Preparation method and cyclic treatment method for high-strength, high-toughness and recyclable bionic structure fiberboard

Abstract

A preparation method and cyclic treatment method for a high-strength, high-toughness and recyclable bionic structure fiberboard. The preparation method and cyclic treatment method for a fiberboard involved in the present invention solve the problem in the prior art of impossible preparation of green, environmentally-friendly, high-strength, high-toughness and recyclable bionic structure fiberboards. The preparation method comprises: 1, pretreatment; 2, swelling treatment; 3, dissociation and dispersion treatments; 4, centrifugal treatment; 5, hydrogel construction; and 6, densification treatment. The cyclic treatment comprises: placing a high-strength, high-toughness and recyclable bionic structure fiberboard in a crusher for crushing treatment, and then repeating swelling treatment, dissociation and dispersion treatments, centrifugal treatment, hydrogel construction and densification treatment. The present invention is used for preparation and cyclic treatment of high-strength, high-toughness and recyclable bionic structure fiberboards.

Description

A preparation method of high-strength, high-toughness, recyclable biomimetic structural fiberboard and its recycling treatment method Technical Field

[0001] The invention relates to a preparation method of fiberboard and a recycling treatment method thereof. Background Art

[0002] Through millions of years of evolution and development, plants and animals in nature have achieved a perfect balance between exquisite structural design and exceptional mechanical properties. Among numerous natural materials, organisms such as shells, bones, and teeth utilize complex, ordered, multi-scale hierarchical structures to achieve strength, hardness, and toughness superior to their native components. The nacre within shells, in particular, serves as a model for high-strength, ultra-tough layered composites. Aragonite layers and organic matter interact through layer-by-layer stacking, forming the "brick-and-mortar" structure commonly used in architecture. This unique assembly and multi-layered structure give nacre a tensile strength 3,000 times greater than that of natural aragonite, while also providing excellent toughening properties. During fracture, the aragonite layers induce frequent crack deflection, triggering organic bridging. This effectively transfers stress and dissipates energy through the slip resistance and fiber pullout between the aragonite layers at the strong interface. This provides design inspiration for the development of new lightweight, high-strength composite materials and is driving the rapid development of biomimetic materials.

[0003] Cellulose fiber is one of the most abundant naturally renewable polymers in plant cell walls. It boasts advantages such as wide availability, high mechanical properties, low thermal expansion, ease of modification, good biocompatibility, and low density. In recent years, the use of natural fibers from wood processing residues as a reinforcing phase to produce environmentally friendly, high-performance composites has been on the rise, finding widespread application in aerospace, industrial construction, home furnishings, product packaging, and other fields. However, current high-strength all-cellulose structural materials are often processed by physical or chemical methods, grinding or oxidizing the cellulose raw material into nanocellulose. This process is not only complex and energy-intensive, but also difficult to scale up to produce large-scale bulk structures due to the gelation behavior of nanocellulose at low concentrations, limiting the production to large fibers or thin films. Other production processes for fiber-reinforced composites that can be produced on a large scale include both adhesive-free and adhesive-based processes. Fiberboard produced using formaldehyde-based adhesives carries the risk of harmful gas release, while inorganic fiberboard produced using cross-linking bonding with inorganic salts, inorganic acids, inorganic bases, metal oxides, and hydroxides also presents challenges in large-scale application due to its high density and processing difficulties. In addition, both of them generally lack the microscopic and macroscopic structural and functional design of the fibers, and have the disadvantages of weak interfacial bonding between cellulose fibers and adhesives (reinforcement phase and matrix material) and low mechanical strength of fiberboard. At the same time, because their composition is relatively complex and difficult to separate and recycle, both of them cannot be recycled.

[0004] In summary, the existing technology cannot produce green, environmentally friendly, high-strength, high-toughness, and recyclable biomimetic structural fiberboard.

[0005] Summary of the Invention

[0006] The present invention aims to solve the problem that the existing technology cannot prepare green, environmentally friendly, high-strength, high-toughness and recyclable biomimetic structural fiberboard, and further provides a preparation method of high-strength, high-toughness and recyclable biomimetic structural fiberboard and its recycling treatment method.

[0007] A preparation method of a high-strength, high-toughness, recyclable biomimetic structural fiberboard and a recycling treatment method thereof are carried out according to the following steps:

[0008] 1. Preprocessing:

[0009] The wood processing residue is subjected to a partial lignin removal and drying treatment in sequence to obtain a wood processing residue from which the partial lignin has been removed;

[0010] 2. Swelling treatment:

[0011] Under room temperature conditions, the wood processing residue from which part of the lignin has been removed is immersed in an activation solution for 30 minutes to 3 hours, and then the activation solution is replaced and the immersion is repeated 1 to 5 times to obtain a swollen wood processing residue;

[0012] 3. Dissociation and dispersion treatment:

[0013] The swollen wood processing residue is added to a cellulose solvent, stirred continuously for 5 to 30 minutes at a temperature of -20 to 150 degrees Celsius, and finally allowed to react for 5 to 10 minutes to obtain a high-viscosity, milky white, multi-scale cellulose mixed solution;

[0014] The density of the high viscosity, milky white multi-scale cellulose mixed solution is 0.8 g / cm 3 ~3g / cm 3 ;

[0015] 4. Centrifugal treatment:

[0016] The high-viscosity, milky white multi-scale cellulose mixed solution is placed in a centrifuge for centrifugation to remove the bottom sediment to obtain a high-viscosity, uniformly dispersed multi-scale cellulose solution;

[0017] The density of the high viscosity, uniformly dispersed multi-scale cellulose solution is 0.5 g / cm 3 ~2g / cm 3 ;

[0018] 5. Hydrogel construction:

[0019] A high-viscosity, evenly dispersed multi-scale cellulose solution is poured into a mold, left to stand for 2 to 10 hours, and then immersed in a regeneration solution for 5 to 20 hours after solidification. Finally, it is washed to obtain a uniform multi-scale cellulose hydrogel.

[0020] 6. Densification treatment:

[0021] The uniform multi-scale cellulose hydrogel is placed in a hot press and hot pressed to obtain a high-strength, high-toughness, recyclable biomimetic structural fiberboard.

[0022] A recycling method for high-strength, high-toughness, recyclable biomimetic structural fiberboard is carried out according to the following steps:

[0023] The high-strength, high-toughness, recyclable bionic structural fiberboard is placed in a crusher for crushing treatment, and then the swelling treatment, dissociation and dispersion treatment, centrifugal treatment, hydrogel construction and densification treatment are repeated to complete the recycling treatment method.

[0024] The beneficial effects of the present invention are:

[0025] The present invention utilizes a dissociation-recombination cellulose fiber method to fully dissociate the cellulose skeleton in the wood processing residue into cellulose fibers, and then uniformly disperses them in a cellulose solution with the help of external force. This process not only avoids the high-energy mechanical grinding and homogenization process used for the same purpose, but also solves the problem of uneven sizing in the traditional fiberboard manufacturing process. After being placed in the regeneration solution, the dissociated and dispersed cellulose fibers are reassembled under the connection of the regenerated nanocellulose network, interweaving to form a multi-scale cellulose hydrogel, realizing an ingenious and reasonable micro / nanostructure design. By utilizing the high contact area, high-density hydrogen bonds and van der Waals forces between the fibers, the multi-scale cellulose hydrogel forms a shell-like "brick-and-mud" structure during the hot pressing process. With the surface-dissolved cellulose fibers as the hard phase material and the regenerated nanocellulose network as the soft phase material, this strong and sophisticated multi-scale micro / nanocellulose network structure replaces the bonding effect of traditional organic and inorganic adhesives, provides ultra-high interfacial strength between the cellulose fibers, and avoids the use of additives and modifiers, simplifying the preparation process, and obtaining an environmentally friendly, biodegradable, lightweight, and high-strength and high-toughness cellulose board. Furthermore, because fiberboard is made entirely of cellulose, it can be recycled and crushed after it has lost its usefulness, reusing it as raw material for the production of new fiberboard. This bottom-up, scalable production method holds great promise for applications in aircraft, construction, automotive, and other fields.

[0026] The invention is used for a preparation method of a high-strength, high-toughness, recyclable biomimetic structural fiberboard and a recycling treatment method thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a photograph of a high-viscosity, uniformly dispersed multi-scale cellulose solution prepared in step 4 of Example 1;

[0028] FIG2 is a photograph of uniform multi-scale cellulose hydrogels after pouring a high-viscosity, uniformly dispersed multi-scale cellulose solution into different molds in step five of Example 1;

[0029] FIG3 is an electron micrograph of the internal network structure of the uniform multi-scale cellulose hydrogel prepared in step 5 of Example 1;

[0030] FIG4 is a photograph of the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1;

[0031] FIG5 is a scanning electron micrograph of a cross-section of a high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1, where 1 is cellulose fiber and 2 is regenerated nanocellulose;

[0032] FIG6 is a graph showing bending stress-strain curves, wherein 1-1 is a high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1, 1-2 is a pure fiberboard prepared in Comparative Experiment 1, and 1-3 is a regenerated fiberboard without cellulose fibers prepared in Comparative Experiment 2;

[0033] FIG7 is a cross-sectional fracture electron microscope image of the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1;

[0034] FIG8 is a fracture toughness bar graph, 1-1 is a high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1, 1-2 is a pure fiberboard prepared in Comparative Experiment 1, and 1-3 is a cellulose-free regenerated fiberboard prepared in Comparative Experiment 2;

[0035] FIG9 is a tensile stress-strain curve of the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1;

[0036] FIG10 is a photo of fiber sheets used as raw materials after the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1 is crushed in Example 2;

[0037] FIG11 is a photograph of the uniform multi-scale cellulose hydrogel prepared in step 5 of Example 2;

[0038] FIG12 is a scanning electron microscope image of a cross section of a high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared by recycling in Example 2, where 1 is cellulose fiber and 2 is regenerated nanocellulose;

[0039] FIG13 is a bending stress-strain curve of the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared by recycling in Example 2;

[0040] FIG14 is a photograph of a high-strength, high-toughness, recyclable biomimetic structural fiber cup or bowl prepared in Example 3;

[0041] FIG15 is a load-bearing photograph of the high-strength, high-toughness, recyclable biomimetic structural fiber bowl prepared in Example 3. DETAILED DESCRIPTION

[0042] Specific embodiment 1: This embodiment provides a method for preparing a high-strength, high-toughness, recyclable biomimetic structural fiberboard and its recycling treatment method, which is carried out in the following steps:

[0043] 1. Preprocessing:

[0044] The wood processing residue is subjected to a partial lignin removal and drying treatment in sequence to obtain a wood processing residue from which the partial lignin has been removed;

[0045] 2. Swelling treatment:

[0046] Under room temperature conditions, the wood processing residue from which part of the lignin has been removed is immersed in an activation solution for 30 minutes to 3 hours, and then the activation solution is replaced and the immersion is repeated 1 to 5 times to obtain a swollen wood processing residue;

[0047] 3. Dissociation and dispersion treatment:

[0048] The swollen wood processing residue is added to a cellulose solvent, stirred continuously for 5 to 30 minutes at a temperature of -20 to 150 degrees Celsius, and finally allowed to react for 5 to 10 minutes to obtain a high-viscosity, milky white, multi-scale cellulose mixed solution;

[0049] The density of the high viscosity, milky white multi-scale cellulose mixed solution is 0.8 g / cm 3 ~3g / cm 3 ;

[0050] 4. Centrifugal treatment:

[0051] The high-viscosity, milky white multi-scale cellulose mixed solution is placed in a centrifuge for centrifugation to remove the bottom sediment to obtain a high-viscosity, uniformly dispersed multi-scale cellulose solution;

[0052] The density of the high viscosity, uniformly dispersed multi-scale cellulose solution is 0.5 g / cm 3 ~2g / cm 3 ;

[0053] 5. Hydrogel construction:

[0054] A high-viscosity, evenly dispersed multi-scale cellulose solution is poured into a mold, left to stand for 2 to 10 hours, and then immersed in a regeneration solution for 5 to 20 hours after solidification. Finally, it is washed to obtain a uniform multi-scale cellulose hydrogel.

[0055] 6. Densification treatment:

[0056] The uniform multi-scale cellulose hydrogel is placed in a hot press and hot pressed to obtain a high-strength, high-toughness, recyclable biomimetic structural fiberboard.

[0057] In step 2, the wood processing residue from which some lignin has been removed is immersed in an activation liquid. After soaking for a period of time, the agglomerates therein are crushed with a glass rod so that they can fully absorb the activation liquid. When the activation liquid is replaced, the wood processing residue is appropriately squeezed to discharge the previously absorbed activation liquid, and then re-immersed to absorb the newly replaced activation liquid, so as to fully weaken the interaction force between the cellulose fibers in the wood processing residue.

[0058] The purpose of step 2 is mainly to fully swell the cellulose fibers in the wood processing residue from which part of the lignin has been removed and to weaken the hydrogen bonding between the cellulose fibers.

[0059] Principle of Step 2: Although wood processing residues vary in macroscopic size and morphology, their microstructure is consistent with that of natural wood, primarily composed of three polymers: cellulose, hemicellulose, and lignin. They are porous, hierarchical, and anisotropic. The basic skeleton of their cell walls is primarily composed of orderly assembled, clustered cellulose molecular chains. Strong hydrogen bonds within and between cellulose molecules hinder contact between the cellulose solvent and the cellulose molecules. However, after treatment with the activation solution, the exposed cellulose microfibrils in the cellulose fibers of wood processing residues partially break open their hydrogen bonds, resulting in a more relaxed molecular chain configuration that increases their contact with the cellulose solvent, thereby promoting the dissociation of the cellulose skeleton and the dissolution of the dissociated cellulose fiber surface.

[0060] In step three, the swollen wood processing residues are added to the cellulose solvent and stirred continuously, so that the wood processing residues precipitated at the bottom are redispersed in the solvent to participate in the dissolution reaction.

[0061] The purpose of step three is to promote the surface dissolution process of the partially delignified wood processing residues.

[0062] Principle of step three: the swelled wood processing residues still maintain an orderly arranged cellulose fiber skeleton. Under the action of external stirring, the partially delignified wood processing residues are fully in contact with the cellulose solvent. Thanks to the previous partial delignification treatment, some cellulose microfibrils are exposed on the surface of the wood processing residues. After being dispersed in the cellulose solvent, a cellulose dissolution reaction occurs on the surface, the hydrogen bonds between the cellulose fibers in the cellulose skeleton of the wood processing residues are broken, and the cellulose is dissolved, which promotes the dissociation of the cellulose skeleton of the wood processing residues. At the same time, due to the presence of a small amount of lignin, the cellulose fibers in the cellulose skeleton of the wood processing residues are avoided from being excessively dissolved. Under the action of external stirring and solvent dissolution, cellulose fibers with surface dissolution and relatively complete cell wall structure are obtained. After regeneration, surface nano-cellulose fibers with a large amount of nanocellulose distributed on the surface can be obtained to increase the contact area and interaction between the interfaces and improve the interface strength.

[0063] In step 4, after placing the milky white multi-scale cellulose into the centrifuge, the large pieces of fibers that are not dissolved and dispersed are precipitated to the bottom, and the upper uniform and slightly transparent cellulose solution is taken to ensure that all the cellulose fibers in the solution participate in the dissolution reaction and are dissociated and dispersed.

[0064] The purpose of step 4 is mainly to obtain a uniformly dispersed surface-dissolved multi-scale cellulose solution.

[0065] Principle of Step 4: The milky white cellulose mixed solution obtained after dissolution and dissociation contains some undecomposed aggregates, which makes it difficult to form a reasonable and effective structural design. It is also very easy to form holes during the densification process, causing structural defects, leading to stress concentration, and thus reducing the strength of the fiberboard. The cellulose mixed solution is placed in a centrifuge. Under the action of external force, the difference in gravity can be used to precipitate and remove the heavier, undispersed fiber blocks, while retaining the cross-linked and entangled cellulose fibers with natural crystalline cellulose (providing reinforcement for the fiberboard), obtaining a uniformly dispersed multi-scale cellulose solution.

[0066] In step five, the multi-scale cellulose hydrogel solidified in the mold is immersed in the regeneration liquid, forming a multi-scale micro / nanocellulose network structure inside the hydrogel, which is formed by interweaving and entanglement of surface nano-sized cellulose fibers and regenerated nano-cellulose networks.

[0067] The purpose of step five is to form a cellulose hydrogel with a multi-scale micro / nanocellulose network structure.

[0068] Principle of step five: The multi-scale cellulose hydrogel is prepared based on the dissociation and dispersion of the cellulose skeleton of the wood processing residue in the early stage, and the cellulose fibers that are exposed to cellulose microfibrils after the delignification process and then undergo surface dissolution. After soaking in the regeneration liquid, the hydrogen bonds within and between the cellulose molecules are reconnected to form a dense nano-scale regenerated cellulose network structure, and the surface nano-cellulose fibers that retain the natural cellulose crystal structure and are uniformly dispersed inside are connected to each other by utilizing the good biocompatibility, large specific surface area, van der Waals force and hydrogen bond network between cellulose fibers, and are reassembled to form a cellulose hydrogel with a multi-scale micro / nano cellulose network structure. Among them, the cellulose fibers play a mechanical supporting role as a skeleton structure, and the regenerated nanocellulose network plays an adhesive effect, laying the foundation for the strong interface between the two phases in the fiberboard with a shell-like structure.

[0069] In step six, during the hot pressing process, the multi-scale cellulose hydrogel continues to shrink and aggregate as the water evaporates, and under the action of external force, forms a high-strength, high-toughness, recyclable biomimetic structural fiberboard.

[0070] The purpose of step six is ​​to densify the multi-scale cellulose hydrogel using hot pressing to obtain a fiberboard with a shell-like "brick-mud" structure with high bending strength and high fracture toughness.

[0071] Principle of step six: During the hot pressing process, as the water evaporates, the fibers continue to shrink and aggregate. The regenerated nanocellulose shrinks violently due to its large specific surface area, forming a dense bonding layer with high hydrogen bond density between the cellulose fibers. Under the action of external force and regenerated nanocellulose, the cellulose fibers that retain natural crystalline cellulose have their internal pores compressed, forming a reinforcement similar to a brick structure, which intersects and stacks layer by layer with the bonding layer formed by the regenerated nanocellulose network. This multi-scale layered structure can produce an effective strengthening and toughening mechanism during the fracture process. It can not only achieve effective transmission of external loads, but also dissipate a large amount of energy through crack deflection, branching, bridging and fiber pull-out, changing the direction of crack propagation, inhibiting crack propagation, delaying the fracture process, and obtaining higher mechanical strength and toughness.

[0072] The beneficial effects of this specific embodiment are:

[0073] This specific embodiment uses a dissociation-recombination cellulose fiber method to fully dissociate the cellulose skeleton in the wood processing residue into cellulose fibers, and then uniformly disperses it in a cellulose solution with the help of external force. This process not only avoids the high-energy mechanical grinding and homogenization process used for the same purpose, but also solves the uneven sizing problem that exists in the traditional fiberboard manufacturing process. After being placed in the regeneration solution, the dissociated and dispersed cellulose fibers are reassembled under the connection of the regenerated nanocellulose network, interweaving to form a multi-scale cellulose hydrogel, realizing an ingenious and reasonable micro / nanostructure design. By utilizing the high contact area, high-density hydrogen bonds and van der Waals forces between the fibers, the multi-scale cellulose hydrogel forms a shell-like "brick-and-mud" structure during the hot pressing process. With the surface-dissolved cellulose fibers as the hard phase material and the regenerated nanocellulose network as the soft phase material, this strong and sophisticated multi-scale micro / nanocellulose network structure replaces the bonding effect of traditional organic and inorganic adhesives, provides ultra-high interfacial strength between cellulose fibers, and avoids the use of additives and modifiers, simplifying the preparation process, and obtaining an environmentally friendly, biodegradable, lightweight, and high-strength and high-toughness cellulose board. Furthermore, because fiberboard is made entirely of cellulose, it can be recycled and crushed after it has lost its usefulness, reusing it as raw material for the production of new fiberboard. This bottom-up, scalable production method holds great promise for applications in aircraft, construction, automotive, and other fields.

[0074] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the size of the wood processing residue in step 1 is 0.3 mm to 2.5 cm. Other aspects are the same as specific embodiment 1.

[0075] The wood processing residues described in this embodiment are softwood and hardwood, and wood powder of 60 mesh and above is removed.

[0076] Specific embodiment three: This embodiment differs from either specific embodiment one or two in that the partial lignin removal described in step one is specifically carried out according to the following steps: immersing the wood processing residue in a delignification solution, heating it in a water bath at a temperature of 60°C to 90°C for 10 to 15 hours, then soaking it in deionized water at a temperature of 20°C to 50°C for 1 to 3 hours, and repeating the deionized water soaking two to four times to obtain the wood processing residue from which the partial lignin has been removed. Other steps are the same as those in specific embodiment one or two.

[0077] Specific embodiment 4: This embodiment differs from Specific embodiments 1 to 3 in that the delignification solution is a mixed solution of sodium chlorite solution and acetic acid buffer, 1% to 30% by mass hydrogen peroxide, 1% to 30% by mass sodium hypochlorite solution, or 1% to 30% by mass anthraquinone solution; and the mixed solution of sodium chlorite solution and acetic acid buffer is a mixture of 5% by mass sodium chlorite solution and acetic acid buffer with a pH of 4.6 in a volume ratio of 30:1. Other aspects are the same as Specific embodiments 1 to 3.

[0078] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the drying process in step 1 is carried out at a temperature of 40° C. to 110° C. for 5 to 15 hours. Other steps are the same as specific embodiments 1 to 4.

[0079] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the activation solution in step 2 is dimethylacetamide, dimethylformamide, or a lithium chloride / dimethylacetamide solution with a lithium chloride mass fraction of 1% to 6%. Other steps are the same as specific embodiments 1 to 5.

[0080] Specific embodiment 7: This embodiment differs from any one of specific embodiments 1 to 6 in that the cellulose solvent in step 3 is one or a mixture of the following: an 85% by mass N-methylmorpholine-N-oxide solution, 1-allyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride, a dimethylacetamide / lithium chloride solution containing 8% to 10% by mass lithium chloride, a sodium hydroxide / urea mixed aqueous solution, a zinc chloride / calcium chloride mixed aqueous solution, and a zinc chloride / aluminum chloride mixed aqueous solution; the sodium hydroxide / urea mixed aqueous solution contains 7% by mass sodium hydroxide and 12% by mass urea; the zinc chloride / calcium chloride mixed aqueous solution contains 72% by mass zinc chloride and 2.2% by mass calcium chloride; and the zinc chloride / aluminum chloride mixed aqueous solution contains 59% by mass zinc chloride and 6.4% by mass aluminum chloride. Other aspects are the same as specific embodiments 1 to 6.

[0081] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the regeneration solution in step 5 is anhydrous ethanol, acetone, distilled water or deionized water. Other aspects are the same as specific embodiments 1 to 7.

[0082] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the hot pressing in step 6 is carried out at a temperature of 30°C to 150°C and a pressure of 1 MPa to 10 MPa for 5 to 50 hours. Other aspects are the same as specific embodiments 1 to 8.

[0083] Specific embodiment 10: This embodiment provides a recycling method for a high-strength, high-toughness, recyclable biomimetic structural fiberboard, which is carried out in the following steps:

[0084] The high-strength, high-toughness, recyclable bionic structural fiberboard is placed in a crusher for crushing treatment, and then the swelling treatment, dissociation and dispersion treatment, hydrogel construction and densification treatment are repeated to complete the recycling treatment method.

[0085] The fiberboard is placed in a crusher to make small-sized fiber sheets. The fiber sheets should not be too large. If there are large block particles, they need to be placed back in the crusher and crushed to obtain fiber sheets.

[0086] The purpose of crushing is to increase the contact area of ​​fiber fragments, improve their swelling, dissociation and dispersion effects, obtain a uniform and viscous multi-scale cellulose mixed solution, form a multi-scale cellulose hydrogel, and after hot pressing, form a high-strength bionic structural fiberboard.

[0087] Principle: Fiberboard is a pure cellulose material, composed of cellulose fibers and regenerated nanocellulose. Cellulose fibers retain some lignin and have a short reaction time in cellulose solvents, so they retain the natural fiber cell wall structure and have a large amount of type I crystalline cellulose. With the high theoretical mechanical strength of type I crystalline cellulose, cellulose fibers act as a reinforcing phase in fiberboards to play a role in mechanical reinforcement. Similarly, a large number of cellulose microfibrils exposed on the surface of regenerated nanocellulose and wood processing residues after partial delignification can be re-dissolved with the help of cellulose solvents to obtain a viscous cellulose solution, which is placed in the regeneration liquid to form a dense regenerated nanocellulose network. Due to its huge specific surface area and high chemical reactivity, the regenerated nanocellulose network acts as a soft phase in the fiberboard to act as a binder. Therefore, the crushed fiberboard can be reused as raw material for the preparation of bionic structural fiberboard.

[0088] The following examples are used to verify the beneficial effects of the present invention:

[0089] Example 1:

[0090] A method for preparing a high-strength, high-toughness, recyclable biomimetic structural fiberboard is carried out according to the following steps:

[0091] 1. Preprocessing:

[0092] The wood processing residue is subjected to a partial lignin removal and drying treatment in sequence to obtain a wood processing residue from which the partial lignin has been removed;

[0093] 2. Swelling treatment:

[0094] At room temperature, the wood processing residue from which some lignin has been removed is immersed in an activation solution for 30 minutes, and then the activation solution is replaced and the immersion is repeated three times to obtain a swollen wood processing residue;

[0095] 3. Dissociation and dispersion treatment:

[0096] The swollen wood processing residue was added to the cellulose solvent and stirred continuously for 20 minutes at 28°C. Finally, it was allowed to react for 6 minutes to obtain a high-viscosity, milky white, multi-scale cellulose mixed solution.

[0097] The density of the high viscosity, milky white multi-scale cellulose mixed solution is 1.02 g / cm 3 ;

[0098] 4. Centrifugal treatment:

[0099] The high-viscosity, milky white multi-scale cellulose mixed solution was placed in a centrifuge and centrifuged at a speed of 2000 r / min for 5 minutes to remove the bottom sediment to obtain a high-viscosity, uniformly dispersed multi-scale cellulose solution;

[0100] The density of the high viscosity, uniformly dispersed multi-scale cellulose solution is 0.99 g / cm 3 ;

[0101] 5. Hydrogel construction:

[0102] A high-viscosity, evenly dispersed multi-scale cellulose solution was poured into a plate-shaped mold, left to stand for 8 hours, solidified, and then immersed in a regeneration solution for 10 hours. Finally, it was washed to obtain a uniform multi-scale cellulose hydrogel.

[0103] 6. Densification treatment:

[0104] The uniform multi-scale cellulose hydrogel was placed in a hot press to obtain a high-strength, high-toughness, recyclable biomimetic structural fiberboard with a length, width and thickness of 20 cm × 7 cm × 0.3 cm.

[0105] The wood processing residue described in step 1 is poplar wood shavings with a size of 0.3 mm to 2.5 cm.

[0106] The removal of part of the lignin described in step 1 is specifically carried out according to the following steps: immersing the wood processing residue in a delignification solution, heating it in a water bath at a temperature of 80°C for 12 hours, and then soaking it in deionized water at a temperature of 30°C for 1 hour, repeating the deionized water soaking 3 times to obtain a wood processing residue from which part of the lignin has been removed.

[0107] The delignification solution is a mixed solution of sodium chlorite solution and acetate buffer solution; the mixed solution of sodium chlorite solution and acetate buffer solution is a mixture of 5% sodium chlorite solution by mass and acetate buffer solution with a pH of 4.6 in a volume ratio of 30:1.

[0108] The drying treatment in step 1 is specifically heating at a temperature of 60° C. for 8 hours.

[0109] The activation solution in step 2 is a lithium chloride / dimethylacetamide solution; the mass percentage of lithium chloride in the lithium chloride / dimethylacetamide solution is 2%.

[0110] The cellulose solvent in step 3 is a dimethylacetamide / lithium chloride solution; the mass percentage of lithium chloride in the dimethylacetamide / lithium chloride solution is 8%.

[0111] The regeneration solution described in step 5 is anhydrous ethanol.

[0112] The hot pressing in step six is ​​specifically performed at a temperature of 80° C. and a pressure of 5 MPa for 15 hours.

[0113] Example 2: This example differs from Example 1 in that the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in step 6 of Example 1 is broken into cellulose flakes <0.8 mm in size. Steps 2 to 6 of Example 1 are then repeated on the cellulose flakes to obtain a recycled high-strength, high-toughness, recyclable biomimetic structural fiberboard. All other aspects are the same as in Example 1.

[0114] Example 3: This example differs from Example 1 in that, in step 5, a high-viscosity, uniformly dispersed multi-scale cellulose solution is poured into a cup- or bowl-shaped mold, left to stand for 8 hours, solidified, and then immersed in a regeneration solution for 10 hours. Finally, it is washed to obtain a uniform multi-scale cellulose hydrogel. Finally, it is dried and formed at room temperature to obtain a high-strength, high-toughness, recyclable biomimetic structural fiber cup or bowl. All other aspects are the same as in Example 1.

[0115] Comparative Experiment 1: This comparative experiment differs from Example 1 in that the wood processing residue from which some lignin was removed prepared in Step 1 of Example 1 was directly subjected to hot pressing in Step 6 to obtain a pure fiberboard. Other aspects are the same as in Example 1.

[0116] Comparative experiment 1 lacks regenerated nanocellulose and structural design, the interface strength between wood processing residues is low, and the cellulose fibers are unevenly distributed, which easily causes structural defects and thus low bending performance.

[0117] Comparative Experiment 2: This comparative experiment differs from Example 1 in that the wood processing residue in step 1 is poplar wood powder with a size of 60 mesh or above, and a cellulose-free regenerated fiberboard is obtained. Other aspects are the same as Example 1.

[0118] In comparative experiment 2, the bending strength of the regenerated fiberboard was lower due to the lack of cellulose fiber reinforcement phase containing natural crystalline cellulose.

[0119] Figure 1 is a photograph of a high-viscosity, uniformly dispersed, multi-scale cellulose solution prepared in step 4 of Example 1. As can be seen from the figure, the cellulose solution has a certain viscosity and is relatively uniform, without obvious stratification. Wood processing residues can be processed into a uniform cellulose mixed solution.

[0120] In step five of Example 1, a high-viscosity, evenly dispersed multiscale cellulose solution was poured into different molds. Figure 2 shows a photograph of the uniform multiscale cellulose hydrogels produced after pouring the high-viscosity, evenly dispersed multiscale cellulose solution into different molds. As can be seen from the figure, the hydrogel can be formed into products of varying shapes using different molds, demonstrating excellent plasticity.

[0121] Figure 3 is an electron micrograph of the internal network structure of the uniform multiscale cellulose hydrogel prepared in step 5 of Example 1. As can be seen from the figure, the hydrogel has a densely packed multiscale micro- and nanofiber network structure, with regenerated cellulose nanofibers densely packed on the cellulose fiber surface, resulting in a high specific surface area.

[0122] Figure 4 is a photograph of the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1. As can be seen from the figure, the fiberboard has a smooth and dense appearance, and the fibers are closely arranged.

[0123] Figure 5 is a scanning electron micrograph of a cross-section of a high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1. Cellulose fibers (1) and regenerated nanocellulose (2) are shown. As can be seen, the partially dissolved cellulose microfibers serve as a reinforcing phase, bonded by the regenerated nanocellulose. The resulting composites form a shell-like "brick-and-mortar" structure, exhibiting a dense, layered structure.

[0124] A high-strength, high-toughness, recyclable biomimetic structural fiberboard was subjected to bending tests according to the national standard for plastic bending properties, GB / T 9341-2008. Figure 6 shows the bending stress-strain curves, with 1-1 showing the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1, 1-2 showing the pure fiberboard prepared in Comparative Experiment 1, and 1-3 showing the cellulose-free recycled fiberboard prepared in Comparative Experiment 2. As can be seen from the figure, the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1 exhibits excellent mechanical strength, with a flexural strength of up to 222 MPa and a strain of 5.2%, demonstrating good toughening.

[0125] Figure 7 is an electron microscope image of the cross-section fracture of the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1. As can be seen from the figure, the fracture cracks of the fiberboard exhibit toughening fracture mechanisms such as crack deflection, branching, and bridging.

[0126] The fracture toughness test of high strength, high toughness and recyclable bionic structural fiberboard was carried out according to the national plane strain fracture toughness K IC The experimental method was conducted in accordance with GB / T 4161-2007. Figure 8 is a fracture toughness bar chart, with 1-1 showing the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1, 1-2 showing the pure fiberboard prepared in Comparative Experiment 1, and 1-3 showing the cellulose-free recycled fiberboard prepared in Comparative Experiment 2. As can be seen from the figure, thanks to its shell-like biomimetic "brick-and-mud" structure and the high interfacial strength between multi-scale fibers, the fiberboard prepared in Example 1 exhibits superior fracture toughness compared to the pure fiberboard and recycled fiberboard, reaching a fracture toughness of 4.4 MPa·m. 0.5 .

[0127] Tensile tests were conducted on the high-strength, high-toughness, recyclable biomimetic structural fiberboard according to the national standard for tensile testing of metallic materials, GB / T 22.1-2010. Figure 9 shows the tensile stress-strain curve of the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1. As can be seen from the figure, the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1 has excellent mechanical strength, with a tensile strength of up to 208 MPa.

[0128] Figure 10 shows the fiber sheets used as raw material after the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1 was broken down in Example 2. As can be seen from the figure, the fiberboard can be broken down into smaller pieces and reused as cellulose-rich raw material to produce fiberboard.

[0129] Figure 11 is a photograph of the uniform multi-scale cellulose hydrogel prepared in step 5 of Example 2. As can be seen from the figure, the fiber fragments obtained after shredding in Example 1 can be cross-linked and reassembled using the same treatment method to obtain a cellulose hydrogel with the same effect as in Example 1.

[0130] Figure 12 is a scanning electron micrograph of a cross-section of the high-strength, high-toughness, recyclable biomimetic fiberboard prepared through recycling in Example 2. 1 is cellulose fiber, and 2 is regenerated nanocellulose. The figure demonstrates that the uniform multi-scale cellulose hydrogel prepared in Step 5 of Example 2, after hot pressing in Step 6, yields a fiberboard with the same biomimetic "brick-and-mortar" structure.

[0131] The recycled high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 2 was subjected to a bending test according to the national standard for plastic bending properties test method GB / T 9341-2008. Figure 13 shows the bending stress-strain curve of the recycled high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 2. As can be seen from the figure, the recycled high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 2 has excellent mechanical strength, with a bending strength of up to 218 MPa.

[0132] Figure 14 is a photo of the high-strength, high-toughness, recyclable biomimetic structural fiber cup or bowl prepared in Example 3. As can be seen from the figure, the hydrogel has good plasticity.

[0133] Figure 15 is a load-bearing photograph of the high-strength, high-toughness, recyclable biomimetic fiber bowl prepared in Example 3. As can be seen from the figure, the two air-dried fiber bowls can withstand the weight of a 50kg adult standing on one leg, demonstrating good mechanical strength.

[0134] Comparative experiment three: Repeat the experiment according to Example 1 in the invention patent with application number 202110396379.2, authorization announcement number CN 113001696 B, and invention name "A method for forming high-strength, formaldehyde-free plywood by self-adhesion without adhesive".

[0135] Thanks to the bottom-up preparation method, Example 1 focuses on the preparation of block-type load-bearing materials. Furthermore, thanks to the dispersibility of the raw materials and the biomimetic design of the structure, the pretreatment process, reaction time, and process of Example 1 are further shortened and improved. The resulting samples are larger in size, more diverse in shape, have better mechanical strength, and more uniform structure. Therefore, it has a wider range of applications and greater potential for industrial production. In contrast, Experiment 3 is limited by the natural size and defects of the wood (knots, insect bites, diagonal grain, etc.), and the resulting product structure and mechanical properties are prone to unevenness and reduction.

[0136] Based on the high interfacial interaction formed by the physical entanglement, van der Waals forces and strong hydrogen bonds between highly dense multi-scale fibers, the Shore D hardness of the high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared in Example 1 is 90.8, while the Shore D hardness of the plywood in Comparative Experiment 3 is 85; at the same time, the fiberboard in Example 1 exhibits a tensile strength comparable to that of the plywood, which is 208 MPa, while the tensile strength of the plywood in Comparative Experiment 3 is 200 MPa.

[0137] With the help of a simple and efficient preparation process and a high cellulose fiber content, the fiberboard obtained in Example 1 can be fully prepared into a fiberboard with the same bionic structure and mechanical properties through a simple crushing process. In contrast, the plywood obtained in Experiment 3 cannot achieve the same recycling process to repeatedly obtain plywood with the same performance.

Claims

1. A method for preparing a high-strength, high-toughness, recyclable bionic structural fiberboard, characterized in that It is carried out in the following steps:

1. Preprocessing: The wood processing residue is subjected to a partial lignin removal and drying treatment in sequence to obtain a wood processing residue from which the partial lignin has been removed; 2. Swelling treatment: Under room temperature conditions, the wood processing residue from which part of the lignin has been removed is immersed in an activation solution for 30 minutes to 3 hours, and then the activation solution is replaced, and the immersion is repeated 1 to 5 times to obtain a swollen wood processing residue; 3. Dissociation and dispersion treatment: The swollen wood processing residue is added to the cellulose solvent, and the mixture is continuously stirred for 5 to 30 minutes at a temperature of -20 to 150 degrees Celsius, and finally allowed to stand for reaction for 5 to 10 minutes to obtain a high-viscosity, milky white, multi-scale cellulose mixed solution; The density of the high-viscosity, milky white multi-scale cellulose mixed solution is 0.8 g / cm 3 ~3g / cm 3 ; 4. Centrifugal treatment: The high-viscosity, milky white multi-scale cellulose mixed solution is placed in a centrifuge for centrifugation to remove the bottom sediment to obtain a high-viscosity, uniformly dispersed multi-scale cellulose solution; The density of the high-viscosity, uniformly dispersed multi-scale cellulose solution is 0.5 g / cm 3 ~2g / cm 3 ; 5. Hydrogel construction: A high-viscosity, uniformly dispersed multi-scale cellulose solution is poured into a mold, left to stand for 2 hours to 10 hours, and after solidification, immersed in a regeneration solution for 5 hours to 20 hours, and finally washed to obtain a uniform multi-scale cellulose hydrogel; 6. Densification treatment: The uniform multi-scale cellulose hydrogel is placed in a hot press and hot pressed to obtain a high-strength, high-toughness, recyclable bionic structural fiberboard.

2. The method for preparing a high-strength, high-toughness, recyclable bionic structural fiberboard according to claim 1, characterized in that The size of the wood processing residue described in step 1 is 0.3 mm to 2.5 cm.

3. The method for preparing a high-strength, high-toughness, recyclable bionic structural fiberboard according to claim 1, characterized in that The removal of part of the lignin described in step one is specifically carried out according to the following steps: immersing the wood processing residue in a delignification solution, heating it in a water bath at a temperature of 60°C to 90°C for 10h to 15h, then soaking it in deionized water at a temperature of 20°C to 50°C for 1h to 3h, repeating the deionized water soaking 2 to 4 times to obtain the wood processing residue from which part of the lignin has been removed.

4. The method for preparing a high-strength, high-toughness, recyclable bionic structural fiberboard according to claim 3, characterized in that The delignification solution is a mixed solution of sodium chlorite solution and acetic acid buffer, 1% to 30% by mass of hydrogen peroxide, 1% to 30% by mass of sodium hypochlorite solution or 1% to 30% by mass of anthraquinone solution; the mixed solution of sodium chlorite solution and acetic acid buffer is a mixture of 5% by mass of sodium chlorite solution and 4.6 pH acetic acid buffer in a volume ratio of 30:

1.

5. The method for preparing a high-strength, high-toughness, recyclable bionic structural fiberboard according to claim 1, characterized in that The drying treatment described in step 1 is specifically heating at a temperature of 40° C. to 110° C. for 5 h to 15 h.

6. The method for preparing a high-strength, high-toughness, recyclable biomimetic structural fiberboard according to claim 1, characterized in that The activation solution in step 2 is dimethylacetamide, dimethylformamide or a lithium chloride / dimethylacetamide solution with a lithium chloride mass fraction of 1% to 6%.

7. The method for preparing a high-strength, high-toughness, recyclable bionic structural fiberboard according to claim 1, characterized in that The cellulose solvent described in step 3 is one of 85% by mass N-methylmorpholine-N-oxide solution, 1-allyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride, 8% to 10% by mass dimethylacetamide / lithium chloride solution, sodium hydroxide / urea mixed aqueous solution, zinc chloride / calcium chloride mixed aqueous solution and zinc chloride / aluminum chloride mixed aqueous solution, or a mixture of several thereof; The mass fraction of sodium hydroxide in the sodium hydroxide / urea mixed aqueous solution is 7%, and the mass fraction of urea is 12%; the mass fraction of zinc chloride in the zinc chloride / calcium chloride mixed aqueous solution is 72%, and the mass fraction of calcium chloride is 2.2%; the mass fraction of zinc chloride in the zinc chloride / aluminum chloride mixed aqueous solution is 59%, and the mass fraction of aluminum chloride is 6.4%.

8. The method for preparing a high-strength, high-toughness, recyclable bionic structural fiberboard according to claim 1, characterized in that The regeneration solution described in step 5 is anhydrous ethanol, acetone, distilled water or deionized water.

9. The method for preparing a high-strength, high-toughness, recyclable biomimetic structural fiberboard according to claim 1, characterized in that The hot pressing described in step six is ​​specifically performed at a hot pressing temperature of 30° C. to 150° C. and a pressure of 1 MPa to 10 MPa for 5 h to 50 h.

10. A recycling method for a high-strength, high-toughness, recyclable biomimetic structural fiberboard prepared as claimed in claim 1, characterized in that It is carried out in the following steps: The high-strength and high-toughness, recyclable bionic structural fiberboard is placed in a crusher for crushing treatment, and then the swelling treatment, dissociation and dispersion treatment, centrifugal treatment, hydrogel construction and densification treatment are repeated to complete the recycling treatment method.

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