The variation of hardness of HAF loaded and
unloaded NBR/EPDM blend as a function of irradiation
dose is illustrated in Fig. 4. Also, the data
for unirradiated loaded rubber were introduced in
the same figure for comparison. It may be observed
that the values of hardness of latter composition
have increased effectively with increasing the degree
of loading with the filler. Similar behavior has been
attained for radiation vulcanized composites when comparing its hardness values at the same irradiation
dose. On the other hand, comparatively a limited
increase has been attained in the value of
hardness for one and the same composition,
whether loaded or unloaded, on increasing the irradiation
dose from 50 kGy to 250 kGy. These data
indicate clearly that contribution to hardness values
from radiation- induced cross-linking that has taken
place in the totally amorphous rubber matrix of
NBR/EPDM blend is a limited one. On the other
hand, the main contribution to the hardness value
is affiliated with the occurrence of the filler in its
aggregated solid and distinct phase, that is, its
‘‘structured’’ form as mentioned before.