Clay Dispersion Assessment via FT-Rheology for Polypropylene/Clay Nanocomposites Fabricated by an Electric Field

Nonlinear viscoelastic parameters obtained from a large-amplitude oscillatory shear (LAOS) test have widely received attention in polymer nanocomposite (PNC) characterization. Previously, we reported that nonlinear parameters, Q0 and NLR (nonlinear–linear viscoelastic ratio) from FT-rheology, better-characterized filler dispersion in PNCs than the linear viscoelastic parameters of the small-amplitude oscillatory shear (SAOS) test and concluded that nonlinear parameters could detect the interfacial area much more sensitively than linear parameters [Kim, M. Macromolecules 2019, 52, 8604]. To confirm this, we systemically manipulated clay dispersion states of polypropylene (PP)/clay PNCs in this study by applying an electric field (EF). An EF can easily manipulate the dispersion quality of clays, i.e., tactoid, intercalation, and exfoliation in a polymer matrix, by controlling the application time. The clay dispersion was examined using the rheological properties of SAOS and LAOS tests. The linear viscoelastic properties (|G*|) from the SAOS test increased monotonically with increasing clay content and EF application time. In contrast, the nonlinear rheological properties (Q0) by FT-rheology from the LAOS test exhibited more prominent and sensitive growth. When the concentration of clay increased without EF application (φ = 1, 3, and 5 wt %), |G*|(φ)/|G*|(PP) increased from 1 to 2.05, whereas Q0(φ)/Q0(PP) increased from 1 to 22.8. In 5 wt % clay PNC, EF was applied in increments of 3, 7, 10, 20, and 30 min. With increasing EF application time, |G*|(5 wt %)/|G*|(PP) increased from 1 to 3.24, while Q0(5 wt %)/Q0(PP) increased significantly from 1 to 13,540.