Spray-assisted self-gluing plywood and preparation method thereof

Abstract

The present invention relates to the technical field of preparation of artificial boards, and specifically to a spray-assisted self-gluing plywood and a preparation method thereof. The preparation method of the spray-assisted self-gluing plywood provided by the present invention self-assembles positively charged chitosan and negatively charged soy protein isolate on the surface of a single board by spraying, adopts layer-by-layer assembly technology, utilizes the electrostatic interaction of positive and negative charges and the self-adhesive properties, and the plywood can be prepared only by a hot pressing process. The entire process is simple to operate and the conditions are mild. All of the materials are natural biomass materials with a wide range of sources. No additional processing aids are introduced, and the materials are green, environmentally friendly, renewable and low in cost. At the same time, the use of aldehyde substances is not involved. In particular, the plywood obtained by the spray-assisted technology of the present invention has high bonding strength and can effectively meet the application requirements of high-performance plywood.

Description

Technical Field

[0001] The invention relates to the technical field of artificial board preparation, and in particular to a spray-assisted self-gluing plywood and a preparation method thereof. Background Art

[0002] Plywood is one of the commonly used materials in construction and furniture making, and is one of the three major types of man-made boards. The textures of adjacent veneers of plywood are crisscrossed, and the veneers are assembled and glued together in a perpendicular direction to the wood grains of adjacent layers. In the production and application of plywood, a large amount of adhesive is inevitably used.

[0003] At present, my country's plywood manufacturing is still mainly based on formaldehyde adhesives such as urea-formaldehyde resin (UF), phenol-formaldehyde resin (PF), and melamine formaldehyde resin (MF). However, formaldehyde adhesives release harmful volatile organic compounds during use and production, which can easily induce a variety of diseases and seriously endanger human life and health. In addition, the raw materials of formaldehyde adhesives are mostly derived from petroleum-based fossil resources and are non-renewable. Therefore, the use of biomass-based adhesives and glue-free bonding technology has attracted much attention and has broad prospects in the field of plywood preparation.

[0004] The traditional glue-free gluing technology uses the material's own components and activates the surface of wood fibers through certain processing to make it self-adhesive. These activations mainly include oxidation, nitration, hydrolysis, polycondensation, dehydration, degradation and free radical initiation of lignin and carbohydrates. Under hot pressing conditions, the cellulose, lignin, hemicellulose and other materials in the raw materials react to form adhesive-like substances, so that the raw materials self-glue to form glue-free boards. The above-mentioned glue-free gluing process often involves many additives and reactions, and there are problems such as complex preparation process, expensive equipment or additives, and it is mostly used in fiberboards and is not suitable for fast-growing wood (such as eucalyptus, poplar, pine, etc.).

[0005] Therefore, a method for preparing glue-free plywood is provided, the raw materials of which are more environmentally friendly, the preparation method is simple, the equipment requirements are low, the cost is low, and it is suitable for fast-growing wood, and has greater application value in industrial production. Summary of the invention

[0006] Based on the above problems, one of the purposes of the present invention is to provide a method for preparing a spray-assisted self-adhesive plywood, which adopts a layer-by-layer assembly technology, utilizes the electrostatic interaction of positive and negative charges and the self-adhesive characteristics, and can produce plywood only through a hot pressing process. The entire process is simple to operate and the conditions are mild. It is all biomass materials with a wide range of sources, does not require the introduction of additional processing aids, is green and environmentally friendly, renewable and low in cost, and does not involve the use of aldehyde substances. In particular, the plywood obtained by the spray-assisted method of the present invention has high bonding strength and can effectively meet the application requirements of high-performance plywood.

[0007] A second object of the present invention is to provide a spray-assisted self-gluing plywood having excellent gluing strength.

[0008] The technical purpose of the present invention is achieved by adopting the following technical solutions:

[0009] A method for preparing a spray-assisted self-gluing plywood comprises the following steps:

[0010] (1) taking a wood veneer to be glued, spraying a chitosan aqueous solution on the surface of the wood veneer, and then drying to obtain a chitosan-modified veneer;

[0011] (2) spraying the soy protein isolate aqueous solution on the surface of the chitosan modified veneer obtained in step (1), and then drying to obtain a chitosan-soy protein isolate modified veneer;

[0012] (3) taking the spraying and drying steps in step (1) and step (2) as one operation cycle, taking the chitosan-soy protein isolate modified veneer obtained in step (2), and repeating the operation cycle 3 to 5 times; after spraying the soy protein isolate aqueous solution in the last operation cycle, selecting a portion of the veneer without drying treatment, and then drying the other portion of the veneer and additionally spraying the chitosan aqueous solution;

[0013] (4) taking the veneer obtained after the soy protein isolate aqueous solution is finally sprayed in step (3) and the veneer obtained after the chitosan aqueous solution is finally sprayed, assembling them in a vertical grain manner, keeping the aqueous solutions sprayed last time between adjacent veneers different, and then hot pressing them to obtain a spray-assisted self-bonding plywood.

[0014] Further preferably, in step (1), the wood veneer is selected from one or more of fast-growing poplar, fast-growing eucalyptus, and fast-growing pine; and the wood veneer is pre-cleaned and dried before spraying. Furthermore, the cleaning is performed with water.

[0015] Further preferably, in step (1), the concentration of the chitosan aqueous solution is 3-10 g / L and the pH is 3-4.

[0016] More preferably, the chitosan used in the chitosan aqueous solution has a deacetylation degree of ≥95% and a viscosity of 100-200 mPa·s.

[0017] Further preferably, in step (1), the amount of chitosan aqueous solution sprayed per square centimeter of wood veneer is 0.05-0.2 mL, and the spraying distance is 12-20 cm. More preferably, the amount of chitosan aqueous solution sprayed per square centimeter of wood veneer is 0.1 mL, and the spraying distance is 15 cm.

[0018] Further preferably, in step (2), the concentration of the soy protein isolate aqueous solution is 3 to 10 g / L.

[0019] Further preferably, in step (2), the amount of the soy protein isolate aqueous solution sprayed per square centimeter of the chitosan modified single board is 0.05-0.2 mL, and the spraying distance is 12-20 cm. More preferably, the amount of the soy protein isolate aqueous solution sprayed per square centimeter of the chitosan modified single board is 0.1 mL, and the spraying distance is 15 cm.

[0020] More preferably, in steps (1) to (3), the drying temperature is 50 to 80°C.

[0021] Further preferably, in step (4), the temperature of hot pressing molding is 100-120° C., the hot pressing pressure is 1.1-1.3 MPa, and the hot pressing time is 30-50 min.

[0022] The spray-assisted self-gluing plywood is prepared by the above preparation method.

[0023] The beneficial effects of the above technical solution of the present invention are:

[0024] The method for preparing the spray-assisted self-bonding plywood provided by the present invention utilizes the layer-by-layer self-assembly technology and uses the electrostatic force as the driving force to self-assemble the positively charged chitosan and the negatively charged soy protein isolate on the surface of the veneer by spraying, and adsorbs the anionic and cationic biomass on the surface of the veneer by the attraction between the positive and negative charges, and repeats the spraying several times. When assembling, the charges of the adjacent veneers are opposite, and the electrostatic interaction and self-bonding characteristics of the positive and negative charges are utilized, and the plywood can be prepared only by the hot pressing process.

[0025] The above-mentioned preparation concept of the present invention, through spray-assisted layer-by-layer self-assembly technology, utilizes electrostatic interaction and self-adhesive properties, and can achieve successful preparation of plywood without additional gluing. Therefore, the present invention realizes glue-free gluing between veneers, not only does not require adhesives, but also simplifies the production process, and can be used for connecting different types of fast-growing wood materials.

[0026] Moreover, when preparing plywood, the chitosan and soy protein isolate used in the present invention are all natural and degradable biomass materials, which are widely available, low in cost, and do not contain harmful gases such as formaldehyde. Moreover, the preparation process and principle of the present invention are simple, and the solvents used are all water solvents, which are green and recyclable. At the same time, the spray-assisted method of the present invention is efficient and simple, has low equipment requirements, is feasible, and is suitable for industrial production. In particular, the spray-assisted self-gluing plywood prepared by the above method of the present invention has excellent gluing performance and can effectively meet the application requirements of high-performance plywood.

[0027] Therefore, the present invention can provide a safe, simple and environmentally friendly preparation method for the production of plywood, which can not only solve the problem that traditional formaldehyde adhesives can harm human health, but also improve the defects of the traditional glue-free gluing technology with complicated operation process, while improving the gluing performance of plywood, and has great application potential and development prospects. DETAILED DESCRIPTION

[0028] The technical scheme and technical effects of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, it should be understood by those skilled in the art that the embodiments are only used to illustrate the technical scheme of the present invention and should not be regarded as limiting the scope of protection of the present invention. Based on the following embodiments, all other implementation schemes obtained by ordinary technicians in the field without making creative work, such as modification, deformation or simple replacement, should belong to the scope of protection of the present invention.

[0029] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the raw materials used are all commonly used in the art, available to the public or commercially available, unless otherwise specified.

[0030] In the following examples and comparative examples, the chitosan used in the chitosan aqueous solution has a deacetylation degree of ≥95% and a viscosity of 100-200 mPa·s. The preparation method of the positively charged chitosan aqueous solution is as follows: 5 g of chitosan is dissolved in 1 L of deionized water, the pH is adjusted to 3-4 with acetic acid solution, and then magnetically stirred until the solution is clear and transparent to obtain a positively charged chitosan aqueous solution with a concentration of 5 g / L.

[0031] In the following examples and comparative examples, the soy protein isolate used in the soy protein isolate aqueous solution is from Shanghai MacLean Biochemical Technology Co., Ltd., Cas No.: 9010-10-0. The preparation method of the negatively charged soy protein isolate aqueous solution is as follows: 5 g of soy protein isolate is dissolved in 1 L of deionized water, and magnetic stirring is performed until the soy protein isolate is uniformly dispersed to obtain a 5 g / L negatively charged soy protein isolate aqueous solution.

[0032] In the following comparative examples, tea polyphenols (purity 99%) were purchased from Shanghai MacLean Biochemical Technology Co., Ltd. Banana peel powder was purchased from Shaanxi Hengling Natural Biological Products Co., Ltd.

[0033] In the following embodiments 1 to 3 of the present invention, the preparation method of plywood is mainly described by taking 3-layer plywood as an example. In other embodiments, those skilled in the art can prepare plywood with other numbers of layers to meet the use requirements, such as 4 to 10 layers, etc., and they only need to ensure that the last spraying solution between adjacent veneers is different during assembly.

[0034] Example 1

[0035] The spray-assisted self-bonding plywood provided in this embodiment is prepared by a method comprising the following steps:

[0036] (1) Material preparation: Three pieces of eucalyptus veneers with a size of 300 mm × 300 mm × 2 mm were washed and dried at a drying temperature of 60° C. to obtain pretreated eucalyptus veneers;

[0037] (2) Spraying a chitosan aqueous solution (concentration 5 g / L) on both sides of the pretreated eucalyptus veneer and drying it at 60° C. to obtain a chitosan-modified veneer; the amount of chitosan aqueous solution sprayed was 0.1 mL per square centimeter of wood veneer, and the spraying distance was 15 cm;

[0038] (3) spraying a soy protein isolate aqueous solution (concentration 5 g / L) on both sides of the chitosan modified veneer and then drying the veneer at a drying temperature of 60° C. to obtain a chitosan-soy protein isolate modified veneer; the spraying amount of the soy protein isolate aqueous solution per square centimeter of the chitosan modified veneer was 0.1 mL, and the spraying distance was 15 cm;

[0039] (4) taking the spraying and drying treatment in step (2) and step (3) as one operation cycle, repeating the operation cycle, processing 5 cycles in total, after the last spraying of the soy protein isolate aqueous solution, selecting two single boards without drying, and spraying the chitosan aqueous solution once more on both sides of the remaining single board, and not performing the drying treatment;

[0040] (5) Eucalyptus plywood was prepared by pressing according to the standard of GB / T 9846.7-2015 "Ordinary Plywood", and three layers of plywood were assembled in a vertical grain manner, with one veneer sprayed with chitosan aqueous solution as the core board of the middle layer, and two veneers sprayed with soy protein isolate aqueous solution as the outer layer boards, ensuring that the last spraying solution of adjacent veneers was different during assembly. After assembly, hot pressing was performed, and the process parameters of hot pressing were: hot pressing temperature of 100° C., pressure of 1.3 MPa, and hot pressing time of 30 min. After hot pressing, the spray-assisted self-bonding plywood of Example 1 was obtained.

[0041] Example 2

[0042] The spray-assisted self-bonding plywood provided in this embodiment is prepared by a method comprising the following steps:

[0043] (1) Material preparation: Three pieces of eucalyptus veneers with a size of 300 mm × 300 mm × 2 mm were washed and dried at a drying temperature of 60° C. to obtain pretreated eucalyptus veneers;

[0044] (2) Spraying a chitosan aqueous solution (concentration 5 g / L) on both sides of the pretreated eucalyptus veneer and drying it at 60° C. to obtain a chitosan-modified veneer; the amount of chitosan aqueous solution sprayed was 0.1 mL per square centimeter of wood veneer, and the spraying distance was 15 cm;

[0045] (3) spraying a soy protein isolate aqueous solution (concentration 5 g / L) on both sides of the chitosan modified veneer and then drying the veneer at a drying temperature of 60° C. to obtain a chitosan-soy protein isolate modified veneer; the spraying amount of the soy protein isolate aqueous solution per square centimeter of the chitosan modified veneer was 0.1 mL, and the spraying distance was 15 cm;

[0046] (4) taking the spraying and drying treatment in step (2) and step (3) as one operation cycle, repeating the operation cycle, processing 5 cycles in total, after the last spraying of the soy protein isolate aqueous solution, selecting two single boards without drying, and spraying the chitosan aqueous solution once more on both sides of the remaining single board, and not performing the drying treatment;

[0047] (5) Eucalyptus plywood was prepared by pressing according to the standard of GB / T 9846.7-2015 "Ordinary Plywood", and three layers of plywood were assembled in a vertical grain manner, with one veneer sprayed with chitosan aqueous solution as the core board of the middle layer, and two veneers sprayed with soy protein isolate aqueous solution as the outer layer boards, ensuring that the last spraying solution of adjacent veneers was different during assembly. After assembly, hot pressing was performed, and the process parameters of hot pressing were: hot pressing temperature of 110°C, pressure of 1.3MPa, and hot pressing time of 30min. After hot pressing, the spray-assisted self-bonding plywood of Example 2 was obtained.

[0048] Example 3

[0049] The spray-assisted self-bonding plywood provided in this embodiment is prepared by a method comprising the following steps:

[0050] (1) Material preparation: Three pieces of eucalyptus veneers with a size of 300 mm × 300 mm × 2 mm were washed and dried at a drying temperature of 60° C. to obtain pretreated eucalyptus veneers;

[0051] (2) Spraying a chitosan aqueous solution (concentration 5 g / L) on both sides of the pretreated eucalyptus veneer and drying it at 60° C. to obtain a chitosan-modified veneer; the amount of chitosan aqueous solution sprayed was 0.1 mL per square centimeter of wood veneer, and the spraying distance was 15 cm;

[0052] (3) spraying a soy protein isolate aqueous solution (concentration 5 g / L) on both sides of the chitosan modified veneer and then drying the veneer at a drying temperature of 60° C. to obtain a chitosan-soy protein isolate modified veneer; the spraying amount of the soy protein isolate aqueous solution per square centimeter of the chitosan modified veneer was 0.1 mL, and the spraying distance was 15 cm;

[0053] (4) taking the spraying and drying treatment in step (2) and step (3) as one operation cycle, repeating the operation cycle, processing 5 cycles in total, after the last spraying of the soy protein isolate aqueous solution, selecting two single boards without drying, and spraying the chitosan aqueous solution once more on both sides of the remaining single board, and not performing the drying treatment;

[0054] (5) Eucalyptus plywood was prepared by pressing according to the standard of GB / T 9846.7-2015 "Ordinary Plywood", and three layers of plywood were assembled in a vertical grain manner, with one veneer sprayed with chitosan aqueous solution as the core board of the middle layer, and two veneers sprayed with soy protein isolate aqueous solution as the outer layer boards, ensuring that the last spraying solution of adjacent veneers was different during assembly. After assembly, hot pressing was performed, and the process parameters of hot pressing were: hot pressing temperature of 120°C, pressure of 1.3MPa, and hot pressing time of 30min. After hot pressing, the spray-assisted self-bonding plywood of Example 3 was obtained.

[0055] Comparative Example 1

[0056] This comparative example provides a plywood, which is prepared by a method comprising the following steps:

[0057] (1) Material preparation: Three pieces of eucalyptus veneers with a size of 300 mm × 300 mm × 2 mm were washed and dried at a drying temperature of 60° C. to obtain pretreated eucalyptus veneers;

[0058] (2) Spraying a chitosan aqueous solution (concentration 5 g / L) on both sides of the pretreated eucalyptus veneer and drying it at 60° C. to obtain a chitosan-modified veneer; the amount of chitosan aqueous solution sprayed was 0.1 mL per square centimeter of wood veneer, and the spraying distance was 15 cm;

[0059] (3) The spraying and drying process in step (2) is regarded as one operation cycle, and the operation cycle is repeated for a total of 5 cycles, and no drying is required after the last spraying;

[0060] (4) Eucalyptus plywood was prepared by pressing according to the standard of GB / T 9846.7-2015 "Ordinary Plywood". Three layers of plywood were assembled in a vertical grain manner. After assembly, hot pressing was performed. The process parameters of hot pressing were: hot pressing temperature of 110° C., pressure of 1.3 MPa, and hot pressing time of 30 min. After hot pressing, the plywood of this comparative example was obtained.

[0061] Comparative Example 2

[0062] This comparative example provides a plywood, which is prepared by a method comprising the following steps:

[0063] (1) Material preparation: Three pieces of eucalyptus veneers with a size of 300 mm × 300 mm × 2 mm were washed and dried at a drying temperature of 60° C. to obtain pretreated eucalyptus veneers;

[0064] (2) spraying a soy protein isolate aqueous solution (concentration 5 g / L) on both sides of the pretreated eucalyptus veneer and drying it at 60° C. to obtain a soy protein isolate modified veneer; the spraying amount of the soy protein isolate aqueous solution per square centimeter of the wood veneer was 0.1 mL, and the spraying distance was 15 cm;

[0065] (3) The spraying and drying process in step (2) is regarded as one operation cycle, and the operation cycle is repeated for a total of 5 cycles, and no drying is required after the last spraying;

[0066] (4) Eucalyptus plywood was prepared by pressing according to the standard of GB / T 9846.7-2015 "Ordinary Plywood". Three layers of plywood were assembled in a vertical grain manner. After assembly, hot pressing was performed. The process parameters of hot pressing were: hot pressing temperature of 110° C., pressure of 1.3 MPa, and hot pressing time of 30 min. After hot pressing, the plywood of this comparative example was obtained.

[0067] Comparative Example 3

[0068] The comparative example provides a plywood, and the preparation method thereof is carried out with reference to Example 2, except that a tea polyphenol aqueous solution (concentration 5 g / L) is used instead of a soy protein isolate aqueous solution (concentration 5 g / L), and the rest is the same as Example 2 to prepare the plywood of the comparative example. The preparation method of the tea polyphenol aqueous solution is as follows: 5 g of tea polyphenol is dissolved in 1 L of deionized water, and magnetically stirred until the solution is clear, to obtain a 5 g / L tea polyphenol aqueous solution, and the prepared tea polyphenol aqueous solution is negatively charged.

[0069] Comparative Example 4

[0070] The comparative example provides a plywood, and the preparation method thereof is carried out with reference to Example 2, except that: banana peel powder aqueous solution (concentration 5 g / L) is used instead of soy protein isolate aqueous solution (concentration 5 g / L), and the rest is the same as Example 2 to prepare the plywood of the comparative example. The preparation method of the banana peel powder aqueous solution is: 5 g of banana peel powder is dissolved in 1 L of deionized water, and magnetic stirring is performed until the solution is clear to obtain a 5 g / L banana peel powder aqueous solution, and the prepared banana peel powder aqueous solution is negatively charged.

[0071] Test Example 1

[0072] According to the Class II plywood bonding strength test method specified in 4.17 of GB / T 17657-2022 "Test methods for physical and chemical properties of wood-based panels and veneer wood-based panels", the bonding strength test was performed on the plywood prepared in Examples 1 to 3 and Comparative Examples 1 to 4. The results are shown in Table 1.

[0073] Table 1 Gluing strength of eucalyptus plywood prepared in the examples and comparative examples

[0074]

[0075] As shown in Table 1, the bonding strength of the plywood product prepared by the preparation method of the present invention is 0.98-2.83MPa. The hot pressing temperature will have a certain impact on the bonding strength, but within a reasonable hot pressing temperature (100-120°C), the obtained plywood meets the relevant standards of national Class II plywood (≥0.7MPa). In addition, after the test of spraying chitosan and soy protein isolate separately in Comparative Examples 1 and 2, the present invention found that the use of chitosan and soy protein isolate alone cannot achieve the effect and standard of preparing plywood. Comparative Examples 3 and 4 use different anionic biomass materials (tea polyphenols, banana peel powder) and chitosan to self-assemble on the surface of the veneer. The test found that they all have no self-bonding effect. After hot pressing, the veneer is not sticky and cannot be hot pressed into plywood.

[0076] In the present invention, chitosan solution is positively charged under pH=3-4, and soy protein isolate is negatively charged under neutral conditions, and there is electrostatic attraction between the positive and negative charges. In addition, soy protein isolate will expose more active sites under hot pressing conditions, including hydroxyl (-OH), amino (-NH 3 ), etc., while chitosan contains abundant hydroxyl (-OH) and amino (-NH 3 ), these functional groups will form a cross-linked network structure between the soy protein isolate molecules and the chitosan molecules through non-covalent interactions, such as the formation of hydrogen bonds, hydrophobic interactions, etc., thereby enhancing the bonding force between the single boards. After the soy protein isolate is sprayed and hot-pressed, the single boards already have a certain viscosity. The present invention uses chitosan to perform self-assembly spraying with it, and the cross-linked network structure formed is more stable, and its viscosity is also greatly improved.

[0077] In summary, the spray-assisted self-gluing plywood prepared by the present invention has excellent bonding strength, and the whole process does not involve the use of any aldehyde compounds or adhesives. The raw materials used are all biomass materials, which are green and recyclable. At the same time, the spray-assisted method is simpler and faster, and has the possibility of industrial production. It provides a safe, simple and environmentally friendly preparation method for the production of plywood, which not only solves the problem that traditional formaldehyde adhesives can harm human health, but also improves the defects of the complicated operation process of traditional glue-free gluing technology, and at the same time improves the gluing performance of plywood.

[0078] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a spray-assisted self-gluing plywood, characterized in that: The following steps are involved: (1) taking a wood veneer to be glued, spraying a chitosan aqueous solution on the surface of the wood veneer, and then drying to obtain a chitosan-modified veneer; (2) spraying the soy protein isolate aqueous solution on the surface of the chitosan modified veneer obtained in step (1), and then drying to obtain a chitosan-soy protein isolate modified veneer; (3) taking the spraying and drying steps in step (1) and step (2) as one operation cycle, taking the chitosan-soy protein isolate modified veneer obtained in step (2), and repeating the operation cycle 3 to 5 times; after spraying the soy protein isolate aqueous solution in the last operation cycle, selecting a portion of the veneer without drying treatment, and then drying the other portion of the veneer and additionally spraying the chitosan aqueous solution; (4) The veneer obtained after the soy protein isolate aqueous solution is finally sprayed in step (3) and the veneer obtained after the chitosan aqueous solution is finally sprayed are assembled in a vertical grain manner, the aqueous solutions sprayed for the last time between adjacent veneers are kept different, and then hot-pressed to obtain a spray-assisted self-bonding plywood.

2. The method for preparing the spray-assisted self-gluing plywood according to claim 1, characterized in that: In step (1), the wood veneer is selected from one or more of fast-growing poplar, fast-growing eucalyptus, and fast-growing pine; and the wood veneer is pre-cleaned and dried before spraying.

3. The method for preparing the spray-assisted self-gluing plywood according to claim 1, characterized in that: In step (1), the concentration of the chitosan aqueous solution is 3-10 g / L, and the pH is 3-4.

4. The method for preparing the spray-assisted self-gluing plywood according to claim 3, characterized in that: The chitosan used in the chitosan aqueous solution has a deacetylation degree of ≥95% and a viscosity of 100-200 mPa·s.

5. The method for preparing the spray-assisted self-gluing plywood according to claim 1, characterized in that: In step (1), the spraying amount of chitosan aqueous solution is 0.05-0.2 mL per square centimeter of wood veneer, and the spraying distance is 12-20 cm.

6. The method for preparing the spray-assisted self-bonding plywood according to any one of claims 1 to 5, characterized in that: In step (2), the concentration of the soy protein isolate aqueous solution is 3-10 g / L.

7. The method for preparing the spray-assisted self-bonding plywood according to any one of claims 1 to 5, characterized in that: In step (2), the spraying amount of the soy protein isolate aqueous solution is 0.05-0.2 mL per square centimeter of the chitosan modified veneer, and the spraying distance is 12-20 cm.

8. The method for preparing the spray-assisted self-bonding plywood according to any one of claims 1 to 5, characterized in that: In steps (1) to (3), the drying temperature is 50 to 80°C.

9. The method for preparing a spray-assisted self-bonding plywood according to any one of claims 1 to 5, characterized in that: In step (4), the temperature of hot pressing is 100-120°C, the hot pressing pressure is 1.1-1.3 MPa, and the hot pressing time is 30-50 min.

10. The spray-assisted self-bonding plywood prepared according to the preparation method according to any one of claims 1 to 9.

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