Defoamer is also called defoamer, anti-foam agent, defoamer is actually the meaning of eliminating foam, it is a low surface tension and high surface activity, can inhibit or eliminate the foam in the system of substances. In the industrial production process will produce a lot of harmful foam, seriously hinder the progress of production, then you need to add defoamer to eliminate these harmful foam.






Reaction mechanism of defoamer






The local surface tension of the foam decreases and the foam bursts


Some people studied the defoaming process of polysiloxane in the oil system. They continuously took photos of the foam system at the speed of 1/1000 seconds, and the photos were enlarged 100 times. The schematization of the four photos taken in succession can be seen that the droplets of silicone oil defoaming agent arrived on the foam film, and the surface of the foam film burst and merged into a large bubble. Finally, the gas and liquid are rapidly separated, the large bubble is destroyed, and the bubble is broken at 4. This also objectively explains why a drop of defoamer goes down and a series of bubbles burst.






When the defoamer is attached to the bubble film, it is immersed in the bubble film liquid, which will significantly reduce the surface tension there. Because in the water system, the solubility of the active ingredient of the defoamer to water is small, the reduction of the surface tension is limited to the local part of the bubble film, and the surface tension around the bubble film hardly changes. The part of the surface tension is reduced, which is strongly pulled around and extended, and finally causes the bubble to burst.










The defoamer can destroy the elasticity of the membrane and cause the bubble to burst


Due to the adsorption of surfactant on the surface of the membrane, the surface tension is reduced. Therefore, under local pressure, the membrane becomes locally thin at the same time, and the surface tension will increase due to the thinning of the surfactant. It is because of the difference in surface tension between the new surface and the original surface that the elastic recovery force is generated when the membrane is thinned by the external impact, and the membrane is not broken and plays a role in stabilizing the bubble. If we manage to break this elasticity, we can break the stability of the foam. Some experts believe that the role of defoamer is to destroy the elasticity of the bubble film. When the defoamer is added to the foam system, it diffuses to the gas-liquid interface, which makes it difficult for the surfactant with foam stabilization function to restore the elasticity of the membrane.






The defoamer can cause the liquid film to drain, thus causing the bubble to burst


The substance (defoamer) that accelerates the liquid discharge of the bubble membrane can be added to defoamer. If the bubble film is thick, the process of drainage to 30~40nm is long, and the self-healing effect of the bubble film is strong, and the elasticity of the bubble film is good, so the foam life of the thick bubble film is long, and the liquid drainage rate of the bubble film can reflect the stability of the foam. The liquid film discharge rate is fast, so that the liquid film becomes thin, thin to a certain extent, the foam burst.






The addition of hydrophobic solid particles can cause the bubble to burst


In the foaming water system, the addition of hydrophobic silica (that is, hydrophobic white carbon black) particles alone has the effect of defoaming. The hydrophobic white carbon black particles attract the hydrophobic end of the surfactant on the bubble surface, and the hydrophobic particles become hydrophilic particles and enter the aqueous phase, completing the defoamization. The solid particles of hydrophobic silica are generally white carbon black particles treated with methyl silicone oil, silazane or DMC, which are locally immersed on the surface of the bubble, making the surface tension of the local bubble smaller, coupled with the effect of solid particles, like the tip of a needle inserted into the bubble, accelerating the collapse of the bubble. Therefore, the defoamer containing hydrophobic white carbon black generally has a better foaming effect.






Solubilizing foaming surfactant can cause bubbles to burst


Some low molecular substances that can be fully mixed with the solution can make the bubble surfactant solubilized and reduce its effective concentration. Low molecular substances with this effect, such as octanol, ethanol, propanol and other alcohols, can not only reduce the surfactant concentration of the surface layer, but also dissolve into the surfactant adsorption layer, reducing the tightness of the surfactant molecules, thus weakening the stability of the foam.


The electrolyte disintegrates and the double layer of surfactant collapses the bubble


For the interaction of the two electric layers of the surfactant with the help of foam to produce a stable foaming solution, the addition of ordinary electrolytes can disintegrate the double electric layer of the surfactant to act as a defoamer.






Composition of defoamer






Active ingredient


Function: bubble breaking, defoaming, reduce surface tension:


Representatives: silicone oil, polyethers, high alcohols, mineral oil, vegetable oil, etc.






emulsifier


Function: Disperse the active ingredients into small particles, easy to disperse in water, better play the anti-foam, anti-foam effect.


Representatives: nonyl (octyl) phenol polyoxyethylene ether, soap salt, op series, Twain series, Pan series, etc.






carrier


Function: helps to combine the carrier and the foaming system, easy to disperse into the foaming system, combine the two, its own surface tension is low, helps to suppress the foam, and can reduce the cost.


Representative: solvents other than water, such as aliphatic hydrocarbons, aromatic hydrocarbons, oxygen-containing solvents, etc






Emulsifying agent


Function: Make the emulsification effect better.


Representative: dispersant (hydrophobic silica, etc.); Tackifier: (CMC, polyethylene ether, etc.).






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How to choose defoamer






Insoluble or insoluble in a foaming solution






In order to burst the foam, the defoamer should be concentrated and concentrated on the bubble film. For the case of defoaming agent, it should be concentrated and concentrated in an instant, and for the case of defoaming agent, it should always be maintained in this state. Therefore, the defoamer is supersaturated in the foaming solution, and only insoluble or insoluble is easy to achieve supersaturation. Insoluble or insoluble, it is easy to gather at the gas-liquid interface, it is easy to concentrate on the bubble film, and it can play a role at a lower concentration. For the defoamer used in water systems, the molecules of the active ingredients must be strong hydrophobic and weak hydrophilic, and the HLB value should be in the range of 1.5-3 for the best effect.






The surface tension is lower than that of the foaming solution






Only when the intermolecular force of the defoamer is small and the surface tension is lower than that of the foaming solution, the defoamer particles can be immersed and expanded on the foam film. It is worth noting that the surface tension of the foaming solution is not the surface tension of the solution, but the surface tension of the foaming solution.






It has a certain degree of affinity with foaming liquid


Since the defoaming process is actually a competition between the speed of foam collapse and the speed of foam formation, the defoaming agent must be able to disperse quickly in the foaming solution in order to quickly play a wider range of roles in the foaming solution. In order to make the defoamer diffusion faster, the active ingredient of the defoamer must have a certain degree of affinity with the foaming solution. The active ingredient of defoamer is too close to the foaming solution and will dissolve. Too sparse and difficult to disperse. The effectiveness is good only when the intimacy is right.






No chemical reaction with the foaming solution


The defoamer reacts with the foaming solution, on the one hand, the defoamer will lose its effect, on the other hand, harmful substances may be produced, affecting the growth of microorganisms.


Low volatility, long action time






Emulsifying agent


First of all, it is necessary to determine the system that needs to use defoamer, whether it is a water-based system or an oil-based system. If the fermentation industry, it is necessary to use oil-based defoamer, such as polyether modified silicon or polyether. Water-based coating industry must use water-based defoamer, silicone defoamer. Select the defoamer, compare the added amount, and get the most suitable and economical defoamer product at the reference price.






The amount of defoamer added






There are many types of defoamer, and the amount of addition required for different types of defoamer is different.


Alcohol defoamer


When alcohol defoamer is used, the dosage is generally within 0.01-0.10%.






Oil defoamer


The addition amount of oil defoamer is between 0.05-2%, and the addition amount of fatty acid ester defoamer is between 0.002-0.2%.






Amide defoamer


The effect of amide defoamer is better, and the addition amount is generally within 0.002-0.005%.






Phosphoic acid defoamer


Phosphoic acid defoamer is most commonly used in fibers and lubricants, and the amount added is between 0.025 and 0.25%.






Amine defoamer


Amine defoamer is mainly used in fiber processing, with an added amount of 0.02-2%.






Ether defoamer


Ether defoamer is used more in paper printing and dyeing and cleaning, and the addition amount is generally 0.025-0.25%.






Advantages and disadvantages of defoamer






Silicone defoamer


This defoamer is easy to source, the price is relatively the cheapest, although cheap, but the effect is very good, defoamer fast, foam suppression time lasting, non-toxic and harmless is a good defoamer for most industrial defoamer. The method of use is also very simple, that is, it is not easy to store and easy to deteriorate, and is incompatible with a small number of systems.






Polyether defoamer


Polyether defoamer is relatively the most stable type, good compatibility with most systems is the most stable defoamer type, basically what type of foam can be found in polyether defoamer, foam suppression time is stronger than silicone, but the disadvantage is that the defoamer speed is relatively slow.






High carbon alcohol defoamer


More effective defoamer Some foams that are difficult to eliminate can be eliminated with high-carbon alcohol defoamer.






Silicon defoamer


It can either eliminate foam or inhibit the production of foam, and is one of the few anti-foam agents that can fundamentally solve industrial foam.






Polyether modified silicon


It combines the advantages of the first two defoaming agents, and is non-toxic and harmless, which is a cost-effective product.