Characterisation of rubbers, rubber contact traces and tyre prints by fluorescence spectroscopy

Abstract

Fluorescent contact traces are transferred from many rubber articles, and may be characterised, after extraction, by synchronously excited fluorescence emission spectroscopy. The fluorescence is due mainly to extender and process oils, to antioxidants, and to polynuclear aromatic hydrocarbons. Variation in these components in tyre treads, caused by variation in manufacture and wear, enables tread rubbers, and their prints, to be efficiently distinguished from one another. Fluorescent tyre print formation is controlled by the nature of the surface, and by contact time and pressure. Some of the fluorescent material solvent-extracted from such prints is present initially as non-fluorescent particles of rubber. Tyre sidewall rubbers are distinguished from tread rubbers by differences in the extraneous polynuclear aromatic hydrocarbon emissions and, in the case of radial tyres, principally by differences in extender oil emissions. The techniques described are also applied to traces left by footwear and by erasers, to the detection of mineral oil in failed brake seals, and can be generally applied in the comparative examination of rubbers.