What qualities should a good defoamer have

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What qualities should a good defoamer have?

In the mortar material, due to the low viscosity of the slurry, the bubbles rise by buoyancy, the bubble liquid film moved to the surface due to gravity and produce pressure difference, the thickness of the film becomes thin, and the bubbles eventually burst. This method of degassing cement-based materials alone cannot meet the comprehensive performance requirements of products such as self-compacting concrete or self-leveling mortar, and appropriate defoamers must be selected for further defoaming treatment.

The functions of defoaming agents include foam suppression and defoaming. Foam suppression means that when the defoamer is added to the system, its molecules are scattered on the surface of the liquid, inhibiting the formation of elastic film, that is, inhibiting the generation of bubbles. Defoaming means that when the system produces a large number of bubbles, adding defoaming agent, its molecules immediately spread on the surface of the foam, spreading rapidly, forming a very thin double film layer, further diffusion, penetration, layered invasion, thus replacing the thin wall of the original bubble film. Because of its low surface tension, easy to flow to the high surface tension of the liquid, so that the rapid thinning of the liquid film, the bubble at the same time by the strong traction of the surrounding surface tension of the film, resulting in the bubble by the stress imbalance, so as to defoaming. The defoamer molecules insoluble in the system reach the surface of another bubble film again, and so on. In the process of mixing dry mortar with water, the air introduced is wrapped by wet mortar to form bubbles. At the same time, admixtures such as water reducing agent, redispersible latex powder and cellulose ether have hydrophilic groups, which can reduce the surface tension of liquid, cause bubble aggregation and increase the stability of bubbles.

The defoamer has certain pertinence and specificity. The foaming mechanism and process conditions of each foaming system are different, and the defoaming agent required is also different, but no matter what kind, as a defoaming agent should have the following characteristics:

(1) strong defoaming force, less dosage;
(2) after joining does not affect the basic nature of the system;
(3) the surface tension is small;
(4) Good balance with the surface;
(5) good diffusion and permeability;
(6) good heat resistance, acid and alkali resistance;
(7) stable chemical properties, strong oxidation resistance;
(8) Good gas solubility and permeability;
(9) The solubility is small in the foaming solution;
(10) high physiological safety.

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