Effects of different ionic liquids on the electrospinning of a polyacrylonitrile polymer solution

Additives have been proven to be useful in improving electrospinnability and controlling fiber morphology through the modification of solution properties, including the conductivity, viscosity, and surface tension. In this study, the effects of adding small amounts of four different types of ionic liquids [i.e., 1‐butyl‐3‐methylimidazolium chloride (C₄MIMCl), 1‐dodecyl‐3‐methylimidazolium chloride (C₁₂MIMCl), 1‐ethyl‐3‐methylimidazolium bromide (C₂MIMBr), and 1‐ethyl‐3‐methylimidazolium phosphate (C₂MIM)₃PO₄] on the solution properties, electrospinning process, and characteristics of polyacrylonitrile (PAN) were investigated. The results show that the solution conductivities significantly increased with the addition of different ionic liquids with concentrations varying from 0.1 to 1.0 wt %, and the tendency depended on the structures of the ionic liquids. (C₂MIM)₃PO₄ showed the highest conductivity value; this was followed by C₂MIMBr, C₄MIMCl, and C₁₂MIMCl. The ionic liquids formed visible crystals; this made the fiber surfaces rough, and some fiber segments underwent partial aggregation. A regular varying tendency between the minimum mean diameter of the PAN/ionic liquid fibers and the structure of the ionic liquid was found. The PAN/N,N‐dimethylformamide (DMF)/(C₂MIM)₃PO₄ solution showed the highest conductivity among the four systems with different ionic liquids added, and the thinnest minimum diameter of the PAN/(C₂MIM)₃PO₄ fibers appeared with a relatively low ionic liquid concentration of 0.25 wt %, whereas the PAN/DMF/C₁₂MIMCl solution had the lowest conductivity, and the minimum mean diameter of PAN/C₁₂MIMCl fibers appeared at a relatively high ionic liquid concentration of 0.8 wt %. Although the conductivity of the PAN/DMF/C₂MIMBr solution was higher than that of the PAN/DMF/C₄MIMCl solution, the minimum mean diameters of the PAN/C₂MIMBr and PAN/C₄MIMCl fibers appeared at the same ionic liquid concentration of 0.5 wt % because of the similar ionic activities of C₂MIMBr and C₄MIMCl. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2359–2368, 2013     

Effect of annealing‐induced interfacial demixing on crystallization of PEO confined in coaxial electrospun nanofibers

Glassy polymer nanofibers with spatially confined poly(ethylene oxide) (PEO) were fabricated by coaxial electrospinning of PEO with polyacrylonitrile (PAN) or polystyrene. The effect of melt‐annealing on the crystallization behavior of the confined PEOs was studied using differential scanning calorimetry. It is found that the crystallization behavior of the confined PEOs varies with annealing temperature (T_a), annealing time (t_a), and molecular weight of PEO. Notably, it is observed that the crystallization temperature (T_c) and melting temperature (T_m) of PEO increase with prolongation of t_a, for PEO600K/PAN and PEO2K/PAN coaxial electrospun fibers. This phenomenon can be interpreted by the annealing‐induced demixing at the core‐sheath interface. After the coaxial electrospinning, the core and sheath of the PEO/PAN coaxial fibers are partially compatible due to the miscible solvents used for the core and sheath polymers. Upon annealing, demixing occurs at the core‐sheath interface, leading to improved crystallizability of PEO. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45760.     

Needleless emulsion electrospinning for scalable fabrication of core–shell nanofibers

This article reports a new needleless emulsion electrospinning method for scale‐up fabrication of ultrathin core–shell polyacrylonitrile (PAN)/isophorone diisocyanate (IPDI) fibers. These core–shell fibers can be incorporated at the interfaces of polymer composites for interfacial toughening and self‐repairing due to polymerization of IPDI triggered by environmental moisture. The electrospinnable PAN/IPDI emulsion was prepared by blending PAN/N,N‐dimethylformamide and IPDI/N,N‐dimethylformamide solutions (with the solute mass fraction of 1 : 1). The electrospinning setup consisted of a pair of aligned metal wires as spinneret (positive electrode) to infuse the PAN/IPDI emulsion and a rotary metal disk as fiber collector (negative electrode). The formed ultrathin core–shell PAN/IPDI fibers were collected with the diameter in the range from 300 nm to 3 μm depending on the solution concentration and process parameters. Optical microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy were used to characterize the core–shell nanostructures. Dependencies of the fiber diameter on the PAN/IPDI concentration, wire spacing, and wire diameter were examined. Results show that needleless emulsion electrospinning provides a feasible low‐cost manufacturing technique for scalable, continuous fabrication of core–shell nanofibers for potential applications in self‐repairing composites, drug delivery, etc. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40896.     

Studies on the synthesis of electrospun PAN‐Ag composite nanofibers for antibacterial application

We have successfully synthesized polyacrylonitrile (PAN) nanofibers impregnated with Ag nanoparticles by electrospinning method at room temperature. Briefly, the PAN‐Ag composite nanofibers were prepared by electrospinning PAN (10% w/v) in dimethyl formamide (DMF) solvent containing silver nitrate (AgNO₃) in the amounts of 8% by weight of PAN. The silver ions were reduced into silver particles in three different methods i.e., by refluxing the solution before electrospinning, treating with sodium borohydride (NaBH₄), as reducing agent, and heating the prepared composite nanofibers at 160°C. The prepared PAN nanofibers functionalized with Ag nanoparticles were characterized by field emission scanning electron microscopy (FESEM), SEM elemental detection X‐ray analysis (SEM‐EDAX), transmission electron microscopy (TEM), and ultraviolet‐visible spectroscopy (UV‐VIS) analytical techniques. UV‐VIS spectra analysis showed distinct absorption band at 410 nm, suggesting the formation of Ag nanoparticles. TEM micrographs confirmed homogeneous dispersion of Ag nanoparticles on the surface of PAN nanofibers, and particle diameter was found to be 5–15 nm. It was found that all the three electrospun PAN‐Ag composite nanofibers showed strong antibacterial activity toward both gram positive and gram negative bacteria. However, the antibacterial activity of PAN‐Ag composite nanofibers membrane prepared by refluxed method was most prominent against S. aureus bacteria. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Comparatively Thermal and Crystalline Study of Poly(methyl‐methacrylate)/Polyacrylonitrile Hybrids: Core–Shell Hollow Fibers,Porous Fibers,and Thin Films

The polyacrylonitrile/polymethyl‐methacrylate (PMMA/PAN) porous fibers, core–shell hollow fibers, and porous thin films are prepared by coaxial electrospinning, single electrospinning, and spin‐coating technologies, respectively. The different morphologies arising from different processes display great influences on their thermal and crystalline properties. The adding of PMMA causes porous structure due to the microphase‐separation structure of immiscible PMMA and PAN phases. The lower weight loss, higher degradation temperature, and glass‐transition temperatures of porous thin films than those of porous fibers and core–shell hollow fibers are obtained, evidencing that the polymer morphologies produced from the different process can efficiently influence their physical properties. The orthorhombic structure of PAN crystals are found in the PMMA/PAN porous thin films, but the rotational disorder PAN crystals due to intermolecular packing are observed in the PMMA/PAN porous fibers and core–shell hollow fibers, indicating that different processes cause different types of PAN crystals.

     

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.     

Optimization and investigation of the governing parameters in electrospinning the home‐made poly(l‐lactide‐co‐ε‐caprolactone‐diOH)

Poly(l ‐lactide‐co‐ε‐caprolactone‐diOH) (PCLA) with (ABA)_n type is synthesized using poly(lactic acid) (PLA) and poly(ε‐caprolactone) di‐OH (PCL‐diOH) via chain extending method. FT‐IR, ¹H‐NMR, and GPC data demonstrate that PLA and PCL‐diOH have reacted completely. The product is electrospun into ultrafine fibers subsequently. The optimum electrospinning parameters obtain from an orthogonal experiment are a solvent ratio (DMF/DCM) of 5/5, a polymer concentration of 28 wt %, a collector distance of 20 cm and a voltage of 18 kV. As a result, the average diameter of fibers is 0.77 µm and the uniformity is above 80%. Via range analysis, it is found that the order of the influence on diameter is solvent ratio, applied voltage, collector distance, and polymer concentration, successively. Single effect of the four governing factors on diameter and morphology is also experimentally investigated. This may provide clues for obtaining fibers with various structures by controlling the parameters. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3600–3610, 2013     

Carbon fibers derived from wet‐spinning of equi‐component lignin/polyacrylonitrile blends

Equi‐component blends of polyacrylonitrile (PAN) and lignin, i.e., with a lignin content as large as 50 wt %, were successfully used as precursors to produce carbon fibers. Rheological measurements demonstrated that increasing lignin content in spinning solution reduced shear viscosity and normal stress, indicating a decrease of viscoelastic behavior. This was confirmed by Fourier transform infrared results that show no discernable chemical reaction or crosslinking between PAN and lignin in the solution. However, the resulting carbon fibers display a large I_D/I_G ratio (by Raman spectroscopy) indicating a larger disordered as compared to that from pure PAN. The macro‐voids in the lignin/PAN blend fibers typically generated during wet‐spinning were eliminated by adding lignin in the coagulant bath to counter‐balance the out‐diffusion of lignin. Carbon fibers resulting from lignin/PAN blends with 50 wt % lignin content displayed a tensile strength and modulus of 1.2 ± 0.1 and 130 ± 3 GPa, respectively, establishing that the equi‐component wet‐spun L/P‐based carbon fibers possessed tensile strength and modulus higher than 1 and 100 GPa. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45903.     

Electrospun polyacrylonitrile nanocomposite fibers reinforced with Fe3O4 nanoparticles: Fabrication and property analysis

The manufacturing of pure polyacrylonitrile (PAN) fibers and magnetic PAN/Fe₃O₄ nanocomposite fibers is explored by an electrospinning process. A uniform, bead-free fiber production process is developed by optimizing electrospinning conditions: polymer concentration, applied electric voltage, feedrate, and distance between needle tip to collector. The experiments demonstrate that slight changes in operating parameters may result in significant variations in the fiber morphology. The fiber formation mechanism for both pure PAN and the Fe₃O₄ nanoparticles suspended in PAN solutions is explained from the rheologial behavior of the solution. The nanocomposite fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectrophotometer, and X-ray diffraction (XRD). FT-IR and XRD results indicate that the introduction of Fe₃O₄ nanoparticles into the polymer matrix has a significant effect on the crystallinity of PAN and a strong interaction between PAN and Fe₃O₄ nanoparticles. The magnetic properties of the nanoparticles in the polymer nanocomposite fibers are different from those of the dried as-received nanoparticles.     

Coaxial Electrospinning with Triton X‐100 Solutions as Sheath Fluids for Preparing PAN Nanofibers

Coaxial electrospinning using surfactants as sheath fluid for preparing high‐quality polymer nanofibers is studied. PAN nanofibers are fabricated using this process with Triton X‐100 solutions in DMF. FESEM demonstrates that the Triton X‐100 solution has a significant influence on the quality of the nanofibers. The nanofiber diameters can be controlled by adjusting the concentration of Triton X‐100 in the sheath fluids with a scaling law D = 640 C^?0.32. The mechanism of the influence of Triton X‐100 solutions on the formation of PAN fibers is discussed and it is demonstrated that coaxial electrospinning with surfactant solution is a facile method for achieving high‐quality polymer nanofibers.

     

Influence of processing conditions on polymorphic behavior,crystallinity, and morphology of electrospun poly(VInylidene fluoride) nanofibers

The polymorphism and crystallinity of poly(vinylidene fluoride) (PVDF) membranes, made from electrospinning of the PVDF in pure N,N‐dimethylformamide (DMF) and DMF/acetone mixture solutions are studied. Influence of the processing and solution parameters such as flow rate, applied voltage, solvent system, and mixture ratio, on nanofiber morphology, total crystallinity, and crystal phase content of the nanofibers are investigated using scanning electron microscopy, wide‐angle X‐ray scattering, differential scanning calorimetric, and Fourier transform infrared spectroscopy. The results show that solutions of 20% w/w PVDF in two solvent systems of DMF and DMF/acetone (with volume ratios of 3/1 and 1/1) are electrospinnable; however, using DMF/acetone volume ratio of 1/3 led to blockage of the needle and spinning process was stopped. Very high fraction of β‐phase (～79%–85%) was obtained for investigated nanofiber, while degree of crystallinity increased to 59% which is quite high due to the strong influence of electrospinning on ordering the microstructure. Interestingly, ultrafine fibers with the diameter of 12 and 15 nm were obtained in this work. Uniform and bead free nanofiber was formed when a certain amount of acetone was added in to the electrospinning solution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42304.     

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.     

Orientation‐Dependence of Thermal Depolarization and Phase Development in Bi1/2Na1/2TiO3‐BaTiO3 Single Crystals

The direction‐dependence of pyroelectric properties of (1 ? x)Bi_1/2Na_1/2TiO₃ ? xBaTiO₃ (BNT ? 100xBT) is investigated, using single crystal samples with well‐defined orientations for x = 0.036 and x = 0.063. The results are compared with those of temperature‐dependent measurements of the ferroelectric and dielectric hysteresis. The depolarization temperature T_d of each crystal composition is found to depend on crystal orientation, a fact that is explained by differences in the stability of respective domain configurations. A rationalization is offered for the observation that T_d differs from the ferroelectric‐relaxor transition temperature, depending on orientation. The hysteresis curves of BNT ? 3.6BT are typical for a rhombohedral system with a ferroelectric‐relaxor transition, with polarization reversal close to T_d occurring in a multistep process that includes decay of ferroelectric domains into polar nanoregions and re‐formation of domains. BNT ? 6.3BT, a composition in the region of the morphotropic phase boundary, shows the same feature, but additionally is characterized by a field‐induced transition between rhombohedral and tetragonal symmetry. This combination results in an effective piezoelectric coefficient of pm/V.     

Effect of different salts on electrospinning of polyacrylonitrile (PAN) polymer solution

Electrospinning is a relatively simple method to produce submicron fibers from solutions of different polymers and polymer blends. If the solution is absolutely insulating, or the applied voltage is not high enough that electrostatic force cannot overcome the surface tension, then no fiber can be produced by electrospinning; however, if some salt is added in the solution, the problem can be overcome. The effect of different salts on electrospinning of polyacrlonitrile (PAN) polymer solution was investigated in this article. The various inorganic salts used in this work include LiCl, NaNO₃, NaCl, and CaCl₂.The results show that when the salts were added, respectively, into different concentrations of PAN solution, the order of conductant was LiCl > NaNO₃ > CaCl₂ > NaCl > no salt added. Viscosity and shearing strength of electrospinning solutions are slightly affected by the adding of salts and mainly affected by the changes in concentration of PAN electrospinning solutions. The diameter of nanofibers electrospun by solutions with different salts size down as follows: LiCl > NaNO₃ > CaCl₂ > NaCl. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3865–3870, 2007     

Fabrication of large‐scale superhydrophobic composite films with enhanced tensile properties by multinozzle conveyor belt electrospinning

Large‐scale superhydrophobic composite films with enhanced tensile properties were prepared by multinozzle conveyor belt electrospinning. First, a strategy of conveyor belt electrospinning was introduced for large‐scale fabrication since the conveyor belt can expand the electrospinning area unlimitedly. During the electrospinning (or electrospraying) process, certain kinds of fibers are combined on the conveyor belt in one electrospinning (or electrospraying) step. The superhydrophobicity of electrospun film can be achieved by the presence of PS beads and bead‐on‐string PVDF fibers, while submicron PAN fibers are responsible for the improvement of mechanical properties. The result shows that CA value of the surface comprising of PS beads and bead‐on‐string PVDF fibers could reach up to 155.0°. As the submicron PAN fibers increased, the value of CA decreased, changing from 155.0° to 140.0°, meanwhile the tensile strength of composite film was enhanced from 1.14 to 4.12 MPa correspondingly which is beneficial to putting the films into practice. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39735.     

High temperature‐insensitive ferro‐/piezoelectric properties and nanodomain structures of Pb(In1/2Nb1/2)O3–PbZrO3–Pb(Mg1/3Nb2/3)O3–PbTiO3 relaxor single crystals

For rhombohedral (R) Pb(In_1/2Nb_1/2)O₃–PbZrO₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PIN–PZ–PMN–PT) relaxor single crystal, high temperature‐insensitive behaviors under different external stimuli were observed (remnant polarization P_r from 30°C to 180°C and piezoelectric strain d₃₃* from 30°C to 116°C). When electric field E ≥ 50 kV/cm in the case of an activation field E_a = 40‐50 kV/cm was applied, it was found that the domain switching was accompanied by a phase transition. The high relaxor nature of the R phase PIN–PZ–PMN–PT was speculated to account for the large E_a and high piezoelectric response. The short‐range correlation lengths extracted from the out‐of‐plane (OP) and in‐plane (IP) nanodomain images, were 64 nm and 89 nm, respectively, which proved the high relaxor nature due to In³⁺ and Zr⁴⁺ ions entering the B‐site in the ABO₃‐lattice and enhancing the disorder of B‐site cations in the R phase PIN–PZ–PMN–PT. The switching process of R nanodomain variants under the step‐increased tip DC voltage was visually revealed. Moreover, the time‐dependent domain evolution confirmed the high relaxor nature of the R phase PIN–PZ–PMN–PT single crystal.     

Catalytic hydrolysis of p-nitrophenyl acetate by electrospun polyacrylamidoxime nanofibers

Modification of polyacrylonitrile (PAN) by hydroxylamine resulted in polyacrylamidoxime (PANOx), the oxime groups of which are nucleophilic and capable of hydrolyzing esters. PANOx fiber mats with submicrometer fiber diameters ranging from tens to 300 nm were produced by electrospinning a suspension of PANOx blended with PAN (1:1 by weight) in a mixture of N,N-dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) (85:15 by weight). Catalytic properties of the PANOx nanofibers were tested by the hydrolysis of p-nitrophenyl acetate (PNPA), which mimics toxic organophosphate nerve agents and insecticides. The presence of PANOx fibers significantly accelerated the hydrolysis of PNPA compared to its spontaneous hydrolysis. The rate constants for the hydrolysis (k₁) and the deacetylation (k₂) reactions for the fibers were obtained using a proposed kinetic model. The effect of the fiber size on reaction rate indicated that intra-fiber diffusional resistances might limit the accessibility of the oxime catalytic sites in the fibers and affect their catalytic activity.     

Electrospinning of poly(l‐lactide‐co‐dl‐lactide) copolymers: Effect of chemical structures and spinning conditions

Nanofibers of poly(L ‐lactide‐co‐DL ‐Lactide) (PDLLA_x) copolymers with DL‐lactate (DLLA) contents of 0, 2.5, 7.5, and 50%, which exhibit strong structure/properties correlation, were fabricated by electrospinning. Effect of the copolymer structure and electrospinning conditions on morphology and properties of the fibers were examined by SEM, DSC, XRD, and tensile measurements. Bead‐free fibers of PDLLA_x prepared from a DMF/CHCl₃ mixed solvent are roughly 10‐times smaller in size (600–800 nm), with lower degree of surface porosity, compared to those of CHCl₃. When CHCl₃ is employed, an increase in size (2.4–5.5 μm) and surface porosity (0–45%) with relative humidity value is observed in crystallizable copolymers, whereas an amorphous copolymer shows a reverse trend. Thermal properties and chain arrangements of the electrospun fibers are critically affected by DLLA content of the copolymers and electrospinning conditions, as a result from interplay between intermolecular and intramolecular hydrogen bonding. Contents of crystalline domains and “physical crosslinks” generated from DL lactate segments are proposed as the origin of this phenomenon. Fiber mats of PDLLA with 50% DLLA content show a large improvement in all aspects of mechanical properties, which are suitable for various biomedical applications. POLYM. ENG. SCI., 54:472–480, 2014. © 2013 Society of Plastics Engineers     

Electrospinning of poly(γ‐benzyl–α,L‐glutamate) microfibers for piezoelectric polymer applications

One of the latest developments in the field of piezoelectric polymers is the use of poly(γ‐benzyl‐α,L‐glutamate) (PBLG), a poly(amino acid) that can be poled along its α‐helical axis and fabricated into thermally stable piezoelectric microfibers via electrospinning. This study demonstrates a method for improving the piezoelectricity of electrospun PBLG microfibers by controlling the orientation of fibers using a method based on a concentrated electric field. The piezoelectricity is verified via customized quasi‐static and dynamic measurement methods, while the correlation between fiber alignment and the piezoelectric constant, d₃₃, in the longitudinal mode of the electrospun PBLG fibers is investigated. When the level of alignment was varied from 50% to 90%, the piezoelectric constant increased linearly, showing a maximum d₃₃ of 27 pC N^?1 and a maximum force sensitivity of 65 mV N^?1 at peak alignment. A fabricated flexible prototype based on electrospun PBLG fibers provides a new solution for the use of PBLG fibers in wearable energy harvesters or composites based on piezoelectric polymer fibers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46440.     

Toughening of epoxy resin with functionalized core‐sheath structured PAN/SBS electrospun fibers

Core‐sheath structured electrospun fibers with styrene‐butadiene‐styrene (SBS) block copolymer as a rubbery core and polyacrylonitrile (PAN) as a hard sheath were prepared by coaxial electrospinning, and used to improve the toughness of epoxy resin. The surface of the fibers was aminated by reacting PAN with diethylenetriamine to improve the interfacial interaction between the fibers and epoxy. Scanning and transmission electron microscopies confirm the core‐sheath structure of the PAN/SBS fibers. The Charpy impact energy is increased by the addition of electrospun fibers. When the content of aminated core‐sheath fibers is 4 wt %, the Charpy impact energy is increased by 150%. Dynamic mechanical analysis shows that the glass transition temperature of epoxy is not decreased by the addition of core‐sheath fibers. The high impact resistance is attributed to the rubbery core of the fibers that can absorb and dissipate impact energy, and the chemical bonding between the fibers and epoxy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41119.