Alteration of the Optical and Mechanical Characteristics of Cellulose Nanofibre Films Under Thermal Treatment

Abstract Nanocelluloses and their different designs, such as films and nanopapers, have gained considerable interest in many application areas due to their unique properties. For many purposes, such as for packaging and electronics, the thermal stability of nanocellulose materials is a crucial characteristic. In this study, the effects of heat treatment (100ºC, 150ºC and 200ºC) on the optical and mechanical properties of 2,2,6,6-tetramethylpiperidinyl-1-oxy radical-oxidised cellulose nanofibre (TO-CNF) films were investigated, especially the alteration of the colour, complex refractive index and birefringence of the films. Exposing TO-CNF films to high temperatures (> 150ºC) induced permanent transformations in the CNF structure, leading to an increase in the refractive index, decreases in the birefringence and crystallinity index, colour darkening and significant deterioration of the mechanical properties.