Chapter 8
Dynamic Rheological Properties
Abstract
In this chapter melt rheological behaviour of
nylonEPDM blends has been investigated. The effect of blend
composition, compatibilisation and dynamic vulcanisation on
the rheological behaviour is discussed in detail. The interfacial
tension between the polymers is calculated from the storage
modulus of the blends using Palierne model and Choi-
Schowalter equation. The effect of compatibilisation on the
interfacial tension between the polymers is discussed. Attempts
were made to correlate the phase morphology with rheology.
276 Chapter 8
8.1 Intraduction
Rheological studies are useful for optimising processing conditions
and understanding the effect of various parameters on flow behavoiur of
materials. Knowledge about the processability of a blend under high
frequency is essential for the fabrication of articles of good finish and
dimensional stability. Now a days dynamic rheological measurement has
received much attention as an extremely powerful rheological technique,
which offers several advantageous over the conventional steady shear
rheometry because of its unique ability to assess and provide important
dependence of rheological properhes and on the physical and micro structure
of materials without disturbing the conformation of the material. In this
technique, a sinusoidal varying strain is imposed on the polymeric material
and the resulting stress is separated into pure elastic and viscous responses
from which useful information on the melt rheology and processing
characteristics can be obtained.
The rheological properties of the components in immiscible
polymer blends affect the processing, morphology and property
relationships [I-31. A large number of studies have been reported on the
melt flow behaviour of TPEs from plasticfrubber blends. Danesi and Porter
141 reported on the rheology-morphology relationships in the blends of
polypropylene (PP) and ethylene propylene rubbers (EPR). Utracki and
Kamal [5] have reviewed the rheological behaviour of m y polymer
blends. Increase in the viscosity upon the incorporation of rubber in a
plastic phase has been reported in PVClENR 161, PP/NR 171, HDPE/NR
[8], and PPfEPDM 191 systems [6-111. Melt rheology and morphology of
nylon6lethylene propylene rubber (EPR) blends were studied as a function of
composition, temperature and compatibiliser loading by Oornmen et al. /12].
Dynamic Rhsologrgrcd Prope&'es 277
Recently many researchers reported about the rheological investigations of
different polymer blends [I 3- 191.
It has been reported in the literature that reactive compatibilisation
has extensive impact on the rheological properties [20-231. Hong et al. [21]
studied the compatibilisation effect on a recycled PPPA blend processed
with reactive copoIymtrs on the basis of morphological, and rheological
characteristics.
Several researchers have studied the effect of dynamic
vulcanization on the rheological behaviour of rubber/plastic blends [24-281.
It has been reported that the viscosity of the blends increased as the
crooslink density [24]. Kumar et al. 1251 studied the effect of various
vulcanizing agents on the rheoIogicd behaviour of nylon/NBR blends.
The rheology and morphology of multiphase polymer blends are
strongly affected by interfacial characteristics. Several models have been
proposed to describe the influence of compatibilisers on the deformation of
dispersed phase to rheological parameters such as the complex shear
modulus (G*), the storage modulus (G') and the loss modulus (G") [29-361.
Palieme model has widely been employed to depict the rheological
response of various blend systems [37-421. Friedrich et d. [38] reported
that the particle size distribution could be derived from measured data if the
interfacial tension is known. On h e other hand, interfacial tension can also
be estimated from particle size distribution using the Palierne model as
shown by Asthma et d. [37] and Shi et al. [40] Asthana and Jayaraman
[373 have investigated the rheology of reactively compatibilised polymer
blends with varying extent of interfacid reaction and found that the
rheology of the reactive blends fit to the Palierne theory to infer vaIues of
the equilibrium interfacial tension. Shi et al. [40] used PaIierne emulsion
278 Chapter 8
type model to describe the relationship between the rheological response to
small amplitude oscillatory deformation and morphology of PPPA6 blends
compatibilised witb maleic anhydride grafted PP.
In this chapter, we made an effort to investigate the rheological
properties of the nylon EPDM blends. Using dynamic rheological method,
viscoelastic properties such as complex viscosity, storage modulus and loss
modulus of uncornpatibilised, cornpatibilised and dynamically vulcanised
blends were evaluated. Attempts were made to correlate the phase
morphology with rheological data. Finally, the experimental results were
used to determine the interfacial tension using and Palierne model Choi-
Schowalter model.
8.2 Results and Discussion
8.2.1 Uncompatibilised blends
The frequency dependence of the complex viscosity (q*) of
uncompatibilised blends at 190°C is depicted in the Fig. 8.1. It is evident from
the curve that the complex viscosity of the pure components and their blends
decreases witb increase in frequency. This is an indication of the pseudoplastic
behaviour of the polymer and their blends. With the increase in the frequency
the shear rate increases. The pseudoplastic nature of polymers arises from the
randomly oriented and entangled nature of polymer chains that, on application
of high shear rate, becomes disentangled and oriented in the direction of shear
1431. As a result of this, the resistance of the chains moving past on another
decreases. It is seen from the figure that EPDM has got a much higher
viscosity than nylon in all range of frequency carried out in this experiment.
The complex viscosity of all the blends is found to be intermediate between
the neat polymers in such a way that addition of EPDM into nylon increases
the complex viscosity. The greater the content of EPDM was, the higher was
Dynamic Rheological Propertr'es 279
the viscosity. Such an increase in viscosity on incorporation of rubber phase
has been reported for several systems [6- 1 11. The increase in viscosity is due to
the entanglement of molecular chains of bath nylon and EPDM. Because of
the suf5cient long and flexible molecular chains, EPDM chains can entangle
themselves and also with the nylon chains. These entanglements oppose
severely the flow of the melt at low shear rates, and consequently, the viscosity
becomes higher [44]. However, the disentangling effect is much greater than
entangling one at high shear r a m , because the repulsion between EPDM chain
and the segment of nylon arises from incompatibilisation of both of them [45].
As a result, nylon/EPDM blends showed lower viscosities than pure EPDM.
In polymer blends, the viscosity depends on the interfacial adhesion in addition
to the characteristics of the component polymers. This is because, in polymer
blends there is an interlayer slip along with the orientation and
disentanglement on the application of shear stress. From the Fig. 8.1 it is seen
that the complex viscosity of the nylon/EPDM blends shows a negative
deviation and this indicates the incompatibility of the blends.
0 1 , .1.0 -0.6 0.0 0.6 1.0 1 6 20
Log Frequency (Hz)
Figure 8.1: Effect of blend ratio on the complex viscosity of uncompatibilised nylon/EPDM blends
280 Chapter 8
Utracki and Sammut [46] showed that, positive or negative deviations of
the measured viscosity is an indication of strong or weak interactions
between the phases of the blend according to the relation
In (q, ) blend = C W- (?,p ) i i
where W, is the weight fraction of the ith component of the blend. They
indicated that immiscible blends show negative deviation due to
heterogeneous nature of the components. Thus the observed negative
deviation is due to the incompatibility between the phase and interlayer slip.
It is also important to note that the viscosity ratio of EPDM and
nylon is very much sensitive to the frequency fluctuation due to their highly
incompatible nature. This is evidenced from the Table 8.1, which shows h e
viscosity ratio of the polymers at selected frequencies.
Table 8.1: Viscosity ratio of EPDM and PA at various frequencies
ratio ( ~ E P D M ~ PA)
38.1
14.4
9.6
4.2
3.0
2.6
2.4
2.1
1.9
Frequency (Hz)
0. I
0.5
1
5
10
15
20
30
50
Complex viscosity (q *)Pa.s
EPDM
1 13000
40200
24900
8360
5020
3700
3030
2200
1520
Nylon
2960
2800
2590
20 10
1660
1450
1280
1080
800
As the frequency increases the viscosity ratio decreases. It should also be
noted that the viscosity difference between the polymers has significant
impact on the phase morphology of the blends. The SEM micrographs of
the bIends are given in the Chapter 3, Fig. 3.2.The large difference in
viscosity with respect to frequency will reflect on the phase morphology
stability of the blends and thereby the ultimate properties. If the minor
component has lower viscosity compared to the major one, it will be finely
and uniformly dispersed in the major continuous phase owing to the
diffusional restrictions imposed by the matrix 1471 and othemise coarsely
dispersed.
Wu's equation
(where D is the droplet diameter 77, the viscosity of the matrix, p the
viscosity ratio of the droplet phase to the matrix, j the shear rate and r the
interfacial tension.) suggests that minimum particle size is achieved when the
viscosities of the two phases are closely matched and the dispersed particles
become larger [48] as the viscosity moves away form unity in either direction.
Since there is a large difference between the viscosities of the two polymers as
seen in Table 8.1 one can expect a considerable difference between the phase
morphologies of nylon rich and EPDM rich blends and a co-continuous
morphology. Since the polymers in molten state are sensitive to frequency
change and therefore to shear rate, it can be expected that the phase
morphology of nylon/EPDM uncompatibilised blends will be coarse, non-
uniform and unstable. All these facts are found to be true in nylon/EPDM
system and thus it is believed that there is perfect correlation between the
morphology and rheology of uncompatibilised nylon/EPDM blends.
282 Chapter 8
Lag Frequency (Hz)
Figure 82: Effect of blend ratio on the storage modulus of uncompatibilised nylonlEPDM blends
Figs. 8.2 and 8.3 show the storage modulus (G') and loss modulus (G") of
various nyloriEPDM blends with different compositions at 190°C as a
function of frequency. It is found that storage and loss moduli show similar
variations with the composition of the blends. Both storage and loss moduli
are greater for EPDM compared to nylon. As seen from the graph, storage
and loss moduli increase with frequency. This is due to the fact that the
polymer chains get less relaxation time with the increase in frequency. Here
also the storage modulus and loss modulus of all the blends are found to be
intermediate between the neat polymers. As we know, G' can reflect the
elasticity of the samples, it is confirmed that elasticity is enhanced with the
incorporation of EPDM. At higher frequencies storage modulus and loss
modulus of nylon increased substantially.
Dynumic Rheological Properties 283
Log Fquency (Hz)
Figure8.3: Effect of blend ratio on the loss modulus of uncompatibilised nylon EPDM blends
Nylon melt shows q*, G' and G" values lower than that of EPDM
rubber. It was reported that all the dynamic viscoelastic property values
would increase with molecular weight increase, at a given frequency [49j.
Here the results inhcated that nylon could have molecular weight very
much lower than that of EPDM rubber. It is well evident in the Chapter 2.
The molecular weight of nylon copolymer is about 38,000 and that of
EPDM is 1,68,000glmol.
8.2.2 Compatibilised blends
The effect of compatibiliser incorporation on the rheological
properties of 70130 blend of nylon and EPDM is shown in the Figs. 8.4-8.6.
As shown in the Fig. 8.4, the complex viscosity of the blends increased as the
amount of compatibiliser loading increases up to critical micelle
concentration (CMC) in the whole frequency range. The increase in complex
viscosity can be taken as an evidence for the compatibilising action of EPM-
g-MA. The viscosity increase is due to the grafting reaction which takes
place betweensanhydride group in EPM-g-MA and arnine group in nylon.
The increase of molecular weight through the grafting reaction is believed to
be the major reason for the viscosity increase of blends. In fact, the
compatibiliser decreases the interfacial tension, and interaction between
nylon and EPDM is greatly enhanced. The graft copolymer locates at the
blend interface and thereby holds the two phases together. The localization of
the compatibiliser at the interface makes the interface less mobile, more
broad and stable. This has been schematically shown in the Fig. 8.7
--- . . -
-0- N,,
Figure 8.4: Effect of compatibilisation on complex viscosity of NTO nylon/EPDM blends containing different levels of compatibiliser
5 -
4- - $ 3 - U
Y 2 -
1 -.
0 - 1 . .O 5 0.0 0.5 1 0 5 2.0
Log GIPa)
Figure 8.5: Effect of compatibilisation on the storage modulus of N70 nylo W D M blends containing different levels of cornpatibiliser
I
, 1
--. - N,,
-O- Nm.1
- *- Nm,2,,
-v- %>,S
-O- N,,,
Dy-ic Rkeological Properties 285
Log Frequency (Hz)
Figure 8.6: Effect of compatibilisation on the loss modulus of N70 nylonEPDM blends containing different levels of compatibiliser
(a) In the absence of copolymer
I ntniface
EPDM
Nylon
Narrow and mobile interface
Big dispersed phase size
High interfacial tension
286 Chapter 8
(b) In the presence of compatibiliser (below CMC)
J- Nylon
Broad and less mobile interface Small dispersed phase size
a Smaller interfacial tension
(c) In the presence of compatibiliser (above CMC)
a Broad and less mobile interface Small dispersed phase size Smaller interfacial tension
Figure 8.7: Schematic representation of the interface in the absence and presence of a compatibiliser
Similar observations were reported by Wang et al. 1201 for PA6/EPDM-
g-MA, Hong et a1.[2 11 for PA6PP systems and Van et al. [SO]. In the case of an
incornpatibile blend, due to the presence of sharp interface and poor interaction
between the homopolymer phases, there occours a high extent of interlayer
slippage between the phaqes. Upon the addition of the compatibiliser, there will
be less slippage at the interface. However, it should be noted that, beyond CMC,
at high concentration of the compatibiliser (lo%), the complex viscosity is even
Dynamic Rkeoiogical Propsdies 287
lower than that of the uncompatibilised blends. The decrease in the viscosity
may be due to the cumulative effect of the micelle formation and the lower
viscosity of the EPM-g-MA. These observations are in perfect correlation with
the phase morphology of the blends in Chapter 4, Fig. 4.5.
Figs. 8.5 & 8.6 show the effect of compatibilisation on the storage and
loss moduli of the 7W30 nylon and EPDM blends. It is obvious from the Fig. 8.5
that storage modulus of compatibilised blends shows a linear increase than that
of uncompatibilised blends. The increase in storage modulus is an indication of
the pronounced elastic properties of the blends due to enhanced interfacial
adhesion in the presence of compatibiliser. It should be noted that beyond CMC,
the storage modulus decreases. Here also the above reason (section 3.2) holds
good. As shown in the Fig. 8.6, the tendency of the loss modulus is similar to
that of the storage modulus.
Only a very few studies have been published on the systematic
investigation of the effect of the frequency on the rheologid properties of
dynamically vulcanised rubkr/plastic blends [51,52]. It was shown that fully
cured thermoplastic vulcanisates exhibit highly pseudoplastic behaviour. Han
and White [26] have studied the rheological behaviour by various measurement
techniques and concluded that the dynamically vulcanised blends show
behaviour, which is characteristic of materials with a rest state structure.
Mainovic et al. (531 confullled that stronger crosslinking contributes to the
formation of more rigid EPDM domains dispersed in the continuous phase.
Figs. 8.8, 8.9 and 8.10 illustrate results of complex viscosity rl*,
storage modulus G' and loss modulus G" versus frequency for the
nylon/EPDM for simple and dynamically cured samples prepared in an
internd mixer. Different crosslinking system under investigation is sulphur,
288 Chapter 8
peroxide, a mixture of sulphur + peroxide and a mixture of sulphur + peroxide + compatibiliser. The types of crosslinks formed during vulcanization were
desmibed in (Chapter 5, Fig. 5.7). The type of crosslinking system on the
complex viscosity of 70130 blend of nylon/EPDM is presented in Fig. 8.8. All the
curves indicate that the viscosity decreases with inmasing frequency, which
shows pseudo plastic kehaviour of the system. The i n a w e in the viscosity of the
vulcanised samples compared to the unvulcanised system is due to the decrease
in the mobility of the polymer chains due to the three dimensional crosslinks
formed durbg vulcanization. Among the four vulcanised systems used, it is
found that viscosity is highest for sulphur cured system followed by mixed -t
compatibiliser system, mixed system and DCP cured system. In the case of
peroxide there is a little chance for the degradation of nylon at higher
temperame, As a result, viscosity decreases. In the mixed system the degradation
of nylon over shadows the effect of crosslinking. In the mixed system with
compatibiliser, in addition to the crosslinks some chemical bonds also present.
This also helps to enhance the viscosity of the system.
o c -1.0 0.5 0.0 0.5 1.0 1.5 2.0
Log Frequency (Hz)
Figure 8.8: Effect of dynamic vulcanization on complex viscosity of N70 nylon/EPDM blends containing different types of crosslinking systems
Dynamic Rheological Properties 289
One can notice that crosslink density (Chapter 5 Table.5.2) plays an
important role in the viscosity change. The morphology of crosslinked
samples was shown in the Fig. 5.2 (Chapter 5). The nylon/EPDM blend
vulcanised with sulphur system has got the lowest domain size while the
blend vulcanised with peroxide has got the highest. The blend vulcanised
with mixed system and mixed with compatibiliser has got a domain size in
between those of sulphur and peroxide cured systems.
-1.0 4 . 5 0 0 0 6 0 1'5 2:0
Log Frequency (Hz)
Figure 8.9: Effect of dynamic vulcanisation on storage modulus of N7rj nylonlEPDM blends containing different types of crosslinking systems
. -
crosslinking systems
6 -
4 -
4 e ,- J b
9 2 -
1 - O d
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Log Frequency(H2) Figure 8.10: Effect of dynamic vulcanization on loss modulus of N7"
nylonlEPDM blends containing different types of
,
N , - N,lS -+ N,D +- Nn,SD -0- N,SDtComp
Fig. 8.9 and Fig. 8.10 show the storage modulus (G') and loss
modulus (G") of vulcanised nylonlEPDM blends. By comparing these
results, one can clearly notice that the melt viscoelastic properties of the
TPV samples, are considerably different from those shown by the simple
blend sample. From the figure it is clear that the storage modulus and loss
modulus of vulcanised blends are higher than that of the nylon /EPDM
binary blends. The increase in the values shows the same trend as in the
case of complex viscosities. During dynamic vulcanisation the crosslinked
rubber phase becomes finely and uniformly distributed in the plastic matrix
and attains a stable morphology. The morphological transformation as a
result of dynamic crosslinlung is schematically shown in Fig. 8.1 1. It can
be concluded that the increase in the vdues is due to the improved
miscibility of the nylon and EPDM because of the vulcanisation.
Sulphur eroarlinksd
EPDM domains Nylon Phase Ctooslinksd E PD M domains
Flylan
DCP crosslinked
domains
Figure 8.11: Schematic representation of the morphology of nylon/EPDM blends vulcanised with sulphur and peroxide
8.2.4 Palierne model
8.2.4.1 Theoritical basis
Palierne model describes the linear viscoelastic behaviour of
viscoelastic fluids. It has been shown to be very useful for predicting the
rheolagicd behaviour of the immiscible blends [34, 32, 35, 54-56)]. The
model was used to determine the interfacial tension between the
components [34,57], to determine the volume average radius of the
dispersed particles [58]. to calculate the sphere-size distribution from
rheological data [38], to analyse the deformation of droplets under
elongational flow 1591. Pdierne derived an equation for predicting the
complex modulus of molten (emulsion type) blends (Gb*), which is a
function of the complex moduli of both phases G,* (for the matrix) and
a* (for the inclusions or dispersed phase) Palierne model has taken into
account of the viscoelasticity of phases, the hydrodynamics interactions, the
droplet size and size distribution and the interfacial tension of a multiphase
system.
Jacobs et al. [60] developed an extended fonn of the Palierne
model, written as,
in which
292 Chapter 8
and
D(O, R) = [ 2 ~ : (co) + 3G: ( m ) ] [ l g ~ ; ( m ) + l6G: (a)]
where, Gl (o) , G: ( w ) and Gi (a) represent complex modulus of blend,
matrix and dispersed phase, respectively. P1(o) and ~ " ( o ) are the
complex interfacial dilation and shear moduli, respectively, U(R) denotes
the particle size distribution function while R, a and u, are particle radius,
interfacial tension, and strain frequency, respectively. When the
deformation of dispersed phase is small enough so that viscoelastic
properties remain linear, we can set both fl1 (o) and 0" (LO) to zero.
Graebling et al. [34] by assuming the particle size distribution to be
narrow (R/R" <- 2)) and interfacial tension to be independent of shear and
interfacial area variation, simplified equation as:
where
(4a/~,)(~~,(m)+5~;(fl))+(~~(~)-~;(~))(~~~:(~)+l~~~(m)) ---,-A- ...( 8.7) H' (#) - ( 4 0 a / ~ i ) ( ~ : (a ) + G: (N) ) + ( 2 ~ ; (a) - 3G. (#))(]%, (a)+ 19~: (.))
Dynamic Rheological Properties 293
in which, Ri and #i denote the ith particle fraction radius and the ith volume
fraction of dispersed phase, respectively. The interfacial tension can then be
estimated by fitting the experimental data to the Palierne model. Using ( a )
as fitting parameter, the best fit gives the interfacial tension.
8.2.4.2 Interfacial tension calculations
The interfacial tension can be calculated on the basis of the
weighted relaxation spectrum (.cH{,,) with the relaxation time (T) for
nylonlEPDM blends. In order to get the weighted relaxation spectrum the
following equations were used:
the relaxation spectrum can be determined using Tschoegle approximation
[6 1 ] as given in following equation:
where crl is the frequency and z is the relaxation time. It should be noted for
neat polymer one will get one relaxation time where as for blends two r
( r , and z,) will be there corresponding to the component polymers. The
difference in the values (z, -t,) was used to calculate the interfacial
tension between the polymers in the presence and absence of
compatibilisers. The interfacial tension ( a ) was calculated using two
294 Chapter 8
methods:(i) Palierne [29] (equation 8.1 1 and (ii) Choi-Schowalter [30]
(equation 8.12).
where rl, is the viscosity of the matrix, # is the volume fraction of the
dispersed phase, K is the viscosity ratio and is given as K = r~d/??, (% is
the viscosity of the dispersed phase).
Table 8.2: Interfacial tension values of uncompatibilised nylon/EPDM blends
The interfacial tension values of nylonlEPDM blends calculated from these
equations are given in Table 8.2. In both cases, Palierne model gives lower
values. It should be noted that in both methods, the blends show different
a values. It is believed that the difference between the a values arises
from the parameter R,, which is derived from the phase morphology. Since
both the blends are not dilute systems, the average particle size (Rv)
contains contributions from interfacial tension as well as coalescence
effect.
Blend
N3o
N ~ o
Interfacial tension (mN/m)
Palierne
13.03
17.46
Choi-Schowalter
14.2 1
20.33
Dvnamic Rheoioaical Proaerhrhes 295
Table 8.3: Effect of compatibilisation on the interfacial tension of N70 blend
Table 8.3 shows the effect of compatibilisation on the interfacial
tension between the two components in NTO blends. On the basis of phase
morphology studies (chapter 4), we concluded that addition of
cornpatibiliser decreases the interfacial tension sharply up to CMC and
beyond that a levelling off in interfacial tension occurs. Theoretical
predictions of Noolandi and Hong, and Leibier also supported this fact. So
based on the phase morphology, we expect a sharp decrease in interfacial
tension with initial addition of compatibiliser. It is obvious from the table
that there is a very good correlation between the phase morphology and
rheology. Addition of even 1 wt% compatibiliser decreases a remarkably
and this continues upto the CMC. Beyond CMC, the interfacial tension
shows an increase at higher compatibiliser concentration.
Blend
N7u
N ~ o , I
N70,z.s
N70,s
N70.10
8.3 Condusions
In this chapter, the dynamic rheology of nylontEPDM blends was
analyzed with special reference to blend ratio, compatibilisation and
dynamic vulcanization. It was found that complex viscosity of EPDM was
maximum and that of nylon was minimum. The complex viscosities of
Interfacial tension (mN/m)
Palierne
17.46
0.637
0.318
0.792
1.166
Choi-Schowalter
20,33
0.7 14
0.356
0.888
1.307
2% Chapter 8
uncompatibilised blends were found to be intermediate. All the blends
showed a decrease in viscosity with increase of frequency, indicated the
pseudoplastic behaviour. The viscosity ratio between the polymers was
very sensitive to frequency, which gives an indirect idea about the unstable
morphology. The elastic properties such as storage and loss moduli were
also maximum for EPDM. The elastic properties showed similar variations
with the composition of the blends. A good correlation was found between
the rheology and morphology.
Effect of compati bilisation on the rheologicd properties revealed
that complex viscosity increased with increase in compatibiliser
concentration up to critical micelle concentration (CMC). Beyond CMC we
observed a reduction in complex viscosity. The micelle formation is
believed to be responsible for the decrease in viscosity at higher
compatibiliser loading. This increased viscosity for the compati bilised
blends has been attributed to the increased interaction between the nylon
and EPDM as a result of decrease interfacial tension and coalescence due to
the introduction of the compatibiliser. It was found that, the rheology and
phase morphology of the compatibilised blends were intimately related.
Dynamically vulcanised blends also registered an increase in viscosity
with crosslinking. Among the dynamic crosslinked blends, the sulphur
crosslinked blends showed the highest viscosity.
The interfacial tension of the blends in the presence and absence of
compatibiliser was determined using Palieme and Choi-Schowalter
methods. Both the methods were successful and gave reasonably good
values. The interfacial tension drastically decreased with the addition of
compatibiliser up to CMC. It was also found that the minimum value was
found at CMC.
Dynamic Rheologicai Properties 297
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