morphological and contact angle studiesshodhganga.inflibnet.ac.in/bitstream/10603/7079/13/13_chapter...

Chapter 5.1

Morphological and Contact Angle Studies

Abstract Transmission electron microscopy and contact angle measurements have bee

performed on EVA-calcium phosphate nanocomposites. Transmission electron

microscopic images of the nanocomposites showed good dispersion in the

nanocomposites. Contact angle measurements of the composites with water and

methylene iodide were calculated. Various wetting parameters such as total solid

surface free energy, work of adhesion, interfacial free energy and spreading

coefficient were analysed. The interaction parameter between the polymer and the

liquid has been calculated using the Girifalco-Good’s equation.

The results of this chapter have been submitted for publication in Polymer

180 Chapter 5.1

5.1.1 Introduction

Recently, ethylene vinyl acetate (EVA)-based nanocomposites have attracted a lot

of attention as a simple and cost effective method of enhancing polymer

properties by the addition of a small amount of properly designed filler, leading to

the creation of composite materials where the reinforcing particles can be

distributed in the polymeric matrix at the nanometer level [1-8].

Contact angle measurements of solids are a frequently accepted characterization

technique for their surface energy properties such as wettability and adhesion.

Using this technique one can measure the surface free energy, interfacial free

energy as well as polar and dispersion energy contributions. The contact angle is

measured as the tangent angle formed between a liquid drop and its supporting

surface. Wettable solid surfaces are of great interest in applications such as

biocompatibility, printing, coating, oil recovery, membranes for reverse osmosis,

food technology etc. Several researchers studied the contact angle behavior of

polymer blends, membranes and composites in recent times. Varughese et al

studied the contact angle behavior of poly vinyl chloride epoxidised natural rubber

miscible blends and related the decrease in contact angle or the increase in

surface free energy to the improved chain mobility and the accumulation of excess

polar sites at the surface through conformational alterations resulting from the

specific interactions of the blend components [9]. Park and Jin studied the effects

of silane coupling agent treatments on the fiber surface properties in terms of the

surface energetics of the fibers and the mechanical interfacial properties, including

ILSS and KIC, of the unsaturated polyester composites [10]. From the experimental

results, it is noted that the silane coupling agent containing the amino silane does

lead to an increasing of the mechanical interfacial properties of composites. Also,

the study of surface free energies and their components determined from the

multiple testing liquids seems to correlate with the study of mechanical interfacial

properties which clearly resulted in increasing the specific component of surface

free energy for the intermolecular or physical bonding properties among three, not

identical, elements of the composites. Saihi et al performed the wettability studies

on PET fibres according to the Wilhelmy method [11]. They obtained qualitative

and quantitative indications about the degree of the water and oil repellency and

Morphological and Contact Angle Studies 181

of the surface free energy of the grafted surface. The wetting force, the contact

angles averages and the hysteresis between the advancing and the receding

forces provide information on the surface heterogeneities and the effect of the

grafting on the surface fiber.

Very recently Gulec et al [12] analyzed the surface properties of food contacting

materials by a novel technique so called plasma polymerization. A simple captive

bubble method was employed to measure the surface hydrophilicity of solids by

measuring the contact angle of air and n-octane on the solid under water. This

method is used to determine the effects of glow-discharge plasma on the solid

surfaces. The modification of various substrate surfaces by plasma polymerization

technique using various monomers caused significant negative changes on the air

contact angle, and positive changes on surface free energy. Modification of glass

substrates by phenol plasma caused some increase of the air contact angle, and

the decrease of surface free energy (SFE). Based on the contact angle and

surface free energy results, it has been shown that SFE values increased related

to decrease in contact angles. Neema et al developed the nano-epoxy matrices

having stable surface energy levels because the solutions are homogeneous and

uniform, which are different from the non-functionalized nanofibers filled epoxy

matrices [13].

This chapter deals with the TEM examination and the wetting behavior of the

poly(ethylene-co-vinyl acetate)/calcium phosphate nanocomposites with respect to water and methylene iodide. This study focuses on the effect of weight percentage

of nanofiller on wetting characteristics such as work of adhesion, total surface free

energy, interfacial free energy and spreading coefficient. The change in contact

angle of water on the polymer surface was also measured. The TEM analysis

showed the dispersion of the nanoparticles in the polymer matrix.

5.1.2 Results and discussion 5.1.2.1. Transmission electron microscopy studies Transmission electron microscopic images of the nanocomposites are given in

figure 5.1.1 (a-e). The neat EVA gives a clear picture in the TEM image. From the

182 Chapter 5.1

TEM images of the nanocomposites, the nanoparticles are shown to be dispersed

well in the matrix.

Figure 5.1.1. TEM images of EVA-Calcium phosphate nanocomposites a) Neat

EVA and b) 1%, c) 3%, d) 5% and e) 10% filled systems (magnification 100 nm).

(d)

(b) (c)

(e)

(a)


As we go from the low filler loading, say 1%, we can see small groups of particles

in the matrix. In 7% filled composites the particle agglomerates can be seen.

When there is good interaction between the polymer matrix and filler the chances

for agglomeration will be less. But owing to the large surface energy for the

nanoparticles the increase in the amount of fillers causes more particle-particle

interaction, which increased agglomeration of the particles in the matrix. This is

clearly seen in the TEM images.

5.1.2.2. Contact angle measurements Contact angle measurements of nanocomposites of EVA with calcium phosphate

were done at room temperature with water and methylene iodide as the liquids.

Various parameters from these measurements were calculated. At first, the

contact angles were measured for each specimen for at least six to ten times. The

average is taken as the contact angle for the particular specimen. Figure 5.1.2

shows the representative pictures of the measurements. In 5.2.2(a) the contact

angle for the neat EVA is given and 5.1.2(b) and (c) represent the same for E5

and E10 respectively. Here the tilt angle is always kept as 0 and an average of the

left hand side and right hand side contact angles is given as the true contact

angle. In most of the measurements the left and right hand side values are similar.

In figure 5.1.3 the change in contact angle with respect to the filler content is

plotted.

Figure 5.1.2. Representative figures of contact angle measurements of (a) EVA (b) E5 and (c) E10 with water as liquid. Corresponding contact angles are given in parenthesis.

(a) (63.33)0 (b) (77.54)0 (c) (74.84)0

184 Chapter 5.1

0 2 4 6 8 1066

68

70

72

74

76

78

watermethylene iodide

Weight % of filler

θ, d

egre

e

42

44

46

48

θ, degree

Figure 5.1.3. Variation of contact angle of water and methylene iodide with respect to filler loading

The values given in the curves are the averages of the similar measurements.

Here we can see that the filled composites show increased contact angle for all

compositions. Concomitantly, the work of adhesion, WA, which is the work

required to separate the solid and liquid, decreases (Figure 5.1.4). The contact

angles for both water and methylene iodide increases with respect to the filler

content. For water, θ increases from 68 to 78 and show a decrement to 73 for

higher loading.


As we go from the low filler loading, say 1%, we can see small groups of particles

in the matrix. In 7% filled composites the particle agglomerates can be seen.

When there is good interaction between the polymer matrix and filler the chances

for agglomeration will be less. But owing to the large surface energy for the

nanoparticles the increase in the amount of fillers causes more particle-particle

interaction, which increased agglomeration of the particles in the matrix. This is

clearly seen in the TEM images.

5.1.2.2. Contact angle measurements Contact angle measurements of nanocomposites of EVA with calcium phosphate

were done at room temperature with water and methylene iodide as the liquids.

Various parameters from these measurements were calculated. At first, the

contact angles were measured for each specimen for at least six to ten times. The

average is taken as the contact angle for the particular specimen. Figure 5.1.2

shows the representative pictures of the measurements. In 5.2.2(a) the contact

angle for the neat EVA is given and 5.1.2(b) and (c) represent the same for E5

and E10 respectively. Here the tilt angle is always kept as 0 and an average of the

left hand side and right hand side contact angles is given as the true contact

angle. In most of the measurements the left and right hand side values are similar.

In figure 5.1.3 the change in contact angle with respect to the filler content is

plotted.

Figure 5.1.2. Representative figures of contact angle measurements of (a) EVA (b) E5 and (c) E10 with water as liquid. Corresponding contact angles are given in parenthesis.

(a) (63.33)0 (b) (77.54)0 (c) (74.84)0

184 Chapter 5.1

0 2 4 6 8 1066

68

70

72

74

76

78

watermethylene iodide

Weight % of filler

θ, d

egre

e

42

44

46

48θ, degree

Figure 5.1.3. Variation of contact angle of water and methylene iodide with respect to filler loading

The values given in the curves are the averages of the similar measurements.

Here we can see that the filled composites show increased contact angle for all

compositions. Concomitantly, the work of adhesion, WA, which is the work

required to separate the solid and liquid, decreases (Figure 5.1.4). The contact

angles for both water and methylene iodide increases with respect to the filler

content. For water, θ increases from 68 to 78 and show a decrement to 73 for

higher loading.


0 2 4 6 8 1086

88

90

92

94

96

98

100

102

water methylene iodide

Weight % of the filler

WA,

mJ/

m2

85

86

87

88

89W

A , mJ/m

2

Figure 5.1.4. Variation of work of adhesion of water and methylene iodide with

respect to filler loading

This indicates that composites’ affinity towards water decreases and thereby

increases the hydrophobic nature. In the case of methylene iodide, the original

θ value was 42 and it also shows an increasing trend. For the composites up to

3% filler loading, the values are almost same. But for the 5 and 10% filled

composites θ increased to 470 and 460 respectively. This means that the

composites show less affinity towards methylene iodide also. Thus filler loading

has an effect on the contact angles of these liquids. Ultimately we can say that the rate of the increase for contact angle is high for water compared to methylene

iodide. Also the wetting of water and methylene iodide on the EVA

nanocomposites specimens decreased.

Figure 5.1.5 shows the variation in total solid surface free energy, γs, with respect

to the filler loading. When we increase the filler loading the total solid surface free

energy decreases which means that the wetting of liquids is less compared to the

neat specimens. Also the dispersive and polar components were calculated by

solving the harmonic mean equations given earlier. For neat EVA the γs value was

186 Chapter 5.1

50.80 and it decreased up to 44.20 for the 5% filled composites and shows an

increase to 46.80. This means that the nature of the forces acting on the surface of

the composites is different.

0 2 4 6 8 10

44

45

46

47

48

49

50

51

τ s, m

J/m

2

Weight % of filler

Figure 5.1.5. Variation of total solid surface free energy with respect to filler loading for water and methylene iodide

From Table 5.1.1, we can see that the dsγ values do not show considerable

variation with respect to the filler loading while psγ values show much difference.

The polar forces acting on the surface of the composites decreased compared to

the neat polymer and thus the total solid surface free energy decreased. Again for

the 10% filled systems the value is slightly higher compared to other filled

compositions, which accounted for the increase in the total solid surface free

energy. The filler dispersion in the polymer matrix may also have affected the

surface properties. Here the initial loadings have good dispersion behavior while

particle agglomeration occurred in the higher loading. This might have caused the

increment in psγ values for the higher loading. So the hydrophobic nature of the

composites became more prominent with the nanofiller addition.


0 2 4 6 8 1086

88

90

92

94

96

98

100

102


Weight % of the filler

WA,

mJ/

m2

85

86

87

88

89

WA , m

J/m2

Figure 5.1.4. Variation of work of adhesion of water and methylene iodide with


This indicates that composites’ affinity towards water decreases and thereby

increases the hydrophobic nature. In the case of methylene iodide, the original

θ value was 42 and it also shows an increasing trend. For the composites up to

3% filler loading, the values are almost same. But for the 5 and 10% filled

composites θ increased to 470 and 460 respectively. This means that the

composites show less affinity towards methylene iodide also. Thus filler loading

has an effect on the contact angles of these liquids. Ultimately we can say that the rate of the increase for contact angle is high for water compared to methylene

iodide. Also the wetting of water and methylene iodide on the EVA

nanocomposites specimens decreased.

Figure 5.1.5 shows the variation in total solid surface free energy, γs, with respect

to the filler loading. When we increase the filler loading the total solid surface free

energy decreases which means that the wetting of liquids is less compared to the

neat specimens. Also the dispersive and polar components were calculated by

solving the harmonic mean equations given earlier. For neat EVA the γs value was

186 Chapter 5.1

50.80 and it decreased up to 44.20 for the 5% filled composites and shows an

increase to 46.80. This means that the nature of the forces acting on the surface of

the composites is different.

0 2 4 6 8 10

44

45

46

47

48

49

50

51

τ s, m

J/m

2

Weight % of filler

Figure 5.1.5. Variation of total solid surface free energy with respect to filler loading for water and methylene iodide

From Table 5.1.1, we can see that the dsγ values do not show considerable

variation with respect to the filler loading while psγ values show much difference.

The polar forces acting on the surface of the composites decreased compared to

the neat polymer and thus the total solid surface free energy decreased. Again for

the 10% filled systems the value is slightly higher compared to other filled

compositions, which accounted for the increase in the total solid surface free

energy. The filler dispersion in the polymer matrix may also have affected the

surface properties. Here the initial loadings have good dispersion behavior while

particle agglomeration occurred in the higher loading. This might have caused the

increment in psγ values for the higher loading. So the hydrophobic nature of the

composites became more prominent with the nanofiller addition.


Composites dsγ psγ γs wφ mφ

E0 36.42 14.29 50.71 0.82 0.37

E1 37.28 10.57 47.85 0.77 0.38

E3 36.23 10.47 46.70 0.77 0.38

E5 34.06 10.12 44.19 0.77 0.38

E10 34.58 12.23 46.82 0.80 0.37

Table 5.1.1. Surface free energy and Girifalco-Good’s interaction parameter of

EVA/CP nanocomposites

The interfacial free energy between the polymer surface and the test liquids, water

and methylene iodide, were calculated and the curves are shown in figure 5.1.6.

The behavior of the liquids is just opposite to each other as one is polar and the

other is non-polar. For water, γsw, increases with respect to the filler loading and

shows a maximum for 1% filled system and thereafter it decreases. For methylene

iodide, γsm, decrease from the neat sample, reaches a minimum for 3% filled

systems and increase for the higher filled systems. The abnormal values for the

10% filled systems is due to the high value for polar component obtained by the

analysis of the equations.

188 Chapter 5.1

0 2 4 6 8 1022

24

26

28

30

water methyleneiodide

Weight % of filler

γ sl,

mJ/

m2

8

9

10

11

12

13

14

γsl , mJ/m

2

Figure 5.1.6. Variation of interfacial free energy of water and methylene iodide

with respect to filler loading

In figure 5.1.7 the spreading coefficient of the liquids; according to equation (4.1.7)

in chapter 4.1; with respect to the filler loading is given. If the value is positive the

implication is that the liquid will spontaneously wet and spread on a solid surface

and if it is negative the lack of wetting and spreading can be ascertained. This

means the existence of a finite contact angle (θ>0). From figure 5.1.7, we can

deduce that as we increase the filler content the spreading coefficient values

become more negative for both the systems. Overall the wetting decreased with

the addition of fillers. Comparing water and methylene iodide, the less negative

value is given by methylene iodide, which means that it is a better wetting agent

for the current composites.

In order to understand the degree of interaction between the test liquid and

polymer surface, Girifalco-Good’s interaction parameter was calculated using the

equation (4.1.8) in chapter 4.1 and the values are given in Table 5.1.1. Generally

a higher value indicates greater interaction and vice versa. wφ and mφ are the

Girifalco-Good’s interaction parameters due to water and methylene iodide,

respectively. From the values one can see that the interaction between water and


Composites dsγ psγ γs wφ mφ

E0 36.42 14.29 50.71 0.82 0.37

E1 37.28 10.57 47.85 0.77 0.38

E3 36.23 10.47 46.70 0.77 0.38

E5 34.06 10.12 44.19 0.77 0.38

E10 34.58 12.23 46.82 0.80 0.37

Table 5.1.1. Surface free energy and Girifalco-Good’s interaction parameter of

EVA/CP nanocomposites

The interfacial free energy between the polymer surface and the test liquids, water

and methylene iodide, were calculated and the curves are shown in figure 5.1.6.

The behavior of the liquids is just opposite to each other as one is polar and the

other is non-polar. For water, γsw, increases with respect to the filler loading and

shows a maximum for 1% filled system and thereafter it decreases. For methylene

iodide, γsm, decrease from the neat sample, reaches a minimum for 3% filled

systems and increase for the higher filled systems. The abnormal values for the

10% filled systems is due to the high value for polar component obtained by the

analysis of the equations.

188 Chapter 5.1

0 2 4 6 8 1022

24

26

28

30

water methyleneiodide

Weight % of filler

γ sl,

mJ/

m2

8

9

10

11

12

13

14γsl , m

J/m2

Figure 5.1.6. Variation of interfacial free energy of water and methylene iodide

with respect to filler loading

In figure 5.1.7 the spreading coefficient of the liquids; according to equation (4.1.7)

in chapter 4.1; with respect to the filler loading is given. If the value is positive the

implication is that the liquid will spontaneously wet and spread on a solid surface

and if it is negative the lack of wetting and spreading can be ascertained. This

means the existence of a finite contact angle (θ>0). From figure 5.1.7, we can

deduce that as we increase the filler content the spreading coefficient values

become more negative for both the systems. Overall the wetting decreased with

the addition of fillers. Comparing water and methylene iodide, the less negative

value is given by methylene iodide, which means that it is a better wetting agent

for the current composites.

In order to understand the degree of interaction between the test liquid and

polymer surface, Girifalco-Good’s interaction parameter was calculated using the

equation (4.1.8) in chapter 4.1 and the values are given in Table 5.1.1. Generally

a higher value indicates greater interaction and vice versa. wφ and mφ are the

Girifalco-Good’s interaction parameters due to water and methylene iodide,

respectively. From the values one can see that the interaction between water and


polymer surface is more compared to methylene iodide and the surface. For water

as we increase the filler loading the parameter show decrease and for methylene

iodide the interaction parameter show a slight increase. Thus, for the polar liquid

the interaction between the polymer surface and liquid decrease while the

opposite is shown for the non-polar liquid. This is can be evidenced also from

figure 5.1.6 showing the behavior of interfacial free energy of the composites.

0 2 4 6 8 10-44

-46

-48

-50

-52

-54

-56

-58


Weight % filler

Sc,

mJ/

m2

-12

-13

-14

-15

-16

-17

Sc , m

J/m2

Figure 5.1.7. Variation of spreading coefficient of water and methylene iodide with


The variation of the contact angle of water with time on the surface of the neat

EVA and nanocomposites were analyzed. The curves are shown in figure 5.1.8.

All curves show similar behavior. In the initial region we can see a sharp decrease

in contact angle. Thereafter the contact angles regularly decrease. The surface of

the specimens and the liquid has some interaction over a time of period and is

expected to reach a saturation point. The surface free energy of polymers and

polymer composites decays due to the conformational alterations and surface

restructuring as the contact time of the liquid increases [14, 15]. Lavielle and

Schultz [14] have noted in acrylic grafted polyethylene samples undergo surface

190 Chapter 5.1

free energy changes when it is in long time contact with water. In this case dsγ initially increased and then decreased, whereas

psγ decreased continuously

with the contact time. In this context, the filler addition in EVA may also bring

about some surface restructuring. Also the presence of filler particles on the

surface may lower the contact angle over a period of time.

0 100 200 300 400 500 600 70050

55

60

65

70

75

80

85

θ, d

egre

e

Time (sec)

E0 E1 E3 E5 E10

Figure 5.1.8. Variation in contact angle of water with respect to time

5.1.3. Conclusion TEM images of the nanocomposites clearly showed dispersion of the fillers in the

EVA matrix. For lower filler loading, the filler particles do not agglomerate but

while increasing the loading they agglomerate. This is mainly due to the filler interaction between them to reduce the free energy. Contact angle measurements

of EVA/calcium phosphate nanocomposites with water and methylene iodide

showed increase in the contact angles both liquids. The hydrophobic nature of the

composites increased with the addition of nanofillers. The solid surface free

energy of the composites increased and thereby decreases the work of adhesion.

The interaction between the liquid and solid surface became less compared to the

neat polymer. With respect to time the contact angle of water decreased for


sometime and leveled off which indicated some interaction between the

surface and water. Methylene iodide showed less negative value for the

spreading coefficient than water and it is a good wetting agent than water.

Overall the hydrophobicity increased. Also the particle dispersion has a say

among the various parameters measured as each one of them changed

according to the filler loading.

5.1.4. References

1. FP La Mantia, N Tzankova Dintcheva, Polym Test 25 (2006) 701

2. S Peeterbroeck, F Laoutid, B Swoboda, J Lopez-Cuesta, N Moreau, JB

Nagy, M Alexandre, P Dubois, Macromol Rapid Commun 28 (2007) 260

3. F Bellucci, G Camino, A Frache, V Ristori, L Sorrentino, S Iannace, X

Bian, M Guardasole, S Vaccaro, e-Polymers 014 (2006) 1

4. R Prasad, RK Gupta, F Cser, SN Bhattacharya, J Appl Polym Sci 101 (2006) 2127

5. B R Guduri, A S Luyt, J Appl Polym Sci 103 (2007) 4095

6. H Zou, Q Ma, Y Tian, S Wu, J Shen, Polym Compos 27 (2006) 529

7. SK Srivastava, M Pramanik, H Acharya, J Polym Sci Part B: Polym Phys

44 (2006) 471

8. M Valera-Zaragoza, E Ramý´rez-Vargas, FJ Medellýn-Rodrýguez, BM

Huerta-Martýnez, Polym Degrad Stab 91 (2006) 1319

9. KT Varughese, PP De, SK Sanyal, J Adhes Sci Technol 3 (1989) 541

10. SJ Park, JS Jin, J Colloid Interface Sci 242 (2001) 174

11. D Saihi, A El-Achari, A Ghenaim, C Caze, Polym Test 21 (2002) 615

12. HA Gulec, K Sariog¡lu, M Mutlu, J Food Eng 75 (2006) 187

192 Chapter 5.1

13. S Neema, A Salehi-Khojin, A Zhamu, WH Zhong, S Jana, YX Gan, J

Colloid Interface Sci (in press)

14. L Lavielle, J Schultz, J Colloid Interface Sci 106 (1985) 438

15. E Ruckenstein, SH Lee, J Colloid Interface Sci 120 (1987) 153

Chapter 5.2

Mechanical and Dynamic Mechanical Properties

Abstract Mechanical properties such as tensile strength, tensile modulus, tear strength etc

were measured. Dynamic mechanical properties of the composites were analyzed

with respect to the filler loading. Storage modulus showed improvement over all

temperatures up to glass transition. Dissipation factor (tanδ) showed a positive

shift indicating good filler/matrix interaction. The peak height of the tanδ curve

decreased upon filler loading indicating decrease in chain flexibility. Finally the

activation energy for the glass transition temperature and some theoretical

predictions of storage modulus were computed.

The results of this chapter have been submitted for publication in Polymer

194 Chapter 5.2

5.2.1 Introduction

EVA-based nanocomposites can be readily obtained by melt intercalation using

nanofillers such as inorganic oxides, organoclay, nanosilica etc [1-4]. Alexandre et al

studied the EVA/clay nanocomposites and a semi-intercalated semi-exfoliated

structure is observed by means of TEM, which shows both structures whatever be

the relative contribution [5]. La Mantia et al studied the mechanical properties of

EVA nanocomposites and found that the Young’s modulus of the obtained

nanocomposites increased significantly by the addition of even 5 wt.-% of

nanofiller [6,7].

Zhang et al synthesized EVA/clay nanocomposites by using organophilic clays as

reinforcement via melt blending [8]. They found that with the vinyl acetate (VA)

content and the basic spacing of the OMMT increasing, the chains of the EVA are

more easily intercalated into sheets of the clays to form intercalated or partially

exfoliated nanocomposites. For EVA28/clay nanocomposites, the intercalated and

the partially exfoliated nanocomposites both have a more obvious increase of their

mechanical and thermal properties compared to other nanocomposites. Moreover,

partially exfoliated nanocomposites has more obvious improvement of thermal and

mechanical properties than intercalated nanocomposites. Therefore the polarity of

the EVA and the basal spacing of OMMT are of importance to the morphology and

properties of EVA/clay nanocomposites.

In most of the EVA nanocomposites studied so far, the mechanical properties

such as tensile strength, elongation at break, tensile modulus etc are reported with

respect to the concentration of the fillers [5, 9-12].

Thus we can conclude that EVA based nanocomposites show good mechanical

as well as dynamic mechanical properties. Most of the works deals with layered

clays and modified clays etc. This chapter deals with the mechanical and dynamic

mechanical properties of poly[ethylene-co-(vinyl acetate)] (EVA copolymer) based

nanocomposites as a function of nano calcium phosphate filler loading.

Mechanical and Dynamic Mechanical Properties 195

5.2.2 Results and Discussion

5.2.2.1. Mechanical properties

Stress-strain behavior of the EVA/calcium phosphate nanocomposites is given in

figure 5.2.1. The stress is plotted against the strain percentage in x–axis. All

curves show similar stress strain behavior. In the initial region of the curves the

stress increases linearly with respect to the strain (Hookean region). Thereafter

the strain goes on increasing and the finally the material breaks. The tensile

strength values of the nanocomposites are plotted against the filler content in

figure 5.2.2. Tensile strength increases upon addition of nanofillers. On addition of

0.5 wt% of nanofiller the tensile strength increased about 50% of the pure

polymer. But on increasing the weight percentage of nanofiller the values

decreased. This is attributed to the filler agglomeration during processing. Figure

5.2.3 depicts the strain at break values against filler weight percentage.

Interestingly it is seen that the strain at break values increase upon addition of 1%

nanofiller. After 1 wt% filler loading it decreases. Srivastava et al studied the

properties of EVA nanocomposites in detail and found that the tensile strength and

elongation at break increase upon nanofiller addition up to a certain extent [12],

thereafter both these values show a dip. This behavior is explained in terms of two

aspects. In the initial region, the filler and polymer matrix show good interaction.

The strong interfacial interaction between the filler and the matrix forms some

shear zones when the composites are under stress and strain. Because of the

strong interaction and development of shear zones, tensile strength of the

nanocomposites is increased. But for the increased filler loading both these

parameters show a decreasing trend. This can be explained in terms of filler

agglomeration.

196 Chapter 5.2

0 100 200 300 400 500 600 700 800 900 10000

2

4

6

8

10

12

14

16

18

20

Stre

ss (M

Pa)

Strain(%)

E0 E.5 E1 E3 E5 E7

Figure 5.2.1. Stress-strain curves of EVA/calcium phosphate nanocomposites

Although there is no direct correlation between the filler particle size and the

composite properties, it plays an important role due to the increase in surface area

of the inclusions. Generally, the elastic modulus increases with augmenting filler

volume fraction, while all other tensile properties such as the yield stress and

strain, the ultimate stress, and strain almost invariably decrease with increasing

filler volume fraction [13–16].


0 1 2 3 4 5 6 712

13

14

15

16

17

18

Tens

ile S

treng

th (M

Pa)

Weight % of CP

Figure 5.2.2. Tensile strength curve of EVA/calcium phosphate nanocomposites

0 1 2 3 4 5 6 7

680

720

760

800

840

880

Stra

in a

t bre

ak (%

)

Weight % of CP

Figure 5.2.3. Strain at break curve of EVA/calcium phosphate nanocomposites

The nanofilled composites generally show an increase in modulus values. The

increase in modulus can be explained due to the good interaction between the

filler and the matrix. The nanofillers have high surface area compared to the

198 Chapter 5.2

conventional fillers and better chance for good interaction with the polymer chains.

The tensile modulus values of the nanocomposites are plotted in figure 5.2.4. The

modulus values increase upon filler addition up to 5% filler loading. For higher

loadings the modulus decreases marginally.

0 1 2 3 4 5 6 7140

160

180

200

220

240

260

280

300

Tens

ile m

odul

us (M

Pa)

Weight % CP

Figure 5.2.4. Tensile Modulus curve of EVA/calcium phosphate nanocomposites

The tear strength of the nanocomposites is plotted in figure 5.2.5 with respect to

the weight percentage of the filler. The tear strength values improved upon filler

addition. Up to 3wt% filler loading the values increased and thereafter the values

decreased. Tear strength increased around 35% for E3 composites. After 3% the

strength decrease which may be due to the agglomeration of the fillers.


0 1 2 3 4 5 6 7

52

54

56

58

60

62

64

66

68

70

Tear

stre

ngth

(N/m

m)

Weight % of CP

Figure 5.2.5. Tear strength curve of EVA/calcium phosphate nanocomposites

Very recently Zou et al examined the structure and properties of EVA-MMT

nanocomposites [17]. They analyzed the mechanical properties of melt processed

EVA with respect to the filler amount, mixing time and temperature. The tear

strength of EVA/modified MMT nanocomposites increased with MMT content, but

reached the maximal value at 5% content, and then decreased with further

increase in MMT content because of the aggregation of some silicate layers in

EVA matrix. Karger-Kocsis and coworkers evaluated the effect of organoclay

loading on tear strength of NR/ENR 50/organoclay nanocomposites [18]. The tear

strength increased gradually and remains relatively high up to 4 phr. This trend is

similar to the elongation at break to which the tear strength is related. At lower

filler content, the filler can be dispersed well in the polymer matrix. At higher filler

content, the filler tends to form agglomerates. Such agglomerates may work as

stress concentrators and thus reduce the tear strength [19].

200 Chapter 5.2

5.2.2.2. Dynamic mechanical analysis

Dynamic mechanical behavior of the EVA nanocomposites with respect to

temperature and frequency is studied. The temperature regime was –100 to 1500C

and the frequencies were 0.1, 1 and 10 Hz.

-100 -50 0 50 100 150-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 03.10

3.15

3.20

3.25

3.30

3.35

3.40

3.45

3.50

3.55

3.60

logε

' (M

Pa)

Temperature 0C

E0 E1 E3 E5 E7

Figure 5.2.6. Storage modulus curves of the EVA nanocomposites

Storage modulus

Storage modulus curves of the nanocomposites are given in figure 5.2.6. All

composites show an increased modulus values in the whole temperature regime

compared to the neat polymer. Up to around 00C all the curves show marginal

decrease from the starting values. A sharp decrease in the storage modulus is

seen between 0 and 1000C. This is basically the glass transition region of the

polymer. After 1000C, the rubbery region of the composites is seen. Here modulus

values are stood clearly apart from each other.

The increase in storage modulus of the nanocomposites can be related to

interaction of the nanofiller with the polymer matrix. Zhang and coworkers earlier

reported this type of behavior on EVA/organoclay systems [8]. The storage

modulus shows an irregular behavior above the Tg. It is because of the fact that


when the temperature increases beyond the Tg, chains of EVA becomes flexible.

Storage modulus curves of the E3 nanocomposites for three different frequencies

are given in figure 5.2.7. It is seen that all the three curves show similar behavior.

The low frequency scan, 0.1 Hz showed some noise in the initial region. In the

glass transition and rubbery regions the curves show some difference from each

other. In general high frequency region shows high values for the storage modulus

as expected.

-100 -50 0 50 100 150-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

logε

' (M

Pa)

Temperature, (0C)

.1 1 10

Figure 5.2.7: Storage modulus curves of the E3 nanocomposites at three different frequencies of 0.1, 1, 10 Hz

Storage modulus values of the five different temperatures of the current

measurement are compared (Table 5.2.1). The normalized values are also given.

Except for 1000C, all composites showed higher values compared to the virgin

polymer. In the more rubbery region a definite trend is not shown by the filler

addition.

202 Chapter 5.2

Unnormalised (log E’, MPa) Normalised w.r.to matrix

0C -100 -50 0 50 100 -100 -50 0 50 100

E0 3.37 3.23 2.33 1.44 0.19 1 1 1 1 1

E1 3.41 3.26 2.36 1.45 0.18 1.01 1.01 1.01 1.01 0.97

E3 3.43 3.28 2.37 1.44 0.21 1.01 1.01 1.07 1.00 1.08

E5 3.45 3.29 2.35 1.46 0.26 1.024 1.02 1.01 1.02 1.34

E7 3.48 3.32 2.37 1.47 0.18 1.03 1.03 1.08 1.02 0.94

Table 5.2.1. Unnormalised and normalised values of storage modulus values

The change in storage modulus at 300C with respect to the filler loading is given in

figure 5.2.8. One can see that the storage modulus changes with respect to the

filler content. It rather increases for all concentrations but from E5 onwards the

values are seemed to be almost same.

0 1 2 3 4 5 6 7 8

50

52

54

56

58

60

E' (M

Pa)

Weight % of filler

Figure 5.2.8. Storage modulus values of the EVA nanocomposites at 300C


Loss modulus

Loss modulus curves for the nanocomposites are shown in figure 5.2.9. All the

loss modulus curves show a plateau in the glassy region and a peak in the glass

transition region. The peak corresponds to the glass transition temperature (Tg) of

the polymer.

-100 -50 0 50 100 150-20

0

20

40

60

80

100

120

140

160

180

200

-50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0

80

100

120

140

160

180

E" (M

Pa)

Temperature 0C

E0 E1 E3 E5 E7

Figure 5.2.9. Variation of loss modulus curves of the EVA nanocomposites at a

frequency of 1 Hz

The loss modulus peaks show not much shift to the higher temperature compared

to the neat EVA. Loss modulus curves of the E3 nanocomposites with respect to

frequency is given in figure 5.2.10. It is seen that the curves shift to the right hand

side.

204 Chapter 5.2

-100 -50 0 50 100 150

-20

0

20

40

60

80

100

120

140

160

180

200

220

240

ε'' (M

Pa)

Temperature 0C

.1 1 10

Figure 5.2.10. Variation of loss modulus of E3 nanocomposites as a function of temperature at three different frequencies of 0.1, 1 and 10 Hz

Dissipation factor (tanδ)

The curves plotted from the values of damping factor (tanδ) versus temperature

for EVA and EVA nanocomposites are shown in figure 5.2.11. For more clarity the

peak regions are shown in the inset of the picture. Here we can see that the neat

polymer gives the larger peak among all the curves. This means that the neat EVA

shows maximum damping behavior. All other curves are well below compared to

it. This decrease in peak height in tanδ is attributed to the better filler-matrix

interaction. Also while examining the tanδ peaks we can see that the Tg is shifted

to the right hand side of the curves. For neat EVA, the Tg corresponds to –100C

while the corresponding values for E3 and E5 are –6 respectively. This behavior is

also due to the good filler dispersion into the matrix. The same reason can be

applied to the decrease in the peak height of the tanδ peak. We can see that the

neat polymer showed a tanδ peak height of 0.25 while it decreased for all filled

systems. For example, for E7 it changed to 0.2.


-100 -80 -60 -40 -20 0 20 40 60 80 100

0.00

0.05

0.10

0.15

0.20

0.25

0.30

-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10

0.20

0.25

ta

nδ

Temperature 0C

E0 E1 E3 E5 E7

Figure 5.2.11. Variation of tanδ of the EVA nanocomposites

While changing the frequency of the measurement the tanδ curves shifted to the

right hand side and Tg showed some increment (figure 5.2.12). It appears that the

addition of nanofiller actually limited the mobility of the polymeric chains. The

adsorption of polymer onto a surface restricts molecular motion, changes the density of packing of polymer chains, and modifies the conformation and

orientation of chain segments in the neighborhood of the surface [15]. Thus

damping of the composites reduces. With increasing of filler content, the glass

transition region of EVA nanocomposite broadens considerably.

206 Chapter 5.2

-100 -80 -60 -40 -20 0 20 40 60 80 100

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

tanδ

Temperature 0C

.1 1 10

Figure 5.2.12. Variation of tanδ of E3 nanocomposites at three different

frequencies as a function of temperature at 0.1, 1 and 10 Hz

Activation energy

Activation energy for the glass transition for the composites was computed

according to Arrhenius equation

0

( / )e E RTf f −= (5.2.1)

where f is the measuring frequency, fo is the frequency when T approaches infinity

and T is the temperature corresponding to the maximum of the tanδ curve. The

activation energy (E) values are given in table 5.2.2.

Composites Activation energy (kJ/mol)

E0 108.8

E1 131.0

E3 139.2

E5 123.7

E7 112.7

Table 5.2.2. Activation energy for glass transition of composites


-100 -80 -60 -40 -20 0 20 40 60 80 100

0.00

0.05

0.10

0.15

0.20

0.25

0.30

-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10

0.20

0.25

tanδ

Temperature 0C

E0 E1 E3 E5 E7

Figure 5.2.11. Variation of tanδ of the EVA nanocomposites

While changing the frequency of the measurement the tanδ curves shifted to the

right hand side and Tg showed some increment (figure 5.2.12). It appears that the

addition of nanofiller actually limited the mobility of the polymeric chains. The

adsorption of polymer onto a surface restricts molecular motion, changes the density of packing of polymer chains, and modifies the conformation and

orientation of chain segments in the neighborhood of the surface [15]. Thus

damping of the composites reduces. With increasing of filler content, the glass

transition region of EVA nanocomposite broadens considerably.

206 Chapter 5.2

-100 -80 -60 -40 -20 0 20 40 60 80 100

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

tanδ

Temperature 0C

.1 1 10

Figure 5.2.12. Variation of tanδ of E3 nanocomposites at three different

frequencies as a function of temperature at 0.1, 1 and 10 Hz

Activation energy

Activation energy for the glass transition for the composites was computed

according to Arrhenius equation

0

( / )e E RTf f −= (5.2.1)

where f is the measuring frequency, fo is the frequency when T approaches infinity

and T is the temperature corresponding to the maximum of the tanδ curve. The

activation energy (E) values are given in table 5.2.2.

Composites Activation energy (kJ/mol)

E0 108.8

E1 131.0

E3 139.2

E5 123.7

E7 112.7

Table 5.2.2. Activation energy for glass transition of composites


These values indirectly represent the filler matrix interaction. The activation

energies for E1 and E3 are high compared to the other composites. When the

interaction between the polymer and the filler higher relaxation needs more energy

and thus the activation energy increases. Later the activation energy is coming

down due to the less filler matrix interaction.

Theoretical modeling

The theoretical predictions and the experimental results of storage modulus and

tanδ are given in table 5.2.3 and 5.2.4 (the corresponding equations are given in

4.2.4). In the case of storage modulus the experimental results differ from the

theoretical predictions. Also for the tanδ values, the experimental results are

much lower than the theoretical ones. This is also due to the better interaction of

the filler and matrix, which lowers the damping characteristics.

Volume fraction Einstein Guth Experimental

0 1.72 1.72 1.72

0.0056 1.73 1.73 1.75

0.017 1.75 1.76 1.77

0.028 1.78 1.80 1.74

0.04 1.80 1.84 1.74

Table 5.2.3. Theoretical predictions of storage modulus

Volume fraction Eq. 4.2.12 Eq. 4.2.13 Experimental

0 0.24 0.24 0.24

0.0056 0.24 0.24 0.24

0.017 0.24 0.23 0.23

0.028 0.24 0.23 0.22

0.04 0.23 0.23 0.20

Table 5.2.4. Theoretical prediction of tanδ

208 Chapter 5.2

5.2.3. Conclusion

The major conclusions from the present study are

1. Mechanical properties of the composites showed improvement by the

addition of 3wt% of nanofillers due to the better filler dispersion. The

particle agglomeration in the higher loadings caused decrease in the

mechanical properties.

2. Dynamic mechanical analysis of the EVA nanocomposites showed

increase in storage modulus for an appreciable range of temperatures.

The good dispersion of the filler into the polymer matrix being the reason

for this. The glass transition temperature of the composites also increased

with respect to the filler loading. This change is also supported by the

good filler-matrix adhesion. The theoretical predictions from the

experimental results deviated due to the better filler- matrix interaction.

5.2.4. References

1. A Riva, M Zanetti, M Braglia, G Camino, L Falqui, Polym Degrad Stab 77 (2002) 299

2. CH Jeon, SH Ryu, YW Chang, Polym Int 52 (2003)153

3. M Valera-Zaragoza, E Ramý´rez-Vargas, FJ Medellý´n-Rodrý´guez, BM

Huerta-Martý´nez, Polym Degrad Stab 91 (2006) 1319

4. M Alexandre, P Dubois, Mater Sci Eng Reports 28 (2000) 1

5. M Alexandre, G Beyer, C Henrist, R Cloots, A Rulmont, R Jerome, P

Dubois, Macromol Rapid Commun 22 (2001) 643

6. FP La Mantia, S Lo Verso, N T Dintcheva, Macromol Mater Eng 287 (2002) 909

7. M Zanetti, G Camino, R Thomann, R Mulhaupt, Polymer 42 (2001) 4501

8. W Zhang, D Chen, Q Zhao, Y Fang, Polymer 44 (2003) 7953


9. M Alexandre, G Beyer, C Henrist, R Cloots, A Rulmont, R Jerome, P

Dubois, Chem Mater 13 (2001) 3830

10. M. Pramanik, S. K. Srivastava, B. K. Samantaray, A. K. Bhowmick, J

Mater Sci Lett 20 (2001) 1377

11. Y Tang, Y Hu, J Wang, R Zong, Z Gui, Z Chen, Y Zhuang, W Fan, J Appl

Polym Sci 91 (2004) 2416

12. SK Srivastava, M Pramanik, H Acharya, J Polym Sci Part B: Polym Phys

44 (2006) 471

13. B Pukanszky, Polypropylene structure, blends and composites, vol 3,

London, Chapman and Hall, (1995)

14. PHT Vollenberg, D Heikens, Polymer 30 (1989) 1656

15. Z Bartczak, AS Argon, RE Cohen, M Weinberg, Polymer 40 (1999) 2347

16. B Pukanszky, New Polym Mater 3 (1992) 205

17. H Zou, Q Ma, Y Tian, S Wu, J Shen, J Shen, Polym Compos, 27 (2006) 529

18. PL Teh, ZA Mohd Ishak, AS Hashim, J Karger-Kocsis, US Ishiaku, J Appl

Polym Sci, 100 (2006) 1083

19. US Ishiaku, CS Chong, H Ismail, Polym Test 19 (2000) 507

Chapter 5.3

Differential Scanning Calorimetric and Thermogravimetric Studies

Abstract Crystallization and thermal behavior of the EVA nanocomposites was analyzed by

DSC and TGA. From DSC the melting and crystallization temperatures were

calculated and it was found that both these parameters do not show much

variation with respect to the filler loading. The TGA traces showed two

degradation peaks corresponding to the degradation of acetic acid and the

polyene backbone. The composites showed better thermal stability due to the

nanoreinforcement. Activation energies for the decomposition of the components

were also calculated.

Results of this chapter have been communicated for publication in Polymer Degradation and Stability

212 Chapter 5.3

5.3.1 Introduction

The thermal stability of any polymer system is an important property for designing

the material for a particular use in a specific field. In particular, in the case of

nanocomposites, the dispersion of filler particles in a polymer matrix plays a

significant role in changing the thermal behavior. The filler matrix interaction can

be well studied using differential scanning calorimetry (DSC) and thermal

analyses. From the heating and cooling curves, we can estimate the melting and

crystallization peaks of the polymeric material and its composites.

It has been well established by different research groups that EVA’s exhibits two-

step decompositions on thermal degradation process. The first step corresponds

to the deacetylation reaction, whereas the second one is associated with the

formation of trans-vinylenes accompanied by the main chain scission. The

mechanism of this two-step decomposition has been presented elsewhere [1,2].

Several reports on the thermal degradation of the EVA nanocomposites appeared in

the literature very recently [3-11]. Almost all of these reports suggests that nanofiller

addition enhances the thermal stability of the EVA based nanocomposites.

This chapter deals with the differential scanning calorimetric and thermal

degradation behavior of the nanocomposites with respect to the nanofiller loading.

5.3.2 Results and discussion

5.3.2.1 Differential Scanning Calorimetric Studies

DSC studies of the EVA nanocomposites were carried out from –50 to 2000C. The

first heating curves were not used for analysis to avoid the influence of the history

of the current samples. The second heating curves of the individual curves are

given in figure 5.3.1. From the heating curves no significant difference in the

behavior of the curves were noted. The melting temperature (Tm) of the

composites was calculated and the corresponding values for neat polymer and the

composites are given in table 5.3.1. It is seen that Tm of the composites shows no

appreciable change with respect to the nanofiller addition.

Chapter 5.3

Differential Scanning Calorimetric and Thermogravimetric Studies

Abstract Crystallization and thermal behavior of the EVA nanocomposites was analyzed by

DSC and TGA. From DSC the melting and crystallization temperatures were

calculated and it was found that both these parameters do not show much

variation with respect to the filler loading. The TGA traces showed two

degradation peaks corresponding to the degradation of acetic acid and the

polyene backbone. The composites showed better thermal stability due to the

nanoreinforcement. Activation energies for the decomposition of the components

were also calculated.

Results of this chapter have been communicated for publication in Polymer Degradation and Stability

212 Chapter 5.3

5.3.1 Introduction

The thermal stability of any polymer system is an important property for designing

the material for a particular use in a specific field. In particular, in the case of

nanocomposites, the dispersion of filler particles in a polymer matrix plays a

significant role in changing the thermal behavior. The filler matrix interaction can

be well studied using differential scanning calorimetry (DSC) and thermal

analyses. From the heating and cooling curves, we can estimate the melting and

crystallization peaks of the polymeric material and its composites.

It has been well established by different research groups that EVA’s exhibits two-

step decompositions on thermal degradation process. The first step corresponds

to the deacetylation reaction, whereas the second one is associated with the

formation of trans-vinylenes accompanied by the main chain scission. The

mechanism of this two-step decomposition has been presented elsewhere [1,2].

Several reports on the thermal degradation of the EVA nanocomposites appeared in

the literature very recently [3-11]. Almost all of these reports suggests that nanofiller

addition enhances the thermal stability of the EVA based nanocomposites.

This chapter deals with the differential scanning calorimetric and thermal

degradation behavior of the nanocomposites with respect to the nanofiller loading.

5.3.2 Results and discussion

5.3.2.1 Differential Scanning Calorimetric Studies

DSC studies of the EVA nanocomposites were carried out from –50 to 2000C. The

first heating curves were not used for analysis to avoid the influence of the history

of

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