Waterproof medium density fiberboard and method for manufacturing the same

Abstract

The application discloses a waterproof medium-density fiberboard and a preparation method thereof, and comprises the following steps: S1, pretreatment and activation of wood fibers; S2, modification of the wood fibers; S3, preparation of an organic silicon modified epoxy resin adhesive; S4, sizing treatment; S5, paving, pre-pressing and hot-pressing forming. The preparation method of the waterproof medium-density fiberboard has the advantages that the pretreated wood fibers are subjected to oxidation and activation treatment, the organic silicon modified epoxy resin adhesive is added, and fillers, sodium silicate and trimellitic anhydride are supplemented, so that the obtained medium-density fiberboard has good mechanical properties, good size stability, water resistance and durable water resistance, and can meet the requirements of the industry and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of artificial board, and particularly relates to a waterproof medium density fiberboard and a preparation method thereof. BACKGROUND

[0002] Fiberboard is a kind of artificial board, which is roughly divided into hard density fiberboard, medium density fiberboard and soft fiberboard (low density fiberboard) according to the density. The fiberboard is made of wood fiber or other plant fiber as raw material, and is made by crushing and pressing after wood, branches and other objects are soaked in water, and is made by applying adhesive, fiber separation, molding, hot pressing and other processes.

[0003] The density of medium density fiberboard (MDF) is usually 500-880 kg / m 3 , and the thickness is usually 5-30 mm. With the improvement of people's consumption level, higher requirements are put forward for the performance of MDF, such as better water resistance and other performances. Due to the porous space between wood fibers, once water and moisture are absorbed, water molecules will enter the voids of MDF, causing deformation, expansion and strength reduction, affecting the application range and service life of MDF, so it is necessary to add waterproof agent in the MDF forming process to improve the water resistance of MDF. The general waterproof agent uses solid paraffin as the base body, and the main function is to block part of the voids between fibers, which is a physical measure, and although it can play a waterproof effect to a certain extent, it cannot form a film. Moreover, when the amount of solid paraffin is small, the waterproof effect is not good, and when the amount of solid paraffin is large, the internal bonding strength of MDF is reduced.

[0004] Chinese patent application No. 202110009285.5 discloses a preparation method of a moisture-proof and water-resistant fiber board. The preparation method of the moisture-proof and water-resistant fiber board comprises the following steps: S1, placing raw materials into a pulverizer for pulverization, and then screening through a screening machine to obtain wood fibers; S2, placing urea-formaldehyde resin glue, MF water-resistant resin, formaldehyde scavenger, phenolic resin, and industrial alkali into a reaction kettle for mixing to obtain a glue mixture. The glue mixture is prepared by mixing urea-formaldehyde resin glue, MF water-resistant resin, formaldehyde scavenger, phenolic resin, and industrial alkali, which increases the adhesive property of the glue. In addition, the fiber board is made of camphor wood shavings, elm branches, and locust wood chips, which can increase the strength of the fiber board and make the fiber board suitable for various occasions. The fiber board has certain practicality. The water-based paint is prepared by mixing polyacrylamide, acrylate, styrene-acrylate, wood wax oil, and mineral glue, which can achieve good moisture-proof effect. Chinese patent application No. 202211326076.4 discloses a waterproof high-density fiber board and a preparation method thereof. The preparation method comprises the following steps: placing plant raw materials into a cooking cylinder for cooking; uniformly mixing the plant fiber raw materials with a first mixed solution and a second mixed solution to obtain a mixed fiber slurry; drying the mixed fiber slurry, and adding waterproof powder, urea-formaldehyde resin with a solid content of 40%-50%, ammonium chloride, aluminum hydroxide powder with a particle size of 200-500 mesh, and a synergist into the mixed fiber slurry during the drying process to obtain dried fiber material; pre-pressing and hot-pressing the dried fiber material after being laid and formed, and cooling to obtain a semi-finished fiber board; uniformly coating a waterproof and flame-retardant coating on the surface of the semi-finished fiber board, and the coating thickness is 0.3-0.6 mm, and the waterproof high-density fiber board product is obtained after drying. The prepared high-density fiber board has good waterproof effect and is not easy to be damp, and has long service life. However, the above-mentioned patents improve the water resistance of the fiber board by adding water-based waterproof paint, and the water resistance of the wood fiber itself is not improved. After long-term use, the falling off of the waterproof paint may cause the waterproof performance to decrease, and it is not clear from the specification how much the waterproof effect of the fiber board is improved. Therefore, the waterproof performance and mechanical properties of the medium-density fiber board need to be further improved. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a waterproof medium-density fiber board and a preparation method thereof. The medium-density fiber board has excellent water resistance and long-lasting water resistance, and also has good mechanical properties, which has good application prospect.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions.

[0007] A preparation method of a waterproof medium-density fiber board comprises the following steps:

[0008] S1, pretreatment and activation of wood fibers: the pretreated wood fibers are added to deionized water, then hydrogen peroxide solution and potassium permanganate are added for activation reaction, after the reaction is completed, the mixture is filtered, washed and dried to obtain activated wood fibers;

[0009] S2, modification of wood fibers: the activated wood fibers in step S1 are added to an ethanol aqueous solution, then γ-mercaptopropyltrimethoxysilane is added for stirring reaction, after the reaction is completed, the mixture is filtered, washed and dried to obtain a solid product, then the solid product is added to N,N-dimethylformamide, followed by adding 4-(trifluoromethyl)styrene and dibenzoyl peroxide for constant temperature reaction, after the reaction is completed, the mixture is filtered, washed and dried to obtain modified wood fibers;

[0010] S3, preparation of silicone-modified epoxy resin adhesive: after the epoxy resin is uniformly mixed in toluene, γ-aminopropyltriethoxysilane, aminosilicone and stannous octoate are added for heating reaction, and the silicone-modified epoxy resin adhesive is obtained after the reaction is completed;

[0011] S4, sizing treatment: the fillers, sodium silicate, trimellitic anhydride and the silicone-modified epoxy resin adhesive in step S3 are uniformly mixed and stirred, and then added to the modified wood fibers in step S2, and uniformly mixed to obtain a premix;

[0012] S5, laying, pre-pressing and hot-pressing molding: the premix is added to a mold, and after laying, pre-pressing and hot-pressing molding are performed, the edges are trimmed and polished to obtain a medium density fiberboard.

[0013] Preferably, the pretreated fibers in step S1 specifically include the following steps: 70-80 parts of wood fibers and 20-30 parts of straw powder are uniformly mixed, then 800-1000 parts of a sodium hydroxide solution with a mass concentration of 7-10% is added, and the mixture is immersed at 40-50°C for 0.5-1h, after the immersion is completed, the mixture is filtered, washed and dried to obtain pretreated wood fibers.

[0014] Preferably, the straw powder is one or more of corn straw, sorghum straw, wheat straw and rice straw.

[0015] In the present application, the pretreatment can dissolve part of the cellulose on the surface of the wood fibers and straw powder, remove impurities and non-fiber substances on the surface of the wood fibers, change the surface properties of the fibers, and the alkaline solution can penetrate into the interior of the fibers, partially dissolve part of the cellulose of the wood fibers, change the pore structure in the interior of the fibers, and facilitate the subsequent reaction.

[0016] Preferably, the mass fraction of the hydrogen peroxide in step S1 is 15-20%, the mass ratio of the pretreated fiber, deionized water, hydrogen peroxide solution, and potassium permanganate is 100:800-1000:100-200:5-8; the temperature of the activation reaction is 80-90℃, and the time is 1-2h.

[0017] More preferably, the mass fraction of the hydrogen peroxide in step S1 is 15-20%, the mass ratio of the pretreated fiber, deionized water, hydrogen peroxide solution, and potassium permanganate is 100:800-900:150-200:6-8; the temperature of the activation reaction is 85-90℃, and the time is 1-1.5h.

[0018] In the present application, the oxidation activation reaction can cause the oxidation reaction of the wood fiber surface, increase the reaction sites of the wood fiber surface, and provide better conditions for the subsequent grafting reaction.

[0019] Preferably, the volume ratio of ethanol to water in the ethanol aqueous solution in step S2 is 7-8:2-3, the mass ratio of the activated wood fiber and γ-mercaptopropyl trimethoxysilane is 100:5-10, the temperature of the stirring reaction is 50-60℃, and the time is 2-4h.

[0020] More preferably, the volume ratio of ethanol to water in the ethanol aqueous solution in step S2 is 7-8:2-3, the mass ratio of the activated wood fiber and γ-mercaptopropyl trimethoxysilane is 100:8-10, the temperature of the stirring reaction is 55-60℃, and the time is 2-3h.

[0021] In the present application, the addition of γ-mercaptopropyl trimethoxysilane can introduce mercapto groups to the wood fiber surface, which is conducive to the subsequent reaction, and the introduced long carbon chain can improve the hydrophobicity of the wood fiber.

[0022] Preferably, the mass ratio of the solid product, 4-(trifluoromethyl)styrene, and dibenzoyl peroxide in step S2 is 100:4-7:0.1-0.3, the temperature of the constant temperature reaction is 70-80℃, and the time is 4-6h.

[0023] More preferably, the mass ratio of the solid product, 4-(trifluoromethyl)styrene, and dibenzoyl peroxide in step S2 is 100:6-7:0.2-0.3, the temperature of the constant temperature reaction is 75-80℃, and the time is 4-5h.

[0024] In the present application, the double bond contained in 4-(trifluoromethyl)styrene can react with the mercapto groups in the wood fiber, thereby introducing fluorine-containing groups to the wood fiber surface, thereby significantly improving the hydrophobicity of the wood fiber.

[0025] Preferably, the mass ratio of the epoxy resin, toluene, gamma-aminopropyl triethoxysilane, aminosilicone, stannous octoate in step S3 is 60-70:25-35:15-25:5-10:0.3-0.6.

[0026] More preferably, the mass ratio of the epoxy resin, toluene, gamma-aminopropyl triethoxysilane, aminosilicone, stannous octoate in step S3 is 65-70:25-30:15-20:8-10:0.4-0.6.

[0027] In the present application, the epoxy resin is modified by silicone, thereby introducing a silicone structure into the epoxy resin system. Due to the hydrophobicity and stability of the silicone structure, the penetration of water molecules can be effectively prevented, and the water resistance of the resin is improved. Moreover, the amino groups in the gamma-aminopropyl triethoxysilane and aminosilicone can react with the epoxy groups in the epoxy resin, realizing the grafting of silicone and epoxy resin, and further improving the long-term water resistance of the epoxy resin.

[0028] Preferably, the temperature of the heating reaction in step S3 is 60-80℃, and the time is 3-5h.

[0029] More preferably, the temperature of the heating reaction in step S3 is 70-80℃, and the time is 3-4h.

[0030] Preferably, the filler in step S4 is one or more of light calcium carbonate, talcum powder, perlite, and barite; and the mass ratio of the filler, sodium silicate, trimellitic anhydride, silicone-modified epoxy resin adhesive, and modified wood fiber is 10-15:3-6:10-15:80-90:50-60.

[0031] More preferably, the filler in step S4 is one or more of light calcium carbonate, talcum powder, perlite, and barite; and the mass ratio of the filler, sodium silicate, trimellitic anhydride, silicone-modified epoxy resin adhesive, and modified wood fiber is 12-15:5-6:12-15:85-90:55-60.

[0032] In the present application, the added filler can increase the mechanical strength of the fiberboard, improve the wear resistance of the fiberboard, and adjust the density of the fiberboard, making the fiberboard more solid and durable.

[0033] Preferably, the temperature of the pre-pressing in step S5 is 60-70℃, the pressure is 3-5MPa, and the time is 30-50s; and the temperature of the hot-pressing treatment is 130-150℃, the pressure is 4-6MPa, and the time is 1-2min.

[0034] The present application also protects a waterproof medium-density fiberboard prepared by the above method.

[0035] Compared with the prior art, the present application has the following advantages:

[0036] (1) The preparation method of the waterproof medium density fiberboard provided by the present application first performs alkali treatment on wood fibers and straw powder to destroy the hydrogen bonds inside the fibers, degrade lignin, and increase the specific surface area of the fibers, which is beneficial to subsequent reactions and improves the bonding strength between the wood fibers and the adhesive, thereby improving the mechanical properties and durability of the fiberboard; then the wood fibers are subjected to oxidation and activation treatment with hydrogen peroxide and potassium permanganate, so that the functional groups such as hydroxyl groups and carbonyl groups on the surface of the wood fibers will undergo oxidation reactions to form more active functional groups and oxides, thereby increasing the specific surface area and reactivity of the wood fibers, and the gas generated during the oxidation and activation process can change the chemical properties of the surface of the wood fibers, making the surface more easily roughened and producing a micro concave-convex structure to increase the roughness and further improve the bonding force between the adhesive and the wood fibers; then the activated wood fibers are reacted with γ-mercaptopropyltrimethoxysilane to obtain mercapto-functionalized wood fibers, which can improve the hydrophobicity of the wood fibers and facilitate subsequent reactions, and then the mercapto-functionalized wood fibers are reacted with 4-(trifluoromethyl)styrene to introduce fluorine-containing groups onto the surface of the wood fibers, which can significantly improve the water resistance of the wood fibers, and the phenyl group contained in 4-(trifluoromethyl)styrene can also improve the weather resistance of the fiberboard; the hydrophobic groups are introduced onto the surface of the wood fibers by chemical grafting, so that the medium density fiberboard prepared has good and durable water resistance.

[0037] (2) The preparation method of the waterproof medium density fiberboard provided by the present application adds an organic silicon-modified epoxy resin adhesive, which uses epoxy resin as a raw material and introduces silane groups into the epoxy resin by adding γ-aminopropyltriethoxysilane and aminosilicone, thereby improving the water resistance of the epoxy resin, and the epoxy groups in the epoxy resin can also react with the mercapto groups introduced into the wood fibers, thereby significantly improving the bonding strength between the adhesive and the wood fibers and making the fiberboard have better mechanical properties.

[0038] (3) The preparation method of the waterproof medium density fiberboard provided by the present application performs oxidation and activation treatment on the pretreated wood fibers, simultaneously adds an organic silicon-modified epoxy resin adhesive, and is supplemented with fillers, sodium silicate and trimellitic anhydride, so that the obtained medium density fiberboard has good mechanical properties, good dimensional stability, water resistance and durable water resistance, etc., can meet the requirements of the industry, and has good application prospects. DETAILED DESCRIPTION

[0039] The technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0040] The epoxy resin is purchased from Wanqing Chemical Technology Co., Ltd., and the brand is E-51.

[0041] Example 1

[0042] A preparation method of a waterproof medium-density fiberboard, comprising the following steps:

[0043] S1, pretreatment and activation of wood fibers: 75 g of wood fibers and 25 g of corn straw powder are uniformly mixed, then 900 g of a sodium hydroxide solution with a mass concentration of 8% is added, and impregnation is carried out at 45℃ for 1 h. After impregnation, filtration, washing and drying are performed to obtain pretreated wood fibers. 100 g of the pretreated wood fibers is added to 900 g of deionized water, then 150 g of a hydrogen peroxide solution with a mass fraction of 20% and 7 g of potassium permanganate are added, and activation reaction is carried out at 85℃ for 1.5 h. After reaction, filtration, washing and drying are performed to obtain activated wood fibers;

[0044] S2, modification of wood fibers: 100 g of the activated wood fibers in step S1 is added to 1500 g of an ethanol aqueous solution (the volume ratio of ethanol to water is 8:2), then 8 g of γ-mercaptopropyltrimethoxysilane is added, and stirring reaction is carried out at 55℃ for 3 h. After reaction, filtration, washing and drying are performed to obtain a solid product. Then 100 g of the solid product is added to 1000 g of N,N-dimethylformamide, then 6 g of 4-(trifluoromethyl)styrene and 0.2 g of dibenzoyl peroxide are added, and constant-temperature reaction is carried out at 75℃ for 5 h. After reaction, filtration, washing and drying are performed to obtain modified wood fibers;

[0045] S3, preparation of a silicone-modified epoxy resin adhesive: 65 g of an epoxy resin is uniformly mixed in 30 g of toluene, then 20 g of γ-aminopropyltriethoxysilane, 8 g of aminosilicone and 0.5 g of stannous octoate are added, and reaction is carried out at 70℃ for 4 h. After reaction, a silicone-modified epoxy resin adhesive is obtained;

[0046] S4, sizing treatment: 13 g of light calcium carbonate, 5 g of sodium silicate, 13 g of trimellitic anhydride and 85 g of the silicone-modified epoxy resin adhesive in step S3 are uniformly mixed and stirred, and then added to 55 g of the modified wood fibers in step S2 to obtain a premix;

[0047] S5, paving, pre-pressing and hot-pressing: the premix is added to the mold, and after paving, it is pre-pressed at 65℃ and 4MPa for 40s, and after pre-pressing, it is hot-pressed at 140℃ and 5MPa for 2min, and after molding, it is trimmed and polished to obtain medium density fiberboard.

[0048] Example 2

[0049] A preparation method of waterproof medium density fiberboard, comprising the following steps:

[0050] S1, pretreatment and activation of wood fibers: 75g of wood fibers, 250g of sorghum straw powder are uniformly mixed, then 900g of 9% sodium hydroxide solution is added, and immersed at 45℃ for 0.5h, after immersion, filtration, washing and drying, pretreated wood fibers are obtained; 100g of pretreated wood fibers is added to 900g of deionized water, then 150g of 15% hydrogen peroxide solution and 6g of potassium permanganate are added, and the mixture is activated at 85℃ for 1.5h, after reaction, filtration, washing and drying, activated wood fibers are obtained;

[0051] S2, modification of wood fibers: 100g of activated wood fibers in step S1 is added to 1500g of ethanol aqueous solution (volume ratio of ethanol to water is 7:3), then 8g of γ-mercaptopropyltrimethoxysilane is added, and the mixture is stirred at 55℃ for 3h, after reaction, filtration, washing and drying, solid product is obtained, then 100g of solid product is added to 1000g of N,N-dimethylformamide, then 6g of 4-(trifluoromethyl)styrene and 0.2g of dibenzoyl peroxide are added, and the mixture is reacted at 75℃ for 5h, after reaction, filtration, washing and drying, modified wood fibers are obtained;

[0052] S3, preparation of silicone-modified epoxy resin adhesive: 65g of epoxy resin is uniformly mixed with 30g of toluene, then 20g of γ-aminopropyltriethoxysilane, 7g of aminosilicone and 0.4g of stannous octoate are added, and the mixture is reacted at 70℃ for 4h, after reaction, silicone-modified epoxy resin adhesive is obtained;

[0053] S4, sizing treatment: 12g of talc, 4g of sodium silicate, 12g of trimellitic anhydride and 85g of silicone-modified epoxy resin adhesive in step S3 are uniformly mixed and stirred, and then added to 55g of modified wood fibers in step S2, and uniformly mixed to obtain a premix;

[0054] S5, paving, pre-pressing and hot-pressing: the premix is added to the mold, and after paving, it is pre-pressed at 65℃ and 4MPa for 40s, and after pre-pressing, it is hot-pressed at 140℃ and 5MPa for 2min, and after molding, it is trimmed and polished to obtain medium density fiberboard.

[0055] Example 3

[0056] A preparation method of waterproof medium density fiberboard, comprising the following steps:

[0057] S1, pretreatment and activation of wood fibers: 70 g of wood fibers, 30 g of wheat straw powder are uniformly mixed, then 800 g of 7% mass concentration sodium hydroxide solution is added, and impregnated at 40℃ for 1 h, after impregnation, filtration, washing and drying, pretreated wood fibers are obtained; 100 g of pretreated wood fibers is added to 800 g of deionized water, then 100 g of 20% mass fraction hydrogen peroxide solution and 5 g of potassium permanganate are added, and the reaction is activated at 80℃ for 2 h, after the reaction is completed, filtration, washing and drying are carried out, and activated wood fibers are obtained;

[0058] S2, modification of wood fibers: 100 g of activated wood fibers in step S1 is added to 1500 g of ethanol aqueous solution (volume ratio of ethanol to water is 7:3), then 5 g of γ-mercaptopropyl trimethoxysilane is added, and the reaction is stirred at 50℃ for 4 h, after the reaction is completed, filtration, washing and drying are carried out, and a solid product is obtained, then 100 g of the solid product is added to 1000 g of N,N-dimethylformamide, then 4 g of 4-(trifluoromethyl) styrene and 0.1 g of dibenzoyl peroxide are added, and the reaction is carried out at 70℃ for 6 h, after the reaction is completed, filtration, washing and drying are carried out, and modified wood fibers are obtained;

[0059] S3, preparation of silicone modified epoxy resin adhesive: 60 g of epoxy resin is uniformly mixed in 25 g of toluene, then 15 g of γ-aminopropyl triethoxysilane, 5 g of aminosilicone and 0.3 g of stannous octoate are added, and the reaction is carried out at 60℃ for 5 h, after the reaction is completed, the silicone modified epoxy resin adhesive is obtained;

[0060] S4, sizing treatment: 10 g of barite, 3 g of sodium silicate, 10 g of trimellitic anhydride and 80 g of silicone modified epoxy resin adhesive in step S3 are uniformly mixed and stirred, and then added to 50 g of modified wood fibers in step S2, and uniformly mixed to obtain a premix;

[0061] S5, laying, pre-pressing and hot-pressing forming: the premix is added to a mold, laid, pre-pressed at 60℃ and 3 MPa for 50 s, hot-pressed at 130℃ and 4 MPa for 2 min after pre-pressing is completed, and then edge cutting and polishing treatment are carried out, and a medium density fiberboard is obtained.

[0062] Example 4

[0063] A preparation method of waterproof medium density fiberboard, comprising the following steps:

[0064] S1, pretreatment and activation of wood fibers: 80 g of wood fibers, 20 g of rice straw powder were mixed uniformly, then 1000 g of 10% mass concentration sodium hydroxide solution was added, and the mixture was immersed at 50°C for 0.5 h. After the immersion was completed, the mixture was filtered, washed, and dried to obtain pretreated wood fibers. 100 g of pretreated wood fibers was added to 1000 g of deionized water, followed by the addition of 200 g of 15% mass fraction hydrogen peroxide solution and 8 g of potassium permanganate. The mixture was activated at 90°C for 1 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain activated wood fibers.

[0065] S2, modification of wood fibers: 100 g of activated wood fibers from step S1 was added to 1500 g of ethanol aqueous solution (volume ratio of ethanol to water was 8:2), followed by the addition of 10 g of γ-mercaptopropyltrimethoxysilane. The mixture was stirred at 60°C for 2 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a solid product. Then, 100 g of the solid product was added to 1000 g of N,N-dimethylformamide, followed by the addition of 7 g of 4-(trifluoromethyl)styrene and 0.3 g of dibenzoyl peroxide. The mixture was reacted at 80°C for 4 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified wood fibers.

[0066] S3, preparation of silicone-modified epoxy resin adhesive: 70 g of epoxy resin was mixed with 35 g of toluene, followed by the addition of 25 g of γ-aminopropyltriethoxysilane, 10 g of aminosilicone, and 0.6 g of stannous octoate. The mixture was reacted at 80°C for 3 h. After the reaction was completed, a silicone-modified epoxy resin adhesive was obtained.

[0067] S4, sizing treatment: 15 g of perlite, 6 g of sodium silicate, 15 g of trimellitic anhydride, and 90 g of the silicone-modified epoxy resin adhesive from step S3 were mixed and stirred uniformly. The mixture was added to 60 g of the modified wood fibers from step S2, and the mixture was mixed uniformly to obtain a premix.

[0068] S5, laying, pre-pressing, and hot-pressing molding: the premix was added to a mold, and after laying, the mixture was pre-pressed at 70°C and 5 MPa for 30 s. After the pre-pressing was completed, the mixture was hot-pressed at 150°C and 6 MPa for 1 min. After molding, the edges were trimmed and polished to obtain a medium density fiberboard.

[0069] Comparative Example 1

[0070] A method for preparing a waterproof medium density fiberboard, comprising the following steps:

[0071] S1, pretreatment and activation of wood fiber: 75 g of wood fiber and 25 g of corn straw powder were uniformly mixed, then 900 g of sodium hydroxide solution with a mass concentration of 8% was added, and impregnation was carried out at 45°C for 1 h. After impregnation, filtration, washing and drying were carried out to obtain pretreated wood fiber. 100 g of pretreated wood fiber was added to 900 g of deionized water, then 150 g of hydrogen peroxide solution with a mass fraction of 20% and 7 g of potassium permanganate were added, and activation reaction was carried out at 85°C for 1.5 h. After the reaction was completed, filtration, washing and drying were carried out to obtain activated wood fiber;

[0072] S2, preparation of silicone-modified epoxy resin adhesive: 65 g of epoxy resin was uniformly mixed in 30 g of toluene, then 20 g of γ-aminopropyl triethoxysilane, 8 g of aminosilicone and 0.5 g of stannous octoate were added, and reaction was carried out at 70°C for 4 h. After the reaction was completed, a silicone-modified epoxy resin adhesive was obtained;

[0073] S3, sizing treatment: 13 g of light calcium carbonate, 5 g of sodium silicate, 13 g of trimellitic anhydride and 85 g of silicone-modified epoxy resin adhesive in step S2 were uniformly mixed and stirred, and then added to 55 g of activated wood fiber in step S1 to obtain a premix;

[0074] S4, laying, pre-pressing and hot pressing: the premix was added to a mold, laid, pre-pressed at 65°C and 4 MPa for 40 s, hot-pressed at 140°C and 5 MPa for 2 min after pre-pressing, and then edge cutting and polishing were carried out to obtain a medium density fiberboard.

[0075] Comparative Example 2

[0076] A preparation method of a waterproof medium density fiberboard, comprising the following steps:

[0077] S1, pretreatment and activation of wood fiber: 75 g of wood fiber and 25 g of corn straw powder were uniformly mixed, then 900 g of sodium hydroxide solution with a mass concentration of 8% was added, and impregnation was carried out at 45°C for 1 h. After impregnation, filtration, washing and drying were carried out to obtain pretreated wood fiber. 100 g of pretreated wood fiber was added to 900 g of deionized water, then 150 g of hydrogen peroxide solution with a mass fraction of 20% and 7 g of potassium permanganate were added, and activation reaction was carried out at 85°C for 1.5 h. After the reaction was completed, filtration, washing and drying were carried out to obtain activated wood fiber;

[0078] S2, modification of wood fibers: 100 g of activated wood fibers in step S1 were added to 1500 g of an ethanol aqueous solution (volume ratio of ethanol to water was 8:2), followed by adding 8 g of γ-mercaptopropyltrimethoxysilane, and stirring and reacting at 55°C for 3 h. After the reaction was completed, filtration, washing, and drying were performed to obtain a solid product. Subsequently, 100 g of the solid product was added to 1000 g of N,N-dimethylformamide, followed by adding 6 g of 4-(trifluoromethyl)styrene and 0.2 g of dibenzoyl peroxide, and constant temperature reaction at 75°C for 5 h. After the reaction was completed, filtration, washing, and drying were performed to obtain modified wood fibers;

[0079] S3, sizing treatment: 13 g of light calcium carbonate, 5 g of sodium silicate, 13 g of trimellitic anhydride, and 85 g of epoxy resin were uniformly mixed and stirred, and then added to 55 g of the modified wood fibers in step S2 to obtain a premix;

[0080] S4, laying, pre-pressing, and hot-pressing molding: the premix was added to a mold, laid, pre-pressed at 65°C and 4 MPa for 40 s, and then hot-pressed at 140°C and 5 MPa for 2 min after the pre-pressing was completed. After molding, edge cutting and polishing were performed to obtain a medium density fiberboard.

[0081] The medium density fiberboards prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to performance tests. The internal bond strength and static bending strength were tested according to the standard LY / T 1611-2023 “Fiberboard for floor base material”. The water absorption thickness swelling rate was tested according to the standard GB / T 17657-2022 “Test methods of physical and chemical properties of wood-based panels and veneered wood-based panels”-water absorption thickness swelling rate test-method 1. The test results are shown in Table 1 below.

[0082] Table 1

[0083] Density / kg / m 3 ]] Internal bond strength / MPa Modulus of rupture / MPa Water thickness expansion rate / % Example 1 821 1.37 36.1 3.2 Example 2 809 1.33 35.9 3.4 Example 3 796 1.24 34.8 3.7 Example 4 815 1.31 35.4 3.5 Comparative Example 1 818 1.06 29.6 7.2 Comparative Example 2 823 1.29 34.5 6.1

[0084] As can be seen from Table 1 above, the medium density fiberboard prepared in the present application has high internal bond strength and static bending strength, and also has a small water absorption thickness swelling rate, and has good water resistance.

[0085] The medium density fiberboards prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to durability water resistance tests. The method was as follows: the sample was immersed in static water at 20±1°C for 72 h, and the upper part of the sample was placed 2 cm under water. Then, the sample was drained for 5-10 min, and then placed in an ice point temperature of-12±1°C for 24 h. Subsequently, the sample was placed in an aging oven with a temperature of 70±1°C for 72 h. The above steps were repeated for 3 times. Finally, the water absorption thickness swelling rate after aging was tested. The test results are shown in Table 2 below.

[0086] Table 2

[0087] Group Water thickness expansion rate after aging / % Example 1 4.9 Example 2 5.4 Example 3 5.8 Example 4 5.5 Comparative Example 1 11.6 Comparative Example 2 9.2

[0088] From the above Table 2, it can be seen that the medium density fiberboard prepared by the present application has good long-term water resistance, and after aging of the fiberboard, it also has good water resistance, and has good application prospect.

[0089] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for producing a waterproof medium density fiberboard, characterized by, The method comprises the following steps: S1, pretreatment and activation of wood fibers: 70-80 parts of wood fibers, 20-30 parts of straw powder are uniformly mixed, then 800-1000 parts of sodium hydroxide solution with a mass concentration of 7-10% is added, and the mixture is soaked at 40-50 DEG C for 0-1 h; after the soaking is completed, the mixture is filtered, washed and dried to obtain pretreated wood fibers; The pretreated wood fibers are added into deionized water, then hydrogen peroxide solution and potassium permanganate are added, and an activation reaction is performed; after the reaction is completed, the mixture is filtered, washed and dried to obtain activated wood fibers; S2, modification of wood fibers: the activated wood fibers in step S1 are added into an ethanol aqueous solution, then gamma-mercaptopropyltrimethoxysilane is added, and a stirring reaction is performed; after the reaction is completed, the mixture is filtered, washed and dried to obtain a solid product; then the solid product is added into N, N-dimethylformamide, then 4-(trifluoromethyl) styrene and dibenzoyl peroxide are added, and a constant temperature reaction is performed; after the reaction is completed, the mixture is filtered, washed and dried to obtain modified wood fibers; S3, preparation of silicone modified epoxy resin adhesive: epoxy resin is uniformly mixed in toluene, then gamma-aminopropyltriethoxysilane, aminosilicone and stannous octoate are added, and a heating reaction is performed; after the reaction is completed, a silicone modified epoxy resin adhesive is obtained; S4, sizing treatment: fillers, sodium silicate and trimellitic anhydride are uniformly mixed with the silicone modified epoxy resin adhesive in step S3, and then the mixture is added into the modified wood fibers in step S2, and uniformly mixed to obtain a premix; S5, paving, pre-pressing and hot-pressing forming: the premix is added into a mold, and after paving, pre-pressing and hot-pressing forming are performed; after forming, edge cutting and polishing treatments are performed to obtain a medium density fiberboard; In step S2, the mass ratio of the solid product, 4-(trifluoromethyl) styrene and dibenzoyl peroxide is 100:4-7:0.1-0.3, the temperature of the constant temperature reaction is 70-80 DEG C, and the time is 4-6 h.

2. The production method according to claim 1, characterized by, In step S1, the mass fraction of the hydrogen peroxide solution is 15-20%, and the mass ratio of the pretreated wood fibers, deionized water, hydrogen peroxide solution, potassium permanganate is 100:800-1000:100-200:5-8; the temperature of the activation reaction is 80-90 DEG C, and the time is 1-2 h.

3. The preparation method according to claim 1, characterized in that, In step S2, the volume ratio of ethanol to water in the ethanol aqueous solution is 7-8:2-3, the mass ratio of the activated wood fibers and gamma-mercaptopropyltrimethoxysilane is 100:5-10, and the temperature of the stirring reaction is 50-60 DEG C, and the time is 2-4 h.

4. The method of claim 1, wherein, In step S3, the mass ratio of the epoxy resin, toluene, gamma-aminopropyltriethoxysilane, aminosilicone and stannous octoate is 60-70:25-35:15-25:5-10:0.3-0.

6.

5. The preparation method according to claim 1, characterized in that, In step S3, the temperature of the heating reaction is 60-80 DEG C, and the time is 3-5 h.

6. The method of claim 1, wherein, The filler in step S4 is one or more of light calcium carbonate, talcum powder, perlite, and barite; and the mass ratio of the filler, sodium silicate, trimellitic anhydride, modified silicone epoxy resin adhesive, and modified wood fiber is 10-15:3-6:10-15:80-90:50-60.

7. The preparation method according to claim 1, characterized in that, In step S5, the pre-pressing temperature is 60-70℃, the pressure is 3-5MPa, and the time is 30-50s; the hot-pressing temperature is 130-150℃, the pressure is 4-6MPa, and the time is 1-2min.

8. A waterproof medium density fiberboard prepared by the method of any one of claims 1-7.