Nano-particle dispersion and crystal structure in semi-crystalline polymer nano-composites

Quantification of nano-particle dispersion in polymer nanocomposites is challenging since a statistically relevant measure of a nano-property must be averaged over macroscopic sample dimensions. For the ternary system presented by semi-crystalline nanocomposites the situation is even more complex. Polymer crystals in the thickness and potentially lateral dimensions are of similar size to the reinforcing filler so it could be expected that some interaction between filler and crystals is to be expected. It is believed that adequate dispersion of nano-additives is required to maximize properties. In this study, dispersion is quantified through the use of x-ray scattering on high density polylethylene (HDPE)/N110 carbon black composites produced by different melt mixing techniques. An analog of the second virial coefficient, which describes binary interactions, is compared with other dispersion measurement techniques. A comprehensive presentation of the crystalline morphology (thickness, width, stacking order, and disorder), carbon black structure (primary size, branch content, tortuosity, aggregate size), as well as a quantitative measure of dispersion are obtained as a function of thermal history and concentration of filler.