When a defoamer does not perform as expected, the chemistry is not always the cause. Very often, it is the physical form that does not suit the application. A silicone defoamer comes in four distinct forms, which do not belong in the same places and are not dosed in the same way.
The compound, at 100 % active matter
It is meant to be emulsified before use, generally between 10 and 20 % active, with a thickener such as xanthan gum to secure the stability of the emulsion. Final dosage usually lies between 0.1 and 0.5 % silicone.
It retains its efficiency up to 95 °C and holds durably in acidic as well as alkaline media, with good compatibility in concentrates rich in surfactants, solvents and electrolytes. This is the product for formulators who prepare their own emulsion, in pulp and paper or in industry. Poured neat into an aqueous bath, however, it does not disperse and leaves oily spots: probably the most frequent mistake we come across.
The ready-to-use emulsion
Nonionic, at around 28 % solids and pH 6-9, it disperses easily, including in hard water, with no oily spots or lumps. It is the simplest form to work with, and it is found in paper, detergents, carpet cleaning, chemical distillation and wastewater treatment.
The powder, granulated on a carrier
At 15 % active and a particle size of 1.0 to 1.4 mm, it is incorporated at 0.5-2 % into a powder detergent. Its value rests on two properties: it does not migrate within the pack, and it controls foam throughout the wash cycle, in cold and hot washes alike. An aqueous emulsion would not be suitable in this application, however good its chemistry.
The food grades
These are emulsions at 10, 20 or 30 % silicone, dosed between 150 and 300 ppm and acceptable under UK and US food regulations. They cover fermentation, filtration, fruit and vegetable washing, brines, syrups and effluent treatment.
De-aerators, an often under-used lever
There is a fifth, less familiar family which does not replace the defoamer but improves the way it works: de-aerators. These are silicone polyether copolymers added at 0.5-1.5 % into the defoamer formulation itself. They inhibit micro-bubbles, improve the dispersibility of the defoamer, limit silicone deposition and favour drainage.
Their selection rests on two parameters: the balance between ethylene oxide and propylene oxide in the copolymer, and its molecular weight. Together, these two settings determine the cloud point, that is, the temperature at which the product ceases to be soluble in water. A fully ethoxylated copolymer of low molecular weight, in the order of 3,000 g/mol, remains strongly hydrophilic: its cloud point sits around 10 °C. A copolymer richer in propylene oxide and much heavier, around 17,000 g/mol, raises it to about 40 °C.
And it is precisely above its cloud point that the additive becomes active: as long as it stays dissolved, it does nothing; once insolubilised, it separates into fine droplets that destabilise foam films and help micro-bubbles coalesce. Choosing a de-aerator therefore means choosing the temperature window in which it will work. In brown stock washing, this is often what separates an adequate defoamer from one that lasts.
The mechanism is the same one that limits fatty alcohol ethoxylates in alkaline cleaning, described in our article on alkyl polyglucosides — except that here, insolubilisation is not the problem: it is the desired effect.
Choosing the right form
| Form | Active matter | Implementation | Typical applications |
|---|---|---|---|
| Compound | 100 % | To be emulsified, 10-20 % active | Pulp and paper, industry, equipped formulators |
| Emulsion | ~28 % solids | Ready to use, dispersible | Detergents, paper, wastewater treatment |
| Granulated powder | 15 % | 0.5-2 % into the powder | Powder detergents |
| Food grade | 10, 20 or 30 % | 150-300 ppm | Fermentation, filtration, food processing |
| De-aerator | Silicone polyether copolymer | 0.5-1.5 % into the defoamer | Brown stock washing, micro-bubble processes |
In practice
These products come from Cyrachem, in Geneva, a company founded in 2009 by chemists from GE’s, later Momentive’s, silicone centre of excellence, and now present in five countries. We distribute their range in France, alongside our other silicone derivatives.
If your defoamer leaves oily spots, loses efficiency with temperature or does not last, tell us which form you are using and in what medium. The answer is often to be found there, and we can make a sample available for trial.