Two cords were used, cord 1 and cord 2 as illustrated inFig. 2,
to investigate the effect of manobond and KMR promoters and
their concentrations on the static adhesion between NR and the
brass-coated steel cord. The relation between the pull-out force of
the rubber mixes and the different concentrations of the two
promoters using cord 1 and cord 2 are shown inFig. 5a and b,
respectively. FromFig. 5a, it can be seen that the adhesion force
increases with the increase of the promoter concentration in the
rubber mix till it reaches a maximum value at 1.5 and 1.0 phr for
manobond and KMR, respectively. Further increase in promoter
concentration is accompanied by a decrease in the adhesion force.
The presence of 1.0 phr of KMR increased the pull-out force by
about 71% while the use of 1.5 phr of manobond increased the
pull-out force by only 31%. Thus, the optimum concentration of
KMR increased the adhesion force more than twice that of
manobond promoter. This may be due to the higher chelation
affinity of iron metal present in KMR and its reaction with
nitrogen and sulfur, present in the rubber mix, compared to
cobalt metal present in manobond. In addition, the iron sulfide
growth rate is faster than that of cobalt sulfide resulting in higher
growth rate and better adhesion properties for mixes containing
KMR than those containing manobond[33].
In case of cord 2, Fig. 5b shows that the use of manobond
promoter leads only to slight improvement, 7%, of adhesion force
regardless of the concentration added to the rubber mix. While in
case of KMR promoter, an increase in adhesion force of more than
30% is achieved when using 1.0 phr of the promoter. This increase
in the adhesion force may be attributed to the high mechanical
properties of the rubber mix, modulus in particular, which leads
to the increase of the adhesion force [33] as well as better