Effect of fill factor and validation of characterizing the degree of mixing in polymer nanocomposites

Polymer nanocomposites have been studied extensively, but few references mention the importance of processing and how to characterize the degree of mixing. In this work, we report the influence of fill factor on the degree of mixing and thermal properties for a nanocomposite system consisting of alumina nanoparticles in polyethylene terephthalate (PET) prepared in a batch mixer. The degree of mixing for the resultant polymeric nanocomposites was quantified by three different techniques; TEM particle density, Morisita's index, and skewness. All of these methods quantify the degree of mixing based on the number of the particles in selected areas of TEM images using image analysis software. TEM particle density and skewness gave similar results, with a maximum in the degree of mixing around a fill factor of 0.70, while Morisita's index displayed a constant increase in degree of mixing with increasing fill factor. Tg was depressed by the filler and with increasing degree of mixing. The depression of Tg in the composite was maximized at a fill factor of 0.70, confirming that the analysis of TEM particle density and skewness are valid techniques to assess the degree of mixing. POLYM. ENG. SCI., 47:2049–2056, 2007. © 2007 Society of Plastics Engineers