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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