Electrospinning and crosslinking of zein nanofiber mats

Electrospinning processing can be applied to fabricate fibrous polymer mats composed of fibers whose diameters range from several microns down to 100 nm or less. In this article, we describe how electrospinning was used to produce zein nanofiber mats and combined with crosslinking to improve the mechanical properties of the as‐spun mats. Aqueous ethanol solutions of zein were electrospun, and nanoparticles, nanofiber mats, or ribbonlike nanofiber mats were obtained. The effects of the electrospinning solvent and zein concentration on the morphology of the as‐spun nanofiber mats were investigated by scanning electron microscopy. The results showed that the morphologies of the electrospun products exhibited a zein‐dependent concentration. Optimizing conditions for zein produced nanofibers with a diameter of about 500 nm with fewer beads or ribbonlike nanofibers with a diameter of approximately 1–6 μm. Zein nanofiber mats were crosslinked by hexamethylene diisocyanate (HDI). The tensile strength of the crosslinked electrospun zein nanofiber mats was increased significantly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:380–385, 2007     

Enhancement of heavy metal ion adsorption using electrospun polyacrylonitrile nanofibers loaded with ZnO nanoparticles

This article describes the adsorption and tensile behavior of electrospun polyacrylonitrile (PAN) nanofiber mats loaded with different amounts of ZnO [0.5, 1.0, 2.0, and 5.0 wt%] nanoparticles. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transforminfrared (FTIR) spectroscopy, and thermal gravimetric analysis (TGA) were utilized to characterize the resulting composite nanofibers. Microscopic investigations revealed that the increase in surface roughness and diameter of the electrospun PAN nanofibers was due to the addition of ZnO nanoparticles. Adsorption results indicated that the fabricated PAN/ZnO (2.0 wt%) composite nanofiber mats showed the best adsorption performance with 261% and 167% increase in adsorption capacities for Pb(II) and Cd(II) from aqueous solutions, respectively, compared to pristine PAN nanofibers. The adsorption equilibrium was reached within 60 min, and the process could be described using the nonlinear pseudo-second-order kinetic model. The adsorption isotherm study was better represented by the Langmuir model, which suggested a homogeneous distribution of the monolayer adsorptive sites on the surface of the composite nanofibers. Mechanical testing revealed that the decrease in tensile strength and elongation at breakof the PAN/ZnO composite nanofiber mats was due to the formation of some bead defects and agglomerates within the structure of the PAN nanofibers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47209.     

Crosslinked,electrospun chitosan–poly(ethylene oxide) nanofiber mats

Mechanical characterization of nanofiber mats is an underexplored area in biomaterial engineering. In this study, a chitosan–poly(ethylene oxide) copolymer blend was electrospun and crosslinked with glutaraldehyde (GA) for various time periods. The tensile and compressive mechanical integrity of the nanofibers was analyzed with increasing exposure to vapor crosslinking. Solubility, scanning electron microscopy characterization, Fourier transform infrared, uniaxial tensile tests, and nanoindentation analyses were used to identify these trends. The mechanical studies confirmed that the GA vapor crosslinking increased the stiffness and decreased the ductility of the electrospun mats. Increased exposure time to crosslinking led to changes in the mat surface color and resistance to dissolution. Scanning electron microscopy fiber counts verified that exposure to GA vapor crosslinking increased the average fiber diameter. By the use of vapor phase deposition, mechanical properties continued to change throughout the study. The crosslinking exposure time could be chosen to accommodate in vivo mechanical loading. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Improving Mechanical Properties of Carbon/Epoxy Composite by Incorporating Functionalized Electrospun Polyacrylonitrile Nanofibers

Electrospun functionalized polyacrylonitrile grafted glycidyl methacrylate (PAN‐g‐GMA) nanofibers are incorporated between the plies of a conventional carbon fiber/epoxy composite to improve the composite's mechanical performance. Glycidyl methacrylate (GMA) is successfully grafted onto polyacrylonitrile (PAN) polymer powder via a free radical mechanism. Characterization of the electrospun PAN and PAN‐g‐GMA nanofibers indicates that the grafting of GMA does not significantly alter the tensile properties of the PAN nanofibers but results in an increase in the diameter of nanofibers. Statistical analysis of the mechanical characterization studies on PAN‐carbon/epoxy hybrid composites conclusively shows that the composite reinforced with functionalized PAN nanofibers has greater mechanical properties than that of both the neat PAN nanofiber enriched hybrid composite and control composite (without nanofibers). The improved performance is attributed to the grafted glycidyl groups on PAN, leading to stronger interactions between the nanofibers and the epoxy matrix. PAN‐g‐GMA nanofiber reinforced composite outperforms their neat PAN counterparts in tensile strength, short beam shear strength, flexural strength, and Izod impact energy absorption by 8%, 9%, 6%, and 8%, respectively. Compared to the control composite, the improvements resulting from the PAN‐g‐GMA nanofiber incorporation are even more pronounced at 28%, 41%, 32%, and 21% in the corresponding tests, respectively.

     

Densifying and strengthening of electrospun polyacrylonitrile‐based nanofibers by uniaxial two‐step stretching

The effects of alignment of polyacrylonitrile (PAN) nanofibers and a two‐step drawing process on the mechanical properties of the fibers were evaluated in the current study. The alignment was achieved using a high‐speed collector in electrospinning synthesis of the nanofibers. Under optimal two‐step drawing conditions (e.g., hot‐water and hot‐air stretching), the PAN nanofiber felts exhibited large improvements in both alignment and molecular chain‐orientation. Large increase in crystallinity, crystallite size, and molecular chain orientation were observed with increasing draw ratio. Optimally, stretched PAN‐based nanofibers exhibited 5.3 times higher tensile strength and 6.7 times higher tensile modulus than those of the pristine one. In addition, bulk density of the drawn PAN nanofibers increased from 0.19 to 0.33 g/cm³. Our results show that fully extended and oriented polymer chains are critical in achieving the highest mechanical properties of the electrospun PAN nanofibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43945.     

Sea‐island polyurethane/polycarbonate composite nanofiber fabricated through electrospinning

Sea‐island polyurethane (PU)/polycarbonate (PC) composite nanofibers were obtained through electrospinning of partially miscible PU and PC in 3 : 7 (v/v) N,N‐dimethylformamide (DMF) and tetrahydrofuran (THF) mixture solvent. Their structures, mechanical, and thermal properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric (TG), and differential scanning calorimetry (DSC). The structures and morphologies of the nanofibers were influenced by composition ratio in the binary mixtures. The pure PC nanofiber was brittle and easy to break. With increasing the PU content in the PU/PC composite nanofibers, PU component not only facilitated the electrospinning of PC but improved the mechanical properties of PU/PC nanofibrous mats. In a series of nanofibrous mats with varied PU/PC composition ratios, PU/PC 70/30 showed excellent tensile strength of 9.60 Mpa and Young's modulus of 55 Mpa. After selective removal of PC component in PU/PC composite nanofibers by washing with acetone, the residual PU maintained fiber morphology. However, the residual PU nanofiber became irregular and contained elongated indents and ridges along the fiber surface. PU/PC composite fibers showed sea‐island nanofiber structure due to phase separation in the spinning solution and in the course of electrospinning. At PC content below 30%, the PC domains were small and evenly dispersed in the composite nanofibers. As PC content was over 50%, the PC phases became large elongated aggregates dispersed in the composite nanofibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Magnetic‐field‐assisted electrospinning highly aligned composite nanofibers containing well‐aligned multiwalled carbon nanotubes

Composite nanofiber meshes of well‐aligned polyacrylonitrile (PAN)/polyvinylpyrrolidone (PVP) nanofibers containing multiwalled carbon nanotubes (MWCNTs) were successfully fabricated by a magnetic‐field‐assisted electrospinning (MFAES) technology, which was confirmed to be a favorable method for preparation of aligned composite nanofibers in this article. The MFAES experiments showed that the diameters of composite nanofibers decreased first and then increased with the increase of voltage and MWCNTs content. With the increase of voltage, the degree of alignment of the composite nanofibers decreased, whereas it increased with increasing MWCNTs concentration. Transmission electron microscopy observation showed that MWCNTs were parallel and oriented along the axes of the nanofibers under the low concentration. A maximum enhancement of 178% in tensile strength was manifested by adding 2 wt % MWCNTs in well‐aligned composite nanofibers. In addition, the storage modulus of PAN/PVP/MWCNTs composite nanofibers was significantly higher than that of the PAN/PVP nanofibers. Besides, due to the highly ordered alignment structure, the composite nanofiber meshes showed large anisotropic surface resistance, that is, the surface resistance of the composite nanofiber films along the fiber axis was about 10 times smaller than that perpendicular to the axis direction. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41995.     

Cocontinuous cellulose acetate/polyurethane composite nanofiber fabricated through electrospinning

Cocontinuous cellulose acetate (CA)/polyurethane (PU) composite nanofibers were obtained through electrospinning of partially miscible CA and PU in 2:1 N,N‐dimethylacetamide (DMAc)/acetone mixture solvent. Their structures, mechanical, and thermal properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The structures and morphologies of the nanofibers were affected by component ratio in the binary mixtures. PU component not only facilitated the electrospinning of CA at CA concentration down to 12 wt%, but reinforced the tensile strength of CA/PU nanofibrous mats, while semirigid component CA in the composite nanofibers could greatly improve the rigidity and dimensional stability of CA/PU nanofibrous mats. In a series of nanofibrous mats with varied CA/PU composition ratios, CA/PU 20/80 showed excellent tensile strength and Young's modulus. The residual product after selective removal of any one of the components in CA/PU composite nanofibers by washing with proper solvent maintained the fiber structure but greatly reduced the fiber size, suggesting CA/PU composite fibers showed a cocontinuous nanofiber structure due to phase separation in the spinning solution and in the course of electrospinning. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Enhancing water swelling ability and mechanical properties of water‐swellable rubber by PAA/SBS nanofiber mats

Investigation of the potential use of nanofibers to reinforce composites has gained significance in many applications. In this article, the nanofiber mats of poly(acrylic acid) (PAA) and styrene–butadiene–styrene (SBS) triblock copolymer with composites structure were interweaved by double needle electrospinning process. The multiple nanofiber mats were added to conventional water‐swellable rubber (WSR). Improved mechanical and physical properties of WSR were obtained. Enhancement of the swellability of WSR + PAA/SBS nanofiber mats was derived from the PAA constituent absorbing water from the surface into the bulk and introducing random internal water channels between discontinuous superabsorbent polymers. The role of SBS nanofibers in the composite of WSR + PAA/SBS nanofiber mats was more related to the mechanical properties, where the breaking force of the composite increased to twice that of the conventional WSR. Interestingly, after immersion of the WSR + PAA/SBS nanofiber mats in water for 1 week, there was only a slight decrease in their mechanical properties of less than 5% compared to the dry state. The mechanisms and effects of the nanofiber mats in enhancing the mechanical and water swelling properties of WSR are also discussed. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44213.     

Conjugate electrospinning of continuous nanofiber yarn of poly(L‐lactide)/nanotricalcium phosphate nanocomposite

The continuous nanofiber yarns of poly(L ‐lactide) (PLLA)/nano‐β‐tricalcium phosphate (n‐TCP) composite are prepared from oppositely charged electrospun nanofibers by conjugate electrospinning with coupled spinnerets. The morphology and mechanical properties of PLLA/n‐TCP nanofiber yarns are characterized by scanning electron microscope, transmission electron microscope, and electronic fiber strength tester. The results show that PLLA/n‐TCP nanofibers are aligned well along the longitudinal axis of the yarn, and the concentration of PLLA plays a significant role on the diameter of the nanofibers. The thicker yarn of PLLA/n‐TCP composite with the weight ratio of 10/1 has been produced by multiple conjugate electrospinning using three pairs of spinnerets, and the yarn has tensile strength of 0.31cN/dtex. A preliminary study of cell biocompatibility suggests that PLLA/n‐TCP nanofiber yarns may be useable scaffold materials. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Electrospinning of polyacrylonitrile solutions containing diluted sodiumthiocyanate

The effect of NaSCN salt on the spinnability of polyacrylonitrile (PAN) solutions, its resulting morphology, mechanical property, and the flame resistance of the resulting electrospun nanofibers were studied. The intent was to develop a method to produce nanosized carbon fiber precursors with good properties. Electrospun PAN nanofibers from 9.7–9.9 wt% PAN/sodiumthiocyanate (NaSCN) (aq)/Dimethylformamide (DMF) solutions with 1.0–2.9 wt% NaSCN (aq), and 10–15 wt% PAN/DMF solutions without salt exhibited good spinnability and morphology with no beading in the range of applied voltage (18–20 kV) and take‐up velocity (9.8–12.3 m/s). The relatively high take‐up velocity produced good yarn alignment. The diameter distributions of the PAN nanofibers containing the NaSCN salt were narrower than those of the PAN/DMF nanofibers without the salt. It was determined that the maximum content of salt for production of electrospun PAN nanofibers with good morphology was below 3.8 wt% (40 wt% based on PAN). The salt concentration can positively influence on the narrow diameter distributions of the resulting electrospun fibers. Also, it could be confirmed that the salt effect on mechanical property and flame resistance of electrospun PAN nanofibers. In particular, the elongation of the PAN nanofiber with 2.9 wt% NaSCN (aq) was significantly increased as much as 186% compared with that of 10 wt% PAN nanofiber without the salt. The flame resistance and mechanical properties of the stabilized PAN nanofibers with NaSCN (aq) increased after oxidization process. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.     

Thermal conductivities of electrospun polyimide‐mesophase pitch nanofibers and mats

In this article, we report the preparation and thermal properties of polyimide–mesophase pitch (MP) composite nanofibers and associated nanofiber nonwoven mats produced using an electrospinning process. The addition of MP increased the thermal conductivities of both the individual composite nanofibers and the in‐plane conductivities of the nanofiber mats. The out‐of‐plane conductivity of the mats remained relatively low due to low through thickness connectivity between the nanofibers. These nanofiber mats are flexible and very thin and are good candidates for thermal management films for future flexible electronic devices. POLYM. ENG. SCI., 54:977–983, 2014. © 2013 Society of Plastics Engineers     

Preparation and antibacterial activity of PET/chitosan nanofibrous mats using an electrospinning technique

The nanofiber deposition method, by electrospinning, was employed to introduce antibacterial activity and biocompatibility to the surface of poly (ethylene terephthalate) (PET) textiles. The polymer blends of PET and chitosan were electrospun on to the PET micro‐nonwoven mats for biomedical applications. The PET/chitosan nanofibers were evenly deposited on to the surface, and the diameter of the nanofibers was in the range between 500 and 800 nm. The surface of the nanofibers was characterized using SEM, ESCA, AFM, and ATR‐FTIR. The wettability of the PET nanofibers was significantly enhanced by the incorporation of chitosan. The antibacterial activity of the samples was evaluated utilizing the colony counting method against Staphylococcus aureus and Klebsiella pneumoniae. The results indicated that the PET/chitosan nanofiber mats showed a significantly higher growth inhibition rate compared with the PET nanofiber control. In addition, the fibroblast cells adhered better to the PET/chitosan nanofibers than to the PET nanofibers mats, suggesting better tissue compatibility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

An applicable electrospinning process for fabricating a mechanically improved nanofiber mat

Engineered polymer scaffolds play an important role in tissue engineering. An ideal scaffold should have good mechanical properties and provide a biologically functional implant site. Considering their large surface area and high porosity, nanofibers have good potential as biomimetic scaffolds. However, the main shortcomings of scaffolds consisting of nanofibers are their mechanical inability to sustain a stress environment for neotissues and shape‐ability to form a variety of shapes and sizes. In this study, we produced design‐based poly (ε‐carprolactone) (PCL) nanofiber mats using an electrospinning method with various auxiliary electrodes and an x‐y moving system. To achieve stable initial solution at a nozzle tip of the electrospinning, various types of auxiliary electrodes were introduced. To characterize the effect of the electrodes in the electric‐field distribution near the nozzle tip, we calculated the electric field concentration factor and compared it with the experimental results. The nanofiber mat produced using the moving x‐y target system demonstrated orthotropic mechanical properties due to the fiber orientation, and human dermal fibroblasts seeded on the structure tended to grow according to nanofiber orientation. POLYM. ENG. SCI., 47:707–712, 2007. © 2007 Society of Plastics Engineers.     

Single‐wall carbon nanotubes dispersion behavior and its effects on the morphological and mechanical properties of the electrospun nanofibers

The dispersion behavior of single‐walled carbon nanotube (SWCNT) has important effects on morphological and mechanical properties of SWCNT composite nanofibers. The relationship of the dispersion conditions with morphological and mechanical characteristics for SWCNT / polyacrylonitrile (PAN) / polyvinylpyrrolidone (PVP) composite nanofibers have been examined. The SEM and TEM analyses of the nanofibers revealed that the deformation in the nanofiber structures increases with increasing concentration of SWCNTs. Tensile results showed that only 2 wt% SWCNT loading to the electrospun composite nanofibers gave rise to 10‐fold and 3‐fold increase in the tensile modulus and tenacity of nanofiber layers, respectively. Essentially, high mechanical properties and uniform morphology of the composite nanofibers were found at SWCNT concentration of ∼2 wt% due to their stable and individual dispersion. POLYM. COMPOS., 33:1951–1959, 2012. © 2012 Society of Plastics Engineers     

Effect of air blowing on the morphology and nanofiber properties of blowing‐assisted electrospun polycarbonates

Polycarbonate (PC) nanofibers are prepared using the air blowing‐assisted electrospinning process. The effects of air blowing pressure and PC solution concentration on the physical properties of fibers and the filtration performance of the nanofiber web are investigated. The air blowing‐assisted electrospinning process produces fewer beads and smaller nanofiber diameters compared with those obtained without air blowing. Uniform PC nanofibers with an average fiber diameter of about 0.170 μm are obtained using an applied voltage of 40 kV, an air blowing pressure of 0.3 MPa, a PC solution concentration of 16%, and a tip‐to‐collection‐screen distance (TCD) of 25 cm. The filtration efficiency improvement of the air blowing‐assisted electrospun web can be attributed to the narrow distribution of fiber diameter and small mean flow pore size of the electrospun web. Performance results show that the air blowing‐assisted electrospinning process can be applied to produce PC nanofiber mats with high‐quality filtration. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of PEI nanofiber membrane based on in situ and solution crosslinking technology and their adsorption properties

Two kinds of PEI (Polyethyleneimine) nanofibers membrane were successfully prepared by electrospinning and crosslinking technology, which were insoluble in water. One Polyethyleneimine/ Epichlorohydrin/ Polyacrylonitrile nanofibrous films (abbreviated as PEI/ EPI/ PAN NFs) was prepared by in situ crosslinking of PEI/PAN nanofiber containing of EPI, and the other PEI/ PAN/ EPI NFs was prepared by crosslinking PEI/ PAN nanofibers using EPI solution. The composition and morphology of nanofibers before and after crosslinking were investigated by infrared spectroscopy and scanning electron microscopy. PEI/EPI/PAN nanofibers exhibited excellent adsorption properties toward heavy metal ions and methyl orange dyes, which can also be reused multiple times. The adsorption rate of methyl orange remained around 75% after 4 cycles, meanwhile, the adsorption rate of copper and lead still remained around 90% after 5 cycles. In addition, we found that PEI/ PAN/ EPI nanofibers prepared by solution crosslinking technology solved the problem of easy gel formation in in situ crosslinking technology and facilitated the continuous production of PEI/ EPI/ PAN nanofibers, which is better than in situ crosslinking technology. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48279.     

Highly Aligned Centrifugal Spun Polyacrylonitrile Nanofibers Collected and Processed with Automated Tracks

A parallel automated track collector is integrated with a rationally designed centrifugal spinning head to collect aligned polyacrylonitrile (PAN) nanofibers. Centrifugal spinning is an extremely promising nanofiber fabrication technology due to high production rates. However, continuous oriented fiber collection and processing presents challenges. Engineering solutions to these two challenges are explored in this study. A 3D-printed head design, optimized through a computational fluid dynamics simulation approach, is utilized to limit unwanted air currents that disturb deposited nanofibers. An automated track collecting device has pulled deposited nanofibers away from the collecting area. This results in a continuous supply of individual aligned nanofibers as opposed to the densely packed nanofiber mesh ring that is deposited on conventional static post collectors. The automated track collector allows for simple integration of the postdraw processing step that is critical to polymer fiber manufacturing for enhancing macromolecular orientation and mechanical properties. Postdrawing has enhanced the mechanical properties of centrifugal spun PAN nanofibers, which have different crystalline properties compared with conventional PAN microfiber. These technological developments address key limitations of centrifugal spinning that can facilitate high production rate commercial fabrication of highly aligned, high-performance polymer nanofibers.     

Investigation on jet stability,fiber diameter,and tensile properties of electrospun polyacrylonitrile nanofibrous yarns

Electrospinning is a flexible and efficient method for producing nanofibers by using relatively dilute polymer solution. However, there are many parameters related to material and processing that influence the morphology and property of the nanofibers. This study investigates the influence of electric field and flow rate on diameter and tensile properties of nanofibers produced using polyacrylonitrile (PAN)‐dimethylformamide (DMF) solution. Stability of the spinning jet is investigated via fiber current measurement and an image system at different electric fields and solution flow rates. It is observed that a set of electric field and flow rate conditions favor producing thinnest, strongest, and toughest nanofibers during electrospinning process. Other conditions may lead to instability of the Taylor cone, discontinuous jet, larger diameter fiber, and lower mechanical properties. Finally, a simple dynamic whipping model is adopted to correlate the nanofiber diameter with volumetric charge density and is found to be excellent validating our experimental results. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41918.     

Investigation of nanoyarn preparation by modified electrospinning setup

Higher ordered structures of nanofibers, including nanofiber‐based yarns and cables, have a variety of potential applications, including wearable health monitoring systems, artificial tendons, and medical sutures. In this study, twisted assemblies of polyacrylonitrile (PAN), polyvinylidene fluoride trifluoroethylene (PVDF‐TrFe), and polycaprolactone (PCL) nanofibers were fabricated via a modified electrospinning setup, consisting of a rotating cone‐shaped copper collector, two syringe pumps, and two high voltage power supplies. The fiber diameters and twist angles varied as a function of the rotary speed of the collector. Mechanical testing of the yarns revealed that PVDF‐TrFe and PCL yarns have a higher strain‐to‐failure than PAN yarns, reaching 307% for PCL nanoyarns. For the first time, the porosity of nanofiber yarns was studied as a function of twist angle, showing that PAN nanoyarns are more porous than PCL yarns. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44813.