Dispersibility of freeze-drying unmodified and modified TEMPO-oxidized cellulose nanofibrils in organic solvents

Cellulose nanofibrils (TOCNF) with a width of 20 $\pm$ 6 nm and a length of 809 $\pm$ 98 nm were prepared using 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidation. Two modifying agents were used to functionalize the TOCNF surface in aqueous media: alkyl ketene dimer (AKD) and 3-aminopropyltriethoxysilane (APS). The hydrophilic aerogel L-TOCNF, hydrophobic aerogels L-TOCNF-AKD and L-TOCNF-APS with water contact angles of 0, 139 $\pm$ 2, and 133 $\pm$ 2$^\circ$, respectively, were prepared by freeze-drying of the aqueous dispersions. The elemental composition, morphology, sizes and crystal structure were determined by EDX analysis, scanning electron microscopy and X-ray diffraction, respectively. The process of redispersion of lyophilized samples in water and four organic solvents was investigated. The effect of TOCNF modification and solvent polarity on the redispersibility of lyophilized samples was revealed: the dispersibility of hydrophobic L-TOCNF-AKD and L-TOCNF-APS in organic solvents was significantly improved.