Green Barrier Materials from Cellulose Nano Fibers

In this study we prepared high grammage, robust, and structurally dense CNF (Cellulose nano fibrils) films with and without wet strength crosslinker KymeneTM (PAE, a polyamide-epichlorohydrin resin). Both selfcrosslink of PAE network and hetero crosslink between cellulose and PAE were formed at elevated temperature. Besides expected wet strength improvement, we also discovered unique stress-strain behavior for dry crosslinked films, which has never been before. This stress-strain behavior indicates varying stress bearing mechanisms at different levels of crosslinker addition due to formation of new bonds by crosslinking. Crosslinking increased dry strength by approximately 2.5 fold compared to pure CNF films. Wet strength enhancement was also quite significant; wet strength of crosslinked films was observed to be very close to pure dry CNF films, approximately 35MPa. Additionally, the crosslinked films showed a transition of both surface and bulk properties from hydrophobic to hydrophilic. Water contact angle increased from 50° to 110°, while the water retention value for the crosslinked films decreased by approximately 25%. Moreover, water vapor permeability also decreased by two fold. As previously shown, some of the increase in hydrophobic nature can be attributed to induced hornification during the 3 hour heating period for crosslinking at 120°C. Possible mechanisms for the changes in behavior are discussed in detail.