dose, the mobility of metal free radicals is too low and hence no
additional bonds will be formed. On the other hand, rubber under-goes chain scissions or crosslink scissions especially at 2500 Gy and
at higher radiation doses. Samples show the best adhesion recovery
at 7500 and 5000 Gy for manobond and KMR, respectively which can
be explained as on exposing to controlled gamma radiation, free
radicals are formed in the rubber bulk and on the brass surface in
contact with rubber (the interface). These free radicals which have
considerable mobility activate excess sulfur in rubber and copper in
brass forming additional bonds[42–44].
Fig. 7(c) and (d) shows the effect of gamma radiation on the
pull-out force for samples containing different concentrations of
manobond and KMR promoters and having cord 2 as a reinforcing
material. It is clear that most samples show good stability
towards exposure to g-radiation. Samples containing the two
types of promoters, manobond and KMR, show adhesion
improvement upon exposure to moderate radiation doses
(2500–5000 Gy) that might be due to the formation of extra
bonds between the rubber mixes and the steel cords through
formation of active free radicals and that enhance crosslinking
between the sulfur in the rubber mix and the brass plated
steel cords.