Walnut green seedcase carbon nanorod modified soybean protein adhesive and preparation method thereof

Abstract

The invention discloses a walnut green seedcase carbon nanorod modified soybean protein adhesive and a preparation method thereof, and belongs to the technical field of bio-based wood adhesives. Walnut green seedcase is used as a carbon source to prepare a carbon nanorod, and the carbon nanorod is used as a functional nanofiller to be blended with soybean protein at room temperature to prepare the walnut green seedcase carbon nanorod modified soybean protein adhesive. Under the conditions of no pretreatment and no chemical cross-linking agent, a non-covalent network structure is constructed through a hydrogen-bond interaction, an electrostatic adsorption effect, a hydrophobic interface effect and a nano confinement effect between the carbon nanorod and the soybean protein, so that the water resistance and the bonding strength of the adhesive are remarkably improved. The preparation process is simple, the energy consumption is low, and the obtained adhesive is formaldehyde-free, environment-friendly and suitable for bonding of plywood.

Description

Technical Field

[0001] This invention belongs to the field of bio-based wood adhesive technology, and particularly relates to a walnut green husk carbon nanorod modified soybean protein adhesive and its preparation method. Background Technology

[0002] Soy protein adhesives, as a typical bio-based wood adhesive material, have advantages such as wide availability of raw materials, renewability, no formaldehyde release, and environmental friendliness, showing promising application prospects in the manufacturing of plywood, fiberboard, and other engineered wood products. However, soybean protein molecules have a high content of hydrophilic groups and insufficient hydrophobicity. The molecular chains are mainly maintained by weak interactions such as hydrogen bonds, resulting in a relatively loose internal structure. Under the influence of moisture, they are prone to swelling, structural damage, or interfacial dissociation, leading to poor water resistance and low wet bonding strength, thus limiting their application in high-performance and water-resistant engineered wood products.

[0003] To improve the mechanical and water resistance properties of soybean protein adhesives, existing technologies typically employ methods such as chemical crosslinking, enzymatic modification, alkali treatment, and reinforcement with inorganic or organic nanofillers. Among these, chemical modification systems often rely on crosslinking agents such as aldehydes and isocyanates to form a covalent crosslinking network, which can significantly improve adhesive strength; however, its potential environmental and health risks limit its application in the field of green engineered wood products. Enzymatic modification and alkali treatment usually require relatively harsh reaction conditions, resulting in complex processes, high costs, and are unfavorable for continuous industrial production.

[0004] In recent years, carbon-based nanomaterials have attracted attention due to their wide availability, relatively simple preparation methods, low cost, and rich surface functional groups such as hydroxyl, carboxyl, and amino groups. The application of carbon nanodots in soybean protein adhesives has been reported, but they mainly exist as zero-dimensional dot structures, making it difficult to construct a continuous reinforcing network in the adhesive layer, thus limiting the reinforcing effect. In contrast, carbon nanorods possess a one-dimensional rod-like structure and a high aspect ratio, resulting in a larger interfacial contact area in the polymer matrix, making it easier to form physical support and stress transfer channels, and therefore exhibiting greater reinforcing potential.

[0005] However, a review of existing literature revealed no publicly available reports on the introduction of carbon nanorods into soybean protein adhesive systems and their reinforcing effects and mechanisms of action. The structural role of carbon nanorods in soybean protein adhesives, their interaction with soybean protein molecules, and their impact on the microstructure and water resistance of the adhesive layer remain unclear, indicating a significant gap in this technological field.

[0006] Therefore, there is an urgent need to develop a method for preparing carbon nanorod-modified soybean protein adhesive with a controllable structure and a clear mechanism of action. Under the premise of avoiding the use of toxic crosslinking agents, a stable and dense adhesive layer structure can be constructed by rationally designing the structural features of carbon nanorods and their interaction with soybean protein molecules, thereby achieving a synergistic improvement in the mechanical properties and water resistance of the adhesive. Summary of the Invention

[0007] To address the technical problems of existing soybean protein adhesives, such as poor water resistance, low wet bonding strength, and insufficient mechanical properties, this invention proposes a walnut green husk carbon nanorod modified soybean protein adhesive and its preparation method, so as to achieve the preparation of a green, environmentally friendly, and high-performance adhesive.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a soybean protein adhesive modified with walnut green husk carbon nanorods includes the following steps: (1) Carbon nanorod solution was prepared by hydrothermal treatment using walnut green skin as carbon source and water as solvent; (2) The carbon nanorod solution was fully dispersed with water at room temperature, and then soybean protein powder was added and stirred evenly at room temperature to obtain walnut green skin carbon nanorod modified soybean protein adhesive.

[0009] Beneficial effects: The carbon nanorod solution prepared from walnut green skin can form a stable weak interaction network with soybean protein molecules through non-covalent interactions such as hydrogen bonding, electrostatic adsorption, and van der Waals forces, which can significantly improve the structural stability, water resistance and wet mechanical properties of the adhesive system.

[0010] Optionally, the mass concentration of the green walnut husk in water in step (1) is 1-4 wt%.

[0011] Furthermore, the mass concentration of the green walnut husk in water is 2 wt%.

[0012] Optionally, the hydrothermal treatment in step (1) is performed at a temperature of 160°C for 6-10 hours.

[0013] Furthermore, the hydrothermal treatment is performed at a temperature of 160°C for 8 hours.

[0014] Optionally, the carbon nanorods in the carbon nanorod solution are one-dimensional rod-shaped nanostructures with a length of 50-2000 nm and a diameter of 5-200 nm.

[0015] Optionally, the mass ratio of the carbon nanorod solution, water and soybean protein powder in step (2) is 1-6:9.5-14.5:3. The three are mixed evenly and stirred at room temperature for 10 minutes to obtain an adhesive.

[0016] Furthermore, the mass ratio of the carbon nanorod solution, water, and soybean protein powder is 5:10.5:3.

[0017] Optionally, the stirring time at room temperature in step (2) is 10 min.

[0018] Furthermore, the temperature of the room temperature stirring is 20-30℃.

[0019] A walnut green husk carbon nanorod modified soybean protein adhesive is prepared by the above preparation method.

[0020] Optionally, the carbon nanorods form a cross-linked network structure with soybean protein molecules through non-covalent interactions (such as hydrogen bonds).

[0021] The application of the above-mentioned walnut green husk carbon nanorod modified soybean protein adhesive in the preparation of plywood.

[0022] A method for preparing a water-resistant plywood, comprising the following steps: The veneer is prepared by coating the surface of a veneer with a modified soybean protein adhesive made from walnut green husk carbon nanorods, stacking the veneers according to the principle of interlayer texture cross, and then placing them in a flat vulcanizing machine for hot pressing and curing.

[0023] Optionally, the hot-press curing conditions are: hot pressing at 120°C and 1.2 MPa for 6 min.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects: This invention modifies soybean protein using carbon nanorods prepared from walnut husks. By utilizing the surface-active groups of the carbon nanorods to form a non-covalent network structure with the protein molecules, the dry and wet bonding strength of the adhesive is significantly enhanced.

[0025] After the plywood is prepared, the dry shear strength can reach 1.99 MPa and the wet shear strength can reach 0.79 MPa, which is significantly better than traditional soybean protein adhesives.

[0026] The adhesive preparation process of this invention is simple, requiring no high temperature or complex chemical crosslinking agents. All raw materials used are derived from biomass resources, meeting green and environmentally friendly requirements, and have good potential for industrialization.

[0027] By constructing a non-covalent network structure, the adhesive achieves performance improvement while maintaining environmental friendliness, providing a green and sustainable adhesive solution for high-performance wood products. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The mechanical properties of the plywood prepared by the adhesives of Example 1, Comparative Examples 1, 2, and 3 of this invention are shown.

[0029] Figure 2 The wet bonding strength of the plywood prepared with the adhesives obtained in Example 1 and Comparative Examples 4 and 5 is given.

[0030] Figure 3 The wet bonding strength of plywood prepared with the adhesives obtained in Example 1 and Comparative Examples 6-10 is measured.

[0031] Figure 4 The structure and mechanism of action of the adhesives obtained in Example 1 and Comparative Example 1 are characterized, where a is the FT-IR spectrum, b is the XPS spectrum, c is the DSC curve, d is the low-field nuclear magnetic relaxation time distribution (T2 distribution) spectrum of the sample, e is the comparison of the average T2 value and τc, and f is the TGA spectrum.

[0032] Figure 5 The images show cross-sectional SEM images of the adhesives obtained in Example 1 and Comparative Example 1.

[0033] Figure 6 This is a TEM image of the formation process of carbon nanorods obtained from walnut green skin through hydrothermal treatment in step S1 of Example 1. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] This invention discloses a method for preparing a soybean protein adhesive modified with walnut green husk carbon nanorods, comprising the following steps: (1) Carbon nanorod solution was prepared by hydrothermal treatment using walnut green skin as carbon source and water as solvent; (2) Disperse the carbon nanorod solution with water at room temperature, then add soybean protein powder and continue to stir evenly at room temperature to obtain soybean protein-carbon nanorod adhesive (i.e., walnut green skin carbon nanorod modified soybean protein adhesive).

[0040] In some alternative embodiments, the walnut husks account for 2 wt% of the water content, the hydrothermal treatment temperature is 160°C, and the treatment time is 8 h.

[0041] In some alternative embodiments, after the carbon nanorod solution and water are mixed evenly at a mass ratio of 5:10.5, 3 g of soybean protein powder is added and the mixture is stirred at room temperature for 10 min to obtain a soybean protein-carbon nanorod adhesive.

[0042] This invention also discloses a plywood, the preparation process of which is as follows: the adhesive obtained in step (2) above is applied to the surface of the plywood veneer, the veneers are stacked according to the principle of interlayer texture cross, and the plywood is prepared by hot pressing and curing in a flat vulcanizing machine.

[0043] In some alternative embodiments, the hot-press curing conditions are as follows: three-layer plywood is prepared by hot-pressing at 120°C and 1.2 MPa for 6 minutes.

[0044] In summary, a non-covalent cross-linked network structure is formed through hydrogen bonding, electrostatic adsorption, and nano-confinement effects between the hydroxyl and carboxyl groups on the surface of carbon nanorods and soybean protein molecules, thereby significantly improving the water resistance and mechanical properties of the adhesive.

[0045] Unless otherwise specified, "room temperature" in this invention refers to 20-30℃.

[0046] All raw materials used in this invention were purchased from the market. The walnut green husk powder was purchased from a specialty store in Taihang Water Town and did not undergo any special chemical treatment; the soybean protein powder was purchased from Shandong Yuwang Ecological Food Industry Co., Ltd.

[0047] The technical solution of the present invention will be further illustrated by the following embodiments.

[0048] Example 1 A method for preparing a soybean protein adhesive modified with walnut green husk carbon nanorods includes the following steps: S1. Add 2 g of walnut green skin powder to 100 mL of deionized water and place it in a pressure-resistant reactor for hydrothermal treatment (160℃, 8 h). After the reaction is completed, cool it naturally to room temperature to obtain a walnut green skin carbon nanorod solution (wherein, the length and diameter of the carbon nanorods correspond to a length of 50-2000 nm and a diameter of 5-200 nm, respectively). S2. Take 5 g of the walnut green husk carbon nanorod solution obtained in step S1, add 10.5 g of deionized water and mix thoroughly. Then add 3 g of soybean protein powder and mechanically stir at room temperature for 10 min to obtain soybean protein-walnut green husk carbon nanorod adhesive.

[0049] Comparative Example 1 The preparation steps of unmodified soybean protein adhesive are as follows: Take 3 g of soybean protein powder, add 15.5 g of deionized water, and mechanically stir for 10 min at room temperature to obtain unmodified soybean protein adhesive.

[0050] Comparative Example 2 The preparation steps of 1% concentration walnut green husk carbon nanorod modified soybean protein adhesive are as follows: S1. Add 1 g of walnut green skin powder to 100 mL of deionized water and place it in a pressure-resistant reactor for hydrothermal treatment (160℃, 8 h). After the reaction is completed, cool it naturally to room temperature to obtain walnut green skin carbon nanorod solution. S2. Take 5 g of the walnut green husk carbon nanorod solution obtained in step S1, add 10.5 g of deionized water and mix thoroughly. Then add 3 g of soybean protein powder and mechanically stir at room temperature for 10 min to obtain soybean protein-walnut green husk carbon nanorod adhesive.

[0051] Comparative Example 3 The preparation steps of 4% concentration walnut green husk carbon nanorod modified soybean protein adhesive are as follows: S1. Add 4 g of walnut green skin powder to 100 mL of deionized water and place it in a pressure-resistant reactor for hydrothermal treatment (160℃, 8 h). After the reaction is completed, cool it naturally to room temperature to obtain walnut green skin carbon nanorod solution. S2. Take 5 g of the walnut green husk carbon nanorod solution obtained in step S1, add 10.5 g of deionized water and mix thoroughly. Then add 3 g of soybean protein powder and mechanically stir at room temperature for 10 min to obtain soybean protein-walnut green husk carbon nanorod adhesive.

[0052] Comparative Example 4 The preparation steps of the walnut green husk carbon nanorod modified soybean protein adhesive after 6 hours of hydrothermal treatment are as follows: S1. Add 2 g of walnut green skin powder to 100 mL of deionized water and place it in a pressure-resistant reactor for hydrothermal treatment (160℃, 6 h). After the reaction is completed, cool it naturally to room temperature to obtain walnut green skin carbon nanorod solution. S2. Take 5 g of the walnut green husk carbon nanorod solution obtained in step S1, add 10.5 g of deionized water and mix thoroughly. Then add 3 g of soybean protein powder and mechanically stir at room temperature for 10 min to obtain soybean protein-walnut green husk carbon nanorod adhesive.

[0053] Comparative Example 5 The preparation steps of the walnut green skin carbon nanorod modified soybean protein adhesive after 10 hours of hydrothermal treatment are as follows: S1. Add 2 g of walnut green skin powder to 100 mL of deionized water and place it in a pressure-resistant reactor for hydrothermal treatment (160℃, 10 h). After the reaction is completed, cool it naturally to room temperature to obtain walnut green skin carbon nanorod solution. S2. Take 5 g of the walnut green husk carbon nanorod solution obtained in step S1, add 10.5 g of deionized water and mix thoroughly. Then add 3 g of soybean protein powder and mechanically stir at room temperature for 10 min to obtain soybean protein-walnut green husk carbon nanorod adhesive.

[0054] Comparative Example 6 The preparation steps for a carbon nanorod-modified soybean protein adhesive with a carbon nanorod concentration of 2% and a carbon nanorod solution addition of 1 g are as follows: S1. Add 2 g of walnut green skin powder to 100 mL of deionized water and place it in a pressure-resistant reactor for hydrothermal treatment (160℃, 8 h). After the reaction is completed, cool it naturally to room temperature to obtain walnut green skin carbon nanorod solution. S2. Take 1 g of the walnut green husk carbon nanorod solution obtained in step S1, add 14.5 g of deionized water and mix thoroughly. Then add 3 g of soybean protein powder and mechanically stir at room temperature for 10 min to obtain soybean protein-walnut green husk carbon nanorod adhesive.

[0055] Comparative Example 7 The preparation steps for a carbon nanorod-modified soybean protein adhesive with a carbon nanorod concentration of 2% and a carbon nanorod solution addition of 2 g are as follows: S1. Add 2 g of walnut green skin powder to 100 mL of deionized water and place it in a pressure-resistant reactor for hydrothermal treatment (160℃, 8 h). After the reaction is completed, cool it naturally to room temperature to obtain walnut green skin carbon nanorod solution. S2. Take 2 g of the walnut green husk carbon nanorod solution obtained in step S1, add 13.5 g of deionized water and mix thoroughly. Then add 3 g of soybean protein powder and mechanically stir at room temperature for 10 min to obtain soybean protein-walnut green husk carbon nanorod adhesive.

[0056] Comparative Example 8 The preparation steps for a carbon nanorod-modified soybean protein adhesive with a carbon nanorod concentration of 2% and a carbon nanorod solution addition of 3 g are as follows: S1. Add 2 g of walnut green skin powder to 100 mL of deionized water and place it in a pressure-resistant reactor for hydrothermal treatment (160℃, 8 h). After the reaction is completed, cool it naturally to room temperature to obtain walnut green skin carbon nanorod solution. S2. Take 3 g of the walnut green husk carbon nanorod solution obtained in step S1, add 12.5 g of deionized water and mix thoroughly. Then add 3 g of soybean protein powder and mechanically stir at room temperature for 10 min to obtain soybean protein-walnut green husk carbon nanorod adhesive.

[0057] Comparative Example 9 The preparation steps for a carbon nanorod-modified soybean protein adhesive with a carbon nanorod concentration of 2% and a carbon nanorod solution addition amount of 4 g are as follows: S1. Add 2 g of walnut green skin powder to 100 mL of deionized water and place it in a pressure-resistant reactor for hydrothermal treatment (160℃, 8 h). After the reaction is completed, cool it naturally to room temperature to obtain walnut green skin carbon nanorod solution. S2. Take 4 g of the walnut green husk carbon nanorod solution obtained in step S1, add 11.5 g of deionized water and mix thoroughly. Then add 3 g of soybean protein powder and mechanically stir at room temperature for 10 min to obtain soybean protein-walnut green husk carbon nanorod adhesive.

[0058] Comparative Example 10 The preparation steps for a carbon nanorod-modified soybean protein adhesive with a carbon nanorod concentration of 2% and a carbon nanorod solution addition of 6 g are as follows: S1. Add 2 g of walnut green skin powder to 100 mL of deionized water and place it in a pressure-resistant reactor for hydrothermal treatment (160℃, 8 h). After the reaction is completed, cool it naturally to room temperature to obtain walnut green skin carbon nanorod solution. S2. Take 6 g of the walnut green husk carbon nanorod solution obtained in step S1, add 9.5 g of deionized water and mix thoroughly. Then add 3 g of soybean protein powder and mechanically stir at room temperature for 10 min to obtain soybean protein-walnut green husk carbon nanorod adhesive.

[0059] Effect verification: Application example: The adhesives prepared in Example 1 and Comparative Examples 1-10 above are used in the preparation of three-layer poplar plywood. The specific preparation process is as follows: The adhesive is applied to the surface of the plywood veneer, the veneers are stacked according to the principle of interlayer texture cross, and then placed in a flat vulcanizing machine for hot pressing and curing to prepare plywood. During the preparation process, the amount of adhesive applied to one side of the core board was controlled at 260-280 g / m²; the hot-pressing curing conditions were: pressure 1.2 MPa, time 6 min, and temperature 120℃. After hot pressing, the plywood was left to stand at room temperature for 24 h.

[0060] The prepared plywood was then subjected to a bonding strength test; the test included: 1. Dry bond strength; 2. Wet bond strength (bonding strength was measured after wet heat treatment (immersion in 63℃ warm water for 3 h)).

[0061] The adhesive strength is calculated according to formula (1): (1); The dry shear strength and wet shear strength of the plywood prepared using the adhesives of Example 1, Comparative Examples 1-10 are shown in Table 1.

[0062] Table 1 In summary, the test results in Table 1 show that the walnut husk carbon nanorod-modified soybean protein adhesive prepared in Example 1 exhibits the best bonding performance. Its dry shear strength (dry bonding strength) and wet shear strength (wet bonding strength) are significantly higher than those of the unmodified adhesive (Comparative Example 1). Notably, the wet shear strength of the adhesive prepared in Example 1 reaches 0.79 MPa, meeting the application requirements of Class II wood-based panel adhesives in the national standard GB / T 17657-2022 (bonding strength ≥ 0.7 MPa). This indicates that the concentration, amount, and degree of carbon nanorods significantly affect the mechanical properties of plywood. With changes in the structure and content of carbon nanorods, the degree of crosslinking, interfacial bonding state, and toughening mechanism of the adhesive system also change, leading to differences in the final mechanical properties. Therefore, rationally optimizing the preparation conditions of carbon nanorods and their dosage in the adhesive is a crucial factor in obtaining high-performance plywood.

[0063] Figure 1 The mechanical properties of plywood prepared using adhesives from Example 1, Comparative Examples 1, 2, and 3 of this invention are presented. The results show that the dry bonding strengths of the adhesives prepared without carbon nanorods and with different carbon nanorod concentrations (1 wt%, 2 wt%, and 4 wt%) were 1.21 MPa, 1.63 MPa, 1.99 MPa, and 1.57 MPa, respectively; and the wet bonding strengths were 0.53 MPa, 0.70 MPa, 0.79 MPa, and 0.60 MPa, respectively. This is because an appropriate amount of carbon nanorods can form hydrogen bonds, electrostatic interactions, and physical nanoconfining effects with soybean protein molecules, increasing the crosslinking density and interfacial bonding ability of the adhesive, thereby significantly enhancing its water resistance and mechanical properties. Especially when the carbon nanorod concentration is 2 wt%, the carbon nanorods are uniformly dispersed in the matrix, effectively filling the pores between protein molecules and strengthening the network structure, allowing the adhesive to achieve optimal performance. When the concentration of carbon nanorods is further increased to 4 wt%, the excess carbon nanorods are prone to agglomeration, which reduces their ability to effectively participate in interfacial interactions, resulting in a decrease in the integrity of the network structure. Therefore, the bonding strength is actually reduced.

[0064] Figure 2The wet bond strength of plywood prepared with the adhesives obtained in Example 1 and Comparative Examples 4 and 5 was measured. The results showed that as the carbonization time of the walnut green husk carbon nanorods at 160 °C increased from 6 h to 8 h, the wet bond strength significantly increased from 0.56 MPa to 0.79 MPa. However, when the carbonization time was further extended to 10 h, the wet bond strength decreased to 0.68 MPa. The reason is that the carbon nanorods obtained by shorter carbonization time (6 h) are not sufficiently graphitized, have a loose structure, and although there are many surface groups, their stability is relatively weak, resulting in limited interfacial interaction with soybean protein. When carbonized for 8 h, the carbon core structure and surface functional groups of the carbon nanorods reach a better balance, which not only has good dispersibility, but also can form a stable and dense non-covalent network with the protein through hydrogen bonding, electrostatic adsorption, and nano-confinement effect, thus the enhancement effect is the most significant. However, when the carbonization time is extended to 10 h, the carbon nanorods are over-carbonized, the surface polar groups decrease, the hydrophilicity and dispersibility decrease, the interfacial interaction with protein molecules weakens, resulting in a decrease in the integrity of the gel layer structure, thus causing a decline in mechanical properties.

[0065] Figure 3 The wet bond strength of plywood prepared with the adhesives obtained in Example 1 and Comparative Examples 6-10 was determined. Figure 3 As can be seen, the material properties show a continuous improvement trend as the amount of carbon nanorods added gradually increases from 1 g (SM-carbon nanorod 1) to 5 g (SM-carbon nanorod 5, Example 1), with SM-carbon nanorod 5 reaching the highest value (0.79 MPa). This indicates that an appropriate amount of carbon nanorods can form sufficient interfacial interactions with the matrix, significantly strengthening the network structure of the system. When the amount added is further increased to 6 g (SM-carbon nanorod 6), the performance decreases slightly (0.75 MPa), mainly because excessive carbon nanorods tend to aggregate in the system, thereby reducing their effective dispersion and interaction sites, disrupting the construction efficiency of the continuous network, and making it difficult to further improve the reinforcing effect. The above results show that carbon nanorods have a clear optimal addition range in the system: insufficient amount results in limited reinforcing effect, while excessive amount leads to decreased structural strengthening efficiency due to impaired dispersibility. Therefore, only within a suitable range can the best reinforcing effect be achieved.

[0066] Figure 4 In Figure a, the FT-IR spectra of the adhesives obtained in Example 1 and Comparative Example 1 are shown. It can be seen that after the addition of carbon nanorods, the adhesive in Example 1 exhibits better performance at 3300 cm⁻¹. -1 The nearby –NH2 / –OH stretching vibration peak is 3342 cm⁻¹, compared to Comparative Example 1. -1 Redshifted to 3298cm -1 This indicates that the hydroxyl and carboxyl groups on the surface of the carbon nanorods formed stronger hydrogen bonds with soybean protein molecules, leading to enhanced hydrogen bond energy and a shift of the absorption peak to lower wavenumbers. Simultaneously, at 1655 cm⁻¹... -1(Amide I band, C=O stretching vibration) shifted to 1661 cm -1 The accompanying increase in peak intensity indicates that the introduction of carbon nanorods alters the microenvironment surrounding protein molecules, enhancing interactions between protein segments and resulting in a more compact structure. Furthermore, the shifts and changes in these characteristic peaks collectively suggest the formation of a stable non-covalent interaction network between the carbon nanorods and the protein, which is beneficial for improving the mechanical properties and water resistance of the adhesive.

[0067] Figure 4 Figure b shows the XPS spectra of the adhesives obtained in Example 1 and Comparative Example 1. Compared with Comparative Example 1, the binding energies of C=O and C–O / C–N in Example 1 show a slight shift (e.g., from 288.0 eV to 287.99 eV), indicating that the oxygen-containing functional groups on the surface of carbon nanorods interact with the amino groups in soybean protein molecules, thereby changing the electronic cloud environment of the relevant functional groups, suggesting that non-covalent interactions such as hydrogen bonds may form in the system.

[0068] Figure 4 Figure c shows the DSC curves of the adhesives obtained in Example 1 and Comparative Example 1. The modified adhesive did not show any new strong exothermic peaks, only a change in the position of the characteristic thermal transition peak, indicating that no significant chemical cross-linking reaction occurred during the modification process. Compared with the comparative example, its glass transition temperature increased from approximately 150 °C to 160 °C, indicating that the introduction of carbon nanorods significantly restricted the movement of soybean protein molecular chains. This is mainly attributed to the multi-point hydrogen bond interactions formed between the hydrophilic functional groups on the surface of the carbon nanorods and the protein molecules, which enhanced the intermolecular interaction strength, enabling the system to exhibit higher thermal stability while maintaining its non-covalent network characteristics.

[0069] Depend on Figure 4 As can be seen from the data in Figure 1, the T2 distribution peak of Example 1 shifts towards a shorter relaxation time compared to Comparative Example 1, and the signal intensity in the long T2 region is significantly weakened, indicating that the free water content in the system is reduced and the movement of water molecules is more restricted. Figure 4 Further, it is shown that the average T2 value of Example 1 is significantly reduced, while the crosslinking density-related parameter τc is significantly increased, indicating that the internal network structure of the adhesive is more compact and the molecular chain motion is suppressed.

[0070] also, Figure 4 Figure f shows the TGA spectra of the adhesives obtained in Example 1 and Comparative Example 1. It can be seen that after adding carbon nanorods, the pyrolysis residue rate of Example 1 is significantly improved compared to Comparative Example 1. This is because carbon nanorods have a high degree of carbonization and thermal stability, and can form a more stable carbonaceous structure during pyrolysis, slowing down the decomposition of soybean protein molecules, thereby improving the thermal stability of the adhesive.

[0071] Figure 5The images show scanning electron microscope (SEM) images of the cross-sectional structures of the adhesives in Example 1 and Comparative Example 1. As can be seen from the images, the cross-sectional structure of the adhesive in Comparative Example 1 is relatively loose, with obvious pores; while the cross-sectional structure of the adhesive in Example 1 is more dense and continuous, with a significantly reduced number of pores. These results indicate that the introduction of carbon nanorods helps improve the internal structure of the adhesive, enhancing interfacial bonding through multi-point non-covalent interactions between the nanorods and soybean protein molecules, thereby constructing a denser and more stable adhesive layer structure.

[0072] Figure 6 This is a TEM image of the formation process of carbon nanorods obtained from walnut green husks through hydrothermal treatment in step S1 of Example 1 (i.e., the formation process of carbon nanorods is shown from left to right, from carbon nanoparticles to a network and then curled and sewn into nanorods). Under hydrothermal conditions, walnut green husks first carbonize to form carbon nanoparticles, and then further form rod-shaped nanostructures, i.e., carbon nanorods, through self-assembly and orientation growth. The specific mechanism of carbon nanorod formation is as follows: Under hydrothermal conditions, the organic components in walnut green husks first carbonize and generate small carbon nanoparticles. As the reaction proceeds, due to the presence of functional groups such as hydroxyl and carboxyl groups on the surface, the carbon nanoparticles undergo phase separation and gradually aggregate through hydrogen bonding, electrostatic interactions, and van der Waals forces to form a two-dimensional carbon nanonetwork structure. In the hydrothermal environment of the closed reactor, due to the temperature gradient and solution convection inside the system, the reaction medium is in a continuous turbulent state. This dynamic environment provides an external driving force for the further growth and structural rearrangement of the carbon nanonetwork. Under the combined influence of external forces and non-covalent interactions, carbon nanonetworks undergo local curling, folding, and gradual orientation growth along specific directions. Ultimately, under the "stitching" effect of weak interactions such as hydrogen bonds, stable one-dimensional rod-shaped carbon nanostructures, namely carbon nanorods, are formed.

[0073] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a soybean protein adhesive modified with walnut green husk carbon nanorods, characterized in that, Includes the following steps: (1) Carbon nanorod solution was prepared by hydrothermal treatment using walnut green skin as carbon source and water as solvent; (2) The carbon nanorod solution was fully dispersed with water at room temperature, and then soybean protein powder was added and stirred evenly to obtain the walnut green skin carbon nanorod modified soybean protein adhesive.

2. The preparation method of the walnut green husk carbon nanorod modified soybean protein adhesive according to claim 1, characterized in that, In step (1), the mass concentration of the green walnut skin in water is 1-4 wt%.

3. The preparation method of the walnut green husk carbon nanorod modified soybean protein adhesive according to claim 1, characterized in that, In step (1), the hydrothermal treatment temperature is 160℃ and the time is 6-10 h.

4. The preparation method of the walnut green husk carbon nanorod modified soybean protein adhesive according to claim 3, characterized in that, The hydrothermal treatment time is 8 hours.

5. The preparation method according to claim 1, characterized in that, The carbon nanorods in the solution are one-dimensional rod-shaped nanostructures with a length of 50-2000 nm and a diameter of 5-200 nm.

6. The preparation method of the walnut green husk carbon nanorod modified soybean protein adhesive according to claim 1, characterized in that, In step (2), the mass ratio of the carbon nanorod solution, water and soybean protein powder is (1-6):(9.5-14.5):

3. The three are mixed evenly and stirred at room temperature for 10 minutes to obtain an adhesive.

7. A walnut green husk carbon nanorod modified soybean protein adhesive, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. The walnut husk carbon nanorod modified soybean protein adhesive according to claim 7, characterized in that, The carbon nanorods form a cross-linked network structure with soybean protein molecules through non-covalent interactions.

9. A water-resistant plywood, characterized in that, The preparation steps are as follows: The walnut green husk carbon nanorod modified soybean protein adhesive described in claim 7 or 8 is coated on the surface of a single board, and the single boards are stacked according to the principle of interlayer texture cross-lamination, and then hot-pressed and cured to prepare the product.

10. A water-resistant plywood according to claim 9, characterized in that, The hot-press curing conditions are as follows: hot-press curing at 120℃ and 1.2 MPa for 6 min.

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