Method for regenerating cotton pulp by using waste textile fabrics

Abstract

The invention discloses a method for regenerating cotton pulp by using waste textiles, and belongs to the technical field of waste textile reutilization, and the method is characterized in that the waste textiles are sequentially soaked in a sodium hydroxide aqueous solution containing hydrogen peroxide, an alkaline hydrogen peroxide solution, a polar solvent and an acidic aqueous solution. According to the method provided by the invention, the alkali treatment, the bleaching treatment, the solvent treatment and the acid treatment are sequentially carried out, so that the polyester-cotton fabric dyed by the reactive dye can be thoroughly stripped, the white and high-purity cotton pulp is obtained, the whiteness of the obtained cotton pulp can reach 72% or above, no polyester component is left, and the cotton pulp is environment-friendly. And during downstream application, the wood pulp can be partially replaced to be used as a raw material of viscose or lyocell fibers.

Description

Technical Field

[0001] The invention belongs to the technical field of recycling waste textiles, and in particular relates to a method for regenerating cotton pulp by utilizing waste textiles. Background Art

[0002] Polyester-cotton blended fabric is one of the most common clothing fabrics. The resource recycling of polyester-cotton waste can help reduce the consumption of petroleum resources and reduce carbon emissions.

[0003] Dissolving pulp is the raw material for preparing regenerated cellulose fibers such as viscose or lyocell, and is mainly prepared by purifying and decolorizing cellulose extracted from wood. In view of the fact that polyester-cotton waste is rich in cotton cellulose, extracting cotton cellulose to prepare cotton pulp to replace wood pulp in the preparation of viscose or lyocell fibers is one of the effective ways to achieve high-value utilization of polyester-cotton waste. For example, the Chinese invention patent with publication number CN113226579A discloses a method for recovering cellulose raw materials from mixed textile waste, wherein the mixed textile waste is treated in an aqueous alkaline treatment medium at 100-200°C to degrade at least one synthetic polymer component, and the cellulose raw materials are obtained from the treated mixed textile waste. For another example, the invention patent with publication number CN110088140A discloses a method for recycling textiles containing cellulose. Mixed textile waste is treated in an aqueous sodium hydroxide solution containing sodium dithionite (hydrogen hydrosulfite) at 50-100°C. The resulting product is bleached with oxygen under alkaline conditions or with ozone under acidic conditions to finally obtain purified cellulose that can be used to prepare viscose fibers. Another example is the Chinese invention patent with publication number CN117986687A, which discloses a method for separating and recovering a polyester-cotton mixture, comprising the following steps: mixing waste polyester-cotton mixture textiles with a high-boiling-point environmentally friendly solvent in proportion, stirring and heating to 160°C~220°C to dissolve the polyester, and separating the cotton fiber and the polyester solution; removing the solvent from the polyester solution, and drying to recover the polyester; or adding a catalyst to the polyester solution to carry out a depolymerization and cyclization reaction, and recovering cyclic oligoethylene terephthalate, wherein the high-boiling-point solvent is a green and environmentally friendly solvent such as 1,3-dimethyl-2-imidazolidinone that does not contain halogens and aromatic groups.

[0004] These methods currently used in production have good results when treating indigo-dyed polyester-cotton denim, and can produce white, high-purity cotton pulp. However, when treating polyester-cotton blended fabrics dyed with reactive dyes, the results are unsatisfactory, and the resulting cotton pulp is limited in downstream applications due to incomplete color stripping. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for regenerating cotton pulp from waste polyester-cotton blended fabrics which can be used for dyeing with reactive dyes.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for regenerating cotton pulp using waste textiles, comprising the following steps: S1. Immersing the waste textile in an aqueous sodium hydroxide solution containing hydrogen peroxide; S2, immersing the product obtained in S1 in an alkaline hydrogen peroxide solution; S3, immersing the product obtained in S2 in a polar solvent; S4. Immerse the product obtained in S3 in an acidic aqueous solution.

[0007] The beneficial effects of the present invention are as follows: the method provided by the present invention can realize the complete stripping of polyester-cotton fabric dyed with reactive dyes by sequentially performing alkali treatment, bleaching treatment, solvent treatment and acid treatment to obtain white, high-purity cotton pulp, the whiteness of the obtained cotton pulp can reach 72% or more, the type A cellulose content reaches 95% or more, the iron ion content is below 15ppm, the polymerization degree is 500-800, and the obtained cotton pulp has no polyester component residue, can partially replace wood pulp as a raw material for viscose or lyocell fiber, prepare high-quality recycled products, and effectively realize the efficient regeneration of waste textiles. DETAILED DESCRIPTION

[0008] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in conjunction with the implementation modes.

[0009] The method for regenerating cotton pulp using waste textiles comprises the following steps: S1. Immersing or immersing the waste textile in an aqueous sodium hydroxide solution containing hydrogen peroxide under stirring; S2, immersing the product obtained in S1 in an alkaline hydrogen peroxide solution or immersing it under stirring; S3, immersing the product obtained in S2 in a polar solvent or immersing it under stirring; S4. Immerse the product obtained in S3 in an acidic aqueous solution or immerse it in an acidic aqueous solution under stirring.

[0010] After each impregnation, the liquid of the previous step is squeezed out, that is, solid-liquid separation is performed to collect the solid part for the next treatment step. Whether to stir during the impregnation process can be selected according to the equipment and the weight of the object to be treated. The stirring rate does not affect the treatment effect, and the purpose is to ensure sufficient impregnation.

[0011] From the above description, it can be seen that the beneficial effect of the present invention is that: the method provided by the present invention first uses a sodium hydroxide aqueous solution containing hydrogen peroxide for alkali treatment to first remove part of the dyes on the cotton cellulose and the polyester fiber, then performs a bleaching treatment in an alkaline hydrogen peroxide solution to further remove the dyes on the cotton fiber, then undergoes a polar solvent treatment to remove the residual dyes on the cotton fiber, and finally uses an acidic aqueous solution to treat and remove metal ions, thereby obtaining a cotton pulp with a degree of polymerization of 500 to 800, a whiteness of ≥72%, a cellulose methyl content of ≥95%, an iron ion content of ≤15 ppm, and no residual polyester components. In the entire treatment process, the order of the steps is crucial and cannot be adjusted arbitrarily. They must be performed in sequence. For example, bleaching treatment cannot be performed first and then alkali treatment can lead to incomplete removal of dyes, affecting whiteness and other problems.

[0012] Furthermore, the waste textiles are polyester-cotton fabrics dyed with reactive dyes.

[0013] From the above description, it can be seen that the method provided by the present invention has a good treatment effect on polyester-cotton fabrics dyed with reactive dyes, but can also be used for polyester-cotton fabrics dyed with indigo dyes.

[0014] Furthermore, S1 specifically comprises: immersing or immersing the waste textile in a sodium hydroxide aqueous solution containing hydrogen peroxide at 130-180° C. for 1-5 hours, preferably at 140-160° C. for 1.5-3 hours, under stirring.

[0015] Furthermore, the concentration of sodium hydroxide in the sodium hydroxide aqueous solution containing hydrogen peroxide in S1 is 5-10wt%, and the concentration of hydrogen peroxide is 0.1-0.5wt%.

[0016] From the above description, it can be seen that selecting an appropriate alkali treatment process can ensure that part of the dye and polyester are removed without affecting the content of methyl cellulose.

[0017] Furthermore, S2 is specifically: immersing the product obtained in S1 or immersing it in an alkaline hydrogen peroxide solution at 50-100° C. for 1-2 hours under stirring.

[0018] Furthermore, the concentration of hydrogen peroxide in the alkaline hydrogen peroxide solution in S2 is 0.1-0.5wt%, and the pH of the alkaline hydrogen peroxide solution is 10-12.

[0019] It can be seen from the above description that bleaching treatment under the above conditions can ensure a good decolorization effect while reducing the oxidative degradation of cotton fibers.

[0020] Furthermore, S3 is specifically: immersing the product obtained in S2 in a polar solvent at 130-160° C. for 0.5-2 h or immersing it under stirring.

[0021] Furthermore, the polar solvent is N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAc).

[0022] From the above description, it can be seen that polar solvents such as DMF or DMAc will cause cotton cellulose to swell slightly, which can promote the dissolution and release of residual colored substances on cotton cellulose. At the same time, they have excellent dissolution effects on the residual chromogenic substances on cotton cellulose after alkali treatment and bleaching and decolorization, and can further remove the residual dyes on cotton fibers.

[0023] Furthermore, S4 specifically comprises: immersing the product obtained in S3 in an acidic aqueous solution at 30-50° C. for 30-40 minutes.

[0024] Furthermore, the pH value of the acidic aqueous solution is less than or equal to 2.

[0025] It can be seen from the above description that the above pH and treatment temperature can ensure the complete removal of metal ions, while avoiding the degradation of cotton fibers, which would result in substandard polymerization degree.

[0026] Embodiment 1: The method for regenerating cotton pulp using waste textiles comprises the following steps: S0. Add 10g each of blue, red and military green polyester-cotton blended fabrics into the reactor; Among them, the polyester-cotton blended fabrics of various colors are dyed with disperse dyes for polyester and reactive dyes for cotton, with a cotton content of 65% and a polyester content of 35%, and are woven fabrics with a gram weight of 160g / m 2 ; S1, then add 600g of sodium hydroxide aqueous solution containing hydrogen peroxide into the reactor, and treat at 150°C for 1.5h; Among them, the concentration of NaOH is 5wt%, and the concentration of H2O2 is 0.2wt%; S2, take 15g of the product obtained in S1, and treat it in 450g of a hydrogen peroxide solution with a pH of 12 at 90°C for 1h; The concentration of H2O2 in the hydrogen peroxide solution was 0.15wt%, and the pH was adjusted with sodium hydroxide; S3, taking 10 g of the product obtained in S2, treating it in 250 g of N,N-dimethylacetamide (DMAc) at 150°C for 1 h; S4. Take the product obtained in S3 and treat it in a sulfuric acid aqueous solution with a pH of 2 at 40° C. for 30 minutes.

[0027] Embodiment 2: S0. Add 10g each of blue, red and military green polyester-cotton blended fabrics into the reactor; Among them, the polyester-cotton blended fabrics of various colors are dyed with disperse dyes for polyester and reactive dyes for cotton, with a cotton content of 65% and a polyester content of 35%, and are woven fabrics with a gram weight of 160g / m 2 ; S1, then add 600g of sodium hydroxide aqueous solution containing hydrogen peroxide into the reactor, and treat at 150°C for 1.5h; Among them, the concentration of NaOH is 10wt%, and the concentration of H2O2 is 0.5wt%; S2, take 15g of the product obtained in S1, and treat it in 450g of a hydrogen peroxide solution with a pH of 12 at 90°C for 1h; The concentration of H2O2 in the hydrogen peroxide solution was 0.5wt%, and the pH was adjusted with sodium hydroxide; S3, take 10 g of the product obtained in S2 and treat it in 250 g of DMAc at 150 °C for 1 h; S4. Take the product obtained in S3 and treat it in a sulfuric acid aqueous solution with a pH of 2 at 40° C. for 30 minutes.

[0028] Embodiment 3: S0. Add 10g each of blue, red and military green polyester-cotton blended fabrics into the reactor; Among them, the polyester-cotton blended fabrics of various colors are dyed with disperse dyes for polyester and reactive dyes for cotton, with a cotton content of 65% and a polyester content of 35%, and are woven fabrics with a gram weight of 160g / m 2 ; S1, then add 600g of sodium hydroxide aqueous solution containing hydrogen peroxide into the reactor, and treat at 150°C for 1.5h; Among them, the concentration of NaOH is 5wt%, and the concentration of H2O2 is 0.2wt%; S2, take 15g of the product obtained in S1, and treat it in 450g of a hydrogen peroxide solution with a pH of 12 at 90°C for 1h; The concentration of H2O2 in the hydrogen peroxide solution was 0.5wt%, and the pH was adjusted with sodium hydroxide; S3, take 10g of the product obtained in S2 and treat it in 250g of DMF at 150°C for 1h; S4. Take the product obtained in S3 and treat it in a sulfuric acid aqueous solution with a pH of 2 at 40° C. for 30 minutes.

[0029] Embodiment 4: The method for regenerating cotton pulp using waste textiles comprises the following steps: S0. Add 10g each of blue, red and military green polyester-cotton blended fabrics into the reactor; Among them, the polyester-cotton blended fabrics of various colors are dyed with disperse dyes for polyester and reactive dyes for cotton, with a cotton content of 65% and a polyester content of 35%, and are woven fabrics with a gram weight of 160g / m 2 ; S1, then add 600g of sodium hydroxide aqueous solution containing hydrogen peroxide into the reactor and treat at 140°C for 3h; Among them, the concentration of NaOH is 10wt%, and the concentration of H2O2 is 0.1wt%; S2, taking the product obtained in S1, treating it in 450g of a hydrogen peroxide solution with a pH of 10 at 70°C for 1h; The concentration of H2O2 in the hydrogen peroxide solution was 0.1wt%, and the pH was adjusted with sodium hydroxide; S3, take the product obtained in S2 and treat it in 250g DMF at 130°C for 2h; S4. Take the product obtained in S3 and treat it in a sulfuric acid aqueous solution with a pH of 1 at 30° C. for 30 minutes.

[0030] Embodiment 5: The method for regenerating cotton pulp using waste textiles comprises the following steps: S0. Add 10g each of blue, red and military green polyester-cotton blended fabrics into the reactor; Among them, the polyester-cotton blended fabrics of various colors are dyed with disperse dyes for polyester and reactive dyes for cotton, with a cotton content of 65% and a polyester content of 35%, and are woven fabrics with a gram weight of 160g / m 2 ; S1, then add 600g of sodium hydroxide aqueous solution containing hydrogen peroxide into the reactor and treat at 160°C for 2h; Among them, the concentration of NaOH is 6wt%, and the concentration of H2O2 is 0.4wt%; S2, taking the product obtained in S1, treating it in 450g of a hydrogen peroxide solution with a pH of 11 at 50°C for 1h; The concentration of H2O2 in the hydrogen peroxide solution was 0.35wt%, and the pH was adjusted with sodium hydroxide; S3, take the product obtained in S2 and treat it in 250g DMAc at 140°C for 1.5h; S4. Take the product obtained in S3 and treat it in a sulfuric acid aqueous solution with a pH of 1.5 at 50° C. for 35 minutes.

[0031] Embodiment 6: The method for regenerating cotton pulp using waste textiles comprises the following steps: S0. Add 15g each of blue, red and military green polyester-cotton blended fabrics into the reactor; Among them, the polyester-cotton blended fabrics of various colors are dyed with disperse dyes for polyester and reactive dyes for cotton, with a cotton content of 65% and a polyester content of 35%, and are woven fabrics with a gram weight of 160g / m 2 ; S1, then add 800g of sodium hydroxide aqueous solution containing hydrogen peroxide into the reactor, and treat at 155°C for 2.5h; Among them, the concentration of NaOH is 8wt%, and the concentration of H2O2 is 0.3wt%; S2, taking the product obtained in S1, treating it in 500 g of a hydrogen peroxide solution with a pH of 12 at 100° C. for 1 h; The concentration of H2O2 in the hydrogen peroxide solution was 0.5wt%, and the pH was adjusted with sodium hydroxide; S3, take the product obtained in S2 and treat it in 300g DMF at 160°C for 0.5h; S4. Take the product obtained in S3 and treat it in a sulfuric acid aqueous solution with a pH of 2 at 40° C. for 40 minutes.

[0032] Embodiment 7: The only difference from Example 1 is that S1 is: 600 g of sodium hydroxide aqueous solution containing hydrogen peroxide is added into the reaction kettle, and the reaction is carried out at 180° C. for 1 hour.

[0033] Embodiment 8: The only difference from Example 1 is that S1 is: 600 g of sodium hydroxide aqueous solution containing hydrogen peroxide is added into the reaction kettle, and the reaction is carried out at 130° C. for 5 hours.

[0034] Comparative Example 1: The only difference from Example 1 is that in S1, the solution used for immersion is added with only NaOH but no H2O2, but the pH of the solutions used for immersion in the two methods is the same.

[0035] Comparative Example 2: The only difference from Example 1 is that the concentration of NaOH in S1 is 3%.

[0036] Comparative Example 3: The only difference from Example 1 is that the concentration of H2O2 in S2 is 0.05wt%.

[0037] Comparative Example 4: The only difference from Example 1 is that 250 g of anhydrous ethanol is used instead of DMAc in S3.

[0038] Comparative Example 5: The only difference from Example 1 is that 250 g of dimethyl sulfoxide (DMSO) is used instead of DMAc in S3.

[0039] Comparative Example 6: The only difference from Example 1 is that S3 is not performed, that is, after being treated with the hydrogen peroxide solution, it is directly treated in a sulfuric acid solution with a pH of 2.

[0040] Comparative Example 7: The only difference from Example 1 is that the raw material added in S1 is replaced by polyester / cotton interwoven denim of equal weight, the cotton fiber is dyed with indigo dye, the polyester fiber is not dyed, the polyester content is 30%, the cotton content is 70%, the woven fabric has a gram weight of 180g / m 2 , and no solvent treatment is performed.

[0041] The treatments described in all the above embodiments and comparative examples are all immersion, after which solid-liquid separation is performed, and the solid portion is taken for the next step of treatment.

[0042] The physical properties of the cotton pulp obtained in Examples 1 to 3 and Comparative Examples 1 to 7 were tested, and the results are shown in Table 1. The whiteness was tested in accordance with "FZ / T 50010.7-1998 Pulp for viscose fibers - Determination of whiteness"; the degree of polymerization was tested in accordance with "FZ / T 50010.3-2011 Pulp for viscose fibers - Determination of viscosity"; the cellulose alpha content was tested in accordance with "FZ / T50010.4-2011 Pulp for viscose fibers - Determination of cellulose alpha content"; the polyester residue was confirmed based on the infrared spectrum of the pulp, and the molecular structure of the polyester fiber contained a carbonyl absorption peak at 1720 cm- 1 The cellulose in cotton fiber has no absorption peak here. Therefore, according to the infrared spectrum of cotton pulp, the absorption peak at 1720 cm -1 Check whether there is an absorption peak at the location to confirm whether there is any polyester residue.

[0043] Table 1

[0044] In summary, the method for regenerating cotton pulp using waste textiles provided by the present invention can treat polyester-cotton blended fabrics dyed with reactive dyes and obtain good treatment effects. The waste polyester-cotton blended fabrics treated by the method of the present invention can be recycled to obtain cotton pulp with high whiteness (≥72%), no polymer residue, high type A cellulose content (≥95%) and low iron ion content (≤15ppm). Cotton pulp can partially replace wood pulp as a raw material for viscose or lyocell fibers, thereby realizing the recycling of resources and helping to further promote the green development of the industry.

[0045] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention specification, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for regenerating cotton pulp using waste textiles, characterized in that: The following steps are involved: S1. Immersing the waste textile in an aqueous sodium hydroxide solution containing hydrogen peroxide; S2, immersing the product obtained in S1 in an alkaline hydrogen peroxide solution; S3, immersing the product obtained in S2 in a polar solvent; S4. Immerse the product obtained in S3 in an acidic aqueous solution.

2. The method for regenerating cotton pulp from waste textiles according to claim 1, characterized in that: The waste textiles are polyester-cotton fabrics dyed with reactive dyes.

3. The method for regenerating cotton pulp from waste textiles according to claim 1, characterized in that: S1 specifically comprises: immersing the waste textile in a sodium hydroxide aqueous solution containing hydrogen peroxide at 130-180° C. for 1-5 hours.

4. The method for regenerating cotton pulp from waste textiles according to claim 1 or 3, characterized in that: The concentration of sodium hydroxide in the sodium hydroxide aqueous solution containing hydrogen peroxide in S1 is 5-10 wt %, and the concentration of hydrogen peroxide is 0.1-0.5 wt %.

5. The method for regenerating cotton pulp from waste textiles according to claim 1, characterized in that: S2 specifically comprises: immersing the product obtained in S1 in an alkaline hydrogen peroxide solution at 50-100° C. for 1-2 hours.

6. The method for regenerating cotton pulp from waste textiles according to claim 1 or 5, characterized in that: The concentration of hydrogen peroxide in the alkaline hydrogen peroxide solution in S2 is 0.1-0.5 wt %, and the pH of the alkaline hydrogen peroxide solution is 10-12.

7. The method for regenerating cotton pulp from waste textiles according to claim 1, characterized in that: S3 specifically comprises: immersing the product obtained in S2 in a polar solvent at 130-160° C. for 0.5-2 h.

8. The method for regenerating cotton pulp from waste textiles according to claim 1 or 7, characterized in that: The polar solvent is N,N-dimethylformamide or N,N-dimethylacetamide.

9. The method for regenerating cotton pulp from waste textiles according to claim 1, characterized in that: S4 is specifically as follows: immersing the product obtained in S3 in an acidic aqueous solution at 30-50° C. for 30-40 minutes.

10. The method for regenerating cotton pulp from waste textiles according to claim 1 or 9, characterized in that: The pH value of the acidic aqueous solution is less than or equal to 2.

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