Mutual dispersion of graphite–silica binary fillers and its effects on curing, mechanical, and aging properties of natural rubber composites

Abstract

Rubber composites deliver unsatisfactory mechanical performance if the rubber matrices, such as natural rubber, lack appropriate dispersion of fillers such as silica. This study explored the dispersion and reinforcement performance of binary fillers in natural rubber. Graphite powder was used as a solid lubricating silica filler in the rubber matrix, and shear force was applied using a conventional two-roll mixing mill. The curing, mechanical, and morphological properties were studied to evaluate the mechanism of binary filler dispersion in the rubber matrix. Binary fillers comprising silica and graphite offered better mutual dispersion, which was observed by scanning electron microscopy and mechanical testing and confirmed by atomic force microscopy. Better filler dispersion in natural rubber improved the mechanical and age resistance properties. The modulus at 100% strain and stress at break of unfilled rubber were increased by nearly 110% and 15%, respectively, when 20 phr (per hundred gram of rubber) of binary filler in a 1:1 weight ratio was used, and the composite exhibited better aging resistance and mechanical properties, compared to those of composites with single-filler systems, which may be attributable to the excellent filler dispersion in the rubber matrix.