A green and facile method was designed to isolate a type of cellulose nanocrystal (CNC) with carboxylated surfaces from native cellulose materials. Because isolation and modification processes of cellulosic particles are generally performed separately using harmful chemicals and multiple steps, the one-pot approach employed in this work is interesting from both an economical and ecological point of view. The reaction is carried out by adding hydrogen peroxide as an oxidant and copper(II) sulfate as a catalyst in acidic medium under mild thermal conditions. The charge content of the carboxylated CNC is about 1.0 mmol g-1, measured by a conductometric titration. Fourier transform infrared spectroscopy also proved the presence of carboxyl groups on the CNC particles. Atomic force microscopy along with optical polarized microscopy readily showed a rod shape morphology for the cellulosic particles. An average length of 263 nm and width of 23 nm were estimated by transmission electron microscopy. Dynamic laser scattering on carboxylated CNC suspensions by adding salt confirmed that nanoparticles are electrostatically stable. Carboxylated CNCs were furthermore characterized by solid carbon-13 nuclear magnetic resonance and X-ray spectroscopy.
Keywords: catalyst; cellulose nanocrystal; hydrogen peroxide; oxidation reactions.