Introduction to organic bentonite
Organic bentonite has been produced and applied in China for more than 30 years. It is a smectite/organic ammonium composite, which uses bentonite as raw material, and utilizes the lamellar structure of montmorillonite in bentonite and its ability to swell and disperse into colloidal grade clay characteristics in water or organic solvent, through ion exchange. The technology is intercalated with an organic covering agent.
Organic bentonite can form gel in various organic solvents, oils and liquid resins, and has good thickening, thixotropic, suspension stability, high temperature stability, lubricity, film formation, water resistance and chemical stability. Especially important in the coatings industry. It is also widely used in industries such as inks, greases, metallurgy, oil drilling and polymers.
English name  :organic bentonite
Chinese alias: organic montmorillonite, organic clay, referred to as OMMT
Relative density: 1.7~1.8 g/cm3
Appearance: white or off-white powder
Solubility: Soluble in hydrocarbon solvent, adding a small amount of polar solvent such as methanol, ethanol, acetone, etc., can make the quaternary ammonium hydrocarbon chain between the montmorillonite layers bridge by hydrogen bond, and obtain effective solvation, so that the layer The thixotropic gel is expanded, dispersed, and formed into a card structure, preventing precipitation of the inorganic filler.
Application: Thickeners, thixotropic agents and stabilizers used as solvent-based adhesives and sealants, with a reference dosage of 5-10 parts. Add organic bentonite directly, stir for 1 hour, then add a small amount (2% ~ 3%) of polar solvent (methanol or ethanol, etc.).
The recommended method is to first make the organic bentonite into a pre-gel (or organic bentonite gel), and then use the organic bentonite pre-gel to dilute to a suitable concentration for the product. The preparation process of the organic bentonite gel is shown in the following table ( Using a high speed disperser):
The main parameters Number of reports: Operating: Feeding amount (mass percentage) 1.Solvent (solvent oil) mixing 85-88 Organic bentonite Mix for 5 minutes 8-10 3. Polar activator Mix for 10 minutes 3-5
The solvent was first introduced, the mixing was started, organic bentonite was added for 5 minutes, and a polar activator (polar additive) was added to continue mixing for 10 minutes. The amount of organic bentonite can be increased or decreased, and for the convenience of operation, 10% is the highest amount. Through testing, the best polar additives are 95% methanol, 95% ethanol and propylene carbonate. The recommended dosages are as follows:
Methanol/water (95/5), 30-35% of organic bentonite
Ethanol/water (95/5), 30-40% of organic bentonite
Propylene carbonate, 40-50% of organic bentonite
In order to obtain the best gel efficiency, both methanol and ethanol need to contain 5% water. Using methanol or ethanol containing water, the viscosity is rapidly increased, while using anhydrous methanol or ethanol, the gel effect is not satisfactory.
The principle of preparation of organic bentonite is: montmorillonite is a unique aluminosilicate mineral composed of two layers of Si-O tetrahedral sheets sandwiched by a layer of AIO(OH) dioctahedral sheets. Si4+ in the montmorillonite structural unit layer can be replaced by Al3+, and Al3+ in the octahedral layer is often replaced by multivalent ions such as Mg2+, Fe3+, Zn2+, etc., so that the charge in the crystal lattice is unbalanced, resulting in residual negative charge, so that The ability to adsorb cations and exchange anions has a high hydration energy, and the interaction between the oxygen layer and the oxygen layer between the crystal layers of the C-axis (layer stacking direction) is small, and a good dissociation surface can be formed. The layers are easily immersed in water molecules or other polar molecules, causing expansion in the C-axis direction. This is a property not found in other non-swelling clays. Due to this property, the montmorillonite layer is filled with interlayer water and exchangeable cations, which are the driving force for the expansion of montmorillonite.
However, for bentonites with different ore-forming conditions, the types of exchangeable cations between the montmorillonite layers and the exchange capacity (CEC) are quite
different. Among them, the interlayer valence cation (Ca2+, Mg2+, etc.) montmorillonite double layer hydration film is thin, the expansion ratio is low; the low-cost cation (Na+, Li+, etc.) hydrated film thickness, high expansion ratio. Generally, it is named after the main type of cation adsorption between montmorillonite layers. For example, Ca2+ is mainly called calcium-based bentonite, Na+ is called sodium bentonite, and organic cation is called organic bentonite. . The cation-exchanged property of montmorillonite can be used to convert a calcium-based montmorillonite or a magnesium group into a sodium group and then react it with an organic ammonium cation to form an organic bentonite. The preparation process of organic bentonite is generally divided into: wet process and dry process (also called semi-dry process), and the most commonly used is wet process.
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