Thermo-oxidative stress relaxation in carbon-filled SBR

ABSTRACT The thermo-oxidative stress relaxation in carbon-filled styrene-butadiene rubber is investigated using a two-step strategy consisting in homogeneous aging identification followed by heterogeneous aging prediction. Experimental observations of the chemical relaxation effects on the permanent deformation and on the equilibrium stiffness are reported on flat samples, containing various amounts of carbon-black fillers and aged at various temperatures and exposure times. The thermally activated degradation, implying scission-reformation mechanisms of links at a constant stretch at high temperature, is modelled from network decomposition under homogeneous aging conditions. An equivalent aging time, using the consumed oxygen across the thickness of bulk structures, is then introduced into the network alteration kinetics in order to predict the diffusion-limited oxidation effects on a bulk sample. Thanks to the model, the macroscopic chemical relaxation response and the heterogeneous damage patterns are discussed in connection to aging conditions and carbon-black filler content.