Preparation method of wood fiber modified plate

Abstract

The invention belongs to the technical field of plate modification processes, and particularly relates to a preparation method of a wood fiber modified plate, which mainly comprises the following steps: S2, stirring for 2-3 hours at the temperature of 50-70 DEG C by adopting a NaOH solution with the concentration of 3%-5%, and removing fatty acid through saponification with the removal rate being greater than or equal to 90%, the retention rate of lignin being greater than or equal to 85% and the retention rate of hemicellulose being greater than or equal to 70%; s3, washing with warm water at 40-60 DEG C until the solution is neutral, and removing residual alkali liquor and small molecule degradation products, wherein the pH value is 6.5-7.5; s4, performing hot air drying for 4-6 hours under the condition of 105-120 DEG C, so that the water content is reduced to be less than 5%; s5, urea resin or phenolic resin is adopted for dipping for 30-60 minutes under the pressure of 0.5-1.0 MPa, the penetration depth is larger than or equal to 80% of the volume of a cell cavity, the defects in the prior art are overcome, the agriculture and forestry waste branch fibers are treated through an alkali treatment method, fatty acid in the agriculture and forestry waste branch fibers is removed, lignin and hemicelluloses cannot be decomposed, the strength of the fibers is kept, and the service life of the fibers is prolonged. The compressive strength of the fiber material is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of board modification technology, and particularly relates to a method for preparing a wood fiber modified board. Background Art

[0002] Sheet materials are flat rectangular building material boards made of standard size, used in the construction industry to make components of walls, ceilings or floors. It also refers to metal plates made by forging, rolling or casting. The dimensional stability of unmodified sheet materials decreases by 8% to 10% per year under an environment of 80°C / 95% RH. In addition, it is difficult for traditional sheet materials to simultaneously meet multifunctional requirements such as flame retardancy (flame retardancy grade > B1) and antibacterial (antibacterial rate > 99%). The mainstream technology of existing wood fiber modified sheet materials uses strong acid (such as H2SO4) or strong alkali (such as NaOH concentration > 8%) to treat the fiber under high temperature (> 100°C) conditions to achieve modification by removing lignin and hemicellulose. However, traditional alkali treatment results in a lignin loss rate of 30% to 40%, and a decrease in fiber breaking strength by 20% to 30%.

[0003] Therefore, it is necessary to develop a new wood fiber modification method that can remove fatty acids without decomposing lignin and hemicellulose to meet market demand. Summary of the Invention

[0004] The present invention aims to provide a method for preparing a modified wood fiber board, overcoming the shortcomings of the prior art. By treating waste agricultural and forestry branch fibers with an alkali treatment method, fatty acids are removed without decomposing lignin and hemicellulose, maintaining the fiber's inherent strength and improving the compressive strength of the fiber material. Heat treatment reduces the moisture content of the wood fiber to below 5%. A resin is then pressurized to penetrate the cell cavity and cell wall of the wood fiber. The resin forms hydrogen bonds or covalent bonds with the hydroxyl groups (-OH) on the fiber surface, improving the compatibility between the fiber and the resin matrix. After curing, a three-dimensional network structure is formed (the resin forms hydrogen bonds with the hydroxyl groups on the fiber surface), reducing hygroscopic expansion and enhancing mechanical strength.

[0005] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0006] A method for preparing a wood fiber modified board, characterized in that it comprises the following steps:

[0007] S1: Raw material pretreatment: Select waste branches from agriculture and forestry, with a diameter of ≤5cm, and process them into fibers of 2-5mm in length using a crusher. Sieve and remove impurities, with the impurity content required to be <0.5%;

[0008] S2: Alkali treatment process: using 3% to 5% NaOH solution, stirring at 50-70℃ for 2-3 hours to remove fatty acids through saponification reaction, with a removal rate of ≥90%, while maintaining the structural integrity of lignin and hemicellulose, with a lignin retention rate of ≥85% and a hemicellulose retention rate of ≥70%;

[0009] S3: Hot water elution: Wash with warm water at 40-60°C until the pH reaches 6.5-7.5 to remove residual alkali and small molecular degradation products;

[0010] S4: Hot press drying: hot air drying at 105-120°C for 4-6 hours to reduce the moisture content to below 5%;

[0011] S5: Resin impregnation: Use urea-formaldehyde resin or phenol-formaldehyde resin, impregnate for 30-60 minutes at a pressure of 0.5-1.0 MPa, and allow the resin to penetrate into the fiber cell cavity, with a penetration depth of ≥80% of the cell cavity volume;

[0012] S6: Hot pressing curing: Press at 140-160°C and 1.5-2.5 MPa for 10-15 minutes to form a density of 0.6-0.8 g / cm 3 of board.

[0013] Preferably, the liquid-to-solid ratio of the NaOH solution is 10:1 to 15:1.

[0014] Preferably, the moisture content in S4 is precisely controlled to be in the range of 4% to 5%.

[0015] Preferably, the solid content of urea-formaldehyde resin is 60% to 65%.

[0016] Preferably, the solid content of the phenolic resin is 55% to 60%.

[0017] Preferably, the alkali treatment process adopts countercurrent rinsing technology and is equipped with a plate heat exchanger to recover waste heat.

[0018] Preferably, after the alkali treatment, a silane coupling agent treatment is added, wherein the concentration of KH-550 is 1% to 2%, the treatment temperature is 60° C., and the treatment time is 30 minutes to form -Si-OC bonding.

[0019] Preferably, microwave pretreatment is added before step S4, with a microwave power of 2 to 3 kW and a treatment time of 10 to 15 minutes.

[0020] Preferably, the urea-formaldehyde resin is a melamine-urea-formaldehyde resin, the free formaldehyde content of the melamine-urea-formaldehyde resin is ≤0.1%, and 5%-10% of nano-SiO2 particles are added, and the particle size of the nano-SiO2 particles is 50-100nm.

[0021] Preferably, the resin is immersed in a vacuum of -0.09 MPa for 20 minutes, and then pressurized to 1.5 MPa for 40 minutes to achieve deep penetration of the resin.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The fiber of agricultural and forestry waste branches is treated by alkali treatment (3% to 5% NaOH solution at 50 to 70°C), which not only removes the fatty acids but also does not decompose the lignin and hemicellulose (quality retention rate ≥85%, fiber breaking strength retention rate ≥90%), thus maintaining the strength of the fiber itself and improving the compressive strength of the fiber material.

[0024] 2. Heat treatment reduces the moisture content of wood fiber to below 5%. The resin penetrates into the cell cavity and cell wall of the wood fiber through a pressurized process. The resin forms hydrogen bonds or covalent bonds with the hydroxyl groups (-OH) on the fiber surface, improving the compatibility between the fiber and the resin matrix. After curing, a three-dimensional network structure is formed (the resin forms hydrogen bonds (bond energy of about 20 to 40 kJ / mol) and covalent bonds (bond energy > 200 kJ / mol) with the hydroxyl groups on the fiber surface, and the interface shear strength is increased by 40% to 60%), reducing hygroscopic expansion and enhancing mechanical strength.

[0025] 3. Add 5% to 10% nano-SiO2 (particle size 50 to 100 nm) to inhibit crack propagation through the "pinning effect" and increase the impact strength by 20% to 25%.

[0026] 4. Wastewater reuse system: Countercurrent rinsing technology makes the alkali solution reuse rate ≥70% and the wastewater COD concentration is reduced to <1000mg / L.

[0027] 5. Microwave-assisted drying: Energy consumption in the pretreatment stage is reduced by 30% to 40%, and drying time is shortened from 6 hours to 4 hours. DETAILED DESCRIPTION

[0028] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] Example 1

[0030] The method for preparing a wood fiber modified board according to the present invention specifically comprises the following steps:

[0031] 1. Raw material pretreatment: Select agricultural and forestry waste branches (diameter ≤ 5 cm), process them into fiber length 2-5 mm by crusher, and sieve to remove impurities (metal, sand and gravel content < 0.5%).

[0032] 2. Alkali treatment process: Use 3% to 5% concentration NaOH solution (liquid-to-solid ratio 10:1 to 15:1) and stir at 50-70°C for 2-3 hours to remove fatty acids through saponification reaction (removal rate ≥ 90%) while maintaining the structural integrity of lignin (retention rate ≥ 85%) and hemicellulose (retention rate ≥ 70%).

[0033] 3. Hot water elution: Wash with warm water at 40-60°C until neutral (pH = 6.5-7.5) to remove residual alkali and small molecular degradation products.

[0034] 4. Hot press drying: Hot air drying at 105-120°C for 4-6 hours to reduce the moisture content to below 5% (precisely controlled to the range of 4%-5%).

[0035] 5. Resin impregnation: Use urea-formaldehyde resin (solid content 60% to 65%) or phenolic resin (solid content 55% to 60%), impregnate for 30 to 60 minutes at a pressure of 0.5 to 1.0 MPa, and allow the resin to penetrate into the fiber cell cavity (penetration depth ≥ 80% of the cell cavity volume).

[0036] 6. Hot pressing curing: Press at 140-160℃ and 1.5-2.5MPa pressure for 10-15 minutes to form a density of 0.6-0.8g / cm 3 of board.

[0037] Example 2

[0038] 1. Improved alkali treatment: adopt countercurrent rinsing technology (alkali solution reuse rate ≥ 70%), and use a matching plate heat exchanger to recover waste heat (energy saving 20% ​​to 30%).

[0039] 2. Microwave-assisted drying: Add microwave pretreatment (power 2-3kW, processing time 10-15 minutes) before traditional hot air drying to shorten the drying time by 30%-40%.

[0040] 3. Low-toxicity resin system: Use modified melamine-urea-formaldehyde resin (free formaldehyde content ≤ 0.1%) and add 5% to 10% nano-SiO2 particles (particle size 50 to 100 nm) to improve toughness.

[0041] Process parameters:

[0042]

[0043] Example 3

[0044] 1. Complex modification treatment: after alkali treatment, increase silane coupling agent treatment (KH-550 concentration 1%~2%, treatment temperature 60℃, time 30 minutes), form ~Si~O~C bond.

[0045] 2. Vacuum pressure impregnation: impregnate under 0.09 MPa vacuum for 20 minutes, then pressurize to 1.5 MPa and maintain for 40 minutes, realize resin deep penetration (cell wall penetration rate ≥70%).

[0046] Process parameters:

[0047]

[0048] Performance comparison with prior art

[0049]

[0050] It is apparent for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, but can be implemented in other concrete forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all aspects as illustrative and not restrictive, the scope of the present application being defined by the appended claims rather than the above description, and all changes falling within the meaning and range of equivalency of the essential elements of the claims are intended to be embraced therein. Any mark in the claims should not be considered as limiting the claims involved.

Claims

1. A method for preparing a wood fiber modified board, characterized in that: The steps include: S1: Raw material pretreatment: Select waste branches from agriculture and forestry with a diameter of ≤5 cm, process them into fibers with a length of 2-5 mm using a crusher, and sieve to remove impurities, wherein the impurity content is required to be less than 0.5%; S2: Alkali treatment process: using 3% to 5% NaOH solution, stirring at 50-70°C for 2-3 hours to remove fatty acids by saponification reaction, with a removal rate of ≥90%, while maintaining the structural integrity of lignin and hemicellulose, with the retention rate of lignin being ≥85% and the retention rate of hemicellulose being ≥70%; S3: Hot water elution: Wash with warm water at 40-60°C until the pH reaches 6.5-7.5 to remove residual alkali and small molecular degradation products; S4: Hot press drying: hot air drying at 105-120°C for 4-6 hours to reduce the moisture content to below 5%; S5: Resin impregnation: Use urea-formaldehyde resin or phenol-formaldehyde resin, impregnate for 30-60 minutes at a pressure of 0.5-1.0 MPa, and allow the resin to penetrate into the fiber cell cavity, with a penetration depth of ≥80% of the cell cavity volume; S6: Hot pressing curing: Press at 140-160°C and 1.5-2.5 MPa for 10-15 minutes to form a density of 0.6-0.8 g / cm 3 of board.

2. The method for preparing a wood fiber modified board according to claim 1, characterized in that: The liquid-to-solid ratio of the NaOH solution is 10:1 to 15:

1.

3. The method for preparing a wood fiber modified board according to claim 1, characterized in that: The moisture content in the S4 is precisely controlled to be in the range of 4% to 5%.

4. The method for preparing a wood fiber modified board according to claim 1, characterized in that: The solid content of the urea-formaldehyde resin is 60% to 65%.

5. The method for preparing a wood fiber modified board according to claim 1, characterized in that: The solid content of the phenolic resin is 55% to 60%.

6. The method for preparing a wood fiber modified board according to claim 1, characterized in that: The alkali treatment process adopts countercurrent rinsing technology and is equipped with a plate heat exchanger to recover waste heat.

7. The method for preparing a wood fiber modified board according to claim 1, characterized in that: After the alkali treatment, a silane coupling agent treatment is added, wherein the concentration of KH-550 is 1% to 2%, the treatment temperature is 60° C., and the treatment time is 30 minutes to form -Si-OC bonding.

8. The method for preparing a wood fiber modified board according to claim 1, characterized in that: Before the step S4, microwave pretreatment is added, the microwave power is 2-3 kW, and the treatment time is 10-15 minutes.

9. The method for preparing a wood fiber modified board according to claim 1, characterized in that: The urea-formaldehyde resin is a melamine-urea-formaldehyde resin, the free formaldehyde content of the melamine-urea-formaldehyde resin is less than or equal to 0.1%, and 5% to 10% of nano-SiO2 particles are added, and the particle size of the nano-SiO2 particles is 50 to 100 nm.

10. The method for preparing a wood fiber modified board according to claim 1, characterized in that: In the step S5, the resin is immersed in a vacuum of -0.09 MPa for 20 minutes, and then pressurized to 1.5 MPa for 40 minutes to achieve deep penetration of the resin.

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