Alkaline Cellulose Nanofibrils from Streamlined Alkali Treated Rice Straw

Alkali treatment (4% NaOH, 70 °C, 5 min, twice) of dewaxed rice straw was effective in removing most hemicelluloses, lignin and silica to yield 47.6% cellulose-rich solid. Optimal TEMPO oxidation (7.5 mmol NaClO per gram of alkaline cellulose) followed by mechanical defibrillation (30 min) produced 36.5% alkaline cellulose nanofibrils (ACNFs), higher than the 29.1% CNFs from sodium chlorite oxidation-alkali leaching as well as the 33.7% HCNFs from sodium chlorite oxidation. At the same 5 mmol NaClO level, ACNFs were similar in lateral dimensions (1.25 ± 0.47 nm) and crystallinity (68%), but less surface oxidized (65%) than CNFs and HCNFs (1.55 ± 0.54 and 1.36 ± 0.62 nm, 69% and 68% CrI, 85% and 69% surface oxidization, respectively). While the residual noncellulosics consumed oxidizing agents, their presence led to longer ACNFs and HCNFs, higher thermal stability, and thinner self-assembling fibers (197 and 94 nm, respectively) than CNFs (497 nm). Therefore, this facile alkali pretreatment is not only highly efficient in preparing ACNFs with attributes similar to CNFs and HCNFs, but like HCNFs due to their less pristine nature, also present some unique properties that are promising for advanced applications.