Preparation method and application of caffeic acid chitosan bionic adhesive

Abstract

The invention discloses a preparation method and application of a caffeic acid chitosan bionic adhesive, and belongs to the field of wood adhesives. The invention aims to solve the problems of high viscosity, poor water resistance, low bonding strength, and complex method, high cost, low efficiency and no environmental protection in the modification process of the existing traditional bio-based adhesive. The method comprises the following steps: 1, preparing a chitosan acid solution; 2, adding caffeic acid; and 3, standing. According to the application, the caffeic acid chitosan bionic adhesive is used for preparing a wood composite material. The invention is used for preparation and application of the caffeic acid chitosan bionic adhesive.

Description

Technical Field

[0001] The invention belongs to the field of wood adhesives. Background Art

[0002] Wood has attracted more and more attention due to its unique advantages of being renewable, fixing carbon, storing carbon, being lightweight and having high strength. The utilization of wood is inseparable from the use of adhesives. However, most traditional wood adhesives rely on formaldehyde-based adhesives, such as urea-formaldehyde resin (UF), phenol-formaldehyde resin (PF) and melamine formaldehyde (MF) adhesives. The raw materials of such adhesives are derived from non-renewable petroleum resources, and during use, they are prone to release harmful volatile substances such as toxic formaldehyde, which may cause health problems such as respiratory irritation, allergic reactions and even cancer. At the same time, with the urgent demand for a healthy living environment and increasingly stringent environmental regulations, the traditional wood industry based on formaldehyde-based adhesive technology is facing the risk of industry shrinkage. Therefore, it is urgent to develop high-performance formaldehyde-free adhesives to help the transformation and upgrading of the wood industry.

[0003] In order to solve the above problems, many researchers are committed to developing sustainable formaldehyde-free bio-based adhesives, such as cellulose-based adhesives, lignin-based adhesives, starch-based adhesives, and soy protein adhesives. These adhesives are based on renewable raw materials, are non-toxic and biodegradable, and are in line with environmental protection concepts. Chitosan, as a natural polymer compound, is rich in active groups such as amino and hydroxyl groups in its molecular structure, and can interact with hydroxyl and carboxyl groups on the surface of the adherend to form hydrogen bonds and other chemical bonds, so it exhibits good adhesion to a variety of materials. At the same time, its non-toxic and environmentally friendly characteristics make it have great application potential in the field of formaldehyde-free adhesives. However, due to its high molecular weight and strong hydrogen bonding, chitosan will face problems such as extremely high viscosity and difficulty in control, poor water resistance, etc. when directly used to bond wood, so it is difficult to replace formaldehyde-based adhesives. Although traditional chemical modification methods can solve these problems to a certain extent, they are often accompanied by the disadvantages of increased costs and reduced efficiency, and may even introduce toxic substances, leading to new environmental pollution. For example, adding glutaraldehyde as a crosslinking agent to chitosan bio-based adhesives can improve adhesive performance to a certain extent, but it has high biological toxicity. During the use of adhesives, unreacted glutaraldehyde may be released into the environment, which may irritate human skin, eyes and respiratory tract, cause allergic reactions, and long-term exposure may even have potential carcinogenic risks.

[0004] Currently, chitosan-based adhesives are used to bond wood, and their viscosity increases exponentially with the increase in the solid content of chitosan. Generally, in chitosan-based adhesives, when the mass fraction of chitosan reaches six or seven percent or more, sizing cannot be carried out due to excessive viscosity. The increase in chitosan content can significantly increase the bonding strength and the performance of wood-based panels. Therefore, for adhesives with a large mass fraction of chitosan, reducing the system viscosity to make it easy to apply sizing is an important challenge in the current use of chitosan-based adhesives. Summary of the Invention

[0005] The present invention aims to solve the problems of existing traditional bio-based adhesives, such as high viscosity, poor water resistance, low bonding strength, and complex methods, high cost, low efficiency, and environmental unfriendliness during the modification process. Furthermore, a preparation method and application of a caffeic acid-chitosan bionic adhesive are provided.

[0006] A preparation method of a caffeic acid-chitosan bionic adhesive is carried out according to the following steps:

[0007] I. Preparation of chitosan acid solution:

[0008] Dissolve chitosan in an acid solution to obtain a chitosan acid solution;

[0009] The mass percentage of chitosan in the chitosan acid solution is 1% - 15%;

[0010] II. Addition of caffeic acid:

[0011] Add caffeic acid to the chitosan acid solution and stir, then adjust the pH value to 1.0 - 6.5 using a pH regulator to obtain a homogenized glue solution;

[0012] The mass ratio of chitosan to caffeic acid in the chitosan acid solution is (1 - 20):1;

[0013] III. Standing:

[0014] Let the homogenized glue solution stand for defoaming to obtain a caffeic acid-chitosan bionic adhesive.

[0015] An application of a caffeic acid-chitosan bionic adhesive, where the caffeic acid-chitosan bionic adhesive is used for the preparation of wood-based composites.

[0016] The beneficial effects of the present invention are as follows:

[0017] (1) This adhesive is based on a caffeic acid-chitosan composite adhesive system, completely abandoning traditional aldehyde-based resins, achieving zero formaldehyde release, and its raw materials are derived from renewable biomass resources.

[0018] (2) This adhesive is prepared by a simple one-pot method with acid catalysis, without the participation of organic solvents or post-treatment purification steps, significantly reducing energy consumption and waste emissions.

[0019] (3) The adhesive constructs a hydrophobic barrier with a hierarchical network structure through the cross-linking and curing mechanism of caffeic acid quinone oxidation and chitosan, greatly improving the water resistance, adhesive strength, and structural stability of plywood, meeting the requirements of Class I plywood in GB / T 9846-2015.

[0020] (4) In the adhesive, caffeic acid and chitosan form a small molecule - polymer solution system, and the non-covalent bond force between them produces a plasticizing effect, significantly reducing the viscosity of the system; the viscosity is regulated by adjusting the mass ratio of chitosan to caffeic acid and the solid content, achieving adaptability to various processing methods such as spraying and roll coating.

[0021] (5) The adhesive is used for plywood, and excellent artificial boards can be prepared under different temperature conditions from normal temperature cold pressing to high temperature hot pressing, saving energy and reducing consumption. Description of the Drawings

[0022] Figure 1 It is the preparation flow chart of the caffeic acid chitosan bionic adhesive of the present invention;

[0023] Figure 2 It is the viscosity comparison chart of the chitosan acid solution prepared in Comparative Example 3 and the caffeic acid chitosan bionic adhesive prepared in Example 8. Detailed Embodiments

[0024] Detailed Embodiment 1, in combination with Figure 1 Specifically described as follows: A preparation method of a caffeic acid chitosan bionic adhesive in this embodiment is carried out according to the following steps:

[0025] I. Preparation of chitosan acid solution:

[0026] Dissolve chitosan in an acid solution to obtain a chitosan acid solution;

[0027] The mass percentage of chitosan in the chitosan acid solution is 1% - 15%;

[0028] II. Addition of caffeic acid:

[0029] Add caffeic acid to the chitosan acid solution and stir, then adjust the pH value to 1.0 - 6.5 using a pH regulator to obtain a homogenized adhesive solution;

[0030] The mass ratio of chitosan to caffeic acid in the chitosan acid solution is (1 - 20):1;

[0031] III. Standing:

[0032] Let the homogenized adhesive solution stand for defoaming to obtain a caffeic acid chitosan bionic adhesive.

[0033] In this specific embodiment, caffeic acid is introduced into the chitosan-based adhesive system, and a dynamic supramolecular network can be constructed through multiple intermolecular non-covalent interactions (including hydrogen bonding, electrostatic interaction, π-π stacking, and cation-π interaction). Among them, caffeic acid, as a functional small molecule additive, has specific interactions with the amino and hydroxyl groups on the chitosan chain, effectively reducing the viscosity of the system and improving the processing performance. Mechanism studies have shown that under acidic conditions, the catechol structure of caffeic acid can be partially oxidized to a quinone structure, and this redox activity enables it to form covalent couplings with functional groups such as phenolic hydroxyl and carboxyl groups on the wood surface, and at the same time, it undergoes chemical cross-linking with the active sites on the chitosan molecular chain.

[0034] Based on the current application status and technical bottlenecks of caffeic acid, caffeic acid is insoluble in water at room temperature. Traditional methods rely on coupling agents or catalysts to carry out dissolution reactions on caffeic acid to achieve molecular grafting. Although it can carry out biomimetic modification on its catechol structure, there are very few studies on its application in wood adhesives, and there are almost no relevant studies on improving the water resistance of wood adhesives using caffeic acid. In addition, the intrinsic solubility characteristics of caffeic acid (slightly soluble in cold water and conventional acid solutions) directly restrict its application efficiency in adhesive systems based on acidic solvents, often resulting in a decrease in the homogeneity of the system due to insufficient dissolution. This specific embodiment innovatively constructs a chitosan-caffeic acid co-solubilization system, breaking through the above-mentioned technical barriers through multiple molecular mechanisms. In an acidic medium, the amino group of chitosan is protonated to form a positively charged polycationic chain, which has strong ion-dipole interactions with polar groups such as the carboxylic acid group and catechol hydroxyl group in the caffeic acid molecule, forming a stable soluble complex. At the same time, a three-dimensional hydrogen bond system is constructed between the hydroxyl network of the chitosan backbone, the phenolic hydroxyl group of caffeic acid, and water molecules, significantly enhancing molecular dispersion. This dynamic action mechanism not only realizes an order-of-magnitude increase in the solubility of caffeic acid, but also produces a unique rheological effect through intermolecular synergy: the effective solubilization of caffeic acid can reduce the viscosity of the system, and this viscosity regulation effect directly optimizes the processing performance of the system, providing a new strategy for the development of functional adhesives with high solid content and easy processing.

[0035] It is worth noting that the three-dimensional interpenetrating network structure formed during the curing process of this embodiment exhibits a significant synergistic strengthening effect: the linear polysaccharide chain of chitosan provides a structural backbone, while the aromatic ring structure of caffeic acid effectively inhibits water penetration through hydrophobic interactions and intermolecular stacking. Therefore, modifying chitosan with caffeic acid can control the viscosity of the adhesive, improve the water resistance and bonding strength of the adhesive, and precisely adjust its properties.

[0036] The beneficial effects of this embodiment are:

[0037] (1) The adhesive based on the caffeic acid-chitosan composite adhesive system completely abandons traditional aldehyde-based resins, achieving zero formaldehyde release, and its raw materials are derived from renewable biomass resources.

[0038] (2) The adhesive is prepared by a simple one-pot method with acid catalysis, without the participation of organic solvents or post-treatment purification steps, significantly reducing energy consumption and three-waste emissions.

[0039] (3) Through the cross-linking and curing mechanism of caffeic acid quinone oxidation and chitosan, the adhesive constructs a hydrophobic barrier with a hierarchical network structure, greatly improving the water resistance, bonding strength, and structural stability of plywood, meeting the requirements of Class I plywood in GB / T9846-2015.

[0040] (4) In the adhesive, caffeic acid and chitosan form a small molecule-polymer solution system, and the non-covalent bond force between them produces a plasticizing effect, significantly reducing the viscosity of the system; the viscosity is regulated by adjusting the mass ratio of chitosan to caffeic acid and the solid content, achieving adaptability to various processing methods such as spraying and roll coating.

[0041] (5) The adhesive is used for plywood, and excellent artificial boards can be prepared under different temperature conditions from normal temperature cold pressing to high temperature hot pressing, saving energy and reducing consumption.

[0042] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the acid solution described in Step 1 is one or a combination of two of organic acids and inorganic acids. Others are the same as Specific Embodiment 1.

[0043] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that the mass percentage of the acid solution described in Step 1 is 1% - 30%. Others are the same as Specific Embodiment 1 or 2.

[0044] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 1 to 3 is that the organic acid is one or a combination of two of acetic acid and citric acid; the inorganic acid is one or a combination of two of hydrochloric acid and phosphoric acid. Others are the same as Specific Embodiment 3.

[0045] Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 1 to 4 is that the stirring described in Step 2 is specifically carried out under the conditions of room temperature to 80°C and a stirring speed of 200 rpm - 1000 rpm for 0.5 h - 3.0 h. Others are the same as Specific Embodiments 1 to 4.

[0046] Specific Embodiment 6: The difference between this embodiment and one of Specific Embodiments 1 to 5 is that the pH regulator described in Step 2 is a basic reagent. Others are the same as Specific Embodiments 1 to 5.

[0047] Embodiment 7: The difference between this embodiment and any one of Embodiments 1 to 6 is that the basic reagent is one or a combination of several of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate. Others are the same as those in Embodiments 1 to 6.

[0048] Embodiment 8: The difference between this embodiment and any one of Embodiments 1 to 7 is that the total time for stirring and pH adjustment in Step 2 does not exceed 6 h. Others are the same as those in Embodiments 1 to 7.

[0049] Embodiment 9: Application of a caffeic acid chitosan bionic adhesive. The caffeic acid chitosan bionic adhesive is used for the preparation of wood-based composites.

[0050] Embodiment 10: The difference between this embodiment and Embodiment 9 is that the caffeic acid chitosan bionic adhesive is used for the preparation of wood-based composites, and specifically, it is carried out according to the following steps: at a sizing amount of 100 g / m 2 ~600 g / m 2 , under the conditions of a curing pressure of 0.5 MPa to 2 MPa and a curing temperature of 25 °C to 230 °C, plywood, blockboard, and laminated wood are laminated and bonded to obtain wood-based composites. Others are the same as those in Embodiment 9.

[0051] The following examples are used to verify the beneficial effects of the present invention:

[0052] Example 1:

[0053] A preparation method of a caffeic acid chitosan bionic adhesive, which is carried out according to the following steps:

[0054] I. Preparation of a chitosan acid solution:

[0055] 3 g of chitosan is added to 96 g of an acid solution and dissolved to obtain a chitosan acid solution;

[0056] The acid solution is a hydrochloric acid solution with a mass percentage of 1%;

[0057] II. Addition of caffeic acid:

[0058] Under the conditions of room temperature and a stirring speed of 500 rpm, 1 g of caffeic acid is added to the chitosan acid solution and stirred for 2 h, and then the pH value is adjusted to 6 with a pH regulator to obtain a homogenized adhesive solution;

[0059] III. Standing:

[0060] The homogenized adhesive solution is allowed to stand for defoaming to obtain a caffeic acid chitosan bionic adhesive.

[0061] The pH regulator in Step II is NaOH or NaHCO3 。

[0062] In Step 2, the total time for stirring and pH adjustment does not exceed 6 h.

[0063] Example 2: The difference between this example and Example 1 is that in Step 2, a pH regulator is used to adjust the pH value to 5. Others are the same as in Example 1.

[0064] Example 3: The difference between this example and Example 1 is that in Step 2, a pH regulator is used to adjust the pH value to 4. Others are the same as in Example 1.

[0065] Example 4: The difference between this example and Example 1 is that in Step 1, 3 g of chitosan is added to 94 g of acid solution; in Step 2, 3 g of caffeic acid is added to the chitosan acid solution. Others are the same as in Example 1.

[0066] Example 5: The difference between this example and Example 1 is that in Step 1, 5 g of chitosan is added to 92 g of acid solution; the acid solution described in Step 1 is a hydrochloric acid solution with a mass percentage of 2%; in Step 2, 3 g of caffeic acid is added to the chitosan acid solution. Others are the same as in Example 1.

[0067] Example 6: The difference between this example and Example 1 is that in Step 1, 5 g of chitosan is added to 92 g of acid solution; the acid solution described in Step 1 is an acetic acid solution with a mass percentage of 2%; in Step 2, 3 g of caffeic acid is added to the chitosan acid solution. Others are the same as in Example 1.

[0068] Example 7: The difference between this example and Example 1 is that in Step 1, 5 g of chitosan is added to 92 g of acid solution; the acid solution described in Step 1 is a citric acid solution with a mass percentage of 20%; in Step 2, 3 g of caffeic acid is added to the chitosan acid solution. Others are the same as in Example 1.

[0069] Example 8: The difference between this example and Example 1 is that in Step 1, 7 g of chitosan is added to 90 g of acid solution; the acid solution described in Step 1 is a hydrochloric acid solution with a mass percentage of 3%; in Step 2, 3 g of caffeic acid is added to the chitosan acid solution. Others are the same as in Example 1.

[0070] Example 9: The difference between this example and Example 1 is that in Step 1, 12 g of chitosan is added to 85 g of acid solution; the acid solution described in Step 1 is a hydrochloric acid solution with a mass percentage of 3%; in Step 2, at a temperature of 50 °C and a stirring speed of 500 rpm, 3 g of caffeic acid is added to the chitosan acid solution and stirred for 30 min. Others are the same as in Example 1.

[0071] Example 10: The differences between this example and Example 1 are as follows: In step one, 12 g of chitosan is added to 85 g of acid solution; the acid solution in step one is a hydrochloric acid solution with a mass percentage of 3%; in step two, 3 g of caffeic acid is added to the chitosan acid solution; in step two, a pH regulator is used to adjust the pH value to 4. Others are the same as in Example 1.

[0072] Example 11: The differences between this example and Example 1 are as follows: In step one, 12 g of chitosan is added to 85 g of acid solution; the acid solution in step one is a hydrochloric acid solution with a mass percentage of 3%; in step two, 3 g of caffeic acid is added to the chitosan acid solution; in step two, a pH regulator is used to adjust the pH value to 2. Others are the same as in Example 1.

[0073] Example 12: Under the condition of a sizing amount of 300 g / m 2 The caffeic acid chitosan bionic adhesive prepared in Example 1 is coated on birch wood, and then hot-pressed for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-ply plywood.

[0074] Example 13: Under the condition of a sizing amount of 300 g / m 2 The caffeic acid chitosan bionic adhesive prepared in Example 2 is coated on birch wood, and then cold-pressed for 4 h under the conditions of a curing pressure of 1 MPa and room temperature to obtain a three-ply plywood.

[0075] Example 14: Under the condition of a sizing amount of 300 g / m 2 The caffeic acid chitosan bionic adhesive prepared in Example 3 is coated on birch wood, and then hot-pressed for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-ply plywood.

[0076] Example 15: Under the condition of a sizing amount of 300 g / m 2 The caffeic acid chitosan bionic adhesive prepared in Example 4 is coated on birch wood, and then hot-pressed for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-ply plywood.

[0077] Example 16: Under the condition of a sizing amount of 300 g / m 2 The caffeic acid chitosan bionic adhesive prepared in Example 5 is coated on birch wood, and then hot-pressed for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-ply plywood.

[0078] Example 17: Under the condition of a sizing amount of 300 g / m 2Under the condition of, coat the caffeic acid chitosan biomimetic adhesive prepared in Example 6 on birch wood, and then hot press for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-layer plywood.

[0079] Example 18: Under the condition of a sizing amount of 300 g / m 2 coat the caffeic acid chitosan biomimetic adhesive prepared in Example 7 on birch wood, and then hot press for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-layer plywood.

[0080] Example 19: Under the condition of a sizing amount of 300 g / m 2 coat the caffeic acid chitosan biomimetic adhesive prepared in Example 8 on birch wood, and then hot press for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-layer plywood.

[0081] Example 20: Under the condition of a sizing amount of 300 g / m 2 coat the caffeic acid chitosan biomimetic adhesive prepared in Example 8 on birch wood, and then cold press for 4 h under the conditions of a curing pressure of 1 MPa and room temperature to obtain a three-layer plywood.

[0082] Example 21: Under the condition of a sizing amount of 300 g / m 2 coat the caffeic acid chitosan biomimetic adhesive prepared in Example 9 on birch wood, and then hot press for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-layer plywood.

[0083] Example 22: Under the condition of a sizing amount of 300 g / m 2 coat the caffeic acid chitosan biomimetic adhesive prepared in Example 9 on birch wood, and then cold press for 4 h under the conditions of a curing pressure of 1 MPa and room temperature to obtain a three-layer plywood.

[0084] Example 23: Under the condition of a sizing amount of 300 g / m 2 coat the caffeic acid chitosan biomimetic adhesive prepared in Example 10 on birch wood, and then hot press for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-layer plywood.

[0085] Example 24: Under the condition of a sizing amount of 300 g / m 2 coat the caffeic acid chitosan biomimetic adhesive prepared in Example 11 on birch wood, and then hot press for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-layer plywood.

[0086] Comparative Example 1: 5 g of chitosan was added to 95 g of an acid solution and dissolved to obtain a chitosan acid solution; the acid solution was a hydrochloric acid solution with a mass percentage of 2%.

[0087] Comparative Example 2: 5 g of chitosan was added to 95 g of an acid solution and dissolved to obtain a chitosan acid solution; the acid solution was an acetic acid solution with a mass percentage of 2%.

[0088] Comparative Example 3: 7 g of chitosan was added to 93 g of an acid solution and dissolved to obtain a chitosan acid solution; the acid solution was a hydrochloric acid solution with a mass percentage of 2%.

[0089] Comparative Example 4: Under the condition of a sizing amount of 300 g / m 2 , the chitosan acid solution prepared in Comparative Example 1 was coated on birch, and then hot-pressed for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-layer plywood.

[0090] Comparative Example 5: Under the condition of a sizing amount of 300 g / m 2 , the chitosan acid solution prepared in Comparative Example 2 was coated on birch, and then hot-pressed for 3 min under the conditions of a curing pressure of 1 MPa and a curing temperature of 140 °C to obtain a three-layer plywood.

[0091] Comparative Example 6: Under the condition of a sizing amount of 300 g / m 2 , the caffeic acid chitosan bionic adhesive prepared in Comparative Example 1 was coated on birch, and then cold-pressed for 4 h under the conditions of a curing pressure of 1 MPa and room temperature to obtain a three-layer plywood.

[0092] Comparative Example 7: Under the condition of a sizing amount of 300 g / m 2 , the caffeic acid chitosan bionic adhesive prepared in Comparative Example 2 was coated on birch, and then cold-pressed for 4 h under the conditions of a curing pressure of 1 MPa and room temperature to obtain a three-layer plywood.

[0093] Regarding the description of the boiling water resistance strength test of plywood, according to the requirements of the boiling test in the national standard GB / T 17657-2022 "Test Methods for Physical and Chemical Properties of Wood-Based Panels and Decorative Wood-Based Panels": boiling water immersion - drying - boiling water immersion (boil - dry - boil): Immerse in boiling water for 4 h, take out and place in a forced-draft drying oven at (60 ± 3) °C for 16 h, then immerse in boiling water for another 4 h, and then cool in cold water below 30 °C. Finally, conduct physical and mechanical property tests on the boards, and take the average value of 6 samples measured in parallel each time. According to the requirement of the bonding strength of Class I birch plywood in the national standard GB / T 9846—2015 "General Plywood", its boiling water resistance strength should be greater than or equal to 1.00 MPa to be qualified.

[0094] Table 1: Mechanical properties of birch three-layer plywood in each example

[0095]

[0096]

[0097] Through the comparison of the bonding strength, the caffeic acid / chitosan bionic adhesive has good boiling water resistance, and the plywood made under the condition of cold pressing at room temperature also has good bonding strength.

[0098] Using a rotational viscometer, the viscosity of the prepared adhesive was tested, and the test results are shown in Table 2.

[0099] Table 2: Comparison of the viscosity and solid content of the adhesive

[0100]

[0101] Through the viscosity test, the caffeic acid / chitosan bionic adhesive shows a lower viscosity. The viscosity can be controlled by adjusting the dosage of caffeic acid to improve the processability, and the solid content can also be increased according to the process requirements. While the unmodified chitosan adhesive has a very high viscosity, poor processability, is difficult to apply glue, and has limited uses.

[0102] Figure 2 Viscosity comparison chart of the chitosan acid solution prepared for Comparative Example 3 and the caffeic acid chitosan bionic adhesive prepared in Example 8; Figure 2 The viscosity comparison of the unmodified chitosan adhesive and the caffeic acid / chitosan bionic adhesive modified by adding caffeic acid is shown. Among them, the unmodified chitosan adhesive was prepared by dissolving chitosan in a dilute hydrochloric acid solution, and the viscosity is 637000 mPa·s; the caffeic acid / chitosan bionic adhesive was prepared by adding caffeic acid to the chitosan solution, and the viscosity is 19900 mPa·s. It can be intuitively seen from the figure that the viscosity of the chitosan adhesive modified by adding caffeic acid is significantly lower than that before modification.

Claims

1. A method for preparing a caffeic acid chitosan biomimetic adhesive, characterized in that It is carried out in the following steps:

1. Prepare chitosan acid solution: dissolving chitosan in an acid solution to obtain a chitosan acid solution; The mass percentage of chitosan in the chitosan acid solution is 1% to 15%; 2. Addition of Caffeic Acid: Adding caffeic acid to the chitosan acid solution and stirring, and then adjusting the pH value to 1.0-6.5 with a pH adjuster to obtain a homogenized gel solution; The mass ratio of chitosan to caffeic acid in the chitosan acid solution is (1-20):1; 3.Stand still: The homogenized adhesive solution is allowed to stand for degassing to obtain the caffeic acid chitosan biomimetic adhesive.

2. The method for preparing a caffeic acid chitosan biomimetic adhesive according to claim 1, characterized in that The acid solution described in step 1 is one or a combination of organic acid and inorganic acid.

3. The method for preparing a caffeic acid chitosan biomimetic adhesive according to claim 2, characterized in that The mass percentage of the acid solution described in step 1 is 1% to 30%.

4. The method for preparing a caffeic acid chitosan biomimetic adhesive according to claim 3, characterized in that The organic acid is one of acetic acid and citric acid or a combination of both; the inorganic acid is one of hydrochloric acid and phosphoric acid or a combination of both.

5. The method for preparing a caffeic acid chitosan biomimetic adhesive according to claim 1, characterized in that The stirring in step 2 is specifically stirring at room temperature to 80° C. and a stirring speed of 200 rpm to 1000 rpm for 0.5 h to 3.0 h.

6. The method for preparing a caffeic acid chitosan biomimetic adhesive according to claim 1, characterized in that The pH adjusting agent described in step 2 is an alkaline agent.

7. The method for preparing a caffeic acid chitosan biomimetic adhesive according to claim 6, characterized in that The alkaline reagent is one of sodium hydroxide, potassium hydroxide, sodium carbonate and sodium bicarbonate or a combination of several of them.

8. The method for preparing a caffeic acid chitosan biomimetic adhesive according to claim 1, characterized in that The total time for stirring and pH adjustment in step 2 does not exceed 6 hours.

9. The use of a caffeic acid chitosan biomimetic adhesive prepared as claimed in claim 1, characterized in that Caffeic acid chitosan biomimetic adhesive is used in the preparation of wood composite materials.

10. The use of a caffeic acid chitosan biomimetic adhesive according to claim 9, characterized in that The caffeic acid chitosan bionic adhesive is used to prepare the wood composite material, which is specifically carried out in the following steps: applying the adhesive at a rate of 100 g / m 2 ~600g / m 2 Under the conditions of a curing pressure of 0.5MPa to 2MPa and a curing temperature of 25°C to 230°C, plywood, blockboard and integrated materials are laminated and bonded to obtain a wood composite material.

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