A softwood thermomechanical pulp (TMP) was suspended in water and oxidized with sodium hypochlorite and catalytic amounts of sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) at pH 10. When the NaClO addition levels were 20–26 mmol g-1 of the TMP, the yields of water-insoluble TEMPO-oxidized TMPs fractions were approximately 40%. Sugar composition and other analyses revealed that most of the lignin and hemicellulose components in the TMP were removed as water-soluble fractions by the oxidation. Thus, almost pure TEMPO-oxidized celluloses can also be prepared from TMP, although the addition levels of NaClO are much higher than for the TEMPO-mediated oxidation of pure celluloses. The water-soluble fractions were analyzed by NMR, showing that polyuronic acids formed from glucomannan and cellulose by oxidation were the main compounds. The water-insoluble fractions of TEMPO-oxidized TMPs prepared with NaClO of 20–26 mmol g-1 had carboxylate contents of approximately 1.2 mmol g-1, and had the same cellulose I allomorph and the same crystal widths as in the original TMP. Transparent and highly viscous gels were obtained by disintegration of these TEMPO-oxidized TMPs in water, and the gels consisted of individual nanofibers 4–6 nm in width. Thus, TEMPO-oxidized cellulose nanofibers can also be prepared from TMP.
Holzforschung is an international scholarly journal that publishes cutting-edge research on the biology, chemistry, physics and technology of wood and wood components. High quality papers about biotechnology and tree genetics are also welcome. Rated year after year as one of the top scientific journals in the category of Pulp and Paper (ISI Journal Citation Index), Holzforschung represents innovative, high quality basic and applied research.