Studies on Epoxy Resin Systems Modified with - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/6790/10/10...morphology of multiphase polymer melts is a complex function of blend

3.1. Introduction Morphology control plays a key role in optimising the performance

of multi component polymer blends. The evolution of blend morphology

from pellet or powder sized particles to the sub micrometer droplets

depends on several processing parameters including the rheology,

interfacial properties and composition of the blend [1-6]. The competing

processes of drop break-up and coalescence during processing of polymer

blends determine the final morphology of these mixtures as explained in a

growing body of literature on this subject [6-15]. The interface has a crucial

role in controlling the morphology and final properties of an immiscible

polymer blend. The interfacial tension is the most basic parameter, which

characterises the interface between polymers [16-18]. Owing to the high

molecular weights of the component polymers and negligible combinatorial

entropy during mixing, most of the blends are characterised by coarse,

unstable morphology and poor interfacial adhesion between the phases.

Hence the major challenge in blending involves the manipulation of blend

morphology via judicious control of mixing parameters and the interfacial

interactions.

By the incorporation of suitable block or graft copolymers referred

to as compatibilisers polymer-polymer interface can be modified, which in

turn, will facilitate the control of morphology development. The

compatibilisers, either pre-made or produced in-situ during reactive

processing, the latter being the industrially preferred method results in the

cost-effective production of new multiphase polymeric materials with

72 Chapter 3

outstanding physical and chemical properties. The basic principle involved

in reactive compatibilisation includes the use of functionalities present in

one or more polymers to form graft or block co-polymers in-situ during

melt processing [19-57]. Compatibilisers improve the degree of dispersion

and stabilise the morphology (by suppressing the coalescence) [38-42] in

addition to strengthening the interface (by reducing the interfacial tension)

[43-46] between the component phases. The compatibilisation efficiency of

the copolymers, in turn depends on several factors such as the type and

amount of functional groups present, reactive group content and end group

configuration of the polymer, the miscibility of the compatibiliser with one

of the phases and its conformation, molecular architecture and stability at

the interface [22, 27-30, 47-55].

This chapter is devoted to the investigations on phase morphology

of compatibilised as well as uncompatibilised PA/PS blends. The effect of

blend composition on the phase morphology development in

uncompatibilised blends has been analysed. Reactive compatibilisation

strategy has been employed making use of amine-anhydride reaction.

Several reports [24-36] based on reactive compatibilisation via amine-

anhydride reaction are available in literature. The compatibilisers used

include, SMA8, SMA28 and SEBS-g-MA. The characteristics of the

compatibilisers are given in Table 2.1. (Chapter2). The effect of reactive

compatibilisation on the phase morphology development of the blends was

analysed. Compatibilisation efficiency of the different compatibilisers has

been discussed. Attempts have also been made to compare the experimental

observations with compatibilisation theories.

Phase Morphology Studies 73

3.2. Results and Discussion

3.2.1. Uncompatibilised blends

3.2.1.1. Analysis using scanning electron microscopy [SEM] The scanning electron micrographs [SEM] of the cryogenically

fractured surfaces of the uncompatibilised blends are given in Figure 3.1. It

is evident from the micrographs that all the blends exhibit two phase

morphology typical of the uncompatibilised blends. Except N50, all the

other compositions exhibit droplet/matrix morphology, with the minor

phase forming the dispersed phase and the major phase forming the matrix.

N50 blends possess a co-continuous phase structure in which both the PA

as well as the PS exist as continuous phases.

X1000X1000 X1000

N20 N30 N50

X1000 X1000

N70 N80

Figure 3.1: SEM micrographs of uncompatibilised PA/PS blends

The effect of blend composition on the average domain diameter is

shown in Figure 3.2. The figure shows that the domain size is small in

74 Chapter 3

blends where PA is the dispersed phase. This can be explained on the

basis of the difference in the melt viscosities of the component phases.

Favis [56] reported that if the minor component has lower viscosity

compared to the major one, it will be finely and uniformly dispersed in

the major continuous phase and otherwise will be coarsely dispersed. It

can be observed from Figure 3.3. that PS possesses higher viscosity than

PA. Therefore when the high viscous PS forms the matrix, the diffusion

of the dispersed PA particles is restricted, thus retarding their coalescence

resulting in smaller particle size. On the other hand, when the high

viscous PS dispersed in a low viscous PA phase, there is a high

probability of particle coalescence leading to large domains.

20 30 40 50 60 70 800

2

4

6

8

10

Aver

age

dom

ain

diam

eter

(μm)

Wt% of PA

Dn Dw Ds

PA dispersed PS dispersed

co-continuous

Figure 3.2: Effect of blend ratio on dispersed particle size of uncompatibilised

PA/PS blends


1.5 1.8 2.1 2.4 2.7 3.0

2.2

2.4

2.6

2.8

3.0

logη

(Pas

)

logγ .(s-1)

N0 N100

Figure 3.3. Melt viscosity of PA and PS as a function of shear stress

The SEM micrographs (Figure 3.1.) reveal that the uncompatibilised blends

exhibit a non- uniform and unstable morphology. Figure 3.2 shows that

with the increase in the wt% of the dispersed phase, the domain size

increases. As discussed earlier, development and stability of the

morphology of multiphase polymer melts is a complex function of blend

composition, interfacial characteristics, rheological properties, shear

conditions etc. [1-6]. In the early 1930s, Taylor developed a theory for the

break-up of individual droplets for Newtonian fluids [57, 58]. A

relationship was established between the capillary number, Ca, a ratio of

shear to interfacial forces and the viscosity ratio ηr = ηd/ηm

ma

γη DC

2Γ= [3.1]

where γ is the shear rate, D is the diameter of the droplet, Γ is the

interfacial tension, ηd is the dispersed phase viscosity, and ηm is the matrix

phase viscosity. The predicted drop size for a simple shear field is

proportional to the interfacial tension and inversely proportional to shear

76 Chapter 3

rate and matrix phase viscosity. If Ca is small, the interfacial forces

dominate and a steady drop shape develops. When Ca exceeds a critical

value, Cacrit the drop deforms and subsequently breaks down under the

influence of interfacial tension. According to Tokita [5] when coalescence and

break down balance, the equilibrium particle size (de) can be expressed as,

de ≅ 24PrΓ/ πτ12 {φd + [4PrEdk/πτ12] φd2 } [3.2]

where τ12 is the shear stress, Γ is the interfacial tension, Edk is bulk

breaking energy, φd is the volume fraction of the dispersed phase and Pr the

probability for a collision to result in coalescence. Tokita’s expression

incorporates the composition variable and predicts that particle size at

equilibrium diminishes as the magnitude of the stress field increases

between the component phases and volume fraction of the dispersed phase

result in an enhancement of particle size.

The increase in particle size with dispersed phase concentration of

PA/PS blends can be attributed to the increase in coalescence. Therefore, it

can be concluded that the non-uniform and unstable morphology of PA/PS

blends stem from the high interfacial tension and coalescence conditions.

3.2.1.2. Region of phase inversion

The development of continuity as described by percolation theory

can be summarised as follows: Initially at low concentrations, there is a

dispersion of particles in the matrix. As the concentration of the minor

phase increases, particles become close enough to behave as if they were

connected. Further addition of minor phase material extends the continuity

network until the minor phase is continuous throughout the sample.


In the present study, the continuity of the dispersed phase is

calculated by solvent dissolution method [59]. When PA forms the matrix,

the minor phase PS was extracted using toluene and when PS forms the

matrix, the minor phase PA was extracted using formic acid. The continuity

of the component is defined as the ratio of the difference of the weight of

the component present initially and the calculated weight of the residual

component after extraction to the weight of the component present initially.

Initial weight of the component ---Weight after extraction Continuity = Initial weight of the component

[3.3]

The results are summarised in Table 3.1. From the values it is

evident that the continuity of both the phases is close to 90% in N40 and

above 90% in N50 and N60 blends. This suggests that N40, N50 and N60

exhibit co-continuous morphology. For all the other blend compositions

(N10, N20, N30, N70, N80 and N90), the continuity is less than 30%,

suggesting matrix/droplet morphology.

Table 3.1: Percentage of continuity by solvent dissolution

Concentration of PS phase

Continuity (%) of PS phase

Concentration of PA phase

Continuity (%) of PA phase

PS dispersed PA dispersed

10 9 10 3

20 26 20 14

30 50 30 16

40 94 40 85

50 97 50 94

78 Chapter 3

Various models have been applied for the prediction of a continuity

point. Jordhamo et al. [60] developed an empirical model based on the melt

viscosity ratio, (ηd/ηm), and the volume fractions (φ), of each phase for

predicting the phase inversion in immiscible polymer blends. According to

this model, phase inversion should occur when

11

2

2

1 =φφ

ηη

[3.4]

Chen and Su [61] proposed the following equation taking into account the

fact that Jordhamo model over estimates the volume fraction of the high

viscosity phase.

3.0

2.1 ⎟⎟⎠

⎞⎜⎜⎝

⎛=

lv

hv

lv

hv

ηη

φφ [3.5]

where hv denotes the high viscous and lv, the low viscous phase.

The region of phase inversion can also be modeled using a modified Chen

and Su model by avoiding 1.2 from the above equation [62].

3.0

⎟⎟⎠

⎞⎜⎜⎝

⎛=

lv

hv

lv

hv

ηη

φφ [3.6]

The volume fractions of PS and PA at their phase inversion points

as predicted by these models are given in Table 3.2. All the models agree

well with the experimental observation at low viscosity ratios. When the

viscosity ratio is less than 2, all the three models predict values close to the

experimental values. At higher viscosity ratios, all the models show some

variations.


Table 3.2: Modeling of phase inversion.

Jordhamo Chen & Su Chen & Su (modified) η ratio

φPS φN φPS φN φPS φN

2.7 0.73 0.27 0.38 0.62 0.57 0.43

2.4 0.7 0.3 0.44 0.56 0.4 0.6

2 0.6 0.44 0.6 0.40 0.55 0.45

1.5 0.4 0.6 0.58 0.42 0.53 0.47

1.2 0.55 0.45 0.56 0.44 0.51 0.49

Experimental observation of phase inversion is found to occur at φPS = 0.52, 0.62 and φN =0.48, 0.38

3.2.2. Compatibilised blends

3.2.2.1. Compatibilisation strategy

Owing to the lack of favourable interfacial interactions resulting

from their polarity difference [note that PA is a polar polymer and PS a

simple hydrocarbon polymer], PA/PS blends are immiscible. This often

leads to a coarse unstable morphology which will be reflected in poor

performance of the blends. This problem can be alleviated via

compatibilisation. Compatibilisation improves morphological stability

primarily by introducing a steric hindrance to coalescence. An effective

compatibiliser tends to reside at the interface and consequently serves as

phase emulsifier to reduce the interfacial tension, leading to smaller

dispersed phase domains in the blend. As a result, the fine phase domains

are stabilised against coalescence and the interfacial adhesion between two

immiscible polymers is enhanced.

80 Chapter 3

Since one of the components is PA with potential functionalities

due to the presence of amine and carboxyl and groups as well as the amide

linkage, reactive route can be successfully employed in compatibilising the

blends. Imidisation is a very well known amine /anhydride reaction. It is a

spontaneous reaction which does not require any molecular catalyst and can

take place even in the absence of solvents, at high temperatures. In our

system we have selected SMA8, SMA28 and SEBS-g-MA as

compatibilisers, which ensure compatibility by imidisation reaction. These

compatibilisers consist of anhydride groups which can react with the

functionalities of the PA. All the three compatibilisers employed possess a

PS part which is expected to be miscible with the PS phase.

The mechanism of the interfacial reaction is based on (1) the amine

–anhydride reaction which involves an acid /amide intermediate that cyclises to

produce an imide group and a water molecule (Scheme 3.1), or (2) amide-

anhydride mechanism which involves an acid/imide intermediate which

cyclises, leading to a cyclic imide and an acid chain end (Scheme 3.2) [63].

O

O

O

+ H2N PA

OH

NHO

O

PA

N

O

O

PA + H2O

Low temperature < 120 C0

High temperature Scheme 3.1: Amine -anhydride mechanism


O

O

O

+

N

O

O

PA

PA HNCO PA

OH

O PA

PAO

O

HOOC PA+

Scheme 3.2: Amide -anhydride mechanism

3.2.2.2. Morphology refinement on compatibilisation with SMA8 The compatibilisation efficiency of SMA8 is well evident from the

SEM micrographs shown in Figure 3.4. The micrographs show that particle

size has been considerably reduced with the incorporation of the

compatibiliser. From the SEM micrographs, morphological parameters

such as average domain diameter (Dn and Dw), domain distribution,

interfacial area per unit volume (Ai) and interparticle distance (IPD) have

been calculated using equations given in chapter 2.

82 Chapter 3

X2000 X2000 X2000

SMA8 (0.5%)N80 SMA8 (1%)

X2000X2000

SMA8 (2%) SMA8 (4%)

Figure 3.4: SEM micrographs of N80 blends compatibilised with SMA8

Figure 3.5 shows the effect of compatibiliser concentration on the

dispersed particle size of N80 blends. It can be observed from the figure

that with the incorporation of SMA8, domain size decreases. The reduction

in domain diameter is significant till 2% addition of SMA8, beyond which

a quasi-equilibrium state is observed. Hence it can be suggested that by the

addition of 2% SMA8, critical micelle concentration (CMC) is reached

beyond which a leveling off in particle size can be observed. The influence

of compatibiliser on the domain distribution is depicted in Figure 3.6 which

reveals that compatibilisation resulted in narrowing of domain distribution.

The effect of compatibilisation on interfacial area per unit volume (Ai) and

interparticle distance (IPD) are given in Table 3.3. The incorporation of

SMA8 resulted in an increase in interfacial area per unit volume, which

suggests that the compatibiliser could effectively locate at the interface


between the components thereby increasing the interfacial thickness. The

IPD values decreased upon compatibilisation.

0 1 2 3 4 5

1

2

3

4

5

Aver

age

Dom

ain

Dia

met

er (μ

m)

Wt% of SMA8

Dn Dw

Figure 3.5: Effect of SMA8 on the dispersed particle size of N80 blends.

0 1 2 3 4 5 6 70

10

20

30

40

50

% d

istri

butio

n

Dn (μm)

N80 SMA8 (0.5) SMA8 (1) SMA8 (2) SMA8 (4)

Figure 3.6: Effect of SMA8 on the domain distribution of N80 blends

84 Chapter 3

Table 3.3: Effect of SMA8 on Ai and IPD of N80 blends

Sample Ai (μm-1)

IPD (μm)

N80 0.31 4.65

SMA8 (0.5%) 0.40 3.54

SMA8 (1%) 0.47 3.02

SMA8 (2%) 1.23 1.17

SMA8 (4%) 1.21 1.19

The SEM micrographs showing the effect of addition of SMA8 on

the morphology of N20 blends are shown in Figure 3.7. The effect of

compatibiliser concentration on particle size is shown in Figure 3.8. As

discussed earlier, the high viscous PS matrix restricts the diffusion of

dispersed PA particles thereby hindering their coalescence. Consequently,

the uncompatibilised blends with the PA dispersed phase consist of

relatively smaller domains. Hence the effect of compatibiliser in reducing

the domain size is not prominent as in the case of N20 blends as evident

from Figures 3.7 and 3.8. However, particle size decreases upon SMA8

addition till CMC (0.5%) beyond which a leveling off is observed. The

effect of compatibilisation on Ai and IPD of N20 blends is presented in

Table 3.4 where we can observe an increase in Ai and decrease in IPD on

addition of SMA8.


X1000 X1000 X1000

N20 SMA8 (0.1%) SMA8 (0.2%)

X1000 X1000

SMA8 (0.5%) SMA8 (1%)


0.0 0.2 0.4 0.6 0.8 1.0 1.2

1.2

1.4

1.6

Aver

age

Dom

ain

Dia

met

er (μ

m)

Wt% of SMA8

Dn Dw

Figure 3.8: Effect of SMA8 on the dispersed particle size of N20 blends.

86 Chapter 3


Sample Ai (μm-1)

IPD (μm)

N20 0.82 1.68

SMA8 (0.1%) 0.83 1.67

SMA8 (0.2%) 0.89 1.55

SMA8 (0.5%) 0.95 1.46

SMA8 (1%) 0.92 1.5

3.2.2.3. Morphology refinement on compatibilisation with SEBS-g-MA Compatibilisation of N80 blends has been carried out employing

SEBS-g-MA as compatibiliser. The effect of SEBS-g-MA on the

morphology of N80 blends is demonstrated in SEM micrographs shown

below (Figure 3.9). The influence of SEBS-g-MA on particle size as well

as domain distribution is shown in Figures 3.10 and 3.11 respectively.

Effect of SEBS-g-MA addition on the Ai and IPD of N80 blends is

presented in Table 3.5.


X1000 X1000 X1000

N80 SEBS-g-MA (0.2%) SEBS-g-MA (1%)

X1000 X1000X1000

SEBS-g-MA (3%) SEBS-g-MA (5%) SEBS-g-MA (8%)

Figure 3.9: SEM micrographs of N80 blends compatibilised with SEBS-g-MA

0 2 4 6 82

3

4

Aver

age

Dom

ain

Dia

met

er (μ

m)

Wt% of SEBS-g-MA

Dn Dw

Figure 3.10: Effect of SEBS-g-MA on the dispersed particle size of N80 blends

88 Chapter 3

1 2 3 4 5 6 70

10

20

30

40

50

% d

istri

butio

n

Dn (μm)

N80 SEBS-g-MA (0.2) SEBS-g-MA (1) SEBS-g-MA (3) SEBS-g-MA (5) SEBS-g-MA (8)

Figure 3.11: Effect of SEBS-g-MA on the domain distribution of N80

blends

Table 3.5: Effect of SEBS-g-MA on Ai and IPD of N80 blends

Sample Ai (μm-1)

IPD (μm)

N80 0.31 4.65

SEBS-g-MA (0.2%) 0.36 4

SEBS-g-MA (1%) 0.40 3.5

SEBS-g-MA (3%)) 0.48 2.9

SEBS-g-MA (5%)) 0.6 2.5

SEBS-g-MA (8%)) 0.57 2.4

It is evident from Figure 3.10 that the addition of SEBS-g-MA

contributed towards reduction in domain size of the N80 blends. The

reduction was significant till 5% addition, beyond which the particle size

almost levels off. The effect of compatibiliser on domain distribution


(Figure 3.11) suggests that the distribution becomes narrow by 3% addition

of SEBS-g-MA. The Ai increases with compatibiliser addition which

confirms the ability of SEBS-g-MA to modify the interface. Beyond CMC

the Ai value decreases which is an indication of interfacial saturation. The

IPD decreases upon compatibiliser loading.

3.2.2.4. Morphology refinement on compatibilisation with SMA28 In addition to SMA8 and SEBS-g-MA, compatibilisation efficiency

of SMA28, a styrene copolymer with high MA content is also analysed.

SEM micrographs showing the effect of SMA28 on the morphology of N80

blends are shown in Figure 3.12. The influence of SMA28 on particle size

as well as domain distribution of N80 blends is shown in Figure 3.13 and

3.14 respectively. The effect of SMA28 on modifying the interface of N80

blends can be evaluated from the Ai and IPD values given in Table 3.6.

N80 SMA28 (0.1%) SMA28 (0.2%)

SMA28 (0.5%) SMA28 (1%) SMA28 (2%)


90 Chapter 3

0.0 0.5 1.0 1.5 2.01.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Wt% of SMA28

Aver

age

dom

ain

diam

eter

(μm

) Dn Dw

Figure 3.13: Effect of SMA28 on the dispersed particle size of N80 blends

1 2 3 4 5 6 7 8

5

10

15

20

25

30

35

% d

istri

butio

n

Dn (μm)

N80 SMA28 (0.1) SMA28 (0.2) SMA28 (0.5) SMA28 (1) SMA28 (2)

Figure 3.14: Effect of SMA28 on the domain distribution of N80 blends



Sample Ai (μm-1)

IPD (μm)

N80 0.31 4.65

SMA28 (0.1%) 0.50 2.86

SMA28 (0.2%) 0.52 2.75

SMA28 (0.5%) 0.67 2.14

SMA28 (1%) 0.57 2.52

SMA28 (2%) 0.53 2.7

It can be observed from Figure 3.13 that SMA28 could reduce the

particle size of the dispersed phase. However, it is interesting to note that

unlike the other two compatibilisers, after a CMC of 0.5%, further addition

of compatibilisers has resulted in a considerable increase in domain size. It

should be noted that even the Ai values registered a decrease at higher

compatibiliser loading. This increase in particle size has resulted in

deterioration of properties as discussed in the coming chapters.

The poor performance of SMA28 as compatibiliser in PA/PS blends

can be attributed to the high MA content of the copolymer. The

compatibiliser contains 28% MA, which makes it slightly polar. Studies by

several researchers have proved the inefficiency of highly functionalised

SMA copolymers in various systems. According to Dedecker [29] SMA-

types with a low MA content are expected to be miscible with PS as both

the polymers are chemically identical. Paul and co-workers [53] reported

92 Chapter 3

that miscibility of the blend PS/SMA becomes worse by increasing the

MA content of SMA. The increase in particle size can also be interpreted

as follows; during the initial addition of very low concentration of

SMA28 (say 0.1%), only a very little amount of SMA28 will be close

enough to the PA/PS interface to react immediately. With further addition

more SMA28, the copolymers are susceptible to reach the interface and

can undergo the interfacial reaction resulting in reduction of particle size.

As the amount of SMA28 increases more than the optimum level, the

reaction at the interface will be significantly high leading to the formation

of heavily grafted copolymer at the interface. These grafts possess an

energetically unbalanced structure with a high PA content. Therefore

there is a greater chance for these grafts to be expelled from the interface

so that it can reside in the PA phase where it is expected to be

thermodynamically more stable.

Literature reports similar observations in various systems.

Triaca et al. [48] in their study related to PA/ABS blends reported that,

full reaction of the SMA25 used as the compatibiliser result in an extreme

level of grafting per molecule which is hard to imagine to be sited for an

interfacial role. They found that beyond an optimum level of SMA25

resulted in deterioration in mechanical properties as well a loss in

optimum morphology. Recently Huang et al. [54] studied the

compatibilisation efficiency of styrene-glycidyl methacrylate copolymers

(SGMA copolymer) on poly (ethylene-2,6-naphthalate) /PS blends . They

reported that in blends compatibilised with the SG copolymer containing

high MA content, heavily grafted copolymers could be produced. The

length of the styrene segments in this heavily grafted copolymer will be too


short to penetrate deep enough into the PS phase to form effective

entanglements, resulting in lower compatibilisation efficiency which is

manifested in morphology as well as mechanical performances. According

to Groeninckx and co-workers [55] the compatibiliser can easily be rejected

from the interface because of its energetically unbalanced design. They

studied the effect of reactive compatibilisation employing SMA

copolymers on the morphology of PA6 with poly(methyl methacrylate)

[PMMA], poly(phenylene oxide) [PPO] and PS blends and found that in

those cases where SMA copolymer reacts more quantitatively, an un-

balanced graft copolymer richer in PA6 is built up. It has a strong tendency

to be driven out from the interface into the PA6 phase, thus leading to the

so called ‘decompatibilisation’ process.

This study implies that the stability of the copolymer at the interface

may be altered, when the balance of interaction between its own sequences

and the individual phases of the blend is not suitable or when the

copolymer organise into micelles in one of the phases. Therefore, the

inefficiency of SMA28 at high loadings can be attributed to the

immiscibility with PS phase owing to the high functionality as well as the

expulsion of the energetically unbalanced graft formed at the interface due

to the high extent of reaction.

3.2.3. Compatibilisation efficiency- comparison.

From the SEM micrographs and plots showing the effect of

compatibilisation on the particle size, we found that the dispersed particle

size decreases with the addition of compatibilisers. A leveling off at higher

concentration is observed in the case of SMA8 and SEBS-g-MA

compatibilisers while an increase in particle size was observed for SMA28.

94 Chapter 3

The reduction in particle size with the addition of compatibilisers is due to

the stabilisation of the blend morphology by the graft copolymers formed

during melt-mixing. The formed graft copolymer locates at the interface

and reduces both the interfacial tension and thus the particle size, and more

importantly, introducing a steric hindrance to coalescence. In addition, the

presence of the graft copolymer at the blend interface broadens the

interfacial region through the penetration of the copolymer chain segments

into the corresponding phases.

The equilibrium concentration of the compatibilisers at which there

is domain size leveling off in domain size is refers to as the so-called

critical micelle concentration (CMC), i.e., the concentration at which

micelles are formed which can be estimated from a plot of interfacial

tension versus compatibiliser concentration. The copolymer covers a part of

the interface when its concentration is small. It should cover the whole

interface for a certain concentration, presumably the CMC, and the

interfacial tension should reach a minimum. As the interfacial tension is

directly proportional to the domain size, the estimation of CMC from the

plot of domain size versus copolymer concentration is warranted [64-66].

From our results, it is seen that CMC for SMA8, SMA28 and SEBS-g-MA

is 2, 0.5 and 5% respectively. It is interesting to note that the interfacial

area per unit volume increased with the compatibiliser concentration up to

CMC followed by a slight decrease upon further addition of the

compatibiliser which suggesting interfacial saturation.

The particle distribution curve obtained for uncompatibilised and

compatibilised N80 blends are shown in Figure 3.15. The Figure shows that

the domain distribution becomes narrow on compatibilisation, the


narrowest being obtained for SMA8 which confirms its supremacy over

SEBS-g-MA and SMA28 in morphology refinement.

0 1 2 3 4 5 6 7 80

10

20

30

40

50

% d

istri

butio

n

Dn(μm)

N80 SMA8 SEBS-g-MA SMA28

Figure 3.15: Effect of compatibilisation on the domain distribution of N80 blends

3.2.4. Phase coarsening (coalescence) under quiescent conditions For a compatibiliser to be effective it should be able to produce a

fine and uniform morphology which is stable. Reports show that reactive

compatibilisers locate at the interface as static stabilisers and offer stability

against static coalescence [8,11,24]. In an attempt to assess the effect of

compatibilisers to provide steric stability against coalescence, we evaluated

the phase coarsening of uncompatibilised and compatibilised N80 blends

under quiescent conditions. The samples were annealed at 180°C for

60min. The SEM micrographs for the N80 blends (uncompatibilised and

compatibilised with SMA8, SEBS-g-MA and SMA28) are presented in

Figure 3.16. Effect of annealing on the average domain size of

uncompatibilised and compatibilised N80 blends is given in Table 3.7.

96 Chapter 3

(a) N80 N80 (annealed)

(b) SMA8 (2%) SMA8 (2%: annealed)

(c) SEBS-g-MA (5%) SEBS-g-MA (5%:annealed)

(d) SMA28 (0.5%) SMA28 (0.5% : annealed)

Figure 3.16: SEM micrographs showing the effect of annealing on the dispersed particle size of (a) uncompatibilised N80 blends (b) N80 blends with 2% SMA8 (c) N80 blends with 5% SEBS-g-MA (d) N80 blends with 0.5% SMA28


Table 3.7: Effect of annealing on the particle size of compatibilised and uncompatibilised N80 blends.

Average domain diameter (Dn) μm Blend

Unannealed Annealed for 60 min

% increase in size

N80 4.06 7.6 87

SMA8 (2%) 1.02 1.1 8

SEBS-g-MA (5%) 2.1 2.7 28

SMA28 (0.5%) 1.9 3.2 63

It can be observed from Figure 3.16 and Table 3.7 that

uncompatibilised N80 blend depicted the maximum coalescence owing to

the weak interface between the phases. SMA8 was found to be the most

effective in providing a stabilised morphology. It seems that in the case of

SMA8 compatibilised blend, the dispersed phase remains almost unaffected

upon annealing. The blend compatibilised with SEBS-g-MA showed a

marginal increase in domain size. Macosko et al. [11] reported that the

compatibiliser surface coverage required for stabilizing blend morphologies

during static coalescence is predominantly higher than that needed at the

time of mixing. This disparity arises from the longer contact times which

allow a greater extent of molecular rearrangement at the interface. The

blends compatibilised with SMA28 also showed an enhancement in drop

dimension. As discussed earlier, the energetically unbalanced design of the

copolymer (owing to the high functionality) at the interface might have lead

to its expulsion from the interface during annealing. Groeninckx et al. [55]

98 Chapter 3

reported the phase morphology coarsening during annealing as a result of

expulsion of copolymer from the interface. These observations suggested

that all the three styrenic copolymers were able to locate at the interface

producing a fine, uniform and stable morphology.

Of the three compatibilisers, SMA8 was found to be the most

effective in preventing the static coalescence, reflecting an unaffected

morphology on annealing. SEBS-g-MA produced a 28% increase and

SMA28 resulted in 63% increase in domain size which can be attributed to

the decompatibilisation process taking place in the case of SMA28. The

energetically unbalanced design of the graft copolymer due to the high

functionality of SMA28 makes it more susceptible to get rejected from the

interface. The compatibilisation efficiency of SMA8 is again confirmed

from the morphology stability of compatibilised N80 blends against the

action of shear and is discussed in chapter 7.

3.2.5. Comparison of the experimental compatibilisation data with theory

Noolandi and coworkers [67–69] and Leibler [70, 71] have

proposed the thermodynamic theories concerning the compatibilising effect

of copolymers in binary polymer blends. The model proposed by Noolandi

was based on the assumption that part of the copolymer that does not

localise at the interface will be randomly distributed in the bulk of the

homopolymer phases as micelles. Localisation of the copolymer however

results in a decrease in the entropy and ultimately limits the amount of

copolymer at the interface. The efficiency of the copolymer is mainly

influenced by a series of factors such as lowering the interaction energy

between the immiscible homopolymers, the broadening of the interface


between the homopolymers, decrease in energy of interaction of the two

blocks with each other and a large decrease in the interaction energy of the

oriented blocks with the homopolymers.

Various other factors such as mixing conditions, interaction of the

compatibiliser with the dispersed phase, molecular weight and composition

of the compatibiliser etc. contribute towards the localisation of the

compatibiliser at the interface and thereby reducing the interfacial tension.

The separation of the blocks and the consequent stretching of the blocks

into corresponding homopolymers also cause a decrease of entropy.

However, the main contribution to the interfacial tension reduction is the

entropy loss of the copolymer that localises at the interface. The loss of

conformational entropy of both the copolymer and homopolymer chains at

the interface was shown to contribute very little to the interfacial tension

reduction. An analytical expression (eqn. 3.7) for the interfacial tension

reduction was derived by Noolandi and Hong by neglecting the loss of

conformational entropy [68, 69].

( )1 2 1 1 exp 2c c c cd Z Z Zφ χ χΔΓ = + −⎡⎣ ⎤⎦ (3.7)

where d is the width at half height of the copolymer profile reduced by the

Kuhn statistical segment length, cφ the bulk copolymer volume fraction of

the copolymer in the system, cZ is the degree of polymerisation of the

copolymer and χ the Flory-Huggins interaction parameter between A and

B segments. Although the theory was developed for the action of a

symmetrical diblock copolymer, A-b-B, in incompatible binary blends

(A/B), it can be very well applied to other systems also, where the

compatibilising action is not strictly by the addition of block copolymers

100 Chapter 3

[24,72,73]. Since the interfacial tension reduction is directly proportional to

the particle size reduction ( ) [64, 65], it can be argued that, DΔ

( )1 2 1 exp 2c c cD Kd Z ZχΔ = Φ +⎡⎣ χ ⎤⎦ (3.8)

where, K is a proportionality constant.

The plot of domain size reduction as a function of the volume

fraction of the compatibilisers for N80 blends is shown in Figures 3.17.

(a, b and c).

(a) (b)

0.000 0.005 0.010 0.015 0.020-2.5

-2.0

-1.5

-1.0

-0.5

0.0

Dom

ain

size

redu

ctio

n,ΔD

n (μ

m)

Volume fraction of SMA28 (c)

Figure 3.17: Effect of compatibilisers on domain size reduction of N80 blends (a) SMA8 (b) SEBS-g-MA (c) SMA28


Figures 3.17. (a) and (b) indicate that below CMC, almost a linear

drop in domain diameter is observed which levels off beyond CMC, thus

agreeing well with Noolandi’s predictions. However, in the case of

SMA28, instead of a leveling off we observed an increase in the ΔD values.

This deviation of SMA28 compatibilised system can be attributed to the

immiscibility of SMA28 with PS phase owing to its high polarity being

worsened at high concentrations.

The interfacial area occupied per compatibiliser molecule [Σ] has

been calculated using the equation

3 MRNWφ⎛ ⎞Σ = ⎜ ⎟

⎝ ⎠ (3.9)

where N is Avogadro number, M is the number average molecular weight

of the compatibiliser, R is the average radius of the dispersed phase, φ is

the volume fraction of the dispersed phase and W is the weight of the

compatibiliser required per unit volume of the blend. The effect of

compatibiliser concentration on Σ is given in Figure 3.18. It can be seen

that in the case of SEBS-g-MA and SMA28, Σ decreased with increase in

compatibiliser concentration. This is due to the fact that as the

concentration of the compatibiliser increases the interface will be more

occupied so that the conformation of the copolymer at the interface changes

so as to include the additional molecules. This in turn reduces the

interfacial area occupied by each compatibililiser molecule. Among all the

compatibilisers, SMA8 showed the lowest value for Σ.

102 Chapter 3

0 2 4 6 80

10

20

30

40

50

60In

terfa

cial

are

a/ c

ompa

tibili

ser m

olec

ule(

nm2 )

Wt% of the compatibiliser

SMA8 SEBS-g-MA SMA28

Figure 3.18: Effect of compatibiliser concentration on the interfacial area

occupied per molecule of the compatibiliser in N80 blends.

According to Leibler [70, 71], the reduction of interfacial tension

caused by the emulsifying action of an A–B copolymer at the interface in

an immiscible blend of polymers A and B can be expressed by the

following relation.

( )( ) ( ) ( )5 31 32 2 2 33 4 CA A CB BkT a a Z Z Z Z− −ΔΓ = − Σ + 2 3− (3.10)

where CAZ and CBZ are the number of A and B units in the copolymer

respectively, AZ and BZ the degree of polymerisation of A and B

respectively, a the monomer’s unit length, Σ , the interfacial area per

copolymer. Leibler suggested that at equilibrium, the droplet size

distribution is controlled by rigidity and spontaneous curvature of radius of

the interphase, both dependent on the copolymer’s molecular constitution.


Between the two brush limits in Leibler’s theory [71], prediction

based on dry brush limit in which the homopolymer does not penetrate the

brush formed by the copolymer, has been used. Based on the assumption

that the reaction between reactive compatibiliser and the polymer with a

different functional group occurs near the interface, the following equation

which is independent of the homopolymer molecular weights can be used

for the interfacial tension reduction (ΔΓ).

( ) 1 23 2

0

489 Nμ χ −ΔΓ ⎛ ⎞= ⎜ ⎟Γ ⎝ ⎠

(3.11)

where is the interfacial tension of polymer blend without a compatibiliser

and

0Γ

μ is the chemical potential which is given by the equation:

ln f Nμ φ χ+= + (3.12)

where f is the volume fraction of the component in copolymer which is

miscible to homopolymer forming the dispersed phase and

( ){ }0

expm d A BN Nφ

φφ φ χ

+ =⎡ ⎤+ −⎣ ⎦

(3.13)

where 0φ , mφ and dφ r resent the volume fraction of the copolymer, matrix

and dispersed phase, respectively, AN and are the number of segments

of the component in the copolymer miscible with the homopolymer

forming the dispersed phase and that miscible with the homopolymer

forming the matrix phase, respectively. Since the value

of

ep

)

BN

({ }exp ANχ − BN is negligible compared to mφ , φ+ is expressed by

0 mφ φ . As the dispersed particle size reduction is directly proportional to

the interfacial tension reduction [64,65], the following equation can be used

104 Chapter 3

( ) ( )0

0 0 0

D DDD D

Γ − Γ −ΔΓ Δ= ≈ =

Γ Γ0 (3.14)

Figure 3.19 shows the effect of compatibiliser concentration on the

χ values of N80 blends. It can be observed from the figure that all the

compatibilisers registered a decrease in χ with increase in concentration.

This implies that the interaction between the component phases in the blend

has been considerably increased on compatibilisation.

0 2 4 6 80.0

0.4

0.8

1.2

Wt % of the compatibiliser

Inte

ract

ion

para

met

er (χ

)

SMA8 SEBS-g-MA SMA28

Figure 3.19: Effect of compatibilisation on the χ values calculated by the

dry brush limit of Leibler’s theory.

3.3. Conclusion In this chapter, we presented a detailed investigation on the phase

morphology analysis of compatibilised and uncompatibilised PA/PS

system. The techniques employed were SEM and solvent dissolution

method. The SEM micrographs revealed that 80/20, 70/30, 30/70 and 20/80

PA/PS blends exhibited dispersed phase morphology while 50/50 PA/PS


blends showed co-continuous phase morphology. The solvent dissolution

method also supported the morphological observation from SEM which

revealed that the blends exhibit a co-continuous morphology when the

concentration of nylon approaches to 40%. Theoretical modeling of

continuity agreed well with the experimental observations especially at low

viscosity ratios. The morphology analysis indicated that the blend possesses

a non-uniform morphology with large domains especially at high PA

concentrations which implies that the system is highly immiscible. This can

be attributed to the polarity difference of the component polymers where

PA is a polar polymer and PS is a non-polar polymer.

Exploiting the inherent functionality of PA, PA/PS blends were

subjected to compatibilisation via reactive route. Maleic modified styrene

copolymers including SMA8, SEBS-g-MA and SMA28 were used as

compatibilisers. These copolymers located at the PA/PS interface through

the chemical reaction between their anhydride groups and the amine end

groups of PA. All the three compatibilisers were found to be effective in

providing a stable, uniform morphology on account of the several

parameters evaluated. The domain size was found to decrease considerably

upon compatibilisation and the domain distribution was narrowed. The

interfacial area per unit volume of the blends increased with the

incorporation of compatibilisers. From these observations, we can conclude

that the compatibilisers used were able to suppress the coalescence between

the dispersed domains as well as to reduce the interfacial tension between

the component polymers.

We compared the efficiency of the three copolymers in N80 blends.

With the incorporation of compatibilisers an initial decrease followed by a

106 Chapter 3

leveling off at higher concentrations beyond critical micelle concentration

(CMC) was observed in the case of SMA8 and SEBS-g-MA, while an

increase in particle size was observed for SMA28 after CMC. The CMC for

SMA8, SEBS-g-MA and SMA28 were 2, 5 and 0.5% respectively. The

minimum particle size was obtained for SMA8 which resulted in a 75%

reduction while SEBS-g-MA and SMA 28 could produce 48 and 53%

reduction in particle size. The domain distribution narrowed upon

compatibilisation, the narrowest being obtained for SMA8 which confirms

its supremacy over SEBS-g-MA and SMA28 in morphology refinement.

However, it is interesting to note that, unlike the other two

compatibilisers, after a CMC of 0.5%, further addition of SMA28 resulted

in a significant increase in domain size. The poor performance of SMA28

as compatibiliser in PA/PS blends could be attributed to the high MA

content of the copolymer. The inefficiency of SMA28 at higher loadings

may be due to the immiscibility with PS phase owing to the polarity

difference between them arising from the high functionality of SMA28.

Another possibility is that the heavily grafted copolymer might be expelled

from the interface due to the energetically unbalanced graft formed at the

interface due to the high extend of reaction. The compatibilised and

uncompatibilised blends were subjected to phase coarsening under

quiescent conditions. We observed a remarkable coalescence in

uncompatibilised blends. The phase dimensions remain almost unaltered in

blends compatibilised with SMA8. The blends compatibilised with SEBS-

g-MA and SMA28 showed an increase in domain size upon annealing.

SMA28 exhibited the highest increase in size which again suggests the

energetically unbalanced design of the copolymer at the interface.


The experimental compatibilisation data have been compared with

the theoretical predictions given by Noolandi and Hong, Paul and Newman

and Leibler. The experimental observations showed good agreement with

theory especially for the blends compatibilised with SMA8 and SEBS-g-

MA. The interaction parameter values were the lowest for blends

compatibilised with SMA8. Therefore, we can conclude that among the

three compatibilisers studied, SMA8 is the most suitable compatibiliser in

PA/PS system based on phase morphology studies.

3.4. References

1. B.D Favis, J.P Chalifoux, Polymer. 29, 1761,1988.

2. K. Min, J.L White, J.F Fellers, Polym. Eng .Sci ., 24,1327,1984.

3. S. Wu. Polym Eng Sci., 27,335,1987.

4. J.L White, K .Min. Adv. Polym. Tech., 5, 225, 1985.

5. N .Tokita, Rubber Chem. Technol., 50, 292, 1977.

6. G. Wildes, H. Keskkula, D.R. Paul, Polymer. 40, 5609, 1999.

7. B. Majumdar, D.R Paul, A.J Oshinski, Polymer, 38, 1787, 1997.

8. U. Sundararaj, C.W, Macosko, Macromolecules, 28, 2647, 1995.

9. I .Fortelny, A. Zivny, Polymer, 36, 4113, 1995.

10. J.J. Elmendorp, A.K. van der Vegt. In, L.A.Utracki, editors. Two-phase

polymer systems, ch. 6. Munich: Carl Hanser, 1991.

11. C.W. Macosko, P. Guegan, A. Khandpur, A. Nakayama, P. Marechal, T.

Inoue, Macromolecules, 29, 5590, 1996.

12. L.A. Utracki,. Polymer alloys and blends. Munich: Carl Hanser/ Dusseldorf:

VDI Verlag, 1989.

108 Chapter 3

13. I.Fortelny, J. Kovar, M.J. Stephan, Elast Plast, 28, 106, 1996.

14. J.M.H. Janssen, H.E.H. Meijer, Polym. Eng.. Sci., 35, 1766, 1987.

15. C.C. Chen, E. Fontan, K. Min, J. White. Polym. Eng. Sci., 28, 69, 1988.

16. L. Minkova, Hr. Yordanov, S. Filippi, N. Grizzuti, Polymer 44, 7925, 2003.

17. S.E. Harton, F.A. Stevie, H.Ade, Macromolecules, 38, 9, 2005

18. H. Pernot, M. Baumert, F .Court, L. Leibler, Nat. Mater., 1, 54, 2002.

19. C.Nakason, P.Wannavilai, A. Kaesaman, J. Appl. Polym. Sci., 100, 4729,

2006.

20. K. Kuniaki, T. Yoshihisa, J. Appl. Polym. Sci., 100, 4375, 2006.

21. B. Lin, U. Sundararaj, P. Guegan, Polym.Eng. Sci., 46, 691, 2006.

22. H.K. Jeon, B.J. Feist, S.B. Koh, K. Chang, C.W. Macosko , R.P. Dion,

Polymer,45, 197, 2004.

23. S.H. Jafari, P. Pötschke, M. Stephan, H. Warth H. Alberts, Polymer, 43,

6985, 2002.

24. S. Thomas, G. Groeninckx, Polymer 40, 5799, 1999.

25. F. Ide, A. Hasegawa, J. Appl. Polym. Sci., 18, 963, 1974.

26. O. Okada, H. Keskkula, D.R Paul, Polymer, 42, 8715, 2001.

27. K. Dedecker , G. Groeninckx, Polymer, 39, 4985,1998.

28. K. Dedecker, G. Groeninckx, T. Inoue, Polymer, 39, 5001, 1998.

29. K. Dedecker, Ph.D. Thesis, Katholieke University, Leuven. 1998

30. K. Dedecker, G. Groeninckx, Macromolecules, 32, 2472, 1999.

31. S. M Hong, S. S. Hwang, J. S. Choi, H. J Choi, J. Appl. Polym. Sci., 101,

1188, 2006.


32. L-T.Yan, J. Sheng, Polymer, 47, 2894, 2006.

33. W.Yang, Y. Yuming, L. Binyao, H. Yanchun, J. Appl. Polym. Sci., 100,

3187, 2006.

34. S. Jose, B. Francis, S. Thomas, J. Karger-Kocsis, Polymer, 47, 3874, 2006.

35. L. Hongzhi, X. Tingxiu, Z. Ying, O. Yuchun, Y. Guisheng, J. Polym. Sci.,

Part B: Polym. Phys., 44, 1050, 2006.

36. S. Jose, S.V. Nair, S. Thomas, J. Karger-Kocsis, J. Appl. Polym. Sci., 99,

2640, 2006.

37. U. Sundararaj, C.W. Macosko, Macromolecules, 28, 2647, 1995.

38. S.P. Lyu, F.S. Bates, C.W. Macosko, AIChE J., 46, 229, 2000.

39. A. Nandi, D.V. Khakhar, A. Mehra, Langmuir, 17, 2647, 2001.

40. S.P. Lyu, T.D. Johns, C.W. Macosko, F.S. Bates, Macromolecules, 35,

7845, 2002.

41. S. Lyu, Macromolecules, 36, 10052, 2003.

42. W. Hu, J.T. Koberstein, J.P. Lingelser, Y. Gallot, Macromolecules, 28, 5209,

1995.

43. J.C. Lepers, B.D. Favis, R.J. Taber, J. Polym. Sci. B: Polym. Phys., 35, 2271,

1997.

44. S.P. Lyu, J.J. Cernohous, F.S. Bates, C.W. Macosko, Macromolecules, 32, 106,

1999.

45. Z. Khattari, Macromol. Theory Simul., 8, 191, 1999.

46. W. Hu, J.T. Koberstein, J.P. Lingelser, Y. Gallot, Macromolecules, 28, 5209,

1995.

110 Chapter 3

47. S.P. Lyu, J.J. Cernohous, F.S. Bates, C.W. Macosko, Macromolecules, 32, 106,

1999.

48. V.J. Triaca, S.Ziaee, J.W. Barlow, H. Keskkula, D.R. Paul, Polymer, 32, 8,

1991.

49. N.K. Kitayama, H. Keskkula, D.R. Paul, Polymer, 41, 8053, 2000.

50. L. Pan, T. Chiba, T. Inoue, Polymer, 42, 8825, 2001.

51. C. Laurens, C. Creton, L. Léger, Macromolecules, 37, 6814, 2004.

52. D.H. Kho, S.H. Chae, U. Jeong, H.Y. Kim, J.K. Kim, Macromolecules, 38, 3820,

2005.

53. J.H. Kim, J.W. Barlow, D.R. Paul; J. Polym. Sci.; Part B: Polym. Physics, 27,

223, 1989.

54. J-M. Huang, M-Y. Ju, C-J. Hung, W-C. Luoh, F.C.Chang, J. Appl. Polym. Sci.,

87, 967, 2003.

55. C. Harrats, K. Dedecker, G. Groeninckx, R. Jérôme; Macromol. Symp., 198,

183, 2003.

56. B.D. Favis, in Polymer Blends, Volume 1, D.R.Paul, C.B.Bucknall Eds.

Wiley Interscience, NewYork, 2000

57. G.I. Taylor, Proc R Soc., A 138, 41, 1932.

58. G.I. Taylor, Proc R Soc., A 146, 501, 1934.

59. B. Favis, J. Polym. Sci. Part B. Polym. Phys., 36, 1889, 1998.

60. G.M. Jordhamo, J.A. Manson, L.H. Sperling, Polym. Eng Sci., 26, 517,

1986.

61. T.H. Chen, A.C. Su., Polymer, 34, 4826, 1993.

62. V. Everaet, L. Aerts, G. Groeninckx, Polymer, 43, 6627, 1999.


63. B.D. Roover, J. Devaux, R.J. Legras, J. Polym. Sci. A: Polym. Chem., 35,

901, 1997.

64. S. Wu, Polymer, 26,1855, 1985.

65. S.Wu, Polym. Eng. Sci., 27, 342, 1987.

66. S. Thomas, R.E.Prud’homme, Polymer, 33, 4260, 1992.

67. J. Noolandi, Polym. Eng. Sci., 24, 70, 1984.

68. J. Noolandi, K.M. Hong, Macromolecules, 15, 482, 1982.

69. J. Noolandi, K.M. Hong, Macromolecules, 17, 1531, 1984.

70. L. Leibler, Macromolecules, 13, 1602, 1980.

71. L. Leibler, Makromol. Chem. Macromol, Symp., 16, 1, 1988.

72. Z. Oommen, M.R.G. Nair, S. Thomas, Polym. Eng. Sci., 36, 151, 1996.

73. S.J.K. Kim, S. Kim, C.E. Park, Polymer, 38, 2155, 1997.

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