Effects of processing parameters on morphology of electrospun polystyrene nanofibers

This study focused on the preparation of electrospun polystyrene (PS) nanofibers. PS solutions were prepared in single (dimethylformamide; DMF, dimethylacetamide; DMAc or tetrahydrofuran; THF) and mixed solvent (DMF/THF and DMAc/THF) systems with and without tetrabutylammonium bromide (TBAB) salt. The effects of PS concentration, solvent system, the addition of salt, appearance and diameter of PS fibers were examined. The average diameter of the as-spun fibers increased upon increasing PS concentration. The morphology of the fibers significantly depended on the properties of the solvents. The obtained fibers were smooth without any beads and their diameters were affected by the amount of THF in the solvent and PS concentration. The beads in the fibers disappeared and the fiber diameter significantly decreased after the addition of TBAB. The smallest diameter and the narrowest diameter distribution of PS nanofibers (376±36 nm) were obtained from 15% PS solution in DMAc with 0.025% w/v TBAB.     

Solvent dyeing of acrylic fibers. Process variables and mechanisms based on rates of dyeing and diffusion studies using cationic dyestuffs

Diffusion coefficients of selected cationic dyes are calculated for one aqueous and six organic solvent dye systems. The concentrations of dyestuffs sorbed by the fibers as functions of dyeing times are plotted for the various dyeing systems. Results indicate that dye sorption decreases and the diffusion coefficient increases as the concentration of the cosolvent increases. The results were determined by comparing the Crank and Olofsson equations for diffusion.     

Studies on the electrospun submicron fibers of SIS and its mechanical properties

The submicron fibers were prepared via electrospinning the styrene–isoprene–styrene (SIS) triblock copolymer from a pure solvent of tetrahydrofuran (THF) and a mixed solvent of THF and N, N‐dimethylformamide (DMF). The addition of DMF to THF resulted in a beneficial effect on the fiber formation and the electrospinnability. The obtained results revealed that the fibers were only formed in a narrow solution concentration range of 8–15 wt %; the morphology, diameter, structure, and mechanical performance of as‐spun fibers from PS and SIS solutions were affected by the composition weight ratio and the solution properties; and those from the solution at the intermediate concentration of 10 wt % exhibited a maximum tensile strength and strain at break. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrospinning and structural characterization of ultrafine poly(butylene succinate) fibers

Biodegradable ultrafine poly(butylene succinate) (PBS) fibers were continuously electrospun for the first time from PBS solutions in chloroform (CF)/2-chloroethanol (CE) (7/3, w/w), CF/CE (6/4, w/w), dichloromethane (DM)/CE (7/3, w/w), DM/CE (6/4, w/w), and CF/3-chloro-1-propanol (9/1, w/w). These mixed solvents had an appropriate evaporation rate for the continuous electrospinning of PBS. The ultrafine PBS fibers had very high crystallinity and their average diameters were in the range of 125-315 nm. The annealed ultrafine PBS fibers exhibited a lamellar stack morphology containing crystalline and amorphous layers.     

The effects of solution properties and polyelectrolyte on electrospinning of ultrafine poly(ethylene oxide) fibers

The effects of solution properties and polyelectrolyte on the electrospinning of poly(ethylene oxide) (PEO) solutions were investigated. Ultrafine PEO fibers without beads were electrospun from 3, 4, 7 and 7 wt% PEO solutions in chloroform, ethanol, (dimethylformamide) DMF and water, respectively. At these concentrations, the values of [η]C were ∼10 for all solutions. The average diameters of PEO fibers were ranged from 0.36 to 1.96 μm. The higher the dielectric constant of solvent was, the thinner PEO fiber was. The average diameters of electrospun PEO fibers from PEO/water solutions were decreased and their distributions were narrowed by adding 0.1 wt% poly(allylamine hydrochloride) (PAH) and poly(acrylic acid sodium salt) (PAA) due to the increased charge density in solutions. The addition of PAH and PAA lowered the minimum concentration for electrospinning of a PEO/water solution to 6 wt%.     

Mechanical,morphology, and thermal properties of carbon fiber reinforced poly(butylene succinate) composites

Biodegradable poly(butylene succinate) (PBS)/carbon fiber (CF) composites were prepared by melt blending method using twin‐screw extruder followed by injection molding. Mechanical properties, crystallization behavior, morphology, crystal structure, and thermal stability of PBS/CF composites were investigated with different CF contents (0, 5, 10, 15, and 20 wt%). It was found that the tensile and impact properties of the composites were improved markedly with the addition of CF; while too much CF would lead to agglomeration and thus weaken the improvement. Scanning electron microscopic photographs on the fracture surfaces showed superior interfacial adhesion between fibers and PBS matrix. Crystallization peak temperature of PBS in its composites was increased due to the heterogeneous effect of CF. The spherulite size of PBS/CF composites decreased and the nucleation density increased drastically. The crystal structure was not affected by the incorporation of CF, as confirmed from the wide‐angle X‐ray diffraction analysis. thermogravimetric analysis showed that the thermal stability of PBS/CF composites was also enhanced. POLYM. COMPOS., 36:1335–1345, 2015. © 2014 Society of Plastics Engineers     

Preparation of the chitosan containing nanofibers by electrospinning chitosan–gelatin complexes

Electrospinning is an interesting technique, which provides a facile and an effective mean in producing nonwoven fibrous materials; however, for producing nanofibers, investigation of the electrospinning conditions is very important. In this study, chitosan, gelatin, and their polyelectrolyte complexes (PECs) were electrospun to prepare nonwoven nanofibrous mats. The concentrations of chitosan and gelatin solutions and electric field (kV/cm) were optimized. The solutions were then blended in different ratios (0–100%) to get electrospun nanofibrous mats. Solution concentration and electric field showed pronounced effect on the electrospinnability and fiber diameter of these systems. Mostly large beads coexisted with the fibers were observed for chitosan at 1 wt% solution concentration, which then showed good electrospinnability at 2 wt% (nanofiber diameter was 145 and 122 nm at 15 and 20 kV/10 cm, respectively), whereas gelatin showed no electrospinnability below 15 wt% solution concentration and a homogenous fibers network at 15 wt% (149 nm at 20 kV/10 cm). The morphology and diameter of chitosan–gelatin PEC nanofibers varied with the chitosan/gelatin ratio. The crystallinity of chitosan was also observed to reduce with electrospinning and addition of gelatin. POLYM. ENG. SCI. 50:1887–1893, 2010. © 2010 Society of Plastics Engineers     

Electrospinning of polycaprolactone nanofibers using H2O as benign additive in polycaprolactone/glacial acetic acid solution

Considerable efforts have been devoted to the production of polycaprolactone (PCL) nanofibrous structures by electrospinning. However, some toxic solvents have often been used to achieve bead‐free nanofibers. At present, a benign solvent such as glacial acetic acid (GAC) only leads to beaded or microscale fibers. Therefore a study is done to extend the electrospinnability of the PCL/GAC system by the addition of H₂O. The solution properties of conductivity, viscosity, and surface tension were altered by the addition of H₂O, especially increasing the conductivity and viscosity. These properties essential to electrospinning could remain stable for 6 h when the H₂O content was less than or equal to 9 vol %. Then ultrafine PCL fibers with diameters from 188 to 200 nm, 10 times smaller than when dissolved in pure GAC, were electrospun from solutions of PCL with concentrations in the range of 17 to 20 wt % with H₂O content at 9 vol %. Finally, the crystallinity and crystallite size of the resulting fibers were smaller than that of raw PCL pellets. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45578.     

Morphology, structure and properties of conductive PS/CNT nanocomposite electrospun mat

The morphologies and properties of Polystyrene (PS)/Carbon Nanotube (CNT) conductive electrospun mat were studied in this paper. Nanocomposite fibers were obtained through electrospinning of PS/Di-Methyl Formamide (DMF) solution containing different concentrations and types of CNTs. The dispersion condition of CNTs was correlated to morphologies and properties of nanocomposite fibers. A copolymer as an interfacial agent (SBS, Styrene-butadiene-styrene type) was used to modify the dispersion of CNTs in PS solution before electrospinning. The results showed that the presence of the copolymer significantly enhances CNT dispersion. The fiber diameters varied between 200 nm and 800 nm depending on CNT type, polymer concentration and copolymer. The final morphological study of the fibers showed that CNT addition caused a decrease in beads formation along fiber axis before percolation threshold. However, addition of CNTs above percolation increased the beads formation, depending on the dispersion condition. The presence of SBS modified the dispersion, reduced the fiber diameter and the number of bead structures. Electrical conductivity measurements on nanocomposite mats of 15-300 μm in thickness showed an electrical percolation threshold around 4 wt% MWCNT; while the samples containing SBS showed higher values of conductivities below percolation compared to the samples with no compatibilizer. Enhancement in mechanical properties was observed by the addition of CNTs at concentrations below percolation.     

High electromagnetic interference shielding with high electrical conductivity through selective dispersion of multiwall carbon nanotube in poly (ε‐caprolactone)/MWCNT composites

This study presents the preparation of electrically conducting poly(ε‐caprolactone) (PCL)/multiwall carbon nanotube (MWCNT) composites with very low percolation threshold (p_c). The method involves solution blending of PCL and MWCNT in the presence of commercial PCL beads. The PCL beads were added into high viscous PCL/MWCNT mixture during evaporation of solvent. Here, the used commercial PCL polymer beads act as an ‘excluded volume’ in the solution blended PCL/MWCNT region. Thus, the effective concentration of the MWCNT dramatically increases in the solution blended region and a strong interconnected continuous conductive network path of CNT−CNT is assumed throughout the matrix phase with the addition of PCL bead which plays a crucial role to improve the electromagnetic interference shielding effectiveness (EMI SE) and electrical conductivity at very low MWCNT loading. Thus, high EMI SE value (∼23.8 dB) was achieved at low MWCNT loading (1.8 wt %) in the presence of 70 wt % PCL bead and the high electrical conductivity of ∼2.49×10⁻² S cm⁻¹ was achieved at very low MWCNT loading (∼0.15 wt %) with 70 wt % PCL bead content in the composites. The electrical conductivity gradually increased with increasing the PCL bead concentration, as well as, MWCNT loading in the composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42161.     

The change of bead morphology formed on electrospun polystyrene fibers

Polystyrene (PS) dissolved in the mixture of tetrahydrofuran (THF) and N,N-dimethyl formamide (DMF) was electrospun to prepare fibers of sub-micron in diameters. Electropinning parameters such as polymer concentration, applied voltage and tip-to-collector distance were controlled. From these parameters it was determined that while the surface tension of polymer solution had linear correlation with the critical voltage, throughput was dependent on electric conductivity. The electrospun PS fibers produced contained irregular beads and electrospinning certainly was enhanced with increasing DMF content. The bead concentration was also controlled by DMF content. The aspect ratio of the formed beads and the diameter of fibers were increased with increasing solution concentration. When PS was dissolved in only THF, an unexpected half hollow spheres (HHS) structure appeared. Also, different shape forms of PS non-woven mats have been prepared by controlling electrospinning parameters.     

Complex stability of sugars and sugar alcohols with NA + , CA 2+ , and LA 3+ in chromatographic separations using poly(styrene- CO -divinylbenzene) resins and aqueous organic eluents

The complex formation between metal ions and carbohydrates in solvent mixtures has been studied by chromatographic measurements. The effect of noncomplexing partition was decreased by attaching the active groups only on the shell of the stationary phase particles. Poly(styrene- co -divinylbenzene) resin beads were surface-sulfonated for that purpose. Thus the inner part of the sulfonated bead remained inactive and nonswellable. The counter-ions examined were Na + , Ca 2+ , and La 3+ , and the organic cosolvents were ethanol and acetonitrile. The stability constants of the very weakly complexing D -glucose, D -xylose, and L -rhamnose, the weakly complexing D -fructose and L -arabinose, and the strongly complexing xylitol and D -sorbitol were determined. The increasing organic cosolvent content increased the retention times, which is explained by the increased complex stability between the complexing solute and the counter-ion. The effect was greatest for the complex-forming sugars in the Ca 2+ form and for the sugar alcohols in the La 3+ form. The organic cosolvent had only a minor effect on the weakly complexing components, whereas the complex stability of the strongly complexing xylitol and sorbitol in 50 wt% ethanol solution in the La 3+ resin was more than five times higher compared to the stability measured in pure water.     

Electrospinning of poly(MMA-co-MAA) copolymers and their layered silicate nanocomposites for improved thermal properties

Copolymers consisting of methyl methacrylate (MMA) and methacrylic acid (MAA) and their layered silicate nanocomposites were electrospun to form fibers with diameters in the sub-micron range. The presence of MAA increased the T_g and thermal stability of the copolymers through formation of anhydrides upon heating. Fibers of uniform diameters were obtained for the poly(MMA-co-MAA) copolymers and nanocomposites containing montmorillonite (MMT), while protrusions were observed on the electrospun fibers from nanocomposites containing fluorohectorite (FH). The electrospinnability of copolymer solutions and nanocomposite dispersions predicted based on both rheological analyses and conductivity measurements correlates well with the experimental electrospinning observations. Dispersion of clays within the nanocomposites improved the electrospinnability of the nanocomposite dispersions. MMT is predominantly exfoliated and well distributed within the fiber and oriented along the fiber axis. Char formation was observed when the MMT-containing fibers were heated above the decomposition temperature, indicating a potential for reduced flammability and increased self-extinguishing properties, whereas the FH-containing materials disintegrated into either film or powder form.     

Electrospinning polymer blend of PLA and PBAT: Electrospinnability–solubility map and effect of polymer solution parameters toward application as antibiotic‐carrier mats

Electrospinning of a biodegradable polymer blend of poly(lactic acid) (PLA) and poly(butylene adipate‐co‐terephthalate) (PBAT) is reported for the first time. Effects of several solution parameters on electrospinning are explored, including types of single and binary solvents, binary solvent mixing ratio, polymer blend concentration, polymer blending ratio, and loading content of tetrabutyl titanate as a compatibilizer. An electrospinnability–solubility map of the PLA/PBAT blend is firstly developed for the facile selection of a suitable binary solvent system, thus simplifying the laborious, time‐consuming, trial‐and‐error process. A particular binary solvent system derived from good and non‐solvent serves as the most suitable medium for the successful preparation of homogeneous bead‐free electrospun PLA/PBAT nanofibers. It is revealed that the compatibilizer acts not only as a diameter size tuner for the PLA/PBAT fibers but also as a mechanical property enhancer for the immiscible PLA/PBAT electrospun mats. Moreover, the antibacterial activity of the drug‐loaded PLA/PBAT fibrous mats suggests their potential application as antibiotic‐carrier mats. Preparation of the composite mats comprising bead‐free fibers with an average size at sub‐micrometer scale is also demonstrated, additionally promoting the possibility of using the PLA/PBAT‐based electrospun mats as a matrix of various additives for a wide range of applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46486.     

COMPLEX STABILITY OF SUGARS AND SUGAR ALCOHOLS WITH Na + , Ca 2+ , and La 3+ IN CHROMATOGRAPHIC SEPARATIONS USING POLY(STYRENE- CO -DIVINYLBENZENE) RESINS AND AQUEOUS ORGANIC ELUENTS

The complex formation between metal ions and carbohydrates in solvent mixtures has been studied by chromatographic measurements. The effect of noncomplexing partition was decreased by attaching the active groups only on the shell of the stationary phase particles. Poly(styrene- co -divinylbenzene) resin beads were surface-sulfonated for that purpose. Thus the inner part of the sulfonated bead remained inactive and nonswellable. The counter-ions examined were Na + , Ca 2+ , and La 3+ , and the organic cosolvents were ethanol and acetonitrile. The stability constants of the very weakly complexing D -glucose, D -xylose, and L -rhamnose, the weakly complexing D -fructose and L -arabinose, and the strongly complexing xylitol and D -sorbitol were determined. The increasing organic cosolvent content increased the retention times, which is explained by the increased complex stability between the complexing solute and the counter-ion. The effect was greatest for the complex-forming sugars in the Ca 2+ form and for the sugar alcohols in the La 3+ form. The organic cosolvent had only a minor effect on the weakly complexing components, whereas the complex stability of the strongly complexing xylitol and sorbitol in 50 wt% ethanol solution in the La 3+ resin was more than five times higher compared to the stability measured in pure water.     

Effects of Poly(ethylene glycol), Inorganic Salt,Sodium Dodecyl Sulfate,and Solvent System on Electrospinning of Poly(ethylene oxide)

Summary: The effects of PEO concentration, addition of PEG of various molecular weights (1 000–35 000 g · mol^?1), inorganic salt of various types (i.e., NaCl, LiCl, KCl, MgCl₂, and CaCl₂), or SDS, and the solvent system (i.e., mixed solvents of distilled water and methanol, ethanol, or 2‐propanol) on the bead formation and/or morphological appearance of electrospun PEO fibers were investigated using SEM. The formation of beaded fibers upon addition of low‐molecular‐weight PEGs into the PEO solution suggested that the very short relaxation time and/or the plasticizing effect of these low‐molecular‐weight PEGs contributed to the formation of the bead‐on‐string morphology of the as‐spun fibers. On the other hand, the observed improvement in the electro‐spinnability of the PEO solution with increasing PEO concentration and upon addition of NaCl and SDS suggested that the observed increase in the viscosity and conductivity and the observed decrease in the surface tension of the solution were indispensable for total suppression of the beads. However, when the conductivity of the solution increased only marginally, beads could still be obtained.

SEM image of as‐spun PEO fibers from a solution of PEO in distilled water at 5% w/v without (left) and with (right) 5% w/v PEG of 2 000 g · mol^?1.     

The influence of electrospinning parameters on the structural morphology and diameter of electrospun nanofibers

Electrospinning is a simple method of producing nanofibers by introducing electric field into the polymer solutions. We report an experimental investigation on the influence of processing parameters and solution properties on the structural morphology and average fiber diameter of electrospun poly ethylene oxide (PEO) polymer solution. Experimental trials have been conducted to investigate the effect of solution parameters, such as concentration, molecular weight, addition of polyelectrolyte in PEO solution, solvent effect, as well as governing parameter, such as applied voltage. The concentration of the aqueous PEO solution has shown noteworthy influence on the fiber diameter and structural morphology of electrospun nanofibers. At lower concentrations of PEO polymer solution, the fibers showed irregular morphology with large variations in fiber diameter, whereas at higher concentrations, the nanofibers with regular morphology and on average uniform fiber diameter were obtained. We find that the addition of polyelectrolytes, such as sodium salt of Poly acrylic acid (PAA) and Poly allylamine hydrochloride (PAH), increases the conductivity of PEO solutions and thereby decreases the bead formation in electrospun nanofibers. The increase in applied voltage has been found to affect the structural morphology of nanofiber while the addition of ethanol in PEO solution diminishes the bead defects. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Immiscible liquid–liquid slug flow characteristics in the generation of aqueous drops within a rectangular microchannel for preparation of poly(2-hydroxyethylmethacrylate) cryogel beads

The microchannel liquid-flow focusing and cryo-polymerization is an efficient method for the preparation of cryogel beads with a narrow diameter distribution. In order to prepare cryogel beads with expected diameters, it is necessary to get insights in the liquid–liquid immiscible flow characteristics of the flow-focusing fluid and the monomer solution in microchannels. In this work, the slug flow behaviors of two immiscible liquids regarding the preparation of poly(2-hydroxyethylmethacrylate) (pHEMA) cryogel beads in a rectangular cross-junction microchannel were investigated experimentally by the high-speed imaging method. Correlations of the immiscible liquid–liquid slug flow parameters like the aqueous slug velocity and length, the aqueous slug nose and tail lengths, the water-immiscible slug length as well as the aqueous droplet size were obtained. The pHEMA cryogel beads were prepared under certain flow conditions and the bead sizes were measured by laser particle size analyzer. The obtained correlations were then employed to estimate the bead sizes and compared with those obtained experimentally. The results showed that the present correlations gave reasonable estimations of the mean bead diameters at various conditions and thus, could be useful and helpful in the preparation of cryogel beads with expected size distributions in rectangular microchannels.     

Processing and characterization of electrospun poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) nanofibrous membranes

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) nanofibrous membranes were first fabricated via electrospinning from chloroform (CHCl₃) or CHCl₃/dimethylformamide (DMF) polymer solutions. The electrospinning conditions such as the polymer concentration, the solvent composition, and the applied voltage were optimized in order to get smooth and nano-sized fibers. The crystalline structure, the melting behaviors and the mechanical properties of the obtained nanofibrous membranes were characterized. With pure CHCl₃ as the solvent in the electrospinning process, the finest smooth PHBHHx fibers were about 1 μm in diameter. When DMF is added to CHCl₃ as a co-solvent, the conductivity and volatility of the solution increased and reduced, respectively, and the electrospinnability of the polymer solution increased as a result. The averaged diameters of PHBHHx fibers could be reduced down to 300-500 nm when the polymer concentration was kept at 3 wt%, the ratio of DMF/CHCl₃ was maintained at 20/80 (wt%), and the applied voltage was fixed at 15 kV during electrospinning. WAXD and DSC results indicated that the crystallization of the PHBHHx nanofibers was restricted to specific crystalline planes due to the molecular orientation along the axial direction of the fibers. The crystallization behaviors of the electrospun nanofibers were significantly different from that of the cast membranes because of the rapid solidification and the one-dimensional fiber size effect in the electrospinning process. Mechanically, the electrospun PHBHHx nanofibrous membranes were soft but tough, and their elongation at break averaged 240-300% and could be up to 450% in some cases. This study demonstrated how the size of electrospun PHBHHx fibers could be reduced by adding DMF in the solvent and gave a clue of the presence of oriented molecular chain packing in the crystalline phase of the electrospun PHBHHx fibers.     

Impact of electrospinning process parameters on the measured current and fiber diameter

In this article, polycaprolactone (PCL) nanofibres were processed by electrospinning using a 3:1 ratio of tetrahydrofuran to methanol as solvent. The solvent choice was motivated by the possibility of greener alternatives to the halogenated compounds most often used for electrospinning. The morphologies and fiber diameters resulting from the electrospinning of PCL solutions at room temperature under various conditions are presented in this article. The material morphology was characterized using scanning electron microscopy and a measuring software. The process was optimized for smaller fibers with a narrower fiber diameter distribution by studying parameters such as polymer concentration, applied voltage, the tip to collector distance (TCD), and the solution flow rate. A comparison analysis was used to separate the current resulting from whipping and that resulting from spraying at high voltage. The fiber diameters obtained under various processing conditions were effectively modeled using the terminal jet theory, referenced in several works. Process parameters were optimal for a 20% PCL concentration spun at a flow rate of 0.5 mL/h, with a TCD of 15 cm and an applied voltage of 8 kV. Fibers spun under these conditions displayed diameters of 546 ± 173 nm. POLYM. ENG. SCI., 55:2576–2582, 2015. © 2015 Society of Plastics Engineers