Thermally enhanced high performance cellulose nano fibril barrier membranes

Reported here is a method of thermal treatment to enhance the barrier properties of membranes made from Cellulose Nano Fibrils (CNFs). CNF membranes of 75 +/- 5 mu m thickness were prepared by evaporation of water from a suspension of CNFs. This was followed by thermal treatment at different temperatures (100 degrees C, 125 degrees C, 150 degrees C, and 175 degrees C) for 3 hours and subsequent conditioning at 23 degrees C and 50% relative humidity for 24 hours. Increasing thermal treatment temperature correlated with enhanced barrier properties; the oxygen and water vapor permeability decreased by 25 fold and 2 fold respectively after treatment at 175 degrees C. The reduction in permeability was attributed to an increase in crystallinity, reduction of the inter fibril space or porosity, and increase in hydrophobicity. These effects were also demonstrated to be analogous to hornification of cellulose fibers.