Tea polyphenol-phenolated lignin, ultraviolet sunscreen agent and preparation method and application thereof

Abstract

The application discloses a tea polyphenol phenolated lignin, an ultraviolet sunscreen agent and a preparation method and application thereof; the tea polyphenol phenolated lignin is obtained by reacting lignin and tea polyphenol in an acid solution at 50-100 DEG C for 0.5-6 h; the tea polyphenol phenolated lignin is dissolved in an organic solvent / aqueous solution, then is dropped into pure water, the organic solvent is naturally volatilized and concentrated to obtain a suspension of the tea polyphenol phenolated lignin, finally, the suspension of the tea polyphenol phenolated lignin is mixed with a small molecule sunscreen agent and a surfactant, ultrasonic cavitation is carried out to obtain a tea polyphenol phenolated lignin / small molecule sunscreen agent ultraviolet sunscreen agent mixed emulsion, a precipitate is removed by centrifugation to obtain the ultraviolet sunscreen agent; the tea polyphenol phenolated lignin significantly improves the anti-ultraviolet performance and the antioxidation performance; then, the small molecule chemical sunscreen agent is compounded and embedded to realize synergistic sunscreen, the sunscreen coefficient is improved, and the anti-permeation performance is good.

Description

Technical Field

[0001] This invention belongs to the field of fine chemicals technology, specifically relating to a tea polyphenol phenolized lignin, an ultraviolet sunscreen agent, its preparation method and application. Background Technology

[0002] In recent decades, industrial development has damaged the ozone layer, leading to a gradual increase in ultraviolet (UV) radiation reaching the Earth's surface. This has exacerbated the health problems caused by excessive UV radiation, often resulting in a range of skin lesions such as sunburn, photoaging, and melanoma. Protecting the skin from excessive UV radiation and mitigating its side effects has been a pressing issue for a considerable period. The first line of defense against UV damage is melanin; however, in some cases, the amount of melanin produced by the skin is insufficient for protection. Therefore, alternative methods to protect the skin from UV radiation are urgently needed. To date, various feasible methods have been proposed, including sun-protective clothing, UV-protective swimwear, sun hats, and sun-protective cosmetics, to prevent UV damage to the skin. Among these, the development of sunscreens offers a strategy that utilizes effective sun-protective ingredients to protect the skin from damage, providing a convenient and robust way to alleviate UV-related problems.

[0003] Currently, sunscreens on the market are mainly divided into three categories based on their sunscreen ingredients: physical sunscreens, chemical sunscreens, and combined physical and chemical sunscreens. Commonly used physical sunscreen ingredients include titanium dioxide, silica, kaolin, and talc. Physical sunscreens utilize reflective particles to physically block, reflect, or scatter ultraviolet (UV) rays, reducing the amount of UV rays reaching the skin to achieve sun protection. They offer good stability and a broad range of filtered wavelengths. However, they have some inherent problems, such as a grainy feel, photoinduced free radicals leading to skin aging, and specific application time and amount requirements. They are often sticky and difficult to wash off, causing clogged pores and poor comfort, severely limiting their further application. Common chemical sunscreen ingredients include benzophenone, ethylhexyl salicylate, homosalate, cinnoxalate, disodium phenyl dibenzimidazole tetraxanate, butyl methoxydibenzoylmethane, ethylhexyl methoxycinnamate, and some patented ingredients from group laboratories, such as Mexoryl. Chemical sunscreens work by forming a UV-absorbing barrier on the skin's surface using other film-forming substances, absorbing and neutralizing UV rays to prevent them from penetrating the skin. It's worth noting that these small organic molecules may undergo photodegradation during use, potentially penetrating the skin and causing toxicity and side effects (Green Chem., 2021, 23, 4633-4646). Alternatively, sunscreens can be prepared using a combination of physicochemical and chemical methods, with functions and advantages falling between the two. This is the most common type of sunscreen on the market, offering more comprehensive sun protection, but its ingredients are relatively complex, posing a higher potential risk. The environmental and human health impacts of traditional sunscreens have become a central topic in this field. To address these issues, using nature-inspired plant components as alternatives to the active ingredients in sunscreens has emerged as a promising solution.

[0004] Lignin is one of the three major components of lignocellulose biomass and the second largest renewable resource after cellulose. Furthermore, lignin is the only natural aromatic raw material that can be obtained in large quantities from terrestrial plants. The various functional groups of lignin, such as phenolic hydroxyl groups, aliphatic hydroxyl groups, and aldehyde groups, endow lignin with a variety of attractive properties, such as amphiphilicity, UV protection, and antioxidant functions. Utilizing the physicochemical properties of lignin, researchers have begun to explore its high-value application in preparing high-performance broad-spectrum sunscreens. However, the sun protection performance of lignin itself is not satisfactory and cannot meet the daily needs of sunscreens. Therefore, it is necessary to modify lignin to improve its physicochemical properties in the field of sun protection. When lignin sunscreens are used in harsh environments, they can be mixed with chemical or physical sunscreens because lignin and chemical sunscreens have a synergistic effect, which can effectively improve the sun protection performance of commercial sunscreens. However, this may lead to potential health threats because these small-molecule sunscreens may come into contact with and penetrate the skin. Encapsulating chemical sunscreens with lignin can enhance their resistance to photodegradation and their permeability, thus mitigating the risk of toxic ingredients penetrating the skin to some extent. Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing tea polyphenol-phenolized lignin.

[0006] The UV resistance and antioxidant capacity of lignin are closely related to the content of phenolic hydroxyl groups in its biopolymers. Phenolic hydroxyl groups are also the main functional units determining the reactivity and amphiphilicity of lignin. The reaction between lignin and phenols can be acid-catalyzed. During this process, the carbocations on the lignin side chains initially form protons through acid catalysis. The lignin side chains with carbocations then condense with phenol molecules through electrophilic attack. The para or ortho positions of the phenolic hydroxyl groups in phenolic substances are usually active sites connected to lignin in the form of carbon-carbon bonds, leading to lignin phenolization. This invention uses an acid method to modify the lignin structure through polyphenol phenolization, resulting in a significant increase in the number of phenolic hydroxyl groups in the lignin structure, thereby improving the UV resistance and antioxidant properties of lignin.

[0007] Another objective of this invention is to provide a tea polyphenol-modified lignin / small molecule sunscreen agent and its preparation method.

[0008] Another object of the present invention is to provide the application of the above-mentioned tea polyphenol phenolated lignin and tea polyphenol phenolated lignin / small molecule sunscreen UV sunscreen in the preparation of sunscreen products.

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

[0010] A method for preparing phenol-modified lignin from tea polyphenols includes the following steps:

[0011] Lignin and tea polyphenols are reacted in an acidic solution at 50–100°C for 0.5–6 h to obtain tea polyphenol-phenolized lignin.

[0012] Preferably, the mass ratio of tea polyphenols to lignin is 2-15:1-5;

[0013] More preferably, the mass ratio of tea polyphenols to lignin is 0.5:1 to 3:1.

[0014] Preferably, the mass ratio of lignin to acidic solution is 1-5:5-20;

[0015] More preferably, the mass ratio of lignin to acidic solution is 1 to 2:10.

[0016] Preferably, the lignin is at least one of organic solvent lignin, alkali lignin, and enzymatically hydrolyzed lignin.

[0017] More preferably, the organic solvent lignin is at least one of pine pulp lignin, poplar pulp lignin, eucalyptus pulp lignin, corn stalk lignin, and wheat straw pulp lignin.

[0018] Most lignin research currently focuses on industrial lignin, namely lignin extracted from biomass or recovered from industrial byproducts. The primary source of industrial lignin is sulfate lignin (KL), but several other types exist, such as enzymatically hydrolyzed lignin (EL), organic solvent lignin (OL), alkali lignin (AL), and lignin sulfonate (LS). The composition, molecular weight, and properties of these industrial lignins vary depending on their source and extraction method. ① Sulfate lignin mainly originates from wastewater from the sulfuric acid pulping process. It is produced in large quantities, exhibits relatively severe structural condensation, and has poor reactivity, generally used as fuel. ② Alkali lignin mainly comes from alkaline pulping wastewater and has a similar structure and properties to sulfate lignin. ③ Enzymatically hydrolyzed lignin is a lignin preparation obtained by removing sugars (carbohydrates) through enzymatic hydrolysis. Compared to sulfate and alkali lignin, it does not undergo high-temperature and high-pressure treatment, thus better preserving the basic structure and activity of phenolic and alcoholic hydroxyl groups. ④ Organic solvent lignin is a type of lignin obtained by separation and extraction using organic solvents such as alcohols, ketones, and lipids at a certain temperature. It has high purity, abundant active groups, and good modification ability. ⑤ Lignosulfonates are derived from waste liquid from the sulfite pulping process and have good water solubility.

[0019] Preferably, the acidic solution is at least one of hydrochloric acid, acetic acid, and sulfuric acid, more preferably a sulfuric acid solution.

[0020] Preferably, the mass concentration of the acidic solution is 70-80%;

[0021] Preferably, the reaction temperature is 75–95°C and the reaction time is 1–3 hours.

[0022] Preferably, after the reaction, the product is cooled, then completely dissolved, precipitated, and dried to obtain a solid product, which is tea polyphenol phenolized lignin.

[0023] More preferably, the method of complete dissolution, precipitation and drying specifically involves: dissolving the reaction product mixture in 1,4-dioxane, filtering or centrifuging to remove solid residue after complete dissolution, adding the filtrate to diethyl ether to precipitate and washing, and then freeze-drying to obtain the solid product.

[0024] The tea polyphenol phenolized lignin prepared by the above preparation method.

[0025] A method for preparing a tea polyphenol-phenolized lignin / small molecule sunscreen UV sunscreen includes the following steps:

[0026] The above-mentioned tea polyphenol phenolized lignin was dissolved in an organic solvent / aqueous solution, and then added dropwise to pure water. The organic solvent evaporated naturally and was concentrated to obtain a suspension of tea polyphenol phenolized lignin. Finally, the suspension of tea polyphenol phenolized lignin was compounded and mixed with a small molecule sunscreen and a surfactant. After ultrasonic cavitation, a mixed emulsion of tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen was obtained. The precipitate was removed by centrifugation to obtain tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen.

[0027] Preferably, the organic solvent is at least one of acetone and methanol; more preferably, it is acetone.

[0028] Preferably, the volume ratio of organic solvent to water in the organic solvent / water solution is 6:4 to 8:2.

[0029] Preferably, the mass-volume ratio of the tea polyphenol phenolized lignin to the organic solvent / water solution is 0.5g:20-40mL; more preferably, it is 0.5g:30mL.

[0030] Preferably, the volume ratio of the pure water to the organic solvent / aqueous solution is 8-12:1;

[0031] Preferably, the concentration is a rotary evaporation concentration;

[0032] Preferably, the concentration of the tea polyphenol-phenolized lignin suspension is 5-20 wt%.

[0033] Preferably, the small molecule sunscreen agent is at least one of chemical sunscreen agents such as isooctyl methoxycinnamate, avobenzone, and homosalate.

[0034] Preferably, the weight ratio of the suspension of tea polyphenol-phenolized lignin to the small molecule sunscreen agent is 1:1 to 8:1, more preferably 2:1 to 6:1, and most preferably 5:1.

[0035] Preferably, the amount of surfactant added accounts for 3 to 12% of the total weight of the suspension of tea polyphenol phenolized lignin and the small molecule sunscreen; more preferably, it is 6%.

[0036] Preferably, the surfactant is at least one selected from Tween, alkyl polyglycosides, and sucrose esters.

[0037] Preferably, the ultrasonic cavitation power is 200-1000W and the time is 1-20min; more preferably, ultrasonic cavitation is performed at 400-800W for 3-6min.

[0038] Preferably, the tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen mixed emulsion is centrifuged to remove excess lignin and unencapsulated substances, thereby obtaining the tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen.

[0039] Preferably, the centrifugation rate is 5000–10000 r / min, and the centrifugation time is 10–20 min. More preferably, it is 8000 r / min and 15 min.

[0040] This invention provides a tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen prepared by the above preparation method.

[0041] The above-mentioned tea polyphenol phenolized lignin and the above-mentioned tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen are used in the preparation of sunscreen products.

[0042] Preferably, the sunscreen is a sunscreen cream;

[0043] Preferably, the amount of the tea polyphenol phenolized lignin / small molecule sunscreen / UV sunscreen added is 10%-40%.

[0044] The tea polyphenol phenolized lignin / small molecule sunscreen of the present invention has a spherical structure with a particle size of 100-700nm, and has good ultraviolet absorption and antioxidant properties, as well as good stability and anti-permeability properties.

[0045] This invention provides the application of the above-mentioned tea polyphenol phenolized lignin / small molecule sunscreen agent in the field of sun protection, and more preferably in the application of sunscreen skin care products.

[0046] Lignin is a multifunctional bio-aromatic polymer with great potential in the preparation of sunscreen products due to its UV resistance and antioxidant properties. However, the high heterogeneity of lignin severely hinders its practical application. This invention modifies lignin, which has a limited hydroxyl content and a wide molecular weight distribution, by utilizing the selective phenolization of tea polyphenols. This not only significantly increases the phenolic hydroxyl content but also makes the lignin structure more uniform. Furthermore, its antioxidant properties and UV absorption performance are significantly improved. Single tea polyphenol-phenolized lignin has poor sunscreen performance and needs to be compounded to enhance its performance. This invention utilizes the anti-solvent method and ultrasonic cavitation technology to prepare tea polyphenol-phenolized lignin nanoparticles to encapsulate chemical sunscreen agents, thus preparing tea polyphenol-phenolized lignin-based microcapsules. By leveraging the synergistic effect of tea polyphenol-modified lignin nanoparticles and small-molecule sunscreens, the amount of small-molecule sunscreen required is reduced while simultaneously enhancing the sunscreen performance of tea polyphenol-modified lignin and lightening the color of the lignin. Furthermore, due to the encapsulation effect of tea polyphenol-modified lignin on small-molecule sunscreens, not only is photodegradation of the small-molecule sunscreens effectively prevented, but a natural barrier is also formed between the chemical sunscreen and the skin, preventing contact damage from chemical sunscreens. The modified lignin microcapsules were mixed with a non-sunscreen face cream, and the performance of the sunscreen was evaluated, achieving excellent sun protection efficiency. The tea polyphenol-modified lignin-based sunscreen performs well in preventing skin damage, improves safety, and can well meet consumers' daily needs.

[0047] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0048] (1) This invention employs an economical and feasible phenolation process to modify lignin, reducing the heterogeneity of low-cost industrial lignin and significantly increasing the content of phenolic hydroxyl groups. Since the UV resistance and antioxidant capacity of lignin are closely related to the content of phenolic hydroxyl groups in biopolymers, the UV resistance and surface activity of lignin are improved. Using tea polyphenol-phenolized lignin as a solid surfactant, ultrasonic cavitation technology is used to effectively encapsulate small-molecule chemical sunscreens, achieving synergistic sun protection and improving the sun protection factor.

[0049] (2) This invention introduces tea polyphenols with abundant phenolic hydroxyl groups into the lignin structure through acid-catalyzed phenolation. Compared with other methods, the acid catalysis system has relatively low energy consumption, high phenolation efficiency, and is easy to operate and scale up production. The phenolized lignin not only has significantly improved UV resistance but also plays a role in scavenging free radicals, significantly enhancing the antioxidant properties of lignin. Using tea polyphenol-phenolized lignin to encapsulate small molecule sunscreens can effectively improve the phenomenon of free radical damage to the skin caused by the photodegradation of small molecule sunscreens, achieving safer sun protection.

[0050] (3) The reactivity and hydrophilicity of the tea polyphenol-phenolized lignin prepared by this invention are improved. The tea polyphenol-phenolized lignin nanoparticles / small molecule sunscreen emulsion prepared by antisolvent method and ultrasonic cavitation have good stability. The UV sunscreen has good anti-permeation properties when applied to sunscreen. In addition, the formation of the encapsulation structure reduces the amount of chemical sunscreen agent used and lightens the color of lignin. This invention is of great significance for expanding the high-end, high-value, and high-efficiency application of lignin in the field of sun protection and skin care. Attached Figure Description

[0051] Figure 1 This is a schematic diagram (left) of the preparation of tea polyphenol phenolized lignin obtained in Example 1, and Fourier transform infrared spectra of tea polyphenol phenolized lignin and original lignin (right).

[0052] Figure 2 The images show the UV spectra of the polyphenol-phenolized lignin, the original lignin, and the physical blend of the original lignin and polyphenols (mass ratio 1:2) obtained in Example 1 at 250–400 nm.

[0053] Figure 3 The curves show the DPPH free radical scavenging rates of the tea polyphenol-phenolized lignin, the original lignin, and the physical blend of the original lignin and tea polyphenol (mass ratio of 1:2) obtained in Example 1 at different concentrations.

[0054] Figure 4 The images show the tea polyphenol phenolized lignin / small molecule sunscreen (emulsion after centrifugation) (left) and the sunscreen cream (right) obtained in Example 1.

[0055] Figure 5 The images are SEM images (left) of tea polyphenol phenolized lignin prepared in step (1) of Example 1 and optical microscope images (right) of tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen (emulsion after centrifugation).

[0056] Figure 6 The images show the UV spectra of the tea polyphenol-phenolized lignin / small molecule sunscreen, the lignin / small molecule sunscreen, and the lignin-free sunscreen obtained in Example 1 in the range of 290–400 nm.

[0057] Figure 7 The figures show the DPPH free radical scavenging rate curves of the tea polyphenol-phenolized lignin / small molecule sunscreen, lignin / small molecule sunscreen, and lignin-free sunscreen obtained in Example 1 at different concentrations.

[0058] Figure 8These are laser confocal test images of the sunscreens obtained in Example 1, namely, the tea polyphenol-phenolized lignin / small molecule sunscreen, the lignin / small molecule sunscreen, and the sunscreen without lignin / small molecule.

[0059] Figure 9 The image shows the UV spectrum of the tea polyphenol-phenolized lignin / small molecule sunscreen obtained in Comparative Example 1 in the range of 290–400 nm. Detailed Implementation

[0060] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the raw materials and reagents used in the present invention are commercially available.

[0061] A method for preparing phenol-modified lignin from tea polyphenols includes the following steps:

[0062] A mixture containing lignin, a corresponding amount of tea polyphenols, and an acidic solution (75%) was placed in a three-necked flask equipped with a reflux condenser and a magnetic stirrer. After reacting at 50–100°C for 0.5–6 hours, the mixture was cooled, then completely dissolved, precipitated, and dried to obtain a solid product of tea polyphenol-phenolized lignin.

[0063] A method for preparing a tea polyphenol-phenolized lignin / small molecule sunscreen UV sunscreen includes the following steps:

[0064] The polyphenol-modified lignin was dissolved in an organic solvent / aqueous solution (volume ratio of 10:0 to 0:10), and then slowly dripped into an appropriate amount of pure water. The organic solvent evaporated naturally and was concentrated to obtain a lignin suspension. Finally, the lignin suspension was compounded and mixed with chemical sunscreen and surfactant. After ultrasonic cavitation, a mixed emulsion of polyphenol-modified lignin / small molecule sunscreen UV sunscreen was obtained. After centrifugation to remove impurities, the polyphenol-modified lignin / small molecule sunscreen UV sunscreen was obtained.

[0065] Example 1

[0066] (1) A mixture containing 1.0 g of organic solvent lignin (poplar pulp lignin), a corresponding amount (2 g) of tea polyphenols, and 10 mL of sulfuric acid (75%) was placed in a three-necked flask equipped with a reflux condenser and a magnetic stirrer. After reacting at 90 °C for 2 h, the flask was rapidly cooled with cold tap water, and 25 mL of 1,4-dioxane was added. After complete dissolution, solid impurities were removed by centrifugation. Then, the centrifuged liquid was dropwise added to 150 mL of diethyl ether to precipitate the modified lignin. The precipitate was washed three times with diethyl ether and then freeze-dried. The solid product obtained was tea polyphenol phenolized lignin (see preparation diagram). Figure 1 (Left image).

[0067] Figure 1 The right figure shows the Fourier transform infrared (FTIR) spectra of the prepared tea polyphenol-modified lignin and the original lignin. Compared with the original lignin, the tea polyphenol-modified lignin exhibits higher fluorescence intensity at 3420 cm⁻¹. -1 The absorption peak signal at the point of absorption is significantly enhanced, indicating a substantial increase in the hydroxyl content of lignin. The positions and intensities of other absorption peaks in the Fourier transform infrared spectrum do not change significantly, indicating that the main structure of lignin is maintained. Lignin undergoes acid catalysis to generate carbocations on its side chains. These carbocation-containing lignin side chains can then condense with the para- or ortho-position of phenolic hydroxyl groups in tea polyphenols through electrophilic attack, leading to lignin phenolization.

[0068] Figure 2 The UV absorption spectra of the tea polyphenol-modified lignin obtained in Example 1, the original lignin / tea polyphenol physical blend (mass ratio 1:2), and the original lignin in the 250–400 nm range were measured using a Shimadzu UV-2600 UV-Vis spectrophotometer (Japan). The figures show that the UV absorption of the tea polyphenol-modified lignin is significantly greater than that of the original lignin and the original lignin / tea polyphenol physical blend, indicating that it has a better absorption effect on ultraviolet light.

[0069] Figure 3 The antioxidant capacity of phenol-treated lignin, virgin lignin / tea polyphenol physical blend (mass ratio 1:2), and virgin lignin was determined by testing DPPH free radical scavenging ability. For a specific amount of lignin, the DPPH free radical scavenging rate of the tested samples was as follows: phenol-treated lignin > virgin lignin / tea polyphenol physical blend > virgin lignin, corresponding to the order of phenolic hydroxyl content. The free radical scavenging ability increased with increasing lignin concentration.

[0070] (2) Dissolve 0.5g of the tea polyphenol phenolized lignin from step (1) in 30mL of acetone / water mixed solution (volume ratio 7:3). Add the mixed solution dropwise into ten times the volume of pure water. Let stand for 24 hours to allow the acetone to evaporate naturally. Concentrate by rotary evaporation to obtain a 5wt% solution. Add 6g of isooctyl methoxycinnamate and avobenzone (mass ratio 4:1) and 0.7g of Tween. Sonicate at 600W for 5min to obtain the tea polyphenol phenolized lignin / small molecule sunscreen emulsion. Centrifuge at 8000r / min for 15min to remove unreacted solid residue to obtain the tea polyphenol phenolized lignin / small molecule chemical sunscreen UV sunscreen (emulsion state). Mix this UV sunscreen with a blank cream (baby moisturizing face cream) without sunscreen active ingredients at a ratio of 1:4 to prepare a UV sunscreen cream.

[0071] The preparation process of lignin / small molecule sunscreen UV sunscreen is the same as above, except that the phenol-modified lignin of tea polyphenols is replaced with unphenol-modified organic solvent lignin.

[0072] Preparation process of lignin-free / small molecule sunscreen: 6g of isooctyl methoxycinnamate, avobenzone (mass ratio 4:1), and 0.7g of Tween were added to 10g of water. The mixture was ultrasonically cavitated at 600W for 5min to obtain a lignin-free / small molecule sunscreen emulsion. Unreacted solid residue was removed by centrifugation at 8000r / min for 15min to obtain a lignin-free / small molecule chemical sunscreen UV sunscreen (emulsion state). This UV sunscreen was then mixed with a blank cream (baby moisturizing face cream) without sunscreen active ingredients at a ratio of 1:4 to prepare the UV sunscreen.

[0073] Figure 4 The images show the emulsion (left) and sunscreen (right) prepared from the tea polyphenol-phenolized lignin / small molecule sunscreen agent obtained in Example 1. It can be seen that the emulsion prepared with the tea polyphenol-phenolized lignin / small molecule sunscreen agent has a slightly darker color, indicating a significant increase in the phenolic hydroxyl content within the lignin. Furthermore, the sunscreen cream prepared with the tea polyphenol-phenolized lignin / small molecule chemical sunscreen agent has a relatively light color, meeting the requirements of most consumers for sunscreens.

[0074] Figure 5 The images show an SEM image (left) of the tea polyphenol phenolized lignin prepared in step (1) of Example 1, and an optical microscope image (right) of the tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen (emulsion after centrifugation). The tea polyphenol phenolized lignin has a good spherical morphology, and the tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen forms a well-defined spherical encapsulated emulsion.

[0075] Figure 6 The UV transmittance of the sunscreens obtained in Example 1, namely, the sunscreens containing tea polyphenol-phenolized lignin / small molecule sunscreens, lignin / small molecule sunscreens, and sunscreens without lignin / small molecule sunscreens, was measured in the 290–400 nm range using a Shimadzu UV-2600 UV-Vis spectrophotometer. As shown in the figure, the UV transmittance of the tea polyphenol-modified lignin / small molecule sunscreen is significantly lower than that of the original lignin / small molecule sunscreen and the sunscreen without lignin / small molecule sunscreen, indicating that it has a better UV blocking effect. Converted to UV Protection Factor (SPF), the SPF value of the tea polyphenol-modified lignin / small molecule sunscreen is 101.1, while the SPF values ​​of the original lignin / small molecule sunscreen and the sunscreen without lignin / small molecule sunscreen are 86.6 and 61.8, respectively.

[0076] Figure 7The antioxidant capacity of sunscreens containing tea polyphenol-modified lignin / small molecule sunscreens, lignin / small molecule sunscreens, and lignin-free sunscreens was determined by testing their DPPH free radical scavenging ability. It is evident that the tea polyphenol-modified lignin / small molecule sunscreen has a better free radical scavenging ability, indicating that this sunscreen can effectively mitigate the skin damage caused by free radicals generated from the photodegradation of small molecule chemical sunscreens, achieving safer sun protection.

[0077] Figure 8 The study involved sectioning pig skin tissue coated with sunscreen and observing the cross-sectional laser confocal fluorescence images to assess the skin penetration performance of the sunscreen. Under laser confocal microscopy, lignin-based sunscreens emitted fluorescence. Microcapsules of pig skin coated with lignin-free / small molecule sunscreens showed fluorescence beneath the stratum corneum, confirming the penetration of small molecule sunscreens. Simultaneously, lignin / small molecule sunscreens also showed slight penetration, with fluorescence clearly visible beneath the stratum corneum. Conversely, polyphenol-modified lignin / small molecule sunscreens remained on the stratum corneum of the pig skin, with almost no microcapsules penetrating into the epidermis or dermis. The experimental results indicate that polyphenol-modified lignin / small molecule sunscreens can retain small sunscreen molecules on the skin surface, effectively preventing them from penetrating the skin and harming human health.

[0078] Example 2

[0079] (1) A mixture containing 1.0 g of alkali lignin (pine pulp lignin), a corresponding amount (1 g) of tea polyphenols and 10 mL of sulfuric acid (75%) was placed in a three-necked flask equipped with a reflux condenser and a magnetic stirrer. After reacting at 75 °C for 3 h, the flask was quickly cooled with cold tap water and 25 mL of 1,4-dioxane was added. After complete dissolution, solid impurities were removed by centrifugation. Then, the centrifuged liquid was dropped into 150 mL of diethyl ether to precipitate the modified lignin. The precipitate was washed three times with diethyl ether and then freeze-dried to obtain the solid product, which was tea polyphenol phenolized lignin.

[0080] (2) Dissolve 0.5g of tea polyphenol phenolized lignin in 30mL of acetone / water mixed solution (volume ratio 6:4). Add ten times the volume of pure water to the mixed solution and let it stand for 24 hours to allow the acetone to evaporate naturally. Concentrate by rotary evaporation to obtain a 10wt% solution. Add 6g of isooctyl methoxycinnamate and humosalilate (mass ratio 4:1) and 0.8g of sucrose ester. Ultrasonic cavitation is performed at 400W for 6min to obtain the tea polyphenol phenolized lignin / small molecule chemical sunscreen emulsion. Centrifuge at 8000r / min for 15min to remove unreacted solid residue to obtain the tea polyphenol phenolized lignin / small molecule chemical sunscreen emulsion (emulsion state). Mix this sunscreen with a blank cream (baby moisturizing face cream) without sunscreen active ingredients at a ratio of 1:4 to prepare a sunscreen cream.

[0081] Using the same lignin modification process, tea polyphenol-modified lignin / small molecule chemical sunscreen UV sunscreen preparation process as in Example 1, Fourier transform infrared spectroscopy, UV-Vis spectroscopy, DPPH free radical scavenging ability, and laser confocal microscopy tests, the results were compared with those in Example 1. Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 They are basically the same. The SPF value of the sunscreen made with tea polyphenols, phenolic lignin, and chemical sunscreens (UV sunscreens) is 99.1.

[0082] Example 3

[0083] (1) A mixture containing 1.0 g of enzymatically hydrolyzed lignin (corn straw lignin), the corresponding amount (3 g) of tea polyphenols and 10 mL of sulfuric acid (75%) was placed into a three-necked flask equipped with a reflux condenser and a magnetic stirrer. After reacting at 95 °C for 1 h, the flask was quickly cooled with cold tap water and 25 mL of 1,4-dioxane was added. After complete dissolution, solid impurities were removed by centrifugation. Then, the centrifuged liquid was dropped into 150 mL of diethyl ether to precipitate the modified lignin. The precipitate was washed three times with diethyl ether and then freeze-dried to obtain the solid product, which was tea polyphenol phenolized lignin.

[0084] (2) Dissolve 0.5g of tea polyphenol phenolized lignin in 30mL of acetone / water mixture (volume ratio 8:2). Add ten times the volume of pure water to the mixture and let it stand for 24 hours to allow the acetone to evaporate naturally. Concentrate by rotary evaporation to obtain a 20wt% solution. Add 6g of avobenzone and homosalate (mass ratio 4:1) and 0.9g of alkyl polyglycoside. Sonicate at 800W for 3min to obtain the tea polyphenol phenolized lignin / chemical sunscreen emulsion. Centrifuge at 8000r / min for 15min to remove unreacted solid residue to obtain the tea polyphenol phenolized lignin / chemical sunscreen emulsion. Mix this sunscreen with a blank cream (baby moisturizing face cream) without sunscreen active ingredients at a ratio of 1:4 to prepare a sunscreen cream.

[0085] Using the same lignin modification process, UV sunscreen preparation process, Fourier transform infrared spectroscopy, UV-Vis spectroscopy, DPPH free radical scavenging ability, and laser confocal microscopy as in Example 1, the results are respectively compared with those in Example 1. Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 They are basically the same. The SPF value of the sunscreen made with tea polyphenols, phenolic lignin, and small molecule chemical sunscreens is 94.1.

[0086] Comparative Example 1

[0087] (1) A mixture containing 1.0 g of organic solvent lignin (poplar pulp lignin), a corresponding amount (0.4 g) of tea polyphenols and 10 mL of sulfuric acid (60%) was placed into a three-necked flask equipped with a reflux condenser and a magnetic stirrer. After reacting at 90 °C for 2 h, the flask was quickly cooled with cold tap water and 25 mL of 1,4-dioxane was added. After complete dissolution, solid impurities were removed by centrifugation. Then, the centrifuged liquid was dropped into 150 mL of diethyl ether to precipitate the modified lignin. The precipitate was washed three times with diethyl ether and then freeze-dried to obtain the solid product, which was tea polyphenol phenolized lignin.

[0088] (2) Dissolve 0.5g of tea polyphenol phenolized lignin in 30mL of acetone / water mixture (volume ratio 7:3). Add ten times the volume of pure water to the mixture and let it stand for 24 hours to allow the acetone to evaporate naturally. Concentrate by rotary evaporation to obtain a 5wt% solution. Add 6g of isooctyl methoxycinnamate and avobenzone (mass ratio 4:1) and 0.7g of Tween. Sonicate at 600W for 5min to obtain the tea polyphenol phenolized lignin / small molecule sunscreen emulsion. Centrifuge at 8000r / min for 15min to remove unreacted solid residue to obtain the tea polyphenol phenolized lignin / small molecule sunscreen emulsion. Mix this sunscreen with a blank cream (baby moisturizing face cream) without sunscreen active ingredients at a ratio of 1:4 to prepare a sunscreen cream (1g:0.4g).

[0089] Figure 9 This is the UV-Vis spectrum of the tea polyphenol-phenolized lignin / small molecule sunscreen (1g:0.4g) obtained in this comparative example. As can be seen from the figure, due to the insufficient supply of tea polyphenols and a sufficiently concentrated acidic solution during the reaction, the degree of lignin phenolization was low, resulting in no significant increase in the content of phenolic hydroxyl groups. Consequently, the SPF of the subsequently prepared tea polyphenol-phenolized lignin / small molecule sunscreen was only 89.2, and the sun protection performance was not improved.

[0090] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing phenolic lignin from tea polyphenols, characterized in that, Includes the following steps: Lignin and tea polyphenols are reacted in an acidic solution at 50-100℃ for 0.5-6 h to obtain phenol-modified lignin by tea polyphenols; the mass ratio of tea polyphenols to lignin is 1:1 to 3:

1. The lignin is at least one of organic solvent lignin, alkali lignin, and enzymatically hydrolyzed lignin; The mass ratio of lignin to acidic solution is 1~5:5~20; The mass concentration of the acidic solution is 70-80%. The acidic solution is sulfuric acid.

2. The preparation method according to claim 1, characterized in that, The reaction is carried out at a temperature of 75-95 °C for 1-3 h. After the reaction, the product is cooled, then completely dissolved, precipitated, and dried to obtain a solid product, tea polyphenol phenolized lignin. The method for complete dissolution, precipitation and drying is as follows: the reaction product mixture is dissolved in 1,4-dioxane, and after complete dissolution, the solid residue is removed by filtration or centrifugation. The filtrate is then added dropwise to diethyl ether to precipitate and washed. The solid product is obtained by freeze-drying.

3. The tea polyphenol phenolized lignin prepared by the preparation method according to any one of claims 1-2.

4. A method for preparing a tea polyphenol-phenolized lignin / small molecule sunscreen UV sunscreen, characterized in that, Includes the following steps: The tea polyphenol phenolized lignin described in claim 3 is dissolved in an organic solvent / aqueous solution, and then dropped into pure water. The organic solvent evaporates naturally and is concentrated to obtain a suspension of tea polyphenol phenolized lignin. Finally, the suspension of tea polyphenol phenolized lignin is compounded and mixed with a small molecule sunscreen and a surfactant. After ultrasonic cavitation, a mixed emulsion of tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen is obtained. The precipitate is removed by centrifugation to obtain tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen.

5. The preparation method according to claim 4, characterized in that, The organic solvent is at least one of acetone and methanol; The volume ratio of organic solvent to water in the organic solvent / aqueous solution is 6:4 to 8:

2. The mass-to-volume ratio of the tea polyphenol phenolized lignin to the organic solvent / aqueous solution is 0.5 g: 20-40 mL; The volume ratio of pure water to organic solvent / aqueous solution is 8-12:1; The concentration is a rotary evaporation concentration; The concentration of the suspension of tea polyphenol-phenolized lignin is 5-20 wt%.

6. The preparation method according to claim 4, characterized in that, The small molecule sunscreen agent is at least one of isooctyl methoxycinnamate, avobenzone and homosalate; The surfactant is at least one of Tween, alkyl polyglycosides and sucrose esters; The weight ratio of the suspension of tea polyphenol-phenolized lignin to the small molecule sunscreen agent is 1:1 to 8:

1. The amount of surfactant added is 3 to 12% of the total weight of the suspension of tea polyphenol phenolized lignin and the small molecule sunscreen. The ultrasonic cavitation power is 200 ~ 1000 W, and the time is 1 ~ 20 min; The centrifugation rate is 5000~10000 r / min, and the centrifugation time is 10~20 min.

7. The tea polyphenol phenolized lignin / small molecule sunscreen UV sunscreen prepared by the preparation method according to any one of claims 4-6.

8. The application of the tea polyphenol phenolized lignin of claim 3 and the tea polyphenol phenolized lignin / small molecule sunscreen / UV sunscreen of claim 7 in the preparation of sunscreen products.

9. The application according to claim 8, characterized in that, The sunscreen is a sunscreen cream; the amount of the added tea polyphenol phenolized lignin / small molecule sunscreen agent UV sunscreen agent is 10%-40%.

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