Modified protein adhesive based on nano-hybrid dynamic cross-linked network as well as preparation method and application of modified protein adhesive

Abstract

The invention discloses a modified protein adhesive based on a nano-hybrid dynamic cross-linked network, and belongs to the technical field of adhesives. The invention relates to a water-based paint, which is prepared from the following ingredients in parts by weight: 25 to 35 parts of vegetable protein meal, 65 to 75 parts of dispersion media, 4 to 6 parts of branched epoxy-terminated polyurethane cross-linking agents, 3 to 7 parts of linear polyurethane cross-linking agents and 0.05 to 0.1 part of metal nanometer oxides. The adhesive is subjected to co-crosslinking modification by using a dual crosslinking agent as a crosslinking enhancing element, an energy dissipation element taking a nano metal oxide as a dynamic crosslinking ligand is constructed, the energy dissipation element and protein molecules are subjected to a crosslinking reaction, and the bonding strength and the bonding toughness can be directionally regulated and controlled by regulating and controlling the proportion of the two crosslinking agents; the method has high efficiency and industrial operability, and is convenient for industrial practical application.

Description

Technical Field

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

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

[0003] The use of agricultural and forestry biomass resources to prepare wood adhesives can solve the problem of formaldehyde release from the source and get rid of dependence on fossil resources. Among them, soy protein has shown great potential in the field of bio-based wood adhesives due to its advantages such as wide sources, large output and easy processing. However, due to the presence of a large number of hydrophilic groups and weak curing network defects, it has poor water resistance in application. To address this problem, current researchers mainly improve the bonding performance through the following methods: (1) Cross-linking network design: by designing and preparing cross-linking agents with different structures and functional groups, protein molecules are induced to build a stable cross-linking network to improve bonding performance; (2) Nanohybrid modification, using nanofillers as the modification unit, constructing a nano-enhanced curing structure by adjusting the type of nanofillers, surface groups, etc.; (3) High-performance resin blending: blending resins with excellent bonding properties into the protein matrix to improve the bonding properties of the protein adhesive by taking advantage of the excellent properties of the added resin; (4) Bionic structure design, simulating the functional structure of organisms with excellent water-resistant adhesion properties, preparing bionic adhesive cross-linking structures to improve water-resistant bonding performance. In the above method, by modifying the stability of the cross-linking network of protein adhesives, the bonding strength and water resistance are significantly improved, but the improvement of the cross-linking network stability also increases the mechanical rigidity of the adhesive curing structure, making the protein adhesive more brittle, resulting in an increase in the scrap rate of the bonded artificial board products in the processing and transportation links.

[0004] 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.

[0005] 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.

[0006] In summary, the current wood adhesives have the following disadvantages: 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; 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; 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

[0007] In view of this, in order to solve the above-mentioned technical problems existing in the prior art, in the first aspect, the present invention provides a modified protein adhesive based on a nano-hybrid dynamic cross-linking network, in which the adhesive is co-cross-linked and modified by using a double cross-linking agent as a cross-linking enhancement unit, and an energy dissipation unit with nano-metal oxide as a dynamic cross-linking ligand is constructed to react with the protein molecules by cross-linking. By adjusting the ratio of the two cross-linking agents, the bonding strength and bonding toughness can be directionally regulated. The adhesive has high efficiency and industrial operability, and is convenient for practical industrial applications.

[0008] To achieve the above object, the present invention provides the following technical solutions: A modified protein adhesive based on a nano-hybrid dynamic cross-linked network comprises the following components by weight: 25-35 parts of plant 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.

[0009] Preferably, the branched end epoxy polyurethane crosslinking agent is a hyperbranched epoxy polyurethane crosslinking agent.

[0010] Preferably, the linear polyurethane crosslinking agent is an epoxy-imidazole double-terminated polyurethane crosslinking agent.

[0011] Preferably, the metal nano-oxide is nano-zinc oxide.

[0012] Preferably, the plant protein meal is soybean meal.

[0013] Preferably, 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 a neutralizer to neutralize, and then add water to emulsify.

[0014] Preferably, 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 to react, and then 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.

[0015] Preferably, the dispersion medium is demineralized water.

[0016] In a second aspect, the present invention also provides a method for preparing the above-mentioned wood adhesive based on the nano-hybrid dynamic cross-linking network, which comprises uniformly mixing the plant protein meal with the dispersion medium; adding a branched end epoxy polyurethane cross-linking agent, a linear polyurethane cross-linking agent and a metal nano-oxide, and subjecting the mixture to high-pressure homogenization to obtain a modified protein adhesive.

[0017] In a third aspect, the present invention also provides the use of the modified protein adhesive based on the nano-hybrid dynamic cross-linking network in wood manufacturing.

[0018] Beneficial Effects

[0019] In view of the above-mentioned shortcoming ①: the present invention uses a double cross-linking agent as a cross-linking enhancement unit and a nano-metal oxide as an energy dissipation unit to cross-link with protein molecules. The strength and toughness can be regulated by simply adjusting the addition amount, which is convenient for practical industrial application.

[0020] Specifically, the co-crosslinking curing agent used in the present invention is a crosslinking agent of two structural types, namely, a branched end epoxy polyurethane crosslinking agent (such as a hyperbranched epoxy polyurethane crosslinking agent) and a linear polyurethane crosslinking agent (such as an epoxy-imidazole double-terminated polyurethane crosslinking agent). Among them, the branched end epoxy polyurethane crosslinking agent is used as one of the crosslinking agents. By virtue of the characteristics of its rich end group sites in the branched structure, the branched crosslinking agent is prepared by modifying the epoxy group, inducing the protein molecules to form a dense crosslinking structure and improving the mechanical stability of the structure; wherein, the linear polyurethane crosslinking agent is used as another crosslinking agent, one end of which is modified with an epoxy group, and is used to co-curing and crosslinking the protein molecules with the branched epoxy crosslinking agent, and the other end is modified with a group that can react with metal ions to form a dynamic crosslinking energy dissipation unit in the co-curing crosslinking structure. The two crosslinking agents can be designed with different structures and mixed and added in different proportions to construct a co-crosslinking curing system, which is convenient for regulating the strength and toughness properties and convenient for practical industrial applications.

[0021] In response to the above-mentioned shortcoming ②: The co-cross-linking curing agents used in the present invention are all polyurethane elastomers with excellent molecular motion ability. Under this action, the dynamic cross-linking effect constructed can efficiently realize energy dissipation through dynamic bonding with the help of molecular motion, thereby significantly improving toughness.

[0022] In response to the above-mentioned shortcoming ③: The present invention uses metal nanooxides as dynamic cross-linking ligands. The high specific surface area of ​​the nanomaterials provides a large number of surface metal ion reaction sites, which cooperate with the functional coordination groups at the end groups of the polyurethane to construct a high-density dynamic cross-linking reaction and form an energy dissipation center, thereby promoting energy dissipation in an orderly and efficient manner and achieving toughness modification.

[0023] In summary, the modified protein adhesive based on the nano hybrid dynamic cross-linking network provided by the present invention uses a double cross-linking agent as a cross-linking enhancement unit to co-cross-link the adhesive, and constructs an energy dissipation unit with nano metal oxide as a dynamic cross-linking ligand to cross-link with protein molecules. By adjusting the ratio of the two cross-linking agents, the bonding strength and bonding toughness can be directionally adjusted. It has universality, high efficiency, industrial ease of operation and scalable application characteristics, and is convenient for industrial practical application. It can effectively solve the above technical problems existing in the prior art. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the embodiments.

[0025] Explanation of terms Nanohybridization: A method of hybridizing and modifying the cross-linked network of materials using nanofillers.

[0026] Dynamic crosslinking: This concept is set relative to traditional covalent chemical crosslinking. Traditional chemical crosslinking has the characteristics of stable structure and non-reprocessable chemical bonds. Dynamic crosslinking uses non-covalent chemical bonds, such as physical hydrogen bonds, coordination bonds, etc., to construct a dynamic crosslinking network by taking advantage of its dynamic crosslinking characteristics.

[0027] Nanohybrid dynamic crosslinking: Using nanofillers as crosslinking ligands, synergistically combining the functional groups in the polymer molecular chains, a dynamic crosslinking network dominated by nanofillers is constructed.

[0028] The simultaneous modification of strengthening and toughening of soy protein adhesives focuses on improving the energy dissipation performance of the cross-linked curing network while maintaining the bonding strength. In the existing toughening modification method, a single curing system with energy dissipation primitives is constructed. Although the toughness can be improved, the toughness modification effect is limited due to defects such as low dynamic cross-linking efficiency and lack of molecular mobility, and it is at the expense of a certain mechanical strength. At the same time, the single curing cross-linking system requires precise control of the chemical cross-linking and dynamic cross-linking formed inside it to achieve toughness improvement.

[0029] The modified protein adhesive of the present invention is based on a nano-hybrid dynamic cross-linking network, which is a nano-hybrid dynamic cross-linking network formed based on nano-hybridization and dynamic cross-linking, and can efficiently and simultaneously improve the stability of the cross-linked curing structure and the energy dissipation performance, thereby realizing efficient enhancement and toughening modification of soybean protein adhesives. The present invention starts from the design of the cross-linking network of the adhesive and uses a double cross-linking agent to co-cross-link and modify the adhesive. By designing the cross-linking agent structure and constructing an energy dissipation mechanism with nano-metal oxides as dynamic cross-linking ligands, the bonding strength and bonding toughness can be directionally regulated by adjusting the ratio of the two cross-linking agents, and it has high efficiency and industrial ease of operation.

[0030] The modified protein adhesive based on the nano-hybrid dynamic cross-linked network of the present invention comprises the following components by weight: 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.

[0031] In the present invention, the plant protein meal is preferably soybean meal; the dispersion medium is preferably softened water; and the branched end epoxy polyurethane crosslinking agent is a hyperbranched epoxy polyurethane crosslinking agent.

[0032] 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 catalyst are reacted under nitrogen protection. The reaction conditions are preferably 80°C for 3 hours; Among them, the isocyanate is preferably isophorone diisocyanate; the polyol is preferably polytetramethylene oxide with an average molecular weight of 2900; and the catalyst is preferably dibutyltin dilaurate.

[0033] Secondly, after cooling, adding a small molecule polyol chain extender to continue the reaction, and adding an epoxy group-containing alcohol monomer to continue the reaction; preferably, the temperature is lowered to 70°C; the reaction conditions are preferably 70°C for 2h; Among them, the small molecule polyol chain extender is preferably propylene glycol. The epoxy group-containing alcohol monomer is preferably glycidol.

[0034] Finally, the mixture is cooled to room temperature, a neutralizing agent is added for neutralization, the neutralization reaction is preferably performed for 45 minutes, and water is added for emulsification.

[0035] Among them, the neutralizing agent is preferably triethylamine.

[0036] The invention provides a specific preparation method of a branched end epoxy polyurethane crosslinking agent. The method comprises the following steps: reacting 23.53 kg of isophorone diisocyanate, 58 kg of polytetramethylene glycol 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; cooling to 70° C., adding 1.59 kg of propylene glycol and reacting for 5 h; adding 3.14 kg of glycidol and reacting at 70° C. for 2 h; cooling to room temperature, adding 3.93 kg of triethylamine and reacting for 45 min; and emulsifying with water.

[0037] In the present invention, the linear polyurethane crosslinking agent is preferably an epoxy-imidazole double-terminated polyurethane crosslinking agent, and the preparation method thereof comprises the following steps: 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 hours.

[0038] Among them, the isocyanate is preferably isophorone diisocyanate; the polyol is preferably polytetramethylene glycol ether with an average molecular weight of 2900. The catalyst is preferably dibutyltin dilaurate.

[0039] Secondly, after cooling down, 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; preferably, the temperature is lowered to 70°C; the reaction conditions are preferably 70°C for 2h.

[0040] Among them, the small molecule polyol chain extender is preferably 1,4-butanediol; the epoxy group-containing alcohol monomer is preferably glycidol; the epoxy group-containing alcohol monomer is preferably glycidol; and the metal ion coordination group-containing reaction monomer is preferably 1-(3-aminopropyl)imidazole.

[0041] Finally, cool to room temperature, add a neutralizer to neutralize, and then add water to emulsify.

[0042] Among them, the neutralizing agent is preferably triethylamine.

[0043] The invention provides a specific preparation method of a linear polyurethane crosslinking agent. 23.53 kg of isophorone diisocyanate, 58 kg of polytetramethylene glycol ether, 5.20 kg of 2,2-bis(hydroxymethyl)propionic acid and 0.43 kg of dibutyltin dilaurate are reacted at 80°C for 3 hours under nitrogen protection; the temperature is lowered to 70°C, 2.34 kg of 1,4-butanediol is added and the reaction is carried out for 5 hours; 1.57 kg of glycidol and 2.65 kg of 1-(3-aminopropyl)imidazole are added and the reaction is carried out at 70°C for 2 hours; the temperature is lowered to room temperature, 3.93 kg of triethylamine is added and the reaction is carried out for 45 minutes, and water is added for emulsification.

[0044] In a second aspect, the present invention also provides a method for preparing the above-mentioned wood adhesive based on the nano-hybrid dynamic cross-linking network, which comprises uniformly mixing the plant protein meal with the dispersion medium; adding a branched end epoxy polyurethane cross-linking agent, a linear polyurethane cross-linking agent and a metal nano-oxide, and subjecting the mixture to high-pressure homogenization to obtain a modified protein adhesive.

[0045] In a third aspect, the present invention also provides the use of the modified protein adhesive based on the nano-hybrid dynamic cross-linking network in wood.

[0046] Example 1

[0047] The modified protein adhesive based on nano-hybrid dynamic cross-linking is composed of the following components: 75 kg of softened water, 25 kg of soybean meal, 4 kg of hyperbranched epoxy polyurethane cross-linking agent, 3 kg of epoxy-imidazole double-terminated polyurethane cross-linking agent, and 0.05 kg of nano zinc oxide. The preparation method thereof comprises the following steps: S1. In a reactor equipped with a stirrer, add softened water and soybean meal according to the ratio and stir evenly; S2, adding a hyperbranched epoxy polyurethane crosslinking agent and an epoxy-imidazole double-terminated polyurethane crosslinking agent according to a ratio, and stirring evenly to obtain an adhesive mucus; S3 adds nano zinc oxide according to the proportion and performs homogenizer treatment. The homogenization pressure is 25MPa. The obtained glue is used to prepare artificial boards.

[0048] Three batches of parallel samples were prepared using the same process, and the performance quality indicators of the obtained adhesives are shown in Table 1.

[0049] Example 2

[0050] The modified protein adhesive based on nano-hybrid dynamic cross-linking is composed of the following components: 70 kg of softened water, 30 kg of soybean meal, 5 kg of hyperbranched epoxy polyurethane cross-linking agent, 5 kg of epoxy-imidazole double-terminated polyurethane cross-linking agent, and 0.075 kg of nano zinc oxide.

[0051] The method for preparing the adhesive solution is the same as in Example 1. Three batches of parallel samples are prepared using the same process. The performance quality indicators of the obtained adhesive are shown in Table 1.

[0052] Example 3

[0053] The modified protein adhesive based on nano-hybrid dynamic cross-linking is composed of the following components: 65 kg of softened water, 35 kg of soybean meal, 6 kg of hyperbranched epoxy polyurethane cross-linking agent, 7 kg of epoxy-imidazole double-terminated polyurethane cross-linking agent, and 0.1 kg of nano zinc oxide.

[0054] The method for preparing the adhesive solution is the same as in Example 1. Three batches of parallel samples are prepared using the same process. The performance quality indicators of the obtained adhesive are shown in Table 1.

[0055] Comparative Example 1

[0056] Protein adhesive, composed of the following components: 75 Kg of softened water, 25 Kg of soybean meal.

[0057] The adhesive solution preparation method was the same as in Example 1 except that the hyperbranched epoxy polyurethane crosslinking agent, epoxy-imidazole double-terminated polyurethane crosslinking agent, and nano zinc oxide were not added. Three batches of parallel samples were prepared using the same process. The performance quality indicators of the obtained adhesive are shown in Table 1.

[0058] Comparative Example 2

[0059] The protein adhesive is composed of the following components: 70 kg of softened water and 30 kg of soybean meal.

[0060] The adhesive solution preparation method was the same as in Example 1 except that the hyperbranched epoxy polyurethane crosslinking agent, epoxy-imidazole double-terminated polyurethane crosslinking agent, and nano zinc oxide were not added. Three batches of parallel samples were prepared using the same process. The performance quality indicators of the obtained adhesive are shown in Table 1.

[0061] Comparative Example 3

[0062] Protein adhesive, composed of the following components: 65 Kg of softened water, 35 Kg of soybean meal.

[0063] The adhesive solution preparation method was the same as in Example 1 except that the hyperbranched epoxy polyurethane crosslinking agent, epoxy-imidazole double-terminated polyurethane crosslinking agent, and nano zinc oxide were not added. Three batches of parallel samples were prepared using the same process. The performance quality indicators of the obtained adhesive are shown in Table 1.

[0064] Comparative Example 4

[0065] The protein adhesive is composed of the following components: 75 kg of softened water, 25 kg of soybean meal, and 4 kg of hyperbranched epoxy polyurethane crosslinking agent.

[0066] The adhesive solution preparation method was the same as in Example 1 except that the epoxy-imidazole double-terminated polyurethane crosslinking agent and nano zinc oxide were not added. Three batches of parallel samples were prepared using the same process. The performance quality indicators of the obtained adhesive are shown in Table 1.

[0067] Comparative Example 5

[0068] The protein adhesive is composed of the following components: 70 kg of softened water, 30 kg of soybean meal, and 5 kg of hyperbranched epoxy polyurethane crosslinking agent.

[0069] The adhesive solution preparation method was the same as in Example 1 except that the epoxy-imidazole double-terminated polyurethane crosslinking agent and nano zinc oxide were not added. Three batches of parallel samples were prepared using the same process. The performance quality indicators of the obtained adhesive are shown in Table 1.

[0070] Comparative Example 6

[0071] 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.

[0072] The adhesive solution preparation method was the same as in Example 1 except that the epoxy-imidazole double-terminated polyurethane crosslinking agent and nano zinc oxide were not added. Three batches of parallel samples were prepared using the same process. The performance quality indicators of the obtained adhesive are shown in Table 1.

[0073] Experimental example

[0074] Three-layer 400 mm×400 mm plywood was manufactured using the adhesives of Examples 1-3 and Comparative Examples 1-6, respectively.

[0075] The material selected for preparing the plywood is poplar veneer with a moisture content of 8% and a size of 400mm×400mm×2mm.

[0076] Gluing method: double-sided gluing of core board, glue coating amount is 300-360g / m 2 .

[0077] Aging method and time: closed aging, 30 minutes.

[0078] Hot pressing pressure: 1.0MPa, hot pressing temperature: 120℃, hot pressing time: 70s / mm.

[0079] The plywood prepared by the above process was tested for formaldehyde emission, bonding strength and water resistance according to the method of GB / T 9846-2015 (Type II plywood). The test results are shown in Table 1: Table 1 Adhesive formulation and test performance data

[0080] The above are only preferred specific implementations of the present invention; however, the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, shall make equivalent replacements or changes according to the technical solutions and improved concepts of the present invention, which shall be covered within 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 plant 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.

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 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 a neutralizer to neutralize, and then add water to emulsify.

7. 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 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.

8. 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.

9. A method for preparing a wood 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.

10. 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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