Scaling up the production rate of nanofibers by needleless electrospinning from multiple ring

Mass production of nanofibers is crucial in both laboratory research and industry application of nanofibers. In this study, multiple ring spinnerets have been used to generate needleless electrospinning. Multiple polymer jets were produced from the top of each ring in the spinning process, resulting in thin and uniform nanofibers. Production rate of nanofibers increased gradually with the increase of the number of rings in the spinneret. Spinning performance of multiple ring electrospinning, namely the quality and production rate of the as-spun nanofibers, was dependent on experimental parameters like applied voltage and polymer concentration. Electric field analysis of multiple ring showed that high concentrated electric field was formed on the surface of each ring. Fiber diameter together with production rate of needleless electrospinning was dependent on the strength and distribution of the electric field of the spinneret. Needleless electrospinning from multiple ring can be further applied in both laboratory research and industry where large amount of nanofibers must be employed simultaneously.     

Comparison of two electrospinning processes in obtaining finer polymer nanofibers

Two different electrospinning processes (traditional single fluid one and a modified coaxial electrospinning with organic solvent as sheath fluid) are investigated in relation to their capability of producing thinner nanofibers. Both the modified coaxial electrospinning and single fluid electrospinning can produce thinner nanofibers with polyvinylpyrrolidone (PVP) as a polymer model and using a poor volatile solvent N, N-dimethylacetamide (DMAc) in different ways. However the traditional single fluid process was less effective compared to the modified coaxial process, as it suffered more from the limitation of polymer chain entanglement threshold for maintaining structural uniformity of nanofibers. Using DMAc as sheath fluid in the modified process facilitated formation of thinner nanofibers without sacrificing their quality. The mechanism should be that an appropriate DMAc surrounding to the core polymer jet helps to retain it in a fluid state to experience a longer time electrical drawing, with little adverse influence on the polymer chain entanglements. Nanofiber diameters could also be tailored in a linear manner using the modified coaxial process simply through manipulating the sheath solvent flow rates. The modified coaxial process described here extends the capability of electrospinning process and opens a new way to obtain thinner nanofibers with fine structural uniformity.     

Spinline behavior and web morphology in multi-nozzle electrospinning of PAN/DMF solution

The spinline behavior, the web morphology and the crystallinity in multi-nozzle electrospinning were investigated using photography, SEM and XRD. It was found that the spinlines of each nozzle had skewed bell shapes and changed along the nozzle alignment and location. The alignment of the nozzles showed significant effects on both the spinline shape and the fiber web morphology. The fiber diameter and the crystallinity were changed along the collected position. They were resulted from the balance of the self-induced and the mutual Coulombic interactions of the spinlines.     

Uniaxially well-aligned nanofiber arrays fabricated by electrospinning with a stable and low moving velocity jet

Aligned fibers in micro-/nano-scale have attracted more attention especially in tissue engineering field because cells can orientation growth along the fiber. However, it is still a huge technological challenge in achieving it as a result of the inherent bending instability of an electrospinning jet. Herein, we report a novel and simple spinning approach, in which low dielectric constant of dioxane was judiciously used as solvent for spinning dope, to obtain electrospinning jet with low induced charge, therefore eliminating electrically and aerodynamically driven bending instability, and forming a stable and low forward-moving velocity jet longer than 100 cm. This consequently allows for readily collecting and fabricating individual fibers, well-aligned ultrafine fiber arrays over large areas. Our approach has proved to be effective in preparing well-aligned ultrafine fibers from biodegradable poly(D, L-lactic acid) with different molecular mass, natural polymer acetyl cellulose and synthesized non-biodegradable polymer polystyrene.     

Preparation of new polymer nanocomposites based on poly(lactic acid)/fatty nitrogen compounds modified clay by a solution casting process

In this study, different organoclays (OMMTs) were prepared using various fatty nitrogen compounds (FNCs) and natural clay, sodium montmorillonite (MMT). The clay modification was carried out by stirring the clay particles in an aqueous solution of fatty amides (FA), fatty hydroxamic acids (FHA), and carbonyl difatty amides (CDFA). These OMMTs were then used for nanocomposites production to improve the property balance of poly(lactic acid) (PLA) by solution casting process. All sets of OMMTs and nanocomposites were characterized using various apparatuses. In the nanocomposites, where the clay surface is pretreated with FA, FHA and CDFA, the basal spacing of the clay increased to 2.94, 3.26 and 3.80 nm, respectively The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirmed the production of nanocomposites. PLA modified clay nanocomposites show higher thermal stability and significant improvement of mechanical properties in comparison with pure PLA.     

RGO/Nylon-6 composite mat with unique structural features and electrical properties obtained from electrospinning and hydrothermal process

In this work, the reduced graphene oxide (RGO) sheets were effectively uploaded through nylon-6 fibers using combined process of electrospinning and hydrothermal treatment. Good dispersion of graphene oxide (GO) with nylon-6 solution could allow to upload GO sheets through nylon-6 fibers and facilitate the formation of spider-wave-like nano-nets during electrospinning. GO sheets present on/into nylon-6 spider-wave-like nano-nets were further reduced to RGO using hydrothermal treatment. The impregnated GO sheets into nylon-6 nanofibers and their reduction during hydrothermal treatment were confirmed by FE-SEM, TEM, FT-IR and Raman spectra. The electrical characteristics of pristine nylon-6, GO/nylon-6 and RGO/nylon-6 nanofibers were investigated and it was found that RGO/nylon-6 composite mat had better electrical conductivity than others. The formation of spider-wave-like nano-nets as well as indirect route of incorporation of RGO sheets on electrospun nylon-6 mat may open a new direction for future graphene/polymer electronics.     

Rheological behavior and spinnability of ethylamine hydroxyethyl chitosan/cellulose co-solution in N-methylmorpholine-N-oxide system

In this work, the novel chitosan derivative ethylamine hydroxyethyl chitosan (EHC) was synthesized and blended with cellulose in an aqueous N-methylmorpholine-N-oxide (NMMO) solution in order to fabricate antibacterial chitosan/cellulose fiber. The rheological behaviors of the obtained co-solution in both steady and dynamic states were carefully investigated to determine the spinnability of the co-solution. In steady state, the addition of EHC was found to preserve the power-law flow characteristics of cellulose in the aqueous NMMO solution, while broadening the first Newtonian fluid-flow area. Under dynamic conditions, both Han-plot and viscoelastic analyses indicated the homogeneity of the co-solution. EHC/cellulose antibacterial fibers were successfully spun via the lyocell process using aqueous NMMO as the solvent, confirming the excellent spinnability of the EHC/cellulose co-solution. Scanning electron microscopy was used to observe the morphology of the obtained EHC/cellulose fibers; they were also investigated for antibacterial activity. The obtained EHC/cellulose fiber exhibited good spinning consistency and strong antibacterial activity against Escherichia coli, demonstrating potential applications for the material in antibacterial textiles.     

Solution electrospinning of polypropylene-based fibers and their application in catalysis

Since the dissolution of polyolefins is a chronic problem, melt processing has been tacitly accepted as an obligation. In this work, polypropylene (PP) was modified on molecular level incorporating poly(ethylene glycol) (PEG) as graft segment (PP-g-PEG) in a range of 6 to 9 mol%. Gold nanoparticles were nucleated in the presence of the copolymer chains via redox reaction. The dissolution of the amphiphilic comb-type graft copolymers containing gold nanoparticles (80 nm in diameter) was achieved in toluene and successfully electrospun from its solution. The diameter of composite fibers was in the range from 0.3 to 2.5 μm. The design of the structurally organized copolymer fiber mats provided a support medium for the nanoparticles enhancing the active surface area for the catalytic applications. The resulting composite fibers exhibited rapid catalytic reduction of methylene blue (MB) dye in the presence of sodium borohydride (NaBH₄) compared to corresponding composite cast film.     

Three dimensional simulation of viscoelastic polymer melts flow in a cast film process

Three-dimensional simulation of the cast film process for viscoelastic polymer materials was carried out using the finite element method. The flow between the extrusion die and chill roll was assumed to be steady-state and isothermal and the rheological property of material was characterized by a single-mode PTT model. Gravity and inertial flow were considered in the simulation work, but neglecting die swell at the die exit, surface tension, crystallization, transient disturbance and film sag. Simulation results of the cast film production line were compared with the experimental data on the velocity profiles and neck-in values. Neck-in and edge bead was well predicted and the influence of strain-hardening nature, elasticity of materials and operation conditions on the final film shape was also investigated. It was found that the effect of strain-hardening nature was masked for the material with a very low relaxation time when the single-mode PTT model was adopted. Greater elasticity helped to produce a film with smaller neck-in and less waste edge. When the air gap length was increased, it was predicted that neck-in phenomenon would be promoted as well. Moreover, it was found that ratio of neck-in values under different air gap lengths was approximately equal to that of air gap lengths, which was consistent with experimental evidence.     

Design and process optimization of polymer filling for bevel guard based on numerical analysis

Injection molding has been widely used in the manufacturing of various polymer products, including housewares, home appliances, and automotive parts. A disposable medical device based on polymeric material at a low cost is another important area for injection molding. The numerical analysis was performed to predict the potential problem, often occurring during the manufacturing process of the medical device. Computer-aided engineering model was developed using industry-standard molding software, MOLDFLOW®. The flow pattern of the molten polymer was investigated in the replication of butterfly shaped Catheter Support for various catheterization. The flow pattern and temperature distribution of the molded part were investigated through a series of analysis. The results of analysis with original design predicted non-uniform polymer flow with a poor weld line, unbalanced cavity filling, and uneven temperature distribution of the part. An appropriate gate location to achieve uniform flow pattern for mold filling was determined on the base of the predicted results and experience, considering the performance of the product and limitation of the production.     

Electrospinning of polycaprolatone nanofibers with DMF additive: The effect of solution proprieties on jet perturbation and fiber morphologies

Electrospinning is a straightforward method to produce sub-micrometer or nanoscale fiber. Polycaprolactone (PCL), an important polymer in biomedical applications, has been electrospun in several solvent systems. N,Ndimethylformamide (DMF) is often used as an additive in the solvent system to prepare PCL nanofibers. The adding of the DMF changes the physical properties of the solution. To trace and understand the influence of these changes on the jet formation as well as the resultant fibers morphologies, a model of jet perturbation based on the Plateau-Rayleigh Instability theory was established to explicate the formation of the particles/fibers and some experiments for testing the solution properties and fibers morphologies were carried out. With the adding of DMF in dichloromethane (DCM)/DMF mixed solvents, the solution surface tensions increase while solution viscosities decrease, which triggers the change of electrospinning to electrospraying in general. However, according to the obtained results, the addition of the DMF makes it easier to induce the transformation of particles electrospraying to fibers electrospinning with smaller diameter. This is attributed to the higher dielectric constant, lower vapor pressure, and higher electric conductivity of DMF. The theoretical model and experimental results strengthen the relations of solution properties, jet moving behaviors, and the resultant fiber morphologies.     

电极液pH值控制对土壤Cd和Pb动电过程的影响

研究了控制阴阳极液pH值对Cd和Pb在土壤中动电过程的影响。结果表明,控制阴阳极液pH值明显改变了动电过程中的电流密度、电渗流量、土壤层pH值和Cd与Pb在土壤层的分配;显著增加了总Cd和Pb及其有效态的去除率,总Cd和Pb平均去除率分别为87%和51%,有效态Cd和Pb的平均去除率分别为97%和73%;与单元素Cd或Pb的动电效果对比,Cd的去除率上升,Pb的去除率下降。     

Mechanical properties and in vitro degradation of PLGA suture manufactured via electrospinning

The current research discusses the efforts to achieve a Poly(lactide-co-glycolide)(PLGA) nanofiber yarn using two differently charged nozzles with potential application as surgery suture. First, electrospinning parameters such as solution concentration, applied voltage, feed rate were optimized to produce yarn with smooth nanofibers. In order to improve the properties of produced suture, heat setting setup was developed. Two heat setting techniques, including hot water and dry heat were applied, and the influence of the heat setting process on the mechanical properties of yarn was studied. The results showed that heat setting with boiling water was the best method. At first strength, E-modulus and extension of prepared suture were 36.6 MPa, 0.9 GPa and 68.8 % respectively. After improvement with heat setting, strength and E-modulus increased to 63.7 MPa, 2.7 GPa respectively and extension decreased to 29.7 %. Finally, in order to analyze knot performance, two types of surgical knot (square and surgeon) were used, and mechanical properties were investigated. The presence of knot lessens mechanical properties for each two type. Square knot showed better mechanical properties than surgeon’s knot. With square knot strength, E-modulus and extension were 62.1 MPa, 2.1 GPa, 28.6 %, respectively. In vitro study of nanofiber yarn degradation behavior showed that the mechanical properties were decreased. This could be due to greater surface area of nanofibers exposed to surrounding environment.     

An investigation on the comparison of wet spinning and electrospinning: Experimentation and simulation

Polysulfonamide (PSA) has been widely used in many fields because of its excellent thermodynamic properties. In this study, PSA fibers were prepared separately via two different spinning ways, including conventional wet spinning and electrospinning. Fluid motion of wet spinning and electrostatic field of electrospinning were modeled using finite element analysis to investigate the spinning process. The properties of fabricated PSA fibers were characterized systematically by scanning electron microscope (SEM), fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), thermal gravity analysis (TGA) and electronic strength tester. Based on the simulation and theoretical analysis of spinning process, it was found that the extruding force of the wet spinning is larger than that of the electrospinning. The larger extruding force makes the alignment of macromolecules inside fiber relatively uniform, and a higher proportion of crystallization happens. Accordingly, the mechanical properties and thermal stability of PSA fibers could be improved due to a higher proportion of crystallization. The experimental results of mechanical strength and TG test are coincided with the simulation results. PSA fiber prepared by wet spinning has better thermal stability and mechanical properties than that fabricated by electrospinning.     

Mapping the influence of electrospinning parameters on the morphology transition of short and continuous nanofibers

A theoretical model for the morphology transition of short and continuous nanofibers by electrospinning has been proposed. The influences of polymer concentration, applied voltage, and flow rate on the fabrication of short and continuous nanofibers were mapped for use as a reference in the design and construction of the theoretical model. The morphology transition of short and continuous nanofibers occurred mainly due to changes in the flow rate and voltage. According to the concentration of the polymer in the solution, the map of the short nanofiber region was narrowed as the polymer concentration increased. The theoretical model derived from the conservation of kinetic energy and potential energy experienced by the polymer solution resulted in an equation that could be used to calculate the voltage and flow rates under certain boundary conditions when cutting nanofibers. The boundary conditions for voltage were 4.7-4.9 kV, and the boundary conditions for flow rate were 0.1-1.1 µl/min.     

Design and fabrication of tubular scaffolds via direct writing in a melt electrospinning mode

Flexible tubular structures fabricated from solution electrospun fibers are finding increasing use in tissue engineering applications. However it is difficult to control the deposition of fibers due to the chaotic nature of the solution electrospinning jet. By using non-conductive polymer melts instead of polymer solutions the path and collection of the fiber becomes predictable. In this work we demonstrate the melt electrospinning of polycaprolactone in a direct writing mode onto a rotating cylinder. This allows the design and fabrication of tubes using 20 μm diameter fibers with controllable micropatterns and mechanical properties. A key design parameter is the fiber winding angle, where it allows control over scaffold pore morphology (e.g. size, shape, number and porosity). Furthermore, the establishment of a finite element model as a predictive design tool is validated against mechanical testing results of melt electrospun tubes to show that a lesser winding angle provides improved mechanical response to uniaxial tension and compression. In addition, we show that melt electrospun tubes support the growth of three different cell types in vitro and are therefore promising scaffolds for tissue engineering applications.     

An investigation on the effects of twist on geometry of the electrospinning triangle and polyamide 66 nanofiber yarn strength

The formation of a symmetric electrospinning triangle zone (E-triangle) via a technique based on using two oppositely charged nozzles is described for fabricating continuous twisted nanofiber yarn of polyamide (Nylon 66). This study shows how changing the dimensions and geometry of the E-triangle influences the distribution of nanofiber tension and diameter in this zone, and consequently how it affects the nanofiber yarn strength. The twist effect on the E-triangle geometry was investigated by changing the rotational speed of the twister plate of values of 96, 160, 224 and 288 rpm. The results showed that by increasing the twist rate, the apex angle of the E-triangle increased, whereas the height and width of the Etriangle decreased. An energy method was adopted to study the distribution of tension on nanofibers in the E-triangle. Considering a constant spinning tension, it was observed that the gradient of the nanofiber tension curve was steeper and the extreme values of tension on nanofibers were increased by increasing the twist rate. Furthermore, the mean diameter reduction of nanofibers confirmed these results. It is concluded that mechanical properties of nanofiber yarn have been considerably improved by increasing the twist rate and changing the shape of the E-triangle.     

Modeling the process and costs of fuel ethanol production by the corn dry-grind process

The corn dry-grind process is the most widely used method in the U.S. for generating fuel ethanol by fermentation of grain. Increasing demand for domestically produced fuel and changes in the regulations on fuel oxygenates have led to increased production of ethanol mainly by the dry-grind process. Fuel ethanol plants are being commissioned and constructed at an unprecedented rate based on this demand, though a need for a more efficient and cost-effective plant still exists.A process and cost model for a conventional corn dry-grind processing facility producing 119 million kg/year (40 million gal/year) of ethanol was developed as a research tool for use in evaluating new processing technologies and products from starch-based commodities. The models were developed using SuperPro Designer^® software and they handle the composition of raw materials and products, sizing of unit operations, utility consumptions, estimation of capital and operating costs, and the revenues from products and coproducts. The model is based on data gathered from ethanol producers, technology suppliers, equipment manufacturers, and engineers working in the industry. Intended applications of this model include: evaluating existing and new grain conversion technologies, determining the impact of alternate feedstocks, and sensitivity analysis of key economic factors. In one sensitivity analysis, the cost of producing ethanol increased from US$ 0.235 l⁻¹ to US$ 0.365 l⁻¹ (US$ 0.89 gal⁻¹ to US$ 1.38 gal⁻¹) as the price of corn increased from US$ 0.071 kg⁻¹ to US$ 0.125 kg⁻¹ (US$ 1.80 bu⁻¹ to US$ 3.20 bu⁻¹). Another example gave a reduction from 151 to 140 million l/year as the amount of starch in the feed was lowered from 59.5% to 55% (w/w).This model is available on request from the authors for non-commercial research and educational uses to show the impact on ethanol production costs of changes in the process and coproducts of the ethanol from starch process.     

Biomedical exploitation of chitin and chitosan via mechano-chemical disassembly, electrospinning, dissolution in imidazolium ionic liquids, and supercritical drying

Recently developed technology permits to optimize simultaneously surface area, porosity, density, rigidity and surface morphology of chitin-derived materials of biomedical interest. Safe and ecofriendly disassembly of chitin has superseded the dangerous acid hydrolysis and provides higher yields and scaling-up possibilities: the chitosan nanofibrils are finding applications in reinforced bone scaffolds and composite dressings for dermal wounds. Electrospun chitosan nanofibers, in the form of biocompatible thin mats and non-wovens, are being actively studied: composites of gelatin + chitosan + polyurethane have been proposed for cardiac valves and for nerve conduits; fibers are also manufactured from electrospun particles that self-assemble during subsequent freeze-drying. Ionic liquids (salts of alkylated imidazolium) are suitable as non-aqueous solvents that permit desirable reactions to occur for drug delivery purposes. Gel drying with supercritical CO(2) leads to structures most similar to the extracellular matrix, even when the chitosan is crosslinked, or in combination with metal oxides of interest in orthopedics.