Modified poplar veneer with flame-retardant and mildew-proof functions and manufacturing method of modified poplar veneer

Abstract

The invention discloses a modified poplar veneer with flame-retardant and mildew-proof functions and a manufacturing method of the modified poplar veneer. The method comprises the following steps: pretreating poplar bark to remove lignin and open cell wall holes; preparing a modified solution from phytic acid, amino silane modified chitosan and a metal cation cross-linking agent; the modifier forms a gradient protection structure in the poplar bark through vacuum-pressure impregnation; and after flexible drying, the modified poplar veneer is attached to a base material, and hot press molding is conducted at the temperature of 120-150 DEG C. And hot-pressing and high-temperature triggering esterification and polycondensation reaction are carried out, and a P-N-Si hybrid network is constructed in situ on wood cell walls. According to the prepared veneer, a P-N-Si network contains phosphorus, nitrogen and silicon elements and is covalently combined with wood cell wall hydroxyl, efficient integration of flame retardance, mildew prevention and interface bonding enhancement of the poplar veneer is successfully achieved, and the defects that traditional modification is prone to loss and strength is reduced are overcome.

Description

Technical Field

[0001] This invention relates to the field of wood processing and modification technology, specifically to a modified poplar veneer panel with flame-retardant and mildew-resistant functions and its manufacturing method. Background Technology

[0002] Poplar, a common fast-growing tree species, is characterized by its short growth cycle, abundant resources, and ease of rotary cutting, making it widely used in surface finishing materials (wood veneer) for engineered wood products. However, poplar's natural low density, high porosity, and high nutrient content result in flammability and susceptibility to moisture and mold, limiting its application in building decoration, furniture manufacturing, and other fields.

[0003] In existing technologies, wood is typically impregnated with flame retardants containing elements such as phosphorus, nitrogen, and boron, as well as various mildew inhibitors, to improve its flame retardant and mildew-resistant properties. However, traditional physical impregnation methods have drawbacks: water-soluble agents lack chemical bonding with the internal functional groups of the wood, making them prone to migration and loss in humid environments, leading to a decline in flame retardant and mildew-resistant effects over time. While surface coatings can prevent agent loss to some extent, they can obscure the natural grain of the wood, resulting in a loss of the visual and tactile appeal of the veneer. Furthermore, after treatment with preservatives and flame retardants, the agents often occupy the active functional groups on the wood surface or form an isolation layer, hindering the penetration and curing of adhesives during subsequent processing. This leads to a decrease in the bonding strength of the modified veneer when hot-pressed with the substrate, resulting in quality problems such as delamination and blistering. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a modified poplar veneer panel with flame retardant and mildew-proof functions and its manufacturing method, aiming to solve the problems of easy loss of preservative and flame retardant agents in existing modified wood and the decrease in bonding strength after modification.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a method for manufacturing a modified poplar veneer panel with flame-retardant and mildew-resistant functions, comprising the following steps:

[0006] Step 1: Preprocessing; Pretreatment of poplar veneer raw materials is carried out to remove lignin barriers and open the cell wall pits of the wood. Step 2: Preparation of the modified solution; Phytic acid was used as the acidic building block, aminosilane-modified chitosan was used as the basic building block, and metal cations were added as crosslinking bridging agents. The mixture was then thoroughly mixed to form a stable colloidal modified liquid. Step 3: Vacuum-pressure impregnation; The poplar bark pretreated in step 1 is placed in the modified solution prepared in step 2 and subjected to vacuum-pressure impregnation treatment, so that small molecules in the modified solution enter the cell wall and large molecules remain in the cell cavity, forming a gradient protective structure inside the poplar bark. Step 4: Gentle drying; The impregnated poplar bark is dried, and the drying speed is controlled so that the modifier that has entered the cell wall and remains in the cell cavity undergoes primary crystallization, preventing the modifier from migrating and crystallizing on the surface during subsequent hot pressing. Step 5: Hot pressing; The modified poplar veneer, after being dried flexibly, is attached to a substrate and hot-pressed at a temperature of 120℃~150℃. The high temperature triggers the esterification reaction and the siloxane condensation reaction, and a PN-Si hybrid network is constructed in situ in the wood cell wall to obtain a modified poplar veneer veneer panel with flame retardancy, mildew resistance and reinforcement.

[0007] Furthermore, in step 1, the pretreatment involves soaking the poplar bark raw material in a mixed solution containing 1% to 5% hydrogen peroxide and 1% to 3% glacial acetic acid for 30 to 120 minutes.

[0008] Furthermore, in step 2, the metal cation is selected from Mg²⁺. + Zn² + or Ca² + One or more of the following; the molar ratio of phytic acid, aminosilane-modified chitosan to metal cations is (1~3):(1~2):(0.1~0.5).

[0009] Furthermore, in step 3, the vacuum-pressure impregnation process is as follows: first, vacuum is drawn at -0.08MPa to -0.1MPa for 15 to 30 minutes, then the modified liquid is injected and pressurized to 0.5MPa to 1.0MPa, and the pressure is maintained for 60 to 120 minutes. Finally, the pressure is released and the poplar bark is removed.

[0010] Furthermore, in step 4, the flexible drying adopts a stepped heating drying method, with the initial temperature controlled at 40℃~50℃, and then the temperature is increased to 70℃~85℃ at a rate of 2℃ / min~5℃ / min until the moisture content of the poplar bark is reduced to 8%~12%.

[0011] Furthermore, in step 5, the hot pressing pressure is 1.0MPa~2.5MPa, and the hot pressing time is 3~8 minutes; the substrate includes one of MDF, particleboard, plywood or solid wood board.

[0012] A modified poplar veneer panel with flame-retardant and mildew-resistant functions is prepared by the above-described manufacturing method. The panel comprises a substrate and modified poplar veneer attached to the substrate. The modified poplar veneer has a gradient protective structure, and its cell walls have an in-situ constructed PN-Si hybrid network. The PN-Si hybrid network contains phosphorus, nitrogen, and silicon elements, which are covalently bonded to the hydroxyl groups of the poplar veneer cell walls. The PN-Si hybrid network uses phytic acid as the acidic unit, aminosilane-modified chitosan as the basic unit, and elements selected from Mg²⁺. + Zn² + or Ca² + One or more metal cations in the mixture act as crosslinking bridges and undergo esterification and polycondensation reactions to generate the product.

[0013] Furthermore, this modified poplar veneer panel has the following microstructural characteristics: (1) The cell wall surface and interior of the modified poplar veneer are covered with inorganic mineralized particles composed of the PN-Si hybrid network. A large number of inorganic mineralized particles are densely aggregated and block the tiny pores of the wood to form a physical anti-mold barrier. The PN-Si hybrid network inhibits the activity of mold enzymes by chelating the metal ions necessary for mold growth, thereby achieving chemical anti-mold. (2) The bonding interface between the modified poplar veneer and the substrate has a mechanical interlocking structure formed by the in-situ generated nanoparticle group and the adhesive matrix. The siloxane groups of the aminosilane modified chitosan react with the functional groups of the adhesive to build a cross-interface covalent bridge at the bonding interface.

[0014] Furthermore, the modified poplar veneer panel has a limiting oxygen index (LOI) ≥ 28%, and its bonding strength is increased by 10% to 30% compared with the unmodified poplar veneer panel.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention pre-treats poplar bark to open the pits in the wood cell walls, enabling the modified liquid system to penetrate efficiently into the interior of the wood cell walls, thus providing a reaction space for subsequent in-situ network construction.

[0016] 2. This invention achieves the effect of constructing a gradient protective structure inside poplar veneer by controlling the distribution difference between small molecules and macromolecules in the modified liquid inside the wood.

[0017] 3. This invention triggers esterification and siloxane polycondensation reactions through high-temperature hot pressing at 120℃~150℃, constructing a PN-Si hybrid network containing phosphorus, nitrogen, and silicon elements in situ within the cell wall. The modified agent is then covalently bonded to the hydroxyl groups of the wood cell wall, achieving long-term fixation of the modified agent within the wood. This solves the problem of easy loss of traditional water-soluble agents when exposed to water, and achieves a stable flame-retardant effect.

[0018] 4. This invention forms inorganic mineral particles on and inside the cell wall of wood through a PN-Si hybrid network, which are then densely aggregated to achieve a physical barrier effect that blocks the micropores of wood. At the same time, the hybrid network structure chelates the metal cations necessary for mold growth to inhibit mold enzyme activity, thus achieving a chemical anti-mold effect. The combination of these two methods achieves a physical-chemical synergistic anti-mold effect for poplar veneer.

[0019] 5. This invention achieves the construction of an interfacial mechanical interlocking structure by in-situ generating nanoparticle clusters at the bonding interface between modified poplar veneer and the substrate, which then entangle with the adhesive matrix. Simultaneously, it achieves the construction of a cross-interfacial covalent bridge by chemically reacting the siloxane groups of chitosan modified with aminosilane with the functional groups of the adhesive. These two mechanisms work synergistically to improve the bonding strength of the modified poplar veneer veneer panel, overcoming the defect of decreased bonding performance caused by traditional wood preservative and flame-retardant modifications. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the manufacturing method of the modified poplar veneer panel with flame-retardant and mildew-resistant functions according to the present invention. Figure 2 These are scanning electron microscope (SEM) comparison images of the microstructure of poplar veneer before and after modification according to the present invention. Among them, (a) is the microstructure of unmodified poplar veneer, and (b) is the microstructure of modified poplar veneer. Detailed Implementation

[0021] The following is in conjunction with the appendix Figure 1 and attached Figure 2 The technical solution of this invention is described in detail below. This invention provides a modified poplar veneer panel with flame-retardant and mildew-resistant functions, mainly comprising modified poplar veneer and a substrate. The panel is manufactured through a specific impregnation and hot-pressing process, and the overall manufacturing steps are as follows.

[0022] Step 1: Pretreatment of poplar bark raw materials. The poplar bark is immersed in a mixed solution containing 1%–5% hydrogen peroxide and 1%–3% glacial acetic acid for 30–120 minutes. During this process, the oxidizing effect of hydrogen peroxide and the acidic swelling effect of glacial acetic acid synergistically degrade the lignin in the poplar bark tissue and dissolve a small amount of extractives. This reaction removes physical barriers in the wood pores, opening the pits on the wood cell walls, thereby improving the wood's liquid permeability and providing channels for the deep penetration of subsequent macromolecular and small molecule reagents.

[0023] Step 2, Preparation of the Modification Solution. The modification solution system consists of acidic building blocks, basic building blocks, and a crosslinking bridging agent. Phytic acid is selected as the acidic building block; phytic acid molecules contain six phosphate groups, exhibiting strong metal ion chelating ability and thermally catalytic charging effect. Aminosilane-modified chitosan is selected as the basic building block; the chitosan molecular chain provides film-forming properties and a nitrogen source, while the incorporated silane groups provide thermal stability. A crosslinking bridging agent is selected from Mg²⁺. + Zn² + or Ca² + One or more metal cations are used as crosslinking bridging agents. Phytic acid, aminosilane-modified chitosan, and metal cations are mixed uniformly at a molar ratio of (1~3):(1~2):(0.1~0.5). In solution, the negatively charged phytic acid and the positively charged aminosilane-modified chitosan are combined through electrostatic attraction and hydrogen bonding, while the metal cations form coordination chelate bonds between them, and the system ultimately maintains a stable colloidal state.

[0024] Step 3, Vacuum-Pressure Impregnation. The poplar veneer treated in Step 1 is completely immersed in the modified solution prepared in Step 2. First, a vacuum is created for 15-30 minutes under a negative pressure of -0.08 MPa to -0.1 MPa to forcibly expel air from the cell cavities and pores of the wood. Then, the modified solution is injected and the environment is switched to positive pressure, pressurized to 0.5 MPa to 1.0 MPa, and maintained for 60-120 minutes. Under this pressure, the modified solution penetrates into the poplar veneer. Due to differences in molecular size, small molecules (phytic acid and metal cations) in the modified solution penetrate the micropores of the cell wall and enter the cell wall interior, while the larger molecular weight aminosilane-modified chitosan mainly remains near the cell cavities and pits, resulting in a gradient protective structure from the inside out in the microscopic thickness direction of the poplar veneer.

[0025] Step 4, Gentle Drying. After impregnation, the poplar bark is removed and subjected to a stepped temperature-controlled drying process. The initial temperature is controlled at 40℃~50℃, allowing the surface moisture of the wood to evaporate slowly. The temperature is then steadily increased to 70℃~85℃ at a rate of 2℃ / min~5℃ / min, until the moisture content of the poplar bark decreases to 8%~12%. This stepped, slow temperature increase prevents internal stress concentration caused by violent boiling of moisture and inhibits the rapid migration of solutes to the surface with the moisture. At this time, the modifiers that have entered the cell walls and remained in the cell cavities undergo primary concentration and crystallization in situ, maintaining the gradient distribution pattern formed during the impregnation stage.

[0026] Step 5: Hot Pressing and In-situ Network Construction. The dried modified poplar veneer is coated with adhesive and attached to a substrate (such as MDF, particleboard, plywood, or solid wood) and placed in a hot press. It is held at a pressure of 1.0 MPa to 2.5 MPa and a temperature of 120°C to 150°C for 3 to 8 minutes. Under the stimulation of the high temperature during hot pressing, complex chemical cross-linking reactions occur. The phosphate groups in phytic acid molecules undergo esterification with the free hydroxyl groups on the cellulose and hemicellulose of the wood cell walls; simultaneously, the silanol groups in the aminosilane-modified chitosan undergo dehydration condensation reactions with the hydroxyl groups on the wood surface. These multiple reactions intertwine to construct an in-situ PN-Si hybrid network containing phosphorus, nitrogen, and silicon within the poplar veneer. This hybrid network is firmly anchored to the wood matrix in the form of covalent bonds.

[0027] Combination Figure 2 The comparison images of the microstructure obtained by scanning electron microscopy (SEM) show that... Figure 2 In (a), the unmodified poplar bark cell wall surface is relatively smooth. However, after the above treatment steps, as shown... Figure 2 As shown in (b), a large number of inorganic mineralized particles composed of PN-Si hybrid networks are generated and attached in situ on the cell wall surface and inside of the modified poplar bark.

[0028] The flame-retardant, mildew-resistant, and reinforcing mechanisms of modified poplar veneer panels are as follows. Regarding flame retardancy, during combustion, the PN-Si hybrid network promotes the dehydration and carbonization of the wood matrix, forming a dense char layer. Nitrogen decomposes upon heating, releasing non-flammable gases to dilute oxygen, and silicon transforms into a heat-resistant silica protective layer at high temperatures. These three elements work synergistically in both the gas and solid phases to achieve a limiting oxygen index (LOI) of over 28%. Regarding mildew resistance… Figure 2(b) The densely aggregated inorganic mineralized particles physically seal the micropores on and inside the wood, blocking the path of moisture intrusion and mold spore attachment. Simultaneously, the PN-Si hybrid network possesses strong chelating properties, actively capturing and chelating free metal cations essential for mold growth and metabolism, inhibiting the activity of extracellular decay enzymes in mold. Regarding adhesive reinforcement, at the interface between the modified poplar veneer and the substrate (i.e., the adhesive interface), the in-situ generated inorganic mineralized particle community significantly increases the micro-roughness of the interface. During hot-pressing, the adhesive intertwines and wraps with these particle groups, forming a strong mechanical interlocking structure after curing. Based on this, the active siloxane groups on the aminosilane-modified chitosan segments undergo chemical coupling reactions with the polar functional groups in the adhesive (such as urea-formaldehyde resin or polyurethane adhesive), constructing a cross-interface covalent bridge between the interfaces. The superposition of physical interlocking and chemical bonding significantly improves the adhesive strength of this veneer compared to the unmodified veneer.

[0029] Example 1 In the pretreatment stage, poplar bark is completely immersed in a mixed solution containing 3% hydrogen peroxide and 2% glacial acetic acid for 60 minutes at room temperature, then removed and rinsed with water. In the preparation of the modification solution stage, phytic acid, aminosilane-modified chitosan, and Zn²⁺ are mixed... + The poplar veneer was mixed in a molar ratio of 2:1:0.2. During the impregnation stage, the poplar veneer was placed in an impregnation tank and vacuumed at -0.09 MPa for 20 minutes. Then, the modified liquid was injected and pressurized to 0.8 MPa, maintaining the pressure for 90 minutes. During the drying stage, the temperature was increased from 45°C to 80°C in stages at a rate of 3°C / min until the moisture content reached 10%. During the hot-pressing stage, the modified poplar veneer was stacked with a MDF substrate and hot-pressed at 135°C and 1.5 MPa for 5 minutes to complete the veneer manufacturing. Test results showed that the veneer prepared in this example had a limiting oxygen index (LOI) of 29.5%, achieved a mold resistance level of 0 (no mold growth), and exhibited an 18% increase in bonding strength compared to the untreated poplar veneer veneer.

[0030] Example 2 In the pretreatment stage, poplar bark was soaked in a mixed solution containing 5% hydrogen peroxide and 3% glacial acetic acid for 30 minutes. In the preparation of the modification solution stage, phytic acid, aminosilane-modified chitosan, and Mg²⁺ were mixed... + The mixture was prepared in a molar ratio of 3:2:0.5. During the impregnation stage, a vacuum was applied at -0.1 MPa for 15 minutes, followed by pressurization to 1.0 MPa and holding for 60 minutes. In the drying stage, the temperature was increased from 50°C to 85°C at a rate of 5°C / min until the moisture content reached 8%. In the hot-pressing stage, the modified poplar veneer was stacked with the plywood substrate and hot-pressed at 150°C and 2.0 MPa for 3 minutes. Test results showed that the limiting oxygen index (LOI) of the veneer reached 31.2%, the mildew resistance test was grade 0, and the bonding strength was improved by 25%.

[0031] Example 3 In the pretreatment stage, poplar bark was soaked in a mixed solution containing 1% hydrogen peroxide and 1% glacial acetic acid for 120 minutes. In the preparation of the modification solution stage, phytic acid, aminosilane-modified chitosan, and Ca²⁺ were mixed... + The components were mixed in a molar ratio of 1:1:0.1. During the impregnation stage, a vacuum was applied at -0.08 MPa for 30 minutes, followed by pressurization to 0.5 MPa and holding for 120 minutes. In the drying stage, the temperature was increased from 40°C to 70°C at a rate of 2°C / min until the moisture content reached 12%. In the hot-pressing stage, the components were stacked with a particleboard substrate and hot-pressed at 120°C and 1.0 MPa for 8 minutes. Test results showed that the limiting oxygen index (LOI) reached 28.3%, the mildew resistance test was grade 0, and the bonding strength was improved by 12%.

[0032] In summary, the modified poplar veneer panels prepared by the method and embodiments provided by this invention all achieved a limiting oxygen index (LOI) of over 28%, demonstrating excellent flame retardant properties. Simultaneously, their mildew resistance rating reached level 0, confirming their long-lasting mildew resistance. Furthermore, the bonding strength of the modified veneer panels was generally increased by 12% to 25% compared to untreated veneer panels. The above embodiments and test data fully demonstrate that this invention, through in-situ construction of a PN-Si hybrid network and an interfacial cross-linking mechanism, effectively overcomes the technical defects of traditional wood preservative and flame-retardant modification processes, such as easy agent loss and decreased bonding performance, successfully achieving a highly efficient integration of flame retardancy, mildew resistance, and enhanced bonding in wood veneer panels.

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing a modified poplar veneer panel with flame-retardant and mildew-resistant functions, characterized in that, Includes the following steps: Step 1: Pre-treat the poplar veneer raw material to remove lignin barriers and open the cell wall pores of the wood; Step 2: Using phytic acid as the acidic building block, aminosilane-modified chitosan as the basic building block, and adding metal cations as crosslinking bridging agents, mix evenly to form a stable colloidal modified liquid system. Step 3: Place the pretreated poplar bark from Step 1 into the modified solution prepared in Step 2 and perform vacuum-pressure impregnation treatment, so that small molecules in the modified solution enter the cell wall and large molecules remain in the cell lumen, forming a gradient protective structure inside the poplar bark. Step 4: Dry the impregnated poplar bark, controlling the drying speed to allow the modifier that has entered the cell wall and remains in the cell cavity to undergo primary crystallization, preventing the modifier from migrating and crystallizing on the surface during subsequent hot pressing; Step 5: Attach the flexible and dried modified poplar veneer to the substrate and hot-press it at a temperature of 120℃~150℃. Utilize the high temperature to trigger the esterification reaction and siloxane polycondensation reaction to construct a PN-Si hybrid network in situ in the wood cell wall, thereby obtaining a modified poplar veneer decorative panel with integrated flame retardancy, mildew resistance, and reinforcement.

2. The method for manufacturing the modified poplar veneer panel with flame-retardant and mildew-resistant functions according to claim 1, characterized in that: In step 1, the pretreatment involves soaking the poplar bark raw material in a mixed solution containing 1% to 5% hydrogen peroxide and 1% to 3% glacial acetic acid for 30 to 120 minutes.

3. The method for manufacturing the modified poplar veneer panel with flame-retardant and mildew-resistant functions according to claim 1, characterized in that: In step 2, the metal cation is selected from Mg²⁺. + Zn² + or Ca² + One or more of the following; the molar ratio of phytic acid, aminosilane-modified chitosan to metal cations is (1~3):(1~2):(0.1~0.5).

4. The method for manufacturing the modified poplar veneer panel with flame-retardant and mildew-resistant functions according to claim 1, characterized in that: In step 3, the vacuum-pressure impregnation process is as follows: first, vacuum is drawn at -0.08MPa to -0.1MPa for 15 to 30 minutes, then the modified liquid is injected and pressurized to 0.5MPa to 1.0MPa, and the pressure is maintained for 60 to 120 minutes. Finally, the pressure is released and the poplar bark is removed.

5. The method for manufacturing the modified poplar veneer panel with flame-retardant and mildew-resistant functions according to claim 1, characterized in that: In step 4, the flexible drying adopts a stepped heating drying method, with the initial temperature controlled at 40℃~50℃, and then the temperature is increased to 70℃~85℃ at a rate of 2℃ / min~5℃ / min until the moisture content of poplar bark is reduced to 8%~12%.

6. The method for manufacturing the modified poplar veneer panel with flame-retardant and mildew-resistant functions according to claim 1, characterized in that: In step 5, the hot pressing pressure is 1.0MPa~2.5MPa, and the hot pressing time is 3~8 minutes; the substrate includes one of MDF, particleboard, plywood or solid wood board.

7. A modified poplar veneer panel with flame-retardant and mildew-resistant functions, characterized in that, The decorative panel is manufactured by the manufacturing method according to any one of claims 1 to 6, comprising a substrate and modified poplar veneer attached to the substrate; the modified poplar veneer has a gradient protective structure internally, and its cell walls have an in-situ constructed PN-Si hybrid network; the PN-Si hybrid network contains phosphorus, nitrogen, and silicon elements, which are covalently bonded to the hydroxyl groups of the poplar veneer cell walls; the PN-Si hybrid network uses phytic acid as an acidic unit, aminosilane-modified chitosan as a basic unit, and elements selected from Mg²⁺. + Zn² + or Ca² + One or more metal cations in the mixture act as crosslinking bridges and undergo esterification and polycondensation reactions to generate the product.

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