In the first story, softwood bleached kraft pulp (SBKP) and microcrystalline cellulose (MCC) were oxidized using a TEMPO-mediated system in water at pH 10 under various conditions. The TEMPO-oxidized SBKP prepared with 10 mmol/g NaClO had a higher mass recovery ratio and higher carboxylate content than the other TEMPO-oxidized celluloses including TEMPO-oxidized MCCs. The TEMPO-oxidized SBKP was then sonicated in water for 10–120 min to prepare aqueous dispersions of needle-like TEMPO-oxidized cellulose nanocrystals (TEMPO-CNCs) with homogenous width of 3.5–3.6 nm and average lengths of ~200 nm. The average chain lengths of the cellulose molecules that make up the TEMPO-CNCs were less than half the average lengths of the TEMPO-CNCs. Compared with conventional CNCs prepared from SBKP by acid hydrolysis, the TEMPO-CNCs prepared by the acid-free and dialysis-free process exhibited higher mass recovery ratios, significantly higher amounts of surface anionic groups, and smaller and more homogeneous widths. These characteristics of TEMPO-CNCs prepared from TEMPO-oxidized SBKP may be advantageous for obtaining increased solid contents in aqueous dispersions and for mass production processes at the industrial level as well as applications such as fillers in polymer composites.<br/><br/>In the second story, layer-by-layer peeling of surface molecules of native cellulose microfibrils was performed using a repeated sequential process of TEMPO-mediated oxidation followed by hot alkali extraction. Both highly crystalline algal and tunicate celluloses and low-crystalline cotton and wood celluloses were investigated. Initially, the C6-hydroxy groups of the outermost surface molecules of each algal cellulose microfibril facing the exterior had the gauche-gauche (gg) conformation, whereas those facing the interior had the gauche-trans (gt) conformation. All the other C6-hydroxy groups of the cellulose molecules inside the microfibrils contributing to crystalline cellulose I had the trans-gauche (tg) conformation. After surface peeling, the originally 2nd-layer molecules from the microfibril surface became the outermost surface molecules, and the original tg conformation changed to gg and gt conformations. The plant cellulose microfibrils likely had disordered structures for both the outermost surface and 2nd-layer molecules, as demonstrated using the same layer-by-layer peeling technique.

Advanced TEMPO-mediated oxidation of cellulose: Preparation of TEMPO-CNCs and layer-by-layer peeling of surface cellulose molecules on cellulose microfibrils

256th National Meeting (2018)

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