A method for electro-promoted in situ epoxidation of a styrene-butadiene emulsion

Abstract

The present application relates to the technical field of styrene butadiene emulsion modification, and particularly relates to a method for in-situ epoxidation of electrically promoted styrene butadiene rubber emulsion, and the preparation steps comprise the following steps: 1) raw material preparation; 2) device assembly; 3) in-situ epoxidation reaction; and 4) product post-treatment. The method is suitable for preparing styrene butadiene rubber with an epoxy degree of 10% to 15%, high mechanical elasticity and green environmental protection, and can be widely applied to high-end fields such as tires, sealing elements and high-performance rubber pipes.

Description

Technical Field

[0001] This invention relates to the field of styrene-butadiene rubber (SBR) emulsion modification technology, specifically to a method for in-situ epoxidation of SBR emulsion by electro-promoting. This method is suitable for preparing SBR with an epoxy degree of 10% to 15%, high mechanical elasticity, and environmental friendliness, and can be widely used in high-end fields such as tires, seals, and high-performance hoses. Background Technology

[0002] Styrene-butadiene rubber (SBR), one of the most produced synthetic rubbers, possesses excellent processing and mechanical properties and is widely used in tires, seals, and rubber products. However, the presence of double bonds in its molecular chain structure results in poor aging resistance, oil resistance, and compatibility with polar materials, limiting its application in high-end fields. Epoxidation modification is an effective means to improve the properties of SBR. By introducing epoxy groups onto the double bonds, its polarity, compatibility, and mechanical strength can be significantly enhanced. Studies have shown that SBR with an epoxy degree in the range of 10%–15% can effectively balance polarity improvement and high mechanical elasticity, making it an ideal raw material for tire tread rubber and high-performance hoses. However, there is a significant technological gap in the efficient and environmentally friendly preparation of SBR within this epoxy degree range using existing epoxidation methods.

[0003] Currently, the epoxidation methods for styrene-butadiene rubber (SBR) are mainly divided into organic peroxy acid oxidation and transition metal catalytic oxidation. 1. Organic acid peroxidation method: Domestic and foreign patents such as RU2623274C2 and CN104530837A disclose the use of organic peroxy acid oxidation method to prepare epoxidized styrene-butadiene rubber. This type of method requires the use of a large amount of organic solvents and peroxy acids, which not only increases the production cost, but also generates a large amount of organic waste and pollutes the environment.

[0004] 2. Transition metal catalytic oxidation method: In this method, although the degree of epoxy can be controlled to a certain extent, the catalyst residue will lead to a decrease in the elasticity of styrene-butadiene rubber, which cannot meet the requirements of tires and rubber hoses for high mechanical elasticity and safety. Moreover, the catalyst recovery process is highly complex, and the economics of industrial application are extremely poor. Therefore, developing a green and low-cost styrene-butadiene rubber (SBR) emulsion epoxidation technology route with no catalyst residue, mild reaction conditions, and precise controllable epoxy degree (10%–15%) is the key to solving the problem of green preparation of high-performance SBR and is also the core research and development goal of this invention.

[0005] After multiple experiments and optimizations by the inventors, the "alternating current + mesh electrode array + in-situ generation of active species by chloride ions" route was innovatively proposed, successfully breaking through the existing technical bottlenecks and achieving remarkable results. Summary of the Invention

[0006] The purpose of this invention is to address the problems of high cost, significant pollution, difficulty in catalyst separation, and difficulty in precise control of epoxy degree in existing technologies. This invention provides a low-cost method for in-situ electro-promoted epoxidation of styrene-butadiene rubber emulsion. By generating oxidizing agents in situ through electrochemical processes, it eliminates the need for adding large amounts of organic peroxy acids or transition metal catalysts, thereby achieving green, energy-saving, and efficient epoxidation modification of styrene-butadiene rubber.

[0007] The technical solution is a method for in-situ epoxidation of styrene-butadiene rubber latex by electro-promoting, characterized in that an AC electrolysis system constructed by a mesh electrode array is used to induce an epoxidation reaction in situ in an aqueous medium containing chloride ions, selectively oxidizing double bonds in the molecular chain and precisely achieving epoxy group modification.

[0008] Specific reaction mechanisms include: In-situ generation of active species at the electrode: Under the action of an alternating electric field, chloride ions in the electrolyte undergo a transient electrochemical reaction on the surface of the mesh electrode to generate highly active hypochlorous acid (HClO) molecules and their precursor species.

[0009] Microphase interface diffusion and reaction: Periodic perturbations generated by alternating current promote the penetration of active species through the emulsion double layer and diffusion into the interior of styrene-butadiene rubber emulsion microspheres, selectively adding to the double bonds on the molecular chain to form epoxy groups.

[0010] Precise process control: By adjusting the current density, frequency, and electrolyte concentration of the alternating current, the generation rate and diffusion flux of active species are controlled, thereby precisely controlling the epoxy content of styrene-butadiene rubber within the range of 10% to 15%.

[0011] The specific technical solution is as follows: A method for preparing raw materials for in-situ epoxidation modification of styrene-butadiene rubber (SBR) is characterized by taking an SBR emulsion obtained by emulsion polymerization under the action of a nonionic surfactant (such as fatty alcohol polyoxyethylene ether), and adding a small amount of halide salt solution to make the chloride ion concentration of the system 0.01~0.03 mol / L. The halide salt can be one or a mixture of several chlorides such as potassium chloride, sodium chloride, lithium chloride and tetrabutylammonium chloride.

[0012] Using nonionic surfactants improves the chemical stability of emulsions. Styrene-butadiene emulsions have a solid content of 10%-30%, which reduces viscosity and improves mass transfer efficiency. Precise control of chloride ion concentration prevents premature salting out.

[0013] Electrolysis device electrodes: titanium-based mesh electrodes (possessing high catalytic activity, conductivity, and chemical stability).

[0014] An assembly method for an electrolytic device adapted for in-situ epoxidation modification of styrene-butadiene rubber is characterized by employing high-surface-area electrodes adapted for kilogram-scale electrolytic cells, wherein the electrodes are arranged in a parallel and symmetrical manner as multiple high-surface-area electrode arrays; the area of ​​a single electrode array is 1.0-2.0 m². 2 The electrode spacing is 5-10 cm. The multi-electrode array integrates synchronous temperature control, allowing real-time adjustment of electrode temperature to prevent localized overheating or temperature unevenness from affecting the reaction system. It also provides stable support for the synergistic coupling of the AC frequency and the reaction system. The electrode material is a titanium-based electrode with a conductive ceramic fluorine-doped tin dioxide surface modified. The high-surface-area multi-electrode array can employ a mesh electrode structure. The electrode material can be fluorine-doped tin dioxide, modified by being attached to the titanium-based electrode material as a surface coating. The electrode anti-polarization pretreatment employs dilute acid activation and inert gas purging processes.

[0015] Power supply: AC power, frequency 45-65 Hz. (This serves to "suppress electrode polarization and achieve uniform distribution of active free radicals / ions through periodic polarity switching," thus preventing emulsion coagulation caused by drastic local pH changes). Reaction vessel: Kilogram-scale electrolytic cell, equipped with nitrogen gas introduction device and stirring device, such as Figure 1 As shown.

[0016] Process steps (1) Raw material preparation: Take the styrene-butadiene rubber latex obtained by conventional emulsion polymerization, slowly add chloride solution to it under constant temperature stirring, stir and mix, adjust the chloride ion concentration to 0.01-0.03 mol / L, and obtain the reaction solution; (2) Assembly of the device: Install the mesh electrodes in multiple arrays in parallel and symmetrical arrangement in the electrolytic cell, ensuring uniform electrode spacing, and connect to AC power supply; (3) In-situ epoxidation reaction: Transfer the reaction solution obtained in process step (1) to the electrolytic cell, start the stirring device, set the stirring speed to 500-1000 r / min, introduce nitrogen to replace the air in the system and maintain the nitrogen atmosphere; turn on the power supply, set the electrolysis voltage to 2.0-3.0 V and the current density to 10-20 mA / cm 2 React at 45±5 ℃ for 5-10 h; (4) Post-processing of product: After the reaction is completed, the power supply and nitrogen gas are turned off, the reaction solution is transferred to the demulsification device, and conventional demulsification methods (such as salting out or acid precipitation) are used for treatment. After washing and drying, epoxidized styrene-butadiene rubber product is obtained.

[0017] The above process parameter range was determined to be the optimal range through parameter sensitivity analysis. Arbitrary adjustments can easily lead to insufficient epoxy content, epoxy ring-opening and double bond cross-linking side reactions, and a decrease in mechanical properties.

[0018] Technical features The epoxidation method for styrene-butadiene rubber latex disclosed in this invention application is based on an innovative electro-promoted in-situ epoxidation technology, and has multiple advantages such as high performance, green and low carbon footprint, and high industrial adaptability. Its core technical features are as follows: A groundbreaking original breakthrough in the core reaction mechanism addresses industry pain points at their source: The innovative use of an electro-promoted in-situ epoxidation mechanism, employing an AC electrolysis system constructed with a mesh electrode array, generates hypochlorous acid, an active oxide, in situ without the need for organic peroxy acids or transition metal catalysts. This fundamentally distinguishes it from existing organic peroxy acid methods (such as RU2623274C2 and CN104530837A) and transition metal catalytic methods. It avoids the damage to rubber properties caused by metal residues, resolving industry pain points such as pollution, additive residues, and high costs associated with existing technologies.

[0019] The epoxy degree is precisely controllable and the reaction uniformity is excellent: by adjusting process parameters such as current density, frequency, and electrolyte concentration, the epoxy degree can be precisely and uniformly controlled within the ideal range of 10% to 15%, and the epoxy grafting modification amount of the product is ≥10%, which fully matches the application requirements of high-end rubber products. Green, low-carbon, and environmentally friendly, with significant environmental benefits: The reaction system is a pure aqueous phase, with no organic solvent emissions, zero catalyst input, solvent costs reduced by more than 60%, and environmental treatment costs extremely low, resulting in significant environmental benefits.

[0020] With excellent modification effects and outstanding advantages in both cost and performance: epoxy-modified styrene-butadiene rubber has comparable effects to traditional peroxy acid oxidation, with better mechanical properties, increasing modulus at a given elongation by nearly 10%, tensile strength by nearly 30%, and elongation at break by more than 10%. It also has better fatigue life and resilience, meeting the requirements of high-end fields such as rubber hoses and tires. Process costs are reduced by more than 70%, making it highly practical for industrial use and competitive in the market. Attached Figure Description

[0021] Figure 1 Schematic diagram of an electrolysis unit; Figure 2 Nuclear magnetic resonance and infrared spectroscopy characterization results; Figure 3 SEM images (a) Comparative Example 1; (b) Example 1. Detailed Implementation

[0022] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. It should be noted that, unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used in the following embodiments, unless otherwise specified, can be purchased commercially. Where specific conditions are not specified in the embodiments, they are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially. To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0023] Example 1 (1) Raw material preparation: Take 1 L of styrene-butadiene rubber latex (solid content 30%) obtained by conventional emulsion polymerization, add 100 ml of aqueous solution containing 0.37 g of potassium chloride solid and 1.29 g of tetrabutylammonium chloride, stir and mix well to make the chloride ion concentration 0.01 mol / L; (2) Device assembly: A mesh titanium base electrode with fluorine-doped tin dioxide surface modification is used (single electrode area 1.0 m²). 2 The electrodes are arranged symmetrically in three arrays with a spacing of 5 cm, and installed in a 2 L kg electrolytic cell, connected to an AC power supply (frequency 50 Hz). (3) In-situ epoxidation reaction: The above emulsion was transferred to an electrolytic cell, and stirring was started (500 r / min). Nitrogen gas was introduced for 30 min to replace the air and maintain the nitrogen atmosphere; the power supply was turned on and the voltage was set to 2.4 V and the current density to 10 mA / cm. 2 The reaction was carried out at 35 ℃ for 5 h. (4) Post-processing of the product: After the reaction was completed, a 10% (w / w) calcium chloride solution was added to the reaction solution for salting out and demulsification. The mixture was allowed to stand and separate into layers. The rubber phase was collected, washed three times with deionized water, and dried under vacuum at 60 °C for 8 h to obtain epoxidized styrene-butadiene rubber. The epoxy degree (ED) of the product was found to be 10%.

[0024] (5) Application and testing: Using epoxidized emulsion styrene-butadiene rubber as the matrix, highly dispersed silica is added as a reinforcing filler, and silane coupling agent, process oil, antioxidant, vulcanization system and other additives are mixed in an internal mixer and vulcanized in a flat vulcanizing machine to prepare 2 mm thick dumbbell-shaped rubber sheets. The 100% constant modulus, tensile strength and elongation at break are measured.

[0025] Examples 2-5 Take the reaction parameters shown in Table 1: Table 1 Parameters of Epoxidation Reaction of Emulsion Styrene-Butadiene Rubber in Examples 2-5 The preparation method in Example 1 was used for the epoxidation of emulsion styrene-butadiene rubber. The reaction parameter ratios were different for each group, but the formulations in Table 1 were followed, and all other steps were the same.

[0026] Comparative Example 1 The difference from Example 1 is that an un-epoxidized emulsion styrene-butadiene rubber and silica and other additives were blended and vulcanized.

[0027] Comparative Example 2 The difference from Example 1 is that the styrene-butadiene rubber emulsion obtained by epoxidation modification with 60 mol% peroxyformic acid at 40°C was demulsified and then blended and vulcanized with silica and other additives.

[0028] Comparative Example 3 The difference from Example 1 is that, after demulsifying 10 kg of styrene-butadiene rubber latex, it was dissolved in 200 L of toluene, and acetic acid (CH3COOH) was added as the reaction medium. Subsequently, a 30% hydrogen peroxide (H2O2) solution containing sodium tungstate (Na2WO4) was added dropwise under stirring conditions (40°C). The amount of sodium tungstate was 1 mol% of the styrene-butadiene rubber, acetic acid was 100 mol%, and hydrogen peroxide was 300 mol%. After demulsification, it was blended and vulcanized with silica and other additives.

[0029] Comparative Examples 4-6 Table 2 Parameters of Epoxidation Reaction of Emulsion Styrene-Butadiene Rubber in Comparative Examples 4-6

[0030] The preparation method in Example 1 was used for the epoxidation of emulsion styrene-butadiene rubber. The reaction parameter ratios were different for each group, but the formulations in Table 1 were followed, and all other steps were the same.

[0031] Product characterization was performed using nuclear magnetic resonance and infrared spectroscopy to characterize the epoxidized styrene-butadiene rubber. The results are as follows: Figure 2 .

[0032] 1 ¹H NMR spectroscopy showed that the epoxidized raw material exhibited characteristic hydrogen peaks of epoxy groups at δ 2.5–2.8 ppm, confirming that the butadiene double bond was successfully converted into epoxy groups, and that the styrene segment structure remained unchanged.

[0033] Epoxidation products at 1630–1650 cm⁻¹ -1 The C=C double bond stretching vibration peak at 820–950 cm⁻¹ is significantly weakened, while the peak at 820–950 cm⁻¹ is significantly weakened. -1 The region shows characteristic vibrational peaks of epoxy groups (C–O–C); the benzene ring-related absorption peaks remain basically unchanged, indicating that the epoxidation reaction mainly occurs in the butadiene double bond, the styrene chain segment remains stable, the product structure is clear and there are few side reactions.

[0034] Comparative Example 1 and Example 1 were prepared, and then the two samples were characterized using scanning electron microscopy. The results are as follows: Figure 3 As shown.

[0035] The dispersion state of silica filler in the ESBR rubber matrix was investigated by scanning electron microscopy (SEM). The results showed that in Comparative Example 1, the silica particles formed distinct large-sized clusters (…). Figure 3 (a); In contrast, in Example 1 with epoxidation modification, the dispersion uniformity of the silica filler was significantly improved ( Figure 3 (b). This improvement is attributed to the strong interaction between the hydroxyl (-OH) groups and epoxy groups on the silica surface.

[0036] Test Example 1 The samples prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to performance tests according to the test methods in Example 1. The test items and methods are as follows: 100% elongation modulus: GB / T 528-2009; Tensile strength: GB / T 528-2009; Elongation at break: GB / T 528-2009; The test results are shown in Table 3: Table 3 Test results of the anti-corrosion coatings obtained in Examples 1-5 and Comparative Examples 1-3 Analysis of the data in the table above shows that, compared with the comparative product, the epoxy-modified emulsion styrene-butadiene rubber of the present invention has the advantages of high tensile modulus, high tensile strength and good toughness, indicating that it has a better application effect on silica substrate and can be widely used in high-performance water-based adhesives, rubber blends and coatings.

[0037] Table 4. Properties of products from Comparative Examples 4-6

[0038] 1 Through nuclear magnetic resonance 1 H-spectral characterization showed no obvious transformation of epoxy functional groups in the product.

[0039] The experimental results in the table above show that, compared with the product in the examples, changes in reaction conditions easily trigger a series of side reactions, leading to reaction failure. Increased chloride ion concentration leads to demulsification, and lower decomposition voltage and reaction time cannot effectively promote the electrolysis reaction.

[0040] Economic benefits and industrial applicability analysis: Based on production practice and comprehensive cost accounting (Table 5), the electro-promoted in-situ epoxidation method described in this invention (Example 1) has a comprehensive production process cost of only about RMB 7,000 per ton of product when preparing products with an epoxy degree of 10%–15%. Compared with the traditional organic peroxyacid method (Comparative Example 2, RMB 25,000 / ton), the cost is reduced by about 70%, and compared with the transition metal catalytic method (Comparative Example 3, RMB 48,000 / ton), the cost is reduced by nearly 85%.

[0041] This significant economic advantage stems from the fact that this invention employs an electrochemical in-situ induction mechanism to generate active oxide species, achieving low-volume (0.1 million yuan / ton) main reaction reagents and zero catalyst input. Simultaneously, because the reaction is carried out in a pure aqueous emulsion system, it completely avoids the large-scale procurement and recycling costs of organic solvents introduced in Comparative Example 3 for dissolving rubber, resulting in a dramatic reduction in solvent / medium costs from 0.3 million yuan / ton to 0.1 million yuan / ton.

[0042] Table 5. Comparison of Production Process Costs between Example 1 and Comparative Examples 2-3 1

[0043] 1 The cost figures in the table are calculated based on an output of 10,000 yuan per ton. Styrene-butadiene rubber latex, as a common raw material, is not included in the process cost.

[0044] Furthermore, while significantly reducing environmental treatment and energy consumption costs, this process avoids the damage to molecular chains caused by transition metal residues. The modified styrene-butadiene rubber exhibits excellent mechanical elasticity and polarity balance: its modulus at a given elongation is increased by nearly 10%, and its tensile strength is increased by 30%. In summary, this invention not only solves the bottleneck problems of catalyst residue and environmental pollution in the preparation of high-performance styrene-butadiene rubber, but also realizes the possibility of large-scale green industrialization of this material at extremely low production costs.

[0045] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for in-situ epoxidation of styrene-butadiene emulsion via electro-promoted oxidation, the technical solution of which is as follows: (1) Raw material preparation: Take the styrene-butadiene rubber latex obtained by conventional emulsion polymerization, slowly add chloride solution to it under constant temperature stirring, stir and mix to obtain a styrene-butadiene rubber latex with a final chloride ion concentration of 0.01~0.03 mol / L; (2) Device assembly: High surface area mesh electrodes adapted to kilogram-level electrolytic cells are used. The mesh electrodes are installed in multiple parallel and symmetrical arrays in the electrolytic cell, ensuring uniform electrode spacing of 5-10 cm and a single electrode area of ​​1.0-2.0 m². 2 Connect to an AC power supply with a voltage of 2.0-3.0 V to assemble an electrolysis device; the electrode material of the mesh electrode is fluorine-doped tin dioxide, which is modified by being attached to the titanium-based electrode material in the form of a surface coating; the mesh electrode undergoes anti-polarization pretreatment, which adopts a dilute acid activation and inert gas purging process. (3) In-situ epoxidation reaction: Transfer the reaction solution obtained in step (1) to an electrolytic cell, start the stirring device, control the stirring rate at 500-1000 r / min, introduce nitrogen to replace the air in the system and maintain a nitrogen atmosphere; turn on the power supply and react for 5-10 h at an electrolytic voltage of 2.0-3.0 V, controlling the current density at 10-20 mA / cm². 2 The frequency of the alternating current is 45~65 Hz, the reaction temperature is maintained at 40±5 ℃, and the pH value of the system is adjusted to 5.0-7.0; (4) Post-processing of product: After the reaction is completed, the power supply and nitrogen gas are turned off, the reaction liquid is transferred to the demulsification device, and conventional demulsification method is used for processing. After washing and drying, epoxidized styrene-butadiene rubber product is obtained.

2. The method for in-situ electro-promoted epoxidation of styrene-butadiene emulsion according to claim 1, characterized in that, The specific process for preparing the raw materials is as follows: Take the styrene-butadiene rubber latex obtained by emulsion polymerization under the action of a nonionic surfactant, add a chloride solution to it, and adjust the chloride ion concentration in the system to 0.01~0.03 mol / L; the chloride is a mixture of one or more of potassium chloride, sodium chloride, lithium chloride and tetrabutylammonium chloride.

Images