Method for regenerating cellulose from waste cotton based on ion solvation pretreatment and application thereof

Abstract

The application discloses a method for regenerating cellulose from waste cotton based on ion solvation pretreatment and application thereof, and belongs to the technical field of high-value utilization of biomass resources. The method is characterized in that waste cotton fabric is immersed in a metal halide aqueous solution for ion solvation pretreatment, and then subjected to mild decolorization by a reduced decoloring agent, and then high-polymerization-degree cotton cellulose after decolorization is dissolved in a cellulose solvent system to obtain a high-transparency and high-activity cellulose solution. The cellulose solution can be widely applied to the fields of regenerated cellulose fiber spinning, nanocellulose preparation, functional aerogel / hydrogel construction and high-performance gel electrolyte. The application overcomes the problem that the thoroughness of decolorization and the retention of polymerization degree of regenerated waste cotton textiles are difficult to be considered simultaneously, and realizes efficient decolorization, high-polymerization-degree retention and efficient dissolution of waste colored cotton textiles in various solvent systems.

Description

Technical Field

[0001] This invention relates to the fields of resource recycling of waste textiles and cellulose chemistry, specifically to a method for regenerating cellulose from waste cotton based on ion solvation pretreatment, and the application of the cellulose solution prepared by this method in the preparation of diverse materials such as regenerated fibers, nanocellulose, cellulose membranes, aerogels, and gel electrolytes. Background Technology

[0002] With the rapid development of the global textile industry and the popularization of the "fast fashion" consumption model, the amount of waste textiles generated each year is exploding. Statistics show that more than 92 million tons of textile waste are generated globally each year, of which cotton and cotton blends and other natural fiber products account for about 30%. Most of these waste cotton textiles are disposed of through landfill or incineration, causing not only serious resource waste but also significant environmental pollution problems. Under the background of "carbon peaking and carbon neutrality," achieving high-value recycling of waste cotton textiles has become a key issue for the green transformation of the textile industry. The core component of cotton textiles is natural cellulose, which has a typical cellulose type I crystal structure and extremely high degree of polymerization (DP usually >2000), making it a high-quality raw material for preparing regenerated fibers, nanocellulose, and functional cellulose materials. However, the high-value recycling of waste colored cotton textiles faces two major challenges: First, the difficulty of deep dye removal. Modern textile printing and dyeing widely uses reactive dyes (such as azo and anthraquinone dyes), which are firmly bound to cellulose hydroxyl groups through covalent bonds and deeply embedded between the microfibrils inside the fiber. Traditional decolorization processes, such as the strong oxidizing system of hydrogen peroxide (H2O2), can achieve a certain degree of decolorization. However, the non-specific attack of hydroxyl radicals (-OH) on cellulose glycosidic bonds leads to a sharp decrease in the degree of polymerization (typically exceeding 40%), severely damaging the mechanical properties of recycled materials. Even with relatively mild reducing decolorizing agents (such as sodium dithionite), the dense crystalline structure and strong hydrogen bond network of cotton fibers make it difficult for the decolorizing agent to penetrate deep into the fiber, often resulting in incomplete decolorization and residual obvious base color. Secondly, the dissolution of high-polymerization-degree cotton fibers is difficult. Existing cellulose solvent systems, such as NMMO (N-methylmorpholine-N-oxide), ionic liquids (such as [BMIM]Cl), and low-temperature NaOH / urea systems, while showing good performance in dissolving low-DP cellulose (such as microcrystalline cellulose and pulp cellulose), often fail to disrupt the crystalline structure of natural cotton fibers with dense supramolecular structures and extremely high DP, leading to incomplete dissolution, turbid solutions, and even gelation.

[0003] While there are existing reports on the use of LiBr metal halide aqueous solutions to dissolve cellulose (e.g., CN112812343A "A method for preparing regenerated cellulose membranes using lithium bromide, its products and applications"), these processes typically require high temperatures, resulting in high energy consumption and significant LiBr residue, making recycling difficult. There are also reports on the use of strong oxidants such as sodium hypochlorite and hydrogen peroxide to decolorize colored cotton fabrics (e.g., CN110804855A "An efficient decolorization method for waste cotton textiles" and CN104499266A "A pretreatment method for waste cotton clothing"). However, while these methods achieve thorough decolorization, they often fail to maintain the degree of polymerization of cellulose. Strong oxidation easily leads to the breakage of glycosidic bonds, significantly reducing the degree of polymerization. Furthermore, patent document CN115747991A, "A Method for Recycling Cellulose from Waste Cotton Fabrics for Use as Raw Material for Regenerated Fibers," discloses a waste cotton fabric recycling process. However, its process route involves complex operations such as multi-step pretreatment and supercritical extraction, making it difficult to control the degree of polymerization of the regenerated cellulose, resulting in some losses. In summary, developing a new method for recycling waste colored cotton textiles that can simultaneously achieve efficient decolorization, high degree of polymerization retention, and efficient dissolution in various solvent systems, and applying the resulting highly active cellulose solution to the preparation of diversified high-value products, has significant scientific and engineering value for realizing the recycling of waste textiles. Summary of the Invention

[0004] This invention addresses two major technical bottlenecks in the recycling process of waste colored cotton textiles: the difficulty in simultaneously achieving deep decolorization and maintaining the degree of polymerization, and the difficulty in achieving efficient homogeneous dissolution of high-polymerization cotton cellulose under mild conditions. It provides a structure-protective recycling method for waste cotton cellulose based on ion solvation pretreatment.

[0005] The present invention is achieved through the following technical solution.

[0006] One aspect of the present invention provides a method for pretreating waste cotton cellulose using ion solvation, comprising the following steps: (a) Cut, dust, wash, and dry the waste cotton fabrics for later use; (b) The dried waste cotton fabric is immersed in a metal halide aqueous solution for treatment, and the pretreated cotton fibers are obtained by filtration and separation. (c) The amount of reducing decolorizing agent added is 1% to 15% of the mass of the pretreated cotton fiber. The pretreated cotton fiber is added to an alkaline aqueous solution containing reducing decolorizing agent and decolorized under stirring or shaking conditions. It is then washed with alternating hot and cold water until neutral to obtain decolorized cotton fiber. (d) According to the mass ratio of decolorized cotton fiber to cellulose solvent of 1:9 to 1:19, the decolorized cotton fiber is added to the cellulose solvent system, and the cellulose solution is obtained by wetting, dissolving and mechanically dispersing treatment that is compatible with the selected solvent system.

[0007] According to an exemplary embodiment of the present invention, the waste cotton fabric includes colored cotton fabric, cotton yarn, or cotton-blended fabric.

[0008] According to an exemplary embodiment of the present invention, the metal halide in the aqueous solution is selected from lithium bromide, lithium chloride, zinc chloride, calcium chloride, and a complex of calcium chloride and zinc chloride; the total mass fraction of the metal halide in the aqueous solution is 5 wt.% to 20 wt.%; when using a complex aqueous solution of calcium chloride and zinc chloride, the mass ratio of calcium chloride to zinc chloride is 1:4 to 4:1.

[0009] According to an exemplary embodiment of the present invention, the concentration of the reducing decolorizing agent in the alkaline aqueous solution is 20-40 g / L, and the pH value of the alkaline aqueous solution containing the reducing decolorizing agent is 9-13.

[0010] According to an exemplary embodiment of the present invention, the reducing decolorizing agent is selected from one or more of sodium dithionite, sodium borohydride, sodium bisulfite, and thiourea dioxide.

[0011] The alkaline substance in the alkaline aqueous solution is selected from one or more of sodium hydroxide and sodium carbonate.

[0012] In step (a), the sample is cleaned with deionized water or an ethanol / water mixture.

[0013] In step (b), the waste cotton fabric is immersed in a metal halide aqueous solution at a temperature of 25~100°C for a time of 0.5 h~6 h; the bath ratio is 1:10~1:50 g / mL.

[0014] In step (c), the pH value of the decolorization system under stirring or shaking conditions is 9~13, the decolorization temperature is 50~90°C, and the decolorization time is 20~120 min.

[0015] According to an exemplary embodiment of the present invention, the cellulose solvent system is a low-temperature alkali / urea / water system or a non-low-temperature alkali / urea / water system; The low-temperature alkali / urea / water system is a NaOH / urea / H2O, LiOH / urea / H2O, or NaOH / urea / thiourea / H2O system. The non-low-temperature alkali / urea / water system is an N-methylmorpholine-N-oxide / water, N,N-dimethylacetamide / lithium chloride, 1-allyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium chloride ionic liquid system. In the NaOH / urea / H2O, LiOH / urea / H2O, and NaOH / urea / thiourea / H2O systems: NaOH or LiOH: 5-10 wt.%, urea or urea + thiourea: 8-15 wt.%, water: 75-87 wt.%; In the N-methylmorpholine-N-oxide / water system and the N,N-dimethylacetamide / lithium chloride system: N-methylmorpholine-N-oxide:water = (75-95):(5-25); N,N-dimethylacetamide:lithium chloride = (90-95):(5-10).

[0016] When a low-temperature alkali / urea / water system is used, the pre-cooling temperature of the cellulose solvent system is -20 to -5°C, the immersion time of the decolorized cotton fibers in the pre-cooled solvent is 2 to 4 hours, and a uniform cellulose solution is obtained by mechanical shearing or stirring dispersion. When using a non-low-temperature alkali / urea / water system, the dissolution temperature of the N-methylmorpholine-N-oxide / water system is 70–120°C, and the dissolution time is 0.5–6 h; the dissolution temperature of the N,N-dimethylacetamide / lithium chloride system is 60–100°C, and the dissolution time is 2–24 h; the dissolution temperature of the 1-allyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium chloride ionic liquid system is 70–120°C, and the dissolution time is 0.5–6 h.

[0017] In another aspect, the present invention provides a regenerated cellulose from waste cotton prepared by the method described above, based on ion-solvent pretreatment.

[0018] In another aspect, the present invention provides a method for preparing regenerated cellulose materials based on the application of ion-solvent pretreatment of waste cotton regenerated cellulose, comprising: Regenerated cellulose fiber: A cellulose solution is regenerated and solidified by wet spinning or dry-wet spinning, and then solidified by coagulation bath to obtain filaments or staple fibers; Nanocellulose: Cellulose nanocrystals or cellulose nanofibers are prepared by diluting, acid hydrolyzing, mechanical shearing, high-pressure homogenization or ultrasonic treatment of cellulose solution; Regenerated cellulose membrane: A transparent regenerated cellulose membrane is obtained by casting or coating a cellulose solution into a film and then regenerating it in a coagulation bath. Cellulose hydrogels / aerogels: Cellulose hydrogels or aerogels are obtained by chemically cross-linking or physically freezing a cellulose solution, followed by atmospheric pressure or freeze-drying. Cellulose-based gel electrolyte: A dual-network gel electrolyte is obtained by in-situ polymerization of a cellulose solution with polymerizable monomers, which is used in flexible energy storage devices.

[0019] The present invention, by adopting the above technical solution, has the following beneficial effects: 1. Through a cascade process of ion solvation pretreatment and mild reduction decolorization, using the initial DP of raw cotton cellulose as a benchmark, the DP retention rate after treatment by this method can reach more than 90%, that is, the DP reduction rate is controlled within 10%. In the preferred embodiment, the DP reduction rate can be further controlled within 5%, which is significantly better than the traditional strong oxidation decolorization process and the single reduction decolorization process. It fully preserves the high molecular weight advantage of natural cotton cellulose and provides a good mechanical property basis for subsequent recycled materials.

[0020] 2. The mass transfer channel constructed through pretreatment significantly reduces the spatial confinement resistance of dye removal. Waste cotton textiles dyed with various reactive dyes such as red, blue, and black can achieve deep decolorization within 60 to 90 minutes. XPS detection shows that the signals of dye characteristic elements (such as S 2p) are attenuated to near the background level. The decolorization uniformity is good, with no obvious residual color. The decolorization is efficient and thorough.

[0021] 3. The supramolecular structure of cotton cellulose after pretreatment and decolorization is in a relaxed state, exhibiting excellent solubility in the NaOH / urea / H2O low-temperature solvent system verified by the examples. The dissolution rate is improved, and the resulting solution has high transparency, moderate viscosity and good stability, avoiding the incomplete dissolution and gelation problems in the traditional high DP cotton cellulose dissolution process.

[0022] 4. The entire pretreatment and decolorization process is mainly carried out in an aqueous phase under medium and low temperature conditions, without the need for strong oxidants or high temperature and high pressure conditions. The chemical reagents have the potential for recycling and meet the requirements of green chemistry. The resulting highly active decolorized cotton cellulose can be used as a general precursor for subsequent cellulose dissolution and functional material construction, and the matching dissolution process conditions can be selected according to the specific solvent system.

[0023] 5. The prepared highly active cellulose solution can be directly used in high-value fields such as wet spinning of regenerated cellulose fibers, preparation of nanocellulose, construction of functional membranes / aerogels, and flexible energy storage gel electrolytes, realizing the leap from "low-value treatment" to "high-value regeneration" of waste cotton textiles, with significant resource conservation, environmental benefits and economic value. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the process flow for the preparation of regenerated cellulose from waste colored cotton fabrics based on ion solvation pretreatment and its multi-path high-value application according to the present invention. Figure 2These are before-and-after photos of waste cotton fabrics of different colors before and after ion solvation pretreatment and reduction decolorization.

[0025] Figure 3 A comparison chart showing the decrease in the degree of polymerization of cotton cellulose after different decolorization treatments.

[0026] Figure 4 The figure shows the simulation results of molecular or ion interactions during ion solvation pretreatment and reduction decolorization.

[0027] Figure 5 This is a macroscopic diagram showing the dissolution effect of decolorized cotton fibers in the NaOH / urea / H2O system.

[0028] Figure 6 This is a polarized light microscope comparison image of cotton fibers after ion solvation pretreatment and before pretreatment, showing the results of dissolution.

[0029] Figure 7 The figures show the morphology and mechanical properties of the regenerated cellulose fibers prepared from the cellulose solution of the present invention, wherein (a1) is a longitudinal surface SEM image, (a2) is a cross-sectional SEM image, (b) is a stress-strain curve, and (c) is tensile strength and Young's modulus.

[0030] Figure 8 The diagram shows the structure, interface adaptability, and cycle performance of the cellulose-based gel electrolyte and flexible zinc-air battery of the present invention. (a) is a schematic diagram of the battery structure, (b) shows the adhesion effect of the gel electrolyte to different substrates, and (c) shows the charge-discharge cycle curves. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0032] Figure 1 The overall technical route of this invention is illustrated, including ion solvation pretreatment of waste colored cotton fabrics, mild reduction decolorization, washing and drying, and cellulose dissolution processes. The resulting highly active decolorized cotton cellulose and its homogeneous solution can be used as general intermediates, depending on the processing method, for spinning regenerated cellulose fibers, preparing regenerated cellulose membranes and nanocellulose, constructing functional hydrogels or aerogels, and preparing gel electrolytes.

[0033] Figure 1 As shown, this embodiment of the invention provides a method for regenerating cellulose from waste cotton based on ion solvation, comprising the following steps: Step 1, Pre-treatment of waste colored cotton textiles: Waste cotton fabrics (colored cotton fabrics, cotton yarns, or cotton-blended fabrics) are cut, dusted, and washed with deionized water or an ethanol / water mixture to remove surface dust, sizing, and soluble impurities, and then dried for later use.

[0034] In the ion solvation pretreatment process, waste colored cotton textiles are immersed in a metal halide aqueous solution for pretreatment. The hydrogen bond network at the edge of the cellulose crystal region is competitively replaced and relaxed by the ion solvation effect, and a continuous mass transfer channel is constructed without significantly degrading the cellulose molecular chain, thus obtaining pretreated cotton fibers.

[0035] Step 2, Ion solvation pretreatment: The dried waste cotton fabric is immersed in a metal halide aqueous solution at a temperature of 25–100°C, preferably 60–85°C, for 0.5–6 h, preferably 1–3 h, with a bath ratio of 1:10–1:50. This allows the ionic solvation structure to penetrate the fiber interior and relax the cellulose hydrogen bond network. After treatment, the pretreated cotton fibers are obtained by filtration. The filtrate can be recycled for the next batch after salt replenishment or concentration.

[0036] The metal halide is selected from lithium bromide, lithium chloride, zinc chloride, calcium chloride, and calcium chloride complexes.

[0037] The mass fraction of metal halides in aqueous solutions ranges from 5 wt.% to 20 wt.%.

[0038] When using a mixed aqueous solution of calcium chloride and zinc chloride, the mass ratio of calcium chloride to zinc chloride is 1:4 to 4:1.

[0039] Step 3, gentle reduction and decolorization: Pretreated cotton fibers are added to an alkaline aqueous solution containing a reducing bleaching agent, the amount of which is 1% to 15% of the weight of the pretreated cotton fibers, preferably 3% to 8%. Bleaching is carried out under stirring or shaking conditions at a pH of 9 to 13, a bleaching temperature of 50 to 90°C, and a bleaching time of 20 to 120 minutes, preferably 60 to 90 minutes, allowing the reducing agent to penetrate into the fiber and selectively reduce or cleave the dye chromophores. After the reaction is complete, the fibers are washed alternately with hot and cold water until neutral to obtain bleached cotton fibers.

[0040] The reducing decolorizing agent is selected from one or more of sodium dithionite (Na2S2O4), sodium borohydride (NaBH4), sodium bisulfite (NaHSO3), and thiourea dioxide.

[0041] The alkaline substance in the alkaline aqueous solution is selected from one or more of sodium hydroxide and sodium carbonate.

[0042] In the mild reduction decolorization process, the pretreated cotton fibers are placed in an alkaline reduction decolorization system. Utilizing the constructed mass transfer channels, the reducing decolorizing agent penetrates into the fiber interior and selectively reduces and cleaves the dye chromophores, yielding decolorized cotton fibers. After pretreatment and decolorization, the decrease in the degree of cellulose polymerization of the obtained decolorized cotton fibers is stably controlled within 5%.

[0043] Step 4, cellulose dissolution: According to the mass ratio of bleached cotton fiber to cellulose solvent of 1:9 to 1:19, the bleached cotton fiber is added to the cellulose solvent system for impregnation, dissolution and mechanical dispersion to obtain a homogeneous cellulose solution.

[0044] The cellulose solvent system is either a low-temperature alkali / urea / water system or a non-low-temperature alkali / urea / water system.

[0045] The low-temperature alkali / urea water system is NaOH / urea / H2O, LiOH / urea / H2O, or NaOH / urea / thiourea / H2O. The solvent system is first pre-cooled to -20 to -5°C, preferably -18 to -10°C, and then decolorized cotton fibers are added and soaked for 2 to 4 hours. Subsequently, mechanical stirring or high-speed shearing is used to promote the deentanglement of cellulose chains and homogeneous dispersion.

[0046] Non-low-temperature alkali / urea / water systems are N-methylmorpholine-N-oxide / water systems, N,N-dimethylacetamide / lithium chloride systems, or ionic liquid systems. Non-low-temperature alkali / urea / water systems do not use the low-temperature pre-cooling steps of the above-mentioned low-temperature alkali / urea / water systems. Instead, they are dissolved under temperature, moisture content, salt content, and mechanical dispersion conditions that match the corresponding solvent system.

[0047] When using a non-low-temperature alkali / urea / water system, the dissolution temperature of the N-methylmorpholine-N-oxide / water system is 70–120°C, and the dissolution time is 0.5–6 h; the dissolution temperature of the N,N-dimethylacetamide / lithium chloride system is 60–100°C, and the dissolution time is 2–24 h; the dissolution temperature of the 1-allyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium chloride ionic liquid system is 70–120°C, and the dissolution time is 0.5–6 h.

[0048] Among them, in the NaOH / urea / H2O, LiOH / urea / H2O, and NaOH / urea / thiourea / H2O systems: NaOH or LiOH is 5-10 wt.%, urea or urea + thiourea is 8-15 wt.%, and water is 75-87 wt.%.

[0049] In the N-methylmorpholine-N-oxide / water system and the N,N-dimethylacetamide / lithium chloride system: N-methylmorpholine-N-oxide:water = (75-95):(5-25), preferably 87:13; N,N-dimethylacetamide:lithium chloride = (90-95):(5-10), preferably 92:8.

[0050] The cellulose solvent system contains 5 wt.% to 10 wt.% of cellulose by mass. Based on the initial degree of polymerization of cellulose in the waste cotton fabric in step (a), the DP retention rate of the decolorized cotton cellulose obtained after treatment in steps (b) and (c) is ≥90%, i.e., the DP decrease rate is ≤10%; preferably, the DP retention rate is ≥95%, i.e., the DP decrease rate is ≤5%; the transmittance of the obtained cellulose solution at a wavelength of 500 nm is not less than 80%, and the zero-shear viscosity at 25°C is 1 to 50 Pa·s.

[0051] This invention proposes an ion solvation pretreatment method as a "structural relaxation" technique for the regeneration of waste colored cotton textiles. It employs an aqueous solution of metal halides (preferably a high-concentration lithium bromide solution) for ion solvation pretreatment, utilizing the ion solvation effect to competitively replace and relax the hydrogen bond network at the edges of cellulose crystal regions, constructing continuous mass transfer channels without significantly degrading the cellulose molecular chains. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations reveal that, under suitable conditions, high-concentration lithium bromide and other metal halide hydrates can effectively relax the hydrogen bond network at the edges of cellulose crystal regions, thus constructing continuous mass transfer channels. + It forms a strong ion-dipole interaction with oxygen-rich sites such as cellulose pyran epoxide and glycosidic oxygen, Br - Competing for hydrogen bonds with hydroxyl hydrogen, it preferentially relaxes the supramolecular hydrogen bond network at the edges of cellulose crystalline regions and in amorphous regions, constructing a continuous mass transfer channel with minimal disruption to the cellulose molecular chain. This channel significantly enhances the penetration of subsequent reducing and decolorizing agents into the fiber interior, while also creating conditions for efficient dissolution in various solvent systems.

[0052] Building upon this foundation, the subsequently added Na2S2O4 reducing decolorizing agent penetrates into the fiber interior with extremely low diffusion resistance. DFT calculations revealed a HOMO-LUMO band gap of 3.68 eV for the relevant system, indicating its electron transfer reactivity. This allows for selective electron transfer to the azo-conjugated chromophore system (-N=N-) through the constructed mass transfer channels, achieving efficient penetration and selective cleavage of the dye chromophores within the fiber. This reduces the dye to colorless -NH-NH- or bond-breaking products, while avoiding attack on glycosidic bonds. Ultimately, the pretreated and decolorized cotton fibers, due to their pre-relaxed supramolecular structure, can rapidly achieve homogeneous dissolution in a low-temperature NaOH / urea system, yielding a highly transparent, high-polymerization-degree cellulose solution, laying the foundation for diversified and high-value downstream applications.

[0053] This invention is preferably applicable to waste cotton fabrics dyed with reactive dyes, especially cotton fabrics dyed with azo reactive dyes that form covalent bonds with cellulose hydroxyl groups and whose chromophores can be selectively reduced or cleaved by reducing agents. For anthraquinone reactive dyes or other dye systems, adaptation treatment can be performed based on the mass transfer channels formed by the ion solvation pretreatment described in this invention, but the specific decolorization conditions and effects should be verified by the corresponding examples.

[0054] The preparation of cellulose materials according to the present invention will be further illustrated below through different embodiments.

[0055] Example 1: Pretreatment, decolorization, dissolution, and cellulose preparation of waste red cotton fabric 1) After washing and drying the waste cotton fabric dyed with red reactive dye, cut it into small pieces no larger than 3 mm × 3 mm.

[0056] 2) Weigh 10 g of cotton fabric and add it to 300 mL of a 10 wt.% LiBr aqueous solution. Immerse the fabric at 25°C for 6 h at a liquor ratio of 1:30 g / mL. After treatment, perform vacuum filtration and collect the LiBr filtrate for recovery. Wash the resulting cotton fibers five times with deionized water and vacuum dry them at 60°C to constant weight. 3) Add the pretreated cotton fibers to a 30 g / L Na2S2O4 aqueous solution at a liquor ratio of 1:30. The amount of reducing decolorizing agent Na2S2O4 added is 3% of the mass of the pretreated cotton fibers. Treat the fibers at a pH of 9 in a 90°C constant temperature water bath shaker at 500 rpm for 90 min. After decolorization, wash the fibers sequentially with 60°C hot water and room temperature deionized water until neutral. Then, air dry the fibers at 25°C for 24 h to obtain the decolorized cotton fibers.

[0057] 4) Prepare a ternary solvent system with NaOH / urea / H2O in a mass ratio of 7:12:81 and pre-cool it at -18°C for 2 hours. Add the decolorized cotton fiber to the pre-cooled cellulose solvent at a mass ratio of 1:19, and disperse the cellulose chains by high-speed mechanical shearing to obtain a transparent and homogeneous cellulose solution.

[0058] Figure 4 For Li + / Br - Simulation results of the interaction between cellulose hydrogen bonding network and Na2S2O4 and dye chromophores. The results showed that the decrease in cellulose polymerization degree after pretreatment-reduction decolorization in this embodiment was approximately 1.5%, significantly lower than that of the strong oxidative decolorization process. The resulting gel electrolyte achieved an elongation at break of 510% and a tensile strength of 222 kPa. Using this gel electrolyte to assemble a flexible zinc-air battery, a peak power density of 57 mW·cm⁻¹ was achieved. -2The specific capacity can reach 720 mAh·g -1 The battery can cycle stably for 61 hours.

[0059] Example 2: Structural Protective Regeneration of Waste Blue Cotton Fabric 1) After washing and drying the blue-dyed waste cotton fabric, cut it into small pieces.

[0060] 2) Weigh 5 g of sample and add it to a 5 wt.% LiBr aqueous solution. Treat at 60°C for 1 h with a bath ratio of 1:10. After filtration, wash thoroughly with deionized water to obtain pretreated cotton fibers.

[0061] After processing, vacuum filtration was performed, and the LiBr filtrate was collected for recovery. The resulting cotton fibers were washed five times with deionized water and then vacuum dried at 60°C to constant weight.

[0062] 3) The pretreated cotton fibers were placed in a 20 g / L NaBH4 aqueous solution. The amount of reducing decolorizing agent NaBH4 added was 8% of the mass of the pretreated cotton fibers. The system was adjusted to a weakly alkaline state with sodium carbonate, and the pH value was 10. The decolorization was carried out at 80°C for 60 min. After decolorization, the fibers were thoroughly washed with 70°C hot water and 20°C cold water and dried for 24 h to obtain decolorized cotton fibers.

[0063] 4) Prepare a ternary solvent system with a LiOH / urea / H2O mass ratio of 5:15:80 and pre-cool it at -15°C for 3 hours. Add the decolorized cotton fiber to the pre-cooled cellulose solvent at a mass ratio of 1:9. Disperse the cellulose chains by high-speed mechanical shearing to obtain a transparent and homogeneous cellulose solution. This solution can be used to prepare cellulose membranes through casting and coagulation regeneration, or to prepare regenerated cellulose fibers through wet or dry-wet spinning.

[0064] The decolorized cotton fibers obtained in this embodiment have virtually no residual color, and the degree of cellulose polymerization decreases by less than 5%. The cellulose solution obtained has a transmittance of not less than 80% at a wavelength of 500 nm, and can be used for subsequent casting to prepare regenerated cellulose membranes or for preparing regenerated cellulose fibers by wet spinning.

[0065] Example 3: Decolorization of waste black cotton fabric and preparation of nanocellulose 1) Cut and dust off the black waste cotton fabric, wash and dry it with deionized water or ethanol / water mixture.

[0066] 2) The sample was added to a 20 wt.% ZnCl2 aqueous solution and treated at 85°C for 3 h at a liquor ratio of 1:20 g / mL. After treatment, the sample was filtered and washed to obtain pretreated cotton fibers.

[0067] 3) The pretreated cotton fibers were added to a 40 g / L NaHSO3 + Na2S2O4 aqueous solution. The amount of reducing decolorizing agent NaHSO3 + Na2S2O4 added was 15% of the mass of the pretreated cotton fibers. The mixture was treated at 50°C for 120 min at a pH of 11. After the reaction was completed, the fibers were washed alternately with 80°C hot water and 35°C cold water until neutral. The fibers were then naturally dried at 25°C for 24 h to obtain decolorized cotton fibers.

[0068] Because the pretreatment process reduces the mass transfer resistance inside the fiber, the reducing agent can fully enter the fiber and act on the deep dye chromophores, resulting in a significant fading of the fabric color after treatment.

[0069] 4) Prepare a cellulose solvent system with a NaOH / urea / thiourea / H2O mass ratio of 10:7:8:75 and pre-cool it at -10°C for 3.5 h. Add bleached cotton fibers at a mass ratio of 1:19 to the cellulose solvent, and obtain a transparent and homogeneous cellulose solution through high-speed mechanical shearing. After coagulation regeneration and thorough washing, this solution can be further processed by controlled acid hydrolysis to prepare regenerated cellulose nanocrystals, or by mechanical shearing, high-pressure homogenization, or ultrasonic treatment to prepare regenerated cellulose nanofibers.

[0070] The solution can be further diluted, mechanically sheared, or homogenized under high pressure to prepare cellulose nanofibers; after physical freezing or chemical cross-linking and freeze drying, cellulose aerogel materials can be obtained.

[0071] Example 4: Decolorization of waste red cotton fabric and preparation of functional hydrogel or aerogel precursors 1) Cut and dust off the red waste cotton fabric, wash and dry it with deionized water or ethanol / water mixture.

[0072] 2) The sample was added to a CaCl2 / ZnCl2 mixed aqueous solution with a total mass fraction of 15 wt.% and a mass ratio of 1:1. The solution was treated at 100°C for 0.5 h with a bath ratio of 1:50 g / mL. After treatment, the sample was filtered and washed to obtain pretreated cotton fibers.

[0073] 3) Add the pretreated cotton fibers to an aqueous solution of sodium hydroxide containing 40 g / L thiourea dioxide, where the amount of thiourea dioxide added is 1% of the mass of the pretreated cotton fibers; adjust the pH of the system to 13 and treat at 80°C for 70 min. After the reaction is complete, wash alternately with 55°C hot water and 25°C cold water until neutral, and air dry at 25°C for 20 h to obtain decolorized cotton fibers.

[0074] Because the pretreatment process reduces the mass transfer resistance inside the fiber, the reducing agent can fully enter the fiber and act on the deep dye chromophores, resulting in a significant fading of the fabric color after treatment.

[0075] 4) Prepare a cellulose solvent system with an N-methylmorpholine-N-oxide / water ratio of 87:13 and dissolve it at 90°C for 3 h. Add decolorized cotton fibers at a mass ratio of 1:19 to cellulose solvent, and obtain a homogeneous cellulose solution by high-speed mechanical shearing. The resulting solution can be used to form hydrogels through physical gelation or chemical cross-linking, or functional aerogels can be prepared after gelation by solvent replacement and freeze-drying or supercritical drying.

[0076] Example 5: Decolorization of waste black cotton fabrics and preparation of functional hydrogel or aerogel precursors 1) Cut and dust off the black waste cotton fabric, wash and dry it with deionized water or ethanol / water mixture.

[0077] 2) The sample was added to a CaCl2 / ZnCl2 mixed aqueous solution with a total mass fraction of 10 wt.% and a mass ratio of 1:4. The solution was treated at 40°C for 5 h with a bath ratio of 1:40 g / mL. After treatment, the sample was filtered and washed to obtain pretreated cotton fibers.

[0078] 3) Add the pretreated cotton fibers to a sodium carbonate aqueous solution containing 40 g / L sodium bisulfite, with the amount of sodium bisulfite added being 5% of the mass of the pretreated cotton fibers. Adjust the pH of the system to 12 and treat at 70°C for 85 min. After the reaction is complete, wash alternately with 65°C hot water and 35°C cold water until neutral, and air dry at 25°C for 20 h to obtain decolorized cotton fibers.

[0079] Because the pretreatment process reduces the mass transfer resistance inside the fiber, the reducing agent can fully enter the fiber and act on the deep dye chromophores, resulting in a significant fading of the fabric color after treatment.

[0080] 4) Prepare a cellulose solvent system with an N-methylmorpholine-N-oxide / water ratio of 95:5 and dissolve it at 70°C for 6 h. Add decolorized cotton fibers at a mass ratio of 1:19 to the cellulose solvent, and obtain a homogeneous cellulose solution by high-speed mechanical shearing. The resulting solution can be used to form hydrogels through physical gelation or chemical cross-linking, or functional aerogels can be prepared after gelation by solvent replacement and freeze-drying or supercritical drying.

[0081] Example 6: Decolorization of waste red cotton fabric and preparation of functional hydrogel or aerogel precursors 1) Cut and dust off the red waste cotton fabric, wash and dry it with deionized water or ethanol / water mixture.

[0082] 2) The sample was added to an 18 wt.% CaCl2 aqueous solution and treated at 40°C for 2 h at a liquor ratio of 1:40 g / mL. After treatment, the sample was filtered and washed to obtain pretreated cotton fibers.

[0083] 3) The pretreated cotton fibers were added to an aqueous solution of sodium carbonate containing 40 g / L thiourea dioxide, with the amount of thiourea dioxide added being 3% of the mass of the pretreated cotton fibers. The pH of the system was adjusted to 12, and the mixture was treated at 60°C for 100 min. After the reaction was completed, the fibers were washed alternately with 65°C hot water and 35°C cold water until neutral, and then naturally dried at 25°C for 20 h to obtain decolorized cotton fibers.

[0084] Because the pretreatment process reduces the mass transfer resistance inside the fiber, the reducing agent can fully enter the fiber and act on the deep dye chromophores, resulting in a significant fading of the fabric color after treatment.

[0085] 4) Prepare a cellulose solvent system with an N-methylmorpholine-N-oxide / water ratio of 75:25 and dissolve it at 120°C for 1 h. Add decolorized cotton fibers at a mass ratio of 1:19 to cellulose solvent, and obtain a homogeneous cellulose solution by high-speed mechanical shearing. The resulting solution can be used to form hydrogels through physical gelation or chemical cross-linking, or functional aerogels can be prepared after gelation by solvent replacement and freeze-drying or supercritical drying.

[0086] Example 7: Decolorization of waste blue cotton fabrics and preparation of functional hydrogel or aerogel precursors 1) Cut and dust the blue waste cotton fabric, wash and dry it with deionized water or ethanol / water mixture.

[0087] 2) The sample was added to a CaCl2 / ZnCl2 mixed aqueous solution with a total mass fraction of 12 wt.% and a mass ratio of 4:1. The solution was treated at 70°C for 4 hours with a bath ratio of 1:40 g / mL. After treatment, the sample was filtered and washed to obtain pretreated cotton fibers.

[0088] 3) Add the pretreated cotton fibers to an aqueous solution containing 40 g / L sodium bisulfite, with the amount of sodium bisulfite added being 12% of the mass of the pretreated cotton fibers; adjust the pH of the system to 10, and treat at 70°C for 85 min. After the reaction is complete, wash alternately with 65°C hot water and 35°C cold water until neutral, and air dry at 25°C for 20 h to obtain decolorized cotton fibers.

[0089] Because the pretreatment process reduces the mass transfer resistance inside the fiber, the reducing agent can fully enter the fiber and act on the deep dye chromophores, resulting in a significant fading of the fabric color after treatment.

[0090] 4) Prepare a cellulose solvent system with an N,N-dimethylacetamide / lithium chloride mass ratio of 92:8 and dissolve it at 100°C for 12 h. Add decolorized cotton fibers at a mass ratio of 1:19 to the cellulose solvent, and obtain a homogeneous cellulose solution by high-speed mechanical shearing. The resulting solution can be used to form hydrogels through physical gelation or chemical cross-linking, or functional aerogels can be prepared after gelation by solvent replacement and freeze-drying or supercritical drying.

[0091] Example 8: Decolorization of waste black cotton fabrics and preparation of functional hydrogel or aerogel precursors 1) Cut and dust off the black waste cotton fabric, wash and dry it with deionized water or ethanol / water mixture.

[0092] 2) The sample was added to a CaCl2 / ZnCl2 mixed aqueous solution with a total mass fraction of 12 wt.% and a mass ratio of 2:1. The solution was treated at 75°C for 1 h with a bath ratio of 1:30 g / mL. After treatment, the sample was filtered and washed to obtain pretreated cotton fibers.

[0093] 3) Add the pretreated cotton fibers to an alkaline aqueous solution containing a mixed reducing agent of sodium dithionite and sodium bisulfite (40 g / L), wherein the mass ratio of sodium dithionite to sodium bisulfite is 1:1, and the amount of the mixed reducing agent added is 10% of the mass of the pretreated cotton fibers; adjust the pH of the system to 11, and treat at 80°C for 20 min. After the reaction is complete, wash alternately with 65°C hot water and 35°C cold water until neutral, and air dry at 25°C for 20 h to obtain decolorized cotton fibers.

[0094] Because the pretreatment process reduces the mass transfer resistance inside the fiber, the reducing agent can fully enter the fiber and act on the deep dye chromophores, resulting in a significant fading of the fabric color after treatment.

[0095] 4) Prepare a cellulose solvent system containing 1-allyl-3-methylimidazolium chloride and dissolve it at 100°C for 6 hours. Add decolorized cotton fibers at a mass ratio of 1:19 to cellulose solvent, and obtain a homogeneous cellulose solution by high-speed mechanical shearing. The resulting solution can be used to form hydrogels through physical gelation or chemical cross-linking, or functional aerogels can be prepared after gelation by solvent replacement and freeze-drying or supercritical drying.

[0096] Figure 2 The color changes of waste cotton fabrics of different colors in Examples 1-8 before and after pretreatment and reduction decolorization are shown.

[0097] The preparation of the material of the present invention is further illustrated below by comparing it with the embodiments of the present invention through comparative examples.

[0098] Comparative Example 1: Decolorization of Na2S2O4 without LiBr pretreatment The same red waste cotton fabric as in Example 1 was added directly to a 30 g / L Na2S2O4 aqueous solution without LiBr pretreatment and treated at 90°C for 90 min. The treated fabric still showed obvious residual color and localized color spots, indicating that without establishing mass transfer channels, the reducing agent could not fully penetrate the deep dye regions within the fiber.

[0099] Furthermore, increasing the decolorization time or temperature can easily lead to a further decrease in the degree of polymerization of cellulose. Compared with Example 1, this comparative example illustrates that the ion solvation pretreatment step plays a crucial role in improving decolorization uniformity, shortening the deep decolorization time, and maintaining the cellulose molecular chain structure.

[0100] Comparative Example 2: Traditional H2O2 strong oxidative decolorization treatment The same red waste cotton fabric as in Example 1 was directly placed in an alkaline H2O2 decolorization system for treatment. Specifically, an aqueous solution containing 30 g / L H2O2 and 2 g / L NaOH was prepared, the pH of the system was adjusted to 11-12, the bath ratio was 1:30 g / mL, and the mixture was treated at 90°C with shaking at 500 rpm for 60 min. After treatment, the fabric was washed sequentially with 60°C hot water and room temperature deionized water until neutral, and then dried at 25°C for 24 h.

[0101] Test results showed that after strong oxidation treatment, the DP of cellulose decreased from 2350 ± 35 to 1302 ± 61, with a DP reduction rate of approximately 44.6%, which was significantly higher than the pretreatment-reduction decolorization method in Example 1. This result indicates that while the H2O2 strong oxidation system can improve fabric whiteness, it causes significant degradation of the cellulose backbone, which is detrimental to the subsequent construction of high-performance recycled materials.

[0102] Comparative Example 3: Dissolution of untreated cotton fibers in a NaOH / urea / H2O system Waste colored cotton fibers that had not undergone LiBr pretreatment or effective decolorization were directly added to a NaOH / urea / H2O ternary solvent system and dissolved under the same pre-cooling and shearing conditions. After dissolution, the system was turbid, and a large number of undissolved fiber fragments were found at the bottom after centrifugation. The fiber outlines could be clearly observed under a polarizing microscope. Figure 5 and Figure 6 The results are shown in Example 1 and Comparative Example 3, along with the results observed under a polarizing microscope.

[0103] Figure 3This figure compares the rate of decrease in degree of polymerization in Example 1, Comparative Example 1, and Comparative Example 2. As can be seen from the figure, compared to the transparent and homogeneous cellulose solution obtained in Example 1, this comparative example demonstrates that ionic solvation pretreatment and gentle decolorization not only improve the decolorization process but also significantly enhance the solubility of high-polymerization-degree cotton cellulose in low-temperature solvent systems.

[0104] Performance Tests and Results The samples obtained in Examples 1-8 and Comparative Examples 1-3 were tested for decolorization effect, DP retention rate, solution transmittance, zero-shear viscosity, dissolution state, and application performance. The degree of polymerization of cellulose was determined using the copper ethylenediamine (CED) viscosity method: the washed and dried cellulose sample was dissolved in a CED solution, and the eluent time was measured using an Ubbelohde viscometer at 25 ± 0.1°C. The intrinsic viscosity [η] was calculated, and the viscosity-average degree of polymerization was converted according to the Mark-Houwink relation [η] = K·DP^α; where K and α were fixed according to the adopted test standard or calibration method and remained consistent in the tests of each sample. If gel permeation chromatography was used, the cellulose sample was dissolved in DMAc / LiCl or other suitable mobile phase, and the molecular weight was calibrated using cellulose or polysaccharide standard samples.

[0105] The transmittance of the cellulose solution was measured at a wavelength of 500 nm using a UV-Vis spectrophotometer; the zero-shear viscosity was measured at 25°C using a rotational rheometer and obtained by extrapolation from the low-shear rate plateau region; the dissolution state was evaluated by centrifugation observation and polarized light microscopy; the gel tensile properties were measured using a universal testing machine; and the performance of the flexible zinc-air battery was tested using an electrochemical workstation.

[0106] Table 1. Effects of different treatment methods on the recycling efficiency of waste cotton textiles

[0107] As shown in Table 1, this invention overcomes the technical contradiction in traditional waste cotton textile recycling processes where it is difficult to simultaneously achieve "thorough decolorization" and "preservation of polymerization degree" through the synergistic effect of ion solvation pretreatment and mild reduction decolorization. After pretreatment and decolorization, the decrease rate of cellulose polymerization degree can be controlled at a low level, and the solubility of decolorized cotton fibers in different cellulose solvent systems is significantly improved. Compared with no pretreatment or strong oxidation treatment, the method of this invention can significantly reduce damage to the cellulose backbone and improve solution homogeneity.

[0108] Furthermore, this invention provides application examples using cellulose solutions.

[0109] The cellulose solution prepared using this invention can be directly used for wet spinning, casting, nanocellulose preparation, aerogel / hydrogel construction, or for in-situ polymerization with monomers such as acrylamide to prepare cellulose-based gel electrolytes.

[0110] Regenerated cellulose materials include: (1) Regenerated cellulose fiber: The cellulose solution is regenerated and solidified by wet spinning or dry-wet spinning, and then solidified by coagulation bath to obtain filaments or short fibers.

[0111] (2) Cellulose nanocrystals: Cellulose nanocrystals (CNC) or cellulose nanofibers (CNF) are prepared by diluting, acid hydrolyzing, mechanical shearing, high pressure homogenization or ultrasonic treatment of cellulose solution.

[0112] (3) Regenerated cellulose membrane: A cellulose solution is cast or coated into a membrane and then regenerated in a coagulation bath to obtain a transparent regenerated cellulose membrane.

[0113] (4) Cellulose hydrogel / aerogel: Cellulose hydrogel or aerogel is obtained by chemically cross-linking or physically freezing a cellulose solution and then further drying it under normal pressure or freeze-drying.

[0114] The preparation of cellulose hydrogels / aerogels specifically includes: Cellulose solution, acrylamide, potassium persulfate and N,N'-methylenebisacrylamide were stirred until homogeneous, degassed and polymerized to obtain cellulose-PAM dual-network hydrogel; the cellulose-PAM dual-network hydrogel was immersed in an electrolyte of 4.0~8.0 mol / L KOH and 0.1~0.3 mol / L Zn(CH3COO)2 for equilibrium swelling and ion exchange to obtain cellulose-based gel electrolyte.

[0115] Taking the preparation of cellulose-based gel electrolytes from cellulose solution in Example 1 as an example.

[0116] Take 10 g of cellulose solution, add 2.13 g of acrylamide, 0.008 g of potassium persulfate and 0.014 g of N,N'-methylenebisacrylamide, mechanically stir until homogeneous, degas, pour into a mold and thermally initiate polymerization to obtain a cellulose-PAM dual-network hydrogel. Immerse the hydrogel in an electrolyte containing 6.0 mol / L KOH and 0.2 mol / L Zn(CH3COO)2 for equilibrium swelling and ion exchange to obtain a cellulose-based gel electrolyte.

[0117] In the cellulose solution used to prepare the gel electrolyte, the cellulose DP is based on the initial degree of polymerization of cellulose in the waste cotton fabric in step (a), and the retention rate is not less than 90%, preferably not less than 95%; in the preferred embodiment, the cellulose DP of the raw cotton is 2350 ± 35, and the DP after ion solvation pretreatment and reduction decolorization is 2315 ± 31, with a DP retention rate of 98.5% ± 1.1%; the transmittance of the solution at a wavelength of 500 nm is not less than 80%, and the zero shear viscosity at 25°C is 1 to 50 Pa·s.

[0118] Cellulose-based gel electrolytes are used to assemble flexible zinc-air batteries, with an elongation at break of not less than 400%, a tensile strength of not less than 200 kPa, and a peak power density of not less than 50 mW·cm⁻¹. -2 Specific capacity not less than 700mAh·g -1 .

[0119] (5) Cellulose-based gel electrolyte: A dual-network gel electrolyte is obtained by in-situ polymerization of a cellulose solution with a polymerizable monomer, which is used in flexible energy storage devices. The polymerizable monomer is selected from one or more of acrylamide, acrylic acid, and N-isopropylacrylamide.

[0120] Table 2 below shows a comparison of the performance of the cellulose-based gel electrolyte and flexible zinc-air battery prepared using the cellulose solution in Example 1 with existing technologies.

[0121] Table 2 Performance of cellulose-based gel electrolyte and flexible zinc-air battery

[0122] As shown in Table 2, the cellulose-PAM dual-network gel electrolyte constructed using the high-polymerization degree cellulose solution obtained in this invention has both high mechanical properties and good electrochemical application performance, proving that the regenerated cellulose solution can serve as an effective precursor for functional materials of flexible energy storage devices.

[0123] Figure 7 The structure and mechanical properties of regenerated cellulose fibers prepared from the cellulose solution of the present invention are demonstrated. Figure 7 (a1) shows that the longitudinal surface of the fiber is continuous and relatively flat, and no obvious large-sized holes or fracture defects were observed. Figure 7 The cross-section shown in (a2) exhibits a relatively dense fibrous aggregate structure, indicating that the obtained cellulose solution has good regenerative molding ability. Figure 7 (b) shows the stress-strain curves of the Cot and Cot-S samples, where Cot is the original cotton fiber control and Cot-S is the regenerated fiber prepared from the cellulose solution of this invention. Cot-S still maintains a tensile strength of approximately 82 MPa. Figure 7 (c) Further, it is shown that the Young's modulus of Cot-S is about 6.9 GPa, which is higher than that of the Cot sample, indicating that the obtained regenerated fiber has better strength and stiffness.

[0124] Figure 8 The application of Cellulose-PAM gel electrolyte in flexible zinc-air batteries was demonstrated. Figure 8 (a) is a schematic diagram of a flexible zinc-air battery structure consisting of an air electrode, a Cellulose-PAM gel electrolyte, and a zinc negative electrode. Figure 8(b) shows that the gel electrolyte can maintain good adhesion to different material surfaces such as carbon cloth, rubber, zinc sheet, plastic, glass and wood block, indicating that it has good flexibility and interface adaptability. Figure 8 (c) The assembled flexible zinc-air battery maintains a relatively stable charge-discharge voltage plateau during approximately 61 h of cycling, without a significant increase in rapid polarization, indicating that the gel electrolyte can support relatively stable battery operation.

[0125] The above embodiments and comparative examples demonstrate that the present invention is not limited to specific colors, specific types of reactive dyes, or specific downstream applications. Conventional substitutions and modifications made by those skilled in the art based on the technical solutions disclosed in this invention, concerning the types of metal halides, reducing decolorizing agents, cellulose solvent systems, polymer monomers, or application forms, should all fall within the scope of protection of this invention.

Claims

1. A method for regenerating cellulose from waste cotton based on ion solvation pretreatment, characterized in that, Includes the following steps: (a) Cut, dust, wash, and dry the waste cotton fabrics for later use; (b) The dried waste cotton fabric is immersed in a metal halide aqueous solution for treatment, and the pretreated cotton fibers are obtained by filtration and separation. (c) The amount of reducing decolorizing agent added is 1% to 15% of the mass of the pretreated cotton fiber. The pretreated cotton fiber is added to an alkaline aqueous solution containing reducing decolorizing agent and decolorized under stirring or shaking conditions. It is then washed with alternating hot and cold water until neutral to obtain decolorized cotton fiber. (d) The decolorized cotton fibers are added to the cellulose solvent system at a mass ratio of 1:9 to 1:19, and the cellulose solution is obtained by wetting, dissolving and mechanically dispersing the cotton fibers in accordance with the cellulose solvent system.

2. The method for regenerating cellulose from waste cotton based on ion solvation pretreatment according to claim 1, characterized in that, The waste cotton fabrics are colored cotton fabrics, cotton yarns, or cotton-blend fabrics dyed with reactive dyes.

3. The method for regenerating cellulose from waste cotton based on ion solvation pretreatment according to claim 1, characterized in that, The metal halide in the aqueous solution is one of lithium bromide, lithium chloride, zinc chloride, calcium chloride, or a complex of calcium chloride and zinc chloride; the total mass fraction of the metal halide in the aqueous solution is 5 wt.% to 20 wt.%. When using a mixed aqueous solution of calcium chloride and zinc chloride, the mass ratio of calcium chloride to zinc chloride is 1:4 to 4:

1.

4. The method for regenerating cellulose from waste cotton based on ion solvation pretreatment according to claim 1, characterized in that, The concentration of the reducing decolorizing agent in the alkaline aqueous solution is 20–40 g / L, and the pH value of the alkaline aqueous solution containing the reducing decolorizing agent is 9–13.

5. The method for regenerating cellulose from waste cotton based on ion solvation pretreatment according to claim 4, characterized in that, The reducing decolorizing agent is selected from one or more of sodium dithionite, sodium borohydride, sodium bisulfite, and thiourea dioxide; The alkaline substance in the alkaline aqueous solution is selected from one or more of sodium hydroxide and sodium carbonate.

6. The method for regenerating cellulose from waste cotton based on ion solvation pretreatment according to claim 1, characterized in that, In step (a), the sample is cleaned with deionized water or an ethanol / water mixture. In step (b), the waste cotton fabric is immersed in a metal halide aqueous solution at a temperature of 25~100°C for 0.5 h~6 h; the bath ratio is 1:10~1:50 g / mL. In step (c), the pH value of the decolorization system under stirring or shaking conditions is 9~13, the decolorization temperature is 50~90°C, and the decolorization time is 20~120 min.

7. The method for regenerating cellulose from waste cotton based on ion solvation pretreatment according to claim 1, characterized in that, The cellulose solvent system is either a low-temperature alkali / urea / water system or a non-low-temperature alkali / urea / water system; The low-temperature alkali / urea / water system is a NaOH / urea / H2O, LiOH / urea / H2O, or NaOH / urea / thiourea / H2O system. The non-low-temperature alkali / urea / water system is an N-methylmorpholine-N-oxide / water, N,N-dimethylacetamide / lithium chloride, 1-allyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium chloride ionic liquid system. In the NaOH / urea / H2O, LiOH / urea / H2O, and NaOH / urea / thiourea / H2O systems: NaOH or LiOH: 5-10 wt.%, urea or urea + thiourea: 8-15 wt.%, water: 75-87 wt.%; In the N-methylmorpholine-N-oxide / water system and the N,N-dimethylacetamide / lithium chloride system: N-methylmorpholine-N-oxide:water = (75-95):(5-25); N,N-dimethylacetamide:lithium chloride = (90-95):(5-10).

8. The method for regenerating cellulose from waste cotton based on ion solvation pretreatment according to claim 7, characterized in that, When a low-temperature alkali / urea / water system is used, the pre-cooling temperature of the cellulose solvent system is -20 to -5°C, the immersion time of the decolorized cotton fibers in the pre-cooled solvent is 2 to 4 hours, and a uniform cellulose solution is obtained by mechanical shearing or stirring dispersion. When using a non-low-temperature alkali / urea / water system, the dissolution temperature of the N-methylmorpholine-N-oxide / water system is 70–120°C, and the dissolution time is 0.5–6 h; the dissolution temperature of the N,N-dimethylacetamide / lithium chloride system is 60–100°C, and the dissolution time is 2–24 h; the dissolution temperature of the 1-allyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium chloride ionic liquid system is 70–120°C, and the dissolution time is 0.5–6 h.

9. A regenerated cellulose solution based on ion-solvent pretreatment of waste cotton, prepared by the method according to any one of claims 1 to 8.

10. An application of the waste cotton regenerated cellulose solution based on ion solvation pretreatment as described in claim 9, characterized in that, The preparation of regenerated cellulose materials includes: Regenerated cellulose fiber: A cellulose solution is regenerated and solidified by wet spinning or dry-wet spinning, and then solidified by coagulation bath to obtain filaments or staple fibers; Nanocellulose: Cellulose nanocrystals or cellulose nanofibers are prepared by diluting, acid hydrolyzing, mechanical shearing, high-pressure homogenization or ultrasonic treatment of cellulose solution; Regenerated cellulose membrane: A transparent regenerated cellulose membrane is obtained by casting or coating a cellulose solution into a film and then regenerating it in a coagulation bath. Cellulose hydrogels / aerogels: Cellulose hydrogels or aerogels are obtained by chemically cross-linking or physically freezing a cellulose solution, followed by atmospheric pressure or freeze-drying. Cellulose-based gel electrolyte: A dual-network gel electrolyte is obtained by in-situ polymerization of a cellulose solution with polymerizable monomers, which is used in flexible energy storage devices.

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