High-strength branched PBAT and preparation method thereof

Abstract

The application provides a high-strength branched PBAT and a preparation method thereof. The preparation method comprises the following steps: performing esterification reaction on terephthalic acid and succinic acid, and then adding adipic acid to perform esterification reaction. The method adopts branched monomers with different carbon chain lengths and different functional groups to modify the straight chain of the PBAT molecule, and constructs a PBAT main chain structure containing different branched sites. The performance of the prepared branched PBAT is greatly improved, and the branched PBAT has excellent tensile strength and elongation at break.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of high-strength branched PBAT and its preparation method, belong to high polymer synthesis technical field. BACKGROUND

[0002] With the development of society, degradable materials are favored, PBAT is a thermoplastic fully biodegradable material, is the most potential polyethylene substitute product, is also one of the important ways to solve polyethylene pollution, especially the substitution effect of PBAT on polyethylene agricultural film makes the research of PBAT become the focus.If you want PBAT to replace polyethylene and other non-degradable products comprehensively, PBAT is currently lacking in performance, for example, the blow molding processing performance is not as good as polyethylene, and the tensile strength also has a big gap with polyethylene.If you want to achieve the comprehensive substitution of PBAT to polyethylene, you must optimize the performance of PBAT.

[0003] Researchers try to add fillers, chain extenders or blend with other polymer materials in PBAT, so as to improve the performance of PBAT, but in the process of use, small molecules are lost, migrated or have poor compatibility with other polymer materials.Long-term research shows that molecular structure determines the performance of polymer materials, and the modification of PBAT molecular structure is the most possible and effective means to improve the performance of PBAT.Grafting branched small molecules in the form of chemical bond on PBAT molecular chain can modify and modify PBAT molecular chain, and because different modifiers have different modification properties for polymer structure, therefore the selection of modifier becomes the most important. SUMMARY

[0004] In order to solve the above problems, the purpose of the present application is to provide a kind of high-strength branched PBAT and its preparation method, the high-strength branched PBAT prepared by the preparation method has high mechanical strength, excellent tensile strength and elongation at break, and the reaction is relatively complete.

[0005] In order to achieve the above purpose, the present application provides a kind of preparation method of high-strength branched PBAT, which includes the following steps: first esterification of terephthalic acid and succinic acid, then adding adipic acid for esterification.

[0006] According to the specific embodiment of the present application, preferably, the above preparation method includes the following steps:

[0007] (1) first esterification: terephthalic acid is mixed with butanediol, after the first addition of catalyst, first esterification is carried out at 210-240 DEG C (preferably 215 DEG C) under the protection of gas atmosphere;

[0008] (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 150-190°C (preferably 150°C);

[0009] (3) Pre-condensation reaction: After the second esterification reaction is completed, the temperature is lowered to below 140°C, and the catalyst is added for the third time. The condensation reaction is carried out at 220-260°C (preferably 230°C) below 100 Pa. After the reaction is completed, the high-strength branched PBAT is obtained.

[0010] When the boiling point of the branching agent is ≥200℃, the branching agent is added in step (1); when the boiling point of the branching agent is ≤200℃, the branching agent is added in step (2).

[0011] The branching agent comprises diols and / or 1,2-epoxy compounds; more preferably, the diol comprises one or more combinations of 1,2-propanediol, 1,2-butanediol, 1,2-hexanediol, 7-octen-1,2-diol, butenyldiol, 2,2-diisobutyl-1,3-propanediol, 1,2-octanediol, 1,2-decanediol, 1,2-dodecanediol, 1,2-tetradecanediol, and 2-butyl-2-ethyl-1,3-propanediol; the 1,2-epoxy compounds comprise one or more combinations of 1,2-epoxybutane, 1,2-epoxyhexane, 1,2-epoxyoctane, butyl glycidyl ether, octyl glycidyl ether, tert-butyl glycidyl ether, and allyl glycidyl ether.

[0012] According to a specific embodiment of the present invention, preferably, in step (1), the molar ratio of titanium in the catalyst added for the first time to the sum of the molar amounts of terephthalic acid and adipic acid is 1:500-1:10000.

[0013] 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.

[0014] According to a specific embodiment of the present invention, preferably, in step (1), the butanediol is 1,4-butanediol.

[0015] According to a specific embodiment of the present invention, preferably, the branching agent is one or a combination of two or more of 1,2-hexanediol, 1,2-epoxyoctane, and butyl glycidyl ether.

[0016] According to a specific embodiment of the present invention, preferably, in step (2), the molar ratio of titanium in the catalyst added for the second time to the sum of the molar amounts of terephthalic acid and adipic acid is 1:500-1:10000.

[0017] 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.

[0018] According to a specific embodiment of the present invention, preferably, in step (3), the molar ratio of the sum of the molar amounts of titanium and terephthalic acid and adipic acid in the catalyst added for the third time is 1:500-1:10000.

[0019] According to a specific embodiment of the present invention, preferably, the catalyst added in steps (1) to (3) is a multinuclear catalyst, preferably including titanium-silicon-zinc multinuclear catalyst and / or titanium-silicon-aluminum multinuclear catalyst.

[0020] 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.

[0021] This invention reconstructs the PBAT molecular chain in a novel form by reacting a branching agent onto the main molecular chain of PBAT, thus preparing PBAT with different linear molecular structures and improving PBAT performance by controlling the PBAT molecular architecture. The branching agent used in this invention is preferably a diol and / or a 1,2-epoxy compound (i.e., a compound containing a 1,2-epoxy group). More preferably, the diol includes one or more combinations of 1,2-propanediol, 1,2-butanediol, 1,2-hexanediol, 7-octen-1,2-diol, butenyldiol, and 2,2-diisobutyl-1,3-propanediol; the 1,2-epoxy compound includes one or more combinations of 1,2-epoxybutane, 1,2-epoxyhexane, 1,2-epoxyoctane, butyl glycidyl ether, octyl glycidyl ether, tert-butyl glycidyl ether, and allyl glycidyl ether. Among them, 1,2-epoxyhexane and butyl glycidyl ether are branching agents with boiling points below 200℃, while the other listed branching agents are branching agents with boiling points above 200℃.

[0022] 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 0.5:100-15:100.

[0023] According to a specific embodiment of the present invention, the above preparation method includes the following specific steps:

[0024] (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 agents with different chain lengths or different structures, and then add a certain proportion of catalyst (if the boiling point of the branching agent is lower than 200℃, the branching agent is not added in this step). Place the three-necked flask in an oil bath that has been preheated to 50℃.

[0025] (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 of the oil bath is raised to about 190°C and kept at that temperature for a certain period of time. Then, the temperature is raised to 210-240°C (e.g., 215°C) until the first step of esterification reaction is completed. (Raising the temperature to 190°C and keeping it at that temperature for a certain period of time means: keeping it at 190°C for more than 20 minutes, and then directly raising the temperature to 210-240°C (e.g., 215°C) 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 of branching agent to carboxylic acid is M. 支化剂 M 羧酸 = 0.5:100-15:100, the molar ratio of catalyst to carboxylic acid ranges from M 催化剂 M 羧酸 =1:10000-1:500, 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 ratio of terephthalic acid and adipic acid is the sum of their molar amounts. Excessive content of the branching agent and catalyst significantly deepens the product color, changing it from white or pale yellow to deep red or yellowish-red. Insufficient content prevents the branching reaction from achieving its intended effect, resulting in no performance improvement compared to the unbranched product. Furthermore, insufficient catalyst content drastically increases reaction time, leading to incomplete catalysis and consequently, no improvement in material performance. Excessive terephthalic acid content negatively impacts degradation performance, while insufficient terephthalic acid content (below 30% of the total molar ratio of terephthalic acid and adipic acid) results in a melting point below 60°C, affecting its performance in summer. Therefore, using the molar ratio of this invention ensures that the resulting branched PBAT possesses excellent mechanical properties. Additionally, increasing the temperature from 190°C to the esterification temperature range at a rate of 5-20°C / 30min during the reaction effectively suppresses side reactions and the loss of reacting components.

[0026] (3) Second step esterification reaction: After the first step esterification is completed, the temperature of the oil bath is lowered to below 140°C, and the catalyst is added to the three-necked flask for the second time, along with a certain proportion of adipic acid (if the boiling point of the branching agent is ≤200°C, the branching agent is added in this step). The temperature of the oil bath is then raised to a certain temperature until the second step esterification reaction is completed (the reaction temperature is controlled below the boiling point of the added branching agent). Lowering the temperature to below 140°C 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.

[0027] (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 220-260°C (e.g., 230°C) to carry out the condensation reaction until the condensation reaction is completed.

[0028] The present invention also provides a high-strength branched PBAT prepared by the above preparation method.

[0029] According to a specific embodiment of the present invention, preferably, the branching degree of the high-strength branched PBAT is 0.5-15%, more preferably 2-6%.

[0030] According to a specific embodiment of the present invention, preferably, the branch length of the high-strength branched PBAT is 2-10 carbon atoms, more preferably 2-6 carbon atoms.

[0031] This invention uses monomers of different lengths and structures as modifiers for the linear PBAT chain to branch and entangle the linear PBAT chain, constructing PBAT molecular chains with different molecular structures and degrees of branching. This allows for the improvement of PBAT performance by controlling the PBAT molecular structure, and has the following beneficial effects:

[0032] (1) High-strength branched PBAT prepared by branching agents with different chain lengths or different structures as described in this invention can effectively improve the mechanical strength of PBAT through the role of branching in the molecular structure of PBAT.

[0033] (2) High-strength branched PBAT prepared by branching agents with different chain lengths or different structures in this invention has different effects on improving the performance of PBAT due to the different branch lengths and structures of the branching agents. The molecular structure of PBAT can be designed according to the different improvement effects.

[0034] (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

[0035] Figure 1 This is a flowchart of the PBAT synthesis process of the present invention;

[0036] Figure 2 The results of esterification are shown for different addition sequences. Figure 2 Photograph of the white emulsion obtained after esterification reaction with adipic acid added first and then terephthalic acid for 6 hours (a). Figure 2 Photograph of a clear, transparent liquid obtained after adding terephthalic acid first and then adipic acid, followed by esterification reaction for 2 hours (b).

[0037] Figure 3 The graph shows the results when the catalyst is added at different temperatures; Figure 3 Figure a shows the catalyst atomization phenomenon caused by hydrolysis when the catalyst is added at 160℃. Figure 3 Figure b shows the phenomenon of no atomization due to hydrolysis when the catalyst is added below 140℃;

[0038] Figure 4 Comparison of tensile properties of branched PBAT and pure PBAT (unbranched) in Examples 1, 2, and 3;

[0039] Figure 5 Figures showing the mechanical properties of PBAT after branching with different degrees of branching and different branch chain lengths; Figure 5 In Figure 'a', the mechanical properties of PBAT with different degrees of branching are shown. Figure 5 In Figure b, the mechanical properties of PBAT with different branch lengths are shown.

[0040] Figure 6 The intrinsic viscosity and melt flow index results of branched PBAT and pure PBAT in Examples 1, 2 and 3 are shown in the figure.

[0041] Figure 7 Photographs of samples with excessively high levels of catalysts and branching agents;

[0042] Figure 8 The mechanical properties of multifunctional branched PBAT are shown in the diagram. Detailed Implementation

[0043] 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.

[0044] The catalysts used in the following examples and comparative examples are all titanium-based composite polynuclear catalysts 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 preparation method is 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 evenly 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.

[0045] The preparation method of the titanium-silicon-zinc polynuclear catalyst used below includes the following steps:

[0046] (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;

[0047] (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;

[0048] (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.

[0049] (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%.

[0050] The preparation method of the titanium-silicon-aluminum polynuclear catalyst used below includes the following steps:

[0051] (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;

[0052] (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;

[0053] (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.

[0054] (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%.

[0055] Example 1

[0056] This embodiment provides a high-strength branched PBAT, the preparation method of which includes the following steps, the process of which is as follows: Figure 1 As shown:

[0057] (1) Sample weighing and mixing: Weigh 18.675g of terephthalic acid and 26.1g of 1,4-butanediol and add them to a three-necked flask, then add 1.18g of 1,2-hexanediol, and then add 30μL of titanium-silicon-zinc polynuclear catalyst. Place the three-necked flask in an oil bath preheated to 50℃.

[0058] (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 the oil bath temperature is gradually increased to 215℃ at a rate of 5℃ every 20 min, and kept at 215℃ until the first step of esterification reaction is completed.

[0059] (3) Second esterification reaction: After the first esterification is completed, the oil bath temperature is lowered to below 140℃, and 20μL of titanium-silicon-zinc polynuclear catalyst is added to the three-necked flask for the second time. At this time, the catalyst will not exhibit atomization (e.g., Figure 3 As shown in Figure b), after adding 20.06g of adipic acid, the bath temperature was raised to 185℃ and the reaction was carried out for 2 hours. The second step of esterification was completed, and the melt was clear and transparent, as shown in Figure b. Figure 2 As shown in b;

[0060] (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℃ to carry out the polycondensation reaction until the polycondensation reaction is completed, and the branched PBAT is obtained.

[0061] (5) Finally, the obtained PBAT is removed from the three-necked flask and dried to obtain branched PBAT.

[0062] Example 2

[0063] This embodiment provides a high-strength branched PBAT, the preparation method of which includes the following steps:

[0064] (1) Sample weighing and mixing: Weigh 18.675g of terephthalic acid and 26.1g 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℃.

[0065] (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 the oil bath temperature is gradually increased to 215℃ at a rate of 5℃ every 20 min, and kept at 215℃ until the first step of esterification reaction is completed.

[0066] (3) Second step esterification reaction: After the first step esterification is completed, the temperature of the oil bath is lowered to below 140°C. 20 μL of titanium silicon zinc polynuclear catalyst is added to the three-necked flask for the second time. At this time, the catalyst will not atomize. After adding 1.3 g of butyl glycidyl ether, 19.27 g of adipic acid is added and the temperature of the bath is raised to 185°C until the second step esterification reaction is completed. The melt is clear and transparent.

[0067] (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℃ to carry out the polycondensation reaction until the polycondensation reaction is completed, and the branched PBAT is obtained.

[0068] (5) Finally, the obtained PBAT is removed from the three-necked flask and dried to obtain branched PBAT.

[0069] Example 3

[0070] This embodiment provides a high-strength branched PBAT, the preparation method of which includes the following steps:

[0071] (1) Sample weighing and mixing: Weigh 18.675g of terephthalic acid and 26.1g 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℃.

[0072] (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 the oil bath temperature is gradually increased to 215℃ at a rate of 5℃ every 20 min, and kept at 215℃ until the first step of esterification reaction is completed.

[0073] (3) Second step esterification reaction: After the first step esterification is completed, the temperature of the oil bath is lowered to below 140℃, and 20μL of titanium silicon aluminum polynuclear catalyst is added to the three-necked flask for the second time. At this time, the catalyst will not atomize. Then 1.28g of 1,2-epoxyoctane is added, followed by 20.06g of adipic acid. The temperature of the bath is then raised to 185℃ until the second step esterification reaction is completed. The melt is clear and transparent.

[0074] (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-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℃ to carry out the polycondensation reaction until the polycondensation reaction is completed, and the branched PBAT is obtained.

[0075] (5) Finally, the obtained PBAT is removed from the three-necked flask and dried to obtain branched PBAT.

[0076] Comparative Example 1

[0077] This comparative example provides a branched PBAT, the preparation method of which includes the following steps:

[0078] (1) Sample weighing and mixing: Weigh 19.27g of adipic acid and 26.1g of 1,4-butanediol and add them to a three-necked flask. Add 60μL of titanium-silicon-aluminum polynuclear catalyst and place the three-necked flask in an oil bath preheated to 50℃.

[0079] (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 160℃ and kept at 20 min, and then the oil bath temperature is gradually increased to 185℃ at a rate of 5℃ every 20 min. The first step of esterification reaction is carried out at 185℃ until it is completed. The esterification time is 2 h, and a clear and transparent liquid is obtained.

[0080] (3) Second step esterification reaction: After the first step esterification is completed, the oil bath temperature is lowered to below 140℃. 35μL of titanium-silicon-aluminum polynuclear catalyst is added to the three-necked flask for the second time. At this point, the catalyst does not exhibit atomization. After adding 1.3g of butyl glycidyl ether, 18.675g of terephthalic acid is added, and the oil bath temperature is raised to 215℃. The esterification reaction is carried out for more than 6 hours, but a clear and transparent melt is not obtained. Figure 2 As shown in Figure a;

[0081] (4) Low-compression polycondensation reaction: After the second esterification reaction is completed, the temperature is lowered to below 140℃ again, and 72μL 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℃ to carry out polycondensation reaction until the polycondensation reaction is completed, and branched PBAT is obtained.

[0082] (5) Finally, the obtained PBAT is removed from the three-necked flask and dried to obtain branched PBAT.

[0083] Comparative Example 2

[0084] This comparative example provides a branched PBAT, the preparation method of which includes the following steps:

[0085] (1) Sample weighing and mixing: Weigh 18.675g of terephthalic acid and 26.1g of 1,4-butanediol and add them to a three-necked flask. Add 50μL of titanium-silicon-zinc polynuclear catalyst and place the three-necked flask in an oil bath preheated to 50℃.

[0086] (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 the oil bath temperature is gradually increased to 215℃ at a rate of 5℃ every 20 min, and kept at 215℃ until the first step of esterification reaction is completed.

[0087] (3) Second step esterification reaction: After the first step esterification is completed, the oil bath temperature is lowered to 160℃, and 30μL of titanium-silicon-zinc polynuclear catalyst is added to the three-necked flask for the second time. At this time, the catalyst will atomize due to the high temperature (e.g., Figure 3 As shown in Figure a), some catalysts are lost due to mist or deactivated by hydrolysis; then 1.3g of butyl glycidyl ether is added, followed by 19.27g of adipic acid, and the bath temperature is raised to 185℃ until the second esterification reaction is completed;

[0088] (4) Low-compression polycondensation reaction: After the second esterification reaction is completed, the temperature is lowered to below 140℃ again, and 60μL 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℃ to carry out polycondensation reaction until the polycondensation reaction is completed, and branched PBAT is obtained.

[0089] (5) Finally, the obtained PBAT is removed from the three-necked flask and dried to obtain branched PBAT.

[0090] Comparative Example 3

[0091] This comparative example provides a branched PBAT, the preparation method of which includes the following steps:

[0092] (1) Sample weighing and mixing: Weigh 18.675g of terephthalic acid and 26.1g of 1,4-butanediol and add them to a three-necked flask. Add 150μL of titanium-silicon-zinc polynuclear catalyst and place the three-necked flask in an oil bath preheated to 50℃.

[0093] (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 the oil bath temperature is gradually increased to 215℃ at a rate of 5℃ every 20 min, and kept at 215℃ until the first step of esterification reaction is completed.

[0094] (3) Second step esterification reaction: After the first step esterification is completed, the temperature of the oil bath is lowered to below 140℃, and 100μL of titanium silicon zinc polynuclear catalyst is added to the three-necked flask for the second time. At this time, the catalyst will not atomize. Then 4.425g of 1,2-hexanediol is added, followed by 20.06g of adipic acid. The temperature of the bath is then raised to 185℃ until the second step esterification reaction is completed. The melt is clear and transparent.

[0095] (4) Low-compression polycondensation reaction: After the second esterification reaction is completed, the temperature is lowered to below 140℃ again, and 100μL 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℃ to carry out polycondensation reaction. During the polycondensation process, the melt turns yellow-red until the polycondensation reaction is completed, and branched PBAT is obtained.

[0096] (5) Finally, the obtained PBAT is removed from the three-necked flask and dried to obtain yellow-red branched PBAT, as shown in the figure. Figure 7 As shown.

[0097] Comparative Example 4

[0098] This comparative example provides a branched PBAT, prepared using the same method as in Example 1, but with 30% terephthalic acid added, i.e., a molar ratio of terephthalic acid to adipic acid of 3:7. The resulting branched PBAT has a melting temperature of 52°C, which is below 60°C, affecting its performance in summer.

[0099] evaluate:

[0100] 1. The mechanical tensile properties, melt index, and intrinsic viscosity of the branched PBAT prepared in Examples 1, 2, and 3 were evaluated. Unless otherwise specified, the PBAT used in the following tests was prepared according to the preparation process of Example 1, with the differences being that no branching agent was added during preparation, different amounts of branching agent were added, and different numbers of carbon atoms of branching agent were added.

[0101] 2. Test methods and conclusions:

[0102] (1) Tensile property test

[0103] The prepared branched PBAT was dried in an oven at 60℃ and then molded at 160℃ 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 number missing]. Figure 4 , Figure 5 ;in, Figure 4 In the middle, taking the vertical part on the right as the reference, the curves from left to right are PBAT (i.e., unbranched PBAT), Example 1, Example 3, and Example 2; Figure 5 In the diagram, 3, 4, 5, 6, and 7 represent branching agents comprising 3%, 4%, 5%, 6%, and 7% of the total molar amount of acid added, respectively. PBAT represents unbranched PBAT. 2C-10C represent the unreacted carbon chain lengths of the same branching agent, ranging from 2 to 10 carbon atoms (the branching agents are, in order, 1,2-butanediol, 1,2-hexanediol, 1,2-octanediol, 1,2-decanediol, and 1,2-dodecanediol). Figure 5 Taking the vertical portion on the right as a reference, the curves from left to right are 7, PBAT, 4, 3, 5, and 6. Figure 5 Taking the vertical portion on the right as a reference, the curves from left to right are 4C, 2C, 8C, 10C, and 6C. As can be seen from the figure, under the same conditions, the branched PBAT exhibits significantly improved tensile strength and elongation at break compared to the unbranched PBAT.

[0104] (2) Melt Flow Index Test

[0105] The prepared branched PBAT was dried in an oven at 60℃ and cut into small particles. Melt index tests were then conducted at 190℃ and 2.16 kg. The results are as follows: Figure 6 As can be seen from the figure, under the same conditions, compared with unbranched PBAT (which was prepared in the same way as in Example 1 without the addition of any branching agent), the melt index of branched PBAT is significantly reduced, and the melt index of different branched structures varies greatly under the same conditions.

[0106] (3) Intrinsic viscosity performance test

[0107] The prepared branched PBAT 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 number missing]. Figure 6 As can be seen from the figure, under the same conditions, the intrinsic viscosity of branched PBAT is increased compared with that of unbranched PBAT, which is consistent with the melt index. Moreover, the intrinsic viscosity of different branched structures differs under the same conditions.

[0108] 3. PBAT branched with different branching agents was pressed into standard specimens according to GB / T1040.2-2006, and its mechanical properties were tested according to the test methods in GB / T1040.2-2006. The PBAT involved below is prepared in the same way as in Example 1, except that different branching agents are added and the amount of branching agents added is different.

[0109] See results Figure 8 , Figure 8 The 2-OH to 6-OH groups indicated in the text represent branched monomers with dihydroxy to hexahydroxy functional groups prepared from PBAT (the branched monomers represented by 2-butyl-1,3-propanediol, trimethylolpropane, pentaerythritol, and dipentaerythritol, respectively). 0.5%, 0.1%, 1%, and 0.2% indicate that the branching agent is 0.5%, 0.1%, 1%, and 0.2% of the total molar amount of acid added, respectively. Figure 8 Taking the vertical part on the right as the reference, the curves from left to right are 4-OH-0.2%, 3-OH-1%, 3-OH-0.5%, 4-OH-0.1%, 6-OH, and 2-OH.

[0110] 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.

[0111] 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 high-strength branched PBAT, comprising 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 210-240℃ 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 150-190℃; (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 below 100 Pa. After the reaction is completed, the high-strength branched PBAT is obtained. When the boiling point of the branching agent is ≥200℃, the branching agent is added in step (1); when the boiling point of the branching agent is ≤200℃, the branching agent is added in step (2). The branching agent comprises diols and / or 1,2-epoxy compounds; the diols comprise one or more combinations of 1,2-propanediol, 1,2-butanediol, 1,2-hexanediol, 7-octen-1,2-diol, butenyldiol, 2,2-diisobutyl-1,3-propanediol, 1,2-octanediol, 1,2-decanediol, 1,2-dodecanediol, 1,2-tetradecanediol, and 2-butyl-2-ethyl-1,3-propanediol; the 1,2-epoxy compounds comprise one or more combinations of 1,2-epoxybutane, 1,2-epoxyhexane, 1,2-epoxyoctane, butyl glycidyl ether, octyl glycidyl ether, tert-butyl glycidyl ether, and allyl glycidyl ether. The molar ratio of adipic acid to terephthalic acid is 70:30-48:52; The molar ratio of the branching agent to the sum of the molar amounts of the terephthalic acid and the adipic acid is 3:100-7:100; The catalyst is prepared by the following steps: First, titanate, 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 evenly to obtain a liquid titanium-silicon composite multinuclear catalyst; the molar ratio of ligand two to Ti atoms in solution C is 0-3:1; the co-catalyst is selected from at least one of triisopropyl aluminate, aluminum acetylacetonate, tribenzyl aluminate, zinc acetylacetonate, magnesium acetylacetonate, and neodymium acetylacetonate; 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.

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 1:500-1:10000.

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 sum of the molar amounts of titanium and terephthalic acid and adipic acid in the catalyst added for the second time is 1:500-1:10000.

5. The preparation method according to claim 1, wherein, In step (3), the molar ratio of the sum of the molar amounts of titanium and terephthalic acid and adipic acid in the catalyst added for the third time is 1:500-1:10000.

6. High-strength branched PBAT prepared by the preparation method according to any one of claims 1-5.

7. The high-strength branched PBAT according to claim 6, wherein, The branching degree of the high-strength branched PBAT is 0.5-15%.

8. The high-strength branched PBAT according to claim 6, wherein, The branching degree of the high-strength branched PBAT is 2-6%.

9. The high-strength branched PBAT according to claim 6, wherein, The branch length of the high-strength branched PBAT is 2-10 carbon atoms.

10. The high-strength branched PBAT according to claim 6, wherein, The branch length of the high-strength branched PBAT is 2-6 carbon atoms.

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