Decolorization recovery method for polyethylene terephthalate-containing articles

Abstract

The present application provides a kind of decolorization recycling treatment method of polyethylene terephthalate component product, which is to heat treatment at least 1 hour under the temperature condition of 80-260 DEG C for plastic, polyester fabric or mixed fabric containing polyethylene terephthalate component in decoloring agent, after time reaches, obtain the recycled product after decolorization by removing dye and filtering;The decoloring agent is at least one of gamma-butyrolactone, gamma-valerolactone and delta-valerolactone.The method innovatively applies the decoloring agent with lactone structure to the decolorization of polyethylene terephthalate component product, and the decoloring agent can be recycled and reused, and the key is to control the degradation and morphology of recycled product by controlling the decolorization treatment condition, which lays the foundation for the high-value application of recycled polyethylene terephthalate component product, and is expected to realize industrial application.

Description

Technical Field

[0001] This invention belongs to the field of polyester product recycling technology, and relates to a decolorization and recycling method for products containing polyethylene terephthalate. Background Technology

[0002] Polyethylene terephthalate (PET) possesses excellent mechanical, thermal, and chemical resistance properties, and is widely used in the manufacture of packaging containers, synthetic fibers, and films. In 2022, China's annual production exceeded 60 million tons. On the one hand, as a typical petroleum-based polymer, PET consumes a large amount of petrochemical resources from production to use, generating substantial carbon emissions. On the other hand, the high consumption of PET often results in enormous waste. Currently, less than 30% of PET is recycled as a renewable resource after its initial use; the remainder is incinerated or discarded into the natural environment, posing a significant threat to the ecological environment. Recycling used PET helps conserve resources and protect the environment, making the development of green and effective waste PET recycling methods of great importance.

[0003] Physical recycling is currently the main technology for recycling waste polyester, but it reduces the thermal and mechanical properties of the recycled polyester, limiting its application in high-value products. Chemical recycling technology depolymerizes waste polyester into oligomers or monomers through hydrolysis, glycolysis, or methanololysis. These oligomers or monomers can be used as raw materials for repolymerization to produce PET, thus achieving closed-loop recycling of waste polyester. The purity of the monomers obtained from degradation and recycling is crucial for the repolymerization process; when the purity is too low, the performance of the repolymerized material will deteriorate. Dyes contained in waste polyester products are one of the main sources of monomer impurities; therefore, dyes must be removed before recycling waste PET products.

[0004] Taking polyester fabric as an example, its bright colors usually come from the firm adhesion of fat-soluble dyes to the polyester surface through physical processes such as hydrogen bonding and van der Waals forces. Dyes not only greatly reduce the quality and value of recycled waste polyester products, but also cause serious environmental and health problems throughout the recycling process. In the process of decolorizing polyester fabrics, oxidants (ozone and nitric acid) and reducing agents (such as sodium formaldehyde sulfonate) are usually used to destroy the chromophores in the dye molecules. However, in most cases, the damaged dye molecules are more toxic than the original dye molecules. Another method is to "dissolve" the dye. For example, Chen et al. used ethylene glycol vapor to repeatedly dissolve dye molecules and separate them from the PET chain (Chen, Z., Sun, H., Kong, W., Chen, L., Zuo, W., 2023. Closed-loop utilization of polyester in the textile industry. Green Chemistry 25(11), 4429-4437.). In addition, dimethyl sulfoxide, benzyl alcohol, and other solvents with similar solubility parameters to PET based on Hildebrand and Hansen have been used to weaken the physical interaction between dyes and polyesters, thereby achieving the separation of dyes and polyesters. This method can not only successfully remove dyes from polyesters but also maintain the chemical and physical properties of the polyesters. However, most of the solvents used in the existing dissolution methods are non-green solvents, and they cannot control the morphology of the recovered polyesters while decolorizing, thus greatly limiting the practical application of this recovery method. Summary of the Invention

[0005] The purpose of this invention is to solve the problems in the background art mentioned above, and to provide a decolorization and recycling method for products containing polyethylene terephthalate (PET). This method innovatively applies a decolorizing agent with a lactone structure to decolorize PET products. Moreover, while the decolorizing agent is recyclable and reusable, the key point is that the degradation and morphology of the recycled products can be controlled by adjusting the decolorization treatment conditions. This lays the foundation for the high-value application of PET-containing products and is expected to achieve industrial application.

[0006] To achieve the above objectives, the present invention employs a technical solution consisting of the following technical measures.

[0007] A method for decolorizing and recycling products containing polyethylene terephthalate involves heating plastic, polyester fabric or blended fabric containing polyethylene terephthalate in a decolorizing agent at a temperature of 80-260°C for at least 1 hour. After the time is up, the decolorized recycled product is obtained by removing the dye and filtering.

[0008] The decolorizing agent is at least one of gamma-butyrolactone, gamma-valerolactone, and delta-valerolactone, or a mixed solution in which at least one of gamma-butyrolactone, gamma-valerolactone, and delta-valerolactone is used as a solute and the mass concentration of the solute is not less than 80%.

[0009] In this document, the term "plastic, polyester fabric, or blended fabric containing polyethylene terephthalate" generally refers to articles or materials containing polyethylene terephthalate (PET) and that have been dyed, especially plastic articles, polyester fabrics, or blended fabrics. Such articles or materials typically require decolorization before reuse. Generally, the decolorization and recycling method described in this invention targets scraps / waste from the production process of the aforementioned plastic, polyester fabric, or blended fabrics, as well as discarded / used articles or materials. Those skilled in the art can determine, based on common knowledge, whether the recycled articles or materials contain polyethylene terephthalate and have been dyed, thus meeting the criteria for selection as the target material for the decolorization and recycling method of this invention.

[0010] In this article, the decolorization refers to the removal of dyes (dyeing agents) and other colored processing aids from plastics, polyester fabrics, or blended fabrics containing polyethylene terephthalate, so that the color of the decolorized recycled product is very close to white, which is beneficial for subsequent reuse.

[0011] In one technical solution, the plastic, polyester fabric, or blended fabric containing polyethylene terephthalate can be pretreated before heat treatment, including washing. This pretreatment mainly removes impurities from the surface of the plastic, polyester fabric, or blended fabric. If necessary, non-polyethylene terephthalate materials (such as buttons and zippers) should also be removed. Those skilled in the art can perform specific treatments based on the actual condition of the product or material to be reused and in accordance with existing technologies.

[0012] It should be further noted that in the plastic or blended fabric containing polyethylene terephthalate described herein, the content of polyethylene terephthalate is generally not less than 1 wt%, so that the decolorizing agent with a lactone structure used in this invention can fully exert its decolorizing effect.

[0013] The inventive point of this invention lies in the innovative application of decolorizing agents with a lactone structure (such as gamma-valerate) to decolorize dyed products or materials containing polyethylene terephthalate. Such decolorizing agents with a lactone structure are biomass-derived solvents that can be obtained from cellulose and hemicellulose. They are highly stable and, compared with solvents currently reported for polyester decolorization, have lower acute toxicity to aquatic organisms and are readily biodegradable, making them a "green" solvent.

[0014] In further research, the inventors discovered that when using decolorizing agents with lactone structures for decolorization treatment of polyester or blended fabrics containing polyethylene terephthalate (PET), they unexpectedly found that different morphologies of white recycled PET products could be obtained under different temperatures and pressures during heat treatment. Analysis revealed two types: woven and granular. The woven structure can be directly recycled and redyed for use as fabric, while the granular structure, with its large specific surface area and mesoporous structure, is suitable as a functional material matrix for modification and preparation of high-value products. Furthermore, NMR and IR characterization confirmed that the PET polymer chain structure remained intact after the decolorization and recycling treatment of this invention, and viscosity testing confirmed that the molecular weight did not decrease to the monomer molecular weight, indicating that the decolorizing agent with lactone structure used in this invention did not have a degradation effect. In addition, when plastic or blended fabrics containing PET form a granular structure through the above decolorization and recycling treatment, the separation of non-PET components can be achieved simultaneously, facilitating subsequent recycling and reuse.

[0015] It should be noted that, according to a review of the technical literature in this field, the existing methods for decolorizing waste polyester mostly use toxic solvents and cannot control the morphology of the recycled PET matrix, which are very harmful to the environment and easily leave dye residues on the fabric after decolorization. Therefore, environmentally friendly decolorization and green functionalization modification of polyester fabrics are also key issues that need to be addressed in the current solvent-based decolorization and recycling of polyester fabrics.

[0016] In addition, through comparative experiments on the variable of heat treatment time, the inventors also found that when the heat treatment time exceeds 10 hours, the dye attached to the surface will gradually denature, causing the decolorization effect to gradually deteriorate. Therefore, the decolorization treatment time is preferably no more than 10 hours.

[0017] Based on the above-mentioned points of invention, in order to ensure that the recycled product after decolorization retains its original morphology as much as possible, in one preferred technical solution, the plastic, polyester fabric or blended fabric containing polyethylene terephthalate is heated in a decolorizing agent at a temperature of 80-160°C for 1-10 hours.

[0018] Based on the above-mentioned points of invention, in order to form a granular structure in the decolorized recycled product, in one preferred technical solution, the plastic, polyester fabric, or blended fabric containing polyethylene terephthalate is placed in a decolorizing agent and subjected to a closed heat treatment at a temperature of 160–260°C for at least 1 hour, accompanied by stirring at a speed in the range of 100–1000 rpm. The pressure environment of the closed heat treatment and the accompanying stirring cause the recycled product to form a granular structure. The stirring treatment is a conventional stirring method in this technical field, and those skilled in the art can select it according to existing process conditions, such as magnetic stirring or mechanical stirring.

[0019] Based on the above-mentioned points of invention, in order to make the decolorizing agent have sufficient decolorizing performance, the decolorizing agent is a mixed solution in which at least one of gamma-butyrolactone, gamma-valerolactone and delta-valerolactone is used as the solute and the mass concentration of the solute is not less than 80%. The solvent selection includes any one or more of methanol, acetone, chloroform, ethanol, dimethyl sulfoxide, dichloroethane, dimethylformamide, dichloromethane and toluene.

[0020] Based on the above-mentioned points of invention, in order to further improve the decolorization effect, the selection of the decolorizing agent was taken as a variable. Through comparative experiments, it was found that the most preferred decolorizing agent is gamma-valerolactone.

[0021] In this paper, the removal of dye is a conventional process operation in the decolorization process using a decolorizing agent. In this invention, the decolorizing agent used can efficiently remove dyes (dyeing agents) and other colored processing aids and dissolve them in the decolorizing agent. Therefore, the removal of dye is essentially the removal of the decolorizing agent containing the dye from the decolorized recycled product. Those skilled in the art can directly use existing technology / common knowledge / conventional processes to select a suitable dye removal process, especially the methods in conventional decolorization processes in this field.

[0022] The second inventive point of this invention lies in the fact that, by applying such a decolorizing agent with a lactone structure for decolorization treatment, a non-solvent miscible with the decolorizing agent (a non-solvent for plastics, polyester fabrics, or blended fabrics containing polyethylene terephthalate) can be further added during the dye removal process to remove the decolorizing agent. The purpose is to dilute and remove the dye-containing decolorizing agent from the recycled product after heat treatment, facilitating the subsequent acquisition of a recycled product free of decolorizing agent, and enabling the recycling and reuse of the decolorizing agent to reduce costs. Based on the above description and common knowledge in the art, those skilled in the art should understand that after filtering to obtain the recycled product, conventional cleaning and drying processes are usually performed to completely remove any residual non-solvents from the recycled product.

[0023] Based on this invention, in one technical solution, the dye removal is achieved by adding a non-solvent that is compatible with the decolorizing agent and is specific to polyester to remove the dye dissolved in the decolorizing agent. The non-solvent that is compatible with the decolorizing agent and is specific to polyester is preferably a conventional industrial organic reagent that is compatible with the decolorizing agent, in order to facilitate subsequent cleaning and other operations.

[0024] Based on this inventive point, in one preferred embodiment, the non-solvent that is compatible with the decolorizing agent and is suitable for polyester includes any one or more of methanol, acetone, chloroform, ethanol, dimethyl sulfoxide, dichloroethane, dimethylformamide, dichloromethane, and toluene.

[0025] Based on this inventive point, in one technical solution, the addition of a non-solvent miscible with the decolorizing agent and specific to polyester to remove the dissolved dye, followed by final filtration to obtain a recovered product, further includes collecting the filtrate and separating the decolorizing agent from the filtrate for reuse. This filtrate typically consists of the decolorizing agent, the non-solvent, and the dye, and can be further purified using conventional methods such as distillation to obtain a colorless and transparent decolorizing agent again.

[0026] In one more preferred technical solution, in order to better recycle and reuse the decolorizing agent to reduce costs, the addition of a non-solvent that is compatible with the decolorizing agent and is specific to polyester is used to remove the dye dissolved in the decolorizing agent. Specifically, a non-solvent with a volume of 1 to 4 times that of the decolorizing agent is added and ultrasonically treated for 10 to 120 minutes, filtered, and the resulting precipitate is soaked in a non-solvent for 12 to 96 hours and then filtered again. The resulting solid is dried to obtain a non-degradable recycled product. The filtrate from the two filtrations is collected, and the non-solvent is removed by a first distillation and then purified by a second distillation to obtain a colorless and transparent decolorizing agent.

[0027] In one preferred embodiment, in order to further improve the decolorization effect, the ratio of the plastic, polyester fabric or blended fabric containing polyethylene terephthalate to the decolorizing agent is at least 1 kg: 3 L, more preferably 1 kg: (3 to 120) L, that is, the solid-liquid ratio (kg: L) ranges from 1: (3 to 120).

[0028] The decolorization and recycling method of this invention can be directly applied to the field of polyethylene terephthalate recycling and reuse technology, especially to the field of recycling and reuse of polyethylene terephthalate polymer material systems.

[0029] The present invention has the following beneficial effects:

[0030] (1) This invention provides a decolorization and recycling method for products containing polyethylene terephthalate. This method innovatively uses a decolorizing agent with a lactone structure to decolorize products containing polyethylene terephthalate. Moreover, the decolorizing agent can be reused multiple times and has excellent application value, and is expected to be used industrially.

[0031] (2) This invention provides a decolorization and recycling method for products containing polyethylene terephthalate. It was found that white PET recycling products with different morphologies can be obtained under different temperature and pressure conditions during heat treatment. After analysis, they can be divided into two types: woven structure and granular structure. The woven structure can be directly recycled and redyed for use as fabric, while the granular structure has a large specific surface area and mesoporous structure, which is suitable as a functional material matrix for modification to prepare high-value products. At the same time, other non-PET components can be separated.

[0032] (3) The present invention provides a decolorization and recycling method for products containing polyethylene terephthalate. In one of the technical solutions, when the decolorizing agent is reused, the dissolved dye is easily treated in a centralized manner to avoid secondary release into the environment and causing pollution.

[0033] (4) The polyester fabric decolorized by the technical solution of the present invention can reach a brightness value of 95 or above. The recycled product with a granular structure is irregularly spherical with a size range of 1 to 10 micrometers and mesopores (10 to 40 nm) on the surface, which has the potential for modification and application. Attached Figure Description

[0034] Figure 1 This is a schematic flowchart of the decolorization and recycling process in Embodiment 1 of the present invention.

[0035] Figure 2 These are comparison images of the microstructure of five different colored polyester fabrics before and after decolorization and recycling treatment in Examples 1-5 of the present invention.

[0036] Figure 3 Figure 1 shows the BET characterization results of the white granular recovered product obtained in Example 1 of this invention. Figure 1(a) shows the N2 adsorption-desorption isotherm characterization results, and Figure 1(b) shows the pore size distribution characterization results. Detailed Implementation

[0037] To further understand the present invention, preferred embodiments are described below with reference to examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. Those skilled in the art can refer to the content of this document to appropriately improve the process parameters. In particular, it should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of the present invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to realize and apply the technology of the present invention. Although it is believed that those skilled in the art will fully understand the following terms, the following definitions are set forth to help illustrate the subject matter disclosed in the present invention.

[0038] A method for decolorizing and recycling products containing polyethylene terephthalate involves heating plastic, polyester fabric or blended fabric containing polyethylene terephthalate in a decolorizing agent at a temperature of 80-260°C for at least 1 hour. After the time is up, the decolorized recycled product is obtained by removing the dye and filtering.

[0039] The decolorizing agent is at least one of gamma-butyrolactone, gamma-valerolactone, and delta-valerolactone, or a mixed solution in which at least one of gamma-butyrolactone, gamma-valerolactone, and delta-valerolactone is used as a solute and the mass concentration of the solute is not less than 80%.

[0040] In this document, the term "plastic, polyester fabric, or blended fabric containing polyethylene terephthalate" generally refers to articles or materials containing polyethylene terephthalate (PET) and that have been dyed, especially plastic articles, polyester fabrics, or blended fabrics. Such articles or materials typically require decolorization before reuse. Generally, the decolorization and recycling method described in this invention targets scraps / waste from the production process of the aforementioned plastic, polyester fabric, or blended fabrics, as well as discarded / used articles or materials. Those skilled in the art can determine, based on common knowledge, whether the recycled articles or materials contain polyethylene terephthalate and have been dyed, thus meeting the criteria for selection as the target material for the decolorization and recycling method of this invention.

[0041] In this article, the decolorization refers to the removal of dyes (dyeing agents) and other colored processing aids from plastics, polyester fabrics, or blended fabrics containing polyethylene terephthalate, so that the color of the decolorized recycled product is very close to white, which is beneficial for subsequent reuse.

[0042] In one embodiment, the plastic, polyester fabric, or blended fabric containing polyethylene terephthalate may be pretreated, including washing, before heat treatment. This pretreatment mainly removes impurities from the surface of the plastic, polyester fabric, or blended fabric. If necessary, non-polyethylene terephthalate materials (such as buttons and zippers) may also be removed. Those skilled in the art can perform specific treatments based on the actual condition of the product or material to be reused and in accordance with existing technologies.

[0043] It should be further noted that in the plastic or blended fabric containing polyethylene terephthalate described herein, the content of polyethylene terephthalate is generally not less than 1 wt%, so that the decolorizing agent with a lactone structure used in this invention can fully exert its decolorizing effect.

[0044] In one embodiment, the plastic, polyester fabric, or blended fabric containing polyethylene terephthalate is heat-treated in a decolorizing agent at a temperature of 80–260°C for at least 1 hour, wherein the temperature is 80–260°C, for example 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, or any range or point value between them; and the heat treatment is for at least 1 hour, for example 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or any point value between them.

[0045] The inventive point of this invention lies in the innovative application of decolorizing agents with a lactone structure (such as gamma-valerate) to decolorize dyed products or materials containing polyethylene terephthalate. Such decolorizing agents with a lactone structure are biomass-derived solvents that can be obtained from cellulose and hemicellulose. They are highly stable and, compared with solvents currently reported for polyester decolorization, have lower acute toxicity to aquatic organisms and are readily biodegradable, making them a "green" solvent.

[0046] In further research, the inventors discovered that when using decolorizing agents with lactone structures for decolorization treatment of polyester or blended fabrics containing polyethylene terephthalate (PET), they unexpectedly found that different morphologies of white recycled PET products could be obtained under different temperatures and pressures during heat treatment. Analysis revealed two types: woven and granular. The woven structure can be directly recycled and redyed for use as fabric, while the granular structure, with its large specific surface area and mesoporous structure, is suitable as a functional material matrix for modification and preparation of high-value products. Furthermore, NMR and IR characterization confirmed that the PET polymer chain structure remained intact after the decolorization and recycling treatment of this invention, and viscosity testing confirmed that the molecular weight did not decrease to the monomer molecular weight, indicating that the decolorizing agent with lactone structure used in this invention did not have a degradation effect. In addition, when plastic or blended fabrics containing PET form a granular structure through the above decolorization and recycling treatment, the separation of non-PET components can be achieved simultaneously, facilitating subsequent recycling and reuse.

[0047] It should be noted that, according to a review of the technical literature in this field, the existing methods for decolorizing waste polyester mostly use toxic solvents and cannot control the morphology of the recycled PET matrix, which are very harmful to the environment and easily leave dye residues on the fabric after decolorization. Therefore, environmentally friendly decolorization and green functionalization modification of polyester fabrics are also key issues that need to be addressed in the current solvent-based decolorization and recycling of polyester fabrics.

[0048] In addition, through comparative experiments on the variable of heat treatment time, the inventors also found that when the heat treatment time exceeds 10 hours, the dye attached to the surface will gradually denature, causing the decolorization effect to gradually deteriorate. Therefore, the decolorization treatment time is preferably no more than 10 hours.

[0049] Based on the above-mentioned points of invention, in order to ensure that the recycled product after decolorization retains its original morphology as much as possible, in one preferred embodiment, the plastic, polyester fabric or blended fabric containing polyethylene terephthalate is heated in a decolorizing agent at a temperature of 80-160°C for 1-10 hours.

[0050] Based on the above-mentioned points of the invention, in order to form a granular structure in the decolorized recycled product, in one preferred embodiment, the plastic, polyester fabric, or blended fabric containing polyethylene terephthalate is subjected to a closed heat treatment in a decolorizing agent at a temperature of 160–260°C for at least 1 hour, accompanied by stirring at a speed in the range of 100–1000 rpm. The pressure environment of the closed heat treatment and the accompanying stirring cause the recycled product to form a granular structure. The stirring treatment is a conventional stirring method in this technical field, and those skilled in the art can select it according to existing process conditions, such as magnetic stirring or mechanical stirring.

[0051] Based on the above-mentioned points of invention, in order to make the decolorizing agent have sufficient decolorizing performance, in one embodiment, the decolorizing agent is a mixed solution in which at least one of gamma-butyrolactone, gamma-valerolactone and delta-valerolactone is used as the solute and the mass concentration of the solute is not less than 80%. The solvent selection includes any one or more of methanol, acetone, chloroform, ethanol, dimethyl sulfoxide, dichloroethane, dimethylformamide, dichloromethane, and toluene.

[0052] Based on the above-mentioned points of invention, in order to further improve the decolorization effect, the selection of the decolorizing agent was taken as a variable. Through comparative experiments, it was found that the most preferred decolorizing agent is gamma-valerolactone.

[0053] In this paper, the removal of dye is a conventional process operation in the decolorization process using a decolorizing agent. In this invention, the decolorizing agent used can efficiently remove dyes (dyeing agents) and other colored processing aids and dissolve them in the decolorizing agent. Therefore, the removal of dye is essentially the removal of the decolorizing agent containing the dye from the decolorized recycled product. Those skilled in the art can directly use existing technology / common knowledge / conventional processes to select a suitable dye removal process, especially the methods in conventional decolorization processes in this field.

[0054] The second inventive point of this invention lies in the fact that, by applying such a decolorizing agent with a lactone structure for decolorization treatment, a non-solvent miscible with the decolorizing agent (a non-solvent for plastics, polyester fabrics, or blended fabrics containing polyethylene terephthalate) can be further added during the dye removal process to remove the decolorizing agent. The purpose is to dilute and remove the dye-containing decolorizing agent from the recycled product after heat treatment, facilitating the subsequent acquisition of a recycled product free of decolorizing agent, and enabling the recycling and reuse of the decolorizing agent to reduce costs. Based on the above description and common knowledge in the art, those skilled in the art should understand that after filtering to obtain the recycled product, conventional cleaning and drying processes are usually performed to completely remove any residual non-solvents from the recycled product.

[0055] Based on this invention, in one embodiment, the dye removal is achieved by adding a non-solvent that is compatible with the decolorizing agent and is specific to polyester to remove the dye dissolved in the decolorizing agent. The non-solvent that is compatible with the decolorizing agent and is specific to polyester is preferably a conventional industrial organic reagent that is compatible with the decolorizing agent, in order to facilitate subsequent cleaning and other operations.

[0056] Based on this inventive point, in one preferred embodiment, the non-solvent that is compatible with the decolorizing agent and is suitable for polyester includes any one or more of methanol, acetone, chloroform, ethanol, dimethyl sulfoxide, dichloroethane, dimethylformamide, dichloromethane, and toluene.

[0057] Based on this invention, in one embodiment, the addition of a non-solvent miscible with the decolorizing agent and specific to polyester to remove the dissolved dye, followed by final filtration to obtain a recovered product, further includes collecting the filtrate and separating the decolorizing agent from the filtrate for reuse. This filtrate typically consists of the decolorizing agent, the non-solvent, and the dye, and can be further purified using conventional methods such as distillation to obtain a colorless and transparent decolorizing agent again.

[0058] In one more preferred embodiment, in order to better recycle and reuse the decolorizing agent to reduce costs, the addition of a non-solvent that is compatible with the decolorizing agent and is specific to polyester is used to remove the dye dissolved in the decolorizing agent. Specifically, a non-solvent with a volume of 1 to 4 times that of the decolorizing agent is added and ultrasonically treated for 10 to 120 minutes, filtered, and the resulting precipitate is soaked in a non-solvent for 12 to 96 hours and then filtered again. The resulting solid is dried to obtain a non-degradable recycled product. The filtrate from the two filtrations is collected, and the non-solvent is removed by a first distillation and then purified by a second distillation to obtain a colorless and transparent decolorizing agent.

[0059] In one preferred embodiment, in order to further improve the decolorization effect, the ratio of the plastic, polyester fabric or blended fabric containing polyethylene terephthalate to the decolorizing agent is at least 1 kg: 3 L, more preferably 1 kg: (3 to 120) L, that is, the solid-liquid ratio (kg: L) ranges from 1: (3 to 120).

[0060] The decolorization and recycling method of this invention can be directly applied to the field of polyethylene terephthalate recycling and reuse technology, especially to the field of recycling and reuse of polyethylene terephthalate polymer material systems.

[0061] The present application will be further explained in detail below with reference to embodiments. However, those skilled in the art should understand that these embodiments are provided for illustrative purposes only and are not intended to limit the present application.

[0062] Example

[0063] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the scope of this application. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all commercially available conventional products. This application should not be construed as being limited to the specific embodiments described.

[0064] 1. Raw materials

[0065] gamma-butyrolactone, gamma-valerolactone and delta-valerolactone: Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0066] Polyester fabrics: Dyed polyester fabrics in yellow, red, blue, green and black were collected from waste clothing.

[0067] Blended fabrics: Blended fabrics containing polyester that are recycled from discarded clothing;

[0068] Waste plastics: Waste plastics containing polyethylene terephthalate (PET) components.

[0069] 2. Testing Methods

[0070] (1) Colorimetric characterization

[0071] The polyester particles obtained after dissolution and decolorization were characterized using a YS6010 benchtop spectrophotometer from Shenzhen Sanenshi Technology Co., Ltd.

[0072] (2) Characterization of specific surface area and porosity

[0073] The decolorized and precipitated polyester particles were characterized using a BELSORP MAXⅡ specific surface area analyzer from Mickey Bayer, Japan.

[0074] (3) Morphological characteristics

[0075] The surface / cross-sectional morphology of the samples before and after decolorization was observed using a Phenom ProX (Phenom word, Netherlands) desktop scanning electron microscope. EDS was used to determine the elemental distribution of the surface / cross-section. Before observing the cross-sectional morphology of the adsorbent, liquid nitrogen embrittlement was performed. The sample surface was purged with N2 and then sputter-coated with gold. Accelerating voltages of 10 kV and 15 kV were used to determine the surface / cross-sectional morphology and elemental distribution.

[0076] (4) Chemical structure characterization (Fourier transform infrared spectroscopy)

[0077] The structural changes of functional groups in the samples were characterized using a Thermo Nicolet 6700 infrared spectrometer, with a scanning wavenumber range of 4000-400 cm⁻¹. -1 .

[0078] (5) Chemical structure characterization (X-ray diffraction)

[0079] The crystal structure of the sample was characterized using a Rigaku Ultima IV X-ray diffractometer from Japan, under Cu Kα radiation from a 40 kV X-ray source and a working current of 40 mA. The scanning angle range was 5°–90° and the scanning speed was 5° / min.

[0080] (6) Pore structure characterization

[0081] The pore size distribution of the sample was measured using a Quanta PoreMaster 33 mercury porosimeter via mercury intrusion colorimetry.

[0082] (7) Thermal performance characterization

[0083] The samples were tested using a NETZSCH TG 209F1 thermometer (Germany) to evaluate changes in their thermal stability. The test temperature range was 30-800℃, and the heating rate was 10℃ / min. -1 Nitrogen environment.

[0084] (8) Zeta potential tester

[0085] The zeta potential of the sample surface was measured using an Anton Paar Surpass zeta potential analyzer. The pH of the sample surface was adjusted to between 2 and 12 using a 0.1 mol / L hydrochloric acid or sodium hydroxide solution.

[0086] (9) Chemical structure and elemental analysis (X-ray photoelectron spectroscopy)

[0087] The elemental composition and oxidation state of the sample surface were characterized using a Thermo K-Alpha electron spectrometer (USA).

[0088] (10) Nuclear magnetic resonance spectroscopy (NMR)

[0089] The samples were characterized using a Bruker AV II-400 nuclear magnetic resonance spectrometer (Germany), with deuterated DMSO or deuterated TFA as the solvent. The following tests were performed. 1 H and 13 C and two nuclear magnetic resonance spectra.

[0090] (11) Characterization of the viscosity / molecular weight of decolorized polyester

[0091] Heat phenol in a 65°C water bath for 1 hour until it is completely melted into a liquid. Mix 250 mL of phenol solution with 250 mL of tetrachloroethane solution in a 1:1 volume ratio and let stand for 12 hours for later use.

[0092] 0.125g of the test sample (including single-color polyester fiber and rPET obtained after decolorizing polyester fabrics of different colors) was completely dissolved in a small amount of phenol / tetrachloroethane mixed solution at 100℃. The solution was transferred to a 25mL volumetric flask and kept warm in a 25℃ water bath. Before viscosity testing, the volume was adjusted to 25mL. After standing for 5 minutes, the intrinsic viscosity was tested using an Ubbelohde viscometer. Each sample was measured three times under controlled temperature of 25℃. The viscosity and molecular weight were calculated according to formulas (1-1) and (1-2).

[0093]

[0094] [η]=KM α (1-2)

[0095] Where, η sp =η r -1;η r = t / t0 (t0 is the time for pure solvent to flow out); c = 0.5; K = 2.1 × 10 -4 , α=0.82.

[0096] Example 1

[0097] (1) Under laboratory conditions, yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg and 0.3L gamma-valerol were added to a reaction vessel and heated in a closed container at 180℃ for 5h. During this process, stirring was carried out at a stirring rate of 500rpm. The mixture was then cooled to room temperature.

[0098] (2) Add 1L of a non-solvent (ethanol) miscible with the decolorizing agent and specific to polyester to the reaction vessel and sonicate for 10 min. Filter the mixture, soak the resulting precipitate in the non-solvent for 12 h, and filter again. Dry the resulting solid under vacuum at 60℃ to obtain a white granular recycled product with an L* value (the closer to 100, the whiter) of 94, denoted as rPET (spherical particles with a diameter of approximately 10 micrometers and a specific surface area of ​​22.398 m²). 2 g -1 (The surface contains a microporous structure, and the molecular weight is reduced to half that of the original polyester);

[0099] (3) The yellow transparent mixed liquid (Solvent / Non-solvent / Dye) obtained by two filtrations in step (2) is subjected to a first rotary evaporation to collect the non-solvent distilled out. The remaining yellow transparent mixed liquid is then subjected to vacuum distillation to obtain colorless and transparent gamma-valerol (Recycled-GVL) and yellow dye solid (Recycled-dye).

[0100] Example 2

[0101] Example 2 follows the steps of Example 1, but replaces the yellow polyester fabric with red polyester fabric.

[0102] Example 3

[0103] Example 3 follows the steps of Example 1, but replaces the yellow polyester fabric with blue polyester fabric.

[0104] Example 4

[0105] Example 4 follows the steps of Example 1, but replaces the yellow polyester fabric with green polyester fabric.

[0106] Example 5

[0107] Example 5 follows the steps of Example 1, but replaces the yellow polyester fabric with black polyester fabric.

[0108] Example 6

[0109] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.3L gamma-valerol and heated at 120℃ for 3h, and then cooled to room temperature.

[0110] (2) It can be observed that after heat treatment, the yellow polyester fabric is decolorized and retains its original weave structure. The decolorized polyester fabric is taken out and a polyester fabric with the weave structure retained and the molecular weight basically unchanged is obtained. The L* value after decolorization is greater than 95.

[0111] (3) The remaining yellow transparent mixed liquid in step (2) was rotary evaporated to collect gamma-valerol (Recycled-GVL).

[0112] Example 7

[0113] (1) Under laboratory conditions, a blue polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg and 0.4L gamma-butyrolactone were added to a reaction vessel and heated in a closed container at 200℃ for 3h. During this process, stirring was carried out at a stirring rate of 200rpm. The mixture was then cooled to room temperature.

[0114] (2) Add 0.8L of a non-solvent (methanol) that is compatible with the decolorizing agent and is effective against polyester to the reaction vessel and sonicate for 20 min. Filter the mixture and soak the resulting precipitate in a non-solvent for 24 h. Filter the mixture again and dry the resulting solid under vacuum at 80 °C to obtain a white granular recovery product.

[0115] (3) The blue transparent mixed liquid obtained by two filtrations in step (2) is subjected to a first rotary evaporation to collect the non-solvent distilled out. The remaining blue transparent mixed liquid is then subjected to vacuum distillation to obtain colorless and transparent gamma-butyrolactone and blue dye solid.

[0116] Example 8

[0117] (1) Under laboratory conditions, a blue polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg and 0.3L gamma-valerol were added to a reaction vessel and heated in a closed container at 220℃ for 2h. During this process, stirring was carried out at a stirring rate of 400rpm. The mixture was then cooled to room temperature.

[0118] (2) Add 1.2L of a non-solvent (chloroform) that is compatible with the decolorizing agent and is effective against polyester to the reaction vessel and sonicate for 30 min. Filter the mixture and soak the resulting precipitate in a non-solvent for 24 h and then filter it again. Dry the resulting solid under vacuum at 60 °C to obtain a white granular recovery product.

[0119] (3) The blue transparent mixed liquid obtained by two filtrations in step (2) is subjected to a first rotary evaporation to collect the non-solvent distilled out. The remaining blue transparent mixed liquid is then subjected to vacuum distillation to obtain colorless and transparent gamma-valerol and blue dye solid.

[0120] Example 9

[0121] (1) Under laboratory conditions, yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg and 0.3L gamma-valerol were added to a reaction vessel and heated in a closed container at 260℃ for 1h. During this process, stirring was carried out at a stirring rate of 600rpm. The mixture was then cooled to room temperature.

[0122] (2) Add 0.6L of non-solvent (ethanol) that is compatible with the decolorizing agent and is effective against polyester to the reaction vessel and sonicate for 60 min. Filter the mixture and soak the resulting precipitate in a non-solvent for 48 h and then filter it again. Dry the resulting solid under vacuum at 60 °C to obtain a white granular recovery product.

[0123] (3) The yellow transparent mixed liquid obtained by two filtrations in step (2) is subjected to a first rotary evaporation to collect the non-solvent distilled out. The remaining yellow transparent mixed liquid is then subjected to vacuum distillation to obtain colorless and transparent gamma-valerol and yellow dye solid.

[0124] Example 10

[0125] (1) Under laboratory conditions, yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg and 0.3L delta-valerol were added to a reaction vessel and heated in a closed container at 200℃ for 8h. During this process, stirring was carried out at a stirring rate of 800rpm. The mixture was then cooled to room temperature.

[0126] (2) Add 1L of non-solvent (toluene) that is compatible with the decolorizing agent and is effective against polyester to the reaction vessel and sonicate for 30 min. Filter the mixture and soak the resulting precipitate in a non-solvent for 24 h and then filter it again. Dry the resulting solid under vacuum at 60 °C to obtain a white granular recovery product.

[0127] (3) The yellow transparent mixed liquid obtained by two filtrations in step (2) is subjected to a first rotary evaporation to collect the non-solvent distilled out. The remaining yellow transparent mixed liquid is then subjected to vacuum distillation to obtain colorless and transparent delta-valerol and yellow dye solid.

[0128] Example 11

[0129] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.2L gamma-butyrolactone and 0.2L gamma-valerolactone. The mixture was then sealed and heated at 240℃ for 2h, with stirring at a rate of 200rpm. The mixture was then cooled to room temperature.

[0130] (2) Add 1.2L of non-solvent (ethanol) that is compatible with the decolorizing agent and is effective against polyester to the reaction vessel and sonicate for 60 min. Filter the mixture and soak the resulting precipitate in the non-solvent for 24 h and then filter it again. Dry the resulting solid under vacuum at 60 °C to obtain a white granular recovery product.

[0131] (3) The yellow transparent mixed liquid obtained by two filtrations in step (2) is subjected to a first rotary evaporation to collect the non-solvent distilled out. The remaining yellow transparent mixed liquid is then subjected to vacuum distillation to obtain a colorless and transparent mixed solution of gamma-butyrolactone and gamma-valerolactone and a yellow dye solid.

[0132] Example 12

[0133] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.2L delta-valerolactone and 0.2L gamma-valerolactone. The mixture was then sealed and heated at 160℃ for 10h, with stirring at a rate of 100rpm. The mixture was then cooled to room temperature.

[0134] (2) Add 1.2L of non-solvent (ethanol) that is compatible with the decolorizing agent and is effective against polyester to the reaction vessel and sonicate for 60 min. Filter the mixture and soak the resulting precipitate in the non-solvent for 24 h and then filter it again. Dry the resulting solid under vacuum at 60 °C to obtain a white granular recovery product.

[0135] (3) The yellow transparent mixed liquid obtained by two filtrations in step (2) is subjected to a first rotary evaporation to collect the non-solvent distilled out. The remaining yellow transparent mixed liquid is then subjected to vacuum distillation to obtain a colorless and transparent delta-valerolactone and gamma-valerolactone mixed solution and a yellow dye solid.

[0136] Example 13

[0137] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.4L gamma-valerol and heated at 100℃ for 6h, and then cooled to room temperature.

[0138] (2) It can be observed that after heat treatment, the yellow polyester fabric is decolorized and retains its original weave structure. The decolorized polyester fabric can be taken out to obtain a polyester fabric that retains its weave structure and whose molecular weight remains basically unchanged.

[0139] (3) Collect gamma-valerol by rotary evaporation of the remaining yellow transparent mixed liquid from step (2).

[0140] Example 14

[0141] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.4L gamma-butyrolactone and heated at 120℃ for 4h, and then cooled to room temperature.

[0142] (2) It can be observed that after heat treatment, the yellow polyester fabric is decolorized and retains its original weave structure. The decolorized polyester fabric can be taken out to obtain a polyester fabric that retains its weave structure and whose molecular weight remains basically unchanged.

[0143] (3) Collect gamma-butyrolactone by rotary evaporation of the remaining yellow transparent mixed liquid from step (2).

[0144] Example 15

[0145] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.4L delta-valerol and heated at 120℃ for 4h, and then cooled to room temperature.

[0146] (2) It can be observed that after heat treatment, the yellow polyester fabric is decolorized and retains its original weave structure. The decolorized polyester fabric can be taken out to obtain a polyester fabric that retains its weave structure and whose molecular weight remains basically unchanged.

[0147] (3) The remaining yellow transparent mixed liquid from step (2) was rotary evaporated to collect delta-valerol.

[0148] Example 16

[0149] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.5L gamma-valerol and heated at 140℃ for 2h, and then cooled to room temperature.

[0150] (2) It can be observed that after heat treatment, the yellow polyester fabric is decolorized and retains its original weave structure. The decolorized polyester fabric can be taken out to obtain a polyester fabric that retains its weave structure and whose molecular weight remains basically unchanged.

[0151] (3) Collect gamma-valerol by rotary evaporation of the remaining yellow transparent mixed liquid from step (2).

[0152] Example 17

[0153] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg and 0.3Lgamma-valerol were added to a reaction vessel, heated at 160℃ for 1h, and then cooled to room temperature.

[0154] (2) It can be observed that after heat treatment, the yellow polyester fabric is decolorized and retains its original weave structure. The decolorized polyester fabric can be taken out to obtain a polyester fabric that retains its weave structure and whose molecular weight remains basically unchanged.

[0155] (3) Collect gamma-valerol by rotary evaporation of the remaining yellow transparent mixed liquid from step (2).

[0156] Example 18

[0157] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.3L gamma-valerol and heated at 80℃ for 8h, and then cooled to room temperature.

[0158] (2) It can be observed that after heat treatment, the yellow polyester fabric is decolorized and retains its original weave structure. The decolorized polyester fabric can be taken out to obtain a polyester fabric that retains its weave structure and whose molecular weight remains basically unchanged.

[0159] (3) Collect gamma-valerol by rotary evaporation of the remaining yellow transparent mixed liquid from step (2).

[0160] Example 19

[0161] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.2L gamma-butyrolactone and 0.2L gamma-valerolactone. The mixture was heated at 120℃ for 3h and then cooled to room temperature.

[0162] (2) It can be observed that after heat treatment, the yellow polyester fabric is decolorized and retains its original weave structure. The decolorized polyester fabric can be taken out to obtain a polyester fabric that retains its weave structure and whose molecular weight remains basically unchanged.

[0163] (3) After rotary evaporation of the remaining yellow transparent mixed liquid in step (2), collect the mixed solution of gamma-butyrolactone and gamma-valerolactone.

[0164] Example 20

[0165] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.4L of gamma-valerol solution (ethanol as solvent, gamma-valerol mass concentration of 80%). The vessel was sealed and heated at 180℃ for 5h, with stirring during the process at a stirring rate of 100rpm. The vessel was then cooled to room temperature.

[0166] (2) Add 1L of non-solvent (ethanol) that is compatible with the decolorizing agent and is effective against polyester to the reaction vessel and sonicate for 10 min. Filter the mixture and soak the resulting precipitate in a non-solvent for 12 h and then filter it again. Dry the resulting solid under vacuum at 60 °C to obtain a white granular recovery product.

[0167] (3) The yellow transparent mixed liquid obtained by two filtrations in step (2) is subjected to a first rotary evaporation to collect the non-solvent distilled out. The remaining yellow transparent mixed liquid is then subjected to vacuum distillation to obtain colorless and transparent gamma-valerol and yellow dye solid.

[0168] Example 21

[0169] (1) Under laboratory conditions, a yellow polyester fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.4L of gamma-butyrolactone solution (ethanol as solvent, gamma-butyrolactone mass concentration of 80%). The vessel was sealed and heated at 180℃ for 5h, with stirring during the process at a stirring rate of 100rpm. The vessel was then cooled to room temperature.

[0170] (2) Add 1L of non-solvent (ethanol) that is compatible with the decolorizing agent and is effective against polyester to the reaction vessel and sonicate for 10 min. Filter the mixture and soak the resulting precipitate in a non-solvent for 12 h and then filter it again. Dry the resulting solid under vacuum at 60 °C to obtain a white granular recovery product.

[0171] (3) The yellow transparent mixed liquid obtained by two filtrations in step (2) is subjected to a first rotary evaporation to collect the non-solvent distilled out. The remaining yellow transparent mixed liquid is then subjected to vacuum distillation to obtain colorless and transparent gamma-butyrolactone and yellow dye solid.

[0172] Example 22

[0173] (1) Under laboratory conditions, a yellow mixed fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.4L gamma-valerol solution. The mixture was then sealed and heated at 180℃ for 5h, with stirring at a rate of 100rpm. The mixture was then cooled to room temperature.

[0174] (2) Add 1L of non-solvent (ethanol) that is compatible with the decolorizing agent and is effective against polyester to the reaction vessel and sonicate for 10 min. Filter the mixture and soak the resulting precipitate in a non-solvent for 12 h and then filter it again. Dry the resulting solid under vacuum at 60 °C to obtain a white granular recycled product and the separated non-polyester fabric fibers.

[0175] (3) The yellow transparent mixed liquid obtained by two filtrations in step (2) is subjected to a first rotary evaporation to collect the non-solvent distilled out. The remaining yellow transparent mixed liquid is then subjected to vacuum distillation to obtain colorless and transparent gamma-valerol and yellow dye solid.

[0176] Example 23

[0177] (1) Under laboratory conditions, a yellow mixed fabric with a size of 1cm×1cm and a mass of about 0.1kg was added to a reaction vessel along with 0.3L gamma-valerol and heated at 120℃ for 3h, and then cooled to room temperature.

[0178] (2) It can be observed that after heat treatment, the yellow blended fabric is decolorized and retains its original weave structure. The decolorized blended fabric can be taken out to obtain a blended fabric that retains its weave structure and whose molecular weight remains basically unchanged.

[0179] (3) Collect gamma-valerol by rotary evaporation of the remaining yellow transparent mixed liquid from step (2).

[0180] Example 24

[0181] (1) Under laboratory conditions, approximately 0.1 kg of black waste plastic and 0.4 L of gamma-valerol solution were added to a reaction vessel and heated at 180 °C for 5 h with stirring at a rate of 100 rpm. The mixture was then cooled to room temperature.

[0182] (2) Add 1L of non-solvent (ethanol) that is compatible with the decolorizing agent and is effective against polyester to the reaction vessel and sonicate for 10 min. Filter the mixture and soak the resulting precipitate in a non-solvent for 12 h and then filter it again. Dry the resulting solid under vacuum at 60 °C to obtain a white granular recovery product.

[0183] (3) The gray transparent mixed liquid obtained by two filtrations in step (2) is subjected to a first rotary evaporation to collect the non-solvent distilled out. The remaining gray transparent mixed liquid is then subjected to vacuum distillation to obtain colorless and transparent gamma-valerol and black dye solid.

[0184] Example 25

[0185] (1) Under laboratory conditions, approximately 0.1 kg of black waste plastic and 0.3 L of gamma-valerol were added to a reaction vessel, heated at 120 °C for 3 h, and then cooled to room temperature.

[0186] (2) It can be observed that after heat treatment, the black waste plastic is decolorized and retains its original shape. The decolorized plastic is taken out and plastic that retains its original shape and whose molecular weight remains basically unchanged is obtained.

[0187] (3) Collect gamma-valerol by rotary evaporation of the remaining gray transparent mixed liquid from step (2).

[0188] 3. Test Results

[0189] Figure 1 This is a schematic diagram of the decolorization and recycling process in Embodiment 1 of the present invention, including a color comparison of yellow polyester fabric before and after decolorization. In the figure, Yellow polyester is yellow polyester fabric, and the L* value represents the brightness of the rPET pixel after decolorization, with a value range of [0, 100], where 0 and 100 correspond to pure black and pure white, respectively, and can be used as a criterion for judging the decolorization effect. The closer the value is to 100, the closer the rPET is to white. The macroscopic morphology of rPET is white granular, and after characterization, the particle size is in the range of 1 to 10 micrometers. Figure 2 ).

[0190] like Figure 3 As shown, rPET was characterized by BET, and its N2 adsorption-desorption isotherm was a type IV isotherm, indicating that the material is mainly mesoporous. The SBET value was 22.398 m. 2 g -1 rPET has a pore size between 10-40 nm, making it suitable as a matrix for functional materials.

[0191] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for decolorizing and recycling products containing polyethylene terephthalate, characterized in that: Plastics, polyester fabrics, or blended fabrics containing polyethylene terephthalate are placed in a decolorizing agent and heated in a closed environment at 180-190°C for at least 5 hours, accompanied by stirring at a speed of 100-1000 rpm. After the time is reached, the decolorized recycled product is obtained by removing the dye and filtering. The recycled product has a granular structure. The decolorizing agent is gamma-valerol; the solid-liquid ratio of the plastic, polyester fabric or blended fabric containing polyethylene terephthalate to the decolorizing agent is 1 kg: 3 L; The dye removal and filtration process involves adding a non-solvent that is compatible with the decolorizing agent and is targeted at polyester to remove the dye dissolved in the decolorizing agent, ultrasonicating for 10 minutes, filtering, soaking the resulting precipitate in a non-solvent for 12 hours, and filtering again to obtain the decolorized recovered product. The non-solvent that is compatible with the decolorizing agent and is suitable for polyester is ethanol.

2. The decolorization and recycling method according to claim 1, characterized in that: The plastic or blended fabric containing polyethylene terephthalate contains not less than 1 wt% polyethylene terephthalate.

3. The decolorization and recycling method according to claim 1, characterized in that: The process of adding a non-solvent compatible with the decolorizing agent and targeting the polyester to remove the dissolved dye, followed by final filtration to obtain the recovered product, also includes collecting the filtrate and separating the decolorizing agent from the filtrate for reuse.

4. The decolorization and recycling method according to claim 3, characterized in that: The decolorizing agent separated from the filtrate is obtained by distillation.

5. The decolorization and recycling method for products containing polyethylene terephthalate as described in claim 1 is applied to the field of recycling polyethylene terephthalate polymer material systems.

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