Structural and phase separation characterization of poly(lactic acid)/poly(ethylene oxide)/carbon nanotube nanocomposites by rheological examinations

The morphology and phase separation have significant impacts on the properties and applications of polymer blends and nanocomposites. In this study, poly(lactic acid) (PLA)/poly(ethylene oxide) (PEO) blends and PLA/PEO/carbon nanotube (CNT) nanocomposites are prepared by solution mixing and the rheological approach is applied to study the morphology and phase separation of the prepared samples. Scanning electron microscopy (SEM) is also used to study the morphology and structure of samples. Additionally, the miscibility or immiscibility between polymer blends was analyzed through Han plots. The results display the lower critical solution temperature (LCST) phase diagram for the prepared samples demonstrating that the enhancement of temperature promotes phase separation. Moreover, the addition of nanoparticles transfers the LCST diagram to high temperatures. The deformation relaxation of PEO droplets commonly diminishes the modulus at very low frequencies, while the formation of big CNT networks in nanocomposites containing high CNT content results in a constant modulus. Han plots also represent the immiscibility in the samples containing 60 and 75 wt% PLA and the nanocomposites including 90 wt% PLA show homogenous structures. The SEM images verify the outputs of rheological tests conducted for the morphology of samples.