Oxidized sugar modified bean flour adhesive as well as preparation method and application thereof

Abstract

The invention relates to the technical field of adhesive preparation, and particularly discloses an oxidized sugar modified bean flour adhesive as well as a preparation method and application thereof, and the adhesive is prepared from 20-30 parts of bean flour, 5-25 parts of oxidized sugar, 0.2-0.5 part of amino silicon dioxide and 0.6-3 parts of phytic acid. Adding bean flour into a sodium hydroxide solution, carrying out alkali treatment to dissolve the bean flour, adding sucrose into an ammonium persulfate solution, and carrying out a heating oxidation reaction to obtain an oxidized sugar solution; reacting PEI with nano silicon dioxide to obtain aminated silicon dioxide; and adding phytic acid, an oxidized sugar solution and aminated silicon dioxide into the bean flour solution, heating and uniformly stirring to obtain the water-retaining bean flour adhesive. The oxidation pond modified bean flour adhesive disclosed by the invention can be applied to wood plywood, is high in corner strength and water-resistant strength, and also has certain flame retardance; the used raw materials are vegetable protein beans, formaldehyde pollution is avoided, environmental protection and safety are achieved, resources are renewable, the preparation process is simple, the curing time is short, operation is convenient and fast, and the production efficiency is high.

Description

Technical Field

[0001] This invention belongs to the field of adhesive preparation technology, specifically relating to an oxidized sugar modified soybean flour adhesive with water retention, water resistance and flame retardancy, its preparation method and application. Background Technology

[0002] Although my country is a country with relatively scarce timber resources, its wood furniture industry has developed rapidly, driving the vigorous development of the engineered wood products industry. In 2022, my country's engineered wood products output reached 337 million cubic meters, firmly ranking as the world's largest producer, consumer, and trader of engineered wood products. The use of wood adhesives has also increased significantly. It is estimated that by 2024, the consumption of wood adhesives will reach US$73.8 billion. Currently, engineered wood product production mainly relies on formaldehyde-based synthetic resin adhesives, such as urea-formaldehyde resin, phenolic resin, and melamine-formaldehyde resin, which are inexpensive, fast-curing, and have high bonding strength. However, engineered wood products made with these adhesives release harmful formaldehyde during use, threatening human health and affecting indoor environmental safety; moreover, their raw materials largely depend on non-renewable petroleum resources. Therefore, to promote the green and sustainable development of the engineered wood products industry and meet the public's demand for a high-quality living environment, developing non-toxic, environmentally friendly, widely available, and renewable green biomass adhesives has become an important research hotspot in the field of wood adhesives.

[0003] Soybean flour (SF), as an agricultural byproduct, boasts advantages such as low cost, ease of modification, and abundant reactive functional groups, making it a potential alternative to formaldehyde resin adhesives in the preparation of engineered wood products. However, weak intermolecular interactions and inherent hydrophilicity result in low adhesive strength and poor water resistance for SF-based adhesives. Furthermore, water retention is also a crucial performance characteristic of SF-based adhesives. In plywood production, once the veneers are glued and assembled, they are transported to the hot press by factory transport vehicles, awaiting hot pressing. This transportation process takes considerable time. However, SF-based adhesives readily lose water within 0.5-1 hour, significantly reducing the bonding strength, production efficiency, and stability of the plywood. Therefore, developing SF-based adhesives with high water retention and water resistance presents a challenge.

[0004] Liu et al. developed a water-retaining, high-adhesion soybean flour adhesive by enriching soybean protein isolate (SPI) on boron nitride (BN) to form protein-functionalized BN nanosheets (BS) with tight hydrogen bonds. A synthesized epoxy hyperbranched polyester (EHP) water-retaining agent was added. The optimal hot-pressing conditions for Class II plywood were a hot-pressing temperature of 120℃, a hot-pressing time of 6 min, and a hot-pressing pressure of 1.0 MPa. (Liu, Z., X. Zhang, W. Zhou, G. Wang, T. Liu, J. Luo, Q. Gao, J. Luo and J. Li (2023). "Bioinspired water-retaining and strong soybean flour-based adhesive for efficient preparation of plywood." JOURNAL OF CLEANER PRODUCTION 414.) However, this type of adhesive requires high-cost materials, and the synthesis process of the water-retaining agent is complex, thus limiting its practical application. Summary of the Invention

[0005] To address the technical problems faced by existing adhesives, this invention provides an oxidized sugar-modified soybean flour adhesive suitable for improving the water retention and water resistance of soybean flour, as well as its preparation method. This soybean adhesive is applied to plywood, and it is also a flame-retardant adhesive.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: One object of the present invention is to provide an oxidized sugar modified soybean flour adhesive, which is prepared from the following raw materials in parts by weight: 20-30 parts soybean flour, 5-25 parts oxidized sugar, 0.2-0.5 parts amino silica, and 0.6-3 parts phytic acid, wherein the mass ratio of soybean flour, oxidized sugar, amino silica and phytic acid is (75-85):(50-70):1:(3-5).

[0007] Preferably, the bean flour is prepared from one or more of soybeans, mung beans, peas, and broad beans, with a diameter of 80-200 mesh; the oxidized sugar is prepared from one or more of glucose, fructose, sucrose, or maltose.

[0008] More preferably, the oxidized sugar is prepared from sucrose.

[0009] Another object of the present invention is to provide a method for preparing the above-mentioned oxidized sugar modified soybean flour adhesive, the specific steps of which are as follows: (1) Alkali treatment to dissolve soybean flour: Soybean flour and sodium hydroxide are added to deionized water, heated and stirred until uniform to obtain an alkali-treated soybean flour solution; (2) Preparation of oxidized sugar: Sucrose and ammonium persulfate are added to deionized water, heated and stirred to carry out the oxidation reaction, and an oxidized sugar solution is obtained; (3) Preparation of aminated silica: PEI (polyethyleneimine) and nano silica are added to deionized water, pH is adjusted to 5-7, stirred, centrifuged and vacuum dried to obtain aminated silica; (4) Preparation of soybean starch gum: Add phytic acid to the soybean starch solution in step (1) and heat and stir until uniform; (5) Add oxidized sugar solution and aminated silicon dioxide to the soybean flour-phytic acid system in step (4) in sequence, and continue to heat and stir evenly to obtain water-retaining soybean flour adhesive.

[0010] Preferably, in step (1), the mass ratio of soybean flour, sodium hydroxide and deionized water is (9-11):(0.1-0.5):(30-32); the heating and stirring conditions are: heating and stirring at 70-80℃ for 30-60 minutes.

[0011] Preferably, in step (2), the mass ratio of sugar, ammonium persulfate and deionized water is (55-60):(5-7):(35-40); the oxidation reaction temperature is 30-50℃ and the reaction time is 30-60min.

[0012] Preferably, in step (3), the mass ratio of PEI, nano-silica and deionized water is 1:1:8; the vacuum drying temperature is 50-70℃ and the time is 12-24h.

[0013] Preferably, the heating and stirring temperature in step (4) is 40-60℃ and the time is 30-60min.

[0014] More preferably, in step (5), the heating and stirring conditions are: heating and stirring at 70-80℃ for 2-3 hours.

[0015] Another object of the present invention is to provide the application of the above-mentioned oxidized pond modified soybean flour adhesive in wood plywood.

[0016] The oxidized soybean flour adhesive has a solids content of 20-45%. The hot pressing process parameters are: temperature 130-170℃, pressure 0.8-1.2MPa, time 3-6min; The resulting plywood exhibits a dry shear strength ≥2.5 MPa and a wet strength retention rate ≥50% after immersion in water at 63℃ for 3 hours. Storage stability: After being stored at 40℃ and 75% relative humidity for 6 months, the adhesive strength decay rate is <5%.

[0017] Another object of the present invention is to provide a flame-retardant adhesive, which is prepared by compounding the above-mentioned oxidized sugar modified soybean flour adhesive with 5-15 wt% of its own inorganic filler.

[0018] In the aforementioned flame-retardant adhesives, the inorganic filler is one of silicon dioxide, boron nitride, montmorillonite, and titanium dioxide.

[0019] The oxidized sugar modified soybean flour adhesive of the present invention forms a three-dimensional cross-linked network through the reaction of the aldehyde group of oxidized sugar with the amino / hydroxyl group of soybean flour, which significantly improves water retention and thermal stability. Furthermore, amino nano-silica and phytic acid are introduced, and their amino groups and polycarboxylic acids enhance the cross-linking density through hydrogen bonding and ionic interactions. At the same time, they react with the soybean flour molecular chains through Schiff base reactions to form an interpenetrating network structure, which increases the cohesiveness of the adhesive by more than 50% and endows the system with high water resistance and flame retardancy.

[0020] The soybean flour adhesive developed in this invention is formaldehyde-free, and its main raw materials are derived from renewable resources, making it an environmentally friendly adhesive for engineered wood products. This product not only completely solves the formaldehyde pollution problem caused by the use of traditional adhesives, but also maintains excellent water retention, water resistance, and high bonding strength.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. One of the raw materials of this invention—soybean flour—uses protein-based substances, especially defatted soybean protein powder, as a raw material for adhesives used in engineered wood products. It contains no free formaldehyde and releases no formaldehyde during use, fundamentally solving the problem of indoor formaldehyde pollution caused by engineered wood products. Furthermore, protein-based substances are renewable resources; using them as the main raw material for adhesives helps alleviate the dependence of traditional engineered wood product adhesives on fossil fuels, conforming to the principles of environmental protection and sustainable development.

[0022] 2. The adhesive of this invention uses soybean processing residues as the main raw material, achieving efficient resource utilization. This not only reduces production costs but also increases product added value, resulting in significant economic and ecological benefits. The preparation process is simple, the curing time is short, and the operation is convenient, which is conducive to improving production efficiency. Furthermore, this adhesive achieves comprehensive resource utilization, meets the requirements of environmental protection and sustainable development, and has broad application prospects.

[0023] 3. This invention uses protein-oxidized sugar reactants as crosslinking enhancers, which solves the problem of poor water resistance of ordinary soybean flour adhesives, meets the water resistance requirements of adhesives for engineered wood products, and ensures the practical performance of adhesives such as bonding strength; the hydrophilicity of oxidized sugars also further ensures the water retention of the adhesive, and the fiberboard prepared by the adhesive of this invention meets the Class II board standard requirements in the national standard.

[0024] 4. This invention uses soybean flour-oxidized sugar reactant as a cross-linking enhancer. Its main raw material is soybean protein meal, which is derived from the residue after soybean oil extraction. This helps to reduce dependence on synthetic fossil raw materials, alleviate the pressure of resource depletion, and meet the requirements of environmental protection and sustainable development. Attached Figure Description

[0025] Figure 1 The images show the FT-IR spectra of sucrose and oxidized sucrose.

[0026] Figure 2 The images show the FT-IR spectra of silica and amino silica.

[0027] Figure 3 FT-IR spectra of soybean flour and oxidized sucrose-modified soybean flour adhesives.

[0028] Figure 4 This is a SEM image of the soybean flour adhesive.

[0029] Figure 5 This is a SEM image of the soybean flour-oxidized sugar adhesive of Example 1 of the present invention.

[0030] Figure 5 contrast Figure 4 It can be seen that the adhesive layer of the soybean flour-oxidized sugar adhesive improved by this invention has a denser surface, which helps to significantly enhance water resistance and strong cohesion. Figure 6 A comparative graph showing the heat release rate (HRR) and total heat release (HHR) of soybean flour and the soybean flour oxidized sugar adhesive of Example 1 of this invention under combustion test.

[0031] Figure 7 A comparative graph showing the smoke production rates of soybean flour and the soybean flour oxidized sugar adhesive of Example 1 of this invention under combustion tests. Detailed Implementation

[0032] The technical solution of the present invention will be further illustrated below through specific embodiments and usage examples. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0033] The preparation of the oxidized sugar modified soybean flour adhesive of the present invention first involves the processing of raw materials. The raw materials used, soybean flour, sodium hydroxide, sucrose, ammonium persulfate, deionized water, PEI, silicon dioxide, and phytic acid, can all be purchased and obtained on the market.

[0034] The present invention first performs the following preparation steps, 1. Alkali treatment to dissolve soybean flour: Add 90g soybean flour and 1g sodium hydroxide to 310g deionized water, heat and stir at 75℃ for 45min until uniform, to obtain an alkali-treated soybean flour solution.

[0035] 2. Preparation of oxidized sucrose: 115g of sucrose and 12g of ammonium persulfate were added to 75g of deionized water and heated and stirred at 40℃ for 45min to carry out the oxidation reaction, so as to obtain oxidized sucrose solution.

[0036] 3. Preparation of aminated silica: 10g of PEI and 10g of nano silica were added to 80g of deionized water, the pH value was adjusted, the mixture was stirred, centrifuged and vacuum dried to obtain aminated silica.

[0037] Example 1 (1) Gelatinization treatment: First, add 75g of water to 25g of defatted soybean powder, stir evenly and let stand for 1 hour, then heat to 50℃, add 0.6g of phytic acid, and continue to keep warm at 50℃ and stir for 30 minutes to obtain modified defatted soybean powder solution. (2) Modification: Add 20g of oxidized sucrose and 0.3g of aminated nano-silica to the modified defatted soybean powder solution, heat to 80℃ and stir for 120min to obtain the modified soybean powder adhesive.

[0038] Example 2 The only difference between Example 2 and Example 1 is that the amount of oxidized sucrose is 25g, while the content of other components and the preparation method remain unchanged.

[0039] Example 3 The only difference between Example 3 and Example 1 is that the amount of oxidized sucrose is 15g, while the content of other components and the preparation method remain unchanged.

[0040] Example 4 The only difference between Example 4 and Example 1 is that the amount of oxidized sucrose is 10g, while the content of other components and the preparation method remain unchanged.

[0041] Example 5 The only difference between Example 5 and Example 1 is that the amount of oxidized sucrose is 5g, while the content of other components and the preparation method remain unchanged.

[0042] Example 6 The only difference between Example 6 and Example 1 is that the amount of phytic acid is 3g, while the content of other components and the preparation method remain unchanged.

[0043] Example 7 The only difference between Example 7 and Example 1 is that the amount of phytic acid is 2.4g, while the content of other components and the preparation method remain unchanged.

[0044] Example 8 The only difference between Example 8 and Example 1 is that the amount of phytic acid is 1.8g, while the content of other components and the preparation method remain unchanged.

[0045] Example 9 The only difference between Example 9 and Example 1 is that the amount of phytic acid is 1.2g, while the content of other components and the preparation method remain unchanged.

[0046] Comparative Example 1 The only difference from Example 1 is that defatted soybean flour was not added to the raw materials of Comparative Example 1, while the content of other components and the preparation method remained unchanged.

[0047] Comparative Example 2 The only difference from Example 1 is that the soybean flour in Comparative Example 2 is undefatted soybean flour, while the content of other components and the preparation method remain unchanged.

[0048] Comparative Example 3 The only difference from Example 1 is that the raw materials of Comparative Example 3 do not contain phytic acid, while the content of other components and the preparation method remain unchanged.

[0049] Comparative Example 4 The only difference from Example 1 is that the raw materials of Comparative Example 4 do not contain anoxidized sucrose, while the content of other components and the preparation method remain unchanged.

[0050] Comparative Example 5 The only difference from Example 1 is that the sucrose used in the raw materials of Comparative Example 5 is unoxidized, while the content of other components and the preparation method remain unchanged.

[0051] Comparative Example 6 The only difference from Example 1 is that aminated nano-silica was not added to the raw materials of Comparative Example 6, while the content of other components and the preparation method remained unchanged.

[0052] Comparative Example 7 The only difference from Example 1 is that nano-silica was used in the raw materials of Comparative Example 7, while the content of other components and the preparation method remained unchanged.

[0053] Application testing of the oxidized tannin-modified soybean flour adhesive obtained in this invention Adhesives were prepared using Examples 1-9 and Comparative Examples 1-7, respectively, and the performance of the prepared adhesives was tested. The test results are shown in Table 1.

[0054] 1. Adhesive strength test: The prepared adhesive is tested at 280g / m². 2 Three-layer poplar plywood was prepared by applying glue to the plywood. The glue was applied and hot-pressed at 160℃ and 1MPa for 8 minutes, and then left at room temperature for 24 hours before use.

[0055] 2. Water resistance test: The water resistance test shall be conducted in accordance with the method for determining Class II wet strength in GB / T9846-2015. The sample shall be immersed in hot water at 63±3℃ for 3 hours, removed and cooled to room temperature for 10 minutes, and then tested immediately.

[0056] 3. Combustion Reaction Test: The adhesive prepared in Example 1 was subjected to a combustion reaction test using a cone calorimeter (FTTUK, Stanton Ledcroft, UK). The radiant heat flux was 50 kW / m², in accordance with ISO 5660-1 standard. 2 The sample size is 100mm×100mm×4mm.

[0057] Table 1. Adhesion and water resistance properties of the adhesives prepared in Examples 1-9 and Comparative Examples 1-7 of the present invention.

[0058] As can be seen from Examples 1-5 and Comparative Examples 4-5, when the content of oxidized sucrose in the raw materials increases, the adhesive strength of the prepared adhesive first decreases and then increases, and the water resistance also first decreases and then increases. When no oxidized sucrose is added or the sucrose is not oxidized, the angular strength and water resistance of the resulting adhesive are significantly reduced. This is because when the oxidized sucrose content is too low (or sucrose is not oxidized), the aldehyde content is insufficient, the cross-linking reaction between protein molecules is limited, and the molecular chains are still mainly connected by hydrogen bonds or van der Waals forces, resulting in a loose structure and poor adhesive strength and water resistance. When the oxidized sucrose content is moderate (in the gradual increasing stage): the aldehyde groups react with the protein amino groups, but due to the matching problems of pH, temperature, and reaction sites in the reaction system, excessive aldehyde groups will cause partial oxidative degradation of the protein molecular structure or the formation of too many small molecule condensates, destroying the continuous network structure, thereby leading to a decrease in adhesive strength and water resistance. When the oxidized sucrose content is further increased (to a higher proportion): with the increase of aldehyde groups available for cross-linking, a denser three-dimensional cross-linking network can be formed between protein molecules, the internal hydrophobicity is enhanced, the system stability is improved, and therefore the bonding strength and water resistance increase again.

[0059] As can be seen from Examples 1, 6-9, and Comparative Example 3, when the phytic acid content increases, the adhesive strength of the adhesive first decreases and then increases, while the water resistance first increases and then decreases. Without phytic acid, the adhesive strength of the adhesive decreases significantly, while the water resistance is relatively good. This is because, with increasing phytic acid content, the adhesive strength of the soybean flour adhesive shows a trend of first decreasing and then increasing, while the water resistance shows a trend of first increasing and then decreasing. This is because low phytic acid content causes a decrease in the system's pH and excessive protein aggregation, limiting the cross-linking reaction and leading to a decrease in the adhesive layer's bonding force. Appropriate amounts of phytic acid can form ionic or esterified cross-links with protein molecules, improving structural density and interfacial adhesion, thereby enhancing adhesive strength and water resistance. However, when the phytic acid content is too high, excessive phosphate groups in the system increase overall hydrophilicity and may disrupt the continuous structure of the adhesive, leading to a decrease in water resistance. Without phytic acid, the cross-linked network in the system is relatively sparse, resulting in a decrease in adhesive strength, while the water resistance is better due to the absence of hydrophilic groups.

[0060] As can be seen from Example 1 and Comparative Examples 1-2, the adhesive system without defatted soybean flour is mainly composed of oxidized sucrose. The resulting adhesive is essentially an oxidized sucrose adhesive. Oxidized sucrose molecules contain a large number of aldehyde groups (–CHO), which can form a cross-linked structure through acetal or addition reactions, resulting in a dense adhesive layer with tight intermolecular bonding. Therefore, even without soybean flour, a three-dimensional network structure of a certain strength can be formed, exhibiting high bonding strength and water resistance.

[0061] As can be seen from Examples 6-7, the adhesive strength of the adhesives without added aminated nano-silica and without any added nano-silica decreased significantly, while the water resistance of the adhesives without added aminated nano-silica increased. This is because when no aminated nano-silica was added or no nano-silica was added at all, the adhesive strength of the soybean flour adhesive decreased significantly, while the water resistance increased slightly. This is because aminated nano-silica can chemically cross-link with the amino and hydroxyl groups in the soybean flour system and the aldehyde groups in oxidized sucrose through its surface amino groups, forming a dense three-dimensional network structure, thereby significantly enhancing the adhesive strength. However, the amination treatment also introduces a large number of polar –NH2 and –OH groups, increasing the hydrophilicity of the adhesive layer, making the cured structure more prone to water absorption, resulting in a slight decrease in water resistance. In contrast, the unmodified or unadded silica system lacks effective cross-linking, the adhesive layer structure is loose but has low polarity, and water penetration is relatively slow, thus exhibiting relatively better water resistance.

[0062] The adhesive prepared in Example 1 of this invention was subjected to a combustion reaction test in the presence of fire. Data graphs were obtained showing the heat release rate (HRR), total heat release (HHR), and smoke production rate of the adhesive under the combustion test. Simultaneously, a combustion test was conducted on ordinary soybean flour, and the data were compared. The resulting data graphs are shown below. Figure 6 and Figure 7 As shown.

[0063] from Figure 6 As can be seen from the results, compared with adhesives made only from soybean flour, the soybean flour oxidized sugar adhesive of Example 1 of the present invention has a slower heat release rate (HRR) and a smaller total heat release (HHR) under combustion test. This indicates that the adhesive of the present invention has a low calorific value and excellent flame retardant properties.

[0064] from Figure 7 As can be seen, compared with adhesives made only from soybean flour, the soybean flour oxidized sugar adhesive of Example 1 of the present invention has a significantly lower smoke production rate under combustion test, indicating that the adhesive of the present invention not only has good flame retardant properties, but also produces very low smoke, making it more environmentally friendly.

[0065] The above content demonstrates and illustrates the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and these embodiments and the descriptions in the specification are only for illustrating the principles of the invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications should fall within the protection scope defined by the appended claims and their equivalents.

Claims

1. An oxidized sugar-modified soy flour adhesive, characterized by, Prepared from the following raw materials by weight: bean powder 20-30 parts, oxidized sugar 5-25 parts, amino silicon dioxide 0.2-0.5 parts, phytic acid 0.6-3 parts, and the mass ratio of bean powder, oxidized sugar, amino silicon dioxide and phytic acid is (75-85):(50-70):1:(3-5).

2. The oxidized sugar-modified soy flour adhesive according to claim 1, characterized by, The bean powder is prepared from one or more of soybean, mung bean, pea and broad bean, and the diameter size is 80-200 mesh; the oxidized sugar is prepared from one or more of glucose, fructose, sucrose or maltose.

3. The oxidized sugar-modified soy flour adhesive according to claim 2, characterized in that, The oxidized sugar is prepared from sucrose.

4. A method for preparing the oxidized sugar-modified soy flour adhesive according to any one of claims 1 to 3, characterized by, The specific steps are as follows: (1) Alkali treatment and dissolution of bean powder: add bean powder and sodium hydroxide into deionized water, heat and stir until uniform to obtain an alkali-treated bean powder solution; (2) Preparation of oxidized sugar: add sugar and ammonium persulfate into deionized water, heat and stir for oxidation reaction to obtain an oxidized sugar solution; (3) Preparation of amino-silicon dioxide: add PEI and nano-silicon dioxide into deionized water, adjust pH to 5-7, stir, centrifuge and vacuum dry to obtain amino-silicon dioxide; (4) Preparation of bean powder glue: add phytic acid into the bean powder solution in step (1) and heat and stir until uniform; (5) Add the oxidized sugar solution and amino-silicon dioxide into the bean-phytic acid system in step (4) in sequence, continue to heat and stir until uniform to obtain a water-retention bean powder adhesive.

5. The method for preparing the oxidized sugar-modified soy flour adhesive according to claim 4, characterized in that, In step (1), the mass ratio of bean powder, sodium hydroxide and deionized water is (9-11):(0.1-0.5):(30-32); the heating and stirring condition is heating and stirring at 70-80℃ for 30-60 min.

6. The method of preparing oxidized sugar-modified soy flour adhesive according to claim 4, characterized by, In step (2), the mass ratio of sugar, ammonium persulfate and deionized water is (55-60):(5-7):(35-40); the oxidation reaction temperature is 30-50℃, and the reaction time is 30-60 min.

7. The method of preparing oxidized sugar-modified soy flour adhesive according to claim 4, characterized by, In step (3), the mass ratio of PEI, nano-silicon dioxide and deionized water is 1:1:8; the vacuum drying temperature is 50-70℃, and the time is 12-24 h.

8. The method of preparing oxidized sugar-modified soy flour adhesive according to claim 4, characterized by, In step (4), the heating and stirring temperature is 40-60℃, and the time is 30-60 min.

9. The method of preparing the oxidized sugar-modified soy flour adhesive according to claim 4, characterized by, In step (5), the heating and stirring condition is heating and stirring at 70-80℃, and the heating time is 2-3 h.

10. Use of the oxidized pond modified bean powder adhesive according to any one of claims 1-3 in wood plywood.

11. A flame-retardant adhesive, characterized by, The oxidized sugar modified bean powder adhesive according to any one of claims 1-3 is compounded with inorganic fillers at 5-15wt% of its own mass.

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