Highly transparent 100% cellulose nanofibril films with extremely high oxygen barriers in high relative humidity

Highly transparent films with excellent gas barriers are very attractive materials for electronic devices. However, gas barrier properties of conventional cellulose nanofibril films tend to degrade under humid conditions. It is a great challenge to obtain nanocellulose films that simultaneously have very low gas permeability, high transparency, and high moisture and water resistance. In this study, free-standing, highly transparent films with excellent oxygen barrier properties were prepared from cellulose nanofibrils (CNF), followed by post-thermal treatment. Also, reducing agent was introduced to reduce discoloration during heating. CNF films showed high transparency (85-90% at 600 nm). SEM images indicated the loss of porous structure after thermal treatment, resulting in higher gas barriers and lower water retention values. Film showed extremely low oxygen permeability value of 0.007 ml mu m kPa(-1) m(-2) day(-1) at 23 A degrees C and 50% relative humidity (RH) after treatment at 145 A degrees C. Even at 80% RH, the oxygen permeability is only 0.584 ml mu m kPa(-1) m(-2) day(-1), which is 100 times lower than most plastic films such as poly(ethylene terephthalate) and poly(vinyl chloride).