Flame-retardant antibacterial soy protein-based adhesive and preparation method thereof

Abstract

This invention relates to the field of adhesive technology, and discloses a flame-retardant and antibacterial soybean protein-based adhesive and its preparation method. This flame-retardant and antibacterial soybean protein-based adhesive is prepared through the synergistic effect of electrostatic complexation and covalent cross-linking between polymer chains, and is made from raw materials comprising the following parts by weight: deionized water: 800-900 parts; soybean protein isolate powder: 100 parts; 30% sodium hydroxide aqueous solution: 10-20 parts; 69% 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution: 12-21 parts; intumescent flame retardant and rheology-regulating precursor: 40-64 parts; 12.5% ​​polyamide polyamine epichlorohydrin resin aqueous solution: 80-144 parts. This invention anchors the flame-retardant and antibacterial components in the cross-linked backbone to prevent loss, thereby improving the water resistance of the soybean protein-based adhesive while achieving a structurally stable, long-lasting fireproof and mildew-proof function.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a flame-retardant and antibacterial soybean protein-based adhesive and its preparation method. Background Technology

[0002] Soy protein-based adhesives, as a widely available and biodegradable biomass polymer material, have active functional groups such as amino, carboxyl, and hydroxyl groups distributed on their molecular chains. They are often used to replace traditional formaldehyde resins in wood processing and engineered wood products manufacturing. With the increasing environmental and safety standards for building materials, soybean protein, rich in nutrients, is susceptible to microbial attack and mold growth. Furthermore, as an organic polymer, it is easily combustible when exposed to open flames. Therefore, developing adhesives with both flame-retardant and antibacterial functions has become a modern technological necessity.

[0003] Existing technologies for improving the overall performance of such adhesives typically employ physical blending, directly mixing small-molecule mildew inhibitors, inorganic or organic flame retardants with a protein-based liquid, and then processing them with conventional crosslinking agents. This processing technique enables the adhesive layer to possess a certain degree of fire resistance and inhibition of microbial growth during the initial stages of coating and curing, thereby meeting basic standards for use in indoor panel materials.

[0004] However, soybean protein molecules inherently contain numerous hydrophilic groups, and simple physical blending cannot alter the matrix's tendency to absorb water and swell. In humid environments, small-molecule antibacterial agents and flame-retardant components that haven't established stable chemical bonds with the polymer backbone are easily migrated and lost with moisture penetration, causing their anti-mildew and flame-retardant properties to rapidly decline over time. Furthermore, achieving satisfactory flame-retardant effects often requires high amounts of additives, which hinders intermolecular reactions in the resin, disrupts the continuity of the adhesive's internal cross-linking network, and triggers phase separation, resulting in a significant reduction in the water-resistant adhesive strength after curing. Current technologies struggle to maintain the high-strength, water-resistant adhesive properties of soybean protein while simultaneously addressing the issues of functional additive loss and structural degradation.

[0005] Therefore, this invention proposes a flame-retardant and antibacterial soybean protein-based adhesive and its preparation method to overcome the shortcomings of the prior art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a flame-retardant and antibacterial soybean protein-based adhesive and its preparation method. This solves the problems of traditional physical blending methods, which cause antibacterial and flame-retardant components to easily migrate and lose with moisture, and the problems of a large number of free additives damaging the internal cross-linking network of the adhesive, thereby reducing the water-resistant bonding strength.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a flame-retardant and antibacterial soybean protein-based adhesive, employing the following technical solution: A flame-retardant and antibacterial soybean protein-based adhesive is prepared through the synergistic effect of electrostatic complexation and covalent cross-linking between polymer chains. It is made from raw materials comprising the following parts by weight: deionized water: 800-900 parts; soybean protein isolate powder: 100 parts; 30% sodium hydroxide aqueous solution: 10-20 parts; 69% 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution: 12-21 parts; intumescent flame retardant and rheology-modifying precursor: 40-64 parts; 12.5% ​​polyamide polyamine epichlorohydrin resin aqueous solution: 80-144 parts.

[0008] By employing the above technical solution, and using soy protein isolate powder as the main substrate and combining it with specific modifying reagents for a stepwise reaction, this invention constructs a dual cross-linked structure at the molecular level, where a dynamic electrostatic complex network and an irreversible covalent network interpenetrate. This enhances the adhesive's water resistance and bonding strength while also imparting anti-mildew and flame-retardant properties. The formation of this dual network in the reaction solution primarily depends on the following reaction process: Soy protein undergoes uncoiling under heating and in the alkaline environment of sodium hydroxide. This process breaks down the hydrogen and disulfide bonds within the protein spheres, causing the molecular chains to unwind and exposing the previously encapsulated active functional groups such as amino, carboxyl, and hydroxyl groups. These exposed functional groups provide the necessary conditions for subsequent grafting and cross-linking.

[0009] In the subsequent cationization grafting modification, the introduced 3-chloro-2-hydroxypropyltrimethylammonium chloride is converted into an epoxypropyltrimethylammonium chloride intermediate in an alkaline environment. The epoxy group of this intermediate then undergoes a nucleophilic ring-opening substitution reaction with the amino or hydroxyl groups on the aforementioned unfolded protein chain, successfully grafting quaternary ammonium salt groups onto the protein chain. On the one hand, the positive charge of the quaternary ammonium salt groups can adsorb and destroy the negatively charged bacterial cell walls, giving the adhesive a long-lasting antibacterial and antifungal effect; on the other hand, these cations also provide necessary sites for establishing an electrostatic complex network.

[0010] When the intumescent flame retardant and rheology-modifying precursor is added to the base liquid, the anionic groups on the precursor and the quaternary ammonium cations on the protein chain are electrostatically attracted to each other, forming a dynamic physical cross-linking network. This reversible complexation not only improves the initial tack of the adhesive but also enhances its rheological properties, allowing the adhesive to maintain a suitable spreading viscosity during coating to avoid excessive penetration into the substrate.

[0011] Finally, during the cross-linking and curing stage, the nitrogen-containing heterocyclic butyl groups in the added polyamide polyamine epichlorohydrin resin molecular chain undergo nucleophilic ring-opening reactions with the remaining active amino and carboxyl groups on the protein molecular chain. This irreversible covalent bond constructs a dense three-dimensional network, which synergistically fuses with the aforementioned electrostatic complex network, effectively reducing the number of hydrophilic groups in the adhesive layer and hindering the intrusion path of water molecules, thereby improving the water-resistant adhesive strength.

[0012] Preferably, the flame-retardant and antibacterial soybean protein-based adhesive is made from the following raw materials in parts by weight: deionized water: 850 parts; soybean protein isolate powder: 100 parts; sodium hydroxide aqueous solution with a mass fraction of 30%: 15 parts; 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution with a mass fraction of 69%: 16 parts; intumescent flame retardant and rheology modulating precursor: 50 parts; polyamide polyamine epichlorohydrin resin aqueous solution with a mass fraction of 12.5%: 112 parts.

[0013] By adopting the above technical solution, the raw material ratio is within a relatively reasonable stoichiometric range. Under this specific ratio, the amount of sodium hydroxide added is sufficient to fully unwind the protein without causing excessive degradation; the proportion of quaternary ammonium salt modifier satisfies the need to inhibit microbial growth while also retaining a sufficient number of amino groups for subsequent covalent cross-linking of the resin; the amount of cross-linking agent is matched with the number of active sites in the mixture, resulting in a moderate cross-linking density and uniform stress distribution in the adhesive layer after curing, thus achieving a good balance between bonding strength and water resistance.

[0014] Preferably, the expansion flame retardant and rheology-modifying precursor is made from raw materials comprising the following parts by weight: 24-36 parts of phytic acid aqueous solution with a mass fraction of 50%; 4-8 parts of glycerol; 8-12 parts of tannic acid powder; and 4-8 parts of urea powder.

[0015] By adopting the above technical solution, a synergistic intumescent flame-retardant structure is formed inside the precursor. The flame-retardant effect is achieved because, in this precursor, phytic acid, as an acid source, catalyzes the dehydration of the matrix into carbon at high temperatures; urea, as a gas source, releases non-combustible gases such as ammonia and carbon dioxide upon thermal decomposition, promoting the foaming and expansion of the molten carbon layer; tannic acid, as a carbon source, provides a polyphenolic ring structure to participate in the formation of a dense carbon layer; and glycerol, as a phase solvent and rheology modifier, promotes the uniform dispersion of the above components and prevents crystallization.

[0016] When this precursor is added to the adhesive, the negative charge ionized from the phosphate groups in the phytic acid molecules directly undergoes the aforementioned electrostatic complexation reaction with the quaternary ammonium cations in the protein base solution. Simultaneously, the abundant phenolic hydroxyl groups in tannic acid not only form hydrogen bonds with the protein molecular chains to enhance the initial tack of the adhesive, but also covalently bond with the nitrogen-containing heterocyclic butyl groups of the polyamide polyamine epichlorohydrin resin during curing. Through this mechanism, the intumescent flame-retardant component is anchored within the three-dimensional network framework of the adhesive via chemical bonds and electrostatic attraction. This alleviates the migration and loss of small-molecule flame retardants in humid environments and allows for the rapid formation of an intumescent, insulating carbon layer upon contact with fire to block heat and oxygen transfer, thus exerting its flame-retardant effect.

[0017] Secondly, the present invention provides a method for preparing a flame-retardant and antibacterial soybean protein-based adhesive, using the following technical solution: A method for preparing a flame-retardant and antibacterial soybean protein-based adhesive includes the following steps: S1, dispersing soybean protein isolate powder in deionized water and stirring to initially disperse the soybean protein isolate powder, obtaining a soybean protein isolate suspension; S2, heating the soybean protein isolate suspension, adding sodium hydroxide aqueous solution to adjust the pH value of the soybean protein isolate suspension, and stirring under constant temperature conditions to fully de-curl the soybean protein isolate, obtaining an alkaline depolymerized soybean protein solution; S3, adding 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution dropwise to the alkaline depolymerized soybean protein solution. After the addition is complete, the reaction is continued under constant temperature and pH conditions to obtain a cationic soybean protein derivative base liquid; S4, the cationic soybean protein derivative base liquid is cooled, and the expansion flame retardant and rheology regulation precursor is pumped into the cationic soybean protein derivative base liquid, where electrostatic complexation occurs between the polymer chains to obtain a dynamic electrostatic complexed protein base liquid; S5, a polyamide polyamine epichlorohydrin resin aqueous solution is added to the dynamic electrostatic complexed protein base liquid, and a ring-opening chain extension and covalent cross-linking reaction is carried out at a constant temperature. After the ring-opening chain extension and covalent cross-linking reaction is completed, the mixture is cooled, filtered, degassed, and discharged to obtain a flame-retardant and antibacterial soybean protein base adhesive.

[0018] By employing the above-mentioned technical solution, the stepwise preparation method effectively avoids potential side reactions and premature gelation when mixing multiple reactants. The successful construction of the interpenetrating network structure primarily relies on the control of the physical and chemical environment during the specific operational steps. In the dispersion and uncoiling stage of the soybean protein powder, after the raw material powder is wetted in the aqueous phase, the tightly stacked protein spheres gradually unfold due to the alkaline environment provided by sodium hydroxide and the heating conditions. This conformational change exposes the reactive functional groups that were originally encased within the molecules, thus providing sufficient contact sites for subsequent grafting reactions.

[0019] During cationization grafting, maintaining a constant temperature and alkalinity of the mixture promotes the ring-opening substitution reaction of the added 3-chloro-2-hydroxypropyltrimethylammonium chloride, which is then grafted onto the protein backbone. This process successfully introduces quaternary ammonium salt groups with antibacterial activity without damaging the protein's macromolecular backbone.

[0020] Regarding the introduction of the flame-retardant precursor, a cooling and slow pumping process was specifically adopted. The precursor with anionic groups was introduced into the cooled cationic soybean protein derivative base liquid, where it under relatively mild conditions underwent electrostatic attraction with the cations on the protein chains, thereby forming a physical complex network. This effectively prevented flocculation and precipitation caused by excessively high local reactant concentrations.

[0021] During the cross-linking and curing stage, the addition of polyamide-polyamine-epoxychloropropane resin triggers irreversible chemical ring-opening and chain-extending reactions. The cross-linking agent molecules combine with the remaining active groups on the protein chains, locking the previously formed physical complex network within the covalent backbone. Finally, cooling and filtration degassing processes eliminate air bubbles trapped in the adhesive solution and terminate the continued cross-linking reaction, thereby ensuring the storage stability and coating effect of the finished adhesive product.

[0022] Preferably, step S1 is carried out in the main reactor, where the stirring speed of the paddle agitator is set to 150-250 rpm, and the continuous stirring time for dispersing the soy protein isolate powder is 20-30 minutes. In step S2, hot water is introduced into the jacket of the main reactor to raise the temperature of the soy protein isolate suspension to 50-60°C, and the pH value of the soy protein isolate suspension is adjusted to 11.0-11.5. Under the constant temperature condition of 50-60°C, the stirring time for uncoiling the soy protein isolate is 45-75 minutes. In step S3, the dropwise addition time of the 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution is controlled at 20-30 minutes; after the 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution is added, the reaction is continued at 50-60°C and pH value of 11.0-11.5 for 50-70 minutes.

[0023] By employing the above technical solution, the stirring speed and dispersion time set in the main reactor can ensure that the powder is completely wetted by deionized water while avoiding the generation of excessive foam. Controlling the temperature between 50-60℃ and adjusting the pH to 11.0-11.5, this specific hot alkaline environment provides sufficient energy to break the hydrogen bonds within the protein, ensuring conformational unfolding without causing protein backbone breakage or degradation due to excessive temperature or alkalinity. Limiting the dropwise addition of 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution and subsequent reaction time aims to prevent localized reactant accumulation and side reactions such as hydrolysis, allowing the cationization reaction to proceed smoothly and resulting in a more uniform charge distribution on the final protein molecular chain.

[0024] Preferably, in step S4, cooling water is introduced into the jacket of the main reactor to lower the temperature of the cationic soybean protein derivative base liquid to 35-45°C; the high-shear dispersing emulsifier inserted into the main reactor is turned on, and the rotation speed of the high-shear dispersing emulsifier is set to 2000-3000 rpm; the pumping rate of the expansion flame retardant and rheology-controlled precursor is 10-20 L / h, and the pH value of the dynamic electrostatic complexed protein base liquid is stabilized at 7.0-7.5. In step S5, the high-shear dispersing emulsifier is turned off, and only the paddle agitator of the main reactor is kept running, with the rotation speed of the paddle agitator set to 100-150 rpm; the temperature of the ring-opening chain extension and covalent crosslinking reaction in the main reactor is controlled at 40-50°C, and the reaction time of the ring-opening chain extension and covalent crosslinking reaction is 30-50 minutes; after the ring-opening chain extension and covalent crosslinking reaction is completed, the final adhesive mixture is cooled, filtered through a filter screen to remove bubbles, and discharged.

[0025] By employing the above technical solution, temperature control and shear force regulation at specific stages directly affect the molding quality of the double crosslinked network. Lowering the temperature of the cationic soybean protein derivative base solution to 35-45℃ before pumping in the high-viscosity precursor slows the molecular chain movement rate, thereby inhibiting excessive local crosslinking caused by rapid component encounters. The high shear force generated by operating the high-shear dispersion emulsifier instantly breaks up and disperses the pumped precursor droplets in the base solution. Combined with a controlled pumping rate of 10-20 L / h, this ensures uniform electrostatic complexation reaction, and the pH of the mixture gradually decreases to near neutral. In the subsequent covalent crosslinking stage, shutting down the high-shear dispersion emulsifier and relying on a paddle agitator running at low speed prevents the high-intensity mechanical forces from severing the newly formed chemical bond network. Maintaining the crosslinking reaction temperature at 40-50℃ keeps the crosslinking reaction of the polyamide polyamine epichlorohydrin resin at a reasonable rate, avoiding excessive internal crosslinking of the adhesive before discharge, which would result in loss of the required fluidity for coating.

[0026] Preferably, the expansion flame retardant and rheology-controlled precursor described in S4 is prepared in advance by the following steps: (1) phytic acid aqueous solution and glycerol are added to the auxiliary preparation vessel, and stirring is turned on to mix evenly to obtain a transparent binary mixed solution; (2) the binary mixed solution is heated, and tannic acid powder is continuously added at the temperature after the temperature is raised to disperse and dissolve the tannic acid powder to obtain a ternary suspension; (3) the temperature in the auxiliary preparation vessel is maintained after the temperature is raised, urea powder is added to the ternary suspension, and then the ternary suspension is stirred at a constant temperature in a closed state until the ternary suspension is transformed into a homogeneous transparent high-viscosity fluid without visible particles, thus obtaining the expansion flame retardant and rheology-controlled precursor. In step (1), the stirring speed of the auxiliary mixing vessel is set to 300-500 rpm; in step (2), the binary mixed solution is heated to 55-65℃, and the tannic acid powder is continuously added within 10-15 minutes; in step (3), the temperature inside the auxiliary mixing vessel is maintained at 55-65℃, and the constant temperature stirring time after the urea powder is added is 40-60 minutes.

[0027] By employing the above technical solution, various flame-retardant raw materials are pre-blended, which helps to obtain a stable mixed solution in advance. Considering the different solubilities among the components, glycerol is used as a bridging solvent, and a heating environment of 55-65℃ is maintained, allowing tannic acid and urea powder to gradually dissolve in the phytic acid aqueous solution. A closed-loop, temperature-controlled stirring process is used to prevent excessive evaporation of moisture and the escape of trace gases generated by heating urea, ensuring thorough mixing of the raw materials in the liquid phase and the establishment of intermolecular hydrogen bonds. After a specified mild reaction time, the mixture transforms from a suspension containing solid particles into a homogeneous, transparent, high-viscosity fluid. This pre-blending step avoids the problem of crystallization caused by uneven dispersion when flame-retardant raw materials are directly added to the protein adhesive, ensuring that the flame-retardant components are uniformly anchored in the adhesive network.

[0028] This invention provides a flame-retardant and antibacterial soybean protein-based adhesive and its preparation method. It has the following beneficial effects: 1. This invention constructs a dual network structure of physical electrostatic complexation and chemical covalent cross-linking interpenetrating resin by alkaline uncoiling and cationic grafting modification of soybean protein, combined with a stepwise reaction of precursor and cross-linking resin. This cross-linking process consumes hydrophilic groups on the molecular chains, forming a dense framework that hinders the penetration of water molecules. This structural feature directly improves the water-resistant adhesive strength of the soybean protein-based product, overcoming the defect of conventional bio-adhesives that are prone to delamination when exposed to moisture.

[0029] 2. This invention introduces a modified reagent with quaternary ammonium salt groups, causing it to undergo a nucleophilic ring-opening substitution reaction with the protein molecular chain, thereby preparing an antibacterial material with a long-lasting protective mechanism. The quaternary ammonium cations grafted onto the main chain adsorb and destroy the negatively charged bacterial cell walls due to their own positive charge. This technique of covalently binding active groups to the polymer backbone effectively prevents the migration and loss of added small-molecule antifungal agents in humid environments.

[0030] 3. This invention introduces a precursor composed of phytic acid, urea, and tannic acid into the reaction solution, utilizing chemical bonds and electrostatic attraction to anchor the expanding flame-retardant components within the network framework. When exposed to fire and heat, phytic acid catalyzes the formation of char in the matrix, urea releases non-flammable gases to promote foaming of the char layer, and tannic acid participates in the formation of a dense char layer. The multi-component synergistic generation of an insulating char layer blocks heat and oxygen transfer, fundamentally ensuring the fireproof and heat-insulating properties of the finished adhesive in high-temperature environments. Attached Figure Description

[0031] Figure 1 These are verification diagrams of local physicochemical properties during the preparation process of Examples 1-3 of the present invention; wherein, (a) records the dynamic decay trajectory of the pH value of the mixed liquid in the main reactor over time when the expansion flame retardant and rheology-controlled precursor is continuously pumped in by the high-pressure metering pump in step (4) of Examples 1, 2 and 3; (b) shows the steady-state shear rheological characteristics of the soybean protein-based adhesive finally obtained in Examples 1, 2 and 3 under a constant temperature environment of 25℃; Figure 2 This is a diagram showing the viscosity evolution of the soybean protein-based adhesive at room temperature during storage according to the present invention. Figure 3 This is a line graph showing the dry / wet mechanical bonding strength test results of the plywood of this invention; Figure 4 This is a line graph comparing the limiting oxygen index of different groups of adhesives according to the present invention; Figure 5 This is a comparative bar chart showing the evolution of the antibacterial rates of Escherichia coli and Staphylococcus aureus with the number of water washing cycles; wherein, (a) is a comparative chart of the antibacterial rates of Escherichia coli, and (b) is a comparative chart of the antibacterial rates of Staphylococcus aureus. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0034] Soy protein isolate (CAS No.: 9010-10-0), a commercially available food-grade powder product with a protein mass fraction greater than or equal to 90%.

[0035] 3-Chloro-2-hydroxypropyltrimethylammonium chloride (CAS No.: 3327-22-8), a commercially available industrial grade product, is an aqueous solution with a mass fraction of 69%.

[0036] Phytic acid (CAS No.: 83-86-3), a commercially available industrial-grade product, is an aqueous solution with a mass fraction of 50%.

[0037] Tannic acid (CAS No.: 1401-55-4), commercially available industrial-grade powder product.

[0038] Urea (CAS No.: 57-13-6), commercially available analytical grade powder product.

[0039] Glycerol (CAS No.: 56-81-5), a commercially available analytical grade liquid product.

[0040] Polyamide polyamine epichlorohydrin resin, a commercially available industrial-grade adhesive crosslinking resin, is an aqueous solution with a mass fraction of 12.5%. Its main chain is a water-soluble polymer obtained by the condensation of adipic acid and diethylenetriamine to form a polyamide polyamine skeleton and then crosslinking it with epichlorohydrin. Its structure contains amide bonds and nitrogen-containing heterocyclic butyl groups with high reactivity.

[0041] Sodium hydroxide (CAS No.: 1310-73-2), a commercially available analytical grade solid product, should be prepared into a 30% aqueous solution with deionized water before use.

[0042] Preparation Example 1: This preparation example provides a method for preparing an intumescent flame retardant and rheology-modified precursor, including the following steps: (1) At room temperature, 30 parts by weight of 50% phytic acid aqueous solution and 5 parts by weight of glycerol are added to an auxiliary mixing vessel with a temperature-controlled water bath jacket and stirring function. Stirring is started and the speed is set to 400 rpm. The mixture is mixed evenly to obtain a transparent binary mixed solution.

[0043] (2) The above binary mixed solution is heated to 60°C within 15 minutes. At this temperature, 10 parts by weight of tannic acid powder are continuously added within 12 minutes. The tannic acid powder gradually disperses and initially dissolves to obtain a brownish-red ternary suspension.

[0044] (3) Maintain the temperature inside the auxiliary mixing vessel at 60°C, add 5 parts by weight of urea powder to the above ternary suspension, and then stir at a constant temperature for 50 minutes in a closed state. The mixture gradually changes from a suspension to a brownish-red homogeneous transparent high-viscosity fluid without visible particles, thus obtaining the expansion flame retardant and rheology regulation precursor, which is then sealed and kept warm for later use.

[0045] Preparation Example 2: This preparation example provides a method for preparing an intumescent flame retardant and rheology-modified precursor, including the following steps: (1) At room temperature, 24 parts by weight of 50% phytic acid aqueous solution and 4 parts by weight of glycerol were added to an auxiliary mixing vessel with a temperature-controlled water bath jacket and stirring function. The stirring was turned on and the speed was set to 300 rpm. The mixture was mixed evenly to obtain a transparent binary mixed solution.

[0046] (2) The above binary mixed solution is heated to 55°C within 10 minutes. At this temperature, 8 parts by weight of tannic acid powder are continuously added within 10 minutes. The tannic acid powder gradually disperses and initially dissolves to obtain a brownish-red ternary suspension.

[0047] (3) Maintain the temperature inside the auxiliary mixing vessel at 55°C, add 4 parts by weight of urea powder to the above ternary suspension, and then stir at a constant temperature for 40 minutes in a closed state. The mixture gradually changes from a suspension to a brownish-red homogeneous transparent high-viscosity fluid without visible particles, thus obtaining the expansion flame retardant and rheology regulation precursor, which is then sealed and kept warm for later use.

[0048] Preparation Example 3: This preparation example provides a method for preparing an intumescent flame retardant and rheology-modified precursor, including the following steps: (1) At room temperature, 36 parts by weight of 50% phytic acid aqueous solution and 8 parts by weight of glycerol were added to an auxiliary mixing vessel with a temperature-controlled water bath jacket and stirring function. Stirring was started and the speed was set to 500 rpm. The mixture was mixed evenly to obtain a transparent binary mixed solution.

[0049] (2) The above binary mixed solution is heated to 65°C within 20 minutes. At this temperature, 12 parts by weight of tannic acid powder are continuously added within 15 minutes. The tannic acid powder gradually disperses and initially dissolves to obtain a brownish-red ternary suspension.

[0050] (3) Maintain the temperature inside the auxiliary mixing vessel at 65°C, add 8 parts by weight of urea powder to the above ternary suspension, and then stir at a constant temperature for 60 minutes in a closed state. The mixture gradually changes from a suspension to a brownish-red homogeneous transparent high-viscosity fluid without visible particles, thus obtaining the expansion flame retardant and rheology regulation precursor, which is then sealed and kept warm for later use.

[0051] Example 1: This example provides a method for preparing a flame-retardant and antibacterial soybean protein-based adhesive, comprising the following steps: (1) Add 850 parts by weight of deionized water to the main reactor equipped with a paddle stirrer and a jacket, turn on the paddle stirrer of the main reactor, set the speed to 200 rpm, add 100 parts by weight of soy protein isolate powder at a uniform speed, and stir continuously for 25 minutes to initially disperse the soy protein isolate powder and obtain soy protein isolate suspension.

[0052] (2) Hot water is introduced into the jacket of the main reactor to raise the temperature of the above soybean protein isolate suspension to 55°C. Using a liquid metering pump, 15 parts by weight of a 30% sodium hydroxide aqueous solution are added dropwise over 15 minutes to adjust the pH of the soybean protein isolate suspension to 11.2. Under this constant temperature condition, the suspension is kept warm and stirred for 60 minutes to fully de-coil the soybean protein isolate and obtain an alkaline depolymerized soybean protein solution.

[0053] (3) 16 parts by weight of a 69% aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added dropwise to the above alkaline depolymerized soybean protein solution at a constant rate using a constant flow feed pump. The addition time was controlled at 25 minutes. After the addition was completed, the reaction was continued for 60 minutes with stirring at 55°C and pH 11.2 to obtain the cationic soybean protein derivative base solution.

[0054] (4) Cooling water was introduced into the jacket of the main reactor to steadily reduce the temperature of the above-mentioned cationic soybean protein derivative base liquid to 40°C. The working head of the high-shear dispersing emulsifier, which extends below the liquid surface of the main reactor, was turned on and the rotation speed was set to 2500 rpm. Using a high-pressure metering pump, 50 parts by weight of the intumescent flame retardant and rheology-modifying precursor prepared in Preparation Example 1 were pumped into the cationic soybean protein derivative base liquid at a rate of 15 L / h. As the intumescent flame retardant and rheology-modifying precursor was continuously pumped in, the pH value of the liquid gradually decreased until it finally stabilized at 7.2. At this point, uniform electrostatic complexation occurred between the polymer chains, and a dynamically electrostatically complexed protein base liquid was obtained.

[0055] (5) Turn off the working head of the high-shear dispersing emulsifier, leaving only the paddle agitator of the main reactor running at a speed of 125 rpm. Add 112 parts by weight of a 12.5% ​​polyamide polyamine epichlorohydrin resin aqueous solution to the above dynamic electrostatic complexed protein base liquid at one time, control the temperature inside the main reactor at 45°C, and carry out the ring-opening chain extension and covalent cross-linking reaction for 40 minutes. After the reaction is completed, cool the final adhesive liquid to 25°C, filter it through a 100-mesh filter to remove bubbles, and then discharge it to obtain the flame-retardant and antibacterial soybean protein-based adhesive.

[0056] Example 2: This example provides a method for preparing a flame-retardant and antibacterial soybean protein-based adhesive, comprising the following steps: (1) Add 800 parts by weight of deionized water to the main reactor equipped with a paddle stirrer and a jacket, turn on the paddle stirrer, set the speed to 150 rpm, add 100 parts by weight of soy protein isolate powder at a uniform speed, and stir continuously for 20 minutes to initially disperse the soy protein isolate powder and obtain soy protein isolate suspension.

[0057] (2) Hot water is introduced into the jacket of the main reactor to raise the temperature of the above soybean protein isolate suspension to 50°C. Using a liquid metering pump, 10 parts by weight of a 30% sodium hydroxide aqueous solution are added dropwise over 10 minutes to adjust the pH of the soybean protein isolate suspension to 11.0. Under this constant temperature condition, the suspension is kept warm and stirred for 45 minutes to fully de-coil the soybean protein isolate and obtain an alkaline depolymerized soybean protein solution.

[0058] (3) 12 parts by weight of a 69% aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added dropwise to the above alkaline depolymerized soybean protein solution at a constant rate using a constant flow feed pump. The addition time was controlled at 20 minutes. After the addition was completed, the reaction was continued for 50 minutes with stirring at 50°C and pH 11.0 to obtain the cationic soybean protein derivative base solution.

[0059] (4) Cooling water was introduced into the jacket of the main reactor to steadily reduce the temperature of the above-mentioned cationic soybean protein derivative base liquid to 35°C. The working head of the high-shear dispersing emulsifier, which extends below the liquid surface of the main reactor, was turned on and the rotation speed was set to 2000 rpm. Using a high-pressure metering pump, 40 parts by weight of the intumescent flame retardant and rheology-modifying precursor prepared in Preparation Example 2 were pumped into the cationic soybean protein derivative base liquid at a rate of 10 L / h. As the intumescent flame retardant and rheology-modifying precursor was continuously pumped in, the pH value of the liquid gradually decreased until it finally stabilized at 7.0. At this point, uniform electrostatic complexation occurred between the polymer chains, and a dynamically electrostatically complexed protein base liquid was obtained.

[0060] (5) Turn off the working head of the high-shear dispersing emulsifier, leaving only the paddle agitator of the main reactor running at a speed of 100 rpm. Add 80 parts by weight of a 12.5% ​​polyamide polyamine epichlorohydrin resin aqueous solution to the above dynamic electrostatic complexed protein base liquid, control the temperature inside the main reactor at 40°C, and carry out the ring-opening chain extension and covalent cross-linking reaction for 30 minutes. After the reaction is completed, cool the final adhesive liquid to 25°C, filter it through a 100-mesh filter to remove bubbles, and then discharge it to obtain the flame-retardant and antibacterial soybean protein-based adhesive.

[0061] Example 3: This example provides a method for preparing a flame-retardant and antibacterial soybean protein-based adhesive, comprising the following steps: (1) Add 900 parts by weight of deionized water to the main reactor equipped with a paddle stirrer and a jacket, turn on the paddle stirrer, set the speed to 250 rpm, add 100 parts by weight of soy protein isolate powder at a uniform speed, and stir continuously for 30 minutes to initially disperse the soy protein isolate powder and obtain soy protein isolate suspension.

[0062] (2) Hot water is introduced into the jacket of the main reactor to raise the temperature of the above soy protein isolate suspension to 60°C. Using a liquid metering pump, 20 parts by weight of a 30% sodium hydroxide aqueous solution are added dropwise over 20 minutes to adjust the pH of the soy protein isolate suspension to 11.5. Under this constant temperature condition, the suspension is kept warm and stirred for 75 minutes to fully de-coil the soy protein isolate and obtain an alkaline depolymerized soy protein solution.

[0063] (3) 21 parts by weight of a 69% aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added dropwise to the above alkaline depolymerized soybean protein solution at a constant rate using a constant flow feed pump. The addition time was controlled at 30 minutes. After the addition was completed, the reaction was continued for 70 minutes with stirring at 60°C and pH 11.5 to obtain the cationic soybean protein derivative base solution.

[0064] (4) Cooling water was introduced into the jacket of the main reactor to steadily reduce the temperature of the above-mentioned cationic soybean protein derivative base liquid to 45°C. The working head of the high-shear dispersing emulsifier, which extends below the liquid surface of the main reactor, was turned on, and the rotation speed was set to 3000 rpm. Using a high-pressure metering pump, 64 parts by weight of the intumescent flame retardant and rheology-modifying precursor prepared in Preparation Example 3 were pumped into the cationic soybean protein derivative base liquid at a rate of 20 L / h. As the intumescent flame retardant and rheology-modifying precursor was continuously pumped in, the pH value of the liquid gradually decreased until it finally stabilized at 7.5. At this point, uniform electrostatic complexation occurred between the polymer chains, and a dynamically electrostatically complexed protein base liquid was obtained.

[0065] (5) Turn off the working head of the high-shear dispersion emulsifier, leaving only the paddle agitator of the main reactor running at a speed of 150 rpm. Add 144 parts by weight of a 12.5% ​​polyamide polyamine epichlorohydrin resin aqueous solution to the above dynamic electrostatic complexed protein base liquid at one time, control the temperature inside the main reactor at 50°C, and carry out the ring-opening chain extension and covalent cross-linking reaction for 50 minutes. After the reaction is completed, cool the final adhesive liquid to 25°C, filter it through a 100-mesh filter to remove bubbles, and then discharge it to obtain the flame-retardant and antibacterial soybean protein-based adhesive.

[0066] Comparative Example 1: Compared with Example 1, the difference is that the intumescent flame retardant and rheology-modifying precursors were not prepared in advance. Specifically, in step (4), the intumescent flame retardant and rheology-modifying precursors were not added. Instead, under the condition that the working head of the high-shear dispersing emulsifier rotates at 2500 rpm, 30 parts by weight of 50% phytic acid aqueous solution, 5 parts by weight of glycerol, 10 parts by weight of tannic acid powder and 5 parts by weight of urea powder were added dropwise to the cationic soybean protein derivative base liquid within 20 minutes. The dropping or feeding time of each raw material was controlled within 5 minutes, and the rest were the same.

[0067] Comparative Example 2: Compared with Example 1, the difference is that glycerol was not added when preparing the intumescent flame retardant and rheology-modifying precursor. Specifically, the intumescent flame retardant and rheology-modifying precursor was prepared only from 30 parts by weight of 50% phytic acid aqueous solution, 10 parts by weight of tannic acid powder and 5 parts by weight of urea powder. The mixing and heating process, stirring speed, time and temperature and other process conditions were completely consistent with those of Example 1. In step (4), 45 parts by weight of the corresponding intumescent flame retardant and rheology-modifying precursor without glycerol was pumped into the cationic soybean protein derivative base liquid. All other aspects were the same.

[0068] Comparative Example 3: Compared with Example 1, the difference is that the cationization grafting reaction of soybean protein in step (3) was omitted. Specifically, after obtaining the alkaline depolymerized soybean protein solution in step (2), cooling water was directly introduced into the jacket of the main reactor to steadily reduce the temperature to 40°C. Then, the working head of the high-shear dispersion emulsifier, which extends below the liquid surface of the main reactor, was turned on, and 50 parts by weight of the expansion flame retardant and rheology-modifying precursor prepared in Preparation Example 1 was pumped into the alkaline depolymerized soybean protein solution at a rate of 15 L / h. No 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution was added throughout the process, and everything else was the same.

[0069] Comparative Example 4: Compared with Example 1, the difference is that urea was not added when preparing the intumescent flame retardant and rheology-modifying precursor. Specifically, the intumescent flame retardant and rheology-modifying precursor was prepared only from 30 parts by weight of 50% phytic acid aqueous solution, 5 parts by weight of glycerol and 10 parts by weight of tannic acid powder. The mixing and heating process, stirring speed, time and temperature and other process conditions were completely consistent with those of Example 1. In step (4), 45 parts by weight of the corresponding urea-free intumescent flame retardant and rheology-modifying precursor were pumped into the cationic soybean protein derivative base liquid. All other aspects were the same.

[0070] Comparative Example 5: Compared with Example 1, the difference is that the traditional physical blending route is used instead of the in-situ grafting and expansion flame retardant and rheology-controlled precursor complexation system of the present invention. Specifically, steps (3) and (4) are omitted. After obtaining the alkaline depolymerized soybean protein solution in step (2), the main reactor is cooled to 45°C, and its pH value is adjusted back to 7.2 using a 10% hydrochloric acid aqueous solution. Then, only the paddle stirrer of the main reactor is kept running and the speed is set to 125 rpm. 112 parts by weight of a 12.5% ​​polyamide polyamine epichlorohydrin resin aqueous solution are added at once, and 50 parts by weight of ammonium polyphosphate (CAS No.: 68333-79-9) powder is directly physically mixed in. Under these conditions, the mixture is physically stirred and blended at a constant temperature for 40 minutes. Finally, the temperature is lowered to 25°C and the mixture is discharged. The rest is the same.

[0071] Test Example 1: Experimental Objective: This experiment aims to objectively verify the in-situ grafting of quaternary ammonium salt cations onto the protein macromolecular backbone in Examples 1 to 3 through electrodynamics, online pH monitoring, and rheological physics testing, and to verify the acid-releasing neutralization and dielectric shielding rheological regulation mechanism played by the intumescent flame retardant and rheology-regulated precursors in the adhesive preparation process.

[0072] Experimental steps: Three key node products from the preparation process of Examples 1, 2 and 3 were selected as test objects: the alkaline depolymerized soybean protein liquid obtained at the end of step (2), the cationic soybean protein derivative base liquid obtained at the end of step (3), and the final flame-retardant and antibacterial soybean protein base adhesive obtained in step (5).

[0073] Take a small amount of alkaline depolymerized soybean protein solution obtained in step (2) of Examples 1 to 3 and cationic soybean protein derivative base solution obtained in step (3). Dilute each sample with deionized water to a solid content of about 0.1%. Use a nanoparticle size and zeta potential analyzer to measure the zeta potential of the two stage products in a constant temperature measuring cell at 25°C. Repeat the test three times for each sample and take the average value.

[0074] In step (4) of Examples 1 to 3, during the time period when the intumescent flame retardant and rheology-regulating precursor is pumped into the aforementioned cationic soybean protein derivative base liquid using a high-pressure metering pump, the electrode probe of the existing industrial online pH meter is directly inserted below the liquid surface of the main reactor. The data acquisition terminal is turned on to record the change of pH value of the mixed liquid over time. The initial stable pH value of the liquid before pumping is recorded. Subsequently, the sampling frequency is set to record once every 2 minutes until the intumescent flame retardant and rheology-regulating precursor is completely pumped in and the pH value of the mixed liquid reaches the final stable state. The final pH value in this state is recorded.

[0075] Take 20 mL of each of the flame-retardant and antibacterial soybean protein-based adhesives finally prepared in step (5) of Examples 1 to 3, and conduct steady-state shear tests using a rotational rheometer with a parallel plate fixture under constant temperature conditions of 25°C. The shear rate scan range is set to 0.1 s. -1 up to 100s -1 The dynamic physical quantity of shear stress in a liquid as a function of shear rate was continuously recorded, with the shear rate recorded as 0.1 s⁻¹. -1 The apparent viscosity of the adhesive at that time.

[0076] Experimental results (see Table 1): Table 1: Test results of physicochemical parameters of key preparation nodes in Examples 1-3

[0077] Test conclusion: According to Table 1 and Figure 1 According to the data, after the soy protein isolate was subjected to decoiling treatment in a strong alkaline environment of sodium hydroxide, its internal polypeptide chains unfolded, exposing nucleophilic groups such as free carboxyl groups. This microstructural change was reflected in the electrokinetic measurements as a negative potential of -28.9 mV to -35.6 mV in the alkaline depolymerized soy protein solution of the product in step (2) of Examples 1 to 3. If a polyvalent inorganic acid is added directly to the protein solution with a high negative charge density at this stage, an isoelectric point salting-out effect will be triggered at the contact interface, leading to flocculation of the system. To avoid this problem and to impart antibacterial ability to the adhesive layer, 3-chloro-2-hydroxypropyltrimethylammonium chloride was introduced for modification in step (3) of Examples 1 to 3. The data showed that the zeta potential of the cationized soy protein derivative base solution obtained in step (3) changed to a positive range of +13.7 mV to +21.9 mV. The reversal of charge polarity thermodynamically confirms that the quaternary ammonium salt cationic groups with lipophilic long chains have been grafted onto the protein backbone through nucleophilic substitution reactions. This provides non-migrating contact active sites for the final flame-retardant and antibacterial soybean protein-based adhesive to resist mold.

[0078] Observation of pH changes during the preparation process revealed that phytic acid, as an acid source for flame retardants, exhibits a strong tendency to induce aggregation. Online monitoring data showed that during the pumping of the intumescent flame retardant and rheology-controlled precursor, the pH value of the mixtures from Examples 1 to 3 steadily decreased from the initial pH value (11.0-11.5) to the final pH value (7.0-7.5), without the sharp decrease observed during conventional strong acid-base neutralization. This gradual transition confirms that the hydrogen bond network constructed by tannic acid and urea played a physical masking role, temporarily confining the protons of phytic acid molecules within the intumescent flame retardant and rheology-controlled precursor. The protons, constrained by their dissociation constant, were slowly released, thereby eliminating the protein gelation phenomenon caused by local pH imbalance.

[0079] For the rheological performance evaluation of the final product, the steady-state rheological shear data and the apparent viscosity of the adhesive in Table 1 provide objective feedback on the compatibility of the system. The final adhesive products of Examples 1 to 3 all exhibit pseudoplastic fluid characteristics of polymeric materials; with increasing shear rate, the shear stress shows a nonlinear increase, and the fluid maintains a shear-thinning flow mechanism. Introducing phytic acid and other polyphosphate anions into a soybean protein base containing a high concentration of quaternary ammonium polycations typically generates strong electrostatic attraction of polyelectrolytes, causing a sharp increase in system viscosity or loss of fluidity. Figure 1 (b) Continuous rheological curves and the apparent viscosity values ​​of the normal adhesive, ranging from approximately 28,000 to 42,000 mPa·s in Table 1, confirm that the polyhydroxy structure of glycerol in the intumescent flame-retardant and rheology-regulated precursor plays a dielectric shielding role. In the microscopic region where anions and cations interact electrostatically, glycerol constructs a solvated hydrated shell, blocking the rigid bonding between positive and negative charges. Combined with the disruptive effect of urea on the hydrophobic association of polypeptide chains, it transforms the originally fixed electrostatic crosslinking into a dynamic and reversible ionic bond network, ultimately ensuring that the high-solids-content flame-retardant and antibacterial soybean protein-based adhesive possesses the flowability required for wood processing coating.

[0080] Test Example 2: Experimental Objective: This experiment aims to objectively evaluate the engineering applicability of the products of Examples 1 to 3 by monitoring the viscosity evolution and macroscopic phase change of each group of flame-retardant and antibacterial soybean protein-based adhesives under room temperature storage conditions, and to compare the destructive effects of Comparative Examples 1 and 2 on the homogeneous stability of the adhesives.

[0081] Experimental steps: Collect 500 mL each of the flame-retardant and antibacterial soybean protein-based adhesives finally prepared in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2, and put them into standard polyethylene wide-mouth sealed bottles.

[0082] Take 20 mL of each of the above adhesive products and perform steady-state shear tests using a rotational rheometer with a parallel plate fixture at a constant temperature of 25°C. Record the shear rate as 0.1 s⁻¹. -1 The initial apparent viscosity of each sample at that time.

[0083] Polyethylene wide-mouth sealed bottles containing each group of adhesive products were placed in a constant temperature incubator at 25°C for continuous room temperature storage. Each day, the sealed bottles were removed at regular intervals, and the adhesive products inside were slowly stirred manually with a glass rod. The time it took for large, visible flocculent matter, irreversible gel clumps, or complete loss of macroscopic fluidity to appear inside the adhesive products was observed and recorded. This time period was recorded as the room temperature storage period.

[0084] On day 7 of constant temperature storage, 20 mL of the sample that had not yet fully gelled and solidified was taken again, and its apparent viscosity after 7 days was measured under the same rheological testing conditions. The specific viscosity change rate was calculated by combining the initial apparent viscosity. The formula for this index is: Viscosity change rate = [(apparent viscosity after 7 days - initial apparent viscosity) / initial apparent viscosity] × 100%. If some of the comparative adhesive products had completely gelled and lost fluidity within 7 days, the rheological test for that group was terminated and recorded as untestable in the record sheet.

[0085] Experimental results (see Table 2): Table 2: Homogeneous stability and pot life test data of adhesives in Examples 1-3 and Comparative Examples 1-2

[0086] Test conclusion: According to Table 2 and Figure 2 Based on the data, the flame-retardant and antibacterial soybean protein-based adhesives finally prepared in Examples 1 to 3 exhibited extremely stable rheological characteristics. During a sealed storage period at room temperature for more than 30 days, no obvious phase separation or gel solidification was observed in the adhesive products of Examples 1 to 3, and the viscosity change rate after 7 days was strictly controlled within a narrow range of 4.76% to 6.16%. In daily production in the wood processing industry, due to the large molecular weight of soybean protein and its rich polar functional groups, the adhesive is prone to shortening the effective coating time due to spontaneous excessive cross-linking between polypeptide chains after the addition of polyvalent salts or modified resins. The fundamental reason why Examples 1 to 3 can maintain homogeneous flow for a long time lies in the multiple hydrogen bond network inside the pre-prepared intumescent flame-retardant and rheology-controlled precursor, which plays a sustained-release function for highly reactive free protons. This mechanism allows the macromolecular skeleton to complete morphological reorganization under acidic masking conditions, avoiding irreversible salting-out of protein molecules caused by local instantaneous enrichment of strong acids.

[0087] Compared to the adhesive product of Comparative Example 1, which was produced without pre-prepared intumescent flame retardant and rheology-modifying precursors but with each component added dropwise, the experimental data revealed severe engineering failure. The initial apparent viscosity of Comparative Example 1 increased sharply to 142650 mPa·s at the beginning of preparation, and within less than one day, it completely lost its macroscopic fluidity, forming a gel block, making subsequent apparent viscosity and viscosity change rate impossible to measure. When a 50% phytic acid aqueous solution was directly added to a strongly alkaline cationic soybean protein derivative base solution, the instantaneous and violent neutralization reaction at the contact interface caused the local pH to rapidly exceed the isoelectric point of the protein macromolecules. This direct physical blending operation stripped away the stable charged hydration layer on the protein surface, thereby directly inducing the entanglement of molecular chains and the complete collapse of the phase.

[0088] For the adhesive product of Comparative Example 2, which lacked glycerol in its intumescent flame retardant and rheology-controlled precursor formulation, laboratory monitoring revealed that although it did not completely gel on the day of preparation like Comparative Example 1, its initial apparent viscosity of 86320 mPa·s significantly exceeded the rheological requirements for normal sizing. With prolonged storage, obvious gel clumps precipitated inside the adhesive product of Comparative Example 2 on the 9th day, and the viscosity change rate within a 7-day statistical period reached as high as 134.8%. Phytic acid molecules carry six polyphosphate groups. When these polyvalent anionic groups come into contact with quaternary ammonium cations grafted onto protein polypeptide chains, a strong electrostatic attraction of polyelectrolytes spontaneously occurs in the high charge density region. Because the polyhydroxy structure of glycerol was removed from the formulation of Comparative Example 2, the reaction network could not self-assemble around the ionic interaction sites to form a solvated hydrated shell with a high dielectric constant. Without dielectric isolation, a direct, rigid electrostatic anchoring occurs between positive and negative charges. The crosslinking density increases exponentially with the natural creep of the molecular chains, ultimately manifesting as a sharp increase in apparent viscosity over time at the macroscopic level. Examples 1 to 3 effectively utilize the solvated hydration shell constructed with glycerol to break this rigid adsorption, ensuring that the high-solids-content adhesive product can still meet the coating requirements of the wood industry under long-term storage conditions.

[0089] Test Example 3: Experimental Objective: Based on the national standards for the physical and chemical properties of wood-based panels, this experiment quantitatively evaluates the mechanical performance and hydrolysis resistance of the flame-retardant and antibacterial soybean protein-based adhesives prepared in Examples 1 to 3 at the wood bonding interface by measuring the shear strength of the prepared three-layer plywood under the following conditions: dry state at room temperature, immersion in warm water at 63℃, and boiling in water at 100℃. The results are compared with those of Comparative Example 5, which uses traditional physical blending of ammonium polyphosphate powder, to verify the actual effect of the in-situ three-dimensional semi-interpenetrating network of the present invention in overcoming the defect of reduced bonding strength caused by inorganic powders.

[0090] Experimental steps: Prepare a knot-free poplar veneer with dimensions of 400mm×400mm×1.5mm and place it in a constant temperature and humidity chamber to treat it so that the moisture content of the poplar veneer is balanced to between 8% and 10%.

[0091] The flame-retardant and antibacterial soybean protein-based adhesives obtained in Examples 1 to 3 and Comparative Example 5 were extracted. Using poplar veneer as the substrate, each group of adhesives from Examples 1 to 3 and Comparative Example 5 was independently and evenly coated on both sides of its corresponding poplar veneer core. Mixing or coating different groups of adhesives on the same core was strictly prohibited. The amount of adhesive applied on both sides was strictly controlled at 300 g / m². 2 .

[0092] Two un-glued poplar veneers were stacked perpendicularly to the grain direction of their respective glued core boards to form three-layer plywoods corresponding to Examples 1 to 3 and Comparative Example 5, respectively. The assembled plywoods were then fed into a cold press and subjected to a cold-pressing pre-compression treatment at a pressure of 1.0 MPa for 15 minutes.

[0093] After cold pressing, the plywood is transferred to a hot press for high-temperature curing. The hot pressing temperature is set to 120℃, the unit hot pressing pressure is 1.2MPa, and the hot pressing time is set to 5 minutes. After hot pressing, the plywood is removed and placed in an indoor environment at 25℃ and 65% relative humidity for 7 days to release residual thermal stress and allow the adhesive layer to fully mature.

[0094] According to the standard "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels" (GB / T 17657-2022), the cured three-layer plywood of each group was cut into standard plywood shear strength test specimens. At least 30 specimens were prepared for each group of three-layer plywood and randomly divided into three parts for strength testing under the following three working conditions.

[0095] Dry shear strength test: At room temperature, a computer-controlled universal testing machine was used to tensile each group of specimens at a loading rate of 10.0 mm / min until the specimens failed, and the dry shear strength of each group of specimens was recorded.

[0096] Test the Class II wet shear strength: Immerse each group of specimens completely in a constant temperature water bath at 63±3℃ for 3 hours. After removal, allow them to cool at room temperature for 10 minutes. Then, use the above-mentioned microcomputer-controlled universal testing machine to stretch the specimens at a tensile loading rate of 10.0 mm / min until the specimens fail. Record the shear failure load during this process and calculate the Class II wet shear strength of each group of specimens.

[0097] Test the Class I wet shear strength: Place each group of specimens in boiling water (100℃) for 4 hours, remove them and dry them in a constant temperature drying oven at 63±3℃ for 20 hours, then put them back into boiling water for another 4 hours. After cooling to room temperature, use a microcomputer-controlled universal testing machine to set a tensile loading speed of 10.0 mm / min to stretch the specimens until they fail. Record the shear failure load and calculate the Class I wet shear strength of each group of specimens.

[0098] Experimental results (see Table 3): Table 3: Dry / Wet Bond Strength Test Data of Plywood in Examples 1-3 and Comparative Example 5

[0099] Test conclusion: According to Table 3 and Figure 3Data shows that the mechanical properties of wood processing adhesives are prone to significant degradation after the introduction of flame-retardant components, which has long been a technical bottleneck hindering the industrialization of multifunctional protein adhesives. In laboratory studies on the modification of conventional soybean protein adhesives, researchers often find that the direct addition of inorganic powders greatly disrupts the continuity of the adhesive layer. Observing the test results of Examples 1 to 3, their dry shear strength reached a relatively high level of 1.75 MPa to 1.91 MPa. After undergoing extremely stringent Class I wet boiling water cycles, their Class I wet shear strength remained between 0.88 MPa and 1.02 MPa, demonstrating excellent interlayer bonding stability. This excellent hydrolysis resistance is attributed to the successful assembly of a three-dimensional semi-interpenetrating polymer network within the adhesive. During the hot-pressing curing stage at 120℃, the highly active nitrogen-containing heterocyclic butyl groups on the polyamide polyamine epichlorohydrin resin molecular chain not only crosslink with the free carboxyl groups and other functional groups remaining in the depolymerized soybean protein matrix, but also further form in-situ covalent open-ring network bridges with the tannic acid polyphenol hydroxyl groups and even the aliphatic hydroxyl groups of glycerol introduced in the expansion flame retardant and rheology regulation precursors. The covalent network of the protein backbone, the dynamic electrostatic complex network between phytic acid and quaternary ammonium salt, and the interpenetrating covalent locks constructed with tannic acid collectively play a role in dispersing external shear stress. The high-density covalent bonds and dynamic ionic bonds inside the adhesive film synergistically seal the polar hydrophilic groups, and the dense network structure effectively prevents high-temperature water molecules from penetrating into the adhesive matrix on a macroscopic level.

[0100] Compared with the test data of Comparative Example 5, this method of directly mixing ammonium polyphosphate powder into the adhesive solution using the traditional physical blending approach reveals serious defects in mechanical properties. The dry shear strength of Comparative Example 5 was only 1.12 MPa, and the Class II wet shear strength dropped directly to 0.53 MPa, making it a substandard product. Furthermore, in boiling water cycling, the specimens experienced adhesive layer dissolution and natural delamination even before the test. Due to the lack of chemical bonding between the ammonium polyphosphate powder and the soybean protein matrix, a large amount of free inorganic powder occupied the free volume inside the adhesive film, creating dense microscopic phase separation regions and stress concentration points at the interface between the adhesive and wood fibers. These interfacial pores left by physical doping constitute natural capillary channels for water intrusion. Once placed in a high-temperature water environment, not only can water molecules penetrate in large quantities and disrupt the hydrogen bonds at the wood interface, but the ammonium polyphosphate itself also undergoes a certain degree of hydrolysis and dissolution. This dual destruction directly tore apart the physical structure of the adhesive layer, causing Comparative Example 5 to completely lose the adhesive load-bearing capacity between the wood layers in an extreme water environment, thereby further confirming the mechanical gain advantages of Examples 1 to 3 of the present invention in terms of phase control and in-situ chemical engineering modification.

[0101] Test Example 4: Experimental Objective: This experiment quantitatively characterizes the combustion behavior of the flame-retardant and antibacterial soybean protein-based adhesives prepared in Examples 1 to 3 under the influence of heat radiation and open flame using limiting oxygen index (LOI) testing and cone calorimetry. By comparing Comparative Examples 3 and 4, the synergistic flame-retardant char formation mechanism of multiple components in the macromolecular network in the condensed and gas phases is revealed.

[0102] Experimental steps: Select 3mm thick knot-free poplar veneer and cut it into 130mm×6.5mm poplar substrate for limiting oxygen index testing and 100mm×100mm conical poplar substrate for calorimetry testing. Place both substrates in a constant temperature drying oven and treat them until they are completely dry.

[0103] The adhesive products finally obtained in Examples 1 to 3, Comparative Example 3, and Comparative Example 4 were extracted. Each group of adhesives from Examples 1 to 3, Comparative Example 3, and Comparative Example 4 was independently and uniformly coated onto one side of its corresponding poplar substrate for limiting oxygen index testing and conical calorimetry testing. Mixing or coating different groups of adhesives onto the same substrate was strictly prohibited. The coating amount on one side of each substrate was strictly controlled to be 250 g / m². 2 .

[0104] The poplar substrates for the limiting oxygen index test and the poplar substrates for the cone calorimetry test, after being coated with adhesive, were placed horizontally in a forced-air constant temperature drying oven and cured at 120°C under normal pressure for 30 minutes. This allowed the moisture in the adhesive on the wood surface to fully evaporate and cross-link, forming a stable cured film. Subsequently, all substrates were placed at room temperature for 24 hours to balance the moisture. The substrates after balancing the moisture were used as standard specimens for subsequent flame retardant performance tests.

[0105] According to the standard "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test" (GB / T 2406.2), the limiting oxygen index (LOI) test specimens of the corresponding groups were tested using an oxygen index meter. The volume percentage of oxygen in the minimum oxygen-nitrogen mixture required to maintain stable combustion of the specimen material was recorded; this value is the limiting oxygen index (LOI) for each group of adhesives. Fifteen standard specimens were tested for each group of adhesives, and the arithmetic mean was taken as the final recorded data.

[0106] After curing and equilibration of moisture, each group of cone calorimeter test specimens was placed horizontally on the test platform of the cone calorimeter. Flame retardant performance tests were conducted according to the standard "Reaction test for fire - Heat release, smoke production and mass loss rate - Part 1: Heat release rate (cone calorimeter method)" (equivalent to ISO international standard: ISO 5660-1:2002). The externally applied heat radiation flux was set to 50 kW / m². 2The igniter triggers the sample. During this combustion process, the cone calorimeter, based on the classical oxygen consumption principle, continuously collects and monitors changes in oxygen concentration and gas volume flow rate in the exhaust gas through a gas analyzer in the exhaust pipe. Based on this, the dynamic heat release rate of each group of samples is calculated in real time. The highest value reached during the entire test is recorded as the peak heat release rate. The dynamic heat release rate over time is then mathematically integrated to calculate the total heat release. Simultaneously, the instrument uses a high-precision weighing sensor connected to the bottom of the sample holder to synchronously record the mass decay of each group of samples during the thermal degradation process. After the test is completely finished and the open flame is extinguished, the mass of the residual carbon layer remaining on the holder is divided by the initial mass of the sample before the test to obtain the residual char rate of each group of samples.

[0107] Experimental results (see Table 4): Table 4: Flame retardant performance test data of adhesives in Examples 1-3 and Comparative Examples 3-4

[0108] Test conclusion: According to Table 4 and Figure 4 The data shows that the lack of cationized soybean protein grafting leads to severe agglomeration and phase separation of the flame-retardant precursor within the adhesive, preventing the formation of a uniform flame-retardant protective layer. Observing the test results of Comparative Example 3, under the influence of an external heat source, its limiting oxygen index was only 22.1%, falling within the flammable range where it can sustain combustion in air. In the cone calorimetry test, the peak heat release rate of Comparative Example 3 reached 312.4 kW / m³. 2 The total heat release is as high as 42.18 MJ / m³. 2 Furthermore, the final char residue rate was only 11.3%, indicating that the cured adhesive film, due to its extremely poor compatibility and complete failure of flame retardancy, rapidly pyrolyzed at high temperatures. The generated volatile combustible gases directly exacerbated the combustion of the wood substrate. Researchers have found in their long-term development of fire-resistant engineered wood panels that single inorganic flame retardants often fail to form a continuous thermal insulation barrier on the wood surface. Examples 1 to 3, by introducing in-situ multi-component compound intumescent flame retardants and rheology-controlled precursors, completely altered the pyrolysis pathway of the adhesive film. The limiting oxygen index of Examples 1 to 3 remained stable between 31.8% and 33.7%, and the peak heat release rate significantly decreased to 149.3 kW / m³. 2 Up to 165.2kW / m 2 The range indicates that the combustion inertness of the cured adhesive film has been substantially improved.

[0109] A deeper analysis of the chemical evolution behind this flame-retardant performance reveals that it can be attributed to the combined interception effect of the phosphorus-nitrogen-carbon three-dimensional intumescent flame-retardant network in both the condensed and gas phases. When the cured adhesive films of Examples 1 to 3 are subjected to high temperatures, the polyphosphate groups abundant in the phytic acid structure undergo dehydration condensation first, generating polyphosphoric acid or pyrophosphoric acid with strong dehydration catalytic ability. These acidic intermediates promote the cross-linking and char formation reaction of the oxygen-containing groups in the soybean protein molecular chain and the hydroxyl groups of glycerol. Simultaneously, the quaternary ammonium cations grafted onto the protein backbone and the urea in the intumescent flame-retardant and rheology-regulating precursors decompose as gas-phase flame-retardant sources, releasing a large amount of non-flammable ammonia and nitrogen. These non-flammable gases dilute the oxygen concentration in the flame zone while driving the volume expansion of the char formation intermediates being generated in the condensed phase. The synergistic effect of the multiple components rapidly constructs a dense and porous char layer of a certain thickness on the adhesive surface. This char network is visually represented in Table 4 as an increase in the char residue rate of Examples 1 to 3 to 29.8% to 34.2%.

[0110] The lack of integrity in the intumescent flame retardant and rheology-controlled precursor components directly weakens the protective efficacy of the intumescent char layer. In Comparative Example 4, the urea component, which is the main gas source, was removed from the formulation, and its peak heat release rate rebounded to 245.9 kW / m³. 2 Due to the lack of sufficient foaming gas support, Comparative Example 4 could only generate a flat, poorly dense thin layer of char during combustion, relying solely on the catalytic effect of phytic acid. This thin char layer was prone to cracking under continuous heat radiation and internal volatile matter erosion, failing to effectively isolate the bottom wood substrate from the heat source. The flame-retardant mechanisms of Examples 1 to 3 not only relied on the physical addition of a single component but also on the homogeneous network structure formed by in-situ reaction. The covalent and non-covalent connections between the macromolecular skeleton and the flame-retardant groups ensured the uniform molecular-level distribution of flame-retardant elements within the film, thus exhibiting consistent and efficient heat barrier and smoke suppression and charring capabilities under macroscopic combustion conditions.

[0111] Test Example 5: Experimental Objective: To evaluate the contact antibacterial activity and antifungal durability of the flame-retardant and antibacterial soybean protein-based adhesives prepared in Examples 1 to 3 under repeated water washing conditions. By comparing Comparative Example 1 and Comparative Example 3, the anchoring and locking mechanism of the cationic antibacterial groups by the macromolecular cross-linking network is revealed.

[0112] Experimental steps: Knotless poplar veneers with a thickness of 3mm were selected and cut into 50mm × 50mm pieces for antibacterial and antifungal durability testing. These pieces were then placed in a constant temperature drying oven until completely dry. The adhesive products obtained in Examples 1 to 3, Comparative Example 1, and Comparative Example 3 were extracted. Each adhesive group was independently and evenly coated onto one side of the corresponding group of poplar substrates. Cross-group mixing was strictly prohibited, and the adhesive application amount on one side was strictly controlled at 250g / m². 2 .

[0113] After applying the adhesive, each group of test substrates was placed horizontally in a forced-air constant-temperature drying oven and cured at 120℃ under normal pressure for 30 minutes to promote cross-linking and formation of the internal polymer chain segments. Subsequently, they were left to stand at room temperature for 24 hours to equilibrate the moisture. Each group of substrates after moisture equilibration served as the standard specimens required for subsequent tests.

[0114] The cured specimens were divided into three batches to establish different water washing aging gradients. The first batch of specimens served as a control group and underwent no water washing treatment. The second batch of specimens was completely immersed in a water bath with deionized water and continuously shaken and rinsed at 25°C and 100 rpm for 24 hours, which was recorded as one water washing cycle. A total of three cycles were repeated. The third batch of specimens under the same conditions underwent five water washing cycles. After each cycle, the specimens were removed and placed in a ventilated area to air dry naturally until constant weight.

[0115] The antibacterial rate was evaluated using the film application method in the standard "Test Methods and Antibacterial Effects of Antibacterial Plastics" (QB / T 2591-2003). *Escherichia coli* (representative of Gram-negative bacteria) and *Staphylococcus aureus* (representative of Gram-positive bacteria) were used as test species, with a concentration of 1.0 × 10⁻⁶. 5 CFU / mL bacterial suspensions were inoculated onto the surfaces of the first, second, and third batches of specimens, respectively. After covering with a sterile polyethylene film, the specimens were incubated at 37°C for 24 hours. Viable colonies were eluted and recovered, and viable counts were performed. In this test, a poplar substrate of the same size, without any adhesive coating and subjected to the same sterilization pretreatment, was used as a blank control. By comparing the number of viable bacteria recovered from each group of specimens with this blank control, the antibacterial rates of *E. coli* and *Staphylococcus aureus* were calculated for each group of specimens after 0, 3, and 5 washes.

[0116] The anti-mold grade was evaluated according to the standard "Test Method for the Control Efficacy of Anti-mold Agents against Wood Molds and Discoloration Fungi" (GB / T 18261-2013). The first, second, and third batches of specimens were placed in sterile petri dishes inoculated with a mixed spore suspension of Aspergillus niger and Trichoderma, and then incubated for 28 days at a constant temperature and humidity of 28℃ and 90% relative humidity. After the incubation period, the percentage of fungal hyphae infection area on the wood surface was visually observed, and the anti-mold grade of each group of specimens was evaluated based on this. The anti-mold efficacy evaluation standards are defined as follows: Grade 0 represents no surface contamination; Grade 1 represents contaminated area less than 25%; Grade 2 represents contaminated area greater than or equal to 25% and less than 50%; Grade 3 represents contaminated area greater than or equal to 50% and less than 75%; Grade 4 represents contaminated area greater than or equal to 75%.

[0117] Experimental results (see Table 5): Table 5: Test data of long-lasting water-washable antibacterial and antifungal properties of adhesives in Examples 1-3 and Comparative Examples 1 and 3

[0118] Test conclusion: According to Table 5 and Figure 5 The data discrepancies are readily observable, demonstrating that unmodified soy protein readily becomes a carrier for the proliferation of microorganisms. Taking Comparative Example 3 as an example, due to the lack of quaternary ammonium cation groups, its initial antibacterial rates against *Escherichia coli* and *Staphylococcus aureus* were only 35.6% and 42.1%, respectively. After five washes, these rates dropped significantly, with the anti-mold rating remaining at the most severely damaged level 4. The free amino acids and polysaccharides abundant in natural soy protein rapidly absorb moisture from the surrounding environment under humid conditions. This is a common obstacle in previous studies of the weather resistance of woodworking adhesives, accelerating the colonization and proliferation of pathogens on the surface of wood-based substrates. Examples 1 to 3, by precisely covalently grafting 3-chloro-2-hydroxypropyltrimethylammonium chloride onto the soy protein backbone, fundamentally severed the fungal propagation pathway. Data shows that in the initial state of zero water washing, the antibacterial rate of the two strains reached 98.4% or above, and maintained an excellent anti-mold state of level 0 under the strong infection environment of pathogenic mold for 28 days.

[0119] Further analysis of the intrinsic physicochemical mechanism underlying this long-lasting contact sterilization performance reveals that it is primarily attributed to the strong anchoring of high-density positive charges within the cross-linked network. When the negatively charged bacterial cell membrane touches the surface of the cured adhesive film from Examples 1 to 3, the strong electrostatic attraction generated by the quaternary ammonium salt groups directly tears apart the lipid bilayer of the bacteria, forcing the cell contents to leak out and causing rapid death. Compared to the traditional method of directly physically mixing in small-molecule bactericides, this in-situ grafting and complexation mechanism greatly eliminates the risk of hydrolytic stripping. In contrast, Comparative Example 1, which directly adds raw materials without undergoing a precursor pre-complexation process, exhibits excessively loose and disordered polymer chain entanglement. Although Comparative Example 1 achieved a 97.2% antibacterial rate against E. coli in the initial stage, external moisture easily penetrates into the adhesive film along its loose structure, breaking the already fragile non-covalent bonds, resulting in severe loss of free protein chains with antibacterial activity with the water flow. After five water washing cycles, the antibacterial rate of the two strains in Comparative Example 1 plummeted to 64.3% and 61.5%, and its antifungal performance also deteriorated to level 3, nearing failure. Examples 1 to 3, with their dual-locking structure of multiple covalent cross-linking and dynamic electrostatic complexation, firmly encapsulated the antibacterial active sites within an insoluble three-dimensional network. Even under continuous alternating attacks of water flow shearing and swelling, Examples 1 to 3 maintained a high bactericidal rate of 94.1% or higher, effectively solving the problem of long-term protection for biomass adhesives in water-related environments.

[0120] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flame-retardant and antibacterial soybean protein-based adhesive, characterized in that, The flame-retardant and antibacterial soybean protein-based adhesive is prepared through the synergistic effect of electrostatic complexation and covalent cross-linking between polymer chains, and is made from raw materials comprising the following parts by weight: Deionized water: 800-900 parts; Soy protein isolate powder: 100 parts; 10-20 parts of a 30% sodium hydroxide aqueous solution; 12-21 parts of an aqueous solution of 69% (w / w) 3-chloro-2-hydroxypropyltrimethylammonium chloride; Intumescent flame retardant and rheology modulating precursor: 40-64 parts; Aqueous solution of polyamide polyamine epichlorohydrin resin with a mass fraction of 12.5%: 80-144 parts.

2. The flame-retardant and antibacterial soybean protein-based adhesive according to claim 1, characterized in that, The flame-retardant and antibacterial soybean protein-based adhesive is made from raw materials comprising the following parts by weight: Deionized water: 850 parts; Soy protein isolate powder: 100 parts; 15 parts of a 30% sodium hydroxide aqueous solution; 16 parts of an aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride with a mass fraction of 69%; Intumescent flame retardant and rheology modulating precursor: 50 parts; 112 parts of an aqueous solution of polyamide polyamine epichlorohydrin resin with a mass fraction of 12.5%.

3. The flame-retardant and antibacterial soybean protein-based adhesive according to claim 1, characterized in that, The intumescent flame retardant and rheology-modifying precursor is made from raw materials comprising the following parts by weight: A 50% phytic acid aqueous solution: 24-36 parts; Glycerol: 4-8 parts; Tannic acid powder: 8-12 parts; Urea powder: 4-8 parts.

4. A method for preparing a flame-retardant and antibacterial soybean protein-based adhesive as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Disperse soy protein isolate powder in deionized water and stir to initially disperse the soy protein isolate powder to obtain a soy protein isolate suspension. S2. Heat the soy protein isolate suspension, add sodium hydroxide aqueous solution to adjust the pH value of the soy protein isolate suspension, and keep it at a constant temperature and stir to fully unwind the soy protein isolate, thereby obtaining an alkaline depolymerized soy protein solution. S3. Add 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution dropwise to the alkaline depolymerized soybean protein solution. After the addition of 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution is complete, continue stirring the reaction while maintaining constant temperature and pH to obtain the cationic soybean protein derivative base solution. S4. Cool the cationic soybean protein derivative base liquid, and pump the expansion flame retardant and rheology regulation precursor into the cationic soybean protein derivative base liquid. Electrostatic complexation occurs between the polymer chains to obtain a dynamic electrostatic complexed protein base liquid. S5. Add polyamide polyamine epichlorohydrin resin aqueous solution to the dynamic electrostatic complexed protein base liquid, and carry out ring-opening chain extension and covalent cross-linking reaction at constant temperature. After the ring-opening chain extension and covalent cross-linking reaction is completed, cool down, filter and degas to discharge the material to obtain flame-retardant and antibacterial soybean protein base adhesive.

5. The preparation method according to claim 4, characterized in that, Step S1 is carried out in the main reactor, and the stirring speed of the paddle agitator in the main reactor is set to 150-250 rpm. The continuous stirring time for dispersing the soy protein isolate powder is 20-30 minutes. In step S2, hot water is introduced into the jacket of the main reactor to raise the temperature of the soy protein isolate suspension to 50-60°C. The pH value of the soy protein isolate suspension is adjusted to 11.0-11.

5. Under the constant temperature condition of 50-60°C, the soy protein isolate is kept warm and stirred for 45-75 minutes to unwind.

6. The preparation method according to claim 5, characterized in that, In step S3, the dripping time of the 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution is controlled at 20-30 minutes; after the 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution is completely added, the reaction is continued to be stirred at 50-60°C and pH 11.0-11.5 for 50-70 minutes.

7. The preparation method according to claim 6, characterized in that, In step S4, cooling water is introduced into the jacket of the main reactor to lower the temperature of the cationic soybean protein derivative base liquid to 35-45℃; the high-shear dispersion emulsifier extending into the main reactor is turned on, and the rotation speed of the high-shear dispersion emulsifier is set to 2000-3000 rpm; the pumping rate of the expansion flame retardant and rheology-controlled precursor is 10-20 L / h, and the pH value of the dynamic electrostatic complexed protein base liquid is stabilized at 7.0-7.

5.

8. The preparation method according to claim 7, characterized in that, In step S5, the high-shear dispersing emulsifier is shut down, and only the paddle agitator of the main reactor is kept running. The speed of the paddle agitator is set to 100-150 rpm, and the temperature of the ring-opening chain extension and covalent crosslinking reaction in the main reactor is controlled at 40-50℃. The reaction time of the ring-opening chain extension and covalent crosslinking reaction is 30-50 minutes. After the ring-opening chain extension and covalent crosslinking reaction is completed, the final adhesive mixture is cooled down, filtered through a filter screen to remove bubbles, and then discharged.

9. The preparation method according to claim 4, characterized in that, The expansion flame retardant and rheology-controlled precursor described in S4 is prepared in advance through the following steps: (1) Add phytic acid aqueous solution and glycerol to the auxiliary preparation vessel, turn on the stirring and mix evenly to obtain a transparent binary mixed solution; (2) Heat the binary mixed solution, and continuously add tannic acid powder at the temperature after heating to disperse and dissolve the tannic acid powder to obtain a ternary suspension. (3) Maintain the temperature inside the auxiliary preparation vessel after heating, add urea powder to the ternary suspension, and then stir at a constant temperature in a closed state until the ternary suspension is transformed into a homogeneous transparent high-viscosity fluid without visible particles, thus obtaining the expansion flame retardant and rheology regulation precursor.

10. The preparation method according to claim 9, characterized in that, In step (1), the stirring speed of the auxiliary mixing vessel is set to 300-500 rpm; in step (2), the binary mixed solution is heated to 55-65℃, and the tannic acid powder is continuously added within 10-15 minutes; in step (3), the temperature inside the auxiliary mixing vessel is maintained at 55-65℃, and the constant temperature stirring time after the urea powder is added is 40-60 minutes.

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