Compatibilization of NBR/SBR blends using amphiphilic montmorillonites

Sodium-montmorillonite (Mont-0) was partially/completely cation exchanged with appropriate amounts of cetyltrimethylammonium bromide to yield amphiphilic montmorillonites bearing different ratios of both hydrophilic and lipophilic segments. The lipophilicity/hydrophilicity range extended progressively up to the highly hydrophobic form (Mont-100), where all of the sodium cation content was replaced by the cetyltrimethylammonium cation. The produced amphiphilic forms can be arranged in the order of Mont-0 > Mont-25 > Mont-50 > Mont-75 > Mont-100, according to the decrease in hydrophilicity. Subsequently, the different montmorillonites were employed as reinforcing agents for acrylonitrile-butadiene rubber/styrene-butadiene rubber (50/50) rubber blend, which is known to be physically incompatible. We found from our previous reports that the mechanical properties of blends comprising a fixed loading of each montmorillonite form (20 phr) displayed remarkable improvements up to different levels indicating different compatibility influences between the rubber components by the inserted clays. In the current report, these results are intensively studied using dynamic mechanical thermal analysis and complemented by differential scanning calorimetry. Additionally, the network characteristics of the vulcanized rubber networks were determined for the neat blends (in absence of any clay) as well as for reinforced blends with different clay forms. Based on the obtained data, it could be concluded that the montmorillonite forms can bind both phases of the blend through interfacial interactions at the boundaries between the blend components but with different potentials. This effect was associated in the mean time by the hindrance of phase separation thus enhancing the compatibility. These findings were further supported using scanning electron microscopy, which confirmed that the compatibilization effect may have been achieved through lowering of the interfacial tension between the components.