Performance requirements for defoaming agents for mortar products
(1) Requirements for the overall defoaming agent
It has defoaming effect, no serious side effects, stable storage, easy to release active ingredients, economical, and meets environmental protection requirements.
(2) Requirements for active ingredients of defoaming agents
1) Insoluble or difficult to dissolve in the foaming liquid. Most excellent defoaming agents are insoluble in the foaming liquid. Especially for the anti-foaming effect, the defoaming agent must be in a supersaturated state in the foaming liquid. Defoaming agents in water-based systems have the best HLB value of 1.5~3;
2) The surface tension is lower than that of the foaming liquid: Only when the intermolecular force of the defoaming agent is small and the surface tension is lower than that of the foaming liquid, can the defoaming agent particles be able to immerse and expand on the bubble film. It is worth noting that the surface tension of the foaming liquid is not the surface tension of the solution, but the surface tension of the foaming solution.
3) It has a certain affinity with the foaming liquid, and the defoaming agent can be quickly dispersed: Since the defoaming process is actually a competition between the foam collapse speed and the foam generation speed, the defoaming agent must be able to be quickly dispersed in the foaming liquid. , in order to quickly play a role in a wider range of foaming liquid. To make the defoaming agent diffuse quickly, the active ingredient of the defoaming agent must have a certain degree of affinity with the foaming liquid. If the active ingredient of the defoaming agent is too close to the foaming liquid, it will dissolve; if it is too sparse, it will be difficult to disperse. Only when the distance is appropriate can the effect be good.
4) No chemical reaction with the foaming liquid: If the defoaming agent reacts with the foaming liquid, on the one hand the defoaming agent will lose its effect, and on the other hand it may produce harmful substances that affect the growth of microorganisms.
5) Low volatility: First, determine the system that requires the use of defoaming agents, whether it is a water-based system or an oil-based system. For example, in the fermentation industry, oil-based defoaming agents, such as polyether modified silicone or polyether, must be used. The water-based coating industry requires water-based defoamer and silicone defoamer.
6) The relative density is smaller than that of foaming liquid (because foam generally accumulates on the liquid surface);
7) Non-toxic and no harm to the environment;
8) Resistant to high and low temperatures;
9) It is not easy to adhere to the wall of the container; the amount of addition is small.
Characteristics of silicone defoamer:
1) The surface tension is small. The surface tension of dimethyl silicone oil is lower than that of water, surfactant aqueous solution and general oils, so it has a very strong defoaming effect. The dosage is 5~200ppm (referring to the active content) of the foaming liquid;
2) Non-polar, insoluble in water, animal and vegetable oils, and high boiling point mineral oil, and has high activity. When a drop of silicone oil in a toluene solution is placed on the water, it will expand on the water and significantly reduce the surface tension of the water. It has a defoaming effect on most foaming systems, and the foam suppression is also very sustainable;
3) Good chemical stability and heat resistance;
4) Physiologically inert and can be used in a variety of industries;
5) There are many varieties and models, and a variety of foaming systems are available.
