Cellulose which is a linear homopolymer of D-anhydro glucopyranose unit (AGU) polymerized via P-1, 4-linkage (Fig. 16.1), can be obtained from plant biomass, bacteria and marine animals called tunicates. During its biosynthesis, cellulose is formed as linear and highly crystalline fibrils at nanoscale with outstanding me­chanical properties via intra and intermolecular hydrogen bonding and organized into microscale elementary fibril-bundles separated and cemented by noncrystalline regions containing lignin, pectin, hemicelluloses. The highly crystalline nanofibrils which exhibit higher axial mechanical properties (strength and modulus), can be obtained by eliminating the other amorphous components or defibrillating them via acid hydrolysis, enzymatic hydrolysis, oxidation, mechanical treatment, ultrasonic treatment or combinations thereof.2728

Depending on the source of cellulose and the isolation protocol used and the sources, they can be obtained as shorter cellulose nanocrystals (CNC) or whiskers (with 5-20 x 500 nm), longer cellulose nanofibers (CNF) or nanofibrillated cellu­lose (NFC) (3-20 nm x few microns) and microfibrillated cellulose (20-100 nm x few microns). In addition, nano-scale cellulose can also be directly by microorgan­isms.27 Bacterial cellulose (BC) is an emerging and unique biopolymer character­ized by very long polymer chains with a degree of polymerization in the range of 4000-10,000, high crystallinity, and high purity with an extremely large amount of water containing. The individual nanofibrils of BC exhibit a high tensile strength of equivalent to that of steel or Kevlar.2931