Preparation method of acetal lignin-based imine resin

Abstract

The invention discloses a preparation method of acetal lignin-based imine resin, which comprises the following specific steps: firstly, in the extraction process of lignin, dialdehyde compounds such as glyoxal and glutaraldehyde are introduced as acetal protective agents, and lignin molecules with low condensation degree are extracted from lignocellulose through acetal reaction under the action of excessive acid; and carrying out a Schiff base reaction with polyether amine to prepare the acetal lignin-based imine resin. The lignin-based imine resin obtained by the invention has excellent mechanical properties, the glass transition temperature is 70-130 DEG C, and the lignin-based imine resin is expected to replace petroleum-based plastics. The preparation method is simple, raw material sources are green, and the method has great application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of biomass-based degradable materials and relates to a method for preparing a lignin-based imine resin. Background Art

[0002] Currently, petroleum-based plastics have been widely used in industrial fields and human daily life. However, traditional petroleum-based plastics lack sustainability because their raw materials come from non-renewable fossil resources. In addition, they are difficult to degrade even after hundreds of years under natural conditions, resulting in serious environmental pollution. Therefore, it is very urgent to increase the use of sustainable raw materials and develop degradable and recyclable alternatives to petroleum-based plastics. Lignin, as the most abundant natural aromatic polymer on earth, is widely derived from inexpensive by-products of the pulp and paper industry.

[0003] The biggest problem in the current preparation of lignin in the field of materials is that the lignin extracted from papermaking waste liquor has a large molecular weight and a serious degree of intramolecular condensation, resulting in poor dispersibility in other polymer matrices and poor reactivity of itself. Therefore, many current studies add lignin as an additive component to polymer materials such as epoxy resins and polyurethanes (CN102585531A, CN105916915A), and use modified lignin in the preparation of imine resins. Due to its poor mechanical properties and difficulty in forming, most of them are used as coatings or adhesives (CN119331352B).

[0004] Therefore, the existing technology has limitations in the high-value utilization of lignin. How to convert lignin into high-value-added products (including biofuels, biomass-based materials, and biochemical products) through simple and inexpensive methods has become a major research hotspot. Summary of the Invention

[0005] The object of the present invention is to overcome the problems of high degree of condensation of current lignin molecules and low addition amount in material preparation, and provide a method for preparing a lignin-based imine resin, to prepare a low-condensation and high-activity lignin and an imine resin with a high lignin content prepared therefrom, and directly realize the conversion of acetal lignin into imine resin.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A method for preparing an acetal lignin-based imine resin specifically includes the following steps: (1) Preparation of aldehyde-group lignin: Mix sawdust, a solvent, a dialdehyde compound, and a hydrochloric acid solution, react at 80 °C for 5 h, filter, wash the residue until the filtrate is colorless, then adjust the pH of the washed filtrate, and finally add deionized water to precipitate lignin. After washing the lignin with water, aldehyde-group modified lignin is obtained; (2) Preparation of imine plastics: The aldehyde group lignin obtained in step (1) is first dissolved in a solvent, and then polyetheramine is added and reacted at 80 °C for 2 h. The obtained mixture is precipitated in water, and after repeated extraction, filtration, washing, drying, and hot pressing, lignin-based imine plastics can be obtained.

[0007] Further, the solvent in step (1) is dioxane, and the mass fraction of the hydrochloric acid solution is 37 wt%.

[0008] Further, the dosage ratio of wood chips, dialdehyde compound, and hydrochloric acid in step (1) is 15 g: (0.1~0.2) mol: (6~8) mL Further, the dialdehyde compound in step (1) is any one of glyoxal, glutaraldehyde, and terephthalaldehyde.

[0009] Further, in step (1), NaHCO3 is used to adjust the pH to 2~4.

[0010] Further, in step (2), the mass ratio of aldehyde group lignin to polyetheramine is 4:1~1:1. The polyetheramine is one of terminal amine polypropylene glycol trimethylolpropane ether, polypropylene glycol bis(2-aminopropyl ether), and polypropylene glycol bis(2-aminopropyl ether); the solvent is dimethyl sulfoxide or 1,4-dioxane.

[0011] The acetal lignin-based imine resin prepared by the above preparation method has a glass transition temperature of 70-130 °C, a lignin content of 50~80%, and a mechanical property of 37~50 MPa.

[0012] The advantages of the present invention are as follows: First, in the process of lignin extraction, dialdehyde compounds such as glyoxal, glutaraldehyde, and terephthalaldehyde are introduced as acetal protecting agents, and lignin molecules with low condensation degree are extracted from lignocellulose through acetal reaction under the action of excessive acid. Then, they are simply blended with polyetheramine, and acetal lignin-based imine resin is prepared through Schiff base reaction. The obtained lignin-based imine resin has excellent mechanical properties, and its glass transition temperature is between 70-130 °C, and it is expected to replace petroleum-based plastics. The preparation method of the present invention is simple, and the raw material source is green, which solves the problem that the addition amount of lignin is low in the field of material preparation due to high condensation degree of lignin. The lignin content in the lignin-based imine resin prepared by the present invention can reach more than 70% at most, and it can also maintain excellent mechanical properties, which has important significance for the high-value utilization of lignin. Description of the Drawings

[0013] Figure 1 It is the infrared spectrogram of glutaraldehyde lignin and its imine resin.

[0014] Figure 2 Tan d curve of glutaraldehyde lignin imine resin

[0015] Figure 3 Tensile property curve of glutaraldehyde lignin imine resin Specific implementation mode

[0016] To better understand the technical solution of the present invention, the following further details are described in combination with specific embodiments and drawings, but it does not limit the protection scope of the present invention.

[0017] Unless otherwise specified, the methods used in the present invention are all conventional technical means.

[0018] Example 1 (1)Preparation of aldehyde lignin: Add 15 g of air-dried wood chips (<20 mesh) and 170 ml of dioxane solvent into a round-bottom flask, then add 25 ml of glutaraldehyde solution (50 wt%) and 6.3 ml of hydrochloric acid solution (37 wt%), and react at 80 °C for 5 h. After the reaction, filter, wash the residue with 1,4-dioxane until the filtrate is colorless, then add solid NaHCO3 to the washed filtrate to adjust the pH to about 3, continue to add a large amount of deionized water to precipitate lignin, and wash it repeatedly with water until neutral to obtain glutaraldehyde-modified lignin molecules. As can be seen from Figure 1 it that there is a characteristic absorption peak of C=O in the infrared spectrum of glutaraldehyde lignin.

[0019] (2)Preparation of imine plastic: Weigh 10 g of the above-mentioned glutaraldehyde-modified lignin and dissolve it in 150 mL of dimethyl sulfoxide, then add 3 g of polyamine ether (amine-terminated polypropylene glycol trimethylolpropane ether), react at 80 °C for 2 h, and precipitate the obtained mixture in a large amount of water to form a precipitate. After repeated filtration and washing to further remove the excess solvent, dry and hot press to obtain lignin imine plastic (lignin content 10 / 13). As can be seen from Figure 1 it that in the infrared spectrum of the imine resin, the characteristic absorption peak of C=O of glutaraldehyde lignin disappears, and the characteristic absorption peak of C=N appears, indicating the occurrence of the Schiff base reaction. The glass transition temperature of the obtained imine plastic is 112 °C ( Figure 2 ), the breaking strength is 49.3 MPa, and the Young's modulus is 1.85 GPa ( Figure 3 ).

[0020] Example 2 (1)Preparation of aldehyde lignin: Add 15 g of air-dried wood chips (<20 mesh) and 170 ml of dioxane solvent into a round-bottom flask, then add 18 ml of glyoxal and 6.3 ml of hydrochloric acid solution (37 wt%). React at 80 °C for 5 h. After the reaction, filter, wash the residue with 1,4-dioxane until the filtrate is colorless. Then add solid NaHCO3 to the washed filtrate to adjust the pH to about 3, and continue to add a large amount of deionized water to precipitate lignin. Wash with water repeatedly until neutral to obtain glyoxal-modified lignin molecules.

[0021] (2)Preparation of imine plastic: Weigh 15 g of the above glyoxal-modified lignin and dissolve it in 150 mL of 1,4-dioxane. Then add 5 g of polyetheramine-400 (polypropylene glycol bis(2-aminopropyl ether), molecular weight 400). React at 80 °C for 2 h. Precipitate the resulting mixture in a large amount of water to form a precipitate. After repeated filtration and washing to further remove the excess solvent, dry and hot-press to obtain lignin-based imine plastic (lignin content 15 / 20). The glass transition temperature of the obtained imine plastic is 102 °C, the breaking strength is 37.6 MPa, and the Young's modulus is 1.21 GPa.

[0022] Example 3 (1)Preparation of aldehyde lignin: Add 15 g of air-dried wood chips (<20 mesh) and 170 ml of dioxane solvent into a round-bottom flask, then add 17 g of terephthalaldehyde and 6.3 ml of hydrochloric acid solution (37 wt%). React at 80 °C for 5 h. After the reaction, filter, wash the residue with 1,4-dioxane until the filtrate is colorless. Then add solid NaHCO3 to the washed filtrate to adjust the pH to about 3, and continue to add a large amount of deionized water to precipitate lignin. Wash with water repeatedly until neutral to obtain terephthalaldehyde-modified lignin molecules.

[0023] (2)Preparation of imine plastic: Weigh 8 g of the above terephthalaldehyde-modified lignin and dissolve it in dimethyl sulfoxide. Then add 8 g of terminal polyetheramine-2000 (polypropylene glycol bis(2-aminopropyl ether), molecular weight 2000). React at 80 °C for 2 h. Precipitate the resulting mixture in a large amount of water to form a precipitate. After repeated filtration and washing to further remove the excess solvent, dry and hot-press to obtain lignin-based imine plastic (lignin content 8 / 16). The glass transition temperature of the obtained imine plastic is 88 °C, the breaking strength is 40.8 MPa, and the Young's modulus is 0.98 GPa.

[0024] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. A preparation method of an acetal lignin-based imine resin, characterized in that: Specifically, it includes the following steps: (1) Preparation of aldehyde lignin: Sawdust, solvent, dialdehyde compound, and hydrochloric acid solution are mixed and reacted at 80 °C for 5 h. After filtration, the residue is washed until the filtrate is colorless. Then, the pH of the washed filtrate is adjusted, and finally, deionized water is added for precipitation to obtain lignin. After washing with water, aldehyde-modified lignin is obtained; (2) Preparation of imine plastic: The aldehyde lignin obtained in step (1) is first dissolved in a solvent, and then polyetheramine is added and reacted at 80 °C for 2 h. The obtained mixture is precipitated in water, and after repeated extraction, filtration, washing, drying, and hot pressing, lignin-based imine plastic can be obtained.

2. The preparation method according to claim 1, characterized in that: In step (1), the solvent is dioxane, and the mass fraction of the hydrochloric acid solution is 37 wt%.

3. The preparation method according to claim 1, characterized in that: In step (1), the dosage ratio of sawdust, dialdehyde compound, and hydrochloric acid is 15 g: (0.1 - 0.2) mol: (6 - 8) mL.

4. The preparation method according to claim 1, characterized in that: In step (1), the dialdehyde compound is any one of glyoxal, glutaraldehyde, and terephthalaldehyde.

5. The preparation method according to claim 1, wherein: In step (1), NaHCO3 is used to adjust the pH to 2 - 4.

6. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of aldehyde lignin to polyetheramine is 4:1 - 1:

1. The polyetheramine is one of terminal amine polypropylene glycol trimethylolpropane ether, polypropylene glycol bis(2-aminopropyl ether), and polypropylene glycol bis(2-aminopropyl ether); the solvent is dimethyl sulfoxide or 1,4-dioxane.

7. Acetal lignin-based imine resin prepared by the preparation method according to any one of claims 1 - 6.

8. The acetal lignin-based imine resin according to claim 7, characterized in that: The glass transition temperature of the acetal lignin-based imine resin is 70 - 130 °C.

9. The acetal lignin-based imine resin according to claim 7, characterized in that: The lignin content in the acetal lignin-based imine resin is 50 - 80%.

10. The acetal lignin-based imine resin according to claim 7, characterized in that: The mechanical properties of the acetal lignin-based imine resin are 37 - 50 MPa.

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