Modified lignin as well as preparation method and application thereof

Abstract

The invention relates to modified lignin and a preparation method and application thereof, and the preparation method comprises the following steps: mixing a wood fiber raw material, resorcinol and an organic acid solution, and stirring and reacting for 0.2-6 hours at 60-200 DEG C under a closed condition to obtain a reaction mixture; the mass ratio of the wood fiber raw material to the resorcinol to the organic acid solution is 1: (0.5-2): (2-20); organic acid in the organic acid solution is a nucleophilic reagent; and filtering the reaction mixture, collecting filtrate, and adding water into the filtrate to adjust the pH value until precipitate is separated out, so that the precipitate is the modified lignin. The preparation method of the modified lignin provided by the invention is mild in process, simple and convenient in flow, green and environment-friendly, and the prepared modified lignin is high in brightness, complete in structure, high in activity and good in dispersity and has multiple functional characteristics of sun protection, oxidation resistance, tyrosinase inhibition, bacterium resistance and the like.

Description

Technical Field

[0001] This invention relates to the field of biomass refining, and in particular to a modified lignin, its preparation method, and its application. Background Technology

[0002] Lignin is the second largest renewable resource in nature after cellulose and is an important chemical component of the cell walls of higher plants. Its molecular structure is rich in functional groups such as aromatic rings, phenolic hydroxyl groups, and methoxy groups, giving it the ability to absorb ultraviolet rays, resist oxidation, and inhibit tyrosinase activity. Therefore, it has broad development value in the fields of sunscreen materials, anti-aging additives, and functional cosmetics.

[0003] However, due to the high cross-linking of natural lignin with cellulose and hemicellulose in plant cell walls, traditional lignin separation methods (such as the alkali method and the sulfite method) often rely on harsh extraction conditions such as strong acids, strong alkalis, and high temperatures. Under these harsh extraction conditions, the lignin molecular structure is prone to condensation or degradation reactions, leading to a darker product color, more complex structure, and loss of activity. This type of lignin is not only difficult to further modify, but also fails to meet the application requirements for aesthetics and high activity, especially limiting its use in high-end daily chemical products such as cosmetics. Furthermore, structural condensation results in poor hydrophilicity and uneven particle size distribution of lignin, leading to poor stability and low compatibility in emulsions, thus restricting its practical application as a functional additive.

[0004] Therefore, it is of great significance to develop a modified lignin that can be used in high-end daily chemical products such as cosmetics. Summary of the Invention

[0005] The main objective of this invention is to provide a modified lignin, its preparation method, and its application. The technical problem to be solved is how to provide a modified lignin that is highly active, has high UV barrier properties, high antioxidant capacity, and high tyrosinase inhibition capacity, while also exhibiting good dispersibility in emulsions and a light color, making it suitable for application in high-end daily chemical products such as cosmetics, thus making it more practical.

[0006] The objective of this invention and the technical problem it solves are achieved through the following technical solution. A method for preparing modified lignin according to this invention includes the following steps:

[0007] The wood fiber raw material, resorcinol, and organic acid solution are mixed and stirred at 60℃~200℃ under closed conditions for 0.2~6h to obtain a reaction mixture; by mass, the ratio of the aforementioned wood fiber raw material: resorcinol: organic acid solution is 1:0.5~2:2~20; the organic acid in the aforementioned organic acid solution is a nucleophile.

[0008] The aforementioned reaction mixture was filtered, and the filtrate was collected. Water was added to the filtrate to adjust the pH value until a precipitate was formed. The precipitate was the aforementioned modified lignin.

[0009] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0010] Preferably, in the aforementioned method for preparing modified lignin, the lignin fiber raw material is derived from at least one of wood, bamboo, crop straw, fruit shells, fruit shell waste, sugarcane bagasse, hemp plants, cotton stalks, and hemp stalks.

[0011] Preferably, in the aforementioned method for preparing modified lignin, the acid in the organic acid solution is at least one selected from formic acid, acetic acid, propionic acid, lactic acid, citric acid, and tartaric acid.

[0012] Preferably, in the aforementioned method for preparing modified lignin, the mass of the aforementioned organic acid solution is 100%, and the mass of the acid in the aforementioned organic acid solution is 20% to 100%.

[0013] Preferably, in the aforementioned method for preparing modified lignin, the specific steps for collecting the aforementioned filtrate are as follows: after filtration, the residue is washed out with water to remove the aforementioned filtrate remaining in the residue.

[0014] Preferably, the specific steps in the aforementioned method for preparing modified lignin, after washing the aforementioned precipitate to obtain the aforementioned modified lignin, are as follows:

[0015] The aforementioned precipitate was centrifuged at 3000–10000 rpm for 5–30 min, and then washed with water 2–5 times to obtain the aforementioned modified lignin.

[0016] The objective of this invention and the technical problem it solves are also achieved by the following technical solution. A modified lignin according to this invention, prepared by any of the aforementioned methods, has a brightness value greater than 60 and a phenolic hydroxyl content greater than 2.0 mmol / g.

[0017] The objective of this invention and the technical problem it solves are also achieved by the following technical solution. A cosmetic product according to this invention contains the aforementioned modified lignin.

[0018] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0019] Preferably, the aforementioned cosmetic is one of lotion, cream and sunscreen, the sun protection factor of the aforementioned cosmetic is 10 to 200, and the mass of the aforementioned modified lignin is 0.01 to 30% of the mass of the aforementioned cosmetic.

[0020] The objective of this invention and the technical problem it solves are also achieved by the following technical solution. This invention proposes the application of the aforementioned modified lignin in polymer composite materials.

[0021] By employing the above technical solution, the modified lignin of the present invention, its preparation method, and its application have at least the following advantages:

[0022] 1. The modified lignin preparation method proposed in this invention involves mixing and reacting lignocellulose raw materials, resorcinol, and an organic acid solution. The organic acid, acting as a nucleophile, induces the formation of a benzyl carbocation intermediate at the α-position of lignin. Resorcinol, a strongly nucleophilic aromatic compound, captures this intermediate during the reaction, forming an aryl structure. This inhibits the condensation reaction following the breaking of the β-O-4 aryl ether bond, achieving a gentle and efficient protective separation and one-step phenolic modification of lignin. This not only significantly improves the brightness, activity, and recovery rate of lignin but also, by increasing its phenolic hydroxyl content, endows it with excellent multifunctional properties such as sun protection, antioxidant, tyrosinase inhibition, and antibacterial properties, expanding the application prospects of lignin in high-value fields such as sun protection, antioxidant, and emulsion stabilization. Furthermore, the modification process improves the dispersibility and compatibility of lignin with the emulsion system, solving the problems of lignin aggregation and precipitation in emulsions or oil-water systems. It can be used as a natural sunscreen additive for stable dispersion, which is beneficial for achieving lightweight and stable cosmetic formulations. The modified lignin preparation method provided by this invention is mild and efficient, simple in process, uses less chemicals, and is green and environmentally friendly.

[0023] 2. The modification method and product provided by this invention have good adaptability and are applicable to different wood fiber raw materials (such as bamboo, straw, sugarcane bagasse, etc.). They are also suitable for various sunscreen or skin care product forms (lotion, spray, essence, etc.), with a wide range of additions, providing flexibility for formulation development.

[0024] 3. Lignin, as an abundant renewable resource in nature, is currently still treated as a low-value-added form or as industrial waste, failing to effectively improve or enhance its value. This is due to two main reasons: firstly, industrial lignin has low activity, making direct modification difficult; and secondly, there is still a lack of efficient methods for directly separating high-brightness, high-activity lignin. This invention proposes a technical solution that can directly separate modified lignin from wood fiber raw materials and convert the modified lignin into a functional sunscreen additive, significantly improving the resource utilization rate and economic added value of lignin.

[0025] 4. The resorcinol used in this invention has good water solubility, is easy to remove after reaction, has a simple process flow, and produces products with high purity.

[0026] 5. Chemical sunscreens such as avobenzone, oxybenzone, and octocrylene have potential skin irritation and proven environmental toxicity (e.g., coral bleaching); physical sunscreens such as titanium dioxide (TiO2) and zinc oxide (ZnO) face problems such as poor application and whitening, and the photocatalytic activity of inorganic nanoparticles may cause potential health risks such as cellular oxidative damage. The modified lignin isolated in this invention is based on natural wood fibers. Resorcinol is water-soluble and can be easily removed during extraction, ensuring the safety of the modified lignin in cosmetics. Simultaneously, this modified lignin has high brightness, good hydrophilicity, and multifunctional properties, which will help expand its multifunctional applications in cosmetics.

[0027] 6. The current market lacks sunscreen ingredients that combine natural origin, biodegradability, safety, non-toxicity, and environmental friendliness. The modified lignin provided by this invention, as a sunscreen additive, not only has excellent effects, but also uses natural, green, and low-carbon raw materials, making it suitable for sustainable skincare product development. Furthermore, it possesses multifunctional properties, including anti-UV, antioxidant, whitening, and antibacterial properties.

[0028] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Detailed Implementation

[0029] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following detailed description, in conjunction with preferred embodiments, provides a modified lignin, its preparation method, and its specific implementation methods, structures, features, and effects according to the present invention. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable manner.

[0030] The present invention provides a method for preparing modified lignin, which includes the following steps:

[0031] The wood fiber raw material, resorcinol, and organic acid solution are mixed and stirred at 60℃~200℃ under closed conditions for 0.2~6h to obtain a reaction mixture; by mass, the ratio of the aforementioned wood fiber raw material: resorcinol: organic acid solution is 1:0.5~2:2~20; the organic acid in the aforementioned organic acid solution is a nucleophile.

[0032] The aforementioned reaction mixture was filtered, and the filtrate was collected. Water was added to the filtrate to adjust the pH value until a precipitate was formed. The precipitate was the aforementioned modified lignin.

[0033] Specifically, the lignocellulose raw material can be derived from at least one of wood, bamboo, crop straw, fruit shells, fruit shell waste, bagasse, hemp plants, cotton stalks, and hemp stalks. To improve the reaction rate, the lignocellulose raw material is a dry powder or granule. The organic acid in the aforementioned organic acid solution is a nucleophile. The acid in the organic acid solution is at least one of formic acid, acetic acid, propionic acid, lactic acid, citric acid, and tartaric acid. As a nucleophile, the organic acid causes the formation of a benzyl carbocation intermediate at the α-position of lignin. Resorcinol, a strongly nucleophilic aromatic compound, captures the benzyl carbocation intermediate during the reaction, forming an arylated structure, thereby inhibiting the condensation reaction after the cleavage of the β-O-4 aryl ether bond, achieving a mild and efficient protective separation and one-step phenolic modification of lignin.

[0034] Preferably, based on the aforementioned organic acid solution (mass of 100%), the mass of the acid in the aforementioned organic acid solution is 20% to 100%. By mass, the ratio of wood fiber raw material to resorcinol is 1:0.5 to 2. If the resorcinol content is too low, the limited reaction sites of resorcinol will not be able to fully protect the lignin, leading to further cross-linking of the lignin and thus a decrease in the performance of the modified lignin. If the resorcinol content is too high, it will result in reagent waste. By mass, the ratio of wood fiber raw material to organic acid solution is 1:2 to 20, wherein the mass of the acid in the organic acid solution is 20% to 100%, and this concentration is adjusted according to the properties of the organic acid. If the organic acid content is too low, the product yield will be too low; if the organic acid content is too high, it will result in reagent waste. The reaction temperature is 60℃~200℃, and the reaction time is 0.2~6h. If the reaction temperature is below 60℃, the reaction rate is too low. If the reaction temperature is above 200℃, it is easy to cause condensation or degradation of the chemical structure of lignin. If the reaction time is less than 0.2h, the product yield is too low. If the reaction time is greater than 6h, the production efficiency is too low.

[0035] The aforementioned reaction mixture is filtered, and the filtrate is collected. Water is added to the filtrate to adjust the pH until a precipitate forms. This precipitate is the modified lignin. Modified lignin dissolves in a strongly acidic solution. Adding water to the filtrate to raise the pH causes the modified lignin to precipitate. The precipitate precipitates when the pH is adjusted to approximately 5-7. Preferably, the aforementioned reaction mixture is filtered, and the residue is washed with water to remove the remaining filtrate. The filtrate obtained from the first filtration and the washed filtrate are collected as the total filtrate. This method improves the yield. Preferably, the acid in the aforementioned acidic solution is a volatile acid. The total filtrate is concentrated to obtain a concentrate, and then water is added. This method improves the yield while reducing the amount of water added, making it easier to operate. For example, the volume ratio of the concentrate to the total filtrate is 1:3-5. Water is then added to the concentrate, with the volume ratio of the concentrate to water being 1:8-15, causing the precipitate to precipitate. The aforementioned precipitate was centrifuged at 3000–10000 rpm for 5–30 min, and then washed with water 2–5 times to obtain the aforementioned modified lignin.

[0036] The modified lignin preparation method proposed in this invention not only significantly improves the brightness, structural integrity, and recovery rate of lignin, but also endows it with multiple functional properties such as sun protection, anti-oxidation, inhibition of tyrosinase activity, and antibacterial properties by increasing its phenolic hydroxyl content, thus expanding the application prospects of lignin in high-value fields such as sun protection, anti-oxidation, and emulsion stabilization. Furthermore, the modification process improves the dispersibility and compatibility of lignin with the emulsion system, solving the problems of lignin aggregation and precipitation in emulsions or oil-water systems. It can be used as a natural sunscreen additive to achieve stable dispersion, which is beneficial for achieving cosmetic formulations with a lightweight feel and strong stability. The modified lignin preparation method provided by this invention is mild, efficient, simple, uses few chemicals, and is environmentally friendly.

[0037] The present invention proposes a modified lignin, which is prepared by any of the aforementioned methods, and has a brightness value greater than 60 and a phenolic hydroxyl content greater than 2.0 mmol / g.

[0038] The present invention provides a cosmetic containing the aforementioned modified lignin. Preferably, the aforementioned cosmetic is one of a lotion, cream, and sunscreen, the sun protection factor (SPF) of the aforementioned cosmetic is 10-200, and the mass of the aforementioned modified lignin is 0.01-30% of the mass of the aforementioned cosmetic.

[0039] Chemical sunscreens such as avobenzone, oxybenzone, and octocrylene have potential skin irritation and proven environmental toxicity (e.g., coral bleaching). Physical sunscreens such as titanium dioxide (TiO2) and zinc oxide (ZnO) suffer from poor application and whitening effects, and the photocatalytic activity of inorganic nanoparticles poses potential health risks such as cellular oxidative damage. The modified lignin provided in this invention is based on natural wood fibers, and resorcinol is water-soluble, allowing for easy removal during extraction, thus ensuring the safety of the modified lignin in cosmetics. Furthermore, this modified lignin possesses multifunctional properties, which will help expand its multifunctional applications in cosmetics.

[0040] The current market lacks sunscreen ingredients that combine natural origin, biodegradability, safety, non-toxicity, and environmental friendliness. The modified lignin provided by this invention, as a sunscreen additive, not only boasts excellent efficacy but also utilizes natural, green, and low-carbon raw materials, making it suitable for sustainable skincare product development. Furthermore, it possesses multifunctional properties, including anti-UV, antioxidant, whitening, and antibacterial effects.

[0041] This invention proposes the application of the aforementioned modified lignin in polymer composite materials. Modified lignin can also be used in polymer composite materials such as tires, rubber, and packaging materials to improve their UV resistance, antioxidant properties, or antibacterial properties.

[0042] The present invention will be further described below with reference to specific embodiments, but this should not be construed as a limitation on the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0043] Unless otherwise specified, all materials and reagents mentioned below are commercially available products well known to those skilled in the art; unless otherwise specified, all methods described are methods known in the art. Unless otherwise defined, the technical or scientific terms used should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0044] In the following embodiments, NMR stands for Nuclear Magnetic Resonance.

[0045] DPPH radical scavenging rate is an effective method for evaluating the antioxidant capacity of substances. The antioxidant activity of a sample is reflected by detecting changes in the absorbance of the DPPH radical solution. DPPH (1,1-diphenyl-2-trinitrophenylhydrazine) is a stable organic free radical; its methanol solution is deep purple and has a maximum absorption peak at 517 nm. In the experiment, dioxane / water (9:1, v:v) was used as the solvent system for modifying lignin. When the modified lignin reacts with DPPH radicals, unpaired electrons are neutralized, the solution decolorizes, and the absorbance decreases. The formula for calculating the free radical scavenging activity is:

[0046]

[0047] Among them, A S A represents the absorbance of the mixture after the reaction. B A represents the absorbance of a mixture of 0.1 mL lignin solution and 3.9 mL methanol. c The absorbance is the absorbance of a mixture of 0.1 mL dioxane / water and 3.9 mL DPPH / methanol.

[0048] The half-maximum inhibitory concentration (IC50) was calculated by plotting the relationship between free radical scavenging activity and modified lignin concentration. 50 Value, calculated by IC 50 The reciprocal of the value yields the free radical scavenging index.

[0049] The method for testing tyrosinase activity inhibition is as follows: L-DOPA (1.5 mM, dissolved in PBS buffer) was used as the substrate, and p-hydroxybenzaldehyde (pHB) was used as a positive control to evaluate the inhibitory effect of modified lignin samples on tyrosinase. The specific experimental steps are as follows: First, different masses of samples (1–12 mg) were weighed and completely dissolved in 1 mL of dimethyl sulfoxide. Then, 9 mL of phosphate buffer (PBS, pH 6.8) was added to prepare a series of modified lignin solutions of varying concentrations. 1 mL of the modified lignin solution was mixed with 1 mL of L-DOPA / PBS solution (1.5 mM) and reacted at 25 ± 0.5 °C for 5 min to ensure thorough substrate mixing. Then, 1 mL of tyrosinase solution (PBS, 50 U / mL, PBS buffer) was added to the mixture, and incubation continued at the same temperature for 5 min. After the reaction, the absorbance of the mixture was immediately measured at 475 nm using a UV-Vis spectrophotometer. Finally, the inhibition rate of modified lignin on tyrosinase was calculated using a formula.

[0050]

[0051] A, B, C, and D represent the absorbance of the following four systems: A: absorbance of the L-DOPA / lignin / tyrosinase system; B: absorbance of the L-DOPA / lignin / PBS system; C: absorbance of the L-DOPA / DMSO+PBS / tyrosinase system; D: absorbance of the L-DOPA / PBS / PBS system.

[0052] Lignin 31 P NMR analysis: Lignin was recorded using an AVIII 400MHz nuclear magnetic resonance spectrometer at 25°C. 31P NMR spectroscopy. Derivatization was required prior to testing. Briefly, lignin samples were derivatized in anhydrous pyridine / deuterated chloroform (1.6:1 v / v) mixed solvent, with cyclohexanol as an internal standard, chromium acetylacetone as a relaxant, and 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxophosphazenecyclopentane (TMDP) as a phosphating agent. The mass of lignin was 20.0 mg, and the integrated area of ​​the internal standard was set to 1.0. The areas of each signal peak were analyzed by integration, including aliphatic hydroxyl (149.0 ppm to 146.0 ppm), phenolic hydroxyl (144.0 ppm to 137.4 ppm), S-type (141.7 ppm to 140.2 ppm), G-type (140.2 ppm to 138.8 ppm), H-type (138.8 ppm to 137.4 ppm), and -COOH (136.0 ppm to 133.6 ppm) signals.

[0053] Sun Protection Factor (SPF) Testing and Calculation of Lignin: The SPF of sunscreen samples was calculated using their transmittance data in the ultraviolet band. In the experiment, 3M Transpore tape was first applied to a 2mm thick quartz plate, and then... (The sentence is incomplete and requires more context to translate accurately.) 2 The prepared lignin-based sunscreen was evenly coated onto the surface of the tape using the specified amount of product. After the sample was allowed to stand and dry for 10 minutes at room temperature (25±1℃), its ultraviolet transmittance in the wavelength range of 290–400 nm was measured using an ultraviolet-visible spectrophotometer equipped with an integrating sphere.

[0054] Before testing, baseline calibration was performed using a quartz plate with blank adhesive tape to effectively eliminate interference from the tape and substrate on UV absorption. Subsequently, measurements were taken on four different regions of the sample surface at a scan step of 1 nm. Based on the UV transmittance data, the SPF of the lignin sunscreen was calculated using the following formula.

[0055]

[0056] In the formula, E λ Indicates the effectiveness of the erythema spectrum, S λ Indicating the effectiveness of the solar spectrum, T λ This indicates the transmittance of the sample.

[0057] Example 1

[0058] This embodiment provides a modified lignin, its preparation method, and its application in sunscreen cosmetics.

[0059] (1) Preparation of modified lignin

[0060] 100g of dried bamboo powder, 100g of resorcinol, and 2000g of formic acid solution were mixed and stirred at 500rpm for 1.0h under sealed conditions at 100℃ to obtain the reaction mixture. The mass of formic acid in the formic acid solution was 1760g.

[0061] After the reaction was complete, the reaction mixture was filtered, and the residue was washed with 500 mL of water. All filtrates were collected. The filtrate was concentrated under reduced pressure to 1 / 5 of its original volume to obtain a concentrated filtrate. 1500 mL of deionized water was added to the concentrated filtrate to precipitate the precipitate. The precipitate was separated by centrifugation at 8000 rpm for 10 min. The separated precipitate was washed three times by centrifugation at 8000 rpm, using 1000 mL of deionized water each time for 5 min, to remove residual acid and unreacted resorcinol. The precipitate was then dried to obtain a light pink modified lignin.

[0062] (2) Performance evaluation of modified lignin

[0063] The brightness value of the modified lignin, measured using a colorimeter, was 74.6. Quantitative analysis was then performed. 31 The phenolic hydroxyl content of the modified lignin was determined to be 4.73 mmol / g by P NMR. The DPPH radical scavenging rate of the modified lignin was determined by UV spectrophotometry; compared to 2.4 for the reference 2,6-di-tert-butyl-p-cresol (BHT), the radical scavenging index of the modified lignin was 39.6. The tyrosinase inhibition ability of the modified lignin was determined by UV spectrophotometry; compared to the IC50 of the reference p-hydroxybenzaldehyde (pHB), the DPPH radical scavenging index of the modified lignin was 39.6. 50 The value was 175 μg / mL, and the IC50 of modified lignin was... 50 The value was 14.5 μg / mL.

[0064] (3) Application of modified lignin in sunscreen cosmetics

[0065] Take 10g of the modified lignin prepared in step (1) and 90g of a commercially available sunscreen with an SPF of 15 as the sunscreen base. Mix the two together and homogenize them in a homogenizer to obtain a lignin-based sunscreen. The transmittance of the lignin-based sunscreen was tested using a UV spectrophotometer, and the SPF value of the sunscreen was calculated. The SPF value of the lignin-based sunscreen was 57.0. The stability of the sunscreen was observed by the static method. No lignin precipitation or emulsion stratification was observed after standing at room temperature for 72 hours, indicating that the lignin-based sunscreen was stable.

[0066] Example 2:

[0067] This embodiment provides a modified lignin, its preparation method, and its application in sunscreen cosmetics.

[0068] (1) Preparation of modified lignin

[0069] 20g of dried bamboo shoot shell powder, 28g of resorcinol, and 200g of acetic acid solution were mixed and reacted at 110℃ under sealed conditions with stirring at 600rpm for 2 hours to obtain the reaction mixture. The mass of acetic acid in the acetic acid solution was 180g.

[0070] After the reaction was complete, the reaction mixture was filtered, and the residue was washed with 100 mL of water. All filtrates were collected. The filtrate was concentrated under reduced pressure to 1 / 4 of its original volume to obtain a concentrated filtrate. 400 mL of deionized water was added to the concentrated filtrate, and a precipitate was precipitated. The precipitate was separated by centrifugation at 9000 rpm for 15 min. The separated precipitate was washed three times by centrifugation at 9000 rpm, using 200 mL of deionized water each time for 5 min, to remove residual acid and unreacted resorcinol. The precipitate was then dried to obtain a light pink modified lignin.

[0071] (2) Performance evaluation of modified lignin

[0072] The brightness value of the modified lignin was measured to be 68.1 using a colorimeter. Quantitative analysis was then performed. 31 The phenolic hydroxyl content of the modified lignin was determined to be 4.74 mmol / g by pNMR. The DPPH radical scavenging rate of the modified lignin was determined by UV spectrophotometry; the radical scavenging index of the reference 2,6-di-tert-butyl-p-cresol (BHT) was 2.4, while that of the modified lignin was 30.5. The ability of the modified lignin to inhibit tyrosinase activity was determined by UV spectrophotometry; the IC50 of the reference p-hydroxybenzaldehyde (pHB) was [not specified in the original text]. 50 The value was 175 μg / mL, and the IC50 of modified lignin was... 50 The value was 16.1 μg / mL.

[0073] (3) Application of modified lignin in sunscreen cosmetics

[0074] Take 5g of the modified lignin prepared in step (1); 35g of the oil phase (ethylhexyl palmitate); and 60g of the aqueous phase, including 54.7g of water, 4g of emulsifier (cetyl alcohol), 1g of thickener (xanthan gum), and 0.3g of preservative (phenoxyethanol). Mix the modified lignin with the oil and aqueous phases and heat to 50°C. Then, homogenize the mixture in a homogenizer at 15,000 rpm for 20 minutes to obtain a lignin-based sunscreen emulsion. The transmittance of the lignin-based sunscreen emulsion was tested by a UV spectrophotometer, and its sun protection factor (SPF) was calculated. The SPF of the lignin-based sunscreen emulsion was 26.3. The stability of the emulsion was observed by the static method. No lignin precipitation or emulsion stratification was observed after standing at room temperature for 72 hours, indicating that the emulsion was stable.

[0075] Example 3

[0076] This embodiment provides a modified lignin, its preparation method, and its application in sunscreen cosmetics.

[0077] (1) Preparation of modified lignin

[0078] 100g of dried eucalyptus wood powder, 80g of resorcinol, and 1500g of tartaric acid solution were mixed and reacted at 150℃ under sealed conditions for 2.0 hours with stirring at 800rpm to obtain the reaction mixture. The mass of tartaric acid in the tartaric acid solution was 800g.

[0079] After the reaction was complete, the reaction mixture was filtered, and the residue was washed with 500 mL of water. All filtrates were collected. The filtrate was concentrated under reduced pressure to 1 / 4 of its original volume to obtain a concentrated filtrate. 1000 mL of deionized water was added to the concentrated filtrate, and a precipitate was precipitated. The precipitate was separated by centrifugation at 6000 rpm for 15 min. The separated precipitate was washed three times by centrifugation at 6000 rpm, using 500 mL of deionized water each time for 10 min, to remove residual acid and unreacted resorcinol. The precipitate was then dried to obtain a light pink modified lignin.

[0080] (2) Evaluation of Lignin Properties

[0081] The brightness value of the modified lignin was measured to be 72 using a colorimeter. Quantitative analysis was then performed. 31 The phenolic hydroxyl content of the modified lignin was determined to be 4.50 mmol / g by pNMR. The DPPH radical scavenging rate of the modified lignin was determined by UV spectrophotometry; compared to 2,6-di-tert-butyl-p-cresol (BHT) with a radical scavenging index of 2.4, the modified lignin had a radical scavenging index of 56.8. The ability of the modified lignin to inhibit tyrosinase activity was determined by UV spectrophotometry; compared to the IC50 of p-hydroxybenzaldehyde (pHB), the modified lignin exhibited a similar activity. 50 The value was 175 μg / mL, and the IC50 of modified lignin was... 50 The value was 11.8 μg / mL.

[0082] (3) Application of modified lignin in sunscreen cosmetics

[0083] Take 5g of the modified lignin prepared in step (1); 25g of the oil phase (jojoba oil); and 75g of the aqueous phase, including 71.3g of water, 3g of emulsifier (Tween-20), 0.5g of thickener (hydroxyethyl cellulose), and 0.2g of preservative (sodium benzoate). Mix the modified lignin with the oil and aqueous phases at room temperature and homogenize using a homogenizer to obtain a lignin-based sunscreen emulsion. Test the transmittance of the sunscreen emulsion with a UV spectrophotometer and calculate the sun protection factor (SPF) value. The SPF value of this lignin-based sunscreen emulsion is 20. Observe its stability by standing. No precipitation or stratification was observed after standing at room temperature for 72 hours, indicating that the emulsion is stable.

[0084] Example 4

[0085] This embodiment provides a modified lignin, its preparation method, and its application in sunscreen cosmetics.

[0086] (1) Preparation of modified lignin

[0087] Mix 25g of rice straw powder, 12.5g of resorcinol and 50g of lactic acid, and react them at 130℃ under sealed conditions with a stirring speed of 600rpm for 2.5h to obtain the reaction mixture.

[0088] After the reaction was complete, the reaction mixture was filtered, and the filtrate was collected. 400 mL of deionized water was added to the filtrate, causing a precipitate to form. The precipitate was separated by centrifugation at 5000 rpm for 15 min. The separated precipitate was washed three times by centrifugation at 5000 rpm, using 100 mL of deionized water each time for 10 min, to remove residual acid and unreacted resorcinol. The precipitate was then dried to obtain a light red modified lignin.

[0089] (2) Evaluation of Lignin Properties

[0090] The L* brightness value of the modified lignin was measured to be 70.1 using a colorimeter. Quantitative analysis was then performed. 31 The phenolic hydroxyl content of the modified lignin was determined to be 3.9 mmol / g by pNMR. The DPPH radical scavenging rate of the modified lignin was determined by UV spectrophotometry; the radical scavenging index of the reference 2,6-di-tert-butyl-p-cresol (BHT) was 2.4, while that of the modified lignin was 45.2. The ability of the modified lignin to inhibit tyrosinase activity was determined by UV spectrophotometry; the IC50 of the reference p-hydroxybenzaldehyde (pHB) was [not specified in the original text]. 50 The value was 175 μg / mL, and the IC50 of modified lignin was... 50 The value was 18 μg / mL.

[0091] (4) Application of modified lignin in sunscreen cosmetics:

[0092] Take 5g of the modified lignin prepared in step (1) and 45g of a commercially available chemical sunscreen with an SPF of 50 as the sunscreen base. Mix the two together and homogenize them in a homogenizer to obtain a lignin-based sunscreen. The transmittance of the lignin-based sunscreen was tested using a UV spectrophotometer, and the SPF value of the sunscreen was calculated. The SPF value of this lignin-based sunscreen was 165. The stability of the sunscreen was observed by the static method. No precipitation or stratification was observed after standing at room temperature for 48 hours.

[0093] The technical features in the claims and / or specification of this invention can be combined, and the combination is not limited to the combinations obtained through reference in the claims. Technical solutions obtained by combining the technical features in the claims and / or specification are also within the scope of protection of this invention.

[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing modified lignin, characterized in that, It includes the following steps: A mixture of lignocellulose raw material, resorcinol, and organic acid solution is stirred and reacted at 60℃~200℃ under sealed conditions for 0.2~6h to obtain a reaction mixture; by mass, the ratio of lignocellulose raw material:resorcinol:organic acid solution is 1:0.5~2:0.2~1; the organic acid in the organic acid solution is a nucleophile. The reaction mixture is filtered, the filtrate is collected, and water is added to the filtrate to adjust the pH value until a precipitate is formed. The precipitate is the modified lignin.

2. The method according to claim 1, characterized in that, The wood fiber raw material is derived from at least one of wood, bamboo, crop straw, fruit shells, fruit shell waste, sugarcane bagasse, hemp plants, cotton stalks, and hemp stalks.

3. The method according to claim 1, characterized in that, The acid in the organic acid solution is at least one of formic acid, acetic acid, propionic acid, lactic acid, citric acid, and tartaric acid.

4. The method according to claim 1, characterized in that, With the organic acid solution having a mass of 100%, the mass of the acid in the organic acid solution is 20% to 100%.

5. The method according to claim 1, characterized in that, The specific steps for collecting the filtrate are as follows: after filtration, the filtrate remaining in the residue is washed out with water.

6. The method according to claim 1, characterized in that, The specific steps for obtaining the modified lignin after washing the precipitate are as follows: The precipitate was centrifuged at 3000-10000 rpm for 5-30 min, and then washed with water 2-5 times to obtain the modified lignin.

7. A modified lignin, characterized in that, The product is prepared by the method according to any one of claims 1 to 6, and has a brightness value greater than 60 and a phenolic hydroxyl content greater than 2.0 mmol / g.

8. A cosmetic product, characterized in that, It contains the modified lignin as described in claim 7.

9. The cosmetic product according to claim 8, characterized in that, The cosmetic is one of lotion, cream and sunscreen, the sun protection factor of the cosmetic is 10 to 200, and the mass of the modified lignin is 0.01 to 30% of the mass of the cosmetic.

10. The application of the modified lignin according to claim 7 in polymer composite materials.

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