This paper reports an investigation of the effects of solvent system, solution concentration, and applied electrostatic field
strength (EFS) on the morphological appearance and/or size of as-spun cellulose acetate (CA) products. The single-solvent
systems were acetone, chloroform, N,N-dimethylformamide (DMF), dichloromethane (DCM), methanol (MeOH), formic acid, and pyridine. The mixed-solvent systems were
acetone–DMAc, chloroform–MeOH, and DCM–MeOH. Chloroform, DMF, DCM, MeOH, formic acid, and pyridine were able to dissolve CA,
forming clear solutions (at 5% w/v), but electrospinning of these solutions produced mainly discrete beads. In contrast, electrospinning of the solution of
CA in acetone produced short and beaded fibers. At the same solution concentration of 5% (w/v) electrospinning of the CA solutions was improved by addition of MeOH to either chloroform or DCM. For all the solvent systems
investigated smooth fibers were obtained from 16% (w/v) CA solutions in 1:1, 2:1, and 3:1 (v/v) acetone–DMAc, 14–20% (w/v) CA solutions in 2:1 (v/v) acetone–DMAc, and 8–12% (w/v) CA solutions in 4:1 (v/v) DCM–MeOH. For the as-spun fibers from CA solutions in acetone–DMAc the average diameter ranged between 0.14 and 0.37 μm
whereas for the fibers from solutions in DCM–MeOH it ranged between 0.48 and 1.58 μm. After submersion in distilled water
for 24 h the as-spun CA fibers swelled appreciably (i.e. from 620 to 1110%) but the physical integrity of the fibrous structure
remained intact. 相似文献
In the present study, cellulose acetate (CA) nanofibers were prepared by electrospinning technique. Alkaline hydrolysis was introduced for conversion of CA nanofibers to cellulose nanofibers. Nanofibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). Furthermore, silver nanoparticles (AgNPs) were incorporated on regenerated cellulose nanofibers with different concentrations and used as an antimicrobial agent against Gram negative Escherichia coli BH5 α , Gram positive Spectromyces arenus, and Aspergillus flavus. Strong inhibition activities were determined. 相似文献
Composite chitosan nanofibers containing 20 wt % chitin nanofibrils and 10 wt % PEO are obtained via the electrospinning method. Additions of 0.5–20.0 wt % chitin nanofibrils into chitosan solutions with concentrations of 3–7 wt % in acetic acid (70 vol %) insignificantly increase the electrical conductivity, surface-tension coefficient, and viscosity of these mixed solutions. Decreases in the viscosities of chitosan solutions containing chitin nanofibrils with increases in shear rate provide evidence for the structuring of solutions and the orientation of chitosan macromolecules and chitin nanofibrils in the shear flow. The effects of shear stress and a high-voltage electric field on chitosan solutions containing chitin nanofibrils and PEO result in a decrease in the imperfection of composite nanofibers. The introduction of chitin nanofibrils allows the content of PEO in the composite nanofibers to be reduced. 相似文献
Curaua nanofibers extracted under different conditions were investigated. The raw fibers were mercerized with NaOH solutions;
they were then submitted to acid hydrolysis using three different types of acids (H2SO4, a mixture of H2SO4/HCl and HCl). The fibers were analyzed by cellulose, lignin and hemicellulose contents; viscometry, X-ray diffraction (XRD)
and thermal stability by thermogravimetric analysis (TG). The nanofibers were morphologically characterized by transmission
electron microscopy (TEM) and their surface charges in suspensions were estimated by Zeta-potential. Their degree of polymerization
(DP) was characterized by viscometry, crystallinity by XRD and thermal stability by TG. Increasing the NaOH solution concentration
in the mercerization, there was a decrease of hemicellulose and lignin contents and consequently an increase of cellulose
content. XRD patterns presented changes in the crystal structure from cellulose I to cellulose II when the fibers were mercerized
with 17.5% NaOH solution. All curaua nanofibers presented a rod-like shape, an average diameter (D) of 6–10 nm and length
(L) of 80–170 nm, with an aspect ratio (L/D) of around 13–17. The mercerization of fibers with NaOH solutions influenced the
crystallinity index and thermal stability of the resulting nanofibers. The fibers mercerized with NaOH solution 17.5% resulted
in more crystalline nanofibers, but thermally less stable and inferior DP. The aggregation state increases with the amount
of HCl introduced into the extraction, due to the decrease of surface charges (as verified by Zeta Potential analysis). However,
this release presented nanofibers with better thermal stability than those whose acid hydrolysis was carried out using only
H2SO4. 相似文献
The aim of this study was to develop cellulose nanofibers with hydrophobic surface characteristics using chemical modification.
Kenaf fibers were modified using acetic anhydride and cellulose nanofibers were isolated from the acetylated kenaf using mechanical
isolation methods. Fourier transform infrared spectroscopy (FTIR) indicated acetylation of the hydroxyl groups of cellulose.
The study of the dispersion demonstrated that acetylated cellulose nanofibers formed stable, well-dispersed suspensions in
both acetone and ethanol. The contact angle measurements showed that the surface characteristics of nanofibers were changed
from hydrophilic to more hydrophobic when acetylated. The microscopy study showed that the acetylation caused a swelling of
the kenaf fiber cell wall and that the diameters of isolated nanofibers were between 5 and 50 nm. X-ray analysis showed that
the acetylation process reduced the crystallinity of the fibers, whereas mechanical isolation increased it. The method used
provides a novel processing route for producing cellulose nanofibers with hydrophobic surfaces. 相似文献
Rapid global industrialization has worsened the heavy metal contamination of aquatic ecosystems globally. In this study, green, ultrafine cellulose-based porous nanofibrous membranes for efficient heavy metal removal were obtained by incorporating chitosan (CS) and using conventional and core–shell electrospinning ways. The relationship between the parameters of the electrospinning solution, the micro-morphology and porosity, the chemically active sites, the thermal stability, and the adsorption performance of the biocomposite nanofibrous membranes were analyzed. The adsorption effects of the copper ions, including the initial concentration, solution pH, and interaction time, were investigated. The results show that the average diameters of the conventional and core–shell ultrafine nanofibers with 50% and 30% CS loading are 56.22 nm and 37.28 nm, respectively. The core–shell cellulose acetate (CA)/CS biocomposite nanofibrous membranes showed the weaker thermal stability with a 48.2 °C lower maximum thermal decomposition temperature and induced the surface aggregation of more copper ions compared to the conventional one. A more uniform distribution of the chemical adsorption sites is obtained by conventional single-nozzle electrospinning than by core–shell electrospinning, which effectively promotes the adsorption performance of copper ions and decreases the surface shrinkage of the nanofibrous membranes during adsorption. The 30% CS conventional nanofibrous membranes at an aqueous solution pH of 5 showed the optimum adsorption capacity of copper ions (86.4 mg/g). The smart combination of renewable biomass with effective chemical adsorption sites, electrospinning technology that produces an interwoven porous structure, and an adsorption method with low cost and facile operation shows a promising prospect for water treatment.
Cellulose and chitin exist in nature as highly crystalline nanofibers. Previously, we reported preparing unique hydrogels from cellulose nanofibers by a simple NaOH treatment without use of any specific solvents or cross-linking agents. In the present study, a similar gel preparation was applied to β-chitin nanofibers extracted from purified squid pen powder. The crystal structure of chitin nanofibers was transformed from β-chitin to α-chitin by NaOH(aq) treatment above 30 wt%. The crystal conversion involving the interdigitation among adjacent nanofibers caused the formation of stable hydrogels with a α-chitin nanofiber network. The use of ethanol voided the dissolution during neutralization and enabled preparation of a higher crystalline hydrogel with high mechanical strength. It achieved a Young’s modulus of 16.6 MPa, a tensile strength of 7 MPa and a strain at break of 52.2 %, on average. Finally, we note that the shrinkage of the cellulose I and β-chitin nanofibers in aqueous NaOH solutions was caused by the release of tensile residual stress due to the intracrystalline swelling in NaOH solutions. 相似文献
Chitosan/poly(ethylene oxide) (PEO) (5:1) nanofibers with cellulose nanocrystals (CNCs) were produced using an electrospinning technique. The addition of CNCs to the chitosan/PEO solutions allowed the production of uniform fibers (without beads) with a high proportion of chitosan. The fiber diameters were influenced by the concentration of CNCs in the chitosan/PEO solutions. The solutions containing 10% (w/w) of CNCs produced thinner fibers compared to solutions containing 5% (w/w) of CNCs. Thermogravimetric analysis indicated that the nanofibers were thermally stable, despite the CNCs having an effect on the PEO decomposition. Results from the cell assay in cultures of 3T3 fibroblasts indicated that the chitosan/PEO nanofibers (with 10% CNCs) promoted cell attachment with changes in the cytoskeletal organization. The results obtained in this work highlight the favorable effect of CNCs in electrospinning of chitosan/PEO. As expected, the influence of nanofibers on 3T3 fibroblasts F-actin and β-tubulin network revealed alterations in cytoskeleton, leading to changes in cell morphology and spreading. 相似文献
Cellulose nanofibers with a diameter of 70 nm and lengths of approximately 400 nm were fabricated from partly mercerized cotton fibers by acid hydrolysis. Morphological evolution of the hydrolyzed cotton fibers was investigated by powder X-ray diffraction, Fourier transform infrared analysis and field emission scanning electron microscopy. The XRD results show that the cellulose I was partially transformed into cellulose II by treatment with 15 % NaOH at 150° for 3 h. The crystallinity of this partially mercerized sample was lower than the samples that were converted completely to cellulose II by higher concentrations of NaOH. The intensities of all of the diffraction peaks were noticeably increased with increased hydrolysis time. Fourier transform infrared results revealed that the chemical composition of the remaining nanofibers of cellulose I and II had no observable change after acidic hydrolysis, and there was no difference between the hydrolysis rates for cellulose I or II. The formation of cellulose nanofibers involves three stages: net-like microfibril formation, then short microfibrils and finally nanofibers. 相似文献
Cellulose (Cell) nanofibrous membranes were prepared by nucleophilic reaction of the cellulose hydroxyl with the triazinyl chloride of Cibacron Blue F3GA (CB) ligand and studied as affinity membranes for lipase enzyme. Cell nanofibrous membranes containing fibers with 200 nm average diameters were prepared by electrospinning of cellulose acetate (CA), followed by alkaline hydrolysis. The CB capacity of the Cell nanofibrous membranes was optimized by lengthening the nucleophilic reaction time and increasing CB concentration and ionic strength. The equilibrium adsorption isotherms of CB on the Cell nanofibrous membranes followed a typical Langmuir monolayer adsorption behavior. At 242 mg CB/g of Cell, the maximum lipase adsorption capacity (qm) and the dissociation constant (Kd) values were 41.02 mg/g and 0.25 mg/mL, respectively. Optimal lipase adsorption capacity was obtained at pH 4.0, its isoelectric point, with added NaCl on Cell membranes 86 mg CB capacity per g of Cell. A facile lipase loading capacity of 16.21 mg/g of CB–Cell was achieved under moderated conditions and could be optimized to reach at least 150 mg/g. The CB–Cell bound lipase had similar catalytic rate and retained 86.2% activity as in its free form. These findings clearly show that the CB bound Cell nanofibrous membrane is a highly efficient ultra-high specific porous support for lipase enzyme and is potentially versatile for immobilizing other enzymes and as affinity membrane for proteins. 相似文献
Nowadays, encapsulated dyes in a polymeric matrix have opened up new perspectives in many applications such as filtration of subatomic particles, composite reinforcement, multifunctional membranes, tissue engineering scaffolds, wound dressing, coatings, medical purposes as well as sensors. In the presented work, we report on electrospinning neat peryelene dianhydride based thermoplastic elastomers. Perylene‐3, 4,9, 10‐tetracarboxylic dianhydride (PDA) is encapsulated into cellulose acetate (CA) electrospun fibers, which was prepared from 12 % cellulose acetate solution, at 20 kV with a distance of 10 cm. The flow rate was 0.2 ml · h–1. These water repellent nanofibrous coatings are anticipated to serve as hydrophobic coatings. Scanning electron microscope is used to study the properties of the electrospun PDA‐CA nanofibers. 相似文献
Fairly uniform chitosan (CS)/poly(ethylene oxide) (PEO) ultrafine fibers containing silver nanoparticles (AgNPs) were successfully
prepared by electrospinning of CS/PEO solutions containing Ag/CS colloids by means of in situ chemical reduction of Ag ions.
The presence of AgNPs in the electrospun ultrafine fibers was confirmed by X-ray diffraction patterns. The AgNPs were evenly
distributed in CS/PEO ultrafine fibers with the size less than 5 nm observed under a transmission electron microscope. X-ray
photoelectron spectroscopy suggested that the existence of Ag―O bond in the composite ultrafine fibers led to the tight combination
between Ag and CS. Evaluation of antimicrobial activities of the electrospun Ag/CS/PEO fibrous membranes against Escherichia coli showed that the AgNPs in the ultrafine fibers significantly enhanced the inactivation of bacteria. 相似文献
Carbon nanofibers with new structural features, e.g. nanoporosity, hollow, U-shape cross-section, were generated by utilizing the phase separation behavior of polymer additive with polyacrylonitrile (PAN). The approach involved the formation of precursor fibers by electrospinning of binary mixtures of PAN with poly(ethylene oxide) (PEO), cellulose acetate (CA) or poly(methyl methacrylate) (PMMA), the removal of the polymer and the carbonization of the remaining PAN. The carbon nanofiber yield was ca 50% of PAN in all cases. Nanoporous carbon nanofibers with an average diameter of 100 nm were generated from the water treated PAN/PEO precursors. Multi-channel hollow fibers (90-190 nm diameters) were produced from the acetone treated PAN/CA precursors. Carbon fibers produced from the chloroform treated PAN/PMMA precursors were 250-400 nm in diameters and consisted of varied hollow structures, i.e., hollow and U-shape cross-sections from those containing 30% and 50% PAN, respectively, and multi-channel hollow fibers from the 70/30 PAN/PMMA precursor. Carbonization of equal-mass PAN/PMMA as-spun fibers also produced similarly U-shape cross-sections as the chloroform treated ones, showing promise of direct carbonization. This simple and yet versatile approach to create new structural features in carbonized fibers has shown to depend on the distinct phase separation as well as the pyrolytic behaviors of the second polymer component. 相似文献
Hybrid nanofibers from chitosan or N‐carboxyethylchitosan (CECh) and silver nanoparticles (AgNPs) were prepared by electrospinning using HCOOH as a solvent. AgNPs were synthesized in situ in the spinning solution. HCOOH slowed down the cross‐linking of the polysaccharides with GA enabling the reactive electrospinning in the presence of poly(ethylene oxide) (PEO). EDX analyses showed that AgNPs are uniformly dispersed in the nanofibers. Since AgNPs hampered the cross‐linking of chitosan and CECh with GA in the hybrid fibers, the imparting of water insolubility to the fibers was achieved at a second stage using GA vapors. The surface of chitosan/PEO/AgNPs nanofibers was enriched in chitosan and 15 wt.‐% of the incorporated AgNPs were on the fiber surface as evidenced by XPS.
A series of novel human‐made functional fibers (biofibers) based on chitin and chitosan are prepared by the wet‐spinning and the post chemical modification of chitosan fiber. The wet‐spinning gives rise to a series of biofibers: chitin, chitosan, chitin‐cellulose, chitosan‐cellulose, chitin‐silk fibroin, chitin‐glycosaminoglycans, chitin‐cellulose‐silk fibroin, chitosan‐tropocollagen, and chitin‐cellulose‐silk fibroin. The post chemical modification of chitosan fiber gives rise to a series of chemically modified fibers: N ‐acylchitosans, N ‐arylidene‐ and N ‐alkylidene‐chitosans, N ‐acetylchitosan (chitin)‐tropocollagen, and chitosan‐transition metal complexes. Some of the current and potential applications of these biofibers are described. 相似文献
This work reports production of nanofibers of cellulose acetate (CA) via electrospinning (ES) technology. Optimal operating conditions to produce nanofibers have been found to involve CA solutions at 20 wt% concentration, flow rate 1.0 mL h?1, a distance between needle tip-collector target of 15 cm and an applied voltage at 20 kV. Under these experimental conditions, nanofibers were produced by ES a solution containing a low concentration of a luminescent fluorene-based cationic conjugated polyelectrolyte. Electronic and optical microscopies were used to characterize their morphology and the diameter of fibers (over 260 nm). Composite fibers with excellent luminescence properties have been obtained and studied in the solid state. Potential applications in a sensing device for nitrobenzene have been tested. 相似文献