Hydrophilic Cellulose Nanofibers Research Articles

Ultra-stable high-internal-phase emulsions fabricated solely by hydrophilic cellulose nanofiber via inter-droplet jamming

High-internal-phase emulsions (HIPEs) has been increasing interest owing to their large surface area and controllable flow behavior, however, their heavy addition of emulsifiers, e.g., surfactants and surface-active particles, leads to high cost and emulsifier abuse. To solve these issues, we report a new strategy to prepare HIPEs by solely adding a surface-inactive, hydrophilic cellulose nanofiber (CNF). Compared to conventional HIPEs, the highly flocculated CNF is closely packed in the liquid films between oil droplets instead of anchoring at the oil-water interfaces, as referred to the inter-droplet jamming. An efficient jamming behavior is observed at a low CNF concentration (as low as 0.075 wt%) and at very high volume fractions of oil (near 0.85), maintaining the HIPEs over timescales of two years, without the liquid drainage or phase separation. This unexpected stability is mainly attributed to the increase by dozen orders of magnitude in the viscoelasticity of the jammed films as compared with that in the bulk phase, generating a significantly spatial barrier to prevent the depletion attraction between droplets. This simple approach should offer a new pathway to achieve nature-inspired, pure and controlled materials.

Sustainable cellulose nanofiber/hydrophobic silica nanoparticle coatings with robust hydrophobic and water-resistant properties for wood substrates

Hydrophobization of wood is pivotal for enhancing the utility of wood products. Traditional hydrophobic coatings, primarily petrochemical-based, are now being replaced by environmentally friendly silane-coupled inorganic nanoparticles. However, these alternatives face challenges like poor dispersion stability and weak wood surface adhesion. Our research introduces cellulose nanofibers (CNFs) into the condensation process of silica nanoparticles, creating a CNFs/silica nanoparticle composite. This composite exhibits remarkable dispersion stability and adjustable viscosity, leading to an improved hydrophobic silica/CNFs coating. Its versatility allows for various application methods, including spray, dip, and brush coating. Remarkably, the composite maintains a water contact angle of about 151°, demonstrating excellent water repellency, even with hydrophilic CNFs. The CNFs also enhance the interaction with wood surfaces, boosting the durability of the coating. This innovative approach not only improves storage stability and workability but also ensures uniform hydrophobicity and durable coating formation. Our findings suggest that CNFs derived from lignocellulosic biomass could ultimately be incorporated into environmentally friendly wood coating materials, significantly improving the shortcomings of conventional hydrophobic coatings while reducing dependence on petroleum-based products.

Wood Cellulose Nanofibers Grafted with Poly(ε-caprolactone) Catalyzed by ZnEu-MOF for Functionalization and Surface Modification of PCL Films.

Renewable cellulose nanofiber (CNF)-reinforced biodegradable polymers (such as polycaprolactone (PCL)) are used in agriculture, food packaging, and sustained drug release. However, the interfacial incompatibility between hydrophilic CNFs and hydrophobic PCL has limited further application as high-performance biomaterials. In this work, using a novel ZnEu-MOF as the catalyst, graft copolymers (GCL) with CNFs were grafted with poly(ε-caprolactone) (ε-CL) via homogeneous ring-opening polymerization (ROP), and used as strengthening/toughening nanofillers for PCL to fabricate light composite films (LCFs). The results showed that the ZnEu-MOF ([ZnEu(L)2(HL)(H2O)0.39(CH3OH)0.61]·H2O, H2L is 5-(1H-imidazol-1-yl)-1,3-benzenedicarboxylic acids) was an efficient catalyst, with low toxicity, good stability, and fluorescence emissions, and the GCL could efficiently promote the dispersion of CNFs and improve the compatibility of the CNFs and PCL. Due to the synergistic effect of the ZnEu-MOF and CNFs, considerable improvements in the mechanical properties and high-intensity fluorescence were obtained in the LCFs. The 4 wt% GCL provided the LCF with the highest strength and elastic modulus, which increased by 247.75% and 109.94% compared to CNF/PCL, respectively, showing the best elongation at break of 917%, which was 33-fold higher than CNF/PCL. Therefore, the ZnEu-MOF represented a novel bifunctional material for ROP reactions and offered a promising modification strategy for preparing high-performance polymer composites for agriculture and biomedical applications.

In-situ polycondensate-coated cellulose nanofiber heterostructure for polylactic acid-based composites with superior mechanical and thermal properties

Renewable yet biodegradable natural fiber (e.g., cellulose nanofiber (CNF)) reinforced bio-based polymers (e.g., polylactic acid (PLA)) are being applied for the manufacture of clean packaging products. The interface incompatibility between hydrophilic CNF and hydrophobic PLA still restricts the promotion of high-performance bio-based products. Herein, a polycondensate-coated CNF hybrid, wherein silane, aluminate, and titanate coupling agent monomers were in-situ polymerized onto the CNF surface via dehydration self-condensation, was designed and further employed as strengthening/toughening nanofillers for fabricating the CNF-reinforced PLA composite. Results showed that the polycondensate coatings could efficiently promote the dispersion of CNFs and enhance interfacial compatibility between CNFs and PLA. Attributing to the synergistic effect of polycondensate coatings and CNFs, a considerable improvement in processing, mechanical and thermal properties was obtained in resultant CNF/PLA composites. With adding 2.5 wt% polycondensate-coated CNFs, the tensile strength, Young's modulus, and tensile toughness of CNF-reinforced PLA composites was raised by about 27 %, 51 % and 68 %, respectively; also, such composite possessed greater elasticity and higher melt strength than pure PLA. This study provides a novel interface control strategy to fabricate low-cost yet high-performance PLA-based composites for sustainable packaging application.

Introducing hydrophilic cellulose nanofiber as a bio-separator for “water-in-salt” based energy storage devices

There has been enormous interest in energy storage devices in recent years, with the emergence of “water-in-salt” based electrolytes coming to the fore in the context of supercapacitors, and lithium-ion batteries. In fact, the “water-in-salt” electrolyte exhibits a wide voltage window; unfortunately, it shows a low intrinsic wettability on the carbon surface, exhibiting hydrophobic properties on the typical separator. In this work, we introduced carboxylate-modified cellulose for utilization as a novel hydrophilic separator in energy storage devices, especially “water-in-salt” electrolytes. The cellulose was modified through the esterification with succinic anhydride followed by microfluidization to obtain cellulose succinate nanofiber (SCNF). The SCNF increases negative surface charges, enhancing the strong electrostatic repulsion between fibrils and facilitating ion transportation. We successfully fabricated the SCNF separators with a high porosity (60%) and the carboxylate content of SCNF (∼3.9 mmol g−1), giving a hydrophilic surface. The applicability of the separator was demonstrated in “water-in-salt” electrolyte, which shows relatively hydrophobic on the commercial separator. Interestingly, the prepared SCNF separator can improve capacitive properties by reducing the cell resistance. It is found that the capacitance can be enhanced up to 2 to 7 times when compared with the supercapacitor fabricated using a commercial separator. This work could strongly advance the research and development of SCNF separators, and “water-in-salt” based electrolytes in the context of energy storage applications.

Highly robust separation for aqueous oils enabled by balsa wood-based cellulose aerogel with intrinsic superior hydrophilicity

Owing to the strong adsorption capacity, cellulose aerogel has emerged as a promising material in the field of oil–water separation. In this study, we have taken advantage of the inherent superior hydrophilicity of balsa wood-based cellulose aerogel for the separation of various aqueous oils. A facile approach to preserve inherent hydrophilic cellulose nanofibers was achieved by removing lignin and hemicellulose fractions from natural wood, resulting in flexible cellulose aerogel with lamellar architecture. As a result, the separation efficiency of cellulose aerogel can achieve 99.97% for immiscible aqueous oils, and 98.45% even for water-in-oil emulsions. Moreover, the as-prepared cellulose aerogel exhibits remarkable mechanical properties, with stress decay of 7% after 60 compression cycles making it recycle feasible. When exposed to several complex environments including acid, alkaline and salt for a long time, the cellulose aerogel remains stable superoleophobicity with underwater oil contact angle of 153.2 ± 1.2°. Given the low operating cost, high separation efficiency and durability and stability of cellulose aerogel, this work provides a promising material for aqueous oils purification.

Structure Optimization of Cellulose Nanofibers/Poly(Lactic Acid) Composites by the Sizing of AKD.

Recently, cellulose nanofibers (CNF) are used as one novel fillers to reinforce poly(lactic acid) (PLA) matrix and form PLA green nanocomposites. In the present work, alkyl ketene dimer (AKD) was used as the sizing of CNF to improve the interfacial compatibility between the hydrophilic CNF and the hydrophobic PLA. The interactions between the AKD and CNF were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), which showed the formation of ketone ester structure between AKD and the hydroxyl groups of CNF. Thermo gravimetric analysis (TGA) showed the little reduced thermal stability of the AKD-CNF/PLA composites. The AKD-CNF/PLA morphology has rough surfaces due to the incorporation of cellulose nanofibers. The mechanical properties of AKD-CNF/PLA were tested by tensile testing, which discovered more AKD-CNF content enhances stress–strain performance. The highest tensile strength of composites was obtained for PLA with 5.0 wt.% AKD-cellulose, which is almost nine times higher than that of the pure PLA.

Highly dispersive Co3O4 nanoparticles incorporated into a cellulose nanofiber for a high-performance flexible supercapacitor.

Transition metal oxides used as electrode materials for flexible supercapacitors have attracted huge attention due to their high specific capacitance and surface-to-volume ratio, specifically for cobalt oxide (Co3O4) nanoparticles. However, the low intrinsic electronic conductivity and aggregation of Co3O4 nanoparticles restrict their electrochemical performance and prevent these electrode materials from being commercialized. Herein, a facile, advantageous, and cost effective sol-gel synthetic route for growing Co3O4 nanoparticles uniformly over a low cost and eco-friendly one-dimensional (1D) hydrophilic cellulose nanofiber (CNF) surface has been reported. This exhibits high conductivity, which enables the symmetric electrode to deliver a high specific capacitance of ∼214 F g-1 at 1 A g-1 with remarkable cycling behavior (∼94% even after 5000 cycles) compared to that of pristine CNF and Co3O4 electrodes in an aqueous electrolyte. Furthermore, the binder-free nature of 1D Co3O4@CNF (which was carbonized at 200 °C for about 20 min under a H2/Ar atmosphere) shows great potential as a hybrid flexible paper-like electrode and provides a high specific capacitance of 80 F g-1 at 1 A g-1 with a superior energy density of 10 W h kg-1 in the gel electrolyte. This study provides a novel pathway, using a hydrophilic 1D CNF, for realizing the full potential of Co3O4 nanoparticles as advanced electrode materials for next generation flexible electronic devices.

Cellulose Nanofiber/Carbon Nanotube-Based Bicontinuous Ion/Electron Conduction Networks for High-Performance Aqueous Zn-Ion Batteries.

Despite their potential as a next-generation alternative to current state-of-the-art lithium (Li)-ion batteries, rechargeable aqueous zinc (Zn)-ion batteries still lag in practical use due to their low energy density, sluggish redox kinetics, and limited cyclability. In sharp contrast to previous studies that have mostly focused on materials development, herein, a new electrode architecture strategy based on a 3D bicontinuous heterofibrous network scaffold (HNS) is presented. The HNS is an intermingled nanofibrous mixture composed of single-walled carbon nanotubes (SWCNTs, for electron-conduction channels) and hydrophilic cellulose nanofibers (CNFs, for electrolyte accessibility). As proof-of-concept for the HNS electrode, manganese dioxide (MnO2 ) particles, one of the representative Zn-ion cathode active materials, are chosen. The HNS allows uniform dispersion of MnO2 particles and constructs bicontinuous electron/ion conduction pathways over the entire HNS electrode (containing no metallic foil current collectors), thereby facilitating the redox kinetics (in particular, the intercalation/deintercalation of Zn2+ ions) of MnO2 particles. Driven by these advantageous effects, the HNS electrode enables substantial improvements in the rate capability, cyclability (without structural disruption and aggregation of MnO2 ), and electrode sheet-based energy (91Wh kgelectrode -1 )/power (1848 W kgelectrode -1 ) densities, which lie far beyond those achievable with conventional Zn-ion battery technologies.

Transparent films by ionic liquid welding of cellulose nanofibers and polylactide: Enhanced biodegradability in marine environments

We introduce a green and facile method to compatibilize hydrophobic polylactide (PLA) with hydrophilic cellulose nanofibers (CNF) by using ionic liquid ([DBNH][OAc]) welding with a cosolvent system (gamma-valerolactone). Such welding affords strong (230 MPa tensile strength), flexible (13% elongation at break), transparent (>90%) and defect-free CNF/PLA films. The films are biodegradable in marine environments (70% degradation in 7 weeks), facilitating the otherwise slow PLA decomposition. Physical, chemical and structural features of the films before and after welding are compared and factored in the trends observed for degradation in seawater. The results point to the possibility of PLA-based films forming a co-continuous system with nanocellulose to achieve an improved performance. The role of film morphology, hydrophobicity, and crystallinity is discussed to add to the prospects for packaging materials that simultaneously display accelerated degradability in marine environments.

Evaluation of hydrophilic cellulose nanofiber dispersions in a hydrophobic isotactic polypropylene composite

AbstractAn effective approach for the evaluation of dispersed hydrophilic cellulose nanofibers (CNFs) in hydrophobic isotactic polypropylene (iPP) is presented using scattering and microscopic techniques for fiber analysis on nanometer and micrometer scales. iPP composites reinforced with CNF fibrous fillers were characterized by small‐angle light scattering, small‐angle X‐ray scattering, and polarized optical microscopy measurements in the molten state in order to evaluate the shape of CNF fillers and/or larger aggregates formed from these fibers. The best dispersion results in the molten state coincided with low concentrations of CNFs. We observed the effect of CNFs on the acceleration of iPP crystal growth using wide‐angle X‐ray scattering and differential scanning calorimeter measurements. It was even possible to observe the nucleation morphology around CNF fibrous fillers using transmission electron microscopy.

Multi-interface engineering of solar evaporation devices via scalable, synchronous thermal shrinkage and foaming

Abstract Recent years have witnessed continuing advances in solar evaporation technologies to achieve strong synergy among sufficient water supply, efficient light absorption, and favorable heat localization. Still, challenges remain in the fabrication of solar evaporation devices with synergistic performance in a scalable fashion. Herein, we develop a scalable fabrication process involving multi-scale and multi-interface engineering to achieve high-performance and large-area solar evaporation devices. At nanoscale, light-absorbing carbon nanotubes (CNTs) are complexed with hydrophilic cellulose nanofibers (CNFs) to form the nanocomposite inks of CNT-CNF (c-CNT) with tunable viscosity for doctor blading on ethanol-diffused polystyrene (E-PS) films. Through one-step thermal treatment, device shrinkage and substrate foaming are triggered at multi-interfaces to synchronously induce (1) the creation of microscale crumpled c-CNT textures with dual-improved water supply and light absorption and (2) the generation of mesoscale pores in PS substrates with dual-suppressed thermal conduction and radiation. Contributed by the synergistic designs, the solar evaporation device demonstrates a high evaporation rate of 1.41 kg m−2 h−1 and a conversion efficiency of 95.8% at an extremely low loading of photothermal materials (0.25 mg cm−2). A large-area solar evaporation panel is realized to highlight the practical consideration toward more impactful solar evaporation exploitation.

Amphiphilic cellulose nanofiber-interwoven graphene aerogel monolith for dyes and silicon oil removal

Monolithic graphene oxide (GO) and reduced GO (rGO) aerogel is recently receiving a great deal of concern as a promising adsorbent, whose structure and surface properties, however, are anticipated to be improved and adapted to the adsorption of organic contaminants with various polarities and ionic properties. Herein, super strong and hydrophilic cellulose nanofiber (CNF) was exploited as a cross-linker to interweave in between rGO layers so as to tune and balance the structural and surface properties (hydrophilicity and hydrophobicity) of the monolith. It was found that mechanical property of the monolith changes stepwise with the addition of CNF and can be greatly improved by proportion with CNF irrespective of a little sacrifice in electrical conductivity. Filling and further formation of aggregating bundle structure of CNFs in rGO monolith gradually decreases porosity at compensation of a slight increase in monolithic volume. CNF plays a critical role in separating rGO layers, leading to formation of the exposed and uniformly dispersed rGO layers in the monoliths. It can increase the amount of oxygen containing groups at the same time to generate carbonized moieties, thus ameliorating both hydrophilicity and hydrophobicity of the monolithic aerogel. The unique structural change and improved amphiphile surface property due to the addition of CNF can greatly enhance affinity of the hybridized monolith toward the adsorption of not only hydrophilic (both anionic and cationic) dyes but also hydrophobic organic oil.

Nanocellulose Modified Polyethylene Separators for Lithium Metal Batteries.

Poor cycling stability and safety concerns regarding lithium (Li) metal anodes are two major issues preventing the commercialization of high-energy density Li metal-based batteries. Herein, a novel tri-layer separator design that significantly enhances the cycling stability and safety of Li metal-based batteries is presented. A thin, thermally stable, flexible, and hydrophilic cellulose nanofiber layer, produced using a straightforward paper-making process, is directly laminated on each side of a plasma-treated polyethylene (PE) separator. The 2.5 µm thick, mesoporous (≈20 nm average pore size) cellulose nanofiber layer stabilizes the Li metal anodes by generating a uniform Li+ flux toward the electrode through its homogenous nanochannels, leading to improved cycling stability. As the tri-layer separator maintains its dimensional stability even at 200 °C when the internal PE layer is melted and blocks the ion transport through the separator, the separator also provides an effective thermal shutdown function. The present nanocellulose-based tri-layer separator design thus significantly facilitates the realization of high-energy density Li metal-based batteries.

Surface Engineering of Cellulose Nanofiber by Adsorption of Diblock Copolymer Dispersant for Green Nanocomposite Materials

An effective approach for the dispersion of hydrophilic cellulose nanofiber (CNF) in hydrophobic high-density polyethylene (HDPE) is presented using adsorption of a diblock copolymer dispersant. The dispersant consists of both resin compatible poly(lauryl methacrylate) (PLMA) and cellulose interactive poly(2-hydroxyethyl methacrylate) blocks. The PLMA-adsorbed CNFs are characterized by FT-IR and contact angle measurement, revealing successful hydrophobization. X-ray CT imaging shows there are apparently less CNF aggregates in the nanocomposites if adding amount of the dispersant was enough. The good dispersion results in a high mechanical reinforcement, corresponding to 140% higher Young's modulus and 84% higher tensile strength than the neat HDPE. This approach is broadly applicable and allows for easy manufacturing process for strong and lightweight CNF-reinforced nanocomposite materials.

Antimicrobial Activity of Silver Ions Released from Zeolites Immobilized on Cellulose Nanofiber Mats.

In this study, we exploit the high silver ion exchange capability of Linde Type A (LTA) zeolites and present, for the first time, electrospun nanofiber mats decorated with in-house synthesized silver (Ag(+)) ion exchanged zeolites that function as molecular delivery vehicles. LTA-Large zeolites with a particle size of 6.0 μm were grown on the surface of the cellulose nanofiber mats, whereas LTA-Small zeolites (0.2 μm) and three-dimensionally ordered mesoporous-imprinted (LTA-Meso) zeolites (0.5 μm) were attached to the surface of the cellulose nanofiber mats postsynthesis. After the three zeolite/nanofiber mat assemblies were ion-exchanged with Ag(+) ions, their ion release profiles and ability to inactivate Escherichia coli (E. coli) K12 were evaluated as a function of time. LTA-Large zeolites immobilized on the nanofiber mats displayed more than an 11 times greater E. coli K12 inactivation than the Ag-LTA-Large zeolites that were not immobilized on the nanofiber mats. This study demonstrates that by decorating nanometer to micrometer scale Ag(+) ion-exchanged zeolites on the surface of high porosity, hydrophilic cellulose nanofiber mats, we can achieve a tunable release of Ag(+) ions that inactivate bacteria faster and are more practical to use in applications over powder zeolites.