Processing and characterization of biodegradable polymer nanocomposites: detection of dispersion state

Nanobiocomposites of poly(lactic acid) (PLA) with 3-5 wt% organically modified montmorillonite (OMMT) were prepared by melt compounding in two different mixers, miniature twin-screw extruder and internal batch mixer, leading to different degrees of dispersion. The progress of dispersion was characterized by melt rheology coupled with light attenuation. Processed PLA/OMMT samples showed percolating networks in the melt, detected by a step increase in low-frequency elastic moduli. The melt elasticity of nanocomposites increased, while the light attenuation coefficient and the loss tangent decreased progressively with mixing energy and reached saturation that can be attributed to the maximum level of clay dispersion achieved in the present experimental conditions. Results showed that a combination of low-frequency loss tangent and light attenuation coefficient provides a potentially sensitive method for the characterization of the degree of clay dispersion. The direct correlation between light attenuation coefficient and loss tangent follows linear dependence and may open an approach for the rapid inline analysis of the degree of dispersion in melt-processed nanocomposites.