Method for producing poly(butylene adipate-co-terephthalate)

Abstract

FIELD: biodegradable plastics.SUBSTANCE: method for producing poly(butylene adipate-co-terephthalate) is described, in which terephthalic acid, adipic acid, 1,4-butanediol and tetrabutyl titanate are used as raw materials and poly(butylene adipate-co-terephthalate) is obtained by sequentially carrying out two stages of esterification and polycondensation, characterized in that after two stages of esterification, a pre-polycondensation stage is carried out before the polycondensation stage, in the first stage of the esterification reaction, terephthalic acid, tetrabutyl titanate and 1,4-butanediol are placed in a reactor in a nitrogen atmosphere in a ratio of 0.8-1.2: 0.0002: 2.4-3.6 mol respectively and stirred at 80°C for 0.5 h, then the esterification reaction is carried out at a temperature of 200-210°C for 3 hours until homogenization of the mixture consisting of 1,4-butanediol and terephthalic acid is achieved, and then the first stage of the esterification reaction is continued for another 2 hours at this temperature; in the second stage of the esterification reaction, adipic acid, tetrabutyl titanate and 1,4-butanediol are added to the reactor in a ratio of 0.8-1.2: 0.0002: 0.3-0.5 mol respectively, then the temperature is increased to 180°C, and the reaction mixture is stirred in a nitrogen atmosphere for 3-4 hours, then tetrabutyl titanate is added in an amount of 0.0002 mol and the reaction mixture is heated to 210-220°C and the pre-polycondensation stage is carried out at a pressure of 50-150 torr for 2-3 hours, then the pressure is reduced to 3-5 torr and pre-polycondensation is carried out for another 2-3 hours, after which the temperature of the reaction mixture is increased to 230-240°C and carry out a polycondensation reaction at a pressure of 0.1-0.5 torr for 3-4 hours.EFFECT: reduction in the presence of low-molecular substances in the final product and, as a result, an improvement in the mechanical characteristics of the product.1 cl, 1 dwg, 1 tbl, 3 ex

Description

[0001] The invention relates to the field of biodegradable plastics, in particular, to a method for producing high-molecular poly(butylene adipate-co-terephthalate), hereinafter PBAT, for the production of plastic products such as packaging boxes for food and beverages, agricultural mulching films, supermarket shopping bags, cosmetic outer packaging, and medical supplies.

[0002] A known method for producing PBAT with a low content of terminal carboxyl groups includes the stages of esterification of 1,4-butanediol, adipic acid and terephthalic acid in the presence of a water-soluble catalyst and a polyhydric alcohol, followed by polycondensation in an inert atmosphere (Application CN 103408739 A, IPC C08G 63 / 20, C08G 63 / 78, published on November 27, 2013). The disadvantage of this invention is the incompleteness of the esterification reaction and the deterioration of the product properties due to a single introduction of the entire volume of 1,4-butanediol at the stage of co-esterification of adipic and terephthalic acids. This approach does not allow for the compensation of butanediol consumption in side reactions, in particular the formation of tetrahydrofuran (THF), which predominantly accompanies the esterification of terephthalic acid. As a result, the actual butanediol / acid molar ratio is lower than calculated.An additional technological limitation is the co-esterification of poorly soluble terephthalic acid and highly soluble adipic acid, limiting the efficiency of ester formation. Furthermore, the use of a single-stage high vacuum (0.23-0.75 Torr) during the polycondensation step disrupts the specified monomer ratio due to the distillation of low-molecular-weight compounds. These characteristics of this PBAT production method result in low strength properties of the material (~15-20 MPa).

[0003] A method for synthesizing high-molecular PBAT is known (Application CN 109134832 A, IPC C08G 63 / 183, C08G 63 / 78, C08G 63 / 80, published on 04.01.2019), which includes introducing a polyhydric alcohol as a chain extender at the stage of esterification of adipic acid and carrying out a three-stage process: esterification, transesterification / secondary esterification and polycondensation in the melt using a combined catalytic system based on titanates and zinc compounds. A disadvantage of this invention is the reduced mechanical properties of the product, as well as the difficulty in obtaining a product with the stated upper molecular weight limit of the resulting polymer. This is apparently caused by the uncompensated introduction of 1,4-butanediol, which does not take into account its consumption in the side cyclization reaction to form THF. This leads to an uncontrolled decrease in the actual excess of butanediol in the system, potentially reducing the completeness of the esterification reaction.

[0004] The closest technical solution selected as a prototype is the method for synthesizing PBAT (Application CN 118126303 A, IPC C08G 63 / 85, C08G 63 / 183, published on 04.06.2024), including preliminary esterification of 1,4-butanediol with adipic acid, secondary esterification with terephthalic acid and polycondensation in the presence of a combined catalytic system based on titanium and zirconium compounds, as well as using epoxy chain extenders. The disadvantages of this invention are insufficient synthesis efficiency and obtaining a final product with reduced mechanical properties, which is a consequence of a single introduction of the entire volume of 1,4-butanediol at the stage of esterification of adipic acid. This introduction does not take into account its consumption in the side reaction of cyclization with the formation of THF.An additional factor limiting the efficiency of the synthesis is the lack of detailed specification of the vacuum process during the polycondensation stage. Only the need for a gradual reduction in pressure to ≤0.38 Torr is indicated, with no specific parameters for the vacuum rate or gradient. This leads to low tensile strength values ​​of 16.9 MPa (Example 8). Thus, there is a technical problem with the uncontrolled reduction of excess 1,4-butanediol in the reaction system due to its additional consumption in side reactions, which potentially reduces the degree of esterification, leads to the presence of low-molecular-weight substances in the final product, and degrades the properties of the final product.

[0005] The objective of the proposed invention is to obtain a purer high molecular weight poly(butylene adipate-co-terephthalate).

[0006] The technical result is a reduction in the presence of low-molecular substances in the final product and, as a result, an improvement in the mechanical characteristics of the product.

[0007] The technical result of the claimed invention is achieved by producing a linear PBAT copolymer through a two-stage melt esterification and polycondensation reaction. The first stage of esterification is carried out with terephthalic acid with the addition of 1,4-butanediol and tetrabutyl titanate. The second stage of esterification is carried out by adding adipic acid, tetrabutyl titanate, and, additionally, 1,4-butanediol, in an amount equal to the released THF. Then, the pre-polycondensation stage is carried out, where catalytic amounts of tetrabutyl titanate are added and pre-polycondensation is carried out by heating the reaction mixture while regulating the pressure. Subsequently, the polycondensation process is carried out by adding a catalytic amount of tetrabutyl titanate and, by regulating the temperature and pressure, the final product is obtained.The addition of 1,4-butanediol in the second esterification stage prevents the uncontrolled reduction of excess 1,4-butanediol in the system due to its additional consumption in side reactions. The consumption of 1,4-butanediol in side processes affects the conversion of acids used in the esterification reaction and the binding of butylene terephthalate and butylene adipate fragments, which reduces the degree of esterification, leads to the presence of low-molecular-weight substances in the final product, and degrades the properties of the final product.

[0008] The linear copolymer PBAT, according to the claimed method, is obtained by a two-stage esterification reaction, a melt polycondensation stage and a melt polycondensation stage.

[0009] To carry out the first stage of esterification, terephthalic acid, tetrabutyl titanate and 1,4-butanediol in a ratio of (0.8-1.2):(0.0002):(2.4-3.6) mol, respectively, are placed in a reactor under a nitrogen atmosphere connected to a vacuum pump through a trap and equipped with a condenser, thermometer and overhead stirrer, stirred at 80°C for 0.5 h. Then the reaction is carried out at a temperature of 200-210°C for 3 hours until the transparency point is reached (homogenization of the mixture of 1,4-butanediol and terephthalic acid) and then for another 2 hours at this temperature, respectively. The esterification process is carried out until more than 90% of the theoretical yield of water is released.

[0010] Terephthalic acid at high temperatures of approximately 200°C and above actively catalyzes the side process of 1,4-butanediol cyclization to form THF. The THF content in the distillation liquid reaches 50-60%. The consumption of 1,4-butanediol in side processes affects the conversion of acids used in the esterification reaction and the binding of butylene terephthalate and butylene adipate fragments. Therefore, in the second stage of esterification, adipic acid, tetrabutyl titanate, and additional 1,4-butanediol are added to the reactor, which is equivalent to the amount of tetrahydrofuran released. Adipic acid, tetrabutyl titanate, and 1,4-butanediol were introduced in a ratio of (0.8-1.2):0.0002:(0.3-0.5) mol, respectively. The temperature is raised to 180°C, and the reaction mixture is stirred under a nitrogen atmosphere for 3-4 hours. The esterification process is continued until more than 90% of the theoretical water yield has been recovered.

[0011] For the next stage of pre-polycondensation, catalytic amounts of tetrabutyl titanate are added - 0.0002 mol and the reactor is connected to a vacuum pump through a trap, then the reaction mass is heated at 210-220 °C and pre-polycondensation is carried out at a pressure of 50-150 Torr for 2-3 hours, then the pressure is reduced to 3-5 Torr and pre-polycondensation is carried out for another 2-3 hours.

[0012] Next, the polycondensation stage begins: the temperature of the reaction mixture is raised to 230-240°C and the polycondensation reaction is carried out at a pressure of 0.1-0.5 Torr for 3-4 hours. The hot copolymer melt is removed from the reactor and cooled to ambient temperature.

[0013] The combination of the above essential features results in a cleaner final product, poly(butylene adipate-co-terephthalate), with more complete conversion of monomers.

[0014] The illustrations attached to the description show:

[0015] Fig. - TGA curves of synthesized PBAT: (1) - with a single introduction of 1,4-butanediol and (2) - with additional introduction of 1,4-butanediol at the second stage of esterification.

[0016] Fig. shows the results of thermogravimetric analysis (TGA), where curve (1) shows the presence of weight loss from 25°C to 360°C due to the destruction of unreacted monomers and oligomers of PBAT with a single introduction of 1,4-butanediol; curve (2) shows a low weight loss from 25°C to 360°C with additional introduction of 1,4-butanediol, which indicates an insignificant content of low molecular weight products in the final PBAT.

[0017] Example 1 The linear copolymer PBAT is synthesized by a two-stage reaction of esterification, pre-polycondensation and melt polycondensation.

[0018] Terephthalic acid (1 mol), 1,4-butanediol (2.7 mol), and tetrabutyl titanate (0.0002 mol) are placed in a 1000 ml glass three-necked flask equipped with a condenser, thermometer, and overhead stirrer under a nitrogen atmosphere and stirred at 80°C for 0.5 hours. The reaction is then carried out at 210°C for 3 hours until the clear point is reached (homogenization of the mixture of 1,4-butanediol and terephthalic acid), and then for another 2 hours at this temperature, respectively. The esterification process is carried out until more than 90% of the theoretical water yield is released. In the second stage of esterification, 1.2 mol of adipic acid, 0.0002 mol of tetrabutyl titanate, and an additional 0.4 mol of 1,4-butanediol, equivalent to the amount of tetrahydrofuran released, are added to the reactor. The temperature is increased to 180°C, and the reaction mixture is stirred at this temperature under a nitrogen atmosphere for 3 hours.The esterification process is continued until more than 90% of the theoretical water yield is released. In the subsequent pre-polycondensation stage, after the addition of a catalytic amount of 0.0002 mol tetrabutyl titanate, the flask is connected to a vacuum pump via a trap, and the reaction mixture is heated to 210°C and pre-polycondensation is carried out at a pressure of 100 Torr for 3 hours. The pressure is then reduced to 5 Torr, and the reaction is carried out for an additional 3 hours. The temperature of the reaction mixture is then increased to 230°C, and the polycondensation stage is carried out at a pressure of 0.2 Torr for 3 hours. The hot copolymer melt is unloaded from the flask, cooled, and subjected to mechanical testing. The material properties are listed in Table 1.

[0019] Example 2 Linear copolymer PBAT is synthesized by a two-stage reaction of esterification, pre-polycondensation and melt polycondensation.

[0020] Terephthalic acid (1.2 mol), 1,4-butanediol (3.6 mol), and tetrabutyl titanate (0.0002 mol) are placed in a 1000 ml glass three-necked flask equipped with a condenser, thermometer, and overhead stirrer under a nitrogen atmosphere and stirred at 80°C for 0.5 hours. The reaction is then carried out at 210°C for 3 hours until the clear point is reached (homogenization of the mixture of 1,4-butanediol and terephthalic acid), and then for another 2 hours at this temperature, respectively. The esterification process is carried out until more than 90% of the theoretical water yield is released. In the second stage of esterification, 0.8 mol of adipic acid, 0.0002 mol of tetrabutyl titanate, and an additional 0.5 mol of 1,4-butanediol, equivalent to the amount of tetrahydrofuran released, are added to the reactor. The temperature is increased to 180°C, and the reaction mixture is stirred at this temperature under a nitrogen atmosphere for 4 hours.The esterification process is continued until more than 90% of the theoretical water yield is released. In the subsequent pre-polycondensation stage, after the addition of a catalytic amount of 0.0002 mol tetrabutyl titanate, the flask is connected to a vacuum pump via a trap, and the reaction mixture is heated to 220°C and pre-polycondensation is carried out at a pressure of 50 Torr for 2 hours. The pressure is then reduced to 3 Torr, and the reaction is carried out for an additional 3 hours. The temperature of the reaction mixture is then increased to 240°C, and the polycondensation stage is carried out at a pressure of 0.1 Torr for 3 hours. The hot copolymer melt is unloaded from the flask, cooled, and subjected to mechanical testing. The material properties are listed in Table 1.

[0021] Example 3 Linear copolymer PBAT is synthesized by a two-stage reaction of esterification, pre-polycondensation and melt polycondensation.

[0022] Terephthalic acid (0.8 mol), 1,4-butanediol (2.4 mol), and tetrabutyl titanate (0.0002 mol) are placed in a 1000 ml glass three-necked flask equipped with a condenser, thermometer, and overhead stirrer under a nitrogen atmosphere and stirred at 80°C for 0.5 hours. The reaction is then carried out at 200°C for 3 hours until the clear point is reached (homogenization of the mixture of 1,4-butanediol and terephthalic acid), and then for another 2 hours at this temperature, respectively. The esterification process is carried out until more than 90% of the theoretical water yield is released. In the second stage of esterification, 1.2 mol of adipic acid, 0.0002 mol of tetrabutyl titanate, and an additional 0.3 mol of 1,4-butanediol, equivalent to the amount of tetrahydrofuran released, are added to the reactor. The temperature is increased to 180°C, and the reaction mixture is stirred at this temperature under a nitrogen atmosphere for 3 hours.The esterification process is continued until more than 90% of the theoretical water yield is recovered. In the subsequent pre-polycondensation stage, after the addition of a catalytic amount of 0.0002 mol tetrabutyl titanate, the flask is connected to a vacuum pump via a trap, and the reaction mixture is heated to 220°C and pre-polycondensation is carried out at a pressure of 150 Torr for 3 hours. The pressure is then reduced to 5 Torr, and the reaction is continued for another 3 hours. The reaction mixture temperature is then increased to 240°C, and the polycondensation stage is carried out at a pressure of 0.5 Torr for 4 hours. The hot copolymer melt is removed from the flask, cooled, and subjected to mechanical testing. The material properties are listed in Table 1.

[0023] Table 1 - Mechanical properties of PBAT films.

[0024] № Film thickness, µm Tensile strength, MPa Young's modulus, MPa Relative elongation at break, % Example 1 47±9 25±1 42±2 1210±80 Example 2 63±10 30±5 114±1 1040±40 Example 3 60±12 11±1 46±5 820±140

[0025] Thus, the proposed method results in a purer final product, high molecular weight poly(butylene adipate-co-terephthalate), with more complete conversion of monomers.

Claims

A method for producing poly(butylene adipate-co-terephthalate) in which terephthalic acid, adipic acid, 1,4-butanediol and tetrabutyl titanate are used as raw materials and poly(butylene adipate-co-terephthalate) is obtained by sequentially carrying out two stages of esterification and polycondensation, characterized in that after two stages of esterification, a pre-polycondensation stage is carried out before the polycondensation stage, in the first stage of the esterification reaction, terephthalic acid, tetrabutyl titanate and 1,4-butanediol are placed in a reactor in a nitrogen atmosphere in a ratio of 0.8-1.2: 0.0002: 2.4-3.6 mol, respectively, and stirred at 80 °C for 0.5 h, then the esterification reaction is carried out at a temperature of 200-210 °C for 3 h until homogenization of the mixture consisting of 1,4-butanediol and terephthalic acid is achieved, and then the first stage of the esterification reaction is continued for another 2 h at this temperature, in the second stage of the esterification reaction, adipic acid, tetrabutyl titanate and 1,4-butanediol are added to the reactor in a ratio of 0.8-1.2: 0.0002: 0.3-0.5 mol, respectively, then the temperature is increased to 180 °C, and the reaction mixture is stirred in a nitrogen atmosphere for 3-4 h, after which tetrabutyl titanate is added in an amount of 0.0002 mol and the reaction mass is heated to 210-220 °C and a pre-polycondensation stage is carried out under pressure 50-150 Torr for 2-3 hours, then the pressure is reduced to 3-5 Torr and pre-polycondensation is carried out for another 2-3 hours, after which the temperature of the reaction mixture is increased to 230-240 °C and the polycondensation reaction is carried out at a pressure of 0.1-0.5 Torr for 3-4 hours.

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