N.M. Stark, R.C. Sabo, L.M. Matuana R.A. Lafia-Araga
U.S. Forest Service,
Keywords: cellulose nanofibrils (CNFs), esterification, polylactic acid (PLA), surface modification, tensile properties, barrier properties
Summary:Packaging films may be required to be transparent, flexible, have good tensile strength, and have good barrier properties. Conventional packaging films are produced from petroleum-derived polymers, however the demand for sustainable packaging is increasing. Because cellulose nanomaterials (CNs) are derived from sustainable, biobased materials they are ideally suited to meet the needs of sustainable packaging films, particularly when combined with biopolymers such as polylactic acid (PLA). Commercial polymer packaging films are produced by combining dry raw materials using techniques such as extrusion. However, the dispersion of dry hydrophilic CNs into hydrophobic polymers has been challenging. We have investigated processing nanocomposites using a technique referred to as wet-compounding, in which aqueous suspensions of CNs are directly compounded with PLA. In this study, we also attempted a water-based catalyzed esterification of the CNF was attempted using lactic acid. The unmodified and modified CNFs were both used to make cast films without a polymer matrix to evaluate the effectiveness of the modification. Compared with unmodified CNF films, the modified CNF has higher tensile modulus, lower tensile strength and elongation, and better barrier properties. We then produced nanocomposites using both injection molding and cast film extrusion. PLA composites containing modified CNFs appeared to exhibit better dispersion and improved transparency compared with PLA composites containing unmodified CNFs. Therefore, the combination of esterification of CNFs in aqueous medium and direct wet-compounding may provide packaging films that meet performance requirements for these applications and demand for sustainability.