Poly(lactide) nanofibers produced by a melt‐electrospinning system with a laser melting device

A new melt‐electrospinning system equipped with a CO₂‐laser melting device was developed. Rod‐like samples were prepared from poly(lactide) pellets, and then fibers were produced from the samples using the new system. The effects of producing conditions on the fiber diameter were investigated. Furthermore, the physical properties of the fibers were investigated. The following conclusions were obtained: (i) in a special case, fibers having an average fiber diameter smaller than 1 μm could be obtained using the system developed; (ii) the fiber diameter could be decreased with increased laser output power, but the physical properties of the fibers such as the melting point and the molecular weight were decreased; and (iii) the electrospun fibers exhibited an amorphous state, and the annealed fibers exhibited an isotropic crystal orientation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1640–1645, 2007     

Effects of ethylene content of poly(ethylene‐co‐vinyl alcohol) on diameter of fibers produced by melt‐electrospinning

Rodlike samples were made from four kinds of poly(ethylene‐co‐vinyl alcohol) (EVAL) pellets with different ethylene contents. From these rodlike samples, fibers were produced using a melt‐electrospinning system equipped with a CO₂‐laser melting device. The effects on the fiber diameter of the ethylene content and the moisture regain of the rodlike samples were investigated. Furthermore, the physical properties of the fibers were investigated. The following conclusions were reached: (i) EVAL fibers having an average fiber diameter smaller than 1 μm can be obtained using the system developed; (ii) the diameter of EVAL fiber is influenced by the ethylene content and the moisture regain of the starting rods; (iii) the laser heating does not greatly decrease the melting point and the molecular weight of EVAL; and (iv) preferred crystal orientation can be seen in electrospun EVAL fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1368–1375, 2007     

Electrospun plasma‐modified chitosan/poly(ethylene terephthalate)/ferrocenyl‐substituted N‐acetyl‐2‐pyrazoline fibers for phosphate anion sensing

Two ferrocenyl‐substituted N‐acetyl‐2‐pyrazolines, N‐acetyl‐3‐(2‐furyl)‐5‐ferrocenyl‐2‐pyrazoline (Fc‐1) and N‐acetyl‐3‐(2‐thienyl)‐5‐ferrocenyl‐2‐pyrazoline (Fc‐2) electrospun fibers, were produced in the presence of plasma‐modified chitosan (PMCh)/poly(ethylene terephthalate) (PET) supporting polymers with an electrospinning method. The morphological and chemical characterizations of the PMCh/PET/Fc‐1 and PMCh/PET/Fc‐2 electrospun fibers were determined by scanning electron microscopy coupled with energy‐dispersive X‐ray spectroscopy analysis. Thermogravimetric analysis results indicated the presence of ferrocene within the PMCh/PET nanofibers. The electrochemical behavior of the PMCh/PET/Fc‐1 and PMCh/PET/Fc‐2 electrospun fibers were investigated by cyclic voltammetry measurements based on the ferrocene/ferrocenium redox couple. The new PMCh/PET/Fc‐1 and PMCh/PET/Fc‐2 electrospun fibers aggregated on the indium tin oxide were used for phosphate anion sensing. The highest oxidation peak currents were observed for the PMCh/PET/Fc‐1 electrospun fibers at about 0.56 V in 0.1M phosphate buffer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43344.     

Spinnability and physical properties of in situ composite fibers based on thermotropic liquid crystalline polymer

In situ composite fibers based on poly(ethylene 2,6‐naphthalate) (PEN) and a thermotropic liquid crystalline polymer (Vectra A950) were prepared using a single‐screw extruder. The fibers were taken up at selected speeds. The spinnability, thermal behavior, mechanical properties, and morphologies of the PEN/Vectra A950 blend were investigated. The results showed that the PEN/Vectra A950 blends were partly miscible, and the miscibility increased with the increased concentration of Vectra in the blend. The DSC measurements indicated that Vectra enhanced the crystallization process of PEN by performing as a nucleating agent. The Instron tensile property study, coupled with scanning electron microscopy, revealed that the mechanical properties of the PEN matrix were significantly improved when Vectra existed as long and continuous fibrils. The laser Raman results showed that the Vectra orientation began to develop at take‐up speeds above 500 m/min. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 795–811, 2002     

Preparation and properties of PET/SiO2 composite micro/nanofibers by a laser melt-electrospinning system

Poly(ethylene terephthalate) (PET)/SiO₂ composite micro/nanofibers were successfully prepared by a laser melt-electrospinning system. The fibers with diameter ranging from 500 nm to 7 μm were obtained. The effect of laser current and applied voltage on the fibers morphologies was investigated by scanning electron microscopy (SEM), and the results showed that the relationship of process parameters and fibers diameter was complicated. The EDS analysis confirmed the presence of SiO₂ in the PET fibers matrix. The crystallization behavior of the electrospun PET/SiO₂ micro/nanofibers was investigated using X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC), and it was found that the as-electrospun fibers exhibited an amorphous phase. After heat-treatment at 120 and 160°C for 1 h, respectively, the fibers showed a high crystallinity. The thermal properties of fibers were studied using thermogravimetry-differential thermal analysis (TG–DTA), and showed the electrospun PET/SiO₂ composite fibers was not effective difference of thermostability compared with PET fibers when used for fibers materials. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of interface and confinement size on the crystallization behavior of PLLA confined in coaxial electrospun fibers

Poly(l ‐lactide)/polyacrylonitrile (PLLA/PAN) core‐sheath composite fibers were fabricated by coaxial electrospinning. The crystallization behavior of PLLA within the coaxial electrospun fibers was studied by differential scanning calorimetry (DSC). The PLLA/PAN coaxial electrospun fiber with a PLLA diameter of ～32 nm (C1) exhibits a crystallization temperature (T_c) of 22.5 °C higher but a cold‐crystallization temperature (T_cc) of 10 °C lower than bulk PLLA. The crystallinity of C1 fiber is also higher than bulk PLLA. In both isothermal melt‐ and cold‐crystallization, PLLA in C1 fiber crystallizes faster than the bulk PLLA, as revealed by the smaller half crystallization times (t_1/2). The enhanced crystallizability of PLLA in the C1 fiber may be attributed to the increased nuclei number and crystal growth rate induced by the PAN surface, i.e., surface‐induction effect. However, PLLA also suffers a nano‐confinement effect exerted by PAN sheath in the coaxial electrospun fiber, which can suppress PLLA crystallization. When the diameter of PLLA is too small (< 32 nm), the nano‐confinement effect may prevail over the surface‐induction effect, leading to a slower crystallization rate and smaller crystallinity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45980.     

Electrospinning of poly(hydroxybutyrate‐co‐hydroxyvalerate) fibrous tissue engineering scaffolds in two different electric fields

Poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) was electrospun into ultrafine fibrous nonwoven mats. Different from the conventional electrospinning process, which involves a positively charged conductive needle and a grounded fiber collector (i.e., positive voltage (PV) electrospinning), pseudo‐negative voltage (NV) electrospinning, which adopted a setup such that the needle was grounded and the fiber collector was positively charged, was investigated for making ultrafine PHBV fibers. For pseudo‐NV electrospinning, the effects of various electrospinning parameters on fiber morphology and diameter were assessed systematically. The average diameters of PHBV fibers electrospun via pseudo‐NVs were compared with those of PHBV fibers electrospun via PVs. With either PV electrospinning or pseudo‐NV electrospinning, the average diameters of electrospun fibers ranged between 500 nm and 4 μm, and they could be controlled by varying the electrospinning parameters. The scientific significance and technological implication of fiber formation by PV electrospinning and pseudo‐NV electrospinning in the field of tissue engineering were discussed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Melt electrospinning from poly(L‐lactide) rods coated with poly(ethylene‐co‐vinyl alcohol)

Rodlike poly(L ‐lactide) (PLLA) samples coated with poly(ethylene‐co‐vinyl alcohol) (EVOH) were made. Fibers were produced from these rodlike samples by using a melt electrospinning system equipped with a laser irradiating device, and the effects of EVOH content and the processing parameters of the melt electrospinning on fiber diameters were investigated. We also studied the fiber formation mechanism from the rods during the laser melt electrospinning process. The following conclusions were reached: (i) coating of EVOH on PLLA rods has a remarkable effect on decreasing fiber diameter from 3 μm to around 1 μm; (ii) increases in the electric field strength and temperature of spinning space decrease the average diameter of fibers produced from pure PLLA rods, and longer collector distance leads to lager PLLA fiber diameter; and (iii) the migration of PLLA component from the core to the surface of electrospun fibers takes place during the fiber formation process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrospun nanofibers of block copolymer of trimethylene carbonate and ϵ‐caprolactone

The electrospinning behavior of a block copolymer of trimethylene carbonate (TMC) and ε‐caprolactone dissolved in N,N‐dimethylformamide (DMF) and methylene chloride (MC) was studied. The effects of the blended solvent volume ratio, concentration, voltage, and tip–collector distance (TCD) on the morphology of the electrospun fibers were investigated by scanning electron microscopy. The results indicated that the diameter of the electrospun fibers decreased with a decreasing molar ratio of MC to DMF, but beads formed gradually. With a decreasing concentration of the solution, the fiber diameter decreased; at the same time, beads also appeared and changed from spindlelike to spherical. A higher voltage and larger TCD favored the formation of smaller diameter electrospun fibers. The results of differential scanning calorimetry and X‐ray diffraction showed that the crystallinity and melting point of the electrospun fibers decreased when increasing the TMC content in the copolymer. Compared with the corresponding films, the crystallinity and melting point of the electrospun fibers were obviously increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1462–1470, 2006     

Development of a Transcrystalline Phase in Poly(propylene) at the PET Interface

An isothermal crystallization behavior is observed for poly(propylene) (PP) on the surface of poly(ethylene terephthalate) (PET) fibers. The extensive nucleation on the fiber surface is followed by the development of a transcrystalline phase, while normal PP spherulites appear much later than the transcrystalline phase in regions far from the interface. The crystallization kinetics is followed by spot‐intensity measurements at selected areas on the picture frame near the fibers, showing that the kinetics in the transcrystalline zone is quite different from that in the PP bulk. Furthermore, a preferential orientation of the b‐axis and/or bc‐planes of PP crystallites along the c‐axis of PET fibers is found, suggesting that the crystal structure of the fiber material could also influence the development of this phase.     

Electrical conductivity and rheology of carbon fiber/liquid crystal polymer composites

One emerging market for electrically conductive resins is for bipolar plates for use in fuel cells. Adding carbon fillers to thermoplastic resins increases composite electrical conductivity and viscosity. Current technology often adds as much of a single type of carbon filler as possible to achieve the desired conductivity, while still allowing the material to be extruded and molded into a bipolar plate. In this study, varying amounts of two different types of polyacrylonitrile (PAN) based carbon fiber (Fortafil 243 and Panex 30) were added to Vectra A950RX liquid crystal polymer. The resulting single fiber composites were then tested for electrical conductivity and rheological properties. The electrical conductivity followed the behavior typically seen in composites with a percolation threshold at 5 vol% for Fortafil 243 and at 13 vol% for Panex 30. Viscosity increased with increasing filler volume fraction for all shear rates, but was more rapid for the Fortafil 243 composites. Over the range of shear rates studied, the viscosity followed a shear‐thinning power law model with power‐law exponent (n – 1) = –0.5 for neat Vectra A950RX. Panex 30 had no effect on the power‐law exponent and Fortafil 243 changed (n – 1) to −0.6. POLYM. COMPOS., 28:168–174, 2007. © 2007 Society of Plastics Engineers     

Electrospun hydroxypropyl methyl cellulose phthalate (HPMCP)/erythromycin fibers for targeted release in intestine

Ultrafine fiber mats of hydroxypropyl methyl cellulose phthalate (HPMCP) were successfully electrospun and explored as drug delivery vehicles using erythromycin as a model drug. The morphology of the electrospun fiber and the drug release process in the artificial gastric juice and in the artificial intestinal juice were investigated. With the same drug‐to‐matrix ratio (HPMCP/erythromycin = 9/1), all the fibers were electrospun into a tape‐like or ribbon shape and the average fiber diameter (AFD) was increased with the HPMCP concentration. Because of the pH‐sensitive property of HPMCP, erythromycin was released from the erythromycin‐containing electrospun HPMCP fiber mats by a slowly diffusion process in the artificial gastric juice, while it was released in nearly first‐order kinetics in the artificial intestinal juice because of the first‐order kinetics dissolution of the HPMCP fibers in the artificial intestinal juice. And the rate of erythromycin released in the artificial intestinal juice was about more than 2.5 times faster than that in the artificial gastric juice. The diameter of the fibers plays an important role on the rate and the total amount of the drug released both in stomach and in intestine, the rate and the total amount of the drug released decreasing with increasing AFD. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of solution properties on nanofibrous structure of electrospun poly(lactic‐co‐glycolic acid)

Electrospinning of poly(lactic‐co‐glycolic acid) (PLGA) in chloroform or 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) was investigated, focusing on its solution parameters, to develop nonwoven biodegradable nanofibrous structures for tissue engineering. PLGA nanofibers were obtained by electrospinning of 15 wt % PLGA solution and the resulting average fiber diameters were varied with the range of 270–760 nm, depending on solution property. When small amounts of benzyl triethylammonium chloride (BTEAC) was added to the PLGA/chloroform solution, the average diameter was decreased from 760 to 450 nm and the fibers were densely amounted in a straight shape. In addition, the average fiber diameter (270 nm) of nanofibers electrospun from polar HFIP solvent was much smaller than that (760 nm) of nanofibers electrospun from nonpolar chloroform solvent. Therefore, it could be concluded that conductivity or dielectric constant of the PLGA solution was a major parameter affecting the morphology and diameter of the electrospun PLGA fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1214–1221, 2006     

Preparation and properties of TPU micro/nanofibers by a laser melt‐electrospinning system

Laser melt electrospinning is a novel technology to fabricate scaffolds in the tissue engineering applications. The melt electrospinning is much safer than the conventional solution electrospinning due to without solvent effect. In this study, thermoplastic polyurethane (TPU) micro/nanofibers were successfully prepared by using this method. The effects of laser current and applied voltage on the fibers morphologies were investigated by scanning electron microscopy. The thermal behaviors and crystallization conditions of the TPU under different states were demonstrated by differential scanning calorimetry and X‐ray diffraction analysis. The mechanical property and the specific surface area of the TPU fibers membranes were also studied. All the analysis results showed that the effects of laser current and applied voltage on the average fiber diameter were complicated, the average fiber diameter ranging from 1.70 to 2.53 µm; the TPU is not an easily crystallized material; the electrospun fibers exhibited an amorphous phase; the average elongation at break laser of the electrospun TPU fiber membranes is about 134%; the average tensile strength is about 1.02 MPa and the specific surface area of the electrospun TPU fiber membrane is about 199 m²/g. POLYM. ENG. SCI., 54:1412–1417, 2014. © 2013 Society of Plastics Engineers     

Direct Laser Patterning of β‐BaB2O4 Crystals with High Orientation in the Inside of Glass Fiber

The laser‐induced crystallization method was applied to pattern β‐BaB₂O₄ crystals (β‐BBO) in the inside of bulk glass plate and fibers of 8Sm₂O₃–42BaO–50B₂O₃, in which the focal position of continuous wave (CW) Yb:YVO₄ fiber lasers (power: 0.9–1.0 W, scanning speed: 2 μm/s) with a wavelength of 1080 nm was moved gradually from the surface to the inside. It was confirmed from micro‐Raman scattering spectra, second harmonic generation, and transmission electron microscope observations that β‐BBO crystals are patterned in the inside of glass plate and fibers (diameter: 110 μm) and are highly oriented that is c‐axis orientation, along the laser scanning direction. This study proposes the direct and simple processing for the fabrication of glass fibers consisting of optical functional crystal cores.     

Effect of platinum salt concentration on the electrospinning of polyacrylonitrile/platinum acetylacetonate solution

The preparation and characterization of electrospun polyacrylonitrile (PAN)/platinum(II) acetylacetonate composite nanofibers were investigated. The solution properties, such as viscosity, surface tension, and conductivity, of Pt‐acetylacetonate‐added PAN solutions in N,N‐dimethylformamide were measured, and their influences on the resulting fiber structure were also determined. At low Pt salt concentrations, the addition of Pt salt increased the fiber diameter but did not change the fiber diameter distribution. However, the fiber diameter decreased, and the fiber diameter distribution became broader when the Pt salt concentration went beyond a critical value. The structure of the electrospun fibers was determined by the formation of polymer–salt– solvent interactions, which changed the balance among the viscosity, surface tension, and conductivity of the solutions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

PET microfiber prepared by carbon dioxide laser heating

In preliminary experiments to optimize the condition of a laser heating, zone drawing for poly(ethylene terephthalate) (PET) fiber, a microfiber was prepared by a continuous‐wave carbon dioxide (CW CO₂) laser heating. CW CO₂ laser heating was carried out at an extremely low applied tension (σ_a) at a higher laser power density (PD) as compared to the optimum condition for the laser heating, zone drawing of PET fiber reported previously. The microfibers were obtained by CO₂ laser heating carried out at a PD of 15.8 W cm^?2 and under a σ_a of 0.66 MPa or lower. The diameter of the fiber decreased with a decreasing σ_a and increasing PD. The smaller the diameter, the higher was its birefringence. The smallest diameter fiber obtained at σ_a = 0.17 MPa at PD = 21 W cm^?2 had a diameter of 4.5 μm and a birefringence of 0.112, and its draw ratio estimated from the diameter reached 3086 fold. Such a high draw ratio was not previously attained by any drawing method. In a wide‐angle X‐ray diffraction photograph of the smallest diameter fiber, indistinct reflections due to oriented crystallites were observed. An SEM micrograph of the smallest diameter fiber showed a smooth surface without any crack and was uniform in diameter. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3297–3283, 2003     

Fabricating novel thermal crosslinked ultrafine fibers via electrospinning

In this article, we report the preparation of a kind of novel crosslinked ultrafine fiber by electrospinning of unsaturated polyester macromonomers (UPM) and subsequent thermal crosslinking. The UPM is prepared via a two‐step reaction with poly(2‐methyl‐1,3‐propyleneadipate) diol terminated (PMPA), isophorone‐diisocyanate (IPDI) and 2‐hydroxyethyl methacrylate (HEMA). Poly(3‐hydroxyl‐butyrate‐co‐3‐hydroxylvalerate) (PHBV) is chosen to improve the processability of the UPM. UPM/PHBV blend ultrafine fibers are successfully electrospun with a proper mass ratio of UPM to PHBV in dichloromethane solution. The fibers are thermally crosslinked after electrospinning. Measurement results indicate that the average diameter of the fibers is about 1 μm and the crosslinked fibers have good solvent‐stability and thermal‐stability. This novel fiber has potential applications in filtration and protective coating. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 107:2142–2149, 2008     

Biocompatibility and antibacterial activity of chitosan and hyaluronic acid immobilized polyester fibers

Poly(ethylene terephthalate) (PET) fibers were treated with ⁶⁰Co‐γ‐ray and grafted with acrylic acid. The resulting fibers were further grafted with chitosan (CS) via esterification. Afterward, hyaluronic acid (HA) was immobilized onto CS‐grafting fibers. The antibacterial activity of CS against S. aureus, E. coli, and P. aeruginosa was preserved after HA‐immobilization. After immobilizing HA, the L929 fibroblasts cell proliferation was improved forCS‐grafting PET fiber. The results indicate that by grafting with CS and immobilizing with HA, PET fibers not only exhibit antibacterial activity, but also improve the cell proliferation for fibroblast. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 220–225, 2007     

Structure and properties of melt‐spun PET/MWCNT nanocomposite fibers

Polyethylene terephthalate (PET) melt‐spun fibers were modified with multiwall carbon nanotubes (MWCNT) to obtain conductive microfibers smaller than 90 μm in diameter. Physical properties such as crystallinity and orientation of as‐spun fibers were studied by X‐ray diffraction, Raman spectroscopy, and microscopy techniques at different draw ratios (DR) and MWCNT concentrations. Morphological and orientation analysis of MWCNT after melt‐spinning process showed agglomerates formation and highly oriented CNTs. The study of the orientation of PET crystalline phase in drawn fibers proved that the addition of nanoparticles decreases the orientation of crystalline units inside the fibers. The orientation of MWCNT as well as that of PET chains was studied using Raman spectroscopy at different DR and a high degree of CNT orientation was observed under high DR conditions. Mechanical and electrical properties of as‐spun fibers were also investigated. Our results showed that it was possible to achieve conductive fibers at a MWCNT concentration of 2% w/w, and more conductive fibers using higher DR were also obtained without increasing the MWCNT concentration. Mechanical properties results showed interestingly high value of maximum tensile strain at break (ε_max) of nanocomposite fibers, up to three times more than pure PET fibers. POLYM. ENG. SCI., 50:1956–1968, 2010. © 2010 Society of Plastics Engineers