Cellulose nanocrystals, a class of fascinating bio-based nanoscale materials, have received a tremendous amount of interest both in industry and academia owing to its unique structural features and impressive physicochemical properties such as biocompatibility, biodegradability, renewability, low density, adaptable surface chemistry, optical transparency, and improved mechanical properties. This nanomaterial is a promising candidate for applications in fields such as biomedical, pharmaceuticals, electronics, barrier films, nanocomposites, membranes, supercapacitors, etc. New resources, new extraction procedures, and new treatments are currently under development to satisfy the increasing demand of manufacturing new types of cellulose nanocrystals-based materials on an industrial scale. Therefore, this review addresses the recent progress in the production methodologies of cellulose nanocrystals, covering principal cellulose resources and the main processes used for its isolation. A critical and analytical examination of the shortcomings of various approaches employed so far is made. Additionally, structural organization of cellulose and nomenclature of cellulose nanomaterials have also been discussed for beginners in this field.

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Recent progress in cellulose nanocrystals: sources and production

A simple approach was developed to isolate cellulose nanocrystals (CNCs) with carboxylic groups from microcrystalline cellulose (MCC). The effect of reaction time on the morphology, microstructure, and thermal stability of isolated CNCs was investigated. The rod-like CNCs with size of 200–250 nm in length and about 15–20 nm in width were obtained by one-step citric/hydrochloric acid (C6H8O7/HCl) hydrolysis of MCC. The CNCs extracted at 4 h showed the highest carboxylic group content which led to a high absolute zeta potential value up to 46.63 mV. Moreover, these CNCs may be used as cationic dye adsorbent (methylene blue) and efficient flocculants with excellent coagulation–flocculation capability to kaolin suspension with a turbidity removal of 99.5%.

New Approach for Single-Step Extraction of Carboxylated Cellulose Nanocrystals for Their Use As Adsorbents and Flocculants

The recent strategies in preparation of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) were described. CNCs and CNFs are two types of nanocelluloses (NCs), and they possess various superior properties, such as large specific surface area, high tensile strength and stiffness, low density, and low thermal expansion coefficient. Due to various applications in biomedical engineering, food, sensor, packaging, and so on, there are many studies conducted on CNCs and CNFs. In this review, various methods of preparation of CNCs and CNFs are summarized, including mechanical, chemical, and biological methods. The methods of pretreatment of cellulose are described in view of the benefits to fibrillation.

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Recent Strategies in Preparation of Cellulose Nanocrystals and Cellulose Nanofibrils Derived from Raw Cellulose Materials

Extraction and comparison of carboxylated cellulose nanocrystals from bleached sugarcane bagasse pulp using two different oxidation methods.

Functionalized Cellulose for Water Purification, Antimicrobial Applications, and Sensors

An efficient and low-cost approach to prepare spherical cellulose nanocrystals (SCNCs) is presented through chemical hydrolysis of lyocell fibers in an ammonium persulfate (APS) solution. The as-prepared cellulose nanoparticles were characterized by scanning electron microscopy, atomic force microscopy, laser light scattering particle analysis, wide angle X-ray diffraction, Fourier transform infrared spectrometry and thermal gravimetric analysis. Effects of hydrolysis conditions, such as reaction time and temperature, and APS concentration on the morphology, microstructure, and thermal stability of cellulose nanoparticles are discussed. Moreover, it is found that under mild reaction conditions, cellulose nanoparticles are spherical particles with a narrow diameter distribution, and have a cellulose II polymorphic crystalline structure with surface carboxyl groups. The optimal hydrolysis time was found to be around 16 h for hydrolysis at 80 °C with a 1 M APS aqueous solution.

Efficient extraction of carboxylated spherical cellulose nanocrystals with narrow distribution through hydrolysis of lyocell fibers by using ammonium persulfate as an oxidant

Superparamagnetic iron oxide coated on the surface of cellulose nanospheres for the rapid removal of textile dye under mild condition

Keywords: Electrospinning; Cellulose acetate; Nanofibrous mat; Tissue scaffold; MG-63 cell Abstract. The cellulose acetate (CA) nanofibrous mat was fabricated by electrospinni ng under optimized spinning conditions in this work. The morphology, chemical structure, thermal stability and hydrophilic property of as-prepared CA nanofibrous mat were characterized by scanning electron microscopy, Fourier transform infrared spectrometry, thermal gravimetric analysis and water contact angel measurement. Moreover, its cytocompatibility was evaluated through the cultivation of the MG-63 cells. The result shows the CA nanofibrous mat exhibits excellent biocompatibility and possesses a great potential in biomedical application as the tissue scaffold.

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Yunfeng Qin

Papers

Efficient extraction of carboxylated spherical cellulose nanocrystals with narrow distribution through hydrolysis of lyocell fibers by using ammonium persulfate as an oxidant

Superparamagnetic iron oxide coated on the surface of cellulose nanospheres for the rapid removal of textile dye under mild condition

Electrospun Cellulose Acetate Nanofibrous Mat as the Tissue Scaffold

Conductive Polyaniline/Cellulose Nanocrystals Composite for Ammonia Gas Detection