Influence on mechanical and rheometric properties through different methods of chemical modification of silica applied to natural rubber compounds

The chemical modification of fillers has been an alternative to reach new levels of mechanical and rheometric properties. In this study, three methods of chemical modification of silica Zeosil 1165 PM, used as a reinforcing filler in elastomeric formulations, were evaluated by using the organosilane coupling agent, bis-(3-triethoxysilylpropyl) tetrasulphane (TESPT) compared to the reference, without addition of the TESPT named F1. The modification methods adopted were the chemical modification of the time-temperature-controlled greenhouse silica, named F2, the modification of the silica in the Banbury mixing process, named F3, and the use of the nanoclay-modified silica and incorporation of the TESPT in Banbury, named F4. Modification of greenhouse silica was monitored by thermogravimetry and Fourier-transform infrared spectrophotometry to define the modification parameters used for further incorporation of the filler in Banbury. Regarding the morphological properties, a large reduction of silica aggregates and agglomerates in TESPT formulations was evidenced by scanning electron microscopy, ranging from 100 nm to 500 nm (F1) to aggregates below 100 nm (F2, F3, and F4). On the other hand, improvements in rheometric, rheological, physical, and mechanical properties were also observed, comparing F2, F3, and F4 with F1, such as a reduction in Mooney viscosity by 40.2%, 51.1%, and 47.8%, a reduction in the optimal cure time by 41.1%, 48.9%, and 44.4%, a reduction in permanent deformation by 47.1%, 31.3%, and 41.6%, an increase in hardness by 15.3%, 16.4%, and 21.6%, increase in the reinforcement character by 32.4%, 51.7%, and 66.0%, and an increase in resistance to traction by 26.6%, 16.1%, and 63.9%. The best results for reinforcing character and tensile strength were verified in the modified nanoclay silica (F4). Thus, all results converge to a significant improvement in the properties of the formulations with the use of TESPT.