 min). The vacuum degree is -0.099 MPa. Devolatilization parameters are adjusted based on feedback from an online molecular weight monitoring system. After devolatilization, the product undergoes melt filtration, metered extrusion, and underwater pelletizing to obtain a controllable degradable copolyester product. Product properties: Number-average molecular weight 132,000 g / mol, molecular weight distribution index 2.2, glass transition temperature -24℃, tensile strength 36 MPa, elongation at break 560%; weight loss rate after 3 months of natural soil degradation is 32%, and after 12 months, it is 94%.

[0022] Example 5: A continuous polymerization method for bio-based controlled degradable copolyester is as follows: Step 1, Raw material pretreatment: PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol (number average molecular weight 4000 g / mol) were vacuum dried in a molar ratio of 1:0.65:0.23:0.16. The drying temperature was 96℃, the vacuum degree was -0.098MPa, and the drying time was 2.5h. The moisture content of the raw materials after drying was ≤35ppm. Step 2, continuous prepolymerization: The pretreated raw materials are continuously fed into the first-stage prepolymerization reactor, and high-purity nitrogen gas (purity 99.99%, rate 1.4 L / min) is introduced. The reaction temperature is controlled at 180℃, the absolute pressure at 0.48 MPa, the stirring speed at 95 r / min, and the reaction is kept at this temperature for 1.6 h to prepare a prepolymer product with a number average molecular weight of 30000 g / mol and a molecular weight distribution index of 1.7. Step 3, continuous chain extension: The prepolymer product is continuously fed into the second chain extension reactor, and 1.6% of the prepolymer product mass of bio-based HDI is added as a chain extender. 0.045% of the total mass of the raw materials of the supported titanium-zinc composite catalyst is added. The reaction temperature is controlled at 220℃, the absolute pressure is 0.1MPa, the stirring speed is 110r / min, and the reaction is kept at this temperature for 1.2h to prepare a chain extension product with a number average molecular weight of 100,000 g / mol. Step 4, Continuous Post-processing: The chain-extended product is continuously fed into the third-stage devolatilization reactor, where a gradient temperature devolatilization process is used (225℃ for 25 min → 235℃ for 25 min → 245℃ for 30 min). The vacuum degree is -0.099 MPa. Devolatilization parameters are adjusted based on feedback from an online molecular weight monitoring system. After devolatilization, the product undergoes melt filtration, metered extrusion, and underwater pelletizing to obtain a controllable degradable copolyester product. Product properties: Number-average molecular weight 145,000 g / mol, molecular weight distribution index 2.3, glass transition temperature -22℃, tensile strength 37 MPa, elongation at break 580%; weight loss rate after 3 months of natural soil degradation is 35%, and after 12 months, it is 96%.

[0023] Example 6: A continuous polymerization method for bio-based controlled degradable copolyester is as follows: Step 1, Raw material pretreatment: PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol (number average molecular weight 4000 g / mol) were vacuum dried in a molar ratio of 1:0.65:0.26:0.18. The drying temperature was 96℃, the vacuum degree was -0.099MPa, and the drying time was 2.5h. The moisture content of the raw materials after drying was ≤32ppm. Step 2, continuous prepolymerization: The pretreated raw materials are continuously fed into the first-stage prepolymerization reactor, and high-purity nitrogen gas (purity 99.99%, rate 1.5L / min) is introduced. The reaction temperature is controlled at 182℃, the absolute pressure at 0.49MPa, the stirring speed at 98r / min, and the reaction is maintained at this temperature for 1.5h to obtain a prepolymer product with a number average molecular weight of 30000 g / mol and a molecular weight distribution index of 1.68. Step 3, continuous chain extension: The prepolymer product is continuously fed into the second chain extension reactor, and 1.7% by mass of bio-based MDI is added as a chain extender. 0.045% by mass of the total raw materials is added, and the reaction temperature is controlled at 222℃, the absolute pressure is 0.10MPa, the stirring speed is 115r / min, and the reaction is kept at this temperature for 1.1h to prepare a chain extension product with a number average molecular weight of 105000 g / mol. Step 4, Continuous Post-processing: The chain-extended product is continuously fed into the third-stage devolatilization reactor, where a gradient temperature devolatilization process is used (225℃ for 25 min → 235℃ for 25 min → 245℃ for 30 min). The vacuum degree is -0.099 MPa. Devolatilization parameters are adjusted based on feedback from an online molecular weight monitoring system. After devolatilization, the product undergoes melt filtration, metered extrusion, and underwater pelletizing to obtain a controllable degradable copolyester product. Product properties: Number-average molecular weight 150,000 g / mol, molecular weight distribution index 2.3, glass transition temperature -21℃, tensile strength 38 MPa, elongation at break 590%; weight loss rate after 3 months of natural soil degradation is 36%, and after 12 months, it is 97%.

[0024] Example 7: A continuous polymerization method for bio-based controlled degradable copolyester is as follows: Step 1, Raw material pretreatment: PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol (number average molecular weight 4000 g / mol) were vacuum dried in a molar ratio of 1:0.75:0.29:0.20. The drying temperature was 99℃, the vacuum degree was -0.099MPa, and the drying time was 2.2h. The moisture content of the raw materials after drying was ≤30ppm. Step 2, continuous prepolymerization: The pretreated raw materials are continuously fed into the first-stage prepolymerization reactor, and high-purity nitrogen gas (purity 99.99%, rate 1.5L / min) is introduced. The reaction temperature is controlled at 184℃, the absolute pressure at 0.52MPa, the stirring speed at 98r / min, and the reaction is maintained at this temperature for 1.5h to obtain a prepolymer product with a number average molecular weight of 30000 g / mol and a molecular weight distribution index of 1.65. Step 3, continuous chain extension: The prepolymer product is continuously fed into the second chain extension reactor, and 1.9% of the prepolymer product mass of bio-based HDI is added as a chain extender. 0.055% of the total mass of the raw materials of the supported titanium-zinc composite catalyst is added. The reaction temperature is controlled at 224℃, the absolute pressure is 0.11MPa, the stirring speed is 118r / min, and the reaction is kept at this temperature for 1.0h to prepare a chain extension product with a number average molecular weight of 110000 g / mol. Step 4, Continuous Post-processing: The chain-extended product is continuously fed into the third-stage devolatilization reactor, where a gradient temperature devolatilization process is used (225℃ for 25 min → 235℃ for 25 min → 245℃ for 30 min). The vacuum degree is -0.099 MPa. Devolatilization parameters are adjusted based on feedback from an online molecular weight monitoring system. After devolatilization, the product undergoes melt filtration, metered extrusion, and underwater pelletizing to obtain a controllable degradable copolyester product. Product properties: Number-average molecular weight 155,000 g / mol, molecular weight distribution index 2.3, glass transition temperature -20℃, tensile strength 38 MPa, elongation at break 600%; weight loss rate after 3 months of natural soil degradation is 37%, and after 12 months, it is 97%.

[0025] Example 8: A continuous polymerization method for bio-based controlled degradable copolyester is as follows: Step 1, Raw material pretreatment: PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol (number average molecular weight 3000 g / mol) were vacuum dried in a molar ratio of 1:0.75:0.27:0.19. The drying temperature was 97℃, the vacuum degree was -0.098MPa, and the drying time was 2.3h. The moisture content of the raw materials after drying was ≤31ppm. Step 2, continuous prepolymerization: The pretreated raw materials are continuously fed into the first-stage prepolymerization reactor, and high-purity nitrogen gas (purity 99.99%, rate 1.4 L / min) is introduced. The reaction temperature is controlled at 183℃, the absolute pressure at 0.51 MPa, the stirring speed at 95 r / min, and the reaction is maintained at this temperature for 1.5 h to obtain a prepolymer product with a number average molecular weight of 29000 g / mol and a molecular weight distribution index of 1.62. Step 3, continuous chain extension: The prepolymer product is continuously fed into the second chain extension reactor, and 1.8% of the prepolymer product mass of bio-based HDI is added as a chain extender. 0.05% of the total mass of the raw materials of supported titanium-zinc composite catalyst is added. The reaction temperature is controlled at 223℃, the absolute pressure is 0.10MPa, the stirring speed is 115r / min, and the reaction is kept at this temperature for 1.0h to prepare a chain extension product with a number average molecular weight of 108000 g / mol. Step 4, Continuous Post-processing: The chain-extended product is continuously fed into the third-stage devolatilization reactor, where a gradient temperature devolatilization process is used (225℃ for 25 min → 235℃ for 25 min → 245℃ for 30 min). The vacuum degree is -0.099 MPa. Devolatilization parameters are adjusted based on feedback from an online molecular weight monitoring system. After devolatilization, the product undergoes melt filtration, metered extrusion, and underwater pelletizing to obtain a controllable degradable copolyester product. Product properties: Number-average molecular weight 152,000 g / mol, molecular weight distribution index 2.2, glass transition temperature -21℃, tensile strength 37 MPa, elongation at break 590%; weight loss rate after 3 months of natural soil degradation is 36%, and after 12 months, it is 96%.

[0026] Example 9: A continuous polymerization method for bio-based controlled degradable copolyester is as follows: Step 1, Raw material pretreatment: PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol (number average molecular weight 4000 g / mol) were vacuum dried in a molar ratio of 1:0.85:0.32:0.22. The drying temperature was 105℃, the vacuum degree was -0.099MPa, and the drying time was 2h. The moisture content of the raw materials after drying was ≤28ppm. Step 2, continuous prepolymerization: The pretreated raw materials are continuously fed into the first-stage prepolymerization reactor, and high-purity nitrogen gas (purity 99.99%, rate 1.6 L / min) is introduced. The reaction temperature is controlled at 185℃, the absolute pressure at 0.55 MPa, the stirring speed at 105 r / min, and the reaction is maintained at this temperature for 1.5 h to prepare a prepolymer product with a number average molecular weight of 30000 g / mol and a molecular weight distribution index of 1.7. Step 3, continuous chain extension: The prepolymer product is continuously fed into the second chain extension reactor, and 2.2% by mass of bio-based MDI is added as a chain extender. 0.055% by mass of the total raw materials is added to the supported titanium-zinc composite catalyst. The reaction temperature is controlled at 225℃, the absolute pressure at 0.12MPa, the stirring speed at 120r / min, and the reaction is kept at this temperature for 1h to prepare a chain extension product with a number average molecular weight of 110000 g / mol. Step 4, Continuous Post-processing: The chain-extended product is continuously fed into the third-stage devolatilization reactor, where a gradient temperature devolatilization process is used (225℃ for 25 min → 235℃ for 25 min → 245℃ for 30 min). The vacuum degree is -0.099 MPa. Devolatilization parameters are adjusted based on feedback from an online molecular weight monitoring system. After devolatilization, the product undergoes melt filtration, metered extrusion, and underwater pelletizing to obtain a controllable degradable copolyester product. Product properties: Number-average molecular weight 160,000 g / mol, molecular weight distribution index 2.3, glass transition temperature -18℃, tensile strength 38 MPa, elongation at break 600%; weight loss rate after 3 months of natural soil degradation is 38%, and after 12 months, it is 98%.

[0027] This invention successfully solves the technical bottlenecks in existing PBAT-based copolyester preparation technologies by constructing an integrated technology system of "bio-based raw materials - heterogeneous green catalysis - three-stage continuous polymerization - online feedback control". This system addresses the issues of poor continuous production stability, low precision in degradation rate control, insufficient greenness of the catalytic system, and poor mechanical property uniformity.

[0028] The core innovations of this invention are: first, the use of a bio-based chain extender and a supported titanium-zinc heterogeneous composite catalytic system significantly reduces catalytic residue and enhances the greenness of the product, aligning with the current cutting-edge development direction of green chemistry; second, the integration of a three-stage continuous polymerization process with online molecular weight monitoring and feedback control ensures product molecular weight uniformity and production stability, improving industrial adaptability; and third, through the precise introduction of hydroxyl-terminated functionalized polyethylene glycol and the control of monomer ratios, a wide range of precise control over the degradation cycle of 3-12 months is achieved, adapting to the needs of different application scenarios. Nine embodiments, through systematic control of key conditions such as monomer ratios, reaction parameters, and catalyst dosage, verified the stability, controllability, and universality of the process of this invention. The prepared copolyester achieved synergistic optimization of degradation performance and mechanical properties, with product performance superior to existing similar products.

[0029] The process of this invention is simple and controllable, easy to scale up industrially, and the product can be widely used in fields such as controllable degradable agricultural mulch film and food contact packaging materials. It has significant industrial value and environmental benefits, and is in line with the cutting-edge development trend of biodegradable polymer materials.

Claims

1. A continuous polymerization process for a bio-based, controllable degradable copolyester, characterized in that, Includes the following steps: Step 1: Raw material pretreatment. Bio-based PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol are vacuum dried separately. The drying temperature is 85-105℃, the vacuum degree is ≤-0.097MPa, the drying time is 2.5-4h, and the moisture content of the raw materials after drying is ≤50ppm. Step 2, continuous prepolymerization: The pretreated raw materials are continuously fed into the first-stage prepolymerization reactor according to the set molar ratio. High-purity nitrogen is introduced for inert protection. The reaction temperature is controlled at 165-185℃, the absolute pressure at 0.35-0.55MPa, the stirring speed at 65-105r / min, and the reaction is maintained at this temperature for 1.5-2.5h to prepare a prepolymer product with a number average molecular weight of 20000-30000 g / mol. Step 3, continuous chain extension: The prepolymer product is continuously fed into the second chain extension reactor, and the chain extender and heterogeneous composite catalyst are added sequentially. The reaction temperature is controlled at 205-225℃, the absolute pressure at 0.06-0.12MPa, the stirring speed at 80-120r / min, and the reaction is maintained at this temperature for 1-1.8h to prepare a chain extension product with a number average molecular weight of 60000-100000 g / mol. Step 4, continuous post-processing: The chain-extended product is continuously fed into the third-stage devolatilization reactor. A gradient temperature vacuum devolatilization mode is adopted, and an online molecular weight monitoring and feedback control system is introduced to control the devolatilization temperature at 225-245℃, the vacuum degree at ≤-0.099MPa, and the devolatilization time at 0.6-1.2h. After devolatilization, the product is obtained by melt filtration, metering extrusion, and underwater pelletizing to prepare the bio-based controllable degradable modified copolyester product.

2. The process according to claim 1, characterized in that, In step 1, the molar ratio of PBAT prepolymer, L-lactic acid, bio-based adipic acid, and hydroxyl-terminated functionalized polyethylene glycol is 1:0.35-0.85:0.12-0.32:0.06-0.22; the number average molecular weight of the hydroxyl-terminated functionalized polyethylene glycol is 1000-4000 g / mol, and the hydroxyl-terminated content is ≥98%.

3. The process according to claim 1, characterized in that, The chain extender mentioned in step 3 is a bio-based isocyanate compound selected from bio-based 4,4'-diphenylmethane diisocyanate or bio-based hexamethylene diisocyanate. The amount of chain extender used is 0.6-2.2% of the mass of the prepolymer product. The chain extender is prepared by transesterification reaction of aliphatic diamine with dimethyl carbonate and has a bio-based content of ≥75%.

4. The process according to claim 1, characterized in that, The heterogeneous composite catalyst mentioned in step 3 is a supported titanium-zinc composite catalyst. The support is modified mesoporous SiO2, the mass ratio of the active component tetrabutyl titanate to zinc powder is 3:1, and the loading of the active component is 5-10% of the support mass. The catalyst dosage is 0.015-0.055% of the total raw material mass. The supported titanium-zinc composite catalyst is prepared by the sol-gel method and has a specific surface area ≥200 m². 2 / g.

5. The process according to claim 1, characterized in that, In step 2, the nitrogen gas introduction rate is 0.6-1.6 L / min. The first prepolymer reactor adopts a jacketed heating and internal coil cooling temperature control mode with a temperature control accuracy of ±1℃. The molecular weight distribution index of the prepolymer product is 1.5-1.

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6. The process according to claim 1, characterized in that, The gradient temperature vacuum devolatilization mode in step 4 is as follows: first, hold at 225℃ for 25 min, then raise the temperature to 235℃ and hold for 25 min, and finally raise the temperature to 245℃ and hold for 30 min; the online molecular weight monitoring and feedback control system monitors the molecular weight of the product online through gel permeation chromatography, and automatically adjusts the temperature and vacuum parameters of the third stage reactor when the molecular weight deviates from the set range of ±5%.

7. The controllable degradable copolyester prepared according to the process described in claim 1, characterized in that, The copolyester has a number-average molecular weight of 85,000-160,000 g / mol, a molecular weight distribution index of 1.8-2.3, a glass transition temperature of -32 to -18℃, and a melting temperature of 110-130℃; the copolyester has a crystallinity of 25-35% and a thermal decomposition temperature of ≥320℃.

8. The controllable degradable copolyester according to claim 7, characterized in that, Under the natural soil degradation conditions specified in GB / T 19277.1-2011, the weight loss rate is 22-38% after 3 months of degradation, 55-70% after 6 months of degradation, and 88-98% after 12 months of degradation; under the test conditions specified in GB / T 1040.3-2006, the tensile strength is 30-38 MPa and the elongation at break is 480-600%.

9. The application of the controllable degradable copolyester according to claim 7 in controllable degradable agricultural mulch films, food contact grade packaging materials or disposable biodegradable tableware.

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