Abstract :
Zinc oxide and copper/zinc sulphide layers are formed during vulcanisation and moulding of rubber to brass-coated steel tyre reinforcing cords.
Previous studies have described how zinc diffuses through the rubber–brass interface to form zinc sulphide, and combines with oxygen to create
zinc oxide during dezincification. The zinc is usually assumed to originate in the brass of the tyre cord, however, zinc oxide is also present in the
rubber formulation.We reveal how zinc from these sources is distributed within the interfacial bonding layers, before and after heat and humidity
ageing.
Zinc oxide produced using 64Zn-isotope depleted zinc was mixed in the rubber formulation in place of the natural ZnO and the zinc isotope
ratios within the interfacial layers were followed by secondary ion mass spectroscopy (SIMS) depth profiling. Variations in the relative ratios of the
zinc isotopes during depth profiling were measured for unaged, heat-aged and humidity-aged wire samples and in each case a relatively large
proportion of the zinc incorporated into the interfacial layer as zinc sulphide was shown to have originated from ZnO in the rubber compound.
