New insights into the morphology of silica and carbon black based on their different dispersion behavior

Precipitated silica in combination with bifunctional organosilanes almost fully replaces currently the commonly used carbon black fillers in modern passenger car tire tread compounds to improve tire properties such as wet traction (safety) and rolling resistance (fuel consumption). However, it is still challenging to reach a sufficient level of abrasion resistance (service life). An optimum macrodispersion quality of the silica is a fundamental precondition for an optimum abrasion resistance. This goal can be reached by the development of new tailor-made highly dispersible silica grades. In order to achieve this, it is essential to be aware of the analytical silica parameters, which affect the dispersion process. One of these parameters known from carbon black is the structure of the filler. To gain deeper insights into the in-rubber dispersibility of the silica, the structure was investigated by two different methods, the DOA measurement and the void volume measurement. The results were correlated to the in-rubber macrodispersion. In contrast to carbon black filled compounds, no sufficient correlation of the structure with the macrodispersion could be found for the silica-filled compounds. Therefore, it was concluded that the morphology of silica differs from that one that is claimed for carbon black. Additional investigations like TEM, FT-IR and X-ray diffraction measurements were carried out. Carbon black shows a more elastic structure, which can withstand the external forces during the mixing process in a better way. Silica contains a much higher void volume in the structure even after exposed to high forces. These new findings will help to understand the macrodispersion process in rubber in a better way

Comparison and evaluation of different analytical methods to predict the in-rubber dispersibility of silica

The aim of the present investigation was to find a correlation between one single analytical parameter of precipitated silica and its in-rubber dispersibility. Therefore, 25 different types of silica with a variety of analytical parameters and dosage forms were investigated by means of standard analytical methods (CTAB, BET, DOA, pH and moisture content) as well as t*wo new methods, the sedimentation test and the in-situ cluster fragmentation. Moreover, all types of silica *were mixed inside a typical Green Tire formulation filled with 80 phr of silica. The macro-dispersion quality was evaluated by means of two dispersion measurement systems, the Topography where the surface roughness of a rubber sample is scanned mechanically by a probe and the Dispertester where the sample is investigated by an optical light microscope. No significant linear correlation between the standard analytical parameter and the macro-dispersion quality could be found whereas the sedimentation method and in-situ cluster fragmentation provides promising approaches. However, it was not possible to directly predict the in-rubber dispersibility of silica by means of one single analytical parameter with a very high correlation coefficient. Finally, different aspects which limit the general approach were discussed. Taking all these facts into account it becomes obvious that a linear correlation of one single analytical parameter with the dispersion quality cannot be found