Supramolecular Structure Characterization of Cellulose II Nanowhiskers Produced by Acid Hydrolysis of Cellulose I Substrates

Micromorphology reformation of regenerated cellulose nanofibers from corn (Zea Mays) stalk pith in urea solution with high-speed shear induced

Nanocellulose is a kind of renewable natural polymer material with high specific surface area, high crystallinity, and strong mechanical properties. RC nanofibers (RCNFs) have attracted an increasing attention in various applications due to their high aspect ratio and good flexibility. Herein, a novel and facile strategy for RCNFs preparation with high-speed shear induced in urea solution through "bottom-up" approach was proposed in this work. Results indicated that the average diameter and yield of RCNF was approach to 136.67 nm and 53.3 %, respectively. Meanwhile, due to the regular orientation RC chains and arrangement micro-morphology, RCNFs exhibited high crystallinity, strong mechanical properties, stable thermal degradation performance, and excellent UV resistance. In this study, a novel regeneration process with high-speed shear induced was developed to produce RCNFs with excellent properties. This study paved a strategy for future low-energy production of nanofibers and high value-added conversion applications of agricultural waste.

Exploring hydrogen-bond structures in cellulose during regeneration with anti-solvent through two-dimensional correlation infrared spectroscopy

Cellulose, renowned for its excellent biocompatibility, finds extensive applications in both industrial and laboratory settings. However, few studies have specifically addressed the mechanistic evolution of hydrogen bond networks in cellulose during the dissolution and regeneration processes. In this research, the regeneration mechanism of cellulose in water and ethanol is investigated through molecular dynamics simulations. The results indicate that the ability of water molecules to disrupt hydrogen bonds between cellulose and ionic liquids is stronger than that of ethanol, which is more conducive to promoting the regeneration of cellulose. Besides, the Fourier transform infrared spectroscopy coupled with two-dimensional correlation infrared spectroscopy techniques are employed to unveil the evolution sequence of hydrogen bonds during dissolution and regeneration: ν(OH) (absorbed water) → ν(O3-H3···O5) (intrachain) → ν(O6-H6···O3') (interchain) → ν(O2-H2···O6) (intrachain) → ν(OH) (free). This study not only enhances our understanding of the intricate hydrogen bond dynamics in cellulose dissolution and regeneration but also provides a foundation for the expanded application of cellulose in diverse fields.

Effects of hydrolysis conditions on the morphology of cellulose II nanocrystals (CNC-II) derived from mercerized microcrystalline cellulose

The properties of cellulose nanocrystals with allomorph II (CNC-II) vary with the sources and the treatments received. In this work, the influences of hydrolysis time, temperature, and the applied acid concentration on the crystal size of CNC-II were investigated by the surface response experimental design. The results showed that temperature was the most significant factor affecting the crystal size of CNC-II during hydrolysis from mercerized cellulose. Then the morphology and colloidal properties of CNC-II were revealed by dynamic laser scattering (DLS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), etc. XRD results indicated that CNC-II had slightly lower crystallinity (80.89 % vs 82.7 %) and larger crystallite size (5.21 vs. 5.13 nm) than CNC-I. TEM and AFM results showed that the morphology of CNC-II were disc-like and rod-like particles, with an average diameter of 14.6 ± 4.7 nm (TEM) and a thickness of 4- 8 nm (AFM). TG and XPS revealed the reduced thermal stability was due to the introduced sulfate groups in CNC-II during hydrolysis. This investigation has addressed the features of CNC-II derived from mercerized cellulose, and it would be promising in fabricating advanced materials.

Multiscale structure of cellulose microfibrils in regenerated cellulose fibers

Cellulose in solution can be assembled into textile fibers by wet-spinning (Viscose etc.) or dry-jet wet spinning (Lyocell, Ioncell etc.), which leads to significant differences in the mechanical properties of fibers. We use scanning X-ray microdiffraction (SXM) to reveal regenerated fibers having a "skin-core" morphology. The "core" region comprises microfibrils (MFs) with ~100 nm in diameter. The cellulose forms elementary fibrils having a ribbon-like cross sectional shape of about 6 × 2 nm, which are packed into MFs. Our SXM studies demonstrate that MFs within Ioncell fibers are composed of elementary fibrils with homogeneous morphologies. Furthermore, the stacking of cellulose molecular sheets within elementary fibrils of Viscose fibers is preferentially along the 010 direction, while those of Ioncell fibers preferably stack in the 1-10 direction. The better structural regularities and distinct morphologies of elementary fibrils give Ioncell fibers enhanced mechanical properties and a wet strength far superior to those of Viscose fibers.

Structural Color from Cellulose Nanocrystals or Chitin Nanocrystals: Self-Assembly, Optics, and Applications

Widespread concerns over the impact of human activity on the environment have resulted in a desire to replace artificial functional materials with naturally derived alternatives. As such, polysaccharides are drawing increasing attention due to offering a renewable, biodegradable, and biocompatible feedstock for functional nanomaterials. In particular, nanocrystals of cellulose and chitin have emerged as versatile and sustainable building blocks for diverse applications, ranging from mechanical reinforcement to structural coloration. Much of this interest arises from the tendency of these colloidally stable nanoparticles to self-organize in water into a lyotropic cholesteric liquid crystal, which can be readily manipulated in terms of its periodicity, structure, and geometry. Importantly, this helicoidal ordering can be retained into the solid-state, offering an accessible route to complex nanostructured films, coatings, and particles. In this review, the process of forming iridescent, structurally colored films from suspensions of cellulose nanocrystals (CNCs) is summarized and the mechanisms underlying the chemical and physical phenomena at each stage in the process explored. Analogy is then drawn with chitin nanocrystals (ChNCs), allowing for key differences to be critically assessed and strategies toward structural coloration to be presented. Importantly, the progress toward translating this technology from academia to industry is summarized, with unresolved scientific and technical questions put forward as challenges to the community.

Controlling the nanocellulose morphology by preparation conditions

Nanocellulose (NC) is the desired building block for novel biomaterials. The morphology of NC is one of the core parameters impacting the functionality and property of engineered functional materials. This work aims to reveal the relationship between the product morphology and sulfuric acid hydrolysis conditions (including acid concentration, temperature and time), and to realize morphological regulation of obtained NC. Three representative products were obtained from microcrystalline cellulose via sulfuric acid hydrolysis, which are cellulose nanocrystals with broad size distribution (W-CNC, 383.9 ± 131.7 nm in length, 6 ± 2.1 nm in height) obtained by 61 % H2SO4, 55 °C and 90 min, cellulose nanospheres (CNS, 61.3 ± 15.9 nm in diameter) obtained by 64 % H2SO4, 35 °C and 75 min, and CNC with narrow size distribution (N-CNC, 276.1 ± 28.7 nm in length, 4.1 ± 0.6 nm in height), obtained by 64 % H2SO4, 45 °C and 45 min. The results showed that the crystallographic form of W-CNC and N-CNC are cellulose I, while cellulose I and II coexist in CNS. Only W-CNC and N-CNC can form chiral nematic structures through evaporation-induced self-assembly strategy and reflected light with specific wavelengths. In addition, the formation mechanism of CNS with cellulose I/II was proposed, which provided a better understanding of NC morphology regulation.

Extraction of the cellulose nanocrystals via ammonium persulfate oxidation of beaten cellulose fibers

The effect of beating starting pulp was investigated on the oxidation efficiency of ammonium persulfate (APS), the yield, and the properties of the CNCs. The beaten pulp and the subsequent CNCs were characterized, respectively, by different techniques. The CNCs were classified as CNC1 and CNC2, dependent on ultrasonication. It showed that the beating exposed more free OH groups in the pulp and enhanced the yield and surface charges of CNCs. Compared to the CNC2, the CNC1 had a higher surface charge, higher crystallinity, higher thermal stability, shorter length, smaller length distribution, and slightly larger width. The CNC1 and CNC2 had similar rheological properties. For the beaten pulp with a beating degree of 25°SR, the yields of the CNC1 and the total CNCs reached the maximum, 42.65 and 34.11 %, respectively. The surface charges of the CNC1 and the CNC2 also reached the maximum, -44.5 and - 33.6 mV, respectively. Their crystallinity indexes were 80.07 and 75.42 %, respectively. The lengths of the CNC1 and the CNC2 were 157.31 ± 30.61 and 214.92 ± 65.52 nm, and their widths were 10.13 ± 2.74 and 9.43 ± 2.99 nm, respectively. Therefore, proper beating enhanced the APS oxidation efficiency and influenced the CNCs properties.

Effect of Acetylation of Two Cellulose Nanocrystal Polymorphs on Processibility and Physical Properties of Polylactide/Cellulose Nanocrystal Composite Film

Polylactide (PLA) has become a popular alternative for petroleum-based plastics to reduce environmental pollution. The broader application of PLA is hampered by its brittle nature and incompatibility with the reinforcement phase. The aim of our work was to improve the ductility and compatibility of PLA composite film and investigate the mechanism by which nanocellulose enhances PLA polymer. Here, we present a robust PLA/nanocellulose hybrid film. Two different allomorphic cellulose nanocrystals (CNC-I and CNC-III) and their acetylated products (ACNC-I and ACNC-III) were used to realize better compatibility and mechanical performance in a hydrophobic PLA matrix. The tensile stress of the composite films with 3% ACNC-I and ACNC-III increased by 41.55% and 27.22% compared to pure PLA film, respectively. Compared to the CNC-I or CNC-III enhanced PLA composite films, the tensile stress of the films increased by 45.05% with 1% ACNC-I and 56.15% with 1% ACNC-III. In addition, PLA composite films with ACNCs showed better ductility and compatibility because the composite fracture gradually transitioned to a ductile fracture during the stretching process. As a result, ACNC-I and ACNC-III were found to be excellent reinforcing agents for the enhancement of the properties of polylactide composite film, and the replacement some petrochemical plastics with PLA composites would be very promising in actual life.

A nitrocellulose/cotton fiber hybrid composite membrane for paper-based biosensor

Nitrocellulose (NC) membrane was fabricated and tested for its potential use in various paper-based biosensors for use in point-of-care testing. However, contemporary technologies are complex, expensive, non-scalable, limited by conditions, and beset with potentially adverse effects on the environment. Herein, we proposed a simple, cost-effective, scalable technology to prepare nitrocellulose/cotton fiber (NC/CF) composite membranes. The NC/CF composite membranes with a diameter of 20 cm were fabricated in 15 min using papermaking technology, which contributes to scalability in the large-scale production of these composites. Compared with existing commercial NC membranes, the NC/CF composite membrane is characterized by small pore size (3.59 ± 0.19 μm), low flow rate (156 ± 55 s/40 mm), high dry strength (up to 4.04 MPa), and wet strength (up to 0.13 MPa), adjustable hydrophilic-hydrophobic (contact angles ranged from 29 ± 4.6 to 82.8 ± 2.4°), the good adsorption capacity of protein (up to 91.92 ± 0.07 μg). After lateral flow assays (LFAs) detection, the limit of detection is 1 nM, which is similar to commercial NC membrane (Sartorius CN 140). We envision the NC/CF composite membrane as a promising material for paper-based biosensors of point-of-care testing applications.

Preparation of Cellulose Nanocrystals: Controlling the Crystalline Type by One-Pot Acid Hydrolysis

Cellulose nanocrystals (CNCs) have aroused increasing interest owing to their renewable origin and excellent properties derived from their size and morphology. Based on their chain orientation, CNCs can be prepared as two main allomorphs (I or II). However, achieving pure CNC allomorphs still requires enhanced control on the CNCs synthesis process and improved understanding of the involved reaction parameters. In this work, we study in detail a set of parameters for CNC synthesis using one-pot acid hydrolysis and evaluate their influence on the outcome with respect to yield, purity, and repeatability. We also demonstrate that a fast, nondestructive, and accurate methodology based on dynamic light scattering is an efficient alternative to the usual structural analysis of the synthesis outcome. Finally, we provide an improved protocol to reliably obtain each allomorph with mass yields of 25% for type I and 40% for type II. Emphasis is put on the reduction of the environmental impact and the overall preparation time.

The influence of temperature on cellulose swelling at constant water density

We have in this paper investigated how water sorbs to cellulose. We found that both cellulose nanofibril (CNF) and cellulose nanocrystal (CNC) films swell similarly, as they are both mainly composed of cellulose. CNF/CNC films subjected to water at 0.018 kg/m³ at 25 °C and 39 °C, showed a decrease in swelling from ~ 8 to 2%. This deswelling increased the tensile index of CNF-films by ~ 13%. By molecular modeling of fibril swelling, we found that water sorbed to cellulose exhibits a decreased diffusion constant compared to bulk water. We quantified this change and showed that diffusion of sorbed water displays less dependency on swelling temperature compared to bulk water diffusion. To our knowledge, this has not previously been demonstrated by molecular modeling. The difference between bulk water diffusion (D_WW) and diffusion of water sorbed to cellulose (D_CC) increased from D_WW - D_CC ~ 3 × 10^-5 cm/s² at 25 °C to D_WW - D_CC ~ 8.3 × 10^-5 cm/s² at 100 °C. Moreover, water molecules spent less successive time sorbed to a fibril at higher temperatures.

Fabrication and Properties of Tree-Branched Cellulose Nanofibers (CNFs) via Acid Hydrolysis Assisted with Pre-Disintegration Treatment

In this paper, the novel morphology of cellulose nanofibers (CNFs) with a unique tree-branched structure was discovered by using acid hydrolysis assisted with pre-disintegration treatment from wood pulps. For comparison, the pulps derived from both softwood and hardwood were utilized to extract nanocellulose in order to validate the feasibility of proposed material fabrication technique. The morphology, crystalline structures, chemical structures, and thermal stability of nanocellulose were characterized by means of transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR), as well as thermogravimetric analysis (TGA). Prior to acid hydrolysis, softwood and hardwood pulps underwent the disintegration treatment in the fiber dissociator. It has been found that nanocellulose derived from disintegrated pulps possesses much longer fiber length (approximately 5-6 μm) and more evident tree-branched structures along with lower degree of crystallinity when compared with those untreated counterparts. The maximum mass loss rate of CNFs takes place at the temperature level of approximately 225 °C, and appears to be higher than that of cellulose nanowhiskers (CNWs), which might be attributed to an induced impact of amorphous content. On the other hand, disintegration treatment is quite beneficial to the enhancement of tensile strength of nanocellulose films. This study elaborates a new route of material fabrication toward the development of well-tailored tree-branched CNFs in order to broaden the potential widespread applications of nanocellulose with diverse morphological structures.

Nanocellulose for Sustainable Water Purification

Nanocelluloses (NC) are nature-based sustainable biomaterials, which not only possess cellulosic properties but also have the important hallmarks of nanomaterials, such as large surface area, versatile reactive sites or functionalities, and scaffolding stability to host inorganic nanoparticles. This class of nanomaterials offers new opportunities for a broad spectrum of applications for clean water production that were once thought impractical. This Review covers substantial discussions based on evaluative judgments of the recent literature and technical advancements in the fields of coagulation/flocculation, adsorption, photocatalysis, and membrane filtration for water decontamination through proper understanding of fundamental knowledge of NC, such as purity, crystallinity, surface chemistry and charge, suspension rheology, morphology, mechanical properties, and film stability. To supplement these, discussions on low-cost and scalable NC extraction, new characterizations including solution small-angle X-ray scattering evaluation, and structure-property relationships of NC are also reviewed. Identifying knowledge gaps and drawing perspectives could generate guidance to overcome uncertainties associated with the adaptation of NC-enabled water purification technologies. Furthermore, the topics of simultaneous removal of multipollutants disposal and proper handling of post/spent NC are discussed. We believe NC-enabled remediation nanomaterials can be integrated into a broad range of water treatments, greatly improving the cost-effectiveness and sustainability of water purification.

Understanding the Drying Behavior of Regenerated Cellulose Gel Beads: The Effects of Concentration and Nonsolvents

The drying behavior of regenerated cellulose gel beads swollen with different nonsolvents (e.g., water, ethanol, water/ethanol mixtures) is studied in situ on the macroscopic scale with an optical microscope as well as on nanoscale using small-angle/wide-angle X-ray scattering (SAXS/WAXS) techniques. Depending on the cellulose concentration, the structural evolution of beads during drying follows one of three distinct regimes. First, when the cellulose concentration is lower than 0.5 wt %, the drying process comprises three steps and, regardless of the water/ethanol mixture composition, a sharp structural transition corresponding to the formation of a cellulose II crystalline structure is observed. Second, when the cellulose concentration is higher than 5.0 wt %, a two-step drying process is observed and no structural transition occurs for any of the beads studied. Third, when the cellulose concentration is between 0.5 and 5.0 wt %, the drying process is dependent on the nonsolvent composition. A three-step drying process takes place for beads swollen with water/ethanol mixtures with a water content higher than 20%, while a two-step drying process is observed when the water content is lower than 20%. To describe the drying behavior governed by the cellulose concentration and nonsolvent composition, a simplified phase diagram is proposed.

Insights into coloration enhancement of mercerized cotton fabric on reactive dye digital inkjet printing

Mercerization can improve the utilization rate of dyes in the dyeing process, and reduce the discharge of washing wastewater. However, the effect and mechanism of mercerization is not clear on digital inkjet printing of cotton fabric. In this work, two kinds of cotton fabrics (original and mercerized) were used for reactive dye digital inkjet printing, and the color improvement mechanism of caustic soda mercerization was investigated. It was found that the crystallinity of cotton fibre was adjusted from 73.9% to 58.5% by caustic mercerization, and the breaking strength did not decrease compared with original cotton fibre. Thus, the accessible reactive hydroxyl groups and the wettability were enhanced for treated cotton fibres, which promoted the inks' wick into the fibres. Interestingly, the penetration of ink droplets between the yarns and fibres after caustic mercerization was decreased, thus the dyes mainly gathered on the surface of cotton fabric. The cotton fibres' cross section structure changed from flat oval to round, which increased the contact area between reactive dyes and fibres. At a certain amount of ink, the optimal K/S value of 23.47 was achieved for treated cotton fabrics, which was higher than that of untreated cotton fabrics (17.15). Meanwhile, the printed fabrics displayed good washing fastness, rubbing fastness and glossiness. This work has important theoretical guiding significance for producing high quality mercerized cotton fabric digital printing products and reducing printing wastewater discharge.

Mercerization can control the crystallinity of cotton fiber, promote the absorption of ink droplets' wick into the fiber and inhibit ink droplets from penetrating the back of fabric. Therefore, the printing quality was extremely enhanced.

Preparation and Characterization of Chinese Leek Extract Incorporated Cellulose Composite Films

This study aimed to prepare microcrystalline cellulose (MCC) films with good mechanical properties via plasticization using a Chinese leek (CL, Allium tuberosum) extract. The microstructure, crystal structure, mechanical properties, barrier ability, and thermal properties of the films were investigated. The chemical structure analysis of CL extract showed the existence of cellulose, lignin, and low-molecular-weight substances, such as polysaccharides, pectins, and waxes, which could act as plasticizers to enhance the properties of MCC:CL biocomposite films. The results of scanning electron microscopy and atomic force microscopy analyses indicated the good compatibility between MCC and CL extract. When the volume ratio of MCC:CL was 7:3, the MCC:CL biocomposite film exhibited the best comprehensive performance in terms of water vapor permeability (2.11 × 10^-10 g/m·s·Pa), elongation at break (13.2 ± 1.8%), and tensile strength (24.7 ± 2.5 MPa). The results of a UV absorption analysis demonstrated that the addition of CL extract improved the UV-shielding performance of the films. Therefore, this work not only proposes a facile method to prepare MCC films with excellent mechanical properties via plasticization using CL extract but also broadens the potential applications of MCC films in the packaging area.

Facile one-step fabrication of all cellulose composites with unique optical performance from wood and bamboo pulp

Cellulosic substrates completely originating from biomass have gained increasing attention for utilization in photoelectric devices due to their biodegradability, sustainability, and renewability. Herein, a simple one-step strategy was used to fabricate transparent (84.2%-90% at 550 nm) all-cellulose composites (ACCs) with customized optical haze (14.7%-83.7% at 550 nm) from wood and bamboo pulp due to their variable solubility. Surface roughness, coagulation bath composition, and the size of the undissolved cellulose fibers contributed to optical haze regulation. Fabricated ACCs demonstrated water resistance, thermal stability, and good mechanical properties. Moreover, an enhancement in the power conversion efficiency of a perovskite solar cell was achieved by simple attachment. Compared with non-sustainable petroleum base materials, ACCs exhibit biodegradability and renewability, which makes the composites promising in large-scale production and various applications due to their tunable haze.

Chemically Functionalized Cellulose Nanocrystals as Reactive Filler in Bio-Based Polyurethane Foams

Cellulose Nanocrystals, CNC, opportunely functionalized are proposed as reactive fillers in bio-based flexible polyurethane foams to improve, mainly, their mechanical properties. To overcome the cellulose hydrophilicity, CNC was functionalized on its surface by linking covalently a suitable bio-based polyol to obtain a grafted-CNC. The polyols grafted with CNC will react with the isocyanate in the preparation of the polyurethane foams. An attractive way to introduce functionalities on cellulose surfaces in aqueous media is silane chemistry by using functional trialkoxy silanes, X-Si (OR)3. Here, we report the synthesis of CNC-grafted-biopolyol to be used as a successful reactive filler in bio-based polyurethane foams, PUFs. The alkyl silanes were used as efficient coupling agents for the grafting of CNC and bio-polyols. Four strategies to obtain CNC-grafted-polyol were fine-tuned to use CNC as an active filler in PUFs. The effective grafting of the bio polyol on CNC was evaluated by FTIR analysis, and the amount of grafted polyol by thermogravimetric analysis. Finally, the morphological, thermal and mechanical properties and hydrophobicity of filled PUFs were thoughtfully assessed as well as the structure of the foams and, in particular, of the edges and walls of the cell foams by means of the Gibson-Ashby model. Improved thermal stability and mechanical properties of PU foams containing CNC-functionalized-polyol are observed. The morphology of the PU foams is also influenced by the functionalization of the CNC.

Temperature-triggered formation of a cellulose II nanocrystal network through regioselective derivatization

The two ends of rodlike cellulose II nanocrystals (CNC-II) were regioselectively functionalized either with gold nanoparticles or thermosensitive polymer chains. In the first case, after the introduction of sulfur atoms at both ends of the rods, CNC-II were labelled using a method based on the in situ nucleation and growth of gold nanoparticles (AuNPs) from soluble derivatives. Transmission electron microscopy (TEM) images showed that such a method resulted in the grafting of one monodisperse AuNP at each extremity of the CNC-II, i.e. to the formation of hybrid dumbbell-shaped objects. No AuNP was detected on the lateral surfaces of the CNC-II and almost all observed CNC-II exhibited this dual labeling. This result confirmed with a good statistics when compared to previous works the possibility to derivatize only the two ends of the CNC-II, thanks to the antiparallel arrangement of cellulose chains in these nanoparticles. In the second case, the localized grafting of temperature-sensitive macromolecules onto the ends of the CNC-II was performed using an oxidation reaction followed by a peptide coupling. This end-specific grafting of thermosensitive chains onto CNC-II enhanced their colloidal stability when the temperature was below the lower critical solution temperature (LCST) of the polymer. Above the LCST, the TEM images revealed the formation of a network extending to tens of microns resulting from end-to-end associations of the derivatized rods through attractive interactions between collapsed polymer chains. Rheology experiments further evidenced a temperature-induced sol-gel transition from a liquid-like (sol) behavior below the LCST to solid-like (gel) behavior above the LCST, in agreement with a change from purely repulsive interactions to interconnections via the hydrophobic collapsed chains. Importantly, all results concurred with a full reversibility of the phenomena upon cooling and reproducibility when samples were subjected to temperature cycles around the LCST. This work reveals that the dual site-specific derivatization of CNC-II can provide symmetric hybrid particles with innovative assembling and macroscopic properties that cannot be obtained through homogeneous chemical modifications.

Facile preparation of all-cellulose composites from softwood, hardwood, and agricultural straw cellulose by a simple route of partial dissolution

In this study, we report a novel, facile, and green method that was used for creating a new all-cellulose composite (ACC) based on inorganic molten salt solvent. Three representatively native fibers from softwood (Pinus kesiya), hardwood (Eucalyptus globulus), and agricultural straw (Zea mays) were selected to verify the effect of the method. The welded sheets were thoroughly characterized and compared. Cellulose sheets from the pine exhibited excellent mechanical properties (σb 16.94 MPa) and thermal stability (T_max 265 °C) after the welding process, while the corn stalk sheets displayed more robust and thermostable features than the eucalyptus. The welding technique using inorganic metal salt hydrate provides a promising and convenient route to obtain firm sheet-materials with micro- or nano-structures from nature fibers.

New insights into the autofluorescence properties of cellulose/nanocellulose

This work explored the fluorescence properties of nano/cellulose isolated from bleached softwood kraft pulp by TEMPO oxidation. Fluorescence spectra showed that all samples exhibited a typical emission peak at 574 nm due to the probabilistic formation of unsaturated bonds by glycosidic bonds independent of lignin. Increasing the excitation wavelengths (510-530 nm) caused red shift of fluorescence emission peaks (570-585 nm) with unchanged fluorescence intensity. Conversely, changing acid/alkaline conditions led to an increase of fluorescence intensity with no shifting of fluorescence emission peak. This can be attributed to an increase in the polarity of the solution environment but does not cause interaction of functional groups within the system identified by generalized two-dimensional correlation fluorescence spectroscopy. This study provides new insight in applying nano/cellulose with special luminous characteristics in biomedicine area such as multi-color biological imaging and chemical sensing.

Biodegradable cellulose I (II) nanofibrils/poly(vinyl alcohol) composite films with high mechanical properties, improved thermal stability and excellent transparency

Cellulose nanofibrils (CNFs) with cellulose I and II allomorphs were efficiently prepared by sulfuric acid hydrolysis of eucalyptus cellulose under three different conditions followed by mechanical treatments: (i) classical sulfuric acid hydrolysis of cellulose I (CNF-I), (ii) sulfuric acid hydrolysis of mercerized cellulose II (MNF-II), and (iii) solubilization and hydrolysis of cellulose I by concentrated sulfuric acid and subsequent recrystallization in water (RNF-II). Crystal structure, surface chemistry, morphology and thermal properties of three CNFs were investigated and compared. Three CNFs of 2-10 wt% were mixed with PVA to prepare biodegradable composite films. CNF allomorph had significant impact on crystal structure, mechanical and thermal properties of the PVA composites. The maximum Young's modulus of CNF-I/PVA, RNF-II/PVA and MNF-II/PVA were increased by 62, 32 and 44%, respectively. Addition of CNFs raised onset degradation temperature (T_onset) and thermal decomposition temperature (T_max) of PVA nanocomposite, while decreased the melting temperature (T_m). Temperature window (T_onset - T_m) for the melt processing of nanocomposites (10 wt% CNF loading) were increased 2.8, 3.2 and 2.5 times for CNF-I/PVA, RNF-II/PVA and MNF-II/PVA, respectively. All composite films remained excellent transparency with addition of CNFs. This comparative study provided important knowledge of selecting CNF allomorph for fabrication of high-performance CNF/PVA composites.

Palladium nanoparticles dispersed on functionalized macadamia nutshell biomass for formic acid-mediated removal of chromium(VI) from aqueous solution

Driven by the need for sustainably sourced catalysts and the use of reaction systems that generate environmentally benign by-products, the present study aimed to deposit stable, dispersed palladium (Pd) nanoparticles on the modified surfaces of granular macadamia nutshell (MNS) biomass for catalytic reduction of hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)). Through wet impregnation with Pd(II) ions and subsequent hydrazine-mediated reduction to Pd(0), Pd nanoparticles were embedded in a scaffold of polyethyleneimine grafted on bleached MNS previously coated with a chemically bound layer of polyglycidyl methacrylate. Imagery from scanning electron microscopy showed the formation of different layers of the polymeric coating and dispersed palladium resulting from surface modification and palladium nanoparticle synthesis, respectively. X-ray diffraction analysis confirmed the formation of Pd on the modified MNS surface and suggested an estimated crystallite size of 5.0 nm. The supported nanoparticles exhibited catalytic activity in formic acid-mediated Cr(VI) reduction and showed promising stability with consecutive reuse. These findings set the stage for advanced studies into performance optimization.

Orienting Cellulose Nanocrystal Functionalities Tunes the Wettability of Water-Cast Films

Cellulose nanocrystal (CNC)-based materials display apparently erratic wetting behaviors with contact angle (CA) variations as large as 30° from sample to sample. This work hypothesizes that it is the orientation of CNC amphiphilic functionalities at the interface with air that causes the variability in CA. By exploiting relationships with the Hansen solubility parameter theory, a set of surface tension parameters is proposed for both the polar and the non-polar surfaces of cellulose I_β nanocrystals. These coefficients elucidate the wettability of CNC materials by establishing a correlation between the wetting properties of the air/sample interface and its chemical composition in terms of non-polar moieties. Advancing/receding CA experiments suggest that, while spin-coating CNC suspensions yield purely polar films, oven-casting them produces amphiphilic surfaces. We proposed a mechanism where the state of dispersion (individual or agglomerated) in which CNCs reach the air/water interface during casting is the determining factor: while individual nanocrystals find it more stable to orient their non-polar surfaces toward the interface, the aspect ratio of CNC agglomerates favors an orientation of their polar surfaces. This represents the first compelling evidence of CNC orientation at an interface and can be applied to Pickering emulsions and nanocomposites and to the production of CNC materials with tuned wettability.

Microwave-assisted alkali hydrolysis for cellulose isolation from wheat straw: Influence of reaction conditions and non-thermal effects of microwave

Microwave-assisted hydrolysis has been widely studied for cellulose fiber isolation, but the influence of reaction conditions and the microwave non-thermal effect are not well clarified. In this study, a series of well-designed experiments were carried out to measure the effects of reaction conditions including temperature, duration and alkali concentration. Compared to the other parameters, temperature was more relevant to the cellulose content in fiber. It could reach the maximum purity of 90.66 % when the temperature was up to 140 °C. Moreover, the existence of non-thermal effect of microwave has been confirmed through extensive determination and characterization of the fibers obtained from parallel controlled experiments conducted with or without microwave assistance. Approximately 50 %-75 % reduction in reaction time or 67 % of that in chemical costs would be realized under microwave with respect to traditional heating hydrolysis. Therefore, this work provides both deep insight and efficiency strategy into the microwave-assisted cellulose isolation.

Patience is a virtue: self-assembly and physico-chemical properties of cellulose nanocrystal allomorphs

Cellulose nanocrystals (CNCs) are bio-based rod-like nanoparticles with a quickly expanding market. Despite the fact that a variety of production routes and starting cellulose sources are employed, all industrially produced CNCs consist of cellulose I (CNC-I), the native crystalline allomorph of cellulose. Here a comparative study of the physico-chemical properties and liquid crystalline behavior of CNCs produced from cellulose II (CNC-II) and typical CNC-I is reported. CNC-I and CNC-II are isolated by sulfuric acid hydrolysis of cotton and mercerized cotton, respectively. The two allomorphs display similar surface charge densities and ζ-potentials and both have a right-handed twist, but CNC-II have a slightly smaller average length and aspect ratio, and are less hygroscopic. Interestingly, the self-assembly behavior of CNC-I and CNC-II in water is different. Whilst CNC-I forms a chiral nematic phase, CNC-II initially phase separates into an upper isotropic and a lower nematic liquid crystalline phase, before a slow reorganization into a large-pitch chiral nematic texture occurs. This is potentially caused by a combination of factors, including the inferred faster rotational diffusion of CNC-II and the different crystal structures of CNC-I and CNC-II, which are responsible for the presence and absence of a giant dipole moment, respectively.

Macro- and Microstructural Evolution during Drying of Regenerated Cellulose Beads

The macro- and microstructural evolution of water swollen and ethanol swollen regenerated cellulose gel beads have been determined during drying by optical microscopy combined with analytical balance measurements, small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS). Two characteristic length scales, which are related to the molecular dimension of cellulose monomer and elongated aggregates of these monomers, could be identified for both types of beads by SAXS. For ethanol swollen beads, only small changes to the structures were detected in both the SAXS and WAXS measurements during the entire drying process. However, the drying of cellulose from water follows a more complex process when compared to drying from ethanol. As water swollen beads dried, they went through a structural transition where elongated structures changed to spherical structures and their dimensions increased from 3.6 to 13.5 nm. After complete drying from water, the nanostructures were characterized as a combination of rodlike structures with an approximate size of cellulose monomers (0.5 nm), and spherical aggregates (13.5 nm) without any indication of heterogeneous meso- or microporosity. In addition, WAXS shows that cellulose II hydrate structure appears and transforms to cellulose II during water evaporation, however it is not possible to determine the degree of crystallinity of the beads from the present measurements. This work sheds lights on the structural changes that occur within regenerated cellulose materials during drying and can aid in the design and application of cellulosic materials as fibers, adhesives, and membranes.

Simple and environmentally friendly preparation of cellulose hydrogels using an ionic liquid

In this study, we developed an easy process for the production of cellulose hydrogels over a wide concentration range by using an ionic liquid/DMSO mixed solution that can easily be recycled at room temperature and has low environmental impact. Cellulose was completely dissolved at 6 to 20 wt% with respect to the [BMIm][OAc]/DMSO mixed solution at room temperature and ambient pressure. Placing the cellulose solution in a mold and immersing it in deionized water caused solvent replacement of the [BMIm][OAc]/DMSO mixed solution with deionized water, making it easy to obtain a cellulose hydrogel without using a crosslinking agent. Approximately 80% of the ionic liquid could be reused by constructing a system that recovers the ionic liquid discharged from the cellulose solution during solvent replacement. The pore size, water content and mechanical strength of the cellulose hydrogel strongly depended on the concentration of the cellulose solution prepared using the [BMIm][OAc]/DMSO mixture. However, the crystallinity and thermal stability did not show a concentration dependence.

Effects of Preparation Method on the Physicochemical Properties of Cationic Nanocellulose and Starch Nanocomposites

Nanocellulose (NC) has attracted attention in recent years for the advantages offered by its unique characteristics. In this study, the effects of the preparation method on the properties of starch films were investigated by preparing NC from cationic-modified microcrystalline cellulose (MD-MCC) using three methods: Acid hydrolysis (AH), high-pressure homogenization (HH), and high-intensity ultrasonication (US). When MD-MCC was used as the starting material, the yield of NC dramatically increased compared to the NC yield obtained from unmodified MCC and the increased zeta potential improved its suspension stability in water. The NC prepared by the different methods had a range of particle sizes and exhibited needle-like structures with high aspect ratios. Fourier transform infrared (FTIR) spectra indicated that trimethyl quaternary ammonium salt groups were introduced to the cellulose backbone during etherification. AH-NC had a much lower maximum decomposition temperature (T_max) than HH-NC or US-NC. The starch/HH-NC film exhibited the best water vapor barrier properties because the HH-NC particles were well-dispersed in the starch matrix, as demonstrated by the surface morphology of the film. Our results suggest that cationic NC is a promising reinforcing agent for the development of starch-based biodegradable food-packaging materials.

Characterization and Cellular Internalization of Spherical Cellulose Nanocrystals (CNC) into Normal and Cancerous Fibroblasts

The aim was to isolate cellulose nanocrystals (CNC) from commercialized oil palm empty fruit bunch cellulose nanofibre (CNF) through sulphuric acid hydrolysis and explore its safeness as a potential nanocarrier. Successful extraction of CNC was confirmed through a field emission scanning electron microscope (FESEM) and attenuated total reflection Fourier transmission infrared (ATR-FTIR) spectrometry analysis. For subsequent cellular uptake study, the spherical CNC was covalently tagged with fluorescein isothiocyanate (FITC), resulting in negative charged FITC-CNC nanospheres with a dispersity (Ð) of 0.371. MTT assay revealed low degree cytotoxicity for both CNC and FITC-CNC against C6 rat glioma and NIH3T3 normal fibroblasts up to 50 µg/mL. FITC conjugation had no contribution to the particle's toxicity. Through confocal laser scanning microscope (CLSM), synthesized FITC-CNC manifested negligible cellular accumulation, indicating a poor non-selective adsorptive endocytosis into studied cells. Overall, an untargeted CNC-based nanosphere with less cytotoxicity that posed poor selectivity against normal and cancerous cells was successfully synthesized. It can be considered safe and suitable to be developed into targeted nanocarrier.

Soft cellulose II nanospheres: sol-gel behaviour, swelling and material synthesis

High axial aspect crystalline nanomaterials have emerged as polymeric building blocks for the construction of supermaterials. In contrast to this form, amorphous nanospheres have remained largely untapped. This is especially peculiar in the context of material assembly, due to the wide range of opportunities they offer by virtue of their soft particle characteristics, high volume ratio at low solid content and their highly swollen and accessible structure. In the context of cellulose, these colloids represent a new field in the family of nanocelluloses. We report an organic solvent-free, heterogeneous and simple synthesis of spherical carboxylated nanoparticles bearing a distinctive, amorphous outer shell structure. The particle shape is evaluated by atomic force microscopy, cryo-transmission electron microscopy, dynamic light scattering and small-angle X-ray scattering. The soft shell structure of the particles and their responsiveness to ionic strength and pH are quantified by the combination of quartz-crystal microgravimetry and atomic force microscopy. Aqueous dispersions of the nanocolloids feature distinctive sol/gel behaviour: at solid content <2 wt% they behave as a low viscous liquid (sol state), whereas at higher concentrations the shells dominate the interparticle interactions, causing an exponential increase in viscosity, typical of a gel state (hydrogel). Gelation is reversible and can be triggered alternatively by protonation of the carboxylate groups under acidic conditions. Supercritical drying of the hydrogels yields a highly porous, isotropic aerogel composed of aggregated nanoparticles. In contrast, ambient drying results in an anisotropic, fully transparent film. These colloids will allow the study of the interaction between soft cellulose and rigid matter, and have high potential as toughening additives in composites. Furthermore, the amorphous nature of this new class of cellulose nanocolloids makes them attractive as support materials for catalysts and enzymes.

Use of CeO₂ Nanoparticles to Enhance UV-Shielding of Transparent Regenerated Cellulose Films

The major challenge in preparing polymer nanocomposites is to prevent the agglomeration of inorganic nanoparticles (NPs). Here, with regenerated cellulose (RC) films as supporting medium, UV-shielding and transparent nanocomposite films with hydrophobicity were fabricated by in situ synthesis of CeO₂ NPs. Facilitated through the interaction between organic and inorganic components revealed by X-ray diffraction (XRD) and Fourier transformation infrared spectroscopy (FTIR) characterization, it was found that CeO₂ NPs were uniformly dispersed in and immobilized by a cellulose matrix. However some agglomeration of CeO₂ NPs occurred at higher precursor concentrations. These results suggest that the morphology and particle size of CeO₂ and the corresponding performance of the resulting films are affected by the porous RC films and the concentrations of Ce(NO₃)₃·6H₂O solutions. The optimized nanocomposite film containing 2.95 wt% CeO₂ NPs had more than 75% light transmittance (550 nm), high UV shielding properties, and a certain hydrophobicity.