Water-resistant vegetable protein adhesive as well as preparation method and application thereof

Abstract

The invention discloses a water-resistant vegetable protein adhesive as well as a preparation method and application thereof. The water-resistant vegetable protein adhesive is prepared from the following raw materials: cake meal, cake meal protein isolate, choline alfoscerate and a modifier, the modifier is prepared from the following raw materials: urea and a sulfamic acid compound. According to the water-resistant vegetable protein adhesive provided by the invention, separation of cakes and meal is avoided, and meanwhile, the flame retardance, the antibacterial property and the mechanical property of an artificial board are improved.

Description

Technical Field

[0001] The invention belongs to a plate modifier, and specifically relates to a water-resistant plant protein adhesive and a preparation method and application thereof. Background Art

[0002] Wood and bamboo materials, such as poplar plantations, have the advantages of high yield and fast growth, but their low wood density, poor mechanical strength, low surface hardness, low wear resistance and poor corrosion resistance limit their use. Compared with natural forest wood, their material properties and decorative properties are far different. Therefore, it is extremely necessary to chemically modify fast-growing forest wood. At present, the use of chemical raw materials to prepare wood adhesives has become the mainstream of the industry, especially formaldehyde-based resins (such as urea-formaldehyde resin (UF), melamine-formaldehyde resin (MF), phenolic resin (PF), etc.), which account for about 90% of the proportion in wood adhesives due to excellent bonding strength and water resistance and weather resistance. However, a fatal defect of "formaldehyde-based" resins is the harm of formaldehyde to the human body and the environment. With the continuous improvement of domestic economic level and people's quality of life, especially under the background conditions of increasingly stringent laws and regulations, the disadvantages of "formaldehyde-based" resin adhesives have attracted more and more attention and concern from people, and the development of non-toxic, green and environmentally friendly new wood adhesives has far-reaching significance for the development of the industry. With the continuous improvement of people's environmental awareness and the continuous improvement of the environmental protection requirements of artificial boards, environmentally friendly biomass-based adhesives such as plant protein adhesives, lignin adhesives, tannin adhesives and starch adhesives have received more and more attention. At present, the raw materials for preparing protein-based adhesives are mainly plant proteins and plant protein cakes. The extraction process of plant protein isolates is complicated and expensive, which limits industrial applications. Therefore, in the production of artificial boards, protein-based adhesives are mostly prepared from plant protein cakes with relatively low protein content and low cost. In order to improve the water resistance of protein-based adhesives, at the same time, most of the existing preparation methods are based on the modification of protein molecules in plant protein cakes, and less on the modification of carbohydrates. The traditional method requires the separation of cakes and the separation of components that are difficult to react (cellulose, hemicellulose and lignin) from the protein components before the protein components can be used for subsequent glue making processes. The process is complicated and difficult to achieve large-scale utilization.

[0003] In summary, it is urgent to develop a water-resistant plant protein adhesive with a simple preparation process. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a water-resistant plant protein adhesive, which avoids the separation of cake and dregs and improves the flame retardancy, antibacterial property and mechanical properties of artificial boards.

[0005] According to a first aspect of the present invention, a water-resistant plant protein adhesive is provided. The raw materials for preparing the water-resistant plant protein adhesive include: cake, cake protein isolate, choline glycerol and a modifier;

[0006] The raw materials for preparing the modifier include urea and aminosulfonic acid compounds.

[0007] According to some embodiments of the present invention, the aminosulfonic acid compound includes at least one of aminosulfonic acid and p-aminobenzenesulfonic acid.

[0008] According to the embodiments of the first aspect of the present invention, there are at least the following beneficial effects:

[0009] In the traditional process, the cake needs to be separated, and the components that are difficult to react (cellulose, hemicellulose and lignin) must be separated from the protein component before the protein component can be used for the subsequent glue making process. Because cellulose, hemicellulose and lignin have low reaction activity, they cannot participate in the subsequent reaction. In the present invention, in the above-mentioned preparation raw materials, the aminosulfonic acid compound reacts with the hydroxyl groups of each component in the cake (mainly cellulose, hemicellulose, lignin and protein), thereby enhancing the physical and chemical properties of the cake, improving the functional characteristics of the cake and making the subsequent reaction more effective; the choline phosphate degrades and dissolves the protein components in the cake, increasing the availability and biocompatibility of the cake separated protein, and the role of the choline phosphate is to react with the protein to reconstruct the protein and improve the performance of the adhesive.

[0010] Specifically, the aminosulfonic acid compound and urea react with the cellulose, hemicellulose and lignin in the cake in the first step, and the three elements can be depolymerized and converted into water-soluble substances. After adding choline glycerol, the three elements are converted into main water-soluble substances due to the treatment of step S1, so that the coated protein component is fully exposed, which is conducive to the further treatment of choline glycerol (if there is no treatment of step S1, only choline glycerol or related methods are used for treatment, the protein component in the cake cannot be fully treated and reconstructed; at the same time, the treatment of step S1 converts and separates the three elements, grafts them, and protects the three elements from participating in subsequent reactions, thereby fully retaining the reaction activity).

[0011] According to some embodiments of the present invention, the cake protein isolate includes at least one of tung oil cake protein, camellia oil cake protein, soybean protein and litsea cubeba cake protein.

[0012] The cake protein isolate has high reactivity and can undergo condensation reaction with the hydroxyl and amino groups in the protein, thereby reducing the water absorption and hygroscopicity of the adhesive and enhancing the mechanical properties of the cured adhesive.

[0013] According to an embodiment of the second aspect of the present invention, a method for preparing a water-resistant plant protein adhesive is proposed, comprising the following steps:

[0014] S1. dispersing the modifier and heating and mixing the cake at a pH value of 5.0 to 6.0 to obtain component A;

[0015] S2. At a pH value of 10 to 11, heating and mixing choline glycerol and component A, and removing impurities to obtain a modified cake;

[0016] S3. The modified cake and cake protein isolate are mixed and reacted to obtain a modified plant protein-based adhesive.

[0017] In step S1, the pH value is controlled at 5.0-6.0. In a weak acid environment, urea and aminosulfonic acid compounds can better react with the hydroxyl groups on lignin, cellulose and hemicellulose; in a weak acid environment, the protein components are protected from premature excessive degradation. If the pH value is not within this range, the reaction cannot be promoted, and the inhibition of the reaction can also be avoided.

[0018] According to some embodiments of the present invention, in step S1, the method for preparing the modifier comprises:

[0019] After mixing the aminosulfonic acid compound and urea, heat to 120-135°C for reaction.

[0020] According to some embodiments of the present invention, in step S2, the molar ratio of the cake to the modifier is 1:10-20.

[0021] According to some embodiments of the present invention, in step S1, the heating temperature is 80-90°C.

[0022] According to some embodiments of the present invention, in step S2, the heating temperature is 120-130°C.

[0023] According to some embodiments of the present invention, in step S2, the mass concentration of the cake protein isolate is 5-10%wt.

[0024] According to an embodiment of the third aspect of the present invention, a man-made board is provided, wherein the raw materials for preparing the man-made board include the water-resistant plant protein adhesive mentioned above. DETAILED DESCRIPTION

[0025] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below by reference are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0026] The meal proteins in the examples are all commercially available.

[0027] Example 1

[0028] This embodiment discloses a method for preparing a water-resistant plant protein adhesive, and the specific steps are as follows:

[0029] S1. Aminosulfonic acid and urea are mixed uniformly in a mass ratio of 1:2, put into a flask, and stirred continuously. After heating in an oil bath to 120°C and reacting until the liquid is uniform, the mixture is blended with water in a mass ratio of 0.5:1.5. After fully dissolved, the pH value of the blended solution is adjusted to between 5.0 and 6.0 using oxalic acid to obtain a modifier, and then the cake and the obtained modifier are mixed in a mass ratio of 1:10. Under heating conditions (80°C), the mixture is rapidly stirred for 6 hours to obtain a mixture, and urea is added at 0.1wt% of the mixture to terminate the reaction to obtain component A;

[0030] S2. Component A is adjusted to a pH value between 10 and 11 using aqueous ammonia to obtain a mixed system, 0.5 wt% of choline glycerol is added to the mixed system, the mixture is stirred evenly, and then the mixture is stirred rapidly for 3 h under heating conditions (120° C.). After sufficient reaction, the heating is stopped, the mixture is rapidly cooled to room temperature, centrifuged, and dialyzed using a dialysis tube and deionized water to remove excess modifier, and then the solid component is obtained by centrifugation and freeze-drying to obtain a modified cake;

[0031] S3. The modified cake was mixed with water to obtain a 10%wt modified cake mixture, and the mixture was evenly mixed to obtain a mixture. Tung oil cake protein was added according to 0.5wt% of the mixed system, and stirring was continued until uniform to obtain a modified plant protein-based adhesive.

[0032] Example 2

[0033] This embodiment discloses a method for preparing a water-resistant plant protein adhesive, and the specific steps are as follows:

[0034] S1. Aminosulfonic acid and urea are mixed uniformly in a mass ratio of 1:3, put into a flask, and stirred continuously. After heating in an oil bath to 120°C and reacting until the liquid is uniform, the mixture is blended with water in a ratio of 0.5:1.5. After being fully dissolved, the pH value of the blended solution is adjusted to between 5.0 and 6.0 using oxalic acid to obtain a modifier. Then, the cake and the obtained modifier are mixed in a ratio of 1:10. After rapid stirring for 6 hours under heating conditions (80°C), an appropriate amount of urea is added to terminate the reaction to obtain component A.

[0035] S2. After adjusting the pH value of component A to between 10 and 11 with ammonia water, 0.5% wt of choline glycerophosphate was added, the mixture was mixed and stirred evenly, and then the mixture was rapidly stirred for 3 hours under heating conditions (120° C.). After sufficient reaction, the heating was stopped, the mixture was rapidly cooled to room temperature, centrifuged, and dialyzed with a dialysis tube and deionized water to remove excess modifier, and then the solid component was obtained by centrifugation and freeze-drying to obtain a modified cake;

[0036] S3. The modified cake was mixed with water to obtain a 10% wt modified cake mixture, and after mixing evenly, 5% wt of tung oil cake protein was added, and stirring was continued until uniform to obtain a modified plant protein-based adhesive.

[0037] Example 3

[0038] This embodiment discloses a method for preparing a water-resistant plant protein adhesive, and the specific steps are as follows:

[0039] S1. Aminosulfonic acid and urea are mixed uniformly in a mass ratio of 1:5, put into a flask, and stirred continuously. After heating to 120°C in an oil bath and reacting until the liquid is uniform, the mixture is blended with water in a ratio of 0.5:1.5. After being fully dissolved, the pH value of the blended solution is adjusted to between 5.0 and 6.0 using oxalic acid to obtain a modifier. Then, the cake and the obtained modifier are mixed in a ratio of 1:10. After rapid stirring for 6 hours under heating conditions (80°C), an appropriate amount of urea is added to terminate the reaction to obtain component A.

[0040] S2. After adjusting the pH value of component A to between 10 and 11 with ammonia water, 0.5% wt of choline glycerophosphate was added, the mixture was mixed and stirred evenly, and then the mixture was rapidly stirred for 3 hours under heating conditions (120° C.). After sufficient reaction, the heating was stopped, the mixture was rapidly cooled to room temperature, centrifuged, and dialyzed with a dialysis tube and deionized water to remove excess modifier, and then the solid component was obtained by centrifugation and freeze-drying to obtain a modified cake;

[0041] S3. The modified cake was mixed with water to obtain a 10% wt modified cake mixture, and after mixing evenly, 5% wt of tung oil cake protein was added, and stirring was continued until uniform to obtain a modified plant protein-based adhesive.

[0042] Example 4

[0043] This embodiment discloses a method for preparing a water-resistant plant protein adhesive, and the specific steps are as follows:

[0044] S1. Aminosulfonic acid (CAS No.: 226-218-8) and urea are mixed uniformly in a mass ratio of 1:2, put into a flask, and continuously stirred. After heating to 120°C in an oil bath and reacting until the liquid is uniform, the mixture is blended with water in a mass ratio of 0.5:1.5. After being fully dissolved, the pH value of the blended solution is adjusted to between 5.0 and 6.0 using oxalic acid to obtain a modifier. Then, the cake and the obtained modifier are mixed in a mass ratio of 1:10. After rapid stirring for 6 hours under heating conditions (80°C), an appropriate amount of urea is added to terminate the reaction to obtain component A.

[0045] S2. After adjusting the pH value of component A to between 10 and 11 with ammonia water, 0.2% wt of choline glycerol was added, the mixture was mixed and stirred evenly, and then the mixture was rapidly stirred for 3 hours under heating conditions (120° C.). After sufficient reaction, the heating was stopped, the mixture was rapidly cooled to room temperature, centrifuged, and dialyzed with a dialysis tube and deionized water to remove excess modifier, and then the solid component was obtained by centrifugation and freeze-drying to obtain a modified cake;

[0046] S3. The modified cake was mixed with water to obtain a 10% wt modified cake mixture, and after mixing evenly, 5% wt of tung oil cake protein was added, and stirring was continued until uniform to obtain a modified plant protein-based adhesive.

[0047] Example 5

[0048] This embodiment discloses a method for preparing a water-resistant plant protein adhesive, and the specific steps are as follows:

[0049] S1. Aminosulfonic acid and urea are mixed uniformly in a mass ratio of 1:2, put into a flask, and stirred continuously. After heating in an oil bath to 120°C and reacting until the liquid is uniform, the mixture is blended with water in a ratio of 0.5:1.5. After being fully dissolved, the pH value of the blended solution is adjusted to between 5.0 and 6.0 using oxalic acid to obtain a modifier. Then, the cake and the obtained modifier are mixed in a ratio of 1:10. After rapid stirring for 6 hours under heating conditions (80°C), an appropriate amount of urea is added to terminate the reaction to obtain component A.

[0050] S2. After adjusting the pH value of component A to between 10 and 11 with ammonia water, 0.9% wt of choline glycerophosphate was added, the mixture was mixed and stirred evenly, and then the mixture was rapidly stirred for 3 hours under heating conditions (120° C.). After sufficient reaction, the heating was stopped, the mixture was rapidly cooled to room temperature, centrifuged, and dialyzed with a dialysis tube and deionized water to remove excess modifier, and then the solid component was obtained by centrifugation and freeze-drying to obtain a modified cake;

[0051] S3. The modified cake was mixed with water to obtain a 10% wt modified cake mixture, and after mixing evenly, 5% wt of tung oil cake protein was added, and stirring was continued until uniform to obtain a modified plant protein-based adhesive.

[0052] Comparative Example 1

[0053] This comparative example discloses a method for preparing a water-resistant plant protein adhesive. The difference between this comparative example and Example 1 is that p-toluenesulfonic acid is used instead of the aminosulfonic acid compound, and the other conditions are the same.

[0054] Comparative Example 2

[0055] This comparative example discloses a method for preparing a water-resistant plant protein adhesive. The difference between this comparative example and Example 1 is that aminosulfonic acid is not added, and the other conditions are the same.

[0056] Comparative Example 3

[0057] This comparative example discloses a method for preparing a water-resistant plant protein adhesive. The difference between this comparative example and Example 1 is that choline chloride is used instead of choline glycerophosphate, and the other conditions are the same.

[0058] Comparative Example 4

[0059] This comparative example discloses a method for preparing a water-resistant plant protein adhesive. The difference between this comparative example and Example 1 is that in step S1, no adjustment is made to the pH value, and the other conditions are the same.

[0060] Comparative Example 5

[0061] This comparative example discloses a method for preparing a water-resistant plant protein adhesive. The difference between this comparative example and Example 1 is that in step S2, no adjustment is made to the pH value, and the other conditions are the same.

[0062] Comparative Example 6

[0063] This comparative example discloses a method for preparing a water-resistant plant protein adhesive. The difference between this comparative example and Example 1 is that the pH value is not adjusted in steps S1 and S2, and the other conditions are the same.

[0064] Comparative Example 7

[0065] This comparative example discloses a method for preparing a water-resistant plant protein adhesive. The difference between this comparative example and Example 1 is that steps S1 and S2 are interchanged, and the other conditions are the same.

[0066] Comparative Example 8

[0067] This comparative example discloses a method for preparing a water-resistant plant protein adhesive. The difference between this comparative example and Example 1 is that there is no step S1, and the other conditions are the same.

[0068] Comparative Example 9

[0069] This comparative example discloses a method for preparing a water-resistant plant protein adhesive. The difference between this comparative example and Example 1 is that there is no step S2, and the other conditions are the same.

[0070] Comparative Example 10

[0071] This embodiment discloses a method for preparing a water-resistant plant protein adhesive, and the specific steps are as follows:

[0072] S1. P-aminobenzenesulfonic acid and urea are mixed uniformly in a mass ratio of 1:2, put into a flask, and continuously stirred. After heating to 120°C in an oil bath and reacting until the liquid is uniform, the mixture is blended with water in a ratio of 0.5:1.5. After being fully dissolved, the pH value of the blended solution is adjusted to between 5.0 and 6.0 using oxalic acid to obtain component A. The cake is then mixed with component A in a ratio of 1:10. After rapid stirring for 6 hours under heating conditions (80°C), an appropriate amount of urea is added to terminate the reaction to obtain component B.

[0073] S2. After adjusting the pH value of component B to between 10 and 11 with ammonia water, 0.5% wt of choline glycerophosphate was added, mixed and stirred evenly, and then stirred rapidly for 3 hours under heating conditions (120° C.). After sufficient reaction, heating was stopped, and the mixture was rapidly cooled to room temperature and centrifuged and then dialyzed with a dialysis tube and deionized water to remove excess modifier. The solid component was obtained by centrifugation and freeze-drying to obtain a modified cake;

[0074] S3. The modified cake was mixed with water to obtain a 10% wt modified cake mixture, and after mixing evenly, 5% wt of tung oil cake protein was added, and stirring was continued until uniform to obtain a modified plant protein-based adhesive.

[0075] Comparative Example 11

[0076] This comparative example discloses a method for preparing a water-resistant plant protein adhesive. The difference between this comparative example and Example 1 is that the pH value in step S1 is between 3 and 4, and the other conditions are the same.

[0077] Comparative Example 12

[0078] This comparative example discloses a method for preparing a water-resistant plant protein adhesive. The difference between this comparative example and Example 1 is that the pH value in step S1 is between 10 and 11, and the other conditions are the same.

[0079] Test Example 1

[0080] This test example tests the performance of the adhesives obtained in the examples and comparative examples when applied to the board, and the specific steps are as follows:

[0081] ① Preparation of thin bamboo particleboard:

[0082] Raw materials: bamboo shavings or wood shavings.

[0083] Thin wood shavings refer to boards with a thickness of 2 to 8 mm, with a raw material length of 0.8 to 4 mm, an aspect ratio of 15 mm, and a thickness of 0.2 to 0.25 mm. This board is generally produced by rolling instead of flat pressing. This board can replace plywood as furniture bottom board, partition board, and can also be used as the core board of plywood.

[0084] Hot pressing conditions: hot pressing temperature 120-135°C, hot pressing time 180-300s, hot pressing pressure 0.8-1.2MPa.

[0085] Table 1 Adhesive storage stability test (15-day storage test)

[0086]

[0087] Example 5 increases the amount of choline glycerol added, which allows the cake protein to be fully depolymerized and reconstructed in the S2 treatment, but also causes excessive depolymerization and reconstruction of the protein components, which significantly increases the viscosity of the adhesive product compared to other examples.

[0088] The p-toluenesulfonic acid in Comparative Example 1 cannot react with the three major elements (cellulose, lignin and hemicellulose), so the cellulose, hemicellulose and lignin in the cake do not change at all, and they cannot form a homogeneous emulsion in the aqueous solution, so precipitation and stratification will occur in the storage test.

[0089] In step S1 of comparative example 2, aminosulfonic acid is not added, so that the simple adjustment of pH value cannot react with the cellulose, hemicellulose and lignin in the cake, resulting in the inability to convert the three major elements into major water-soluble substances. Therefore, in the subsequent steps, cellulose, hemicellulose and lignin exist as water-insoluble particulate matter in the emulsion system of the adhesive. After a certain period of storage, the cellulose, hemicellulose and lignin particles settle, resulting in stratification.

[0090] Comparative Example 3 Choline chloride is unstable in an alkaline environment and is easily degraded. It cannot react with the protein components in the cake. Since the protein components in the cake are relatively stable and generally have low water solubility, the cake protein particles that have not been treated in any way will also settle and stratify as the storage time increases.

[0091] In comparative example 4, step S1 does not adjust the pH value, and the reaction between aminosulfonic acid and the three elements needs to be carried out in a weakly acidic environment, and H +, it is easy to degrade in an acidic environment to promote the reaction; however, if the acidity is too low, the reaction cannot proceed smoothly, because the acid treatment with too low pH value will cause a certain degree of carbonization on the surface of the cellulose and hemicellulose particles, hindering the infiltration and deep reaction of the modifier to the cake particles, so the cellulose, hemicellulose and lignin particles in the cake are not completely reacted and cannot be converted into water-soluble substances. They will always exist as water-insoluble particulate matter in subsequent reactions and adhesive emulsion systems, and will settle and stratify during long-term storage; excessive alkalinity will lead to excessive degradation of the protein structure, and some of it may be degraded into amino acid structure or further dehydrated and carbonized, so water-insoluble particulate matter is formed, which gradually settles and stratifies during long-term storage.

[0092] In step S2 of comparative example 5, no adjustment is made to the pH value. The reaction of choline glycerol to protein requires optimal treatment and highest reaction activity in an alkaline environment. Therefore, the protein component in the cake cannot be depolymerized and reconstructed in step S2. Its water solubility is poor, and it is difficult to fully dissolve and mix with the adhesive emulsion system. Long-term storage will cause sedimentation and stratification.

[0093] In comparative example 6, no adjustment was made to the pH value in steps S1 and S2, resulting in the inability of aminosulfonic acid and choline glycerol to transform the three major element components and the protein component in S1 and S2, maintaining the water-insoluble granular state, and causing sedimentation and stratification during long-term storage.

[0094] In Comparative Example 7, the processing steps were replaced. Due to the coating and steric hindrance effects of cellulose, hemicellulose and lignin in the cake, the protein in the cake was not completely treated by choline glycerophosphate in the first step, and the reaction efficiency was low. Most of the protein did not complete the depolymerization and reconstruction reactions and remained in the state of water-insoluble particles, which made it impossible to completely dissolve and mix in the adhesive emulsion system, and sedimentation and stratification occurred after long-term storage.

[0095] In Comparative Example 8, since there is no S1 step, cellulose, hemicellulose and lignin remain in the state of water-insoluble particles, so that they cannot be completely dissolved and mixed in the adhesive emulsion system, and sedimentation and stratification occur after long-term storage.

[0096] In Comparative Example 9, since there is no S2 step, the cake protein component remains in the state of water-insoluble particles with poor reactivity, so that it cannot be completely dissolved and mixed in the adhesive emulsion system, and sedimentation and stratification occur after long-term storage.

[0097] The p-aminobenzenesulfonic acid of comparative example 10 has weak reactivity with the three major elemental hydroxyl groups. At the same time, p-aminobenzenesulfonic acid has a large molecular structure and poor water solubility. Due to large steric hindrance and poor solubility during the reaction, even if there is a certain degree of reaction, it cannot achieve full reaction, so that cellulose, hemicellulose and lignin react insufficiently and incompletely, and some of them remain in the state of water-insoluble particles, and sedimentation and stratification occur after long-term storage.

[0098] The pH value in step S1 in Comparative Example 11 is between 3 and 4. Acid treatment at too low a pH value will cause a certain degree of carbonization on the surface of the cellulose hemicellulose particles, hindering the infiltration and deep reaction of the modifier on the cake particles. As a result, the cellulose, hemicellulose and lignin particles in the cake do not react completely and cannot be converted into water-soluble substances. They remain as water-insoluble particulate matter in subsequent reactions and adhesive emulsion systems, and sedimentation and stratification occur during long-term storage.

[0099] Comparative Example 12: Aminosulfonic acid is prone to reaction and transformation in alkaline conditions and cannot react with the three major elements, so cellulose, hemicellulose and lignin remain in the state of water-insoluble particles, cannot be dissolved and blended in the adhesive emulsion system, and are prone to sedimentation and stratification after long-term storage.

[0100] The test results are shown in Table 2:

[0101] Table 2 Performance test of board modifier in bamboo and wood thin particle board

[0102]

[0103]

[0104] Example 5 increases the amount of choline glycerol added, which allows the cake protein to be fully depolymerized and reconstructed in the S2 treatment, but it also causes excessive depolymerization and reconstruction of the protein components, resulting in a decrease in some indicators of physical and mechanical properties compared to other examples.

[0105] The p-toluenesulfonic acid in Comparative Example 1 cannot react with the three major elements (cellulose, lignin and hemicellulose), so the cellulose, hemicellulose and lignin in the cake do not react at all, and they cannot form a homogeneous emulsion in the aqueous solution. In addition, the cellulose, hemicellulose and lignin particles are purely physically filled in the subsequent adhesive curing reaction, and no covalent bonds are formed, so the mechanical properties are poor. At the same time, the reason for the poor LOI is that although related substances are added, they are unevenly distributed in the emulsion system due to no reaction, resulting in a low LOI value.

[0106] In comparative example 2, no aminosulfonic acid is added and the cellulose, hemicellulose and lignin in the cake cannot react, resulting in the inability to convert the three major elements into major water-soluble substances. Therefore, the cellulose, hemicellulose and lignin are still in the state of water-insoluble particles and cannot participate in the subsequent curing reaction. No covalent bonds are formed between the substances, resulting in poor physical and mechanical properties.

[0107] Comparative Example 3 Choline chloride is unstable in an alkaline environment, easily degraded, and unable to further react with protein, so that adjusting the pH value in S2 has a negative effect on it. As a result, the protein in the cake cannot be depolymerized and reconstructed to form active reaction substances, and it is also water-soluble, making the cake protein component easy to settle in the emulsion system, unable to be evenly distributed, and unable to participate in the subsequent curing reaction of various substances, unable to form a cross-linked network, resulting in poor physical and mechanical properties of the board.

[0108] In comparative example 4, step S1 does not adjust the pH value, and the reaction between aminosulfonic acid and the three elements needs to be carried out in a weakly acidic environment, and H + , it is easy to degrade in an acidic environment to promote the reaction; however, if the acidity is too low, the reaction cannot proceed smoothly. Excessive acid treatment will cause a certain degree of carbonization on the surface of the cellulose and hemicellulose particles, hindering the infiltration and full reaction of the modifier to the cake particles. As a result, the cellulose, hemicellulose and lignin particles in the cake components do not react fully, remain in a water-insoluble particle state, and cannot participate in the subsequent curing reaction, affecting the formation of the cross-linked network structure, resulting in poor physical and mechanical properties of the board.

[0109] In comparative example 5, step S2 does not make any adjustment to the pH value. The reaction of choline glycerol to protein requires an alkaline environment to achieve optimal treatment and the highest reaction activity. Therefore, the protein component in the cake cannot be depolymerized and reconstructed in step S2. Its water solubility is poor, which affects the formation of the cross-linked network structure, resulting in poor physical and mechanical properties of the board.

[0110] In comparative example 6, no adjustment is made to the pH value in steps S1 and S2, resulting in the inability of aminosulfonic acid and choline glycerol to convert the three major element components and the protein component in S1 and S2. Therefore, in the final curing reaction, the components cannot be connected by covalent bonds, and no cross-linked network structure is formed, resulting in poor physical and mechanical properties of the board.

[0111] In Comparative Example 7, the processing steps were replaced. Due to the coating and steric hindrance effects of cellulose, hemicellulose and lignin in the cake, the protein in the cake was not completely treated by choline glycerophosphate in the first step, and the reaction efficiency was low. Most of the protein did not complete the depolymerization and reconstruction reactions and could not participate in the subsequent curing reaction, which affected the formation of the cross-linked network structure and resulted in poor physical and mechanical properties of the board.

[0112] In Comparative Example 8, since there is no S1 step, cellulose, hemicellulose and lignin remain in the state of water-insoluble particles and cannot react with other components in subsequent reactions to form covalent bonds and affect the formation of a cross-linked network structure.

[0113] In Comparative Example 9, since there is no S2 step, the cake protein component remains in a water-insoluble particle state with poor reactivity and cannot fully and effectively react with other components in the subsequent reaction, affecting the formation of the cross-linked network structure.

[0114] The p-aminobenzenesulfonic acid of comparative example 10 has weak reactivity with the three major hydroxyl groups. At the same time, p-aminobenzenesulfonic acid has a large molecular structure and poor water solubility. Due to large steric hindrance and poor solubility during the reaction, even if there is a certain degree of reaction, it cannot achieve full reaction, so that cellulose, hemicellulose and lignin react insufficiently and incompletely, and some of them remain in the state of water-insoluble particles. In the subsequent reaction, they cannot react with other components to form covalent bonds and affect the formation of a cross-linked network structure.

[0115] In Comparative Example 11, the pH value of step S1 is between 3 and 4. Acid treatment at too low a pH value will cause a certain degree of carbonization on the surface of the cellulose hemicellulose particles, hindering the infiltration and deep reaction of the modifier on the cake particles. As a result, the cellulose, hemicellulose and lignin particles in the cake do not react completely and cannot be converted into water-soluble substances. They remain as water-insoluble particulate matter in subsequent reactions and the adhesive emulsion system, hindering the smooth progress of the reaction.

[0116] Comparative Example 12: Aminosulfonic acid is prone to reaction transformation in alkaline conditions and cannot react with the three major elements. It is also unable to react with other components in subsequent reactions to form covalent bonds and affect the formation of a cross-linked network structure.

[0117] The embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A water-resistant plant protein adhesive, characterized in that: The raw materials for preparing the water-resistant plant protein adhesive include: cake, cake protein isolate, choline glycerol and a modifier; The raw materials for preparing the modifier include urea and aminosulfonic acid compounds.

2. The water-resistant plant protein adhesive according to claim 1, characterized in that: The aminosulfonic acid compound includes aminosulfonic acid.

3. The water-resistant plant protein adhesive according to claim 1, characterized in that: The cake protein isolate comprises at least one of tung oil cake protein, camellia oil cake protein, soybean protein and litsea cubeba cake protein.

4. A method for preparing a water-resistant plant protein adhesive as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: S1. dispersing the modifier and heating and mixing the cake at a pH value of 5.0 to 6.0 to obtain component A; S2. At a pH value of 10 to 11, heating and mixing choline glycerol and component A, and removing impurities to obtain a modified cake; S3. The modified cake and cake protein isolate are mixed and reacted to obtain a modified plant protein-based adhesive.

5. The preparation method according to claim 4, characterized in that: In step S1, the preparation method of the modifier comprises: After mixing the aminosulfonic acid compound and urea, heat to 120-135°C for reaction.

6. The preparation method according to claim 4, characterized in that: In step S2, the molar ratio of the cake to the modifier is 1:10-20.

7. The preparation method according to claim 4, characterized in that: In step S1, the heating temperature is 80-90°C.

8. The preparation method according to claim 4, characterized in that: In step S2, the heating temperature is 120-130°C.

9. The preparation method according to claim 4, characterized in that: In step S2, the mass concentration of the cake protein isolate is 5-10%wt.

10. A wood-based panel, characterized in that: The raw material for preparing the artificial board includes the water-resistant plant protein adhesive according to any one of claims 1 to 3.

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