A borate and wood flour composite modified soybean protein adhesive, its preparation method and application

Abstract

This invention relates to the field of adhesive technology, and more particularly to a borate and wood flour composite modified soybean protein adhesive, its preparation method, and its application. The soybean protein adhesive provided by this invention is prepared from raw materials including soybean protein, wood flour, borate, and a dispersion medium; the amount of soybean protein is 10-30% of the total mass of the raw materials used to prepare the soybean protein adhesive; the amount of wood flour is 3-50% of the soybean protein mass; and the amount of borate is 2.5-50% of the soybean protein mass. The soybean protein adhesive provided by this invention uses a scientifically formulated blend of specific types and amounts of raw materials to achieve synergistic effects among multiple components. Utilizing the combined action of the active ingredients in the wood flour and the borate, a dense and stable three-dimensional chemical cross-linking network is constructed in the soybean protein system, thereby simultaneously and significantly improving the adhesive's comprehensive properties such as water resistance, mildew resistance, and flame retardancy without introducing harmful substances such as formaldehyde.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and more particularly to a borate and wood flour composite modified soybean protein adhesive, its preparation method, and its application. Background Technology

[0002] Adhesives are essential materials in the fields of engineered wood products, furniture manufacturing, and building decoration. Currently, traditional synthetic adhesives, such as urea-formaldehyde resin and phenolic resin, are still widely used in the market. While these adhesives offer excellent bonding performance and are inexpensive, their production relies heavily on dwindling fossil resources like petroleum, and they inevitably release volatile organic compounds (VOCs) such as formaldehyde during production and use, posing a long-term threat to the ecological environment and human health. With increasing global emphasis on environmental protection and sustainable development, developing renewable, green, and non-toxic biomass adhesives has become an inevitable trend and a research hotspot in the industry.

[0003] Among numerous biomass materials, soybean protein, as a widely available, abundant, and renewable natural polymer, is considered an ideal alternative to traditional synthetic adhesives due to its advantages such as renewable raw materials, low cost, and good biocompatibility, and has been initially applied in fields such as wood processing.

[0004] However, unmodified pure soybean protein adhesives have problems such as poor weather resistance, susceptibility to mold, poor flame retardancy, and significant performance degradation under high temperature and humidity conditions, which greatly limit their large-scale industrial application.

[0005] To overcome these shortcomings, existing technologies typically employ chemical modification methods, such as adding synthetic resins, isocyanates, epichlorohydrin, and other chemical crosslinking agents to improve the water resistance and strength of adhesives. However, these chemical modification methods often introduce new harmful substances, increasing costs and failing to meet the requirements of green and environmentally friendly development. Furthermore, some chemical additives can impair the biodegradability of adhesives, limiting their application in high-end environmentally friendly fields.

[0006] Therefore, finding a green, economical, and efficient modification method that can simultaneously improve the comprehensive properties of soybean protein adhesives, such as water resistance, mildew resistance, and flame retardancy, without introducing toxic or harmful chemicals, is a key technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0007] This invention provides a borate and wood flour composite modified soybean protein adhesive, its preparation method, and its application, in order to solve the common performance defects of existing soybean protein adhesives, such as poor water resistance, easy mold growth, and lack of flame retardancy, as well as the problem that traditional chemical modification methods introduce harmful substances and are not green and environmentally friendly enough.

[0008] According to a first aspect of the present invention, the present invention provides a borate and wood flour composite modified soybean protein adhesive, which is prepared from raw materials including soybean protein, wood flour, borate and a dispersion medium; wherein the amount of soybean protein is 10-30% of the total mass of the raw materials for preparing the soybean protein adhesive; the amount of wood flour is 3-50% of the mass of the soybean protein; and the amount of borate is 2.5-50% of the mass of the soybean protein.

[0009] The borate and wood flour composite modified soybean protein adhesive provided by this invention uses specific amounts of wood flour and borate in combination with soybean protein. The synergistic effect between the components not only significantly improves the cohesive strength of the adhesive and the interfacial bonding force between the adhesive layer and the substrate, but also has excellent flame retardant properties and long-lasting anti-mildew properties. Moreover, the raw materials are environmentally friendly, fundamentally avoiding the release of harmful substances such as formaldehyde in traditional synthetic adhesives. It comprehensively solves the technical problems of poor water resistance, easy mildew, lack of flame retardancy, and environmentally unfriendly chemical modification methods of existing soybean protein adhesives.

[0010] According to the borate and wood flour composite modified soybean protein adhesive of the present invention, the wood flour contains 1-5% tannin and 9-15% polysaccharides.

[0011] The active ingredients such as tannins in the wood flour of this invention can act as natural cross-linking agents, undergoing a cross-linking reaction with soybean protein molecular chains. An appropriate amount of tannins provides sufficient ortho- and olfactory hydroxyl active sites for efficient cross-linking with soybean protein molecules and borates. The polysaccharides in the wood flour further promote the Maillard reaction, while saponins enhance the surface activity of the material, thus improving reaction efficiency. By limiting these parameters, a uniform and dense chemical cross-linking network is formed between the wood flour, soybean protein, and borates, maximizing the synergistic effect of the three components. This results in excellent bonding strength while imparting stable flame retardant properties and long-lasting anti-mildew characteristics to the adhesive.

[0012] Preferably, the wood powder is selected from one or more of tree trunk powder, bark powder, and branch powder, and more preferably elm bark powder.

[0013] According to the borate and wood flour composite modified soybean protein adhesive of the present invention, the wood flour has a particle size of 80-100 mesh. This particle size range ensures that the wood flour is uniformly dispersed in the adhesive system and forms a stable suspension system, avoiding sedimentation and stratification caused by excessively large particle size or agglomeration caused by excessively small particle size. This optimizes the contact area and interfacial bonding strength between the active components of wood flour and soybean protein and borate, effectively improving the crosslinking density and mechanical property stability of the adhesive.

[0014] Preferably, the amount of wood flour used is 5-35% of the soybean protein content; the amount of borate used is 5-35% of the soybean protein content.

[0015] According to the borate and wood flour composite modified soybean protein adhesive of the present invention, the soybean protein has a protein content of 85-95% and a carbohydrate content of 5-15%.

[0016] This invention controls the protein and carbohydrate content of soybean protein to a specific range, ensuring that the selected soybean protein has a suitable density of reactive sites, good water dispersibility and solubility, so that the active groups can be fully exposed during the adhesive preparation process, and undergo efficient cross-linking reaction with tannins and borates in wood flour to form a uniform and dense solidified network.

[0017] According to the borate and wood flour composite modified soybean protein adhesive of the present invention, the soybean protein has a particle size of less than 200 mesh. This allows it to be rapidly hydrated, fully dissolved, and uniformly dispersed in the dispersion medium, which facilitates the full extension of the protein molecular chains to expose more active reaction sites, thereby achieving a more thorough cross-linking reaction with wood flour and borate, forming a denser and more uniform cured network structure, and providing a foundation for obtaining excellent adhesive strength and stability.

[0018] According to the borate and wood flour composite modified soybean protein adhesive of the present invention, the borate is selected from one or more of monoborate and polyborate, preferably polyborate, and more preferably tetraborate (borax, AR, ≥99.5%). As a core modifier, tetraborate can form stable chemical crosslinks with hydroxyl groups and other groups in soybean protein and wood flour, while its inherent properties endow the adhesive with key flame retardant and mildew-proof functions.

[0019] The borate and wood flour composite modified soybean protein adhesive of the present invention uses water as the dispersion medium. Using water as a solvent avoids the environmental pollution and health risks associated with organic solvents in traditional adhesives, thus meeting the requirements of sustainable development.

[0020] The borate and wood flour composite modified soybean protein adhesive according to the present invention comprises, by weight, 10-30 parts soybean protein, 1-5 parts wood flour, 0.75-5 parts borate and 70-90 parts dispersion medium.

[0021] The borate and wood flour composite modified soybean protein adhesive according to the present invention comprises, by weight, 10-20 parts soybean protein, 1-3 parts wood flour, 0.75-2.25 parts borate, and 80-90 parts dispersion medium; wherein, the wood flour is elm bark powder with a particle size of 80-100 mesh; the soybean protein has a protein content of 85-95% and a carbohydrate content of 5-15%, and a particle size of less than or equal to 200 mesh (preferably 150-200 mesh); and the borate is sodium tetraborate.

[0022] According to a second aspect of the present invention, the present invention also provides a method for preparing the above-mentioned borate and wood flour composite modified soybean protein adhesive, comprising: dispersing soybean protein in a dispersion medium to obtain a soybean protein dispersion; and then dispersing borate and wood flour in the soybean protein dispersion.

[0023] This invention optimizes the preparation method of a soybean protein adhesive modified by borate and wood flour composite. First, the soybean protein is dissolved to fully extend its molecular chains, and then borate is added for preliminary cross-linking and wood flour is dispersed. This facilitates the formation of a uniform, stable, and efficient interpenetrating network structure, thereby improving the performance of the adhesive.

[0024] According to the preparation method of the borate and wood flour composite modified soybean protein adhesive of the present invention, the borate is first dispersed in the soybean protein dispersion, and then the wood flour is dispersed in the soybean protein dispersion.

[0025] This invention adds borate first and then wood flour, which can effectively avoid the problems of excessively high system viscosity and uneven dispersion of subsequent components caused by adding wood flour first, thereby preparing an adhesive with uniform structure and stable performance.

[0026] The preparation method of this invention first disperses soybean protein in a dispersion medium to allow the soybean protein molecular chains to fully stretch and extend, exposing the active groups (such as hydroxyl and amino groups) encapsulated within the protein as much as possible. Next, borates are added, which interact with the fully stretched soybean protein molecular chains to form preliminary cross-links. Finally, wood flour is dispersed in the soybean protein system that has formed a preliminary cross-linked network, allowing the active components in the wood flour (such as tannins) to synergistically interact with the soybean protein and borates at the network nodes, further strengthening and densifying this three-dimensional network, forming a uniform, stable, and efficient interpenetrating network structure.

[0027] According to the preparation method of the borate and wood flour composite modified soybean protein adhesive of the present invention, the borate is first dispersed in the soybean protein dispersion, and then the wood flour is dispersed in the soybean protein dispersion. The temperature is 22-28℃, the stirring power is 60-80r / min, and the total time should be controlled within 2h.

[0028] According to a third aspect of the present invention, the present invention also provides the application of the above-described borate and wood flour composite modified soybean protein adhesive, or the borate and wood flour composite modified soybean protein adhesive prepared by the above-described preparation method, in engineered wood panels.

[0029] The engineered wood products of this invention include any one of plywood, particleboard, fiberboard, blockboard, and decorative panels.

[0030] The beneficial effects of this invention are: The borate and wood flour composite modified soybean protein adhesive provided by this invention uses specific types and amounts of raw materials (soybean protein, wood flour, borate, and dispersion medium) in a scientific formulation to achieve synergistic effects among multiple components. By utilizing the combined effect of active ingredients (such as tannins) in wood flour and borate, a dense and stable three-dimensional chemical cross-linking network is constructed in the soybean protein system, thereby simultaneously and significantly improving the overall performance of the adhesive without introducing harmful substances such as formaldehyde.

[0031] The borate and wood flour composite modified soybean protein adhesive of the present invention has a bonding strength far exceeding the national Class II board standard (dry shear strength up to 2.73 MPa, wet shear strength up to 1.37 MPa), and has excellent flame retardancy (limiting oxygen index LOI up to 27.97%, reaching the flame-retardant level) and long-lasting mildew resistance (mildew resistance test shows no mildew growth for 120 days or more).

[0032] The preparation method of the borate and wood flour composite modified soybean protein adhesive of the present invention is simple, the raw materials are green and renewable, and the cost is controllable. It fundamentally solves the industry technical problems of poor water resistance, easy mold growth, and lack of flame retardancy of traditional soybean protein adhesives, as well as the environmentally unfriendly nature of existing chemical modification methods. It has significant economic and social benefits and broad prospects for industrial application. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 A physical image of the borate and wood flour composite modified soybean protein adhesive provided in Example 1 of this invention applied to plywood.

[0035] Figure 2 The image shows a physical example of the borate and wood flour composite modified soybean protein adhesive provided in Comparative Example 1 of this invention applied to plywood. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0037] The sources of the raw materials used in the following examples and comparative examples are as follows: Elm bark powder, with tannin content of 1-5% and polysaccharide content (hot water extraction method) of 9-15%, has a particle size of 80-100 mesh; origin: Hubei Province; Poplar bark powder, with tannin content less than 1%, polysaccharide content less than 5%, and particle size of 80-100 mesh; origin: Hubei.

[0038] First Soybean Protein: Protein content is 90%, carbohydrate content is 8%, and particle size is 150-200 mesh; Origin: Shandong; Second, soybean protein: 50% protein, 30% carbohydrates, and a particle size of 150-200 mesh. Third, soybean protein: protein content is 42%, carbohydrate content is 33%, and its particle size is 150-200 mesh; Borate: Sodium tetraborate (AR, ≥99.5%); Dispersion medium: deionized water.

[0039] Example 1 This embodiment provides a soybean protein adhesive modified by a combination of borate and wood flour, comprising 15g of first soybean protein, 1.5g of elm bark powder (tannin content of 3% and elm bark polysaccharide content of 9.43%), 0.75g of borate and 85g of water.

[0040] This embodiment also provides a method for preparing the borate and wood flour composite modified soybean protein adhesive, including the following steps: Disperse 15g of first-grade soy protein evenly in 85g of water; then add 0.75g of borate to the soy protein dispersion and stir evenly at 70r / min; finally, add 1.5g of wood flour to the solution and stir evenly at 70r / min.

[0041] Example 2 This embodiment provides a soybean protein adhesive modified with borate and wood flour, which differs from Example 1 in that the amount of borate used is 1.5g.

[0042] Example 3 This embodiment provides a soybean protein adhesive modified with borate and wood flour composite, which differs from Example 1 in that the amount of borate used is 2.25g.

[0043] Example 4 This embodiment provides a soybean protein adhesive modified with borate and wood flour, which differs from Example 1 in that the amount of borate used is 5g.

[0044] Example 5 This embodiment provides a borate and wood flour composite modified soybean protein adhesive, which differs from Example 1 in that the amount of soybean protein used is 10g.

[0045] Example 6 This embodiment provides a borate and wood flour composite modified soybean protein adhesive, which differs from Example 1 in that the amount of soybean protein used is 30g.

[0046] Example 7 This embodiment provides a soybean protein adhesive modified with borate and wood flour, which differs from Example 1 in that the amount of elm bark powder used is 1g.

[0047] Example 8 This embodiment provides a soybean protein adhesive modified with borate and wood flour, which differs from Example 1 in that the amount of elm bark powder used is 3g.

[0048] Example 9 This embodiment provides a soybean protein adhesive modified with borate and wood flour, which differs from Example 1 in that the amount of elm bark powder used is 5g.

[0049] Comparative Example 1 This comparative example provides a soybean protein adhesive modified with borate and wood flour composite, which differs from Example 1 in that it does not contain elm bark powder and borate.

[0050] Comparative Example 2 This comparative example provides a borate and wood flour composite modified soybean protein adhesive, which differs from Example 1 in that no borate is added.

[0051] Comparative Example 3 This comparative example provides a soybean protein adhesive modified with borate and wood flour composite, which differs from Example 1 in that it does not contain elm bark powder.

[0052] Comparative Example 4 This comparative example provides a soybean protein adhesive modified by a combination of borate and wood flour, which differs from Example 1 in that poplar bark powder is used instead of elm bark powder. The poplar bark powder contains 0.8% tannin and 4.5% polysaccharides.

[0053] Comparative Example 5 This comparative example provides a soybean protein adhesive modified with borate and wood flour composite, which differs from Example 1 in that boric acid is used instead of tetraborate.

[0054] Comparative Example 6 This comparative example provides a borate and wood flour composite modified soybean protein adhesive, which differs from Example 1 in that a second soybean protein replaces the first soybean protein.

[0055] Comparative Example 7 This comparative example provides a borate and wood flour composite modified soybean protein adhesive, which differs from Example 1 in that a third soybean protein replaces the first soybean protein.

[0056] The properties of the borate and wood flour composite modified soybean protein adhesives in the examples and comparative examples were determined as follows: The prepared soybean protein adhesive was evenly applied to poplar veneer at a rate of 180 g / m². 2 Next, hot-pressed sheets were required (1MPa, 120℃, 330s). Strength testing was performed using an electronic universal testing machine (Shimadzu Instruments (Suzhou) Co., Ltd., AGS-X-10K, 337-01261-31) according to the Chinese national standard (GB / T 9846-2015). After pressing, the sheets were left to stand for more than 24 hours before sawn timber testing. Dry shear strength was tested directly; wet shear strength was tested by hot water immersion: soaking in (63±3)℃ hot water for 3 hours, followed by cooling to room temperature for 10 minutes before testing. The performance test results are shown in Table 1.

[0057] Table 1 category Viscosity (Pa∙s) Dry shear strength (MPa) Wet shear strength (MPa) Overlap shear strength (MPa) LOI (%) Example 1 248.25 2.58 1.00 1.79 26.13 Example 2 329.86 2.73 1.37 1.98 27.54 Example 3 381.63 2.51 1.27 1.91 27.97 Example 4 466.62 2.55 1.18 1.41 28.71 Example 5 256.37 1.86 1.01 1.66 26.35 Example 6 653.21 1.62 0.99 1.26 25.74 Example 7 323.02 1.74 0.88 1.72 25.89 Example 8 462.55 2.53 1.03 1.78 26.21 Example 9 504.72 1.61 0.79 1.56 26.34 Comparative Example 1 13.32 1.42 0.58 1.53 22.46 Comparative Example 2 42.15 2.39 1.20 2.46 23.64 Comparative Example 3 165.20 2.60 1.12 1.84 26.89 Comparative Example 4 4.85 1.42 0.98 1.61 - Comparative Example 5 43.73 1.42 0.74 0.81 - Comparative Example 6 694.29 1.55 0.39 0.91 - Comparative Example 7 826.89 1.44 0.27 0.88 - As can be seen from the experimental results of the examples and Comparative Example 1 in the table, when the soybean protein adhesive provided by the present invention is applied to plywood, the dry shear strength of the plywood can reach up to 2.73 MPa, the wet shear strength can reach 1.37 MPa, and the lap shear strength can reach 1.98 MPa. It also exhibits excellent flame retardancy and high water resistance. The soybean protein adhesive of the present invention can achieve the above-mentioned technical effects, possibly because: firstly, elm bark powder has viscosity, which can increase the cohesive force of the adhesive to a certain extent during bonding; secondly, borate ions form hydrogen bonds with hydroxyl groups, and through heating condensation reaction, form strong COB and BOB covalent bonds, achieving chemical cross-linking and enhancing bonding strength. Furthermore, due to the excellent flame retardancy and mildew resistance of borate, its addition to the soybean protein adhesive resulted in a limiting oxygen index (LOI) of 27.97% (LOI > 27% indicates a flame-retardant material). Mildew resistance tests showed that the adhesive of the present invention did not exhibit mold growth for more than four months.

[0058] Compared with Example 1 and Comparative Example 1, the dry shear strength, wet shear strength, and lap shear strength of the present invention, after adding wood flour and borate, are significantly increased compared with traditional soybean protein adhesive, all exceeding the national Class II standard (wet shear strength ≥ 0.7 MPa). It also achieves flame retardancy and mildew resistance of the adhesive, ensuring the stability of the material's performance during use. Figure 1 and Figure 2 It can be seen Figure 1 The surface has slight wrinkles, which confirms the formation of the internal cross-linking structure. At the same time, the surface is condensed, which has good water resistance. Figure 2 The smooth surface and lack of obvious agglomeration confirm its poor wet shear strength. Adjusting the amount of wood flour and borate added allows for targeted control of adhesive strength, facilitating the preparation of adhesives suitable for different types of boards. Comparing Example 1 and Comparative Example 1, the use of wood flour and borate to reinforce soybean protein adhesive significantly reduced modification costs, and the prepared adhesive is formaldehyde-free and environmentally friendly.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A soybean protein adhesive modified with borate and wood flour, characterized in that, It is prepared from raw materials including soybean protein, wood flour, borate and dispersion medium; wherein, the amount of soybean protein is 10-30% of the total mass of the raw materials for preparing soybean protein adhesive; the amount of wood flour is 3-50% of the soybean protein mass; and the amount of borate is 2.5-50% of the soybean protein mass.

2. The borate and wood flour composite modified soybean protein adhesive according to claim 1, characterized in that, The wood flour contains 1-5% tannins and 9-15% polysaccharides.

3. The borate and wood flour composite modified soybean protein adhesive according to claim 1 or 2, characterized in that, The wood powder is selected from one or more of tree trunk powder, bark powder, and branch powder, with elm bark powder being more preferred.

4. The borate and wood flour composite modified soybean protein adhesive according to any one of claims 1-3, characterized in that, The wood flour has a particle size of 80-100 mesh.

5. The borate and wood flour composite modified soybean protein adhesive according to any one of claims 1-4, characterized in that, The amount of wood flour used is 5-35% of the soybean protein content; the amount of borate used is 5-35% of the soybean protein content.

6. The borate and wood flour composite modified soybean protein adhesive according to any one of claims 1-5, characterized in that, The soy protein contains 85-95% protein and 5-15% carbohydrates.

7. The borate and wood flour composite modified soybean protein adhesive according to any one of claims 1-6, characterized in that, The borate is selected from one or more monoborates and polyborates, preferably polyborates; And / or, the dispersion medium is water.

8. The method for preparing the borate and wood flour composite modified soybean protein adhesive according to any one of claims 1-7, characterized in that, include: Soy protein is dispersed in a dispersion medium to obtain a soybean protein dispersion. Then, borates and wood flour are dispersed in the soybean protein dispersion.

9. The method for preparing the borate and wood flour composite modified soybean protein adhesive according to claim 8, characterized in that, The borate is first dispersed in the soybean protein dispersion, and then the wood flour is dispersed in the soybean protein dispersion.

10. The application of the borate and wood flour composite modified soybean protein adhesive according to any one of claims 1-7, or the borate and wood flour composite modified soybean protein adhesive prepared by the preparation method according to claim 8 or 9, in engineered wood panels.

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