Urea-formaldehyde resin-based adhesive for carbon crystal artificial board, preparation method and application thereof

Abstract

The application discloses a urea-formaldehyde resin-based adhesive for carbon crystal artificial board, a preparation method and application. The urea-formaldehyde resin-based adhesive is prepared from the following components: 60-80 parts of urea-formaldehyde resin, 80-100 parts of glyoxal, 15-40 parts of dicyandiamide, 4-10 parts of polyvinyl alcohol, 10-20 parts of lignin, 6-15 parts of epoxy soybean oil, 12-25 parts of lye, 6-15 parts of nano-modified silicon powder, 2-10 parts of curing agent, 2-8 parts of catalyst and 2-8 parts of dispersing agent. The prepared urea-formaldehyde resin-based adhesive is mixed with wood fibers, uniformly falls and lays on a board blank belt, and then is sequentially subjected to preheating and pressurizing, constant-temperature pressurizing and temperature-reducing pressurizing to obtain a carbon crystal artificial board blank. The prepared adhesive can improve the water resistance, interfacial bonding strength and durability of the carbon crystal artificial board, effectively reduces the formaldehyde release of the carbon crystal artificial board, and is especially suitable for the production of carbon crystal artificial boards with high requirements on physical properties and environmental protection. The adhesive preparation process is simpler and more efficient.

Description

Technical Field

[0001] This invention belongs to the field of adhesive preparation technology, and in particular relates to a urea-formaldehyde resin-based adhesive for carbon crystal artificial boards, its preparation method and application. Background Technology

[0002] With socio-economic development, consumers' demands for the environmental performance of home furnishing products have gradually increased. In recent years, with the growing demand for green buildings and environmentally friendly home furnishings, carbon crystal engineered wood panels (commonly known as carbon crystal boards or bamboo charcoal boards) have become a new type of environmentally friendly decorative board. Carbon crystal engineered wood panels have been widely used in high-end fields such as building materials, the automotive industry, and aerospace. Carbon crystal engineered wood panels are mainly made from wood fibers or other plant fibers, processed by adding carbon crystal powder and adhesives, and then pressed under heat and pressure to form a composite material. Carbon crystal engineered wood panels have advantages such as lightweight, high strength, and corrosion resistance, effectively improving product performance and lifespan. They are an environmentally friendly material actively promoted and widely used in Europe and America. In China, with the country's high emphasis on the new materials industry, research and development in the field of carbon crystal new materials has gradually become a focus, especially in the fields of building decoration and high-performance manufacturing. The application of carbon crystal engineered wood panels is showing a rapid growth trend. Carbon crystal engineered wood panel products have superior performance in terms of heat resistance, moisture resistance, and corrosion resistance, and by replacing traditional materials, they effectively improve the environmental performance and service life of building materials. Meanwhile, the domestic carbon crystal artificial board production process has been continuously optimized, and the cost has gradually decreased, which has promoted its popularity in the market.

[0003] With the improvement of social development and the enhancement of people's environmental awareness, the requirements for carbon crystal engineered wood panels are becoming increasingly stringent. Although China has made certain achievements in the research and application of carbon crystal engineered wood panels, there are still some technological gaps compared with international advanced levels. These gaps are mainly reflected in the higher production costs of high-performance carbon crystal engineered wood panels, and the need to improve their mechanical properties, thermal management capabilities, scratch resistance, and water and moisture resistance. Traditional carbon crystal engineered wood panel production processes primarily use polyurethane (PU / PUR), cyanuramide-modified urea-formaldehyde resin (MUF), and phenolic resin adhesive (PF) as main raw materials. These adhesives exhibit low strength, high brittleness, poor water resistance, and low density during fiber bonding, resulting in deficiencies in waterproofing and structural stability. Furthermore, they have poor flame retardant properties and release harmful substances such as formaldehyde and phenol, posing risks to human health and polluting the air, thus compromising the durability and safety of carbon crystal products. Therefore, researching a green and environmentally friendly urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels to improve their durability and safety is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels, its preparation method, and its application. This adhesive improves the water resistance, interfacial bonding strength, and durability of the adhesive, while effectively reducing formaldehyde release. It is particularly suitable for the production of carbon crystal engineered wood panels with stringent requirements for physical properties and environmental friendliness. The adhesive preparation process is simpler and more efficient. To achieve the above objectives, this invention adopts the following technical solution: This invention also provides a urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels. The urea-formaldehyde resin-based adhesive is prepared from the following components: 60-80 parts urea-formaldehyde resin, 80-100 parts glyoxal, 15-40 parts dicyandiamide, 4-10 parts polyvinyl alcohol, 10-20 parts lignin, 6-15 parts epoxidized soybean oil, 12-25 parts alkali solution, 6-15 parts nano-modified silica powder, 2-10 parts curing agent, 2-8 parts catalyst, and 2-8 parts dispersant. Lignin contains a large number of phenolic hydroxyl groups and a small number of carboxyl groups, which can react rapidly with polyisocyanates (-NCO) to form stable polyurethane bonds and urea bonds. Simultaneously, during the adhesive curing process, the epoxy groups of epoxidized soybean oil can form a complex, highly cross-linked epoxy-polyurethane network structure with the phenolic hydroxyl groups of lignin, the silanol groups after hydrolysis of the silane coupling agent, and the isocyanate, which can greatly enhance the stability and adhesion of the adhesive.

[0005] In a further preferred embodiment of the above scheme, the alkaline solution is a sodium hydroxide solution or a triethanolamine solution; the alkaline solution is preferably a sodium hydroxide solution with a mass fraction of 25%–30%; the curing agent is a mixture of ammonium chloride and ammonium dihydrogen phosphate, with a mass ratio of ammonium chloride to ammonium dihydrogen phosphate of 1:1–3; the curing agent can enhance the curing ability of the adhesive and also enhance the water resistance of the carbon crystal board; the catalyst is one or more of titanium dioxide, diatomaceous earth, or manganese-based catalysts, and the addition of the catalyst enhances the density of the adhesive layer and the interfacial bonding force with the carbon crystal board. During the board manufacturing process, the catalyst can also continuously degrade trace amounts of formaldehyde released; the dispersant is one or more of nano-alumina, nano-tin oxide, or polyphosphate.

[0006] In a further preferred embodiment of the above scheme, the lignin is a lignin sulfonate with a number average molecular weight of 1500 g / mol to 4000 g / mol, and the polyvinyl alcohol has a degree of alcoholysis of 87% to 89% and a degree of polymerization of 500 to 1700.

[0007] In a further preferred embodiment of the above scheme, the nano-modified silicon powder is obtained by treating active microsilica powder with a particle size of 20-100 nm with a silane coupling agent, and the apparent density of the active microsilica powder is 0.1-0.2 g / cm³. 3The silane coupling agent is vinyltrimethoxysilane or γ-mercaptopropyltrimethoxysilane. Modified active microsilica powder can significantly improve the hardness, strength, heat resistance, and water resistance of the adhesive layer. It also greatly enhances the interfacial bonding force between the adhesive and the carbon crystal plate. In a further preferred embodiment of the above scheme, the total mass of the silane coupling agent is 2% to 5% of the mass of the active microsilica powder; the active microsilica powder and the silane coupling agent are mixed and treated at 80℃ to 100℃ and a rotation speed of 800 rpm to 1500 rpm for 20 min to 40 min. Active microsilica powder is a non-toxic, odorless, and pollution-free hydrophobic and oleophilic high-purity white micropowder with excellent properties such as good temperature resistance, acid and alkali corrosion resistance, low expansion, and stable chemical properties. Under the action of the silane coupling agent, the surface of the active microsilica powder is modified, thereby changing the surface adhesion of the active microsilica powder, improving the mechanical properties and weather resistance of the adhesive. Modifying the surface of the active microsilica powder alters its original physical properties, causing a ring-opening reaction with lignin and epoxidized soybean oil, which can significantly improve the rigidity, hardness, heat resistance, and water resistance of the adhesive layer, and enhance the surface adhesion and interfacial hydrophobicity of the adhesive.

[0008] According to another aspect of the present invention, the present invention provides a method for preparing a urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels, the preparation method comprising the following steps: The enzymatically hydrolyzed lignin was mixed with deionized water and stirred at 70℃~80℃ for 1h~2h to obtain an aqueous lignin solution for later use. Polyvinyl alcohol is mixed with deionized water and completely dissolved at 80℃~95℃ to obtain a polyvinyl alcohol solution with a mass fraction of 5%~10%, which is then cooled to below 60℃ for later use. The glyoxal solution was adjusted to pH 8.0–8.5 with alkaline solution, then heated to 80–90°C. Urea-formaldehyde resin was added, and the mixture was ultrasonically mixed for 10–30 minutes. The mixture was then cooled to 60–75°C, and dicyandiamide was added and stirred for 30–90 minutes. Epoxidized soybean oil and lignin aqueous solution were then added and mixed thoroughly. The reaction was carried out at 70–85°C for 15–30 minutes. The pH was then adjusted to 7.5–8.5, and the reaction was continued at 70–85°C for another 30 minutes. After cooling to 50℃-60℃, add polyvinyl alcohol solution and stir thoroughly at a constant temperature for 60-90 minutes. Cool to 35℃-45℃ and irradiate with ultraviolet light. Add catalyst and dispersant, mix evenly, let stand for 1-2 hours, and then cool to room temperature to obtain urea-formaldehyde resin-based polymer. Adding catalyst and dispersant under ultraviolet light and mixing evenly can reduce the free formaldehyde content in urea-formaldehyde resin under the action of the catalyst. The degradation efficiency is better than that of natural light irradiation, which can significantly improve the environmental performance of adhesives.

[0009] After mixing the nano-modified silica powder and the curing agent evenly, add them to the urea-formaldehyde resin base and stir thoroughly for 5 to 15 minutes. Then let it stand and cool to room temperature to obtain the finished urea-formaldehyde resin-based adhesive.

[0010] In a further preferred embodiment of the above scheme, the placement involves standing at 40℃~60℃ for 20min~60min, followed by cooling to room temperature.

[0011] In a further preferred embodiment of the above scheme, the temperature during the settling process is maintained at 35℃~45℃, and the mixture is stirred once every 10 minutes; the ultraviolet irradiation time is 0.5h~1.5h, the wavelength of the ultraviolet light is controlled at 200 nm~300 nm, and the irradiation intensity is not less than 80μW / cm². 2 .

[0012] According to another aspect of the present invention, the present invention provides a method for applying urea-formaldehyde resin-based adhesive for carbon crystal artificial board in the production of carbon crystal artificial board. The dried wood fibers are fed into a mixer. During the falling process of the wood fibers, the urea-formaldehyde resin-based adhesive is sprayed onto the mixer along the peripheral wall of the mixer in proportion, so that the urea-formaldehyde resin-based adhesive and the wood fibers are mixed. Then, the glued wood fibers are evenly fallen from the mixer and spread flat on the board blank conveyor belt. Then, the board blank is hot-pressed sequentially through the inlet preheating and pressurizing section, the middle section heat preservation and pressurizing section, the middle section heating and pressurizing section, and the outlet heating and depressurizing section to obtain the carbon crystal artificial board blank.

[0013] In a further preferred embodiment of the above scheme, the temperature of the inlet preheating and pressurizing section is 180℃~200℃, the pressure is 0.8~2.0MPa, and the hot-pressing time is 2min~5min; the temperature of the middle section heat preservation and pressurizing section is 220℃±2℃, the hot-pressing time is 5min~8min, and the pressure is 1.5MPa~3MPa; the temperature of the middle section heating and pressurizing section is 222℃~230℃, the hot-pressing time is 2min~2min, and the pressure is 2MPa~4.5MPa; and the temperature of the outlet heating and depressurizing section is 235℃~260℃, and the pressure is 0.3~1.3MPa.

[0014] In this invention, the solid content of the aqueous solution of urea-formaldehyde resin is 46%–55%. Urea-formaldehyde resin contains abundant hydrophilic functional groups. After curing, it is essentially insoluble in water. Using ordinary urea-formaldehyde resin as the matrix promotes resin curing and enhances resin density. Glyoxal (a low-toxicity dialdehyde) and dicyandiamide are used as basic network reaction monomers. The aldehyde group of glyoxal first copolymerizes with the urea-formaldehyde resin to remove free formaldehyde and other substances, and then undergoes a nucleophilic addition condensation reaction with the amino (-NH2) and imino (-NH) groups on dicyandiamide. Finally, lignin (polyphenolic hydroxyl groups), epoxidized soybean oil (polyepoxy groups), and polyvinyl alcohol (polyhydroxyl groups) are introduced into the basic network... Through multi-dimensional chemical reactions and physical entanglement, a rigid-flexible, organically interwoven urea-formaldehyde resin-based polymer reinforcement network is formed. This network exhibits significantly superior toughness, hydrolysis resistance, and durability compared to the network structures formed by traditional polyurethane (PU / PUR), cyanuramide-modified urea-formaldehyde resin (MUF), or phenolic resin adhesive (PF). During the urea-formaldehyde resin-based polymer reinforcement network process, the two aldehyde groups (-CHO) in glyoxal can react with the amino groups (-NH2) or hydroxymethyl groups (-CH2OH) in urea-formaldehyde resin to form a three-dimensional cross-linked network structure of hemiacetal or acetal. This causes the urea-formaldehyde resin molecular chains to grow or cross-link, increasing the molecular weight and degree of cross-linking of the resin, and improving the water resistance and mechanical properties of the adhesive.

[0015] Among them, the amino group (-NH2) in the dicyandiamide molecule can undergo an addition reaction with the aldehyde group of glyoxal to generate hydroxymethyl dicyandiamide intermediate, and can also undergo a condensation reaction with the hydroxymethyl group of urea-formaldehyde resin to form a methylene bridge (-CH2-) or a cyano bridge, which improves the thermal stability and chemical resistance of the adhesive and enhances the stability of the reaction system. The polyvinyl alcohol (PVA) introduced has a large number of hydroxyl groups on its chain that can not only form an acetal structure with glyoxal, but the hydroxyl groups (-OH) in PVA can also form hydrogen bonds with the hydroxymethyl or amino groups of urea-formaldehyde resin, which improves the viscosity, film-forming properties and water resistance of the resin, and plays a significant role in toughening and crack resistance, overcoming the disadvantage of high brittleness of traditional amino resins. The phenolic hydroxyl groups (-OH) or active sites on the aromatic rings of lignin can react with the aldehyde groups of glyoxal to form hydroxymethyl lignin intermediates. Subsequently, through dehydration condensation, methylene ether bonds or carbon-carbon bonds are formed, which increases or cross-links the lignin molecular chains, improving the reactivity and compatibility of lignin. At the same time, the epoxy groups of epoxidized soybean oil can react with the phenolic hydroxyl groups of lignin, the silanol groups after hydrolysis of silane coupling agents, and dicyandiamide during the adhesive curing process to form a highly cross-linked interpenetrating network structure, which effectively improves and enhances the toughness of the adhesive.

[0016] In summary, due to the adoption of the above technical solutions, the present invention has the following significant effects: (1) The urea-formaldehyde resin-based polymer composed of urea-formaldehyde resin, glyoxal, dicyandiamide, polyvinyl alcohol, lignin, epoxidized soybean oil and other components in the adhesive of the present invention forms a complex three-dimensional cross-linked network. In terms of chemical bond type (such as forming C-C bonds, ether bonds, etc.), network rigidity, reactivity and adhesion mechanism to the substrate, it fundamentally solves the problems of high brittleness and poor impact resistance of traditional resins formed by formaldehyde, urea, melamine and other materials, and endows the adhesive layer with excellent toughness, crack resistance and fatigue resistance. (2) The urea-formaldehyde resin-based adhesive for carbon crystal artificial boards of the present invention can improve the water resistance, interfacial bonding strength and durability of the adhesive, while effectively reducing formaldehyde release. It is particularly suitable for the production of carbon crystal artificial boards with strict requirements for physical properties and environmental protection. The processing technology of the urea-formaldehyde resin-based adhesive for carbon crystal artificial boards of the present invention is simpler and more efficient than the traditional process of preparing urea-formaldehyde resin adhesive using formaldehyde, urea, melamine and other raw materials. (3) This invention uses non-toxic and non-volatile glyoxal to partially replace formaldehyde as a raw material, thereby reducing the harm of formaldehyde release to the environment and human health from the source. The adhesive achieves formaldehyde-free addition from the source. Its key properties such as dry and wet bonding strength and boiling water resistance are comprehensively superior to traditional adhesives prepared with formaldehyde, urea, melamine and other raw materials. It is particularly suitable for the manufacture of carbon crystal artificial boards with high requirements for environmental protection and physical performance. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, preferred embodiments will be listed below to provide a clear and complete description of the invention. However, it should be noted that the embodiments in this specification are preferred examples, not all examples. Furthermore, many details listed in this specification are merely to provide the reader with a deep understanding of the key issues of this invention; the invention can be implemented even without these specific details.

[0018] Example 1 This embodiment provides a urea-formaldehyde resin-based adhesive for carbon crystal artificial boards. The urea-formaldehyde resin-based adhesive is prepared from the following components: 60 parts urea-formaldehyde resin, 90 parts glyoxal, 15 parts dicyandiamide, 4 parts polyvinyl alcohol, 10 parts lignin, 6 parts epoxidized soybean oil, 12 parts alkali solution, 6 parts nano-modified silica powder, 2 parts curing agent, 2 parts catalyst, and 2 parts dispersant. The alkaline solution is a sodium hydroxide solution or a triethanolamine solution, the curing agent is a mixture of ammonium chloride and ammonium dihydrogen phosphate, the catalyst is titanium dioxide, diatomaceous earth or a manganese-based catalyst, and the dispersant is one or more of nano-alumina, nano-tin oxide or polyphosphate.

[0019] The lignin is a lignin sulfonate with a number average molecular weight of 1500 g / mol to 4000 g / mol, and the polyvinyl alcohol has a degree of alcoholysis of 87% to 89% and a degree of polymerization of 500 to 1700.

[0020] The nano-modified silicon powder is obtained by treating active microsilica powder with a particle size of 20 nm with a silane coupling agent; the total mass of the silane coupling agent is 2% of the mass of the active microsilica powder; the active microsilica powder and the silane coupling agent are mixed and treated at 80°C and 1500 rpm for 40 min.

[0021] This embodiment provides a method for preparing a urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels, comprising the following steps: Step 1: Weigh the raw materials for urea-formaldehyde resin-based adhesive according to the following mass proportions: 60 parts urea-formaldehyde resin, 90 parts glyoxal, 15 parts dicyandiamide, 4 parts polyvinyl alcohol, 10 parts lignin, 6 parts epoxidized soybean oil, 12 parts alkali solution, 6 parts nano-modified silica powder, 2 parts curing agent, 2 parts catalyst, and 2 parts dispersant. Step 2: Mix the enzymatically hydrolyzed lignin with deionized water and stir at 70°C for 2 hours to obtain an aqueous lignin solution for later use. Step 3: Mix polyvinyl alcohol with deionized water and dissolve it completely at 80°C to obtain a 5% polyvinyl alcohol solution by mass. Cool the solution to below 60°C for later use. Step 4: Adjust the pH of the glyoxal solution to 8.0 with alkaline solution, then heat to 80℃. Add urea-formaldehyde resin and ultrasonically mix for 30 minutes. Cool to 60℃, add dicyandiamide, and mix and stir for 90 minutes. Add epoxidized soybean oil and lignin aqueous solution, mix thoroughly, and react at 70℃ for 30 minutes. Adjust the pH to 7.5 and continue reacting at 70℃ for 60 minutes. Cool to 50℃, add polyvinyl alcohol solution, and stir thoroughly at a constant temperature for 90 minutes. Cool to 35℃ and irradiate with ultraviolet light for 0.5 hours. Add catalyst and dispersant, mix thoroughly, let stand for 1 hour, and then cool to room temperature to obtain the urea-formaldehyde resin-based polymer. During the standing process, maintain the temperature at 35℃ and stir every 10 minutes. Control the wavelength of the ultraviolet light to 200nm-300nm and the irradiation intensity to be not less than 80μW / cm. 2 ; Step 5: Mix the nano-modified silica powder and curing agent evenly, then add them to the urea-formaldehyde resin base and stir thoroughly for 5 minutes. After standing at 40°C for 60 minutes, cool to room temperature to obtain the finished urea-formaldehyde resin adhesive.

[0022] Example 2 This embodiment provides a urea-formaldehyde resin-based adhesive for carbon crystal artificial boards. The urea-formaldehyde resin-based adhesive is prepared from the following components: 80 parts urea-formaldehyde resin, 100 parts glyoxal, 40 parts dicyandiamide, 10 parts polyvinyl alcohol, 20 parts lignin, 15 parts epoxidized soybean oil, 25 parts alkali solution, 15 parts nano-modified silica powder, 10 parts curing agent, 8 parts catalyst, and 8 parts dispersant. The alkaline solution is a sodium hydroxide solution or a triethanolamine solution, the curing agent is a mixture of ammonium chloride and ammonium dihydrogen phosphate, the catalyst is titanium dioxide, diatomaceous earth or a manganese-based catalyst, and the dispersant is one or more of nano-alumina, nano-tin oxide or polyphosphate.

[0023] The lignin is a lignin sulfonate with a number average molecular weight of 1500 g / mol to 4000 g / mol, and the polyvinyl alcohol has a degree of alcoholysis of 87% to 89% and a degree of polymerization of 500 to 1700.

[0024] The nano-modified silicon powder is obtained by treating active microsilica powder with a particle size of 100 nm with a silane coupling agent; the total mass of the silane coupling agent is 5% of the mass of the active microsilica powder; the active microsilica powder and the silane coupling agent are mixed and treated at 100°C and 800 rpm for 20 min.

[0025] The preparation method of a urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels according to this embodiment includes the following steps: Step 1: Weigh the raw materials for urea-formaldehyde resin-based adhesive according to the following mass proportions: 80 parts urea-formaldehyde resin, 100 parts glyoxal, 40 parts dicyandiamide, 10 parts polyvinyl alcohol, 20 parts lignin, 15 parts epoxidized soybean oil, 25 parts alkali solution, 15 parts nano-modified silica powder, 10 parts curing agent, 8 parts catalyst, and 8 parts dispersant. Step 2: Mix the enzymatically hydrolyzed lignin with deionized water and stir at 80°C for 1 hour to obtain an aqueous lignin solution for later use. Step 3: Mix polyvinyl alcohol with deionized water and dissolve completely at 95°C to obtain a 10% polyvinyl alcohol solution by mass. Cool to below 60°C for later use. Step 4: Adjust the pH of the glyoxal solution to 8.5 with alkaline solution, then heat to 90℃. Add urea-formaldehyde resin and ultrasonically mix for 10 minutes. Cool to 75℃, add dicyandiamide, and mix and stir for 30 minutes. Add epoxidized soybean oil and lignin aqueous solution, mix thoroughly, and react at 85℃ for 15 minutes. Adjust the pH to 8.5 again and continue the reaction at 85℃ for 30 minutes. Cool to 60℃, add polyvinyl alcohol solution, and stir thoroughly at a constant temperature for 60 minutes. Cool to 45℃ and irradiate with ultraviolet light for 1.5 hours. Add catalyst and dispersant, mix thoroughly, let stand for 2 hours, and then cool to room temperature to obtain the urea-formaldehyde resin-based polymer. During the standing process, maintain the temperature at 45℃ and stir every 10 minutes. Control the wavelength of ultraviolet light to 200nm~300nm and the irradiation intensity to be not less than 80μW / cm. 2 ; Step 5: After mixing the nano-modified silica powder and curing agent evenly, add them to the urea-formaldehyde resin base and stir thoroughly for 15 minutes. After placing at 60°C for 20 minutes, cool to room temperature to obtain the finished urea-formaldehyde resin adhesive.

[0026] Example 3 This embodiment provides a urea-formaldehyde resin-based adhesive for carbon crystal artificial boards. The urea-formaldehyde resin-based adhesive is prepared from the following components: 70 parts urea-formaldehyde resin, 80 parts glyoxal, 30 parts dicyandiamide, 8 parts polyvinyl alcohol, 18 parts lignin, 10 parts epoxidized soybean oil, 18 parts alkali solution, 10 parts nano-modified silica powder, 7 parts curing agent, 6 parts catalyst, and 5 parts dispersant. The alkaline solution is a sodium hydroxide solution or a triethanolamine solution, the curing agent is a mixture of ammonium chloride and ammonium dihydrogen phosphate, the catalyst is titanium dioxide, diatomaceous earth or a manganese-based catalyst, and the dispersant is one or more of nano-alumina, nano-tin oxide or polyphosphate.

[0027] The lignin is a lignin sulfonate with a number average molecular weight of 1500 g / mol to 4000 g / mol, and the polyvinyl alcohol has a degree of alcoholysis of 87% to 89% and a degree of polymerization of 500 to 1700.

[0028] The nano-modified silicon powder is obtained by treating active micro-silica powder with a particle size of 60nm to 80nm with a silane coupling agent; the total mass of the silane coupling agent is 4% of the mass of the active micro-silica powder; the active micro-silica powder and the silane coupling agent are mixed and treated at 85°C and 1200rpm for 30min.

[0029] The preparation method of a urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels according to this embodiment includes the following steps: Step 1: Weigh the raw materials for urea-formaldehyde resin-based adhesive according to the following mass proportions: 70 parts urea-formaldehyde resin, 80 parts glyoxal, 30 parts dicyandiamide, 8 parts polyvinyl alcohol, 18 parts lignin, 10 parts epoxidized soybean oil, 18 parts alkali solution, 10 parts nano-modified silica powder, 7 parts curing agent, 6 parts catalyst, and 5 parts dispersant. Step 2: Mix the enzymatically hydrolyzed lignin with deionized water and stir at 75°C for 1.5 hours to obtain an aqueous lignin solution for later use. Step 3: Mix polyvinyl alcohol with deionized water and dissolve completely at 90°C to obtain a polyvinyl alcohol solution with a mass fraction of 8%. Cool to below 60°C for later use. Step 4: Adjust the pH of the glyoxal solution to 8.2 with alkaline solution, then heat to 85℃. Add urea-formaldehyde resin and ultrasonically mix for 20 minutes. Cool to 70℃, add dicyandiamide, and mix and stir for 60 minutes. Add epoxidized soybean oil and lignin aqueous solution, mix thoroughly, and react at 80℃ for 20 minutes. Adjust the pH to 8 and continue reacting at 80℃ for 40 minutes. Cool to 55℃, add polyvinyl alcohol solution, and stir thoroughly at a constant temperature for 70 minutes. Cool to 40℃ and irradiate with ultraviolet light for 1 hour. Add catalyst and dispersant, mix thoroughly, let stand for 1.5 hours, and then cool to room temperature to obtain the urea-formaldehyde resin-based polymer. During the standing process, maintain the temperature at 40℃ and stir every 10 minutes. Control the wavelength of ultraviolet light to 200 nm–300 nm and the irradiation intensity to be not less than 80 μW / cm. 2 ; Step 5: Mix the nano-modified silica powder and curing agent evenly, then add them to the urea-formaldehyde resin base and stir thoroughly for 10 minutes. Place at 40℃~60℃ for 20 minutes~60 minutes, then cool to room temperature to obtain the urea-formaldehyde resin base adhesive product.

[0030] The application of the urea-formaldehyde resin-based adhesive prepared in Examples 1 to 3 of this invention in the production of carbon crystal artificial boards mainly includes the following process: Dried wood fibers are fed into a mixer. During the falling process, the urea-formaldehyde resin-based adhesive is sprayed onto the mixer along the periphery of the mixer in proportion, allowing the urea-formaldehyde resin-based adhesive to mix with the wood fibers. The glued wood fibers are then evenly dropped from the mixer and spread on a board conveyor belt. The board is then sequentially passed through an inlet preheating and pressurizing section, a middle section heat preservation and pressurizing section, a middle section heating and pressurizing section, and an outlet heating and depressurizing section for hot pressing to obtain carbon crystal artificial boards. The process involves the following steps: The inlet preheating and pressurizing section has a temperature of 180℃~200℃, a pressure of 0.8~2.0MPa, and a hot-pressing time of 2min~5min; the middle insulation and pressurizing section has a temperature of 220℃±2℃, a hot-pressing time of 5min~8min, and a pressure of 1.5MPa~3MPa; the middle heating and pressurizing section has a temperature of 222℃~230℃, a hot-pressing time of 2min~2min, and a pressure of 2MPa~4.5MPa; and the outlet heating and depressurization section has a temperature of 235℃~260℃ and a pressure of 0.3~1.3MPa.

[0031] The performance of the urea-formaldehyde resin-based adhesive of the present invention was tested in accordance with the national standards GB / T14732-2017 Urea-formaldehyde, phenol-formaldehyde, and melamine-formaldehyde resins for wood industry and GB / T14074-2017 Test methods for adhesives and their resins for wood industry. A comparative example was made with an adhesive prepared from melamine-modified urea-formaldehyde resin. The test results are shown in Table 1.

[0032] Table 1 Performance Indicators of Urea-Formaldehyde Resin-Based Adhesives Particleboard (commonly 18mm thick) was prepared using the urea-formaldehyde resin-based adhesive of the present invention. The performance of the particleboard was tested according to GB / T17657-2022 Test Method for Physicochemical Properties of Wood-based Panels and Decorative Wood-based Panels, and the safety of the particleboard of the present invention was tested according to GB18580-2017 Formaldehyde Emission Limits in Wood-based Panels and Their Products for Interior Decoration. The test results are shown in Table 2.

[0033] Table 2. Performance comparison indicators of particleboard prepared in the embodiments of the present invention and comparative embodiments. The urea-formaldehyde resin-based adhesive used in this invention produces particleboard with significantly better mechanical properties than the comparative examples. Its wet strength and dimensional stability (low water absorption and swelling rate) are greatly improved, and its formaldehyde and ammonia release is significantly lower than the comparative examples, demonstrating outstanding environmental protection and safety performance. While its internal bond strength is comparable to the comparative examples, its wet bond strength is significantly better, proving its superior water resistance. This urea-formaldehyde resin-based adhesive exhibits balanced performance, good physical, mechanical, and water resistance properties, and is a novel adhesive with no significant formaldehyde or ammonia release. Without using formaldehyde, urea, or melamine, the adhesive of this invention achieves a dry bond strength equivalent to commercially available melamine-modified urea-formaldehyde resin (MUF), and its wet strength is significantly better than ordinary UF adhesive, comparable to or even slightly better than E0 grade MUF adhesive. Most importantly, its formaldehyde and ammonia release are both "undetectable," indicating an environmental protection level far exceeding that of the comparative examples. Boiling water resistance test shows that it has excellent durability, which also fully proves that the raw material system proposed in this invention can fully achieve and partially exceed the performance targets of adhesives prepared by traditional "formaldehyde, urea and melamine", and fundamentally solves the environmental protection problem.

[0034] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Therefore, for those skilled in the art, any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels, characterized in that: The urea-formaldehyde resin-based adhesive is prepared from the following components: 60-80 parts urea-formaldehyde resin, 80-100 parts glyoxal, 15-40 parts dicyandiamide, 4-10 parts polyvinyl alcohol, 10-20 parts lignin, 6-15 parts epoxidized soybean oil, 12-25 parts alkali solution, 6-15 parts nano-modified silica powder, 2-10 parts curing agent, 2-8 parts catalyst, and 2-8 parts dispersant.

2. The urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels according to claim 1, characterized in that: The alkaline solution is a sodium hydroxide solution or a triethanolamine solution, the curing agent is a mixture of ammonium chloride and ammonium dihydrogen phosphate, the catalyst is one or more of titanium dioxide, diatomaceous earth or manganese-based catalyst, and the dispersant is one or more of nano-alumina, nano-tin oxide or polyphosphate.

3. The urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels according to claim 1, characterized in that: The lignin is a lignin sulfonate with a number average molecular weight of 1500 g / mol to 4000 g / mol, and the polyvinyl alcohol has a degree of alcoholysis of 87% to 89% and a degree of polymerization of 500 to 1700.

4. The urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels according to claim 1, characterized in that: The nano-modified silicon powder is obtained by treating active micro-silicon powder with a particle size of 20-100 nm with a silane coupling agent.

5. The urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels according to claim 4, characterized in that: The total mass of the silane coupling agent is 2% to 5% of the mass of the active microsilica powder; the active microsilica powder and the silane coupling agent are mixed and treated at 80℃ to 100℃ and at a rotation speed of 800 rpm to 1500 rpm for 20 min to 40 min.

6. A method for preparing a urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels according to any one of claims 1 to 5, characterized in that: The preparation method includes the following steps: The enzymatically hydrolyzed lignin was mixed with deionized water and stirred at 70℃~80℃ for 1h~2h to obtain an aqueous lignin solution for later use. Polyvinyl alcohol is mixed with deionized water and completely dissolved at 80℃~95℃ to obtain a polyvinyl alcohol solution with a mass fraction of 5%~10%, which is then cooled to below 60℃ for later use. After adjusting the pH of the glyoxal solution to 8.0–8.5 with alkaline solution, the temperature is raised to 80–90°C. Urea-formaldehyde resin is added and ultrasonically mixed for 10–30 minutes. Then, the temperature is cooled to 60–75°C, and dicyandiamide is added and mixed for 30–90 minutes. Subsequently, epoxidized soybean oil and lignin aqueous solution are added and mixed evenly. The reaction is carried out at 70–85°C for 15–30 minutes. The pH is then adjusted to 7.5–8.5, and the reaction is continued at 70–85°C for 30–60 minutes. After cooling to 50–60°C, polyvinyl alcohol solution is added and the mixture is stirred and reacted at a constant temperature for 60–90 minutes. After cooling to 35–45°C, ultraviolet light is applied. Catalyst and dispersant are added and mixed evenly. After standing for 1–2 hours, the mixture is cooled to room temperature to obtain the urea-formaldehyde resin-based polymer. After mixing the nano-modified silica powder and the curing agent evenly, add them to the urea-formaldehyde resin base and stir thoroughly for 5 to 15 minutes. Then let it stand and cool to room temperature to obtain the finished urea-formaldehyde resin-based adhesive.

7. The method for preparing a urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels according to claim 5, characterized in that: The placement involves standing at 40℃~60℃ for 20min~60min, followed by cooling to room temperature.

8. A method for preparing a urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels according to claim 5, characterized in that: The temperature during the standing process is maintained at 35-45°C, and the stirring is performed every 10 minutes; the time for the ultraviolet irradiation is 0.5-1.5 hours, the wavelength of the ultraviolet is controlled at 200-300 nm, and the irradiation intensity is not less than 80 μW / cm 2 .

9. A method for applying the urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels as described in claim 1 in the manufacture of carbon crystal engineered wood panels, characterized in that: The dried wood fibers are fed into the mixer. During the falling process, urea-formaldehyde resin-based adhesive is sprayed onto the mixer along the wall of the mixer in proportion, so that the urea-formaldehyde resin-based adhesive is mixed with the wood fibers. The glued wood fibers are then evenly dropped from the mixer and spread on the board conveyor belt. The boards are then hot-pressed sequentially through the inlet preheating and pressurizing section, the middle heat preservation and pressurizing section, the middle heating and pressurizing section, and the outlet heating and depressurizing section to obtain carbon crystal artificial board blanks.

10. The method for applying the urea-formaldehyde resin-based adhesive for carbon crystal engineered wood panels according to claim 9 in the manufacture of carbon crystal engineered wood panels, characterized in that: The inlet preheating and pressurizing section has a temperature of 180℃~200℃, a pressure of 0.8~2.0MPa, and a hot-pressing time of 2min~5min; the middle section heat preservation and pressurizing section has a temperature of 220℃±2℃, a hot-pressing time of 5min~8min, and a pressure of 1.5MPa~3MPa; the middle section heating and pressurizing section has a temperature of 222℃~230℃, a hot-pressing time of 2min~2min, and a pressure of 2MPa~4.5MPa; and the outlet heating and depressurizing section has a temperature of 235℃~260℃ and a pressure of 0.3~1.3MPa.

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