Original article date: Aug. 19, 2016
Updated Oct. 29, 2021
Originally, this article was written about five years ago, and with most things, there have been advancements in new technologies for the use of defoamers and antifoams, as well as the composition of the additives due to greater regulatory restrictions and the need for different technology for different uses. There is some essential information below and more can be found in the endnotes.
Both antifoams and defoamers are used for foam control. Given their similarities in function, they often have similar chemistries. The main difference between them is the timing of application. In order to prevent it, antifoams are designed to be applied before the formation of foam, while defoamers are designed to be applied after foam formation in order to destroy it. Below, we provide a closer look at antifoam and defoamer chemistry.
For this article, defoamers and antifoam agents are focused on use in paints, inks, adhesives and even construction products. Defoamers are very important in the growing market of oil recovery applications but fall outside of the scope of this paper. There are food-grade defoamers and even ones designated as kosher or halal, but they are mentioned but not discussed here.I
Dependent upon the application and performance requirements, defoamers consist of polydimethylsiloxanes and other silicones, insoluble oils, waxes, stearates and glycols, as well as inorganics, such as silicates and talc. The regulatory requirements of zero VOC, or close to it, have changed the landscape of defoamers. The further development of bio-based products has also resulted in variations which might include the use of a soy-based oil instead of a non-vegetable oil.
There are many types of antifoams available, and they are often lumped into two broad categories:
Silicone antifoams are normally composed of hydrophobized silica that is finely dispersed within a silicone fluid. The resulting compound is then stabilized into a water-based or oil-based emulsion. These antifoams are highly effective due to their general chemical inertness, potency even in low concentrations, and ability to spread over a foam film. If needed, they can be combined with other hydrophobic solids and liquids to improve their defoaming properties.
Non-silicone antifoams generally contain surfactants, which enhance their dispersal capabilities and effectiveness in foaming water. They can be water-based, oil-based, or surfactant-based. These antifoams can be used for a wide range of industries. Compared to silicone antifoams, they are sometimes more readily biodegradable and less prone to causing certain problems such as discoloration, spotting, and negative membrane effects.
As far as new technologies, examples are:
FOAMSTAR® ST 2400 is a series of defoamers based on new defoamer chemistry developed and patented by BASF. It is the first new defoamer chemistry in over 30 years. It is based on a hyper-branched polymer with a 3-dimensional star-shaped structure containing hydrophilic as well as hydrophobic elements. FoamStar® technology breaks down foam on a molecular level. It acts as a unique surfactant interacting with the foam-related surfactants and destabilizes the foam bubbles.
Soy-based defoamers are the preferred choice for biobased defoamers but can also be made from other vegetable sources instead of petroleum. Besides providing bio preferred labeling, there is a push for low or no VOC products.
Processing with defoamers
In industrial processes, foams pose serious problems. They cause defects on surface coatings. They prevent the efficient filling of containers. Some of the sources of foam formation include:
- Filtration through a sieve or anything with air on the surface
- Introduction of air through substrate wetting (wood coatings, other highly porous substrates)
- Inclusion of air through agitation during production, filling, mixing of 2-pack systems. Often high viscosity (epoxies, adhesives)
- Air inclusion on pigment surface resulting in poor wetting of pigments
- Application: Roller, spraying, brushing
It is suggested that the following is considered if you require a more thorough understanding of the subject of foam generation, defoamer composition, mechanisms, etc.:
- Test Methods
- Paints
- Inks
- Adhesives
- Construction Products
- Selection Guidelines
- Process
- Application
- Foam stabilization
- Composition and Mode of Action of Defoamers
- Coatings Defects
Chemical defoamers similarly have analogous methods, which are in the form of composition rather than processes. In-process, they can either consolidate small foam to larger bubbles which can then break at the air/liquid interface and break bubbles during mixing and shear. During application, they disrupt the bubble wall, or cause increased drainage. In many cases, the choice of a chemical defoamer is a balance between highest efficiency and lowest undesired side effects, coupled with a preferred mechanical process, if available.
Mechanical dissipation of foam, as well as the chemical elimination of foam, is important in processing. Bubble consolidation is achieved with lower shear mixing, which will put the microfoam in contact, especially at surface (vortex) and foam will consolidate to larger bubbles that break more easily. Vibration using a rotosieve or other vibration tools will reduce the surface tension at the air/liquid interface in processes such as filtration of latexes; utilizing a very fine mist of water spray, the bubble walls will be disrupted and break them; or vacuum such as a RotoVap or Ross Mill homogenizer and vacuum.
There are many considerations in the choice of a defoamer. For paints, persistency over a long shelf-life is required, but the defoamer cannot affect color uniformity, such as rub-up. For water-borne flexographic inks, the preferred defoamers are based on glycols and polyglycol (ethers). Silicone defoamers are used in solvent-borne and high viscosity systems and are used more in the grind stage of pigment dispersion rather than in the letdown.
In summary, defoamers are essential ingredients in a paint formulation avoiding foam formation and stabilization in water-borne as well as solvent-borne paints. Proper selection of defoamer quality and quantity is essential for optimal defoamer performance. Defoamers compete with foam stabilizing ingredients in order to be effective in a coating system. The proper defoaming results in paint quality properties, and it is important that test methodologies are appropriate for the specific application or process.
References
- Coatings Additives – Defoamers, Adhesion Promoters & UV Protection | Prospector Knowledge Center (ulprospector.com) October 16, 2015
- Defoamers (ulprospector.com) October 9, 2019
- WEBINAR: Solve compatibility issues with slip and mar, anti-blocking and foam control additives (ulprospector.com) December 8, 2020
1 Food Contact Compliant Defoamers & Deaerators for Water-Based Coatings and Inks | Prospector Knowledge Center (ulprospector.com) July 21, 2021
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Your still the man when it comes to defamers. Good job.
Thanks, Fred. You are too kind.
Very good explanation. THANKS
Thanks for this article. We have a thick aliphatic polymer with no polarity, that generates air bubbles upon mixing – where do we look for defoamers for such a resin?
When you say “generates bubbles”, are you referring to a chemical reaction where gas is produced, or is this air generated by the method of mixing? If this is only process-oriented, from a mechanical standpoint, you could use something like a Ross-Miles mixer fitted with a vacuum. The vacuum will pull the air to the surface.
From a chemical standpoint, it is somewhat trial-and-error also because the defoamer can effect performance or appearance. For your type of viscosity, you can try Efka PB2001, WorleeAdd678 and BYK 1794. Talk to the suppliers for their recommendations. Good luck.
Nice and precise. Thanks.
Hi Marc
Excellent article Can you kindly assist with formulation of mineral oil based defoamer?
excellent article
Very informative article.
Would like to know how to improve performance of mineral oil based defoamer with hydrophobic particles? What is to be added to get that performance.
I am sure that there are patents you can refer to, and also easier to purchase from a supplier already made. But basically a simple defoamer would consist of mineral oil, bis-stearamide and hydrophobic silica. You will need to heat the mix to melt the bis- and reduce the viscosity to be able to add in silica. Evonik and others sell treated silica. You can reduce the viscosity overall with an OMS 9odorless mineral spirit) as there are several MW’s. All then is process through a sand mill or horizontal mill/homogenizer. Something with sufficient shear to fully homogenize. That is the basic concept. Many people don’t make their own as it is time-consuming, and you need the equipment. Good luck.
Wonderful article. I have always enjoyed your articles and often times I felt like it should never end.
I am new to understanding defoamers and the best way to dispel foams. I have worked in the paint industries where we have very small issues with foams and defoamers. However, currently I work in the ink industry and this happens to be a very critical and important aspect. As a matter of fact, sometimes defoamers tend to introduce pinholes in some coatings and inks. the task therefore, is to find that balance between having excessive/inadequate/adequate defoamer that will eliminate foam without introducing pinholes into product.
One question that I have is, at what stage in the production process is it most optimal to use defoamer? I have often times suggested that it should be t he last ingredient while antifoam show be before adding a foam forming raw material but an expert knowledge will go a long way.
Just a quick one we make foamed parts for a major car company, we have been doing this for two years now and we have only just stated to get voids in are parts , we have tried different methods like increasing foam decreasing foam playing around with the heat of the chemical, even tried ratio , we have even tryed shimming the tool
My apologies that for whatever reason, I hadn’t seen this question. A lot really depends on the type of defoamer, what type of processing you are using (shear), etc. As an example, a much stronger silicone/polysiloxanes defoamer could be used if there were high shear in processing the ink. Otherwise, you want something very dispersible, such as an ester defoamer.
I am answering this even though you asked Fred.
I really don’t understand what you are asking. Here’s my guess: Foaming creates small voids. So you are saying that the voids are either consolidating to large ones or large ones are being created? Second, is this a polyol/PI system to make PU foam? You may want to increase mixing shear to create smaller foam and perhaps add a surfactant to stabilize/increase small foam that won’t collapse to larger bubbles.
Hi Marc Hirch
Can you help me to make mineral oil defoamer
Dear Marc,
Thanks for your valuable advices as above mentioned.
I am working on two component pu for wood imitation
pu, where foaming is not wanted.
Foaming occurs with the beginning of the urethane reaction.
What kind anti foam(brand?) would you recoomend
for the problem I mentioned?
Thanks in advance,
Kursun Kursunoglu
Orjin Kimya/Turkey
I am sorry for my slow response as I just saw this. I can suggest some general defoamers, but it is probably best for you to contact local suppliers of defoamers, share your problem and have them suggest what to use. They may even provide some technical support in the labs. If I suggest defoamers that aren’t available to you in Turkey, those recommendations would be pretty useless to you.
Dependent upon how and when the gassing occurs, as I had previously suggested, a Ross-Miles dispersator or other blending equipment fitted with a vacuum apparatus would be the easier way to remove bubbles without introducing an additive that could affect your performance. Hope that this helps.
any recommendations for ethanol soluble laminating adhesives ?
I should be asking you for advice considering you work for Henkel. But seriously, I would think you would be more worried about FDA food contact. So if I had this problem, I would first look at recommendations from suppliers with the FDA clearances that you need. I am guessing 175.105. And I would not necessarily look at suppliers in the US since there shouldn’t be any ITAR restrictions. And Europe does have different defoamers than the US. And different raw materials to make same
Thanks for sharing your valuable feedback I’m grateful to you.