A lignin sunscreen material and its preparation method and application

Abstract

The present invention relates to the technical field of sunscreen preparation, and the present invention discloses a lignin sunscreen material and its preparation method and application. The lignin sunscreen material includes ZIF-8 and lignin encapsulated inside ZIF-8. Lignin, Zn(OAC)2·2H2O and 2-methylimidazole are put into a beaker and completely dissolved using a one-pot method, and then stirred for reaction for at least 8-9 hours. After the reaction is completed, the product is centrifuged, washed and dried to obtain a Z2L lignin sunscreen material. The obtained Z2L not only has a lighter color, making lignin suitable for use in cosmetics, but also solves the problem that the dark color of lignin is not conducive to use in sunscreen cosmetics; and the material has excellent sun protection and antioxidant properties that exceed lignin itself under both neutral and acidic conditions, which can reduce the use of other chemical reagents that may cause skin risks, reduce skin allergies and the risk of inflammation, and has a simple preparation method and is suitable for promotion and application.

Description

Technical Field

[0001] The present invention relates to the technical field of sunscreen preparation, and in particular to a lignin sunscreen material, a preparation method and application thereof. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] Yunnan, located on the Yunnan-Guizhou Plateau, is at a high altitude, with thin air and strong ultraviolet radiation. Providing effective sun protection has always been a social concern. Sunscreens currently on the market typically contain zinc oxide (ZnO) and titanium dioxide (TiO2) or various organic chemicals to block UV radiation.

[0004] Over the past 20 years, most sunscreens on the market have been composed of organic UV sunscreens (such as avobenzone, oxybenzone, octadecene, and octyl methoxycinnamate). However, these sunscreens may cause allergic and photoallergic contact dermatitis. Some studies have shown that they can pass through the stratum corneum or penetrate hair follicles to reach epidermal cells, which may lead to systemic absorption and accumulation in adipose tissue. To avoid these problems, inorganic UV sunscreens (zinc oxide and titanium dioxide) are currently more widely used. However, the disadvantage of sunscreens containing these inorganic filters is that they make the skin appear white when used. To overcome this problem, it is necessary to reduce their particle size or add these sunscreens to microparticles and nanoparticles. For example, the prior art CN113101235B discloses a kind of in-situ titanium dioxide-coated lignin composite particles. Another disadvantage of organic and inorganic sunscreens is that they may increase the production of ROS after ultraviolet exposure, which is harmful to cells and may induce cancer.

[0005] Due to the side effects of synthetic UV-blocking agents on skin tissue, natural sunscreens are gaining increasing attention. Many natural extracts have been investigated as UV blockers. However, most natural polyphenol extracts are of low purity, have poor photostability, and are partial-spectrum sunscreens, failing to block the full spectrum of UV light. Lignin, the most abundant natural polyphenol, is a waste product recovered from pulp and paper production and biorefining processes. It has diverse applications in cosmetics, including antioxidant activity, sun protection factor enhancement, and antimicrobial activity. Lignin in plants is difficult to degrade under UV radiation, and its content increases with increasing exposure to UVB radiation. In addition to its excellent UV absorption properties, lignin's free radical scavenging ability contributes to its excellent antioxidant properties. Furthermore, studies have demonstrated that purified industrial lignin is non-cytotoxic and exhibits good biocompatibility.

[0006] The dark color of industrial lignin has hindered the market adoption of lignin-based sunscreens. Whitening lignin to an acceptable color is essential for widespread use in sunscreen products. Although natural lignin in wood is nearly colorless, its darkening occurs due to the formation of chromophores within its structure, and separation and processing techniques can also contribute to its darkening. Furthermore, the dark color is also attributed to an increase in lignin's degree of conjugation. To reduce lignin's color, various methods have been successfully developed and reported, including fractionation, acetylation, and the preparation of lignin microstructures or nanostructures. Currently, most color reduction methods involve bleaching pulp, decolorizing pulping waste liquor, and degrading industrial lignin. However, these processes aim to remove or destroy as many lignin molecules as possible, making these products unsuitable for further modification and subsequent use as lignin dispersants. Degraded lignin, after bleaching, struggles to retain its UV absorption capacity, making it unsuitable for use as a sunscreen ingredient. UV irradiation has been used to decolorize lignin with considerable success, but this work is conducted at low concentrations and requires the use of large amounts of solvent. Furthermore, due to the low UV penetration rate, the reaction rate is unsatisfactory, resulting in a long time to reduce the color of lignin. Lignin fractionation alone to degrade the condensed structure of lignin does not appear to be effective enough to reduce the color of lignin to an acceptable level for further use of lignin in sunscreens.

[0007] The prior art CN113662880B also discloses improving the structure of lignin and then mixing it with sunscreens to prepare catechol / chemical sunscreen microcapsules, etc., to improve the sun protection of lignin and use chemical reagents to encapsulate lignin to achieve the purpose of color reduction. However, this method has a complicated preparation process and requires the use of chemical solvents to treat lignin. The preparation process is long and ultimately must still be compounded with a sunscreen to achieve the desired effect. Summary of the Invention

[0008] The purpose of the present invention is to provide a lignin sunscreen material and its preparation method and application to address the current problem of difficulty in reducing the color of lignin, thereby solving the dark color problem of lignin and the problems of light instability and skin penetration of existing sunscreens during the skin protection process.

[0009] The technical solutions of the present invention are as follows:

[0010] In one aspect, the present invention provides a lignin sunscreen material, comprising ZIF-8 and lignin encapsulated in the ZIF-8.

[0011] According to a preferred embodiment, the drug loading of ZIF-8 to lignin is 25-28%.Drug loading=lignin mass / ZIF-8 mass×100%.

[0012] Another aspect of the present invention provides a method for preparing a lignin sunscreen material, comprising the following steps:

[0013] Step (1): 50 mg to 250 mg of lignin, 0.4390 g of Zn(OAC)2·2H2O, and 2-methylimidazole were placed in a beaker and mixed, 40 mL of deionized water was added, and the mixture was ultrasonically treated in an ultrasonic cleaner to completely dissolve the solid;

[0014] Step (2): The solution is then transferred into a round-bottom flask and stirred for reaction for at least 8-9 hours. After the reaction is completed, the product is centrifuged and washed three times with an aqueous solution. The powder product is dried at 60° C. for 12-36 hours to obtain the Z2L sunscreen material.

[0015] According to a preferred embodiment, the molar ratio of Zn(OAC)2·2H2O:2-methylimidazole in step (1) is 1:1.5-1:16, preferably 1:4-1:16.

[0016] In step (1), the preferred ratio is 1:4, 1:8, 1:12, or 1:16; more preferably 1:8.

[0017] According to a preferred embodiment, the mass of the lignin in step (1) is 50 mg, 75 mg, 100 mg, 125 mg, 175 mg, 225 mg to 250 mg.

[0018] According to a preferred embodiment, the mass of the lignin is 225 mg.

[0019] According to a preferred embodiment, in step (2), the stirring reaction time is 9 hours.

[0020] Another aspect of the present invention provides an application of a lignin sunscreen material in the preparation of sunscreen cosmetics.

[0021] Preferably, the sunscreen cosmetics include sunscreen cream and sunscreen spray.

[0022] Compared with the existing technology, the beneficial effects of the present invention are:

[0023] 1. A lignin sunscreen material, its preparation method, and application. To address the problems of lignin being too dark in color and prone to agglomeration, the lignin is encapsulated inside ZIF-8 to disperse and lighten the lignin color, while also achieving a high lignin loading rate. To address the problems of current lignin color reduction methods being ineffective, complex to prepare, and the small size of the prepared lignin, a one-pot method is used to prepare a lignin composite material. This method is easy to operate, can control the size of the composite material, and can effectively lighten the color of the lignin.

[0024] 2. A lignin sunscreen material, its preparation method, and application, which uses ZIF-8 to disperse and load lignin. The combination not only maintains the sunscreen and antioxidant properties of lignin, but also improves the overall antioxidant properties of the prepared Z2L sunscreen material, which is conducive to the promotion and application of lignin.

[0025] 3. A lignin sunscreen material, its preparation method, and its application. Addressing skin safety concerns, lignin, as a natural, stable, and biocompatible sunscreen ingredient, reduces the risk of skin allergies and inflammation. The lignin composite material also possesses antioxidant and antibacterial properties, reducing the use of other chemical agents that may cause skin risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Comparison of the color of Z2L prepared by the preparation method of the lignin sunscreen material prepared in Example 1 of this application with the color of the original lignin;

[0027] Figure 2 The UV blocking ability of the Z2L sunscreen material prepared in Example 1 of the present application at different pH values;

[0028] Figure 3 The SPF and UVA PF values ​​of the sunscreen prepared using the Z2L sunscreen material prepared in Example 1 of the present application;

[0029] Figure 4 Comparison of the antioxidant capacity of the Z2L sunscreen material prepared in Example 1 of the present application and lignin alone;

[0030] Figure 5 TEM images of ZIF-8 synthesized in different solvents, where (A) uses water as solvent and (B) uses methanol as solvent;

[0031] Figure 6 TEM images of Z2L sunscreen materials synthesized in different solvents, where (A) uses water as solvent and (B) uses methanol as solvent;

[0032] Figure 7 The toxic effects of different concentrations of Z2L sunscreen material and ZIF-8 on HACAT cells in Example 5;

[0033] Figure 8 The effect of different lignin addition amounts on the drug loading of Z2L sunscreen material in Example 3. DETAILED DESCRIPTION

[0034] The specific embodiments listed in the present invention are only examples of the present invention, and the present invention is not limited to the specific embodiments described below. For those skilled in the art, any equivalent modifications and substitutions to the embodiments described below are also within the scope of the present invention. Therefore, equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be included within the scope of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. All reagents or instruments without the manufacturer specified are conventional products that can be purchased commercially. In order to better illustrate the present invention, numerous specific details are given in the specific embodiments below. Those skilled in the art should understand that the present invention can also be implemented without certain specific details. In other embodiments, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present invention.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art. Unless otherwise specified, the units used in this specification are International Standard Units, and the numerical values ​​and numerical ranges appearing in this invention should be understood to include the inevitable systematic errors in industrial production.

[0036] The cream of this application uses Nivea's hand cream, and other creams can also be used instead.

[0037] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0038] Example 1

[0039] A method for preparing a lignin sunscreen material comprises the following steps:

[0040] Step (1): Take a 50 mL beaker, pour 20 mL of deionized water into it, accurately weigh 0.4390 g of Zn(OAC)2·2H2O and 225 mg of lignin, add them to the deionized water, and then sonicate in an ultrasonic cleaner for 5 minutes to completely dissolve the solid. Take another 50 mL beaker, add 20 mL of deionized water into it, weigh 0.6565 g of the organic linker 2-methylimidazole, add it to the deionized water, and sonicate in an ultrasonic cleaner for 5 minutes to completely dissolve the solid.

[0041] Step (2): The solution is then transferred into a round-bottom flask and stirred at 1000 rpm for 24 hours. After the reaction is completed, the product is centrifuged at 10,000 rpm and washed three times with a certain amount of aqueous solution. The powder product is dried at 60° C. for 24 hours to obtain the Z2L sunscreen material.

[0042] Figure 1 This is the color comparison between lignin and Z2L. The dark color of lignin has always been one of the reasons why it has been troubled in the application of sun protection. Figure 1 We can observe that unencapsulated lignin appears dark black, but when encapsulated by ZIF-8, its color is greatly reduced to light yellow. Therefore, encapsulating lignin in ZIF-8 can effectively reduce the color of lignin, which is conducive to the promotion of lignin as a sunscreen.

[0043] like Figure 2 As shown, the UV absorption ability of Z2L was tested at different pH. Z2L was dissolved in PBS solutions of different pH values, and the UV absorption ability of Z2L under different pH conditions was compared by comparing the color changes of the UV test cards. From the figure, we can observe that the color of the UV card of the Control group darkened in a short period of time under the irradiation of the UV lamp, indicating that a large amount of ultraviolet rays were irradiated onto the UV card. In the control group, the color of the UV card did not change significantly in the first 30 minutes of UV lamp irradiation, but as the irradiation time increased, the color of the UV cards in the pH=2 and pH=5 groups gradually darkened. This is because ZIF-8 itself is an acid-sensitive MOFs, which is digested in an acidic environment, resulting in the weakening of Z2L's UV absorption ability. However, due to the presence of lignin, it still has a certain anti-UV ability even under acidic conditions. Compared with the former, Z2L is dissolved in PBS with a pH=7.4, and still has a high anti-UV ability under UV lamp irradiation. Figure 2 It can be observed that even after two hours of UV light exposure, the color of the UV test card does not change much.

[0044] like Figure 3 As shown, Z2L was incorporated into a cream to prepare a sunscreen for sun protection efficacy testing. A cream without Z2L served as the control group. S1, S5, and S10 were sunscreens with 1%, 5%, and 10% Z2L incorporation, respectively. The results showed that as the concentration of Z2L increased, the SPF and UVA PF of the sunscreen also increased accordingly. As people's understanding of sun protection continues to improve, they are increasingly concerned about the UVA protection provided by sunscreen products. UVA can penetrate the skin and induce the production of reactive oxygen species (ROS), which can significantly damage skin cells and potentially lead to cancer risks. Therefore, sunscreens must have sufficient UVA PF to protect against UVA damage.

[0045] Figure 4The DPPH scavenging ability of Z2L and lignin is shown. Lignin exhibits a certain degree of free radical scavenging capacity, and within the evaluated range, its antioxidant capacity increases with increasing lignin concentration. At a lignin concentration of 100 μg / mL, the DPPH scavenging rate of lignin was 51.8%. Similarly, within the evaluated range, the DPPH scavenging rate of Z2L also increased with increasing concentration. Furthermore, Z2L exhibited superior DPPH scavenging ability compared to free lignin.

[0046] Example 2

[0047] The amounts of 2-methylimidazole and Zn(OAC)2·2H2O in step (1) were kept unchanged, and the amount of lignin added was changed to: 50 mg, 75 mg, 100 mg, 125 mg, 175 mg, 225 mg to 250 mg. Step (2) was the same as in Example 1. The results were as follows: Figure 8 As shown in the figure, with the increase of the amount of lignin added, the drug loading of Z2L first increased and then decreased. When the amount of lignin added was 225 mg, the drug loading rate was the highest, reaching 27.19%.

[0048] Example 3

[0049] A method for preparing a lignin sunscreen material comprises the following steps:

[0050] The amount of lignin added in step (1) was kept constant at 225 mg and the mass of Zn(OAC)2·2H2O was kept constant at 0.4390 g, and the amount of 2-methylimidazole added was changed to 1.756 g, 3.512 g, 5.268 g, and 7.024 g, respectively, so that the molar ratio of Zn(OAC)2·2H2O to 2-methylimidazole was 1:4, 1:8, 1:12, and 1:16. The results showed that the particle size of ZIF-8 decreased with increasing ligand (2-methylimidazole). When the molar ratio of Zn(OAC)2·2H2O to 2-methylimidazole was 1:4, the particle size of the ZIF-8 nanocrystals was approximately 800 nm. When the molar ratio of Zn(OAC)2·2H2O to 2-methylimidazole was 1:8, the particle size of the ZIF-8 nanocrystals was approximately 400 nm. When the molar ratio of Zn(OAC)2·2H2O to 2-methylimidazole was 1:12, the particle size of the ZIF-8 nanocrystals was approximately 250 nm. When the molar ratio of Zn(OAC)2·2H2O to 2-methylimidazole was 1:16, the particle size of the ZIF-8 nanocrystals was approximately 150 nm. Furthermore, as the particle size decreased, the color depth of the particles gradually increased, indicating that the appropriate particle size can be selected to achieve a balanced color.

[0051] When the molar ratio of Zn(OAC)2·2H2O and 2-methylimidazole is 1:8, the particle size is not easy to penetrate the skin, and the color of the nanoparticles is lighter, making them easy to apply.

[0052] Example 4

[0053] The difference between Example 4 and Example 1 is that the stirring reaction time in the round-bottom flask in step (2) is changed to 2-24 hours. The results show that the optimal structure of the Z2L sunscreen material can be obtained by controlling the reaction time to at least 8 hours, preferably 9 hours.

[0054] Example 5

[0055] Different concentrations of Z2L and ZIF-8 were used to test the cytotoxicity of HACAT cells. Figure 7 As shown, with the increase of concentration, the cell survival rate was not significantly affected, indicating that the Z2L and ZIF-8 of the present application would not have toxic effects on cells.

[0056] Comparative Example 1: ZIF-8 nanoparticles were prepared in a different manner.

[0057] Preparation of ZIF-8 nanoparticles using methanol as solvent:

[0058] Step (1): Weigh 0.439 g of Zn(OAC)2·2H2O and dissolve it in 20 mL of anhydrous methanol solution, labeled as solution E. Weigh 1.313 g of an organic linker 2-methylimidazole and dissolve it in 20 mL of anhydrous methanol solution, labeled as solution F.

[0059] Step (2): Solution E and Solution F were sequentially poured into a 100 mL round-bottom flask and stirred at 1000 rpm for 24 hours. After the reaction was complete, the product was collected by centrifugation at 10,000 rpm, washed three times with anhydrous methanol, and dried in an oven at 60°C for 24 hours to obtain ZIF-8 nanoparticles.

[0060] Preparation of ZIF-8 nanoparticles using deionized water as solvent:

[0061] Step (1): Weigh 0.439 g of Zn(OAC)2·2H2O and dissolve it in 20 mL of deionized water, labeled as solution E. Weigh 1.313 g of the organic linker 2-methylimidazole and dissolve it in 20 mL of deionized water, labeled as solution F.

[0062] Step (2): Solution E and Solution F were sequentially poured into a 100 mL round-bottom flask and stirred at 1000 rpm for 24 hours. After the reaction was complete, the product was collected by centrifugation at 10,000 rpm, washed three times with deionized water, and dried in an oven at 60°C for 24 hours to obtain ZIF-8 nanoparticles.

[0063] The TEM images of ZIF-8 nanoparticles prepared using methanol and deionized water as solvents are shown in Figure 2. Figure 5 As shown, (A) uses water as the solvent, and (B) uses methanol as the solvent. ZIF-8 nanoparticles were synthesized in both deionized water and methanol. The ZIF-8 nanoparticles prepared in methanol solution have more regular morphology. Comparative Example 2 uses different methods to prepare Z2L sunscreen material.

[0064] Preparation of Z2L sunscreen material using methanol as solvent:

[0065] Step (1): Take a 50 mL beaker, pour 20 mL of anhydrous methanol solution into it, accurately weigh 0.4390 g of Zn(OAC)2·2H2O and 225 mg of lignin, add them to the methanol solution, and then sonicate in an ultrasonic cleaner for 5 minutes to completely dissolve the solid. Take another 50 mL beaker, add 20 mL of anhydrous methanol solution into it, weigh 0.6565 g of organic linker 2-methylimidazole, add it to the anhydrous methanol solution, and sonicate in an ultrasonic cleaner for 5 minutes to completely dissolve the solid.

[0066] Step (2): The two solutions were transferred to a 100 mL round-bottom flask and stirred at 1000 rpm for 9 hours. After the reaction, the product was centrifuged at 10,000 rpm and collected. The product was washed three times with a certain amount of methanol solution. The powdered product was dried at 60°C for 24 hours to obtain a sample synthesized in methanol.

[0067] Preparation of Z2L sunscreen material using deionized water as solvent:

[0068] Step (1): Take a 50 mL beaker, pour 20 mL of deionized water into it, accurately weigh 0.4390 g of Zn(OAC)2·2H2O and 225 mg of lignin, add them to the deionized water, and then sonicate in an ultrasonic cleaner for 5 minutes to completely dissolve the solid. Take another 50 mL beaker, add 20 mL of deionized water into it, weigh 0.6565 g of the organic linker 2-methylimidazole, add it to the deionized water, and sonicate in an ultrasonic cleaner for 5 minutes to completely dissolve the solid.

[0069] Step (2): The two solutions were transferred to a 100 mL round-bottom flask and stirred at 1000 rpm for 9 hours. After the reaction, the product was centrifuged at 10,000 rpm and collected. The product was then washed three times with a certain amount of deionized water. The powdered product was dried at 60°C for 24 hours to obtain a sample synthesized in deionized water.

[0070] TEM images of Z2L sunscreen materials in two solvents are shown in Figure 2. Figure 6 As shown, (A) is water as solvent and (B) is methanol as solvent. It can be seen from the figure that the use of methanol solution as solvent failed to successfully prepare the Z2L sunscreen material, while the use of deionized water as solvent successfully prepared the Z2L sunscreen material with regular structure and loaded with lignin; it can be seen that the conditions for preparing Z2L sunscreen material are different from those for preparing ZIF-8 nanoparticles, and need to be explored according to actual conditions.

[0071] The above-described embodiments merely represent specific implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection of the present application. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the technical concept of the present application, and all such variations and improvements fall within the scope of protection of the present application.

Claims

1. Application of a lignin sunscreen material in the preparation of sunscreen cosmetics, characterized in that: The lignin sunscreen material includes ZIF-8 and lignin encapsulated inside the ZIF-8; The preparation method of the lignin sunscreen material comprises the following steps: Step (1): 50 mg to 250 mg of lignin, 0.4390 g of Zn(OAC)2·2H2O, and 2-methylimidazole were placed in a beaker and mixed, 40 mL of deionized water was added, and the mixture was ultrasonically treated in an ultrasonic cleaner to completely dissolve the solid. Step (2): The solution is then transferred into a round-bottom flask and stirred for reaction for at least 8 hours. After the reaction is completed, the product is centrifuged and washed three times with an aqueous solution. The powder product is dried at 60°C for 12-36 hours to obtain the Z2L sunscreen material.

2. The use according to claim 1, characterized in that The sunscreen cosmetics include sunscreen cream and sunscreen spray, and the amount of lignin sunscreen material added to the sunscreen cream is 10%.

3. The use according to claim 1, characterized in that The drug loading capacity of ZIF-8 on lignin is 25wt%-28wt%.

4. The use according to claim 1, characterized in that The molar ratio of Zn(OAC)2•2H2O:2-methylimidazole in step (1) is 1:1.5-1:

16.

5. The use according to claim 4, characterized in that The molar ratio of Zn(OAC)2•2H2O:2-methylimidazole is 1:4, 1:8, 1:12 or 1:

16.

6. The use according to claim 1, characterized in that The mass of the lignin in step (1) is 50 mg, 75 mg, 100 mg, 125 mg, 175 mg, 225 mg or 250 mg.

7. The use according to claim 6, characterized in that The mass of the lignin in step (1) is 225 mg.

8. The use according to claim 1, characterized in that The stirring reaction time in step (2) is 9 hours.

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