Influence of a mixing solvent with tetrahydrofuran and N,N‐dimethylformamide on electrospun poly(vinyl chloride) nonwoven mats

We evaluated the effects of the solvent composition with respect to the solution concentration, applied electric field, and tip‐to‐collector distance on the morphology of electrospun poly(vinyl chloride) (PVC) fibers. The solvent volume ratio was strongly correlated with the diameter of the electrospun fibers with respect to the other processing parameters. Electrospun PVC fibers dissolved in tetrahydrofuran (THF) had diameters ranging from 500 nm to 6 μm; those dissolved in N,N‐dimethylformamide (DMF) had an average diameter of 200 nm. The diameters of the electrospun fibers were obtained from narrow to broad distributions with the solvent composition. Also, the diameters of fibers electrospun from a mixed solvent of THF and DMF were less than 1 μm. The mechanical properties of electrospun PVC nonwoven mats depended on the fiber orientation and linear velocity of the drum surface. With increasing linear velocity of the drum surface, electrospun PVC fibers were arranged toward the machine direction, and the dimensions of the spiral path were shorter. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2259–2268, 2002     

Thermally induced color change in electrospun fiber mats

Electrospinning is a process that employs a high static electrical potential to produce polymeric fibers of nanoscale diameter. The process has been utilized to achieve color change by electrospinning black polymer solutions to produce white fiber mats. When subsequently heated, the electrospun mats undergo a color change from white to black. This phenomenon is demonstrated with three polymer/solvent systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 752–757, 2004     

Preparation of electrospun nanofibers from solutions of different gelatin types using a benign solvent mixture composed of water/PBS/ethanol

The feasibility of using phosphate buffer saline (PBS)/ethanol mixtures as a benign solvent to electrospin three types of gelatin was studied. Gelatins with different chemical properties, such as Bloom, were selected and the effect of the gelatin nature and its concentration on the electrospinnability of the dope solution and on the fiber diameter of the electrospun mats were studied. Viscosity of the gelatin solution, which follows a power law relationship with the gelatin concentration, was found to significantly influence the morphology of the mats and the fiber diameter. It was demonstrated that the PBS/ethanol solvent interacted with the gelatins as a good solvent with a Flory exponent of 0.65. In addition, the effect of the solvent composition on the fiber formation process was evaluated corroborating that the ionic strength of the medium and the PBS/ethanol ratio significantly affected the morphology and the diameter of the electrospun fibers. Chemical structure and thermal stability of the electrospun gelatin mats were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Finally, cytotoxicity of the electrospun mats was analyzed by the Alamar Blue assay, using human foreskin fibroblasts (BJ‐5ta), resulting in a high cell viability (80–90%) regardless the type of gelatin. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermal shrinkage of electrospun PVP nanofibers

This paper outlines the shrinkage of electrospun polyvinylpyrrolidone (PVP) fiber mats during thermal treatment. The thermal behavior and phase changes within the fibers were investigated by DSC and TGA/DTA. Five precursors with different PVP loading in ethanol were electrospun. The mats shrinkage as function of temperature was measured in the RT–200 °C range. Shrinkage rate drastically increased above the polymer glass transition point, T_g (150–180 °C), due to increase in polymer chain mobility. Mats shrinkage at 200 °C as function of PVP concentration showed a minimum at ∼10%wt. Below 10% PVP the mats morphology is non‐uniform, consisting of beads and fibers. Above 10% PVP, only flat and uniform fibers were observed. This paper outlines the dominant mechanism governing the mats shrinkage during heating. In addition, the effect of PVP concentration on the expansion of fibers diameter was investigated and found to be consistent with the linear shrinkage observing a minimum at ∼10% PVP. The effect of applied voltage on mat shrinkage was investigated, and showed a minimum at 12 kV. Understanding the interplay between fibers morphology and thermal shrinkage allows precursor composition and system optimization needed for minimizing shrinkage negative effects on the structure and properties of electrospun fiber mats. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 248–254     

Polyaniline/poly(methyl methacrylate) coaxial fibers: The fabrication and effects of the solution properties on the morphology of electrospun core fibers

Electrically conductive polyaniline (PANi)/poly(methyl methacrylate) (PMMA) coaxial fibers were prepared through the chemical deposition of PANi onto preformed PMMA fibers via in situ polymerization. PMMA fibers were prepared as core materials via electrospinning. Spectral studies and scanning electron microscopy observations indicated the formation of PANi/PMMA coaxial fibers with a diameter of approximately 290 nm and a PANi layer thickness of approximately 30 nm. The conductivity of the PANi/PMMA coaxial fibers was significantly higher than that of electrospun fibers of PANi/poly(ethylene oxide) blends and blend cast films of the same PANi composition. To reproducibly generate uniform‐core polymer fibers, the organic solution properties that affected the morphology and diameter of the electrospun fibers were investigated. The polymer molecular weight, solution concentration, solvent dielectric constant, and addition of soluble organic salts were strongly correlated to the morphology of the electrospun fiber mat. In particular, the dielectric constants of the solvents substantially influenced both the fiber diameter and bead formation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3934–3942, 2004     

Characterization of poly(methyl methacrylate) nanofiber mats by electrospinning process

In this study, the aim is to describe the influence of electrospinning parameters on the morphology, the water wetting property and dye adsorption property of poly(methyl methacrylate) nanofiber mats. Specifically, the effects of solution concentration, solvent type, applied voltage, distance between the electrodes and particulate reinforcement on the diameter and shape of the nanofibers were investigated. All poly(methyl methacrylate) nanofiber mats contained beaded nanofiber structures. With increasing the polymer solution concentration, the average fiber diameter also increased. Poly(methyl methacrylate) nanofiber mat electrospun from dimethylformamide solution resulted in thicker fibers when compared with the mat electrospun from acetone solution. Increasing the electric potential difference between the collector and the syringe tip did not increase the average fiber diameter. Besides increasing the distance between the electrodes resulted in a decrease in the average fiber diameter. When compared with PMMA nanofiber mat, thicker fibers were obtained with silica nanoparticles reinforced nanofiber mat. According to the water contact angle measurements, all poly(methyl methacrylate) nanofiber mats revealed hydrophobic surface property. PMMA nanofiber mat with the highest water contact angle gave rise to the highest dye adsorption capacity.     

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     

Diameter control of electrospun polyacrylonitrile/iron acetylacetonate ultrafine nanofibers

Electrospinning is the process of producing ultrafine fibers by overcoming the surface tension of a polymer solution using high voltage. In this work, the effects of both solution properties (viscosity, conductivity, and surface tension) and operational conditions (voltage, feed rate, and spinneret‐collector distance), on the structure of electrospun polyacrylonitrile nanofibers, were systematically investigated. Iron acetylacetonate was added to the electrospinning solution to control fiber diameter by selectively adjusting solution properties. It was found that, with increased salt concentration, the fiber diameter increases and then passes through a maximum due to changes in solution viscosity, conductivity, and surface tension. In addition, the fiber diameter increases with increase in voltage, feed rate, and spinneret‐collector distance. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1611–1618, 2008     

Transport properties of electrospun nylon 6 nonwoven mats

In this work, we evaluate the physical properties of nylon 6 nonwoven mats produced from solutions with formic acid. Nonwoven electrospun mats from various solutions with different concentration are examined regarding their morphology, pore size, surface area, and gas transport properties. Each nonwoven mat with average fiber diameters from 90 to 500 nm was prepared under controlled electrospinning process parameters. From the results, it was observed that the fiber diameter was strongly affected by the polymer concentration (polymer viscosity). In additional the results showed that the pore size, Brunauer-Emmett-Teller (BET) surface area, and gas transport property of electrospun nylon 6 nonwoven mats were affected by the fiber diameter.     

二氧化碳-环氧丙烷共聚物电纺纤维形貌研究

利用电纺丝技术制备了二氧化碳环氧丙烷共聚物超细纤维,研究了喷丝口电势、纺丝距离、浓度、溶剂等因素对纤维形貌、直径及均一性的影响.实验结果表明,利用电纺丝法可以制备直径在小于200nm到7μm二氧化碳环氧丙烷共聚物纤维;喷丝口电势和浓度对于共聚物电纺丝纤维是否形成串珠结构有重要影响;电势、距离和纺丝液浓度都对纤维直径及分散系数有较大影响,在一定范围内,随着喷丝口电势增加,纤维平均直径变大而分散系数变小;纺丝距离增大使得纤维平均直径变小,分散系数变大;浓度的增大使得纤维平均直径变大,分散系数变小;不同溶剂配制的溶液体系制备的电纺丝纤维形貌有很大差异,在二氯甲烷和丁酮的体系中,分别观察到了两组较为集中的直径分布.     

Electrospinning of poly(vinylidene fluoride)/dimethylformamide solutions with carbon nanotubes

For conductive carbon nanotube (CN)/polymer composite fibers to be obtained, CNs were incorporated into poly(vinylidene fluoride) (PVDF) in dimethylformamide (DMF) solutions and electrospun to form CN/PVDF fiber mats. The thinnest fiber was 70 nm thick. The percolation threshold for the insulator‐to‐conductor transition was 0.003 wt % CN for CN/PVDF/DMF solutions, 0.015 wt % CN for CN/PVDF spin‐coated films, and 0.04 wt % CN for CN/PVDF electrospun fiber mats. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1572–1577, 2003     

Structural characterization and mechanical properties of electrospun silk fibroin nanofiber mats

The regenerated silk fibroin dissolved in formic acid was electrospun into nanofiber mats. Structural characteristics of the spun as received and methanol and ethanol treated fibers were examined using the Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction. Mechanical properties and air permeability of the electrospun mats were also studied. IR spectroscopy and X-ray diffractometry showed random coil conformation and amorphous structure for as-spun fibers while typical FTIR spectra and X-ray diffractograms of β-sheet crystalline structure were recorded for the methanol and ethanol treated fibers. The mechanical properties of the mats were found to be dependent on fiber diameter. The mats containing fibers with smaller diameter had higher tensile strength but lower breaking strain. Methanol and ethanol treatment enhanced tensile strengths of the mats at the expenses of their breaking strain. Air permeability and pore size of the mats are strongly associated with diameter of the electrospun fibers.     

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.     

Centrifugally spun poly(ethylene oxide) fibers rival the properties of electrospun fibers

Centrifugal force spinning (CFS), also known as centrifugal spinning, forcespinning, or rotary jet spinning, provides considerably higher production rates than electrospinning (ES), but the more widespread use of CFS as an alternative depends on the ability to produce fibers with robust thermal and mechanical properties. Here, we report the CFS of poly(ethylene oxide) (PEO) fibers made using a spinning dope formulated with acetonitrile (AcN) as the volatile solvent, and we describe the thermal and mechanical properties of the centrifugally-spun fibers. Even though the formation, diameter, and morphology of electrospun and centrifugally-spun PEO fibers are relatively well-studied, the article presents three crucial contributions: the pioneering use of PEO solutions in AcN as spinning dope, characterization of crystallinity and mechanical properties of the centrifugally-spun PEO fibers, and a comparison with the corresponding properties of electrospun fibers. We find that fiber formation occurrs for the chosen CFS conditions if polymer concentration exceeds the entanglement concentration, determined from the measured specific viscosity. Most significantly, the centrifugally spun PEO fibers display crystallinity, modulus, elongation-at-break, and fiber diameter that rival the properties of electrospun PEO fibers reported in the literature.     

Effect of polymer molecular weight on the fiber morphology of electrospun mats

In this work, different fractions of solvent-induced polymer degraded solution were mixed with freshly prepared solution of same polymer, and its effect on fiber morphology of electrospun mats was investigated. Nylon-6 solution in formic acid was allowed to degrade for 3 weeks and different fractions of it were mixed with freshly prepared nylon-6 solution to get the electrospun mats. FE-SEM images of the mats indicated that the a large amount of sub-nanofibers (<50 nm in diameter) in the form of spider-net like structures were achieved by tailoring the amount of solvent degraded polymer solution in the freshly prepared nylon-6 solution. Large quantity of these ultrafine sub-nanofibers present in electrospun nylon-6 mats could increase its hydrophilicity and mechanical strength. The decreased average pore diameter and increased BET surface area of the mat, caused by spider-net like structure, can make it as a potential candidate for air/water filtration.     

Controlling electrospun nanofiber morphology and mechanical properties using humidity

Electrospinning is a fiber spinning technique used to produce nanoscale polymeric fibers with superior interconnectivity and specific surface area. The fiber diameter, surface morphology, and mechanical strength are important properties of electrospun fibers that can be tuned for diverse applications. In this study, the authors investigate how the humidity during electrospinning influences these specific properties of the fiber mat. Using two previously uninvestigated polymers, poly(acrylonitrile) (PAN) and polysulfone (PSU) dissolved in N,N‐Dimethylformamide (DMF), experimental results show that increasing humidity during spinning causes an increase in fiber diameter and a decrease in mechanical strength. Moreover, surface features such as roughness or pores become evident when electrospinning in an atmosphere with high relative humidity (RH). However, PAN and PSU fibers are affected differently. PAN has a narrower distribution of fiber diameter regardless of the RH, whereas PSU has a wider and more bimodal distribution under high RH. In addition, PSU fibers spun at high humidity exhibit surface pores and higher specific surface area whereas PAN fibers exhibit an increased surface roughness but no visible pores. These fiber morphologies are caused by a complex interaction between the nonsolvent (water), the hygroscopic solvent (DMF), and the polymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Solvent Influences the Morphology and Mechanical Properties of Electrospun Poly(L-lactic acid) Scaffold for Tissue Engineering Applications

Electrospun micro- and nanofiber scaffolds have gained interest in biomedical applications, especially in tissue engineering, because they can be used to reproduce the structure of the extracellular matrix (ECM) of natural tissue. The selection of the solvent is an important factor which affects the diameter, the surface morphology and the crystallinity of the electrospun fibers, and, accordingly, their mechanical properties as well as their degradation kinetics. Furthermore, the surface morphology of the electrospun fibres can be controlled by solvent vapour pressure to produce porous structures which might be helpful for cell adhesion and proliferation. In the present work, poly (L-lactic acid) (PLLA) has been electrospun using solvents with different vapour pressures to investigate the influences of the solvent vapour pressure on morphology, diameter, crystallinity and mechanical properties of the electrospun fiber scaffolds. The results show that the vapour pressure of the solvents (or solvent mixtures) play an important role in the fiber diameter and crystallinity. Furthermore, the crystallinity of the fibers is increased by lowering the vapour pressure of the used solvent. In addition, the mechanical properties (e.g., tensile strength and Young's modulus) are strongly dependent on morphological features such average fibers diameter. The smaller the average diameter, the higher the tensile strength and Young's modulus.     

静电纺丝法制备聚甲醛纳米纤维

以六氟异丙醇为溶剂, 用静电纺丝的方法制备了聚甲醛纳米纤维. 利用场发射扫描电镜对纤维形貌进行了表征, 纤维的直径为0.3~1.2 μm. 讨论了溶液浓度、接收距离、电压和温度等纺丝参数对纤维形貌的影响. 用DSC方法对电纺纤维膜的结晶性能进行了研究, 并与溶液浇铸膜的进行了比较. 结果表明, 电纺纤维膜的熔点与溶液浇铸膜的相同, 与溶液的浓度无关, 但结晶度比溶液浇铸膜的低. 力学性能用拉伸试验进行了测试, 观察到很长的断裂伸长率.     

Fluorescent PMMA/MEH‐PPV electrospun nanofibers: Investigation of morphology,solvent, and surfactant effect

Electrospinning is a powerful technique to produce nanofibers of tunable diameter and morphology for medicine and biotechnological applications. By doping electrospun nanofibers with inorganic and organic compounds, new functionalities can be provided for technological applications. Herein, we report a study on the morphology and optical properties of electrospun nanofibers based on the conjugated polymer poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV) and poly(methylmethacrylate) (PMMA). Initially, we investigate the influence of the solvent, surfactant, and the polymer concentration on electrospinning of PMMA. After determining the best conditions, 0.1% MEH‐PPV was added to obtain fluorescent nanofibers. The optical characterizations display the successful impregnation of MEH‐PPV into the PMMA fibers without phase separation and the preservation of fluorescent property after fiber electrospinning. The obtained results show the ability of the electrospinning approach to obtain fluorescent PMMA/MEH‐PPV nanofibers with potential for optical devices applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1388–1394     

Effect of side‐chain length on the electrospinning of perfluorosulfonic acid ionomers

The effect of the side‐chain length (short side chain and long side chain, SSC and LSC, respectively) of perfluorosulfonic acid (PFSA) ionomers on the properties of nanofibers obtained by electrospinning ionomer dispersions in high dielectric constant liquids has been investigated with a view to obtaining electrospun webs as components of fuel cell membranes. Ranges of experimental conditions for electrospinning LSC and SSC PFSAs have been explored, with a scoping of solvents, carrier polymer and PFSA ionomer concentrations, and carrier polymer molecular weight. Under optimal conditions, the electrospun mats derived from SSC and from LSC PFSA show distinct fiber dimensions that arise from the different chain lengths of the respective ionomers. Enhanced interchain interactions in SSC PFSA with low equivalent weight compared to LSC PFSA result in a considerably lower average fiber diameter and a markedly narrower fiber size distribution. The proton conductivity of nanofiber mats of SSC and LSC PFSA with equivalent weights of 830 and 900 g mol^?1, respectively, are 102 and 58 mS cm^?1 at 80°C and 95% relative humidity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013