Pulp Fiber-Reinforced Polylactic Acid (PLA) Nanocomposites Prepared by In Situ Extrusion Fibrillation

Pulp fiber-reinforced polymer nanocomposites have received considerable R&D interest, with a notable challenge in achieving good nanofiber dispersion. One particularly successful approach is through the in situ fibrillation of the pulp fibers into nanofibers in the presence of polymers during extrusion compounding. The extrusion fibrillation of bleached/unbleached pulp fibers and old corrugated container was investigated with polylactic acid (PLA) for improving fiber dispersion. Extrusion fibrillation generated both fibrillated nanofibers and unfibrillated pulp fibers, which were well dispersed in the PLA matrix. PLA’s crystallinity increased as fiber loading increased, attributable to the nucleating effect of cellulose. Heat deflection temperature increased from 53 °C to 57 °C with fiber presence at high loading. Higher fiber loading also increased the viscosity of composite melts because of increased fiber−fiber and fiber−polymer interactions. The biocomposites formed were found to have improved tensile strength (∼75 MPa) and stiffness (∼5.5 GPa) by 15% and 53%, respectively, at a 30 wt. % fiber loading relative to the neat PLA polymer, without any loss in impact strength. The improvement in composites’ mechanical properties comes from well-dispersed nanofibers, increased interfacial interaction, and higher polymer matrix crystallinity. This research shows the potential of extrusion fibrillation for recycling old corrugated containers as a reinforcing material in PLA composites.