Nanocellulose, a tiny fiber with huge applications Tiffany Abitbol 1,3 , Amit Rivkin 1,3 , Yifeng Cao 1,3 , Yuval Nevo 1 , Eldho Abraham 1 , Tal Ben-Shalom 1 , Shaul Lapidot 2 and Oded Shoseyov 1 Nanocellulose is of increasing interest for a range of applications relevant to the fields of material science and biomedical engineering due to its renewable nature, anisotropic shape, excellent mechanical properties, good biocompatibility, tailorable surface chemistry, and interesting optical properties. We discuss the main areas of nanocellulose research: photonics, films and foams, surface modifications, nanocomposites, and medical devices. These tiny nanocellulose fibers have huge potential in many applications, from flexible optoelectronics to scaffolds for tissue regeneration. We hope to impart the readers with some of the excitement that currently surrounds nanocellulose research, which arises from the green nature of the particles, their fascinating physical and chemical properties, and the diversity of applications that can be impacted by this material. Addresses 1 Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel 2 Melodea Ltd, Rehovot 76100, Israel Corresponding author: Shoseyov, Oded ([email protected]) 3 These authors contributed equally to this work. Current Opinion in Biotechnology 2016, 39:76–88 This review comes from a themed issue on Nanobiotechnology Edited by Michael Nash and Oded Shoseyov http://dx.doi.org/10.1016/j.copbio.2016.01.002 0958-1669/# 2016 Elsevier Ltd. All rights reserved. Introduction Increased demand for high-performance materials with tailored mechanical and physical properties, makes nanocellulose the most attractive renewable material for advanced applications. Cellulose is the product of biosynthesis from plants, animals, or bacteria, while the general term ‘nanocellulose’ refers to cellulosic extracts or processed materials, having defined nano-scale structural dimensions. Nanocellulose can be divided to three types of materials: (I) cellulose nanocrystals (CNCs), also re- ferred to as nanocrystalline cellulose (NCC) and cellulose nanowhiskers (CNWs), (II) cellulose nanofibrils (CNFs), also referred to as nano-fibrillated cellulose (NFC), and (III) bacterial cellulose (BC). Different approaches are used to extract nanoparticles from cellulose sources, resulting in particles with varied crystallinities, surface chemistries, and mechanical properties [1]. See Figure 1 for electron microscope images of the three types of nanocellulose. Currently, CNCs are mainly produced by acid hydrolysis/ heat controlled techniques, with sulfuric acid being the most utilized acid. Extraction of the crystals from cellulose fibers involves selective hydrolysis of amor- phous cellulose regions, resulting in highly crystalline particles with source-dependent dimensions, for exam- ple, 5–20 nm 100–500 nm for plant source CNCs. Sul- furic acid hydrolysis grafts negatively charged sulfate half-ester groups onto the surface of the particles, which act to prevent aggregation in aqueous suspensions due to electrostatic repulsion between particles. Furthermore, the rod-like shape of CNCs leads to concentration- dependent liquid crystalline self-assembly behavior. CNFs are micrometer-long entangled fibrils that contain both amorphous and crystalline cellulose domains, unlike CNCs which have near-perfect crystallinity (ca. 90%). Entanglement of the long particles gives highly viscous aqueous suspensions at relatively low concentrations (be- low 1 wt%). The extraction of CNFs from cellulosic fibers can be achieved by three types of processes: (I) mechani- cal treatments (e.g. homogenization, grinding, and mill- ing), (II) chemical treatments (e.g. TEMPO oxidation), and (III) combination of chemical and mechanical treat- ments [2]. BC is produced extracellularly by microorganisms, with Gluconacetobacter xylinum being the most efficient amongst cellulose-producing microorganisms. Different from plant-source nanocellulose, which may require pre- treatment to remove lignin and hemicellulosics before hydrolysis, BC is synthesized as pure cellulose. BC nano- fibers, characterized by average diameters of 20–100 nm and micrometer lengths, entangle to form stable network structures (see Figure 1). The different types of nanocellulose exhibit distinct properties which dictate their applicability and function- ality, that is, certain types of nanocellulose are better suited for specific applications than others. The unique properties of nanocellulose include high Young’s modu- lus/tensile strength (e.g. 150 GPa/10 GPa for CNCs), a range of aspect ratios that can be accessed depending on Available online at www.sciencedirect.com ScienceDirect Current Opinion in Biotechnology 2016, 39:76–88 www.sciencedirect.com
Nanocellulose, a tiny fiber with huge applications
Jun 17, 2023
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