Chemically and mechanically isolated nanocellulose and their self-assembled structures

Cellulose nanocrystals (CNCs) and nanofibrils (CNFs) have been isolated from pure rice straw cellulose via sulfuric acid hydrolysis, mechanical blending and TEMPO-mediated oxidation to 16.9%, 12% and 19.7% yields, respectively. Sulfuric acid hydrolysis produced highly crystalline (up to 90.7% Crl) rod-like (3.96-6.74 nm wide, 116.6-166 nm long) CNCs with similarly negative surface charges (-67 to -57 mV) and sulfate contents but decreasing yields and dimensions with longer hydrolysis time. Mechanical defibrillated CNFs were 82.5% crystalline and bimodally distributed in sizes (2.7 nm wide and 100-200 nm long; 8.5 nm wide and micrometers long). TEMPO mediated oxidation liberated the most uniform, finest (1.7 nm) and micrometer long, but least crystalline (64.4% Crl) CNFs. These nanocellulose self-assembled into submicron (153-440 nm wide) fibers of highly crystalline (up to 90.9% CH) cellulose 113 structure upon rapid freezing (-196 degrees C) and freeze-drying. The self-assembling behaviors were analyzed based on nanocellulose dimensions, specific surfaces and surface chemistries. (C) 2013 Elsevier Ltd. All rights reserved.