Preparation method of a lignin-based natural sunscreen complex

Abstract

The present invention provides a method for preparing a lignin-based natural sunscreen composite, which specifically includes the following steps: First, sodium silicate is used as the silicon source and tetrabutyl titanate is used as the titanium source to prepare an amino-modified composite silica / titania sol by an in-situ modification method; Secondly, the amino-modified composite silica / titania sol is reacted with lignin to prepare a silica / titania / lignin sunscreen composite; The silica, titania, and lignin are compounded, and their components are superimposed on each other to jointly exert their effects, so that the sunscreen range is wider, and the ultraviolet rays in the entire wavelength band can be blocked more effectively, achieving a good sunscreen effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of sunscreen product processing, and particularly relates to a preparation method of a lignin-based natural sunscreen complex. Background Art

[0002] Lignin is one of the three major components forming the plant skeleton, and it widely exists in plant tissues. The annual global lignin production is close to 50 million tons, mainly from the traditional pulp and paper industry and biomass refining residues. With lignin biomass being used to produce renewable fuels and chemicals as a sustainable alternative to petroleum, this quantity may continue to increase in the future. However, currently, more than 95% of industrial lignin is only used as fuel, and less than 5% is utilized industrially. The burned lignin is directly discharged into the environment, which is not only a waste of resources but also causes certain pollution to the environment, contrary to the national development concept. Therefore, it is urgent to develop and utilize lignin to make it effectively and reasonably applied.

[0003] Lignin is a complex organic polymer with functional groups such as aromatic groups, phenolic hydroxyl groups, alcoholic hydroxyl groups, carbonyl groups, and methoxy groups in its molecular structure. Therefore, it can undergo various chemical reactions, endowing lignin with certain properties such as ultraviolet absorption, antibacterial, and antioxidant properties. At the same time, lignin has characteristics such as natural, non-toxic, renewable, and biodegradable, and has great utilization value. Currently, lignin or lignin after modification can be used to prepare fertilizers, additives, adhesives, etc., and has certain applications in the fields of medicine, metallurgy, metal industry, printing and dyeing industry, construction field, etc., but the overall utilization rate is still not high, and more high-value-added products of lignin need to be developed.

[0004] Nowadays, more and more people begin to pay attention to sun protection, and using sunscreen products has become an increasingly common thing. Sunscreen can not only prevent sunburn and suntan, but more importantly, it can resist oxidation and aging. Sunscreen products can block ultraviolet rays and weaken the harm brought by ultraviolet rays to the skin, thereby slowing down skin aging. The current sunscreen products on the market are mainly divided into physical sunscreen and chemical sunscreen, among which most are chemical sunscreen. Such sunscreen products are likely to irritate the skin and may have certain side effects on the skin. Therefore, using lignin as a natural ultraviolet blocker to prepare a sunscreen coating is expected to further improve the comprehensive utilization rate of lignin.

[0005] Lignin has properties such as scavenging free radicals, absorbing ultraviolet rays, antibacterial, and antioxidant, and is considered a natural antioxidant. Using it as a natural ultraviolet blocker to prepare a sunscreen coating can increase the additional utilization value of lignin. However, the dark color of lignin limits its application range, and its absorption effect on ultraviolet rays as a plant sunscreen is not ideal enough. Nano-TiO₂ particles are commonly used physical sunscreens and have good absorption, scattering, and reflection abilities for ultraviolet rays. However, there is a phenomenon of nanoparticle aggregation during the preparation of nano-TiO₂ particles, which reduces the physical barrier performance of nano-TiO₂ to ultraviolet rays. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a preparation method of a lignin-based natural sunscreen composite, which specifically includes the following steps:

[0007] (1) Preparation of composite silica / titania sol:

[0008] 1.1) Take water glass and add acid to adjust the pH of the system to 8-9 to obtain a silica precursor solution;

[0009] 1.2) Disperse tetrabutyl titanate in absolute ethanol to obtain a dispersion liquid. Dropwise add the dispersion liquid into the silica precursor solution in step 1.1), stir and react, and then dropwise add an amino silane coupling agent thereto. After stirring and reacting, a composite silica / titania sol can be obtained;

[0010] (2) Place enzymatically hydrolyzed lignin in a sodium hydroxide solution; then add glyoxal thereto, and then add the composite silica / titania sol thereto under stirring conditions; stir and react at 60 °C for 6-8 h, filter, wash, and dry to obtain a lignin-based natural sunscreen composite;

[0011] In step 1.1), the water glass is an aqueous silicate solution with a modulus of 2.0; the concentration of the aqueous silicate solution is calculated based on silica, and the mass concentration of silica in the aqueous silicate solution is 5%; the silicate is one or two of sodium silicate and potassium silicate;

[0012] The molar ratio of tetrabutyl titanate, silica in the water glass solution, and amino groups in the amino silane coupling agent is 5∶1∶3;

[0013] The amino silane coupling agent is aminopropyltriethoxysilane or bis(aminopropyl)triethoxysilane;

[0014] The mass ratio of the enzymatically hydrolyzed lignin to silica in the water glass solution is 0.8-1.2∶1;

[0015] The mass ratio of the enzymatically hydrolyzed lignin to glyoxal is 10∶1;

[0016] The drying described in step (2) is spray drying;

[0017] The present invention also aims to provide a lignin-based natural sunscreen complex prepared by the above method;

[0018] The application of the described lignin-based natural sunscreen complex in sunscreen products.

[0019] The present invention uses water glass as the silicon source of silicon dioxide, and through adjusting the pH, it undergoes preliminary hydrolysis to obtain a silicon dioxide precursor solution; tetrabutyl titanate is added to the silicon dioxide precursor solution to undergo hydrolysis to form a silicon dioxide / titanium dioxide precursor; the precursor undergoes polycondensation at a certain temperature to form nano-silicon dioxide / nano-titanium dioxide composite nanoparticles; and the surface of the composite nanoparticles has reactive groups such as amino groups; nano-titanium dioxide and nano-silicon dioxide interpenetrate each other, improving the stability of the nanoparticles, avoiding secondary aggregation, and effectively increasing the specific surface area of the nanoparticles, so that without using complex instruments or reagents and with simple operation, it can significantly improve the physical barrier performance of nano-TiO2 to ultraviolet rays.

[0020] The composite nanoparticle sol is reacted with lignin and glyoxal at a certain temperature. The composite nanoparticles undergo a bonding reaction with lignin through groups such as amino groups and hydroxyl groups on the surface, improving the binding strength and compatibility between the nanoparticles and lignin; at the same time, the presence of lignin significantly reduces the secondary aggregation of the nanoparticles during the formation process, improves the dispersibility of the nanoparticles, further avoids the aggregation of the nanoparticles, and improves the sunscreen performance.

[0021] Beneficial effects

[0022] The present invention prepares a nano-titanium dioxide / nano-silicon dioxide / lignin complex by an in-situ composite method; the three act synergistically, endowing stronger light stability, and thus preparing a sunscreen coating with full-band ultraviolet ray blocking. Moreover, the lignin-based natural sunscreen complex has a more excellent ultraviolet ray absorption effect than a simple mixture of nano-titanium dioxide, nano-silicon dioxide, and lignin, and can effectively reduce the transmittance of ultraviolet rays.

[0023] In the lignin-based natural sunscreen complex of the present invention, nano-titanium dioxide, nano-silicon dioxide, and lignin undergo chemical bonding, improving their dispersibility and stability in the sunscreen coating. Moreover, the white nano-titanium dioxide and nano-silicon dioxide also neutralize the color of lignin, breaking through the limitation of difficult color blending due to the deep color, resulting in a better makeup effect and a wider application range; at the same time, the three are compounded, and the components are superimposed on each other to jointly exert their functions, making the sunscreen range wider, more effectively blocking ultraviolet rays in the full band, and achieving a good sunscreen effect.

[0024] The lignin-based natural sunscreen complex of the present invention is used for preparing sunscreen products, which improves the additional utilization value of lignin and has very important significance for improving the comprehensive utilization level of lignin. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a physical picture of the commercial Cetaphil lotion, the lignin-based sunscreen complex prepared in Examples 1-3 of the present invention, and the commercial lotion Cetaphil after being mixed for 15 minutes at 30°C.

[0026] Figure 2 It is a schematic diagram of the change in UV transmittance of the mixed sunscreen coating of the lignin-based sunscreen complex prepared in Example 2 of the present invention and the commercial Cetaphil lotion and two commercially available sunscreen products.

[0027] Wherein a. the mixed sunscreen coating of the lignin-based sunscreen complex prepared in Example 2 of the present invention and the commercial Cetaphil lotion; b. Missha Clear Fit Whitening Sunscreen; c. Olay Total Effects Sunscreen. DETAILED DESCRIPTION OF THE INVENTION

[0028] The technical solutions of the present invention will be elaborated in detail below in conjunction with specific embodiments. The raw materials used in the present invention can be obtained commercially without special instructions.

[0029] Example 1

[0030] A preparation method of a lignin-based natural sunscreen complex specifically includes the following steps:

[0031] (1) Preparation of composite silica / titania sol:

[0032] 1.1) Take 300 g of sodium silicate solution (the concentration is recorded as 5% in terms of the mass concentration of silicon dioxide, and the modulus is 2), add sulfuric acid to adjust the pH of the system to 8-9 to obtain a silica precursor solution;

[0033] 1.2) Disperse 1.25 mol of tetrabutyl titanate in an equal mass of absolute ethanol to obtain a dispersion liquid. Gradually add the dispersion liquid to the silica precursor solution in step 1.1), stir evenly, and then dropwise add an ethanol solution of 3-aminopropyltriethoxysilane thereto, and stir and react for 3 h to obtain a composite silica / titania sol; the ethanol solution of 3-aminopropyltriethoxysilane is obtained by dispersing 0.75 mol of 3-aminopropyltriethoxysilane into an equal weight of absolute ethanol and stirring evenly.

[0034] (2) Take 18.75 g of enzymatically hydrolyzed lignin and place it in a sodium hydroxide solution; then add 1.875 g of glyoxal thereto, and then add the composite silica / titania sol in step (1) thereto under stirring conditions; after reacting at 60 °C for 6 - 8 h, filter, wash, and then obtain the lignin-based natural sunscreen composite through spray drying.

[0035] Example 2

[0036] (1) Preparation of the composite silica / titania sol:

[0037] 1.1) Take 300 g of sodium silicate solution (the concentration is recorded as 5% in terms of the mass concentration of silicon dioxide and the modulus is 2), add sulfuric acid thereto to adjust the pH of the system to 8 - 9 to obtain a silicon dioxide precursor solution;

[0038] 1.2) Disperse 1.25 mol of tetrabutyl titanate in an equal mass of absolute ethanol to obtain a dispersion liquid, gradually add the dispersion liquid to the silicon dioxide precursor solution in step 1.1), stir evenly, and then dropwise add an ethanol solution of aminopropyltriethoxysilane thereto, and stir and react for 3 h to obtain the composite silica / titania sol; the ethanol solution of aminopropyltriethoxysilane is obtained by dispersing 0.75 mol of aminopropyltriethoxysilane into an equal weight of absolute ethanol and stirring evenly;

[0039] (2) Take 15 g of enzymatically hydrolyzed lignin and place it in a sodium hydroxide solution; then add 1.5 g of glyoxal thereto, and then add the composite silica / titania sol in step (1) thereto under stirring conditions; after reacting at 60 °C for 6 - 8 h, filter, wash, and then obtain the lignin-based natural sunscreen composite through spray drying.

[0040] Example 3

[0041] (1) Preparation of the composite silica / titania sol:

[0042] 1.1) Take 300 g of sodium silicate solution (the concentration is recorded as 5% in terms of the mass concentration of silicon dioxide and the modulus is 2), add sulfuric acid thereto to adjust the pH of the system to 8 - 9 to obtain a silicon dioxide precursor solution;

[0043] 1.2) Disperse 1.25 mol of tetrabutyl titanate in an equal mass of absolute ethanol to obtain a dispersion liquid, gradually add the dispersion liquid to the silicon dioxide precursor solution in step 1.1), stir evenly, and then dropwise add an ethanol solution of aminopropyltriethoxysilane thereto, and stir and react for 3 h to obtain the composite silica / titania sol; the ethanol solution of aminopropyltriethoxysilane is obtained by dispersing 0.75 mol of aminopropyltriethoxysilane into an equal weight of absolute ethanol and stirring evenly;

[0044] (2) Weigh 12.5 g of enzymatically hydrolyzed lignin and place it in a sodium hydroxide solution. Then add 1.25 g of glyoxal to it, and subsequently add the composite silica / titania sol from step (1) thereto under stirring conditions. After reacting at 60 °C for 6 - 8 h, filter, wash, and then obtain the lignin-based natural sunscreen composite by spray drying.

[0045] Comparative Example 1

[0046] A preparation method of a lignin-based natural sunscreen composite specifically comprises the following steps:

[0047] (1) Preparation of composite silica / titania nanoparticles:

[0048] 1.1) Take 300 g of sodium silicate solution (with a silica mass concentration of 5% and a modulus of 2), add sulfuric acid to adjust the pH of the system to 8 - 9 to obtain a silica precursor solution;

[0049] 1.2) Disperse 1.25 mol of tetrabutyl titanate in an equal mass of absolute ethanol to obtain a dispersion. Gradually add the dispersion to the silica precursor solution in step 1.1), stir evenly, and then dropwise add an ethanol solution of 3-aminopropyltriethoxysilane thereto. After stirring and reacting at 60 °C for 5 h, filter and wash until the washing liquid contains no sulfate ions, and then obtain the composite silica / titania nanoparticle powder by spray drying; the ethanol solution of 3-aminopropyltriethoxysilane is obtained by dispersing 0.75 mol of 3-aminopropyltriethoxysilane into an equal weight of absolute ethanol and stirring evenly;

[0050] (2) Take 15 g of enzymatically hydrolyzed lignin and place it in a sodium hydroxide solution. Then add 1.5 g of glyoxal to it, and subsequently add the composite silica / titania nanoparticles from step (1) thereto under stirring conditions. After reacting at 60 °C for 6 - 8 h, filter, wash, and then obtain the lignin-based natural sunscreen composite by spray drying.

[0051] Comparative Example 2

[0052] A preparation method of a lignin-based natural sunscreen composite specifically comprises the following steps:

[0053] (1) Preparation of composite silica / titania sol:

[0054] 1.1) Take 300 g of sodium silicate solution (with a silica mass concentration of 5% and a modulus of 2), add sulfuric acid to adjust the pH of the system to 8 - 9 to obtain a silica precursor solution;

[0055] 1.2) Disperse 1.25 mol of tetrabutyl titanate in an equal mass of absolute ethanol to obtain a dispersion, and gradually add the dispersion to the silica precursor solution in step 1.1). After stirring evenly, continue stirring and reacting for 3 h to obtain a composite silica / titania sol;

[0056] (2) Take 15 g of enzymatically hydrolyzed lignin and place it in a sodium hydroxide solution; then add 1.5 g of glyoxal to it, and then add the composite silica / titania sol in step (1) thereto under stirring conditions; react at 60 °C for 6 - 8 h, filter, wash, and then obtain a lignin-based natural sunscreen composite through spray drying.

[0057] Comparative Example 3

[0058] A preparation method of a lignin-based natural sunscreen composite specifically includes the following steps:

[0059] (1) Disperse 1.25 mol of tetrabutyl titanate in an equal mass of absolute ethanol to obtain a dispersion;

[0060] (2) Take 15 g of enzymatically hydrolyzed lignin and place it in a sodium hydroxide solution; then add 1.5 g of glyoxal to it, and then add the tetrabutyl titanate dispersion in step (1) thereto under stirring conditions; react at 60 °C for 6 - 8 h, filter, wash, and then obtain a lignin-based natural sunscreen composite through spray drying.

[0061] Testing the in vitro sun protection index of the lignin-based natural sunscreen composite prepared in the present invention:

[0062] Disperse the lignin-based sunscreen composites prepared in Examples 1 - 3 and Comparative Examples 1 - 3 of the present invention in the commercially available product Cetaphil lotion, and stir and mix for 15 min at 30 °C to obtain a sunscreen coating; the physical diagram of the sunscreen coating of the lignin-based sunscreen composite prepared in the examples of the present invention is as Figure 1 shown;

[0063] Take the sunscreen coatings of the lignin-based sunscreen composites prepared in Examples 1 - 3 and Comparative Examples 1 - 3 of the present invention as the test groups; measure their UV transmittance, and use the commercially available Cetaphil lotion as the reference group; the test results are shown in Table 1.

[0064] Table 1

[0065] UV Transmittance (%) Example 1 16.18 Example 2 15.66 Example 3 16.75 Comparative Example 1 21.97 Comparative Example 2 25.59 Comparative Example 3 29.78

[0066] It can be seen from the data in Table 1 that the lignin-based sunscreen composites prepared in Examples 1 - 3 of the present invention have a lower UV transmittance as sunscreen coatings, indicating that the sunscreen composite coating of the present invention has excellent anti-ultraviolet performance.

[0067] Compared with Example 2, the ultraviolet transmittance of the composite coatings in Comparative Examples 1-3 is higher than that of the sunscreen coating in Example 2; the composite sunscreen coating in Comparative Example 1 is prepared by mixing and reacting composite nanoparticle powder with lignin to obtain a sunscreen composite; during the preparation of the composite nanoparticles, secondary aggregation of the nanoparticles reduces the contact probability between nano-silica and nano-titanium dioxide and ultraviolet rays, thereby reducing the absorption rate of ultraviolet rays; in Comparative Example 2, amino-silane coupling agent is not added during the preparation of the composite sol. On the one hand, this increases the aggregation of the composite nanoparticles. On the other hand, the surface of the composite nanoparticles does not contain reactive groups of amino. During the compounding process with lignin, the reactivity is reduced, and the compatibility between the nanoparticles and lignin is poor, resulting in poor stability of the sunscreen composite coating; Comparative Example 3 is to obtain a sunscreen composite by compounding nano-titanium dioxide particles with lignin. The sunscreen composite does not contain nano-silica, and the ultraviolet transmittance of the obtained sunscreen coating increases; therefore, the present invention uses an in-situ composite method to first prepare a nano-silica / nano-titanium dioxide precursor (composite silica / titanium dioxide sol); then in-situ compound the sol with lignin to obtain a lignin-based natural sunscreen composite. The lignin-based composite formed in the in-situ synthesis has better stability than the simple mixture of nanoparticles and lignin when forming a coating in the emulsion. At the same time, the dispersion of the nanoparticles is better, and the function of absorbing ultraviolet rays can be more fully exerted, and the ultraviolet transmittance will be significantly reduced; it shows a good barrier effect on ultraviolet rays.

[0068] Meanwhile, the UV transmittance of the lignin-based sunscreen composite sunscreen coating prepared in Example 2 of the present invention and two commercially available sunscreen products was tested in vitro, and the transmittance change curve is as Figure 2 shown;

[0069] The light with a wavelength of 400nm - 10nm in the sun is ultraviolet light, and 98.7% of the ultraviolet light reaching the earth's surface is UVA (ultraviolet A, wavelength 400nm - 320nm); it can be Figure 2 seen that within this wavelength range, the ultraviolet transmittance of the commercially available Mamonde Clear White Tone Up Sunscreen (curve b) and Olay Total Effects Sunscreen (curve c) is much higher than that of the lignin-based sunscreen composite sunscreen coating (curve a) prepared in Example 2 of the present invention; and the ultraviolet transmittance of the commercially available Olay Total Effects Sunscreen fluctuates greatly in the full wavelength range, and the stability is poor; therefore, the lignin-based sunscreen composite prepared in Example 2 of the present invention has better sunscreen effect than the two commercially available sunscreen products, and shows a good ultraviolet blocking effect in the full wavelength range.

[0070] The above embodiments are only preferred specific embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any simple variations or equivalent substitutions of technical solutions that can be obviously obtained by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope of the present invention.

Claims

1. A preparation method of a lignin-based natural sunscreen complex, characterized in that, Specifically, it includes the following steps: (1) Preparation of composite silica / titania sol: 1.1) Take water glass, add acid to adjust the pH of the system to 8 - 9 to obtain a silica precursor solution; 1.2) Disperse tetrabutyl titanate in absolute ethanol to obtain a dispersion. Dropwise add the dispersion into the silica precursor solution in step 1.1), stir and react, then dropwise add an amino silane coupling agent, and stir and react to obtain a composite silica / titania sol; (2) Place enzymatically hydrolyzed lignin in a sodium hydroxide solution; then add glyoxal to it, and then dropwise add the composite silica / titania sol under stirring conditions; stir and react at 60 °C for 6 - 8 h, then filter, wash and dry to obtain a lignin-based natural sunscreen composite; Among them, the molar ratio of tetrabutyl titanate, silica in the water glass solution, and amino groups in the amino silane coupling agent is 5:1:

3.

2. The preparation method of the lignin-based natural sunscreen complex according to claim 1, characterized in that, In step 1.1), the water glass is an aqueous silicate solution with a modulus of 2.0; the concentration of the aqueous silicate solution is calculated based on silica, and the mass concentration of silica in the aqueous silicate solution is 5%.

3. The preparation method of the lignin-based natural sunscreen complex according to claim 2, characterized in that, The silicate is one or two of sodium silicate and potassium silicate.

4. The preparation method of the lignin-based natural sunscreen complex according to claim 1, characterized in that, The amino silane coupling agent is aminopropyltriethoxysilane or bis(aminopropyl)triethoxysilane.

5. The preparation method of the lignin-based natural sunscreen complex according to claim 1, characterized in that, The mass ratio of enzymatically hydrolyzed lignin to silica in the water glass solution is 0.8 - 1.2:

1.

6. The preparation method of the lignin-based natural sunscreen complex according to claim 1, characterized in that, The mass ratio of enzymatically hydrolyzed lignin to glyoxal is 10:

1.

7. The preparation method of the lignin-based natural sunscreen complex according to claim 1, characterized in that, The drying in step (2) is spray drying.

8. A lignin-based natural sunscreen composite prepared by the method according to any one of claims 1 - 7.

9. Use of the lignin-based sunscreen composite according to claim 8 in sunscreen products.

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