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% CrI) 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% CrI) CNFs. These nanocellulose self-assembled into submicron (153–440 nm wide) fibers of highly crystalline (up to 90.9% CrI) cellulose Iβ structure upon rapid freezing (−196 °C) and freeze-drying. The self-assembling behaviors were analyzed based on nanocellulose dimensions, specific surfaces and surface chemistries.