A wood surface photochromic coating and a method for preparing the same

Abstract

The application discloses a kind of wood surface photochromic coating and its preparation method, preparation method includes the following steps: preparation chitosan solution and transition metal oxide solution, wood is placed in the container with chitosan solution, the top and bottom of container are placed anode and cathode in parallel, direct current electric field is applied in the direction perpendicular to the surface to be loaded of substrate, after drying, wood is placed in the container with transition metal oxide solution, the top and bottom of container are placed cathode and anode in parallel, direct current electric field is applied in the direction perpendicular to the surface to be loaded of substrate, with the first chitosan and the first transition metal oxide solution of loading as a cycle, repeat cycle loading 5~10 times, obtain the wood substrate with photochromic coating, the application can quickly complete on the surface of wood substrate photochromic coating, sample is irradiated by ultraviolet light for about 15min, discoloration phenomenon is remarkable, color is basically restored after 24h shading.

Description

Technical Field

[0001] This invention relates to the field of wood technology, specifically to a photochromic coating for wood surfaces and its preparation method. Background Technology

[0002] Due to the inherent chemical composition and structural characteristics of wood, wood products are susceptible to quality problems caused by environmental factors, resulting in decreased aesthetics and reduced physical and mechanical properties. Ultraviolet (UV) radiation accelerates the degradation of lignin and other components within the wood, shortening the lifespan of wood products. Compared to opaque coatings that obscure the natural grain of wood, less effective transparent varnishes, and less environmentally friendly organic UV absorbers, inorganic nanoparticles primarily provide physical shielding against UV radiation, offering advantages such as low toxicity, high stability, and strong shielding effectiveness. Modifying the wood surface with inorganic nanoparticles can effectively improve the wood's resistance to photoaging and extend the lifespan of wood products. Certain inorganic nanoparticles can also produce color changes while absorbing UV light, exhibiting the characteristic of "photochromism." Wood can produce corresponding color changes under different light sources, demonstrating a certain degree of intelligent response capability, which can significantly expand the scope of intelligent applications for wood and has excellent application prospects. Therefore, photochromic modification of wood is of great significance for expanding the application range of wood, improving its use value, and achieving sustainable development.

[0003] Chinese patent document CN201710520522.8 describes a method for preparing organic-inorganic hybrid photoresponsive wood: 1. Dissolve phosphomolybdic acid in anhydrous ethanol and stir until homogeneous to obtain coating solution A; 2. Add chitosan to acetic acid solution, stir magnetically, and then let stand at room temperature to obtain coating solution B; 3. Mix coating solution A and coating solution B, stir magnetically, and then obtain a coating mixture solution; vacuum the mixture to obtain a defoamed coating mixture solution; 4. Impregnate wood in the defoamed coating mixture solution under vacuum, remove and let stand to dry to obtain organic-inorganic hybrid photoresponsive wood. This method is complex, time-consuming, and unsuitable for large-scale industrial production. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a photochromic coating for wood surfaces and its preparation method. This method is simple to operate, quick to prepare, low in cost, easy to mass-produce, and can be carried out at room temperature.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a photochromic coating on a wood surface includes the following steps:

[0007] (1) Immerse the wood in a container containing chitosan solution. Place the positive and negative electrodes parallel to each other at the top and bottom of the container. Apply a DC electric field in a direction perpendicular to the substrate surface to be loaded, so that the chitosan with positive charge on the surface moves toward the substrate surface to be loaded and is directionally adsorbed onto the surface to be loaded. Perform first-stage impregnation to obtain the first wood product.

[0008] (2) Take out the first wood product and dry it, then immerse it in a container containing a solution of transition metal oxides. The top and bottom of the container are placed parallel to the negative and positive electrodes. Apply a DC electric field in a direction perpendicular to the substrate surface to be loaded, so that the transition metal oxides with negative charges on the surface move toward the substrate surface to be loaded and are oriented to be adsorbed on the surface to be loaded. Perform secondary impregnation to obtain the second wood product.

[0009] (3) Take out the second wood product and dry it. Then repeat steps (1) to (2) 5 to 10 times to obtain a photochromic coating on the wood surface.

[0010] Preferably, in step (1), the method for preparing the chitosan solution includes the following steps: dissolving chitosan in water, adjusting the pH value to 2-6 with hydrochloric acid, and performing ultrasonic dispersion to obtain a chitosan solution; the ultrasonic dispersion time is 5-30 min, and the power is 400-1000 W.

[0011] Preferably, in step (1), the mass fraction of the chitosan solution is 0.2-1%.

[0012] Preferably, in step (2), the method for preparing the transition metal oxide solution includes the following steps: dissolving the transition metal oxide in water, adjusting the pH value to 7-11 with sodium hydroxide, and performing ultrasonic dispersion to obtain the transition metal oxide solution; the ultrasonic dispersion time is 5-30 min and the power is 400-1000 W.

[0013] Preferably, in step (2), the transition metal oxide is nano-tungsten trioxide or nano-cerium dioxide, and the mass fraction of the transition metal oxide solution is 0.2~1%.

[0014] Preferably, in step (2), the particle size of the transition metal oxide is <100nm.

[0015] Preferably, the voltage of the DC electric field is 10~100V.

[0016] Preferably, the time for both primary and secondary immersion is 5 to 60 minutes.

[0017] Preferably, the drying temperature is 60~80℃ and the time is 0.5~2h.

[0018] The present invention also claims protection for a photochromic coating on a wood surface prepared using the aforementioned preparation method.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This invention provides a method for preparing a photochromic coating on a wood surface. The coating is prepared by chitosan and transition metal oxides under a direct current electric field. Chitosan molecules, selected in this invention, have excellent adsorption properties and, as the only naturally occurring positively charged polymer, are easily assembled and arranged under an electric field during coating preparation. Wood fibers themselves are uncharged; however, when the fibers are suspended in water, some anionic groups on the fibers undergo a certain degree of ionization, resulting in a negative charge on the fibers. The positively charged chitosan can then be electrostatically adsorbed onto the wood surface, further adsorbing negatively charged inorganic transition metal oxide nanoparticles. The photochromic material selected in this invention is inorganic transition metal oxide nano-tungsten trioxide or nano-cerium dioxide. Under the application of an external electric field, the inorganic nanoparticles can be distributed and arranged along a specific direction. By changing the concentration of chitosan and transition metal oxides, their surface charge, and the applied electric field conditions, the thickness and particle orientation of the loaded coating can be controlled.

[0021] This invention provides a method for preparing a photochromic coating on a wood surface. Compared with photochromic coatings prepared by ordinary impregnation modification methods, the DC electric field deposition method disclosed in this invention can obtain ordered polyelectrolytes (chitosan) and inorganic transition metal oxides, promote particle orientation dispersion, improve the photochromic performance of composite materials with low filler content, and improve the smoothness of the photochromic coating. In addition, the method provided by this invention can quickly construct a photochromic coating on the surface of a wood substrate. The color change phenomenon is already very significant after the sample is irradiated with ultraviolet light for about 15 minutes, and the color is basically restored after 24 hours of shading. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some schematic diagrams of certain embodiments of the present invention, and therefore should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 AFM testing of the photochromic coatings on the wood surface obtained in Comparative Example 1(a) and Example 3(b);

[0024] Figure 2 The examples and comparative examples illustrate the color change of the photochromic coating on the wood surface as a function of light.

[0025] Figure 3 The image shows the fading of the photochromic coating on the wood surface after light-shielding treatment, as shown in the examples and comparative examples. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Unless otherwise specified, all chemical reagents and materials in this invention are purchased from the market or synthesized from raw materials purchased from the market.

[0028] Chitosan is a low-viscosity chitosan with a viscosity of <200 mPa·s.

[0029] The present invention will be further described below through specific embodiments.

[0030] Example 1

[0031] A method for preparing a photochromic coating on a wood surface, characterized by comprising the following steps:

[0032] (1) Dissolve chitosan in water and adjust the pH to 3 with 0.1 mol / L HCl solution. Then, perform ultrasonic dispersion for 30 min at a power of 1000 W to obtain a chitosan solution with a mass fraction of 0.2% and a positive charge.

[0033] (2) Dissolve tungsten trioxide in water and adjust the pH to 11 with a 0.1 mol / L NaOH solution. Then, perform ultrasonic dispersion for 30 min at a power of 1000 W to obtain a 0.2% tungsten trioxide solution with a negative charge.

[0034] (3) The raw poplar wood was repeatedly rinsed with distilled water and dried at 60°C for 40 min to obtain a wood material with a negative charge on the surface;

[0035] (4) Pour the chitosan solution into a petri dish between two horizontally arranged electrode plates. Connect the upper electrode plate to the positive terminal of the power supply and the lower electrode plate to the negative terminal of the power supply. Place the poplar wood specimen in the dish. The solution level should be slightly higher than the surface of the wood. The voltage between the two electrodes is 100V and the energizing time is 30min. Then rinse repeatedly with distilled water and dry at 60℃ for 40min to obtain the first wood product.

[0036] (5) Pour the tungsten trioxide solution into a petri dish between two horizontally arranged electrode plates. Connect the upper electrode plate to the negative terminal of the power supply and the lower electrode plate to the positive terminal of the power supply. Place the first wood product in the dish. The solution level should be slightly higher than the surface of the wood. The voltage between the two electrodes is 100V and the energizing time is 30min. Then rinse repeatedly with distilled water and dry at 60℃ for 40min to obtain the second wood product.

[0037] (6) Repeat steps (4) to (5) 5 times to obtain a photochromic coating on the wood surface.

[0038] Example 2

[0039] A method for preparing a photochromic coating on a wood surface, characterized by comprising the following steps:

[0040] (1) Dissolve chitosan in water and adjust the pH to 3 with 0.1 mol / L HCl solution. Then, perform ultrasonic dispersion for 30 min at a power of 1000 W to obtain a chitosan solution with a mass fraction of 0.2% and a positive charge.

[0041] (2) Dissolve tungsten trioxide in water and adjust the pH to 9 with a 0.1 mol / L NaOH solution. Then, perform ultrasonic dispersion for 30 min at a power of 1000 W to obtain a 0.2% tungsten trioxide solution with a negative charge.

[0042] (3) The raw poplar wood was repeatedly rinsed with distilled water and dried at 60°C for 40 min to obtain a wood material with a negative charge on the surface;

[0043] (4) Pour the chitosan solution into a petri dish between two horizontally arranged electrode plates. Connect the upper electrode plate to the positive terminal of the power supply and the lower electrode plate to the negative terminal of the power supply. Place the poplar wood specimen in the dish. The solution level should be slightly higher than the surface of the wood. The voltage between the two electrodes is 50V and the energizing time is 15min. Then rinse repeatedly with distilled water and dry at 60℃ for 40min to obtain the first wood product.

[0044] (5) Pour the tungsten trioxide solution into a petri dish between two horizontally arranged electrode plates. Connect the upper electrode plate to the negative terminal of the power supply and the lower electrode plate to the positive terminal of the power supply. Place the first wood product in the dish. The solution level should be slightly higher than the surface of the wood. The voltage between the two electrodes is 50V and the energizing time is 15min. Then rinse repeatedly with distilled water and dry at 60℃ for 40min to obtain the second wood product.

[0045] (6) Repeat steps (4) to (5) 10 times to obtain a photochromic coating on the wood surface.

[0046] Example 3

[0047] A method for preparing a photochromic coating on a wood surface, characterized by comprising the following steps:

[0048] (1) Dissolve chitosan in water and adjust the pH to 3 with 0.1 mol / L HCl solution. Then, perform ultrasonic dispersion for 30 min at a power of 1000 W to obtain a chitosan solution with a mass fraction of 0.2% and a positive charge.

[0049] (2) Dissolve tungsten trioxide in water and adjust the pH to 7 with a 0.1 mol / L NaOH solution. Then, perform ultrasonic dispersion for 30 min at a power of 1000 W to obtain a 0.2% tungsten trioxide solution with a negative charge.

[0050] (3) The raw poplar wood was repeatedly rinsed with distilled water and dried at 60°C for 40 min to obtain a wood material with a negative charge on the surface;

[0051] (4) Pour the chitosan solution into a petri dish between two horizontally arranged electrode plates. Connect the upper electrode plate to the positive terminal of the power supply and the lower electrode plate to the negative terminal of the power supply. Place the poplar wood specimen in the dish. The solution level should be slightly higher than the surface of the wood. The voltage between the two electrodes is 30V and the energizing time is 5min. Then rinse repeatedly with distilled water and dry at 60℃ for 40min to obtain the first wood product.

[0052] (5) Pour the tungsten trioxide solution into a petri dish between two horizontally arranged electrode plates. Connect the upper electrode plate to the negative terminal of the power supply and the lower electrode plate to the positive terminal of the power supply. Place the first wood product in the dish. The solution level should be slightly higher than the surface of the wood. The voltage between the two electrodes is 30V and the energizing time is 5min. Then rinse repeatedly with distilled water and dry at 60℃ for 40min to obtain the second wood product.

[0053] (6) Repeat steps (4) to (5) 5 times to obtain a photochromic coating on the wood surface.

[0054] Comparative Example 1

[0055] A method for preparing a photochromic coating on a wood surface, characterized by comprising the following steps:

[0056] (1) Dissolve chitosan in water and adjust the pH to 3 with 0.1 mol / L HCl solution. Then, perform ultrasonic dispersion for 30 min at a power of 1000 W to obtain a chitosan solution with a mass fraction of 0.2% and a positive charge.

[0057] (2) Dissolve tungsten trioxide in water and adjust the pH to 11 with a 0.1 mol / L NaOH solution. Then, perform ultrasonic dispersion for 30 min at a power of 1000 W to obtain a 0.2% tungsten trioxide solution with a negative charge.

[0058] (3) The raw poplar wood was repeatedly rinsed with distilled water and dried at 60°C for 40 min to obtain a wood material with a negative charge on the surface;

[0059] (4) Immerse the wood material in a positively charged chitosan solution for a first-stage impregnation for 60 min, then rinse repeatedly with distilled water and dry at 60°C for 40 min to obtain the first wood product;

[0060] (5) The first wood product is immersed in a negatively charged tungsten trioxide solution for a second immersion of 60 min, then rinsed repeatedly with distilled water and dried at 60°C for 40 min to obtain the second wood product;

[0061] (6) Repeat steps (4) to (5) 5 times to obtain a photochromic coating on the wood surface.

[0062] AFM analysis of the photochromic coatings on the wood surfaces prepared in Comparative Example 1 and Example 3 showed that the roughness of the composite film in the sample with an applied DC electric field was less than that in the sample without an applied electric field. After applying the electric field, the smoothness of most areas improved and the roughness decreased. The possible reason for this result is that the continuous application of the electric field caused more nanoparticles to be deposited on the wood surface, filling the gaps and thus making the surface smoother than the sample without an applied electric field.

[0063] like Figure 2 As shown, under the same light source, the color difference values ​​of the samples prepared by electric field-assisted self-assembly were all greater than those of the samples prepared by self-assembly without an applied electric field. With increasing irradiation time, significant color changes occurred. When the irradiation time reached 20 minutes, the photochromic coating prepared in Example 2 reached its deepest color. Upon continued irradiation, the sample color hardly changed. This indicates that electric field-assisted self-assembly effectively improved the photochromic performance of the samples.

[0064] After stopping the UV light irradiation, the discolored samples were placed in a dark box for 24 hours of light-blocking treatment. All samples returned to their original color. Figure 3 It can be seen that the fading efficiency of the self-assembled samples with an applied electric field is higher than that of the self-assembled samples without an applied electric field.

[0065] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for the preparation of a wood surface photochromic coating, characterized by, It comprises the following steps: (1) immerse the wood into a container containing a chitosan solution, place the positive and negative electrodes at the top and bottom of the container in parallel, apply a direct current electric field in the direction perpendicular to the surface of the substrate to be loaded, so that the chitosan with positive charges on the surface moves to the surface of the substrate to be loaded and is oriented and adsorbed on the surface to be loaded, carry out primary immersion, and obtain a first wood product; (2) take out the first wood product and dry it, then immerse it into a container containing a transition metal oxide solution, place the negative and positive electrodes at the top and bottom of the container in parallel, apply a direct current electric field in the direction perpendicular to the surface of the substrate to be loaded, so that the transition metal oxide with negative charges on the surface moves to the surface of the substrate to be loaded and is oriented and adsorbed on the surface to be loaded, carry out secondary immersion, and obtain a second wood product; (3) take out the second wood product and dry it, then repeat steps (1) to (2) for 5 to 10 times to obtain a wood surface photochromic coating; In step (2), the transition metal oxide is nano tungsten trioxide or nano cerium dioxide, and the mass fraction of the transition metal oxide solution is 0.2 to 1%; In step (1), the preparation method of the chitosan solution comprises the following steps: dissolving chitosan in water, adjusting the pH value to 2 to 6 with hydrochloric acid, and ultrasonic dispersion to obtain a chitosan solution; the ultrasonic dispersion time is 5 to 30 min, and the power is 400 to 1000 W; In step (2), the preparation method of the transition metal oxide solution comprises the following steps: dissolving the transition metal oxide in water, adjusting the pH value to 7 to 11 with sodium hydroxide, and ultrasonic dispersion to obtain a transition metal oxide solution; the ultrasonic dispersion time is 5 to 30 min, and the power is 400 to 1000 W.

2. The production method according to claim 1, characterized by, In step (1), the mass fraction of the chitosan solution is 0.2 to 1%.

3. The preparation method according to claim 1, characterized in that, In step (2), the particle size of the transition metal oxide is <100 nm.

4. The production method according to claim 1, characterized by, The voltage of the direct current electric field is 10 to 100 V.

5. The method of claim 1, wherein, The time of primary and secondary immersion is 5 to 60 min.

6. The method of claim 1, wherein, The drying temperature is 60 to 80℃, and the time is 0.5 to 2 h.

7. A wood surface photochromic coating prepared by the preparation method of any one of claims 1 to 6.

Images