The change of tensile stress, elongation and 100% modulus upon
ageing with nitric acid vapor are given in Figs. 10–12. First a sharp
decrease in tensile strength and elongation is observed and then
the rate of decay decreases. The influence of nitric acid vapor are
more pronounced at the exposed surface of the sample rather than
inside. Therefore although the appearance seemed effected from
nitric acid vapor heavily (Fig. 5), the overall properties are not affected
to the same extent. Increase in 100% modulus values and
after about 300 h of ageing a stabilization followed by a slight decrease
was observed. Retention of tensile strength, elongation and
100% modulus are given in Table 7. SBR-2 seems to be slightly affected
from nitric acid vapor especially at higher exposure times.