Application of strain–time correspondence as a tool for structural analysis of acrylonitrile–butadiene copolymer nanocomposites with various organoclay loadings

Abstract

Acrylonitrile–butadiene copolymer (NBR) nanocomposites were prepared with varied silicate loadings by the melt mixing between NBR and organoclays (OCs) containing intercalants with different polarity and chain length. WXRD exhibited that the NBR nanocomposites had an intercalated structure with distinct differences in gallery height depending on the intercalant characteristics. However, WXRD failed to show a structural change with increasing silicate contents. Hence, tensile strain–stress measurements were carried out at various strain rates (0.162, 0.0975, and 0.0187 s −1), and then the results of tensile measurement applied to the strain–time correspondence (STC) principle, resulting in the tensile modulus master curves of the NBR nanocomposites as a function of time. For pure NBR, a master curve was constructed using only the horizontal shift factor, indicating that the material was structurally homogeneous. However, the NBR nanocomposites required both vertical shift (modulus shift, Γ( α)) and horizontal shift to form the master curves, indicating structural heterogeneity ascribed to the domain structure such as silicate tactoid. From master curves, we found that NBR nanocomposite with OC having polar organic intercalant, NBROC30B, had the lowest n value in the nanocomposites. This indicates that NBROC30B had the most dispersive silicate structure in the nanocomposites due to the polar interaction, being in good agreement with WXRD results. In particular, STC was not applicable at all nanocomposites with silicate loadings over 8 wt%, regardless type of organoclay, and tensile strength and toughness of the nanocomposites with silicate loading of 8 wt% were better than expected. These could be explained as the network-like percolation of the silicate tactoids in all nanocomposites with silicate loadings over 8 wt%, which were consistent with the results observed from HR-TEM.