Improving the dispersion of MWCNT and MMT in PVDF melts employing controlled extensional flows

Poly (vinylidene fluoride) (PVDF) has been widely explored to produce polymer nanocomposites possessing outstanding combinations of properties. In this work, the impact of extensional melt flows on the dispersion, relaxation and crystallinity of PVDF nanocomposites filled with multiwalled carbon nanotubes (MWCNT) and montmorillonites (MMT) was studied. Extrusion was employed to produce nanocomposites containing 3 wt% of fillers, named: (i) PVDF/3 wt% MWCNT, (ii) PVDF/3wt%MMT, and (iii) PVDF/1.5wt%MWCNT/1.5 wt% MMT. The results showed that applying a sequence of extensional flows through the melts improved the dispersion of both fillers in the PVDF matrix. Moreover, extensional flows significantly enhanced the viscosity and relaxation of MWCNT nanocomposite, but had marginal effects on MMT nanocomposite. On the other hand, MMT favored the crystallization of the β piezoelectric phase of PVDF over the α phase and the extensional flow enhanced its crystallinity content. Therefore, these new insights prospect a vast horizon toward the use of extensional flows for tailoring synergic combinations of properties in hybrid PVDF/MWCNT/MMT systems.