A highly bio-based mildew-proof, antibacterial and water-resistant soybean protein adhesive and its application

Abstract

The present invention discloses a high-biobased content mildew-proof, antibacterial and water-resistant soy protein adhesive and its application. The preparation method is as follows: first, polyphenol and soluble metal salt are dissolved in water, and a chelation reaction is performed to obtain a functional modification reagent containing polyphenol chelated metal nanoparticles. Then, a soy protein aqueous solution is prepared, the pH is adjusted, and heated and stirred. Finally, a functional modification reagent containing polyphenol chelated metal nanoparticles is added, the pH is adjusted with acid, and a bio-based cross-linking agent is added. The cross-linking reaction is stirred and mixed, and the material is uniformly discharged to obtain a high-biobased content soy protein adhesive. Different from most existing studies that use a large amount of petrochemical-based modification additives, the present invention has a higher biomass content. The dry and wet strengths of plywood made from the high-biobased content adhesive can reach up to 2.83MPa and 1.78MPa, respectively, and it has high water resistance, heat resistance, flame retardancy, mildew resistance, and antibacterial capabilities.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesive preparation, in particular to a highly bio-based mildew-proof, antibacterial and water-resistant soybean protein adhesive and its application. Background Art

[0002] Soy protein is widely available, inexpensive, and readily available. Its biodegradable properties are unmatched by other petrochemical-based materials, offering significant potential for application in the food industry, coatings, papermaking, and adhesives. Soy protein, a natural macromolecule, possesses a protein-based quaternary structure and contains numerous hydrophilic groups, resulting in poor water resistance. Plywood made with pure soy protein-based adhesives lacks the required wet strength. Furthermore, the strong intermolecular forces, hydrogen bonds, and disulfide bonds within soy protein molecules contribute to high viscosity and poor flowability, making application difficult. As an edible nutrient, soy protein is susceptible to microbial degradation, resulting in poor storage stability and prone to deterioration. These drawbacks have hindered the commercialization of traditional soy protein adhesives within the wood industry, significantly limiting their development and widespread adoption. Therefore, considering their practical applications in everyday life, ensuring the adhesive's water resistance and mildew and antibacterial properties is a key issue that needs to be addressed.

[0003] To improve the water and heat resistance of soy protein adhesives, the primary approach is to add substances containing aldehyde groups, which react with the amino groups of soy protein to form a Schiff base reaction, creating strong covalent bonds. Furfural, a bio-aldehyde primarily derived from the residual waste of agricultural processing byproducts such as corn and sugarcane, contains a stable furan ring structure and highly reactive aldehyde groups. The chemical crosslinking provided by furfural strengthens the internal network structure of soy protein, thereby enhancing its water and heat resistance. Furthermore, furfural can undergo a polycondensation reaction with tannic acid, forming a multi-component network and increasing crosslink density.

[0004] Existing invention CN103881633A discloses a composite adhesive and its preparation method. The method comprises mixing molten phenol, sodium hydroxide, and soy protein powder, heating and refluxing for 60 minutes, then adding formaldehyde solution and refluxing for 60 minutes at 90°C, adding urea and continuing the refluxing for 60 minutes, and finally adding an appropriate amount of distilled water, cooling and discharging to obtain the composite adhesive. The temperature conditions required for this invention are relatively high, and a complicated reflux device needs to be set up, which is not conducive to practical promotion. In addition, the modifiers used are all petroleum-based chemical resources with low biomass content, which is not in line with the current green environmental protection concept. At the same time, the viscosity of the adhesive of this invention is basically within the range of 65 to 160 mPa∙s. Too low a viscosity value will lead to excessive penetration of the adhesive, which is not conducive to practical application.

[0005] CN 113480970 A discloses a method for preparing a fully bio-based, two-component soy adhesive and its application. The method involves adding a crosslinking curing agent to pretreated soy protein powder to produce the desired soy protein adhesive. The crosslinking curing agent includes furfuryl alcohol, or a mixture of furfuryl alcohol and one or more of furfural, 5-hydroxyfurfuryl alcohol, and 5-hydroxyfurfural. Plywood produced using this adhesive achieves a maximum dry and wet strength of only 1.61 MPa and 1.47 MPa, respectively. No evidence exists regarding the adhesive's mildew and antibacterial properties, potentially hindering its practical application and promotion.

[0006] CN 110964478 A discloses a hyperbranched polyester and borate-modified soy protein adhesive. The invention first synthesizes the hyperbranched polyester and then uses it to modify the soy protein. The hyperbranched polyester prepared by this method has a complex process flow, uses a large amount of chemical reagents, has multiple steps, and consumes high energy. Furthermore, the resulting soy protein adhesive has low water resistance and mediocre mechanical properties, with a maximum wet strength of only 0.91 MPa.

[0007] CN 112300756 A discloses a method for preparing a modified nanocellulose-reinforced soy protein adhesive. This method first produces epoxy-containing nanocellulose, which is then used to modify soy protein. This method requires nanocellulose, the primary modifier, which is expensive and uneconomical. Furthermore, the resulting adhesive has a high viscosity, reaching a maximum of 10,019 mPa∙s, making it difficult to store and use. The maximum wet strength reaches only 1.17 MPa, and it lacks good water resistance.

[0008] CN115262234A discloses a method for preparing a high-strength, corrosion-resistant soy protein adhesive. This method involves synthesizing an organic-inorganic hybrid enhancer, dispersing the organic-inorganic hybrid enhancer and a tannic acid modifier in water and stirring. Soy protein and a glycerol triglycidyl ether crosslinker are then added and stirred to produce the soy protein adhesive. The organic-inorganic hybrid enhancer used in this method is complex and requires numerous steps, and requires the use of large amounts of organic solvents and chemical reagents, which can lead to significant cost increases and environmental pollution. Furthermore, the resulting adhesive has poor mildew resistance, extending its shelf life to only approximately 72 hours.

[0009] Therefore, the existing preparation method of soy protein adhesive has the following technical deficiencies:

[0010] 1. The modifiers used in soy protein adhesives are overly dependent on petrochemical resources and have low biomass content. The production and discharge processes are prone to produce substances harmful to the human body, affecting human health. This also does not conform to the current healthy concept of green chemistry pursuing sustainable development.

[0011] 2. Soy protein adhesives have low bonding performance and poor water resistance, and cannot meet the national standard requirements for first-class plywood, so they can only be used indoors;

[0012] 3. Soy protein adhesives have poor mildew and antibacterial properties, generally only lasting 7 days. There is little research on the antibacterial and flame retardant properties of adhesives, which can easily limit the application and promotion of soy protein adhesives in real life.

[0013] 4. The preparation process of soy protein adhesive is cumbersome, and the modifier used also requires a complex synthesis method. On the one hand, it wastes too much resources and causes a large amount of energy loss, and is only suitable for laboratory research; on the other hand, it is not conducive to the industrial production and application of soy protein adhesives, limiting its promotion.

[0014] References:

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[0016] [2] Jin, S., Li, K., Gao, Q., Zhang, W., Chen, H., Li, J., Shi, SQ, 2020. Multiple crosslinking strategy to achieve high bonding strength and antibacterial properties of double-network soy adhesive. Journal of CleanerProduction 254.

[0017] [3] Koopmann, A.-K., Bartschmid, T., Hüsing, N.,Elsaesser, MS, 2023. Renewable, Organic and Related Carbon Aerogel Monoliths from the Polycondensation of Tannin with 5-(Hydroxymethyl)furfural. Journal ofSol-GelScience and Technology.

[0018] [4] Lei, Z., Jiang, K., Chen, Y., Qi, J., Xie, J.,Huang, X., Jiang,Y., Zhang, S., Jia, S., Xiao, H., 2022. Developing a high-strengthantibacterial soy protein adhesive by adding low amount oftetraepoxy l-tyrosine. Polymer Testing 112.

[0019] [5] Li, J., Li, J., Wei, J., Zhu, X., Qiu, S.,Zhao, H., 2021. CopperTannic Acid-Coordinated Metal-Organic Nanosheets for SynergisticAntimicrobial and Antifouling Coatings. ACS Appl Mater Interfaces 13,10446-10456.

[0020] [6] Li, Y., Yan, L., Cai, L., Xu, Y., Li, J., Li, J.,Shi, S.Q., Gao,Q., 2022. Low-temperature curable and strong soy protein / allicin adhesivewith excellent mildewresistance via a free-radical-polymerization curingsystem. Industrial Crops and Products 189.

[0021] [7] Quan, TH, Benjakul, S., Sae-leaw, T., Balange, AK, Maqsood,S., 2019. Protein–polyphenol conjugates: Antioxidant property, functionalities and their applications. Trends in Food Science&Technology 91,507-517.

[0022] [8] Shirmohammadli, Y., Efhamisisi, D., Pizzi, A., 2018. Tannins as asustainable raw material for green chemistry: A review. Industrial Crops andProducts126, 316-332.

[0023] [9] Zhang, J., Liu, B., Zhou, Y., Essawy, H.,Chen, Q., Zhou, X., Du, G., 2021. Preparation of a starch-based adhesive cross-linked with furfural, furfuryl alcohol and epoxy resin. International Journal of Adhesion and Adhesives 110.

[0024]

[10] Wang Haijie. Research progress on modification technology of soy protein-based wood-based panel adhesives. Henan University of Technology. 2019

[0025]

[11] Zhang Zeyu. Research progress of modified soy protein-based adhesives. Beihua University. 2021. Summary of the Invention

[0026] The purpose of the present invention is to overcome at least one deficiency of the prior art and provide a high-biobased content mildew-proof, antibacterial and water-resistant soy protein adhesive and its application.

[0027] The technical solution adopted by the present invention is:

[0028] The present invention provides a highly bio-based mildew-proof, antibacterial and water-resistant soybean protein adhesive, the preparation method of which comprises the following steps:

[0029] 1) Dissolve the soy protein raw material in water, adjust the pH to 10-11, and heat and stir to react to obtain a soy protein base liquid;

[0030] 2) dissolving the polyphenol and a soluble metal salt in water to carry out a chelation reaction to obtain a functional modified reagent containing polyphenol-chelated metal nanoparticles, wherein the metal salt can be reduced to a zero-valent metal element by the polyphenol;

[0031] 3) Adding a polyphenol chelated metal nanoparticle modification functional reagent to the soy protein base liquid obtained in step 1), adjusting the pH to 4.5-6 with acid, then adding a bio-based cross-linking agent, stirring and mixing to cause a cross-linking reaction, and uniformly discharging the material to obtain a high-biobased content soy protein adhesive.

[0032] In some examples, the polyphenols in step 2) are selected from at least one of tannic acid, flavonoids, and lignin.

[0033] In some examples, the soluble metal salt in step 2) is selected from at least one of Cu salt and Ag salt.

[0034] In some examples, the bio-based cross-linking agent in step 3) is selected from at least one of furfural and furfuryl alcohol.

[0035] In some examples, based on weight, the soy protein raw material is 10 to 50 parts, the polyphenol is 1 to 10 parts, the soluble metal salt is 1 to 5 parts, and the bio-based cross-linking agent is 1 to 10 parts.

[0036] In some examples, based on weight, the soy protein raw material is 15 to 40 parts, the polyphenol is 2 to 7 parts, the soluble metal salt is 0.25 to 1 part, and the bio-based cross-linking agent is 3 to 7 parts.

[0037] In some examples, the chelating reaction conditions in step 2) are: reacting at 60-70° C. for 1-2 hours.

[0038] In some examples, the pH value in step 1) is adjusted using at least one of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0039] In some examples, the acid in step 3) is selected from at least one of hydrochloric acid, sulfuric acid, and acetic acid.

[0040] In another aspect, the present invention provides an adhesive for the wood industry, which contains the soy protein adhesive.

[0041] The beneficial effects of the present invention are:

[0042] (1) The present invention adopts a simple one-pot method to prepare soy protein adhesives, using tannic acid chelated metal nanoparticles and furfural as the main functional modifiers. Unlike most existing studies that use a large amount of petrochemical-based modification additives, the present invention has a high biomass content while ensuring relatively excellent mechanical properties. All raw materials used (except a small amount of metal ions) are derived from biomass resources, are non-toxic, environmentally sustainable and friendly, low in cost, and the simple preparation process is conducive to industrial promotion and future practical application.

[0043] (2) The present invention utilizes tannic acid and a small amount of metal ions to self-assemble into tannic acid-chelated metal nanoparticles through a simple preparation method, which fill the internal network structure of soybean protein molecules. The nanoparticles can regulate the interaction between soybean protein molecules, reduce the viscosity of the glue, thereby increasing the permeability of the adhesive and further improving mechanical anchoring;

[0044] (3) The soy protein adhesive prepared by the present invention has a moderate viscosity, which is conducive to the penetration and infiltration of the adhesive into the pores of wood. The plywood made from this high bio-based content adhesive can achieve dry and wet strengths of up to 2.83 MPa and 1.78 MPa, respectively. It can also pass the aging test and meet the national standards for outdoor Class I boards, and has high water resistance and heat resistance.

[0045] (4) The soybean protein adhesive of the present invention has good flame retardant properties and excellent mildew resistance, the mildew resistance time can be extended to 15 days, and it also has certain antibacterial properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a digital photo of the prepared soy protein adhesive with high bio-based content.

[0047] Figure 2 These are the test results for the residual rate of the cured adhesive of the prepared high-biobased soy protein adhesive.

[0048] Figure 3 This is a scatter plot of the viscosity of the prepared soy protein adhesive with high bio-based content.

[0049] Figure 4 This is the cone calorimetry test result of the plywood made of the prepared high-biobased soy protein adhesive, where a is the total heat release value, b is the total smoke release value, c is the peak heat release rate, and d is the peak smoke release rate.

[0050] Figure 5 These are the test results of the anti-corrosion performance of the prepared soy protein adhesive with high bio-based content.

[0051] Figure 6 These are the test results of antibacterial properties of the prepared soy protein adhesive with high bio-based content. DETAILED DESCRIPTION

[0052] A highly bio-based mildew-proof, antibacterial and water-resistant soy protein adhesive, the preparation method of which comprises the following steps:

[0053] 1) Dissolve the soy protein raw material in water, adjust the pH to 10-11, and heat and stir to react to obtain a soy protein base liquid;

[0054] 2) dissolving the polyphenol and a soluble metal salt in water to carry out a chelation reaction to obtain a functional modified reagent containing polyphenol-chelated metal nanoparticles, wherein the metal salt can be reduced to a zero-valent metal element by the polyphenol;

[0055] 3) Adding a polyphenol chelated metal nanoparticle modification functional reagent to the soy protein base liquid obtained in step 1), adjusting the pH to 4.5-6 with acid, then adding a bio-based cross-linking agent, stirring and mixing to cause a cross-linking reaction, and uniformly discharging the material to obtain a high-biobased content soy protein adhesive.

[0056] In the embodiments of the present invention, the soy protein raw material used is not limited in terms of molecular weight, type, or source, and is preferably soy protein concentrate powder, textured soy protein powder, soy protein isolate powder, or a mixture thereof, and more preferably soy protein isolate powder. The soy protein powder is preferably present in an amount of 10 to 50 parts by weight, more preferably 15 to 40 parts by weight. Furthermore, to prepare the soy protein aqueous solution, deionized water is preferably present in an amount of 50 to 100 parts, more preferably 70 to 90 parts by weight.

[0057] In the embodiment of the present invention, the alkali used is an alkali treatment agent for soy protein, whose main function is to release the active groups in the soy protein molecules to obtain more reaction sites, preferably sodium hydroxide, potassium hydroxide, calcium hydroxide or a mixture of their aqueous solutions; by weight, the alkali treatment agent is preferably 1 to 5 parts; more preferably 1 to 2.7 parts.

[0058] In the embodiment of the present invention, the polyphenol in the modified enhancer is preferably tannic acid, flavonoids, lignin or a mixture thereof, more preferably tannic acid; by weight, the polyphenol is preferably 1 to 10 parts; more preferably 2 to 7 parts.

[0059] There are no specific requirements for the type of soluble metal salt. For environmental and health reasons, non-toxic metal salts are preferred. In some embodiments, the soluble metal salt in step 2) is selected from at least one of Ni salts, Co salts, Zn salts, Cu salts, Ag salts, Fe salts, and Mn salts. The soluble metal salt is preferably present in an amount of 1 to 5 parts by weight, more preferably 0.25 to 1 part by weight.

[0060] In some examples, the bio-based cross-linking agent in step 3) is selected from at least one of furfural and furfuryl alcohol, more preferably furfural; the bio-based cross-linking agent is preferably 1 to 10 parts by mass, more preferably 3 to 7 parts by mass.

[0061] In some examples, based on weight, the soy protein raw material is 10 to 50 parts, the polyphenol is 1 to 10 parts, the soluble metal salt is 1 to 5 parts, and the bio-based cross-linking agent is 1 to 10 parts.

[0062] In some examples, based on weight, the soy protein raw material is 15 to 40 parts, the polyphenol is 2 to 7 parts, the soluble metal salt is 0.25 to 1 part, and the bio-based cross-linking agent is 3 to 7 parts.

[0063] In some examples, the chelating reaction conditions in step 2) are: reacting at 60-70° C. for 1-2 hours.

[0064] In some examples, the pH in step 1) is adjusted using at least one of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0065] In some examples, the acid in step 3) is selected from at least one of hydrochloric acid, sulfuric acid, and acetic acid.

[0066] In the embodiment of the present invention, the soluble metal salt in the modifier is preferably Ni 2+ 、Co 2+ 、Zn 2+ 、Cu 2+ 、Ag 1+ 、Fe 2+ 、Mn 2+ One or more of the following.

[0067] In the embodiment of the present invention, the acid used as the initiator is preferably hydrochloric acid, sulfuric acid, acetic acid or a mixture of their aqueous solutions; the acid initiator is preferably 1 to 10 parts by mass, more preferably 1 to 4.5 parts by mass.

[0068] The following disclosure provides many different embodiments or examples for realizing different solutions of the present invention. Unless otherwise specified, the reagents used in the examples can be purchased from the market.

[0069] Comparative Example 1: Preparation of unmodified soy protein sample (SPI)

[0070] Add 20 g of soy protein isolate powder (protein weight percentage ≥ 90%) and 80 g of deionized water into a 250 mL beaker, and mechanically stir at 600 r / min for 20 min to obtain the target soy protein gel, which is recorded as SPI.

[0071] Comparative Example 2: Preparation of samples without metal ions (SF / T)

[0072] (1) Add 20 g of soy protein isolate powder (protein weight percentage ≥ 90%) and 80 g of deionized water into a 250 mL beaker, stir and mix, then add 1.7 g of 40 wt% sodium hydroxide aqueous solution, adjust the pH to 10, and react at 65 ° C and 600 r / min for 1 h;

[0073] (2) Weigh 4 g of tannic acid and add it to the reaction in step (1) for 1 h. Then add 4.5 g of 19 wt% hydrochloric acid solution and adjust the pH to 5. Then add 3 g of furfural and continue stirring for 30 min to obtain the target soybean protein adhesive, which is recorded as SF / T.

[0074] Example 3: Preparation and application of high bio-based soy protein adhesive (SF / T-Ag)

[0075] (1) Add 20 g of soy protein isolate powder (protein weight percentage ≥ 90%) and 60 g of deionized water into a 250 mL beaker, stir and mix, then add 2 g of 40 wt% sodium hydroxide aqueous solution, adjust the pH to 11, and react at 55 ° C and 600 r / min for 1 h;

[0076] (2) Weigh 4 g of tannic acid, 0.25 g of AgNO3, and 20 g of deionized water and stir at 1000 rpm for 1 h in a nitrogen atmosphere.

[0077] (3) The reaction solution of step (2) was transferred to step (1) and reacted under the original reaction conditions for 1 h. 3 g of 19 wt % hydrochloric acid solution was added to adjust the pH to 4.5. Then, 3 g of furfural was added and stirred for 30 min to obtain the target soybean protein adhesive, which was recorded as SF / T-Ag.

[0078] Example 4: Preparation method and application of high bio-based soy protein adhesive (SF / T-Cu)

[0079] (1) Add 20 g of soy protein isolate powder (protein weight percentage ≥ 90%) and 60 g of deionized water into a 250 mL beaker, stir and mix, then add 1.7 g of 40 wt% sodium hydroxide aqueous solution, adjust the pH to 10, and react at 65 ° C and 600 r / min for 2 h;

[0080] (2) Weigh 4 g of tannic acid, 0.5 g of CuCl₂⋅2H₂O, and 20 g of deionized water and stir mechanically at 1000 rpm for 1 h in a nitrogen atmosphere.

[0081] (3) The reaction solution of step (2) was transferred to step (1) and reacted under the original reaction conditions for 1 h. 2.5 g of 19 wt % hydrochloric acid solution was added to adjust the pH to 5. Then 3 g of furfural was added and stirred for 30 min to obtain the target soybean protein adhesive, which was recorded as SF / T-Cu.

[0082] Example 5: Preparation method and application of high bio-based soy protein adhesive (SF / T-Ca)

[0083] (1) Add 20 g of soy protein isolate powder (protein weight percentage ≥ 90%) and 60 g of deionized water into a 250 mL beaker, stir and mix, then add 2 g of 40 wt% sodium hydroxide aqueous solution, adjust the pH to 11, and react at 75 ° C and 600 r / min for 3 h under mechanical stirring;

[0084] (2) Weigh 4 g of tannic acid, 0.75 g of CaCl2, and 20 g of deionized water and stir mechanically at 1000 rpm for 1 h in a nitrogen atmosphere.

[0085] (3) The reaction solution of step (2) was transferred to step (1) and reacted under the original reaction conditions for 1 h. 1.5 g of 19 wt % hydrochloric acid solution was added to adjust the pH to 5.5. Then, 3 g of furfural was added and stirred for 30 min to obtain the target soybean protein adhesive, which was recorded as SF / T-Ca.

[0086] Example 6: Preparation method and application of high bio-based soy protein adhesive (SF / T-Mn)

[0087] (1) Add 20 g of soy protein isolate powder (protein weight percentage ≥ 90%) and 60 g of deionized water into a 250 mL beaker, stir and mix, then add 1.7 g of 40 wt% sodium hydroxide aqueous solution, adjust the pH to 10, and react at 85 ° C and 600 r / min for 1 h;

[0088] (2) Weigh 4 g of tannic acid, 1 g of MnCl2, and 20 g of deionized water and stir mechanically at 1000 rpm for 1 h in a nitrogen atmosphere.

[0089] (3) The reaction solution of step (2) was transferred to step (1) and reacted under the original reaction conditions for 1 h. 0.5 g of 19 wt % hydrochloric acid solution was added to adjust the pH to 6. Then 3 g of furfural was added and stirred for 30 min to obtain the target soybean protein adhesive, which was recorded as SF / T-Mn.

[0090] Bond strength performance test

[0091] Tested in accordance with the national standard GB / T9846-2015 (≥0.7 MPa), the specific data are shown in Table 1.

[0092] Table 1 Comparison of properties of different soy protein adhesives

[0093] serial number Dry bonding strength (MPa) Type II wet bond strength (MPa) Type I wet bond strength (MPa) Wood breakage rate (%) Comparative Example 1 2.52 0.47 0 5 Comparative Example 2 1.52 1.71 1.19 70 Example 3 2.45 1.29 0.55 30 Example 4 2.83 1.78 1.22 85 Example 5 2.41 1.40 0.76 40 Example 6 1.69 1.31 0.69 20

[0094] As can be seen from the table, the bonding strength can reach a maximum of 1.78 MPa and the dry strength is 2.83 MPa according to the Type II plywood test, and it meets the strength standard of Type I plywood. The soy protein adhesive of the present invention effectively improves the water-resistant bonding performance of the prepared plywood. Since the nanoparticles generated by the chelation of metal salts and natural polyphenols have a high specific surface area, they can better penetrate into the interior of the wood to form a larger contact area, thereby producing stronger mechanical anchoring, which shows that the reinforcing effect of the adhesive is significant.

[0095] Residual rate test comparison

[0096] The residual rate test method was used to study the crosslinking degree and water resistance of soy protein adhesives. The fully cured adhesive was dried to constant weight (M), then immersed in cold water at room temperature (25°C) for 24 hours and then dried at 103±3°C to constant weight (m). The residual rate was calculated as m / M*100%. Each sample was tested three times and the average value was recorded. The results are shown in Tables 2 and 3. Figure 2 shown.

[0097] Table 2 Comparison of residual rates of different soy protein adhesives

[0098] serial number Residual rate (%) Comparative Example 1 73.75 Comparative Example 2 81.25 Example 3 81.19 Example 4 82.66 Example 5 84.01 Example 6 84.39

[0099] From Table 2 and Figure 2 It can be seen that the unmodified soy protein adhesive in Comparative Example 1 has the lowest residual rate, only 73.75%, while Example 6 shows a very high hydrolyzability, up to 84.39%. The residual rate of the modified adhesive is improved, and the addition of metal ions can improve water resistance, indicating that the modified sample has good water resistance. The multiple cross-linked network constructed by metal salt nanoparticles, soy protein and other components effectively blocks the invasion of moisture and successfully enhances the water resistance of the adhesive.

[0100] Adhesive Viscosity Comparison

[0101] The apparent viscosity of the adhesives was evaluated using a rotational rheometer at 25 °C with shear rates ranging from 0.1 to 100 s -1 , every 10 s -1 Repeat the test 3 times for each sample and record the average value. The results are shown in Table 3 and Figure 3 shown.

[0102] Table 3 Comparison of viscosity of different soy protein adhesives

[0103] serial number Viscosity (mPa∙s) Comparative Example 1 8643 Comparative Example 2 128.2 Example 3 583.4 Example 4 941.4 Example 5 1207.4 Example 6 7779

[0104] Combined with Table 3 and Figure 3 It can be seen that the viscosity of the original soy protein adhesive is as high as 8643 mPa∙s, while the viscosity of the modified SF / T adhesive drops to 128.2 mPa∙s. The viscosity of the adhesive increases after the introduction of metal ions, indicating that the introduction of an appropriate amount of metal ions can improve the viscosity characteristics of the adhesive. This is because the generated metal salt nanoparticles interact with the active groups of the soy protein, reducing the formation of hydrogen bonds and molecular chain entanglement within the adhesive, effectively reducing the viscosity.

[0105] Flame retardancy comparison

[0106] The total heat release, total smoke release rate, peak heat release rate, and peak smoke release rate of plywood prepared with a flame-retardant and mildew-resistant high-biobased soy protein adhesive were measured using a cone calorimeter (Modisco Combustion Technology Instrument Co., Ltd., Kunshan, China). Standard metal frames and aluminum foil were used to protect the edges of the samples, leaving the coated surface exposed to the fire. All samples were 100 x 100 x 40 mm in size. 3 The test pieces are all at 50 Kw / m 2 The test was carried out under horizontal exposure heat flow conditions. Each sample was treated with 3 replicates. The results are shown in Table 4 and Figure 4 shown.

[0107] Table 4 Comparison of flame retardant properties of different soy protein adhesives

[0108] serial number <![CDATA[Total Heat Release / THR (MJ / m 2 )]]> <![CDATA[Peak heat release rate / HRR (Kw / m 2 )]]> <![CDATA[Total smoke production / TSP (m 2 )]]> <![CDATA[Peak smoke production rate / SPR (m 2 / s)]]> Comparative Example 1 47 386 2.37 0.041 Comparative Example 2 46 359 2.31 0.037 Example 3 45 325 2.24 0.033 Example 4 42 322 2.23 0.032 Example 5 40 318 2.20 0.031 Example 6 37 305 1.87 0.029

[0109] From Table 4 and Figure 4 As can be seen from the results, compared to the unmodified soy protein adhesive in Comparative Example 1, the total heat release and heat release rate of the particleboard plywood prepared with the modified soy protein adhesive were both reduced. Its total smoke release value and peak smoke release rate also decreased, demonstrating that the flame retardancy of the plywood prepared with this adhesive was improved. This is because the metal salt nanoparticles catalyze the cracking of soy protein molecules during combustion, altering the thermal cracking process of the soy protein molecules, reducing the production of combustibles and promoting charring, thereby improving the flame retardancy of the adhesive to a certain extent.

[0110] Comparison of anti-mildew performance

[0111] The anti-mildew performance of soy protein adhesive was evaluated by the Petri dish method. The same weight of freshly prepared adhesive was placed in a Petri dish and stored at a constant temperature of 30±2℃ and a relative humidity of 95%±2%. The mold status of the adhesive sample was observed and recorded every day. Figure 5 shown.

[0112] from Figure 5 As can be seen, after 168 hours of storage, the surfaces of Comparative Examples 1 and 2 were largely colonized by mold, accompanied by a strong, foul, rancid odor. However, no mold was observed on the surfaces of Examples 3-6, demonstrating the excellent mold-resistant properties of the modified soy protein adhesives of the present invention. This is because the metal ions in the metal salt nanoparticles effectively inhibit the growth of mold, destroying the mold cell walls and inactivating them, thereby achieving the mold-resistant effect.

[0113] Comparison of antibacterial properties

[0114] The solid-medium inhibition zone test method was used to evaluate its antibacterial effect on Staphylococcus aureus. First, the bacterial strain was cultured in LB culture medium overnight. The bacterial suspension was then diluted 3 times in a gradient and spread on the surface of a culture dish with LB solid agar. The sample was then placed on an LB solid agar plate cultured with Staphylococcus aureus to conduct a solid-medium inhibition zone test. The results are as follows: Figure 6 shown.

[0115] from Figure 6 It can be seen that the unmodified soy protein sample of Comparative Example 1 did not produce an antibacterial zone, the modified Comparative Example 2 produced an antibacterial zone with a diameter of 1.63 cm, and the diameter of the inhibition zone of sample Example 4 with the introduction of metal ions against Staphylococcus aureus was significantly increased to 2.34 cm. This is because metal ions can cause the cell membrane of bacteria to rupture, induce oxidative stress, and cause them to lose their normal physiological functions and thus lead to death. This shows that the antibacterial activity of the adhesive is significantly enhanced after the introduction of metal ions.

[0116] The above is a further detailed description of the present invention and should not be considered as a limitation on the specific implementation of the present invention. For those skilled in the art, simple deductions or substitutions that do not depart from the concept of the present invention are within the scope of protection of the present invention.

Claims

1. A highly bio-based mildew-proof, antibacterial and water-resistant soybean protein adhesive, characterized in that: The soy protein raw material is 10 to 50 parts by mass, the natural polyphenol is 1 to 10 parts by mass, the soluble metal salt is 1 to 5 parts by mass, and the bio-based cross-linking agent is 1 to 10 parts by mass. The preparation method comprises the following steps: 1) Dissolve the soy protein raw material in water, adjust the pH to 10-11, and heat and stir to react to obtain a soy protein base liquid; 2) dissolving a polyphenol and a soluble Cu salt in water to perform a chelation reaction to obtain a functionalized reagent containing polyphenol-chelated metal nanoparticles, wherein the Cu salt can be reduced to a zero-valent metal element by the polyphenol, wherein the polyphenol is selected from at least one of tannic acid, flavonoids, and lignin; 3) Adding a polyphenol chelated metal nanoparticle modification functional reagent to the soy protein base liquid obtained in step 1), adjusting the pH to 4.5-6 with acid, then adding a bio-based crosslinking agent, stirring and mixing to cause a crosslinking reaction, and uniformly discharging the material to obtain a high-biobased content soy protein adhesive, wherein the bio-based crosslinking agent is selected from at least one of furfural and furfuryl alcohol.

2. The soybean protein adhesive according to claim 1, characterized in that Calculated by mass, the soybean protein raw material is 15 to 40 parts, the polyphenol is 2 to 7 parts, the soluble Cu salt is 0.25 to 1 part, and the bio-based cross-linking agent is 3 to 7 parts.

3. The soybean protein adhesive according to claim 1, characterized in that The chelating reaction conditions in step 2) are: reacting at 60-70° C. for 1-2 hours.

4. The soybean protein adhesive according to claim 1, characterized in that In step 1), at least one of sodium hydroxide, potassium hydroxide, and calcium hydroxide is used to adjust the pH.

5. The soybean protein adhesive according to claim 1, characterized in that The acid in step 3) is selected from at least one of hydrochloric acid, sulfuric acid, and acetic acid.

6. An adhesive for wood industry, characterized in that: Contains the soybean protein adhesive according to any one of claims 1 to 5.

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