Method for modifying high-performance environment-friendly urea-formaldehyde resin adhesive through enzymolysis of soybean protein

Abstract

The invention discloses a soybean protein modified high-performance environment-friendly urea-formaldehyde resin adhesive and a preparation method thereof, and relates to the technical field of adhesive preparation. The adhesive comprises a modified soybean protein solution, paraformaldehyde and urea, wherein the modified soybean protein solution is obtained through enzymolysis and ultrasonic treatment. The adhesive is prepared by the following steps: reacting soybean protein and paraformaldehyde, and then sequentially adding urea for four times to react. According to the preparation method, biomass macromolecules in the soybean protein are subjected to enzymolysis, and the enzymolysis product is subjected to ultrasonic treatment, so that the cross-linking reaction capacity of the soybean protein and urea-formaldehyde resin molecules is improved, the adhesive property of urea-formaldehyde resin is enhanced, and the free formaldehyde content of the urea-formaldehyde resin is reduced, and therefore, the environment-friendly urea-formaldehyde resin adhesive with excellent performance is prepared.

Description

Technical Field

[0001] The invention relates to the technical field of adhesive preparation, and in particular to a method for enzymatically hydrolyzing soybean protein to modify a high-performance environmentally friendly urea-formaldehyde resin adhesive. Background Art

[0002] Urea-formaldehyde resin has the advantages of high reactivity, fast curing time, low cost, clear color, good bonding strength, etc., and is widely used in the field of wood processing. However, urea-formaldehyde resin releases carcinogenic formaldehyde during use and is easily hydrolyzed under high temperature and high air humidity conditions, which limits the application of urea-formaldehyde resin adhesives.

[0003] Soybean meal is a byproduct of the soybean industry and has a wide range of sources. Soybean meal contains a large amount of crude protein, so soybean protein isolate with high protein content can be extracted. The spherical structure of soybean protein isolate contains rich -NH2, -CONH and other groups, which can undergo copolymerization with urea-formaldehyde resin and can be used as a green and environmentally friendly modifier to improve the bonding strength of urea-formaldehyde resin adhesives. However, unmodified soy protein is directly added to urea-formaldehyde resin, and its cross-linking reaction ability with formaldehyde and urea-formaldehyde resin is poor, so it can only play the role of filler and affect the water resistance of urea-formaldehyde resin. Therefore, through modification treatment, the viscosity of soy protein solution is reduced, its complex structure is unfolded, active groups and hydrophobic groups are increased, and bonding performance and water resistance are improved. It is of great significance for modifying urea-formaldehyde resin and preparing high-performance green and environmentally friendly urea-formaldehyde resin. Summary of the invention

[0004] In view of the above shortcomings, the present invention provides a soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive and a preparation method thereof. The present invention improves the cross-linking reaction ability of soybean protein and urea-formaldehyde resin molecules by enzymatic hydrolysis of biomass macromolecules in soybean protein and ultrasonic treatment of the enzymatic hydrolysis product, thereby enhancing the bonding performance of urea-formaldehyde resin and reducing its free formaldehyde content, thereby preparing an environmentally friendly urea-formaldehyde resin adhesive with excellent performance.

[0005] The specific technical solutions of the present invention are as follows:

[0006] A soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive, comprising the following components: modified soybean protein solution, paraformaldehyde and urea;

[0007] The preparation method of the modified soybean protein solution comprises the following steps:

[0008] (1) Dissolving: dissolving the soy protein isolate in water to obtain a soy protein source solution;

[0009] (2) Enzymatic hydrolysis: adding biological enzymes to the soy protein source solution, and adjusting the pH of the solution to alkaline for enzymatic hydrolysis to obtain an enzymatic hydrolysis solution; the effect of enzymatic hydrolysis is to promote the degradation of soy protein into small molecular peptides, reduce the viscosity of the soy protein solution, and increase its reaction activity;

[0010] (3) Ultrasound: The enzymatic hydrolysis solution is subjected to ultrasonic treatment to obtain the modified soy protein solution.

[0011] Furthermore, the added mass of the soy protein source solution accounts for 0.5-1.0% of the total mass of the soy protein modified urea-formaldehyde resin adhesive.

[0012] Furthermore, in step (1), the protein content of the soy protein isolate is 70-80%, and the mass concentration of the soy protein source solution is 5-10%.

[0013] Furthermore, in step (2), the biological enzyme is one or more of papain, laccase, and cellulase.

[0014] Furthermore, in step (2), the biological enzymes include papain, cellulase and laccase, and the mass ratio of the papain, the cellulase and the laccase is 1:1:1.

[0015] Furthermore, in step (2), the amount of the biological enzyme added is 0.1%-0.3% of the mass of the soy protein source solution.

[0016] Furthermore, in step (2), the enzymatic hydrolysis has a pH of 8.0-8.5, a temperature of 40-60° C., and a time of 1-3 h.

[0017] Furthermore, in step (3), the power of the ultrasound is 360W, the temperature is room temperature, and the time is 10-30 minutes.

[0018] In the present invention, the mass concentration, enzymolysis temperature, enzymolysis time, and enzymolysis pH control of the above-mentioned soy protein source solution can ensure the best enzymolysis effect. If the concentration of the soy protein source solution is too high or too low, the temperature is not within the range of enzyme activity, and the reaction time and reaction pH are improperly controlled, the degradation efficiency, product type, and product molecular weight of the macromolecules in the soy protein will be affected. And the control of the above-mentioned ultrasonic time can effectively unfold the complex structure of the soy protein. If the ultrasonic time is too long, it will increase energy consumption. If the ultrasonic time is too low, the complex structure of the soy protein cannot be unfolded, and in the later adhesive synthesis process, it affects the cross-linking degree with formaldehyde and urea-formaldehyde molecules. In addition, the present invention introduces a soy protein source, which can reduce the usage of paraformaldehyde and urea, but its content should be controlled within the scope of the present invention. If the mass fraction of the soy protein source in the adhesive is too low, the environmental protection improvement effect is not obvious, and if the soy protein source accounts for too high a content of the adhesive, a gel is directly formed in the formaldehyde solution so that the subsequent synthesis of the adhesive cannot be performed.

[0019] The present invention also provides a method for preparing the soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive, which comprises the following steps:

[0020] S1: adding paraformaldehyde to the modified soy protein solution, adjusting the pH to 8.0-8.5, heating to 38-40° C. for reaction, and then adding the first portion of urea for reaction to obtain a first reaction solution;

[0021] S2: After heating the first reaction solution to 86-90° C., keeping the temperature for 18-22 min, adjusting the pH value to 4.8-5.0, and when the viscosity increases to 45-50 mPa·, obtaining the second reaction solution;

[0022] S3: adjusting the pH of the second reaction solution to 5.8-6.0, then adding the second portion of urea, and when the viscosity thereof increases to 50-55 mPa·s, obtaining a third reaction solution;

[0023] S4: adjusting the pH of the third reaction solution to 7.0-7.5 and cooling the solution to 75-80° C., then adding a third portion of urea to react to obtain a fourth reaction solution;

[0024] S5: adjusting the temperature of the fourth reaction liquid to 65-70° C., then adding a fourth portion of urea to react, and cooling after the reaction to obtain the soy protein modified environmentally friendly urea-formaldehyde resin adhesive.

[0025] Furthermore, the mass ratio of the first portion of urea, the second portion of urea, the third portion of urea and the fourth portion of urea is (4.3-5.0): (2.0-2.5): (1.2-1.8): (0.9-1.2).

[0026] Furthermore, in the above preparation method, the pH value of the solution is adjusted using an acid regulator or an alkaline regulator, wherein the acid regulator is one or more of hydrochloric acid, sulfuric acid or formic acid, and the alkaline regulator is sodium hydroxide and / or potassium hydroxide.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention solves the problem that soybean protein is insoluble in water and has low reactivity by enzymolysis of biomass macromolecules in soybean protein and ultrasonic modification of the enzymolysis product, and improves the reactivity of soybean protein by controlling the reaction conditions of enzymolysis and ultrasonic modification, and realizes that it can be copolymerized with urea-formaldehyde resin, thereby preparing an environmentally friendly urea-formaldehyde resin adhesive with excellent performance. Among them, soybean protein is depolymerized by biological enzymes, and soybean protein can be degraded into small molecule peptides. Combined with the control of enzymolysis conditions, the spherical structure of protein molecules is unfolded, so that soybean protein exposes more active groups such as amino groups and hydroxyl groups, and more reactive sites are generated on the polypeptide chain, so that chemical bonding can be generated with formaldehyde and reaction intermediates hydroxymethyl (-CH2-OH) and aminomethylene bonds (-NH-CH2-NH-) in the synthesis process of urea-formaldehyde resin, and the viscosity of soybean protein solution is reduced by ultrasonic modification, so that modified soybean protein and urea-formaldehyde resin are cross-linked, so that more soybean protein peptides participate in the cross-linking reaction with paraformaldehyde, and a tighter cross-linked network structure is established, thereby improving the performance of urea-formaldehyde resin.

[0029] 2. In the preparation method of the present invention, soybean protein is introduced at the early stage of urea-formaldehyde resin synthesis, so that the active groups exposed after depolymerization can undergo cross-linking reaction with formaldehyde and urea-formaldehyde resin molecules, thereby improving the bonding performance of urea-formaldehyde resin and the environmental protection level of its artificial board.

[0030] 3. The preparation method of the soybean protein modified urea-formaldehyde resin adhesive of the present invention does not require changing the existing urea-formaldehyde resin synthesis process, nor does it require adjusting the artificial board production process. The entire process does not emit wastewater, waste gas, etc., and is clean and pollution-free.

[0031] 4. The preparation steps of the soybean protein modified urea-formaldehyde resin adhesive of the present invention are simple, the reaction conditions are easy to achieve, and it has broad market application prospects. DETAILED DESCRIPTION

[0032] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0033] Example 1

[0034] A soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive comprises the following components: modified soybean protein solution, paraformaldehyde and urea. It is prepared according to the following method:

[0035] 1) Preparation of modified soy protein solution:

[0036] (1) Dissolution: Weigh 17 g of wet soy protein with a protein content of 80%, dissolve the soy protein isolate in 83 g of water to obtain a soy protein source solution with a mass concentration of 5%;

[0037] (2) Enzyme hydrolysis: add 0.2 g of biological enzyme (the biological enzyme includes 0.1 g of papain and 0.1 g of laccase) to the soy protein source solution, then adjust the pH to 8.5 with a 30% sodium hydroxide aqueous solution, react at 55° C. for 2 h, and stir continuously during the reaction to obtain an enzymatic solution;

[0038] (3) Ultrasound: The enzymatic hydrolysis solution was subjected to ultrasound treatment (power of 360 W) for 30 min at room temperature to obtain the modified soy protein solution.

[0039] 2) adding 222 g of paraformaldehyde and 283 g of water to the modified soy protein solution, and then adjusting the pH to 8.5 with a 30% sodium hydroxide aqueous solution, heating the solution under heating conditions, and stirring the solution at a stirring rate of 200 rpm. When the temperature reaches 38° C., adding the first portion of urea (207.27 g), and keeping the temperature for 20 minutes to obtain a first reaction solution;

[0040] 3) After heating the first reaction solution to 88° C., the temperature was kept for 20 min, and then the pH value was adjusted to 4.8 with 15% formic acid solution. When the viscosity of the solution increased to 45 mPa·s, a second reaction solution was obtained;

[0041] 4) adjusting the pH of the second reaction solution to 6.0 with a 30% sodium hydroxide aqueous solution, and then adding a second portion of urea (107.73 g), and when the viscosity of the solution increases to 50 mPa·s, obtaining a third reaction solution;

[0042] 5) adjusting the pH of the third reaction solution to 7.5 with a 30% sodium hydroxide aqueous solution and cooling the solution to 80° C., then adding 70.91 g of the third portion of urea and keeping the temperature for 15 minutes to obtain a fourth reaction solution;

[0043] 6) The temperature of the fourth reaction liquid was lowered to 67° C., and then 45.82 g of the fourth portion of urea was added. After keeping the temperature for 15 min, the reaction liquid was cooled to 40° C. to obtain the soy protein modified environmentally friendly urea-formaldehyde resin adhesive.

[0044] Example 2

[0045] A soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive comprises the following components: modified soybean protein solution, paraformaldehyde and urea. It is prepared according to the following method:

[0046] 1) Preparation of modified soy protein solution:

[0047] (1) Dissolution: Weigh 34 g of wet soy protein with a protein content of 75%, dissolve the soy protein isolate in 66 g of water to obtain a soy protein source solution with a mass concentration of 10%;

[0048] (2) Enzyme hydrolysis: add 0.2 g of biological enzyme (the biological enzyme includes 0.1 g of papain) to the soy protein source solution, then adjust the pH to 8.0 with a 30% sodium hydroxide aqueous solution, react at 40° C. for 3 h, and stir continuously during the reaction to obtain an enzymatic hydrolysis solution;

[0049] (3) Ultrasound: The enzymatic hydrolysis solution is subjected to ultrasound treatment (power of 360 W) for 20 min at room temperature to obtain the modified soy protein solution.

[0050] 2) Add 222 g of paraformaldehyde and 288 g of water to the modified soy protein solution, then adjust the pH to 8.3 using a 30% sodium hydroxide aqueous solution, start heating under heating conditions, and stir the solution at a stirring rate of 200 rpm. When the temperature reaches 39° C., add 220.35 g of the first portion of urea, and keep warm for 20 minutes to obtain a first reaction solution;

[0051] 3) After heating the first reaction solution to 90° C., the temperature was kept for 20 min, and then the pH value was adjusted to 4.9 with a 10% sulfuric acid solution. When the viscosity of the solution increased to 48 mPa·s, a second reaction solution was obtained;

[0052] 4) adjusting the pH of the second reaction solution to 5.9 with a 30% sodium hydroxide aqueous solution, and then adding a second portion of urea (102.49 g), until the viscosity of the solution increases to 53 mPa·s, to obtain a third reaction solution;

[0053] 5) adjusting the pH of the third reaction solution to 7.2 with a 30% sodium hydroxide aqueous solution and cooling the solution to 78° C., then adding 61.49 g of the third portion of urea and keeping the temperature for 15 minutes to obtain a fourth reaction solution;

[0054] 6) The temperature of the fourth reaction liquid was lowered to 65° C., and then 46.12 g of the fourth portion of urea was added. After keeping the temperature for 15 minutes, the mixture was cooled to 40° C. to obtain the soy protein modified environmentally friendly urea-formaldehyde resin adhesive.

[0055] Example 3

[0056] A soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive comprises the following components: modified soybean protein solution, paraformaldehyde and urea. It is prepared according to the following method:

[0057] 1) Preparation of modified soy protein solution:

[0058] (1) Dissolution: Weigh 27.2 g of wet soy protein with a protein content of 80%, dissolve the soy protein isolate in 72.8 g of water to obtain a soy protein source solution with a mass concentration of 8%;

[0059] (2) Enzyme hydrolysis: add 0.2 g of biological enzyme (the biological enzyme includes 0.1 g of papain and 0.2 g of cellulase) to the soy protein source solution, then adjust the pH to 8.0 with a 30% sodium hydroxide aqueous solution, react at 60° C. for 1 h, and stir continuously during the reaction to obtain an enzymatic solution;

[0060] (3) Ultrasound: The enzymatic hydrolysis solution was subjected to ultrasound treatment (power of 360 W) for 10 min at room temperature to obtain the modified soy protein solution.

[0061] 2) adding 222 g of paraformaldehyde and 283 g of water to the modified soy protein solution, and then adjusting the pH to 8.0 with a 30% potassium hydroxide aqueous solution, heating the solution under heating conditions, and stirring the solution at a stirring rate of 200 rpm. When the temperature reaches 40° C., adding 191.58 g of the first portion of urea, and keeping the temperature for 20 minutes to obtain a first reaction solution;

[0062] 3) After heating the first reaction solution to 86° C., the temperature was kept for 20 min, and then the pH value was adjusted to 5.0 with a 10% hydrochloric acid solution. When the viscosity of the solution increased to 50 mPa·s, a second reaction solution was obtained;

[0063] 4) adjusting the pH of the second reaction solution to 5.8 with a 30% sodium hydroxide aqueous solution, and then adding a second portion of urea (95.79 g), until the viscosity of the solution increases to 55 mPa·s, to obtain a third reaction solution;

[0064] 5) adjusting the pH of the third reaction solution to 7.0 with a 30% sodium hydroxide aqueous solution and cooling the solution to 75° C., then adding 68.97 g of the third portion of urea and keeping the temperature for 15 minutes to obtain a fourth reaction solution;

[0065] 6) The temperature of the fourth reaction liquid was lowered to 70° C., and then 45.98 g of the fourth portion of urea was added. After keeping the temperature for 15 minutes, the reaction liquid was cooled to 40° C. to obtain the soy protein modified environmentally friendly urea-formaldehyde resin adhesive.

[0066] Example 4

[0067] The difference between the adhesive of Example 4 and Example 1 is that in step (2), the biological enzymes used include 0.1 g of papain, 0.1 g of cellulase and 0.1 g of laccase.

[0068] Comparative Example 1

[0069] The adhesive in Comparative Example 1 is urea-formaldehyde resin. Except that the modified soy protein solution is not used, the other preparation processes are the same as those in Example 1. The specific preparation method is as follows:

[0070] 1) dissolving 222 g of paraformaldehyde in 378 g of water, adjusting the pH to 8.5 with a 30% sodium hydroxide aqueous solution, heating the solution under heating conditions, stirring the solution at a stirring rate of 200 rpm, and when the temperature rises to 38° C., adding the first portion of urea (207.27 g), keeping the temperature for 20 min, to obtain a first reaction solution;

[0071] 2) After the first reaction solution is heated to 88° C., a 15% formic acid solution is used to adjust the pH value to 4.8, and when the viscosity of the solution reaction solution increases to 45 mPa·s, a second reaction solution is obtained;

[0072] 3) adjusting the pH value of the second reaction solution to 6.0 with a 30% sodium hydroxide aqueous solution, adding 107.73 g of the second portion of urea, and obtaining a third reaction solution when the viscosity of the reaction solution increases to 50 mPa·s;

[0073] 4) adjusting the pH of the third reaction solution to 7.5 with a 30% sodium hydroxide aqueous solution and cooling the solution to 80° C., adding 70.91 g of the third portion of urea, and keeping the temperature for 15 minutes to obtain a fourth reaction solution;

[0074] 5) The temperature of the fourth reaction liquid was lowered to 67° C., 45.82 g of the fourth portion of urea was added, the mixture was kept warm for 15 min, and the mixture was cooled to 40° C. to obtain a urea-formaldehyde resin adhesive.

[0075] Comparative Example 2

[0076] The difference between the adhesive of Comparative Example 2 and Example 1 is that the preparation method does not include step (2) and step (3), that is, the soy protein source solution is not subjected to enzymatic hydrolysis and ultrasonic treatment, and the other steps are the same as those of Example 1.

[0077] Comparative Example 3

[0078] Compared with the adhesive of Example 1, the difference between Comparative Example 3 and the adhesive of Example 1 is that there is no step (2) in the preparation method, that is, the soy protein source solution is not subjected to ultrasonic treatment, and the other steps are the same as those of Example 1.

[0079] Comparative Example 4

[0080] The difference between the adhesive of Comparative Example 4 and Example 1 is that the order of steps (2) and (3) in the preparation method is exchanged, that is, the soy protein source solution is first subjected to ultrasonic treatment and then to enzymatic treatment, and the other steps are the same as those of Example 1.

[0081] Comparative Example 5

[0082] The difference between Comparative Example 5 and the adhesive of Example 4 is that in step (2), the biological enzymes used include 0.1 g of acid protease, 0.1 g of cellulase and 0.1 g of laccase.

[0083] Effect verification

[0084] 1. Adhesive property testing

[0085] (1) Experimental subjects: the adhesives of Examples 1-4 and Comparative Examples 1-5 above.

[0086] (2) Test items: solid content, viscosity, pH, curing time and free formaldehyde content of the adhesive.

[0087] The characteristics of the above groups of adhesives were tested according to the testing methods specified by the state / industry. The test results are shown in Table 1 below.

[0088] Table 1 Test results of adhesive properties of each group

[0089]

[0090]

[0091] As can be seen from Table 1, the adhesive properties of Examples 1-4 are significantly better than those of Comparative Examples 1-5, indicating that the modified soy protein prepared by the present invention can effectively modify urea-formaldehyde resin and improve the quality and environmental friendliness of urea-formaldehyde resin.

[0092] 2. Performance testing of fiberboard after adhesive application

[0093] (1) The adhesives of Examples 1-4 and Comparative Examples 1-5 were pressed in the same manner to obtain fiberboards, the fiberboards having a thickness of 12 mm and a density of 780 kg / m 3 .

[0094] (2) Test items: formaldehyde emission, internal bonding strength and 24h water absorption thickness expansion rate of fiberboard.

[0095] (3) Test method: The method specified in the national standard GB / T17657-2022.

[0096] The test results are shown in Table 2 below.

[0097] Table 2 Performance test results of each group of fiberboard

[0098] Group Formaldehyde emission, mg / 100g Internal bonding strength, MPa 24h water absorption thickness expansion rate, % Example 1 3.7 0.85 6.7 Example 2 4.6 0.70 7.4 Example 3 4.0 0.75 7.0 Example 4 3.5 0.89 6.2 Comparative Example 1 7.5 0.6 9.0 Comparative Example 2 5.6 0.63 8.2 Comparative Example 3 5.0 0.67 7.7 Comparative Example 4 5.1 0.66 7.9 Comparative Example 5 5.0 0.68 7.6

[0099] It can be seen from Table 2 that the performance of the fiberboards of Examples 1-4 is significantly better than that of Comparative Examples 1-5, indicating that the use of the adhesives of Examples 1-4 of the present invention can significantly improve the bonding performance and waterproof performance of urea-formaldehyde resin.

[0100] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A soybean protein modified high performance environmentally friendly urea-formaldehyde resin adhesive, It is characterized in that The invention comprises the following components: modified soybean protein solution, paraformaldehyde and urea; The preparation method of the modified soybean protein solution comprises the following steps: (1) Dissolving: dissolving the soy protein isolate in water to obtain a soy protein source solution; (2) Enzymatic hydrolysis: adding biological enzymes to the soy protein source solution, and adjusting the pH of the solution to alkaline for enzymatic hydrolysis to obtain an enzymatic hydrolysis solution; (3) Ultrasound: The enzymatic hydrolysis solution is subjected to ultrasonic treatment to obtain the modified soy protein solution.

2. A soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive according to claim 1, It is characterized in that The added mass of the soy protein source solution accounts for 0.5-1.0% of the total mass of the soy protein modified urea-formaldehyde resin adhesive.

3. A soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive according to claim 1, It is characterized in that In step (1), the protein content in the soy protein isolate is 70-80%, and the mass concentration of the soy protein source solution is 5-10%.

4. A soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive according to claim 1, It is characterized in that In step (2), the biological enzyme is one or more of papain, laccase, and cellulase.

5. A soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive according to claim 4, It is characterized in that In step (2), the biological enzymes include papain, cellulase and laccase, and the mass ratio of the papain, the cellulase and the laccase is 1:1:

1.

6. A soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive according to claim 1, It is characterized in that In step (2), the added amount of the biological enzyme is 0.1%-0.3% of the mass of the soybean protein source solution.

7. A soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive according to claim 1, It is characterized in that In step (2), the enzymatic hydrolysis has a pH of 8.0-8.5, a temperature of 40-60° C., and a time of 1-3 h.

8. A soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive according to claim 1, It is characterized in that In step (3), the power of the ultrasound is 360W, the temperature is room temperature, and the time is 10-30min.

9. A method for preparing a soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive according to any one of claims 1 to 8, It is characterized in that The following steps are involved: S1: adding paraformaldehyde to the modified soy protein solution, adjusting the pH to 8.0-8.5, heating to 38-40° C. for reaction, and then adding the first portion of urea for reaction to obtain a first reaction solution; S2: After heating the first reaction solution to 86-90° C., keeping the temperature for 18-22 min, adjusting the pH value to 4.8-5.0, and when the viscosity increases to 45-50 mPa·, obtaining the second reaction solution; S3: adjusting the pH of the second reaction solution to 5.8-6.0, then adding the second portion of urea, and when the viscosity thereof increases to 50-55 mPa·s, obtaining a third reaction solution; S4: adjusting the pH of the third reaction solution to 7.0-7.5 and cooling the solution to 75-80° C., then adding a third portion of urea to react to obtain a fourth reaction solution; S5: adjusting the temperature of the fourth reaction liquid to 65-70° C., then adding a fourth portion of urea to react, and cooling after the reaction to obtain the soy protein modified environmentally friendly urea-formaldehyde resin adhesive.

10. A method for preparing a soybean protein modified high-performance environmentally friendly urea-formaldehyde resin adhesive according to claim 9, It is characterized in that The mass ratio of the first portion of urea, the second portion of urea, the third portion of urea and the fourth portion of urea is (4.3-5.0): (2.0-2.5): (1.2-1.8): (0.9-1.2).

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