Preparation method and application of mildew-proof bamboo wood with high strength and stable size

Abstract

The invention provides a preparation method of mildew-proof bamboo wood with high strength and stable size, which comprises the following steps: carrying out alkali pretreatment on bamboo wood to be treated, dissolving chitosan in an acetic acid aqueous solution, then dispersing in distilled water, adjusting the pH value to 4.8-5.0, adding AgNO3 and tannic acid to obtain a chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew-proof agent, and then adding the chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew-proof agent to obtain the mildew-proof bamboo wood with high strength and stable size. And spraying on the surface of the bamboo wood subjected to alkali pretreatment, and carrying out spraying and drying circular treatment for 8 times. The invention further provides application for preparing furniture such as tables and chairs and kitchen utensils. The bamboo wood prepared through the method is good in mildew protection effect, the mechanical property and the size stability of the material are enhanced, and the treatment method is environmentally friendly, efficient and capable of adapting to industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of bamboo material processing, and particularly relates to a preparation method and application of high-strength, dimensionally stable mildew-proof bamboo material. Background Art

[0002] Bamboo, a natural, renewable biomass material, is widely used in construction, furniture, and other fields due to its rapid growth, abundant resources, and high strength. It not only alleviates the imbalance between supply and demand in the timber market but also serves as a carbon storage medium, playing a significant role in reducing CO2 emissions and mitigating climate change. Consequently, it has garnered significant attention. However, bamboo's inherent hygroscopicity and high concentration of nutrients, such as polysaccharides and proteins, create favorable conditions for the reproduction and growth of microorganisms, leading to surface mold, dimensional deformation, and degradation of mechanical properties. Mold can even cause allergies and infections in humans, posing a serious threat to health and safety.

[0003] Currently, common methods for preventing mold in bamboo include chemical impregnation and biological control. Chemical impregnation involves soaking the bamboo in a solution of a mildew inhibitor, allowing it to penetrate deep into the material. These mildew inhibitors often contain ingredients such as copper, chromium, arsenic, and pentachlorophenol, which can have adverse effects on human health and the environment. Furthermore, the complex processing conditions may hinder their industrial applicability. Heat treatment involves using high temperatures (typically above 220°C) to reduce the content of nutrients such as starch within the bamboo structure, thereby preventing mold growth. However, this method can easily lead to a loss of mechanical properties, and the high energy consumption of the heat treatment process restricts its application. Biological control methods primarily involve functionally modifying bamboo using microorganisms such as fungi and bacteria, or natural extracts. These methods have attracted widespread attention due to their mild processing conditions, low energy consumption, and environmental friendliness. However, natural mildew inhibitors pose challenges such as high cost, inconsistent mildew prevention effectiveness, and difficulty in large-scale production.

[0004] Inorganic nanoparticles are a new class of materials that have been widely used in chemical, biological, and energy fields due to their unique nano-properties. Metal nanoparticles (Ag, Cu, Zn) and photocatalytic nanomaterials (TiO2, ZnO) have become promising antibacterial candidates due to their broad-spectrum antibacterial effects and photocatalytic oxidation capabilities. However, inorganic nanoantimicrobial agents face key technical limitations: (1) Inherent agglomeration seriously affects the stability of dispersion. (2) Weak interfacial bonding with the matrix leads to nanoparticle shedding, resulting in rapid attenuation of the antibacterial effect. These limitations collectively hinder the formation of durable protective coatings, thereby limiting their green engineering applications in bamboo modification. Bio-based inorganic nanocomposites composed of natural polymers and inorganic nanoparticles address these issues through multi-scale synergy. The polymer matrix promotes the stabilization of nanoparticles through hydrogen bonding and π-π stacking interactions, while enhancing mechanical properties and dimensional stability. Crucially, the hybrid coatings exhibit durable antibacterial properties and excellent hydrophobicity. This approach can minimize the loss of metal nanoparticles in the environment, meeting the requirements of green development. In addition, the current method of modifying bamboo and wood with mildew inhibitors usually adopts the immersion method. In order to ensure that the bamboo is completely immersed in the mildew-proof aqueous solution, more antibacterial and mildew-proof aqueous solution is often required, resulting in low solution utilization. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and provide a method for preparing high-strength, dimensionally stable mildew-resistant bamboo material and its application. The bamboo material prepared by this method has good mildew protection effect, and enhances the mechanical properties and dimensional stability of the material. The processing method is green and efficient and can be adapted to industrial production.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing high-strength, dimensionally stable mildew-proof bamboo material, the method comprising:

[0007] S1. Cut bamboo timber 1m above the ground, remove the green and yellow bamboo, and cut it into boards according to the requirements;

[0008] S2, cutting the board obtained in S1 into blank sizes, such as the preliminary shapes of components such as tabletops and chair legs, and then planing, slotting, and carving to obtain blank bamboo materials;

[0009] S3, using a deburring tool to remove burrs from the blank bamboo material obtained in S2, washing with water to remove dust, and drying to obtain the bamboo material to be processed;

[0010] S4, immersing the bamboo material to be treated obtained in S3 in an alkali pretreatment solution at a temperature of 80° C., washing with deionized water, and drying to obtain alkali-pretreated bamboo material;

[0011] The present invention removes some nutrients from the bamboo through alkali pretreatment, enlarging its pores. The treated bamboo is sugar- and starch-free, but contains fibrous pores. This reduces the nutrients available for mold growth, inhibiting mold growth to a certain extent and improving the bamboo's mold resistance. Furthermore, the alkali treatment exposes a large number of hydroxyl groups in the cellulose, providing anchoring conditions for the subsequent spraying of CS / TA / Ag. This creates a stable, compact, and uniform cross-linked structure on the bamboo surface through bonding, filling the bamboo's natural defects and improving the material's mechanical properties and dimensional stability.

[0012] S5, dissolving chitosan (CS) in an acetic acid aqueous solution to obtain a chitosan acetic acid solution, and then dispersing it in distilled water, adjusting the pH value to 4.8-5.0, and then adding AgNO3 and tannic acid (TA), and stirring at room temperature to obtain a chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor (abbreviated as CS / TA / Ag);

[0013] The present invention significantly improves the mildew resistance, dimensional stability and mechanical properties of bamboo through the synergistic effect of alkaline pretreatment and chitosan / tannic acid / silver bio-based organic-inorganic hybrid system;

[0014] Under acidic conditions, the amino groups (-NH2) of chitosan are protonated to -NH3 + , combines with the phenolic hydroxyl groups in tannic acid through electrostatic adsorption; at the same time, the amino hydroxyl groups (-OH) on the chitosan molecular chain form a dense hydrogen bond network with the phenolic hydroxyl groups (-OH) of tannic acid through hydrogen bonding; the catechol groups in tannic acid reduce silver ions to silver particles (Ag) in situ, and anchor them in the chitosan long chain through electrostatic and coordination bonds, thereby improving the dispersibility of silver particles in the system and improving its anti-loss performance; in the present invention, tannic acid and chitosan are both natural polymer materials, which avoid the toxicity problem of traditional chemical reducing agents (such as sodium borohydride), and the polyphenol structure of tannic acid can reduce Ag + , and can limit particle growth through the capping effect, thereby obtaining ultra-small size and high density silver particles, which enable them to exert excellent antibacterial effects. In addition, the silver particles formed by in-situ reduction are fixed in chitosan through chemical bonds, avoiding the migration and aggregation of particles. CS / TA / Ag as a reinforcing phase expands the interface area of ​​bamboo, effectively transmits and disperses stress, forms a more uniform stress distribution, and improves the mechanical properties of the material. At the same time, silver particles release silver ions and reactive oxygen species (ROS), which increases cell permeability and leakage of contents, effectively inhibiting the growth of mold;

[0015] S6. Using a spray gun, spray the chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor obtained in S5 onto the surface of the alkali-pretreated bamboo material obtained in S4, and then dry it at 80° C. for 10 to 15 minutes. The spraying and drying processes are repeated 8 times, and the final drying is performed at 103° C. for 7 to 8 hours to obtain a high-strength, dimensionally stable mildew-resistant bamboo material.

[0016] The spraying conditions are: air pressure of 0.5 MPa, spraying distance of 20 cm to 50 cm;

[0017] The high-strength, dimensionally stable, mildew-proof bamboo material is assembled into a finished product, and the assembly method can be through mortise and tenon joints, screws or gluing.

[0018] The present invention also provides an application of the high-strength, dimensionally stable, mildew-resistant bamboo material prepared by the above-mentioned preparation method. The high-strength, dimensionally stable, mildew-resistant bamboo material is used to prepare furniture such as tables and chairs, and kitchen tableware.

[0019] The invention deposits a chitosan-tannic acid-silver (CS / TA / Ag) bio-based organic-inorganic hybrid mildew inhibitor in situ on the surface of bamboo by precise spraying.

[0020] The present invention adopts a spraying process to fix the bio-based inorganic composite mildew inhibitor on the surface of the bamboo material, which saves dosage, reduces costs and is suitable for large-scale industrial production.

[0021] Preferably, the bamboo material in S1 is 3-5 year old moso bamboo.

[0022] Preferably, the drying temperature in S3 is 60° C. to 100° C., and the drying time is 12 h to 24 h.

[0023] Preferably, the alkaline pretreatment liquid in S4 is a sodium hydroxide aqueous solution with a mass fraction of 4%, and the immersion treatment time is 30 minutes to 40 minutes.

[0024] Preferably, the moisture content of the bamboo material after the alkali pretreatment in S4 is 8% to 12%.

[0025] Preferably, the acetic acid aqueous solution in S5 is an acetic acid aqueous solution with a mass fraction of 2%.

[0026] Preferably, the stirring time in S5 is 10 h to 12 h.

[0027] Preferably, the final concentration of chitosan in the chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor in S5 is 1 g / L to 5 g / L, and the final concentration of tannic acid is 1 g / L to 10 g / L; the molar ratio of silver nitrate to tannic acid is 1:15.

[0028] Preferably, the high-strength, dimensionally stable mildew-proof bamboo material in S6 has a modulus of rupture of 178.18 MPa to 187.23 MPa, and an elastic modulus of 6.97 Gpa to 7.55 Gpa; the high-strength, dimensionally stable mildew-proof bamboo material has an efficacy of 82.50% to 93.75% against citrinum in a simulated environmental condition of 28°C and 85% relative humidity for 28 days, and an efficacy of 100% against citrinum.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] The present invention first pre-treats bamboo with an alkaline solution to remove nutrients. A chitosan-tannic acid-silver (CS / TA / Ag) bio-based organic-inorganic hybrid mildew inhibitor is then deposited in situ on the bamboo surface via precision spraying. Compared to impregnation, the spraying process is simpler to operate, offers high agent utilization, and is suitable for large-scale production. The bamboo produced by this method exhibits excellent mildew resistance, significant anti-bleeding properties, suitability for large-scale industrial production, and low cost. It also enhances the bamboo's mechanical properties and dimensional stability, effectively addressing the problem of bamboo's susceptibility to mildew and decay in high-humidity or outdoor environments.

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The macromorphology (first row), SEM images (the third row is an enlarged view of the corresponding details in the second row), and EDS images (the fourth row) of Example 1 and Comparative Examples 1 and 3 of the present invention are shown. Note: Natural bamboo (a1-a4); Alk from Comparative Example 1 (b1-b4); Alk / CS / TA / Ag-Sp from Example 1 (c1-c4); Alk / CS / TA / Ag-Im from Comparative Example 3 (d1-d4).

[0033] Figure 2 The bamboo samples before and after modification of Example 1 and Comparative Examples 1-3 are at 500-4000cm -1 FTIR spectrum of .

[0034] Figure 3 1 and 2 are X-ray diffraction patterns of bamboo samples before and after modification according to Example 1 of the present invention and Comparative Examples 1-3.

[0035] Figure 4 Graphs showing the modulus of rupture (a) and elastic modulus (b) of bamboo samples before and after modification according to Example 1 of the present invention and Comparative Examples 1-3.

[0036] Figure 5 Graph showing the growth of Penicillium citrinum on the surface of bamboo samples within 28 days in Example 1 of the present invention and Comparative Examples 1-3.

[0037] Figure 6 Graph showing the growth of Trichoderma viride on the surface of bamboo samples within 28 days in Example 1 of the present invention and Comparative Examples 1-3. DETAILED DESCRIPTION

[0038] Example 1

[0039] The method for preparing the high-strength, dimensionally stable, mildew-resistant bamboo material of this embodiment comprises the following steps:

[0040] S1. Cut 2m of bamboo timber 1m above the ground foundation, remove the green bamboo and yellow bamboo, and cut them into boards;

[0041] The bamboo material is 5-year-old moso bamboo;

[0042] S2, cutting the board obtained in S1 into blank size, and then planing, slotting, and carving to obtain blank bamboo material;

[0043] S3, using a deburring tool to remove burrs from the blank bamboo material obtained in S2, washing with water to remove dust, and drying at a temperature of 60 ° C for 24 h to obtain a bamboo material to be processed;

[0044] S4. Immersing the bamboo material obtained in S3 in a 4% by mass sodium hydroxide aqueous solution at 80° C. for 30 minutes, washing with deionized water, and drying to obtain an alkali-pretreated bamboo material having a moisture content of 8%;

[0045] In this embodiment, tannic acid and chitosan are both natural polymer materials, which avoid the toxicity problem of traditional chemical reducing agents (such as sodium borohydride). The polyphenol structure of tannic acid can reduce Ag. +The capping effect also limits particle growth, resulting in ultra-small, high-density silver particles that exert excellent antibacterial properties. Furthermore, the silver particles formed by in-situ reduction are chemically fixed to the chitosan, preventing particle migration and aggregation. The CS / TA / Ag reinforcement phase expands the bamboo's interfacial area, effectively transferring and dispersing stress, creating a more uniform stress distribution and improving the material's mechanical properties. At the same time, the silver particles release silver ions and reactive oxygen species (ROS), thereby increasing cell permeability and causing leakage of contents, thereby effectively inhibiting mold growth. S5. Chitosan (CS) is dissolved in a 2% acetic acid aqueous solution to obtain a chitosan acetic acid solution, which is then dispersed in distilled water. The pH value is adjusted to 5.0 with a 4% sodium hydroxide solution, and then AgNO3 and tannic acid (TA) are added. After stirring at room temperature for 10 hours, a chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor (abbreviated as CS / TA / Ag) is obtained. The final concentration of chitosan in the chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor is 5 g / L, and the final concentration of tannic acid is 1 g / L. The molar ratio of silver nitrate to tannic acid is 1:15.

[0046] This example significantly improves the mildew resistance, dimensional stability, and mechanical properties of bamboo through the synergistic effect of alkaline pretreatment and chitosan / tannic acid / silver bio-based organic-inorganic hybrid system.

[0047] Under acidic conditions, the amino groups (-NH2) of chitosan are protonated to -NH3 + , combined with the phenolic hydroxyl groups in tannic acid through electrostatic adsorption; at the same time, the amino hydroxyl groups (-OH) on the chitosan molecular chain form a dense hydrogen bond network with the phenolic hydroxyl groups (-OH) of tannic acid through hydrogen bonding; the catechol groups in tannic acid reduce silver ions to silver particles in situ. Tannic acid and chitosan are both natural polymer materials, avoiding the toxicity of traditional chemical reducing agents (such as sodium borohydride). The polyphenol structure of tannic acid can reduce Ag + , and can limit particle growth through the end-capping effect, thereby obtaining ultra-small size and high density silver particles, which play an excellent antibacterial role. In addition, the silver particles formed by in-situ reduction are fixed in chitosan through chemical bonds, avoiding particle migration and aggregation, and are anchored in the long chitosan chain through electrostatic interaction and coordination bonds, improving the dispersion of silver particles in the system and improving its resistance to loss.

[0048] The porous structure and weak acidity of bamboo (pH usually <5) promote the protonation of amino groups in chitosan (-NH3 +) and enhances electrostatic adsorption with bamboo hydroxyl groups. Simultaneously, tannic acid tightly binds to chitosan through hydrogen bonding, and the reducing property of phenolic hydroxyl groups in situ reduces silver particles, forming a cross-linked network structure that blocks external moisture and mold intrusion. CS / TA / Ag tightly cross-links with bamboo through hydrogen and covalent bonding, forming a stable cross-linked structure within the pores and surface. This reduces the cell cavity and intercellular spaces, acts as a barrier to moisture, and slows water diffusion within the bamboo, thereby improving its dimensional stability. Furthermore, the reinforcing phase of CS / TA / Ag expands the interfacial area of ​​the bamboo, effectively transferring and distributing stress, resulting in a more uniform stress distribution. Furthermore, the strong intermolecular interaction between Ag and CS results in a more compact structure. The TA-reduced Ag is encapsulated by CS molecular chains and anchored to the bamboo surface through electrostatic and coordination bonds. Due to the ductility and rigidity of Ag, it requires more energy to break when subjected to an external load, thereby increasing the modulus of rupture. S6. Using a spray gun, spray the chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor obtained in S5 onto the surface of the alkali-pretreated bamboo material obtained in S4, followed by drying at 80° C. for 10 minutes. The spraying and drying processes were repeated 8 times, with the final drying at 103° C. for 7 hours to obtain a high-strength, dimensionally stable mildew-resistant bamboo material (denoted as Alk / CS / TA / Ag-Sp).

[0049] The spraying conditions are: air pressure of 0.5 MPa, spraying distance of 20 cm;

[0050] The high-strength, dimensionally stable, mildew-proof bamboo material is assembled into a finished product, and the assembly method can be through mortise and tenon joints, screws or gluing.

[0051] In this embodiment, a chitosan-tannic acid-silver (CS / TA / Ag) bio-based organic-inorganic hybrid mildew inhibitor is in situ deposited on the surface of bamboo by precision spraying.

[0052] This embodiment uses a spraying process to fix the bio-based inorganic composite mildew inhibitor on the surface of the bamboo material, which saves dosage, reduces costs and is suitable for large-scale industrial production.

[0053] The high-strength, dimensionally stable, mildew-resistant bamboo material prepared in this embodiment has a mildew inhibition rate of up to 100%, a rupture modulus of 187.23 MPa, and an elastic modulus of 7.55 GPa.

[0054] Comparative Example 1

[0055] This comparative example is a method for preparing modified bamboo material. The method is the same as steps S1-S4 in Example 1. The prepared bamboo material after alkali pretreatment is the modified bamboo material of this comparative example, which is denoted as Alk.

[0056] Comparative Example 2

[0057] The preparation method of the modified bamboo material in this comparative example is the same as that in Example 1, except that the alkaline solution immersion treatment operation in step S4 is omitted. The prepared modified bamboo material is recorded as CS / TA / Ag-Sp.

[0058] Comparative Example 3

[0059] The preparation method of the modified bamboo material of this comparative example, steps S1-S5 are the same as those of Example 1, except that step S6 is as follows: the bamboo material pretreated with alkali obtained in S4 is immersed in the chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor obtained in S5 for 60 minutes, and then dried at a temperature of 103° C. for 12 hours to obtain a modified bamboo material, which is recorded as Alk / CS / TA / Ag-Im.

[0060] (1) Electron microscope image:

[0061] like Figure 1 The SEM and EDS images of bamboo before and after treatment of Example 1 and Comparative Examples 1-3 are shown. The cell structure of natural bamboo (control) consists of fiber bundles, thin-walled cells and vessels ( Figure 1 a2), these components form a honeycomb arrangement through a matrix composed of lignin and hemicellulose (such as Figure 1 a3 arrow), its thin-walled cells are rich in starch. Figure 1 b2), sodium hydroxide degrades some of the hemicellulose and lignin in the bamboo, and gaps appear on the surface ( Figure 1 b3 arrows), the fiber bundles are largely exposed. Due to the loss of the bonding effect of hemicellulose, the fiber bundles are warped and deformed. After further spraying CS / TA / Ag on the bamboo surface, it can be seen that CS / TA / Ag successfully fills the pores ( Figure 1 c3 arrows), covering the surface of the fiber bundle to form a rough coating ( Figure 1 c2). It is worth noting that after the bamboo surface was impregnated with CS / TA / Ag, it was observed that there were still large gaps on the surface ( Figure 1 d3), indicating that the CS / TA / Ag impregnation is uneven, further confirming that the modification effect of the spraying treatment is better than that of the impregnation treatment. In addition, EDS surface scanning confirmed the presence of Ag elements in both Alk / CS / TA / Ag-Sp and Alk / CS / TA / Ag-Im, indicating that the silver particles have penetrated into the entire sample ( Figure 1 c4, d4).

[0062] (2) Infrared spectrum:

[0063] The natural bamboo material, i.e. the unmodified bamboo material of Example 1, was used as the control. The functional group changes of the samples of Example 1 and Comparative Examples 1-3 before and after modification were tested by Fourier transform infrared spectroscopy (FTIR). Figure 2 As shown. 3400cm -1 and 2895cm -1 The characteristic peaks at 3400cm are the stretching vibration peaks of -OH and CH. -1 There is a slight shift at 1728cm, which confirms that the CS / TA / Ag composite modifier is bound to the cell wall through hydrogen bonding. -1 The characteristic peak at 1600 cm is the result of CO stretching vibration in hemicellulose and lignin. It is worth noting that after alkali pretreatment, the vibration peak intensity of the samples (Example 1, Comparative Example 1, Comparative Example 3) is significantly weakened, indicating that some hemicellulose and lignin in the bamboo material have been degraded during the alkali pretreatment process. In addition, the samples CS / TA / Ag-Sp (Comparative Example 2), Alk / CS / TA / Ag-Sp (Example 1) and Alk / CS / TA / Ag-Im (Comparative Example 3) have a peak at 1600 cm -1 and 1560cm -1 The characteristic peak at 1238cm shifted, which was mainly attributed to the stretching vibration of C=O and C=N in chitosan and tannic acid, indicating that chitosan and tannic acid were successfully cross-linked through the alkaline Schiff reaction. -1 The characteristic peak at is attributed to the stretching vibration of CO in lignin. The vibration signals of the samples after alkali pretreatment are weakened, which further confirms that alkali pretreatment removes the lignin and hemicellulose components in bamboo.

[0064] (3) X-ray diffraction pattern:

[0065] Taking natural bamboo as control, the XRD patterns of the samples of Example 1 and Comparative Examples 1-3 are as follows: Figure 3 As shown. Two broad peaks are shown at 15.7° and 22.0°, which belong to the diffraction peaks of cellulose I in the bamboo component, corresponding to the (110) and (200) crystal planes, respectively. Compared with the control sample (Control), no disappearance or position shift of the peak was observed in all modified samples, indicating that the alkali pretreatment and the amorphous structure of CS / TA / Ag have no effect on the crystalline region of cellulose. Samples CS / TA / Ag-Sp (Comparative Example 2), Alk / CS / TA / Ag-Sp (Example 1) and Alk / CS / TA / Ag-Im (Comparative Example 3) have new diffraction peaks at 38.1°, 44.3°, 64.5° and 77.4°, corresponding to the (111), (200), (220) and (311) lattice planes of silver particles, respectively, indicating that silver is successfully doped on the bamboo surface.

[0066] Bamboo is mainly composed of cellulose, hemicellulose and lignin, of which cellulose accounts for about 50%. Cellulose I is the main crystalline form of natural cellulose and is widely present in the fiber structure of plant cell walls.

[0067] (IV) Mechanical properties test: The mechanical properties of bamboo materials with different treatments were tested by three-point bending test, such as Figure 5 As shown in the table. Compared with natural bamboo (Control), the modulus of rupture (MOR) and modulus of elasticity (MOE) of sample Alk (Comparative Example 1) treated with 4wt% sodium hydroxide alone decreased by 9.92% and 9.82%, respectively. This is because during the alkali pretreatment process, a large amount of lignin and hemicellulose degraded, causing the connection of the cell wall to become loose, the fibers to easily slip and debond, and tiny cracks to appear. Under the action of external force, the stress cannot be evenly dispersed, resulting in local fracture. It is worth noting that the modulus of rupture (MOR) and modulus of elasticity (MOE) of sample CS / TA / Ag-Sp (Comparative Example 2) increased by 9.85% and 14.78%, respectively, compared with natural bamboo. This shows that CS / TA / Ag multi-component modified bamboo can effectively improve the mechanical properties of the material. A more interesting finding is that in the co-modification system of alkali pretreatment and CS / TA / Ag composite modifier, the mechanical properties showed a more significant improvement. The modulus of rupture (MOR) and modulus of elasticity (MOE) of samples Alk / CS / TA / Ag-Sp (Example 1) and Alk / CS / TA / Ag-Im (Comparative Example 3) increased by 38.79% and 42.83%, and by 25.44% and 20.60%, respectively. This is mainly attributed to two aspects:

[0068] (1) Alkali pretreatment exposes a large amount of cellulose, increasing the specific surface area and forming a large number of reactive groups between cellulose chains. The large amount of hydroxyl groups (-OH) in cellulose can react with the amino groups (-NH 2 ) and hydroxyl groups (-OH) form intermolecular hydrogen bonds, thereby building a stable cross-linked network structure on the surface. This structure acts as a reinforcing phase to expand the interfacial area of ​​the bamboo material, effectively transferring and dispersing stress, and forming a more uniform stress distribution.

[0069] (2) The strong intermolecular interaction between silver particles and CS leads to a more compact structure. TA-reduced silver particles are wrapped by CS molecular chains and anchored to the bamboo fiber surface through electrostatic interactions and coordination bonds. Due to the ductility and rigidity of Ag NPs, when an external load is applied, more energy is required to break, thereby increasing the modulus of rupture.

[0070] The phenolic hydroxyl groups in tannic acid form a dynamic crosslinked network with amino or hydroxyl groups on chitosan through hydrogen bonding and coordination, altering the chitosan chain structure to form a denser three-dimensional crosslinked network. This network then tightly binds to the hydroxyl groups in bamboo cellulose. Furthermore, the catechol groups in tannic acid possess strong reducing properties, reducing silver ions to silver particles in situ, thus forming a CS / TA / Ag crosslinked structure on the bamboo surface.

[0071] By spraying chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor, a uniform and stable cross-linked structure is formed on the surface of bamboo. Silver particles are evenly distributed in the surface film and are protected by TA and CS. They can release Ag in time when they come into contact with mold. + and active oxygen, quickly preventing mold from invading the interior of the bamboo. The impregnation of antifungal agent causes silver to disperse inside the bamboo, releasing Ag + It needs to diffuse to the surface to be effective, and the antibacterial efficiency is low. In addition, the silver distributed inside may migrate and lose due to the moisture absorption and expansion of the bamboo, resulting in a weakened antibacterial ability. Table 1 Mechanical properties of bamboo materials in Example 1 and Comparative Examples 1-3

[0072] project Modulus of rupture MPa Elastic modulus GPa Control (unmodified bamboo material of Example 1) 134.59 5.29 Comparative Example 1 (Alk) 121.51 4.77 Comparative Example 2 (CS / TA / Ag-Sp) 148.18 6.07 Example 1 (Alk / CS / TA / Ag-Sp) 187.23 7.55 Comparative Example 3 (Alk / CS / TA / Ag-Im) 169.21 6.38

[0073] (5) Anti-mildew performance test:

[0074] In a simulated environment of 28° C. and 85% relative humidity, the anti-mildew performance of natural bamboo (Control) and modified bamboo samples (Example 1, Comparative Examples 1-3) was evaluated for 28 days, and the growth of mold was recorded and observed every day.

[0075] Figure 5-6 Shows the mildew condition of bamboo surface within 28 days ( Figure 5 Penicillium citrinum, Figure 6Green Trichoderma). The anti-mildew effect of natural bamboo (Control) is extremely poor. It can be seen that it is infected with both Citric Acid and Green Trichoderma within 7 days, and the mycelium coverage rate on the surface reaches 98% within 14 days. This is because the natural bamboo is rich in nutrients such as polysaccharides, starch and protein, and its own hygroscopicity is strong, which provides suitable conditions for the growth and reproduction of molds. Under the heating treatment of 4wt% NaOH aqueous solution, the infection value of Citric Acid and Green Trichoderma on bamboo is significantly reduced within 28 days, and the infection value is as low as 2. The inhibition rate of sample CS / TA / Ag-Sp (Comparative Example 2) on Citric Acid and Green Trichoderma within 28 days is 37.50% and 18.52% respectively, and the infection value reaches 3 on the 14th day, indicating that the anti-mildew effect is not ideal. This shows that the use of CS / TA / Ag alone cannot significantly enhance the anti-mildew performance of bamboo, which may be due to the weak bonding of CS / TA / Ag to bamboo. In the CS / TA / Ag co-modification system for bamboo after alkali pretreatment, the sample Alk / CS / TA / Ag-Sp (Example 1) showed an infection value and control efficacy against Penicillium citrinum and 93.75%, respectively, while the infection value and control efficacy against Penicillium citrinum and 0% and 100%, respectively. The sample Alk / CS / TA / Ag-Im (Comparative Example 3) showed mold infection within 7 days, and within 28 days, the infection value and control efficacy against Penicillium citrinum and Trichoderma viride were 2 and 4, 62.5% and 11.11%, respectively, and the mold infection area on the bamboo surface reached more than 75%. This result shows that the anti-mildew effect of the bamboo treated with the spray modification strategy (Example 1, Comparative Example 2) is far superior to that of the immersion treatment (Comparative Example 3).

[0076] Compared with chitosan, tannic acid, and silver ions alone, the chemical composition of the chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor in this embodiment has changed. First, chitosan acts as a stabilizer and end-capping agent during the synthesis of silver particles. The -NH +2 The -OH groups interact with the surface of the formed silver cores, preventing them from agglomerating due to electrostatic repulsion and steric hindrance. Secondly, the catechol groups of the natural polymer tannic acid reduce silver ions to silver particles in situ, anchoring them within the chitosan structure to form a stable cross-linked network. The stable and evenly distributed silver particles within the chitosan structure exert an antibacterial effect. When the chitosan / tannic acid / silver bond is tightly integrated with bamboo, it improves mechanical properties by filling the bamboo's micropores or interfiber gaps, reducing material defects, while also enhancing overall stiffness through the dispersion-enhancing effect of the silver particles.

[0077] The chitosan (deacetylation degree ≥95%, viscosity 100-200 mPa.s) used in the present invention is obtained by deacetylation of chitin. Its molecular chain is rich in amino groups (-NH2), which can easily combine with tannic acid and silver through chemical bonds to achieve a broad-spectrum antibacterial (including fungal) effect. The ingredients are safe and non-toxic.

[0078] The core functionality of the chitosan (CS) and tannic acid (TA) combination in this invention focuses on controlling the synthesis of in-situ reduced silver particles and enhancing their long-lasting antifungal properties. The multifunctional chemical properties of tannic acid guide the synthesis and stabilization of Ag, and synergize with chitosan to enhance antibacterial and antioxidant properties.

[0079] Example 2

[0080] Preparation method of high-strength, dimensionally stable mildew-resistant bamboo material of this embodiment - This embodiment finally assembles the prepared mildew-resistant bamboo material into furniture such as tables and chairs. The mildew-resistant bamboo material preparation method is as follows:

[0081] S1. Cut 2m of bamboo timber 1m above the ground foundation, remove the green bamboo and yellow bamboo, and cut them into boards;

[0082] The bamboo material is 3-year-old moso bamboo;

[0083] S2, cutting the board obtained in S1 into blank sizes and preliminary shapes of components such as tabletops and chair legs, and then planing, slotting, and carving to obtain blank bamboo materials;

[0084] S3, using a deburring tool to remove burrs from the blank bamboo material obtained in S2, washing with water to remove dust, and drying at a temperature of 100° C. for 12 hours to obtain a bamboo material to be processed;

[0085] S4. Immersing the bamboo material obtained in S3 in a 4% by mass sodium hydroxide aqueous solution at 80° C. for 40 minutes, washing with deionized water, and drying to obtain alkali-pretreated bamboo material having a moisture content of 12%;

[0086] S5. Dissolving chitosan (CS) in a 2% acetic acid aqueous solution to obtain a chitosan acetic acid solution, then dispersing the solution in distilled water, adjusting the pH to 4.8 with a 4% sodium hydroxide solution, then adding AgNO3 and tannic acid (TA), and stirring at room temperature for 12 hours to obtain a chitosan-tannic acid-silver bio-based inorganic nano-mildew inhibitor (abbreviated as CS / TA / Ag); the final concentration of chitosan in the chitosan-tannic acid-silver nano-bio-based inorganic nano-mildew inhibitor is 1 g / L, and the final concentration of tannic acid is 1 g / L; the molar ratio of silver nitrate to tannic acid is 1:15;

[0087] S6. Using a spray gun, spray the chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor obtained in S5 onto the surface of the alkali-pretreated bamboo material obtained in S4, and then dry it at 80° C. for 15 minutes. The spraying and drying processes are repeated 8 times, and the final drying is performed at 103° C. for 8 hours to obtain a high-strength, dimensionally stable mildew-resistant bamboo material.

[0088] The spraying conditions are: air pressure of 0.5 MPa, spraying distance of 50 cm;

[0089] The high-strength, dimensionally stable, mildew-proof bamboo material is assembled into finished products (table and chair furniture) by means of mortise and tenon joints, screws, and gluing.

[0090] The high-strength, dimensionally stable, mildew-resistant bamboo material prepared in this example has a modulus of rupture of 178.18 MPa and an elastic modulus of 6.97 GPa. After 28 days in a simulated environment at 28°C and 85% relative humidity, it demonstrated 82.50% efficacy against Penicillium citrinum and 100% efficacy against Penicillium citrinum. The assembled tables and chairs offer a mildew-resistant lifespan of up to five years.

[0091] Example 3

[0092] Preparation method of high-strength, dimensionally stable mildew-resistant bamboo material of this embodiment - This embodiment finally assembles the prepared mildew-resistant bamboo material into kitchen utensils (cutting boards, chopsticks, spoons). The mildew-resistant bamboo material preparation method is as follows:

[0093] S1. Cut 2m of bamboo timber 1m above the ground foundation, remove the green bamboo and yellow bamboo, and cut them into boards;

[0094] The bamboo material is 3-year-old moso bamboo;

[0095] S2, cutting the board obtained in S1 into blank size, and then planing, slotting, and carving to obtain blank bamboo material;

[0096] S3, using a deburring tool to remove burrs from the blank bamboo material obtained in S2, washing with water to remove dust, and drying at a temperature of 80° C. for 20 h to obtain a bamboo material to be processed;

[0097] S4. Immersing the bamboo material obtained in S3 in a 4% by mass sodium hydroxide aqueous solution at 80° C. for 35 minutes, washing with deionized water, and drying to obtain alkali-pretreated bamboo material having a moisture content of 10%;

[0098] S5. Dissolving chitosan (CS) in a 2% acetic acid aqueous solution to obtain a chitosan acetic acid solution, then dispersing the solution in distilled water, adjusting the pH to 4.9 with a 4% sodium hydroxide solution, then adding AgNO3 and tannic acid (TA), and stirring at room temperature for 10 hours to obtain a chitosan-tannic acid-silver bio-based inorganic nano-mildew inhibitor (abbreviated as CS / TA / Ag); the final concentration of chitosan in the chitosan-tannic acid-silver nano-bio-based inorganic nano-mildew inhibitor is 3 g / L, and the final concentration of tannic acid is 5 g / L; the molar ratio of silver nitrate to tannic acid is 1:15;

[0099] S6. Using a spray gun, spray the chitosan-tannic acid-silver nanobio-based inorganic mildew inhibitor obtained in S5 onto the surface of the alkali-pretreated bamboo material obtained in S4, and then dry it at 80° C. for 10 minutes. The spraying and drying processes are repeated 8 times, and the final drying is performed at 103° C. for 8 hours to obtain a high-strength, dimensionally stable mildew-resistant bamboo material.

[0100] The spraying conditions are: air pressure of 0.5 MPa, spraying distance of 30 cm;

[0101] The high-strength, dimensionally stable, mildew-proof bamboo material is assembled into finished products (kitchen utensils: cutting boards, spoons, and chopsticks).

[0102] The high-strength, dimensionally stable, mildew-resistant bamboo material prepared in this example has a modulus of rupture of 180.34 MPa and an elastic modulus of 7.28 GPa. After 28 days in a simulated environment at 28°C and 85% relative humidity, it demonstrated 91.28% efficacy against Penicillium citrinum and 100% efficacy against Penicillium citrinum. Kitchenware assembled into the material can maintain mildew resistance for up to five years.

[0103] Bamboo has abundant hydrophilic groups and a large porosity, making it highly hygroscopic. Exposure to humid environments can easily lead to dimensional changes, affecting its usability. Alkali treatment and combined CS / TA / Ag treatment of the bamboo creates a tight crosslinking effect through hydrogen and covalent bonding, forming a stable crosslinked structure within the pores and surface. This reduces the cell cavity and intercellular spaces, creating a barrier to moisture and slowing its diffusion within the bamboo. This, in turn, improves the bamboo's dimensional stability, enhancing its stability and suitability in humid environments.

[0104] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing high-strength, dimensionally stable mildew-resistant bamboo material, characterized in that: The method is: S1. Cut bamboo timber 1m above the ground, remove the green and yellow bamboo, and cut them into boards; S2, cutting the board obtained in S1 into blank size, and then planing, slotting, and carving to obtain blank bamboo material; S3, removing burrs from the blank bamboo material obtained in S2, rinsing with water, and drying to obtain the bamboo material to be processed; S4, immersing the bamboo material to be treated obtained in S3 in an alkali pretreatment solution at a temperature of 80° C., washing with deionized water, and drying to obtain alkali-pretreated bamboo material; S5, dissolving chitosan in an acetic acid aqueous solution to obtain a chitosan acetic acid solution, and then dispersing the solution in distilled water, adjusting the pH value to 4.8-5.0, and then adding AgNO3 and tannic acid. After stirring at room temperature, a chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor is obtained; S6. Spray the chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor obtained in S5 onto the surface of the alkali-pretreated bamboo material obtained in S4, and then dry it at 80°C for 10 to 15 minutes; the spraying and drying processes are repeated 8 times, and the last drying is performed at a temperature of 103°C for 7 to 8 hours to obtain a high-strength, dimensionally stable mildew-proof bamboo material; the spraying conditions are: an air pressure of 0.5 MPa and a spraying distance of 20 to 50 cm.

2. The method for preparing high-strength, dimensionally stable, mildew-resistant bamboo material according to claim 1, characterized in that: The bamboo material described in S1 is 3 to 5-year-old moso bamboo.

3. The method for preparing high-strength, dimensionally stable, mildew-resistant bamboo material according to claim 1, characterized in that: The drying temperature in S3 is 60° C. to 100° C., and the drying time is 12 h to 24 h.

4. The method for preparing high-strength, dimensionally stable, mildew-resistant bamboo material according to claim 1, characterized in that: The alkaline pretreatment liquid in S4 is a sodium hydroxide aqueous solution with a mass fraction of 4%; the immersion treatment time is 30 minutes to 40 minutes.

5. The method for preparing high-strength, dimensionally stable, mildew-resistant bamboo material according to claim 1, characterized in that: The moisture content of the bamboo material after alkali pretreatment in S4 is 8% to 12%.

6. The method for preparing high-strength, dimensionally stable, mildew-resistant bamboo material according to claim 1, characterized in that: The acetic acid aqueous solution in S5 is an acetic acid aqueous solution with a mass fraction of 2%.

7. The method for preparing high-strength, dimensionally stable, mildew-resistant bamboo material according to claim 1, characterized in that: The stirring time in S5 is 10 h to 12 h.

8. The method for preparing high-strength, dimensionally stable, mildew-resistant bamboo material according to claim 1, characterized in that: The final concentration of chitosan in the chitosan-tannic acid-silver bio-based organic-inorganic hybrid mildew inhibitor described in S5 is 1g / L~5g / L, and the final concentration of tannic acid is 1g / L~10g / L; the molar ratio of the silver nitrate to tannic acid is 1:

15.

9. The method for preparing high-strength, dimensionally stable, mildew-resistant bamboo material according to claim 1, wherein: The high-strength, dimensionally stable, mildew-proof bamboo material described in S6 has a modulus of rupture of 178.18 MPa to 187.23 MPa, and an elastic modulus of 6.97 Gpa to 7.55 Gpa; the high-strength, dimensionally stable mildew-proof bamboo material has an efficacy of 82.50% to 93.75% against citrinum in a simulated environmental condition of 28°C and 85% relative humidity for 28 days, and an efficacy of 100% against citrinum.

10. An application of high-strength, dimensionally stable, mildew-resistant bamboo material prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The high-strength, dimensionally stable, mildew-proof bamboo material is used for preparing furniture such as tables and chairs, and kitchen utensils.

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