2.2 Mixing and measurements of cure
characteristics
Mixing was carried out using a laboratory
two-roll mill in accordance with ASTM
method designation D 3184-80. The cure
characteristics of the mixes were determined
by using a Monsanto Rheometer model MDR
2000 at 140 oC. The respective cure time (t90),
and scorch times (t2) values were obtained
from the rheograph. The compounds were
then compression molded at 140 oC based
on respective t90 values.
2.3 Measurement of mechanical
properties
Specimens for tensile and tear testing were
punched out from the vulcanized sheets.
Tensile testing was done as per ASTM D412,
using dumb-bell specimens and at a rate of
grip separation of 500 50 mm/min. For the
hardness test, a Shore A type durometer was
employed to find out the hardness of the
vulcanizates. The method adopted is the same
as that of ASTM D 2240 and the readings
were taken after 5 s of indentation. Resilience
was done according to ASTM D 2632 using
a Vertical Rebound. Figure 1, that plot of
stress versus strain. Measures the area under-
neath the stress-strain curve called toughness.
Toughness is really a measure of the energy a
sample can absorb before specimen breaks.