Glueless Fiberboard Based on Fiber Pretreatment and Its Preparation Method

Abstract

A glue-free plywood based on fiber pretreatment and its preparation method are provided, comprising: immersing wood fibers in a 0.8-1.5% NaOH solution and loosening them at 85-95℃ for 2-4 hours; immersing the loosened fibers in a NaOH / urea / water solution with a mass ratio of (5-9):12:(79-83) and dissolving them at -5--18℃ for 4-8 hours, followed by regeneration with a low-concentration acid at room temperature; rinsing the regenerated fibers with water until pH neutral, filtering, and drying them at 50-70℃ to a moisture content of 8-15% to obtain pretreated fibers; and hot-pressing the pretreated fibers after spreading and laying them out at a temperature of 180-200℃ and a pressure of 5-9 MPa. The material-to-liquid ratio in the loosening and dissolving steps is 1 g:(50-100) mL. This yields a high-performance glue-free plywood.

Description

Technical Field

[0001] This invention belongs to the field of engineered wood products technology, specifically relating to a glue-free plywood and its preparation method, and more particularly to a glue-free plywood based on fiber pretreatment and its preparation method. Background Technology

[0002] my country is a major producer and consumer of engineered wood products, with plywood being the largest and fiberboard the second largest. The production of engineered wood products primarily uses urea-formaldehyde resin, phenolic resin, and melamine resin as adhesives, all of which contain formaldehyde. Fiberboard, in particular, uses urea-formaldehyde resin adhesives in 90% of its production, making formaldehyde pollution a primary concern for consumers. In recent years, formaldehyde-free engineered wood products have become an important development direction, including the use of biomass adhesives and polyisocyanate resin (MDI) adhesives to replace aldehyde-based adhesives. However, these generally suffer from high hygroscopicity, poor dimensional stability, and high costs. Furthermore, biomass adhesives, primarily based on soybean meal, are prone to mold growth, while MDI adhesives are brittle. Therefore, the market share of formaldehyde-free fiberboard is very low. Consequently, developing new formaldehyde-free or even glue-free fiberboards has become an urgent need for the fiberboard industry to achieve green production and improve quality and efficiency.

[0003] The main raw material for fiberboard is wood and bamboo fiber, which contains components such as cellulose, lignin, and hemicellulose. During hot pressing, lignin and hemicellulose degrade under the influence of hygrothermal stress, and the degradation products self-glued to form glue-free plywood. However, because the surface of cellulose contains a large number of hydroxyl groups, these hydroxyl groups do not play a role in improving performance during gluing. Moreover, due to the hygroscopic nature of hydroxyl groups, the formed board easily absorbs water and swells, resulting in poor board performance. Therefore, the development of the glue-free plywood industry needs to improve the stability of its performance.

[0004] Fiber pretreatment can significantly improve self-gluing efficiency; however, general pretreatment methods aim to enhance the degradation efficiency of lignin and hemicellulose, allowing the degradation products to act as adhesives. However, cellulose fails to participate in the self-gluing process, which is a significant factor affecting self-gluing performance. Therefore, effective fiber pretreatment technologies and methods for preparing high-performance glue-free fiberboard remain to be developed. Summary of the Invention

[0005] In view of the above problems, the present invention was developed to provide a preparation method based on fiber pretreatment and a glue-free plywood with excellent mechanical properties and water resistance.

[0006] To achieve the above-mentioned objective, this invention provides a method for preparing a glue-free fiberboard, comprising: immersing wood fibers in a NaOH aqueous solution with a mass concentration of 0.8%–1.5%, subjecting them to a disintegration treatment at 85°C–95°C for 2–4 hours, and then filtering to obtain disintegrated fibers; immersing the disintegrated fibers in a NaOH / urea / aqueous solution with a mass ratio of (5–9):12:(79–83), subjecting them to a fiber dissolution treatment at -18°C–-5°C for 4–8 hours, then adding a certain amount of low-concentration acid at room temperature for ciliary regeneration treatment, and filtering to obtain ciliated regenerated fibers; rinsing the ciliated regenerated fibers with water until the pH is neutral, filtering, and then drying them at 50°C–70°C until the fiber moisture content is 8%–15% to obtain pretreated fibers; and then hot-pressing the pretreated fibers to obtain the glue-free fiberboard, wherein the hot-pressing temperature is 180°C–200°C and the hot-pressing pressure is 5 MPa–9 MPa.

[0007] Furthermore, the ratio of wood fiber to NaOH aqueous solution is 1 g:(50-100) mL. Alternatively, the ratio of disintegrated fiber to NaOH / urea / aqueous solution is 1 g:(50-100) mL. Since the mass change of wood fiber during disintegration is negligible, an alternative ratio of wood fiber to NaOH / urea / aqueous solution of (50-100) mL can also be used. Even further, the ratio of wood fiber to NaOH aqueous solution is 1 g:70 mL. The ratio of disintegrated fiber to NaOH / urea / aqueous solution is 1 g:70 mL.

[0008] Furthermore, the mass concentration of the NaOH aqueous solution was 1%, the decomposition treatment temperature was 90℃, and the treatment time was 3h; the mass ratio of NaOH / urea / aqueous solution was 7:12:81, the fiber dissolution treatment temperature was -12℃, and the treatment time was 6h.

[0009] Furthermore, the drying temperature is 55℃~65℃, and even further, the drying temperature is 60℃.

[0010] If the ratio of wood fiber to NaOH aqueous solution is too low, it is difficult to completely wet the fiber, resulting in poor dissolution effect; if it is too high, it will waste the alkaline solution. If the dissolution time is too short, the lignin and hemicellulose will not depolymerize sufficiently, affecting the dissolution and regeneration of cellulose at low temperature. If the temperature is too high or the time is too long, it will lead to excessive degradation of lignin and hemicellulose, and the lignin will be lost in small molecules, affecting the bonding performance.

[0011] If the specific gravity of the solution between the fiber and the NaOH aqueous solution is too low, the fiber will not be fully wetted during the treatment process. If it is too high, the solution will have excessive permeability on the fiber surface, severely damaging the crystallinity of the surface cellulose and reducing its self-adhesive properties. If the dissolution treatment time is too short, less cellulose on the fiber surface will dissolve and regenerate into filaments, making it difficult to form strong hydrogen bonds. If the time is too long, more surface cellulose will dissolve, affecting the overall crystallinity of the fiber and reducing its self-adhesive properties. Therefore, limiting the appropriate solution-to-solid ratio and treatment time is crucial to ensure optimal dissolution results.

[0012] The treated fibers are used to make self-adhesive fiberboard. Therefore, excessively high drying temperatures cause the fibers to clump together severely, which is not conducive to fiber laying and will also lead to uneven density of self-adhesive boards. On the other hand, excessively low drying temperatures result in excessively long drying times for the fibers, thereby increasing manufacturing energy consumption.

[0013] By maintaining a fiber moisture content of 8%–15%, water molecules act as plasticizers during the hot-pressing process of preparing glue-free fiberboard. This lowers the glass transition temperature of lignin degradation products, promotes lignin flow, and improves the self-adhesion efficiency of hemicellulose and lignin degradation products. Furthermore, water molecules act as interfacial transition agents during hot-pressing evaporation, promoting the formation of a stable solid-liquid interface towards a solid-solid interface. However, if the moisture content is too high, it is difficult to remove the moisture within a short hot-pressing time, leading to blistering in the self-adhesive fiberboard.

[0014] It is preferable to ensure that the fiber moisture content is 12% to 15% during the drying process. This can better ensure that water acts as a medium for solid-liquid exchange between the solid regenerated fibers during the hot pressing process. During the exchange process, water molecules introduce a hydroxyl group and form a hydrogen bond with another hydroxyl group during the departure process, thus achieving fiber self-bonding.

[0015] If the hot-pressing temperature is too low, lignin and hemicellulose are difficult to degrade, and the self-adhesive properties of the degradation products decrease. If the hot-pressing temperature is too high, the fiber surface is easily carbonized, and the self-adhesive fiberboard turns black.

[0016] Similarly, hot-pressing pressure is also a very important factor. If the hot-pressing pressure is too low, it is difficult for the hydroxyl groups on the fibrillated surface to form strong hydrogen bonds. Boards with weak hydrogen bonds are prone to absorbing water and swelling under high humidity, which affects the performance of self-adhesive boards.

[0017] Furthermore, the hot pressing temperature is 185℃~195℃, and the hot pressing pressure is 6MPa~8MPa. Even further, the hot pressing temperature for hot pressing is 190℃, and the hot pressing pressure is 7MPa.

[0018] Among them, the H of low concentration acid + The content of NaOH in NaOH / urea / aqueous solution - The molar ratio of the contents is (0.5~1):1, and the H+ content of low-concentration acid is...+ The ion concentration is 0.8 mol / L to 1.3 mol / L.

[0019] The low-concentration acid can be a hydrochloric acid solution or a sulfuric acid solution.

[0020] As a specific example, the low-concentration acid is a sulfuric acid solution with a mass concentration of 4% to 6%, and further, the sulfuric acid solution has a mass concentration of 5%.

[0021] As another specific example, the low-concentration acid is a sulfuric acid solution with a molar concentration of 0.43 mol / L to 0.64 mol / L, and further, the molar concentration of the sulfuric acid solution is 0.54 mol / L.

[0022] Furthermore, the addition of low-concentration acid can maintain a treatment time of 0.1h to 1h.

[0023] The low concentration of acid can be set according to the specific amount of NaOH / urea / aqueous solution added. Once the low concentration of acid is added, it will neutralize the NaOH and quickly regenerate the fiber. Therefore, the treatment time can be unlimited.

[0024] Specifically, the wood fiber can be one or more of the following: eucalyptus fiber, poplar fiber, fir fiber, Masson pine fiber, mixed wood fiber, and bamboo fiber.

[0025] Specifically, the drying process is carried out in a constant temperature and humidity environment, with a relative humidity of 60% to 80%.

[0026] As a further specific example, the constant temperature and humidity environment is achieved using a constant temperature and humidity drying oven, with a drying temperature of 60℃ and a relative humidity of 70%.

[0027] Specifically, the pretreated fiber has a layup thickness of 2mm to 12mm and a density of 0.8 to 1.2 g / cm³. 3 The hot-pressing time is 2–4 mm / min. More specifically, the paving thickness is 8 mm–10 mm, and the density is 0.8–1.0 g / cm³. 3 .

[0028] The present invention also provides a glue-free fiberboard prepared by any of the above preparation methods.

[0029] According to the inventors' research, the improved self-gluing performance of fibers is due to two factors. First, lignin and hemicellulose in the fibers degrade under certain temperature and humidity conditions to form small molecules, and the degradation products self-glued. Second, cellulose melt regeneration forms filaments on the fiber surface, and surface fibrillation greatly enhances the hydroxyl groups and activity on the fiber surface. The hydroxyl groups form hydrogen bonds, which improves the self-gluing performance.

[0030] After high-temperature treatment with an alkaline solution, the hemicellulose and lignin on the fiber surface partially degrade, exposing more cellulose on the fiber surface. Low-temperature treatment with alkali / urea promotes cellulose dissolution and regeneration under acidic conditions, forming cellulose filaments on the fiber surface. This enhances the activity of surface hydroxyl groups and significantly increases the area of ​​the self-gluing interface. Following high and low temperature pretreatment, during glueless bonding, not only do the degradation products of hemicellulose and lignin self-glu, but the cellulose filaments also self-glu, forming cellulose filaments through hydrogen bonding. The three major cellulose components in the fiber each play a self-gluing role, significantly improving the performance of glueless plywood. Among these factors, the time, temperature, and concentration of the high-temperature alkaline solution treatment are important influencing factors, while the concentration, temperature, and time of the low-temperature alkali / urea treatment are the most important influencing factors for cellulose dissolution and regeneration. Insufficient high-temperature treatment results in cellulose being encapsulated, making it difficult to dissolve and regenerate in subsequent high-temperature processes. Excessive high-temperature treatment leads to lignin degradation and loss, affecting the self-gluing of lignin degradation products. Insufficient low-temperature treatment makes it difficult for cellulose to dissolve, while excessive low-temperature treatment time leads to excessive cellulose dissolution, which can damage the cellulose crystal structure and reduce the fiber's mechanical strength. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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.

[0032] In the following examples and comparative examples, the static bending strength testing process of the prepared boards is as follows:

[0033] Cut the plate into 5mm×60mm×t (t is the thickness). Adjust the support span of the mechanical testing machine to be at least 20 times the thickness of the specimen. Place the specimen on the support, with the long axis of the specimen perpendicular to the support roller and the center point of the specimen below the loading roller. Apply constant loading to the entire specimen. Adjust the loading speed to reach the maximum load within 1 minute. Record the maximum load and take the average value of 5 parallel tests.

[0034] static bending strength formula:

[0035] σ: Static bending strength of the specimen, MPa;

[0036] F max : Maximum load at which the specimen fails, in N;

[0037] l: Distance between the two supports, mm;

[0038] b: Specimen width, mm;

[0039] t: Specimen thickness, mm.

[0040] The elastic modulus test method for the prepared plates is the same as that for static bending strength.

[0041] Elastic modulus formula:

[0042] E b : Elastic modulus of the specimen, MPa;

[0043] l: Distance between the two supports, mm;

[0044] b: Specimen width, mm;

[0045] t: Specimen thickness, mm;

[0046] F2-F1: The increase in load within the straight segment of the load-deflection curve, in N;

[0047] a2-a1: The increase in deformation at the middle of the specimen, i.e., the amount of deformation of the specimen in the force range of F2 to F1, in mm.

[0048] The test method for the water absorption swelling rate of the prepared board is as follows:

[0049] Cut the board into 20mm×20mm pieces and immerse them in a water bath with a pH of 7±1 and a temperature of (20±1)℃. The upper part of the specimen is (25±5)mm below the water surface. Soak for 24 hours. After soaking, take out the specimen, wipe off the water adhering to the surface, and measure its thickness at the original measurement point. The water absorption swelling rate is the ratio of the increase in thickness after water absorption to the thickness before water absorption.

[0050] Formula for water absorption swelling rate:

[0051] T: Water absorption thickness swelling rate, %;

[0052] t1: Specimen thickness before immersion in water, mm;

[0053] t2: Specimen thickness after immersion in water, mm.

[0054] Example 1

[0055] (1) 16g of poplar fiber was immersed in 800mL of 0.8% NaOH aqueous solution, heated to 85℃ and kept for 2h for decomposition treatment, and filtered to obtain decomposition fiber.

[0056] (2) Prepare a NaOH / urea / water solution with a mass ratio of 5:12:79. Immerse the poplar fiber disintegrated in step (1) in 800 mL of NaOH / urea / water solution, cool it to -5℃ and keep it for 4 h for fiber dissolution treatment, restore it to room temperature of 25℃, add 100 mL of 4% sulfuric acid solution and keep it for 10 min for fiber regeneration treatment, and filter to obtain fiber regenerated fibers.

[0057] (3) Rinse the regenerated fibers with water until the pH is neutral, filter them and place them in a constant temperature and humidity oven. Set the drying temperature to 50℃ and the relative humidity to 60% for drying. Monitor the fiber moisture content during the process. Stop drying when the moisture content reaches 8% and take out the pretreated fibers.

[0058] (4) After the pretreated fibers are broken up, they are laid in a hot press mold with mold dimensions of 100mm×100mm×2mm and a density of 0.8g / cm³. 3 Hot pressing is performed at a temperature of 180℃, a pressure of 5MPa, and a time of 2mm / min. After standing at room temperature, glue-free laminated poplar fiberboard is obtained.

[0059] performance:

[0060] Static bending strength: 76MPa

[0061] Elastic modulus: 3.5 GPa

[0062] 24-hour moisture absorption expansion rate: 8.1%

[0063] Example 2

[0064] (1) Immerse 16g of bamboo fiber in 1600mL of 1.5% NaOH aqueous solution, heat to 95℃ and maintain for 4h for decomposition treatment, and filter to obtain decomposition fiber.

[0065] (2) Prepare a NaOH / urea / water solution with a mass ratio of 9:12:83. Immerse the poplar fiber disintegrated in step (1) in 1600 mL of NaOH / urea / water solution, cool it to -18℃ and keep it for 8 hours to dissolve the fiber. After restoring it to room temperature of 25℃, add 400 mL of 6% sulfuric acid solution and keep it for 60 minutes to regenerate the cilia. Filter to obtain the regenerated cilia fiber.

[0066] (3) Rinse the regenerated fibers with water until the pH is neutral, filter them and place them in a constant temperature and humidity oven. Set the drying temperature to 70℃ and the relative humidity to 80% for drying. Monitor the fiber moisture content during the process. Stop drying when the moisture content reaches 12% and take out the pretreated fibers.

[0067] (4) After the pretreated fibers are broken up, they are laid in a hot press mold with mold dimensions of 100mm×100mm×12mm and a density of 1.2g / cm³. 3 Hot pressing is performed at a temperature of 200℃, a pressure of 9MPa, and a time of 4mm / min. After standing at room temperature, glue-free laminated bamboo fiberboard is obtained.

[0068] performance:

[0069] Static bending strength: 125MPa

[0070] Elastic modulus: 9.2 GPa

[0071] 24-hour moisture absorption expansion rate: 6.2%

[0072] Example 3

[0073] (1) Immerse 16g of Chinese fir fiber in 800mL of 0.8% NaOH aqueous solution, heat to 85℃ and maintain for 2h for decomposition treatment, and filter to obtain decomposition fiber.

[0074] (2) Prepare a NaOH / urea / water solution with a mass ratio of 5:12:79. Immerse the poplar fiber disintegrated in step (1) in 800 mL of NaOH / urea / water solution, cool it to -5℃ and keep it for 4 h for fiber dissolution treatment. After restoring it to room temperature of 25℃, add 100 mL of 3% hydrochloric acid solution and keep it for 30 min for cilia regeneration treatment. Filter to obtain cilia regenerated fiber.

[0075] (3) Rinse the regenerated fibers with water until the pH is neutral, filter them and place them in a constant temperature and humidity oven. Set the drying temperature to 55℃ and the relative humidity to 60% for drying. Monitor the fiber moisture content during the process. Stop drying when the moisture content reaches 12% and take out the pretreated fibers.

[0076] (4) After the pretreated fibers are broken up, they are laid in a hot press mold with mold dimensions of 100mm×100mm×8mm and a density of 1.0g / cm³. 3 The wood was hot-pressed at a temperature of 185℃, a pressure of 6MPa, and a time of 2mm / min, and then allowed to stand at room temperature to obtain glue-free laminated fir fiberboard.

[0077] performance:

[0078] Static bending strength: 109 MPa

[0079] Elastic modulus: 6.5 GPa

[0080] 24-hour moisture absorption expansion rate: 7.6%

[0081] Example 4

[0082] (1) 16g of fir fiber was immersed in 800mL of 1.2% NaOH aqueous solution, heated to 95℃ and kept for 4h for decomposition treatment, and filtered to obtain decomposition fiber.

[0083] (2) Prepare a NaOH / urea / water solution with a mass ratio of 5:12:79. Immerse the poplar fiber disintegrated in step (1) in 800 mL of NaOH / urea / water solution, cool it to -18℃ and keep it for 6 h for fiber dissolution treatment, restore it to room temperature of 25℃, add 400 mL of 4% sulfuric acid solution and keep it for 30 min for cilia regeneration treatment, and filter to obtain cilia regenerated fiber.

[0084] (3) Rinse the regenerated fibers with water until the pH is neutral, filter them and place them in a constant temperature and humidity oven. Set the drying temperature to 65℃ and the relative humidity to 80% for drying. Monitor the fiber moisture content during the process. Stop drying when the moisture content reaches 15% and take out the pretreated fibers.

[0085] (4) After the pretreated fibers are broken up, they are laid in a hot press mold with mold dimensions of 100mm×100mm×10mm and a density of 0.9g / cm³. 3 The wood was hot-pressed at a temperature of 195℃, a pressure of 8MPa, and a time of 4mm / min, and then allowed to stand at room temperature to obtain glue-free laminated fir fiberboard.

[0086] performance:

[0087] Static bending strength: 90MPa

[0088] Elastic modulus: 3.8 GPa

[0089] 24-hour moisture absorption expansion rate: 9.4%

[0090] Example 5

[0091] (1) 16g of poplar fiber was immersed in 1000mL of 1% NaOH aqueous solution, heated to 90℃ and kept for 3h for decomposition treatment, and filtered to obtain decomposition fiber.

[0092] (2) Prepare a NaOH / urea / water solution with a mass ratio of 7:12:81. Immerse the poplar fiber disintegrated in step (1) in 1000 mL of NaOH / urea / water solution, cool it to -12℃ and keep it for 6 hours to dissolve the fiber. After restoring it to room temperature (25℃), add 200 mL of 5% sulfuric acid solution and keep it for 30 minutes to regenerate the cilia. Filter to obtain the regenerated cilia fiber.

[0093] (3) Rinse the regenerated fibers with water until the pH is neutral, filter them and place them in a constant temperature and humidity oven. Set the drying temperature to 60℃ and the relative humidity to 70% for drying. Monitor the fiber moisture content during the process. Stop drying when the moisture content reaches 12% and take out the pretreated fibers.

[0094] (4) After the pretreated fibers are broken up, they are laid in a hot press mold with mold dimensions of 100mm×100mm×8mm and a density of 0.8g / cm³. 3 Hot pressing is performed at a temperature of 190℃, a pressure of 7MPa, and a time of 3mm / min. After standing at room temperature, glue-free laminated poplar fiberboard is obtained.

[0095] performance:

[0096] Static bending strength: 89MPa

[0097] Elastic modulus: 6.8 GPa

[0098] 24-hour moisture absorption expansion rate: 7.6%

[0099] Comparative Example 1

[0100] Fiberboard was prepared using untreated poplar fiber, following the same method as in Example 5. Test results:

[0101] Static bending strength: 32MPa

[0102] Elastic modulus: 2.0 GPa

[0103] 24-hour moisture absorption expansion rate: 40.5%

[0104] Comparative Example 2

[0105] The difference from Example 5 is that the drying process was carried out until the fiber moisture content was 8%, and the test results were as follows:

[0106] Static bending strength: 65MPa

[0107] Elastic modulus: 4.8 GPa

[0108] 24-hour moisture absorption expansion rate: 10.5%

[0109] Comparative Example 3

[0110] The difference from Example 5 is that the drying process was carried out until the fiber moisture content was 7%, and the test results were as follows:

[0111] Static bending strength: 57MPa

[0112] Elastic modulus: 3.1 GPa

[0113] 24-hour moisture absorption expansion rate: 15.8%

[0114] Comparative Example 4

[0115] The difference from Example 1 is that the NaOH aqueous solution was 700 mL, and the detection results are as follows:

[0116] Static bending strength: 68MPa

[0117] Elastic modulus: 2.4 GPa

[0118] 24-hour moisture absorption expansion rate: 12.8%

[0119] Comparative Example 5

[0120] The difference from Example 1 is that the sludge removal time was 1 hour, and the test results are as follows:

[0121] Static bending strength: 70MPa

[0122] Elastic modulus: 3.4 GPa;

[0123] 24-hour moisture absorption expansion rate: 11.4%

[0124] Comparative Example 6

[0125] The difference from Example 4 is that the dissolution time was 5 hours and the dissolution temperature was 100°C. The test results are as follows:

[0126] Static bending strength: 82MPa

[0127] Elastic modulus: 3.7 GPa

[0128] 24-hour moisture absorption expansion rate: 15.1%

[0129] Comparative Example 7

[0130] The difference from Example 1 is that the NaOH / urea / aqueous solution was 700 mL. Detection results:

[0131] Static bending strength: 70MPa

[0132] Elastic modulus: 2.8 GPa

[0133] 24-hour moisture absorption expansion rate: 17.2%

[0134] Comparative Example 8

[0135] The difference from Example 1 is that the dissolution time was 3 hours, and the test results are as follows:

[0136] Static bending strength: 73MPa

[0137] Elastic modulus: 3.3 GPa

[0138] 24-hour moisture absorption expansion rate: 9.4%

[0139] Comparative Example 9

[0140] The difference from Example 2 is that the dissolution time was 9 hours, and the test results are as follows:

[0141] Static bending strength: 94MPa

[0142] Elastic modulus: 6.5 GPa

[0143] 24-hour moisture absorption expansion rate: 7.5%

[0144] Comparative Example 10

[0145] The difference from Example 2 is that the drying temperature was 80°C, and the test results are as follows:

[0146] Static bending strength: 115MPa

[0147] Elastic modulus: 9.9 GPa

[0148] 24-hour moisture absorption expansion rate: 5.9%

[0149] Comparative Example 11

[0150] The difference from Example 1 is that the hot-pressing temperature was 170°C, and the test results are as follows:

[0151] Static bending strength: 64MPa

[0152] Elastic modulus: 2.5 GPa

[0153] 24-hour moisture absorption expansion rate: 35.2%

[0154] Comparative Example 12

[0155] The difference from Example 2 is that the hot-pressing temperature was 210°C, and the test results are as follows:

[0156] black

[0157] Static bending strength: 117MPa

[0158] Elastic modulus: 9.5 GPa

[0159] 24-hour moisture absorption expansion rate: 3.2%

[0160] Comparative Example 13

[0161] The difference from Example 1 is that the hot-pressing pressure was 4 MPa, and the test results are as follows:

[0162] Static bending strength: 72MPa

[0163] Elastic modulus: 5.1 GPa

[0164] 24-hour moisture absorption expansion rate: 12.5%

[0165] Comparative Example 14

[0166] The difference from Example 2 is that the hot-pressing pressure was 10 MPa, and the test results are as follows:

[0167] Bubbling

[0168] Static bending strength: 120MPa

[0169] Elastic modulus: 10.5 GPa

[0170] 24-hour moisture absorption expansion rate: 8.5%.

Claims

1.A method for preparing a glue-free fiberboard based on fiber pretreatment, comprising: immersing wood fibers in an aqueous NaOH solution with a mass concentration of 0.8%-1.5%, and performing a defibration treatment at a temperature of 85-95 ℃ for 2-4 h to obtain defibrated fibers by filtration; immersing the defibrated fibers in an NaOH / urea / water solution with a mass ratio of (5-9) : 12 : (79-83), and performing a fiber dissolution treatment at a temperature of -18- -5 ℃ for 4-8 h, then adding a certain amount of low-concentration acid at room temperature to perform a fiber regeneration treatment, and obtaining regenerated fibers by filtration; washing the regenerated fibers with water until the pH is neutral, and performing a drying treatment at a temperature of 50-70 ℃ until the moisture content of the fibers is 12%-15% to obtain pretreated fibers; and hot-pressing the pretreated fibers after being scattered and laid to obtain the glue-free fiberboard, wherein the hot-pressing temperature is 185-195 ℃, and the hot-pressing pressure is 6-8 MPa. characterized in that In the method, the solid-liquid ratio of the wood fibers to the aqueous NaOH solution is 1 g : (50-100) mL; and the solid-liquid ratio of the defibrated fibers to the NaOH / urea / water solution is 1 g : (50-100) mL. 2.The method of claim 1, wherein the mass concentration of the aqueous NaOH solution is 1%, the defibration treatment temperature is 90 ℃, and the treatment time is 3 h; the mass ratio of the NaOH / urea / water solution is 7:12:81, the fiber dissolution treatment temperature is -12 ℃, and the treatment time is 6 h; the solid-liquid ratio of the wood fibers to the aqueous NaOH solution is 1 g : 70 mL; the solid-liquid ratio of the defibrated fibers to the NaOH / urea / water solution is 1 g : 70 mL; the drying treatment temperature is 60 ℃; the hot-pressing temperature is 190 ℃, and the hot-pressing pressure is 7 MPa. 3.The method of claim 1, wherein the low-concentration acid is a hydrochloric acid solution or a sulfuric acid solution. 4.The method of claim 1, wherein H of the low concentration acid + The molar ratio of the OH content of the low concentration acid to the OH content of NaOH in the NaOH / urea / water solution is (0.5-1):1 - The molar ratio of the OH content of the low concentration acid to the OH content of NaOH in the NaOH / urea / water solution is (0.5-1):1 + The ion concentration is 0.8-1.3 mol / L. the wood fibers are one or more of eucalyptus wood fibers, poplar wood fibers, fir wood fibers, pine wood fibers, mixed wood fibers, and bamboo fibers. 5.The method of claim 1, wherein the drying treatment is performed in a constant temperature and humidity environment with a relative humidity of 60%-80%. 6.A glue-free fiberboard prepared by the method of any one of claims 1-5. ​ ​ ​ ​ ​