Preparation of water-soluble cellulose derivatives using TEMPO radical-mediated oxidation at extended reaction time

摘要

Four types of cellulosic samples, including cotton linters, microcrystalline, never-dried sulfite pulp, and viscose, were tested as potential sources to prepare cellulose-based derivatives, able to be used in homogeneous systems. In this way, by employing water as a solvent, can surpass one of the major drawbacks of native cellulose, its recalcitrance towards common solvents. The chosen derivatization procedure implies the chemical oxidation using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical, sodium hypochlorite, and sodium bromide. Following this treatment, each cellulose sample was processed in such a way as to maximize the content of water-soluble fractions. Therefore, for each cellulose type (except viscose), we could isolate three oxidized samples All of these samples were thoroughly characterized using spectral analyses (FT-IR, H-1 NMR, C-13 NMR), content of negatively charged groups, and degree of polymerization. The morphology of the oxidized products has been evaluated by means of scanning electron microscopy (SEM), and crystallinity was assessed by using X-ray diffraction (XRD). The thermal analyses for the pure and oxidized cellulose samples were also performed. The limit of the solubility in water for the oxidized fractions was checked by using a low-voltage electron microscopy (LVEM).