Bead‐to‐fiber transition in electrospun polystyrene

The morphological transition, namely bead‐to‐fiber transition, of electrospun polymer was examined for polystyrene, with its molecular weight ranging from 19,300 to 1,877,000 g/mol. Tetrahydrofuran and N,N‐dimethylformamide were used as solvents to examine the effects of solvent properties on the morphological variations. Polymer molecular weight and solvent properties had a significant effect on the morphology of beads as well as fibers. Observation of fiber diameter and its distribution suggested that the effect of molecular weight and solvent may be independent. The critical concentrations at which incipient and complete fibers were observed were found to decrease significantly with molecular weight, as can be expected. The effect of solvents on these critical concentrations was minimal for moderate to high‐molecular‐weight (>100,000 g/mol) solutions. For low‐molecular‐weight solutions, the transition occurred at concentrations much lower than those predicted by a model, based exclusively on chain entanglements. Rapid solidification of jet which is expected to occur with concentrated solutions may play a vital role in establishing stable fibers during electrospinning. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Sulfonated and cross-linked polystyrene ultrafine fibers for the esterification of palmitic acid for biodiesel production

For the need of green and sustainable development, a fibrous solid acid catalyst was developed for the transformation of low cost oils to biodiesel in an efficient and green manner. Polystyrene was electrospun into ultrafine fibers with mean diameter of ~1.34 μm, and then simultaneously cross-linked and sulfonated in sulfuric acid/acetic acid mixed solvent with paraformaldehyde as the external cross-linker. The cross-linking and sulfonation degrees were controllable by changing the ratio of sulfuric acid/acetic acid. After sulfonation and cross-linking, the solvent resistance, chemical structure, and composition of these fibers were separately characterized by scanning electron microscopy, infrared spectroscopy, and elemental analysis. At last, this novel fibrous solid acid catalyst was used to catalyze the esterification reaction of palmitic acid and methanol for biodiesel production. After optimizing the reaction conditions, this fibrous solid acid catalyst can catalyze the esterification of palmitic acid and methanol with the conversion up to 92% under mild reaction conditions. Moreover, due to the fibrous structure, this fibrous solid acid catalyst could be readily separated and reused.     

Electrospinning of gelatin fibers using solutions with low acetic acid concentration: Effect of solvent composition on both diameter of electrospun fibers and cytotoxicity

Gelatin fibers were prepared by electrospinning of gelatin/acetic acid/water ternary mixtures with the aim of studying the feasibility of fabricating gelatin nanofiber mats at room temperature using an alternative benign solvent by significantly reducing the acetic acid concentration. The results showed that gelatin nanofibers can be optimally electrospun with low acetic acid concentration (25%, v/v) combined with gelatin concentrations higher than 300 mg/mL. Both gelatin solutions and electrospun gelatin mats (prepared with different acetic acid aqueous solutions) were analyzed by Fourier transform infrared spectroscopy and differential scanning calorimetry techniques to determine the chemical and structural changes of the polymer. The electrospun gelatin mats fabricated from solutions with low acetic acid content showed some advantages as the maintenance of the decomposition temperature of the pure gelatin (～ 230°C) and the reduction of the acid content on electrospun mats, which allowed to reach a cell viability upper than 90% (analyzed by cell viability test using human dermal fibroblast and embryonic kidney cells). This study has also analyzed the influence of gelatin and acetic acid concentration both on the solution viscosity and the electrospun fiber diameter, obtaining a clear relationship between these parameters. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42115.     

Preparation and characterization of ultrafine electrospun polyacrylonitrile fibers and their subsequent pyrolysis to carbon fibers

The present contribution reports the fabrication and characterization of ultrafine polyacrylonitrile (PAN) fibers by electrospinning and further development of the as‐spun PAN fibers into ultrafine carbon fibers. The effects of solution conditions (i.e., solution concentration, viscosity, conductivity, and surface tension) and process parameters (i.e., applied electrostatic field strength, emitting electrode polarity, nozzle diameter, and take‐up speed of a rotating‐drum collector) on morphological appearance and average diameter of the as‐spun PAN fibers were investigated by optical scanning (OS) and scanning electron microscopy (SEM). The concentration, and hence the viscosity, of the spinning solutions significantly affected the morphology and diameters of the as‐spun PAN fibers. The applied electrostatic field strength and nozzle diameter slightly affected the diameters of the as‐spun fibers, while the emitting electrode polarity did not show any influence over the morphology and size of the as‐spun fibers. Utilization of the rotating‐drum collector enhanced the alignment of the as‐spun fibers. Within the investigated concentration range, the average diameter of the fibers ranged between 80 and 725 nm. Finally, heat treatment of the as‐spun fibers with their average diameter of about 450 nm was carried out at 230 and 1000 °C, respectively. Various characterization techniques revealed successful conversion into carbon fibers with an average diameter of about 250 nm. Copyright © 2006 Society of Chemical Industry     

Durable adhesives based on electrospun poly(vinylidene fluoride) fibers

Herein, the fabrication of poly(vinylidene fluoride) (PVDF) fibrous membrane using electrospinning is reported and its use for dry‐adhesive applications is demonstrated. The shear and normal adhesion performance of the samples was investigated using an Instron tensile tester and an atomic force microscope (AFM) respectively. For shear adhesion measurements, the electrospun membrane was finger pressed on to a glass slide and pulled in shear mode using a tensile tester. The thickness of the electrospun membrane was varied and the effect of thickness on shear adhesion was investigated. The shear adhesion strength increased when the thickness of the samples was reduced. Shear adhesion strength of a 200 µm thick sample was determined to be approximately 0.165 N/cm. For normal adhesion measurements, a flat tipless cantilever was used to indent the sample and then retract back to measure the pull‐off force. High shear adhesion strength and normal pull‐off force recorded are attributed to the fine size of the fibers that conform to the asperities present on the surfaces of the glass slide and the AFM cantilever. The durability of the adhesive was also verified by repeating the AFM adhesion measurements over 1000 consecutive attachment–detachment cycles. The pull‐off force was seen to be constant over 1000 attachment–detachment cycles. Our results indicate that these electrospun fibrous membranes can potentially be used as reusable dry‐adhesives. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44393.     

Directional self‐assembly by electrospun wet fibers

In this study, we examined directional self‐assembly by electrospun wet fibers. The landing point of the wet fibers was controllable as its trajectory was strictly limited by the adjustment of the parameters of electrospinning. The wet fibers would not stack on the grounded plate in an irregular pattern but in the direction of an electric field in sequence. The preliminary wet fibers deposited and erected on the ground plate to form a controllable circle. The subsequent wet fibers traveled to the top of the circle directionally to organize a mesh tube. The apical circle of the mesh tube was the precise landing point of the subsequent wet fibers. With the wet fibers landing continuously, the mesh tube grew longer and longer. Finally, the controllable circle grew to be the growing mesh tube step by step. We discovered that the mesh tube was assembled by fibers spontaneously in the electrostatic field. In this article, we also try to explain the mechanism of self‐assembly and the formation of wet fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43003.     

Olive leaf extract as a crosslinking agent for the preparation of electrospun zein fibers

Incorporating active agents, reinforcing structure by crosslinking, thus changing release properties, can be listed as possible modifications in preparation methods of biopolymer fibers. This study introduces oleuropein, major component of olive leaf extract (OLE), as a natural functional crosslinker for electrospun zein fibers, owing to its antioxidant and antimicrobial properties. Incorporation of OLE causes morphological and structural changes indicated by a decrease in fiber diameter up to 27%, an increase in intensity of NH bending region due to interaction with –OH groups and observation of characteristic oleuropein bands. Extract addition also enhances thermal stability. Zein fibers without OLE is fully degraded at 600°C, whereas 10% of OLE loaded zein fibers is left undegraded. Fifty percent of initial phenolic content loaded into fibers is released which indicate the effect of OLE incorporation as accumulation of oleuropein. OLE‐incorporated fibers immersed in PBS are less fused than pure zein fibers, due to the crosslinking effect. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41338.     

Micromechanical properties and ductile behavior of electrospun polystyrene nanofibers

Using electrospinning technique polystyrene (PS) nanofibers in the thickness range from 150 to 800 nm have been produced. Electron microscope inspections reveal the relatively uniform thickness of the obtained fibers. The mechanical deformation mechanisms have been studied in tension tests using micro-tensile devices for a scanning electron microscope (SEM) and a transmission electron microscope (TEM). A characteristic change in the deformation behavior from the typical craze formation of PS to a micro necking and cold drawing has been found with decreasing fiber thickness. There is a surprisingly sharp fiber thickness limit between both deformation types in the range of 220–225 nm: nanofibers thicker than ∼ 225 nm deform with formation of crazes, nanofibers thinner than ∼ 225 nm show necking and cold drawing. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Acrylamide‐plasma treated electrospun polystyrene nanofibrous adsorbents for cadmium and nickel ions removal from aqueous solutions

The aim of this work was to prepare novel electrospun polystyrene (PS) nanofibrous samples functionalization with acrylamide monomer (AAm) as promising nanoadsorbents by the use of nitrogen gas plasma. To investigate the performance evaluation of the samples for adsorbing cadmium (Cd²⁺) and nickel (Ni²⁺) ions, a series of tests in terms of ATR‐FTIR spectroscopy, FE‐SEM, water contact angle (WCA) measurements and atomic adsorption spectroscopy were carried out. The ATR‐FTIR results showed that nitrogen (N₂) plasma was an efficient tool because of the formation of functionalized AAm‐PS nanofibrous samples by providing amide (?NCO) and amine (?NH?) groups onto their surfaces. The WCA measurements demonstrated that the N₂ plasma‐modified samples in the presence of AAm had a lower contact angle of 42.8º than the other samples. Moreover, FE‐SEM micrpgraph images of AAm‐treated PS nanofibrous samples indicated that approperiate amount of the functional groups onto the samples surfaces were deposited. Afterwards, AAS analysis along with Langmuir and Freundlich's isotherm models revealed that a high adsorption of the ions was occurred at pH 5 in the order Cd²⁺ (10 mg g^?1) > Ni²⁺ (4.9 mg g^?1) by using the nanoadsorbents dosage 1 g L^?1 and the metal ions concentration 25 mg L^?1. In addition, the obtained results exhibited the Cd²⁺ and Ni²⁺ ions removal efficiencies (%R) were increased up to 96% and 94%, respectively with raising the nanoadsorbents dosage. Moreover, the equilibrium adsorption of the ions showed the best fitting by the Freundlich's model. Finally, the desorption of the optimized samples for regenerating them owing to the effective removal of the ions has been confirmed by applying the recyclability test. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42944.     

Palladium complex embedded crosslinked polystyrene nanofibers as a green and efficient heterogeneous catalyst for coupling reactions

A simple and green chemical modification coupled with electrospinning technique has been developed to incorporate tetrakis(triphenylphosphine)palladium [Pd(PPh₃)₄] inside crosslinked polystyrene nanofibers (Pd@CPS) as an efficient and stable heterogeneous palladium catalyst. The catalytic activities and recyclabilities of the prepared Pd@CPS catalyst have been evaluated by using Suzuki and Heck reactions of various aromatic halides separately with phenylboronic acid and alkenes. The Pd@CPS exhibited high-catalytic activities for the Suzuki and Heck reactions of aromatic iodides to afford the products in excellent yields (coupling yields >88%). The catalytic activities and the nanofiber structure remained essentially unchanged even after recycling for five times. The high activities and stabilities of the prepared Pd@CPS catalyst can be attributed to the ultrafine fiber and embedment of palladium active species inside the nanofibers.     

Characterization of composites based on recycled expanded polystyrene reinforced with curaua fibers

This study evaluated the mechanical, thermal, rheological, and morphological properties of virgin and recycled matrices and their composites with 20 wt % of curaua fiber. The recycling process of postconsumer polystyrene was carried out by grinding and extrusion. It was found that the recycling of expanded polystyrene did not have a major influence on the mechanical properties; however, the thermal stability was increased. The addition of curaua fibers led to increases in the tensile strength, modulus of elasticity, rigidity, thermal stability and melt viscosity of the composites. The composites made with the recycled matrix revealed higher thermal stability and melt viscosity than those made with the virgin matrix. Scanning electron microscopy characterization showed empty spaces where the curaua fibers had pulled out of the matrices in the fractured regions, indicating poor interfacial adhesion without the use of a coupling agent. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of reversed arrangement of electrodes on electrospun nanofibers

The process of electrospinning can be affected by various parameters, leading to as‐prepared nanofibers with different morphology and properties. In order to explore the impact of DC(+) high‐voltage position on the resultant nanofibers, two setups with DC(+) high‐voltage individually tethered to the needle (S‐1) and the collecting plate (S‐2) were fabricated. Nanofibers produced by both setups under the same conditions were examined to distinguish their differences in morphology and electrostatic properties. It was found that the nanofibers with positive surface potential produced by the S‐1 setup have a larger surface coverage and porosity, smaller average diameter, and wider distribution of diameters. Furthermore, the differences between both setups in the trajectory of flying jets and the distribution of electric field intensity were studied. The results showed that the volume charge density (VCD) of the flying jets plays a crucial role in determining the morphology and electrostatic properties of the resultant nanofibers. The relationship between the position of DC(+) high‐voltage and the VCD of flying jets was then discussed, which could develop a better understanding of the process of electrospinning and deliver more accurate control over the production of various functional nanofibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44687.     

Synthesis of ultrafine poly(styrene‐maleic anhydride) and polystyrene fibers by electrospinning

Fiber formation from atactic polystyrene (aPS) and alternating poly(styrene‐maleic anhydride) (PSMA) synthesized by free radical polymerization (AIBN, 90°C, 4 h) were investigated by electrospinning from various solutions. aPS was soluble in dimethylformamide (DMF), tetrahydrofuran (THF), toluene, styrene, and benzene, whereas PSMA was soluble in acetone, DMF, THF, dimethylsulfoxide (DMSO), ethyl acetate, and methanol. aPS fibers could be electrospun from 15 to 20% DMF and 20% THF solutions, but not from styrene nor toluene. PSMA, on the other hand, could be efficiently electrospun into fibers from DMF and DMSO at 20 and 25%, respectively. Few PSMA fibers were, however, produced from acetone, THF, or ethyl acetate solutions. Results showed that solvent properties and polymer–solvent miscibility strongly influenced the fiber formation from electrospinning. The addition of solvents, such as THF, generally improved the fiber uniformity and reduced fiber sizes for both polymers. The nonsolvents, however, had opposing effects on the two polymers, i.e., significantly reducing PSMA fiber diameters to 200 to 300 nm, creating larger and irregularly shaped aPS fibers. The ability to incorporate the styrene monomer and divinylbenzene crosslinker in aPS fibers as well as to hydrolyze PSMA fibers with diluted NaOH solutions demonstrated potential for post‐electrospinning reactions and modification of these ultrafine fibers for reactive support materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Simple fabrication of an electrospun polystyrene microfiber filter that meets N95 filtering facepiece respirator filtration and breathability standards

During the global spread of COVID-19, high demand and limited availability of melt-blown filtration material led to a manufacturing backlog of N95 Filtering Facepiece Respirators (FFRs). This shortfall prompted the search for alternative filter materials that could be quickly mass produced while meeting N95 FFR filtration and breathability performance standards. Here, an unsupported, nonwoven layer of uncharged polystyrene (PS) microfibers was produced via electrospinning that achieves N95 performance standards based on physical parameters (e.g., filter thickness) alone. PS microfibers 3–6 μm in diameter and deposited in an ~5 mm thick filter layer are favorable for use in FFRs, achieving high filtration efficiencies (≥97.5%) and low pressure drops (≤15 mm H₂O). The PS microfiber filter demonstrates durability upon disinfection with hydroxyl radicals (•OH), maintaining high filtration efficiencies and low pressure drops over six rounds of disinfection. Additionally, the PS microfibers exhibit antibacterial activity (1-log removal of E. coli) and can be modified readily through integration of silver nanoparticles (AgNPs) during electrospinning to enhance their activity (≥3-log removal at 25 wt% AgNP integration). Because of their tunable performance, potential reusability with disinfection, and antimicrobial properties, these electrospun PS microfibers may represent a suitable, alternative filter material for use in N95 FFRs.     

Blends of polypropylene and modified polystyrene for dyeable fibers

Blends of polypropylene (PP) and modified atactic polystyrene (PS) with good processability were studied for dyeable fine and superfine fibers. Acrylic acid and butyl acrylate monomers were added to PS by radical suspension copolymerization. The dispersion of the additives in the PP crystal was investigated. The rheology curves of the blends were similar to that of PP under the testing conditions. Fine and superfine PP filaments were processed from these blends, and they had practical mechanical properties. The dyeability of the fabrics from the fibers was studied. The increased amorphous content and the interface between PP and modified PS allowed the dyes to penetrate the fibers. These two effects helped to improve the color intensity. The color fastness was also improved by the presence of polar groups introduced by the modified PS components. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2360–2366, 2005     

Morphologies of electrospun fibers of lignin in poly(ethylene oxide)/N,N‐dimethylformamide

The effects of polyethylene oxide (PEO) molecular weight (Mv), and volume fraction ( ) on the morphology of electrospun sulfur free softwood lignin nanofibers were investigated. Small amounts of PEO were used during preparations of the solutions to aid the electrospinning process. It was found that tripling the PEO volume fraction resulted in a transition from semi‐dilute un‐entangled to semi‐dilute entangled solutions. Conversely, the solution remained in the semi‐dilute un‐entangled regime as the molecular weight was increased by five times. The effects of molecular weight and volume fraction of PEO both on entanglement density and fiber morphology were unified by scaling PEO viscosities as a function of . We investigated and discussed conditions that would produce smooth fibers and conditions that would produce fibers with beads. In the case of beads‐on‐a‐string formation, bead widths remained constant regardless of the molecular weight and concentration of PEO, but the bead length changed. Additionally, we observed a decrease in the diameter of the fibers and the dimension of beads (length and width of beads) with an increase in the electric field used for electrospinning. The aspect ratio of beads increased with increases to both the electric field and the PEO molecular weight or concentration. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44172.     

The electrospun polyhydroxybutyrate fibers reinforced with cellulose nanocrystals: Morphology and properties

Polyhydroxybutyrate (PHB) has been used in the biomedical field. However, the poor mechanical properties of PHB have limited its application. Here, electrospun fibrous nanocomposite mats reinforced with cellulose nanocrystals (CNCs) were fabricated by using PHB as polymeric matrix. The morphological, thermal, mechanical properties, as well as cytotoxicity were characterized. Increasing the concentration of CNCs caused a decrease in diameter of the electrospun fibers. Moreover, thermal analysis indicated that melting temperature of PHB/CNCs electrospun fibers were improved with the increased CNCs content. The addition of CNCs gradually enhanced the tensile strength till 8 wt % content followed by a gradual decrease at higher CNCs content (12–22 wt %) in tensile strength. The PHB/CNCs electrospun fibers were nontoxic to L‐929 and capable of supporting cell proliferation in all conditions. This study demonstrates that fibrous PHB/CNCs electrospun fibers are cytocompatible and potentially useful mechanical properties for biomedical application. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43273.     

A study on the effect of the collector properties on the fabrication of magnetic polystyrene nanocomposite fibers using the electrospinning technique

The role of the collector properties in changing the fiber morphology in electrospinning has not been completely understood yet. In this work, we studied the effect of different collectors on the helicity of the magnetic polystyrene nanocomposite fibers containing superparamagnetic magnetite nanoparticles. Aluminum and ice were used as solid collectors. Ethanol, ethanol-deionized (DI) water mixture, sodium dodecyl sulfate, Triton X-100, deionized water, and NaCl baths were used as liquid collectors. Ice, when surrounded by a conductive foil, produced excellent fiber alignment, but increased local humidity, inhibiting the continuous jet formation. The deionized water and NaCl bath exhibited minimum helicity. The surfactant bath produced different structures such as coiled, helical, and zig-zag with varied diameters. Ethanol and DI/Ethanol baths were found to retain the structure of the deformed fiber formed due to jet instability. The helicity of the fibers was observed to increase with decreasing surface tension. Incorporation of the magnetic phase affected the viscosity of the polymer solution and the hydrophobicity of the polystyrene fibers further influencing the obtained morphologies.     

Fabrication of electrospun fibers from a waterborne soy-based polyurethane employing polyethylene oxide as a coformer

The fabrication of electrospun fibers made from aqueous dispersions of polyurethane obtained from renewable sources is an eco-friendly method to produce porous membranes for different applications. Polyethylene oxide (PEO) has been already employed in formulations for allowing fiber formation, but its role was not yet completely understood. In this work the fabrication of electrospun fibers made from biobased polyurethane aqueous dispersion with PEO in order to obtain regular fibers is performed. The role of PEO was studied by thermal analysis, infrared and Raman spectroscopy, rheology, and fiber morphology. Polyurethane fibers were obtained only when PEO was added, otherwise the dispersion is electrosprayed and particles are formed. It was observed that PEO modifies the rheology of dispersion and assists coalescence of polyurethane particles. On the other hand, polyurethane fibers conserved their diameter and their homogeneous structure after removal of PEO by immersion in water, which indicates that the distribution of both polymers was even within the fibers. This work provides both an insight on the role of PEO and a route for the fabrication of eco-friendly biobased polyurethane microfibers from aqueous dispersions.     

The morphology of electrospun polystyrene fibers

Electrospinning is a process of electrostatic fiber formation which uses electrical forces to produce polymer nanofibers from polymer solution. The electrospinning system consists of a syringe feeder system, a collector system, and a high power supplier. The important parameters in the morphology of electrospun polystyrene fibers are concentration, applied voltage, and solvent properties. Higher concentrations of the polymer solution form thicker fibers and fewer beads. When the concentration is 7 wt%, electrospun fibers have an average diameter of 340 nm, but as the concentration of PS increases to 17 wt%, the fiber diameter gradually thickens to 3,610 nm. The fiber morphology under different solvent mixture ratios and solvent mixtures has also been studied.