Morphology evolution and macroscopic behaviour of PLA-organoclay nanocomposites during extensional rheology: Experimental study

Changes in morphology and macroscopic behaviour of polylactide (PLA)-organoclay nanocomposites in extensional melt deformation were studied as a function of nanoparticle weight fraction and strain rate. Extensional rheology at different strain rates from 0.1 s−1 to 10 s−1 was used to determine the macroscopic response of the nanocomposites, while the associated changes in nanocomposite morphology were characterised through wide-angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). The average nanoparticle reorientation was found to increase with increased strain and strain rate, irrespective of the organoclay mass fraction. Reduction in the tactoid thickness and increased effective tactoid length were found with increased strain, although the strain rate was found to have larger influence on the effective length. Moreover, non-Newtonian macroscopic extensional thinning was found for the nanocomposites, and attributed to the enhanced local shear deformations in the polymer matrix caused by the presence of the nanoparticles.