A strong light-resistant nanolignin-based composite coating and a preparation method and application thereof

Abstract

The application discloses a kind of strong light resistance nanolignin-based composite coating and its preparation method and application, belong to timber protection technical field.Compared with traditional unmodified lignin, the strong light resistance nanolignin-based composite coating prepared by using the lignin nanoparticles prepared from quaternary ammonium lignin and nano-TiO2 as raw materials has more excellent light resistance;The strong light resistance nanolignin-based composite coating provided by the application can retain the original texture of wood, effectively compensate for the shortcomings of traditional protection methods.In addition, the preparation method of the strong light resistance nanolignin-based composite coating provided by the application saves raw materials and has high resource utilization rate.The strong light resistance nanolignin-based composite coating can significantly improve the aging resistance of wood and expand its application prospect in outdoor landscape building materials, durable furniture and wood packaging.

Description

Technical Field

[0001] This invention belongs to the field of wood protection technology, and in particular relates to a highly light-resistant nano-lignin-based composite coating, its preparation method, and its application. Background Technology

[0002] Ultraviolet (UV) absorbers can absorb UVA (320-400 nm) and UVB (280-320 nm) ultraviolet radiation while maintaining their structural integrity. By coating or incorporating them into materials, they can effectively shield wood from UV radiation and protect it from damage. UV absorbers are classified into organic and inorganic types. Evans et al. (Photoprotection of Wood Using Polyester-Type UV-Absorbers Derived from the Reaction of 2-hydroxy-4(2,3-epoxypropoxy)-benzophenone with Dicarboxylic Acid Anhydrides, J. Wood Chem. Technol. 30 (2010) 186-204.) synthesized a polyester-type organic UV absorber (2HBTF) that significantly inhibits wood photodegradation and reduces light transmittance in the 380-405 nm wavelength range. However, organic UV absorbers are prone to migration and decomposition, reducing their long-term protective ability. Yi et al. (Role of α / γ Fe2O3 and ZnO nano-particles in reducing photodegradation of wood components, Wood Sci. Technol. 57 (2023) 427-446) treated radiata pine with Fe2O3 and ZnO nano-solutions, both of which protected the wood surface from UV damage. Inorganic UV absorbers mainly absorb, reflect, and scatter UV rays, effectively blocking them from penetrating coatings and reaching the interior of the wood, but they pose risks to respiratory and eye health, limiting their applicability.

[0003] While traditional UV absorbers can improve the lightfastness of wood to some extent, they suffer from poor compatibility with wood matrices, are prone to migration or decomposition under long-term UV exposure, and some products also exhibit toxicity, making it difficult to meet the demands of green and environmentally friendly applications. Lignin, as a natural and renewable biological resource, is environmentally friendly and has few side effects. Developing lignin-based composite materials can not only effectively reduce environmental pollution caused by lignin waste in the paper industry and alleviate resource waste pressure, but also realize the high-value utilization of lignin and expand its application areas. As a natural phenolic polymer, lignin, rich in aromatic rings and conjugated functional groups in its molecular structure, has a strong characteristic absorption peak in the 280-380 nm UV region, enabling it to absorb UV light and serve as a natural UV blocker. However, its complex macromolecular structure limits the high-value application of lignin, thus its effectiveness often requires modification and compounding. Converting lignin into lignin nanoparticles (LNPs) is an important strategy to overcome this limitation. LNPs not only retain abundant UV-absorbing groups but also significantly improve specific surface area and surface activity due to nanoscale effects. Wu et al. (The mechanism of self-assembly of lignin in deep eutectic solvent based on sulfamic acid and urea through molecular dynamics simulation, Int. J. Biol. Macromol. 253 (2023)) prepared aminated LNPs by modifying them with a deep eutectic solvent of aminosulfonic acid and urea. The micro-nano-scale rough structure can broaden the light propagation path, enhance the ultraviolet absorption rate of the coating, and inhibit the long-term ultraviolet degradation of wood. However, the chemical properties of the aminosulfonic acid-urea deep eutectic solvent may affect the life of the coating under certain environmental conditions. Song et al. (Valorization of Lignin from Biorefinery: Colloidal Lignin Micro-Nanospheres as Multifunctional Bio-Based Fillers for Waterborne Wood Coating Enhancement, ACS Sustainable Chem. Eng. 10 (2022) 11655-11665) prepared colloidal lignin micro-nanospheres (LMNS) using a self-assembly process. These LMNS effectively block ultraviolet rays and provide excellent protection for the color of wood. However, the structural stability of LMNS itself is insufficient, and the UV protection efficiency of the coating will gradually decrease after long-term use.

[0004] TiO2 possesses excellent ultraviolet absorption properties and is a commonly used ultraviolet shielding agent in polymer materials. However, TiO2 itself suffers from strong polarity and easy aggregation, and its poor compatibility with polymer materials greatly limits its performance. Yu et al. (Preparation of lignin / TiO2 composite nanoparticles and their sunscreen application [J]. Fine Chemicals, 2019, 36(10):2089-2095.DOI:10.13550) used a one-step hydrothermal esterification reaction to encapsulate lignin on the surface of TiO2, utilizing the good interfacial compatibility between lignin and TiO2 to improve the dispersibility of TiO2. Lignin and TiO2 undergo a redox reaction to generate Ti 3+ The semiquinone structure enhances the UV absorption capacity of the composite nanoparticles, but the complexity of the one-step hydrothermal esterification process may pose challenges for large-scale applications.

[0005] Guo et al. (Highly Efficient UV Protection of the Biomaterial Wood by A Transparent TiO2 / Ce Xerogel. ACS Appl Mater Interfaces. 2017;9(44):39040-39047. doi:10.1021 / acsami.7b12574) prepared TiO2 / Ce coated wood, which was protected under UV-A radiation at 340 nm with an intensity of 1.87 W / (m²). 2· (nm)) and 313nm band (UV-B, irradiance 2.43W / (m) 2 Irradiation under ultraviolet light conditions of ·nm) for 672h showed that the total color difference ΔE of the TiO2 / Ce gel-coated wood was... The value was 7.15. Shi et al. (Weathering properties of wood treated with 3-isocyanatopropyltriethoxysilane-TiO2. Eur.J. Wood Prod. 81, 1011–1020 (2023)) deposited TiO2 nanoparticles onto the surface of wood using 3-isocyanatopropyltriethoxysilane (IPTS). The artificial aging process used an ultraviolet light wavelength of 340 nm and a radiation intensity of 0.77 W / (m2·nm). After 192 h of artificial weathering, the color difference ΔE of the IPTS-TiO2 treated wood was... The value is 12.

[0006] Patent CN115652616A discloses a photo-aging resistant protective radiation-cooling filler particle and coating, its preparation method, and applications. It utilizes highly selective radiation-inorganic materials to modify lignin, increasing the material's reflectivity to sunlight and reducing the temperature rise of lignin due to light absorption, thus achieving efficient radiation-cooling effects for lignin-based materials. Simultaneously, leveraging lignin's excellent antioxidant and UV-resistant properties, it eliminates free radicals generated by inorganic particles during light exposure, preventing damage to the coating and imparting UV protection. Ultimately, this achieves photo-aging resistance, breaking through the application barriers of lignin materials in the field of radiation-cooling for the first time. It is mainly used on the surfaces of various materials such as sun umbrellas, outdoor clothing, and tents, but its compatibility with wood materials is insufficient.

[0007] Currently available UV absorbers for wood light protection often have significant performance shortcomings and application limitations: organic absorbers, while able to inhibit wood photodegradation to some extent, are prone to migration and decomposition, resulting in weak long-term protection; inorganic absorbers, although possessing UV shielding effects, are highly polar, prone to aggregation, and have poor compatibility with wood matrices, with some inorganic materials posing risks to respiratory and eye health. Traditional UV absorber modification or composite technologies often suffer from cost-efficiency imbalances, and the synthesized materials have low UV absorption efficiency, while their production and use can easily generate environmental burdens, failing to meet the needs of green development. Existing wood light-resistant protective materials often face challenges in large-scale promotion in practical applications, failing to adapt to large-scale application scenarios such as outdoor building materials, limiting their widespread adoption in furniture manufacturing, landscaping, and other fields, and also hindering the promotion of high-value utilization of wood resources. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a highly light-resistant nano-lignin-based composite coating, its preparation method, and its applications. This composite coating uses natural, renewable lignin as a raw material, prepared by quaternizing lignin into LNP, and then compounded with nano-TiO2. It not only possesses advantages such as readily available raw materials, simple synthesis methods, and low production costs, but also exhibits excellent broad-spectrum UV absorption and interfacial compatibility, effectively adsorbing and blocking ultraviolet rays to protect wood from photodegradation. Compared with traditional UV absorbers, the highly light-resistant nano-lignin-based composite coating provided by this invention has significant advantages in terms of environmental friendliness and resource conservation, greatly reducing production and application costs, and promoting the popularization and application of green wood light-resistant protection technology in furniture, outdoor building materials, and timber-framed buildings.

[0009] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a highly light-resistant nano-lignin-based composite coating, comprising the following steps: adding a surfactant to an ethanol solution containing a silane coupling agent, adding nano-titanium dioxide and LNP (lignin nanoparticles) to the resulting mixed solution, mixing to obtain a dispersion, and spraying the dispersion onto a substrate to obtain the highly light-resistant nano-lignin-based composite coating.

[0011] Furthermore, the particle size of the nano-titanium dioxide is 30 nm; the particle size of the lignin nanoparticles is 174 nm.

[0012] Furthermore, the surfactant is selected from sodium dodecyl sulfate; the silane coupling agent is selected from γ-glycidoxypropyltrimethoxysilane.

[0013] Furthermore, the ratio of the surfactant, silane coupling agent, and ethanol solution is 7 mg: 1.4 mg: 20 mL; the mass ratio of the surfactant to lignin nanoparticles is 1: 10; and the mass ratio of the lignin nanoparticles to nano-titanium dioxide is 1: (0.5-2).

[0014] Furthermore, the mass ratio of the lignin nanoparticles to the nano-titanium dioxide is 1:2.

[0015] Further, the preparation method of the lignin nanoparticles includes the following steps: dissolving alkali lignin in sodium hydroxide solution, adding 3-chloro-2-hydroxypropyltrimethylammonium chloride solution dropwise after initial stirring, heating and stirring to obtain quaternized lignin solution, performing initial dialysis purification and initial freeze-drying sequentially to obtain quaternized lignin; adding the quaternized lignin to an organic solvent, stirring at room temperature, adding concentrated nitric acid to the resulting suspension until the solution pH is 5.5, and then performing ultrasonic treatment, secondary dialysis purification and secondary freeze-drying sequentially to obtain lignin nanoparticles.

[0016] The synthesis principle of quaternized lignin in this invention is as follows: the active hydrogen on the phenolic hydroxyl group in lignin is replaced by quaternary ammonium, resulting in an etherification reaction, as detailed below:

[0017]

[0018] The nano-sizing of lignin can improve its high-value applications. LNP has excellent physical and chemical properties, exhibiting uniform dispersion and abundant surface functional groups. By quaternization modification, lignin nanoparticles can be prepared, which can reduce the color of lignin and retain its original texture when sprayed on wood.

[0019] The combination of LNP and nano-TiO2 to obtain a highly light-resistant nano-lignin-based composite coating effectively solves the problem of poor compatibility between traditional inorganic materials and wood matrices. The natural aromatic structure of lignin and the UV-shielding properties of TiO2 work synergistically, giving the coating excellent broad-spectrum UV absorption, protecting wood from photodegradation. Simultaneously, the combination system of natural lignin and TiO2 is environmentally friendly, with no additional harmful emissions during production and use, reducing environmental burden and meeting the requirements of green development.

[0020] Preparing quaternized lignin into nanoparticles and combining them with TiO2 to form a highly light-resistant nano-lignin-based composite coating can effectively solve the problem of easy aggregation of TiO2, significantly improve the absorption and blocking effect of ultraviolet rays in the UVA and UVB bands, enhance the light resistance of wood, and provide ideas for the development of green and environmentally friendly wood protective materials.

[0021] Furthermore, the ratio of alkali lignin to 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is 4 g: 3.3 mL, the mass concentration of 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is 60 wt.%; and / or, the heating and stirring temperature is 85 °C, and the time is 4 h.

[0022] Furthermore, the substrate is selected from wood materials.

[0023] Secondly, the present invention provides a highly light-resistant nano-lignin-based composite coating prepared by the above preparation method.

[0024] Thirdly, the present invention provides an application of the above-mentioned highly light-resistant nano-lignin-based composite coating in the preparation of green and environmentally friendly wood protective materials.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] Compared to traditional unmodified lignin, the highly light-resistant nano-lignin-based composite coating prepared by this invention using lignin nanoparticles obtained from quaternized lignin and nano-TiO2 as raw materials exhibits superior light resistance. This highly light-resistant nano-lignin-based composite coating provides the ability to retain the original texture of wood, effectively compensating for the shortcomings of traditional protective methods. Furthermore, the preparation method of this highly light-resistant nano-lignin-based composite coating saves raw materials and has a high resource utilization rate. This highly light-resistant nano-lignin-based composite coating can significantly improve the aging resistance of wood and expand its application prospects in outdoor landscape building materials, durable furniture, and wooden packaging. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram illustrating the preparation of the highly light-resistant nano-lignin-based composite coating in Example 1;

[0029] Figure 2 The color difference changes during photoaging of wood chips coated with a strong light-resistant nano-lignin-based composite coating in Examples 1-3, wood chips coated with a nano-TiO2 coating in Comparative Example 1, untreated wood chips, wood chips sprayed with an alkali lignin coating in Comparative Example 2, and wood chips sprayed with a quaternized lignin coating in Comparative Example 3 are shown.

[0030] Figure 3 The images show the textures of the wood and raw wood coated with a strong light-resistant nano-lignin-based composite coating in Example 1, where a is a texture image of the wood coated with the strong light-resistant nano-lignin-based composite coating in Example 1, and b is a texture image of the raw wood. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0034] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0035] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0036] Regarding enhancing the lightfastness of wood, traditional methods involve applying a protective coating to the wood surface using functional additives (organic UV absorbers and inorganic nanoparticles). While this improves lightfastness, it suffers from drawbacks such as poor compatibility, easy migration or decomposition under UV irradiation, and toxicity. Therefore, this invention proposes the development of an environmentally friendly, high-performance light stabilizer. This is achieved by quaternizing lignin to prepare lignin nanoparticles, which are then compounded with nano-TiO2 to create a highly lightfast nano-lignin-based composite coating. This modification significantly enhances the lightfastness of wood. Specifically, quaternized lignin stabilizes the wood surface structure to a certain extent, slowing down the rate at which surface lignin produces dark substances due to photodegradation, and the nanoparticle preparation effectively reduces the color of the lignin. The carboxyl groups of the lignin nanoparticles undergo esterification with the carboxyl groups of nano-TiO2, and the introduced silane coupling agent (KH560) enhances the adhesion of the composite coating to the wood surface. The composite coating absorbs and scatters UV light, thus slowing down the degradation of the wood.

[0037] This invention provides a method for preparing a highly light-resistant nano-lignin-based composite coating, which includes the following steps: First, alkali lignin is modified by quaternization to prepare lignin nanoparticles (LNP). Then, surfactant, silane coupling agent, LNP, and nano titanium dioxide are dissolved in an ethanol solution with a mass concentration of 33 wt.%, and stirred continuously for 4 hours to form a stable dispersion. The dispersion is then sprayed onto the surface of wood to obtain a highly light-resistant nano-lignin-based composite coating.

[0038] In some preferred embodiments, the nano-titanium dioxide has a particle size of 30 nm; the lignin nanoparticles have a particle size of 174 nm.

[0039] In some preferred embodiments, the surfactant is selected from sodium dodecyl sulfate; the silane coupling agent is selected from γ-glycidoxypropyltrimethoxysilane.

[0040] In some preferred embodiments, the ratio of the surfactant, silane coupling agent, and ethanol solution is 7 mg:1.4 mg:20 mL; the mass ratio of the surfactant to lignin nanoparticles is 1:10; and the mass ratio of the lignin nanoparticles to nano-titanium dioxide is 1:(0.5-2). For example, the mass ratio of the lignin nanoparticles to nano-titanium dioxide is 1:0.5, 1:1, and 1:2.

[0041] In some preferred embodiments, the specific preparation method of the lignin nanoparticles includes the following steps: dissolving alkali lignin in sodium hydroxide solution, adding 3-chloro-2-hydroxypropyltrimethylammonium chloride solution dropwise after initial stirring, heating and stirring to obtain a quaternized lignin solution, and sequentially performing initial dialysis purification and initial freeze-drying to obtain quaternized lignin; adding the quaternized lignin to an organic solvent, stirring at room temperature, adding concentrated nitric acid to the resulting suspension until the solution pH is 5.5, and then sequentially performing ultrasonic treatment, secondary dialysis purification, and secondary freeze-drying to obtain lignin nanoparticles. The ratio of alkali lignin to 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is 4 g: 3.3 mL, and the mass concentration of the 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is 60 wt.%; the heating and stirring temperature is 85°C, and the time is 4 h.

[0042] This invention also provides a highly light-resistant nano-lignin-based composite coating prepared by the above-described method.

[0043] This invention also provides the application of the above-mentioned highly light-resistant nano-lignin-based composite coating in the preparation of green and environmentally friendly wood protective materials.

[0044] This invention places coated wood in an environment equipped with 40W / m 2 Accelerated aging tests were conducted for 672 hours in a UV-340 high-intensity UV lamp UV aging chamber. The results showed that when the ratio of LNP to nano-TiO2 was 1:2, the total color difference ΔE after UV aging was [missing value]. The lowest value, 4.14, indicates that the highly light-resistant nano-lignin-based composite coating prepared in this invention can effectively improve the color stability of wood and has excellent anti-UV aging properties. According to GB / T 23983-2009, the reference irradiance for wood lightfastness testing is 0.68 W / m². 2 The actual irradiance of this invention reaches 40W / m². 2 Under these conditions, ΔE The value is only 4.14, indicating that the strong light-resistant nano-lignin-based composite coating provided by the present invention can effectively improve the light aging resistance of wood.

[0045] The room temperature in this invention refers to 25±2℃.

[0046] The alkali lignin used in the embodiments of this invention was purchased from Beijing Huamaike Biotechnology Co., Ltd., and the nano TiO2 was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0047] The particle size of the nano-TiO2 in this embodiment of the invention is 30 nm.

[0048] Example 1: A method for preparing a highly light-resistant nano-lignin-based composite coating

[0049] S1. Preparation of quaternized lignin: 4g of alkali lignin was dissolved in a NaOH solution prepared by 6g of NaOH and 25mL of water. After stirring, 3.3mL of 3-chloro-2-hydroxypropyltrimethylammonium chloride solution (60wt.%) was added dropwise, and the mixture was stirred at 85℃ for 4h to obtain a quaternized lignin solution. After dialyzing with distilled water for 4 days, the solution was filtered and then freeze-dried at -40℃ to obtain quaternized lignin powder.

[0050] S2. Preparation of lignin nanoparticles: 0.5 g of the quaternized lignin powder prepared in S1 was dissolved in 100 mL of ethylene glycol and stirred at 600 rpm for 30 min at room temperature to obtain a quaternized lignin powder suspension. Subsequently, concentrated nitric acid was slowly added to the suspension dropwise until the pH of the solution reached 5.5. The resulting mixture was treated with ultrasound at 55 Hz for 1 h. The solution was then placed in a dialysis bag (molecular weight cutoff of 3500 Da) and dialyzed with deionized water for 4 days to remove residual impurities and small molecule products. Finally, the dialyzed solution was freeze-dried at -50 °C using a freeze dryer to obtain lignin nanoparticles (particle size of 174 nm).

[0051] S3. Preparation of nano-lignin coating: 1.4 mg KH-560 (γ-glycidoxypropyltrimethoxysilane) was added to 20 mL of 33 wt.% ethanol solution and stirred for 15 min. Then, 7 mg SDS (sodium dodecyl sulfate) was added and stirred to fully dissolve the SDS in the mixed solution. 70 mg of nano-TiO2 was added and stirred for 1 h. The mixture was then sonicated at 55 Hz for 1 h. Subsequently, 70 mg of lignin nanoparticles prepared in S2 was added and stirred continuously for 4 h to ensure uniform mixing of the components, forming a dispersion with a lignin nanoparticle to nano-TiO2 ratio of 1:1. Finally, the dispersion was sprayed 10 cm away from the surface of a small wood chip with dimensions of 100 mm × 40 mm × 0.5 mm using an air compressor pump (pressure of 4 bar) and a spray tool (nozzle diameter of 0.3 mm) to obtain a highly light-resistant nano-lignin-based composite coating.

[0052] Figure 1 This is a diagram illustrating the preparation of the highly light-resistant nano-lignin-based composite coating in Example 1. Figure 1 The preparation process of quaternized lignin is not included.

[0053] Example 2

[0054] S1. Preparation of quaternized lignin: Same as in Example 1;

[0055] S2. Preparation of lignin nanoparticles: Same as in Example 1;

[0056] S3. Preparation of nano-lignin coating: 1.4 mg KH-560 (γ-glycidoxypropyltrimethoxysilane) was added to an ethanol solution (33%, volume fraction). KH-560 was dispersed in the ethanol solution by stirring. Then, 7 mg SDS (sodium dodecyl sulfate) was added and stirred to fully dissolve the SDS in the mixed solution. 35 mg of nano-TiO2 was added and stirred for 1 h. After stirring, the mixture was ultrasonically treated at 55 Hz for 1 h. Then, 70 mg of lignin nanoparticles prepared in S2 was added and stirred continuously for 4 h to ensure uniform mixing of the components, forming a dispersion with a lignin nanoparticle to nano-TiO2 ratio of 2:1. Finally, the dispersion was sprayed 10 cm away from the surface of a small wood chip with dimensions of 100 mm × 40 mm × 0.5 mm using an air compressor pump (pressure of 4 bar) and a spray tool (nozzle diameter of 0.3 mm) to obtain a highly light-resistant nano-lignin-based composite coating.

[0057] Example 3

[0058] S1. Preparation of quaternized lignin: Same as in Example 1;

[0059] S2. Preparation of lignin nanoparticles: Same as in Example 1;

[0060] S3. Preparation of a high-light-resistant nano-lignin-based composite coating: 1.4 mg of KH-560 (γ-glycidyl etheroxypropyltrimethoxysilane) was added to an ethanol solution (33%, volume fraction). KH-560 was dispersed in the ethanol solution by stirring. Then, 7 mg of SDS (sodium dodecyl sulfate) was added and stirred to fully dissolve the SDS in the mixed solution. 140 mg of nano-TiO2 was added and stirred for 1 h. The mixture was then sonicated at 55 Hz for 1 h. Subsequently, 70 mg of lignin nanoparticles prepared in S2 was added and stirred continuously for 4 h to ensure uniform mixing of the components, forming a dispersion with a lignin nanoparticle to nano-TiO2 ratio of 1:2. Finally, the dispersion was sprayed 10 cm away from the surface of a small wood chip with dimensions of 100 mm × 40 mm × 0.5 mm using an air compressor pump (pressure of 4 bar) and a spray tool (nozzle diameter of 0.3 mm) to obtain a high-light-resistant nano-lignin-based composite coating.

[0061] Comparative Example 1: Preparation method of nano-TiO2 coating

[0062] 7 mg SDS was dissolved in 20 mL of 33 wt.% ethanol solution and stirred for 15 min. Then, 70 mg of nano TiO2 was added and stirred for 1 h. The mixture was then sonicated at 55 Hz for 1 h. 1.4 mg of KH-560 was added and stirred for another 4 h. The resulting dispersion was then sprayed evenly onto the surface of wood chips to prepare a nano TiO2 coating.

[0063] Comparative Example 2: Preparation method of alkali lignin coating

[0064] 0.5 g of alkali lignin was dissolved in 100 mL of ethylene glycol to prepare an alkali lignin solution with a concentration of 5.0 mg / mL. The solution was stirred at 500 rpm for 30 min to obtain an alkali lignin suspension. Subsequently, concentrated nitric acid was slowly added to the suspension dropwise until the pH of the solution reached 5.5. The resulting mixture was treated with ultrasound at 55 Hz for 1 h. The solution was then placed in a dialysis bag and dialyzed with deionized water for 4 days to remove residual impurities and small molecule products. Finally, the dialyzed solution was freeze-dried at -50 °C using a freeze dryer to obtain alkali lignin nanoparticles. 7 mg of alkali lignin nanoparticles were dissolved in 20 mL of 33 wt.% ethanol solution and stirred for 15 min. Then, 1.4 mg of KH-560 was added, and stirring was continued for 4 h. The resulting dispersion was uniformly sprayed onto the surface of wood chips to prepare an alkali lignin coating.

[0065] Comparative Example 3: Preparation method of quaternized lignin coating

[0066] S1. Preparation of quaternized lignin: Same as in Example 1;

[0067] S2. Dissolve 7 mg of quaternized lignin nanoparticles prepared in S1 in 20 mL of 33 wt.% ethanol solution, stir for 15 min, then add 1.4 mg of KH-560, continue stirring for 4 h, and spray the resulting dispersion evenly onto the surface of wood chips to prepare a quaternized lignin coating.

[0068] Performance testing

[0069] 1. Artificial accelerated aging test:

[0070] Wood chips coated with strong light-resistant nano-lignin-based composite coating in Examples 1-3, wood chips coated with nano-TiO2 coating in Comparative Example 1, untreated wood chips, wood chips coated with alkali lignin coating in Comparative Example 2, and wood chips coated with quaternized lignin coating in Comparative Example 3 were all placed in an ultraviolet aging test chamber equipped with a 40W UV-340 ultraviolet lamp for artificial accelerated aging test. The aging time was 672 hours, and there were 5 samples of wood chips in each group. Figure 2 The color difference changes during photoaging of wood chips coated with a strong light-resistant nano-lignin-based composite coating in Examples 1-3, wood chips coated with a nano-TiO2 coating in Comparative Example 1, untreated wood chips, wood chips coated with an alkali lignin coating in Comparative Example 2, and wood chips coated with a quaternized lignin coating in Comparative Example 3 are shown.

[0071] Aging tests revealed that all the wood samples exhibited rapid color changes in the early stages of aging, with the rate of change slowing down in the middle stages and becoming more gradual in the later stages. The ΔE values ​​for untreated wood chips, Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 2, Example 1, and Example 3 are also shown. The values ​​after 672 hours of accelerated photoaging were 17.62, 14.66, 13.91, 5.62, 4.27, 4.57, and 4.14, respectively. Compared with other samples, the ΔE of the nano-lignin:TiO2=1∶2 coating material was significantly higher. With the lowest value, it more effectively improves the light aging resistance of wood.

[0072] 2. Investigate the effect of highly light-resistant nano-lignin-based composite coatings on the original texture of wood.

[0073] Figure 3 In Figure a, there is a photograph of the wood texture coated with a strong light-resistant nano-lignin-based composite coating in Example 1, and in Figure b, there is a photograph of the original wood texture. By comparison, it can be seen that the strong light-resistant nano-lignin-based composite coating provided by the present invention can retain the original wood texture.

[0074] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a highly light-resistant nano-lignin-based composite coating, characterized in that, Includes the following steps: A surfactant is added to an ethanol solution containing a silane coupling agent. Nano-titanium dioxide and lignin nanoparticles are added to the resulting mixed solution and mixed to obtain a dispersion. The dispersion is then sprayed onto a substrate to obtain the highly light-resistant nano-lignin-based composite coating. The mass ratio of the lignin nanoparticles to the nano-titanium dioxide is 1:2; The preparation method of the lignin nanoparticles includes the following steps: alkali lignin is dissolved in sodium hydroxide solution, and after initial stirring, 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is added dropwise, and the mixture is heated and stirred to obtain a quaternized lignin solution. This solution is then subjected to initial dialysis purification and initial freeze-drying to obtain quaternized lignin. The quaternized lignin is added to an organic solvent and stirred at room temperature. Concentrated nitric acid is added to the resulting suspension until the pH of the solution reaches 5.

5. The solution is then subjected to ultrasonic treatment, secondary dialysis purification, and secondary freeze-drying to obtain lignin nanoparticles. The substrate is selected from wood materials; The surfactant is selected from sodium dodecyl sulfate; the silane coupling agent is selected from γ-glycidoxypropyltrimethoxysilane.

2. The method for preparing the highly light-resistant nano-lignin-based composite coating according to claim 1, characterized in that, The nano-titanium dioxide has a particle size of 30 nm; the lignin nanoparticles have a particle size of 174 nm.

3. The method for preparing the highly light-resistant nano-lignin-based composite coating according to claim 1, characterized in that, The ratio of the surfactant, silane coupling agent, and ethanol solution is 7 mg: 1.4 mg: 20 mL; the mass ratio of the surfactant to lignin nanoparticles is 1:

10.

4. The method for preparing the highly light-resistant nano-lignin-based composite coating according to claim 1, characterized in that, The ratio of alkali lignin to 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is 4 g : 3.3 mL, and the mass concentration of 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is 60 wt.%; and / or, the heating and stirring temperature is 85 °C and the time is 4 h.

5. A highly light-resistant nano-lignin-based composite coating prepared by the preparation method according to any one of claims 1-4.

6. The application of the strong light-resistant nano-lignin-based composite coating as described in claim 5 in the preparation of green and environmentally friendly wood protective materials.

Images