A white carbon black reinforced recycled rubber material and a method of making the same

Abstract

The present application relates to the field of reinforcing reclaimed rubber, and discloses a white carbon black reinforced reclaimed rubber material and a preparation method thereof, raw materials of which include, in parts by weight, 100 parts of waste rubber powder, 1-20 parts of a functionalized modifier, and 5-30 parts of modified white carbon black; the modified white carbon black is prepared by sequentially reacting white carbon black with a silane coupling agent and 4-(2-allyl)-catechol; the mass of the silane coupling agent is 1-3% of the mass of the white carbon black; and the molar ratio of the silane coupling agent to 4-(2-allyl)-catechol is 2-3:1. The present application performs synergistic surface modification on white carbon black by using 4-(2-allyl)-catechol and a silane coupling agent, and applies the white carbon black to the production of reclaimed rubber, so that the hygroscopicity and dispersibility of the white carbon black can be significantly improved, and the white carbon black can be connected to rubber molecular chains through chemical bonds, thereby improving the reinforcing effect of the white carbon black.

Description

Technical Field

[0001] This invention relates to the field of reinforced reclaimed rubber technology, and in particular to a silica-reinforced reclaimed rubber material and its preparation method. Background Technology

[0002] Silica is a commonly used rubber reinforcing agent. Reinforcing rubber with silica can significantly improve its tensile strength, tear strength, and abrasion resistance. Silica is mainly prepared using two methods: calcination and precipitation. Calcination-processed silica, also known as fumed silica or dry-process silica, is produced by thermally decomposing polyhalides (SiClx) at high temperatures, resulting in a gas-phase reaction. Fumed silica has fewer impurities and better reinforcing properties, but its preparation is complex and costly, and it is mainly used in silicone rubber. Precipitated silica is generally produced by the neutralization and precipitation reaction of silicates with inorganic acids. It has silanol groups on its surface, numerous micropores, and stronger hygroscopicity than fumed silica, but it is cheaper, has better processing performance, and can be used alone in general-purpose rubbers such as NR and SBR.

[0003] Due to its large specific surface area, silica tends to aggregate, and its high hygroscopicity in the air leads to strong hydrogen bonding between hydroxyl groups, further increasing particle cohesion. Therefore, when used as a rubber reinforcing agent, silica is difficult to mix and disperse, and in large quantities, it easily forms gels, causing the rubber compound to harden. Furthermore, silica has poor compatibility with rubber. Existing technologies generally use silane coupling agents to modify its surface, improving its hygroscopicity and rubber compatibility. For example, patent CN112143057A discloses a silane coupling agent modified silica pre-dispersed masterbatch, its preparation method, and its application, composed of the following raw materials in parts by weight: 50-90 parts silane coupling agent modified silica, 5-50 parts carrier rubber, 1-10 parts softening oil, and 1-5 parts dispersant.

[0004] However, silane coupling agents lack groups that react with rubber molecular chains, making it impossible to form a chemical bridge between silica and rubber, and thus their effect on regulating the interfacial interaction between rubber and silica is poor. Summary of the Invention

[0005] This invention aims to overcome the aforementioned problems existing in the prior art when using silica to reinforce rubber, and provides a silica-reinforced reclaimed rubber material and its preparation method. The silica is synergistically surface-modified with 4-(2-allyl)-catechol and a silane coupling agent, and then applied to reclaimed rubber production. This significantly improves the hygroscopicity and dispersibility of silica, and connects silica to the rubber molecular chain through chemical bonds, thereby enhancing the reinforcing effect of silica.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A silica-reinforced recycled rubber material, by weight, comprises: 100 parts waste rubber powder, 1-20 parts functional modifier, and 5-30 parts modified silica.

[0008] The modified silica is prepared by reacting silica sequentially with a silane coupling agent and 4-(2-allyl)-catechol; the mass of the silane coupling agent is 1-3% of the mass of silica; the molar ratio of the silane coupling agent to 4-(2-allyl)-catechol is 2-3:1.

[0009] This invention uses a silane coupling agent and 4-(2-allyl)-catechol to synergistically modify silica. The silane coupling agent first reacts with the silanol groups on the surface of silica through alkoxy hydrolysis to form a hydrophobic layer, reducing the polarity and hygroscopicity of silica, thereby improving its compatibility with non-polar rubber matrices and reducing its agglomeration in the rubber matrix. Subsequently, the catechol structure of 4-(2-allyl)-catechol can further combine with the residual silanol groups on the surface of silica through hydrogen bonds or covalent bonds to form a double modification layer. The allyl group in 4-(2-allyl)-catechol can undergo a click reaction with the -SH group generated by the pyrolysis of waste rubber powder, thereby achieving chemical bridging between silica and the rubber matrix and improving the interfacial bonding strength.

[0010] This invention uses silane coupling agents and 4-(2-allyl)-catechol to synergistically modify silica, which can significantly improve the dispersibility of silica in the rubber matrix, reduce the Mooney viscosity of reclaimed rubber materials, and have good adhesion. At the same time, the chemical crosslinking of silica-rubber is enhanced by the participation of allyl in vulcanization, thereby improving the reinforcing effect and obtaining high-performance reclaimed rubber materials.

[0011] Preferably, the silane coupling agent is Si-69. Si-69 (bis-[γ-(triethoxysilyl)propyl]tetrasulfide) contains triethoxysilane groups and tetrasulfide segments. The triethoxysilane groups can bind to the surface of silica through silane hydrolysis and condensation, while the sulfide segments can form covalent crosslinks with rubber, significantly improving tensile strength, tear resistance, and abrasion resistance.

[0012] Preferably, the functionalizing modifier includes two or more compounds selected from 3-hydroxycyclopentene, hexadienoic acid, cyclooctadiene, cyclopentadienoic acid, oligomeric pentadienoic acid, and C9-C22 dienoic acid. The functionalizing modifier includes compounds containing unsaturated double bonds and functional groups such as -COOH and -OH. The unsaturated double bonds can undergo click reactions with the -SH groups generated from the pyrolysis of solid waste rubber powder, grafting the functionalizing modifier onto the molecular chain of the product. This results in the product having functional groups such as -COOH and -OH. Under the combined action of these functional groups, a reclaimed rubber with good compatibility with general-purpose rubber, good mechanical properties, and good chemical and physical adhesion is obtained.

[0013] Preferably, the particle size of the waste rubber powder is 10-80 mesh.

[0014] The present invention also provides a method for preparing the above-mentioned silica-reinforced reclaimed rubber material, comprising the following steps:

[0015] (1) 4-(2-allyl)-catechol and silane coupling agent were used to modify silica to obtain modified silica;

[0016] (2) Waste rubber tires are crushed, screened, and impurities are removed to obtain waste rubber powder;

[0017] (3) Mix waste rubber powder with functional modifier and modified silica and stir evenly to obtain a mixture;

[0018] (4) The mixture is desulfurized and extruded to obtain desulfurized rubber compound;

[0019] (5) The desulfurized rubber compound is continuously kneaded in a refining extruder and then pressed into sheets to obtain the silica-reinforced reclaimed rubber material.

[0020] As a preferred embodiment, the modification method in step (1) includes the following steps: dissolving the silane coupling agent in a mixed solvent of ethanol and water, then adding silica, stirring and reacting, then adding 4-(2-allyl)-catechol, continuing to stir and react, and then separating, washing and drying the product to obtain the modified silica.

[0021] Preferably, the volume ratio of ethanol to water in the mixed solvent is 7-9:1; the mass of the silane coupling agent is 10-20% of the mass of the mixed solvent.

[0022] Preferably, the temperature of the reaction after adding silica is 55~65℃ and the reaction time is 1~3h; the temperature of the reaction after adding 4-(2-allyl)-catechol is 55~65℃ and the reaction time is 30~60min.

[0023] Preferably, the temperature during desulfurization extrusion in step (4) is 100~350℃.

[0024] Preferably, the kneading temperature in step (5) is 100~165℃.

[0025] Therefore, the present invention has the following beneficial effects: the present invention uses silane coupling agent and 4-(2-allyl)-catechol to synergistically modify silica, which can significantly improve the hydrophobicity of silica and its dispersibility in the rubber matrix, reduce the Mooney viscosity of the reclaimed rubber material, and have good adhesion; at the same time, the chemical crosslinking of silica-rubber is enhanced by the participation of allyl in vulcanization, thereby improving the reinforcing effect and obtaining high-performance reclaimed rubber material. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments.

[0027] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0028] General Implementation Examples:

[0029] A silica-reinforced recycled rubber material, by weight, comprises: 100 parts waste rubber powder, 1-20 parts functional modifier, and 5-30 parts modified silica.

[0030] The modified silica is prepared by reacting silica sequentially with a silane coupling agent and 4-(2-allyl)-catechol; the mass of the silane coupling agent is 1-3% of the mass of silica; the molar ratio of the silane coupling agent to 4-(2-allyl)-catechol is 2-3:1.

[0031] In one specific embodiment, the silane coupling agent is Si-69.

[0032] In one specific embodiment, the functionalizing modifier includes two or more of the following: 3-hydroxycyclopentene, hexadienoic acid, cyclooctadiene, cyclopentadienoic acid, oligopolypentadienoic acid, and C9-C22 dienoic acid.

[0033] In one specific embodiment, the particle size of the waste rubber powder is 10-80 mesh.

[0034] As one specific implementation method, the raw materials include, by weight: 100 parts waste rubber powder, 1-20 parts functionalized modifier, and 10-20 parts modified silica.

[0035] The preparation method of the above-mentioned silica-reinforced reclaimed rubber material includes the following steps:

[0036] (1) 4-(2-allyl)-catechol and silane coupling agent were used to modify silica to obtain modified silica;

[0037] (2) Waste rubber tires are crushed, screened, and impurities are removed to obtain waste rubber powder;

[0038] (3) Mix waste rubber powder with functional modifier and modified silica and stir evenly to obtain a mixture;

[0039] (4) The mixture is desulfurized and extruded to obtain desulfurized rubber compound;

[0040] (5) The desulfurized rubber compound is continuously kneaded in a refining extruder and then pressed into sheets to obtain the silica-reinforced reclaimed rubber material.

[0041] As a specific implementation method, the modification method in step (1) includes the following steps: dissolving the silane coupling agent in a mixed solvent of ethanol and water, then adding silica, stirring and reacting, then adding 4-(2-allyl)-catechol, continuing to stir and react, and then separating, washing and drying the product to obtain the modified silica.

[0042] In one specific embodiment, the volume ratio of ethanol to water in the mixed solvent is 7~9:1; the mass of the silane coupling agent is 10~20% of the mass of the mixed solvent.

[0043] In one specific embodiment, the temperature of the stirring reaction after adding silica is 55~65℃ and the stirring reaction time is 1~3h; the temperature of the stirring reaction after adding 4-(2-allyl)-catechol is 55~65℃ and the stirring reaction time is 30~60min.

[0044] As one specific implementation, the waste rubber tires mentioned in step (2) are selected from one or more of all-steel truck tires, passenger car tires, bias-ply truck tires and light truck tires.

[0045] As a specific implementation method, in step (2), steel wire cords, fiber cords, metal impurities and inorganic impurities in waste rubber powder are removed by physical methods.

[0046] As a specific implementation method, in step (3), when mixing, first stir at high speed for 5 to 20 minutes at a temperature of 50 to 150°C, and then stir at low speed for 10 to 25 minutes at a temperature of 50 to 150°C. The speed of high-speed stirring is 50 to 600 rpm, and the speed of low-speed stirring is 1 to 50 rpm.

[0047] As a specific implementation method, in step (4), desulfurization extrusion is carried out in a desulfurization extruder, which is a single-screw, twin-screw, or three-screw extruder; the desulfurization extruder has no less than 4 heating zones, and the temperature of each heating zone is controlled at 100~350℃ respectively; the desulfurization extruder speed is 10~120 rpm.

[0048] In one specific implementation, the kneading temperature in step (5) is 100~165℃.

[0049] Example 1:

[0050] A method for preparing a silica-reinforced reclaimed rubber material, comprising the following steps:

[0051] (1) Preparation of modified silica: Si-69 silane coupling agent was dissolved in a mixed solvent of ethanol and water (volume ratio 8:1), and the mass of Si-69 silane coupling agent was 15% of the mass of the mixed solvent; silica was then added, and the mixture was stirred at 60°C for 2 h. 4-(2-allyl)-catechol was then added, and the mixture was stirred for 45 min. The product was then centrifuged, washed three times with anhydrous ethanol, and dried under vacuum at 80°C to obtain modified silica; the mass of the silane coupling agent was 2% of the mass of silica; the molar ratio of the silane coupling agent to 4-(2-allyl)-catechol was 2.5:1.

[0052] (2) The solid waste all-steel radial truck tires are crushed and passed through 20-mesh and 60-mesh sieves. The steel cords, fiber cords, metal impurities and inorganic impurities in the clean rubber are removed by physical methods to obtain waste rubber powder.

[0053] (3) By weight, 100 parts of waste rubber powder are mixed with 5 parts of hexadienoic acid, 5 parts of cyclopentadienoic acid and 15 parts of modified silica, and then fed into a high-speed mixer. The mixture is stirred at high speed for 25 minutes at 100°C with a speed of 150 rpm. The mixture is then fed into a storage tank, kept at 100°C, and stirred at low speed for 25 minutes with a speed of 20 rpm to obtain a uniformly mixed material.

[0054] (4) The mixture is fed into the feed port of the twin-screw desulfurization extruder and extruded to obtain desulfurized rubber at a high temperature. The temperatures of the nine heating zones of the twin-screw desulfurization extruder are 135℃, 170℃, 230℃, 270℃, 270℃, 280℃, 280℃, 230℃, and 170℃, respectively. The speed of the twin-screw desulfurization extruder is 80 rpm. The extruded desulfurized rubber at a high temperature is transferred to a cooler for preliminary cooling to obtain granular desulfurized rubber.

[0055] (5) The granular desulfurized rubber is fed into a twin-screw refining extruder for continuous kneading at a kneading temperature of 150°C; the kneaded rubber is then fed into an extruder for compression molding and sheeting to obtain silica-reinforced reclaimed rubber material.

[0056] Example 2:

[0057] A method for preparing a silica-reinforced reclaimed rubber material, comprising the following steps:

[0058] (1) Preparation of modified silica: Si-69 silane coupling agent was dissolved in a mixed solvent of ethanol and water (volume ratio 7:1), and the mass of Si-69 silane coupling agent was 10% of the mass of the mixed solvent; silica was then added, and the mixture was stirred at 60°C for 2 h. 4-(2-allyl)-catechol was then added, and the mixture was stirred for 45 min. The product was then centrifuged, washed three times with anhydrous ethanol, and dried under vacuum at 80°C to obtain modified silica; the mass of silane coupling agent was 1% of the mass of silica; the molar ratio of silane coupling agent to 4-(2-allyl)-catechol was 2:1.

[0059] (2) The solid waste all-steel radial truck tires are crushed and passed through 20-mesh and 60-mesh sieves. The steel cords, fiber cords, metal impurities and inorganic impurities in the clean rubber are removed by physical methods to obtain waste rubber powder.

[0060] (3) By weight, 100 parts of waste rubber powder are mixed with 5 parts of hexadienoic acid, 5 parts of cyclopentadienoic acid and 10 parts of modified silica, and then fed into a high-speed mixer. The mixture is stirred at high speed for 25 minutes at 100°C with a speed of 150 rpm. The mixture is then fed into a storage tank, kept at 100°C and stirred at low speed for 25 minutes with a speed of 20 rpm to obtain a uniformly mixed material.

[0061] (4) The mixture is fed into the feed port of the twin-screw desulfurization extruder and extruded to obtain desulfurized rubber at a high temperature. The temperatures of the nine heating zones of the twin-screw desulfurization extruder are 135℃, 170℃, 230℃, 270℃, 270℃, 280℃, 280℃, 230℃, and 170℃, respectively. The speed of the twin-screw desulfurization extruder is 80 rpm. The extruded desulfurized rubber at a high temperature is transferred to a cooler for preliminary cooling to obtain granular desulfurized rubber.

[0062] (5) The granular desulfurized rubber is fed into a twin-screw refining extruder for continuous kneading at a kneading temperature of 150°C; the kneaded rubber is then fed into an extruder for compression molding and sheeting to obtain silica-reinforced reclaimed rubber material.

[0063] Example 3:

[0064] A method for preparing a silica-reinforced reclaimed rubber material, comprising the following steps:

[0065] (1) Preparation of modified silica: Si-69 silane coupling agent was dissolved in a mixed solvent of ethanol and water (volume ratio 9:1), and the mass of Si-69 silane coupling agent was 20% of the mass of the mixed solvent; silica was then added, and the mixture was stirred at 60°C for 2 h. 4-(2-allyl)-catechol was then added, and the mixture was stirred for 45 min. The product was then centrifuged, washed three times with anhydrous ethanol, and dried under vacuum at 80°C to obtain modified silica; the mass of the silane coupling agent was 3% of the mass of silica; the molar ratio of the silane coupling agent to 4-(2-allyl)-catechol was 3:1.

[0066] (2) The solid waste all-steel radial truck tires are crushed and passed through 20-mesh and 60-mesh sieves. The steel cords, fiber cords, metal impurities and inorganic impurities in the clean rubber are removed by physical methods to obtain waste rubber powder.

[0067] (3) By weight, 100 parts of waste rubber powder are mixed with 5 parts of hexadienoic acid, 5 parts of cyclopentadienoic acid and 20 parts of modified silica, and then fed into a high-speed mixer. The mixture is stirred at high speed for 25 minutes at 100°C with a speed of 150 rpm. The mixture is then fed into a storage tank, kept at 100°C, and stirred at low speed for 25 minutes with a speed of 20 rpm to obtain a uniformly mixed material.

[0068] (4) The mixture is fed into the feed port of the twin-screw desulfurization extruder and extruded to obtain desulfurized rubber at a high temperature. The temperatures of the nine heating zones of the twin-screw desulfurization extruder are 135℃, 170℃, 230℃, 270℃, 270℃, 280℃, 280℃, 230℃, and 170℃, respectively. The speed of the twin-screw desulfurization extruder is 80 rpm. The extruded desulfurized rubber at a high temperature is transferred to a cooler for preliminary cooling to obtain granular desulfurized rubber.

[0069] (5) The granular desulfurized rubber is fed into a twin-screw refining extruder for continuous kneading at a kneading temperature of 150°C; the kneaded rubber is then fed into an extruder for compression molding and sheeting to obtain silica-reinforced reclaimed rubber material.

[0070] Comparative Example 1 (no modification of silica):

[0071] A method for preparing a silica-reinforced reclaimed rubber material, comprising the following steps:

[0072] (1) The solid waste all-steel radial truck tires are crushed and passed through 20-mesh and 60-mesh sieves. The steel cords, fiber cords, metal impurities and inorganic impurities in the clean rubber are removed by physical methods to obtain waste rubber powder.

[0073] (2) By weight, 100 parts of waste rubber powder are mixed with 5 parts of hexadienoic acid, 5 parts of cyclopentadienoic acid and 15 parts of silica, and then fed into a high-speed mixer. The mixture is stirred at high speed for 25 minutes at 100°C with a speed of 150 rpm. The mixture is then fed into a storage tank, kept at 100°C and stirred at low speed for 25 minutes with a speed of 20 rpm. A uniformly mixed mixture is obtained.

[0074] (3) The mixture is fed into the feed port of the twin-screw desulfurization extruder and extruded to obtain desulfurized rubber at a high temperature. The temperatures of the nine heating zones of the twin-screw desulfurization extruder are 135℃, 170℃, 230℃, 270℃, 270℃, 280℃, 280℃, 230℃, and 170℃, respectively. The speed of the twin-screw desulfurization extruder is 80 rpm. The extruded desulfurized rubber at a high temperature is transferred to a cooler for preliminary cooling to obtain granular desulfurized rubber.

[0075] (4) The granular desulfurized rubber is fed into a twin-screw refining extruder for continuous kneading at a kneading temperature of 150°C; the kneaded rubber is then fed into an extruder for compression molding and sheeting to obtain silica-reinforced reclaimed rubber material.

[0076] Comparative Example 2 (no silane coupling agent added to the modifier):

[0077] A method for preparing a silica-reinforced reclaimed rubber material, comprising the following steps:

[0078] (1) Preparation of modified silica: 4-(2-allyl)-catechol was dissolved in ethanol, and then silica was added. The mixture was stirred at 60°C for 2 hours. The product was then centrifuged, washed three times with anhydrous ethanol, and dried under vacuum at 80°C to obtain modified silica. The mass of 4-(2-allyl)-catechol was 3% of the mass of silica.

[0079] (2) The solid waste all-steel radial truck tires are crushed and passed through 20-mesh and 60-mesh sieves. The steel cords, fiber cords, metal impurities and inorganic impurities in the clean rubber are removed by physical methods to obtain waste rubber powder.

[0080] (3) By weight, 100 parts of waste rubber powder are mixed with 5 parts of hexadienoic acid, 5 parts of cyclopentadienoic acid and 15 parts of modified silica, and then fed into a high-speed mixer. The mixture is stirred at high speed for 25 minutes at 100°C with a speed of 150 rpm. The mixture is then fed into a storage tank, kept at 100°C, and stirred at low speed for 25 minutes with a speed of 20 rpm to obtain a uniformly mixed material.

[0081] (4) The mixture is fed into the feed port of the twin-screw desulfurization extruder and extruded to obtain desulfurized rubber at a high temperature. The temperatures of the nine heating zones of the twin-screw desulfurization extruder are 135℃, 170℃, 230℃, 270℃, 270℃, 280℃, 280℃, 230℃, and 170℃, respectively. The speed of the twin-screw desulfurization extruder is 80 rpm. The extruded desulfurized rubber at a high temperature is transferred to a cooler for preliminary cooling to obtain granular desulfurized rubber.

[0082] (5) The granular desulfurized rubber is fed into a twin-screw refining extruder for continuous kneading at a kneading temperature of 150°C; the kneaded rubber is then fed into an extruder for compression molding and sheeting to obtain silica-reinforced reclaimed rubber material.

[0083] Comparative Example 3 (without 4-(2-allyl)-catechol added to the modifier):

[0084] A method for preparing a silica-reinforced reclaimed rubber material, comprising the following steps:

[0085] (1) Preparation of modified silica: Si-69 silane coupling agent was dissolved in a mixed solvent of ethanol and water (volume ratio 8:1), and the mass of Si-69 silane coupling agent was 15% of the mass of the mixed solvent; then silica was added, and the mixture was stirred at 60°C for 2 hours. The product was then centrifuged, washed three times with anhydrous ethanol, and dried under vacuum at 80°C to obtain modified silica; wherein the mass of the silane coupling agent was 3% of the mass of silica.

[0086] (2) The solid waste all-steel radial truck tires are crushed and passed through 20-mesh and 60-mesh sieves. The steel cords, fiber cords, metal impurities and inorganic impurities in the clean rubber are removed by physical methods to obtain waste rubber powder.

[0087] (3) By weight, 100 parts of waste rubber powder are mixed with 5 parts of hexadienoic acid, 5 parts of cyclopentadienoic acid and 15 parts of modified silica, and then fed into a high-speed mixer. The mixture is stirred at high speed for 25 minutes at 100°C with a speed of 150 rpm. The mixture is then fed into a storage tank, kept at 100°C, and stirred at low speed for 25 minutes with a speed of 20 rpm to obtain a uniformly mixed material.

[0088] (4) The mixture is fed into the feed port of the twin-screw desulfurization extruder and extruded to obtain desulfurized rubber at a high temperature. The temperatures of the nine heating zones of the twin-screw desulfurization extruder are 135℃, 170℃, 230℃, 270℃, 270℃, 280℃, 280℃, 230℃, and 170℃, respectively. The speed of the twin-screw desulfurization extruder is 80 rpm. The extruded desulfurized rubber at a high temperature is transferred to a cooler for preliminary cooling to obtain granular desulfurized rubber.

[0089] (5) The granular desulfurized rubber is fed into a twin-screw refining extruder for continuous kneading at a kneading temperature of 150°C; the kneaded rubber is then fed into an extruder for compression molding and sheeting to obtain silica-reinforced reclaimed rubber material.

[0090] Comparative Example 4 (excessive amount of 4-(2-allyl)-catechol):

[0091] A method for preparing a silica-reinforced reclaimed rubber material, comprising the following steps:

[0092] (1) Preparation of modified silica: Si-69 silane coupling agent was dissolved in a mixed solvent of ethanol and water (volume ratio 8:1), and the mass of Si-69 silane coupling agent was 15% of the mass of the mixed solvent; silica was then added, and the mixture was stirred at 60°C for 2 h. 4-(2-allyl)-catechol was then added, and the mixture was stirred for another 45 min. The product was then centrifuged, washed three times with anhydrous ethanol, and dried under vacuum at 80°C to obtain modified silica; the mass of the silane coupling agent was 2% of the mass of silica; the molar ratio of the silane coupling agent to 4-(2-allyl)-catechol was 1:1.

[0093] (2) The solid waste all-steel radial truck tires are crushed and passed through 20-mesh and 60-mesh sieves. The steel cords, fiber cords, metal impurities and inorganic impurities in the clean rubber are removed by physical methods to obtain waste rubber powder.

[0094] (3) By weight, 100 parts of waste rubber powder are mixed with 5 parts of hexadienoic acid, 5 parts of cyclopentadienoic acid and 15 parts of modified silica, and then fed into a high-speed mixer. The mixture is stirred at high speed for 25 minutes at 100°C with a speed of 150 rpm. The mixture is then fed into a storage tank, kept at 100°C, and stirred at low speed for 25 minutes with a speed of 20 rpm to obtain a uniformly mixed material.

[0095] (4) The mixture is fed into the feed port of the twin-screw desulfurization extruder and extruded to obtain desulfurized rubber at a high temperature. The temperatures of the nine heating zones of the twin-screw desulfurization extruder are 135℃, 170℃, 230℃, 270℃, 270℃, 280℃, 280℃, 230℃, and 170℃, respectively. The speed of the twin-screw desulfurization extruder is 80 rpm. The extruded desulfurized rubber at a high temperature is transferred to a cooler for preliminary cooling to obtain granular desulfurized rubber.

[0096] (5) The granular desulfurized rubber is fed into a twin-screw refining extruder for continuous kneading at a kneading temperature of 150°C; the kneaded rubber is then fed into an extruder for compression molding and sheeting to obtain silica-reinforced reclaimed rubber material.

[0097] Comparative Example 5 (using urushiol instead of 4-(2-allyl)-catechol):

[0098] A method for preparing a silica-reinforced reclaimed rubber material, comprising the following steps:

[0099] (1) Preparation of modified silica: Si-69 silane coupling agent was dissolved in a mixed solvent of ethanol and water (volume ratio 8:1), and the mass of Si-69 silane coupling agent was 15% of the mass of the mixed solvent; silica was then added, and the mixture was stirred at 60°C for 2 h, followed by the addition of urushiol. The mixture was stirred for 45 min, and the product was centrifuged, washed three times with anhydrous ethanol, and dried under vacuum at 80°C to obtain modified silica; the mass of silane coupling agent was 2% of the mass of silica; the molar ratio of silane coupling agent to urushiol was 2.5:1.

[0100] (2) The solid waste all-steel radial truck tires are crushed and passed through 20-mesh and 60-mesh sieves. The steel cords, fiber cords, metal impurities and inorganic impurities in the clean rubber are removed by physical methods to obtain waste rubber powder.

[0101] (3) By weight, 100 parts of waste rubber powder are mixed with 5 parts of hexadienoic acid, 5 parts of cyclopentadienoic acid and 15 parts of modified silica, and then fed into a high-speed mixer. The mixture is stirred at high speed for 25 minutes at 100°C with a speed of 150 rpm. The mixture is then fed into a storage tank, kept at 100°C, and stirred at low speed for 25 minutes with a speed of 20 rpm to obtain a uniformly mixed material.

[0102] (4) The mixture is fed into the feed port of the twin-screw desulfurization extruder and extruded to obtain desulfurized rubber at a high temperature. The temperatures of the nine heating zones of the twin-screw desulfurization extruder are 135℃, 170℃, 230℃, 270℃, 270℃, 280℃, 280℃, 230℃, and 170℃, respectively. The speed of the twin-screw desulfurization extruder is 80 rpm. The extruded desulfurized rubber at a high temperature is transferred to a cooler for preliminary cooling to obtain granular desulfurized rubber.

[0103] (5) The granular desulfurized rubber is fed into a twin-screw refining extruder for continuous kneading at a kneading temperature of 150°C; the kneaded rubber is then fed into an extruder for compression molding and sheeting to obtain silica-reinforced reclaimed rubber material.

[0104] In the tire carcass formulation, the recycled rubber material from the above examples and comparative examples was mixed with natural rubber at a mass ratio of 1:2 and then compounded. The performance of the compounded vulcanized rubber was tested, and the results are shown in Table 1.

[0105] Table 1: Test Results of Compound Rubber Properties

[0106]

[0107] As shown in Table 1, the recycled rubber materials prepared by the method of this invention in Examples 1-3 exhibit good self-adhesion, chemical bonding properties, and high tensile strength after being mixed with natural rubber. However, in Comparative Example 1, the addition of unmodified silica resulted in a significant decrease in the self-adhesion, chemical bonding properties, and tensile strength of the mixed rubber compared to Example 1 due to its high water absorption, tendency to self-polymerize, and poor compatibility with rubber. In Comparative Example 2, only 4-(2-allyl)-catechol was used to modify silica without adding a silane coupling agent, resulting in a decrease in the improvement effect on silica dispersion compared to Example 1, leading to a decrease in all properties of the mixed rubber compared to Example 1. In Comparative Example 3, only a silane coupling agent was used to modify silica without adding 4-(2-allyl)-catechol, preventing the silica from chemically bonding with the rubber and significantly reducing the reinforcing effect compared to Example 1. In Comparative Example 4, the ratio of silane coupling agent and 4-(2-allyl)-catechol in the modifier is outside the scope of this invention. Excessive use of 4-(2-allyl)-catechol will also lead to a decrease in the reinforcing effect. In Comparative Example 5, urushiol was used instead of 4-(2-allyl)-catechol in this application to modify silica. Although it also has a catechol structure and reactive double bonds, its nonpolar long carbon chain weakens the ability of the catechol groups to bond with silica through hydrogen bonds, resulting in insufficient bonding ability between silica and rubber. The reinforcing effect is also lower than that in Example 1.

Claims

1. A method for preparing a silica-reinforced reclaimed rubber material, characterized in that the steps include: include: (1) Silica was reacted sequentially with a silane coupling agent and 4-(2-allyl)-catechol to obtain modified silica; The silane coupling agent is Si-69; the mass of the silane coupling agent is 1-3% of the mass of silica; the molar ratio of the silane coupling agent to 4-(2-allyl)-catechol is 2-3:1; (2) Waste rubber tires are crushed, screened, and impurities are removed to obtain waste rubber powder; (3) By weight, 100 parts of waste rubber powder, 1-20 parts of functional modifier, and 5-30 parts of modified silica are mixed and stirred evenly to obtain a mixture; the functional modifier includes two or more of 3-hydroxycyclopentene, hexadienoic acid, cyclooctadiene, and cyclopentadienoic acid. (4) The mixture is desulfurized and extruded to obtain desulfurized rubber compound; (5) After continuous kneading in a refining extruder, the desulfurized rubber compound is pressed into sheets.

2. The method for preparing silica-reinforced reclaimed rubber material according to claim 1, characterized in that, The functionalizing modifier is 5 parts hexadienoic acid and 5 parts cyclopentadienoic acid.

3. The method for preparing silica-reinforced reclaimed rubber material according to claim 1, characterized in that, The particle size of the waste rubber powder is 10-80 mesh.

4. The method for preparing silica-reinforced reclaimed rubber material according to claim 1, characterized in that, The modification method in step (1) includes the following steps: dissolving the silane coupling agent in a mixed solvent of ethanol and water, then adding silica, stirring and reacting, then adding 4-(2-allyl)-catechol, continuing to stir and react, and then separating, washing and drying the product to obtain the modified silica.

5. The method for preparing silica-reinforced reclaimed rubber material according to claim 4, characterized in that, The volume ratio of ethanol to water in the mixed solvent is 7~9:1; the mass of the silane coupling agent is 10~20% of the mass of the mixed solvent.

6. The method for preparing silica-reinforced reclaimed rubber material according to claim 4 or 5, characterized in that, After adding silica, the reaction temperature is 55-65℃ and the reaction time is 1-3h; after adding 4-(2-allyl)-catechol, the reaction temperature is 55-65℃ and the reaction time is 30-60min.

7. The method for preparing silica-reinforced reclaimed rubber material according to claim 1, characterized in that, The temperature during desulfurization extrusion in step (4) is 100~350℃.

8. The method for preparing silica-reinforced reclaimed rubber material according to claim 1, characterized in that, The kneading temperature in step (5) is 100~165℃.

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