Nanocellulose: From Fundamentals to Advanced Applications

Abstract

Over the past few years, nanocellulose (NC), cellulose in the form of nanostructures, has been proved to be one of the most prominent green materials of modern times. NC materials have gained growing interests owing to their attractive and excellent characteristics such as abundance, high aspect ratio, better mechanical properties, renewability, and biocompatibility. The abundant hydroxyl functional groups allow a wide range of functionalizations via chemical reactions, leading to developing various materials with tunable features. In this review, recent advances in the preparation, modification, and emerging application of nanocellulose, especially cellulose nanocrystals (CNCs), are described and discussed based on the analysis of the latest investigations (particularly for the reports of the past 3 years). We start with a concise background of cellulose, its structural organization as well as the nomenclature of cellulose nanomaterials for beginners in this field. Then, different experimental procedures for the production of nanocelluloses, their properties, and functionalization approaches were elaborated. Furthermore, a number of recent and emerging uses of nanocellulose in nanocomposites, Pickering emulsifiers, wood adhesives, wastewater treatment, as well as in new evolving biomedical applications are presented. Finally, the challenges and opportunities of NC-based emerging materials are discussed.

Keywords: application; cellulose nanocrystals; functionalization; nanocellulose; production.

Figure 1

Cellulose contained in plants or trees has a hierarchical structure from the meter to the nanometer scale, as shown in (A). A schematic diagram of the reaction between cellulose and strong acid to obtain Nanocellulose is shown in (B). Bionanocellulose cultured from cellulose-synthesizing bacteria is shown in (C). Reprinted with permission from Miyashiro et al. (2020) as distributed by creative common license CC BY license, MDPI publisher.

Figure 2

An example of the procedure used to prepare CNC form hardwood. Reprinted with permission from Lin K. H. et al. (2019) as distributed by creative common license CC BY license, MDPI publisher.

Figure 3

SEM micrographs of (a) the raw material (corn stalk) and (b) the extracted cellulose; (c,d) transmission electron microscopy (TEM) micrographs of the cellulose nanocrystals (CNCs). Reprinted from Huang et al. (2017) as distributed by creative common license CC BY license, MDPI publisher.

Figure 4

Transmission electron microscopy (TEM) micrographs of CNC isolated from: filter paper enzyme-treated for (A) 0 h, (B) 2 h, and (C) 10 h and wood pulp enzyme-treated for (D) 0 h, (E) 2 h, and (F) 10 h. Reprinted from Beyene et al. (2018) as distributed by creative common license CC BY license, MDPI publisher.

Figure 5

Schematic representation of the most commonly used surface modification routes of nanocellulose.

Figure 6

Scheme of fullerene C₆₀ (A) and of the preparation and structure of nanocellulose/fullerene composites (B). Reprinted from Bacakova et al. (2020) as distributed by creative common license CC BY license, MDPI publisher.