Top-Down Production of Nanocellulose from Environmentally Friendly Processes

Abstract

The production of nanometric size particles from lignocellulosic pulp or waste and other cellulose biomass involves top-down techniques. The first stage is the fractionation of biomass, which is the first opportunity to apply more environmentally friendly methods. Subcritical water or supercritical CO2 are simple methods to extract hemicelluloses and extractives. A recently developed process involves lignin removal by chemical treatment with gamma-valerolactone to obtain a highly purified cellulosic fraction, avoiding subsequent bleaching stages and facilitating the nanofibrillation process. The most studied green methods for nanocellulose production are the enzymatic pretreatment of cellulosic fibers and alternative oxidant methods. Deep eutectic solvents are more efficient than traditional ones or one-pot oxidative hydrolysis to obtain nanocrystalline sizes that minimize wastewater generation. This chapter covers the most environmentally friendly processes and reagents that have been reported for nanocellulose production, including the fractionation of the raw material. Reported properties of nanocellulose produced by green solvents pretreatments are similar to those obtained by traditional chemical reagents such as TEMPO-oxidation. Then, the future of nanocellulose production from environmentally friendly processes is promising.