Improved method for preparing defoaming agent
The effectiveness of defoamers made with the same ingredients is often different. On the one hand, we need to master the preparation technology and follow the established operating procedures, and also pay attention to the following key issues:
1. Take into account the relationship between activity and stability
Stable silicone oil emulsions have directional arrangement of emulsifier molecules on the interface between silicone oil droplets and the dispersion medium water, with their hydrophilic groups extending to the water phase and their hydrophobic groups extending to the oil phase. In the foaming water system, stable bubbles also have directional arrangement of surfactant molecules on the interface between them and water, with their hydrophilic groups extending into the water phase and their hydrophilic groups extending into the gas phase. Therefore, when silicone oil defoaming emulsion is added to the foaming liquid, the silicone oil droplets and bubbles cannot approach each other because they carry the same charge. Only when the surfactant attached to the silicone droplets is lost in the water phase, can the silicone oil droplets attach to the gas-liquid interface of the bubbles with the help of hydrophilicity and exert their defoaming effect. In this way, silicone oil defoaming emulsions should be stable in the concentrated emulsion state. If it is added directly to the foaming liquid, it will be unstable. That is to say, the surfactant in the concentrated emulsion state is firmly adsorbed on the interface between silicone oil and water. After being added to the foaming agent liquid, the surfactant will quickly diffuse away. In order to achieve the above requirements, it is necessary to control the amount of emulsifier when preparing the defoaming emulsion. When the amount of emulsifier is small, it is easy to diffuse when added to the foaming liquid. But if this is the case, in order to take into account the defoaming activity, the stability of the silicone emulsion will be reduced. Therefore, when preparing, the defoaming activity and emulsion stability must be taken into account. The stability cannot be improved by simply increasing the amount of emulsifier, but according to the requirements for the storage period, the emulsifier should be used as little as possible while ensuring stability.
2. Control the appropriate droplet particle size
If the silicone oil is too coarsely dispersed and the particle size is too large, it will obviously have no defoaming effect. Early researchers have proposed that only when the diameter of the silicone oil dispersed particles is less than 100m, it has defoaming activity. Later, Osipow proposed that only when the diameter of dimethyl silicone oil particles is less than 2 μm, can it have defoaming effect at a low addition amount of 10 mass fraction. In the 1980s, some people found that the defoaming effect was small when the diameter of silicone oil particles was less than 2 μm. This is because such droplets are more stable in the foaming system and are not easy to attach to bubbles. It is also pointed out that in silicone oil emulsion, the dispersed droplet particles with a diameter greater than 50 μm have poor stability. The above statements all point out the importance of controlling the appropriate particle size. However, there are different opinions on the appropriate particle size. The objective factors of each researcher are different, so the bubble film composition is also different.
3. There is a certain relationship between the appropriate particle size and the thickness of the bubble film. When preparing silicone oil emulsion defoamers, the focus should be on not making the particles too coarse, because different researchers have emphasized the harm of “coarse”. As long as they are not too fine, the defoaming activity of silicone oil emulsion will increase with the decrease of droplet diameter. In order to reduce the silicone oil droplets, it is necessary to use ideal emulsification equipment. ③ The concentration of active ingredients in the emulsion should be appropriate. The concentration of active ingredients in the emulsion generally refers to the oil phase content. When the oil phase concentration is high, it is conducive to storage and transportation, and when the concentration is low, it is conducive to dilution and use. However, too high or too low will cause instability and difficulty in preparation. When the mass fraction is 30%~40%, it is more conducive to preparation, and when the mass fraction is less than 10%, it is conducive to use.
