(94d) Strain Hardening in Elongational Flow of Nylon-Clay Nanocomposite Melts

The object of this paper was to compare the nonlinear strain hardening behavior in uniaxial extensional flow of polymer clay nanocomposite melts prepared with the same nylon-6 as the matrix and with different organic modifiers for the montmorillonite clay. The elongational flow tests were carried out with the RME and with the rotary extensional viscosity fixture (EVF) on the TA-ARES instrument. The coupling between the matrix and the clay was evaluated with vanGurp-Palmen plots prepared from dynamic shear tests on the nanocomposites at 235 C. The nylon-6 melt alone did not show any strain hardening. The nanocomposite melt with stronger matrix-nanofiller coupling displayed significant strain hardening.

In contrast, when conventional composites of low density polyethylene or polystyrene with microscale fillers such as glass beads, flakes and whiskers were tested in uniaxial extension [Takahashi et al. 1999], the strain hardening behavior was observed to be weaker than that of the matrix over strain rates of up to 1 s-1. The smaller the particle size, the weaker the strain hardening of the composite melt; the strain hardening also weakened progressively with increasing aspect ratio. Although the extent of orientation of the microscale fillers increased with the Hencky strain up to 1, the change in orientation had no effect on the strain hardening of the composite melt.

Hence the orientation of nanoscale fillers and the molecular chains must be coupled to observe strain hardening in nanocomposites.