Nanocellulose is drawing extensive concern and attention from the academic and industrial circles due to its unique structure and exceptional properties, and it is the research hotspot in the field of new material and cellulose science. Nanocellulose isolated from lignocellulosic biomass can be divided into two main categories: cellulose nanocrystal (CNC) and cellulose nanofibril (CNF). The preparation methods of CNC and CNF are detailedly summarized in this review, with the focus on some new methods developed in recent years, such as the integrated preparation of CNC and CNF via recoverable organic acid hydrolysis, tuneable preparation of lignin-coated CNC and CNF via AVAP method, high efficiency preparation of CNC and CNF via deep eutectic solvents pretreatment combined with mechanical shearing, as well as the controllable isolation of hydrophilic or hydrophobic CNF by mechanical disintegration in polar microenvironment. Meanwhile, the advantages and shortcomings of the preparation methods are discussed, and the industrialization status of nanocellulose production is introduced as well. Finally, it’s believed that the development of green, effective and sustainable preparation methods will be the main trend for manufacturing nanocellulose.
Contents
1 Introduction
2 Preparation of CNC
2.1 Oxidative degradation
2.2 Ionic liquid treatment
2.3 Solid acid hydrolysis
2.4 Organic acid hydrolysis
2.5 Subcritical water hydrolysis
2.6 AVAP method
3 Preparation of CNF
3.1 Mechanical methods
3.2 Pretreatment methods
4 Industrialization status of nanocellulose
5 Conclusion