Preparation method and application of high-cohesiveness environment-friendly antibacterial woodworking glue

Abstract

The invention discloses a preparation method and application of high-cohesiveness environment-friendly antibacterial woodworking glue. The woodworking glue is a water-based emulsion, and is prepared through the processes of prepolymerization of polyisocyanate and polyol, chain extension of a hydrophilic monomer, a chain extender and a silane coupling agent, end capping and neutralization of an imidazole compound, emulsification and post-chain extension. The adhesive developed by the invention takes water as a dispersion medium, does not contain formaldehyde, is low in VOC (Volatile Organic Compounds), and is safe and environment-friendly. A molecular side chain of the adhesive contains hydrolyzable siloxane, a terminal group contains thermal reactive blocked isocyanate, and when the adhesive is applied, self-crosslinking of adhesive molecules can be realized, and covalent bonds can be formed with hydroxyl groups on the surface of wood, so that the adhesive has high cohesive force and strong interface adhesion. A hydrophobic structure formed by siloxane chain segments can further improve the hydrolysis resistance of the adhesive. Besides, the glue system has a cationic characteristic, and the imidazole compound released by curing and the side chain tertiary amine salt have a synergistic effect, so that breeding of microorganisms such as white-rot fungi and the like can be efficiently inhibited. The adhesive is suitable for bonding wood materials, can be heated and cured after being glued and attached, and has good application value in manufacturing of various wood products.

Description

Technical Field

[0001] This invention relates to the field of wood adhesive processing technology, specifically to a method for preparing and applying a highly adhesive, environmentally friendly, antibacterial woodworking adhesive. Background Technology

[0002] Wood, as one of the oldest natural materials used by humankind, occupies an indispensable position in construction, furniture, decoration, and industrial production due to its advantages such as being renewable, easy to process, having a high strength-to-weight ratio, and a warm texture. However, natural wood also has inherent defects such as poor dimensional stability, anisotropy, and susceptibility to cracking and decay. To overcome these shortcomings and maximize the utilization of wood resources, the engineered wood products industry (such as plywood, particleboard, and fiberboard) and modern wood structure engineering have emerged and become the mainstay of the wood industry. In this transformation, wood adhesives, as the key factor in firmly bonding wood or other woody materials, directly determine the performance, quality, application range, and even service life of wood products. For a long time, the adhesives relied upon in the wood processing field have mainly included traditional aldehyde adhesives such as urea-formaldehyde resin, phenolic resin, and melamine-formaldehyde resin. These adhesives are favored by people because of their low cost, excellent bonding strength, and mature processes. However, they release free formaldehyde over a long period of time during use, which has a significant impact on human health. With increasingly stringent environmental regulations and rising consumer awareness of health, the development of environmentally friendly water-based wood adhesives has become a consensus and an urgent need in academia and industry.

[0003] Waterborne polyurethane adhesives, as an ideal alternative to traditional aldehyde adhesives, have attracted widespread attention due to their advantages such as being non-toxic, pollution-free, and having low VOC content. However, most existing waterborne woodworking adhesive technologies struggle to effectively balance environmental friendliness and practicality. For example, ordinary waterborne polyurethane has problems such as poor water resistance, insufficient antibacterial properties, and limited bonding strength in wood products, severely hindering its widespread application. Chinese invention patent CN119410336A discloses a highly weather-resistant, antibacterial, and environmentally friendly waterborne woodworking adhesive and its preparation method. Although some progress has been made in waterborne formaldehyde-free woodworking adhesives, the product still requires the addition of microcapsules to achieve antibacterial function. This physical mixing antibacterial method suffers from problems such as easy migration of antibacterial components and insufficient durability. Meanwhile, while the wood-based panel adhesive disclosed in patent CN115612441A emphasizes antibacterial properties, its formulation contains small molecule substances such as plasticizers, which may lead to a decrease in the adhesive's aging resistance and affect its long-term performance. CN113322041A discloses a waterborne polyurethane adhesive for reconstituted wood, but it relies on external surfactants to achieve external emulsification of polyurethane. After curing, the residual hydrophilic emulsifier molecules will continuously absorb moisture like a sponge, resulting in a significant decrease in the water resistance, chemical resistance and mechanical strength of the adhesive film. At the same time, its stability is poor, and it is sensitive to electrolytes and freeze-thaw cycles. Its overall performance is inferior to internally emulsified products that use chemically bonded hydrophilic groups.

[0004] Furthermore, although commercially available polyvinyl acetate emulsions (white glue) are water-based and environmentally friendly products, the adhesive film is thermoplastic. When exposed to water or continuous high humidity, it will soften, whiten, and lose strength, making it completely unsuitable for outdoor or humid environments. Its softening point is between 60-90℃, exhibiting extremely poor water resistance, insufficient heat resistance, weak adhesion to non-porous materials, and susceptibility to microbial attack. These inherent defects make it unsuitable for any scenario requiring water resistance, heat resistance, or durability. It is only suitable for dry, non-structural applications such as furniture assembly, interior decoration bonding, and paper / fabric bonding. For outdoor, humid, load-bearing, or high-temperature environments, more durable adhesives such as polyurethane, epoxy resin, or phenolic resin must be used. Summary of the Invention

[0005] To address the problems in related technologies, this invention proposes a method for preparing and applying a highly adhesive, environmentally friendly, antibacterial wood adhesive, overcoming the issues of existing wood adhesives being environmentally unfriendly, having poor physical properties, and being prone to bacterial growth. This invention utilizes imidazole compounds, silane coupling agents, and amine hydrophilic chain extenders to prepare an antibacterial reactive waterborne polyurethane adhesive. Its unique cationic structure and imidazole substances effectively inhibit the damage to wood and the adhesive caused by harmful microorganisms such as bacteria and white-rot fungi. Furthermore, due to its thermally activated and self-crosslinking properties, it possesses high interfacial reactivity, adhesion, and cohesion, exhibiting advantages such as high adhesion and hydrolysis resistance.

[0006] A method for preparing and applying a high-adhesion, environmentally friendly, antibacterial wood adhesive includes the following steps: (1) Preparation of prepolymer: In a nitrogen atmosphere, polyisocyanate and vacuum dehydrated polyol are added to the reactor and reacted at 80°C for 2-3 hours; the temperature is lowered to 60°C, hydrophilic monomer and chain extender are added and reacted for 1-2 hours; the temperature is further lowered to a certain level, an appropriate amount of acetone is added to reduce viscosity, and then a silane coupling agent is added and reacted for a period of time. Then an imidazole compound is added to end-cap for 30 minutes-1 hour until the -NCO content of the system reaches the theoretical value and the reaction is stopped to obtain polyurethane prepolymer; (2) Preparation of waterborne polyurethane adhesive: Add acidic neutralizer and neutralize for 20 min. When the pH of the system is maintained between 5 and 7, add an appropriate amount of water, increase the rotation speed to 1500-2000 r / min, and emulsify for 20 min. Add chain extender and continue emulsifying for 20 min to obtain polyurethane emulsion. After standing overnight, remove acetone by vacuum distillation and add deionized water to adjust the solid content to 30%.

[0007] (3) Application of water emulsion in wood bonding: The adhesive emulsion prepared in step (2) is evenly applied to the surface of the wood substrate, and after pressure bonding, it is cured at a certain temperature for a period of time to obtain the adhesive board.

[0008] In step (1), the polyisocyanate is any one or more of toluene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, dicyclohexylmethane diisocyanate, and methylcyclohexyl diisocyanate, preferably one or more of isophorone diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, dicyclohexylmethane diisocyanate, and methylcyclohexyl diisocyanate.

[0009] In step (1), the polyol is one or more of the following: adipic acid polyester diol, polycaprolactone diol, polycarbonate diol, polylactic acid diol, terephthalic acid polyester diol, phthalic anhydride polyester polyol, isophthalic acid polyester diol, polytetrahydrofuran diol, and polytrimethylene ether diol.

[0010] In step (1), the polyol has a molecular weight ≥ 2000, and polyester diols with a molecular weight ≤ 4000 and a molecular weight ≤ 2500 are particularly preferred.

[0011] The hydrophilic monomer in step (1) is diethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N-(n-propyl)diethanolamine, N-butyldiethanolamine, 3-dimethylamino-1,2-propanediol, N,N-bis(2-hydroxyethyl)aniline, N,N-bis(2-hydroxyethyl)-m-toluidine, N,N-bis(2-hydroxypropyl)aniline, N,N-bis(2-hydroxyethyl)aminomethylenephosphonic acid diethyl ester, N,N-dimethyl-N',N'-bis(2-hydroxyethyl)-1,3-propanediamine, and N,N-dimethyl-N',N'-bis(2-hydroxypropyl)-1,3-propanediamine. The preferred choice is any one of N,N-dimethyl-(2-dihydroxymethyl)butamine, N,N-diethyl-(2-dihydroxymethyl)butamine, 1,4-butanediol di(3-diethylamino-2-hydroxypropanol) ether, and 1,2-ethylenediol di(3-diethylamino-2-hydroxypropanol) ether, preferably any one of 3-dimethylamino-1,2-propanediol, N,N-dimethyl-(2-dihydroxymethyl)butamine, N,N-diethyl-(2-dihydroxymethyl)butamine, 1,4-butanediol di(3-diethylamino-2-hydroxypropanol) ether, and 1,2-ethylenediol di(3-diethylamino-2-hydroxypropanol) ether.

[0012] In step (1), the chain extender is any one of 1,4-butanediol, ethylene glycol, neopentyl glycol, trimethylolpropane, glycerol, triethanolamine, triisopropanolamine, and 3,3'-dichloro-4,4'-diaminodiphenylmethane, preferably any one of triethanolamine and triisopropanolamine.

[0013] In step (1), the silane coupling agent is any one or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, γ-diethylenetriaminepropyltrimethoxysilane, γ-ureapropyltriethoxysilane, and phenylaminomethyltriethoxysilane, preferably any one or more of N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, and γ-diethylenetriaminepropyltrimethoxysilane.

[0014] In step (1), the reaction temperature of the silane coupling agent is ≤45℃, and the dropwise reaction time is 20min-50min.

[0015] In step (1), the imidazole compound is any one or more of imidazole, 2-methylimidazolium, 2-ethylimidazolium, 2-isopropylimidazolium, 5-isopropylimidazolium, 2-tert-butylimidazolium, 2-ethyl-4-methylimidazolium, 2-nitroimidazolium, 4-nitroimidazolium, 2-methyl-4-nitroimidazolium, 2-phenylimidazolium, 4-phenylimidazolium, 4,5-dibenzimidazole, 2,4,5-triphenylimidazolium, and 2-(4-thiazolyl)-1H-benzimidazole, preferably any one or more of 2-nitroimidazolium, 4-nitroimidazolium, 2-phenylimidazolium, 4-phenylimidazolium, 4,5-dibenzimidazole, and 2,4,5-triphenylimidazolium.

[0016] In step (1), the molar ratio of polyisocyanate, polyol, hydrophilic monomer, chain extender, silane coupling agent and imidazole compound is 8-15:1-3:3-6:1-1.5:1-1.5:0.5-2.

[0017] In step (2), the acid neutralizing agent is any one or more of 2,3-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,4-dihydroxycinnamic acid, 3-methoxy-4-hydroxycinnamic acid, 3,5-dimethoxy-4-hydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, 4-hydroxybenzoic acid, 2-hydroxybenzoic acid, acetic acid, lactic acid, formic acid, hydrochloric acid, and phosphoric acid, preferably any one or two of 2,3-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,4-dihydroxycinnamic acid, and acetic acid.

[0018] In step (2), the chain extender is any one or more of diethylenetriamine, isophorone diamine, ethylenediamine, and cyclohexane-1,3-dimethyldimethylamine.

[0019] In step (2), the molar ratio of the post-chain extender to the polyurethane prepolymer-NCO prepared in step (1) is 5%-30%.

[0020] In step (3), the curing temperature is 90℃-120℃ and the curing time is 5min-30min.

[0021] Beneficial effects of the present invention (1) Compared with traditional wood glue, the wood glue developed in this invention uses water as the dispersion medium, has low VOC content, does not contain free formaldehyde, etc., and is safe and non-toxic during storage and use.

[0022] (2) The waterborne polyurethane wood adhesive developed in this invention contains hydrolyzable siloxane groups in its molecular side chains, and the end groups of the molecular chains contain thermally reactive groups—blocked isocyanates. During the heating and curing process, self-crosslinking occurs between the polyurethane molecular chains, increasing the cohesive strength of the adhesive. Furthermore, the Si-OH generated by the hydrolysis of siloxane groups in the curing system and the -NCO formed by unblocking react with the abundant hydroxyl groups on the wood surface to form covalent crosslinks. Therefore, the wood adhesive developed in this invention has high cohesive strength, high interfacial reactivity, and exhibits excellent bonding performance.

[0023] (3) Due to the hydrolytic condensation between the siloxane groups on the side chains of polyurethane molecules, special hydrophobic siloxane segments are formed, which act like a protective shield to shield and surround the adjacent ester bonds, effectively reducing the probability of water molecules approaching and attacking the ester bonds in polyurethane molecules. Therefore, the water-based wood glue prepared in this invention has good hydrolysis resistance.

[0024] (4) Traditional wood glues, such as urea-formaldehyde resin, phenolic resin, and white glue, only provide bonding and not protection. Once glued areas, especially gaps and joints, become damp, they are more prone to accumulating moisture and nutrients than solid wood parts, becoming breeding grounds for bacteria and other microorganisms. Especially in the field of wood preservation, the protection requirements against white rot fungi are far higher than those against mold, because their damage is structural and fatal. The waterborne polyurethane developed in this invention is cationic, and its special tertiary amine salt structure gives it excellent antibacterial effect. In particular, the imidazole compounds produced during the curing and unsealing process can effectively prevent the growth of white rot fungi and other saprophytic microorganisms in wood. Attached Figure Description

[0025] Figure 1 The fracture conditions and ultra-depth-of-field 3D images of the glued surfaces of plywood boards in the examples and comparative examples are shown. Figure 2 The images show the antibacterial effects of Examples 1-3 and Comparative Example 1 against white rot fungi, Escherichia coli, and Staphylococcus aureus. Detailed Implementation

[0026] The following description is merely a preferred embodiment of the present invention and is used only to describe the present invention. It should not be construed as limiting the scope of the present invention.

[0027] Example 1 (1) Under a nitrogen atmosphere, 5.8 mol of isophorone diisocyanate and 1 mol of poly(1,4-butanediol adipate) (PBA3000) were added to a three-necked flask and reacted at 80°C for about 2.5 h. The temperature was lowered to 60°C, and 2.13 mol of 3-dimethylamino-1,2-propanediol and 0.61 mol of triethanolamine were added and the reaction continued for about 1 h. The temperature was lowered to 40°C, and 0.66 mol of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane was added dropwise and reacted for 30 min. An appropriate amount of acetone was added to adjust the viscosity, and 0.5 mol of 2-ethylimidazole was added to seal the reaction for 50 min. The -NCO content was measured to be at the theoretical value, and the polyurethane prepolymer was obtained.

[0028] (2) Add 0.8 mol of 2,3-dihydroxybenzoic acid and 1.33 mol of acetic acid, neutralize for 20 min, and wait for the pH of the system to be maintained between 5 and 7. Add an appropriate amount of water, increase the rotation speed to 2000 r / min, emulsify for 20 min, add 0.18 mol of ethylenediamine, and continue emulsifying for 20 min to obtain a polyurethane emulsion. After standing overnight, remove acetone by rotary evaporation, add a small amount of deionized water, and obtain a polyurethane emulsion with a solid content of 30%.

[0029] Example 2 (1) 5.8 mol of isophorone diisocyanate and 1 mol of poly(1,4-butanediol adipate) (PBA3000) were added to a three-necked flask under a nitrogen atmosphere and reacted at 80°C for about 2.5 h. The temperature was lowered to 60°C, and 2.13 mol of N,N-dimethyl-(2-dihydroxymethyl)butylamine and 0.61 mol of triethanolamine were added and the reaction continued for about 1 h. The temperature was lowered to 40°C, and 0.66 mol of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane was added dropwise and reacted for 30 min. An appropriate amount of acetone was added to adjust the viscosity, and 0.5 mol of 4-nitroimidazole was added to seal the reaction for 50 min. The content of -NCO was measured to be at the theoretical value, and the polyurethane prepolymer was obtained.

[0030] (2) Add 1 mol of 3,4-dihydroxybenzoic acid and 1.13 mol of acetic acid, neutralize for 20 min, and wait for the pH of the system to be maintained between 5 and 7. Add an appropriate amount of water, increase the rotation speed to 2000 r / min, emulsify for 20 min, add 0.2 mol of isophorone diamine, and continue emulsifying for 20 min to obtain a polyurethane emulsion. After standing overnight, remove acetone by rotary evaporation, add a small amount of deionized water, and obtain a polyurethane emulsion with a solid content of 30%.

[0031] Example 3 (1) 5.8 mol of isophorone diisocyanate and 1 mol of poly(1,4-butanediol adipate) (PBA3000) were added to a three-necked flask under a nitrogen atmosphere and reacted at 80°C for about 2.5 h. The temperature was lowered to 60°C, and 2.13 mol of 3-dimethylamino-1,2-propanediol and 0.61 mol of triisopropanolamine were added and the reaction continued for about 1.5 h. The temperature was lowered to 45°C, and 0.66 mol of N-(2-aminoethyl)-3-aminopropyltriethoxysilane was added dropwise and reacted for 50 min. An appropriate amount of acetone was added to adjust the viscosity, and 1 mol of 4-nitroimidazole was added to seal the reaction for 1 h. The content of -NCO was measured to reach the theoretical value, and the polyurethane prepolymer was obtained.

[0032] (2) Add 1.2 mol of 3,4-dihydroxybenzoic acid and 0.93 mol of acetic acid, neutralize for 20 min, and wait for the pH of the system to be maintained between 5 and 7. Add an appropriate amount of water, increase the rotation speed to 2000 r / min, emulsify for 20 min, add 0.3 mol of isophorone diamine, and continue emulsifying for 20 min to obtain a polyurethane emulsion. After standing overnight, remove acetone by rotary evaporation, add a small amount of deionized water, and obtain a polyurethane emulsion with a solid content of 30%.

[0033] Comparative Example 1 (1) Under a nitrogen atmosphere, 5.8 mol of isophorone diisocyanate and 1 mol of poly(1,4-butanediol adipate) (PBA3000) were added to a three-necked flask and reacted at 80°C for about 2.5 h. The temperature was lowered to 60°C, and 2.13 mol of 3-dimethylamino-1,2-propanediol and 0.61 mol of triethanolamine were added, and the reaction continued for about 1 h. The temperature was lowered to 40°C, and 0.66 mol of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane was added dropwise. After reacting for 30 min, the -NCO content was measured and found to be at the theoretical value. An appropriate amount of acetone was added to adjust the viscosity, and the polyurethane prepolymer was obtained.

[0034] (2) Add 0.8 mol of 3,4-dihydroxybenzoic acid and 1.33 mol of acetic acid, neutralize for 20 min, and wait for the pH of the system to be maintained between 5 and 7. Add an appropriate amount of water, increase the rotation speed to 2000 r / min, emulsify for 20 min, add 0.2 mol of ethylenediamine, and continue emulsifying for 20 min to obtain a polyurethane emulsion. After standing overnight, remove acetone by rotary evaporation, add a small amount of deionized water, and obtain a polyurethane emulsion with a solid content of 30%.

[0035] Comparative Example 2 (1) In a nitrogen atmosphere, 5.8 mol of isophorone diisocyanate and 1 mol of poly(1,4-butanediol adipate) (PBA3000) were added to a three-necked flask and reacted at 80°C for about 2.5 h. The temperature was lowered to 60°C, and 2.13 mol of 3-dimethylamino-1,2-propanediol and 0.61 mol of triethanolamine were added and the reaction continued for about 1 h. The temperature was lowered to 40°C, and 0.66 mol of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane was added dropwise and reacted for 30 min. An appropriate amount of acetone was added to adjust the viscosity, and 1 mol of methyl ethyl ketone oxime was added to block the reaction for 1 h. The content of -NCO was measured to reach the theoretical value, and the polyurethane prepolymer was obtained.

[0036] (2) Add 1.065 mol of 3,4-dihydroxybenzoic acid and 1.065 mol of acetic acid, neutralize for 20 min, and wait for the pH of the system to be maintained between 5 and 7. Add an appropriate amount of water, increase the rotation speed to 2000 r / min, emulsify for 20 min, add 0.18 mol of isophorone diamine, and continue emulsifying for 20 min to obtain a polyurethane emulsion. After standing overnight, remove acetone by rotary evaporation, add a small amount of deionized water, and obtain a polyurethane emulsion with a solid content of 30%.

[0037] Comparative Example 3 (1) 5.8 mol of isophorone diisocyanate and 1 mol of poly(1,4-butanediol adipate) (PBA3000) were added to a three-necked flask under a nitrogen atmosphere and reacted at 80°C for about 2.5 h. The temperature was lowered to 60°C, and 2.13 mol of 3-dimethylamino-1,2-propanediol and 0.61 mol of triethanolamine were added and the reaction continued for about 1 h. The temperature was lowered to 40°C, and 0.66 mol of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane was added dropwise and reacted for 30 min. An appropriate amount of acetone was added to adjust the viscosity, and 1.5 mol of 4-nitroimidazole was added to seal the reaction for 1 h. The -NCO content was measured to be at the theoretical value, and the polyurethane prepolymer was obtained.

[0038] (2) Add 1.2 mol of 3,4-dihydroxybenzoic acid and 0.93 mol of acetic acid, neutralize for 20 min, and wait for the pH of the system to be maintained between 5 and 7. Add an appropriate amount of water, increase the rotation speed to 2000 r / min, emulsify for 20 min, add 0.18 mol of isophorone diamine, and continue emulsifying for 20 min to obtain a polyurethane emulsion. After standing overnight, remove acetone by rotary evaporation, add a small amount of deionized water, and obtain a polyurethane emulsion with a solid content of 30%.

[0039] Application of Examples and Comparative Products To illustrate the application effect of this invention, according to GB / T 7124-2008, the lap shear strength of wood was tested using the adhesives prepared in the examples and comparative examples. The substrate size was 130mm × 25mm, and the bonding area was 25mm × 5mm. During the experiment, the wood substrate was pressed under a pressure of 500g and dried at 110℃ for 20min. The tensile speed during measurement was 10mm / min. Five sets of tests were performed on each sample in parallel. The minimum and maximum values ​​were removed, and the average value of the remaining three sets was taken. The shear strength test data are listed in Table 1. Simultaneously, the surface morphology of the wood lap joint surface after the test was observed using a depth-of-field method. The results are as follows: Figure 1 As shown.

[0040] Table 1 Shear strength of adhesives in the examples and comparative examples Table 1 shows that the bonding effect of the examples is better than that of the comparative examples, especially the wood shear strength of Example 3, which reaches 6.91 MPa. The surface morphology and 3D images of the wood lap joints after mechanical property testing are also presented. Figure 1 As can be seen, the roughness of the bonded cross section in the embodiments is generally higher than that in the comparative examples, indicating that the bonding effect is better. In particular, the depth ratio of the bonded cross section of the wood in embodiment 3 is the most significant, indicating that the degree of damage at the bonded joint after breakage is the highest and the bonding force is the highest.

[0041] To further illustrate the antibacterial effect of the adhesive prepared in this invention, the antibacterial activity of the adhesives prepared in Examples 1, 2, 3, and Comparative Example 1 against *Escherichia coli* (24h), *Staphylococcus aureus* (24h), and white-rot fungi (4d) was tested using the disc diffusion method. The specific methods are as follows: 1. Preparation of the test film: Weigh 16g of water-based adhesive emulsion, pour it into a polytetrafluoroethylene mold, and dry it at room temperature in a well-ventilated indoor area for 3 days to prepare the film. Then, place the dried film in a vacuum drying oven at 110℃ for 2 hours. Place the dried film in a desiccator to cool naturally. Cut the film into 18mm round pieces for later use.

[0042] 2. Antimicrobial Experiment of White Rot Fungi: First, under aseptic conditions, a small amount of preserved white rot fungal hyphae was picked up with an inoculation needle and inoculated onto potato dextrose agar (PDA) medium. The medium was then incubated at 28°C for 5-7 days until the slant was covered with white, fluffy hyphae, which was then used as activated inoculum. Next, the cultured white rot fungi were re-inoculated onto PDA medium, and a cut piece of gelatin film (18 mm) was placed in the center of the PDA medium. The medium was incubated at 28°C for 4 days. The diameter of the inhibition zone was measured using precision calipers.

[0043] 3. Antibacterial test for Escherichia coli and Staphylococcus aureus: A bacterial cell suspension (approximately 10⁸ CFU mL⁻¹) was evenly spread on Mueller-Hinton agar. Then, the gel film (18 mm) was placed in MT agar. The MT agar plates were incubated at 37°C for 24 hours, and the diameter of the inhibition zone was measured using precision calipers.

[0044] Table 2. Statistics on the diameter of the antibacterial zone of the adhesives prepared in Examples 1-3 and Comparative Example 1 Depend on Figure 2 As shown in Table 2, the adhesive films formed by the adhesives in Examples 1 and 2 (Comparative Example 1) all exhibited inhibition zones, indicating antibacterial properties. However, compared to Comparative Example 1, the adhesive films formed by the adhesives in Examples 1-3 showed larger inhibition zone diameters and better antibacterial effects. In particular, the adhesives in Examples 1-3 demonstrated a particularly significant inhibitory effect on white rot fungi, with inhibition zones exceeding 50 mm in all cases.

Claims

1. A method for preparing a high-bonding, environmentally friendly, antibacterial wood adhesive, characterized by, It comprises the following steps: (1) Preparation of the prepolymer: under the nitrogen atmosphere, the polyisocyanate and the vacuum dehydrated polyol are added into the reactor, and reacted at 80℃ for 2-3h; cooled to 60℃, and the hydrophilic monomer and the chain extender are added and reacted for 1-2h; continuously cooled to a certain temperature, and then a proper amount of acetone is added to reduce the viscosity, and then the silane coupling agent is added and reacted for a period of time, and then the imidazole compound is added and capped for 30min-1h, until the -NCO content of the system reaches the theoretical value, and the reaction is stopped, to obtain the polyurethane prepolymer; (2) Preparation of the water-based polyurethane adhesive: the acidic neutralizer is added, and the neutralization treatment is carried out for 20min, and then the pH of the system is maintained at 5-7, and then a proper amount of water is added, and the rotation speed is increased to 1500-2000r / min, and then the emulsification is carried out for 20min; the post-chain extender is added, and the emulsification is continuously carried out for 20min, to obtain the polyurethane emulsion; after standing overnight, the acetone is removed by the reduced pressure distillation, and then the deionized water is added to adjust the solid content to 30%.

2. The preparation method of the high-adhesion environmentally friendly antibacterial wood glue according to claim 1, characterized in that, The polyisocyanate in the step (1) is any one or more of toluene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, pentaerythritol diisocyanate, dicyclohexylmethane diisocyanate, and methylcyclohexyl diisocyanate; The polyol in the step (1) is one or more of adipic acid-based polyester diol, polycaprolactone diol, polycarbonate diol, polylactic acid diol, terephthalic acid-based polyester diol, phthalic anhydride-based polyester polyol, isophthalic acid-based polyester diol, polytetrahydrofuran diol, and polytrimethylene ether glycol; The molecular weight of the polyol in the step (1) is greater than or equal to 2000; The hydrophilic monomer in the step (1) is any one of diethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N-(n-propyl)diethanolamine, N-butyldiethanolamine, 3-dimethylamino-1,2-propanediol, N,N-bis(2-hydroxyethyl)aniline, N,N-bis(2-hydroxyethyl)-m-toluidine, N,N-bis(2-hydroxypropyl)aniline, N,N-bis(2-hydroxyethyl)aminomethylene phosphonic acid diethyl ester, N,N-dimethyl-N',N'-bis(2-hydroxyethyl)-1,3-propanediamine, N,N-dimethyl-N',N'-bis(2-hydroxypropyl)-1,3-propanediamine, N,N-dimethyl-(2-dihydroxymethyl)butylamine, N,N-diethyl-(2-dihydroxymethyl)butylamine, 1,4-butanediol di(3-diethylamino-2-hydroxypropanol) ether, and 1,2-ethanediol di(3-diethylamino-2-hydroxypropanol) ether; The chain extender in the step (1) is any one of 1,4-butanediol, ethylene glycol, neopentyl glycol, trimethylolpropane, glycerol, triethanolamine, triisopropanolamine, and 3,3'-dichloro-4,4'-diamino diphenyl methane. The silane coupling agent in step (1) is any one or more of γ-aminopropyl triethoxysilane, γ-aminopropyl trimethoxysilane, N-(2-aminoethyl)-3-aminopropyl methyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyl trimethoxysilane, N-(2-aminoethyl)-3-aminopropyl triethoxysilane, γ-divinyltriamine propyl trimethoxysilane, γ-urea propyl triethoxysilane, phenylaminomethyl triethoxysilane; The reaction temperature of the silane coupling agent in step (1) is ≤45℃, and the dropping reaction time is 20min-50min; The imidazole compound in step (1) is any one or more of imidazole, 2-methyl imidazole, 2-ethyl imidazole, 2-isopropyl imidazole, 5-isopropyl imidazole, 2-tert-butyl imidazole, 2-ethyl-4-methyl imidazole, 2-nitro imidazole, 4-nitro imidazole, 2-methyl-4-nitro imidazole, 2-phenyl imidazole, 4-phenyl imidazole, 4,5-diphenyl imidazole, 2,4,5-triphenyl imidazole, 2-(4-thiazolyl)-1H-benzimidazole; The molar ratio of the polyisocyanate, the polyol, the hydrophilic monomer, the chain extender, the silane coupling agent, and the imidazole compound in step (1) is 8-15:1-3:3-6:1-1.5:1-1.5:0.5-2.

3. The method for preparing the high-adhesion, environmentally friendly, antibacterial wood glue according to claim 2, characterized in that, The polyisocyanate in step (1) is one or more of isophorone diisocyanate, hexamethylene diisocyanate, pentaerythritol diisocyanate, dicyclohexyl methane diisocyanate, methylcyclohexyl diisocyanate; The polyol in step (1) is a polyester diol with a molecular weight of 2500≤molecular weight≤4000; The hydrophilic monomer in step (1) is any one of 3-dimethylamino-1,2-propanediol, N,N-dimethyl-(2-dimethylol)butylamine, N,N-diethyl-(2-dimethylol)butylamine, 1,4-butanediol di(3-diethylamino-2-hydroxypropanol) ether, 1,2-ethanediol di(3-diethylamino-2-hydroxypropanol) ether; The chain extender in step (1) is any one of triethanolamine, triisopropanolamine; The silane coupling agent in step (1) is any one or more of N-(2-aminoethyl)-3-aminopropyl methyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyl trimethoxysilane, N-(2-aminoethyl)-3-aminopropyl triethoxysilane, γ-divinyltriamine propyl trimethoxysilane; The imidazole compound in step (1) is any one or more of 2-nitro imidazole, 4-nitro imidazole, 2-phenyl imidazole, 4-phenyl imidazole, 4,5-diphenyl imidazole, 2,4,5-triphenyl imidazole.

4. The preparation method of the high-adhesion environmentally friendly antibacterial wood adhesive according to claim 1, characterized in that, The acid neutralizer in step (2) is any one or more of 2,3-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,4-dihydroxycinnamic acid, 3-methoxy-4-hydroxycinnamic acid, 3,5-dimethoxy-4-hydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, 4-hydroxybenzoic acid, 2-hydroxybenzoic acid, acetic acid, lactic acid, formic acid, hydrochloric acid, and phosphoric acid; The post-chain extender in step (2) is any one or more of diethylenetriamine, isophorone diamine, ethylenediamine, and cyclohexane-1,3-dimethyl dimethylamine; In step (2), the molar ratio of the post-chain extender to the polyurethane prepolymer-NCO prepared in step (1) is 5%-30%.

5. The preparation method of the high-adhesion environmentally friendly antibacterial wood adhesive according to claim 1, characterized in that, The acid neutralizer in step (2) is any one or two of 2,3-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,4-dihydroxycinnamic acid, and acetic acid.

6. The use of the high-tack, environmentally friendly, antibacterial wood adhesive prepared by the method of any one of claims 1-5, characterized in that, The prepared water emulsion is applied to wood adhesion, the adhesive emulsion prepared in step (2) is uniformly coated on the surface of the wood substrate, and after pressing and bonding, it is cured at a certain temperature for a period of time to obtain a bonded board.

7. Use according to claim 6, characterized in that, The curing temperature is 90-120°C, and the curing time is 5-30 min.

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