reasons for the imbalance in carbon black transfer to the BR phase are attributed to
the relatively low viscosity of the BR phase and the relatively strong interaction
between carbon black and the BR phase. An addition of fillers leads to a decrease in
tan δ as a result of the dilution effect, that is, the viscous response of the elastomeric
phase is diluted by the nonviscous response of fillers. Carbon blacks with small and
large particle sizes, N220, N330, and N660, tend to reside preferentially in the BR
phase rather than the NBR phase because of the lower viscosity and non polarity of
BR. For the BR/NBR blend ratio of 20/80, the precipitated silica appears to reside
increasingly in the polar phase (NBR), compared to carbon black, indicating the
strong silica–NBR interaction. However, the filler polarity effect is not observed in
the 50/50 BR/NBR blend. Carbon black distribution in BR/NBR blends is affected
significantly by the difference in polarity between the BR and NBR. The higher the
polarity of the NBR, the smaller the amount of carbon black residing in the NBR
phase [95].
Kader et al. studied the dynamic-mechanical properties of gum and filled acrylic
rubber (ACM), fluorocarbon rubber (FKM), and their blends of varying compositions. DMTA showed a single tan δ peak corresponding to a single phase transition
for both cured and filled blends. The storage modulus of the blend increased from
the gum blend to the filled blend, indicating the presence of polymer–filler interaction. The loss tangent peaks, corresponding to glass-transition temperature of
unfilled blends and of both cured and uncured gum blends were observed at À1.0
C
and 0
C, respectively. However, the corresponding peak for the filled system was
observed at 5
C, with reduction in the loss tangent value, indicating the influence
of filler on the Tg of the blend. The effect of curing and the addition of filler were
also seen with increasing storage modulus values at all measured temperatures
because of the restricted mobility of the polymer chain through crosslinking and
polymer–filler networking, respectively [96].
Chuayjuljit et al., studied the E
0 and tan δ thermograms for the 70/30 XSBR/NR
blend vulcanizate, and those with and without the addition of 3 phr of either nSiO 2
XSBR and NR rubber blends filled with nSiO 2 or PS-nSiO 2 . These are shown in
Fig. 14. The E
0 of the nanocomposite containing nSiO 2 or PS-nSiO 2 in the temperature range from 100
C up to 20
C is the lowest, suggesting insufficient crosslinking. This is presumably caused by the acidic OH groups on the silica surface
adversely affecting the sulfur-mediated curing of the NR. Therefore, the Tg of NR
in this nanocomposite is slightly shifted towards a lower temperature. At a temperature above 20
C, the E
0 of the nanocomposite increases due to the interaction
between the nSiO 2 and XSBR that induces a restricted mobility of XSBR. However,
the nSiO 2 may provide two possible effects: firstly a decrease in the cross-link
density and secondly the restriction of molecular chain mobility. As the PS-nSiO 2
was introduced into the rubber blend matrix, the PS shell improved the compatibility of the nanofiller and the rubber matrix, resulting in a slightly increased E
0
value. Nevertheless, the strong interaction between the nanofillers and the XSBR
may cause microphase separation in the rubber matrix, resulting in an indirect
decrease in the Tg of the soft segment in XSBR. Thus, both the Tg values of XSBR
in the nanocomposites are slightly decreased [97].
108
A.B. Nair et al.
the relatively low viscosity of the BR phase and the relatively strong interaction
between carbon black and the BR phase. An addition of fillers leads to a decrease in
tan δ as a result of the dilution effect, that is, the viscous response of the elastomeric
phase is diluted by the nonviscous response of fillers. Carbon blacks with small and
large particle sizes, N220, N330, and N660, tend to reside preferentially in the BR
phase rather than the NBR phase because of the lower viscosity and non polarity of
BR. For the BR/NBR blend ratio of 20/80, the precipitated silica appears to reside
increasingly in the polar phase (NBR), compared to carbon black, indicating the
strong silica–NBR interaction. However, the filler polarity effect is not observed in
the 50/50 BR/NBR blend. Carbon black distribution in BR/NBR blends is affected
significantly by the difference in polarity between the BR and NBR. The higher the
polarity of the NBR, the smaller the amount of carbon black residing in the NBR
phase [95].
Kader et al. studied the dynamic-mechanical properties of gum and filled acrylic
rubber (ACM), fluorocarbon rubber (FKM), and their blends of varying compositions. DMTA showed a single tan δ peak corresponding to a single phase transition
for both cured and filled blends. The storage modulus of the blend increased from
the gum blend to the filled blend, indicating the presence of polymer–filler interaction. The loss tangent peaks, corresponding to glass-transition temperature of
unfilled blends and of both cured and uncured gum blends were observed at À1.0
C
and 0
C, respectively. However, the corresponding peak for the filled system was
observed at 5
C, with reduction in the loss tangent value, indicating the influence
of filler on the Tg of the blend. The effect of curing and the addition of filler were
also seen with increasing storage modulus values at all measured temperatures
because of the restricted mobility of the polymer chain through crosslinking and
polymer–filler networking, respectively [96].
Chuayjuljit et al., studied the E
0 and tan δ thermograms for the 70/30 XSBR/NR
blend vulcanizate, and those with and without the addition of 3 phr of either nSiO 2
XSBR and NR rubber blends filled with nSiO 2 or PS-nSiO 2 . These are shown in
Fig. 14. The E
0 of the nanocomposite containing nSiO 2 or PS-nSiO 2 in the temperature range from 100
C up to 20
C is the lowest, suggesting insufficient crosslinking. This is presumably caused by the acidic OH groups on the silica surface
adversely affecting the sulfur-mediated curing of the NR. Therefore, the Tg of NR
in this nanocomposite is slightly shifted towards a lower temperature. At a temperature above 20
C, the E
0 of the nanocomposite increases due to the interaction
between the nSiO 2 and XSBR that induces a restricted mobility of XSBR. However,
the nSiO 2 may provide two possible effects: firstly a decrease in the cross-link
density and secondly the restriction of molecular chain mobility. As the PS-nSiO 2
was introduced into the rubber blend matrix, the PS shell improved the compatibility of the nanofiller and the rubber matrix, resulting in a slightly increased E
0
value. Nevertheless, the strong interaction between the nanofillers and the XSBR
may cause microphase separation in the rubber matrix, resulting in an indirect
decrease in the Tg of the soft segment in XSBR. Thus, both the Tg values of XSBR
in the nanocomposites are slightly decreased [97].
108
A.B. Nair et al.