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New methods of bulk and surface modification of polypropylene filaments at the stage of their forming from a melt are presented. Modification of polypropylene filaments by introducing a small amount of stabilized metal-containing nanoparticles into the fiber-forming polymer during the melt generation step is considered. It was found that the modified filaments exhibits high quality characteristics. A method for surface modification based on applying a suspension of finely dispersed polytetrafluoroethylene to the surface of a semi-cured polypropylene filament during the sizing stage is also considered. The modified filament acquires an extremely high chemical resistance and a very low coefficient of friction. [ABSTRACT FROM AUTHOR]

Round hollow fiber membranes have been well established in applications such as gas separation, ultrafiltration and blood dialysis. Yet, it is well known that geometrical topologies can introduce secondary flow patterns counteracting mass transport limitations, stemming from diffusion resistances and fouling. We present a new systematic methodology to fabricate novel membrane architectures. We use the freedom of design by 3D-printing spinnerets, having multiple bore channels of any geometry. First, such spinnerets are stationary to fabricate straight bore channels inside a monolithic membrane. Second, in an even more complex design, a new mechanical system enables rotating the spinneret. Such rotating multibore spinnerets enable (A) the preparation of twisted channels inside a porous monolithic membrane as well as (B) a helical twist of the outside geometry. The spun material systems comprise classical polymer solutions as well as metal-polymer slurries resulting in solid porous metallic monolithic membrane after thermal post-processing. It is known that twisted spiral-type bore channel geometries are potentially superior to straight channels with respect to mass and heat polarization phenomena, however their fabrication was cumbersome in the past. Now, the described methodology enables membrane fabrication to tailor the membrane geometry to the needs of the membrane process. To showcase the delicate interplay between the geometry and radial and axial flow conditions, we report fluid mechanical simulations and flow magnetic resonance imaging measurements for a twisted tri-bore membrane during permeation. [ABSTRACT FROM AUTHOR]

The influence of the spinneret draw ratio and subsequent solid-state stretching of polypropylene multifilament yarns (PMY) on changes in the orientation of crystallites and molecular chains in the polymer amorphous regions was studied using x-ray structure analysis. It was shown that crystallites and molecular chains of amorphous polypropylene (PP) became significantly more oriented already for a yarn spinneret draw ratio of 2400% and changed little if it was increased further. Additional solid-state stretching of yarns at elevated temperature had practically no effect on the orientation of PP crystallites but did halve the misorientation angle of molecular chains in the polymer amorphous regions. This phenomenon suggested that the substantial decrease of the elongation at break and increase of PMY physicomechanical parameters could be attributed to distribution of the applied load onto a larger number of continuous chains. [ABSTRACT FROM AUTHOR]

A structured spinneret comprising two acentric needles nested into a third metal capillary was developed to conduct three-fluid electrospinning processes. With an exterior solvent surrounding two core fluids arranged side-by-side, high quality polyvinylpyrrolidone/shellac Janus nanofibers could be prepared, which was not possible using a standard side-by-side spinneret without this innovation. [ABSTRACT FROM AUTHOR]

The spinning apparatus and silk of Segestria senoculata were stud-ied with the use of scanning electron microscopy and light microscopy, which confirmed the presence of four categories of spigots connected with four types of spinning glands (i.e., Glandulae ampullaceae major, Glandulae ampullaceae minor, Glandulae piriformes and Glandulae pseudaciniformes). New data about the morphology of spinnerets and spigots were obtained for both the adults and nymphal stages of both sexes. For the first time the silken threads of retreats, signal threads and attachment discs of the members of Segestria were subjected to a detailed SEM study. The data resulting from studying the spinning apparatus of S. senoculata was compared to current knowledge of the silk producing systems of families belonging to the Dysderoidea superfamily. Silks that are emitted from spigots in the course of retreat construction are not (similarly to the other dysderoids) processed by the spider’s legs during the subsequent process of hardening. Apart from the major ampullate glands/spigots, segestriids also possess developed minor ampullate glands. Minor ampullate threads are used by S. senoculata spiders when making their signal threads. [ABSTRACT FROM AUTHOR]

Novel CoFe 2 O 4 nanotubes (CFNs) are successfully prepared by the electrospinning technique and subsequent annealing process. When evaluated as anode materials for lithium-ion batteries (LIBs), the CFNs exhibited good electrochemical performance with high specific capacity of 1228 mA h g − 1 , long cycling stability over 160 cycles, and good rate capability (214.7 mA h g −1 at 2 A g −1 ). The improved electrochemical performance can be attributed to the hollow and continuous one dimensional (1D) nanostructure. [ABSTRACT FROM AUTHOR]

In this study, the key factors for controlling the average fiber diameter and diameter distribution of fibers made via simultaneous centrifugal spinning and UV initiated polymerization are elucidated. Through systematic investigation, it was found that the average fiber diameter has a strong dependence on monomer delivery rate through the orifice, which can be intuitively linked to both the orifice diameter and monomer mixture viscosity. On the other hand, the breadth of the fiber diameter distribution can be controlled by the spin speed of the rotating spinneret. Carefully tuning these process parameters allows near independent control of average fiber diameter and its distribution, which could provide access to a widely tailorable range of fibers appropriate for different applications. Finally, under optimized process conditions, crosslinked fibers with average diameters of approximately 1.5 μm can be produced, which are one to two orders of magnitude smaller than photocured fibers fabricated in previous reports and comparable with the smallest melt blown nonwoven fibers produced commercially. Coupled with the advantages of cross-linked fibers made by in-situ photopolymerization, the capability to produce small fibers with tailored diameter distributions by centrifugal spinning could further establish this technology as a competitive alternative to existing approaches. [ABSTRACT FROM AUTHOR]

A novel quadruple spinneret to produce dual-layer hollow fiber membranes by simultaneous spinning of two polymer solutions, using the dual precipitation bath technique is proposed. Hollow fibers aimed at gas separation processes were prepared in extrusion system specifically designed and built for this purpose. A polyurethane polymer was selected as the selective layer (outer-layer), while polyethersulfone was defined as the support (inner-layer). Activated carbon powder was added into the PU solution for further improvement of the transport properties. The hollow fibers showed good adhesion between the polymer layers and a defect-free selective layer. Representative results include a CO2/N2selectivity of 43. [ABSTRACT FROM PUBLISHER]

A family of medicated Janus fibers that provides highly tunable biphasic drug release was fabricated using a side-by-side electrospinning process employing a Teflon-coated parallel spinneret. The coated spinneret facilitated the formation of a Janus Taylor cone and in turn high quality integrated Janus structures, which could not be reliably obtained without the Teflon coating. The fibers prepared had one side consisting of polyvinylpyrrolidone (PVP) K60 and ketoprofen, and the other of ethyl cellulose (EC) and ketoprofen. To modulate and tune drug release, PVP K10 was doped into the EC side in some cases. The fibers were linear and had flat morphologies with an indent in the center. They provide biphasic drug release, with the PVP K60 side dissolving very rapidly to deliver a loading dose of the active ingredient, and the EC side resulting in sustained release of the remaining ketoprofen. The addition of PVP K10 to the EC side was able to accelerate the second stage of release; variation in the dopant amount permitted the release rate and extent this phase to be precisely tuned. These results offer the potential to rationally design systems with highly controllable drug release profiles, which can complement natural biological rhythms and deliver maximum therapeutic effects. [ABSTRACT FROM AUTHOR]

New-typed magnetic and color-tunable bifunctional Janus nanofibers have been successfully fabricated by electrospinning technology using a specially designed parallel spinneret. The Janus nanofiber consists of two strands of nanofibers assembled side-by-side, one strand nanofiber has tuned magnetism and the other one possesses color-tunable photoluminescence. The Janus nanofibers possess superior magnetic and luminescent properties due to their special nanostructure. Tunable colors from bluish green to orange can be realized in the flexible Janus nanofibers by varying the content of Eu(BA)phen complex, and furthermore, white-light-emitting flexible Janus nanofibers are achieved using rare-earth complexes as luminescent centers. In particular, it is the first time to report the influence of FeO nanoparticles on the fluorescent color of the magnetic-fluorescent nanomaterials. The synthesized products have potential applications in color displays, nano-bio-label materials, and anti-counterfeit materials. [ABSTRACT FROM AUTHOR]

The method of statistical modeling is used to determine the relationship between the thickness of filaments and the coefficients of variation for time and density. It is shown that the standard deviation of the outgoing flow is directly proportional to these coefficients individually and in combination. The mathematical model which was constructed allows these relationships to be used to design new systems for controlling the passage of a polymer solution through a spinneret. [ABSTRACT FROM AUTHOR]

The modified near-field electrospinning (NFES) and the conventional NFES have been compared to demonstrate the viability of direct-writing micro/nano structures from PVDF solution systems. The modified NFES shows good capability in writing various orderly micro/nano patterns, such as straight and continuous lines, parallel lines, arc lines, and beads-on-string structures, whereas the conventional NFES is difficult to give a continuous writing process. Besides, the modified NFES also allows a lower electric field due to the jet initiated in a mechanical way. By finely tuning the key parameters during the modified NFES process, such as the solution property, speed of the movable collector, and the distance between the spinneret and the collector, it is likely to construct complex patterns as required on rigid or flexible substrates for a myriad of applications. [ABSTRACT FROM AUTHOR]

A new flexible nanostructure of [CoFe2O4/PVP]@[YAG:7 %Tb3+/PVP] magnetic-luminescent bifunctional coaxial nanofibers is fabricated successfully by electrospinning technology using a homemade coaxial spinneret. The morphologies, structures, and magnetic and luminescent properties of the final products are investigated by modern determination techniques. The results show that the coaxial nanofibers simultaneously provide better magnetic and luminescent properties than CoFe2O4/YAG:7%Tb3+/PVP composite nanofibers owing to the isolation of the YAG:7%Tb3+ luminescent nanofibers from the CoFe2O4 magnetic nanofibers. Furthermore, the luminescent characteristics and saturation magnetizations of the coaxial nanofibers can be tuned by adjusting the contents of luminescent and magnetic compounds. The formation mechanism of coaxial nanofibers is also presented. More importantly, the design concept and construction technology are of universal significance for the fabrication of other bifunctional coaxial nanofibers. [ABSTRACT FROM AUTHOR]

CoMn2O4nanofibers with hollow structures are successfully prepared by the electrospinning technique. These hollow nanofibers are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TG) and Brunauer-Emmett-Teller (BET) analyzer. The temperature-dependent experiments are also carried out to monitor the evolution process of CoMn2O4hollow nanofibers (HNs), and a possible formation mechanism is introduced reasonably based on the investigations. When evaluated as an electrode material for lithium-ion batteries, the results of electrochemical test show that these unique CoMn2O4HNs exhibit admirable lithium storage performances with high specific capacity and excellent rate capability. The hollow and continuous one dimensional (1D) nanostructures of the CoMn2O4HNs make a prominent contribution to the excellent electrochemical performance. [ABSTRACT FROM AUTHOR]

Abstract: We have developed novel tri-bore thin-film composite (TFC) hollow fiber (HF) membranes for forward osmosis (FO) processes by employing a specially designed tri-bore blossom spinneret. The resultant hollow fibers exhibit evenly-distributed three inner bores with an either round or triangle outer geometry. The newly developed triangle tri-bore hollow fibers have impressive mechanical strength with enhanced permeation properties better than the round ones. Further efforts were given to investigate the effects of glycerol treatment and surfactant concentration during the interfacial polymerization. The new developed TFC tri-bore HF membranes exhibit high water fluxes of 50.5LMH and 11.8LMH with salt leakages as low as 3.5gMH and 2.5gMH, in pressure retarded osmosis (PRO) and FO modes, respectively, when using 2M NaCl as the draw solution and pure water as the feed. The potential of using the triangle TFC membrane for desalination is also investigated. It could reach a water flux of 5.8LMH using a 2M NaCl draw solution and a model seawater solution as the feed. In addition, much more fibers can be packed in a FO module if TFC tri-bore HF membranes have a triangle shape instead of a round one. Theoretical calculations suggest that water output of the module consisting of triangle membranes would double the one comprising round membranes at a 40% packing density. This may enlighten the advantages of triangle tri-bore configuration for FO applications. [Copyright &y& Elsevier]

Flexible luminescent-electrical-magnetic trifunctional Janus nanofibers have been successfully fabricated through electrospinning technology by using specially designed parallel spinnerets. The terbium complex [Tb(ba)3(phen)] (BA=benzoic acid, phen=1,10-phenanthroline), polyaniline (PANI), and Fe3O4 nanoparticles (NPs) were incorporated into polyvinyl pyrrolidone (PVP) and electrospun into Janus nanofibers with [Tb(ba)3(phen)]/PVP as one strand of the nanofiber and PANI/Fe3O4/PVP as another. The morphologies and properties of the final products were investigated in detail by XRD, SEM, TEM, fluorescence spectroscopy, Hall effect measurement system, and vibrating sample magnetometry. The [[Tb(ba)3(phen)]/PVP]//[PANI/Fe3O4/PVP] Janus nanofibers, with an average diameter of 180 nm, simultaneously possess enhanced luminescent performance, electrical conduction, and magnetism. Fluorescence emission peaks of Tb3+ are observed in the [[Tb(ba)3(phen)]/PVP]//[PANI/Fe3O4/PVP] Janus nanofibers and assigned to the 5D4→5F6 ( λ=491 nm), 5D4→5F5 ( λ=544 nm), 7D4→5F4 ( λ=585 nm), and 5D4→7F3 ( λ=620 nm) energy-level transitions of Tb3+ ions; the 5D4→5F5 hypersensitive transition at λ=544 nm is the predominant emission peak. The electrical conductivity of Janus nanofibers reaches up to the order of 10−3 S cm−1. The luminescent intensity, electrical conductivity, and magnetic properties of Janus nanofibers can be tunable by adjusting the amounts of rare-earth complex, PANI, and Fe3O4 NPs present. This new type of luminescent-electrical-magnetic trifunctional Janus nanofiber holds potential for a variety of applications, including molecular electronics, microwave absorption, and future nanodevices, owing to their excellent fluorescence, electrical conduction, and magnetism. [ABSTRACT FROM AUTHOR]

Concentrated cellulose/1-butyl-3-methylimidazolium chloride ([bmim]Cl) solution which exhibits typical elasticity has been employed to prepare fibres by dry jet wet spinning technique. In order to design the spinneret, simulation on contraction flow of cellulose/[bmim]Cl solution through spinneret orifice was carried out. Geometry and mathematical models were established according to rheological behaviour and material parameters. The effects of geometry on variation of viscosity and flow pattern were simulated and discussed. The results show that an increase in aspect ratio decreased the apparent viscosity and a decrease in entrance angle reduced the size of 'dead' region. The aspect ratio and entrance angle of spinneret during dry jet wet spinning were optimised. [ABSTRACT FROM AUTHOR]

Electric field plays a key role in producing required nanofibers in electrospinning. This study aims to improve the electric field distribution of the multijet spinning system by designing the spinneret configuration. A novel 19-hole multistep electrospinning configuration is presented. The simulation results show that the electric field strength at the central position is intensified due to the protuberant step on the spinneret, and therefore more uniform electric field is obtained compared with the 19-hole flat spinneret. We demonstrate that the multistep spinneret configuration produces finer fibers and more continuous fiber mats compared with the flat spinneret configuration because of the improved electric field distribution. Jet repulsion in the multijet electrospinning process is studied. It is found that the electric field line distribution, which is determined by the spinneret configuration, plays a dominant role in influencing jet repulsion. Applied voltage is the main factor responsible for jet repulsion for a given spinneret configuration. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new spinneret with Teflon nozzle for implementing electrospinning. [•] The Teflon nozzle facilitates energy transfer to the working fluid. [•] New knowledge about the interfacial interactions between Teflon/metal and fluids. [•] Producing quercetin-loaded composite fibers with higher quality. [•] Nanofibers from the new protocols provide better sustained drug release profile. [Copyright &y& Elsevier]

Abstract: This study reveals and highlights the importance of the electrospinning set-up to avoid the occurrence of ionic interaction between drugs during the preparation of dual drug loaded electrospun fibrous materials. Poly(L-lactide) (PLA)-based fibrous materials containing diclofenac sodium (DS) and lidocaine hydrochloride (LHC) were prepared by dual spinneret electrospinning of two separate solutions each containing one drug only [(PLA/DS and PLA/LHC)] and compared with materials obtained by electrospinning of a common solution (PLA/DS/LHC) using a single spinneret. Interestingly, the dual spinneret approach allowed the ionic interaction between DS and LHC to be obviated. This was evidenced by the absence of NaCl crystals in the case of (PLA/DS+PLA/LHC) membranes as proven by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The XRD and differential scanning calorimetric analyses revealed that the drugs were in the amorphous state regardless of the method of preparation of the fibrous materials. It was found that PLA/DS/LHC and (PLA/DS+PLA/LHC) fibrous materials exhibited antimicrobial activity against Staphylococcus aureus and were cytocompatible with human mesenchymal stem cells. [Copyright &y& Elsevier]

A two-dimensional model is used to study the pressure distribution in a chamber of a spinneret system. Darcy's law is adopted for determining the inlet and outlet velocities of the flow. The pressure distribution on the spinneret plate is obtained, and the dead zone, where no nozzle exists, can be optimally determined. [ABSTRACT FROM AUTHOR]

The thickness of a spinneret is always a geometrical constraint in nozzle design. The geometrical form of a nozzle has a significant effect on the subsequent spinning characteristics. This paper gives an optimal condition for maximal pressure gradient through the nozzle. [ABSTRACT FROM AUTHOR]

Highlights: [•] A Teflon-coated spinneret has been employed in electrospinning for the first time. [•] Finer polymer nanofibers were produced using the new Teflon-coated spinneret. [•] The interfacial tension between the fluid and spinneret was identified as vital to successful electrospinning. [•] A molecular mechanism rationalizing the influence of spinneret composition on electrospinning was proposed. [ABSTRACT FROM AUTHOR]

The present research investigates a modified coaxial process for smoothening electrospinning of cellulose acetate (CA) and obtaining its nanofibers with high quality. With 11 w/v% CA in mixed solvent of acetone and N,N-dimethylacetamide (DMAc) (v:v, 3:1) as electrospinnable core fluid, different solvents (acetone, DMAc and their mixture) are taken as sheath fluids to conduct the modified process. SEM observations demonstrate that the modified process is effective in retarding the clogging of spinneret for a smooth electrospinning and in obtaining high quality CA nanofibers in terms of structural uniformity, diameters, and their distributions. The mechanism about the influence of sheath fluid on the process and the formation of nanofibers is discussed. The key for the modified coaxial process is the reasonable selection of sheath fluids and a sheath-to-core flow rate ratio matching the drawing process of core CA fluid during the electrospinning. The present paper provides a simple method to implement the modified coaxial process for smoothening the electrospinning and obtaining polymer nanofibers with high quality. [ABSTRACT FROM AUTHOR]

We have studied the basic characteristics of spinneretless electrospinning of polyacrylonitrile fibers. We show the effect of the viscosity and the type of solvent on the fiber drawability of the solutions. [ABSTRACT FROM AUTHOR]

A new process technology modified from conventional coaxial electrospinning process has been developed to prepare polymer fibers from a high concentration solution. This process involves a pure solvent concentrically surrounding polymer fluid in the spinneret. The concentric spinneret was constructed simply by inserting a metal needle through a high elastic silica gel tube. Two syringe pumps were used to drive the core polymer solution and the sheath solvent. Using polyvinylpyrrolidone (PVP) as the polymer model, which normally has an electrospinnable concentration of 10% w/v in ethanol, it was possible to electrospin 35% w/v of PVP in the same solvent, when pure N, N-dimethylacetamide (DMAc) was used as sheath fluid. The resultant fibers have a smooth surface morphology and good structural uniformity. The diameter of the fibers was 2.0±0.25 μm when the DMAc-to-polymer-solution flow rate ratio was set as 0.1. The process technology reported here opens a new window to tune the polymer fibers obtained by the electrospinning, and is useful for improving productivity of the electrospinning process. [ABSTRACT FROM AUTHOR]

We present comparative results of tests on commercial and experimental platinum/palladium spinnerets in forming polyacrylonitrile filament yarn of 50 tex. The experimental spinnerets were made with holes of high precision diameter (0.08 ± 0.001 mm). The spinnerets were characterized by their integrated throughput (the flow-through time for distilled water) while the filament yarns were characterized by their linear density. We demonstrate a correlation between the filament linear density and the flow-through time. In this case, the criteria for uniformity of the filament with respect to linear density (variance, range, mean-square deviation, coefficient of variation) are statistically significantly smaller for the experimental spinnerets than for the commercial spinnerets. [ABSTRACT FROM AUTHOR]

Abstract: This study has successfully demonstrated that a proper combination of novel spinneret designs and spinning parameters can effectively counteract the die swell as well as flow instability phenomena, i.e. extrudate distortion, in the hyperbranched polyethersulfone (HPES) hollow fiber spinning. Attempts are also made to unravel the die swell and flow behavior differences between HPES and linear polyethersulfone (LPES) membranes spun using various spinneret designs and spinning conditions. In terms of flow stability, it is revealed that short conical spinnerets with a flow angle of 60° as well as short round flow channel spinneret with a flow angle of 30°, can reduce or eliminate extrudate distortions. Apart from spinneret designs, this study also accentuates the importance of a proper choice of spinning conditions for each specific spinneret to achieve flow stability and reduce die swell, namely: (1) bore fluid composition; (2) dope flow rate; (3) spinning temperature; and (4) take-up speed. Experimental results concluded that a proper combination of spinneret design and these four spinning parameters is the key to stabilize the spinning process. It is found that a high take-up speed spinning and a high non-solvent concentration in the bore fluid can fully eliminate die swell and enhance flow stability in the HPES hollow fiber spinning using short and conical or round spinnerets. [ABSTRACT FROM AUTHOR]

Abstract: A method of obtaining membranes with a developed inner wall structure has been worked-out by establishing appropriate spinning conditions. Obtaining a developed surface of membranes without interference into the spinneret structure is feasible. Membranes with a developed inner surface bear higher ultrafiltration than that of membranes of a smooth surface made from the same membrane-forming solution. No essential differences in the molecular weight cut-off values for both types of membranes were observed. The scanning electron microscope images of membranes of developed inner surface were shown. [Copyright &y& Elsevier]

A calculation scheme is proposed which allows establishing the effect of creep on the sag of the spinneret plate in a spinneret feeder and its lifetime. The sag increases and the feeder lifetime decreases with an increase in the stresses arising when the plate is loaded. [ABSTRACT FROM AUTHOR]

Abstract: A defect-free as-spun hollow fiber membrane with an ultra-thin dense-selective layer is the most desirable configuration in gas separation because it may potentially eliminate post-treatments such as silicone rubber costing, simplify membrane manufacture, and reduce production costs. However, the formation of defect-free as-spun hollow fiber membranes with an ultra-thin dense-selective layer is an extremely challenging task because of the complexity of phase inversion process during the hollow fiber fabrication and the trade-off between the formation of an ultra-thin dense-selective layer and the generation of defects. We have for the first time successfully produced defect-free as-spun Torlon® hollow fiber membranes with an ultra-thin dense layer of around 540Å from only a one polymer/one solvent binary system at reasonable take-up speeds of 10–50m/min. The best O2/N2 permselectivity achieved is much higher than the intrinsic value of Torlon® dense films. This is also a pioneering work systematically studying the effects of spinneret dimension and hollow fiber dimension on gas separation performance. Several interesting and important phenomena have been discovered and never been reported: (1) as the spinneret dimension increases, a higher elongation draw ratio is required to produce defect-free hollow fiber membranes; (2) the bigger the spinneret dimension, the higher the selectivity; (3) the bigger the spinneret dimension, the thinner the dense-selective layer. Mechanisms to explain the above observation have been elaborated. The keys to produce hollow fiber with enhanced permselectivity are to (1) remove die swell effects, (2) achieve finer monodisperse interstitial chain space at the dense-selective layer by an optimal draw ratio, and (3) control membrane formation by varying spinneret dimension. [Copyright &y& Elsevier]

In this communication, we demonstrate that the electrospinning process with a side-by-side dual spinneret can be a simple approach for fabricating bicomponent TiO2/SnO2nanofibers with controllable heterojunctions. Specifically, both of the TiO2and SnO2components in the nanofibers are fully exposed to the surface. This morphology fully utilized the photogenerated holes and electrons during the photocatalytic process, thus leading to a high photocatalytic activity. We believe that this versatile approach can be extended to fabricate other novel high-efficiency bicomponent photocatalysts. [ABSTRACT FROM AUTHOR]

Abstract: Silkworms have been developed over thousands years to optimize folding and crystallization of fibroin under highly controlled conditions which have resulted in their efficient fiber formation. In this paper, we reconstructed the three-dimensional architecture of the spinneret of a wild silkworm Samia cynthia ricini from approximately 1000 optical micrographs of the semi-thin cross sections. The chitin plates and muscles were observed in the silk press part together with large change in the diameter of the spinneret lumen at the press part by large shear stress. This is similar to the case of the spinneret of Bombyx mori silkworm, indicating that the structural change in the silk fibroin of S.c. ricini silkworm occurs exclusively at the silk press part due to large shear stresses. Molecular dynamics (MD) calculations were then performed to study the structural change that occurs in the crystalline region of S.c. ricini silk fibroin under shear stress. Namely, using the peptide AGGAGG(A)12GGAGAG as a model of the crystalline part of the silk fibroin under different shear stresses in the presence of water molecules and followed by molecular mechanics (MM) calculation after removal of water molecules. The simulation indicates that the Ala residues in the model peptides adopt a predominantly β-sheet structure under shear stresses of above 1.0GPa. [Copyright &y& Elsevier]

The scientific principles of direct dissolution of cellulose in the NMMO—water system demonstrate the major possibility of obtaining concentrated spinning solutions and spinning hydrated cellulose fibres from them. The specific features of the properties of NMMO (high boiling point and insufficient thermal stability) that dissolves the NMMO—water system (narrow concentration range, optimum for dissolution of cellulose) makes it necessary to recycle the washing water by evaporating it, which causes high power consumption for this process. It is expedient to examine the possibilities of membrane technologies, including electrodialysis, for solving problems of recycling the solvent and cutting power consumption. However, this path only allows partially concentrating used washing water, since there is the danger of crystallization of NMMO di-and monohydrate. Spinning through an air gap from highly viscous solutions with long relaxation times at high spinneret draw ratios results in highly oriented fibres with high tensile rigidity (high deformation modulus). Fabrication of fibres whose properties correspond to ordinary viscose fibres will perhaps require “going away” from highly viscous solutions to a lower concentration and spinning by the ordinary wet method, but the volume of solvent used increases significantly, recycling it is more difficult, and power consumption increases. For the same reason of high orientation, the fibres exhibit important fibrillation when wet, and a “peach skin” effect is formed in the finished textiles. To reduce fibrillation, special treatments of the fabrics must be used, biofinishing, for example. During use of the articles, fibrillation can reappear, in laundering, for example. The technology for fabricating fibres of the Lyocell type requires solving many problems. Developing research on selecting alternative solvents and dissolving systems for direct dissolution of cellulose to obtain concentrated spinning solutions is simultaneously useful. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate that melt electrospinning can be a feasible way to produce sub-micron scale polylactic acid (PLA) fibers in this paper. This solvent-free approach to produce sub-micron scale fibers is more environmentally benign than common solution electrospinning processes, and has a potential to increase the production rate significantly. Our experimental results show that temperatures at the spinneret and in the spinning region are critical to produce sub-micron sized fibers: a high-speed photographic investigation reveals that when spinning temperature is below glass transition temperature, whipping of the jet is suppressed by fast solidification in the spinning region, leading to a larger jet diameter. Both thermal and mechanical degradations of PLA in melt electrospinning can be significant but no change in chemical composition is found. Due to rapid solidification, melt electrospun PLA fibers are mostly amorphous, and the small presence of β crystals is noted in the sub-micron scale PLA fibers by XRD studies. The highly oriented structure of PLA fibers gives rise to cold crystallization at around 95°C, and the degree of crystallinity of fibers increases with increasing the degree of annealing. Finally, PLA nanofibers have directly been electrospun onto cellulose filter media, and a drastic enhancement in collection efficiency of sub-micron sized dust particles is presented. Melt electrospun PLA nanofiber mats with no residual solvent may serve as better filter media and tissue scaffolds than those obtained from solution electrospinning processes. [Copyright &y& Elsevier]

Heat treatment processes for some tools (knitting needles, travelers for thimbles of spinning and doubling frames, thread-forming spinnerets) used for the production of cloths, hosiery, and other articles) in the knitting and textile industries are considered. Problems of the choice of steel and the kind and parameters of heat treatment are discussed in connection with the special features of tool design and operating conditions. [ABSTRACT FROM AUTHOR]

We have developed almost defect-free Matrimid/polyethersulfone (PES) dual-layer hollow fibers with an ultra-thin outer layer of about 10 × 10-6 m (10 μm), studied the effects of spinneret and coagulant temperatures and dope flow rates on membrane morphology and separation performance, and highlighted the process similarities and differences between single-layer and dual-layer hollow fiber fabrications. The compositions of the outer and inner layer dopes were 26.2/58.8/15.0 (in wt.%) Matrimid/NMP/methanol and 36/51.2/12.8 (in wt.%) PES/NMP/ethanol, respectively. It is found that 25 °C for both spinneret and coagulant is a better condition, and the fibers thus spun exhibit an O2/N2 selectivity of 6.26 which is within the 87% of the intrinsic value and a calculated apparent dense-layer thickness of about 2886 × 10-10 m (2886 Å). These dual-layer membranes also have impressive CO2/CH4 selectivity of around 40 in mixed gas tests. The scanning electron microscopy (SEM) studies show that low coagulant temperatures produce dual-layer hollow fibers with an overall thicker thickness and tighter interfacial structure which may result in a higher substructure resistance and decrease the permeance and selectivity simultaneously. The elemental analysis of the interface skins confirms that a faster inter-layer diffusion occurs when the fibers are spun at higher spinneret temperatures. Experimental results also reveal that the separation performance of dual-layer hollow fiber membranes is extremely sensitive to the outer layer dope flow rate, and the inner layer dope flow rate also has some influence. SEM pictures indicate that the macrovoid formation in dual-layer asymmetric hollow fiber membranes is quite similar to that in single-layer ones. It appears that macrovoids observed in this study likely start from local stress imbalance and weak points. [Copyright &y& Elsevier]

Lead magnesium niobate–lead titanate (PMN–PT) ceramic fibres with the nominal composition of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 were synthesised using PMN–PT single crystal powder and poly(acrylic acid). The fibres were extruded directly by pressing the mixture through a spinneret. The fibres were well crystallised after sintering at 1250 °C and the final diameter was around 300 μm. The microstructural properties of the fibres were investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrical characteristics of the fibre were determined by measuring the hysteresis D–E loop, relative permittivity and impedance spectrum. The measured results showed that this method can be used to fabricate PMN–PT fibres with good performance. [Copyright &y& Elsevier]

To obtain stable spinning of glass and basalt fibres, it is necessary to significantly increase the angle of wetting of the bottom of the spinneret feeder by the spinning melt at the time the fibre is loaded. To increase the angle of wetting in loading the fibre, more intensive cooling in the zone under the spinneret can be used. [ABSTRACT FROM AUTHOR]

The effect of spinneret size and place on diameter and tensile property of cellulose acetate fibers is studied, and a criterion for the maximal breaking energy is obtained, and the spinneret distribution can be optimized for each spinning condition [ABSTRACT FROM AUTHOR]

Abstract: A novel approach to needleless electrospinning of nanofibers has been developed to increase the productivity of nanofibers. Multiple jets were observed to form on the edges of the stepped pyramid-shaped spinneret simultaneously. Compared with the traditional needle based electrospinning, nanofibers produced by the stepped pyramid-shaped spinneret were finer and an enhancement of more than 100 times over the traditionally obtained nanofibers productivity was obtained. The finite element analysis of electric field revealed a strong electric field gradient around the edges of the spinneret. The effect of applied voltage on nanofiber diameter and productivity were also explored. This novel design instrument avoids the possibility of clogging and will benefit to the development of needleless electrospinning. [Copyright &y& Elsevier]

By modeling the movement of viscose rayon through a spinneret by the finite element method, we establish the dependence of the filament quality on the stability of a number of factors. We demonstrate the relationship of the boundary temperature gradients and the shape of the heat flux distribution in the solution. The mathematical model developed allows us to use the identified relationships in synthesis of control systems. [ABSTRACT FROM AUTHOR]

Experimental data supporting the feasibility of application of Poiseuille equation for determining the dimensions of the inner spinneret channel and the height of the hydrostatic melt column above the spinneret plate are reported. These data can be used to develop a method for calculating the strength and rigidity of the key components of the spinneret feeders. [ABSTRACT FROM AUTHOR]

In the usual forcespinning (FS) process, a meso-scale fluid jet is forced through an orifice of a rotating spinneret, where the ambient fluid is air. This leads to the formation of a jet with a curved centerline. In this study we make use of a phenomenological viscosity model, which, in particular, takes into account both extension thinning and thickening of the polymeric jet, to investigate the properties of polymeric fiber jets during FS process. We consider the governing modeling systems for such rotating jets and calculate numerically the expressions for the nonlinear steady solutions for the jet quantities such as radius, speed, stretching rate, strain rate and trajectory versus arc length. We determine these quantities for different values of the parameters that represent effects due to rotation, viscosity and relaxation times for shear and extension. We also carry out experimental investigation for several types of polymeric fluid jets during FS process that provide general agreement with the present theoretical results. [ABSTRACT FROM AUTHOR]

A needleless electrospinning setup named ‘Needleless Twisted Wire Electrospinning’ was developed. The polymer solution is electrospun from the surface of a twisted wire set to a high voltage and collected on a cylindrical collector around the wire. Multiple Taylor cones are simultaneously self-formed on the downward flowing solution. The system is robust and simple with no moving parts aside from the syringe pump used to transport the solution to the top of the wire. The structure and process parameters of the setup and the results on the preparation of polyvinyl pyrrolidone (PVP), hydroxyapatite (HA) and bioglass fibers with the setup are presented. PVP fiber sheets with areas of 40 × 120 cm2 and masses up to 1.15 g were prepared. High production rates of 5.23 g h−1 and 1.40 g h−1 were achieved for PVP and HA respectively. The major limiting factor of the setup is drying of the polymer solution on the wire during the electrospinning process which will eventually force to interrupt the process for cleaning of the wire. Possible solutions to this problem and other ways to develop the setup are discussed. The presented system provides a simple way to increase the production rate and area of fiber sheet as compared with the conventional needle electrospinning. [ABSTRACT FROM AUTHOR]