A branched PBAT and a preparation method thereof

Abstract

The application provides branched PBAT and a preparation method thereof. The preparation method comprises the following steps: performing esterification reaction on terephthalic acid and butanediol, and then adding adipic acid to perform esterification reaction. The preparation method adds branched monomers with different functional groups such as ester groups, carboxyl groups and isomeric carbon chain structures, constructs branched chain structures on the main chain of PBAT through chemical reaction, can effectively improve the branching degree of PBAT, prevents the cross-linking of PBAT molecular chains, and the prepared branched PBAT has good mechanical properties.

Description

Technical Field

[0001] This invention relates to a branched PBAT and its preparation method, belonging to the field of polymer synthesis technology. Background Technology

[0002] Since its initial synthesis, polyethylene has seen increasingly superior performance and has been applied to various aspects of life thanks to in-depth research. However, with social development and the emergence of environmentally friendly concepts, polyethylene's non-biodegradability and subsequent environmental pollution have created a pressing need for a biodegradable material with comparable performance. Polybutylene terephthalate (PBAT) is a fully biodegradable aliphatic-aromatic copolyester. As a fully biodegradable material, it possesses excellent performance characteristics and rapid degradation, making it the most promising and likely environmentally friendly alternative to polyethylene. However, PBAT has significant drawbacks, such as inferior blow molding performance compared to linear low-density polyethylene (LDPE), and lower tensile strength and modulus in film applications, which limits its replacement of polyethylene films in fields such as agricultural mulch films and packaging bags. Studies have found that the molecular structure of polymer materials has a crucial impact on their performance. Modifying or reconstructing the molecular chain structure of PBAT can effectively control its performance. Therefore, in order to make PBAT meet the requirements, modifiers are used to reconstruct and modify the PBAT molecular chain. By connecting the modifiers to the main chain of the PBAT molecule through strong chemical bonds, the molecular chain of PBAT is functionalized, thereby achieving the purpose of regulating PBAT performance and endowing it with the necessary functions. Summary of the Invention

[0003] To address the aforementioned problems of poor blow molding processability and insufficient mechanical properties of PBAT films, the present invention aims to provide a branched PBAT and its preparation method. This preparation method can effectively improve the branching degree of PBAT, prevent cross-linking of PBAT molecular chains, and produce branched PBAT with good mechanical properties, while ensuring a more complete reaction.

[0004] To achieve the above objectives, the present invention provides a method for preparing branched PBAT, which includes the following steps: first, terephthalic acid and butanediol are subjected to an esterification reaction, and then adipic acid is added to carry out an esterification reaction.

[0005] According to a specific embodiment of the present invention, preferably, the above preparation method includes the following steps:

[0006] (1) First step esterification reaction: Terephthalic acid and butanediol are mixed, and after the catalyst is added for the first time, the first step esterification reaction is carried out at 200-240℃ (preferably 215℃) under a protective gas atmosphere;

[0007] (2) Second step esterification reaction: After the first step esterification reaction is completed, the temperature is lowered to below 140°C, adipic acid is added and the catalyst is added for the second time, and the second step esterification reaction is carried out at 160-190°C (preferably 185°C);

[0008] (3) Pre-condensation reaction: After the second esterification reaction is completed, the temperature is lowered to below 140°C, the catalyst is added for the third time, and the condensation reaction is carried out at 220-260°C and below 100 Pa. After the reaction is completed, the branched PBAT is obtained.

[0009] When the boiling point of the branching agent is ≥210℃, the branching agent is added in step (1); when the boiling point of the branching agent is ≤210℃, the branching agent is added in step (2).

[0010] The branching agent includes diester branching agents and / or dicarboxylic acid branching agents; more preferably, the diester branching agent includes one or more of diethyl n-butylmalonate, diethyl dibutylmalonate, dimethyl propylmalonate, dimethyl isobutyl-1,3-malonate, and diethyl diisobutylmalonate; the dicarboxylic acid branching agent includes one or more of butylmalonic acid, propylmalonic acid, propylglutaric acid, and isobutylmalonic acid.

[0011] According to a specific embodiment of the present invention, preferably, in step (1), the molar ratio of the titanium in the catalyst added for the first time to the sum of the molar amounts of the terephthalic acid and adipic acid is 1:10000-3:1000.

[0012] According to a specific embodiment of the present invention, preferably, in step (1), the molar ratio of terephthalic acid to butanediol is 45:100-45:150.

[0013] According to a specific embodiment of the present invention, preferably, the butanediol is 1,4-butanediol and / or 1,2-butanediol.

[0014] According to a specific embodiment of the present invention, preferably, the branching agent is one or a combination of two or more of butyl malonate, butyl malonate, and dimethyl isobutyl malonate.

[0015] According to a specific embodiment of the present invention, preferably, in step (2), the molar ratio of the titanium in the catalyst added for the second time to the sum of the molar amounts of the terephthalic acid and adipic acid is 1:10000-3:1000.

[0016] According to a specific embodiment of the present invention, preferably, in step (2), the molar ratio of adipic acid to terephthalic acid is 70:30-48:52.

[0017] According to a specific embodiment of the present invention, preferably, in step (3), the molar ratio of the titanium in the catalyst added for the third time to the sum of the molar amounts of the terephthalic acid and adipic acid is 1:10000-6:1000.

[0018] According to a specific embodiment of the present invention, preferably, the catalyst added in steps (1) to (3) is a polynuclear catalyst, more preferably including titanium-silicon-zinc polynuclear catalyst and / or titanium-silicon-aluminum polynuclear catalyst.

[0019] According to a specific embodiment of the present invention, preferably, the catalyst added in steps (1) to (3) is the titanium-silicon composite polynuclear catalyst described in invention patent application 202210966547.1.

[0020] This invention grafts branching agents with different structures or functions onto the main chain of PBAT through a chemical reaction, constructing the main chain branching points and functional sites of PBAT in a novel way by integrating the branching agents into the main chain. This results in the preparation of PBAT containing branches with different structural structures, thereby improving the performance of PBAT by controlling its molecular structure. The branching agents used in this invention are preferably diester branching agents and / or dicarboxylic acid branching agents; more preferably, the diester branching agents include one or more combinations of diethyl n-butylmalonate, diethyl dibutylmalonate, dimethyl propylmalonate, dimethyl isobutyl-1,3-malonate, and diisobutylmalonate; the dicarboxylic acid branching agents include one or more combinations of butylmalonic acid, propylmalonic acid, propylglutaric acid, and isobutylmalonic acid. Among them, dimethyl isobutyl-1,3-malonic acid is a branching agent with a boiling point below 215℃, while the other listed branching agents are branching agents with a boiling point above 215℃.

[0021] According to a specific embodiment of the present invention, preferably, the molar ratio of the branching agent to the sum of the molar amounts of terephthalic acid and adipic acid is 1:100 to 10:100.

[0022] According to a specific embodiment of the present invention, the above preparation method includes the following specific steps:

[0023] (1) Weighing and mixing of samples: Weigh terephthalic acid and butanediol in a certain proportion and add them to a three-necked flask. Add a certain proportion of branching agent and catalyst. If the boiling point of the branching agent is ≤210℃, the branching agent is not added in this step. Place the three-necked flask in an oil bath preheated to 50℃. If the boiling point of the branching agent is low, the high temperature will cause the catalyst to vaporize and be lost when the branching agent is added in this step.

[0024] (2) First step of esterification reaction: Nitrogen gas is continuously introduced into the three-necked flask in step (1), the stirring device is turned on, and after setting a suitable stirring rate, the temperature is quickly raised to 190℃ and the esterification reaction is carried out at 190℃ for 20 min. The temperature of the oil bath is gradually increased from 190℃ to between 200-240℃ (e.g., 215℃) until the first step of esterification reaction is completed (gradually increasing to between 200-240℃ means: increasing the temperature at a rate of 5-20℃ / 30min-60min, and holding it at the set temperature of 190℃ for more than 20 min, and then increasing the temperature to between 200-240℃, and maintaining it within the temperature range of 200-240℃ until the first step of esterification reaction is completed. When the predetermined amount of water produced is reached, it indicates that the first step of esterification reaction is completed); the molar ratio range of the branching agent to the carboxylic acid is M 支化剂 M 羧酸 = 1:100-10:100, the molar ratio of catalyst to carboxylic acid ranges from M. 催化剂 M 羧酸 =1:10000-3:1000, the molar ratio of terephthalic acid to butanediol ranges from M. 对苯二甲酸 M 丁二醇 =45:100-45:150, where M 羧酸 The molar amounts of terephthalic acid and adipic acid are combined. Preferably adding terephthalic acid ensures a complete reaction and a clear, transparent solution. Excessive branching agent content significantly reduces melt strength; excessive catalyst content leads to severe coloration in the melt, while insufficient content significantly prolongs esterification and polycondensation times, failing to improve material performance. Excessive terephthalic acid content negatively impacts degradation performance. Taking the sum of the molar amounts of terephthalic acid and adipic acid as 100%, when the terephthalic acid content is below 30%, the crystal structure of PBAT changes from PBT to PBA. In this case, BT acts as a defect, hindering the integrity of the BT crystal, thus reducing the crystallization rate and crystallinity of PBAT, resulting in a decrease in mechanical properties and a melting point below 50°C, severely impacting safety. Therefore, by mixing using the molar ratio of the present invention, the resulting branched PBAT can be guaranteed to have excellent mechanical properties; in addition, gradually increasing the temperature can effectively suppress the occurrence of side reactions and the loss of reacting components.

[0025] (3) Second step esterification reaction: After the first step esterification is completed, the temperature of the oil bath is lowered to below 140℃, the catalyst is added to the three-necked flask for the second time, and a certain proportion of adipic acid is added (if the boiling point of the branching agent is ≤210℃, the branching agent is added in this step). Then the temperature of the oil bath is raised to a certain temperature (the reaction temperature is controlled below the boiling point of the added branching agent) until the second step esterification reaction is completed. Lowering the temperature to below 140℃ can effectively prevent the hydrolysis of the catalyst and the loss of catalyst efficiency caused by the catalyst being carried away by nitrogen after atomization.

[0026] (4) Pre-condensation reaction: After the second esterification reaction is completed, the temperature is lowered to below 140°C again, the catalyst is added to the three-necked flask for the third time, and the pressure inside the three-necked flask is reduced to below 100 Pa. Then, the temperature of the oil bath is raised to between 220-260°C to carry out the condensation reaction until the condensation reaction is completed.

[0027] The present invention also provides branched PBAT prepared by the above preparation method.

[0028] According to a specific embodiment of the present invention, preferably, the branching degree of the branched PBAT is 1%-10% (mole percentage), more preferably 2%-6%.

[0029] According to a specific embodiment of the present invention, preferably, the branch length of the branched PBAT is 2-10 carbon atoms, more preferably 2-6 carbon atoms.

[0030] The preparation method of this invention involves using branching monomers with different functional groups as branching agents to modify the straight chain of PBAT during its synthesis. This novel approach constructs branching points on the main chain of PBAT, resulting in PBAT with varying degrees of branching. This effectively increases the branching degree of PBAT and prevents cross-linking of the PBAT molecular chain, thereby improving PBAT performance by controlling its molecular chain structure. This invention offers the following advantages:

[0031] (1) The branched PBAT prepared by the branching agents with different functional group structures described in this invention can effectively improve the processing performance of PBAT through the effect of the branched chains in the PBAT molecular structure.

[0032] (2) The branched PBAT prepared by the branching agents with different branched structures described in this invention has different effects on improving the performance of PBAT due to the different branched structure of the branching agents. Based on the different improvement effects, the molecular structure of PBAT can be designed for different applications.

[0033] (3) In the preparation method of the present invention, the first step of the esterification reaction is to first react terephthalic acid with butanediol, and then add adipic acid to carry out the second step of the reaction, which can effectively improve the reaction degree of terephthalic acid. Attached Figure Description

[0034] Figure 1 This is a flowchart of the PBAT synthesis process of the present invention;

[0035] Figure 2 This is a diagram of the new PBAT structure constructed after modifying the PBAT backbone with the branching agent used in Example 1;

[0036] Figure 3 This is a comparison chart of the tensile properties of branched PBAT and pure PBAT (unbranched) in Example 1.

[0037] Figure 4 The intrinsic viscosity and melt flow index of branched PBAT and unbranched PBAT under the same conditions are shown in the graphs of Examples 1-3.

[0038] Figure 5 The following are DSC diagrams of branched and unbranched PBAT in Example 1. Figure 5 In the figure, 'a' represents the crystallization curve. Figure 5 In the figure, b represents the melt flow curve;

[0039] Figure 6 This is the melt curve when the terephthalic acid content is 20%. Detailed Implementation

[0040] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0041] The catalysts used in the following examples and comparative examples are all from the titanium-based composite polynuclear catalyst described in patent application 202210966547.1. Specifically, the titanium-silicon-zinc polynuclear catalyst is the product of Example 2 in patent application 202210966547.1, and the titanium-silicon-aluminum polynuclear catalyst is the product of Example 9 in patent application 202210966547.1. The catalyst is prepared as follows: First, titanate ester, co-catalyst, and ligand one are added to a diol and mixed until homogeneous to form solution A; then, an organosilicon source is mixed with ethanol and acidic deionized water to pre-hydrolyze the organosilicon source to form solution B; subsequently, solution B is slowly added dropwise to solution A, and then the low-boiling-point components are removed from the reaction system to obtain solution C; finally, ligand two is added dropwise to solution C and stirred until homogeneous to obtain the liquid titanium-silicon composite polynuclear catalyst; the molar ratio of ligand two to Ti atoms in solution C is (0-3):1. The cocatalyst is selected from at least one of triisopropyl aluminate, aluminum acetylacetonate, tribenzyl aluminate, zinc acetylacetonate, magnesium acetylacetonate, and neodymium acetylacetonate; the ligand one and ligand two are independently selected from at least one of acetylacetonate, 2,2'-bipyridine, acetic acid, L-lactic acid, D-lactic acid, and tartaric acid.

[0042] The preparation method of the titanium-silicon-zinc polynuclear catalyst used below includes the following steps:

[0043] (1) Add 0.05 mol of tetrabutyl titanate, 0.005 mol of zinc acetylacetone and 0.1 mol of L-lactic acid dropwise into 1 mol of 1,4-butanediol and stir thoroughly until homogeneous solution A is formed;

[0044] (2) Mix 0.02 mol of tetraethyl silicate, 0.15 mol of ethanol, and 0.08 mol of acidic deionized water evenly and stir at room temperature for 12 h to form solution B;

[0045] (3) Slowly add solution B to solution A and stir quickly until homogeneous. Then, react the resulting solution at 80°C for 3 hours under a pressure range of 150 Pa to remove low-boiling-point components and obtain solution C.

[0046] (4) Add 0.1 mol of acetylacetone to solution C and stir quickly until homogeneous to obtain liquid titanium-silicon composite multinuclear catalyst with a titanium element mass fraction of 2.12 wt%.

[0047] The preparation method of the titanium-silicon-aluminum polynuclear catalyst used below includes the following steps:

[0048] (1) Add 0.05 mol of isopropyl titanate, 0.005 mol of aluminum acetylacetonate and 0.05 mol of D-lactic acid to 1 mol of 1,4-butanediol and stir thoroughly until homogeneous solution A is formed;

[0049] (2) Mix 0.01 mol of tetraethyl silicate, 0.07 mol of ethanol, and 0.04 mol of deionized water evenly and stir at room temperature for 12 h to form solution B;

[0050] (3) Slowly add solution B to solution A and stir quickly until homogeneous. Then, react the resulting solution at 80°C for 3 hours under a pressure range of 120 Pa to remove low-boiling-point components and obtain solution C.

[0051] (4) Add 0.12 mol of acetylacetone and 0.005 mol of tartaric acid to solution C and stir quickly until homogeneous to obtain liquid titanium-silicon composite multinuclear catalyst with a titanium element mass fraction of 2.08 wt%.

[0052] Example 1

[0053] This embodiment provides a branched PBAT, the preparation method of which includes the following steps, the process of which is as follows: Figure 1 As shown:

[0054] (1) Sample weighing and mixing: Weigh 17.93g of terephthalic acid and 27g of 1,4-butanediol and add them to a three-necked flask. Add 2.16g of diethyl butyl malonate branching agent and 30μL of titanium silicon zinc polynuclear catalyst. Then place the three-necked flask in an oil bath preheated to 50℃.

[0055] (2) First step of esterification reaction: Nitrogen gas is continuously introduced into the three-necked flask in step (1), the stirring device is turned on, the stirring speed is set to 260 r / min, the oil bath is heated to 190℃ and kept at 20 min, and then the oil bath temperature is gradually increased to 215℃ at a rate of 10℃ every 20 min. Esterification is carried out at 215℃ for 60 min. After the water output reaches the predetermined value, the first step of esterification reaction is completed.

[0056] (3) Second step esterification reaction: After the first step esterification is completed, the temperature of the oil bath is lowered to below 140℃, 20μL of titanium silicon zinc polynuclear catalyst is added to the three-necked flask for the second time, and 19.27g of adipic acid is added. The temperature of the bath is then raised to 185℃ and esterified for 120min. The amount of water output reaches the predetermined value, and the second step esterification reaction is completed.

[0057] (4) Low-compression polycondensation reaction: After the second esterification reaction is completed, the temperature is lowered to below 140℃ again, and 35μL of titanium silicon zinc polynuclear catalyst is added to the three-necked flask for the third time. The pressure inside the three-necked flask is pumped to below 100pa, and the oil bath temperature is raised to 230℃ for polycondensation reaction for 1.5h to obtain branched PBAT.

[0058] (5) Finally, the obtained PBAT was removed from the three-necked flask and dried to obtain branched PBAT, with the structure shown in the figure. Figure 2 As shown.

[0059] Example 2

[0060] This embodiment provides a branched PBAT, the preparation method of which includes the following steps:

[0061] (1) Weighing and mixing of samples: Weigh 17.93g of terephthalic acid and 27g of 1,4-butanediol and add them to a three-necked flask. Add 1.6g of butylmalonic acid branching agent and 30μL of titanium silicon zinc polynuclear catalyst. Then place the three-necked flask in an oil bath preheated to 50°C.

[0062] (2) First step of esterification reaction: Nitrogen gas is continuously introduced into the three-necked flask in step (1), the stirring device is turned on, the stirring speed is set to 260 r / min, the oil bath is heated to 190℃ and kept at 20 min, and then the oil bath temperature is gradually increased to 215℃ at a rate of 15℃ every 20 min. Esterification is carried out at 215℃ for 60 min. After the water output reaches the predetermined value, the first step of esterification reaction is completed.

[0063] (3) Second step esterification reaction: After the first step esterification is completed, the temperature of the oil bath is lowered to below 140℃, 20μL of titanium silicon zinc polynuclear catalyst is added to the three-necked flask for the second time, and 19.27g of adipic acid is added. The temperature of the bath is then raised to 185℃ and esterified for 120min. The amount of water output reaches the predetermined value, and the second step esterification reaction is completed.

[0064] (4) Low-compression polycondensation reaction: After the second esterification reaction is completed, the temperature is lowered to below 140℃ again, and 30μL of titanium silicon zinc polynuclear catalyst is added to the three-necked flask for the third time. The pressure inside the three-necked flask is pumped to below 100pa, and the oil bath temperature is raised to 230℃ for polycondensation reaction for 1.5h to obtain branched PBAT.

[0065] (5) Finally, the obtained PBAT is removed from the three-necked flask and dried to obtain branched PBAT.

[0066] Example 3

[0067] This embodiment provides a branched PBAT, the preparation method of which includes the following steps:

[0068] (1) Weighing and mixing of samples: Weigh 17.93g of terephthalic acid and 27g of 1,4-butanediol and add them to a three-necked flask. Add 30μL of titanium-silicon-aluminum polynuclear catalyst and place the three-necked flask in an oil bath preheated to 50°C.

[0069] (2) First step of esterification reaction: Nitrogen gas is continuously introduced into the three-necked flask in step (1), the stirring device is turned on, the stirring speed is set to 260 r / min, the oil bath is heated to 190℃ and kept at 20 min, and then the oil bath temperature is gradually increased to 215℃ at a rate of 20℃ every 30 min. Esterification is carried out at 215℃ for 60 min. After the water output reaches the predetermined value, the first step of esterification reaction is completed.

[0070] (3) Second step esterification reaction: After the first step esterification is completed, the oil bath temperature is lowered to below 140℃, 20μL of titanium-silicon-aluminum polynuclear catalyst is added to the three-necked flask for the second time, and 1.88g of dimethyl isobutyl malonate and 19.27g of adipic acid are added. Then the bath temperature is raised to 185℃ and esterification is carried out for 120min. The amount of water output reaches the predetermined value, and the second step esterification reaction is completed.

[0071] (4) Low-compression polycondensation reaction: After the second esterification reaction is completed, the temperature is lowered to below 140℃ again, and 40μL of titanium-silicon-aluminum polynuclear catalyst is added to the three-necked flask for the third time. The pressure inside the three-necked flask is pumped to below 100pa, and the oil bath temperature is raised to 230℃ for polycondensation reaction for 1.5h to obtain branched PBAT.

[0072] (5) Finally, the obtained PBAT is removed from the three-necked flask and dried to obtain branched PBAT.

[0073] Comparative Example 1

[0074] This comparative example provides a branched PBAT, the preparation method of which includes the following steps:

[0075] (1) Weighing and mixing of samples: Weigh 19.27g adipic acid and 27g 1,4-butanediol and add them to a three-necked flask. Add 50μL of titanium-silicon-zinc polynuclear catalyst, 1.88g of dimethyl isobutyl malonate and 17.93g of terephthalic acid. Then place the three-necked flask in an oil bath preheated to 50℃.

[0076] (2) Esterification reaction: Nitrogen gas was continuously introduced into the three-necked flask in step (1), the stirring device was turned on, the stirring speed was set to 260 r / min, the oil bath was heated to 170℃ and kept at that temperature for 20 min, and then the oil bath temperature was gradually increased to 215℃ at a rate of 5℃ every 20 min. The esterification reaction was carried out at 215℃ for 8 hours, and no clear and transparent melt was obtained.

[0077] (3) Low-compression polycondensation reaction: After the esterification reaction is completed, the temperature is lowered to below 140℃ again, and 40μL of titanium silicon zinc polynuclear catalyst is added to the three-necked flask for the third time. The pressure inside the three-necked flask is pumped to below 100pa, and the oil bath temperature is raised to 230℃ for polycondensation reaction for 2h to obtain branched PBAT.

[0078] (4) Finally, the obtained PBAT is removed from the three-necked flask and dried to obtain branched PBAT.

[0079] Comparative Example 2

[0080] This comparative example provides an unbranched PBAT, the preparation method of which includes the following steps:

[0081] (1) Weighing and mixing of samples: Weigh 17.93g of terephthalic acid and 27g of 1,4-butanediol and add them to a three-necked flask. Add 30μL of titanium-silicon-zinc polynuclear catalyst and place the three-necked flask in an oil bath preheated to 50°C.

[0082] (2) First step of esterification reaction: Nitrogen gas is continuously introduced into the three-necked flask in step (1), the stirring device is turned on, the stirring speed is set to 250 r / min, the oil bath is heated to 190℃ and kept at 20 min, and then the oil bath temperature is gradually increased to 215℃ at a rate of 20℃ every 30 min. Esterification is carried out at 215℃ for 60 min. After the water output reaches the predetermined value, the first step of esterification reaction is completed.

[0083] (3) Second step esterification reaction: After the first step esterification is completed, the temperature of the oil bath is lowered to below 140℃, 20μL of titanium silicon zinc polynuclear catalyst is added to the three-necked flask for the second time, and 19.27g of adipic acid is added. The temperature of the bath is then raised to 185℃ and esterified for 120min. The amount of water output reaches the predetermined value, and the second step esterification reaction is completed.

[0084] (4) Low-compression polycondensation reaction: After the second esterification reaction is completed, the temperature is lowered to below 140℃ again, and 36μL of titanium silicon zinc polynuclear catalyst is added to the three-necked flask for the third time. The pressure inside the three-necked flask is pumped to below 100pa, and the oil bath temperature is raised to 230℃ for polycondensation reaction for 1.5h to obtain branched PBAT.

[0085] (5) Finally, the obtained PBAT is removed from the three-necked flask and dried to obtain unbranched PBAT.

[0086] Comparative Example 3

[0087] This comparative example provides a branched PBAT with minimal pole-climbing behavior, and its preparation method includes the following steps:

[0088] (1) Sample weighing and mixing: Weigh 17.93g of terephthalic acid and 27g of 1,4-butanediol and add them to a three-necked flask. Add 30μL of titanium silicon zinc polynuclear catalyst and 8.4g of butylmalonic acid and place the three-necked flask in an oil bath preheated to 50℃.

[0089] (2) First step of esterification reaction: Nitrogen gas is continuously introduced into the three-necked flask in step (1), the stirring device is turned on, the stirring speed is set to 250 r / min, the oil bath is heated to 190℃ and kept at 20 min, and then the oil bath temperature is gradually increased to 215℃ at a rate of 20℃ every 30 min. Esterification is carried out at 215℃ for 60 min. After the water output reaches the predetermined value, the first step of esterification reaction is completed.

[0090] (3) Second step esterification reaction: After the first step esterification is completed, the temperature of the oil bath is lowered to below 140℃, 20μL of titanium silicon zinc polynuclear catalyst is added to the three-necked flask for the second time, and 19.27g of adipic acid is added. The temperature of the bath is then raised to 185℃ and esterified for 120min. The amount of water output reaches the predetermined value, and the second step esterification reaction is completed.

[0091] (4) Low-compression polycondensation reaction: After the second esterification reaction is completed, the temperature is lowered to below 140℃ again, and 36μL of titanium silicon zinc polynuclear catalyst is added to the three-necked flask for the third time. The pressure inside the three-necked flask is pumped to below 100pa, and the oil bath temperature is raised to 230℃ for polycondensation reaction for 4h. At this time, the PBAT melt climbing phenomenon is not obvious, and the melt viscosity is very low.

[0092] (5) Finally, the obtained PBAT is removed from the three-necked flask and dried to obtain branched PBAT with very low melt viscosity.

[0093] evaluate:

[0094] 1. The mechanical tensile properties, melt index, intrinsic viscosity and DSC of PBAT prepared by branching the ester-based branched structure obtained in Example 1 were evaluated.

[0095] 2. Test methods and conclusions:

[0096] (1) Tensile properties test of PBAT prepared by branching of ester-based branched structure

[0097] The branched butyl malonate (PBAT) obtained was dried in an oven at 60°C and then molded at 160°C to form standard specimens according to GB / T1040.2-2006. The tensile strength was tested using an Instron 5500R universal testing machine at room temperature and a tensile speed of 50 mm / min. The tensile results are shown in […]. Figure 3 ,from Figure 3As can be seen from the figure, under the same conditions, compared with unbranched PBAT (Comparative Example 2, represented as PBAT in the figure), the tensile strength and elongation at break of branched PBAT are significantly improved.

[0098] (2) Melt index test of PBAT prepared by branching structures such as ester groups.

[0099] The branched butyl malonate (PBAT) obtained was dried in an oven at 60°C and cut into small particles. Melt index testing was performed at 190°C and 2.16 kg. The results are as follows: Figure 4 ,from Figure 4 As can be seen, under the same conditions, compared with unbranched PBAT (Comparative Example 2), the melt index of branched PBAT is significantly reduced, and the melt index of different branched structures varies greatly under the same conditions.

[0100] (3) Testing of intrinsic viscosity properties of PBAT prepared by branching structures such as ester-based branches.

[0101] The branched butyl malonate (PBAT) obtained in Example 1 was dried in an oven at 60°C and then dissolved in a solvent composed of phenol and 1,1,2,2-tetrachloroethane in a mass ratio of 1:1, resulting in a 0.5% (w / w) solution. The intrinsic viscosity was measured using an Ubbelohde viscometer and calculated. The results are shown in [Figure / Reference]. Figure 4 ,from Figure 4 As can be seen from the data, under the same conditions, the intrinsic viscosity of branched PBAT is improved compared with that of unbranched PBAT, which is consistent with the melt index. Furthermore, the intrinsic viscosity of different branched structures varies under the same conditions.

[0102] (4) DSC performance testing of PBAT prepared by branching structures such as ester groups and branched chains.

[0103] The branched butyl malonate (PBAT) obtained was dried in an oven at 60°C and tested using a DSC analyzer. The test conditions were as follows: first, the temperature was lowered from 160°C to -50°C at a rate of 10°C / min, held at that temperature for 1 min, and then raised back to 160°C at a rate of 10°C / min. The results are shown in […]. Figure 5 After branching, the crystallization temperature of PBAT decreases (e.g. Figure 5 As shown in a), but its melting temperature is increased (as shown in a). Figure 5 (As shown in b). Figure 6Based on the sum of the molar amounts of terephthalic acid and adipic acid being 100%, PBAT synthesized when the terephthalic acid content is less than 30% (terephthalic acid content is 20%, i.e., molar ratio of terephthalic acid: adipic acid = 2:8, preparation method is the same as Comparative Example 2, only the molar ratio of terephthalic acid and adipic acid is adjusted) has a melting temperature below 50℃. The melting temperature is too low, and its food safety is seriously affected when used in summer.

[0104] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0105] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing branched PBAT, wherein, The preparation method includes the following steps: (1) First step of esterification reaction: Terephthalic acid and butanediol are mixed, and after the catalyst is added for the first time, the first step of esterification reaction is carried out at 200-240℃ under a protective gas atmosphere; (2) Second step esterification reaction: After the first step esterification reaction is completed, the temperature is lowered to below 140℃, adipic acid is added and the catalyst is added for the second time, and the second step esterification reaction is carried out at 160-190℃; (3) Pre-condensation reaction: After the second step of esterification reaction is completed, the temperature is lowered to below 140°C, the catalyst is added for the third time, and the condensation reaction is carried out at 220-260°C below 100 Pa. After the reaction is completed, the branched PBAT is obtained. When the boiling point of the branching agent is ≥210℃, the branching agent is added in step (1); when the boiling point of the branching agent is ≤210℃, the branching agent is added in step (2). The branching agent includes one or more of diethyl butyl malonate, dimethyl isobutyl-1,3-malonate and butyl malonate. The molar ratio of adipic acid to terephthalic acid is 70:30-48:52; The branching degree of the branched PBAT is 2%-6%.

2. The preparation method according to claim 1, wherein, In step (1), the molar ratio of the titanium in the catalyst added for the first time to the sum of the molar amounts of the terephthalic acid and adipic acid is 1:10000-3:1000.

3. The preparation method according to claim 1, wherein, In step (1), the molar ratio of terephthalic acid to butanediol is 45:100-45:

150.

4. The preparation method according to claim 1, wherein, In step (2), the molar ratio of the titanium in the catalyst added for the second time to the sum of the molar amounts of the terephthalic acid and adipic acid is 1:10000-3:1000.

5. The preparation method according to claim 1, wherein, In step (3), the molar ratio of the titanium in the catalyst added for the third time to the sum of the molar amounts of the terephthalic acid and adipic acid is 1:10000-6:1000.

6. The preparation method according to claim 1, wherein, The catalysts added in steps (1) to (3) are polynuclear catalysts.

7. The preparation method according to claim 6, wherein, The multinuclear catalyst includes titanium-silicon-zinc multinuclear catalysts and / or titanium-silicon-aluminum multinuclear catalysts.

8. The preparation method according to claim 6, wherein, The catalyst added in steps (1) to (3) is the titanium-silicon composite polynuclear catalyst described in invention patent application 202210966547.

1.

9. Branched PBAT prepared by any one of claims 1-8.

10. The branched PBAT according to claim 9, wherein, The branched PBAT has a branch length of 2-10 carbon atoms.

11. The branched PBAT according to claim 9, wherein, The branched PBAT has a branch length of 2-6 carbon atoms.

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