Lignin environmentally friendly adhesive, and preparation method and application thereof

Abstract

The present application provides a kind of lignin environmental protection adhesive and its preparation method and application.The method includes the following steps: quaternary ammonium salt surfactant is mixed with organic acid, stirring is uniformly under heating condition, and transparent pre-prepared liquid is obtained;Pre-prepared liquid is mixed with lignin powder, stirring is uniformly, and lignin environmental protection adhesive is obtained.The technical problem to be solved by the present application is how to prepare a kind of lignin environmental protection adhesive, so that the adhesive does not include formaldehyde, phenolic substances, is healthy and environmentally friendly, and at the same time, the wood bonded by it can be carried out at normal temperature and pressure, the operation is convenient, and the bonding strength is excellent, so as to be more suitable for the bonding demand in specific occasions.

Description

Technical Field

[0001] This invention relates to the field of lignin-based formaldehyde-free adhesive manufacturing technology, and in particular to a lignin-based environmentally friendly adhesive, its preparation method, and its application. Background Technology

[0002] Modern home furnishing materials are mostly composite engineered wood products, including plywood, particleboard, and fiberboard. Currently, 70% of formaldehyde globally is used in the production of urea, phenol, and melamine-formaldehyde resin adhesives. Phenolic resin adhesives used in engineered wood products have disadvantages such as high cost, brittleness, high curing temperature, and the release of free formaldehyde and phenol. Formaldehyde is a major chemical in wood products; due to its high volatility and toxicity to humans, it has caused significant environmental problems. As people's demands for home environments increase, they are forced to seek healthy and environmentally friendly adhesives. In recent years, researchers have focused on exploring the use of biomass raw materials (starch, protein, lignin, and tannin) to replace phenol and formaldehyde in the preparation of environmentally friendly green adhesives.

[0003] Lignin is the second largest natural polymer after cellulose, primarily derived from wastewater from industrial papermaking and pulping, and from pretreatment processes in biomass refining. my country's annual lignin production exceeds 10 million tons, with the vast majority recovered as a heat source through alkali recovery, resulting in a significant waste of this natural aromatic resource. Because lignin is a complex compound composed of aromatic ring structural units, its surface possesses various functional groups, such as hydroxyl, methoxy, carbonyl, and methyl groups, making it a potential candidate for bio-based materials. Currently, significant progress has been made in developing lignin-based phenolic environmentally friendly adhesives by partially replacing phenol. However, this method still uses phenol and formaldehyde, and bonding boards requires high temperature and pressure, placing certain demands on equipment and the environment. Therefore, developing a formaldehyde-free and phenol-free lignin-based green and environmentally friendly adhesive is of significant practical importance. Summary of the Invention

[0004] The main objective of this invention is to provide a lignin-based environmentally friendly adhesive, its preparation method, and its application. The technical problem to be solved is how to prepare a lignin-based environmentally friendly adhesive that does not contain formaldehyde or phenolic substances, making it healthy and environmentally friendly. At the same time, the adhesive can bond wood at room temperature and pressure, making it easy to operate and providing excellent bonding strength, thus making it more suitable for bonding needs in specific situations.

[0005] The objective of this invention and the technical problem it solves are achieved through the following technical solution. A method for preparing a lignin-based environmentally friendly adhesive according to this invention includes the following steps:

[0006] S1 mixes quaternary ammonium salt surfactants with organic acids and stirs them evenly under heating conditions to obtain a transparent pre-prepared liquid;

[0007] S2 mixes the pre-prepared liquid with lignin powder and stirs it evenly to obtain lignin-based environmentally friendly adhesive.

[0008] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0009] Preferably, in the aforementioned preparation method, the quaternary ammonium salt surfactant is selected from at least one of 3-chloro-2-hydroxypropyltrimethylammonium chloride, benzyltrimethylammonium chloride, benzyltriethylammonium chloride, and octadecyltrimethylammonium chloride; and the organic acid is selected from at least one of formic acid, acetic acid, and citric acid.

[0010] Preferably, in the aforementioned preparation method, the mass ratio of the quaternary ammonium salt surfactant to the organic acid is 0.5 to 2:1.

[0011] Preferably, in the aforementioned preparation method, the solid content of the pre-prepared liquid is ≥49% by mass percentage.

[0012] Preferably, in the aforementioned preparation method, the heating temperature is 70–100°C.

[0013] Preferably, in the aforementioned preparation method, the mass ratio of the pre-prepared liquid to the lignin powder is 1 to 2:1.

[0014] Preferably, in the aforementioned preparation method, the lignin powder is selected from at least one of alkali lignin, sulfate lignin, and hydrolyzed lignin.

[0015] The objective of this invention and the technical problem it solves are achieved by the following technical solution. According to this invention, a lignin-based environmentally friendly adhesive can be cured at room temperature and pressure; after curing, the lignin-based environmentally friendly adhesive has a bonding strength to wood ≥1 MPa.

[0016] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0017] Preferably, the aforementioned lignin-based environmentally friendly adhesive is prepared by the aforementioned preparation method.

[0018] The objective of this invention and the technical problem it solves are achieved through the following technical solution: An application of the aforementioned lignin-based environmentally friendly adhesive in the field of wood-based panels, according to this invention.

[0019] By employing the above technical solution, the lignin-based environmentally friendly adhesive, its preparation method, and its application proposed in this invention have at least the following advantages:

[0020] This invention proposes a lignin-based environmentally friendly adhesive, its preparation method, and its application. The adhesive involves mixing a quaternary ammonium salt surfactant with an organic acid under heating conditions, allowing them to form a low-co-solubility solvent through hydrogen bonding, thus creating a uniform and stable transparent pre-mixed liquid. Lignin powder is then added to the pre-mixed liquid and stirred. The lignin powder is dispersed under the action of the quaternary ammonium salt surfactant, which also promotes the penetration of the organic acid into the lignin to form hydrogen bonds, thus effectively dissolving the lignin powder and forming a uniform black viscous liquid, which is the lignin-based environmentally friendly adhesive. Due to the long-term stable hydrogen bonding between the quaternary ammonium salt surfactant and the organic acid, it remains in a low-co-solubility system for an extended period, giving the lignin-based environmentally friendly adhesive good flowability, making it easy to store and apply. When this lignin-based environmentally friendly adhesive is applied to the surface of wood... When applied to the wood, the good fluidity of the lignin-based environmentally friendly adhesive allows the organic acids in it to penetrate effectively. The organic acids carry some lignin into the wood, while most of the lignin and quaternary ammonium salt surfactants remain on the wood surface. The lignin and surfactants undergo hydrogen bonding with the wood surface, giving it a certain mechanical strength. As the organic acids gradually penetrate the wood, the hydrogen bonds between them and the quaternary ammonium salt surfactants gradually weaken or even dissolve, reverting to being independent organic acids and quaternary ammonium salt surfactants. As the quaternary ammonium salt surfactants lose their low eutectic effect with the organic acids and gradually solidify, the lignin-based environmentally friendly adhesive can be cured at room temperature and pressure, thus firmly bonding the wood together with strong adhesive properties. This invention eliminates the need for auxiliary heating or pressurization during wood bonding, eliminating the need for expensive specialized equipment, making it convenient and cost-effective.

[0021] Furthermore, the technical solution of the present invention can be applied to a variety of industrial lignins, with a wide range of raw material sources, and the raw materials used are safe, non-toxic, and have good biocompatibility.

[0022] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the bonding strength testing method of the present invention;

[0024] Figure 2 These are XRD patterns of various substances in the lignin-based environmentally friendly adhesive in this embodiment of the invention. Detailed Implementation

[0025] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following detailed description, in conjunction with preferred embodiments, provides a detailed explanation of the specific implementation methods, structure, features, and effects of a lignin-based environmentally friendly adhesive, its preparation method, and its application according to the present invention. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable manner.

[0026] This invention proposes a method for preparing a lignin-based environmentally friendly adhesive, which includes the following steps:

[0027] First, quaternary ammonium salt surfactants and organic acids are stirred evenly under heating conditions to obtain a transparent pre-formed liquid. In this step, for liquid quaternary ammonium salt surfactants and organic acids, they can form a uniform transparent liquid through hydrogen bonding and van der Waals forces. For solid quaternary ammonium salt surfactants and organic acids, although they can also form hydrogen bonding and van der Waals forces at room temperature, the limited molecular mobility of solids results in a slow reaction. This invention preferably uses heating conditions to facilitate the formation of a uniform transparent liquid through hydrogen bonding and van der Waals forces, thereby improving efficiency. While there are chemical interactions such as hydrogen bonding and van der Waals forces between quaternary ammonium salt surfactants and organic acids, no chemical reaction occurs. No new substances are formed in this step; rather, the quaternary ammonium salt surfactants and organic acids form low-co-solubility solvent ligands through hydrogen bonding and van der Waals forces, lowering the melting point of the system. This allows the system to remain stable in liquid form even after cooling to room temperature, forming a transparent pre-formed liquid.

[0028] In the above steps, to ensure sufficient interaction between the quaternary ammonium salt surfactant and the organic acid, forming a greater number of hydrogen bonds and van der Waals forces, this invention preferably involves thorough stirring for at least 2 hours during mixing. If the stirring time is too short, sufficient hydrogen bonds and van der Waals forces may not form, resulting in an insufficient low-co-solubility solvent system. Conversely, excessively long stirring times are unnecessary from an energy-saving perspective. Therefore, in subsequent embodiments of this invention, the stirring time is fixed at 2 hours.

[0029] Extensive experimental testing has revealed that when quaternary ammonium salt surfactants are selected from at least one of 3-chloro-2-hydroxypropyltrimethylammonium chloride, benzyltrimethylammonium chloride, benzyltriethylammonium chloride, and octadecyltrimethylammonium chloride, and organic acids are selected from at least one of formic acid, acetic acid, and citric acid, the resulting low eutectic solvent system is particularly stable and can be stored stably at room temperature for extended periods, which is beneficial for the storage of adhesives.

[0030] In the above steps, quaternary ammonium salt surfactants and organic acids are preferably selected from raw materials with high purity. Higher raw material concentrations allow for denser hydrogen bonds and van der Waals forces, resulting in a better pre-prepared solution. However, some raw materials, such as 3-chloro-2-hydroxypropyltrimethylammonium chloride, are more expensive with higher purity. Therefore, this invention uses commercially available raw materials with a mass concentration of 65%. Considering the cost-effectiveness of different commercially available raw materials, and taking into account factors such as the bonding performance and application cost of the final adhesive product, this invention preferably uses a pre-prepared solution with a mass solid content ≥49%. When the solid content meets this condition, the pre-prepared solution can be used to prepare lignin-based environmentally friendly adhesives with excellent performance indicators. Furthermore, the applicant has found that as the solid content of the pre-prepared solution increases, the bonding performance of the final lignin-based environmentally friendly adhesive improves, the bonding time is shortened, and the efficiency is higher. Therefore, this invention further preferably uses a pre-prepared solution with a mass solid content ≥78%. However, increasing the solid content of the pre-formulated liquid gradually increases its viscosity. As the viscosity increases, the spreadability of the adhesive gradually decreases, leading to an increase in the amount of adhesive applied, which in turn increases costs. Therefore, this invention preferably uses a pre-formulated liquid with a solid content of 78-85% to ensure a better balance between performance, efficiency, and cost; the preferred application rate is 12-18 g / m³. 2 .

[0031] In the above steps, in order for the quaternary ammonium salt surfactant and the organic acid to form sufficient hydrogen bonds and van der Waals forces, the molecular numbers of the two should be basically matched. This avoids the difficulty in forming a low-co-solubility solvent due to the insufficient amount of one raw material, which would increase the difficulty in forming the pre-formed solution. Therefore, the present invention preferably uses a mass ratio of quaternary ammonium salt surfactant to organic acid of 0.5 to 2:1. When the ingredients are mixed within this ratio range, more hydrogen bonds and van der Waals forces can be formed between the two, and the resulting low-co-solubility solvent ligand is more stable.

[0032] In the above steps, due to the differences in properties between different quaternary ammonium salt surfactants and organic acids, to ensure that each of the above combinations can quickly form a low co-soluble solvent ligand, the preferred heating temperature in this invention is 70–100°C. At lower heating temperatures, the molecular activity of some raw materials is restricted, thus limiting the hydrogen bonding and van der Waals forces between the quaternary ammonium salt surfactant and the organic acid, resulting in inefficiency; while excessively high temperatures may lead to energy waste. The choice of heating temperature only affects production efficiency and energy consumption, and has little impact on the adhesive properties. For ease of data comparison, the heating temperature is fixed at 80°C in subsequent embodiments.

[0033] After the pre-prepared liquid is prepared, it is mixed with lignin powder and stirred evenly to obtain the lignin-based environmentally friendly adhesive. In the above steps, the lignin powder does not need to be added in stages; adding all the lignin powder at once ensures its complete dissolution. This is because the pre-prepared liquid contains a large amount of quaternary ammonium salt surfactants. The lignin powder is dispersed under the action of these surfactants, and the surfactants also promote the penetration of organic acids into the lignin to form hydrogen bonds, thus allowing the lignin powder to dissolve well and form a uniform, black, viscous liquid, which is the lignin-based environmentally friendly adhesive.

[0034] Extensive experimental testing has shown that when the mass ratio of the pre-mixed liquid to lignin powder is within the range of 1 to 2:1, the resulting adhesive exhibits particularly excellent spreadability, curing time, and bonding strength.

[0035] In the above technical solution, lignin powder does not chemically react with quaternary ammonium salt surfactants or organic acids; they interact only through hydrogen bonds and van der Waals forces. Specifically, lignin powder is dispersed under the action of quaternary ammonium salt surfactants, which also promote the penetration of organic acids into the lignin to form hydrogen bonds, thus enabling the lignin powder to be dissolved effectively. Therefore, the structure and functional groups of lignin itself have little impact on the adhesive, making the technical solution of this invention applicable to various industrial lignins. Considering the availability and cost of lignin powder, this invention preferably selects lignin powder from at least one of alkali lignin, sulfate lignin, and hydrolyzed lignin. Lignin powder has a wide range of raw material sources, is safe and non-toxic, and has good biocompatibility.

[0036] To illustrate the technical solution of this invention, XRD analysis was performed on an adhesive system consisting of alkali lignin, formic acid, and benzyltriethylammonium chloride. The results are shown in the attached figure. Figure 2 As shown in (a) and (b) in the figure; the horizontal axis is the diffraction angle 2-Theat (Bragg angle), in degrees, used to represent the diffraction direction of different crystal planes in the crystal; the vertical axis Intensity is the diffraction intensity, in arbitrary units, used to represent the intensity of the diffraction peak at the corresponding diffraction angle, and the intensity is related to factors such as crystal structure and composition. In the figure, AL represents alkali lignin, FA represents formic acid, and AL... -F It is a mixture of alkali lignin and formic acid; TEBAC is benzyltriethylammonium chloride; AL -F-T It is a mixture of alkali lignin, formic acid, and benzyltriethylammonium chloride, AL -T It is a mixture of alkali lignin and benzyltriethylammonium chloride.

[0037] Adding AL to FA yields AL. -F Mixture, by attached Figure 2 As shown in (a), AL -F The diffraction peaks of the mixture are basically consistent with those of FA, which indicates that the intermolecular hydrogen bonding of AL is weakened, and also indicates that AL -F No new diffraction peaks appeared in the mixture system, meaning no new substances were formed; compared with FA, AL -F The diffraction peak intensities at 13° and 29.8° decreased slightly; these results indicate that FA weakens the intermolecular hydrogen bonds of AL, while AL only slightly alters the crystal structure of FA. There are few covalent cross-linking reactions between FA and AL, and no new chemical structures are formed between them.

[0038] Add AL to TEBAC to obtain AL -T The system, consisting of appendices Figure 2 As shown in (b), AL -T The system exhibited entirely new diffraction peaks, indicating that the intermolecular hydrogen bonding of AL was weakened, and that the strong crystal structure of TEBAC formed a new peak shape with AL. These results suggest that there is a strong covalent cross-linking reaction between TEBAC and AL.

[0039] From the appendix Figure 2 As shown in (b), compared to AL -T With the addition of TEBAC, FA, and AL, the system... -F-T The intensity of the crystal peaks in the system decreased significantly; studies have shown that covalent cross-linking reactions hinder the formation of an ordered crystal structure; therefore, AL -F-T The significant decrease in the intensity of the crystal peaks in the system indicates that the mixed system with all three components exhibits the most cross-linking reactions.

[0040] In summary, the combined addition of TEBAC and FA significantly weakens the intermolecular hydrogen bonds of Al and simultaneously forms new free intermolecular hydrogen bonds, disrupting the crystalline structure of Al and ultimately leading to Al... -F-T The system exhibits a viscous mixed liquid state.

[0041] After the viscous liquid mixture is evenly applied to the wood, the small amount of moisture from the FA dries in the air, causing the free intermolecular hydrogen bonds to tightly arrange themselves between the wood molecules, exhibiting an AL (Al₂O₃) effect. -F-T Adhesive effect with wood.

[0042] The present invention also proposes a lignin-based environmentally friendly adhesive prepared by the aforementioned preparation method, which can be cured at room temperature and pressure; the lignin-based environmentally friendly adhesive has a bonding strength to wood of ≥1MPa after curing.

[0043] This invention also proposes an application of the aforementioned lignin-based environmentally friendly adhesive in the field of wood-based panels. Wood-based panels prepared using the lignin-based environmentally friendly adhesive of this invention do not contain formaldehyde or phenolic substances, making them healthy and environmentally friendly. Furthermore, the bonding of wood using this adhesive can be carried out at room temperature and pressure, making the process convenient and resulting in excellent bonding strength.

[0044] The present invention will be further described below with reference to specific embodiments, but this should not be construed as a limitation on the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0045] Unless otherwise specified, all materials and reagents mentioned below are commercially available products well known to those skilled in the art; unless otherwise specified, all methods described are methods known in the art. Unless otherwise defined, the technical or scientific terms used should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0046] Example 1

[0047] This embodiment prepares a lignin-based environmentally friendly adhesive, and the specific steps are as follows:

[0048] 1) Preparation of adhesive prepreg: Mix benzyltriethylammonium chloride and formic acid at a mass ratio of 1:1 at 80°C, stir until uniform, and store at room temperature for later use.

[0049] 2) Mix the pre-prepared adhesive liquid with Longli Industrial lignin powder at a mass ratio of 2:1, stir evenly, add a small amount of water to adjust its solid content, and obtain a black mixed viscous liquid, which is the lignin environmentally friendly adhesive, which can be stored at room temperature for later use.

[0050] The bonding performance of the lignin-based environmentally friendly adhesive prepared in this embodiment was tested, and the steps are as follows:

[0051] 1) Cut the beechwood planks into strips that are 20mm wide, 80mm long, and 5mm thick;

[0052] 2) Apply the lignin-based environmentally friendly adhesive to ten beechwood boards. The coating area of ​​the lignin adhesive on each beechwood board is 20mm × 10mm, and the application rate is 15g / m². 2 ;

[0053] 3) Join the coatings on each pair of beechwood boards together and secure them with clips, then let them stand at room temperature for 24 hours;

[0054] 4) According to BS EN 205:2016 Timber Lap Joint Methods, single-layer lap joint specimens were subjected to parallel tensile and shear tests using a universal tensile testing machine, as shown in the attached figure. Figure 1As shown, when clamping the specimen into the tensile testing machine, shims or appropriately designed clamps should be used to ensure that the applied force is applied on the plane of the joint line and centered. Figure 1 In the diagram, l1 represents the length of the test specimen, which is 150mm ± 2mm; b represents the width of the test specimen, which is 20mm ± 0.2mm; l3 represents the length of the test piece, which is 80mm ± 2mm; s represents the thickness of the test piece, which is 5mm ± 0.1mm; and l2 represents the bonding length of the overlap between the test pieces, which is 10mm ± 0.2mm.

[0055] The lignin-based environmentally friendly adhesive prepared in this embodiment has a bond strength of 4.36 ± 0.13 MPa. The solids content was tested using conventional methods in the art.

[0056] Examples 2-16

[0057] Same as Example 1, except for the types and proportions of raw materials in the lignin-based environmentally friendly adhesive, as detailed in Table 1; the test results are shown in Table 1.

[0058] Comparative Example 1

[0059] Longli Industrial lignin powder was stirred evenly with formic acid to obtain a black mixed liquid, which was then stored at room temperature. The mixture was tested according to the method shown in Example 1, and the results are shown in Table 1.

[0060] Comparative Example 2

[0061] Longli Industrial lignin powder was mixed with deionized water to obtain a black mixed liquid, which was then stored at room temperature. The mixture was tested according to the method described in Example 1, and the results are shown in Table 1.

[0062] Comparative Example 3

[0063] Longli Industrial lignin powder was mixed with benzyltriethylammonium chloride to obtain a black mixed liquid, which was then stored at room temperature. The mixture was tested according to the method described in Example 1, and the results are shown in Table 1.

[0064] Table 1

[0065]

[0066]

[0067] As can be seen from the test results of the above embodiments and comparative examples, the adhesive prepared by the technical solution of the present invention has excellent bonding performance, and its bonding strength after curing at room temperature and pressure is ≥1MPa, as in Examples 1 to 16; furthermore, when formic acid is preferred as the organic acid, its bonding strength can reach more than 3MPa, as in Examples 1 to 8 and Examples 11 to 16. However, when only a surfactant is added without adding an organic acid, the adhesive has certain bonding performance, but the bonding strength is low, as in Comparative Example 3; furthermore, when only an organic acid is added without adding a surfactant, it has no bonding strength, as in Comparative Example 1; when neither organic acid nor surfactant is added, it has no bonding strength, as in Comparative Example 2.

[0068] As can be seen from the test results of the above embodiments and comparative examples, the adhesive prepared by the technical solution of the present invention has good bonding performance when the solid content is ≥49%, as in Examples 1 to 16; furthermore, when the solid content is ≥78%, the adhesive has good bonding performance, fast drying speed, and improved construction efficiency, as in Examples 1, 3 to 6, 8 to 10, and 12 to 16.

[0069] The technical features in the claims and / or specification of this invention can be combined, and the combination is not limited to the combinations obtained through reference in the claims. Technical solutions obtained by combining the technical features in the claims and / or specification are also within the scope of protection of this invention.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a lignin-based environmentally friendly adhesive, characterized in that, It includes the following steps: S1. A quaternary ammonium salt surfactant is mixed with an organic acid and stirred evenly under heating conditions to obtain a transparent pre-prepared solution. The quaternary ammonium salt surfactant is selected from at least one of 3-chloro-2-hydroxypropyltrimethylammonium chloride, benzyltrimethylammonium chloride, benzyltriethylammonium chloride, and octadecyltrimethylammonium chloride. The organic acid is selected from at least one of formic acid and acetic acid. The mass ratio of the quaternary ammonium salt surfactant to the organic acid is 0.5~2:

1. The pre-prepared solution is a eutectic solvent formed by the quaternary ammonium salt surfactant and the organic acid through hydrogen bonding. S2. The pre-prepared liquid is mixed with lignin powder and stirred evenly. The lignin powder is dispersed under the action of quaternary ammonium salt surfactant. At the same time, the quaternary ammonium salt surfactant can promote the organic acid to penetrate into the lignin and form hydrogen bonds with it, so that the lignin powder can be dissolved well, and lignin environmentally friendly adhesive is obtained. The mass ratio of the pre-prepared liquid to lignin powder is 1~2:

1. The lignin powder is selected from at least one of alkali lignin, sulfate lignin and hydrolyzed lignin.

2. The preparation method according to claim 1, characterized in that, The solid content of the pre-prepared liquid is ≥49% by mass percentage.

3. The preparation method according to claim 1, characterized in that, The heating temperature is 70~100℃.

4. A lignin-based environmentally friendly adhesive prepared by the preparation method according to any one of claims 1 to 3, characterized in that, It can be cured at room temperature and pressure; the lignin-based environmentally friendly adhesive has a bonding strength to wood of ≥1 MPa after curing.

5. The application of the lignin-based environmentally friendly adhesive according to claim 4 in the field of wood-based panels.

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