An investigation into the influence of electrospinning parameters on the diameter and alignment of poly(hydroxybutyrate‐co‐hydroxyvalerate) fibers

Electrospinning is an effective technology for the fabrication of ultrafine fibers, which can be the basic component of a tissue engineering scaffold. In tissue engineering, because cells seeded on fibrous scaffolds with varying fiber diameters and morphologies exhibit different responses, it is critical to control these characteristics of electrospun fibers. The diameter and morphology of electrospun fibers can be influenced by many processing parameters (e.g., electrospinning voltage, needle inner diameter, solution feeding rate, rotational speed of the fiber‐collecting cylinder, and working distance) and solution properties (polymer solution concentration and conductivity). In this study, a factorial design approach was used to systematically investigate the degree of influence of each of these parameters on fiber diameter, degree of fiber alignment, and their possible synergetic effects, using a natural biodegradable polymer, poly(hydroxybutyrate‐co‐hydroxyvalerate), for the electrospinning experiments. It was found that the solution concentration invoked the highest main effect on fiber diameter, whereas both rotational speed of the fiber‐collecting cylinder and addition of a conductivity‐enhancing salt could significantly affect the degree of fiber alignment. By carefully controlling the electrospinning parameters and solution properties, fibrous scaffolds of desired characteristics could be made to meet the requirements of different tissue engineering applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Properties of aligned poly(L‐lactic acid) electrospun fibers

Poly(L‐lactic acid) (PLLA)‐aligned fibers with diameters in the nano‐ to micrometer size scale are successfully prepared using the electrospinning technique from two types of solutions, different material parameters and working conditions. The fiber quality is evaluated using scanning electron microscopy (SEM) to judge fiber diameter, diameter uniformity, orientation, and appearance of defects or beads. The smoothest fibers, most uniform in diameter and defect free, were found to be produced from 10% w/v chloroform/dimethylformamide solution using an accelerating voltage from 10–20 kV. Addition of 1.0% multiwalled carbon nanotubes (MWCNT) into the electrospinning solution decreases fiber diameter, improves diameter uniformity, and slightly increases molecular chain alignment. The fibers were cold crystallized at 120°C and compared with their as‐spun counterparts. The influences of the crystalline phase and/or MWCNT addition were examined using fiber shrinkage, temperature‐modulated calorimetry, X‐ray diffraction, and dynamic mechanical analysis. Crystallization increases the glass transition temperature, T_g, slightly, but decreases the overall fiber alignment through shrinkage‐induced buckling of the fibers when heated above T_g. MWCNT addition has little impact on T_g, but significantly increases the orientation of crystallites. MWCNT addition slightly reduces the dynamic modulus, whereas crystallization increases the modulus in both neat‐ and MWCNT‐containing fibers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41779.     

熔体直写电纺聚己内酯纤维有序沉积工艺

目前聚合物熔体电纺技术制备的纤维大多以杂乱无序的无纺布形式存在,限制了电纺技术在组织工程支架以及机器人等需要有序结构领域的应用。本文将熔体电纺技术与三维运动平台相结合,采用自主设计的熔体电纺可控成型实验装置,对聚己内酯（PCL）进行熔体直写静电纺丝,获得了有序纤维。研究了喷头移动速度、接收距离和纺丝电压对熔体直写电纺纤维沉积形貌的影响。结果表明,纤维直径随着喷头移速、接收距离和纺丝电压的增大而减小,其中接收距离的改变对直径的影响最为显著;接收距离的增大虽然有利于纤维的细化,但是距离过大会使纤维沉积的有序性变差;当射流下落速度与喷头移动速度相匹配时,射流才能实现有序沉积;增大接收距离和纺丝电压会引起射流鞭动,需要相应地增大喷头移动速度才能实现有序沉积。     

Preparation and characterization of ultrafine electrospun polyacrylonitrile fibers and their subsequent pyrolysis to carbon fibers

The present contribution reports the fabrication and characterization of ultrafine polyacrylonitrile (PAN) fibers by electrospinning and further development of the as‐spun PAN fibers into ultrafine carbon fibers. The effects of solution conditions (i.e., solution concentration, viscosity, conductivity, and surface tension) and process parameters (i.e., applied electrostatic field strength, emitting electrode polarity, nozzle diameter, and take‐up speed of a rotating‐drum collector) on morphological appearance and average diameter of the as‐spun PAN fibers were investigated by optical scanning (OS) and scanning electron microscopy (SEM). The concentration, and hence the viscosity, of the spinning solutions significantly affected the morphology and diameters of the as‐spun PAN fibers. The applied electrostatic field strength and nozzle diameter slightly affected the diameters of the as‐spun fibers, while the emitting electrode polarity did not show any influence over the morphology and size of the as‐spun fibers. Utilization of the rotating‐drum collector enhanced the alignment of the as‐spun fibers. Within the investigated concentration range, the average diameter of the fibers ranged between 80 and 725 nm. Finally, heat treatment of the as‐spun fibers with their average diameter of about 450 nm was carried out at 230 and 1000 °C, respectively. Various characterization techniques revealed successful conversion into carbon fibers with an average diameter of about 250 nm. Copyright © 2006 Society of Chemical Industry     

Isotactic polypropylene hollow microfibers prepared by CO2 laser‐thinning

An isotactic polypropylene hollow microfiber was continuously produced by using a carbon dioxide (CO₂) laser‐thinning method. To prepare the hollow microfiber continuously, the apparatus used for the thinning of the solid fiber was improved so that the laser can circularly irradiate to the hollow fiber. Original hollow fiber with an outside diameter (OD) of 450 μm and an internal diameter (ID) of 250 μm was spun by using a melt spinning machine with a specially designed spinneret to produce the hollow fiber. An as‐spun hollow fiber was laser‐heated under various conditions, and the OD and the ID decreased with increasing the winding speed. For example, when the hollow microfiber obtained by irradiating the CO₂ laser to the original hollow fiber supplied at 0.30 m min^?1 was wound up at 800 m min^?1, the obtained hollow microfiber had an OD of 6.3 μm and an ID of 2.2 μm. The draw ratio calculated from the supplying and the winding speeds was 2667‐fold. The hollow microfibers obtained under various conditions had the hollowness in the range of 20–30%. The wide‐angle X‐ray diffraction patterns of the hollow microfibers showed the existence of the highly oriented crystallites. Further, the OD and ID decreased, and the hollowness increased by drawing hollow microfiber obtained with the laser‐thinning. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2600–2607, 2006     

Influence of the spinning conditions on the structure and properties of polyamide 12/carbon nanotube composite fibers

The inclusion of nanoparticles in polymer fibers is potentially useful for improving or bringing new properties such as mechanical strength, electrical conductivity, piezoresistivity, and flame retardancy. In this study, composite fibers made of polyamide 12 and multiwall carbon nanotubes were investigated. The fibers were spun via a melt‐spinning process and stretched at different draw ratios. The influence of several spinning factors, including spinning speed, extrusion rate, and draw ratio were investigated and correlated to the structure and properties of the fibers. X‐ray diffraction analyses and mechanical tests indicated that the spinning speed barely affected the structure and mechanical properties of the fibers under tension. The spinning speed, however, is critical for future industrial applications because it determines the possible production rates. By contrast, drawing during spinning or after spinning strongly affected the polymer chain alignment and fiber mechanical properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Recent studies on electrospinning preparation of patterned,core–shell,and aligned scaffolds

Electrospinning is one of the most important ways to prepare continuous, high porosity, large specific surface area, and uniform diameter micro‐ and nanoscale fibers. So, it has been widely used in the preparation of micro/nano‐sized polymer scaffolds for tissue engineering in recent years. In addition to the versatility in material selection and the processing variables, electrospinning also provides a lot of methods to regulate fiber structure and scaffolds morphology. For example, the near‐field electrospinning can provide a method to solve the problem of uncontrollable fiber path; the melt electrospinning eliminates the risk of solvent residue in the construct; the addition of different auxiliary electrodes can make the fiber patterned. This review introduces the underlying principle and characteristics of above electrospinning applied in biomedicine. Herein, we highlight a comprehensive understanding of the technical aspect of this technology for versatile fibers with patterned, core–shell and aligned morphology. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46570.     

Numerical approach to modeling fiber motion during melt blowing

Melt blowing involves applying a jet of hot air to an extruding polymer melt and drawing the polymer stream into microfibers. This study deals with the dynamic modeling of the instabilities and related processes during melt blowing. A bead‐viscoelastic element model for fiber formation simulation in the melt blowing process was proposed. Mixed Euler‐Lagrange approach was adopted to derive the governing equations for modeling the fiber motion as it is being formed below a melt‐blowing die. The three‐dimensional paths of the fiber whipping in the melt blowing process were calculated. Predicted parameters include fiber diameter, fiber temperature, fiber stress, fiber velocity, and the amplitude of fiber whipping. The mathematical model provides a clear understanding on the mechanism of the formation of microfibers during melt blowing. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Nano and submicrometric fibers of poly(D,L‐lactide) obtained by solution blow spinning: Process and solution variables

Nano and submicrometric fibers of poly(D ,L ‐lactide) (PDLLA or PLA) were spun from solutions using a solution blow spinning (SBS) apparatus. Fiber morphology and diameter were investigated by scanning electron microscopy as a function of polymer concentration, feed rate, and air pressure. A more systematic understanding of the SBS process parameters was obtained, and a quantitative relationship between these parameters and average fiber diameter was established by design of experiments and response surface methodology. It was observed that polymer concentration played an important role in fiber diameter, which ranges from 70 to 2000 nm, and its distribution. Lower polymer concentration tended to increase the formation of bead‐on‐string structures, whereas smooth fibers were formed at higher concentrations. Fiber diameter tended to increase with polymer concentration and decrease with feed rate. Based on these results, optimal conditions could be obtained for solution‐blow spun fibers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Structure and properties of partially cyclized polyacrylonitrile‐based carbon fiber—precursor fiber prepared by melt‐spun with ionic liquid as the medium of processing

Carbon fiber has many excellent properties. Currently, the precursor fiber of polyacrylonitrile (PAN)‐based carbon fiber is made from solution by wet or dry spinning process that requires expensive solvents and costly solvent recovery. To solve this problem, we developed a melt‐spun process with ionic liquid as the medium of processing. The melt‐spun precursor fiber exhibited partially cyclized structure. The structure and properties of the melt‐spun PAN precursor fiber were analyzed by combination of scanning electron microscope, Fourier transform infrared spectroscopy, differential scanning calorimetry, X‐ray diffraction, thermogravimetry, ultraviolet spectroscopy, flotation technique, sound velocity orientation test, linear density, and tensile strength tests. The results showed that the tensile strength of melt‐spun PAN precursor fiber was fairly high reached up to 7.0 cN/dtex. The reason was the low imperfect morphology and a cyclized structure formed by in situ chemical reaction during melt‐spun process. Due to the existence of partially cyclized structure in the melt‐spun PAN precursor fiber, exothermic process was mitigated and the heat evolved decreased during thermal stabilization stage in comparison with commercial precursor fibers produced by solution‐spun, which could shorten the residence time of thermal stabilization and reduce the cost of final carbon fiber. POLYM. ENG. SCI., 55:2722–2728, 2015. © 2015 Society of Plastics Engineers     

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

Here, 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.     

Effect of copolymer mixing on elongation property of as‐spun PET fibers

The change of elongation property in the melt spinning process of polyethylene terephthalate (PET) fibers, mixed with small amount of additive copolymer less than 5% by weight, was studied. The additive polymer was synthesized to improve the extensibility of matrix PET in the spinning process. The amount, molecular weight of additive polymer, and spinning conditions were changed to investigate the extensibility of as‐spun fibers. Experimental results show that the blend of copolymer improves the extensibility of as‐spun PET fibers. The elongation at break of as‐spun fibers increases with molecular weight and amount of additive polymer. The additive polymer prevents the fiber orientation and this causes the increase of extensibility of as‐spun fibers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1426–1431, 2006     

Electrospinning functional nanoscale fibers: a perspective for the future

Over the past decade, electrospinning has grown from a small niche process to a widely used fiber formation technique. Applying a strong electric potential on a polymer solution or melt produces nanoscale fibers. These nanofibers form non‐woven textile mats, oriented fibrous bundles and even three‐dimensional structured scaffolds, all with large surface areas and high porosity. Major applications of electrospun membranes include tissue engineering, controlled drug delivery, sensing, separations, filtration, catalysis and nanowires. This perspective article highlights many recent advances in electrospun fibers for functional applications, with an emphasis on the advantages and proposed technologies for these non‐woven fibrous scaffolds. Copyright © 2007 Society of Chemical Industry     

Investigation of a postprocessing method to tailor the mechanical properties of carbon nanotube/polyamide fibers

The incorporation of carbon nanotubes to thermoplastic fibers can potentially improve mechanical, thermal and electrical properties. In this article, a methodology to tailor the mechanical properties of carbon nanotube/nylon fibers is presented. Multiwalled nanotubes (MWNT) were combined to polyamide 12 through melt compounding and twin‐screw extrusion. Pellets containing between 0 and 5.0 wt % MWNT were extruded and subsequently melt spun with a capillary rheometer to produce filaments. To further promote the alignment of the polymer chains and MWNTs, postdrawing parameters were systematically investigated: temperature, drawing speed and elongation. The best improvements in terms of elastic modulus and yield strength were measured at 140°C and 500% elongation, whereas drawing speed was shown to have a negligible effect. It was confirmed through electron microscopy and X‐ray diffraction that these enhancements were mainly induced by the alignment of the polymer chains along the fibers' axis. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4375–4382, 2013     

静电纺工艺参数对聚己内酯纳米纤维直径的影响

用静电纺丝法制备组织工程所需的纳米纤维及材料,在实验中主要研究了基本的工艺参数对所获纤维直径的影响。纤维或非织造膜由两种溶剂系统所制备:氯仿与N,N-二甲基甲酰胺(DMF)的混合剂及含少量(约40μg)嘧啶的乙酸溶液。为了研究聚合物浓度、DMF含量、施加电压、极距、溶剂系统等因素的影响,使用了扫描电子显微镜、溶液黏度仪、溶液电导率测试仪等。结果表明:随着聚合物浓度上升,纤维的直径先增加后减小;随着溶液中DMF含量的增加,纤维直径不断减小;电压对纤维直径无明显的影响;极距需适中,过大过小都会产生珠状纤维;含少量嘧啶(40μg的乙酸溶剂所获得的聚己内酯(PCL)纳米纤维比由氯仿和DMF的混合溶剂所获得的PCL纳米纤维更加细而均匀。     

Solution blow spinning: A new method to produce micro‐ and nanofibers from polymer solutions

A solution blow spinning technique was developed using elements of both electrospinning and melt blowing technologies as an alternative method for making non‐woven webs of micro‐ and nanofibers with diameters comparable with those made by the electrospinning process with the advantage of having a fiber production rate (measured by the polymer injection rate) several times higher. The diameters of fibers produced ranged from 40 nm for poly(lactic acid) to several micrometers for poly(methyl methacrylate). This solution blow spinning method uses a syringe pump to deliver a polymer solution to an apparatus consisting of concentric nozzles whereby the polymer solution is pumped through the inner nozzle while a constant, high velocity gas flow is sustained through the outer nozzle. Analysis of the process showed that pressure difference and shearing at the gas/solution interface jettisoned multiple strands of polymer solution towards a collector. During flight, the solvent component of the strands rapidly evaporates forming a web of micro and nanofibers. The effect of injection rate, gas flow pressure, polymer concentration, working distance, and protrusion distance of the inner nozzle was investigated. Polymer type and concentration had a greater effect on fiber diameter than the other parameters tested. Injection rate, gas flow pressure, and working distance affected fiber production rate and/or fiber morphology. Fibers were easily formed into yarns of micro‐ and nanofibers or non‐woven films that could be applied directly onto biological tissue or collected in sheets on a rotating drum. Indeed, virtually any type of target could be used for fiber collection. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Factorial optimization of the effects of extrusion temperature profile and polymer grade on as‐spun aliphatic–aromatic copolyester fibers. II. Crystallographic order

By using factorial experimental design, a range of crystallographic orders for as‐spun linear aliphatic–aromatic copolyester fibers have been characterized with the aid of wide angle X‐ray diffraction measurements. Full‐Width Half‐Maximum of an X‐ray scattering profile (FWHM) has been quantitatively assessed as responses to polymer grades denoted by melt flow index (MFI) and to extrusion temperature zones in the extrusion equipment used to produce the as‐spun fibers. With the advantages of the factorial experimental design in the development of fiber process technology, the enhanced statistical approach specifies the direction of change of the polymer's melt flow index and extrusion temperature profile for increasing or reducing crystallographic order. The produced as‐spun aliphatic aromatic copolyester fiber is an environmentally‐friendly attractive, alternative to conventional chemical fibers for different applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure and properties of thermotropic liquid crystal polymer and poly(ethylene 2,6‐naphthalate) blend fibers

BACKGROUND: The melt blending of thermotropic liquid crystal polymers (TLCPs) using conventional thermoplastics has attracted much attention due to the improved strength and tensile modulus of the resulting polymer composites. Moreover, because of their low melt viscosity, the addition of small amounts of TLCPs can reduce the melt viscosity of polymer blends, thereby enhancing the processability. RESULTS: In this study, TLCP/poly(ethylene 2,6‐naphthalate) (PEN) blend fibers were prepared by melt blending and melt spinning to improve fiber performance and processability. The relation between the structure and the mechanical properties of TLCP/PEN blend fibers and the effect of annealing on these properties were also investigated. The mechanical properties of the blend fibers were improved by increasing the spinning speed and by adding TLCP. These properties of the blend fibers were also improved by annealing. The tensile strength of TLCP5/PEN spun at a spinning speed of 2.0 km h^?1 and annealed at 235 °C for 2 h was about three times higher than that of TLCP5/PEN spun at a spinning speed of 0.5 km h^?1. The double melting behavior observed in the annealed fibers depended on the annealing temperature and time. CONCLUSION: The improvement of the mechanical properties of the blend fibers with spinning speed, by adding TLCP and by annealing was attributed to an increase in crystallite size, an increase in the degree of crystallinity and an improvement in crystal perfection. The double melting behavior was influenced by the distribution in lamella thickness that occurred because of a melt‐reorganization process during differential scanning calorimetry scans. Copyright © 2007 Society of Chemical Industry     

Process Optimization and Empirical Modeling for Electrospun Poly(D,L‐lactide) Fibers using Response Surface Methodology

Summary: Ultrafine fibers were spun from poly(D ,L ‐lactide) (PDLA) solution using a homemade electrospinning set‐up. Fibers with diameter ranging from 350 to 1 900 nm were obtained. Morphologies of fibers and distribution of fiber diameters were investigated varying concentration and applied voltage by scanning electron microscopy (SEM). Average fiber diameter and distribution were determined from about 100 measurements of the random fibers with an image analyzer (SemAfore 5.0, JEOL). A more systematic understanding of process parameters of the electrospinning was obtained and a quantitative relationship between electrospinning parameters and average fiber diameter was established by response surface methodology (RSM). It was concluded that the concentration of polymer solution played an important role in the diameter of fibers and standard deviation of fiber diameter. Lower concentration tended to facilitate the formation of bead‐on‐string structures. Fiber diameter tended to increase with polymer concentration and decrease with applied voltage. Fibers with lower variation in diameter can be obtained at lower concentration regardless of applied voltage. Fibers with uniform diameter and lower variation in diameter can be obtained at higher concentration and higher applied voltage. Process conditions for electrospinning of PDLA could be chosen according to the model in this study.

Contour plots of average fiber diameter as a function of concentration and applied voltage.     

Structural changes in the melt spinning,cold drawing,and annealing of poly(4‐methylpentene‐1) fibers

Isotactic poly(4‐methylpentene‐1) melt‐spun fibers were investigated. Prior investigators of melt‐spun fibers found that these fibers have a tetragonal unit cell (Form I). We obtained the same unit cell structure in melt‐spun fibers. We found that higher draw‐down‐ratio fibers had d‐spacings closer to the previously cited values of Form I. We also found that cold‐drawn fibers had similar values to those of melt‐spun fibers. However, after these were annealed at 200°C, the unit cell was changed. It is possible that this new unit cell was the orthorhombic form of He and Porter. We also observed the birefringence of these fibers. The values changed after the melt‐spun fibers were cold drawn and annealed. The melt‐spun fiber values reached 0.006. The values for the drawn fibers were as high as 0.007. We suggest that the intrinsic birefringence is about 0.0075. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 130–137, 2005