This document gives a brief description on defoamer chemicals used in industry. Foaming is a problem in processing industry like, food, paper and pulp, paint and coating, printing, dyeing, oil drilling, boiler steam production, water treatment, waste management, etc.

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Defoamers and Applications
Chandran Udumbasseri
Technical Consultant
chandran.udumbasseri@gmail.com.
Introduction
Defoamers are chemical additives that eliminate existing foam that has been formed
and antifoam is the additive that prevents the foam formation. Foam is defined as
dispersed air or gas in a liquid. Surface active agents stabilize foam
Foam is a desired property in the case of soaps, detergents and beverages. But it is
not acceptable in the case of paint, coating, printing, etc. In usual processes like
mixing, blending, and distillation foaming creates process problem and takes a lot of
production hours to accommodate the foaming character of a liquid. Foaming
creates craters, fish eyes, pin holes and such surface irregularities when surface
coating, painting or printing is performed. The following situations cause foam
formation:
 Air inclusion during processing like mixing
 Air adhesion to pigment surface this causes poor wetting of pigments.
 During roller application, spraying and brushing air enters and mixes.
 During filtration in atmospheric condition the air above the liquid surface get
mixed up with the liquid..
 Chemical process which liberates gas/air can form foaming. ,
 When giving coating to porous surface and wood surfaces air from
atmosphere enter the process of coating.
There are two types of defoaming methods, mechanical means and adding chemical
additives. In the former, there are several effective methods:
 At a low level shear mixing micro-foams get into contact and make larger
foams which breaks more easily.
 Vibrating sieves have reduced surface tension at the air/liquid interface.
Process like filtration using rotosieve reduce the surface tension at the
air/liquid interface and promote any foam breaking.
 Using a very fine mist of water spray to disrupt and break the bubble walls.
 Vacuuming, such as with a RotoVap or Ross Mill homogenizer.
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
(flocculants), which can then break at the air/liquid interface or
 break bubbles during mixing and shear
 disrupt the bubble wall or cause increased drainage
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
Surface tension and defoamer performance
Surface active agents like emulsifiers, detergents, wetting agents tend to reduce the
surface tension of a liquid. These chemicals have amphiphilic nature (hydrophobic
and hydrophilic parts in a molecule) and accumulate at the interface of gas/liquid
interface, retard coalescence of bubbles and stabilize the foam.

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Surface tension of liquids
Water 72mN/m
Xylene 30
Butyl acetate 25
White spirit 24
Solutions (0.5% solution
Fatty alcohol ethoxylate) 24
Silicone wetting agent 24
Fluorinated surfactant 22
Sulfosuccinate 27
Steps involved during defoaming:
 When a defoamer droplet moves to the foam it enters at foam lamella
 It spreads at the air/liquid/surfactant interface
 Destabilization and rupture of the foam lamella.
When a solid like hydrophobic silica is added with the defoamer the surfactant
around gas phase cannot wet the silica and gets dehydrated. This causes shrinkage
of the surfactant and thus destabilizes the foam lamella and rupture.
Types of defoamers
1. Oil based
Oil based defoamers have an oil carrier. The oil carrier may be mineral oil (white
spirit) or vegetable oil or any oil that is insoluble in the foaming medium. Solids like
silica and wax can boost the performance of the defoamer. Typical waxes
are ethylene bisstearamide (EBS), paraffin waxes, ester waxes and fatty
alcohol waxes. The presence of surfactants help emulsification between solid and oil
phase.
2. Water based
Water based defoamers contain fatty alcohols, fatty acid soap and its esters. In the
dispersed phase oil and waxes are also present.
3. Silicone based
Silicone-based defoamers are polymers with silicon backbones. The silicone
compound consists of hydrophobic silica dispersed in silicone oil. Emulsifiers are
added to ensure that the silicone spreads fast and well in the foaming medium. The

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silicone compound contains siloxane glycols, modified polydimethyl siloxane, silicone
polyoxyalkylene oxide copolymer, organo polysiloxane, etc.
Silicone defoamers are good at both knocking down surface foam and releasing
entrained air.
4. EO/PO based
EO/PO based defoamers contain polyethylene glycol and polypropylene
glycol copolymers. EO/PO copolymers have good dispersing properties. They are
suitable in cases when deposit problems are an issue.
5. Polyacrylates
Alkyl polyacrylates are suitable as defoamers in non-aqueous systems where air
release is important.
6. Powder
Powder defoamers are used especially in detergents, cement and plastering mix.
When water is added to these products it is natural to promote foaming. Powdered
silica is one defoamer used in these products.
Chemistry of defoamers
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Defoamer application
1. Water treatment
Foams are formed in most of the water treatment processes like boiler steam
production, cooling water evaporation, waste water disposing, and sea water
evaporation to produce drinking water.
Polyoxylakylene glycol is used in boiler foam control as antifoaming additive. In
waste water effluent treatment a blend of polypropylene glycol, wax, fatty acid, seal
oil and hydrocarbon solvent mixture is used. Polypropylene glycol, polyethylene
glycol dioleate ester and surfactant blend is used in sea water evaporation units to
control foaming during drinking water production from sea water.
2. Paper and Pulp industry
Defoamers are the requirements in the paper and pulp industry, petroleum industry,
water treatment, paints and coatings, food and beverage processing, the mining
industry, textiles, agriculture, and the like.
Common defoamer compositions are generally composed of a carrier fluid, a
defoaming agent and miscellaneous additives
Foaming problems are solved by using compositions containing various petroleum
oil-based compositions with an alkylene diamide and/or hydrophobic silica (silicone
coated silica), as well as silicone emulsions and concentrates. The effective carrier
fluid is mineral oil. Water is also used in some preparations.
Oil based diamide defoamers (in paper and pulp industry) contain two
ingredients.wax of high melting point and carrier fluid (over 80%). Ethylene bis di
stearamide (3 to 10%) is used as wax diamide.
Usually silicone based defoamers are not recommended for paper industry as they
can cause deposition.
Polymers of Acrylate and methacrylate based defoamers are recommended for
paper industry. The formulation contains carrier, additive and surfactant apart from
acrylate polymer.
This formulation shows good controlling and destroying foaming in
 Kraft pulping process,
 sulfite pulping process,
 thermo-mechanical pulping (TMP) process
 chemical TMP (CTMP) process,
 ground-wood pulping process,
 carbonate pulping process,
 paper machine applications,
 screen room applications
 bleach plant applications, etc.
It prevents inhomogeneity such as craters and rough appearances due to entrained
air during the manufacturing of
 Paints and/or coatings for metal, wood, plastics, concrete, etc.
Methacrylates outperform acrylate polymer based defoamers. The most robust
performance is observed when the polymer contains acrylic acid as well as an alkyl
acrylate and a hydroxyalkyl acrylate.
In the soda and kraft pulping processes wood chips are cooked at elevated
temperature and pressure in a solution composed of sodium hydroxide (soda
process), or sodium hydroxide and sodium sulfate (kraft process). After draining off

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the spent cooking liquid (black liquor), the resulting fibre suspension, or pulp, is
washed free of residual black liquor in multi-stage, counter-current brown stock
washers. The washed pulp is then screened to remove knots, incompletely cooked
fibre clumps, and other foreign material. Black liquor has a strong tendency to foam,
even in dilute concentrations. Because of this, the control of foaming in black liquor-
containing liquids is a common problem in alkaline pulp mill
So defoamer composition used in black liquor should be applicable to control
foaming at high temperature, high pH of black liquor in soda and kraft brown stock
washers.
The defoamer compositions contain solid fatty acid diamide, hydrophobic silica
particles, and, optionally, silicone oil dispersed in a water insoluble liquid
hydrocarbon, together with a suitable non-ionic emulsifier.
Formulation
Recipe:
Mineral oil 13%
Hydrophobic silica 0.5%
N,N'-ethylene bis-distearamide 8%
Non-ionic emulsifier
(polyoxyethylene stearyl ether HLB 9.5) 2.5%
Water 76%
The resulting aqueous emulsion, containing 24% by wt. disperse phase, is superior
in effectiveness of controlling foaming of high temperature, high .pH black liquor in
the first stage brown stock washers of a West Coast kraft pulp mill when compared
with oil-based defoamer
Virtually all segments of the papermaking process generate entrained air and
surface foam which are extremely undesirable due to their harmful effect upon
process efficiency and the finished product.
A defoamer composition having concentrated active ingredients, such as a polyether
surfactant and a polyhydric alcohol fatty acid ester is particularly advantageous for
foam control and drainage enhancement in paper and pulp processes, general wet-
end foam control, ground wood/mechanical pulp systems, secondary fibre systems,
and bleach plants/screen rooms.
Defoamer composition to avoid deposition
The defoamer composition given does not contain oil, amides, hydrophobic silica or
silicone additives, thereby avoiding deposition and felt filling problems. The
suggested composition is;
 10-90% by weight of a polyether surfactant (polyoxyalkylated glycerol,
polyoxyalkylated sorbitol or sorbitan, polyoxyalkylated sucrose)
 10-90% by weight of a polyhydric alcohol fatty acid ester(diester of
polyethylene glycol and/or polypropylene glycol)
 Defoamer composition is added in a concentration in the range between
about 0.01-10.0 pounds per ton of paper produced
An antifoam formulation is recommended to make oil in water emulsion by using 30
to 50 percentage of defoaming agent (consisting essentially of particulate
hydrophobic Silica) in oil carrier, 2 to 5 % non-ionic surfactant (mixture of sorbitan
monooleate and sorbitan monolaurate, HLB number of between about 2 to 8.) and
remaining water.

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3. Dyeing bath
A silicone based antifoam formulation is suggested for dyeing bath to avoid uneven
dyeing with oil spots on the dyed product.
 60-70% of polyalkylene modified diorganopolysiloxane
 10-20% of a mixture of 85-95% of polydimethylsiloxane and 15%-5% of finally
divided silica powder.
 10-20% of poly(oxyethylene oxypropylene) copolymer having average mol
weight of 500-1000
 5-15% of polydimethylsiloxane (viscosity 10 to 5000cSt) with dimethyl
hydroxyl silyl terminal group.
4. Paint and Coating industry
A defoamer is often an essential component to a paint or coating. Without a
defoamer, bubbles will form in the paint or coating. When the paint or coating is
applied to the substrate, the bubbles will dry on the substrate. These dried bubbles
are not aesthetically pleasing. Furthermore, a substrate with dried bubbles is not
effectively covered and protected from the environment.
A defoamer composition with following items is recommended for paint & coating
industry:
(a) hydrophobic silica;
(b) a linear polysiloxane having end-blocked polyoxypropylene groups;
(c) a polysiloxane having a pendant polyoxypropylene group;
(d) a non-ionic Surfactant; and
(e) an inert diluent
The pendant group of component (c) is a polyoxypropylene group, and does not
contain a polyoxyethylene group.
An advantage of the defoamer is that it can be added to the paint formulation after it
is formulated and will not degrade even after an extended shelf life.
The defoamers can be stored at temperatures of 0o
C. to 40° C. for several months
(typically up to six or even twelve months) before using them without a phase
separation.
Typical formulation:
1. Polypropylene glycol (MW 2000) 48.6%
2. Hydrophobic silica 5.4%
3. Linear Polysiloxane where x = 15 11.9%
4. Pendant Polysiloxane where x = 65 and y = 8 24.1%
5. Polyethylene glycol monooleate 10%
5. Printing inks
Organopolysiloxane copolymers are used as defoamers for aqueous coating
systems and printing inks. For all water-based systems the use of defoamers is
widespread and often indispensible
Preparation: (US6,858,663B2) Butynediol etherified with about 1.1 mol of ethylene
oxide is reacted with a pendant hydrogen siloxane (SiH content: 4.62 eq/kg) at
140o
C in presence of catalyst (HPtCl4. 6H2O and RuCl3 H2O in isopropanol) at
10ppm of Pt and 10ppm Ru. The exothermic reaction is controlled by drop-wise
addition of SiH-siloxane. The reaction is quantitative. A clear, amber-colored liquid
having a viscosity of 639 mPas at 25o
C.was isolated as final product.

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The organopolysiloxanes for use can be employed, for the defoaming of polymer
dispersions, paints, and printing inks.
6. Food application
The below recommended formulation is used in food applications such as potato
washing, fermenting operations, or sugar production, applications in pharmacy, for
example, in the fermentation of penicillin or as an antiflatulence agent, in detergents
and cleaning products, in the control of foam in wastewater plants, in textile dyeing
processes, in the scrubbing of natural gas, in polymer dispersions, and when
defoaming aqueous media that are obtained in the production of cellulose.
Preparation: (US2006/0160908A1) Trimethylsiloxy-terminated polydimethylsiloxane
having a viscosity of 1000 mPas is mixed with pyrogenic silica (having a BET surface
area of 200 m/g) and precipitated silica (having a BET surface area of 165 m/g) and
demineralized water. The mixture is then homogenized at 1500 rpm for 5 minutes
(Water content of 0.08%). This mixture is baked at 150° C. for a period of 2 hours.
This gave an opaque formulation having a viscosity of 2240 mPas. The activity of the
defoamer formulation prepared is given below.
Antifoam index test
Above sample AFI = 2150
Comparative sample (commercial) = 5120
Testing
AFI determination
200 ml of 4% strength by weight aqueous solution of a sodium alkyl sulfonate
containing 10 mg of the test defoamer (in solution in 10 times the amount of methyl
ethyl ketone) is taken and shaken to foam for 1 minute using two counter-rotating
stirrers. Subsequently the collapse of the foam is recorded through a system of light
barriers and evaluated using a PC. The area of the plot of foam height versus time is
used to calculate the antifoam index (AFI) (The lower this index, the more effective
the defoamer).
References