Reinforcement of maleated natural rubber by precipitated silica

Graft copolymers of maleic anhydride and natural rubber or so-called maleated natural rubbers (MNRs) were prepared in a molten state with varying maleic anhydride contents from 4 to 10 phr. In this work, the filler-filler and filler-rubber interactions of the MNR and precipitated silica were investigated. The MNR compounds containing 40 phr of silica both with and without 9 wt % of silane coupling agent were prepared. By increasing the maleic anhydride contents, the Mooney viscosity and cure times were increased, but the torque differences and cure rate indices were decreased. Bound rubber was increased with increasing maleic anhydride content, indicating an increase of filler-rubber interaction. In case of the compounds without silane, the MNR with 6 phr of maleic anhydride showed the lowest filler-filler interaction as indicated by a decrease of storage modulus upon an increase of strain in the filled compound i.e., Payne effect. This MNR compound also yielded the optimum mechanical properties. It has been demonstrated that a use of MNR with appropriate maleic anhydride content can reduce filler-filler interaction dramatically and hence improve a silica dispersion, as confirmed by SEM micrographs, resulting in an enhancement of the mechanical and dynamical properties.