Macrodispersion of amorphous precipitated silica micropearls in an elastomer matrix: Role of silica intrinsic parameters

Abstract : The development of highly dispersible silica micropearls by Rhodia led to the introduction of silica as a reinforcing filler in Green tyres in 1992 by Michelin. However new environmental constraints imply to further improve the silica dispersion process. The objective of the present work was to investigate the role of silica intrinsic parameters on its dispersibility in order to determine key parameters to improve the silica dispersion. The behaviour of different silica grades was thus investigated: two classical silica micropearl grades for tyre applications different in their specific area (silica Z1165MP with a high specific area and silica Z1115MP with a lower specific area), the same grades chemically modified with a covering agent (silane), and pilot grades (same specific area, same aggregate structure as Z1165MP) synthesized by Rhodia where the physico-chemistry of the silica surface was modified during the silica process. The dispersion behaviour was characterized in model conditions: in air (impact on wall) and under shear in a SBR matrix (rheo-optical device). The direct observation of dispersion mechanism in a SBR matrix under shear showed that the Z1115MP dispersed via an efficient mechanism of disintegration with the sudden breakage of the micropearl into micron size fragments above a low critical stress whereas the Z1165MP ruptured into a few large fragments at a higher stress. The post-chemical modification of the silica surface using silane had no effect on the silica dispersion compared to raw materials. However the modification of the physico-chemistry of the silica surface during the silica process implied changes in the internal organisation of the micropearl and allowed to modify the dispersion mechanism. This work was performed in the framework of DURAMAT project, programme of AXELERA for innovative, durable and environmental friendly materials. The authors thank the other partners of the project (LRMP-IMP, LTDS/ECL in Lyon) for their collaboration.