final synopsis of the proposed thesis -...

The results presented in this chapter have been published in

Abstract

This chapter presents the results of author’s investigations

on miscibility and morphological studies on SAN/PMMA,

PVC/SAN, PS/PMMA, PP/HDPE, PVC/EVA, PVC/PS and

SAN/EVA polymer blends, derived from free volume

measurements, DSC and SEM techniques. Limitations in the

use of free volume data, DSC and SEM with regard to

miscibility are discussed. Major objective of this study is to

determine the composition dependent miscibility level in

miscible, partially miscible and immiscible polymer blends

using hydrodynamic interaction approach.

interaction approach.

Microstructure, morphology and miscibility

studies of polymer blends

Chapter 4

Polymer, 53 (2012) 4539-4546.

Journal of Applied Polymer Science, 127 (2013) 190-199.

Journal of Physics: C, 443 (2013) 012048-1- 012048-4.

Morphology, microstructure and miscibility studies 110

4.1 Introduction

As mentioned in Chapter 1, the practical applications of partially miscible

and immiscible blends are often limited by the fact that they have poor

mechanical strength since the adhesion strength at the interface will not be

strong [Macknight et al., 1978; Gisbergen, 1989; Van Gisbergen and Meijer, 1991;

Van Gisbergen et al., 1991; Folkes and Hope, 1993; Utracki, 2002; Senatore et al.,

2008]. Many investigations were directed to find new path ways to strengthen

the polymer-polymer interface in immiscible blends through different

compatibilization routes. In order to realize the effectiveness of compatibilization

method, comprehensive knowledge of the interface is required and a

sophisticated method to determine the level of miscibility.

One of the commonly used methods is DSC measurement through the

determination glass transition temperature (Tg) of the blends. Secondly,

morphology investigation also plays an important role in the study of polymer

blends, and scanning electron microscopy (SEM) is generally used for this

purpose.

Of late Positron Annihilation Lifetime Spectroscopy (PALS) is emerging as

one of the important methods for miscibility study in polymer blends. Further, it

has been found that this technique is a better one for understanding of the

microstructure of the blends compared to any other available techniques.

Let us understand the limitations of the above mentioned methods in

determining the composition dependent miscibility level. In this chapter, the

miscibility level in binary polymer blends using hydrodynamic approach through

free volume measurements from the PALS technique is presented. The binary

polymer blends selected for the study are SAN/PMMA, PVC/SAN, PS/PMMA,

PP/HDPE, PVC/EVA, PVC/PS and SAN/EVA covering all the three types of

polymer blends namely miscible, partially miscible and immiscible blends.

4.2 Experimental

4.2.1 Differential Scanning Calorimetric Measurements (DSC)

The glass transition temperatures of pristine polymers and 80/20, 50/50 and

20/80 blends of SAN/PMMA, PVC/SAN, PS/PMMA, PVC/PS were measured using

Morphology, microstructure and miscibility studies 111 Mettler FP90 DSC instrument available at the Department of Physics, University

of Mysore, Mysore. For PP/HDPE, PVC/EVA and SAN/EVA blends, with negative

Tg values, DSC measurements were performed at Indian Institute of Science

(IISc), Bengaluru using METTLER-TOLEDO DSC1 - 2920 MDSC V2.6A instrument

connected to liquid nitrogen cooling accessory with a nitrogen purge.

4.2.2 Scanning Electron Microscopy (SEM)

The surface morphology of the polymer blends under study was scanned

using the ULTRA 55, Field Emission Scanning Electron Microscope (Karl Zeiss)

available at Indian Institute of Science (IISc) Bengaluru, India.

4.2.3 PALS: Lifetime measurements and free volume determination

Positron annihilation lifetime spectra were recorded for SAN, PS, PMMA,

PVC, EVA polymers and the blends of 80/20, 50/50, 20/80 compositions using

Positron Lifetime Spectrometer. The description of the positron lifetime

spectrometer used in this investigation is given in Chapter 3 with full details. All

lifetime measurements were performed at room temperature with more than a

million counts under each spectrum. For each sample, three lifetime spectra were

accumulated and analyzed with PATFIT-88 [Kirkegaard et al., 1989] computer

program. The average of these three measurements is used in the further analysis

namely o-Ps lifetimes (τ3) and intensities (I3). Further, all these spectra were

analyzed using another computer program CONTIN-PALS2 [Gregory, 1995] which

facilitates the determination of lifetime distributions from the same annihilation

lifetime measurements. More details on the PATFIT-88 and CONTIN-PALS2

programs can be found in chapter 3, sub-section 3.2.1.5. In the present work, the

results of positron lifetime measurements will be presented as free volume

radius or size distributions with a comparison that the average values of o-Ps

lifetime and intensity values are reproducible from both the analysis.

4.3 Results and Discussion

4.3.1 SAN/PMMA blends

The polymer, Poly(methyl methacrylate) (PMMA), with the chemical

structure as shown in Figure 4.1, is an optically clear amorphous thermoplastic. It

Morphology, microstructure and miscibility studies 112 is widely used as a substitute for inorganic glass [Demir et al., 2006].

Poly(styrene-co-acrylonitrile) (SAN), whose chemical structure is also shown in

Figure 4.1, exhibits the combined properties of the ease of processing of

polystyrene and the rigidity and chemical resistance of polyacrylonitrile [Jang

and Wilkie., 2005].

The properties of SAN vary with the concentration of AN content in the

copolymer. Generally it has been observed that the lower bound of AN content in

SAN to be miscible with other polymers is 3.5 wt%, and the upper bound is 28

wt%. In the present study we have used SAN containing 25 wt% of AN to blend

with PMMA.

Figure 4.1: Illustration of chemical structures of SAN and PMMA polymers.

(a) DSC results of SAN/PMMA blends

Presence of single Tg in a blend’s thermogram is an indication of its

miscibility while presence of two Tg points to its immiscibility [Macknight et al.,

1978; Folkes and Hope, 1993; Utracki, 2002]. This inference is based on literature

reports, that binary immiscible blends would show two distinct glass transitions

(Tg) and partially miscible (phase separated) binary blends show a single broad

glass transition temperature [Macknight et al., 1978; Senatore et al., 2008]. If the

difference in the two Tg’s of the blend components is ΔTg, then on

compatibilization of the blend, it is expected that ΔTg will decrease possibly due

to favorable interactions between the blend constituents due to compatibilizer.

Let us look into the DSC results of the present blend from this background.

The DSC thermograms of pristine polymers of SAN and PMMA and the blends

with different compositions namely 80/20, 50/50 and 20/80 are shown in Figure

Morphology, microstructure and miscibility studies 113 4.2. From the figure we notice that the glass transition of SAN is at 100 0C and

PMMA exhibits a broad glass transition that starts around 84 0C and extends up to

98 0C. A point to be noted is that, all the three compositions exhibit single glass

transition but appears to be slightly broadened.

Figure 4.2: DSC scans of pristine SAN, PMMA and blends of SAN/PMMA

at 80/20, 50/50 and 20/80 compositions.

The blend compositions 80/20 and 50/50 exhibit single but slightly

broadened transitions at around 90 0C and 87 0C respectively suggesting miscible

nature of the blends. There is a considerable shift in their glass transition

temperatures with reference to PMMA glass transition temperature. But 20/80

blend exhibits Tg around 85 0C, with a marginal shift of about only 1 0C from the

Tg of PMMA. Based on glass transition temperatures, it can be inferred that

SAN/PMMA blends are miscible at all the three compositions, but the miscibility

level whether it decreases or increases with increase in PMMA content cannot be

inferred.

(b) SEM micrographs

In Figure 4.3 SEM micrographs are displayed for the SAN/PMMA blends of

composition 80/20, 50/50 and 20/80. The micrographs show almost complete

homogeneity and lack discernible separated domains in the blends. This can be

Morphology, microstructure and miscibility studies 114 inferred as due to good mixing of SAN and PMMA polymers resulting in

miscibility of the blends.

Figure 4.3: SEM images of SAN/PMMA blends of composition (a) (80/20)

(b) (50/50) and (c) (20/80).

(c) PALS results

The lifetime spectra were resolved into three lifetime components 1, 2 and

3 with intensities I1, I2 and I3 respectively by free analysis using PATFIT-88

program. The general attribution of the three positron lifetime components in

polymers is as follows [Jean, 1990]; The shortest lifetime component 1 (0.130–

0.170 ns) with intensity I1 (45–50%) is attributed to contribution from para-

Positronium (p-Ps) and free positron annihilations in the medium. The

intermediate lifetime component 2 (0.410–0.470 ns) with intensity I2 (25–35%)

is considered to be due to the annihilation of positrons trapped at defects present

in the crystalline regions or trapped at the crystalline-amorphous boundaries

[Goldanskii et al., 1987]. For polymers, 1 and 2 do not provide any information

with regard to free volume, they are not the main focus of the present work and

hence these lifetime components are not discussed in this work. The longest-lived

component 3 (1.57 - 2.37 ns) with intensity I3 (15 – 29%) is due to pick-off

annihilation of the ortho-Positronium (o-Ps) in the free volume cavities present

mainly in the amorphous regions of the polymer under investigation [Nakanishi

et al., 1989]. As described in chapter 2, a simple relation developed by Nakanishi

et al. [1988] connects o-Ps lifetime (3) to the free volume hole radius R. This

equation is recalled here.

τ

Morphology, microstructure and miscibility studies 115 where, is an adjustable parameter and found to be equal to

1.656 Å by fitting the experimentally measured 3 values to known free volume

hole sizes in porous materials like zeolites [Eldrup, 1982; Nakanishi and Ujihira,

1982; Abbe et al., 1988]. With this value of R, free volume cavity radius R is

evaluated. The average free volume hole size (Vf) is then calculated using the

relation

The fractional free volume FV or the free volume content of the given polymer is

calculated as

where C = 0.0018 Å-3 is a constant whose value suggested by Jean et al. is used

[1990].

Free volume in polymeric materials evolves due to chain folding and the

molecular architecture of the polymer chains. Therefore, the free volume hole

size and the free volume fraction depend on the chain structure, spacing and

molecular orientations. Polymeric materials with ordered arrangement of chains

with close packing give rise to small size free volume holes. When two polymers

are blended, and if any specific interactions between the chains of the constituent

polymers are involved, this results in reduced free volume in the material.

Therefore, the average free volume hole size, Vf evaluated from o-Ps lifetime is

certainly expected to depend on chain arrangement, orientation and packing.

More the compact packing, smaller is the Vf and vice versa in any polymer.

The o-Ps lifetime and intensity results derived from the lifetime analysis are

tabulated in Table 4.1. From thetable it can be seen that as SAN concentration in

the blend increases free volume hole size (Vf) decreases. This means that there is

close packing with the increase in SAN content, which may be due to

conformational changes between the constituents since no specific interaction

between SAN and PMMA have been reported so far.

The behavior of fractional free volume (FV) is more or less similar to that of

free volume size (Vf). From 20 wt% to 80 wt% of SAN in the blend, the value of FV

Morphology, microstructure and miscibility studies 116 shows decrease just as Vf. As described before, the changes in FV reveals that the

molecular orientation and arrangement of the chains are such that it produces

some close packing.

Table 4.1: o-Ps lifetime, intensity and free volume parameters of the SAN/PMMA

polymer blend determined from PATFIT-88 and CONTIN-PALS2 analysis.

SAN/PMMA

PATFIT-88 CONTIN-PALS2

(Averages derived from moments)

3 0.01 (ns)

I3 0.14 (%)

Vf 0.8 (Å3)

FV 0.04 (%)

3 0.03 (ns)

I3 0.2 (%)

Vf 2 (Å3)

FV0.05 (%)

0/100 2.19 24.09 115.8 5.02 2.14 24.90 114.9 5.14

20/80 2.06 23.00 103.00 4.26 2.01 23.60 101.2 4.30

50/50 1.93 21.10 92.00 3.45 1.88 21.60 90.5 3.52

80/20 1.92 20.10 90.00 3.25 1.89 20.60 88.7 3.29

100/0 1.91 19.87 89.00 3.18 1.88 19.10 88.20 3.03

From literature we learn that in SAN/PMMA system, the miscibility occurs

due to the intramolecular repulsion between the styrene group and acrylonitrile

(CN) groups of SAN [Fowler et al., 1987; Robertson and Wilkes, 2001]. Due to this

repulsion, the SAN chains are pushed apart and the PMMA chains can slide in

between SAN chains. This is how close packing and hence miscibility results.

Lifetime parameters derived from CONTIN-PALS2 analyses of PAL spectra

given in Table 4.1 show that, they are consistent with the PATFIT-88 results. It

may be noted that in deducing lifetime distributions for the pristine polymers and

different blend compositions, a constant alpha () regularizer was used to ensure

that the shapes of the resulting lifetime distributions are least affected by the

extent of data smoothening and hence reflect promptly the respective

microstructures. This has been strongly advocated by researchers who have

developed this program.

In Figure 3.10 (chapter 3), a typical positron annihilation rate PDF (λ) of

SAN/PMMA blend is shown, in which peak 3 is o-Ps annihilation rate PDF. Peak 1

and 2 are respectively related to annihilation of positrons with free electrons and

p-Ps and positrons trapped in defect sites or crystalline-amorphous regions. For

the present discussion only peak 3 is important.


Figure 4.4: Plot of (a) o-Ps lifetime PDF resolved from lifetime spectra with

cavity radius in the upper x-axis and lifetime in the lower x-axis (b) free volume

size (Vf) PDF for SAN/PMMA blends.

Transformation from annihilation rate probability density function (PDF) into the

corresponding free volume radius PDF and free volume size PDF were

accomplished by the method of Gregory [1991, 1995]. The expressions used to

obtain free volume radius PDF and free volume size PDF are

Δ

where ΔR has the same meaning as defined earlier in equation 4.1. Figure 4.4a,

displays the distribution of lifetime and free volume radius, and in Figure. 4.4b

the free volume size (Vf) distribution are shown for SAN/PMMA blends of 80/20,

Morphology, microstructure and miscibility studies 118 50/50 and 20/80 compositions. As can be seen from the figures, the distribution

of lifetime (τ3), free volume radius (R) and free volume size (Vf) in 80/20 and

50/50 compositions are narrower (FWHM = 24 Å3 and 25 Å3 respectively)

compared to 20/80 composition (FWHM = 30 Å3) and the distribution has shifted

towards the pristine PMMA free volume size. The narrower FWHMs of 80/20 and

50/50 composition clearly suggest close packing of the chains leading to high

level of miscibility than that for 20/80 composition.

4.3.2 PVC/SAN blends

Poly (vinyl chloride) (PVC) is a versatile polymer, used in flexible, semi

rigid and rigid forms. The rapid expansion and consumption of PVC is due

to lower cost, greater availability, good mechanical properties and diversity of

its properties [Titow, 1984]. Low service temperature of PVC limits its practical

usage in industries. At this point blending PVC with styrene–acrylonitrile (SAN)

copolymer series are expected to increase its heat-deflection temperature. It is

well known that PVC is not miscible with either polystyrene or polyacrylonitrile

and several other polymers. However, SAN series (depending on the AN content)

is expected to result in miscible or partially miscible blend with PVC. [Schneider

and Calugaru, 1976; Kim et al., 1989].

(a) DSC results

The DSC scans of pristine PVC and SAN and the selected compositions

(80/20, 50/50 and 20/80) of their blends are shown in Figure 4.5. As can be seen

the pristine PVC and SAN exhibits glass transition temperature (Tg) at 85 0C and

100 0C respectively. Blend composition 80/20 shows a broad glass transition

where as 50/50 and 20/80 show two Tgs with very little gap between them

suggesting that 80/20 composition produces miscible blend while 50/50 and

20/80 compositions are immiscible. Therefore composition dependant

miscibility is observed in the blend [Macknight, 1978; Moon et al., 2007].


Figure 4.5: DSC scans of pristine PVC, SAN and blends of PVC/SAN


(b) SEM micrographs

Figure 4.6: SEM images of PVC/SAN blends of composition (a) (80/20),

(b) (50/50) and (c) (20/80).

From the SEM micrographs shown in Figure 4.6 it is observed that both

homogeneous and heterogeneous phase structures are clear depending on the

blend composition. For composition of 80/20, higher degree of dispersion is seen

while 50/50 and 20/80 compositions show phase separated structures with a

high degree of anisotropy.

(c) PALS Results

Similar to the previous blends, for this series also three lifetime components

were resolved. For comparison, the results of analysis from PATFIT-88 and

CONTIN-PALS2 programs are tabulated in Table 4.2.

From the results in table it can be noticed that, the positron annihilation

parameters τ3, Vf and FV show increasing trend with increase in SAN content. This

Morphology, microstructure and miscibility studies 120 suggests that addition of SAN into PVC results to the increase in the average free

volume cavity size and the free volume fraction in the blend. As per the previous

discussion, free volume is related to the microstructure of the system and if there

is interaction between dissimilar chains of the component polymers of the blend,

including change in segmental conformation, close packing results leading to

decrease in FV values.

Table 4.2: o-Ps lifetime, intensity and free volume parameters of the PVC/SAN


PVC/SAN PATFIT-88

CONTIN-PALS2 (Averages derived from moments)

3 (ns) I3 (%) Vf (Å3) FV (%) 3 (ns) I3 (%) Vf (Å3) FV (%)

100/0 1.72 6.12 72.2 0.79 1.74 6.90 73.0 0.90

80/20 1.78 8.8 72.7 1.15 1.77 8.20 76.7 1.13

50/50 1.86 14.3 84.2 2.16 1.87 14.70 85.7 2.19

20/80 1.92 18.7 89.8 2.90 1.90 17.80 90.3 2.95

0/100 1.91 19.87 89.0 3.18 1.88 19.10 88.2 3.03

Supporting evidence comes from the radius and free volume hole size (Vf)

PDF curves (as can be seen from Figure 4.7) show remarkable difference in their

FWHMs. For the blend with SAN at 20 wt% composition, we observe narrow

distribution having FWHM = 30 Å3. As the SAN content in the blend increases the

PDF curves become broad in 50 wt% and 80 wt% compositions resulting in

FWHM = 35 Å3 and 39 Å3 respectively.

For the changes observed in the blends of PVC, SAN polymers, the possible

interactions between PVC and SAN are shown in Figure 4.8. The favorable

interactions between the polymer are the chlorine of PVC with α-hydrogen of

benzene ring and or hydrogen bond between PVC and C≡N group of SAN [Moon

et al., 2007]. The composition 80/20 of PVC/SAN is miscible due to least FV in this

case which is due to increased interactions between the components. The other

two compositions results in immiscibility due to unfavorable interactions.



cavity radius in the upper x-axis and lifetime in the lower x-axis (b) free volume

size (Vf) PDF for PVC/SAN blends.

Figure 4.8: Illustration of chemical structure of PVC and SAN with the

possible sites of interaction shown by arrows.

Morphology, microstructure and miscibility studies 122 4.3.3 PS/PMMA blends

Polystyrene (PS) and poly(methyl methacrylate) (PMMA) both are flexible

thermoplastics with various optical and electronic properties and vital for

various device fabrication technologies. However, the literature indicates that the

blends of these two produce partially miscible blends. It would be technically

important that if the level of miscibility at different composition is known, then

through compatibilization improved interfacial adhesion can be achieved. The

improved interfacial adhesion would make these blends suitable for many

applications such as, in the fabrication of high density magnetic storage media etc

[Elbaum, 2000].

(a) DSC results

The DSC scans of the pristine polymers and their blends are shown in Figure

4.9. The DSC curves show that PS has Tg around 103 0C and PMMA showing a

broad glass transition from 84 0C to 98 0C. It is also evident that 80/20 and 50/50

composition of PS/PMMA blends exhibit two Tgs whereas 20/80 composition has

single glass transition.

Figure 4.9: DSC scans of pristine PS, PMMA and blends of PS/PMMA


Morphology, microstructure and miscibility studies 123 Similar to the previous blend, in this case also Tg of the blend constituents is

20 0C, the single glass transition observed for 20/80 composition seems to

mislead whether the system has single phase with a true single glass transition or

a phase separated one with the overlap of the two glass transitions. Due to the

observation of single broad glass transition at 20/80 composition, we can

conclude this composition produces miscible blend.

(b) SEM micrographs

SEM images of PS/PMMA blends of composition 80/20, 50/50 and 20/80 are

shown in Figure 4.10 (a,b,c) respectively. The compositions 50/50 and 80/20

exhibit clear phase separated domains of the dispersed phase, as a result of weak

interaction between the constituent polymers. But the micrograph representing

20/80 composition shows no signs of phase separation. This can be attributed to

homogenous dispersion of the dispersed phases in the matrix.

Figure 4.10: SEM images of PS/PMMA blends of composition (a) (80/20),

(b) (50/50) and (c) (20/80).

(c) PALS results

Table 4.3 presents the average lifetime parameters of PS/PMMA blends,

obtained from the PATFIT-88 and CONTIN-PALS2 computer programs.

Table 4.3: o-Ps lifetime, intensity and free volume parameters of the PS/PMMA


PS/PMMA PATFIT-88

CONTIN-PALS 2 (Averages derived from moments)


100/0 2.01 32.2 98.2 5.68 2.04 33.4 99.1 5.95

80/20 2.08 22.3 105.1 4.23 2.06 22.8 104.8 4.30

50/50 2.07 19.9 105.1 3.80 2.05 20.3 104.9 3.83

20/80 2.04 21.3 100.8 3.86 2.03 21.6 100.0 3.89


0/100 2.19 24.1 115.8 5.02 2.14 24.9 114.9 5.14

It can be noticed that the average value of free volume size Vf is same for

80/20 and 50/50 compositions (~105 Å3) but slightly less (101 Å3) for 20/80

composition. However, the fractional free volume FV shows decrease in the co-

continuous phase (50/50) and increases slightly at 20/80 composition.

Figure 4.11: Plot of (a) o-Ps lifetime PDF resolved from lifetime spectra

with cavity radius in the upper x-axis and lifetime in the lower x-axis (b)

free volume size (Vf) PDF for PS/PMMA blends.

From the o-Ps lifetime and free volume hole size distribution, (see Figure

4.11(a and b) obtained using the CONTIN-PALS 2 analysis it can be observed that

the free volume size PDF curve for PS/PMMA at 80/20 and 50/50 blend

compositions show broader distribution with FWHM equal to 36 and 38 Å3

Morphology, microstructure and miscibility studies 125 respectively compared to 20/80 composition which exhibits full width at half

maximum (FWHM) equal to 30 Å3. Similar trend can be seen in the lifetime

distribution curves also. The smaller FWHM and the small fractional free volume

(FV) value of PS/PMMA blend at 20/80 composition suggest close packing of the

constituent chains in that blend.

The positron results clearly support the DSC results where we observed only

a single broader Tg for 20/80 composition and the blend is termed as miscible.

The possible interactions for this miscibility may be either due to conformational

changes in the constituent polymer chains, or perhaps the interactions involving

the C=O carbonyl group of PMMA with hydrogen of PS [Callaghan and Paul, 1993;

Arlen and Dadmun, 2003] as shown in the Figure 4.12

Therefore based on the above discussions, it can be concluded that the

miscibility of the PS/PMMA blend is only at 20/80 composition, but the level of

miscibility compared to other polymer blends is not clear from these results.

Figure 4.12: Illustration of chemical structure of PS and PMMA,

the arrows indicate the possible sites of interaction.

4.3.4 PP/HDPE blends

Relatively low cost and adaptable properties make the polyolefins one of the

principal commodity thermoplastics [Dumoulin and Carreau, 1987]. As a

consequence, their blends have attracted great interest [Shanks et al., 2000;

Schimdt et al., 2001]. One such blend is PP/HDPE. It is well known that the impact

strength of PP increases at low temperatures through the addition of HDPE

[Flaris et al., 1993); Teh et al., 1994]. Unfortunately, PP and HDPE are highly

Morphology, microstructure and miscibility studies 126 immiscible resulting in poor properties of the final product [Rachtanapun et al.,

2003]. The huge worldwide annual consumption requirements of PP and HDPE

have resulted in continuous research efforts directed towards improving the final

products. The figure below gives the chemical structure of PP and HDPE pristine

polymers.

Figure 4.13: Illustration of chemical structure of PP and HDPE polymers.

(a) DSC results

HDPE is a semicrystalline polymer, which exhibits a well-defined crystalline

melting point at 135 0C with Hm = 109 J/g, Hm is the change in enthalpy of the

system. DSC scans of pristine PP, HDPE and their blends are shown in Figure 4.14.

We observe that PP has Tg at -20 0C and HDPE exhibits a clear melting at 135 0C.

Figure 4.14: DSC thermograms of pristine PP, HDPE and blends of PP/HDPE


Morphology, microstructure and miscibility studies 127 The DSC scans of the blends at all the compositions exhibit that, Tg

corresponding to PP seems to be not seen while only the Tm of HDPE is at the

same temperature making it difficult to infer the status of the blends like

miscible, immiscible or partially miscible by just following the general

interpretation of the DSC results in blends.

(b) SEM micrographs

The SEM pictures of the three compositions studied are shown in Figure 4.15

and show that they exhibit heterogeneous and coarse morphology with sharp

interfaces which certainly indicates the immiscible nature may be due to the

absence of any intermolecular interactions between PP and HDPE. This may

support the DSC measurements showing that blends are of immiscible nature.

Figure 4.15: SEM images of PP/HDPE blends of composition (a) (80/20),

(b) (50/50) and (c) (20/80).

(c) PALS results

The positron results for PP/HDPE blends from PATFIT-88 and CONTIN-

PALS2 computer programs are summarized in Table 4.4. For the blend of

PP/HDPE with 80/20 composition, which means HDPE is the disbursed phase;

the o-Ps lifetime is shorter than at the other two compositions namely 50/50 and

20/80.

Table 4.4: o-Ps lifetime, intensity and free volume parameters of the PP/HDPE

polymer blends determined from PATFIT-88 and CONTIN-PALS2 analysis.

PP/HDPE PATFIT-88



100/0 2.10 15.0 108.1 2.91 2.13 15.7 109.0 3.08 80/20 2.19 15.9 115.0 3.29 2.17 16.2 114.1 3.32

50/50 2.23 16.9 132.9 4.04 2.20 17.3 131.6 4.02


20/80 2.25 17.7 121.0 3.86 2.21 18.1 120.3 3.90

0/100 2.38 20.03 133.9 4.82 2.35 19.40 133.0 4.64

Secondly, the free volume size distributions obtained from CONTIN-PALS2

shown in Figure 4.16 are broader for 50/50 and 20/80 blend compositions with

FWHM = 42 Å3 and 40 Å3 respectively than 80/20 composition which exhibits a

narrower FWHM=35 Å3. Increase of free volume with the addition of HDPE

suggests additional free volume is being created and indicates the incompatibility

of the two components of the blend. The broader distribution of the free volume

hole size in PP/HDPE blends further supports the incompatibility.


cavity radius shown in the upper x-axis and lifetime in the lower x-axis (b)

free-volume size (Vf) PDF for PP/HDPE blends.


4.3.5 PVC/EVA blends

The authors investigation on the fifth blend system, of the present study,

namely PVC/EVA is discussed here. The two polymers chemical structure is

shown in Figure 4.17. As already mentioned earlier, all the desirable properties of

PVC are masked by its poor processability and impact strength. Generally to

overcome the poor processability PVC is mixed with plasticizers to increase the

processing temperature. These problems can be solved successfully by the

addition of small amounts of polymeric modifiers [1975; Lutz, 1983; Robeson,

1990]. One such modifier is ethylene-co-vinyl acetate (EVA) [Hammer 1971;

Siegmann and Hiltner, 1984]. It is essential that before the blend could be put into

practical use, understanding the compatibility between the constituents is

necessary.

Figure 4.17: Illustration of chemical structures of PVC and EVA polymers.

(a) DSC results

DSC scans of pristine PVC and EVA and their blend compositions of 80/20,

50/50 and 20/80 are shown in Figure 4.18.


Figure 4.18: DSC scans of pristine PVC, EVA and blends of PVC/EVA


From the scans, for PVC and EVA, we observe two clear glass transitions at

85 0C and -40 0C respectively. For the blends of all the three compositions, we

observe clearly two Tgs indicating the immiscible nature of the blends suggesting

lack of interaction between the constituent polymers.

(b) SEM micrographs

Phase morphology of different compositions of PVC/EVA blends is shown in

from the SEM micrographs (Figure 4.19). All the three images display phase

separated morphology which is possibly due to agglomeration of dispersed

phase. These results are in line with the DSC results discussed above.

Figure 4.19: SEM images of PVC/EVA blends of composition (a) (80/20),

(b) (50/50) and (c) (20/80).

(c) PALS results

Comparison of the average values of 3, I3, Vf and Fv values derived from

PATFIT-88 and CONTIN-PALS2 computer programs are summarized in Table 4.5.

For the PVC/EVA blends, we notice that the free volume hole size V f shows

Morphology, microstructure and miscibility studies 131 increasing trend as the EVA content increases suggesting additional free volume

created at the phase boundaries due to poor interfacial adhesion.

Table 4.5: o-Ps lifetime, intensity and free volume parameters of the PVC/EVA


PVC/EVA PATFIT-88



100/0 1.72 6.12 72.2 0.79 1.74 6.9 73.00 0.91

80/20 2.08 7.00 107.10 1.35 2.13 6.8 112.74 1.38

50/50 2.23 8.82 119.70 1.91 2.26 8.7 125.79 1.97

20/80 2.29 15.6 125.70 3.51 2.32 15.0 131.85 3.56

0/100 2.46 20.83 143.1 5.36 2.43 20.2 142.6 5.18

Similar trend is reflected in the radius and Vf distribution PDF curves

exhibited in Figure 4.20. It is to be noted that for this blend the distributions are

broader but appears to be symmetric curves unlike in other blends discussed so

far. Among these curves, 80/20 composition curve is narrower with FWHM = 35

Å3 and as EVA content increases to 50 and 80 composition distribution curve gets

slightly broader with FWHM = 37 Å3 and 40 Å3 respectively (see Figure 4.20b).

Presence of two Tgs seen from DSC, phase separated morphology from SEM

images, increasing Vf and FV values and broader distribution curves of radius and

free volume size all indicate the lack of interaction between PVC and EVA

components and the immiscibility of the blend at all compositions.



cavity radius shown in the upper x-axis and lifetime in the lower x-axis

(b) free volume size (Vf) PDF for PVC/EVA blends.

4.3.6 PVC/PS blends

The polymers polyvinyl Chloride (PVC) and polystyrene (PS) chemical

structures are shown in Figure 4.21. These two polymers form immiscible blends.

An appropriate compatibilization is essential to make these blends useful in the

practical use of the blends particularly to improve the blend’s temperature

performance and processability. Prior knowledge of the level of

miscibility/immiscibility at different compositions will make the selection of

compatibilizer easy.


Figure 4.21: Illustration of chemical structure of PVC and PS.

(a) DSC results

In Figure 4.22 DSC scans of pristine PVC, PS, and PVC/PS blends of

composition 80/20, 50/50 and 20/80 are shown.

Figure 4.22: DSC scans of pristine PVC, PS and blends of PVC/PS


Pristine PVC and PS polymers exhibit Tg at 85 0C and 98 0C respectively while

their blends show two glass transitions for all the three compositions. The two

glass-transition temperatures observed are above and below the Tg of PVC and PS

except at 20/80 composition which shows Tg close to that of 100 wt% PS. These

results infer that the blends are immiscible at all the three compositions.

(b) SEM micrographs

Morphology, microstructure and miscibility studies 134 Figure 4.23(a, b, c) are the SEM images showing the phase morphology of the

PVC/PS blends of composition 80/20, 50/50 and 20/80 respectively.

Figure 4.23: SEM images of PVC/PS blends of composition (a) (80/20),

(b) (50/50) and (c) (20/80).

These scans indicate the phase separated domains with a high degree of

anisotropy of the dispersed parts. Scan (c) which corresponds to 80 wt% PS,

phase separation is very clear and the domain sizes are bigger compared to the

other two compositions. The absence of compatibility between the constituent

polymers is demonstrated.

(c) PALS results

Table 4.6: o-Ps lifetime, intensity and free volume parameters of the PVC/PS


PVC/PS PATFIT-88



100/0 1.72 6.12 72.2 0.79 1.74 6.9 73.0 0.91

80/20 1.98 13.40 95.2 2.30 1.96 12.7 93.1 2.13

50/50 2.01 21.00 98.2 3.70 1.99 19.9 96.4 3.50

20/80 1.99 30.90 96.1 5.34 1.96 29.8 94.5 5.11

0/100 2.01 32.20 98.2 5.68 2.04 33.4 99.1 5.95

Data presented in Table 4.6 are the average lifetime parameters obtained

from PATFIT-88 and CONTIN-PALS2 computer programs. Similar to the previous

two blends which are immiscible, for this blend also analogous behaviour is

observed. That is with the increase in PS (having higher Vf and FV than PVC)

increase the average free volume cavity size and the free volume fraction. From

Figure 4.24 it can be seen that free volume radius and free volume hole size

distributions are wider for the 20/80 composition (FWHM = 42 Å3) while 50/50

Morphology, microstructure and miscibility studies 135 and 80/20 compositions show narrow (FWHMs 32 and 30 Å3) distribution

among themselves.


cavity radius shown in the upper x-axis and lifetime in the lower x-axis

(b) free-volume size (Vf) PDF for PVC/PS blends.

The increase in fractional free volume FV with increase in PS content in the

blend suggests the absence of any intermolecular interactions between PVC and

PS and additional free volume is generated with blending. Broadening of FWHM

of free volume size PDFs, with higher content of PS in the blend was also

observed by Liu [1995] so that it can be inferred that blends are immiscible in

nature.

4.3.7 SAN/EVA blends

Poly(styrene-co-acrylonitrile) (SAN) is a polar thermoplastic polymer with

high transparency, excellent gloss, high mechanical strength, and good chemical

Morphology, microstructure and miscibility studies 136 resistance. Poly(ethylene vinyl acetate) (EVA) copolymers, due to their rubbery

and resin properties, are used for several applications, such as packaging films,

adhesive coatings, cable insulation etc. Further, blends of these two polymers are

shown to increase the processing temperature and hence find variety of

applications. However, these two are also incompatible with each other.

(a) DSC

DSC scans of SAN and EVA system are presented in Figure 4.25. From this we

observe that Tg of SAN is 100 0C and that of EVA is -40 0C and the SAN/EVA

blends of composition 80/20, 50/50 and 20/80 exhibit two clear glass transitions

each one corresponding to their homopolymer glass transitions. This confirms

that SAN/EVA blends are immiscible systems.

Figure 4.25: DSC scans of pristine SAN, EVA and blends of SAN/EVA


(b) SEM micrographs

The SEM scans of SAN/EVA blends are given in Figure 4.26 for 80/20, 50/50

and 20/80 compositions. Absence of interaction between the constituent

polymers resulting in immiscibility, as is evident from the images showing phase

separated morphology consisting of micro domains of glassy SAN and rubbery

EVA parts.


Figure 4.26: SEM images of SAN/EVA blends of composition (a) (80/20),

(b) (50/50) and (c) (20/80).

(c) PALS results

Positron results from the analysis by PATFIT-88 and CONTIN-PALS2

programs for the blends of SAN/EVA are summarized in Table 4.7. Once again the

two programs are complementary to each other producing the same average

values. From the tabulated values, we observe that, as the EVA content in

SAN/EVA blends increases from 20 to 80%, the lifetime parameter, fractional free

volume increase which is a typical case of immiscible blends in which fee volume

content increase is normally due to additional free volume being generated upon

blending.

Table 4.7: o-Ps lifetime, intensity and free volume parameters of the SAN/EVA


SAN/EVA PATFIT-88



100/0 1.91 19.87 89.0 3.18 1.88 19.1 88.2 3.03

80/20 2.10 16.0 110.0 3.16 2.14 17.0 112.0 3.42

50/50 2.21 16.5 116.5 3.46 2.29 17.8 117.9 3.77

20/80 2.30 17.9 123.0 4.00 2.37 18.3 124.6 4.10

0/100 2.46 20.83 143.1 5.36 2.43 20.2 142.6 5.18

We have plotted in Figure 4.27, the free volume radius and volume

distribution PDFs from which the FWHM values have been derived. These widths

are wide with FWHMs 48, 51 and 55 Å3 for 80/20, 50/50 and 20/80 blend

compositions respectively. Compared to all other blends studied in this work,

Morphology, microstructure and miscibility studies 138 these widths are very large suggesting high incompatibility of the component

polymers.

Figure 4.27: Plot of (a) o-Ps lifetime PDF resolved from lifetime spectra and

cavity radius is shown in the upper x-axis and lifetime in lower x-axis (b) free

volume size (Vf) PDF for SAN/EVA blends.

Limitations of the methods (described in this chapter) in understanding

miscibility

The most common method used in the field of polymer blends to establish

polymer miscibility is Differential Scanning Calorimetry (DSC) in which

determination of the glass transition temperature (Tg) or the depression in the

melting temperature allow one to obtain details of the mixing or the well

dispersed environment of the blend [Utracki, 2002]. DSC of course comes with

the limitation that it is not sensitive below 15 nm domain size of the dispersed

Morphology, microstructure and miscibility studies 139 phase of the blend. Further, when the glass transitions of the component

polymers of the blend are close to each other (i.e., Tgs differ by 20 0C, example

PVC/SAN blend), Tg measurement may mislead due to overlap of the two Tgs

resulting in a broader single Tg. This happens due to the inadequacy of DSC in

resolving the Tgs, thereby forcing one to infer the blend as miscible. Therefore,

there is an argument that measurement of Tg in blends give only the degree of

dispersion but not true thermodynamic miscibility. Also, Tg measurement

becomes insensitive when the amount of the dispersed component is less than

about 10 wt%.

SEM is also frequently used to study miscibility but the information it yields

is limited. With this technique one can only examine the surface level information

regarding the distribution of dispersed phase in the matrix but not really sure

whether it holds good to the bulk of the sample.

However the use of PALS in the study of polymer blends has generated lot of

interest and also data since it is a highly sensitive and sophisticated technique for

characterizing defects, micro voids or free volume holes of smaller dimensions.

We have seen in the discussion of PALS results of the seven polymer blends

reported in this chapter that mere free volume measurement by PALS will not

provide information whether the free volume changes upon blending are within

the component polymers or the blend as whole, in particular at the interface of

the two components which is very important from the miscibility point of view.

The literature survey also indicates that the interchain interaction parameter

, proposed by Liu et al., [1995] (discussed in chapter 2 sub-section 2.5.1) and

calculated from the fractional free volume did not exhibit any systematic to infer

that a particular composition is optimum to produce high level miscibility [Raj

and Ranganathaiah, 2009; Ranganathaiah and Kumaraswamy,2009]. Therefore,

parameter’s utility in the study of miscibility turns out to be little help.

Thus, merely on the basis of DSC, SEM and PAL results at different

compositions, one cannot judge which composition of a blend produces good

interface adhesion so that its miscibility level is highest. This becomes an

Morphology, microstructure and miscibility studies 140 important issue with regard to polymer blends in particular immiscible and

partially miscible blends.

To overcome this inadequacy in the characterization methods, in recent

years a new method based on hydrodynamic interaction approach was developed

by Ranganathaiah et al. [Ranganathaiah and Kumaraswamy, 2009; Jamieson et al.,

2012; Ramya and Ranganathaiah (2012, 2013)] which uses the same free volume

parameters derived from o-Ps lifetime data to determine the composition

dependent miscibility level of blends. This method introduces two parameters

namely the geometric factor γ and hydrodynamic interaction characterized by

parameter. The γ parameter signifies the geometrical architecture of the chain

configuration of the polymer blend. The hydrodynamic interaction parameter,

from the Wolf et al. theory [Schnell and Wolf, (2000, 2001)] developed for

polymer blends in solution has been suitably modified to polymer blends in solid

phase and its usefulness in determining the composition dependent miscibility

level is well explored for a number of polymer blends. [Raj and Ranganathaiah,

2009; Ranganathaiah and Kumaraswamy, 2009; Jamieson et al., 2012; Meghala

and Ranganathaiah, 2012; Ramya and Ranganathaiah (2012, 2013)]. This theory

is based on hydrodynamic interaction between the constituent polymers of the

blend at the interfaces. Complete details of the hydrodynamic theory is provided

in Chapter 2 sub-section 2.5.2

4.4 Miscibility determination via hydrodynamic interaction

The hydrodynamic interaction parameter by definition quantifies the

excess friction developed at the interface between component 1 and 2 of the

blend especially between unlike polymer chains.

The hydrodynamic interaction parameter , geometric parameter γ are

calculated by using the experimentally measured fractional free volumes of the

pristine components and the blends, and volume fractions by recalling the

relevant equations from chapter 2; we have

Morphology, microstructure and miscibility studies 141 where FV1 and FV2 are the fractional free volumes and ϕ1 and ϕ2 are volume

fractions of constituent polymer 1 and 2 of the blend. FV is the fractional free

volume of the blend, and δ is expressed in terms of fractional free volumes of the

component polymers as

The final expression employed for the determination of hydrodynamic

interaction parameter is

(4.8)

here ΔFV is defined as

i.e., difference in the reciprocal fractional free volumes of the constituent polymer

1 and 2 of the blends. Complete details of the derivation can be found in chapter

2.

In case of favourable interactions (the case for miscible blends) the

monomers (beads as per the bead-spring theory) are brought closer to each other

due to attractive interactions and as a result excess friction is generated at the

interface (as depicted in Figure 1.10). This leads to increased dissipation of

energy and less tension at the interface. The energy dissipation is indicated by

the negative sign of the hydrodynamic interaction parameter (α). If

miscibility is high at certain composition of the blend, takes on large values

[Ranganathaiah and Kumaraswamy, 2009; Jamieson et al., 2012; Meghala and

Ranganathaiah, 2012; Ramya and Ranganathaiah (2012, 2013)]. On the other

hand, for immiscible blends, values are small or close to zero or even become

positive. This indicates the absence of any favourable interactions between the

constituent polymers, and hence very little or no friction is generated at the

interface (see Figure 1.10). As a consequence, can be considered as a measure

Morphology, microstructure and miscibility studies 142 of excess friction between the molar surfaces of the component polymer chains.

With this prescription of hydrodynamic interaction parameter the above seven

polymer blends are again discussed with regards to composition dependent

miscibility level in the following paragraphs.

4.4.1 SAN/PMMA blends

The geometric factor (γ) and hydrodynamic interaction parameter, are

calculated from equation (4.6) and (4.8) respectively. These values for the three

compositions of the blend are tabulated in Table 4.8.

Table 4.8: Geometric parameter and hydrodynamic interaction parameter

for SAN/PMMA blends.

SAN/PMMA Geometric factor

(γ)

Hydrodynamic interaction parameter ()

80/20 -0.80 -63.40

50/50 -0.76 -12.40

20/80 -0.72 -2.15

To understand the meaning of these results, let us look in to the important

observation made by different techniques on this particular blend (SAN/PMMA);

that is this blend has been found to be miscible throughout the concentration

range, but none of them have indicated the extent or degree of miscibility at

different compositions.

From the Table 4.8 we observe that the parameter varies with composition

and it is negative. A large value of 63.4 at 20 wt% PMMA concentration indicates

that the hydrodynamic interaction is strong between the chains of the component

polymers at this composition. So the friction at the interface is high and energy

dissipation occurs, hence tension is reduced. Therefore it can be inferred that

degree of miscibility is maximum at this composition.

The interpretation is as follows: At 20 wt% of PMMA, SAN is the matrix and

PMMA is the dispersed phase. Further, the repulsive forces between styrene and

acrylonitrile groups of SAN chains make it easy for PMMA chains to slide fast

between the chains of SAN, and hence a fine dispersion results. But as the SAN

Morphology, microstructure and miscibility studies 143 content decreases and PMMA content increases, the net repulsive force decrease,

and hence the friction also decreases. Alongside, since the PMMA content is large,

its chains tend to form their own domains instead of getting associated with the

SAN chains. Secondly one more important point to be noted is that SAN has large

molecular weight (1,65,000 g/mol) compared to PMMA (15,000 g/mol). The

relatively large molecular weight of SAN also restricts its easy entry into the

PMMA matrix.

Therefore, we can infer that 20 wt% PMMA is the optimum composition,

resulting in good dispersion and excess friction; so a high degree of miscibility in

the SAN/PMMA blends. Other important point is that, the blend miscibility is not

due to any specific interactions between SAN and PMMA chains but because of

fine dispersion of PMMA in SAN matrix according to the description given above.

4.4.2 PVC/SAN blends

PVC/SAN is a partially miscible blend well supported through DSC and SEM

and PALS results. Let us try to understand from the hydrodynamic interaction

perspective ( values from Table 4.9).


for PVC/SAN blends.

PVC/SAN Geometric factor

(γ)


80/20 1.23 -2.10

50/50 1.50 -0.73

20/80 2.51 -0.27

Only at 20 wt% of SAN in PVC/SAN blend, shows higher value of 2.1

indicative of interaction between PVC and SAN, while at 50/50 and 20/80, the

values are small but still negative. Since values are small and close to zero,

these two compositions produce immiscible blends. The γ parameter is positive

at all compositions and greater than unity.

The observed variation in this blend are due to the interaction between

SAN and PVC which is influenced by the acrylonitrile (AN) concentration in SAN

Morphology, microstructure and miscibility studies 144 owing to self-association of AN groups and steric effects [Kim et al., 1996]. Also

there are two more possible interactions, namely an induced dipole interaction

between the aromatic quadrupole (benzene ring) of SAN and halogen (chlorine)

of the PVC as well as hydrogen bonding between the AN and the α-hydrogen of

PVC as depicted in Figure 4.8 [Moon et al., 2007].

4.4.3 PS/PMMA blends

The values of γ and hydrodynamic interaction parameter , evaluated using

equation (4.8) for PS/PMMA blends at three compositions are tabulated in Table

4.10.

Table 4.10: Geometric parameter () and hydrodynamic interaction parameter ()

for PS/PMMA blends.

PS/PMMA Geometric factor

(γ)


80/20 1.04 -0.42

50/50 0.37 -0.28

20/80 -0.71 -1.75

PS/PMMA blend is known to be partially miscible that is, it exhibits

miscibility at some compositions and become immiscible at other compositions.

As already mentioned for this blend, there exists a possible interaction (see

Figure 4.12) between the carbonyl group (C=O) of PMMA and -hydrogen of PS

[Callaghan and Paul, 1993; Arlen and Dadmun, 2003]. From Table 4.10 we can

observe that, has large value of 1.75 at 20 wt% of PS and decreases as the PS

content in the system increases. In comparison with miscible SAN/PMMA system

for which has the highest value of 64 and the partially miscible PVC/SAN

system which has a maximum value of equal to 2.1, the value of at PS/PMMA-

20/80 composition is low (1.75). Even then this composition produces highest

miscibility in PS/PMMA blend and the other two compositions are immiscible.

According to Wolf et al. theory, is independent of composition of the system

[Schnell and Wolf, (200,2001)]. However, since depends on the molecular

surfaces and volumes in the system and blend composition influences the phase

Morphology, microstructure and miscibility studies 145 morphology, molecular arrangement and orientation it is expected that shall

vary with the blend composition. This has been confirmed from the variation in

the values of γ parameter in all the three polymer blends mentioned above.

Nevertheless, we observe that does not show any systematic behaviour with

respect to blend compositions. Further it is evident that parameter do not

reveal any information regarding the composition dependent changes in the

interface.

4.4.4 PP/HDPE blends

It is well documented that PP and HDPE are incompatible polymers and

produce immiscible blends. Results from DSC, SEM and free volume results have

supported this inference. In Table 4.11, we have tabulated the hydrodynamic

interaction parameter, and geometric parameter, γ for the three compositions

of the blend.

Recalling the prescription given to parameter earlier, that is, it is a measure

of friction generated at the interface and it provides the composition dependent

attractive or repulsive interaction level at the interface. We observe the values of

parameter in Table 4.11.


for PP/HDPE blends.

PP/HDPE Geometric factor

(γ)


80/20 -1.55 -0.85

50/50 -2.90 -0.16

20/80 -3.90 -0.21

For all the three compositions values are negative but less than unity or it

is close to zero and hence the PP/HDPE blend is termed immiscible at all the

compositions.

4.4.5 PVC/EVA blends

Morphology, microstructure and miscibility studies 146 PVC/EVA blend has been shown to be an immiscible blend. The values of

parameter tabulated in Table 4.12, similar to PP/HDPE blend, are less than

unity/close to zero but negative for all the three compositions hence confirming

the immiscible nature at all the compositions of this blend. Thus, verifying the

absence of any kind of interaction between the constituent polymers.


for PVC/EVA blends.

PVC/EVA Geometric factor

(γ)


80/20 5.65 -0.62

50/50 2.06 -0.41

20/80 5.93 -0.12

4.4.6 PVC/PS blends

The blend system PVC/PS is also known to be immiscible blend due to lack of

interaction among its constituents and this is well supported by the present DSC,

SEM and free volume data. For this blend we can expect values to be smaller

and may be closer to zero. The values calculated for PVC/PS blend systems at

different composition are presented in Table 4.13. The data shows that the value

of is close to zero at all compositions and hence infer that the blend is

immiscible throughout the composition range. The interesting point is that the γ

parameter assumes positive and higher value around 6 irrespective of the

composition indicating the geometrical arrangement of the chains in the blends

do not vary very much for this blend compared to the previous blends.

Table 4.13: Geometric parameter and hydrodynamic interaction parameter for

PVC/PS blends

PVC/PS Geometric factor

(γ)



80/20 6.40 -0.48

50/50 6.98 -0.06

20/80 6.83 -0.006

4.4.7 SAN/EVA blends

DSC, SEM and free volume results indicate the absence of any kind of

interactions between SAN/EVA blend components. According to the prescription

for an immiscible blend, the value is expected to be small or may be close to

zero. Table 4.14 data for this blend do indeed proves this. The important point to

be noted is value is very small and is very large at 80 wt% of EVA.

Table 4.14: Geometric parameter and hydrodynamic interaction parameter for

SAN/EVA blends

SAN/EVA Geometric factor

(γ)


80/20 -3.67 -0.00148

50/50 -5.15 -0.00144

20/80 -8.35 -0.00072

This is an obvious indication of non-mixing of the components leading to no

friction or no contact at the interfaces of the dissimilar polymer chains in the

blend confirming the dearth of interactions in it.

4.5 Conclusions

Morphological, microstructural and miscibility study of three types of

polymer blends namely (i) Miscible, (ii) Partially Miscible and (iii) Immiscible

blends have been studied using DSC, SEM and Positron Lifetime Techniques.

Based on the results and the discussions above, the following conclusions are

drawn:

DSC, SEM and positron lifetime parameters give an overall view of the blend

like a blend is miscible or immiscible but, they are inadequate to resolve


which composition produces better interfacial adhesion in the blend

resulting in higher level of miscibility.

The hydrodynamic interaction parameter, derived from free volume data

proved to be a parameter of choice to monitor the interface changes and

hence determine which composition results in high miscibility. But the

geometric factor due to its arbitrary variations could not be considered as

an indicator of the level of miscibility of a given system.

The studied blends fall in to the three categories mentioned above.

SAN/PMMA is miscible and at 20 wt% of PMMA produces highest miscibility.

Secondly PVC/SAN, PS/PMMA blends exhibit partially miscible character and

finally PP/HDPE, PVC/EVA, PVC/PS and SAN/EVA blends are immiscible. Out

of 4 immiscible blends studied, SAN/EVA blend is highly immiscible for

which the hydrodynamic interaction parameter is very small and gamma

parameter is highest meaning the two components SAN and EVA are highly

incompatible.

From the present study, it is clear that through determination we get the

information, not only on the particular composition of a polymer blend which

produces highest miscibility but also provide an opportunity to select a

suitable method for compatibilization to fine tune the blend in this

composition.

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final synopsis of the proposed thesis -...

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