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     

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     

Orientation of poly(vinyl alcohol) nanofiber and crystallites in non-woven electrospun nanofiber mats under uniaxial stretching

The development of macroscopic nanofiber orientation and microscopic crystallite and molecular chain orientation have been investigated during uniaxial stretching of electrospun poly(vinyl alcohol) (PVA) non-woven nanofiber mats. Scanning electron microscopy and stress-strain/small-angle X-ray scattering show that the macroscopic nanofiber orientation significantly increases during the initial stage of deformation, and approaches a plateau on the way of stretching. Detailed analyses of the stress-strain/wide-angle X-ray diffraction measurement and polarized Fourier transform infrared spectroscopy indicate that the microscopic crystallite and molecular chain orientation rapidly increase at the initial stage of stretching due to macroscopic nanofiber orientation. At higher deformation, the microscopic modes of orientation continuously develop as a result of the nanofiber stretching. The complicated deformation process of non-woven nanofiber mats is discussed in terms of macroscopic nanofiber orientation and the microscopic crystallite and molecular chain orientation.     

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     

Distance transform algorithm for measuring nanofiber diameter

This paper describes a new distance transform method used for measuring fiber diameter in electrospun nanofiber webs. In this algorithm, the effect of intersection is eliminated, which brings more accuracy to the measurement. The method is tested by a series of simulated images with known characteristics as well as some real webs obtained from electrospinning of PVA. Our method is compared with the distance transform method. The results obtained by our method were significantly better than the distance transform, indicating that the new method could successfully be used to measure electrospun fiber diameter.     

Prediction of nanofiber diameter for improvements in incorporation of multilayer electrospun nanofibers

The fabrication of novel multilayer electrospun nanofiber web is demonstrated. Under optimized processing conditions, the interface between these webs can be sustained for long time, yielding layers with distinct compartments. Simultaneous control over internal fiber architecture makes these multilayer nano-webs potential candidates for applications such as clothing and industrial filters.     

基于纤维取向的纳米纤维滤料设计及其性能

通过基于霍夫变换的图像分析法获取静电纺纳米纤维取向分布信息,分析纤维取向对纳米纤维滤料性能的影响,并据此设计制备了中间为杂乱纤维层、两侧为相互垂直的取向纤维层构成的复合纳米纤维膜滤料。采用扫描电镜对纳米纤维膜形貌进行观察并获取SEM图像,进行了透气性、拉伸性能、孔径尺寸和过滤性能测试。结果表明,纳米纤维膜纤维分布方向拉伸断裂强度高,纤维取向各向异性比例理论值和实验值相吻合,纤维取向是影响纳米纤维膜力学各向异性的主要参数;取向纳米纤维膜滤料孔径较大且有许多微粒可逃逸的通道,其过滤效率和过滤阻力均较低,与文献中报道的数值模拟结果相一致;所设计制备的复合纳米纤维膜滤料结合了取向纳米纤维膜滤料力学性能优良和杂乱纳米纤维膜滤料过滤效率高的优点,其纵向和横向断裂强度分别为8.85MPa和8.71MPa,气流流速为25L/min时过滤效率高达99.691%。     

A comparative experimental study of the hygroscopic and mechanical behaviors of electrospun nanofiber membranes and solution-cast films of polybenzimidazole

This article reports a comparative experimental study of the hygroscopic and mechanical behaviors of electrospun polybenzimidazole (PBI) nanofiber membranes and solution-cast PBI films. As-electrospun nonwoven PBI nanofiber mats (with the nanofiber diameter of ~250 nm) were heat-pressed under controlled temperature, pressure and duration for the study; lab-made solution-cast PBI films and commercially available PBI films (the PBI Performance Product Inc., Charlotte, NC) were used as the control samples. Thermogravimetric and microtensile tests were utilized to characterize the hygroscopic (moisture absorption) and mechanical properties of the PBI nanofiber membranes at varying heat-pressing conditions, which were further compared to those of solution-cast PBI films. Experimental results indicated that the PBI nanofiber membranes carried slightly higher thermal stability and less hygroscopic properties than those of solution-cast PBI films. In addition, heat-pressing conditions significantly influenced the mechanical properties of the resulting PBI nanofiber membranes. The stiffness and tensile strength increase with increasing either the heat-pressing pressure or duration, and relevant mechanisms were explored. The present study provides a rational understanding of the hygroscopic and mechanical behaviors of electrospun PBI nanofiber membranes and solution-cast PBI films that are beneficial to their reliable cutting-edge applications in high-temperature filtration, polymer electrolyte membranes (PEMs), etc.     

Charge storage of electrospun fiber mats of poly(phenylene ether)/polystyrene blends

Nonwoven fiber mats composed of poly(phenylene ether) (PPE) and polystyrene (PS) blends were prepared by electrospinning of PPE/PS solutions in a mixture of chloroform and hexafluoroisopropanol. The blends showed higher electrospinnability and led to thinner fibers (200 nm–1.3 μm) than the pure components, because of a proper balance of electrical conductivity and interaction with the electrospinning solvent. The charge retention of the electrospun fibers was evaluated and related to the blend composition and the electret properties of the components. It was found that the nonwoven mats were able to retain up to 60% of the initial surface potential after several days of annealing at temperatures as high as 140°C, which is markedly higher than the charge retention of corona‐charged compact films. The capability of the electrospinning technique, to inject charges into the bulk of the material and to orientate the dipoles of the PPE phase in the field direction at the same time, was related to the good surface potential stability of the PPE/PS electrospun fiber mats. The possibility of creating thin PPE/PS fibers with excellent charge retention capabilities makes these materials ideal candidates for electret filter and sensing applications. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Spider-net within the N6, PVA and PU electrospun nanofiber mats using salt addition: Novel strategy in the electrospinning process

Electrospun nanofibers are promising candidates in the nanotechnological applications due to the advantages of the nanofibrous morphology. Therefore, many attempts were reported to modify the electrospun mats to gain more beneficial properties. In the present study, we are introducing a strategy to synthesize electrospun polymeric nanofiber mats containing spider-net binding the main nanofibers. Addition with long stirring time of a metallic salt having tendency to ionize rather than formation of sol–gel in the host polymer solution reveals to synthesize a spider-net within the electrospun nanofibers of the utilized polymer. Nylon6, polyurethane and poly(vinyl alcohol) have been utilized; NaCl, KBr, CaCl₂ and H₂PtCl₆ have been added to the polymeric solutions. In the case of nylon6 and poly(vinyl alcohol), addition of the inorganic salts resulted in the formation of multi-layers spider-network within the electrospun nanofibers mats. The synthesized spider-nets were almost independent on the nature of the salt; the optimum salt concentration was 1.5 wt%. The metallic acid led to form trivial spider-nets within both of nylon6 and poly(vinyl alcohol) nanofibers. In a case of polyurethane, few spider-nets were formed after salt addition due to the low polarity of the utilized solvents. According to TEM analysis, the synthesized spider-net consisted of joints; the later issued from the main nanofibers at Taylor's cone zone. The spider-net improved the mechanical properties and the wetability of the nylon6 nanofiber mats, accordingly a mat having amphiphilic feature has been prepared.     

Filter life comparison of different levels of nanofiber coated cleanable-surface filter for gas turbine

High-efficiency air filtration is a basic requirement for the most cost-effective operation of high-efficiency gas turbines. The filtration system protects the gas turbine from damaging debris. In gas turbine/dust collector applications, higher efficiency filtration could be achieved with nanofibers, which provide higher equipment protection than traditional media. With a nanofiber performance filter layer, the dust accumulates on the surface of the filtration media rather than within the media and could be cleaned off easily with a back pulse resulting in long filter life and a low-operating pressure drop. In this study five type of gas tribune nanofiber coated corrugated cellulose/synthetic filter media were developed. Nanofiber coating was adjusted for five filtration efficiency level, 50 ≤ E < 60, 60 ≤ E < 70, 70 ≤ E < 85, 85 ≤ E < 95 and 95 ≤ E, pore size and filter-life of the developed media were evaluated. One of the developed nanofiber coated media was also compared with two other commercial nanofiber coated gas tribune filter media, a glass fiber type filter media and a commercial fine fiber gas tribune filter media. It was seen that, with decreasing penetration levels due to nanofiber coating level, initial 30 cycle durations of filter life evaluation could reach about 229.9 to 250.7 min. Highest final cycle duration of 188.7 min belonged to cellulose/synthetic blend corrugated filter media with penetration of 13.66%. Nanofiber based surface filter media was cleaned up better than fine fiber media and final 30 cycle sequences were significantly higher. Surface of the nanofiber coated media was smoother when compared to fine fiber media and during the initial and final cycle test dust could not penetrate inside and could not hang to this smooth surface. So, with back pulse cleaning cake releasing have performed easily. It was also seen that, for higher filter life nanofiber coating should be uniform and robust to back pulse cleaning.     

PHBV／Ecoflex共混体系电纺成形及其热性能研究

采用静电纺丝技术制备了聚（3-羟基丁酸酯-co-3-羟基戊酸酯）（PHBV）／Econ“共混体系的超细纤维毡。通过扫描电镜（SEM）照片，分析了Ecoflex的加入对电纺纤维的平均直径和直径分布的影响。通过比较各体系的最低纺丝溶液浓度，发现PHBV在共混体系PHBV／Ecoflex中的含量越高，溶液的可纺性越好。对比研究了PHBV和PHBV／Ecoflex的溶液浇铸膜和电纺纤维毡的热性能，结果发现，出现在溶液浇铸膜DSC图谱中低温处的小熔融峰，在电纺纤维的DSC图谱中消失。     

Structure and process relationship of electrospun bioabsorbable nanofiber membranes

An electrospinning method was used to fabricate bioabsorbable amorphous poly(d,l-lactic acid) (PDLA) and semi-crystalline poly(l-lactic acid) (PLLA) nanofiber non-woven membranes for biomedical applications. The structure and morphology of electrospun membranes were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and synchrotron wide-angle X-ray diffraction/small angle X-ray scattering. SEM images showed that the fiber diameter and the nanostructured morphology depended on processing parameters such as solution viscosity (e.g. concentration and polymer molecular weight), applied electric field strength, solution feeding rate and ionic salt addition. The combination of different materials and processing parameters could be used to fabricate bead-free nanofiber non-woven membranes. Concentration and salt addition were found to have relatively larger effects on the fiber diameter than the other parameters. DSC and X-ray results indicated that the electrospun PLLA nanofibers were completely non-crystalline but had highly oriented chains and a lower glass transition temperature than the cast film.     

Poly(butylene terephthalate) electrospun/melt‐blown composite mats for white blood cell filtration

In this research, poly(butylene terephthalate) (PBT) electrospun nanofibrous mats were prepared for white blood cell (WBC) filtration after the blood was collected from donors. The feasibility of using PBT electrospun mats used as WBC filtration materials was studied. The average fiber diameter and mean pore diameter of the PBT electrospun mats were much lower than those of melt‐blown mats, and such properties were found to be beneficial for the functions of filtration and cell absorbency. A layer of PBT electrospun mats was added before the exit of filter; this formed a kind of compound material with different pore diameters and fibers diameters in the direction of blood flow. The WBC filtration efficiency of the newly designed filter and a traditional filter were also compared. The results show that filters with electrospun PBT fibers reduced the number of WBCs to 10⁴/L, whereas the remaining WBCs after flow through the traditional filter was about 10⁵L^?1. The existence of electrospun fibers increased the filtration resistance at the same time, and this led to a longer filtration time. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electrospinning fabrication and characterization of poly(vinyl alcohol)/waterborne polyurethane nanofiber membranes in aqueous solution

Poly(vinyl alcohol) (PVA)/waterborne polyurethane (WBPU) nanofiber mats were prepared using electrospinning method with aqueous solutions. Scanning electron microscopy (SEM), X‐ray diffraction (XRD), thermal gravimetric analyzer (TGA), and tensile strength testing machine (ZWICK) were used to characterize the morphology and properties of the PVA/WBPU nanofiber mats. The results showed that the morphologies of PVA/WBPU nanofiber mats changed with the total solid concentration and the mass ratio of PVA/WBPU in the spinning solution. The tensile strength and thermal stability of the fibers could be significantly affected by the WBPU contents. The electrospun PVA/WBPU membranes showed higher water uptake, which would have potential applications in wound dressings. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Atmospheric plasma application to improve adhesion of electrospun nanofibers onto protective fabric

Nylon 6 electrospun nanofibers were deposited on plasma-pretreated woven fabric substrates with the objective of improving adhesion between them. The prepared samples were evaluated for adhesion strength and durability of nanofiber mats by carrying out peel strength, flex resistance, and abrasion resistance tests. The test results showed significant improvement in the adhesion of nanofiber mats on woven fabric substrates due to atmospheric plasma pretreatment. The samples also exhibited good flex and abrasion resistance characteristics. X-ray photoelectron spectroscopy and water contact angle analyses indicate that plasma pretreatment introduces radicals, increases the oxygen content on the substrate surface, and leads to formation of active chemical sites that may be responsible for enhanced cross-linking between the substrate fabric and the electrospun nanofibers, which in turn increases the adhesion properties. The work demonstrates that the plasma treatment of the substrate fabric prior to deposition of electrospun nanofiber mats is a promising method to prepare durable functional materials.     

On the electrospinning of PVDF: influence of the experimental conditions on the nanofiber properties

The characteristics of poly(vinylidene fluoride) (PVDF) nanofibers, prepared by applying the electrospinning technique from N,N‐dimethylformamide/acetone mixtures, were studied by varying the experimental conditions. The nanofiber morphology was assessed by scanning electron microscopy, while wide angle X‐ray diffraction and infrared spectroscopy were performed to study the crystallinity. The influence of the electrospinning conditions, such as kind of solvent mixture, polymer concentration, voltage tension, airflow and humidity, on nanofiber morphology was studied. In particular, the latter parameter, generally not considered, was found to modify the electrospun mat structure in a relevant way. Generally, the above technique turns out to be capable of strongly affecting the polymorphism of the polymer, namely β phase formation was higher in the electrospun mats compared with cast films, which displayed a non‐polar α crystal phase. As far as the influence of the electrospinning conditions on PVDF crystal structure is concerned, modification of the experimental parameters did not affect the α/β ratio. Nevertheless, comparing the behavior of two commercial PVDF samples with similar molecular masses, our results show that the polymer which forms a higher content of β phase in its cast films allowed electrospun mats characterized by almost complete formation of β phase to be obtained. Copyright © 2012 Society of Chemical Industry     

静电纺丝法纺制聚乳酸纳米纤维无纺毡

采用静电纺丝法制备了生物降解聚乳酸(PLLA)纳米纤维无纺毡。分析了纺丝液浓度、电压、接收距离、挤出速度等因素对纤维形态的影响。结果表明:纺丝液的浓度和挤出速度对纤维直径的影响较为明显,溶液挤出速度增大,所得纤维微孔含量及尺寸也增大;适当的电压和接收距离有利于收集无液滴纤维;随着纤维直径的减小,无纺毡的孔径呈减小趋势。在PLLA质量分数为5．7％、挤出速度0．8 mL／h、接受距离 15．5 cm、电压8 kV的静电纺丝条件下,可制备纤维直径为200-400 nm的PLLA纳米纤维无纺毡。     

Fabrication of nanofibers by a modified air-jet electrospinning method

A modified air-jet electrospinning (MAE) setup was demonstrated for contributing to the large-scale nanofibers production. With this single nozzle air-jet electrospinning device, the productivity of nanofibers can be increased more than forty times as compared with using the single-needle electrospinning (SNE) setup. When compared with other needle-less electrospinning setups, the benefits of this setup include ability to keep stable concentration of electrospun solution and to produce more uniform and thinner fibers, controlling of the jets formed speed and position, higher throughput, lower critical voltage, easier assembling, simpler operation, and so on. Four different parts of the fiber generator were, respectively, charged as electrospun electrodes to produce fibers. The distributions of the electric field with different electrodes were simulated and investigated for explaining the experimental results including the fibers productivity, the deposition area of nanofiber mats, as well as the surface morphology of the fibers. When the whole nozzle was charged, as compared with charging other electrodes, the MAE system produced thinner fibers with larger standard deviation on a much larger scale. By reduction of charged area, the received fibers presented lower productivity and thicker diameter with lower standard deviation. Especially, when a half of the nozzle was charged, the deposition area of nanofiber mats was larger than charging other electrodes. Besides, when a half of the nozzle was charged, the influences of electrospinning parameters such as applied voltage, collecting distance and the flow rate of air on nanofibers morphology were also investigated. Furthermore, based on this spinning unit, multi-nozzle air-jet electrospinning setup can be designed for larger production of nanofibers.     

Toughened electrospun nanofibers from crosslinked elastomer‐thermoplastic blends

A crosslink‐able elastomeric polyester urethane (PEU) was blended with a thermoplastic, polyacrylonitrile (PAN), and electrospun into nanofibers. The effects of the PEU/PAN ratio and the crosslinking reaction on the morphology and the tensile properties of the as‐spun fiber mats were investigated. With the same overall polymer concentration (9 wt %), the nanofiber containing higher composition of PEU shows a slight decrease in the average fiber diameter, but the tensile strength, the elongation at break and tensile modulus of the nanofiber mats are all improved. These tensile properties are further enhanced by slight crosslinking of the PEU component within the nanofibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007