**4. Conclusions**

The present work has discussed the influence of in-situ silica and precipitated silica on friction, abrasion, and crack growth properties of SSBR rubber. For better understanding of the significance of silane in the silica-filled elastomer systems, the TESPT silane coupling agen<sup>t</sup> was incorporated. The silanization a ffected the friction characteristics (wet grip performance) of precipitated silica-filled rubber. However, no significant e ffect was observed in the in-situ silica systems. Lower friction coe fficients were observed for the in-situ silica systems, which is very vital for low rolling resistance (better fuel e fficiency) applications. The precipitated silica compounds displayed better abrasion characteristics and the incorporation of a silane coupling agen<sup>t</sup> plays a significant role by improving the filler-rubber interaction. The crack propagation results initially indicated that the precipitated silica system has higher resistance to crack propagation. However, upon comparing samples with similar crosslink densities, much better resistance to crack growth was observed for the in-situ silica systems, which is further improved by an additional silane modification. As a consequence of the results described in this paper, it can be stated that rubber compounds using a masterbatch containing in-situ silica (instead of the classical silica/silane mixing process) may have the potential to be used in the future in the industrial production of technical rubber articles or car tires. Yet, further research efforts are required for this implementation, in particular to ensure the scale-up of the process to industrial dimensions.

**Author Contributions:** Conceptualization, S.R.V., G.H., A.D., and K.W.S. Methodology, S.R.V., E.S.B., F.X., and S.W. Validation, G.H., A.D., and K.W.S. Formal Analysis, S.R.V., E.S.B., and F.X. Investigation, S.R.V. Resources, G.H. and S.W. Writing—Original Draft Preparation, S.R.V. Writing—Review and Editing, G.H., A.D., and K.W.S. Visualization, S.R.V. and E.S.B. Supervision, G.H., A.D., and K.W.S. Project Administration, S.R.V., A.D., and K.W.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding. **Acknowledgments:** The authors express their thanks to Manfred Klüppel and Andrej Lang at Deutsches Institut für Kautschuktechnologie (DIK), Hannover for conducting the friction experiments and useful discussions. For the electron microscopy images, many thanks are given to Regine Boldt and Maria auf der Landwehr. The support of René Jurk in the Elastomer lab is gratefully acknowledged (all Leibniz-Institut für Polymerforschung Dresden).

**Conflicts of Interest:** The authors declare no conflict of interest.
