Diffusion of Thyme, Cinnamon and Oregano essential oils in different nanocellulose matrices

Solubility and diffusivity of Thyme, Cinnamon and Oregano essential oils in nanocellulose films, with different carboxymethylation degree, were investigated in view of potential use in active packaging applications. Solubility of liquid essential oils resulted to increase with the carboxymethylation degree for both Oregano and Thyme, while it was non-monotonous for Cinnamon. Thyme showed the higher solubility (about 20%wt) fol-lowed by Cinnamon and Oregano. The sorption kinetics of liquid essential oils was substantially Fickian. The diffusivity also increased with the increase of the carboxymethylation degree, going from 9.6 x 10-9 cm2 forward slash s, observed for oregano in pure nano -cellulose, to 2.0 x 10-8 cm2 forward slash s, measured for Cinnamon in the most charged one. The release in vapor phase showed two different kinetics: a faster one dominating at short times and a slower one visible at long times. Fickian diffusion described the behaviour of most of the samples even if in some case data were better fitted by using exponential functions. In general, Diffusivities values ranged from 10-9 to 10-11 cm2 forward slash s for the fast process and from 10-11 to 10-13 cm2 forward slash s, for the slow one. Carboxymethylation degree also affected the release kinetics of antimicrobial essential oils, which therefore can be tuned by appropriate choice of the nanocellulose material.