3.7. Effect of thermal ageing
The effect of thermal ageing on the mechanical properties,
namely TS, Eb and hardness of NBR vulcanizates cured by sulfur,
peroxide, peroxide/coagent and radiation/coagent is shown in Figs.
11–13, respectively. The values of TS for sulfur and radiation/coagent
(150 kGy) cured systems at 150 kGy were found slightly reduced
on ageing while the other cured systems were not
affected. On the other hand, only the values of Eb for sulfur cured
system decreased on ageing. Meanwhile, the hardness values for
all NBR vulcanizates encountered a slight alteration on ageing.
The decrease in values of TS and Eb in case of sulfur vulcanized
samples may be attributed to the fact that the polysulfidic crosslinks
cleave and rearrange into shorter crosslinks [30]. Also, the decrease
in values of TS of NBR vulcanizates cured by radiation/
coagent may be attributed to chain scission by thermal ageing.
Moreover, compared to sulfur vulcanized samples, radiation/coagent
vulcanized samples are more resistant to heating due to the
nature of networks, as CAC linkage is more stable possessing higher
bond energy than CASAC linkage. It is also well known that
polysulfidic linkage is of relatively low bond strength, i.e. poorer
thermal ageing resistant.
3.7. Effect of thermal ageingThe effect of thermal ageing on the mechanical properties,namely TS, Eb and hardness of NBR vulcanizates cured by sulfur,peroxide, peroxide/coagent and radiation/coagent is shown in Figs.11–13, respectively. The values of TS for sulfur and radiation/coagent(150 kGy) cured systems at 150 kGy were found slightly reducedon ageing while the other cured systems were notaffected. On the other hand, only the values of Eb for sulfur curedsystem decreased on ageing. Meanwhile, the hardness values forall NBR vulcanizates encountered a slight alteration on ageing.The decrease in values of TS and Eb in case of sulfur vulcanizedsamples may be attributed to the fact that the polysulfidic crosslinkscleave and rearrange into shorter crosslinks [30]. Also, the decreasein values of TS of NBR vulcanizates cured by radiation/coagent may be attributed to chain scission by thermal ageing.Moreover, compared to sulfur vulcanized samples, radiation/coagentvulcanized samples are more resistant to heating due to thenature of networks, as CAC linkage is more stable possessing higherbond energy than CASAC linkage. It is also well known thatpolysulfidic linkage is of relatively low bond strength, i.e. poorerthermal ageing resistant.
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