Lignin-cuprous oxide composite microspheres modified reconstituted bamboo and preparation method thereof

Abstract

The application discloses lignin-cuprous oxide composite microspheres modified reconstituted bamboo and a preparation method thereof, and the lignin-cuprous oxide composite microspheres with a core-shell structure are prepared by a solvent exchange method, and are uniformly dispersed in a phenolic resin to prepare a modified phenolic resin adhesive with excellent gluing performance, long-acting mildew-proof performance and good hydrophobic performance. The adhesive is used for the preparation of reconstituted bamboo, and a mildew-proof component can be directly introduced into the inside of the bamboo during a hot-pressing forming stage, so that the defects of poor thermal stability, easy decomposition and surface treatment only of a traditional mildew-proof agent are overcome. The reconstituted bamboo composite material has a mildew-proof grade of 0 for Penicillium citrinum, and a mildew-proof grade of 1 for Trichoderma viride, Aspergillus niger and mixed molds, and meanwhile, the gluing strength and bending resistance of the reconstituted bamboo composite material are significantly improved, the surface hydrophobicity is enhanced, and the comprehensive performance is excellent. The application realizes high-value utilization of biomass resources, and has simple process, environmental friendliness and wide application prospect in the field of bamboo processing.

Description

Technical Field

[0001] This invention relates to the field of bamboo processing and biomass materials technology, specifically to a lignin-cuprous oxide composite microsphere modified recombinant bamboo and its preparation method. Background Technology

[0002] Bamboo, as a fast-growing and renewable biomass resource, boasts outstanding advantages such as a short growth cycle, excellent mechanical properties, and environmental friendliness, making it an ideal material to replace wood. Reconstituted bamboo is a high-performance bamboo-based composite material made by assembling bamboo bundles or fibrous bamboo veneers along the grain direction, followed by gluing and pressing. It has shown great application potential in fields such as green building and structural engineering.

[0003] However, bamboo is rich in nutrients such as starch and protein, and its molecular structure contains a large number of hydrophilic hydroxyl groups, making it highly susceptible to moisture absorption and mold growth. Mold growth not only affects the appearance of bamboo but also severely reduces its mechanical properties and service life, becoming a key bottleneck limiting the large-scale outdoor application of reconstituted bamboo. To address this issue, existing technologies typically employ physical methods (such as heat treatment and surface coating), chemical methods (such as preservative impregnation), or biological methods to treat bamboo for mold prevention. For example, anti-mold agents are applied to the surface of reconstituted bamboo after molding, or anti-mold varnish is used for post-treatment. However, these methods have significant drawbacks: first, anti-mold agents can only act on the surface of the material and cannot penetrate into the interior, thus failing to provide long-term protection; second, most organic anti-mold agents have poor thermal stability and cannot be added before the high-temperature hot pressing (usually >140℃) molding of reconstituted bamboo, otherwise they are prone to decomposition and ineffectiveness; third, while natural anti-mold components are environmentally friendly, they suffer from insufficient stability and poor slow-release effects.

[0004] Phenolic resin (PF) is one of the most commonly used adhesives in the manufacture of reconstituted bamboo. While it possesses certain heat resistance and mechanical strength, its anti-mold properties are limited. If anti-mold components could be directly introduced into the phenolic resin system, allowing it to be uniformly distributed within the bamboo along with the adhesive during hot pressing, it could potentially solve the anti-mold problem of reconstituted bamboo fundamentally. However, designing a composite system that possesses good thermal stability, compatibility with phenolic resin, and the ability to achieve long-term sustained release of anti-mold components remains a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing lignin-cuprous oxide composite microspheres modified reconstituted bamboo. The method involves coating cuprous oxide with lignin to form core-shell structured microspheres, which are then uniformly dispersed in phenolic resin to obtain a modified phenolic resin adhesive with excellent bonding properties, long-lasting anti-mold properties, and good hydrophobicity. Using this adhesive in the preparation of reconstituted bamboo allows for the direct introduction of anti-mold components into the bamboo during the hot-pressing stage. The resulting reconstituted bamboo composite material exhibits a level 0 anti-mold rating against Penicillium citrinum and a level 1 anti-mold rating against Trichoderma viride, Aspergillus niger, and mixed molds. Simultaneously, its bonding strength and bending resistance are significantly improved, surface hydrophobicity is enhanced, and its overall performance is excellent.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a lignin-cuprous oxide composite microsphere modified reconstituted bamboo material, wherein the reconstituted bamboo material is obtained by impregnating bamboo bundles with a lignin-cuprous oxide composite microsphere modified phenolic resin adhesive and then hot-pressing them. The lignin-cuprous oxide composite microsphere modified phenolic resin adhesive includes phenolic resin and lignin-cuprous oxide composite microspheres dispersed in the phenolic resin. The lignin-cuprous oxide composite microspheres have a core-shell structure, comprising a cuprous oxide core and a lignin shell coating the surface of the cuprous oxide core.

[0007] Furthermore, the lignin-cuprous oxide composite microspheres have a particle size of 200-2000 nm. This particle size range allows them to easily penetrate the pores (approximately 1000-10000 nm) of bamboo and enter the interior of the bamboo, achieving comprehensive internal protection.

[0008] Furthermore, in the synthesis process of the lignin-cuprous oxide composite microspheres, the mass ratio of lignin raw material to cuprous oxide raw material is 1:(0.8-1.2). Preferably, it is 1:1. This ratio is beneficial for forming a complete and stable coating layer and ensures sufficient cuprous oxide content to guarantee the anti-mildew effect.

[0009] The mass ratio of the lignin-cuprous oxide composite microspheres to phenolic resin is 1:(8-12), preferably 1:10. This ratio imparts excellent anti-mildew properties while ensuring the adhesive bonding strength.

[0010] This invention uses bamboo bundles as raw material and introduces lignin@cuprous oxide microspheres into phenolic resin adhesive to produce hot-pressed reconstituted bamboo engineered wood panels. The presence of the lignin microsphere shell enables the slow release of substances from the internal core material and also demonstrates lignin's strong drug-carrying capacity and environmental performance. This invention successfully achieves long-lasting mildew resistance in reconstituted bamboo. The lignin-coated cuprous oxide microspheres exhibit excellent slow-release properties. The mildew-resistant bamboo sheets achieve a level 0 mildew resistance standard against Penicillium citrinum and a level 1 mildew resistance standard against Trichoderma viride, Aspergillus niger, and mixed molds. Compared to directly adding Cu2O to the phenolic resin, the mildew resistance is significantly improved. Furthermore, this invention uses infrared and XPS analyses to confirm the stability of the lignin@cuprous oxide microsphere system, enabling it to persist in the substrate for a long time. Simultaneously, the addition of lignin@cuprous oxide microspheres also improves the mechanical and hydrophobic properties of the engineered wood panels, greatly expanding the application environment of the panels. By adding the mildew inhibitor to the adhesive before pressing, mildew resistance is achieved before pressing, making the process simpler and more convenient.

[0011] The present invention also provides a method for preparing the above-mentioned modified recombinant bamboo, comprising the following steps: (1) Mix lignin with cuprous oxide powder of micron size in an organic solvent, stir and disperse to obtain a mixture; (2) Add water to the mixture obtained in step (1) to carry out solvent exchange reaction. Utilize the π-π interaction between lignin molecules to enable it to self-assemble and coat on the surface of cuprous oxide. After the organic solvent has completely evaporated, perform solid-liquid separation on the reaction solution to obtain lignin-cuprous oxide composite microspheres (Lignin@Cu2O). (3) The dried lignin-cuprous oxide composite microsphere powder obtained in step (2) is mixed with phenolic resin and stirred evenly to obtain lignin-cuprous oxide composite microsphere modified phenolic resin adhesive. (4) After the bamboo bundles are impregnated with lignin-cuprous oxide composite microsphere modified phenolic resin adhesive, they are taken out and dried. The dried bamboo bundles are hot-pressed in the same direction as the grain to obtain modified reconstituted bamboo boards.

[0012] Furthermore, in step (1), the organic solvent is acetonitrile, which is miscible with water and is the basis for solvent exchange; the mass ratio of lignin to cuprous oxide powder is 1:(0.8-1.2); the stirring speed is 800-1000 rpm to ensure sufficient dispersion.

[0013] Furthermore, in step (2), the water is added at a rate of 15-25 mL / min; the ratio of water to organic solvent is (4-6):1; the solvent exchange reaction is carried out at room temperature. Controlling the water addition rate helps to form microspheres with uniform particle size and complete coating.

[0014] Further, in step (3), the mass ratio of the lignin-cuprous oxide composite microsphere powder to the phenolic resin is 1:(8-12).

[0015] Furthermore, the bamboo bundles are impregnated for 20-40 minutes to allow the adhesive to fully soak the bamboo bundles; the hot pressing temperature is 140-150℃, and the bamboo bundles are first hot-pressed at 5MPa for 5 minutes to set the shape, and then held at 15-20MPa for 25-35 minutes.

[0016] The lignin-cuprous oxide composite microspheres used in this invention have excellent thermal stability (the thermal decomposition temperature is much higher than the hot pressing process temperature of reconstituted bamboo), and can maintain structural integrity under these high temperature and high pressure conditions, and are firmly anchored inside the bamboo as the adhesive cures.

[0017] Experiments have verified that the reconstituted bamboo board has a mold resistance level of 0 against Penicillium citrinum and a mold resistance level of 1 against Trichoderma viride, Aspergillus niger, and mixed molds, thus meeting the mold resistance requirements.

[0018] The static bending strength of the reconstituted bamboo board is more than 20% higher than that of the reconstituted bamboo material prepared with pure phenolic resin adhesive without lignin-cuprous oxide composite microsphere modification, indicating that the introduction of lignin not only did not reduce the mechanical properties, but also synergistically enhanced them.

[0019] Lignin, the second most abundant natural polymer in the world, possesses abundant functional groups, good hydrophobicity, and certain antibacterial activity, making it an ideal microcapsule shell material. Cuprous oxide (Cu2O), as an inorganic antibacterial agent, has advantages such as broad-spectrum antibacterial properties, low toxicity, and low cost. Its antifungal mechanism mainly relies on the slow-released copper ions disrupting the cell membrane of microorganisms. Combining the two holds promise for constructing a novel, environmentally friendly, and long-lasting antifungal system. However, the core innovation of this invention lies in how to stably introduce the lignin-cuprous oxide composite system into phenolic resin adhesives and ensure its structural integrity and functional performance under the hot-pressing process of reconstituted bamboo.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention utilizes the π-π interactions between lignin molecules to self-assemble a dense lignin shell on the surface of cuprous oxide via solvent exchange, successfully preparing core-shell composite microspheres with a particle size of 200-2000 nm. The thermal decomposition temperature of these microspheres is much higher than that of the hot-pressing process of reconstituted bamboo (thermogravimetric analysis shows that they only experience trace weight loss below 200℃), enabling them to maintain structural integrity during high-temperature and high-pressure molding and uniformly distribute within the bamboo material along with the phenolic resin adhesive. Simultaneously, the lignin shell, through its three-dimensional network structure, regulates the release rate of copper ions in cuprous oxide, achieving long-term, stable, and sustained release of the antifungal components, overcoming the shortcomings of traditional antifungal agents such as poor sustained-release effect and short protection period.

[0021] (2) The recombinant bamboo composite material treated with the lignin-cuprous oxide composite microsphere modified phenolic resin adhesive of the present invention was tested for mildew resistance according to GB / T 18261-2013 standard. During the 28-day incubation period, it exhibited excellent mildew resistance: the mildew resistance level against *Penicillium citrinum* reached level 0, and the mildew resistance levels against *Trichoderma viride*, *Aspergillus niger*, and a mixture of the three mildews all reached level 1, fully meeting the mildew resistance requirements for engineered wood products. In contrast, the unmodified pure phenolic resin control group showed severe mildew growth under the same conditions, with a mildew resistance level of level 4; the modified group with only cuprous oxide added but without lignin coating still showed unsatisfactory mildew resistance against *Penicillium citrinum*, and even worse resistance to other mildews. This result indicates that lignin and cuprous oxide form a synergistic mildew-inhibiting system—the lignin shell not only achieves slow release, but its own antibacterial activity and the hydrophobic interface formed with the phenolic resin also jointly enhance the overall mildew resistance.

[0022] (3) The lignin shell material in this invention serves as an interfacial bridge. Its molecular structure contains a large number of active functional groups, which can undergo chemical cross-linking reactions with the hydroxymethyl groups in the phenolic resin to form a stable composite crosslinking system. Scanning electron microscopy observation shows that the surface of the reconstituted bamboo modified with lignin-cuprous oxide composite microspheres is more dense and smooth, and the microspheres are well bonded to the resin matrix. Mechanical property test results show that the bending resistance of the modified reconstituted bamboo of this invention is more than 20% higher than that of the unmodified control group, while the bending resistance of the control group with directly added cuprous oxide is significantly reduced. This indicates that the introduction of lignin not only does not weaken, but also synergistically enhances the bonding strength and overall mechanical properties of the adhesive system.

[0023] (4) Bamboo itself is rich in hydroxyl groups and has strong hydrophilicity, making it easy to absorb moisture and become a breeding ground for mold. This invention utilizes the natural hydrophobic properties of lignin (its molecular structure contains aromatic rings and hydrophobic side chains that can effectively reduce the surface energy of the material) to increase the water contact angle of the recombinant bamboo composite material from 111° in the control group to approximately 114°, further enhancing the surface hydrophobicity. The improved hydrophobicity helps reduce the adsorption and penetration of moisture on the bamboo surface, reducing the humidity conditions for mold growth from the source, and forming a dual protection mechanism of physical barrier + chemical inhibition with the anti-mold component. Attached Figure Description

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0025] Figure 1 Scanning electron microscope (SEM) image, transmission lens image, and EDS image of lignin-cuprous oxide microspheres; Figure 2 SEM images and corresponding EDS spectra of blank recombinant bamboo, Cu2O-modified recombinant bamboo, and Ligin@Cu2O-modified recombinant bamboo; Figure 3 FTIR spectra of Ligin@Cu2O powder and Ligin@Cu2O modified phenolic resin; Figure 4 X-ray photoelectron spectroscopy analysis of Ligin@Cu2O powder and Ligin@Cu2O modified phenolic resin; Figure 5 Thermogravimetric curves (A) and thermogravimetric differential curves (B) of Ligin@Cu2O powder and Ligin@Cu2O modified phenolic resin were analyzed. Figure 6 Three-point mechanical tests were conducted on blank reconstituted bamboo, Cu2O-modified reconstituted bamboo, and Liglin@Cu2O-modified reconstituted bamboo. Figure 7 Wetting tests were conducted on blank reconstituted bamboo, Cu2O-modified reconstituted bamboo, and Liglin@Cu2O-modified reconstituted bamboo. Figure 8 The images show the mold growth of blank reconstituted bamboo, Cu2O-modified reconstituted bamboo, and Liglin@Cu2O-modified reconstituted bamboo within 28 days. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Both the reconstituted bamboo and phenolic resin were provided by Zhejiang Jiahe Bamboo Industry Technology Co., Ltd. Example 1

[0028] Purification of lignin by enzymatic hydrolysis: The enzymatic hydrolysis of lignin involves purchasing crude lignin from the market and then extracting and purifying it using tetrahydrofuran.

[0029] The purification process of lignin by enzymatic hydrolysis is as follows: 1. Washing: Take 50-100g of enzymatically hydrolyzed lignin, and successively crush, dissolve in hot water, and wash three times with water. Then filter using a Büchner funnel and wash again with water. After each washing, it needs to be re-crushed and then placed in an oven to dry.

[0030] The first step of water washing (hot water dissolution and multiple filtrations) effectively removes most water-soluble impurities and some low-molecular-weight components, significantly improving the purity of lignin. High-purity lignin is a crucial prerequisite for achieving stable and uniform coating of cuprous oxide in the subsequent process—the presence of impurities interferes with the π-π self-assembly behavior between lignin molecules, leading to irregular microsphere morphology, incomplete coating, or even aggregation and precipitation. Therefore, this purification step ensures the controllability of the morphology and structural stability of the lignin-cuprous oxide composite microspheres from the source.

[0031] 2. Acetonitrile dissolution: After washing and drying, the completely hydrolyzed lignin is pulverized again, poured into a three-necked flask, acetonitrile is added, and the mixture is refluxed and stirred for 12 hours at 120°C.

[0032] The hydrophobicity of lignin is a key driving force behind its self-assembly and coating of hydrophobic cuprous oxide surfaces during solvent exchange. However, residual hydrophilic polysaccharides and hydroxylated small molecules in industrial lignin weaken its hydrophobic properties. Acetonitrile reflux extraction further removes polar small molecules and some oligosaccharides physically bound to lignin, fully exposing hydrophobic groups such as hydrophobic aromatic rings and methoxy groups in the lignin molecular structure, significantly enhancing its hydrophobic properties. This enhanced hydrophobicity directly improves the affinity and coating efficiency of lignin for cuprous oxide particles in the acetonitrile / water solvent exchange system, resulting in a more dense and uniform core-shell structure of the obtained microspheres.

[0033] 3. Filtration of the solution: Using a sintered metal funnel (three-necked steel), after the solution has been fully cooled, the supernatant (clear liquid) is drawn off. If the filtrate is turbid, it can be washed again (using the original funnel), and the filter residue can be returned to the three-necked flask for reflux.

[0034] 4. Rotary evaporation: Rotary evaporation at 50°C, under reduced pressure, recover all acetonitrile. The solid in the straight bottle shows no obvious flow. Place it in an oven to dry. Example 2

[0035] Preparation of lignin-cuprous oxide composite microspheres and their modified phenolic resin adhesive: 1. Preparation of lignin-cuprous oxide composite microspheres (Lignin@Cu2O): Enzymatically hydrolyzed lignin (2.5 g) and cuprous oxide powder (2.5 g) were added to 200 mL of acetonitrile solution at a mass ratio of 1:1. The mixture was stirred at 850 rpm for 30 min at room temperature to ensure thorough mixing and dispersion. Then, 1000 mL of deionized water was slowly added to the mixture at a flow rate of 20 mL / min using a peristaltic pump. During the addition process, lignin molecules gradually self-assembled on the surface of the hydrophobic cuprous oxide particles due to their hydrophobic interactions and intermolecular π-π interactions, forming a coating layer.

[0036] After the acetonitrile in the mixture has completely evaporated, the remaining suspension is vacuum filtered to collect the solid powder, which is then washed several times with deionized water and dried to obtain core-shell structured lignin-cuprous oxide composite microspheres.

[0037] 2. Preparation of lignin-cuprous oxide composite microsphere modified phenolic resin adhesive: The lignin-cuprous oxide composite microsphere powder prepared above was dried to absolute dryness, and then mixed with commercially available phenolic resin (PF) at a mass ratio of 1:10. The mixture was stirred at room temperature for 2 hours using a high-speed disperser until the microspheres were uniformly dispersed in the phenolic resin without agglomeration, thus obtaining the lignin-cuprous oxide modified phenolic resin adhesive. Example 3

[0038] Preparation of reconstituted bamboo composite materials: The reconstituted bamboo bundles were cut to a uniform length and dried in an oven until the moisture content met the requirements. The dried bamboo bundles were then divided into three groups: Control group: Bamboo bundles were impregnated with pure phenolic resin for 30 minutes, then removed and placed in a ventilated place to dry naturally.

[0039] The preparation process of the Cu2O modified group: cuprous oxide modified phenolic resin adhesive is as follows: cuprous oxide powder and commercially available phenolic resin (PF) are mixed at a mass ratio of 1:10. The mixture is stirred at room temperature for 2 hours using a high-speed disperser until the microspheres are uniformly dispersed in the phenolic resin without agglomeration. A 30-minute impregnation experiment was conducted on bamboo bundles using the cuprous oxide modified phenolic resin adhesive. After removal, the bundles were placed in a ventilated area to allow for natural drying.

[0040] Lignin@Cu2O Modified Group: Bamboo bundles were impregnated with the lignin-cuprous oxide composite microsphere modified phenolic resin adhesive prepared in Example 2 for 30 minutes. After being removed, they were placed in a ventilated place to dry naturally.

[0041] Subsequently, the resin-impregnated bamboo bundles are assembled along the grain and placed into a hot press for hot pressing. The hot pressing process is as follows: at a temperature of 145℃, a pressure of 5MPa is first applied for 5 minutes for pre-pressing and shaping, then the pressure is increased to 15-20MPa and held for 30 minutes for curing. After hot pressing, the mixture is allowed to cool naturally to room temperature to obtain reconstituted bamboo boards.

[0042] 1. Microstructure analysis and characterization: The morphology of the samples was observed using scanning electron microscopy (SEM) (FEI, Hillsboro, OR, USA) and transmission electron microscopy (TEM). The chemical composition of the lignin-cuprous oxide microspheres was analyzed using Fourier transform infrared spectroscopy (FTIR) (PerkinElmer, Waltham, MA, USA). The static water wettability of the reconstituted bamboo surface was tested using a water contact angle meter. Five water droplets were randomly dropped onto each sample to measure the water contact angle (WCA) and roll-off angle (SA), and the average value was taken.

[0043] 2. Mechanical Experiment Design The mechanical properties of reconstituted bamboo boards were determined using the three-point bending method according to the national standard GB / T 17657-2013. The specimen dimensions were set to 100mm (longitudinal) × 80mm × 11mm, with a span of 80mm. The test environment was room temperature, and the test was conducted at a loading rate of 10mm / min. The static bending strength (MOR) and modulus of elasticity (MOE) of the specimens were calculated by measuring the maximum load and deflection change. Six specimens were used in each group, and the maximum and minimum values ​​were removed to ensure data reliability.

[0044] 3. Experimental Design for Mold Prevention Wood samples were cut to standard dimensions of 50mm (longitudinal) × 20mm × 5mm, and reconstituted bamboo composite materials were prepared using experimental methods. Three groups of samples (including a control group, a Cu2O modified group, and a Lignin@Cu2O modified group) were set up to determine the anti-mildew level. Each group contained three parallel samples to ensure data reliability. According to GB / T 18261-2013 standard, this experiment mainly used Aspergillus niger (AN), Penicillium citrinum (PC), Trichoderma viride (TV), and a mixed mold (AN, PC, and TV mixed in a 1:1:1 ratio) (MM).

[0045] Weigh 46g of PDA powder, dissolve it in 1000mL of deionized water, heat until completely dissolved, dispense into narrow-mouthed Erlenmeyer flasks, and then sterilize in a high-temperature, high-pressure autoclave under the following conditions: temperature 121℃, pressure 0.1MPa, sterilization time 90min. Finally, pour the prepared potato dextrose agar nutrient solution into the culture medium for culturing the inoculum. Open the activated inoculum, perform the inoculation operation, and seal and mark the flasks. Place the inoculated culture dishes in a constant temperature and humidity incubator (25±0.5℃, 85±3%RH) and incubate in the dark for 7 days until the mycelium completely covers the surface of the culture medium. Place two U-shaped rods in the culture medium, and place the wooden block sample in the culture medium for incubation, taking photos every 2 days. After inoculation, incubate the fungus at 25℃ and 85% relative humidity for 28 days. During the incubation process, quantify the mold coverage rate on the sample surface.

[0046] Table 1 Grading of Mold Growth on Surface of Wood-based Panel Specimens 0 Not grown No mold growth was observed on the surface, and no mold growth was observed under a low-power (50×) biological optical microscope. 1 Trace growth A few hyphae were present on the surface of the specimen, but the infected area was ≤10%. 2 slight growth Slight mold hyphae growth was observed, with the infected area on the specimen surface exceeding 10% but less than 30%. 3 Moderate growth Moderate mold hyphae growth was observed, with the infected area on the specimen surface >30% but ≤60%. 4 Severe growth Mold hyphae are growing severely, with the infected area on the specimen surface exceeding 60%. According to the mold growth classification of the test specimens, those at grade 0 or 1 met the mold prevention requirements.

[0047] Experimental test results: This invention employs a solvent exchange method to prepare microspheres with lignin as the outer shell and cuprous oxide as the core material. Lignin molecules aggregate and coat cuprous oxide particles through π-π interactions, producing lignin-cuprous oxide microspheres (Lignin@Cu2O) with a particle size between 200-2000 nm. Their regular spherical structure provides a certain degree of surface roughness, and the slow release of the internal metal oxide substances achieves a long-lasting anti-mildew effect. Subsequently, reconstituted bamboo bundles are impregnated in an adhesive mixture of LCMs and phenolic resin, and reconstituted bamboo engineered wood panels are prepared by hot pressing along the grain.

[0048] Depend on Figure 1 Scanning electron microscope image of lignin-cuprous oxide microspheres (Lignin@Cu2O) Figure 1 In the images (a, b, c) and transmission lens images (h, i, j), it can be observed that the lignin-cuprous oxide microsphere powder exhibits a complete spherical shape, indicating that lignin has successfully coated the cuprous oxide. The average diameter reaches 200-2000 nm. It is understood that the pore size of most bamboo is between 1000-10000 nm. The diameter of the microspheres allows them to easily penetrate the interior of the bamboo, achieving long-lasting and comprehensive anti-mold release. Furthermore, with the support of phenolic resin adhesive, the microspheres can be anchored extensively within the bamboo, effectively improving anti-mold performance. In the energy dispersive spectroscopy (EDS) images (…), the microspheres exhibit a complete spherical shape, demonstrating that lignin has successfully coated the cuprous oxide. Figure 1(d, e, f) The presence of a large amount of Cu can be clearly observed, indicating that Cu2O can be uniformly distributed in the composite system; at the same time, the presence of C also confirms the effectiveness of the lignin shell, which provides conditions for improving the hydrophobic and mechanical properties of the engineered wood panel.

[0049] Figure 2 SEM images of blank reconstituted bamboo (control group), Cu2O-modified reconstituted bamboo (Cu2O modified group), and lignin-cuprous oxide microsphere-modified reconstituted bamboo (Lignin@Cu2O modified group) are shown. Reconstituted bamboo treated with pure phenolic resin (… Figure 2 The surface of A1-A3 is relatively smooth. Cu2O modified reconstituted bamboo ( Figure 2 On the surface of B1-B3, Cu2O particles were observed to be uniformly distributed in the hot-pressed reconstituted bamboo. Simultaneously, the surface roughness of the Cu2O-modified reconstituted bamboo was also observed to be relatively high. Meanwhile, the lignin-cuprous oxide microsphere-modified reconstituted bamboo (… Figure 2 The surface roughness of C1-C3 bamboo is significantly reduced, making it smoother than Cu2O-modified reconstituted bamboo. This is the reason for its high hydrophobicity. The addition of lignin-cuprous oxide microspheres allows lignin and phenolic resin to form a composite crosslinking system, improving the mechanical properties and hydrophobicity of the resin system. Furthermore, the presence of microsphere morphology is clearly visible on the surface of the lignin-cuprous oxide microsphere-modified reconstituted bamboo, indicating that lignin has successfully coated cuprous oxide to form a composite structure. Energy dispersive spectroscopy (EDS) analysis... Figure 2 (D1-D3) confirmed that the Cu element was evenly distributed and the C element signal was enhanced in the Lignin@Cu2O modified group, further confirming the successful introduction of lignin-cuprous oxide composite microspheres.

[0050] like Figure 3 As shown, lignin-cubic oxide microspheres (Lignin@Cu2O) mainly exhibit four characteristic peaks, among which the peak at 1526 cm⁻¹ is the most prominent. -1 The peak at 2871 cm⁻¹ is the most typical aromatic characteristic peak of lignin. -1 The asymmetric stretching characteristic peak of -CH2 at 1030 cm⁻¹ -1 Stretching vibrations of primary alcohols or ether bonds (CO) are also strong evidence for the presence of lignin; a 472 cm⁻¹ vibration can be observed after the addition of Cu₂O. -1 The stretching vibration of the Cu-O bond appears at this point, with Cu2O being the most prominent characteristic peak, corresponding to the symmetric vibration mode of Cu-O in its cubic crystal system. Then, lignin-cuprous oxide microspheres (Lignin@Cu2O) are mixed with phenolic resin (RF) and subjected to [a process] at 1250 cm⁻¹. -1 The CO bond (phenolic hydroxyl group linked to the benzene ring) vibration peak observed in phenolic resin is a key peak that distinguishes it from other resins; at 1509 cm⁻¹ -1The presence of C=C stretching vibrations in the aromatic ring of the phenol unit at the point indicates the existence of a benzene ring structure in the resin.

[0051] from Figure 4 XPS spectra of two samples (lignin-cuprous oxide microsphere powder (Lignin@Cu2O) and lignin-cuprous oxide microsphere-modified phenolic resin (Lignin@Cu2O@PF)) show that, due to the presence of lignin, C and O elements can be observed at (284.8 eV) and (532.8 eV), while Cu2p (932.5 eV) confirms the successful introduction of Cu2O. The C1s region is mainly composed of the following chemical bonds: C=O, CO, CC, and COC. The introduction of phenolic resin enhances all characteristic peaks, but the CO proportion (286.5 eV) decreases after the co-condensation of lignin and PF. These analytical results demonstrate the structural stability and confirm the successful preparation of this composite system.

[0052] The TGA and DTG curves of lignin-cuprous oxide microsphere powder (Lignin@Cu2O) and lignin-cuprous oxide microsphere-modified phenolic resin (Lignin@Cu2O@PF) are shown below. Figure 5 A and Figure 5 As shown in B, the mass loss within 150 ℃ is due to the evaporation of residual moisture in the sample. The main decomposition region for each element is between 200-450 ℃. The presence of Cu₂O accelerates the breaking of CO bonds in lignin, resulting in a slight decrease in decomposition temperature (within...). Figure 5 (As shown in Figure B, the DTG peak shifts to the left), but most of the overall mass loss still occurs after 242℃. Simultaneously, Cu₂O catalyzes the decomposition of phenolic resin and lignin, leading to an overlap in the decomposition ranges of lignin (200-400℃) and phenolic resin (250-450℃) (showed in the DTG plot that both decompose simultaneously at 258℃), resulting in a bimodal DTG curve and synergistic carbonization. Its mass loss also occurs earlier at 214℃. The 400-800℃ range is the carbonization stage, where Cu₂O / Cu embeds into the carbon matrix, leading to an increase in residual char. Thermogravimetric analysis results show that phenolic resin has a higher total carbon mass fraction, while phenolic resin and lignin have a greater advantage in terms of carbon yield.

[0053] In the performance evaluation system of engineered wood products, mechanical properties are the core quality indicator. The main adhesives for engineered wood products are urea-formaldehyde resin, phenolic resin, and polyurethane, with urea-formaldehyde resin being the most widely used. Currently, establishing the structure-property relationship between mechanical properties and other functional characteristics (such as mildew resistance and dimensional stability) is one of the current research hotspots in the market during material development and product upgrades.

[0054] In this experiment, the blank reconstituted bamboo was a reconstituted bamboo engineered wood panel directly bonded with phenolic resin. The other two groups were made by hot-pressing reconstituted bamboo engineered wood panels using phenolic resins modified with Cu2O and Liglin@Cu2O, respectively. Under thermocatalytic conditions, the hydroxymethyl groups in the phenolic resin adhesive system can undergo multi-stage condensation reactions with the active groups in the lignin structure, thereby improving its bonding strength. Figure 6 As can be seen, the bending resistance of Lignin@Cu2O modified reconstituted bamboo is significantly improved compared to unmodified reconstituted bamboo, with a maximum yield point reaching 1.68 kN. This is because the addition of lignin improves the mechanical properties of the glued reconstituted bamboo. However, the bending resistance of reconstituted bamboo modified with only Cu2O is poor, showing a significant reduction compared to unmodified reconstituted bamboo engineered wood panels. This is because cuprous oxide itself is a brittle phase, has poor interfacial compatibility, and its hardness differs greatly from that of the resin, thus disrupting the material's homogeneity. Therefore, it can be concluded that Lignin@Cu2O modified reconstituted bamboo retains the anti-mildew and antibacterial properties of Cu2O while maintaining good mechanical properties.

[0055] Figure 7 Water contact angle analysis was performed on Ligin@Cu2O modified reconstituted bamboo, Cu2O modified reconstituted bamboo, and blank reconstituted bamboo. From... Figure 7 As can be seen, after adding the silane modifier, the water contact angle of all samples exceeded 90°. This is because the silane modifier can reduce the surface energy of the reconstituted bamboo chips, thus making the bamboo chips hydrophobic. The average water contact angle of the blank group was 111°, because the glue on the surface of the reconstituted bamboo formed a smooth glue layer during hot pressing after impregnation, resulting in a larger hydrophobic angle. The reconstituted bamboo modified with Liglin@Cu2O showed a slight improvement in hydrophobicity compared to the blank control group because lignin itself possesses hydrophobic properties; however, the average water contact angle of the Cu2O-modified reconstituted bamboo was only 102.8° because the addition of Cu2O made the glue layer surface rougher, reducing its hydrophobicity. Bamboo surfaces are rich in hydroxyl groups, exhibiting strong hydrophilicity, causing liquids to penetrate rapidly through capillary action and hydrogen bonding, reaching high moisture content in a short time. While this characteristic is beneficial for modification treatment, it significantly affects dimensional stability. Therefore, when wood is in a humid environment for a long time, it is easily damaged by mold, and its mechanical properties cannot be guaranteed. Therefore, modifying the hydrophobic properties of bamboo surfaces is essential.

[0056] Anti-mold performance is one of the key indicators for evaluating the practical value of wood-based materials. This study evaluated the anti-mold performance of Liglin@Cu2O microspheres by incorporating them into phenolic resin for hot-pressed reconstituted bamboo, using unmodified blank reconstituted bamboo panels as a control group. The microspheres were cultured for 28 days in PC, AN, TV, and MM media, respectively, and the presence of mold growth on the surface was observed. After 28 days of culture, all four control groups showed obvious signs of various mold growth. Cu2O-modified reconstituted bamboo exhibited good anti-mold ability against Penicillium citrinum (PC), while other molds showed signs of growth. However, no obvious signs of fungal growth were observed on or around the surface of Liglin@Cu2O-modified reconstituted bamboo, fully demonstrating the superior anti-mold properties of Liglin@Cu2O microspheres. Since both lignin and phenolic resin have weak anti-mold properties, the synergistic anti-mold system constructed by combining Cu2O and lignin effectively inhibits mold growth. The anti-mold mechanism of Cu2O is mainly based on its slow-release copper ion properties: In humid environments, Cu2O continuously releases Cu⁺ / Cu²⁺ ions through controlled dissolution (extremely low solubility). These ions can penetrate the cell membrane of microorganisms, bind to intracellular enzymes or proteins, disrupt their metabolic activity, and lead to mold death. The lignin coating layer reduces the diffusion rate of copper ions through its three-dimensional network structure, achieving long-lasting anti-mold effect. This synergistic effect allows this anti-mold system to maintain a high anti-mold rate while effectively controlling the amount of copper ion leaching.

[0057] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A lignin-cuprous oxide composite microsphere-modified reconstituted bamboo material, characterized in that, The reconstituted bamboo material is made by impregnating bamboo bundles with lignin-cuprous oxide composite microspheres modified phenolic resin adhesive, and then hot-pressing them. The lignin-cuprous oxide composite microsphere modified phenolic resin adhesive includes phenolic resin and lignin-cuprous oxide composite microspheres dispersed in the phenolic resin. The lignin-cuprous oxide composite microspheres have a core-shell structure, comprising a cuprous oxide core and a lignin shell coating the surface of the cuprous oxide core.

2. The modified reconstituted bamboo according to claim 1, characterized in that, The particle size of the lignin-cuprous oxide composite microspheres is 200-2000 nm.

3. The modified reconstituted bamboo according to claim 2, characterized in that, In the synthesis of the lignin-cuprous oxide composite microspheres, the solid content ratio of lignin raw material to cuprous oxide raw material is 1:(0.8-1.2); the solid content ratio of the lignin-cuprous oxide composite microspheres to phenolic resin is 1:(8-12).

4. A method for preparing modified reconstituted bamboo as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Mix lignin and cuprous oxide powder in an organic solvent, stir and disperse to obtain a mixture; (2) Add water to the mixture obtained in step (1) to carry out solvent exchange reaction, so that lignin self-assembles and coats on the surface of cuprous oxide. After the organic solvent has completely evaporated, the reaction solution is separated into solid and liquid to obtain lignin-cuprous oxide composite microspheres. (3) The dried lignin-cuprous oxide composite microsphere powder obtained in step (2) is mixed with phenolic resin and stirred evenly to obtain lignin-cuprous oxide composite microsphere modified phenolic resin adhesive. (4) After the bamboo bundles are impregnated with lignin-cuprous oxide composite microsphere modified phenolic resin adhesive, they are taken out and dried. The dried bamboo bundles are hot-pressed in the same direction as the grain to obtain modified reconstituted bamboo boards.

5. The method for preparing modified reconstituted bamboo according to claim 4, characterized in that, In step (1), the organic solvent is acetonitrile; the mass ratio of lignin to cuprous oxide powder is 1:(0.8-1.2); and the stirring speed is 800-1000 rpm.

6. The method for preparing modified reconstituted bamboo according to claim 4, characterized in that, In step (2), the water is added at a rate of 15-25 mL / min; the ratio of water to organic solvent is (4-6):1; the solvent exchange reaction is carried out at room temperature.

7. The method for preparing modified reconstituted bamboo according to claim 4, characterized in that, In step (3), the mass ratio of the lignin-cuprous oxide composite microsphere powder to the phenolic resin is 1:(8-12).

8. The method for preparing modified reconstituted bamboo according to claim 4, characterized in that, In step (4), the soaking time of the bamboo bundle is 20-40 min; the hot pressing temperature is 140-150℃, first hot pressing with 5MPa pressure for 5 min to set the shape, and then holding the pressure with 15-20MPa pressure for 25-35 min.

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