Flame-retardant medium density fiberboard and method of making same

Abstract

The application discloses a kind of flame-retardant medium density fiberboard and preparation method thereof, by weight parts, including the following raw materials: modified wood fiber 100-120 parts, modified flame retardant 30-40 parts, adhesive 50-60 parts, filler 5-10 parts, sodium silicate 5-9 parts, curing agent 15-20 parts.The flame-retardant medium density fiberboard provided by the application, by oxidation activation treatment to pretreated wood fiber, then graft modification is carried out, improve the flame retardancy of wood fiber, while adding modified flame retardant, and supplemented by filler, sodium silicate, epoxy resin and curing agent, so that the medium density fiberboard obtained has good mechanical properties and flame retardant performance, has good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of engineered wood products technology, specifically relating to a flame-retardant medium-density fiberboard and its preparation method. Background Technology

[0002] Fiberboard is a type of engineered wood product, broadly categorized by density into hardboard, medium-density fiberboard (MDF), and softboard (low-density fiberboard). Fiberboard is made from wood fibers or other plant fibers. Wood, branches, and other materials are soaked in water, crushed, and pressed together, then adhesives are applied. The process involves fiber separation, shaping, and hot pressing. Medium-density fiberboard (MDF) typically has a density between 500-880 kg / m³. 3 The thickness is usually 5-30mm. Its main advantages are that it is relatively inexpensive compared to logs, easy to process, has uniform material, good physical properties, and can be waterproof and moisture-proof after adding paraffin and other substances.

[0003] However, medium-density fiberboard (MDF) is mainly made of wood fiber or straw fiber, which are flammable materials. Its extensive use indoors increases the risk of fire. Furthermore, this natural fiber material is untreated and has poor water resistance, which leads to poor dimensional stability and weather resistance of the fiberboard. It also causes a series of problems such as low mechanical properties of the fiberboard.

[0004] Currently, flame-retardant treatment of fiberboard mainly involves adding chemical flame retardants. However, this method significantly increases the cost of fiberboard, and the board's durability is poor. Over time, the flame retardant is prone to leach out, losing its flame-retardant effect. Furthermore, excessive addition of flame retardants can significantly affect the various physical and mechanical properties of the fiberboard. These factors greatly limit the widespread application of traditional flame-retardant fiberboard, especially in furniture and interior decoration materials.

[0005] Chinese Patent Application No. 201710864209.6 discloses a flame-retardant fiberboard and its manufacturing method. The flame-retardant fiberboard comprises a wood core layer, a flame-retardant coating layer sprayed onto the wood core layer, and a flame-retardant material layer disposed between the wood core layers. The flame-retardant coating layer is made of a resin, vinylidene chloride copolymer emulsion, ammonium polyphosphate, organohalophosphate, titanium dioxide, antimony dioxide, and SiO2. The flame-retardant material layer is made of tricresyl phosphate, β-trichloroethylene phosphate, magnesium hydroxide, aluminum hydroxide, decabromobiphenyl acid, tetrabromobisphenol A, chlorinated paraffin, and SiO2. The flame-retardant fiberboard of this invention has the advantages of being thicker, less prone to breakage, having better heat insulation, and better flame retardant properties. This patent increases the thickness of the flame-retardant fiberboard and improves its heat insulation by setting a double-layer wood board structure. It also enhances the flame-retardant ability of the fiberboard by adding a flame-retardant material layer between the wood board layers. However, the multi-layer structure may result in low bonding strength between the flame-retardant layer and the wood board layer, poor mechanical properties of the fiberboard layer, and easy delamination. Furthermore, the flame-retardant effect of the fiberboard is not disclosed in the patent specification. Chinese patent application number 202311430274.X discloses a high-density flame-retardant fiberboard and its preparation method, comprising a high-density flame-retardant fiberboard. The raw materials for preparing the high-density flame-retardant fiberboard, by mass percentage, consist of 40% wood fiber, 20% softwood pulp, 30% flame retardant, and 5% mildew inhibitor. In this invention, flame retardant is added during the production of wood fiberboard, thus initially giving the wood fiberboard good flame-retardant properties. Furthermore, flame-retardant coating is sprayed onto both sides of the wood fiberboard using a spraying machine to finally produce a flame-retardant limiting plate, thereby further enhancing the flame-retardant performance of the fiberboard. However, the flame retardant content in this patent is as high as 30% or more, which may lead to a deterioration in the mechanical properties of the fiberboard.

[0006] Therefore, there is an urgent need in this field to develop a medium-density fiberboard with good flame retardant properties and excellent mechanical properties. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a flame-retardant medium-density fiberboard and its preparation method. This medium-density fiberboard has good flame-retardant properties, as well as good dimensional stability and high strength, and has good application prospects.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A flame-retardant medium-density fiberboard, comprising the following raw materials by weight:

[0010] 100-120 parts modified wood fiber, 30-40 parts modified flame retardant, 50-60 parts adhesive, 5-10 parts filler, 5-9 parts sodium silicate, and 15-20 parts curing agent.

[0011] Preferably, a flame-retardant medium-density fiberboard comprises, by weight, the following raw materials:

[0012] 110-120 parts modified wood fiber, 35-40 parts modified flame retardant, 55-60 parts adhesive, 8-10 parts filler, 7-9 parts sodium silicate, and 17-20 parts curing agent.

[0013] Preferably, the method for preparing the modified wood fiber includes the following steps:

[0014] S1. Pretreatment and activation of wood fiber: Add the pretreated wood fiber to deionized water, then add hydrogen peroxide solution and potassium permanganate to carry out the activation reaction. After the reaction is completed, filter, wash and dry to obtain activated wood fiber.

[0015] S2. Modification of wood fiber: The activated wood fiber from step S1 is added to an aqueous ethanol solution, followed by the addition of γ-aminopropyltriethoxysilane. The mixture is stirred and reacted. After the reaction is complete, the mixture is filtered, washed, and dried to obtain a solid product. The solid product is then added to N,N-dimethylformamide, followed by the addition of 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid and concentrated sulfuric acid. The mixture is subjected to a constant temperature reaction. After the reaction is complete, the mixture is filtered, washed, and dried to obtain modified wood fiber.

[0016] Preferably, the pretreated fiber in step S1 specifically includes the following steps: 70-80 parts of wood fiber and 20-30 parts of straw powder are mixed evenly, and then added to 800-1000 parts of sodium hydroxide solution with a mass concentration of 7-10%, and impregnated at 40-50℃ for 0.5-1h. After impregnation, the mixture is filtered, washed, and dried to obtain pretreated wood fiber.

[0017] Preferably, the straw powder is one or more of corn straw, sorghum straw, wheat straw, and rice straw.

[0018] In this invention, the pretreatment can partially dissolve the cellulose on the surface of wood fibers and straw powder, while removing impurities and non-fibrous substances from the surface of wood fibers, thereby changing the surface properties of the fibers. Furthermore, the alkaline solution can penetrate into the interior of the fibers, partially dissolving some of the cellulose in the wood fibers, thus altering the internal pore structure of the fibers and facilitating subsequent reactions.

[0019] Preferably, in step S1, the mass fraction of hydrogen peroxide is 15-20%, and the mass ratio of the pretreated fiber, deionized water, hydrogen peroxide solution, and potassium permanganate is 100:800-1000:100-200:5-8; the activation reaction temperature is 80-90℃, and the time is 1-2 hours.

[0020] More preferably, in step S1, the mass fraction of hydrogen peroxide is 15-20%, and the mass ratio of the pretreated fiber, deionized water, hydrogen peroxide solution, and potassium permanganate is 100:800-900:150-200:6-8; the activation reaction temperature is 85-90℃, and the time is 1-1.5h.

[0021] In this invention, the oxidation activation reaction can cause oxidation on the surface of wood fibers, increasing the reaction sites on the surface of wood fibers and providing better conditions for subsequent grafting reactions.

[0022] Preferably, in step S2, the volume ratio of ethanol to water in the aqueous ethanol solution is 7-8:2-3, the mass ratio of the activated wood fiber to γ-aminopropyltriethoxysilane is 100:5-10, the temperature of the stirring reaction is 50-60℃, and the time is 2-4h; the mass ratio of the solid product, 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid, and concentrated sulfuric acid is 100:10-15:5-10, and the temperature of the isothermal reaction is 90-100℃, and the time is 4-6h.

[0023] In this invention, the added γ-aminopropyltriethoxysilane is a silicon-containing compound that can form a silicon oxide layer at high temperatures. This silicon oxide layer can form a sealed protective layer, reducing the conduction of oxygen and heat, thereby slowing down the combustion rate.

[0024] In this invention, the added 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid has a carboxyl group that can react with an amino group, introducing nitrogen and phosphorus elements into the surface of the wood fiber. The fiberboard decomposes at high temperature to produce nitrogen and phosphorus compounds, forming a protective layer and slowing down the burning rate.

[0025] Preferably, the modified flame retardant is prepared by the following method:

[0026] Diatomaceous earth was added to hydrochloric acid solution and impregnated at room temperature for 4-6 hours. After impregnation, the mixture was filtered, washed, dried, and calcined to obtain pretreated diatomaceous earth. The pretreated diatomaceous earth was then added to an aqueous ethanol solution, followed by the addition of vinyltriethoxysilane, and the mixture was subjected to a constant-temperature reaction. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a solid product. The solid product was then added to dimethyl sulfoxide, followed by the addition of triallyl phosphate and bis(phthaloyl)peroxide, and the mixture was heated to react. After the reaction was completed, the mixture was filtered, washed, and dried to obtain the modified flame retardant.

[0027] In this invention, by modifying diatomaceous earth, the dispersibility of diatomaceous earth in adhesives can be improved. At the same time, the introduced phosphorus element can also play a synergistic role with diatomaceous earth, thereby improving the flame retardant effect of the modified flame retardant.

[0028] Preferably, the hydrochloric acid solution has a mass concentration of 5-10%, the calcination temperature is 300-350℃, and the time is 1-2 hours; the volume ratio of ethanol to water in the ethanol-water solution is 3:1-2, the mass ratio of the pretreated diatomaceous earth to vinyltriethoxysilane is 50:5-10, the isothermal reaction temperature is 60-70℃, and the time is 2-4 hours; the mass ratio of the solid product, triallyl phosphate, and bis(phthaloyl)peroxide is 50:4-8:0.3-0.5, and the heating reaction temperature is 90-100℃, and the time is 3-5 hours.

[0029] Preferably, the adhesive is an epoxy resin adhesive, the filler is one or more of light calcium carbonate, talc, perlite, and barite, and the curing agent is one or more of ethylenediamine, triethylenetetramine, maleic anhydride, and acetic anhydride.

[0030] This invention also protects a method for preparing flame-retardant medium-density fiberboard as described above, comprising the following steps:

[0031] Weigh the raw materials according to the formula, mix the modified flame retardant, adhesive, filler and sodium silicate evenly, then add the modified wood fiber and curing agent, and continue to mix evenly to obtain a premix. Then add the premix into the mold, lay it up and pre-press it at 60-70℃ and 3-5MPa for 40-60s, then hot press it at 140-150℃ and 5-7MPa for 3-5min to form it. After forming, trim the edges and polish it to obtain flame-retardant medium density fiberboard.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The flame-retardant medium-density fiberboard provided by this invention first involves alkali treatment of wood fibers and straw powder to break hydrogen bonds within the fibers, degrade lignin, and increase the specific surface area of ​​the fibers. This benefits subsequent reactions and improves the bonding strength between the wood fibers and the adhesive, thereby improving the mechanical properties and durability of the fiberboard. Subsequently, the wood fibers are oxidized and activated with hydrogen peroxide and potassium permanganate, causing the hydroxyl and carbonyl functional groups on the surface of the wood fibers to undergo oxidation reactions, forming more active functional groups and oxides, thereby increasing the specific surface area and reactivity of the wood fibers. At the same time, the gas generated during the oxidation and activation process can change the chemical properties of the wood fiber surface, making it easier to roughen the surface, producing a micro-uneven structure, increasing roughness, and further improving the bonding force between the adhesive and the wood fibers. Then, the activated wood fibers are further oxidized with hydrogen peroxide and potassium permanganate. γ-aminopropyltriethoxysilane is reacted to obtain aminated wood fibers. This process introduces silicon into the surface of the wood fibers and facilitates subsequent reactions. The aminated wood fibers are then reacted with 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid to introduce nitrogen and phosphorus into the surface of the wood fibers. This causes the wood fibers to decompose at high temperatures, releasing phosphorus and nitrogen compounds to form a protective layer that prevents flame spread. Furthermore, the nitrogen and phosphorus elements in 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid can synergistically enhance the flame retardant properties of the wood fibers with silicon, significantly improving their flame retardant performance. The introduced fluorine also improves the water resistance of the wood fibers. This invention introduces silicon, nitrogen, and phosphorus into the surface of wood fibers through chemical grafting, which significantly improves the flame retardant properties of medium-density fiberboard.

[0034] (2) The flame-retardant medium-density fiberboard provided by this invention incorporates diatomaceous earth as the modified flame retardant. Diatomaceous earth possesses unique diatom shell structure, strong adsorption, large specific surface area, high porosity, and high temperature resistance, among other excellent properties. During combustion, it maintains skeletal stability, protecting the char layer. Furthermore, diatomaceous earth contains a large amount of silicon, which is itself an excellent non-halogenated flame-retardant element with excellent flame-retardant effects. First, the diatomaceous earth is acid-treated to unclog its internal pores, thereby increasing its specific surface area and adsorption capacity, which is beneficial for subsequent reactions and also provides flame-retardant and smoke-suppressing effects. Then… Pretreated diatomaceous earth is modified with vinyltriethoxysilane to introduce double bond groups on its surface, which also improves its dispersibility in adhesives. Then, triallyl phosphate is reacted with it to introduce it onto the surface of the diatomaceous earth. As a phosphorus-containing surfactant, triallyl phosphate can increase the surface energy of diatomaceous earth and improve its adhesion to epoxy resin, thus avoiding the decrease in the mechanical properties of fiberboard due to the addition of flame retardants. At the same time, triallyl phosphate and diatomaceous earth can have a synergistic effect, thereby improving the flame retardancy of medium-density fiberboard.

[0035] (3) The flame-retardant medium-density fiberboard provided by the present invention improves the flame retardancy of the wood fibers by oxidizing and activating the pretreated wood fibers and then grafting them. At the same time, a modified flame retardant is added, along with fillers, sodium silicate, epoxy resin and curing agent, so that the medium-density fiberboard has good mechanical properties and flame retardant properties and has good application prospects. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] The diatomaceous earth was purchased from Chengdu Yuang Chemical Co., Ltd., with a mesh size of 325; the epoxy resin was purchased from Wanqing Chemical Technology Co., Ltd., with the grade E-51.

[0038] Example 1

[0039] A method for preparing flame-retardant medium-density fiberboard includes the following steps:

[0040] Weigh the raw materials according to the formula, mix 35g of modified flame retardant, 55g of epoxy resin, 8g of light calcium carbonate and 7g of sodium silicate evenly, then add 110g of modified wood fiber and 20g of ethylenediamine, and continue to mix evenly to obtain a premix. Then add the premix into the mold, lay it up and pre-press it at 65℃ and 4MPa for 50s, then hot press it at 145℃ and 6MPa for 4min to form it. After forming, trim the edges and polish it to obtain flame-retardant medium density fiberboard.

[0041] The preparation method of the modified flame retardant is as follows:

[0042] 50g of diatomaceous earth was added to 300g of a 10% hydrochloric acid solution and impregnated at room temperature for 5 hours. After impregnation, the mixture was filtered, washed, and dried, and then calcined at 320℃ for 1.5 hours to obtain pretreated diatomaceous earth. 50g of the pretreated diatomaceous earth was added to 800g of an aqueous ethanol solution (ethanol to water volume ratio of 3:1), followed by the addition of 8g of vinyltriethoxysilane. The mixture was reacted at 65℃ for 3 hours. After the reaction, the mixture was filtered, washed, and dried to obtain a solid product. Then, 50g of the solid product was added to 600mL of dimethyl sulfoxide, followed by the addition of 6g of triallyl phosphate and 0.4g of bis(phthaloyl)peroxide. The mixture was reacted at 95℃ for 4 hours. After the reaction, the mixture was filtered, washed, and dried to obtain the modified flame retardant.

[0043] The method for preparing the modified wood fiber includes the following steps:

[0044] S1. Pretreatment and activation of wood fiber: Mix 75g of wood fiber and 25g of corn stalk powder evenly, then add 900g of 8% sodium hydroxide solution and soak at 45℃ for 1h. After soaking, filter, wash and dry to obtain pretreated wood fiber. Add 100g of pretreated wood fiber to 900g of deionized water, then add 150g of 20% hydrogen peroxide solution and 7g of potassium permanganate, and activate at 85℃ for 1.5h. After the reaction is completed, filter, wash and dry to obtain activated wood fiber.

[0045] S2. Modification of wood fiber: 100g of activated wood fiber from step S1 was added to 1300g of ethanol aqueous solution (ethanol to water volume ratio of 7:3), followed by 8g of γ-aminopropyltriethoxysilane. The mixture was stirred at 55℃ for 3h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a solid product. Then, 100g of the solid product was added to 1000g of N,N-dimethylformamide, followed by 13g of 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid and 8g of concentrated sulfuric acid. The mixture was kept at 95℃ for 5h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified wood fiber.

[0046] Example 2

[0047] A method for preparing flame-retardant medium-density fiberboard includes the following steps:

[0048] Weigh the raw materials according to the formula, mix 35g of modified flame retardant, 55g of epoxy resin, 7g of talc powder and 7g of sodium silicate evenly, then add 110g of modified wood fiber and 15g of triethylenetetramine, and continue to mix evenly to obtain a premix. Then add the premix into the mold, lay it out and pre-press it at 65℃ and 4MPa for 50s, then hot-press it at 15℃ and 6MPa for 4min to form it. After forming, trim the edges and polish it to obtain flame-retardant medium density fiberboard.

[0049] The preparation method of the modified flame retardant is as follows:

[0050] 50g of diatomaceous earth was added to 300g of a 5% hydrochloric acid solution and impregnated at room temperature for 5 hours. After impregnation, the mixture was filtered, washed, and dried, and then calcined at 330℃ for 1.5 hours to obtain pretreated diatomaceous earth. 50g of the pretreated diatomaceous earth was added to 800g of an aqueous ethanol solution (ethanol to water volume ratio of 3:2), followed by the addition of 8g of vinyltriethoxysilane. The mixture was reacted at 65℃ for 3 hours. After the reaction, the mixture was filtered, washed, and dried to obtain a solid product. Then, 50g of the solid product was added to 600mL of dimethyl sulfoxide, followed by the addition of 6g of triallyl phosphate and 0.4g of bis(phthaloyl)peroxide. The mixture was reacted at 95℃ for 3-5 hours. After the reaction, the mixture was filtered, washed, and dried to obtain the modified flame retardant.

[0051] The method for preparing the modified wood fiber includes the following steps:

[0052] S1. Pretreatment and activation of wood fiber: 75g of wood fiber and 25g of sorghum straw powder were mixed evenly, and then added to 900g of 9% sodium hydroxide solution. The mixture was soaked at 45℃ for 0.5h. After soaking, the mixture was filtered, washed, and dried to obtain pretreated wood fiber. 100g of pretreated wood fiber was added to 900g of deionized water, followed by 150g of 15% hydrogen peroxide solution and 7g of potassium permanganate. The mixture was activated at 85℃ for 1.5h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain activated wood fiber.

[0053] S2. Modification of wood fiber: 100g of activated wood fiber from step S1 was added to 1300g of ethanol aqueous solution (ethanol to water volume ratio of 8:2), followed by 8g of γ-aminopropyltriethoxysilane. The mixture was stirred at 55℃ for 3h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a solid product. Then, 100g of the solid product was added to 1000g of N,N-dimethylformamide, followed by 13g of 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid and 8g of concentrated sulfuric acid. The mixture was kept at 95℃ for 5h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified wood fiber.

[0054] Example 3

[0055] A method for preparing flame-retardant medium-density fiberboard includes the following steps:

[0056] Weigh the raw materials according to the formula, mix 30g of modified flame retardant, 50g of epoxy resin, 5g of perlite and 5g of sodium silicate evenly, then add 100g of modified wood fiber and 18g of maleic anhydride, and continue to mix evenly to obtain a premix. Then add the premix into the mold, lay it up and pre-press it at 60℃ and 3MPa for 60s, then hot press it at 140℃ and 5MPa for 5min to form it. After forming, trim the edges and polish it to obtain flame-retardant medium density fiberboard.

[0057] The preparation method of the modified flame retardant is as follows:

[0058] 50g of diatomaceous earth was added to 300g of a 5% hydrochloric acid solution and impregnated at room temperature for 6 hours. After impregnation, the mixture was filtered, washed, and dried, and then calcined at 300℃ for 2 hours to obtain pretreated diatomaceous earth. 50g of the pretreated diatomaceous earth was added to 800g of an aqueous ethanol solution (ethanol to water volume ratio of 3:1), followed by the addition of 5g of vinyltriethoxysilane. The mixture was reacted at 60℃ for 4 hours. After the reaction, the mixture was filtered, washed, and dried to obtain a solid product. Then, 50g of the solid product was added to 600mL of dimethyl sulfoxide, followed by the addition of 4g of triallyl phosphate and 0.3g of bis(phthaloyl)peroxide. The mixture was reacted at 90℃ for 5 hours. After the reaction, the mixture was filtered, washed, and dried to obtain the modified flame retardant.

[0059] The method for preparing the modified wood fiber includes the following steps:

[0060] S1. Pretreatment and activation of wood fiber: Mix 70g of wood fiber and 30g of wheat straw powder evenly, then add 800g of 7% sodium hydroxide solution and soak at 40℃ for 1h. After soaking, filter, wash and dry to obtain pretreated wood fiber. Add 100g of pretreated wood fiber to 800g of deionized water, then add 100g of 20% hydrogen peroxide solution and 5g of potassium permanganate, and activate at 80℃ for 2h. After the reaction is completed, filter, wash and dry to obtain activated wood fiber.

[0061] S2. Modification of wood fiber: 100g of activated wood fiber from step S1 was added to 1300g of ethanol aqueous solution (ethanol to water volume ratio of 7:3), followed by 5g of γ-aminopropyltriethoxysilane. The mixture was stirred at 50℃ for 4h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a solid product. Then, 100g of the solid product was added to 1000g of N,N-dimethylformamide, followed by 10g of 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid and 5g of concentrated sulfuric acid. The mixture was kept at 90℃ for 6h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified wood fiber.

[0062] Example 4

[0063] A method for preparing flame-retardant medium-density fiberboard includes the following steps:

[0064] Weigh the raw materials according to the formula, and mix 40g of modified flame retardant, 60g of epoxy resin, 10g of barite and 9g of sodium silicate evenly. Then add 120g of modified wood fiber and 20g of acetic anhydride, and continue to mix evenly to obtain a premix. Then add the premix into the mold, lay it up and pre-press it at 70℃ and 5MPa for 40s, and then hot press it at 150℃ and 7MPa for 3min to form it. After forming, trim the edges and polish it to obtain flame-retardant medium density fiberboard.

[0065] The preparation method of the modified flame retardant is as follows:

[0066] 50g of diatomaceous earth was added to 300g of a 10% hydrochloric acid solution and impregnated at room temperature for 4 hours. After impregnation, the mixture was filtered, washed, and dried, and then calcined at 350℃ for 1 hour to obtain pretreated diatomaceous earth. 50g of the pretreated diatomaceous earth was added to 800g of an aqueous ethanol solution (ethanol to water volume ratio of 3:2), followed by the addition of 10g of vinyltriethoxysilane. The mixture was reacted at 70℃ for 2 hours. After the reaction, the mixture was filtered, washed, and dried to obtain a solid product. Then, 50g of the solid product was added to 600mL of dimethyl sulfoxide, followed by the addition of 8g of triallyl phosphate and 0.5g of bis(phthaloyl)peroxide. The mixture was reacted at 100℃ for 3 hours. After the reaction, the mixture was filtered, washed, and dried to obtain the modified flame retardant.

[0067] The method for preparing the modified wood fiber includes the following steps:

[0068] S1. Pretreatment and activation of wood fiber: Mix 80g of wood fiber and 20g of rice straw powder evenly, then add 1000g of 10% sodium hydroxide solution and soak at 50℃ for 0.5h. After soaking, filter, wash and dry to obtain pretreated wood fiber. Add 100g of pretreated wood fiber to 1000g of deionized water, then add 200g of 15% hydrogen peroxide solution and 8g of potassium permanganate, and activate at 90℃ for 1h. After the reaction is completed, filter, wash and dry to obtain activated wood fiber.

[0069] S2. Modification of wood fiber: 100g of activated wood fiber from step S1 was added to 1300g of ethanol aqueous solution (ethanol to water volume ratio of 8:2), followed by the addition of 10g of γ-aminopropyltriethoxysilane. The mixture was stirred at 60℃ for 2h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a solid product. Subsequently, 100g of the solid product was added to 1000g of N,N-dimethylformamide, followed by the addition of 15g of 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid and 10g of concentrated sulfuric acid. The mixture was kept at 100℃ for 4h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified wood fiber.

[0070] Comparative Example 1

[0071] A method for preparing flame-retardant medium-density fiberboard includes the following steps:

[0072] Weigh the raw materials according to the formula, and mix 35g of modified flame retardant, 55g of epoxy resin, 8g of light calcium carbonate and 7g of sodium silicate evenly. Then add 110g of activated wood fiber and 20g of ethylenediamine, and continue to mix evenly to obtain a premix. Then add the premix into the mold, lay it up and pre-press it at 65℃ and 4MPa for 50s, and then hot press it at 145℃ and 6MPa for 4min to form it. After forming, trim the edges and polish it to obtain flame-retardant medium density fiberboard.

[0073] The preparation method of the modified flame retardant is as follows:

[0074] 50g of diatomaceous earth was added to 300g of a 10% hydrochloric acid solution and impregnated at room temperature for 5 hours. After impregnation, the mixture was filtered, washed, and dried, and then calcined at 320℃ for 1.5 hours to obtain pretreated diatomaceous earth. 50g of the pretreated diatomaceous earth was added to 800g of an aqueous ethanol solution (ethanol to water volume ratio of 3:1), followed by the addition of 8g of vinyltriethoxysilane. The mixture was reacted at 65℃ for 3 hours. After the reaction, the mixture was filtered, washed, and dried to obtain a solid product. Then, 50g of the solid product was added to 600mL of dimethyl sulfoxide, followed by the addition of 6g of triallyl phosphate and 0.4g of bis(phthaloyl)peroxide. The mixture was reacted at 95℃ for 4 hours. After the reaction, the mixture was filtered, washed, and dried to obtain the modified flame retardant.

[0075] The method for preparing the activated wood fiber includes the following steps:

[0076] Mix 75g of wood fiber and 25g of corn stalk powder evenly, then add to 900g of 8% sodium hydroxide solution and soak at 45℃ for 1h. After soaking, filter, wash and dry to obtain pretreated wood fiber. Add 100g of pretreated wood fiber to 900g of deionized water, then add 150g of 20% hydrogen peroxide solution and 7g of potassium permanganate, and activate the reaction at 85℃ for 1.5h. After the reaction is completed, filter, wash and dry to obtain activated wood fiber.

[0077] Comparative Example 2

[0078] A method for preparing flame-retardant medium-density fiberboard includes the following steps:

[0079] Weigh the raw materials according to the formula, and mix 35g flame retardant, 55g epoxy resin, 8g light calcium carbonate and 7g sodium silicate evenly. Then add 110g modified wood fiber and 20g ethylenediamine, and continue to mix evenly to obtain a premix. Then add the premix into the mold, lay it up and pre-press it at 65℃ and 4MPa for 50s, and then hot press it at 145℃ and 6MPa for 4min to form it. After forming, trim the edges and polish it to obtain flame retardant medium density fiberboard.

[0080] The method for preparing the modified wood fiber includes the following steps:

[0081] S1. Pretreatment and activation of wood fiber: Mix 75g of wood fiber and 25g of corn stalk powder evenly, then add 900g of 8% sodium hydroxide solution and soak at 45℃ for 1h. After soaking, filter, wash and dry to obtain pretreated wood fiber. Add 100g of pretreated wood fiber to 900g of deionized water, then add 150g of 20% hydrogen peroxide solution and 7g of potassium permanganate, and activate at 85℃ for 1.5h. After the reaction is completed, filter, wash and dry to obtain activated wood fiber.

[0082] S2. Modification of wood fiber: 100g of activated wood fiber from step S1 was added to 1300g of ethanol aqueous solution (ethanol to water volume ratio of 7:3), followed by 8g of γ-aminopropyltriethoxysilane. The mixture was stirred at 55℃ for 3h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a solid product. Then, 100g of the solid product was added to 1000g of N,N-dimethylformamide, followed by 13g of 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid and 8g of concentrated sulfuric acid. The mixture was kept at 95℃ for 5h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified wood fiber.

[0083] The flame retardant is composed of 50g of diatomaceous earth and 6g of triallyl phosphate.

[0084] The flame-retardant medium-density fiberboards prepared in Examples 1-4 and Comparative Examples 1-2 of this invention were subjected to performance tests. The internal bond strength and static bending strength were tested according to standard LY / T 1611—2023 "Fiberboard for Flooring Substrates". The water absorption thickness swelling rate was tested according to method 1 of standard GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels". The limiting oxygen index was tested according to standard GB / T 2406.2-2009. The test results are shown in Table 1 below.

[0085] Table 1

[0086]

[0087] As can be seen from Table 1 above, the flame-retardant medium-density fiberboard provided by the present invention has excellent internal bond strength, static bending strength, water resistance and flame retardancy, and has good application prospects.

[0088] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flame-retardant medium-density fiberboard, characterized in that, By weight, it includes the following ingredients: 100-120 parts modified wood fiber, 30-40 parts modified flame retardant, 50-60 parts adhesive, 5-10 parts filler, 5-9 parts sodium silicate, and 15-20 parts curing agent; The method for preparing the modified wood fiber includes the following steps: S1. Pretreatment and activation of wood fiber: Add the pretreated wood fiber to deionized water, then add hydrogen peroxide solution and potassium permanganate to carry out the activation reaction. After the reaction is completed, filter, wash and dry to obtain activated wood fiber. S2. Modification of wood fiber: The activated wood fiber from step S1 is added to an aqueous ethanol solution, followed by the addition of γ-aminopropyltriethoxysilane. The mixture is stirred and reacted. After the reaction is complete, the mixture is filtered, washed, and dried to obtain a solid product. The solid product is then added to N,N-dimethylformamide, followed by the addition of 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid and concentrated sulfuric acid. The mixture is subjected to a constant temperature reaction. After the reaction is complete, the mixture is filtered, washed, and dried to obtain modified wood fiber.

2. The flame-retardant medium-density fiberboard according to claim 1, characterized in that, By weight, it includes the following ingredients: 110-120 parts modified wood fiber, 35-40 parts modified flame retardant, 55-60 parts adhesive, 8-10 parts filler, 7-9 parts sodium silicate, and 17-20 parts curing agent.

3. The flame-retardant medium-density fiberboard according to claim 1, characterized in that, The pretreatment of wood fiber in step S1 specifically includes the following steps: 70-80 parts of wood fiber and 20-30 parts of straw powder are mixed evenly, and then added to 800-1000 parts of sodium hydroxide solution with a mass concentration of 7-10%, and impregnated at 40-50℃ for 0.5-1h. After impregnation, the mixture is filtered, washed, and dried to obtain pretreated wood fiber.

4. The flame-retardant medium-density fiberboard according to claim 1, characterized in that, In step S1, the mass fraction of hydrogen peroxide is 15-20%, and the mass ratio of the pretreated wood fiber, deionized water, hydrogen peroxide solution, and potassium permanganate is 100:800-1000:100-200:5-8; the activation reaction temperature is 80-90℃, and the time is 1-2 hours.

5. The flame-retardant medium-density fiberboard according to claim 1, characterized in that, In step S2, the volume ratio of ethanol to water in the aqueous ethanol solution is 7-8:2-3, the mass ratio of the activated wood fiber to γ-aminopropyltriethoxysilane is 100:5-10, the stirring reaction temperature is 50-60℃, and the time is 2-4h; the mass ratio of the solid product, 5-[(diethoxyphosphino)difluoromethyl]-1H-indole-2-carboxylic acid, and concentrated sulfuric acid is 100:10-15:5-10, and the isothermal reaction temperature is 90-100℃, and the time is 4-6h.

6. The flame-retardant medium-density fiberboard according to claim 1, characterized in that, The modified flame retardant is prepared as follows: Diatomaceous earth was added to hydrochloric acid solution and impregnated at room temperature for 4-6 hours. After impregnation, the mixture was filtered, washed, dried, and calcined to obtain pretreated diatomaceous earth. The pretreated diatomaceous earth was then added to an aqueous ethanol solution, followed by the addition of vinyltriethoxysilane, and the mixture was subjected to a constant-temperature reaction. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a solid product. The solid product was then added to dimethyl sulfoxide, followed by the addition of triallyl phosphate and bis(phthaloyl)peroxide, and the mixture was heated to react. After the reaction was completed, the mixture was filtered, washed, and dried to obtain the modified flame retardant.

7. The flame-retardant medium-density fiberboard according to claim 6, characterized in that, The hydrochloric acid solution has a mass concentration of 5-10%, the calcination temperature is 300-350℃, and the time is 1-2 hours; the volume ratio of ethanol to water in the ethanol-water solution is 3:1-2, the mass ratio of the pretreated diatomaceous earth to vinyltriethoxysilane is 50:5-10, the isothermal reaction temperature is 60-70℃, and the time is 2-4 hours; the mass ratio of the solid product, triallyl phosphate, and bis(phthaloyl)peroxide is 50:4-8:0.3-0.5, and the heating reaction temperature is 90-100℃, and the time is 3-5 hours.

8. The flame-retardant medium-density fiberboard according to claim 1, characterized in that, The adhesive is an epoxy resin adhesive, the filler is one or more of light calcium carbonate, talc, perlite, and barite, and the curing agent is one or more of ethylenediamine, triethylenetetramine, maleic anhydride, and acetic anhydride.

9. A method for preparing flame-retardant medium-density fiberboard as described in any one of claims 1-8, characterized in that, Includes the following steps: Weigh the raw materials according to the formula, mix the modified flame retardant, adhesive, filler and sodium silicate evenly, then add the modified wood fiber and curing agent, and continue to mix evenly to obtain a premix. Then add the premix into the mold, lay it up and pre-press it at 60-70℃ and 3-5MPa for 40-60s, then hot press it at 140-150℃ and 5-7MPa for 3-5min to form it. After forming, trim the edges and polish it to obtain flame-retardant medium density fiberboard.

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