A defoamer or an anti-foaming agent is a chemical additive that reduces and hinders the formation of

foam Foams are two-phase materials science, material systems where a gas is dispersed in a second, non-gaseous material, specifically, in which gas cells are enclosed by a distinct liquid or solid material. Note, this source focuses only on liquid ...

in industrial process liquids. The terms anti-foam agent and defoamer are often used interchangeably. Strictly speaking, defoamers eliminate existing foam and anti-foamers prevent the formation of further foam. Commonly used agents are insoluble oils, polydimethylsiloxanes and other silicones, certain alcohols, stearates and glycols. The additive is used to prevent formation of foam or is added to break a foam already formed. In industrial processes, foams pose serious problems. They cause defects on surface coatings and prevent the efficient filling of containers. A variety of chemical formulae are available to prevent formation of foams.

Properties

Generally a defoamer is insoluble in the foaming medium and has surface active properties. An essential feature of a defoamer product is a low

viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...

and a facility to spread rapidly on foamy surfaces. It has affinity to the air-liquid surface where it destabilizes the foam lamellas. This causes rupture of the air bubbles and breakdown of surface foam. Entrained air bubbles are agglomerated, and the larger bubbles rise to the surface of the bulk liquid more quickly.

History

The first defoamers were aimed at breaking down visible foam at the surface.

Kerosene Kerosene, or paraffin, is a combustibility, combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in Aviation fuel, aviation as well as households. Its name derives from the Greek (''kērós'') meaning " ...

fuel oil Fuel oil is any of various fractions obtained from the distillation of petroleum (crude oil). Such oils include distillates (the lighter fractions) and residues (the heavier fractions). Fuel oils include heavy fuel oil (bunker fuel), marine f ...

and other light oil products were used to break down foam.

Vegetable oil Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of edible plants. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed ...

s also found some use.

Fatty alcohol Fatty alcohols (or long-chain alcohols) are usually high-molecular mass, straight-chain primary alcohols, but can also range from as few as 4–6 carbon atoms to as many as 22–26, derived from natural fats and oils. The precise chain length vari ...

s (C7 – C22) were effective but expensive antifoams. They were added to oil products to boost the efficiency.

Milk Milk is a white liquid food produced by the mammary glands of lactating mammals. It is the primary source of nutrition for young mammals (including breastfeeding, breastfed human infants) before they are able to digestion, digest solid food. ...

and

cream Cream is a dairy product composed of the higher-fat layer skimmed from the top of milk before homogenization. In un-homogenized milk, the fat, which is less dense, eventually rises to the top. In the industrial production of cream, this proces ...

were forebears for modern-day emulsion type defoamers. During the 1950s, experiments with

silicone In Organosilicon chemistry, organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (, where R = Organyl group, organic group). They are typically colorless oils or elastomer, rubber ...

-based defoamers started. These were based on

polydimethylsiloxane Polydimethylsiloxane (PDMS), also known as dimethylpolysiloxane or dimethicone, is a silicone polymer with a wide variety of uses, from cosmetics to industrial lubrication and passive daytime radiative cooling. PDMS is particularly known for its ...

(silicone oil) dispersed in water or light oil. Silicone oils worked well, but caused surface disturbances in many applications like

paint Paint is a material or mixture that, when applied to a solid material and allowed to dry, adds a film-like layer. As art, this is used to create an image or images known as a painting. Paint can be made in many colors and types. Most paints are ...

s and

papermaking Papermaking is the manufacture of paper and cardboard, which are used widely for printing, writing, and packaging, among many other purposes. Today almost all paper is Pulp and paper industry, made using industrial machinery, while handmade pape ...

. In 1963 the first antifoams with

hydrophobic In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, thu ...

particles ( hydrophobic silica) in light oil were patented. In the early 1970s, hydrophobic waxes like ethylene bis stearamide dispersed in oils developed. These types of defoamers were very efficient, but the oil crisis of 1973 made these too expensive and resulted in a push for reduction of the oil content. The solution was adding

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

. So water-extended (water in oil emulsion) and water-based (oil in water emulsion) defoamers appeared. The development of silicone-based defoamers has continued, using different emulsifiers and modified silicone oils. In the early 1990s, silicone emulsion defoamers that caused less surface disturbance were used in the

wood pulp Pulp is a fibrous Lignocellulosic biomass, lignocellulosic material prepared by chemically, semi-chemically, or mechanically isolating the cellulose fiber, cellulosic fibers of wood, fiber crops, Paper recycling, waste paper, or cotton paper, rag ...

ing industry with great success. These caused better washing, reduced biological oxygen demand (BOD) in effluent and reduced deposits.

Classification

Oil-based defoamers

Oil-based defoamers have an oil carrier. The oil might be

mineral oil Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils. The name 'mineral oil' by itself is imprecise, ...

vegetable oil Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of edible plants. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed ...

or any other oil that is insoluble in the foaming medium, except

silicone oil A silicone oil is any liquid polymerized siloxane with organic side chains. The most important member is polydimethylsiloxane. These polymers are of commercial interest because of their relatively high thermal stability and their lubricating prop ...

. An oil-based defoamer also contains a wax and/or hydrophobic silica to boost the performance. Typical waxes are ethylene bis stearamide (EBS),

paraffin wax Paraffin wax (or petroleum wax) is a soft colorless solid derived from petroleum, coal, or oil shale that consists of a mixture of hydrocarbon molecules containing between 20 and 40 carbon atoms. It is solid at room temperature and melting poi ...

es, ester waxes and

fatty alcohol Fatty alcohols (or long-chain alcohols) are usually high-molecular mass, straight-chain primary alcohols, but can also range from as few as 4–6 carbon atoms to as many as 22–26, derived from natural fats and oils. The precise chain length vari ...

waxes. These products might also have surfactants to improve emulsification and spreading in the foaming medium. These are heavy duty defoamers and are normally best at knocking down surface foam.

Powder defoamers

Powder defoamers are in principle oil-based defoamers on a particulate carrier like

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

. These are added to powdered products like

cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mi ...

plaster Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English, "plaster" usually means a material used for the interiors of buildings, while "re ...

and

detergent A detergent is a surfactant or a mixture of surfactants with Cleanliness, cleansing properties when in Concentration, dilute Solution (chemistry), solutions. There are a large variety of detergents. A common family is the alkylbenzene sulfonate ...

Water-based defoamers

Water-based defoamers are different types of oils and waxes dispersed in a water base. The oils are often mineral oil or vegetable oils and the waxes are long chain

fatty acid In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an ...

soap Soap is a salt (chemistry), salt of a fatty acid (sometimes other carboxylic acids) used for cleaning and lubricating products as well as other applications. In a domestic setting, soaps, specifically "toilet soaps", are surfactants usually u ...

s or

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

s. These are normally best as deaerators, which means they are best at releasing entrained air.

Silicone-based defoamers

Silicone In Organosilicon chemistry, organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (, where R = Organyl group, organic group). They are typically colorless oils or elastomer, rubber ...

-based defoamers are polymers with silicon backbones. These might be delivered as an oil or a water-based emulsion. The silicone compound consists of a hydrophobic silica dispersed in a

. Emulsifiers are added to ensure that the silicone spreads fast and well in the foaming medium. The silicone compound might also contain silicone glycols and other modified silicone fluids. These are also heavy duty defoamers and are good at both knocking down surface foam and releasing entrained air. PmdsStructure

Silicone-based defoamers are also suitable in non-aqueous foaming systems like

crude oil Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring u ...

and

oil refining An oil refinery or petroleum refinery is an industrial processes, industrial process Factory, plant where petroleum (crude oil) is transformed and refining, refined into products such as gasoline (petrol), diesel fuel, Bitumen, asphalt base, ...

. For very demanding applications fluorosilicones may be suitable. EO/PO-based defoamers contain polyethylene glycol and

polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer Propene, propylene. Polypropylene belongs to the group of polyolefin ...

glycol copolymers. They are delivered as oils, water solutions, or water-based emulsions. EO/PO copolymers normally have good dispersing properties and are often well suited when deposit problems are an issue.

Alkyl polyacrylates

Alkyl polyacrylates are suitable for use as defoamers in non-aqueous systems where air release is more important than the breakdown of surface foam. These defoamers are often delivered in a

solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...

carrier like

petroleum Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...

distillates.

Glycol based defoamers

Combination polyglycol and fatty acid is used as defoamer in many applications such as control of foam in aqueous alkaline protein, starch, synthetic resin solutions.

Industrial problems

The most noticeable form of foam is foam floating on the stock surface. It is easy to monitor and relatively easy to handle and is more a cosmetic issue. Surface foam may cause problems with liquid levels and give overflow leading to pools of oils around the equipment which is a safety concern. Additionally, this might reduce the process speed and availability of process equipment. The main mechanical problem tends to be when foam enters the system as air is a poor lubricant, meaning metal to metal contact can occur.

Mechanical problem factors

Air or other gas dissolved in the fluid can come out of solution as small bubbles (entrained air). If these small bubbles have sufficient

buoyancy Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...

, they can rise to the surface and together form foam. Mechanical factors that may generate entrapped air: * Leaky seals on pumps * High pressure pumps * Poor system design (tank, pump inlet, outlet and

manifold In mathematics, a manifold is a topological space that locally resembles Euclidean space near each point. More precisely, an n-dimensional manifold, or ''n-manifold'' for short, is a topological space with the property that each point has a N ...

design) *

Pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...

release

Foam in process and coolant liquids

Foam, entrained and dissolved air that are present in coolants and processing liquids, may cause various kinds of problems, including: * Reduction of

pump A pump is a device that moves fluids (liquids or gases), or sometimes Slurry, slurries, by mechanical action, typically converted from electrical energy into hydraulic or pneumatic energy. Mechanical pumps serve in a wide range of application ...

efficiency (

cavitation Cavitation in fluid mechanics and engineering normally is the phenomenon in which the static pressure of a liquid reduces to below the liquid's vapor pressure, leading to the formation of small vapor-filled cavities in the liquid. When sub ...

) * Reduced capacity of pumps and storage tanks *

Bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

l growth * Dirt flotation / deposit formation * Reduced effectiveness of the fluid solution(s) * Eventual downtime to clean tanks * Drainage problems in sieves and filters * Formation problems (i.e. in a

paper mill A paper mill is a factory devoted to making paper from vegetable fibres such as wood pulp, old rags, and other ingredients. Prior to the invention and adoption of the Fourdrinier machine and other types of paper machine that use an endless belt ...

it may cause the

fibers Fiber (spelled fibre in British English; from ) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often inco ...

to form an

inhomogeneous Homogeneity and heterogeneity are concepts relating to the uniformity of a substance, process or image. A homogeneous feature is uniform in composition or character (i.e., color, shape, size, weight, height, distribution, texture, language, i ...

sheet) * Cost of replenishing the liquid * Cost of entire material rejection due to imperfections

Test methods

There are several ways to test defoamers. The easiest is looking at the surface foam. All that is needed is a system for generating foam. This might be done with a round pumping system with a nozzle and a cylinder or an air injection system into a cylinder. The cylinder is fitted with a scale to measure the foam height. This equipment may have a heater to control the temperature. Entrained air can be tested with similar equipment that has a

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

meter that can record changes of the liquid density over time. Drainage can be tested with a filter system for measuring the time to drain a liquid through the filter. The filter might be pressurized or have a

vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...

Applications

Detergents

Anti-foams are added in certain types of

s to reduce

ing that might decrease the action of the detergent. For example,

dishwasher A dishwasher is a machine that is used to clean dishware, cookware, and cutlery automatically. Unlike dishwashing, manual dishwashing, which relies on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying hot wat ...

detergents have to be low foaming for the dishwasher to work properly. Defoamer is added into the recovery tank of carpet extractors to prevent too much-foaming damage to the vac motor.

Food

When used as an ingredient in

food Food is any substance consumed by an organism for Nutrient, nutritional support. Food is usually of plant, animal, or Fungus, fungal origin and contains essential nutrients such as carbohydrates, fats, protein (nutrient), proteins, vitamins, ...

, antifoaming agents are intended to curb

effusion In physics and chemistry, effusion is the process in which a gas escapes from a container through a hole of diameter considerably smaller than the mean free path of the molecules. Such a hole is often described as a ''pinhole'' and the escape ...

or effervescence in preparation or serving. The agents are included in a variety of foods and in materials for food preparation;

McDonald's McDonald's Corporation, doing business as McDonald's, is an American Multinational corporation, multinational fast food chain store, chain. As of 2024, it is the second largest by number of locations in the world, behind only the Chinese ch ...

includes

(a type of

) in its oil to mitigate hazardous splashes of oil caused by foaming in fryers, so it has been listed as an ingredient in their chicken nuggets, french fries, and other fried menu items.

Industrial use

Defoamers are used in many industrial processes and products:

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses, Feces#Other uses, herbivore dung, or other vegetable sources in water. Once the water is dra ...

industrial wastewater treatment Industrial wastewater treatment describes the processes used for Wastewater treatment, treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reus ...

food processing Food processing is the transformation of agricultural products into food, or of one form of food into other forms. Food processing takes many forms, from grinding grain into raw flour, home cooking, and complex industrial methods used in the mak ...

oil drilling An oil well is a drillhole boring (earth), boring in Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produ ...

machine tool A machine tool is a machine for handling or machining metal or other rigid materials, usually by cutting, Boring (manufacturing), boring, grinding (abrasive cutting), grinding, shearing, or other forms of deformations. Machine tools employ some s ...

industry, oils cutting

tools A tool is an object that can extend an individual's ability to modify features of the surrounding environment or help them accomplish a particular task. Although many animals use simple tools, only human beings, whose use of stone tools dates ...

hydraulics Hydraulics () is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counterpart of pneumatics, which concer ...

, etc. Besides, for many building materials, such as cement, mortar, self-leveling compound, or tile adhesive, foam can be an unwanted side effect that disrupts the subsequent work steps and may even undermine the stability of the construction. It needs defoamers to eliminate or reduce the formation of bubbles and ensure smooth processing of the compound.

Pharmaceuticals

Antifoaming agents are also sold commercially to relieve

bloating Abdominal bloating (or simply bloating) is a short-term disease that affects the gastrointestinal tract. Bloating is generally characterized by an excess buildup of gas, air or fluids in the stomach. A person may have feelings of tightness, pressu ...

. A familiar example is the drug

simethicone Simeticone (International Nonproprietary Name, INN), also known as simethicone (United States Adopted Name, USAN), is an anti-foaming agent used to reduce bloating, discomfort or pain caused by excessive gas. Medical uses Simeticone is used to ...

, which is the active ingredient in drugs such as Gas-X.

References

{{reflist, 30em Foams Industrial processes Colloidal chemistry Food additives Lubricants Oil additives Process chemicals