Method for recycling and utilizing waste cotton-polyester blended fabric and application thereof

Abstract

This invention provides a method for recycling waste cotton-polyester blended fabrics and its application. The method includes the following steps: dissolving cellulose raw materials in a superbasic acetate ionic solvent to obtain a first solution; the cellulose raw materials are obtained from the processing of waste cotton-polyester blended fabrics; adding a viscosity reducer to the first solution and mixing thoroughly to obtain a second solution; performing solid-liquid separation on the second solution to obtain a cellulose solution and insoluble polyester; regenerating and drying the cellulose solution to obtain regenerated cellulose material; and washing and drying the insoluble polyester to obtain regenerated polyester material. The technical problem solved is how to recycle waste cotton-polyester blended fabrics, enabling efficient separation of cellulose and polyester from waste cotton fabrics to obtain regenerated cellulose and polyester materials, achieving full-component resource utilization of waste cotton-polyester blended fabrics; simultaneously, this method achieves decolorization and dissolution in a single process, with simple steps and is environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of waste textile recycling technology, and in particular to a method for recycling waste cotton-polyester blended fabrics and its application. Background Technology

[0002] The global fast fashion industry drives rapid iteration in clothing, generating massive amounts of waste textiles. Cotton-polyester blends, combining the comfort of cotton with the durability of polyester, are widely used in clothing, home furnishings, and other fields, accounting for over 60% of total waste textiles. Currently, this type of waste is mostly disposed of through incineration or landfill, which not only wastes cellulose resources (cotton fiber contains over 90% cellulose) but also causes land pollution and secondary environmental problems, highlighting the urgent need for efficient recycling technologies.

[0003] The efficient separation and recycling of waste cotton textiles presents a significant challenge due to the tight bonding between different fibers and the substantial differences in chemical properties between cotton fibers (cellulose) and polyester fibers (polyester). Furthermore, the complex dyeing processes involved in the production of waste textiles further complicate recycling. Physical and mechanical methods (such as opening and screening) struggle to achieve complete fiber separation, resulting in low purity recycled materials. Chemical methods (such as acid hydrolysis and alkali hydrolysis) are often targeted at single components (e.g., recovering only cellulose or only polyester) and are prone to environmental pollution. Waste textiles typically contain dyes, requiring existing technologies to first undergo physical or chemical decolorization before dissolution and separation, a complex process that can damage the fiber structure. Traditional solvents for dissolving cellulose, such as cuprammonium phosphate solution and strong alkaline solutions, suffer from high toxicity and low recovery rates, failing to meet the demands of green and sustainable development. Moreover, most processes only recover one type of fiber (cellulose or polyester), failing to achieve full resource utilization of blended fabrics and resulting in resource waste.

[0004] In recent years, ionic solvents (such as ionic liquids and eutectic solvents) have shown potential in the field of textile recycling as a new type of green solvent system due to their high solubility for cellulose and environmental friendliness. However, the following problems still exist: First, the high viscosity of the solution after dissolution is not conducive to subsequent separation; second, dye residue will lead to poor color of recycled materials, requiring additional decolorization steps. Summary of the Invention

[0005] The main objective of this invention is to provide a method for recycling waste cotton-polyester blended fabrics and its application. The technical problem to be solved is how to recycle waste cotton-polyester blended fabrics, so that cellulose and polyester in waste cotton fabrics can be efficiently separated, and recycled cellulose materials and recycled polyester materials can be prepared through this method, realizing the resource utilization of all components of waste cotton-polyester blended fabrics. At the same time, the method achieves decolorization and dissolution in one pot, with simple process steps, green and environmentally friendly, thus making it more suitable for practical use.

[0006] The objective of this invention and the technical problem it solves are achieved through the following technical solution. A method for recycling waste cotton-polyester blended fabrics according to this invention includes the following steps:

[0007] S11 involves adding cellulose raw material to a superbasic acetate ionic solvent, stirring to dissolve and decolorize, to obtain a first solution; the cellulose raw material is obtained from waste cotton-polyester blended fabric.

[0008] S12 Add a viscosity reducer to the first solution, mix well, and obtain the second solution;

[0009] S13 performs solid-liquid separation on the second solution to obtain a cellulose solution and an insoluble polyester;

[0010] S14 regenerates and dries the cellulose solution to obtain regenerated cellulose material; insoluble polyester is washed and dried to obtain regenerated polyester material.

[0011] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0012] Preferably, in the aforementioned recycling method, the cellulose raw material is a powdered, filamentous, or wavy fabric obtained by crushing colored waste cotton-polyester blended fabric with a degree of polymerization of 500 to 1000.

[0013] Preferably, in the aforementioned recycling method, the cation in the superbasic acetate ionic solvent is selected from at least one of 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

[0014] Preferably, in the aforementioned recycling method, in step S11, the mass of the cellulose raw material is 2.6-12% based on the mass of the ionic solvent being 100%.

[0015] Preferably, in the aforementioned recycling method, in step S11, the dissolution temperature is 70–90°C and the dissolution time is 2–4 hours.

[0016] Preferably, in the aforementioned recycling method, in step S12, when the viscosity reducer is added, the temperature of both the viscosity reducer and the first solution is 40-60°C.

[0017] Preferably, in the aforementioned recycling method, the viscosity reducer is selected from at least one of dimethyl sulfoxide, γ-valerolactone, and sulfolane.

[0018] Preferably, in the aforementioned recycling method, the mass ratio of the viscosity reducer to the ionic solvent is 0.3 to 1:1; and the mass solid content of the cellulose raw material is 2 to 6%, based on the total mass of the ionic solvent and the viscosity reducer being 100%.

[0019] The objective of this invention and the technical problem it solves are achieved by the following technical solution: A regenerated cellulose material obtained according to the aforementioned recycling method, based on this invention.

[0020] The objective of this invention and the technical problem it solves are achieved by the following technical solution: A recycled polyester material obtained according to the aforementioned recycling method.

[0021] The objective of this invention and the technical problem it solves are achieved through the following technical solution: An application of the aforementioned regenerated cellulose material in the fields of food packaging, filtration and adsorption, functional sensing, or thermal insulation.

[0022] By employing the above technical solution, the recycling method for waste cotton-polyester blended fabrics and its application proposed in this invention have at least the following advantages:

[0023] This invention achieves efficient treatment of waste cotton-polyester blended fabrics through the selective dissolution and decolorization of ultrabasic acetate ionic solvents, and has the following advantages:

[0024] 1. This invention utilizes a superbasic acetate ionic solvent to dissolve cellulose raw materials. Taking advantage of its highly selective solubility for cellulose, cotton fibers (cellulose) dissolve into the solution phase, while polyester fibers (polyester) remain in a solid state, allowing for complete separation through simple solid-liquid separation. Compared to physical-mechanical methods (incomplete separation, low purity) and traditional chemical methods (requiring strong acids and bases, resulting in significant pollution), this method achieves efficient separation through solvent selectivity, simplifies the separation process, and yields higher purity recycled materials. The superbasic acetate ionic solvent possesses a "superbasic" structure, and its intramethylene groups such as amidine and guanidine groups have extremely strong proton accepting (H) groups. +The superbasic cation has a much higher alkalinity than ordinary organic amines. Dyes in fabrics typically exhibit color through conjugated double bonds, and these conjugated structures are highly sensitive to proton environments. The superbasic cation can catalytically remove active hydrogen protons from dye molecules, thereby disrupting their conjugated double bond system and causing the dye to lose its color-producing ability, thus achieving decolorization. Simultaneously, the superbasic acetate ionic solvent causes significant swelling during the dissolution of cellulose. Solvent molecules, especially cations, can penetrate into the cellulose molecular chains, breaking the hydrogen bonds between cellulose molecules, making the fiber structure looser and increasing the inter-chain gaps. Since dyes in fabrics are mostly adsorbed or chemically bonded within the cellulose fibers, the binding force between the dye and the fiber weakens after the cellulose swells, making it easier for the dye to detach from the fiber network and enter the solvent phase. This invention, by selecting a specific ionic solvent, achieves efficient separation and decolorization of components in waste cotton-polyester blended fabrics in a one-pot process, thus avoiding the complex process of separate decolorization pretreatment required in traditional processes, representing a significant improvement and possessing substantial advantages.

[0025] 2. This invention solves the problem of high viscosity and difficulty in separation of cellulose solutions after dissolution by introducing a viscosity reducer. Compared with the complex process of additional viscosity treatment after dissolution in existing technologies, this method directly improves solution fluidity through the synergistic effect of the viscosity reducer and solvent, making solid-liquid separation more efficient, significantly shortening the process cycle, and reducing the operational difficulty of industrial production.

[0026] 3. This invention simultaneously obtains "cellulose solution" and "insoluble polyester" through a "solid-liquid separation" step, and then regenerates them into "regenerated cellulose material" and "regenerated polyester material," respectively. Compared to existing technologies that only recover a single component (such as only cellulose or only polyester), this method achieves the complete recovery of both core components in cotton-polyester blended fabrics, avoiding resource waste, significantly improving the utilization efficiency of waste textiles, and conforming to the sustainable development concept of "whole industrial chain recycling."

[0027] 4. The superbasic acetate ionic solvent in this invention is an environmentally friendly solvent. Compared with traditional toxic and harmful solvents such as copper ammonia solution and strong alkaline solution used to dissolve cellulose, it has better biocompatibility and can be recycled through subsequent treatment. At the same time, the entire process does not require the use of corrosive reagents such as strong acids and strong oxidants, which reduces the discharge of "three wastes" and reduces the potential harm to operators and the ecological environment, meeting the needs of the textile industry's clean transformation.

[0028] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0029] Figure 1 This invention provides a photo comparison of colored fabrics before and after dissolving and decolorizing them.

[0030] Figure 2 This is a polarized light microscope image of the dissolution process of cotton fiber components in the cotton-polyester blended fabric of the present invention.

[0031] Figure 3 This is a photograph of the insoluble polyester filtered out by this invention;

[0032] Figure 4 This is a polarized light microscope image of the cellulose solution after the insoluble polyester has been removed by filtration according to the present invention.

[0033] Figure 5 It is the regenerated cellulose membrane obtained by the blade coating method in Embodiment 2 of the present invention;

[0034] Figure 6 These are the infrared spectra of the insoluble polyester and pure polyester components obtained by filtration in Example 1 of the present invention;

[0035] Figure 7 It is the regenerated cellulose membrane obtained by casting in Example 4 of this invention;

[0036] Figure 8 The polarization and color change of the colored fabric in Comparative Example 1 of this invention after being dissolved in an ionic solvent for 10.5 hours are shown.

[0037] Figure 9 These are photographs of the dye decolorization experiment in Comparative Example 1 of this invention (the left image is "1-allyl-3-methylimidazolium chloride ionic solvent", and the right image is "superbasic acetate ionic solvent in this invention"). Detailed Implementation

[0038] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with preferred embodiments, details the specific implementation methods, structures, features, and effects of a method for recycling waste cotton-polyester blended fabrics proposed according to the present invention. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0039] This invention proposes a method for recycling waste cotton-polyester blended fabrics, which includes the following steps:

[0040] The first step is the dissolution and decolorization of cellulose raw materials: the cellulose raw materials are added to a superbasic acetate ionic solvent and stirred to dissolve while simultaneously decolorizing, resulting in the first solution.

[0041] In this step, the cellulose raw material is obtained from waste cotton-polyester blended fabrics, with the aim of recycling these fabrics. This invention is applicable to the recycling of waste cotton-polyester blended fabrics containing azo dyes, vat dyes, anthraquinone dyes, phthalocyanine dyes, and / or sulfur dyes.

[0042] In some specific embodiments of the present invention, before the cellulose raw material is dissolved, the colored cotton-polyester blended fabric raw material is preferably pulverized into powder, filament, or flocculent (cotton-like) raw material by a pulverizing process. This raw material form can increase its contact area with the solvent, improve the dissolution efficiency, and thus promote the swelling and rapid dissolution and separation of the cellulose raw material.

[0043] This invention uses superbasic acetate ionic solvent to dissolve cellulose raw materials. By utilizing its highly selective solubility of cellulose, cotton fibers (cellulose) dissolve into the solution phase, while polyester (polyester) remains in solid form because it does not dissolve. The two can be completely separated by simple solid-liquid separation.

[0044] Superbasic acetate ionic solvents possess a "superbasic" structure, and their intramolecular groups such as the amidine and guanidine groups have extremely strong proton-accepting (H) groups. + The superbasic cation has a much higher alkalinity than ordinary organic amines. Dyes in fabrics typically exhibit color through conjugated double bonds, and these conjugated structures are highly sensitive to proton environments. The superbasic cation can catalytically remove active hydrogen protons from dye molecules, thereby disrupting their conjugated double bond system and causing the dye to lose its color-producing ability, thus achieving decolorization. Simultaneously, the superbasic acetate ionic solvent causes significant swelling during the dissolution of cellulose. Solvent molecules, especially cations, can penetrate into the cellulose molecular chains, disrupting the hydrogen bonds between cellulose molecules, making the fiber structure looser and increasing the inter-chain gaps. Since dyes in fabrics are mostly adsorbed or chemically bonded within the cellulose fibers, the binding force between the dye and the fiber weakens after the cellulose swells, making it easier for the dye to detach from the fiber network and enter the solvent phase. This invention, by selecting a specific ionic solvent, achieves efficient separation and decolorization of components in waste cotton-polyester blended fabrics in a one-pot process, thus avoiding the complex process of separate decolorization pretreatment required in traditional methods. In Comparative Examples 1 and 4, decolorization could not be achieved because superbasic acetate ionic solvents were not used, further demonstrating that the strong alkalinity of superbasic cations is the core factor in decolorization.

[0045] In some specific embodiments of the present invention, the degree of polymerization of cellulose is preferably between 500 and 1000. The degree of polymerization of cellulose directly affects its molecular chain length and crystallinity. When the degree of polymerization is below 500, the cellulose molecular chains are too short, the crystalline structure is severely damaged, and more solvent is often required to prevent molecular chain entanglement. Although it is easily soluble, the mechanical properties (such as strength and toughness) of the recycled material may decrease significantly. When the degree of polymerization is above 1000, the hydrogen bonding between its molecular chains is strong, and the crystallinity is high, leading to difficulty in dissolution. Excessive solvent is often required to destroy the crystalline structure, and higher temperatures or longer times are needed to dissolve it. On the one hand, this increases energy consumption, and on the other hand, it may also cause cellulose degradation, thereby affecting the performance of the recycled material. The present invention preferably uses cellulose with a degree of polymerization of 500 to 1000 so that it has suitable solubility while retaining sufficient molecular chain length to ensure the performance of the recycled material.

[0046] When cotton-polyester blended fabrics are dissolved, if the cellulose polymerization degree is too high, undissolved cellulose fragments may encapsulate polyester fibers, potentially leading to incomplete component separation. However, with cellulose of 500-1000, after complete dissolution, the polyester exists as intact particles. Subsequent processes can achieve efficient component separation and improve component purity simply through filtration.

[0047] To balance raw material dissolution efficiency, solution operability, and recycled material performance, this invention preferably uses an ionic solvent mass of 100% and a cellulose raw material mass of 2.6–12%. Superbasic acetate ionic solvents have an upper limit to their solubility of cellulose. If the cellulose raw material proportion exceeds 12%, the solvent cannot completely break the hydrogen bonds between cellulose molecules, resulting in some cellulose remaining undissolved and reducing the recovery rate of the cellulose component. Unrecovered cellulose may encapsulate insoluble polyester, causing incomplete subsequent solid-liquid separation and thus reducing the purity of the recycled polyester material. In Comparative Example 2, the cellulose raw material mass accounted for 16% of the ionic solvent, and "difficulty in stirring and dissolving" occurred during dissolution, confirming that an excessively high proportion leads to incomplete cellulose dissolution. Setting an upper limit of 12% ensures that cellulose can be fully swollen and dissolved by the ionic solvent at a set dissolution temperature, providing a uniform cellulose solution for subsequent separation and regeneration. The lower limit is set to ensure that the performance of the recycled cellulose material meets the usage requirements.

[0048] During dissolution, colored waste cotton-polyester blended fabric raw materials are mixed with an ionic solvent, allowing the cellulose to fully swell at 70–90°C. The mixture is stirred at this temperature to ensure complete dissolution of the cellulose, resulting in a cotton-polyester blended fabric solution, also known as the first solution. If the dissolution temperature is too low or the time is too short, the cellulose may be difficult to dissolve, while if the dissolution temperature is too high or the dissolution time is too long, the cellulose may degrade at high temperatures or the solvent may evaporate. The preferred dissolution temperature of this invention is 70–90°C, and the preferred dissolution time is 2–4 hours.

[0049] To ensure the dissolution efficiency and quality of cellulose, the cation in the superbasic acetate ionic solvent system of this invention is preferably at least one of 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

[0050] The second step is to add a certain amount of viscosity reducer to the first solution, which is the dissolved and decolorized cotton-polyester blended fabric solution, and mix it evenly to obtain the second solution. The purpose of adding the viscosity reducer is to lower the viscosity of the cotton-polyester blended fabric solution, so as to facilitate subsequent filtration and thus achieve the separation of cellulose components.

[0051] In some specific embodiments of the present invention, the viscosity reducer is selected from at least one of dimethyl sulfoxide (DMSO), γ-valerol (GVL), and sulfolane. These viscosity reducers can disrupt the hydrogen bonds between cellulose molecules, reducing solution viscosity. Furthermore, these viscosity reducers are mostly polar organic solvents, and the oxygen atoms contained in their molecules (such as the sulfoxide group of DMSO and the ester group of GVL) can form hydrogen bonds with the hydroxyl groups on the cellulose molecular chain, or undergo solvation binding with cellulose through dipole interactions. This effect weakens the hydrogen bonds or van der Waals forces between cellulose and dye molecules (dyes in fabrics are mostly adsorbed or chemically bonded to the interior of cellulose), creating solvation competition. The viscosity reducer molecules occupy the binding sites of cellulose, forcing dye molecules to dissociate from the cellulose network and enter the solution phase. This allows the dye molecules to better contact with superbasic cations for decolorization and facilitates subsequent separation with the solvent, further enhancing the in-situ decolorization effect. For example, in both Example 2 and Comparative Example 2, 1,5-diazabicyclo[4.3.0]non-5-ene acetate ionic solvent was used to dissolve cotton-polyester fabrics. In Example 2, the viscosity reducer γ-valerol was added for synergistic decolorization, and its decolorization effect L reached 63, while in Comparative Example 2, no viscosity reducer was added for synergistic decolorization, and its decolorization effect L was only 31. In both Example 3 and Comparative Example 3, 1,5,7-triazabicyclo[4.4.0]dec-5-ene acetate ionic solvent was used to dissolve cotton-polyester fabrics. In Example 3, the viscosity reducer sulfolane was added for synergistic decolorization, and its decolorization effect L reached 72, while in Comparative Example 3, no viscosity reducer was added for synergistic decolorization, and its decolorization effect L was only 55.

[0052] When adding viscosity reducers, it is best to control the temperature between 40 and 60°C. If the temperature is too low, it may cause difficulty in stirring, which in turn may lead to difficulties in subsequent separation. If the temperature is too high, it may cause cellulose degradation and volatilization of the viscosity reducer.

[0053] Using the above-mentioned viscosity reducer, at a temperature of 40–60°C, the viscosity of the solution can be reduced from >50000 mPa·s to 804.7–39723 mPa·s, thereby greatly improving the solid-liquid separation efficiency.

[0054] In the above steps, the preferred amount of viscosity reducer added is 30-100% of the mass of the ionic solvent. If the amount added is too low, the required low viscosity for filtration will not be achieved; if the amount added is too high, reagent waste will occur, and the low cellulose solids content will affect the performance of the regenerated cellulose membrane. This invention preferably controls the added viscosity reducer to 30-100% of the mass of the ionic solvent to ensure sufficient viscosity reduction and aid in decolorization, while avoiding increased solvent costs due to excessive viscosity reducer.

[0055] The mass of cellulose raw material in the first solution is 2.6-12%; after adding 30-100% of the mass of viscosity reducer in an ionic solvent, the mass solid content of cellulose raw material in the second solution is 2-6%.

[0056] Dyes in waste textiles are typically adsorbed within cellulose fibers. When cellulose with a degree of polymerization of 500–1000 swells in a superbasic acetate ionic solvent, the inter-chain gaps increase moderately. This facilitates the "superbasic" structure to abstract active hydrogen protons from dye molecules, disrupting their conjugated double bond system and causing the dye to lose its color-producing ability. Simultaneously, it allows viscosity-reducing agents to penetrate and strip dye molecules, thus achieving decolorization. Experiments show that the decolorization rate in this degree of polymerization range is significantly higher than that of high-degree-of-polymerization cellulose.

[0057] When dissolving cellulose raw materials, the mass concentration of the cellulose solution should generally be controlled so that it can facilitate subsequent film laying. In this invention, a superbasic acetate ionic solvent is first used to treat waste cotton-polyester blended fabrics before cellulose and insoluble polyester components can be separated. The dissolved component is cellulose. The mass concentration of the cellulose solution is affected by the mass concentration of the blended fabric dissolved by the superbasic acetate ionic solvent. Because the superbasic acetate ionic solvent has limited dissolving power and insoluble polyester components are present in the raw materials, it is difficult to achieve a high mass concentration of the cellulose solution used for film coating. When the mass concentration of the cellulose solution is too low, the cellulose membrane forming effect is poor and it is difficult to achieve high mechanical strength. In order to successfully lay the membrane and obtain a regenerated cellulose membrane with excellent physicochemical properties, this invention preferably controls the mass solid content of cellulose raw materials in the first solution to be 2.6-12% and the mass solid content of cellulose raw materials in the second solution to be 2-6%. By setting this range, the dissolution efficiency and solution viscosity can be balanced, avoiding insufficient cellulose dissolution due to excessive solid content or increased solvent costs due to excessively low solid content. Further preferably, the mass solid content of cellulose raw materials in the second solution is 2-4%; even more preferably, it is 4%. To facilitate membrane regeneration in subsequent processes, the present invention preferably controls the zero-shear viscosity of the cellulose solution to be 800–40000 mPa·s.

[0058] After the second solution is thoroughly mixed, the insoluble polyester component is filtered out, yielding a cellulose solution and insoluble polyester. A custom-made pressure filtration device is used for the filtration operation; the pressure is not limited, and normal filtration can be performed within the maximum pressure range. During the filtration process, the temperature can be appropriately increased to accelerate the filtration process.

[0059] The present invention also proposes a regenerated cellulose material obtained according to the aforementioned recycling method, which may be in the form of a film.

[0060] After filtering the blended fabric solution, the resulting cellulose solution is used to lay a membrane, regenerate, and dry to obtain a regenerated cellulose film.

[0061] In the above film-making process, the specific film-making process is not specifically limited. Normal casting or blade coating methods are acceptable, as long as the cellulose solution can be prepared into a film.

[0062] In the above membrane-forming process, the original solution membrane is immersed in a coagulation bath to regenerate the nascent cellulose membrane. When the cellulose solution encounters the coagulation bath liquid, a slow solvent-non-solvent dual diffusion effect occurs, disrupting the hydrogen bonding between the ionic solvent and cellulose, resulting in slow solidification and regeneration of the cellulose. Subsequently, the coagulation bath is replaced 1–10 times, with each residence time ranging from 0.5 to 4 hours. Multiple replacements of the coagulation bath thoroughly wash away the ionic solvent, reducing solvent residue in the regenerated material. To better balance quality and efficiency, replacing the coagulation bath 4–5 times is further optimized. The coagulation bath is selected from at least one of tert-butanol, ethanol, and water.

[0063] In the above-described membrane-making process, the final step is to oil and dry the nascent cellulose membrane to obtain a regenerated cellulose membrane. The process for this step in this invention can be controlled using conventional processes in the prior art, and this invention does not impose specific limitations on it.

[0064] In a specific embodiment of the present invention, the oil concentration in the oiling step is preferably 2-5%; the drying step is preferably drying at room temperature and pressure or high temperature, with the high temperature drying temperature being 20-150°C and the time being 5-60 minutes. Low temperature and slow drying can reduce film cracking, while high temperature and fast drying are suitable for industrial production; the present invention further preferably uses a drying temperature of 100-120°C and a drying time of 8-25 minutes. If the drying time is too short, the film will not dry completely; if the drying time is too long, the film strength will decrease.

[0065] The regenerated cellulose material of the present invention can also be processed into fiber or aerogel forms according to actual needs. Its regeneration process is not specifically limited.

[0066] The present invention also proposes an application of the aforementioned regenerated cellulose material in the fields of food packaging, filtration and adsorption, functional sensing, or thermal insulation.

[0067] The regenerated cellulose membrane of this invention conforms to GB 4806.6-2016 "National Food Safety Standard for Plastic Resins for Food Contact", with a heavy metal content of <0.1mg / kg (test data from Example 3) and a migration amount of <10mg / dm³. 2 It meets the safety requirements in the food packaging field.

[0068] The regenerated cellulose membrane of this invention has an average pore size of 0.2–1.5 μm (data from Example 4) and an adsorption capacity of 200–300 mg / g for methylene blue (adsorption experiment in Example 5), making it suitable for treating dye wastewater in the field of filtration and adsorption.

[0069] The regenerated cellulose membrane of this invention has a humidity response time of <5s (test data from Example 2) and an electrical conductivity of 10. -4 ~10 -3S / cm (data from Example 3) can be used as a humidity sensor material in the field of functional sensing.

[0070] The thermal conductivity of recycled polyester fiber is 0.03 to 0.05 W / (m·K) (test data from Example 5), which meets the performance requirements in the field of thermal insulation.

[0071] Its biocompatibility allows it to be used in food packaging, its porous structure allows it to be used for filtration and adsorption, its ion responsiveness allows it to be used for functional sensing, and its low thermal conductivity allows it to be used in thermal insulation.

[0072] This invention also proposes a recycled polyester material obtained according to the aforementioned recycling method. The infrared spectrum of the recycled polyester material exhibits characteristic peaks of polyester and essentially maintains the original chemical structure of the polyester, as shown in the attached figure. Figure 6 The image shows the infrared spectra of the insoluble polyester and pure polyester components obtained by filtration in Example 1 of the present invention.

[0073] This invention fully utilizes the selective solubility characteristics of superbasic acetate ionic solvents on cotton fibers (cellulose) to achieve efficient separation of cotton-polyester blend components. Compared with traditional acid-base hydrolysis methods, it is more environmentally friendly and avoids fiber damage. By using superbasic cations to capture active hydrogen protons from dye molecules, the conjugated double bond system is destroyed, causing the dye to lose its color-emitting ability. Furthermore, the dissolution of cellulose by superbasic acetate ionic solvents is accompanied by severe swelling. Solvent molecules penetrate into the cellulose molecular chains, destroying the hydrogen bonds between cellulose molecules, making the fiber structure loose and increasing the gaps between molecular chains. The dye in the fabric is mostly adsorbed or chemically bonded inside the cellulose fibers. After the cellulose swells, the binding force between the dye and the fiber weakens, making it easier to detach from the fiber network and enter the solvent phase. Furthermore, by adding a viscosity reducer to the solution, this invention promotes the dissociation of dye molecules from the cellulose network and reduces the solution viscosity to facilitate subsequent separation. The "one-step dissolution + decolorization" process of this invention breaks through the limitations of traditional step-by-step operations. The technical solution of this invention can not only obtain regenerated cellulose materials (such as membranes, fibers, etc.), but also directly use the separated polyester as recycled material, realizing the full resource utilization of blended fabrics.

[0074] The introduction of viscosity reducer in the technical solution of this invention has the dual functions of viscosity reduction and decolorization, solving the problems of high viscosity and dye residue of ionic solvents.

[0075] The present invention will be further described below with reference to specific embodiments, but this should not be construed as a limitation on the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0076] Unless otherwise specified, all materials and reagents mentioned below are commercially available products well known to those skilled in the art; unless otherwise specified, all methods described are methods known in the art. Unless otherwise defined, the technical or scientific terms used should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0077] Superbasic acetate ionic solvents exhibit good technical effects in the one-pot dissolution and decolorization of cotton-polyester fabrics with a degree of polymerization of 500-1000. In the specific embodiments below, the colored blended fabrics used are commercially available cotton-polyester fabrics with a degree of polymerization of 578, containing 85% cellulose and 15% polyester by mass; these degrees of polymerization and contents are merely illustrative and do not constitute a limitation on the specific scope of the present invention.

[0078] Example 1

[0079] Add 4.8g of filamentous colored blended fabric to 60g of 1,8-diazabicyclo[5.4.0]undec-7-ene acetate ionic solvent, mix thoroughly, and stir at 80°C until the cellulose is completely dissolved. Figure 1 As shown, the left photo is before dissolution and decolorization, and the right photo is after dissolution and decolorization. Samples were taken periodically and observed under a polarizing microscope to monitor the dissolution of cellulose. After 3.5 hours, complete dissolution of cellulose was observed under the polarizing microscope. The dissolution process is as follows: Figure 2 As shown, the long fibers are insoluble polyester components and exhibit color under polarized light. The four images are polarized microscope images taken at different times. Figure 2 It was observed that less and less cellulose dissolved, while the polyester remained undissolved, thus achieving separation of cellulose and polyester. Simultaneously, the color of the blended fabric solution gradually lightened during the cellulose dissolution process. Then, 60g of the viscosity reducer dimethyl sulfoxide was added to the solution at 60℃, and after mixing until no obvious lumps remained, the insoluble polyester component and cellulose solution were separated by hydraulic filtration. Figure 3 The image shown is of insoluble polyester. Figure 4 The image shown is a polarized light image of a cellulose solution with a viscosity of 5663.2 mPa·s. The cellulose solution was coated using a blade coating method and then regenerated in a tert-butanol coagulation bath. The tert-butanol coagulation bath was replaced every 1–2 hours, for a total of 4 times, to remove ionic solvents from the solution. Subsequently, an oil was applied at a concentration of 3 g / L, and the film was dried in an oven at 120°C to obtain a regenerated cellulose membrane with high transparency, such as… Figure 5 The image shows a cellulose membrane through which the object behind the membrane can be clearly seen. The insoluble polyester component is washed and dried to obtain recycled polyester material.

[0080] The specific properties of the regenerated cellulose membrane obtained in this embodiment after the above steps are shown in Table 1.

[0081] The filtered polyester was subjected to infrared spectroscopy testing. Figure 6 The infrared spectra of the insoluble polyester obtained by filtration and the pure polyester component are shown. The results show that the infrared spectra of the filtered polyester and the pure polyester are almost identical, and they have the typical characteristic peaks of polyester materials, indicating that cellulose and polyester were efficiently separated in this embodiment.

[0082] Example 2

[0083] 4.8g of filamentous colored blended fabric was thoroughly mixed with 80g of 1,5-diazabicyclo[4.3.0]non-5-ene acetate ionic solvent, and stirred at 80℃ until the cellulose was completely dissolved. Samples were taken periodically and observed under a polarizing microscope to monitor the cellulose dissolution. After 3 hours, complete cellulose dissolution was observed under the polarizing microscope, and the color of the blended fabric solution gradually lightened during the cellulose dissolution process. Then, 40g of the viscosity reducer γ-valerolactone was added to the solution at 40℃ and mixed until no obvious lumps remained. The insoluble polyester component and cellulose solution were separated by hydraulic filtration, with the cellulose solution having a viscosity of 39723 mPa·s. The cellulose solution was then coated using a blade coating method and regenerated in an ethanol coagulation bath. The ethanol coagulation bath was replaced every 1–2 hours, for a total of 4 times, to remove the ionic solvent from the solution. Subsequently, an oil with a concentration of 3g / L was applied, and the membrane was dried in an oven at 120℃ to obtain the regenerated cellulose membrane.

[0084] The specific properties of the regenerated cellulose membrane obtained in this embodiment after the above steps are shown in Table 1.

[0085] Example 3

[0086] 4.8 g of filamentous colored blended fabric was thoroughly mixed with 90 g of 1,5,7-triazabicyclo[4.4.0]dec-5-ene acetate ionic solvent. The mixture was stirred at 80 °C until the cellulose was completely dissolved. Samples were taken periodically and observed under a polarizing microscope to monitor the cellulose dissolution. After 2.5 h, complete cellulose dissolution was observed under the polarizing microscope, and the color of the blended fabric solution gradually lightened during the cellulose dissolution process. Then, 30 g of viscosity reducer sulfolane was added to the solution at 40 °C and mixed thoroughly until no obvious lumps remained. The insoluble polyester component and cellulose solution were separated by hydraulic filtration. The viscosity of the cellulose solution was 34588 mPa·s. The cellulose solution was then coated onto a film using a scraping method and regenerated in an ethanol coagulation bath. The ethanol coagulation bath was replaced every 1–2 h, for a total of 4 times, to remove the ionic solvent from the solution. Subsequently, an oil with a concentration of 3 g / L was applied, and the film was dried in an oven at 120 °C to obtain the regenerated cellulose membrane.

[0087] The specific properties of the regenerated cellulose membrane obtained in this embodiment after the above steps are shown in Table 1.

[0088] Example 4

[0089] 2.4g of filamentous colored blended fabric was thoroughly mixed with 60g of 1,8-diazabicyclo[5.4.0]undec-7-ene acetate ionic solvent. The mixture was stirred at 80℃ until the cellulose was completely dissolved. Samples were taken periodically and observed under a polarizing microscope to monitor the cellulose dissolution. After 2 hours, complete cellulose dissolution was observed under the polarizing microscope, and the color of the blended fabric solution gradually lightened during the cellulose dissolution process. Then, 60g of dimethyl sulfoxide (DMSO), a viscosity reducer, was added to the solution at 60℃. After mixing until no obvious lumps remained, the solution was separated by hydraulic filtration to separate the insoluble polyester component and the cellulose solution. The viscosity of the cellulose solution was 804.7 mPa·s. The cellulose solution was then cast into a film using a casting method and regenerated in an ethanol coagulation bath. The coagulation bath needed to be replaced every 1-2 hours, for a total of 4 times, to remove the ionic solvent from the solution. Subsequently, an oil was applied at a concentration of 3g / L. After drying at room temperature and pressure, a regenerated cellulose membrane was obtained. Figure 7 The image shown is a photograph of the membrane. The specific properties of the regenerated cellulose membrane obtained in this embodiment after the above steps are shown in Table 1.

[0090] Example 5

[0091] 4.8g of filamentous colored blended fabric was thoroughly mixed with 60g of 1,5,7-triazabicyclo[4.4.0]dec-5-ene acetate ionic solvent, and stirred at 80℃ until the cellulose was completely dissolved. Samples were taken periodically and observed under a polarizing microscope to monitor the cellulose dissolution. After 3.5 hours, complete cellulose dissolution was observed under the polarizing microscope, and the color of the blended fabric solution gradually lightened during the cellulose dissolution process. Then, 60g of the viscosity reducer γ-valerolactone was added to the solution at 60℃ and mixed until no obvious lumps remained. The insoluble polyester component and cellulose solution were separated by hydraulic filtration, with the cellulose solution having a viscosity of 5487.6 mPa·s. The cellulose solution was then coated using a scraping method and regenerated in a hydrocoagulation bath. The hydrocoagulation bath was replaced every 1–2 hours, for a total of 4 times, to remove the ionic solvent from the solution. Subsequently, an oil with a concentration of 3g / L was applied, and the membrane was dried in an oven at 120℃ to obtain the regenerated cellulose membrane. The specific properties of the regenerated cellulose membrane obtained in this embodiment after the above steps are shown in Table 1.

[0092] Comparative Example 1

[0093] 4.8g of filamentous colored cotton-polyester blended fabric was mixed with 60g of 1-allyl-3-methylimidazolium chloride ionic solvent and allowed to swell fully. The mixture was stirred at 80℃, and samples were taken periodically for observation of cellulose dissolution under a polarizing microscope. After 10.5 hours, most of the cellulose remained undissolved. It was also observed that the colored fabric raw material did not decolorize in this ionic solvent. Figure 8As shown, the left image is a polarized light image of cellulose after 10.5 hours of dissolution, and the right image is a photograph of the corresponding cellulose dissolution. Furthermore, after mixing an appropriate amount of 1-allyl-3-methylimidazolium chloride ionic solvent with the fabric dye at 80°C and reacting for a period of time, no significant color change was observed in the mixture. Figure 9 As shown, the left image shows the color after the reaction of the dye with the 1-allyl-3-methylimidazolium chloride ionic solvent, and the right image shows the color after the reaction of the dye with the superbasic acetate ionic solvent of this invention. No viscosity reducer was added in this comparative example; the final colored fabric raw material content was 8% based on 100% ionic solvent mass. The specific experimental phenomena of this embodiment after the above steps are shown in Table 1.

[0094] Comparative Example 2

[0095] 9.6g of filamentous colored blended fabric was thoroughly mixed with 60g of 1,5-diazabicyclo[4.3.0]non-5-ene acetate ionic solvent, and stirred at 90°C. Samples were taken periodically and observed under a polarizing microscope to check the dissolution of the sizing agent. It was found that although the color of the cotton-polyester blended fabric solution lightened, the high fabric concentration made stirring and dissolution difficult, hindering the next step of component separation. No viscosity reducer was added in this comparative example; with the ionic solvent mass as 100%, the final content of the colored fabric raw material was 16%. The specific experimental phenomena observed in this embodiment after the above steps are shown in Table 1.

[0096] Comparative Example 3

[0097] 4.8g of filamentous colored cotton-polyester blended fabric was mixed with 60g of 1,5,7-triazabicyclo[4.4.0]dec-5-ene acetate ionic solvent and allowed to swell fully. The mixture was stirred at 100°C until the cellulose was completely dissolved. Samples were taken periodically and observed under a polarizing microscope to monitor the cellulose dissolution. After 3.5 hours, the cellulose was found to be completely dissolved. Filtration was performed directly without a viscosity reducer, and the viscosity of the solution was found to be too high. Transferring the solution from the beaker to the filtration equipment and filtering the insoluble polyester were extremely difficult. The high viscosity led to prolonged filtration time and filter clogging, making subsequent operations difficult. In this comparative example, no viscosity reducer was added, and the final content of the colored fabric raw material was 8% based on the mass of the ionic solvent being 100%. The specific experimental phenomena observed in this example after the above steps are shown in Table 1.

[0098] Comparative Example 4

[0099] 4.8g of filamentous colored cotton-polyester blended fabric was mixed with 60g of eutectic solvent and allowed to swell fully. The mixture was stirred at 80°C, and samples were taken periodically for observation of cellulose dissolution under a polarizing microscope. It was found that dissolution was difficult and the viscosity was high, making further component separation difficult. Simultaneously, it was observed that the colored fabric raw material did not decolorize in this ionic solvent. Furthermore, after mixing an appropriate amount of eutectic solvent with the fabric dye at 80°C and reacting for a period of time, no significant color change was observed in the mixture. No viscosity reducer was added in this comparative example; based on the ionic solvent mass being 100%, the final mass content of the colored fabric raw material was 8%. The specific experimental phenomena observed in this embodiment after the above steps are shown in Table 1.

[0100] Unless otherwise specified, the performance testing methods of the above embodiments and comparative examples were all conducted using conventional testing methods in the art.

[0101] Decolorization effect test: Under the same conditions, the color change during the cellulose dissolution process was recorded, and the color Lab value was extracted by software. In this invention, the L (brightness) value is mainly recorded to indicate that the colored fabric undergoes decolorization during the dissolution process. The larger the L value, the lighter the color. It is known that after the colored cellulose raw material and cellulose solvent are mixed evenly, the L value is 8. The L values ​​in Table 1 are measured after the cellulose is dissolved (the experiment for undissolved cellulose is conducted at the end of the dissolution stirring operation).

[0102] Transparency Test: The transmittance of the cellulose film was tested according to GB / T2410-2008, using a UV-Vis spectrophotometer with an integrating sphere, with a wavelength range of 400-800 nm. The transmittance calculation formula is as follows:

[0103]

[0104] Where T represents transmittance, T1 is incident light flux, and T2 is the total transmitted light flux through the sample.

[0105] Cellulose recovery rate: The filtered polyester is washed, dried, and weighed to obtain the mass of dissolved cellulose. The cellulose recovery rate is calculated by comparing this mass with the mass of the initially added cellulose.

[0106] Table 1

[0107]

[0108]

[0109] As can be seen from the above examples and comparative test data, in Examples 1 to 5, the separation of cotton and polyester components and color removal of the fabric can be achieved simultaneously during the process of dissolving the colored cotton-polyester blended fabric in a superbasic acetate ionic solvent. The resulting cellulose solution can be regenerated and dried to obtain a regenerated cellulose membrane.

[0110] Compared with Comparative Example 2, Examples 1-5 show that when the concentration of the cotton-polyester blended fabric raw material is too high, the fabric is difficult to fully dissolve, while when it is too low, the mechanical properties of the regenerated cellulose membrane are poor. The present invention preferably uses a cellulose solution mass concentration of 4% to achieve better dissolution.

[0111] Examples 1-3 show that the content of viscosity reducer not only affects the ease of filtration, but also the mechanical properties of the regenerated cellulose membrane. When the added viscosity reducer is 50% of the mass of the ionic solvent, the viscosity of the solution can be effectively reduced to meet the filtration requirements. The tensile strength of the resulting regenerated cellulose membrane reaches 115.6 MPa and the elongation at break is 34.4%.

[0112] A comparison of Examples 2 and 4-5 revealed that the regenerated cellulose membrane obtained under the conditions of ethanol coagulation bath and high-temperature drying at 120°C had higher strength.

[0113] As can be seen from the test data of the above embodiments, in Examples 1 to 5 and Comparative Example 3, the use of raw materials with different solid contents and different amounts of viscosity reducers during the dissolution process will affect the dissolution and the ease of filtration. However, it can be found that in the experiment using superbasic acetate ionic solvent as cellulose solvent, the fabric color faded. The removal of dye color is mainly due to the oxidation of dye molecules by specific ionic solvent components, causing them to lose hydrogen protons, resulting in the disappearance of color.

[0114] As can be seen from the test data of the above comparative examples, in Comparative Examples 1 and 4, the ionic solvents selected were 1-allyl-3-methylimidazolium chloride ionic solvent and eutectic solvent, respectively. It was found that the cellulose was not completely dissolved in the end, and the color of the colored fabric did not change significantly during the dissolution process. If decolorization is required, other bleaching experiments need to be carried out. This fully demonstrates the innovation of the present invention in using superbasic acetate ionic solvent to achieve integrated component separation and color removal of colored waste cotton-polyester blended fabrics.

[0115] As can be seen from the test data of the above comparative examples, in Comparative Example 2, although the cellulose could not be fully swollen and dissolved in the ionic solvent due to the excessively high mass concentration of the fabric raw material, and the next step of viscosity reduction and separation could not be carried out, it was found that the color of the fabric became lighter during the experiment, indicating that the superbasic acetate ionic solvent in this invention can decolorize colored fabrics under suitable conditions.

[0116] As can be seen from the test data of the above comparative examples, in Comparative Example 3, the solvent only had a cellulose dissolving system and no viscosity reducing agent. This resulted in the cotton-polyester blended fabric solution obtained after the fabric was swollen and stirred having too high a viscosity. It was difficult to transfer the solution to the filtration equipment and to perform subsequent filtration operations. This indicates that the use of a viscosity reducing agent is necessary in the technical solution of this invention. Furthermore, it was found that when the blended fabric solution was dissolved at 100°C, the resulting solution was reddish in color. This may be due to excessive degradation of cellulose caused by excessively high temperature.

[0117] The technical features in the claims and / or specification of this invention can be combined, and the combination is not limited to the combinations obtained through reference in the claims. Technical solutions obtained by combining the technical features in the claims and / or specification are also within the scope of protection of this invention.

[0118] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for recycling waste cotton-polyester blended fabrics, characterized in that, It includes the following steps: S11 involves adding cellulose raw material to a superbasic acetate ionic solvent and stirring to dissolve it, achieving efficient separation and decolorization of components in waste cotton-polyester blended fabrics in a one-pot process to obtain a first solution; the cellulose raw material is obtained by processing waste cotton-polyester blended fabrics; the cation in the superbasic acetate ionic solvent is selected from at least one of 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene; S12 Add a viscosity reducer to the first solution and mix thoroughly to obtain a second solution; through the synergistic effect of the viscosity reducer and the solvent, the dye molecules are promoted to dissociate from the cellulose network, while the solution viscosity is reduced; the viscosity reducer is selected from at least one of dimethyl sulfoxide, γ-valerolactone and sulfolane; S13 performs solid-liquid separation on the second solution to obtain a cellulose solution and an insoluble polyester; S14 regenerates and dries the cellulose solution to obtain regenerated cellulose material; insoluble polyester is washed and dried to obtain regenerated polyester material.

2. The recycling method according to claim 1, characterized in that, The cellulose raw material is a powdered, filamentous, or flocculent fabric obtained by crushing colored waste cotton-polyester blended fabrics with a degree of polymerization of 500-1000.

3. The recycling method according to claim 1, characterized in that, In step S11, the mass of the cellulose raw material is 2.6-12% based on the mass of the ionic solvent being 100%.

4. The recycling method according to claim 1, characterized in that, In step S11, the dissolution temperature is 70~90℃ and the dissolution time is 2~4 h.

5. The recycling method according to claim 1, characterized in that, In step S12, when the viscosity reducer is added, the temperature of both the viscosity reducer and the first solution is 40~60℃.

6. The recycling method according to claim 1, characterized in that, The mass ratio of the viscosity reducer to the ionic solvent is 0.3 to 1:1; based on the total mass of the ionic solvent and the viscosity reducer being 100%, the mass solid content of the cellulose raw material is 2 to 6%.

7. A regenerated cellulose material obtained by the recycling method according to any one of claims 1 to 6.

8. A recycled polyester material obtained by the recycling method according to any one of claims 1 to 6.

9. The application of the regenerated cellulose material according to claim 7 in the fields of food packaging, filtration and adsorption, functional sensing, or thermal insulation.

Images