Abstract
ABSTRACT Organo-montmorillonite (OMMT) increases the elastic modulus of elastomers such as natural rubber (NR) by a very large amount at low strains, but this decreases as the rubber is extended. Silane coupling agents, widely used with silica-filled rubbers, were added to NR/OMMT nanocomposites to increase the effects of OMMT on modulus at high strains. Both bis(triethoxysilylpropyl)tetrasulfide (TESPT) and 3-mercaptopropyl di(tridecan-1-oxy-13-penta(ethylene oxide))ethoxysilane (MPDES) increase tensile modulus significantly at strains greater than 30%. The coupling agents strengthen the rubber–filler interface, reducing cavitation around OMMT particles and preventing NR molecules from sliding at the interface. Evidence for a stronger rubber–filler interaction is provided by measurements of bound rubber content and use of network visualization transmission electron microscopy (NVTEM). OMMT also affects the dynamic properties of NR differently from other fillers. One aspect of this is the appearance of a peak in tan δ between 20 °C and 60 °C, attributed to the glass transition of intercalated and adsorbed NR molecules. The intensity of this peak is diminished by the addition of TESPT or MPDES, implying that they are restricting the intercalation of the rubber between the clay sheets. The coupling agents also have a small effect on vulcanization behavior compared with that of OMMT.
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