Classification and properties of organosilicon defoamers


Oil (ointment) defoamer


Oil defoamer is a direct defoamer using silicone oil. It is mainly used in oil-phase foaming systems where dispersants and emulsifiers are not allowed to exist. It is generally believed that silicone oil with different viscosity has different defoaming effects on the same foaming system. Low viscosity silicone oil defoamer has fast defoaming effect, but poor persistence, while high viscosity silicone oil defoamer has slow defoaming effect, but good persistence. Oil-paste defoamer is a kind of defoamer in the form of ointment, which is made up of silicon oil with silica, aluminium trioxide and other micro-powders. It is mainly used for defoaming in non-aqueous system.


The defoaming effect of dimethyl silicone oil depends on the dispersion degree of silicone oil in the foaming system. The higher the dispersion degree of silicone oil in the foaming system, the better the defoaming effect. In order to improve the dispersion, mechanical stirring, such as high-speed stirring under heating, colloidal mill can be used to prepare a uniform dispersant of silicone oil-mineral oil, or oil paste defoamer can be prepared from silicone oil and white carbon black powder in advance, which can be used by the dispersion of white carbon black powder.


Solution defoamer


Dimethyl silicone oil can be dissolved in appropriate solvents to produce silicone defoamer. Organosilicon defoamers made from organic solvents such as polychlorinated ethane, toluene and xylene can be used for defoaming of oil-soluble media, and organosilicon defoamers made from water-soluble organic solvents such as hexanediol and glycerol can be used for defoaming of aqueous solutions. The preparation process of solution organosilicon defoamer is very simple. It is easy to use. Silicone oil disperses in the foaming fluid with organic solvents, and some solvents also play a defoaming role in the diffusion process. However, this method has not been widely used, mainly because the large use of defoamers will increase the cost, while possibly causing environmental pollution.


Emulsion defoamer


Silicone oil emulsion, which is made of silicone oil or silicon paste under strong stirring or emulsifying agent, can effectively improve the dispersion of silicone oil in aqueous phase. Therefore, it is widely used as defoamer in water system. Emulsion defoamer is also the most widely used and defoaming agent of silicone defoamer.


Emulsion type organosilicon defoamer is generally made up of two methyl silicone oil, emulsifier, emulsion stabilizer and deionized water. The emulsifiers used are mainly non-ionic emulsifiers with low foaming property, such as sipan, tween and polyethylene glycol. The effect of mixed emulsifier is better than that of single emulsifier. The particle size of silicone oil emulsion is the most important control index of emulsion type silicone defoamer. For silicone oil emulsion with high defoaming efficiency and good storage stability, it is usually required that the particle size is less than 10 m.


Therefore, besides choosing suitable emulsifiers and mixed grinding conditions, thickeners such as polyvinyl alcohol and methyl cellulose can be added to improve the viscosity of continuous phase.


When using emulsion type organosilicon defoamer, we should first understand the temperature and acid-base of the foaming system, because they will affect the stability of emulsion and even lead to demulsification.


Although emulsion type organosilicon defoamer is difficult to store for a long time, it is easy to be layered and easy to deteriorate. However, it has the characteristics of convenient operation, wide application, excellent defoaming effect and moderate price. All of them are still welcomed by users. With the progress of technology, the emulsion type organosilicon defoamer will have more room for development.


Solid defoamer


Solid silicone defoamer has the characteristics of good storage stability, easy transportation and easy use. It can be used not only in the production of non-foaming and low foaming detergent powder, but also in other occasions where defoaming operation is needed.


There are three preparation methods of solid silicone defoamer: (1) organic silicone oil is directly dispersed on the surface of solid carrier; (2) organic silicone oil is melted with fatty alcohols, fatty acids, fatty amides, fatty acid esters or paraffins with lower softening point, and then the melt is attached to the surface of solid carrier; (3) organic silicone oil is mixed with film-forming substances to encapsulate the film-forming substances in organic matrix. Dispersed solid particles are formed outside the defoaming components of silicone oil.


Modified Silicone Oil Defoamer


Modified silicone oil introduced a part of hydrophilic polyether chain methyl silicone oil, which can be changed into self-emulsifying defoamer. It can keep dispersion in the foaming system for a long time and prolong the service life of defoamer. At present, polyether silicone oil, fluoroalkyl silicone oil and long chain alkyl silicone oil are commonly used as defoamers. Their applications and effects are noticeable.


End-base, side-base and branched-chain polyether silicone oil can be used as defoamer. They all have a clear cloud point. Only above the cloud point can they have a strong defoaming effect, while below the cloud point, they can promote the foaming effect. In addition, using the strong emulsifying ability of polyether silicone oil and silicone paste, it can self-emulsify into a stable and efficient defoamer in water system. It has been widely used in high temperature dyeing of polyester fibers, defoaming of various lubricants, cutting oils, antifreeze and strong acid systems.


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


The surface tension of fluoroalkyl silicone oil is lower than that of other silicone oil, so the defoamer made of fluoroalkyl silicone oil is more effective in reducing the surface tension of various foaming systems.