The advantages and disadvantages of silicone defoamer

Advantages:


1) Wide application: Due to the special chemical structure of silicone oil, it is neither soluble with water or substances containing polar groups, nor is it soluble with hydrocarbons or hydrocarbon-based organic compounds. Because of the insolubility of silicone oil to various substances, it is widely used, which can be used for water system defoaming and oil system.






2) Small surface tension: the surface capacity of silicone oil is generally 20-21 dyne/cm, which is smaller than the surface tension of water (72 dyne/cm) and general foaming liquid, and the antifoam effect is good.


3) Good thermal stability: Taking the commonly used dimethyl silicone oil as an example, it can withstand 150 ° C for a long time, and can withstand more than 300 ° C for a short time, and its Si-O bond does not decompose. This ensures that the silicone defoamer can be used over a wide temperature range.


4) Good chemical stability: Because the Si-O bond is relatively stable, the chemical stability of silicone oil is very high, and it is difficult to chemically react with other substances. Therefore, as long as the preparation is reasonable, the silicone defoamer is allowed to be used in the system containing acid, alkali and salt.


5) Physiological inertia: silicone oil has been shown not to be toxic to humans and animals, and its semi-lethal dose is greater than 34 g/kg. Therefore, silicone defoamer (in the combination of suitable non-toxic emulsifiers, etc.) can be safely used in food, medical, pharmaceutical and cosmetics industries.


6) Strong defoaming power: silicone defoaming agent can not only effectively break the foam that has been generated, but also significantly inhibit the foam and prevent the formation of foam. Its use is very small, as long as the weight of the foaming medium is added one millionth (1ppm), that can produce defoaming effect. Its common range is 1 to 100 PPM. Not only the cost is low, but also does not pollute the defoaming material




Cons:


1) Polysiloxane dispersion is more difficult: polysiloxane is difficult to dissolve in water, hindering its dispersion in the water system, dispersant must be added, dispersant added more, the emulsion is stable, the defoaming effect will become worse, it is necessary to use less emulsifier, so that the defoaming effect is good, and the emulsion is stable.


2) Silicone is oil-soluble, reducing its defoaming effect in the oil system.


3) Long-term high temperature resistance and strong alkaline resistance






Classification and properties of organosilicon defoamer


Oil (ointment) type defoamer


Oil type defoamer is the direct use of silicone oil as defoamer. It is mainly used in oil phase foaming systems that do not allow the presence of dispersants and emulsifiers. It is generally believed that silicone oils with different viscosity show different defoaming effects on the same foaming system. Low viscosity silicone oil defoamer has fast defoamer effect but poor continuity, while high viscosity silicone oil defoamer has slow defoamer effect but good continuity. Ointment type defoamer is an ointment type defoamer prepared by adding silica, aluminum oxide and other micro-powders into silicone oil, which is mainly used for defoamer of non-aqueous system.


The defoaming effect of dimethylsilicone oil depends on the degree of dispersion of silicone oil in the foaming system. In order to improve the degree of dispersion, mechanical agitation can be used, such as high-speed agitation under heating, or a uniform dispersion of silicone oil and mineral oil can be configured with a colloid mill in advance. Or pre-mix silicone oil with white carbon black and other micro-powder into a cream type defoamer, which is used by means of the dispersion of micro-powder such as white carbon black.






Solution type defoamer


Silicone solution defoamer can be prepared by dissolving dimethylsilicone oil in appropriate solvent. Silicone defoamer prepared with organic solvents such as polychloroethane, toluene and xylene is selected. Can be used for oil soluble media defoaming operation; The silicone defoamer is prepared with organic solvent which is easily soluble in water, such as hexanediol and glycerol. It can be used for defoaming of aqueous solution. The preparation process of solution silicone defoamer is very simple. Easy to use, silicone oil dispersed in the foaming liquid with organic solvents to play a defoaming role, while some solvents in the diffusion process will also play a certain defoaming role. However, this method is not widely used, mainly because a large number of use will increase the cost of defoamer, while it may cause environmental pollution.




Emulsion type defoamer


The dispersion of silicone oil in aqueous phase can be effectively improved by making silicone oil emulsion with strong stirring or emulsifier. Therefore, it is widely used as a defoamer in water system. Emulsion type defoamer is also the most widely used and the largest amount of silicone defoamer.


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


Therefore, in addition to the selection of appropriate emulsifiers and mixed grinding conditions, thickening agents such as polyvinyl alcohol and methyl cellulose can also be added to improve the viscosity of continuous phase.


When using emulsion 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 emulsion silicone defoamer has the disadvantages of difficult long-term storage, easy stratification and easy deterioration, it has the characteristics of convenient use, wide application, obvious defoamer effect and moderate price, all of which are still welcomed by users, and with the progress of process technology, emulsion silicone defoamer will have a larger space for development




Modified silicone oil type defoamer


The modified silicone oil introduces some methyl silicone oil of hydrophilic polyether chain segment, which can become a self-emulsifying defoamer, and maintain the dispersibility in the foaming system for a long time, extending the service life of the defoamer. At present, the modified silicone oils commonly used as defoamer are polyether silicone oil, fluoroalkyl silicone oil and long chain alkyl silicone oil, and their application and effect are remarkable.


End group, side group and branch chain polyether silicone oil can be used as defoamer. They all have a clear cloud point, only above the cloud point has a strong defoaming, and below the cloud point has the effect of promoting foaming. In addition, the use of polyether silicone oil strong emulsifying ability, and silicon paste, in the water system can be self-emulsified into a stable, efficient defoamer, has been widely used as polyester fiber high temperature dyeing, a variety of lubricating oil, cutting oil, antifreeze and strong acid system defoamer.


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


The surface tension of fluoroalkyl silicone oil is lower than that of other silicone oils, so the defoamer prepared by fluoroalkyl silicone oil is more effective in reducing the surface tension of various foaming systems, and the effect is better than other silicone oil defoamer. It is mainly used for foaming medium of non-aqueous system with strong solubility to methyl silicone oil or methyl phenyl silicone oil, such as aliphatic hydrocarbon, aromatic hydrocarbon and naphtha.



Silicone defoamer not only has good defoaming and defoaming effect, but also has the characteristics of low dosage, good chemical inertia, and can play a role under harsh conditions. In recent years, it has achieved rapid development, and new varieties and models suitable for different use environments are constantly produced, and the application surface is constantly expanding. In the future, new high-efficiency silicone defoamer with strong applicability and can further improve product quality and equipment utilization will be further developed, especially polyether modified silicone defoamer and emulsion defoamer with excellent performance will occupy a major position in the market.