The defoaming effect of dimethyl silicone oil depends on the degree of dispersion of the silicone oil in the foaming system. The defoaming effect of the silicone oil is only when the silicone oil is dispersed below 100 m, and the dispersion system is stable when the dispersion is below 20 m. In order to improve the degree of dispersion, mechanical stirring, such as high-speed stirring under heating, can be used, or a homogeneous dispersion of silicone oil and mineral oil can be prepared in advance with a colloid mill. Or make silicone oil and white carbon black and other micropowders into an ointment type defoamer in advance, and use it with the help of the dispersion of white carbon black and other micropowders.

2.2 Solution type defoamer

Silicone solution type defoamer can be prepared by dissolving dimethyl silicone oil in a suitable solvent. Use organic silicon defoamer prepared from organic solvents such as polychloroethane, toluene and xylene. It can be used for defoaming operation of oil-soluble medium; and the organic silicon defoaming agent prepared from water-soluble organic solvents such as hexylene glycol and glycerin is selected. Can be used for defoaming of aqueous solutions. The preparation process of solution type silicone defoamer is very simple. Easy to use. The silicone oil is dispersed in the foaming liquid with the help of organic solvent to defoam. At the same time, some solvents will also play a certain defoaming effect during the diffusion process. However, this method has not been widely used, mainly because large-scale use will increase the cost of defoaming agents and may cause environmental pollution.

2.3 Emulsion type defoamer

The silicone oil or silicone paste is made into silicone oil emulsion under the action of strong stirring or emulsifier, which can effectively improve the dispersibility of silicone oil in the water phase. Therefore, it is widely used as a defoamer in water systems. Emulsion-type defoamer is also the most widely used and most widely used defoamer of silicone defoamer.

Emulsion-type silicone defoamer is generally prepared from dimethyl silicone oil, emulsifier, emulsion stabilizer and deionized water. The emulsifiers used are mainly non-ionic emulsifiers with low foaming properties, such as Span, Tween and polyethylene glycol. The effect of using a mixed emulsifier is better than that of a single emulsifier. The particle size of silicone oil emulsion is the most important control index for emulsion type silicone defoamer. In order to obtain a silicone oil emulsion with high defoaming efficiency and good storage stability, the particle size is usually required to be less than 10 μm.

Therefore, in addition to selecting suitable emulsifiers and mixing and grinding process conditions, thickeners such as polyvinyl alcohol and methyl cellulose can also be added to increase the viscosity of the continuous phase.

When using emulsion type silicone defoamer. The temperature, acidity and alkalinity of the foaming system should be understood first, because they will affect the stability of the emulsion and even lead to demulsification.

Although the emulsion type silicone defoamer has the disadvantages of being difficult to store for a long time, easy to delaminate and easy to deteriorate, it has the characteristics of convenient use, wide application, obvious defoaming effect and moderate price. With the advancement of technology, emulsion-type silicone defoamer will still have a large space for development.
2.4 Solid type defoamer

Solid silicone defoamer has the characteristics of good storage stability, easy transportation, and convenient use.

There are three preparation methods of solid silicone defoamer: (1) Disperse silicone oil directly on the surface of solid carrier; (2) Mix silicone oil with fatty alcohols, fatty acids, fatty amides, fatty acid esters with a lower softening point Or paraffin and other substances are melted together, and then the melt is attached to the surface of the solid carrier; (3) The silicone oil is mixed with the film-forming substance, so that the film-forming substance is encapsulated outside the silicone oil defoaming component to form dispersed solid particles.

2.5 Modified silicone oil type defoamer

The modified silicone oil introduces methyl silicone oil with some hydrophilic polyether segments, which can become a self-emulsifying defoamer, maintain dispersibility in the foaming system for a long time, and prolong the service life of the defoamer. The commonly used modified silicone oils currently used as defoaming agents include polyether silicone oil, fluorocarbon-based silicone oil and long-chain alkyl silicone oil, and their applications and effects are eye-catching.

End group, side group and branched polyether silicone oil can be used as defoamer. They all have a clear cloud point, and only above the cloud point have strong defoaming properties. Below the cloud point, it promotes foaming. In addition, using the strong emulsifying ability of polyether silicone oil and compounding with silicone paste, it can self-emulsify into a stable and efficient defoamer in the water system. It has been widely used for high-temperature dyeing of polyester fibers, various lubricating oils, cutting Defoaming of oil, antifreeze and strong acid systems.

Long-chain alkyl silicone oil defoamer can be used in fields such as fermentation, food addition, medical treatment, textile, petroleum, synthetic rubber and resin, coating and ink. Due to its good affinity for organic materials, long-chain alkyl silicone oil defoamer will not affect the post-processing properties of the product. However, the surface tension increases with the increase of carbon chain, and the defoaming performance decreases accordingly, so it is very important to choose the appropriate carbon chain length. Long-chain alkyl silicone oils are used in defoaming of both non-aqueous and aqueous systems.

The surface tension of fluorocarbon-based silicone oil is lower than that of other silicone oils, so the defoamer formulated from it is more effective in reducing the surface tension of various foaming systems, and the effect is better than other silicone oil defoamers. Mainly used for the foaming medium of non-aqueous systems with strong solubility to methyl silicone oil or methyl phenyl silicone oil, such as aliphatic hydrocarbons, aromatic hydrocarbons and naphtha.

3. Conclusion

Silicone defoamer not only has good defoaming and anti-foaming effects, but also has the characteristics of low dosage, good chemical inertness, and can function under harsh conditions. In recent years, it has developed rapidly, and new varieties and models suitable for different use environments Continue to produce. The application area is also constantly expanding. In the future, new high-efficiency silicone defoamers with strong applicability and can further improve product quality and equipment utilization will be further developed, especially polyether-modified silicone defoamer and emulsion type defoamer with excellent performance. The market occupies a dominant position.