Method for preparing petg biodegradable copolyester from waste pet polyester

Abstract

The application discloses a method for preparing PETG biodegradable copolyester from waste PET polyester. The method comprises the following steps: mixing waste PET polyester, alcoholysis agent and catalyst, heating to perform alcoholysis reaction, controlling alcoholysis reaction conditions to stop the reaction when the PET polyester is depolymerized into an oligomer with a number average molecular weight of 1000-2000 g / mol and a polymerization degree of 5-8, then supplementing monomers, and completing polycondensation reaction under high vacuum conditions to obtain PETG copolyester. The scheme has the advantages of simple process route, small catalyst consumption, no need to supplement catalyst during polycondensation reaction, low energy consumption, realization of conversion of non-degradable PET into biodegradable copolyester, and important significance for relieving plastic pollution problems.

Description

Technical Field

[0001] This invention relates to the field of waste material recycling. More specifically, it relates to a method for preparing PETG biodegradable copolyester from waste PET polyester. Background Technology

[0002] Polyethylene terephthalate (PET) is a thermoplastic widely used in beverage bottles, food packaging, textiles, and engineering plastics due to its excellent mechanical properties, chemical stability, and good transparency. While PET has a long lifespan, its slow degradation makes waste PET a global challenge, especially since plastic bottles and packaging materials often enter the environment as waste, imposing a long-term burden on ecosystems.

[0003] To address the PET waste problem, recycling technologies have gained increasing attention. Currently, PET recycling is mainly divided into two methods: mechanical recycling and chemical recycling. Mechanical recycling refers to cleaning, crushing, and melting waste PET materials before reprocessing them into new PET products. While this method is simple and economical, the recycled PET often suffers from performance degradation and inevitably accumulates impurities, limiting its reuse scope. In contrast, chemical recycling degrades PET into its monomers or oligomers through hydrolysis and alcoholysis, achieving high-quality reuse. However, existing recycling methods are usually limited to the reuse of raw materials, lacking effective enhancement and functional modification of the recycled PET's performance.

[0004] Patent CN118374057A discloses a method for preparing PET copolyester through alcoholysis and polymerization of waste PET. However, different catalysts are required in the alcoholysis and polymerization stages, and stabilizers and antioxidants need to be added to the polymerization system, making the operation complex. Patent CN112441917A discloses a method for recovering terephthalic acid esters by transesterification of waste PET with alkyl alcohols, but the product requires multiple processing steps, resulting in a complex process and high energy consumption. Therefore, a simpler method for PET recycling is needed.

[0005] PETG, as a biodegradable copolyester material, is increasingly favored by the market due to its good processing performance and superior physical properties. Therefore, converting PET into biodegradable polyester PETG through upgraded recycling technologies has become an important direction for enhancing the recycling value of PET. Summary of the Invention

[0006] Based on the above problems, the first objective of this invention is to provide a method for preparing PETG biodegradable copolyester from waste PET polyester. This method uses waste PET polyester as raw material, and under the action of an alcoholysis agent and a catalyst, the alcoholysis reaction conditions are controlled to obtain the alcoholysis product. After adding monomer, a polycondensation reaction can be directly carried out to obtain PETG biodegradable copolyester.

[0007] The second objective of this invention is to provide a PETG biodegradable copolyester prepared from waste PET.

[0008] To achieve the first objective mentioned above, the present invention adopts the following technical solution:

[0009] This invention discloses a method for preparing PETG copolyester from waste PET polyester. The method uses waste PET polyester as raw material and includes the following steps:

[0010] Waste PET polyester, alcoholysis agent and catalyst are mixed and heated to carry out alcoholysis reaction. The alcoholysis reaction conditions are controlled to depolymerize the PET polyester to oligomers with a number average molecular weight of 1000-2000 g / mol and a degree of polymerization of 5-8, and the reaction is stopped. Then monomers are added and polycondensation reaction is completed under high vacuum conditions to obtain PETG copolyester.

[0011] Furthermore, the alcoholysis agent is selected from ethylene glycol.

[0012] Furthermore, the catalyst is selected from one or more of antimony-based catalysts, germanium-based catalysts, rare earth catalysts, and titanium-based catalysts, preferably a titanium-based bimetallic catalyst. The titanium-based bimetallic catalyst is prepared according to CN108034046A. The titanium-based bimetallic catalyst selected in this invention can catalyze both the alcoholysis of PET polyester and the synthesis of copolyesters, making it a highly efficient catalyst with dual catalytic activity.

[0013] Furthermore, the monomer is selected from glycolic acid or methyl glycolate.

[0014] Furthermore, the amount of the alcoholysis agent used is 0.5-10 times the mass of the waste PET polyester.

[0015] Further, the amount of catalyst used is 0.01-0.5% of the mass of waste PET polyester. Exemplarily, the amount of catalyst used can also be 0.01-0.1%, 0.01-0.2%, 0.01-0.3%, 0.01-0.4%, 0.05-0.1%, 0.05-0.2%, 0.05-0.3%, 0.05-0.4%, 0.05-0.5%, 0.1-0.2%, 0.1-0.3%, 0.1-0.4%, 0.1-0.5%, 0.2-0.3%, 0.2-0.4%, 0.2-0.5%, 0.3-0.4%, 0.3-0.5%, 0.4-0.5%, etc., of the mass of waste PET polyester.

[0016] Furthermore, the mass ratio of monomer to PET polyester is 0.01-1. Exemplarily, the mass ratio of monomer to waste PET polyester can also be 0.05-0.1, 0.05-0.2, 0.05-0.3, 0.05-0.4, 0.05-0.5, 0.05-0.6, 0.05-0.7, 0.05-0.8, 0.05-0.9, 0.05-1, 0.1-0.2, 0.1-0.3, 0.1-0.4, 0.1-0.5, 0.1-0.6, 0.1-0.7, 0.1-0.8, 0.1-0.9, 0.1-1, etc.

[0017] Furthermore, the reaction temperature of the alcoholysis reaction is 180-230℃, and the reaction time of the alcoholysis reaction is 1.0-8.0 h.

[0018] Furthermore, the vacuum degree in the polycondensation reaction is controlled at 10-100 Pa, the reaction temperature of the polycondensation reaction is 240-260℃, and the reaction time of the polycondensation reaction is 0.5-5.0 h.

[0019] Furthermore, the waste PET polyester is selected from one or more of waste PET bottles, waste PET films and waste PET fibers, and its number average molecular weight is 10-40 kg / mol.

[0020] To achieve the second objective mentioned above, the present invention adopts the following technical solution:

[0021] This invention discloses a PETG biodegradable copolyester prepared by the method described above, the structural formula of which is shown below:

[0022]

[0023] Where x is 5-8, y is 1-2, and the number-average molecular weight of the PETG biodegradable copolyester is 10000-50000 g / mol.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention provides a rapid and effective method for preparing PETG biodegradable copolyester from waste PET polyester. Waste PET polyester is directly polycondensed after alcoholysis to form oligomers of a certain molecular weight. Compared to existing technologies that involve alcoholysis of PET into monomers, followed by esterification and polycondensation to finally generate copolyester, this method has a simpler process, requires less catalyst, has lower energy consumption, and produces a biodegradable copolyester. This method realizes the transformation of non-degradable PET into biodegradable copolyester, which is of great significance for alleviating environmental pollution problems.

[0026] After the alcoholysis reaction is completed, the system does not require any separation steps and can skip the esterification stage to directly carry out the polycondensation reaction, which greatly simplifies the process and reduces time costs.

[0027] The catalyst selected in this invention (e.g., a titanium-based bimetallic catalyst) can catalyze both the alcoholysis of PET polyester and the synthesis of copolyesters. This allows for the use of a single catalyst in both the alcoholysis and polycondensation processes, with the catalyst added only once during alcoholysis. This achieves a successful transition from alcoholysis to polycondensation without the need for secondary additions of the polycondensation catalyst throughout the entire process. Furthermore, the relatively small amount of catalyst used in the alcoholysis reaction and the absence of additional catalyst in the subsequent polycondensation reaction ensures a low metal content in the recovered polymer.

[0028] The waste PET polyester used in this invention has a wide range of sources, including waste PET bottles, waste PET films, and waste PET fibers. This method realizes the recycling of PET waste into biodegradable copolyester. Detailed Implementation

[0029] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0030] The molecular weight and distribution of the polymer were determined using a gel permeation chromatography system (GPC, e2695, Waters, USA) with chloroform and o-chlorophenol as a mixed solvent, chloroform as the mobile phase, and PMMA as the reference standard.

[0031] The content of metal elements in the polymer was determined using an inductively coupled plasma mass spectrometer (ICP-MS-2030, Shimadzu, Japan) with trifluoroacetic acid as the solvent.

[0032] Using nuclear magnetic resonance hydrogen spectroscopy (NMR) 1The structure of the polymer was tested by 1H NMR (Advance 400, Bruker, Germany), and the content of GA units in the copolyester was calculated.

[0033] The titanium-based bimetallic catalysts used in the following specific examples of the present invention were prepared according to the preparation conditions of Example 1 in CN108034046A.

[0034] Examples 1-8

[0035] The structural formula of PETG copolyester is shown below:

[0036] Where x is 5-8, y is 1-2, and the number-average molecular weight of the copolyester is 10000-50000 g / mol.

[0037] The steps for preparing PETG copolyester by alcoholysis and polymerization of waste PET polyester are as follows:

[0038] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and titanium-based bimetallic catalyst (0.15g) were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The stirring speed was 300rpm, and after reacting at a certain temperature for a certain time, oligomers with a number average molecular weight of about 1000-2000g / mol and a degree of polymerization of 5-8 were obtained.

[0039] (2) Polymerization: Add glycolic acid (20g), use an oil pump to reduce the pressure of the reaction system to below 100Pa, increase the stirring speed to 450rpm, and carry out the polycondensation reaction at a certain temperature. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30N·cm, the reaction is considered to have reached the endpoint, and PETG copolyester is obtained.

[0040] In Examples 1-8, the alcoholysis temperature, alcoholysis time, molecular weight of the alcoholysis product, polycondensation temperature and polycondensation time of each example are shown in Table 1, and the molecular weight of the PETG copolyester obtained in each example is shown in Table 2.

[0041] Table 1. Reaction parameters in Examples 1-8

[0042]

[0043]

[0044] Table 2. Molecular weight of PETG copolyesters in Examples 1-8

[0045]

[0046] Examples 9-11

[0047] The steps for preparing PETG copolyester by alcoholysis and polymerization of waste PET polyester are as follows:

[0048] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and a certain amount of titanium-based bimetallic catalyst were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200℃ and the stirring speed at 300rpm. After reacting for a period of time, oligomers with a number average molecular weight of approximately 1500g / mol were obtained.

[0049] (2) Polymerization: Add glycolic acid (20g), use an oil pump to reduce the pressure of the reaction system to below 100Pa, raise the temperature of the oil bath to 250℃, and increase the stirring speed to 450rpm to carry out the polycondensation reaction. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30N·cm, the reaction is considered to have reached the endpoint, and PETG copolyester is obtained.

[0050] In Examples 9-11, the amount of catalyst, alcoholysis time, polycondensation time, and molecular weight of the obtained PETG copolyester are shown in Table 3.

[0051] Table 3. Reaction parameters and product information in Examples 9-11

[0052]

[0053] Examples 12-16

[0054] The steps for preparing PETG copolyester by alcoholysis and polymerization of waste PET polyester are as follows:

[0055] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and titanium-based bimetallic catalyst (0.15g) were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200℃ and the stirring speed at 300rpm. After reacting for 3.5h, oligomers with a number average molecular weight of approximately 1500g / mol were obtained.

[0056] (2) Polymerization: A certain amount of glycolic acid was added, and the pressure of the reaction system was reduced to below 100 Pa using an oil pump. The temperature of the oil bath was raised to 250°C, and the stirring speed was increased to 450 rpm to carry out the polycondensation reaction. When the viscosity of the polymer increased significantly and the torque of the stirring device reached 30 N·cm, the reaction was considered to have reached its endpoint, and PETG copolyester was obtained.

[0057] The reaction parameters and product details in Examples 12-16 are shown in Table 4.

[0058] Table 4. Reaction parameters and product information in Examples 12-16

[0059]

[0060] Comparative Example 1

[0061] The preparation of PETG copolyester by alcoholysis and polymerization of waste PET polyester differs from Example 7 in that the reaction time is extended to hydrolyze the polyester into monomers before polymerization. The steps are as follows:

[0062] (1) Alcohololysis: Waste PET (100.0 g), ethylene glycol (300.0 g), and titanium-based bimetallic catalyst (0.15 g) were added to a 500 mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200 °C and the stirring speed at 300 rpm. After 6.0 h of reaction, the yield of the monomer product diethyl terephthalate was 80.3%.

[0063] (2) Polymerization: Add glycolic acid (20g), and carry out esterification reaction at 200-240℃ for 3 hours under normal pressure and stirring speed of 450rpm. Then, use an oil pump to reduce the pressure of the reaction system to below 100Pa, and carry out polycondensation reaction at 250℃ for about 90 minutes. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30N·cm, the reaction is considered to have reached the endpoint, and PETG copolyester is obtained.

[0064] Comparative Example 2

[0065] The preparation of PETG copolyester by alcoholysis and polymerization of waste PET polyester differs from Comparative Example 1 in that the reaction time is shortened to hydrolyze the polyester into oligomers with higher molecular weight before polymerization. The steps are as follows:

[0066] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and titanium-based bimetallic catalyst (0.15g) were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200℃ and the stirring speed at 300rpm. After reacting for 2.5h, oligomers with a number average molecular weight of approximately 4000g / mol were obtained.

[0067] (2) Polymerization: Add glycolic acid (20g), use an oil pump to reduce the pressure of the reaction system to below 100Pa, raise the temperature of the oil bath to 250℃, and increase the stirring speed to 450rpm to carry out the polycondensation reaction. The polycondensation reaction lasts for about 80min. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30N·cm, the reaction is considered to have reached the endpoint, and PETG copolyester is obtained.

[0068] The reaction parameters and product information for Examples 7 and Comparative Examples 1-2 are shown in Table 5.

[0069] Table 5. Reaction parameters and product information in Example 7 and Comparative Examples 1-2

[0070]

[0071] The comparison reveals that depolymerizing polyester into monomers before polymerization significantly prolongs the alcoholysis and polymerization times. Conversely, shortening the alcoholysis time to obtain larger molecular weight oligomers results in longer ET segments in the PETG copolyester, potentially leading to decreased biodegradability.

[0072] Comparative Example 3

[0073] The preparation of PETG copolyester by alcoholysis and polymerization of waste PET polyester differs from Example 7 in that the catalyst used in the reaction is tetrabutyl titanate, and the steps are as follows:

[0074] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and tetrabutyl titanate (0.19g) were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200℃ and the stirring speed at 300rpm. After reacting for 6.0h, oligomers with a number average molecular weight of approximately 1500g / mol were obtained.

[0075] (2) Polymerization: Add glycolic acid (20g), use an oil pump to reduce the pressure of the reaction system to below 100Pa, raise the temperature of the oil bath to 250℃, and increase the stirring speed to 450rpm to carry out the polycondensation reaction. The polycondensation reaction lasts for about 130min. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30N·cm, the reaction is considered to have reached the endpoint, and PETG copolyester is obtained.

[0076] Comparative Example 4

[0077] The preparation of PETG copolyester by alcoholysis and polymerization of waste PET polyester differs from Comparative Example 3 in the amount of tetrabutyl titanate used. The steps are as follows:

[0078] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and tetrabutyl titanate (0.32g) were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200℃ and the stirring speed at 300rpm. After reacting for 3.5h, oligomers with a number average molecular weight of approximately 1500g / mol were obtained.

[0079] (2) Polymerization: Add glycolic acid (20g), use an oil pump to reduce the pressure of the reaction system to below 100Pa, raise the temperature of the oil bath to 250℃, and increase the stirring speed to 450rpm to carry out the polycondensation reaction. The polycondensation reaction lasts for about 110min. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30N·cm, the reaction is considered to have reached the endpoint, and PETG copolyester is obtained.

[0080] Comparative Example 5

[0081] The preparation of PETG copolyester by alcoholysis and polymerization of waste PET polyester differs from Comparative Example 4 in that tetrabutyl titanate is added in two separate steps, alcoholysis and polymerization, as follows:

[0082] (1) Alcohololysis: Waste PET (100.0g), ethylene glycol (300.0g), and tetrabutyl titanate (0.16g) were added to a 500mL three-necked flask, which was then placed in an oil bath equipped with a mechanical stirrer. The reaction temperature was controlled at 200℃ and the stirring speed at 300rpm. After reacting for 6.5h, oligomers with a number average molecular weight of approximately 1500g / mol were obtained.

[0083] (2) Polymerization: Add glycolic acid (20g) and tetrabutyl titanate (0.16g) to the three-necked flask. Use an oil pump to reduce the pressure of the reaction system to below 100Pa, raise the temperature of the oil bath to 250℃, and increase the stirring speed to 450rpm to carry out the polycondensation reaction. The polycondensation reaction lasts for about 110min. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30N·cm, the reaction is considered to have reached the endpoint, and PETG copolyester is obtained.

[0084] The reaction parameters and product details for Examples 7 and Comparative Examples 3-5 are shown in Table 6.

[0085] Table 6. Reaction parameters and product information in Example 7 and Comparative Examples 3-5

[0086]

[0087]

[0088] The comparison reveals that when tetrabutyl titanate is used as a catalyst, the reaction efficiency is relatively lower than that of titanium-based bimetallic catalysts. A longer alcoholysis time or more catalysts are required to obtain a copolyester comparable to that in the examples. However, increasing the amount of catalyst may result in a higher metal content in the prepared copolyester.

[0089] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a PETG biodegradable copolyester from waste PET polyester, characterized by, The method comprises the following steps: The waste PET polyester, alcoholysis agent and catalyst are mixed, heated to carry out alcoholysis reaction, the alcoholysis reaction condition is controlled to make the PET polyester depolymerize to the oligomer with number average molecular weight of 1000-2000 g / mol and polymerization degree of 5-8, then monomer is added to complete the polycondensation reaction under high vacuum condition, and the PETG copolyester is obtained; The catalyst is titanium-based bimetallic catalyst; The vacuum degree in the polycondensation reaction is controlled to be 10-100 Pa; The monomer is selected from glycolic acid or methyl glycolate.

2. The method of claim 1, wherein, The alcoholysis agent is selected from ethylene glycol.

3. The method of claim 1, wherein, The amount of the alcoholysis agent is 0.5-10 times of the mass of the waste PET polyester.

4. The method of claim 1, wherein, The amount of the catalyst is 0.01-0.5% of the mass of the waste PET polyester.

5. The method of claim 1, wherein, The mass ratio of the monomer to the waste PET polyester is 0.01-1.

6. The method of claim 1, wherein, The reaction temperature of the alcoholysis reaction is 180-230 DEG C, and the reaction time of the alcoholysis reaction is 1.0-8.0 h.

7. The method of claim 1, wherein, The reaction temperature of the polycondensation reaction is 240-260 DEG C, and the reaction time of the polycondensation reaction is 0.5-5.0 h.

8. A PETG biodegradable copolyester characterized in that, The method is prepared by the method in any one of claims 1-7, and the structural formula is as follows: ； Wherein, x is 5-8, y is 1-2, and the number average molecular weight of the PETG biodegradable copolyester is 10000-50000 g / mol.

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