border of CR and EPDM, as observed i.e. from transmission electron microscopy.
The extra-ordinary improvement of dynamic modulus can also be understood by a
very strong filler–filler networking that we observed in strain sweep experiments.
Moreover, we found that the compatibilized blends exhibit an extra dynamicmechanical relaxation process at higher temperatures (~T + 130 K). The suggested
method for compatibilization of incompatible rubber blends offers routes to the
design of new rubber based technical products for diversified applications [106].
Figure 26 shows TEM images of CR/EPDM blend at the ratio of 75/25, 50/50
and 25/75, respectively, with 10 phr clay. Every blend is prepared by incorporating
all the clay in the EPDM rubber and, subsequently, the resulting composites were
mixed with CR. It is obvious from Fig. 26a, b that two phases of CR and EPDM
co-exist with a large number of exfoliated and intercalated clay platelets at the
interfaces. The dark phase is the CR phase with higher electron density due to the
presence of chlorine atoms in the rubber chains. Remarkably, it is found that there
are almost no clay layers in the bright phase rather than in the dark phase. CR, being
a polar rubber, forces to migrate the clay particles into it, rendering the EPDM
phase poor, despite the fact that all the clay was premixed with EPDM. Migration of
inorganic clay layers is taken place from non-polar EPDM to polar CR and, as far as
viscosity mismatch (Mooney viscosity) is concerned, the migration is also driven
by viscosity difference since the Mooney viscosity of EPDM is higher than the
viscosity of CR. The migration of clay from EPDM to CR phase can also be well
explained as a wetting/dewetting process between polymers and filler. Hereby, the
driving force is the difference of the interfacial tensions between the rubbers and
clay [106].
The dependence of storage elastic modulus (E
0 ) on the strain amplitude at very
low strain values delivers an understanding about the impact of the filler networking
within the rubber matrix. Generally, E
0 remains unaltered with increasing strain for
an unfilled rubber system. However, for a filled system, the storage modulus
decreases with increasing strain. This nonlinear behaviour of a filled rubber system
is called ‘Payne effect’ and yields information about filler–filler networking in the
rubber matrix. In the present investigations, the plots of E
0 versus double strain
amplitude of the CR/EPDM blends are shown in Fig. 27a. It is evident from this
figure that the gum-blend without any filler does not undergo any change in E
0 with
increasing strain. However, a strong dependency can be observed for all filled
samples. Here, all rubber blends are filled with only 10 phr of clay and, obviously,
these clay particles, being either exfoliated and/or intercalated, build a strong filler–
filler network in the rubber matrix. The preferential localization of the clay at the
interface fulfils the demand to remain in contact with hydrogen bonding by the
virtue of hydroxyl group of clay (end-to-end coupling). Moreover, it is quite
interesting to discuss the very high value of E
0 at the low strain region. These
findings can be only explained if a large amount of delaminated silicate particles are
coming out from the nanoclay stacks by exfoliation process. Here, it can be
observed that with the increase of the EPDM content the filler–filler networking
decreases which can be attributed to relatively smaller space availability
(CR phase) for the clay particles at a fixed volume and, consequently, the clay
particles are forced to remain in nonintercalated–exfoliated form. TEM in
120
A.B. Nair et al.
The extra-ordinary improvement of dynamic modulus can also be understood by a
very strong filler–filler networking that we observed in strain sweep experiments.
Moreover, we found that the compatibilized blends exhibit an extra dynamicmechanical relaxation process at higher temperatures (~T + 130 K). The suggested
method for compatibilization of incompatible rubber blends offers routes to the
design of new rubber based technical products for diversified applications [106].
Figure 26 shows TEM images of CR/EPDM blend at the ratio of 75/25, 50/50
and 25/75, respectively, with 10 phr clay. Every blend is prepared by incorporating
all the clay in the EPDM rubber and, subsequently, the resulting composites were
mixed with CR. It is obvious from Fig. 26a, b that two phases of CR and EPDM
co-exist with a large number of exfoliated and intercalated clay platelets at the
interfaces. The dark phase is the CR phase with higher electron density due to the
presence of chlorine atoms in the rubber chains. Remarkably, it is found that there
are almost no clay layers in the bright phase rather than in the dark phase. CR, being
a polar rubber, forces to migrate the clay particles into it, rendering the EPDM
phase poor, despite the fact that all the clay was premixed with EPDM. Migration of
inorganic clay layers is taken place from non-polar EPDM to polar CR and, as far as
viscosity mismatch (Mooney viscosity) is concerned, the migration is also driven
by viscosity difference since the Mooney viscosity of EPDM is higher than the
viscosity of CR. The migration of clay from EPDM to CR phase can also be well
explained as a wetting/dewetting process between polymers and filler. Hereby, the
driving force is the difference of the interfacial tensions between the rubbers and
clay [106].
The dependence of storage elastic modulus (E
0 ) on the strain amplitude at very
low strain values delivers an understanding about the impact of the filler networking
within the rubber matrix. Generally, E
0 remains unaltered with increasing strain for
an unfilled rubber system. However, for a filled system, the storage modulus
decreases with increasing strain. This nonlinear behaviour of a filled rubber system
is called ‘Payne effect’ and yields information about filler–filler networking in the
rubber matrix. In the present investigations, the plots of E
0 versus double strain
amplitude of the CR/EPDM blends are shown in Fig. 27a. It is evident from this
figure that the gum-blend without any filler does not undergo any change in E
0 with
increasing strain. However, a strong dependency can be observed for all filled
samples. Here, all rubber blends are filled with only 10 phr of clay and, obviously,
these clay particles, being either exfoliated and/or intercalated, build a strong filler–
filler network in the rubber matrix. The preferential localization of the clay at the
interface fulfils the demand to remain in contact with hydrogen bonding by the
virtue of hydroxyl group of clay (end-to-end coupling). Moreover, it is quite
interesting to discuss the very high value of E
0 at the low strain region. These
findings can be only explained if a large amount of delaminated silicate particles are
coming out from the nanoclay stacks by exfoliation process. Here, it can be
observed that with the increase of the EPDM content the filler–filler networking
decreases which can be attributed to relatively smaller space availability
(CR phase) for the clay particles at a fixed volume and, consequently, the clay
particles are forced to remain in nonintercalated–exfoliated form. TEM in
120
A.B. Nair et al.