Role of Starch In Improving the Fatigue Life of Carbon Black Filled SBR Composites

This paper deals with the fatigue resistance of carbon black (N330 CB) filled SBR. We found that 5 phr starch, replacing the same amount of N330 CB, can greatly improve the tensile fatigue life of SBR composites. Starch was added in form of starch/SBR masterbatch prepared by latex compounding method, to ensure the fine dispersion of starch. To investigate the underlying mechanism, the influence of starch was compared with that of other fillers with different particle sizes and surface activity, such as modified starch, silica, CaCO₃, and N990 CB, in terms of crack growth rate, tearing strength, stress-strain curves, filler network, crosslinking density. The measurements of cyclic crack growth of single-edge notched samples in uniaxial tension showed that modified starch exhibited the highest resistance against crack propagation, and the overall order is modified starch > starch > silica > N330 > N990 > CaCO₃. This order is consistent with the results of the fatigue life and SEM observation of fatigue fractured surface. Rubber processing analyzer testings showed that replace of 5 phr N330 carbon black reduced the filler network. The effects of filler deformation, filler particle size and interfacial interaction on the fatigue life were discussed, and it was suggested that the starch deformation, due to its polymeric characteristic, should play an important role in improving the fatigue life. These findings are of high importance for designing rubber composites with high fatigue resistance and extending the application of starch as filler. The results are also expected to provide further insights into the influence of filler on crack growth in elastomeric materials.