CN1079409C - Process for preparing clay-rubber nm-class composite material - Google Patents

Abstract

The invention relates to a preparation method of clay/rubber nano composite material. The method of the present invention is based on the advantage that most rubbers have their own emulsion form. The aqueous suspension of clay is used to blend with the rubber emulsion, and a coagulant is added for flocculation to remove water, thereby obtaining the clay/rubber nanocomposite material. The method of the invention has the advantages of simple operation, low cost, wide applicability and easy industrialization, and the clay can be uniformly dispersed in the form of nanometer in the rubber matrix by using the method of the invention.

Description

Preparation method of clay/rubber nanocomposite

The invention relates to a preparation method of a polymer-based nanocomposite material, especially a method for preparing a rubber-based nanocomposite material. More specifically, the present invention relates to a method for dispersing nano-sized platelets contained in clay particles in rubber.

The traditional reinforcing agents in the rubber industry have always been carbon black and silica, especially the former, which occupies an important position in the rubber industry. The size of the primary particles of these two reinforcing agents is very small. For example, the particle size of carbon black before N600 grade is less than 60nm, and the particle size of precipitated white carbon black is generally between 20-40nm. It can be said that the particle size is the first factor affecting its ability to reinforce rubber. After the particle size exceeds 1000nm, even if the surface treatment method is used to produce excellent interfacial adhesion between the two, it is difficult to reach the level of carbon reinforcement. Levels of black and silica reinforcement. The research on a large number of inorganic fillers has strongly proved this point. Up to now, it has not been possible to find a new type of filler with a reinforcing ability that exceeds these two reinforcing agents. The reason is that the particle size of the newly developed fillers is relatively small. big.

However, people have never stopped efforts to develop new rubber reinforcement methods and reinforcing agents. This is because the traditional reinforcing agent has the following disadvantages: (1) The processing is highly polluting. Due to the low apparent density of these two reinforcing agents, it is easy to generate flying when they are added to the rubber. Therefore, even if a closed rubber mixer is used, it is difficult to ensure the cleanliness of the mixing workshop and avoid harm to the health of workers. damage. (2) The processing time is long and the energy consumption of mixing is large. Because the powders of these two reinforcing agents are extremely fine and easy to aggregate, it takes a long time to disperse in the rubber, and at the same time the extremely low apparent density leads to a short time for them to mix into the rubber (or eat people). Longer, accounting for almost 1/2 of the whole process of rubber mixing. (3) The color of the product is single. This mainly refers to carbon black reinforcement. High-grade carbon black generally has better comprehensive reinforcing ability than white carbon black, so it is more commonly used in the rubber industry. But the black tone of the finished product cannot be changed. (4) Some performances are still lacking. For example, these two reinforcing agents are difficult to give rubber products higher hardness, better air permeability resistance and so on. (5) Due to dependence on petroleum, the resources of carbon black are gradually decreasing. It is impossible for white carbon black to completely replace carbon black, and the price is more expensive. If the surface is treated with a silane coupling agent (many times this is required), the price will be even higher.

Therefore, the development trend of new reinforcing agents is to have good processing performance and better comprehensive reinforcing ability, preferably light-colored fillers, and the price should be low. The research results of clay polymer-based nanocomposites have made people see the dawn of the solution to this problem.

The research on clay/polymer-based nanocomposites is a hot spot in the field of polymer materials today. It has shown people a series of excellent physical and mechanical properties of this type of material, and has achieved industrialization results, such as Japan The clay/nylon 6 nanocomposite produced by Ube Industries has extremely high stiffness, high heat distortion temperature and tensile strength. Clay nanocomposites of a series of polymer matrices have been prepared in the laboratory, including nylon 6, epoxy resin, polystyrene and so on. The acquisition of these nanocomposites is obtained by uniformly dispersing the unique lamellar structure contained in the clay particle structure in the polymer matrix by using appropriate technical methods. Since the thickness of the clay sheet is about 1nm, in the final composite material, the thickness of the dispersed phase (clay sheet single layer or sheet aggregate) can be kept below 100nm, so this material is called a nanocomposite material. . These nanocomposites not only have good tensile properties and processing properties, but also have excellent air permeability resistance due to the existence of clay sheets. Recent studies have shown that the flame retardancy of composites is also very good. outstanding. In short, these studies provide a good idea for people to find new rubber reinforcement methods and reinforcement agents.

The vast majority of clay/polymer-based nanocomposites are prepared by in situ polymerization. The method of in-situ polymerization means that the continuous phase and the nanoscale dispersed phase are simultaneously obtained during the chemical reaction. For example, Fukushima et al. used the cations of 12-aminododecanoic acid to intercalate between the clay crystal layers to obtain organoclay, and then initiated the polymerization of caprolactam, the monomer infiltrated between the crystal layers, to successfully prepare clay/nylon 6 nanocomposites. The 96105362.3 patent applied by the Institute of Chemistry of the Chinese Academy of Sciences also discloses a one-time in-situ polymerization preparation method of polyamide/clay nanocomposites. However, in many cases, it is not always possible to find a monomer like caprolactam that easily enters the clay layer to polymerize in situ to form a nanocomposite. Therefore, this preparation method has certain limitations in terms of applicability, and this method has high cost and complex and unstable process. Difficult to realize industrialized production.

Clay/rubber-based nanocomposites have been less studied compared to clay/plastic-based nanocomposites. US4889885 (Document 1) discloses two methods for preparing clay/rubber nanocomposites. One is the in-situ polymerization method, that is, firstly modify the properties of the clay sheet with a vinyl-terminated quaternary ammonium salt, and then disperse the modified clay in N,N-dimethylformamide solvent, add A large amount of isoprene monomer and a corresponding proportion of free radical type initiator. The isoprene is then polymerized into polyisoprene rubber between the clay sheets, and the solvent is removed, so that the clay/isoprene rubber nanocomposite material is obtained. The second is to disperse the liquid-terminated amino-acrylonitrile-butadiene rubber with a lower molecular weight in a mixed solvent composed of water and dimethyl sulfide, then add an acid to form an amine salt, and then mix it with the aqueous suspension of clay , and finally remove the water and solvent to form a clay/liquid nitrile rubber nanocomposite. Chinese patent application No. 94192043.7 (document 2) discloses a method for preparing clay/liquid nitrile rubber nanocomposites for tire innerliners and inner tubes. Specifically, at first the clay is evenly dispersed in water, acid is added to make the surface of the sheet absorb hydrogen ions, and then mixed with the toluene solution of liquid-terminated amino-acrylonitrile-butadiene rubber, during the mixing process, the hydrogen ions on the sheet and The terminal amine groups of the nitrile rubber react, so that the clay sheets are dispersed in the liquid nitrile rubber, and the solvent is removed to form a nanocomposite.

Theoretically speaking, the higher the dispersion of clay flakes in rubber, the higher the hardness of the resulting material, the lower the elongation, the higher the strength, the worse the elasticity, the better the flame retardancy, and the better the air permeability resistance. . Therefore, for most rubber products, it is not necessary for the clay flakes to form a complete single-layer dispersion state, although the resulting composite material has very good tensile properties. If the clay flakes are dispersed in the rubber as certain aggregates (such as several layers or even dozens of layers), the size of which is several nanometers to tens of nanometers, and the clay/rubber nanocomposite material with very good comprehensive properties can be obtained. Compared with the method of Document 2, the two methods of Document 1 have a higher degree of dispersion of clay, but the obtained material is less elastic. Document 2 overcomes this point. In the obtained clay-rubber nanocomposite, the clay flakes exist as aggregates to a certain extent, which not only meets the required air permeability resistance, but also has good elasticity. In terms of method implementation, the in-situ polymerization method mentioned in Document 1 is too complicated to realize industrialization. Although the second method of Document 2 and Document 1 has a slightly simplified process, it is still relatively complicated, and the required amine-terminated nitrile rubber is more expensive, and the process requires a large amount of more expensive solvents. More importantly, the obtained nanocomposite must be blended with other solid rubbers due to the strength and price problems of liquid nitrile rubber, and liquid nitrile rubber and many solid rubbers (such as natural rubber, styrene-butadiene rubber) , butadiene rubber, ethylene propylene rubber, etc.) have poor compatibility, which will damage the performance of the final composite material.

The purpose of the present invention is to propose a new clay/rubber nanocomposite technology with simple operation, low cost, wide applicability and easy industrialization, so that clay can be uniformly dispersed in the form of nanoscale in the rubber matrix.

The method of the present invention is based on the advantage that most rubbers have their own emulsion form. The aqueous suspension of clay is used to blend with the rubber emulsion, and a coagulant is added for flocculation to remove water, thereby obtaining the clay/rubber nanocomposite material.

The preparation method of the clay/rubber nanocomposite of the present invention comprises the following steps in turn, A: mixing the suspension of clay and water having a layered crystal layer overlapping structure with the rubber emulsion to form a uniform mixed solution; B: adding an optional The coagulant used to demulsify the rubber emulsion is used for flocculation; C: The clay/rubber nanocomposite is obtained by dehydrating and drying the flocs.

The clay used in the present invention can be natural or synthetic clay, including smectite, montmorillonite, talcum powder, beidellite, hectorite, silica and halloysite, wherein the preferred interlayer cation of the present invention is sodium Ionic clays such as sodium bentonite. The clay used needs to have an overlapping structure of lamellar crystal layers so that it can be separated and dispersed in the rubber at a nanometer size. Adjacent crystal layers of this type of clay are negatively charged, therefore, cations are generally adsorbed between clay crystal layers. This structure allows water and other polar molecules to enter between clay crystal layers, and exchange between external cations and internal cations can occur. Stirring and mixing the clay with water results in a stable clay suspension in water in which the clay crystal layers are separated from each other by the hydration of the interlayer cations. When the rubber latex is mixed, the clay crystal layer and the latex particles will be interspersed and isolated from each other. At this time, a coagulant that can demulsify the rubber emulsion is added for flocculation, and the micro-nano composite structure of the two will be preserved, thereby forming a clay/rubber nano-composite material.

The dispersion distance of clay flakes in water depends on its concentration, the concentration should not be too high, the higher the concentration, the smaller the dispersion distance, the harder it is for latex particles to intersperse and isolate them, and the size of the nano-dispersed phase will increase. However, if the concentration is too low, the coagulation of the final clay/emulsion mixture will be difficult. Therefore, the content of the clay-water suspension should be controlled at 0.2-20% by weight.

After the clay is mixed with water, it can be left to stand for a period of time after being stirred, so that some extremely difficult-to-disperse clay particles with large specific gravity and gravel containing belts will settle down, so that the clay water suspension obtained is more delicate. But whether to stand still and the length of time to stand still can be determined according to the quality and nature of the clay.

The present invention has no special requirements on the coagulant used, but it can be different according to the type of latex used, and the coagulant required for the industrial coagulation of the corresponding type of latex can be used. For example, styrene-butadiene rubber emulsion can use about 1.5% (weight) of hydrogen chloride solution, and nitrile rubber emulsion can use about 2% (weight) of calcium chloride solution.

The method of the present invention has no special requirements on the rubber emulsion, which can be the emulsion before coagulation in the rubber synthesis process, or a rubber re-emulsified product, and the variety is not limited, and the solid content of the latex is not limited. Such as: styrene-butadiene rubber emulsion, nitrile rubber emulsion, neoprene rubber emulsion, acrylate rubber emulsion and so on. A mixture of two or more emulsions can also be used to obtain a nanocomposite material with a wider range of mixed matrix materials. Some plastic matrices in emulsion form can also be used to prepare clay/plastic matrix nanocomposites by the method of the present invention. Such as: polyvinyl chloride emulsion, polystyrene emulsion and so on.

The method of the present invention can also apply microwaves or ultrasonic waves in step A, so that the clay sheets can be better dispersed in the rubber matrix.

In the method of the present invention, a substance having a coupling effect can also be added in step A to enhance the interface effect between the clay sheet and the rubber matrix. Such as commercially available triethanolamine, silane coupling agent, titanate coupling agent, etc., the dosage is 0.2-5% (weight) of the clay dosage.

The method for preparing the clay/rubber nano composite material of the invention has simple process, low cost and no pollution in the production process. The clay/rubber nanocomposite material prepared by the method of the present invention has a dispersed phase of clay single-layer or sheet-layer aggregate with a thickness below 100nm. Has excellent physical and mechanical properties, processing performance. And it also has quite good air permeability resistance, which can replace expensive butyl rubber or chlorinated butyl rubber and be used on the inner tube of the tire or the inner layer of the tubeless tire. Utilize the clay/rubber nanocomposite material that the method for the present invention makes, both can directly add vulcanization system, softening system etc. and apply, also can add other types of raw rubber or reinforcing agent (as: carbon black, white carbon black , calcium carbonate, clay, etc.) to be applied.

In addition, since the clay flakes have been uniformly dispersed in the rubber matrix in advance as a reinforcing agent, no carbon black or a small amount of carbon black can be added, which will greatly reduce the environmental pollution caused by flying dust during the rubber mixing process, and at the same time Reduce mixing time and reduce mixing energy consumption. In particular, this kind of rubber is also very good for eating humans of other compounding agents. Compared with the methods of Document 1 and Document 2, the method of the present invention has simple process, no solvent pollution, and no need for expensive liquid nitrile rubber as the "matrix" of the composite material and then dispersed in the general-purpose rubber matrix.

Embodiment 1: commercially available sodium-based bentonite is stirred in water, and the time is 4 hours, after mixing uniformly, let it stand for 24 hours, and the final concentration (solid content) is controlled at about 2% (weight); 200 grams of above-mentioned suspensions are mixed with 250 grams of nitrile rubber latex (the weight content of acrylonitrile is 26%, the solid content is 40%) is stirred and mixed, and the temperature is at room temperature; then flocculated with 2% hydrochloric acid solution. Flush the flocs to neutral. Dry in an oven at 80° C. for about 10 hours to obtain a clay/nitrile rubber nanocomposite material with a clay content of about 4 grams of clay/100 grams of nitrile rubber. Observation under a transmission electron microscope shows that more than 80% of the thickness of the clay flakes is less than 30 nm. The composite material was kneaded and processed, and after vulcanization, the tensile strength was 15.0 MPa, and the elongation at break was 520%. And add 10 parts by weight of high wear-resistant carbon black (N330) of the nitrile rubber, its tensile strength is only 6.0MPa, and the tensile elongation is 480%.

Embodiment 2: change the nitrile butadiene rubber latex in embodiment 1 into styrene-butadiene rubber latex, solid content is 5% clay suspension 400 grams and 500 grams of styrene-butadiene rubber latex (solid content is 20%) carry out stirring and mixing, Coagulation is carried out with about 2% hydrogen chloride solution. Other steps are the same as in Example 1. A nanocomposite material with a clay content of 20 grams of clay/100 grams of styrene-butadiene rubber was obtained. After kneading and vulcanization, the tensile strength is 12.0MPa, and the elongation at break is 400%. However, the tensile strength of styrene-butadiene rubber added with 20 parts by weight of high wear-resistant carbon black (N330) is only 10.0 MPa, and the tensile elongation is 420%.

Embodiment 3: in embodiment 2, when clay aqueous suspension and styrene-butadiene rubber latex are mixed, add the silane coupling agent KH560 of 0.8 gram (epoxy silane coupling agent, Nanjing Shuguang chemical factory production), other Step is with embodiment 2. The obtained composite material is mixed and processed. After vulcanization, the tensile strength is 14.8MPa, and the elongation at break is 300%. The tensile strength without coupling agent is 12.0MPa, and the elongation at break is 400%. . However, the tensile strength of styrene-butadiene rubber added with 20 parts by weight of high wear-resistant carbon black (N330) is only 10.0 MPa, and the elongation at break is 420%.

Embodiment 4: be that 10% clay suspension 200 grams and 250 grams of nitrile rubber latex (solid content is 40%) carry out stirring and mixing with solid content, other steps are with embodiment 1. A nanocomposite material with a clay content of 20 grams of clay/100 grams of nitrile rubber is obtained. After kneading and vulcanization, the tensile strength is 19.5MPa, and the elongation at break is 570%. And add 20 parts by weight of high wear-resistant carbon black (N330) of nitrile rubber, its tensile strength is only 11.0MPa, elongation at break is 500%. The gas permeability resistance of the obtained material is 2.2 times that of the carbon black compound, and the air tightness of the chlorinated butyl rubber inner liner rubber for radial tires provided by the Beijing Tire Factory has increased by 30%.

Embodiment 5: be that 5% clay suspension 250 grams and 500 grams of styrene-butadiene rubber latex (solid content is 20%) are stirred and mixed with solid content, other steps are with embodiment 2. A nanocomposite material with a clay content of 40 grams of clay/100 grams of styrene-butadiene rubber was obtained. After kneading and vulcanization, the tensile strength is 17.0MPa, and the elongation at break is 380%. However, the tensile strength of styrene-butadiene rubber added with 40 parts by weight of N550 carbon black is only 13.0 MPa, and the elongation at break is 410%. The anti-air permeability of the obtained material is 1.7 times that of the carbon black compound, which is 40% higher than the air tightness of the natural rubber inner tube compound provided by the Beijing Tire Factory.

Embodiment 6: In embodiment 1, the mixture of clay suspension and rubber emulsion is subjected to ultrasonic waves for 10 minutes (using the CX-250 ultrasonic cleaner produced by Beijing Medical Equipment No. 2 Factory), and other steps are the same as in embodiment 1. The obtained material was mixed and processed, and after vulcanization, the tensile strength was 17.0 MPa, and the elongation at break was 490%, while the tensile strength without ultrasonic waves was 15.0 MPa, and the elongation at break was 520%. And add 10 parts by weight of high wear-resistant carbon black (N330) of the nitrile rubber, its tensile strength is only 6.0MPa, elongation at break is 480%.

Claims (7)

1. the preparation method of a clay-rubber nm-class composite material in turn includes the following steps, A: will have the clay of stratiform crystal layer overlay structure and the suspension of water and mix with rubber latex, and form uniform mixed solution; B: adding can make the flocculation agent of rubber latex breakdown of emulsion flocculate; C: throw out dehydration, oven dry are made clay-rubber nm-class composite material.

2. preparation method according to claim 1 is characterized in that: the weight percentage of the suspension medium clay soil of said clay and water is 0.2-20%.

3. preparation method according to claim 1 is characterized in that: said flocculation agent is an electrolyte solution.

4. preparation method according to claim 1 is characterized in that: said clay is terre verte, polynite, talcum powder, beidellite, hectorite, silica or halloysite.

5. preparation method according to claim 1 is characterized in that: said clay is a sodium bentonite.

6. according to the described any preparation method of claim 1-5, it is characterized in that: in steps A, apply microwave or ultrasonic wave.

7. according to the described any preparation method of claim 1-5, it is characterized in that: adding has the material that can make generation coupled action between clay and rubber macromolecule in steps A.