The adhesion between virgin textile cords and rubber is always weak, because of significant differences between fiber and rubber in modulus, elongation, polarity as well as reactivity. In order to improve the adhesion, it is common to use adhesive systems, which act as bridges between elastomer and reinforcement. These are commonly based on Resorcinol/Formaldehyde/Latex (RFL) dips. Despite the fact that this technique was invented in 1938 and no major improvements have been achieved since then, the mechanism by which the adhesion is obtained is still unclear. This paper contributes more fundamental understanding of RFL to rubber bonding. In previous work an enrichment of curatives at the RFL-rubber interface was observed by use of a Scanning Electron Microscope coupled to an Energy Dispersive X-ray spectrometer. In the present paper, the same method is used to determine the degree of enrichment for several RFL formulations, based on latices with varying vinyl-pyridine (VP) contents. The vinyl-pyridine content is varied by copolymerization of various VP terpolymers. Adhesion decreases with increasing vinyl-pyridine content for most rubber compounds. For aN NR compound with low accelerator content and a NR/SBR blend, an optimum vinyl-pyridine content of 10% is observed.

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