An environmentally friendly wood bleaching treatment method using ultraviolet photocatalysis

Abstract

An environmentally friendly wood bleaching treatment method using ultraviolet photocatalysis is disclosed, belonging to the field of wood bleaching. This invention aims to solve the problems of low efficiency, yellowing of bleached wood, excessive bleaching waste liquid, and severe reduction in mechanical properties associated with existing bleaching methods. The treatment method includes: 1. Coating with bleaching solution; 2. Catalytic bleaching. This invention is used for environmentally friendly wood bleaching treatment using ultraviolet photocatalysis.

Description

Technical Field

[0001] This invention belongs to the field of wood bleaching. Background Technology

[0002] my country is a country with relatively little forest cover. With socio-economic development, population growth, and improved living standards, the demand for forest products is constantly increasing. At the same time, with the strengthening of public ecological awareness and increased national forest protection efforts, logging has been subject to certain restrictions. It is estimated that my country's timber consumption in 2020 was approximately 500 million cubic meters. 3 Domestic timber production is only 100 million cubic meters. 3 There is a huge gap between supply and demand in the timber market. Currently, my country is the world's largest importer of timber, accounting for about a quarter of the global timber import trade. Therefore, how to efficiently utilize wood products, enhance their commercial value, and alleviate the supply-demand imbalance in the domestic timber market has become one of the urgent issues to be addressed in the development of my country's timber industry in the new era.

[0003] Discoloration of wood is a common phenomenon in nature. Whether it's mature trees during their growth, logs after logging, processed boards and timber, or wood after drying and use, surface or internal discoloration is frequently observed. This not only affects the wood's aesthetics but also alters its hardness, making it more brittle in some cases. Discoloration also impacts subsequent processing and manufacturing processes, reducing the wood's usability and commercial value. Therefore, bleaching wood is essential.

[0004] There are many reasons for wood discoloration, which can be mainly divided into four categories based on the cause: chemical discoloration, physical discoloration, physiological discoloration, and microbial discoloration. However, from the perspective of wood composition, the discoloration of wood is due to changes in the internal chemical composition of the wood. The color of wood is mainly due to the presence of chromophores and auxochromes. Chromophores are groups that cause compounds to absorb light in the ultraviolet and visible light regions, regardless of whether they exhibit color. For example, unsaturated groups containing π bonds such as C=C, C≡C, benzene rings, and C=O are chromophores. Auxochromes are groups with lone pairs of electrons, such as -OH, -OR, -NH2, -NHR, -Cl, -Br, and -I. They themselves cannot absorb light greater than 200nm, but when they are attached to chromophores, they shift the absorption peak of the chromophore towards longer wavelengths and increase its absorption intensity. Chromophores and auxochromes are mainly found in lignin and extracts, and in small amounts in ash. Wood bleaching is the process of destroying the chromophores or auxochromes and other color-related components in wood through oxidation, reduction, and devalence reduction by bleaching agents, thereby achieving the purpose of decolorization.

[0005] Based on the characteristics of the bleaching process, it can be divided into brush bleaching and impregnation bleaching. Brush bleaching is mainly used to remove surface contaminants from wood and adjust the surface color. It is simple to operate, but the bleach solution does not penetrate deeply into the wood, only affecting the surface. For example, furniture is bleached before applying a transparent finish to make the surface color more uniform. Brush bleaching often requires a high concentration of bleach solution. Although an excessively high concentration of sodium hydroxide can promote the decomposition rate of hydrogen peroxide, the bleached wood surface will be contaminated by the high sodium hydroxide concentration, requiring rinsing with water, increasing the bleaching process, generating more rinsing waste liquid, and the high concentration of sodium hydroxide can damage the wood surface, leading to a decrease in mechanical properties. Impregnation bleaching can change the surface color of wood and can also perform deep treatment, but since the internal color changes of wood cannot be directly reflected on the surface, it is not very meaningful. Furthermore, impregnation bleaching requires more impregnation solution, generating more impregnation waste liquid, making it more polluting to the environment than brush bleaching, and the bleaching time is longer, reducing industrial production efficiency. Therefore, it is particularly important to find a highly efficient cleaning and bleaching method that can effectively reduce bleaching time and waste liquid generation. Summary of the Invention

[0006] This invention aims to solve the problems of low efficiency, yellowing of wood color after bleaching, excessive bleaching waste liquid, and severe reduction in mechanical properties of existing bleaching methods, and to provide an environmentally friendly wood bleaching treatment method using ultraviolet photocatalysis.

[0007] An environmentally friendly wood bleaching treatment method catalyzed by ultraviolet light, comprising the following steps:

[0008] 1. Apply bleach solution:

[0009] A 5%–10% sodium hydroxide solution and a 25%–35% hydrogen peroxide solution, or a mixed solution of sodium hydroxide and hydrogen peroxide, are sequentially coated onto a wooden board to obtain the coated wooden board.

[0010] The sodium hydroxide and hydrogen peroxide mixed solution is prepared by mixing a sodium hydroxide solution of 5% to 10% by mass and a hydrogen peroxide solution of 25% to 35% by mass in a mass ratio of (0.5 to 2):1.

[0011] II. Catalytic bleaching:

[0012] Under the conditions of UV lamp power of 50W to 500W and UV wavelength of 200nm to 400nm, the coated wood board is irradiated with UV lamp for 0.5h to 5h, and finally dried, thus completing the environmentally friendly wood bleaching treatment method of UV photocatalysis.

[0013] The beneficial effects of this invention are:

[0014] This invention provides a novel method for bleaching wood surfaces. Depending on the specific needs, one or both sides of the wood can be treated. The method primarily uses a combination of sodium hydroxide and hydrogen peroxide at a certain concentration as a bleaching agent, bleaching the wood surface under ultraviolet light irradiation of a certain intensity. Sodium hydroxide plays two main roles: firstly, it reacts with lignin and tannins in the wood, increasing the permeability of the bleaching solution; secondly, it adjusts the pH value of hydrogen peroxide, causing it to generate more free radicals. Hydrogen peroxide mainly functions by decomposing to generate free radicals that react with chromophores and auxochromes in the wood, achieving the bleaching effect. Ultraviolet light catalyzes and further stimulates the decomposition of hydrogen peroxide, increasing the efficiency of free radical activation. Additionally, some unstable groups in lignin, such as conjugated double bonds and quinone groups, can absorb the photoelectron energy of ultraviolet light, becoming free radicals that react more effectively with hydrogen peroxide, further improving bleaching efficiency. Bleaching under ultraviolet light can, to some extent, reduce the use of alkaline substances such as sodium hydroxide, mitigating the damage to wood caused by these substances and reducing the loss of mechanical properties. The use of low-concentration sodium hydroxide reduces the residue of alkaline substances on the wood surface, eliminating the need for cleaning. Because some unstable groups in lignin and extracts are excited into free radicals and bleached by absorbing ultraviolet light energy during the initial bleaching process, the bleached product is less prone to discoloration due to ultraviolet radiation during subsequent use, slowing down the yellowing process.

[0015] The bleaching solution of this invention is applied by brushing or spraying, which reduces the generation of impregnation waste compared to soaking. Furthermore, under ultraviolet light catalysis, it increases the efficiency of hydrogen peroxide in generating free radicals and accelerates the reaction rate between chromophores, auxochromes, and hydrogen peroxide in the wood, reducing bleaching time and increasing whiteness. The whiteness after bleaching can reach up to 89.3, and the total color difference ΔE before and after bleaching can reach up to 27.6. It reduces the use of alkaline substances such as sodium hydroxide, lowering the concentration of sodium hydroxide commonly used in industry (20%–35% by mass) to 5%–10%, thus avoiding the need for cleaning the wood surface after bleaching. Additionally, ultraviolet light has a certain heating effect, reducing the drying time of the wood compared to the absence of ultraviolet light catalysis. The wood bleaching treatment method of this embodiment has been used to bleach different tree species, producing good bleaching effects with whiteness Wh reaching over 80, while effectively reducing the loss of mechanical properties. Furthermore, after bleaching, oak, poplar, and balsa wood under UV accelerated aging for 36 hours, the ΔE value was only 12.2–18.7.

[0016] Instruction manual illustrations

[0017] Figure 1The images show a comparison of wood before and after bleaching treatment. a is oak before bleaching in Example 1, b is poplar before bleaching in Example 2, c is balsa wood before bleaching in Example 3, d is oak after bleaching in Example 1, e is poplar after bleaching in Example 2, and f is balsa wood after bleaching in Example 3.

[0018] Figure 2 The images show a comparison of poplar wood treated with different bleaching methods and then subjected to accelerated UV aging. a is poplar wood before bleaching in Example 2, b is poplar wood after bleaching in Example 2, c is poplar wood after bleaching in Example 2 subjected to accelerated UV aging for 36 hours, d is poplar wood before bleaching in Comparative Experiment 1, e is poplar wood after bleaching in Comparative Experiment 1, f is poplar wood after bleaching in Comparative Experiment 1 subjected to accelerated UV aging for 36 hours, g is poplar wood before industrial bleaching in Comparative Experiment 2, h is poplar wood after industrial bleaching in Comparative Experiment 2, and i is poplar wood after industrial bleaching in Comparative Experiment 2 subjected to accelerated UV aging for 36 hours after bleaching.

[0019] Figure 3 Images of oak veneer after bleaching using different methods: a) bleached oak surface in Example 4; b) industrially bleached oak surface in Comparative Experiment 4; c) bleached oak surface in Example 4 under a 50x super depth-of-field microscope; d) industrially bleached oak surface in Comparative Experiment 4 under a 50x super depth-of-field microscope; e) scanning electron microscope image of bleached oak in Example 4; f) industrially bleached oak surface in Comparative Experiment 4. Detailed Implementation

[0020] Specific Implementation Method 1: This implementation method is an environmentally friendly wood bleaching treatment method catalyzed by ultraviolet light, which is carried out according to the following steps:

[0021] 1. Apply bleach solution:

[0022] A 5%–10% sodium hydroxide solution and a 25%–35% hydrogen peroxide solution, or a mixed solution of sodium hydroxide and hydrogen peroxide, are sequentially coated onto a wooden board to obtain the coated wooden board.

[0023] The sodium hydroxide and hydrogen peroxide mixed solution is prepared by mixing a sodium hydroxide solution of 5% to 10% by mass and a hydrogen peroxide solution of 25% to 35% by mass in a mass ratio of (0.5 to 2):1.

[0024] II. Catalytic bleaching:

[0025] Under the conditions of UV lamp power of 50W to 500W and UV wavelength of 200nm to 400nm, the coated wood board is irradiated with UV lamp for 0.5h to 5h, and finally dried, thus completing the environmentally friendly wood bleaching treatment method of UV photocatalysis.

[0026] Unstable chromophores and auxochromes in lignin and extracts of wood can absorb ultraviolet photon energy and become free radicals under ultraviolet light, reacting with oxygen and other substances in the environment. Hydrogen peroxide is unstable under alkaline conditions and easily decomposes to produce free radicals. Furthermore, under ultraviolet light, hydrogen peroxide can accelerate the generation of free radicals (such as O· and HOO·), reacting more quickly with the unstable groups in the wood to achieve a bleaching effect. Moreover, the oxygen and water produced after the decomposition of hydrogen peroxide do not harm human health or the environment, aligning with the concept of green development. This embodiment is based on the above theory, using sodium hydroxide and hydrogen peroxide to bleach wood by brushing, catalyzed by ultraviolet light. Compared to brushing high-concentration sodium hydroxide and hydrogen peroxide to bleach wood, this method uses a relatively low concentration of sodium hydroxide, and the bleached wood surface is clean, bright, and has a high whiteness, eliminating the need for water rinsing and reducing the generation of cleaning waste liquid. Compared to bleaching with low-concentration sodium hydroxide and hydrogen peroxide, the method described in this embodiment uses less bleaching solution, saving costs and avoiding environmental pollution. It also reduces bleaching time, improves production efficiency, meets the requirements of large-scale industrial production, and is therefore feasible.

[0027] The beneficial effects of this embodiment are:

[0028] This embodiment provides a novel method for bleaching wood surfaces. Depending on the specific needs, one or both sides of the wood can be treated. The method primarily uses a combination of sodium hydroxide and hydrogen peroxide at a certain concentration as a bleaching agent, bleaching the wood surface under ultraviolet light irradiation of a certain intensity. Sodium hydroxide plays two main roles: firstly, it reacts with lignin and tannins in the wood, increasing the permeability of the bleaching solution; secondly, it adjusts the pH value of hydrogen peroxide, causing it to generate more free radicals. Hydrogen peroxide mainly functions by decomposing to generate free radicals that react with chromophores and auxochromes in the wood, achieving the bleaching effect. Ultraviolet light catalyzes and more easily activates the decomposition of hydrogen peroxide, increasing the activation efficiency of free radicals. Furthermore, some unstable groups in lignin, such as conjugated double bonds and quinone groups, can absorb the photoelectron energy of ultraviolet light, becoming free radicals that react more effectively with hydrogen peroxide, further improving bleaching efficiency. Bleaching under ultraviolet light can, to some extent, reduce the use of alkaline substances such as sodium hydroxide, mitigating the damage to wood caused by these substances and reducing the loss of mechanical properties. The use of low-concentration sodium hydroxide reduces the residue of alkaline substances on the wood surface, eliminating the need for cleaning. Because some unstable groups in lignin and extracts are excited into free radicals and bleached by absorbing ultraviolet light energy during the initial bleaching process, the bleached product is less prone to discoloration due to ultraviolet radiation during subsequent use, slowing down the yellowing process.

[0029] The bleaching solution in this embodiment is applied by brushing or spraying, which reduces the generation of impregnation waste compared to soaking. Furthermore, under ultraviolet light catalysis, the efficiency of hydrogen peroxide in generating free radicals is increased, and the reaction rate between chromophores, auxochromes, and hydrogen peroxide in the wood is accelerated, reducing bleaching time and increasing whiteness. The whiteness after bleaching can reach up to 89.3, and the total color difference ΔE before and after bleaching can reach up to 27.6. The use of alkaline substances such as sodium hydroxide is reduced, decreasing the concentration of sodium hydroxide commonly used in industry (20%–35% by mass) to 5%–10%, avoiding the need for cleaning the wood surface after bleaching. Additionally, ultraviolet light has a certain heating effect, reducing the drying time of the wood compared to the absence of ultraviolet light catalysis. The wood bleaching treatment method in this embodiment has been used to bleach different tree species, producing good bleaching effects with whiteness Wh reaching over 80, while effectively reducing the loss of mechanical properties. Furthermore, after bleaching, oak, poplar, and balsa wood under UV accelerated aging for 36 hours, the ΔE value was only 12.2–18.7.

[0030] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the coating process in step one is performed by brushing or spraying. Everything else is the same as in Specific Implementation Method One.

[0031] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: in step one, when sequentially coating the wooden board with a sodium hydroxide solution of 5%–10% by mass and a hydrogen peroxide solution of 25%–35% by mass, the coating amount of the 5%–10% sodium hydroxide solution is 50 g / m². 2 ~100g / m 2 The coating amount of hydrogen peroxide solution with a mass percentage of 25%–35% is 60 g / m². 2 ~120g / m 2 Everything else is the same as in specific implementation method one or two.

[0032] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step one, when sequentially coating the wooden board with a 5%–10% sodium hydroxide solution and a 25%–35% hydrogen peroxide solution by mass, the 5%–10% sodium hydroxide solution is first applied to the wooden board and allowed to stand at room temperature for 5–30 minutes. Then, the 25%–35% hydrogen peroxide solution is applied and allowed to stand at room temperature for 0–5 minutes, resulting in the coated wooden board. Everything else is the same as in Specific Implementation Methods One to Three.

[0033] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: in step one, when coating the wooden board with a mixed solution of sodium hydroxide and hydrogen peroxide, the coating amount of the mixed solution of sodium hydroxide and hydrogen peroxide is 50 g / m². 2 ~150g / m 2 Everything else is the same as in specific implementation methods one through four.

[0034] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: in step one, when coating the wooden board with a mixed solution of sodium hydroxide and hydrogen peroxide, after coating the wooden board with the mixed solution of sodium hydroxide and hydrogen peroxide, it is allowed to stand at room temperature for 0 to 5 minutes to obtain the coated wooden board. Everything else is the same as in Specific Implementation Methods One to Five.

[0035] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the drying process in step two is specifically carried out at a drying temperature of 60℃ to 105℃ for 1 hour to 24 hours. Everything else is the same as in Specific Implementation Methods One to Six.

[0036] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the wood material used in Step One is oak, poplar, balsa wood, rosewood, cedar, rubberwood, pine, eucalyptus, walnut, elm, willow, birch, beech, cypress, paulownia, linden, hemlock, or oak. Everything else is the same as in Specific Implementation Methods One to Seven.

[0037] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that, in step two, the coated wooden board is irradiated with ultraviolet light for 0.5 to 2 hours under the conditions of an ultraviolet lamp power of 200W to 500W and an ultraviolet wavelength of 250nm to 400nm. Everything else is the same as in Specific Implementation Methods One to Eight.

[0038] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that, in step two, the coated wooden board is irradiated with ultraviolet light for 1 to 5 hours under conditions of ultraviolet lamp power of 50W to 500W and ultraviolet wavelength of 200nm to 350nm. Everything else is the same as in Specific Implementation Methods One to Nine.

[0039] The beneficial effects of the present invention are verified using the following embodiments:

[0040] Example 1:

[0041] An environmentally friendly wood bleaching treatment method catalyzed by ultraviolet light, comprising the following steps:

[0042] 1. Apply bleach solution:

[0043] First, a 10% sodium hydroxide solution was brushed onto the wooden board and left to stand at room temperature for 15 minutes. Then, a 30% hydrogen peroxide solution was brushed onto the board and left to stand at room temperature for 2 minutes to obtain the coated wooden board.

[0044] The coating amount of the 10% sodium hydroxide solution was 70 g / m². 2 The coating amount of a 30% hydrogen peroxide solution is 80 g / m². 2 ;

[0045] II. Catalytic bleaching:

[0046] Under the conditions of UV lamp power of 350W and UV wavelength of 340nm, the coated wood board was irradiated with UV lamp for 2 hours and then dried to obtain bleached oak.

[0047] The wood mentioned in step one is a clean, tangentially cut oak board with a thickness of 5mm.

[0048] The drying process described in step two specifically involves drying at a temperature of 80°C for 3 hours, followed by drying at a temperature of 103°C for 4 hours.

[0049] In Example 1, with a total bleaching time of 2 hours, the whiteness of the oak tangential plank surface increased from 57.7 to 83.9. After bleaching, the oak was treated in an accelerated UV aging apparatus for 36 hours, and the ΔE was 16.6 (the conditions of the accelerated UV aging apparatus were 0.77 W / m²). 2 (The temperature is 60℃, and the wavelength is 340nm).

[0050] Example 2:

[0051] An environmentally friendly wood bleaching treatment method catalyzed by ultraviolet light, comprising the following steps:

[0052] 1. Apply bleach solution:

[0053] First, a 5% sodium hydroxide solution was brushed onto the wooden board and left to stand at room temperature for 10 minutes. Then, a 30% hydrogen peroxide solution was brushed onto the board and left to stand at room temperature for 2 minutes to obtain the coated wooden board.

[0054] The coating amount of the 5% sodium hydroxide solution was 70 g / m². 2 The coating amount of a 30% hydrogen peroxide solution is 80 g / m². 2 ;

[0055] II. Catalytic bleaching:

[0056] Under the conditions of UV lamp power of 350W and UV wavelength of 340nm, the coated wooden board was irradiated with UV lamp for 1 hour and then dried to obtain bleached poplar wood.

[0057] The wood mentioned in step one is a clean and neat poplar veneer with a thickness of 5mm.

[0058] The drying process described in step two specifically involves drying at a temperature of 60°C for 3 hours, followed by drying at a temperature of 103°C for 3 hours.

[0059] In Example 2, with a total bleaching time of 1 hour, the whiteness of poplar tangential veneer increased from 68.7 to 84.9. After bleaching, the poplar was treated in an accelerated UV aging apparatus for 36 hours, and the ΔE was 18.7 (the conditions of the accelerated UV aging apparatus were 0.77 W / m²). 2 (The temperature is 60℃, and the wavelength is 340nm).

[0060] Comparative Experiment 1: This comparative experiment differs from Example 2 in that: in step one, a 5% sodium hydroxide solution (by mass) is first brushed onto the wooden board, and after standing at room temperature for 10 minutes, a 30% hydrogen peroxide solution (by mass) is brushed onto it, and it is left to stand at room temperature for 180 minutes to ensure that the bleach reacts completely with the wood; step two is omitted. Everything else is the same as in Example 2.

[0061] Comparative Experiment 2:

[0062] This comparative experiment differs from Example 2 in that, in step one, bleaching solution A was first brushed onto the wood board and allowed to stand at room temperature for 10 minutes. Then, bleaching solution B was brushed onto the board and allowed to stand at room temperature for 180 minutes to ensure complete reaction between the bleaching solutions and the wood. Step two was omitted, resulting in industrially bleached poplar wood. Bleaching solution A was identified as component A of a wood whitening liquid produced by Musen Wood Products Co., Ltd. in Heshan City, Guangdong Province. Testing revealed that the main active ingredient in bleaching solution A was a 21.6% sodium hydroxide solution by mass, and it also contained other additives. The coating amount of bleaching solution A was 70 g / m². 2 The bleaching solution B mentioned above is the wood whitening solution B component produced by Guangdong Heshan Musen Wood Products Co., Ltd. Testing revealed that the main effective component of bleaching solution B is a 32.1% (w / w) hydrogen peroxide solution, and it also contains other additives. The coating amount of bleaching solution B is 80 g / m². 2 Everything else is the same as in Example 2.

[0063] Example 3:

[0064] An environmentally friendly wood bleaching treatment method catalyzed by ultraviolet light, comprising the following steps:

[0065] 1. Apply bleach solution:

[0066] First, a 10% sodium hydroxide solution was brushed onto the wooden board and left to stand at room temperature for 5 minutes. Then, a 25% hydrogen peroxide solution was brushed onto the board and left to stand at room temperature for 2 minutes to obtain the coated wooden board.

[0067] The coating amount of the 10% sodium hydroxide solution is 50 g / m². 2 The coating amount of the 25% hydrogen peroxide solution is 60 g / m². 2 ;

[0068] II. Catalytic bleaching:

[0069] Under the conditions of UV lamp power of 200W and UV wavelength of 340nm, the coated wood board was irradiated with UV lamp for 0.5h and then dried to obtain bleached balsa wood.

[0070] The wood mentioned in step one is a clean and neat balsa wood tangential board with a thickness of 10mm.

[0071] The drying process described in step two specifically involves drying at a temperature of 80°C for 1 hour.

[0072] In Example 3, with a total bleaching time of 0.5 hours, the whiteness of the balsa wood tangential section increased from 74.9 to 89.3. After bleaching, the balsa wood was treated in an accelerated UV aging apparatus for 36 hours, and the ΔE was 12.2 (the conditions of the accelerated UV aging apparatus were 0.77 W / m²). 2 (The temperature is 60℃, and the wavelength is 340nm).

[0073] Example 4:

[0074] An environmentally friendly wood bleaching treatment method catalyzed by ultraviolet light, comprising the following steps:

[0075] 1. Apply bleach solution:

[0076] First, spray an 8% sodium hydroxide solution onto the wooden board and let it stand at room temperature for 10 minutes. Then, spray a 30% hydrogen peroxide solution onto the board and let it stand at room temperature for 2 minutes to obtain the coated wooden board.

[0077] The coating amount of the 8% sodium hydroxide solution was 50 g / m². 2 The coating amount of a 30% hydrogen peroxide solution is 60 g / m². 2 ;

[0078] II. Catalytic bleaching:

[0079] Under the conditions of UV lamp power of 350W and UV wavelength of 340nm, the coated wood board was irradiated with UV lamp for 1 hour and then dried to obtain bleached oak.

[0080] The wood mentioned in step one is a clean and neat oak tangential board with a thickness of 1mm.

[0081] The drying process described in step two specifically involves drying at a temperature of 60°C for 1 hour, followed by drying at a temperature of 103°C for 1 hour.

[0082] In Example 4, the whiteness of oak tangential planks increased from 56.9 to 84.4 with a total bleaching time of 1 hour. The flexural modulus of the bleached oak was tested using a universal testing machine. The sample dimensions were 100mm × 30mm (with the fiber direction as the length direction) and 1mm thick. The testing speed was 2mm / min, and the span was 40mm. The calculation results were based on GB / T9341-2008 standard, yielding a flexural modulus of 2.16 GPa. After 36 hours of treatment in an accelerated UV aging chamber, the whiteness of the bleached oak decreased to 69.5, with a ΔE of 15.7 (the accelerated UV aging chamber conditions were 0.77 W / m²). 2 (The temperature is 60℃, and the wavelength is 340nm).

[0083] Comparative Experiment 3: This comparative experiment differs from Example 4 in that: in step one, an 8% sodium hydroxide solution by mass is first sprayed onto the wooden board, and after standing at room temperature for 10 minutes, a 30% hydrogen peroxide solution by mass is sprayed onto it, and after standing at room temperature for 180 minutes, the bleaching solution is allowed to react completely with the wood; step two is omitted. Everything else is the same as in Example 4.

[0084] Comparative Experiment 4:

[0085] This comparative experiment differs from Example 4 in that, in step one, bleaching solution A is sprayed onto the wood board first, and after standing at room temperature for 10 minutes, bleaching solution B is sprayed onto it and left to stand at room temperature for 180 minutes to ensure complete reaction between the bleaching solution and the wood. Step two is omitted, resulting in industrially bleached oak. Bleaching solution A is wood whitening solution A component produced by Guangdong Heshan Musen Wood Products Co., Ltd. Testing revealed that the main effective component of bleaching solution A is a 21.6% sodium hydroxide solution by mass, and it also contains other additives. The coating amount of bleaching solution A is 50 g / m². 2 The bleaching solution B mentioned above is the wood whitening solution B component produced by Guangdong Heshan Musen Wood Products Co., Ltd. Testing revealed that the main effective component of bleaching solution B is a 32.1% (w / w) hydrogen peroxide solution, and it also contains other additives. The coating amount of bleaching solution B is 60 g / m². 2 Everything else is the same as in Example 4.

[0086] Example 5:

[0087] An environmentally friendly wood bleaching treatment method catalyzed by ultraviolet light, comprising the following steps:

[0088] 1. Apply bleach solution:

[0089] After spraying a mixed solution of sodium hydroxide and hydrogen peroxide onto a wooden board, the board was left to stand at room temperature for 2 minutes to obtain the coated wooden board.

[0090] The sodium hydroxide and hydrogen peroxide mixed solution is prepared by mixing 8% sodium hydroxide solution and 30% hydrogen peroxide solution in a mass ratio of 1:1.

[0091] Furthermore, the coating amount of the mixed solution of sodium hydroxide and hydrogen peroxide is 100 g / m². 2 ;

[0092] II. Catalytic bleaching:

[0093] Under the conditions of UV lamp power of 500W and UV wavelength of 340nm, the coated wooden board was irradiated with UV lamp for 1 hour and then dried to obtain bleached poplar wood.

[0094] The wood mentioned in step one is a clean and neat poplar tangential board with a thickness of 2mm.

[0095] The drying process described in step two specifically involves drying at a temperature of 80°C for 2 hours, followed by drying at a temperature of 103°C for 1 hour.

[0096] In Example 5, the whiteness of the poplar surface increased from 67.1 to 85.9 when the total bleaching time was 1 hour.

[0097] Figure 1 The figures show a comparison of wood before and after bleaching treatment. a) Oak before bleaching in Example 1; b) Poplar before bleaching in Example 2; c) Balsa wood before bleaching in Example 3; d) Oak after bleaching in Example 1; e) Poplar after bleaching in Example 2; and f) Balsa wood after bleaching in Example 3. As can be seen from the figures, the bleaching method has a good bleaching effect on different types and densities of tree species.

[0098] Table 1. Changes in color parameters of different tree species before and after bleaching.

[0099]

[0100] Note: L* is lightness, a* is red-green magenta index, b* is yellow-blue magenta index, Wh is whiteness, and ΔE is the total color difference before and after bleaching.

[0101] As shown in the table, this bleaching method has a good bleaching effect on different types and densities of tree species. The whiteness (Wh) of the bleached wood can reach over 80.

[0102] Figure 2The images show a comparison of poplar wood treated with different bleaching methods and then subjected to accelerated UV aging. a) Poplar wood before bleaching in Example 2; b) Poplar wood after bleaching in Example 2; c) Poplar wood after bleaching in Example 2 subjected to accelerated UV aging for 36 hours; d) Poplar wood before bleaching in Comparative Experiment 1; e) Poplar wood after bleaching in Comparative Experiment 1; f) Poplar wood after bleaching in Comparative Experiment 1 subjected to accelerated UV aging for 36 hours; g) Poplar wood before industrial bleaching in Comparative Experiment 2; h) Poplar wood after industrial bleaching in Comparative Experiment 2; i) Poplar wood after industrial bleaching in Comparative Experiment 2 subjected to accelerated UV aging for 36 hours after bleaching.

[0103] Table 2 Comparison of bleaching and aging in Example 2 with different bleaching methods

[0104]

[0105] As shown in the table, in Example 2, the whiteness of the bleached poplar reached 84.9, and the ΔE before and after bleaching was 16.2. In contrast, the whiteness of the poplar boards bleached using the industrial bleaching method in Comparative Experiment 1 (without UV photocatalysis) and Comparative Experiment 2 (using the commonly used industrial bleaching method) was only around 78, and the ΔE before and after bleaching was only around 9.0, fully demonstrating the importance of UV photocatalysis. The bleached poplar obtained from the three different treatment methods were placed in a UV accelerated aging instrument for 36 hours of accelerated aging. The ΔE of the poplar bleached using the commonly used industrial bleaching method reached 25.5, and the ΔE of the poplar bleached without UV photocatalysis even reached 28.3. In contrast, the ΔE of the bleached poplar in Example 2 was only 18.7. This indicates that UV photocatalysis can, to a certain extent, prevent the aging of bleached wood and the occurrence of "yellowing," further demonstrating the importance of UV photocatalysis in this bleaching method.

[0106] Figure 3 Images show the surface of oak veneer after bleaching using different methods. Image a shows the surface of oak veneer after bleaching in Example 4; image b shows the surface of oak veneer after industrial bleaching in Comparative Experiment 4; image c shows the surface of oak veneer after bleaching in Example 4 under a 50x ultra-depth-of-field microscope; image d shows the surface of oak veneer after industrial bleaching in Comparative Experiment 4 under a 50x ultra-depth-of-field microscope; image e shows the surface of oak veneer after bleaching in Example 4; and image f shows the surface of oak veneer after industrial bleaching in Comparative Experiment 4. As can be seen from the images, the surface of the wood treated with commonly used industrial bleaching agents has a layer of white particles (see the circled areas in images b and d, and the location indicated by the arrow in image f). This substance is caused by the use of high-concentration sodium hydroxide. This bleached oak requires water washing and other steps before use, increasing the processing steps and generating more bleach solution. In Example 4, the oak treated showed no substances other than veneer components, whether viewed from a macroscopic perspective or under a 50x ultra-depth microscope. It had a clean and tidy surface and did not cause any damage to the wood surface, saving the need for subsequent water washing steps. This proves that low-concentration sodium hydroxide does not damage the wood and also demonstrates the environmental friendliness of low-concentration sodium hydroxide.

[0107] Table 3 Comparison of flexural modulus of oak veneer after bleaching using different bleaching methods

[0108]

[0109] Table 3 shows that the flexural modulus of oak veneer treated with commonly used industrial bleaching methods decreased significantly, with the average value decreasing from 2.34 GPa in the blank sample to 1.92 GPa. In contrast, the average flexural modulus of oak veneer treated with bleach only without UV catalytic bleaching was 2.20 GPa. This comparison demonstrates that low-concentration sodium hydroxide can effectively reduce damage to the wood surface and minimize the loss of mechanical properties. In Example 4, compared to oak veneer treated with bleach only without UV catalytic bleaching, the average flexural modulus decreased by only 0.04 GPa, indicating that the UV light in this bleaching method does not damage the wood and cause a significant decrease in mechanical properties. Compared to commonly used industrial bleaching methods, the average flexural modulus of oak veneer in Example 4 increased by 0.24 GPa, demonstrating the superiority of this bleaching method in preserving the mechanical properties of the treated wood.

[0110] Table 4 Comparison of bleaching and aging in Example 4 with different bleaching methods

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[0113] As shown in the table, Example 4 exhibited the highest whiteness improvement after bleaching, with a ΔE reaching 27.6. Even after 36 hours of UV aging, the whiteness remained close to 70, significantly higher than the approximately 55 of Comparative Experiments 3 and 4. Furthermore, the ΔE of Example 4 before and after aging was only 15.7, lower than the 21.6 of Comparative Experiment 3 (bleaching without UV photocatalysis) and the 20.7 of Comparative Experiment 4 (bleaching with industrial bleaching). This demonstrates the superiority of UV photocatalytic bleaching in improving the whiteness of wood surfaces and its resistance to UV aging and yellowing.

Claims

1. An environmentally friendly wood bleaching treatment method using ultraviolet photocatalysis, characterized in that... It is done in the following steps:

1. Apply bleach solution: First, a 5%~10% sodium hydroxide solution is coated on the wooden board. After standing at room temperature for 5 to 15 minutes, a 25%~30% hydrogen peroxide solution is coated on the board and left to stand at room temperature for 2 minutes to obtain the coated wooden board. The coating amount of sodium hydroxide solution with a mass percentage of 5%~10% is 50g / m². 2 ~70g / m 2 The coating amount of hydrogen peroxide solution with a mass percentage of 25%~30% is 60g / m². 2 ~80g / m 2 ; The wood panels are made of oak, poplar, or balsa wood; II. Catalytic bleaching: Under the conditions of UV lamp power of 200W~350W and UV wavelength of 340nm, the coated wood board is irradiated with UV lamp for 0.5h~2h, and finally dried, thus completing the environmentally friendly wood bleaching treatment method of UV photocatalysis.

2. The environmentally friendly wood bleaching treatment method using ultraviolet photocatalysis according to claim 1, characterized in that... The drying process described in step two specifically involves drying at a temperature of 60℃ to 105℃ for 1 hour to 24 hours.

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