Modified lignin, preparation method thereof, rubber composite material and preparation method and application thereof

Abstract

This invention provides a modified lignin and its preparation method, a rubber composite material and its preparation method, and its applications, relating to the field of rubber materials technology. This invention employs sulfur and oil to synergistically surface-functionalize lignin, significantly enhancing its interfacial compatibility with the rubber matrix. Furthermore, the modified lignin, rich in long carbon chains, can form physical entanglements with rubber, and is also rich in polysulfide bonds, enabling chemical cross-linking with rubber at high temperatures to form a stable three-dimensional network structure, effectively improving the mechanical properties of the rubber material. The modified lignin prepared by this invention can replace 10-50% of carbon black and 10-50% of rubber without reducing rubber performance; it also imparts additional functions such as UV resistance and anti-aging properties to rubber materials. The multi-purpose nature of this modified lignin makes it widely applicable in the field of rubber material preparation.

Description

Technical Field

[0001] This invention relates to the field of rubber materials technology, and in particular to a modified lignin and its preparation method, a rubber composite material and its preparation method and application. Background Technology

[0002] Rubber is a key material in tire manufacturing, and the demand is huge. However, the supply of natural rubber is limited, and the production of synthetic rubber is highly dependent on petroleum-based raw materials, facing dual pressures from resources and the environment. In addition, carbon black is usually added as a reinforcing agent in the manufacture of rubber products. Although traditional carbon black filler can improve the performance of rubber, it is mainly produced by the incomplete combustion of fossil fuels. In this process, one ton of carbon black emits 2.5 to 3 tons of CO2, along with pollutants such as sulfides and nitrogen oxides, exacerbating the dilemma of sustainable development in the industry.

[0003] Lignin, as a widely available, renewable, and environmentally friendly bio-based material, holds promise as a substitute for carbon black or rubber, thereby reducing the amount of carbon black added to rubber and dependence on natural rubber. The structure of lignin comprises three phenylpropane units: syringyl, guaiacolyl, and p-hydroxyphenyl. These units form a three-dimensional network structure through complex ether and carbon-carbon bonds. The abundant phenolic hydroxyl groups and conjugated double bonds in the lignin molecule contribute to its excellent ultraviolet absorption capacity. Studies have shown that these chromophores can produce strong absorption in the 290–400 nm wavelength range, through π→π... Electron transitions effectively dissipate ultraviolet energy. This natural ultraviolet shielding mechanism also makes lignin an ideal additive for protecting polymer materials from photoaging.

[0004] However, lignin is a polar phenolic polymer with densely distributed polar functional groups such as phenolic hydroxyl groups, alcoholic hydroxyl groups, carboxyl groups, and methoxy groups on its molecular chain. It has strong hydrophilicity and is unevenly mixed in rubber systems. It is very easy to spontaneously aggregate through intermolecular hydrogen bonds and other forces, forming microscopic "defect points". Furthermore, there is no strong bond between lignin particles and rubber molecules, and there is a clear phase interface, which makes it impossible to effectively transfer stress, thus seriously affecting the mechanical properties of rubber materials. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a modified lignin and its preparation method, a rubber composite material and its preparation method, and its application. The modified lignin prepared by this invention exhibits good interfacial compatibility and uniform dispersion in a rubber matrix, ensuring that the rubber material possesses good mechanical properties.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing modified lignin, comprising the following steps: The modified lignin is obtained by mixing lignin, sulfur, and a solid base catalyst and carrying out a first reaction; the solid base catalyst is sodium oleate, sodium acetate, sodium hydroxide, or sodium carbonate. When the solid base catalyst is sodium acetate, sodium hydroxide, or sodium carbonate, the first reaction further includes mixing the resulting reaction product with an oil to carry out a second reaction; the oil has carbon-carbon unsaturated bonds. The temperatures of the first and second reactions are independently 160~220℃.

[0007] Preferably, the mass ratio of lignin to sulfur is 100:(20~220).

[0008] Preferably, the mass ratio of lignin to solid alkali catalyst is 100:(5~100).

[0009] Preferably, the oil includes one or more of unsaturated acids, unsaturated salts, and bio-oils; the mass ratio of lignin used to prepare the reaction product obtained from the first reaction to the mass of the oil is 100:(5~100).

[0010] Preferably, the reaction time for the first reaction is 4 to 24 hours.

[0011] Preferably, the second reaction takes 6 to 24 hours.

[0012] This invention provides modified lignin prepared by the preparation method described in the above technical solution.

[0013] This invention provides a rubber composite material comprising the following raw materials in parts by weight: 100 parts rubber, 1-100 parts reinforcing filler, 1-100 parts modified lignin, 2-20 parts activator, 0-5 parts silane coupling agent, 0-2 parts accelerator, and 1-5 parts vulcanizing agent; wherein the modified lignin is the modified lignin described in the above technical solution.

[0014] This invention provides a method for preparing the rubber composite material described above, comprising the following steps: Rubber is plasticized to obtain plasticized rubber compound; The plasticized rubber compound is mixed with activator, reinforcing filler, accelerator, modified lignin and silane coupling agent in a first-stage compounding process to obtain a first-stage compound. The first-stage compound is mixed with a vulcanizing agent in a second stage to obtain a second-stage compound. The two-stage compound is vulcanized to obtain the rubber composite material.

[0015] This invention provides the application of the rubber composite material described in the above technical solutions or the rubber composite material prepared by the above technical solutions in tires.

[0016] This invention provides a method for preparing modified lignin. The method employs sulfur and oil (sodium oleate, which also acts as the oil when the solid alkaline catalyst is used) to synergistically modify the surface of lignin. Sulfur-containing hydrophobic segments are successfully grafted onto the lignin molecular framework, improving its oleophilicity and significantly enhancing its interfacial compatibility with the rubber matrix and its dispersion uniformity within the rubber matrix. Furthermore, the modified lignin is rich in long carbon chains (due to the introduction of the oil), which can form physical entanglement with rubber. Simultaneously, the modified lignin is rich in polysulfide bonds, which can chemically crosslink with rubber under high-temperature vulcanization conditions, forming a stable three-dimensional network structure and effectively improving the mechanical properties of the rubber material. Using the modified lignin prepared by this invention in rubber materials can replace 10-50% of carbon black without significantly affecting material performance, and can also partially replace rubber, reducing the amount of rubber used. It also imparts additional functions such as UV resistance and anti-aging properties to rubber materials. The multi-purpose nature of the modified lignin prepared by this invention makes it a promising candidate for application in the field of rubber material preparation. Attached Figure Description

[0017] Figure 1 The UV absorption spectrum of the modified lignin prepared in Example 1 is shown. Detailed Implementation

[0018] This invention provides a method for preparing modified lignin, comprising the following steps: The modified lignin is obtained by mixing lignin, sulfur, and a solid base catalyst and carrying out a first reaction; the solid base catalyst is sodium oleate, sodium acetate, sodium hydroxide, or sodium carbonate. When the solid base catalyst is sodium acetate, sodium hydroxide, or sodium carbonate, the first reaction further includes mixing the resulting reaction product with an oil to carry out a second reaction; the oil has carbon-carbon unsaturated bonds. The temperatures of the first and second reactions are independently 160~220℃.

[0019] Unless otherwise specified, all raw materials involved in this invention are commercially available products well known in the art.

[0020] In this invention, lignin, sulfur, and a solid alkali catalyst are mixed to carry out a first reaction to obtain the reaction product.

[0021] In this invention, the lignin, sulfur, and solid alkali catalyst are preferably used in powder form, and can be crushed into powder separately in a high-speed blender. Before crushing, the lignin and sulfur are preferably dried separately, preferably at a temperature of 80°C for 2-8 hours, specifically in an oven. This invention does not have any special requirements for the lignin; any lignin well-known to those skilled in the art can be used. In this embodiment, the lignin is alkali lignin produced by Rizhao Huatai Paper Industry Co., Ltd.

[0022] In this invention, the mass ratio of lignin to sulfur is preferably 100:(20~220), more preferably 100:(30~50), and can be 100:30, 100:33, 100:35, 100:40, 100:45 or 100:50; the mass ratio of lignin to solid alkali catalyst is preferably 100:(5~100), more preferably 100:(20~50), and can be 100:20, 100:30, 100:38, 100:40 or 100:50.

[0023] The present invention does not have any special requirements for the mixing method of the lignin, sulfur and solid alkali catalyst, as long as the components are mixed evenly.

[0024] In this invention, the temperature of the first reaction is preferably 160~220℃, which can be 180, 190 or 200℃, and the time is preferably 4~24h, which can be 5, 10, 12, 15 or 20h; the first reaction is specifically carried out in a closed reaction vessel.

[0025] When the solid base catalyst is sodium oleate, during the first reaction, under the catalysis of sodium oleate, the eight-membered sulfur ring structure opens to form an active sulfur radical, which undergoes electrophilic substitution with the carbons at the ortho and para positions of the phenolic hydroxyl groups in lignin. On the other hand, the double bond of sodium oleate opens at high temperature and undergoes an addition reaction with the polysulfide bond. When the solid base catalyst is sodium acetate, sodium hydroxide, or sodium carbonate, during the first reaction, under the action of the solid base catalyst, the eight-membered sulfur ring structure undergoes ring opening to generate an active sulfur radical. The sulfur radical undergoes electrophilic substitution with the carbons at the ortho and para positions of the phenolic hydroxyl groups in lignin to form sulfurized lignin.

[0026] In this invention, when the solid base catalyst is sodium acetate, sodium hydroxide or sodium carbonate, the first reaction further includes mixing the obtained reaction product with oil to carry out a second reaction, and after the second reaction, the modified lignin is obtained.

[0027] In this invention, the oilseed has carbon-carbon unsaturated bonds. The oilseed preferably includes one or more of unsaturated acids, unsaturated salts, and bio-oils. The unsaturated acid is preferably an unsaturated fatty acid, and the unsaturated fatty acid is preferably oleic acid. The unsaturated salt is preferably sodium unsaturate, and the sodium unsaturate is preferably sodium oleate. The bio-oil is preferably a vegetable oil, and the vegetable oil is preferably soybean oil. In this invention, the mass ratio of lignin to oilseed used in preparing the reaction product obtained from the first reaction is preferably 100:(5~100), more preferably 100:(20~50), and can be 100:20, 100:25, 100:26, 100:27, 100:30, 100:40, or 100:50.

[0028] Preferably, the reaction product (block solid) obtained from the first reaction is crushed, washed with water (to remove unreacted alkali and by-product salts), and dried in sequence, and then blended with oil.

[0029] In this invention, the temperature of the second reaction is 160~220℃, which can be 180, 190 or 200℃, and the time is preferably 6~24h, which can be 6, 10, 12, 15 or 20h. During the second reaction, the unsaturated bonds in the oil are activated into free radicals at high temperature, and the activated free radicals copolymerize with lignin to form a carbon-carbon crosslinked network.

[0030] This invention provides modified lignin prepared by the preparation method described in the above technical solution. In this invention, the modified lignin is an oleophilic lignin modified by grafting sulfur and oil (when the solid base catalyst is sodium oleate, it also acts as the oil).

[0031] This invention provides a rubber composite material comprising the following raw materials in parts by weight: 100 parts rubber, 1-100 parts reinforcing filler, 1-100 parts modified lignin, 2-20 parts activator, 0-5 parts silane coupling agent, 0-2 parts accelerator, and 1-5 parts vulcanizing agent; wherein the modified lignin is the modified lignin described in the above technical solution.

[0032] The raw materials for preparing the rubber composite material provided by the present invention comprise 100 parts by weight. In the present invention, the rubber can be one or more of natural rubber, styrene-butadiene rubber, and cis-butadiene rubber.

[0033] Based on the mass fraction of the rubber, the raw materials for preparing the rubber composite material provided by the present invention include 1 to 100 parts of reinforcing filler, which can be 10, 40, 50, 55, 56, 64, 68, or 80 parts. In the present invention, the reinforcing filler is preferably carbon black.

[0034] Based on the mass fraction of the rubber, the raw materials for preparing the rubber composite material provided by this invention include 1 to 100 parts of modified lignin, which can be 5, 10, 11, 20, 50, or 70 parts. In this invention, the modified lignin is modified with sulfur and oils, which improves its oleophilicity and significantly improves the interfacial compatibility and dispersion uniformity of lignin in the rubber matrix. Furthermore, since lignin contains a large number of phenolic hydroxyl groups, it can effectively improve the anti-aging properties of the rubber material and can also form physical or chemical crosslinking points with rubber molecules to improve its tear strength. The modified lignin of this invention can not only serve as a reinforcing filler to strengthen the three-dimensional network structure of rubber, but also effectively improve the tensile properties and anti-aging properties of the composite material. The modified lignin can also serve as an effective substitute for carbon black, reducing the amount of carbon black used in the rubber material. Lignin itself has a rigid structure. After crosslinking it with oils containing unsaturated bonds, the unsaturated bonds of the oils provide it with flexible long chains. When added to rubber and vulcanized, a three-dimensional crosslinked network structure can be obtained, which is similar in structure to rubber and can be used to partially replace rubber.

[0035] Based on the mass fraction of the rubber, the raw materials for preparing the rubber composite material provided by the present invention include 2 to 20 parts of activator, which can be 5, 8, 9, 10 or 15 parts. The activator is preferably zinc oxide and stearic acid, and the mass ratio of zinc oxide and stearic acid is preferably (1 to 10):(1 to 10), which can be 5:3.

[0036] Based on the mass fraction of the rubber, the raw materials for preparing the rubber composite material provided by this invention include 0 to 5 parts of silane coupling agent, which can be 0.5, 1, or 2 parts. In this invention, the silane coupling agent is preferably Si-69 (chemical name bis-[γ-(triethoxysilyl)propyl]tetrasulfide). In this invention, the silane coupling agent serves as a dispersant for modified lignin.

[0037] Based on the mass fraction of the rubber, the raw materials for preparing the rubber composite material provided by the present invention include 0 to 2 parts of accelerator, which can be 0.5, 0.6, 1, or 1.4 parts. In the present invention, the accelerator is preferably accelerator DM and / or accelerator CZ.

[0038] Based on the mass fraction of the rubber, the raw materials for preparing the rubber composite material provided by the present invention include 1 to 5 parts of a vulcanizing agent, which can be 1, 1.5, 2, 2.4, 2.5, 2.6, or 3 parts. In the present invention, the vulcanizing agent is preferably sulfur.

[0039] This invention provides a method for preparing the rubber composite material described above, comprising the following steps: Rubber is plasticized to obtain plasticized rubber compound; The plasticized rubber compound is mixed with activator, reinforcing filler, accelerator, modified lignin and silane coupling agent in a first-stage compounding process to obtain a first-stage compound. The first-stage compound is mixed with a vulcanizing agent in a second stage to obtain a second-stage compound. The two-stage compound is vulcanized to obtain the rubber composite material.

[0040] This invention uses a dry rubber mixing method to achieve the mixing of various raw materials.

[0041] In this invention, the preferred specific operation of the plasticizing is to put the rubber into a two-roll mill (rotation speed of 30 rpm) and plasticize for 2 to 5 minutes (or 2 to 3 minutes) until it is wrapped around the roll.

[0042] In this invention, the preferred specific operation of the first-stage mixing is as follows: The open mill speed is set to 20-50 rpm (30 rpm is acceptable). An activator, reinforcing filler, accelerator, modified lignin, and silane coupling agent are added to the plasticized rubber compound. During this process, the rubber is continuously cut and formed into triangular bales until uniformly dispersed. After passing through a thin sheet 4-6 times, the roller gap is reduced to 1-3 mm, and the sheet is produced. In this invention, when the mass fraction of the silane coupling agent and accelerator is 0, the addition of the silane coupling agent and accelerator is omitted.

[0043] In this invention, the preferred specific operation of the two-stage mixing is as follows: after the first-stage mixing material is placed at room temperature for 4 to 12 hours (6 or 8 hours), it is put into an open mill, the speed is set to 30 rpm, and after the rolls are wrapped, the vulcanizing agent is slowly added, and after being mixed evenly, the sheet is produced.

[0044] In this invention, the two-stage compound is preferably allowed to stand for 2-8 hours (5 or 6 hours) before vulcanization. In this invention, the vulcanization temperature is preferably 140-160°C, and the time is preferably 15-20 minutes; the vulcanization can be carried out in a flat vulcanizing machine.

[0045] This invention provides the application of the rubber composite material described in the above technical solutions or the rubber composite material prepared by the above preparation methods in tires. This invention does not impose any particular requirements on the method of application; methods well-known in the art can be used. The rubber composite material provided by this invention, due to the addition of modified lignin, has the characteristic of low price, and lignin, as a green renewable energy source, can reduce carbon emissions in the rubber industry.

[0046] To further illustrate the present invention, the modified lignin and its preparation method, the rubber composite material and its preparation method and application provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of protection of the present invention.

[0047] In all embodiments, "parts" refers to "parts by weight". The lignin and sulfur were dried at 80°C.

[0048] Example 1 Weigh 22g of alkali lignin powder (Rizhao Huatai Paper Co., Ltd.), 11g of sulfur powder and 4.4g of sodium oleate powder, mix them evenly, and then transfer them into a reaction vessel to react at 180℃ for 12h. After the reaction is completed, crush the product, wash it with water and dry it to obtain modified lignin.

[0049] A raw rubber compound was prepared by blending 34 parts of natural rubber, 34 parts of styrene-butadiene rubber, and 32 parts of butadiene rubber. The raw rubber was then added to a two-roll mill (set to 30 rpm) and masticated for 5 minutes. While maintaining the mill speed at 30 rpm, 5 parts of zinc oxide, 3 parts of stearic acid, 64 parts of carbon black, 5 parts of modified lignin, 0.5 parts of Si-69, and 1.4 parts of accelerator CZ were added to the masticated compound. During this process, the rubber was continuously cut and shaped into triangular loops until evenly dispersed. After passing through a thin mill 6 times, the roll gap was reduced to 2 mm, and the compound was sheeted. After standing at room temperature for 8 hours, a second-stage mixing process was performed. The first-stage mixed compound was fed into a two-roll mill (set to 30 rpm). After the rubber wrapped around the rolls, 2.4 parts of vulcanizing agent were slowly added and mixed evenly. The compound was then sheeted and allowed to stand for 6 hours. Finally, the compound with the added vulcanizing agent was transferred to a flat vulcanizing mill and vulcanized at 160℃ for 20 minutes to obtain a rubber composite material.

[0050] Example 2 Weigh 22g of alkali lignin powder (Rizhao Huatai Paper Co., Ltd.), 11g of sulfur powder and 4.4g of sodium oleate powder, mix them evenly, and then transfer them into a reaction vessel to react at 180℃ for 12h. After the reaction is completed, crush the product, wash it with water and dry it to obtain modified lignin.

[0051] 100 parts of natural rubber raw rubber were added to a two-roll mill (set to 30 rpm) and masticated for 5 minutes. While maintaining the mill speed at 30 rpm, 5 parts of zinc oxide, 3 parts of stearic acid, 40 parts of carbon black, 10 parts of modified lignin, 1 part of Si-69, and 0.6 parts of accelerator CZ were added to the masticated compound. During this process, the rubber was continuously cut and shaped into triangular loops until evenly dispersed. After passing through a thin tube 6 times, the roll gap was reduced to 2 mm, and the compound was sheeted. After standing at room temperature for 8 hours, a second-stage mixing process was performed. The first-stage mixed compound was fed into a two-roll mill, set to 30 rpm. After the rubber wrapped around the rolls, 2.4 parts of vulcanizing agent were slowly added and mixed evenly. The compound was then sheeted and allowed to stand for 6 hours. Finally, the compound with the added vulcanizing agent was transferred to a flat vulcanizing mill and vulcanized at 140℃ for 15 minutes to obtain the rubber composite material.

[0052] Example 3 Weigh 15g of alkali lignin powder (Rizhao Huatai Paper Co., Ltd.), 5g of sulfur powder and 5.7g of sodium acetate powder, mix them evenly, and then transfer them to a reaction vessel and react at 180℃ for 12h. After the reaction is completed, crush the product, wash it with water, dry it, mix it with 4g of soybean oil, and then transfer it to a reaction vessel and react at 180℃ for 6h to obtain modified lignin.

[0053] 100 parts of natural raw rubber were added to a two-roll mill (set to 30 rpm) and masticated for 5 minutes. While maintaining the mill speed at 30 rpm, 5 parts of zinc oxide, 3 parts of stearic acid, 40 parts of carbon black, 10 parts of modified lignin, and 0.6 parts of accelerator CZ were added to the masticated compound. During this process, the rubber was continuously cut and shaped into triangular loops until evenly dispersed. After passing through a thin pass 6 times, the roll gap was reduced to 2 mm, and the compound was sheeted. After standing at room temperature for 8 hours, a second-stage mixing process was performed. The first-stage mixed compound was fed into a two-roll mill, set to 30 rpm. After the rubber wrapped around the rolls, 2.4 parts of vulcanizing agent were slowly added and mixed evenly. The compound was then sheeted and allowed to stand for 6 hours. Finally, the compound with the added vulcanizing agent was transferred to a flat vulcanizing mill and vulcanized at 140℃ for 15 minutes to obtain the rubber composite material.

[0054] Example 4 Weigh 15g of alkali lignin powder (Rizhao Huatai Paper Co., Ltd.), 5g of sulfur powder and 5.7g of sodium acetate powder, mix them evenly, and then transfer them to a reaction vessel and react at 180℃ for 12h. After the reaction is completed, crush the product, wash it with water, dry it, mix it with 4g of soybean oil, and then transfer it to a reaction vessel and react at 180℃ for 6h to obtain modified lignin.

[0055] 90 parts of natural raw rubber were added to a two-roll mill (set to 30 rpm) and masticated for 5 minutes. While maintaining the mill speed at 30 rpm, 5 parts of zinc oxide, 3 parts of stearic acid, 50 parts of carbon black, 10 parts of modified lignin, and 0.6 parts of accelerator CZ were added to the masticated compound. During this process, the rubber was continuously cut and shaped into triangular loops until evenly dispersed. After passing through a thin pass 6 times, the roll gap was reduced to 2 mm, and the compound was sheeted. After standing at room temperature for 8 hours, a second-stage mixing process was performed. The first-stage mixed compound was fed into a two-roll mill, set to 30 rpm. After the rubber wrapped around the rolls, 2.4 parts of vulcanizing agent were slowly added and mixed evenly. The compound was then sheeted and allowed to stand for 6 hours. Finally, the compound with the added vulcanizing agent was transferred to a flat vulcanizing mill and vulcanized at 140℃ for 15 minutes to obtain the rubber composite material.

[0056] Comparative Example 1 A raw rubber compound was prepared by blending 34 parts of natural rubber, 34 parts of styrene-butadiene rubber, and 32 parts of butadiene rubber. The raw rubber was then added to a two-roll mill (set to 30 rpm) and masticated for 5 minutes. While maintaining the mill speed at 30 rpm, 5 parts of zinc oxide, 3 parts of stearic acid, 69 parts of carbon black, and 1.4 parts of accelerator CZ were added to the masticated compound. During this process, the rubber was continuously cut and shaped into triangular loops until evenly dispersed. After passing through a thin mill 6 times, the roll gap was reduced to 2 mm, and the compound was sheeted. After standing at room temperature for 8 hours, a second-stage mixing process was performed. The first-stage mixed compound was fed into a two-roll mill (set to 30 rpm). After the rubber wrapped around the rolls, 2.4 parts of vulcanizing agent were slowly added and mixed evenly. The compound was then sheeted and allowed to stand for 6 hours. Finally, the compound with the added vulcanizing agent was transferred to a flat vulcanizing mill and vulcanized at 160℃ for 20 minutes to obtain a rubber composite material.

[0057] Comparative Example 2 100 parts of natural rubber raw rubber were fed into a two-roll mill (set to 30 rpm) and masticated for 5 minutes. Then, maintaining the mill speed at 30 rpm, 5 parts of zinc oxide, 3 parts of stearic acid, 50 parts of carbon black, and 0.6 parts of accelerator CZ were added sequentially to the masticated compound. During this process, the rubber was continuously cut and shaped into triangular loops until the additives were evenly dispersed. The compound was then passed through a thin pass 6 times, and the mill roll gap was adjusted to 2 mm. The compound was sheeted and allowed to stand at room temperature for 8 hours to complete the first stage of mixing. Next, the first stage of mixed compound was fed into the two-roll mill, set to 30 rpm. After the compound wrapped around the rolls, 2.4 parts of vulcanizing agent were slowly added. After thorough mixing, the compound was sheeted and allowed to stand for 6 hours. Finally, the compound with the added vulcanizing agent was transferred to a flat vulcanizing mill and vulcanized at 140℃ for 15 minutes to obtain the rubber composite material.

[0058] Comparative Example 3 100 parts of natural rubber raw rubber were fed into a two-roll mill (set to 30 rpm) and masticated for 5 minutes. Then, maintaining the mill speed at 30 rpm, 5 parts of zinc oxide, 3 parts of stearic acid, 40 parts of carbon black, 10 parts of alkali lignin (unmodified), and 0.6 parts of accelerator CZ were added sequentially to the masticated compound. During this process, the rubber was continuously tapped and shaped into triangular loops until the additives were evenly dispersed. The compound was then passed through a thin pass 6 times, and the mill roll gap was adjusted to 2 mm before sheeting. The mixture was allowed to stand at room temperature for 8 hours to complete the first stage of mixing. Next, the first stage of mixed rubber was fed into the two-roll mill, set to 30 rpm. After the rubber wrapped around the rolls, 2.4 parts of vulcanizing agent were slowly added. After thorough mixing, the mixture was sheeted and allowed to stand for 6 hours. Finally, the rubber compound with the added vulcanizing agent was transferred to a flat vulcanizing mill and vulcanized at 140℃ for 15 minutes to obtain the rubber composite material.

[0059] Table 1 shows the formulation composition of the rubber composite materials in Examples 1-4 and Comparative Examples 1-3.

[0060] Table 1. Formulation composition (parts by mass) of the rubber composite materials in Examples 1-4 and Comparative Examples 1-3.

[0061] Figure 1 The image shows the UV absorption spectrum of the modified lignin prepared in Example 1. The modified lignin exhibits a strong absorption peak in the 200-400 nm range, demonstrating high absorption intensity for UV light. This effectively consumes UV energy and reduces the aging effect of UV light on rubber.

[0062] The performance of the rubber composite materials prepared in Examples 1-4 and Comparative Examples 1-3 was tested, and the test results are shown in Table 2.

[0063] Table 2. Performance test results of the rubber composite materials prepared in Examples 1-4 and Comparative Examples 1-3.

[0064] The testing method is as follows: The tensile properties test was conducted in accordance with GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber". The tensile rate was 500 mm / min, and the test area was dumbbell-shaped with a length of 20 mm, a width of 4 mm, a thickness of 2 mm, and a total length of 75 mm.

[0065] The Shore hardness test was performed according to GB / T 39693.4-2025 "Determination of hardness of vulcanized rubber or thermoplastic rubber - Part 4: Determination of indentation hardness by Shore hardness tester (Shore hardness)". The sample thickness was ≥6mm and the surface was smooth and flat. The instrument was a truncated cone with a cone angle of 35° and a top plane diameter of 0.79mm±0.03mm. The matching indenter had a diameter of 9mm±0.3mm (used to disperse the test force and avoid local deformation of the sample).

[0066] Comparing the data from Example 1 and Comparative Example 1, it can be seen that after the modified lignin replaces carbon black, the tensile strength of the resulting rubber composite material decreases, but the elongation at break increases, and the basic properties are not significantly different. Comparing the data from Example 2 and Comparative Example 2, it can be seen that after the modified lignin replaces carbon black, the tensile properties of the rubber composite material decrease, but the overall performance is still better. Comparing the data from Example 3 and Comparative Example 3, it can be seen that compared with unmodified lignin, the tensile properties of the rubber composite material obtained by replacing carbon black with modified lignin are significantly improved. Comparing the data from Example 4 and Comparative Example 2, it can be seen that after the modified lignin replaces rubber, its mechanical properties are improved to varying degrees.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing modified lignin, characterized in that, Includes the following steps: The modified lignin is obtained by mixing lignin, sulfur, and a solid base catalyst and carrying out a first reaction; the solid base catalyst is sodium oleate, sodium acetate, sodium hydroxide, or sodium carbonate. When the solid base catalyst is sodium acetate, sodium hydroxide, or sodium carbonate, the first reaction further includes mixing the resulting reaction product with an oil to carry out a second reaction; the oil has carbon-carbon unsaturated bonds. The temperatures of the first and second reactions are independently 160~220℃.

2. The preparation method according to claim 1, characterized in that, The mass ratio of lignin to sulfur is 100:(20~220).

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of lignin to solid alkali catalyst is 100:(5~100).

4. The preparation method according to claim 1, wherein the oil comprises one or more of unsaturated acids, unsaturated salts and bio-oils; the mass ratio of lignin used to prepare the reaction product obtained from the first reaction to the mass of the oil is 100:(5~100).

5. The preparation method according to claim 1, characterized in that, The first reaction takes 4 to 24 hours.

6. The preparation method according to claim 1, characterized in that, The second reaction takes 6 to 24 hours.

7. The modified lignin prepared by the preparation method according to any one of claims 1 to 6.

8. A rubber composite material, characterized in that, The preparation raw materials include the following parts by weight: 100 parts rubber, 1-100 parts reinforcing filler, 1-100 parts modified lignin, 2-20 parts activator, 0-5 parts silane coupling agent, 0-2 parts accelerator, and 1-5 parts vulcanizing agent; wherein the modified lignin is the modified lignin as described in claim 7.

9. The method for preparing the rubber composite material according to claim 8, characterized in that, Includes the following steps: Rubber is plasticized to obtain plasticized rubber compound; The plasticized rubber compound is mixed with activator, reinforcing filler, accelerator, modified lignin and silane coupling agent in a first-stage compounding process to obtain a first-stage compound. The first-stage compound is mixed with a vulcanizing agent in a second stage to obtain a second-stage compound. The two-stage compound is vulcanized to obtain the rubber composite material.

10. The application of the rubber composite material of claim 8 or the rubber composite material prepared by the preparation method of claim 9 in tires.

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