Preparation method of lignin-based adhesive

Abstract

The invention belongs to the field of lignin-based adhesives, and provides a preparation method of a lignin-based adhesive, which comprises the following steps: depolymerizing lignin into a micromolecular aromatic compound to obtain a depolymerized product; uniformly mixing the depolymerization product with a curing agent to obtain a lignin-based adhesive; wherein the curing agent is selected from at least one of hydrochloric acid, glacial acetic acid, hydrofluoric acid, phosphoric acid, sulfuric acid, benzenesulfonyl chloride, p-toluenesulfonyl chloride, p-toluenesulfonic acid and benzenesulfonic acid. The adhesive has the characteristics of low cost, thermal stability and good adhesion performance, and the prepared adhesive has the characteristics of high bonding strength, no formaldehyde and the like.

Description

Technical Field

[0001] The invention belongs to the field of lignin-based adhesives and relates to a preparation method of the lignin-based adhesive. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] In recent years, artificial boards, such as particleboard and fiberboard, have become the mainstream substrates for flooring, wallboard, and furniture, leading to a significant increase in adhesive usage. Currently, commercially available adhesives are still primarily based on phenolic, epoxy, acrylic, or polyurethane systems. These chemicals can release volatile organic compounds (VOCs) during synthesis, hot pressing, and long-term use, posing health risks and increasing the depletion of fossil resources.

[0004] Lignin is widely available, inexpensive, biodegradable, non-toxic, and renewable. Therefore, utilizing lignin to develop high-performance, environmentally friendly wood adhesives has become a research hotspot. Currently, lignin is used in adhesives in two ways: by co-modifying lignin with phenolic or urea-formaldehyde resins to produce wood adhesives; and by using lignin itself as an adhesive. While lignin co-modification offers performance advantages, it still requires the use of a large number of toxic chemicals, failing to meet green and environmental requirements. Furthermore, the industrialization of lignin as an adhesive faces multiple challenges. Firstly, lignin's complex structure, wide molecular weight distribution, and low density of active phenolic hydroxyl groups limit crosslinking efficiency, poor solubility and dispersibility, and difficulty forming a uniform and stable network, resulting in poor adhesive properties. Secondly, existing modification methods (such as hydroxymethylation, phenolation, or demethylation) often rely on strong acids and alkalis, high temperatures, and organic solvents, resulting in high energy consumption and heavy wastewater treatment, making them difficult to meet green manufacturing requirements. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a method for preparing a lignin-based adhesive, which has the characteristics of low cost, good thermal stability, high bonding strength, and no formaldehyde.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The first aspect of the present invention provides a method for preparing a lignin-based adhesive, comprising: Depolymerizing lignin into small molecular aromatic compounds to obtain depolymerization products; uniformly mixing the depolymerization product with a curing agent to obtain a lignin-based adhesive; Wherein, the curing agent is selected from at least one of hydrochloric acid, glacial acetic acid, hydrofluoric acid, phosphoric acid, sulfuric acid, benzenesulfonyl chloride, p-toluenesulfonyl chloride, p-toluenesulfonic acid, and benzenesulfonic acid.

[0007] The second aspect of the present invention provides a lignin-based adhesive prepared by the above method.

[0008] The third aspect of the present invention provides the use of the above-mentioned lignin-based adhesive in the preparation of boards, home furnishings and building materials.

[0009] A fourth aspect of the present invention provides a method for preparing a plate, comprising: The above-mentioned lignin-based adhesive is loaded on a single board, and multiple single boards loaded with the lignin-based adhesive are combined and hot-pressed to obtain a board.

[0010] Beneficial effects of the present invention (1) The present invention depolymerizes lignin into small aromatic compounds, overcoming the problems of low lignin reactivity, wide molecular weight span, and large structural differences. The lignin liquid phase depolymerization product is then mixed with a curing agent to prepare an adhesive that relies on the self-crosslinking of the lignin degradation products.

[0011] (2) The present invention utilizes the self-polymerization of lignin degradation products to prepare formaldehyde-free plywood. This method is simple, efficient, and easy to scale up for production.

[0012] (3) The adhesive of the present invention has the characteristics of low cost, good thermal stability, no formaldehyde release and high adhesion strength, which can effectively reduce the formaldehyde release problem existing in decoration and household items.

[0013] (4) The preparation method of the present invention is simple, practical, and easy to promote. DETAILED DESCRIPTION

[0014] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0015] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. The reagents or raw materials used in the present invention can be purchased through conventional channels. Unless otherwise specified, the reagents or raw materials used in the present invention are used in accordance with conventional methods in the art or according to product specifications. Similarly, unless otherwise specified, the test methods of the present invention are also tested in accordance with conventional methods in the art or the common methods or standards in the industry. In addition, any methods and materials similar to or equivalent to the described contents can be applied to the inventive method. The preferred embodiments and materials described herein are for demonstration purposes only.

[0016] The present invention provides a method for preparing a lignin-based adhesive, comprising: Depolymerizing lignin into small molecular aromatic compounds to obtain depolymerization products; uniformly mixing the depolymerization product with a curing agent to obtain a lignin-based adhesive; Wherein, the curing agent is selected from at least one of hydrochloric acid, glacial acetic acid, hydrofluoric acid, phosphoric acid, sulfuric acid, benzenesulfonyl chloride, p-toluenesulfonyl chloride, p-toluenesulfonic acid, and benzenesulfonic acid.

[0017] The curing of the adhesive can be achieved by adding a curing agent. The amount of curing agent added will affect the curing effect and the subsequent bonding strength. Therefore, the present invention studies the amount of curing agent added. In some embodiments, the amount of curing agent added is 1 wt%-15 wt%, based on the mass of the depolymerization product, to obtain a better bonding effect.

[0018] The acid concentration has little effect on the bonding strength, but if the acid concentration is too low, the evaporation of water during the use of the adhesive will affect the bonding of the boards. In some embodiments, the concentration of the curing agent is 20wt%-98wt% to achieve better bonding effect.

[0019] The composition of the depolymerization product affects its adhesive properties and the binding effect with the curing agent. The present invention has found that in some embodiments, when the molecular weight of the small molecule aromatic compound is 100-1200, the obtained depolymerization product has better adhesive properties.

[0020] The present invention does not impose any particular limitation on the specific method of depolymerization. In some embodiments, the depolymerization method is selected from at least one of thermochemical depolymerization, liquefaction degradation, oxidative degradation, hydrogenation degradation, and enzymatic hydrolysis. Those skilled in the art can select the method according to the actual working conditions. In theory, any of the above depolymerization methods can meet the preparation requirements of the adhesive of the present invention.

[0021] In some embodiments, the lignin is selected from at least one of kraft lignin, alkali lignin, hydrolyzed lignin, enzymatically degraded lignin, and organic solvent lignin; Lignin obtained by different treatment methods has different chemical structures and specific properties. The present invention does not impose any particular limitation on the preparation method of lignin. In some embodiments, the preparation method of lignin is: treating biomass raw materials with acid, alkali, supercritical fluid, aqueous two-phase, ionic liquid, organic solvent or enzyme to obtain lignin. In theory, lignin prepared by any of the above methods can meet the preparation requirements of the adhesive of the present invention.

[0022] The present invention does not impose any particular limitation on the source of the lignin raw material. In some embodiments, the biomass is selected from at least one of woody plants, herbaceous plants, and vascular plants. Those skilled in the art can make the selection based on actual working conditions.

[0023] The present invention also provides a method for preparing a plate, comprising: The above-mentioned lignin-based adhesive is loaded on a single board, and multiple single boards loaded with the lignin-based adhesive are combined and hot-pressed to obtain a board.

[0024] The coating amount will affect the bonding strength of the board. Therefore, the present invention has studied the coating amount. In some embodiments, the coating amount is 50-300 g / m 2 , to obtain better bonding strength.

[0025] The hot pressing temperature and pressure will affect the bonding strength, moisture content, deformation degree, etc. of the board. Therefore, the present invention studies the hot pressing conditions. In some embodiments, the hot pressing pressure is 0.5-1.7 MPa, and in some embodiments, the hot pressing temperature is 100-195°C to obtain better board performance.

[0026] As the hot pressing time increases, the mechanical properties of the board are enhanced. However, if the hot pressing time is too long, it will cause deformation of the board or increase energy consumption. Therefore, in some embodiments, the hot pressing time is 3-20 minutes to save energy while ensuring the quality of the board.

[0027] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0028] In the following examples, the lignin is all industrial sulfate lignin, a commercially available product.

[0029] Example 1: The reaction device was heated to 650°C, and lignin was directly added to the reaction device. The reaction device was kept warm for 10 minutes under nitrogen protection at a flow rate of 100 mL / min. The volatiles obtained were purged out of the reaction device by protective gas and condensed. The uncondensed gas was passed into an organic solvent for washing. After the pyrolysis was completed, the pipeline was washed with ethyl acetate and mixed with the washing liquid and then rotary evaporated to obtain pyrolysis oil. Concentrated sulfuric acid (mass concentration of 98%) was added to the lignin pyrolysis oil at a concentration of 2% relative to the mass of the pyrolysis oil and mixed evenly to obtain an adhesive. According to GB / T 17657-2022 "Test methods for physical and chemical properties of artificial boards and veneered artificial boards", the adhesive was evenly applied on the wooden board, with a coating amount of 100 g / m on each side. 2The resulting wood panels were assembled and hot-pressed at 140°C for 12 minutes at a pressure of 1.5 MPa. Plywood was obtained after cooling to room temperature. The measured bonding strength was 3.5 MPa.

[0030] Example 2: The reaction device was heated to 600°C, and lignin was directly added to the reaction device. The reaction device was kept warm for 12 minutes under nitrogen protection at a flow rate of 100 mL / min. The volatiles obtained were purged out of the reaction device by protective gas and condensed. The uncondensed gas was passed into an organic solvent for washing. After the pyrolysis was completed, the pipeline was washed with ethyl acetate and mixed with the washing liquid and then rotary evaporated to obtain pyrolysis oil. Phosphoric acid (mass concentration of 85%) was added to the lignin pyrolysis oil at 5% of the mass of the pyrolysis oil relative to the mass of the pyrolysis oil and mixed evenly to obtain an adhesive. According to GB / T 17657-2022 "Test methods for physical and chemical properties of wood-based panels and veneered wood-based panels", the adhesive was evenly applied on the wood board with a coating amount of 100 g / m2 on each side. 2 The resulting wood panels were assembled and hot-pressed at 140°C for 12 minutes at a pressure of 1.5 MPa. After cooling to room temperature, plywood was obtained. The measured bond strength was 1.03 MPa.

[0031] Example 3: The reaction device was heated to 650°C, and lignin was directly added to the reaction device. The reaction device was kept warm for 10 minutes under nitrogen protection at a flow rate of 100 mL / min. The volatiles obtained were purged out of the reaction device by protective gas and condensed. The uncondensed gas was passed into an organic solvent for washing. After the pyrolysis was completed, the pipeline was washed with ethyl acetate and mixed with the washing liquid and then rotary evaporated to obtain pyrolysis oil. Hydrochloric acid (mass concentration of 36%) was added to the lignin pyrolysis oil at a concentration of 6% relative to the mass of the pyrolysis oil and mixed evenly to obtain an adhesive. According to GB / T 17657-2022 "Test methods for physical and chemical properties of wood-based panels and veneered wood-based panels", the adhesive was evenly applied on the wood board, with a coating amount of 100 g / m on each side. 2 The resulting wood panels were assembled and hot-pressed at 140°C for 12 minutes at a pressure of 1.5 MPa. After cooling to room temperature, plywood was obtained. The measured bond strength was 0.94 MPa.

[0032] Comparative Example 1: According to GB / T 17657-2022 "Test methods for physical and chemical properties of wood-based panels and veneered wood-based panels", apply commercial phenolic resin adhesive evenly on the wood board, with a coating amount of 100 g / m on each side. 2 The resulting wood panels were assembled and hot-pressed at 140°C for 12 minutes at a pressure of 1.5 MPa. Plywood was obtained after cooling to room temperature. The measured bonding strength was 1.63 MPa.

[0033] Comparative Example 2 The difference from Example 1 is that concentrated sulfuric acid was not added. According to GB / T 17657-2022 "Test methods for physical and chemical properties of wood-based panels and veneered wood-based panels", lignin pyrolysis oil without curing agent was evenly applied on the wood board, with a coating amount of 100 g / m on each side. 2 The resulting wood panels were assembled and hot-pressed at 140°C for 12 minutes at a pressure of 1.5 MPa. Plywood was obtained after cooling to room temperature. The measured bonding strength was 0 MPa.

[0034] From the comparison between Example 1 and Comparative Example 1, it can be seen that, under the condition of the same coating amount, the bonding strength of the adhesive prepared by the present invention is better than that of the commercial phenolic resin adhesive.

[0035] From the comparison between Example 1 and Comparative Example 2, it can be seen that without adding a curing agent, the adhesive cannot be cured and the bonding strength is 0 MPa.

[0036] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a lignin-based adhesive, characterized in that: include: Depolymerizing lignin into small molecular aromatic compounds to obtain depolymerization products; uniformly mixing the depolymerization product with a curing agent to obtain a lignin-based adhesive; Wherein, the curing agent is selected from at least one of hydrochloric acid, glacial acetic acid, hydrofluoric acid, phosphoric acid, sulfuric acid, benzenesulfonyl chloride, p-toluenesulfonyl chloride, p-toluenesulfonic acid, and benzenesulfonic acid.

2. The method for preparing a lignin-based adhesive according to claim 1, wherein The added amount of the curing agent is 1 wt%-15 wt%, based on the mass of the depolymerized product.

3. The method for preparing a lignin-based adhesive according to claim 1, wherein: The concentration of the curing agent is 20wt%-98wt%.

4. The method for preparing a lignin-based adhesive according to claim 1, wherein The molecular weight of the small molecule aromatic compound is 100-1200.

5. The method for preparing the lignin-based adhesive according to claim 1, wherein The depolymerization method is selected from at least one of thermochemical depolymerization, liquefaction degradation, oxidative degradation, hydrogenation degradation, and enzymatic degradation.

6. The method for preparing a lignin-based adhesive according to claim 1, wherein: The lignin is selected from at least one of sulfate lignin, alkali lignin, hydrolyzed lignin, enzymatic lignin, and organic solvent lignin; Alternatively, the method for preparing lignin comprises: treating the biomass raw material with acid, alkali, supercritical fluid, aqueous two-phase, ionic liquid, organic solvent or enzyme to obtain lignin; Alternatively, the biomass is selected from at least one of woody plants, herbaceous plants, and vascular plants.

7. A lignin-based adhesive prepared by the method according to any one of claims 1 to 6.

8. Use of the lignin-based adhesive according to claim 7 in the preparation of boards, home furnishings and building materials.

9. A method for preparing a plate, characterized in that: include: The lignin-based adhesive according to claim 7 is loaded onto a single board, and multiple single boards loaded with the lignin-based adhesive are combined and hot-pressed to obtain a board.

10. The method for preparing a plate according to claim 9, wherein: Coating weight is 50-300 g / m 2 ; Alternatively, the hot pressing pressure is 0.5-1.7 MPa; Alternatively, the hot pressing temperature is 100-195°C; Alternatively, the hot pressing time is 3-20 min.