Method for converting lignin into functional dye and application

Abstract

The invention relates to the field of lignin processing, in particular to a method for converting lignin into functional dye and application. The method for converting the lignin into the functional dye comprises the following steps: preparing the lignin into low-molecular-weight lignin by using a reaction solution a containing potassium persulfate and ferric sulfate; adding low-molecular-weight lignin into the reaction liquid b, and reacting under the protection of inert gas to obtain the lignin functional dye. The reaction liquid b is prepared from sodium methoxide, lauryl mercaptan and a solvent. The invention also provides dyeing application of the lignin functional dye. By depolymerizing and demethylating the lignin, the brown dye which is small in molecular weight, high in water solubility and antibacterial is prepared, and a new way is provided for efficient utilization of the lignin.

Description

Technical Field

[0001] The present invention relates to the field of lignin processing, and in particular to a method for converting lignin into a functional dye and its application. Background Art

[0002] Lignin is one of the most abundant aromatic polymers in nature, widely present in plant cell walls and the second largest renewable biomass resource after cellulose. However, lignin's high molecular weight, complex three-dimensional network structure, and low solubility limit its application in high-value-added applications. Currently, lignin is primarily incinerated or discarded as a byproduct of the papermaking industry, resulting in not only a waste of resources but also negative environmental impacts. Therefore, developing efficient technologies for the conversion and utilization of lignin has important economic and environmental implications.

[0003] Lignin molecules contain abundant active groups such as phenolic hydroxyl groups and carboxyl groups, which give them potential antibacterial, antioxidant and UV absorption properties. However, the high molecular weight and low water solubility of natural lignin limit its application in functional fields such as dyes and antibacterial materials. Therefore, how to modify lignin by chemical or biological methods to prepare lignin dyes with low molecular weight, high water solubility and functional properties has become the key to its application in textile dyeing. Through biological or chemical modification means, the molecular weight of lignin can be reduced, its water solubility can be increased, and it can be given better dyeing properties and functional properties. For example, patent CN103703082A discloses a method for preparing sulfur dyes using lignin, and patent US20210285153A1 discloses a method for dyeing textiles with lignin. However, a method for simultaneously giving lignin good dyeing properties and functionality through modification has not been reported. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for converting lignin into functional dyes and its application.

[0005] In order to solve the above technical problems, the present invention provides a method for converting lignin into functional dyes, comprising the following steps:

[0006] 1) Preparation of low molecular weight lignin

[0007] Add lignin (powdered) to reaction solution a, stir and disperse, and then react at 100-140° C. for 3-12 hours (preferably 100-135° C. for 5-10 hours) under stirring; the material-liquid ratio of lignin to reaction solution a is 1 g / 20-150 ml (preferably 1 g / 50-100 ml);

[0008] The reaction solution a is composed of 5% to 15% (preferably 8% to 12%) of potassium persulfate by mass, 0.5% to 1.5% (preferably 0.9% to 1.3%) of ferric sulfate by mass, and a solvent (solvent a) as the balance;

[0009] The obtained reaction product is sequentially extracted, washed, and dried to obtain low molecular weight lignin;

[0010] 2) Preparation of lignin functional dyes

[0011] Add the low molecular weight lignin obtained in step 1) to the reaction solution b, stir to dissolve, and then stir under an inert gas (e.g., nitrogen) at 100-140° C. for 1-6 hours (preferably 100-130° C. for 3-5 hours); the material-liquid ratio of low molecular weight lignin to reaction solution b is 1 g / 20-150 ml (preferably 1 g / 50-10 ml);

[0012] The reaction mixture b is composed of 0.5% to 5% (preferably 2% to 4%) of sodium methoxide by mass, 0.1% to 2% (preferably 0.5% to 1.5%) of dodecyl mercaptan by mass, and a solvent (solvent b) as the balance;

[0013] After the reaction time is up, water is added to the obtained reaction product to terminate the reaction; then the pH is adjusted to 1-2 to perform acid precipitation (to precipitate lignin), and then filtered. The solid obtained by filtration is washed and dried to obtain a lignin functional dye.

[0014] In the present invention, sodium methoxide is used as an alkaline catalyst to assist dodecyl mercaptan in generating sulfur anions (RS-); dodecyl mercaptan is used as a strong nucleophile, and mercaptan removes protons under alkaline conditions to generate RS-, which attacks the methoxy carbon on the aromatic ring of lignin, triggering a demethylation reaction.

[0015] As an improvement to the method for converting lignin into functional dyes of the present invention:

[0016] The solvent in the reaction solution a (solvent a) is composed of ethanol / water at a volume ratio of 1:(1±0.05).

[0017] As a further improvement of the method for converting lignin into functional dyes of the present invention:

[0018] The stirring speed in step 1) is 500±100 rpm.

[0019] As a further improvement of the method for converting lignin into functional dyes of the present invention, in step 1):

[0020] The obtained reaction product was extracted with an equal volume of ethyl acetate, and then washed with a saturated NaCl solution and deionized water in sequence; finally, it was dried at 60±10° C. (to constant weight) to obtain low molecular weight lignin.

[0021] As a further improvement of the method for converting lignin into functional dyes of the present invention: the solvent (solvent b) in the reaction mixture b is N,N-dimethylformamide.

[0022] As a further improvement of the method for converting lignin into functional dyes of the present invention, in step 2):

[0023] An equal volume of deionized water was added to the obtained reaction product to terminate the reaction;

[0024] Use 1 mol / L hydrochloric acid to adjust the pH;

[0025] The solid obtained by filtration was washed with n-hexane;

[0026] The drying step is drying at 45±5° C. (to constant weight).

[0027] The present invention also provides a dyeing application of the lignin functional dye obtained by any of the above methods, comprising the following steps:

[0028] Step 1:

[0029] First, set the mass ratio of lignin functional dye to fabric = 1% to 5% (preferably 2% to 4%);

[0030] dissolving the lignin functional dye in deionized water to obtain a dye solution;

[0031] According to the dye bath ratio of 1:40-60 (preferably 1:50), immerse the fabric in the dye liquor, first heat it to 65-95°C (preferably 70-90°C) in a shaker (oscillation frequency of 150±20rpm), and then keep it warm for 60±5 minutes;

[0032] Then, the fabric is washed with water (the fabric is rinsed with deionized water until the washing water is colorless) to obtain the pretreated fabric;

[0033] Step 2:

[0034] The amount of mordant is set to 0.05-0.07% (preferably 0.06%) of the fabric weight;

[0035] dissolving the mordant in deionized water to obtain a mordant aqueous solution;

[0036] According to the bath ratio of 1:25-35 (preferably 1:30), the pretreated fabric obtained in step ① is immersed in the mordant aqueous solution and treated at 50-80°C (preferably 60-80°C) for 60±5 minutes on a shaking table (oscillation frequency of 150±20rpm);

[0037] Finally, the fabric was taken out and dried at 80±10° C. to obtain the dyed fabric.

[0038] As an improvement to the dyeing application of the lignin functional dye of the present invention: the mordant is alum or aluminum sulfate.

[0039] As a further improvement of the dyeing application of the lignin functional dye of the present invention: the heating rate is 2°C / min.

[0040] This invention organically combines two independent lignin modification technologies, "depolymerization" and "demethylation", for the first time and applies them to the field of dye preparation, achieving the following technological breakthroughs:

[0041] ① Synergistic modification strategy of depolymerization + demethylation

[0042] By first depolymerizing lignin to reduce its molecular weight and increase its water solubility, it imparts excellent dyeing properties. Then, through demethylation treatment, more phenolic hydroxyl groups are introduced to enhance the functional properties of lignin dyes (such as antibacterial properties).

[0043] ② Compared with traditional petroleum-based dyes, the present invention provides a green dye from renewable biomass resources, providing a new way for the high-value-added conversion of lignin.

[0044] In summary, the present invention develops a method for converting lignin into a functional dye, which not only achieves high-value utilization of lignin resources but also provides green, sustainable functional materials for fields such as textiles and medical treatment. By depolymerizing and demethylating lignin, the present invention produces a brown dye with low molecular weight, high water solubility, and antibacterial properties, providing a new approach for the efficient utilization of lignin. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0046] Figure 1 These are the antibacterial performance test results of lignin before and after modification in Example 1. DETAILED DESCRIPTION

[0047] The present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0048] The lignin powder of the present invention can be purchased from Shandong Longli Biotechnology Co., Ltd., for example, and has a molecular weight of about 5000 g / mol.

[0049] The stirring reaction in step 1) is carried out at a rotation speed of 500±100 rpm.

[0050] Example 1: A method for converting lignin into a functional dye, comprising the following steps:

[0051] 1) Preparation of low molecular weight lignin

[0052] In the reactor, reaction solution a was first added, and then lignin powder was added at a material-liquid ratio of 1 g / 50 ml. After stirring and dispersion, the mixture was stirred at a reaction temperature of 120° C. and a rotation speed of 500±100 rpm for 10 h.

[0053] After the reaction, the obtained reaction product was extracted with an equal volume of ethyl acetate, and then washed with a saturated NaCl solution and deionized water in sequence (until the washing solution was colorless and the pH was close to neutral); finally, it was dried at 60°C to a constant weight to obtain low molecular weight lignin.

[0054] The reaction solution a is composed of 8% by mass of potassium persulfate, 1.3% by mass of ferric sulfate, and the balance of solvent a;

[0055] The solvent a is composed of ethanol / water with a volume ratio of 1:1.

[0056] 2) Preparation of lignin functional dyes

[0057] In a reactor, first add reaction solution b, then add the low molecular weight lignin obtained in step 1) at a solid-liquid ratio of 1 g / 100 ml, stir evenly, and then, under nitrogen protection (continuously introduce nitrogen into the reactor), stir and react at 130°C and 500±100 rpm for 5 hours;

[0058] The reaction mixture is composed of 2% by mass of sodium methoxide, 1.5% by mass of dodecyl mercaptan, and the remainder of solvent (N,N-dimethylformamide).

[0059] After the reaction time is up, an equal volume of deionized water is added to the mixture in the reactor to terminate the reaction. The pH of the mixture is adjusted to 1-2 with 1 mol / L hydrochloric acid to perform acid precipitation, and then filtered to collect the resulting solid. The filtered solid is washed once with n-hexane (until the eluent is colorless and has no obvious dodecyl mercaptan odor), and finally dried at 45°C to constant weight to obtain a lignin functional dye.

[0060] 3) Dyeing application of lignin functional dyes

[0061] Step ①: first set the mass ratio of lignin functional dye to fabric = 4%;

[0062] dissolving the lignin functional dye in deionized water to obtain a dye solution;

[0063] The fabric was immersed in the dye liquor at a dye bath ratio of 1:50. The dye liquor temperature was first raised from room temperature to 90°C at a rate of 2°C / min on a shaker (oscillation frequency of 150 rpm), and then kept at this temperature for 60 minutes.

[0064] Then, the fabric is washed with water (the fabric is rinsed with deionized water until the washing water is colorless) to obtain the pretreated fabric;

[0065] Step 2:

[0066] The amount of mordant was set at 0.06% of the fabric weight;

[0067] dissolving the mordant in deionized water to obtain a mordant aqueous solution;

[0068] According to the bath ratio of 1:30, the pretreated fabric obtained in step ① was immersed in the mordant aqueous solution and treated at 60°C for 60 minutes in a shaking table (oscillation frequency of 150 rpm);

[0069] Finally, the fabric was taken out and dried at 80° C. to a constant weight to obtain a dyed fabric (final dyed product).

[0070] The mordant is alum.

[0071] In Examples 2 to 9, relative to Example 1, corresponding process parameters are changed (as described in Table 1 below); the rest are the same as in Example 1.

[0072] Table 1. Example Condition Parameters

[0073]

[0074] Test method:

[0075] The molecular weight of the modified lignin (M n );

[0076] The water solubility of the modified lignin was tested using GB 21845-2008 (at a water temperature of 25°C);

[0077] The release bactericidal effect of modified lignin was tested using AATCC-147, which is expressed as the size of the inhibition zone. Specifically, the sterilized LB agar medium was poured into a sterile petri dish. After the plate solidified, the diluted bacterial solution was evenly spread on the surface of the plate. A 6mm diameter filter paper was soaked in a 1.5mg / mL sample solution for 1 hour and placed on the microbial culture medium. After incubation at 37°C for 24 hours, the diameter of the inhibition zone was measured with a caliper (the bacteria targeted were Gram-negative bacteria: Escherichia coli; Gram-positive bacteria: Staphylococcus aureus).

[0078] The color depth (K / S value) of the front and back of the dyed products was tested using a conventional spectrophotometer. The color fastness of the dyed products to washing was tested using AATCC 61-2003 "Color fastness to home and commercial washing: Rapid method". The antibacterial properties of the fabrics were tested using GB / T 20944.2-2007 (absorption method) (representative bacterial species targeted were Escherichia coli and Staphylococcus aureus). The color fastness to dry and wet rubbing of the dyed fabrics was tested using GB / T 3920-2008 "Textiles - Tests for color fastness - Color fastness to rubbing".

[0079] Dye yield = (mass of lignin powder put into the reactor in step 1 - mass of lignin functional dye obtained in step 2) / mass of lignin powder put into the reactor in step 1.

[0080] Table 2. Implementation Effects

[0081]

[0082]

[0083] Note: Example 2 has the best effect.

[0084] Comparative Example 1: The ratio of potassium persulfate in Example 1 was changed to 2%, while other parameters remained unchanged. The obtained results are shown in Table 3 below.

[0085] It can be seen that a too low proportion of potassium persulfate will significantly affect the molecular weight and solubility of the dye, causing the dyeing effect and antibacterial properties of the fabric to deteriorate. Ultimately, the antibacterial rate of the dyed fabric will not meet the national standard requirements (antibacterial rate not less than 85%).

[0086] Comparative Example 2: The proportion of ferric sulfate in Example 1 was changed to 0.2%, while other parameters remained unchanged. The obtained results are shown in Table 3 below.

[0087] It can be seen that if the proportion of ferric persulfate is too low, it will significantly affect the molecular weight and solubility of the dye, and deteriorate the dyeing effect and antibacterial properties of the fabric.

[0088] Comparative Example 3: The reaction temperature in step 1) of Example 2 was changed to 160° C., while other parameters remained unchanged. The obtained results are shown in Table 3 below.

[0089] It can be seen that the reaction temperature in step 1) is too high, resulting in polymerization between lignin molecules, which will significantly affect the molecular weight and solubility of the dye, making the dyeing effect and antibacterial properties of the fabric worse. Ultimately, the antibacterial rate of the dyed fabric does not meet the national standard requirements (antibacterial rate not less than 85%).

[0090] Comparative Example 4: The reaction time in step 1) in Example 2 was changed to 24 h, while other parameters remained unchanged. The results obtained are shown in the following table.

[0091] It can be seen that if the reaction time in step 1) is too long, polymerization of lignin molecules will occur, which will significantly affect the molecular weight and solubility of the dye, and deteriorate the dyeing effect and antibacterial properties of the fabric.

[0092] Comparative Example 5: The solid-to-liquid ratio of the low molecular weight lignin in step 2) of Example 3 was changed to 1:250, and other parameters remained unchanged. The obtained results are shown in Table 3 below.

[0093] It can be seen that if the solid-liquid ratio in step 2) is too large, the demethylation effect of the dye will be significantly affected, the antibacterial performance of the dye will be deteriorated (the diameter of the inhibition zone of Escherichia coli is 8 mm, and the diameter of the inhibition zone of Staphylococcus aureus is 9 mm), and the antibacterial performance of the fabric will also be deteriorated.

[0094] Comparative Example 6: The reaction temperature in step 2) in Example 3 was changed to 70° C., while other parameters remained unchanged. The obtained results are shown in Table 3 below.

[0095] It can be seen that if the reaction temperature in step 2) is too low, the demethylation effect of the dye will be significantly affected, resulting in a deterioration in the antibacterial performance of the dye (the diameter of the inhibition zone for Escherichia coli is 6 mm, and the diameter of the inhibition zone for Staphylococcus aureus is 8 mm). The antibacterial performance of the dyed fabric will also deteriorate, and the antibacterial rate of the dyed fabric will ultimately fail to meet the national standard requirement (the antibacterial rate is not less than 85%).

[0096] Comparative Example 7: The reaction time in step 2) in Example 3 was changed to 0.5 h, and other parameters remained unchanged. The results obtained are shown in Table 3 below.

[0097] It can be seen that if the reaction time in step 2) is too short, the demethylation effect of the dye will be significantly affected, resulting in a deterioration in the antibacterial performance of the dye (the diameter of the inhibition zone for Escherichia coli is 5 mm, and the diameter of the inhibition zone for Staphylococcus aureus is 6 mm). The antibacterial performance of the dyed fabric will also deteriorate, and the antibacterial rate of the dyed fabric will ultimately fail to meet the national standard requirements (the antibacterial rate is not less than 85%).

[0098] Comparative Example 8: The reaction temperature in step 2) of Example 2 was changed to 180° C., while other parameters remained unchanged. The results obtained are shown in Table 3 below.

[0099] It can be seen that the reaction temperature in step 2) is too high, resulting in polymerization between lignin molecules, which will significantly affect the demethylation effect of the dye, making the antibacterial performance of the dye worse (the diameter of the inhibition zone of Escherichia coli is 8 mm, and the diameter of the inhibition zone of Staphylococcus aureus is 9 mm). It also makes the antibacterial performance of the dyed fabric worse, and the antibacterial rate of the dyed fabric ultimately does not meet the requirements of the national standard (the antibacterial rate is not less than 85%).

[0100] Comparative Example 9: The lignin powder-to-liquid ratio in step 1) of Example 2 was changed to 1:20, while other parameters remained unchanged. The obtained results are shown in Table 3 below.

[0101] It can be seen that the lignin powder-liquid ratio in step 1) is too low, and the lignin dispersibility is poor, which will significantly affect the molecular weight and solubility of the dye, resulting in poor dyeing effect and antibacterial performance.

[0102] Comparative Example 10: The final temperature of the dye solution in step 3) of Example 2 was changed to 50° C., while other parameters remained unchanged. The obtained results are shown in Table 3 below.

[0103] It can be seen that if the final temperature of the dye solution in step 3) is too low, the degree of adsorption of the dye by the fabric will be significantly affected, resulting in poor dyeing color depth and antibacterial performance.

[0104] Comparative Example 11: The amount of sodium methoxide in step 2) in Example 3 was changed to 0.2%, and other parameters remained unchanged. The obtained results are shown in Table 3 below.

[0105] It can be seen that if the concentration of sodium methoxide in step 2) is too low, the demethylation effect of the dye will be significantly affected, resulting in poor antibacterial performance of the dye (the diameter of the inhibition zone for Escherichia coli is 10 mm, and the diameter of the inhibition zone for Staphylococcus aureus is 11 mm). The antibacterial performance of the dyed fabric will also deteriorate, and the antibacterial rate of the dyed fabric will ultimately fail to meet the national standard requirement (the antibacterial rate is not less than 85%).

[0106] Comparative Example 12: The amount of dodecyl mercaptan in step 2) in Example 3 was changed to 0.05%, and other parameters remained unchanged. The obtained results are shown in Table 3 below.

[0107] It can be seen that if the concentration of dodecyl mercaptan in step 2) is too low, the demethylation effect of the dye will be significantly affected, resulting in poor antibacterial performance of the dye (the diameter of the inhibition zone for Escherichia coli is 8 mm, and the diameter of the inhibition zone for Staphylococcus aureus is 9 mm). The antibacterial performance of the dyed fabric is also poor, and the antibacterial rate of the dyed fabric ultimately fails to meet the national standard requirement (the antibacterial rate is not less than 85%).

[0108] Comparative Example 13: The mordanting temperature in step 3) of Example 3 was changed to 30° C., while other parameters remained unchanged. The obtained results are shown in Table 3 below.

[0109] It can be seen that if the mordanting temperature is too low, it will significantly affect the color fixation effect of the dyed fabric, and the final color change and friction fastness of the dyed fabric will not meet the requirements of the national standard (the evaluation level is lower than level 3).

[0110] Table 3, comparative example effect

[0111]

[0112]

[0113] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples and is subject to numerous variations. All variations that can be directly derived or conceived by a person of ordinary skill in the art from the disclosure of the present invention are considered to be within the scope of protection of the present invention.

Claims

1. A method for converting lignin into functional dyes, characterized in that The steps include: 1) Preparation of low molecular weight lignin Add lignin to the reaction solution a, stir and disperse, and then react at 100-140° C. for 3-12 hours under stirring; the material-liquid ratio of lignin to reaction solution a is 1 g / 20-150 ml; The reaction solution a is composed of 5% to 15% by mass of potassium persulfate, 0.5% to 1.5% by mass of ferric sulfate, and a solvent as the balance; The obtained reaction product is sequentially extracted, washed, and dried to obtain low molecular weight lignin; 2) Preparation of lignin functional dyes Add the low molecular weight lignin obtained in step 1) to the reaction solution b, stir to dissolve, and then stir and react at 100-140° C. for 1-6 hours under inert gas protection; the material-liquid ratio of low molecular weight lignin to reaction solution b is 1 g / 20-150 ml; The reaction mixture is composed of 0.5% to 5% by mass of sodium methoxide, 0.1% to 2% by mass of dodecyl mercaptan, and the remainder being a solvent; After the reaction time is up, water is added to the obtained reaction product to terminate the reaction; then the pH is adjusted to 1-2 to perform acid precipitation, and then filtered. The solid obtained by filtration is washed and dried to obtain a lignin functional dye.

2. The method for converting lignin into functional dye according to claim 1, wherein: The solvent in the reaction solution a is composed of ethanol / water with a volume ratio of 1:(1±0.05).

3. The method for converting lignin into functional dye according to claim 2, wherein: The stirring speed in step 1) is 500±100 rpm.

4. The method for converting lignin into functional dyes according to any one of claims 1 to 3, characterized in that In the step 1): The obtained reaction product was extracted with an equal volume of ethyl acetate, and then washed with a saturated NaCl solution and deionized water in sequence; finally, it was dried at 60±10° C. to obtain low molecular weight lignin.

5. The method for converting lignin into functional dyes according to any one of claims 1 to 4, characterized in that: The solvent in the reaction mixture is N,N-dimethylformamide.

6. The method for converting lignin into functional dye according to claim 5, characterized in that In the step 2): An equal volume of deionized water was added to the obtained reaction product to terminate the reaction; Use 1 mol / L hydrochloric acid to adjust the pH; The solid obtained by filtration was washed with n-hexane; The drying is carried out at 45±5°C.

7. The dyeing application of the lignin functional dye obtained by any one of the methods of claims 1 to 6, characterized in that The following steps are involved: Step 1: First, set the mass ratio of lignin functional dye to fabric to 1% to 5%; dissolving the lignin functional dye in deionized water to obtain a dye solution; Immerse the fabric in the dye liquor at a dye bath ratio of 1:40-60, heat it to 65-95°C in a shaker, and then keep it warm for 60±5 minutes; Then, the pretreated fabric is obtained by washing; Step 2: The amount of mordant is set at 0.05-0.07% of the fabric weight; dissolving the mordant in deionized water to obtain a mordant aqueous solution; Immerse the pretreated fabric obtained in step ① in a mordant aqueous solution at a bath ratio of 1:25-35 and treat in a shaker at 50-80°C for 60±5 minutes; Finally, the fabric was taken out and dried at 80±10° C. to obtain the dyed fabric.

8. The dyeing application of the lignin functional dye according to claim 7, characterized in that: The mordant is alum or aluminum sulfate.

9. The dyeing application of the lignin functional dye according to claim 7 or 8, characterized in that: The heating rate is 2°C / min.

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