Vulcanized rubber/brass interface

Analysis of failure surfaces can also lead to information about the reactions which occurred in the interface. Results of an XPS analysis(39) of a vulcanized rubber/brass interface are shown in Figure 34. Products formed at the interface were identified as ZnO, ZnS, and Cu S the latter two were confirmed by X-ray diffraction analysis. The components of the vulcanizing rubber attack the brass leading to the formation of an interfacial film of reaction products, which become an integral part of the rubber-brass bond. Ageing in either steam or oxygen leads to further reaction and the formation of a weak boundary layer and low strength. 

Bonding Agents. These materials are generally only used in wire cable coat compounds. They are basically organic complexes of cobalt and cobalt—boron. In wire coat compounds they are used at very low levels of active cobalt to aid in the copper sulfide complex formation that is the primary adherance structure. The copper sulfide structure builds up at the brass rubber interface through copper in the brass and sulfur from the compound. The dendrites of copper sulfide formed entrap the polymer chains before the compound is vulcanized thus holding the rubber firmly to the wire. 

Cobalt salts used in the wire coat compounds may accelerate the vulcanization rate of high sulfur compounds, and increase the state of cure or crosslink density. The increase in crosslink density increases the pullout force of the wire in the rubber. More important, cobalt salts form Co + ions at the interface of the brass surface during vulcanization, and this will affect copper sulfide formation. 

Brass/Rubber. When rubber containing sulfur curatives is pressed into contact with brass (typical alloy 65% copper, 35% zinc) and then vulcanized, copper diffuses to the brass surface and reacts with sulfur to form cuprous sulfide (51). This interlayer grows outward from the brass surface, strongly interlocking into the rubber phase (52,53). Again, diffusion to an interface and in situ reaction... 

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