Abstract
The isolation of nanocellulose from different agricultural residues is becoming an important research field due to its versatile applications. This work collects different production processes, including conditioning steps, pretreatments, bleaching processes and finally purification for the production of nanocellulose in its main types of morphologies: cellulose nanofiber (CNF) and cellulose nanocrystal (CNC). This review highlights the importance of agricultural wastes in the production of nanocellulose in order to reduce environmental impact, use of fossil resources, guarantee sustainable economic growth and close the circle of resource use. Finally, the possible applications of the nanocellulose obtained as a new source of raw material in various industrial fields are discussed.
Highlights
The social and environmental impact associated with the exploitation of fossil resources has resulted in the search for more environmentally friendly alternatives in recent years [1]
Mishra et al [39] observed that the use of TEMPO agent in the treatment of oxidized cellulose pulp involved an increase in the degree of polymerization, nanocellulose yield and brightness stability due to post-oxidation
These problems can be reduced by using this pretreatment in combination with others, which will result in lower concentration alkaline solutions being required and processing times reduced [49]
Summary
The social and environmental impact associated with the exploitation of fossil resources has resulted in the search for more environmentally friendly alternatives in recent years [1]. Acid hydrolysis and mechanical treatments are the most widely employed methods for obtaining CNC and CNF, respectively; these procedures have some drawbacks related to economic and environmental aspects such as the energy demand of the process and the high amount of water required in the neutralization steps [11]. Another possibility for producing nanocellulose is the use of enzymatic hydrolysis, a promising environmentally friendly and sustainable route due to the advantages of enzymatic treatments, the cost of enzymes may be an inconvenient. The process would consist of a series of stages: (a) conditioning of the biomass (milling, sieving and drying); (b) attainment of cellulose through pretreatments, mainly by alkaline processes, that degrade the structure of the lignocellulosic residue in order to facilitate the release of its monomers; (c) purification and bleaching; and (d) attainment of nanocrystals or nanofibers, mainly by acid hydrolysis
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