Adesão borracha-latão: a influência do cobalto, do sistema HMMM (hexametoximetilmelamina)-resorcinol e da temperatura na interface
Abstract
Using a blank compound as reference and brass coated steel tire cords
with 64 and 68.2 % of cooper content, it was studied the effect of the
ingredients cobalt and the HMMM-resorcinol system, and the vulcanization
temperature on the rubber-brass adhesion. Samples were studied as new
(original), aged in oven, steam and humidity environments. Mechanical
properties, vulcanization kinetics and cross linking density were analyzed in the
compounds. The ingredients, as well as the vulcanization temperature, showed
a strong effect on the compounds properties, however, it did not show relation
with the adhesion. The steel tire cords were evaluated by scanning electron
microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS), being
evident variations on brass deposition, which can lead to adhesion loss. The
adhesion of the samples was evaluated by means of the force and coverage by
pull out tests from a rubber block. The results, for each condition, were
statistically analyzed. For the original condition, the steel cord with high content
of cooper (68.2 %) showed higher adhesion values. In oven, only the effect of
HMMM-resorcinol system was statistically significant. Aging in steam, the most
aggressive condition, showed that the use of cobalt was effective in the
maintenance of the adhesion level. Aging with humidity showed that the
adhesion promoters cobalt and HMMM-resorcinol system were beneficial to the
rubber-brass adhesion. The cords surface, after the extraction of the rubber,
was evaluated by SEM and EDS. The formation of a CuxS structure,
responsible for rubber-brass adhesion was evident. In general, it was not found
a unique combination which guaranteed the maximum adhesion level for the
studied conditions, however, the better balance was achieved using a steel cord
with 64 % of cooper, the adhesion promoters cobalt and HMMM-resorcinol
system, and the vulcanization temperature of 150 ºC.