| Summary: | Several compounds were prepared by melt mixing various formulations of a linear low
density polyethylene, a graft modified polyethylene and an organically modified clay, in
a twin screw extruder. X-ray diffraction, transmission electron microscopy and rheology
were used to characterize the extent of intercalation of the silicate galleries.
Incorporation of minimum weight fraction of 2% clay and 50% maleated polyethylene
was found to introduce radical changes in the rheological behaviour of the
nanocomposites. Broadening peaks in X-ray diffraction indicated increasing dispersion
of silicate nanolayers inside polymer as a function of graft modification. With higher
incorporation of maleated polyethylene, solid-like response begins to appear at low
frequencies indicating possible networking. Flow activation energy was found to
decrease with incorporation of clay. Dual flow behaviour of the nanocomposites beyond
the Newtonian plateau in the form of a filler-like flow at low shear rates and polymer-like
shear thinning flow at high shear rates was observed. Changes in flow energy of
activation with respect to clay and fusabond concentration are analysed. Relaxation
spectra determined using a parsimonious model were found to extend to higher relaxation
time scales with exfoliation. The Cox-Merz rule was found to fail over the whole range
of shear rates for exfoliated compounds, indicating increased interactions in the matrix
resulting in highly anisotropic distribution of individual silicate layers. Fusabond induces
higher elasticity into the composite and increases the tensile stress growth function during
melt elongation. Fusabond exhibits highly ductile failure as opposed to the brittle failure
of polyethylene. Hence, fusabond is observed to contribute towards the ductility of the
nanocomposite. A combination of fusabond and clay was found to be complementary in
initiating strain hardening. The mechanical properties of the nanocomposites did not
show an impressive change at low clay concentrations. A unique dip at 0.1 wt% clay
loadings to complement its role in processing was followed by a steady increase with
increasing clay concentration. While fusabond and higher levels of clay accounted for
the increased toughness of nanocomposites, 0.1 wt% of clay decreased the toughness.
There exists a threshold level of clay concentration above which the intercalation and
exfoliation phenomena play a significant role in enhancing the mechanical properties. === Applied Science, Faculty of === Chemical and Biological Engineering, Department of === Graduate
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