3.4. Radiation/coagent cured NBR
An electron beam accelerator was used to generate free radicals
on the carbon atoms of the NBR and coagent. The radicals may
either be reacting with each other or grafting on the coagent forming
crosslinks. Table 5 shows the results for radiation curing of
NBR by different radiation doses up to 150 kGy in the presence
of 5 phr of PETRA. The M100 was found to increase linearly with
radiation dose indicating the linear relationship of cross-link density
with radiation dose, whereas the latter inversely lowers the
values of Mc. The increase in values of Vr, decrease in Eb, Q and
in solubility were considerable by increasing radiation dose indicating
the increase of cross-link density of vulcanizate. Also there
is an increase in TS up to 100 kGy, beyond which there is a very
slight decrease in TS values dose. The leveling off or decrease in
TS by radiation may be explained as follows: TS of a polymer is
a function of cross-link density and energy dissipation, at higher
crosslinking density, i.e. at 150 kGy, the segments of the macromolecule
become immobile, the system becomes stiffer and the
elasticity decreases [21]. Also, it can be assumed that the rate of
two processes, namely crosslinking and degradation may then occur
with the same rate, hindered mobility of macromolecules due
to increased rate of crosslinking may contribute also to decreasing
the values of TS.3.4. Radiation/coagent cured NBR
An electron beam accelerator was used to generate free radicals
on the carbon atoms of the NBR and coagent. The radicals may
either be reacting with each other or grafting on the coagent forming
crosslinks. Table 5 shows the results for radiation curing of
NBR by different radiation doses up to 150 kGy in the presence
of 5 phr of PETRA. The M100 was found to increase linearly with
radiation dose indicating the linear relationship of cross-link density
with radiation dose, whereas the latter inversely lowers the
values of Mc. The increase in values of Vr, decrease in Eb, Q and
in solubility were considerable by increasing radiation dose indicating
the increase of cross-link density of vulcanizate. Also there
is an increase in TS up to 100 kGy, beyond which there is a very
slight decrease in TS values dose. The leveling off or decrease in
TS by radiation may be explained as follows: TS of a polymer is
a function of cross-link density and energy dissipation, at higher
crosslinking density, i.e. at 150 kGy, the segments of the macromolecule
become immobile, the system becomes stiffer and the
elasticity decreases [21]. Also, it can be assumed that the rate of
two processes, namely crosslinking and degradation may then occur
with the same rate, hindered mobility of macromolecules due
to increased rate of crosslinking may contribute also to decreasing
the values of TS.