Paper Number 3.8
Effect of Aging on the Morphology
of the Rubber-Brass Interfacial Layer
William J. Vanooij
Department of Chemical & Materials Engineering
Adhesion between rubber compound and
brass-plated steel tire cord is a crucial in governing the overall performance
of tires. The rubber-brass interfacial adhesion is influenced by the chemical
composition and thickness of the interfacial layer, which in turn are
influenced by the rubber formulation. Previously, various adhesion promoters
such as organic cobalt salts and resins have been used to impede degradation of
the rubber-brass bonding layer during aging. It has been shown that the
interfacial layer consists mainly of sulfides and oxides of copper and zinc. A
strong correlation exists between the nature of the interfacial layer and the
rubber-brass adhesion. This paper
discusses the effect of changes in the chemical composition and the structure
of the interfacial layers due to addition of adhesion promoter resins. Grazing
incidence X-Ray Diffraction (GIXRD) experiments were run on sulfidized polished
brass coupons previously bonded to six experimental rubber compounds. It was
confirmed that heat and humidity conditions lead to physical and chemical
changes of the rubber-steel tire cord interfacial layer, closely related to the
degree of rubber-brass adhesion. The adhesion promoter resins inhibit the
unfavorable morphological changes in the interfacial layer thus stabilizing it
during aging and prolonging failure. Tire cord adhesion tests illustrated that
the one-component resins improved adhesion after aging using a rubber compound
with lower cobalt loading. Based on the acquired diffraction profiles, these
resins were also found to impede crystallization of the sulfide layer after
aging leading to improved adhesion. Secondary Ion Mass Spectrometry (SIMS)
depth profiles and