Preparation method and application of lignin-based ionic liquid

Abstract

The application discloses a lignin-based ionic liquid preparation method and application thereof. The lignin-based ionic liquid is prepared from raw materials including the following components in mass fraction: lignin 1-100 parts, imidazole and imidazole derivatives 1-100 parts, and solvent 0.01-2000 parts. The application further provides a lignin ionic liquid / natural rubber composite material prepared from raw materials including the following components in mass fraction: natural rubber 100 parts, lignin-based ionic liquid 1-100 parts, elemental sulfur 0.1-1 part, and vulcanization aid 0-12 parts. The application improves the dispersibility and compatibility of lignin in natural rubber by preparing lignin into lignin-based ionic liquid, and enhances the mechanical properties of the composite material. In addition, the application not only significantly reduces the production cost of natural rubber, but also promotes the green production of natural rubber.

Description

Technical Field

[0001] This invention belongs to the field of rubber composite materials technology, specifically relating to a method for preparing lignin-based ionic liquids and their applications. Background Technology

[0002] Natural rubber elastomers are bio-based polymers extracted from the Brazilian rubber tree. Due to their high elasticity, high strength, high impact resistance, and excellent biocompatibility, they are widely used in aviation tires, engineering tires, and medical and health fields, making them an important industrial raw material and strategic resource. However, natural rubber itself has poor mechanical properties and cannot be directly applied industrially. Large amounts of reinforcing agents (usually carbon black) are needed to improve its physical and mechanical properties. Furthermore, natural rubber has poor resistance to thermo-oxidative aging and UV aging, requiring the addition of small-molecule antioxidants, such as hindered phenols and hindered amines. However, small molecules are toxic and easily migrate and leach from the natural rubber matrix, causing harm to the environment and human health. Therefore, developing a green and inexpensive reinforcing agent and antioxidant is of significant economic and environmental importance to the natural rubber industry.

[0003] Lignin is the second largest biomass resource after cellulose. Globally, over 50 million tons of industrial lignin byproducts are generated annually from pulp and paper production and ethanol production from cellulose fermentation. More than 95% of this industrial lignin is used as low-value fuel or directly discharged as waste. Therefore, finding high-value utilization pathways for lignin has become an increasingly important focus for researchers. Lignin is a rigid natural polymer primarily composed of phenylpropane as its basic structural unit, condensed through ether and carbon-carbon bonds. Its molecular structure also contains numerous reactive functional groups, such as phenolic hydroxyl and carboxyl groups. Figure 1 These functional groups (phenolic hydroxyl groups) give it excellent anti-aging properties [Environmental Chemistry Letters, 2023, 21, 2171–2197]. If lignin is used in natural rubber, it can replace carbon black to reinforce natural rubber while reducing the amount of anti-aging agents used in natural rubber.

[0004] However, due to the presence of oxygen-containing functional groups, lignin is prone to agglomeration in natural rubber, and the interfacial forces between polar lignin and non-polar natural rubber are weak. Poor dispersibility and poor compatibility make it difficult for lignin to exert its reinforcing and anti-aging properties in natural rubber. Although there have been many research reports on the preparation of composite materials by blending lignin with rubber at home and abroad, most of the prepared composite materials have poor performance, and the lignin modification process is cumbersome and not conducive to industrial production and application. For example, Bahl et al. used lignin sulfonate to fill styrene-butadiene rubber and found that the polar lignin particles agglomerated seriously in the rubber matrix, which not only reduced the crosslinking density of the rubber, making the reinforcing effect of lignin on non-polar styrene-butadiene rubber not obvious, but also prolonged the curing time of the rubber [Journal of Applied Polymer Science, 2014, 131(7): 1.]; Intapun et al. added classon lignin prepared by high concentration of sulfuric acid (72 wt%) to non-polar natural rubber through a room temperature solid mixing process to enhance its mechanical properties. Studies have shown that when the amount of lignin in the Clarison lignin filler increases to 15 parts, lignin not only exhibits significant agglomeration between natural rubber matrices but also significant phase separation, resulting in a decrease in tensile strength to below 17 MPa; when the filler amount increases to 20 parts, the tensile strength drops sharply to below 14 MPa [Polymers, 2021, 13(7): 1109.]. Therefore, how to simultaneously solve the problems of lignin dispersion and compatibility in natural rubber matrices is the key to preparing high-strength lignin / natural rubber composites. Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide lignin-based ionic liquid materials. By utilizing lignin-based ionic liquids to disrupt the aggregation tendency of lignin particles, and subsequently blending the lignin-based ionic liquid with natural rubber to prepare a composite material, the dispersibility and compatibility of lignin in natural rubber are enhanced, improving the mechanical and anti-aging properties of the composite material. This allows for the substitution of carbon black and anti-aging agents, thereby reducing the production cost of natural rubber and promoting its green production. Another objective of this invention is to provide a method for preparing the aforementioned lignin-based ionic liquid / natural rubber composite material.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a lignin-based ionic liquid.

[0007] The lignin-based ionic liquid is made from raw materials comprising the following components in parts by mass: Lignin 1-100 parts 1-100 parts of imidazole and imidazole derivatives Solvent: 0.01~2000 parts.

[0008] In some embodiments of the present invention, the lignin-based ionic liquid is made from raw materials comprising the following components in parts by mass: Lignin 10-40 parts 2-20 parts of imidazole and imidazole derivatives Solvent: 30-500 parts.

[0009] In some embodiments of the present invention, the lignin-based ionic liquid is made from raw materials comprising the following components in parts by mass: 10 parts lignin 2-10 parts of imidazole and imidazole derivatives Solvent 36-60 parts.

[0010] In some embodiments of the present invention, the lignin may be alkali lignin, a byproduct of alkaline pulping in the papermaking industry, or enzymatically hydrolyzed lignin extracted from lignocellulose by fermentation with ethanol, or organic solvent lignin extracted from lignocellulose by organic solvent method, or low molecular weight lignin (Mw: 700-2000) further extracted from the above lignin by ethanol, ethyl acetate or acetone, etc.

[0011] In some embodiments of the present invention, the imidazole and imidazole derivatives are substances that can react with lignin to generate ionic liquids.

[0012] In some embodiments of the present invention, the imidazole and imidazole derivatives may be imidazole, hydroxyethyl imidazole, 1,2-dimethylimidazolium, N-vinylimidazolium, 1-imidazolium acetic acid, 2-amino-1-methylimidazolium, 2-(methylthio)-1H-imidazolium, benzimidazole, histidine and other derivatives containing an imidazole ring.

[0013] In a specific embodiment of the present invention, the imidazole and imidazole derivatives are 1,2-dimethylimidazolium.

[0014] In some embodiments of the present invention, the solvent is a solvent capable of dissolving lignin and imidazole and imidazole derivatives, selected from at least one of the following: chloroform, dichloromethane, dimethyl sulfoxide, tetrahydrofuran, toluene, methanol, ethanol, N,N-dimethylformamide, etc.

[0015] Secondly, the present invention provides a method for preparing the lignin-based ionic liquid described in the first aspect.

[0016] The method for preparing the lignin-based ionic liquid includes the following steps: mixing the raw materials for preparing the lignin-based ionic liquid in a certain proportion and reacting them to obtain the liquid.

[0017] In some embodiments of the present invention, the reaction temperature is in the range of 25-180 °C.

[0018] In some embodiments of the present invention, the reaction temperature is room temperature (25-30°C), 60°C, 80°C, 100°C, or 180°C.

[0019] In some embodiments of the present invention, the reaction time is 2-24 hours.

[0020] In some embodiments of the present invention, the method further includes the following step: after the reaction is completed, the reaction system is dried until the organic solvent is completely evaporated.

[0021] In some embodiments of the present invention, the drying temperature may be 40 °C.

[0022] Thirdly, the present invention provides a lignin ionic liquid / natural rubber composite material.

[0023] The lignin ionic liquid / natural rubber composite material provided by this invention is made from raw materials comprising the following components in parts by weight: 100 parts natural rubber 1-100 parts of lignin-based ionic liquid Elemental sulfur 0.1-5 parts Vulcanizing aid: 0-12 parts.

[0024] In some embodiments of the present invention, the lignin ionic liquid / natural rubber composite material is made from raw materials comprising the following components in parts by mass: 100 parts natural rubber 10-60 parts of lignin-based ionic liquid 2-4 parts of elemental sulfur Vulcanizing aid 5-10 parts.

[0025] In a specific embodiment of the present invention, the lignin ionic liquid / natural rubber composite material is made from raw materials comprising the following components in parts by mass: 100 parts natural rubber 40 parts of lignin-based ionic liquid 2 parts of elemental sulfur Vulcanizing aid 8 parts.

[0026] In some embodiments of the present invention, the natural rubber is unmodified natural rubber dry rubber or epoxidized natural rubber dry rubber (epoxy degree is 10%-50%).

[0027] In a specific embodiment of the present invention, the natural rubber is mainly composed of cis-1,4-polyisoprene and contains a small amount of non-rubber substances, such as proteins and phospholipids, or some cis-isoprene is oxidized into epoxy groups.

[0028] In some embodiments of the present invention, the vulcanizing aid is selected from one or a mixture of several of N-tert-butyl-2-benzothiazole sulfenamide, zinc oxide, and stearic acid.

[0029] In some embodiments of the present invention, the vulcanization aid is a mixture of N-tert-butyl-2-benzothiazole sulfenamide (accelerator NS), zinc oxide, and stearic acid.

[0030] In some embodiments of the present invention, the mass ratio of sulfur, N-tert-butyl-2-benzothiazole sulfenamide, zinc oxide and stearic acid in the mixture of elemental sulfur, N-tert-butyl-2-benzothiazole sulfenamide, zinc oxide and stearic acid is (1-3):(0.5-2):(3-5):(1-3), preferably (1.5-2.5):(0.7-1.5):(4-5):(1.5-2).

[0031] In a specific embodiment of the present invention, the mass ratio of sulfur, N-tert-butyl-2-benzothiazole sulfenamide, zinc oxide and stearic acid in the mixture of elemental sulfur, N-tert-butyl-2-benzothiazole sulfenamide, zinc oxide and stearic acid is 2:1:5:2.

[0032] Fourthly, the present invention provides a method for preparing the lignin ionic liquid / natural rubber composite material described in the third aspect.

[0033] The method for preparing lignin ionic liquid / natural rubber composite material provided by the present invention includes the following steps: Natural rubber is mixed at 25~110 ℃ for 1~20 min, then lignin ionic liquid, elemental sulfur and vulcanization aids are added and mixed for 5~20 min; the mixture is discharged, pressed into sheets, cured and vulcanized to obtain the lignin ionic liquid / natural rubber composite material.

[0034] In some embodiments of the present invention, the mixing is carried out in a mixer well known in the art.

[0035] In some embodiments of the present invention, the tableting is performed in a mixer well known in the art.

[0036] In some embodiments of the present invention, the vulcanization molding is performed in a flat vulcanizing machine well known in the art.

[0037] In some embodiments of the present invention, the curing time can be adjusted as needed, such as 24 hours.

[0038] In some embodiments of the present invention, the vulcanization molding conditions are vulcanization at 140~180℃ and 10~20 MPa for 10~120 min.

[0039] In a specific embodiment of the present invention, the vulcanization molding conditions are vulcanization at 145 °C and 15 MPa for 20 min.

[0040] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The lignin used in this invention has a large number of polar oxygen-containing functional groups such as hydroxyl and carboxyl groups, which can react with the imidazole ring to form imidazole onium salt, thereby liquefying the lignin and improving the dispersibility and compatibility of lignin in natural rubber.

[0041] 2. The lignin-based ionic liquid described in this invention, as a rubber reinforcing agent, can replace carbon black, reducing costs and carbon footprint. Its polyphenol structure endows it with excellent heat resistance, aging resistance, and UV resistance, improving tire life. The raw materials are inexpensive, non-toxic, renewable, biodegradable, and widely available. Attached Figure Description

[0042] Figure 1 Infrared spectra of lignin and lignin-based ionic liquids; Figure 2 X-ray photoelectron spectroscopy (nitrogen element) of imidazole and lignin-based ionic liquids; Figure 3 This is a scanning electron microscope image of the NR / lignin-based ionic liquid composite material. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0044] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0045] In the following examples, the parts of raw materials refer to parts by mass. The lignin used in the following examples is alkali lignin, a byproduct of industrial alkali pulping.

[0046] Example 1 By mass, lignin and 1,2-dimethylimidazole were added to dichloromethane at room temperature and reacted. The mass parts of lignin, 1,2-dimethylimidazole and dichloromethane were 10 parts, 2 parts and 36 parts respectively. After the reaction was complete (4 hours after reaction), the mixture was placed in a vacuum oven and dried at 40 °C for 20 hours until the organic solvent was completely evaporated, thus obtaining the lignin-based ionic liquid.

[0047] 100 parts of dry natural rubber were added sequentially to a mixer and mixed at 25 °C for 3 min. Then, 40 parts of lignin-based ionic liquid, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid were added and mixed for 15 min before being discharged. The material was then pressed into sheets using a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 °C and 15 MPa for 20 min to obtain the lignin-based ionic liquid / natural rubber composite material.

[0048] Example 2 By mass, lignin and 1,2-dimethylimidazole were added to dichloromethane at room temperature and reacted. The mass parts of lignin, 1,2-dimethylimidazole and dichloromethane were 10 parts, 4 parts and 42 parts respectively. After the reaction was complete, the mixture was placed in a vacuum oven and dried at 40 °C for 20 h until the organic solvent was completely evaporated, thus obtaining a lignin-based ionic liquid.

[0049] 100 parts of dry natural rubber were added sequentially to a mixer and mixed at 25 °C for 3 min. Then, 40 parts of lignin-based ionic liquid, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid were added and mixed for 15 min before discharge. The material was then pressed into sheets using a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 °C and 15 MPa for 20 min to obtain the lignin-based ionic liquid / natural rubber composite material.

[0050] Example 3 By mass, lignin and 1,2-dimethylimidazole were added to dichloromethane at room temperature and reacted. The mass parts of lignin, 1,2-dimethylimidazole and dichloromethane were 10 parts, 6 parts and 48 parts respectively. After the reaction was complete, the mixture was placed in a vacuum oven and dried at 40 °C for 20 h until the organic solvent was completely evaporated, thus obtaining the lignin-based ionic liquid.

[0051] 100 parts of dry natural rubber were added sequentially to a mixer and mixed at 25 °C for 3 min. Then, 40 parts of lignin-based ionic liquid, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid were added and mixed for 15 min before being discharged. The material was then pressed into sheets using a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 °C and 15 MPa for 20 min to obtain the lignin-based ionic liquid / natural rubber composite material.

[0052] Example 4 By mass, lignin and 1,2-dimethylimidazole were added to dichloromethane at room temperature and reacted. The mass parts of lignin, 1,2-dimethylimidazole and dichloromethane were 10 parts, 8 parts and 54 parts respectively. After the reaction was complete, the mixture was placed in a vacuum oven and dried at 40 °C for 20 h until the organic solvent was completely evaporated, thus obtaining the lignin-based ionic liquid.

[0053] 100 parts of dry natural rubber were added sequentially to a mixer and mixed at 25 °C for 3 min. Then, 40 parts of lignin-based ionic liquid, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid were added and mixed for 15 min before being discharged. The material was then pressed into sheets using a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 °C and 15 MPa for 20 min to obtain the lignin-based ionic liquid / natural rubber composite material.

[0054] Example 5 By mass, lignin and 1,2-dimethylimidazole were added to dichloromethane at room temperature and reacted. The mass parts of lignin, 1,2-dimethylimidazole and dichloromethane were 10 parts, 10 parts and 60 parts respectively. After the reaction was complete, the mixture was placed in a vacuum oven and dried at 40 °C for 20 h until the organic solvent was completely evaporated, thus obtaining the lignin-based ionic liquid.

[0055] 100 parts of dry natural rubber were added sequentially to a mixer and mixed at 25 °C for 3 min. Then, 40 parts of lignin-based ionic liquid, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid were added and mixed for 15 min before being discharged. The material was then pressed into sheets using a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 °C and 15 MPa for 20 min to obtain the lignin-based ionic liquid / natural rubber composite material.

[0056] Example 6 By mass, lignin and 1,2-dimethylimidazole were added to chloroform at 80°C and reacted. The mass parts of lignin, 1,2-dimethylimidazole and chloroform were 10 parts, 4 parts and 42 parts respectively. After the reaction was complete, the mixture was placed in a vacuum oven and dried at 40°C for 20 hours until the organic solvent was completely evaporated, thus obtaining the lignin-based ionic liquid.

[0057] 100 parts of dry natural rubber were added sequentially to a mixer and mixed at 25 °C for 3 min. Then, 40 parts of lignin-based ionic liquid, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid were added and mixed for 15 min before being discharged. The material was then pressed into sheets using a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 °C and 15 MPa for 20 min to obtain the lignin-based ionic liquid / natural rubber composite material.

[0058] Example 7 By mass, lignin and 1,2-dimethylimidazole were added to dimethyl sulfoxide at 180°C and reacted. The mass parts of lignin, 1,2-dimethylimidazole and dimethyl sulfoxide were 10 parts, 4 parts and 42 parts respectively. After the reaction was complete, the mixture was placed in a vacuum oven and dried at 40°C for 20 hours until the organic solvent was completely evaporated, thus obtaining the lignin-based ionic liquid.

[0059] 100 parts of dry natural rubber were added sequentially to a mixer and mixed at 25 °C for 3 min. Then, 40 parts of lignin-based ionic liquid, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid were added and mixed for 15 min before being discharged. The material was then pressed into sheets using a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 °C and 15 MPa for 20 min to obtain the lignin-based ionic liquid / natural rubber composite material.

[0060] Example 8 By mass, lignin and 1,2-dimethylimidazole were added to tetrahydrofuran at 60°C and reacted. The mass parts of lignin, 1,2-dimethylimidazole and tetrahydrofuran were 10 parts, 4 parts and 42 parts respectively. After the reaction was complete, the mixture was placed in a vacuum oven and dried at 40°C for 20 hours until the organic solvent was completely evaporated, thus obtaining the lignin-based ionic liquid.

[0061] 100 parts of dry natural rubber were added sequentially to a mixer and mixed at 25 °C for 3 min. Then, 40 parts of lignin-based ionic liquid, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid were added and mixed for 15 min before being discharged. The material was then pressed into sheets using a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 °C and 15 MPa for 20 min to obtain the lignin-based ionic liquid / natural rubber composite material.

[0062] Example 9 By mass, lignin and 1,2-dimethylimidazole were added to toluene at 100°C and reacted. The mass parts of lignin, 1,2-dimethylimidazole and toluene were 10 parts, 4 parts and 42 parts respectively. After the reaction was complete, the mixture was placed in a vacuum oven and dried at 40°C for 20 hours until the organic solvent was completely evaporated, thus obtaining the lignin-based ionic liquid.

[0063] 100 parts of dry natural rubber were added sequentially to a mixer and mixed at 25 °C for 3 min. Then, 40 parts of lignin-based ionic liquid, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid were added and mixed for 15 min before being discharged. The material was then pressed into sheets using a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 °C and 15 MPa for 20 min to obtain the lignin-based ionic liquid / natural rubber composite material.

[0064] Example 10 By mass, lignin and 1,2-dimethylimidazole were added to ethanol at 80°C and reacted. The mass parts of lignin, 1,2-dimethylimidazole and tetrahydrofuran were 10 parts, 4 parts and 42 parts respectively. After the reaction was complete, the mixture was placed in a vacuum oven and dried at 40°C for 20 hours until the organic solvent was completely evaporated, thus obtaining the lignin-based ionic liquid.

[0065] 100 parts of dry natural rubber were added sequentially to a mixer and mixed at 25 °C for 3 min. Then, 40 parts of lignin-based ionic liquid, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid were added and mixed for 15 min before being discharged. The material was then pressed into sheets using a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 °C and 15 MPa for 20 min to obtain the lignin-based ionic liquid / natural rubber composite material.

[0066] Example 11 By mass, lignin and 1,2-dimethylimidazole were added to dichloromethane at room temperature and reacted. The mass parts of lignin, 1,2-dimethylimidazole and dichloromethane were 10 parts, 4 parts and 42 parts respectively. After the reaction was complete, the mixture was placed in a vacuum oven and dried at 40 °C for 20 h until the organic solvent was completely evaporated, thus obtaining a lignin-based ionic liquid.

[0067] 100 parts of dry natural rubber were added to a mixer in sequence and mixed at 25 ℃ for 3 min; then 40 parts of lignin-based ionic liquid were added and mixed for 15 min before being discharged; the material was then pressed into sheets on a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 ℃ and 15 MPa for 120 min to obtain the lignin-based ionic liquid / natural rubber composite material.

[0068] Comparative Example 1 By weight, under normal temperature conditions, 100 parts of dry natural rubber, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide and 2 parts of stearic acid are added sequentially to an internal mixer and mixed for 15 minutes before being discharged. The material is then pressed into sheets on a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 ℃ and 15 MPa for 20 minutes to obtain a natural rubber composite material.

[0069] Comparative Example 2 By weight, under normal temperature conditions, 100 parts of dry natural rubber, 40 parts of lignin, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide and 2 parts of stearic acid are added sequentially to an internal mixer and mixed for 15 minutes before being discharged. The material is then pressed into sheets on a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145℃ and 15 MPa for 20 minutes to obtain a lignin-based / natural rubber composite material.

[0070] Comparative Example 3 By weight, under normal temperature conditions, 100 parts of dry natural rubber, 40 parts of 1,2-dimethylimidazole, 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid are added sequentially to an internal mixer and mixed for 15 minutes before being discharged. The material is then pressed into sheets using a two-roll mill and finally placed into a flat vulcanizing mill and vulcanized at 145 ℃ and 15 MPa for 20 minutes to obtain a natural rubber composite material.

[0071] Comparative Example 4 By weight, at room temperature, 100 parts of dry natural rubber, 40 parts of a mixture of lignin and 1,2-dimethylimidazole (mass ratio 1:0.4), 2 parts of sulfur, 1 part of N-tert-butyl-2-benzothiazole sulfenamide, 5 parts of zinc oxide, and 2 parts of stearic acid were sequentially added to an internal mixer and mixed for 15 minutes before being discharged. The material was then sheeted on a two-roll mill and finally placed in a flat vulcanizing mill and vulcanized at 145 ℃ and 15 MPa for 20 minutes. Natural rubber composite materials can then be obtained.

[0072] The product from the example was made into a specimen conforming to the GB / T 528-2009 standard, and the tensile strength, tensile strength at break and other mechanical properties were tested using an MTS universal testing machine. The results are shown in Table 1.

[0073] Table 1 Tensile property testing of lignin-based ionic liquid / natural rubber composites

[0074] As shown in Figure 1, lignin is present at 1704 cm⁻¹ -1 The infrared absorption peak at this point is a carboxyl vibration absorption peak. Once lignin reacts with imidazole, the carboxyl absorption peak disappears, indicating that the carboxyl group in lignin has undergone a chemical reaction with the imidazole. As shown in Figure 2, compared with imidazole, the N element X-ray photoelectron spectrum of the lignin-based ionic liquid shows a new peak, indicating that the carboxyl group of lignin reacts with the N atom on the imidazole ring to form an onium salt.

[0075] After preparation into composite materials, the tensile strength of the sample with only lignin added (Comparative Example 2, 15.2 MPa) was significantly lower than that of the composite material without filler (Comparative Example 1, 20.3 MPa). This is because lignin is prone to agglomeration and interfacial separation in natural rubber, leading to a deterioration in the material's mechanical properties. In Example 2, after preparing an ionic liquid from lignin and 1,2-dimethylimidazole, the tensile strength of the resulting composite material was significantly increased to 27.5 MPa. This was not only higher than the sample prepared from the original lignin (Comparative Example 2, 15.2 MPa), but also much higher than the control sample of simple blending of the two (Comparative Example 4, 16.8 MPa). This is mainly because the formation of an ionic liquid from lignin and 1,2-dimethylimidazole effectively inhibited the aggregation of lignin itself. Figure 3 (a,c), and the interfacial interaction between liquid lignin ionic liquid and natural rubber is much stronger than that between solid lignin particles and natural rubber. Figure 3 (b,d), thereby significantly enhancing its reinforcing effect on natural rubber.

[0076] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A lignin-based ionic liquid, by weight, made from raw materials comprising the following components: Lignin 1-100 parts 1-100 parts of imidazole and imidazole derivatives Solvent: 0.01~2000 parts.

2. The lignin-based ionic liquid according to claim 1, characterized in that: The lignin is selected from at least one of the following: alkali lignin, enzymatically hydrolyzed lignin, and organic solvent lignin.

3. The lignin-based ionic liquid according to claim 1 or 2, characterized in that: The imidazole and imidazole derivatives mentioned above are substances that can react with lignin to generate ionic liquids; Furthermore, the imidazole and imidazole derivatives are selected from at least one of the following: imidazole, hydroxyethyl imidazole, 1,2-dimethylimidazole, N-vinylimidazole, 1-imidazoleacetic acid, 2-amino-1-methylimidazole, 2-(methylthio)-1H-imidazole, benzimidazole, histidine, and other derivatives containing an imidazole ring.

4. The lignin-based ionic liquid according to any one of claims 1-3, characterized in that: The solvent is a solvent capable of dissolving lignin, imidazole, and imidazole derivatives; Furthermore, the solvent is selected from at least one of the following: chloroform, dichloromethane, dimethyl sulfoxide, tetrahydrofuran, toluene, methanol, ethanol, and N,N-dimethylformamide.

5. A method for preparing the lignin-based ionic liquid according to any one of claims 1-4, comprising the following steps: mixing the raw materials for preparing the lignin-based ionic liquid in a certain proportion and reacting them to obtain the liquid.

6. The preparation method according to claim 5, characterized in that: The reaction temperature is in the range of 25-180 ℃; The reaction time is 2-24 h; The method further includes the following steps: after the reaction is completed, the reaction system is dried until the organic solvent has completely evaporated.

7. A lignin ionic liquid / natural rubber composite material, made from raw materials comprising the following components in parts by weight: 100 parts natural rubber 1-100 parts of lignin-based ionic liquid Elemental sulfur 0.1-5 parts Vulcanizing aid 0-12 parts The lignin-based ionic liquid is the lignin-based ionic liquid according to any one of claims 1-5.

8. The lignin ionic liquid / natural rubber composite material according to claim 7, characterized in that: The natural rubber mentioned is unmodified natural rubber dry rubber or epoxidized natural rubber dry rubber, with an epoxy degree of 10%-50%. The vulcanizing aid is selected from one or a mixture of several of N-tert-butyl-2-benzothiazole sulfenamide, zinc oxide, and stearic acid.

9. A method for preparing the lignin ionic liquid / natural rubber composite material according to claim 7 or 8, comprising the following steps: mixing natural rubber at 25~110 °C for 1~20 min, then adding lignin ionic liquid, elemental sulfur and vulcanization auxiliaries, mixing for 5~20 min; discharging, pressing into sheets, curing, and vulcanizing to obtain the lignin ionic liquid / natural rubber composite material.

10. The preparation method according to claim 9, characterized in that: The vulcanization molding conditions are vulcanization at 140~180℃ and 10~20 MPa for 10~120 min.

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