Individualization of Nano-Sized Plant Cellulose Fibrils by Direct Surface Carboxylation Using TEMPO Catalyst under Neutral Conditions

Periodate oxidation-mediated nanocelluloses: Preparation, functionalization, structural design, and applications

In recent years, the remarkable progress in nanotechnology has ignited considerable interest in investigating nanocelluloses, an environmentally friendly and sustainable nanomaterial derived from cellulosic feedstocks. Current research primarily focuses on the preparation and applications of nanocelluloses. However, to enhance the efficiency of nanofibrillation, reduce energy consumption, and expand nanocellulose applications, chemical pre-treatments of cellulose fibers have attracted substantial interest and extensive exploration. Various chemical pre-treatment methods yield nanocelluloses with diverse functional groups. Among these methods, periodate oxidation has garnered significant attention recently, due to the formation of dialdehyde cellulose derived nanocellulose, which exhibits great promise for further modification with various functional groups. This review seeks to provide a comprehensive and in-depth examination of periodate oxidation-mediated nanocelluloses (PONCs), including their preparation, functionalization, hierarchical structural design, and applications. We believe that PONCs stand as highly promising candidates for the development of novel nano-cellulosic materials.

Structure-properties relationships of defined CNF single-networks crosslinked by telechelic PEGs

The high structural anisotropy and colloidal stability of cellulose nanofibrils' enable the creation of self-standing fibrillar hydrogel networks at very low solid contents. Adding methacrylate moieties on the surface of TEMPO oxidized CNFs allows the formation of more robust covalently crosslinked networks by free radical polymerization of acrylic monomers, exploiting the mechanical properties of these networks more efficiently. This technique yields strong and elastic networks but with an undefined network structure. In this work, we use acrylate-capped telechelic polymers derived from the step-growth polymerization of PEG diacrylate and dithiothreitol to crosslink methacrylated TEMPO-oxidized cellulose nanofibrils (MATO CNF). This combination resulted in flexible and strong hydrogels, as observed through rheological studies, compression and tensile loading. The structure and mechanical properties of these hydrogel networks were found to depend on the dimensions of the CNFs and polymer crosslinkers. The structure of the networks and the role of individual components were evaluated with SAXS (Small-Angle X-ray Scattering) and photo-rheology. A thorough understanding of hybrid CNF/polymer networks and how to best exploit the capacity of these networks enable further advancement of cellulose-based materials for applications in packaging, soft robotics, and biomedical engineering.

Wood waste-derived dual-mode materials paving the way for year-round energy saving in buildings

In the face of the challenges posed by global warming, traditional methods of building heating and cooling contribute significantly to electricity and coal consumption, thereby emitting considerable amounts of greenhouse gases. Here, a dual-mode thermal management structural material is created by processing sustainable cellulose and lignin derived from wood waste into gels, followed by lamination. The cellulose surface of the material exhibits the ability to scatter solar radiation backward while emitting strongly in the mid-infrared wavelengths, whereas the lignin surface absorbs visible and near-infrared light, primarily releasing energy through non-radiative transitions. Consequently, the material can achieve sub-ambient radiative cooling of 6 °C and solar heating of 27.5 °C during the daytime by simply flipping its orientation. This pioneering material showcases the potential to significantly reduce cooling energy consumption by an average of 18% and heating energy consumption by 42%. Moreover, the integration of a thermal-electric generator within the dual-layer structure optimally utilizes the temperature differential between the two layers, converting it into electrical power. Notably, the dual-mode thermal management structural material exhibits impressive mechanical strength, boasting a flexural strength of 102 MPa, surpassing that of natural wood by over 4.8 times. With its dual-mode functionality and embedded thermal-electric generator, this material represents a crucial step towards achieving both thermal comfort and energy autonomy in sustainable building practices, thereby contributing to a more environmentally friendly and efficient future.

Defect Engineering Centrosymmetric 2D Material Flexocatalysts

In this study, the flexoelectric characteristics of 2D TiO2 nanosheets are examined. The theoretical calculations and experimental results reveal an excellent strain-induced flexoelectric potential (flexopotential) by an effective defect engineering strategy, which suppresses the recombination of electron-hole pairs, thus substantially improving the catalytic activity of the TiO2 nanosheets in the degradation of Rhodamine B dye and the hydrogen evolution reaction in a dark environment. The results indicate that strain-induced bandgap reduction enhances the catalytic activity of the TiO2 nanosheets. In addition, the TiO2 nanosheets degraded Rhodamine B, with kobs being ≈1.5 × 10-2  min-1 in dark, while TiO2 nanoparticles show only an adsorption effect. 2D TiO2 nanosheets achieve a hydrogen production rate of 137.9 µmol g-1  h-1 under a dark environment, 197% higher than those of TiO2 nanoparticles (70.1 µmol g-1  h-1 ). The flexopotential of the TiO2 nanosheets is enhanced by increasing the bending moment, with excellent flexopotential along the y-axis. Density functional theory is used to identify the stress-induced bandgap reduction and oxygen vacancy formation, which results in the self-dissociation of H2 O on the surface of the TiO in the dark. The present findings provide novel insights into the role of TiO2 flexocatalysis in electrochemical reactions.

Mechanochemically functionalized and fibrillated microcrystalline cellulose as a filler in silicone foam: An integrated experimental and simulation investigation

Fibrillated celluloses have gained significant attention due to their exceptional mechanical properties and eco-friendly characteristics, which make them suitable for various applications. In this study, we designed a precise approach for producing highly fibrillated microcrystalline cellulose (MCC) via ball-milling treatment using four typical silane coupling agents. The empirical data demonstrate that the fibrillization of MCC and the properties of fibrillated MCC are largely affected by the size and geometry of the functional groups of the silanes. After ball-milling, most MCC displayed enhanced e-beam tolerance and thermal stability, whereas the silane loading amount, surface area, and morphology of fibrillated MCC appeared to be random, which was exemplified by the proportional and non-proportional relationship between the loading amount and surface area of methyl silane- and phenyl silane-treated MCC, respectively. Density functional theory calculations and molecular dynamics simulations were employed to obtain the intricate details. The simulation results were in agreement with the experimental results. Finally, fibrillated MCC was incorporated into silicone foams as an additive. The thermal stability of fibrillated MCC with added silicone was greatly improved, and the tensile strength of fibrillated MCC-containing silicone foam was 44.1 and 5.4 times higher than that of the neat and MCC-containing silicone foams, respectively.

Advances in natural polysaccharides for gold recovery from e-waste: Recent developments in preparation with structural features

The increasing demand for gold because of its high market price and its wide use in the electronic industry has attracted interest in gold recovery from electronic waste (e-waste). Gold is being dumped as solid e-waste which contains gold concentrations ten times higher than gold ores. Adsorption is a widely used approach for extracting gold from e-waste due to its simplicity, low cost, high efficiency, and reusability of adsorbent material. Natural polysaccharides received increased attention due to their natural abundance, multi-functionality, biodegradability, and nontoxicity. In this review, a brief history, and advancements in this technology were evaluated with recent developments in the preparation and mechanism advancements of natural polysaccharides for efficient gold recovery. Moreover, we have discussed some bifunctional modified polysaccharides with detailed gold adsorption mechanisms. The modified adsorbent materials developed from polysaccharides coupled with inorganic/organic functional groups would demonstrate an efficient technology for the development of new bio-based materials for efficient gold recovery from e-waste. Also, future views are recommended for highlighting the direction to achieve fast and effective gold recovery from e-waste in a friendly and sustainable manner.

Synthesis, characterization, and cytotoxicity studies of nanocellulose extracted from okra (Abelmoschus Esculentus) fiber

Nanocellulose, especially originating from a natural source, has already shown immense potential to be considered in various fields, namely packaging, papermaking, composites, biomedical engineering, flame retardant, and thermal insulating materials, etc. due to its environmental friendliness and novel functionalities. Thus, a thorough characterization of nanocellulose is a hot research topic of research communities in a view to judge its suitability to be used in a specific area. In this work, a kind of green and environment-friendly nanocellulose was successfully prepared from okra fiber through a series of multi-step chemical treatments, specifically, scouring, alkali treatment, sodium chlorite bleaching, and sulfuric acid hydrolysis. Several characterization techniques were adopted to understand the morphology, structure, thermal behavior, crystallinity, and toxicological effects of prepared nanocellulose. Obtained data revealed the formation of rod-shaped nanocellulose and compared to raw okra fiber, their size distributions were significantly smaller. X-ray diffraction (XRD) patterns displayed that compared to the crystalline region, the amorphous region in raw fiber is notably larger, and in obtained nanocellulose, the crystallinity index increased significantly. Moreover, variations in the Fourier transform infrared spectroscopy (FTIR) peaks depicted the successful removal of amorphous regions, namely, lignin and hemicelluloses from the surface of fiber. Thermostability of synthesized nanocellulose was confirmed by both Differential Scanning Calorimetry (DSC) analysis, and thermogravimetric analysis (TGA). Cytotoxicity assessment showed that the okra fiber-derived nanocellulose exhibited lower to moderate cellular toxicity in a dose-dependent manner where the LD50 value was 60.60 μg/ml.

Recent advances in TEMPO-oxidized cellulose nanofibers: Oxidation mechanism, characterization, properties and applications

Cellulose is the richest renewable polymer source on the earth. TEMPO-mediated oxidized cellulose nanofibers are deduced from enormously available wood biomass and functionalized with carboxyl groups. The preparation procedure of TOCNFs is more environmentally friendly compared to other cellulose, for example, MFC and CNCs. Due to the presence of functional carboxyl groups, TOCNF-based materials have been studied widely in different fields, including biomedicine, wastewater treatment, bioelectronics and others. In this review, the TEMPO oxidation mechanism, the properties and applications of TOCNFs are elaborated. Most importantly, the recent advanced applications and the beneficial role of TOCNFs in the various abovementioned fields are discussed. Furthermore, the performances and research progress on the fabrication of TOCNFs are summarized. It is expected that this timely review will help further research on the invention of novel material from TOCNFs and its applications in different advanced fields, including biomedicine, bioelectronics, wastewater treatment, and the energy sector.

Construction of metal-organic framework/cellulose nanofibers-based hybrid membranes and their ion transport property for efficient osmotic energy conversion

The development of advanced nanofluidic membranes with better ion selectivity, efficient energy conversion and high output power density remains challenging. Herein, we prepared nanofluidic hybrid membranes based on TEMPO oxidized cellulose nanofibers (T-CNF) and manganese-based metal organic framework (MOF) using a simple in situ synthesis method. Incorporated T-CNF endows the MOF/T-CNF hybrid membrane with a high cation selectivity up to 0.93. Nanoporous MOF in three-dimensional interconnected nanochannels provides massive ion transport pathways. High transmembrane ion flux and low ion permeation energy barrier are correlated with a superior energy conversion efficiency (36 %) in MOF/T-CNF hybrid membrane. When operating under 50-fold salinity gradient by mixing simulated seawater and river water, the MOF/T-CNF hybrid membrane achieves a maximum power density value of 1.87 W m-2. About 5-fold increase in output power density was achieved compared to pure T-CNF membrane. The integration of natural nanofibers with high charge density and nanoporous MOF materials is demonstrated an effective and novel strategy for the enhancement of output power density of nanofluidic membranes, showing the great potential of MOF/T-CNF hybrid membranes as efficient nanofluidic osmotic energy generators.

Rapid, in situ synthesis of ultra-small silicon particles for boosted lithium storage capability through ultrafast Joule heating

High-capacity anodes, especially silicon, suffer from huge volume fluctuations and electrode material pulverization during lithiation/delithiation. An accessible solution to this issue is to construct nano-silicon anodes with optimized particle size and a conductive matrix. In this work, we introduce a novel strategy for the in situ, rapid synthesis of ultra-small silicon nanoparticles uniformly embedded within carbonized nanosheets (us-Si/C) through swift high-temperature thermal radiative heating of sizable silicon nanoparticles (SiNPs). The us-Si/C anode shows ample capability to accommodate volume fluctuations during the lithiation/delithiation processes. The as-prepared anode exhibits a specific capacity of 920 mA h g-1 after 1000 cycles at a current density of 2 A g-1, indicating the advantages of the well-tailored structure. Additionally, the us-Si/C electrode can maintain an areal capacity of approximately 1.55 mA h cm-2 after 200 cycles at a high loading of 3.66 mg cm-2. Moreover, it presents practical applicability when assembled into LFP (lithium iron phosphate)//us-Si/C full cells. This preparation method presents great promise for achieving roll-to-roll manufacturing for practical applications due to its simplicity and efficiency.

Synergistically regulating the separator pore structure and surface property toward dendrite-free and high-performance aqueous zinc-ion batteries

As an emerging electrochemical device, aqueous zinc-ion batteries (ZIBs) present promising potential in safe and large-scale energy storage. However, the large pores of commercial glass fiber (GF) separators result in uneven Zn2+ ion flux, leading to severe dendrite growth issues of Zn metal anodes. Herein, we integrated a multifunctional layer on the GF separator that can synergistically regulate the pore feature and surface property of commercial GF separators. Such modification layer, composed of nanocellulose and SiO2 nanoparticles, exhibited uniform nanoporous structure and abundant negatively charged polar functional groups. These features allow regulating the distribution of Zn2+ ions at the separator-anode interface, facilitating stable and uniform Zn nucleation and growth. Moreover, the electrostatic interaction between the negatively charged functional groups and Zn2+ ions enhanced the Zn2+ ion transport kinetics, preventing the Zn dendrites formation and adverse reactions. Consequently, the modified electrolyte-filled GF separator showed an increased Zn2+ ion transference number of 0.65. The symmetric Zn//Zn batteries utilizing such a separator achieved an impressive cycling life of 500 h at a high current density/capacity of 10 mA cm-2/4 mAh cm-2, nearly nine times longer than the battery using the unmodified GF separator (<55 h). The superior electrochemical performance was verified in both Zn//AC and Zn//LiMn2O4 full battery evaluations. This work presents a novel synergistic modification strategy for developing advanced separators for aqueous ZIBs.

Hornification of cellulose-rich materials - A kinetically trapped state

The fundamental understanding concerning cellulose-cellulose interactions under wet and dry conditions remains unclear. This is especially true regarding the drying-induced association of cellulose, commonly described as an irreversible phenomenon called hornification. A fundamental understanding of the mechanisms behind hornification would contribute to new drying techniques for cellulose-based materials in the pulp and paper industry while at the same time enhancing material properties and facilitating the recyclability of cellulose-rich materials. In the present work, the irreversible joining of cellulose-rich surfaces has been studied by subjecting cellulose nanofibril (CNF) films to different heat treatments to establish a link between reswelling properties, structural characteristics as well as chemical and mechanical analyses. A heating time/temperature dependence was observed for the reswelling of the CNF films, which is related to the extent of hornification and is different for different chemical compositions of the fibrils. Further, the results indicate that hornification is related to a diffusion process and that the reswellability increases very slowly over long time, indicating that equilibrium is not reached. Hence, hornification is suggested to be a kinetically limited phenomenon governed by non-covalent reversible interactions and a time/temperature dependence on their forming and breaking.

Shape-recovering nanocellulose networks: Preparation, characterization and modeling

Development of strong cellulose nanofibril (CNF) networks for advanced applications, such as in the biomedical field, is of high importance owing to the biocompatible nature and plant-based origin of cellulose nanofibrils. Nevertheless, lack of mechanical strength and complex synthesis methods hinder the application of these materials in areas where both toughness and manufacturing simplicity are required. In this work, we introduce a facile method for the synthesis of a low solid content (< 2 wt%), covalently crosslinked CNF hydrogel where Poly (N-isopropylacrylamide) (NIPAM) chains are utilized as crosslinks between the nanofibrils. The resulting networks have the capability to fully recover the shape in which they were formed after various drying and rewetting cycles. Characterization of the hydrogel and its constitutive components was performed using X-ray scattering, rheological investigations and uniaxial testing in compression. Influence of covalent crosslinks was compared with networks crosslinked by the addition of CaCl₂. Among other things the results show that the mechanical properties of the hydrogels can be tuned by controlling the ionic strength of the surrounding medium. Finally, a mathematical model was developed based on the experimental results, which describes and predicts to a decent degree the large-deformation, elastoplastic behavior, and fracture of these networks.

Harnessing Nature's Ingenuity: A Comprehensive Exploration of Nanocellulose from Production to Cutting-Edge Applications in Engineering and Sciences

Primary material supply is the heart of engineering and sciences. The depletion of natural resources and an increase in the human population by a billion in 13 to 15 years pose a critical concern regarding the sustainability of these materials; therefore, functionalizing renewable materials, such as nanocellulose, by possibly exploiting their properties for various practical applications, has been undertaken worldwide. Nanocellulose has emerged as a dominant green natural material with attractive and tailorable physicochemical properties, is renewable and sustainable, and shows biocompatibility and tunable surface properties. Nanocellulose is derived from cellulose, the most abundant polymer in nature with the remarkable properties of nanomaterials. This article provides a comprehensive overview of the methods used for nanocellulose preparation, structure-property and structure-property correlations, and the application of nanocellulose and its nanocomposite materials. This article differentiates the classification of nanocellulose, provides a brief account of the production methods that have been developed for isolating nanocellulose, highlights a range of unique properties of nanocellulose that have been extracted from different kinds of experiments and studies, and elaborates on nanocellulose potential applications in various areas. The present review is anticipated to provide the readers with the progress and knowledge related to nanocellulose. Pushing the boundaries of nanocellulose further into cutting-edge applications will be of particular interest in the future, especially as cost-effective commercial sources of nanocellulose continue to emerge.

Carbon and Cellulose-Based Nanoparticle-Reinforced Polymer Nanocomposites: A Critical Review

Nanomaterials are currently used for different applications in several fields. Bringing the measurements of a material down to nanoscale size makes vital contributions to the improvement of the characteristics of materials. The polymer composites acquire various properties when added to nanoparticles, increasing characteristics such as bonding strength, physical property, fire retardance, energy storage capacity, etc. The objective of this review was to validate the major functionality of the carbon and cellulose-based nanoparticle-filled polymer nanocomposites (PNC), which include fabricating procedures, fundamental structural properties, characterization, morphological properties, and their applications. Subsequently, this review includes arrangement of nanoparticles, their influence, and the factors necessary to attain the required size, shape, and properties of the PNCs.

Visual Colorimetric Detection of Edible Oil Freshness for Peroxides Based on Nanocellulose

Traditional methods for evaluating the edibility of lipids involve the use of organic reagents and complex operations, which limit their routine use. In this study, nanocellulose was prepared from bamboo, and a colorimetric reading strategy based on nanocellulose composite hydrogels was explored to monitor the freshness of edible oils. The hydrogels acted as carriers for peroxide dyes that changed color according to the freshness of the oil, and color information was digitized using UV-vis and RGB analysis. The sensitivity and accuracy of the hydrogel were verified using H₂O₂, which showed a linear relationship between absorbance and H₂O₂ content in the range of 0-0.5 and 0.5-11 mmol/kg with R² of 0.9769 and 0.9899, respectively, while the chromatic parameter showed an exponential relationship with R² of 0.9626. Surprisingly, the freshness of all seven edible oil samples was correctly identified by the hydrogel, with linear correlation coefficients greater than 0.95 in the UV-vis method and exponential correlation coefficients greater than 0.92 in the RGB method. Additionally, a peroxide value color card was established, with an accuracy rate of 91.67%. This functional hydrogel is expected to be used as a household-type oil freshness indicator to meet the needs of general consumers.

Nanolatex architectonics: Influence of cationic charge density and size on their adsorption onto surfaces with a 2D or 3D distribution of anionic groups

HYPOTHESIS

It is theoretically predicted and hypothesized that the charge density and size of spherical nanoparticles are the key factors for their adsorption onto oppositely charged surfaces. It is also hypothesized that the morphology and charge of the surface are of great importance. In-plane 2D (silica) or a volumetric 3D (regenerated TEMPO-oxidized cellulose model surfaces) distribution of charged groups is expected to influence charge compensation and, thus, the adsorption behavior.

EXPERIMENTS

In this work, self-stabilized nanolatexes with a range of cationic charge densities and sizes were synthesized through reversible addition - fragmentation chain-transfer (RAFT) polymerization coupled with polymerization-induced self-assembly (PISA). Their adsorption onto silica and anionic cellulose model surfaces was investigated using stagnation point adsorption reflectometry (SPAR) and quartz crystal microbalance with dissipation (QCM-D).

FINDINGS

Experiments and theory agree and show that the size of the nanolatex and the difference in charge density compared to the substrate determine the charge compensation and, thus, the surface coverage. Highly charged or large nanolatexes overcompensate the surface charge of non-porous substrates leading to a significant repulsive zone where other particles cannot adsorb. For porous substrates like cellulose, the vertical distribution of charged groups in the 3D volume prevents overcompensation and thus increases the adsorption. This systematic study investigates the isolated effect of surface charge and size and paves the way for on-demand particles specifically designed for a surface with particular characteristics.

Six weeks effect of different nanocellulose on blood lipid level and small intestinal morphology in mice

AIMS

Cellulose nanofibrils (CNF, or NFC), cellulose nanocrystals (CNC, or NCC), and Tempo (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidized CNF (Tempo-CNF) were compared for the short-term effect on mice fed with a high-fat and high-sugar (Western diet, WD) to investigate their effect when combined with a sub-optimal diet.

SCOPE

Thirty C57B/C female mice (10 weeks old; 5-6 mice/group) were given water, cellulose, or three types of nanocellulose once daily in a dose of 30 mg/kg body weight by oral gavage. After six weeks, weight changes, fecal output, glucose homeostasis, and gut permeability showed no significant among groups. Serum analysis including triglycerides, cholesterol and total bile acids and small intestinal morphology including villus length, villus width, crypt depth, goblet cell count and goblet cell density were no difference for all groups. Only CNC group had higher excretion of bile acids in the feces.

CONCLUSIONS

These results suggest that current treated dose using three types of nanocellulose had no detrimental effects on blood lipid level and small intestinal morphology.

An All-Natural Wood-Inspired Aerogel

The oriented pore structure of wood endows it with a variety of outstanding properties, among which the low thermal conductivity has attracted researchers to develop wood-like aerogels as excellent thermal insulation materials. However, the increasing demands of environmental protection have put forward new and strict requirements for the sustainability of aerogels. Here, we report an all-natural wood-inspired aerogel consisting of all-natural ingredients and develop a method to activate the surface-inert wood particles to construct the aerogel. The obtained wood-inspired aerogel has channel structure similar to that of natural wood, endowing it with superior thermal insulation properties to most existing commercial sponges. In addition, remarkable fire retardancy and complete biodegradability are integrated. With the above outstanding performances, this sustainable wood-inspired aerogel will be an ideal substitute for the existing commercial thermal insulation materials.

Comparison of pre-treatments mediated by endoglucanase and TEMPO oxidation for eco-friendly low-cost energy production of cellulose nanofibrils

Specific kinds of enzymes have been used as an eco-friendly pre-treatment for mechanical extraction of cellulose nanofibrils (CNFs) from vegetal pulps. Another well-established pre-treatment is the 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-mediated oxidation, which has gained considerable attention. Pre-treatments assist in fiber swelling, facilitating mechanical fibrillation, and reducing energy consumption; however, some of these methods are extremely expensive. This work aimed to evaluate the influence of enzymatic pre-treatment with endoglucanase on the energy consumption during mechanical fibrillation of cellulose pulps. Bleached pulps from Eucalyptus sp. and Pinus sp. were pre-treated with endoglucanase enzyme compared to TEMPO-meditated oxidation. Average diameters of CNFs pre-treated with enzymes were close to that found for TEMPO-oxidized nanofibrils (TOCNFs). Results showed that enzymatic pre-treatment did not significantly modify the pulp chemical and morphological characteristics with efficient stabilization of the CNFs suspension at higher supernatant turbidity. Energy consumption of pulps treated with endoglucanase enzymes was lower than that shown by pulps treated with TEMPO, reaching up to 58% of energy savings. The enzyme studied in the pulp treatment showed high efficiency in reducing energy consumption during mechanical fibrillation and production of films with high mechanical quality, being an eco-friendly option for pulp treatment.

Spatioselective surface chemistry for the production of functional and chemically anisotropic nanocellulose colloids

Maximizing the benefits of nanomaterials from biomass requires unique considerations associated with their native chemical and physical structure. Both cellulose nanofibrils and nanocrystals are extracted from cellulose fibers via a top-down approach and have significantly advanced materials chemistry and set new benchmarks in the last decade. One major challenge has been to prepare defined and selectively modified nanocelluloses, which would, e.g., allow optimal particle interactions and thereby further improve the properties of processed materials. At the molecular and crystallite level, the surface of nanocelluloses offers an alternating chemical structure and functional groups of different reactivity, enabling straightforward avenues towards chemically anisotropic and molecularly patterned nanoparticles via spatioselective chemical modification. In this review, we will explain the influence and role of the multiscale hierarchy of cellulose fibers in chemical modifications, and critically discuss recent advances in selective surface chemistry of nanocelluloses. Finally, we will demonstrate the potential of those chemically anisotropic nanocelluloses in materials science and discuss challenges and opportunities in this field.

Printing Structurally Anisotropic Biocompatible Fibrillar Hydrogel for Guided Cell Alignment

Many fibrous biological tissues exhibit structural anisotropy due to the alignment of fibers in the extracellular matrix. To study the impact of such anisotropy on cell proliferation, orientation, and mobility, it is important to recapitulate and achieve control over the structure of man-made hydrogel scaffolds for cell culture. Here, we report a chemically crosslinked fibrous hydrogel due to the reaction between aldehyde-modified cellulose nanofibers and gelatin. We explored two ways to induce structural anisotropy in this gel by extruding the hydrogel precursor through two different printheads. The cellulose nanofibers in the hydrogel ink underwent shear-induced alignment during extrusion and retained it in the chemically crosslinked hydrogel. The degree of anisotropy was controlled by the ink composition and extrusion flow rate. The structural anisotropy of the hydrogel extruded through a nozzle affected the orientation of human dermal fibroblasts that were either seeded on the hydrogel surface or encapsulated in the extruded hydrogel. The reported straightforward approach to constructing fibrillar hydrogel scaffolds with structural anisotropy can be used in studies of the biological impact of tissue anisotropy.

Enhancing the Matrix-Fiber Interface with a Surfactant Leads to Improved Performance Properties of 3D Printed Composite Materials Containing Cellulose Nanofibrils

Cellulose nanofibrils (CNFs) exhibit characteristics that make them a desirable addition to new composite materials. CNFs are usable in a wide variety of applications such as coatings, personal and healthcare products, packaging, and advanced structural materials. They can also help overcome some performance issues with objects 3D printed by stereolithography (SLA) including dimensional instability and poor mechanical properties. However, CNFs are hydrophilic, making their dispersion in hydrophobic resins common to SLA difficult. Therefore, improvement of performance properties will not be fully realized. In this work, we treated TEMPO-oxidized CNFs (TOCNFs) with the hydrochloride salt of lauroyl arginate ethyl ester (LAE·HCl), a cationic surfactant, to investigate how this coating would affect the performance properties of multicomponent uncured SLA resins and subsequently printed objects. We hypothesized this coating would enhance the dispersion of the cellulose nanomaterials when compared to their uncoated counterparts, which would lead to quantifiable differences among the sample groups. We found that the viscosity of a commercial 3D printing resin (0.34 Pa·s at 30 Hz) increased by nearly an order of magnitude upon addition of even 1 wt % uncoated TOCNFs (2.96 Pa·s at 30 Hz). Moreover, the tensile strength (19.9(5) MPa) and modulus (0.65(5) GPa) of objects printed from the commercial resin decreased when adding 4 wt % uncoated TOCNF (12.5(2) MPa and 0.58(8) GPa, respectively). In contrast, resins having 4 wt % TOCNFs coated with LAE were less viscous (1.25 Pa·s at 30 Hz), and objects printed from them had enhanced tensile strength (24.7(7) MPa) and modulus (0.78(8) GPa) when compared to both the unadulterated resin and that having uncoated TOCNFs. Our findings show the general utility of using a surfactant with cellulose nanomaterials to homogenize multicomponent resins for 3D printing composite materials with enhanced performance properties.

Characteristics of Cellulose Nanofibrils from Transgenic Trees with Reduced Expression of Cellulose Synthase Interacting 1

Cellulose nanofibrils can be derived from the native load-bearing cellulose microfibrils in wood. These microfibrils are synthesized by a cellulose synthase enzyme complex that resides in the plasma membrane of developing wood cells. It was previously shown that transgenic hybrid aspen trees with reduced expression of CSI1 have different wood mechanics and cellulose microfibril properties. We hypothesized that these changes in the native cellulose may affect the quality of the corresponding nanofibrils. To test this hypothesis, wood from wild-type and transgenic trees with reduced expression of CSI1 was subjected to oxidative nanofibril isolation. The transgenic wood-extracted nanofibrils exhibited a significantly lower suspension viscosity and estimated surface area than the wild-type nanofibrils. Furthermore, the nanofibril networks manufactured from the transgenics exhibited high stiffness, as well as reduced water uptake, tensile strength, strain-to-break, and degree of polymerization. Presumably, the difference in wood properties caused by the decreased expression of CSI1 resulted in nanofibrils with distinctive qualities. The observed changes in the physicochemical properties suggest that the differences were caused by changes in the apparent nanofibril aspect ratio and surface accessibility. This study demonstrates the possibility of influencing wood-derived nanofibril quality through the genetic engineering of trees.

Atomic-scale dents on cellulose nanofibers: the origin of diverse defects in sustainable fibrillar materials

Atomic-scale dent structures on the surfaces of cellulose nanofibers were detected by comparing the experimentally measured and computer-simulated widths of single nanofibers. These dent parts constituted at least 30-40% of the total length of the dispersed nanofibers, and deep dents induced the kinking and fragmentation of nanofibers.

A Review of Properties of Nanocellulose, Its Synthesis, and Potential in Biomedical Applications

Cellulose is the most venerable and essential natural polymer on the planet and is drawing greater attention in the form of nanocellulose, considered an innovative and influential material in the biomedical field. Because of its exceptional physicochemical characteristics, biodegradability, biocompatibility, and high mechanical strength, nanocellulose attracts considerable scientific attention. Plants, algae, and microorganisms are some of the familiar sources of nanocellulose and are usually grouped as cellulose nanocrystal (CNC), cellulose nanofibril (CNF), and bacterial nanocellulose (BNC). The current review briefly highlights nanocellulose classification and its attractive properties. Further functionalization or chemical modifications enhance the effectiveness and biodegradability of nanocellulose. Nanocellulose-based composites, printing methods, and their potential applications in the biomedical field have also been introduced herein. Finally, the study is summarized with future prospects and challenges associated with the nanocellulose-based materials to promote studies resolving the current issues related to nanocellulose for tissue engineering applications.

Effect of Surface Modification on the Pulmonary and Systemic Toxicity of Cellulose Nanofibrils

Cellulose nanofibrils (CNFs) have emerged as sustainable options for a wide range of applications. However, the high aspect ratio and biopersistence of CNFs raise concerns about potential health effects. Here, we evaluated the in vivo pulmonary and systemic toxicity of unmodified (U-CNF), carboxymethylated (C-CNF), and TEMPO (2,2,6,6-tetramethyl-piperidin-1-oxyl)-oxidized (T-CNF) CNFs, fibrillated in the same way and administered to mice by repeated (3×) pharyngeal aspiration (14, 28, and 56 μg/mouse/aspiration). Toxic effects were assessed up to 90 days after the last administration. Some mice were treated with T-CNF samples spiked with lipopolysaccharide (LPS; 0.02-50 ng/mouse/aspiration) to assess the role of endotoxin contamination. The CNFs induced an acute inflammatory reaction that subsided within 90 days, except for T-CNF. At 90 days post-administration, an increased DNA damage was observed in bronchoalveolar lavage and hepatic cells after exposure to T-CNF and C-CNF, respectively. Besides, LPS contamination dose-dependently increased the hepatic genotoxic effects of T-CNF.

Highly TEMPO-oxidized cellulose for removal of ionic and complexed cadmium from a complicated water system

TEMPO-NaDCC-oxidized cellulose (TNOCS) with a large surface area and an abundance of carboxyl groups was used to remove heavy metal ions (Cd, Cu, and Pb) and their organic acid complexes [HM-OAs] (OAs, i.e., citric acid (CA) and propionic acid (PA)), and then reveal their adsorption behaviors. Taking Cd and CA as examples, the results showed that some of Cd ions were first adsorbed onto TNOCS, and then, the existence of [Cd-CA^-] complexes formed a coordinated structure with preloaded Cd ions to serve as a bridge for combining TNOCS and [Cd-CA]. The maximum adsorption capacities of TNOCS for Cd and Cd-CA were 16.50 and 22.15 mg/g, respectively. Moreover, adsorption energies and molecular orbital distributions indicated that the adsorption capacity of TNOCS for [Cd-CA] was better than that for Cd alone. TNOCS can maintain greater than 90% adsorption capacity in five times regeneration experiments using EDTA, indicating that it is very efficient and stable. In addition, the electron density, deformation charge, and Mulliken charge distribution were confirmed that the electron transfer direction was from carboxyl groups to cadmium, whether it was cadmium ions or complexed cadmium.

Surface functionalization and size modulate the formation of reactive oxygen species and genotoxic effects of cellulose nanofibrils

BACKGROUND

Cellulose nanofibrils (CNFs) have emerged as a sustainable and environmentally friendly option for a broad range of applications. The fibrous nature and high biopersistence of CNFs call for a thorough toxicity assessment, but it is presently unclear which physico-chemical properties could play a role in determining the potential toxic response to CNF. Here, we assessed whether surface composition and size could modulate the genotoxicity of CNFs in human bronchial epithelial BEAS-2B cells. We examined three size fractions (fine, medium and coarse) of four CNFs with different surface chemistry: unmodified (U-CNF) and functionalized with 2,2,6,6-tetramethyl-piperidin-1-oxyl (TEMPO) (T-CNF), carboxymethyl (C-CNF) and epoxypropyltrimethylammonium chloride (EPTMAC) (E-CNF). In addition, the source fibre was also evaluated as a non-nanosized material.

RESULTS

The presence of the surface charged groups in the functionalized CNF samples resulted in higher amounts of individual nanofibrils and less aggregation compared with the U-CNF. T-CNF was the most homogenous, in agreement with its high surface group density. However, the colloidal stability of all the CNF samples dropped when dispersed in cell culture medium, especially in the case of T-CNF. CNF was internalized by a minority of BEAS-2B cells. No remarkable cytotoxic effects were induced by any of the cellulosic materials. All cellulosic materials, except the medium fraction of U-CNF, induced a dose-dependent intracellular formation of reactive oxygen species (ROS). The fine fraction of E-CNF, which induced DNA damage (measured by the comet assay) and chromosome damage (measured by the micronucleus assay), and the coarse fraction of C-CNF, which produced chromosome damage, also showed the most effective induction of ROS in their respective size fractions.

CONCLUSIONS

Surface chemistry and size modulate the in vitro intracellular ROS formation and the induction of genotoxic effects by fibrillated celluloses. One cationic (fine E-CNF) and one anionic (coarse C-CNF) CNF showed primary genotoxic effects, possibly partly through ROS generation. However, the conclusions cannot be generalized to all types of CNFs, as the synthesis process and the dispersion method used for testing affect their physico-chemical properties and, hence, their toxic effects.

Low-filled suspensions of α-chitin nanorods for electrorheological applications

Highly anisometric α-chitin nanoparticles isolated by TEMPO-oxidation were investigated as filler for electrorheological fluids. The dimensions of rod-like particles were determined by AFM and cryo-TEM methods. The rheological behavior of α-chitin nanoparticles in polydimethylsiloxane changes from viscous to elastic under electric field. The yield stress reaches about 220 Pa at 7 kV/mm for 1.0 wt% fluid. Despite the nanosize of particles, the suspensions sedimentation ratio was found to be low (~23%). The electrorheological behavior of the fluids was discussed in terms of the Mason numbers. The stability of fluids response under switching electric field was shown. The activation energy of polarization processes in suspensions was calculated as 58 ± 2 and 64 ± 1 kJ/mol for 0.5 and 1.0 wt% filler content from the impedance spectra. The high aspect ratio (~70) and dielectric permittivity result in high electrorheological activity of α-chitin suspensions at extremely low concentrations (≤1.0 wt%).

Cavitation Fibrillation of Cellulose Fiber

Cellulose fibrils are the structural backbone of plants and, if carefully liberated from biomass, a promising building block for a bio-based society. The mechanism of the mechanical release─fibrillation─is not yet understood, which hinders efficient production with the required reliable quality. One promising process for fine fibrillation and total fibrillation of cellulose is cavitation. In this study, we investigate the cavitation treatment of dissolving, enzymatically pretreated, and derivatized (TEMPO oxidized and carboxymethylated) cellulose fiber pulp by hydrodynamic and acoustic (i.e., sonication) cavitation. The derivatized fibers exhibited significant damage from the cavitation treatment, and sonication efficiently fibrillated the fibers into nanocellulose with an elementary fibril thickness. The breakage of cellulose fibers and fibrils depends on the number of cavitation treatment events. In assessing the damage to the fiber, we presume that microstreaming in the vicinity of imploding cavities breaks the fiber into fibrils, most likely by bending. A simple model showed the correlation between the fibrillation of the carboxymethylated cellulose (CMCe) fibers, the sonication power and time, and the relative size of the active zone below the sonication horn.

Delignified wood aerogels as scaffolds coated with an oriented chitosan–cyclodextrin co-polymer for removal of microcystin-LR

Nano-porous aerogels are an advantageous approach to produce low-density materials with high surface area, particularly when using biobased materials. Frequently, most biobased aerogels are synthesized through a bottom-up approach, which requires high energy inputs to break and rebuild the raw materials, and for elimination of water. To curb this, this work focused on generating aerogels by a top-down approach through the delignification of a wood substrate while eliminating water by solvent exchange. To diversify the surface chemistry for use in water treatment, the delignified wood–nanowood-was coated with a chitosan–cyclodextrin co-polymer and tested in the capture of microcystin-LR. The generated nanowood structure had 75% porosity after coating, with up to 339% water swelling and an adsorption capacity of 0.12 mg g⁻¹ of the microcystin. This top-down technique enables the generation of low-cost aerogels by reducing steps, using a biobased self-assembled coating with hydrophobic active sites, and avoiding costly energetic input.

Herein, a preassembled chitosan-cyclodextrin was used as a versatile coating onto delignified wood as an alternative for the removal of microcystin-LR. The addition of β-cyclodextrin proved to allow the nanowood scaffold to adsorb up to 0.12 mg g⁻¹.

Mechanical properties of cellulose nanofibril papers and their bionanocomposites: A review

Cellulose nanofibril (CNF) paper has various applications due to its unique advantages. Herein, we present the intrinsic mechanical properties of CNF papers, along with the preparation and properties of nanoparticle-reinforced CNF composite papers. The literature on CNF papers reveals a strong correlation between the intrafibrillar network structure and the resulting mechanical properties. This correlation is found to hold for all primary factors affecting mechanical properties, indicating that the performance of CNF materials depends directly on and can be tailored by controlling the intrafibrillar network of the system. The parameters that influence the mechanical properties of CNF papers were critically reviewed. Moreover, the effect on the mechanical properties by adding nanofillers to CNF papers to produce multifunctional composite products was discussed. We concluded this article with future perspectives and possible developments in CNFs and their bionanocomposite papers.

Efficient homogeneous TEMPO-mediated oxidation of cellulose in lithium bromide hydrates

An appropriate cellulose-dissolving solvent is critical for the homogeneous oxidation of cellulose using TEMPO (2, 2, 6, 6-tetramethylpiperidine-1-oxyl)-mediated system. Herein, TEMPO/NaClO/NaClO₂ system in lithium bromide hydrates (LBHs) was developed for the homogeneous selective-oxidation of cellulose, which was two-stage protocol involving cellulose dissolution and homogeneous oxidation. Specifically, cellulose was firstly dissolved in LiBr·3.5H₂O and offered the optimal pH (5.6) for the subsequent TEMPO/NaClO/NaClO₂ oxidation without precipitation of the cellulose chains. Effect of reaction conditions on cellulose oxidation was investigated. The results showed that high degree of oxidation (DO) and evenly distributed carboxyl could be achieved. The particle size gradually decreased with DO, and oxidized cellulose with high water solubility and amorphous structure could be obtained. Furthermore, FT-IR, ¹³C NMR and fractionation analysis verified that cellulose was successfully converted and the carboxyl uniformly distributed onto the cellulose chains. This TEMPO-mediated system using LBHs as solvent presented an efficient method on the homogeneous selective oxidation of primary hydroxyl in cellulose.

Synthesis, Characterization, and Antifungal Activity of Silver Nanoparticles Embedded in Pullulan Matrices

Steady developments made in nanotechnology-based products have facilitated new perspectives for combating drug-resistant fungi. Silver nanoparticles represent one of the most attractive nanomaterials in biomedicine due to their exclusive optical, electromagnetic, and catalytic properties and antifungal potency compared with other metal nanoparticles. Most studies show that the physicochemical parameters affecting the antifungal potential of AgNPs include the shape, size, surface charge, and concentration and colloidal state. For the present study, pullulan (P) and its oxidized counterpart (PO) have been selected as matrices for the silver nanoparticles’ generation and stabilization (AgNPs). The TEMPO (2,2,6,6-tetramethylpiperidin-1-yl radical)–sodium hypochlorite–sodium bromide system was used for the C6 selective oxidation of pullulan in order to introduce negatively charged carboxylic groups in its structure. The structure and morphology of the synthesized AgNPs were analyzed using FTIR and EDX. The main objective of this study was to elucidate the antifungal activity of AgNPs on the clinical yeasts isolates and compare the performance of AgNPs with the conventional antifungals. In this study, different concentrations of AgNPs were tested to examine antifungal activity on various clinical isolates.

Plant Cellulose Nanofiber-Derived Structural Material with High-Density Reversible Interaction Networks for Plastic Substitute

Ubiquitous petrochemical-based plastics pose a potential threat to ecosystems. In response, bioderived and degradable polymeric materials are being developed, but their mechanical and thermal properties cannot compete with those of existing petrochemical-based plastics, especially those used as structural materials. Herein, we report a biodegradable plant cellulose nanofiber (CNF)-derived polymeric structural material with high-density reversible interaction networks between nanofibers, exhibiting mechanical and thermal properties better than those of existing petrochemical-based plastics. This all-green material has substantially improved flexural strength (∼300 MPa) and modulus (∼16 GPa) compared with those of existing petrochemical-based plastics. Its average thermal expansion coefficient is only 7 × 10^-6 K^-1, which is more than 10 times lower than those of petrochemical-based plastics, indicating its dimension is almost unchanged when heated, and thus, it has a thermal dimensional stability that is better than those of plastics. As a fully bioderived and degradable material, the all-green material offers a more sustainable high-performance alternative to petrochemical-based plastics.

Assembling Native Elementary Cellulose Nanofibrils via a Reversible and Regioselective Surface Functionalization

Selective surface modification of biobased fibers affords effective individualization and functionalization into nanomaterials, as exemplified by the TEMPO-mediated oxidation. However, such a route leads to changes of the native surface chemistry, affecting interparticle interactions and limiting the development of potential supermaterials. Here we introduce a methodology to extract elementary cellulose fibrils by treatment of biomass with N-succinylimidazole, achieving regioselective surface modification of C6-OH, which can be reverted using mild post-treatments. No polymer degradation, cross-linking, nor changes in crystallinity occur under the mild processing conditions, yielding cellulose nanofibrils bearing carboxyl moieties, which can be removed by saponification. The latter offers a significant opportunity in the reconstitution of the chemical and structural interfaces associated with the native states. Consequently, 3D structuring of native elementary cellulose nanofibrils is made possible with the same supramolecular features as the biosynthesized fibers, which is required to unlock the full potential of cellulose as a sustainable building block.

Recent Advances in Cellulose Nanofibers Preparation through Energy-Efficient Approaches: A Review

Cellulose nanofibers (CNFs) and their applications have recently gained significant attention due to the attractive and unique combination of their properties including excellent mechanical properties, surface chemistry, biocompatibility, and most importantly, their abundance from sustainable and renewable resources. Although there are some commercial production plants, mostly in developed countries, the optimum CNF production is still restricted due to the expensive initial investment, high mechanical energy demand, and high relevant production cost. This paper discusses the development of the current trend and most applied methods to introduce energy-efficient approaches for the preparation of CNFs. The production of cost-effective CNFs represents a critical step for introducing bio-based materials to industrial markets and provides a platform for the development of novel high value applications. The key factor remains within the process and feedstock optimization of the production conditions to achieve high yields and quality with consistent production aimed at cost effective CNFs from different feedstock.

Review on Nonconventional Fibrillation Methods of Producing Cellulose Nanofibrils and Their Applications

The production of cellulose nanofibrils (CNFs) continues to receive considerable attention because of their desirable material characteristics for a variety of consumer applications. There are, however, challenges that remain in transitioning CNFs from research to widespread adoption in the industrial sectors, including production cost and material performance. This Review covers CNFs produced from nonconventional fibrillation methods as a potential alternative solution. Pretreating biomass by biological, chemical, mechanical, or physical means can render plant feedstocks more facile for processing and thus lower energy requirements to produce CNFs. CNFs from nonconventional fibrillation methods have been investigated for various applications, including films, composites, aerogels, and Pickering emulsifiers. Continued research is needed to develop protocols to standardize the characterization (e.g., degree of fibrillation) of the lignocellulosic fibrillation processes and resulting CNF products to make them more attractive to the industry for specific product applications.