Figure 1.

Nanocelluloses and examples of their production methods. Plants and microorganisms are two main sources of cellulose. Cellulose fibrils (often chemically pre-treated, e.g., with TEMPO) are disintegrated into nanoscale fibrils, named cellulose nanofibrils (CNF) through rigorous mechanical processing (such as microfluidization and high-pressure homogenization) [13]. When cellulose fibrils are treated with a strong acid, such as sulfuric acid, the amorphous regions of fibrils are hydrolyzed, yielding needle-shaped crystals known as cellulose nanocrystals (CNC) [17]. Moreover, instead of removing amorphous regions, when they are solubilized through oxidation, cellulose fibrils fall apart into CNCs sandwiched between two protruding layers of functionalized cellulose chains. This class of newly emerged nanocelluloses is called hairy CNCs [8,9,18]. Some microorganisms, such as bacteria Acetobacter xylinum, also produce cellulose with a high purity, which may further be processed with a strong acid to yield bacterial CNCs (BCNC) [14,16]. Note that other sources of nanocelluloses are tunicates and algae [19].