Abstract:
Sub-micron thick flakes were obtained by sonication of vermiculite that was first exfoliated by either
thermal shock or chemical treatment with hydrogen peroxide. Dimer fatty acid polyamide
nanocomposites with a mixed morphology were prepared via a solution-dispersion technique. The
large (in the micrometre range) vermiculite flakes assumed random orientations in the matrix. BET
surface area measurements indicated flake thickness below 100 nm but SEM showed that thicker
flakes were also present. Filler content was varied up to 30 wt.%. At this loading, the tensile strength
doubled, the modulus increased five-fold but the elongation-at-break decreased by a factor of ten.
Dynamic mechanical analysis suggests that three stiffening mechanisms were operating. The
reinforcing effect of the high stiffness inorganic flakes is the primary contributor. Together with the
chain confinement effect, that expresses itself in an apparent increase in the glass transition
temperature, this provided an adequate rationalisation of the stiffness variation below Tg. However,
an additional stiffening effect is indicated at temperatures above Tg. The mechanism may involve
dynamic network formation based on fluctuating hydrogen bonding interactions between the matrix
polymer chains and the filler particles.
