Studies on the use of nano zinc oxide and modified silica in NR, CR ...

Mix
Use of antioxidant modified precipitated silica in natural rubber,
chloroprene rubber and styrene butadiene rubber
Table 7.3 Cure characteristics of the mixes
Min torque
dNm
Max torque
dNm
Scorch
time (min)
Optimum cure
time (min)
Cure rate
index (%)
E-1 0.481 9.88 1.39 4.77 29.58
E-2 0.559 9.69 1.06 5.07 24.93
F-1 0.251 8.52 1.15 5.11 25.20
F-2 0.392 8.01 1.10 5.18 24.50
G-1 0.643 9.64 1.55 6.37 20.72
G-2 0.457 8.23 1.39 6.49 19.60
From the Table, it is seen that the cure values of compounds filled
with antioxidants modified silica exhibit higher cure rate and extent of cure
over that of compounds with neat precipitated silica. Chemical surface
groups on fillers play an important role in their effect on rate of cure, with
many vulcanized systems. Physical adsorption activity of the filler surface is
of greater importance than its chemical nature. The polar nature of silica
surface adsorbs a part of the curatives and or silica- zinc ion interaction
leads to slowing down of the curing reaction. 17 But in the case of antioxidant
modified silica, the -OH groups on the surface are already hydrogen bonded
with the NH group of the substituted phenylenediamine antioxidant.
Cure graphs of the three types of antioxidants filled compounds are
shown in the Figure 7.1(a-c). The maximum torque is a measure of crosslink
density and stiffness in the rubber. 18 In general, for all the mixes, the torque
initially decreases and then increases. The increase in torque is due to the
cross linking of rubber. It is found that the antioxidant modified silica
increases the torque compared to the neat precipitated silica. This increase is
due to the presence of silica- rubber crosslink that imparts more restriction to
deformation.
125