Silicone oil emulsion type defoamer

Silicone oil emulsion type defoamer is generally an oil-in-water (O/W) emulsion, that is, water is the continuous phase, and silicone oil is the discontinuous phase. It is to pre-mix silicone oil, emulsifier and thickener, and then gradually add water to mix, and finally grind repeatedly in a colloid mill until the desired emulsion is obtained.

Silicone oil emulsion defoamer is the most widely used and the largest amount of defoamer among silicone defoamers. It is characterized by being easy to disperse in the water system and can be widely used as a defoamer in the water system. When in use, the emulsion can be directly added to the foaming system to obtain a good defoaming effect. In order to improve the defoaming effect of the emulsion and the accuracy of the measurement, it is generally not necessary to directly use the concentrated silicone oil emulsion of more than 10%: instead, it should be diluted to below 10% with cold water or directly with a foaming liquid. It is contraindicated to use hot or cold liquid to dilute, otherwise it will cause the emulsion to break. After the emulsion is diluted, the stability will become poor, and the phenomenon of delamination (bleaching) may also occur during storage, that is, demulsification. Therefore, the diluted lotion should be used up as soon as possible. If desired, thickeners can be added to improve the stability of the emulsion. For batch operation, the silicone oil emulsion can be added at one time before the system runs, or it can be added in batches; for continuous operation, the silicone oil emulsion should be added continuously or intermittently at appropriate parts of the system.

When using an emulsion type defoamer, special consideration should be given to the temperature of the foaming system and conditions such as acid and alkalinity, because the silicone oil emulsion is squeamish, and if it exceeds its use range, the emulsion will break prematurely and become inefficient or ineffective. (The dosage of silicone oil emulsion is generally 10-100ppm of the weight of the foaming liquid (calculated by silicone oil). Of course, under special circumstances, there are also less than 10ppm and more than 100ppm. The optimum dosage is mainly determined by experiments.

The general silicone oil emulsion type defoamer is mostly oil-in-water type. According to the different types of silicone oil, silicone oil emulsion defoamer has the following types:

1. Silicone oil emulsion based on dimethyl silicone oil
This type of defoamer is prepared from dimethyl silicone oil plus emulsifier and water, and can be widely used in fermentation, food, paper, fiber, pharmaceutical, synthetic resin and so on.

2. Silicone oil emulsion based on methyl ethoxy silicone oil
This type of defoamer is made of methyl ethoxy silicone oil and compounding agents.

3. Silicone oil emulsion based on ethyl silicone oil
Silicone defoamers are developing in the direction of silicone-polyether block copolymerization (or graft copolymerization). Since this type of defoamer has the characteristics of both silicone and polyether, the defoaming power is greatly improved; the silicone-polyether copolymerized defoamer can also be called a self-emulsifying silicone Block (or graft) a hydrophilic ethylene oxide chain or ethylene oxide propylene oxide chain in the silicone molecular chain, so that the hydrophobic siloxane part is combined with the hydrophilic polyether, such a molecule has a larger As a defoamer, it has a large spreading coefficient, can be evenly dispersed in the foaming medium, and has high defoaming effect. It is a new type of high-efficiency defoamer. This kind of self-emulsifying silicone oil without the use of emulsifiers, the defoaming effect is quite satisfactory for some systems, and it is especially suitable for those occasions where the use of general silicone oil emulsions is not suitable and the general silicone oil emulsions are incompetent.