Dynamic Mechanical Properties -...

Dynamic Mechanical Properties

5.1. Introduction

5.2. Results and Discussion

5.2.2.1. Uncompatibilised blends Figure 5.1: Variation of storage modulus (E’) of PA and PS with temperature.

Figure 5.2: Variation of tan δ of PA and (PS) with temperature

Figure 5.3: Variation of loss modulus (E”) of PA and polystyrene (PS) with temperature.

Figure 5.4: Variation of storage modulus (E’) of the uncompatibilised PA/ PS blends with temperature

Figure 5.5: Effect of blend composition on E’ values

Figure 5.6 (a): Variation of tan δ of the uncompatibilised (N80, N70 & N50) blends with temperature

Figure 5.6 (b): Variation of tan δ of the uncompatibilised blends (N30 & N20) with temperature

Table 5.1: Tg values for PA and PS from damping curves

Figure 5.6(c): Variation of tanδ max due to PA and PS in uncompatibilised blends with blend composition.

Figure 5.7: Variation of loss modulus (E”) of uncompatibilised (N80, N50 & N20) blends with temperature.

132 Chapter 5

Theoretical modelling of the dynamic mechanical properties Figure 5.8 (a): Experimental and theoretical curves of storage modulus of

uncompatibilised PA/PS blends as a function of wt % of PA at 70°C.

Figure 5.8 (b): Experimental and theoretical curves of storage modulus for N20 blends in the whole temperature range

Figure 5.8 (c): Experimental and theoretical curves of storage modulus for N80 blends in the whole temperature range

Viscoelastic properties of compatibilised blends Figure 5.9: Variation of storage modulus as a function of temperature for

N80 blends compatibilised with SMA8

Figure 5.10: Effect of compatibiliser (SMA8) concentration on the storage modulus of N80 blends

Figure 5.11: Effect of compatibilisation (SMA8) on the damping behaviour of N80 blends

Figure 5.12: Variation of storage modulus as a function of temperature for N20 blends compatibilised with SMA8



Figure 5.15: Loss modulus curves as a function of temperature for N80 and N20 blends compatibilised with SMA8 (1%)

Figure 5.16: Effect of compatibiliser (SEBS-g-MA) concentration on the storage modulus of N80 blends

Figure 5.17: Effect of compatibilisation (SEBS-g-MA) on the damping behaviour of N80 blends

Dynamic Mechanical Properties 133



Figure 5.20: Loss modulus curves as a function of temperature for N80 blends compatibilised with SEBS-g-MA (5%) and SMA28 (0.5%)

Figure 5.21: Storage modulus for uncompatibilised and

compatibilised 80 blends

Table 5.2: Damping properties of compatibilised N80 blends.

Figure 5.22: Storage modulus of compatibilised blends-Comparison with theory

Conclusion

References:

1

Chapter 5

Dynamic Mechanical Properties

5.1. Introduction Scientific interest in polymer blends has intensified in the recent years due to

their application in many technological products. However, the major

challenge in polymer blending is the heterogeneous nature of the blends, due

to the lack of miscibility in polymer blends. Therefore many attempts have

been made to enhance the miscibility in polymer blends and the incorporation

of compatibiliser was proved to be a successful approach [1-22].

Several experimental techniques are being used to characterise polymer

blends. Polymer glass transition temperature (Tg) has been accepted as a

diagnostic aid for determining the miscibility of polymer blends. Dynamic

Mechanical Analysis (DMTA) has the advantages of a thousand-fold

greater sensitivity when studying glass transition phenomena and the ability

to detect all secondary motional transitions at low temperatures which

influence the impact strength characteristics [23-25]. DMA measures the

stiffness and mechanical damping or internal friction/thermal dissipation of

a dynamically deformed material as a function of temperature. Literature

shows that DMA has been accepted as a powerful tool in characterising

polymer blends [7-22].

Very recently Kong and Al-Malaika studied the viscoelastic properties of

PET/EPR blends and found that the peak position of tanδ varies with blend

composition [22]. The dependence of tanδ peak on weight ratios of individual

polymer components of the blends based on different polymer combinations has

2

been reported previously and has been related to the differences in blend

morphology [26-28]. Thomas and co workers reported the effect of

compatibilisation on the viscoelastic properties of various blends [16-21].

The present chapter deals with the viscoelastic properties of nylon

copolymer (PA)/polystyrene (PS) blends. The effect of blend composition

and compatibilisation on the viscoelastic properties has been analysed.

SMA8, SMA28 and SEBS-g-MA are used as compatibilisers. We have

made an attempt to correlate the viscoelastic properties with the phase

morphology of the blends in which the morphology of both the

compatibilised as well as the uncompatibilised blends are accounted. The

experimentally obtained results have been compared with certain

theoretical models.Their correlation has been discussed.

5.2. Results and Discussion

5.2.2.1. Uncompatibilised blends The dynamic mechanical properties such as storage modulus, loss modulus

and damping behaviour of the hompolymers were analysed over a

temperature range of -100 to 150°C at a frequency of 1Hz.The storage

moduli and tanδ for the neat polymers has been plotted in Figures 5.1 and

5.2 respectively.

3

-100 -50 0 50 100 150

0

1

2

3

4

Log

E' (

MP

a)

Temperature°C

N100 N0

Figure 5.1: Variation of storage modulus (E’) of PA and PS with temperature.

The value of E′ signifies the stiffness of the material. At any fixed rate of

deformation, the temperature at which E′ starts to decrease rapidly corresponds

to the glass transition temperature (Tg). PS exhibits higher modulus than PA up

to its Tg. At the transition zone there is drastic decrease in modulus with

temperature. This is because at the transition zone segmental mobility sets in

followed by a corresponding decrease in the E′ values. Thus the storage modulus

drops drastically at about 100°C for PS and for PA the drop is at about 40°C. In

the case of PS there is a drastic fall around Tg, whereas the modulus drop for PA

is less due to its crystalline nature. For crystalline materials only the amorphous

part undergoes segmental motion at Tg while the crystalline regions remain

unaffected till the melting temperature. Thus in the case of PA a rubbery plateau

is observed after Tg

4

-100 -50 0 50 100 150

0

1

2

3

-100 -50 0 50 100 1500.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

tanδ

Temperature °C

Temperature (°C)

N100 N0

tanδ

Figure 5.2: Variation of tan δ of PA and (PS) with temperature

The tanδ curve for PA consists of two peaks. The transition occurring

around high temperature (around 48°C) is the α relaxation and this

corresponds to the glass transition of the amorphous phase. The transition

at the lower temperature (around -50°C) corresponds to the β relaxation

which has been related to movements involving carbonyl groups which

have formed hydrogen bonds with absorbed water [30, 31]. The tan δ curve

for PS shows maxima at 114°C which corresponds to the Tg of PS. The

damping curves indicate that PS has high damping than PA up to it’s Tg

(114°C). The loss modulus curve for PA and PS are presented in Figure

5.3, which shows a loss maximum at 42°C for PA and 104°C for PS. PA

shows a β relaxation peak around -50°C.

5

-100 -50 0 50 100 150-100

0

100

200

300

400

500

600

700

E" (

MPa

)

Temperature °C

N100 N0

Figure 5.3: Variation of loss modulus (E”) of PA and polystyrene (PS) with temperature.

The storage modulus value for the different blend compositions is shown in

Figure 5.4. All the blends show a modulus value in between the component

polymers of which the PS rich blends exhibit moderately large values at room

temperature. The variation of storage modulus as a function of PA concentration

in the blends at 25°C is shown in Figure 5.5. from which it can be observed that

with the increase in PA concentration the storage modulus decreases. The curve

exhibits a negative deviation from the additivity line indicating the immiscibility

of the system. This negative deviation can be attributed to the lack of interfacial

interaction and adhesion between the polar PA phase and the non polar PS

phase. It can also be seen that N50 blends have the lowest storage modulus. This

behaviour can be explained on the basis of the morphology of the system. Phase

morphology analysis of uncompatibilised blends suggest that N50 blends exhibit

a co-continuous morphology whereas in all the other cases the system shows

dispersed phase morphology (chapter 3). The morphological observation

through SEM analysis was further supported by the co-continuity index

6

measurement via solvent extraction technique and is presented in chapter 3.

Hence the tendency of the N50 blends to exhibit the minimum storage modulus

can be attributed to the co-continuous nature of the system at that particular

composition. Castro et al. [32] while anlaysing the low frequency

viscoelastic behaviour in immiscible polymer blends reported that the

decrease in the G’ coincides with the creation of continuous phases in the

blend. The variation of slope in the storage modulus-composition curve at the

phase inversion region is reported by George et al. [21].

-100 -50 0 50 100 1500.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

g(

)

Temperature °C

N80 N70 N50 N30 N20

Figure 5.4: Variation of storage modulus (E’) of the uncompatibilised PA/ PS blends with temperature

7

0 20 40 60 80 1001000

1500

2000

2500

3000

3500

E' (

MP

a)

Wt % of PA

Figure 5.5: Effect of blend composition on E’ values.

The effect of blend compositions on the damping behaviour of blends are shown

in Figure 5.6 (a & b). All the blends show two peaks indicating the

immiscibility between the phases. In the case of PA rich blends (N80 and

N70), the β relaxation peak is also visible. The Tg values for PA and PS from

the damping curves is shown in Table 5.1.The polystyrene Tg remains almost

unaffected on blending. The PA Tg shifts slightly towards the high

temperature range with PS content which may be due to the low moisture

absorption of the blends compared to pure PA. PA rich blends show a β

relaxation peak around -50°C which is due to the absorbed moisture as

discussed earlier [19,20].

8

-100 -50 0 50 100 150

0.0

0.1

0.2

0.3

0.4

0.5

Temperature°C

N80 N70 N50

Figure 5.6 (a): Variation of tan δ of the uncompatibilised (N80, N70 & N50) blends with temperature

-100 -50 0 50 100 150

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Temperature°C

N30 N20

Figure 5.6 (b): Variation of tan δ of the uncompatibilised blends (N30 & N20) with temperature

9

Table 5.1: Tg values for PA and PS from damping curves

Tg (°C) Sample

PA PS

N100 47.7

N80 47.7 112.2

N70 51.8 111.1

N50 52.6 112.2

N30 53.3 111.1

N20 53.2 112.2

N0 113

The effect of blend composition on the damping properties is shown in

Figure 5.6©. It is evident from the figure that tan δ maximum due to the PA and

PS increases with the concentration of the respective phases. It is known that the

height of the dynamic transition of a component of a composite apparently

reflects the relative quantity of the component itself [33-35]. PS is showing high

damping compared to PA in whole range of compositions studied. Even though

brittle, the high damping values shown by PS may be due to its amorphous

nature, while PA which is semi crystalline exhibits poor damping.

10

0 20 40 60 80 100

0.06

0.08

0.10

0.12

0.14

0.16

0.18due to PA due to PS

Wt. farction of PA

tan δ

max

due

to P

A

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

tan δ max due to PS

Figure 5.6©: Variation of tanδ max due to PA and PS in uncompatibilised

blends with blend composition.

Variation of loss modulus with temperature for the blends (N80, N50 and N20)

is shown in Figure 5.7. The plot shows that the blends exhibit two loss maxima

corresponding to the glass transitions of PA (around 50°C) and PS (around

100°C) phases indicating the immiscibility of the blends.

-100 -50 0 50 100 1500

50

100

150

200

250

300

350

E"(

MP

a)

Temperature°C

N80 N50 N20

Figure 5.7: Variation of loss modulus (E”) of uncompatibilised (N80, N50

& N20) blends with temperature.

11

Theoretical modelling of the dynamic mechanical properties Theoretical models including parallel, series and Coran’s model have

been applied to predict the storage modulus of the binary blends. The upper

bound parallel model is given by

E = E1φ1 + E2φ2 (5.1)

Where E is the property of the composite, E1 and E2 are the corresponding

properties of components 1 and 2, respectively. In a parallel model the

components are arranged parallel to one another so that an applied stress

elongates each component by the same amount. In the case of the lower

bound series model, where the components are arranged in series with the

applied stress, the equation is

1

1 2

1

LE E E2φ φ

= + (5.2)

The properties of an incompatible blend usually are in between

upper bound parallel model (MU) and lower bound series model (ML).

According to Coran’s equation [36]

( )U L LM f M M M= − + (5.3)

where f can vary between zero and unity. The value of f is given by

(5.4) ( 1nH Sf V nV= )+

where n contains the aspects of phase morphology. VH and VS are the

volume fractions of the hard phase and soft phase, respectively.

Takayanagi proposed a series-parallel model [37, 38] in which, the concept

of percolation is introduced. It is a phenomenological model consisting of

12

mixing rule between two simple models involving connection in series (Reuss

prediction) or in parallel (Voigt prediction) of the components. According to

this model,

(5.5) E = (1-λ)E1 + λ[ (1-φ)/E1 + (φ/E2)]-1

E1 is the property of the matrix phase, E2 is the property of the dispersed

phase, and φ is the volume fraction of the dispersed phase and is related to

the degree of series-parallel coupling. The degree of parallel coupling of

the model can be expressed by

(5.6) % parallel= [φ (1- λ) / (1- φ λ)] x 100

Experimental and theoretical curves of the storage modulus of the

PA/PS blends at 70°C are shown in Figure 5.8(a). The experimental curve

lies between the parallel and series model. Takayanagi model based on

series parallel coupling gives the best fit with the experimental observation.

This model takes into account the contribution from the respective

components related to their volume fractions. The theoretical values are

calculated on the basis of % parallel coupling obtained using equation (5.6).

For a value of n=5, the Coran’s model agrees well with the experimental

values as evident from the Figure 5.8 (a). This is mainly because Coran’s

model takes into account the aspects of phase morphology and hence shows

good agreement with the experimental values.

13

0 25 50 75 1000

1000

2000

3000

43

Stor

age

mod

ulus

(E')

[MPa

]

Wt % of PA

Experimental parallel [1] series [2] Coran (n=5) [3] Takayanagi [4]

1

2

Figure 5.8 (a): Experimental and theoretical curves of storage modulus of

uncompatibilised PA/PS blends as a function of wt % of PA at 70°C.

Comparison of experimental values with theoretical predictions has been

made for the whole temperature range for N20 and N80 blends and is

plotted in Figure 5.8 (b) and Figure 5.8 (c). Both the N80 and N20 blends

show good agreement with the Takayanagi and Coran’s model especially in

the temperature range in between the Tgs of the component polymers.

Takayanagi shows good agreement with the experimental values for N20

and N80 blends at 5% parallel coupling which accounts the contribution of

each phases relative to their volume fractions. As mentioned earlier the

model considers the morphological aspects of the system and the term ‘f’ in

the equation is a function of phase morphology. If only the soft phase were

continuous, ‘f’ would be low (f=0.02 for N80 blends, where PA forms the

continuous phase), ‘f’is closer to unity if the hard phase is continuous

(f=0.6 for N20 blends, where PS forms the continuous phase). Thus for the

compositions with dispersed phase morphology, the model shows good

14

agreement with the suggested ‘f’ values thus resulting in good correlation

between the experimental and predicted values. The model proposed by

Takayanagi also shows good agreement with the experimental values for

N20 and N80 blends at 5% parallel coupling.

-100 -50 0 50 100 150

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

2

Log

E' (

MP

a)

Temperature (°C)

Expt Parallel [1] Series [2] Coran (n=5) [3] Takayanagi [4]

134

Figure 5.8 (b): Experimental and theoretical curves of storage modulus

for N20 blends in the whole temperature range

-100 -50 0 50 100 1500.5

1.0

1.5

2.0

2.5

3.0

3.5

2

LogE

'(MP

a)

Temperature (°C)

Experimental parallel [1] series [2] Coran (n=5) [3]

N801

3

4

Figure 5.8 (c): Experimental and theoretical curves of storage modulus

for N80 blends in the whole temperature range

15

Viscoelastic properties of compatibilised blends The storage modulus curves for N80 blends compatibilised with SMA8 are

shown in Figure 5.9. The Figure shows that there is an increase in storage

modulus upon compatibiliser addition. The influence of comaptibiliser

concentration on the storage modulus of the blends at three different

temperatures 1. 25°C (below the Tg of both the components); 2. 80°C (in

between the Tg of both the components and 3. 120°C (above the Tg of both

the components) are shown in Figure 5.10.The storage modulus shows high

values below the Tg of the component polymers and shows a drastic drop

beyond the Tgs. The blends exhibited a maximum storage modulus at room

temperature on addition of 2% SMA8. This result shows good correlation

with the morphology of the system, where a minimum particle size is

observed for blends with 2% compatibiliser addition and is discussed in

chapter 3.

-100 -50 0 50 100 1500.5

1.0

1.5

2.0

2.5

3.0

3.5

Log

E' (

MP

a)

Temperature°C

N80 SMA8 (1%] SMA8 (2%) SMA8 (4%)

Figure 5.9: Variation of storage modulus as a function of temperature for

N80 blends compatibilised with SMA8

16

0 1 2 3 4 5

2.0

2.2

2.4

2.6

2.8

3.0

3.2

Log

E'(M

Pa)

Wt% of SMA8

25°C 80°C 120°C

Figure 5.10: Effect of compatibiliser (SMA8) concentration on the storage

modulus of N80 blends

The tan δ curves for compatibilised N80 blends are depicted in Figure 5.11.

The plot shows the α and β relaxation peaks for the polyamide phase. The

Tg of polyamide shifts towards high temperature upon compatibilisation

which indicates that compatibiliser addition resulted in interfacial chemical

reaction. The grafted copolymers that are formed in-situ during melt mixing

preferentially reside at the interface, improve interfacial adhesion through

chemical linkages, and allow a finer dispersion. A minimum domain size was

obtained for 2% compatibiliser loading. Further addition of compatibiliser

does not have much effect on the domain size and we can say that by 2%

addition there is almost a leveling off in particle size (chapter 3). We

obtained a maximum storage modulus for the system compatibilised with

2% SMA which can be attributed to the finest and most uniform dispersion

of PS phase in the PA matrix.

17

-100 -50 0 50 100 150

0.00

0.05

0.10

0.15

0.20

0.25

0.30

tan δ

Temperature (°C)

N80 SMA8 (1%) SMA8 (2%) SMA8 (4%

Figure 5.11: Effect of compatibilisation (SMA8) on the damping behaviour

of N80 blends

Tg of PS does not show any change upon compatibilisation. But the tan δ

maximum corresponding to the PS phase increases upon SMA addition

which can be attributed to the increase in polystyrene concentration with

increased SMA content.

The effect of compatibilisation on the viscoelastic properties of N20 blends

using SMA8 has also been analysed. The influence of SMA loading on the

storage modulus of N20 blends are shown in Figure 5.12. It can be seen

that at temperatures lower than the Tg of PS, the storage modulus increases

upon compatibiliser loading which almost levels off by the addition of

0.5% compatibiliser. The observation is more clearly depicted in Figure 5.13,

where the storage modulus variation at two temperatures for different

compatibiliser loading is plotted. At temperatures beyond Tg of PS the

storage modulus remains almost the same for both the uncompatibilised

and compatibilised blends. In this case also the increase in storage modulus

upon SMA loading can be attributed to the compatibilising action of SMA

18

resulting from the interfacial chemical reaction between anhydride groups

of SMA and amine end groups of PA as depicted in scheme 3.1.

-100 -50 0 50 100 1500

1

2

3

4

N20 SMA8 (0.1%) SMA8 (0.2%) SMA8 (0.5%) SMA8 (1%)

Log

E' (

MP

a)

Temperature (°C)

Figure 5.12: Variation of storage modulus as a function of temperature for N20 blends compatibilised with SMA8

0.0 0.2 0.4 0.6 0.8 1.0

3.20

3.25

3.30

3.35

3.40

3.45

Log

E'(M

Pa)

Wt% of SMA8

25°C 80°C


19

The compatibilising action of the copolymer SMA8 is evident from the

morphology of the compatibilised N20 blends. As in the case of N80 blends

here also the incorporation of SMA has resulted in reduction of domain size

(discussed in chapter 3). The reduction in domain size along with the increase in

storage modulus on compatibilisation suggests that SMA8 can be considered as

a good compatibiliser for PA/PS system.

The variation of tan δ of compatibilised N20 blends is shown in Figure 5.14. We

can see that on compatibiliser loading the Tg of PS is shifted slightly to lower

temperatures which suggest that the blends become more compatible with the

addition of SMA8. The shift in PA Tg is not obvious due to the low PA

concentration in the system, but seems that the peak is slightly broadened which

is an indication of improved compatibility. Thus in N20 system, the Tg of the

components shows a tendency to become closer suggesting the improved

compatibility of the blends upon the addition of SMA8.

The loss modulus curve for N80 and N20 blends compatibilised with SMA8 is

shown in Figure 5.15.

-50 0 50 100 150

0.0

0.4

0.8

1.2

1.6

tan δ

Temperature (°C)

N20 SMA8 (0.2%) SMA8 (0.5%) SMA8 (1%)

20


-100 -50 0 50 100 1500

100

200

300

400

E' (

MP

a)

Temperature (°C)

N80 (SMA8 (1%)] N20 (SMA8 (1%)]

Figure 5.15: Loss modulus curves as a function of temperature for N80 and

N20 blends compatibilised with SMA8 (1%)

In addition to SMA8, influence of SEBS-g-MA and SMA28 on the visco

elastic properties of N80 blends were investigated. Based on phase

morphology studies (chapter 3) and mechanical properties (chapter 4)

SEBS-g-MA proved to be a good compatibiliser in PA/PS blends. In this

section we investigated the compatibilisation efficiency of SEBS-g-MA on

the viscoelastic properties of N80 blends. Effect of addition of SEBS-g-MA

on the storage modulus of N80 blends is shown in Figure 5.16. The storage

modulus of the compatibilised blends is higher than that of the

uncompatibilised blend. But it can be observed from the figure that at

higher loadings of SEBS-g-MA, the modulus reduces which may be due to

the flexible nature of the compatibiliser.

21

-100 -50 0 50 100 1500.5

1.0

1.5

2.0

2.5

3.0

3.5

LogE

' (M

Pa)

Temperature(°C)

N80 SEBS-g-MA (1%) SEBS-g-MA (5%) SEBS-g-MA (8%)

Figure 5.16:Effect of compatibiliser (SEBS-g-MA) concentration on the

storage modulus of N80 blends

The influence of SEBS-g-MA incorporation on the dissipation factor (tan δ)

of N80 blends is given in Figure 5.17. From the Figure it is well evident

that the Tg corresponding to PA experienced a positive shift with the

addition of SEBS-g-MA. This is due to the interfacial chemical reaction

taking place between the MA groups of the compatibiliser and the amine

end groups of PA.

22

-100 -50 0 50 100 1500.00

0.05

0.10

0.15

0.20

0.25

Temperature (°C)

N80 SEBS-g-MA (1%) SEBS-g-MA (5%) SEBS-g-MA (8%)

Figure 5.17: Effect of compatibilisation (SEBS-g-MA) on the damping

behaviour of N80 blends

Effect of compatibilisation using SMA28 on the storage modulus of N80

blends are shown in Figure 5.18. It can be observed from the figure that up to

0.5% addition of the compatibiliser the storage modulus of the blends has been

increased in the whole range of temperature studied. The addition of the

compatibiliser beyond 1% resulted in a decrease of storage modulus. The

phase morphology studies of SMA28 compatibilised blends showed that at

higher concentration, the compatibiliser failed to act as an interfacial modifier

(chapter 3). Analysis of mechanical properties also suggested that after 0.5%

loading SMA28 could not produce enhancement of mechanical properties

(chapter 4). We assume that owing to the high polarity of SMA28, the

compatibiliser at higher concentrations might have formed micelles in the PA

phase instead of locating at the interface [39, 40]. This might have resulted in

the increased domain size and inferior properties. According to the studies of

Harrats et al. [41] the heavily grafted copolymer formed during the interfacial

23

reaction might have been expelled from the interface due to its energetically

unfavourable design and formed micelles.

-100 -50 0 50 100 150

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Log

E' (

MP

a)

Temperature (°C)

N80 SMA28 (0.2%) SMA28 (0.5%] SMA28 (1%) SMA28 (2%)

Figure 5.18: Effect of compatibiliser (SMA28) concentration on the

storage modulus of N80 blends

-100 -50 0 50 100 150

0.00

0.05

0.10

0.15

0.20

0.25

tan δ

Temperature (°C)

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

Figure 5.19: Effect of compatibilisation (SMA28) on the damping

behaviour of N80 blends

The tan δ curves for SMA28 compatibilised N80 blends are plotted in

Figure 5.19.With the incorporation of compatibiliser an increase in the Tg

corresponding to PA is observed. This can be attributed to the interfacial

24

chemical reaction taking place between the compatibiliser and the PA

phase. This in turn reduces the segmental mobility and hence increases the

Tg of the blends as evident from Figure 5.19.

Representative plots showing the variation of loss modulus with temperature

for N80 blends compatibilised with SEBS-g-MA and SMA 28 are given in

Figure 5.20. The plot shows two Tgs corresponding to PA and PS, indicating

that the blends remain immiscible even after compatibilisation with the

styrenic co-polymers.

-100 -50 0 50 100 1500

50

100

150 SEBS-g-MA (5%) SMA28 (0.5%)

E" (M

Pa)

Temperature (°C)

Figure 5.20: Loss modulus curves as a function of temperature for N80

blends compatibilised with SEBS-g-MA (5%) and SMA28 (0.5%)

The efficiency of the three compatibilisers was compared based on their

influence on the viscoelastic properties of the N80 blends. The storage

moduli for N80 blends compatibilised with the three different

compatibilisers are shown in Figure 5.21. The figure indicates that SMA8

resulted in higher storage modulus followed by SMA28 .

25

-100 -50 0 50 100 1501.0

1.5

2.0

2.5

3.0

3.5

N80 SMA8 (2%) SMA28 (0.5%] SEBS-g-MA (5%)

Log

E' (M

Pa)

Temperature (°C)

Figure 5.21: Storage modulus for uncompatibilised and compatibilised 80 blends

The damping properties of the three compatibilisers are shown in Table 5.2.

where tan δ max due to PA and PS in the compatibilised blends are

presented. Damping due to PS seems to be unaffected upon

compatibilisation, whereas tan δ(max) due to PA increases on

compatibilisation. The table indicates, N80 blends compatibilised with

SEBS-g-MA exhibits the maximum damping. This observation can be

devoted to the high damping nature of the rubbery polymer when compared

with the other compatibilisers

26

Table 5.2: Damping properties of compatibilised N80 blends.

Sample tanδ (max) due to PA

tanδ (max) due

to PS

N80 0.151 0.214

SMA8 (2%) 0.157 0.222

SMA28 (0.5%) 0.167 0.210

SEBS-g-MA (5%) 0.175 0.212

The storage modulus obtained for compatibilised blends are compared with

theory. The compatibilised blends exhibited a positive deviation with

respect to Coran’s and Takayanagi models which fit well with the

uncompatibilised blends. The deviation from Coran’s model which was

proposed for incompatible blends suggests that with the incorporation of

the styrenic copolymers the blends have become compatible. The positive

deviation with respect to Takayanagi model can be attributed to the

synergism in storage modulus obtained through compatibilisation.

27

-100 -50 0 50 100 1500.5

1.0

1.5

2.0

2.5

3.0

3.5

Log

E'(M

Pa)

Temperature(°C)

N80 parallel series Coran (n=5) Takayanagi SMA8(2%) SEBS-g-MA[5%] SMA28(0.5%]

Conclusion Blends of PA copolymer/polystyrene were prepared in a brabender

plasticorder. The dynamic mechanical properties such as storage modulus,

loss modulus and damping behaviour of the hompolymers and their blends

were analysed in temperature range of -100 to 150°C.The blends exhibited

two Tgs corresponding to the individual polymers indicating that the blends

are immiscible. All the blends showed modulus value in between the

component polymers of which the PS rich blends exhibited moderately large

values at room temperature. N50 blends with a co continuous morphology

28

showed the lowest value of storage modulus at room temperature. The Tg

of PA phase shifted slightly towards the higher temperature with PS content

which may be due to the low moisture absorption of the blends compared to

neat PA.

While analysing the compatibilised blends (with three different

compatibilisers, SMA8, SEBS-g-MA and SMA28), it was found that the

storage modulus increased up on compatibilisation. A slight shift in the Tg

of PA phase was obtained in the case of compatibilised N80 blends. The

increase in storage modulus as well as the positive shift in Tg can be

attributed to the interfacial chemical reaction. The DMTA results showed

good correlation with the blend morphology. In the case of

compatibilisation with SMA8, for N80 blends the maximum storage

modulus and the minimum particle size was obtained for 2% loading. In the

case of N20 blends with a less amount of compatibiliser (0.5 %) we

obtained a leveling off in the case of storage modulus as well as the domain

size. Upon compatibilisation with SEBS-g-MA, the storage modulus

increased. In this case a decrease in storage modulus was obtained at higher

concentration which can be attributed to the rubbery nature of the

copolymer.

Analysis of viscoelastic properties using SMA28 revealed that beyond 1%

addition the compatibiliser exhibited inferior properties. This could be

attributed to the poor miscibility of the highly polar SMA28 with PS phase

along with the probability of heavily grafted copolymer formed to be

expelled from the interface. The morphology analysis indicated that the

domain size increases with high concentration of SMA28. Among the three

copolymers used for compatibilisation, SMA8 resulted in maximum

29

improvement of storage modulus, while SEBS-g-MA exhibited the

maximum damping behaviour. The results from the dynamic mechanical

analysis showed that with the addition of the compatibilisers, the blends

became more compatible, suggesting that the copolymers function as

interfacial modifiers in the system. Theoretical models were applied to

evaluate the storage modulus of the binary blends of which the Coran’s and

Takayanagi models shows good agreement with the experimental values.

30

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