Introduction to Defoamers – Part 3

Foams Cited from: https://pixabay.com/zh/photos/foam-bubbles-vesicles-waterdrop-998256/

Cover Photo Cited from: https://pixabay.com/zh/photos/waves-sea-water-blue-blue-water-1215449/

We have introduced the detailed mechanisms of defoamers in the last two blog articles. We could see clearly that the defoamers’ mechanisms are still in debate and some of them could be mutually contradict, and the others may be controversial.

Today we will stick to the other aspect of defoamers- the properties and the corresponding categorizations of defoamers, especially for silicone oil defoamers.

Basic Properties of Silicone Oil Defoamers

If we see the defoamers from the structural view, the non-silicon defoamers that include alcohol, aliphatic acid, fatty acid esters, amide, esters, phosphates and metal soaps are the organic compounds that have polar groups on single side or double side of molecules. They are similar with the foaming agents, thus if the way of using is wrong, the materials will have the same effect as the foaming agents. Besides, the using quantity is larger and cannot be used as the additives for food.

However, if we use silicone oil the products processed from silicone oil as the effective components for defoaming agents, there will be some unique features which are different from non-silicon defoamers.

The first feature is the insolubility. Silicone oil has special chemical structure; it belongs to non-polar compounds, and its solubility parameters are way different from organic compounds. Therefore, it is not soluble in water or compounds which contain polar functional groups, and it is not soluble in non-polar compounds. The defoamers which are made from silicone oil are also not soluble in water, fats of animals or plants and mineral oil which have high boiling points. This determines it could both be applied in water system and oil system.

The second feature is the low surface tensile strength. The dimethyl silicone oil which has medium-level viscosity has a surface tensile strength of 20~21mN/m, this is a low value compared to the surface tensile strength of water and common foaming liquid. This is one of the main reasons why silicone oil defoaming agent is applied widely and it has strong defoaming ability.

The third is the excellent thermal stability. To use the methyl silicone oil as the example, it could endure 150℃ for a long time, and endure 300℃ for a short time. Its main Si-O-Si chain will not be destroyed. Therefore, it guarantees the silicone oil defoamers could be used in a large range of temperatures.

Another feature is the high chemical stability. It is due to the Si-O and Si-C keys are more stable, thus the chemical stability of silicone oil is high and it is hard to have chemical reactions with other materials. Therefore, if the design is proper, the silicone oil defoamers are allowed to be used in the system which contains little acids, alkaline or salts.

It also has the inertia. Silicone oil is an inertia material which is confirmed to be the safe materials to humans.

Types of Silicone oil Defoamers

The forms of products of silicone oil could be divided into silicone oil type, silicone ointment type, solvent type, emulsion type, modified silicone oil type and solid type. Among all of these, emulsion type has the largest consumption quantity. But in the recent 10 years, the modified silicone oil type and the solid type also have a rapid development.

For silicone oil type, which means to use silicone oil directly as the defoamers, it is mainly applied in the oil phase foaming system which does not have dispersants or emulsifiers. The main using type is the dimethyl silicone oil which has small tensile strength and medium & low viscosity. The viscosity of silicone oil has a large influence on defoaming effects. The general opinion is that the low–viscosity silicone oil has fast defoaming feature but with a short lasting period; High-viscosity silicone oil has a low defoaming speed rate with a longer lasting period.  

The second type is the silicone ointment type. This type of defoaming agent is made from mixing silicone oil with some certain proposition of micro powders like SiO2, Al2O3, MgO or TiO2 to get the ointment type products. It is due to the existence of micro particles, the dispersion effectiveness of silicone oil is increased and then lead to the increment of defoaming effectiveness.

The third type is the solvent. Solvent defoamers are products that are made from silicone oil or silicon ointments with some kinds of organic solvents. The solvents could be petrol or kerosene or other alkane solvents, or aromatic hydrocarbon solvents like xylene, toluene or benzene; or chlorinated hydrocarbon solvents. When the final solvent is ready, it could increase the dispersion of silicone oil in non-water system foaming agents to increase the corresponding defoaming capacity.

The forth type is the emulsion type. The former 3 types of defoamers above are all hard to be dispersed in the water phase thus are not suitable to be used as water system defoamers. If we shake the silicone oil or silicon ointments to make O/W emulsions, we could increase the dispersions of silicone oil in water phase effectively.

The fifth type is the modified silicone oil. All of the four types mentioned above have the common problem that the dispersed silicone oil micro particles will gather gradually to the larger size in the foaming system and finally lead to the loss of defoaming ability of silicone oil. Then the foams will appear again. How to keep the dispersion status of silicone oil in foaming system for a long time is definitely the key to extend the product life. It is according to it, modified silicone oil, especially for the methyl silicone oil which has partly hydrophilicity polyether chains will become self-emuylsificated defoamers and keeps dispersion forms in foaming system for a longer time.

The last type is the solid type. It is a new developed type of defoamers. It could be divided into powder type or non-powder type according to the corresponding forms. It has the advantages like stable storage and convenient usages.

Summary

From the content above, we could see that defoamer is a large type of products derived from silicone oil and could be applied in so many different industries for different purposes.