Biodegradable copolyester as well as preparation method and application thereof

Abstract

The invention provides biodegradable copolyester as well as a preparation method and application thereof. The preparation method comprises the following steps: simultaneously mixing terephthalic acid, adipic acid, butanediol and a biodegradable monomer, and reacting to obtain the biodegradable copolyester. The biodegradable copolyester with a specific structure is prepared through a one-step polymerization method, the production difficulty of the biodegradable copolyester is reduced, and the degradation performance and the processing performance of the biodegradable copolyester are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of biodegradable materials, and specifically relates to a biodegradable copolyester and a preparation method and application thereof. Background Art

[0002] Biodegradable plastics can be divided into bio-based biodegradable plastics (such as PLA, PHA) and petroleum-based biodegradable plastics (such as PBAT, PBS, PPC, PGA) according to raw materials. Currently, PBAT and PLA are the most widely used. PBAT is slightly softer while PLA is harder. For example, PLA and PBAT are often blended in the preparation of packaging materials or film bags, or PBAT is copolymerized with PLA or lactide to prepare block copolymers.

[0003] CN115418085A discloses a biodegradable PBAT / PLA blended film, the PBAT / PLA blended film comprises the following raw materials in parts by weight: 20-60 parts of PLA, 40-80 parts of PBAT, 0.5-1.5 parts of a compatibilizer, 1 part of nano calcium carbonate, and 4-6 parts of chitosan; the preparation method of the PBAT / PLA blended film comprises: (1) granulation: weighing and fully mixing the raw materials in different proportions in order, feeding them into a twin-screw extruder, and granulating; (2) placing the granulated material obtained in step (1) in a blast drying oven, drying it at 60°C for 6 hours, obtaining a PLA / PBAT blown film material, and then feeding it into a blown film machine for blow molding. In this technical solution, a biodegradable PBAT / PLA blended film is prepared by blending PLA and PBAT, but in this technical solution, the dispersibility of PLA and PBAT is poor, and it is difficult to make PLA and PBAT dispersed evenly, which ultimately leads to poor performance of the film.

[0004] CN107141458A discloses a copolymerization synthesis method of PBAT-PLA copolyester, the method comprising the following steps: after prepolymer PBAT and prepolymer PLA are uniformly blended, they are put into a high vacuum reactor, the vacuum degree is 5-100Pa, heated to 100-110°C for reaction for 0.5-1h; then the temperature is gradually increased to 145-155°C within 1-2h, and the reaction is continued for 5-10h to obtain the product PBAT-PLA copolyester, with a weight average molecular weight of 100000-250000. This technical solution uses prepolymer PBAT and prepolymer PLA as raw materials to prepare PBAT-PLA copolyester, the process is cumbersome, it is difficult to control the degree of reaction, and the performance of the PBAT-PLA copolyester prepared thereby is poor.

[0005] Therefore, how to provide a biodegradable copolyester with a simple preparation process and excellent performance has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a biodegradable copolyester and a preparation method and application thereof. The present invention prepares a biodegradable copolyester with a specific structure by a one-step polymerization method, reduces the production difficulty of the biodegradable copolyester, and improves the degradation performance and processing performance of the biodegradable copolyester.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a biodegradable copolyester, the preparation method comprising the following steps:

[0009] Terephthalic acid and / or terephthalate, adipic acid, butanediol and biodegradable monomers are mixed and reacted simultaneously to obtain the biodegradable copolyester.

[0010] In the present invention, terephthalic acid and / or terephthalate, adipic acid, butanediol and a biodegradable monomer are mixed and reacted simultaneously, and a biodegradable copolyester with a specific structure is prepared by a one-step polymerization method, thereby reducing the production difficulty of the biodegradable copolyester and improving the degradation performance and processing performance of the biodegradable copolyester.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0012] As a preferred technical solution of the present invention, the raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0013]

[0014] In the present invention, by controlling the amount of each component within a specific range, a biodegradable copolyester with a specific structure is prepared, the production difficulty of the biodegradable copolyester is reduced, and the degradation performance and processing performance of the biodegradable copolyester are improved.

[0015] In the present invention, the molar ratio of terephthalic acid and / or terephthalate to adipic acid is further controlled to be ≤1.14, which can further improve the degradation performance of the biodegradable copolyester.

[0016] In the present invention, in the raw materials for preparing the biodegradable copolyester, the weight proportion of the terephthalic acid and / or terephthalate ester can be 25 parts, 26 parts, 27 parts, 28 parts, 29 parts or 30 parts.

[0017] The weight proportions of the adipic acid may be 25 parts, 26 parts, 27 parts, 28 parts, 29 parts or 30 parts, etc.

[0018] The weight proportions of the butanediol may be 30 parts, 31 parts, 32 parts, 33 parts, 34 parts or 35 parts, etc.

[0019] The weight proportions of the biodegradable monomer may be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 parts, etc.

[0020] As a preferred technical solution of the present invention, the terephthalate ester is selected from any one of dimethyl terephthalate, diethyl terephthalate, dipropyl terephthalate, dibutyl terephthalate or dioctyl terephthalate, or a combination of at least two thereof.

[0021] Preferably, the biodegradable monomer comprises lactic acid Methyl lactate Glycolic acid Methyl glycolate Any one or a combination of at least two of the following.

[0022] As a preferred technical solution of the present invention, the raw materials for preparing the biodegradable copolyester also include 0.005 to 0.1 parts of auxiliary agents, for example, 0.005 parts, 0.01 parts, 0.02 parts, 0.03 parts, 0.04 parts, 0.05 parts, 0.06 parts, 0.07 parts, 0.08 parts, 0.09 parts or 0.1 parts, etc.

[0023] Preferably, the auxiliary agent includes an antioxidant.

[0024] Preferably, the antioxidant is selected from any one of tris(2,4-di-tert-butylphenyl)phosphite, triphenyl phosphite or bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite or a combination of at least two thereof.

[0025] As a preferred technical solution of the present invention, the raw materials for preparing the biodegradable copolyester also include 0.05 to 1 part of a catalyst, for example, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 part.

[0026] Preferably, the catalyst comprises n-butyl titanate or isopropyl titanate.

[0027] As a preferred technical solution of the present invention, the polymerization temperature is 130-250°C, for example, it can be 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C or 250°C.

[0028] Preferably, the polymerization time is 5 to 12 hours, for example, it can be 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0029] As a preferred technical solution of the present invention, the polymerization includes a first reaction stage, a second reaction stage and a third polymerization stage.

[0030] Preferably, the temperature of the first reaction stage is 130-150°C (for example, it can be 130°C, 132°C, 134°C, 136°C, 138°C, 140°C, 142°C, 144°C, 146°C, 148°C or 150°C, etc.), and the time is 1-3h (for example, it can be 1h, 1.5h, 2h, 2.5h or 3h, etc.).

[0031] In the present invention, the first reaction stage is carried out under normal pressure (101 KPa).

[0032] Preferably, the temperature of the second reaction stage is 150-230°C (for example, it can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C or 230°C, etc.), the time is 2.5-4h (for example, it can be 2.5h, 3.0h, 3.2h, 3.5h or 4.0h, etc.), and the absolute pressure is 30-70KPa (for example, it can be 30KPa, 35KPa, 40KPa, 45KPa, 50KPa, 55KPa, 60KPa, 65KPa or 70KPa, etc.).

[0033] Preferably, the heating rate from the first reaction stage to the second reaction stage is 30-40°C / h, for example, 30°C / h, 32°C / h, 34°C / h, 36°C / h, 38°C / h, 40°C / h, etc.

[0034] Preferably, the temperature of the third polymerization stage is 230-250°C (for example, it may be 230°C, 232°C, 234°C, 236°C, 238°C, 240°C, 242°C, 244°C, 246°C, 248°C or 250°C, etc.), the time is 3-5h (for example, it may be 3h, 3.5h, 4h, 4.5h or 5h, etc.), and the absolute pressure is less than 500Pa (for example, it may be 10Pa, 50Pa, 100Pa, 150Pa, 200Pa, 250Pa, 300Pa, 350Pa, 400Pa, 450Pa or 490Pa, etc.).

[0035] As a preferred technical solution of the present invention, a pretreatment step is also included before the terephthalic acid and / or terephthalate, adipic acid, butanediol and biodegradable monomer are mixed simultaneously;

[0036] Preferably, the pretreatment method comprises: mixing terephthalic acid and / or terephthalate, adipic acid, butanediol and biodegradable monomers simultaneously to remove water, and then heating and melting.

[0037] Preferably, the dehydration is carried out in a protective gas atmosphere, and the protective gas includes nitrogen and / or argon.

[0038] Preferably, the dehydration temperature is 110-130°C (for example, it can be 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, 122°C, 124°C, 126°C, 128°C or 130°C, etc.), and the time is 1-3h (for example, it can be 1h, 1.5h, 2h, 2.5h or 3h, etc.).

[0039] Preferably, the heating and melting temperature is 130-150°C (for example, it may be 130°C, 132°C, 134°C, 136°C, 138°C, 140°C, 142°C, 144°C, 146°C, 148°C or 150°C, etc.).

[0040] As a preferred technical solution of the present invention, the preparation method of the biodegradable copolyester specifically comprises the following steps:

[0041] At 110-130°C, terephthalic acid and / or terephthalate, adipic acid, butanediol and biodegradable monomers are dehydrated for 1-3 hours, then heated to 130-150°C, and after they are melted, a catalyst and optional auxiliary agents are added thereto, and the reaction is carried out at 130-150°C and normal pressure for 1-3 hours, and then the temperature is increased to 200-230°C at a heating rate of 30-40°C / h, and the reaction is carried out at an absolute pressure of 30-70KPa for 1-4 hours, and then a polymerization reaction is carried out at 230-250°C and an absolute pressure of less than 500Pa for 3-5 hours to obtain the biodegradable copolyester.

[0042] As a preferred technical solution of the present invention, the weight average molecular weight of the biodegradable copolyester is 80,000 to 120,000, for example, it can be 80,000, 85,000, 90,000, 96,000, 100,000, 106,000, 110,000, 114,000, 118,000 or 120,000.

[0043] In a second aspect, the present invention provides a biodegradable copolyester, wherein the molecular chain of the biodegradable copolyester comprises the following repeating units:

[0044] and / or

[0045] Among them, R is selected from or methylene, with dotted lines indicating attachment sites;

[0046] x is a number between 1 and 5, y is a number between 1 and 7, z1 is a number between 1 and 10, and z2 is a number between 1 and 10.

[0047] Preferably, the total degree of polymerization of the repeating units directly connected to the repeating units with a degree of polymerization of x and the repeating units with a degree of polymerization of y is ≤15.

[0048] In the present invention, terephthalic acid and / or terephthalic acid ester react with butanediol to obtain an ester 1 of repeating units with a polymerization degree of x, adipic acid and butanediol react to obtain an ester 2 for forming repeating units with a polymerization degree of y, and a biodegradable monomer reacts with butanediol or the biodegradable monomer self-polymerizes to obtain an ester 3 for forming repeating units with a polymerization degree of z1 and / or Z2. Since terephthalic acid and / or terephthalic acid ester, adipic acid, butanediol and the biodegradable monomer are mixed and reacted at the same time, the ester 3 will be relatively evenly dispersed in the ester system (the ester system is composed of ester 1, ester 2 and ester 3), and then the ester 1, ester 2 and ester 3 containing terminal hydroxyl groups and terminal carboxyl groups are copolymerized to form a copolymer to obtain a biodegradable copolyester with excellent processing performance.

[0049] Wherein, if the biodegradable monomer is selected from lactic acid or methyl lactate, the product having R If the biodegradable monomer is selected from glycolic acid or methyl glycolate, a repeating unit z1 or a repeating unit z2 in which R is a methylene group can be prepared.

[0050] Compared with the prior art, in which terephthalic acid and / or terephthalic acid ester, adipic acid and 1,4-butanediol are first polymerized to obtain a prepolymer, and then the above prepolymer is reacted with a prepolymer formed by a biodegradable monomer, the present invention is to simultaneously mix terephthalic acid and / or terephthalic acid ester, adipic acid, 1,4-butanediol and a biodegradable monomer for reaction, and prepare a biodegradable copolyester by a one-step polymerization method. The repeating units with a degree of polymerization of z1 and / or Z2 formed by the biodegradable copolyester will be inserted between the repeating units with a degree of polymerization of x and the repeating units with a degree of polymerization of y. Therefore, in the biodegradable copolyester prepared by the one-step polymerization provided by the present invention, the total degree of polymerization of the repeating units directly connected with the repeating units with a degree of polymerization of x and the repeating units with a degree of polymerization of y must be less than the total degree of polymerization of the repeating units directly connected with the repeating units with a degree of polymerization of x and the repeating units with a degree of polymerization of y in the copolyester obtained by step-by-step polymerization in the prior art (i.e., the polymer of the prepolymer). The degree of polymerization of the polymer of the prepolymer in the prior art is greater than 15, and may even reach hundreds or thousands. Therefore, in the biodegradable copolyester provided by the present invention, the total degree of polymerization of the repeating units directly connected with the repeating units with a degree of polymerization of x and the repeating units with a degree of polymerization of y is ≤15.

[0051] In the present invention, a biodegradable copolyester with a special structure is prepared by a one-step polymerization method, thereby improving the comprehensive performance of the biodegradable copolymer.

[0052] It should be noted that, since the degrees of polymerization of repeating units x, repeating units y, repeating units z1, and repeating units z2 (i.e., x, y, z1, z2) in the biodegradable copolyester molecular chain are measured by nuclear magnetic resonance, there are multiple repeating units x, repeating units y, repeating units z1, and repeating units z2 in the biodegradable copolyester molecular chain segment, and the degrees of polymerization x, y, and z of each repeating unit x, repeating unit y, repeating unit z1, and repeating unit z2 are not necessarily the same, therefore, the values ​​of x, y, and z in the tested molecular chain of the biodegradable copolyester are all average values ​​and are not necessarily integers.

[0053] In the present invention, in the molecular chain of the biodegradable copolyester, the polymerization degree x of the repeating units x can be independently 1.0, 1.6, 2.3, 3.0, 4.4 or 5.0.

[0054] In the molecular chain of the biodegradable copolyester, the degree of polymerization y of the repeating units y can be independently 1.0, 1.2, 2.4, 3.5, 4.8, 5.6, 6.7 or 7.0.

[0055] In the molecular chain of the biodegradable copolyester, the degree of polymerization z1 of the repeating units z1 can be independently 1.0, 1.3, 2.6, 3.2, 4.4, 5.5, 6.7, 7.0, 8.1, 9.4 or 10.0.

[0056] In the molecular chain of the biodegradable copolyester, the degree of polymerization z1 of the repeating units z1 can be independently 1.0, 1.3, 2.6, 3.2, 4.4, 5.5, 6.7, 7.0, 8.1, 9.4 or 10.0.

[0057] As a preferred technical solution of the present invention, x is a number between 2 and 4 (for example, it can be 2.2, 3.3 or 4.8), y is a number between 2 and 5 (for example, it can be 2.0, 3.3, 4.1 or 5.4), z1 is a number between 3 and 5 (for example, it can be 3.1, 4.2 or 5.6), and z2 is a number between 3 and 5 (for example, it can be 3.1, 4.2 or 5.6).

[0058] In a third aspect, the present invention provides an application of the biodegradable copolyester prepared by the preparation method as described in the first aspect, wherein the biodegradable copolyester is used for preparing packaging materials.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] The present invention prepares a biodegradable copolyester with a specific structure by mixing terephthalic acid and / or terephthalate, adipic acid, butanediol and a biodegradable monomer at the same time, polymerizing them, and using a one-step polymerization method, thereby reducing the production difficulty of the biodegradable copolyester and improving the degradation performance and processing performance of the biodegradable copolyester. DETAILED DESCRIPTION

[0061] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0062] Example 1

[0063] This embodiment provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0064]

[0065] The preparation method of the above-mentioned biodegradable copolyester is as follows:

[0066] Adipic acid, terephthalic acid, methyl lactate and 1,4-butanediol were added to a 1L reactor, and nitrogen was passed through for protection. Water was removed at 120°C for 2 hours, and then the temperature was raised to 140°C. After the materials in the reactor were completely melted, n-butyl titanate was added thereto, and the reaction was carried out at 140°C and normal pressure for 2 hours. The temperature was then raised to 230°C at a heating rate of 35°C / h, and the reaction was carried out at an absolute pressure of 70KPa for 2 hours. Then, a polymerization reaction was carried out at 240°C and an absolute pressure of less than 200Pa for 4 hours to obtain the biodegradable copolyester.

[0067] Example 2

[0068] This embodiment provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0069]

[0070] The preparation method of the above-mentioned biodegradable copolyester is as follows:

[0071] Adipic acid, terephthalic acid, lactic acid and 1,4-butanediol were added to a 1L reactor, and nitrogen was passed through the reactor for protection. After water was removed at 120°C for 2 hours, the temperature was raised to 140°C. After the materials in the reactor were completely melted, isopropyl titanate was added thereto. The reaction was carried out at 140°C and normal pressure for 2 hours. The temperature was then raised to 230°C at a heating rate of 30°C / h. The reaction was carried out at an absolute pressure of 70KPa for 1.5 hours. Then, a polymerization reaction was carried out at 240°C and an absolute pressure of less than 100Pa for 4 hours to obtain the biodegradable copolyester.

[0072] Example 3

[0073] This embodiment provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0074]

[0075]

[0076] The preparation method of the above-mentioned biodegradable copolyester is as follows:

[0077] Adipic acid, terephthalic acid, lactic acid and 1,4-butanediol are added to a 1L reactor, and nitrogen is passed through the reactor for protection. After water is removed at 120°C for 2 hours, the temperature is then raised to 140°C. After the materials in the reactor are completely melted, n-butyl titanate and triphenyl phosphite are added thereto. The reaction is carried out at 140°C and normal pressure for 2 hours. The temperature is then raised to 230°C at a heating rate of 35°C / h. The reaction is carried out at an absolute pressure of 70KPa for 2 hours. Then, a polymerization reaction is carried out at 240°C and an absolute pressure of less than 100Pa for 4 hours to obtain the biodegradable copolyester.

[0078] Example 4

[0079] This embodiment provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0080]

[0081] The preparation method of the above-mentioned biodegradable copolyester is as follows:

[0082] Adipic acid, dimethyl terephthalate, lactic acid and 1,4-butanediol were added to a 1L reactor, and nitrogen was passed through the reactor for protection. Water was removed at 110°C for 3 hours, and then the temperature was raised to 140°C. After the materials in the reactor were completely melted, n-butyl titanate was added thereto, and the reaction was carried out at 140°C and normal pressure for 2.5 hours. The temperature was then raised to 230°C at a heating rate of 30°C / h, and the reaction was carried out at an absolute pressure of 70KPa for 3 hours. Then, a polymerization reaction was carried out at 240°C and an absolute pressure of less than 100Pa for 3 hours to obtain the biodegradable copolyester.

[0083] Example 5

[0084] This embodiment provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0085]

[0086] The preparation method of the above-mentioned biodegradable copolyester is as follows:

[0087] Adipic acid, terephthalic acid, methyl glycolate and 1,4-butanediol are added to a 1L reactor, and nitrogen is passed through the reactor for protection. After water is removed at 130°C for 1 hour, the temperature is raised to 135°C. After the materials in the reactor are completely melted, n-butyl titanate and triphenyl phosphite are added thereto. The reaction is carried out at 135°C and normal pressure for 3 hours, and then the temperature is raised to 230°C at a heating rate of 30°C / h. Under the condition of an absolute pressure of 70KPa, the reaction is carried out for 4 hours, and then a polymerization reaction is carried out at 240°C and an absolute pressure of less than 100Pa for 5 hours to obtain the biodegradable copolyester.

[0088] Example 6

[0089] This embodiment provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0090]

[0091]

[0092] The preparation method of the above-mentioned biodegradable copolyester is as follows:

[0093] Adipic acid, dimethyl terephthalate, lactic acid and 1,4-butanediol were added to a 1L reactor, and nitrogen was passed through the reactor for protection. The reactor was heated to 115°C, and water was removed for 2 hours. The temperature was then continued to rise to 150°C. After the materials in the reactor were completely melted, n-butyl titanate and triphenyl phosphite were added thereto. The reaction was carried out at 150°C and normal pressure for 1 hour. The temperature was continuously raised to 230°C for 3.5 hours, and the reactor was kept at 230°C for 3 hours under a pressure of -0.7 KPa. The temperature was raised to 250°C, and the reaction was slowly carried out to the ultimate vacuum, and gradually to within 100 Pa. The polymerized reactor was polymerized for 4 hours and then the material was discharged to obtain a white biodegradable copolyester.

[0094] Example 7

[0095] This embodiment provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0096]

[0097] The above biodegradable copolyester is the same as that in Example 3.

[0098] Example 8

[0099] This embodiment provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0100]

[0101]

[0102] The above biodegradable copolyester is the same as that in Example 3.

[0103] Example 9

[0104] This embodiment provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0105]

[0106] The above biodegradable copolyester is the same as that in Example 3.

[0107] Example 10

[0108] This embodiment provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0109]

[0110]

[0111] 0.06 parts of n-butyl titanate

[0112] The above biodegradable copolyester is the same as that in Example 3.

[0113] Embodiment 11

[0114] This embodiment provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0115]

[0116] The preparation method of the above biodegradable copolyester is the same as that in Example 3.

[0117] Comparative Example 1

[0118] This comparative example provides a biodegradable copolyester and a preparation method thereof. The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

[0119]

[0120] The preparation method of the above-mentioned biodegradable copolyester is as follows:

[0121] (1) Preparation method of prepolymer PBAT: Adipic acid, terephthalic acid and 1,4-butanediol are added to a reactor, nitrogen is passed through the reactor, and the reactor is heated to 140°C. After the materials in the reactor are completely melted, n-butyl titanate and triphenyl phosphite are added and the temperature is kept for 1 hour; the temperature is continuously raised to 230°C and the temperature is kept for 2.5 hours; the temperature is raised to 240°C, the vacuum degree is gradually controlled at 500-1000 Pa, and the reaction is continued for 4 hours; then the prepolymer PBAT (degree of polymerization is 110) is obtained by discharging the material.

[0122] (2) Preparation method of prepolymer PLA: lactic acid is added to a reactor, and the reaction is heated to 120°C after nitrogen replacement three times. The vacuum degree is gradually controlled at 0.08 MPa, and the reaction is stirred for 3 hours. Then, the catalyst zinc acetate is added, the temperature is gradually increased to 180°C within 2 hours, and the vacuum is evacuated to 800 Pa. The reaction is continued for 4 hours. Then, the prepolymer polylactic acid is obtained by discharging the material.

[0123] (3) Prepolymer PBAT and prepolymer PLA are added to a reaction kettle, the temperature is controlled at 240° C., the vacuum is less than 100 Pa, and the polymerization is carried out for 4 hours to finally obtain a PBAT-PLA copolyester with a weight average molecular weight of 100,000-250,000.

[0124] Comparative Example 2

[0125] This comparative example provides a biodegradable material, which is composed of PBAT (purchased from Zhejiang Huafeng Group Environmental Protection Materials Co., Ltd., model HF101) and PLA (purchased from Zhejiang Hisun Biomaterials Co., Ltd., model REVODE110) in a mass ratio of 80:20.

[0126] The preparation method of the above-mentioned biodegradable material is as follows:

[0127] The biodegradable material is obtained by melting and mixing BAT and PLA.

[0128] The properties of the biodegradable copolyesters provided in the above examples and the biodegradable materials provided in the comparative examples were tested, and the specific testing methods are as follows:

[0129] The polymerization degree x, polymerization degree y and polymerization degree z of the repeating units in the biodegradable copolyester were tested using a Bruker Avance III 400M nuclear magnetic resonance spectrometer and 1H NMR with deuterated chloroform (CDCl3) as the solvent and internal standard.

[0130] Weight average molecular weight: gel chromatography, chloroform as mobile phase, ultraviolet detector.

[0131] Degradability: Refer to the biodegradation rate in GB / T 41010-2021.

[0132] Processability: The processability was tested using a 35 co-rotating twin-screw extruder and a film blowing machine, and the conclusions on processability were obtained. Among them, "excellent" means that the modified plasticization is good and the film blowing is stable, "good" means that the modified plasticization is moderate and the film blowing is stable, and "medium" means that the modified plasticization is poor and the film blowing is unstable.

[0133] The above performance test results are shown in Table 1 below:

[0134] Table 1

[0135]

[0136] From the above content, it can be seen that the present invention prepares a biodegradable copolyester with a specific structure through a one-step polymerization method, and further designs the dosage of each component of the raw material for preparing the biodegradable copolyester within a specific range so that the degree of polymerization of each repeating unit is within a specific range, thereby reducing the production difficulty of the biodegradable copolyester and improving the degradation performance and processing performance of the biodegradable copolyester.

[0137] From the comparison of the data of Examples 1-9 and Examples 10-11, it can be seen that in the present invention, by controlling the degree of polymerization x of the repeating unit within a specific range, the comprehensive performance of the biodegradable copolyester can be further improved.

[0138] It can be seen from the comparison between Examples 1-11 and Comparative Examples 1-2 that in the present invention, a biodegradable copolyester with a specific structure is prepared by a one-step polymerization method, which reduces the production difficulty of the biodegradable copolyester and improves the degradation performance and processing performance of the biodegradable copolyester.

[0139] In summary, the present invention prepares a biodegradable copolyester with a specific structure through a one-step polymerization method, reduces the production difficulty of the biodegradable copolyester, and improves the degradation performance and processing performance of the biodegradable copolyester.

[0140] The applicant declares that the present invention illustrates the detailed process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a biodegradable copolyester, characterized in that: The preparation method comprises the following steps: Terephthalic acid and / or terephthalate, adipic acid, butanediol and a biodegradable monomer are mixed and polymerized to obtain the biodegradable copolyester.

2. The preparation method according to claim 1, characterized in that: The raw materials for preparing the biodegradable copolyester include the following components in parts by weight:

3. The preparation method according to claim 1 or 2, characterized in that: The terephthalate ester is selected from any one of dimethyl terephthalate, diethyl terephthalate, dipropyl terephthalate, dibutyl terephthalate or dioctyl terephthalate, or a combination of at least two thereof; Preferably, the biodegradable monomer includes any one of lactic acid, methyl lactate, glycolic acid, methyl glycolate, or a combination of at least two thereof.

4. The preparation method according to claim 2, characterized in that: The raw materials for preparing the biodegradable copolyester also include 0.005 to 0.1 parts of auxiliary agent; Preferably, the auxiliary agent includes an antioxidant; Preferably, the antioxidant is selected from any one of tris(2,4-di-tert-butylphenyl)phosphite, triphenyl phosphite or bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite or a combination of at least two thereof.

5. The preparation method according to claim 3, characterized in that: The raw materials for preparing the biodegradable copolyester also include 0.05 to 1 part of a catalyst; Preferably, the catalyst comprises n-butyl titanate or isopropyl titanate.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The polymerization temperature is 130-250°C; Preferably, the polymerization time is 5 to 12 hours.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The weight average molecular weight of the biodegradable copolyester is 80,000 to 120,000.

8. A biodegradable copolyester, characterized in that: The molecular chain of the biodegradable copolyester includes the following repeating units: Among them, R is selected from or methylene, with dotted lines indicating attachment sites; x is a number between 1 and 5, y is a number between 1 and 7, z1 is a number between 1 and 10, and z2 is a number between 1 and 10; Preferably, the total degree of polymerization of the repeating units directly connected to the repeating units with a degree of polymerization of x and the repeating units with a degree of polymerization of y is ≤15.

9. The biodegradable copolyester according to claim 8, characterized in that: The x is a number between 1.5 and 5, y is a number between 2 and 5, z1 is a number between 3 and 5, and z2 is a number between 3 and 5.

10. An application of the biodegradable copolyester prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The biodegradable copolyester is used for preparing packaging materials.

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