Charged Cellulose Nanofibrils Research Articles

Study on the Rectification of Ionic Diode Based on Cross-Linked Nanocellulose Bipolar Membranes.

Nanocellulose-based membranes have attracted intense attention in bioelectronic devices due to their low cost, flexibility, biocompatibility, degradability, and sustainability. Herein, we demonstrate a flexible ionic diode using a cross-linked bipolar membrane fabricated from positively and negatively charged cellulose nanofibrils (CNFs). The rectified current originates from the asymmetric charge distribution, which can selectively determine the direction of ion transport inside the bipolar membrane. The mechanism of rectification was demonstrated by electrochemical impedance spectroscopy with voltage biases. The rectifying behavior of this kind of ionic diode was studied by using linear sweep voltammetry to obtain current-voltage characteristics and the time dependence of the current. In addition, the performance of cross-linked CNF diodes was investigated while changing parameters such as the thickness of the bipolar membranes, the scanning voltage range, and the scanning rate. A good long-term stability due to the high density cross-linking of the diode was shown in both current-voltage characteristics and the time dependence of current.

Formulation and stabilization of high internal phase emulsions via mechanical cellulose nanofibrils/ethyl lauroyl arginate complexes

Motivated by the quest for biocompatibility, we report on oil-in-water (O/W), high-internal-phase Pickering emulsions stabilized via complexes of mechanical cellulose nanofibrils (CNF) and food-grade cationic surfactant ethyl lauroyl arginate (LAE). The complexation of oppositely charged CNF and LAE can be held together by electrostatic interaction. Their effect on suspensions electrostatic stabilization, heteroaggregation state, and emulsifying ability was studied and related to properties of resultant interfacial tension between oil and water and 3D printing of emulsions. The Pickering system with adjustable droplet diameter and stability against creaming and oiling-off during storage was achieved resting with LAE loading. Complexes formed by LAE adjustment act as Pickering stabilizers and three-dimensional networks in emulsion system, forming a scaffold with elastoplastic rheological properties that flows above critical stress while, without any additional treatment, exhibiting the required self-standing properties for 3D printing. By understanding the properties of CNF/LAE behavior in bulk and on interfaces, printing edible functional foods of CNF/LAE-based emulgel inks has been demonstrated to enable regulation of oil release.

ZnO microrods sandwiched between layered CNF matrix: Fabrication, stress transfer, and mechanical properties

Functional metal oxide particles are often added to the polymers to prepare flexible functional polymer composites with adequate mechanical properties. ZnO and cellulose nanofibrils (CNF) outstand among these metal oxides and the polymer matrices respectively due to their various advantages. Herein, we in situ prepare ZnO microrods in the presence of CNF, which resultes in a layered composite structure. The ZnO microrods are sandwiched between the CNF layers and strongly bind to highly charged CNF, which provides a better stress transfer during mechanical activity. Digital image correction (DIC) and finite element analysis-based computational homogenization methods are used to investigate the relationship between mechanical properties and composite structure, and the stress transfer to the ZnO microrods. Full-field strain measurements in DIC reveal that the in situ ZnO microrods preparation leads to their homogenous distribution in the CNF matrix unlike other methods, which require external means such as ultrasonication. The computational homogenization technique provides a fairly good insight into the stress transfer between constituents in microstructure as well as a good prediction of macroscopic mechanical properties, which otherwise, would be challenging to be assessed by any ordinary mechanical testing in the layered composites. Finally, we also demonstrate that these composites could be used as physiological motion sensors for human health monitoring.

Thermal insulation and antibacterial foam templated from bagasse nanocellulose /nisin complex stabilized Pickering emulsion

Foam packaging with good thermal insulation and antibacterial properties is promising for cold chain delivery to strengthen food safety. This study reports a novel antibacterial foam with thermal insulation templated from bagasse nanocellulose complex particle-stabilised acrylate epoxy soybean oil (AESO) Pickering emulsions. Nanocellulose/nisin complex particles (N-CNFs) were prepared by loading positively charged nisin onto negatively charged cellulose nanofibrils via electrostatic interactions, that highly enhanced the stability of nanocellulose at the AESO/water interface and imparted the corresponding foam with good antibacterial properties. The results show that the porosity of the foam prepared with N-CNFs increased from 10.9% to 29.9% compared with that of the foam corresponding with bare nanocellulose; the thermal conductivity of the N-CNF foam decreased substantially from 0.431 W/m·K to 0.197 W/m·K. Moreover, the prepared foam exhibited good antibacterial activity, and its bacteriostatic rate against Listeria monocytogenes was 91.33%. The incorporation of antibacterial peptides into nanocellulose has enriched the study of the Pickering emulsion templating method for preparing multifunctional foam materials and is expected to broaden the application of nanocellulose in the field of food packaging.

Charged-cellulose nanofibrils as a nutrient carrier in biodegradable polymers for enhanced efficiency fertilizers

An enhanced efficiency fertilizer (EEF) is essential for sustainable agriculture, and here, we evaluated cellulose nanofibrils (CNF) as a nutrient carrier dispersed in biodegradable polymeric matrices. CNF were functionalized with negative (CNF−) and positive (CNF+) charges to improve (i) the CNF-nutrient and (ii) the CNF-polymeric matrix interactions. The CNF encapsulated the KNO3 nutrient by spray drying (microcapsules) and then inserted into a poly (hydroxybutyrate)/starch-based matrix by melt-compounding (tablets). These materials were morphologically, structurally, and thermally characterized before and after biodegradation. Nutrient release profiles showed the microcapsules released the nutrients for up to 1 h, while the tablets did for 8 h in water and over 80 days in soil. Tablets with CNF− released NO3− faster than K+, and those with CNF+ behaved inversely. Besides, the biodegradation efficiencies were up to 75 % in 120 days. The CNF charges affected nutrient release and the matrix biodegradation, ensuring the matrices were harmless to the environment.

Constructing acid-resistant chitosan/cellulose nanofibrils composite membrane for the adsorption of methylene blue

Facing the serious environmental problem caused by water pollution, it is still challenging to develop a kind of acidic wastewater treatment adsorbent with high adsorption efficiency. In this study, the negative charged cellulose nanofibrils (CNF) were used to enhance the acid-resistance of the positive charged chitosan (CTS) via both ionic and hydrogen-bonding crosslinking interactions. The prepared CTS/CNF composite membrane presented an excellent acid-resistant property (approximately 95% acid-resistant degree) and 14.71 mg/g of adsorption capacity for methylene blue in the strong acidic environment (pH = 1.22), surpassing almost reported adsorbents. Besides, the adsorption process for methylene blue conformed to the pseudo-first-order kinetic model and the Langmuir isotherm model better. Furthermore, the obtained CTS/CNF composite membrane presented excellent recyclability (about 85% desorption rate) after five recycles of adsorption-desorption. Consequently, as a novel and efficient adsorbent, the CTS/CNF composite membrane showed an outstanding application potential in the treatment of acidic wastewater.

Stable Cellulose Nanofibril Microcapsules from Pickering Emulsion Templates.

Electrostatic attractions are essential in any complex formation between the nanofibrils of the opposite charge for a specific application, such as microcapsule production. Here, we used cationized cellulose nanofibril (CCNF)-stabilized Pickering emulsions (PEs) as templates, and the electrostatic interactions were induced by adding oxidized cellulose nanofibrils (OCNFs) at the oil–water interface to form microcapsules (MCs). The oppositely charged cellulose nanofibrils enhanced the solidity of interfaces, allowing the encapsulation of Nile red (NR) in sunflower oil droplets. Microcapsules exhibited a low and controlled release of NR at room temperature. Furthermore, membrane emulsification was employed to scale up the preparation of microcapsules with sunflower oil (SFO) encapsulated by CCNF/OCNF complex networks.

Combining cellulose nanofibrils and galactoglucomannans for enhanced stabilization of future food emulsions

The use of wood-derived cellulose nanofibrils (CNFs) or galactoglucomannans (GGM) for emulsion stabilization may be a way to obtain new environmentally friendly emulsifiers. Both have previously been shown to act as emulsifiers, offering physical, and in the case of GGM, oxidative stability to the emulsions. Oil-in-water emulsions were prepared using highly charged (1352 ± 5 µmol/g) CNFs prepared by TEMPO-mediated oxidation, or a coarser commercial CNF, less charged (≈ 70 µmol/g) quality (Exilva forte), and the physical emulsion stability was evaluated by use of droplet size distributions, micrographs and visual appearance. The highly charged, finely fibrillated CNFs stabilized the emulsions more effectively than the coarser, lower charged CNFs, probably due to higher electrostatic repulsions between the fibrils, and a higher surface coverage of the oil droplets due to thinner fibrils. At a constant CNF/oil ratio, the lowest CNF and oil concentration of 0.01 wt % CNFs and 5 wt % oil gave the most stable emulsion, with good stability toward coalescence, but not towards creaming. GGM (0.5 or 1.0 wt %) stabilized emulsions (5 wt % oil) showed no creaming behavior, but a clear bimodal distribution with some destabilization over the storage time of 1 month. Combinations of CNFs and GGM for stabilization of emulsions with 5 wt % oil, provided good stability towards creaming and a slower emulsion destabilization than for GGM alone. GGM could also improve the stability towards oxidation by delaying the initiation of lipid oxidation. Use of CNFs and combinations of GGM and CNFs can thus be away to obtain stable emulsions, such as mayonnaise and beverage emulsions.

Controlled Polyelectrolyte Association of Chitosan and Carboxylated Nano-Fibrillated Cellulose by Desalting.

We prepared chitosan (CHI) hydrogels reinforced with highly charged cellulose nanofibrils (CNF) by the desalting method. To this end, the screening of electrostatic interactions between CHI polycation and CNF polyanion was performed by adding NaCl at 0.4 mol/L to the chitosan acetate solution and to the cellulose nanofibrils suspension. The polyelectrolyte complexation between CHI polycation and CNF polyanion was then triggered by desalting the CHI/CNF aqueous mixture by multistep dialysis, in large excess of chitosan. Further gelation of non-complexed CHI was performed by alkaline neutralization of the polymer, yielding high reinforcement effects as probed by the viscoelastic properties of the final hydrogel. The results showed that polyelectrolyte association by desalting can be achieved with a polyanionic nanoparticle partner. Beyond obtaining hydrogel with improved mechanical performance, these composite hydrogels may serve as precursor for dried solid forms with high mechanical properties.

Growth factor functionalized biodegradable nanocellulose scaffolds for potential wound healing application

Nanocellulose has been highlighted as one of the most promising biomaterials for biomedical applications with the potential to outperform conventional polymeric materials. However, the design of nanocellulose-based biomaterials for wound healing still requires precise control over biophysical and biochemical cues to direct a series of cellular activities in healing processes. The bioactive cellulose nanofibrils scaffolds with controlled release of basic fibroblast growth factors (bFGFs) were constructed for potential wound healing applications. The Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) analysis revealed the polyion complex interaction between the positively charged bFGFs with the negatively charged cellulose nanofibrils, which mimics the interaction between bFGFs and heparin sulfate in extracellular matrix in the body. Such association enables not only the storage of bFGFs in a readily available form and from where it is slowly released, but also potential protection of it from denaturation. The release profile of bFGFs from the CNF scaffolds was tailored by tuning the CNF surface chemistry and in situ deconstruction of the scaffolds. The in situ enzymatic deconstruction of the scaffolds provides a possibility to tune the bioavailability of bFGFs for cell growth and proliferation, and more importantly, to balance the scaffolds degradation and new tissue formation in wound healing. The MTT assay of cells proliferation and fluorescence imaging of cells cultured in the 3D scaffolds showed that the CNF scaffolds loaded with bFGF can significantly facilitate the proliferation of the cells, even if only a small amount of bFGF was loaded. Enzymatic deconstruction of the CNFs network further increases the bFGFs bioavailability, and promotes cell proliferation. This work may serve as an important step toward the development of nanocellulose-based biomaterials with tailored biophysical and biochemical cues for wound healing and other biomedical applications.

Surface Charges Control the Structure and Properties of Layered Nanocomposite of Cellulose Nanofibrils and Clay Platelets.

The interfacial bonding and structure at the nanoscale in the polymer–clay nanocomposites are essential for obtaining desirable material and structure properties. Layered nanocomposite films of cellulose nanofibrils (CNFs)/montmorillonite (MTM) were prepared from the water suspensions of either CNFs bearing quaternary ammonium cations (Q-CNF) or CNFs bearing carboxylate groups (TO-CNF) with MTM nanoplatelets carrying net surface negative charges by using vacuum filtration followed by compressive drying. The effect of the ionic interaction between cationic or anionic charged CNFs and MTM nanoplatelets on the structure, mechanical properties, and flame retardant performance of the TO-CNF/MTM and Q-CNF/MTM nanocomposite films were studied and compared. The MTM nanoplatelets were well dispersed in the network of TO-CNFs in the form of nanoscale tactoids with the MTM content in the range of 5–70 wt %, while an intercalated structure was observed in the Q-CNF/MTM nanocomposites. The resulting TO-CNF/MTM nanocomposite films had a better flame retardant performance as compared to the Q-CNF/MTM films with the same MTM content. In addition, the effective modulus of MTM for the TO-CNF/MTM nanocomposites was as high as 129.9 GPa, 3.5 times higher than that for Q-CNF/MTM (37.1 GPa). On the other hand, the Q-CNF/MTM nanocomposites showed a synergistic enhancement in the modulus and tensile strength together with strain-to-failure and demonstrated a much better toughness as compared to the TO-CNF/MTM nanocomposites.

Particle Size Distribution and Yield Analysis of Different Charged Cellulose Nanofibrils Obtained by TEMPO-mediated Oxidation

Cellulose Nanofibrils (CNF) was successfully obtained by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation with the addition of different oxidant namely NaClO (Sodium Hypochlorite) i.e. 3, 4, 7, 10 and 15 mL followed by ultra-sonication treatment. Size distribution of nanocellulose was observed using particle size analyzer, while surface charged was measured using zeta potentiometer. At different level of oxidant, CNF obtained different charged with different size distribution. As the amount of oxidant increased, the size distribution of CNF increased which correlated to the higher CNF yield, however it decreased at maximum oxidant addition. Although, in general the yield for nanocellulose was very low. With zeta potential value about -48 mV, it showed very stable suspension in water for more than 8 months observation. An optimum oxidant level promoted thinner and longer CNF which further beneficial for better entanglement in the hydrogel formation application.

Highly Mineralized Biomimetic Polysaccharide Nanofiber Materials Using Enzymatic Mineralization.

Many biological high-performance composites, such as bone, antler, and crustacean cuticles, are composed of densely mineralized and ordered nanofiber materials. The mimicry of even simplistic bioinspired structures, i.e., of densely and homogeneously mineralized nanofibrillar materials with controllable mechanical performance, continues to be a grand challenge. Here, using alkaline phosphatase as an enzymatic catalyst, we demonstrate the dense, homogeneous, and spatially controlled mineralization of calcium phosphate nanostructures within networks of anionically charged cellulose nanofibrils (CNFs) and cationically charged chitin nanofibrils (ChNFs)-both emerging biobased nanoscale building blocks for sustainable high-performance materials design. Our study reveals that anionic CNFs lead to a more homogeneous nanoscale mineralization with very high mineral contents up to ca. 70 wt % with a transition from amorphous to crystalline deposits, while cationic ChNFs yield rod-like crystalline morphologies. The bone-inspired CNF bulk films exhibit a significantly increased stiffness, maintain good flexibility and translucency, and have a significant gain in wet state mechanical properties. The mechanical properties can be tuned both by the enzyme concentration and the mineralization time. Moreover, we also show a spatial control of the mineralization using kinetically controlled substrate uptake in a dialysis reactor, and by spatially selectively incorporating the enzyme into 2D printed filament patterns. The strategy highlights possibilities for spatial encoding of enzymes in tailored structures and patterns and programmed mineralization processes, promoting the potential application of mineralized CNF biomaterials with complex gradients for bone substitutes and tissue regeneration in general.

Stable nanocellulose gels prepared by crosslinking of surface charged cellulose nanofibrils with di- and triiodoalkanes

Nanocellulose gels were prepared by a new chemical crosslinking approach. Carboxy group containing cellulose nanofibrils, which were prepared by (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TEMPO) mediated oxidation, were reacted with two different diiodoalkanes and one triiodoalkane in DMSO/water dispersions at elevated temperatures. Mechanically stable gels were obtained that were characterized with respect to chemical and physical properties. It was confirmed by FTIR spectroscopy that crosslinking of TEMPO oxidized cellulose nanofibrils (TCNF) occurs by the formation of ester bonds. The kinetics of gel formation were evaluated by oscillatory rheology experiments. For long alkyl chain cross-linkers, namely 1,4-diiodobutane and 1,10-diiododecane, the initial gel was formed within a short time (gel point < 5 min) and further evolved upon time for about 0.5–2 h. For the short crosslinker triiodomethane, gel formation was slower and resulted in lower mechanical strength.

Effects of non-solvents and electrolytes on the formation and properties of cellulose I filaments

Coagulation is a critical process in the assembly of cellulose nanofibrils into filaments by wet spinning; however, so far, the role of the coagulation solvent has not been systematically elucidated in this context. This work considers organic non-solvents (ethanol, acetone) and aqueous electrolyte solutions (NaCl(aq), HCl(aq), CaCl2(aq)) for the coagulation of negatively charged cellulose nanofibrils via wet spinning. The associated mechanisms of coagulation with such non-solvents resulted in different spinnability, coagulation and drying time. The properties of the achieved filaments varied depending strongly on the coagulant used: filaments obtained from electrolytes (using Ca2+ and H+ as counterions) demonstrated better water/moisture stability and thermomechanical properties. In contrast, the filaments formed from organic non-solvents (with Na+ as counterions) showed high moisture sorption and low hornification when subjected to cycles of high and low humidity (dynamic vapor sorption experiments) and swelled extensively upon immersion in water. Our observations highlight the critical role of counter-ions and non-solvents in filament formation and performance. Some of the fundamental aspects are further revealed by using quartz crystal microgravimetry with model films of nanocelluloses subjected to the respective solvent exchange.

Influence of TEMPO-oxidised cellulose nanofibrils on the properties of filler-containing papers

In this work, cellulose nanofibrils (CNF) were produced from a Eucalyptus globulus bleached kraft pulp by TEMPO-mediated oxidation and mechanical homogenisation, and their effects in papermaking, namely filler flocculation and retention, dry and wet-web strength and structural properties, were studied in detail. Cellulose nanofibrils possessing 0.6 mmol/g carboxyl groups and a degree of polymerisation (DP) of ca. 550 were found to promote filler flocculation and retention in the fibre mat, whereas the same amount (3 wt%) of CNF having 1.5 mmol/g of carboxyl groups, a DP of ca. 200 and a similar mean diameter exhibited the opposite effect. These results were interpreted with the help of flocculation studies of precipitated calcium carbonate (PCC) in the presence of CNF carried out by laser diffraction spectrometry. In addition, the mechanical and structural properties of the handsheets were analysed, revealing that the less charged CNF led to more closed matrices and, even increasing the filler retention, had a positive role on the tensile strength. A bonding mechanism among eucalypt fibres, PCC, CNF and a linear cationic polyacrylamide is proposed, consistent with the flocculation, retention and paper strength and structural property results. It is concluded that, to be used in papermaking, the CNF must not have a high charge (or a small length) to be able to flocculate the filler particles and, at the same time, to increase the filler-to-cellulosic fibres bonding. A complementary study on the wet-web resistance of handsheets produced with the less charged CNF was conducted for moisture contents between 10 and 70%, showing that these CNF can significantly improve the handsheet wet tensile strength (nearly 100%) even for water contents above 50%. The use of CNF in the paper machine may thus contribute, through the higher wet-web tensile resistance, to reducing breaks and increasing the operating speeds and, through the higher filler retention, to important fibre and cost savings.

Self-assembling of TEMPO Oxidized Cellulose Nanofibrils As Affected by Protonation of Surface Carboxyls and Drying Methods

Self-assembling of cellulose nanofibrils (CNFs) as affected by varying extent of protonation on C6 surface carboxyls was investigated under freeze-drying and air-drying processes. Surface carboxyls were protonated from 10.3 to 100%, all on the same TEMPO oxidized and mechanically blended CNFs with identical geometries and level of oxidation. Upon freeze-drying, all CNFs assembled into amphiphilic mass. The mostly charged CNFs assembled into the finest and most uniform fibers (ϕ = 137 nm) that absorbed significantly more nonpolar toluene than water; whereas the fully protonated CNFs assembled extensively into porous and more thermally stable ultrathin filmlike structures that absorbed water and toluene similarly. Ultrafiltration and air-drying induced cyrstallization led to more thermally stable, semitransparent, and hydrophilic films that showed no affinity toward nonpolar toluene. In essence, CNFs could be tuned by varying the degree of surface carboxyl protonation, along with drying processes, to create...

Preparation of highly charged cellulose nanofibrils using high-pressure homogenization coupled with strong acid hydrolysis pretreatments

Cellulose nanofibrils (CNFs) are attracting much attention for the advantages of excellent mechanical strength, good optical transparency, and high surface area. An eco-friendly and energy-saving method was created in this work to produce highly negative charged CNFs using high-pressure mechanical defibrillation coupled with strong acid hydrolysis pretreatments. The morphological development, zeta potential, crystal structure, chemical composition and thermal degradation behavior of the resultant materials were evaluated by transmission electron microscopy (TEM), zeta potential analysis, X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), and thermogravimetric analysis (TGA). These CNFs were fully separated, surface-charged, and highly entangled. They showed a large fiber aspect ratio compared to traditional cellulose nanocrystrals that are produced by strong acid hydrolysis. Compared to hydrochloric acid hydrolysis, the CNFs produced by sulfuric acid pretreatments were completely defibrillated and presented stable suspensions (or gels) even at low fiber content. On the other hand, CNFs pretreated by hydrochloric acid hydrolysis trended to aggregate because of the absence of surface charge. The crystallinity index (CI) of CNFs decreased because of mechanical defibrillation, and then increased dramatically with increased sulfuric acid concentration and reaction time. FTIR analysis showed that the COSO3 group was introduced on the surfaces of CNFs during sulfuric acid hydrolysis. These sulfate groups accelerated the thermal degradation of CNFs, which occurred at lower temperature than wood pulp, indicating that the thermal stability of sulfuric acid hydrolyzed CNFs was decreased. The temperature of the maximum decomposition rate (Tmax) and the maximum weight-loss rates (MWLRmax) were much lower than for wood pulp because of the retardant effect of sulfuric acid during the combustion of CNFs. By contrast, the CNFs treated with hydrochloric acid had better thermal stability, because no functional groups were introduced on the surface.