A biodegradable polyester copolymer, and a preparation method and application thereof

Abstract

The application provides a biodegradable polyester copolymer and a preparation method and application thereof, and belongs to the technical field of biodegradable plastics. The preparation method comprises the following steps: S1. mixing an aromatic dicarboxylic compound, 1,4-butanediol and a catalyst to perform esterification reaction to obtain esterification product E1, the terminal carboxyl group content of the esterification product E1 being 50-450 mol / t; S2. mixing an aliphatic dicarboxylic compound and 1,4-butanediol to perform esterification reaction to obtain esterification product E2, the terminal carboxyl group content of the esterification product E2 being 500-5000 mol / t; and S3. mixing the esterification product E1, the esterification product E2 and polylactic acid to react to obtain the biodegradable polyester copolymer. The biodegradable polyester copolymer prepared by the application has excellent tensile strength and elongation at break, and good biodegradability.

Description

Technical Field

[0001] This invention relates to the field of biodegradable plastics technology, and in particular to a biodegradable polyester copolymer, its preparation method, and its application. Background Technology

[0002] Aliphatic-aromatic polyesters, represented by PBAT (a copolymer of butylene adipate and butylene terephthalate), possess excellent biodegradability and are among the most widely used biodegradable materials. Aliphatic-aromatic polyesters combine the characteristics of both aliphatic and aromatic polyesters, exhibiting good ductility and elongation at break, but their impact strength is relatively poor, especially at low temperatures.

[0003] Polylactic acid (PLA), also known as polyhydroxypropionic acid or polylactide, is a biodegradable polymer material formed by the condensation polymerization of lactic acid monomers. PLA has high strength, but its toughness is relatively poor, lacking elasticity and flexibility. It is hard and brittle with low elongation at break. Furthermore, PLA has a slow crystallization rate and poor processing performance.

[0004] Blending aliphatic-aromatic polyesters with PLA can, on the one hand, produce biodegradable plastic alloys with high bio-based content; on the other hand, it can achieve complementary properties. PLA can improve the impact strength of aliphatic-aromatic polyesters, while aliphatic-aromatic polyesters can better improve the processing performance and elongation at break of PLA.

[0005] However, PLA and aliphatic-aromatic polyesters have significantly different solubility parameters, resulting in poor compatibility. Without compatibilizers, the overall performance of PLA / aliphatic-aromatic polyester alloys is poor. Even after compatibilization with compatibilizers, the blend still exhibits a phase-separated structure, making it difficult to ensure sufficient refinement of the dispersed phase. Existing technology CN102702696A discloses a fully degradable biomaterial composed of PBAT and PLA, where PBAT accounts for 75–90 wt.% and the remainder is PLA. This fully degradable biomaterial suffers from compatibility issues between PLA and PBAT, making it difficult to guarantee the product's performance and stability, thus hindering long-term use.

[0006] To address the aforementioned problem of poor compatibility between aliphatic-aromatic polyesters and PLA, prior art CN104725620A discloses an unsaturated polylactic acid block copolymer and its preparation method, comprising first preparing an unsaturated copolyester, and then reacting the unsaturated copolyester with lactide under the action of a catalyst to obtain the unsaturated polylactic acid block copolymer. However, the reaction conditions using lactide and unsaturated copolyester are harsh and poorly controllable, resulting in low yield and poor efficiency of the obtained unsaturated polylactic acid block copolymer. Furthermore, the compatibility between PLA and aliphatic-aromatic polyester remains poor, leading to insufficient mechanical properties of the unsaturated polylactic acid block copolymer. Summary of the Invention

[0007] The purpose of this invention is to overcome the defect of poor compatibility between aliphatic-aromatic polyesters and PLA in the prior art, and to provide a biodegradable polyester copolymer.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned biodegradable polyester copolymer.

[0009] Another object of the present invention is to provide applications of the above-mentioned biodegradable polyester copolymer.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for preparing a biodegradable polyester copolymer includes the following steps:

[0012] S1. An aromatic dicarboxylic acid compound, 1,4-butanediol and a catalyst are mixed and subjected to an esterification reaction to obtain esterified product E1. The terminal carboxyl group content of esterified product E1 is 50-450 mol / t.

[0013] S2. An aliphatic dicarboxylic acid compound is mixed with 1,4-butanediol and subjected to an esterification reaction to obtain esterified compound E2. The content of terminal carboxyl groups in esterified compound E2 is 500-5000 mol / t.

[0014] S3. Mix esterified E1, esterified E2 and polylactic acid, add to copolymerization equipment, and react at 200-250℃ and 1000-5000Pa for 1.5-4 hours to obtain a biodegradable polyester copolymer.

[0015] Based on the total molar amount of aromatic dicarboxylic acid compounds and aliphatic dicarboxylic acid compounds, the aromatic dicarboxylic acid compounds account for 38-52 mol%, and the aliphatic dicarboxylic acid compounds account for 48-62 mol%.

[0016] The polylactic acid has a D-type content of 0.4-1.6% and a melting point of 150-180℃.

[0017] In aliphatic-aromatic polyesters, the content of aromatic dicarboxylic acids directly affects the mechanical, thermodynamic, degradation, and processing properties. Based on the total molar amount of aromatic and aliphatic dicarboxylic acids, when aromatic dicarboxylic acids account for 38–52 mol%, the melting point of the aliphatic-aromatic polyester is 105–123 °C.

[0018] The aromatic dicarboxylic acid compounds mentioned in this invention refer to aromatic dicarboxylic acids or their ester derivatives, or mixtures thereof; the aliphatic dicarboxylic acid compounds refer to aliphatic dicarboxylic acids or their ester derivatives, or mixtures thereof.

[0019] Preferably, the aromatic dicarboxylic acid is at least one selected from terephthalic acid, dimethyl terephthalate, diethyl terephthalate, dibutyl terephthalate, dioctyl terephthalate, ethylene glycol terephthalate, butylene glycol terephthalate, isophthalic acid, dioctyl isophthalate, naphthalenedicarboxylic acid, and diphenyl dicarboxylic acid.

[0020] Preferably, the aliphatic dicarboxylic acid is at least one of succinic acid, adipic acid, octanoic acid, and sebacic acid.

[0021] In the preparation method of the biodegradable polyester copolymer of the present invention, aromatic dicarboxylic acid compounds and aliphatic dicarboxylic acid compounds are first subjected to esterification reactions with 1,4-butanediol to obtain two esterified compounds. Then, esterified compounds E1 and E2 are mixed with polylactic acid for copolymerization. During the copolymerization reaction, esterified compounds E1 and E2 react to obtain a copolyester, and polylactic acid also achieves good compatibility with the copolyester. By rationally controlling the esterification reaction conditions and copolymerization reaction conditions, the present invention obtains a biodegradable polyester copolymer that possesses both the high strength of polylactic acid and the high toughness of aliphatic-aromatic polyesters, while also exhibiting good biodegradability.

[0022] The method for determining the content of terminal carboxyl groups in esterified products is in accordance with FZ / T 50012 2006 "Determination of terminal carboxyl group content in polyester by titration analysis": a mixture of o-cresol and chloroform is used as the solvent, with a mass ratio of o-cresol to chloroform of 7:3, and the terminal carboxyl group value is tested using an automatic potentiometric titrator.

[0023] The end carboxyl group content of the esterification compound reflects the degree of esterification. A lower end carboxyl group content indicates a more complete esterification reaction, while a lower end carboxyl group content indicates a lower degree of esterification. The inventors found that controlling the end carboxyl group content of esterification compound E1 to be relatively low (50–450 mol / t) and controlling the end carboxyl group content of esterification compound E2 to be relatively high (500–5000 mol / t) facilitates the copolymerization reaction in the subsequent step S3. When the end carboxyl group content exceeds this range, the copolymerization efficiency is poor, or the PLA phase in the biodegradable polyester copolymer is difficult to disperse well.

[0024] Preferably, in step S1, an aromatic dicarboxylic acid compound is mixed with a portion of 1,4-butanediol to obtain mixture A; the remaining 1,4-butanediol is mixed with a catalyst to obtain mixture B; and mixture A and mixture B are then added to an esterification reaction apparatus for reaction.

[0025] The catalyst has a high viscosity, and direct addition can easily cause it to stick to the catalyst wall, thus affecting the catalytic effect. Dissolving the catalyst in 1,4-butanediol before addition can improve its catalytic performance.

[0026] Preferably, the content of terminal carboxyl groups in the esterified compound E1 is 100–400 mol / t.

[0027] Preferably, the content of terminal carboxyl groups in the esterified compound E2 is 2000-3000 mol / t.

[0028] When the terminal carboxyl group content of esterified E1 and esterified E2 is within the above-mentioned preferred range, the resulting biodegradable polyester copolymer has better mechanical properties.

[0029] Preferably, in step S1, the esterification reaction is carried out at 200–250°C and 30–110 kPa for 1.5–3.5 h.

[0030] Preferably, in step S2, the esterification reaction is carried out at 150–200°C and 30–110 kPa for 2–4 hours.

[0031] Preferably, the catalyst is a titanate catalyst.

[0032] Optionally, the titanate catalyst is at least one of tetrabutyl titanate, tetraethyl titanate, tetraisopropyl titanate, titanoceramsite catalyst, and chelated titanate catalyst.

[0033] Preferably, the intrinsic viscosity of the polylactic acid is 0.2 to 1.2 dL / g, more preferably 0.2 to 1.0 dL / g.

[0034] The intrinsic viscosity of polylactic acid is tested according to GB / T 10247-2008, using chloroform or dichloromethane as the solvent and at a test temperature of 25℃.

[0035] The viscosity of polylactic acid (PLA) should not be too high. If the viscosity is too high, PLA will not readily copolymerize with esterified compounds E1 and E2, or the PLA phase in the resulting biodegradable polyester copolymer will still be poorly compatible. The inventors have discovered that when the viscosity of PLA is 0.2–1.2 dL / g, the copolymerization reaction can proceed efficiently, and the PLA phase in the biodegradable polyester copolymer is well dispersed.

[0036] The D-type content of polylactic acid (PLA) can be detected by the following method: PLA is alcoholyzed in methanol using a catalyst, so that all lactic acid monomers in the molecule are converted into methyl lactate. Then, gas chromatography is used for analysis. The peak area ratio of D-methyl lactate to L-methyl lactate is the D-type content in PLA.

[0037] The D-type content of polylactic acid can be detected by following steps: (1) Weigh 100±10mg of polylactic acid sample and place it in the inner liner of a 25mL pressurized container; (2) Add 10mL of methanol and 1 drop of 20wt.% dilute sulfuric acid; (3) Seal the pressurized container and place it in a 150℃ thermostat for 4h; (4) Remove the pressurized container and wait for it to cool to room temperature before opening the lid; (5) After filtering the sample solution through a membrane filter (pore size 0.22 or 0.45μm), transfer it to a gas chromatography vial and operate according to the equipment manufacturer's instructions; (6) Calculate the D-type content based on the peak area ratio.

[0038] Preferably, the polylactic acid accounts for 8 to 41 wt.% of the total amount of esterified E1, esterified E2 and polylactic acid.

[0039] Preferably, in step S3, the viscosity number (intrinsic viscosity) of the biodegradable polyester copolymer is 1.2 to 1.8 dL / g.

[0040] The present invention also protects a biodegradable polyester copolymer prepared by the above preparation method.

[0041] The biodegradable polyester copolymer has a number-average molecular weight (Mn) of 50,000 to 120,000, preferably 62,000 to 113,000.

[0042] The number-average molecular weight (Mn) of biodegradable polyester copolymers can be measured by gel permeation chromatography (GPC). The determination can be performed using a tandem array of two columns (5 μm and 3 μm particle sizes with mixed porosity), a refractive index detector, chloroform as eluent (flow rate 0.5 ml / min), and polystyrene as a reference standard, with the chromatographic system maintained at 40°C.

[0043] The melting point of biodegradable polyester copolymers can be tested using differential scanning calorimetry (DSC). Specifically, 5-10 mg of sample is weighed and placed in a crucible used for DSC testing. The temperature range is 20-200 °C, and the heating rate is 10 K / min. Two cycles of testing are performed. The peak value corresponding to the melting peak on the second heating curve is the melting point of the sample.

[0044] For physical mixtures of aliphatic-aromatic polyesters and polylactic acid (PLA), due to their poor compatibility, the melting points of the aliphatic-aromatic polyester and PLA will be displayed separately in the second heating curve of the DSC. For the biodegradable polyester copolymer composed of aliphatic-aromatic polyester and PLA described in this invention, the compatibility between the aliphatic-aromatic polyester and PLA is improved during the synthesis process due to the bonding reaction between chemical bonds. For partially compatible systems, two melting point peaks will appear in the second heating curve of the DSC; for completely compatible systems, only one melting point peak will appear, and the corresponding melting point value will be between the individual melting point peaks of the aliphatic-aromatic polyester and PLA. Therefore, the compatibility of aliphatic-aromatic polyester and PLA in the biodegradable polyester copolymer can be determined by the change in the melting point of the sample.

[0045] The difference between the melting point of the polylactic acid component in the biodegradable polyester copolymer and the theoretical melting point of the biodegradable polyester copolymer is η≤22℃, preferably ≤15℃.

[0046] The theoretical melting point of the biodegradable polyester copolymer described in this invention refers to the melting point of the corresponding sample when the aliphatic-aromatic polyester and polylactic acid are completely compatible. The theoretical melting point can be calculated using the formula shown in equation (I):

[0047] M p(理论) =M p1 *W1+M p2 *W2 Formula (I)

[0048] in,

[0049] M p(理论) When aliphatic-aromatic polyesters are completely compatible with polylactic acid, the melting point of biodegradable polyester copolymers is reached.

[0050] M p1 The melting point of aliphatic-aromatic polyesters alone;

[0051] M P2 The melting point of polylactic acid alone;

[0052] W1, the weight percentage of aliphatic-aromatic polyester in the biodegradable polyester copolymer;

[0053] W2 represents the weight percentage of polylactic acid in the biodegradable polyester copolymer.

[0054] The difference η between the melting point of the polylactic acid component in the biodegradable polyester copolymer and the theoretical melting point of the biodegradable polyester copolymer can be calculated using the formula shown in equation (II):

[0055] η = M P2 - M p(理论) Equation (II)

[0056] The biodegradable polyester copolymer prepared by the above method has good tensile strength and elongation at break, and good biodegradability.

[0057] This invention also protects the use of the above-mentioned biodegradable polyester copolymer in the preparation of disposable film bags.

[0058] Compared with the prior art, the beneficial effects of the present invention are:

[0059] This invention provides a biodegradable polyester copolymer comprising a PBAT-type polyester phase and a PLA phase, with good compatibility between the two phases. The biodegradable polyester copolymer has both excellent tensile strength and elongation at break, and good biodegradability. Detailed Implementation

[0060] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any way.

[0061] In the embodiments and comparative examples of the present invention, polylactic acid (hereinafter referred to as PLA for ease of description) was prepared in-house. The preparation method was as follows: lactic acid monomer and initiator (glycerol) were mixed, and then a catalyst was added. The polymerization reaction was carried out at a temperature of 120 to 160°C and a vacuum degree of -0.050 to -0.09 MPa for 10 to 25 hours to obtain PLA. Different viscosities were obtained by controlling different reaction times or different amounts of initiator added.

[0062] Among them: PLA-1, viscosity is 0.5 dL / g, D-type content is 0.5%, melting point is 176℃; PLA-2, viscosity is 1.0 dL / g, D-type content is 0.8%, melting point is 170℃; PLA-3, viscosity is 0.2 dL / g, D-type content is 1.0%, melting point is 165℃; PLA-4, viscosity is 1.2 dL / g, D-type content is 1.2%, melting point is 154℃.

[0063] Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0064] Examples 1-6

[0065] Examples 1-6 each provide a biodegradable polyester copolymer, prepared by the following methods:

[0066] S1. Mix 166 kg of terephthalic acid with 105 kg of 1,4-butanediol to obtain mixture A; mix 3.5 kg of 1,4-butanediol with 0.2 kg of catalyst (n-butyl titanate) to obtain mixture B; then add mixture A and mixture B to the esterification reaction equipment respectively to carry out the esterification reaction to obtain esterified product E1.

[0067] S2. Mix 144 kg of adipic acid with 100 kg of 1,4-butanediol, and add the resulting mixture to an esterification reaction apparatus to carry out the esterification reaction, thereby obtaining esterified product E2;

[0068] S3. Mix 245kg of esterified E1, 210kg of esterified E2 and 152kg of PLA-1, add them to the copolymerization reaction equipment, and carry out the copolymerization reaction to obtain a biodegradable polyester copolymer.

[0069] In other words, in this embodiment, based on the total molar amount of terephthalic acid and adipic acid, terephthalic acid accounts for 50 mol%, and adipic acid accounts for 50 mol%; based on the total amount of esterified E1, esterified E2 and PLA-1, PLA-1 accounts for 25 wt.% by weight.

[0070] The specific reaction conditions are shown in Table 1.

[0071] Table 1

[0072]

[0073] Examples 7-9

[0074] Examples 7-9 each provide a biodegradable polyester copolymer, the preparation method of which differs from that of Example 1 in that:

[0075] In Example 7, the amounts of terephthalic acid and adipic acid were adjusted and controlled to be: based on the total molar amount of terephthalic acid and adipic acid, terephthalic acid accounted for 40 mol% and adipic acid accounted for 60 mol%.

[0076] In Example 8, the amount of PLA added was adjusted and controlled to be 10 wt.% based on the total amount of ester E1, ester E2 and PLA.

[0077] In Example 9, the amount of PLA added was adjusted and controlled to be 40 wt.% based on the total amount of ester E1, ester E2 and PLA.

[0078] Examples 10-12

[0079] Examples 10-12 each provide a biodegradable polyester copolymer, prepared using the same method as in Example 1, except that:

[0080] In Example 10, PLA-1 is replaced with an equal amount of PLA-2;

[0081] In Example 11, PLA-1 is replaced with an equal amount of PLA-3;

[0082] In Example 12, PLA-1 is replaced with an equal amount of PLA-4.

[0083] Comparative Example 1

[0084] Comparative Example 1 provides a biodegradable polyester copolymer, the preparation method of which differs from that of Example 1 in that:

[0085] S1. Mix 166 kg of terephthalic acid with 105 kg of 1,4-butanediol to obtain mixture A; mix 3.5 kg of 1,4-butanediol with 0.2 kg of catalyst (n-butyl titanate) to obtain mixture B; mix 144 kg of adipic acid with 100 kg of 1,4-butanediol to obtain mixture C.

[0086] Mixtures A, B, and C are then added to the esterification reaction apparatus to carry out the esterification reaction, yielding esterified products.

[0087] S3. Mix 455 kg of esterified material and 152 kg of PLA-1, add them to the copolymerization reaction equipment, and carry out the copolymerization reaction to obtain a biodegradable polyester copolymer.

[0088] Comparative Examples 2-5

[0089] Comparative Examples 2-5 provide a biodegradable polyester copolymer. The preparation method differs from that of Example 1 in that the content of terminal carboxyl groups of esterified E1 and esterified E2 is controlled differently in steps S1 and S2. The specific reaction conditions of steps S1 and S2 are shown in Table 2. Step S3 is the same as that of Example 1.

[0090] Table 2

[0091]

[0092]

[0093] Comparative Example 6

[0094] Comparative Example 6 provides a biodegradable polyester copolymer, prepared by the following method:

[0095] 90 kg of PBAT (trademark A400, sourced from Zhuhai Kingfa Biomaterials Co., Ltd.) and 30 kg of PLA (trademark L175, sourced from Total Praxair) were mixed, and 0.3 kg of compatibilizer (ADR 4368) was added. The mixture was then fed into a twin-screw extruder (L / D = 48; diameter 40 mm) for melt-mixing extrusion granulation. The extrusion temperature was 140-200℃, the screw speed was 300 rpm, and the vacuum was -0.50 to -0.65 kg / cm². 2 A biodegradable polyester copolymer was obtained.

[0096] Performance testing

[0097] The performance of the biodegradable polyester copolymers prepared in the above examples and comparative examples was tested, and the specific methods are as follows:

[0098] Tensile strength: Tested according to ISO 527-2-2012 standard method;

[0099] Elongation at break: Tested according to the standard method of ISO 527-2-2012;

[0100] Biodegradation rate: The biodegradable polyester copolymer was prepared into a 12μm±1μm film, and the biodegradation rate was tested after 12 weeks of storage according to standard ISO16929 (2013).

[0101] The test results are shown in Table 3.

[0102] Table 3

[0103]

[0104] According to the test results in Table 3, the biodegradable polyester copolymers prepared in each embodiment of the present invention have good mechanical properties. With PLA accounting for 25 wt.%, the tensile strength of the biodegradable polyester copolymer is ≥33 MPa and the elongation at break is ≥198%. At the same time, the biodegradable polyester copolymers prepared in each embodiment also have good biodegradability.

[0105] According to Examples 1-6, it can be seen that when the end carboxyl group content of esterified E1 obtained in step S1 is controlled to be 50-450 mol / t, and the end carboxyl group content of esterified E2 obtained in step S2 is controlled to be 500-5000 mol / t, the copolymerization reaction in step S3 can proceed effectively, and the PLA phase in the obtained biodegradable polyester copolymer can be uniformly dispersed, resulting in good mechanical properties of the biodegradable polyester copolymer. When the end carboxyl group content of esterified E1 is 100-400 mol / t, and the end carboxyl group content of esterified E2 is 2000-3000 mol / t, the mechanical properties of the obtained biodegradable polyester copolymer are relatively better, with a tensile strength ≥37 MPa and an elongation at break ≥250%.

[0106] According to Comparative Example 1, when aromatic dicarboxylic acid compounds and aliphatic dicarboxylic acid compounds are not controlled to undergo esterification reactions, it is difficult to obtain esters with suitable terminal carboxyl group content, resulting in biodegradable polyester copolymers with poor mechanical properties.

[0107] According to Comparative Examples 2 to 5, when the end carboxyl group content of esterified E1 and esterified E2 exceeds the range defined in this invention, the tensile strength and elongation at break of the prepared biodegradable polyester copolymers are significantly deteriorated.

[0108] According to Examples 1 and 10-12, when the viscosity of PLA is 0.2-1.0 dL / g, the copolymerization reaction in step S3 can proceed efficiently, and the PLA phase in the biodegradable polyester copolymer is better dispersed, resulting in relatively better mechanical properties of the biodegradable polyester copolymer.

[0109] In Comparative Example 6, when PBAT and PLA were directly blended, even with the addition of a compatibilizer for melt enrichment, the PBAT / PLA blend still exhibited a phase-separated structure, and the resulting biodegradable polyester copolymer failed to meet the required mechanical properties.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A process for the preparation of a biodegradable polyester copolymer, characterized in that, The method comprises the following steps: S1. mixing aromatic dicarboxylic acid compound, 1,4-butanediol and catalyst to perform esterification reaction to obtain esterification product E1, the content of terminal carboxyl group of esterification product E1 being 50-450 mol / t; S2. mixing aliphatic dicarboxylic acid compound and 1,4-butanediol to perform esterification reaction to obtain esterification product E2, the content of terminal carboxyl group of esterification product E2 being 500-5000 mol / t; S3. mixing esterification product E1, esterification product E2 and polylactic acid, and adding into copolymerization reaction equipment to perform reaction under the conditions of 200-250 ℃ and 1000-5000 Pa for 1.5-4 h to obtain biodegradable polyester copolymer, wherein, the aromatic dicarboxylic acid compound accounts for 38-52 mol% and the aliphatic dicarboxylic acid compound accounts for 48-62 mol% based on the total moles of the aromatic dicarboxylic acid compound and the aliphatic dicarboxylic acid compound; the D-form content of the polylactic acid is 0.4-1.6%, and the melting point of the polylactic acid is 150-180 ℃.

2. The method for preparing the biodegradable polyester copolymer according to claim 1, characterized in that, In step S1, the esterification reaction is performed under the conditions of 200-250 ℃ and 30-110 KPa for 1.5-3.5 h.

3. The method for preparing the biodegradable polyester copolymer according to claim 1, characterized in that, In step S2, the esterification reaction is performed under the conditions of 150-200 ℃ and 30-110 KPa for 2-4 h.

4. The method for preparing the biodegradable polyester copolymer according to claim 1, characterized in that, The aromatic dicarboxylic acid compound is at least one of terephthalic acid, dimethyl terephthalate, diethyl terephthalate, dibutyl terephthalate, dioctyl terephthalate, ethylene glycol terephthalate, butylene glycol terephthalate, isophthalic acid, isophthalic acid dioctyl ester, naphthalene dicarboxylic acid and diphenyl dicarboxylic acid.

5. The method for preparing the biodegradable polyester copolymer according to claim 1, characterized in that, The aliphatic dicarboxylic acid compound is at least one of butanedioic acid, hexanedioic acid, octanedioic acid and decanedioic acid.

6. The method for preparing the biodegradable polyester copolymer according to claim 1, characterized in that, The intrinsic viscosity of the polylactic acid is 0.2-1.2 dL / g.

7. The method for preparing the biodegradable polyester copolymer according to claim 1, characterized in that, In step S3, the intrinsic viscosity of the biodegradable polyester copolymer is 1.2-1.8 dL / g.

8. The method for preparing the biodegradable polyester copolymer according to claim 1, characterized in that, The weight of the polylactic acid is 8-41 wt.% based on the total amount of esterification product E1, esterification product E2 and polylactic acid.

9. A biodegradable polyester copolymer prepared by the process of any one of claims 1 to 8, characterized in that, The difference η between the melting point corresponding to the polylactic acid component in the biodegradable polyester copolymer and the theoretical melting point of the biodegradable polyester copolymer is ≤22 ℃.

10. Use of the biodegradable polyester copolymer according to claim 9 in preparing disposable film bags.

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