Preparation method and application of modified chitosan silica sol-based intumescent flame retardant coating

Abstract

A preparation method and application of a modified chitosan silica sol-based intumescent flame-retardant coating, the present invention relates to the technical field of intumescent flame-retardant coating preparation, and specifically to a preparation method of an organic-inorganic hybrid composite intumescent flame-retardant coating, and the application of the flame-retardant coating on the surface of a wood board material. The present invention is to solve the problem of flammability of wood. Method: The present invention uses a water bath synthesis method to hybridize and cross-link acidic silica sol and modified chitosan-acetic acid solution, and the chitosan molecules can be interspersed and distributed in the Si-O-Si gap. The formed coating has both inorganic and organic properties, and an organic-inorganic hybrid film-forming agent, i.e., a flame-retardant coating, is obtained. Compared with the existing intumescent flame-retardant coating, the modified chitosan silica sol-based composite flame-retardant coating of the present invention not only has a small amount of intumescent flame retardant added and high flame retardant efficiency, but also has good physical properties while ensuring the high flame retardant performance of the material. The flame-retardant coating prepared by the present invention is used in the field of preparing flame-retardant panels.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of intumescent flame-retardant coatings, and in particular to a method for preparing an organic-inorganic hybrid composite intumescent flame-retardant coating, and application of the flame-retardant coating on the surface of a wood board material. Background Art

[0002] As a natural, environmentally friendly and renewable polymer material, wood has the advantages of high strength-to-weight ratio and easy processing. It is widely used in building materials, artificial boards, home furnishings and other fields. Commonly used wood raw materials in these fields include pine, mahogany, poplar, elm, oak, etc. In recent years, poplar has been widely used in interior decoration, furniture and other fields because of its toughness, high mechanical strength, strong corrosion resistance, moderate hardness and strength, clear texture, smooth planing surface and good appearance. When used in these fields, the fire resistance of wood is an important factor to ensure the safe use of materials. The burning of wood produces a lot of heat, smoke and toxic gases. High temperature accelerates the spread of fire, smoke greatly reduces the visibility at the fire scene, and toxic gases can even cause suffocation and death. Therefore, in order to eliminate this potential fire hazard, it is necessary to flame retardant the wood to improve its fire safety.

[0003] At present, the methods for flame retardant treatment of wood include impregnation, surface modification, sol-gel method, etc. The most commonly used method is to add flame retardants for flame retardant treatment, and the commonly used flame retardants include phosphorus nitrogen boron flame retardants, metal compound flame retardants, resin flame retardants, nano flame retardants and microcapsule flame retardants. Applying flame retardant coating on flammable materials, positioning the flame retardant on the surface of the burning material and maintaining the volume characteristics of the material is a simpler and more effective flame retardant method.

[0004] Flame retardant coating is a functional material that can be used to decorate and protect the substrate. Flame retardant coating is generally composed of two parts: base material and flame retardant. Flame retardant coating is widely used in various industries in many countries, especially in the construction industry. Flame retardant coating has well solved the requirements of safety and fire prevention. At present, there are various types of flame retardant coatings, and requirements have been put forward for the application of flame retardant coatings in various industries. Generally speaking, flame retardant coatings should have many functions such as environmental protection, waterproof, aging resistance, good compatibility with the substrate and aesthetics while meeting the requirements of fire safety. Summary of the invention

[0005] In order to solve the problem of flammable wood, the present invention provides a preparation method and application of a modified chitosan silica sol-based intumescent flame-retardant coating.

[0006] The purpose of the present invention is to provide a modified chitosan silica sol-based composite flame retardant coating. Through a water bath synthesis method, a self-made acidic silica sol and a modified chitosan-acetic acid solution are subjected to a hybrid cross-linking reaction, and the chitosan molecules can be interspersed and distributed in the Si-O-Si gap, and the formed coating has both inorganic and organic properties, thereby obtaining a new organic-inorganic hybrid film-forming agent, which has excellent properties such as strong adhesion, high hardness, crack resistance, and water resistance. On the basis of this film-forming system, other flame retardant systems are introduced, such as ammonium polyphosphate, phytic acid, melamine polyphosphate, and non-flame retardant fillers, to form a complete expansion flame retardant system. After the coating is cured and formed, it has excellent hardness and adhesion, and can achieve a good expansion flame retardant effect.

[0007] Beneficial effects of the present invention:

[0008] (1) Chitosan is one of the most abundant natural polymers on earth. Due to its biodegradability, antibacterial properties and biocompatibility, it is widely used in biosensors, tissue engineering, gas separation membranes, edible packaging films, etc. In the field of intumescent flame retardants, chitosan is also used as a carbon source and gas source provider. However, due to the strong intramolecular and intermolecular hydrogen bonding, the high crystallinity leads to greater brittleness of the chitosan film, and the high crystallinity leads to a high melting temperature of chitosan, which is close to its decomposition temperature. Therefore, when used alone as a film-forming agent for an intumescent flame retardant system, it is difficult to form a melt foaming process. Therefore, chitosan is modified. Glycerol, polyethylene glycol borate, polyethylene glycol, etc. are used as modifiers, which can destroy the hydrogen bonding in chitosan molecules, reduce the crystallinity of chitosan, play a role in lubrication and plasticization, and can not only increase the toughness of the film, but also reduce the melting temperature of chitosan. They can all improve the film-forming properties of chitosan, and the modification effect of polyethylene glycol borate is the best. However, since these modification additives are flammable, the dosage needs to be controlled. If too much is used, the coating is flammable and the hardness is too low, the water resistance is reduced, and it is easy to be affected by moisture; if too little is used, the coating is easy to be brittle and crack. On this basis, in order to further improve the flame retardancy and water resistance of the film-forming agent, silica sol is introduced. Silica sol is a nano-SiO2 dispersion. Nano-SiO2 has small size effect, surface and interface effect, quantum size effect, etc., which leads to the unique physical and chemical properties of nanoparticles. Silica sol is dispersed on the surface of the substrate and particles. As water evaporates, the mSiO2·nH2O particles are dehydrated to form a three-dimensional network coating film with strong Si-O bond cross-linking. The introduction of silicon can not only improve the problem of easy brittle cracking during chitosan film formation, but also improve the flame retardant performance of the coating, while also taking into account the bonding strength between the coating and the material surface, as well as the strength and water resistance of the coating itself. Therefore, the present invention utilizes the excellent film-forming performance of the hybrid system of silica sol and modified chitosan. When the composite expansion flame retardant is added to the system, the film-forming agent can better coat it.

[0009] (2) The present invention utilizes the physicochemical properties and film-forming properties of modified chitosan silica sol to develop a composite flame retardant that has good compatibility with the system and has a significant flame retardant effect. Taking the composite flame retardant of pentaerythritol, ammonium polyphosphate, and melamine polyphosphate as an example, the optimal ratio of the three to produce an intumescent flame retardant effect when chitosan silica sol is used as a film-forming agent is studied, as well as how to fully and evenly mix the composite flame retardant with the chitosan silica sol film-forming agent. Compared with other intumescent flame retardant coatings, the coating has a higher intumescent flame retardant efficiency, and the preparation process is simpler and the preparation conditions are easier to control.

[0010] (3) Compared with the existing intumescent flame retardant coatings, the modified chitosan silica sol-based composite flame retardant coatings not only have a small amount of intumescent flame retardant added and high flame retardant efficiency, but also have good physical properties such as surface adhesion and hardness while ensuring the high flame retardant performance of the material. Moreover, chitosan is a biomass renewable resource, green, non-toxic and environmentally friendly, freeing itself from dependence on petroleum-based raw materials and reducing manufacturing costs.

[0011] The flame retardant coating prepared by the present invention is used in the field of preparing flame retardant panels BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A photograph of the longitudinal cross section of the expanded carbon layer of the flame retardant board obtained by using the coating of Example 1 in the simulated large board combustion test;

[0013] Figure 2 This is a photograph of the expanded carbon layer of the flame-retardant board obtained by using the coating of Example 1 in the late stage of combustion in the simulated large-board combustion test. DETAILED DESCRIPTION

[0014] Specific implementation method 1: This implementation method is a method for preparing a modified chitosan silica sol-based intumescent flame retardant coating, which is specifically carried out in the following steps:

[0015] 1. Add the silica sol precursor to a mixture of anhydrous ethanol, deionized water and silane coupling agent, stir until completely mixed, adjust the pH to 2-3, and then stir in a 50-80°C water bath until fully reacted, cool to room temperature and seal for storage to obtain acidic silica sol;

[0016] 2. Add chitosan powder to acetic acid solution and stir mechanically until completely dissolved, add modifier and stir thoroughly to obtain modified chitosan solution; add acidic silica sol prepared in step 1 to the modified chitosan solution and stir mechanically for 10-30 minutes, control the speed to 800-1500rpm, and then carry out cross-linking reaction in a water bath at 40-60℃ for 4-8h to obtain a uniform translucent solution;

[0017] 3. Add carbon source, acid source and gas source composite flame retardant to the translucent solution prepared in step 2 and stir ultrasonically to mix evenly, then add inorganic filler and stir until mixed evenly to obtain modified chitosan silica sol-based intumescent flame retardant coating to complete the preparation.

[0018] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that: the silica sol precursor in step 1 is ethyl orthosilicate or methyl orthosilicate;

[0019] The silane coupling agent in step 1 is KH560. Others are the same as those in the first embodiment.

[0020] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the molar ratio of the silica sol precursor to the silane coupling agent in step 1 is (1-2):1, the molar ratio of the silica sol precursor to anhydrous ethanol is (0.1-1):4, and the molar ratio of anhydrous ethanol to deionized water is (1-2):1. Others are the same as specific embodiment 1 or 2.

[0021] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that concentrated hydrochloric acid is used to adjust the pH in step 1. The rest is the same as specific embodiments 1 to 3.

[0022] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that: the deacetylation degree of the chitosan powder in step 2 is 80% to 90%;

[0023] The volume concentration of the acetic acid solution is 1-3%.

[0024] Step 2: The mass ratio of the chitosan powder to the acetic acid solution is 1:(20-30). The rest is the same as that of the first to fourth embodiments.

[0025] Specific embodiment 6: This embodiment is different from specific embodiments 1 to 5 in that: the modifier in step 2 is one of glycerol, polyethylene glycol borate, polyvinyl alcohol and polyethylene glycol or a mixture of several thereof; the mass ratio of the modifier to the chitosan powder is 1: (1-10). Others are the same as specific embodiments 1 to 5.

[0026] Specific embodiment 7: This embodiment is different from any one of specific embodiments 1 to 6 in that: the carbon source in step 3 is one or a mixture of several of pentaerythritol, phenolic resin, polyamide, tetramethylene glycol, cyclohexane hexol, starch, maltose and triazine compounds;

[0027] The acid source is an organic acid, an inorganic acid or a compound that generates an inorganic acid when heated to 100-250°C;

[0028] The gas source is one of melamine polyphosphate, dicyandiamide, ammonium phosphate, ammonium polyphosphate and urea or a mixture of several of them;

[0029] In terms of weight, the carbon source in the compound flame retardant is 20-30 parts, the acid source is 50-60 parts, and the gas source is 20-30 parts. The rest is the same as the first to sixth embodiments.

[0030] Specific implementation example 8: This implementation example is different from specific implementation examples 1 to 7 in that: in step 3, the ultrasonic frequency is controlled to be 20 kHz. The rest is the same as specific implementation examples 1 to 7.

[0031] Specific embodiment 9: This embodiment is different from any one of specific embodiments 1 to 8 in that: the inorganic filler in step 3 is one or a mixture of several of aluminum hydroxide, magnesium hydroxide, zirconium oxide, antimony trioxide, sodium tetraborate, hexagonal boron nitride, hydrotalcite, diatomaceous earth, montmorillonite and basalt;

[0032] The mass percentage of the inorganic filler in the modified chitosan silica sol-based intumescent flame retardant coating is 0.1%-1%. The rest is the same as any one of the first to eighth embodiments.

[0033] Specific embodiment ten: This embodiment is an application of a modified chitosan silica sol-based intumescent flame retardant coating, and the modified chitosan silica sol-based intumescent flame retardant coating is used as a coating in the field of preparing flame retardant panels;

[0034] The method for preparing the flame retardant board comprises: applying a modified chitosan silica sol-based intumescent flame retardant coating on the surface of a wood board, and curing the coating to obtain the flame retardant board;

[0035] The wood species is one or a combination of pine, redwood, poplar, birch, rubber wood, peach and elm;

[0036] The brushing standard of the modified chitosan silica sol-based intumescent flame retardant coating is 500g / m 2 dry weight;

[0037] The curing time is 12-24 hours.

[0038] The content of the present invention is not limited to the content of the above-mentioned embodiments. The combination of one or several specific embodiments can also achieve the purpose of the invention.

[0039] Embodiment 1:

[0040] This embodiment is a method for preparing a modified chitosan silica sol-based intumescent flame retardant coating:

[0041] 1. Add 62.5g of tetraethyl orthosilicate to a mixture of 47g of silane coupling agent (KH560), 92g of anhydrous ethanol and 27g of deionized water, control the speed to 800rpm and magnetically stir for 30min, then add 10 drops of concentrated hydrochloric acid with a plastic dropper, adjust the pH to 3, heat in a 50°C water bath and control the speed to 800rpm for magnetic stirring, react for 8h to obtain acidic silica sol;

[0042] 2. Add 3 g of chitosan powder with a deacetylation degree of 90% to 87 g of 3% acetic acid solution, control the speed to 1000 rpm and stir mechanically for 20 min until the chitosan powder is completely dissolved, add 1 g of polyethylene glycol borate, continue to control the speed to 1000 rpm and stir mechanically for 10 min to form a light yellow uniform and transparent viscous solution, i.e., the modified chitosan solution;

[0043] 10 g of the acidic silica sol prepared in step 1 was added to the modified chitosan solution, and the mixture was stirred mechanically at 1000 rpm for 30 min at room temperature to obtain a viscous milky white solution after uniform mixing. The mixture was then placed in a beaker, sealed with plastic wrap, and stirred magnetically at 1000 rpm for 6 h in a 50°C water bath to perform a crosslinking reaction to obtain a viscous yellow translucent solution.

[0044] 3. Add 8g of pentaerythritol, 15g of melamine polyphosphate and 6g of ammonium polyphosphate to the translucent solution prepared in step 2 in sequence, control the speed to 1200rpm for mechanical stirring for 10min, then use an ultrasonic cleaning machine for ultrasonic treatment, control the ultrasonic frequency to 20kHz, and the ultrasonic time to 30min, then add 1g of hexagonal boron nitride powder, continue ultrasonication for 10min, and then mechanically stir at a speed of 600rpm for 10min to eliminate bubbles in the system to obtain a modified chitosan silica sol-based intumescent flame retardant coating to complete the preparation.

[0045] The prepared modified chitosan silica sol-based intumescent flame-retardant coating was applied to the surface of a poplar board with a mass of 25 g and a size of 10 cm×10 cm×0.6 cm and cured for 12 hours. After curing, the board gained 5 g and a white, dense flame-retardant coating was formed on the surface of the board to obtain a flame-retardant board.

[0046] Figure 1 A photograph of the longitudinal cross section of the expanded carbon layer of the flame retardant board obtained by using the coating of Example 1 in the simulated large board combustion test;

[0047] Figure 2 This is a photograph of the expanded carbon layer of the flame-retardant board obtained by using the coating of Example 1 in the late stage of combustion in the simulated large-board combustion test;

[0048] from Figure 1It can be seen that the coating forms a uniform and dense expanded carbon layer in the early stage of combustion, and there is no cavity or collapse in the carbon layer, which shows that the ratio of carbon source, acid source and gas source in the expanded flame retardant coating is appropriate. The formed carbon layer can effectively block the transfer of heat and prevent the flame from penetrating the carbon layer and directly burning the wood surface.

[0049] from Figure 2 It can be seen that during the combustion test, the carbon layer did not peel off and was firmly bonded to the surface of the material. There was no sign of melting on the carbon layer, which proves that the expanded carbon layer has good adhesion and strength. It can also be seen that the flame continuously burns the contact position with the expanded carbon layer. As the expanded carbon layer gradually decomposes and becomes thinner, it begins to burn the surface of the wood, which proves that the thermal insulation effect of the expanded carbon layer is very good and heat cannot be transmitted downward through the carbon layer.

[0050] Embodiment 2:

[0051] This embodiment provides a method for preparing a modified chitosan silica sol-based intumescent flame retardant coating:

[0052] 1. Add 62.5g of tetraethyl orthosilicate to a mixture of 40g of silane coupling agent (KH560), 100g of anhydrous ethanol and 27g of deionized water, control the speed to 800rpm and magnetically stir for 30min, then add 15 drops of concentrated hydrochloric acid with a plastic dropper, adjust the pH to 2, heat in a 60℃ water bath and control the speed to 800rpm and magnetically stir, react for 7h to obtain acidic silica sol;

[0053] 2. Add 3 g of chitosan powder with a deacetylation degree of 90% to 82 g of 3% acetic acid solution, control the speed to 1000 rpm and stir mechanically for 30 min until the chitosan powder is completely dissolved, add 1 g of polyethylene glycol borate, continue to control the speed to 1000 rpm and stir mechanically for 10 min to form a light yellow uniform and transparent viscous solution, i.e., the modified chitosan solution;

[0054] 15 g of the acidic silica sol prepared in step 1 was added to the modified chitosan solution, and the mixture was stirred mechanically at 1000 rpm for 30 min at room temperature to obtain a viscous milky white solution after uniform mixing. The mixture was then placed in a beaker, sealed with plastic wrap, and stirred magnetically at 1000 rpm for 6 h in a 50°C water bath to perform a crosslinking reaction to obtain a viscous yellow translucent solution.

[0055] 3. Add 8g of pentaerythritol, 15g of melamine polyphosphate and 6g of ammonium polyphosphate to the translucent solution prepared in step 2 in sequence, control the speed to 1200rpm for mechanical stirring for 10min, then use an ultrasonic cleaning machine for ultrasonic treatment, control the ultrasonic frequency to 20kHz, and the ultrasonic time to 30min, then add 1g of hexagonal boron nitride powder, continue ultrasonication for 10min, and then mechanically stir at a speed of 600rpm for 10min to eliminate bubbles in the system to obtain a modified chitosan silica sol-based intumescent flame retardant coating to complete the preparation.

[0056] The prepared modified chitosan silica sol-based intumescent flame-retardant coating was applied to the surface of a poplar board with a mass of 25 g and a size of 10 cm×10 cm×0.6 cm and cured for 12 hours. After curing, the board gained 5 g and a white, dense flame-retardant coating was formed on the surface of the board to obtain a flame-retardant board.

[0057] Embodiment three:

[0058] This embodiment provides a method for preparing a modified chitosan silica sol-based intumescent flame retardant coating:

[0059] 1. Add 62.5g of tetraethyl orthosilicate to a mixture of 47g of silane coupling agent (KH560), 92g of anhydrous ethanol and 27g of deionized water, control the speed to 800rpm and magnetically stir for 30min, then add 10 drops of concentrated hydrochloric acid with a plastic dropper, adjust the pH to 3, heat in a 50℃ water bath and control the speed to 800rpm and magnetically stir, react for 8h to obtain acidic silica sol;

[0060] 2. Add 3 g of chitosan powder with a deacetylation degree of 90% to 87 g of 3% acetic acid solution, control the speed to 1000 rpm and stir mechanically for 30 min until the chitosan powder is completely dissolved, add 1 g of glycerol, continue to control the speed to 1000 rpm and stir mechanically for 10 min to form a light yellow, uniform, transparent, viscous solution, i.e., the modified chitosan solution;

[0061] 10 g of the acidic silica sol prepared in step 1 was added to the modified chitosan solution, and mechanical stirring was continued at room temperature at a speed of 1000 rpm for 30 min to obtain a viscous milky white solution after uniform mixing; the solution was then placed in a beaker, sealed with plastic wrap, and magnetically stirred at a speed of 1000 rpm for 6 h in a 50°C water bath for cross-linking reaction to obtain a viscous yellow translucent solution;

[0062] 3. Add 8g of pentaerythritol, 15g of melamine polyphosphate and 6g of ammonium polyphosphate to the translucent solution prepared in step 2 in sequence, control the speed to 1200rpm for mechanical stirring for 10min, then use an ultrasonic cleaning machine for ultrasonic treatment, control the ultrasonic frequency to 20kHz, and the ultrasonic time to 30min, then add 1g of hexagonal boron nitride powder, continue ultrasonication for 10min, and then mechanically stir at a speed of 600rpm for 10min to eliminate bubbles in the system to obtain a modified chitosan silica sol-based intumescent flame retardant coating to complete the preparation.

[0063] The prepared modified chitosan silica sol-based intumescent flame-retardant coating was applied to the surface of a poplar board with a mass of 25 g and a size of 10 cm×10 cm×0.6 cm and cured for 12 hours. After curing, the board gained 5 g and a white, dense flame-retardant coating was formed on the surface of the board to obtain a flame-retardant board.

[0064] Comparative Example 1:

[0065] (1) Add 62.5 g of tetraethyl orthosilicate to a mixed solution of 47 g of silane coupling agent (KH560), 92 g of anhydrous ethanol, and 27 g of deionized water, and stir the mixture with magnetic stirring at a speed of 800 rpm for 30 min. Then, add 10 drops of concentrated hydrochloric acid with a plastic dropper to adjust the pH value of the solution to 3. Heat the mixed solution in a 50° C. water bath and stir the mixture with magnetic stirring at a speed of 800 rpm for 8 h to obtain an acidic silica sol.

[0066] (2) 3 g of chitosan with a deacetylation degree of 90% was added to 87 g of 3% acetic acid solution, and the mixture was mechanically stirred at a speed of 1000 rpm for 20 min until the chitosan was completely dissolved. 1 g of polyethylene glycol borate was added, and the mixture was mechanically stirred at a speed of 1000 rpm for 10 min to form a light yellow, uniform, transparent, viscous solution.

[0067] (3) adding 10 g of the acidic silica sol of step (1) to the modified chitosan solution of step (2), and continuing to mechanically stir at a speed of 1000 rpm for 30 min at room temperature to obtain a viscous milky white solution after uniform mixing;

[0068] (4) placing the milky white solution in step (3) in a beaker, sealing it with plastic wrap, and stirring it with a magnetic force at a speed of 1000 rpm in a 50° C. water bath for 6 h to allow sufficient hybridization and cross-linking reaction to occur, thereby obtaining a viscous yellow translucent solution;

[0069] (5) The solution of step (4) is repeatedly applied to a poplar board with a mass of 25 g and a size of 10 cm×10 cm×0.6 cm using a silicone brush, so that the weight of the board increases by 5 g after curing, and a light yellow transparent flame retardant coating is formed on the surface of the board.

[0070] Comparative Example 2:

[0071] (1) 3 g of chitosan with a deacetylation degree of 90% was added to 97 g of 3% acetic acid solution and mechanically stirred for 20 min until the chitosan was completely dissolved to form a light yellow, uniform, transparent, viscous solution;

[0072] (2) adding 1 g of polyethylene glycol borate to the chitosan solution of step (2), continuing mechanical stirring for 10 min, and obtaining a viscous light yellow translucent solution after uniform mixing;

[0073] (3) placing the solution in step (2) in a beaker, sealing it with plastic wrap, and magnetically stirring it in a 50° C. water bath for 6 h to allow sufficient hybridization and cross-linking reaction to occur, thereby obtaining a viscous yellow translucent solution;

[0074] (4) The solution of step (3) is repeatedly applied to a poplar board with a mass of 25 g and a size of 10 cm×10 cm×0.6 cm using a silicone brush, so that the weight of the board increases by 5 g after curing, and a light yellow transparent flame retardant coating is formed on the surface of the board.

[0075] Performance Testing:

[0076] Flame retardant and smoke suppression performance: The flame retardant and smoke suppression performance of PVC wood-plastic composite materials was tested using a cone calorimeter in accordance with the international standard ISO5660-1-2002, with a radiation power of 50Kw / m 2 , the flame retardant and smoke suppression performance test results are shown in Table 1;

[0077] Wood board burning test: a butane gas spray gun was used to conduct a burning test on the coating surface of the test sample. The test end point was when the back of the wood board was burned through by the flame. The flame retardant performance test results are shown in Table 2.

[0078] Adhesion and hardness test:

[0079] Adhesion test: According to GB / T 4893.4-2013, the adhesion test of the composite coating was tested. A white grid knife (OU4000) was used to cut 5 cuts in the horizontal and vertical directions of the composite film to form 16 small squares of 1cm×1cm. After firmly sticking with 3M 100-grid test tape, it was quickly torn off to observe the degree of coating damage and determine its grade.

[0080] Hardness test: According to the national standard GB / T 6739-1996, the coating hardness is tested using a coating pencil hardness tester (QHQ-A). The sample to be tested is placed horizontally on the test bench. At the same time, the installed pencil hardness tester is gently placed on the coating surface at 45°. Then, starting from the hardest pencil, push 10 cm horizontally at a speed of 5 to 10 cm / min to observe whether there are scratches on the surface. Each level of pencil is scratched 5 times. If 2 of the 5 times can scratch the sample to be tested, a softer numbered pencil is selected until a pencil that can scratch the sample to be tested at most 1 time out of 5 times is selected. The corresponding number of this pencil is the pencil hardness of the sample to be tested. The results of adhesion and hardness tests are shown in Table 3.

[0081] Table 1 Flame retardant and smoke suppression performance test results

[0082]

[0083]

[0084] Table 2 Simulated large plate combustion test results

[0085] Pure wood board Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Coating thickness(mm) 0 1.0 1.0 1.0 1.0 1.0 Burn-through time (min) 1 60 56 59 5 2 Expanded carbon layer thickness (cm) none 3 3.6 3.8 0.2 0.2

[0086] Table 3 Adhesion and hardness test results

[0087] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Adhesion grade 0 0 1 0 0 Pencil hardness 2H 2H 2H H HB

[0088] It can be seen from the data results in the table that the modified chitosan silica sol-based composite flame retardant coating prepared by the present invention can effectively realize the flame retardant protection function of wood. By comparing Comparative Example 1 and Comparative Example 2, it can be concluded that chitosan modified with polyethylene glycol borate has a certain melt foaming effect, indicating that the modified film-forming agent is suitable for the expansion flame retardant system, and the introduction of silica sol significantly increases the flame retardant and smoke suppression properties of the coating, and increases the hardness of the film; by comparing Example 1 with Example 2, it can be concluded that with the increase of the silica sol content in the system, the physical properties of the coating after film formation do not change significantly, while the flame retardant properties decrease, indicating that too much silica sol will limit the expansion flame retardant properties of the coating; by comparing Example 1 with Example 3, it can be seen that the chitosan silica sol-based composite flame retardant coating modified with polyethylene glycol borate has better film-forming properties on the surface of the wooden board, and the flame retardant properties are also slightly improved. The coating modified with propylene glycol has reduced adhesion and slightly reduced flame retardant properties. The reason may be that the degree of hydrogen bonding between propylene glycol and chitosan is higher, combined with a large number of free hydroxyl groups, resulting in a decrease in the bonding strength between the film-forming agent and the wood surface, and the strength of the expanded carbon layer formed during combustion will also be reduced. By comparing Comparative Example 1 with the pure wood board, it can be seen that although the added polyethylene glycol borate is flammable, the entire film-forming system still has certain flame retardant properties. This is because chitosan itself is a flame retardant substance, and the silica network formed by cross-linking silica sol and chitosan can also improve the flame retardant properties of the coating, thereby reducing the negative impact of the addition of the modifier on the flame retardant effect of the coating.

[0089] By observing the three embodiments, no open flame was generated on the surface of the material during the entire process before burning through, and the ignition time was relatively long. The increase in ignition time reduced the probability of fire on the one hand, and increased the escape time when a fire occurred on the other hand. At the same time, the poplar boards using the modified chitosan silica sol-based composite flame retardant coating produced an expanded carbon layer that was dozens of times thicker than the coating itself in the combustion test, indicating that the modified chitosan silica sol-based composite flame retardant coating prepared by the present invention has very excellent flame retardant properties.

[0090] The above is an exemplary description of the embodiments of the present invention. However, the protection scope of the present invention is not limited to the above embodiments. Any modification, equivalent substitution, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a modified chitosan silica sol-based intumescent flame retardant coating, characterized in that The method is specifically carried out in the following steps:

1. Add the silica sol precursor to a mixture of anhydrous ethanol, deionized water and silane coupling agent, stir until completely mixed, adjust the pH to 2-3, and then stir in a 50-80°C water bath until fully reacted, cool to room temperature and seal for storage to obtain acidic silica sol; 2. Add chitosan powder to acetic acid solution and stir mechanically until completely dissolved, add modifier and stir thoroughly to obtain modified chitosan solution; add acidic silica sol prepared in step 1 to the modified chitosan solution and stir mechanically for 10-30 minutes, control the speed to 800-1500rpm, and then carry out cross-linking reaction in a water bath at 40-60℃ for 4-8h to obtain a uniform translucent solution; 3. Add the carbon source, acid source and gas source composite flame retardant to the translucent solution prepared in step 2 and stir ultrasonically to mix evenly, then add the inorganic filler and stir until mixed evenly to obtain a modified chitosan silica sol-based intumescent flame retardant coating, thereby completing the preparation; The molar ratio of the silica sol precursor to the silane coupling agent in step 1 is (1-2):1, the molar ratio of the silica sol precursor to anhydrous ethanol is (0.1-1):4, and the molar ratio of anhydrous ethanol to deionized water is (1-2):1; In step 2, the modifier is one of propylene glycol, polyethylene glycol borate, polyvinyl alcohol and polyethylene glycol, or a mixture of several of them; the mass ratio of the modifier to the chitosan powder is 1: (1-10).

2. The method for preparing a modified chitosan silica sol-based intumescent flame retardant coating according to claim 1, characterized in that The silica sol precursor in step 1 is ethyl orthosilicate or methyl orthosilicate; The silane coupling agent in step 1 is KH560.

3. The method for preparing a modified chitosan silica sol-based intumescent flame retardant coating according to claim 1, characterized in that Step 1: Use concentrated hydrochloric acid to adjust the pH.

4. The method for preparing a modified chitosan silica sol-based intumescent flame retardant coating according to claim 1, characterized in that The deacetylation degree of the chitosan powder in step 2 is 80% to 90%; The volume concentration of the acetic acid solution is 1-3%; In step 2, the mass ratio of the chitosan powder to the acetic acid solution is 1:(20-30).

5. The method for preparing a modified chitosan silica sol-based intumescent flame retardant coating according to claim 1, characterized in that The carbon source in step 3 is one or a mixture of pentaerythritol, phenolic resin, polyamide, tetramethylene glycol, cyclohexanehexol, starch, maltose and triazine compounds; The acid source is an organic acid, an inorganic acid or a compound that generates an inorganic acid when heated to 100-250°C; The gas source is one of melamine polyphosphate, dicyandiamide, ammonium phosphate, ammonium polyphosphate and urea or a mixture of several of them; In terms of weight percentage, the carbon source in the compound flame retardant is 20-30 parts, the acid source is 50-60 parts, and the gas source is 20-30 parts.

6. The method for preparing a modified chitosan silica sol-based intumescent flame retardant coating according to claim 1, characterized in that Step three: control the ultrasonic frequency to 20kHz.

7. The method for preparing a modified chitosan silica sol-based intumescent flame retardant coating according to claim 1, characterized in that The inorganic filler in step 3 is one or a mixture of several of aluminum hydroxide, magnesium hydroxide, zirconium oxide, antimony trioxide, hexagonal boron nitride, hydrotalcite, diatomaceous earth, montmorillonite and basalt; The mass percentage of the inorganic filler in the modified chitosan silica sol-based intumescent flame retardant coating is 0.1%-1%.

8. The use of the modified chitosan silica sol-based intumescent flame retardant coating prepared by the method for preparing a modified chitosan silica sol-based intumescent flame retardant coating as claimed in claim 1, characterized in that The modified chitosan silica sol-based intumescent flame-retardant coating is used as a coating in the field of preparing flame-retardant panels; The method for preparing the flame retardant board comprises: applying a modified chitosan silica sol-based intumescent flame retardant coating on the surface of a wood board and curing the coating to obtain the flame retardant board; The wood board is one or a combination of pine, redwood, poplar, birch, rubber wood, peach and elm; The brushing standard of the modified chitosan silica sol-based intumescent flame retardant coating is 500g / m 2 dry weight; The curing time is 12-24 hours.

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