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Foam Control Technology
Historical Defoamers/Antifoam
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Fat/Lard
Kerosene
Silicone fluid
Refined petroleum distillates
Why Is Foam A Problem?
 Equipment failure
 Loss of plant efficiency
 Product defects
 Voids in inks, paints and coatings
 Adhesion loss
 Spots in textiles
 Safety hazard
 Eyesore
 Environmental hazard
What Causes Foam?
 Foam is a result of contamination of a pure
liquid
 Contaminants
 Dirt
 Surfactants
 Pigments
 Metabolized waste
Important Things To Remember
 Foam Control is generally physical,
not chemical
 Foam Control works because it is not
similar to the foaming media
 Defoamers/antifoams must be somewhat
insoluble in the foaming media
Surfactant Chemistry
 Surfactants are a
chemical entity
consisting of a
hydrophillic
(water-loving) and
hydrophobic
(water insoluble) tail
Foam Origins
 A gas is entrained into
the media
 Mechanical
 Mixers inducting air
 Pump cavitation
 Chemical
 Reaction produces a gas
Bubble Physics
 Ability of entrained air to escape depends upon
Stokes Law.
V = r2/η
V=
r=
η=
Rate of rise
Radius of bubble
Viscosity of media
Foam Formation
 Once a bubble is
formed, it begins to
rise to the surface
 As it rises, surfactants
are trapped between
the surface of the
media and the
surface of the bubble
Foam Stabilization
 As the bubble rises it
comes in close proximity
to the surface of the
media
 A liquid lamella forms
between the surface of
the bubble and the media
surface
 The surfactants begin to
orient themselves to the
lowest thermodynamically
stable state
Surfactant Orientation & Result
 The hydrophillic end
of the surfactant
extends into the liquid
lamella
 The hydrophobic end
resides at the surface
of the media and the
surface of the media
Stable Foam
 The interaction of the charges associated with the
hydrophillic heads result in a force towards the surface of
the media and the surface of the bubble
 Atmospheric pressure exerted on the media surface
results in a force pushing in towards the media
 Gas pressure from within the bubble exerts a force
towards the media
 Result is stable foam that can and will shut down most
major equipment
Defoamer Vs. Antifoam
 Defoamer is a term usually associated with a
non-silicone foam control agent
 Antifoam is usually associated with a silicone or
silicone emulsion
 Any foam control agent added to a pre-existing
foam works as a defoamer
 Any foam control agent added before the
formation of foam to help prevent it is an
antifoam
Defoamer Method Of Action
 A defoamer is added to a
foaming system and
quickly spreads to a
monolayer across the
surface
 Due to the rapid
spreading, the underlying
liquid is pulled in the
direction of the spreading
Foam Control Begins
 As the underlying liquid is
pulled apart by the
spreading of the defoamer,
the outer lamellar wall
begins to thin until it finally
breaks and a hole develops
in the wall
 The defoamer then spills
thru the hole into the liquid
lamella and quickly begins
to spread across the inner
lamella wall
Foam Destabilization
 As the defoamer spills
into the lamella, the
particulate in the
defoamer attaches to the
outer wall which prevents
the wall from reforming
due to elasticity
 This repeats as the inner
wall is broken
Bubble Rupture
 As the particulate attaches to
the inner wall, the lamellar fluid
is expelled due the surface
charge associated with the
particulate
 The lamlla quickly drains and
thins until the the inner and
outer walls are all that is left
 The two walls pull away from
the particulate and the gas is
released
Factors Required For Defoaming
 The liquid phase of the defoamer must have a
degree of incompatability with the media into
which it is dosed
 The liquid must have a rapid spreading
coefficient so that it spreads across the media
 The hydrophobic particle works on a semispecific contact angle, so it must be the correct
size and shape
Defoamer Chemistry
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Defoamers consist of three main
components
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Liquid vehicle
Emulsifier/spreading agent
Hydrophobic particle
Building Foam Control Products
The Vehicle
 Does the bulk of the work
 Requirements
 Must be a liquid
 Must have a high spreading rate coefficient
 Must have some degree of incompatibility with
the media
Building Foam Control Products
The Vehicle
 Can be
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Silicone/organosilicone oil
Vegetable oil or some derivation thereof
Synthetic polymer or ester thereof
Mineral oil/white oil
 Aliphatic (paraffinic)
 Naphthenic
 Aromatic (mineral seal oil)
 LOPS
Building Foam Control Products
The Vehicle
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Silicone/organo silicone oil
Vegetable oil or some derivation thereof
Synthetic polymer or ester thereof
Mineral oil/white oil
Hydrophobicity
 Hydrophobic character
Building Foam Control Products
The Emulsifier/Spreading Agent
 Chemical entities
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Silicone/organo surfactants
Ethoxylates
Fatty esters
Alcohols
Building Foam Control Products
The Activator/Hydrophobic Particle
 Chemical entities
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Fatty amides
Fatty esters
Fatty alcohols
Fatty acids
Metal stearates
Silica
Urea compounds
Foam Control Technology