Modified protein adhesive based on nano-hybrid dynamic crosslinking network, its preparation method and application

Abstract

The present invention discloses a modified protein adhesive based on a nano-hybrid dynamic crosslinked network, belonging to the technical field of adhesives. By weight, the present invention comprises the following components: 25-35 parts of plant protein meal, 65-75 parts of dispersion medium, 4-6 parts of branched-terminal epoxy polyurethane crosslinking agent, 3-7 parts of linear polyurethane crosslinking agent, and 0.05-0.1 part of metal nano-oxide. The present invention carries out co-crosslinking modification on the adhesive by using dual crosslinking agents as crosslinking enhancement elements, constructs an energy dissipation element with nano-metal oxide as the dynamic crosslinking ligand, and reacts with protein molecules in crosslinking. By regulating the ratio of the two crosslinking agents, the bonding strength and gluing toughness can be directionally regulated, which has high efficiency and easy industrial operation, and is convenient for practical industrial application.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and particularly to a modified protein adhesive based on a nano-hybrid dynamic crosslinked network, a preparation method thereof, and an application thereof in wood manufacturing. Background Art

[0002] At present, trialdehyde adhesives (urea-formaldehyde resin, phenolic resin, melamine-formaldehyde resin) still dominate the wood adhesive industry. However, the problem of formaldehyde harmful substance release therefrom has caused serious harm to human health. Therefore, the development of formaldehyde-free wood adhesives has received wide attention.

[0003] Preparing wood adhesives using agroforestry biomass resources can solve the problem of formaldehyde release from the source and get rid of the dependence on fossil resources. Among them, soy protein shows great potential in the field of bio-based wood adhesives due to its wide source, large yield, and easy processing. However, due to the large number of hydrophilic groups and the weak curing network, it shows poor water resistance in applications. To address this problem, current researchers mainly improve the bonding performance in the following ways:

[0004] (1) Crosslinked network design: By designing and preparing crosslinking agents with different structures and functional groups, inducing protein molecules to construct a stable crosslinked network to improve the bonding performance;

[0005] (2) Nano-hybrid modification: Using nano-fillers as modification elements, constructing a nano-enhanced curing structure by adjusting the type, surface groups, etc. of the nano-fillers;

[0006] (3) High-performance resin blending: Blending resins with excellent bonding performance into the protein matrix, and improving the bonding performance of the protein adhesive by virtue of the excellent performance of the added resins;

[0007] (4) Bionic structure design: Simulating the functional mechanisms of organisms with excellent water-resistant adhesion performance, and preparing a bionic adhesive crosslinked structure to improve the water-resistant bonding performance. Among the above methods, by modifying the crosslinked network stability of the protein adhesive, the bonding strength and water resistance have been significantly improved. However, the improvement of the crosslinked network stability has also increased the mechanical rigidity of the curing structure of the adhesive, making the protein adhesive more brittle and resulting in an increase in the defective rate of the artificial board products during processing, transportation, etc.

[0008] At present, introducing an energy dissipation mechanism into the protein cross-linking network is an effective way to achieve simultaneous modification of soy protein adhesives for strengthening and toughening. For example, the invention patent with publication number CN118931491A discloses a mildew-proof, flame-retardant, antioxidant and tough soy protein adhesive and its preparation method and application, and uses gallic acid-modified seaweed nanofibers and metal ion compounds to modify soy protein adhesives. The formation of multiple cross-links improves structural stability, while the chelate bonds between gallic acid and metal ion compounds promote energy dissipation, achieving simultaneous modification of adhesive strength and toughness. However, the chelate bonds need to rely on the movement of molecular chains to present the best energy dissipation effect. Most of the designs are rigid elements, which is not conducive to a significant improvement in toughness. For example, the invention patent with authorization announcement number CN111171277B discloses polyurethane elastic crosslinking agents and high-strength and tough plant protein adhesives and their applications. The terminal isocyanate groups of the plant polyphenol branched modified polyurethane are protected by bisulfite end-capping, so that the isocyanate groups are exposed during the curing process to cross-link the protein molecules, and the phenolic hydroxyl groups of the plant polyphenols are synergistically used to construct a physical, covalent double cross-linked network. The molecular movement of the flexible chain segments of the polyurethane is used to efficiently exert the energy dissipation effect of the physical network induced by the phenolic hydroxyl groups, thereby effectively improving the strength and toughness.

[0009] Obviously, in the current research on strengthening and toughening modification, most of the schemes are to modify the structural stability and energy dissipation performance of the protein adhesive cross-linking network through the covalent and non-covalent molecular bonding network formed by a single curing cross-linking system. The contradictory structural requirements of strength and toughness are difficult to achieve through a single curing cross-linking system, and the modification of toughness is mostly achieved at the expense of strength. At the same time, the energy dissipation designs such as physical cross-linking and metal ion coordination cross-linking reported so far have low bonding density, which is not conducive to the rapid energy dissipation effect.

[0010] In summary, the current wood adhesives have the following disadvantages:

[0011] Disadvantage ①: Most of the existing soy protein adhesive enhancement and toughening modification schemes are based on a single curing and cross-linking system, and it is difficult to simultaneously improve strength and toughness through a single system;

[0012] Disadvantage ②: The construction of energy dissipation mechanism is mostly based on rigid cross-linking system. In this case, the energy dissipation effect shows rigid cross-linking effect due to the lack of molecular mobility, and the toughness improvement formed by energy dissipation is not utilized;

[0013] Disadvantage ③: The energy dissipation mechanism is mostly constructed through the bonding form of physical hydrogen bonds and metal ion coordination bonds. This form has disadvantages such as randomness and low bonding density, resulting in a lack of efficient and orderly energy dissipation centers under the action of external forces to promote energy dissipation and achieve significant improvement in toughness. Summary of the invention

[0014] In view of this, to solve the above technical problems existing in the prior art, in a first aspect, the present invention provides a modified protein adhesive based on a nano-hybrid dynamic crosslinking network. The adhesive is co-crosslinked and modified by using a dual crosslinking agent as a crosslinking enhancement element, and an energy dissipation element with nano-metal oxide as a dynamic crosslinking ligand is constructed to react with protein molecules. By regulating the ratio of the two crosslinking agents, the bonding strength and gluing toughness can be directionally regulated, which has high efficiency and easy industrial operation and is convenient for practical industrial applications.

[0015] To achieve the above object, the present invention provides the following technical solutions:

[0016] A modified protein adhesive based on a nano-hybrid dynamic crosslinking network, by weight, comprises the following components:

[0017] 25-35 parts of plant protein meal, 65-75 parts of dispersion medium, 4-6 parts of branched-end epoxy-based polyurethane crosslinking agent, 3-7 parts of linear polyurethane crosslinking agent, and 0.05-0.1 part of metal nano-oxide.

[0018] Preferably, the branched-end epoxy-based polyurethane crosslinking agent is a hyperbranched epoxy polyurethane crosslinking agent.

[0019] Preferably, the linear polyurethane crosslinking agent is an epoxy-imidazole double-capped polyurethane crosslinking agent.

[0020] Preferably, the metal nano-oxide is nano-zinc oxide.

[0021] Preferably, the plant protein meal is soybean meal.

[0022] Preferably, the preparation method of the branched-end epoxy-based polyurethane crosslinking agent comprises the following steps:

[0023] First, isocyanate, polyol, 2,2-bis(hydroxymethyl)propionic acid, and a catalyst are reacted under nitrogen protection;

[0024] Secondly, after cooling, a small molecule polyol chain extender is added to continue the reaction, and an alcohol monomer containing an epoxy group is added to continue the reaction;

[0025] Finally, it is cooled to room temperature, neutralized with a neutralizing agent, and emulsified with water.

[0026] Preferably, the preparation method of the linear polyurethane crosslinking agent comprises the following steps:

[0027] First, isocyanate, polyol, 2,2-bis(hydroxymethyl)propionic acid, and a catalyst are reacted under nitrogen protection;

[0028] Secondly, after cooling, a small molecule polyol chain extender is added for reaction, and an alcohol monomer containing an epoxy group and a reaction monomer containing a metal ion coordination group are added, and the reaction is continued;

[0029] Finally, it is cooled to room temperature, neutralized with a neutralizing agent, and emulsified with water.

[0030] Preferably, the dispersion medium is softened water.

[0031] In a second aspect, the present invention also provides a preparation method of the above-mentioned wood adhesive based on a nano-hybrid dynamic crosslinked network, mixing plant protein meal with a dispersion medium evenly; adding a branched terminal epoxy group polyurethane crosslinking agent, a linear polyurethane crosslinking agent and a metal nano-oxide, and performing high-pressure homogenization treatment to obtain a modified protein adhesive.

[0032] In a third aspect, the present invention also provides an application of the above-mentioned modified protein adhesive based on a nano-hybrid dynamic crosslinked network in wood manufacturing.

[0033] Beneficial effects

[0034] Aiming at the above-mentioned shortcoming ①: By using a dual crosslinking agent as a crosslinking enhancement element and a nano-metal oxide as an energy dissipation element to crosslink and react with protein molecules, the present invention can realize the regulation of strength and toughness by simply adjusting the addition amount, which is convenient for industrial practical applications.

[0035] Specifically: The co-crosslinking curing agent used in the present invention is a crosslinking agent of two structural types, namely a branched terminal epoxy group polyurethane crosslinking agent (such as a hyperbranched epoxy polyurethane crosslinking agent) and a linear polyurethane crosslinking agent (such as an epoxy-imidazole double-capped polyurethane crosslinking agent). Among them, the branched terminal epoxy group polyurethane crosslinking agent, as one of the crosslinking agents, by virtue of its characteristic of rich end group sites in the branched structure, is prepared into a branched crosslinking agent through epoxy group modification, inducing protein molecules to form a dense crosslinked structure and improving the mechanical stability of the structure; among them, the linear polyurethane crosslinking agent, as another crosslinking agent, is modified with an epoxy group at one end for co-curing crosslinking of protein molecules with the branched epoxy crosslinking agent, and is modified with a group capable of coordinating with metal ions at the other end for forming a dynamic crosslinked energy dissipation element in the co-curing crosslinked structure. The two crosslinking agents can construct a co-crosslinking curing system by different structural designs and different proportion blending, which is convenient for regulating strength and toughness properties and convenient for industrial practical applications.

[0036] Aiming at the above-mentioned shortcoming ②: The co-crosslinking curing agents used in the present invention are all polyurethane elastomers with excellent molecular motion ability. Under this action, the constructed dynamic crosslinking action can efficiently dissipate energy through dynamic bonding by means of molecular motion, thereby significantly improving toughness.

[0037] Regarding the above-mentioned drawback ③: The present invention utilizes metal nano-oxides as dynamic crosslinking ligands. The high specific surface area of the nano-materials provides a large number of surface metal ion reaction sites, which cooperate with the terminal functional coordination groups of polyurethane to construct a high-density dynamic crosslinking reaction, forming an energy dissipation center, thereby promoting energy dissipation in an orderly and efficient manner and achieving toughness modification.

[0038] In summary, the modified protein adhesive based on the nano-hybrid dynamic crosslinking network provided by the present invention co-crosslinks and modifies the adhesive by using dual crosslinking agents as crosslinking enhancement elements, and constructs an energy dissipation element with nano-metal oxides as dynamic crosslinking ligands to react with protein molecules. By regulating the ratio of the two crosslinking agents, the bonding strength and gluing toughness can be directionally regulated. It has the characteristics of universality, high efficiency, easy industrial operation and scalable application, facilitating the practical application in industry. It can effectively solve the above-mentioned technical problems existing in the prior art. Detailed implementation manners

[0039] The present invention will be further described below in conjunction with embodiments.

[0040] Term explanations

[0041] Nano-hybridization: A method of hybridizing and modifying the crosslinking network of materials using nano-fillers.

[0042] Dynamic crosslinking: This concept is set relative to traditional covalent chemical crosslinking. Traditional chemical crosslinking has characteristics such as stable structure and non-reprocessable chemical bonds. Dynamic crosslinking utilizes non-covalent chemical bonds, such as physical hydrogen bonds, coordination bonds, etc., and constructs a dynamic crosslinking network by virtue of its characteristics of being able to crosslink dynamically.

[0043] Nano-hybrid dynamic crosslinking: Using nano-fillers as crosslinking ligands to cooperate with the functional groups in polymer molecular chains to construct a nano-filler-dominated dynamic crosslinking network.

[0044] The synchronous modification of enhancing and toughening of soy protein adhesives focuses on improving the energy dissipation performance of the crosslinked curing network while maintaining the bonding strength. Among the toughening modification methods in the prior art, by constructing a single curing system with energy dissipation elements, although the toughness can be improved, due to defects such as low dynamic crosslinking efficiency and lack of molecular motion ability, the toughening modification effect is limited, and it is achieved at the cost of sacrificing a certain mechanical strength. At the same time, precise control of the chemical crosslinking and dynamic crosslinking formed inside the single curing crosslinking system is required to achieve toughness improvement.

[0045] The modified protein adhesive based on the nano-hybrid dynamic crosslinking network of the present invention is a nano-hybrid dynamic crosslinking network formed based on nano-hybridization and dynamic crosslinking, which can efficiently and synchronously improve the structural stability of crosslinking and curing and the energy dissipation performance, and realize the efficient enhancement and toughening modification of the soybean protein adhesive. Starting from the design of the crosslinking network of the adhesive, the present invention uses a dual crosslinking agent to carry out co-crosslinking modification on the adhesive. By designing the structure of the crosslinking agent and constructing an energy dissipation mechanism with nano-metal oxides as dynamic crosslinking ligands, the bonding strength and gluing toughness can be directionally regulated by adjusting the ratio of the two crosslinking agents, which has high efficiency and industrial operability.

[0046] The modified protein adhesive based on the nano-hybrid dynamic crosslinking network of the present invention, by weight, comprises the following components:

[0047] 25-35 parts of plant protein meal, 65-75 parts of dispersion medium, 4-6 parts of branched-terminal epoxy group polyurethane crosslinking agent, 3-7 parts of linear polyurethane crosslinking agent, and 0.05-0.1 part of metal nano-oxide.

[0048] In the present invention, the plant protein meal is preferably soybean meal; the dispersion medium is preferably softened water; the branched-terminal epoxy group polyurethane crosslinking agent is a hyperbranched epoxy polyurethane crosslinking agent.

[0049] The preparation method of the branched-terminal epoxy group polyurethane crosslinking agent comprises the following steps:

[0050] First, isocyanate, polyol, 2,2-bis(hydroxymethyl)propionic acid and a catalyst are reacted under nitrogen protection. The reaction conditions are preferably 80 °C for 3 h;

[0051] Among them, the isocyanate is preferably isophorone diisocyanate; the polyol is preferably polytetrahydrofuran ether with an average molecular weight of 2900; the catalyst is preferably dibutyltin dilaurate.

[0052] Secondly, after cooling, a small molecule polyol chain extender is added to continue the reaction, and an alcohol monomer containing an epoxy group is added to continue the reaction; preferably cooled to 70 °C; the reaction conditions are preferably 70 °C for 2 h;

[0053] Among them, the small molecule polyol chain extender is preferably glycerol. The alcohol monomer containing an epoxy group is preferably glycidol.

[0054] Finally, it is cooled to room temperature, neutralized with a neutralizing agent, preferably for 45 min of neutralization reaction, and emulsified with water.

[0055] Among them, the neutralizing agent is preferably triethylamine.

[0056] The present invention provides a specific preparation method of a branched terminal epoxy polyurethane crosslinking agent. React 23.53 Kg of isophorone diisocyanate, 58 Kg of polytetrahydrofuran ether, 5.20 Kg of 2,2-bis(hydroxymethyl)propionic acid, and 0.43 Kg of dibutyltin dilaurate at 80°C for 3 h under nitrogen protection; cool down to 70°C, add 1.59 Kg of glycerol and react for 5 h; add 3.14 Kg of glycidol and react at 70°C for 2 h; cool to room temperature, add 3.93 Kg of triethylamine and react for 45 min; add water for emulsification.

[0057] In the present invention, the linear polyurethane crosslinking agent is preferably an epoxy-imidazole double-ended polyurethane crosslinking agent, and its preparation method includes the following steps:

[0058] First, react isocyanate, polyol, 2,2-bis(hydroxymethyl)propionic acid and a catalyst under nitrogen protection; the reaction conditions are preferably reacting at 80°C for 3 h.

[0059] Among them, the isocyanate is preferably isophorone diisocyanate; the polyol is preferably polytetrahydrofuran ether with an average molecular weight of 2900. The catalyst is preferably dibutyltin dilaurate.

[0060] Secondly, after cooling down, add a small molecule polyol chain extender to react, add an alcohol monomer containing an epoxy group and a reaction monomer containing a metal ion coordination group, and continue to react; preferably cool down to 70°C; the reaction conditions are preferably reacting at 70°C for 2 h.

[0061] Among them, the small molecule polyol chain extender is preferably 1,4-butanediol; the alcohol monomer containing an epoxy group is preferably glycidol. The alcohol monomer containing an epoxy group is preferably glycidol; the reaction monomer containing a metal ion coordination group is preferably 1-(3-aminopropyl)imidazole.

[0062] Finally, cool to room temperature, add a neutralizing agent for neutralization, and then add water for emulsification.

[0063] Among them, the neutralizing agent is preferably triethylamine.

[0064] The present invention provides a specific preparation method of a linear polyurethane crosslinking agent. React 23.53 Kg of isophorone diisocyanate, 58 Kg of polytetrahydrofuran ether, 5.20 Kg of 2,2-bis(hydroxymethyl)propionic acid, and 0.43 Kg of dibutyltin dilaurate at 80°C for 3 h under nitrogen protection; cool down to 70°C, add 2.34 Kg of 1,4-butanediol and react for 5 h; add 1.57 Kg of glycidol and 2.65 Kg of 1-(3-aminopropyl)imidazole and react at 70°C for 2 h; cool to room temperature, add 3.93 Kg of triethylamine and react for 45 min, and then add water for emulsification.

[0065] Second aspect, the present invention also provides a preparation method of the above-mentioned wood adhesive based on a nano-hybrid dynamic crosslinked network, which uniformly mixes vegetable protein meal with a dispersion medium; adds a branched terminal epoxy group polyurethane crosslinking agent, a linear polyurethane crosslinking agent, and metal nano-oxides, and obtains a modified protein adhesive through high-pressure homogenization treatment.

[0066] Third aspect, the present invention also provides the application of the above-mentioned modified protein adhesive based on a nano-hybrid dynamic crosslinked network in wood.

[0067] Example 1

[0068] The modified protein adhesive based on nano-hybrid dynamic crosslinking is composed of the following components: 75 Kg of softened water, 25 Kg of soybean meal, 4 Kg of hyperbranched epoxy polyurethane crosslinking agent, 3 Kg of epoxy-imidazole double-capped polyurethane crosslinking agent, and 0.05 Kg of nano-zinc oxide. Its preparation method includes the following steps:

[0069] S1. In a reaction kettle equipped with a stirrer, add softened water and soybean meal according to the ratio and stir evenly;

[0070] S2. Add the hyperbranched epoxy polyurethane crosslinking agent and the epoxy-imidazole double-capped polyurethane crosslinking agent according to the ratio and stir evenly to obtain an adhesive mucus;

[0071] S3. Add nano-zinc oxide according to the ratio and perform homogenization treatment. The pressure of the homogenization treatment is 25 MPa, and the obtained glue liquid is used for preparing artificial boards.

[0072] Prepare three batches of parallel samples by the same process, and the performance quality indexes of the obtained adhesives are shown in Table 1.

[0073] Example 2

[0074] The modified protein adhesive based on nano-hybrid dynamic crosslinking is composed of the following components: 70 Kg of softened water, 30 Kg of soybean meal, 5 Kg of hyperbranched epoxy polyurethane crosslinking agent, 5 Kg of epoxy-imidazole double-capped polyurethane crosslinking agent, and 0.075 Kg of nano-zinc oxide.

[0075] The preparation method of the adhesive glue liquid is the same as that in Example 1. Prepare three batches of parallel samples by the same process, and the performance quality indexes of the obtained adhesives are shown in Table 1.

[0076] Example 3

[0077] The modified protein adhesive based on nano-hybrid dynamic crosslinking is composed of the following components: 65 Kg of softened water, 35 Kg of soybean meal, 6 Kg of hyperbranched epoxy polyurethane crosslinking agent, 7 Kg of epoxy-imidazole double-capped polyurethane crosslinking agent, and 0.1 Kg of nano-zinc oxide.

[0078] The preparation method of the adhesive glue liquid is the same as that in Example 1. Three batches of parallel samples are prepared by the same process. The performance and quality indexes of the obtained adhesive are shown in Table 1.

[0079] Comparative Example 1

[0080] The protein adhesive consists of the following components: 75 Kg of softened water and 25 Kg of soybean meal.

[0081] Except for not adding hyperbranched epoxy polyurethane crosslinking agent, epoxy-imidazole double-capped polyurethane crosslinking agent, and nano-zinc oxide, the preparation method of the adhesive glue liquid is the same as that in Example 1. Three batches of parallel samples are prepared by the same process. The performance and quality indexes of the obtained adhesive are shown in Table 1.

[0082] Comparative Example 2

[0083] The protein adhesive consists of the following components: 70 Kg of softened water and 30 Kg of soybean meal.

[0084] Except for not adding hyperbranched epoxy polyurethane crosslinking agent, epoxy-imidazole double-capped polyurethane crosslinking agent, and nano-zinc oxide, the preparation method of the adhesive glue liquid is the same as that in Example 1. Three batches of parallel samples are prepared by the same process. The performance and quality indexes of the obtained adhesive are shown in Table 1.

[0085] Comparative Example 3

[0086] The protein adhesive consists of the following components: 65 Kg of softened water and 35 Kg of soybean meal.

[0087] Except for not adding hyperbranched epoxy polyurethane crosslinking agent, epoxy-imidazole double-capped polyurethane crosslinking agent, and nano-zinc oxide, the preparation method of the adhesive glue liquid is the same as that in Example 1. Three batches of parallel samples are prepared by the same process. The performance and quality indexes of the obtained adhesive are shown in Table 1.

[0088] Comparative Example 4

[0089] The protein adhesive consists of the following components: 75 Kg of softened water, 25 Kg of soybean meal, and 4 Kg of hyperbranched epoxy polyurethane crosslinking agent.

[0090] Except for not adding epoxy-imidazole double-capped polyurethane crosslinking agent and nano-zinc oxide, the preparation method of the adhesive glue liquid is the same as that in Example 1. Three batches of parallel samples are prepared by the same process. The performance and quality indexes of the obtained adhesive are shown in Table 1.

[0091] Comparative Example 5

[0092] The protein adhesive consists of the following components: 70 Kg of softened water, 30 Kg of soybean meal, and 5 Kg of hyperbranched epoxy polyurethane crosslinking agent.

[0093] Except for not adding epoxy-imidazole double-capped polyurethane crosslinking agent and nano-zinc oxide, the preparation method of the adhesive glue solution is the same as that in Example 1. Three batches of parallel samples are prepared by the same process, and the performance and quality indexes of the obtained adhesives are shown in Table 1.

[0094] Comparative Example 6

[0095] The protein adhesive is composed of the following components: 65 Kg of softened water, 35 Kg of soybean meal, and 6 Kg of hyperbranched epoxy polyurethane crosslinking agent.

[0096] Except for not adding epoxy-imidazole double-capped polyurethane crosslinking agent and nano-zinc oxide, the preparation method of the adhesive glue solution is the same as that in Example 1. Three batches of parallel samples are prepared by the same process, and the performance and quality indexes of the obtained adhesives are shown in Table 1.

[0097] Experimental Example

[0098] The adhesives of Examples 1-3 and Comparative Examples 1-6 are respectively used to manufacture three-layer 400mm×400mm plywood.

[0099] The materials for preparing the plywood are selected as poplar veneers, with a moisture content of 8% and a size of 400mm×400mm×2mm.

[0100] Gluing method: double-sided gluing of the core board, and the glue spreading amount is 300-360g / m 2 .

[0101] Aging method and time: closed aging for 30 minutes.

[0102] Hot pressing pressure: 1.0 MPa, hot pressing temperature is 120 °C, and hot pressing time is 70 s / mm.

[0103] The plywood prepared by the above process is tested for formaldehyde release amount, bond strength, and water resistance according to the method of GB / T 9846–2015 (Type II plywood), and the test results are shown in Table 1:

[0104] Table 1 Formulations of adhesives and their test performance data

[0105]

[0106] The above is only a preferred specific embodiment of the present invention; however, the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its improved concept, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A modified protein adhesive based on a nano-hybrid dynamic cross-linked network, characterized in that: By weight, it includes the following components: 25-35 parts of vegetable protein meal, 65-75 parts of dispersion medium, 4-6 parts of branched end epoxy polyurethane crosslinking agent, 3-7 parts of linear polyurethane crosslinking agent and 0.05-0.1 parts of metal nano oxide; The preparation method of the branched end epoxy polyurethane crosslinking agent comprises the following steps: First, isocyanate, polyol, 2,2-bis(hydroxymethyl)propionic acid and a catalyst are reacted under nitrogen protection; Secondly, after cooling, a small molecule polyol chain extender is added to continue the reaction, and an epoxy group-containing alcohol monomer is added to continue the reaction; Finally, cool to room temperature, add neutralizer to neutralize, and then add water to emulsify; The preparation method of the linear polyurethane crosslinking agent comprises the following steps: First, isocyanate, polyol, 2,2-bis(hydroxymethyl)propionic acid and a catalyst are reacted under nitrogen protection; Secondly, after cooling, a small molecule polyol chain extender is added for reaction, and an alcohol monomer containing an epoxy group and a reaction monomer containing a metal ion coordination group are added to continue the reaction; Finally, cool to room temperature, add neutralizer for neutralization, and add water for emulsification.

2. A modified protein adhesive based on a nano-hybrid dynamic cross-linked network according to claim 1, characterized in that: The branched end epoxy polyurethane crosslinking agent is a hyperbranched epoxy polyurethane crosslinking agent.

3. A modified protein adhesive based on a nano-hybrid dynamic cross-linked network according to claim 1, characterized in that: The linear polyurethane crosslinking agent is an epoxy-imidazole double-terminated polyurethane crosslinking agent.

4. A modified protein adhesive based on a nano-hybrid dynamic cross-linked network according to claim 1, characterized in that: The metal nano-oxide is nano-zinc oxide.

5. A modified protein adhesive based on a nano-hybrid dynamic cross-linked network according to claim 1, characterized in that: The plant protein meal is soybean meal.

6. A modified protein adhesive based on a nano-hybrid dynamic cross-linked network according to any one of claims 1 to 5, characterized in that: The dispersion medium is softened water.

7. A method for preparing a modified protein adhesive based on a nano-hybrid dynamic cross-linked network according to any one of claims 1 to 5, characterized in that: The plant protein meal is mixed evenly with a dispersion medium; a branched end epoxy polyurethane crosslinking agent, a linear polyurethane crosslinking agent and a metal nano-oxide are added, and a modified protein adhesive is obtained by high-pressure homogenization.

8. Use of a modified protein adhesive based on a nano-hybrid dynamic cross-linked network according to any one of claims 1 to 5 in wood manufacturing.

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