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Thickeners/Rheology Guide
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Rheology
Rheology is dened as the study o the deormation and fow o materials. When a orce is applied to a liquid, the
liquid will fow to relieve the strain rom this orce. Dierent systems will resist this fow more than others and the
measurement o this resistance is a measure o the viscosity o the system. Newton rst introduced a basic model or
the fow measurement o a liquid between two parallel plates and this is represented in gure 1.
Area A
Upper moveable plate
y
x
Lower fixed plate
Force F
Speed v
gure 1
Newtonian Fluid
Shear Rate
Viscosity
Newtonian Fluid
Shear Rate
SheerStress
02 Scott Bader Thickeners/Rheology
Newtonian Fluids examples include water, certain oils
and dilute resin solutions. The viscosity o a Newtonian
fuid is independent o shear rate or put another way the
rate o deormation is directly proportional to the applied
orce. This is shown in the two dierent plot types below:
Using this model a number o common rheology terms
can be dened as ollows:
Shear Stress the orce experienced by the liquid is
proportional to the area o the upper plate and is dened
as the shear stress, = F/A (Units = Nm-2 or Pascals [Pa])
Shear Rate the velocity gradient or the rate o change
o velocity at which one layer passes over an adjacent
layer is the shear rate, = dv/dx (Units = s-1)
Viscosity this is expressed mathematically as, = shear stress/shear rate and is the measurement o
the resistance to fow o a fuid. Pascal.second (Pa.s) is
the basic unit o viscosity, but Poise or centpoise (cp =
one hundredth o a Poise) is oten used and one cp is
equivalent to a millpascal-second, mPa.s. When quoting
viscosities the shear rate (or measurement method/
equipment used) should be stated together with the
temperature at which the measurement was taken.
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Dilatant Fluid
Shear Rate
Viscosity
4) Rheopexy rheopectic fuids show the oppositebehavior to thixotropic fuids i.e. they increase in
viscosity over time or a given shear orce until a
maximum is reached ollowed by a viscosity reduction
over time when the shear is stopped. This type o
behavior is extremely rare.
Pseudoplastic Fluid
Shear Rate
Viscosity
Pseudoplastic Fluid
Shear Rate
ShearStress
Thixotropy
Shear Rate
Viscosity
hysteresisarea
>
>
Scott Bader Thickeners/Rheology 03
2) Dilatancy dilatant fuids show the opposite type o
behavior to pseudoplastic systems i.e. they show an
increase in viscosity as the shear rate increases (shear
thickening). It is seen in highly concentrated
suspensions or slurries. This type o behavior is
relatively uncommon, but is represented in theplot below:
1) Pseudoplasticity a large number o liquids show alarge decrease in viscosity when the shear rate is
increased and this type o fow is dened as
pseudoplastic or shear thinning behavior. Emulsions,
suspensions and dispersions are typically
pseudoplastic as are many paint, ink and adhesive
systems. At higher shear rates the fow behavior
becomes more linear (Newtonian). A related type o
fow behavior is that o plastic materials, which
initially resist deormation until a certain yield stress
is reached. Beyond this point the fow is then that o a
pseudoplastic fuid. Pseudoplastic behavior is
portrayed below in two dierent plot types:
Non-Newtonian Systems many systems show
behavior that deviates rom that o simple Newtonian
fow and examples o this are dened below:
3) Thixotropy or thixotropic liquids the viscosity
decreases over time or a given shear rate until a
minimum is reached. Once the shearing orce is
stopped the viscosity recovers over time. The degree
o thixotropy can be represented by what is termed a
hysteresis area This is typical o the behavior observed
in gelled paints applied to a vertical surace, where the
viscosity reduces under the shear o the brush or roller
and then recovers to prevent sagging. This is
represented in the plot below:
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Brookfeld Viscometer Low to medium shear
Stormer Medium shear
ICI Cone and Plate High shear
Rheometer Low to high shear
04 Scott Bader Thickeners/Rheology
Practical Rheology or Surace Coatings and
Adhesives ormulators use a number o viscometer
types and methods to measure and understand the
behavior o their systems. Some common viscometer
types are listed below together with the shear ranges
they typically represent:
The Brookeld viscometer is a very common type that is
simple to operate and is oten used as a QC tool to check
a single viscosity measurement at a specied
temperature, and they can also be used to get a basic
rheology prole under lower shear conditions. For a more
complete understanding o the rheology prole o yoursystem it may be necessary to use a rheometer that can
make multiple measurements over a wide shear range. It
is also worth mentioning that various dierent fow cup
types exist and are used as QC tools and to check
viscosities in production. They measure the time taken or
a set volume o fuid to fow through a given size o orice
in the bottom o the cup and are not truly viscometers.
However, the fow time is related to the viscosity o the
liquid and higher viscosity liquids take longer to fow
through the hole.
Many paints and adhesives show either pseudoplastic or
thixotropic behavior and thus show a viscosity reductionwhen sheared. A knowledge o the rheology o a system
can be very useul in understanding its stability and fow
behavior under dierent shear conditions. Settling,
sagging and levelling occur under very low shear
conditions whereas application o the coating or adhesive
generally happens under relatively high shear conditions
e.g. brushing, spraying and rolling. Pumping and general
mixing o ingredients are carried out at low to medium
shear rates. Paints oten require a degree o levelling
ater application, so it may not be desirable to have ast
recovery o viscosity. However, too slow a recovery can
lead to sagging and dripping. Other systems may require
more instantaneous recovery o viscosity. In such cases a
knowledge o the fow behavior imparted by dierent
thickener systems will aid selection o the best product
or the job.
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Stabilizers
Stabilizers
Scott Bader Thickeners/Rheology 05
Scott Bader
Inverse Emulsion Thickeners
Conventional emulsions, in technical terms, are oil-in-
water emulsions i.e the continuous phase is water.
Inverse emulsions are simply the opposite i.e water in oil
emulsions with the continuous phase being an oil. Texipol
inverse emulsions are manuactured directly rom the
pre-neutralized liquid monomers that are intimately
dispersed in the oil phase ollowed by a controlled
polymerization process to yield the liquid thickener. The
diagram below shows the essential dierences between
conventional and inverse emulsions.
Mechanism and Benefts o Texipol
Inverse Emulsion Thickeners
When Texipols are added to water or a waterborne
system, the Texipol inverts with the help o the watersoluble emulsiers and water becomes the continuous
phase. The hydrophilic polymer particles swell rapidly
and the resulting highly swollen structure leads to a rapid
increase in viscosity.
Texipol thickeners are supplied in a pre-neutralized orm
which means there is no requirement or additional alkali
or suractant to achieve thickening. In most applications,
Texipol thickeners can be added at any stage o
ormulating, including post-thickening o systems, thus
allowing greater fexibility when ormulating.
In general terms a thickener has 3 unctions to ull
in a typical ormulation:
a. To increase viscosity
b. To stabilize the dispersion o insoluble components
such as pigments
c. To modiy the fow.
Formulation Guidelines or Texipols:
Product selection: The rheology, fow and viscosity
eciency is dependent on other ingredients in a
ormulation. Dissolved salts and suractants are known to
eect both the fow and eciency o a Texipol thickened
solution.
To determine the concentration level o Texipol
required in a ormulation: The exact amount o
thickener required can only be determined by
experimentation and depends on the required viscosity
and the nature o the other ingredients in the ormulation.
For typical applications o Texipols where paste-like
viscosities are required, start with a 2%
(by weight) addition level o Texipol and increase the
amount until the desired viscosity is achieved. For lower
ormulation viscosities, 1% or less o the Texipol may be
needed. Since the polymer is preneutralised the
thickening eect is almost instantaneous under high
shear stirring and can be added to thicken a ormulation atany stage o the manuacturing process. Additional
Texipol can be added at the end o a batch to conveniently
adjust the viscosity up to the target level.
How to add: The batch to be thickened should
be thoroughly and uniormly mixed to achieve a
homogenous product and to avoid local thickening. High
shear mixing is recommended or the best results.
Problems can arise i the stirrer is too slow or too small
and does not move the total batch (i.e. a localized
thickening eect is noticed around the blade, and the mix
is not homogenous.) Texipol is shear stable, but it does
shear thin.
What to avoid: High concentrations o dissolved salts
and some suractants will dramatically reduce the
viscosity eciency o Texipol. The presence o polyvinyl
alcohol emulsions can cause sharp viscosity increases in
some inverse emulsion thickened compounds.
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1) 63-201: 1% in DI water Brookeld RVT, Spindle 3, 50 rpm, @ 25C. 2) 63-202: 4% in DI water Brookeld RVT, Spindle 6, 5 rpm, @ 25C.3) 63-253: 2% in DI water Brookeld RVT, Spindle 6, 5 rpm, @ 25C. 4) 63-237: 2% in DI water Brookeld RVT, Spindle 6, 5 rpm, @ 25C.5) 63-258: 2.5% in DI water Brookeld RVT, Spindle 6, 5 rpm, @ 25C. 6) 63-510: 4% in DI water Brookeld RVT, Spindle 6, 5 rpm, @ 25C.
Viscosity of water when Mixed with 2% Texipol
Shear rate (s-1)
Viscosity of water when Mixed with 2% Texipol
Shear rate (s-1)
0.01
0.1
1
10
100
1000
0.1 1 10 100 1000
Viscosity(Pa.s=
1,0
00cP)
Texipol 63-201
Texipol 63-202Texipol 63-237
Texipol 63-253
Texipol 63-258
Texipol 63-510
06 Scott Bader Thickeners/Rheology
Texipol Flow Typical thickenedviscosity mPa.s Typical pHusage range
63-201 Long stringy 700 1) 5.0 - 12.0
63-202 Short 35,000 2) 5.5 - 11.0
63-237 Extremely short 30,000 3) 6.0 - 12.0
63-253 Extremely short 45,000 4) 6.0 - 11.0
63-258 Extremely short 100,000 5) 6.5 - 10.0
63-510 Short 100,000 6) 2.0 - 12.0
Rheology Curves :
Texipol selection chart
This chart is intended as a guideline to use when selecting a grade o Texipol or certain applications.
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Effect of pH on the Viscosities of Water and Texipol Solutions
[2.0% Texipol in Water and @50 s-1]
pH of the Solution
Effect of pH on the Viscosities of Water and Texipol Solutions
[2.0% Texipol in Water and @50 s-
pH of the Solution
100
1000
10000
0 1 2 3 4 5 6 7 8 9 10 11 12
Viscosity(Pa.s=
1,0
00cP)
Texipol 63-201
Texipol 63-202Texipol 63-237
Texipol 63-253
Texipol 63-258
Texipol 63-510
Scott Bader Thickeners/Rheology 07
NOTICE: The inormation and recommendations in this publication are, to the best o ouractual knowledge, reliable. Suggestions made concerning uses or applications are only
the opinion o Scott Bader, Inc. and users o these products should make their own tests
to determine the suitability o these products or their own particular purposes. Because
o the numerous actors beyond our control aecting the results o the use o these
products, SCOTT BADER, INC. MAKES NO WARRENTY OF ANY KIND, EXPRESSED OR
IMPLIED, INCLUDING THOSE OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE, OTHER THAN THAT THE PRODUCT CONFORMS TO ITS APPLICABLE CURRENT
STANDARD SPECIFICATION.
Suggestions or uses o our products should not be understood as recommending
the use o our products in violation o any patent.
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Speciality Polymers
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