A method for constructing a flame-retardant superhydrophobic self-cleaning coating on the wood surface

Abstract

The present invention relates to the field of coatings, and discloses a method for constructing a flame-retardant superhydrophobic self-cleaning coating on the surface of wood, which includes: 1) modifying the surface of wood with KH550 to obtain positively charged wood; 2) enabling ammonium polyphosphate to adsorb on the surface of wood through electrostatic interaction to form an APP / KH550 electrostatic composite layer; 3) preparing DOPO-SiO2; 4) preparing a coating from DOPO-SiO2, PDMS, epoxy resin and a curing agent, spraying the coating on the surface of wood, and curing to form a flame-retardant superhydrophobic self-cleaning coating. By the method of the present invention, a flame-retardant superhydrophobic self-cleaning coating can be constructed on the surface of wood. The surface of the coating has a micro-nano hydrophobic structure composed of DOPO-SiO2 in a "semi-embedded" state. Combining with the low surface energy of PDMS, the surface of the coating has a superhydrophobic self-cleaning effect; at the same time, DOPO in the outer layer of the coating and APP in the inner layer have a synergistic flame-retardant effect, which can further improve the flame retardancy of wood.

Description

Technical Field

[0001] The present invention relates to the field of coatings, and particularly to a method for constructing a flame-retardant superhydrophobic self-cleaning coating on the surface of wood. Background Art

[0002] Wood is one of the oldest materials. Due to its light weight, high strength-to-weight ratio, good texture, and thermal insulation and electrical insulation properties, it is commonly used in construction, furniture, and decoration. However, wood is flammable, which to a certain extent limits its application. Impregnating halogen flame retardants into wood pores through physical penetration is a traditional flame retardant treatment method. However, halogen flame retardants will release toxic and corrosive gases during combustion, which will cause harm to the environment and human health and cannot meet the requirements of modern industry for environmental protection and health. Currently, wood flame retardancy mainly relies on applying chemically synthesized flame retardants to wood through vacuum pressure impregnation. Its process includes vacuum pumping, pressurization, and pressure holding, which is relatively complex and has low production efficiency. Although impregnation under normal pressure has low cost, it will result in shallow penetration of the flame retardant into the wood. Therefore, developing efficient and sustainable wood flame retardant coatings is the focus of current wood flame retardant research.

[0003] In practical applications, due to the inherent hygroscopicity of wood and the resulting outflow of flame retardants, the decline of wood flame retardancy is inevitable. Most coatings are easily affected by dirt, moisture, and water, resulting in the destruction of wood flame retardancy and low tolerance to the water environment. Therefore, there is an urgent need to develop durable flame retardant coatings with waterproof and self-cleaning properties for natural wood materials. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for constructing a flame-retardant superhydrophobic self-cleaning coating on the surface of wood. Through the method of the present invention, a flame-retardant superhydrophobic self-cleaning coating can be constructed on the surface of wood. The surface of the coating has a micro-nano hydrophobic structure composed of "semi-embedded" DOPO-SiO2. Combining with the low surface energy of PDMS, the surface of the coating has a superhydrophobic self-cleaning effect. At the same time, since the outer layer of the coating also contains DOPO, which has a synergistic flame retardant effect with APP in the inner layer, the flame retardancy of wood can be further improved.

[0005] The specific technical solution of the present invention is: a method for constructing a flame-retardant superhydrophobic self-cleaning coating on the surface of wood, which specifically includes the following steps:

[0006] 1) Immerse the wood in an alkaline solution, add KH550 ethanol solution, and heat and react to obtain wood with a positively charged surface.

[0007] In step 1), KH550 hydrolyzes to form silanol bonds, which undergo hydrolysis and polycondensation reactions with the hydroxyl groups on the wood surface. The modified wood surface contains positively charged amino groups.

[0008] 2) Immerse the wood in the ammonium polyphosphate solution, heat it, and form an APP / KH550 electrostatic composite layer on the surface of the wood.

[0009] 3) Add the KH570 ethanol solution to the alkaline solution of nano-SiO2 and heat for reaction; add the DOPO ethanol solution and heat for reaction to obtain DOPO-SiO2.

[0010] In step 3), KH570 hydrolyzes to generate silanol bonds, which undergo hydrolysis polycondensation reaction with the hydroxyl groups on the surface of nano-SiO2. The surface of the modified nano-SiO2 contains double bonds and undergoes an addition reaction with the P-H bond of DOPO.

[0011] 4) Mix the dispersion liquid containing DOPO-SiO2 with the mixed liquid containing PDMS and epoxy resin, add the epoxy resin curing agent and the PDMS curing agent to obtain a coating; spray the coating on the surface of the wood obtained in 2), and form a flame-retardant superhydrophobic self-cleaning coating on the surface of the wood after curing.

[0012] In the above preparation process, the present invention first grafts γ-aminopropyltriethoxysilane (KH550) onto wood to make the wood surface positively charged, and then ammonium polyphosphate (APP) with negative charge is adsorbed on the surface of KH550 through electrostatic interaction, thereby forming an APP / KH550 electrostatic composite layer on the wood surface. This method can significantly improve the loading rate of APP on the wood surface during the impregnation process. On the other hand, γ-methacryloxypropyltrimethoxysilane (KH570) is used to modify the surface of nano-SiO2, creating conditions for subsequent grafting of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) flame retardant, and finally obtaining DOPO-SiO2 (with nano-SiO2 as the core and a layer of DOPO coated on its surface). Finally, polydimethylsiloxane (PDMS) and epoxy resin are used as film-forming substances for the coating, and the coating is prepared by mixing DOPO-SiO2, and the coating is sprayed on the wood surface with an APP / KH550 electrostatic composite layer to form a flame-retardant superhydrophobic self-cleaning coating. In the above coating, the inner layer is an APP / KH550 electrostatic composite layer, and APP can endow the wood with flame retardancy; the outer matrix is cured PDMS and epoxy resin, and DOPO-SiO2 is adhered to the surface layer of the matrix. These DOPO-SiO2 are attached to the surface layer of the outer matrix in a "semi-embedded" manner (that is, the bottom of the particles is embedded in the matrix and the top is exposed on the surface of the matrix), thereby constructing a micro-nano surface structure with hydrophobic effect (the nano-scale surface structure is formed by dispersed DOPO-SiO2, and the micro-scale surface structure is formed by partially agglomerated DOPO-SiO2). On this basis, combined with the low surface energy provided by PDMS, the outer coating has superhydrophobic self-cleaning effect (contact angle > 150°, rolling angle < 10°). At the same time, because the outer layer also contains DOPO, which has a synergistic flame-retardant effect with APP, it can further improve the flame retardancy of wood.

[0013] Preferably, in step 3), the dosage ratio of nano-SiO2, KH570 and DOPO is (2.5-3.5 g):(1-2 mL):(3.5-4.5 g).

[0014] Preferably, in step 4), the mass ratio of DOPO-SiO2, epoxy resin and PDMS in the coating is (1-2):(0.5-2):(0.5-2).

[0015] The present invention finds that the dosages of epoxy resin and PDMS relative to DOPO-SiO2 in the coating are crucial for the formation of the micro-nano surface structure. Appropriate dosages of epoxy resin and PDMS can not only firmly fix DOPO-SiO2, but also ensure that most of the DOPO-SiO2 is in a "semi-embedded" state. If the dosages of epoxy resin and PDMS are too small, DOPO-SiO2 cannot be effectively fixed; conversely, if the content is too high, the formed coating will completely cover DOPO-SiO2, resulting in the absence of a micro-nano hydrophobic structure on the coating surface.

[0016] Preferably, in step 1), the wood is basswood.

[0017] Preferably, in step 1), the wood is pretreated by surface roughening. Further preferably, the surface roughening pretreatment is to sand the wood surface with sandpaper, perform ultrasonic washing, and then dry. More preferably, the specification of the sandpaper is 350 - 450 mesh.

[0018] Preferably, in step 1), the volume ratio of KH550 to ethanol in the KH550 ethanol solution is (5 - 7):(36 - 43).

[0019] Preferably, in step 1), the temperature of the heating reaction is 35 - 45°C, and the time is 2 - 2.5 h.

[0020] Preferably, in step 2), the content of ammonium polyphosphate in the ammonium polyphosphate solution is 8 - 12 g / 100 mL.

[0021] Preferably, in step 2), the heating temperature is 45 - 55°C, and the time is 2 - 2.5 h.

[0022] Preferably, in step 3), the particle size of the nano-SiO2 is 300 - 600 nm.

[0023] Preferably, in step 3), the temperature of the first heating reaction is 35 - 40°C, and the time is 25 - 35 min; the temperature of the second heating reaction is 85 - 95°C, and the time is 3.5 - 4.5 h.

[0024] Preferably, in step 4), the solvents of the dispersion liquid and the mixed liquid are ethyl acetate.

[0025] Preferably, in step 4), the curing agent includes an epoxy resin curing agent and a PDMS curing agent.

[0026] Preferably, in step 4), the curing temperature is 80 - 90°C, and the time is 2 - 3 h.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] (1) In the present invention, KH550 is first grafted onto the wood to make the wood surface carry a positive charge, and then the negatively charged APP is adsorbed onto the KH550 surface through electrostatic interaction, thereby forming an APP / KH550 electrostatic composite layer on the wood surface. This method can significantly improve the loading rate of APP on the wood surface during the impregnation process.

[0029] (2) The surface of the coating has a micro-nano hydrophobic surface structure composed of "semi-embedded" DOPO-SiO2. Further combined with the low surface energy provided by PDMS, the surface of the coating has a superhydrophobic self-cleaning effect (contact angle > 150°, rolling angle < 10°). At the same time, since the outer layer of the coating also contains DOPO, which has a synergistic flame retardant effect with APP, it can further improve the flame retardancy of the wood. Description of the Drawings

[0030] Figure 1 It is a schematic diagram of the synthesis of DOPO-SiO2 of the present invention.

[0031] Figure 2 It is an electron microscope image of the nano-SiO2 obtained in Example 1 with a magnification of 20,000 times.

[0032] Figure 3 It is an electron microscope image of the DOPO-SiO2 obtained in Example 1 with a magnification of 20,000 times.

[0033] Figure 4 It is an electron microscope image of the log with a magnification of 500 times.

[0034] Figure 5 It is an electron microscope image of the APP-modified wood obtained in Example 1 with a magnification of 500 times.

[0035] Figure 6 It is an electron microscope image of the flame-retardant superhydrophobic self-cleaning coating on the wood surface obtained in Example 1 with a magnification of 1000 times.

[0036] Figure 7 It is an electron microscope image of the coating on the wood surface obtained in Comparative Example 1 with a magnification of 1000 times.

[0037] Figure 8 It is a contact angle picture of the wood surface treated in Example 1.

[0038] Figure 9 It is the FT-IR spectra of the nano-SiO2, K570-modified SiO2, and DOPO-SiO2 obtained in Example 1.

[0039] Figure 10 It is the combustion digital pictures of the log, Example 1, Comparative Example 3, and Comparative Example 4.

[0040] Figure 11 Digital pictures after the combustion of log (a), Example 1 (b), Comparative Example 3 (c) and Comparative Example 4 (d).

[0041] Figure 12 Self-cleaning performance diagrams of log (a-d) and Example 1 (e-h).

[0042] Figure 13 Digital pictures of Comparative Example 3 (a), Example 1 (b) immersed in water and Comparative Example 3 (c), Example 1 (d) after the completion of impregnation and combustion. Detailed implementation mode

[0043] The present invention will be further described below in conjunction with embodiments.

[0044] A method for constructing a flame-retardant superhydrophobic self-cleaning coating on the surface of wood, which specifically includes the following steps:

[0045] 1) Immerse the wood in an alkaline solution, add KH550 ethanol solution, and heat for reaction to obtain wood with a positively charged surface after the reaction.

[0046] In some specific implementation cases, the wood is basswood, with dimensions of 5 cm × 2.5 cm × 0.15 cm.

[0047] In some specific implementation cases, the wood is pretreated by surface roughening; in some more specific implementation cases, the surface roughening pretreatment is specifically to sand the wood surface with 350-450 mesh sandpaper, wash it with deionized water and ethanol for 2-10 min each under ultrasonic conditions, and dry it at 60-70 °C for standby.

[0048] In some specific implementation cases, the volume ratio of KH550 to ethanol in the KH550 ethanol solution is (5-7):(36-43).

[0049] In some specific implementation cases, the alkaline solution is composed of ammonia water (concentration 25-28%) and water with a volume ratio of (8-12):(45-55).

[0050] In some specific implementation cases, the temperature of the heating reaction is 35-45 °C, and the time of the heating reaction is 2-2.5 h.

[0051] 2) Immerse the wood in ammonium polyphosphate solution, perform heat treatment, and form an APP / KH550 electrostatic composite layer on the wood surface through electrostatic adsorption.

[0052] In some specific implementation cases, the content of ammonium polyphosphate in the ammonium polyphosphate solution is 8-12 g / 100 mL.

[0053] In some specific embodiments, the temperature of the heat treatment is 45 - 55 °C, and the time of the heat treatment is 2 - 2.5 h.

[0054] 3) Add the KH570 ethanol solution to the nano - SiO2 alkaline solution for heating reaction; add the DOPO ethanol solution and further heat - react to obtain DOPO - SiO2 (the reaction principle is as Figure 1 shown).

[0055] In some specific embodiments, the particle size of the nano - SiO2 is 300 - 600 nm.

[0056] In some specific embodiments, the nano - SiO2 alkaline solution is composed of nano - SiO2, ammonia water (concentration 25 - 28%) and water.

[0057] In some specific embodiments, the dosage ratio of nano - SiO2, water, ammonia water, KH570, DOPO and ethanol is (2.5 - 3.5 g):(45 - 55 mL):(8 - 12 mL):(1 - 2 mL):(3.5 - 4.5 g):(450 - 550 mL).

[0058] In some specific embodiments, the temperature of the first heating reaction is 35 - 40 °C, and the time of the heating reaction is 25 - 35 min; the temperature of the second heating reaction is 85 - 95 °C, and the time of the heating reaction is 3.5 - 4.5 h.

[0059] 4) Mix the dispersion liquid containing DOPO - SiO2 with the mixed liquid containing PDMS and epoxy resin, add an epoxy resin curing agent and a PDMS curing agent to obtain a coating; spray the coating on the surface of the wood with the APP / KH550 electrostatic composite layer obtained in 2), and after curing, form a flame - retardant super - hydrophobic self - cleaning coating on the wood surface.

[0060] In some specific embodiments, the solvents of the dispersion liquid and the mixed liquid are ethyl acetate.

[0061] In some specific embodiments, the dosage ratio of DOPO - SiO2, epoxy resin, PDMS and ethyl acetate in the coating is (1 - 2 g):(0.5 - 2 g):(0.5 - 2 g):(20 - 30 mL).

[0062] In some specific embodiments, the curing agent includes an epoxy resin curing agent and a PDMS curing agent.

[0063] In some specific embodiments, the temperature of the curing is 80 - 90 °C, and the time of the curing is 2 - 3 h.

[0064] In some specific implementation cases, the contact angle of the flame-retardant superhydrophobic self-cleaning coating > 150°, and the rolling angle < 10°.

[0065] Specific examples and comparative examples

[0066] Example 1

[0067] (1) Sand the surface of the wood chip (basswood, size 5 cm × 2.5 cm × 0.15 cm) with 400-mesh sandpaper, wash it with deionized water and ethanol for 5 min each under ultrasonic conditions, and dry it at 60 °C to obtain a wood chip with surface roughening pretreatment.

[0068] (2) Add 50 mL of deionized water and 10 mL of ammonia water (concentration 27%) to a beaker, stir at 35 °C at a speed of 450 rpm for 30 min to form an alkaline solution, put the wood chip with surface roughening pretreatment into the beaker, prepare a modification solution containing 6 mL of KH550 and 40 mL of ethanol, dropwise add the modification solution into the beaker, stir at 40 °C at a speed of 450 rpm for 2 h, after the reaction is completed, wash it with ethanol 3 times, and dry it at 60 °C for 10 min to obtain a KH550-modified wood chip.

[0069] (3) Add 100 mL of deionized water and 10 g of APP to a beaker, stir at 50 °C at a speed of 400 rpm until dissolved, then put the KH550-modified wood chip obtained in step (2) into the beaker, continue to stir at 50 °C at a speed of 400 rpm for 2 h, after the reaction is completed, wash it with ethanol 3 times, and dry it at 80 °C for 12 h to obtain a wood chip with an APP / KH550 electrostatic composite layer on the surface, and set it aside.

[0070] (4) Add 200 mL of ethanol, 50 mL of deionized water, and 20 mL of ammonia water (concentration 27%) to a beaker, stir evenly at a speed of 600 rpm, add 8 mL of tetraethyl orthosilicate, continue to stir at a speed of 600 rpm for 4 h, after the reaction is completed, wash it with deionized water and ethanol 3 times respectively, and dry it at 60 °C for 24 h to obtain nano-SiO2.

[0071] (5) Add the 3 g of nano-SiO₂, 50 mL of deionized water, and 10 mL of ammonia water (concentration 27%) obtained in step (4) into a three-necked flask, stir at 35 °C at a speed of 450 rpm for 30 min to form an alkaline solution. Prepare a modification solution containing 1.5 mL of KH570 and 40 mL of ethanol, drop the modification solution into the three-necked flask, and stir at 40 °C at a speed of 450 rpm for 2 h. Prepare a modification solution containing 4 g of DOPO and 100 mL of ethanol, add the modification solution into the three-necked flask, stir at 90 °C at a speed of 450 rpm for 4 h, add 50 mL of ethanol every 0.5 h during this period. After the reaction is completed, wash with deionized water and ethanol three times each, and dry at 60 °C for 24 h to obtain DOPO-SiO₂.

[0072] (6) Add the 1.5 g of DOPO-SiO₂ obtained in step (5) into 10 mL of ethyl acetate solution and ultrasonically disperse for 30 min to obtain dispersion A. Add 1 g of epoxy resin and 1 g of PDMS into 15 mL of ethyl acetate solution and stir at a speed of 400 rpm for 30 min to obtain dispersion B. Then add dispersion A into dispersion B and stir at a speed of 400 rpm for 30 min. Add 0.2 g of epoxy resin curing agent and 0.1 g of PDMS curing agent and continue to stir for 15 min. Finally, spray it onto the surface of the wood chip with an APP / KH550 electrostatic composite layer obtained in step (3), and cure at 80 °C for 2 h to obtain a wood chip with a flame-retardant superhydrophobic self-cleaning coating on its surface.

[0073] Comparative Example 1

[0074] (1) Polish the surface of the wood chip (basswood, size 5 cm × 2.5 cm × 0.15 cm) with 400-mesh sandpaper, wash with deionized water and ethanol under ultrasonic conditions for 5 min each, and dry at 60 °C to obtain a wood chip with surface roughening pretreatment.

[0075] (2) Add 50 mL of deionized water and 10 mL of ammonia water (concentration 27%) into a beaker, stir at 35 °C at a speed of 450 rpm for 30 min to form an alkaline solution. Put the wood chip with surface roughening pretreatment into the beaker. Prepare a modification solution containing 6 mL of KH550 and 40 mL of ethanol, drop the modification solution into the beaker drop by drop, and stir at 40 °C at a speed of 450 rpm for 2 h. After the reaction is completed, wash with ethanol three times and dry at 60 °C for 10 min to obtain a KH550-modified wood chip.

[0076] (3) Add 100 mL of deionized water and 10 g of APP into a beaker. Stir at a speed of 400 rpm at 50 °C until dissolved. Then put the KH550-modified wood chips obtained in step (2) into the beaker and continue to stir at a speed of 400 rpm at 50 °C for 2 h. After the reaction is completed, wash with ethanol three times and dry at 80 °C for 12 h to obtain wood chips with an APP / KH550 electrostatic composite layer on the surface, and set aside.

[0077] (4) Add 200 mL of ethanol, 50 mL of deionized water, and 20 mL of ammonia water (concentration 27%) into a beaker. Stir evenly at a speed of 600 rpm and then add 8 mL of tetraethyl orthosilicate. Continue to stir at a speed of 600 rpm for 4 h. After the reaction is completed, wash with deionized water and ethanol three times respectively and dry at 60 °C for 24 h to obtain nano-SiO₂.

[0078] (5) Add 3 g of the nano-SiO₂ obtained in step (4), 50 mL of deionized water, and 10 mL of ammonia water (concentration 27%) into a three-necked flask. Stir at a speed of 450 rpm at 35 °C for 30 min to form an alkaline solution. Prepare a modified solution containing 1.5 mL of KH570 and 40 mL of ethanol, and drop the modified solution into the three-necked flask. Stir at a speed of 450 rpm at 40 °C for 2 h. Prepare a modified solution containing 4 g of DOPO and 100 mL of ethanol, add the modified solution into the three-necked flask, and stir at a speed of 450 rpm at 90 °C for 4 h. During this period, add 50 mL of ethanol every 0.5 h. After the reaction is completed, wash with deionized water and ethanol three times respectively and dry at 60 °C for 24 h to obtain DOPO-SiO₂.

[0079] (6) Add 1.5 g of the DOPO-SiO₂ obtained in step (5) into 10 mL of ethyl acetate solution and ultrasonically disperse for 30 min to obtain dispersion A. Add 3 g of epoxy resin and 1 g of PDMS into 15 mL of ethyl acetate solution and stir at a speed of 400 rpm for 30 min to obtain dispersion B. Then add dispersion A into dispersion B and stir at a speed of 400 rpm for 30 min. Add 0.6 g of epoxy resin curing agent and 0.1 g of PDMS curing agent and continue to stir for 15 min. Finally, spray it onto the surface of the wood chips with an APP / KH550 electrostatic composite layer on the surface obtained in step (3), and cure at 80 °C for 2 h to obtain wood chips with a flame-retardant superhydrophobic self-cleaning coating on the surface.

[0080] Comparative Example 2

[0081] (1) Polish the surface of the wood chips (basswood, size 5 cm × 2.5 cm × 0.15 cm) with 400-mesh sandpaper, wash with deionized water and ethanol for 5 min each under ultrasonic conditions, and dry at 60 °C to obtain wood chips with surface roughening pretreatment.

[0082] (2) Add 50 mL of deionized water and 10 mL of ammonia water (concentration 27%) into a beaker, stir at 450 rpm for 30 min at 35 °C to form an alkaline solution. Put the pre-treated wood chips with roughened surface into the beaker. Prepare a modification solution containing 6 mL of KH550 and 40 mL of ethanol, and add the modification solution dropwise into the beaker. Stir at 450 rpm for 2 h at 40 °C. After the reaction is completed, wash with ethanol three times and dry at 60 °C for 10 min to obtain KH550-modified wood chips.

[0083] (3) Add 100 mL of deionized water and 10 g of APP into a beaker, stir at 400 rpm at 50 °C until dissolved, then put the KH550-modified wood chips obtained in step (2) into the beaker, and continue to stir at 400 rpm at 50 °C for 2 h. After the reaction is completed, wash with ethanol three times and dry at 80 °C for 12 h to obtain wood chips with an APP / KH550 electrostatic composite layer on the surface, and set aside.

[0084] (4) Add 200 mL of ethanol, 50 mL of deionized water, and 20 mL of ammonia water (concentration 27%) into a beaker, stir evenly at 600 rpm, then add 8 mL of tetraethyl orthosilicate, and continue to stir at 600 rpm for 4 h. After the reaction is completed, wash with deionized water and ethanol three times respectively, and dry at 60 °C for 24 h to obtain nano-SiO₂.

[0085] (5) Add 3 g of nano-SiO₂ obtained in step (4), 50 mL of deionized water, and 10 mL of ammonia water (concentration 27%) into a three-necked flask, stir at 450 rpm for 30 min at 35 °C to form an alkaline solution. Prepare a modification solution containing 1.5 mL of KH570 and 40 mL of ethanol, and drop the modification solution into the three-necked flask. Stir at 450 rpm for 2 h at 40 °C. Prepare a modification solution containing 4 g of DOPO and 100 mL of ethanol, add the modification solution into the three-necked flask, stir at 450 rpm for 4 h at 90 °C, and add 50 mL of ethanol every 0.5 h during this period. After the reaction is completed, wash with deionized water and ethanol three times respectively, and dry at 60 °C for 24 h to obtain DOPO-SiO₂.

[0086] (6) Add 1.5 g of DOPO-SiO₂ obtained in step (5) to 10 mL of ethyl acetate solution and ultrasonically disperse for 30 min to obtain dispersion A. Add 1 g of PDMS to 15 mL of ethyl acetate solution and stir at a speed of 400 rpm for 30 min to obtain dispersion B. Then add dispersion A to dispersion B and stir at a speed of 400 rpm for 30 min. Add 0.1 g of PDMS curing agent and continue to stir for 15 min. Finally, spray it onto the surface of the wood chip with an APP / KH550 electrostatic composite layer obtained in step (3), and cure at 80 °C for 2 h to obtain a wood chip with a flame-retardant superhydrophobic self-cleaning coating on its surface.

[0087] Comparative Example 3

[0088] (1) Sand the surface of the wood chip (basswood, size 5 cm × 2.5 cm × 0.15 cm) with 400-mesh sandpaper, wash it with deionized water and ethanol for 5 min each under ultrasonic conditions, and dry at 60 °C to obtain a wood chip with surface roughening pretreatment.

[0089] (2) Add 50 mL of deionized water and 10 mL of ammonia water (concentration 27%) to a beaker, stir at a speed of 450 rpm at 35 °C for 30 min to form an alkaline solution. Put the wood chip with surface roughening pretreatment into the beaker, prepare a modification solution containing 6 mL of KH550 and 40 mL of ethanol, add the modification solution dropwise to the beaker, stir at a speed of 450 rpm at 40 °C for 2 h. After the reaction is completed, wash it with ethanol 3 times and dry at 60 °C for 10 min to obtain a KH550-modified wood chip.

[0090] (3) Add 100 mL of deionized water and 10 g of APP to a beaker, stir at a speed of 400 rpm at 50 °C until dissolved, then put the KH550-modified wood chip obtained in step (2) into the beaker, continue to stir at a speed of 400 rpm at 50 °C for 2 h. After the reaction is completed, wash it with ethanol 3 times and dry at 80 °C for 12 h to obtain a wood chip with an APP / KH550 electrostatic composite layer on its surface.

[0091] Comparative Example 4

[0092] (1) Sand the surface of the wood chip (basswood) with 400-mesh sandpaper, wash it with deionized water and ethanol for 5 min each under ultrasonic conditions, and dry at 60 °C to obtain a wood chip with surface roughening pretreatment.

[0093] (2) Add 100 mL of deionized water and 10 g of APP into a beaker and stir at 400 rpm at 50 °C until dissolved. Then, place the wood chips pretreated with surface roughening into the beaker and stir at 400 rpm at 50 °C for 2 h. After the reaction is completed, wash with ethanol three times and dry at 80 °C for 12 h to obtain APP-modified wood chips.

[0094] Performance Testing and Characterization

[0095] Figure 2 This is an electron microscope image of the nano-SiO2 obtained in Example 1 with a magnification of 20,000 times. It can be seen that the nano-SiO2 is a regular sphere with an average particle size of 458nm. Figure 4 This is an electron microscope image of DOPO-SiO2 obtained in Example 1 at a magnification of 20,000 times. It can be seen that an irregular layer of DOPO is wrapped on the surface of the nano-SiO2.

[0096] Figure 4 This is an electron microscope picture of the log at a magnification of 500 times. The surface of the log is clearly fibrous and relatively smooth. Figure 5 This is an electron microscope image of the APP-modified wood obtained in Example 1 at a magnification of 500 times. Compared with the original wood, the surface of the APP-modified wood becomes slightly rough, which is mainly due to the adhesion of APP and APP / KH550 to the wood surface. Figure 6 This is an electron microscope image of the flame-retardant super-hydrophobic self-cleaning coating on the wood surface obtained in Example 1 at a magnification of 1000 times. Due to the coverage of DOPO-SiO2 / PDMS / EP, the roughness of the wood surface is significantly increased, and micron- and nano-scale protrusions appear. Figure 7 The electron microscope image of the wood surface coating obtained in Comparative Example 1 at a magnification of 1000 times is shown. The difference between Comparative Example 1 and Example 1 is that 3g of epoxy resin is used. It is found that the addition of excessive epoxy resin wraps the DOPO-SiO2 nanoparticles, and the coating surface is blocky, and the super-hydrophobic effect is not achieved. The difference between Comparative Example 2 and Example 1 is that epoxy resin is not introduced. It is found that although Comparative Example 2 achieves a super-hydrophobic effect, the coating will fall off during the combustion process when using a single PDMS as a bonding layer. Figure 8 The contact angle picture of Example 1 shows that the contact angle of Example 1 is 151.2° and the rolling angle is 5.6°, achieving a super hydrophobic effect. The above results show that the content of epoxy resin in the coating affects the hydrophobicity of the coating and the adhesion of the coating on the substrate. Therefore, as described above, the performance of Example 1 is the best.

[0097] Figure 9 The FT-IR spectra of nano-SiO2, K570-modified SiO2, and DOPO-SiO2 obtained in Example 1. In the FT-IR spectrum of SiO2, the absorption peak is at 1103 cm-1 This is due to the stretching vibration of Si-O-Si, and the absorption peak is at 804 cm -1 and 470 cm -1 This is due to the symmetric stretching vibration and bending vibration of Si-O, at 940 cm -1 The absorption at this position is the bending vibration of Si-OH. In the FT-IR spectrum of K570-modified SiO2, the absorption peaks at 2958 and 2893 cm -1 are the asymmetric stretching vibration peaks of -CH3, and at 3436 cm -1 is the stretching vibration peak of -OH, and at 1721 cm -1 is the vibration peak of -C=O of the silane coupling agent, at 1637 cm -1 is the characteristic peak of C=C. In the FT-IR spectrum of DOPO-SiO2, the disappearance of the characteristic peak of C=C can be explained by the reaction of the P-H bond of DOPO with C=C.

[0098] Figure 10 Digital combustion pictures of the log, Example 1, Comparative Example 3, and Comparative Example 4 are shown. After placing the log on the flame of an alcohol lamp for 10 s and then removing it, the log continued to burn violently until it was completely burned out. After placing the APP / KH550-impregnated wood in Comparative Example 3 and the flame-retardant superhydrophobic self-cleaning coating wood in Example 1 on the flame of an alcohol lamp for 10 s and then removing them, neither of them burned. After placing both of them on the flame again for 10 s and then removing them, flames appeared on the wood chips and the flame spread speed was very slow. The flame on the APP / KH550-impregnated wood self-extinguished 6 s after removal, and the flame on the flame-retardant superhydrophobic self-cleaning coating wood self-extinguished 7 s after removal. The wood directly impregnated with APP in Comparative Example 4 continued to burn for 18 s and then self-extinguished after being removed from the flame of the alcohol lamp for 10 s. After placing it on the flame again for 10 s and then removing it, the wood completely burned out after burning for 20 s.

[0099] Figure 11 Digital pictures after combustion of the log (a), Example 1 (b), Comparative Example 3 (c), and Comparative Example 4 (d) are shown. Figure 11 (a) After the log burned, broken ashes were formed. Figure 11 (b) and Figure 11 (c) show that the degree of damage after combustion of the APP / KH550-impregnated wood is deeper than that of the flame-retardant superhydrophobic self-cleaning coating wood after combustion. Figure 11(d) No ash dropped after the wood directly impregnated with APP was burned. The above results indicate that soaking with APP has a flame retardant effect on wood. The electrostatic action of KH550 increases the loading amount of APP on the wood surface. Therefore, the flame retardant effect of the wood impregnated with APP / KH550 is much better than that of the wood directly impregnated with APP, and the addition of DOPO-SiO2 has a synergistic effect on the flame retardancy of wood. The above results show that the flame retardant effect of Example 1 is the best.

[0100] Figure 12 Self-cleaning performance diagrams of log (a-d) and Example 1 (e-h). Figure 12 (a-d) By dripping water droplets, the soil on the log was not completely removed, and the wood surface was wetted by the water droplets. The liquid containing soil adhered to the surface, making the surface dirtier. Figure 12 (d-f) By dripping water droplets, the soil on the wood coating surface was carried away, indicating that the coating has extremely low adhesion to water and excellent self-cleaning performance.

[0101] Figure 13 Digital pictures of Comparative Example 3 (a) and Example 1 (b) soaked in water, and digital pictures of Comparative Example 3 (c) and Example 1 (d) after impregnation and burning. Figure 13 (a) shows that the clear wood texture can still be seen when the wood impregnated with APP / KH550 is soaked in water. Figure 13 (b) shows a bright silver mirror surface appears on the coating surface because the air trapped by the micro-nano structure will produce total internal reflection of light. After the wood impregnated with APP / KH550 and Example 1 were soaked in water for 2 h, they were respectively placed on an alcohol lamp and burned for 10 s and then removed. Figure 13 (c) shows that the wood impregnated with APP / KH550 continued to burn violently until it was completely burned out. And Figure 13 (d) shows that the wood with the flame retardant superhydrophobic self-cleaning coating in Example 1 showed self-extinguishing phenomenon after 10 s of burning and still had excellent flame retardant performance. The above results indicate that the flame retardant superhydrophobic self-cleaning coating in Example 1 effectively reduces the loss of wood flame retardant.

[0102] The raw materials and equipment used in the present invention are all common raw materials and equipment in the field without special instructions; the methods used in the present invention are all conventional methods in the field without special instructions.

[0103] The above are only the preferred embodiments of the present invention and do not limit the present invention in any way. Any simple modifications, changes and equivalent transformations made to the above embodiments according to the technical essence of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims

1. A method for constructing a flame-retardant superhydrophobic self-cleaning coating on the wood surface, characterized in that Including: 1) Immerse the wood in an alkaline solution, add KH550 ethanol solution, and heat for reaction to obtain wood with a positively charged surface; 2) Immerse the wood in ammonium polyphosphate solution, heat to form an APP / KH550 electrostatic composite layer on the wood surface; 3) Add KH570 ethanol solution to the nano-SiO2 alkaline solution and heat for reaction; add DOPO ethanol solution and heat for reaction to obtain DOPO-SiO2; the dosage ratio of nano-SiO2, KH570 and DOPO is (2.5 - 3.5 g):(1 - 2 mL):(3.5 - 4.5 g); 4) Mix the dispersion containing DOPO-SiO2 with the mixture containing PDMS and epoxy resin, and add a curing agent; spray the obtained coating on the wood surface and cure to form a flame-retardant superhydrophobic self-cleaning coating; the mass ratio of DOPO-SiO2, epoxy resin and PDMS is (1 - 2):(0.5 - 2):(0.5 - 2).

2. The method according to claim 1, characterized in that: In step 1), the wood is basswood; the wood is pretreated by surface roughening.

3. The method according to claim 1, wherein: In step 1), the volume ratio of KH550 to ethanol in the KH550 ethanol solution is (5 - 7):(36 - 43).

4. The method according to claim 1, characterized in that: In step 1), the temperature of the heating reaction is 35 - 45 °C and the time is 2 - 2.5 h.

5. The method according to claim 1, wherein: In step 2), the content of ammonium polyphosphate in the ammonium polyphosphate solution is 8 - 12 g / 100 mL.

6. The method according to claim 1, characterized in that: In step 2), the heating temperature is 45 - 55 °C and the time is 2 - 2.5 h.

7. The method according to claim 1, characterized in that: In step 3), the particle size of the nano-SiO2 is 300 - 600 nm; the temperature of the first heating reaction is 35 - 40 °C and the time is 25 - 35 min; the temperature of the second heating reaction is 85 - 95 °C and the time is 3.5 - 4.5 h.

8. The method according to claim 1, characterized in that: In step 4), the solvents of the dispersion and the mixture are ethyl acetate.

9. The method according to claim 1, characterized in that: In step 4), the curing agent includes an epoxy resin curing agent and a PDMS curing agent.

10. The method according to claim 1, characterized in that: In step 4), the contact angle of the flame-retardant superhydrophobic self-cleaning coating > 150°, and the rolling angle < 10°; the curing temperature is 80 - 90 °C and the time is 2 - 3 h.

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