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

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

Influence of electrospinning parameters on poly(hydroxybutyrate) electrospun membranes fiber size and distribution

Poly(hydroxybutyrate) (PHB) obtained from sugar cane waste was dissolved in a blend of chloroform and dimethylformamide (DMF) and electrospun at 40°C. By adding DMF to the solution, the electrospinning process for the PHB polymer becomes more stable, allowing complete polymer crystallization during the jet travelling between the tip and the grounded collector. The influence of processing parameters on fiber size and distribution was systematically studied. It was observed that an increase of tip inner diameter promotes a decrease of the fiber average size and a broader distribution. Conversely, an increase of the electric field and flow rate produces an increase of fiber diameter until a maximum of ～2.0 µm but for electric fields higher than 1.5 kV cm^?1, a decrease of the fiber diameter was observed. Polymer crystalline phase seems to be independent of the processing conditions and a crystallinity degree of 53% was found. Moreover, thermal degradation of the as‐spun membrane occurs in single step degradation with activation energy of 91 kJ mol^?1. Furthermore, MC‐3T3‐E1 cell adhesion was not inhibited by the fiber mats preparation, indicating their potential use for biomedical applications. POLYM. ENG. SCI., 54:1608–1617, 2014. © 2013 Society of Plastics Engineers     

Crystallinity study of electrospun poly (vinyl alcohol) nanofibers: effect of electrospinning,filler incorporation,and heat treatment

This study aims to explore crystallinity variations of polyvinyl alcohol (PVA) as a result of electrospinning, filler addition, and heat treatment. Pure PVA and PVA nanocomposite fibers containing only nanohydroxy apatite (nHAp) and together with cellulose nanofibers (CNF) were electrospun. Electrospun nanofibers were heat treated at 180 °C for 8 h. The morphology of electrospun fibers was evaluated by scanning electron microscopy (SEM) while Fourier transform infrared spectroscopy, differential scanning calorimetry, and wide angle X-ray scattering were used to analyze nanofibers crystallinity. Un-treated electrospun nanofibers were shrank and lost their porous structure in water, while heat treatment of nanofibers caused stabilization of fibrous mats in boiling water. It was concluded that the crystallinity of electrospun PVA were considerably reduced compared to PVA powder due to formation of metastable—small and/or defective crystals. Adding small content (1 wt%) of nHAp led to increase in electrospun nanofibers crystallinity. However, incorporation of higher content of nHAp and CNF caused reduction of crystallinity most probably due to possible interactions among components which interrupt the orientation of macromolecules. All analyzing methods proved the crystallinity enhancement of nanofibers upon heat treatment which can be attributed mostly to water evaporation from electrospun fibers structure.     

优化操作参数提高窑产量及余热发电量

我公司5000t／d生产线,采用双系列五级预热器带NST-1型分解炉。2006年6月份投产,随着生产技术的提高,生产日趋稳定,熟料产量在5600～5700t／d左右,熟料28d抗压强度为57．6MPa。由于设计时篦冷机冷却风机按5000t／d生产能力配置,随着窑产量大幅度提高,篦冷机冷却效果越来越差,还影响到了余热发电量。     

Improved graphitization and electrical conductivity of suspended carbon nanofibers derived from carbon nanotube/polyacrylonitrile composites by directed electrospinning

Single suspended carbon nanofibers on carbon micro-structures were fabricated by directed electrospinning and subsequent pyrolysis at 900 °C of carbon nanotube/polyacrylonitrile (CNT/PAN) composite material. The electrical conductivity of the nanofibers was measured at different weight fractions of CNTs. It was found that the conductivity increased almost two orders of magnitude upon adding 0.5 wt.% CNTs. The correlation between the extent of graphitization and electrical properties of the composite nanofiber was examined by various structural characterization techniques, and the presence of graphitic regions in pyrolyzed CNT/PAN nanofibers was observed that were not present in pure PAN-derived carbon. The influence of fabrication technique on the ordering of carbon sheets in electrospun nanofibers was examined and a templating effect by CNTs that leads to enhanced graphitization is suggested.     

Effect of phenyl-isocyanate functionalized graphene oxide on the crystalline phases,mechanical and piezoelectric properties of electrospun PVDF nanofibers

Owing to their good flexibility, biocompatibility, and capability to convert mechanical energy to electrical energy, electrospun poly(vinylidene fluoride) nanofibers (PVDFNFs) have attracted considerable attention for energy harvesting as well as wearable and self-powered electronics. However, inadequate mechanical strength and low piezoelectric output are major concerns for their practical application. Herein, we report an effective method for fabricating mechanically robust PVDFNFs with enhanced piezoresponse by incorporating phenyl-isocyanate functionalized graphene oxide (IGO) as an efficient nanofiller. The presence of IGO endowed PVDFNFs with a rough surface morphology, enhanced crystallinity, and electroactive β phase. Excitingly, enhancements of 303% and 332% in the ultimate tensile strength and modulus, respectively, were achieved for the IGO-incorporated PVDFNFs. Furthermore, the acoustic sensitivity of the composites was 63.09% higher than that of the pristine PVDFNFs. The composites had a minimum sensing force of 0.012 N, which was 20% less than the minimum sensing force of the pristine PVDFNFs. The incorporation of IGO enhanced the power generation capability of the composites by 55.23% compared with that of the pristine PVDFNFs. Thus, the as-prepared composites hold great promise for the fabrication of mechanically robust, high-performance piezoelectric composites for mechanical energy conversion applications.     

Influence of molecular weight and rheological behavior on electrospinning cellulose nanofibers from ionic liquids

Dissolving pulp was depolymerized with 2.5M HCl into cellulose fractions with decreasing molecular weight relative to acid treatment time. The cellulose fractions were dissolved at various concentrations in the ionic liquid 1‐ethyl‐3‐methylimidazolium acetate (EmimAc) with co‐solvent DMSO at ratio 1 : 1 (w/w) and electrospun. Size exclusion chromatography was used to evaluate the molecular weight distributions and the rheological properties were characterized with a cone‐and‐plate rheometer. Scanning electron microscope was used to evaluate the fiber morphology, and thereby spinnability. Zero shear viscosity as a function of cellulose concentration show that all the solutions in this study are in the entangled semi‐dilute regime; where the polymer concentration is large enough for significant overlap necessary for chain entanglement. However, within the intervals studied, neither cellulose concentration nor molecular weight seems to be decisive for if a solution can be electrospun into fibers or not. It is rather the viscosity of the solution that is decisive for electrospinnability, even though the solution is in the entangled semi‐dilute regime. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2303–2310, 2013     

Development of carbon nanofibers from aligned electrospun polyacrylonitrile nanofiber bundles and characterization of their microstructural, electrical, and mechanical properties

Carbon nanofibers with diameters of 200-300 nm were developed through stabilization and carbonization of aligned electrospun polyacrylonitrile (PAN) nanofiber bundles. Prior to the oxidative stabilization in air, the electrospun PAN nanofiber bundle was tightly wrapped onto a glass rod, so that tension existed during the stabilization. We also investigated several carbonization procedures by varying final carbonization temperatures in the range from 1000 to 2200 °C. The study revealed that: (1) with increase of the final carbonization temperature, the carbon nanofibers became more graphitic and structurally ordered; (2) the carbon nanofiber bundles possessed anisotropic electrical conductivities, and the differences between the parallel and perpendicular directions to the bundle axes were over 20 times; and (3) the tensile strengths and Young's moduli of the prepared carbon nanofiber bundles were in the ranges of 300-600 MPa and 40-60 GPa, respectively.     

Morphology enhancement of TiO2/PVP composite nanofibers based on solution viscosity and processing parameters of electrospinning method

In this work, different sol solutions with various titanium tetraisopropoxide (TIP)/glacial acetic acid ratios in 2‐propanol with 5 wt % poly(vinyl pyrrolidone) (PVP) (M_w = 360,000 g/mol) were prepared and electrospun. Composition of the prepared sols and as‐spun TiO₂/PVP nanofibers were determined by Fourier transform infrared and Raman spectroscopy methods. Morphology of the electrospun TiO₂/PVP nanofibers was studied by scanning electron microscopy and transmission electron microscopy (TEM) techniques. Rheometry measurements of the sol solutions showed decrease of viscosity upon the addition of TIP to the polymer solutions with constant polymer and acid concentrations. The sol solution having the lowest viscosity (at shear rate 10 s^?1) but the highest TIP/glacial acetic acid ratio showed beaded nanofibers morphology when electrospun under 10 and 12 kV applied voltage while injection rate, needle tip to collector distance, and needle gauge were kept constant. However, smooth electrospun TiO₂/PVP composite nanofibers with the average nanofibers diameters (148 ± 79 nm) were achieved under the same condition when applied voltage increased to 15 kV. TEM micrographs of the electrospun TiO₂/PVP nanofiber showed that the TiO₂ particles with continuous structure are formed at the middle of the nanofiber and distributed along its axis. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46337.     

Investigating the effect of PGA on physical and mechanical properties of electrospun PCL/PGA blend nanofibers

In the field of tissue engineering there is always a need for new engineered polymeric biomaterials which have ideal properties and functional customization. Unfortunately the demands for many biomedical applications need a set of properties that no polymers can fulfill. One method to satisfy these demands and providing desirable new biomaterials is by mixing two or more polymers. In this work, random nanofibrous blends of poly (ε‐caprolactone) (PCL) and polyglycolic acid (PGA) with various PCL/PGA compositions (100/0, 80/20, 65/35, 50/50, and 0/100) were fabricated by electrospinning method and characterized for soft‐tissue engineering applications. Physical, chemical, thermal, and mechanical properties of PCL/PGA blend nanofibers were measured by scanning electron microscopy (SEM), porosimetry, contact angle measurement, water uptake, attenuated total reflectance Fourier transform‐infrared spectroscopy (ATR‐FT‐IR), X‐ray diffraction (XRD), differential scanning calorimetric (DSC), dynamic mechanical thermal analysis (DMTA), and tensile measurements. Morphological characterization showed that the addition of PGA to PCL results in an increase in the average diameter of the nanofibers. According to these results, when the amount of PGA in the blend solution increased, the hydrophilicity and water uptake of the nanofibrous scaffolds increased concurrently, approaching those of PGA nanofibers. Differential scanning calorimetric studies showed that the PCL and PGA were miscible in the nanofibrous structure and the mechanical characterization under dry conditions showed that increasing PGA content results in a tremendous increase in the mechanical properties. In conclusion, the random nanofibrous PCL/PGA scaffold used in this study constitutes a promising material for soft‐tissue engineering. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrospinning of PLA and PLA/POSS nanofibers: Use of Taguchi optimization for process parameters

It is known that electrospinning is the most practical technique to obtain unique nanofibrous structures, such as neat PLA (polylactide) and PLA filled with POSS (Polyhedral Oligomeric Silsesquioxane) particles. On the other hand, due to the so many different process parameters to consider, production of these fibers are extremely difficult and time consuming. That is, use of a certain statistical optimization technique in the design of experiments would be necessary. Therefore, the main purpose of this study was to determine the optimum electrospinning parameters by applying the Taguchi technique first to neat PLA and then to reveal the applicability of these parameters for the electrospinning of PLA/POSS nanofibers. It was observed that instead of conducting 81 experiments to determine the most significant four optimum process parameters for PLA, use of Taguchi L₉ orthogonal array experiment matrix, that is, conducting only nine experiments, reduced time, labor and material consumption considerably. For the smallest electrospun PLA fiber diameter, the optimum parameters determined were; “PLA solution concentration” of 8% w/v, “solution feeding rate” of 1.8 mL/h, “needle-to-collector distance” of 18 cm, and “applied voltage” of 15 kV. Moreover, it was generally concluded that these same parameters could be also used for the electrospinning of PLA/POSS nanofibers after addition of only 3 wt% KCl salt into the polymer solution.     

Investigation of β phase formation in piezoelectric response of electrospun polyvinylidene fluoride nanofibers: LiCl additive and increasing fibers tension

As a piezoelectric polymer, poly (vinylidene fluoride) (PVDF) is attractive in energy conversion applications between electrical and mechanical forms because of its low cost, high flexibility, and biocompatibility. The piezoelectricity of electrospun PVDF polymer is due to changes in the crystalline structure (e.g., creating the β‐phase) during the electrospinning process. This research focuses on two approaches for investigation of β Phase formation: (1) addition of LiCl in different concentrations (0.001, 0.00133, 0.002, 0.004 wt%) as inorganic salt to the polymer solution, (2) increasing tension along the fiber axis by increasing the collector drum speed during the aligning process. Performances of these structures were evaluated by using X‐ray diffraction (XRD), Fourier Transform Infrared (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). A one‐step nano‐generator and cost‐effective package based on electrospun nanofibers was presented to measure output voltages as a performance factor. Results show that the addition of LiCl leads to β Phase formation in the crystalline structure, decreasing fiber diameter to 65 nm, and increment in the work of rupture and piezoelectric output. Moreover, the results show that increasing collector drum speed causes the alignment of β‐crystallites along the fiber axis and subsequently no considerable effect on the formation of β‐phases and output voltage. POLYM. ENG. SCI., 56:61–70, 2016. © 2015 Society of Plastics Engineers     

Studies on the electrospun Nylon 6 nanofibers from polyelectrolyte solutions: 1. Effects of solution concentration and temperature

Polyelectrolyte solutions of Nylon 6 in 99 vol% formic acid were electrospun, and the effect of polymer concentration was studied. Using a laser device to locally heat the needle spinneret, the solution temperature was feasibly elevated up to 66 °C, and its effect on electrospinning was investigated as well. The microstructure of the as-spun products was characterized by several analytical techniques, including electron diffraction, differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. Based on the solution rheology, the entanglement concentration (c_e) was determined to be 1 wt%. To prepare bead-free fibers, the minimum polymer concentration was 8 c_e, which was much higher than that (1.75-2.0 c_e) required for conventional neutral solutions. Increasing the polymer concentration and/or solution temperature led to a gradual change of electrospun products from round fibers with major γ form crystals to ribbon-like fibers in possession of exclusive α form ones. For intermediate concentrations, nanowebs made of nanofibrils with diameters of 20-40 nm were seen. Thin ribbon-like fibers (ca. 40 nm thick) with nanowebs became the dominant products obtained from the 15 wt% solutions at high temperatures. The dramatic variations in morphological features and crystal modification could be thoroughly explained on the basis of the interplay between solvent evaporation at the jet surface and solvent diffusion in the liquid jet. DSC heating traces on the ribbon-like fibers exhibited an unusually high melting temperature of ∼235 °C, which is higher than the equilibrium melting temperature of Nylon 6 crystals of 232 °C.     

Effect of electrospinning on the ionic conductivity of polyacrylonitrile/polymethyl methacrylate nanofibrous membranes: optimization based on the response surface method

A novel fibrous polymer electrolyte membrane was produced based on polymethyl methacrylate/polyacrylonitrile (PMMA/PAN) blend. This was achieved through optimization in the loadings of the two polymers and electrospinning method. Consequently, the effect of PMMA on the ionic conductivity was assessed. A quantitative relationship between ionic conductivity and the important parameters including voltage, solution concentration, and PMMA content was determined. The response surface method (RSM) was employed to obtain the quantitative relationship and to determine the ion conductivity of PAN/PMMA electrospun membrane. Analysis of variance technique was used to study the importance of parameters and their interactions. A regression model was applied to determine the most influential factors on the ionic conductivity and to find the maximum ionic conductivity of the electrolyte membrane as an optimal result. The average fiber diameter was in the range of 206–367 nm, and the membranes were associated with high porosities between 50 and 91 %, and the electrolyte uptakes were in the range of 285–460 %. For all samples, the ionic conductivity of gel polymer electrolytes at 25 °C was above the 1 mS/cm. The ionic conductivity changed with the voltage directly and with the solution concentration inversely. According to the results, the ionic conductivity showed its dependency with the PMMA content, increasing with the PMMA content up to 50 % and smoothly decreasing with PMMA further increases. Some important interactions between the parameters were also detected.     

Design and optimization of carbon-free power generation based on coal hydrogasification integrated with SOFC

The zero emissions coal alliance (ZECA) have proposed a highly efficient integrated coal hydrogasification power producing scheme, where carbon is removed from product gas through a cyclic CaO-CaCO₃ process and electricity is produced with solid oxide fuel cells. In recent years a lot of research effort has been put towards the realisation of the ZECA cycle. This paper has two purposes: (a) to present optimal solutions to the technical challenges of the envisaged cycle, i.e. achieving the required product gas recycling to the gasifier with steam ejector, heat transfer to the calcination process via heat pipes, and required gas cleaning with appropriate sorbents and (b) to re-evaluate the cycle’s performance and operating regime adopting these solutions.The complete power plant was designed in detail using ASPENPLUS™ simulation software and results include all critical operation parameters in order to achieve optimal integration. The maximum realistically achievable net power production efficiency was estimated at ∼40%, with ∼90% decarbonisation.     

Systematic analysis and optimization of power generation in pressure retarded osmosis: Effect of multistage design

This work presents a systematic method for analysis and optimization of specific energy production (SEP) of pressure retarded osmosis (PRO) systems employing single‐stage configuration as well as multistage design with interstage hydro‐turbines. It is shown that the SEP normalized by the draw solution feed osmotic pressure increases with the number of stages as well as a dimensionless parameter . As compared to the single‐stage PRO, the multistage arrangement not only increases flux and volume gain, but also allows a stage‐dependent, progressively decreasing hydraulic pressure, both of which contribute to enhanced SEP and power density. At the thermodynamic limit where γ_tot goes to infinity, the theoretical maximum SEP by an N‐stage PRO system is , where q_tot is the ratio of the draw solution flow rate at the outlet to the inlet on the system level. For single‐stage PRO, it is no more than π₀. For infinite number of stages, the theoretical limit becomes . SEP under realistic conditions and practical constraints on multistage design are discussed. © 2017 American Institute of Chemical Engineers AIChE J, 63: 144–152, 2018     

Combined effect of temperature and thickness on work of fracture parameters of unplasticized PVC film

The combined effect of temperature and thickness on the essential work of fracture (EWF) parameters for an unplasticized poly(vinyl chloride) (uPVC) film was investigated using double edge notched tension specimens. It was found that for the range of temperatures (23°C to 60°C) and thicknesses (0.15 mm to 0.40 mm) studied here, specific essential work of fracture (w_e) was independent of temperature at each thickness but increased with thickness at each temperature. It was found that at each temperature, w_e and its yielding (w_e,y) and necking/tearing components (w_e,nt), all increased linearly with increasing thickness. However, whilet w_e showed no significant variation with respect to temperature, its yielding component (w_e,y) decreased and its necking/tearing component increased (w_e,nt) with increasing temperature. It was found that estimated values of w_e and its components w_e,y and w_e,nt via crack opening displacement values were by and large unsatisfactory, being either much higher or lower than the directly measured values.     

以最佳温度均匀度和最小熵产为目标的航天器热循环试验系统运行参数优化

以数值模拟的方法研究了不同运行参数下航天器热循环试验箱内温度均匀度与熵产的变化规律。结果表明,在4.3×10³≤Re≤8.6×10⁵、4.62×10¹³≤Gr≤1.38×10¹⁴范围内,由于强浮升力的作用,壁面附近出现回流区,温度由上往下降低,中轴线附近气体加速下沉,温度由上往下升高。箱内量纲1温度标准偏差随Reynolds数增大而增大,随Grashof数变化不明显;混合对流过程中流动熵产远小于传热熵产,熵产数值随Reynolds数、Grashof数的增大而增大。提出了壁面Nusselt数、试验箱内量纲1平均温度、量纲1温度标准偏差及量纲1传热熵产随Reynolds数、Grashof数变化的关联式。     

Effect of layer thickness on the electrical parameters and conduction mechanisms of conjugated polymer‐based heterojunction diode

In this study, thickness‐dependent current density–voltage (J–V) characteristics obtained for poly{(9,9‐dioctylfluorene)?2,7‐diyl‐(4,7‐bis(thien‐2‐yl) 2‐dodecyl‐benzo[1,2,3] triazole)} (PFTBT) conjugated copolymer based heterojunction diode fabricated on ITO were investigated in terms of electrical characteristics. In order to analyze J –V plots with ITO/PEDOT:PSS/PFTBT:PC₆₁BM/LiF/Al configuration, the thickness‐dependent J–V measurements were applied in the thickness range between 90 and 200 nm. The effect of PFTBT:PC₆₁BM layer thickness on the forward J –V characteristics were investigated by evaluating electrical parameters such as zero bias barrier height (Φ_Bo), ideality factor (n ), shunt resistance (R _sh), series resistance (R_s ), the interface states density (N _ss), and space‐charge limited mobility. The results show that at PFTBT:PC₆₁BM layer thickness of 90 and 200 nm, ideality factor for ITO/PEDOT:PSS/PFTBT:PC₆₁BM/LiF/Al heterojunction diodes ranged from 2.726 to 3.121 and the thermionic emission over the heterojunction diodes is crucial at low current densities and the intrinsic thermally generated charge carriers controlled the forward current this region of the heterojunction diode. At relatively higher voltage, the current mechanism of ITO/PFTBT:PC₆₁BM/PEDOT:PSS/LiF/Al heterojunction diodes were found to obey a space charge limited (SCLC) conduction mechanism. The values of N_ss and R_s in heterojunction diodes increase with increasing PFTBT:PC₆₁BM layer thickness and effect the main electrical parameters of diodes. In addition, the leakage current of heterojunction diodes are taken and interpreted via Poole‐Frenkel emission and Schottky emission. The leakage current was controlled in ITO/PEDOT:PSS/PFTBT:PC₆₁BM/LiF/Al heterojunction diodes by Poole‐Frenkel emission above 140 nm and by Schottky emission under 140 nm. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44817.