Application Of Cellulose Nanocrystals Research Articles

Application of cellulose nanocrystals in 3D printed alkali-activated cementitious composites

With the rapid development of concrete 3D printing for construction projects, it is crucial to produce sustainable 3D-printed cementitious composites that meet the required fresh and hardened properties. This study develops sustainable 3D-printed cementitious composites of ordinary portland cement and alkali-activated materials using cellulose nanocrystals (i.e., green natural nanomaterials). The extrudability and buildability of the alkali-activated slag-fly ash mixtures were improved and the extrusion pressure was reduced by ~ 35 % by increasing the cellulose nanocrystals content (up to 1 %) suggesting their viscosity-modifying properties in alkali-activated materials. The inclusion of cellulose nanocrystals improves the overall mechanical performance (8–20 % increase) and reduces the porosity of ordinary portland cement and heat-cured alkali-activated samples. Further, the addition of cellulose nanocrystals (up to 0.30 %) in sealed-cured alkali-activated samples improves their flexural strength by 20 %. The ordinary portland cement sample with cellulose nanocrystals densifies the microstructure and has an approximately 25 % increase in the degree of hydration at inner depths indicating cellulose nanocrystals' internal curing potential. The developed 3D-printable alkali-activated composites with cellulose nanocrystals can provide an overall reduction in the environmental impacts by eliminating/reducing the need for chemical admixtures to improve material consistency and stability, and replacing 100 % of portland cement.

Extraction of cellulose nanocrystalline from Camellia oleifera Abel waste shell: Study of critical processes, properties and enhanced emulsion performance

Cellulose nanocrystals (CNCs) extracted from the waste shell of Camellia oleifera Abel (C. oleifera) are gaining attention as valuable materials. In this study, CNCs were extracted from the agricultural waste shell of C. oleifera through phosphoric acid and sulfuric acid hydrolysis, respectively. Firstly, we optimized the alkaline treatment process for cellulose isolation by using response surface methodology. Furthermore, the properties of CNCs were investigated by neutralizing them with NaOH and NH3·H2O, and by dialysis in water. In addition, the characterization methods including FT-IR, TGA, AFM and TEM were used to analysis the properties of the synthesized CNCs. Finally, CNCs were studied for their application in essential oil-based Pickering emulsions. CNCs obtained from sulfuric acid showed the smallest particle size and good dispersibility. Moreover, the release profiles of essential oils in the emulsions were followed by Peppa's kinetic release model. The antibacterial activity of the emulsions against E. coli and S. aureus showed that CNCs-stabilized emulsions enhanced the antibacterial activity of essential oils. Therefore, neutralization treatments may enhance the properties of CNCs, and CNCs stabilized Pickering emulsions can enhance antibacterial activity of essential oil. This study provides insight into the potential application of CNCs derived from C. oleifera waste shells.

Nanocrystalline Cellulose as a Versatile Engineering Material for Extrusion-Based Bioprinting.

Naturally derived polysaccharide-based hydrogels, such as alginate, are frequently used in the design of bioinks for 3D bioprinting. Traditionally, the formulation of such bioinks requires the use of pre-reticulated materials with low viscosities, which favour cell viability but can negatively influence the resolution and shape fidelity of the printed constructs. In this work, we propose the use of cellulose nanocrystals (CNCs) as a rheological modifier to improve the printability of alginate-based bioinks whilst ensuring a high viability of encapsulated cells. Through rheological analysis, we demonstrate that the addition of CNCs (1% and 2% (w/v)) to alginate hydrogels (1% (w/v)) improves shear-thinning behaviour and mechanical stability, resulting in the high-fidelity printing of constructs with superior resolution. Importantly, LIVE/DEAD results confirm that the presence of CNCs does not seem to affect the health of immortalised chondrocytes (TC28a2) that remain viable over a period of seven days post-encapsulation. Taken together, our results indicate a favourable effect of the CNCs on the rheological and biocompatibility properties of alginate hydrogels, opening up new perspectives for the application of CNCs in the formulation of bioinks for extrusion-based bioprinting.

Copolymer-grafted cellulose nanocrystal induced nanocomposite hydrogels with enhanced strength, high elasticity and adhesiveness for flexible strain and pressure sensors

Recently, the application of cellulose nanocrystals (CNCs) in the field of hydrogel sensors has attracted much attention. However, it remains challenging to construct CNC-reinforced conductive hydrogels with a combination of enhanced strength, low hysteresis, high elasticity and remarkable adhesiveness. Herein, we present a facile method to prepare conductive nanocomposite hydrogels with the above-mentioned properties by reinforcing chemically crosslinked poly(acrylic acid) (PAA) hydrogel with rational-designed copolymer-grafted CNCs. The copolymer-grafted CNCs interact with PAA matrix to form carboxyl-amide conventional hydrogen bonds and carboxyl-amino ionic hydrogen bonds, among which the ionic hydrogen bonds with rapid recovery capability are critical to the low hysteresis and high elasticity of hydrogel. The introduction of copolymer-grafted CNCs endowed the hydrogels with enhanced tensile/compressive strength, high resilience (>95 %) during tensile cyclic loading, rapid self-recovery during compressive cyclic loading and improved adhesiveness. Thanks to the high elasticity and durability of hydrogel, the assembled hydrogel sensors exhibited good cycling repeatability and durability in detecting various strains, pressures and human motions. The hydrogel sensors also showed satisfying sensitivity. Hence, the proposed preparation method and the obtained CNC-reinforced conductive hydrogels would open new avenues in flexible strain and pressure sensors for human motion detection and beyond.

Cellulose nanocrystals: source, production and application as a coagulant for water purification

Abstract The coagulation/flocculation technique is an old proven method that utilizes chemical coagulants for water purification but there are health and environmental challenges associated with the long-term application of such coagulants. Cellulose fibre is a renewable, eco-friendly polymer found in many materials. It has been widely researched due to its unique properties, especially when processed in the ‘nano’ form as cellulose nanocrystals (CNCs) but nanocelluloses require surface functionalization in order to improve their suitability for various applications. The aim of this review is to provide an in-depth discussion of the current progress in the synthesis of CNCs with recourse to their source, surface chemistry and extraction procedures. Various techniques used for the conversion of CNCs into coagulants were extensively reviewed while the current development on the potential application of CNCs as a coagulant for water remediation was presented. The results obtained from the potential application of modified CNC-based coagulants demonstrate their remarkable coagulation efficiency for the purification of contaminated water. Therefore, global research into the development of CNC-based coagulants at all levels is crucial in order to generate interest in natural coagulants as a potential replacement for chemical coagulants. Furthermore, potential areas for more research were proposed in this review.

Cellulose Nanocrystals (CNCs) and Cellulose Nanofibers (CNFs) as Adsorbents of Heavy Metal Ions

The isolation of nanocellulose has been extensively investigated due to the growing demand for sustainable green materials. Cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs), which have the same chemical composition but have different morphology, particle size, crystallinity, and other properties depending on the precursor and the synthesis method used. In comparison, CNC particles have a short rod-like shape and have smaller particle dimensions when compared to CNF particles in the form of fibers. CNC synthesis was carried out chemically (hydrolysis method), and CNF synthesis was carried out mechanically (homogenization, ball milling, and grinding), and both can be modified because they have a large surface area and are rich in hydroxyl groups. Modifications were made to increase the adsorption ability of heavy metal ions. The Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric (TG), and dynamic light scattering (DLS) can reveal the characteristics and morphology of CNCs and CNFs. The success and effectiveness of the heavy metal adsorption process are influenced by a few factors. These factors include adsorbent chemical structure changes, adsorbent surface area, the availability of active sites on the adsorbent’s surface, adsorption constants, heavy metal ionic size differences, pH, temperature, adsorbent dosage, and contact time during the adsorption process. In this review, we will discuss the characteristics of CNCs and CNFs synthesized from various precursors and methods, the modification methods, and the application of CNCs and CNFs as heavy metal ion adsorbents, which includes suitable isotherm and kinetics models and the effect of pH on the selectivity of various types of heavy metal ions.

Effect of Different Methods to Synthesize Polyol-Grafted-Cellulose Nanocrystals as Inter-Active Filler in Bio-Based Polyurethane Foams.

Currently, the scientific community has spent a lot of effort in developing "green" and environmentally friendly processes and products, due the contemporary problems connected to pollution and climate change. Cellulose nanocrystals (CNCs) are at the forefront of current research due to their multifunctional characteristics of biocompatibility, high mechanical properties, specific surface area, tunable surface chemistry and renewability. However, despite these many advantages, their inherent hydrophilicity poses a substantial challenge for the application of CNCs as a reinforcing filler in polymers, as it complicates their dispersion in hydrophobic polymeric matrices, such as polyurethane foams, often resulting in aggregate structures that compromise their properties. The manipulation and fine-tuning of the interfacial properties of CNCs is a crucial step to exploit their full potential in the development of new materials. In this respect, starting from an aqueous dispersion of CNCs, two different strategies were used to properly functionalize fillers: (i) freeze drying, solubilization in DMA/LiCl media and subsequent grafting with bio-based polyols; (ii) solvent exchange and subsequent grafting with bio-based polyols. The influence of the two functionalization methods on the chemical and thermal properties of CNCs was examined. In both cases, the role of the two bio-based polyols on filler functionalization was elucidated. Afterwards, the functionalized CNCs were used at 5 wt% to produce bio-based composite polyurethane foams and their effect on the morphological, thermal and mechanical properties was examined. It was found that CNCs modified through freeze drying, solubilization and bio-polyols grafting exhibited remarkably higher thermal stability (i.e., degradation stages > 100 °C) with respect to the unmodified freeze dried-CNCs. In addition, the use of the two grafting bio-polyols influenced the functionalization process, corresponding to different amount of grafted-silane-polyol and leading to different chemico-physical characteristics of the obtained CNCs. This was translated to higher thermal stability as well as improved functional and mechanical performances of the produced bio-based composite PUR foams with respect of the unmodified CNCs-composite ones (the best case attained compressive strength values three times more). Solvent exchange route slightly improved the thermal stability of the obtained CNCs; however; the so-obtained CNCs could not be properly dispersed within the polyurethane matrix, due to filler aggregation.

Responsive Chiral Photonic Cellulose Nanocrystal Materials

AbstractResponsive photonic crystals have attracted significant attention in fundamental scientific research and technological applications. Upon applying external stimuli, such as mechanical, electrical, magnetic, and optical triggers, the optical properties of photonic crystals can be actively tuned. Among a large number of photonic crystals, cellulose nanocrystals (CNCs) are considered one of the most promising materials due to their renewability, simplicity of preparation, and unprecedented chirality. A comprehensive overview of the fundamental design principles, methodologies, responsive mechanisms, and practical applications of responsive chiral photonic CNC materials is presented here. The changes in helix pitch, refractive index, orientation, and resulting structural and optical properties of chiral photonic CNCs in response to various stimuli are discussed. Thereafter, novel applications of responsive chiral photonic CNCs, such as colorimetric sensors, photonic actuators, rewritable photonic papers, and anti‐counterfeiting smart tags are described. We conclude by discussing future challenges and opportunities for developing high‐performance responsive chiral photonic CNC materials.

Surface modifications of cellulose nanocrystals: Processes, properties, and applications

The interest in nanocellulose has recently increased in many fields due to its natural abundance, exceptional mechanical/optical properties, and better biocompatibility. During the production of cellulose nanocrystals (CNCs) via sulfuric acid hydrolysis, sulfate groups are introduced, which decrease the thermal stability of CNCs and, thus, have a profound negative effect on the potential application of CNCs in nanocomposites. Also, mechanical methods exhibit poor morphological properties in CNCs with a reduced degree of crystallinity. Therefore, to improve the processability and performance of CNCs and extend their industrial applications and quality, nano-cellulose undergoes surface modifications by physical and chemical means. Surface modifications of CNCs lower the surface energy, increase hydrophobicity, improve interfacial adhesion, enhance their compatibility between nanocomposite components, and improve their dispersion and interaction. Surface-modified CNCs have wide applications in medicine, catalysis, optics, remediation processes, electronics, textiles, pulp, paper, etc. Other applications of CNCs are: supporting catalysts and sensors, as diaphragms in earphones; for tissue engineering, scaffolds, for toughened paper, as polymer nanocomposites for developing membranes, in flexible panels for flat panel displays, in the optical application and biomimetic foams, and as rheology modifiers. This review provides the latest advances in surface modification of CNCs and the relevant processes, properties, and applications. • Acid hydrolysis of cellulose introduces sulfate groups on cellulose nanocrystals (CNCs) surface, limiting their applications. • Surface modification is an effective method to mitigate the shortcomings of CNCs. • Recent advancements in physical and chemical surface modifications are summarized. • The applications of CNCs, including polymer nanocomposites, are intensively studied.

Cellulose Nanocrystals (CNC)-Based Functional Materials for Supercapacitor Applications

The growth of industrialization and the population has increased the usage of fossil fuels, resulting in the emission of large amounts of CO2. This serious environmental issue can be abated by using sustainable and environmentally friendly materials with promising novel and superior performance as an alternative to petroleum-based plastics. Emerging nanomaterials derived from abundant natural resources have received considerable attention as candidates to replace petroleum-based synthetic polymers. As renewable materials from biomass, cellulose nanocrystals (CNCs) nanomaterials exhibit unique physicochemical properties, low cost, biocompatibility and biodegradability. Among a plethora of applications, CNCs have become proven nanomaterials for energy applications encompassing energy storage devices and supercapacitors. This review highlights the recent research contribution on novel CNC-conductive materials and CNCs-based nanocomposites, focusing on their synthesis, surface functionalization and potential applications as supercapacitors (SCs). The synthesis of CNCs encompasses various pretreatment steps including acid hydrolysis, mechanical exfoliation and enzymatic and combination processes from renewable carbon sources. For the widespread applications of CNCs, their derivatives such as carboxylated CNCs, aldehyde-CNCs, hydride-CNCs and sulfonated CNC-based materials are more pertinent. The potential applications of CNCs-conductive hybrid composites as SCs, critical technical issues and the future feasibility of this endeavor are highlighted. Discussion is also extended to the transformation of renewable and low-attractive CNCs to conductive nanocomposites using green approaches. This review also addresses the key scientific achievements and industrial uses of nanoscale materials and composites for energy conversion and storage applications.

Spider-web-inspired membrane reinforced with sulfhydryl-functionalized cellulose nanocrystals for oil/water separation

The cellulose nanocrystals (CNC) has attracted widespread attention in reinforced materials. However, the application of CNC in electrospinning has been limited due to its self-polymerization. Herein, a cobweb-like nanofibrous membrane was fabricated by electrospinning the polyacrylonitrile (PAN) and sulfydryl-functionalized CNC (SC). The SC content could reach to 48 wt% after the thiolation modification. The membrane with ultrafine fibers and interlaced nets possessed outstanding porosity (91.7%) and underwater superoleophobicity. An ultrahigh permeation flux of 1244 L·m−2·h−1 with a separation efficiency of >99.9% was achieved driven by gravity. The mechanical properties also enhanced significantly with the increase of SC. When the addition amount of SC was 48 wt%, the maximum tensile stress was 2.9 MPa, which was 3.4 times than that of the PAN membrane. The antifouling performance and chemical stability endowed the SC(48)/PAN membrane with intriguing reusability, thus making it exhibit enormous potential in oil/water separation.

Production of bacterial cellulose nanocrystals via enzymatic hydrolysis and evaluation of their coating on alginate particles formed by ionotropic gelation

This study aimed to obtain the bacterial cellulose nanocrystals (CNC) by enzymatic hydrolysis and verify the CNC application as coating material in alginate particles. Therefore, the production of CNC was carried out through two enzymatic hydrolysis methods involving a time period of 48 and 72 h. 0.35 mg of dry mass of cellulose was produced approximately 1.6 × 1011 CNC/mL. The CNC obtained by enzymatic hydrolysis at 72 h (Method II) was applied to cover the alginate particles, obtained by ionotropic gelation. The CNC Zeta potential value was about +15 mV and for alginate particles -26.46 ± 1.48 mV. These results confirmed the application of CNC as coating material for alginate particles. It brings an incremental contribution to the knowledge advancement in the pharmaceutical and food area, allowing the engineering of systems to use a mixed composition of nanobiomaterials to modify the release pattern of drugs, macromolecule, nutrients, stabilizers and target specific drug release.

Effects of cellulose nanocrystals on the vulcanization of natural rubber/cellulose nanocrystals nanocomposite and corresponding regulating strategies

AbstractVulcanization is a vital process in rubber processing, it endows rubber with valuable physical and mechanical properties, making rubber a widely used engineering material. In addition to vulcanization agent, reinforcing fillers play a non‐ignorable influence on the vulcanization of rubber nanocomposites. Herein, the effects of cellulose nanocrystals (CNCs) on the vulcanization of natural rubber (NR)/CNCs nanocomposite was studied. It was found that even though the addition of CNCs can effectively improve the dispersion of ZnO in NR matrix, the vulcanization of NR was inhibited. This may be attributed to the CNCs' adsorption of vulcanizing agents (DM, ZnO) and the acidic chemical environment on the surface of CNCs. In order to improve the vulcanization properties of NR/CNCs nanocomposite, tetramethyldithiochloram (TMTD) and triethanolamine (TEOA) were used as a combination accelerator and curing activator, respectively, and polyethylene glycol (PEG) was introduced to screen hydroxyl groups on the surface of CNCs to prohibit the CNCs' adsorption of vulcanizing agents. The results indicate that TMTD and TEOA effectively improved the vulcanization rate of NR/CNCs nanocomposite and increased the crosslink density by an order of magnitude. Subsequently, the tensile strength, tear strength, and so forth. of NR/CNCs nanocomposite were significantly improved. However, PEG hardly help to improve the vulcanization properties of NR/CNCs nanocomposite. In addition, the control samples without CNCs were prepared and characterized, the comparation between NR and NR/CNCs nanocomposite shows that the synergistic effect of crosslink density and CNCs' reinforcement more effectively improve mechanical properties of NR. This work not only elucidates the inhibiting mechanisms of CNCs on the vulcanization of NR, but also provides practical strategies for improving the vulcanization and properties of NR/CNCs nanocomposite. It may accelerate the application of CNCs as rubber reinforcing filler.

Effect of cellulose nanocrystals on the formation and stability of oil-in-water emulsion formed by octenyl succinic anhydride starch

This study aimed to investigate the effect of cellulose nanocrystals (CNCs) combined with octenyl succinic anhydride modified starch (OSAS) on the stabilization of oil-in-water emulsions. Hydrogen bond and intermolecular electrostatic interaction were found in the formation of CNCs-OSAS complex as characterized by molecular dynamics simulation. A relatively stable emulsion could be formed by ultrasonic emulsification when the concentrations of CNCs-OSAS complex in the weight ratio of 2:8 and oil were 1.5 wt% and 10 wt%, respectively. Increase in Z-average diameter of emulsion prepared with the CNCs-OSAS complex (81.3 nm at 25 °C for 30 days) was considerably less than that of OSAS-stabilized emulsion (116.8 nm at 25 °C). No creaming was observed in emulsion prepared with the CNCs-OSAS complex after 30 days of storage. The apparent viscosity of emulsion stabilized by the CNCs-OSAS complex was 1.4 times as high as that of OSAS-stabilized emulsion when shear rate was 0.01 s−1. Increased viscoelasticity of emulsions in the presence of CNCs probably enhanced the interaction between droplets and delayed the creaming of emulsions. This study provided a new perspective to broaden the application of CNCs and OSAS in "green" emulsion.

Insight into the formation mechanism of soy protein isolate films improved by cellulose nanocrystals

This study aimed to evaluate the effects of cellulose nanocrystals (CNC) on the basic properties of soy protein isolate films, and especially to propose the corresponding formation mechanism. Tensile strength, barrier properties, and water resistance were effectively improved after the formation of nanocomposite films. Incorporating CNC could restrict water mobility and improve the viscoelastic properties of films. Appropriate content of CNC (0.50% and 0.75%) promoted the construction of a more homogeneous and compact film structure, which may be attributed to the CNC-induced conformational modifications and the enhanced hydrophobic and hydrogen-bond interactions. While excessive CNC (1.00%) was not conducive to the integrity and continuity of film structures, resulting in the weakened functional properties. The obtained films were able to decrease total viable counts and total volatile basic nitrogen of stored pork, and extend the shelf-life of strawberry. This work offers a theoretical basis for the application of CNC in packaging industry.

Taming the Photonic Behavior of Laser Dyes Through Specific and Dynamic Self‐Assembly onto Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) display a set of unique properties such as surface charge, nanometric size, and giant dipole moment that have not been considered so far to tame the luminescent properties of organic dyes upon soft and hard photoexcitation. Herein, the first comprehensive analysis on the photonic behavior of laser dyes adsorbed onto CNCs through physically dynamic driving forces is reported. By systematically varying the solvent, the dye molecular structure, and dye/CNC ratios, it is shown that the dye absorption and emission signatures are drastically modified when CNCs are incorporated into the solutions. The photonic characterization, together with molecular dynamic simulations, allows to unravel the labeling interaction processes and unambiguously assigns both the physicochemical properties of the surrounding media and the giant permanent dipole moment of CNCs as the most important factors taming the photophysical and lasing properties of dyes adsorbed on it. Accordingly, a CNC‐induced Stark effect accounts for the absorption and emission spectral changes recorded upon CNC incorporation. Herein, the widely expanding applications of CNCs toward the design of advanced photoactive nanomaterials based on these renewable building blocks are opened up.

Enhanced photocatalytic performance for phenol degradation using ZnO modified with nano-biochar derived from cellulose nanocrystals

Phenol, considered as a stable and refractory organic pollutant, has posed an increasing threat to the environment and human health. Herein, the ZnO was regulated with nano-biochar (CCNC) derived from cellulose nanocrystals (CNCs). The CCNC/ZnO photocatalysts were fabricated via in situ precipitation and carbonization, in which CNCs served as both the templates and carbon source. Meanwhile, Zn2+ ions deposited on the surface of rod-like CNCs by electrostatic interaction. Subsequently, homogeneous dispersed ZnO nanoparticles were anchored onto the surface of CNCs, decreasing the ZnO nanoparticles size. As the CNCs transformed into CCNC, the resultant CCNC/ZnO photocatalysts demonstrated excellent degradation efficiency to phenol, corresponding to 99.8% within 90 min. Additionally, the CCNC/ZnO photocatalysts also displayed a satisfactory stability for five cycles without significant performance being decreased. The calculating and experimental results demonstrated that the conjugated graphitic structures of CCNC effectively reduced the band gap of ZnO from 3.26 to 2.96 eV. Besides, the CCNC remarkably promoted photogenerated electron-hole pairs separation and transfer, thereby improving the photodegradation efficiency for phenol. Furthermore, the efficiency for phenol photodegradation was comprehensively influenced by a combination of the ratio of photocatalyst, initial phenol concentration and catalyst dose, and pH value. This study broadened the application of CNCs in the field of photocatalysis, which provided a new perspective for the preparation of highly efficient photocatalysts using CNCs derived nano-biochar as a template and charge-transport pathway.

Colloidal stability of cellulose nanocrystals in aqueous solutions containing monovalent, divalent, and trivalent inorganic salts

Aggregation kinetics and surface charging properties of rod-like sulfated cellulose nanocrystals (CNCs) have been investigated in aqueous suspensions containing monovalent, divalent, or trivalent inorganic salts. Electrophoresis and time-resolved dynamic light scattering (DLS) were used to characterize the surface charge and colloidal stability of the CNCs, respectively. The surface charge and aggregation kinetics of the sulfated CNCs were found to be independent of solution pH (pH range 2–10). For the monovalent salts (CsCl, KCl, NaCl, and LiCl), the critical coagulation concentration (CCC) followed the order of Cs+ < K+ < Na+ < Li+, which follows the direct Hofmeister series, indicating specific interaction of the cations with the CNCs surface. The experimental aggregation kinetics of CNCs were in very good agreement with predictions based on the classic Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. A Hamaker constant of 3.6 × 10−20 J for the CNCs in aqueous medium was derived, for the first time, from the colloidal stability curves with monovalent salts. This value is consistent with a previous value determined by direct force measurements for cellulose surfaces in aqueous solutions. For the divalent salts (MgCl2, CaCl2, and BaCl2), the CCC values followed the order Mg2+ > Ca2+ > Ba2+, which is in the reverse order of the counterion ionic size. For the trivalent salts (LaCl3, AlCl3, and FeCl3), the CNCs suspension was destabilized much more effectively. The observed complex stability curves with AlCl3 and FeCl3 are attributed to charge neutralization and charge reversal imparted by the adsorption of aluminum and ferric hydrolysis species on the CNC surface. The significant charge reversal induced by the ferric hydrolysis species led to the restabilization of suspensions. Our results on the colloidal stability of CNCs are of central importance to the nanotechnology and materials science communities working on various applications of CNCs.

An eco-friendly approach to preparing cellulose nanocrystals by precisely controlling the dissolution of natural cellulose in TBAH/H2O solvent

Applications of cellulose nanocrystals (CNCs) in various fields of high value have been and are being widely studied. However, research about the fundamental preparation method has come to a standstill. This work aims to introduce a concept of progressive dissolution of cellulosic fibers and an eco-friendly way of preparing CNCs. By controlling TBAH concentration, the amphiphilicity and dissolving capability of TBAH/H2O can be regulated. Through a controlled partial dissolution of cellulose in the solvent, aqueous tetra-butylammonium hydroxide (TBAH), the fiber can be dissolved to make nanoscale particles (CNC suspensions). Polarized light microscopy provides a quantitative evaluation of the progress of dissolution, by which a processing window (43% TBAH/H2O, 30 min dissolution at room temperature) for preparing CNCs from cotton pulp has been determined. The multiscale cellulose products, including micron-scale, nanoscale, and well-dissolved products of cellulose, have been separated with the assistance of the derivatization process. There are interestingly homogeneous materials of cellulose I with a needle-like shape in the nanoscale products extracted. Furthermore, the cellulose raw materials can be extended from cotton pulp to wood pulp, bamboo pulp, straw pulp, and microcrystalline cellulose, indicating it to be a universal method. Analysis of XRD patterns of the raw and CNCs indicates that amorphous and less-crystalline cellulose can be precisely and controllably dissolved by the solvent, leaving CNCs.

Functionalization of Cellulose Nanocrystals with POEGMA Copolymers via Copper-Catalyzed Azide-Alkyne Cycloaddition for Potential Drug-Delivery Applications.

Elongated colloidal nanoparticles (NPs) have significant potential for drug delivery and imaging applications in cancer therapy, but progress depends on developing a deeper understanding of how their physicochemical properties affect their interactions with cells and with tumors. Cellulose nanocrystals (CNCs) are biocompatible, rodlike colloids that are broadly surface-functionalizable, making them interesting as modular drug carriers. In this report, we describe the attachment of a statistical copolymer containing oligoethylene glycol methacrylate (OEGMA; Mn ≈ 500 Da) and small amounts of aminopropylmethacrylamide (APMA) to CNCs. Here, the copolymer is designed to serve as a "stealth" corona to minimize protein adsorption, and the amino groups provide functionality for the attachment of diagnostic or therapeutic moieties. The corona polymer with a terminal azide group was synthesized by atom transfer radical polymerization using tert-butyloxycarbonyl (tBoc)-protected APMA as the comonomer. A key step in this synthesis was the grafting of acetylene groups to the CNC surface via a reaction with NaOH plus propargyl bromide in aqueous dimethyl sulfoxide. The copolymer was attached to the CNCs using copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click" chemistry. By determining the mean number of amino groups per copolymer and amino group content of the CNC sample, we were able to infer that there were on average ca. 300 polymer molecules per CNC. Preliminary evaluation in a human ovarian cancer cell line (HEYA8) and a human breast cancer cell line (MDA-MB-436) demonstrated that these CNCs are nontoxic. We also assessed the cellular uptake of these CNC NPs in the same two cell lines using flow cytometry and distinguished between NPs being internalized by the cell or surface-bound using a trypan blue quenching experiment. These results provide support for applications of polymer-coated CNCs in medicine and are encouraging for further studies in vitro and in vivo to evaluate their potential as drug-delivery vehicles.