Method for cleanly preparing dissolving pulp based on waste cotton textiles

Abstract

The invention discloses a method for cleanly preparing dissolving pulp based on waste cotton textiles, and belongs to the technical field of textile recovery and green chemistry. The preparation method comprises the following steps: taking betaine as a hydrogen bond acceptor, taking organic acid as a hydrogen bond donor, and adding a certain proportion of deionized water to construct a hydrated ternary eutectic solvent system; the pretreated waste cotton fabric is placed in the ternary eutectic solvent system to be subjected to depolymerization treatment, the solvent can be recycled after being blended, then refining treatment is carried out, and finally the regenerated dissolving pulp is obtained. The obtained regenerated dissolving pulp has the following performance indexes: the polymerization degree is 500-700, the alpha cellulose content is more than or equal to 97%, the whiteness is more than or equal to 84%, the iron content is less than or equal to 20ppm, and the fiber length is 26-32%. The method is mild in process condition, simple and convenient to operate, low in energy consumption, recyclable in solvent and free of high-alkali waste liquid, conforms to the green chemistry principle, and provides an economic and environment-friendly effective way for high-valued resource utilization of the waste cotton textiles.

Description

Technical Field

[0001] This invention belongs to the field of textile recycling and green chemistry technology, and in particular relates to a method for preparing dissolving pulp based on waste cotton textiles. Background Technology

[0002] Cotton fiber, as a major natural fiber, is widely used in clothing, home textiles, medical, and industrial fields due to its excellent moisture absorption, breathability, and comfort. With the continuous shortening of textile replacement cycles, the amount of waste cotton textiles generated continues to rise. Existing methods for reusing waste cotton textiles mainly include mechanical methods to produce recycled yarn and as reinforcement in composite materials. However, these two methods result in low added value and limited recycling pathways, making it difficult to achieve closed-loop recycling. Compared to physical recycling, converting waste cotton fibers into recycled dissolving pulp and further spinning it into recycled fibers is an ideal path to achieve high-value and sustainable utilization of waste cotton textiles.

[0003] Dissolving pulp refers to refined chemical pulp with a high cellulose content (90-98%) and extremely low levels of lignin, hemicellulose, minerals, and other components. Waste cotton textiles, as an important cellulose-based biomass resource, typically have a cellulose content >94% and low levels of non-cellulose impurities such as pectin and lignin, making them a potentially high-quality raw material for dissolving pulp preparation. Currently, the main method for preparing cotton pulp from waste cotton textiles is the cooking method, which suffers from problems such as high cooking temperatures, large alkali consumption, long holding times, and difficulties in waste liquid treatment. For example, Chinese patent CN115536754A discloses a wet pulp production process for viscose using recycled cotton textiles. This method uses recycled cotton textiles as raw material and processes such as opening, alkali cooking, beating, metal ion removal, ozone and chlorine dioxide bleaching to obtain pulp. Finally, the bleached pulp is treated to obtain viscose. This method has a long pulping cycle, consumes a lot of energy, and causes some environmental pollution.

[0004] Eutectic solvents, as a novel type of green solvent, offer advantages such as environmental friendliness, low cost, and tunable structure and properties. Typically composed of a mixture of hydrogen bond donors and acceptors in a specific ratio, eutectic solvents possess physicochemical properties similar to ionic liquids, showing great potential for application in biomass pretreatment, depolymerization, and refining. For example, Chinese patent CN112920454A discloses a method for separating and recycling waste polyester-cotton blended fabrics using eutectic solvents. This method uses waste polyester-cotton blended fabrics as raw materials, employing a eutectic solvent to provide a strongly acidic environment for thorough and rapid hydrolysis of cellulose, completely destroying the fiber structure to the micron or nanoscale. Further separation of cellulose and polyester fibers is achieved through ultrasonic treatment and filtration. However, the core of this method lies in the separation of the blended fabrics. Therefore, during the processing, cotton fibers are sacrificially degraded into powdery products, resulting in low added value and poor reprocessing performance, limiting its subsequent application scope and high-value utilization pathways. Therefore, there is an urgent need to develop efficient and clean methods for preparing dissolving pulp that are compatible with the characteristics of waste pure cotton fabrics, so as to promote the high-value utilization and industrial regeneration of waste cotton textiles. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for preparing dissolving slurry based on the cleaning of waste cotton textiles.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing dissolving pulp from waste cotton textiles, comprising the following steps: pre-treating, depolymerizing and refining the waste cotton textiles in sequence to obtain recycled dissolving pulp;

[0008] The depolymerization agent used in the depolymerization process is a ternary eutectic solvent; the ternary eutectic solvent is composed of betaine, organic acid and water.

[0009] Technical Principle: This invention uses waste cotton textiles as raw materials. First, it depolymerizes the textiles to precisely control the degree of polymerization to 500-700. Then, it further refines the depolymerization product to convert it into a dissolving paste that meets the spinning standards for regenerated cellulose fibers. This maximizes the preservation of fiber morphology and utilizes the intrinsic value of the raw materials, solving the problems of high pollution and high energy consumption in traditional pulping processes, and promoting the resource utilization of waste cotton textiles. Specifically, betaine in the ternary eutectic solvent acts as a hydrogen bond acceptor, disrupting the cellulose hydrogen bond network and providing a good buffering effect on solvent acidity. This effectively modulates the overall acidity of the reaction system, making the cellulose depolymerization reaction more mild and controllable, providing the possibility for precisely preparing a dissolving paste with the target degree of polymerization. Organic acids, as hydrogen bond donors, provide a relatively mild acid catalytic environment, promoting the hydrolysis of cellulose glycosidic bonds and having a good swelling effect on the fibers. Water molecules, as hydrogen bond competitors, participate in the construction of the eutectic solvent's hydrogen bond network, regulating the system's acidity and viscosity, promoting the penetration of solvent components into the fiber interior and inhibiting excessive degradation, while further reducing costs.

[0010] Furthermore, the molar ratio of betaine to organic acid is 1:(1-3).

[0011] Furthermore, the water content in the ternary eutectic solvent is 10-40% by mass.

[0012] Furthermore, the organic acid is selected from lactic acid, formic acid, acetic acid, or oxalic acid.

[0013] Furthermore, the temperature of the depolymerization treatment is 75-85°C, the time of the depolymerization treatment is 30-60 minutes, and the material-to-liquid ratio of the depolymerization treatment is 1:(8-12)(g / mL).

[0014] Furthermore, the refining agent used in the refining process comprises hydrogen peroxide, ethylenediaminetetraacetic acid (EDTA), and magnesium sulfate; the mass concentration of hydrogen peroxide in the refining agent is 4-6%, the mass concentration of EDTA is 0.8-1%, and the mass concentration of magnesium sulfate is 0.05-0.1%; the pH value of the refining agent is 9-11.

[0015] Furthermore, the temperature of the refining process is 80-90°C, the time of the refining process is 60-90 minutes, and the material-to-liquid ratio of the refining process is 1:(8-12)(g / mL).

[0016] Furthermore, the depolymerization process also includes a step of recycling and reusing the ternary eutectic solvent.

[0017] Furthermore, the recycling and reuse includes: filtering and separating the product obtained after depolymerization to obtain depolymerized cotton textiles and filtrate; adding 3-5% organic acid by mass to the filtrate, and then reusing it.

[0018] Furthermore, the degree of polymerization of the regenerated dissolving pulp is 500-700, the content of methyl cellulose is ≥97%, the whiteness is ≥84%, the iron content is ≤20ppm, and the fiber length is 26-32%.

[0019] Compared with the prior art, the present invention has the following advantages and technical effects:

[0020] This invention utilizes betaine as a hydrogen bond acceptor and organic acid as a hydrogen bond donor, adding a certain proportion of deionized water to construct a hydrated ternary eutectic solvent system. Pretreated waste cotton fabrics are placed in this ternary eutectic solvent system for depolymerization. The solvent can be recycled after adjustment. Following further refining, a regenerated dissolving pulp is obtained. The resulting regenerated dissolving pulp has the following performance indicators: degree of polymerization 500–700, methyl cellulose content ≥97%, whiteness ≥84%, iron content ≤20 ppm, and fiber length 26–32%.

[0021] This invention addresses the problems of harsh reaction conditions, high alkali consumption, and high environmental impact of existing cooking processes by developing a method for the clean preparation of recycled dissolving pulp from waste cotton textiles under mild conditions. It demonstrates the application potential of ternary eutectic solvents in the resource utilization of waste cotton textiles and provides a new path for the high-value recycling of waste cotton textiles.

[0022] The present invention features mild process conditions and simple operation. Based on a ternary eutectic solvent system, it achieves efficient and directional depolymerization of waste cotton textiles. At the same time, the ternary eutectic solvent can be recycled, which significantly reduces energy consumption. The overall process is environmentally friendly and meets the requirements of green chemical processes. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0024] Figure 1 From left to right, the images show the physical samples of the eutectic solvents prepared in step (2) of Examples 1, 3, and 4.

[0025] Figure 2 The infrared spectra of the waste pure cotton fabric in step (1) of Example 1, the depolymerized cotton fabric obtained in step (2) and the recycled dissolving pulp obtained in step (3) are shown. In this example, raw cotton refers to waste pure cotton fabric, depolymerized cotton refers to depolymerized cotton fabric, and recycled cotton pulp refers to recycled dissolving pulp.

[0026] Figure 3The XRD patterns are of the waste pure cotton fabric in step (1) of Example 1, the depolymerized cotton fabric obtained in step (2), and the recycled dissolving pulp obtained in step (3), where raw cotton refers to waste pure cotton fabric, depolymerized cotton refers to depolymerized cotton fabric, and recycled cotton pulp refers to recycled dissolving pulp. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] This invention provides a method for preparing dissolving pulp from waste cotton textiles, comprising the following steps: pretreatment, depolymerization, and refining of the waste cotton textiles to obtain recycled dissolving pulp. Using waste cotton textiles as raw material, this invention first precisely controls the degree of polymerization to 500-700 through depolymerization, and then further refines the depolymerization product to convert it into dissolving pulp that meets the spinning standards for regenerated cellulose fibers. This maximizes the preservation of fiber morphology and utilizes the intrinsic value of the raw materials, solving the problems of high pollution and high energy consumption in traditional pulping processes, and promoting the resource utilization of waste cotton textiles.

[0030] In a preferred embodiment, the pretreatment includes: washing and disinfecting the waste cotton textiles, and then cutting them into pieces of fabric with a size of 8 to 12 centimeters; the waste cotton textiles are waste pure cotton textiles.

[0031] In a preferred embodiment, the depolymerizing agent used in the depolymerization treatment is a ternary eutectic solvent; the ternary eutectic solvent is composed of betaine, organic acid, and water. Betaine in the ternary eutectic solvent of this invention acts as a hydrogen bond acceptor, which can disrupt the cellulose hydrogen bond network and has a good buffering effect on the acidity of the solvent, effectively modulating the overall acidity of the reaction system. This makes the depolymerization reaction of cellulose more mild and controllable, providing the possibility for the precise preparation of dissolving slurry with the target degree of polymerization. The organic acid acts as a hydrogen bond donor, which can catalyze the hydrolysis of cellulose glycosidic bonds and has a good swelling effect on the fiber. Water molecules, as hydrogen bond competitors, can participate in the construction of the hydrogen bond network of the eutectic solvent, regulating the acidity and viscosity of the system, promoting the penetration of solvent components into the fiber interior and inhibiting excessive degradation, while further reducing costs. Furthermore, betaine is derived from natural plants and has extremely high biocompatibility and biodegradability, meeting the requirements of modern green chemical processes for safety and environmental friendliness.

[0032] In a preferred embodiment, the water content in the ternary eutectic solvent is 10-40% by mass, more preferably 19.50-24.28%. If the water content in the ternary eutectic solvent of this invention is too low, the system viscosity will be too high, which will limit the mass transfer process of the solvent in the fiber; if the water content is too high, it will severely damage the inherent hydrogen bond network structure of the eutectic solvent.

[0033] In a preferred embodiment, the molar ratio of betaine to organic acid is 1:(1-3).

[0034] In a preferred embodiment, the organic acid is selected from lactic acid, formic acid, acetic acid, or oxalic acid; when the organic acid is lactic acid, the molar ratio of betaine to lactic acid is 1:2; when the organic acid is formic acid, the molar ratio of betaine to formic acid is 1:2; when the organic acid is acetic acid, the molar ratio of betaine to acetic acid is 1:3; and when the organic acid is oxalic acid, the molar ratio of betaine to oxalic acid is 1:1.

[0035] In a preferred embodiment, the preparation method of the ternary eutectic solvent includes the following steps: mixing and heating betaine and organic acid to obtain a eutectic solvent; adding water to the eutectic solvent and stirring evenly at room temperature to obtain the ternary eutectic solvent; the mixing and heating temperature is 60-80°C, and the mixing and heating time is 20-30 minutes.

[0036] In a preferred embodiment, the depolymerization treatment includes: placing the pretreated waste cotton textiles in a ternary eutectic solvent, heating and degrading them in a water bath, filtering and separating them after the reaction to obtain filter residue and filtrate; washing and drying the filter residue to obtain depolymerized cotton textiles; the washing temperature is room temperature, the washing reagent is water, and the number of washing cycles is 3 to 5; the drying temperature is 40 to 60°C, the drying time is 4 to 6 hours, and the drying equipment is a vacuum drying oven.

[0037] In a preferred embodiment, the temperature of the depolymerization treatment is 75-85°C, the time of the depolymerization treatment is 30-60 minutes, and the material-to-liquid ratio of the depolymerization treatment is 1:(8-12)(g / mL).

[0038] In a preferred embodiment, the depolymerization process further includes a step of recycling and reusing the ternary eutectic solvent.

[0039] In a preferred embodiment, the recycling and reuse includes: filtering and separating the product obtained after depolymerization to obtain depolymerized cotton textiles and filtrate; adding 3-5% organic acid by mass to the filtrate, and then reusing it.

[0040] In a preferred embodiment, the refining agent used in the refining process comprises hydrogen peroxide, ethylenediaminetetraacetic acid (EDTA), and magnesium sulfate; the mass concentration of hydrogen peroxide in the refining agent is 4-6%, the mass concentration of EDTA is 0.8-1%, and the mass concentration of magnesium sulfate is 0.05-0.1%; the volume concentration of hydrogen peroxide is 30%; the pH value of the refining agent is 9-11, and the pH value of the refining agent is adjusted with sodium hydroxide. The hydrogen peroxide in the refining agent of this invention is used to bleach cotton fabrics and improve the whiteness of the product; magnesium sulfate is a stabilizer in the refining process; and EDTA acts as a metal complexing agent to reduce the iron content in the pulp.

[0041] In a preferred embodiment, the temperature of the refining process is 80-90°C, the time of the refining process is 60-90 minutes, and the material-to-liquid ratio of the refining process is 1:(8-12)(g / mL).

[0042] In a preferred embodiment, the refining process further includes washing, drying, and pulping steps; the washing temperature is room temperature, the washing reagent is water, and the washing is performed 3 to 5 times; the drying temperature is 40 to 60°C, the drying time is 4 to 6 hours, and the drying equipment is a vacuum drying oven; the pulping is performed until the fiber length is 26 to 32%.

[0043] In a preferred embodiment, the degree of polymerization of the regenerated dissolving pulp is 500-700, the content of methyl cellulose is ≥97%, the whiteness is ≥84%, the iron content is ≤20ppm, and the fiber length is 26-32%.

[0044] In this embodiment of the invention, room temperature refers to "25±2℃".

[0045] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0046] In the following examples and comparative examples, 1 mol / L copper ethylenediamine was used as the solvent. The degree of polymerization of cellulose in the regenerated dissolving pulp was determined by the viscosity method; the whiteness of the sample was determined by a whiteness meter; the content of cellulose A in the sample was determined according to "FZ / T50010.4 Determination of Cellulose A Content in Viscose Fiber Pulp"; the iron content of the sample was determined by inductively coupled plasma atomic emission spectrometry; and the fiber length in the regenerated dissolving pulp was determined by a fiber length analyzer.

[0047] Example 1

[0048] A method for preparing dissolving pulp based on the cleaning of waste cotton textiles, the specific steps of which are as follows:

[0049] (1) After washing and disinfecting the waste pure cotton fabric, cut it into pieces of fabric 8-12 cm long and weigh out 10g for later use.

[0050] (2) Weigh 46.86 g of betaine and 72.06 g of lactic acid (the molar ratio of betaine to lactic acid is 1:2) into a 200 mL sample bottle, heat to 80 °C and stir for 20 minutes to form a homogeneous and transparent clear solution. After cooling, a eutectic solvent is obtained. Add 29.73 g of deionized water to the obtained eutectic solvent (i.e., the mass content of water in the ternary eutectic solvent is 20.00%), stir evenly at room temperature to form a homogeneous and clear ternary eutectic solvent.

[0051] (3) Measure 100 mL of the ternary eutectic solvent prepared in step (2) into a 200 mL sample bottle, add 10 g of the waste pure cotton fabric cut in step (1), heat to 80 °C and stir for 40 minutes, then filter the reaction product through a filter membrane under vacuum to obtain filter residue and filtrate; wash the filter residue with water 3 to 5 times, and after washing, place it in a vacuum drying oven at 60 °C and dry for 4 hours to obtain the depolymerized cotton fabric.

[0052] (4) Take 16.67 mL of hydrogen peroxide solution with a mass concentration of 30% into a 200 mL sample bottle, then add 1 g of ethylenediaminetetraacetic acid and 0.08 g of magnesium sulfate, add deionized water to make the total volume of the solution 100 mL, and add sodium hydroxide solution to adjust the pH value of the solution to 10 to obtain the purified preparation.

[0053] (5) Place the depolymerized cotton fabric obtained in step (3) into the refining agent prepared in step (4), heat it to 90°C and keep it warm for 60 minutes, then take the fabric out of the solution with tweezers and wash it with water 3 to 5 times. After washing, place it in a vacuum drying oven at 60°C and dry it for 4 hours to obtain cotton fabric. Pulp the obtained cotton fabric to obtain regenerated dissolving pulp.

[0054] The performance of the recycled dissolving pulp obtained in Example 1 was tested, and the results are as follows: degree of polymerization 547, whiteness 85.8%, methyl cellulose content 98.8%, iron content 16.0 ppm, and fiber length 28%.

[0055] Example 2

[0056] A method for preparing dissolving pulp based on the cleaning of waste cotton textiles, the specific steps of which are as follows:

[0057] (1) After washing and disinfecting the waste pure cotton fabric, cut it into pieces of fabric 8-12 cm long and weigh 8g for later use;

[0058] (2) Add 5% lactic acid by mass fraction to the filtrate obtained in step (3) of Example 1, stir evenly at room temperature to obtain a newly formulated ternary eutectic solvent.

[0059] (3) Measure 80 mL of the ternary eutectic solvent prepared in step (2) into a 200 mL sample bottle, add 8 g of the cotton fabric cut in step (1), heat to 80 °C and stir for 40 minutes, then filter the reaction product through a filter membrane under vacuum to obtain the filter residue and filtrate; wash the filter residue with water 3 to 5 times, and after washing, place it in a vacuum drying oven at 60 °C and dry for 4 hours to obtain the depolymerized cotton fabric.

[0060] (4) Take 13.33 mL of 30% hydrogen peroxide solution into a 200 mL sample bottle, then add 0.8 g of ethylenediaminetetraacetic acid and 0.06 g of magnesium sulfate, add deionized water to make the total solution volume 80 mL, and add sodium hydroxide solution to adjust the pH value of the solution to 10 to obtain the purified preparation.

[0061] (5) Place the depolymerized cotton fabric obtained in step (3) into the refining agent prepared in step (4), heat it to 90°C and keep it warm for 60 minutes, then take the fabric out of the solution with tweezers and wash it with water 3 to 5 times. After washing, place it in a vacuum drying oven at 60°C and dry it for 4 hours to obtain cotton fabric. Pulp the obtained cotton fabric to obtain regenerated dissolving pulp.

[0062] The performance of the recycled dissolving pulp obtained in Example 2 was tested, and the results are as follows: degree of polymerization 565, whiteness 84.9%, methyl cellulose content 98.6%, iron content 16.4 ppm, and fiber length 30%.

[0063] Example 3

[0064] A method for preparing dissolving pulp based on the cleaning of waste cotton textiles, the specific steps of which are as follows:

[0065] (1) After washing and disinfecting the waste pure cotton fabric, cut it into pieces of fabric 8-12 cm long and weigh out 10g for later use.

[0066] (2) Weigh 46.86 g of betaine and 36.83 g of formic acid (the molar ratio of betaine to formic acid is 1:2) into a 200 mL sample bottle, heat to 60 °C and stir for 20 minutes to form a homogeneous and transparent clear solution. After cooling, a eutectic solvent is obtained. Add 27.90 g of deionized water to the obtained eutectic solvent (i.e., the mass content of water in the ternary eutectic solvent is 24.28%), stir evenly at room temperature to form a homogeneous and clear ternary eutectic solvent.

[0067] Steps (3) to (5) are the same as in Example 1.

[0068] The performance of the regenerated dissolving pulp obtained in Example 3 was tested, and the results are as follows: degree of polymerization 528, whiteness 85.2%, methyl cellulose content 98.6%, iron content 17.0 ppm, and fiber length 28%.

[0069] Example 4

[0070] A method for preparing dissolving pulp based on the cleaning of waste cotton textiles, the specific steps of which are as follows:

[0071] (1) After washing and disinfecting the waste pure cotton fabric, cut it into pieces of fabric 8-12 cm long and weigh out 10g for later use.

[0072] (2) Weigh 58.57 g of betaine and 45.02 g of oxalic acid (the molar ratio of betaine to oxalic acid is 1:1) into a 200 mL sample bottle, heat to 80 °C and stir for 20 minutes to form a homogeneous and transparent clear solution. After cooling, a eutectic solvent is obtained. Add 25.90 g of deionized water to the obtained eutectic solvent (i.e., the mass content of water in the ternary eutectic solvent is 19.50%), stir evenly at room temperature to form a homogeneous and clear ternary eutectic solvent.

[0073] (3) Measure 100 mL of the ternary eutectic solvent prepared in step (2) into a 200 mL sample bottle, add 10 g of the waste pure cotton fabric cut in step (1), heat to 75 °C and stir for 40 minutes, then filter the reaction product through a filter membrane under vacuum to obtain filter residue and filtrate; wash the filter residue with water 3 to 5 times, and after washing, place it in a vacuum drying oven at 60 °C and dry for 4 hours to obtain the depolymerized cotton fabric.

[0074] (4) Take 16.67 mL of hydrogen peroxide solution with a mass concentration of 30% into a 200 mL sample bottle, then add 1 g of ethylenediaminetetraacetic acid and 0.08 g of magnesium sulfate, add deionized water to make the total volume of the solution 100 mL, and add sodium hydroxide solution to adjust the pH value of the solution to 10 to obtain the purified preparation.

[0075] (5) Place the depolymerized cotton fabric obtained in step (3) into the refining agent prepared in step (4), heat it to 90°C and keep it warm for 60 minutes, then take the fabric out of the solution with tweezers and wash it with water 3 to 5 times. After washing, place it in a vacuum drying oven at 60°C and dry it for 4 hours to obtain cotton fabric. Pulp the obtained cotton fabric to obtain regenerated dissolving pulp.

[0076] The performance of the regenerated dissolving pulp obtained in Example 4 was tested, and the results are as follows: degree of polymerization was 561, whiteness was 84.8%, methyl cellulose content was 97.3%, iron content was 18.9 ppm, and fiber length was 29%.

[0077] Figure 1 From left to right, the images show physical photos of the eutectic solvents prepared in step (2) of Examples 1, 3, and 4. Figure 1 It can be seen that the eutectic solvents prepared in Examples 1, 3, and 4 are homogeneous and transparent solutions.

[0078] Figure 2 The infrared spectra of the waste pure cotton fabric in step (1) of Example 1, the depolymerized cotton fabric obtained in step (2), and the recycled dissolving pulp obtained in step (3) are shown. Here, "raw cotton" refers to the waste pure cotton fabric, "depolymerized cotton" refers to the depolymerized cotton fabric, and "recycled cotton pulp" refers to the recycled dissolving pulp. Figure 2 It can be seen that the characteristic absorption peak positions of the three are highly consistent, indicating that the pulping process provided by the present invention is mild and does not change the chemical structure of cotton fibers.

[0079] Figure 3 The images show the XRD patterns of the waste pure cotton fabric in step (1) of Example 1, the depolymerized cotton fabric obtained in step (2), and the recycled dissolving pulp obtained in step (3), where raw cotton refers to waste pure cotton fabric, depolymerized cotton refers to depolymerized cotton fabric, and recycled cotton pulp refers to recycled dissolving pulp. Figure 3It can be seen that the crystallinity index (CrI) of waste pure cotton fabric is 79.62%, the crystallinity index (CrI) of depolymerized cotton fabric is 85.64%, and the crystallinity index (CrI) of recycled dissolving pulp is 82.60%. This indicates that the acidic environment provided by the depolymerizing agent can promote local rearrangement of cellulose molecular chains, further improving the orderliness of the crystalline regions. The oxidation of the refining agent leads to molecular chain breakage, and some crystalline regions are destroyed. However, the diffraction peak positions are consistent, and the cellulose crystal form has not changed, still maintaining the cellulose type I structure.

[0080] Comparative Example 1

[0081] A method for preparing dissolving pulp based on the cleaning of waste cotton textiles, differing from Example 1 in that ethylenediaminetetraacetic acid is not added to the refining agent. Specifically, step (4) involves taking 16.67 mL of 30% hydrogen peroxide solution into a 200 mL sample bottle, adding 0.08 g of magnesium sulfate, adding deionized water to a total solution volume of 100 mL, and adding sodium hydroxide solution to adjust the pH value of the solution to 10 to obtain the refining agent. Other steps are the same as in Example 1.

[0082] The performance of the regenerated dissolving pulp obtained in Comparative Example 1 was tested, and the results are as follows: degree of polymerization 545, whiteness 85.4%, methyl cellulose content 98.8%, iron content 31.4 ppm, and fiber length 28%. It can be seen that, compared with Example 1, the iron content in the regenerated dissolving pulp obtained in Comparative Example 1 is significantly increased, indicating that the addition of ethylenediaminetetraacetic acid can effectively remove iron from the pulp.

[0083] Comparative Example 2

[0084] A method for preparing dissolving pulp based on the cleaning of waste cotton textiles, the specific steps of which are as follows:

[0085] (1) After washing and disinfecting the waste pure cotton fabric, cut it into pieces of fabric 8-12 cm long and weigh 8g for later use;

[0086] (2) Measure 80 mL of the filtrate obtained in step (3) of Example 1 into a 200 mL sample bottle, add 8 g of the cotton fabric cut in step (1), heat to 80 °C and stir for 40 minutes, then filter the reaction product through a filter membrane under vacuum to obtain the filter residue and filtrate; wash the filter residue with water 3 to 5 times, and after washing, place it in a vacuum drying oven at 60 °C and dry for 4 hours to obtain the depolymerized cotton fabric.

[0087] (3) Take 13.33 mL of hydrogen peroxide solution with a mass concentration of 30% into a 200 mL sample bottle, then add 0.8 g of ethylenediaminetetraacetic acid and 0.06 g of magnesium sulfate, add deionized water to make the total volume of the solution 80 mL, and add sodium hydroxide solution to adjust the pH value of the solution to 10 to obtain the purified preparation.

[0088] (4) Place the depolymerized cotton fabric obtained in step (2) into the refining agent prepared in step (3), heat it to 90°C and keep it warm for 60 minutes, then take the fabric out of the solution with tweezers and wash it with water 3 to 5 times. After washing, place it in a vacuum drying oven at 60°C and dry it for 4 hours to obtain cotton fabric. Pulp the obtained cotton fabric to obtain regenerated dissolving slurry.

[0089] The performance of the regenerated dissolving slurry obtained in Comparative Example 2 was tested, and the results are as follows: degree of polymerization was 712, whiteness was 83.6%, methyl cellulose content was 97.2%, iron content was 17.5 ppm, and fiber length was 31%. Compared with Example 2, Comparative Example 2 did not add organic acid when recycling the filtrate obtained in step (3) of Example 1, and directly recycled it. The ternary eutectic solvent experienced performance degradation, resulting in a significant decrease in depolymerization efficiency, and the product performance could not meet the requirements.

[0090] Comparative Example 3

[0091] A method for preparing dissolving slurry based on the cleaning of waste cotton textiles differs from Example 1 in that deionized water is not added to the eutectic solvent. Specifically, step (2) is as follows: 41.00 g of betaine and 63.06 g of lactic acid (the molar ratio of betaine to lactic acid is 1:2) are weighed into a 200 mL sample bottle, heated to 80 °C and stirred for 20 minutes to form a homogeneous and transparent clear solution. After cooling, the eutectic solvent is obtained. The rest is the same as in Example 1.

[0092] The performance of the regenerated dissolving pulp obtained in Comparative Example 3 was tested, and the results are as follows: degree of polymerization was 1208, whiteness was 84.6%, methyl cellulose content was 96.3%, iron content was 19.3 ppm, and fiber length was 29%. Compared with Example 1, deionized water was not added to the eutectic solvent in Comparative Example 3, which hindered the solvent from penetrating into the fiber interior, resulting in insufficient depolymerization and an excessively high degree of polymerization in the obtained regenerated dissolving pulp.

[0093] Comparative Example 4

[0094] A method for preparing dissolving slurry based on the cleaning of waste cotton textiles, differing from Example 1 in that step (2) is as follows: 35.14g of betaine and 54.05g of lactic acid (the molar ratio of betaine to lactic acid is 1:2) are weighed into a 200mL sample bottle, heated to 80℃ and stirred for 20 minutes to form a homogeneous and transparent clear solution. After cooling, a eutectic solvent is obtained. 89.19g of deionized water (i.e., the mass content of water in the ternary eutectic solvent is 50.00%) is added to the obtained eutectic solvent and stirred evenly at room temperature to form a homogeneous and clear ternary eutectic solvent. The rest is the same as in Example 1.

[0095] The performance of the regenerated dissolving pulp obtained in Comparative Example 4 was tested, and the results are as follows: degree of polymerization was 1062, whiteness was 85.0%, methyl cellulose content was 96.9%, iron content was 19.1 ppm, and fiber length was 30%. Compared with Example 1, the water content of the ternary eutectic solvent in Comparative Example 4 was too high, causing the inherent hydrogen bond network of the eutectic solvent to disintegrate, greatly weakening the depolymerization efficiency, and resulting in a high degree of polymerization in the obtained regenerated dissolving pulp.

[0096] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing a dissolving pulp based on waste cotton textiles, characterized in that, The method comprises the following steps: The waste cotton textiles are sequentially pretreated, depolymerized and refined to obtain regenerated dissolving pulp; The depolymerization agent used in the depolymerization treatment is a ternary eutectic solvent; the ternary eutectic solvent is composed of betaine, organic acid and water.

2. The method for producing dissolving pulp based on waste cotton textile cleaning according to claim 1, characterized in that, The molar ratio of the betaine and the organic acid is 1:(1-3).

3. The method for producing dissolving pulp based on waste cotton textile cleaning according to claim 1, characterized in that, The mass content of water in the ternary eutectic solvent is 10-40%.

4. The method for producing dissolving pulp based on waste cotton textile cleaning according to claim 1 or 2, characterized in that, The organic acid is selected from lactic acid, formic acid, acetic acid or oxalic acid.

5. The method for producing dissolving pulp based on waste cotton textile cleaning according to claim 1, characterized in that, The temperature of the depolymerization treatment is 75-85℃, the time of the depolymerization treatment is 30-60 minutes, and the solid-liquid ratio of the depolymerization treatment is 1:(8-12)(g / mL).

6. The method for producing dissolving pulp based on waste cotton textile cleaning according to claim 1, characterized in that, The refining agent used in the refining treatment comprises hydrogen peroxide, ethylenediaminetetraacetic acid and magnesium sulfate; the mass concentration of hydrogen peroxide in the refining agent is 4-6%, the mass concentration of ethylenediaminetetraacetic acid is 0.8-1%, and the mass concentration of magnesium sulfate is 0.05-0.1%; the pH value of the refining agent is 9-11.

7. The method for producing dissolving pulp based on waste cotton textile cleaning according to claim 1, characterized in that, The temperature of the refining treatment is 80-90℃, the time of the refining treatment is 60-90 minutes, and the solid-liquid ratio of the refining treatment is 1:(8-12)(g / mL).

8. The method for producing dissolving pulp based on waste cotton textile cleaning according to claim 1, characterized in that, The depolymerization treatment further comprises a step of recycling the ternary eutectic solvent.

9. The method for producing dissolving pulp from waste cotton textiles according to claim 8, characterized in that, The recycling comprises: filtering and separating the product obtained after the depolymerization treatment to obtain depolymerized cotton textiles and filtrate; supplementing the filtrate with 3-5% of the mass of the organic acid and then recycling.

10. The method for producing dissolving pulp based on waste cotton textile cleaning according to claim 1, characterized in that, The regenerated dissolving pulp has a degree of polymerization of 500-700, a content of alpha cellulose of ≥97%, a whiteness of ≥84%, an iron content of ≤20ppm and a fiber length of 26-32%.

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