Final Fiber Diameter Research Articles

Pilot-Scale Melt Electrospinning of Polybutylene Succinate Fiber Mats for a Biobased and Biodegradable Face Mask

The COVID-19 pandemic led to a huge demand for disposable facemasks. Billions were manufactured from nonbiodegradable petroleum-derived polymers, and many were discarded in the environment where they contributed to plastic pollution. There is an urgent need for biobased and biodegradable facemasks to avoid environmental harm during future disease outbreaks. Melt electrospinning is a promising alternative technique for the manufacturing of filter layers using sub-microfibers prepared from biobased raw materials such as polybutylene succinate (PBS). However, it is not yet possible to produce sub-micrometer PBS fibers or uniform nonwoven-like samples at the pilot scale, which hinders their investigation as filter layers. Further optimization of pilot-scale PBS melt electrospinning is therefore required. Here, we tested the effect of different parameters such as electric field strength, nozzle-to-collector distance and throughput on the final fiber diameter and sample uniformity during PBS melt electrospinning on a pilot-scale device. We also studied the effect of a climate chamber and an additional infrared heater on the solidification of PBS fibers and their final diameter and uniformity. In addition, a post-processing step, including a hot air stream of 90 °C for 30 s has been studied and successfully lead to a nonwoven-like structure including filaments that weld together without changing their structure. The finest fibers (1.7 µm in diameter) were produced at an applied electric field strength of −40 kV, a nozzle-to-collector distance of 5.5 cm, and a spin pump speed of 2 rpm. Three uniform nonwoven-like samples were tested as filter layers in a medical face mask by measuring their ability to prevent the transfer of bacteria, but the pore size was too large for effective retention. Our results provide insight into the process parameters influencing the suitability of melt-electrospun nonwoven-like samples as biobased and biodegradable filter materials and offer guidance for further process optimization.

The Effect of Electrical Polarity on the Diameter of Biobased Polybutylene Succinate Fibers during Melt Electrospinning.

Melt electrospinning is a simple, versatile, and widely used technique for the production of microfibers and sub-microfibers. Polybutylene succinate (PBS) is a promising raw material for the preparation of melt-electrospun fibers at the laboratory scale. The inclusion of additives in the PBS melt can reduce the final fiber diameter, but economically feasible larger-scale processes remain challenging. The fiber diameter can also be reduced by machine optimization, although this is expensive due to the complexity of melt-electrospinning devices. Changes in electrical field polarity have provided a low-cost strategy to reduce the diameter of fibers produced by solution-electrospinning, but there is little information about the effect of this parameter on the final diameter of melt-electrospun fibers. We therefore determined the effect of field polarity on the diameter of melt-electrospun PBS fibers at the laboratory scale and investigated the transferability of these results to our 600-nozzle pilot-scale device. Changing the polarity achieved a significant reduction in fiber diameter of ~50% at the laboratory scale and ~30% at the pilot scale, resulting in a minimum average fiber diameter of 10.88 µm. Although the effect of field polarity on fiber diameter was similar at both scales, the fibers in the web stuck together at the laboratory scale but not at the pilot scale. We have developed an inexpensive method to reduce the diameter of melt-electrospun PBS fibers and our data provide insight into the transferability of melt electrospinning from the laboratory to a pilot-scale machine.

Airflow, Fiber Dynamic Whipping, and Final Fiber Diameter in Flush Sharp-Die Melt Blowing with Different Air-Slot Widths

Melt streams were attenuated into microfibers by high-speed airflow during melt blowing. The present work explored the effect of air-slot width on the fiber diameter and diameter evenness in flush sharp-die melt blowing. The airflow in different die melt blowing was first numerically simulated by the CFD approach. Then, the fiber dynamic whipping was captured by high-speed photography. Finally, a spinning experiment was implemented and the fiber diameters were measured. The result reveals that the sharp die with a larger air-slot width produces fibers with a larger diameter, but the uniformity is obviously better. This study reveals that the air flow, fiber whipping, and final fiber diameter are closely related to each other. The quality control of melt-blown fiber can be carried out by controlling the fiber whipping motion.

The Role of Polymer Carrier and Process Parameters for Small Molecule Drug Delivery via Blended Electrospinning

Delivery of therapeutic compounds to the diseased area in the body with minimized adverse effects is the underlying objective behind development of advanced drug delivery systems. Providing disease-specific release patterns is the ultimate goal of any drug delivery system. Electrospinning has been widely used for nanofiber fabrication. Having high aspect ratio and similarity to the extracellular matrix in the body make electrospun nanofibers a great candidate to be used as drug delivery implants. In this study, we report electrospinning to be a tunable technique capable of providing engineered, disease-specific drug release patterns. Using “one factor at a time” and “central composite design” techniques, we respectively demonstrate flow rate and applied voltage to be the two most significant parameters (with [Formula: see text]-values of 512.48 and 42.31) affecting the final fiber diameter, and capillary-to-collector distance as the least important one, by evaluating their influence, individually and combined, on the morphology of electrospun Poly (Lactide-co-Glycolide acid) nanofibers. Using the same two techniques, we also show that hydrophobicity of the polymeric fibrous scaffold, measured by water contact angle (WCA) with the [Formula: see text]-value of 376.44, is the main factor to consider when designing an electrospun fibrous drug delivery system for a specific disease, while fiber diameter can further modulate the release pattern of the drug from hydrophobic polymeric nanofibers. We finally support our hypothesis by comparing our findings with analysis of data derived from the literature. Taken together, our findings suggest electrospinning to be a tunable technique capable of providing various release patterns for any small molecular weight drug on the basis of the requirements of the diseases to be treated.

Simulation of polymer jet motion during melt blowing with phase field method

In the past two decades, a number of models have been built to simulate the motion of polymer jet during melt blowing. Unfortunately, the complex interaction between polymer jet and air flow field has been rarely reported. In this work, a phase-field method was applied to simulate the coupling effects between polymer and air flow during melt blowing and the computed results were compared with the results of the model built through level-set method and experimental results. Velocity in the x direction, velocity in the y direction, whipping amplitude and diameter of polymer jet were discussed, respectively. It was found that the velocity predicted by the present model was higher than that predicted by the level-set method. However, both of them are close to the experimental value. The calculated final fiber diameter based on the phase-field method is much closer with the experimental value than that based on the level set method. Based on the model, the effect of polymer surface tension and slot angle on the polymer jet velocity were discussed.

Extension rate and bending behavior of electrospinning jet: The role of solution conductivity

Two model solutions, one containing organic salt and the other none, of poly(N-isopropylacrylamide) (PNIPAM) in DMF solvent with the same concentration of 17 wt% were electrospun to investigate the extension rate profile in the straight jet as well as the subsequent jet bending (whipping) behavior. Both model solutions have identical rheological properties, while the solution with added salt possesses electrical conductivity 16 fold higher than the other. At a given flow rate of Q, light scattering experiments were carried out to derive the jet diameters of the straight segment dj at different jet positions z so that the z-dependence of jet velocity (vj, = 4Q/πdj2) was feasibly calculated, from which the profile of extension rate (ε˙) was obtained by dvj/dz. Using high speed video imaging, the onset of jet bending was observed, and the motion of the first bend was traced, from which the extension rate of the bending jet could be also estimated.Compared to the neat solution, the solution with salt exhibits a bigger Taylor cone and a shorter straight segment with a larger jet-end diameter to proceed the subsequent jet bending process. Moreover, the magnitudes of ε˙ in the straight jet and in the bending jet are all dramatically enhanced with solution conductivity, yielding PNIPAM fibers with a smaller diameter on the grounded collector. Our results show that it is the extension rate developed in the spin line plays an important role in determining the final fiber diameter. The onset of bending instability is attributed to the local buckling in the end section of the straight jet, which is unambiguously observed by video imaging with a high frame rate of 104 fps. The formation of jet buckling is due to the compressive forces associated with the air drag to resist the electric stretching force induced by the setup electric field. The dynamics of bending jet was elucidated in this work.

Effect of viscoelasticity in polymer nanofiber electrospinning: Simulation using FENE-CR model

The uniaxial elongational flow of a polymer solution in the electrospinning process was investigated numerically and experimentally. The numerical model was constructed taking into account the viscoelasticity of the material. Therefore, governing equations were supported by a finite extensible non-linear elastic constitutive model and for the first time a FENE-CR model was used. This version of FENE model allows a good description of the rheology of extensional flows. For validation purposes, experimental studies were conducted using polymeric solutions of polyamide 6 (PA6). The main emphasis was made in determining the final fiber diameter and how initial polymer concentration acts on it. Further, the effect of the different concentration regimes on thinning dynamics was also examined. The comparative results of the numerical and experimental outcomes are sufficient to prove the predictive ability of the simulations. It can also be observed that the numerical approach adopted in this study captures not only the viscoelastic behavior of the material but also solidification of nanofibers due to solvent evaporation. As predictive quantitative models for electrospinning are lacking, this study gives good insights into the simulation of this process.

Wire Melt Electrospinning of Thin Polymeric Fibers via Strong Electrostatic Field Gradients

AbstractHere, a novel melt electrospinning method to produce few‐micron and nanometer thick fibers is presented, in which a polymer‐coated wire with a sharp tip is used as the polymer source. The polymer coating is melted via Joule heating of the source wire and extracted toward the target via electrostatic forces. The high viscosity and low charge density of polymer melts lower their stretchability in melt. The method relies on confining the Taylor cone and reducing initial jet diameter via concentrated electrostatic fields as a means to reduce the diameter of fibers. As a result, the initial jet diameter and the final fiber diameter are reduced by an order of magnitude of three to ten times, respectively, using wire melt electrospinning compared to syringe‐ and edge‐based electrospinning. The fiber diameter melt electrospun via this novel method is 1.0 ± 0.9 µm, considerably thinner than conventional melt electrospinning techniques. The generation of thin fibers are explained in terms of the electrostatic field around the wire tip, as obtained from finite element analysis (FEA), which controls the size and shape of the melt electrospun jet.

Continuous manufacturing of nanofiber yarn with the assistance of suction wind and rotating collection via needleless melt electrospinning

ABSTRACTNanofiber yarn was continuously manufactured by a needleless melt‐electrospinning method. The suction wind speed was the most important factor influencing the final fiber diameter and determining whether the fibers could be gathered into a well‐aligned strand. The twisting process of the yarn was performed by the adjustment of ratio of the speed of the collecting roller to the speed of the rotating disk. The results show that the higher the assisting suction wind speed was, the smaller the fiber diameter was. The smallest average fiber diameter of 440 nm was obtained at a suction wind speed of 30 m/s. Furthermore, the smaller the ratio of the speed of the collecting roller to the speed of the rotating disk was, the larger the twisting angle of the prepared yarn was. The largest twisting angle obtained in this study was 43 ° at the greatest ratio of the speed of the collecting roller to the speed of the rotating disk. The X‐ray diffraction results show that the alignment degree of the nanofiber twisting and the crystallinity increased with increasing twisting angle. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44820.

The effect of nozzle-exit-channel shape on resultant fiber diameter in melt-electrospinning

In recent decades, electrospinning using a molten poly (ε-caprolactone) resin has gained attention for creating fibrous tissue scaffolds. The topography and diameter control of such electrospun microfibers is an important issue for their different applications in tissue engineering. Charge density, initial nozzle-exit-channel cross-sectional area, nozzle to collector distance, viscosity, and processing temperature are the most important input parameters that affect the final electrospun fiber diameters. In this paper we will show that the effect of nozzle-exit-channel shape is as important as the other effective parameters in a resultant fiber diameter. However, to the best of our knowledge, the effect of nozzle-exit-channel shapes on a resultant fiber diameter have not been studied before. Comparing rectangular and circular nozzles with almost the same exit-channel cross-sectional areas in a similar processing condition showed that using a rectangular nozzle resulted in decreasing final fiber diameter up to 50%. Furthermore, the effect of processing temperature on the final fiber topography was investigated.

Analysis of bending region physics in determining electrospun fiber diameter: effect of relative humidity on evaporation and force balance

This paper explores the role of the bending region and relative humidity (RH) in determining the resulting electrospun fiber diameter through a combined experimental and modeling analysis. Analysis of experimental measurements on PEO/water and PVP/alcohol solutions indicates that the bending region is significant in determining the final fiber diameter. A model is developed, to determine the dominant process physics of the bending region, predicting the final fiber diameter to be within 6% of experimental observations. The experimental analysis reveals that stretching in the bending region accounts for 40–60% of the stretching in the electrospinning process and the significant impact that RH has on fiber diameters. Our modeling analysis reveals the role of both evaporation and stretching in the bending region, and how RH influences both the jet length (stretching time) and force balance to determine the final fiber diameter.

Impact of Entanglement Density on Solution Electrospinning: A Phenomenological Model for Fiber Diameter

The rheological properties of poly(N-isopropylacrylamide, PNIPAM) in dimethylformamide solvent were investigated and correlated with solution electrospinnability. The jet diameter was measured by using the light scattering technique during the electrospinning in the straight jet region prior to the jet whipping. The diameter of the straight jet end is independent of the solution concentration (or viscosity within the range of 15–2000 mPa·s). Thus, the final fiber diameter df observed on the grounded collector is dominantly controlled by the jet-whipping process. According to the present PNIPAM solution and other different polymer solutions, df is correlated with the solution concentration ϕ. A master curve is constructed by using the following equation: df/df,e = (ϕ/ϕe)2.5, where df,e is the diameter of the fibers electrospun from the solutions with an entanglement concentration of ϕe, above which the specific viscosity starts to increase with ϕ according to ϕ3.7 or ϕ4.7, depending upon the given polymer/...

Simplified modeling of the electrospinning process from the stable jet region to the unstable region for predicting the final nanofiber diameter

ABSTRACTElectrospinning allows the production of ultrafine nanofibers through the stretching of a charged polymer jet with an external electrostatic field. In this study, we derived a simplified and accurate model relating the processing parameters, including the solution volumetric flow rate (Q), the applied electric field (E), and the polymer concentration, to the final fiber diameter. The model takes into consideration the jet behavior starting at the stable region and moving to the bending instability region. We validated the model experimentally by performing the electrospinning process with a polyacrylonitrile/N,N‐dimethylformamide solution with different ranges of concentrations (8–11 wt %), Qs (900–1320 μL/h), and Es (88,889–113,889 V/m). The final fiber diameter was measured with scanning electron microscopy. The model predicted the fiber diameter with a relative error of less than 10%. Moreover, a 30% increase in Q resulted in a 15% increase in the fiber diameter, whereas a 30% increase in E resulted in a 14% decrease in the fiber diameter. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44112.

Experimental investigation of melt fiberization from a perforated rotor spinning machine

Fiber formation from molten fructose sugar was investigated experimentally on a spinning machine with a hollow perforated rotor. The fiberization process was visualized by a high-speed camera in different operating points obtained by variation of melt temperature and rotor rotational speed. Contours of the forming fibers were found to significantly depend on the rotor rotational speed and melt temperature, approaching involute shape with little statistical variability at sufficiently high Weber and Rossby numbers. After exiting fiberization orifices, melt jets contracted significantly and over a relatively short distance. Surprisingly, final fiber diameter rose with the Weber number due to an increase in Rossby number reducing the degree of fiber longitudinal stretching. Fiber contours were found to be initially smooth, but developing large amplitude transversal instabilities farther downstream up to a point when fiber structure is completely disrupted, creating random and highly complex new flow structures. A structure optimal for fibrous end products may be attained by controlling initial melt superheat and assuring that fibers are cooled below the glass transition temperature.

Scaling analysis for electrospinning.

Electrospinning refers to the process of generating nanofibers from electrified viscous polymeric jets. Though relatively easy to perform, this process is quite complex in its nature, given the large number of parameters that are involved. This study attempts to derive a relation between the final fiber diameter and the major process parameters. Two new dimensionless numbers describing viscous and surface charge repulsion effects are identified from the scaling analysis of governing equation for the motion of a bent jet. Experimental data for a wide range of polymer solutions exhibit a common slope, when expressed in terms of these new dimensionless numbers. This correlation is used to derive a new scaling expression for the final fiber diameter.

Processing and properties of melt spun polylactide-multiwall carbon nanotube fiber composites

This article reports on the fabrication of oriented composite fibers between polylactide (PLA) and multiwall carbon nanotube (MWNT). The fibers were fabricated using a custom-built melt fiber-drawing setup. The influence of processing parameters on the final fiber diameter and on the orientation were characterized and optimized. Composite fibers were fabricated at various MWNT contents. Addition of low amounts of MWNT (0.25–1 wt %) to PLA did not have a significant effect on the diameters of the fibers. Observations of the composite morphology under STEM indicated preferential orientation of the MWNTs along the draw direction of the fibers. Increasing amounts of MWNTs was found to increase crystallization kinetics and content. The crystalline content had a direct and profound implication on the mechanical properties with 0.5-wt % MWNT fibers having the highest crystalline content and also the highest Young's modulus. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 477–484

Fabrication of styrene–acrylonitrile random copolymer nanofiber membranes from N,N-dimethyl formamide by electrospinning

Ultrafine styrene–acrylonitrile random copolymer (SAN) nanofiber-based membranes were produced from N,N-dimethyl formamide solution by electrospinning. The purpose of this study was to find the optimum values of the electrospinning parameters and the influence of major significant parameters on the electrospun fiber morphology and the average fiber diameter ( Davg) and its standard deviation using design of experiment. A backward elimination model for multiple regression analysis was employed to obtain quantitative interactions among selected electrospinning parameters and the final fiber diameter. The dependence of the Davg and morphology on the critical entanglement concentration was also studied. Morphology of the electrospun nanofiber mats were examined by scanning electron microscopy. Davg of electrospun SAN fibers increased considerably with increasing solution concentration. Fibers with diameters ranging from 40 to 650 nm were obtained. Analysis of variance was utilized to identify the statistically significant parameters ( p < 0.05) and error variance.

Electrospinning of Gelatin/PEO Blends: Influence of Process Parameters in the Nanofiber Properties

AbstractSummary: Results of electrospinning of gelatin/PEO blends from aqueous solutions are presented. The effects of applied electric field (15–25 kV), flow rate (0.25–0.75 mL/h) and gelatin concentration in the final fiber diameter were studied. It was observed that the resulting fiber system presented high polydispersity, where fiber diameters ranged from 150 nm to 1.3 µm. In some cases an adequate fibrous system were not obtained. It was observed that the average diameter decreased mainly when the flow rate and gelatin concentration decreased.

Solvent-free fabrication of three dimensionally aligned polycaprolactone microfibers for engineering of anisotropic tissues

Fabrication of aligned microfiber scaffolds is critical in successful engineering of anisotropic tissues such as tendon, ligaments and nerves. Conventionally, aligned microfiber scaffolds are two dimensional and predominantly fabricated by electrospinning which is solvent dependent. In this paper, we report a novel technique, named microfiber melt drawing, to fabricate a bundle of three dimensionally aligned polycaprolactone microfibers without using any organic solvent. This technique is simple yet effective. It has been demonstrated that polycaprolactone microfibers of 10μm fiber diameter can be directly drawn from a 2mm orifice. Orifice diameter, temperature and take-up speed significantly influence the final linear density and fiber diameter of the microfibers. Mechanical test suggests that mechanical properties such as stiffness and breaking force of microfiber bundles can be easily adjusted by the number of fibers. In vitro study shows that these microfibers are able to support the proliferation of human dermal fibroblasts over 7days. In vivo result of Achilles tendon repair in a rabbit model shows that the microfibers were highly infiltrated by tendon tissue as early as in 1month, besides, the repaired tendon have a well-aligned tissue structure under the guidance of aligned microfibers. However whether these three dimensionally aligned microfibers can induce three dimensionally aligned cells remains inconclusive.

Modeling the melt blowing of viscoelastic materials

Several outstanding issues concerning modeling of melt blowing of viscoelastic materials are addressed in this work. Using a slender-jet model for the melt-blown fiber, we probe the effects of rheology by considering Newtonian, upper-convected Maxwell, Phan-Thien and Tanner (PTT), and Giesekus constitutive equations. The effects of a non-uniform shear stress along the fiber length and heat transfer are also addressed. Our results suggest that by combining the slender-jet approach with a Giesekus (or PTT) constitutive equation, useful engineering predictions can be made concerning the final fiber diameter, even when assuming a constant shear stress and neglecting heat transfer. Finally, questions related to linear stability, nonlinear dynamics, and sensitivity are explored. Steady-state fiber profiles are found to be linearly stable, and numerical simulations indicate that the predictions from linear theory can be carried over into the nonlinear regime. Sensitivity analysis reveals that disturbances are likely to become especially amplified at particular frequencies, with elasticity reducing the magnitude of the amplification but broadening the spectrum of frequencies susceptible to large amplification. This suggests an explanation for the narrower fiber diameter distributions that are observed experimentally.