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What are the factors that affect the rate of hydrolysis of silane coupling agents?
Release Date:
2021-04-07
Silane coupling agent is a kind of alkoxysilane, its alkoxy water will occur hydrolysis reaction, into hydroxyl silane (I. e. silanol), while releasing the reaction by-products-the corresponding alcohol (methoxy silicon hydrolysis reaction after the release of methanol, ethoxy silane hydrolysis reaction after the release of ethanol). This reaction is the hydrolysis reaction of silane coupling agent, and the factors that affect the speed of this reaction are as follows:
1. Solubility of silane coupling agent in water: Different silane coupling agent has different polarity and solubility in water. Silane coupling agent with greater solubility is more dissolved in water and fully contacted with water, so the hydrolysis rate will be relatively fast. In order to achieve this purpose, it is necessary and important to sufficiently stir the silane coupling agent when it is dissolved in water.
2, the concentration of silane coupling agent in water: the same as the general chemical reaction, the greater the concentration of reactants, the faster the chemical reaction. Therefore, a higher silane coupling agent will accelerate the rate of hydrolysis reaction, of course, this will also cause the hydrolysis product self polymerization speed.
3. pH of silane coupling agent aqueous solution: the hydrolysis reaction speed of silane coupling agent is the slowest when the pH of the aqueous solution is equal to 7, I .e. neutral, while acid or alkali has obvious catalytic acceleration effect on the hydrolysis reaction of silane coupling agent, so generally, acid is used to adjust the pH value of the solution to 3~5 before adding silane coupling agent dropwise. However, the aqueous solution of aminosilane is already highly alkaline, therefore, the aminosilane is generally directly added dropwise without adjusting the pH of the aqueous solution with an acid.
4, temperature: the same as the general chemical reaction, the speed of the hydrolysis reaction of silane coupling agent has a positive correlation with the temperature, that is, the higher the temperature, the faster the speed. Therefore, in summer and winter, the change of ambient temperature will also affect the rate of hydrolysis reaction of silane coupling agent.
5. Alcohol cosolvent: Like the general chemical reaction, if some products are added to the reactants, the presence of the products will slow down the speed of the chemical reaction, and the chemical reaction is partially reversible. If some alcohol solvents, such as ethanol, are added to the solution, the hydrolysis reaction rate of the silane coupling agent will be slowed down.
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