Preparation method and application of modified soybean protein adhesive

Abstract

The invention provides a preparation method and application of a modified soybean protein adhesive. According to the method, cross-linking modification of sodium dodecyl sulfate (SDS) and polyethylene glycol diacrylate (PEGDA) and doping modification of TEMPO oxidized nanocellulose (TOCNF) and zinc borate (ZB) have a synergistic effect, so that the mechanical strength and water resistance of the adhesive are effectively improved. The modified soybean protein adhesive is used for preparing the salix psammophila reconstituted wood, the wettability and coating property of the adhesive to salix psammophila fiber and the compactness and uniformity of the internal structure of the material are remarkably improved, the layering phenomenon is avoided, the limit oxygen index of the prepared salix psammophila reconstituted wood reaches 32.7%, the static bending intensity reaches 75.21 MPa, the elastic modulus reaches 15.76 GPa, the internal bonding strength reaches 1.05 MPa, the 24-hour water absorption thickness swelling rate is 9.67%, and the prepared salix psammophila reconstituted wood has the good water absorption performance. The flame retardance, the strength and the water resistance are good.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wood adhesives, and particularly relates to a preparation method and application of a modified soybean protein adhesive. BACKGROUND

[0002] The global wood processing industry has long used formaldehyde-based adhesives to produce sand willow reconstituted wood and other materials due to their excellent performance and low cost. The current mainstream adhesives include urea-formaldehyde resin glue (UF) and phenol-formaldehyde resin glue (PF). The raw materials of urea-formaldehyde resin glue are easy to obtain, the manufacturing process is simple, and the price is relatively low. However, free formaldehyde is released during synthesis and use, the environmental protection performance is poor, and the glue is prone to swelling due to moisture absorption, which causes the deformation or cracking of the board. The molecular structure of phenol-formaldehyde resin glue is stable, and a three-dimensional network structure is formed after curing, which gives the sand willow reconstituted wood excellent water resistance, corrosion resistance and weather resistance, and strong bonding strength. However, high temperature and high pressure (such as 160℃ hot pressing temperature) are required for complete curing, which increases the production energy consumption and equipment requirements, and the price is about 2.5-3 times that of urea-formaldehyde resin glue. Free formaldehyde is also released. With the improvement of environmental protection awareness, the problems of dependence on non-renewable resources and release of formaldehyde harmful to health have become prominent. The contradiction between the "green" properties of sand willow reconstituted wood and the release of formaldehyde needs to be solved urgently. Isocyanate resin glue is made of diphenylmethane diisocyanate (MDI) and other polyphenyl polymethylene cyanates. The molecular structure does not contain formaldehyde groups, and a stable high molecular structure is formed after curing, almost without the release of volatile substances. It is recognized as a non-formaldehyde adhesive, but its activity is high, it is easy to stick to the board, the production process is strict, the production threshold is high, and the price is expensive, about 2.5-3 times that of phenol-formaldehyde resin glue.

[0003] In recent years, with the tightening of environmental protection policies and the increasing demand of consumers for healthy building materials, sand willow reconstituted wood adhesives are developing towards low formaldehyde, high performance and low cost. Researchers have found that bio-based adhesives (such as natural soybean protein glue) are ideal materials to replace formaldehyde-based adhesives, but they face three major problems when applied to the industrialization of reconstituted wood: affecting production efficiency and product mechanical properties, high modification cost, flammable and traditional flame retardants violate the environmental protection concept. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a preparation method and application of a modified soybean protein adhesive to solve the above problems of the prior art. The present application optimizes the performance of soybean protein adhesive by using a synergistic modification strategy, and improves the flame retardancy by adding a green flame retardant, thereby providing a low-cost, high-strength and flame-retardant bio-based adhesive for sand willow reconstituted wood and promoting its industrialization application.

[0005] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a preparation method of a modified soybean protein adhesive, comprising the following steps: Sodium dodecyl sulfate powder is added to deionized water, after being dissolved sufficiently, defatted soybean powder is added, and the mixture is uniformly mixed to obtain a mixed solution; the pH value of the mixed solution is adjusted to 8-10, ethylene glycol and TEMPO oxidized nanocellulose are added, and constant temperature reaction is carried out at 85-95 DEG C for 20-50 min; then polyethylene glycol diacrylate and ammonium persulfate are added in sequence, and the reaction is continuously carried out for 20-40 min; then zinc borate is added, and the reaction is terminated after continuously stirring for 10-30 min, to obtain a modified soybean protein adhesive.

[0006] Preferably, the mass-volume ratio of the sodium dodecyl sulfate powder to deionized water is 1g: (70-90mL).

[0007] Preferably, the mass ratio of the sodium dodecyl sulfate powder to defatted soybean powder is 1: (10-20).

[0008] Preferably, the method for adjusting the pH value of the mixed solution is sodium hydroxide solution adjustment, and the concentration of the sodium hydroxide solution is 1mol / L.

[0009] Preferably, the mass ratio of the defatted soybean powder, ethylene glycol and TEMPO oxidized nanocellulose is (90-100):(40-50):1.

[0010] Preferably, the mass ratio of the defatted soybean powder, polyethylene glycol diacrylate and ammonium persulfate is (190-200):(90-100):1.

[0011] Preferably, the mass ratio of the defatted soybean powder to zinc borate is (3-5):1.

[0012] The application further provides a modified soybean protein adhesive prepared by the above method.

[0013] The application further provides an application of the modified soybean protein adhesive, which is used for preparing sand willow recombination wood.

[0014] Compared with the prior art, the application has the following remarkable technical effects: 1. The application provides a preparation method of a modified soybean protein adhesive, sodium dodecyl sulfate (SDS) and polyethylene glycol diacrylate (PEGDA) are cross-linked and modified to form a cross-linked network structure, and TEMPO oxidized nanocellulose (TOCNF) and zinc borate (ZB) are doped and modified to make nanofibers uniformly embedded in the matrix to form a dense three-dimensional network, and zinc borate particles are dispersed in the cross-linked network to form small-scale agglomerations due to the hydrophobic characteristics and intermolecular forces, and the two synergistically act to effectively improve the mechanical strength and water resistance of the adhesive. In addition, zinc borate is a green and environmentally-friendly non-halogen flame retardant, which has the characteristics of non-toxicity, low water solubility, high thermal stability, small particle size, small specific gravity and good dispersibility, and helps to improve the flame retardant performance.

[0015] 2、The modified soybean protein adhesive of the present application is used for preparing the sand willow recombination wood, which significantly improves the wettability and coating property of the sand willow fiber, the compactness and uniformity of the internal structure of the material, and there is no delamination phenomenon, the interface between the glue layer and the sand willow bundle is continuous, which verifies the optimization effect of the cross-linked network on the internal stress transmission.

[0016] 3、The sand willow recombination wood prepared by using the modified soybean protein adhesive of the present application has an ultimate oxygen index of 32.7%, a static bending strength of 75.21 MPa, an elastic modulus of 15.76 GPa, an internal bonding strength of 1.05 MPa, and a 24 h water absorption thickness expansion rate of 9.67%, and has good flame retardancy, strength and water resistance.

[0017] The present application will be further described in detail below in combination with the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the FTIR spectrum of the preliminary cross-linked modified soybean protein adhesive (SPIA-CL) of the present application comparative example 1, wherein a: SPIA, b: SDS-SPIA, c: SDS-PEGDA-SPIA, d: SDS-PEGDA-APS-SPIA; Figure 2 is the SEM graph of the modified soybean protein adhesive (SPIA-CL-TOCNF-ZB) prepared in the present application example 1 after curing; Figure 3 is the SEM graph of the preliminary cross-linked modified soybean protein adhesive (SPIA-CL) prepared in the present application comparative example 1 after curing; Figure 4 is the SEM graph of the unmodified soybean protein adhesive (SPIA) prepared in the present application comparative example 2 after curing; Figure 5 is the physical picture of the sand willow recombination wood pressed by the modified soybean protein adhesive (SPIA-CL-TOCNF-ZB) of the present application example 1, a: top view, b: side view; Figure 6 is the appearance after burning of the sand willow recombination wood pressed by the modified soybean protein adhesive (SPIA-CL-TOCNF-ZB) of the present application example 1 in the cone calorimeter test. DETAILED DESCRIPTION

[0019] The specifications of the raw materials used in the present application are as follows: The defatted soybean powder is purchased from Beijing Hongrun Baoshun Technology Co., Ltd., and the purity is industrial pure.

[0020] Sodium dodecyl sulfate is purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., and the purity is analytical pure.

[0021] Polyethylene glycol diacrylate was purchased from Shanghai Melin Biochemical Technology Co., Ltd., with a specification of M.W. 400.

[0022] Ammonium persulfate was purchased from Shanghai Melin Biochemical Technology Co., Ltd., with a purity of analytical pure.

[0023] Zinc borate was purchased from Shandong Wuyi Flame Retardant Technology Co., Ltd., with a purity of industrial pure.

[0024] TEMPO-oxidized nanocellulose was self-made in the laboratory, with a diameter distribution within 9-10 nm. The preparation method was as follows: (1) 20 g of treated sand willow wood powder was accurately weighed and slowly added into 650 mL of deionized water. The mixture was heated to 75°C in a water bath, and 7.5 g of sodium chlorite and 5 mL of glacial acetic acid were added at this temperature in four times, with an interval of 1 h each time and sufficient stirring. After the addition was completed, the heating was stopped, and the mixture was left overnight. The reaction product was washed with deionized water repeatedly until it was neutral. After drying, cellulose (CF) was obtained; (2) The water bath temperature was adjusted to 30°C. 3.71 g of sodium carbonate was dissolved in 500 mL of deionized water, and then 1.26 g of sodium bicarbonate was added. The mixture was continuously stirred for 10 min, and then 1 g of sodium bromide and 0.1 g of 2,2,6,6-tetramethylpiperidine oxide (TEMPO) were added. After the mixture was stirred and dissolved, 5 g of the above CF was added and dispersed. Under stirring, 50 mL of sodium hypochlorite solution was added dropwise. After the dropwise addition was completed, the mixture was reacted at 30°C for 4 h. After the reaction was completed, 10 mL of anhydrous ethanol was added, and the heating and stirring were stopped. The mixture was left overnight. The product was washed with deionized water until it was neutral. After drying, oxidized cellulose (TOCF) was obtained; (3) 0.5 g of TOCF was slowly added into an appropriate amount of deionized water, and the mixture was cooled by ice bath. The mixture was treated by an ultrasonic cell crusher at a power of 480 W for 1 h to make it fully dispersed. Finally, oxidized nanocellulose suspension (TOCNF) was obtained. Then, the TOCNF was processed into oxidized nanocellulose powder by a spray dryer.

[0025] Example 1 The present example is a preparation method of a modified soy protein adhesive, which specifically includes the following steps: Take 1 g of sodium dodecyl sulfate (SDS) powder into 80 mL of deionized water, and after it is fully dissolved, add 15 g of defatted soybean powder (SPI) to it, mix well, and obtain a mixed solution. Then, adjust the pH value of the mixed solution to 9 with a 1 mol / L NaOH solution, add 7 g of ethylene glycol (EG) and 0.15 g of TEMPO oxidized nanocellulose (TOCNF), and place it in a 90°C constant temperature water bath for 30 min. After the reaction is completed, add 7.5 g of polyethylene glycol diacrylate (PEGDA) and 0.075 g of ammonium persulfate (APS) in sequence, continue to react for 30 min, and then add 3.5 g of zinc borate (ZB), continue to mechanically stir for 20 min, and terminate the reaction to obtain a modified soy protein adhesive (SPIA-CL-TOCNF-ZB).

[0026] Example 2 The present example is a preparation method of a modified soy protein adhesive, which specifically comprises the following steps: Take 1 g of sodium dodecyl sulfate (SDS) powder into 70 mL of deionized water, and after it is fully dissolved, add 10 g of defatted soybean powder (SPI) to it, mix well, and obtain a mixed solution. Then, adjust the pH value of the mixed solution to 8 with a 1 mol / L NaOH solution, add 4 g of ethylene glycol (EG) and 0.1 g of TEMPO oxidized nanocellulose (TOCNF), and place it in a 85°C constant temperature water bath for 50 min. After the reaction is completed, add 5 g of polyethylene glycol diacrylate (PEGDA) and 0.05 g of ammonium persulfate (APS) in sequence, continue to react for 40 min, and then add 3 g of zinc borate (ZB), continue to mechanically stir for 10 min, and terminate the reaction to obtain a modified soy protein adhesive (SPIA-CL-TOCNF-ZB).

[0027] Example 3 The present example is a preparation method of a modified soy protein adhesive, which specifically comprises the following steps: Take 1 g of sodium dodecyl sulfate (SDS) powder into 90 mL of deionized water, after it is fully dissolved, 20 g of defatted soybean powder (SPI) is added, mixed thoroughly, to obtain a mixed solution. Then, the pH value of the mixed solution is adjusted to 10 with 1 mol / L NaOH solution, 10 g of ethylene glycol (EG) and 0.2 g of TEMPO oxidized nanocellulose (TOCNF) are added, and placed in a 95°C constant temperature water bath for 20 min. After the reaction is completed, 10 g of polyethylene glycol diacrylate (PEGDA) and 0.1 g of ammonium persulfate (APS) are added in turn, and the reaction is continued for 20 min, and then 4 g of zinc borate (ZB) is added, and the reaction is terminated after mechanical stirring for 30 min, to obtain a modified soy protein adhesive (SPIA-CL-TOCNF-ZB).

[0028] Comparative Example 1 The preparation of the preliminary cross-linked modified soy protein adhesive specifically includes the following steps: Take 1 g of sodium dodecyl sulfate (SDS) powder into 80 mL of deionized water, after it is fully dissolved, 15 g of defatted soybean powder (SPI) is added, mixed thoroughly, to obtain a mixed solution. Then, the pH value of the mixed solution is adjusted to 9 with 1 mol / L NaOH solution, and then placed in a 90°C constant temperature water bath for 30 min. After the reaction is completed, 7.5 g of polyethylene glycol diacrylate (PEGDA) and 0.075 g of ammonium persulfate (APS) are added in turn, and the reaction is continued for 30 min, and then the reaction is terminated, to obtain a preliminary cross-linked modified soy protein adhesive (SPIA-CL).

[0029] Figure 1 is the FTIR spectrum of the preliminary cross-linked modified soy protein adhesive (SPIA-CL), wherein a: SPIA, b: SDS-SPIA, c: SDS-PEGDA-SPIA, d: SDS-PEGDA-APS-SPIA. As can be seen from the figure, 1655.8 cm -1 is the C=O stretching vibration (amide band I), 1539.4 cm -1 is the coupling peak of N-H bending vibration and C-N stretching vibration (amide band II) and sulfonamide bond spectrum peak, 3343.9 cm -1 contains -OH, -NH and sulfonamide bond spectrum peak, 1391.1 cm -1 is the sulfonamide bond, COO⁻ characteristic peak, 1070.5 cm -1 and 690.5 cm -1 are used to characterize the amide bond spectrum peak before and after SPI modification; 2900 cm -1 is the CH2 group absorption peak, 1655.8 cm-1 , 1539.4 cm -1 , 690.5 cm -1 Nearby is also the benzene ring and its C-H face in bending vibration characteristic spectrum peak area. Analysis Figure 1 b-d can be seen, SDS modification, 3343.9 cm -1 , 2900 cm -1 and 1391.1 cm -1 Peak left shift and intensity enhancement, indicating the formation of SDS-SPI complex, 1655.8 cm -1 Wave peak position unchanged, slightly increased intensity, to support the benzene ring into the SPI molecular structure; after adding PEGDA modification, 853 cm -1 , 1636.4 cm -1 and 1726.4 cm -1 Nearby PEGDA characteristic new peak, indicating its successful participation in the modification; after APS initiation reaction, 1726.4 cm -1 Peak intensity significantly enhanced, 1636.4 cm -1 Peak shape broadened left shift, 1070.5 cm -1 Peak intensity increased, 3343.9 cm -1 Peak width decreased and intensity decreased, confirming that PEGDA and SPI occur free radical polymerization to form a crosslinked network, which improves the mechanical strength and water resistance of the adhesive.

[0030] Comparative Example 2 Preparation of soy protein adhesive without modification, including the following steps: Take 15 g of defatted soybean powder (SPI) and add 80 mL of deionized water. Mechanically stir to fully dissolve, then place the mixture in a 90°C constant temperature water bath for 30 min. After the reaction is complete, the soy protein adhesive (SPIA) is obtained.

[0031] Figure 2 is the SEM image of the modified soy protein adhesive (SPIA-CL-TOCNF-ZB) prepared in Example 1 after curing.

[0032] Figure 3 is the SEM image of the preliminary cross-linked modified soy protein adhesive (SPIA-CL) prepared in Comparative Example 1 after curing.

[0033] Figure 4 is the SEM image of the unmodified soy protein adhesive (SPIA) prepared in Comparative Example 2 after curing.

[0034] As can be seen, the unmodified soybean protein adhesive (SPIA) has obvious grooves and a rough surface on its fracture surface. This is because the protein molecules are wrapped in a spherical structure and lack effective intermolecular connections, resulting in a loose surface structure of the adhesive. The soybean protein adhesive (SPIA-CL) after preliminary cross-linking modification has a smoother fracture surface, mainly because PEGDA reacts with the protein to form a tighter cross-linked network structure. The fully modified soybean protein adhesive (SPIA-CL-TOCNF-ZB) has a smoother fracture surface, with nanofibers uniformly embedded in the matrix to form a dense three-dimensional network. Zinc borate particles are partially dispersed in the cross-linked network, and small-scale agglomeration occurs in local areas due to hydrophobic properties and intermolecular forces.

[0035] The modified soybean protein adhesive (SPIA-CL-TOCNF-ZB) obtained in Example 1, the pre-crosslinked modified soybean protein adhesive (SPIA-CL) obtained in Comparative Example 1, and the unmodified soybean protein adhesive (SPIA) in Comparative Example 2 were used to prepare reconstituted *Salix psammophila* wood, respectively, according to the following methods: The modified soybean protein adhesive (SPIA-CL-TOCNF-ZB) obtained in Example 1, the pre-crosslinked modified soybean protein adhesive (SPIA-CL) obtained in Comparative Example 1, and the unmodified soybean protein adhesive (SPIA) in Comparative Example 2 were coated onto willow wood bundles and pressed into boards. In the hot pressing stage, the boards were continuously treated at 130°C and 10 MPa for 30 min. Then, they were transferred to the cold pressing process and shaped by maintaining a pressure of 7 MPa for 10 min. After demolding, the formed boards were processed into samples of specified specifications using a band saw according to the testing standards.

[0036] Figure 5 These are images of reconstituted *Salix psammophila* wood pressed using the modified soybean protein adhesive (SPIA-CL-TOCNF-ZB) of Example 1. a and b are the top and side views, respectively. (Top view observation...) Figure 5 a) shows that the sample surface is smooth and flat, the wood bundles are tightly packed and without pores or fiber warping, indicating that the modified adhesive significantly improves its wettability and coating properties to the willow fiber; side view ( Figure 5 (b) Further revealing the compactness and uniformity of the material's internal structure, with no delamination between layers (red dashed box), and continuous bonding between the adhesive layer and the wood bundle interface, directly confirming the optimizing effect of the cross-linking network on internal stress transfer. The reconstituted willow wood board pressed with the pre-cross-linked modified soybean protein adhesive (SPIA-CL) of Comparative Example 1 showed no significant difference from Example 1; while the reconstituted willow wood board pressed with the unmodified soybean protein adhesive (SPIA) of Comparative Example 2 exhibited more severe delamination between layers.

[0037] The performance of the prepared sand willow reconstituted wood was tested. Among them, the mechanical properties such as static bending strength, elastic modulus and internal bonding strength were tested according to GB / T 17657-2022; the flame retardant performance was tested according to standard GB / T 2406.2-2009: <21% is flammable material, between 21%~26% is combustible material, between 27%~32% is self-extinguishing / difficultly flammable material, >32% is difficultly flammable material; the water resistance was tested according to standard GB / T 17657-2022: 24h water absorption thickness expansion rate ≤8% is class I water resistance level, which can be applied to outdoor and high humidity environment; ≤12% is class II water resistance level, which can be applied to indoor humid environment; ≤15% is class III water resistance level, which can be used in indoor dry environment. The results are shown in Table 1: Table 1 Performance test results of sand willow reconstituted wood The results show that compared with Comparative Example 1 and Comparative Example 2, the static bending strength, elastic modulus and internal bonding strength of the sand willow reconstituted wood prepared by the modified soybean protein adhesive (SPIA-CL-TOCNF-ZB) prepared by the application examples 1~3 are significantly improved, indicating that it has better mechanical properties; the 24h water absorption thickness expansion rate is significantly reduced, indicating that it has better water resistance; the limiting oxygen index can reach more than 32, reaching the difficultly flammable level.

[0038] The sand willow reconstituted wood was subjected to cone calorimeter test, and the results are shown in Table 2, wherein: TTI represents ignition time, pk-HRR represents peak heat release rate, average HRR represents average heat release rate, THR represents total heat release amount, and TSP represents total smoke production amount.

[0039] Table 2 Cone calorimeter test parameters of sand willow reconstituted wood Figure 6 is the morphology of the sand willow reconstituted wood after the cone calorimeter test combustion of the sand willow reconstituted wood compressed by the modified soybean protein adhesive (SPIA-CL-TOCNF-ZB) of Example 1. After the sample burns, there is no continuous expansion of carbon layer, mainly in the form of loose ash, which directly reflects the high efficiency of the flame retardant system: on the one hand, zinc borate (ZB) releases crystal water during pyrolysis, effectively cools down and dilutes oxygen and combustible gas, rapidly inhibits flaming combustion; on the other hand, its decomposition products catalyze the oxidation of carbon layer, converting into gas and ash, further consuming heat; both of them shorten the combustion process and prevent stable carbonization.

[0040] The application provides a preparation method of a modified soybean protein adhesive, sodium dodecyl sulfate (SDS) and polyethylene glycol diacrylate (PEGDA) are cross-linked and modified, and TEMPO-oxidized nanocellulose (TOCNF) and zinc borate (ZB) are doped and modified, so that the mechanical strength and water resistance of the adhesive are effectively improved; meanwhile, the zinc borate is a green and environment-friendly non-halogen flame retardant, and the flame retardant performance is effectively improved. The modified soybean protein adhesive is used for preparing a sand willow reconstituted wood, the wettability and coating property of the sand willow fiber are significantly improved, the compactness and uniformity of the internal structure of the material are improved, there is no layering phenomenon, the adhesive layer and the sand willow bundle interface are continuously combined, and the prepared sand willow reconstituted wood has good flame retardant property, strength and water resistance.

[0041] The above description is only a preferred embodiment of the application, and does not limit the application. Any simple modification, change and equivalent change of the above embodiment according to the technical essence of the application are still within the protection scope of the technical scheme of the application.

Claims

1. A method for preparing a modified soybean protein adhesive, characterized in that, Includes the following steps: Sodium dodecyl sulfate powder was added to deionized water and dissolved completely. Then, defatted soybean flour was added and mixed evenly to obtain a mixture. The pH of the mixture was adjusted to 8-10, and ethylene glycol and TEMPO oxidized nanocellulose were added. The mixture was reacted at a constant temperature of 85-95°C for 20-50 minutes. Then, polyethylene glycol diacrylate and ammonium persulfate were added in sequence, and the reaction was continued for 20-40 minutes. Zinc borate was then added, and the reaction was terminated after stirring for 10-30 minutes to obtain a modified soybean protein adhesive.

2. The method according to claim 1, characterized in that, The mass-to-volume ratio of sodium dodecyl sulfate powder to deionized water is 1 g: (70~90 mL).

3. The method according to claim 1, characterized in that, The mass ratio of sodium dodecyl sulfate powder to defatted soybean flour is 1:(10~20).

4. The method according to claim 1, characterized in that, The pH of the mixture is adjusted by adding sodium hydroxide solution, wherein the concentration of the sodium hydroxide solution is 1 mol / L.

5. The method according to claim 1, characterized in that, The mass ratio of defatted soybean flour, ethylene glycol, and TEMPO oxidized nanocellulose is (90~100):(40~50):

1.

6. The method according to claim 1, characterized in that, The mass ratio of defatted soybean flour, polyethylene glycol diacrylate, and ammonium persulfate is (190~200):(90~100):

1.

7. The method according to claim 1, characterized in that, The mass ratio of defatted soybean flour to zinc borate is (3~5):

1.

8. A modified soybean protein adhesive prepared by the method of any one of claims 1 to 7.

9. An application of the modified soybean protein adhesive according to claim 8, characterized in that, The modified soybean protein adhesive is used in the preparation of reconstituted sand willow wood.

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