A method for preparing a petg biodegradable copolyester from a mixed polyester

Abstract

The application discloses a method for preparing a PETG biodegradable copolyester from mixed polyesters. The method comprises the following steps: mixing waste PET polyesters, PGA polyesters, an alcoholysis agent and a catalyst, heating to perform alcoholysis reaction, controlling the alcoholysis reaction conditions to stop the reaction when the number average molecular weight of the PET is 1000-2000 g / mol, and then completing polycondensation reaction under high vacuum conditions to obtain the PETG copolyester. The process route is simple, the catalyst consumption is low, the polycondensation reaction does not require additional catalyst, the energy consumption is low, the conversion from non-degradable PET to biodegradable copolyester is realized, and the method has important significance for relieving the plastic pollution problem.

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 by blending polyesters. Background Technology

[0002] Polyethylene terephthalate (PET) is a thermoplastic polyester material widely used in packaging, fibers, and engineering plastics, favored for its excellent mechanical properties, heat resistance, and transparency. However, the increasing production and consumption of PET has caused serious environmental pollution problems. The accumulation of waste PET not only occupies land resources but also puts considerable pressure on the ecological environment. Therefore, developing effective PET recycling and reuse technologies has become an important research topic in materials science.

[0003] Currently, waste PET recycling methods are mainly divided into physical recycling and chemical recycling. Physical recycling methods include processes such as washing, crushing, melting, and regranulation, which can turn waste PET into recycled pellets. However, due to limitations in raw material purity and impurity content, the performance of the recycled materials often fails to meet the requirements of high-end applications. Chemical recycling, on the other hand, uses chemical reactions to convert waste PET into its raw material monomers, such as hydrolysis, alcoholysis, and pyrolysis. These chemical recycling methods can effectively process complex and mixed PET waste and generate high-purity raw materials that meet high-standard application requirements. Compared to physical recycling, chemical recycling has the advantages of higher recovery rates and greater tolerance to contaminants.

[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] In recent years, with the growing acceptance of the concept of sustainable development, the research and development of biodegradable materials has gradually attracted attention. PETG, as a biodegradable copolyester material, is increasingly favored by the market due to its good processing performance and superior physical properties. Therefore, recycling waste PET to prepare PETG biodegradable copolyester can not only effectively solve the environmental problems caused by waste PET, but also provide a possible solution for the development of new environmentally friendly materials. 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 mixed polyesters. This method uses waste PET polyester and PGA polyester as raw materials, and, under the action of an alcoholysis agent and a catalyst, regulates the alcoholysis reaction conditions so that the alcoholysis products can directly undergo polycondensation reaction to obtain PETG biodegradable copolyester.

[0007] The second objective of this invention is to provide a PETG biodegradable copolyester prepared by the above method.

[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 mixed polyesters. The method uses waste PET polyester and PGA polyester as raw materials and belongs to a mixed polyester system. The method includes the following steps:

[0010] Waste PET polyester, PGA polyester, alcoholysis agent and catalyst are mixed and heated to carry out alcoholysis reaction. The alcoholysis reaction conditions are controlled so that the PET is depolymerized to a number average molecular weight of 1000-2000 g / mol and the reaction is stopped. Then, the polycondensation reaction is completed under high vacuum 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 and PGA polyesters and the synthesis of copolyesters, making it a highly efficient catalyst with dual catalytic activity.

[0013] Furthermore, the amount of the alcoholysis agent used is 0.5-10 times the sum of the mass of waste PET polyester and PGA polyester.

[0014] Further, the amount of catalyst used is 0.01-0.5% of the sum of the mass of waste PET polyester and PGA 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 sum of the mass of waste PET polyester and PGA polyester.

[0015] Furthermore, the mass ratio of PGA polyester to waste PET polyester is 0.02-0.5. Exemplarily, the mass ratio of PGA polyester to waste PET polyester can also be 0.02-0.1, 0.02-0.2, 0.02-0.3, 0.02-0.4, 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.

[0016] Furthermore, the reaction temperature of the alcoholysis reaction is 180-230℃, and the reaction time of the alcoholysis reaction is 0.5-8.0 h.

[0017] Furthermore, the reaction temperature of the polycondensation reaction is 240-260℃, and the reaction time of the polycondensation reaction is 0.5-5.0 h.

[0018] Furthermore, the vacuum level in the polycondensation reaction is controlled at 10-100 Pa.

[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 1-100, y is 1-3, 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 efficient method for preparing PETG biodegradable copolyester from waste PET polyester. Waste PET polyester, PGA polyester, an alcoholysis agent, and a catalyst are mixed and subjected to an alcoholysis reaction to obtain oligomers. Then, a polycondensation reaction is completed under specific reaction temperatures and high vacuum conditions to obtain the PETG copolyester. This method features a simple process route, low catalyst usage, low energy consumption, and the prepared copolyester is biodegradable, realizing the conversion 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 a successful transition from alcoholysis to polycondensation without the need for secondary addition of a polycondensation catalyst throughout the 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) 1 The 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 1-10, y is 1-3, and the number-average molecular weight of the copolyester is 10000-50000 g / mol.

[0037] The following steps are taken to prepare PETG copolyester by alcoholysis and polymerization of waste PET and PGA:

[0038] (1) Alcohololysis: Waste PET (100.0g), PGA (15.0g), ethylene glycol (300.0g), and titanium-based bimetallic catalyst (0.16g) 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 the reaction was carried out at a certain temperature for a certain time to obtain oligomers with a number average molecular weight of approximately 1000-2000g / mol.

[0039] (2) Polymerization: The pressure of the reaction system is reduced to below 100 Pa using an oil pump, and the stirring speed is increased to 450 rpm. Polycondensation reaction is carried out at a certain temperature. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30 N·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 following steps are taken to prepare PETG copolyester by alcoholysis and polymerization of waste PET and PGA:

[0048] (1) Alcohololysis: Waste PET (100.0g), PGA (15.0g), 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 about 2000g / mol were obtained.

[0049] (2) Polymerization: The pressure of the reaction system is reduced to below 100 Pa using an oil pump, the temperature of the oil bath is raised to 250℃, and the stirring speed is increased to 450 rpm to carry out the polycondensation reaction. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30 N·cm, the reaction is considered to have reached its endpoint, and PETG copolyester is obtained.

[0050] In Examples 9-11, the reaction parameters and product details are shown in Table 3.

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

[0052]

[0053] Examples 12-16

[0054] The following steps are taken to prepare PETG copolyester by alcoholysis and polymerization of waste PET and PGA:

[0055] (1) Alcohololysis: Waste PET (100.0g), a certain amount of PGA, ethylene glycol (300.0g), and titanium-based bimetallic catalyst (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 a period of time, oligomers with a number average molecular weight of about 2000g / mol were obtained.

[0056] (2) Polymerization: The pressure of the reaction system is reduced to below 100 Pa using an oil pump, the temperature of the oil bath is raised to 250℃, and the stirring speed is increased to 450 rpm to carry out the polycondensation reaction. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30 N·cm, the reaction is considered to have reached its endpoint, and PETG copolyester is 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] PETG copolyester was prepared by alcoholysis and polymerization of waste PET and PGA. The difference from Example 8 is that the reaction time was extended to hydrolyze the polyester into monomers before polymerization. The steps are as follows:

[0062] (1) Alcohololysis: Waste PET (100.0 g), PGA (15.0 g), ethylene glycol (300.0 g), and titanium-based bimetallic catalyst (0.16 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 75.3%.

[0063] (2) Polymerization: Esterification was carried out at 200-240℃ for 3.0 h under normal pressure with a stirring speed of 450 rpm. Subsequently, the pressure of the reaction system was reduced to below 100 Pa using an oil pump, and polycondensation was carried out at 250℃ for about 60 min. 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.

[0064] Comparative Example 2

[0065] PETG copolyester was prepared by alcoholysis and polymerization of waste PET and PGA. The difference from Example 8 is that the reaction time was shortened to hydrolyze the polyester into oligomers with higher molecular weights before polymerization. The steps are as follows:

[0066] (1) Alcohololysis: Waste PET (100.0g), PGA (15.0g), ethylene glycol (300.0g), and titanium-based bimetallic catalyst (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 2.5h, oligomers with a number average molecular weight of approximately 5000g / mol were obtained.

[0067] (2) Polymerization: The pressure of the reaction system is reduced to below 100 Pa using an oil pump, the temperature of the oil bath is raised to 250℃, and the stirring speed is increased to 450 rpm to carry out the polycondensation reaction. The polycondensation reaction lasts for about 60 minutes. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30 N·cm, the reaction is considered to have reached its endpoint, and PETG copolyester is obtained.

[0068] The reaction parameters and product information for Example 8 and Comparative Examples 1-2 are shown in Table 5.

[0069] Table 5. Reaction parameters and product information in Example 8 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 oligomers with larger molecular weights makes it difficult for GA units to insert into the molecular weight of PET, resulting in a lower GA unit content in the copolyester and affecting its biodegradability.

[0072] Comparative Example 3

[0073] PETG copolyester was prepared by alcoholysis and polymerization of waste PET and PGA. The difference from Example 8 is that tetrabutyl titanate was used as the catalyst in the reaction. The steps are as follows:

[0074] (1) Alcohololysis: Waste PET (100.0g), PGA (15.0g), ethylene glycol (300.0g), and tetrabutyl titanate (0.22g) 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 5.0h, oligomers with a number average molecular weight of approximately 2000g / mol were obtained.

[0075] (2) Polymerization: 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℃, and the stirring speed was increased to 450 rpm to carry out the polycondensation reaction. The polycondensation reaction lasted for about 120 minutes. 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 the endpoint, and PETG copolyester was obtained.

[0076] Comparative Example 4

[0077] PETG copolyester was prepared by alcoholysis and polymerization of waste PET and PGA. The difference from Comparative Example 3 is the amount of tetrabutyl titanate used. The steps are as follows:

[0078] (1) Alcohololysis: Waste PET (100.0g), PGA (15.0g), ethylene glycol (300.0g), and tetrabutyl titanate (0.36g) 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 3.0h, oligomers with a number average molecular weight of approximately 2000g / mol were obtained.

[0079] (2) Polymerization: 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℃, and the stirring speed was increased to 450 rpm to carry out the polycondensation reaction. The polycondensation reaction lasted for about 90 minutes. 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 the endpoint, and PETG copolyester was obtained.

[0080] Comparative Example 5

[0081] PETG copolyester was prepared by alcoholysis and polymerization of waste PET and PGA. The difference from Comparative Example 4 is that tetrabutyl titanate was added in two separate steps, alcoholysis and polymerization, as follows:

[0082] (1) Alcohololysis: Waste PET (100.0g), PGA (15.0g), ethylene glycol (300.0g), and tetrabutyl titanate (0.18g) 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 5.5h, oligomers with a number average molecular weight of approximately 2000g / mol were obtained.

[0083] (2) Polymerization: Add tetrabutyl titanate (0.18 g) to the three-necked flask, reduce the pressure of the reaction system to below 100 Pa using an oil pump, raise the temperature of the oil bath to 250 °C, and increase the stirring speed to 450 rpm to carry out the polycondensation reaction. The polycondensation reaction lasts for about 90 min. When the viscosity of the polymer increases significantly and the torque of the stirring device reaches 30 N·cm, the reaction is considered to have reached its endpoint, and PETG copolyester is obtained.

[0084] The reaction parameters and product details for Example 8 and Comparative Examples 3-5 are shown in Table 6.

[0085] Table 6. Reaction parameters and product information in Example 8 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 PETG biodegradable copolyester from blended polyesters, characterized in that, Includes the following steps: Waste PET polyester, PGA polyester, alcoholysis agent and catalyst are mixed and heated to carry out alcoholysis reaction. The alcoholysis reaction conditions are controlled so that the PET is depolymerized to a number average molecular weight of 1000-2000 g / mol and the reaction is stopped. Then, the polycondensation reaction is completed under high vacuum to obtain PETG copolyester. The alcoholysis agent is selected from ethylene glycol; The catalyst is selected from titanium-based bimetallic catalysts; The amount of the alcoholysis agent used is 0.5-10 times the sum of the mass of waste PET polyester and PGA polyester; The amount of catalyst used is 0.01-0.5% of the sum of the mass of waste PET polyester and PGA polyester.

2. The method according to claim 1, characterized in that, The vacuum level in the polycondensation reaction is controlled at 10-100 Pa.

3. The method according to claim 1, characterized in that, The mass ratio of PGA polyester to waste PET polyester is 0.02-0.

5.

4. The method according to claim 1, characterized in that, The reaction temperature of the alcoholysis reaction is 180-230℃, and the reaction time is 0.5-8.0 h.

5. The method according to claim 1, characterized in that, The reaction temperature of the polycondensation reaction is 240-260℃, and the reaction time is 0.5-5.0 h.

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