Chemical stability is a necessary condition for defoamers, so defoamers in foaming systems generally do not fail due to chemical reactions. Most of the reasons for their failure are caused by changes in the dispersion state. Only by eliminating this cause can the effectiveness of the defoamer be fully exerted.

1. The defoamer particles have become too small

According to the mechanism of action of the defoamer, it is adsorbed on the foam film in the form of particles, and the bubbles are perforated, broken or merged through the crushing of the particles. The diameter of the particles is similar to the thickness of the foam film, and the effect is better. When the defoamer particles repeatedly function and are crushed again and again, the final particle size will become too small compared to the thickness of the foam film, making it difficult to perforate the bubbles and achieve the purpose of breaking them.
In addition, over time, the active ingredients of the defoamer will also be affected by the surface active agent of the foaming liquid, making the particles too small to burst bubbles. If the active ingredients of the defoamer are too ‘affinitive’ to the foaming liquid, the defoamer particles will become too small and will be less effective.

2. Defoamer particles become too large

In the foaming liquid, defoamer particles may merge and coalesce when they collide. In addition, the defoamer accumulates on the bubble film. When a steady stream of foam surges to the surface from the liquid, it acts like ‘flotation’ and concentrates the defoamer particles distributed inside the liquid into the foam layer on the surface of the liquid. After the foam bursts, it turns into a small amount of liquid, and a large amount of defoamer particles accumulate in a small amount of liquid, so it is very easy for the defoamer particles to agglomerate. When the affinity between the active ingredient of the defoamer and the foaming liquid is too weak, the tendency to agglomerate is also greater.
Therefore, the defoamer particles that have agglomerated into larger particles move slowly. They cannot quickly aggregate at the gas-liquid interface of the foam film to exert their defoaming effect, and the activity of the defoamer becomes worse.

3. Changes in the surface properties of the defoamer particles

The foaming liquid’s foam-promoting surfactant attaches to the active particles of the defoamer, solubilising the active ingredients and causing them to form hydrophilic molecular clusters. This reduces the foaming power somewhat by consuming some of the foam-promoting agent, but at the same time changes the surface properties of the active ingredients of the defoamer, rendering them defoaming-inactive. When the concentration of the foam booster in the system increases, defoaming becomes more difficult. This is due to the combination of the enhanced foaming power and the foam booster changing the surface properties of the defoamer.