Investigation of the Rubber-Brass Adhesion Layer Using the Olefin-Metathesis Method

The incorporation of brass-coated steel wires in rubber products such as tires, hydraulic hoses and handrails is a widely used reinforcing method. To attain the highest standards of mechanical properties an outstanding adhesion between rubber and metal is required. This is accomplished by the formation of a Cu_xS-ZnS interface, created during the sulfur vulcanization of the rubber. [1] Thus, the cured rubber is then able to bind mainly mechanically on this interface, and consequently the adhesion properties are influenced by the rubber mixture and the brass surface as well. The additional contribution of covalent bonding to adhesive strength of rubber-brass interfaces is assumed to be rather low. [2]

For a thorough investigation of the rubber-brass interface and for further development a method is needed, where the generated adhesive layer can be released in a non-destructive way. However, due to the strong adhesive strength between the rubber and the brass coated wire, it is difficult to uncover their interface. A method, where the degradation of the rubber compound does not damage the adhesive interface, is based on the olefin-metathesis. Here the rubber macromolecules are cleaved in low-molecular weight components using a ruthenium based Grubbs 2^ndcatalyst (“metathesis degradation”). After careful optimization of the reaction conditions, the rubber-metal interface can be exposed for detailed investigations using e.g. optical microscopy, focus variation microscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX).

This method permits to investigate real rubber-brass interfaces although in the presence of large amounts of fillers and additives in the elastomer matrix. . Therefore, the olefin-metathesis method is promising for future studies in brass reinforced rubber technologies. This will be shown on the basis of selected examples.

 

References

[1]       van Ooij W.J.: Fundamental Aspects of Rubber Adhesion to Brass-Plated Steel Tire Cords, Rubber Chemistry and Technology, Vol. 52, 1979, 605-675

[2]       van Ooij, W. J.: Mechanism and Theories of Rubber Adhesion to Steel Tire Cords, Rubber Chemistry and Technology, Vol. 57, 1984, 421-456