Cellulose Nanofibers Concentrations Research Articles

Development of Hybrid Electrospun Nanofibers: Improving Effects of Cellulose Nanofibers (CNFs) on Electrospinnability of Gelatin

Cellulose nanofibers (CNFs) were used to improve the electrospinnability of the gelatin protein in a water/ethanol/acetic acid (3:2:3, v/v) solution. The effects of different concentrations of CNFs (0.5–4%) on the important physical properties of the gelatin solution (15%), including rheology, conductivity, and surface tension, were investigated. The apparent viscosity and shear-thinning behavior were increased by increasing the CNF concentration from 0 to 4% at a low shear rate (<10 s−1). CNFs also increased the electrical conductivity and surface tension of the gelatin solution. Scanning electron microscopy (SEM) images revealed uniformly ordered structures with good continuity without fracture or bead formation in all hybrid nanofibers. They also showed that the average diameters of fibers decreased from 216 nm in the pure gelatin nanofibers to 175.39 nm in the hybrid gelatin/CNF (4%) ones. Differential scanning calorimetry (DSC) results showed that CNFs increased Tg, and X-ray diffraction (XRD) analysis showed that the electrospinning process caused the formation of more amorphous structures in the gelatin/CNF hybrid nanofibers. The tensile test indicated that by adding 2% CNFs, the ultimate tensile strength (UTS) and strain at break (SB) of nanofiber mats increased from 4.26 to 10.5 MPa and 3.3% to 6.25%, respectively. The current study indicated that incorporating CNFs at the optimal concentration into a gelatin solution can improve the resulting hybrid nanofibers’ morphology, average diameter, and mechanical properties.

Droplet size distribution of oil-in-water Pickering emulsions stabilized by cellulose nanofibers using restricted diffusion NMR

In this study, droplet size distributions (DSDs) of oil-in-water Pickering emulsions stabilized by cellulose nanofibers (CNFs) estimated from NMR diffusion measurements in conjunction with cogent mathematical modelling based on the Gaussian phase distribution (GPD) approximation for diffusion in a sphere. The effects of oil types and Pickering stabilizer loadings on DSDs were investigated by using different n-alkanes (octane to hexadecane) and CNF concentrations (0.5–1%). The NMR diffusion data of the dispersed oil were well-described by the GPD model with a monomodal log-normal distribution. Pickering emulsions composed of higher n-alkane carbon number and/or CNF concentration were found to have smaller median radii, RMedian, and these RMedian estimates were in good agreement with laser scattering data. The volume-based RMedian against the CNF concentrations or the number of hydrocarbon n-alkanes exhibited an approximate exponential relationship.

Applicability of enzymatic and phenol–sulfuric acid methods for determination of cellulose nanofibers in ecotoxicity testing

In parallel with the development of novel materials, such as cellulose nanofibers (CNFs), their effects on aquatic organisms should be evaluated. In ecotoxicity testing, concentration measurements are important to obtain accurate exposure concentrations; however, few studies have measured the concentration and dispersion state of CNFs in test solutions. Therefore, we evaluated the applicability of enzymatic and phenol–sulfuric acid methods for CNF quantification in ecotoxicity testing. In the enzymatic method, CNF content was determined by quantifying the d-glucose produced from the CNFs using cellulase with a glucose assay kit. Three types of cellulases were purchased, and impurities such as d-glucose were identified and removed. The differences in CNF degradation efficiency among the cellulases were evaluated, and a cellulase suitable for CNF degradation was selected. In the phenol–sulfuric acid method, a microplate-based method was employed to handle a large number of samples. We demonstrated that both the enzymatic and phenol–sulfuric acid methods could quantify CNFs in media for ecotoxicity testing. The enzymatic method was able to measure lower CNF concentrations (~ 1 mg/L) than the phenol–sulfuric acid method (~ 10 mg/L) and had less interference with CNF quantification by algae and non-cellulosic polysaccharides.

Algal growth inhibition test with TEMPO-oxidized cellulose nanofibers

Ecotoxicity data on cellulose nanofibers (CNFs) are limited despite their wide potential applications prospects, such as structural and packaging materials, filters, coatings, foods, and cosmetics. In this study, toxicity tests of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized CNFs (TEMPO-CNFs), which are one of the major CNF products commercially available in Japan, on the green alga Raphidocelis subcapitata were conducted. As nanomaterials are considered difficult-to-test substances, the Organisation for Economic Co-operation and Development has released a guidance document that provides considerations regarding ecotoxicity tests of nanomaterials. In the algal growth inhibition tests of TEMPO-CNFs, there were specific issues to be examined, including the effects of medium components on the characteristics of TEMPO-CNFs, CNF interference with algal density measurements, algal interference with CNF measurements, and the effects of ion concentration changes in the test medium by the addition of CNFs on algal growth. To examine these issues, we conducted preliminary studies and established a suitable test method for algal growth inhibition tests of TEMPO-CNFs. We confirmed that the components in the medium for algal growth inhibition tests had negligible effects on the characteristics (zeta-potential, viscosity, and morphology) and concentration stability of TEMPO-CNFs and that in vitro and in vivo fluorescence measurements were applicable for estimating the algal densities, without interference by TEMPO-CNFs. In contrast, we observed that the grown algae interfered with the CNF concentration measurements. Therefore, we established a method to correct the measured CNF concentrations by estimating the algal contribution. Furthermore, we found that the nutrient salt concentrations in the medium changed due to interactions with CNFs; however, this change did not affect algal growth. Based on the results of the preliminary studies, algal growth inhibition tests of TEMPO-CNFs were conducted using in vitro and in vivo fluorescence measurements, along with measurements of CNFs and ion concentrations in the test dispersions. The test results showed that no growth inhibition was observed on growth rate or yield even at the maximum CNF concentration of 100 mg/L, suggesting that the ecological effect of TEMPO-CNFs on algae was relatively low. The results of this study will be valuable for conducting ecotoxicity assessments on additional CNFs and comparable nanomaterials in future studies.

Acute toxicity tests of TEMPO-oxidized cellulose nanofiber using Daphnia magna and Oryzias latipes

Ecotoxicity data on cellulose nanofibers (CNFs) are limited despite their wide application prospects. Herein, acute toxicity tests of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized CNFs to Daphnia magna and Oryzias latipes were conducted according to the Organisation for Economic Co-operation and Development test guidelines, which consider CNF dispersibility during the test. To select a suitable test medium, the interaction between the medium components and CNFs was first evaluated using five test media with different ion concentrations. The viscosity, zeta potential, and concentration uniformity of TEMPO-CNFs changed with increasing ionic concentration. The toxicity test results showed no acute toxicity of TEMPO-CNFs to the two species, even at the highest exposure concentrations in this study. Both the median effective concentration (EC50) and median lethal concentration (LC50) were >100 mg/L. In most cases, the measured CNF concentrations were within 20% of the nominal concentrations and remained largely constant. However, in the D. magna acute toxicity test, the concentration uniformity of TEMPO-CNFs tended to decrease when the CNF concentration was low. Our results demonstrate the importance of measuring CNF concentrations during testing and revealed that the ion concentrations in the test solution changed because of the interaction between the medium components and TEMPO-CNFs. This finding demonstrates the importance of examining the components of the medium to avoid mistaking the effects of depleted medium components for the direct effects of TEMPO-CNFs on aquatic organisms.

Potential use of nanofibrillated cellulose-loaded cationic starch solutions as coating formulation for recycled fluting papers

Effects of cellulose nanofibers (CNF) and cationic starch (CS) were evaluated as coating components relative to the physical and mechanical properties of fluting papersheets fabricated from recycled corrugated cardboard fibers. Fabricated fluting papers were subjected to size press applications by three different coating blends. Coating suspensions were prepared at various concentrations of CNF (0.5%, 1%, 2%, 3%, and 4%) and 4 wt% CS, and the same amounts of CS/CNF. The paper sheets were fabricated using size press machine as three-time repetitive applications, followed by one-time drying section, and compared to uncoated, CS-coated, and CNF-coated papers. The application of CNF suspensions increased tensile indices up to 11.7%. Moreover, CS/CNF suspensions resulted in a 67.2% increase in tensile index values. The coating of CS/CNF suspensions increased the burst index values by 163% at the CS+1%CNF concentration when compared to the control pulp. Surface application of prepared suspensions reduced the porosity of the samples under all conditions. The highest reduction in the air permeability was observed in the CS+4%CNF-coated samples as 91.5%. It can be concluded that the superficial applications of CNF on the physical and mechanical properties of recycled fluting paper was more effective in the presence of CS.

Effect of Powdered Cellulose Nanofiber with Different Particle Sizes on the Physical Properties of Tablets Manufactured via Direct Compression.

Direct compression is a tableting technique that involves a few steps in non-demanding manufacturing conditions. High strength and rapid disintegration of tablet formulations were previously achieved through the addition of cellulose nanofibers (CNFs), which have recently attracted attention as a high-performance biomass material. However, CNF addition results in greater variation in tablet weight and drug content, potentially due to differences in particle size between CNF and other additives. Herein, we used pulverized CNF to evaluate the effect of CNF particle size on the variation in tablet weight and drug content. Tablet formulations consisted of CNF with different particle sizes (approximately 100 µm [CNF100] and 300 µm [CNF300], at 0, 10, 30, or 50%), lactose hydrate, acetaminophen, and magnesium stearate. Ten powder formulations with different particle sizes and CNF concentrations were prepared; thereafter, the tablets were produced using a rotary tableting press with a compression force of 10 kN. The variation in weight and drug content as well as the tensile strength, friability, disintegration time, and drug dissolution of tablets were evaluated. CNF100 addition to the tablets reduced the weight and drug content variation to a greater extent than CNF300 addition. Using CNF300, we produced tablets of sufficient strength and short disintegration time. These properties were also achieved with CNF100 addition. Our findings suggest that adding CNF of small particle size to the tablet formulation can reduce the variation in weight and drug content while maintaining high strength and short disintegration time.

Preparation, characterization, and performance evaluation of composite films of polyvinyl alcohol/ cellulose nanofiber extracted from Imperata cylindrica

In recent years, production of cellulose nanofiber (CNF) from waste materials has achieved great interest owing to their renewable nature, biodegradability, high mechanical properties, economic value, and low density. Because Polyvinyl alcohol (PVA) is a synthetic biopolymer with good water solubility and biocompatibility, the composite material formed of CNF and PVA, is a sustainable way of monetizing to address environmental and economic issues. In this work pure PVA, PVA/CNF0.5, PVA/CNF1.0, PVA/CNF1.5, and PVA/CNF2.0 nanocomposite films were produced using the solvent casting approach with the addition of 0, 0.5, 1.0, 1.5, and 2.0 wt% of CNF concentrations respectively. The strongest water absorption behaviour was found as 25.82% for pure PVA membrane, followed by PVA/CNF0.5 (20.71%), PVA/CNF1.0 (10.26%), PVA/CNF1.5 (9.63%), and PVA/CNF2.0 (4.35%). The water contact angle of 53.1°, 47.8°, 43.4°, 37.7°, and 32.3° was formed between water droplet and the solid-liquid interface of pure PVA, PVA/CNF0.5, PVA/CNF1.0, PVA/CNF1.5, PVA/CNF2.0 composite films respectively. The SEM image clearly shows that a network structure like a tree form at the PVA/CNF0.5 composite film, where the sizes and number of pores are apparent. XRD analysis suggested that unique peaks found at 2θ = 17.5°, 28.1°, 33.4°, and 38° for nanocomposites indicating new crystal plane generated upon cross-linking in presence of malic acid. The maximum loss rate temperature (Td,max) for PVA/CNF0.5, PVA/CNF1.0, PVA/CNF1.5 was determined by TG analysis to be around 273.4 °C. FTIR studies suggested that PVA/CNF0.5 composite film showed the highest peak at 1428 cm−1 as compared to other PVA/CNF composite films representing the presence of higher crystalline band in the composite film matrix. PVA/CNF0.5 composite film was found to have a surface porosity and mean pore size of 27.35% and 0.19 μm respectively, classifying it in the MF membrane category. The maximum tensile strength (TS) of 5.27 MPa was found for PVA/CNF0.5, followed by PVA/CNF1.0, PVA/CNF1.5, pure PVA, and PVA/CNF2.0. The maximum young's modulus (111 MPa) was found for PVA/CNF1.0, followed by PVA/CNF0.5, PVA/CNF2.0, PVA/CNF1.5, and pure PVA, which could be attributed to the cyclization of the molecular structures by cross-linking. PVA/CNF0.5 exhibits greater elongation at break (21.7) than the other polymers, indicating a material's ability to undergo significant deformation before failure. Performance evaluation of the PVA/CNF0.5 composite film showed that 46.3% and 92.8% yield were found in the retentate for 200 mg/L of BSA, and 5 × 107 CFU/mL respectively. However, more than 90% E. coli was retained by PVA/CNF0.5 composite film, therefore absolute rating of this membrane is 0.22 μm. The size of this composite film may be therefore considered in the range of MF.

Emulsion polymerized styrene acrylic/nanocellulose composite coating to improve the strength and hydrophobicity of kraft paper

Improving the mechanical and water repelling property of kraft paper will extend its use for packaging application. In this work, we developed a cellulose nanofiber (CNF)-based colloidal polymer nanocomposite that was used as coating for improving those properties of kraft paper. In this case, the polymer latex was obtained by the mini-emulsion copolymerization of styrene (St), 2-ethyl hexyl acrylate (EHA) initiated by ammonium persulfate. The CNFs were incorporated into the styrene-acrylic copolymer matrix by the in-situ polymerization and ex-situ mixing process keeping the CNF concentration up to 1.0 wt%. All the latexes showed particle size below 100 nm and excellent colloidal stability (Zeta potential > −32 mV) for several months. The nanocomposite films showed improved mechanical properties (tensile strength upto 7.8 MPa, elongation upto 1096 %) than the pristine copolymer. The in-situ prepared nanocomposite at 1.0 wt% CNF showed the highest storage modulus. The latex-coated kraft paper showed improved tensile index (31.0–45.1 Nm/g) compared to the uncoated paper (20.3 Nm/g) and also high hydrophobicity (water contact angle ∼120°) for the ex-situ prepared nanocomposites. The results are quite promising to develop paper-based packaging materials using nanocellulose in combination with synthetic polymers.

Development and characterization of walnut oleogels structured by cellulose nanofiber

Edible oleogels were successfully prepared by cellulose nanofibers (CNFs) as the unique oleogelator through emulsion-templated method at varying CNF concentrations of 0.4–4.0%, without additional thickening agent. The microstructure and physical properties of the oleogels such as oil binding capacity, rheology, texture, thermal and oxidative stability were evaluated, using a variety of tools including confocal laser scanning microscopy, polarizing light microscopy, fourier transform-infrared spectroscopy and X-ray diffractometer. The adsorption and closely packing of CNF crystals on the surfaces of the oil droplets in emulsion decreased the clustering of droplets, and inhibited the oil droplets from destabilization during drying. This formed a more reticulated and denser but less anisotropic network, contributed to a β polymorph of the lipid crystallization. Thus the oil binding capacity and stability of oleogels were greatly enhanced, while stronger gelation strength, higher hardness, lower mobility and opaque appearance of the oleogels were observed. The oil loss of oleogels after processing at cooking temperature of 90 °C was remarkably declined, while the oxidative stability of the oleogels was also improved to a satisfactory level. In summary, these results contributed to a better understanding of the oleogelation in CNF-based oleogels, and benefited the use of healthy walnut oil to develop functional fat products with desired physical properties and oxidative stability.

Evaluating the Stability of Cellulose Nanofiber Pickering Emulsions Using MRI and Relaxometry.

Magnetic resonance imaging (MRI) relaxometry and diffusion methods were used to highlight the instability mechanisms of oil-in-water Pickering emulsions stabilized by cellulose nanofibers (CNFs). Four different Pickering emulsions using different oils (n-dodecane and olive oil) and concentrations of CNFs (0.5 and 1.0wt%) were systematically investigated over a period of one month after emulsification. The separation into a free oil, emulsion layer, and serum layer and the distribution of flocculated/coalesced oil droplets in several hundred micrometers were captured in MR images using fast low-angle shot (FLASH) and rapid acquisition with relaxation enhancement (RARE) sequences. The components of the Pickering emulsions (e.g., free oil, emulsion layer, oil droplets, and serum layer) were observable by different voxelwise relaxation times and apparent diffusion coefficients (ADCs) and reconstructing in the apparent T1, T2, and ADC maps. The mean T1, T2, and ADC of the free oil and serum layer corresponded well with MRI results for pure oils and water, respectively. Comparing the relaxation properties and translational diffusion coefficients of pure dodecane and olive oil obtained from NMR and MRI resulted in similar T1 and ADC but significantly different T2 depending on the sequence used. The diffusion coefficients of olive oil measured by NMR were much slower than dodecane. The ADC of the emulsion layer for dodecane emulsions did not correlate with the viscosity of the emulsions as the CNF concentration increased, suggesting the effects of restricted diffusion of oil/water molecules due to droplet packing.

Reinforcement Behavior of Chemically Unmodified Cellulose Nanofiber in Natural Rubber Nanocomposites

We investigated the reinforcement behavior of small amounts of chemically unmodified cellulose nanofiber (CNF) in eco-friendly natural rubber (NR) nanocomposites. For this purpose, NR nanocomposites filled with 1, 3, and 5 parts per hundred rubber (phr) of cellulose nanofiber (CNF) were prepared by a latex mixing method. By using TEM, a tensile test, DMA, WAXD, a bound rubber test, and gel content measurements, the effect of CNF concentration on the structure-property relationship and reinforcing mechanism of the CNF/NR nanocomposite was revealed. Increasing the content of CNF resulted in decreased dispersibility of the nanofiber in the NR matrix. It was found that the stress upturn in the stress-strain curves was remarkably enhanced when the NR was combined with 1-3 phr CNF, and a noticeable increase in tensile strength (an approximately 122% increase in tensile strength over that of NR) was observed without sacrificing the flexibility of the NR in the NR filled with 1 phr CNF, though no acceleration in their strain-induced crystallization was observed. Since the NR chains were not inserted in the uniformly dispersed CNF bundles, the reinforcement behavior by the small content of CNF might be attributed to the shear stress transfer at the CNF/NR interface through the interfacial interaction (i.e., physical entanglement) between the nano-dispersed CNFs and the NR chains. However, at a higher CNF filling content (5 phr), the CNFs formed micron-sized aggregates in the NR matrix, which significantly induced the local stress concentration and promoted strain-induced crystallization, causing a substantially increased modulus but reduced the strain at the rupture of the NR.

Nondestructive and noncontact evaluation of cellulose nanofiber-reinforced composites using terahertz time-domain spectroscopy

Cellulose nanofibers (CNFs) can be obtained from natural sources, such as plants and wood fibers. Thermoplastic resin composites reinforced with CNFs exhibit various features, including superior mechanical strength. As the mechanical properties of composites reinforced with CNFs are affected by the amount of fiber addition, it is important to determine the concentration of the CNF filler in the matrix after injection or extrusion molding. We confirmed that there was good linearity between the CNF concentration and terahertz absorption. We could distinguish the difference in the 1%-point-CNF concentration with terahertz time-domain spectroscopy. Furthermore, we estimated the mechanical properties of the CNF nanocomposites using terahertz information.

Optimization of the Formulation of Sago Starch Edible Coatings Incorporated with Nano Cellulose Fiber (CNF)

This study aimed to produce new edible coatings based on the mixture of sago starch, cellulose nanofiber (CNF), glycerol, and tween-80.The effect of sago starch (5–10 g of starch/100 ml of distilled water), CNF (0.5–20% w/w), glycerol (10–30% w/w), and tween-80 (0.5–10% w/w) based on sago starch concentration on contact angle (CA), water vapor permeability (WVP), oxygen permeability (PO2) and tensile strength (TS) properties of the edible coatings were optimized using factorial experimental design (2k).The result showed that the linear model for all independent variables was significant (<i>P</i><0.05) on all responses (dependent variable).The sago starch concentration depicted a significant (p < 0.001) positive effect on contact angle; CNF showed a statistically significant effect on WVP, PO2, and TS; tween-80 showed a significant effect on all dependent variables, whereas glycerol only affected WVP. The optimum concentrations of sago starch, CNF, glycerol, and tween-80 were predicted to be 5 g/100 ml distilled water, 20% w/w, 10% w/w, and 0.5% w/w based on sago starch, respectively to obtain the minimum contact angle, WVP, PO2, and the maximum TS. The predicted data for the optimized coating formulation were in good agreement with the experimental value. This work revealed that the potential of sago starch/CNF based coating formulation could be effectively produced and successfully applied for coating of food.

Unexpected Gelation Behavior of Cellulose Nanofibers Dispersed in Glycols

In this study, the gelation behavior of TEMPO-oxidized wood-based cellulose nanofiber (CNF) suspensions in two different glycols, ethylene glycol (EG) and propylene glycol (PG), was investigated near the overlap concentration and compared with that of aqueous CNF suspensions. The flow property of these non-aqueous and aqueous CNF suspensions was characterized by rheological, UV–vis, and rheo-optical techniques. It was found that the CNF(PG) suspensions exhibited stirring-reversible gelation behavior, where gelation could be induced simply by resting (i.e., prolonged holding time). However, this behavior was not observed for CNF(EG) and CNF(aq) suspensions. Higher temperature and higher CNF concentration could accelerate the gelation process of CNFs in PG, but no large-scale phase separation was detected by the optical techniques. Our study suggests that the reduced hydrophilic attraction between CNFs in PG is the main driving force for forming CNF-rich micro-domains, yielding a physically crosslinked network. This study suggests that the choice of solvent can be used to tailor and control the flow behavior of CNF suspensions, leading to designs of new cellulose-enabled nanocomposites for varying applications.

Superinsulating nanocellulose aerogels: Effect of density and nanofiber alignment

Cellulose aerogels are potential alternatives to silica aerogels with advantages in cost, sustainability and mechanical properties. However, the density dependence of thermal conductivity (λ) for cellulose aerogels remains controversial. Cellulose aerogels were produced by gas-phase pH induced gelation of TEMPO-oxidized cellulose nanofibers (CNF) and supercritical drying. Their properties are evaluated by varying the CNF concentration (5–33 mg·cm−3) and by uniaxial compression (9–115 mg·cm−3). The aerogels are transparent with specific surface areas of ~400 m2·g−1, mesopore volumes of ~2 cm3·g−1 and a power-law dependence of the E-modulus (α ~ 1.53, and the highest reported E of ~1 MPa). The dataset confirms that λ displays a traditional U-shaped density dependence with a minimum of 18 mW·m−1·K−1 at 0.065 g·cm−3. For a given density, λ is ~5 mW·m−1·K−1 lower for compressed aerogels due to the alignment of nanofibers, confirmed by small angle X-ray scattering (SAXS).

Tunning matrix rheology and mechanical performance of ultra-high performance concrete using cellulose nanofibers

Abstract With the growing demand for sustainability and rapid development of nanotechnology, nanocellulose materials extracted from natural plants have attracted great attention. The incorporation of nanocellulose materials leads to a change in viscosity and yield stress on ultra-high performance concrete (UHPC). Rheological parameters affect the mechanical strength and steel fiber distribution of UHPC significantly. Therefore, it is essential to adjust the matrix rheology within an appropriate range through nanocellulose materials. This study aims to propose a novel method to optimize steel fiber distribution and mechanical properties of UHPC by adjusting the matrix rheology with cellulose nanofibers (CNFs) suspensions. The relationship among CNF concentration, steel fiber distribution, and the mechanical properties of UHPC was established. Test results showed that the failure mode of UHPC containing CNFs changed from single cracking to multiple cracking, accompanied by 11–23% enhancement in tensile strength. With the increase of CNF concentrations, the probability density distribution functions of steel fiber orientation showed the trend toward the distribution with a larger inclination. The addition of CNF suspensions effectively reduced the number of steel fibers settling to the bottom of the specimens. Scanning electron microscopy analyses demonstrated that the nanoscale reinforcement by CNFs was conducive to improving the mechanical properties of UHPC.

Mechanically robust ionic liquid gels composed of cellulose nanofiber and poly(vinyl alcohol)

In this study, we found that composite ion gels composed of cellulose nanofiber (CNF) and poly (vinyl alcohol) (PVA) using an ionic liquid (IL) as a solvent are mechanically robust and tough. In the composite ion gels, CNF played a significant role in the enhancement of the mechanical strength, so that Young’s moduli of the CNF/PVA ion gels with and without borax attained the values of 13 MPa and 9.9 MPa, respectively, which were 20 and 40 times higher than those of the hydrogel prepared in the freezing-thawing method at the same CNF and PVA concentrations, respectively. Various experimental results clarified that the composite ion gels were dually reinforced by CNF and PVA nanocrystals so that the ion gels were mechanically tough and robust.

Stability of novel cellulose-nanofiber-containing foam as environmentally friendly fracturing fluid

Foam-based fracturing is one of the waterless fracturing technologies that can reduce the environmental issues of water-based fracturing. To utilize foam as a fracturing fluid in oil/gas developments, improving foam stability is essential. To examine whether the environmentally friendly and low-cost cellulose nanofiber (CNF) can be a novel foam stabilizer, we investigated the effect of surfactant on the initial foam volume and stability of CNF-containing foam using four types of surfactants with different electrical properties. Then, we investigated the stability of CNF-containing foam under the high-pressure or high-temperature conditions as well as under the laboratory pressure and temperature condition and compared to the stability of foam containing sodium salt of CMC (NaCMC). In addition, we investigated the stability of CNF-containing foam under the presence of salts. As a result, it was concluded that the initial foam volume and stability of CNF-containing foam strongly depend on the type of surfactant because the CNF surface is negatively charged; the CNF is superior to NaCMC as a foam stabilizer, especially in the CNF concentration range above 0.10 wt%; the stability of CNF-containing foam decreases with increasing temperature and increases with increasing pressure, and it is significantly reduced with the addition of salt because the aggregation of the CNFs is formed due to the interaction between the salt cations and CNFs. Further research is expected to use CNF as a stabilizer for foam-based fracturing fluids as CNF is an attractive biomass substance as a foam stabilizer.

Orally Disintegrating Tablet Manufacture via Direct Powder Compression Using Cellulose Nanofiber as a Functional Additive.

In recent years, orally disintegrating (OD) tablets have been continuously improved to increase efficacy. Herein, we focused on the benefits of cellulose nanofiber (CNF), a highly functional material, in OD tablet manufacturing. We studied its effects on the physical properties of tablets during manufacture. The analyzed tablet formulations included different content CNF (0-50%; 6 preparations), lactose hydrate, acetaminophen, and magnesium stearate (Mg-St). We measured the angles of repose and evaluated the flowability of the powder. Tablets were prepared on a tabletop and rotary tableting presses, whereafter their weight, drug content, hardness, friability, and disintegration time were evaluated. Although CNF addition slightly reduced powder flowability, continuous tableting was feasible via direct powder compression. Tablet hardness (~40 N) was comparable between CNF-containing (20%) tablets and those prepared with crystalline cellulose under 10 kN compression force. Disintegration time (~30 s) was similar between CNF-supplemented tablets and those supplemented with low-substituted hydroxypropyl cellulose, crospovidone, or croscarmellose sodium. At higher CNF fractions, tablet hardness increased, while friability decreased. Adding ≥30% CNF prolonged the tablet disintegration time. To set the optimized manufacturing condition for ensuring the desired tablet physical properties, we created contour plots for evaluating the effects of CNF concentration and compression force on hardness and disintegration time. A CNF concentration of 10-20% and a compression force of 12-13 kN would allow for the preparation of tablets with a hardness ≥30 N and a disintegration time ≤60 s. Altogether, addition of CNF to the OD tablet formulation for direct powder compression enhanced hardness and disintegration.