CN111019198A - Natural rubber/nano silicon dioxide composite material and preparation method thereof - Google Patents
Natural rubber/nano silicon dioxide composite material and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of rubber composite materials, and particularly relates to a natural rubber/nano silicon dioxide composite material and a preparation method thereof. The preparation method of the natural rubber/nano-silica composite material comprises the following steps: (1) soaking the surface-modified nano-silica in alkyl alcohol, dispersing in water, and stirring to obtain a nano-silica dispersion liquid; (2) mixing the nano silicon dioxide dispersion liquid with the natural rubber emulsion, stirring for 1-30min at the temperature of 15-70 ℃, and performing demulsification and flocculation to obtain flocculate; (3) the flocculate is obtained after post-treatment. The invention selects the nano silicon dioxide with surface modification as the filler, and can realize the flocculation of the natural rubber emulsion without adopting a flocculating agent; the flocculation process is simple and convenient, and the flocculated composite micelle (flocculate) can be prepared into the wet-process rubber compound through the procedures of crepe, water washing, hammer milling granulation, drying and the like in the traditional production process.
Description
Technical Field
The invention belongs to the technical field of rubber composite materials, and particularly relates to a wet mixing preparation method of a natural rubber/nano silicon dioxide composite material.
Background
The nano silicon dioxide, also called white carbon black, has reinforcement performance similar to that of carbon black, and is a commonly used reinforcement filler for rubber materials. The surface of the rubber material contains a large amount of silicon hydroxyl, the particle size is small, the specific surface area is large, the polarity is strong, and the rubber material is easy to agglomerate in a nonpolar rubber material, so that the reinforcing effect is reduced. Through proper surface organic modification, the surface polarity of the rubber can be reduced, and the compatibility with rubber is enhanced.
The common method for rubber nano composite material is mainly mechanical blending method, and rubber material and powdered nano silicon dioxide are plasticated and mixed in solid state by adopting mechanical equipment such as a double-roller open mill, an internal mixer and a screw extruder to prepare the rubber nano composite material. In the traditional mechanical blending method, the mixing energy consumption is high, dust is easy to generate, environmental pollution is caused, the loss of filler is large, the dispersion is not uniform, the processing of the composite material is not facilitated, and the stress concentration and the mechanical property of the composite material are directly caused.
The wet mixing is the main development direction of the mixing process of natural rubber, and the natural rubber emulsion and the nano material dispersion liquid are mixed in an emulsion state to form a uniform emulsion system, and then the uniform emulsion system is flocculated by a flocculating agent, co-precipitated or dried at high temperature to prepare the natural rubber nano composite material.
In recent years, various patent technologies relating to the preparation of natural rubber nanocomposites by wet kneading have been disclosed, and can be roughly classified into two main categories: one is a flocculating agent demulsification method, under the action of an emulsifying agent, a nano material is pre-modified at a certain temperature by adopting organic modifying agents such as a silane coupling agent and the like, a nano material dispersion liquid with a certain solid content is prepared, the dispersion liquid and natural rubber emulsion are uniformly blended, and then flocculating agents are added for coprecipitation to prepare a composite material; the other is a high-temperature drying method, firstly preparing nano material emulsion, uniformly mixing the emulsion and natural rubber emulsion, and directly drying at high temperature by the processes of spraying, flash evaporation and the like to prepare the composite material.
Compared with the traditional wet mixing method, the invention can realize the demulsification and flocculation of the natural rubber emulsion without adding a flocculating agent, and can directly relieve the pollution of flocculating agents such as acid, salt and the like to water in the primary processing and washing process of the natural rubber. The invention has simple and convenient process, low energy consumption and simple equipment, and can realize industrial production by simply rebuilding on the basis of the original production line.
Disclosure of Invention
In order to overcome the problems in the prior art, the invention provides a wet mixing preparation method of a natural rubber/nano-silica composite material. The preparation method adopts the surface-modified nano silicon dioxide as the filler, can realize the flocculation of the natural rubber emulsion without adopting a flocculating agent, and is green and environment-friendly.
The invention also provides the natural rubber/nano silicon dioxide composite material prepared by the method.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a preparation method of a natural rubber/nano-silica composite material comprises the following steps:
(1) soaking the surface-modified nano-silica in alkyl alcohol, dispersing in water, and stirring to obtain a nano-silica dispersion liquid;
(2) mixing the nano silicon dioxide dispersion liquid in the step (1) with natural rubber emulsion, stirring for 1-30min at the temperature of 15-70 ℃, and performing demulsification and flocculation to obtain flocculate;
(3) and (3) carrying out after-treatment on the flocculate obtained in the step (2).
Specifically, the step (1) can be carried out at the temperature of 20-70 ℃ with stirring.
Specifically, the stirring speed in the step (2) is 50-2000 rad/min.
Preferably, the mass ratio of the using amount of the surface modified nano silicon dioxide to the dry rubber content in the natural rubber emulsion is (0.05-1): 1; namely, the addition amount of the nano silicon dioxide is 5 to 100phr calculated by the dry rubber content in the natural rubber emulsion being 100 phr.
Preferably, in the step (1), the surface modified nano-silica is one or more of A and/or B, wherein A is obtained by modifying nano-silica by one or more than two short chain compounds of linear chain or branched chain containing 2-8 carbon atoms, and B is obtained by modifying nano-silica by long chain polymer obtained by polymerizing monomers containing 2-8 carbon atoms.
More preferably, the short-chain compound is an organic silane or organic compound containing a methyl group, an ethyl group, an amino group, a vinyl group, an epoxy group, a carboxyl group, a carbonyl group, or the like; the long-chain polymer is polyolefin polymer such as polyethylene, polyvinyl chloride, polyvinyl acetate, polybutadiene or polyisoprene.
Specifically, the surface-modified nanosilica has a modifying group such as: vinyltriethoxysilane, gamma- (2, 3-epoxypropoxy) propyltrimethoxysilane, dimethyldiethoxysilane, bis- (gamma-triethoxysilylpropyl) tetrasulfide, gamma-mercaptopropyltrimethylsilane, polyvinyl acetate, polybutadiene, dimethyldiethoxysilane, and the like.
Further preferably, the content of the modifier grafted on the surface of the nano silicon dioxide is more than 5 percent; i.e. the content of modifier chemically bonded to the silica surface is greater than 5%.
Preferably, the mass fraction of the surface-modified nano-silica in the nano-silica dispersion liquid in the step (1) is 4-35%; more preferably, the mass fraction of the surface-modified nano-silica is 5-30%.
Preferably, the mass fraction of the alkyl alcohol in the nano-silica dispersion liquid in the step (1) is 0-10%, and the alkyl alcohol is one or more of monohydric alcohol or polyhydric alcohol of C1-C5, such as ethanol, methanol, propylene glycol, and the like.
Preferably, the natural rubber emulsion in the step (2) is field latex, ammoniated natural latex, concentrated natural latex or natural rubber skim latex, and the dry rubber content in the natural rubber emulsion is 5-65%.
Specifically, the post-treatment in the step (3) is to crepe, wash, hammer mill and granulate the flocculate, and dehydrate and dry the flocculate (when latex is used); or filtering and washing with water to obtain flocculated micelle (when natural rubber skim latex is used).
Step (2) may be carried out in the following reactor: a stirring reaction kettle, a colloid mill, a testing machine based on a single/double screw extrusion principle, and one or more of the components are used in combination.
The natural rubber/nano-silica composite material prepared by the method is adopted.
It should be noted that: the surface-modified nano-silica is obtained by a liquid-phase in-situ surface modification method, which can be specifically referred to in the literature (Xiaohong Li, Zhi Cao, Zhijun Zhang, Hongxin Dang2applied Surface science.2006, and its structures and triglogic properties; 7856-7861 Fahui Yan, XiiaobingZhang, Feng Liu, Xiaohong Li, Zhijun Zhang, adjusting the properties of silicone fibers with a silicone by changing the surface organic groups of silicone composites Part B, Engineering, 2015; 75,47-52.) or (CN102502663A, CN1704452A, CN1666954A) to prepare nano SiO2The surface contains organic groups; or can be purchased from common commercial products and used after being modified by the modifier.
In the invention, the preparation of uniformly dispersed nano-silica aqueous dispersion is the key for preparing high-performance wet rubber compound, and the method selects the nano-silica with surface modification as the filler, and the nano-silica is wetted by alkyl alcohol and uniformly dispersed in the water solution in an emulsion reaction device. In addition, the main function of the alkyl alcohol in the invention is to rapidly and uniformly disperse the surface organically modified silicon dioxide in the aqueous solution, and the preparation of the dispersion can also be realized by regulating the polarity of the surface of the silicon dioxide without adding an auxiliary agent.
The invention selects the nano silicon dioxide with surface modification as the filler, and the nano silicon dioxide with surface modification reduces the surface energy and surface polarity of the nano silicon dioxide, weakens the agglomeration of the nano filler, greatly improves the affinity of the nano filler with a nonpolar rubber material, and reduces the loss of the silicon dioxide and natural rubber in the wet mixing process.
The surface modified nano silicon dioxide is selected as the filler, and due to the strong adsorption effect of the nano silicon dioxide, the water-soluble protein is peeled from the surface of the rubber molecular chain and is adsorbed on the surface of the rubber molecular chain under the action of two-phase mixing mechanical stirring, so that a filler-rubber network structure is quickly formed, and the demulsification of the natural rubber emulsion is caused.
The outer layer structure of the natural rubber particle is water-soluble protein, phospholipid and the like, the macromolecular chain structure is coated inside, and an electric double layer structure is formed on the surface of the particle due to the ionization effect of the protein and the phospholipid on the surface of the rubber particle, so that the particle has weaker negative charges. After the surface-modified nano silicon dioxide is added into a natural rubber emulsion system, the double electronic layer structure on the surface of the natural rubber emulsion particle is destroyed, and the charge balance is broken, so that the demulsification of the natural rubber emulsion colloid system is caused.
Therefore, the invention can realize the flocculation coprecipitation of the natural rubber/silicon dioxide nano composite material without adding any flocculating agent.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention selects the nano silicon dioxide with surface modification as the filler, which can realize the flocculation of the natural rubber emulsion; the invention has wide application range and can be widely applied to the wet mixing of latexes with different solid contents of natural rubber.
2. According to the invention, the nano-silica and the natural rubber have better affinity by regulating and controlling the modification group, the purpose of flocculation can be achieved by adsorbing natural rubber molecular chains in the emulsion, the flocculation is thorough, the loss amount of the nano-silica in the mixing process can be reduced to below 1%, a flocculating agent is not used in the process, the problem of water pollution in the creping and washing process is avoided due to the fact that the flocculating agent is not used for flocculation, the environment is friendly, and the corrosion of the flocculating agent to equipment can be reduced.
3. The flocculation process of the invention is simple and convenient, the equipment is simple, and the flocculated composite micelle (flocculate) can be prepared into the wet-process rubber compound through the procedures of crepe, water washing, hammer milling granulation, drying and the like in the traditional production process.
4. By adopting the method, the solid content of the natural rubber skim latex can be reduced from about 8 percent to 1-3 percent, and more than 70 percent of colloid components in the natural rubber latex can be flocculated.
Drawings
FIG. 1 scanning electron micrographs and Si distribution plots of composites prepared in examples 1-4;
FIG. 2 is a comparison of the natural rubber skim before and after the reaction in examples 9 to 10.
Detailed Description
The invention is further illustrated, but not limited, by the following examples and the accompanying drawings.
Example 1
Taking 3.75phr of ethanol and 30phr of vinyl triethoxysilane modified nano silicon dioxide (surface modified nano silicon dioxide is infiltrated by ethanol) based on 100phr of dry rubber content of the natural rubber emulsion, then adding the mixture into 116.25phr of distilled water, heating to 50 ℃, stirring for 20min, and preparing 20% solid content nano silicon dioxide alkyl alcohol aqueous solution; mixing with ammonia-added natural latex (dry glue content 25%) 400g, controlling flow (adjustable according to actual conditions) and pumping into a reaction kettle at 50 deg.C, stirring at 200rad/min for 10min to obtain composite micelle (flocculate); and (4) carrying out crepe, washing, crushing and drying on the flocculate to obtain the natural rubber/nano silicon dioxide composite material.
The silica content of the composite material prepared in this example is shown in table 1, and it can be seen from table 1 that the loss amount of the nano silica in the mixing process is 1% or less.
130phr of the natural rubber/nano-silica composite material, 695phr of Si, 5phr of zinc oxide, 1.5phr of stearic acid, 1.5phr of accelerator CBS, 0.5phr of accelerator D and 1.5phr of sulfur, mixing, standing for 12h, vulcanizing under the conditions of 150 ℃ multiplied by 20MPa multiplied by Tc90, and testing the mechanical properties, wherein the results are shown in Table 2.
Example 2
Taking 6.25phr of propanol and 50phr of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane modified nano silicon dioxide (the nano silicon dioxide with the surface modified is infiltrated by the propanol) based on 100phr of dry rubber content of the natural rubber emulsion, then adding the mixture into 193.75phr of distilled water, heating to 60 ℃, stirring for 20min, and preparing 20% solid content nano silicon dioxide alkyl alcohol aqueous solution; mixing with ammonia-added natural latex (dry gel content 25%) 400g, pumping into reaction kettle at 70 deg.C while controlling flow rate, and stirring at 200rad/min for 8min to obtain composite micelle (flocculate); and (4) conducting crepe, washing, crushing and drying on the composite micelle (flocculate) to obtain the natural rubber/nano silicon dioxide composite material.
The silica content of the composite material prepared in this example is shown in table 1. 150phr of the natural rubber/nano-silica composite material, 695phr of Si, 5phr of zinc oxide, 1.5phr of stearic acid, 1.5phr of accelerator CBS, 0.5phr of accelerator D0, 1.5phr of sulfur, mixing, standing for 12h, vulcanizing under the conditions of 150 ℃ multiplied by 20MPa multiplied by Tc90, and testing the mechanical properties, wherein the results are shown in Table 2.
Example 3
Taking 8.75phr of propylene glycol and 70phr of dimethyl diethoxy silane modified nano silicon dioxide (the nano silicon dioxide with the surface modified is infiltrated by the propylene glycol) according to 100phr of the dry rubber content of the natural rubber emulsion, then adding the mixture into 271.25phr of distilled water, heating to 70 ℃, stirring for 20min, and preparing 20% solid content nano silicon dioxide alkyl alcohol aqueous solution; mixing with ammonia-added natural latex (dry gel content 25%) 400g, pumping into reaction kettle at 50 deg.C while controlling flow rate, and stirring at 200rad/min for 15min to obtain composite micelle (flocculate); and (4) conducting crepe, washing, crushing and drying on the composite micelle (flocculate) to obtain the natural rubber/nano silicon dioxide composite material.
The silica content of the composite material prepared in this example is shown in table 1.
170phr of the natural rubber/nano-silica composite material, 695phr of Si, 5phr of zinc oxide, 1.5phr of stearic acid, 1.5phr of accelerator CBS, 0.5phr of accelerator D and 1.5phr of sulfur, mixing, standing for 12h, vulcanizing under the conditions of 150 ℃ multiplied by 20MPa multiplied by Tc90, and testing the mechanical properties, wherein the results are shown in Table 2.
Example 4
Taking 11.25phr of methanol and 90phr of vinyl triethoxysilane nano-silica (surface-modified nano-silica is infiltrated by methanol) based on 100phr of dry rubber content of the natural rubber emulsion, then adding the mixture into 348.75phr of distilled water, stirring the mixture at room temperature for 20min, and preparing 20% solid content nano-silica alkyl alcohol aqueous solution; mixing with ammonia-added natural latex (dry gel content 25%) 400g, pumping into reaction kettle at 50 deg.C while controlling flow rate, and stirring at 200rad/min for 30min to obtain composite micelle (flocculate); and (4) conducting crepe, washing, crushing and drying on the composite micelle (flocculate) to obtain the natural rubber/nano silicon dioxide composite material.
The silica content of the composite material prepared in this example is shown in table 1.
190phr of the natural rubber/nano-silica composite material, 695phr of Si, 5phr of zinc oxide, 1.5phr of stearic acid, 1.5phr of accelerator CBS, 0.5phr of accelerator D and 1.5phr of sulfur, mixing, standing for 12h, vulcanizing under the conditions of 150 ℃ multiplied by 20MPa multiplied by Tc90, and testing the mechanical properties, wherein the results are shown in Table 2.
The scanning electron micrographs and Si distribution plots for the composites prepared in examples 1-4 are shown in FIG. 1: wherein a is1-d1(i.e. a)1、b1、c1、d1) Scanning electron micrographs of the composites of examples 1-4, respectively, a2-d2(i.e. a)2、b2、c2、d2) The Si profiles for the composites of examples 1-4, respectively. From figure a1-d1It is understood that the nanosilica is finely and uniformly dispersed in the rubber mass, and no large-sized aggregates appear in the visual field, as shown in the graph a2-d2Further confirming the uniform dispersion of silica in the rubber mass.
Example 5
Taking 3.75phr of ethanol and 30phr of bis- (gamma-triethoxysilylpropyl) tetrasulfide modified nano-silica (the nano-silica with the surface modified is infiltrated by the ethanol) based on 100phr of dry rubber content of the natural rubber emulsion, then adding the mixture into 116.25phr of distilled water, heating to 50 ℃, stirring for 20min, and preparing 20% solid content nano-silica alkyl alcohol aqueous solution; mixing with ammonia-added natural latex (dry gel content 25%) 400g, pumping into reaction kettle at 50 deg.C while controlling flow rate, and stirring at 200rad/min for 5min to obtain composite micelle (flocculate); and (4) conducting crepe, washing, crushing and drying on the composite micelle (flocculate) to obtain the natural rubber/nano silicon dioxide composite material.
Example 6
Taking 3.75phr of ethanol and 30phr of gamma-mercaptopropyl-trimethyl silane modified nano-silica (the nano-silica with the surface modified is infiltrated by the ethanol) based on 100phr of the dry rubber content of the natural rubber emulsion, then adding the nano-silica into 116.25phr of distilled water, heating to 50 ℃, stirring for 20min, and preparing 20% solid content nano-silica alkyl alcohol aqueous solution; mixing with ammonia-added natural latex (dry gel content 25%) 400g, pumping into reaction kettle at 50 deg.C while controlling flow rate, and stirring at 200rad/min for 10min to obtain composite micelle (flocculate); and (4) conducting crepe, washing, crushing and drying on the composite micelle (flocculate) to obtain the natural rubber/nano silicon dioxide composite material.
Example 7
Taking 3.75phr of ethanol and 30phr of polyvinyl acetate modified nano silicon dioxide (surface modified nano silicon dioxide is soaked by ethanol) based on 100phr of dry rubber content of the natural rubber emulsion, then adding the mixture into 116.25phr of distilled water, heating to 50 ℃, stirring for 20min, and preparing 20% solid content nano silicon dioxide alkyl alcohol aqueous solution; mixing with ammonia-added natural latex (dry gel content 25%) 400g, pumping into reaction kettle at 50 deg.C while controlling flow rate, and stirring at 200rad/min for 20min to obtain composite micelle (flocculate); and (4) conducting crepe, washing, crushing and drying on the composite micelle (flocculate) to obtain the natural rubber/nano silicon dioxide composite material.
Example 8
Taking 3.75phr of ethanol and 30phr of polybutadiene modified nano silicon dioxide (surface modified nano silicon dioxide is infiltrated by ethanol) based on 100phr of dry rubber content of the natural rubber emulsion, then adding the mixture into 116.25phr of distilled water, heating to 50 ℃, stirring for 20min, and preparing 20% solid content nano silicon dioxide alkyl alcohol aqueous solution; mixing with ammonia-added natural latex (dry gel content 25%) 400g, pumping into reaction kettle at 50 deg.C while controlling flow rate, and stirring at 200rad/min for 20min to obtain composite micelle (flocculate); and (4) conducting crepe, washing, crushing and drying on the composite micelle (flocculate) to obtain the natural rubber/nano silicon dioxide composite material.
Example 9
Taking 6.25phr of ethanol and 50phr of dimethyl diethoxy silane modified nano silicon dioxide (surface modified nano silicon dioxide is soaked by ethanol) according to the dry rubber content of the natural rubber emulsion of 100phr, then adding the mixture into 193.75phr of distilled water, heating to 50 ℃, stirring for 20min, and preparing 20% solid content nano silicon dioxide alkyl alcohol aqueous solution; 1176g of natural rubber skim latex (dry gum content is 8.5 percent), the mixture is pumped into a reaction kettle at the same time of controlling the flow rate under the condition of 50 ℃, stirred for 10min at the rotating speed of 200rad/min and flocculated to obtain the composite material; filtering and washing the composite material. The filtrate was pale yellow with a solid content of 2.52% and the upper solid was flocculated micelles.
The organic content and the skim latex separation rate of the filtrate in this example are shown in table 3.
Example 10
Taking 11.25phr of ethanol and 90phr of dimethyl diethoxy silane modified nano silicon dioxide (surface modified nano silicon dioxide is soaked by ethanol) based on 100phr of dry rubber content of the natural rubber emulsion, then adding the mixture into 348.75phr of distilled water, heating to 50 ℃, stirring for 20min, and preparing 20% solid content nano silicon dioxide alkyl alcohol aqueous solution; 1176g of natural rubber skim latex (dry gum content is 8.7 percent), the mixture is pumped into a reaction kettle at the same time of controlling the flow rate under the condition of 50 ℃, stirred for 15min at the rotating speed of 200rad/min and flocculated to obtain the composite material; and (3) carrying out vacuum filtration and washing on the composite material. The filtrate was pale yellow with a solid content of 1.56% and the upper solid was colloidal particles.
The organic content of the filtrate of this example is shown in table 3.
A comparison of the results of examples 9-10 with the natural rubber skim in the reaction is shown in FIG. 2. As can be seen from FIG. 2, the natural rubber skim latex is white due to about 8% of organic components; after the reaction of examples 9-10, the filtrate was yellowish and clear, and the filtered upper solid (i.e., the micelle in FIG. 2) was either lumpy (example 9) or granular (example 10). Example 9 elution of 71.2% of the organic content of the natural rubber skim by a wet mixing process reduced the solids content of the filtrate to; 2.52 percent; in example 10, 82.2% of organic matter in the natural rubber serum was eluted by wet mixing, and the solid content of the filtrate was reduced to 1.56%; the wet mixing process shows that more than 70% of organic matter components in the natural rubber whey are combined with the silicon dioxide to form the natural rubber/silicon dioxide nano composite material with a space network structure.
Example 11
Taking 3.75phr of ethanol and 5phr of vinyl triethoxysilane modified nano silicon dioxide (surface modified nano silicon dioxide is infiltrated by ethanol) based on 100phr of dry rubber content of the natural rubber emulsion, then adding the mixture into 116.25phr of distilled water, heating to 35 ℃, stirring for 20min, and preparing 20% solid content nano silicon dioxide alkyl alcohol aqueous solution; 400g of field latex (with dry glue content of 25 percent), pumping the mixture into a reaction kettle at the same time of controlling the flow rate under the condition of 70 ℃, and stirring the mixture for 1min at the rotating speed of 50rad/min to obtain a composite micelle (flocculate); and (4) carrying out crepe, washing, crushing and drying on the flocculate to obtain the natural rubber/nano silicon dioxide composite material.
Example 12
Taking 6.25phr of ethanol and 100phr of gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane modified nano silicon dioxide (surface modified nano silicon dioxide is infiltrated by ethanol) based on 100phr of dry rubber content of the natural rubber emulsion, then adding the mixture into 193.75phr of distilled water, heating to 70 ℃, stirring for 20min, and preparing 20% solid content nano silicon dioxide alkyl alcohol aqueous solution; 400g of concentrated natural latex (the dry rubber content is 25 percent), pumping the mixture into a reaction kettle at the same time of controlling the flow rate under the condition of 15 ℃, and stirring the mixture for 30min at the rotating speed of 2000rad/min to obtain composite micelle (flocculate); and (4) conducting crepe, washing, crushing and drying on the composite micelle (flocculate) to obtain the natural rubber/nano silicon dioxide composite material.
Comparative example 1
Taking 100phr (cloud label No. 1) of natural rubber dry rubber and SiO modified by vinyl triethoxysilane230phr, Si695phr, zinc oxide 5phr, stearic acid 1.5phr, accelerant CBS 1.5phr, accelerant D0.5phr, sulfur 1.5phr, mixing, standing for 12h, vulcanizing under 150 ℃ x 20MPa x Tc90, testing mechanical properties, and the results are shown in Table 2.
Example 1 differs from comparative example 1 in the preparation method, example 1 is wet mixing and comparative example 1 is conventional dry mixing.
Comparative example 2
Taking 100phr (cloud label No. 1) of natural rubber dry glue and SiO modified by gamma- (2, 3-epoxypropoxy) propyl trimethoxy silane250phr, Si695phr, zinc oxide 5phr, stearic acid 1.5phr, accelerator CBS 1.5phr, accelerator D0.5phr, sulfur 1.5phr, mixing, standing for 12h, vulcanizing at 150 ℃ x 20MPa x Tc90, testing mechanical properties, and the results are shown in Table 2.
Example 2 differs from comparative example 2 in the preparation method, example 2 is wet mixing and comparative example 2 is conventional dry mixing.
Comparative example 3
Taking 100phr (cloud label No. 1) of natural rubber dry rubber and SiO modified by dimethyl diethoxy silane270phr, Si695phr, zinc oxide 5phr, stearic acid 1.5phr, accelerant CBS 1.5phr, accelerant D0.5phr, sulfur 1.5phr, mixing, standing for 12h, vulcanizing under 150 ℃ x 20MPa x Tc90, testing mechanical properties, and the results are shown in Table 2.
Example 3 differs from comparative example 3 in the preparation method, example 3 is wet mixing and comparative example 3 is conventional dry mixing.
Comparative example 4
Taking 30phr of common commercial unmodified nano silicon dioxide based on 100phr of dry rubber content of natural rubber emulsion, adding the common commercial unmodified nano silicon dioxide into 120phr of aqueous solution to prepare silicon dioxide dispersion liquid with the mass percentage content of 20%, pumping the dispersion liquid and ammonia-added natural latex (the dry rubber content is 25%) 400g into a reaction kettle at the same time under the condition of 50 ℃, controlling the flow, stirring for 10min at the rotation speed of 200rad/min, and adding calcium chloride flocculant for flocculation; and (4) conducting crepe, washing, crushing and drying on the composite micelle (flocculate) to obtain the natural rubber/nano silicon dioxide composite material.
130phr of the natural rubber/nano-silica composite material, 695phr of Si, 5phr of zinc oxide, 1.5phr of stearic acid, 1.5phr of accelerator CBS, 0.5phr of accelerator D and 1.5phr of sulfur, mixing, standing for 12h, vulcanizing under the conditions of 150 ℃ multiplied by 20MPa multiplied by Tc90, and testing the mechanical properties, wherein the results are shown in Table 2.
Examples 1 to 3 are different from comparative examples 1 to 3 in the preparation method, examples 1 to 3 are composite materials prepared by wet mixing flocculation without a flocculant, and comparative examples 1 to 3 are composite materials prepared by conventional dry mixing. As can be seen from Table 2, examples 1-3 are higher in tensile strength, 100%, 200%, 300% stress at elongation, and tear strength than comparative examples 1-3, because the wet mixing process improves the dispersibility of the silica in the rubber matrix. Meanwhile, as the silicon dioxide is uniformly dispersed, the number of rubber molecular chains adsorbed/wound on the surface of the silicon dioxide is increased, and the interfacial bonding between the filler and the rubber is further enhanced, so that the elongation at break of the composite material prepared by the method is slightly reduced compared with that of the composite material prepared by the traditional dry mixing method.
The difference between the comparative example 4 and the example 1 is that the preparation method is different, and the example 1 can realize the demulsification and flocculation of the natural rubber emulsion without adding a flocculating agent in the wet mixing process; comparative example 4 is the traditional wet mixing process, and the rubber nanocomposite is prepared after the flocculant is added in the mixing process. By comparing the properties of example 1 and comparative example 4 (see table 2), it can be seen that the tensile strength, 100%, 200%, 300% stress at definite elongation, and tear strength of the samples prepared according to the present invention are higher than those of comparative example 4; the elongation at break of the inventive sample is slightly lower than that of comparative example 4, which may be related to the stronger bonding strength of the inventive sample filler to rubber.
Table 1 silica content in composites prepared in examples 1-4
TABLE 2 mechanical properties of examples 1-4 and comparative examples 1-4
Table 3 examples 9-10 organic matter content of filtrate and skim latex separation efficiency
| Sample (I) | Color of filtrate | Organic content (%) | Separation efficiency of skim latex (%) |
| Glue cleaner | Milky white color | 8.75 | / |
| Example 9 | Light yellow and clear | 2.52 | 71.2 |
| Example 10 | Light yellow and clear | 1.56 | 82.2 |
The surface modified nano silicon dioxide is selected, so that the filler-rubber compatibility is good, and the binding force is strong; the flocculation and coprecipitation of the natural rubber/nano silicon dioxide can be realized without a flocculating agent in the wet mixing process, so that the water pollution in the primary processing process of the natural rubber can be greatly reduced, and the ring pressure maintaining is reduced; the wet mixing process has complete demulsification, the loss of silicon dioxide in the wet mixing process is less than 1 percent, the equipment is simple, and the industrial production is easy to realize.
The wet mixing process is used for treating natural rubber skim latex, can flocculate more than 70% of organic matters in the natural rubber skim latex, and provides a new way for treating byproducts prepared from the natural rubber concentrated latex.
Claims (9)
1. A preparation method of a natural rubber/nano-silica composite material is characterized by comprising the following steps:
(1) soaking the surface-modified nano-silica in alkyl alcohol, dispersing in water, and stirring to obtain a nano-silica dispersion liquid;
(2) mixing the nano silicon dioxide dispersion liquid in the step (1) with natural rubber emulsion, stirring for 1-30min at the temperature of 15-70 ℃, and performing demulsification and flocculation to obtain flocculate;
(3) and (3) carrying out after-treatment on the flocculate obtained in the step (2).
2. The method for preparing a natural rubber/nano-silica composite material according to claim 1, wherein the mass ratio of the amount of the surface-modified nano-silica to the dry rubber content in the natural rubber emulsion is (0.05-1): 1.
3. The method for preparing a natural rubber/nano-silica composite material according to claim 1, wherein the surface-modified nano-silica in the step (1) is one or more of a and/or B, wherein a is obtained by modifying nano-silica with one or more short chain compounds of linear chains or branched chains containing 2 to 8 carbon atoms, and B is obtained by modifying nano-silica with a long chain polymer obtained by polymerizing monomers containing 2 to 8 carbon atoms.
4. The method for preparing a natural rubber/nano-silica composite according to claim 3, wherein the short-chain compound is an organic silane or compound containing a methyl group, an ethyl group, an amino group, a vinyl group, an epoxy group, a carboxyl group or a carbonyl group; the long-chain polymer is polyethylene, polyvinyl chloride, polyvinyl acetate, polybutadiene or polyisoprene.
5. The method for preparing a natural rubber/nano-silica composite according to claim 3, wherein the content of the modifier grafted on the surface of the nano-silica is more than 5%.
6. The method for preparing a natural rubber/nano-silica composite according to claim 1, wherein the mass fraction of the surface-modified nano-silica in the nano-silica dispersion liquid of the step (1) is 4 to 35%.
7. The method for preparing the natural rubber/nano-silica composite material according to claim 1, wherein the nano-silica dispersion liquid in the step (1) contains 0-10% by mass of an alkyl alcohol, wherein the alkyl alcohol is one or more of monohydric alcohols and polyhydric alcohols of C1-C5.
8. The method for preparing a natural rubber/nano silica composite material according to claim 1, wherein the natural rubber emulsion of the step (2) is field latex, ammoniated natural latex, concentrated natural latex or natural rubber skim latex, and the dry rubber content in the natural rubber emulsion is 5-65%.
9. A natural rubber/nano-silica composite material prepared by the method of any one of claims 1 to 8.
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