(234b) High Performance Green Barrier Films From Thermal Treatment of Cellulose Nanofibrils

Hornification due to thermal exposure has been shown to be detrimental to the properties of cellulose fibers and the formation of paper. This is due to closure of pores, reduction in hydrophilic nature of fibers due to irreversible hydrogen bonding of the –OH groups of the fibers and increased crystallinity. However, these effects of thermal exposure could be very beneficial in the enhancement of barrier properties of membranes made from Nanocellulosic fibers (NCF) fibers for oxygen and water vapor. In this study we demonstrate that controlled thermal exposure (heat treatment/annealing) after forming membranes from NCF fibers can indeed enhance the barrier properties of these membranes.  We demonstrated 3 hours of thermal exposure (at 175°C) to films of about 75μm thickness results in the improvement in oxygen barrier by almost 25 fold while water vapor permeability could be reduced to half, while being accompanied by all the consistent hornification changes.  The films were found to be decreasing in porosity with increasing heat treatment temperature. The oxygen and water vapor permeability reduced from 0.17 to 0.007 (ml.μm/m2.day.kPa) and 3.12 to 1.544 (kmmol.μm/m2.day.kPa) respectively. Thermal exposure to the films was also accompanied by expected hornification effects, closure of porous structure, increase in size of crystallites by more than 45% (0.067 – 0.099nm) increase in hydrophobicity increase in contact angle from 64° - 96° and decrease in water retention value by more than 55%. This study shows that the barrier and mechanical properties of films made from NCFs can be fine-tuned by controlled thermal exposure.