The Influence of Cation in Organometallic Boroacylate Adhesion Promoters on Physico-Mechanical and Dynamic Mechanical Properties of Steel Cord Skim Rubber Compound

Abstract

In steel cord reinforced radial tyres, mainly a silica-resorcinol-hexamethyl melamine (SRH) system and an organometallic salt (generally boroacylate salts which are the best performers among all anions) are incorporated in order to obtain adequate adhesion and reduce the deleterious effects of the corrosion process encountered by brass coating under different hostile environments. This paper is a report of studies on the effect of nature and concentration of the cations associated with organometallic boroacylate salts on the process-ability and physico-mechanical properties under different ageing conditions, as well as dynamic mechanical properties of steel cord skim formulations. The boroacylate salt of cobalt, nickel and zinc have been chosen for this purpose. In general, the addition of an organometallic adhesion promoter helps in achieving a higher level of curing, enhances crosslink density, and reduces the thermal and oxidative stability of the compound. All the viscoelastic properties, viz., storage modulus (E'), loss modulus (E") and loss tangent (tan γ) are influenced by the presence of these adhesion promoters to different extents depending on the nature of the cation. Irrespective of the test frequency and temperature, cobalt boroacylate exhibits the lowest tan γ. These viscoelastic properties are also influenced by the variation of zinc ion concentration. Tan γ shows a maxima at 0.35 pphr of zinc ion. These promoters are unable to resist the compound degradation due to steam ageing. However, cobalt and nickel salts offer a degree of protection against salt ageing.