Two-component adhesive for shaving board / fiberboard and preparation method of two-component adhesive

Abstract

The invention discloses a two-component adhesive for shaving boards / fiberboards and a preparation method of the two-component adhesive, and relates to the technical field of adhesive preparation. The adhesive disclosed by the invention is prepared by introducing an acrylic acid hydroxyl ester monomer in a VAE copolymerization stage for hydroxylation modification, then mixing with polyether polyol prepolymerization modified pMDI, and matching with nano cellulose and a lignosulfonate reinforced phase, so that the technical problems of low reaction efficiency, short pot life and high cost of an existing VAE / pMDI system are solved. The working life of the prepared adhesive is gt; the wet strength of the shaving board prepared from the adhesive is larger than or equal to 1.1 MPa, the internal bonding strength is larger than or equal to 1.0 MPa, the comprehensive cost is reduced by 30% or above compared with that of a pure pMDI system, and the adhesive is suitable for efficient production of formaldehyde-free artificial boards.

Description

Technical Field

[0001] This invention relates to the field of adhesive preparation technology, and more particularly to a two-component adhesive for particleboard / fiberboard and its preparation method. Background Technology

[0002] With increasingly stringent environmental requirements in the engineered wood products industry (ENF level ≤0.025mg / m³ in GB / T 39600-2021), traditional aldehyde resins (urea-formaldehyde resin, phenol-formaldehyde resin) are no longer able to meet the demands of the high-end market due to formaldehyde release issues. While VAE (vinyl acetate-ethylene copolymer) emulsions, as water-based environmentally friendly adhesives, have achieved industrial application, their linear molecular structure results in insufficient water resistance and low wet strength, limiting their application in engineered wood products used in humid environments. Although pMDI (polymethylene polyphenyl polyisocyanate) possesses excellent bonding strength and water resistance, its high cost, sensitivity to moisture, and poor compatibility with water-based systems hinder its large-scale promotion.

[0003] In the prior art, CN1285695C discloses an adhesive system for direct blending of pMDI and VAE emulsion, but this system has the following technical bottlenecks: (1) Mismatched reaction efficiency: Commercially available VAE (vinyl acetate-ethylene copolymer) emulsions mainly rely on the hydroxyl groups provided by polyvinyl alcohol protective colloids to react with pMDI, resulting in insufficient reaction sites and low activity, limiting the crosslinking density. (2) Short pot life: After pMDI (polymethylene polyphenyl polyisocyanate) is directly added to VAE emulsion, the -NCO groups react rapidly with water, causing the system viscosity to rise sharply, and the working time is less than 30 minutes. (3) Cost and performance imbalance: Although the water resistance can be improved when the pMDI addition exceeds 15%, the cost increases dramatically and the brittleness of the adhesive layer increases. (4) Interface compatibility defects: When pMDI and VAE emulsion are mixed, they are prone to phase separation, resulting in uneven application.

[0004] To address the aforementioned issues, while some studies have attempted to add small-molecule coupling agents or perform simple physical blending, none have fundamentally resolved the two core contradictions: insufficient reactive sites in the VAE molecular structure and the waterborne stability of pMDI. Therefore, developing a VAE / pMDI adhesive system that combines high reactivity, long pot life, excellent water resistance, and controllable cost has become a pressing technical challenge for the industry. Summary of the Invention

[0005] To address the above shortcomings, this invention provides a two-component adhesive for particleboard / fiberboard and its preparation method, solving the problems of low reaction efficiency, short pot life, and cost-performance imbalance of existing adhesives. The specific technical solution is as follows: A two-component adhesive for particleboard / fiberboard, comprising component A and component B; Component A is a modified vinyl acetate-ethylene copolymer emulsion (modified VAE emulsion), which is mainly prepared from the following raw materials in parts by weight: 1-3 parts polyvinyl alcohol, 10-15 parts ethylene, 32-38 parts vinyl acetate, 10-15 parts functional monomer, 0.1-0.3 parts initiator, and 50-60 parts water; the functional monomer is hydroxyethyl acrylate (HEA) and / or hydroxybutyl acrylate (HBA); Component B is a modified polymethylene polyphenyl polyisocyanate prepolymer (modified pMDI prepolymer), which is mainly prepared from the following raw materials in parts by weight: 70-85 parts of polymethylene polyphenyl polyisocyanate and 15-30 parts of polyether polyol.

[0006] Furthermore, in the functional monomer, the mass ratio of hydroxyethyl acrylate to hydroxybutyl acrylate is 1:(0.5-2).

[0007] Furthermore, the degree of alcoholysis of the polyvinyl alcohol is 88-99%, and the degree of polymerization is 500-1700.

[0008] Furthermore, component A also includes 8-12 parts of lignin sulfonate, wherein the weight-average molecular weight of the lignin sulfonate is 10,000.

[0009] Furthermore, component B also includes 1-5 parts of nanocellulose crystals, wherein the nanocellulose crystals have a diameter of 10-50 nm and a length of 200-500 nm.

[0010] Furthermore, the number-average molecular weight of the polyether polyol is 400-800.

[0011] Furthermore, the initiator is ammonium persulfate.

[0012] The present invention also provides a method for preparing the two-component adhesive for particleboard / fiberboard, comprising the following steps: (1) Preparation of component A: By weight, water and polyvinyl alcohol are added to a high-pressure reactor and heated to 90-100°C. After the polyvinyl alcohol is dissolved, the mixture is cooled to 60-80°C, ethylene is added, and the pressure is increased to 4-6 MPa. Then, a mixture of vinyl acetate, functional monomer and initiator is added dropwise. The mixture is kept warm for 1-3 hours. Finally, lignin sulfonate is added and mixed well to obtain component A with a solid content of 50-60%. (2) Preparation of component B: Under nitrogen protection, polymethylene polyphenyl polyisocyanate and polyether polyol are reacted at 70-90℃ for 1.5-3h, and then nanocellulose crystals are added and mixed evenly. The isocyanate content is controlled to be 15-25% to obtain the final product. (3) Save the components A and B separately.

[0013] The present invention also provides the application of the above-mentioned two-component adhesive in the preparation of formaldehyde-free particleboard or fiberboard.

[0014] Furthermore, in the preparation of the particleboard or fiberboard, the adhesive application method is as follows: after mixing component A and component B at a mass ratio of 100:(8-15), the mixture is applied to the surface of the particleboard or fiberboard using a mist spraying method, with an adhesive application amount of 80-120 g / m². 2 (Based on oven-dry solids); During preparation, the moisture content of the wood shavings is controlled at 6-10%, and the moisture content of the fibers is controlled at 8-12%; The hot-pressing process is as follows: temperature 140-180℃, pressure 3-5MPa, time 0.5-2min / mm board thickness.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention prepares a two-component adhesive by hydroxylating VAE molecules, water-based modification of pMDI prepolymer, and in-situ introduction of reinforcing phases such as lignin sulfonate and nanocellulose crystals, thus solving the problems of low reaction efficiency, short pot life, and cost-performance imbalance of existing adhesives.

[0016] 2. In the VAE copolymerization stage, this invention introduces hydroxyethyl acrylate and / or hydroxybutyl acrylate functional monomers, giving the VAE molecular chain a primary hydroxyl group on its side group. The primary hydroxyl group can significantly enhance the reactivity of the modified VAE emulsion with the -NCO in the modified pMDI prepolymer, thereby improving the reaction efficiency of the adhesive. At the same time, by controlling the amount of hydroxyethyl acrylate and hydroxybutyl acrylate functional monomers added, flexible segments can be introduced into the molecular chain to balance the crosslinking density. According to the test, compared with the unmodified product, the internal bond strength is increased by about 100%, the wet strength is increased by about 400%, the boiling water resistance time is increased by about 2 hours, and the pot life is increased by about 3 hours.

[0017] 3. This invention uses low molecular weight polyether polyol (Mn=400-800) to prepolymerize pMDI, which can convert some of the highly active -NCO groups into urethane prepolymer structures, thereby reducing the initial NCO functionality, slowing down the side reaction rate between the modified pMDI prepolymer and water, and extending the pot life of the adhesive to more than 3 hours.

[0018] 4. The nanocellulose crystals in the adhesive of this invention are rich in hydroxyl groups on their surface, which can react simultaneously with the modified VAE emulsion and the modified pMDI prepolymer to construct nano-reinforced crosslinking points and form a hybrid network. The phenolic hydroxyl groups and sulfonic acid groups in the lignin sulfonate can also participate in the crosslinking reaction to form a multi-scale reinforced structure. The multi-layer crosslinked network structure formed by the modified VAE emulsion and the modified pMDI prepolymer with the nanocellulose crystals and lignin sulfonate can enable the adhesive to achieve a wet strength of more than 1.5 MPa and a boiling water resistance time of 4.4-4.5 h, meeting the ENF environmental protection standard and satisfying the application requirements in humid environments.

[0019] 5. The lignin sulfonate of this invention can also improve the wettability of adhesives on wood, thereby reducing the amount of adhesive applied by 10-15% and thus reducing costs. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0021] Example 1 This embodiment provides a two-component adhesive for particleboard / fiberboard, comprising component A and component B; Component A is a modified vinyl acetate-ethylene copolymer emulsion (modified VAE emulsion), which is mainly made from the following raw materials in parts by weight: 1 part polyvinyl alcohol (degree of alcoholysis is 88%, degree of polymerization is 500), 10 parts ethylene, 32 parts vinyl acetate, 8 parts hydroxyethyl acrylate (HEA), 4 parts hydroxybutyl acrylate (HBA), 0.1 parts ammonium persulfate, and 50 parts water. Component B is a modified polymethylene polyphenyl polyisocyanate prepolymer (modified pMDI prepolymer), which is mainly made from the following raw materials in parts by weight: 70 parts of polymethylene polyphenyl polyisocyanate and 15 parts of polyether polyol (number average molecular weight of 400).

[0022] The preparation method of the above-mentioned two-component adhesive for particleboard / fiberboard includes the following steps: (1) Preparation of component A: By weight, water and polyvinyl alcohol are added to a high-pressure reactor and heated to 90°C. After the polyvinyl alcohol is dissolved, the reactor is cooled to 60°C, ethylene is added, the pressure is increased to 4MPa, and then a mixture of vinyl acetate, hydroxyethyl acrylate (HEA), hydroxybutyl acrylate (HBA) and ammonium persulfate is added dropwise. The reactor is kept warm for 1 hour to obtain component A with a solid content of 50%. (2) Preparation of component B: Under nitrogen protection, polymethylene polyphenyl polyisocyanate and polyether polyol were reacted at 70°C for 1.5 h, and the isocyanate content was controlled to be 15% to obtain the component B. (3) Save the components A and B separately.

[0023] Example 2 This embodiment provides a two-component adhesive for particleboard / fiberboard, comprising component A and component B; Component A is a modified vinyl acetate-ethylene copolymer emulsion (modified VAE emulsion), which is mainly made from the following raw materials in parts by weight: 3 parts polyvinyl alcohol (degree of alcoholysis is 99%, degree of polymerization is 1700), 15 parts ethylene, 38 parts vinyl acetate, 8 parts hydroxyethyl acrylate (HEA), 4 parts hydroxybutyl acrylate (HBA), 0.3 parts ammonium persulfate, and 60 parts water. Component B is a modified polymethylene polyphenyl polyisocyanate prepolymer (modified pMDI prepolymer), which is mainly made from the following raw materials in parts by weight: 85 parts of polymethylene polyphenyl polyisocyanate and 30 parts of polyether polyol (number average molecular weight of 800).

[0024] The preparation method of the above-mentioned two-component adhesive for particleboard / fiberboard includes the following steps: (1) Preparation of component A: By weight, water and polyvinyl alcohol are added to a high-pressure reactor and heated to 100°C. After the polyvinyl alcohol is dissolved, the reactor is cooled to 80°C, ethylene is added, the pressure is increased to 6MPa, and then a mixture of vinyl acetate, hydroxyethyl acrylate (HEA), hydroxybutyl acrylate (HBA) and ammonium persulfate is added dropwise. The reactor is kept warm for 3 hours to obtain component A with a solid content of 60%. (2) Preparation of component B: Under nitrogen protection, polymethylene polyphenyl polyisocyanate and polyether polyol were reacted at 90°C for 3 hours, and the isocyanate content was controlled to be 25% to obtain the component B. (3) Save the components A and B separately.

[0025] Example 3 This embodiment provides a two-component adhesive for particleboard / fiberboard, comprising component A and component B; Component A is a modified vinyl acetate-ethylene copolymer emulsion (modified VAE emulsion), which is mainly made from the following raw materials in parts by weight: 2 parts polyvinyl alcohol (degree of alcoholysis is 90%, degree of polymerization is 1000), 12 parts ethylene, 35 parts vinyl acetate, 8 parts hydroxyethyl acrylate (HEA), 4 parts hydroxybutyl acrylate (HBA), 0.1-0.3 parts ammonium persulfate, 50-60 parts water, and 10 parts lignosulfonate (weight average molecular weight is 10000). Component B is a modified polymethylene polyphenyl polyisocyanate prepolymer (modified pMDI prepolymer), which is mainly made from the following raw materials in parts by weight: 80 parts of polymethylene polyphenyl polyisocyanate and 20 parts of polyether polyol (number average molecular weight of 600).

[0026] The preparation method of the above-mentioned two-component adhesive for particleboard / fiberboard includes the following steps: (1) Preparation of component A: By weight, water and polyvinyl alcohol are added to a high-pressure reactor and heated to 90°C. After the polyvinyl alcohol is dissolved, the reactor is cooled to 65°C, ethylene is added, the pressure is increased to 5 MPa, and then a mixture of vinyl acetate, hydroxyethyl acrylate (HEA), hydroxybutyl acrylate (HBA) and ammonium persulfate is added dropwise. The mixture is kept warm for 2 hours. Finally, lignin sulfonate is added and mixed well to obtain component A with a solid content of 55%. (2) Preparation of component B: Under nitrogen protection, polymethylene polyphenyl polyisocyanate and polyether polyol were reacted at 80°C for 2 hours, and the isocyanate content was controlled to be 20% to obtain the component B. (3) Save the components A and B separately.

[0027] Example 4 This embodiment provides a two-component adhesive for particleboard / fiberboard, comprising component A and component B; Component A is a modified vinyl acetate-ethylene copolymer emulsion (modified VAE emulsion), which is mainly made from the following raw materials in parts by weight: 2 parts polyvinyl alcohol (degree of alcoholysis is 90%, degree of polymerization is 1000), 12 parts ethylene, 35 parts vinyl acetate, 8 parts hydroxyethyl acrylate (HEA), 0.1-0.3 parts ammonium persulfate, and 50-60 parts water. Component B is a modified polymethylene polyphenyl polyisocyanate prepolymer (modified pMDI prepolymer), which is mainly made from the following raw materials in parts by weight: 80 parts of polymethylene polyphenyl polyisocyanate, 20 parts of polyether polyol (number average molecular weight of 600), and 3 parts of nanocellulose crystals (diameter 30nm, length 400nm).

[0028] The preparation method of the above-mentioned two-component adhesive for particleboard / fiberboard includes the following steps: (1) Preparation of component A: By weight, water and polyvinyl alcohol are added to a high-pressure reactor and heated to 90°C. After the polyvinyl alcohol is dissolved, the reactor is cooled to 65°C, ethylene is added, the pressure is increased to 5MPa, and then a mixture of vinyl acetate, hydroxyethyl acrylate (HEA) and ammonium persulfate is added dropwise. The reactor is kept warm for 2 hours to obtain component A with a solid content of 55%. (2) Preparation of component B: Under nitrogen protection, polymethylene polyphenyl polyisocyanate and polyether polyol were reacted at 80°C for 2 hours, and then nanocellulose crystals were added and mixed. The isocyanate content was controlled to be 20% to obtain the final product. (3) Save the components A and B separately.

[0029] Example 5 Preparing particleboard: (1) Adjust the moisture content of the wood shavings to 8%; (2) Mix component A and component B of the adhesive in a mass ratio of 100:15 and spray it onto the surface of wood shavings with a moisture content of 8%, with an application rate of 110 g / m² (dry). (3) After laying, pre-press for 30 minutes, hot pressing temperature 170℃, pressure 3.5MPa, time 1min / mm board thickness to obtain 18mm particleboard.

[0030] Example 6 Preparing fiberboard: (1) Adjust the moisture content of the fiber to 10%; (2) Mix component A and component B of the adhesive in a mass ratio of 100:10 and spray the mixture onto the fiber surface with a moisture content of 10%, with an application rate of 100 g / m² (dry). (3) After laying, pre-press for 30 minutes, hot press temperature 180℃, pressure 4MPa, time 2min / mm board thickness to obtain 18mm fiberboard.

[0031] Comparative Example 1: Unmodified VAE was used as component A, and unmodified pMDI was used as component B.

[0032] Comparative Example 2: Unmodified pMDI was used as component B, and component A was the same as in Example 1.

[0033] Comparative Example 3: Unmodified VAE was used as component A, and component B was the same as in Example 1.

[0034] Comparative Example 4: Polyether 2000 was used instead of polyether polyol, and other raw materials and preparation methods were the same as in Example 1. The components of the adhesives in each embodiment and comparative example are shown in Table 1: Table 1. Components of the adhesives in each embodiment and comparative example. Particleboard was prepared using the adhesives listed in Table 1 according to the method in Example 5. The properties of the prepared particleboard were then tested. Internal bond strength, wet strength, and boiling water resistance time were tested according to GB / T 17657-2022 standard, and the pot life was tested according to GB / T 7123.1-2002 standard. The results are shown in Table 2. Table 2 Performance of Adhesives and Particleboard in Each Group Table 2 shows that the data from Examples 1 to 4 of this invention, through hydroxylation modification of VAE molecules and water-based modification of pMDI prepolymer, can improve the performance of the adhesive, resulting in particleboard with an internal bond strength of 2.1-2.2 MPa, a wet strength of 1.1-1.2 MPa, a boiling water resistance time of 4.2-4.4 h, and a pot life of 3.2 h. The in-situ introduction of reinforcing phases such as lignin sulfonate and nanocellulose crystals further enhances its performance, with an internal bond strength exceeding 2.3 MPa, a wet strength exceeding 1.5 MPa, a boiling water resistance time exceeding 4.4 h, and a pot life of 3.3 h. Compared with traditional adhesives (Comparative Example 1), the particleboard produced exhibits approximately double the internal bond strength, approximately four times the wet strength, approximately 2 h longer boiling water resistance time, and approximately 3 h longer pot life.

[0035] The data from Example 1 and Comparative Examples 2 and 3 show that only by modifying VAE molecules and pMDI simultaneously can the performance of the adhesive be improved. This indicates that dual modification has a synergistic effect, giving the adhesive a more stable cross-linked network structure, and ultimately significantly improving the internal bond strength, wet strength, boiling water resistance time, and pot life of the resulting particleboard.

[0036] Data from Example 1 and Comparative Example 4 show that the prepolymerization of pMDI using low molecular weight polyether polyols (Mn=400-800) can extend the pot life of the adhesive by approximately 1 hour. This indicates that compared to high molecular weight polyether 2000, prepolymerization of pMDI using low molecular weight polyether polyols can more effectively slow down the side reaction rate between the modified pMDI prepolymer and water, thereby extending the pot life of the adhesive.

[0037] In summary, this invention prepares a two-component adhesive by hydroxylating VAE molecules, water-based modification of pMDI prepolymer, and in-situ introduction of reinforcing phases such as lignin sulfonate and nanocellulose crystals, thus solving the problems of low reaction efficiency, short pot life, and cost-performance imbalance of existing adhesives.

[0038] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A two-component adhesive for chipboard / fiberboard, characterized in that, comprising a Group A component and a Group B component; the Group A component is a modified vinyl acetate-ethylene copolymer emulsion, which is prepared from the following raw materials in parts by weight: polyvinyl alcohol 1-3 parts, ethylene 10-15 parts, vinyl acetate 32-38 parts, functional monomer 10-15 parts, initiator 0.1-0.3 parts, and water 50-60 parts; the functional monomer is hydroxyethyl acrylate and / or hydroxybutyl acrylate; the Group B component is a modified polymethylene polyphenyl polyisocyanate prepolymer, which is prepared from the following raw materials in parts by weight: polymethylene polyphenyl polyisocyanate 70-85 parts and polyether polyol 15-30 parts.

2. The two-component adhesive for particle / fiber board according to claim 1, characterized in that, In the functional monomer, the mass ratio of hydroxyethyl acrylate to hydroxybutyl acrylate is 1: (0.5-2).

3. The two-component adhesive for particle / fiber board according to claim 1, characterized in that, The polyvinyl alcohol has an alcoholysis degree of 88-99% and a polymerization degree of 500-1700.

4. The two-component adhesive for particle / fiber board according to claim 1, wherein The Group A component further comprises 8-12 parts of lignin sulfonate, which has a weight average molecular weight of 10000.

5. The two-component adhesive for particle / fiber board according to claim 1, wherein The Group B component further comprises 1-5 parts of nanocellulose crystals, which have a diameter of 10-50 nm and a length of 200-500 nm.

6. The two-component adhesive for particle / fiber board according to claim 1, wherein The polyether polyol has a number average molecular weight of 400-800.

7. The two-component adhesive for particle / fiber board according to claim 1, wherein The initiator is ammonium persulfate.

8. A method for preparing a two-component adhesive for particle / fiber board according to any one of claims 1 to 7, characterized in that comprising the following steps: (1) preparing the Group A component: water and polyvinyl alcohol are added to a high-pressure reaction kettle and heated to 90-100°C, after the polyvinyl alcohol is dissolved, the temperature is cooled to 60-80°C, ethylene is added, the pressure is increased to 4-6 MPa, then a mixture of vinyl acetate, functional monomer and initiator is added dropwise, and the reaction is maintained for 1-3 h, finally lignin sulfonate is added and mixed evenly to obtain the Group A component; (2) preparing the Group B component: under the protection of nitrogen, polymethylene polyphenyl polyisocyanate and polyether polyol are reacted at 70-90°C for 1.5-3 h, then nanocellulose crystals are added and mixed evenly, and the isocyanate content is controlled to be 15-25% to obtain the Group B component; (3) the Group A component and the Group B component are stored separately.

9. Use of the two-component adhesive for particle board / fiber board according to any one of claims 1 to 7 or prepared by the preparation method of claim 8 in the preparation of formaldehyde-free particle board or fiber board.

10. Use according to claim 9, characterized in that, The method for applying glue during the preparation of the shaving board or fiber board is: mixing the A component and the B component in a mass ratio of 100: (8-15), and then applying the mixture to the surface of the shaving or fiber by atomization spraying, with the amount of glue applied being 80-120 g / m 2 .

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