Preparation of submicron‐scale,electrospun cellulose fibers via direct dissolution

Cellulose nonwoven mats of submicron‐sized fibers (150 nm–500 nm in diameter) were obtained by electrospinning cellulose solutions. A solvent system based on lithium chloride (LiCl) and N,N‐dimethylacetamide (DMAc) was used, and the effects of (i) temperature of the collector, (ii) type of collector (aluminum mesh and cellulose filter media), and (iii) postspinning treatment, such as coagulation with water, on the morphology of electrospun fibers were investigated. The scanning electron microscopy (SEM) and X‐ray diffraction studies of as‐spun fibers at room temperature reveal that the morphology of cellulose fibers evolves with time due to moisture absorption and swelling caused by the residual salt and solvent. Although heating the collector greatly enhances the stability of the fiber morphology, the removal of salt by coagulation and DMAc by heating the collector was necessary for the fabrication of dry and stable cellulose fibers with limited moisture absorption and swelling. The presence and removal of the salt before and after coagulation have been identified by electron microprobe and X‐ray diffraction studies. When cellulose filter media is used as a collector, dry and stable fibers were obtained without the coagulation step, and the resulting electrospun fibers exhibit good adhesion to the filter media. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1673–1683, 2005     

Electrospinning of ultra-thin polymer fibers

The electrospinning technique was used to spin ultra-thin fibers from several polymer/solvent systems. The diameter of the electrospun fibers ranged from 16 nm to 2 μm. The morphology of these fibers was investigated with an atomic force microscope (AFM) and an optical microscope. Polyethylene oxide) (PEO) dissolved in water or chloroform was studied in greater detail. PEO fibers spun from aqueous solution show a “beads on a string” morphology. An AFM study showed that the surface of these fibers is highly ordered. The “beads on a string” morphology can be avoided if PEO is spun from solution in chloroform; the resulting fibers show a lamellar morphology. Polyvinylalcohol (PVA) dissolved in water and cellulose acetate dissolved in acetone were additional polymer/solvent systems which were investigated. Furthermore, the electrospinning process was studied: different experimental lay-outs were tested, electrostatic fields were simulated, and voltage - current characteristics of the electrospinning process were recorded.     

Controlling the surface structure,mechanical properties,crystallinity, and piezoelectric properties of electrospun PVDF nanofibers by maneuvering molecular weight

Polyvinylidene fluoride (PVDF) is a significant polymer in the formation of nanofiber webs via the electrospinning technique. In this paper, three PVDF-wrinkled fiber webs with different molecular weights (M_Ws) (180000, 275000, and 530000) were generated via the electrospinning method by using tetrahydrofuran/N,N-dimethylformamide at the solvent ratio of 1:1 as a mixed solvent. The formation mechanism of the wrinkled electrospun PVDF fibers is demonstrated. Furthermore, the relationships between the M_W and the surface structure, mechanical properties, crystalline phases, and piezoelectric properties of electrospun PVDF fibers are comprehensively investigated. The results reported that the surface structure, mechanical properties, crystalline phases, and piezoelectric properties of wrinkled electrospun PVDF fibers can be affected intensely by maneuvering the M_W. We believe this study can be served as a good reference for the effect of M_W on the morphology and properties of electrospun fibers.     

EFFECT OF GAS FLOW RATE ON CRYSTAL STRUCTURES OF ELECTROSPUN AND GAS-JET/ELECTROSPUN POLY(VINYLIDENE FLUORIDE) FIBERS

The effect of gas flow rate on crystal structures of electrospun and gas-jet/electrospun poly(vinylidene fluoride) (PVDF) fibers was investigated.PVDF fibers were prepared by electrospinning and gas-jet/electrospinning of its N,N-dimethylformamide (DMF) solutions.The morphology of the PVDF fibers was investigated by scanning electron microscopy (SEM).With an increase of the gas flow rate,the average diameters of PVDF fibers were decreased.The crystal structures and thermal properties of the PVDF fibers w...     

Solvent degradation of nylon-6 and its effect on fiber morphology of electrospun mats

In this work, we studied solvent-induced polymer degradation and its effect on the morphology of electrospun fibers. Nylon-6 in formic acid solvent was allowed to degrade by simply allowing it to stand for a long time, and nanofibrous mats were fabricated by taking a fraction of this solution at different time intervals via electrospinning under the same electrospinning conditions. FE-SEM images of the mats indicate that the nanofiber diameter gradually decreased with the standing time of solution, and large numbers of true nano fibers (<50 nm in diameter) were obtained. MALDI-TOF analysis revealed that the formation of low-molecular weight ions was caused by solvent degradation. FT-IR, DSC, XRD, and TGA analyses of electrospun mats showed that some physical properties, such as bond strength, crystallinity, and thermal stability also depended on solvent degradation. The obtained sub-nanofibrous mat has potential applications in different bioengineering fields.     

PHBV电纺纤维结构与形态的研究

利用电纺丝法制备了超细聚 β 羟基丁酸戊酸酯 (PHBV)纤维 ,通过扫描显微镜 (SEM)、差热分析(DSC)、宽角X射线衍射和偏振红外吸收光谱对产品进行了结构与形态的表征 .研究了纺丝过程中溶液浓度、电压和接收距离 3个参数对纤维形态的影响 .结果表明 ,溶液浓度是决定性的 ,只有高于一个定值才能获得单一的纤维产品 .与流延成型的PHBV相比 ,电纺丝具有较高的取向度和结晶度 .原因可能是 ,电场力下喷丝震荡过程中带来的拉伸作用从而引起分子链的规整排列     

Facilely preparing various new titania electrospun fibers with controllable nanostructures using a three-step method

A facile three-step method is developed to prepare new titania fibers with various special structures using a standard electrospinning equipment. After the traditional electrospinning, a treatment process, such as storing in air and soaking in water, for electrospun composite fibers is added before the calcination. Based on a given electrospinning solution and corresponding composite fiber, the structure of titania fiber is easily adjusted to be rough surface, fiber-in-tube, or a string of many particles by controlling the treating parameters and the calcination temperature, so this method shows a great potential of producing ceramic nanofibers with controlled structures for a large-scale production using a standard electrospinning equipment. The origin behind the morphological change of titania electrospun fibers is intensely studied. The results indicate that the surface structure of titania electrospun fiber formed during the storing period, will become the key factor on the formation of special titania fiber structure during the calcination process with different temperatures.     

原生纤维素静电纺丝的调控

通过电纺非溶剂调控的纤维素溶液, 制备出纤维素电纺纤维. 在N,N-二甲基乙酰胺(DMAc)-氯化锂(LiCl)溶解纤维素体系中, 以DMAc和N,N-二甲基甲酰胺(DMF)作为非溶剂, 添加到高浓度的纤维素溶液中制备电纺溶液. 考察添加非溶剂对纤维素溶液性质和电纺纤维形貌的影响. 结果表明, 添加非溶剂有助于提升纤维素溶液的可纺浓度, 获得分散性较好的电纺纤维, 其中DMF效果最好. 添加非溶剂降低了纤维素溶液的黏度, 使纤维素溶液可纺浓度提高; 添加非溶剂改变了电纺溶液的稳定性, 获得了分散良好的纳米纤维, 从而有助于纤维素射流在电纺过程中快速固化成型.     

Electrospun poly(3‐hexylthiophene)/poly(ethylene oxide)/graphene oxide composite nanofibers: effects of graphene oxide reduction

In this article, we report on the production by electrospinning of P3HT/PEO, P3HT/PEO/GO, and P3HT/PEO/rGO nanofibers in which the filler is homogeneously dispersed and parallel oriented along the fibers axis. The effect of nanofillers' presence inside nanofibers and GO reduction was studied, in order to reveal the influence of the new hierarchical structure on the electrical conductivity and mechanical properties. An in‐depth characterization of the purity and regioregularity of the starting P3HT as well as the morphology and chemical structure of GO and rGO was carried out. The morphology of the electrospun nanofibers was examined by both scanning and transmission electron microscopy. The fibrous nanocomposites are also characterized by differential scanning calorimetry to investigate their chemical structure and polymer chains arrangements. Finally, the electrical conductivity of the electrospun fibers and the elastic modulus of the single fibers are evaluated using a four‐point probe method and atomic force microscopy nanoindentation, respectively. The electrospun materials crystallinity as well as the elastic modulus increase with the addition of the nanofillers while the electrical conductivity is positively influenced by the GO reduction. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrospun PDA‐CA Nanofibers toward Hydrophobic Coatings

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.     

Electrospinning of poly(trimethylene terephthalate)/carbon nanotube composites

Poly(trimethylene terephthalate) (PTT) nanocomposites containing carbon nanotubes (CNTs) with different surface structure and aspect ratio were prepared by melt compounding for electrospinning. The dispersion state of the CNTs in the composites was then examined utilizing rheology tools. The results show that carboxylic surface functionalized CNTs present better dispersion in the matrix than hydroxy surface functionalized CNTs because the former has stronger affinity to the PTT. Besides surface functionalization, the aspect ratio of CNTs is also vital to their final dispersion. The CNTs with lower aspect ratio are dispersed as individuals or small bundles while those with higher aspect ratio are dispersed mainly as flocs with large hydrodynamic radius, showing higher effective volume fraction. The presence of CNTs has a large influence on the morphologies of electrospun fiber and on the appearances of CNTs in the fibers. In the presence of CNTs with lower aspect ratio, continuous composite fibers are obtained. But the structure of those continuous fibers highly depends on the surface group of CNTs. Carboxylic surface functionalized CNTs are well embedded by the PTT and oriented along the fiber axis during electrospinning, leading to bead-free and uniform fiber morphology; while hydroxy surface functionalized CNTs show tortuous conformations with less orientation in the fibers, and as a result, the obtained fibers show beaded and misshaped morphologies. In the case of higher aspect ratio, however, the CNTs prefer to exist as entanglements or knots in the streamlines, and thereby only beaded or even uncontinuous fibers are obtained. Therefore, the formation and fiber morphology of PTT/CNT composite fibers obtained by electrospinning strongly depend on the surface functional groups of the CNTs, as well as on the CNT structure.     

Thermodynamic modeling and investigation of the formation of electrospun collagen fibers

Electrospun type I collagen fibers are very promising materials for tissue scaffold applications, but are typically fabricated from toxic solvents. Recently, electrospinning of type I collagen fibers by using environmentally friendly phosphate buffer saline (PBS)/ethanol solution has been explored. PBS/ethanol solvent systems offer better cell compatibility, but the high surface tension and high boiling point of the solvent system make the collagen difficult to electrospin and can cause inferior fiber morphology. In this study, the influence of solvent surface tension on the morphology of electrospun collagen fibers has been experimentally investigated and analyzed from a thermodynamics perspective. The analytical results indicate that solvents with high surface tension drive the formation of beads along the smaller, thinner fibers. In addition, beads with relatively small angular eccentricity were thermodynamically favorable. The experimental results presented herein corroborate the theoretical analysis and conclusions drawn from this study. The surface tension of the solvent has significant influence on the bead formation, especially in an aqueous system. The environmental humidity for the electrospinning process and the collagen concentration were also investigated. These parameters may result in variations of the evaporation-solidification rates, which consequently impact the formation and morphologies of electrospun collagen fibers. According to the thermodynamic analysis, uniform electrospun collagen fibers without beads can be obtained by manipulating solvent surface tension during the electrospinning process.     

Investigation of nanomechanical and morphological properties of silane-modified halloysite clay nanotubes reinforced polycaprolactone bio-composite nanofibers by atomic force microscopy

There is remarkable interest in the fabrication of polymeric composite nano/micro-fibers by electrospinning for many applications ranging from bioengineering to water/air filtration. In almost all of these applications, the mechanical properties of both the polymer fibers and their assemblies, are significant. In this study, unmodified, 3-Glycidoxypropyltrimethoxysilane (GPTMS) or 3-Aminopropyltriethoxysilane (APTES) modified halloysite clay nanotube (HNT) reinforced polycaprolactone (PCL) nanofibers were successfully synthesized via the electrospinning. The morphology and mechanical features of the obtained electrospun fibers were investigated by atomic force microscopy (AFM) and AFM-based nanoindentation for single fibers in nanoscale, respectively. Besides, scanning electron microscopy and tensile strength tests were used to investigate whole fibrous structures in microscale. The AFMresults, accompanied by SEM and tensile strength, support the conclusion that silane-modification affected positively the morphology and mechanical characteristics of electrospun PCL nanofibers. Therefore, it was concluded that the morphological and mechanical features from the single fibers in the nanofiber mats were related to the whole fibrous structure.     

Morphology,Crystallization Behavior and Tensile Properties of β-Nucleated Isotactic Polypropylene Fibrous Membranes Prepared by Melt Electrospinning

β-nucleated isotactic polypropylene(iPP) fibers with diameters less than 5 μm were prepared through melt electrospinning. The effects of electrospinning process and rare earth β-nucleating agent(WBG) on the crystal structure of iPP fibers were investigated. The results indicate that the addition of WBG can improve the fluidity of iPP melt remarkably and help the formation of fine fibers with thinner diameter, while the electrostatic force applied on the iPP melt is not favorable for the formation of β-crystal in iPP fibers. In addition, the morphology and crystalline structure of WBG/iPP electrospun fibers depended on the content of WBG. Both the crystallinity and the percentage of β-crystal form of WBG/iPP electrospun fibers increase with the rise of the content of nucleating agent, which endows the prepared electrospun fibers excellent mechanical properties. The β-nucleated iPP electrospun fibrous membranes prepared in this study can be used for protective clothing material, filtration media, reinforcement for composites and tissue engineering scaffolds.     

Preparation of polybenzoxazole fibers via electrospinning and postspun thermal cyclization of polyhydroxyamide

Polybenzoxazole (PBO) fibers with a submicron diameter were successfully prepared by electrospinning its precursor, polyhydroxyamide (PHA), solutions to obtain the PHA fibers first, followed by appropriate thermal treatments for cyclization reaction. BisAPAF‐IC PHA with two different molecular weights (MWs) were synthesized from a low temperature polymerization of 2,2′‐bis(3‐amino‐4‐hydroxyphenyl) hexafluoropropane (BisAPAF) and isophthaloyl chloride (IC). Using dimethylacetamide (DMAc) and tetrahydrofuran (THF), solvent effects on the electrospinnability of PHA solutions were investigated. For balancing the solution properties, it was found that DMAc/THF mixture with a weight ratio of 1/9 was the best cosolvent to prepare smooth PHA fibers; uniform PHA fibers with a diameter of 325–720 nm were obtained by using 20 wt % PHA/(DMAc/THF) solutions. For a fixed PHA concentration, solutions with a lower MW of PHA yielded thinner electrospun fibers under the same electrospinning condition. After obtaining the electrospun BisAPAF‐IC PHA fibers, subsequent thermal cyclization up to 350 °C produced the corresponding thermally stable BisAPAF‐IC PBO fibers with a diameter of 305–645 nm. The structure of the precursor fibers and the fully cyclized fibers were characterized by FTIR. For the cyclized BisAPAF‐IC PBO fibers, thermogravimetric analysis showed a 5% weight loss temperature at 523 °C in nitrogen atmosphere. The interconnected fiber structure in the BisAPAF‐IC PBO fiber mats was irrelevant to the curing process, but resulted from the jet merging during the whipping process as revealed by the high speed camera images. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8159–8169, 2008     

Simple fabrication of cellulose nanofibers via electrospinning of dissolving pulp and tunicate

This work demonstrates a simple fabrication of cellulose nanofibers by direct electrospinning of dissolved cellulose solutions. The hard- and softwood pulps and the outer mantles of tunicate were dissolved in a mixture of trifluoroacetic acid and dichloroethane by stirring and ultrasonication to give highly viscoelastic, clear solutions. These solutions were electrospun to form continuous nanofibers made of unsubstituted cellulose, which were confirmed by scanning electron microscopy (SEM) and IR spectroscopy. Statistical analysis of the SEM images of the nanofibers suggested that there are positive correlations between diameters of the nanofibers and concentration of the cellulose solution. The mean diameters of the nanofibers obtained from softwood pulp (DP of cellulose ≈ 1200) solutions were larger than those from hardwood pulp (DP of cellulose ≈ 500) at the same concentrations. This indicates that the DP of cellulose is one of the important parameters to control the diameters of the electrospun cellulose nanofibers.     

Bioactive Electrospun Fibers of Poly(ε-Caprolactone) Incorporating α-Tocopherol for Food Packaging Applications

Antioxidant activity is an important feature for food contact materials such as packaging, aiming to preserve freshness and retard food spoilage. Common bioactive agents are highly susceptible to various forms of degradation; therefore, protection is required to maintain functionality and bioavailability. Poly(ε-caprolactone) (PCL), a biodegradable GRAS labeled polymer, was used in this study for encapsulation of α-tocopherol antioxidant, a major component of vitamin E, in the form of electrospun fibers. Rheological properties of the fiber forming solutions, which determine the electrospinning behavior, were correlated with the properties of electrospun fibers, e.g., morphology and surface properties. Interactions through hydrogen bonds were evidenced between the two components. These have strong effect on structuration of macromolecular chains, especially at low α-tocopherol amounts, decreasing viscosity and elastic modulus. Intra-molecular interactions in PCL strengthen at high α-tocopherol amounts due to decreased solvation, allowing good structural recovery after cease of mechanical stress. Morphologically homogeneous electrospun fibers were obtained, with ~6 μm average diameter. The obtained fibers were highly hydrophobic, with fast release in 95% ethanol as alternative simulant for fatty foods. This induced good in vitro antioxidant activity and significant in vivo reduction of microbial growth on cheese, as determined by respirometry. Therefore, the electrospun fibers from PCL entrapping α-tocopherol as bioactive agent showed potential use in food packaging materials.     

Preparation and Characterization of Aligned PLLA/PCL/HA Composite Fibrous Membranes

Aligned poly(L-lactide) (PLLA)/poly(?-caprolactone) (PCL)/hydroxyapaite (HA) composite fibrous membranes were fabricated by electrospinning. Their morphology, thermal stability, mechanical properties, hydrophilic properties and biocompatibility were investigated. The electrospun fibers are highly aligned and the HA are oriented along the fiber axis. When HA are incorporated, the PLLA/PCL/HA composite fibers become thinner due to the increased conductivity. In addition, the aligned HA reinforce the electrospun fibrous membranes. The larger porosity and higher hydrophilic properties induced by HA in the electrospun fibers have improved the degradation of the PLLA/PCL/HA fibrous membranes which have no toxic effect on proliferation of adipose-derived stem cells.     

Solvent and concentration effects on the properties of electrospun poly(ethylene terephthalate) nanofiber mats

This study describes the preparation and characterization of nanofibrous mats obtained by electrospinning poly(ethylene terephthalate) (PET) solutions in trifluoroacetic acid/dichloromethane (TFA/DCM). Special attention was paid to the effect of polymer concentration and solvent properties on the morphology, structure, and mechanical and thermal properties of the electrospun nonwovens. The results show that the spinnable concentration of PET solution in TFA/DCM solvents is above 10 wt %. Mats have nanofibrous morphology with fibers having an average diameter in the range of 200–700 nm (depending on polymer concentration and solvent composition) and an interconnected pore structure. Higher solution concentration favors the formation of uniform fibers without beads and with higher diameter. Morphology and fiber assembly changed with the solvent properties. Solvent mixtures rich in TFA, i.e., those with higher dielectric constant and lower surface tension, originated fibers with small diameter. However, due to the lower volatility, those solvent mixtures also produced more branched and crosslinking fibers, with less morphologic uniformity. Mechanical properties (Young's modulus, ultimate strength, and elongation at break) and thermal properties (glass transition, crystallization, and melting) have been studied for the PET electrospun nanomats and compared with those of the original polymer. Solvent effect on fiber crystallinity was not significant, but a complex effect was observed on the mechanical properties of the electrospun mats, as a consequence of the different structural organization of the fibers within the mat network. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 460–471, 2008     

Deposition of silver nanoparticles on cellulosic fibers via stabilization of carboxymethyl groups

The stabilizing role of carboxymethyl groups on the conformal deposition of Ag NPs over cellulosic fibers was elucidated while developing a method for the deposition of silver nanoparticles (NPs) on cellulose acetate (CA), cellulose and partially carboxymethylated cellulose (CMC) electrospun fibers. CMC fibers were prepared through judicious anionization of deacetylated cellulose acetate fibers. Ag NPs were chemically reduced from silver nitrate using sodium borohydride and further stabilized using citrate. Ag NPs were directly deposited onto CA, cellulose and CMC electrospun fibers at pH conditions ranging from 2.5 to 9.0. The resulting composites of Ag/fiber were characterized by field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX). The results revealed that the amount of Ag agglomerates and NPs deposited on CMC fibers was higher than that deposited on cellulose fibers at similar pH conditions, and that barely any Ag agglomerates or NPs were deposited on the CA fibers. These results implied that functional groups on the cellulose backbone played two important roles in the deposition of NPs as follows: (1) Hydrogen bonding was the main driving force for agglomeration of NPs when the medium pH was below 4.4, which corresponds to the pKa of carboxylic acid groups; (2) Carboxymethyl groups could replace citrate groups as stabilizers allowing the fabrication of a uniform and evenly distributed Ag NPs layer over CMC fibers at higher pH values. This report also highlights the importance of the substrate’s surface charge and that of the pH of the medium used, on the deposition of NPs. The composite of Ag NPs on CMC electrospun fibers appears to be a promising candidate for wound dressing applications due to its superior antibacterial properties originated by the uniform and even distribution of Ag NPs on the surface of the fibers and the wound healing aptness of the CMC fibers.