PRODUCTION AND CHARACTERIZATION OF CELLULOSE NANOFIBRILS AND BIOPOLYMER COMPOSITES FOR PACKAGING APPLICATIONS

The cellulose reinforced biopolymer composites are emerging as a potential packaging material due to their biodegradability, biocompatibility, and superior material properties. Cellulose Nanofibrils (CNF), a nanostructured cellulose can be reinforced with biopolymers such as chitosan, polylactic acid (PLA) to produce composites for flexible packaging applications. To produce highly dispersible and consistent quality CNF, cellulose pulp was subjected to a combination of mechanical (ball milling) and chemical (Carboxyl methylcellulose, CMC dispersion & NaOH swelling) pretreatments. The pretreated cellulose was fibrillated using a high-pressure homogenizer to produce CNF with up to 6% solid content and uniform fibril width from 20 to 40 nm. The CNF was reinforced with chitosan and crosslinked using citric acid to improve mechanical and hydrophobicity of flexible packaging films. The water uptake and water vapor permeability (WVP) of composite films were reduced by up to 86 and 50% respectively. The optimal amount of CNF and citric acid was determined as 20% and 25% respectively. Cellulose microfibers (CMF) produced from cotton noil was reinforced with PLA biopolymer. The tensile, WVP and UV barrier properties were improved by better dispersion stability and interfacial adhesion of CMF in PLA. The tensile stress and Young’s modulus of 1% CMF reinforcement were 46 and 30% higher than the films without CMF reinforcement and the WVP of 20% CMF reinforcement was less than 29%. The UV light absorbance was improved between 41 and 90% for the CMF reinforcement of 1 to 20%. The environmental benefits of Chitosan-CNF composite films were investigated using a life cycle assessment method to use as a proof-of-concept for large scale production. It was found that about 79% of the environmental impacts were caused by the citric acid and heat energy used in the film manufacturing process. The carbon footprint of composite film manufacturing process was about 7 and 16% less than that of the fossil-based low-density polyethylene (LDPE) and PLA biopolymer films respectively. In overall, micro and nano fibrils of cellulose can be used as a reinforcing agent to improve the mechanical and barrier properties of biopolymer composites without compromising its carbon footprint for flexible packaging applications.

INDEX WORDS: Nano cellulose, Biopolymer composite, Crosslinking, Tensile properties, Barrier properties, Packaging films, Life cycle assessment