Surface and Structure Characteristics, Self-Assembling, and Solvent Compatibility of Holocellulose Nanofibrils

Rice straw holocellulose was TEMPO-oxidized and mechanically defibrillated to produce holocellulose nanofibrils (HCNFs) at 33.7% yield (based on original rice straw mass), 4.6% higher yield than cellulose nanofibril (CNF) generated by the same process from pure rice straw cellulose. HCNFs were similar in lateral dimensions (2.92 nm wide, 1.36 nm thick) as CNF, but longer, less surface oxidized (69 vs 85%), and negatively charged (0.80 vs 1.23 mmol/g). HCNFs also showed higher affinity to hydrophobic surfaces than CNFs while still attracted to hydrophilic surfaces. By omitting hemicellulose/silica dissolution step, the two-step 2:1 toluene/ethanol extraction and acidified NaClO2 (1.4%, pH 3-4, 70 degrees C, 6 h) delignification process for holocellulose was more streamlined than that of pure cellulose, while the resulting amphiphilic HCNFs were more hydrophobic and self-assembled into much finer nanofibers, presenting unique characteristics for new potential applications.