A method for component separation of waste polyester-cotton blended fabrics based on complex acids

Abstract

This invention relates to a method for separating components of waste polyester-cotton blended fabrics based on a complex acid system. Through the synergistic effect of a complex acid system combining organic, inorganic, and Lewis acids, the hydrogen bond network within the cellulose fibers of the waste polyester-cotton blended fabric is effectively disrupted, efficiently depolymerizing cotton fibers and releasing polyester fibers, achieving efficient and precise separation of the waste polyester-cotton blended fabric. This not only improves separation efficiency but also significantly enhances the specificity of degradation selection between components, ensuring high-purity recovery of polyester and cotton fibers. It also helps preserve the original properties of polyester and cotton fibers, providing an effective means for the resource utilization of waste polyester-cotton blended textiles. This invention significantly reduces the required acid quantity and processing time, effectively improves the recovery rate and purity of polyester and cotton fibers, lowers production costs, and significantly enhances environmental performance, providing an economical and green new approach for the recycling and reuse of waste polyester-cotton blended textiles.

Description

Technical Field

[0001] This invention relates to the field of waste polyester-cotton fabric recycling technology, and more specifically to a method for separating components of waste polyester-cotton blended fabrics based on composite acids. Background Technology

[0002] my country's textile industry is large-scale, with a complete industrial chain and abundant resources and technological advantages, playing a vital supporting role in the country's economic development and employment. However, with the continuous increase in textile consumption, the amount of waste textiles is also growing, leading to increasingly serious environmental pollution and resource waste. Polyester is the most abundant component in waste textiles, accounting for approximately 80% of all fibers. Since polyester is predominantly found in polyester-cotton textiles and is difficult to degrade in the natural environment, the recycling of waste polyester-cotton blended textiles is of great significance.

[0003] Currently, various methods have been proposed for separating and recycling waste polyester-cotton blended textiles, such as ionic liquid dissolution, acid hydrothermal methods, alkaline hydrolysis, alcoholysis, and sulfuric acid-mechanical methods. However, each method has its limitations. Some separation methods use strong acids or other chemical reagents, which may lead to equipment corrosion and environmental pollution. For example, although phosphotungstic acid (HPW) is an easily recyclable heteropoly acid, its use still requires caution to avoid secondary pollution. During the separation process, some methods may cause changes in the properties of cellulose or polyester. For example, after sulfuric acid-mechanical treatment, cracks and pores appear on the surface of cotton fibers, and their length and fineness are significantly reduced; the mechanical properties of polyester fibers show a significant decline. This indicates that an inappropriate separation process may affect the final application of the recycled materials. Furthermore, the implementation of any separation technology is accompanied by energy consumption and potential cost issues, especially those methods that require high temperature, high pressure, or specific chemical reagents, which may lead to higher operating costs and energy consumption. With the increasing global emphasis on environmental protection and sustainable development, developing simpler, more efficient, environmentally friendly, and sustainable separation technologies for waste polyester-cotton blended textiles is a very urgent and important research direction. Summary of the Invention

[0004] Therefore, a method for separating components of waste polyester-cotton blended fabrics based on compound acids is needed. This method aims to achieve efficient separation and recovery of polyester and cotton fibers from waste polyester-cotton blended fabrics using low-cost, pollution-free compound acids through simple operations, while ensuring that the structure and properties of polyester and cotton fibers are not damaged during the separation and recovery process. Simultaneously, the organic acids in the compound acid should be effectively recovered for recycling, minimizing the cost for industrial-scale production.

[0005] To achieve the above objectives, the present invention provides a method for separating components of waste polyester-cotton blended fabrics based on composite acids, comprising the following steps:

[0006] The pretreated waste polyester-cotton blended fabric is placed in a composite acid system, which includes organic acids, inorganic acids and Lewis acids, and heated to degrade it, resulting in a reacted polyester-cotton mixture.

[0007] The reacted polyester-cotton mixture was then ultrasonically cleaned.

[0008] Solid-liquid separation is used to recover polyester and cotton fibers separately.

[0009] Waste polyester-cotton blended fabrics, after pretreatment steps such as crushing, washing, and drying, are mixed with a composite acid solution of a certain concentration containing organic acids, inorganic acids, and Lewis acids. The mixture is then heated in an atmospheric pressure container for degradation. Organic acids, as the main solvent for separating the components of waste polyester-cotton blended fabrics, are weakly acidic, and the hydrogen ions generated by ionization have a relatively weak effect on glycosidic bonds, primarily attacking the amorphous regions of cellulose, thus ensuring the integrity of the cotton fibers. The addition of Lewis acids promotes the ring-opening of functional groups on the fiber surface, penetrating into the cellulose to attack and destroy hydrogen bonds. Unsaturated hydrated ions further disrupt hydrogen bonds and disperse the cellulose macromolecular chains, helping cotton fibers peel off from the polyester surface. Inorganic acids, due to their strong oxidizing and catalytic properties, can improve the separation efficiency of the reaction system when used appropriately. Furthermore, organic acids have a relatively small impact on the chemical stability and mechanical properties of fibers, and generally have strong lipophilicity, allowing them to simultaneously remove grease and other contaminants from the fabric surface during the polyester-cotton separation process. The synergistic effect of these three different types of acids, with their individual effects mutually reinforcing each other, works together on cellulose to effectively disrupt its internal hydrogen bond network, reducing the amount of acid required or the processing time. Polyester and cotton fibers in waste polyester-cotton blended fabrics are initially separated during heating degradation; after the reaction is complete, hot water is added to terminate the reaction. Next, the solution mixture is placed in an ultrasonic cleaning device for deep cleaning of the polyester and cotton fibers; then, under vacuum filtration, the polyester and cotton fibers are separated and recovered separately. This not only improves separation efficiency but also helps retain the original properties of the polyester and cotton fibers, ensuring the secondary utilization of the recovered polyester and providing an effective means for the resource utilization of waste polyester-cotton blended textiles. For the remaining filtrate after filtration, the organic acid solvent in the composite acid is recovered using cooling crystallization technology. The recovered organic acid solvent can be reused in the recycling process of new waste polyester-cotton blended textiles, achieving resource recycling.

[0010] Preferably, in the composite acid system, the mass concentration of organic acid is 60-80 wt%, the mass concentration of inorganic acid is 1-5 wt%, the mass concentration of Lewis acid is 1-5 wt%, and the balance is deionized water.

[0011] Preferably, the organic acid is one of oxalic acid, p-toluenesulfonic acid, malic acid, acetic acid, and citric acid; the inorganic acid is one of sulfuric acid, hydrochloric acid, and phosphoric acid; and the Lewis acid is aluminum trichloride or zinc dichloride tetrahydrate.

[0012] Preferably, the organic acid is oxalic acid. Low-cost oxalic acid can be produced industrially from plant resources. It is a naturally abundant, biodegradable, non-volatile, and easily recyclable reagent, making it a sustainable agent.

[0013] Preferably, the heating degradation temperature is 95-115℃, and the time is 1-3 hours. By optimizing the precise control of parameters such as heating degradation temperature and time, the separation effect is improved, and energy consumption and cost are reduced.

[0014] Preferably, the ultrasonic cleaning temperature is 50-70℃ and the time is 10-30 minutes. Before ultrasonic cleaning, hot water at 100℃ is added to the mixing system after the heat preservation is completed to stop the degradation reaction. By optimizing the temperature, time and other conditions of ultrasonic cleaning, dirt and grease on the fiber surface are removed, further improving the separation effect.

[0015] Preferably, the cotton fiber content in the waste polyester-cotton blended fabric is 1-99 wt%.

[0016] Preferably, the solid-liquid separation includes the following steps: pre-filtering the mixed solution after ultrasonic cleaning to obtain recovered polyester fibers and preliminary filtrate; and further filtering and recovering the preliminary filtrate by vacuum suction to obtain cotton fibers.

[0017] Preferably, the solid-liquid mass ratio of the pretreated waste polyester-cotton blended fabric to the composite acid system is 1:10-100.

[0018] Preferably, the method further includes the following steps: recovering the filtrate after solid-liquid separation to obtain a mixed solution containing organic acid crystals, and cooling it in an environment of 2-4°C for 16-24 hours to obtain fully crystallized organic acid, further filtering to obtain moist organic acid crystals, and heating it in a vacuum environment to obtain dry, high-purity organic acid crystals.

[0019] Unlike existing technologies, the above-mentioned technical solution effectively disrupts the hydrogen bond network within the cellulose of waste polyester-cotton blended fabrics through the synergistic effect of a complex acid system combining organic acids, inorganic acids, and Lewis acids. This efficiently depolymerizes cotton fibers, releasing polyester fibers and achieving efficient and precise separation of waste polyester-cotton blended fabrics. This technical solution not only improves separation efficiency but also significantly enhances the specificity of degradation selection between components, ensuring high-purity recovery of polyester and cotton fibers. It also helps preserve the original properties of polyester and cotton fibers, guaranteeing the secondary utilization of recycled polyester and providing an effective means for the resource utilization of waste polyester-cotton blended textiles. This invention significantly reduces the required acid volume and processing time, effectively improves the recovery rate and purity of polyester and cotton fibers, lowers production costs, and significantly enhances environmental performance, providing an economical and green new approach for the recycling and reuse of waste polyester-cotton blended textiles. Attached Figure Description

[0020] Figure 1 Scanning electron microscope image of waste polyester-cotton blended textiles used in a specific embodiment of the present invention;

[0021] Figure 2 This is a scanning electron microscope image of the polyester fiber aggregate obtained after the reaction by the method of the present invention;

[0022] Figure 3 This is a scanning electron microscope image of cotton fibers obtained after the reaction by the method of the present invention;

[0023] Figure 4 The image shows a comparison of Fourier transform infrared (FTIR) spectra of polyester fibers before and after the reaction.

[0024] Figure 5 The image shows a comparison of Fourier transform infrared (FTIR) spectra of cotton fibers before and after the reaction.

[0025] Figure 6 Comparison of Fourier transform infrared (FTIR) spectra of unreacted oxalic acid and recovered oxalic acid recycled 1 to 5 times;

[0026] Figure 7 A comparison chart showing cotton fibers recovered from sulfuric acid separation and recovered from compound acid separation. Detailed Implementation

[0027] To explain in detail the technical content, structural features, objectives, and effects of the technical solution, the following description is provided in conjunction with specific embodiments and accompanying drawings.

[0028] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0029] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0030] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0031] In this application, terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual quantity, hierarchy or order relationship between these entities or operations.

[0032] Unless otherwise specified, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0033] Similar to the interpretation in the Patent Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceeding" are understood to exclude the stated number; expressions such as "above," "below," and "within" are understood to include the stated number. Furthermore, in the description of the embodiments in this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also interpreted in this way, such as "multiple groups" and "multiple times," unless otherwise explicitly specified.

[0034] In the description of the embodiments of this application, the space-related expressions used, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "vertical," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," indicate the orientation or positional relationship based on the orientation or positional relationship shown in the specific embodiments or drawings. They are only for the purpose of describing the specific embodiments of this application or for the reader's understanding, and do not indicate or imply that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0035] Unless otherwise expressly specified or limited, the terms "installation," "connection," "linking," "fixing," and "setting," as used in the description of the embodiments of this application, should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two components or the interaction between two components. For those skilled in the art to which this application pertains, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0036] The various instruments, equipment, raw materials, or reagents used in the specific embodiments of this invention are not limited in their source; they are all conventional products that can be purchased through legitimate commercial channels and can be prepared according to conventional methods well known to those skilled in the art. The waste polyester-cotton blended raw materials used in the following embodiments are waste fabrics recycled from factories. Unless otherwise specified, the chemical reagents used in the following embodiments are commercially available and of analytical grade. Unless otherwise specified, the operations or instruments used in the following embodiments are common operations or instruments in the art. Unless otherwise specified, the proportions, ratios, and contents mentioned in the following embodiments are weight ratios. The recovery rate refers to the ratio of the polyester (or cotton fiber) collected after separation to the polyester (or cotton fiber) content in the untreated waste polyester-cotton textiles.

[0037] The purity of polyester is calculated as follows: The recovered polyester fibers are processed according to the national standard GB / T 2910.11—2009 "Quantitative Chemical Analysis of Textiles—Part 11: Mixtures of Cellulose Fibers and Polyester Fibers (Sulfuric Acid Method)". The cellulose fibers are dissolved and removed from a mixture of known dry mass using sulfuric acid. The residue is collected, washed, dried, and weighed. The percentage of the residue to the dry mass of the mixture is calculated using the corrected mass. The purity of the polyester fibers is calculated as the ratio of the mass of the polyester fibers obtained from the reaction to the mass of the polyester fibers before the reaction.

[0038] The loss rate of polyester is obtained by calculating the difference between the mass of the separated polyester and the polyester content in the original fabric, and then dividing the difference by the mass of the original fabric. The loss rate of cotton fiber is obtained by calculating the difference between the mass of the separated cotton fiber and the cotton fiber content in the original fabric, and then dividing the difference by the mass of the original fabric.

[0039] The intrinsic viscosity and degree of polymerization were tested and calculated according to GB / T 14190—2017 "Test Method for Fiber Grade Polyester (PET) Chips". The PET chips were dissolved in a phenol / tetrachloroethane (mass ratio 50:50) mixture at 90°C. The outflow time of the solvent and the PET solution with a concentration of 0.005 g / ml at 25°C was measured using an Ubbelohde viscometer. The intrinsic viscosity was calculated based on the measured outflow time and the solution concentration of the sample. The degree of polymerization was obtained by the ratio of the average molecular weight of the polymer to the molecular weight of the polymer unit.

[0040] Furthermore, the method of this invention does not involve the use of harmful chemicals or large amounts of expensive solvents. Instead, it uses water as the reaction medium. In addition, the acid solution used is easy to recycle and reuse, which helps to reduce fiber recycling costs, improve production efficiency, and achieve truly "green and environmentally friendly" recycling and reuse of polyester-cotton blended textiles.

[0041] Example 1

[0042] A certain amount of waste polyester-cotton blended fabric raw material with a cotton content of 32% and a polyester content of 68% was thoroughly washed with water, cut or crushed into pieces of approximately 1.0000±0.0002g, thoroughly dried in an oven, and then dried to constant weight in a desiccator to obtain pretreated waste polyester-cotton blended fabric. The pretreated waste polyester-cotton blended fabric was removed and weighed using a weighing bottle. It was then placed in a composite acid system solution consisting of 5wt% oxalic acid, 5wt% sulfuric acid, 5wt% aluminum trichloride, and the remainder being deionized water, with a mass ratio of 1:10 between the pretreated waste polyester-cotton blended fabric and the composite acid system solution. The temperature of the digital display constant temperature oil bath was set to 105℃, and the reaction time was 3 hours to complete the degradation reaction of cotton fibers in the waste polyester-cotton blended fabric. After the reaction was completed, sufficient 100℃ hot water was added to stop the reaction. The mixed solution after the reaction was stopped was placed in an ultrasonic cleaning device for deep ultrasonic cleaning at 60℃ for 20 minutes. Next, preliminary filtration is performed to obtain recycled polyester fibers. The recycled polyester fibers are washed several times with cold water, and the preliminary filtrate is drained through a filter membrane under vacuum suction. The filtrate is then filtered again to recover cotton fibers. Finally, the recovered polyester fibers and cotton fibers are dried in an oven for 4-16 hours, then placed in a desiccator to cool and dry to constant weight. They are then weighed within 2 minutes.

[0043] Example 2

[0044] The difference from Example 1 is that the added composite acid system solution contains 60 wt% oxalic acid, 5 wt% sulfuric acid, and 5 wt% aluminum trichloride, with the balance being deionized water. All other operating steps and parameters are performed according to Example 1.

[0045] Example 3

[0046] The difference from Example 1 is that the added composite acid system solution contains 65 wt% oxalic acid, 5 wt% sulfuric acid, and 5 wt% aluminum trichloride, with the balance being deionized water. All other operating steps and parameters are performed according to Example 1.

[0047] Example 4

[0048] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 5 wt% sulfuric acid, and 5 wt% aluminum trichloride, with the balance being deionized water. All other operating steps and parameters are performed according to Example 1.

[0049] Example 5

[0050] The difference from Example 1 is that the added composite acid system solution contains 80 wt% oxalic acid, 5 wt% sulfuric acid, and 5 wt% aluminum trichloride, with the balance being deionized water. All other operating steps and parameters are performed according to Example 1.

[0051] The recovery rates of polyester and cotton fibers recovered in Examples 1-5 were calculated based on the ratio of the polyester (or cotton fiber) collected after separation to the polyester (or cotton fiber) content in untreated waste polyester-cotton textiles. Using the polyester and cotton fiber recovery rates as evaluation indicators, it was found that the separation effect was best in the mixed solution system containing 70wt% oxalic acid, with a polyester recovery rate of over 99% and a cotton fiber recovery rate as high as 94.01%. The loss rate of recovered polyester and cotton fibers is calculated based on the ratio of the difference between the polyester (or cotton fiber) content collected after separation and the polyester (or cotton fiber) content in untreated waste polyester-cotton textiles, to the polyester (or cotton fiber) content in untreated waste polyester-cotton textiles. The purity of polyester fibers is calculated by the ratio of the mass of polyester fibers obtained from the reaction according to GB / T2910.11—2009 "Quantitative Chemical Analysis of Textiles Part 11: Mixtures of Cellulose Fibers and Polyester Fibers (Sulfuric Acid Method)" to the mass of polyester fibers before the reaction. The polyester purity is 100%, the polyester mass loss rate is less than 1%, and the cotton fiber mass loss rate is less than 5%.

[0052] Example 6

[0053] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 1 wt% sulfuric acid, and 5 wt% aluminum trichloride, with the balance being deionized water. All other operating steps and parameters are performed according to Example 1.

[0054] Example 7

[0055] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid, and 5 wt% aluminum trichloride, with the balance being deionized water. All other operating steps and parameters are performed according to Example 1.

[0056] Example 8

[0057] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid, and 5 wt% aluminum trichloride, with the balance being deionized water. All other operating steps and parameters are performed according to Example 1.

[0058] The recovery rates of polyester and cotton fibers recovered in Examples 6-8 were calculated based on the ratio of the collected polyester (or cotton fiber) after separation to the polyester (or cotton fiber) content in untreated waste polyester-cotton textiles. Using these recovery rates as evaluation indicators, it was found that the separation effect was best in the mixed solution system containing 3 wt% sulfuric acid, with a polyester recovery rate exceeding 99% and a cotton fiber recovery rate reaching a maximum of 94.89%. The purity of the recovered polyester fibers was calculated by comparing the mass of the recovered polyester fibers obtained from the reaction with that of the polyester fibers before the reaction, according to GB / T 2910.11—2009 "Quantitative Chemical Analysis of Textiles—Part 11: Mixtures of Cellulose Fibers and Polyester Fibers (Sulfuric Acid Method)". The polyester purity was 100%, the polyester mass loss rate was less than 1%, and the cotton fiber mass loss rate was less than 5%.

[0059] Example 9

[0060] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid, and 1 wt% aluminum trichloride, with the balance being deionized water. All other operating steps and parameters are performed according to Example 1.

[0061] Example 10

[0062] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid, and 3 wt% aluminum trichloride, with the balance being deionized water. All other operating steps and parameters are performed according to Example 1.

[0063] Example 11

[0064] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid, and 4 wt% aluminum trichloride, with the balance being deionized water. All other operating steps and parameters are performed according to Example 1.

[0065] Example 12

[0066] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid, and 5 wt% aluminum trichloride, with the balance being deionized water. All other operating steps and parameters are performed according to Example 1.

[0067] The recovery rates of polyester and cotton fibers recovered in Examples 9-12 were calculated based on the ratio of the collected polyester (or cotton fiber) after separation to the polyester (or cotton fiber) content in untreated waste polyester-cotton textiles. Using these recovery rates as evaluation indicators, it was found that the separation effect was best in the mixed solution system containing 4 wt% aluminum trichloride, with a polyester recovery rate exceeding 99% and a cotton fiber recovery rate reaching a maximum of 95.05%. The purity of the recovered polyester fibers was calculated by comparing the mass of the recovered polyester fibers obtained from the reaction with that of the polyester fibers before the reaction, according to GB / T 2910.11—2009 "Quantitative Chemical Analysis of Textiles—Part 11: Mixtures of Cellulose Fibers and Polyester Fibers (Sulfuric Acid Method)". The polyester purity was 100%, the polyester mass loss rate was less than 1%, and the cotton fiber mass loss rate was less than 5%.

[0068] Example 13

[0069] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid and 4 wt% aluminum trichloride, with the balance being deionized water. The temperature of the digital display constant temperature oil bath is set to 95°C, and other operating steps and parameters are the same as in Example 1.

[0070] Example 14

[0071] The difference from Example 13 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid and 4 wt% aluminum trichloride, with the remainder being deionized water. The temperature of the digital display constant temperature oil bath is set to 97°C. All other operating steps and parameters are the same as in Example 1.

[0072] Example 15

[0073] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid and 4 wt% aluminum trichloride, with the remainder being deionized water. The temperature of the digital display constant temperature oil bath is set to 100°C, and other operating steps and parameters are performed in accordance with Example 1.

[0074] Example 16

[0075] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid and 4 wt% aluminum trichloride, with the remainder being deionized water. The temperature of the digital display constant temperature oil bath is set to 110°C. All other operating steps and parameters are the same as in Example 1.

[0076] Example 17

[0077] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid and 4 wt% aluminum trichloride, with the balance being deionized water. The temperature of the digital display constant temperature oil bath is set to 115°C. All other operating steps and parameters are the same as in Example 1.

[0078] The recovery rates of polyester and cotton fibers recovered in Examples 13-17 were calculated based on the ratio of the collected polyester (or cotton fiber) after separation to the polyester (or cotton fiber) content in untreated waste polyester-cotton textiles. Using these recovery rates as evaluation indicators, it was found that the separation effect was optimal at a heating degradation temperature of 97°C, with a polyester recovery rate exceeding 99% and a cotton fiber recovery rate reaching a maximum of 97.22%. The purity of the recovered polyester fibers was calculated by comparing the mass of the recovered polyester fibers obtained from the reaction with that of the polyester fibers before the reaction, according to GB / T 2910.11—2009 "Quantitative Chemical Analysis of Textiles—Part 11: Mixtures of Cellulose Fibers and Polyester Fibers (Sulfuric Acid Method)". The polyester purity was 100%, the polyester mass loss rate was less than 1%, and the cotton fiber mass loss rate was less than 5%.

[0079] Example 18

[0080] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid and 4 wt% aluminum trichloride, with the balance being deionized water. The temperature of the digital display constant temperature oil bath is set to 97°C, the reaction time is 1 hour, and other operating steps and parameters are the same as in Example 1.

[0081] Example 19

[0082] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid and 4 wt% aluminum trichloride, with the balance being deionized water. The temperature of the digital display constant temperature oil bath is set to 97°C, the reaction time is 2 hours, and other operating steps and parameters are the same as in Example 1.

[0083] Example 20

[0084] The difference from Example 1 is that the added composite acid system solution contains 70 wt% oxalic acid, 3 wt% sulfuric acid and 4 wt% aluminum trichloride, with the balance being deionized water. The temperature of the digital display constant temperature oil bath is set to 97°C, the reaction time is 3 hours, and other operating steps and parameters are the same as in Example 1.

[0085] The recovery rates of polyester and cotton fibers recovered in Examples 18-20 were calculated based on the ratio of the collected polyester (or cotton fiber) after separation to the polyester (or cotton fiber) content in untreated waste polyester-cotton textiles. Using these recovery rates as evaluation indicators, it was found that a heating degradation time of 1 hour resulted in the best separation effect, with a polyester recovery rate exceeding 99% and a cotton fiber recovery rate reaching a maximum of 96.53%. The purity of the recovered polyester fibers was calculated by comparing the mass of the recovered polyester fibers obtained from the reaction with that of the polyester fibers before the reaction, according to GB / T 2910.11—2009 "Quantitative Chemical Analysis of Textiles—Part 11: Mixtures of Cellulose Fibers and Polyester Fibers (Sulfuric Acid Method)". The polyester purity was 100%, with a polyester mass loss rate of less than 1% and a cotton fiber mass loss rate of less than 5%.

[0086] Example 21

[0087] The difference from Example 1 is that the waste polyester-cotton blended textile raw material used has a cotton fiber content of 1wt%, the added composite acid system solution contains 70wt% oxalic acid, 3wt% sulfuric acid and 4wt% aluminum trichloride, and the balance is deionized water. The temperature of the digital display constant temperature oil bath is set to 97℃ and the reaction time is 1h. Other operating steps and parameters are the same as in Example 1.

[0088] Example 22

[0089] The difference from Example 1 is that the waste polyester-cotton blended textile raw material used has a cotton fiber content of 20wt%, the added composite acid system solution contains 70wt% oxalic acid, 3wt% sulfuric acid and 4wt% aluminum trichloride, and the balance is deionized water. The temperature of the digital display constant temperature oil bath is set to 97℃ and the reaction time is 1h. Other operating steps and parameters are the same as in Example 1.

[0090] Example 23

[0091] The difference from Example 1 is that the waste polyester-cotton blended textile raw material used has a cotton fiber content of 50wt%, the added composite acid system solution contains 70wt% oxalic acid, 3wt% sulfuric acid and 4wt% aluminum trichloride, and the balance is deionized water. The temperature of the digital display constant temperature oil bath is set to 97℃ and the reaction time is 1h. Other operating steps and parameters are the same as in Example 1.

[0092] Example 24

[0093] The difference from Example 1 is that the waste polyester-cotton blended textile raw material used has a cotton fiber content of 80wt%, the added composite acid system solution contains 70wt% oxalic acid, 3wt% sulfuric acid and 4wt% aluminum trichloride, and the balance is deionized water. The temperature of the digital display constant temperature oil bath is set to 97℃ and the reaction time is 1h. Other operating steps and parameters are the same as in Example 1.

[0094] Example 25

[0095] The difference from Example 1 is that the waste polyester-cotton blended textile raw material used has a cotton fiber content of 99wt%, the added composite acid system solution contains 70wt% oxalic acid, 3wt% sulfuric acid and 4wt% aluminum trichloride, and the balance is deionized water. The temperature of the digital display constant temperature oil bath is set to 97℃ and the reaction time is 1h. Other operating steps and parameters are the same as in Example 1.

[0096] The recovery rates of polyester and cotton fibers recovered in Examples 21-25 were calculated based on the ratio of the collected polyester (or cotton fiber) after separation to the polyester (or cotton fiber) content in untreated waste polyester-cotton textiles. Using these recovery rates as evaluation indicators, it was found that for polyester-cotton blended textiles with a cotton fiber content of 1-99 wt%, the method of this invention achieved complete separation of polyester and cotton fibers, with a polyester recovery rate exceeding 99% and a cotton fiber recovery rate reaching a maximum of 96.53%. The purity of the recovered polyester fibers was calculated by comparing the mass of the recovered polyester fibers obtained from the reaction with that of the polyester fibers before the reaction, according to GB / T2910.11—2009 "Quantitative Chemical Analysis of Textiles—Part 11: Mixtures of Cellulose Fibers and Polyester Fibers (Sulfuric Acid Method)". The polyester purity was 100%, the polyester mass loss rate was less than 1%, and the cotton fiber mass loss rate was less than 5%.

[0097] As can be seen from the above embodiments, the preferred process of the present invention for separating waste polyester-cotton blended textiles based on compound acid is as follows: the waste polyester-cotton blended textiles are heated and degraded by a compound acid solution composed of 70% oxalic acid, 3% sulfuric acid and 4% aluminum trichloride. The preferred reaction temperature for heating and degradation is 97°C and the preferred reaction time is 1 hour. The cotton fiber content of the waste polyester-cotton textiles treated by the present invention is 1%-99%, which means it is applicable to most polyester-cotton blended textiles.

[0098] The polyester and cotton fibers obtained from the separation and recovery in Example 22 were subjected to Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) tests. Please refer to [link to relevant documentation]. Figure 1 Scanning electron microscope images of untreated waste polyester-cotton textiles Figure 2Scanning electron microscope images of the polyester fiber assemblies obtained after separation and recovery. Figure 3 Scanning electron microscope images of the recovered cotton fibers show that the polyester and cotton fiber components in the treated waste polyester-cotton textiles were effectively separated, and no cotton fibers were observed in the separated polyester. Figure 2 The polyester and cotton fibers on the surface have completely separated, and the polyester fiber surface remains smooth and undamaged; the cotton fibers have been completely separated from their intertwined state with the polyester, and the separated cotton fibers have broken into curved fiber bodies of different sizes. Figure 3 ).

[0099] Please see Figure 4 The Fourier Transform Infrared (FTIR) spectra of polyester fibers before and after the reaction are shown in the comparison. It can be seen that the FTIR spectra of the polyester fibers obtained after composite acid treatment are consistent with those of pure polyester fibers (the pure polyester fiber fabric is 100% polyester fabric, provided by Fujian Huafeng New Materials Co., Ltd.), with no new peaks appearing. This indicates that the polyester fibers maintained their original chemical structure after composite acid treatment. The pure polyester fibers are 100% polyester fabric, provided by Fujian Huafeng New Materials Co., Ltd.

[0100] Please see Figure 5 The Fourier transform infrared (FTIR) spectra of cotton fibers before and after the reaction are shown in the comparison graph. It can be seen that, compared with untreated pure cotton fabric, the cotton fiber product treated with the composite acid solution exhibits higher spectral density at 1630 cm⁻¹. -1 A distinct carboxyl absorption peak was observed, indicating that the separated product contains carboxyl groups, proving that the cotton fiber was hydrolyzed and oxidized into oxidized cellulose containing carboxyl groups.

[0101] Therefore, the polyester fibers separated from waste polyester-cotton blended fabrics have the same chemical structure as pure polyester fibers (reference material), while the cotton fibers separated from them have a basically the same chemical structure as pure cotton fabrics.

[0102] Referring to GB / T 14190—2017 "Test Methods for Fiber Grade Polyester (PET) Chips", the PET was dissolved in a phenol / tetrachloroethane (mass ratio 50:50) mixture at 90℃. The outflow time of the solvent and the PET solution with a concentration of 0.005 g / ml at 25℃ was measured using an Ubbelohde viscometer. The intrinsic viscosity was calculated based on the measured outflow time and the solution concentration of the sample. The degree of polymerization was obtained by the ratio of the average molecular weight of the polymer to the molecular weight of the polymer unit. Tests on the intrinsic viscosity and degree of polymerization of the polyester fibers before and after treatment showed that the changes in intrinsic viscosity and degree of polymerization were small. The intrinsic viscosity was 0.66 dl / g and 0.70 dl / g, respectively. The degree of polymerization before treatment was 98, and the degree of polymerization after treatment was 106. The separated polyester fibers still exhibited excellent mechanical properties.

[0103] Example 26

[0104] The filtrate containing oxalic acid crystals after the separation of polyester and cotton fibers in Example 1 was cooled at 2-4°C for 16-24 hours to ensure sufficient crystallization of oxalic acid. After crystallization, the oxalic acid crystals were retained on filter paper or a filter, while the aqueous solution flowed out. The filtered oxalic acid crystals still contained some moisture or other impurities. They were heated under vacuum to evaporate the moisture and other volatile substances, yielding 30.4g of dry, high-purity oxalic acid crystals. Observation showed that the obtained oxalic acid was not significantly different in morphology from the unreacted oxalic acid, still appearing as white crystals. The oxalic acid was recovered and recycled five times in a composite acid system solution for the separation of polyester and cotton from waste polyester-cotton blended fabrics. Initially, 32g of fresh oxalic acid was used. Calculations showed that the total amount of oxalic acid gradually decreased with each cycle. However, after five cycles, the total amount of recovered oxalic acid was still 26.5g, with a total recovery rate of 82.8% over five cycles. The oxalic acid recovery rate in each cycle was above 95%. Please refer to [link / reference]. Figure 6 The Fourier transform infrared (FTIR) spectra of unreacted oxalic acid and recovered oxalic acid recycled 1 to 5 times are shown in the diagram. The FTIR analysis demonstrates that the chemical structure of oxalic acid remains unchanged after being recycled and repeated 4 times; its chemical composition remains oxalic acid, and no other significant impurities are generated. This shows that the organic acid solvent used in this invention can be recycled multiple times, ensuring separation efficiency while reducing environmental pollution caused by chemical emissions.

[0105] Comparative Example 1

[0106] Take a certain amount of waste polyester-cotton blended raw material, cut it into pieces of approximately 1.0000±0.0002g, place them in an oven for 4-16 hours, remove them, and dry them in a desiccator until constant weight. Add 350ml of concentrated sulfuric acid (ρ=1.84g / ml) to 150ml of water. After the solution cools to room temperature, add water to 500ml. Separately weigh 15ml of concentrated ammonia and add 187.5ml of water. Prepare a 75% sulfuric acid solution and a dilute ammonia solution. Take out the sample pretreated in the desiccator, weigh it in a weighing bottle and record the mass after drying, place it in an Erlenmeyer flask, add 200mL of the prepared 75% sulfuric acid solution per gram of sample, stopper the flask, shake the flask to fully wet the sample, and then place the flask in a water bath at 50℃±5℃ for 1 hour, shaking it once every 10 minutes. After the reaction is complete, filter the reaction mixture into a glass frosted crucible, remove the liquid under vacuum, and then add a small amount of sulfuric acid to wash the flask. Vacuum suction was used to drain the liquid. Fresh sulfuric acid solution was added to the crucible to wash away the residue. Gravity drainage was performed for at least 1 minute, followed by vacuum suction. The crucible was washed several times with cold water, neutralized twice with dilute ammonia, and then washed with cold water again. Each wash involved gravity drainage followed by vacuum suction. Finally, the crucible and residue were placed in an oven and dried for 4-16 hours. Afterward, they were transferred to a desiccator to cool and dry to constant weight. The residue was then weighed within 2 minutes to obtain 0.6701 g of polyester fabric. Please refer to [reference needed]. Figure 7 A comparison chart of cotton fibers recovered from sulfuric acid separation and recovered from composite acid separation shows that, compared with Example 1, the cotton fibers in the fabric treated in the comparative example were excessively hydrolyzed, and the fiber structure was severely damaged, making it impossible to effectively recover the cotton fibers. This proves that the composite acid solution is more effective in separating the two components in waste polyester-cotton blended textiles and in recycling polyester and cotton fibers with high recovery rates.

[0107] In summary, the component separation method for waste polyester-cotton blended textiles of the present invention is simple, efficient, low-cost, environmentally friendly, and can achieve recycling. It achieves a polyester recovery rate of over 99% and a purity of 100% in waste polyester-cotton blended textiles, with a polyester mass loss rate of less than 1%. The cotton fiber recovery rate is over 95%, making it an ideal and efficient method for separating and recovering components from waste polyester-cotton blended textiles.

[0108] It should be noted that although the above embodiments have been described herein, this does not limit the scope of patent protection of the present invention. Therefore, any changes and modifications made to the embodiments described herein based on the innovative concept of the present invention, or equivalent structural or procedural transformations made using the content of the present invention's specification and drawings, directly or indirectly applying the above technical solutions to other related technical fields, are all included within the scope of patent protection of the present invention.

Claims

1. A method for separating components of waste polyester-cotton blended fabrics based on composite acids, characterized in that, Includes the following steps: The pretreated waste polyester-cotton blended fabric is placed in a composite acid system, which includes organic acid, inorganic acid and Lewis acid. The organic acid mass concentration is 60-80 wt%, the inorganic acid mass concentration is 1-5 wt%, and the Lewis acid mass concentration is 1-5 wt%. The fabric is then heated for degradation at a temperature of 95-115℃ for 1-3 hours to obtain the reacted polyester-cotton blend. The reacted polyester-cotton mixture was then ultrasonically cleaned. Solid-liquid separation was used to recover polyester and cotton fibers separately. The organic acid is oxalic acid, the inorganic acid is sulfuric acid, and the Lewis acid is aluminum trichloride.

2. The method according to claim 1, characterized in that, The ultrasonic cleaning temperature is 50-70℃ and the time is 10-30 minutes.

3. The method according to claim 1, characterized in that, The cotton fiber content in the waste polyester-cotton blended fabric is 1-99 wt%.

4. The method according to claim 1, characterized in that, The solid-liquid separation includes the following steps: The mixed solution after ultrasonic cleaning was initially filtered to obtain recovered polyester fibers and preliminary filtrate. The initial filtrate is then drained under vacuum and filtered again to recover cotton fibers.

5. The method according to claim 1, characterized in that, The solid-liquid mass ratio of the pretreated waste polyester-cotton blended fabric to the composite acid system is 1:10-100.

6. The method according to claim 1, characterized in that, It also includes the following steps: The filtrate after solid-liquid separation is recovered to obtain a mixed solution containing organic acid crystals. This solution is then cooled at 2-4°C for 16-24 hours to obtain fully crystallized organic acid. The solution is further filtered to obtain moist organic acid crystals, which are then heated under vacuum to obtain dry, high-purity organic acid crystals.

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