Investigation of Composition and Processing Parameters on Mechanical Properties of Magadiite/SBR Composites

This work investigates mechanical reinforcement and energy dissipation in styrene-butadiene rubber (SBR) composites containing sulfur-functional, organosilane-modified magadiite (MGD), a layered silicate (Na₂Si₁₄O₂₉ž9H₂O).  Using MGD gives us plate-like active filler particles with surface chemistry similar to precipitated silica.  In previous research, we demonstrated that MGD/SBR elastomers have better mechanical properties than silica/SBR composites with the same filler weight loading.  MGD has significantly higher specific surface area than silica, and both the SI-69 coupling agent and SBR can access the MGD interlayer space, resulting in superior reinforcement.  This work aims for a deeper understanding of reinforcement mechanisms in MGD/SBR composites by investigating the influence of composition and processing parameters on the elastomer structure and properties.  The main composition parameter is the type of alkyl ammonium ion used to prop open the MGD interlayer space.  We treat MGD with cetyl trimethyl ammonium (CTA), dodecyl pyridinium (DP) and hexadecyl ammonium (HDA) cations to produce “organo-MGD” materials with varying initial interlayer spacing.  Using these materials, we explore the hypothesis that larger organo-MGD spacing will permit greater access of SBR into the MGD interlayer gaps.  We investigate a second composition parameter, the phr loading of SI-69, to assess the importance of chemical cross-linking between MGD and SBR.  The main processing parameter is the batch mixing time, to see if longer batch mixing facilitates MGD expansion and ingress of SI-69 and SBR pre-polymer into the interlayers.  We prepare cross-linked MGD/SBR samples with varying organo-MGD materials, varying levels of SI-69 addition, and varying mixing time to study the influence of those factors on mechanical reinforcement.  All samples are characterized by XRD after mixing, milling, and curing steps to help us understand at what stage SBR enters the MGD interlayer.  DMA and tensile testing quantify the mechanical properties.  By exploring the roles of composition and processing factors on the mechanical properties of MGD/SBR composites, this work will help us better understand the impact of non-spherical filler particle shape on reinforcement mechanisms and energy dissipation in platelet-filled elastomers.