|dc.description.abstract||Polymer-clay nanocomposites are attracting global interest principally because
property enhancements are obtained at low clay particle loadings (1-5 wt%).
However there is lack of fundamental understanding of such composites. The aim
of this work is to provide an insight into the interaction between polymer and clay.
This includes the driving force for intercalation, the reinforcement mechanisms and
property-volume fraction relationships.
Functionalised poly(ethylene glycol)-clay, poly(c-caprolactone)-clay and
thermoplastic starch-clay nanocomposites with a range of polymer molecular
weights, clay volume fractions and with different clays were prepared using
solution methods, melt-processing methods, and in situ polymerisation. A reliable
X-ray diffraction technique for low angle basal plane spacing of clay, the essential
parameter for structure determination, was established obtaining ±0.005 Mn
between three diffractometers. The basal plane spacing was found to be unaffected
by polymer molecular weight and preparation method but was affected by the
nature of the polymer and clay. Increasing clay loading could lead to a lower
spacing. As a cautionary observation, poly(ethylene glycol) with high molecular
weight (2: 10,000) was found to undergo degradation readily during preparation of
nanocomposites with and without clay.
Competitive sorption experiments for molecular weight showed that high
molecular weight fractions of polymer intercalate preferentially into clay during
solution preparation. Thermodynamic studies on the intercalation process found
that significant enthalpic change occurred during intercalation, which is coincident
with the observation that heat-treated clays without interlayer water can intercalate
polymer. The calculation of true volume fraction against nominal volume fraction
provided reasonable explanation of property enhancement and helps understand the
relation between nanocomposites and conventional composites. At a given clay
loading, nanocomposites with better dispersion gave more property enhancement
than those with lower dispersion or conventional composites. The crystallinity of
semicrystalline polymer was also affected by varying extents of dispersion of clay.
The use of X-ray diffraction with an internal standard was explored for quantitative
analysis of intercalation and exfoliation.||en_US