A method for preparing a weak alkali bleaching working solution of a manganese-based metal complex for low-temperature oxygen bleaching of cotton fabric

Abstract

The present application belongs to the technical field of textile bleaching, and particularly relates to a manganese-based metal complex weak alkaline bleaching working solution for low-temperature oxygen bleaching of cotton fabrics and a preparation method thereof. In the method, sodium bicarbonate and soluble divalent manganese salt are sequentially added into a base solution containing a refining agent and a penetrating agent to generate a liquid manganese-based precursor in situ; then, citric acid is added to coordinate with manganese ions and form a composite buffer system with sodium bicarbonate; finally, hydrogen peroxide is added, and the manganese-citric acid complex activates the hydrogen peroxide in situ to generate a catalytic reaction, thereby forming a strong bleaching agent and increasing the concentration of bleaching active ingredients. The method combines in-situ coordination reaction of metal-organic acid, in-situ activation and catalytic reaction, and does not require a strong alkaline environment, thereby reducing damage to cotton fabric fibers, shortening bleaching time while reducing bleaching temperature, and further realizing efficient catalytic bleaching. The obtained bleached cotton fabric meets the requirements of high whiteness and high strength retention rate.

Description

Technical Field

[0001] This invention belongs to the field of textile bleaching technology, specifically relating to a manganese-based metal complex weakly alkaline bleaching working solution for low-temperature oxygen bleaching of cotton fabrics and its preparation method. Background Technology

[0002] Hydrogen peroxide, due to its advantages such as pure whiteness, resistance to yellowing, and clean, pollution-free decomposition products, has become the most widely used mainstream bleaching agent in the pretreatment of cotton fabrics. The processing of high-whiteness cotton fabrics requires particularly stringent bleaching effects, typically requiring a whiteness of over 80%. However, because hydrogen peroxide has an extremely low ionization constant at room temperature, traditional oxygen bleaching processes for cotton fabrics require treatment under high-temperature, strongly alkaline conditions (usually 98-100℃, pH=10-12) for more than 60 minutes to ensure that sufficient hydrogen peroxide generates sufficient peroxide ions as an effective bleaching component after the catalytic reaction. However, prolonged high-temperature treatment not only consumes a large amount of steam, which is inconsistent with the current green development trend of energy conservation and emission reduction in the textile printing and dyeing industry; at the same time, the combined effect of a strongly alkaline environment and high temperature accelerates the alkaline oxidative degradation of cotton fibers, leading to decreased fabric strength, rough hand feel, and increased losses, seriously affecting product quality and subsequent processing performance. Therefore, how to achieve low-temperature, rapid, and efficient bleaching of cotton fabrics while ensuring whiteness has become a pressing technical bottleneck for the textile industry.

[0003] Numerous studies have shown that adding activators or catalysts to hydrogen peroxide bleaching systems can potentially lower bleaching temperatures and shorten bleaching times, but their mechanisms are entirely different. Adding an activator to hydrogen peroxide allows it to react and form peroxyacids with stronger bleaching power, offering advantages such as lower bleaching temperatures and reduced fiber damage. Adding a catalyst, on the other hand, allows for a catalytic reaction with hydrogen peroxide, promoting its extensive ionization and increasing the concentration of hydrogen peroxide ions in the bleaching solution. This, to some extent, lowers the temperature while significantly shortening the bleaching time. Because activators and catalysts have vastly different mechanisms of action, their characteristics, advantages, and disadvantages also differ. Activated bleaching systems suffer from drawbacks such as high activator dosage, easy hydrolysis, and high cost. Furthermore, existing catalytic systems exhibit poor adaptability to different water qualities, fabric types, and process conditions, making it difficult to guarantee the stability and reproducibility of the bleaching effect. Additionally, the raw material costs of some highly efficient catalytic systems are relatively high. All of these factors limit the large-scale application of catalysts in the field of cotton fabric bleaching.

[0004] Therefore, the key to achieving the industrial application of low-temperature, high-efficiency bleaching of cotton fabrics lies in developing a bleaching working solution that possesses both catalytic and activating properties under low-temperature, weakly alkaline conditions. Metal complexes, as a class of highly efficient enzyme-like catalysts, have attracted attention in recent decades due to their advantages such as low dosage, high efficiency, and good whiteness of bleached fabrics. Bleaching catalysts based on various soluble transition metals have also been reported. Among these soluble transition metals, manganese, due to its abundant redox states and excellent catalytic activation ability, has become one of the commonly used metals in current bleaching catalysts.

[0005] Although there are currently many technical solutions for synthesizing manganese complexes to catalyze hydrogen peroxide for low-temperature catalytic bleaching, they still exhibit many obvious drawbacks, such as poor stability, low safety, limited functionality, complex formulations, and cumbersome procedures. Studies have shown that complexes formed with manganese and typical ligands such as cyclic polyamines, Schiff bases, pyridines, porphyrins, phthalocyanines, and macrocyclic amides generally require strongly alkaline conditions (pH > 10) to exert their catalytic activity. In this environment, soluble metal ions and metal complexes are easily deactivated and precipitated. Therefore, manganese metal complexes are not only sensitive to changes in water quality, pH, and temperature, but also often require the addition of stabilizers during preparation. Mechanistic investigations reveal that manganese metal complexes possess only a single catalytic effect without any synergistic activation, and they must be in a strongly alkaline environment to undergo a highly efficient catalytic reaction with hydrogen peroxide. If the pH value decreases, the catalytic ionization constant of hydrogen peroxide decreases significantly, leading to a sharp decline in the catalytic bleaching performance of the manganese metal complexes (Wu Shouying et al., Journal of Textile Research, 2021). Meanwhile, although manganese metal complexes can achieve catalytic bleaching at low temperatures, the strong alkaline conditions still cause significant damage to cotton fibers, resulting in a low strength retention rate of only about 80%. This limits the application of such complexes in cotton knitwear processing where high strength is required (Qin Xinbo et al., Journal of Textile Research, 2012). Furthermore, based on existing literature, it is easy to see that transition metal complexes used for low-temperature bleaching of cotton fabrics generally suffer from complex synthesis processes, cumbersome preparation procedures, and high production costs.

[0006] While existing manganese complexes can achieve a certain degree of low-temperature bleaching by catalyzing hydrogen peroxide, they still require a strongly alkaline environment with a pH above 10 to exert their effective activity, making it difficult to simultaneously achieve low temperature and low fiber damage. In contrast, this invention constructs a mild and safe weakly alkaline system (pH 8-9) using sodium bicarbonate. By adding manganese salt, citric acid, and other auxiliaries in the same working solution in one step, the active complex can be generated in situ without the need for pre-synthesis and separation purification, greatly simplifying the process. At the same time, it completely eliminates the dependence on strong alkali while lowering the bleaching temperature, fundamentally solving the contradiction between catalytic activity and fiber protection. Under the same whiteness requirements, it can improve the strength retention rate of fabrics, achieving a balance between high whiteness, low damage, and simple process under mild conditions. Summary of the Invention

[0007] To address the problems in the background art, this invention provides a metal complex weakly alkaline bleaching working solution for low-temperature oxygen bleaching of cotton fabrics and its preparation method. This invention uses soluble manganese salt and mild citric acid as raw materials, employing a dual in-situ reaction preparation process under a weakly alkaline environment. This process forms a substance with strong bleaching ability while increasing the concentration of bleaching active ingredients, ultimately achieving multiple objectives: efficient pigment removal, reduced bleaching temperature, and shortened bleaching time.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a manganese-based metal complex weakly alkaline bleaching working solution, characterized by comprising the following steps:

[0010] (1) Preparation of bleaching working solution: Under room temperature conditions, add penetrant and scouring agent to deionized water while stirring to obtain a mixture. Then continue stirring for 5-10 minutes to fully homogenize the mixture, thus obtaining the bleaching working solution.

[0011] (2) Preparation of weakly alkaline bleaching working solution: Add sodium bicarbonate as a pH buffer to the bleaching working solution obtained in step (1), stir at 35-45℃ for 10-15 minutes, and continue stirring for 10-15 minutes after cooling to room temperature to allow sodium bicarbonate to fully dissociate and disperse evenly in the system, forming a stable HCO3⁻ / CO3 2 ⁻ A buffer system is used to obtain a weakly alkaline bleaching working solution;

[0012] (3) Preparation of liquid-phase manganese-based catalytic precursor: Add soluble divalent manganese salt to the weakly alkaline bleaching working solution obtained in step (2), and stir at 20-40℃ for 10-15 minutes to make manganese ions fully and uniformly dispersed in the weakly alkaline bleaching working solution to form a highly active liquid-phase manganese-based catalytic precursor.

[0013] (4) Preparation of manganese-citric acid complex solution: Add citric acid to the solution obtained in step (3) and stir at 20-40℃ for 20-30 minutes to allow it to fully undergo in-situ coordination reaction with the soluble manganese ions dispersed in the solution, thereby obtaining the manganese-citric acid complex solution;

[0014] (5) Preparation of manganese-based metal complex weak alkaline bleaching working solution: Add hydrogen peroxide to the manganese-citric acid complex solution obtained in step (4), heat to 45-65℃ to carry out in-situ catalytic reaction, continue stirring for 15-20 minutes and then keep warm for 10-15 minutes to produce highly efficient bleaching active ingredients, and finally obtain manganese-based metal complex weak alkaline bleaching working solution.

[0015] Preferably, the soluble divalent manganese salt is one of manganese chloride, manganese sulfate, or manganese acetate.

[0016] Preferably, based on 1L of water, the amounts of the raw material components are as follows:

[0017] The amount of the penetrant is 1.0~3.0g; the amount of the refining agent is 1.0~3.0g; the amount of sodium bicarbonate is 2.0~5.0g; the amount of the soluble divalent manganese salt added is 6~12mmol based on the manganese ions therein; the amount of citric acid is 2.0~4.0g; the hydrogen peroxide is a 25~35% hydrogen peroxide aqueous solution, and the amount is 6.0~12.0g.

[0018] Furthermore, the penetrant is sodium primary alkyl sulfonate; the refining agent is fatty alcohol polyoxyethylene ether;

[0019] Preferably, the penetrant is sodium primary alkyl sulfonate (PAS-80), and the refining agent is fatty alcohol polyoxyethylene ether (AEO-9).

[0020] Preferably, the pH value of the weakly alkaline bleaching working solution is approximately 8.0 to 9.0, with a deviation of ±0.5 allowed, and no additional acid-base adjuster needs to be added.

[0021] A weakly alkaline bleaching working solution of manganese-based metal complex prepared by the above method.

[0022] The manganese-based metal complex weakly alkaline bleaching working solution prepared by the above method is used for low-temperature oxygen bleaching of cotton fabrics.

[0023] The above-mentioned manganese-based metal complex weakly alkaline bleaching working solution was used for low-temperature oxygen bleaching and testing of cotton fabrics. The specific steps are as follows:

[0024] Add the cotton fabric sample to the prepared weakly alkaline bleaching working solution of the manganese-based metal complex, and stir the sample at a constant temperature of 60-80℃ for 30-45 minutes. Then, remove the cotton fabric sample, wash it 2-3 times with hot water at 60-80℃, rinse it with room temperature water until neutral, and place it in an oven to dry in air at 60-80℃ for 1-2 hours. Furthermore, the liquor ratio for the bleaching process is 1:15-25.

[0025] After bleaching, the cotton fabric samples were ironed flat, cooled, and folded into four layers. The whiteness value of the fabric was determined according to GB / T 8424.2—2001 standard. Four different locations were tested for each sample, and the average value was taken as the whiteness value of the cotton fabric sample. The tensile strength of the cotton fabric samples before and after bleaching was determined according to GB / T 3923.1—2013 standard. The tensile speed was 10 cm / min, and each sample was tested five times. The average value was taken as the strength value of the cotton fabric sample.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) The manganese-citric acid metal complex constructed in this invention during the bleaching process of cotton fabrics has the dual functions of a catalyst and an activator. On the one hand, as an activator, the complex can undergo an in-situ activation reaction with hydrogen peroxide to generate a peroxyacid intermediate, the oxidation potential of which is higher than that of hydrogen peroxide itself, thus enhancing the bleaching ability. On the other hand, as a catalyst, the complex reacts with hydrogen peroxide to promote the generation of a large number of hydrogen peroxide ions (HOO⁻), forming a high concentration of bleaching active ingredients. The two reaction pathways proceed synergistically, effectively shortening the bleaching time while reducing the bleaching temperature, overcoming the shortcomings of insufficient efficiency of a single activation or catalytic pathway in traditional systems.

[0028] (2) This invention breaks through the dependence on high temperature and strong alkaline conditions, significantly reducing the bleaching temperature from the traditional 100℃ to 60-80℃, and adjusting the working solution pH from strong alkaline to weak alkaline. Under the dual mild conditions of low temperature and weak alkalinity, not only is steam energy consumption and carbon emissions reduced, but the severe swelling and alkaline oxidative degradation of cotton fibers under high temperature and strong alkalinity are also effectively avoided. The fabric strength retention rate is improved, the hand feel is soft, and the loss is reduced, which meets the requirements of energy conservation, emission reduction and green sustainable development in the textile printing and dyeing industry.

[0029] (3) Compared with existing manganese complex catalytic systems that use artificially synthesized ligands, this invention overcomes the limitations of cumbersome pre-synthesized complex processes. It utilizes commercially available manganese salts and citric acid to generate manganese-citric acid metal complexes in situ in bleaching solutions, eliminating the need for complex ligand synthesis steps and the separation and drying of solid catalysts. The operation is simple, the cost is low, and it is easy to promote industrially. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 The bar chart shows the whiteness and strength retention rates of fabrics bleached with different amounts of sodium bicarbonate in Examples 1-4.

[0032] Figure 2 The bar charts for whiteness and strength retention rates obtained after adding different amounts of manganese chloride to bleach fabrics are shown in Examples 1, 5-7.

[0033] Figure 3 The bar chart shows the whiteness and strength retention rates of fabrics bleached with different amounts of citric acid in Examples 1, 8, and 9.

[0034] Figure 4 For Example 1, bar charts showing the whiteness and strength retention rates of fabrics bleached with different amounts of hydrogen peroxide (10-12).

[0035] Figure 5 The bar chart shows the whiteness and strength retention rates of fabrics bleached at different preparation temperatures in Examples 1, 13, and 14.

[0036] Figure 6 This is a process flow diagram of the method for preparing the weakly alkaline bleaching working solution of the manganese-based metal complex according to the present invention. Detailed Implementation

[0037] To further understand the purpose, content, and advantages of this invention, specific embodiments of the invention are described in detail below. However, these embodiments are not limited to the examples described below and should be freely combined according to actual circumstances. The endpoints and values ​​of the ranges disclosed herein are not limited to the precise ranges and values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0038] The cotton fabric used in the following embodiments of the present invention is pure cotton grey fabric (linear density 18.2 tex, whiteness 42.6%). The penetrant used in the following embodiments of the present invention is sodium primary alkyl sulfonate (PAS-80), industrial grade, purchased from Sinopharm Chemical Reagent Co., Ltd. The scouring agent used in the following embodiments of the present invention is fatty alcohol polyoxyethylene ether (AEO-9), industrial grade, purchased from Sinopharm Chemical Reagent Co., Ltd. Sodium bicarbonate used in the following embodiments of the present invention is analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd. 30% hydrogen peroxide used in the following embodiments of the present invention is analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd. Anhydrous manganese chloride used in the following embodiments of the present invention is analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd. Anhydrous manganese sulfate used in the following embodiments of the present invention is analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd. Manganese acetate used in the following embodiments of the present invention is analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd. Citric acid used in the following embodiments of the present invention is analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0039] However, this patent does not restrict the source of cotton fabrics, penetrants, scouring agents, sodium bicarbonate, hydrogen peroxide, manganese chloride, manganese sulfate, manganese acetate, and citric acid; any commercially available materials are suitable for the method of this patent.

[0040] This invention provides a method for preparing a weakly alkaline bleaching working solution based on manganese metal complexes, comprising the following steps:

[0041] (1) Preparation of bleaching working solution: Under room temperature conditions, add penetrant and scouring agent to deionized water while stirring to obtain a mixture. Then continue stirring for 5-10 minutes to fully homogenize the mixture, thus obtaining the bleaching working solution.

[0042] (2) Preparation of weakly alkaline bleaching working solution: Add sodium bicarbonate as a pH buffer to the bleaching working solution obtained in step (1), stir at 35-45℃ for 10-15 minutes, and continue stirring for 10-15 minutes after cooling to room temperature to allow sodium bicarbonate to fully dissociate and be evenly dispersed in the system to form stable HCO3. - / CO3 2- The buffer system yields a weakly alkaline bleaching working solution;

[0043] (3) Preparation of liquid-phase manganese-based catalytic precursor: Add soluble divalent manganese salt to the weakly alkaline bleaching working solution obtained in step (2), and stir at 20-40℃ for 10-15 minutes to fully hydrate and uniformly disperse manganese ions in the weakly alkaline bleaching working solution to form a highly active liquid-phase manganese-based catalytic precursor.

[0044] (4) Preparation of manganese-citric acid complex solution: Add citric acid to the solution obtained in step (3) and stir at 20-40℃ for 20-30 minutes to allow it to fully undergo in-situ coordination reaction with the soluble manganese ions dispersed in the solution, thereby obtaining the manganese-citric acid complex solution;

[0045] (5) Preparation of manganese-based metal complex weak alkaline bleaching working solution: Add hydrogen peroxide to the manganese-citric acid complex solution obtained in step (4), heat to 45-65℃ to carry out in-situ catalytic reaction, continue stirring for 15-20 minutes and then keep warm for 10-15 minutes to produce highly efficient bleaching active ingredients, and finally obtain manganese-based metal complex weak alkaline bleaching working solution.

[0046] In the preparation method described above, the concentrations of sodium bicarbonate, soluble manganese ions, citric acid, hydrogen peroxide, and in-situ catalytic reaction temperature are key parameters affecting the low-temperature oxygen bleaching degree and strength retention rate of cotton fabrics by the manganese-based metal complex weakly alkaline bleaching working solution. Other factors are non-critical and will not have a significant impact on product performance as long as they are controlled within the specified range (the impact can be ignored).

[0047] More specific examples are as follows:

[0048] Example 1

[0049] Preparation of bleaching working solution: At room temperature, add 2.0 g of sodium primary alkyl sulfonate penetrant and 2.0 g of fatty alcohol polyoxyethylene ether refining agent to 1 L of deionized water while stirring to obtain a mixture. Then continue stirring for 5-10 minutes to fully homogenize the mixture, thus obtaining the bleaching working solution.

[0050] Preparation of a weakly alkaline bleaching working solution: Add 4.0 g of sodium bicarbonate as a pH buffer to the obtained bleaching working solution, stir at 40℃ for 10-15 minutes, stop heating and continue stirring, and after cooling to room temperature, continue stirring for 10-15 minutes to allow the sodium bicarbonate to fully dissociate and be evenly dispersed in the system, forming a stable HCO3-. - / CO3 2- The buffer system yields a weakly alkaline bleaching working solution;

[0051] Preparation of liquid-phase manganese-based catalytic precursor: 1.26 g of manganese chloride, i.e., 10 mmol of manganese ions, was added to the obtained weakly alkaline bleaching working solution. The solution was stirred at 30°C for 10-15 minutes to fully hydrate and uniformly disperse the manganese ions in the weakly alkaline bleaching working solution, forming a highly active liquid-phase manganese-based catalytic precursor.

[0052] Preparation of manganese-citric acid complex solution: 3.0 g of citric acid was rapidly added to the liquid-phase manganese-based catalytic precursor and stirred at 30°C for 20-30 minutes to allow it to fully undergo in-situ coordination reaction with soluble manganese ions dispersed in the solution, thus obtaining the manganese-citric acid complex solution;

[0053] Preparation of a weakly alkaline bleaching working solution based on manganese metal complex: Add 8.0 g of 30% hydrogen peroxide to a manganese-citric acid complex solution at 30℃, raise the temperature to 55℃ to carry out an in-situ catalytic reaction, continue stirring for 15-20 minutes and then keep warm for 10-15 minutes to produce a highly efficient bleaching active ingredient, and finally obtain a weakly alkaline bleaching working solution based on manganese metal complex.

[0054] Low-temperature oxygen bleaching test was conducted on cotton fabrics: 50g of cotton fabric sample was added to a freshly prepared weakly alkaline bleaching working solution containing manganese-based metal complexes at a liquor ratio of 1:20. The sample was stirred at 80℃ for 30-45 minutes. Afterward, the sample was removed and washed 2-3 times with hot water at 60-80℃, then rinsed with room temperature water until neutral. The sample was then placed in an oven and dried in air at 60-80℃ for 1-2 hours. Whiteness and strength tests were performed on the cotton fabric samples before and after bleaching. The results showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 81.3%, and the strength retention rate was 94.5%.

[0055] Example 2

[0056] The difference from Example 1 is that when preparing the weakly alkaline bleaching working solution, the mass of sodium bicarbonate used is 2.0g, and the rest of the operation is the same as in Example 1.

[0057] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 77.5%, and the strength retention rate was 95.2%.

[0058] Example 3

[0059] The difference from Example 1 is that when preparing the weakly alkaline bleaching working solution, the mass of sodium bicarbonate used is 3.0g, and the rest of the operation is the same as in Example 1.

[0060] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 80.6%, and the strength retention rate was 91.8%.

[0061] Example 4

[0062] The difference from Example 1 is that when preparing the weakly alkaline bleaching working solution, the mass of sodium bicarbonate used is 5.0g, and the rest of the operation is the same as in Example 1.

[0063] Tests showed that the whiteness of cotton fabrics after low-temperature oxygen bleaching was 80.8%, and the strength retention rate was 90.5%.

[0064] Example 5

[0065] The difference from Example 1 is that when preparing the liquid-phase manganese-based catalytic precursor, the mass of manganese chloride used is 0.76 g, that is, the amount of manganese ions is 6 mmol. The rest of the operation is the same as in Example 1.

[0066] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 68.5%, and the strength retention rate was 93.2%.

[0067] Example 6

[0068] The difference from Example 1 is that when preparing the liquid-phase manganese-based catalytic precursor, the mass of manganese chloride used is 1.01 g, that is, the amount of manganese ions is 8 mmol. The rest of the operation is the same as in Example 1.

[0069] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 75.2%, and the strength retention rate was 92.7%.

[0070] Example 7

[0071] The difference from Example 1 is that when preparing the liquid-phase manganese-based catalytic precursor, the mass of manganese chloride used is 1.51 g, that is, the amount of manganese ions is 12 mmol. The rest of the operation is the same as in Example 1.

[0072] Tests showed that the whiteness of cotton fabrics after low-temperature oxygen bleaching was 80.3%, and the strength retention rate was 90.1%.

[0073] Example 8

[0074] The difference from Example 1 is that when preparing the manganese-citric acid complex solution, the mass of citric acid used is 2.0 g, and the rest of the operation is the same as in Example 1.

[0075] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 74.6%, and the strength retention rate was 85.2%.

[0076] Example 9

[0077] The difference from Example 1 is that when preparing the manganese-citric acid complex solution, the mass of citric acid used is 4.0 g, and the rest of the operation is the same as in Example 1.

[0078] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 87.5%, and the strength retention rate was 92.2%.

[0079] Example 10

[0080] The difference from Example 1 is that when preparing the manganese-based metal complex weakly alkaline bleaching working solution, the mass of hydrogen peroxide used is 6g, and the rest of the operation is the same as in Example 1.

[0081] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 73.2%, and the strength retention rate was 97.2%.

[0082] Example 11

[0083] The difference from Example 1 is that when preparing the manganese-based metal complex weakly alkaline bleaching working solution, the mass of hydrogen peroxide used is 10g, and the rest of the operation is the same as in Example 1.

[0084] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 81.8%, and the strength retention rate was 92.7%.

[0085] Example 12

[0086] The difference from Example 1 is that when preparing the manganese-based metal complex weakly alkaline bleaching working solution, the mass of hydrogen peroxide used is 12g, and the rest of the operation is the same as in Example 1.

[0087] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 82.3%, and the strength retention rate was 86.2%.

[0088] Example 13

[0089] The difference from Example 1 is that the in-situ catalytic reaction temperature is 45°C when preparing the manganese-based metal complex weakly alkaline bleaching working solution, while the rest of the operation is the same as in Example 1.

[0090] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 82.1%, and the strength retention rate was 89.6%.

[0091] Example 14

[0092] The difference from Example 1 is that the in-situ catalytic reaction temperature is 65°C when preparing the manganese-based metal complex weakly alkaline bleaching working solution, while the rest of the operation is the same as in Example 1.

[0093] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 82.5%, and the strength retention rate was 84.2%.

[0094] Comparative Example 1

[0095] The difference from Example 1 is that sodium bicarbonate was not used as a pH buffer when preparing the weakly alkaline bleaching working solution; the rest of the operations were the same as in Example 1.

[0096] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 65.3%, and the strength retention rate was 89.2%.

[0097] Comparative Example 2

[0098] The difference from Example 1 is that no manganese chloride was added in the preparation of the liquid-phase manganese-based catalytic precursor, while the rest of the operation is the same as in Example 1.

[0099] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 57.7%, and the strength retention rate was 97.4%.

[0100] Comparative Example 3

[0101] The difference from Example 1 is that no citric acid was added when preparing the manganese-citric acid complex solution; the rest of the operation was the same as in Example 1.

[0102] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 61.5%, and the strength retention rate was 84.7%.

[0103] Comparative Example 4

[0104] The difference from Example 1 is that when preparing the manganese-citric acid complex solution, water, sodium bicarbonate, manganese chloride, citric acid, and hydrogen peroxide are added at once, and the temperature is raised to 55°C to react. The rest of the operation is the same as in Example 1.

[0105] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 63.7%, and the strength retention rate was 92.5%.

[0106] Comparative Example 5

[0107] The difference from Example 1 is that a manganese-citric acid complex was prepared in advance. Specifically, 1.26 g of manganese chloride and 3.0 g of citric acid were dissolved in 50 mL of deionized water in a beaker and stirred at 30°C for 20-30 minutes to generate a manganese-citric acid complex. Subsequently, it was directly added to the weakly alkaline bleaching working solution containing penetrant, scouring agent and sodium bicarbonate prepared in steps (1) and (2), and hydrogen peroxide was added for subsequent processing. The remaining operations were the same as in Example 1.

[0108] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 76.3%, and the strength retention rate was 87.6%.

[0109] Comparative Example 6

[0110] The difference from Example 1 is that citric acid is replaced with EDTA in equimolar amounts; the rest of the operation is the same as in Example 1.

[0111] Tests showed that the whiteness of the cotton fabric after low-temperature oxygen bleaching was 71.3%, and the strength retention rate was 85.2%.

[0112] Table 1. Parameter control of Examples 1 to 14 of the present invention and Comparative Examples 1 to 6

[0113]

[0114] Table 2. Test and analysis results of bleached cotton fabrics from Examples 1 to 14 of the present invention and Comparative Examples 1 to 6.

[0115]

[0116] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the scope of the present invention. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a manganese-based metal complex weakly alkaline bleaching working solution, characterized in that, Includes the following steps: (1) Preparation of bleaching working solution: At room temperature, add penetrant and scouring agent to deionized water to obtain a mixture, stir until homogenized, and obtain bleaching working solution; (2) Preparation of weakly alkaline bleaching working solution: Add sodium bicarbonate as a pH buffer to the bleaching working solution obtained in step (1), stir at 35-45℃ for 10-15 minutes, cool to room temperature and continue stirring for 10-15 minutes to form a stable HCO3⁻ / CO3 2 ⁻ A buffer system is used to obtain a weakly alkaline bleaching working solution; (3) Preparation of liquid-phase manganese-based catalytic precursor: Add soluble divalent manganese salt to the weakly alkaline bleaching working solution obtained in step (2), and stir at 20-40℃ to make manganese ions uniformly dispersed in the weakly alkaline bleaching working solution to form a liquid-phase manganese-based catalytic precursor; (4) Preparation of manganese-citric acid complex solution: Add citric acid to the liquid manganese-based catalytic precursor obtained in step (3) and stir at 20-40℃ to allow it to fully undergo in-situ coordination reaction with soluble manganese ions to obtain manganese-citric acid complex solution; (5) Preparation of manganese-based metal complex weak alkaline bleaching working solution: Add hydrogen peroxide to the manganese-citric acid complex solution obtained in step (4), heat to 45-65℃ to carry out in-situ catalytic reaction, continue stirring for 15-20 minutes and then keep warm for 10-15 minutes to produce bleaching active ingredients and obtain manganese-based metal complex weak alkaline bleaching working solution.

2. The method for preparing the weakly alkaline bleaching working solution of manganese-based metal complex according to claim 1, characterized in that, Based on 1L of water, the amounts of raw material components are as follows: The amount of the penetrant is 1.0~3.0g; the amount of the refining agent is 1.0~3.0g; the amount of sodium bicarbonate is 2.0~5.0g; the amount of the soluble divalent manganese salt added is 6~12mmol based on the manganese ions therein; the amount of citric acid is 2.0~4.0g; the amount of hydrogen peroxide is 6.0~12.0g; and the hydrogen peroxide is a hydrogen peroxide aqueous solution with a mass fraction of 25~35%.

3. The method for preparing the weakly alkaline bleaching working solution of manganese-based metal complex according to claim 1, characterized in that, The soluble divalent manganese salt is one of manganese chloride, manganese sulfate, or manganese acetate.

4. The method for preparing the weakly alkaline bleaching working solution of manganese-based metal complex according to claim 1, characterized in that, The penetrant is sodium primary alkyl sulfonate, and the refining agent is fatty alcohol polyoxyethylene ether.

5. The method for preparing the weakly alkaline bleaching working solution of manganese-based metal complex according to claim 1, characterized in that, The pH value of the weakly alkaline bleaching working solution mentioned in step (2) is 8.0~9.

0.

6. A manganese-based metal complex weakly alkaline bleaching working solution prepared by the preparation method according to any one of claims 1-5.

7. The application of the manganese-based metal complex weakly alkaline bleaching working solution according to claim 6 in low-temperature oxygen bleaching of cotton fabrics.

8. The application according to claim 7, characterized in that, The bleaching process includes the following steps: Add the cotton fabric sample to the freshly prepared weakly alkaline bleaching working solution of manganese-based metal complex, control the bath ratio to 1:15-25, stir at a constant temperature of 60-80℃ for 30-45 minutes, then remove the cotton fabric sample, wash it 2-3 times with hot water at 60-80℃, then rinse it with room temperature water until neutral, and finally place it in an oven to dry in an air atmosphere at 60-80℃.

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