Silicone oil emulsion defoamer is generally water-in-oil (O/W) emulsion, that is, water is continuous phase, silicone oil is discontinuous phase.It is the silicone oil, emulsifier and thickening agent for premixing, and then gradually add water to stir evenly, and finally in the colloidal mill repeatedly grinding until the emulsion reaches the requirements.
Silicone oil emulsion defoamer is one of the most widely used silicone defoamer. It is easy to disperse in water system and can be widely used as defoamer in water system. When used, the emulsion is directly added into 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 not recommended to directly use more than 10% concentrated silicone oil emulsion, but firstly use cold water or directly with foaming liquid to dilute to be less than 10%. Contraindicated use overheat or too cold liquid dilution, otherwise will cause emulsion demulsification. Emulsion stability will become worse after dilution, storage process may also occur stratification (oil) phenomenon, that is, demulsification. Therefore, the emulsion after dilution should be used up as soon as possible. If necessary, thickeners can be added to improve the stability of the emulsion. For batch operation, silicone oil emulsion can be added at one time before system operation or in batches. For continuous operation, silicone oil emulsions should be added continuously or intermittently at appropriate parts of the system.
When using emulsion-type antifoaming agent, it is necessary to consider the temperature acid and alkaline. If it exceeds the silicone oil emulsion limits, demulsification will occur and will become low efficiency or invalid (the dosage of silicone oil emulsion, it is commonly the 10 ~ 100 ppm of bubble fluid weight (calculate by silicone oil). Of course, there are special cases where there are less than 10ppm and more than 100ppm. The optimum dosage is mainly determined by experiment.
The general silicone oil emulsion defoamer is mostly water-in-oil. According to the types of silicone oil, silicone oil emulsion defoamer has the following types:
1. Dimethyl silicone oil as the main silicone oil emulsion
This kind of antifoaming agent is made of dimethyl silicone oil, emulsifier and water, etc., and can be widely used in fermentation, food, paper, fiber, pharmaceutical, synthetic resin, etc.
2. Silicone oil emulsion with methyl ethoxy silicone oil
The defoaming agent is made of methyl ethoxy silicone oil and its compounding agent.
3. Silicone oil emulsion with ethyl silicone oil (Something New!!!)
In recent years, silicone defoaming agents are developing towards block copolymerization (or graft copolymerization). This kind of defoaming agent has the characteristics of organosilicone and polyether, so the defoaming ability is greatly increased. Organosiloxane copolymer defoaming agent can also be called self-emulsifying organosiloxane defoaming agent, it is in the organosiloxane molecular chain block (or graft) hydrophilic ethylene oxide chain or ethylene oxide propylene oxidation chain, so that the hydrophobic siloxane part and hydrophilic polyether are boned together. Such molecules have a larger polarity, and coefficient, and can be dispersed evenly in the foam medium, and brings high defoaming efficiency. It is a new type of efficient defoaming agent. This type of self-emulsifying silicone oil has no need to use emulsifier. Its defoaming effect is quite satisfactory for some systems, it is particularly suitable for those condition that are not suitable to use the general silicone oil emulsion and the general silicone oil emulsion.