Process of Electrospinning and Variables - Coursework Example

Name Tutor Course Date Electrospinning Introduction Electrospinning is the process of manufacturing Nano or micro scale fibers from a liquid. Use of electrical charge does electrospinning. The process does not require the conventional environments such as coagulation chemistry neither does it require high temperatures. Thus, electrospinning is a suitable process for the production of fibers of large and complex molecular structure. Electrospinning has become popular than other methods of fabrication of fiber; these include; self-assembly, mechanical drawing, phase separation, and template synthesis (Agarwal et al., 966). Electrospinning has been considered the most versatile hence most valuable and, therefore, the preferred method of polymer production. The attributes that make it preferred are many. The electrospinning process involves the application of a high voltage electric power application into a melt or a solution of polymer liquid. The process results in the extrusion of a stream of the jet stand. The eluting nozzle produces the aircraft and forcefully projected to a ground collector that gets oppositely charged in comparison with the nozzle (Luo, Nangrejo, and Edirisinghe, 1652). Electrospinning is a cognitive operation. In this case, nanofibers polymers with high lengths can be manufactured using a polymer melt (or polymer solution) jet that is driven by electrostatic forces (Pillay, et al. np). Particular working nanostructures including nanowires and nanotubes made by the bare alignment of Nanofibers and electrospun. For the last ten or fewer years, electrospinning process has gained sufficient popularity in the global divide in its application to nanofiber polymer preparation with diameters as little as a few nanometers. The process offers production of nonwovens and Nanofibers with composite structures (Agarwal, Seema, Andreas, and Joachim, Wendorff, 965). Various publications made which cover several topics. Some of these include the governing of polymer formation by variation of operating parameters and materials, amelioration, and developments constructed to spinning devices (Darian, et al., 610-615). Electrospinning is a less complicated and variedly applied method that makes use of electrostatic forces to make fibers of fineness ranging from nanometer diameters to submicron. The method can be utilized to produce a broad variety of architectures of polymer types; natural, no degradable, biodegradable, synthetic. They include the fact that they are affordable, it is easy in comparison to other methods and used in creating fine fibers with much ease than other methods. The uncomplicated step-up production process of developing ultrafine fibers is only easily attainable with electrospinning method and not any other way (Liu, et al., 3). The electric field is used to prevent polymer droplets from adhering to the tip of the capillary due to the effect of the liquid's surface tension. When an electric field gets applied, the electrostatic forces balance the surface tension, and the droplets are stretched to make cones typically referred to as “Taylor comes”. For cases where electric field overcomes surface tension, the Tailor cone ejects a beautiful fiber from the tip. The thread gets set in motion in the atmosphere. Therefore, solvent evaporation is enabled as the deposition of solid fibers happens concurrently on a grounded collector (Agarwal et al., 966). In conventional spinning, the fiber production methods involve the elongation of fibers by subjecting them to aerodynamic, tensile, rheological, inertial or gravitational forces. The electrospinning process utilizes the electric field to develop tensile forces that are directed axially to the polymer jet flow direction, and thus fiber spinning gets attained (Nasri, et al. 127). It got experimentally discovered that, after the jet travel a short distance, stability gets lost. Whipping sets in due to the interaction between the electrostatic field produced by the electric field and the opposing forces resulting from jet surface charges (Zahedi, et al. 4174). The process result is the reduced diameter of fibers and a consequent increase in the length by many-fold In comparison to fiber production by other methods. The overall outcome is the additional reward of electrospun fibers. It makes it more versatile; these advantages include; high porosity, the formation of interlinked porous networks, and a large surface compared to the volume (Agarwal et al., 967). The electrospinning technique got founded in the late 1890s by Rayleigh, and a detailed investigation got done in the early 1900s by Zeleny. The process was patented in the mid-1930s by Formhals after small diameter fabrication of fibers became practical. Kundu and Bherdwaj patented mandrel and other devices that had movable fiber-collectors. However, the fibers could not dry thoroughly because of the reduced distance between the collector and the jet. The distance did not allow enough time for the tissue to dry. The consequence of the incomplete dryness was the sticking of fibers to the collecting surface and other fibers (Senthil, Gibson, and Anandhan, 408). Formhals went on to improve on the drawbacks of his initial apparatus in his second patent. The subsequent patents by Formhals had various aims. The objectives included ameliorating control of fiber lengths, strengthening the fiber achieved by using a rotating funnel to draw threads, and production of composite fibers. It was achievable by the alleviation of spun fibers to the base fibers (Agarwal et al., 967). Researchers have done a lengthy research on the effect of a number of varied variables of processes on the morphology of the electrospun fiber structure and their properties. It has led the researchers coming up with methods to produce small diameter polymeric fibers whose bulk properties and surface characteristics are desirable. The continued research has consequently resulted in the evolvement of the utilization of electrospun nanofibers in more versatile ways. The application in lithium ion batteries as the material for the anode electrode is one use of this process in the electronic field (Agarwal et al., 968). Other materials include magnetic material and excellent conducting fibers, in electrical and optical nanomaterials, and in nano-devices and electronic micro-devices. The ratio of the surface are to volume in electrospun nanofibers has rendered it applicable in it being used as a catalytic substrate (Darian, et al., 610-615). There has been a successful investigation of nanofibrous materials on their possible use as elements of a pollutant (such as benzene and toluene). The use could also get applied to adsorption and water adsorption due to their high adsorption and absorption ability. Another development is the application of electrospun nanofiber membrane use in the prevarication of sensors for; gas detection, anticancer agent drugs and other such drugs, and urea and related chemical substances. Gene delivery, postoperative adhesion prevention, tissue engineering, wound dressing, and drug delivery are some of the areas in which nanofibers have been useful. The use majorly falls in the medical field (Agarwal, et al., 968). The various applications of electrospun nanofibers in tissue engineering include; neutral tissue engineering, bone tissue, ligament and tendon tissue, and contrived vascular graft constructs (Zahedi, et al. 4177). The Process of Electrospinning. This process of electrospinning got developed from electrospraying. It makes use of the same principle of applying an electric potential to a polymer liquid and forcefully projecting the liquid from the tip of the capillary. The projection is majorly in the direction of a collector charged opposite of the capillary tip. If it happens that the liquid polymer has a low viscosity, as the jet accelerates it breaks due to its relatively high surface tension and the product will be polymer droplets instead of polymer fibers. The process got referred to as electrospraying and were useful in the making of aerosols whose sizes are minimal to the extent of submicron range (Agarwal, et al., 969). The electrostatic and pesticide sprayers are a practical application of this technology (Pillay, et al. np). In most cases, liquids under the electric potential have higher viscosity (typically around 200 poise). The likelihood of the jet breaking gets reduced and as a result of increased viscoelastic forces. Such forces would weaken the Rayleigh mechanism of breaking because these forces of viscosity hardly work act opposite to the surface tension forces (Liu, et al., 3). The jet will consequently trace its route to the grounded target as uninterrupted deposits of nanofibers; this entire process amounts to electrons pining. Other than polymer solution and surface tension forces, there are other parameters or processing variables that affect the end product of the procedure and the functionality of the manufactured nanofibers (Nasri, et al. 130). Various processing variables need to get adjusted as much as the electrospinning process may seem technically less complicated and easily manipulated to suit different needs. The variables need to be controlled to avoid the production of beaded morphologies or droplets and produce only fibers. Optimization of the useful variables to attain the sought nanofiber properties and morphology has been an important, challenging factor in the electrospinning process (Agarwal, et al., 975). The various parameters can defined as follows. Effect of Variation in the Applied Voltage. As was observed by Taylor, there is a slight difference between the applied voltage that would destabilize the polymer drop and the applied voltage that will make the polymer drop take the shape of a cone. If the voltage gets increased beyond a value that is considered critical, the polymer jet will be extruded from the cone apex (Agarwal, et al., 979). The critical value is different from different polymer solution. There exist an optimum value of the electric field magnitude also referred to as a voltage with which the nanofiber formation for a given polymer solution is of desired characteristics (Zahedi, et al. 4180). An electric field that is below or above the critical value in strength will result in inhibition of the jet initiation of the polymer or beaded morphologies. An increase in the applied voltage will lead to initially decreased the diameter of the nanofiber and then past a definite point, the diameter increase. The increased applied voltage produced an external field electric strength and magnified repulsion of charges in the jet. It thus results in increased magnitude of jet stretching power, the consequence of this is the initial decreased diameter of the Nanofiber (Neo, et al. 645). At an optimum rate of feed, the polymer length increases with an increase in voltage.According to Baumgarten in his study, the diameter of the nanofiber decreased to the lowest value at first and then increased proportionally. It gets attributed to the rise in the applied voltage at a gap of 50mm between the collector and the capillary (Agarwal, et al., 980). When the difference got increased by 25mm, the diameter of the nanofiber did not decrease to the extent that it reduced when the gap was 50mm. However, the diameter increase as a result of increased voltage was not as significance as when the gap was 50mm. The increase in the applied voltage also made a significant rise in the optimum feed rate of the capillary (Luo, et al. 1655). Solution flow-rate impacts The rate of polymer solution flow via a capillary has a significant impact on the porosity, geometry, and diameter of the nanofiber. Independent studies by Zong and coworkers and Dietzel and colleagues carried out to explain the impression of voltage change (Zahedi, et al. 4182). The amount of drop of polymer decreased within the Taylor cone as the applied voltage got increased. Consequently resulting in the ejection of nanofiber jet from the inside of the capillary and thus the effect of beads set in (Agarwal, et al., 982). Minimizing helps to cover up for the solution loss during the ejection of the Nanofiber jet. Medeski made a demonstration of the increase in diameter and electrospun polystyrene nanofiber pore size, with regards to the increment in the polymer rate of flow. With the rise in the rate of flow, the quantity of the polymer increased. Therefore, it resulted in the growth in diameter of the nanofiber as well as an increase in the size of the pore (Oliveira, et al. 3396) Before collection, increased bead defects were observed because efficient drying of the nanofiber was not well attained when the flow rate of the polymer solution was made too high. Ribbon-shaped and flattened nanofiber morphology can get observed as a consequence of incomplete drying caused by the increased flow rate (Agarwal, et al., 984). The diameter of the nanofiber was proportional to the rate of flow, and the effect of bead defects got reduced with the decrease in the flow rate according to a study conducted by Zong. High flow rates electrospinning resulted in large droplets that caused an increase in the bead diameter. Polymer Concentration and Solution Viscosity impacts. The electrospinning process gets established on stretching of charged jet of the solution uniaxial. The charged jet breaks into distinct droplets way before they are in contact with the collector at lower concentration of the polymer solution. The fragmentation results due to the effect of the surface tension and applied a voltage (Agarwal, et al., 986). The nanofibers get formed under improved entanglement between the chains of polymers when the polymer concentration increase due to the viscosity of the polymer solution. The above explanations show that the concentration of the polymer solution affects both the surface tension and viscosity of the solution. Such are the key parameters in determining the electro spinnability in making nanofibers having prolonged diameters with concentrated polymers (Nasouri, et al. 134). The flow of the polymer solution is however interrupted is an individual limit of viscosity is made extremely high. The formation of nanofiber occurs at optimum concentrations that govern the optimum viscosity of the solution. An increase in the solution viscosity gets accompanied by a subsequent rise in the diameter of the beads and a concurrent decrease in the density of the beads. Higher viscosities of the polymer solution made in spindle-like shaped rather than spherical beads, thereby, resulting in the production of Nanofibers having fewer defects (Neo, et al. 647). Effect of Solvent Selection. Based on solubility, the choice of polymer to use affects how electrospinning transforms a nanofiber. The polymer boiling point affects its volatility, and its solubility affects its solubility in the solvent. The instability of the polymer is a parameter that impact the dehydration of nanofibers as the accelerations occurs to the collector surface from the capillary tip. It, therefore, means that highly volatile polymers exist as preferred for the electrospinning process (Agarwal, et al., 989). However, unstable polymers with very low boiling points should not be used. Such polymers may vaporize at the tip of the capillary and hence causing clogging and inhibiting the rate of the flow of the polymer (Oliveira, et al. 3404). Solvents having very high boiling points may result in an incomplete dehydration before being collected. The effect outcome is flat ribbon-like Nanofiber architecture or Nanofiber conglutination at the boundaries. The separation between phases is at the air-liquid interface as the jet gets projected in the atmosphere before reaching the collector. The air-liquid interface is a mapping of the solvent volatility and is a critical parameter is deciding the porosity of the final nanofiber product. The intended porosity can be attained by mixing two solutions whose boiling points differ. When two solutions gets blended in diverse ratios, the pore density varies downwards with the increased in the quantity of the less volatile co-solvent (Senthil, et al. 416). . Effect of Solution Conductivity. The conductivity of the polymer solution controls the charge carrying capacity of the polymer to a great extent. Therefore, the polymers with high conductivity have a higher load carrying capacity while the low conductivity ones have lower charge carrying capacity (Luo, et al. 1660). The conductivity of a polymer is directly proportional to the eminent tensional force imparted to the jet due to the significant quantity of charge exposure to the applied voltage (Agarwal, et al., 989). The solution conductivity is proportionally consequential to the diameter of the resulting nanofiber diameter. Furthermore, the nanofiber radius has been found to be inversely proportional to the solution electrical conductivity cube root (Neo, et al. 650). By increasing the polymer solution conductivity through the addition of substances such as Sodium Chloride, increases the weight of the charge of the jet thus decreasing the inhibition of the formation of nanofiber jet. The produced nanofibers are smoother due to the effect of the increment in quantity and uniformity of charges resulting from increased density of the electric charge (Agarwal, et al., 990). .Neutralizing the fiber jet charges with oppositely charged ions bead defects become rampant due to reduced electric strength. The addition of salts to the polymer exhibit varied characteristics depending on the size of the ions of the salt added. Ions that have smaller radii show high-density charge carrying capacity and, therefore, subject greater stretching forces to the fiber jet (Oliveira, et al. 3399). Effect of the Capillary and Collector Distance. The distance between the collector and the capillary affects the architecture and size of the formed Nanofibers. The said range should get set at an optimum measure that is efficient for the formation of nanofiber.Variation of this distance either to the negative or to the positive of the optimum range result in electrospraying rather that electrospinning or formation of beads.The Electrospun Nanofiber diameter decreases with the increase in the collector to the capillary distance. When the capillary to collector distance is too small, the solvent is not exposed to complete evaporation for the sufficient time thus the nanofibers formed have flat shapes (Agarwal, et al., 991). The change in the collector to the capillary distance does not significantly affect the diameter of the nanofiber. However, there is a notable formation of beads with a decrease in the distance for the case of polymers that are biodegradable. In the medical field, therefore, the rate of drug delivery can be modulated by selecting a desired polymer(s). It depends on the given rate for the matrix of an electrospun (Senthil, et al. 419). Effects of molecular weight on electrospinning The dissolution of the polymer is mainly dependent on the molecular weight of the polymer. For a proper ending, the polymer to be used should have the smallest molecular weight because solvent dissolution in lighter molecules is much easier due to the minimal resistance offered by the polymer. Resistance to polymer dissolution increase with increase in molecular weight of the polymer, and this makes large molecular weight polymer have high resistance to decomposition. The viscosity of the polymer is also influenced by the molecular weight; a large molecular weight polymer increases the viscosity of the polymer. Furthermore, large molecular weight polymers produce large pores with non-uniform shapes. Conclusion Advancements in manufacturing sector utilize the use of nanotechnology. Thus, electrospinning comes in handy in ensuring the production of desirable nanoscale components. Electrospinning thus has a significant impact in current nanotechnologies. Most of the nanofibers used in the market are electrospinning. The technologies of electrospinning are diverse. However, choice of the best electrospinning technique and the final product desired can always be achieved. The achievement gets based on the proper adjustment of production variables during the electrospinning process; Electrospinning keeps advancing each time becoming more and more sophisticated. Work Cited Agarwal, Seema, Andreas Greiner, and Joachim H. Wendorff. "Functional materials by Electro spinning of polymers." Progress in Polymer Science 38.6 (2013): 963-991. Dabirian, F., et al. "Manufacturing of twisted continuous PAN nanofiber yarn by electrospinning process." Fibers and Polymers 12.5 (2014): 610-615. Liu, Haifeng, et al. "Electrospinning of nanofibers for tissue engineering applications." Journal of Nanomaterials 2013 (2013): 3. Luo, C. J., M. Nangrejo, and M. Edirisinghe. "A novel method of selecting solvents for polymer electrospinning." Polymer 51.7 (2014): 1654-1662. Nasouri, Komeil, et al. "Modeling and optimization of electrospun PAN nanofiber diameter using response surface methodology and artificial neural networks." Journal of Applied Polymer Science 126.1 (2013): 127-135. Neo, Yun Ping, et al. "Influence of solution and processing parameters towards the fabrication of electrospun zein fibers with sub-micron diameter." Journal of Food Engineering 109.4 (2015): 645-651. Oliveira, Juliano E., et al. "Nano and submicrometric fibers of poly (D, L‐lactide) obtained by solution blow spinning: Process and solution variables." Journal of Applied Polymer Science 122.5 (2014): 3396-3405. Pillay, Viness, et al. "A review of the effect of processing variables on the fabrication of electrospun nanofibers for drug delivery applications." Journal of Nanomaterials 2013 (2014). Senthil, T., Gibin George, and S. Anandhan. "Chemical-resistant ultrafine poly (styrene-co- acrylonitrile) fibers by electrospinning: process optimization by design of experiment." Polymer-Plastics Technology and Engineering 52.4 (2013): 407-421. Zahedi, Payam, et al. "Preparation and performance evaluation of tetracycline hydrochloride loaded wound dressing mats based on electrospun nanofibrous poly (lactic acid)/poly (ϵ‐caprolactone) blends." Journal of Applied Polymer Science 124.5 (2012): 4174-4183. Read More

Electrospinning is a less complicated and variedly applied method that makes use of electrostatic forces to make fibers of fineness ranging from nanometer diameters to submicron. The method can be utilized to produce a broad variety of architectures of polymer types; natural, no degradable, biodegradable, synthetic. They include the fact that they are affordable, it is easy in comparison to other methods and used in creating fine fibers with much ease than other methods. The uncomplicated step-up production process of developing ultrafine fibers is only easily attainable with electrospinning method and not any other way (Liu, et al., 3). The electric field is used to prevent polymer droplets from adhering to the tip of the capillary due to the effect of the liquid's surface tension.

When an electric field gets applied, the electrostatic forces balance the surface tension, and the droplets are stretched to make cones typically referred to as “Taylor comes”. For cases where electric field overcomes surface tension, the Tailor cone ejects a beautiful fiber from the tip. The thread gets set in motion in the atmosphere. Therefore, solvent evaporation is enabled as the deposition of solid fibers happens concurrently on a grounded collector (Agarwal et al., 966). In conventional spinning, the fiber production methods involve the elongation of fibers by subjecting them to aerodynamic, tensile, rheological, inertial or gravitational forces.

The electrospinning process utilizes the electric field to develop tensile forces that are directed axially to the polymer jet flow direction, and thus fiber spinning gets attained (Nasri, et al. 127). It got experimentally discovered that, after the jet travel a short distance, stability gets lost. Whipping sets in due to the interaction between the electrostatic field produced by the electric field and the opposing forces resulting from jet surface charges (Zahedi, et al. 4174). The process result is the reduced diameter of fibers and a consequent increase in the length by many-fold In comparison to fiber production by other methods.

The overall outcome is the additional reward of electrospun fibers. It makes it more versatile; these advantages include; high porosity, the formation of interlinked porous networks, and a large surface compared to the volume (Agarwal et al., 967). The electrospinning technique got founded in the late 1890s by Rayleigh, and a detailed investigation got done in the early 1900s by Zeleny. The process was patented in the mid-1930s by Formhals after small diameter fabrication of fibers became practical.

Kundu and Bherdwaj patented mandrel and other devices that had movable fiber-collectors. However, the fibers could not dry thoroughly because of the reduced distance between the collector and the jet. The distance did not allow enough time for the tissue to dry. The consequence of the incomplete dryness was the sticking of fibers to the collecting surface and other fibers (Senthil, Gibson, and Anandhan, 408). Formhals went on to improve on the drawbacks of his initial apparatus in his second patent.

The subsequent patents by Formhals had various aims. The objectives included ameliorating control of fiber lengths, strengthening the fiber achieved by using a rotating funnel to draw threads, and production of composite fibers. It was achievable by the alleviation of spun fibers to the base fibers (Agarwal et al., 967). Researchers have done a lengthy research on the effect of a number of varied variables of processes on the morphology of the electrospun fiber structure and their properties.

It has led the researchers coming up with methods to produce small diameter polymeric fibers whose bulk properties and surface characteristics are desirable. The continued research has consequently resulted in the evolvement of the utilization of electrospun nanofibers in more versatile ways. The application in lithium ion batteries as the material for the anode electrode is one use of this process in the electronic field (Agarwal et al., 968).

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