Biological modification preparation method of flame-retardant moisture-proof plant-based board

Abstract

The invention relates to the technical field of wood processing and functional modification, and discloses a biological modification preparation method of a flame-retardant and moisture-proof plant-based board, which comprises the following steps: firstly, preparing a modification liquid containing phytic acid, a boron source trapping agent, metal salt and plant triglyceride; immersing the plant fiber veneer, adding laccase and lipase, and carrying out vacuum pressure impregnation; then constant-temperature incubation is conducted, lipase is used for catalyzing hydrolysis of triglyceride, the product glycerol is captured in situ to generate flame-retardant glyceryl borate, fatty acid and metal ions are combined to generate hydrophobic metal soap, and meanwhile laccase activates the surface of lignin of the veneer; and finally, carrying out gradient drying and hot press molding to obtain a finished product. Through enzymatic cascade reaction, a compact hydrophobic barrier and a heat-resistant cross-linked network are constructed in the deep layer of the plate, and the self-gluing effect of laccase is cooperated, so that formaldehyde-free manufacturing is realized, and the flame-retardant grade, the water-resistant and moisture-proof performance and the mechanical stability of the plate are improved.

Description

Technical Field

[0001] This invention relates to the field of wood processing and functional modification technology, specifically to a bio-modification preparation method for flame-retardant and moisture-proof plant-based boards. Background Technology

[0002] Plant-based panels are widely used in building decoration, furniture manufacturing, and packaging and transportation due to their natural texture, high specific strength, and ease of processing. However, as a porous biomass material, plant-based units are naturally rich in hydroxyl groups, exhibiting strong hygroscopicity and flammability. In humid environments, the panels are prone to absorbing water, swelling, deformation, and even mold and decay; while in fire scenarios, their flammability poses a serious safety hazard. Therefore, endowing plant-based panels with excellent flame-retardant and moisture-proof properties has always been a research hotspot in this field.

[0003] Current flame-retardant and moisture-proof modification technologies mainly employ physical impregnation or surface coating methods, but technical bottlenecks remain in practical applications. Regarding moisture and hydrophobicity, commonly used paraffin emulsions or hydrophobic oils, due to their large molecular weight and high viscosity, struggle to penetrate the microscopic pores and cell cavities deep within plant fibers. They often only form a surface coating, leaving the interior of the board susceptible to moisture absorption. Furthermore, these physically applied hydrophobic agents are prone to migration or loss due to changes in environmental temperature and humidity over long-term use. In terms of flame retardancy, traditional inorganic flame retardants, while inexpensive, typically exhibit strong hygroscopicity and high water solubility. This not only easily leads to moisture absorption and efflorescence in the board but also causes loss with moisture migration, resulting in a decline in flame-retardant efficacy over time. In addition, existing modification processes often fail to balance adhesive performance. Exogenously added flame retardants and hydrophobic agents tend to form a weak boundary layer on the veneer surface, hindering the wetting and penetration of the adhesive and reducing the internal bond strength of the board.

[0004] More importantly, traditional engineered wood-based panel production relies excessively on aldehyde-based adhesives such as urea-formaldehyde or phenol-formaldehyde resins, inevitably leading to formaldehyde release issues and making it difficult to meet increasingly stringent environmental standards. While laccase-activated lignin self-gluing technology offers a formaldehyde-free solution, single enzyme-activated bonding strength is often low and highly susceptible to interference from other functionalized additives in the system, making it difficult to maintain a high level of mechanical bond strength while introducing highly efficient flame-retardant and moisture-proof functions. Therefore, there is an urgent need to develop a plant-based panel modification method that can achieve deep penetration and fixation, overcome the moisture absorption defects of flame retardants, and is perfectly compatible with formaldehyde-free bio-gluing technology. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a bio-modification preparation method for flame-retardant and moisture-proof plant-based boards. This method solves the problems of existing plant-based board modification technologies, such as the difficulty of deep penetration and fixation of hydrophobic agents, the easy loss of inorganic flame retardants due to moisture absorption and weakening of the bonding interface, and the difficulty of achieving both durable flame-retardant and moisture-proof performance and high mechanical strength in a formaldehyde-free manufacturing system.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a flame-retardant and moisture-proof plant-based board through biomodification, comprising the following steps: S1. Preparation of multifunctional precursor modified liquid: Phytic acid and boron source scavenger were added sequentially to deionized water. After adjusting the pH value, metal salt was added for complexation, followed by the addition of plant triglycerides for shear emulsification to prepare multifunctional precursor modified liquid. S2. Vacuum pressure impregnation treatment: The plant fiber veneer is placed in an impregnation tank, the multifunctional precursor modification liquid is injected, and a biological enzyme preparation containing laccase and lipase is added simultaneously. The impregnation is carried out by first vacuuming and then pressurizing to obtain the impregnated plant fiber veneer. S3. Constant temperature enzymatic cascade incubation: The impregnated plant fiber veneer is placed in a constant temperature and humidity environment for incubation. Lipase is used to catalyze the hydrolysis of plant triglycerides. The generated glycerol is captured in situ by a boron source scavenger. The generated fatty acids combine with metal ions. At the same time, laccase is used to activate the lignin surface of the plant fiber veneer to obtain the incubated plant fiber veneer. S4. Gradient drying: The incubated plant fiber veneer is dried by staged heating until the preset moisture content is reached, and the dried plant fiber veneer preform is obtained. S5. High-temperature hot pressing molding: The dried plant fiber veneer blanks are hot-pressed to cause the internal glycerol borate ester to undergo condensation cross-linking and complete the fixation of the metal soap, thus obtaining flame-retardant and moisture-proof plant-based boards.

[0007] By adopting the above technical solution, and through a modification strategy that combines enzymatic cascade reaction with in-situ chemical capture, excellent dual effects of flame retardancy and moisture resistance are achieved. The specific innovative mechanism is as follows: In-situ transformation and deep fixation of hydrophobic precursors: Traditional methods of directly impregnating macromolecular oils or hydrophobic agents are difficult to penetrate the tiny pores of plant fiber veneers and are prone to seepage. This invention prepares an emulsified plant triglyceride precursor in step S1, utilizing its fluidity to penetrate deep into the wood. During incubation in step S3, lipase is used to hydrolyze the plant triglyceride in situ into glycerol and long-chain fatty acids. At this time, the premixed metal ions in the system rapidly react with the generated long-chain fatty acids, forming in-situ insoluble metal fatty acid salts. This metal soap precipitates and crystallizes in situ within the wood pores, constructing a durable hydrophobic barrier that effectively prevents moisture intrusion.

[0008] Glyceryl Boronate Esters for Capturing and Flame-Retardant Framework Construction: Glyceryl, a byproduct of vegetable oil hydrolysis, is typically hygroscopic, and its residue in the substrate can reduce moisture resistance. This invention utilizes a boron-based scavenger to capture newly generated glyceryl in situ, reacting it to form glyceryl borate esters. This process not only eliminates the hygroscopic potential of glyceryl but also transforms it into an effective char-forming agent. In the high-temperature hot-pressing stage of step S5, the glyceryl borate ester undergoes further dehydration and condensation, forming a heat-resistant organic boron crosslinked network. This network rapidly expands and carbonizes upon combustion, forming a dense glassy char layer that isolates oxygen and heat.

[0009] Synergistic enhancement of phytic acid-metal complexes: Phytic acid introduced into the system has multiple functions. First, as a multidentate ligand, phytic acid forms a dynamically balanced complex with metal ions and boric acid in solution, which helps stabilize metal ions and prevents them from precipitating prematurely before impregnation. Second, during combustion, the phosphorus source provided by phytic acid has a synergistic effect with the boron and metal sources, promoting catalytic char formation and reducing the heat release rate.

[0010] Establishment of a glue-free self-adhesive system: In step S3, laccase introduced enzymatically oxidizes the lignin on the surface of the plant fiber veneer, generating phenolic radicals. During the hot-pressing process in step S5, these radicals undergo a coupling reaction, achieving chemical bonding between the veneers; simultaneously, the in-situ generated glycerol borate ester polymer network interweaves between the fibers, acting as a reinforcing phase. The synergistic effect of these two processes allows the board to achieve excellent internal bond strength without the addition of traditional formaldehyde adhesives.

[0011] Preferably, the amounts of each component, by weight, are as follows: 200-400 parts of deionized water relative to 100 parts of dry plant fiber veneer; the raw materials of the multifunctional precursor modification liquid include: 5.0-15.0 parts of phytic acid, 2.0-5.0 parts of boron source scavenger, 2.0-10.0 parts of metal salt, and 3.0-8.0 parts of plant triglycerides; the amount of the biological enzyme preparation added, based on the oven-dry plant fiber veneer, is: 10-50 U / g of laccase and 100-500 U / g of lipase.

[0012] By adopting the above technical solution, the concentration ratio of the reaction precursors was optimized. The specific ratio of phytic acid to metal salt ensured the stability of the modified solution after pH adjustment, avoiding emulsion demulsification or precipitation; the limited ratio of plant triglycerides to lipase ensured that the oils were fully hydrolyzed within a limited incubation time, providing sufficient fatty acids for constructing the hydrophobic layer, and simultaneously providing sufficient glycerol for constructing the flame-retardant network, thus achieving the best balance between moisture-proof and flame-retardant properties.

[0013] Preferably, in step S1, the boron source scavenger is a mixture of boric acid and sodium tetraborate decahydrate in a mass ratio of 5:1 to 10:1; the metal salt is selected from zinc acetate dihydrate or magnesium chloride hexahydrate; and the vegetable triglyceride is selected from refined soybean oil, linseed oil or tung oil.

[0014] By employing the above technical solutions, the combination of boric acid and boron forms a buffer system, which is beneficial for maintaining the pH environment for enzyme activity, and the synergistic effect of the two can improve the complexation efficiency of glycerol. Zinc acetate or magnesium chloride is chosen as the metal source because the metal soaps formed by zinc / magnesium ions and long-chain fatty acids have extremely low surface energy and excellent hydrophobicity, and their oxides can act as sintering aids at high temperatures to enhance the strength of the carbon layer. Soybean oil, linseed oil, or tung oil with high unsaturation are selected because their long-chain structure is more conducive to forming a dense hydrophobic filling within the pores.

[0015] Preferably, in step S1, the heating temperature during the preparation process is 35–40°C; the pH value is adjusted to a range of 4.8–5.5; the shear emulsification speed is 3000–5000 rpm, and the time is 15–30 minutes. When the metal salt is zinc acetate dihydrate, the pH value is adjusted to a range of 4.8–5.5; when the metal salt is magnesium chloride hexahydrate, the pH value is adjusted to 5.2.

[0016] By employing the above technical solutions, strictly controlling the pH range is crucial to ensuring that metal ions remain in a complexed and dissolved state in the impregnation solution without damaging the enzyme activity. Specific pH adjustment windows are set based on the different solubility product constants of zinc and magnesium salts, ensuring the homogeneity and permeability of the modified solution. The high-shear emulsification process disperses the oil into micron-sized droplets, facilitating its passage through the pits and vessels of the plant fiber veneer.

[0017] Preferably, in step S2, the plant fiber veneer is selected from poplar veneer, eucalyptus veneer, or pine veneer; the laccase is selected from *Trametes versicolor* or *Bacillus subtilis*; and the lipase is selected from *Candida antarcticis* or *Aspergillus oryzae*. The specific procedure for the vacuum pressure impregnation treatment is as follows: first, a vacuum is drawn to -0.08 MPa to -0.09 MPa and maintained for 30–45 minutes; then, atmospheric pressure is restored and pressurized to 0.8 MPa to 1.2 MPa, and maintained for 60–120 minutes.

[0018] By adopting the above technical solution and using a variable pressure impregnation process of negative pressure extraction and positive pressure injection, the air in the plant cell cavity is first discharged. Then, the pressure difference is used to force the high-viscosity emulsion modification liquid to overcome capillary resistance and penetrate deep into the core layer of the plant fiber veneer, thereby achieving uniform modification of the entire cross section and avoiding the core-skin effect.

[0019] Preferably, in step S3, the conditions for the isothermal enzymatic cascade incubation are: temperature 40-50°C, relative humidity 90%-95%, and incubation time 3.0-6.0 hours.

[0020] By adopting the above technical solution, a high-humidity environment was established to prevent the plant fiber veneer from losing moisture too quickly, providing the necessary moisture medium for the enzymatic hydrolysis reaction. The temperature range of 40–50°C covers the high-activity temperature window of the selected lipase and laccase. Under these conditions, the oil hydrolysis rate matches the glycerol capture rate, ensuring the efficient in-situ reaction.

[0021] Preferably, in step S4, the gradient drying specifically includes: drying at 50-60°C for 2.0-4.0 hours, followed by raising the temperature to 70-85°C for continued drying; the preset moisture content is 8%-12%.

[0022] By adopting the above technical solution, the gradient heating strategy avoids substrate cracking or surface hardening caused by rapid evaporation of moisture. At the same time, the low temperature stage helps to maintain some enzyme activity until the early stage of drying, thus prolonging the surface activation effect.

[0023] Preferably, in step S5, the process parameters for high-temperature hot pressing are: hot pressing temperature 165~185℃, unit pressure 2.0~5.0MPa, and hot pressing time controlled at 40~60 seconds / mm plate thickness.

[0024] By employing the above technical solution, under these high temperature and high pressure conditions, physical and chemical changes occur simultaneously: the metal fatty acid salt melts and flows, filling microscopic pores; the glycerol borate ester completes the final cross-linking and curing, forming a rigid skeleton; and the free radical coupling reaction between lignins is completed, giving the board high bonding strength. This step achieves structural integration of the flame-retardant and moisture-proof components with the substrate.

[0025] This invention provides a bio-modification method for preparing flame-retardant and moisture-proof plant-based boards. It has the following beneficial effects: 1. This invention utilizes lipase to hydrolyze plant triglycerides immersed in the interior of plant fiber veneer into long-chain fatty acids in situ, and induces them to react rapidly with pre-placed metal ions to generate insoluble metal fatty acid salt precipitates in situ. These in-situ generated hydrophobic crystals can tightly fill the cell cavities and micropores of wood, constructing a hydrophobic barrier across the entire cross-section. This not only significantly reduces the water absorption thickness swelling rate of the board, but also effectively solves the technical problem that traditional external coating hydrophobic agents are difficult to penetrate and easy to lose.

[0026] 2. This invention innovatively utilizes a boron source scavenger to convert glycerol, a byproduct of oil hydrolysis, into flame-retardant glycerol borate esters in situ. This eliminates the hygroscopic hazards caused by glycerol residue and achieves resource utilization of waste. During high-temperature hot pressing and combustion, the glycerol borate esters undergo cross-linking and condensation to form a heat-resistant skeleton, and form a phosphorus-boron-metal synergistic char-forming system with phytic acid metal complexes. This promotes the rapid formation of a dense and continuous expanded char layer on the surface of the board, effectively isolating heat and oxygen, and improving the flame retardant rating of the board.

[0027] 3. This invention utilizes laccase to enzymatically activate the lignin on the surface of plant fiber veneers, generating highly active phenolic oxygen radicals, which initiate chemical covalent bonding between veneers during hot pressing. Simultaneously, the glycerol borate ester polymer network generated within the system interweaves between the fibers, acting as a reinforcing anchoring effect similar to rivets. This dual bonding mechanism of bio-enzyme-activated chemical cross-linking allows the board to achieve excellent internal bond strength and static bending strength without the addition of traditional urea-formaldehyde / phenolic resin adhesives, thus solving the formaldehyde release problem at its source. Detailed Implementation

[0028] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Examples 1-3: Example

[0030] This embodiment provides a bio-modification preparation method for flame-retardant and moisture-proof plant-based boards, specifically including the following steps: Step S1: Preparation of multifunctional precursor modification liquid Add 200 parts of deionized water (relative to the dry weight of plant fiber veneer) to the solution tank and heat to 35°C. Then add 5.0 parts of phytic acid (70% concentration) and 2.0 parts of boron source scavenging agent in sequence; wherein the boron source scavenging agent is composed of boric acid and sodium tetraborate decahydrate mixed at a mass ratio of 5:1.

[0031] After stirring and dissolving, adjust the pH of the system to 4.8 using 1M NaOH solution.

[0032] Add 2.0 parts of zinc acetate dihydrate to the solution and stir at low speed for 20 minutes to perform metal complexation. Turn on the high shear disperser at 3000 rpm and slowly add 3.0 parts of refined soybean oil dropwise, and disperse at low speed for 15 minutes to obtain the precursor emulsion.

[0033] Step S2: Vacuum pressure impregnation treatment Select fast-growing poplar veneer (300mm×300mm×1.5mm) with a moisture content of 10% as plant fiber veneer, and weigh 100 parts by dry weight.

[0034] The veneer was placed into an impregnation tank, a precursor emulsion was injected, and biological enzyme preparations were added simultaneously; the amount of laccase added was 10 U / g, and the amount of lipase added was 100 U / g.

[0035] The impregnation procedure is as follows: First, vacuum to -0.08MPa and maintain for 30 minutes; then restore to normal pressure and pressurize to 0.8MPa, maintain for 60 minutes; finally, depressurize and drain the liquid from the surface of the veneer.

[0036] Step S3: Isothermal enzymatic cascade incubation The impregnated veneer was placed in a constant temperature and humidity chamber, with the temperature set at 40℃ and the relative humidity at 90%, and the incubation time at 3 hours.

[0037] During this stage, lipase catalyzes the hydrolysis of soybean oil, and the product glycerol is captured in situ by boric acid, while fatty acids bind with zinc ions; at the same time, laccase activates the lignin surface.

[0038] Step S4: Gradient drying After incubation, the veneer is placed in an oven and dried at 50°C for 2 hours. Then, the temperature is increased to 70°C and the drying continues until the moisture content of the veneer drops to 10%-12%.

[0039] Step S5: High-temperature hot pressing molding After drying, the veneers are assembled into three layers according to their cross-grain pattern, without applying any external adhesive between the veneers.

[0040] Place the plate into a hot press for hot pressing at a temperature of 165℃ and a unit pressure of 2.0MPa. The hot pressing time is controlled at 40 seconds per mm of plate thickness.

[0041] Step S6: Post-processing After hot pressing, the board is allowed to cool naturally to room temperature, then trimmed and sanded to obtain the finished product. Example

[0042] This embodiment provides a bio-modification preparation method for flame-retardant and moisture-proof plant-based boards, specifically including the following steps: Step S1: Preparation of multifunctional precursor modification liquid Add 250 parts of deionized water (relative to the dry weight of plant fiber veneer) to the solution tank and heat to 40°C. Then add 10.0 parts of phytic acid (70% concentration) and 3.5 parts of boron source scavenging agent in sequence; wherein the boron source scavenging agent is composed of boric acid and sodium tetraborate decahydrate mixed at a mass ratio of 8:1.

[0043] After stirring and dissolving, adjust the pH of the system to 5.2 using 1M NaOH solution.

[0044] Add 4.0 parts of magnesium chloride hexahydrate to the solution and stir at medium speed for 20 minutes to establish a complex system.

[0045] Turn on the high-shear disperser at 4000 rpm and slowly add 5.0 parts of flaxseed oil. Shear disperse for 20 minutes to obtain the precursor emulsion.

[0046] Step S2: Vacuum pressure impregnation treatment Eucalyptus veneer with a moisture content of 10% (size 300mm×300mm×1.7mm) was selected as plant fiber veneer, and 100 parts of dry weight were weighed.

[0047] The veneer was placed into an impregnation tank, the precursor emulsion was injected, and biological enzyme preparations were added simultaneously; the amount of laccase added was 30 U / g, and the amount of lipase added was 300 U / g.

[0048] The impregnation procedure is as follows: First, evacuate to -0.09 MPa and maintain for 40 minutes; then restore to normal pressure and pressurize to 1.0 MPa, and maintain for 90 minutes.

[0049] Step S3: Isothermal enzymatic cascade incubation The impregnated veneer was placed in a constant temperature and humidity chamber, with the temperature set at 45℃, relative humidity at 95%, and incubation time at 4.5 hours.

[0050] During this stage, flaxseed oil is hydrolyzed to produce glycerol and fatty acids. Glycerol is captured by boric acid to form glycerol borate esters, and magnesium ions react with fatty acids to form metal soap precipitates.

[0051] Step S4: Gradient drying After incubation, the veneer is placed in an oven and dried at 55°C for 2.5 hours. Then, the temperature is raised to 75°C and the drying continues until the moisture content of the veneer drops to 9%-10%.

[0052] Step S5: High-temperature hot pressing molding After drying, the veneers are assembled into 5 layers with the grain arranged in a crisscross pattern, without applying any external adhesive.

[0053] Place the plate into a hot press for hot pressing at a temperature of 175℃ and a unit pressure of 3.5MPa. The hot pressing time is controlled at 50 seconds per mm of plate thickness.

[0054] Step S6: Post-processing After hot pressing, the sheet material undergoes stacking heat treatment, cooling, edge trimming, and sanding to obtain the finished product. Example

[0055] This embodiment provides a bio-modification preparation method for flame-retardant and moisture-proof plant-based boards, specifically including the following steps: Step S1: Preparation of multifunctional precursor modification liquid Add 400 parts of deionized water (relative to the dry weight of plant fiber veneer) to the solution tank and heat to 40°C. Then add 15.0 parts of phytic acid (70% concentration) and 5.0 parts of boron source scavenging agent in sequence; wherein the boron source scavenging agent is composed of boric acid and sodium tetraborate decahydrate mixed at a mass ratio of 10:1.

[0056] After stirring and dissolving, adjust the pH of the system to 5.5 using 1M NaOH solution.

[0057] Add 10.0 parts of zinc acetate dihydrate to the solution and stir at high speed for 30 minutes to form a complex system.

[0058] Turn on the high shear disperser at 5000 rpm and slowly add 8.0 parts of tung oil. Shear disperse for 30 minutes to obtain the precursor emulsion.

[0059] Step S2: Vacuum pressure impregnation treatment Select pine veneer (300mm×300mm×2.0mm) with a moisture content of 8% as plant fiber veneer, and weigh 100 parts of dry weight.

[0060] The veneer was placed into an impregnation tank, the precursor emulsion was injected, and biological enzyme preparations were added simultaneously; among them, the amount of laccase added was 50U / g, and the amount of lipase added was 500U / g.

[0061] The impregnation procedure is as follows: First, evacuate to -0.09 MPa and maintain for 45 minutes; then restore to normal pressure and pressurize to 1.2 MPa, and maintain for 120 minutes.

[0062] Step S3: Isothermal enzymatic cascade incubation The impregnated veneer was placed in a constant temperature and humidity chamber, with the temperature set at 50℃ and the relative humidity at 95%, and the incubation time at 6 hours.

[0063] During this stage, tung oil hydrolyzes, glycerol is captured by boric acid, and zinc ions and fatty acids form a zinc soap layer in situ.

[0064] Step S4: Gradient drying After incubation, the veneer is placed in an oven and dried at 60°C for 4 hours. Then, the temperature is raised to 85°C and the drying continues until the moisture content of the veneer drops to 8%-10%.

[0065] Step S5: High-temperature hot pressing molding After drying, the veneers are assembled into 7 layers according to the cross-grain pattern, without applying any external adhesive.

[0066] The wood is placed in a hot press at 185℃ and 5.0 MPa, with the pressing time controlled at 60 seconds per mm of board thickness. Under these conditions, glycerol borate esters cross-link with the wood components.

[0067] Step S6: Post-processing After hot pressing, the boards are stacked for insulation, cooled, trimmed, and sanded to obtain the finished product.

[0068] Comparative Examples 1-6: Comparative Example 1: Compared with Example 2, the difference is that no chemical modification components and biological enzyme preparations are added. Only deionized water is used instead of the multifunctional precursor modification liquid for the same vacuum pressure impregnation, drying and hot pressing treatment. Everything else is the same.

[0069] Comparative Example 2: Compared with Example 2, the difference is that plant triglycerides and biological enzyme preparations (lipase, laccase) are not added. Instead, oleic acid (long-chain fatty acid) and glycerol (glycerol) in the same molar amount as the theoretical yield of Example 2 are directly added to the modified solution. After strong emulsification and dispersion, the solution is impregnated. All other process parameters are the same.

[0070] Comparative Example 3: Compared with Example 2, the difference is that no boron source scavenging agent (boric acid and sodium tetraborate) was added to the modified solution, while the other components and preparation process are the same.

[0071] Comparative Example 4: Compared with Example 2, the difference is that no biological enzyme preparations (laccase and lipase) were added during the impregnation process, or an inactivated enzyme solution that had been inactivated by high temperature was added, while the other components and process parameters were the same.

[0072] Comparative Example 5: Compared with Example 2, the difference is that no plant triglycerides and lipase were added to the modified solution (phytic acid, boron source, metal salt and laccase were retained), while the other process parameters were the same.

[0073] Comparative Example 6: Compared with Example 2, the difference is that no polyvalent metal salt (magnesium chloride hexahydrate) was added to the modified solution, while the other components and process parameters are the same.

[0074] Test Example 1-3: Test Example 1: Process Feasibility and Loss Resistance Test Experimental description: This test verifies the fixation stability of the chemically modified system within the plant substrate. Boards prepared in Examples 1-3 and Comparative Examples 1-6 were selected and cut into 100mm × 100mm samples, with 5 parallel samples per group. The samples were dried in an oven at 103±2℃ to constant weight, and the initial dry weight was recorded. Initial limiting oxygen index The dried sample was then completely immersed in deionized water at a ratio of 1:20 and a temperature of 25±2℃ for 24 hours, with the water stirred every 8 hours. The sample was then removed, its surface moisture was removed with absorbent paper, and it was dried in an oven at 103±2℃ until constant weight. The dry weight after immersion was recorded. And the limiting oxygen index after immersion was measured. Calculate the mass loss rate. and flame retardant efficacy retention rate , where 19.0 is the baseline value for the limiting oxygen index of untreated plant substrate.

[0075] Experimental data: Table 1. Results of water wash-resistance test Group <![CDATA[Initial dry weight m0 (g)]]> <![CDATA[Dry weight m1 (g) after immersion in water]]> Quality loss rate (%) Initial LOI (%) LOI (%) after immersion in water Flame retardant efficacy retention rate (%) Example 1 18.42 18.16 1.41 29.4 28.5 91.3 Example 2 19.05 18.89 0.84 33.6 32.9 95.2 Example 3 20.11 19.98 0.65 35.8 35.3 97 Comparative Example 1 15.6 15.32 1.79 19.2 19.1 / Comparative Example 2 18.98 16.45 13.33 32.1 21.4 18.3 Comparative Example 3 18.55 17.88 3.61 28.3 24.1 54.8 Comparative Example 4 18.8 17.2 8.51 21.5 20.2 / Comparative Example 5 17.5 16.65 4.86 30.2 23.5 40.2 Comparative Example 6 18.25 16.9 7.4 31 22.8 31.7 (Note: The data is the average value of parallel samples) Results analysis: Table 1 shows the following: The mass loss rate in Examples 1-3 ranged from 0.65% to 1.41% after washing. The flame retardant efficacy retention rate was above 90% in all cases, with no decrease in the flame retardant value. Comparative Example 2, using a physical addition method, showed a mass loss rate of 13.33% and a flame retardant efficacy retention rate of only 18.3%, indicating that physically mixed oleic acid and glycerol could not form an effective adhesion within the wood pores, easily dissolving or floating in water, leading to functional failure. The metal fatty acid salts and glycerol borate esters generated through enzymatic reactions in the examples are non-water-soluble, achieving component fixation.

[0076] In Comparative Example 3, without the addition of a boron source scavenger, the mass loss rate increased to 3.61%, and the flame retardant efficacy retention rate decreased to 54.8%. This indicates that the lack of boric acid complexation with glycerol leads to increased product water solubility, and the lack of borophytic acid synergistic effect reduces the system's water resistance.

[0077] Comparative Example 4: No biological enzymes added, initial The value (21.5%) was lower than that of the example. The vegetable oil did not undergo hydrolysis, and the metal ions could not be converted into precipitated fatty acid salts. They mostly existed in the form of water-soluble salts, resulting in a high mass loss rate (8.51%), which made it impossible to construct a hydrophobic flame retardant network.

[0078] Data confirms that the synergistic reaction of lipase hydrolysis, metal ion precipitation, and boric acid complexation is key to ensuring the water-resistant fixation of the modified components within the plant substrate.

[0079] Test Example 2: Flame Retardant Performance Test Experimental description: Plate samples prepared in Examples 1-3 and Comparative Examples 1-6 were selected to evaluate their combustion behavior and char formation performance. The plates were cut into strips measuring 150 mm × 10 mm × plate thickness. Using an oxygen index meter, the flow rate of the oxygen-nitrogen mixture was adjusted to determine the minimum oxygen concentration at which combustion was just maintained, and this was recorded as the limiting oxygen index (UOI). The sheet metal was cut into 100mm × 100mm × sheet thickness square samples, the bottom and sides of which were wrapped with aluminum foil, and placed on the sample stage of the cone calorimeter. The thermal radiation flux was set to 50kW / m². 2 Record the ignition time (TTI), peak heat release rate (PHRR), total heat release (THR), and char yield (Char Yield).

[0080] Experimental data: Table 2. Flame retardant and combustion performance test data Group Limiting Oxygen Index (LOI) (%) Ignition time TTI (s) <![CDATA[Peak heat release rate PHRR (kW / m 2 )]]> <![CDATA[Total Heat Release THR (MJ / m 2 )]]> Carbon residue rate (%) Example 1 29.1 18 148.2 41.5 30.8 Example 2 33.4 23 120.5 29.3 41.2 Example 3 35.6 29 98.7 23.4 45.9 Comparative Example 1 19.2 9 291.4 68.9 10.8 Comparative Example 2 25.1 12 224.3 55.6 20.5 Comparative Example 3 26.5 16 179.8 48.1 23.7 Comparative Example 4 21.3 11 245.6 62.3 14.9 Comparative Example 5 27.9 17 161.2 44.5 28.1 Comparative Example 6 23.7 13 203.4 51.7 18.6 (Note: The data is the arithmetic mean of three independent tests.) Results analysis: Table 2 shows the following: Examples 1-3 The value increased from 29.1% to 35.6% with increasing precursor concentration, and the PHRR increased from 148.2 kW / m³. 2 Reduced to 98.7kW / m 2 The char residue rate showed an increasing trend. Compared with Comparative Example 1, the PHRR of Example 3 decreased by approximately 66%, and the char residue rate increased by approximately 4 times.

[0081] Comparative Example 2 had a higher PHRR (224.3 kW / m²). 2 The residual char rate (20.5%) was lower than that of the example. The physically added glycerol was easily volatilized upon heating and failed to effectively participate in the construction of the char skeleton; furthermore, the fatty acids that did not undergo complexation with metal ions were unevenly distributed within the substrate, leading to accelerated local thermal decomposition. In the example, the in-situ generated glycerol borate ester and metal soap network promoted the dehydration and char formation of the matrix during thermal decomposition, and this chemical bonding improved the flame retardant efficiency.

[0082] The char residue of Comparative Example 3 (23.7%) was lower than that of Example 1. The lack of a boron source resulted in the failure to capture the enzymatic hydrolysis product glycerol, thus preventing the formation of borate ester cross-linked structures. The limited catalytic char formation effect of the single phytic acid component indicates that the formation of glassy oxides by boron at high temperatures and its synergistic effect with phosphate char formation are crucial for suppressing heat release.

[0083] Comparative Example 4 showed performance close to Comparative Example 1. The vegetable oil in the modified solution did not undergo hydrolysis in an enzyme-free environment, and no metal soaps or glycerol were generated. The residual oil released heat in the early stage of combustion, resulting in a higher PHRR and a shorter TTI.

[0084] Comparative Example 5 The value was 27.9%, but both THR and PHRR were higher than in Example 1. This indicates that the in-situ generated metal fatty acid salt and glycerol borate ester network, in addition to providing hydrophobicity, also participated in the construction of a dense char layer during combustion, increasing the char layer's ability to block heat and oxygen.

[0085] Data show that the metal-phytate-boronate-fatty acid salt hybrid network constructed by enzymatic reaction can form a stable expanded carbon layer at high temperature, thereby reducing the heat release rate and increasing the residual carbon content.

[0086] Test Example 3: Moisture-proof and Physical / Mechanical Performance Test Experimental description: This test evaluated the dimensional stability, surface hydrophobicity, and internal bonding quality of the modified substrate. Substrates prepared in Examples 1-3 and Comparative Examples 1-6 were selected. The samples were cut to a size of 50mm × 50mm. When determining the thickness swelling rate (TS), the center thickness of the sample was measured, and the sample was completely immersed in deionized water at 20±2℃ for 24 hours. After drying the surface, the thickness was measured again, and the percentage increase was calculated. When determining the surface contact angle (CA), a 5mm drop was applied to the sample surface using the seated drop method. Deionized water was used, and the static contact angle was recorded after 3 seconds. The average value of 5 points was taken. When determining the internal bond strength (IB), the sample surface was glued to the metal clip, and a tensile force was applied at a speed of 10 mm / min along the direction perpendicular to the plate surface on a universal testing machine until failure. The maximum load was recorded and the strength value was calculated.

[0087] Experimental data: Table 3. Results of moisture-proof and mechanical performance tests Group 24h water absorption thickness swelling rate TS (%) Surface contact angle CA (°) Internal bond strength IB (MPa) Example 1 11.8 104.5 0.82 Example 2 8.5 116.2 1.05 Example 3 7.1 121.4 1.18 Comparative Example 1 26.4 42.1 0.58 Comparative Example 2 19.3 88.7 0.32 Comparative Example 3 16.7 92.5 0.74 Comparative Example 4 22.1 61.3 0.41 Comparative Example 5 21.5 56.8 0.94 Comparative Example 6 18.2 78.4 0.63 (Note: The data represents the average value of valid samples.) Results analysis: Table 3 shows the following: The thickness swelling rate (TS) of Examples 1-3 ranged from 7.1% to 11.8%, which was better than that of Comparative Example 1 (26.4%). With the increase of hydrophobic components, the contact angle (CA) increased to 121.4° and the internal bond strength (IB) increased to 1.18 MPa, indicating that the modification treatment improved the moisture resistance and enhanced the internal structure.

[0088] Comparative Example 2, using a physical mixing method, showed limited improvement in TS (19.3%) and a decrease in IB to 0.32 MPa. The physically added oils did not undergo chemical transformation and remained in a free state at the fiber interface, acting as a barrier and hindering inter-fiber bonding, leading to a significant decrease in strength. The examples used enzymatic reactions to convert oils into metal soap precipitates and glycerol borate cross-links. The former provides a hydrophobic barrier, while the latter acts as an adhesive reinforcing component, achieving a synergistic effect of moisture resistance and strength. Comparative Example 4, without added enzymes, had a TS of 22.1%, a contact angle of only 61.3°, and a low IB (0.41 MPa). Due to the lack of enzymatic catalysis, the vegetable oil did not undergo hydrolysis, failing to generate hydrophobic metal soaps, and the unreacted oil weakened interlayer bonding. Comparative Example 5, without added vegetable oil, achieved an IB of 0.94 MPa, indicating that laccase activation and phytic acid cross-linking contributed to strength, but the TS was as high as 21.5%, and the contact angle was low, confirming that vegetable triglycerides and their enzymatic hydrolysis products are key components imparting moisture resistance to the board. Comparative Example 6, lacking metal ions, had a TS of 18.2%. Fatty acids cannot form crystalline metallic soaps and exist only as free acids, making it difficult to effectively seal the pores of wood. They are also prone to migration when moisture penetrates, resulting in a less effective moisture-proof effect than in the examples.

[0089] Data shows that the metal fatty acid salts and glycerol borate polymers generated by the enzymatic reaction not only impart hydrophobic and moisture-proof properties to the board, but also enhance mechanical properties through a cross-linking network, thus avoiding the negative impact of directly adding oily substances on the bonding strength.

Claims

1. A method for preparing flame-retardant and moisture-proof plant-based boards through biomodification, characterized in that, Includes the following steps: S1. Preparation of multifunctional precursor modified liquid: Phytic acid and boron source scavenger were added sequentially to deionized water. After adjusting the pH value, metal salt was added for complexation, followed by the addition of plant triglycerides for shear emulsification to prepare multifunctional precursor modified liquid. S2. Vacuum pressure impregnation treatment: The plant fiber veneer is placed in an impregnation tank, the multifunctional precursor modification liquid is injected, and a biological enzyme preparation containing laccase and lipase is added simultaneously. The impregnation is carried out by first vacuuming and then pressurizing to obtain the impregnated plant fiber veneer. S3. Constant temperature enzymatic cascade incubation: The impregnated plant fiber veneer is placed in a constant temperature and humidity environment for incubation. Lipase is used to catalyze the hydrolysis of plant triglycerides. The generated glycerol is captured in situ by a boron source scavenger. The generated fatty acids combine with metal ions. At the same time, laccase is used to activate the lignin surface of the plant fiber veneer to obtain the incubated plant fiber veneer. S4. Gradient drying: The incubated plant fiber veneer is dried by staged heating until the preset moisture content is reached, and the dried plant fiber veneer preform is obtained. S5. High-temperature hot pressing molding: The dried plant fiber veneer blanks are hot-pressed to cause the internal glycerol borate ester to undergo condensation cross-linking and complete the fixation of the metal soap, thus obtaining flame-retardant and moisture-proof plant-based boards.

2. The method for preparing a flame-retardant and moisture-proof plant-based board according to claim 1, characterized in that, The components of the flame-retardant and moisture-proof plant-based board are expressed in parts by weight as follows: Use 200-400 parts of deionized water relative to 100 parts of dry weight of plant fiber veneer; The raw materials of the multifunctional precursor modification liquid include: 5.0-15.0 parts of phytic acid, 2.0-5.0 parts of boron source scavenger, 2.0-10.0 parts of metal salt, and 3.0-8.0 parts of plant triglycerides; The amount of the added biological enzyme preparation, calculated based on the oven-dried plant fiber veneer, is: laccase 10-50 U / g, lipase 100-500 U / g.

3. The method for preparing a flame-retardant and moisture-proof plant-based board according to claim 1, characterized in that, In step S1, the boron source scavenger is a mixture of boric acid and sodium tetraborate decahydrate in a mass ratio of 5:1 to 10:1; the metal salt is selected from zinc acetate dihydrate or magnesium chloride hexahydrate; and the vegetable triglyceride is selected from refined soybean oil, linseed oil or tung oil.

4. The method for preparing a flame-retardant and moisture-proof plant-based board according to claim 1, characterized in that, In step S1, the heating temperature during the preparation process is 35–40°C; the pH value is adjusted to a range of 4.8–5.5; the rotation speed of the shear emulsification is 3000–5000 rpm, and the time is 15–30 minutes.

5. The method for preparing a flame-retardant and moisture-proof plant-based board according to claim 1, characterized in that, In step S2, the vacuum pressure impregnation treatment is specifically performed as follows: first, the vacuum is evacuated to -0.08MPa to -0.09MPa and maintained for 30 to 45 minutes, then the pressure is restored to normal and pressurized to 0.8MPa to 1.2MPa, and maintained for 60 to 120 minutes.

6. The method for preparing a flame-retardant and moisture-proof plant-based board according to claim 1, characterized in that, In step S3, the conditions for the isothermal enzymatic cascade incubation are: temperature 40–50°C, relative humidity 90%–95%, and incubation time 3.0–6.0 hours.

7. The method for preparing a flame-retardant and moisture-proof plant-based board according to claim 6, characterized in that, In step S4, the gradient drying specifically includes: first drying at 50-60°C for 2.0-4.0 hours, then raising the temperature to 70-85°C for continued drying; the preset moisture content is 8%-12%.

8. The method for preparing a flame-retardant and moisture-proof plant-based board according to claim 1, characterized in that, In step S5, the process parameters for high-temperature hot pressing are as follows: the hot pressing temperature is 165-185℃, the unit pressure is 2.0-5.0MPa, and the hot pressing time is controlled at 40-60 seconds / mm plate thickness.

9. The method for preparing a flame-retardant and moisture-proof plant-based board according to claim 3, characterized in that, When the metal salt is zinc acetate dihydrate, the pH value is adjusted in step S1 to a range of 4.8 to 5.5; when the metal salt is magnesium chloride hexahydrate, the pH value is adjusted to 5.2 in step S1.

10. The method for preparing a flame-retardant and moisture-proof plant-based board according to claim 1, characterized in that, In step S2, the plant fiber veneer is selected from poplar veneer, eucalyptus veneer or pine veneer; the laccase is selected from Trametes versicolor or Bacillus subtilis; and the lipase is selected from Candida antarctica or Aspergillus oryzae.