Disruptive enzyme-based strategies to isolate nanocelluloses: a review

The use of cellulases has been explored for several decades to depolymerize cellulosic materials to their monosaccharide units and use them to produce fuels, chemicals and biomaterials, among others. The use of cellulases to obtain nanocellulose (NC) actively began during the last decade due to the increasing interest in the development of industrial-scale processes based on a more environmentally friendly approach. Since then, a myriad of studies reported green strategies using cellulases for isolating cellulose nanofibrils and cellulose nanocrystals from a wide variety of cellulosic materials. Most of these studies use reaction conditions similar to those employed for the complete depolymerization of cellulose, resulting in low yields and particles that are heterogeneous in size and crystallinity. To overcome this, the classical synergism between cellulases must be revisited in order to enhance NC yields and properties. Some recent works have demonstrated that unusual reaction conditions employing enzymes from different organisms and modified enzyme systems, assisted or not by mild biomass pretreatment techniques, were able to modify the classical enzyme mode of action and these may be potentially explored to improve NC isolation. In this work, the use of enzymes (mostly cellulases) for optimal NC isolation is reviewed. Also, unconventional strategies used to boost hydrolysis efficiency are discussed in the light of their potential to improve yields and properties of the resulting nanocellulosic materials.