Polymer nanocomposites, consisting of a polymer matrix with dispersed nanoparticles, have been researched extensively in recent years for their enhanced mechanical, electrical, optical and thermal properties. The objective of this thesis, Microstructure Modification in Model Polymer Nanocomposite Systems, was to explore the effect of the nano-sized particles on the polymer's crystalline structure. The purpose of this research was to develop a model to be used to predict the effect of the nanoparticles on the crystalline structure of nanocomposites studied in future research.
The nanocomposites formed for this thesis were based on a polyhydroxybutyrate (PHB) matrix with either montmorillonite (MMT) or fluoromica clay nanoparticles dispersed throughout. Nanocomposites with a loading of 1wt% and 3wt% clay were formed using melt mixed and solution methods.
Thin film samples were analysed using optical microscopy under polarised light to determine the effect of the clay on the PHB spherulites. Differential Scanning Calorimetry (DSC) was also used to indicate the level of crystallinity of the samples, while analysis with X-Ray Diffraction (XRD) provided a means of characterizing the nanocomposites as immiscible, intercalated or exfoliated.
The conclusion most relevant to the thesis objective was that both MMT and fluoromica clay particles caused local nucleation within the PHB matrix. This was observed as concentrated growth of spherulites on a much smaller scale than the larger spherulites in the pure PHB samples, with sizes of approximately 100 µm compared to 1500 µm in pure PHB.
However, it was also found that the two mixing methods produced nanocomposites with inadequate dispersion of the clay particles. A number of possible experimental procedures have been recommended to rectify this in future work, including pre-grinding the PHB and clay powders and drying them in a vacuum oven, the use of an autoclave for the solution method, and premixing the powders adequately before melt mixed extrusion. Another finding was that XRD was not adequate as the sole means of characterizing the polymer nanocomposites. This was attributed to disorder within the samples, low loadings of clay, degradation of the surfactant used to treat the clay, or possible complete exfoliation, which does not register using XRD. Extensions to this thesis were recommended to use XRD in conjunction with scanning electron microscopy (SEM), as well as transmission electron microscopy (TEM) in order to adequately characterize the nanocomposites.