This work examines the mechanisms by which magadiite (MGD), a synthetic layered silicate, acts as an active filler to provide high levels of mechanical reinforcement in styrene-butadiene rubber (SBR) composites. Cetyltrimethylammonium (CTA(+)) expands the MGD layer spacing and promotes intercalation of SBR and silane coupling agent (Si69); the resulting CMGD/SBR composites have greater tensile moduli than comparable silica/SBR composites. CMGD was reacted in solution with Si69 (or MPTES) to prepare pre-grafted MGD with varying levels of interlayer silane functionalization (SMGD). If the silane graft density is relatively low, the resulting SMGD/SBR composite has mechanical properties comparable to CMGD composites prepared with Si69 added during batch mixing. However, SMGD with high silane graft density does not permit SBR intercalation and produces composites with inferior mechanical properties, demonstrating the necessity of silane-mediated interlayer grafting. Omitting Si69 from the formulation dramatically reduces the level of mechanical reinforcement as measured by DMA and tensile testing. Adding extra bulk sulfur (to replace sulfur omitted with Si69) does not produce composites with mechanical properties comparable to CMGD/SBR or SMGD/SBR prepared with Si69. This work demonstrates that silane-mediated SBR-MGD grafts within the MGD interlayer space are essential for achieving high levels of mechanical reinforcement in MGD/SBR composites. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45025.
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