Aliphatic-aromatic copolyester and application thereof

Abstract

The invention provides aliphatic-aromatic copolyester and application thereof. The aliphatic-aromatic copolyester comprises dibasic acid residues and dihydric alcohol residues, the dibasic acid residues comprise 8-92 mol% of terephthalic acid residues and 8-92 mol% of succinic acid residues in terms of the total molar percentage content of the dibasic acid residues being 100 mol%; the dihydric alcohol residues are selected from aliphatic dihydric alcohol residues which are at least equal to the dibasic acid residues in molar weight; the mass percentage content of an oligomer obtained through a volume exclusion chromatography test in the aliphatic-aromatic copolyester is less than or equal to 2.4%. In the invention, a film prepared from the aliphatic-aromatic copolyester has excellent water vapor barrier property, low haze and fewer film crystal points.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to an aliphatic-aromatic copolyester and its applications. Background Technology

[0002] Poly(1,4-butanediol) terephthalic acid-adipic acid copolymer (PBAT) is a biodegradable polyester based on terephthalic acid, adipic acid, and butanediol monomers. This material exhibits excellent biodegradability, good flexibility, and compostability, making it suitable for various processing techniques such as injection molding, extrusion molding, and blown film production. It currently has wide applications in the field of film and bag products.

[0003] However, the ductility, flatness, and barrier properties of PBAT films still need improvement, and their optical properties such as haze cannot meet current commercial needs. These limitations, to some extent, hinder the wider promotion and application of PBAT materials.

[0004] Therefore, developing an aliphatic-aromatic copolyester that combines high water vapor barrier properties, low haze, and fewer crystal points in the film after film formation is an urgent problem to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an aliphatic-aromatic copolyester and its applications. This aliphatic-aromatic copolyester solves the problem that PBAT films in the prior art cannot simultaneously possess high water vapor barrier properties, low haze, and a small number of film crystal points.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides an aliphatic-aromatic copolyester comprising diacid residues and diol residues; based on a total molar percentage of 100 mol% for the diacid residues, the diacid residues comprise 8-92 mol% for terephthalic acid residues and 8-92 mol% for succinic acid residues; the diol residues are selected from aliphatic diol residues in at least an equimolar amount with the diacid residues; and the mass percentage of oligomers obtained by volume exclusion chromatography in the aliphatic-aromatic copolyester is ≤2.4%.

[0007] In this invention, succinic acid residues are used instead of adipic acid residues and compounded with terephthalic acid residues to form an aliphatic-aromatic copolyester with high water vapor barrier properties. Furthermore, oligomers can act as heterogeneous nucleation sites to promote polyester crystallization, which is beneficial to further improve the water vapor barrier properties of the polyester and reduce the haze of the material. By controlling the oligomer content in the aliphatic-aromatic copolyester within a specific range, the polyester can crystallize more uniformly during film formation, resulting in a material that combines low haze, excellent water vapor barrier properties, and fewer crystal points.

[0008] In this invention, the mass percentage of oligomers obtained by volume exclusion chromatography in the aliphatic-aromatic copolyester is ≤2.4%, for example, it can be 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.3% or any range of the above values; preferably, the mass content of oligomers in the aliphatic-aromatic copolyester is 0.6~2.3%.

[0009] In this invention, if the oligomer content obtained by volume exclusion chromatography is too high, the overall molecular chain regularity of the polyester is destroyed, the spherulite morphology varies greatly, and the haze increases. In addition, it will affect the crystallization uniformity and increase the number of crystal points. If the content is too low, the polyester crystallizes slowly and secondary crystallization is more likely to occur, which also leads to increased haze. Furthermore, it affects the crystallization rate, resulting in reduced processing performance and poor water vapor barrier performance.

[0010] In this invention, the number-average molecular weight of the oligomers obtained by volume exclusion chromatography is ≤3000 g / mol.

[0011] Preferably, the aliphatic-aromatic copolyester contains oligomers with a molecular weight ≤3000 g / mol as determined by mass spectrometry, for example, 172 g / mol, 344 g / mol, 516 g / mol, 688 g / mol, 860 g / mol, 1032 g / mol, 1204 g / mol, 1376 g / mol, 1548 g / mol, 1720 g / mol, 1892 g / mol, 2064 g / mol, 2236 g / mol, 2408 g / mol, 2580 g / mol, 2752 g / mol, 2924 g / mol, or any range of the above values.

[0012] The oligomers with a molecular weight ≤3000 g / mol obtained by mass spectrometry testing include oligomers with a molecular weight of 500~1000 g / mol, and their mass percentage content in the oligomers with a molecular weight ≤3000 g / mol is more than 50%, for example, it can be 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95% or any range of the above values, preferably 55~88%, more preferably 70~85%.

[0013] In this invention, the mass percentage of oligomers with a molecular weight of 500-1000 g / mol obtained by mass spectrometry within oligomers with a molecular weight of ≤3000 g / mol is within a specific range, which is beneficial for balancing a smaller number of crystal points, high water vapor barrier performance, and low haze. If the proportion of oligomers with a molecular weight of 500-1000 g / mol is too high, the crystallization will be uneven and the number of crystal points will increase; if the proportion is too low, the water vapor barrier performance will be poor and the number of crystal points will also increase.

[0014] In this invention, based on a total molar percentage of 100 mol% for the dicarboxylic acid residues, the dicarboxylic acid residues comprise 8-92 mol% of terephthalic acid residues (for example, 10 mol%, 15 mol%, 20 mol%, 25 mol%, 30 mol%, 35 mol%, 40 mol%, 45 mol%, 50 mol%, 55 mol%, 60 mol%, 65 mol%, 70 mol%, 75 mol%, 80 mol%, 85 mol%, 90 mol%, or any range of the above values) and 8-92 mol% of succinic acid residues (…). For example, it can be 10 mol%, 15 mol%, 20 mol%, 25 mol%, 30 mol%, 35 mol%, 40 mol%, 45 mol%, 50 mol%, 55 mol%, 60 mol%, 65 mol%, 70 mol%, 75 mol%, 80 mol%, 85 mol%, 90 mol%, or any range of the above values), more preferably, the total molar percentage of the dicarboxylic acid residues is 100 mol%, and the dicarboxylic acid residues include 28-72 mol% terephthalic acid residues and 28-72 mol% succinic acid residues.

[0015] Preferably, the aliphatic diol residues include at least one of ethylene glycol residues, 1,3-propanediol residues, 1,4-butanediol residues, 1,5-pentanediol residues, 1,6-hexanediol residues, and 1,10-decanediol residues, and more preferably at least 1,4-butanediol residues.

[0016] It should be noted that, in this invention, "residue" refers to any organic structure introduced into the polymer molecular chain by the relevant monomer through a polycondensation reaction, that is, an organic structure derived from the relevant monomer; for example, diacid residues refer to structures in copolyesters derived from diacid monomers.

[0017] In this invention, terephthalic acid and / or terephthalic acid derivatives are introduced into the molecular chain of the copolyester through a polymerization reaction to form terephthalic acid residues; succinic acid and / or succinic acid derivatives are introduced into the molecular chain of the copolyester through a polymerization reaction to form succinic acid residues; the terephthalic acid derivatives include dialkyl terephthalate, and exemplarily, the dialkyl terephthalate includes, but is not limited to, dimethyl terephthalate, diethyl terephthalate, di-n-propyl terephthalate, and dimethyl terephthalate. The succinic acid derivative comprises at least one of diisopropyl formate, di-n-butyl terephthalate, di-n-pentyl terephthalate, and di-n-hexyl terephthalate; the succinic acid derivative includes dialkyl succinates, which include, but are not limited to, at least one of dimethyl succinate, diethyl succinate, di-n-propyl succinate, diisopropyl succinate, di-n-butyl succinate, diisobutyl succinate, di-tert-butyl succinate, di-n-pentyl succinate, diisopentyl succinate, and di-n-hexyl succinate.

[0018] Preferably, the intrinsic viscosity of the aliphatic-aromatic copolyester is 1~1.5 dL / g, for example, it can be 1 dL / g, 1.02 dL / g, 1.05 dL / g, 1.08 dL / g, 1.1 dL / g, 1.12 dL / g, 1.15 dL / g, 1.18 dL / g, 1.2 dL / g, 1.22 dL / g, 1.25 dL / g, 1.26 dL / g, 1.28 dL / g, 1.3 dL / g, 1.32 dL / g, 1.35 dL / g, 1.38 dL / g, 1.4 dL / g, 1.42 dL / g, 1.45 dL / g, 1.48 dL / g, or any range of the above values.

[0019] In this invention, the intrinsic viscosity test method is as follows: according to GB / T 17931-1999 standard, the intrinsic viscosity of aliphatic-aromatic polyester in a mixed solution of phenol and tetrachloroethane (mass ratio w / w=3 / 2) at 25±0.01℃ is tested, and the mass concentration of aliphatic-aromatic polyester is 0.005g / mL.

[0020] In this invention, the preparation method of the aliphatic-aromatic copolyester is not particularly limited, and any method capable of preparing the aliphatic-aromatic copolyester with oligomer content and specific structural composition of this invention is acceptable; preferably, the preparation method of the copolyester includes the following steps: (1) Esterification reaction of terephthalic acid and / or terephthalic acid derivatives, succinic acid and / or succinic acid derivatives with diol to obtain esterified products; (2) Polycondensation reaction of the esterified products, followed by post-treatment, to obtain the aliphatic-aromatic copolyester.

[0021] In this invention, the ratio of the total molar amount of terephthalic acid and / or terephthalic acid derivatives and succinic acid and / or succinic acid derivatives to the molar amount of diol in step (1) is 1:(1.2~1.4).

[0022] In this invention, the source of the terephthalic acid and / or terephthalic acid derivatives, succinic acid and / or succinic acid derivatives, and diols is not particularly limited. They can be derived from bio-based terephthalic acid and / or terephthalic acid derivatives, succinic acid and / or succinic acid derivatives, and diols (i.e., the raw material for preparation is biomass resources), or from petroleum-based terephthalic acid and / or terephthalic acid derivatives, succinic acid and / or succinic acid derivatives, and diols (i.e., the raw material for preparation is petroleum resources). The choice can be made according to actual needs.

[0023] In this invention, the esterification reaction in step (1) is carried out in the presence of a protective atmosphere, which includes, but is not limited to, nitrogen; the temperature of the esterification reaction is 220~242℃, the time is 1~6h, the pressure is atmospheric pressure, and the stirring rate is 30~40Hz; the temperature of the polycondensation reaction in step (2) is 230~255℃, the pressure is 10~100Pa, the polymerization reaction is carried out in the forward direction by removing the water formed, and the polycondensation reaction is stopped when the stirring power reaches a fixed torque value (the fixed torque value is 8~18Hz / 200W, preferably 9~16Hz / 200W).

[0024] In this invention, the post-processing in step (2) includes: washing and / or refluxing the product obtained from the polycondensation reaction; the washing method includes: treating the product obtained from the polycondensation reaction with an organic solvent under ultrasonic conditions (room temperature, ultrasonic power of 50~150W) for 4min~65min; the organic solvent includes tetrahydrofuran and / or alcohol compounds; the alcohol compounds include, but are not limited to, ethanol; the organic solvent includes tetrahydrofuran and alcohol compounds, and the volume ratio of tetrahydrofuran and alcohol compounds is (5~9):(1~5); the reflux temperature is 50~90℃, and the time is 10~80min.

[0025] In this invention, the aliphatic-aromatic copolyester can also be prepared by a stepwise esterification method. Exemplarily, the preparation method includes the following steps: (S1) A diol with a molar ratio of (1.2~1.4):1 and succinic acid are placed in a stainless steel reactor and esterified for 1~5 hours at 150~180℃ and atmospheric pressure under a protective atmosphere to obtain an esterified product; then the temperature is raised to 220~260℃ and a prepolymerization reaction is carried out at 100~600Pa. During the reaction, the intrinsic viscosity of the prepolymer is tested. When the intrinsic viscosity reaches 0.2~0.8dL / g, the reaction is stopped to obtain prepolymer A. (S2) A diol with a molar ratio of (1.2~1.4):1 and terephthalic acid are placed in a stainless steel reactor and esterified at 200~260℃ and atmospheric pressure for 1~8 hours under a protective atmosphere to obtain the esterified product; then the temperature is raised to 220~280℃ and a prepolymerization reaction is carried out at 100~500Pa. During the reaction, the intrinsic viscosity of the prepolymer is tested. When the intrinsic viscosity reaches 0.2~0.8dL / g, the reaction is stopped to obtain prepolymer B. (S3) Prepolymer A and prepolymer B are mixed, and then optional catalyst and stabilizer are added. The polymerization reaction is carried out in the forward direction by removing the water formed at 230~260°C and 10~100Pa. The polymerization reaction is stopped when the stirring power reaches a fixed torque value (the fixed torque value is 8~18Hz / 200W, preferably 9~16Hz / 200W) to obtain the aliphatic-aromatic polyester.

[0026] In this invention, the raw materials for the esterification reaction in step (1) and the polycondensation reaction in step (S3) each independently include at least one of a catalyst or a stabilizer; the mass percentage of the catalyst is 0.005~1wt% based on a total mass of 100wt% of the diacid and diol; the catalyst includes, but is not limited to, at least one of tin-based catalysts, antimony-based catalysts, germanium-based catalysts, titanium-based catalysts, or aluminum-based catalysts; the tin-based catalyst includes at least one of dimethyltin oxide, stannous isooctanoate, dibutyltin oxide, monobutyltriisooctanoate, and dioctyltin oxide; the antimony-based catalyst includes antimony acetate, antimony trioxide, antimony glycol, and polyethylene glycol. At least one of antimony alkoxides; the germanium-based catalyst includes germanium dioxide; the titanium-based catalyst includes at least one of tetrabutyl titanate, isopropyl titanate, titanium dioxide, and inorganic supported titanium catalyst; the aluminum-based catalyst includes aluminum chloride and / or aluminum oxide; the stabilizer has a mass percentage content of 0.02~2wt% based on a total mass of 100wt% of diacids and diols; the stabilizer includes, but is not limited to, phosphorus-based stabilizers; the phosphorus-based stabilizers include at least one of diphenyl phosphate, triphenyl phosphite, trimethyl phosphate, dimethyl phosphate, triphenyl phosphate, diphenyl phosphite, ammonium phosphite, ammonium dihydrogen phosphate, phosphorous acid, hypophosphite, pyrophosphate, and ammonium phosphate.

[0027] In this invention, in the esterification reaction in step (1) and the polycondensation reaction in step (S3), the catalysts each independently include tetrabutyl titanate and / or dibutyltin oxide. The mass ratio of the tetrabutyl titanate and dibutyltin oxide is (1.8~4.2):(5.8~8.2).

[0028] In this invention, the aliphatic-aromatic copolyester can also be prepared by the following method: (I) The aliphatic-aromatic copolyester with an oligomer content >2.4% obtained by volume exclusion chromatography was prepared by post-treatment.

[0029] In this invention, the post-processing method in step (I) includes washing and / or reflux.

[0030] In this invention, the washing and reflux methods used in step (I) are selected from the same range as those in step (2).

[0031] In a second aspect, the present invention provides a film or bag comprising the aliphatic-aromatic copolyester described in the first aspect.

[0032] Preferably, the water vapor permeability coefficient of the membrane or bag is ≤450g / 24h·m 2 More preferably, it is 316~440 g / 24h·m 2 .

[0033] Preferably, the haze of the membrane or bag is ≤40%, more preferably 22~37%.

[0034] In this invention, the mass percentage of aliphatic-aromatic copolyester in the film or bag is ≥50%; the film or bag may also contain additives as needed; the additives include, but are not limited to, at least one of antioxidants, lubricants, or light stabilizers.

[0035] In this invention, the types of additives are not limited too much; conventional additives can be used. For example, the antioxidants include, but are not limited to, any one of antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant 164, antioxidant DLTP, or antioxidant TPP.

[0036] The light stabilizers include, but are not limited to, at least one of hindered amine light stabilizers (such as light stabilizer 770, light stabilizer 622, light stabilizer 944, etc.), benzophenone light stabilizers (such as UV531), or benzotriazole light stabilizers.

[0037] The lubricant includes, but is not limited to, at least one of esters (such as polyethylene glycol esters, polyol esters), lignite salts, ethylene bis-stearamide, or polyethylene wax.

[0038] In this invention, based on 100 parts by weight of the aliphatic-aromatic copolyester, the mass of the auxiliary agent can be 0.1 to 10 parts.

[0039] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows: The aliphatic-aromatic copolyester provided by the present invention uses succinic acid residues instead of adipic acid residues and is compounded with terephthalic acid residues. At the same time, the mass content of oligomers in the aliphatic-aromatic copolyester is controlled within a specific range, so that the material including the aliphatic-aromatic copolyester has excellent water vapor barrier properties, low haze and fewer film crystal points. Detailed Implementation

[0041] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0042] In this invention, all materials used can be purchased commercially or prepared using conventional methods. Unless otherwise specified, the materials used in this invention are as follows, and unless otherwise specified, dicarboxylic acid and diol refer to ortho-dicarboxylic acid and ortho-diol.

[0043] Terephthalic acid: Dixin Chemical, purity > 99.0%.

[0044] Succinic acid: Shandong Landian, bio-based, purity > 99.0%.

[0045] Adipic acid: Huafeng Group, refined adipic acid.

[0046] 1,4-Butanediol: Tunhe, Lanshan, Xinjiang, with a purity of 99.7%.

[0047] Ethylene glycol: Hualu Hengsheng, polyester grade ethylene glycol.

[0048] Tetrabutyl titanate, trimethyl phosphate, and dibutyltin oxide are all commercially available.

[0049] In this invention, the structural composition of the aliphatic-aromatic copolyester, the content of oligomers with a number average molecular weight ≤3000 g / mol, and the mass percentage of oligomers with a molecular weight of 500~1000 g / mol in the oligomers with a molecular weight ≤3000 g / mol obtained by mass spectrometry are tested as follows.

[0050] 1. Structural Composition In this invention, a proton nuclear magnetic resonance (NMR) spectrometer (manufacturer: Bruker, model: AV500) was used to characterize the structure of the copolyester. Specifically, 20-50 mg of the copolyester sample was dissolved in deuterated chloroform containing tetramethylsilane, and then the structure of the copolyester was determined using a proton NMR spectrometer at room temperature. 1 HNMR; the characteristic peaks of diacids are integrated, and the composition of diacid residues in aliphatic-aromatic copolyesters is obtained by the proportion of peak areas; wherein the molar ratio of diacid residues to diol residues is 1:1.

[0051] For example, taking terephthalic acid residues and succinic acid residues as examples, the characteristic chemical shift peaks of terephthalic acid residues and succinic acid residues (the characteristic chemical shift of succinic acid residues is approximately 2.63 ppm, representing the hydrogen on the methylene group in succinic acid; the characteristic chemical shift of terephthalic acid residues is approximately 8.10 ppm, representing the hydrogen on the benzene ring) are integrated, and the composition of dicarboxylic acid residues in the aliphatic-aromatic copolyester is obtained by the proportion of peak areas. For example, if the integrated area of ​​succinic acid residues is I1 and the integrated area of ​​terephthalic acid residues is I2, then the molar percentage of succinic acid residues in the aliphatic-aromatic copolyester, calculated as 100 mol% of the total molar percentage of succinic acid residues and terephthalic acid residues, is I1 / (I1+I2)×100%. The structural composition of the aliphatic-aromatic copolyester is shown in Tables 1-3.

[0052] 2. Oligomer content with a number average molecular weight ≤ 3000 g / mol The test was performed using volume exclusion chromatography (SEC), referring to GB / T 36214.1-2018. Specifically, 1~2 mg of aliphatic-aromatic copolyester sample was dissolved in 1 mL of chloroform, and then tested using volume exclusion chromatography (manufacturer: Agilent, model: PL-GPC220) at 40℃.

[0053] When quantifying oligomer content, an Agilent narrow-distribution low molecular weight polystyrene standard (nominal molecular weight 162-7000 Da) needs to be used to establish a molecular weight standard curve for the oligomers. A linear relationship is obtained by fitting the retention time logarithm-average molecular weight. Subsequently, the sample is tested and the peak area (A) of the molecular weight ≤3000 is integrated. ≤3000 ) and total polymer peak area (A totalThe formula for calculating the oligomer content is: (A) ≤3000 / A total )×100%.

[0054] 3. Mass percentage of oligomers with a molecular weight of 500-1000 g / mol in oligomers with a molecular weight ≤3000 g / mol as determined by mass spectrometry. High-resolution mass spectrometry (LC-TOF-MS) was used for detection (waters, Xevo G3). Acetonitrile and water were used as the mobile phase in liquid chromatography at a flow rate of 0.4 mL / min, and the mass spectrometry was performed in positive ion mode. Aliphatic-aromatic copolyester samples were dissolved in a 1:1 volume ratio of THF to acetonitrile (concentration 1 ppm) and filtered through a 0.22 μm filter membrane before injection.

[0055] Examples 1-14, Comparative Examples 1-2 Examples 1-14 and Comparative Examples 1-2 each provide an aliphatic-aromatic copolyester, wherein the aliphatic-aromatic copolyester has a structural composition and an oligomer content (labeled as M) of a number-average molecular weight ≤3000. ≤3000 The mass percentage of oligomers with a molecular weight of 500~1000 g / mol in oligomers with a molecular weight of ≤3000 g / mol (labeled as M). 500-1000 As shown in Tables 1-3; “ / ” indicates that the aliphatic-aromatic copolyester does not contain this residue.

[0056] The preparation methods of aliphatic-aromatic copolyesters provided in Examples 1-5 of this invention include: Diol and diacid were added to a stainless steel reactor according to the formula, followed by tetrabutyl titanate and trimethyl phosphate. The mixture was stirred for 3 hours at 230°C, atmospheric pressure, and a stirring rate of 35 Hz under high-purity nitrogen protection. The temperature was then increased to 240°C under stirring, and the pressure was gradually reduced to 80 Pa under constant temperature of 240°C. The polymerization reaction was carried out in the forward direction by removing the water formed. When the torque of the stirring paddle reached the target value (10 Hz / 200 W), the pressure was gradually reduced to atmospheric pressure and the material was discharged. The obtained material was washed for 5 minutes at room temperature and under ultrasonic conditions (ultrasonic power of 100 W) with a mixed solvent of ethanol and tetrahydrofuran (volume ratio of tetrahydrofuran to ethanol of 7:3) to obtain the aliphatic-aromatic copolyester. The molar ratio of diol to diacid is 1.3:1, the mass of tetrabutyl titanate is 0.1% of the total mass of diacid and diol, and the mass of trimethyl phosphate is 0.05% of the total mass of diacid and diol.

[0057] Table 1 Table 2 Table 3 In the preparation method of aliphatic-aromatic copolyester provided in Example 6, the polycondensation temperature is 250°C, that is, the pressure is gradually reduced to 80 Pa under constant temperature conditions of 250°C, and other parameters are the same as in Example 1.

[0058] In the preparation method of the aliphatic-aromatic copolyester provided in Comparative Example 1, the esterification reaction temperature is 235°C, the time is 4h, and the polycondensation temperature is 245°C, that is, stirring at 235°C for 4h under high-purity nitrogen protection, and then raising the temperature to 245°C under stirring, and gradually reducing the pressure to 80Pa under constant temperature at 245°C. Other parameters are the same as in Example 3.

[0059] The preparation methods for Examples 7-14 and Comparative Example 2 are as follows: Example 7 Diol and diacid were added to a stainless steel reactor according to the formula, followed by tetrabutyl titanate and trimethyl phosphate. The mixture was stirred for 3 hours at 230°C, atmospheric pressure, and a stirring rate of 35 Hz under high-purity nitrogen protection. The temperature was then increased to 240°C under stirring, and the pressure was gradually reduced to 80 Pa under constant temperature of 240°C. The polymerization reaction was carried out in the forward direction by removing the water formed. When the torque of the stirring paddle reached the target value (10 Hz / 200 W), the pressure was gradually reduced to atmospheric pressure and the material was discharged. The obtained material was washed for 1 hour at room temperature and under ultrasonic conditions (ultrasonic power of 100 W) with a mixed solvent of ethanol and tetrahydrofuran (volume ratio of tetrahydrofuran to ethanol of 7:3) to obtain the aliphatic-aromatic copolyester. The molar ratio of diol to diacid is 1.3:1, the mass of tetrabutyl titanate is 0.1% of the total mass of diacid and diol, and the mass of trimethyl phosphate is 0.05% of the total mass of diacid and diol.

[0060] Example 8 Diol and diacid were added to a stainless steel reactor according to the formula, followed by tetrabutyl titanate and trimethyl phosphate. The mixture was stirred for 3 hours at 230°C, atmospheric pressure, and a stirring rate of 35 Hz under high-purity nitrogen protection. The temperature was then increased to 240°C under stirring, and gradually reduced to 80 Pa under constant temperature of 240°C. The resulting water was removed to allow the polymerization reaction to proceed in the forward direction. When the torque of the agitator reached the target value (10 Hz / 200 W), the pressure was gradually reduced to atmospheric pressure, and the material was discharged. The obtained material was washed ultrasonically for 20 minutes with a mixed solvent of ethanol and tetrahydrofuran (volume ratio of tetrahydrofuran to ethanol 7:3) to obtain the aliphatic-aromatic copolyester. The molar ratio of diol to diacid was 1.3:1, the mass of tetrabutyl titanate was 0.1% of the total mass of the diacid and diol, and the mass of trimethyl phosphate was 0.05% of the total mass of the diacid and diol.

[0061] Example 9 The aliphatic-aromatic copolyester obtained in Comparative Example 2 was washed with tetrahydrofuran at room temperature and under ultrasonic conditions (ultrasonic power of 100W) for 30 minutes to obtain the aliphatic-aromatic copolyester.

[0062] Example 10 (S1) 1,4-Butanediol and succinic acid in a molar ratio of 1.3:1 were placed in a stainless steel reactor and esterified at 160°C and atmospheric pressure for 3 hours under high-purity nitrogen protection to obtain the esterified product; then the temperature was raised to 240°C and a prepolymerization reaction was carried out at 400 Pa. During the reaction, samples were taken and the intrinsic viscosity of the prepolymer was tested using the aforementioned method. When the intrinsic viscosity reached 0.45 dL / g, the reaction was stopped to obtain prepolymer A. (S2) 1,4-Butanediol and terephthalic acid in a molar ratio of 1.3:1 were placed in a stainless steel reactor and esterified at 230°C and atmospheric pressure for 4 hours under high-purity nitrogen protection to obtain the esterified product. Then, the temperature was raised to 240°C and a prepolymerization reaction was carried out at 300 Pa. During the reaction, samples were taken and the intrinsic viscosity of the prepolymer was tested using the aforementioned method. When the intrinsic viscosity reached 0.42 dL / g, the reaction was stopped to obtain prepolymer B. (S3) Prepolymer A and prepolymer B are mixed, and then a catalyst and trimethyl phosphate are added. The pressure is gradually reduced to 80 Pa under constant temperature of 240°C. The polymerization reaction proceeds in the forward direction by removing the water formed. When the torque of the agitator reaches the target value (10 Hz / 200 W), the pressure is gradually reduced to atmospheric pressure and the product is discharged to obtain the aliphatic-aromatic copolyester. The mass of the catalyst is 0.1% of the total mass of the diacid and diol. The catalyst is composed of tetrabutyl titanate (TBT) and dibutyltin oxide (DBTO, Merck, 98%) in a mass ratio of 3:7. The mass of trimethyl phosphate is 0.05% of the total mass of the diacid and diol.

[0063] Example 11 (S1) 1,4-Butanediol and succinic acid in a molar ratio of 1.3:1 were placed in a stainless steel reactor and esterified at 160°C and atmospheric pressure for 3 hours under high-purity nitrogen protection to obtain the esterified product; then the temperature was raised to 240°C and a prepolymerization reaction was carried out at 400 Pa. During the reaction, samples were taken and the intrinsic viscosity of the prepolymer was tested using the aforementioned method. When the intrinsic viscosity reached 0.6 dL / g, the reaction was stopped to obtain prepolymer A. (S2) 1,4-Butanediol and terephthalic acid in a molar ratio of 1.3:1 were placed in a stainless steel reactor and esterified at 230°C and atmospheric pressure for 4 hours under high-purity nitrogen protection to obtain the esterified product. Then, the temperature was raised to 240°C and a prepolymerization reaction was carried out at 300 Pa. During the reaction, samples were taken and the intrinsic viscosity of the prepolymer was tested using the aforementioned method. When the intrinsic viscosity reached 0.52 dL / g, the reaction was stopped to obtain prepolymer B. (S3) Prepolymer A and prepolymer B are mixed, and then a catalyst and trimethyl phosphate are added. The pressure is gradually reduced to 80 Pa under constant temperature of 240°C. The polymerization reaction proceeds in the forward direction by removing the water formed. When the torque of the agitator reaches the target value (10 Hz / 200 W), the pressure is gradually reduced to atmospheric pressure and the product is discharged to obtain the aliphatic-aromatic copolyester. The mass of the catalyst is 0.1% of the total mass of the diacid and diol. The catalyst is composed of tetrabutyl titanate (TBT) and dibutyltin oxide (DBTO, Merck, 98%) in a mass ratio of 4:6. The mass of trimethyl phosphate is 0.05% of the total mass of the diacid and diol.

[0064] Example 12 (S1) 1,4-Butanediol and succinic acid in a molar ratio of 1.3:1 were placed in a stainless steel reactor and esterified at 160°C and atmospheric pressure for 3 hours under high-purity nitrogen protection to obtain the esterified product; then the temperature was raised to 240°C and a prepolymerization reaction was carried out at 500 Pa. During the reaction, samples were taken and the intrinsic viscosity of the prepolymer was tested using the aforementioned method. When the intrinsic viscosity reached 0.68 dL / g, the reaction was stopped to obtain prepolymer A. (S2) 1,4-Butanediol and terephthalic acid in a molar ratio of 1.3:1 were placed in a stainless steel reactor and esterified at 230°C and atmospheric pressure for 3 hours under high-purity nitrogen protection to obtain the esterified product. Then, the temperature was raised to 240°C and a prepolymerization reaction was carried out at 400 Pa. During the reaction, samples were taken and the intrinsic viscosity of the prepolymer was tested using the aforementioned method. When the intrinsic viscosity reached 0.62 dL / g, the reaction was stopped to obtain prepolymer B. (S3) Prepolymer A and prepolymer B are mixed, and then tetrabutyl titanate and trimethyl phosphate are added. The pressure is gradually reduced to 80 Pa under constant temperature of 235°C. The polymerization reaction proceeds in the forward direction by removing the water formed. When the torque of the agitator reaches the target value (10Hz / 200W), the pressure is gradually reduced to atmospheric pressure and the product is discharged to obtain the aliphatic-aromatic copolyester. The mass of tetrabutyl titanate is 0.1% of the total mass of the diacid and diol, and the mass of trimethyl phosphate is 0.05% of the total mass of the diacid and diol.

[0065] Example 13 Diol and diacid were added to a stainless steel reactor according to the formula, followed by tetrabutyl titanate and trimethyl phosphate. The mixture was stirred for 3 hours at 230°C, atmospheric pressure, and a stirring rate of 35 Hz under high-purity nitrogen protection. The temperature was then increased to 240°C under stirring, and the pressure was gradually reduced to 80 Pa under constant temperature of 240°C. The polymerization reaction was carried out in the forward direction by removing the water formed. When the torque of the stirring paddle reached the target value (15 Hz / 200 W), the pressure was gradually reduced to atmospheric pressure and the material was discharged. The obtained material was washed with tetrahydrofuran at room temperature under ultrasonic conditions (ultrasonic power of 100 W) for 10 minutes, and then heated and refluxed at 70°C for 30 minutes to obtain the aliphatic-aromatic copolyester. The molar ratio of diol to diacid is 1.3:1, the mass of tetrabutyl titanate is 0.12% of the total mass of diacid and diol, and the mass of trimethyl phosphate is 0.05% of the total mass of diacid and diol.

[0066] Example 14 Diol and diacid were added to a stainless steel reactor according to the formula, followed by a catalyst and trimethyl phosphate. The mixture was stirred for 3 hours at 230°C, atmospheric pressure, and a stirring rate of 35 Hz under high-purity nitrogen protection. The temperature was then increased to 240°C under stirring, and gradually reduced to 80 Pa under constant temperature of 240°C. The resulting water was removed to allow the polymerization reaction to proceed in the forward direction. When the stirring torque reached the target value (10 Hz / 200 W), the pressure was gradually reduced to atmospheric pressure, and the product was discharged to obtain the aliphatic-aromatic copolyester. The molar ratio of diol to diacid was 1.3:1, the catalyst mass was 0.09% of the total mass of the diacid and diol, and the catalyst was a combination of TBT and DBTO with a mass ratio of 2:8; the trimethyl phosphate mass was 0.05% of the total mass of the diacid and diol.

[0067] Comparative Example 2 Diol and diacid were added to a stainless steel reactor according to the formula, followed by tetrabutyl titanate and trimethyl phosphate. The mixture was stirred for 3 hours at 245°C, atmospheric pressure, and a stirring rate of 35 Hz under high-purity nitrogen protection. The temperature was then increased to 250°C and gradually reduced to 80 Pa under constant temperature of 250°C. The resulting water was removed to allow the polymerization reaction to proceed in the forward direction. When the torque of the agitator reached the target value (5 Hz / 200 W), the pressure was gradually reduced to atmospheric pressure, and the product was discharged to obtain the aliphatic-aromatic copolyester. The molar ratio of diol to diacid was 1.45:1, the mass of tetrabutyl titanate was 0.1% of the total mass of the diacid and diol, and the mass of trimethyl phosphate was 0.05% of the total mass of the diacid and diol.

[0068] Performance testing The aliphatic-aromatic copolyesters provided in the examples and comparative examples were used to prepare polyester films with a thickness of 30 micrometers. The specific process included: drying the copolyester resin raw material, heating and melting it through an extruder (temperature 120~160℃), then injecting compressed air into the film tube for inflation. By adjusting the inflation ratio (2.5~3) and the traction speed (5~15m / min), the polyester film was stretched laterally and longitudinally. It was then flattened and folded by traction rollers. The process parameters were monitored and adjusted in real time using an online thickness gauge to ensure that the film thickness was uniform and stable at 30 micrometers. Finally, the film was wound up. Then, the water vapor barrier properties, haze, and mechanical properties of the film were tested.

[0069] (1) Water vapor barrier performance: Under constant temperature and humidity conditions, the water vapor transmission coefficient of the film was tested using a water vapor transmission rate tester (manufacturer model: Labthink, W3 / 031). The specific method was as follows: the principle of the permeation cup weighing method was adopted. At a certain temperature, a specific humidity difference was formed on both sides of the sample. Water vapor passed through the sample in the permeation cup and entered the dry side. The water vapor transmission coefficient (WVTR) of the sample was calculated by measuring the change in weight of the permeation cup over time. The calculation formula is: WVTR = m / (t×A); where, m is the change in weight of the permeation cup during the test period (g); t is the test time (24h); A is the effective permeation area of ​​the membrane (m²). 2 ).

[0070] (2) Haze: Tested in accordance with GB / T 2410-2008 standard.

[0071] (3) Thin film crystal points: Observe the uniformity and number of crystal points on a thin film with a length of 1m and a width of 40cm. The crystal point diameter is 0.1mm-0.3mm. The number of crystal points is 0~10, which is grade 1; the number of crystal points is 10~20, which is grade 1.5; the number of crystal points is 20~30, which is grade 2; the number of crystal points is 30~40, which is grade 2.5; and the number of crystal points is above 40, which is grade 3.

[0072] The specific test results are shown in Table 4.

[0073] Table 4 As shown in Table 4, the aliphatic-aromatic copolyester provided by this invention, by using succinic acid residues instead of adipic acid residues and compounding it with terephthalic acid residues, while controlling the mass content of oligomers in the aliphatic-aromatic copolyester within a specific range, enables materials containing the aliphatic-aromatic copolyester to possess excellent water vapor barrier properties, low haze, and fewer film crystal points; the water vapor permeability coefficient of the membrane or bag is ≤450g / 24h·m. 2 The haze of the membrane or bag is ≤40%, and the crystal point level is less than 3.

[0074] As can be seen from Examples 3, 7-9 and Comparative Example 2, the oligomer can act as a heterogeneous nucleation point to promote polyester crystallization. By controlling its mass percentage content to ≤2.4%, the overall molecular chain regularity of the polyester can be avoided, and the spherulite morphology difference can be avoided. This is beneficial to make the film have lower haze and fewer crystal points, while also ensuring good water vapor barrier performance.

[0075] As can be seen from Examples 8 and 10-14, controlling the mass percentage of oligomers with a molecular weight of 500-1000 g / mol within the range of 55-88% is beneficial to further improve the water vapor barrier performance of the film and reduce the number of crystal points. If the percentage is too high, the crystallization will be uneven and the number of crystal points will increase; if the percentage is too low, the water vapor barrier performance will be worse and the number of crystal points will also increase.

[0076] As can be seen from Comparative Example 1, the aliphatic-aromatic copolyester provided by the present invention has better water vapor barrier properties than PBAT.

[0077] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An aliphatic-aromatic copolyester, characterized in that, The aliphatic-aromatic copolyester contains diacid residues and diol residues; Based on a total molar percentage of 100 mol% for dicarboxylic acid residues, the dicarboxylic acid residues comprise 8-92 mol% terephthalic acid residues and 8-92 mol% succinic acid residues. The diol residues are selected from aliphatic diol residues in at least an equimolar amount with the dicarboxylic acid residues; The mass percentage of oligomers obtained by volume exclusion chromatography in the aliphatic-aromatic copolyester is ≤2.4%.

2. The aliphatic-aromatic copolyester according to claim 1, characterized in that, The mass content of oligomers obtained by volume exclusion chromatography in the aliphatic-aromatic copolyester is 0.6-2.3%.

3. The aliphatic-aromatic copolyester according to claim 1, characterized in that, The aliphatic-aromatic copolyester contains oligomers with a molecular weight ≤3000 g / mol as determined by mass spectrometry. The oligomers with a molecular weight ≤3000 g / mol as determined by mass spectrometry contain oligomers with a molecular weight of 500~1000 g / mol, and their mass percentage content in the oligomers with a molecular weight ≤3000 g / mol is ≥50%, preferably 55~88%, more preferably 70~85%.

4. The aliphatic-aromatic copolyester according to claim 1, characterized in that, Based on a total molar percentage of 100 mol% for the dicarboxylic acid residues, the dicarboxylic acid residues comprise 28-72 mol% terephthalic acid residues and 28-72 mol% succinic acid residues.

5. The aliphatic-aromatic copolyester according to claim 1, characterized in that, The aliphatic diol residues include at least one of ethylene glycol residues, 1,3-propanediol residues, 1,4-butanediol residues, 1,5-pentanediol residues, 1,6-hexanediol residues, and 1,10-decanediol residues, preferably including at least 1,4-butanediol residues.

6. A method for preparing an aliphatic-aromatic copolyester according to any one of claims 1 to 5, characterized in that, The preparation method includes the following steps: (1) Esterification reaction of terephthalic acid and / or terephthalic acid derivatives, succinic acid and / or succinic acid derivatives with diols to obtain esterified products; (2) The esterified product is subjected to polycondensation reaction, and then post-processed to obtain the aliphatic-aromatic copolyester; or, (S1) Succinic acid and / or succinic acid derivatives are reacted with diols via esterification and prepolymerization to obtain prepolymer A; (S2) Terephthalic acid and / or terephthalic acid derivatives are reacted with diols by esterification and prepolymerization to obtain prepolymer B; (S3) The prepolymer A and prepolymer B are subjected to a polycondensation reaction to obtain the aliphatic-aromatic copolyester; or, (I) The aliphatic-aromatic copolyester with an oligomer content >2.4% obtained by volume exclusion chromatography was prepared by post-treatment.

7. The preparation method according to claim 6, characterized in that, The ratio of the total molar amount of terephthalic acid and / or terephthalic acid derivatives and succinic acid and / or succinic acid derivatives to the molar amount of diol in step (1) is 1:(1.2~1.4); Preferably, the esterification reaction in step (1) is carried out at a temperature of 220~242℃ for 1~6h. Preferably, the temperature of the polycondensation reaction in step (2) is 230~255℃, the pressure is 10~100Pa, and the reaction continues until the stirring power reaches a fixed torque value, wherein the fixed torque value is 8~18Hz / 200W; Preferably, the post-processing in step (2) includes: washing and / or refluxing the product obtained from the polycondensation reaction; Preferably, the organic solvent used for washing includes tetrahydrofuran and / or alcohol compounds; Preferably, the organic solvent comprises tetrahydrofuran and an alcohol compound, wherein the volume ratio of the tetrahydrofuran to the alcohol compound is (5~9):(1~5); Preferably, the washing time is 4 to 65 minutes; Preferably, the reflux temperature is 50~90℃ and the time is 10~80min; Preferably, the esterification reaction in step (S1) is carried out at a temperature of 150-180°C for 1-5 hours. Preferably, the temperature of the prepolymerization reaction in step (S1) is 220~260℃, the pressure is 100~600Pa, and the reaction continues until the intrinsic viscosity reaches 0.2~0.8dL / g; Preferably, the esterification reaction in step (S2) is carried out at a temperature of 200-260°C for 1-8 hours. Preferably, the temperature of the prepolymerization reaction in step (S2) is 220~280℃, the pressure is 100~500Pa, and the reaction continues until the intrinsic viscosity reaches 0.2~0.8dL / g; Preferably, the temperature of the polycondensation reaction in step (S3) is 230~260℃, the pressure is 10~100Pa, and the reaction continues until the stirring power reaches a fixed torque value, wherein the fixed torque value is 8~18Hz / 200W. Preferably, the post-processing method in step (I) includes washing and / or reflux.

8. A film or bag, characterized in that, The film or bag comprises the aliphatic-aromatic copolyester as described in any one of claims 1 to 5.

9. The membrane or bag according to claim 8, characterized in that, The water vapor permeability coefficient of the membrane or bag is ≤450g / 24h·m 2 More preferably, it is 338~440 g / 24h·m 2 .

10. The film or bag according to claim 8 or 9, characterized in that, The haze of the membrane or bag is ≤40%, more preferably 22~37%.

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