(Fig. 21). This indicates that the blends are not compatible and so form a two phase
structure in the blend and nanocomposites. The Tg for both NR and XSBR of each
rubber nanocomposite tended to increase with increasing CNT loading levels, and
so the thermal motion of the rubber chain segments was constrained by the CNT
particles.
With respect to the variations in the E
0 with temperature, the E
0 of each
composition decreased with increasing temperatures due to the decrease in stiffness
of the samples (Fig. 21). A significant influence of the CNT content on the E
0 occurs
at a temperature below the Tg of NR. At À80
C, a temperature selected below the
Tg of NR, the E
0 of the nanocomposites tends to increase considerably with
increasing CNT loadings in comparison with that of the neat rubber blend, most
likely due to the stiffening of the rubber matrix, as described previously. Thus, the
data for the changes in E
0 with increasing CNT loading levels are in agreement with
that for the tensile modulus [100].
Kueseng et al. prepared 50/50 NR/NBR blends with various MWCNT loadings
by mixing with MWCNT/NR master batches on a two-roll mill and sheeted off at
the smallest nip gap. Then, the effect of milling direction, machine direction
(MD) and transverse direction (TD), on the mechanical and electrical properties
of the blends was elucidated. Results from dynamic mechanical tests also showed
that the maximum tan δ in the MD sample was lower than that in the corresponding
TD sample. In addition, the storage modulus at 30
C for the MD sample containing
4 phr MWCNT was 1.15 higher than that of the corresponding TD sample. This
stronger reinforcement efficiency resulted from the combination of the greater
alignment and dispersion of most MWCNTs in the MD sample [101].
The plots of tan δ of the blends versus temperature are displayed in Fig. 22. It is
evident that there are two Tg; around À56
C and À14
C corresponding to NR and
NBR phases, respectively. It is found that MWCNT loading and alignment direction slightly influence the Tgs of both phases. However, the tan δ max of both
phases tends to reduce with increasing MWCNT loading, regardless of the alignment direction. The dilution effect could be used to explain this finding. It is also
observed that tan δ in the MD of both phases is lower than that in the TD. Figure 23
shows the average storage modulus values at 30
C for the blends. It appears that the
storage modulus of all blends in MD is higher than that of the corresponding TD
samples. This result may be explained by the higher reinforcement efficiency for
MWCNT aligned in the longitudinal direction. These results correspond well with
the moduli and tear strength of the blends.
Le et al., developed ternary blends based on SBR, NBR and NR. And also
studied the characterization of the kinetics of CNT dispersion and distribution in
ternary blends [102].
The similarity in morphology of four blends can be proved by the DMA
investigation. In Fig. 24 elastic modulus and tan δ of four blends are presented.
The dynamic-mechanical behavior of the investigated blends does not differ from
each other. It was found that CNTs mainly reside in the polar NBR and non-polar
NR but not in weak polar SBR. Such unusual localization of CNTs in ternary
SBR/NBR/NR can be explained by taking into consideration the presence of
116
A.B. Nair et al.
structure in the blend and nanocomposites. The Tg for both NR and XSBR of each
rubber nanocomposite tended to increase with increasing CNT loading levels, and
so the thermal motion of the rubber chain segments was constrained by the CNT
particles.
With respect to the variations in the E
0 with temperature, the E
0 of each
composition decreased with increasing temperatures due to the decrease in stiffness
of the samples (Fig. 21). A significant influence of the CNT content on the E
0 occurs
at a temperature below the Tg of NR. At À80
C, a temperature selected below the
Tg of NR, the E
0 of the nanocomposites tends to increase considerably with
increasing CNT loadings in comparison with that of the neat rubber blend, most
likely due to the stiffening of the rubber matrix, as described previously. Thus, the
data for the changes in E
0 with increasing CNT loading levels are in agreement with
that for the tensile modulus [100].
Kueseng et al. prepared 50/50 NR/NBR blends with various MWCNT loadings
by mixing with MWCNT/NR master batches on a two-roll mill and sheeted off at
the smallest nip gap. Then, the effect of milling direction, machine direction
(MD) and transverse direction (TD), on the mechanical and electrical properties
of the blends was elucidated. Results from dynamic mechanical tests also showed
that the maximum tan δ in the MD sample was lower than that in the corresponding
TD sample. In addition, the storage modulus at 30
C for the MD sample containing
4 phr MWCNT was 1.15 higher than that of the corresponding TD sample. This
stronger reinforcement efficiency resulted from the combination of the greater
alignment and dispersion of most MWCNTs in the MD sample [101].
The plots of tan δ of the blends versus temperature are displayed in Fig. 22. It is
evident that there are two Tg; around À56
C and À14
C corresponding to NR and
NBR phases, respectively. It is found that MWCNT loading and alignment direction slightly influence the Tgs of both phases. However, the tan δ max of both
phases tends to reduce with increasing MWCNT loading, regardless of the alignment direction. The dilution effect could be used to explain this finding. It is also
observed that tan δ in the MD of both phases is lower than that in the TD. Figure 23
shows the average storage modulus values at 30
C for the blends. It appears that the
storage modulus of all blends in MD is higher than that of the corresponding TD
samples. This result may be explained by the higher reinforcement efficiency for
MWCNT aligned in the longitudinal direction. These results correspond well with
the moduli and tear strength of the blends.
Le et al., developed ternary blends based on SBR, NBR and NR. And also
studied the characterization of the kinetics of CNT dispersion and distribution in
ternary blends [102].
The similarity in morphology of four blends can be proved by the DMA
investigation. In Fig. 24 elastic modulus and tan δ of four blends are presented.
The dynamic-mechanical behavior of the investigated blends does not differ from
each other. It was found that CNTs mainly reside in the polar NBR and non-polar
NR but not in weak polar SBR. Such unusual localization of CNTs in ternary
SBR/NBR/NR can be explained by taking into consideration the presence of
116
A.B. Nair et al.