A fiber pretreatment method and the application of the treated fibers

Abstract

This invention discloses a fiber pretreatment method and the application of the pretreated fibers. The method involves dissolving the fibers in dimethylacetamide at room temperature to obtain dissolved fibers. These dissolved fibers are then treated in a LiCl / DMAc solution. After removing the reagents by squeezing, the fibers are washed, filtered, and dried to obtain pretreated fibers. These pretreated fibers are then used in the preparation of glue-free laminated fiberboard. The LiCl / DMAc solution treatment significantly increases the area of ​​the self-bonding interface of the fibers and enhances the surface hydroxyl activity. During the glue-free bonding process, not only do the degradation products of hemicellulose and lignin self-bond, but cellulose also melts and regenerates to form filaments, which then self-bond under hydrogen bonding, significantly improving the performance of the glue-free laminated board.

Description

Technical Field

[0001] This invention relates to the field of fiberboard manufacturing technology, and more specifically to a fiber pretreatment method and the application of the treated fibers. Background Technology

[0002] my country is the world's largest producer and consumer of fiberboard, with an annual output of 50 million cubic meters. 90% of fiberboard production uses urea-formaldehyde resin adhesives, posing a risk of formaldehyde pollution. A smaller portion uses isocyanate adhesives, but these are costly and prone to cracking. From both environmental and economic perspectives, developing adhesive-free fiberboard has become an urgent need for green production and improved efficiency in the fiberboard industry under the "dual-carbon" strategy.

[0003] Glue-free plywood refers to engineered fiberboard made by hot-pressing wood fibers or other plant fibers without adding adhesives. Because the fibers rely on their own binding force during hot pressing to form the board, and the fibers themselves have low adhesive content, pretreatment is necessary. Commonly used acid and alkali pretreatment methods can damage the fiber's crystalline structure, affecting its properties. This results in glue-free fiberboard having inferior mechanical properties and water resistance compared to traditional fiberboard. Furthermore, acid and alkali pretreatment can corrode equipment, and the chemical residues remain in the fibers, causing the glue-free fiberboard to degrade too quickly in acidic or alkaline environments, thus shortening its lifespan.

[0004] Therefore, green and sustainable fiber pretreatment technologies and methods for preparing high-performance glue-free plywood still need to be developed. Summary of the Invention

[0005] In view of this, the present invention provides a recyclable fiber pretreatment method and the application of the pretreated fibers. By changing the surface structure through pretreatment, the fibers can be applied to the preparation of fiberboard to obtain glue-free plywood with excellent mechanical properties and water resistance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] First, this invention provides a fiber pretreatment method, comprising the following steps:

[0008] (1) The fiber was placed in dimethylacetamide at room temperature to dissolve it, and dissolved fiber was obtained;

[0009] (2) Dissolve lithium chloride in dimethylacetamide to obtain a solution;

[0010] (3) Place the fibrous material from step (1) into the solution from step (2), heat it for a period of time, and then cool it to room temperature for further treatment.

[0011] (4) Remove the reagent by physical squeezing the fiber after treatment in step (3), rinse the fiber with water and filter it, and then dry it to obtain pretreated fiber.

[0012] Preferably, the fiber in step (1) includes one or more of eucalyptus fiber, poplar fiber, fir fiber, Masson pine fiber, mixed wood fiber, and bamboo fiber, more preferably poplar fiber and moso bamboo fiber.

[0013] Preferably, in step (1), the ratio of fiber to dimethylacetamide is 1g:10mL to 1g:100mL, and the dissolution time is 2h to 12h. More preferably, the ratio of fiber to dimethylacetamide is 1g:50mL, and the dissolution time is 6h to 8h.

[0014] The advantages of the above-mentioned preferred technical solution are: if the material-to-liquid ratio is too low, it is difficult to completely wet the fiber and the dissolution effect is poor; if it is too high, it will cause solvent waste.

[0015] Preferably, in step (2), the lithium chloride has a mass fraction of 5% to 8% in dimethylacetamide, more preferably 6% to 7%.

[0016] Preferably, in step (3), the ratio of the fiber to the solution is 1g:10mL to 1g:100mL, more preferably 1g:50mL. The treatment process is to first treat at 80℃ to 90℃ for 1h to 2h, preferably at 85℃ for 1.5h, and then cool to room temperature for 12 to 18h.

[0017] The advantages of the above-mentioned preferred technical solution are as follows: If the material-to-liquid ratio is too low, the processing process will not be able to completely wet the fibers; if it is too high, the solution will have excessively high permeability on the fiber surface, severely damaging the crystallinity of the surface cellulose and reducing its self-adhesive properties. Conversely, if the processing 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 material-to-liquid ratio and processing time appropriately ensures the optimal dissolution effect.

[0018] Preferably, in step (4), the drying is carried out by sun-drying or drying at 40°C to 60°C until the moisture content is 8% to 12%. More preferably, the drying temperature is 50°C and the moisture content is 10%.

[0019] The advantages of the above-mentioned preferred technical solutions are as follows: When the treated fibers are used in the production of self-adhesive fiberboard, excessively high drying temperatures cause severe fiber clumping, hindering fiber laying and leading to uneven density in the self-adhesive board. Conversely, excessively low drying temperatures result in prolonged drying times, increasing manufacturing energy consumption. While air drying is an energy-saving method, it is not optimal due to its long processing time. Furthermore, hot-pressing the preparation of self-adhesive fiberboard at a high moisture content of 8%–12% allows water molecules to disrupt the hydrogen bonds of cellulose in the fibers, facilitating the release of hydroxyl sites on the cellulose surface and promoting more hydrogen bonding with the activated fiber surface. Simultaneously, water molecules act as an interfacial transition 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 moisture within a short hot-pressing time, leading to bubbling in the self-adhesive fiberboard. Conversely, if the moisture content is too low, the role of water molecules is insufficient.

[0020] The present invention also provides a pretreated fiber obtained by the method described in the above technical solution.

[0021] The present invention also provides a pretreated fiber obtained by the method described above, or the application of the pretreated fiber in the preparation of glue-free plywood.

[0022] Furthermore, the application includes the following steps: breaking up and laying the pretreated fibers, and hot-pressing them into shape.

[0023] Preferably, the paving thickness is 2mm to 12mm, and the density is 0.8 to 1.2g / cm³. 3 The hot pressing temperature is 150℃~190℃, the hot pressing pressure is 4~8MPa, and the hot pressing time is 2~4mm / min.

[0024] More preferably, the hot pressing temperature is 180°C and the time is 3 mm / min.

[0025] The effects of the above-mentioned preferred technical solution are as follows: the improvement of fiber self-adhesion performance depends on two factors. First, lignin and hemicellulose in the fiber degrade under certain temperature and humidity to form small molecules, and the degradation products self-adhede. 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-adhesion performance.

[0026] Therefore, 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.

[0027] 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.

[0028] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a fiber pretreatment method and the application of the pretreated fibers in the preparation of fiberboard, which has the following beneficial effects:

[0029] After treatment with LiCl / DMAc solution, the hemicellulose and lignin on the fiber surface are degraded, cellulose dissolves, and after rinsing with water, cellulose regenerates, forming cellulose filaments on the fiber surface. This significantly increases the area of ​​the self-gluing interface and enhances the surface hydroxyl activity. During the glue-free gluing process, not only do the degradation products of hemicellulose and lignin self-glu, but the cellulose filaments also self-glu through hydrogen bonding. The three major cellulose components in the fiber each play a self-gluing role, significantly improving the performance of glue-free gluing boards. The treatment time, temperature, and concentration of the LiCl / DMAc solution are crucial influencing factors. Too low a concentration, temperature, or time results in poor cellulose dissolution, while too high a concentration, temperature, or time leads to excessive cellulose dissolution, which can disrupt the cellulose crystal structure and reduce the fiber's mechanical strength. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0031] Figure 1 A schematic diagram showing the difference between fiber pretreatment and pretreatment;

[0032] Figure 2 Scanning electron microscope images showing the difference between wood fiber pretreatment and pretreatment. Detailed Implementation

[0033] 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.

[0034] In the following examples and comparative examples, the static bending strength testing process of the prepared boards is as follows:

[0035] 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.

[0036] static bending strength formula:

[0037] σ: Static bending strength of the specimen, MPa;

[0038] F max : Maximum load at which the specimen fails, in N;

[0039] l: Distance between the two supports, mm;

[0040] b: Specimen width, mm;

[0041] t: Specimen thickness, mm.

[0042] The elastic modulus test method for the prepared plates is the same as that for static bending strength.

[0043] Elastic modulus formula:

[0044] E b : Elastic modulus of the specimen, MPa;

[0045] l: Distance between the two supports, mm;

[0046] b: Specimen width, mm;

[0047] t: Specimen thickness, mm;

[0048] F2-F1: The increase in load within the straight segment of the load-deflection curve, in N;

[0049] 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.

[0050] The test method for the water absorption swelling rate of the prepared board is as follows:

[0051] 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.

[0052] Formula for water absorption swelling rate:

[0053] T: Water absorption thickness swelling rate, %;

[0054] t1: Specimen thickness before immersion in water, mm;

[0055] t2: Specimen thickness after immersion in water, mm.

[0056] Example 1

[0057] (1) Place 16g of poplar fiber in 800mL of dimethylacetamide (DMAc) and let it dissolve at room temperature for 6h;

[0058] (2) Dissolve lithium chloride (LiCl) in DMAc to prepare 800 mL of a 6% (w / w) LiCl / DMAc solution;

[0059] (3) Place the poplar fiber that was loosened in step (1) in the solution of step (2), treat it at 85°C for 1 hour, and then cool it to room temperature for another 12 hours.

[0060] (4) Physically squeeze the poplar fiber treated in step (3) to remove LiCl / DMAc, and recover the LiCl / DMAc reagent for reuse. Rinse the filtered poplar fiber with water and dry the poplar fiber in an oven at 50°C until the moisture content is 8%.

[0061] (5) Spread the dried poplar fibers in a mold with dimensions of 100mm×100mm×2mm and a density of 0.8g / cm³. 3 The hot-pressing temperature was 150℃, the hot-pressing pressure was 4MPa, and the hot-pressing time was 1min, resulting in glue-free laminated poplar fiberboard.

[0062] The obtained poplar fiberboard was tested and found to be:

[0063] Static bending strength: 36 MPa;

[0064] Elastic modulus: 3.2 GPa;

[0065] 24-hour moisture absorption expansion rate: 8%.

[0066] Example 2

[0067] (1) Place 50g of bamboo fiber in 2000mL of dimethylacetamide (DMAc) and let it dissolve at room temperature for 7h;

[0068] (2) Dissolve lithium chloride (LiCl) in DMAc to prepare 2000 mL of a 7% (w / w) LiCl / DMAc solution;

[0069] (3) Place the bamboo fiber that was loosened in step (1) in the solution of step (2), treat it at 85°C for 1.5h, and then cool it to room temperature for 15h.

[0070] (4) Physically squeeze the bamboo fiber in step (3) to remove LiCl / DMAc, and recycle the LiCl / DMAc for reuse. Rinse the bamboo fiber with water and dry it in the sun until the moisture content is 10%.

[0071] (5) Spread the dried bamboo fibers out in a mold with dimensions of 100mm×100mm×5mm and a density of 1.0g / cm³. 3 The hot-pressing temperature was 180℃, the hot-pressing pressure was 5MPa, and the hot-pressing time was 2.5min, resulting in glue-free laminated bamboo fiberboard.

[0072] The obtained bamboo fiberboard was tested and found to be:

[0073] Static bending strength: 96 MPa;

[0074] Elastic modulus: 12 GPa;

[0075] 24-hour moisture absorption expansion rate: 3%.

[0076] Example 3

[0077] (1) Place 120g of cedar fiber in 1200mL of dimethylacetamide (DMAc) and let it dissolve at room temperature for 8h;

[0078] (2) Dissolve lithium chloride (LiCl) in DMAc to prepare 1200 mL of 8% LiCl / DMAc solution;

[0079] (3) Place the cedar fiber that was loosened in step (1) in the solution of step (2), treat it at 90°C for 2 hours, and then cool it to room temperature for 18 hours.

[0080] (4) Physically squeeze the poplar fiber treated in step (3) to remove LiCl / DMAc, and recover the LiCl / DMAc reagent for reuse. Rinse the fir fiber with water and dry the fir fiber in an oven at 50°C until the moisture content is 12%.

[0081] (5) Spread the dried cedar fibers in a 100mm×100mm×10mm size, with a density of 1.2g / cm³. 3 The hot-pressing temperature was 190℃, the hot-pressing pressure was 6MPa, and the hot-pressing time was 2.5min, resulting in glue-free laminated fir fiberboard.

[0082] The obtained fir fiberboard was tested and found to be:

[0083] Static bending strength: 110 MPa;

[0084] Elastic modulus: 15 GPa;

[0085] 24-hour moisture absorption expansion rate: 2.5%.

[0086] Example 4

[0087] (1) Place 50g of poplar fiber in 5000mL of dimethylacetamide (DMAc) and let it dissolve at room temperature for 7h;

[0088] (2) Dissolve lithium chloride (LiCl) in DMAc to prepare 5000 mL of a 7% (w / w) LiCl / DMAc solution;

[0089] (3) Place the poplar fiber that was loosened in step (1) in the solution of step (2), treat it at 85°C for 1.5 h, and then cool it to room temperature for another 15 h.

[0090] (4) Physically squeeze the poplar fiber treated in step (3) to remove LiCl / DMAc, and recover the LiCl / DMAc reagent for reuse. Rinse the filtered poplar fiber with water and dry the poplar fiber in an oven at 50°C until the moisture content is 12%.

[0091] (5) Loosen and lay the dried poplar fibers in a mold with dimensions of 100mm × 100mm × 5mm and a density of 1.0g / cm³. 3 The hot-pressing temperature was 180℃, the hot-pressing pressure was 8MPa, and the hot-pressing time was about 1.6min, resulting in glue-free laminated poplar fiberboard.

[0092] The obtained poplar fiberboard was tested and found to be:

[0093] Static bending strength: 104 MPa;

[0094] Elastic modulus: 11 GPa;

[0095] 24-hour moisture absorption expansion rate: 2.8%.

[0096] Comparative Example 1

[0097] Fiberboard was prepared using poplar wood fibers that had not been treated with LiCl / DMAc solution, following the same method as in Example 4. The test results were as follows:

[0098] Static bending strength: 55 MPa;

[0099] Elastic modulus: 2 GPa;

[0100] 24-hour moisture absorption expansion rate: 25%.

[0101] Comparative Example 2

[0102] The difference from Example 4 is that the hot-pressing temperature was 100°C, and the test results are as follows:

[0103] Static bending strength: 73 MPa;

[0104] Elastic modulus: 5 GPa;

[0105] 24-hour moisture absorption expansion rate: 11%.

[0106] Comparative Example 3

[0107] The difference from Example 4 is that the hot-pressing temperature was 200°C, and the test results are as follows:

[0108] blackened surface

[0109] Static bending strength: 54 MPa;

[0110] Elastic modulus: 12 GPa

[0111] 24-hour moisture absorption expansion rate: 2%.

[0112] Comparative Example 4

[0113] The difference from Example 4 is that the sample was dried to a moisture content of 7%, and the test results were as follows:

[0114] Static bending strength: 79 MPa;

[0115] Elastic modulus: 6 GPa;

[0116] 24-hour moisture absorption expansion rate: 9%.

[0117] Comparative Example 5

[0118] The difference from Example 4 is that the sample was dried to a moisture content of 13%, and the test results were as follows:

[0119] Bubbling;

[0120] Static bending strength: 44 MPa;

[0121] Elastic modulus: 4 GPa;

[0122] 24-hour moisture absorption expansion rate: 19%.

[0123] Experimental Example 1

[0124] The fibers treated in Example 4 and the untreated fibers in Comparative Example 1 were tested, and the results are shown in the appendix. Figure 2 As shown, Figure 2 In the figures, the top two images are fiber morphology diagrams of Comparative Example 1 without treatment, and the bottom two images are fiber morphology diagrams after treatment in Example 4. As can be seen from the figures, the surface of the treated fiber is rough, it is fibrillated, the cellulose filaments are exposed, and the surface hydroxyl groups are increased, while the surface of the untreated fiber is smooth.

[0125] The various embodiments described in this specification are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for producing a glueless fiberboard, characterized by, The method comprises the following steps: dispersing and paving pretreated fibers, hot-pressing forming, paving thickness 2mm-12mm, density 0.8-1.2g / cm 3 , hot-pressing temperature 150℃-190℃, hot-pressing pressure 4-8MPa, hot-pressing time 2-4mm / min; wherein the fiber pretreatment method comprises the following steps: (1) The fiber was placed in dimethylacetamide at room temperature to dissolve it, and the fiber to dimethylacetamide ratio was 1g:10mL to 1g:100mL, and the dissolving time was 2h to 12h. (2) Dissolve lithium chloride in dimethylacetamide to obtain a solution, wherein the mass fraction of lithium chloride in dimethylacetamide is 5% to 8%; (3) Place the sloughed fiber from step (1) into the solution from step (2), heat it for a period of time, and then cool it down to room temperature for further treatment. The material-liquid ratio of the sloughed fiber to the solution is 1g:10mL~1g:100mL. The treatment process is to first treat it at 80℃~90℃ for 1h~2h, and then cool it down to room temperature for 12~18h. (4) Remove the reagent by physical squeezing the fiber after treatment in step (3), rinse the fiber with water to filter it, form cellulose filaments on the fiber surface, and then dry it by sun drying or drying at 40℃~60℃ to a moisture content of 8%~12% to obtain pretreated fiber.

2. The method for preparing a glue-free plywood according to claim 1, characterized in that, The fibers mentioned in step (1) include one or more of the following: eucalyptus fiber, poplar fiber, fir fiber, Masson pine fiber, mixed wood fiber, and bamboo fiber.

3. A pretreated fiber obtained by the method according to any one of claims 1-2.

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