Method for extracting light-color lignin and application of light-color lignin in sunscreen cream

Abstract

The invention belongs to the technical field of lignin separation and high-value utilization thereof, and particularly relates to a method for extracting light-color lignin and application of the light-color lignin in sunscreen cream. The method for extracting the light-colored lignin comprises the following steps: performing extraction treatment on a lignin raw material by adopting a deep eutectic solvent containing oxalic acid and polyethylene glycol and hydrogen peroxide, collecting filtrate, and mixing the filtrate with water to separate out solid, namely the light-colored lignin, the color difference value of the light-color lignin is less than 40. The sunscreen cream contains the light-colored lignin. The method is characterized in that a specific polyethylene glycol-oxalic acid eutectic solvent and hydrogen peroxide synergistic extraction system is adopted, light-color lignin with a light color is successfully extracted from a lignin raw material, and the light-color lignin has good ultraviolet absorption performance and good biocompatibility with sunscreen cream components; when the natural sun-screening agent is added into a sun-screening formula, the sun-screening coefficient can be remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lignin separation and high-value utilization, and particularly relates to a method for extracting light-colored lignin and application of the method in sunscreen. Background Art

[0002] With the global emphasis on sustainable development and green chemistry, the development and high-value utilization of natural biomass resources have become a common focus of scientific and industrial attention. Lignin, a natural aromatic polymer second only to cellulose in abundance, is widely present in plant cell walls and possesses excellent UV absorption, antioxidant properties, and biodegradability. However, its complex cross-linked structure and chromophores (such as phenolic hydroxyl groups and conjugated double bonds) result in a dark color (typically tan to black), severely limiting its commercial application in high-end packaging, bio-based dyes, and high-value-added products. Its potential in light-colored sunscreen products, in particular, has yet to be fully explored.

[0003] Currently, conventional decolorization strategies mainly focus on areas such as pulp bleaching process optimization, pulping wastewater color control, and lignin directional degradation. However, these methods can easily lead to deep damage to the lignin molecular structure. Ultraviolet radiation technology has shown certain potential in the field of lignin color regulation, but due to the insufficient penetration of ultraviolet light, the process must be implemented in an extremely low concentration system (usually <1wt%), resulting in a surge in solvent consumption and high energy consumption for subsequent concentration. At the same time, there are problems such as insufficient reaction activity and low decolorization efficiency. Continuous irradiation for 6 to 12 hours is often required to achieve the target color, limiting its industrial feasibility.

[0004] In recent years, deep eutectic solvents, as a new type of green solvent system, have provided an innovative approach for the mild extraction and functional modification of lignin due to their low toxicity, designability, and ability to efficiently dissolve biomass. It is worth noting that the synergistic effect of deep eutectic solvents and hydrogen peroxide has opened up a new direction for the green extraction and lightening of lignin. However, the lignin extracted by the existing deep eutectic solvent and hydrogen peroxide synergistic system still has the problem of being too dark in color to meet the requirements of sunscreen applications, or being too light in color but with weak UV absorption properties and poor compatibility with sunscreen products, which limits its high-value applications. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a method for extracting light-colored lignin to address the problems that lignin extracted by the synergistic system of deep eutectic solvent and hydrogen peroxide used in the prior art is still dark in color and cannot meet the requirements of sunscreen applications, or is light in color but has weak ultraviolet absorption performance and poor compatibility with sunscreen products. The extracted light-colored lignin not only retains good ultraviolet absorption performance, but also has good compatibility with sunscreen products. When added to sunscreen products as an additive, it can significantly improve their sun protection factor, thereby achieving high-value applications.

[0006] Specifically, the method for extracting light-colored lignin provided by the present invention comprises the following steps: extracting the lignin raw material using a low eutectic solvent containing oxalic acid and polyethylene glycol and hydrogen peroxide, collecting the filtrate, mixing the filtrate with water, and the solid precipitated is the light-colored lignin; the color difference value of the light-colored lignin is below 40.

[0007] In a preferred embodiment, the molar ratio of oxalic acid to polyethylene glycol in the deep eutectic solvent is 1:(1-3).

[0008] In a preferred embodiment, the preparation method of the deep eutectic solvent comprises: stirring and mixing oxalic acid and polyethylene glycol at 70-90° C., and the resulting mixture is the deep eutectic solvent.

[0009] In a preferred embodiment, the number average molecular weight of the polyethylene glycol is 150 to 350 g / mol.

[0010] In a preferred embodiment, the mass ratio of the lignin raw material to the deep eutectic solvent is (0.5-2):20.

[0011] In a preferred embodiment, the amount of hydrogen peroxide used is 10 to 50 wt % of the mass of the deep eutectic solvent.

[0012] In a preferred embodiment, the lignin raw material is selected from at least one of wood, bamboo, crops, and herbaceous plant raw materials.

[0013] In a preferred embodiment, the method for pretreating the lignin raw material comprises: washing and drying the lignin raw material, and then mechanically grinding and sieving the lignin raw material to obtain a powdered lignin raw material.

[0014] In a preferred embodiment, the extraction treatment conditions include: temperature of 100-120° C. and time of 1-3 hours.

[0015] The second object of the present invention is to provide light-colored lignin prepared by the above method.

[0016] In a preferred embodiment, the particle size of the light-colored lignin is 100 to 300 nm.

[0017] A third object of the present invention is to provide a sunscreen containing the light-colored lignin.

[0018] In a preferred embodiment, the content of light-colored lignin in the sunscreen is 1.0-2.0 wt%.

[0019] Beneficial effects: The key to the present invention is the use of a polyethylene glycol-oxalic acid deep eutectic solvent and a hydrogen peroxide extraction system to successfully extract light-colored lignin from the lignin raw material. The light-colored lignin not only has good ultraviolet absorption properties but also has good biocompatibility with sunscreen components. When added to sunscreen formulas as a natural sunscreen, it can significantly improve the sun protection factor, promote the high-value utilization of biomass resources, and lay a theoretical and practical foundation for replacing synthetic sunscreen ingredients and developing efficient, safe and environmentally friendly natural sunscreen products. It is speculated that the reason may be that: through the synergistic effect of polyethylene glycol-oxalic acid low eutectic solvent and hydrogen peroxide, the chromophores in lignin (such as conjugated phenol-type structures and carbonyl compounds) are selectively degraded during the lignin extraction process, thereby avoiding lignin condensation and reducing the chromaticity of lignin. At the same time, the mild depolymerization effect of polyethylene glycol-oxalic acid low eutectic solvent retains the aromatic skeleton and ultraviolet absorption active groups of lignin, so that the obtained light-colored lignin exhibits excellent light protection properties. Moreover, the light-colored lignin has a smaller particle size and better suspension stability, which improves its compatibility with sunscreen components, so that it can replace synthetic sunscreen ingredients and be added to sunscreen formulas to improve its sun protection performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is a graph showing the particle size and potential test results of the lignin obtained in Preparation Examples 2 to 6 and Comparative Example Preparation Example 2.

[0021] Figure 2 This is a graph showing the molecular weight test results of the lignin obtained in Preparation Examples 2 to 6 and Comparative Example Preparation Example 2.

[0022] Figure 3 It is the Fourier transform infrared (FTIR) spectrum of the lignin obtained in Preparation Examples 2 to 6 and Comparative Example Preparation Example 2.

[0023] Figure 4 The lignin obtained in Preparation Examples 2 to 6 and Comparative Example Preparation Example 2 is 31 P NMR nuclear magnetic spectrum.

[0024] Figure 5 This is a two-dimensional nuclear magnetic resonance spectrum of the side chain region and aromatic region of the lignin (DH-L-10) obtained in Preparation Example 2.

[0025] Figure 6 This is a two-dimensional nuclear magnetic resonance spectrum of the side chain region and aromatic region of the lignin (DH-L-20) obtained in Preparation Example 3.

[0026] Figure 7 This is a two-dimensional nuclear magnetic resonance spectrum of the side chain region and aromatic region of the lignin (DH-L-30) obtained in Preparation Example 4.

[0027] Figure 8 This is a two-dimensional nuclear magnetic resonance spectrum of the side chain region and aromatic region of the lignin (DH-L-40) obtained in Preparation Example 5.

[0028] Figure 9 This is a two-dimensional nuclear magnetic resonance spectrum of the side chain region and aromatic region of the lignin (DH-L-50) obtained in Preparation Example 6. DETAILED DESCRIPTION

[0029] The method for extracting light-colored lignin provided by the present invention comprises the following steps: extracting a lignin raw material using a deep eutectic solvent containing oxalic acid and polyethylene glycol and hydrogen peroxide, collecting the filtrate, and mixing the filtrate with water to obtain a solid precipitated as light-colored lignin. The light-colored lignin has a color difference value of less than 40. In the present invention, a TS7700 spectrophotometer (Shenzhen Sannshi Technology) is preferably used to evaluate the color of the lignin. Existing low eutectic solvents such as choline chloride-polyethylene glycol-oxalic acid, choline chloride-polyethylene glycol, choline chloride-oxalic acid, etc. are prone to lignin condensation problems during the extraction process (lignin condensation causes dark color). Compared with the existing low eutectic solvent system, the present invention adopts an oxalic acid-polyethylene glycol low eutectic solvent and a hydrogen peroxide extraction system, which can effectively remove the conjugated carbonyl groups of lignin (one of the important reasons for the dark color of lignin) during the extraction process, while avoiding lignin condensation and reducing the phenolic hydroxyl content of lignin. The decrease in the phenolic OH content helps to reduce the p-π conjugated structure formed by the phenolic OH and the benzene ring in the lignin, reduce the color of the lignin, and obtain light-colored lignin.

[0030] In the present invention, the molar ratio of oxalic acid to polyethylene glycol in the deep eutectic solvent is preferably 1:(1-3). In this case, the polyethylene glycol-oxalic acid deep eutectic solvent system is more stable and more conducive to improving the extraction rate of lignin. Based on the content of oxalic acid in the deep eutectic solvent as 1 mol, the content of polyethylene glycol in the deep eutectic solvent is preferably 1-3 mol, such as 1 mol, 1.5 mol, 2 mol, 2.5 mol, 3 mol, or any value therebetween.

[0031] In the present invention, the low eutectic solvent containing oxalic acid and polyethylene glycol is preferably obtained by mixing oxalic acid and polyethylene glycol. The preparation method of the low eutectic solvent specifically comprises: stirring and mixing oxalic acid and polyethylene glycol at 70-90°C, and the resulting mixed solution is a low eutectic solvent. The temperature of the mixing treatment is preferably 70-90°C, such as 70°C, 75°C, 80°C, 85°C, 90°C or any value therebetween, which is more conducive to mixing oxalic acid and polyethylene glycol to obtain a uniform and transparent low eutectic solvent. The time of the mixing treatment may not be specifically limited, and is based on the uniform and transparent mixed solution obtained after oxalic acid and polyethylene glycol are evenly mixed, preferably 1-2h, such as 1h, 1.2h, 1.5h, 1.8h, 2h or any value therebetween.

[0032] In the present invention, the number average molecular weight (Mn) of the polyethylene glycol is preferably 150 to 350 g / mol, such as 150 g / mol, 200 g / mol, 250 g / mol, 300 g / mol, 350 g / mol or any value therebetween. In the present invention, the mass ratio of the lignin raw material to the deep eutectic solvent is preferably (0.5 to 2):20. Based on the amount of the deep eutectic solvent being 20 g, the amount of the lignin raw material is preferably 0.5 to 2 g, such as 0.5 g, 0.8 g, 1 g, 1.5 g, 2 g or any value therebetween.

[0033] In the present invention, the amount of hydrogen peroxide is preferably 10-50 wt% of the mass of the deep eutectic solvent, such as 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt% or any value therebetween. This is more conducive to the safe and efficient extraction of light-colored lignin.

[0034] In the present invention, the lignin raw material can be selected from at least one of wood, bamboo, crops and herbaceous plants. The source of the lignin raw material can be directly purchased from pretreated lignin raw materials, or the lignin raw material to be extracted can be obtained by pretreating the original lignin raw material. The pretreatment method may include: washing and drying the lignin raw material, mechanically grinding it, and sieving it to obtain a powdered lignin raw material. The lignin raw material used in the present invention is preferably obtained by pretreating waste crops. The specific processing process includes: first, rinsing the tea stems with deionized water, then drying them at 70-90°C, mechanically grinding them, and passing them through an 80-mesh sieve to obtain tea residue powder. The tea residue powder is the lignin raw material and can be directly used for subsequent extraction.

[0035] In the present invention, the extraction treatment conditions preferably include: a temperature of 100-120°C, such as 100°C, 105°C, 110°C, 115°C, 120°C or any value therebetween; and a time of 1-3h, such as 1h, 1.5h, 2h, 2.5h, 3h or any value therebetween.

[0036] The present invention provides light-colored lignin prepared by the method.

[0037] In the present invention, the particle size of the light-colored lignin is preferably 100 to 300 nm, such as 100 nm, 150 nm, 2000 nm, 250 nm, 300 nm, or any value therebetween. When the particle size of the light-colored lignin is within this preferred range, it exhibits improved suspension stability, which helps improve compatibility with sunscreen ingredients. Thus, it can be added to sunscreen formulations to replace synthetic sunscreens and impart excellent sun protection to the sunscreen.

[0038] The present invention provides a sunscreen containing the above-mentioned light-colored lignin.

[0039] In the present invention, the content of light-colored lignin in the sunscreen is preferably 1.0-2.0 wt%, such as 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2.0 wt%, or any value therebetween. This is more conducive to ensuring that the color of the sunscreen is bright enough, acceptable to consumers, and has good sun protection performance.

[0040] In the present invention, the method for preparing the sunscreen may include: mixing the light-colored lignin with pure cream in the dark to obtain the sunscreen containing the light-colored lignin. The pure cream may be a non-sunscreen cream without the addition of synthetic sunscreens, such as a moisturizing cream, or a cream with a certain sunscreen function.

[0041] In the preparation process of the sunscreen, the mixing process preferably includes: a rotation speed of 500 to 700 rpm, such as 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, or any value therebetween; and a mixing time of 18 to 30 hours, such as 18 hours, 20 hours, 24 hours, 28 hours, 30 hours, or any value therebetween. This is more conducive to uniform mixing of the light-colored lignin and the pure cream, thereby imparting good sun protection properties to the resulting sunscreen.

[0042] The present invention will be described in detail below through specific examples. The examples of the embodiments are intended to explain the present invention and are not to be construed as limiting the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this field or the product specifications are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0043] Preparation Example 1

[0044] This preparation example is used to illustrate the preparation of a powdered lignin raw material - tea slag powder. The specific process is as follows: first, the tea stems are rinsed with deionized water, then heat-dried at 80°C to remove moisture, and then mechanically ground and passed through an 80-mesh sieve to obtain tea slag powder.

[0045] Preparation Example 2

[0046] This preparation example is used to illustrate the preparation of a light-colored lignin, and the specific process is as follows:

[0047] Oxalic acid and PEG200 (polyethylene glycol, Mn = 200 g / mol, purchased from Shanghai Aladdin Reagent Co., Ltd., China, catalog number P103718) were mixed in a molar ratio of 1:2. The resulting mixture was vigorously stirred at 80° C. to form a translucent mixed solution. After cooling to room temperature, a deep eutectic solvent was obtained.

[0048] 1.0 g of the tea residue powder obtained in Preparation Example 1, 20.0 g of a deep eutectic solvent, and 2 g of hydrogen peroxide were mixed in a 100 mL high-pressure reactor and subjected to extraction at 100° C. for 2 h. The cooled mixture was separated by vacuum filtration to obtain a cellulose-rich solid component and a lignin-rich filtrate. The resulting lignin-rich filtrate was subjected to rotary evaporation to remove the organic solvent from the filtrate, and then diluted with 200 mL of deionized water to precipitate the lignin. The precipitated solid was freeze-dried for 24 h to obtain a light-colored lignin, designated DH-L-10 (10 indicates a 10% hydrogen peroxide addition), and stored at 4° C. for future use.

[0049] Preparation Example 3

[0050] This preparation example is used to illustrate the preparation of a light-colored lignin, and the specific process is as follows:

[0051] Light-colored lignin was prepared according to the method of Preparation Example 2, except that the amount of hydrogen peroxide used was 4 g. The other conditions were the same as those in Preparation Example 2. Thus, light-colored lignin was prepared and was recorded as DH-L-20 (20 means that the amount of hydrogen peroxide added was 20%).

[0052] Preparation Example 4

[0053] This preparation example is used to illustrate the preparation of a light-colored lignin, and the specific process is as follows:

[0054] Light-colored lignin was prepared according to the method of Preparation Example 2, except that the amount of hydrogen peroxide used was 6 g. The other conditions were the same as those in Preparation Example 2. Thus, light-colored lignin was prepared and was recorded as DH-L-30 (30 means that the amount of hydrogen peroxide added was 30%).

[0055] Preparation Example 5

[0056] This preparation example is used to illustrate the preparation of a light-colored lignin, and the specific process is as follows:

[0057] Light-colored lignin was prepared according to the method of Preparation Example 2, except that the amount of hydrogen peroxide used was 8 g. The other conditions were the same as those in Preparation Example 2. Thus, light-colored lignin was prepared and recorded as DH-L-40 (40% means that the amount of hydrogen peroxide added was 40%).

[0058] Preparation Example 6

[0059] This preparation example is used to illustrate the preparation of a light-colored lignin, and the specific process is as follows:

[0060] Light-colored lignin was prepared according to the method of Preparation Example 2, except that the amount of hydrogen peroxide used was 10 g. The other conditions were the same as those in Preparation Example 2. Thus, light-colored lignin was prepared and recorded as DH-L-50 (50% means that the amount of hydrogen peroxide added was 50%).

[0061] Preparation Example 7

[0062] This preparation example is used to illustrate the preparation of a light-colored lignin, and the specific process is as follows:

[0063] Light-colored lignin was prepared according to the method of Preparation Example 3, except that the extraction treatment was carried out at 110°C. The other conditions were the same as those in Preparation Example 3. Thus, light-colored lignin was prepared and recorded as DH-L-110°C.

[0064] Preparation Example 8

[0065] This preparation example is used to illustrate the preparation of a light-colored lignin, and the specific process is as follows:

[0066] Light-colored lignin was prepared according to the method of Preparation Example 3, except that the extraction treatment was carried out at 120°C. The other conditions were the same as those in Preparation Example 3. Thus, light-colored lignin was prepared and recorded as DH-L-120°C.

[0067] Comparative Preparation Example 1

[0068] This preparation example is used to illustrate the preparation of a reference lignin, and the specific process is as follows:

[0069] Reference lignin was prepared according to the method of Preparation Example 3, except that water of the same mass was used instead of hydrogen peroxide. The other conditions were the same as those of Preparation Example 3. Thus, reference lignin was prepared and recorded as DL-1.

[0070] Comparative Preparation Example 2

[0071] This preparation example is used to illustrate the preparation of groundwood lignin. The specific process is as follows:

[0072] Take 5g of the tea residue powder of Preparation Example 1 and put it into a 100mL beaker. Add 50mL of dioxane aqueous solution (the volume ratio of water to dioxane is 96:4). The beaker is sealed and vibrated in the dark for 24h, centrifuged, and the filtrate is retained. Repeat the above experiment, place the two filtrates on a rotary evaporator, heat at 50°C to remove dioxane, and concentrate the filtrate to 3mL. In the 3mL concentrated filtrate, 9mL of 95% ethanol solution is added dropwise, centrifuged after sufficient vibration, and the filtrate is rotary evaporated to 3mL. This step is repeated three times. 30mL of hydrochloric acid solution with pH=2 is added dropwise, centrifuged, and the solid matter is dried. The above-mentioned dried solid matter is fully dissolved in a mixed solution of dichloroethane and ethanol (v:v=2:1), and is added dropwise to 10 times the volume of anhydrous ether to obtain a precipitate, which is groundwood lignin (MWL), which is dried for standby use.

[0073] Examples 1 to 5 and Comparative Example 1

[0074] The lignin obtained in the above preparation examples and comparative example preparation examples was mixed with pure cream (purchased from NIVEA NIVEA refreshing and soft moisturizing cream) and stirred at 600 rpm for 24 hours. The entire mixing process was carried out in a dark room at room temperature to obtain a sunscreen. The specific type of lignin and the amounts of lignin and pure cream used are shown in Table 1.

[0075] Table 1

[0076]

[0077]

[0078] Test Case

[0079] (1) Lignin color evaluation: The color of lignin was evaluated using a TS7700 spectrophotometer (Shenzhen Sanenshi Technology). After the device was powered on, the color of the colorimeter was calibrated using a black light absorber and a white plate. After calibration, the test was started, and the color parameter values ​​of the test sample were recorded as L*, a*, and b*. The total color difference (ΔE) was calculated using the following formula: ΔE = [(ΔL*) 2 +(Δa*) 2 +(Δb*)2] 1 / 2, where ΔL*, Δa*, and Δb* are the differences in L*, a*, and b* between a white reference and the sample in the spectrophotometer. Color was measured at five points on each sample and the average was taken. The results are shown in Table 2. The test results show that the lignin prepared using the method provided by the present invention has a lighter color, with a color difference within 40, which better meets the application requirements of sunscreen.

[0080] (2) Particle size and zeta potential test: The particle size and zeta potential of the lignin obtained in Preparation Examples 2 to 6 and Comparative Example 2 were tested using a Malvern laser particle size analyzer ZS90. The results are shown in Table 2 and Figure 1 As shown. Molecular weight test of lignin: The molecular weight distribution of lignin in Preparation Examples 2 to 6 and Comparative Example Preparation Example 2 was determined using Waters 1515 gel permeation chromatography (GPC) combined with Agilent PLgel 5μm mixed c column and differential refractive index detector. The results are shown in Figure 2 shown.

[0081] from Figure 1 It can be seen that with the increase in the amount of H2O2 added, the particle size of lignin gradually decreases, and the particle size of lignin after 50% pretreatment is 167nm, which is much smaller than the particle size of groundwood lignin (1234nm). Lignin is negatively charged at neutral pH due to its phenolic and carboxyl groups. The higher their negative Zeta potential, the less likely they are to aggregate. At different amounts of H2O2 added, the Zeta potential of lignin ranges from -4.19mV to -26.17mV, and the potential of 50% lignin is -15.4mV, which is higher in absolute value than that of groundwood lignin. This phenomenon may be because the lignin obtained by DES-H2O2 treatment produces more carboxyl groups and is negatively charged at neutral pH. The higher their negative Zeta potential, the less likely they are to aggregate, and they exhibit smaller particle sizes. From Figure 2 It can be seen that the PDI values ​​of the lignin components obtained by DES-H2O2 treatment are all greater than those of the MWL. This is likely due to the cleavage of β-O-4 bonds during DES-H2O2 treatment, but the simultaneous repolymerization of the broken lignin leads to an increase in the PDI of the DES lignin. In summary, the lignin obtained by DES-H2O2 treatment has a smaller particle size and better suspension stability, and has the potential to improve compatibility with sunscreen ingredients.

[0082] Table 2

[0083] project ΔE-lignin Particle size (nm) project ΔE-lignin Particle size (nm) Preparation Example 2 39.86 310 Preparation Example 7 37.59 - Preparation Example 3 37.57 206 Preparation Example 8 38.88 - Preparation Example 4 35.43 229 Comparative Preparation Example 1 42.83 - Preparation Example 5 32.67 206 Comparative Preparation Example 2 60.49 1234 Preparation Example 6 31.15 167 - - -

[0084] (3) Fourier transform infrared (FTIR) spectroscopy: Nicolet 50 FTIR spectrometer was used to test the lignin of Preparation Examples 2 to 6 and Comparative Example Preparation Example 2. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the lignin and groundwood lignin (MWL) obtained by DES-H2O2 treatment are both at 1625 cm -1 、1531cm -1 and 1452cm -1 The typical absorption peak of aromatic skeleton was observed at 1700 cm -1 The absorption peak at is attributed to the stretching vibration absorption of conjugated carbonyl groups. The higher the conjugated carbonyl content, the darker the color of the lignin. However, the lignin obtained by DES-H2O2 treatment does not show this peak, indicating that DES-H2O2 treatment can decompose the conjugated carbonyl groups in lignin, resulting in a light color.

[0085] (4) 31 P NMR nuclear magnetic spectrum test: AVANCE 600MHz nuclear magnetic resonance spectrometer (Bruker, Germany) was used to test the lignin obtained in Preparation Examples 2 to 6 and Comparative Example Preparation Example 2. The results are as follows: Figure 4 As shown. Figure 4 It can be seen that the aliphatic hydroxyl content of lignin DH-L-10 to DH-L-50 is lower than that of MWL, and the content of carboxyl OH is significantly increased after DES-H2O2 pretreatment, indicating that the degree of H2O2 oxidation of lignin is high. This may be because under the H2O2 oxidation conditions, the ketone groups in lignin are oxidized to carboxylic acids, which will reduce the 1700 cm-1 in FTIR. -1 The conjugated carbonyl group (C=O of ketone) at the end of the reaction was removed, while the -OH of the carboxylic acid was increased, resulting in an enhancement in the NMR spectrum, which is consistent with the FTIR results. According to the quantitative analysis results, the total phenolic OH content was calculated by adding S-type OH, G-type OH (such as guaiacol hydroxyl) and H-type OH (such as p-hydroxyphenyl hydroxyl). The results showed that the total phenolic OH content of lignin DH-L-10 to DH-L-50 decreased with the increase of H2O2 addition, and the decrease in phenolic OH content will help reduce the p-π conjugated structure formed by phenolic OH and benzene ring in lignin, resulting in light color.

[0086] (5) Two-dimensional nuclear magnetic resonance spectroscopy test: The lignin obtained in Preparation Examples 2 to 6 was tested using two-dimensional heteronuclear single quantum coherence (2D-HSQC) nuclear magnetic resonance (NMR) spectroscopy analysis. The results are as follows: Figures 5 to 9 shown.

[0087] In the side chain region (δC / δH 43-93 / 5.7-2.8), it can be seen that the methoxy signal of lignin is significantly weakened, which indicates that the DES-H2O2 treatment can effectively cut off the methoxy group on the benzene ring. At the same time, the xylan signal is also weakened or disappears to varying degrees (part of the xylan is oxidized in the harsh pulping and covalently bonded to the lignin to form a larger and stronger conjugate, also known as the lignin carbohydrate complex (LCC), which leads to the dark color of the lignin). At the same time, with the increase in the addition amount, 50% of the lignin appears a new characteristic peak of AGα (δC / δH48.9 / 4.4ppm). The reason is that the active C5 position of the G unit is grafted to the Cα position to form a stable structure, thereby protecting the β-O-4 bond from damage and preventing the condensation of the lignin unit. In the aromatic region, lignin only has signals of G and H structural units, and the S unit and S condensation unit structure signals do not exist at all. 31 The results of the P NMR spectra are consistent, indicating that the DES-H2O2 treatment successfully inhibits the condensation of lignin, while retaining the G-type structural units and maintaining the UV absorption properties of lignin. In summary, the use of DES-H2O2 treatment helps prevent the cleavage and condensation of lignin bonds, resulting in the extracted lignin exhibiting a lighter color and good UV absorption properties.

[0088] (6) Sun protection factor SPF test:

[0089] Medical tape was attached to one side of a quartz glass slide. A disposable syringe was used to evenly apply the sunscreen sample on the tape surface at a density of 2 mg / cm. 2 A UV-visible spectrophotometer (Q-6, Yuanxi, Shanghai) equipped with a solid sample holder was used to measure the transmittance of UV-visible light within the range of 290-400 nm and the UV transmittance within the range of UVB (290-320 nm) to UVA (320-400 nm). Four points were scanned for each sample. After measuring the UV transmittance, the sun protection factor was calculated using the following formula:

[0090]

[0091] Where Eλ = erythema spectrum effect, Sλ = solar spectrum efficiency, and Tλ = spectral transmittance of the sample. The results are shown in Table 3.

[0092] Table 2

[0093] project ΔE-sunscreen SPF project ΔE-sunscreen SPF Example 1 30.88 24.94 Example 4 47.84 56.76 Example 2 41.41 34.02 Example 5 53.05 40.59 Example 3 46.21 43.02 Comparative Example 1 18.67 17.62

[0094] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A method for extracting light-colored lignin, characterized in that: The method comprises the following steps: extracting a lignin raw material using a low eutectic solvent containing oxalic acid and polyethylene glycol and hydrogen peroxide, collecting a filtrate, mixing the filtrate with water, and precipitating a solid, which is light-colored lignin; the color difference value of the light-colored lignin is below 40.

2. The method for extracting light lignin according to claim 1, wherein The molar ratio of oxalic acid to polyethylene glycol in the deep eutectic solvent is 1:(1-3); Preferably, the preparation method of the deep eutectic solvent comprises: stirring and mixing oxalic acid and polyethylene glycol at 70-90° C., and the resulting mixed solution is the deep eutectic solvent.

3. The method for extracting light lignin according to claim 1, wherein The number average molecular weight of the polyethylene glycol is 150 to 350 g / mol.

4. The method for extracting light lignin according to claim 1, wherein The mass ratio of the lignin raw material to the deep eutectic solvent is (0.5-2):20; Preferably, the amount of hydrogen peroxide used is 10 to 50 wt% of the mass of the deep eutectic solvent.

5. The method for extracting light lignin according to claim 1, characterized in that The lignin raw material is selected from at least one of wood, bamboo, crops, and herbaceous plants; Preferably, the pretreatment method of the lignin raw material comprises: washing and drying the lignin raw material, and then mechanically grinding and sieving the lignin raw material to obtain a powdered lignin raw material.

6. The method for extracting light lignin according to claim 1, characterized in that The extraction treatment conditions include: temperature of 100-120° C. and time of 1-3 hours.

7. Light-colored lignin prepared by the method according to any one of claims 1 to 6.

8. The light-colored lignin according to claim 7, characterized in that The particle size of the light-colored lignin is 100-300 nm.

9. A sunscreen, characterized in that: The sunscreen contains the light-colored lignin according to claim 7 or 8.

10. The sunscreen according to claim 9, characterized in that The content of light-colored lignin in the sunscreen is 1.0-2.0 wt%.

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