A powder formaldehyde-free adhesive for multilayer boards and preparation method thereof

Abstract

The present invention relates to the technical field of adhesives, and in particular to a powder formaldehyde-free adhesive for multilayer boards and a preparation method thereof. The powder formaldehyde-free adhesive for multilayer boards is prepared from the following raw materials: modified plant meal, calcium chloride, potassium silicate, polyacrylamide, and trimethylolpropane trimethacrylate; the modified plant meal is obtained from trimethylolpropane tris (3-mercaptopropionate) and dodecanethiol modified and washed plant meal. The present invention effectively utilizes plant meal, overcomes the problems of insufficient adhesive strength, poor wet strength, and poor anti-aging performance of traditional plant meal adhesives, and realizes the combination of environmental protection and high performance.

Description

Technical Field

[0001] The invention relates to the technical field of adhesives, and in particular to a powdered formaldehyde-free adhesive for multilayer boards and a preparation method thereof. Background Art

[0002] In recent years, with the increasing awareness of environmental protection and the popularization of the concept of sustainable development, the adhesive industry has an increasing demand for formaldehyde-free and environmentally friendly adhesives. Traditional urea-formaldehyde adhesives are gradually being phased out or reduced in use because of the threat to the environment and human health posed by the formaldehyde they release. In this context, the development of formaldehyde-free, environmentally friendly, high-performance adhesives has become an important direction for the industry's technological development.

[0003] Plant meal refers to the solid residue remaining after pressing or solvent extraction during the vegetable oil extraction process. It is mainly formed by oil extraction from plant seeds or fruits, and is rich in protein, cellulose, minerals and other nutrients. Common plant meal includes soybean meal, rapeseed meal, cottonseed meal and peanut meal. Plant meal is a renewable resource. Using plant meal as an adhesive raw material helps reduce dependence on petrochemical resources and reduce environmental pollution. In addition, the protein and cellulose in plant meal can be chemically modified to improve its bonding properties, making it have broad application prospects in formaldehyde-free adhesives. Although plant meal adhesives are environmentally friendly, they have problems such as insufficient bonding strength, poor wet strength, insufficient durability and aging resistance, which limit their scope of application. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a powder formaldehyde-free adhesive for multilayer boards and a preparation method thereof, so as to solve the problems of insufficient bonding strength, poor wet strength, insufficient durability and aging resistance of plant meal adhesives.

[0005] Based on the above purpose, the present invention provides a powder formaldehyde-free adhesive for multilayer boards, which is prepared from the following raw materials by weight: 20-30 parts of modified plant meal, 8-15 parts of calcium chloride, 4-12 parts of potassium silicate, 2.8-3.5 parts of polyacrylamide, and 1.8-2.4 parts of trimethylolpropane trimethacrylate;

[0006] Furthermore, the preparation method of the modified plant meal is as follows:

[0007] (1) washing the vegetable meal with deionized water and centrifuging to obtain a decontaminated vegetable meal;

[0008] (2) Add the decontaminated plant meal to deionized water, stir for 1.5-2.5 hours, adjust the pH to 8.3-8.8 with an aqueous sodium hydroxide solution, and let stand at room temperature for 20-28 hours to obtain a plant meal dispersion. Then, add trimethylolpropane tris(3-mercaptopropionate) and dodecanethiol to anhydrous ethanol, raise the temperature to 40-50°C, and stir for 20-40 minutes to obtain a modified solution. Then, add the modified solution dropwise to the plant meal dispersion at a shear rate of 5000-7000 rpm. After the addition is completed, continue to shear at a shear rate of 5000-7000 rpm for 2-4 minutes, and then high-pressure homogenize at 80-120 MPa for 2-4 times, centrifuge, dry, and finally crush through an 80-120 mesh sieve to obtain a modified plant meal.

[0009] Preferably, the plant meal in step (1) is one or a mixture of soybean meal, rapeseed meal, cottonseed meal and peanut meal.

[0010] Preferably, in step (1), the vegetable meal is ground and crushed through a 200-mesh sieve before washing.

[0011] Preferably, the centrifugal speed in step (1) is 6000 rpm and the time is 5 min.

[0012] Preferably, in step (2), the ratio of the decontaminated plant meal, deionized water, trimethylolpropane tris(3-mercaptopropionate), dodecanethiol and anhydrous ethanol is 50 g:400-600 mL:3-7 g:2-3 g:50-100 mL.

[0013] Preferably, the concentration of the sodium hydroxide aqueous solution in step (2) is 1 mol / L.

[0014] Furthermore, the present invention provides a method for preparing a powder formaldehyde-free adhesive for multilayer boards, comprising the following steps: placing modified plant meal, calcium chloride, potassium silicate, polyacrylamide, and trimethylolpropane trimethacrylate in a high-speed mixer for high-speed mixing at a speed of 800-1200 rpm for 8-12 minutes to obtain a powder formaldehyde-free adhesive for multilayer boards.

[0015] Beneficial effects of the present invention:

[0016] The present invention adopts trimethylolpropane tris (3-mercaptopropionate) as a modifier, which effectively improves the dry strength of the adhesive. The coordinated use of dodecanethiol not only maintains high dry strength, but also significantly improves wet strength and anti-aging performance, which is attributed to the regulation of the crosslinking density and hydrophobicity by both.

[0017] After 5 cycles of accelerated aging tests, the dry strength decrease rate of the powdered formaldehyde-free adhesive for multilayer boards provided by the present invention is lower than that of conventional urea-formaldehyde adhesives, showing excellent anti-aging performance. This allows the adhesive to maintain good stability during long-term and multiple uses.

[0018] The invention effectively utilizes the plant meal, overcomes the problems of insufficient adhesive strength, poor wet strength and poor anti-aging performance of traditional plant meal adhesives, and realizes the combination of environmental protection and high performance. DETAILED DESCRIPTION

[0019] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0020] Example 1: (1) 100 g of peanut meal was ground and pulverized, passed through a 200-mesh sieve, added to 1 L of deionized water, stirred for 30 min, centrifuged at a speed of 6000 rpm for 5 min, and finally the solid after centrifugation was dried at 50° C. for 12 h to obtain a decontaminated vegetable meal;

[0021] (2) Add 50 g of decontaminated plant meal to 500 mL of deionized water, stir for 2 h, adjust the pH to 8.5 with 1 mol / L sodium hydroxide aqueous solution, and let stand at room temperature for 24 h to obtain a plant meal dispersion. Then, add 5 g of trimethylolpropane tris(3-mercaptopropionate) and 2.5 g of dodecanethiol to 75 mL of anhydrous ethanol, heat to 45 °C, and stir for 30 min to obtain a modified solution. Then, add the modified solution dropwise to the plant meal dispersion at a shear rate of 6000 rpm. After the addition is complete, continue to shear at a shear rate of 6000 rpm for 3 min, and then high-pressure homogenize at 100 MPa for 3 times, centrifuge, dry, and finally pulverize through a 100-mesh sieve to obtain a modified plant meal.

[0022] (3) 25 g of modified plant meal, 12 g of calcium chloride, 8 g of potassium silicate, 3.2 g of polyacrylamide, and 2.1 g of trimethylolpropane trimethacrylate were mixed in a high-speed mixer at a speed of 1000 rpm for 10 min to obtain a powdered formaldehyde-free adhesive for multilayer boards.

[0023] Example 2: (1) 100 g of peanut meal was ground and pulverized, passed through a 200-mesh sieve, added to 1 L of deionized water, stirred for 30 min, and centrifuged at a speed of 6000 rpm for 5 min. Finally, the solid after centrifugation was dried at 50° C. for 12 h to obtain a decontaminated vegetable meal.

[0024] (2) Add 50 g of decontaminated plant meal to 400 mL of deionized water, stir for 2 h, adjust the pH to 8.3 with 1 mol / L sodium hydroxide aqueous solution, and let stand at room temperature for 20 h to obtain a plant meal dispersion. Then, add 3 g of trimethylolpropane tris(3-mercaptopropionate) and 2 g of dodecanethiol to 50 mL of anhydrous ethanol, heat to 40 °C, and stir for 40 min to obtain a modified solution. Then, add the modified solution dropwise to the plant meal dispersion at a shear rate of 5000 rpm. After the addition is complete, continue to shear at a shear rate of 5000 rpm for 4 min, and then high-pressure homogenize at 80 MPa for 4 times, centrifuge, dry, and finally pulverize through an 80-mesh sieve to obtain a modified plant meal.

[0025] (3) 20 g of modified plant meal, 8 g of calcium chloride, 4 g of potassium silicate, 2.8 g of polyacrylamide, and 1.8 g of trimethylolpropane trimethacrylate were mixed in a high-speed mixer at a speed of 800 rpm for 12 min to obtain a powdered formaldehyde-free adhesive for multilayer boards.

[0026] Example 3: (1) 100 g of peanut meal was ground and pulverized, passed through a 200-mesh sieve, added to 1 L of deionized water, stirred for 30 min, centrifuged at a speed of 6000 rpm for 5 min, and finally the solid after centrifugation was dried at 50° C. for 12 h to obtain a decontaminated vegetable meal;

[0027] (2) Add 50 g of decontaminated plant meal to 600 mL of deionized water, stir for 2 h, adjust the pH to 8.8 with 1 mol / L sodium hydroxide aqueous solution, and let stand at room temperature for 28 h to obtain a plant meal dispersion. Then, add 7 g of trimethylolpropane tris(3-mercaptopropionate) and 3 g of dodecanethiol to 100 mL of anhydrous ethanol, heat to 50 °C, and stir for 40 min to obtain a modified solution. Then, add the modified solution dropwise to the plant meal dispersion at a shear rate of 7000 rpm. After the addition is complete, continue to shear at a shear rate of 7000 rpm for 2 min, and then high-pressure homogenize twice at 120 MPa, centrifuge, dry, and finally pulverize through a 120-mesh sieve to obtain a modified plant meal.

[0028] (3) 30 g of modified vegetable meal, 15 g of calcium chloride, 12 g of potassium silicate, 3.5 g of polyacrylamide, and 2.4 g of trimethylolpropane trimethacrylate were mixed in a high-speed mixer at a speed of 1200 rpm for 8 min to obtain a powdered formaldehyde-free adhesive for multilayer boards.

[0029] Example 4: (1) 60 g of cottonseed meal and 40 g of soybean meal were ground and pulverized, passed through a 200-mesh sieve, added to 1 L of deionized water, stirred for 30 min, and centrifuged at a speed of 6000 rpm for 5 min. Finally, the solid after centrifugation was dried at 50 °C for 12 h to obtain a decontaminated vegetable meal.

[0030] (2) Add 50 g of decontaminated plant meal to 500 mL of deionized water, stir for 2 h, adjust the pH to 8.5 with 1 mol / L sodium hydroxide aqueous solution, and let stand at room temperature for 24 h to obtain a plant meal dispersion. Then, add 5 g of trimethylolpropane tris(3-mercaptopropionate) and 2.5 g of dodecanethiol to 75 mL of anhydrous ethanol, heat to 45 °C, and stir for 30 min to obtain a modified solution. Then, add the modified solution dropwise to the plant meal dispersion at a shear rate of 6000 rpm. After the addition is complete, continue to shear at a shear rate of 6000 rpm for 3 min, and then high-pressure homogenize at 100 MPa for 3 times, centrifuge, dry, and finally pulverize through a 100-mesh sieve to obtain a modified plant meal.

[0031] (3) 25 g of modified plant meal, 12 g of calcium chloride, 8 g of potassium silicate, 3.2 g of polyacrylamide, and 2.1 g of trimethylolpropane trimethacrylate were mixed in a high-speed mixer at a speed of 1000 rpm for 10 min to obtain a powdered formaldehyde-free adhesive for multilayer boards.

[0032] Comparative Example 1:

[0033] The difference between Comparative Example 1 and Example 1 is that: trimethylolpropane tris(3-mercaptopropionate) is not added in step (2);

[0034] The specific preparation steps are as follows:

[0035] (1) Grind 100 g of peanut meal, pass it through a 200-mesh sieve, add it to 1 L of deionized water, stir it for 30 min, centrifuge it at a speed of 6000 rpm for 5 min, and finally dry the solid after centrifugation at 50 °C for 12 h to obtain decontaminated vegetable meal;

[0036] (2) Add 50 g of decontaminated plant meal to 500 mL of deionized water, stir for 2 h, adjust the pH to 8.5 with 1 mol / L sodium hydroxide aqueous solution, and let stand at room temperature for 24 h to obtain a plant meal dispersion. Then, add 2.5 g of dodecanethiol to 75 mL of anhydrous ethanol, heat to 45 °C, and stir for 30 min to obtain a modified solution. Then, add the modified solution dropwise to the plant meal dispersion at a shear rate of 6000 rpm. After the addition is complete, continue to shear at a shear rate of 6000 rpm for 3 min, and then high-pressure homogenize at 100 MPa for 3 times, centrifuge, dry, and finally crush through a 100-mesh sieve to obtain a modified plant meal.

[0037] (3) 25 g of modified plant meal, 12 g of calcium chloride, 8 g of potassium silicate, 3.2 g of polyacrylamide, and 2.1 g of trimethylolpropane trimethacrylate were mixed in a high-speed mixer at a speed of 1000 rpm for 10 min to obtain a powdered formaldehyde-free adhesive for multilayer boards.

[0038] Comparative Example 2:

[0039] The difference between Comparative Example 2 and Example 1 is that: dodecanethiol is not added in step (2);

[0040] The specific preparation steps are as follows:

[0041] (1) Grind 100 g of peanut meal, pass it through a 200-mesh sieve, add it to 1 L of deionized water, stir it for 30 min, centrifuge it at a speed of 6000 rpm for 5 min, and finally dry the solid after centrifugation at 50 °C for 12 h to obtain decontaminated vegetable meal;

[0042] (2) Add 50 g of decontaminated plant meal to 500 mL of deionized water, stir for 2 h, adjust the pH to 8.5 with 1 mol / L sodium hydroxide aqueous solution, and let stand at room temperature for 24 h to obtain a plant meal dispersion. Then, add 5 g of trimethylolpropane tris(3-mercaptopropionate) to 75 mL of anhydrous ethanol, heat to 45 °C, and stir for 30 min to obtain a modified solution. Then, add the modified solution dropwise to the plant meal dispersion at a shear rate of 6000 rpm. After the addition is complete, continue to shear at a shear rate of 6000 rpm for 3 min, and then high-pressure homogenize at 100 MPa for 3 times, centrifuge, dry, and finally crush through a 100-mesh sieve to obtain a modified plant meal.

[0043] (3) 25 g of modified plant meal, 12 g of calcium chloride, 8 g of potassium silicate, 3.2 g of polyacrylamide, and 2.1 g of trimethylolpropane trimethacrylate were mixed in a high-speed mixer at a speed of 1000 rpm for 10 min to obtain a powdered formaldehyde-free adhesive for multilayer boards.

[0044] Comparative Example 3:

[0045] The difference between Comparative Example 3 and Example 1 is that the plant meal is not modified;

[0046] The specific preparation steps are as follows:

[0047] (1) Grind 100 g of peanut meal, pass it through a 200-mesh sieve, add it to 1 L of deionized water, stir it for 30 min, centrifuge it at a speed of 6000 rpm for 5 min, and finally dry the solid after centrifugation at 50 °C for 12 h to obtain decontaminated vegetable meal;

[0048] (2) 25 g of decontaminated plant meal, 12 g of calcium chloride, 8 g of potassium silicate, 3.2 g of polyacrylamide, and 2.1 g of trimethylolpropane trimethacrylate were mixed in a high-speed mixer at a speed of 1000 rpm for 10 min to obtain a powdered formaldehyde-free adhesive for multilayer boards.

[0049] Comparative Example 4:

[0050] The difference between Comparative Example 4 and Example 1 is that: calcium chloride is not added in step (3);

[0051] The specific preparation steps are as follows:

[0052] (1) Grind 100 g of peanut meal, pass it through a 200-mesh sieve, add it to 1 L of deionized water, stir it for 30 min, centrifuge it at a speed of 6000 rpm for 5 min, and finally dry the solid after centrifugation at 50 °C for 12 h to obtain decontaminated vegetable meal;

[0053] (2) Add 50 g of decontaminated plant meal to 500 mL of deionized water, stir for 2 h, adjust the pH to 8.5 with 1 mol / L sodium hydroxide aqueous solution, and let stand at room temperature for 24 h to obtain a plant meal dispersion. Then, add 5 g of trimethylolpropane tris(3-mercaptopropionate) and 2.5 g of dodecanethiol to 75 mL of anhydrous ethanol, heat to 45 °C, and stir for 30 min to obtain a modified solution. Then, add the modified solution dropwise to the plant meal dispersion at a shear rate of 6000 rpm. After the addition is complete, continue to shear at a shear rate of 6000 rpm for 3 min, and then high-pressure homogenize at 100 MPa for 3 times, centrifuge, dry, and finally pulverize through a 100-mesh sieve to obtain a modified plant meal.

[0054] (3) 25 g of modified vegetable meal, 8 g of potassium silicate, 3.2 g of polyacrylamide, and 2.1 g of trimethylolpropane trimethacrylate were mixed in a high-speed mixer at a speed of 1000 rpm for 10 min to obtain a powdered formaldehyde-free adhesive for multilayer boards.

[0055] Comparative Example 5:

[0056] The difference between Comparative Example 5 and Example 1 is that: potassium silicate is not added in step (3);

[0057] The specific preparation steps are as follows:

[0058] (1) Grind 100 g of peanut meal, pass it through a 200-mesh sieve, add it to 1 L of deionized water, stir it for 30 min, centrifuge it at a speed of 6000 rpm for 5 min, and finally dry the solid after centrifugation at 50 °C for 12 h to obtain decontaminated vegetable meal;

[0059] (2) Add 50 g of decontaminated plant meal to 500 mL of deionized water, stir for 2 h, adjust the pH to 8.5 with 1 mol / L sodium hydroxide aqueous solution, and let stand at room temperature for 24 h to obtain a plant meal dispersion. Then, add 5 g of trimethylolpropane tris(3-mercaptopropionate) and 2.5 g of dodecanethiol to 75 mL of anhydrous ethanol, heat to 45 °C, and stir for 30 min to obtain a modified solution. Then, add the modified solution dropwise to the plant meal dispersion at a shear rate of 6000 rpm. After the addition is complete, continue to shear at a shear rate of 6000 rpm for 3 min, and then high-pressure homogenize at 100 MPa for 3 times, centrifuge, dry, and finally pulverize through a 100-mesh sieve to obtain a modified plant meal.

[0060] (3) 25 g of modified vegetable meal, 12 g of calcium chloride, 3.2 g of polyacrylamide, and 2.1 g of trimethylolpropane trimethacrylate were mixed in a high-speed mixer at a speed of 1000 rpm for 10 min to obtain a powdered formaldehyde-free adhesive for multilayer boards.

[0061] Comparative Example 6:

[0062] The difference between Comparative Example 6 and Example 1 is that: trimethylolpropane trimethacrylate is not added in step (3);

[0063] The specific preparation steps are as follows:

[0064] (1) Grind 100 g of peanut meal, pass it through a 200-mesh sieve, add it to 1 L of deionized water, stir it for 30 min, centrifuge it at a speed of 6000 rpm for 5 min, and finally dry the solid after centrifugation at 50 °C for 12 h to obtain decontaminated vegetable meal;

[0065] (2) Add 50 g of decontaminated plant meal to 500 mL of deionized water, stir for 2 h, adjust the pH to 8.5 with 1 mol / L sodium hydroxide aqueous solution, and let stand at room temperature for 24 h to obtain a plant meal dispersion. Then, add 5 g of trimethylolpropane tris(3-mercaptopropionate) and 2.5 g of dodecanethiol to 75 mL of anhydrous ethanol, heat to 45 °C, and stir for 30 min to obtain a modified solution. Then, add the modified solution dropwise to the plant meal dispersion at a shear rate of 6000 rpm. After the addition is complete, continue to shear at a shear rate of 6000 rpm for 3 min, and then high-pressure homogenize at 100 MPa for 3 times, centrifuge, dry, and finally pulverize through a 100-mesh sieve to obtain a modified plant meal.

[0066] (3) 25 g of modified plant meal, 12 g of calcium chloride, 8 g of potassium silicate, and 3.2 g of polyacrylamide were mixed in a high-speed mixer at a speed of 1000 rpm for 10 min to obtain a powdered formaldehyde-free adhesive for multilayer boards.

[0067] Data testing:

[0068] Gluing test: 30g of the powdered formaldehyde-free adhesive prepared in the embodiment and comparative example and commercially available conventional urea-formaldehyde glue were added to 65g of deionized water and stirred for 10min to obtain liquid formaldehyde-free glue. The 1.6mm thick poplar board was used for pressing, the single-sided glue coating amount was 175g / m³, the pressing temperature was 135℃ for 8min, and the pressure was 1.2mpa to obtain a plywood;

[0069] Gluing performance: According to the standard GB / T 9845-2015, the dry strength and wet strength of the plywood prepared by the pressing test were determined by a universal mechanical testing machine. The wet strength test was to place the pressed board in a constant temperature water bath at 63°C for 3 hours, then take it out and cool it at room temperature for 10 minutes, and then test the bonding strength, which is the wet strength. The results are shown in Table 1.

[0070] Anti-aging performance: (1) The specimens were immersed in water at room temperature. The specimens were completely submerged in water. After 12 hours, they were taken out and the surface moisture was wiped off. (2) The immersed specimens were placed in a drying oven and dried at 120°C until they were absolutely dry. After completing steps (1) and (2), one dry-wet cycle of accelerated aging was completed. A total of 5 dry-wet cycles of accelerated aging were performed. The dry strength after each dry-wet cycle of accelerated aging was tested, and the decrease rate of dry strength relative to that without accelerated aging test was calculated to evaluate the anti-aging performance. The results are shown in Table 1.

[0071] Table 1 Performance test data

[0072]

[0073] Data Analysis:

[0074] It can be seen from the data of Examples 1-4 and conventional urea-formaldehyde glue in Table 1 that the powder formaldehyde-free adhesive for multilayer boards provided by the present invention has high dry strength and wet strength, which is comparable to conventional urea-formaldehyde glue, realizes the effective utilization of plant meal, overcomes the problem of insufficient bonding strength of traditional plant meal adhesives, especially poor wet strength, and the powder formaldehyde-free adhesive for multilayer boards provided by the present invention has excellent anti-aging properties. After 5 cycles of accelerated aging tests, the dry strength decrease rate is lower than that of conventional urea-formaldehyde glue.

[0075] It can be seen from the data of Example 1 and Comparative Example 1 in Table 1 that trimethylolpropane tris(3-mercaptopropionate) can improve dry strength.

[0076] It can be seen from the data of Example 1 and Comparative Example 2 in Table 1 that dodecanethiol can significantly improve wet strength and anti-aging properties.

[0077] From the data of Example 1 and Comparative Example 3 in Table 1, it can be seen that trimethylolpropane tris(3-mercaptopropionate) and dodecanethiol synergistically regulate the adhesive strength of the powder formaldehyde-free adhesive for multilayer boards, and improve the wet strength and anti-aging properties while achieving higher dry strength. This is mainly because trimethylolpropane tris(3-mercaptopropionate) and dodecanethiol regulate the crosslinking density on the one hand, and regulate the hydrophobic properties on the other hand.

[0078] From the data of Example 1 and Comparative Example 4 in Table 1, it can be seen that calcium chloride effectively improves the adhesive strength of the powder formaldehyde-free adhesive for multilayer boards, which is mainly due to the cross-linking effect of calcium ions.

[0079] From the data of Example 1 and Comparative Example 5 in Table 1, it can be seen that potassium silicate has a significant effect on the wet strength of the powder formaldehyde-free adhesive for multilayer boards, which is mainly due to the hydrolysis and cross-linking effect of potassium silicate.

[0080] From the data of Example 1 and Comparative Example 6 in Table 1, it can be seen that trimethylolpropane trimethacrylate effectively improves the adhesive strength of the powder formaldehyde-free adhesive for multilayer boards. This is mainly because trimethylolpropane trimethacrylate can be cross-linked with the modified plant meal during the hot pressing process.

[0081] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A powder formaldehyde-free adhesive for multilayer boards, characterized in that: The invention is prepared from the following raw materials by weight: 20-30 parts of modified plant meal, 8-15 parts of calcium chloride, 4-12 parts of potassium silicate, 2.8-3.5 parts of polyacrylamide, and 1.8-2.4 parts of trimethylolpropane trimethacrylate; The preparation method of the modified plant meal is as follows: (1) washing the vegetable meal with deionized water and centrifuging to obtain a decontaminated vegetable meal; (2) Add the decontaminated plant meal to deionized water, stir for 1.5-2.5 hours, adjust the pH to 8.3-8.8 with sodium hydroxide aqueous solution, and let stand at room temperature for 20-28 hours to obtain a plant meal dispersion, then add trimethylolpropane tris(3-mercaptopropionate) and dodecanethiol to anhydrous ethanol, heat to 40-50°C, stir for 20-40 minutes, and obtain a modified solution; Then, the modified liquid is added dropwise to the plant meal dispersion at a shear rate of 5000-7000 rpm. After the addition is completed, the modified liquid is sheared at a shear rate of 5000-7000 rpm for 2-4 minutes, and then the modified liquid is homogenized at a high pressure of 80-120 MPa for 2-4 times, centrifuged, dried, and finally crushed through a 80-120 mesh sieve to obtain a modified plant meal. In step (1), the plant meal is one or a mixture of soybean meal, rapeseed meal, cottonseed meal and peanut meal; In the step (2), the amount ratio of the decontaminated plant meal, deionized water, trimethylolpropane tris(3-mercaptopropionate), dodecanethiol and anhydrous ethanol is 50g:400-600mL:3-7g:2-3g:50-100mL.

2. The powder formaldehyde-free adhesive for multilayer boards according to claim 1, characterized in that: In the step (1), the vegetable meal is ground and crushed through a 200-mesh sieve before being washed.

3. The powder formaldehyde-free adhesive for multilayer boards according to claim 1, characterized in that: The centrifugal speed in step (1) is 6000 rpm and the time is 5 min.

4. The powder formaldehyde-free adhesive for multilayer boards according to claim 1, characterized in that: The concentration of the sodium hydroxide aqueous solution in step (2) is 1 mol / L.

5. A method for preparing the powder formaldehyde-free adhesive for multilayer boards according to any one of claims 1 to 4, characterized in that: The following steps are involved: The modified plant meal, calcium chloride, potassium silicate, polyacrylamide and trimethylolpropane trimethacrylate are mixed in a high-speed mixer at a speed of 800-1200 rpm for 8-12 minutes to obtain a powder formaldehyde-free adhesive for multilayer boards.

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