Waterproof antibacterial fiberboard

Abstract

This invention discloses a waterproof and antibacterial fiberboard, belonging to the field of fiberboard processing technology. The fiberboard has a thickness of 1-2 mm and employs a three-layer composite structure consisting of a functional surface layer, a toughening inner layer, and another functional surface layer. The functional surface layer is composed of a mixture of periodate-oxidized wood fibers and unoxidized wood fibers, grafted with linear polyethyleneimine through a reducing amination reaction, and then reacted with C8-C18 halogenated hydrocarbons to form a chemically bonded hydrophobic and antibacterial surface. The toughening inner layer is composed of unoxidized wood fibers and hyperbranched polyethyleneimine grafted with flexible segments, serving to toughen and assist in formaldehyde fixation. This fiberboard is prepared through a process involving specific proportions of compounding, sequential spraying of functionalizing agents, pre-curing, and two-stage hot pressing. The fiberboard obtained by this invention possesses excellent durable hydrophobicity, highly efficient contact antibacterial properties, high mechanical strength, and ultra-low formaldehyde emission, making it particularly suitable for thin-sheet materials with stringent requirements for hygiene, weather resistance, and environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of fiberboard processing technology, and specifically relates to a waterproof and antibacterial fiberboard. Background Technology

[0002] Wood fiberboard (WFPC) is a type of engineered wood product made from wood fibers or other plant fibers, bonded with synthetic resin adhesives, and then hot-pressed. It is widely used in furniture manufacturing, interior decoration, construction, and packaging. However, the inherent chemical composition and structural characteristics of wood fibers also present various technical challenges. First, cellulose and hemicellulose, the main components of the fibers, contain a large number of hydrophilic hydroxyl groups, making the board highly susceptible to moisture absorption, leading to problems such as thickness expansion, dimensional deformation, and decreased strength. Second, humid environments and organic substrates easily breed mold and bacteria.

[0003] Currently, the most direct method is to add hydrophobic substances, such as paraffin emulsions, asphalt, or organosilicon compounds, to the fibers, or to apply waterproof coatings to the surface of the finished boards. However, the fundamental drawback is that under long-term humid and hot cycling, external friction, or internal stress, the additives are prone to migration, volatilization, or precipitation, leading to a rapid decline in waterproof performance. More importantly, such methods cannot impart active and long-lasting antibacterial properties to the boards. For example, Chinese patent CN111958744A discloses a method for producing moisture-proof high-density fiberboard. This technology uses a complex hydrothermal method and spin coating process to first prepare nano-zinc oxide on conductive glass, and then composite it with positively charged nano-graphene to obtain nanocomposite particles. These positively charged nanocomposite particles are introduced into a melamine-modified urea-formaldehyde resin adhesive, where electrostatic self-assembly forms a dense structural layer at the fiber-resin interface, physically blocking moisture intrusion. This method has achieved significant progress in improving the dimensional stability and moisture resistance of the boards. However, its antibacterial properties rely solely on the photocatalytic or zinc ion slow-release effect that nano zinc oxide may possess. This effect is passive, unstable, and has limited efficiency. In particular, it is barely effective under conditions of no light or rapid water flow, and cannot achieve active, efficient, and long-lasting contact sterilization.

[0004] Currently, selective oxidation technology using sodium periodate is particularly prominent. This reaction specifically breaks the C2-C3 bonds on the glucose rings of cellulose, converting hydroxyl groups into two highly reactive aldehyde groups with minimal damage to the fiber skeleton. These aldehyde groups can undergo covalent cross-linking reactions with hydroxyl and amino groups on adjacent fibers during hot pressing, thus achieving "self-gluing" without the addition of synthetic resins. The resulting boards exhibit excellent mechanical properties and significant water resistance. This technology is not only environmentally friendly but, more importantly, provides a large number of customizable chemical reaction sites for the surface functionalization of fibers. However, this technical route does not actively integrate antibacterial functions. Furthermore, excessive oxidation treatment can lead to a decrease in the toughness of the fiberboard, weakening the inherent strength of the fibers.

[0005] Therefore, there is an urgent need in this field for an innovative technical solution that can create thin, high-performance fiberboard with durable hydrophobicity, strong contact antibacterial properties, and excellent flexibility through a relatively simple, controllable process suitable for large-scale production. Summary of the Invention

[0006] In view of this, the present invention specifically relates to a waterproof and antibacterial fiberboard.

[0007] The objective of this invention can be achieved through the following technical solution: a waterproof and antibacterial fiberboard, wherein the fiberboard is 1-2 mm thick and comprises a three-layer structure consisting of a functional surface layer, a toughening inner layer, and another functional surface layer; wherein the fibers in the functional surface layer are composed of a mixture of long wood fibers treated with periodate oxidation and unoxidized long wood fibers; the aldehyde content on the surface of the fibers in the functional surface layer is 0.8-2.0 mmol / g; the functional surface layer is grafted with linear polyethyleneimine through a reductive amination reaction, and the grafted polyethyleneimine further undergoes a quaternization reaction with C8-C18 halogenated hydrocarbons to form a hydrophobic and antibacterial surface; the number average molecular weight of the linear polyethyleneimine is 5000-50000. g / mol; the fibers in the toughening inner layer are composed of unoxidized long wood fibers and hyperbranched polyethyleneimine grafted with flexible chain segments; the functional surface layer and the toughening inner layer also contain urea-formaldehyde resin adhesive and are bonded by hot pressing process, wherein the formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive is (1.05-1.20):1.

[0008] In traditional wood-based panel manufacturing, the F / U molar ratio of urea-formaldehyde resin adhesives is typically high (approximately 1.3-1.5:1). Excess formaldehyde can generate more hydroxymethyl groups, increasing crosslinking density and initial tack, but at the cost of a large amount of free formaldehyde remaining in the board, which continues to be released through hydrolysis during use. Actively reducing the molar ratio significantly below 1.20 minimizes free formaldehyde at the molecular level: promoting the reaction between formaldehyde and urea reduces the presence of free formaldehyde, fundamentally lowering the risk of long-term formaldehyde release. Above the upper limit of 1.20, even with an amino group trapping mechanism, the initial formaldehyde content is still excessive due to the presence of aldehyde groups internally. Below the lower limit of 1.05, the formaldehyde content is insufficient to fully hydroxymethylate urea, resulting in low resin condensation degree, sparse crosslinking network after curing, and severely weakening adhesive strength, internal bond strength, and static bending strength.

[0009] Furthermore, the long wood fiber is coniferous wood fiber or broadleaf wood fiber, and its fiber length is 1.0~2.0 mm.

[0010] Furthermore, the mass ratio of unoxidized long wood fibers to oxidized long wood fibers in the functional surface layer is (1~4):1.

[0011] Oxidized fibers provide chemically reactive aldehyde groups; unoxidized fibers retain the strength and toughness of natural fibers. The preferred mass ratio is (1~4):1. Within this range, excessive oxidized fibers will not lead to excessive surface rigidity, reducing the bending strength of the ultrathin fiberboard and causing easy warping, while insufficient oxidized fibers will not significantly affect the anchoring of polyethyleneimine, thus affecting the important target performance of this product such as waterproofness, hydrophobicity, and antibacterial properties.

[0012] Furthermore, the aldehyde content on the surface of the mixed fibers in the functional surface layer is 0.8-2.0 mmol / g; the number-average molecular weight of the linear polyethyleneimine is 5000-50000 g / mol.

[0013] If the concentration is below 0.8 mmol / g, there are too few sites, and the grafted linear polyethyleneimine is distributed in an island-like pattern, failing to form an effective hydrophobic-antibacterial barrier. Periodate oxidation, while introducing aldehyde groups, also cleaves the cellulose chains. Excessive oxidation exceeding 2.0 mmol / g will cause a sharp decrease in fiber strength, making it brittle, and severely deteriorating the overall mechanical properties of the board.

[0014] Furthermore, in the hyperbranched polyethyleneimine grafted with flexible segments, the flexible segments are polyethylene oxide or polypropylene oxide, the number average molecular weight of the flexible segments is 1000-2000 g / mol, and the mass grafting rate of the flexible segments on the hyperbranched polyethyleneimine backbone is 5%-20%.

[0015] To ensure the toughening effect, the chain segments must have sufficient length and degrees of freedom. If the molecular weight is too low and the chain segments are too short, their mobility is limited, resulting in negligible toughening effect, essentially equivalent to ineffective grafting. Excessively long flexible chain segments lead to excessive aggregation and phase separation between the hyperbranched polyethyleneimine backbone and the fiber / resin matrix, creating weak points at the interface and impairing mechanical properties. Furthermore, excessively long chain segments increase steric hindrance, hindering uniform dispersion in the fiber slurry and affecting the uniformity of the final board properties.

[0016] Further, the preparation steps of the waterproof and antibacterial fiberboard are as follows: S1. Oxidized long wood fibers with a surface aldehyde content of 0.8-2.0 mmol / g are compounded with unoxidized long wood fibers and then mixed evenly with urea-formaldehyde adhesive to obtain a functional surface layer prepolymer; S2. Flexible segment grafted hyperbranched polyethyleneimine, accounting for 5%-12% of the oven-dry weight of the inner layer unoxidized long wood fibers, is uniformly compounded with the inner layer unoxidized long wood fibers and urea-formaldehyde adhesive to obtain a toughened inner layer prepolymer; S3. The surface layer prepolymer is laid as the upper and lower surface layers, and the inner layer prepolymer is laid as the middle layer to form a three-layer board blank; S4. Linear polyethyleneimine solution is sprayed sequentially on the upper and lower surface layers of the laid board blank, and the spraying amount is controlled to have a molar ratio of amino groups to aldehyde groups of the surface oxidized fibers of (0.4~0.5 mmol / g). .6):1; reducing agent solution; C8-C18 halohydrocarbon solution, the spraying amount of which controls the molar ratio of halohydrocarbon to the linear polyethyleneimine amino to be (0.8~1.2):1; S5. Place the sprayed board blank in an environment of 80-100℃ and 70%-90% relative humidity for 3-8 minutes for curing; S6. Hot press the cured board blank, the hot pressing curing adopts a two-stage heating program: the first stage is held at 165-180℃ and 2.0MPa unit pressure for 30-90 seconds; the second stage is heated to 180-195℃ and the unit pressure is increased to 3.0MPa to complete the curing and obtain waterproof and antibacterial fiberboard.

[0017] Adding 5%-12% by oven-dry weight of flexible segments grafted with hyperbranched polyethyleneimine allows these flexible segments to act as "nanosprings" to disperse stress. The hyperbranched structure forms an entangled network with fibers and adhesives. Simultaneously, its abundant amine groups can capture formaldehyde released from urea-formaldehyde resin adhesives, forming localized covalent anchors to ensure its toughening effect.

[0018] First, spray linear polyethyleneimine to bring it into contact with the aldehyde groups; then spray a reducing agent to reduce the unstable Schiff base to a stable CN bond; finally, spray a haloalkane to react with the amine groups on the cured linear polyethyleneimine. The molar ratio (0.4~0.6):1 ensures that most of the aldehyde groups are reacted while the linear polyethyleneimine is not excessive. If the ratio is too low, the aldehyde group reaction will be incomplete; if the ratio is too high, excess linear polyethyleneimine will be physically adsorbed rather than chemically bonded, affecting subsequent reactions and surface properties. A molar ratio (0.8~1.2):1 aims to maximize the conversion of available amine groups on the linear polyethyleneimine into quaternary ammonium salts. This ensures the conversion of primary amines to generate highly reactive quaternary ammonium salts.

[0019] During curing, maintain a temperature of 80-100℃: This provides sufficient kinetic energy to promote the rapid initial completion of the reductive amination reaction, while also enhancing the activity of reagent molecules. Maintain a relative humidity of 70%-90%: This high-humidity environment prevents fiber drying and, through capillary action, drives the functional reagents in the surface solution to penetrate into the interior of the slab and towards the surface-to-inner layer interface. 3-8 minutes: This is the optimal time window for the initial completion of the reaction and adequate reagent penetration. Too short a time results in insufficient reaction and penetration; too long a time may lead to excessive inward migration of reagents, affecting the surface functional density.

[0020] During the adhesive application process, the surface layer uses a low amount of adhesive. The cross-linking of the aldehyde groups of the oxidized fiber with linear polyethyleneimine already contributes to the "self-adhesive" strength. Excessive adhesive may block the surface functionalization reaction, leading to a decrease in performance. The inner layer uses a higher amount of adhesive, which is derived from pure physical bonding. Sufficient adhesive is required to form a strong skeleton to support the overall mechanical strength.

[0021] Furthermore, the reducing agent is sodium cyanoborohydride or sodium borohydride; the halohydrocarbon is dissolved in an organic solvent to form a spray solution. Beneficial effects

[0022] In the functional surface layer of this invention, linear polyethyleneimine forms a stable covalent bond with the aldehyde groups of oxidized fibers through reductive amination. The abundant amino groups on its molecular chain further undergo alkylation reactions with haloalkanes, constructing a dense and robust quaternary ammonium salt hydrophobic layer in situ on the fiber surface. This hydrophobic structure, anchored by chemical bonds, avoids the migration and precipitation of traditional physical additives, giving the board extremely low water absorption thickness swelling rate and extremely low water absorption rate.

[0023] The quaternary ammonium salt structure generated through a chemical reaction on the surface of this invention can disrupt microbial cell membranes through electrostatic interactions. Because the antibacterial groups are fixed by covalent bonds, its antibacterial activity exhibits remarkable durability, remaining intact even after water immersion and friction.

[0024] The flexible segments grafted with hyperbranched polyethyleneimine introduced into the toughening inner layer of this invention have the following effects: on the one hand, the flexible segments can effectively absorb and disperse stress; on the other hand, the hyperbranched structure forms physical entanglement and hydrogen bonds and covalent bonds with the fiber and urea-formaldehyde resin adhesive, which can play a role in toughening and strengthening, ensuring that the solution can still produce 1-2 mm ultrathin fiberboard under the high rigidity conditions caused by oxidized long fibers.

[0025] This invention employs a functional surface layer composed of oxidized and unoxidized fibers, allowing functionalized reagents to partially penetrate inwards. During hot pressing, cross-linking reactions occur between the aldehyde groups of the oxidized surface fibers, the inner adhesive, and the functionalized reagents, forming a "gradient transition interface" at the surface-core layer interface where chemical composition and mechanical properties continuously change. This eliminates stress concentration caused by a clear interface, significantly improving interlayer bonding strength and overall structural stability. Furthermore, by oxidizing the cellulose hydroxyl groups, the amount of formaldehyde used in conventional fiberboard production is reduced, decreasing formaldehyde release at the adhesive source. Specific Implementation

[0026] The technical solutions 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. Example 1

[0027] Step S1: Disperse 300g of oven-dry long wood fibers in deionized water, add 60g of sodium periodate, and stir and react for 5 hours at 45℃ in the dark. Wash and vacuum dry to obtain oxidized long wood fibers. After determining the surface aldehyde content to be 1.5 mmol / g by the hydroxylamine hydrochloride method, mix 110g of the above oxidized long wood fibers with 400g of unoxidized long wood fibers, and then add 21.6g of urea-formaldehyde resin adhesive and mechanically stir evenly to obtain a functional surface prepolymer. The formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive is 1.05:1.

[0028] Step S2: Under nitrogen protection, 100g of hyperbranched polyethyleneimine was dissolved in tetrahydrofuran, and 12g of carboxyl-terminated polypropylene oxide monobutyl ether with a molecular weight of 1800, 1.2g of dicyclohexylcarbodiimide, and 0.12g of 4-dimethylaminopyridine were added. The mixture was reacted at 65°C for 8 hours. After the reaction was completed, the mixture was purified and dried to obtain PPO-grafted hyperbranched polyethyleneimine with a grafting rate of 12%.

[0029] 440g of unoxidized long wood fibers with an oven-dry weight, 85g of urea-formaldehyde adhesive, and PPO-g-hyperbranched polyethyleneimine from step S2 were stirred and mixed evenly, and dried at 60°C to obtain the inner fiber layer. The formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive was 1.10:1.

[0030] Step S3: 140g of surface fiber and 440g of inner fiber are laid in a three-layer slab structure of "surface-inner-surface".

[0031] Step S4: Spray 105g of 10% linear polyethyleneimine aqueous solution, 20g of 6% sodium cyanoborohydride aqueous solution, and 20.5g of 16% hexadecane ethanol solution onto the upper and lower surfaces of the laid slab in sequence.

[0032] Step S5: Transfer the slab treated in S4 to a curing chamber and treat it for 6 minutes at 90°C and 80% relative humidity to allow the initial reduction amination and alkylation reactions to proceed, and the functional reagents to partially penetrate and fix.

[0033] After curing, the slab is fed into a hot press, following the procedure: First stage: Hold pressure at 170℃ and 2.0MPa for 60 seconds. Then, raise the temperature to 185℃ and simultaneously increase the pressure to 3.0MPa, holding for 120 seconds. After hot pressing, the slab is depressurized, cooled, trimmed, and sanded to obtain a waterproof and antibacterial fiberboard of the target thickness. Example 2

[0034] Step S1: Disperse 300g of oven-dried long wood fibers in deionized water, add 60g of sodium periodate, and stir and react for 5 hours at 45℃ in the dark. Wash and vacuum dry to obtain oxidized long wood fibers. After determining the surface aldehyde content to be 1.5 mmol / g using the hydroxylamine hydrochloride method, the above oxidized long wood fibers are compounded with unoxidized long wood fibers at a mass ratio of 1:1. Then, 16.5g of urea-formaldehyde resin adhesive is added and mechanically stirred until homogeneous to obtain surface fibers. The formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive is 1.20:1.

[0035] Step S2: Under nitrogen protection, 100g of hyperbranched polyethyleneimine was dissolved in tetrahydrofuran, and 12g of carboxyl-terminated polypropylene oxide monobutyl ether with a molecular weight of 1800, 1.2g of dicyclohexylcarbodiimide, and 0.12g of 4-dimethylaminopyridine were added. The mixture was reacted at 65°C for 8 hours. After the reaction was completed, the mixture was purified and dried to obtain PPO-grafted hyperbranched polyethyleneimine with a grafting rate of 12%.

[0036] 440g of unoxidized long wood fibers with an oven-dry weight, 85g of urea-formaldehyde adhesive, and 30g of PPO-g-hyperbranched polyethyleneimine from step S2 were stirred and mixed evenly, and dried at 60°C to obtain the inner fiber layer. The formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive was 1.15:1.

[0037] Step S3: 140g of surface fiber and 440g of inner fiber are laid in a three-layer slab structure of "surface-inner-surface".

[0038] Step S4: Spray 105g of 10% linear polyethyleneimine aqueous solution, 20g of 6% sodium borohydride aqueous solution, and 30.0g of 16% bromooctane ethanol solution sequentially onto the upper and lower surfaces of the laid slab.

[0039] Step S5: Transfer the slab treated in S4 to a curing chamber and treat it for 6 minutes at 90°C and 80% relative humidity to allow the initial reduction amination and alkylation reactions to proceed, and the functional reagents to partially penetrate and fix.

[0040] After curing, the slab is fed into a hot press, following the procedure: First stage: Hold pressure at 180℃ and 2.0MPa for 60 seconds. Then, raise the temperature to 195℃ and simultaneously increase the pressure to 3.0MPa, holding for 120 seconds. After hot pressing, the slab is depressurized, cooled, trimmed, and sanded to obtain a waterproof and antibacterial fiberboard of the target thickness. Example 3

[0041] Step S1: Disperse 300g of oven-dried long wood fibers in deionized water, add 60g of sodium periodate, and stir and react for 5 hours at 45℃ in the dark. Wash and vacuum dry to obtain oxidized long wood fibers. After determining the surface aldehyde content to be 2.0 mmol / g by the hydroxylamine hydrochloride method, the above oxidized long wood fibers and unoxidized long wood fibers are compounded at a mass ratio of 1:1. Then, 18.5g of urea-formaldehyde resin adhesive is added and mechanically stirred evenly to obtain surface fibers. The formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive is 1.05:1.

[0042] Step S2: Under nitrogen protection, 100g of hyperbranched polyethyleneimine was dissolved in an appropriate amount of tetrahydrofuran, and 20g of carboxyl-terminated polypropylene oxide monobutyl ether with a molecular weight of 2000, 1.2g of dicyclohexylcarbodiimide, and 0.12g of 4-dimethylaminopyridine were added. The mixture was reacted at 65℃ for 8 hours. After the reaction was completed, the mixture was purified and dried to obtain PPO-grafted hyperbranched polyethyleneimine with a grafting rate of 20%.

[0043] 440g of unoxidized long wood fibers with an oven-dry weight, 100g of urea-formaldehyde adhesive, and 30g of PPO-g-hyperbranched polyethyleneimine from step S2 were stirred and mixed evenly, and dried at 60°C to obtain the inner fiber layer. The formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive was 1.15:1.

[0044] Step S3: 140g of surface fiber and 440g of inner fiber are laid in a three-layer slab structure of "surface layer, inner layer, surface layer".

[0045] Step S4: Spray 105g of 10% linear polyethyleneimine aqueous solution, 20g of 6% sodium cyanoborohydride aqueous solution, and 40.0g of 10% octadecane ethanol solution sequentially onto the upper and lower surfaces of the laid slab.

[0046] Step S5: Transfer the slab treated in S4 to a curing chamber and treat it for 6 minutes at 90°C and 80% relative humidity to allow the initial reduction amination and alkylation reactions to proceed, and the functional reagents to partially penetrate and fix.

[0047] After curing, the slab is fed into a hot press, following the procedure: First stage: Hold pressure at 165℃ and 2.0MPa for 60 seconds. Then, raise the temperature to 180℃ and simultaneously increase the pressure to 3.0MPa, holding for 120 seconds. After hot pressing, the slab is depressurized, cooled, trimmed, and sanded to obtain a waterproof and antibacterial fiberboard of the target thickness. Example 4

[0048] Step S1: Disperse 300g of oven-dried long wood fibers in deionized water, add 60g of sodium periodate, and stir and react for 5 hours at 45℃ in the dark. Wash and vacuum dry to obtain oxidized long wood fibers. After determining the surface aldehyde content to be 2.0 mmol / g by the hydroxylamine hydrochloride method, the above oxidized long wood fibers and unoxidized long wood fibers are compounded at a mass ratio of 1:1. Then, 18.5g of urea-formaldehyde resin adhesive is added and mechanically stirred evenly to obtain surface fibers. The formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive is 1.05:1.

[0049] Step S2: Under nitrogen protection, 100g of hyperbranched polyethyleneimine was dissolved in an appropriate amount of tetrahydrofuran, and 12g of carboxyl-terminated polypropylene oxide monobutyl ether with a molecular weight of 2000, 1.2g of dicyclohexylcarbodiimide, and 0.12g of 4-dimethylaminopyridine were added. The mixture was reacted at 65℃ for 8 hours. After the reaction was completed, the mixture was purified and dried to obtain PPO-grafted hyperbranched polyethyleneimine with a grafting rate of 12%.

[0050] 440g of unoxidized long wood fibers with an oven-dry weight, 100g of urea-formaldehyde adhesive, and 30g of PPO-g-hyperbranched polyethyleneimine from step S2 were stirred and mixed evenly, and dried at 60°C to obtain the inner fiber layer. The formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive was 1.20:1.

[0051] Step S3: 140g of surface fiber and 440g of inner fiber are laid in a three-layer slab structure of "surface layer, inner layer, surface layer".

[0052] Step S4: Spray 105g of 10% linear polyethyleneimine aqueous solution, 20g of 6% sodium cyanoborohydride aqueous solution, and 40.0g of 10% octadecane ethanol solution sequentially onto the upper and lower surfaces of the laid slab.

[0053] Step S5: Transfer the slab treated in S4 to a curing chamber and treat it for 6 minutes at 90°C and 80% relative humidity to allow the initial reduction amination and alkylation reactions to proceed, and the functional reagents to partially penetrate and fix.

[0054] After curing, the slab is fed into a hot press, following the procedure: First stage: Hold pressure at 165℃ and 2.0MPa for 60 seconds. Then, raise the temperature to 180℃ and simultaneously increase the pressure to 3.0MPa, holding for 120 seconds. After hot pressing, the slab is depressurized, cooled, trimmed, and sanded to obtain a waterproof and antibacterial fiberboard of the target thickness. Example 5

[0055] Step S1: Disperse 300g of oven-dried long wood fibers in deionized water, add 60g of sodium periodate, and stir and react for 5 hours at 45℃ in the dark. Wash and vacuum dry to obtain oxidized long wood fibers. After determining the surface aldehyde content to be 2.0 mmol / g by the hydroxylamine hydrochloride method, the above oxidized long wood fibers and unoxidized long wood fibers are compounded at a mass ratio of 1:1. Then, 18.5g of urea-formaldehyde resin adhesive is added and mechanically stirred evenly to obtain surface fibers. The formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive is 1.05:1.

[0056] Step S2: Under nitrogen protection, 100g of hyperbranched polyethyleneimine was dissolved in an appropriate amount of tetrahydrofuran, and 12g of carboxyl-terminated polypropylene oxide monobutyl ether with a molecular weight of 2000 was added. The reaction was carried out at 65°C for 8 hours under the action of a catalyst. After the reaction was completed, the mixture was purified and dried to obtain PPO-grafted hyperbranched polyethyleneimine with a grafting rate of 12%.

[0057] 440g of unoxidized long wood fibers with an oven-dry weight, 100g of urea-formaldehyde adhesive, and 30g of PPO-g-hyperbranched polyethyleneimine from step S2 were stirred and mixed evenly, and dried at 60°C to obtain the inner fiber layer. The formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive was 1.10:1.

[0058] Step S3: 140g of surface fiber and 440g of inner fiber are laid in a three-layer slab structure of "surface layer, inner layer, surface layer".

[0059] Step S4: Spray 105g of 10% linear polyethyleneimine aqueous solution, 20g of 6% sodium cyanoborohydride aqueous solution, and 40.0g of 10% octadecane ethanol solution sequentially onto the upper and lower surfaces of the laid slab.

[0060] Step S5: Transfer the slab treated in S4 to a curing chamber and treat it for 6 minutes at 90°C and 80% relative humidity to allow the initial reduction amination and alkylation reactions to proceed, and the functional reagents to partially penetrate and fix.

[0061] After curing, the slab is fed into a hot press, following the procedure: First stage: Hold pressure at 165℃ and 2.0MPa for 60 seconds. Then, raise the temperature to 180℃ and simultaneously increase the pressure to 3.0MPa, holding for 120 seconds. After hot pressing, the slab is depressurized, cooled, trimmed, and sanded to obtain a waterproof and antibacterial fiberboard of the target thickness.

[0062] Comparative Example 1 differs from Example 1 in that the long wood fibers are not subjected to oxidation treatment.

[0063] Comparative Example 2 differs from Example 1 in that linear polyethyleneimine is not sprayed on the surface.

[0064] Comparative Example 3 differs from Example 1 in that hyperbranched polyethyleneimine is not added to the inner layer.

[0065] Comparative Example 4 differs from Example 1 in that no halogenated hydrocarbons are added to the surface layer.

[0066] One hundred fiberboard samples were prepared using the process method provided in Example 1, with fiberboard dimensions of 1200×800×1mm. Performance tests were then conducted on the fiberboard samples according to national standard requirements. The test results are shown in Table 1: Fiberboard Samples Provided in Example 1 Table 1

[0067] The water absorption rate and thickness swelling rate of the example are far superior to those of the comparative example. The 98% antibacterial rate and Grade 0 mildew resistance are outstanding, with the antibacterial and mildew-resistant properties stemming from the firmly attached quaternary ammonium salt bactericidal groups on the surface. Through the "self-adhesive" effect of the oxidized fibers combined with a low molar ratio urea-formaldehyde resin adhesive, the formaldehyde emission level reaches that of E1 grade boards.

[0068] Note: Moisture content determination shall be performed according to the method specified in 4.3 of GB / T17657-2013. Static bending strength and modulus of elasticity determination shall be performed according to the method specified in 4.7 of GB / T17657-2013, and specimen balancing treatment shall be performed. If the specimen does not fail, the maximum load-bearing capacity shall be used as Fmax for static bending strength calculation. Internal bond strength determination shall be performed according to the method specified in 4.11 of GB / T17657-2013, and specimen balancing treatment shall be performed. Water absorption thickness swelling rate determination shall be performed according to method 1 of water absorption swelling rate determination specified in 4.4 of GB / T17657-2013, requiring an immersion time of 24h ± 5min, and the measurement after immersion shall be completed within 10min. Water absorption rate shall be determined according to the 24h water absorption rate determination method specified in 4.6 of GB / T17657-2013. Formaldehyde emission was determined according to the formaldehyde emission test specifications in GB18580-2017. Quantitative antibacterial testing was conducted according to ISO 22196:2011, using Staphylococcus aureus as the bacterial strain. Antifungal performance testing was conducted according to GB / T24346-2009.

Claims

1. A waterproof and antibacterial fiberboard, characterized in that, The fiberboard has a thickness of 1-2 mm and consists of three layers: a functional surface layer, a toughening inner layer, and another functional surface layer. The fibers in the functional surface layer are a mixture of long wood fibers treated with periodate oxidation and unoxidized long wood fibers. The functional surface layer contains 0.8-2.0 mmol / g of aldehyde groups on the fiber surface; the functional surface layer is grafted with linear polyethyleneimine through a reducing amination reaction, and the grafted polyethyleneimine further undergoes a quaternization reaction with C8-C18 halogenated hydrocarbons to form a hydrophobic and antibacterial surface; the number average molecular weight of the linear polyethyleneimine is 5000-50000 g / mol; the toughening inner layer is composed of unoxidized long wood fibers and hyperbranched polyethyleneimine grafted with flexible segments; the functional surface layer and the toughening inner layer also contain urea-formaldehyde resin adhesive, and the board is bonded and formed by hot pressing, and the formaldehyde to urea molar ratio of the urea-formaldehyde resin adhesive is (1.05-1.20):

1.

2. The waterproof and antibacterial fiberboard according to claim 1, characterized in that, The long wood fibers are coniferous or broadleaf fibers, with a fiber length of 1.0~2.0 mm.

3. The waterproof and antibacterial fiberboard according to claim 1, characterized in that, The mass ratio of unoxidized long wood fibers to oxidized long wood fibers in the functional surface layer is (1~4):

1.

4. The waterproof and antibacterial fiberboard according to claim 1, characterized in that, In the hyperbranched polyethyleneimine grafted with flexible segments, the flexible segments are polyethylene oxide or polypropylene oxide; the number average molecular weight of the flexible segments is 1000-2000 g / mol, and the mass grafting rate of the flexible segments on the hyperbranched polyethyleneimine backbone is 5%-20%.

5. The waterproof and antibacterial fiberboard according to claim 1, characterized in that, The method for preparing the waterproof and antibacterial fiberboard includes the following steps: S1. Oxidized long wood fibers with a surface aldehyde content of 0.8-2.0 mmol / g are compounded with unoxidized long wood fibers and then mixed evenly with urea-formaldehyde adhesive to obtain a functional surface layer prepolymer; S2. Flexible segment grafted hyperbranched polyethyleneimine, accounting for 5%-12% of the oven-dry weight of the inner layer unoxidized long wood fibers, is uniformly compounded with the inner layer unoxidized long wood fibers and urea-formaldehyde adhesive to obtain a toughened inner layer prepolymer; S3. The functional surface layer prepolymer is laid as the upper and lower surface layers, and the toughened inner layer prepolymer is laid as the middle layer to form a three-layer board; S4. Linear polyethyleneimine solution is sprayed sequentially on the upper and lower surface layers of the laid board, and the spraying amount is controlled to have a molar ratio of amino groups to aldehyde groups of the surface oxidized fibers of (0.8-2.0 mmol / g) of the solution. 4~0.6):1; reducing agent solution; C8-C18 halohydrocarbon solution, the spraying amount of which controls the molar ratio of halohydrocarbon to the linear polyethyleneimine amino to be (0.8~1.2):1; S5. Place the sprayed slab in an environment of 80-100℃ and 70%-90% relative humidity for 3-8 minutes for curing; S6. Hot press the cured slab, the hot pressing curing adopts a two-stage heating program: the first stage is at 165-180℃ and 2.0MPa unit pressure for 30-90 seconds; the second stage is heated to 180-195℃ and 3.0MPa unit pressure to complete the curing and obtain waterproof and antibacterial fiberboard.

6. The waterproof and antibacterial fiberboard according to claim 5, characterized in that, In step S4, the reducing agent is sodium cyanoborohydride or sodium borohydride; the haloalkane is dissolved in an organic solvent to form a spray solution.

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