Rheological and mechanical properties of polylactide nanocomposites reinforced with the cellulose nanofibers with various surface treatments

Abstract

As green composites, cellulose nanofiber (CNF) reinforced polylactide (PLA) systems have attracted increasing attention recently. In this work, three forms of CNFs, including pristine, coupled and acetylated ones, were incorporated with PLA through solution casting and injection molding to prepare PLA nanocomposites with different polymer-fiber affinities, and with different dispersion states and orientation levels of fibers. Rheological and mechanical properties of those systems were studied then in terms of fiber loadings and phase compatibility. Some interesting results are shown here. Surface acetylation can improve phase affinity of CNFs to PLA more evidently as compared to coupling reaction, but it also has diluent effect on the shear flow of nanocomposites, and therefore acetylated CNFs show better dispersion and higher orientation levels relative to coupled ones. However, the linear dynamical shear flow responses of nanocomposites, especially the percolation behaviors, are not sensitive to improved fiber dispersion, but are highly dependent on fiber loadings. All three forms of CNFs exhibit good reinforcement of PLA, and acetylated CNFs provide the best outcome. The relationships between properties of nanocomposites and hierarchical structures of CNFs are then established through the mechanical model.