A formaldehyde-free wood adhesive and a method for preparing the same

Abstract

This invention discloses a formaldehyde-free wood adhesive and its preparation method, belonging to the field of polymer material synthesis technology. The formaldehyde-free wood adhesive is made from the following raw materials in parts by weight: 15-50 parts deionized water, 0.35-2.2 parts composite emulsifier, 0.1-0.35 parts initiator, 35-55 parts nano-calcium carbonate modified polyacrylate emulsion, 15-25 parts vinyl acetate, 2-8 parts acrylic acid, 0.2-2 parts sodium hydroxypropanesulfonate functional monomer, 0.1-0.7 parts sodium alginate functional monomer, 0.07-0.28 parts crosslinking agent, and 0.1-5 parts pH adjuster. The adhesive prepared by this invention has the advantages of being formaldehyde-free and environmentally friendly, having high bonding strength, good water resistance, fast drying speed, and wide applicability, and can be widely used in artificial boards, wood decoration, plywood bonding, and other scenarios.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis technology, specifically relating to a formaldehyde-free wood adhesive and its preparation method. Background Technology

[0002] Wood adhesives are core materials for wood processing and engineered wood products manufacturing, and their current development is characterized by a pattern of "traditional dominance, environmental upgrading, and performance pursuit".

[0003] Urea-formaldehyde (UF), phenolic (PF), and melamine-formaldehyde (MF) adhesives have long dominated the wood industry, especially the market for engineered wood products, due to their low raw material costs, mature production processes, and good bonding performance.

[0004] With increasingly stringent global environmental regulations (such as China's GB / T39600-2021 "Classification of Formaldehyde Emission from Wood-based Panels and Their Products") and rising consumer health awareness, the market demand for "formaldehyde-free" products is growing rapidly. This has driven the research and application of formaldehyde-free adhesives such as waterborne polyurethane (PU), soybean protein adhesive, isocyanate (MDI), and various waterborne acrylic copolymers.

[0005] Current research and development focuses on improving the performance of environmentally friendly adhesives, especially water resistance and bonding strength, to overcome the gap with traditional "three-aldehyde" adhesives. It also aims to achieve faster curing speed, better workability, and additional functions such as storage stability, wetting properties, and antibacterial and antifungal properties.

[0006] Several key technical challenges currently facing the transition of wood adhesives towards formaldehyde-free formulations: 1. Formaldehyde release problem Traditional formaldehyde-based adhesives continuously release free formaldehyde during manufacturing and use, posing a serious threat to human health and the indoor environment. Although modification can reduce the release amount, it cannot eliminate it completely.

[0007] 2. Bond strength and durability issues Formaldehyde-free adhesives need to achieve or even surpass the mechanical properties of traditional adhesives. The challenge lies in how to form a strong and lasting bond with wood. This involves the adhesive's wetting and penetration into the wood, its chemical bonding or physical anchoring ability with wood fibers, and the cohesive strength of the adhesive layer itself.

[0008] 3. Insufficient water resistance Many early or simple water-based formaldehyde-free adhesives, such as some starch adhesives and polyvinyl alcohol adhesives, have poor water resistance. Their bonding strength drops sharply when exposed to humid environments or after immersion in water, limiting their application in humid environments such as kitchens and bathrooms or in outdoor furniture.

[0009] 4. Wetting and permeability issues with porous substrates Wood is a porous material, and adhesives need good wettability to fully penetrate into the pores of the wood and form an effective mechanical interlock. Some adhesives with mismatched surface tension or improper viscosity will result in poor wetting and affect the final bonding effect.

[0010] 5. Performance defects caused by reliance on small molecule emulsifiers To form a stable emulsion, existing water-based emulsion adhesives typically require the addition of small-molecule emulsifiers, such as sodium dodecyl sulfate. However, these emulsifiers are physically adsorbed on the surface of polymer particles and are not chemically bonded. After film formation and drying or exposure to water, these small molecules are prone to migration or precipitation, becoming weak hydrophilic points in the adhesive film, thereby impairing the film's water resistance, scrub resistance, and long-term durability.

[0011] 6. Storage stability and construction issues Adhesives must remain uniform, without settling or stratification, and with stable viscosity during storage. Existing complex systems or natural polymer adhesives are prone to spoilage, gelation, or performance degradation. Summary of the Invention

[0012] This invention aims to overcome the shortcomings of existing technologies and provide a formaldehyde-free wood adhesive and its preparation method. This invention solves the problems of formaldehyde release, insufficient bonding strength, poor water resistance, poor wettability to porous wood, performance degradation due to reliance on easily migrating small molecule emulsifiers, and storage stability of existing wood adhesives by combining self-emulsifying copolymerization with inorganic-organic hybrid crosslinking.

[0013] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A formaldehyde-free wood adhesive uses nano-calcium carbonate modified polyacrylate emulsion as the base colloid. It is modified by copolymerization of vinyl acetate and acrylic acid, and employs specific functional monomers (sodium hydroxypropanesulfonate methacrylate and sodium alginate) and a crosslinking agent (sodium metasilicate) to construct a formaldehyde-free polymer network system with "self-emulsifying" properties, high crosslinking density, and strong adhesion to wood. It is made from the following raw materials in parts by weight: 15-50 parts deionized water, 0.35-2.2 parts composite emulsifier, 0.1-0.35 parts initiator, 35-55 parts nano-calcium carbonate modified polyacrylate emulsion, 15-25 parts vinyl acetate, 2-8 parts acrylic acid, 0.2-2 parts sodium hydroxypropanesulfonate functional monomer, 0.1-0.7 parts sodium alginate functional monomer, 0.07-0.28 parts crosslinking agent, and 0.1-5 parts pH adjuster.

[0014] The composite emulsifier is composed of a reactive emulsifier and an anionic emulsifier in a mass ratio of 2:1; the reactive emulsifier is sodium allyl hydroxypropyl sulfonate, and the anionic emulsifier is any one or two of sodium dodecyl sulfate, disodium alkyl polyoxyethylene ether monoester sulfonate, and sodium dicyclohexyl succinate sulfonate.

[0015] The initiator is ammonium persulfate or potassium persulfate.

[0016] The nano-calcium carbonate modified polyacrylate emulsion is prepared by the method disclosed in patent CN116836407A.

[0017] The crosslinking agent is sodium metasilicate.

[0018] The pH adjuster is ammonia water with a mass fraction of 25-28%.

[0019] The method for preparing the formaldehyde-free wood adhesive includes the following steps: (1) Add the initiator to 80-100 times the volume of deionized water to obtain an initiator solution; (2) Preparation of reaction solution: Deionized water and composite emulsifier are placed in a container at room temperature and homogenized and emulsified for 20-30 minutes using a dispersion homogenizer. Nano-calcium carbonate modified polyacrylate emulsion is added and stirred for 10-20 minutes to obtain the reaction solution. (3) Add the above reaction solution to the reaction flask, start stirring, heat to 60-80℃, add vinyl acetate, acrylic acid and 90% of the initiator solution in sequence, and react for 100-180 minutes; (4) Add the functional monomers sodium hydroxypropanesulfonate methacrylate and sodium alginate, and react for 60-90 minutes; (5) Heat to 85-90℃, add the remaining 10% of the initiator solution, and react for 30-60 minutes; (6) When the temperature of the reaction system drops to 60-70℃, add sodium metasilicate as a crosslinking agent and react for 20-30 minutes; (7) Add ammonia water to make the pH value of the system 6-8, cool to below 50℃ and discharge to obtain the product.

[0020] The preparation method employs emulsion polymerization, and the process design aims to ensure that each component reacts fully and its function is realized sequentially, as detailed below: Pre-emulsification: The nano-calcium carbonate modified polyacrylate emulsion is first pre-emulsified under the action of a composite emulsifier to obtain a reaction solution.

[0021] Gradient crosslinking polymerization and functional introduction: The above reaction solution and host monomers (vinyl acetate and acrylic acid) are polymerized at a moderate temperature; then, two functional monomers are added in the intermediate stage to effectively integrate them into the polymer chain; finally, the reaction is completed by raising the temperature and adding an initiator, thereby improving the monomer conversion rate.

[0022] Post-crosslinking and finished product conditioning: Sodium metasilicate, a crosslinking agent, is added in the later stages of the reaction. The crosslinking reaction is carried out at a relatively mild temperature to avoid rapid polymerization. Finally, ammonia water is used to adjust the pH to neutral to slightly alkaline, resulting in a stable and ready-to-use finished adhesive.

[0023] Nano-calcium carbonate modified polyacrylate emulsion: Using nano-calcium carbonate modified polyacrylate emulsion as the main film-forming substance provides basic adhesion and film-forming properties. Vinyl acetate and acrylic acid are introduced for copolymerization. Vinyl acetate improves the wettability and penetration of the adhesive into wood and enhances flexibility; acrylic acid provides carboxyl active sites, laying the foundation for subsequent crosslinking reactions.

[0024] Composite emulsifier: Sodium allyl hydroxypropyl sulfonate contains sulfonic acid groups and allyl oxy groups in its molecular structure, making it a reactive emulsifier. In polymerization reactions, besides acting as an emulsifier, it can also copolymerize with acrylate monomers and functional monomers, permanently bonding to the polymer emulsion particles. This overcomes the residue left by conventional emulsifiers in the polymer, while simultaneously improving the conversion rate of reactive monomers, optimizing emulsion particle size distribution and mechanical stability, and enhancing adhesive strength and water resistance. Anionic emulsifiers such as sodium dodecyl sulfate, disodium alkyl polyoxyethylene ether succinate monoester sulfonate, and sodium dicyclohexyl succinate sulfonate are used in conjunction with it to improve the system's stability, wettability, water resistance, and scrub resistance.

[0025] Vinyl acetate: As a comonomer, it reduces costs and improves wettability of porous sheets, as well as the flexibility, bond strength and water resistance of adhesives.

[0026] Functional monomer sodium hydroxypropanesulfonate methacrylate: (1) Excellent emulsion stabilizer and emulsifying aid: The strong hydrophilic sulfonic acid group (-SO3Na) in the molecule can effectively improve the stability of the monomer pre-emulsion. Beneficial effect: Significantly enhances the mechanical stability and storage stability of the emulsion. (2) Permanently introduces hydrophilic groups through chemical bonding to achieve "self-emulsification": The methacryloyl group in its molecule can participate in free radical copolymerization reaction and be permanently bonded to the polymer backbone through covalent bonds. The sulfonic acid group is fixed on the polymer chain as a hydrophilic group. Beneficial effect: Forms a self-emulsifying polymer system, which can be stably dispersed in water without relying on physically adsorbed emulsifiers, fundamentally solving the migration problem of traditional small molecule emulsifiers, and greatly improving the water resistance and solvent resistance of the adhesive film.

[0027] Sodium alginate, a functional monomer, is a natural high-molecular-weight functional monomer. The sodium alginate molecule contains a sodium carboxylate group (-COO-Na). + The adhesive reacts with groups such as carboxyl groups (-COOH) and carbon-carbon double bonds (C=C) in the acrylate monomers to form graft copolymers, enhancing the bond strength between the adhesive and the wood. After drying, it forms a uniform film that protects the wood and extends its service life. Stability: Prevents adhesive delamination / sedimentation, ensuring stable performance during long-term storage and use.

[0028] Crosslinking agent sodium metasilicate: silicate ions (SiO3) generated by hydrolysis 2- It reacts with the carboxyl groups (-COOH) or free radicals of acrylates to form a siloxane network, which enhances the adhesive strength of the polymer through polymerization and crosslinking. The formed siloxane bonds (Si-O-Si) can effectively improve the water resistance of the adhesive.

[0029] Compared with the prior art, the present invention has the following beneficial effects: This invention, through the implementation of the above-mentioned technical solutions, eliminates formaldehyde release at the source, achieving complete formaldehyde-free status; multiple chemical bonds, copolymerization, grafting, cross-linking, and physical anchoring achieve high bonding strength; the "self-emulsifying" structure avoids the hydrophilic points of small molecule emulsifiers, and the hydrophobic effect of the siloxane cross-linking network achieves excellent water resistance; the stabilizing effect of the composite emulsion system and functional monomers achieves good storage and construction stability; the nano-calcium carbonate modified polyacrylate emulsion and natural sodium alginate components used endow the product with certain antibacterial and antifungal properties and environmental protection attributes; it has good wetting and bonding effects on porous wood, engineered wood, etc.

[0030] The adhesive prepared by this invention has the advantages of being formaldehyde-free and environmentally friendly, having high bonding strength, good water resistance, fast drying speed, and wide applicability. It can be widely used in artificial boards, wood decoration, plywood bonding and other scenarios. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. 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. Example 1

[0032] This embodiment provides a nano-calcium carbonate modified polyacrylate emulsion, which is prepared by the method disclosed in patent CN116836407A. Specifically, it is made from the following raw materials in parts by weight: 35 parts ethyl acrylate, 25 parts n-butyl acrylate, 8 parts dimethylolpropionic acid, 10 parts acrylic acid, 8 parts 1,6-hexanediol diacrylate, 0.5 parts modified nano-calcium carbonate emulsion, 3 parts composite emulsifier, 0.32 parts potassium persulfate, 2.5 parts styrax resin, 0.2 parts ethylene glycol, 2.5 parts sodium hydroxide solution with a mass fraction of 2%, and 105 parts deionized water.

[0033] The composite emulsifier is composed of alkylphenol polyoxyethylene ether (OP-10) and allyloxynonylphenol polyoxyethylene (10) ether ammonium sulfate (DNS-86) in a mass ratio of 1:2.5. The modified nano-calcium carbonate emulsion is made from the following raw materials: nano-calcium carbonate, anhydrous ethanol, acryloyloxyethyltrimethylammonium chloride, deionized water, dispersant, and pH adjuster.

[0034] The modified nano-calcium carbonate emulsion is made from the following raw materials in parts by weight: 11 parts nano-calcium carbonate, 42 parts anhydrous ethanol, 42 parts deionized water, 0.8 parts acryloyloxyethyltrimethylammonium chloride, 0.4 parts dispersant, and 0.2 parts pH adjuster. The preparation method of the modified nano-calcium carbonate emulsion includes the following steps: (1) Place nano-calcium carbonate and anhydrous ethanol in a single-necked flask and sonicate for 30 min. Place the mixture in a three-necked flask with a stirrer, add acryloyloxyethyltrimethylammonium chloride, sonicate for 15 min, heat to 80±2℃, sonicate for 2 h, pour out the suspension, filter and wash, and place the filter cake in a vacuum oven at 105℃ for 2 h to dry, thus obtaining modified nano-calcium carbonate. (2) Add modified nano-calcium carbonate, deionized water and dispersant to a beaker, adjust the pH value to 7.2 with 2% sodium hydroxide solution, and emulsify for 10 min with Onni AD500S-H dispersion homogenizer to obtain modified nano-calcium carbonate emulsion.

[0035] The preparation method of the above-mentioned nano-calcium carbonate modified polyacrylate emulsion includes the following steps: (1) Add potassium persulfate to 90 times the amount of deionized water and stir well to obtain an initiator solution; (2) Add the remaining deionized water and composite emulsifier to the four-necked reaction flask, and stir for 30 minutes at 60°C. (3) Heat to 80±2℃, add ethyl acrylate, n-butyl acrylate, functional monomer, modified nano calcium carbonate emulsion, styrax resin and ethylene glycol to the reaction flask in sequence, add 70% potassium persulfate solution dropwise over 60 minutes, keep the temperature for 60 minutes; add 20% potassium persulfate solution at once, react for 100 minutes; then add the remaining 10% potassium persulfate solution at once, heat to 88-90℃, react for 60 minutes; (4) Add 2% sodium hydroxide solution to adjust the pH of the reaction system to 3.9, stir for 10 minutes, cool to room temperature, and discharge the product. Example 2

[0036] This embodiment provides a formaldehyde-free wood adhesive, which is made from the following raw materials in parts by weight: 35 parts deionized water, 1.2 parts composite emulsifier, 0.22 parts ammonium sulfate initiator, 45 parts nano-calcium carbonate modified polyacrylate emulsion, 20 parts vinyl acetate, 5 parts acrylic acid, 1.1 parts sodium hydroxypropanesulfonate functional monomer, 0.4 parts sodium alginate functional monomer, 0.18 parts sodium metasilicate crosslinking agent, and 2.5 parts pH adjuster (ammonia water with a mass fraction of 26%).

[0037] The composite emulsifier is composed of sodium allyl hydroxypropyl sulfonate, a reactive emulsifier, and sodium dodecyl sulfate, an anionic emulsifier, in a mass ratio of 2:1.

[0038] The method for preparing the formaldehyde-free wood adhesive includes the following steps: (1) Add the initiator to 90 times the volume of deionized water to obtain an initiator solution; (2) Preparation of reaction solution: Deionized water and composite emulsifier were placed in a container at room temperature and homogenized and emulsified for 25 minutes using a dispersion homogenizer. Nano-calcium carbonate modified polyacrylate emulsion was added and stirred for 15 minutes to obtain the reaction solution. (3) Add the above reaction solution to the reaction flask, start stirring, heat to 72°C, add vinyl acetate, acrylic acid and 90% of the initiator solution in sequence, and react for 140 minutes; (4) Add the functional monomers sodium hydroxypropanesulfonate methacrylate and sodium alginate, and react for 75 minutes; (5) Heat to 86°C, add the remaining 10% of the initiator solution, and react for 45 minutes; (6) When the temperature of the reaction system drops to 65°C, add sodium metasilicate as a crosslinking agent and react for 25 minutes; (7) Add ammonia water to make the pH value of the system 7.0, cool to below 50°C and discharge to obtain the product. Example 3

[0039] This embodiment provides a formaldehyde-free wood adhesive, which is made from the following raw materials in parts by weight: 15 parts deionized water, 2.2 parts composite emulsifier, 0.1 parts potassium sulfate initiator, 35-55 parts nano-calcium carbonate modified polyacrylate emulsion, 25 parts vinyl acetate, 2 parts acrylic acid, 2 parts sodium hydroxypropanesulfonate functional monomer, 0.1 parts sodium alginate functional monomer, 0.28 parts sodium metasilicate crosslinking agent, and 0.1 parts pH adjuster (ammonia water with a mass fraction of 25%).

[0040] The composite emulsifier is composed of sodium allyl hydroxypropyl sulfonate, a reactive emulsifier, and disodium alkyl polyoxyethylene ether monoester sulfonate, an anionic emulsifier, in a mass ratio of 2:1.

[0041] The method for preparing the formaldehyde-free wood adhesive includes the following steps: (1) Add the initiator to 80 times the volume of deionized water to obtain an initiator solution; (2) Preparation of reaction solution: Deionized water and composite emulsifier were placed in a container at room temperature and homogenized and emulsified for 20 minutes using a dispersion homogenizer. Nano-calcium carbonate modified polyacrylate emulsion was added and stirred for 20 minutes to obtain the reaction solution. (3) Add the above reaction solution to the reaction flask, start stirring, heat to 71°C, add vinyl acetate, acrylic acid and 90% of the initiator solution in sequence, and react for 180 minutes; (4) Add the functional monomers sodium hydroxypropanesulfonate methacrylate and sodium alginate, and react for 60 minutes; (5) Heat to 88°C, add the remaining 10% of the initiator solution, and react for 60 minutes; (6) When the temperature of the reaction system drops to 68°C, add sodium metasilicate as a crosslinking agent and react for 30 minutes; (7) Add ammonia water to make the pH value of the system 6.9, cool to below 50°C and discharge to obtain the product. Example 4

[0042] This embodiment provides a formaldehyde-free wood adhesive, which is made from the following raw materials in parts by weight: 50 parts deionized water, 0.35 parts composite emulsifier, 0.35 parts ammonium sulfate initiator, 35 parts nano-calcium carbonate modified polyacrylate emulsion, 25 parts vinyl acetate, 2 parts acrylic acid, 2 parts sodium hydroxypropanesulfonate functional monomer, 0.1 parts sodium alginate functional monomer, 0.28 parts sodium metasilicate crosslinking agent, and 0.1 parts pH adjuster (ammonia water with a mass fraction of 28%).

[0043] The composite emulsifier is composed of sodium allyl hydroxypropyl sulfonate, a reactive emulsifier, and sodium allyl hydroxypropyl sulfonate, an anionic emulsifier, in a mass ratio of 2:1.

[0044] The method for preparing the formaldehyde-free wood adhesive includes the following steps: (1) Add the initiator to 100 times the volume of deionized water to obtain an initiator solution; (2) Preparation of reaction solution: Deionized water and composite emulsifier were placed in a container at room temperature and homogenized and emulsified for 30 minutes using a dispersion homogenizer. Nano-calcium carbonate modified polyacrylate emulsion was added and stirred for 10 minutes to obtain the reaction solution. (3) Add the above reaction solution to the reaction flask, start stirring, heat to 78°C, add vinyl acetate, acrylic acid and 90% of the initiator solution in sequence, and react for 100 minutes; (4) Add the functional monomers sodium hydroxypropanesulfonate methacrylate and sodium alginate, and react for 90 minutes; (5) Heat to 88°C, add the remaining 10% of the initiator solution, and react for 30 minutes; (6) When the temperature of the reaction system drops to 70°C, add sodium metasilicate as a crosslinking agent and react for 20 minutes; (7) Add ammonia water to make the pH value of the system 7.8, cool to below 50°C and discharge to obtain the product. Example 5

[0045] This embodiment provides a formaldehyde-free wood adhesive, which is made from the following raw materials in parts by weight: 35 parts deionized water, 1.2 parts composite emulsifier, 0.25 parts potassium persulfate initiator, 40 parts nano-calcium carbonate modified polyacrylate emulsion, 21 parts vinyl acetate, 6 parts acrylic acid, 0.8 parts sodium hydroxypropanesulfonate functional monomer, 0.6 parts sodium alginate functional monomer, 0.218 parts sodium metasilicate crosslinking agent, and 2 parts pH adjuster (ammonia water with a mass fraction of 26%).

[0046] The composite emulsifier is composed of sodium allyl hydroxypropyl sulfonate, a reactive emulsifier, sodium dodecyl sulfate, an anionic emulsifier, and sodium dicyclohexyl succinate sulfonate, in a mass ratio of 2:0.5:0.5.

[0047] The method for preparing the formaldehyde-free wood adhesive includes the following steps: (1) Add the initiator to 85 times the volume of deionized water to obtain an initiator solution; (2) Preparation of reaction solution: Deionized water and composite emulsifier were placed in a container at room temperature and homogenized and emulsified for 24 minutes using a dispersion homogenizer. Nano-calcium carbonate modified polyacrylate emulsion was added and stirred for 18 minutes to obtain the reaction solution. (3) Add the above reaction solution to the reaction flask, start stirring, heat to 72°C, add vinyl acetate, acrylic acid and 90% of the initiator solution in sequence, and react for 160 minutes; (4) Add the functional monomers sodium hydroxypropanesulfonate methacrylate and sodium alginate, and react for 70 minutes; (5) Heat to 87°C, add the remaining 10% of the initiator solution, and react for 50 minutes; (6) When the temperature of the reaction system drops to 68°C, add sodium metasilicate as a crosslinking agent and react for 28 minutes; (7) Add ammonia water to make the pH value of the system 7.2, cool to below 50°C and discharge to obtain the product. Example 6

[0048] This embodiment provides a formaldehyde-free wood adhesive, which is made from the following raw materials in parts by weight: 45 parts deionized water, 1.6 parts composite emulsifier, 0.24 parts ammonium sulfate initiator, 38 parts nano-calcium carbonate modified polyacrylate emulsion, 22 parts vinyl acetate, 4 parts acrylic acid, 1.6 parts sodium hydroxypropanesulfonate functional monomer, 0.3 parts sodium alginate functional monomer, 0.15 parts sodium metasilicate crosslinking agent, and 3 parts pH adjuster (ammonia water with a mass fraction of 25-28%).

[0049] The composite emulsifier is composed of sodium allyl hydroxypropyl sulfonate, a reactive emulsifier, and sodium dicyclohexyl succinate, an anionic emulsifier, in a mass ratio of 2:1.

[0050] The method for preparing the formaldehyde-free wood adhesive includes the following steps: (1) Add the initiator to 95 times the volume of deionized water to obtain an initiator solution; (2) Preparation of reaction solution: Deionized water and composite emulsifier were placed in a container at room temperature and homogenized and emulsified for 28 minutes using a dispersion homogenizer. Nano-calcium carbonate modified polyacrylate emulsion was added and stirred for 12 minutes to obtain the reaction solution. (3) Add the above reaction solution to the reaction flask, start stirring, heat to 74°C, add vinyl acetate, acrylic acid and 90% of the initiator solution in sequence, and react for 160 minutes; (4) Add the functional monomers sodium hydroxypropanesulfonate methacrylate and sodium alginate, and react for 70 minutes; (5) Heat to 86°C, add the remaining 10% of the initiator solution, and react for 40 minutes; (6) When the temperature of the reaction system drops to 68°C, add sodium metasilicate as a crosslinking agent and react for 25 minutes; (7) Add ammonia water to make the pH value of the system 7.3, cool to below 50°C and discharge to obtain the product.

[0051] Comparative Example 1 This embodiment provides a formaldehyde-free wood adhesive. In this embodiment, no nano-calcium carbonate modified polypropylene resin emulsion is added; everything else is the same as in Example 1, and will not be repeated here.

[0052] Comparative Example 2 This embodiment provides a formaldehyde-free wood adhesive. In this embodiment, an unmodified polyacrylate emulsion without nano-calcium carbonate is added. Everything else is the same as in Example 1, and will not be repeated here.

[0053] Comparative Example 3 This embodiment provides a formaldehyde-free wood adhesive. In this embodiment, the emulsifier used is sodium dodecyl sulfate, and the other components are the same as in Example 1, and will not be repeated here.

[0054] Comparative Example 4 This embodiment provides a formaldehyde-free wood adhesive. In this embodiment, the functional monomer sodium hydroxypropanesulfonate methacrylate is not added. Everything else is the same as in Example 1, and will not be repeated here.

[0055] Comparative Example 5 This embodiment provides a formaldehyde-free wood adhesive. In this embodiment, the functional monomer sodium alginate is not added. Everything else is the same as in Example 1, and will not be repeated here.

[0056] Comparative Example 6 This embodiment provides a formaldehyde-free wood adhesive. In this embodiment, no crosslinking agent sodium metasilicate is added. Everything else is the same as in Example 1, and will not be repeated here.

[0057] Performance testing The performance of the wood adhesives prepared in Examples 2-6 and Comparative Examples 1-6 was tested.

[0058] The test results are as follows: ; Test method for wood adhesive bonding strength: determined according to national standard GB / T 7124-2008. Water resistance test: determined according to national standard GB / T 14074-2017, Class II plywood (water-resistant plywood: suitable for humid environments) bonding strength test method, referring to GB / T 17657-2013. Specific implementation method: the specimen needs to be immersed in water at (63±3)℃ for 3 hours, and after being removed, cooled at room temperature for 10 minutes before testing.

[0059] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the preferred embodiments have been described in detail, those skilled in the art can still make appropriate modifications or equivalent substitutions to the solutions of the present invention, and such modifications or substitutions should be considered to still fall within the spirit and scope of the technical solutions of the present invention.

Claims

1. A formaldehyde-free wood adhesive, characterized in that... It is made from the following raw materials in parts by weight: 15-50 parts deionized water, 0.35-2.2 parts composite emulsifier, 0.1-0.35 parts initiator, 35-55 parts nano-calcium carbonate modified polyacrylate emulsion, 15-25 parts vinyl acetate, 2-8 parts acrylic acid, 0.2-2 parts sodium hydroxypropanesulfonate functional monomer, 0.1-0.7 parts sodium alginate functional monomer, 0.07-0.28 parts crosslinking agent, and 0.1-5 parts pH adjuster.

2. The formaldehyde-free wood adhesive according to claim 1, characterized in that: The composite emulsifier is composed of a reactive emulsifier and an anionic emulsifier in a mass ratio of 2:1; the reactive emulsifier is sodium allyl hydroxypropyl sulfonate, and the anionic emulsifier is any one or two of sodium dodecyl sulfate, disodium alkyl polyoxyethylene ether monoester sulfonate, and sodium dicyclohexyl succinate sulfonate.

3. The formaldehyde-free wood adhesive according to claim 1, characterized in that: The initiator is ammonium persulfate or potassium persulfate.

4. The formaldehyde-free wood adhesive according to claim 1, characterized in that: The crosslinking agent is sodium metasilicate.

5. The formaldehyde-free wood adhesive according to claim 1, characterized in that: The pH adjuster is ammonia water with a mass fraction of 25-28%.

6. A method for preparing the formaldehyde-free wood adhesive according to any one of claims 1-5, characterized in that... Includes the following steps: (1) Add the initiator to 80-100 times the volume of deionized water to obtain an initiator solution; (2) Preparation of reaction solution: Deionized water and composite emulsifier are placed in a container at room temperature and homogenized and emulsified for 20-30 minutes using a dispersion homogenizer. Nano-calcium carbonate modified polyacrylate emulsion is added and stirred for 10-20 minutes to obtain the reaction solution. (3) Add the above reaction solution to the reaction flask, start stirring, heat to 60-80℃, add vinyl acetate, acrylic acid and 90% of the initiator solution in sequence, and react for 100-180 minutes; (4) Add the functional monomers sodium hydroxypropanesulfonate methacrylate and sodium alginate, and react for 60-90 minutes; (5) Heat to 85-90℃, add the remaining 10% of the initiator solution, and react for 30-60 minutes; (6) When the temperature of the reaction system drops to 60-70℃, add sodium metasilicate as a crosslinking agent and react for 20-30 minutes; (7) Add ammonia water to make the pH value of the system 6-8, cool to below 50℃ and discharge to obtain the product.