A flexible formaldehyde-free fiberboard and a method of manufacturing the same

Abstract

The present application relates to a kind of flexible formaldehyde-free fiberboard and its manufacturing method, belong to functional composite material manufacturing field and artificial board processing field.Flexible formaldehyde-free fiberboard is composed of special fiber and flexible adhesive system, special fiber includes wood, bamboo, straw and / or straw fiber, flexible adhesive system includes isocyanate compound, the number average molecular weight between 500-5000 of polyol and the molecular weight between 30-500 of small molecule polyol, polyamine or polyacid anhydride;Adhesive system is applied to the surface of special fiber using high-pressure vapor deposition technology, then the fiber containing glue special fiber is laid into three-dimensional network fiber network layer by pneumatic-pole process, and flexible formaldehyde-free fiberboard is prepared by hot pressing.Flexible ultra-thin fiberboard has flexible sponge-like porous structure between fiber.The present application is simple and easy to operate, low in production cost, green and environmentally friendly, and is conducive to the application of fiberboard in large-radius curved surface, improves the added value of fiberboard.

Description

Technical Field

[0001] This invention relates to a novel flexible formaldehyde-free fiberboard and its manufacturing method, specifically to a wood fiber reinforced resin-based environmentally friendly formaldehyde-free composite material and its preparation method, belonging to the fields of functional composite material manufacturing and artificial board processing. Background Technology

[0002] Fiberboard products are widely used in various industries in my country. Previous research and development mainly focused on medium-density fiberboard (MDF), with products primarily used in traditional sectors such as furniture, cabinets, and wood flooring. This resulted in product homogenization and uniformity. Therefore, there is an urgent need to develop new, high-performance products to broaden the application areas of fiberboard and address the problem of product homogenization.

[0003] Currently, the decoration of engineered wood products mainly uses decorative paper, resin film, and wood veneer for surface finishing. With the development of engineered wood product technology, my country has developed thin high-density fiberboard (HDF) with a thickness of less than 1.5mm. This type of fiberboard features thinness, a smooth surface, and customizable cutting dimensions, making it a viable alternative to large-format natural wood veneers and paper-based decorative materials. It shows great promise in areas such as plywood veneer, significantly expanding the new uses and fields for fiberboard. However, because ultra-thin fiberboard uses rigid adhesives such as urea-formaldehyde resin and phenolic resin, the cured board is highly rigid (the group standard for ultra-thin high-density fiberboard (T / CNFPIA3007-2019) requires an elastic modulus of ≥3800MPa), resulting in poor flexibility. While suitable for veneer applications with minimal curvature, ultra-thin fiberboard cannot be effectively used in applications with significant curvature due to its insufficient flexibility.

[0004] Patent (CN 201580036706.6) discloses a flexible fiberboard made from wheat straw fiber, corn straw fiber, rice straw fiber, oat straw fiber, barley straw fiber, and rye straw fiber, along with thermoplastic elastomer resin. The manufacturing method involves mixing the straw fiber and thermoplastic resin powder, extruding and granulating the mixture, and then hot-pressing the granules to form a board. This manufacturing method employs extrusion granulation and pressing processes common in the plastics industry, resulting in slow efficiency and low output. This is incompatible with the large-scale development of my country's engineered wood products industry and cannot be applied in practical industries. Furthermore, the patent does not disclose the bending radius of the fiberboard, making it impossible to effectively assess its flexibility. Therefore, it is essential to develop a product and its manufacturing technology that offers high flexibility, efficient manufacturing processes, and is compatible with the scale of my country's engineered wood products industry. This will promote the transformation and upgrading of my country's engineered wood products industry, broaden its application areas, and address the problem of product homogenization. Summary of the Invention

[0005] To address the application of fiberboard in the decorative field, and to enable its application on large curved surfaces, thereby increasing the added value of fiberboard in the decorative field, this invention provides a novel flexible formaldehyde-free fiberboard and its manufacturing method.

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

[0007] A flexible formaldehyde-free fiberboard is composed of special fibers and a flexible adhesive system. The special fibers include biomass materials such as wood, bamboo, straw, and / or rice straw. The flexible adhesive system includes isocyanate compounds, polyols with a number average molecular weight between 500 and 5000, and small molecule polyols, polyamines, or polyanhydrides with a molecular weight between 30 and 500. The adhesive system is applied to the surface of the special fibers using high-pressure vapor deposition technology, and then the adhesive-containing special fibers are laid into a three-dimensional network fiber layer using a pneumatic-roller process. The flexible formaldehyde-free fiberboard is then prepared by hot pressing.

[0008] Furthermore, the special fiber accounts for 50% to 95% of the mass fraction of the fiberboard, and the flexible adhesive system accounts for 50% to 5% of the mass fraction of the fiberboard; preferably, the flexible adhesive system accounts for 5-20% of the mass fraction, and more preferably, 5-15% of the mass fraction.

[0009] Furthermore, the special fibers are composed of biomass material fibers such as wood, bamboo, straw, and / or rice straw, in any proportion. The special fibers are biomass material fibers of various types, including fir, poplar, eucalyptus, moso bamboo, green bamboo, hemp bamboo, corn straw, wheat straw, rice straw, and / or upland rice straw, and their types are not specifically limited.

[0010] Furthermore, in the special fiber, more than 80% of the fiber has a length of 0.5-7mm and more than 80% of the fiber has a diameter of 0.05-0.3mm; preferably, more than 80% of the fiber has a length of 1-4.5mm and more than 80% of the fiber has a diameter of 0.08-0.2mm.

[0011] Furthermore, in the flexible adhesive system, by weight, the isocyanate compound is 5-30 parts, preferably 5-20 parts, more preferably 10-20 parts; the polyol with a number average molecular weight between 500 and 5000 is 60-85 parts, preferably 60-80 parts, more preferably 70-80 parts; and the small molecule polyol, polyamine, or polyacid anhydride with a molecular weight between 30 and 500 is 1-10 parts, preferably 1-8 parts, more preferably 3-5 parts.

[0012] Further, the isocyanate compound includes one or more of the following: toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), TDI or MDI or HDI or IPDI modified epoxy resin, and prepolymers of TDI or MDI or HDI or IPDI reacted with polyether.

[0013] Furthermore, the polyols with a number average molecular weight between 500 and 5000 include one or more of diols or polyol polymers such as polytetrahydrofuran ether diol, polyethylene glycol, and polypropylene glycol, with a preferred number average molecular weight of 500-3000, and a more preferred number average molecular weight of 1000-2000.

[0014] Furthermore, the polyols, polyamines, or polyacid anhydrides with a molecular weight between 30 and 500 include one or more of the following: 1,4-butanediol, 1,3-butanediol, ethylene glycol, ethylenediamine, 3,3'-dichloro-4,4-diamino-diphenylmethane, pyromellitic anhydride, phthalic anhydride, phthalic anhydride, and trimellitic anhydride glyceride.

[0015] Furthermore, the flexible adhesive system further includes a foaming agent and / or a toughening agent; the foaming agent includes inorganic foaming agents (carbonates such as calcium carbonate, magnesium carbonate, and sodium bicarbonate) and organic foaming agents (organic solvents such as azo compounds, sulfonyl hydrazides, nitroso compounds, n-hexane, n-heptane, dichloromethane, and trichloromethane); the amount added is 1-10% of the total mass of the adhesive system. The toughening agent includes rubbers such as liquid polysulfide rubber, liquid acrylate rubber, liquid polybutadiene rubber, nitrile rubber, ethylene propylene rubber, and styrene-butadiene rubber, as well as polyurethane, styrene, polyolefin, polyester, syndiotactic 1,2-polybutadiene, and polyamide products, and also includes low-molecular-weight polyamides and low-molecular-weight inactive toughening agents, such as phthalates; the amount added is 1-10% of the total mass of the adhesive system.

[0016] Furthermore, the flexible adhesive system can be used in a solvent-free state or in a solvent-dissolved and diluted state. That is, the flexible adhesive system may also contain a solvent, which may be one or more of tetrahydrofuran, acetone, ethyl acetate, ethanol, methanol, N,N'-dimethylformamide, N,N'-dimethylacetamide, dimethyl sulfoxide, chloroform, dichloromethane, trichloromethane, and tetrachloromethane. The amount of solvent added is 10%-95% of the total mass of the flexible adhesive system.

[0017] Further, the thickness of the flexible formaldehyde-free fiberboard is less than or equal to 10 mm, and the bending radius is less than or equal to 10 mm. Preferably, the thickness of the flexible formaldehyde-free fiberboard is 0.1-10 mm, and the bending radius is 0.1-10 mm. More preferably, the thickness of the flexible formaldehyde-free fiberboard is 0.5-3 mm, and the bending radius is 2-8 mm.

[0018] The manufacturing method of the above-mentioned flexible formaldehyde-free fiberboard includes the following steps:

[0019] (1) Preparation of special fibers: Wood, bamboo, straw and / or rice straw and other biomass materials are put into a digester and cooked. After the biomass materials soften, they are put into a grinder containing an alkaline solution and ground into fine fibers. The size requirements of the fine fibers are: more than 80% of the length is between 0.5-7mm and more than 80% of the diameter is between 0.05-0.3mm.

[0020] (2) Preparation of flexible adhesive system: The flexible adhesive system contains isocyanate compounds, polyols with a number average molecular weight between 500 and 5000, and small molecule polyols, polyamines, or polyanhydrides with a molecular weight between 30 and 500; the adhesive system is composed of polymers formed by chemical reactions of one or more of the above mixtures or mixtures thereof.

[0021] (3) Preparation of formaldehyde-free fiberboard: The adhesive system is applied to the surface of special fibers using high-pressure vapor deposition technology, and then the adhesive-containing special fibers are laid into a three-dimensional network fiber layer by pneumatic-roller process, and then hot-pressed to prepare flexible formaldehyde-free fiberboard.

[0022] In step (1), the preferred size requirements for the fine fibers are: the length of the fine fibers is between 1 and 4.5 mm, accounting for more than 80%, and the diameter of the fine fibers is between 0.08 and 0.2 mm, accounting for more than 80%.

[0023] In step (1), the alkaline solution is a solution composed of one or more of NaOH, KOH, Ca(OH)2, Na2SO3 and Na2S, and the mass fraction of the solute in the solution is 0.5%-50%, and the proportion of the mixture is not limited.

[0024] In step (2), the flexible adhesive system further includes a solvent, such as tetrahydrofuran, acetone, ethyl acetate, ethanol, methanol, N,N'-dimethylformamide, N,N'-dimethylacetamide, dimethyl sulfoxide, chloroform, dichloromethane, trichloromethane, and / or tetrachloromethane. The amount of solvent added is 10-95% of the total mass of the flexible adhesive system.

[0025] The flexible adhesive system further includes foaming agents and / or toughening agents; the foaming agents include inorganic foaming agents (calcium carbonate, magnesium carbonate, sodium bicarbonate and other carbonate substances) and organic foaming agents (azo compounds, sulfonyl hydrazide compounds, nitroso compounds, n-hexane, n-heptane and other organic solvents, added at 1-10% of the total adhesive system mass); the toughening agents include liquid polysulfide rubber, liquid acrylate rubber, liquid polybutadiene rubber, nitrile rubber, ethylene propylene rubber and styrene-butadiene rubber and other rubber products, as well as polyurethane, styrene, polyolefin, polyester, syndiotactic 1,2-polybutadiene and polyamide products, and also include low molecular weight polyamides and low molecular weight inactive toughening agents, such as phthalates, added at 1-10% of the total adhesive system mass.

[0026] In step (3), the special fiber accounts for 50% to 90% of the mass fraction of the fiberboard, and the adhesive system accounts for 50% to 10% of the mass fraction of the fiberboard; preferably, the adhesive system accounts for 5-20% of the mass fraction, and more preferably, 5-15% of the mass fraction.

[0027] The high-pressure vapor deposition technology described herein employs a high-pressure gas-assisted deposition process, using air of a certain energy and flow intensity to bombard the adhesive system, dispersing the adhesive into micro- and nano-sized particles. Through the cascade collision effect between air and the deposited particles, the migration ability of the deposited particles is increased, thereby improving the adhesion of the particles to the fiber surface.

[0028] The pneumatic-roller process described above uses a slow wedge-angle exhaust and a one-time heavy-duty pre-compression method to optimize the roller diameter and exhaust angle parameters, and uses a large-diameter steel belt pre-compression system to solve the problem of uniform laying of wood fiberboard.

[0029] The aforementioned three-dimensional network fiber layer employs a pneumatic-paddle process, where the adhesive-containing fibers interweave in the X, Y, and Z directions to form a three-dimensional fluffy interpenetrating network fiber felt.

[0030] The hot pressing process involves a temperature of 50-200℃ and a pressure of 0.5-5MPa, which causes the hydroxyl groups on the fiber surface to react chemically with functional groups such as isocyanates and anhydrides, forming chemical bonds such as urethane functional groups and carboxyl groups. This improves the bonding force between the adhesive and the fiber, and enhances the mechanical properties of the board.

[0031] During the hot-pressing process, a large amount of gas is released due to the action of the foaming agent and / or the reaction between isocyanate and water and / or isocyanate and acid anhydride. This gas expands at high temperatures, creating numerous pores within the soon-to-cure adhesive. Because the adhesive itself is flexible, this forms a sponge-like flexible porous network structure, giving the board its flexibility. The resulting flexible fiberboard has an internal porosity ≥25%, and the fibers exhibit a sponge-like porous flexible network structure.

[0032] The beneficial effects of this invention are:

[0033] (1) This invention discloses a method for manufacturing flexible fiberboard, which uses a flexible adhesive system to prepare fiberboard, overcoming the problem of rigidity of traditional fiberboard and is beneficial to the application of fiberboard in curved surfaces.

[0034] (2) This invention discloses a method for preparing an ultra-thin flexible fiberboard, which is beneficial for the application of fiberboard in the field of expanding curvature and breaking through the added value of fiberboard.

[0035] (3) This invention discloses a method for preparing a flexible ultra-thin fiberboard. The fiberboard is isotropic and flexible, which is beneficial for applying the fiberboard to the surface decoration of plywood, overcoming the problem of anisotropy of plywood veneer, and suppressing the problem of cracking of plywood surface veneer during use.

[0036] (4) The flexible ultra-thin fiberboard of the present invention has a flexible sponge-like porous structure between the fibers, which is beneficial to the fiberboard having stretchability when subjected to external force, and prevents the fiberboard from breaking. Attached Figure Description

[0037] Figure 1 The length distribution of the fibers;

[0038] Figure 2 This refers to the diameter distribution of the fibers;

[0039] Figure 3 A schematic diagram of a traditional 1mm thick ultrathin fiberboard and its bending performance test;

[0040] Figure 4 A schematic diagram of the flexible ultrathin fiberboard in Embodiment 1 of the present invention and its bending performance test;

[0041] Figure 5 The sponge-like foam between the fibers of the flexible ultrathin fiberboard in Embodiment 1 of the present invention;

[0042] Figure 6 A schematic diagram of the flexible ultrathin fiberboard in Embodiment 2 of the present invention and its bending performance test;

[0043] Figure 7 This is a schematic diagram of the flexible ultrathin fiberboard in Embodiment 4 of the present invention and a bending performance test.

[0044] Figure 8 This is a schematic diagram of the flexible ultrathin fiberboard in Embodiment 6 of the present invention and a bending performance test.

[0045] Figure 9 A schematic diagram of a traditional 3mm thick ultrathin fiberboard and its bending performance test. Detailed Implementation

[0046] The principles and specific steps of the present invention will be described in detail and completely below with reference to embodiments of the present invention. However, the described embodiments are only a part of the present invention, not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention, through simple repetition without creative effort, are within the scope of protection of the present invention.

[0047] The method for preparing the flexible formaldehyde-free fiberboard of the present invention includes the following steps:

[0048] (1) Preparation of special fibers: Biomass materials such as wood, bamboo, straw, and rice straw are placed in a digester and cooked until the biomass material softens. Then, it is placed in a grinder containing an alkaline solution and ground into fine fibers. The size requirements for the fine fibers are as follows: Figure 1 As shown, the fiber length distribution (horizontal axis unit mm) shows that fibers with a length between 0.5-7 mm account for more than 80%. Figure 2 As shown, the fiber diameter distribution (horizontal axis unit mm) shows that more than 80% of the fibers have a diameter between 0.05-0.3 mm, with a length between 1-4.5 mm being preferred and a diameter between 0.08-0.2 mm being even more preferred.

[0049] Biomass materials such as timber, bamboo, straw, and rice straw refer to biomass materials of various kinds, including fir, poplar, eucalyptus, moso bamboo, green bamboo, hemp bamboo, corn stalks, wheat stalks, rice, and upland rice, without any specific restrictions on the types.

[0050] Alkaline solutions are solutions containing one or more of the following: NaOH, KOH, Ca(OH)2, Na2SO3, and Na2S. The mass fraction of the solute in the solution is 0.5%-50%, and there are no restrictions on the proportion of the mixture.

[0051] (2) Preparation of flexible adhesive system: The flexible adhesive system contains isocyanate compounds, polyols with a number average molecular weight between 500 and 5000, small molecule polyols or polyamines or polyanhydrides with a molecular weight between 30 and 500, foaming agents, toughening agents, etc. The adhesive system is composed of polymers formed by the chemical reaction of one or more of the above mixtures.

[0052] The isocyanate compound is characterized by including toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), TDI or MDI or HDI or IPDI modified epoxy resin, and prepolymers of TDI or MDI or HDI or IPDI reacted with polyether.

[0053] Polyols with a number average molecular weight between 500 and 5000, characterized in that they are diols or polyol polymers such as polytetrahydrofuran ether diol, polyethylene glycol, and polypropylene glycol, with a preferred number average molecular weight of 500-3000, and more preferably a number average molecular weight of 1000-2000.

[0054] Polyols, polyamines, or polyacid anhydrides with molecular weights between 30 and 500, characterized by 1,4-butanediol, 1,3-butanediol, ethylene glycol, ethylenediamine, 3,3'-dichloro-4,4-diamino-diphenylmethane, pyromellitic anhydride, phthalic anhydride, trimellitic anhydride glycerides, etc.

[0055] An adhesive system refers to an adhesive that can be used in a solvent-free state or in a state where it is dissolved and diluted with a solvent. Solvents include tetrahydrofuran, acetone, ethyl acetate, ethanol, methanol, N,N'-dimethylformamide, N,N'-dimethylacetamide, dimethyl sulfoxide, chloromethane, dichloromethane, trichloromethane, tetrachloromethane, etc.

[0056] (3) Preparation of formaldehyde-free fiberboard: The adhesive system is applied to the surface of special fibers using high-pressure vapor deposition technology, and then the adhesive-containing special fibers are laid into a three-dimensional network fiber layer by pneumatic-roller process, and then hot-pressed to prepare flexible formaldehyde-free fiberboard.

[0057] The special fibers account for 50% to 90% of the mass of the fiberboard, and the adhesive accounts for 50% to 10% of the mass of the fiberboard, with a preferred adhesive mass fraction of 5-20%, and a more preferred mass fraction of 5-15%.

[0058] High-pressure vapor deposition (HPV) technology employs a high-pressure gas-assisted deposition process, using air of a certain energy and flow intensity to bombard the adhesive system, dispersing the adhesive into micro- and nano-sized particles. Through the cascading collision effect between air and the deposited particles, the migration ability of the deposited particles is increased, improving their adhesion to the fiber surface. The pneumatic-roller process is characterized by slow wedge-angle venting and a one-time heavy-duty pre-compression method, optimizing roller diameter and venting angle parameters, and using a large-diameter steel belt pre-compression system to ensure uniform installation of wood fiberboard. The three-dimensional network fiber layer is characterized by a pneumatic-roller process where adhesive-containing fibers interweave in the X, Y, and Z directions, forming a three-dimensional, fluffy, interpenetrating network fiber mat.

[0059] The hot-pressing temperature is 50-200℃, and the hot-pressing pressure is 0.5-5MPa. This causes the hydroxyl groups on the fiber surface to react chemically with functional groups such as isocyanates and acid anhydrides, forming chemical bonds such as urethane functional groups and carboxyl groups. This improves the bonding force between the adhesive and the fiber, and enhances the mechanical properties of the board. During the hot-pressing process, due to the action of the foaming agent and / or the reaction between isocyanates and water and / or isocyanates and acid anhydrides, a large amount of gas is released. The gas expands at high temperatures, causing numerous pores to form inside the adhesive that is about to cure. Because the adhesive itself is flexible, this forms a sponge-like flexible porous network structure, giving the board its flexibility.

[0060] The thickness of the flexible fiberboard is less than or equal to 10mm, and the bending radius is less than or equal to 10mm.

[0061] Flexible fiberboard has an internal porosity of ≥25% and a sponge-like porous flexible network structure between the fibers.

[0062] Example 1

[0063] Poplar wood was selected as the raw material. It was first steamed and boiled until the wood softened. Then, it was ground in a pulper containing NaOH solution (NaOH mass fraction of 5%) to obtain fibers with a length of 0.5-4.5 mm accounting for 85% and a diameter of 0.05-0.2 mm accounting for 82%. The fibers were then dried.

[0064] An adhesive system was prepared using toluene diisocyanate, polytetrahydrofuran ether diol (number average molecular weight Mn = 1000), and ethylene glycol in a mass ratio of 35:200:3.1. The components were stirred until homogeneous. The adhesive was then applied to the surface of the fibers using high-pressure vapor deposition (HPV). After application, the glued fiber preform was hot-pressed at 120°C for 2 hours to cure, resulting in a flexible ultrathin fiberboard with a thickness of 1 mm and an adhesive mass fraction of 20%.

[0065] Example 2

[0066] Poplar wood was selected as the raw material. It was first steamed and boiled until the wood softened. Then, it was ground in a pulper containing KOH solution (KOH mass fraction of 5%) to obtain fibers with a length of 0.5-4.5 mm accounting for 85% and a diameter of 0.05-0.2 mm accounting for 82%. The fibers were then dried.

[0067] An adhesive system was prepared using 4,4'-diphenylmethane diisocyanate (MDI), polytetrahydrofuran ether glycol (number average molecular weight Mn = 1000), and ethylene glycol in a mass ratio of 50:100:6.2. The components were stirred until homogeneous. The adhesive was then applied to the surface of the fibers using high-pressure vapor deposition (HPV). After application, the glued fiber preform was hot-pressed at 120°C for 2 hours to cure, resulting in a flexible ultrathin fiberboard with a thickness of 1 mm and an adhesive mass fraction of 20%.

[0068] Example 3

[0069] Poplar wood was selected as the raw material. It was first steamed and boiled until the wood softened. Then, it was ground in a pulper containing NaOH solution (10% by mass) to obtain fibers with a length of 4.5-7.0 mm accounting for 90% and a diameter of 0.2-0.3 mm accounting for 85%. The fibers were then dried.

[0070] 50g of 4,4'-diphenylmethane diisocyanate and 200g of polytetrahydrofuran ether diol were reacted at 80°C for 2 hours. Then, 20g of pyromellitic anhydride and 50g of acetone were added and the mixture was stirred further to form an adhesive system.

[0071] The adhesive was applied to the surface of the fiber using a high-pressure vapor deposition process. After the adhesive was applied, the fiber preform containing the adhesive was hot-pressed at 150°C for 3 hours to cure and obtain a flexible ultra-thin fiberboard with a thickness of 1 mm and an adhesive mass fraction of 20%.

[0072] Example 4

[0073] Bamboo is selected as the raw material. The green part of the bamboo is removed, and the yellow part is steamed until it softens. Then, it is ground in a pulper containing a mixed solution of NaOH and Na2SO3 (20% NaOH and 10% Na2SO3 by mass) to obtain fibers with a length of 0.5-4.5 mm accounting for 85% and a diameter of 0.05-0.2 mm accounting for 82%. The fibers are then dried.

[0074] An adhesive system was prepared using 4,4'-diphenylmethane diisocyanate (MDI), polytetrahydrofuran ether glycol (number average molecular weight Mn = 1000), and ethylene glycol in a mass ratio of 50:100:6.2. The components were stirred until homogeneous. The adhesive was then applied to the surface of the fibers using high-pressure vapor deposition (HPV). After application, the glued fiber preform was hot-pressed at 120°C for 2 hours to cure, resulting in a flexible ultrathin fiberboard with a thickness of 0.5 mm and an adhesive mass fraction of 30%.

[0075] Example 5

[0076] Fir wood is selected as the raw material. It is first steamed and boiled until the wood softens. Then, it is ground in a pulper containing NaOH solution (NaOH mass fraction of 5%) to obtain fiber with a length of 4.5-7.0 mm accounting for 90% and a diameter of 0.2-0.3 mm accounting for 85%. The fiber is then dried.

[0077] 50g of 4,4'-diphenylmethane diisocyanate and 50g of polytetrahydrofuran ether diol (number average molecular weight Mn = 2000) were reacted at 80℃ for 2 hours. Then, this mixture was added to 500g of epoxy resin (E51) and stirred for 4 hours. Finally, 50g of acetone and 200g of ethylenediamine were added and stirred until homogeneous to form an adhesive system. The adhesive was applied to the surface of the fibers using high-pressure vapor deposition (HPV). After adhesive application, the glued fiber preform was hot-pressed at 120℃ for 2 hours to cure, resulting in a flexible ultrathin fiberboard with a thickness of 0.5mm and an adhesive mass fraction of 20%.

[0078] Example 6

[0079] Poplar wood was selected as the raw material. It was first steamed and boiled until the wood softened. Then, it was ground in a pulper containing a mixed solution of NaOH and Na2S (20% NaOH and 5% Na2S by mass) to obtain fibers with a length of 4.5-7.0 mm accounting for 90% and a diameter of 0.2-0.3 mm accounting for 85%. The fibers were then dried.

[0080] An adhesive system was prepared using 4,4'-diphenylmethane diisocyanate (MDI), polypropylene glycol (number average molecular weight Mn = 1000), and 1,4-butanediol in a mass ratio of 50:100:4.5. The components were stirred until homogeneous. The adhesive was then applied to the surface of the fibers using high-pressure vapor deposition (HPV). After application, the glued fiber preform was hot-pressed at 120°C for 2 hours to cure, resulting in a flexible ultrathin fiberboard with a thickness of 3 mm and an adhesive mass fraction of 30%.

[0081] Example 7

[0082] Eucalyptus wood is selected as the raw material. It is first steamed and boiled until the wood softens. Then, it is ground in a pulper containing a Ca(OH)2 solution (Ca(OH)2 mass fraction is 5%) to obtain fibers with a length of 0.5-4.5 mm accounting for 90% and a diameter of 0.05-0.2 mm accounting for 85%. The fibers are then dried.

[0083] An adhesive system was prepared using 4,4'-diphenylmethane diisocyanate (MDI), polytetrahydrofuran ether diol (number average molecular weight Mn = 1000), and 1,4-butanediol in a mass ratio of 50:100:4.5. The components were stirred until homogeneous. The adhesive was then applied to the surface of the fibers using high-pressure vapor deposition (HPV). After application, the glued fiber preform was hot-pressed at 120°C for 2 hours to cure, resulting in a flexible ultrathin fiberboard with a thickness of 3 mm and an adhesive mass fraction of 40%.

[0084] The flexible ultrathin fiberboards obtained in the above embodiments were tested for properties such as bending radius, board thickness, and board porosity. The bending radius was tested as follows: the fiberboard was rolled up, and the radius of the arc corresponding to the point where the fiberboard was about to crack was the bending radius. The board porosity was tested using a high-pressure mercury porosimeter. Figure 4 , 6 As shown in Figures 7 and 8, bending performance tests were conducted on the flexible ultrathin fiberboards in Embodiments 1, 2, 4, and 6 of the present invention; Figure 5 As shown, this is a sponge-like foam between the fibers of the flexible ultrathin fiberboard in Embodiment 1 of the present invention; as Figure 3 , 9 As shown in Table 1, bending performance tests were conducted on traditional 1mm and 3mm thick ultrathin fiberboards. The test results are shown in Table 1. It can be seen that the product of this invention has an extremely low bending radius, demonstrating the good flexibility of the board and giving the fiberboard high added value.

[0085] Table 1. Bending radius, thickness, and porosity of ultra-thin fiberboard and traditional ultra-thin fiberboard in the embodiments of the present invention.

[0086]

[0087] This invention grinds biomass materials into fibers of a specific size and shape. A flexible adhesive system is applied to the surface of these fibers using high-pressure vapor deposition (HPV). The adhesive-containing fibers are then laid into a three-dimensional network using a pneumatic-roller process, followed by hot pressing to produce a flexible, formaldehyde-free fiberboard. The flexible, ultra-thin fiberboard exhibits a flexible, sponge-like porous structure between the fibers, which enhances its flexibility under external forces and prevents breakage. This invention is simple, cost-effective, and environmentally friendly. The resulting product overcomes the rigidity problem of traditional fiberboards, facilitating their application on large-radius curved surfaces and increasing their added value.

Claims

1. A flexible formaldehyde-free fiberboard, characterized in that: Composed of special fibers and a flexible adhesive system, the flexible adhesive system includes isocyanate compounds, polyols with a number average molecular weight between 500 and 5000, and small molecule polyols, polyamines, or polyanhydrides with a molecular weight between 30 and 500. The adhesive system is applied to the surface of the special fibers using high-pressure vapor deposition technology, and then the adhesive-containing special fibers are laid into a three-dimensional network fiber web layer using a pneumatic-roller process. The flexible formaldehyde-free fiberboard is then prepared by hot pressing. The high-pressure vapor deposition technology disperses the adhesive into micro- and nano-sized particles. Through the cascade collision effect between air and the deposited particles, the migration ability of the deposited particles is increased, and the adhesion of the particles to the fiber surface is improved. The three-dimensional network fiber layer, using the pneumatic-roller process, has adhesive fibers interwoven in the XYZ directions to form a three-dimensional fluffy interwoven network fiber felt; The hot pressing temperature is 50-200℃, and the hot pressing pressure is 0.5-5MPa; The flexible formaldehyde-free fiberboard has an internal porosity of ≥25%, and the fibers have a sponge-like porous flexible network structure. The flexible formaldehyde-free fiberboard has a thickness of less than or equal to 10 mm and a bending radius of 0.1 to 10 mm. The special fibers account for 50% to 95% of the mass of the fiberboard, and the flexible adhesive system accounts for 50% to 5% of the mass of the fiberboard; the special fibers are fir, poplar, eucalyptus, moso bamboo, green bamboo, hemp bamboo, corn stalks, and wheat stalks; Of the special fibers mentioned above, more than 80% have a length of 0.5-7 mm and more than 80% have a diameter of 0.05-0.3 mm; In the aforementioned flexible adhesive system, by weight, the isocyanate compound comprises 5-30 parts, the polyol with a number average molecular weight between 500 and 5000 comprises 60-85 parts, and the small molecule polyol, polyamine, or polyanhydride with a molecular weight between 30 and 500 comprises 1-10 parts.

2. The flexible formaldehyde-free fiberboard according to claim 1, characterized in that: The isocyanate compounds include toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI); the polyols with a number average molecular weight between 500 and 5000 include polytetrahydrofuran ether glycol, polyethylene glycol, and / or polypropylene glycol; the polyols, polyamines, or polyacid anhydrides with a molecular weight between 30 and 500 include 1,4-butanediol, 1,3-butanediol, ethylene glycol, ethylenediamine, pyromellitic anhydride, and phthalic anhydride.

3. The flexible formaldehyde-free fiberboard according to claim 1, characterized in that: The flexible adhesive system further includes a solvent, which is tetrahydrofuran, acetone, ethyl acetate, ethanol, methanol, N,N'-dimethylformamide, N,N'-dimethylacetamide, dimethyl sulfoxide, chloroform, dichloromethane, trichloromethane, and / or tetrachloromethane, and the amount of solvent added is 10-95% of the total mass of the flexible adhesive system; the flexible adhesive system also includes a foaming agent and / or a toughening agent, the foaming agent includes inorganic foaming agents and organic foaming agents, and the amount added is 1-10% of the total mass of the adhesive system; the toughening agent includes liquid polysulfide rubber, liquid acrylate rubber, liquid polybutadiene rubber, nitrile rubber, ethylene propylene rubber, and styrene-butadiene rubber, and the amount added is 1-10% of the total mass of the adhesive system.

4. A method for manufacturing a flexible formaldehyde-free fiberboard according to any one of claims 1-3, comprising the following steps: (1) Preparation of special fibers: Wood, bamboo and straw biomass materials are put into a steamer and steamed. After the biomass material softens, it is put into a grinder containing an alkaline solution and ground into fine fibers. The size requirements of the fine fibers are: the length is between 0.5-7mm and more than 80% are between 0.05-0.3mm and more than 80% are between 0.05-0.3mm. (2) Preparation of flexible adhesive system: The flexible adhesive system contains isocyanate compounds, polyols with a number average molecular weight between 500 and 5000, small molecule polyols or polyamines or polyanhydrides with a molecular weight between 30 and 500, foaming agents and / or toughening agents; the adhesive system is composed of a mixture of the above or a polymer formed by the chemical reaction of the above mixtures; (3) Preparation of formaldehyde-free fiberboard: The adhesive system is applied to the surface of special fibers using high-pressure vapor deposition technology, and then the adhesive-containing special fibers are laid into a three-dimensional network fiber layer by pneumatic-roller process, and the flexible formaldehyde-free fiberboard is prepared by hot pressing.

5. The method for manufacturing flexible formaldehyde-free fiberboard according to claim 4, characterized in that: The alkaline solution is one or more of NaOH, KOH, Ca(OH)2, Na2SO3 and Na2S, and the mass fraction of the solute in the solution is 0.5%-50%.

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