Nanocellulose preperation by TEMPO / NaCIO / NaBr oxidation method

Cellulose nanofibrils (NFC) are obtained mainly from wood biomass and typically by mechanical disintegration of bleached wood pulp in aqueous medium. However, the use of these methods alone requires high cost and energy consumption as well as low efficiency. These problems have been solved for various chemical and biological pretreatment. Recently, it was reported that 2,2,6,6- tetramethylpiperidine-1-oxyl (TEMPO) -mediated oxidation of cellulose fibers, allowed for controlable and high efficiency process accompanied by low energy mechanical disintegration of the oxidized fibers in aqueous suspensions. In this study, TEMPO-mediated oxidized cellulose (TOC) were produced by oxidation of bleached wood pulp with basic TEMPO / NaBr / NaClO system was carried out under different amounts of NaClO primary oxidant. Being an important success criterion, contributing to energy consumption and calculated by titration conductivity measurements the value of 1.68 mmol/g for –COONa sodium carboxylate groups per D-glucose unite was obtained. Subsequently, diluted TOC samples were subjected to ultrasonication and high pressure homogenization to obtain TEMPO-mediated oxidized cellulose nanofibril (TOCN) suspension. By applying centrifugation to separate non/partially fibrillated portions, the TOCN solution (supernatant) also known as NFC, was produced. It was confirmed by XRD measurements that the crystal structure and the interplanar distance (d200) of the original cellulose was maintained during the nanofibrillation process (4.39 nm, 4.26 nm and 3.53 nm in MFC, TOC and TOCN cellulose samples respectively). The mean hydrodynamic sizes, distribution percentages and homogeneity of TOCNs in solution were observed by DLS measurements. The trimodal size distribution of the TOC sample was changed to bimodal size distribution with smaller averages of 100 nm and 700 nm. The wet films of the TOCN solutions was obtained by vacuum filtration, subsequenly dried by two drying techniques.