Optical Properties of Cellulose Nanofibre Films at High Temperatures

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 packaging and electronics, the thermal stability and optical properties of nanocellulose materials are crucial characteristics. In this study, the effects of heat treatment (100 ºC, 150 ºC and 200 ºC) 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. Exposing TO-CNF films to high temperatures (> 150 ºC) 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. Graphical abstract

Optimization of spray-coated nanochitin/nanocellulose films as renewable oxygen barrier layers via thermal treatment

“…43 For instance, it has been found that the RIs for cellulose and chitin are ∼1.54 and ∼1.56, respectively. 44,45 At a higher temperature, the RI for cellulose increases while that for chitin decreases, 46,47 so the RI difference between CNC and ChNW likely decreases with an increasing temperature, which may cause an decrease in haze. A decrease in transmittance at shorter wavelengths was especially pronounced for S100T40.…”

Modification of Nanocellulose

“…Besides, the formation of hydrophilic groups caused by thermal degradation is also implied in the contact angle measurements, which showed a considerable decrease in films treated at 200 C (WCA of 35 ). A reduction in strength and strain was noticeable at higher temperatures (Niskanen et al 2022).…”