A low-alkali agent system natural plant indigo mud reduction dyeing method

Abstract

The application discloses a low-alkali agent system natural plant indigo mud reduction dyeing method and relates to the technical field of natural dye dyeing. The application controls the pH of a reduction system in a low-alkali interval of 11.5-12.5, uses glucose as a reducing agent, compensates for insufficient reduction power under low-alkali conditions through temperature rise, reduces reaction activation energy, accelerates electron transfer and promotes dye depolymerization, and realizes sufficient reduction of natural plant indigo mud. Meanwhile, a 10-110 g / L wide-concentration self-adaptive reduction mechanism is constructed, corresponding reduction temperatures are matched according to dyeing liquid concentrations, and process applicability is improved; a high-temperature reduction and low-temperature dyeing coupling process is adopted, and the oxidation and agglomeration of leuco bodies are effectively inhibited. The process is green and environmentally friendly and has strong adaptability, the obtained fabric has high dyeing depth and excellent uniformity, and is suitable for clean industrial application of natural indigo mud.

Description

Technical Field

[0001] This invention relates to the field of natural dyeing technology, and in particular to a method for reducing dyeing with natural plant indigo mud using a low-alkali agent system. Background Technology

[0002] Natural plant-based indigo dyes are the earliest and most widely used plant dyes, produced from indigo plants such as Polygonum tinctorium, Isatis tinctoria, Indigofera tinctoria, and Strobilanthes cusia through traditional processes including fermentation, reduction, and precipitation. Currently, industrial applications are dominated by synthetic indigo, while the use of natural plant-based indigo is gradually declining. Compared to natural plant-based indigo, synthetic indigo has a higher environmental impact due to its raw material sources and production processes, while natural plant dyes are more in line with the industry trends of green chemistry and sustainable development.

[0003] Traditional plant-based indigo dyeing relies on fermentation of rice wine and alkali agents (such as white alkali, quicklime, and wood ash) to build fermentation vats. This method has several drawbacks, including the fact that the vat-building conditions are greatly affected by the environment, the fermentation cycle is uncontrollable, and the fermentation effect is judged subjectively based solely on the color of the dye solution and the state of the indigo flowers. As a result, it is difficult to achieve stable industrial application. To address the shortcomings of traditional dyeing methods, such as low efficiency and poor stability, several improvement schemes have been proposed: Patent CN109098011A uses sodium hydrosulfite to reduce natural indigo for denim yarn dyeing, resulting in fast reduction and stable dyeing effects. However, sodium hydrosulfite has poor chemical stability, decomposing to produce large amounts of sulfates and sulfites, significantly increasing the salinity of wastewater and reducing dissolved oxygen, thus posing a significant environmental burden. Patent CN108951204A uses electrochemical reduction to dye conductive yarn with indigo, reducing the use of chemical agents and wastewater discharge, but it relies on electrode power, leading to high industrial production costs. Patent CN113564943A uses electron-medium-enhanced whole-cell biological reduction to construct a green and low-consumption dyeing system, but it has stringent requirements for the activity of microorganisms and enzymes, resulting in unstable reduction conversion rates.

[0004] Reducing sugars, as chemical reducing agents, are simple to operate and highly safe, but their reducing ability is weak, requiring the addition of excessive alkali to fully reduce indigo. The use of large amounts of alkali severely reduces the application value of natural dyes: on the one hand, a highly alkaline environment causes excessive swelling of cellulose fibers, leading to a decrease in fiber strength and affecting the performance of textiles; on the other hand, the subsequent neutralization of highly alkaline dyeing wastewater requires a large amount of acid, significantly increasing environmental treatment costs. Therefore, developing a natural plant-based indigo mud reduction dyeing process that requires no additional alkali, is highly efficient in reduction, and is adaptable to a wide concentration range has become crucial for overcoming the shortcomings of existing technologies and promoting the clean industrial dyeing of natural indigo. Summary of the Invention

[0005] The purpose of this invention is to provide a low-alkali system for natural plant indigo mud reduction dyeing, so as to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution: This invention provides a method for reducing and dyeing natural indigo mud using a low-alkali agent system, comprising the following steps: (1) Preparation of dye solution: Natural plant indigo mud is prepared into an indigo dye solution with a concentration of 10-110 g / L, glucose is added as a reducing agent, and the pH of the indigo dye solution is adjusted to 11.5-12.5 with acid to obtain a low-alkali reducing system; (2) Reduction treatment: The low-alkali reduction system of step (1) is subjected to high-temperature reduction at 50-80℃ to reduce indigo to water-soluble leuco form, and the reduced dye solution is obtained. (3) Dyeing treatment: Cool the reduced dye liquor to 20-30℃ for fabric dyeing; (4) Post-treatment: The dyed fabric is oxidized, washed and dried to obtain the dyed fabric.

[0007] Furthermore, the indigo dye solution employs a concentration-adaptive reduction process: When the concentration of the indigo dye solution is 10-40 g / L, but not 40 g / L, the reduction temperature is 50-70℃ and the reduction time is 60-80 min; more preferably, the reduction time is 70 min. When the concentration of the indigo dye solution is 40-80 g / L, but not 80 g / L, the reduction temperature is 60-80℃ and the reduction time is 60-80 min; more preferably, the reduction time is 70 min. When the concentration of the indigo dye solution is 80-110 g / L, the reduction temperature is 70-80℃, the reduction time is 60-80 min, and more preferably the reduction time is 70 min.

[0008] Furthermore, the concentration of the indigo dye solution is 70 g / L; the pH value of the indigo dye solution in step (1) is 12; the high-temperature reduction temperature in step (2) is 80 °C, and the reduction time is 70 min.

[0009] Furthermore, the concentration of glucose added to the low-alkaline reducing system is 10 g / L.

[0010] Furthermore, acetic acid is used for pH adjustment in step (1).

[0011] Furthermore, in step (3), the staining bath ratio is 1:100 and the staining time is 20 min; in step (4), the oxidation method is air oxidation.

[0012] Furthermore, the air oxidation time is 10 minutes; deionized water is used for washing; and the drying method is natural drying or low-temperature drying.

[0013] Furthermore, the fabric undergoes a desizing pretreatment before dyeing. The desizing solution used in the desizing pretreatment contains: sodium hydroxide at a mass concentration of 10 g / L and penetrant JFC at an addition amount of 1 g / L; the conditions for the desizing pretreatment are: a liquor ratio of 1:50, a temperature of 95℃, and a time of 60 min.

[0014] The present invention also provides a dyed fabric prepared by the above-mentioned low-alkali agent system natural plant indigo mud reduction dyeing method.

[0015] This invention achieves significant technological breakthroughs in the following aspects: High-temperature compensation replaces high-alkali reduction, achieving clean, low-alkali production: This invention controls the pH of the reduction system within the low-alkali range of 11.5-12.5. Compared to traditional processes that require large amounts of alkali, this invention compensates for insufficient reduction kinetics of indigo under low-alkali conditions by increasing the temperature, thus constructing a green, low-alkali dyeing process. Low-alkali environments easily lead to increased reduction potential and decreased electron transfer efficiency, causing indigo molecules to easily aggregate and become difficult to fully reduce. Increasing the temperature effectively reduces the Gibbs free energy and activation energy of the reaction, accelerates the electron transfer rate, weakens the intermolecular forces of dye molecules, and promotes the deagglomeration of aggregates, achieving full reduction of natural plant-based indigo mud even with low alkali usage.

[0016] Concentration-adaptive mechanism significantly improves process adaptability: This invention elucidates the adaptation rules of reduction parameters for indigo dye liquor within a wide concentration range of 10-110 g / L. In low-concentration dye liquor (10-40 g / L, but not exceeding 40 g / L), the number of indigo molecules is small, the intermolecular distance is large, and the degree of aggregation is low. Moderate heating can avoid the aggregation from hindering the reduction reaction. If the alkali content is too low, the reduction potential will rise sharply, and the driving force for electron transfer of the reducing agent will be severely insufficient. In medium-to-high concentration dye liquor (40-110 g / L), the dye molecules are dense and the aggregation phenomenon is significant, and the reduction resistance and mass transfer barrier are significantly increased. This invention compensates for the reduction kinetic gap caused by low alkali by high temperature, while promoting the depolymerization of dye aggregates and accelerating the reaction rate. This eliminates the need for additional alkali and ensures complete reduction of high-concentration indigo, achieving a balance between environmental friendliness and high efficiency.

[0017] This invention couples high-temperature reduction with low-temperature dyeing to improve dyeing uniformity and color depth. For dye liquor with an optimal application concentration of 70 g / L, a high temperature of 80℃ is used to achieve full dye reduction, followed by low-temperature dyeing at 30℃ to inhibit premature oxidation and secondary aggregation of leuco pigments. This allows the fabric to achieve a K / S value of over 8 in a single dyeing process, with a color difference ΔE ≤ 0.5, and significantly improved dyeing uniformity and color depth.

[0018] The present invention discloses the following technical effects: This invention addresses the problems of high alkali consumption and poor dyeing uniformity in natural plant indigo mud reduction dyeing by using a low-alkali system, high-temperature compensation reduction, and temperature control coupling to achieve clean and efficient dyeing.

[0019] This invention controls the pH of the reduction system within a low-alkali range of 11.5-12.5, using temperature increase to compensate for insufficient reduction kinetics caused by low alkali, reducing the activation energy of the reaction, accelerating electron transfer and promoting dye depolymerization, thus achieving full reduction of natural plant indigo mud with low alkali dosage, and significantly improving environmental friendliness.

[0020] Meanwhile, this invention establishes a wide concentration adaptive reduction mechanism of 10-100 g / L, matching the appropriate reduction temperature according to the dye liquor concentration, taking into account the reduction driving force of the low concentration system and the depolymerization and mass transfer efficiency of the medium and high concentration system, ensuring the complete reduction of high concentration dyes while reducing the use of alkali agents, and greatly expanding the application range of the process. Detailed Implementation

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0022] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included within the scope of this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0023] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0024] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0025] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0026] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0027] In the following embodiments and comparative examples of this invention, all raw materials used are commercially available conventional products: the cotton fabric used is 140 g / m². 2 The fabric is made of 32S cotton twill; the glucose and acetic acid used are of analytical grade; the natural indigo mud used has a solid content of 43.8%.

[0028] Example 1 This embodiment provides a low-alkali reduction staining method using a 20 g / L low-concentration staining solution, the steps of which are as follows: (1) Pretreatment of cotton fabrics: Take cotton fabric raw material and dry it until the weight is constant. Put it into the pre-prepared desizing solution and immerse it at a constant temperature of 95℃ for 60 minutes to allow the sizing on the fabric to fully swell and decompose. After desizing, the greige fabric is removed and washed step by step using graded water washing: first, it is washed twice with hot water above 85 ℃ to fully remove undecomposed sizing agents and chemical residues from the fabric surface; then, it is washed with warm water at 50~60 ℃ to further remove surface adhering substances; finally, it is repeatedly rinsed with room temperature water until the pH value of the washing solution is close to neutral; after washing, the greige fabric is transferred to an oven to dry to constant weight and is ready for use. The desizing solution was prepared under the following conditions: water was used as the solvent, the bath ratio was 1:50 (the ratio of the mass of the cotton fabric to the volume of the treatment solution), the sodium hydroxide mass concentration was 10 g / L, and the amount of penetrant JFC added was 1 g / L. All components were stirred until completely dissolved to obtain a uniform and stable treatment solution.

[0029] (2) Dye solution preparation: Take natural indigo mud and prepare a dye solution with a mass concentration of 20 g / L. Adjust the pH value of the dye solution to 12.5, add glucose with a mass concentration of 10 g / L, stir evenly, and obtain a low-alkali reduction system.

[0030] (3) Reduction treatment: Place the prepared dye solution in a 60℃ constant temperature water bath and stir for 70 min until the dye solution turns yellow-green, indicating that the indigo has been fully reduced to the leuco form.

[0031] (4) Low temperature dyeing: The dye solution after reduction is rapidly cooled to 30°C. The pretreated cotton fabric is then immersed in the dye solution at a liquor ratio of 1:100 and dyed for 20 min.

[0032] (5) Post-treatment: Take out the dyed cotton fabric and oxidize it in the air for 10 min; then rinse it with deionized water 3 times and air dry it at room temperature to obtain the dyed cotton fabric.

[0033] According to the test results, the dyed cotton fabric obtained in this embodiment has a dyeing K / S value of 3.638, a color difference ΔE=0.4575, a lightness L value of 52.24, a vividness C value of 21.686, and a hue H value of 257.654.

[0034] Example 2 This embodiment provides a low-alkali reduction staining method using a medium-concentration dye solution of 60 g / L, the steps of which are as follows: (1) Pretreatment of cotton fabric: Same as in Example 1.

[0035] (2) Dye solution preparation: Prepare a dye solution with a mass concentration of 60 g / L, adjust the pH value of the dye solution to 12.0, add glucose with a mass concentration of 10 g / L, stir evenly, and obtain a low-alkali reducing system.

[0036] (3) Reduction treatment: Place the prepared dye solution in a 70℃ constant temperature water bath and stir for 70 min until the dye solution turns yellow-green, indicating that the indigo has been fully reduced to the leuco form.

[0037] (4) Low temperature dyeing: The dye solution after reduction is rapidly cooled to 30°C. Take the pretreated cotton fabric and immerse it in the dye solution at a bath ratio of 1:100 for 20 minutes.

[0038] (5) Post-treatment: Take out the dyed cotton fabric and oxidize it in the air for 10 min; then rinse it with deionized water 3 times and air dry it at room temperature to obtain the dyed cotton fabric.

[0039] According to the test results, the dyed cotton fabric obtained in this embodiment has a dyeing K / S value of 6.398, a color difference ΔE=0.375, a lightness L value of 43.214, a vividness C value of 21.346, and a hue H value of 259.666.

[0040] Example 3 This embodiment provides a low-alkali reduction staining process using a 100 g / L high-concentration dye solution. The specific steps are as follows: (1) Pretreatment of cotton fabric: Same as in Example 1.

[0041] (2) Dye solution preparation: Prepare a dye solution with a mass concentration of 100 g / L, adjust the pH value of the dye solution to 11.5, add glucose with a mass concentration of 10 g / L, stir evenly, and obtain a low-alkali reducing system.

[0042] (3) Reduction treatment: Place the prepared dye solution in an 80℃ constant temperature water bath and stir for 70 min until the dye solution turns yellow-green, indicating that the indigo has been fully reduced to the leuco form.

[0043] (4) Low temperature dyeing: The dye solution after reduction is rapidly cooled to 30°C. Take the pretreated cotton fabric and immerse it in the dye solution at a bath ratio of 1:100 for 20 minutes.

[0044] (5) Post-treatment: Take out the dyed cotton fabric and oxidize it in the air for 10 min; then rinse it with deionized water 3 times and air dry it at room temperature to obtain the dyed cotton fabric.

[0045] According to the test results, the dyed cotton fabric obtained in this embodiment has a dyeing K / S value of 7.99, a color difference ΔE=0.475, a lightness L value of 39.726, a vividness C value of 21.512, and a hue H value of 261.404.

[0046] Example 4 This embodiment provides a low-alkali reduction dyeing process using a dye solution with a dyeing equilibrium concentration of 70 g / L (where dye molecules reach dynamic equilibrium through adsorption and desorption on the fabric surface). The specific steps are as follows: (1) Pretreatment of cotton fabric: Same as in Example 1.

[0047] (2) Dye solution preparation: Prepare a dye solution with a mass concentration of 70 g / L, adjust the pH value of the dye solution to 12.0, add glucose with a mass concentration of 10 g / L, stir evenly, and obtain a low-alkali reducing system.

[0048] (3) Reduction treatment: Place the prepared dye solution in an 80℃ constant temperature water bath and stir for 70 min until the dye solution turns yellow-green, indicating that the indigo has been fully reduced to the leuco form.

[0049] (4) Low temperature dyeing: The dye solution after reduction is rapidly cooled to 30°C. Take the pretreated cotton fabric and immerse it in the dye solution at a bath ratio of 1:100 for 20 minutes.

[0050] (5) Post-treatment: Take out the dyed cotton fabric and oxidize it in the air for 10 min; then rinse it with deionized water 3 times and air dry it at room temperature to obtain the dyed cotton fabric.

[0051] According to the test results, the dyed cotton fabric obtained in this embodiment has a dyeing K / S value of 8.618, a color difference ΔE=0.288, a lightness L value of 38.712, a vividness C value of 21.146, and a hue H value of 260.124.

[0052] In this embodiment, 70 g / L is selected as the concentration of indigo mud dye solution. This concentration is the optimal application concentration, which can balance dyeing depth, dyeing uniformity and production cost. Under the low-alkali reduction system of this invention, the best dyeing effect can be achieved.

[0053] Comparative Example 1 This comparative example provides a low-alkali reduction staining process using 70 g / L dye solution without temperature compensation. The specific steps are as follows: (1) Pretreatment of cotton fabric: Same as in Example 1.

[0054] (2) Dye solution preparation: Prepare a dye solution with a mass concentration of 70 g / L, adjust the pH value of the dye solution to 12.0, add glucose with a mass concentration of 10 g / L, stir evenly, and obtain a low-alkali reducing system.

[0055] (3) Reduction treatment: Place the prepared dye solution in a 40℃ constant temperature water bath and stir for 70 min to reduce.

[0056] (4) Low temperature dyeing: The dye solution after reduction is rapidly cooled to 30°C. Take the pretreated cotton fabric and immerse it in the dye solution at a bath ratio of 1:100 for 20 minutes.

[0057] (5) Post-treatment: Take out the dyed cotton fabric and oxidize it in the air for 10 min; then rinse it with deionized water 3 times and air dry it at room temperature to obtain the dyed cotton fabric.

[0058] The dyed cotton fabric obtained in this comparative example has a K / S value of 4.416, a color difference ΔE = 0.5725, a lightness L value of 47.32, a vividness C value of 20.158, and a hue H value of 258.342.

[0059] This invention constructs a low-alkali reduction system and establishes an adaptive matching mechanism between dye concentration and reduction parameters. While reducing the amount of alkali agent used, it ensures the dyeing depth and uniformity, reduces fiber damage, and achieves clean and industrialized dyeing of natural indigo.

[0060] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for reducing and dyeing natural plant indigo mud using a low-alkali agent system, characterized in that, Includes the following steps: (1) Preparation of dye solution: Natural plant indigo mud is prepared into an indigo dye solution with a concentration of 10-110 g / L, glucose is added as a reducing agent, and the pH of the indigo dye solution is adjusted to 11.5-12.5 with acid to obtain a low-alkali reducing system; (2) Reduction treatment: The low-alkali reduction system of step (1) is subjected to high-temperature reduction at 50-80℃ to reduce indigo to water-soluble leuco form, and the reduced dye solution is obtained. (3) Dyeing treatment: Cool the reduced dye liquor to 20-30℃ for fabric dyeing; (4) Post-treatment: The dyed fabric is oxidized, washed and dried to obtain the dyed fabric.

2. The method for reducing and dyeing natural plant indigo mud using a low-alkali agent system according to claim 1, characterized in that, The indigo dye solution employs a concentration-adaptive reduction process. When the concentration of the indigo dye solution is 10-40 g / L, but not 40 g / L, the reduction temperature is 50-70℃ and the reduction time is 60-80 min. When the concentration of the indigo dye solution is 40-80 g / L, but not 80 g / L, the reduction temperature is 60-80℃ and the reduction time is 60-80 min. When the concentration of the indigo dye solution is 80-110 g / L, the reduction temperature is 70-80℃ and the reduction time is 60-80 min.

3. The method for reducing and dyeing natural plant indigo mud using a low-alkali agent system according to claim 1, characterized in that, The concentration of the indigo dye solution is 70 g / L; the pH value of the indigo dye solution in step (1) is 12; the high-temperature reduction temperature in step (2) is 80 °C and the reduction time is 70 min.

4. The method for reducing and dyeing natural plant indigo mud using a low-alkali agent system according to claim 1, characterized in that, The concentration of glucose added to the low-alkaline reducing system is 10 g / L.

5. The method for reducing and dyeing natural plant indigo mud using a low-alkali agent system according to claim 1, characterized in that, In step (3), the staining bath ratio is 1:100 and the staining time is 20 min; in step (4), the oxidation method is air oxidation.

6. The method for reducing and dyeing natural plant indigo mud using a low-alkali agent system according to claim 1, characterized in that, The fabric undergoes a desizing pretreatment before dyeing.

7. The method for reducing and dyeing natural plant indigo mud using a low-alkali agent system according to claim 6, characterized in that, The desizing solution used in the desizing pretreatment has the following composition: sodium hydroxide concentration of 10 g / L and JFC penetrant addition of 1 g / L; the conditions for the desizing pretreatment are: bath ratio of 1:50, temperature of 95℃, and time of 60 min.

8. A dyed fabric prepared by the natural plant indigo mud reduction dyeing method according to any one of claims 1-7 using a low-alkali agent system.