TEMPO-mediated oxidation of cellulose has received considerable attention, either as a pre-treatment in the production of nanocellulose, e.g. nanofibrillated cellulose (NFC), or for post-production surface modification of cellulose nanocrystals and nanofibers. The oxidation is specific for the C6 primary alcohols and is considered to be unable to penetrate into the crystalline interior of the nanocellulose materials, resulting in surface-confined carboxylic acid or carboxylate groups. The conventional method involves stoichiometric amounts of cooxidants, e.g. NaClO, NaBrO and NaClO2, which continuously generate TEMPO+, the oxoammonium ion form of TEMPO, that carries out the cellulose oxidation (Fig. 1). A more environmentally friendly approach is to completely remove the cooxidants and instead generate TEMPO+ electrochemically through electrogeneration (Fig. 1). In this work we used electrogeneration of TEMPO+ in order to oxidize highly crystalline Cladophora sp. nanocellulose. We demonstrate that complete surface oxidation can be achieved in approximately the same time as with a conventional TEMPO-mediated oxidation with cooxidants. The degree of surface oxidation could easily be controlled by varying the oxidation time, i.e. controlling the oxidation charge. The fiber width, specific surface area (&gt;115 m2/g), and the pore characteristics of the resulting dried water-insoluble fibrous particles was unaffected by oxidation. However, if the oxidation was carried out for longer times than required for completely oxidizing the surface, significant amounts of water-soluble products formed, indicating that the oxidation in fact may proceed beyond the surface.

Cooxidant-free TEMPO-mediated oxidation of highly crystalline Cladophora nanocellulose

249th National Meeting (2015)

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