A white lignin, its extraction method and application

Abstract

This invention discloses a method for extracting white lignin, comprising the following steps: first, washing and drying white fruit shells, crushing and sieving them to obtain pulverized materials of different sizes; then, pre-treating the pulverized materials by filtration to obtain filter residue; enzymatically hydrolyzing the filter residue to obtain lignin-rich residue; finally, adding an alcoholic organic solvent, centrifuging, and precipitating white lignin. This invention also discloses a method for extracting white lignin and its applications, solving the problem of not being able to directly extract white lignin from plants. Low reaction temperature and short reaction time can reduce the damage to the lignin substructure during processing, avoiding the generation of multiple chromophores, resulting in a dark brown lignin product. This achieves effective extraction of white lignin under mild conditions. The extracted white lignin has a whiteness between 80 and 90.4 degrees and can be used as an active ingredient or additive in products with strict color requirements, expanding the application fields of lignin.

Description

Technical Field

[0001] This invention belongs to the field of biomass refining technology, specifically relating to a white lignin and its extraction method and application. Background Technology

[0002] With the ever-increasing consumption of fossil resources, resource scarcity has led to a series of environmental pollution problems, increasing the demand for alternative and sustainable resources. Lignin is the second largest biomass resource in the plant kingdom after cellulose. It has a natural three-dimensional network structure, high carbon content, good renewability and degradability, and its source is natural, safe, green, and readily available. If applied to production and daily life, it could have good economic benefits, while also making rational use of natural resources, thus showing promising application prospects.

[0003] Natural lignin is white or nearly colorless, but due to stringent extraction techniques (high temperature, high alkali, high acid value, etc.), and even the destruction of its original structure, various chromophores are generated, causing lignin products to appear dark brown. The dark appearance of lignin easily stains products, which greatly limits its development and utilization in fields such as sunscreens, dispersants, coatings, and packaging.

[0004] To improve the high-value utilization of lignin resources, it is necessary to reduce the color of lignin-based polymers. Therefore, scholars both domestically and internationally have conducted research on how to obtain light-colored lignin. Zhang Hui (Color Reduction of Lignin and its Application in Lignin-Based Chemicals, Doctoral Dissertation, South China University of Technology, 2018) investigated the influence of structural changes on macroscopic color by studying the preparation methods and microscopic dimensions of lignin, finding that the microstructure of lignin has a certain relationship with its apparent color; Lee et al. (Preparation and Application of Light-Colored Lignin Nanoparticles for Broad-Spectrum) Sunscreens, Polymers, 2020, 12:699) used rice husks as raw material, treated with cellulase, and then extracted in a solvent under mild conditions to finally obtain lignin with a lighter color; Chinese patent publication CN115838482A disclosed a two-step high-boiling alcohol-acid catalytic method for extracting light-colored lignin; Cui Ying et al. (Optimization of process for rapid extraction of light-colored sugarcane bagasse lignin in one step, Fine Chemicals, 2020, 37(09):1864-1869+1925) used p-toluenesulfonic acid (p-TsOH) to separate and extract sugarcane bagasse and prepare lignin with a lighter color.

[0005] While there are some methods for extracting light-colored lignin, no literature reports on the extraction of white lignin. Preventing discoloration of natural lignin during preparation is crucial for producing white lignin. Therefore, new methods for separating and extracting lignin must be further developed. Summary of the Invention

[0006] In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a method for extracting white lignin, which solves the problem that the lignin extracted from plants by the existing technology is dark in color.

[0007] Another object of the present invention is to provide a white lignin.

[0008] Another object of the present invention is to provide an application of white lignin.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A method for extracting white lignin, comprising the following steps:

[0011] (1) Wash and dry the white fruit shells, crush and sieve them to obtain crushed materials of different sizes;

[0012] (2) Prepare sodium hydroxide solution by mixing the pulverized material in step (1) with the sodium hydroxide solution to obtain a mixture. After the mixture is reacted under low temperature conditions, it is neutralized by acid addition, filtered and washed to obtain filter residue.

[0013] (3) Prepare a buffer solution. Mix the filter residue from step (2) with the buffer solution, add cellulase and hemicellulase, react in a water bath shaker for 72 hours, and then centrifuge and wash until neutral to obtain a residue rich in lignin.

[0014] (4) Mix the lignin-rich residue from step (3) with an alcoholic organic solvent, add an inorganic base, heat and centrifuge to obtain the supernatant, adjust the pH of the supernatant, let stand for 2-12 hours, and precipitate a white lignin precipitate.

[0015] (5) Wash the white lignin precipitate from step (4) with an acidic aqueous solution to remove excess acid and salt, add an antioxidant and a polyol to obtain a white paste, and freeze-dry the white paste to obtain white lignin.

[0016] Preferably, the white fruit shell is a discarded fruit shell or seed coat that is white or light yellow in appearance.

[0017] Preferably, the white shell includes one or more of the following: ginkgo shell, pumpkin seed shell, pistachio shell, white hyacinth bean skin, white lima bean skin, safflower seed skin, and white toothpick melon seed skin.

[0018] Preferably, the specific steps of drying in step (1) are as follows: the washed white fruit shells are dried in a hot air oven at 50-70°C for 4-8 hours.

[0019] Preferably, the specific steps of crushing and sieving in step (1) are as follows:

[0020] The white nut shells are crushed into 40-80 mesh powder, then ground in a ball mill at 500 r / min for 6-24 hours, and finally sieved through a 100-300 mesh sieve to obtain the crushed material.

[0021] Preferably, the specific steps for neutralizing with acid in step (1) are as follows:

[0022] Add an acidic aqueous solution to the mixture to adjust the pH to neutral.

[0023] Preferably, the concentration of the sodium hydroxide solution in step (2) is 3-10 wt%.

[0024] Preferably, the mass ratio of the pulverized material to the sodium hydroxide solution in step (2) is 1:1 to 20.

[0025] Preferably, the specific steps for the reaction of the mixture in step (2) under low-temperature conditions are as follows:

[0026] Stir the mixture at -15 to 0°C for 1 to 5 hours, then freeze for 10 to 24 hours, and finally place it at room temperature to thaw. Stir the thawed mixture at room temperature.

[0027] More preferably, the specific stirring step is to stir at a speed of 200-800 r / min for 6-24 hours.

[0028] Preferably, the mass ratio of the filter residue to the buffer solution in step (3) is 1:1 to 20.

[0029] Preferably, the concentration of the buffer solution in step (3) is 0.1–1 mol·L⁻¹. -1 The pH ranges from 4.3 to 6.5.

[0030] More preferably, the buffer solution comprises one or more of sodium acetate, sodium phosphate, and sodium citrate.

[0031] Preferably, the amount of cellulase used in step (3) is 1 to 10 wt%, and the amount of hemicellulase used is 0.1 to 3 wt%.

[0032] Preferably, the cellulase and hemicellulase include cellulase and hemicellulase supplied by Novozymes, Sinocare, or Gmet.

[0033] Preferably, the water temperature of the water bath shaker reaction in step (3) is 40-50°C and the speed is 100-220 r / min.

[0034] Preferably, the specific steps of centrifugation in step (3) are centrifugation at 3000-10000 r / min for 10-20 min.

[0035] Preferably, the alcohol organic solvent in step (4) includes one or more of 1,4-butanediol, 1,3-butanediol, glycerol, ethylene glycol, propylene glycol, and isopropanol.

[0036] Preferably, the solid-liquid ratio of the lignin-rich residue to the organic solvent is 1g:10-20mL.

[0037] Preferably, the inorganic base in step (4) includes one or more of NaOH, KOH, Na2CO3, Ba(OH)2, Ca(OH)2, Mg(OH)2 and NaHCO3.

[0038] Preferably, the heating step (4) involves heating to 60-100°C using an oil bath or water bath and maintaining the temperature for 1-3 hours.

[0039] More preferably, the heating temperature is 60°C, and the heat preservation reaction time is 3 hours.

[0040] Preferably, the specific steps for adjusting the pH value of the supernatant in step (4) are as follows:

[0041] Add an acidic solution to adjust the pH of the supernatant to 2-4.

[0042] More preferably, the acidic solution includes one or more of acetic acid, hydrochloric acid, and citric acid.

[0043] Preferably, the acidic aqueous solution in step (5) includes one or more of glycolic acid, malic acid, citric acid, and acetic acid.

[0044] More preferably, the concentration of the acidic aqueous solution is 0.1 to 0.5 wt%.

[0045] Preferably, the mass ratio of the antioxidant to the white lignin precipitate in step (5) is 1:2 to 10.

[0046] More preferably, the antioxidant is ascorbic acid.

[0047] More preferably, the concentration of the ascorbic acid is 0.1 to 0.4 wt%.

[0048] Preferably, the concentration of the polyol is 0.1 to 0.4 wt%.

[0049] Preferably, the mass ratio of the polyol to the white lignin precipitate is 1g:2-10mL.

[0050] A white lignin, extracted using a white lignin extraction method.

[0051] An application of a white lignin in the cosmetics, 3D printing, and film manufacturing industries.

[0052] The present invention has the following advantages and beneficial effects compared with the prior art:

[0053] (1) This invention discloses a method for extracting white lignin, which directly extracts white lignin from plants. In the early stage, the fruit shell powder is alkalized and freeze-thawed to improve the enzymatic hydrolysis efficiency and retain more lignin, thus facilitating lignin extraction. Enzymatic hydrolysis is used to remove cellulose and hemicellulose, and then organic solvents are used to dissolve the lignin. The low reaction temperature and short reaction time can reduce the damage to the lignin substructure during the process and avoid the generation of multiple chromophores, so that the lignin product is dark brown. This achieves efficient extraction of white lignin under mild conditions. The whiteness of the extracted white lignin is between 80 and 90.4 degrees, and it can be mixed with other components to prepare lignin-based biocomposite materials.

[0054] (2) The process for extracting white lignin provided by the present invention is simple and feasible, and the lignin obtained has high purity. It can be widely used in various industrial and agricultural products to realize the high added value utilization of lignin in multiple fields. In addition, white lignin has certain ultraviolet absorption properties and can be used in the field of sun protection.

[0055] (3) This invention utilizes waste materials such as ginkgo shells, pumpkin seed shells, pistachio shells, white hyacinth bean skins, safflower seed skins, or white toothpick melon seed skins to make resource utilization of biomass. This method is in line with the concept of green development, can effectively alleviate environmental pressure, and the production process is simple to operate and easy to control, with low equipment requirements and low reagent costs, showing good industrialization potential. Attached Figure Description

[0056] Figure 1 This is a flowchart of a method for extracting white lignin according to the present invention.

[0057] Figure 2 This is a color comparison diagram of white lignin and commercial lignin in Example 1 of the present invention.

[0058] Figure 3 The infrared absorption spectra of white lignin and commercial lignin in Example 1 of this invention are shown.

[0059] Figure 4The UV absorption spectra of white lignin and commercial lignin in Example 1 of this invention are shown. Detailed Implementation

[0060] The inventive objective of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described in detail here, but the implementation of the present invention is not limited to the following embodiments.

[0061] (1) Wash the pistachio shells, dry them in a hot air oven at 50°C for 8 hours, then mechanically crush them using a household mixer, and continue to ball mill them in a planetary ball mill for 8 hours. Finally, pass them through a 150-mesh sieve to obtain the crushed material.

[0062] (2) Weigh 20g of the material obtained in step (1), mix it with 300mL of sodium hydroxide solution with a concentration of 5wt%, stir at -6℃ for 3h, freeze in a refrigerator for 10h, stir at room temperature for 12h after the material is thawed, and then filter and wash to obtain filter residue.

[0063] (3) Mix the filter residue obtained in step (2) with 150 mL of 0.1 mol·L⁻¹ solution. -1 Mix with sodium acetate buffer solution, adjust pH to 6.4, add 0.45g cellulase and 0.15g hemicellulase (Novozymes enzyme), react in a water bath shaker at 45℃ and 200r / min for 72h, then centrifuge at 4000r / min for 10min, and wash with distilled water until neutral.

[0064] (4) The material obtained in step (3) is mixed with 135 mL of 90 wt% glycerol / water solution, and then 2 g of sodium hydroxide is added as a catalyst. After heating to 60 °C and reacting for 3 h, the supernatant is obtained by centrifugation. Acetic acid water solution is added to make the pH of the supernatant 2.3. After standing for 24 h, white lignin precipitate is obtained.

[0065] (5) Wash the lignin precipitate obtained in step (4) with 0.5wt% acetic acid solution to remove excess acid and salt, add 10mL of 0.2wt% ascorbic acid and polyvinyl alcohol solution to obtain a white paste, and freeze-dry it to obtain the white lignin.

[0066] The whiteness of the white lignin extracted in this embodiment was tested.

[0067] Whiteness test results are as follows:

[0068] The lignin powder was compressed into tablets, and its infrared spectrum was measured using a Fourier transform infrared spectrometer (Nicolet IS50-Nicolet Continuum, Thermo Fisher Scientific, USA), with a scanning range of 4000–4000 cm⁻¹. -1The white lignin extracted in this embodiment was dissolved in DMSO solution, and its UV absorbance in UVB (290-320nm) and UVA (320-400nm) was measured using a UV-1780 UV spectrometer (Shimadzu, Japan). The lignin powder was tested using an X-Rite 500 series colorimeter, and the color parameters L*, a*, and b* of the test samples were recorded after calibration. Each sample was tested five times, and the data were averaged. The L* value represents the brightness of the color, ranging from 0 (black) to 100 (white); a* represents the red and green of the lignin, with positive values ​​for red and negative values ​​for green; b* represents the yellow and blue of the lignin, with positive values ​​for yellow and negative values ​​for blue. Whiteness (WI) was calculated using the following formula:

[0069]

[0070] Color data are shown in Table 1. The whiteness value of the lignin was measured to be 90.40.

[0071] Example 2

[0072] (1) Wash the white hyacinth bean skins, dry them in a hot air oven at 50℃ for 8 hours, mechanically crush them and then ball mill them for 8 hours, and then pass them through a 100-mesh sieve.

[0073] (2) Weigh 20g of the material obtained in step (1), mix it with 300mL of sodium hydroxide solution with a concentration of 4wt%, stir at -6℃ for 3h, freeze in a refrigerator for 10h, stir at room temperature for 12h after the material is thawed, and then filter and wash to obtain filter residue.

[0074] (3) Mix the filter residue obtained in step (2) with 150 mL of 0.1 mol·L⁻¹ solution. -1 The sodium dihydrogen phosphate / sodium phosphate buffer solution was mixed and the pH was adjusted to 6.0. 0.45g cellulase and 0.15g hemicellulase (Sindeli enzyme) were added and reacted in a water bath shaker at 45℃ and 200r / min for 72h. Then, the mixture was centrifuged at 4000r / min for 10min and washed with distilled water until neutral.

[0075] (4) The material obtained in step (3) is mixed with 135 mL of 90 wt% ethylene glycol / water solution, and 2 g of sodium phosphate is added as a catalyst. After heating to 60 °C and reacting for 3 h, the supernatant is obtained by centrifugation. Acetic acid water solution is added to make the pH of the supernatant 2.3. After standing for 24 h, white lignin precipitate is obtained.

[0076] (5) The lignin precipitate obtained in step (4) was washed with 0.5 wt% citric acid solution to remove excess acid and salt. 10 mL of 0.1 wt% ascorbic acid and low molecular weight chitosan solution was added to obtain a white paste. After freeze-drying, the white lignin was obtained. The whiteness of the white lignin extracted in this embodiment was tested using the same method as in Example 1. The color data are shown in Table 1. The test results showed that the whiteness value of the lignin was 82.30.

[0077] Example 3

[0078] (1) Wash the ginkgo shells, dry them in a hot air oven at 50°C for 8 hours, mechanically crush them, ball mill them for 8 hours, and then pass them through a 100-mesh sieve.

[0079] (2) Weigh 20g of the material obtained in step (1), mix it with 300mL of sodium hydroxide solution with a concentration of 3wt%, stir at -6℃ for 3h, freeze in a refrigerator for 10h, stir at room temperature for 12h after the material is thawed, and then filter and wash to obtain filter residue.

[0080] (3) Mix the filter residue obtained in step (2) with 150 mL of 0.1 mol·L⁻¹ solution. -1 Mix with sodium citrate buffer solution, adjust pH to 6.3, add 0.45g cellulase and 0.15g hemicellulase (Gometase), react in a water bath shaker at 45℃ and 200r / min for 72h, then centrifuge at 4000r / min for 10min, and wash with distilled water until neutral.

[0081] (4) The material obtained in step (3) is mixed with 135 mL of 90 wt% 1,3-butanediol / water solution, and 2 g of sodium carbonate is added as a catalyst. After heating to 60 °C and reacting for 3 h, the supernatant is obtained by centrifugation. Acetic acid water solution is added to make the pH of the supernatant 2.3. After standing for 24 h, white lignin precipitate is obtained.

[0082] (5) The lignin precipitate obtained in step (4) was washed with 0.5 wt% citric acid solution to remove excess acid and salt. 15 mL of 0.3 wt% ascorbic acid and 1,4-butanediol solution was added to obtain a white paste. After freeze-drying, the white lignin was obtained. The whiteness of the white lignin extracted in this example was tested using the same method as in Example 1. The color data are shown in Table 1. The results showed that the whiteness value of the lignin was 89.91.

[0083] Example 4

[0084] (1) Wash the white pumpkin seed skin, dry it in a hot air oven at 50℃ for 8 hours, mechanically crush it and then ball mill it for 8 hours, and then pass it through a 100-mesh sieve.

[0085] (2) Weigh 20g of pulverized material and mix it with 300mL of 3wt% sodium hydroxide solution. Stir at -6℃ for 3h, freeze in a refrigerator for 10h, stir at room temperature for 12h after thawing, and then filter and wash to obtain filter residue.

[0086] (3) Mix the filter residue obtained in step (2) with 150 mL of 0.1 mol·L⁻¹ solution. -1 Mix with sodium acetate buffer solution, adjust pH to 6.2, add 0.45g cellulase and 0.15g hemicellulase (Novozymes enzyme), react in a water bath shaker at 45℃ and 200r / min for 72h, then centrifuge at 4000r / min for 10min, and wash with distilled water until neutral.

[0087] (4) The material obtained in step (3) is mixed with 135 mL of 90 wt% 1,4-butanediol / water solution, and then 2 g of sodium hydroxide is added as a catalyst. After heating to 60 °C and reacting for 3 h, the supernatant is obtained by centrifugation. Acetic acid water solution is added to make the pH of the supernatant 2.3. After standing for 24 h, white lignin precipitate is obtained.

[0088] (5) The lignin precipitate obtained in step (4) was washed with 0.5 wt% citric acid solution to remove excess acid and salt. 10 mL of 0.1 wt% ascorbic acid and polyethylene glycol 4000 solution was added to obtain a white paste. After freeze-drying, the white lignin was obtained. The whiteness of the white lignin extracted in this example was tested using the same method as in Example 1. The color data are shown in Table 1. The test results showed that the whiteness value of the lignin was 87.24.

[0089] Example 5

[0090] (1) Wash the white hyacinth bean skins, dry them in a hot air oven at 50℃ for 8 hours, mechanically crush them and then ball mill them for 8 hours, and then pass them through a 100-mesh sieve.

[0091] (2) Weigh 20g of the material obtained in step (1), mix it with 300mL of sodium hydroxide solution with a concentration of 3wt%, stir at -6℃ for 3h, freeze in a refrigerator for 10h, stir at room temperature for 12h after the material is thawed, and then filter and wash to obtain filter residue.

[0092] (3) Mix the filter residue obtained in step (2) with 150 mL of 0.1 mol·L⁻¹ solution. -1 Mix with sodium acetate buffer solution, adjust pH to 6.2, add 0.45g cellulase and 0.15g hemicellulase, react in a water bath shaker at 45℃ and 200r / min for 72h, then centrifuge at 4000r / min for 10min, and wash with distilled water until neutral.

[0093] (4) The material obtained in step (3) is mixed with 135 mL of 90 wt% glycerol / water solution, and then 2 g of sodium hydroxide is added as a catalyst. After heating to 60 °C and reacting for 3 h, the supernatant is obtained by centrifugation. Acetic acid water solution is added to make the pH of the supernatant 2.3. After standing for 24 h, white lignin precipitate is obtained.

[0094] (5) The lignin precipitate obtained in step (4) was washed with 0.5 wt% citric acid solution to remove excess acid and salt. 10 mL of 0.2 wt% ascorbic acid and polyethylene glycol 200 solution was added to obtain a white paste. After freeze-drying, the white lignin was obtained. The whiteness of the white lignin extracted in this example was tested using the same method as in Example 1. The color data are shown in Table 1. The test results showed that the whiteness value of the lignin was 80.11.

[0095] Comparative Example 1

[0096] The commercial lignin was named alkaline lignin and was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., product number L832292-100g.

[0097] The whiteness of commercial lignin was tested using the same procedure as in Example 1, and the color data are shown in Table 1.

[0098] Comparative Example 2

[0099] Pistachio shells were crushed and passed through a 150-mesh sieve. Then, 10g of pistachio shell powder was added to 200mL of pyruvic acid solution (mass fraction 50%) and treated at 100℃ for 1h to obtain light-colored lignin.

[0100] The whiteness of light-colored lignin was tested, and the testing steps were the same as in Example 1. The color data are shown in Table 1.

[0101] Comparative Example 3

[0102] The camellia fruit shells were crushed and passed through a 150-mesh sieve. Then, 10g of camellia fruit shell powder was added to 200mL of pyruvic acid solution (mass fraction 50%) and treated at 100℃ for 1h to obtain pale yellow lignin.

[0103] The whiteness of the pale yellow lignin was tested, and the testing procedure was the same as in Example 1. The color data are shown in Table 1.

[0104] Comparative Example 4

[0105] (1) Wash the camellia fruit shells, dry them in a hot air oven at 50°C for 8 hours, mechanically crush them with a household mixer, and then continue to ball mill them in a planetary ball mill for 8 hours before passing them through a 150-mesh sieve to obtain the crushed material.

[0106] (2) Weigh 20g of the material obtained in step (1), mix it with 300mL of sodium hydroxide solution with a concentration of 5wt%, stir at -6℃ for 3h, freeze in a refrigerator for 10h, stir at room temperature for 12h after the material is thawed, and then filter and wash to obtain filter residue.

[0107] (3) Mix the filter residue obtained in step (2) with 150 mL of 0.1 mol·L⁻¹ solution. -1 Mix with sodium acetate buffer solution, adjust pH to 6.4, add 0.45g cellulase and 0.15g hemicellulase (Novozymes enzyme), react in a water bath shaker at 45℃ and 200r / min for 72h, then centrifuge at 4000r / min for 10min, and wash with distilled water until neutral.

[0108] (4) The material obtained in step (3) is mixed with 135 mL of 90 wt% glycerol / water solution, and 2 g of sodium hydroxide is added as a catalyst. After heating to 60 °C and reacting for 3 h, the supernatant is obtained by centrifugation. Acetic acid water solution is added to make the pH of the supernatant 2.3. After standing for 24 h, a light brown lignin precipitate is obtained.

[0109] (5) The lignin precipitate obtained in step (4) was washed with 0.5 wt% acetic acid solution to remove excess acid and salt. 10 mL of 0.2 wt% ascorbic acid and polyvinyl alcohol solution was added to obtain a light brown precipitate. After freeze-drying, light brown lignin was obtained. The determination results showed that the whiteness value of the lignin was 44.85.

[0110] Comparative Example 5

[0111] (1) Wash the peanut shells, dry them in a hot air oven at 50°C for 8 hours, then mechanically crush them using a household mixer, and then continue to ball mill them in a planetary ball mill for 8 hours before passing them through a 150-mesh sieve to obtain the crushed material.

[0112] (2) Weigh 20g of the material obtained in step (1), mix it with 300mL of sodium hydroxide solution with a concentration of 5wt%, stir at -6℃ for 3h, freeze in a refrigerator for 10h, stir at room temperature for 12h after the material is thawed, and then filter and wash to obtain filter residue.

[0113] (3) Mix the filter residue obtained in step (2) with 150 mL of 0.1 mol·L⁻¹ solution. -1 Mix with sodium acetate buffer solution, adjust pH to 6.4, add 0.45g cellulase and 0.15g hemicellulase (Novozymes enzyme), react in a water bath shaker at 45℃ and 200r / min for 72h, then centrifuge at 4000r / min for 10min, and wash with distilled water until neutral.

[0114] (4) The material obtained in step (3) is mixed with 135 mL of 90 wt% glycerol / water solution, and then 2 g of sodium hydroxide is added as a catalyst. After heating to 60 °C and reacting for 3 h, the supernatant is obtained by centrifugation. Acetic acid water solution is added to make the pH of the supernatant 2.3. After standing for 24 h, a yellow lignin precipitate is obtained.

[0115] (5) The lignin precipitate obtained in step (4) was washed with 0.5 wt% acetic acid solution to remove excess acid and salt. 10 mL of 0.2 wt% ascorbic acid and polyvinyl alcohol solution was added to obtain a yellow flocculent substance. After freeze-drying, yellow lignin was obtained. The determination results showed that the whiteness value of the lignin was 42.94.

[0116] Table 1

[0117]

[0118] Table 1 shows the color data for each embodiment. A comparative analysis of the data from Example 1 and Comparative Example 1 indicates that the white lignin extracted by this method is significantly superior in whiteness to commercially available lignin. A comparison of Example 1 with Comparative Examples 2 and 3 shows that the lignin extracted by the acid method has a deeper color. Examples 1 with Comparative Examples 4 and 5 show that different biomass raw materials treated with the same method yield different degrees of whiteness, and white lignin is not present in all types of lignin. Therefore, this invention is highly efficient in improving lignin whiteness, providing an important basis for further application development.

[0119] Figure 2 This is a color comparison diagram of commercial lignin in Comparative Example 1 and white lignin in Example 1, by... Figure 2 It is known that commercial lignin is dark in color, appearing as blackish-brown, while the lignin extracted by the method of this invention is white. This indicates that the extraction method proposed in this invention can effectively improve the whiteness of lignin, with a whiteness value as high as 90.40.

[0120] Figure 3 The images show the infrared absorption spectra of white lignin in Example 1 and commercial lignin in Comparative Example 1. As can be seen from the images, at 3358 cm⁻¹... -1 Characteristic peaks for OH groups on the lignin benzene ring and side chain, 2940 cm⁻¹ -1 and 2872cm -1 This is a characteristic peak for CH in methyl and methylene groups. 1653 cm⁻¹ -1 1503cm -1 and 1462cm -1 This is a characteristic peak of the lignin aromatic ring framework. 1329cm -1 1225cm -1 1126cm -1 and 1051cm-1 The peaks represent the characteristic structural units of lignin, indicating that white lignin possesses a typical lignin compound structure. Furthermore, the figure shows that the peak intensity of commercial lignin increases with the increase of chromophores or auxochromes, which may be the reason for the blackening of lignin.

[0121] Figure 4 The UV absorption spectra of the commercial lignin in Comparative Example 1 and the white lignin in Example 1 demonstrate that the white lignin can effectively absorb ultraviolet radiation and is suitable for use in the field of sun protection in cosmetics.

[0122] The above-described specific embodiments are preferred embodiments of the present invention and are not intended to limit the present invention. Any other changes or equivalent substitutions made without departing from the technical solution of the present invention are included within the protection scope of the present invention.

Claims

1. A method for extracting white lignin, characterized in that, Includes the following steps: (1) Wash and dry the white fruit shells, crush and sieve them to obtain crushed materials of different sizes; (2) Prepare sodium hydroxide solution by mixing the pulverized material in step (1) with the sodium hydroxide solution to obtain a mixture. After the mixture is reacted under low temperature conditions, it is neutralized by acid addition, filtered and washed to obtain filter residue. (3) Prepare a buffer solution, mix the filter residue from step (2) with the buffer solution, add cellulase and hemicellulase, react in a water bath shaker for 72 h, then centrifuge and wash until neutral to obtain a residue rich in lignin. (4) Mix the lignin-rich residue from step (3) with an alcoholic organic solvent, add an inorganic base, heat and centrifuge to obtain the supernatant, adjust the pH of the supernatant, let it stand for 2-12 h, and precipitate a white lignin precipitate. (5) Wash the white lignin precipitate from step (4) with an acidic aqueous solution to remove excess acid and salt, add an antioxidant and a polyol to obtain a white paste, and freeze-dry the white paste to obtain white lignin; The white shell mentioned in step (1) includes one or more of the following: ginkgo shell, pumpkin seed shell, pistachio shell, white hyacinth bean skin, white lima bean skin, and safflower seed skin; The specific steps for the reaction of the mixture under low-temperature conditions in step (2) are as follows: Stir the mixture at -15~0℃ for 1~5 h, then freeze for 10~24 h, and finally place it at room temperature to thaw, and stir the thawed mixture at room temperature.

2. The method for extracting white lignin according to claim 1, characterized in that, The mass ratio of the filter residue to the buffer solution in step (3) is 1:1~20.

3. The method for extracting white lignin according to claim 1, characterized in that, The amount of cellulase used in step (3) is 1~10 wt%, and the amount of hemicellulase used is 0.1~3 wt%.

4. The method for extracting white lignin according to claim 1, characterized in that, The alcoholic organic solvents mentioned in step (4) include one or more of 1,4-butanediol, 1,3-butanediol, glycerol, ethylene glycol, propylene glycol, and isopropanol.

5. The method for extracting white lignin according to claim 1, characterized in that, The solid-liquid ratio of the lignin filter residue to the alcohol organic solvent in step (4) is 1 g: 10~20 mL.

6. The method for extracting white lignin according to claim 1, characterized in that, The specific heating steps in step (4) are to heat to 60~100℃ using an oil bath or water bath and keep the temperature for 1~3 hours.

7. A white lignin, characterized in that, It is extracted by the extraction method of white lignin according to any one of claims 1-6.

8. The application of the white lignin according to claim 7, characterized in that, It is used in the cosmetics, 3D printing and thin film manufacturing industries.

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