THE MECHANISM OF ADHESION BETWEEN TYRE-CORDS AND RUBBER, AS GOVERNED BY INTERFACIAL PHENOMENA
Chemical Product Design and Engineering (CPD&E)
CPD&E Keynote Lectue 2
Keywords: Rubber technology, RFL formulations, Tyres
J.W.M. NOORDERMEER, W.B. WENNEKES AND R.N. DATTA
Tyres need reinforcement with textile and metal cords in order to withstand internal pressure and to stabilize the tread. The adhesion between virgin textile cords and rubber is always poor, because of significant differences between fibre and rubber in modulus, elongation, polarity as well as in chemical reactivity. In order to improve this adhesion, it is common to use adhesive systems, which act as bridges in the interface between elastomer and reinforcing cord. These are commonly based on Resorcinol/Formaldehyde/Rubber-Latex (RFL) dip systems. Although this system dates back as far as 1938 and is commonly used for rubber reinforcement till today, the mechanism by which the adhesion is obtained is still unclear.
The paper provides new fundamental insights into RFL to rubber bonding. Enrichment by migration of rubber vulcanization ingredients to the RFL-rubber interface can be observed by use of Scanning Electron Microscopy, coupled with an Energy Dispersive X-ray spectrometer. The same method is used to determine the degree of enrichment for several RFL formulations, based on rubber-latices with varying polar vinylpyridine-contents. The vinylpyridine-content in the RFL indeed turns out to be the governing factor for the enrichment. The vinylpyridine-content also turns out to influence the adhesion: for most rubber compounds adhesion decreases with increasing vinylpyridine content. For a Natural Rubber / Styrene Butadiene Rubber blend, an optimum vinylpyridine content of 10% is observed.
A new mechanism of RFL-rubber adhesion is proposed based on the experimental results. The mechanism is explained in terms of unwanted embrittlement of the interfacial layer between the RFL dip and the rubber compound for high vinylpyridine containing RFL formulations, due to over-cure by excessive migration of curatives to the interface.
Presented Thursday 20, 08:45 to 09:15, in session CPD&E Keynote Lectue 2.
