Characterization of the Interface in Rubber/Silica Composite Materials

Abstract: in the rubber industry, especially tyre production, the most widely used elastomer is styrene-butadiene rubber (SBR) in which the styrene units generally are present at 25 wt.%. The unit repeats are random distributed along the macromolecular chains and the configuration of the butadiene units is mostly 1,4-trans. The elastomer blends are mixed with fillers, acting as reinforcing agents, and the effect that silica particles have on their physical and mechanical properties is now well established. One of the most important parameters in determining the performance of such composite materials is the degree of adhesion at the rubber/silica interface. In this context, the interface characterization has been performed through a spectroscopic investigation (XPS/x-ray-induced Auger electron spectroscopy) in order to derive information from core-level and Auger line chemical shifts. A series of composite rubbers have been examined by means of a detailed curve-fitting procedure that allows the determination of intrinsic and extrinsic structures connected to each photopeak and the spectroscopic results compared with those of reference compounds. The changes in the C 1s lineshape and shake-up region of the polymers and the reduced binding energies of silicon, oxygen and sulphur core lines have provided clear evidence of interfacial reactions. Moreover, the Auger parameters of silicon show systematic shifts that can be interpreted on a chemical state plot in terms of initial- and final-state contributions and used for theoretical investigation of the local chemical environment. Copyright (C) 2002 John Wiley Sons, Ltd.