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.     

Formation of melt and solution spun polycaprolactone fibers by centrifugal spinning

Nano‐ and microfibers have a myriad of applications ranging from filtration, composites, energy harvesting, to tissue engineering and drug delivery. Electrospinning, the most common method to produce such fibers, has many limitations including low fiber output and solvent dependency. Centrifugal spinning is a new technique that uses centrifugal forces to form nano‐ and microfibers both from solution and the melt. In this work, the effect of melt temperature, collector distance, rotation speed, and concentration (for polymer solutions) of polycaprolactone were evaluated with respect to fiber morphology, diameter, alignment, and crystallinity. The fiber diameter generally decreased with increasing rotation speed and reduced concentration. Crystallinity for spun fibers decreased compared to the bulk polymer. Fiber alignment was improved with rotation speed for the melt‐spun fibers. The fiber mats were evaluated as tissue scaffolds with neuronal PC12 cells. The cells adhered and extended neurites along the fibers for both melt and solution‐spun scaffolds. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41269.     

Poly(lactic acid) fibers obtained by solution blow spinning: Effect of a greener solvent on the fiber diameter

Poly(lactic acid) (PLA) fibers has been obtained by solution blow spinning (SBS) using different solvents, however most of them are toxic and can be dangerous to human health or cause harm to the environment. Therefore, this work aimed to evaluate the use of dimethyl carbonate (DMC), a greener solvent, on the production of PLA fibers by SBS using surface response analysis to evaluate and compare the influence of three solvents (chloroform, DMC, and 1,1,1,3,3,3‐hexafluoro‐2‐propanol, HFP) in the average fiber diameter. Scanning electron microscopy (SEM) was used to analyze the fiber morphology and different ranges of fiber diameter was observed when varying the solvents (chloroform: 260–970 nm; DMC: 240–650 nm; and HFP: 220–470 nm). Regression analysis showed the polymer concentration was significant for all solvents and the air pressure was significant when using chloroform and HFP. Regardless of the air pressure, increasing the PLA concentration increased the average fiber diameters for all solvents. Chloroform and HFP indicated a tendency of reduction on the average fiber diameter when the air pressure was decreased, however this behavior was not observed for DMC. It was also observed that the standard deviation indicated to be more affected by the polymer concentration than by the air pressure. The results also indicated that lower surface tension and viscosity can reduce fiber thickness. All solvents showed to be feasible to produce PLA fibers by SBS and DMC can be used to produce PLA fibers with an affordable price using a greener process. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43379.     

Poly(vinyl pyrrolidone) sub-microfibers produced by solution blow spinning

In this study, poly(vinyl pyrrolidone) (PVP) polymeric fibers were obtained by the solution blow-spinning (SBS) technique using PVP of low molecular weight. The fabrication of nano-microfibers of polymers with low molecular weights by using the SBS or electrospinning (ES) techniques is not common. Most theoretical studies suggest that only high-molecular-weight polymers can be produced because of their rheological properties. The influence of solution parameters (concentration, solvent volatility, and viscosity) and processing parameters (injection rate, collector rotation, gas pressure, and needle size protuberance) on the formation, morphology, and physical properties of the PVP fibers was investigated using the images obtained by scanning electron microscopy (SEM), thermal analysis (DSC/TG), x-ray diffraction (XRD) patterns, and Fourier-transform infrared spectroscopy (FTIR) spectra. The results showed no significate changes in the polymer properties because of fiber processing. Additionally, the fiber diameter frequency distribution was analyzed for each condition studied, and the behaviors of the fiber diameters with higher occurrences were evaluated as a function of the variables in the study, revealing that there is no simple relationship between the fiber diameter and processing conditions.     

Air permeability of electrospun polyacrylonitrile nanoweb

Ultrafine fibers were spun from polyacrylonitrile (PAN) solution in N,N‐dimethylformamide using a homemade electrospinning setup. Fibers with diameter ranging from 80 to 340 nm were obtained. Fiber size and fiber size distribution were investigated for various concentration, applied voltage, and tip‐to‐collector distance using image analysis. The diameters of the electrospun fibers increase when increasing the solution concentration and decrease slightly when increasing the voltage and needle tip‐to‐collector distance. Porosity and air permeability are vital properties in applications of electrospun nanofibrous structures. In this study, effects of process parameters on the porosity and air permeability of electrospun nanoweb were investigated as well. Results of statistical analysis showed that solution concentration and applied voltage have significant influences on pore diameters. It was concluded that nanofiber diameter played an important role on the diameter of pores formed by the intersections of nanofibers. A more realistic understanding of porosity was obtained and a quantitative relationship between nanoweb parameters and its air permeability was established by regression analysis. Two separate models were constructed for predicting air permeability in relation to process parameters. Optimization of electrospinning process for producing nanoweb with desirable air permeability is well achieved by these models. The models presented in this study are of high importance for their ability to predict the air permeability of PAN nanoweb both by process or structure parameters. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Effect of solution concentration in microfiltration properties of PLA mats produced by solution blow spinning

In order to remediate the difficulty of access to safe drinking water by 1/3 of the world population, mats produced by solution blow spinning (SBS) have a great potential for use in liquid filtration due to their small pores and high porosity, being capable of filtrating water by retaining particles and even microorganisms. In this context, this work aims the production and characterization of poly (lactic acid) mat obtained by SBS to be morphologically, thermally, and mechanically evaluated, as well as to observe water flux properties. The correlation between structure-processing-properties is an important part of the work, which shows that lower concentration of polymeric solution leads to mats with smaller average fiber diameter, greater crystallinity, impacting on their greater tensile strength. The water flux performance shows that mats obtained from higher polymer concentration solutions present less resistance to the water flow, which indicates larger pore diameters.     

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     

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     

Generation of nanofibers via electrostatic‐Induction‐assisted solution blow spinning

Increasing attention has been given to nanofiber fabrication techniques. Solution blow spinning (SBS) is an innovative, simple, and effective method for producing nanofibers, and it only uses the drawing force of high‐velocity airflow. However, solution‐blown nanofibers easily form bundles; this results in an uneven distribution of nanofibers and an inhomogeneity of nanofiber mats. In this study, electrostatic‐induction‐assisted solution blow spinning (EISBS) was established by the introduction of an additional electrostatic field with an induction circle electrode into the SBS system. The effects of the electrostatic force on the fiber configuration and structure were examined. The results indicate that the electrostatic field effectively separated the fibers. Response surface methodology, based on the four‐factor, three‐level Box–Behnken design, was used to facilitate a more systematic understanding of the processing parameters of EISBS. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42326.     

Electrospinning of methacrylate‐based copolymers: Effects of solution concentration and applied electrical potential on morphological appearance of as‐spun fibers

Three methacrylate‐based copolymers [i.e., poly(methacrylic acid‐co‐methyl methacrylate), poly(ethyl acrylate‐co‐methyl methacrylate‐co‐trimethyl‐ammonioethyl methacrylate chloride), and poly(butyl methacrylate–co‐(2‐dimethylaminoethyl) methacrylate‐co‐methyl methacrylate)] were successfully electrospun into fibers using ethanol as the solvent. For a given applied electrical potential, increasing the concentration of the spinning solutions caused the morphology of the as‐spun products to change from discrete droplets to a combination of beaded and smooth fibers and finally to completely smooth fibers. For a given spinning solution having a low concentration, increasing the applied electrical potential increased the electro‐spinnability of the spinning solution. The average diameters for all of the as‐spun fibers were found to range between about 0.2 and 5.5 μm. Generally, for a given applied potential, the average fiber diameter increased with increasing concentration of the spinning solutions, and for a given solution concentration the average fiber diameter increased with increasing applied electrical potential. POLYM. ENG. SCI., 45:1073–1080, 2005. © 2005 Society of Plastics Engineers     

Processing,structure, and properties of gel spun PAN and PAN/CNT fibers and gel spun PAN based carbon fibers

Polyacrylonitrile (PAN) and PAN/carbon nanotube (PAN/CNT) fibers were manufactured through dry‐jet wet spinning and gel spinning. Fiber coagulation occurred in a solvent‐free or solvent/nonsolvent coagulation bath mixture with temperatures ranging from ?50 to 25°C. The effect of fiber processing conditions was studied to understand their effect on the as‐spun fiber cross‐sectional shape, as well as the as‐spun fiber morphology. Increased coagulation bath temperature and a higher concentration of solvent in the coagulation bath medium resulted in more circular fibers and smoother fiber surface. as‐spun fibers were then drawn to investigate the relationship between as‐spun fiber processing conditions and the drawn precursor fiber structure and mechanical properties. PAN precursor fiber tows were then stabilized and carbonized in a continuous process for the manufacture of PAN based carbon fibers. Carbon fibers with tensile strengths as high as 5.8 GPa and tensile modulus as high as 375 GPa were produced. The highest strength PAN based carbon fibers were manufactured from as‐spun fibers with an irregular cross‐sectional shape produced using a ?50°C methanol coagulation bath, and exhibited a 61% increase in carbon fiber tensile strength as compared to the carbon fibers manufactured with a circular cross‐section. POLYM. ENG. SCI., 55:2603–2614, 2015. © 2015 Society of Plastics Engineers     

Effects of different coagulation conditions on polyacrylonitrile fibers wet spun in a system of dimethylsulphoxide and water

Polyacrylonitrile (PAN) precursors were prepared by the wet spinning way. The effects of the coagulation conditions, such as coagulation temperature, coagulation ratio, and coagulation concentration, are discussed in detail. While keeping the coagulation bath concentration constant, as the coagulation bath temperature increased, the cross section deviated less from a circular form, and the as‐spun fiber diameter decreased. Measurement to the rate of the boundary movement has been calculated depending on the coagulation rate. While keeping the coagulation bath temperature constant, high coagulation bath concentration can cause more coagulant to diffuse into the solution to the polymer precipitated consequently, which led to a faster coagulation rate. The as‐spun fiber from high coagulation concentration was compacted than those from low concentration. The character of the formed structure reflected the system mobility and capability to crystallize. Improvement in fiber density in the as‐spun fiber resulted in improvements in the tensile strength of the as‐spun fiber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3723–3729, 2007     

Predicting poly(vinyl pyrrolidone)'s solubility parameter and systematic investigation of the parameters of electrospinning with response surface methodology

The solubility parameters were used to choose the solvent for poly(vinyl pyrrolidone) (PVP) in electrospinning. In this study, a novel method for predicting the contribution value of the pyrrolidone group (a typical part of the PVP molecular structure) was proposed. The solubility parameters of PVP were calculated by this method, and accordingly, ethanol was chosen as the solvent for PVP. What is more, response surface methodology was used to facilitate a systematic investigation on the influence of the PVP solution concentration, feed rate, distance between the tip and collector, and operating voltage on the fiber diameter and morphology in electrospinning. The predicted fiber diameters by the response regression model, and the experimental values were in close proximity. The solution concentration and feed rate both had significant effects on the PVP fiber diameter, and there was some interaction between the solution concentration and the feed rate in this system. In addition, this study provided a train of thought for the electrospinning of polymer fibers with controllable and predictable fiber diameters. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40304.     

Gel‐spun polyacrylonitrile fiber from pregelled spinning solution

Polyacrylonitrile (PAN) fibers have been gel spun from pregelled PAN spinning solution. The pregelled solution had network structure with elevated spinnability, the as‐spun fiber from which had more circular cross‐section and reduced skin‐core difference. Drawing was more effective in inducing the segmental orientation and crystallization in gel‐spun fiber than in dry–wet spun fiber. The mechanical properties of the gel‐spun fiber were better than those of the dry–wet spun fiber after multi‐stage drawing. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Wettability behavior of solution blow spun polysulfone by controlling morphology

Solution blow spinning (SBS) is used to prepare polysulfone materials (PSf) with different morphologies changing the processing conditions. Morphological study is done by scanning electron microscopy. Materials mainly constituted by beads and fibers are obtained. An optimization strategy based on desirability function approach together with Box–Behnken design is employed to find the best processing conditions to produce PSf materials with tailored morphology. Feed rate and air pressure are the variables of SBS processing conditions with the highest influence on the relative amount of fibers produced while air pressure and a particular balance between work distance and feed rate have the highest impact on the size of fibers. Contact angle measurements are used to understand SBS PSf wettability as a function of morphology. It is demonstrated the possibility of designing PSf materials with particular wettability behavior induced by tailored morphologies obtained from a particular election of SBS processing conditions.     

Impact of electrospinning process parameters on the measured current and fiber diameter

In this article, polycaprolactone (PCL) nanofibres were processed by electrospinning using a 3:1 ratio of tetrahydrofuran to methanol as solvent. The solvent choice was motivated by the possibility of greener alternatives to the halogenated compounds most often used for electrospinning. The morphologies and fiber diameters resulting from the electrospinning of PCL solutions at room temperature under various conditions are presented in this article. The material morphology was characterized using scanning electron microscopy and a measuring software. The process was optimized for smaller fibers with a narrower fiber diameter distribution by studying parameters such as polymer concentration, applied voltage, the tip to collector distance (TCD), and the solution flow rate. A comparison analysis was used to separate the current resulting from whipping and that resulting from spraying at high voltage. The fiber diameters obtained under various processing conditions were effectively modeled using the terminal jet theory, referenced in several works. Process parameters were optimal for a 20% PCL concentration spun at a flow rate of 0.5 mL/h, with a TCD of 15 cm and an applied voltage of 8 kV. Fibers spun under these conditions displayed diameters of 546 ± 173 nm. POLYM. ENG. SCI., 55:2576–2582, 2015. © 2015 Society of Plastics Engineers     

Ultra-high-modulus fibers from solution spinning

Ultra-high-modulus fibers such as Du Pont PRD-49 (initial modulus up to ～1000 g/den) and Monsanto X-500 (initial modulus up to ～600 g/den) are spun from solutions. Both polymers are characterized by a high intrinsic rigidity of individual molecular chains and considerable orientation along the fiber axis. The thermodynamics of solution for rigid and semirigid macromolecules is critically reviewed in order to illustrate conditions under which spontaneous formation of highly oriented fibers is expected. In the case of semirigid polymers, the free energy of (random) mixing pure solvent and parallellized polymer may, according to Flory, become positive for some critical value of a “flexibility parameter.” Formation of an ordered phase for semirigid polymers is not, however, observed by lowering temperature or increasing polymer concentration. In the case of rod-like polymers, still according to Flory, at some critical value of polymer concentration (which decreases with the axial ratio of the macromolecule) the isotropic solution of rods undergoes phase separation with formation of a partly ordered solution. This theoretical prediction is satisfactorily verified by data. While Du Pont fibers are spun from this anisotropic solution, Monsanto's X-500 only yields an isotropic solution at room temperature up to the limit of polymer concentration at which crystallization occurs. This inability of X-500 to form anisotropic solutions at the expected critical concentration is attributed to a partial degree of flexibility. Mechanical properties and orientation of fibers spun from the anisotropic solution appear to be superior to those obtained by spinning from isotropic solution, according to Du Pont's results. When a polymer has a partial degree of flexibility, alteration of physico-chemical variables such as solvent type, solvent composition, temperature, and polymer concentration may still be used in order to increase its rigidity. Theoretical arguments and data supporting this contention are discussed. Moreover, alteration of these variables may also be used to alter the crystallization temperature, allowing formation of the anisotropic solution to occur at a high enough polymer concentration. This expectation was verified in the case of X-500. Finally, the all important role of mechanical orientation of solutions is emphasized. According to Hermans, under high enough shear stress, the difference between the isotropic and the anisotropic solution vanishes. In line with these consideration, drawing techniques are particularly useful in order to achieve almost-perfect orientation and theoretical moduli.     

Factorial optimization of the effects of melt‐spinning conditions on biodegradable as‐spun aliphatic–aromatic copolyester fibers. III. Diameter,tensile properties,and thermal shrinkage

To model the melt‐spinning process of biodegradable as‐spun linear aliphatic–aromatic copolyester fibers, a fraction factorial experimental design and appropriate statistical analysis for the 32 screening trials involving five control parameters were used. Because of their central role in the production processes and end use textiles, it is important to simulate the mechanical and thermal shrinkage properties of AAC fibers. Concise statistical models of fiber behavior are based on factorial experimental design data. Process's data are collected, analyzed, and mathematical models created to predict the diameter, tenacity, elongation at break, modulus, and thermal shrinkage of the spun fiber in terms of random variables and their associated probability distributions. The theoretical regression models obtained form the main source code in the enhanced forecasting program, which presents the melt‐spinning process of aromatic–aliphatic copolyester fibers. Factorial statistical approaches, based on over indicated region levels of melt‐spinning process parameters, are given in terms of assumptions and theory to produce biodegradable, environmentally friendly fibers for different applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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。