What properties should a high-quality defoamer have?

Dec. 20, 2024

In mortar materials, due to the low viscosity of the slurry, bubbles rise due to buoyancy, and the bubble liquid film that moves to the surface produces a pressure difference due to gravity, the thickness of the film becomes thinner, and the bubbles eventually burst. This method of degassing cement-based materials alone cannot meet the comprehensive performance required by products such as self-compacting concrete or self-leveling mortar. It is necessary to select a suitable defoamer for further defoaming treatment.

The functions of defoamers include foam suppression and defoaming. Foam suppression means that when the system is added with a defoamer, its molecules are randomly distributed on the surface of the liquid, inhibiting the formation of an elastic film, that is, inhibiting the generation of bubbles. Defoaming means that when a large number of bubbles are generated in the system, a defoamer is added, and its molecules are immediately spread on the surface of the foam, spreading rapidly to form a very thin double film layer, which further diffuses, penetrates, and invades in layers, thereby replacing the thin wall of the original bubble film. Due to its low surface tension, it is easy to flow to the liquid with high surface tension, making its liquid film thinner rapidly. At the same time, the bubbles are strongly pulled by the surrounding film layer with high surface tension, causing the stress of the bubbles to be unbalanced, thereby defoaming. The defoamer molecules that are insoluble in the system will reach the surface of another bubble membrane again, and this process will be repeated. During the mixing process of dry-mixed mortar with water, the introduced air is wrapped by the wet mortar to form bubbles. At the same time, admixtures such as water reducers, redispersible latex powders and cellulose ethers have hydrophilic groups, which can reduce the surface tension of the liquid, cause bubble aggregation, and increase the stability of the bubbles.

Defoamers have certain specificity and speciality. The foaming mechanism and process conditions of each foaming system are different, and the required defoaming agent is also different. However, no matter which type it is, the defoaming agent should have the following characteristics:

(1) Strong defoaming power and small dosage;

(2) Does not affect the basic properties of the system after addition;

(3) Low surface tension;

(4) Good balance with the surface;

(5) Good diffusion and permeability;

(6) Good heat resistance, acid and alkali resistance;

(7) Stable chemical properties and strong oxidation resistance;

(8) Good gas solubility and permeability;

(9) Low solubility in the foaming solution;

(10) High physiological safety.

What properties should a high-quality defoamer have?cid=4