Nanocellulose

Nanocellulose is a term referring to nano-structured cellulose. This may be either cellulose nanocrystal (CNC or NCC), cellulose nanofibers (CNF) also called microfibrillated cellulose (MFC), or bacterial nanocellulose, which refers to nano-structured cellulose produced by bacteria. Nanocellulose is a term referring to nano-structured cellulose. This may be either cellulose nanocrystal (CNC or NCC), cellulose nanofibers (CNF) also called microfibrillated cellulose (MFC), or bacterial nanocellulose, which refers to nano-structured cellulose produced by bacteria. CNF is a material composed of nanosized cellulose fibrils with a high aspect ratio (length to width ratio). Typical fibril widths are 5–20 nanometers with a wide range of lengths, typically several micrometers. It is pseudo-plastic and exhibits thixotropy, the property of certain gels or fluids that are thick (viscous) under normal conditions, but become less viscous when shaken or agitated. When the shearing forces are removed the gel regains much of its original state. The fibrils are isolated from any cellulose containing source including wood-based fibers (pulp fibers) through high-pressure, high temperature and high velocity impact homogenization, grinding or microfluidization (see manufacture below). Nanocellulose can also be obtained from native fibers by an acid hydrolysis, giving rise to highly crystalline and rigid nanoparticles which are shorter (100s to 1000 nanometers) than the nanofibrils obtained through homogenization, microfluiodization or grinding routes. The resulting material is known as cellulose nanocrystal (CNC). The terminology microfibrillated/nanocellulose or (MFC) was first used by Turbak, Snyder and Sandberg in the late 1970s at the ITT Rayonier labs in Whippany, New Jersey, USA to describe a product prepared as a gel type material by passing wood pulp through a Gaulin type milk homogenizer at high temperatures and high pressures followed by ejection impact against a hard surface. The terminology first appeared publicly in the early 1980s when a number of patents and publications were issued to ITT Rayonier on a new nanocellulose composition of matter. In later work Herrick at Rayonier also published work on making a dry powder form of the gel. Rayonier has been one of the world's premier producers of purified pulps interested in creating new uses and new markets for pulps and not to compete with new customers. Thus, as the patents issued, Rayonier gave free license to whoever wanted to pursue this new use for cellulose. Rayonier, as a company, never pursued scale-up. Rather, Turbak et al. pursued 1) finding new uses for the MFC/nanocellulose. These included using MFC as a thickener and binder in foods, cosmetics, paper formation, textiles, nonwovens, etc. and 2) evaluate swelling and other techniques for lowering the energy requirements for MFC/Nanocellulose production. After ITT closed the Rayonier Whippany Labs in 1983–84, Herric worked on making a dry powder form of MFC at the Rayonier labs in Shelton, Washington, USA In the mid 1990s the group of Taniguchi and co-workers and later Yano and co-workers pursued the effort in Japan. and a host of major companies, see numerous U.S. patents issued to P&G, J&J, 3M, McNeil, etc. using U.S. patent search under inventor name Turbak search base. Nanocellulose, which is also called cellulose nanofibers (CNF), microfibrillated cellulose (MFC) or cellulose nanocrystal (CNC), can be prepared from any cellulose source material, but woodpulp is normally used. The nanocellulose fibrils may be isolated from the wood-based fibers using mechanical methods which expose the pulp to high shear forces, ripping the larger wood-fibres apart into nanofibers. For this purpose, high-pressure homogenizers, ultrasonic homogenizers, grinders or microfluidizers can be used. The homogenizers are used to delaminate the cell walls of the fibers and liberate the nanosized fibrils. This process consumes very large amounts of energy and values over 30 MWh/tonne are not uncommon. To address this problem, sometimes enzymatic/mechanical pre-treatments and introduction of charged groups for example through carboxymethylation or TEMPO-mediated oxidation are used. These pre-treatments can decrease energy consumption below 1 MWh/tonne. Recently, a new method 'Nitro-oxidation' has been developed to prepare carboxycellulose nanofibers directly from raw plant biomass. Owing to fewer processing steps to extract nanocellulose, the Nitro-oxidation method has found to be a cost-effective, less-chemically oriented and efficient method to extract carboxycellulose nanofibers. Functionalized nanofibers obtained using nitro-oxidation has found excellent substrate to remove heavy metal ions impurities such as lead cadmium uranium