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-
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
-
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)
-
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)
-
Morphological and Contact Angle Studies 183
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.
-
Morphological and Contact Angle Studies 183
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.
-
Morphological and Contact Angle Studies 185
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.
-
Morphological and Contact Angle Studies 185
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
89
WA , m
J/m2
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.
-
Morphological and Contact Angle Studies 187
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
-
Morphological and Contact Angle Studies 187
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
-
Morphological and Contact Angle Studies 189
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
water methylene iodide
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
respect to filler loading
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
-
Morphological and Contact Angle Studies 189
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
water methylene iodide
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
respect to filler loading
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
-
Morphological and Contact Angle Studies 191
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
-
Morphological and Contact Angle Studies 191
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.
-
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].
-
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].
-
Mechanical and Dynamic Mechanical Properties 197
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.
-
Mechanical and Dynamic Mechanical Properties 197
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.
-
Mechanical and Dynamic Mechanical Properties 199
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
-
Mechanical and Dynamic Mechanical Properties 199
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
-
Mechanical and Dynamic Mechanical Properties 201
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
-
Mechanical and Dynamic Mechanical Properties 201
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
-
Mechanical and Dynamic Mechanical Properties 203
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.
-
Mechanical and Dynamic Mechanical Properties 203
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.
-
Mechanical and Dynamic Mechanical Properties 205
-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
-
Mechanical and Dynamic Mechanical Properties 205
-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
-
Mechanical and Dynamic Mechanical Properties 207
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
-
Mechanical and Dynamic Mechanical Properties 207
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
-
Mechanical and Dynamic Mechanical Properties 209
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