Method for stripping cotton component in waste fabric and upgrading and recycling cellulose acetate

Abstract

The invention belongs to the field of organic polymers, and discloses a method for stripping a cotton component in a waste fabric and upgrading and recycling cellulose acetate, which is characterized in that the cotton component in the waste fabric (including pure cotton and blended fabric) is acetylated by using an acetic acid / acetic anhydride solvent system and is stripped from a chemical fiber component at the same time, and the acetylated product of the cotton component is the cellulose acetate. The method is easy to operate, the obtained cellulose acetate can be widely applied to water purification membranes, textiles, cigarette filters and the like, and the method is wide in application range and suitable for stripping of most blended yarns in the market.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of organic polymers, and relates to a method for stripping and upgrading cellulose acetate from cotton components in waste fabrics. BACKGROUND

[0002] Overall, textile materials can be divided into two categories: natural fibers and chemical fibers. Among them, cotton is the most common natural fiber, and polyester (PET) is the most common chemical fiber. Although there are pure cotton and pure polyester fiber fabrics, in order to balance the comfort of skin and air permeability of cotton and the advantages of wrinkle resistance, shape retention and elasticity of polyester fiber, the market provides blended products of cotton and polyester fiber to meet social needs. When these blended fabrics are discarded, it poses a great challenge to classification management, because it is difficult to separate these blends by physical methods. At present, the separation of blends basically adopts chemical methods. Chemical methods can be divided into polyester-first and cellulose-first routes. The polyester-first route usually uses methanolysis or glycolysis to selectively depolymerize PET into dimethyl terephthalate or bis-hydroxyethyl terephthalate, but due to the difficulty in separation and purification of these two monomers, the energy consumption and cost are high. The cellulose-first route usually uses N-methyl morpholine-N-oxide (NMMO), inorganic mixed solvents, ionic liquids, deep eutectic solvents, etc., but most of these solvents use complex metals or organic ions, and when dealing with waste fabrics containing various pigments, additives and impurities, their recycling usability faces great challenges. If these solvents cannot be efficiently recovered, both the economic cost and the environmental cost are uncontrollable. Therefore, it is of great significance to develop a route with simple system and efficient solvent recovery for recycling complex blended fabrics, making full use of waste resources and relieving environmental pressure. SUMMARY

[0003] The present application aims to provide a method for stripping and upgrading cellulose acetate from cotton components in waste fabrics, which uses acetic acid and acetic anhydride as activators and acetylating agents, respectively, to achieve acetylation of cotton components in waste fabrics. The acetylated cotton components are fully dissolved in acetic acid solution to form a homogeneous fluid and separate from chemical fiber components, while most chemical fiber components (including polyester, polyamide, polyurethane, etc.) remain unaffected in solid form.

[0004] To achieve the purpose, the present application adopts the following technical solutions: The application discloses a method for stripping and upgrading cellulose acetate from cotton components in waste fabrics, and belongs to the field of waste fabric recycling.

[0005] Further, the blended fabric comprises cotton components and chemical fiber components (such as polyester, polyamide, polyurethane and the like).

[0006] The cotton components comprise repeating structural units as shown in formula (1): (1) ; In formula (1), the main component is a long-chain fiber formed by connecting glucose through β-1,4-glycosidic bonds.

[0007] The polyester comprises repeating structural units as shown in formula (2): (2) ; In formula (2), m=1-3. Preferably, when m=1, the polymer is polyethylene terephthalate (PET), and when m=2, the polymer is polybutylene terephthalate (PBT).

[0008] The polyamide comprises repeating structural unit fragments as shown in formula (3): (3) ; In formula (3), m=1-7. Preferably, when m=1, the polymer is nylon 6, when m=6, the polymer is nylon 11, and when m=7, the polymer is nylon 12.

[0009] Alternatively, the polyamide polymer comprises repeating structural unit fragments as shown in formula (4): (4) ; In formula (4), R1 is a substituent group with 4-10 carbon atoms, R2 is a substituent group with 4-12 carbon atoms, and R1 and R2 can be the same or different. Preferably, when R1 is a C4 linear alkyl group and R2 is a C4 linear alkyl group, the polymer is nylon 46; when R1 is a C4 linear alkyl group and R2 is a C6 linear alkyl group, the polymer is nylon 66; when R1 is a C8 linear alkyl group and R2 is a C6 linear alkyl group, the polymer is nylon 610; when R1 is a C10 linear alkyl group and R2 is a C6 linear alkyl group, the polymer is nylon 612; when R1 is a C8 linear alkyl group and R2 is a C10 linear alkyl group, the polymer is nylon 1010; when R1 is a C6 phenyl group and R2 is a C6 linear alkyl group, the polymer is nylon 6T; and when R1 is a C6 phenyl group and R2 is a C6 phenyl group, the polymer is aramid 1313 or aramid 1414.

[0010] The polyurethane comprises a repeating structural unit fragment as shown in formula (5): (5) ; In formula (5), R1 comprises an aromatic ring structure, such as diphenylmethane and toluene, and the corresponding monomers are diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI), respectively.

[0011] In the above-mentioned formula (1) to formula (5), n only represents the polymer repeating unit in each formula, and the specific value of n in each formula is independent of each other; similarly, m in formula (2) and formula (3) is independent of each other, and R1 in formula (4) and formula (5) is also independent of each other, and only represents the group in each formula.

[0012] The chemical fiber component can further comprise any form of polymer (for example, polyolefin can be present) other than polyester, polyamide, and polyurethane structure, and will not affect the peeling of the cotton component.

[0013] Preferably, the waste fabric includes, but is not limited to, the polyester products currently consumed in the market.

[0014] Preferably, the activator used is an acetic acid solution containing various inorganic acid catalysts or organic acid catalysts. The inorganic acid catalysts include, but are not limited to, hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. The organic acid catalysts include, but are not limited to, methanesulfonic acid, benzenesulfonic acid, and p-toluenesulfonic acid.

[0015] Preferably, the mass ratio of the catalyst to the waste fabric is 0.005-0.1 g:1 g, and the volume ratio of the activator to the waste fabric is 1-100 mL:1 g.

[0016] Preferably, the acetylating agent used is acetic anhydride or an acetic acid solution of acetic anhydride. The mass ratio of the acetic anhydride to the waste fabric is 0.1-100 g:1 g.

[0017] Preferably, the pre-activation reaction temperature is 50-100℃, and the reaction time is 0.5-10 hours.

[0018] Preferably, the acetylation reaction temperature is 50-100℃. The reaction time is 0.5-10 hours.

[0019] Compared with the prior art, the present application has the following advantages: The present application mixes the waste fabric with an activating agent and heats for a period of time, then adds acetic anhydride and continues to stir until the acetylation is complete, thereby achieving cotton peeling. The operation is simple, and the obtained acetylated product is cellulose acetate, which is a high-value second-generation artificial cellulose and is widely used in water purification membranes, textiles, cigarette filters, etc. The method of the present application has a wide range of applications and is suitable for peeling of most blended fabrics on the market. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic diagram of the operation process of the method of the present application; Figure 2 is a 1H NMR spectrum of cellulose acetate obtained according to the method of the present application, wherein DS is the degree of substitution of the cellulose acetate product, and the 1.5-2.2 ppm shift is the chemical shift of the methyl group on the acetyl group, and the 3.5-5.2 ppm is the chemical shift of the cellulose skeleton and unsubstituted hydroxyl hydrogen. 1 H NMR spectrum, wherein DS is the degree of substitution of the cellulose acetate product, and the 1.5-2.2 ppm shift is the chemical shift of the methyl group on the acetyl group, and the 3.5-5.2 ppm is the chemical shift of the cellulose skeleton and unsubstituted hydroxyl hydrogen. DETAILED DESCRIPTION

[0021] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. In addition, it should be understood that after reading the content of the present application, those skilled in the art can make various modifications or modifications to the present application, and these equivalent forms also fall within the scope defined by the present application.

[0022] The present application provides a method for peeling and upgrading cellulose acetate from cotton components in waste fabric, and the core technology is to use acetic anhydride as an acetylation reagent to peel the cotton components. The obtained product is cellulose acetate. The degree of substitution of cellulose acetate is characterized by nuclear magnetic resonance.

[0023] Example 1 In a 250 mL conical flask, 10 g of shredded cotton / polyester blend with a blend ratio of cotton / PET = 2 / 8 was added. A sulfuric acid / acetic acid solution (0.5 g of sulfuric acid dissolved in 50 mL of acetic acid) was prepared and added to the conical flask, which was then heated to 70 °C and maintained for 30 minutes. Subsequently, 20 g of acetic anhydride was added, and stirring was continued at 70 °C for another 30 minutes. Upon completion of the reaction, the viscous fluid was collected by simple suction filtration, while the PET was retained. To the viscous fluid, 150 mL of purified water was added to re-precipitate the cellulose acetate. After suction filtration and drying, cellulose acetate powder was obtained, with a yield of 92.3% (calculated based on the cotton component). The degree of substitution was tested by nuclear magnetic resonance hydrogen spectrum using deuterated DMSO as the solvent (results shown in Table 1). Figure 2 . .

[0024] Example 2 In a 250 mL conical flask, 3 g of shredded cotton and 7 g of PET fabric were added. A sulfuric acid / acetic acid solution (0.5 g of sulfuric acid dissolved in 50 mL of acetic acid) was prepared and added to the conical flask, which was then heated to 70 °C and maintained for 30 minutes. Subsequently, 20 g of acetic anhydride was added, and stirring was continued at 70 °C for another 30 minutes. Upon completion of the reaction, the viscous fluid was collected by simple suction filtration, while the PET was retained. To the viscous fluid, 150 mL of purified water was added to re-precipitate the cellulose acetate. After suction filtration and drying, cellulose acetate powder was obtained, with a yield of 91.5% (calculated based on the cotton component).

[0025] Example 3 In a 250 mL conical flask, 10 g of shredded cotton / polyester blend with a blend ratio of cotton / PET = 3.5 / 6.5 was added. A sulfuric acid / acetic acid solution (0.5 g of sulfuric acid dissolved in 50 mL of acetic acid) was prepared and added to the conical flask, which was then heated to 70 °C and maintained for 30 minutes. Subsequently, 20 g of acetic anhydride was added, and stirring was continued at 70 °C for another 30 minutes. Upon completion of the reaction, the viscous fluid was collected by simple suction filtration, while the PET was retained. To the viscous fluid, 150 mL of purified water was added to re-precipitate the cellulose acetate. After suction filtration and drying, cellulose acetate powder was obtained, with a yield of 91.1% (calculated based on the cotton component).

[0026] Example 4 In a 250 mL conical flask, 10 g of shredded cotton / polyester blend with a blend ratio of cotton / PET = 8 / 2 was added. A sulfuric acid / acetic acid solution (0.5 g of sulfuric acid dissolved in 50 mL of acetic acid) was prepared and added to the conical flask, which was then heated to 70 °C and maintained for 30 minutes. Subsequently, 20 g of acetic anhydride was added, and stirring was continued at 70 °C for another 30 minutes. Upon completion of the reaction, the viscous fluid was collected by simple suction filtration, while the PET was retained. To the viscous fluid, 150 mL of purified water was added to re-precipitate the cellulose acetate. After suction filtration and drying, cellulose acetate powder was obtained, with a yield of 90.9% (calculated based on the cotton component).

[0027] Example 5 In a 250 mL conical flask, 10 g of broken cotton cloth was added. A sulfuric acid / acetic acid solution (0.5 g of sulfuric acid dissolved in 50 mL of acetic acid) was prepared and added to the above conical flask, which was then warmed to 70 °C and maintained for 30 minutes. Subsequently, 20 g of acetic anhydride was added, and stirring was continued at 70 °C for 30 minutes. Upon completion of the reaction, the viscous fluid was collected by simple suction filtration. To the viscous fluid, 150 mL of purified water was added to re-precipitate the cellulose acetate. The cellulose acetate powder was obtained by suction filtration and drying, with a yield of 92.0% (calculated based on the cotton component).

[0028] Example 6 In a 250 mL conical flask, 10 g of broken cotton / polyester blend (blend ratio: cotton / PET = 3.5 / 6.5) was added. A phosphoric acid / acetic acid solution (1 g of phosphoric acid dissolved in 50 mL of acetic acid) was prepared and added to the above conical flask, which was then warmed to 70 °C and maintained for 30 minutes. Subsequently, 20 g of acetic anhydride was added, and stirring was continued at 70 °C for 30 minutes. Upon completion of the reaction, the viscous fluid was collected by simple suction filtration, with the PET being trapped. To the viscous fluid, 150 mL of purified water was added to re-precipitate the cellulose acetate. The cellulose acetate powder was obtained by suction filtration and drying, with a yield of 88.9% (calculated based on the cotton component).

[0029] Example 7 In a 250 mL conical flask, 10 g of broken cotton / polyester blend (blend ratio: cotton / PET = 3.5 / 6.5) was added. A p-toluenesulfonic acid / acetic acid solution (0.25 g of p-toluenesulfonic acid dissolved in 50 mL of acetic acid) was prepared and added to the above conical flask, which was then warmed to 70 °C and maintained for 30 minutes. Subsequently, 20 g of acetic anhydride was added, and stirring was continued at 70 °C for 30 minutes. Upon completion of the reaction, the viscous fluid was collected by simple suction filtration, with the PET being trapped. To the viscous fluid, 150 mL of purified water was added to re-precipitate the cellulose acetate. The cellulose acetate powder was obtained by suction filtration and drying, with a yield of 91.2% (calculated based on the cotton component).

[0030] Example 8 In a 250 mL conical flask, 10 g of high-density crash cloth (NC cloth) was added (blend ratio: cotton / nylon = 2 / 8). A sulfuric acid / acetic acid solution (0.5 g of sulfuric acid dissolved in 50 mL of acetic acid) was prepared and added to the above conical flask, which was then warmed to 70 °C and maintained for 30 minutes. Subsequently, 20 g of acetic anhydride was added, and stirring was continued at 70 °C for 30 minutes. Upon completion of the reaction, the viscous fluid was collected by simple suction filtration, with the nylon being trapped. To the viscous fluid, 150 mL of purified water was added to re-precipitate the cellulose acetate. The cellulose acetate powder was obtained by suction filtration and drying, with a yield of 83.3% (calculated based on the cotton component).

[0031] Example 9 In a 250 mL conical flask, 10 g of cotton and spandex blended fabric was added, the blending ratio was cotton / spandex = 95 / 5. A sulfuric acid / acetic acid solution (0.5 g of sulfuric acid was dissolved in 50 mL of acetic acid) was prepared and added to the above conical flask, and the temperature was raised to 70°C and kept for 30 minutes. Then, 20 g of acetic anhydride was added, and the stirring was continued at 70°C for 30 minutes. After the reaction was completed, the viscous fluid was collected by simple suction filtration, while the spandex was intercepted. To the viscous fluid, 150 mL of pure water was added to re-precipitate the cellulose acetate. After suction filtration and drying, cellulose acetate powder was obtained, with a yield of 91.9% (based on the cotton component).

[0032] As can be seen from the above examples, the method for stripping and upgrading cellulose acetate from waste fabric provided by the present application has the following advantages: whether it is pure cotton fabric or cotton and PET, nylon, spandex and other blended fabrics, the simple process of "pre-activation with catalyst-containing acetic acid solution-acetylation with acetic anhydride" can achieve efficient treatment, and the cellulose acetate yield based on the cotton component reaches 92.3%. During the reaction, the acetylated cotton component is in the form of a homogeneous fluid, and the chemical fiber component remains in a solid state, which can be easily separated by suction filtration, achieving complete separation. The method not only realizes the conversion of cotton component to high-value cellulose acetate, but also provides conditions for the subsequent reuse of intercepted chemical fiber components. The entire process only requires conventional reaction and separation equipment, the raw materials are widely available and low-cost, the reaction conditions are mild, and the operation is simple. The method can effectively solve the problems of difficult separation and low utilization value of waste blended fabric, and has feasibility and promotional value in industrial application.

[0033] The above only describes exemplary embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for stripping cotton components from waste fabrics and recycling cellulose acetate, characterized in that: The waste fabric is pure cotton fabric or a blended fabric containing cotton and chemical fiber components. First, the cotton component in the waste fabric is pre-activated using an acetic acid solution containing a catalyst as an activator. Then, the pre-activated cotton component is acetylated using an acetylation reagent. The acetylated cotton component dissolves in the acetic acid solution, and the resulting acetylation product is cellulose acetate.

2. The method for stripping cotton components from waste fabrics and upgrading and recovering cellulose acetate according to claim 1, characterized in that: The chemical fiber component includes at least one of polyester, polyamide, and polyurethane.

3. The method for stripping cotton components from waste fabrics and upgrading and recovering cellulose acetate according to claim 1, characterized in that: The catalyst is an inorganic acid or an organic acid.

4. The method for stripping cotton components from waste fabrics and recycling cellulose acetate according to claim 1, characterized in that: The acetylation reagent is acetic anhydride or an acetic acid solution of acetic anhydride.

5. The method for stripping cotton components from waste fabrics and upgrading and recovering cellulose acetate according to claim 1, characterized in that: The volume ratio of the activator to the mass ratio of the waste fabric is 1~100mL:1g, and the mass ratio of the catalyst to the mass ratio of the waste fabric is 0.005~0.1g:1g.

6. The method for stripping cotton components from waste fabrics and upgrading and recovering cellulose acetate according to claim 4, characterized in that: The mass ratio of the acetic anhydride to the waste fabric is 0.1~100g:1g.

7. The method for stripping cotton components from waste fabrics and upgrading and recovering cellulose acetate according to claim 1, characterized in that: The pre-activation reaction temperature is 50~100℃, and the reaction time is 0.5~10 hours.

8. The method for stripping cotton components from waste fabrics and upgrading and recovering cellulose acetate according to claim 1, characterized in that: The acetylation reaction temperature is 50~100℃, and the reaction time is 0.5~10 hours.

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