3D printed poly(lactic acid) composites with grafted cellulose nanofibers: Effect of nanofiber and post-fabrication annealing treatment on composite flexural properties

Poly(lactic acid) (PLA) and PLA grafted cellulose nanofibers (PLA-g-CNFs) mixture were extruded into filaments, and subsequently 3D printed into composites. As-3D printed composites were then thermally annealed at a temperature above PLA glass transition temperature (T-g). Dynamic mechanical analysis, including temperature ramp, frequency sweep, and creep for annealed composites, confirmed the enhanced responses to various viscoelastic factors. Such enhancements were ascribed to the presence of PLA crystalline regions containing both alpha and alpha' phases, which were induced and developed through the annealing treatment. After 3-point bending test at 70 degrees C, unannealed composites were partially damaged, while annealed composites preserved the originally well-integrated layer structures. Experimental creep and recovery data essentially fitted to the Burger's model and Weibull's distribution function, respectively. The calculated parameters (e.g., moduli) from numerical fitting curves demonstrated the synergetic effect of PLA-g-CNFs and annealing treatment on the enahncement of flexural properties for 3D printed PLA composites.