Flocculation method of epoxidized natural latex and epoxidized natural rubber prepared by using method

Abstract

The invention discloses a flocculation method of epoxidized natural latex and epoxidized natural rubber prepared by using the method, and relates to the technical field of epoxidized natural latex preparation, and the method comprises the following steps: mixing a clay mineral solution and the epoxidized natural latex, stirring and flocculating. It is found for the first time that the clay substance can demulsify and flocculate the epoxidized natural latex, the flocculated rubber is granular, the flocculation speed is high, the flocculation is complete, the flocculated water phase is completely clear, formic acid can be fully recycled, and the flocculation method is simple, low in cost and capable of being carried out at normal temperature and normal pressure. The clay mineral with the layered structure is used as the flocculating agent of the epoxidized natural latex, the clay mineral with the layered structure can flocculate the epoxidized natural latex under the conditions of normal temperature and normal pressure, the flocculation method is high in flocculation efficiency, simple in process and low in flocculation cost, 80% of formic acid can be recycled after post-treatment, and the ring opening rate is lower.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of epoxidized natural latex. Further, it relates to a flocculation method for epoxidized natural latex and epoxidized natural rubber prepared by using this method. Background Art

[0002] The industrial preparation of epoxidized natural rubber (ENR) can be divided into a solution method and a latex method. Initially, people used the solution method for preparation, that is, dissolving natural rubber (NR) in a homogeneous solution and adding an oxidant for oxidation. However, due to many disadvantages of the solution method, such as easy swelling of NR in the solvent and incomplete dissolution, people now choose the latex method to epoxidize natural rubber. The in-situ epoxidation method of using formic acid and hydrogen peroxide to in-situ generate peroxyformic acid is used to epoxidize natural latex. The latex method has advantages such as a simple production process and low cost.

[0003] During the epoxidation process of natural latex, an emulsifier (also known as a stabilizer) needs to be added to stabilize the latex. Otherwise, the addition of formic acid will cause the latex to directly demulsify. Currently, the most commonly used by scientific researchers is still a non-ionic emulsifier as the stabilizer of the latex. Non-ionic surfactants refer to a class of surfactants that can generate non-electrostatic particles in water, with high stability, strong resistance to hard water, and not restricted by pH.

[0004] In terms of the flocculation of epoxidized natural latex, in addition to the traditional use of alcohols for flocculation in the laboratory, the flocculation method of epoxidized latex can also use boiling water flocculation or steam flocculation. When the latex is heated to a relatively high temperature, the latex system will lose stability and demulsify.

[0005] In terms of the flocculation effect, the effects of boiling water flocculation and steam flocculation are equivalent. However, both methods require a large amount of heat when flocculating the latex, with extremely high actual production costs, and the flocculated rubber blocks are compact, and it is difficult to thoroughly elute substances such as formic acid. Thailand has achieved the industrial production of epoxidized natural rubber. Patent PCT / GB2008 / 050272 describes the treatment method of steam flocculation of epoxidized natural latex, and China has not achieved the industrialization of epoxidized natural rubber.

[0006] Zeng Zong-Qiang et al. compared and studied the effects of steam flocculation and ethanol flocculation on the properties of epoxidized natural rubber in Effects of Coagulation Processes on Properties of Epoxidized Natural Rubber, and found that compared with the ENR flocculated by steam, the ENR flocculated by ethanol has higher elastic modulus and elastic torque, longer stress relaxation time, and the processing performance, antioxidant performance and curing characteristics of the composition of the ENR coagulated by ethanol are all worse than those of the ENR coagulated by steam.

[0007] At present, in the laboratory research stage of epoxidized natural latex, dehydrating agents such as methanol and ethanol are mostly used to flocculate the latex. The rubber blocks flocculated by alcohol are relatively compact, and it is difficult to wash out residual substances such as formic acid. Moreover, the cost of using alcohol flocculation in industrial production is huge, and the environmental protection pressure is also great, which is not suitable for industrial production.

[0008] Therefore, on the premise of ensuring the stability of the basic properties of epoxidized natural rubber, exploring a flocculation method with simple process and low cost is of great significance to the industrial production of epoxidized natural rubber. Summary of the Invention

[0009] In order to solve the problems existing in the prior art, the present invention provides a flocculation method for epoxidized natural latex and epoxidized natural rubber prepared by using this method. The method of the present invention makes the process of epoxidized natural latex more concise and efficient in the flocculation and post-treatment stages, can make the flocculation stage of epoxidized natural rubber preparation easier to control, the flocculated rubber particles are granular, and this method of flocculation can wash out substances such as formic acid in the rubber more thoroughly.

[0010] One of the purposes of the present invention is to provide a flocculation method for epoxidized natural latex.

[0011] The flocculation method for epoxidized natural latex described in the present invention includes:

[0012] Mix and stir the clay mineral solution with the epoxidized natural latex for flocculation.

[0013] Preferably,

[0014] When using a clay mineral with a layered structure for flocculation, it needs to be configured into a uniform aqueous dispersion with a certain concentration. The clay mineral solution is an aqueous dispersion of clay minerals. Preferably, the concentration of the clay mineral solution is 0.1 wt% - 10 wt%, preferably 1 wt% - 5 wt%.

[0015] Preferably,

[0016] The dosage of the clay mineral solution is 0.5 wt% - 100 wt% of the epoxidized natural latex, preferably 80 wt% - 100 wt%.

[0017] Preferably,

[0018] The clay mineral has a layered structure.

[0019] Preferably,

[0020] The clay mineral is at least one of sodium-based clay, calcium-based clay, lithium-based clay, kaolin, muscovite, hydrotalcite, vermiculite, and inorganically modified montmorillonite.

[0021] Preferably,

[0022] The epoxidized natural latex is prepared by the latex method commonly used in the art. Using natural latex as the raw material, in the presence of an emulsifier, formic acid, and hydrogen peroxide, epoxidized natural latexes with different degrees of epoxidation are obtained by controlling the reaction temperature and time. Specifically, it can be prepared by stabilizing natural latex with an emulsifier and then adding deionized water, formic acid, and hydrogen peroxide under stirring conditions for epoxidation reaction.

[0023] Preferably,

[0024] The natural latex is concentrated latex or fresh latex. Preferably, the total solid content of the concentrated latex is 20 - 60%; and / or,

[0025] The emulsifier is at least one of non-ionic emulsifiers, cationic emulsifiers, and anionic emulsifiers.

[0026] The non-ionic emulsifiers, such as nonylphenol polyoxyethylene ether (OP-10), Tween 80, TXT-100, AEO-7, AEO-9, NP-4, etc.;

[0027] The cationic emulsifiers, such as octadecyl trimethyl ammonium chloride, cetyl trimethyl ammonium bromide, dodecyl amine chloride, cationic emulsifier E-11, etc.

[0028] The anionic emulsifiers, such as sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, etc.

[0029] Preferably,

[0030] The reaction temperature of the epoxidation reaction is 20°C - 60°C, and / or the reaction time is 1 - 24 h.

[0031] Preferably,

[0032] The stirring time is 1 - 5 min, preferably 2 - 3 min.

[0033] Specifically, the following scheme can be adopted:

[0034] Use a layered clay mineral to flocculate the epoxidized natural latex. Stir with a stirring device or manually stir with a glass rod. The flocculation can be completed within 5 min.

[0035] The second object of the present invention is to provide an epoxidized natural rubber.

[0036] The epoxidized natural rubber described in the present invention is obtained by flocculating by the above-mentioned flocculation method, followed by separation, washing, and drying.

[0037] Specifically, the following scheme can be adopted:

[0038] After completely flocculating the epoxidized natural latex, the flocculated rubber particles are completely separated from the aqueous phase. The separation methods include, but are not limited to, filtration using a filter screen, suction filtration, centrifugation, etc. After completely separating the flocculated rubber particles from the aqueous phase, the rubber particles need to be washed. The washing methods include, but are not limited to, thoroughly washing with deionized water or soaking with a sodium carbonate solution, and finally washing until neutral, and then drying to obtain dry epoxidized natural rubber.

[0039] Compared with the existing technology, the present invention firstly discovers that clay substances can cause the demulsification and flocculation of epoxidized natural latex. After flocculation, the rubber is in granular form, the flocculation speed is fast, the flocculation is complete, the aqueous phase is completely clear after flocculation, formic acid can be fully recovered, the flocculation method is simple, the cost is low, and it can be carried out at normal temperature and pressure.

[0040] The present invention uses a layered clay mineral as a flocculant for epoxidized natural latex. The layered clay mineral can cause the flocculation of epoxidized natural latex under the conditions of normal temperature and pressure. This flocculation method has high flocculation efficiency, simple process and low flocculation cost. The post-treatment can recover 80% of formic acid and has a lower ring-opening rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is the effect diagram after completely flocculating the epoxidized natural latex by using the sodium-based montmorillonite PNG aqueous dispersion in Example 1;

[0042] As can be seen from the figure, after adding the clay dispersion to the epoxidized natural latex, the latex has been completely flocculated within a short time;

[0043] Figure 2 It is the effect diagram of soaking the flocculated rubber block in the sodium carbonate solution after completely flocculating the epoxidized natural latex by using the sodium-based montmorillonite clay SMP aqueous dispersion in Example 4. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] The present invention will be specifically described below in conjunction with specific drawings and embodiments. It is necessary to point out here that the following embodiments are only used for further illustration of the present invention and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the content of the present invention still fall within the protection scope of the present invention.

[0045] The raw materials used in the embodiments and comparative examples of the present invention are all commercially available products, and the specific information is shown in Table 1 below:

[0046] Table 1

[0047] Raw material Source Sodium montmorillonite PNG NANOCOR montmorillonite from the United States Clay DK-NF Zhejiang Fenghong New Materials Co., Ltd. Clay BP-188 Zhejiang Fenghong New Materials Co., Ltd. Clay SMP Zhejiang Fenghong New Materials Co., Ltd. Domestic bentonite Jilin Liufangzi Bentonite Technology Co., Ltd. Concentrated natural latex Shandong Xufuyuan Chemical Co., Ltd. Nonylphenol polyoxyethylene ether OP-10 Shanghai Macklin Biochemical Co., Ltd. Octadecyl trimethyl ammonium chloride Shanghai Macklin Biochemical Co., Ltd. Sodium dodecyl sulfate Shanghai Macklin Biochemical Co., Ltd. Tween 80 Shanghai Macklin Biochemical Co., Ltd. Cationic emulsifier E-11 Nouryon Chemicals (Boxing) Co., Ltd. Fresh latex Hainan Rubber Group

[0048] Example 1

[0049] Weigh 100 parts by weight of concentrated natural rubber latex with a total solid content of 60%, add 3.4 parts by weight of non-ionic emulsifier - nonylphenol polyoxyethylene ether (OP-10), then add 70 parts by weight of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, and react at 30 °C for 8 hours. After the reaction is completed, take 30 g of sodium montmorillonite PNG aqueous dispersion with a concentration of 5 wt%, and slowly add it to 50 g of the epoxidized natural rubber latex prepared above under stirring. Wait until the epoxidized natural rubber latex is completely flocculated. The flocculation effect is as Figure 1 shown. The complete flocculation time is 1 min. Filter out the rubber particles with a filter screen, recover the aqueous phase, wash the flocculated rubber particles thoroughly with deionized water, and recover the aqueous phase. After the washing is completed, soak the rubber block in a sodium carbonate solution with a mass concentration of 2% for 6 h. After the soaking is completed, perform multiple water washes, and then dry it to obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxy degree of this epoxidized natural rubber dry rubber is 28%, and the ring-opening rate is 1.2%; the formic acid recovery rate is 60% obtained by titrating the recovered aqueous acid solution with sodium hydroxide.

[0050] Example 2

[0051] Weigh 100 parts by weight of concentrated natural rubber latex with a total solid content of 60%, add 3.4 parts by weight of cationic emulsifier - octadecyltrimethylammonium chloride (OTAC), then add 70 parts by weight of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, and react at 20 °C for 10 hours. After the reaction is completed, take 40 g of sodium-based clay - clay DK-NF aqueous dispersion with a concentration of 5 wt%, and slowly add it to 50 g of the epoxidized natural rubber latex prepared above under stirring. Wait until the epoxidized natural rubber latex is completely flocculated. The complete flocculation time is 1 min. Filter out the rubber particles with a filter screen, recover the aqueous phase, wash the flocculated rubber particles thoroughly with deionized water, recover the aqueous phase. After the washing is completed, soak the rubber block in a sodium carbonate solution with a mass concentration of 2% for 4 h. After the soaking is completed, perform multiple water washes, and then dry it to obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxy degree of this epoxidized natural rubber dry rubber is 25%, and the ring-opening rate is 1.1%; the formic acid recovery rate is 65% obtained by titrating the recovered aqueous acid solution with sodium hydroxide.

[0052] Example 3

[0053] Weigh 100 parts by weight of concentrated natural rubber latex with a total solid content of 60%, add 3.4 parts by weight of an anionic emulsifier - sodium dodecyl sulfate (SDS), then add 70 parts by weight of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, and react at 40 °C for 6 hours. After the reaction is completed, take 50 g of an aqueous dispersion of inorganic modified montmorillonite - clay BP-188 with a concentration of 5 wt%, and slowly add it to 50 g of the epoxidized natural rubber latex prepared above under stirring. Wait until the epoxidized natural rubber latex is completely flocculated, and the complete flocculation time is 1 min. Centrifuge the mixture of the latex and the clay mineral dispersion. The centrifugation parameters are: centrifuge speed 500 RPM, centrifugation time 10 min. After centrifugation, use a filter screen to filter to separate the rubber particles from the aqueous phase, recover the aqueous phase, and wash the flocculated rubber particles thoroughly with deionized water, and recover the aqueous phase. After washing to neutrality, carry out drying to obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxy degree of this epoxidized natural rubber dry rubber is 28%, and the ring-opening rate is 1.2%; the formic acid recovery rate is 59% obtained by titrating the recovered aqueous acid solution with sodium hydroxide.

[0054] Example 4

[0055] Weigh 100 parts by weight of concentrated natural rubber latex with a total solid content of 60%, add 1.7 parts by weight of a non-ionic emulsifier - nonylphenol polyoxyethylene ether (OP-10) and 1.7 parts by weight of a cationic emulsifier OTAC, then add 70 parts by weight of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, and react at 50 °C for 6 hours. After the reaction is completed, take 50 g of an aqueous dispersion of inorganic modified montmorillonite - clay SMP with a concentration of 0.5 wt%, and slowly add it to 50 g of the epoxidized natural rubber latex prepared above under stirring. Wait until the epoxidized natural rubber latex is completely flocculated, and the complete flocculation time is 1 min. Centrifuge the mixture of the latex and the clay mineral dispersion. The centrifugation parameters are: centrifuge speed 500 RPM, centrifugation time 10 min. After centrifugation, use a filter screen to filter to separate the rubber particles from the aqueous phase, recover the aqueous phase, and wash the flocculated rubber particles thoroughly with deionized water, and recover the aqueous phase. After the washing is completed, immerse the rubber block in a sodium carbonate solution with a mass concentration of 2% for 5 h. After the immersion is completed, carry out multiple water washings and granulation, and then drying can obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxy degree of this epoxidized natural rubber dry rubber is 33%, and the ring-opening rate is 1.1%; the formic acid recovery rate is 63% obtained by titrating the recovered aqueous acid solution with sodium hydroxide.

[0056] Example 5

[0057] Weigh 100 parts by weight of concentrated natural rubber latex with a total solid content of 60%, add 3.4 parts by weight of non-ionic emulsifier - Tween 80, then add 70 parts by weight of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, and react at 60 °C for 4 hours. After the reaction is completed, take 50 g of an aqueous dispersion of inorganic modified montmorillonite - domestic bentonite with a concentration of 2 wt%, and slowly add it to 50 g of the epoxidized natural rubber latex prepared above under stirring. Wait until the epoxidized natural rubber latex is completely flocculated, and the complete flocculation time is 1 min. Centrifuge the mixture of the latex and the clay mineral dispersion. The centrifugation parameters are: centrifuge speed 1000 RPM, centrifugation time 8 min. After centrifugation, use a suction filtration device to separate the rubber particles from the aqueous phase, recover the aqueous phase, and thoroughly wash the flocculated rubber particles with deionized water repeatedly under suction filtration, recover the aqueous phase. After washing to neutrality, granulate and dry to obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxy degree of this epoxidized natural rubber dry rubber is 32%, and the ring-opening rate is 1.01%; the formic acid recovery rate is 80% obtained by titrating the recovered aqueous acid solution with sodium hydroxide.

[0058] Example 6

[0059] Weigh 100 parts by weight of concentrated natural rubber latex with a total solid content of 60%, add 1.7 parts by weight of non-ionic emulsifier - nonylphenol polyoxyethylene ether (OP-10) and 1.7 parts by weight of anionic emulsifier - sodium dodecyl sulfate (SDS), then add 70 parts by weight of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, and react at 30 °C for 8 hours. After the reaction is completed, take 10 g of an aqueous dispersion of clay BP-188 with a concentration of 6 wt%, and slowly add it to 50 g of the epoxidized natural rubber latex prepared above under stirring. Wait until the epoxidized natural rubber latex is completely flocculated, and the complete flocculation time is 1 min. Centrifuge the mixture of the latex and the clay mineral dispersion. The centrifugation parameters are: centrifuge speed 1000 RPM, centrifugation time 8 min. After centrifugation, use a suction filtration device to separate the rubber particles from the aqueous phase, recover the aqueous phase, and thoroughly wash the flocculated rubber particles with deionized water under suction filtration, recover the aqueous phase. After the washing is completed, soak the rubber block in a sodium carbonate solution with a mass concentration of 2% for 6 h. After the soaking is completed, perform multiple water washes, granulation, and then drying to obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxy degree of this epoxidized natural rubber dry rubber is 28%, and the ring-opening rate is 0.98%; the formic acid recovery rate is 58% obtained by titrating the recovered aqueous acid solution with sodium hydroxide.

[0060] Example 7

[0061] Weigh 100 parts by weight of concentrated natural rubber latex with a total solid content of 60%, add 2 parts by weight of non-ionic emulsifier - Tween 80 and 1.4 parts by weight of cationic emulsifier E-11, then add a certain amount of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, and react at 40 °C for 6 hours. After the reaction is completed, take 50 g of clay SMP aqueous dispersion with a concentration of 3 wt%, and slowly add it to 50 g of the epoxidized natural rubber latex prepared above under stirring. Wait until the epoxidized natural rubber latex is completely flocculated, and the complete flocculation time is 1 min. Use a suction filtration device to separate the rubber particles from the aqueous phase, recover the aqueous phase, and wash the flocculated rubber particles thoroughly with deionized water under suction filtration, recover the aqueous phase. After washing to neutrality, granulate and dry to obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxy degree of this epoxidized natural rubber dry rubber is 28%, and the ring-opening rate is 1.4%; the formic acid recovery rate is obtained by titrating the recovered aqueous acid solution with sodium hydroxide to be 61%.

[0062] Example 8

[0063] Weigh 100 parts by weight of concentrated natural rubber latex with a total solid content of 60%, add 2 parts by weight of non-ionic emulsifier - Tween 80 and 1.4 parts by weight of anionic emulsifier sodium dodecyl sulfate (SDS), then add a certain amount of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, and react at 60 °C for 6 hours. After the reaction is completed, take 50 g of clay DK-NF aqueous dispersion with a concentration of 3 wt%, and slowly add it to 50 g of the epoxidized natural rubber latex prepared above under stirring. Wait until the epoxidized natural rubber latex is completely flocculated, and the complete flocculation time is 1 min. Use a suction filtration device to separate the rubber particles from the aqueous phase, recover the aqueous phase, and wash the flocculated rubber particles thoroughly with deionized water under suction filtration, recover the aqueous phase. After the washing is completed, immerse the rubber block in a sodium carbonate solution with a mass concentration of 2% for 12 h. After the immersion is completed, perform multiple water washes and granulation, and then dry to obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxy degree of this epoxidized natural rubber dry rubber is 51%, and the ring-opening rate is 1.8%; the formic acid recovery rate is obtained by titrating the recovered aqueous acid solution with sodium hydroxide to be 63%.

[0064] Example 9

[0065] Weigh 100 parts by weight of fresh latex, add 3.4 parts by weight of a non-ionic emulsifier - nonylphenol polyoxyethylene ether (OP-10), then add a certain amount of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, and react at 55 °C for 7 hours. After the reaction is completed, take 50 g of a 2.5 wt% aqueous dispersion of clay DK-NF, and slowly add it to 50 g of the epoxidized natural rubber latex prepared above under stirring. Wait until the epoxidized natural rubber latex is completely flocculated. The complete flocculation time is 1 min. Use a suction filtration device to separate the rubber particles from the aqueous phase, recover the aqueous phase, and wash the flocculated rubber particles thoroughly with deionized water under suction filtration. Recover the aqueous phase. After washing to neutrality, granulate and dry to obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxide degree of this epoxidized natural rubber dry rubber is 43%, and the ring-opening rate is 1.5%; by performing a sodium hydroxide titration test on the recovered aqueous acid solution, the formic acid recovery rate is 60%.

[0066] Example 10

[0067] Weigh 100 parts by weight of fresh latex, add 3.4 parts by weight of a non-ionic emulsifier - nonylphenol polyoxyethylene ether (OP-10), then add a certain amount of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, and react at 55 °C for 7 hours. After the reaction is completed, take 0.5 g of a 10 wt% aqueous dispersion of clay DK-NF, and slowly add it to 100 g of the epoxidized natural rubber latex prepared above under stirring. Wait until the epoxidized natural rubber latex is completely flocculated. The complete flocculation time is 2 min. Use a suction filtration device to separate the rubber particles from the aqueous phase, recover the aqueous phase, and wash the flocculated rubber particles thoroughly with deionized water under suction filtration. Recover the aqueous phase. After washing to neutrality, granulate and dry to obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxide degree of this epoxidized natural rubber dry rubber is 42%, and the ring-opening rate is 1.3%; by performing a sodium hydroxide titration test on the recovered aqueous acid solution, the formic acid recovery rate is 65%.

[0068] Comparative Example 1

[0069] Weigh 100 parts by weight of concentrated natural rubber latex with a total solid content of 60%, add 3.4 parts by weight of a non-ionic emulsifier - nonylphenol polyoxyethylene ether (OP-10), then add 70 parts by weight of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, react at 30 °C for 8 hours. After the reaction, flocculate the latex with 500 mL of ethanol for 2 minutes. Wash the flocculated rubber blocks thoroughly with deionized water. After the washing, immerse the rubber blocks in a sodium carbonate solution with a mass concentration of 2% for 6 hours. After the immersion, perform multiple water washes, and then dry to obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxy degree of this epoxidized natural rubber dry rubber is 27%, and the ring-opening rate is 2.2%.

[0070] Comparative Example 2

[0071] Weigh 100 parts by weight of concentrated natural rubber latex with a total solid content of 60%, add 3.4 parts by weight of a cationic emulsifier - octadecyltrimethylammonium chloride (OTAC), then add 70 parts by weight of deionized water under stirring, successively add 18.85 parts by weight of formic acid and 78.9 parts by weight of hydrogen peroxide, react at 20 °C for 10 hours. After the reaction, flocculate the latex with 500 mL of ethanol for 2 minutes. Wash the flocculated rubber blocks thoroughly with deionized water. After the washing, immerse the rubber blocks in a sodium carbonate solution with a mass concentration of 2% for 4 hours. After the immersion, perform multiple water washes, and then dry to obtain epoxidized natural rubber dry rubber. According to NMR characterization, the epoxy degree of this epoxidized natural rubber dry rubber is 24%, and the ring-opening rate is 2.2%.

[0072] It can be seen from Comparative Example 1 and Comparative Example 2 that a large amount of ethanol is contained in the water phase separated after flocculation with ethanol, and the ethanol therein cannot be removed alone, making the formic acid unable to be effectively recovered; moreover, the amount of ethanol consumed for flocculation with ethanol is very large, and a small amount of ethanol cannot effectively flocculate the latex. A large amount of ethanol is used in the actual production process, resulting in extremely high costs.

[0073] Comparative Example 3

[0074] Weigh 100 g of concentrated natural rubber latex (solid content 60%), take 50 g of a 2.5 wt% aqueous dispersion of clay PNG, and slowly add it to 50 g of the above natural rubber latex under stirring, and the latex does not flocculate.

[0075] Comparative Example 4

[0076] Weigh 50 g of concentrated natural rubber latex (solid content 60%), dilute it with deionized water to a solid content of 30%, take 100 g of a 5 wt% aqueous dispersion of clay PNG, and slowly add it to 100 g of the above natural rubber latex under stirring, and the latex does not flocculate.

[0077] As can be seen from Comparative Example 3 and Comparative Example 4, directly adding a clay dispersion into the latex does not affect the stability of the latex, and the mixing of clay and pure latex does not cause the latex to break.

[0078] In the examples and comparative examples of the present invention, the "parts" are all "parts by weight". Each example in this specification is described in a progressive manner. The key point of each example is to illustrate the differences from other examples. For the same and similar parts among the examples, reference can be made to each other. For the devices disclosed in the examples, since they correspond to the methods disclosed in the examples, the description is relatively simple, and reference can be made to the description in the method part for relevant parts.

[0079] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A flocculation method for epoxidized natural rubber latex, the method comprising: Mixing and stirring a clay mineral solution with epoxidized natural rubber latex for flocculation.

2. The flocculation method according to claim 1, characterized in that: The clay mineral solution is an aqueous dispersion of clay minerals. Preferably, the concentration of the clay mineral solution is 0.1 wt% to 10 wt%, preferably 1 wt% to 5 wt%.

3. The flocculation method according to claim 1, characterized in that: The dosage of the clay mineral solution is 0.5 wt% to 100 wt% of the epoxidized natural rubber latex, preferably 80 wt% to 100 wt%.

4. The flocculation method according to claim 2, characterized in that: The clay mineral has a layered structure.

5. The flocculation method according to claim 2, characterized in that: The clay mineral is at least one of sodium-based clay, calcium-based clay, lithium-based clay, kaolin, muscovite, hydrotalcite, vermiculite, and inorganically modified montmorillonite.

6. The flocculation method according to claim 1, characterized in that: The epoxidized natural rubber latex is prepared by stabilizing natural rubber latex with an emulsifier and then adding deionized water, formic acid, and hydrogen peroxide for epoxidation reaction under stirring.

7. The flocculation method according to claim 6, characterized in that: The natural rubber latex is concentrated latex or fresh latex. Preferably, the total solid content of the concentrated latex is 20 to 60%; and / or, The emulsifier is at least one of non-ionic emulsifier, cationic emulsifier, and anionic emulsifier.

8. The flocculation method according to claim 6, characterized in that: The reaction temperature of the epoxidation reaction is 20°C to 60°C, and / or the reaction time is 1 to 24 h.

9. The flocculation method according to claim 1, characterized in that: The stirring time is 1 to 5 min, preferably 2 to 3 min.

10. An epoxidized natural rubber, characterized in that The epoxidized natural rubber is prepared by flocculating with the flocculation method according to any one of claims 1-9, followed by separation, washing, and drying.

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