Lignin for rubber additive and preparation method thereof

Abstract

The present application relates to the field of rubber additives, and in particular to a lignin for rubber additives and a preparation method thereof. The preparation method of lignin for rubber additives of the present application uses bamboo as raw material, and through biological decomposition, compression and rubbing separation, purification and modification of lignin, the prepared lignin has a smaller particle size and better compatibility with rubber, forming a chemical bonding effect, and can replace carbon black to reinforce rubber. The preparation method provided by the present application has a simple preparation process, green and environmentally friendly raw materials, and low cost. The prepared modified lignin has a double bond structure and has good compatibility with rubber. As a rubber reinforcing agent, it has a significant reinforcing effect on rubber and can significantly improve the mechanical properties and antioxidant properties of rubber.

Description

Technical Field

[0001] The present application relates to the field of rubber additives, and in particular to lignin for rubber additives and a preparation method thereof. Background Art

[0002] Carbon black is the most commonly used traditional raw material for rubber reinforcement. Fossil fuels are the main raw materials for the production of carbon black. However, fossil energy is gradually being over-consumed, environmental pollution is becoming more and more serious, and the burning of fossil fuels will emit greenhouse gases and pollutants related to environmental degradation and human health hazards. Therefore, there is an urgent need for cleaner, sustainable and environmentally friendly materials to replace carbon black. Natural biomass raw materials have attracted widespread attention due to their wide distribution, abundant resources, low pollution and renewable advantages.

[0003] Lignin is a natural polymer compound with a three-dimensional network structure. Its content in nature is second only to cellulose. However, as a byproduct of the papermaking industry, lignin is usually burned as fuel, resulting in resource waste and environmental pollution. Lignin molecules have a rigid aromatic structure and have the potential to replace carbon black as a rubber reinforcing agent. However, rubbers represented by natural rubber are mostly non-polar polymers, while lignin has polar functional groups such as hydroxyl and carboxyl groups, and has a large particle size. It has poor compatibility and dispersibility in the natural rubber matrix, resulting in poor reinforcement effect of lignin as a rubber reinforcing agent, which limits the application of lignin in rubber reinforcement. Patent CN112831059B mentions that lignin and acetylenic compounds are reacted in an organic solvent to obtain a reaction solution containing modified lignin. Patent CN116333516A mentions a method for preparing a lignin-based nano carbon black: alkali and additives synergistically catalyze and degrade phenolic lignin to obtain an alcohol filtrate containing degraded phenolic lignin, ultrasound synergizes with organic solvent self-assembly to prepare lignin nanoparticles; lignin carbon with aromatic ring organic characteristic structure is prepared by impregnation and nitrogen doping, low-temperature carbon fixation and dehydration; and nitrogen-doped nano carbon black is prepared by heat treatment. The above preparation methods involve organic solvent treatment or high temperature and high pressure treatment, the preparation process is relatively complicated, the risk factor of preparing raw materials is relatively high, the preparation method is costly, easy to cause resource waste and environmentally unfriendly. Summary of the invention

[0004] In view of the existing problems, the present application provides a lignin that can be used as a rubber additive and a preparation method thereof. The preparation method of the present application uses bamboo as a raw material, and through biological decomposition, compression and rubbing separation, purification and modification of lignin, the prepared lignin has a smaller particle size and better compatibility with rubber, forming a chemical bonding effect, and can replace carbon black to reinforce rubber. In addition, the preparation method provided by the present application has a simple preparation process, green and environmentally friendly raw materials, and low cost. The prepared modified lignin has a double bond structure and has good compatibility with rubber. As a rubber reinforcing agent, it has a significant reinforcing effect on rubber and can significantly improve the mechanical properties and antioxidant properties of rubber.

[0005] In the first aspect, the present application provides a method for preparing lignin for rubber additives, using the following technical scheme: A method for preparing lignin for rubber additives comprises the following steps: S1. Select bamboo as raw material and crush it into bamboo powder with particle size of 20-80 mesh; S2, biodegrading the bamboo powder to obtain a fermentation liquid; S3, separating the fermentation liquid by pressing and rubbing to obtain a crude lignin liquid; S4, purifying and separating the crude lignin solution by ultrafiltration membrane technology to obtain a pure lignin solution, and placing the pure lignin solution into a dialysis bag with a molecular weight of 1000Da, and dialyzing it in distilled water for 72-80h; collecting the retentate in the dialysis bag, and then rotary evaporating the retentate to obtain lignin; S5, modifying the lignin obtained in step S4 to obtain lignin for rubber additive.

[0006] By adopting the above technical scheme, step S1: select bamboo as raw material and crush it into bamboo powder with a particle size of 20-80 mesh. The main function of this step is to prepare the raw material so that it is suitable for subsequent biodegradation treatment. Bamboo is a rich biomass resource, containing a large amount of cellulose, hemicellulose and lignin, which are the basic materials for producing lignin. Step S2: biodegradation treatment of bamboo powder to obtain fermentation liquid. This step uses microorganisms (such as Bifidobacterium adolescentis) to perform anaerobic fermentation on bamboo fiber to decompose the cellulose and hemicellulose therein and release lignin. This process not only improves the purity of lignin, but also increases its functional group content, thereby improving the antioxidant properties of lignin. Step S3: The fermentation liquid is separated by pressing and rubbing to obtain a crude lignin liquid. The main purpose of this step is to preliminarily separate lignin from the fermentation liquid and remove other impurities, such as cellulose and hemicellulose residues, for further purification. Step S4: Purify and separate the crude lignin solution using ultrafiltration membrane technology to obtain a pure lignin solution, and put it into a dialysis bag with a molecular weight of 1000da, and dialyze it in distilled water for 72-80 hours. This step further purifies the lignin through ultrafiltration and dialysis technology, removes small molecular impurities, and improves the purity and quality of the lignin. The retentate after dialysis is subjected to rotary evaporation to finally obtain pure lignin. Step S5: Modify the lignin obtained in step S4 to obtain lignin for rubber additives. This step uses a modifier to cause lignin to undergo an ester exchange reaction, giving lignin a double bond structure so that it can form a chemical bond with rubber, thereby significantly improving the mechanical properties and antioxidant properties of the rubber. The entire preparation process uses bamboo as raw material, and through biodegradation, compression and separation, purification and modification, a modified lignin with a double bond structure is finally obtained. This modified lignin has good compatibility with rubber, can replace carbon black to reinforce rubber, and significantly improves the mechanical properties and antioxidant properties of rubber. In addition, the preparation method is simple, low-cost, and the raw materials are green and environmentally friendly, and it has high application prospects.

[0007] Preferably, in step S2, the method for biodegrading bamboo powder comprises the following steps: S31, according to the mass fraction, put 10 parts of bamboo powder into a cooking pot, add 100 parts of distilled water, rotate the cooking pot without heating, mix the bamboo powder and distilled water thoroughly, then heat to 170-180° C., keep warm for 2-3 hours, after the reaction is completed, separate the solid and liquid to obtain a pre-hydrolyzed liquid; S32, according to the mass parts, 1000 parts of the pre-hydrolyzed liquid were added to the reactor, and then 10 parts of casein peptone, 12 parts of beef extract, 5 parts of yeast extract, 20 parts of glucose, 5 parts of anhydrous sodium acetate, 2 parts of diamine hydrogen citrate, 1 part of Tween 80, 2 parts of K2HPO4, 0.2 parts of MgSO4·H2O, 0.05 parts of MnSO4·H2O, 1 part of L-cysteine ​​and 1 part of sodium thioglycolate were added respectively, and stirred evenly to obtain solution A; S33, add OD to solution A 600 =0.6 of Bifidobacterium adolescentis, and then anaerobically fermented in an anaerobic incubator at 37°C for 72-80h; after the anaerobic fermentation, solid-liquid separation was performed by centrifugation to obtain a fermentation liquid.

[0008] By adopting the above technical solution, the biological decomposition treatment in step S2 is the key link of the entire lignin preparation process, and its main purpose is to convert the complex organic matter in the bamboo powder into lignin that is easier to separate and purify through the action of microorganisms. Pre-hydrolysis treatment: First, the bamboo powder is mixed with distilled water and hydrolyzed at high temperature. This step helps to destroy the structure of bamboo fiber and release lignin and other components therein. Preparation of culture medium: Then, the pre-hydrolyzate is mixed with other nutrients (such as casein peptone, beef extract, yeast extract, etc.) to prepare a culture medium suitable for microbial growth. These nutrients provide the necessary carbon source, nitrogen source and other growth factors for subsequent microbial fermentation. Anaerobic fermentation: Then, Bifidobacterium adolescentis inoculated into the above culture medium and fermented for a long time under anaerobic conditions. Bifidobacterium adolescentis a bacterium that can grow in an anaerobic environment and can decompose complex organic matter into simpler compounds through metabolic activities. In this process, lignin is selectively enriched, while other non-lignin components are utilized or converted by microorganisms. Solid-liquid separation: Finally, the fermented liquid is separated from the solid residue by physical methods such as centrifugation to obtain a fermentation liquid rich in lignin. In the entire preparation method, the biological decomposition treatment in step S2 plays a vital role. It not only effectively extracts lignin from bamboo powder, but also improves the purity and functional group content of lignin through the selective metabolism of microorganisms, thereby enhancing its antioxidant properties. In addition, due to the use of environmentally friendly microorganisms such as Bifidobacterium adolescentis, the whole process is greener and more sustainable, which meets the requirements of modern industry for environmental protection and resource recycling.

[0009] Preferably, in step S3, the pressure of the pressing and rubbing separation is 10-15 MPa.

[0010] Preferably, in step S5, the preparation method of modifying lignin comprises, by weight, 100 parts of lignin, 15-20 parts of modifier, 2-4 parts of catalyst, pH adjuster A and pH adjuster B, and 400-450 parts of water.

[0011] By adopting the above technical solution, lignin: as a basic material, providing a modified skeleton structure. Modifier: participates in the transesterification reaction, introduces a double bond structure, and improves compatibility with rubber. Catalyst: accelerates the transesterification reaction and improves the reaction efficiency. pH regulators A and B: adjust the pH value of the reaction system to ensure that the reaction is carried out under optimal conditions. Water: as a solvent, helps the raw materials to mix and react fully. Through the above modification treatment, the prepared lignin can be better compatible with rubber and form an effective bonding effect, thereby significantly improving the mechanical properties and antioxidant properties of the rubber.

[0012] Preferably, the modifier is composed of methyl methacrylate, glycidyl methacrylate and dimethylaminoethyl methacrylate in a mass ratio of 3:4:2-4.

[0013] By adopting the above technical scheme, in the preparation process of lignin for rubber additives, the modifier is composed of methyl methacrylate (MMA), glycidyl methacrylate (GMA) and dimethylaminoethyl methacrylate (DMAEMA), and the mass ratio is 3:4:2-4. These components play an important role in the modification process: Methyl methacrylate (MMA): MMA is an important chemical raw material. It has good polymerization properties and can be copolymerized with other monomers to improve the hardness and weather resistance of the material. Glycidyl methacrylate (GMA): GMA is a multifunctional monomer containing epoxy groups and can react with a variety of polymers to improve the weather resistance, high temperature resistance and bonding properties of the material. Dimethylaminoethyl methacrylate (DMAEMA): DMAEMA contains tertiary amino groups and ester groups, and amino groups can be introduced through ester exchange reactions to improve the crosslinking density and mechanical properties of the material. It also has good water solubility and adhesion, and is suitable for the modification of coatings and adhesives. During the modification process, lignin undergoes an ester exchange reaction with MMA, GMA and DMAEMA, so that the modified lignin has a double bond structure and can form a chemical bond with rubber, thereby significantly improving the mechanical properties and antioxidant properties of the rubber. The different functional groups of MMA, GMA and DMAEMA cooperate with each other to improve the comprehensive performance of the modified lignin through ester exchange reactions and copolymerization. MMA provides hardness and weather resistance, GMA improves weather resistance and adhesion, and DMAEMA increases crosslinking density and mechanical strength. The three work together to make the modified lignin have excellent compatibility and reinforcement effects with rubber. In summary, methyl methacrylate, glycidyl methacrylate and dimethylaminoethyl methacrylate jointly improve the performance of the modified lignin through ester exchange reactions and copolymerization in the process of modifying lignin, making it an efficient rubber reinforcing agent.

[0014] Preferably, the catalyst is potassium hydroxide.

[0015] Preferably, the pH adjuster A is a sodium bicarbonate solution with a mass concentration of 5%; and the pH adjuster B is a hydrochloric acid solution with a mass concentration of 7%.

[0016] Preferably, the preparation method of the modified lignin comprises the following steps: S81, mixing lignin and water according to weight fractions, and emulsifying for 1-2 hours to obtain a lignin emulsion; S82, adding pH regulator A to the lignin emulsion according to the mass fraction, adjusting the pH to 8.5-9.2, to obtain a lignin alkaline emulsion, and then stirring and heating to 110-120° C., keeping the temperature for 5-6 hours, adding a catalyst and a modifier, and reacting at 110-120° C. for 6-8 hours to obtain a pre-product; S83, adding pH regulator B to the pre-product, adjusting the pH of the system to 2-3, and obtaining a modified lignin solution, and finally post-treating the modified lignin solution to obtain lignin for rubber additives.

[0017] By adopting the above technical scheme, the modified lignin is subjected to an ester exchange reaction by using a modifier, so that the modified lignin has a double bond structure and can be bonded with rubber, thereby having good compatibility with rubber and having a significant reinforcing effect when used as a rubber reinforcing agent.

[0018] Preferably, the post-treatment is: using a vacuum pump to filter the modified lignin solution under reduced pressure, then washing with 50-60°C pure water as a washing liquid, and then drying in a 60-70°C vacuum drying oven for 8-10h; wherein the vacuum degree of the reduced pressure filtration is 0.05MPa, and the amount of the washing liquid is 1-2 times the volume of the modified lignin solution.

[0019] In a second aspect, the present application provides a lignin for rubber additive, using the following technical solution: As a general technical concept, the present application also provides the above-mentioned lignin for rubber additive, which is prepared by the above-mentioned preparation method of lignin for rubber additive.

[0020] In summary, the beneficial technical effects of this application are: 1. Environmental protection and cost-effectiveness: The preparation method uses bamboo as raw material, which is a renewable resource and is more environmentally friendly than traditional non-renewable raw materials. In addition, the wide availability and low-cost characteristics of bamboo also make the cost of the entire production process low. 2. Simple process: The preparation process includes steps such as biological decomposition, compression and separation, purification and modification. It is easy to operate and easy to industrialize and mass produce. 3. Performance improvement: The prepared modified lignin has a double bond structure, which enables it to form a chemical bond with rubber, significantly improving the mechanical properties and antioxidant properties of rubber. This modified lignin can effectively replace carbon black as a rubber reinforcing agent, not only improving the physical and mechanical properties of rubber, but also enhancing its aging resistance. 4. Good compatibility: The modified lignin has a smaller particle size and better compatibility with rubber. It can be evenly dispersed in the rubber matrix, thereby improving the overall performance of the composite material. DETAILED DESCRIPTION

[0021] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0022] In the following examples, 1 portion means 1 kg.

[0023] Example 1 A method for preparing lignin for rubber additives comprises the following steps: S1, select bamboo as raw material, and crush it into bamboo powder with particle size of 60 mesh; S2, biodegrading the bamboo powder, comprising the following steps: S31, according to the mass fraction, put 10 parts of bamboo powder into a cooking pot, add 100 parts of distilled water, rotate the cooking pot without heating, mix the bamboo powder and distilled water thoroughly, then heat to 170° C., keep warm for 3 hours, after the reaction is completed, separate the solid and liquid to obtain a pre-hydrolyzed liquid; S32, according to the mass parts, 1000 parts of the pre-hydrolyzed liquid were added to the reactor, and then 10 parts of casein peptone, 12 parts of beef extract, 5 parts of yeast extract, 20 parts of glucose, 5 parts of anhydrous sodium acetate, 2 parts of diamine hydrogen citrate, 1 part of Tween 80, 2 parts of K2HPO4, 0.2 parts of MgSO4·H2O, 0.05 parts of MnSO4·H2O, 1 part of L-cysteine ​​and 1 part of sodium thioglycolate were added respectively, and stirred evenly to obtain solution A; S33, add OD to solution A 600 =0.6 of Bifidobacterium adolescentis, and then anaerobically fermented in an anaerobic incubator at 37°C for 72h; after the anaerobic fermentation, solid-liquid separation was performed by centrifugation to obtain a fermentation liquid.

[0024] S3, separating the fermented liquid by squeezing and kneading, wherein the pressure of squeezing and kneading separation is 10 MPa, to obtain a crude lignin liquid; S4, purifying and separating the crude lignin solution by ultrafiltration membrane technology to obtain a pure lignin solution, and placing the pure lignin solution into a dialysis bag with a molecular weight of 1000Da, and dialyzing it in distilled water for 72 hours; collecting the retentate in the dialysis bag, and then rotary evaporating the retentate to obtain lignin; S5. The lignin prepared in step S4 is modified. The raw materials include, by weight, 100 parts of lignin, 15 parts of a modifier, 2 parts of potassium hydroxide, a sodium bicarbonate solution with a mass concentration of 5%, a hydrochloric acid solution with a mass concentration of 7%, and 400 parts of water. The modifier is composed of methyl methacrylate, glycidyl methacrylate and dimethylaminoethyl methacrylate in a mass ratio of 3:4:2. The preparation method of the modified lignin includes the following steps: S81, mixing lignin and water according to weight fractions, and emulsifying for 1 hour to obtain a lignin emulsion; S82, adding a 5% sodium bicarbonate solution to the lignin emulsion according to the mass fraction, adjusting the pH to 8.5 to obtain a lignin alkaline emulsion, and then stirring and heating to 110° C., keeping the temperature for 6 hours, adding a catalyst and a modifier, and reacting at 110° C. for 8 hours to obtain a pre-product; S83. Add a hydrochloric acid solution with a mass concentration of 7% to the pre-product, adjust the pH of the system to 2, and obtain a modified lignin solution. Finally, the modified lignin solution is post-treated, and the post-treatment is as follows: use a vacuum pump to reduce the pressure and filter the modified lignin solution, then wash it with 50°C pure water as a washing liquid, and then dry it in a vacuum drying oven at 60°C for 10 hours; wherein the vacuum degree of the reduced pressure and filtration is 0.05MPa, and the amount of the washing liquid is 1 times the volume of the modified lignin solution, to obtain lignin for rubber additives.

[0025] Example 2 A method for preparing lignin for rubber additives comprises the following steps: S1, select bamboo as raw material, and crush it into bamboo powder with particle size of 60 mesh; S2, biodegrading the bamboo powder, comprising the following steps: S31, according to the mass fraction, put 10 parts of bamboo powder into a cooking pot, add 100 parts of distilled water, rotate the cooking pot without heating, mix the bamboo powder and distilled water thoroughly, then heat to 180° C., keep warm for 2 hours, after the reaction is completed, separate the solid and liquid to obtain a pre-hydrolyzed liquid; S32, according to the mass parts, 1000 parts of the pre-hydrolyzed liquid were added to the reactor, and then 10 parts of casein peptone, 12 parts of beef extract, 5 parts of yeast extract, 20 parts of glucose, 5 parts of anhydrous sodium acetate, 2 parts of diamine hydrogen citrate, 1 part of Tween 80, 2 parts of K2HPO4, 0.2 parts of MgSO4·H2O, 0.05 parts of MnSO4·H2O, 1 part of L-cysteine ​​and 1 part of sodium thioglycolate were added respectively, and stirred evenly to obtain solution A; S33, add OD to solution A 600=0.6 of Bifidobacterium adolescentis, and then anaerobically fermented in an anaerobic incubator at 37°C for 80 hours; after the anaerobic fermentation, solid-liquid separation was performed by centrifugation to obtain a fermentation liquid.

[0026] S3, separating the fermented liquid by squeezing and kneading, wherein the pressure of squeezing and kneading separation is 15 MPa, to obtain a crude lignin liquid; S4, purifying and separating the crude lignin solution by ultrafiltration membrane technology to obtain a pure lignin solution, and placing the pure lignin solution into a dialysis bag with a molecular weight of 1000Da, and dialyzing it in distilled water for 80 hours; collecting the retentate in the dialysis bag, and then rotary evaporating the retentate to obtain lignin; S5. The lignin prepared in step S4 is modified. The raw materials include, by weight, 100 parts of lignin, 20 parts of a modifier, 4 parts of potassium hydroxide, a sodium bicarbonate solution with a mass concentration of 5%, a hydrochloric acid solution with a mass concentration of 7%, and 450 parts of water. The modifier is composed of methyl methacrylate, glycidyl methacrylate and dimethylaminoethyl methacrylate in a mass ratio of 3:4:4. The preparation method of the modified lignin includes the following steps: S81, mixing lignin and water according to mass fractions, and emulsifying for 2 hours to obtain a lignin emulsion; S82, adding a 5% sodium bicarbonate solution to the lignin emulsion according to the mass fraction, adjusting the pH to 9.2 to obtain a lignin alkaline emulsion, and then stirring and heating to 120° C., keeping the temperature for 5 hours, adding a catalyst and a modifier, and reacting at 120° C. for 6 hours to obtain a pre-product; S83. Add a hydrochloric acid solution with a mass concentration of 7% to the pre-product, adjust the pH of the system to 3, and obtain a modified lignin solution. Finally, the modified lignin solution is post-treated, and the post-treatment is as follows: use a vacuum pump to reduce the pressure and filter the modified lignin solution, then wash it with 60°C pure water as a washing liquid, and then dry it in a vacuum drying oven at 70°C for 8 hours; wherein the vacuum degree of the reduced pressure and filtration is 0.05MPa, and the amount of the washing liquid is twice the volume of the modified lignin solution, to obtain lignin for rubber additives.

[0027] Example 3 A method for preparing lignin for rubber additives comprises the following steps: S1, select bamboo as raw material, and crush it into bamboo powder with particle size of 60 mesh; S2, biodegrading the bamboo powder, comprising the following steps: S31, according to the mass fraction, put 10 parts of bamboo powder into a cooking pot, add 100 parts of distilled water, rotate the cooking pot without heating, mix the bamboo powder and distilled water thoroughly, then heat to 175° C., keep warm for 2.3 hours, after the reaction is completed, separate the solid and liquid to obtain a pre-hydrolyzed liquid; S32, according to the mass parts, 1000 parts of the pre-hydrolyzed liquid were added to the reactor, and then 10 parts of casein peptone, 12 parts of beef extract, 5 parts of yeast extract, 20 parts of glucose, 5 parts of anhydrous sodium acetate, 2 parts of diamine hydrogen citrate, 1 part of Tween 80, 2 parts of K2HPO4, 0.2 parts of MgSO4·H2O, 0.05 parts of MnSO4·H2O, 1 part of L-cysteine ​​and 1 part of sodium thioglycolate were added respectively, and stirred evenly to obtain solution A; S33, add OD to solution A 600 =0.6 of Bifidobacterium adolescentis, and then anaerobically fermented in an anaerobic incubator at 37°C for 75h; after the anaerobic fermentation, solid-liquid separation was performed by centrifugation to obtain a fermentation liquid.

[0028] S3, separating the fermented liquid by squeezing and kneading, wherein the pressure of squeezing and kneading separation is 12 MPa, to obtain a crude lignin liquid; S4, purifying and separating the crude lignin solution by ultrafiltration membrane technology to obtain a pure lignin solution, and placing the pure lignin solution into a dialysis bag with a molecular weight of 1000Da, and dialyzing it in distilled water for 75 hours; collecting the retentate in the dialysis bag, and then rotary evaporating the retentate to obtain lignin; S5. The lignin prepared in step S4 is modified. The raw materials include, by weight, 100 parts of lignin, 17 parts of a modifier, 3 parts of potassium hydroxide, a sodium bicarbonate solution with a mass concentration of 5%, a hydrochloric acid solution with a mass concentration of 7%, and 430 parts of water. The modifier is composed of methyl methacrylate, glycidyl methacrylate and dimethylaminoethyl methacrylate in a mass ratio of 3:4:3. The preparation method of the modified lignin includes the following steps: S81, mixing lignin and water according to mass fractions, and emulsifying for 1.5 hours to obtain a lignin emulsion; S82, adding pH regulator A to the lignin emulsion according to the mass fraction to adjust the pH to 9 to obtain a lignin alkaline emulsion, then stirring and heating to 115° C., keeping the temperature for 5.6 hours, adding a catalyst and a modifier, and reacting at 115° C. for 7 hours to obtain a pre-product; S83. Add pH adjusting agent B to the pre-product, adjust the pH of the system to 2.5, and obtain a modified lignin solution. Finally, the modified lignin solution is post-treated, and the post-treatment is as follows: reduce the pressure and filter the modified lignin solution with a vacuum pump, then wash it with 55°C pure water as a washing liquid, and then dry it in a vacuum drying oven at 65°C for 9 hours; wherein the vacuum degree of the reduced pressure and filtration is 0.05MPa, and the amount of the washing liquid is 1.5 times the volume of the modified lignin solution, to obtain lignin for rubber additives.

[0029] Comparative Example 1 The same as Example 3, except that in step S5, the modifier is methyl methacrylate.

[0030] Comparative Example 2 The same as Example 3, except that in step S5, the modifier is glycidyl methacrylate.

[0031] Comparative Example 3 The same as Example 3, except that in step S5, the modifier is dimethylaminoethyl methacrylate.

[0032] Performance Testing The rubber additive lignin prepared in Example 1, Example 3 and Comparative Examples 1-3 was sampled and applied to the rubber raw material. The rubber formula was, by weight, 100 parts of natural rubber, 45 parts of carbon black, 7 parts of rubber additive lignin, 2 parts of aromatic oil, 2 parts of stearic acid, 3 parts of zinc oxide, 1.5 parts of sulfur, 0.1 parts of scorch retarder CTP, and 1.4 parts of accelerator TMTD. The above raw materials were mixed to obtain the corresponding rubber products, and the following evaluation tests were performed. The test results are shown in Table 1.

[0033] Tensile strength: test method see GB / T 528-2009; Elongation at break: test method see GB / T 528-2009; Tensile strength: test method see GB / T 528-2009; Hardness (Shore A): Test method see GB / T 531.1-2008; Antioxidant effect: Based on the test of rubber oxidation induction time, the longer the rubber oxidation induction time, the better the antioxidant effect.

[0034] Table 1 Performance test Analyzing the data in Table 1, we can see that: 1) The lignin for rubber additives prepared in Examples 1 to 3 has a double bond structure and is highly compatible with rubber. As a rubber reinforcing agent, it has a significant reinforcing effect on rubber and can significantly improve the mechanical properties and antioxidant properties of rubber.

[0035] 2) The performance comparison analysis of the lignin for rubber additives prepared in combination with Example 3 and Comparative Examples 1-3 shows that the modifier is composed of methyl methacrylate, glycidyl methacrylate and dimethylaminoethyl methacrylate in a mass ratio of 3:4:3. During the modification process, lignin undergoes an ester exchange reaction with MMA, GMA and DMAEMA, so that the modified lignin has a double bond structure and can form a chemical bond with the rubber, thereby significantly improving the mechanical properties and antioxidant properties of the rubber. The different functional groups of MMA, GMA and DMAEMA cooperate with each other, and through ester exchange reaction and copolymerization, the performance of the modified lignin is jointly improved, making it an efficient rubber reinforcing agent.

[0036] The above embodiments are only used to explain the technical solutions of the present application rather than to limit them. Although the above embodiments provide a specific description of the present application, relevant technical personnel should understand that the specific implementation methods of the present application can still be modified or replaced by equivalents, and any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing lignin for rubber additives, characterized in that: The following steps are involved: S1. Select bamboo as raw material and crush it into bamboo powder with particle size of 20-80 mesh; S2, biodegrading the bamboo powder to obtain a fermentation liquid; S3, separating the fermentation liquid by pressing and rubbing to obtain a crude lignin liquid; S4, purifying and separating the crude lignin solution by ultrafiltration membrane technology to obtain a pure lignin solution, and then placing the pure lignin solution into a dialysis bag with a molecular weight of 1000Da, and dialyzing it in distilled water for 72-80 hours; collecting the retentate in the dialysis bag, and then rotary evaporating the retentate to obtain lignin; S5, modifying the lignin obtained in step S4 to obtain lignin for rubber additive.

2. The method for preparing lignin for rubber additive according to claim 1, characterized in that: In step S2, the method for biodegrading bamboo powder comprises the following steps: S31, according to the mass fraction, put 10 parts of bamboo powder into a cooking pot, add 100 parts of distilled water, rotate the cooking pot without heating, mix the bamboo powder and distilled water thoroughly, then heat to 170-180° C., keep warm for 2-3 hours, after the reaction is completed, separate the solid and liquid to obtain a pre-hydrolyzed liquid; S32, according to the mass parts, 1000 parts of the pre-hydrolyzed liquid were added to the reactor, and then 10 parts of casein peptone, 12 parts of beef extract, 5 parts of yeast extract, 20 parts of glucose, 5 parts of anhydrous sodium acetate, 2 parts of diamine hydrogen citrate, 1 part of Tween 80, 2 parts of K2HPO4, 0.2 parts of MgSO4·H2O, 0.05 parts of MnSO4·H2O, 1 part of L-cysteine ​​and 1 part of sodium thioglycolate were added respectively, and stirred evenly to obtain solution A; S33, add OD to solution A 600 =0.6 of Bifidobacterium adolescentis, and then anaerobically fermented in an anaerobic incubator at 37°C for 72-80h; after the anaerobic fermentation, solid-liquid separation was performed by centrifugation to obtain the fermentation liquid.

3. The method for preparing lignin for rubber additive according to claim 1, characterized in that: In step S3, the pressure of the pressing and rubbing separation is 10-15 MPa.

4. The method for preparing lignin for rubber additive according to claim 1, characterized in that: In step S5, the preparation method of modifying lignin comprises, by weight, 100 parts of lignin, 15-20 parts of modifier, 2-4 parts of catalyst, pH regulator A and pH regulator B, and 400-450 parts of water.

5. The method for preparing lignin for rubber additive according to claim 4, characterized in that: The modifier is composed of methyl methacrylate, glycidyl methacrylate and dimethylaminoethyl methacrylate in a mass ratio of 3:4:2-4.

6. The method for preparing lignin for rubber additive according to claim 4, characterized in that: The catalyst is potassium hydroxide.

7. The method for preparing lignin for rubber additive according to claim 4, characterized in that: The pH regulator A is a sodium bicarbonate solution with a mass concentration of 5%; the pH regulator B is a hydrochloric acid solution with a mass concentration of 7%.

8. The method for preparing lignin for rubber additive according to claim 4, characterized in that: The preparation method of the modified lignin comprises the following steps: S81, mixing lignin and water according to weight fractions, and emulsifying for 1-2 hours to obtain a lignin emulsion; S82, according to the mass fraction, add pH regulator A to the lignin emulsion, adjust the pH to 8.5-9.2, to obtain a lignin alkaline emulsion, then stir and heat to 110-120 ° C, keep warm for 5-6h, add a catalyst and a modifier, react at 110-120 ° C for 6-8h to obtain a pre-product; S83, adding pH regulator B to the pre-product, adjusting the pH of the system to 2-3, and obtaining a modified lignin solution, and finally post-treating the modified lignin solution to obtain lignin for rubber additives.

9. The method for preparing lignin for rubber additive according to claim 8, characterized in that: The post-treatment is as follows: using a vacuum pump to perform vacuum filtration on the modified lignin solution, then washing with 50-60°C pure water as a washing liquid, and then drying in a 60-70°C vacuum drying oven for 8-10 hours; wherein the vacuum degree of the vacuum filtration is 0.05MPa, and the amount of the washing liquid is 1-2 times the volume of the modified lignin solution.

10. A lignin for rubber additive, characterized in that: The lignin for rubber additive is prepared by the preparation method of lignin for rubber additive according to any one of claims 1 to 9.

Images