A bio-based rubber dispersant and its use in rubber compositions

Abstract

This invention provides a bio-based rubber dispersant and its application in rubber compositions, belonging to the technical field of rubber dispersants. It comprises the following raw materials in parts by weight: 18-26 parts of low molecular weight carboxyl-modified lignin, 3-6 parts of N-cocoyl-1,3-propylenediamine, 40-52 parts of pentaerythritol stearate, and 24-34 parts of plasticizer. This invention can reduce the Mooney viscosity of rubber compositions, improve scorch safety, improve the dispersibility of silica, and enhance the overall mechanical properties of vulcanized rubber.

Description

Technical Field

[0001] This invention relates to the field of rubber dispersant technology, and more specifically to a bio-based rubber dispersant and its application in rubber compositions. Background Technology

[0002] In the tire industry and rubber products sector, large-scale filling with high-specific-surface-area silica (precipitated silica) is a key technological approach to achieving low rolling resistance and high wet skid resistance in green tires. However, the densely packed silanol groups on the surface of silica are prone to severe self-agglomeration during the mixing process due to strong hydrogen bonding. This agglomeration not only causes a sharp increase in Mooney viscosity, increasing energy consumption and equipment load in the mixing process, but also results in low modification efficiency of silane coupling agents, as the silanol groups on the silica surface are masked by their own hydrogen bond network, making it difficult for the coupling agent to fully contact and react. Furthermore, the accumulation of thermal history and premature formation of local active sites can easily lead to early vulcanization, resulting in a significant reduction in scorch time. At the same time, the filler is prone to secondary agglomeration and extremely poor dispersion, ultimately leading to increased hysteresis loss in the vulcanized rubber and a significant decrease in fatigue life and wear resistance.

[0003] Existing technologies have attempted to improve the aforementioned defects by introducing bio-based dispersants such as lignin sulfonates or simple carboxyl-modified lignin. However, due to the large number of polar hydroxyl and carboxyl groups in lignin molecules, they exhibit strong competitive adsorption with the silanol groups of silica during the initial mixing stage. This strong adsorption not only fails to effectively disperse the filler but also exacerbates the aggregation of the filler network. Furthermore, during the subsequent high-temperature vulcanization stage, these conventional bio-based dispersants cannot effectively release their activity to participate in the construction of the cross-linked network, making dynamic control of the entire process impossible.

[0004] Patent application CN103333378A discloses a silica dispersant comprising C8-C22 fatty acids, protective wax, fatty acid esters, inorganic fillers, and antioxidants. This dispersant improves the dispersibility of rubber compounds containing highly active silica and avoids the environmental problems associated with zinc-containing dispersants. While this type of dispersant can reduce compound viscosity and improve processing fluidity during the mixing stage, it primarily relies on lubrication, coating, and physical dispersion. It lacks sufficient ability to provide phased control over the active groups on the silica surface, making it difficult to simultaneously achieve low viscosity, scorch safety, and post-curing interfacial reinforcement in high-silica-filled systems.

[0005] Therefore, there is a need to provide a bio-based rubber dispersant and its application in rubber compositions to solve the problems existing in the prior art. Summary of the Invention

[0006] In view of this, the present invention provides a bio-based rubber dispersant and its application in rubber compositions, which can reduce the Mooney viscosity of rubber compositions, improve scorch safety, improve the dispersibility of silica and enhance the overall mechanical properties of vulcanized rubber.

[0007] To achieve the above objectives, the present invention provides a bio-based rubber dispersant comprising the following raw materials in parts by weight: 18-26 parts of low molecular weight carboxyl-modified lignin, 3-6 parts of N-cocoyl-1,3-propanediamine, 40-52 parts of pentaerythritol stearate, and 24-34 parts of plasticizer; It was prepared using the following method: Step S1: Add alkali lignin to deionized water, adjust the pH, add Co-Mn bimetallic oxide nanocatalyst, ultrasonically disperse, transfer to a reaction vessel, introduce air, heat and stir the reaction, cool down, separate and recover the catalyst, and perform acid precipitation, filtration, washing, drying and pulverizing on the reaction solution to obtain low molecular weight carboxyl modified lignin. Step S2: Mix low molecular weight carboxyl-modified lignin with N-cocoyl-1,3-propanediamine to obtain pretreated lignin; add pentaerythritol stearate and plasticizer to a reaction vessel, heat and stir, add pretreated lignin, heat and stir, granulate to obtain bio-based rubber dispersant.

[0008] Using Co-Mn bimetallic oxide nanocatalysts to oxidize alkali lignin in the air can activate and break the ether bonds in the lignin molecule, and oxidize the phenolic hydroxyl groups and side chain structures, thereby simultaneously reducing the molecular weight and increasing the carboxyl content.

[0009] Low molecular weight carboxyl-modified lignin serves as a bio-based active framework. Its low molecular weight facilitates diffusion and dispersion in the molten continuous phase and rubber matrix. Its high carboxyl content provides active sites for subsequent silica interface anchoring. After N-cocoyl-1,3-propylenediamine forms ion pairs with the carboxyl groups, it enhances the compatibility of lignin with the rubber phase using long-chain alkyl groups. Furthermore, it constructs a thermally reversible masking layer to shield the strongly polar carboxyl groups, preventing premature strong hydrogen bond adsorption between the lignin and silica silanol groups during the low-temperature mixing stage.

[0010] Further, PETS (pentaerythritol stearate) and plasticizers are used to form a low-melting-point lubricating continuous phase, which can quickly soften and provide boundary lubrication at the rubber mixing temperature, thereby reducing internal friction and filler agglomeration resistance in the rubber compound. After pretreated lignin is coated in this continuous phase, it can form pre-dispersed particles that are easy to feed and disperse, so that the dispersant can play a lubricating and viscosity-reducing role in the low-temperature mixing stage, and be demasked by heat and release carboxyl activity in the high-temperature vulcanization stage.

[0011] Preferably, the plasticizer is a mixture of zinc stearate and zinc oleate, wherein the mass ratio of zinc stearate to zinc oleate is 1:(0.5-2).

[0012] Preferably, in step S1, the preparation of the Co-Mn bimetallic oxide nanocatalyst includes the following steps: Alkali lignin solution was added to a mixed solution of Co(NO3)2·6H2O and Mn(NO3)2·4H2O, citric acid monohydrate was added and the pH was adjusted to form a mixed sol. The mixed sol was concentrated and dried to obtain a dry gel, which was then calcined in stages under nitrogen and air atmospheres, cooled, ground and sieved to obtain Co-Mn bimetallic oxide nanocatalyst.

[0013] Alkali lignin macromolecules are dispersed in a sol. During the nitrogen atmosphere calcination stage, the lignin undergoes pyrolysis and carbonization, forming a rigid carbon framework that isolates the Co-Mn oxide nanocrystals from each other. In subsequent further calcination in an air atmosphere, the carbon framework is oxidized to CO2 and escapes, forming a porous network that increases the specific surface area, facilitating lignin contact with the active sites inside the catalyst. Simultaneously, the reducing gases (CO2, H2) generated during lignin pyrolysis can partially remove Co... 3+ / Mn 4+ In-situ reduction to more reactive Co 2+ / Mn 3+ This process generates oxygen vacancies; while the residual trace amounts of bio-carbon doping into the metal oxide lattice interface can improve the electronic conductivity of the material, accelerate electron transfer during the catalytic process, and improve catalytic efficiency.

[0014] Preferably, the mass ratio of the alkali lignin, Co(NO3)2·6H2O, Mn(NO3)2·4H2O and citric acid monohydrate is 2.50:43.65:12.55:42.04; and the pH of the mixed sol is 7.0-8.0.

[0015] Preferably, in step S1, the concentration temperature is 75-85℃ and the time is 4-6h; the drying temperature is 105-115℃ and the time is 10-14h; the heating rate of calcination under nitrogen atmosphere is 1.5-2.5℃ / min, the calcination temperature is 280-320℃, and the calcination time is 0.8-1.2h; the heating rate of calcination under air atmosphere is 1.5-2.5℃ / min, the calcination temperature is 400-440℃, and the calcination time is 1.5-2.5h.

[0016] The nitrogen atmosphere roasting stage enables alkali lignin to undergo pyrolysis and carbonization, forming a temporary carbon skeleton that isolates and confines Co-Mn oxide grains. The air atmosphere roasting stage removes the carbon skeleton and generates a porous structure, while promoting the multivalent transformation of Co and Mn and the formation of oxygen vacancies, thereby improving the catalyst's ability to adsorb and activate oxygen.

[0017] Preferably, in step S1, the pH is adjusted to 10.0-11.0; the pressure of the heated and stirred reaction is 0.3-0.5 MPa, the temperature is 85-95℃, the speed is 300-400 rpm, and the time is 3-4 h; the pH of the acid precipitation is 2.0-3.0.

[0018] The above-mentioned catalytic oxidation conditions enable alkali lignin to fully dissolve and come into contact with reactive oxygen species, which is beneficial to promoting the simultaneous degradation and carboxylation of lignin.

[0019] Preferably, in step S1, the mass ratio of alkali lignin to Co-Mn bimetallic oxide nanocatalyst is 100:(0.4-0.8).

[0020] Preferably, in step S2, the mixing speed is 1200-1800 rpm and the time is 15-25 min.

[0021] Preferably, in step S2, the heating and stirring temperature is 100-110℃, the speed is 200-300rpm, and the time is 25-35min; the heating and stirring temperature is 125-130℃, the speed is 380-420rpm, and the time is 20-30min.

[0022] Temperature control at 125-130℃, far below the dissociation initiation temperature of the carboxylic acid-ammonium ion pair, ensures the stability of the masked structure throughout the granulation process. PETS and plasticizer remain completely liquid at this temperature, resulting in optimal fusion uniformity. Combined with high-speed stirring, this allows the masked lignin to achieve molecular-level interpenetration in the continuous phase.

[0023] The present invention also provides the application of the above-mentioned bio-based rubber dispersant in a rubber composition, wherein the rubber composition comprises the following raw materials in parts by weight: 100 parts of natural rubber SMR20, 45-60 parts of precipitated silica VN3, 4-6 parts of bis-[3-(triethoxysilyl)propyl]-tetrasulfide, 3-5 parts of the bio-based rubber dispersant according to any one of claims 1-9, 3-5 parts of zinc oxide, 1.5-2.5 parts of stearic acid, 1-2 parts of antioxidant 4020, 1-2 parts of accelerator CBS, and 1-2 parts of sulfur.

[0024] When the bio-based rubber dispersant of the present invention is added to the natural rubber / fumed silica rubber composition, the viscosity of the rubber compound and the scorch time can be reduced and the mixture extended due to the combined effect of ion masking and low-melting-point lubricating continuous phase during the mixing stage. During the vulcanization stage, after the temperature rises, the carboxylic acid-ammonium ion pair undergoes thermally triggered demasking, and the exposed carboxyl groups can form hydrogen bonds with the silanol groups of fumed silica to inhibit secondary agglomeration of fumed silica, thereby improving the tensile strength, tensile stress at a given elongation and abrasion resistance of the vulcanized rubber.

[0025] The above-described technical solution of the present invention has at least the following beneficial effects: 1. Co-Mn bimetallic oxide nanocatalysts can activate oxygen in the air and generate reactive oxygen species, promoting the ether bond cleavage and side chain oxidation in alkali lignin, enabling lignin to simultaneously achieve low molecular weight and high carboxylation, providing a basis for subsequent ion masking and silica interface anchoring.

[0026] 2. Low molecular weight carboxyl-modified lignin forms a carboxylic acid-ammonium ion pair with N-cocoyl-1,3-propanediamine, which can mask the strong polar carboxyl groups in the early stage of mixing, reduce the premature competitive adsorption of lignin and silica silanol groups, and allow bis-[3-(triethoxysilane)propyl]-tetrasulfide to more fully modify the silica surface.

[0027] 3. PETS and plasticizers form a low-melting-point lubricating continuous phase, which can quickly soften and improve filler wetting and rubber flowability during the mixing stage, thereby reducing Mooney viscosity and mixing energy consumption. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments.

[0029] Example 1 Add 2.50g of alkali lignin to 50mL of deionized water, add 2mL of ammonia (25%wt) dropwise, stir to dissolve, and prepare an alkali lignin solution. 43.65 g Co(NO3)2·6H2O and 12.55 g Mn(NO3)2·4H2O were dissolved in 200 mL of deionized water and stirred to obtain a bimetallic salt solution. Alkali lignin solution was added and stirred for 30 min. 42.04 g citric acid monohydrate was added and stirred to mix. The pH of the solution was adjusted to 7.5 with ammonia water to obtain a mixed sol. The sol was stirred in a constant temperature water bath at 80 °C for 5 h, then transferred to an oven and dried at 110 °C for 12 h to obtain a dry gel. The gel was placed in a corundum boat and placed in a tube furnace. Nitrogen gas was introduced to purge air, and the temperature was increased to 300 °C at a rate of 2.0 °C / min. The calcination was carried out for 1.0 h. The atmosphere was switched to compressed air (flow rate 200 mL / min), and the temperature was increased to 420 °C at a rate of 2.0 °C / min. The calcination was carried out for 2.0 h. The gel was cooled, ground, and passed through a 200-mesh sieve to obtain a Co-Mn bimetallic oxide nanocatalyst.

[0030] 100g of alkali lignin was dissolved in 800mL of deionized water, and NaOH was added to adjust the pH to 10.5. The mixture was stirred and dissolved, and 0.6g of Co-Mn bimetallic oxide nanocatalyst was added. The mixture was ultrasonically dispersed for 15min, transferred to a reaction vessel, and air was introduced to a pressure of 0.4MPa. The temperature was raised to 90℃, and the reaction was carried out at 350rpm for 3.5h. The mixture was cooled to room temperature, centrifuged to obtain the supernatant, and the pH was adjusted to 2.5. The precipitate was precipitated, filtered, washed with deionized water until neutral, dried under vacuum at 60℃, and pulverized through a 200-mesh sieve to obtain low molecular weight carboxyl-modified lignin.

[0031] 20g of low molecular weight carboxyl-modified lignin and 4.5g of N-cocoyl-1,3-propanediamine were added to a high-speed mixer and mixed at 1500rpm for 20min at room temperature to obtain pretreated lignin.

[0032] 46g of PETS and 29g of plasticizer (zinc stearate to zinc oleate mass ratio 1:1) were added to the reactor and heated to 105℃. The mixture was stirred at 250rpm for 30min to obtain a homogeneous melt. Stirring continued, and pretreated lignin was slowly added in three portions, with an interval of 10min between each addition. The temperature was then slowly increased to 128℃ at a rate of 5℃ / min, and the mixture was stirred at 400rpm for 25min to obtain a mixed fluid. This fluid was then pumped to the die head of a water ring pelletizer and pelletized at 20℃ to obtain a bio-based rubber dispersant.

[0033] Take 100g of natural rubber SMR20, 52g of precipitated silica VN3, 5.0g of bis-[3-(triethoxysilyl)propyl]-tetrasulfide, 4.0g of bio-based rubber dispersant, 4.0g of zinc oxide, 2.0g of stearic acid, and antioxidant 4020. 1.5g of natural rubber, 1.5g of accelerator CBS, and 1.5g of sulfur were added and plasticized for 1 minute. When the rubber temperature reached 75℃, a bio-based rubber dispersant was added. Silica VN3 and bis-[3-(triethoxysilyl)propyl]-tetrasulfide were added in two batches and mixed for 2 minutes. Then zinc oxide, stearic acid, and antioxidant 4020 were added and mixed for another 3 minutes. When the temperature reached 140℃, the rubber was discharged, sheeted, and cooled to room temperature. The rolling temperature of the open mill was controlled at 55℃, sulfur and accelerator CBS were added, and the mixture was passed through a thin mill 6 times and formed into triangular bundles 3 times. The final rubber was sheeted and left to stand at 23±2℃ and 50±5% relative humidity for 12 hours. The final rubber was cut and placed in a mold, and vulcanized at 165℃ and 15MPa to obtain a rubber composition.

[0034] Example 2 Add 2.50g of alkali lignin to 50mL of deionized water, add 2mL of ammonia (25%wt) dropwise, stir to dissolve, and prepare an alkali lignin solution. 43.65 g Co(NO3)2·6H2O and 12.55 g Mn(NO3)2·4H2O were dissolved in 200 mL of deionized water and stirred to obtain a bimetallic salt solution. Alkali lignin solution was added and stirred for 30 min. 42.04 g citric acid monohydrate was added and stirred to mix. The pH of the solution was adjusted to 8.0 with ammonia water to obtain a mixed sol. The sol was stirred in a constant temperature water bath at 85 °C for 6 h, then transferred to an oven and dried at 115 °C for 14 h to obtain a dry gel. The gel was placed in a corundum boat and placed in a tube furnace. Nitrogen gas was introduced to purge air, and the temperature was increased to 320 °C at a rate of 2.5 °C / min. The calcination was carried out for 1.2 h. The atmosphere was switched to compressed air (flow rate 200 mL / min), and the temperature was increased to 440 °C at a rate of 2.5 °C / min. The calcination was carried out for 2.5 h. The gel was cooled, ground, and passed through a 200-mesh sieve to obtain a Co-Mn bimetallic oxide nanocatalyst.

[0035] 100g of alkali lignin was dissolved in 800mL of deionized water, and NaOH was added to adjust the pH to 11.0. The mixture was stirred until dissolved, and 0.8g of Co-Mn bimetallic oxide nanocatalyst was added. The mixture was ultrasonically dispersed for 15min, transferred to a reaction vessel, and air was introduced to a pressure of 0.5MPa. The temperature was raised to 95℃, and the mixture was reacted at 400rpm for 4h. The mixture was cooled to room temperature, centrifuged to obtain the supernatant, and the pH was adjusted to 3.0. The precipitate was precipitated, filtered, washed with deionized water until neutral, dried under vacuum at 60℃, and pulverized through a 200-mesh sieve to obtain low molecular weight carboxyl-modified lignin.

[0036] 22g of low molecular weight carboxyl-modified lignin and 6g of N-cocoyl-1,3-propanediamine were added to a high-speed mixer and mixed at 1800rpm for 25min at room temperature to obtain pretreated lignin.

[0037] 52g of PETS and 34g of plasticizer (zinc stearate to zinc oleate mass ratio 1:1) were added to the reactor and heated to 110°C. The mixture was stirred at 300 rpm for 35 min to obtain a homogeneous melt. Stirring continued, and pretreated lignin was slowly added in three portions, with an interval of 10 min between each addition. The temperature was then slowly increased to 130°C at a rate of 5°C / min, and the mixture was stirred at 420 rpm for 30 min to obtain a mixed fluid. This fluid was then pumped to the die head of a water ring pelletizer and pelletized at 25°C to obtain a bio-based rubber dispersant.

[0038] Take 100g of natural rubber SMR20, 60g of precipitated silica VN3, 6g of bis-[3-(triethoxysilyl)propyl]-tetrasulfide, 5g of bio-based rubber dispersant, 5g of zinc oxide, 2.5g of stearic acid, 2g of antioxidant 4020, and accelerator CBS. Add 2g of sulfur and natural rubber to the mixture and masticate for 1 minute. When the rubber temperature reaches 75℃, add the bio-based rubber dispersant, and add fumed silica VN3 and bis-[3-(triethoxysilyl)propyl]-tetrasulfide in two batches. Mix for 2 minutes, then add zinc oxide, stearic acid and antioxidant 4020, and continue mixing for 3 minutes. When the temperature reaches 140℃, discharge the rubber, sheet it, and cool it to room temperature. Control the rolling temperature of the open mill at 60℃, add sulfur and accelerator CBS, pass through the mill 6 times, and form a triangular bundle 3 times. Sheet the rubber to obtain the final compound. Let it stand for 12 hours at 23±2℃ and 50±5% relative humidity. Cut the final compound and place it in a mold. Vulcanize it at 165℃ and 15MPa to obtain the rubber composition.

[0039] Example 3 Add 2.50g of alkali lignin to 50mL of deionized water, add 2mL of ammonia (25%wt) dropwise, stir to dissolve, and prepare an alkali lignin solution. 43.65 g Co(NO3)2·6H2O and 12.55 g Mn(NO3)2·4H2O were dissolved in 200 mL of deionized water and stirred to obtain a bimetallic salt solution. Alkali lignin solution was added and stirred for 30 min. 42.04 g citric acid monohydrate was added and stirred to mix. The pH of the solution was adjusted to 7.0 with ammonia water to obtain a mixed sol. The sol was stirred in a constant temperature water bath at 75 °C for 4 h, then transferred to an oven and dried at 105 °C for 10 h to obtain a dry gel. The gel was placed in a corundum boat and placed in a tube furnace. Nitrogen gas was introduced to purge air, and the temperature was increased to 280 °C at a rate of 1.5 °C / min. The calcination was carried out for 0.8 h. The atmosphere was switched to compressed air (flow rate 200 mL / min), and the temperature was increased to 400 °C at a rate of 1.5 °C / min. The calcination was carried out for 1.5 h. The gel was cooled, ground, and passed through a 200-mesh sieve to obtain a Co-Mn bimetallic oxide nanocatalyst.

[0040] 100g of alkali lignin was dissolved in 800mL of deionized water, and NaOH was added to adjust the pH to 10.0. The mixture was stirred until dissolved, and 0.4g of Co-Mn bimetallic oxide nanocatalyst was added. The mixture was ultrasonically dispersed for 15min, transferred to a reaction vessel, and air was introduced to a pressure of 0.3MPa. The temperature was raised to 85℃, and the mixture was reacted for 3h with stirring at 300rpm. The mixture was cooled to room temperature, centrifuged to obtain the supernatant, and the pH was adjusted to 2.0. The precipitate was precipitated, filtered, washed with deionized water until neutral, dried under vacuum at 60℃, and pulverized through a 200-mesh sieve to obtain low molecular weight carboxyl-modified lignin.

[0041] 18g of low molecular weight carboxyl-modified lignin and 3g of N-cocoyl-1,3-propanediamine were added to a high-speed mixer and mixed at 1200rpm for 15min at room temperature to obtain pretreated lignin.

[0042] 40g of PETS and 24g of plasticizer (zinc stearate to zinc oleate mass ratio 1:0.5) were added to the reactor and heated to 100℃. The mixture was stirred at 200rpm for 25min to obtain a homogeneous melt. Stirring continued, and pretreated lignin was slowly added in three portions, with an interval of 10min between each addition. The temperature was then slowly increased to 125℃ at a rate of 5℃ / min, and the mixture was stirred at 380rpm for 20min to obtain a mixed fluid. This fluid was then pumped to the die head of a water ring pelletizer and pelletized at 15℃ to obtain a bio-based rubber dispersant.

[0043] Take 100g of natural rubber SMR20, 45g of precipitated silica VN3, 4g of bis-[3-(triethoxysilyl)propyl]-tetrasulfide, 3g of bio-based rubber dispersant, 3g of zinc oxide, 1.5g of stearic acid, 1g of antioxidant 4020, and 1g of accelerator CBS. Add 1g of natural rubber and 1g of sulfur; add natural rubber and masticate for 1 minute. When the rubber temperature rises to 75℃, add bio-based rubber dispersant, add silica VN3 and bis-[3-(triethoxysilyl)propyl]-tetrasulfide in two batches, mix for 2 minutes, then add zinc oxide, stearic acid and antioxidant 4020, continue mixing for 3 minutes, discharge the rubber when the temperature rises to 140℃, sheet it and cool it to room temperature; control the rolling temperature of the open mill at 50℃, add sulfur and accelerator CBS, pass through the mill 6 times and make triangular wraps 3 times, and sheet it to obtain the final rubber compound. Let it stand for 12 hours at 23±2℃ and 50±5% relative humidity; cut the final rubber compound and put it into a mold, vulcanize it at 165℃ and 15MPa to obtain the rubber composition.

[0044] Example 4 Add 2.50g of alkali lignin to 50mL of deionized water, add 2mL of ammonia (25%wt) dropwise, stir to dissolve, and prepare an alkali lignin solution. 43.65 g of Co(NO3)2·6H2O and 12.55 g of Mn(NO3)2·4H2O were dissolved in 200 mL of deionized water and stirred to obtain a bimetallic salt solution. Alkali lignin solution was added and stirred for 30 min. 42.04 g of citric acid monohydrate was added and stirred to mix. The pH of the solution was adjusted to 7.2 with ammonia water to obtain a mixed sol. The sol was stirred in a constant temperature water bath at 78 °C for 4.5 h, then transferred to an oven and dried at 108 °C for 11 h to obtain a dry gel. The gel was placed in a corundum boat and placed in a tube furnace. Nitrogen gas was introduced to purge air, and the temperature was increased to 290 °C at a rate of 1.8 °C / min. The calcination was carried out for 0.9 h. The atmosphere was switched to compressed air (flow rate 200 mL / min), and the temperature was increased to 410 °C at a rate of 1.8 °C / min. The calcination was carried out for 1.8 h. The gel was cooled, ground, and passed through a 200-mesh sieve to obtain a Co-Mn bimetallic oxide nanocatalyst.

[0045] 100g of alkali lignin was dissolved in 800mL of deionized water, and NaOH was added to adjust the pH to 10.2. The mixture was stirred until dissolved, and 0.5g of Co-Mn bimetallic oxide nanocatalyst was added. The mixture was ultrasonically dispersed for 15min, transferred to a reaction vessel, and air was introduced to a pressure of 0.35MPa. The temperature was raised to 88℃, and the reaction was carried out at 320rpm for 3.2h. The mixture was cooled to room temperature, centrifuged to obtain the supernatant, and the pH was adjusted to 2.2. The precipitate was precipitated, filtered, washed with deionized water until neutral, dried under vacuum at 60℃, and pulverized through a 200-mesh sieve to obtain low molecular weight carboxyl-modified lignin.

[0046] 19g of low molecular weight carboxyl-modified lignin and 4g of N-cocoyl-1,3-propanediamine were added to a high-speed mixer and mixed at 1400rpm for 18min at room temperature to obtain pretreated lignin.

[0047] 43g of PETS and 26g of plasticizer (zinc stearate to zinc oleate mass ratio 1:1.5) were added to the reactor and heated to 102℃. The mixture was stirred at 230rpm for 28min to obtain a homogeneous melt. Stirring continued, and pretreated lignin was slowly added in three portions, with an interval of 10min between each addition. The temperature was then slowly increased to 126℃ at a rate of 5℃ / min and stirred at 390rpm for 22min to obtain a mixed fluid. This fluid was then pumped to the die head of a water ring pelletizer and pelletized at 18℃ to obtain a bio-based rubber dispersant.

[0048] Take 100g of natural rubber SMR20, 48g of precipitated silica VN3, 4.5g of bis-[3-(triethoxysilyl)propyl]-tetrasulfide, 3.5g of bio-based rubber dispersant, 3.5g of zinc oxide, 1.8g of stearic acid, and antioxidant 4020. 1.2g of natural rubber, 1.2g of accelerator CBS, and 1.2g of sulfur were added and plasticized for 1 minute. When the rubber temperature reached 75℃, a bio-based rubber dispersant was added. Silica VN3 and bis-[3-(triethoxysilyl)propyl]-tetrasulfide were added in two batches and mixed for 2 minutes. Zinc oxide, stearic acid, and antioxidant 4020 were then added and mixed for another 3 minutes. When the temperature reached 140℃, the rubber was discharged, sheeted, and cooled to room temperature. The rolling temperature of the open mill was controlled at 52℃. Sulfur and accelerator CBS were added, and the mixture was passed through a thin mill 6 times and formed into triangular bundles 3 times. The final rubber was sheeted and left to stand at 23±2℃ and 50±5% relative humidity for 12 hours. The final rubber was cut and placed in a mold, and vulcanized at 165℃ and 15MPa to obtain a rubber composition.

[0049] Example 5 Add 2.50g of alkali lignin to 50mL of deionized water, add 2mL of ammonia (25%wt) dropwise, stir to dissolve, and prepare an alkali lignin solution. 43.65 g Co(NO3)2·6H2O and 12.55 g Mn(NO3)2·4H2O were dissolved in 200 mL of deionized water and stirred to obtain a bimetallic salt solution. Alkali lignin solution was added and stirred for 30 min. 42.04 g citric acid monohydrate was added and stirred to mix. The pH of the solution was adjusted to 7.8 with ammonia to obtain a mixed sol. The sol was stirred in a constant temperature water bath at 82 °C for 5.5 h, then transferred to an oven and dried at 112 °C for 13 h to obtain a dry gel. The gel was placed in a corundum boat and placed in a tube furnace. Nitrogen gas was introduced to purge air, and the temperature was increased to 310 °C at a rate of 2.2 °C / min. The calcination was carried out for 1.1 h. The atmosphere was switched to compressed air (flow rate 200 mL / min), and the temperature was increased to 430 °C at a rate of 2.2 °C / min. The calcination was carried out for 2.2 h. The gel was cooled, ground, and passed through a 200-mesh sieve to obtain a Co-Mn bimetallic oxide nanocatalyst.

[0050] 100g of alkali lignin was dissolved in 800mL of deionized water, and NaOH was added to adjust the pH to 10.8. The mixture was stirred until dissolved, and 0.7g of Co-Mn bimetallic oxide nanocatalyst was added. The mixture was ultrasonically dispersed for 15min, transferred to a reaction vessel, and air was introduced to a pressure of 0.45MPa. The temperature was raised to 92℃, and the reaction was carried out at 380rpm for 3.8h. The mixture was cooled to room temperature, centrifuged to obtain the supernatant, and the pH was adjusted to 2.8. The precipitate was precipitated, filtered, washed with deionized water until neutral, dried under vacuum at 60℃, and pulverized through a 200-mesh sieve to obtain low molecular weight carboxyl-modified lignin.

[0051] 21g of low molecular weight carboxyl-modified lignin and 5g of N-cocoyl-1,3-propanediamine were added to a high-speed mixer and mixed at 1600rpm for 22min at room temperature to obtain pretreated lignin.

[0052] 49g of PETS and 32g of plasticizer (zinc stearate to zinc oleate mass ratio 1:1) were added to the reactor and heated to 108℃. The mixture was stirred at 280rpm for 32min to obtain a homogeneous melt. Stirring continued, and pretreated lignin was slowly added in three portions, with an interval of 10min between each addition. The temperature was then slowly increased to 129℃ at a rate of 5℃ / min, and the mixture was stirred at 410rpm for 28min to obtain a mixed fluid. This fluid was then pumped to the die head of a water ring pelletizer and pelletized at a cooling water temperature of 22℃ to obtain a bio-based rubber dispersant.

[0053] Take 100g of natural rubber SMR20, 56g of precipitated silica VN3, 5.5g of bis-[3-(triethoxysilyl)propyl]-tetrasulfide, 4.5g of bio-based rubber dispersant, 4.5g of zinc oxide, 2.2g of stearic acid, and antioxidant 4020. 1.8g of natural rubber, 1.8g of accelerator CBS, and 1.8g of sulfur were added and plasticized for 1 minute. When the rubber temperature reached 75℃, a bio-based rubber dispersant was added. Silica VN3 and bis-[3-(triethoxysilyl)propyl]-tetrasulfide were added in two batches and mixed for 2 minutes. Zinc oxide, stearic acid, and antioxidant 4020 were then added and mixed for another 3 minutes. When the temperature reached 140℃, the rubber was discharged, sheeted, and cooled to room temperature. The rolling temperature of the open mill was controlled at 58℃. Sulfur and accelerator CBS were added, and the mixture was passed through a thin mill 6 times and formed into triangular bundles 3 times. The final rubber was sheeted and left to stand at 23±2℃ and 50±5% relative humidity for 12 hours. The final rubber was cut and placed in a mold, and vulcanized at 165℃ and 15MPa to obtain a rubber composition.

[0054] Example 6 Add 2.50g of alkali lignin to 50mL of deionized water, add 2mL of ammonia (25%wt) dropwise, stir to dissolve, and prepare an alkali lignin solution. 43.65 g Co(NO3)2·6H2O and 12.55 g Mn(NO3)2·4H2O were dissolved in 200 mL of deionized water and stirred to obtain a bimetallic salt solution. Alkali lignin solution was added and stirred for 30 min. 42.04 g citric acid monohydrate was added and stirred to mix. The pH of the solution was adjusted to 7.6 with ammonia water to obtain a mixed sol. The sol was stirred in a constant temperature water bath at 80 °C for 5 h, then transferred to an oven and dried at 110 °C for 12 h to obtain a dry gel. The gel was placed in a corundum boat and placed in a tube furnace. Nitrogen gas was introduced to purge air, and the temperature was increased to 300 °C at a rate of 2.0 °C / min. The calcination was carried out for 1.0 h. The atmosphere was switched to compressed air (flow rate 200 mL / min), and the temperature was increased to 420 °C at a rate of 2.0 °C / min. The calcination was carried out for 2.0 h. The gel was cooled, ground, and passed through a 200-mesh sieve to obtain a Co-Mn bimetallic oxide nanocatalyst.

[0055] 100g of alkali lignin was dissolved in 800mL of deionized water, and NaOH was added to adjust the pH to 10.6. The mixture was stirred until dissolved, and 0.6g of Co-Mn bimetallic oxide nanocatalyst was added. The mixture was ultrasonically dispersed for 15min, transferred to a reaction vessel, and air was introduced to a pressure of 0.4MPa. The temperature was raised to 90℃, and the mixture was reacted at 360rpm for 3.5h. The mixture was cooled to room temperature, centrifuged to obtain the supernatant, and the pH was adjusted to 2.5. The precipitate was precipitated, filtered, washed with deionized water until neutral, dried under vacuum at 60℃, and pulverized through a 200-mesh sieve to obtain low molecular weight carboxyl-modified lignin.

[0056] 20g of low molecular weight carboxyl-modified lignin and 4.5g of N-cocoyl-1,3-propanediamine were added to a high-speed mixer and mixed at 1500rpm for 20min at room temperature to obtain pretreated lignin.

[0057] 46g of PETS and 29g of plasticizer (zinc stearate to zinc oleate mass ratio 1:2) were added to the reactor and heated to 105℃. The mixture was stirred at 250rpm for 30min to obtain a homogeneous melt. Stirring continued, and pretreated lignin was slowly added in three portions, with an interval of 10min between each addition. The temperature was then slowly increased to 128℃ at a rate of 5℃ / min, and the mixture was stirred at 400rpm for 25min to obtain a mixed fluid. This fluid was then pumped to the die head of a water ring pelletizer and pelletized at 20℃ to obtain a bio-based rubber dispersant.

[0058] Take 100g of natural rubber SMR20, 54g of precipitated silica VN3, 5.0g of bis-[3-(triethoxysilyl)propyl]-tetrasulfide, 4.0g of bio-based rubber dispersant, 4.0g of zinc oxide, 2.0g of stearic acid, and antioxidant 4020. 1.5g of natural rubber, 1.5g of accelerator CBS, and 1.5g of sulfur were added and plasticized for 1 minute. When the rubber temperature reached 75℃, a bio-based rubber dispersant was added. Silica VN3 and bis-[3-(triethoxysilyl)propyl]-tetrasulfide were added in two batches and mixed for 2 minutes. Then zinc oxide, stearic acid, and antioxidant 4020 were added and mixed for another 3 minutes. When the temperature reached 140℃, the rubber was discharged, sheeted, and cooled to room temperature. The rolling temperature of the open mill was controlled at 55℃, sulfur and accelerator CBS were added, and the mixture was passed through a thin mill 6 times and formed into triangular bundles 3 times. The final rubber was sheeted and left to stand at 23±2℃ and 50±5% relative humidity for 12 hours. The final rubber was cut and placed in a mold, and vulcanized at 165℃ and 15MPa to obtain a rubber composition.

[0059] The present invention also includes comparative examples and related experiments.

[0060] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that no bio-based rubber dispersant is added to the rubber composition; the other components and preparation methods are the same as in Example 1.

[0061] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that N-cocoyl-1,3-propanediamine was not added for the preparation of pretreated lignin. Instead, low molecular weight carboxyl-modified lignin was directly used to prepare the bio-based rubber dispersant. The other components and preparation methods were the same as in Example 1.

[0062] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that alkali lignin that has not been treated with Co-Mn bimetallic oxide nanocatalyst oxidation is used instead of low molecular weight carboxyl-modified lignin. The other components and preparation methods are the same as in Example 1.

[0063] Performance testing The performance of the rubber composition samples prepared in Examples 1-6 and Comparative Examples 1-3 was tested.

[0064] (1) Mooney viscosity and Mooney scorch: Mooney viscosity was determined according to GB / T 1232.1-2016, and the test conditions were 100℃ and ML 1+4; Mooney scorch was determined according to GB / T 1232.2-2025, and the test temperature was 120℃, and t5 was recorded; (2) Vulcanization characteristics: The test was conducted using a rotorless vulcanizer in accordance with GB / T 16584-1996. The test temperature was 160℃ and the amplitude was ±0.5°. The values ​​of ML, MH, t10 and T90 were recorded. (3) Physical and mechanical properties: Tensile properties were determined according to GB / T 528-2009, using type I dumbbell plates, with a tensile speed of 500 mm / min; Hardness was determined according to GB / T 531.1-2008, using a Shore A hardness tester; Abrasion resistance was determined according to GB / T9867-2008. (4) Macroscopic dispersion of silica: The dispersion grade of the vulcanized rubber was evaluated by observing the cross-section of the vulcanized rubber using a reflected light microscope in accordance with ISO 11345 standard. The test results are summarized in Table 1-4.

[0065] Table 1. Mooney viscosity and Mooney scorch test results

[0066] As shown in Table 1 above, compared with Comparative Example 1 (without added bio-based rubber dispersant), Example 1 significantly reduced the viscosity of the rubber compound and prolonged the scorch time. This indicates that the synergistic effect of PETS, zinc stearate / zinc oleate lubricating continuous phase, and pretreated lignin can improve the wetting of silica and the flowability of the rubber compound, and reduce the risk of early scorch. Compared with Comparative Example 2 (without N-coco-1,3-propylenediamine pretreatment), Example 1 had a lower Mooney viscosity and a longer scorch time, indicating that the ion masking effect of N-coco-1,3-propylenediamine on carboxyl groups can reduce the premature adsorption of silica silanol groups by carboxyl groups during the low-temperature mixing stage, thus balancing processing flowability and scorch safety. Compared with Comparative Example 3 (without catalytic oxidation of alkali lignin), Example 1 still showed a lower Mooney viscosity and a longer scorch time, indicating that the low molecular weight carboxyl-modified lignin treated with Co-Mn bimetallic oxide nanocatalyst has better dispersion adaptability and interface regulation effect.

[0067] Table 2. Results of vulcanization characteristic tests

[0068] As shown in Table 2, compared with Example 1, the ML of Comparative Example 1 increased from 4.8 dN·m to 6.2 dN·m, the MH decreased from 18.2 dN·m to 17.2 dN·m, the t10 shortened from 1.8 min to 1.0 min, and the T90 extended from 8.9 min to 10.5 min. This indicates that without the addition of the bio-based rubber dispersant, the initial flowability of the rubber compound was poor, the early vulcanization tendency was enhanced, but the efficiency of effective crosslinking network formation was insufficient in the later stage. In Comparative Example 2, the ML increased to 5.7 dN·m, the MH decreased to 17.2 dN·m, the t10 shortened to 1.2 min, and the T90 extended to 9.8 dN·m. The presence of N-cocoyl-1,3-propanediamine pretreatment indicates that the highly polar carboxyl groups in the low molecular weight carboxyl-modified lignin are not effectively masked, which can easily interfere with the surface modification of silica and the stability of the sulfurization system during mixing and the early stage of sulfurization. The ML of Comparative Example 3 is 5.0 dN·m, which is close to that of Example 1, but MH is significantly reduced to 14.8 dN·m, t10 is extended to 3.1 min, and T90 is extended to 11.0 min. This indicates that the alkali lignin without catalytic oxidation treatment has insufficient active sites, making it difficult to effectively participate in the anchoring and reinforcing network construction of silica interface during the sulfurization stage, resulting in a decrease in sulfurization efficiency and final crosslinking degree.

[0069] Table 3 Comprehensive Mechanical Performance Test Results

[0070] As shown in Table 3, compared with Example 1, the tensile strength, 300% elongation stress, and Shore A hardness of Comparative Example 1 all decreased, while the DIN abrasion increased. This indicates that without the addition of bio-based rubber dispersant, the dispersion and reinforcing effects of silica were insufficient, leading to a decrease in both the strength and abrasion resistance of the vulcanizate. The tensile strength and 300% elongation stress of Comparative Example 2 decreased slightly, while the DIN abrasion increased to 110 mm. 3 This indicates that, although the lignin still contains low molecular weight carboxyl-modified lignin after pretreatment with N-cocoyl-1,3-propylenediamine, its interfacial release is not controllable, resulting in insufficient overall reinforcement and wear resistance improvement. Comparative Example 3 showed significant decreases in tensile strength, 300% elongation stress, and Shore A hardness, with DIN wear increasing to 140 mm. 3 This indicates that alkali lignin without catalytic oxidation has a high molecular weight and insufficient active carboxyl sites, making it difficult to effectively improve the interfacial bonding between silica and rubber.

[0071] Table 4 Results of silica dispersion test

[0072] Table 4 shows that, compared with Example 1, the dispersion grade of silica in Comparative Example 1 decreased from 8 to 5, indicating that without the addition of bio-based rubber dispersant, silica agglomeration was significant, and the uniformity of filler dispersion in the rubber matrix was poor. The dispersion grade of Comparative Example 2 decreased to 6, indicating that when only low molecular weight carboxyl-modified lignin was used without N-cocoyl-1,3-propylenediamine pretreatment, the early strong adsorption of lignin carboxyl groups affected the sufficient dispersion of silica and the effect of silane coupling agents. The dispersion grade of Comparative Example 3 decreased to 5, indicating that alkali lignin without Co-Mn catalytic oxidation modification could not effectively provide low molecular weight, highly active interfacial anchoring sites, making it difficult to inhibit secondary agglomeration of silica. This shows that the low molecular weight carboxyl-modified lignin, N-cocoyl-1,3-propylenediamine, and PETS / zinc stearate-zinc oleate lubricating continuous phase in Example 1 have a synergistic effect, which can improve the dispersion effect of silica in natural rubber.

[0073] Characterization test of low molecular weight carboxyl-modified lignin Molecular weight, carboxyl content, and acid value were tested for alkali lignin and the low molecular weight carboxyl-modified lignin prepared in Examples 1-6. Molecular weight was determined by gel permeation chromatography. Before testing, the samples were vacuum-dried, acetylated, and dissolved in tetrahydrofuran. Calibration was performed using polystyrene standard samples, and the weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution index (PDI) were recorded. Carboxyl content was determined by potentiometric titration. Titration with NaOH standard solution was performed, and the blank sample was subtracted. The carboxyl content in the sample was calculated based on the titration consumption. Acid value was calculated based on the amount of KOH consumed per gram of sample containing carboxyl groups. The test results are shown in Table 5.

[0074] Table 5. Characterization results of alkali lignin and low molecular weight carboxyl-modified lignin

[0075] As shown in Table 5, after air oxidation treatment with Co-Mn bimetallic oxide nanocatalyst, the weight-average molecular weight of the modified lignin obtained in Examples 1-6 decreased from 8650 g / mol of alkali lignin to 2860-4210 g / mol, the carboxyl content increased from 0.78 mmol / g to 2.10-2.95 mmol / g, and the acid value increased from 43.8 mg KOH / g to 117.8-165.5 mg KOH / g. This indicates that the above catalytic oxidation treatment can simultaneously achieve the reduction of molecular weight and carboxylation of alkali lignin. The lower molecular weight is beneficial for the diffusion and dispersion of modified lignin in the PETS / plasticizer continuous phase and the rubber matrix. The higher carboxyl content can provide active sites for subsequent interfacial anchoring with the silanol groups on the surface of silica, thus providing a structural basis for reducing Mooney viscosity, improving silica dispersion, and enhancing the mechanical properties of vulcanizates.

Claims

1. A bio-based rubber dispersant, characterized in that, The raw materials include the following parts by weight: 18-26 parts of low molecular weight carboxyl-modified lignin, 3-6 parts of N-cocoyl-1,3-propanediamine, 40-52 parts of pentaerythritol stearate, and 24-34 parts of plasticizer; It was prepared using the following method: Step S1: Add alkali lignin to deionized water, adjust the pH, add Co-Mn bimetallic oxide nanocatalyst, ultrasonically disperse, transfer to a reaction vessel, introduce air, heat and stir the reaction, cool down, separate and recover the catalyst, and perform acid precipitation, filtration, washing, drying and pulverizing on the reaction solution to obtain low molecular weight carboxyl modified lignin. Step S2: Mix low molecular weight carboxyl-modified lignin with N-cocoyl-1,3-propanediamine to obtain pretreated lignin; add pentaerythritol stearate and plasticizer to a reaction vessel, heat and stir, add pretreated lignin, heat and stir, granulate to obtain bio-based rubber dispersant.

2. The bio-based rubber dispersant according to claim 1, characterized in that, The plasticizer is a mixture of zinc stearate and zinc oleate, wherein the mass ratio of zinc stearate to zinc oleate is 1:(0.5-2).

3. The bio-based rubber dispersant according to claim 1, characterized in that, In step S1, the preparation of the Co-Mn bimetallic oxide nanocatalyst includes the following steps: Alkali lignin solution was added to a mixed solution of Co(NO3)2·6H2O and Mn(NO3)2·4H2O, citric acid monohydrate was added and the pH was adjusted to form a mixed sol. The mixed sol was concentrated and dried to obtain a dry gel, which was then calcined in stages under nitrogen and air atmospheres, cooled, ground and sieved to obtain Co-Mn bimetallic oxide nanocatalyst.

4. The bio-based rubber dispersant according to claim 3, characterized in that, The mass ratio of the alkali lignin, Co(NO3)2·6H2O, Mn(NO3)2·4H2O and citric acid monohydrate is 2.50:43.65:12.55:42.04; the pH of the mixed sol is 7.0-8.

0.

5. The bio-based rubber dispersant according to claim 3, characterized in that, In step S1, the concentration temperature is 75-85℃ and the time is 4-6h; the drying temperature is 105-115℃ and the time is 10-14h; the heating rate of calcination under nitrogen atmosphere is 1.5-2.5℃ / min, the calcination temperature is 280-320℃, and the calcination time is 0.8-1.2h; the heating rate of calcination under air atmosphere is 1.5-2.5℃ / min, the calcination temperature is 400-440℃, and the calcination time is 1.5-2.5h.

6. The bio-based rubber dispersant according to claim 1, characterized in that, In step S1, the pH is adjusted to 10.0-11.0; the pressure of the heated and stirred reaction is 0.3-0.5 MPa, the temperature is 85-95℃, the speed is 300-400 rpm, and the time is 3-4 h; the pH of the acid precipitation is 2.0-3.

0.

7. The bio-based rubber dispersant according to claim 1, characterized in that, In step S1, the mass ratio of alkali lignin to Co-Mn bimetallic oxide nanocatalyst is 100:(0.4-0.8).

8. The bio-based rubber dispersant according to claim 1, characterized in that, In step S2, the mixing speed is 1200-1800 rpm and the time is 15-25 min.

9. The bio-based rubber dispersant according to claim 1, characterized in that, In step S2, the heating and stirring temperature is 100-110℃, the speed is 200-300rpm, and the time is 25-35min; the heating and stirring temperature is 125-130℃, the speed is 380-420rpm, and the time is 20-30min.

10. The use of a bio-based rubber dispersant according to any one of claims 1-9 in a rubber composition, characterized in that, The bio-based rubber dispersant is used in a natural rubber / fumed silica rubber composition; the rubber composition comprises the following raw materials in parts by weight: 100 parts of natural rubber SMR20, 45-60 parts of precipitated silica VN3, 4-6 parts of bis-[3-(triethoxysilyl)propyl]-tetrasulfide, 3-5 parts of the bio-based rubber dispersant according to any one of claims 1-9, 3-5 parts of zinc oxide, 1.5-2.5 parts of stearic acid, 1-2 parts of antioxidant 4020, 1-2 parts of accelerator CBS, and 1-2 parts of sulfur.

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