Stimulation-responsive surfactant, epoxidized rubber and preparation method thereof

Abstract

The invention provides a stimulus-responsive surfactant, epoxidized rubber and a preparation method of the stimulus-responsive surfactant and the epoxidized rubber. The stimulation-responsive surface active agent comprises a surface active agent and nano particles; the preparation method comprises the following steps: mixing a surfactant, nanoparticles and a solvent, dispersing and self-assembling to obtain the stimulus-responsive surfactant, the preparation method of the epoxidized rubber comprises the following steps: adding a stimulus-responsive surfactant into raw materials for preparing the epoxidized rubber, and demulsifying and separating the stimulus-responsive surfactant after reaction to obtain the epoxidized rubber. The stimulus-responsive surfactant prepared by the invention has good stability to rubber emulsion and can ensure that the reaction time is relatively long, so that the epoxy degree of the prepared epoxidized rubber is relatively high, meanwhile, the problems of difficult flocculation and long rubber washing time after the epoxidation reaction of latex is completed are solved, and the economical efficiency is better.

Description

Technical Field

[0001] The present invention relates to the technical field of epoxidized rubber, and more particularly to a stimulus-responsive surfactant, epoxidized rubber and a preparation method thereof. Background Art

[0002] Rubber is typically epoxidized in the form of latex or liquid rubber. Compared to liquid rubber prepared by dissolving rubber in an organic solvent, latex rubber avoids the use of organic solvents, making it a popular choice. Before the epoxidation process begins, surfactants must be added to stabilize the latex to ensure smooth, complete epoxidation. After the reaction is complete, it is desirable to facilitate flocculation of the latex to obtain the final product and to remove the surfactant from the final product, a task difficult to achieve with traditional surfactants.

[0003] Chinese invention patent CN113072652A discloses a quantitative epoxidized rubber and its preparation method. The process involves epoxidizing a fatty alcohol polyoxyethylene ether as a stabilizer. After the reaction is complete, stirring is stopped, the system is heated to a boil, and the pH of the system is adjusted to neutral to allow the latex to precipitate. The epoxidized rubber is then collected by centrifugation. Chinese invention patent CN101654488A discloses a process for preparing epoxidized rubber. The process involves epoxidizing a sorbitol polyoxyethylene ether as a stabilizer. After the reaction is complete, the pH of the system is adjusted to neutral with ammonia, steam is introduced and heated until the latex coagulates, followed by dehydration, rinsing, granulation, and drying. Chinese invention patent CN101942043A discloses a process for preparing epoxidized rubber. Polyoxyethylene laurate ether is added, the system is stabilized for 2 hours, and then epoxidation is carried out. After the reaction is complete, the epoxidized natural rubber latex is adjusted to a pH of 8-9 with ammonia, coagulated with ethanol, dehydrated, rinsed, granulated, and dried. Chinese invention patent CN117186270 A uses a cationic emulsifier as a stabilizer during the preparation of epoxidized natural rubber, making the reaction process easier to control. The epoxidized natural rubber dry rubber is obtained by ethanol flocculation, followed by alkaline soaking, water washing, drying, and post-processing. All of the aforementioned methods require the addition of surfactants to stabilize the latex during the epoxidation process, which requires a large amount. This results in high demulsification conditions after the reaction is complete, making flocculation difficult. Flocculation requires the addition of steam or the use of an organic solvent, anhydrous ethanol, which is costly, complex, and requires flocculation equipment. Furthermore, post-flocculation processing is tedious, requiring multiple washes to remove residual surfactants, which is not environmentally friendly.

[0004] Therefore, it is necessary to study a surfactant that can not only effectively stabilize rubber latex and allow the epoxidation reaction to proceed smoothly, but also solve the problems of difficult flocculation and long rubber washing time after the latex epoxidation reaction is completed. While ensuring that the above two points can be achieved, the economy is better. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides a stimulus-responsive surfactant, epoxidized rubber and a preparation method thereof.

[0006] This invention modifies the surface of nanoparticles with surfactants through physical interactions, creating stimuli-responsive surfactants. This allows for responsive emulsification and demulsification of the emulsion in response to external stimuli. The process is simple, efficient, environmentally friendly, and low-cost, resolving the difficult issue of ensuring latex stability during epoxidation while ensuring easy demulsification after the reaction is complete.

[0007] One of the objects of the present invention is to provide a stimulus-responsive surfactant.

[0008] The stimulus-responsive surfactant comprises a surfactant and nanoparticles;

[0009] The surfactant is at least one of a cationic surfactant, an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, and a special surfactant, preferably at least one of a cationic surfactant, an amphoteric surfactant, and a special surfactant;

[0010] The nanoparticles are nanoparticles with electric charge in an aqueous medium, and are preferably at least one of nano-silicon dioxide, nano-aluminum oxide, nano-iron oxide, nano-zinc oxide, nano-titanium dioxide, and nano-calcium carbonate.

[0011] In a preferred embodiment of the present invention,

[0012] The cationic surfactant is at least one of an amine salt type, a quaternary ammonium salt type, a heterocyclic type, and a phosphite type; preferably at least one of cetyltrimethylammonium bromide (CTAB), cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium iodide (CTAI), cetyltrimethylammonium fluoride (CTAF), octadecyltrimethylammonium bromide (OTAB), octadecyltrimethylammonium chloride (OTAC), octadecyltrimethylammonium iodide (OTAI), and octadecyltrimethylammonium fluoride (OTAF);

[0013] The anionic surfactant is at least one of carboxylate, sulfate, sulfonate, and phosphate; preferably at least one of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and sodium α-olefinsulfonate-AOS;

[0014] The nonionic surfactant is at least one of polyoxyethylene type, polyol type, polyether type, and alkylolamide type; preferably at least one of Tween-80, alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and isomeric alcohol polyoxyethylene ether;

[0015] The amphoteric surfactant is at least one of amino acids, betaines, imidazolinium salts, and amine oxides; preferably at least one of dodecylaminopropionic acid, dodecyldimethyl betaine, octadecyldimethyl sulfoethyl betaine, dodecylethoxysulfobetaine, dodecylhydroxypropylsulfobetaine, and dodecylsulfopropyl betaine;

[0016] The special surfactant is a novel surfactant with special functions, preferably at least one of N'-dodecyl-N,N-dimethylacetamidine (DDAA), N'-hexadecyl-N,N-dimethylacetamidine (HDAA) corresponding carbonate, and dodecyltetramethylguanidine;

[0017] The average particle size of the nanoparticles is 5 to 100 nm, preferably 10 to 85 nm, and more preferably 15 to 40 nm.

[0018] In a preferred embodiment of the present invention,

[0019] The stimulus-responsive surfactant further comprises a solvent, and the solvent is preferably water;

[0020] In the stimulus-responsive surfactant, the concentration of the surfactant is 0.0001 to 0.3 mol / L, preferably 0.001 to 0.07 mol / L, more preferably 0.003 to 0.05 mol / L;

[0021] In the stimulus-responsive surfactant, the concentration of the nanoparticles is 0.1 to 15 wt.%, preferably 0.1 to 10 wt.%, and more preferably 0.9 to 9 wt.%.

[0022] A second object of the present invention is to provide a method for preparing a stimulus-responsive surfactant, comprising:

[0023] The surfactant, nanoparticles, and solvent are mixed and dispersed and self-assembled to obtain the stimulus-responsive surfactant; preferably,

[0024] The dispersion method is at least one of ultrasonic dispersion, homogenizer dispersion, stirrer dispersion, ball mill dispersion, and rotor-stator mixer dispersion, and ultrasonic dispersion is more preferred.

[0025] In the preparation method, the surfactant and the solvent may be prepared into a surfactant solution first, and then mixed with the nanoparticles.

[0026] The stimuli-responsive surfactant is obtained by modifying nanoparticles with a surfactant.

[0027] In a preferred embodiment of the present invention,

[0028] The frequency of the ultrasonic dispersion is 5 to 100 KHz, preferably 10 to 60 KHz;

[0029] The ultrasonic dispersion time is 5 to 60 minutes, preferably 5 to 30 minutes;

[0030] The temperature of the ultrasonic dispersion is 20-60°C, preferably 25-45°C;

[0031] The preferred ultrasonic dispersion method of the present invention is ultrasonic cavitation, which generates high shear force and can break down particle agglomerates into individual dispersions. Ultrasonic dispersion is easy to implement and can be quickly converted from laboratory to industrial production.

[0032] In the stimulus-responsive surfactant, the solvent is water;

[0033] In the stimulus-responsive surfactant, the concentration of the surfactant is 0.0001 to 0.3 mol / L, preferably 0.001 to 0.07 mol / L, more preferably 0.003 to 0.05 mol / L;

[0034] In the stimulus-responsive surfactant, the concentration of the nanoparticles is 0.1 to 15 wt.%, preferably 0.1 to 10 wt.%, and more preferably 0.9 to 9 wt.%.

[0035] A third object of the present invention is to provide a stimulus-responsive surfactant obtained by the above preparation method.

[0036] A fourth object of the present invention is to provide a method for preparing epoxidized rubber, comprising: adding a stimulus-responsive surfactant to the raw materials for preparing the epoxidized rubber, breaking the emulsion after the reaction to separate the stimulus-responsive surfactant, and obtaining the epoxidized rubber; the stimulus-responsive surfactant is as described above.

[0037] Demulsification requires the application of a stimulus to the system. The stimulus-responsiveness of stimuli-responsive surfactants refers to their sensitivity to externally applied conditions, such as pH, CO₂, N₂, temperature, light, magnetism, and surfactants, after the epoxidation reaction is complete, leading to the demulsification and flocculation of the product.

[0038] In a preferred embodiment of the present invention,

[0039] The preparation method comprises the following steps:

[0040] (1) adding a stimulus-responsive surfactant, an oxidant, and an epoxidation catalyst to rubber latex to carry out an epoxidation reaction to obtain epoxidized rubber latex;

[0041] (2) applying a stimulus to the epoxidized rubber latex obtained in step (1) to demulsify the latex, thereby obtaining the epoxidized rubber; preferably, separating and recovering the stimulus-responsive surfactant.

[0042] In a preferred embodiment of the present invention,

[0043] In step (1),

[0044] The rubber in the rubber latex is a rubber containing double bonds; preferably, the double bond content in the rubber is 0.05 to 2 mol double bonds / 100 g rubber, more preferably 0.05 to 1.85 mol double bonds / 100 g rubber; further preferably, the rubber latex is at least one of styrene-butadiene latex, nitrile-butadiene latex, natural rubber latex, butadiene-pyrrolidone latex, chloroprene latex, butyl latex, carboxylated styrene-butadiene latex, EPDM latex, and carboxylated chloroprene latex;

[0045] The solid content of the rubber latex is 10-70%, preferably 20-60%;

[0046] The oxidant is at least one of hydrogen peroxide, hypochlorous acid, sodium hypochlorite, nitric acid, peracetic acid, m-chloroperbenzoic acid, and ammonium persulfate, preferably at least one of hydrogen peroxide, peracetic acid, and m-chloroperbenzoic acid;

[0047] The epoxidation catalyst is at least one of an organic acid, a heteropoly acid salt, a lipase, a metal oxide, and a metal salt, preferably at least one of formic acid, manganese sulfate, sodium bicarbonate, a quaternary ammonium salt of a phosphotungstic heteropoly acid, a lipase, methyl rhenium trioxide, molybdenum trioxide, and a porphyrin metal salt;

[0048] The ratio of the stimulus-responsive surfactant to the rubber latex is 0.5 to 100 ml of the stimulus-responsive surfactant per 100 g of rubber latex, preferably 5 to 20 ml of the stimulus-responsive surfactant per 100 g of rubber latex;

[0049] The mass ratio of the oxidant to the rubber in the rubber latex is (5-480):100, preferably (5-90):100;

[0050] The mass ratio of the epoxidation catalyst to the rubber in the rubber latex is (0.1-80):100, preferably (0.5-60):100, more preferably (10-60):100;

[0051] The temperature of the epoxidation reaction is 20 to 70°C, preferably 25 to 50°C;

[0052] The epoxidation reaction time is 0.5 to 12 hours, preferably 0.5 to 8 hours, more preferably 2 to 8 hours;

[0053] The epoxidation reaction is carried out under stirring, preferably, the stirring speed is 100-800 r / min, more preferably 200-500 r / min;

[0054] The drying can be carried out by any drying method that can remove the solvent, preferably at least one of vacuum drying, atmospheric pressure drying, microwave drying, and spray drying;

[0055] In step (2),

[0056] The method of stimulating demulsification is at least one of adjusting pH, irradiation, changing temperature, introducing CO2, introducing N2, increasing magnetic field, and adding surfactants of opposite charge; preferably at least one of adjusting pH, adding surfactants of opposite charge, introducing CO2, and introducing N2;

[0057] The choice of the above different stimulation methods for demulsification is related to the properties of the surfactant itself. For example, increasing the magnetic field is suitable for magnetic nanoparticles, and adding surfactants with opposite charges is suitable for charged surfactants.

[0058] More preferably,

[0059] The pH value is adjusted to be greater than or equal to 7;

[0060] The surfactant with opposite charge is added. For example, if a cationic surfactant is added to the stimulus-responsive surfactant, an anionic surfactant with opposite charge is added during demulsification, such as an anionic surfactant sodium dodecyl sulfate (SDS), and the added anionic surfactant is equimolar to the cationic surfactant.

[0061] The separation method is to separate the stimulus-responsive surfactant from the epoxidized rubber by filtering, centrifuging or the like.

[0062] A fifth object of the present invention is to provide an epoxidized rubber obtained by the above preparation method.

[0063] The resulting epoxidized rubber can be used to prepare an epoxidized rubber composite material by mixing it with components including rubber additives and then vulcanizing it. The rubber additives are conventional additives in the art, such as antioxidants, and can be added by those skilled in the art based on actual conditions. The mixing and vulcanization process conditions are also conventional process conditions in the art and can be adjusted by those skilled in the art based on actual conditions.

[0064] The prepared epoxidized rubber nanocomposite material can be applied to rubber products such as tires, sealing rings, hoses and tapes.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] 1. The present invention uses commercial surfactants with a concentration far below the critical micelle concentration to self-assemble with nanoparticles in a solution to obtain stimulus-responsive surfactants. No complicated chemical modification is required, the preparation method is simple, and the feasibility is good.

[0067] 2. The stimulus-responsive surfactant prepared by the present invention makes the nanoparticles amphiphilic by modifying the surfactant on the surface of the nanoparticles, thereby replacing the conventional surfactant in the epoxidation reaction. It has good stability for the rubber emulsion and can ensure a long reaction time, thereby ensuring that the prepared epoxidized rubber has a high epoxidation degree.

[0068] 3. The stimulated demulsification method used in the present invention is simple and feasible, and does not require the use of organic flocculants, boiling water, or steam flocculation, thereby solving the problems of difficult flocculation after the latex epoxidation reaction is completed and the long rubber washing time. In addition, the prepared stimulus-responsive surfactant can be recycled by separation, which is more economical.

[0069] 4. The stimulus-responsive surfactant prepared by the present invention changes its own activity to achieve a stimulus-responsive effect, thereby making the preparation of epoxidized rubber green, low-cost, simple in process, high in process efficiency, and low in energy consumption. DETAILED DESCRIPTION

[0070] The present invention will be described in detail below with reference to specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art to the present invention based on the contents of the present invention still fall within the scope of protection of the present invention.

[0071] N'-dodecyl-N,N-dimethylacetamidine and dodecylaminopropionic acid were made in the laboratory. The remaining raw materials used in the examples and comparative examples were conventional commercially available raw materials. The main raw materials are shown in Table 1:

[0072] Table 1 Specifications of main raw materials

[0073]

[0074] Preparation of N'-dodecyl-N,N-dimethylacetamidine (DDAA):

[0075] N,N-dimethylacetamide (87 g, 1 mol) and dimethyl sulfate (126 g, 1 mol) were reacted at 70-80°C under nitrogen for 3 h to obtain a complex of the two.

[0076] Sodium methoxide was prepared by reacting 23g of sodium metal with 317mL of methanol. The mixture was then cooled in an ice-water bath. The resulting complex was added dropwise to the sodium methoxide with vigorous stirring for 3 hours. After the reaction was complete, the mixture was stirred at room temperature (25°C) for 20 hours, followed by 20 hours of undisturbed reaction. Approximately 65g of the product was obtained by distillation. The product was N,N-dimethylacetamide dimethyl acetal (an intermediate).

[0077] N'-dodecyl-N,N-dimethylacetamidine was prepared by reacting equimolar amounts of dodecylamine and N,N-dimethylacetamide dimethyl acetal (intermediate) at 60-70°C for 15 minutes.

[0078] Preparation of dodecylaminopropionic acid (DAP):

[0079] To a reactor equipped with a stirrer, thermometer, and heater, add 1 mol of dodecylamine until it melts. Then, slowly add 1.1-1.2 mol of methyl acrylate dropwise at 50°C with stirring for 1 hour. After the addition is complete, the mixture is kept warm for 5 hours. Excess methyl acrylate is removed by vacuum distillation to yield the intermediate N-dodecyl-β-aminopropionic acid methyl ester. The intermediate is then added dropwise to an alkaline solution containing 1 mol of sodium hydroxide heated to 90-100°C with rapid stirring to undergo a saponification reaction for approximately 1 hour. The reaction is then cooled to 70°C, and the generated methanol is removed under reduced pressure. The pH is adjusted to neutral with hydrochloric acid to yield dodecylaminopropionic acid (DAP).

[0080] Test method:

[0081] Nuclear magnetic resonance (NMR) 1 H-NMR) analysis:

[0082] The AVANCE III analyzer produced by Bruker Corporation of the United States was used to test 1 H-NMR quantitatively characterizes the epoxidation degree of epoxidized rubber, and its value can be calculated based on the integrated area of ​​each characteristic peak in the double bond:

[0083]

[0084] Among them, E is the epoxy degree of the sample, A epoxy 、A C＝C They are epoxy group and double bond respectively;

[0085] The test conditions are as follows:

[0086] Solvent: deuterated chloroform (CDC 13 ); spectral width: 0ppm~16ppm; center frequency: 8ppm; number of sampling times: 16.

[0087] Example 1

[0088] SiO2 particles (average particle size 20 nm) were dispersed in a CTAB aqueous solution and ultrasonically dispersed at 40°C for 15 min at a frequency of 45 kHz. The concentration of SiO2 particles in the obtained stimulus-responsive surfactant was 5.0 wt.%, and the concentration of CTAB was 0.03 mol / L.

[0089] 16 ml of the resulting stimuli-responsive surfactant was then added to 100 g of natural rubber latex (30% solids content, 1.45 mol of double bonds per 100 g of dry rubber) and stirred for 20 minutes. Then, 13 g of formic acid (85% by mass) and 46 g of H₂O₂ (30% by mass) were added. The reaction was set at 300 rpm and allowed to react at 35°C for 5 hours. 16 ml of SDS (0.03 mol / L) solution was added, stirred to break the emulsion, filtered, washed, and dried under atmospheric pressure to obtain the epoxidized natural rubber.

[0090] Example 2

[0091] Al2O3 particles (average particle size 25 nm) were dispersed in a CTAC aqueous solution and ultrasonically dispersed at 28°C for 30 min at a frequency of 45 kHz. The concentration of Al2O3 particles in the resulting stimulus-responsive surfactant was 9.0 wt.%, and the concentration of CTAC was 0.05 mol / L.

[0092] Then, 10 ml of the resulting stimuli-responsive surfactant was added to 100 g of styrene-butadiene rubber latex (30% solids content, 0.63 mol of double bonds per 100 g of dry rubber) and stirred for 20 minutes. Then, 15 g of NaHCO₃, 2 g of MnSO₄, and 50 g of H₂O₂ (30% by mass) were added. The reaction was set at 400 rpm and allowed to react at 45°C for 5 hours. 5 ml of sodium dodecyl sulfate (0.1 mol / L) solution was added, stirred to break the emulsion, filtered, washed, and dried under atmospheric pressure to obtain the epoxidized styrene-butadiene rubber.

[0093] Example 3

[0094] SiO2 particles (average particle size 20 nm) were dispersed in an aqueous solution of dodecylaminopropionic acid (DAP) and ultrasonically dispersed at 40°C for 15 min. The frequency of ultrasonic dispersion was 45 kHz. The concentration of SiO2 particles in the obtained stimulus-responsive surfactant was 8.0 wt.%, and the concentration of dodecylaminopropionic acid was 0.05 mol / L.

[0095] 6 ml of the resulting stimuli-responsive surfactant was then added to 100 g of EPDM rubber latex (25% solids content, 0.15 mol of double bonds per 100 g of dry latex) and stirred for 20 minutes. Subsequently, 12 g of formic acid (85% by mass) and 30 g of H₂O₂ (30% by mass) were added, and the reaction was set at 320 rpm and 40°C for 5 hours. The emulsion was then stirred to break the pH at 7, filtered, washed, and vacuum-dried to obtain the epoxidized EPDM rubber.

[0096] Example 4

[0097] SiO2 particles (average particle size 25 nm) were dispersed in N'-dodecyl-N,N-dimethylacetamidine (DDAA) solution and ultrasonically dispersed at 40°C for 30 min. The frequency of ultrasonic dispersion was 45 kHz. The concentration of SiO2 particles in the obtained stimulus-responsive surfactant was 2 wt.%, and the concentration of N'-dodecyl-N,N-dimethylacetamidine (DDAA) was 0.011 mol / L.

[0098] 8 ml of the resulting stimuli-responsive surfactant was then added to 100 g of butylpyrrolidone rubber latex (40% solids content, 0.73 mol of double bonds per 100 g of dry rubber) and stirred for 20 minutes. Subsequently, 10 g of formic acid (85% by mass) and 45 g of H₂O₂ (30% by mass) were added, and the reaction was set at 350 rpm and allowed to react at 25°C for 5 hours. The mixture was stirred in an ice bath at 0-5°C with nitrogen purge, demulsified, centrifuged, washed, and dried at atmospheric pressure to obtain the epoxidized butylpyrrolidone rubber.

[0099] Example 5

[0100] TiO2 particles (average particle size 30 nm) were dispersed in an OTAB aqueous solution and ultrasonically dispersed at 45°C for 10 min at a frequency of 45 kHz. The concentration of TiO2 particles in the obtained stimulus-responsive surfactant was 1.8 wt.%, and the concentration of OTAB was 0.007 mol / L.

[0101] 8 ml of the resulting stimuli-responsive surfactant was then added to 100 g of butyl rubber latex (40% solids content, 0.16 mol of double bonds per 100 g of dry rubber) and stirred for 20 minutes. Then, 6 g of formic acid (85% by mass) and 22 g of H₂O₂ (30% by mass) were added. The reaction was set at 500 rpm and 35°C for 5 hours. 8 ml of SDS (0.007 mol / L) solution was added, stirred to break the emulsion, filtered, washed, and microwave-dried to obtain the epoxidized butyl rubber.

[0102] Example 6

[0103] ZnO particles (average particle size 20 nm) were dispersed in a CTAB aqueous solution and ultrasonically dispersed at 40°C for 15 min at a frequency of 45 kHz. The concentration of ZnO particles in the obtained stimulus-responsive surfactant was 1.5 wt.%, and the concentration of CTAB was 0.003 mol / L.

[0104] Then, 20 ml of the resulting stimuli-responsive surfactant was added to 100 g of chloroprene rubber latex (solids content 40%, 1.1 mol of double bonds per 100 g of dry rubber) and stirred for 20 minutes. Then, 13 g of formic acid (85% by mass) and 46 g of H₂O₂ (30% by mass) were added. The reaction was set at 200 rpm and allowed to react at 40°C for 7 hours. 5 ml of SDS (0.012 mol / L) solution was added, stirred to break the emulsion, filtered, washed, and dried under atmospheric pressure to obtain the epoxidized natural rubber.

[0105] Example 7

[0106] TiO2 particles (average particle size 30 nm) were dispersed in a CTAC aqueous solution and ultrasonically dispersed at 45°C for 10 min at a frequency of 45 kHz. The concentration of TiO2 particles in the obtained stimulus-responsive surfactant was 0.9 wt.%, and the concentration of CTAC was 0.006 mol / L.

[0107] Then, 20 ml of the resulting stimuli-responsive surfactant was added to 100 g of nitrile rubber latex (55% solids content, 0.93 mol of double bonds per 100 g of dry rubber) and stirred for 20 minutes. Then, 8 g of formic acid (85% by mass) and 20 g of H₂O₂ (30% by mass) were added, and the reaction was set at 200 rpm and 45°C for 5 hours. 20 ml of SDS (0.006 mol / L) solution was added, stirred to break the emulsion, filtered, washed, and microwave-dried to obtain the epoxidized nitrile rubber.

[0108] Comparative Example 1

[0109] The difference from Example 1 is that the surfactant used is a 0.03 mol / L CTAB aqueous solution, rather than a stimulus-responsive surfactant prepared by combining a CTAB aqueous solution with nano-SiO2 particles.

[0110] Specifically:

[0111] Add 16 ml of a 0.03 mol / L CTAB aqueous solution to 100 g of natural rubber latex (30% solids content, 1.45 mol of double bonds per 100 g of dry rubber) and stir for 20 minutes. Then, add 13 g of formic acid (85% by mass) and 46 g of H₂O₂ (30% by mass). Set the speed to 300 rpm and react at 35°C for 50 minutes until the latex destabilizes and breaks.

[0112] Comparative Example 2

[0113] The difference from Example 2 is that the surfactant used is a 0.05 mol / L CTAC aqueous solution, rather than a stimulus-responsive surfactant prepared by combining a CTAC aqueous solution with nano-Al2O3 particles.

[0114] Specifically:

[0115] Add 10 ml of a 0.05 mol / L CTAC aqueous solution to 100 g of styrene-butadiene rubber latex (30% solids content, 0.63 mol of double bonds per 100 g of dry latex) and stir for 20 minutes. Then, add 15 g of NaHCO₃, 2 g of MnSO₄, and 50 g of H₂O₂ (30% by mass). Set the speed to 400 rpm and react at 45°C for 20 minutes until the latex destabilizes and breaks.

[0116] Comparative Example 3

[0117] The difference from Example 3 is that the surfactant used is a 0.05 mol / L dodecylaminopropionic acid (DAP) aqueous solution, rather than a stimulus-responsive surfactant prepared by combining a DAP aqueous solution with nano-SiO2 particles.

[0118] Specifically:

[0119] Add 6 ml of a 0.05 mol / L aqueous solution of dodecylaminopropionic acid (DAP) to 100 g of EPDM rubber latex (25% solids content, 1.45 mol of double bonds per 100 g of dry latex) and stir for 20 minutes. Then, add 12 g of formic acid (85% by mass) and 30 g of H₂O₂ (30% by mass). Set the speed to 320 rpm and react at 40°C for 15 minutes until the latex destabilizes and breaks.

[0120] Comparative Example 4

[0121] The difference from Example 1 is that the surfactant used is 20 ml of 0.03 mol / L OP-10 aqueous solution, rather than the stimulus-responsive surfactant prepared by CTAB aqueous solution and nano-SiO2 particles.

[0122] Specifically:

[0123] 20 ml of a 0.03 mol / L OP-10 aqueous solution was added to 100 g of natural rubber latex (solids content 30%, 1.45 mol of double bonds per 100 g of dry rubber) and stirred for 20 minutes. Then, 13 g of formic acid (85% by mass) and 46 g of H₂O₂ (30% by mass) were added. The reaction was set at 300 rpm and 35°C for 0.5 hours. 300 g of anhydrous ethanol was added for flocculation, the mixture was filtered, washed, and dried under normal pressure to obtain the epoxidized natural rubber.

[0124] The epoxidation degrees of the epoxidized rubbers of Examples 1 to 7 and Comparative Examples 1 to 4 calculated and measured based on H NMR spectroscopy are shown in Table 2.

[0125] Table 2 Ring opening rates calculated from H NMR tests of Examples 1 to 7 and Comparative Examples 1 to 4

[0126] Epoxy degree (%) Example 1 13 Example 2 6 Example 3 24 Example 4 5 Example 5 5 Example 6 17 Example 7 16 Comparative Example 1 3 Comparative Example 2 2 Comparative Example 3 0.5 Comparative Example 4 3

[0127] Comparing Comparative Example 1 with Example 1, the epoxidation reaction in Comparative Example 1 destabilized and demulsified after 50 minutes at 35°C, while the epoxidation reaction in Example 1 continued at 35°C for 5 hours. This demonstrates that the stimuli-responsive surfactant prepared in Example 1 provides superior latex stability. Demulsification can be achieved by simply adding an SDS solution and stirring after the reaction, providing a simple demulsification method. Compared to Comparative Example 4, this method solves the problems of difficult flocculation and long rubber washing times after the epoxidation reaction.

[0128] Compared with Example 2, the epoxidation reaction of Comparative Example 2 became unstable and demulsified after reacting at 45°C for 20 minutes, while the epoxidation reaction of Example 2 was reacted at 45°C for 5 hours, which also proved that the stimulus-responsive surfactant prepared in Example 2 had better stability to the latex. After the reaction was completed, SDS solution was added and stirred to break the emulsion.

[0129] Compared with Example 3, the epoxidation reaction of Comparative Example 3 became unstable and demulsified after 15 minutes of reaction at 40°C, while the epoxidation reaction of Example 3 was reacted at 40°C for 5 hours. This also proves that the stimulus-responsive surfactant prepared in Example 3 has better stability to the latex. After the reaction is completed, the pH is adjusted to 7 and the emulsion can be broken by stirring. The demulsification method is also simple.

[0130] Comparative Example 4 uses a traditional method to prepare epoxidized rubber, which requires a large amount of alcohol solvent for flocculation after the reaction, making flocculation difficult.

[0131] As can be seen from Table 2, the epoxidized rubbers prepared in Examples 1 to 7 have an epoxidation degree of 5 to 24%, while the epoxidized rubbers prepared in Comparative Examples 1 to 3 have an epoxidation degree of only 0.5 to 3% due to the instability of the latex and the short epoxidation reaction time. The epoxidized rubber prepared in Comparative Example 4 also has an epoxidation degree of only 3%, demonstrating the importance of the stimuli-responsive surfactant prepared in the present invention in the epoxidation reaction.

[0132] The stimulus-responsive surfactants prepared in Examples 1 to 7, when used to prepare different epoxidized rubbers, have good stability to the rubber latex, can ensure a longer reaction time, and can prepare epoxidized rubber with a higher epoxidation degree. At the same time, the demulsification operation is simple, which solves the problem of difficult flocculation after the latex epoxidation reaction is completed and the long rubber washing time.

Claims

1. A stimuli-responsive surfactant comprising a surfactant and nanoparticles; The surfactant is at least one of a cationic surfactant, an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, and a special surfactant; The nanoparticles are nanoparticles with electric charge in an aqueous medium, and are preferably at least one of nano-silicon dioxide, nano-aluminum oxide, nano-iron oxide, nano-zinc oxide, nano-titanium dioxide, and nano-calcium carbonate.

2. The stimuli-responsive surfactant according to claim 1, wherein: The cationic surfactant is at least one of an amine salt type, a quaternary ammonium salt type, a heterocyclic type, and a phosphonium salt type; preferably at least one of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, cetyltrimethylammonium iodide, cetyltrimethylammonium fluoride, octadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, octadecyltrimethylammonium iodide, and octadecyltrimethylammonium fluoride; and / or, The anionic surfactant is at least one of carboxylate, sulfate, sulfonate, and phosphate; preferably at least one of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and sodium α-olefin sulfonate-AOS; and / or, The nonionic surfactant is at least one of polyoxyethylene type, polyol type, polyether type, and alkylolamide type; preferably at least one of Tween-80, alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and isomeric alcohol polyoxyethylene ether; and / or, The amphoteric surfactant is at least one of amino acids, betaines, imidazolinium salts, and amine oxides; preferably at least one of dodecylaminopropionic acid, dodecyldimethyl betaine, octadecyldimethyl sulfoethyl betaine, dodecylethoxysulfobetaine, dodecylhydroxypropylsulfobetaine, and dodecylsulfopropyl betaine; and / or, The special surfactant is at least one of N'-dodecyl-N,N-dimethylacetamidine, N'-hexadecyl-N,N-dimethylacetamidine corresponding carbonate, and dodecyltetramethylguanidine; and / or, The average particle size of the nanoparticles is 5 to 100 nm, preferably 10 to 85 nm, and more preferably 15 to 40 nm.

3. The stimuli-responsive surfactant according to claim 1, wherein: The stimulus-responsive surfactant further comprises a solvent, and the solvent is preferably water; In the stimulus-responsive surfactant, the concentration of the surfactant is 0.0001 to 0.3 mol / L, preferably 0.001 to 0.07 mol / L, more preferably 0.003 to 0.05 mol / L; and / or, In the stimulus-responsive surfactant, the concentration of the nanoparticles is 0.1 to 15 wt.%, preferably 0.1 to 10 wt.%, and more preferably 0.9 to 9 wt.%.

4. A method for preparing the stimulus-responsive surfactant according to any one of claims 1 to 3, comprising: The surfactant, nanoparticles, and solvent are mixed and dispersed and self-assembled to obtain the stimulus-responsive surfactant; preferably, The dispersion method is at least one of ultrasonic dispersion, homogenizer dispersion, stirrer dispersion, ball mill dispersion, and rotor-stator mixer dispersion.

5. The method for preparing a stimuli-responsive surfactant according to claim 4, wherein: The frequency of the ultrasonic dispersion is 5 to 100 KHz, preferably 10 to 60 KHz; and / or, The ultrasonic dispersion time is 5 to 60 minutes, preferably 5 to 30 minutes; and / or, The temperature of the ultrasonic dispersion is 20 to 60° C., preferably 25 to 45° C.; and / or, In the stimulus-responsive surfactant, the solvent is water; and / or In the stimulus-responsive surfactant, the concentration of the surfactant is 0.0001 to 0.3 mol / L, preferably 0.001 to 0.07 mol / L, more preferably 0.003 to 0.05 mol / L; and / or, In the stimulus-responsive surfactant, the concentration of the nanoparticles is 0.1 to 15 wt.%, preferably 0.1 to 10 wt.%, and more preferably 0.9 to 9 wt.%.

6. A stimulus-responsive surfactant obtained by the preparation method according to claim 4 or 5.

7. A method for preparing epoxidized rubber, comprising: Adding a stimulus-responsive surfactant to the raw materials for preparing the epoxidized rubber, breaking the emulsion after the reaction to separate the stimulus-responsive surfactant, and obtaining the epoxidized rubber; The stimulus-responsive surfactant is as described in any one of claims 1 to 3 and 6.

8. The method for preparing epoxidized rubber according to claim 7, wherein: The preparation method comprises the following steps: (1) adding a stimulus-responsive surfactant, an oxidant, and an epoxidation catalyst to rubber latex to carry out an epoxidation reaction to obtain epoxidized rubber latex; (2) applying a stimulus to the epoxidized rubber latex obtained in step (1) to demulsify the latex, thereby obtaining the epoxidized rubber; preferably, separating and recovering the stimulus-responsive surfactant.

9. The method for preparing epoxidized rubber according to claim 8, wherein: In step (1), The rubber in the rubber latex is a rubber containing double bonds; preferably, the double bond content in the rubber is 0.05 to 2 mol double bonds / 100 g rubber, more preferably 0.05 to 1.85 mol double bonds / 100 g rubber; further preferably, the rubber latex is at least one of styrene-butadiene latex, nitrile-butadiene latex, natural rubber latex, butyl latex, chloroprene latex, butyl latex, carboxylated styrene-butadiene latex, EPDM latex, and carboxylated chloroprene latex; and / or, The rubber latex has a solid content of 10 to 70%, preferably a solid content of 20 to 60%; and / or, The oxidant is at least one of hydrogen peroxide, hypochlorous acid, sodium hypochlorite, nitric acid, peracetic acid, meta-chloroperbenzoic acid, and ammonium persulfate, preferably at least one of hydrogen peroxide, peracetic acid, and meta-chloroperbenzoic acid; and / or The epoxidation catalyst is at least one of an organic acid, a heteropoly acid salt, a lipase, a metal oxide, and a metal salt, preferably at least one of formic acid, manganese sulfate, sodium bicarbonate, a quaternary ammonium salt of a phosphotungstic heteropoly acid, a lipase, methylrhenium trioxide, molybdenum trioxide, and a porphyrin metal salt; and / or, The ratio of the stimulus-responsive surfactant to the rubber latex is 0.5 to 100 ml of the stimulus-responsive surfactant per 100 g of rubber latex, preferably 5 to 20 ml of the stimulus-responsive surfactant per 100 g of rubber latex; and / or, The mass ratio of the oxidant to the rubber in the rubber latex is (5-480):100, preferably (5-90):100; and / or, The mass ratio of the epoxidation catalyst to the rubber in the rubber latex is (0.1-80):100, preferably (0.5-60):100, more preferably (10-60):100; and / or, The epoxidation reaction temperature is 20 to 70° C., preferably 25 to 50° C.; and / or, The epoxidation reaction time is 0.5 to 12 hours, preferably 0.5 to 8 hours, more preferably 2 to 8 hours; and / or, The epoxidation reaction is carried out under stirring, preferably at a stirring speed of 100 to 800 r / min, more preferably 200 to 500 r / min; and / or, The drying may be carried out by any drying method capable of removing the solvent, preferably at least one of vacuum drying, atmospheric pressure drying, microwave drying, and spray drying; and / or, In step (2), The method of stimulating demulsification is at least one of adjusting pH value, illumination, changing temperature, introducing CO2, introducing N2, increasing magnetic field, and adding surfactant with opposite charge. The separation method is to separate the stimulus-responsive surfactant from the epoxidized rubber by filtration and centrifugation.

10. An epoxidized rubber obtained by the preparation method according to any one of claims 7 to 9.

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