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How does Defoamer Defoam

Nov 2, 2020

Papermaking water treatment, paper pulping, pulp washing, color paste, degassing, du paper coating zhi coating sizing, coating coating, printing pictorial paper after calendering, deinking washing, defoaming in paper coating polymer system And deaeration, art paper, slurry defoaming, paper surface sizing and pressing process, glue, coating process defoaming, deinking process defoaming, paper machine wet end use, degassing and defoaming during paper production, etc.

Anti-foaming agents generally eliminate foam through the following two methods.

1. The defoamer diffuses in the zhi foam and forms a double-layer film on the foam wall during diffusion. During this diffusion process, the stabilizing surfactant is discharged, which reduces the local surface tension of the foam and destroys the foam’s self The healing effect makes the bubble burst.

2. The defoamer may enter the foam wall, but only spread to a very limited extent, forming a mixed monolayer with the foaming agent. If the cohesion of this monolayer is not good, the foam will burst.

Dosage and usage of defoamer
Silicone defoamers with a defoaming active content of 100% are less directly used in the production process. This is not only due to high cost, but also difficult to work when used in small amounts, and large amounts can cause pollution problems. Therefore, most commonly used antifoam emulsions are formulated into silicone with a mass fraction of 1% to 2%. The amount is appropriately changed according to the process conditions.

In terms of use, it is easy to operate. Of course, it is best to add the defoamer to the solution at once to control the foam during the entire process. But sometimes this does not work well. This is because the defoamer must expel the foam stabilizer at the interface between liquid and air in order to defoam. In this process, there are many factors that can remove the defoamer from the surface, that is, it will slowly dissolve or emulsify into the liquid over time, and lose the defoaming ability (the speed of the defoamer dissolving emulsification speed and the following factors Related); shear force, surfactant type and concentration, temperature, pH value, solvent type and content, and some special substances that may exist).

Therefore, the safest and most effective way to use defoamers is to add low-concentration dilute emulsions in a continuous or semi-continuous manner during the production process. In this way, it can prevent both foaming and oil contamination of silicone. If you must add enough silicone defoamer at the beginning of the operation, you must avoid excess.

Choice of defoamer
1. Insoluble or insoluble in foaming liquid
To break the foam, the defoamer should be concentrated and concentrated on the foam film. In the case of foam breaker, it should be concentrated and concentrated in an instant, and in the case of foam suppression, it should be kept in this state frequently. Therefore, the defoamer is supersaturated in the foaming liquid, and only insoluble or insoluble can it easily reach the supersaturated state. Insoluble or poorly soluble, it is easy to gather at the gas-liquid interface, it is easy to concentrate on the bubble film, and it can work at a lower concentration. For defoamers used in water systems, the molecules of the active ingredients must be strong hydrophobic and weakly hydrophilic, with an HLB value in the range of 1.5-3 for the best effect.

2. The surface tension is lower than the foaming liquid.
Only when the defoamer has a small intermolecular force and the surface tension is lower than that of the foaming liquid, the defoamer particles can be immersed and expanded on the foam 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 degree of affinity with foaming liquid.
Since the defoaming process is actually a competition between the foam collapse speed and the foam generation speed, the defoamer must be able to quickly disperse in the foaming liquid in order to quickly play a role in a wider range of the foaming liquid. To make the defoamer diffuse faster, the active ingredients of the defoamer must have a certain degree of affinity with the foaming liquid. The active ingredient of the defoamer is too close to the foaming liquid and will dissolve; too thin and difficult to disperse. The effectiveness will be good only if the relationship is suitable.

4. No chemical reaction with foaming liquid.
The defoamer reacts with the foaming liquid. On the one hand, the defoamer will lose its effect, and on the other hand, it may produce harmful substances that affect the growth of microorganisms.

5. Low volatility and long action time.
First of all, determine whether the system that needs to use defoamer is water-based or oily. Such as the fermentation industry, it is necessary to use oily defoamers, such as polyether modified silicon or polyether. Water-based paint industry needs water-based defoamer, silicone defoamer. Choose the defoamer, compare the addition amount, and get the most suitable and economical defoamer product at the reference price.

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