(376a) Exploiting Synergies of Anionic and Cationic Biomaterials for Oxygen and Water Vapor Barrier Properties

There is strong interest in the introduction of renewable sources of packaging into global society. In particular, flexible barrier packaging and coatings are of interest due to their prevalence in the supply chain, e.g., at least 40% of all packaging is nonrenewable/nonrecycled flexible plastic. Forest-derived cellulose nanocrystals (CNCs) are a promising renewable source, and have been shown to be coatable as films with high oxygen barrier properties. Generally, CNCs are derived by acid hydrolysis processing that leaves pendant sulfate groups, imparting negative charge in aqueous media. Recent work in our group has shown that combining anionic CNCs with renewably sourced cationic nanofibers is a promising approach to developing manufacturable barrier films. Notably, chitin nanofibers (ChNFs) and nanowhiskers (ChNWs), which can be derived from renewable sources including crustacean food waste and fungi, are cationic and form complexes with CNCs that lead to dense barrier films. This talk describes recent innovations in optimizing the synergy between ChNWs and CNCs through careful tuning of the ChNW density and length. We find that optimal deacetylation of the ChNWs leads to formation of layered ChNW/CNC structures with oxygen permeability lower than poly(ethylene terephthalate) (PET). We also explore the use of thermal treatment and spray temperature to further improve the film structures. Finally, we will discuss an application of the bilayer films to PET film, to form PET/ChNW/CNC layered structures that have combined low oxygen permeability and low water vapor transport rate.