Method for separating polyester and cotton from blended textiles

Abstract

The present disclosure provides a method for oxidizing cotton and retaining PET by chemical (hydrogen peroxide) and biological (oxidase) methods, thereby achieving the separation of cotton and PET in PET-cotton blends. The method provides a green, non-toxic and energy-saving treatment method for cotton / PET blended fabrics.

Description

Technical Field

[0001] The present disclosure relates to a method for separating polyester (polyethylene terephthalate (PET)) and cotton from mixed textiles. More specifically, the present disclosure relates to a method for separating PET and cotton from mixed textiles through oxidation reaction. Background Art

[0002] Disposal of textile waste is a prominent issue, causing negative environmental impacts through landfill and incineration. In addition, mixed textile waste is challenging to recycle due to the different physical and chemical properties of the fibers.

[0003] To solve this problem, several separation methods of PET and cotton have been developed by selectively dissolving or degrading one of PET and cotton to achieve separation and reuse of the selected PET or cotton. These methods include degrading cotton by (i) using acid or microorganisms, or (ii) dissolving cotton with ionic liquids or N-methylmorpholine N-oxide, which is expensive. A method of depolymerizing polyester while retaining cotton using hydrolysis and alcoholysis of polyester has also been proposed. In the existing separation methods of PET-cotton mixed fabrics, cellulose and PET cannot be retained at the same time.

[0004] Green separation methods for PET-cotton blends are limited. Existing recycling or reuse methods may require organic / ionic solvents, high temperatures, or high costs. Moreover, the above methods have little impact on the recycled material by changing its inherent properties. Summary of the invention

[0005] Therefore, the object of the present disclosure is to provide a method for preparing a novel nanostructured carbon nanotube by chemical oxidation (based on H 2 O 2 The invention discloses a method for separating cotton and PET in PET-cotton blended fabrics by using oxidase (oxidation of laccase) and oxidase (laccase).

[0006] In a first aspect, the present invention provides a method based on H 2 O 2 The oxidation method is used for the oxidation of 2 O 2 The cotton was subjected to oxidation in the presence of 2,2,6,6-tetramethylpiperidinium-N-oxide (TEMPO) as a catalyst, so that the cotton fibers were changed into cotton powder, while PET remained in the fiber form during this process.

[0007] The present disclosure provides a method for separating PET and cotton in a PET-cotton blended fabric, comprising the following steps: contacting the blended fabric with hydrogen peroxide or an oxidase in the presence of TEMPO; wherein the method of contacting with hydrogen peroxide is referred to as a hydrogen peroxide method, and the method of contacting with an oxidase (e.g., laccase) is referred to as an oxidase method.

[0008] According to some embodiments, in the hydrogen peroxide method, the PET-cotton blended fabric is treated with hydrogen peroxide (H2O) at a concentration of 1% to 10% (v / H2O v). 2 O 2 ), in the presence of 0.1% to 5.0% (w / v) TEMPO, at a temperature of 55° C. to 65° C., pH 8 to 10, with stirring, the liquid ratio of the reaction system is 1:50 to 1:300, and the reaction time is 6-48 hours.

[0009] According to some embodiments, the concentration of hydrogen peroxide is 8% to 10%. According to some embodiments, the concentration of hydrogen peroxide is 10%.

[0010] According to some embodiments, the concentration of TEMPO is 0.5% to 2.0% (w / v). According to some embodiments, the concentration of TEMPO is 0.8% to 1.5% (w / v). According to some embodiments, the concentration of TEMPO is 0.1% to 1.0% (w / v). According to some embodiments, the concentration of TEMPO is 1.0% (w / v)

[0011] According to some embodiments, the pH value of the reaction system is 8 to 10. According to some embodiments, the pH value of the reaction system is 9 to 10. According to some embodiments, the pH value of the reaction system is 10.

[0012] According to some embodiments, the reaction time is 6-30 hours. According to some embodiments, the reaction time is 6-24 hours. According to some embodiments, the reaction time is 24 hours.

[0013] According to some embodiments, the reaction temperature is 60 to 65°C. According to some embodiments, the reaction temperature is 65°C.

[0014] According to some embodiments, the liquid ratio of the reaction system is 1:75 to 1:250. According to some embodiments, the liquid ratio of the reaction system is 1:100 to 1:200. According to some embodiments, the liquid ratio of the reaction system is 1:100 to 1:150. According to some embodiments, the liquid ratio of the reaction system is 1:100.

[0015] According to some embodiments, in the oxidase method, the PET-cotton blended fabric is incubated with an oxidase (e.g., laccase), the concentration of the enzyme is 0.5 to 55 mg / mL, the concentration of TEMPO is 3.75 mg / mL to 60 mg / mL, the working temperature of the enzyme is 20°C to 60°C, the pH range is 3 to 6, the liquid ratio of the reaction system is 1:50 to 1:300, and the reaction time is 2-72 hours.

[0016] According to some embodiments, the weight ratio of oxidase to TEMPO is 0.5-8: 1. According to some embodiments, the weight ratio of oxidase to TEMPO is 1-4: 1. According to some embodiments, the weight ratio of oxidase to TEMPO is 1-3: 1. According to some embodiments, the weight ratio of oxidase to TEMPO is 2: 1.

[0017] According to some embodiments, the oxidase is laccase.

[0018] According to some embodiments, the concentration of the oxidase is 25 to 50 mg / mL. According to some embodiments, the concentration of the oxidase is 30 to 45 mg / mL. According to some embodiments, the concentration of the oxidase is 30 to 40 mg / mL. According to some embodiments, the concentration of the oxidase is 30 mg / mL.

[0019] According to some embodiments, the concentration of TEMPO is 7.5 to 30 mg / mL. According to some embodiments, the concentration of TEMPO is 10 to 22.5 mg / mL. According to some embodiments, the concentration of TEMPO is 15 mg / mL.

[0020] According to some embodiments, the operating temperature of the oxidase is 40°C to 60°C. According to some embodiments, the operating temperature of the oxidase is 40°C to 55°C. According to some embodiments, the operating temperature of the oxidase is 40°C to 50°C.

[0021] According to some embodiments, the working pH of the oxidase is 3 to 4. According to some embodiments, the working pH of the oxidase is 4 to 5. According to some embodiments, the working pH of the oxidase is 4 to 4.5. According to some embodiments, the working pH of the oxidase is 4.

[0022] According to some embodiments, in the oxidase method, the liquid ratio of the reaction system is 1:50-1:250. According to some embodiments, in the oxidase method, the liquid ratio of the reaction system is 1:100-1:200. According to some embodiments, in the oxidase method, the liquid ratio of the reaction system is 1:100-1:150. According to some embodiments, in the oxidase method, the liquid ratio of the reaction system is 1:100.

[0023] According to some embodiments, the reaction time of the oxidase method is 5 to 50 hours. According to some embodiments, the reaction time of the oxidase method is 8 to 48 hours. According to some embodiments, the reaction time of the oxidase method is 8 to 36 hours. According to some embodiments, the reaction time of the oxidase method is 36 hours. According to some embodiments, the reaction time of the oxidase method is 8 hours.

[0024] In some embodiments, H is studied by a gradient from 1% to 10% (v / H2O v).2 O 2 In the reaction, H 2 O 2 Decomposes and generates a hydroxyl radical, which attacks the carbon atom on the cellulose, causing the hydroxyl to form a carboxyl group. Therefore, the cellulose fibers are cut into cellulose powder to achieve separation purposes.

[0025] In some embodiments, H 2 O 2 The oxidation capacity of TEMPO was catalyzed by TEMPO, and the catalytic effect of TEMPO was studied by varying its concentration from 0.1% to 5.0% (w / H2O v).

[0026] In some embodiments, the effect of temperature on separation efficiency was studied by varying the reaction temperature from 55°C to 65°C.

[0027] In some embodiments, due to pH and H 2 O 2 The decomposition rates of were highly correlated, so the pH effect was elucidated by changing the reaction from pH 8 to pH 10.

[0028] In some embodiments, the relationship between separation efficiency and reaction time is studied.

[0029] In some embodiments, the liquid ratio is varied from 1:50 to 1:200 to verify the reaction behavior and separation performance.

[0030] In some embodiments, the cotton powder and PET fibers are separated by simple filtration, followed by washing and drying. The separation efficiency is defined as the weight percentage of the separated product (cotton or PET) collected to the cotton or PET in the original textile.

[0031] In some embodiments, the separated cotton and PET are further identified and characterized by FTIR and SEM to show the quality and purity of the products.

[0032] The oxidase method provided herein can utilize the laccase / TEMPO system. In short, the laccase from Aspergillus is selected to implement the method. In the presence of the catalyst TEMPO, the laccase acts as an oxidant to selectively oxidize the cellulose fibers into cellulose powder. The presence of oxygen in the air can cause the oxidation of the laccase, followed by the oxidation of the hydroxyl groups on TEMPO and cellulose, thereby forming cellulose powder, while PET still exists in the form of fibers.

[0033] In some embodiments, the concentration of laccase varies from 0.5 to 45 mg / mL.

[0034] In some embodiments, the effect of TEMPO catalytic ability is demonstrated by a weight ratio of laccase to TEMPO of 0.5 to 8:1 (wt / wt).

[0035] In some embodiments, the oxidation reaction by oxidase is studied by varying the reaction temperature from room temperature to 55°C.

[0036] In some embodiments, the reaction time is monitored for 4 hours to 3 days to demonstrate the extent of separation.

[0037] In some embodiments, the pH of the reaction is varied between 4 and 6 to investigate the effect of pH.

[0038] In some embodiments, the liquid ratio is varied from 1:50 to 1:200 to investigate the reaction behavior and separation performance.

[0039] In some embodiments, the cotton powder and PET fibers are separated by simple filtration, followed by washing and drying. The separation efficiency is defined as the weight percentage of the collected separation product (cotton or PET) and the cotton or PET in the original textile.

[0040] In some embodiments, the separated cotton and PET are further identified and characterized by FTIR and SEM to show the quality and purity of the product.

[0041] A textile with a ratio of PET / cotton = 52:48 (wt / wt) was used as a test sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present disclosure is described in detail below with reference to the accompanying drawings.

[0043] Figure 1 The results show that in the hydrogen peroxide method, under the conditions of 0.1% TEMPO (w / H2O v), pH 10, 55°C, liquid ratio 1:100, and 24 hours of reaction, H 2 O 2 Relationship between concentration and separation efficiency.

[0044] Figure 2 It shows that in the hydrogen peroxide method, at 55°C, 10% H 2 O 2 Effects of pH and reaction time on separation under the conditions of 1:100 liquid ratio and 0.1% TEMPO (w / H2O v).

[0045] Figure 3 It is shown that in the hydrogen peroxide method, at pH 8, 10% H 2 O 2The effect of temperature on separation under the conditions of (v / H2O v), 1% TEMPO (w / H2O v), liquid ratio of 1:100, and 24h reaction.

[0046] Figure 4 It is shown that in the hydrogen peroxide method, at pH 8, 55°C, 10% H 2 O 2 The relationship between TEMPO concentration and separation efficiency under the conditions of (v / H2O v), liquid ratio of 1:100, and 24 h reaction time.

[0047] Figure 5 The results show that the reaction was carried out at pH 8 and 65 °C for 24 hours using 10% H 2 O 2 The effect of 1% TEMPO on the liquid ratio on the separation efficiency.

[0048] Fig. 6A Photographs and SEM images of fibers (PET) and powder (cellulose) separated in the hydrogen peroxide process are shown.

[0049] Figure 6B Fourier transform infrared (FTIR) spectra of fibers and powder separated in the hydrogen peroxide process are shown exemplarily, and compared with the spectra of their raw materials.

[0050] Figure 7 The effect of laccase concentration on separation in an oxidation reaction performed at 40°C, pH 4, laccase:TEMPO = 1:1 (wt / wt), liquid ratio 1:200, for 72 hours is shown.

[0051] Figure 8 The catalytic effect of TEMPO in the laccase oxidation system was shown, wherein the concentration of laccase was kept at 30 mg / mL, and the reaction was carried out at 40°C and pH 4 for 8 hours to maintain the optimal concentration of laccase.

[0052] Fig. 9 The effect of temperature on the laccase oxidation system is shown at a laccase to TEMPO ratio of 2:1 (wt / wt) at 40°C and pH 4 for 72 h.

[0053] Fig.10 The relationship between the reaction time and the separation efficiency of the laccase oxidation system is shown, and the separation efficiency was monitored from 2 to 48 hours under the optimal conditions.

[0054] Fig.11 The effect of pH in oxidase separations is shown (pH 4 to 6).

[0055] Fig.12 The relationship between the liquid ratio and the separation efficiency in the oxidase method is shown.

[0056] Fig.13A Photographs and SEM images of oxidase-separated fibers (PET) and powder (cellulose) are shown.

[0057] Fig. 13B Fourier transform infrared (FTIR) spectra of oxidase-separated fibers and powders are shown and compared with the spectra of their raw materials.

[0058] Detailed description

[0059] The scope of the present disclosure is not limited by any specific embodiments described herein.The following embodiments are described only as examples.

[0060] The separation method disclosed in the present invention is developed for the separation of PET-cotton blends. It involves two mentioned mechanisms, including a hydrogen peroxide system and an oxidase system, to slightly change the cellulose fibers into cellulose powder, and achieve green separation and recovery of these materials by simple filtration.

[0061] In the present disclosure, the above two separation methods have great potential to separate different ratios of PET-cotton blends through these no-pretreatment and no-selection methods.

[0062] The hydrogen peroxide method and the oxidase method mentioned both involve oxidation of cellulose in the presence of a catalyst TEMPO to produce short cellulose fibers. Thus, the long PET fibers can be separated from the short cotton fibers by simple filtration.

[0063] These separation methods are not limited to the ratio of cotton to PET, and fabrics of any ratio of these two materials can be converted into cellulose powder and PET fibers by the above method.

[0064] In the hydrogen peroxide method, the cotton-PET blend is simply placed in H 2 O 2 -TEMPO solution, and then the oxidation reaction of cotton was started under mild heating and stirring. 2 O 2 The color of the -TEMPO solution changed from orange to colorless, indicating the completion of the reaction.

[0065] H 2 O 2 It plays an important role in controlling separation efficiency. Figure 1 As shown, with H 2 O 2 The separation efficiency increases with the increase of H concentration (especially from 8% to 10%). 2 O 2 The rapid decomposition of 2 O 2Complete separation can be achieved.

[0066] In the hydrogen peroxide separation, pH also affects H 2 O 2 Decomposition of. Figure 2 As shown in Figure 2, by comparing the overall performance of the separation system under different pH conditions, the decomposition at pH 10 is always better than that at pH 9 and pH 8. 2 O 2 The decomposition of is pH dependent, with higher pHs causing faster decomposition. Therefore, higher pHs favor the reaction.

[0067] like Figure 2 As shown, the optimal reaction time for hydrogen peroxide separation is 24h, and the fabric can be completely separated.

[0068] The effect of temperature on the separation efficiency of the hydrogen peroxide method is that the separation efficiency increases with temperature. Figure 3 As shown, the temperature increased from 55°C to 65°C and TEMPO increased from 0.1% to 1%, allowing the separation to occur at pH 8 (a more neutral environment), which provides more energy to initiate the oxidation reaction. In addition, the increase in TEMPO, i.e., free radicals, also catalyzes the oxidation reaction. In the presence of hydrogen peroxide, TEMPO first transfers to the nitro cation and then forms hydroxylamine. TEMPO goes through its reaction cycle and continues to induce the decomposition of H2O2. The optimal reaction temperature is 65°C.

[0069] The role of TEMPO in the hydrogen peroxide method is clear. Figure 4 As shown, the presence of TEMPO increases the separation efficiency from 0.1% to 1%, however, excess TEMPO inhibits the separation by hydrogen peroxide method.

[0070] The liquor ratio, i.e. the ratio of fabric weight to solvent (e.g. water) weight, is optimized for the hydrogen peroxide process to maximize reactivity and minimize cost. Figure 5 As shown in the figure, for a liquid ratio less than 1:100, the separation efficiency is reduced by 50%, which clearly indicates that there is insufficient solvent. However, when the sample is incubated in the solution at 1:100 and 1:200, the separation efficiency remains 100%. Therefore, a liquid ratio of 1:100 is selected, which maintains high separation efficiency and minimizes solvent (separation agent) consumption.

[0071] Microscopic images were captured by SEM. At pH 8, there was little damage to the PET fibers, showing excellent performance in maintaining the original PET fibers. The separated cellulose powder and PET fibers were characterized by SEM. After the oxidation reaction, the surface of the PET fibers remained smooth, while the cotton became short cellulose fragments. Fig. 6A shown.

[0072] The separated cellulose powder and PET were identified by FTIR. The separated fibers were identified as pure PET, and the separated powder was identified as pure cotton, such as Figure 6B shown.

[0073] In the oxidase method, the biological enzyme laccase is applied to the chemical enzymatic modification of cellulose. In the presence of TEMPO as a mediating substance, cellulose fibers are oxidized into small cellulose powders under mild aqueous conditions. In this aerobic reaction, laccase induces TEMPO oxidation, and the oxidized TEMPO then reacts with cellulose. At the same time, TEMPO+ is continuously regenerated by reacting with laccase, so C6 on cellulose continues to oxidize until all cellulose is oxidized to form cellulose powder. The PET fiber remains unchanged in the reaction of the oxidase.

[0074] First, the concentration of laccase was optimized by varying the concentration from 0.5 mg / mL to 45 mg / mL. Figure 7 As shown, the separation efficiency increased significantly with the increase of laccase concentration until its concentration reached 30 mg / mL. This shows that laccase concentration is one of the key factors for the oxidase separation. 30 mg / mL laccase is the optimal concentration for this reaction.

[0075] The weight ratio of laccase to TEMPO also affects the separation efficiency. Figure 8 As shown, small changes in the ratio have a large impact on the separation performance in the oxidase separation. The preferred weight ratio of laccase to TEMPO is 2:1, which helps to further improve the separation efficiency of 30 mg / mL laccase solution and promote the complete separation of cotton / PET mixture.

[0076] like Fig. 9 As shown, the oxidase showed consistency in separation efficiency at a working temperature range of 40°C to 55°C. The temperature of 40°C to 50°C is considered to be the optimal reaction temperature for this separation system, which matches the properties of laccase, and the enzyme activity is highest in this temperature range.

[0077] For the oxidase reaction, lowering the temperature from 40°C to room temperature resulted in low laccase activity and required additional reaction time to complete the separation.

[0078] Monitoring of oxidase separations, such as Fig.10 As shown, complete separation was found at 8 h, indicating that this method can achieve rapid separation.

[0079] The pH value affects the properties of the enzyme (laccase). The present disclosure studies the effect of pH on the system of oxidase. Fig.11 As shown, separation occurs between pH 4 and 6, for example between pH 4 and 5. The optimum pH is believed to be pH 4, and an increase in pH affects the degree of separation. This may be due to the loss of enzyme activity at high pH.

[0080] Similar to the previous hydrogen peroxide reactions, the liquid ratios for the oxidase separations were investigated to minimize reagent consumption. Fig.12 As shown, the separation efficiency is optimized at different liquid ratios, where the liquid ratio is between 1:50 and 1:200, and the optimal liquid ratio is 1:100, which can achieve complete separation with minimal reagent consumption.

[0081] The PET and cellulose powders separated by the oxidase reaction were subjected to SEM imaging and FTIR analysis, and the results are shown in Fig.13A and Fig. 13B The results were similar to those of the hydrogen peroxide method, showing a high degree of consistency between the two reactions.

[0082] The present disclosure selects PET-cotton (52:48 weight ratio) blend as an example to demonstrate the success of the hydrogen peroxide separation method. DETAILED DESCRIPTION

[0083] The separation methods disclosed herein are described below by way of example, but are not intended to be limiting in any way.

[0084] Example 1

[0085] Hydrogen Peroxide Method

[0086] 1 kg of TEMPO and 100 L of 10% HO were added. 2 O 2 Mixed with 1 kg of the textile to be treated (cotton and PET mixed ratio of 52:48), stirred for 24 hours under the conditions of pH 8, 65°C, and liquid ratio of 1:100, then filtered to separate the cotton powder and PET fibers. After washing and drying, 0.52 kg of PET and 0.48 kg of cotton powder were obtained respectively. Photos and SEM images of separated PET fibers and cotton powder (cellulose) are shown in Fig. 6A , Fourier transform infrared (FTIR) spectrum and its comparison with the spectrum of raw materials see Figure 6B .

[0087] Example 2

[0088] Oxidase method

[0089] 15 mg / mL TEMPO and 30 mg / mL laccase were mixed with 1 kg of the textile to be treated (the mixing ratio of cotton to PET was 52:48), stirred for 8 h at 40 °C, pH 4, and a liquid ratio of 1:100, and then filtered to separate the cotton powder and PET fibers. After washing and drying, 0.52 kg of PET and 0.48 kg of cotton powder were obtained, respectively. Photos and SEM images of the separated PET fibers and cotton powder (cellulose) are shown in Fig.13A, Fourier transform infrared (FTIR) spectrum and its comparison with the spectrum of raw materials see Fig. 13B .

[0090] Industrial Applicability

[0091] The method provided by the present disclosure is a fast, energy-saving and non-toxic separation method for cotton-PET mixtures. The separated PET still has good properties and can be directly reused in the textile industry, while the cellulose powder becomes a short fiber form that can be spun into long fibers and filaments for future use.

Claims

1. A method for separating and obtaining PET and cotton from a PET-cotton blended fabric, characterized in that: The method comprises the following steps: in the presence of TEMPO, the blended fabric is contacted with hydrogen peroxide or oxidase to generate an oxidation reaction; the method of contacting with hydrogen peroxide is called a hydrogen peroxide method, and the method of contacting with oxidase is called an oxidase method, wherein in the hydrogen peroxide method, the weight volume ratio concentration of TEMPO is 0.8% to 1.5%; in the oxidase method, the oxidase is laccase, and the weight ratio of the oxidase to TEMPO is 1-3:

1.

2. The method according to claim 1, characterized in that In the hydrogen peroxide method, a PET-cotton blended fabric is treated with hydrogen peroxide having a volume ratio concentration of 1% to 10% in the presence of TEMPO at a temperature of 55°C to 65°C, a pH of 8 to 10, with stirring, a liquid ratio of the reaction system of 1:50 to 1:300, and a reaction time of 6 to 48 hours.

3. The method according to claim 1 or 2, characterized in that: In the hydrogen peroxide method, the concentration of hydrogen peroxide is 8% to 10%; or the pH is 9 to 10; or the reaction time is 6-24 hours; or the reaction temperature is 60-65° C.; or the liquid ratio is 1:100 to 1:

200.

4. The method according to claim 3, characterized in that In the hydrogen peroxide method, the concentration of hydrogen peroxide is 10%; or the concentration of TEMPO is 1.0%; or the pH is 10; or the reaction time is 24 hours; or the reaction temperature is 65° C.; or the liquid ratio is 1:

100.

5. The method according to claim 1, characterized in that In the oxidase method, PET-cotton blended fabric is incubated with oxidase, the concentration of the oxidase is 0.5 to 55 mg / mL, the weight-to-volume concentration of TEMPO is 3.75 mg / mL to 60 mg / mL, the working temperature of the oxidase is 20°C to 60°C, the pH range is 3 to 6, the liquid ratio of the reaction system is 1:50 to 1:300, and the reaction time is 2-72 hours.

6. The method according to claim 5, characterized in that The concentration of the oxidase is 25-50 mg / mL; or the working temperature of the oxidase is 40° C. to 55° C.; or the pH range of the reaction system is 4 to 5; or the liquid ratio of the reaction system is 1:100-1:200; or the reaction time is 8 to 48 hours.

7. The method according to claim 5, characterized in that The concentration of the oxidase is 30 mg / mL; or the working temperature of the oxidase is 40° C. to 50° C.; or the pH range of the reaction system is 4; or the liquid ratio of the reaction system is 1:100; or the reaction time is 8 hours.

8. The method according to claim 1, characterized in that In the oxidase method, the weight ratio of the oxidase to TEMPO is 2:1.

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