Shear rheology of polylactide (PLA)-cellulose nanocrystal (CNC) nanocomposites

A simple method for the preparation of polymer-cellulose nanocrystal (CNC) nanocomposite is shown to yield good dispersion of CNCs within a polylactide (PLA) matrix, which consequently resulted in the lowest rheological percolation threshold reported so far for polymer-CNC systems. The rheological behavior of the nanocomposites was determined in dynamic, transient, and steady-shear flow fields in the molten state. The complex viscosity and storage modulus of the nanocomposites increased markedly with CNC content, particularly at low frequencies; the samples were highly shear thinning and exhibited a transition from liquid- to solid-like behavior as the CNC concentration increased. Larger values for steady-state viscosity, yield stress, shear stress, and first normal stress difference were reported for the more concentrated nanocomposites. Also, pronounced overshoots in the transient start-up viscosity of the nanocomposites were observed. These results could be ascribed to the formation of an interconnected CNC network within the PLA matrix.