A method for efficient gradient pulping recycling and reuse of waste cotton textiles and preparation of functional fibers.

Abstract

This invention discloses a method for the efficient gradient pulping recycling and reuse of waste cotton textiles and the preparation of functional fibers. This invention belongs to the field of textile printing and dyeing processing. After being cut, waste cotton textiles undergo pre-impregnation with chemical agents, followed by gradient pulping treatment using a disc mill and a Walli beater, and bleaching to obtain cotton pulp fibers prepared from waste cotton textiles. This invention uses the various mechanical forces generated by the pulping machine to cause certain physical changes in the fibers, further refining, swelling, kneading, and crushing them, promoting the formation of individual fibers. Further bleaching removes color and other impurities to achieve fiber whiteness. Pulping increases the hydrogen bonding force between fibers, improving the strength and softness of the paper sheet, meeting the requirements for normal papermaking. Simultaneously, the high-quality cellulose obtained after treatment can be further chemically modified to prepare functional cellulose, providing more directions for cellulose reuse.

Description

Technical Field

[0001] This invention belongs to the field of textile printing and dyeing processing, specifically relating to a method for efficient gradient pulping recycling and reuse of waste cotton textiles and preparation of functional fibers. Background Technology

[0002] With the improvement of economic and living standards, people's consumption of clothing has increased rapidly, leading to a shortened lifespan of textiles and a large waste of textile waste. This waste not only wastes resources but also causes environmental pollution. In the past, textile waste was mainly disposed of through methods such as stockpiling, landfilling, and incineration. However, these methods have drawbacks: stockpiling waste occupies land and is prone to collapse; stockpiled waste exposed to the air accumulates dust and impurities, affecting environmental sanitation; under the action of rainwater, dyes and other harmful components on the textile waste leach out and seep into the ground, polluting groundwater. Landfilling, while not affecting the surface environment, leaves almost unusable sites in cities and incurs additional costs; due to the non-degradability of chemical fibers, especially synthetic fibers, landfilling chemical fiber waste causes soil compaction and hardening; similarly, harmful substances on the waste seep into the soil and groundwater with water, polluting the soil and groundwater. Burning waste textiles produces large amounts of dust and harmful gases that pollute the atmosphere, impacting environmental hygiene. Furthermore, the chemical fiber residues left after incineration are difficult to dispose of. Therefore, the recycling and reuse of waste textiles has become a key concern.

[0003] my country is the world's largest textile producer, accounting for over 50% of global textile fiber processing. Cotton textiles are popular due to the excellent moisture absorption, breathability, superior feel, and strength of cotton fibers. With the continuous increase in per capita fiber consumption, my country generates a large amount of waste textiles annually. The recycling of waste textiles is of great significance for resource conservation, pollution reduction, and carbon reduction. It is an important measure to effectively supplement the raw material supply of my country's textile industry, alleviate resource and environmental constraints, and is a crucial component of establishing a sound green, low-carbon, and circular economic development system. During the recycling and reuse of waste cotton textiles, the color of the textiles can affect their subsequent use. Therefore, it is necessary to avoid excessive depolymerization of cellulose during pulping.

[0004] Cotton pulp has a wide range of applications in many fields. Currently, the main raw materials for preparing cotton pulp come from waste cotton and cotton linters from the textile industry. This cotton pulp contains relatively pure cellulose, with long, thin, and elastic fibers that are tough, durable, and have good absorbency. The paper made from it is fine and soft, highly opaque, and can be preserved for a long time. It is used to manufacture banknotes and other high-value items; unbleached cotton pulp is used to manufacture steel paper base paper, etc.; bleached cotton pulp is mainly used to manufacture filter paper, absorbent paper, drawing paper, security paper, banknotes, and other high-grade printing papers. Due to its very high cellulose content, cotton pulp can also be used as a raw material for derivatives such as rayon, cellulose acetate, cellulose nitrate, and carboxymethyl cellulose.

[0005] In traditional pulping and papermaking, the pulp, after washing, bleaching, and purification, contains many fiber bundles that have not been refined using a disc refiner and Wallix beater. These fibers are too coarse and long, with a smooth, stiff, and elastic surface, a small specific surface area, and poor binding properties. If this uncrushed pulp is used directly for papermaking, it is difficult to distribute evenly on the wire, resulting in loose, porous paper with a rough, fuzzy surface, very low bonding strength, and extremely poor paper performance, thus failing to meet usage requirements. Therefore, it is necessary to design the pulping process based on the characteristics of waste cotton textile raw materials; there is an urgent need to develop methods for preparing cotton pulp specifically tailored to the characteristics of waste cotton textile raw materials, as well as methods for further chemically modifying the recovered cellulose to prepare functional cellulose. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing recycling and reuse technologies for waste cotton textiles and to overcome problems such as excessively coarse and long fibers, small specific surface area, and lack of binding energy in the traditional cotton pulp preparation process.

[0007] This invention proposes a novel method for preparing high-quality cotton pulp by using a refiner and a Wali refiner to refine the cotton pulp at different gradients, based on the use of clean cooking aids such as hydrogen peroxide, sodium hexametaphosphate, and benzoquinone as cooking aids. The high-quality cotton pulp is then further chemically modified to prepare functional cellulose.

[0008] To achieve the above objectives, this invention provides a method for preparing cotton pulp from waste cotton textiles using a gradient refining process with compound penetrating aids such as magnesium sulfate and sodium hexametaphosphate. The method involves obtaining high-quality cotton pulp through the refining action of a refiner and a Wali beater, followed by further modification treatment of the high-quality cotton pulp. The main contents include the following steps:

[0009] (1) Disperse the cotton pulp after cooking and decolorizing waste cotton textiles in an aqueous solution containing magnesium sulfate, sodium hexametaphosphate, and benzoquinone to obtain a mixed system, and soak it thoroughly for 30-60 minutes. Filter the soaked cloth pieces through a perforated sieve, remove them, drain the water, and then grind and pulp the cloth pieces using a Walley pulper and a disc mill. After filtration through a sieve, collect the pulped cotton fibers, bleach them, and dry them to obtain high-quality cotton pulp prepared from waste cotton textiles. Disperse the obtained high-quality cotton pulp in DMAC and fully activate it. Add an appropriate amount of anhydrous lithium chloride and stir thoroughly. After the fibers are completely dissolved, cool to 8°C and add a mixture of DMAC and triethylamine. Then, add dropwise a DMAC solution containing p-toluenesulfonic acid acyl chloride and stir at 8°C for 24 hours to obtain TsCell. Dissolve the obtained TsCell in DMSO, add ethylenediamine to the system and stir for 6 hours. The product precipitates in acetone, washes with ethanol and dries to obtain NCell.

[0010] Furthermore, in step (1), the amount of magnesium sulfate used accounts for 0.5-10% of the mass fraction of waste cotton textiles by weight percentage.

[0011] Furthermore, in step (1), the amount of sodium hexametaphosphate used accounts for 0.01-5% of the mass fraction of waste cotton textiles by weight percentage.

[0012] Further, in step (1), the solid-liquid ratio of the mixed system is 1:4-20 by weight percentage.

[0013] Furthermore, during gradient grinding in step (1): the slits of the disc mill are 2.0 mm, 0.5 mm, and 0.1 mm, respectively; the Wali pulper is used for 3 min, 10 min, and 15 min, respectively. The Wali pulper and the mill are used for continuous processing for 2-20 minutes in sequence.

[0014] Furthermore, step (1) also includes bleaching the pulp after it has been ground by a pulper and a Wali pulper with hydrogen peroxide. The amount of hydrogen peroxide used accounts for 2-10% of the mass fraction of waste cotton textiles. The treatment temperature is 60-90℃ and the treatment time is 60 minutes.

[0015] Furthermore, in step (1), the solid-liquid ratio of the mixed system during hydrogen peroxide bleaching is 1:4-20 by weight percentage.

[0016] Further, in step (1), the molar ratio of cellulose glucose unit to p-toluenesulfonyl chloride is 1:1-2.

[0017] Further, in step (1), the mass-to-volume ratio of lithium chloride to high-quality cotton pulp is 1 mL / 1 g; the mass ratio of triethylamine to high-quality cotton pulp is 2:1; and the molar ratio of ethylenediamine to TsCell is 25:1.

[0018] Furthermore, in step (1), the reaction temperature is 100°C and the time is 6 hours.

[0019] Beneficial effects

[0020] This invention discloses a method for the efficient gradient pulping recycling and reuse of waste cotton textiles and the preparation of functional fibers, which has at least the following advantages compared with the prior art:

[0021] (1) The present invention discloses a method for efficient gradient pulping recycling and reuse of waste cotton textiles and a method for preparing functional fibers. The fibers undergo a certain amount of physical changes under the mechanical action of a disc mill and a Wali pulping machine, which further refines, swells, rubs and crushes them, and promotes the fuzzing of individual fibers (increases the surface area of ​​the fibers).

[0022] (2) The present invention can increase the hydrogen bonding force between fibers through pulping, which can improve the strength and softness of the paper sheet and meet the requirements of normal papermaking;

[0023] (3) The present invention can adjust the grinding specific pressure according to the grinding raw materials and grinding quality process requirements, while taking into account the cutting of fibers and the internal friction of fibers, so as to make the fibers separate into bristles, thereby achieving stable high-concentration grinding quality and energy-saving effect.

[0024] (4) The product obtained by this invention is close to the performance requirements of traditional pulping products, reduces pulping energy consumption, and is conducive to the development of subsequent recycling processes such as pulping of waste cotton textiles.

[0025] (5) The functional cellulose obtained by this invention can be further synthesized with other products, which is beneficial to the reuse of waste cotton textiles. Attached Figure Description

[0026] Figure 1 The process flow for recycling and pulping waste cotton textiles.

[0027] Figure 2 shows the effect of different refining methods on fiber morphology; (a) refining with a Wali refining machine for 30 min; (b, c) the effect of refining machine spacing of 2 mm and 1 mm on cotton fiber morphology; (d) fiber state under an optical microscope after refining with a Wali refining machine for 30 min; (ef) fiber state under an optical microscope after refining machine spacing of 2 mm and 1 mm; (gi) white light photographs of air-dried pulp after different refining methods.

[0028] Figure 3 Microscopic images showing the effects of different refining slits and beating times on fiber morphology. (ac) Refining slits of the disc mill were 2.0 mm, 0.5 mm, and 0.1 mm, respectively; (df) Beating times of the Walley beater were 3 min, 10 min, and 15 min, respectively.

[0029] Figure 4 SEM images showing the effects of different refining slits and beating times on fiber morphology: (ac) disc mill refining slits are 2.0 mm, 0.5 mm, and 0.1 mm; (df) Walley beater beating times are 3 min, 10 min, and 15 min.

[0030] Figure 5 This diagram illustrates the process of preparing functional fibers from recycled cotton pulp.

[0031] Figure 6 The image shows the infrared spectrum of TsCell.

[0032] Figure 7 This is an NCell infrared spectrum. Detailed Implementation

[0033] The present invention will now be described in detail. Before proceeding with the description, it should be understood that the terminology used in this specification and the appended claims should not be construed as limited to its general or dictionary meaning, but rather should be interpreted according to the meaning and concept corresponding to the technical aspects of the invention, based on the principle that the inventors are allowed to appropriately define the terminology for the best interpretation. Therefore, the description presented herein is merely illustrative of preferred examples and is not intended to limit the scope of the invention; thus, it should be understood that other equivalents or modifications can be obtained therefrom without departing from the spirit and scope of the invention.

[0034] The following examples further illustrate the outstanding advantages and significant features of the present invention, but the present invention is by no means limited to the following examples and does not constitute any limitation on the present invention. Those skilled in the art will understand that modifications that do not depart from the spirit and concept of the present invention fall within the protection scope of the present invention. Unless otherwise specified, the reagents and instruments used in the following examples are all commercially available products.

[0035] The basic procedure of this invention is as follows: After washing and drying waste cotton textiles, buttons, zippers, and other accessories are removed; the textiles are cut into 5 cm × 5 cm pieces and placed in a resealable bag overnight (to balance moisture), and the moisture content is tested. 0.5 kg of the oven-dry waste cotton textile pieces are weighed and prepared; a 30 g / L sodium hydroxide solution is prepared and prepared. The textile pieces are thoroughly soaked in 5-10 times their volume of water, with 0.2-10% hydrogen peroxide, 0.01-5% sodium hexametaphosphate, and 0.01-0.5% benzoquinone added, and soaked for 30-60 minutes. Then, sodium hydroxide is added to a concentration of 20-60 g / L, and the volume is adjusted to 5 L. The solution is then transferred to a pressure-resistant digester and kept at a constant temperature for 0.5-3 hours. After the digester is closed, the solution is diluted with water, washed, and filtered through a perforated sieve. Further grinding is performed using a mill at different gradients, followed by sieve filtration to obtain high-quality cotton pulp. High-quality cotton pulp (1.0 g) was dispersed in DMAC and activated at 160°C. The mixture was then cooled to 100°C, and an appropriate amount of anhydrous lithium chloride (2.0 g) was added. After thorough stirring and cooling to room temperature until the high-quality cotton pulp was completely dissolved, the cellulose solution was cooled to 8°C. A mixture of DMAC (2.1 ml) and triethylamine (3 ml) was added, followed by dropwise addition of a DMAC solution containing p-toluenesulfonyl chloride (2.118 g). The mixture was stirred at 8°C for 24 hours. The product was poured into 150 ml of ice water to precipitate, and the mixture was filtered to obtain TsCell (cellulose p-benzenesulfonate). TsCell (1.0 g) was then dissolved in DMSO solution, and 25 molar amounts of ethylenediamine were added to the system. The mixture was stirred at 100°C for 6 hours and then cooled to room temperature. The product was precipitated in acetone, then washed with ethanol and dried to obtain NCell (aminocellulose).

[0036] Example 1

[0037] Weigh 0.5 kg of waste cotton textile fabric and soak it in a 2 L aqueous solution containing 2% hydrogen peroxide, 0.1% benzoquinone, and 1% sodium hexametaphosphate for half an hour. Then add sodium hydroxide to a concentration of 30 g / L, bring the volume to 5 L, and transfer it to a high-pressure reactor. Under rotating conditions, heat the reactor to 160°C at a rate of 4-6°C / min and maintain the temperature for 3 hours to carry out the oxidation, decolorization, and degradation reaction of the cotton fibers. After the reaction is complete, turn off the electric heater and rotary switch. After the reactor cools to room temperature, open the reactor and remove the reaction product. Filter the reaction product through a sieve to obtain cotton pulp fiber aggregates. Then, vacuum filter the remaining mixture through a filter membrane to obtain cotton pulp fibers. The cotton pulp aggregates are then processed by a refiner and a Wali beater to become reusable fiber raw materials. During gradient grinding, the Wali beater and refiner are processed sequentially and continuously. The disc mill slits were 2.0 mm, 0.5 mm, and 0.1 mm respectively, and the treatment time was 5 minutes; the Wali pulper was used for pulping for 3 minutes, 10 minutes, and 15 minutes respectively.

[0038] Example 2

[0039] Weigh 0.5 kg of waste cotton textile fabric and soak it in a 5 L aqueous solution containing 1% hydrogen peroxide, 0.5% benzoquinone, and 2% sodium hexametaphosphate for half an hour. Then add sodium hydroxide to 40 g / L, bring the volume to 5 L, and transfer it to a high-pressure reactor. Under rotating conditions, heat the reactor to 160℃ at a rate of 4-6℃ / min and maintain the temperature for 140 min to carry out the oxidation, decolorization, and degradation reaction of the cotton fibers. After the reaction is complete, turn off the electric heater and rotary switch. After the reactor cools to room temperature, open the reactor and remove the reaction product. Filter the reaction product through a sieve to obtain cotton pulp fiber aggregates. The cotton pulp aggregates are then processed by a refiner and a Wali beater to become reusable fiber raw materials. During gradient grinding, the Wali beater and refiner are processed sequentially and continuously. The disc mill slits were 2.0 mm, 0.5 mm, and 0.1 mm in sequence, and the treatment time was 2 minutes; the Wali pulper was used for pulping for 3 minutes, 10 minutes, and 15 minutes in sequence.

[0040] Example 3

[0041] Weigh 0.5 kg of waste cotton textile fabric and soak it in a 5 L aqueous solution containing 1% hydrogen peroxide, 0.5% benzoquinone, and 3% sodium hexametaphosphate for half an hour. Then add sodium hydroxide to 50 g / L, bring the volume to 5 L, and transfer it to a high-pressure reactor. Under rotating conditions, heat the reactor to 160℃ at a rate of 4-6℃ / min and maintain the temperature for 180 min to carry out the oxidation, decolorization, and degradation reaction of the cotton fibers. After the reaction is complete, turn off and rotate the switch. After the reactor cools to room temperature, open the reactor and remove the reaction product. Filter the reaction product through a sieve to obtain cotton pulp fiber aggregates. The cotton pulp aggregates are then mechanically processed by a refiner and a power beater with an electric heater to become reusable fiber raw materials. During gradient grinding, the power beater and refiner are processed sequentially and continuously. The slits for grinding pulp in the disc mill were 2.0 mm, 0.5 mm, and 0.1 mm respectively, and the treatment time was 10 minutes; the pulping machine in the Wali pulping machine was used for 3 minutes, 10 minutes, and 15 minutes respectively.

[0042] High-quality cotton pulp (1.0 g) was dispersed in DMAC and activated at 160°C. The mixture was then cooled to 100°C, and an appropriate amount of anhydrous lithium chloride (2.0 g) was added. After thorough stirring and cooling to room temperature until the high-quality cotton pulp was completely dissolved, the cellulose solution was cooled to 8°C. A mixture of DMAC (2.1 ml) and triethylamine (3 ml) was added, followed by dropwise addition of a DMAC solution containing p-toluenesulfonyl chloride (2.118 g). The mixture was stirred at 8°C for 24 hours. The product was poured into 150 ml of ice water to precipitate, and the mixture was filtered to obtain TsCell (cellulose p-benzenesulfonate). TsCell (1.0 g) was then dissolved in DMSO solution, and 25 molar amounts of ethylenediamine were added to the system. The mixture was stirred at 100°C for 6 hours and then cooled to room temperature. The product was precipitated in acetone, then washed with ethanol and dried to obtain NCell (aminocellulose).

[0043] Figure 1 The process flow for recycling and pulping waste cotton textiles involves: first, pre-treatment of the waste textiles, followed by gradient pulping, and then bleaching to obtain high-quality fibers.

[0044] Figure 2 To investigate the effects of different refining methods on fiber morphology, cotton fibers were pulped and refined using a Wali beater and a refiner, respectively, and the morphological changes were observed under a microscope. (a) Wali beater pulping for 30 min; (b, c) Effects of refiner spacing of 2 mm and 1 mm on cotton fiber morphology; (d) Fiber state under an optical microscope after Wali beater pulping for 30 min; (ef) Fiber state under an optical microscope with refiner spacing of 2 mm and 1 mm; (gi) White light photographs of air-dried pulp after different refining methods.

[0045] Figure 3 Microscopic images showing the effects of different refining slits and beating times on fiber morphology were obtained. Cooked cotton pulp was refined with slits of 2.0 mm, 0.5 mm, and 0.1 mm, and then beaten with a Walley beater for 3 min, 10 min, and 15 min, respectively. The pulp was then observed under a microscope. (ac) Disc mill refining slits: 2.0 mm, 0.5 mm, and 0.1 mm; (df) Walley beater beating times: 3 min, 10 min, and 15 min.

[0046] Figure 4 SEM images showing the effects of different refining slits and beating times on fiber morphology: (ac) disc mill refining slits were 2.0 mm, 0.5 mm, and 0.1 mm; (df) Walley beater beating times were 3 min, 10 min, and 15 min.

[0047] Figure 5For the preparation of functional fibers from recycled cotton pulp, high-quality cotton pulp (1.0 g) was dispersed in DMAC and fully activated at 160°C. The temperature was then lowered to 100°C, and an appropriate amount of anhydrous lithium chloride (2.0 g) was added. After thorough stirring and cooling to room temperature until the high-quality cotton pulp was completely dissolved, the cellulose solution was cooled to 8°C. A mixture of DMAC (2.1 ml) and triethylamine (3 ml) was added, followed by dropwise addition of a DMAC solution containing p-toluenesulfonyl chloride (2.118 g). The mixture was stirred at 8°C for 24 hours. The product was poured into 150 ml of ice water to precipitate and filtered to obtain TsCell. TsCell (1.0 g) was then dissolved in DMSO solution, and 25 molar amounts of ethylenediamine were added to the system. The mixture was stirred at 100°C for 6 hours and then cooled to room temperature. The product was precipitated in acetone, then washed with ethanol and dried to obtain NCell.

[0048] Figure 6 TsCell infrared spectrum, γ=2900 cm⁻¹ -1 The TsCell curve shows that the peak of the CH2 symmetric stretching vibration associated with the hydroxyl group is significantly weakened and broadened at this point, and at γ=1362 cm⁻¹. -1 and 1174 cm -1 A new peak appears; this is the absorption peak of SO2. At γ = 1597 cm⁻¹ -1 1500 cm -1 and 1456 cm -1 The new peak that appears is the C peak of the benzene ring in the p-toluenesulfonyl group, which indicates that the -OH part of cellulose is replaced by the p-toluenesulfonyl group.

[0049] Figure 7 The infrared spectrum of NCell is shown. NCell at γ=1320 cm⁻¹ -1 The SO2 absorption peak at γ = 3500~3000 cm⁻¹ weakens, and the absorption peak at γ = 3500~3000 cm⁻¹ decreases. -1 A new absorption peak appears, which is the absorption peak of the primary amine. Simultaneously, γ = 812 cm⁻¹. -1 The characteristic absorption peak of p-toluenesulfonate in cellulose was significantly weakened, indicating that NH2 substituted p-toluenesulfonyl group.

Claims

1. A method for efficient gradient refining recycling and reuse of waste cotton textiles and preparation of functional fibers, characterized by, It comprises the following steps: (1) washing, airing and cutting the waste cotton textiles into pieces; (2) dispersing the pieces in a water solution system containing magnesium sulfate, benzoquinone, sodium hexametaphosphate and hydrogen peroxide to obtain a mixed system, and then performing gradient grinding and pulping treatment on the pieces by pre-impregnation; during the gradient grinding, the grinding gap of the grinder is 2.0 mm, 0.5 mm and 0.1 mm respectively, and the beating gap of the Valli beater is 3 min, 10 min and 15 min respectively, and the grinder and the Valli beater are sequentially treated for 2-20 min; (3) filtering through a screen, collecting, bleaching, washing and airing the cotton fibers after grinding to obtain high-quality cotton pulp prepared from the waste cotton textiles; (4) chemically modifying the high-quality cotton pulp to obtain functional cellulose; the chemical modification comprises dispersing the cotton pulp in DMF, adding lithium chloride, then adding triethylamine, and then adding p-toluenesulfonic acid chloride dropwise, stirring at 8℃ to obtain cellulose p-toluenesulfonate, and then adding ethylenediamine to obtain amino cellulose; according to the molar ratio, the molar ratio of the cellulose glucose unit to the p-toluenesulfonic acid chloride is 1:1-2.

2. The production method according to claim 1, characterized by, According to the weight percentage, the amount of magnesium sulfate accounts for 0.5-10% of the mass fraction of the waste cotton textiles.

3. The preparation method according to claim 1, characterized in that, According to the weight percentage, the amount of sodium hexametaphosphate accounts for 0.01-5% of the mass fraction of the waste cotton textiles.

4. The method of claim 1, wherein, According to the weight percentage, the amount of hydrogen peroxide accounts for 0.01-5% of the mass fraction of the waste cotton textiles.

5. The method of claim 1, wherein, According to the weight percentage, the amount of hydrogen peroxide accounts for 2-10% of the mass fraction of the waste cotton textiles.

6. The method of claim 1, wherein, The mass-volume ratio of lithium chloride to high-quality cotton pulp is 1 mL / 1 g; the mass ratio of triethylamine to high-quality cotton pulp is 2:1; and the molar ratio of ethylenediamine to cellulose p-toluenesulfonate is 25:

1.

7. The method of claim 1, wherein, The temperature during the reaction is 100℃, and the reaction time is 6 hours.

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