(734c) Magadiite Silylated With Sulfur-Functional Organosilanes: Investigation of Structure and Interlayer Accessibility

Sodium magadiite (Na-MGD) is a prospective active filler for elastomer applications.  In this work, Na-MGD was functionalized with sulfur-containing silane coupling agents, either bifunctional (bis (triethoxysilylpropyl) polysulfide, Si69) or monofunctional (3-mercaptopropyltriethoxysilane, MPTES) using cetyltrimethylammonium bromide modified MGD (CTA-MGD) as the intermediate.  During grafting, the organosilanes displace CTA⁺ cations from CTA-MGD surface, leading to a decrease in the interlayer spacing as measured by XRD; however, some CTA⁺ cations remain in the MGD interlayer.  The amounts of organosilane molecules grafted on MGD surface indicate that MPTES leads to a higher grafting density than Si69.   Having functionalized the MGD interlayer surfaces, the accessibility of the sulfur-functional interlayer was evaluated using squalene, a model compound for natural rubber.  Various sulfur-functional MGD materials (CTA-MGD, Si69-MGD, and MPTES-MGD) were reacted with pure liquid squalene.  FTIR results show that new Si-O-C bonds are formed after reaction of squalene with sulfur-functional MGDs, but not with CTA-MGD.  TGA and elemental analysis were used to quantify the amount CTA+, silane, and squalene in the products.  XRD results demonstrate that squalene can access the interlayer sulfur only when the silane graft density is relatively low.  This work shows the value of using squalene as a model compound for characterizing the structure and properties of sulfur-functional MGD prior to preparation of MGD-based elastomer composites.