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Cellulose nanofibrils (CNFs) are versatile materials, but their sensitivity to humidity affects performance. Esterification with fatty acids enhances the hydrophobicity of CNF films. This study compared gas- and liquid-phase esterification using three fatty acid chlorides at different dosages. Gas-phase esterification minimally affected cellulose crystallinity, maintaining a crystallinity index exceeding 55.8%, whereas liquid-phase esterification significantly reduced crystallinity. Gas-phase esterification achieved hydrophobicity (water contact angle >100°) with less fatty acid chlorides (0.50 eq/OH) compared to liquid-phase esterification (1.00 eq/OH). Tensile strength significantly dropped in the liquid phase (68.4–6 MPa) and up to an 8-fold decrease in the elastic modulus. Conversely, gas-phase esterification maintained tensile strength over 40 MPa, and elastic modulus increased by a minimum of 2.5 times. However, gas-phase esterification resulted in a 5-fold reduction in elongation at break (%). Thermogravimetric analysis indicated a high of 362°C for liquid-phase esterified samples and a substantial 24.9% residual weight for gas-phase esterified samples.

In this study, the effect of lignin esterification with fatty acid chloride on the properties of lignin and lignin/poly(lactic acid) (PLA) composites was investigated. Lignocellulose (Pinus densiflora S. et Z.) was treated using a deep eutectic solvent (DES) with choline chloride (ChCl)/lactic acid (LA). From the DES-soluble fraction, DES-lignin (DL) was isolated by a regeneration process. Lignin esterification was conducted with palmitoyl chloride (PC). As the PC loading increased for DL esterification, the Mw of esterified DL (EDL) was increased, and the glass transition temperature (Tg) was decreased. In DL or EDL/PLA composite films, it was observed that EDL/PLA had cleaner and smoother morphological characteristics than DL/PLA. The addition of DL or EDL in a PLA matrix resulted in a deterioration of tensile properties as compared with neat PLA. The EDL/PLA composite film had a higher tensile strength and elastic modulus than the DL/PLA composite film. DL esterification decreased water absorption with lower water diffusion coefficients. The effect of lignin esterification on improving the compatibility of lignin and PLA was demonstrated. These results are expected to contribute to the development of high-strength lignin composites.

Esterified nanofibrillated cellulose (eNFC) with varying degrees of substitution was prepared using fatty acid chloride. Furthermore, the effect of esterification on properties of pure NFC and its composites with polybutylene succinate (PBS) was investigated. Lauroyl chloride (LC) with 12 carbon atoms was used for esterification. An increase in the amount of LC increased the degree of substitution (DS), which significantly decreased the water contact angle and improved the hydrophobicity of NFC. The addition of fatty acid to NFCs lowered their crystallinity. However, the fatty acid increased the hydrophobicity of NFCs, thereby improving their dispersibility in nonpolar solvents. Compared with pure NFCs, eNFC exhibited enhanced compatibility with PBS, and the addition of eNFC with an appropriate DS increased the tensile strength and elastic modulus of PBS. These findings suggest the potential of NFC esterification for improving the performance of NFC-based composite materials.

Cellulose nanofibrils (CNF) were esterified using long-chain fatty acid chlorides (octanoyl chloride, lauroyl chloride, and palmitoyl chloride) and composited with a biodegradable polymer, polybutylene succinate (PBS). The composite material was fabricated into nano-scale fibers and films via electrospinning and electrospraying processes using chloroform as a solvent. The influence of process conditions, CNF type and CNF amount on morphologies were investigated. The diameter of the electrospun fibers was ranged from 648 to 975 nm and fibers with the lowest diameters were produced at 10% concentration, 15 kV voltage and 30 µL/min flow rate. Further, PBS to CNF ratio of 95/5 and CNF esterified with lauryl chloride produced the best results. Electrospraying was achieved at a concentration of 5% or less and the tensile properties of the resulting electrosprayed films were investigated. The highest increase in tensile strength was observed at a PBS to CNF ratio of 99/1, while the most significant enhancement in elastic modulus occurred at the 95/5 ratio.

Lignin, the most abundant aromatic biopolymer on Earth, has great potential to replace petrochemical-based polymers in the production of value-added products. However, lignin is difficult to extract from lignocellulose because of the recalcitrance of the latter. Herein, the extraction of lignin from lignocellulose using deep eutectic-like solvents (DESs) as green solvents was investigated. Three types of DESs were used, and the effects of treatment temperature (100, 110, and 130 °C) and time (6, 12, and 24 h) on lignin yield and its characteristics were studied. For each DES, the yield of DES-lignin increased with reaction temperature and time. At the same time, the lignin yield obtained using different DESs decreased in the order of choline chloride/lactic acid > betaine/lactic acid > K2CO3/glycerol. At higher temperatures and longer reaction times, lignin with a high molecular weight was produced, which was attributed to the recondensation of lignin fragments. Furthermore, the methoxyl and hydroxyl group contents decreased with increasing reaction temperature and time. Thermal stability studies revealed that the increased molecular weight of DES-lignin enhanced its thermal resistance.

Wet spinning was studied for lignocellulose nanofibrils (TOLCNF) obtained by TEMPO oxidation and mechanical defibrillation of deep eutectic-like solvent-treated lignocellulose. First, the morphological characteristics, water retention value, and specific surface area of the TOLCNF were studied. The effects of the TOLCNF concentration (1.5, 2.0, and 2.5 wt%) and spinning rate (0.1, 1.0, and 10 mL/min) on the wet-spun filament diameter, orientation index, and tensile properties were studied. With an increase in the TOLCNF concentration, the average diameter increased, whereas the orientation index and tensile strength decreased. An increased spinning rate resulted in an increased orientation index and tensile strength but a decrease in the average diameter. To further extend their applicability, Ag nanoparticles (AgNPs) were grown in situ on the filament surface using UV irradiation. Spherical AgNPs with diameters of 30 to 90 nm were observed using scanning electron microscopy. An increased AgNP content improved the tensile strength and elastic modulus of the filaments.

Ionic liquids (ILs) have been widely used for lignocellulose fractionation and lignin isolation. However, the effect of IL treatment on lignin structure has been less explored. This study aimed to explore the chemical structure of lignin isolated by widely used imidazolium based ILs and compare it with the well-known milled wood lignin structure (MWL). Four types of ILs were used, and the effects of the treatment conditions on the isolated lignin (ILL) characteristics were evaluated. As the treatment temperature was increased from 60 to 140 °C, the ILL yield increased, whereas the molecular weight and hydroxyl group content decreased. Among the ILs, [EMIM]Ac produced the highest lignin yield (5.28%), and the ILL obtained had the lowest hydroxyl content (1.27 mM/g) and a molecular weight (Mw) of 29,500 g/mol. Esterification of the ILL isolated with [EMIM]Ac was performed using three fatty acid chlorides, octanoyl chloride (C8), lauroyl chloride (C12), and palmitoyl chloride (C16), to extend its applicability. The effects of esterification on the characteristics of ILL were evaluated, and successful esterification was confirmed using Fourier transform infrared and nuclear magnetic resonance spectroscopies.

Background Herein, we report a green, microwave irradiated synthesis of gold nanoparticles by using a simple, low cost and ecofriendly technique. The green technique has been developed for the synthesis of gold nanoparticles (AuNPs) from HAuCl 4 using papaya leaf extract. The papaya leaf extract served both as a reductant and a stabilizer. Method The synthesized AuNPs had been characterized by UV-Visible spectrophotometer, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Zeta potential and Transmission electron microscopy (TEM) techniques. Results The results indicated that the synthesized nanoparticles were crystalline, stable, well dispersed and spherical in shape and had an average diameter of 15 ± 2 nm. The AuNPs showed excellent catalytic activity for the reduction of p-nitrophenol (4-NP) to p-aminophenol (4-AP) in the presence of NaBH 4 . The effects of concentration of NaBH 4 , catalyst dose and temperature on the formation of nanoparticles were studied. The activation energy was found to be 28.15 ± 1.14 kJ/mol. Conclusions The papaya leaf extract capped AuNPs are highly stable, and have showed effective catalytic activity in the reduction of 4-NP to 4-AP and antimicrobial activity on both gram-positive and gram-negative bacteria.

Simultaneous fluorometric determination of iron(III) and copper(II) without the use of any masking agent or additional treatment is achieved by using N-doped carbon dots (NCDs). The NCDs were hydrothermally prepared, have strongest excitation/emission peaks at 320/406 nm and a 47% quantum yield. Excitation-tunable emission is found to depend on solution pH values. This supports the involvement of surface states in the origin of the excitation dependent nature. The NCDs were employed as a fluorescent probe for the simultaneous determination of Fe(III) with a linear response in the 3–60 μM concentration range and a 0.31 μM detection limit (LOD). The probe also responds linearly to Cu(II) in the 0.5–15 μM concentration range and with a 56 nM LOD. With the addition of Cu(II), the absorption spectra of NCDs presented a clear decrease in the intensity at 312 nm followed by an increase at 360 nm. This is not observed in the presence of Fe(III). The fluorescence lifetime of NCDs (5.8 ns) is reduced by Fe(III) but not by Cu(II). Thus, the two metal ions can be simultaneously detected without the need for any reagents. The probe was employed to quantify Fe(III) and Cu(II) in spiked water, serum, and urine samples. Graphical abstract Schematic representation of hydrothermal synthesis of highly fluorescent N-doped carbon dots with novel pH dependent emission and their application for the simultaneous determination of Cu(II) and Fe(III) with individual ion discrimination.

Background A facile and eco-friendly method for green synthesis of silver nanoparticles (AgNPs) has been developed using gum tragacanth (GT) (Astragalus gummifer), an abundantly available natural phyto-exudate in India, employing a novel method of ultrasonication process. Methods Silver nanoparticles were prepared by the reduction of silver nitrate solution by the aqueous extract of gum tragacanth by ultrasonication method at 45 °C for about 45 min. The aqueous extract of the gum acts as a reducing as well as stabilizing agent. Results The resultant AgNPs were characterized by ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. The influence of gum concentration and silver precursor concentration on the synthesis of AgNPs was studied. The role and effectiveness of nanoparticles in the catalytic reduction of a cationic dye methylene blue (MB), and an anionic azo dye Congo red (CR), were also studied. FTIR analysis revealed that –OH groups present in the gum matrix might be responsible for the reduction of Ag+ into AgNPs. The X-ray diffraction studies indicated that the resulting AgNPs were highly crystalline with face-centered cubic geometry. TEM studies showed that the average particle size of the synthesized AgNPs was 18 ± 2 nm. Conclusions The study highlights the green synthesis of GT-capped AgNPs and the rapid reduction of carcinogenic and toxic contaminants such as MB and CR with the help of GT-capped AgNPs in an eco-friendly manner.