Facile crosslinking methods for water-durable oven-dried cellulose nanofibril foams and their application as dye adsorbents.

The potential applications of cellulose nanofibril-based foam materials can be expanded by their enhanced water durability. This study proposes two crosslinking methods to improve the water durability of the oven-dried carboxymethylated cellulose nanofibril (CMCNF) foam. The first method involves the addition of a crosslinker, polyamideamine epichlorohydrin. The second method is the self-crosslinking of CMCNFs via heat treatment at 140 °C for less than an hour, which is a simple way to crosslink CMCNF-based materials. Both crosslinking methods resulted in excellent water durability and wet resilience of the foams, which also exhibited high water absorbency. Furthermore, neither method affected the structural nor mechanical properties of the oven-dried CMCNF foams. In particular, self-crosslinking by heat treatment proved to be as effective as using a crosslinking agent. Compared to the freeze-dried foam, the oven-dried foam exhibited slower methylene blue (MB) dye adsorption but a higher maximum adsorption capacity (238-250 mg/g), attributed to the closed pore structure and a larger specific surface area. In addition, the isotherm and reusability of the foam for MB adsorption were investigated. These crosslinking processes expanded the potential use of oven-dried CMCNF foams as adsorbents for cationic dyes.

Deep-Learning Segmentation of Urinary Stones in Noncontrast Computed Tomography.

Background: Noncontrast CT (NCCT) relies on labor-intensive examinations of CT slices to identify urolithiasis in the urinary tract, and, despite the use of deep-learning algorithms, false positives remain. Materials and Methods: A total of 410 NCCT axial scans from patients undergoing surgical treatment for urolithiasis were used for model development. The deep learning model was customized to combine a urolithiasis segmentation with per-slice classification for screening. Prediction models of the axial, coronal, and sagittal views were trained, and an additive model with an intersection of the coronal and sagittal predictions added to the axial outcome was introduced. Automated quantification of clinical metrics was evaluated in three-dimensional models of urinary stones. Results: The axial model detected 88.92% of urinary stones and produced a dice similarity coefficient of 87.56% in the urolithiasis segmentation. For urolithiasis (>5 mm), the sensitivity of the axial model reached 95.10%. False positives were reduced to 0.34 per patient using an ensemble of individual models. The additive model improved the sensitivity to 90.97% by detecting more small urolithiasis (<5 mm). All clinical metrics of size, long-axis diameter, volume, mean stone density, stone heterogeneity index, and skin-to-stone distance showed a strong correlation of R2 > 0.964. Conclusions: The proposed system could reduce the burden on the physician for imaging diagnosis and help determine treatment strategies for urinary stones through automated quantification of clinical metrics with high accuracy and reproducibility.

A waterproof cellulose nanofibril sheet prepared by the deposition of an alkyl ketene dimer on a controlled porous structure.

This study prepared a waterproof cellulose nanofibril (CNF) sheet via the deposition of an alkyl ketene dimer (AKD) on the sheet's controlled porous structure. The porosity of the CNF sheet was controlled by drying under different conditions, which included hot-press drying (HD) and solvent-exchange drying (SD), and the effect on the hydrophobization and water-related barrier performance of the sheet were investigated. When the SD sheet was immersed in an AKD wax solution, the sheet exhibited super-hydrophobicity and a lower water vapor transmission rate, compared with the HD sheet. This indicated that the porous structure of the SD sheet enabled AKD to be adsorbed on both the surface and the inner surface and it filled in the pores of the sheet, thereby giving rise to excellent waterproofing properties. The performance of a hydrophobized SD sheet as a water barrier material was comparable to a linear low-density polyethylene film. This study confirms the possibility for AKD wax to be immersed in a porous CNF sheet and used as a potential barrier material in hydrogel packaging.

Deep-learning segmentation of ultrasound images for automated calculation of the hydronephrosis area to renal parenchyma ratio.

PURPOSE: We investigated the feasibility of measuring the hydronephrosis area to renal parenchyma (HARP) ratio from ultrasound images using a deep-learning network. MATERIALS AND METHODS: The coronal renal ultrasound images of 195 pediatric and adolescent patients who underwent pyeloplasty to repair ureteropelvic junction obstruction were retrospectively reviewed. After excluding cases without a representative longitudinal renal image, we used a dataset of 168 images for deep-learning segmentation. Ten novel networks, such as combinations of DeepLabV3+ and UNet++, were assessed for their ability to calculate hydronephrosis and kidney areas, and the ensemble method was applied for further improvement. By dividing the image set into four, cross-validation was conducted, and the segmentation performance of the deep-learning network was evaluated using sensitivity, specificity, and dice similarity coefficients by comparison with the manually traced area. RESULTS: All 10 networks and ensemble methods showed good visual correlation with the manually traced kidney and hydronephrosis areas. The dice similarity coefficient of the 10-model ensemble was 0.9108 on average, and the best 5-model ensemble had a dice similarity coefficient of 0.9113 on average. We included patients with severe hydronephrosis who underwent renal ultrasonography at a single institution; thus, external validation of our algorithm in a heterogeneous ultrasonography examination setup with a diverse set of instruments is recommended. CONCLUSIONS: Deep-learning-based calculation of the HARP ratio is feasible and showed high accuracy for imaging of the severity of hydronephrosis using ultrasonography. This algorithm can help physicians make more accurate and reproducible diagnoses of hydronephrosis using ultrasonography.

Linear and nonlinear oscillatory rheology of chemically pretreated and non-pretreated cellulose nanofiber suspensions.

Linear and nonlinear rheological properties of cellulose nanofiber (CNF) suspensions were measured under small and large amplitude oscillatory shear (SAOS and LAOS) flow. Four different CNFs were produced, two by only mechanical disintegration and two with chemical pretreatments. Linear viscoelastic properties distinguished chemically treated CNFs from two untreated fibers via a different scaling exponent of the elastic modulus. However, different mechanical fibrillation degree was not characterized via linear viscoelastic properties. In contrast, nonlinear viscoelastic properties reflected both effects of chemical pretreatments and mechanical fibrillation. More fibrillated CNFs exhibited nonlinear rheological phenomena at larger deformations. In addition, chemically treated CNFs exhibited greater network stiffness and higher network recovery rates due to the presence of charged functional groups on the fiber surfaces. A material-property co-plot showed that network stiffness and recovery rate were in a trade-off relationship.

Improving the Barrier Properties of Packaging Paper by Polyvinyl Alcohol Based Polymer Coating-Effect of the Base Paper and Nanoclay.

The poor barrier properties and hygroscopic nature of cellulosic paper impede the wide application of cellulosic paper as a packaging material. Herein, a polyvinyl alcohol (PVA)-based polymer coating was used to improve the barrier performance of paper through its good ability to form a film. Alkyl ketene dimer (AKD) was used to enhance the water resistance. The effect of the absorptive characteristics of the base paper on the barrier properties was explored, and it was shown that surface-sized base paper provides a better barrier performance than unsized base paper. Nanoclay (Cloisite Na+) was used in the coating formulation to further enhance the barrier performance. The results show that the coating of PVA/AKD/nanoclay dispersion noticeably improved the barrier performance of the paper. The water vapor transmission rate of the base paper was 533 g/m2·day, and it decreased sharply to 1.3 g/m2·day after the application of a double coating because of the complete coverage of the base paper by the PVA-based polymer coating. The coated paper had excellent water resistance owing to its high water contact angle of around 100°. The grease resistance and mechanical properties of the base paper also improved after coating. This work may provide inspiration for improving the barrier properties of packaging paper through the selection of a suitable base paper and coating formulation.

Comparison of Effects of Sodium Chloride and Potassium Chloride on Spray Drying and Redispersion of Cellulose Nanofibrils Suspension.

Cellulose nanofibrils (CNFs) were exposed to the same levels of potassium chloride (KCl) and sodium chloride (NaCl) before being subjected to spray drying. The effect of NaCl and KCl on the size of atomized droplets and the hydrogen bond retardation between CNFs was investigated by characterizing product morphology, particle size distribution, dispersion stability in aqueous system, and surface chemistry. The results showed that the CNF suspensions treated with KCl could be atomized into smaller droplets during spray drying, and then CNF powder with smaller sizes could be obtained. As the agglomeration was less, and the CNF with KCl addition had good dispersion stability after redispersion compared with CNF treated by NaCl. Therefore, KCl treatment was an effective method to reduce the agglomeration of CNF during spray drying.

Incorporation of CNF with Different Charge Property into PVP Hydrogel and Its Characteristics.

Cellulose nanofibril (CNF)-added polyvinylpyrrolidone (PVP) hydrogels were prepared using different types of CNFs and their properties were investigated. CNFs with different morphology and surface charge properties were prepared through quaternization and carboxymethylation pretreatments. The quaternized CNF exhibited the narrow and uniform width, and higher viscoelastic property compared to untreated and carboxymethylated CNF. When CNF was incorporated to PVP hydrogel, gel contents of all hydrogels were similar, irrespective of CNF addition quantity or CNF type. However, the absorptivity of the hydrogels in a swelling medium increased by adding CNF. In particular, the quaternized CNF-added PVP hydrogel exhibited the highest swelling ability. Unlike that of hydrogels with untreated and carboxymethylated CNFs, the storage modulus of PVP hydrogels after swelling significantly increased with an increase in the content of the quaternized CNF. These indicate that a PVP hydrogel with a high absorptivity and storage modulus can be prepared by incorporating the proper type of CNF.

Diatom Bio-Silica and Cellulose Nanofibril for Bio-Triboelectric Nanogenerators and Self-Powered Breath Monitoring Masks.

The application of biodegradable and biocompatible materials to triboelectric nanogenerators (TENGs) for harvesting energy from motions of the human body has been attracting significant research interest. Herein, we report diatom bio-silica as a biomaterial additive to enhance the output performance of cellulose nanofibril (CNF)-based TENGs. Diatom frustules (DFs), which are tribopositive bio-silica having hierarchically porous three-dimensional structures and high surface area, have hydrogen bonds with CNFs, resulting in enhanced electron-donating capability and a more roughened surface of the DF-CNF composite film. Hence, DFs were applied to form a tribopositive composite film with CNFs. The DF-CNF biocomposite film is mechanically strong, electron-rich, low-cost, and frictionally rough. The DF-CNF TENG showed an output voltage of 388 V and time-averaged power of 85.5 mW/m2 in the contact-separation mode with an efficient contact area of 4.9 cm2, and the generated power was sufficient for instantaneous illumination of 102 light-emitting diodes. In addition, a cytotoxicity study and biocompatibility tests on rabbit skin suggested that the DF-CNF composite was biologically safe. Moreover, a practical application of the DF-CNF TENG was examined with a self-powered smart mask for human breathing monitoring. This study not only suggests high output performance of biomaterial-based TENGs but also presents the diverse advantages of the DFs in human body-related applications such as self-powered health monitoring masks, skin-attachable power generators, and tactile feedback systems.

Analysis of Spotty Deposits on Fine Paper and Investigation of Key Factors Affecting Alkyl Ketene Dimer Spot Formation.

Defect spots degrade paper quality and often cause sheet breaks and other problems in the subsequent coating process. We encountered sporadic surges of defect spots on paper from a paper machine producing printing and writing grades of paper. We found that white or light-colored filler spots and waxy, translucent, elliptical spots accounted for 27.3 and 34.4% of these defects, respectively, and that both types of defect contained unhydrolyzed AKD as a major component. Paper machine's wet-end deposits, however, did not contain unhydrolyzed AKD as a deposit component. We hypothesized that the colloidal stability of AKD was the main factor causing the increase in spot defects, and we verified this by deposit testing experiments. Among the papermaking additives tested, bentonite caused the most significant increase in AKD deposition during testing, which was attributed to its causing the electrostatic coagulation of cationically charged AKD emulsion particles. In contrast, anionically charged AKD emulsions showed improved stability and less deposit formation in the presence of bentonite.

UV/Vis Spectrometry-Based Analysis of Alkyl Ketene Dimer (AKD) Retention to Solve the Waxy Spot Problem in the Papermaking Process.

A sudden surge in the number of translucent and oval-shaped waxy spots caused a serious production loss of the papermaking process. The investigation of the spots revealed that the alkyl ketene dimer (AKD) sizing agent caused the waxy spot problem. A ultraviolet/visible (UV/vis) spectrometry method for the quantitative analysis of AKD was developed and used to reduce the waxy spot problem in paper products. The results showed that the method could be used to quantify AKD in both papermaking stock and white water. The major factors in the papermaking wet end that were associated with the waxy spot problem were evaluated, and practical approaches to solving the AKD retention problem and the waxy spot problem were proposed and implemented. The dosage of a retention aid was found to be the principal factor controlling AKD retention. However, varying the retention aid dosage resulted in the deterioration of the paper formation; therefore, this was not a suitable solution to the waxy spot problem. The type of fixing agent and AKD used was found to be the secondary factor affecting the AKD retention and papermaking system cleanliness. Mill trials were conducted on a paper machine to examine the effects of different fixing agents and AKD types on AKD retention and the waxy spot count at the reel. This approach identified a combination of fixing agent and AKD type that substantially improved AKD retention and reduced the formation of translucent waxy spots in the resulting paper products.

Preparation of Transparent and Thick CNF/Epoxy Composites by Controlling the Properties of Cellulose Nanofibrils.

Cellulose nanofibrils (CNFs) have been used as reinforcing elements in optically transparent composites by combination with polymer matrices. In this study, strong, optically transparent, and thick CNF/epoxy composites were prepared by immersing two or four layers of CNF sheets in epoxy resin. The morphology of the CNF, the preparation conditions of the CNF sheet, and the grammage and layer numbers of the CNF sheets were controlled. The solvent-exchanged CNF sheets resulted in the production of a composite with high transparency and low haze. The CNF with smaller width and less aggregated fibrils, which are achieved by carboxymethylation, and a high number of grinding passes are beneficial in the production of optically transparent CNF/epoxy composites. Both the grammage and number of stacked layers of sheets in a composite affected the optical and mechanical properties of the composite. A composite with a thickness of 450-800 µm was prepared by stacking two or four layers of CNF sheets in epoxy resin. As the number of stacked sheets increased, light transmittance was reduced and the haze increased. The CNF/epoxy composites with two layers of low grammage (20 g/m2) sheets exhibited high light transmittance (>90%) and low haze (<5%). In addition, the composites with the low grammage sheet had higher tensile strength and elastic modulus compared with neat epoxy and those with high grammage sheets.

Biological Activity of Thyme White Essential Oil Stabilized by Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) are produced by sulfonic acid hydrolysis and used for the formation of Pickering emulsion (PE) with thyme white essential oil (EO). Highly volatile and hydrophobic thyme white is encapsulated in PE by the amphiphilicity of CNCs. Encapsulation of EO in a CNC shell is determined by confocal microscopy with distinct fluorescent labelling. The amount of CNC affects the size distribution of PE, and the emulsion stability is confirmed by rheological property. The antimicrobial activity of the emulsion is evaluated against Escherichia coli and Staphylococcus aureus by minimal inhibitory concentration and minimum bactericidal concentration. The larvicidal activity is also investigated against Aedes albopictus by dispersing the emulsion in water.

Utilization of lignin fractions in UV resistant lignin-PLA biocomposites via lignin-lactide grafting.

Lignin was fractionated with several organic solvents and fractions were utilized for UV resistant lignin-PLA composites. First, soda lignin (SL) was sequentially fractionated into six fractions: ethyl acetate (F1), 2-butanone (F2), methanol (F3), acetone (F4), dioxane/water (F5), and an insoluble fraction (INS). Molecular weight of the fractions increased from F1 to F5 and phenolic hydroxyl contents decreased with increasing molecular weight of fractions. Five lignin fractions (SL, F1, F3, F5, and INS) were grafted with l-lactide to produce lignin-grafted poly-l-lactide (PLLA) copolymers. Conversion ratio of l-lactide to PLLA chains increased from 88.3% for F5-PLLA copolymer to 91.2% for F1-PLLA copolymer as the content of hydroxyl groups in the fraction increased, while the molecular weight of the copolymers showed the reverse tendency. Each copolymer was mixed with PLA 2002D, and mechanical and optical properties of the composites were investigated. Composites of F1, F3, and F5 showed a tensile strength around 65 MPa, which is similar to that of neat PLA. The elastic modulus increased from 2197.7 for F1 to 2503.4 MPa for F5. According to the investigation of UV-VIS transmittance of the composite films, composites of F3 and F5 showed better UV blocking ability than the other composites, and this UV blocking ability increased with increasing concentration of lignin copolymer.

Recycling of isopropanol for cost-effective, environmentally friendly production of carboxymethylated cellulose nanofibrils.

An approach to recycling isopropanol used in the carboxymethylation of pulp fiber was investigated as a cost-effective and environmentally friendly method of producing cellulose nanofibrils (CNF). Carboxymethylation of pulp fiber was carried out using isopropanol (IPA) as the sole solvent. IPA was recovered after carboxymethylation reaction and recycled in the next carboxymethylation reaction. Simple recycling of IPA decreased the reaction efficiency of carboxymethylation due to the increase of water content in the IPA. To dehydrate the recovered IPA, a 4 Å molecular sieve was used as a drying material. It was shown that dehydration restored carboxymethylation efficiency to the same level as when fresh IPA was used. The characteristics of the carboxymethylated CNFs produced using the recycled IPA were evaluated, including fibrillation tendency, average width, and width distribution, and it was shown that the use of recycled IPA after dehydration treatment did not cause any changes in carboxymethylated CNF properties. Recycling IPA after simple dehydration using a molecular sieve is thus a cost-effective and environmentally friendly method of producing carboxymethylated CNF.

Fractionation of lignin macromolecules by sequential organic solvents systems and their characterization for further valuable applications.

Lignin solvent fractionation is one of the promising methods for homogenizing and utilizing lignin commercially. In this work, fractionation characteristics of two lignin fractions were compared to investigate the potential of utilization of fractionated lignin. Two lignins [milled wood lignin(MWL) and organosolv lignin(OL) from yellow poplar] were sequentially fractionated with ethyl acetate(F1), 2-butanone(F2), methanol(F3), acetone(F4), and dioxane/water(F5). Yields of five MWL fractions F1 to F5 were 11.7%, 11.7%, 15.3%, 11.8%, and 49.6%, respectively, and yields of OL fractions were 26.2%, 26.1%, 18.7%, 3.7% and 25.4%. Average molecular weight of F1 (lowest molecular weight fraction) ranged from 1000 to 2400Da, whereas that of F5 (highest molecular weight fraction) was above 10000Da. According to functional group analysis, contents of phenolic hydroxyl groups and methoxyl groups decreased gradually with increasing molecular weight. DFRC analysis was performed to investigate the frequency of ß-O-4 linkages and it revealed that the higher molecular weight fractions yielded larger amounts of DFRC monomers, indicating that those fractions more frequently contain aryl ether linkages. TG/DTG showed that the low molecular weight fractions generally have lower initial thermal stability. Tg of the fractions ranged from 126°C to 156°C, increasing as the molecular weight of the lignin fraction increased.

Subnanomolar Sensitivity of Filter Paper-Based SERS Sensor for Pesticide Detection by Hydrophobicity Change of Paper Surface.

As a cost-effective approach for detecting trace amounts of pesticides, filter paper-based SERS sensors have been the subject of intensive research. One of the hurdles to overcome is the difficulty of retaining nanoparticles on the surface of the paper because of the hydrophilic nature of the cellulose fibers in paper. This reduces the sensitivity and reproducibility of paper-based SERS sensors due to the low density of nanoparticles and short retention time of analytes on the paper surface. In this study, filter paper was treated with alkyl ketene dimer (AKD) to modify its property from hydrophilic to hydrophobic. AKD treatment increased the contact angle of the aqueous silver nanoparticle (AgNP) dispersion, which consequently increased the density of AgNPs. The retention time of the analyte was also increased by preventing its rapid absorption into the filter paper. The SERS signal was strongly enhanced by the increased number of SERS hot spots owing to the increased density of AgNPs on a small contact area of the filter surface. The reproducibility and sensitivity of the SERS signal were optimized by controlling the distribution of AgNPs on the surface of the filter paper by adjusting the concentration of the AgNP solution. Using this SERS sensor with a hydrophobicity-modified filter paper, the spot-to-spot variation of the SERS intensity of 25 spots of 4-aminothiophenol was 6.19%, and the limits of detection of thiram and ferbam as test pesticides were measured to be 0.46 nM and 0.49 nM, respectively. These proof-of-concept results indicate that this paper-based SERS sensor can serve for highly sensitive pesticide detection with low cost and easy fabrication.