Defoamer / Anti Defoamer

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

Types of Defoamers

Oil based defoamers

Oil based defoamers have an oil carrier. The oil might be mineral oil, vegetable oil, white oil or any other oil that is insoluble in the foaming medium, except silicone oil. An oil based defoamer also contains a wax and/or hydrophobic silica to boost the performance. Typical waxes are ethylene bis stearamide , paraffin waxes, ester waxes and fatty alcohol waxes. These products might also have surfactants to improve emulsification and spreading in the foaming medium.

Powder defoamers

Powder defoamers are in principle oil based defoamers on a particulate carrier like silica. These are added to powdered products like cement, plaster and detergents.

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 alcohol, fatty acid soaps or esters. These are normally best as deaerators, which means they are best at releasing entrained air.

Silicone based defoamers

Silicone-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 silicone oil. 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.

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 carrier like petroleum distillates.

Mechanical problem factors

Mechanical factors that may generate foam and entrapped air:

• Leaky seals on pumps
• High pressure pumps
• Poor system design (tank, pump inlet, outlet and manifold design)
• Pressure release

The main classes of air that are of concern to the mechanical systems are:

• Dissolved air behaves as part of the fluid phase, except that it can come out of solution as small bubbles (entrained air)
• Entrained air consists of bubbles that are small enough to collect on top of a fluid
• Bubbles that have sufficient buoyancy to rise to the surface and are described as foam

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 efficiency (cavitation)
• Reduced capacity of pumps and storage tanks
• Bacterial 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 it may cause the fibers to form an inhomogeneous sheet)
• Cost of replenishing the liquid
• Cost of entire material rejection due to imperfections

Detergents

Anti-foams are added in certain types of detergents to reduce foaming that might decrease the action of the detergent. For example, dishwasher 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, antifoaming agents are intended to curb effusion or effervescence in preparation or serving. The agents are included in a variety of foods and in materials for food preparation; McDonald’s includes polydimethylsiloxane (a type of silicone) 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: wood pulp, paper, paint, industrial wastewater treatment, food processing, oil drilling, machine tool industry, oils cutting tools, hydraulics, etc.

Pharmaceuticals

Antifoaming agents are also sold commercially to relieve bloating. A familiar example is the drug Simethicone, which is the active ingredient in drugs such as Maalox, Mylanta, and Gas-X.

Also use in applications such as

• Hair conditioner
• Bath/shower gel
• Cold wave
• Acid cleaner
• Ammonia
• Chlorine
• Detergent powder
• Liquid detergent
• Fabric softener
• Candles
• Pot pourri