Inquire Into The Research Progress of Electrospinning Technology
[Introduction] Summary: electrospinning technology is a method of directly, continuously manufacture polymer nanofiber at present. It has the advantages such as simple process, convenient operation, quick manufacture speed, etc.
Foshan Lepton Precision Measurement And Control Technology Co.,Ltd 528225
Summary: ectrospinning technology is a method to directly, continuously manufacture polymer nanofiber at present. It has the advantages such as simple process, convenient operation, quick manufacture speed, etc. It’s extensive applied to medical and environmental areas. This article introduced electrospinning technology in recent years and its application’s research progress, summarized the electrospinning theory and influencing factors, are proposed the prospects of the electrospinning technology application in the future.
Keywords: electrospinning; nanofiber; progress
Foreword
In the strict sense, nanofiber means the ultra minimum fiber whose diameter is less than 100nm. Its feature is high specific surface area and high porosity. Therefore, it can be extensive applied to the areas like high-efficiency filter materials, biological materials, high precision instruments, protective materials, nano composites, etc. In the 1990s, the research of nanotechnology was heated up, making the nanofiber manufacture become the research hot spot quickly. Electrospinning polymer nanofiber has the features like simple equipment, easy operation, etc. Up to now, it’s one of the most important methods of manufacturing polymer nanofiber.
1. Electrospinning
The figure of the electrospinning equipment is showed as Diagram1. It’s mainly composed of three parts: high voltage power supply, nozzle and fiber collection device. Usually adopted direct-current power supply instead of alternating current power supply for high voltage power. Electrospinning needed for high voltage power 1～30kV. The syringe (or pipette) deliver the solution or melt to the nozzle in the terminal. The nozzle is a very thin metal tube with electrode. The collection device or collection plate is used for collecting nanofiber. Through changing the geometric dimensioning and shape of the collection device, we can change the nanofiber arrays form.
2. Electrospinning Technology Theory
Back to 1882, Ｒaleigh found that liquid drop with electric was unstable in the electric field. After entering the electric field, because of the electric field force, the liquid drop is easy to split into smaller liquid drops. Taylor’s research showed that liquid drop with electricity entered the electric field through the nozzle, under the combined action of electric field force and surface tension of liquid, the liquid drop gradually stretched, forming a cone (Taylor Cone) with a 49.3° angle.
In the process of electrospinning, the polymer solution or melt is extruded to the nozzle, because of the actions of electric field force and surface tension. There forms a Taylor Cone on the nozzle. Along with the spinning solution pushed into the electric field, it will spray out from the top of the Taylor Cone, In the electric field, it will be continue stretched under the electric field force. When the jet-flow is stretched to a certain extent, it will overcome the surface tension, curve unstably and be stretched and split into thinner jet-flows. At the moment, the jet-flow’s specific surface is increasing quickly, making the solvent volatilize quickly. At last it’s collected by the collection device, solidify and form the nonwoven cloth shape fibrofelt.
3. The Influencing Factors of Electrospinning
The influencing factors of electrospinning mainly include solution properties (such as viscosity, thickness, apparent molecular weight distribution, elastic conductivity, dielectric constant, surface tension, etc.), process conditions (such as voltage, press ratio, the distance between nozzle and collection device, nozzle diameter, etc.) and environmental factors (such as temperature, humidity, gas flow rate, etc.). In this respect, many people did the research.
The existing research result showed that in the electrospinning process, the main process parameters which influencing the fiber property mainly are: polymer solution thickness, spinning voltage, solidify distance ( the distance between nozzle and collection device), solvent volatility and extruded velocity, etc.
（1）Polymer Solution Concentration
The higher the polymer solution concertration, the higher the viscosity and surface tension. After leaving the nozzle, the splitting ability of the liquid drop is decreasing along with the surface tension increasing. Usually, when other conditions are unchanged, the fiber’s diameter will increase along with the polymer solution concentration increase.
（2）Spinning Voltage
Along with the voltage to the polymer solution increased , the system’s electrostatic force increased, the splitting ability of the liquid drop increased, the fiber diameter decreased.
（3）Solidify Distance
After spraying out from the nozzle, the polymer liquid drop along with the solvent volatilize in the air, concentrate and solidify to fiber, at last collected by the collection device. In different system, the solidify distance has different influence to the fiber diameter. Such as, the research of PS/THF system showed that changing the solidify distance, the influence to the fiber diameter is unapparent. But for the PAN/N, N-DMF system, the fiber diameter decreased along with the collection distance increased.
（4）Solvent
Similar with the regular solution spinning, the solvent property has a big influence to the forming, structure and property of the solution electrospinning fiber. The volatility of the solvent is very important to the fiber shape.
4. The Application of Electrospinning Technology
With the development of nanotechnology, electrospinning as a simple, effective nanofiber manufacture new process technology, it will play a significant role in the biomedical materials, filtration and protection, catalysis, energy, photoelectricity, food engineering and cosmetics areas.
① In the biomedicine area, the nanofiber’s diameter is smaller than cell, can simulate the structure and biological function of natural cell epimatrix; the form and structure of many human tissues, organs are similar to the nanofiber. That makes the nanofiber be possible to be used for repairing of the tissues and organs. Some electrospinning materials have good biocompatibility and degradability, can be the carrier to enter human body, is easy to be absorbed. Besides, the electrospinning nanofiber has high specific surface, high porosity and other good features. Therefore, it caused continue concern by the researchers in the biomedicine area, and well applied to drug delivery system, wound repair, biological tissue engineering and other aspects.
② The filter efficiency of the fiber filter material will improve along with the decrease of the fiber diameter. Therefore, decreasing the fiber diameter becomes an effective method to improve the filtering quality of fiber filter materials. Electrospinning fiber has many advantages, such as small diameter, small hole diameter, high porosity, uniform fiber etc. That makes it have great application potential in air filtration, liquid filtration and individual protection areas.
③ Electrospinning can effectively regulate and control fiber’s fine structure, combining with low surface energy materials, can get super hydrophobic materials, and is hopeful to apply to the ship hull, petroleum pipeline inwall, high-rise glass, automotive glass, etc. But if electrospinning fiber materials want to achieve the above application in the self-cleaning field, have to improve the intensity, abradability and the binding strength of the fiber membrane material and substrate material, etc.
④ Catalyst granule with nano structure is easy to unite, thus influencing its dispersibility and utilization ratio. Therefore electrospinning fiber material can be the formwork to uniformly disperse the granule. At the same time, it can also exert the flexibility and operational ease of the polymer carrier, as well as utilizing the composition of catalytic material and polymer surface in micro nano size, producing quite strong synergistic effect, improving the catalytic effect.
⑤ Electrospinning nanofiber has quite high specific surface and porosity, can increase the active area of sensing materials and detected objects. It’s hopeful to increase the sensor’s performance substantially. Besides, electrospinning nanofiber can also be applied to many areas like energy, photoelectricity, food engineering etc.
5. The Technology Progress of Electrospinning
5.1. The Technological Improvement of Electrospinning Method
（1）Combination Electrospinning
In 2003, Philip University, Germany and Israel Zussman developed the combination electrospinning technology together. There are two solutions and two nozzles in this spinning technology. On the front end of the nozzles formed the combination liquid drop, produced the jet-flow, the inner liquid drop also added into the jet-flow. Therefore, it’s difficult to control the liquid drop. If controlling well, it can produce core-shell structure fiber and hollow fiber.
（2）The Development of TUFT
TUFT is the abbreviation of tubular fiber template. It used polymer to manufacture nanofiber, made other polymer, metal, ceramic attach to the nanofiber, then removed the original polymer, made the fiber become hollow. It can also make composite layer to manufacture nano capacitor. For example, if adding polymer on the outside of the palladium particles, then can get nanocables which inside is electric conductor, outside is insulating layer. If making the aluminum attach to the polymer, then can get expoxy aluminum tube. If making the chromium attach to the polymer, then can get chromium tube.
（3）Composite Nozzle
Electrospinning basically adopted nozzle as its spinning way. The University of Shiga Prefecture, Japan developed composite nozzle. In order to continue to manufacture nanofiber nonwoven fabric, composite nozzle is indispensable. Because of the distance between the top, bottom, left and right is big, the electrostatic repulsion’s influence decrease. Therefore, usually set the nozzle according to this distance: left and right 10mm, top and bottom 50mm. The nozzle adopted diameter 0.5mm stainless steel tube, used good drug resistance fluorine rubber hose to delivery solution to each steel tube . Each steel tube inserted to the hole on the copper tube, applied high voltage to the copper tube. For this, the stainless steel tube need to connect to the copper tube firmly, but detachable. At present, the nozzle is linear arrangement.
5.2 M-ESP’s Development
F.Ko connected the nozzle of the extruder to the ground, applied high voltage to the collector, electrostatic jet spinning PP. But using this device couldn’t get average diameter less than 1μm fiber. Besides, the fiber on the collector can’t be taken out in the high voltage status. It’s a problem of industrialization. Warner used plastic pipe to wind the PP filled syringe, made the heat carrier circularly manufacture melt, the spinning cabinet was in heating status, applied high voltage to the area between syringe nozzle and collector, then got the nanofiber first time. Joo added PLA to the syringe, manufactured a device which can control syringe temperature, spinning temperature, collector temperature, successfully manufactured PLA nanofiber. Above-mentioned research device, manufactured polymer melt in the container, set the nozzle on the container. This is only changing the solution to melt of the S-ESP. This method is the extending of S-ESP.
University of Fukui, Japan developed a device which lasing polymer rod from a distance, melting a part of it, and applied high voltage to the melt. This device’s action principle is supplying polymer rod material (diameter less than 1mm) to the melt part in a certain speed (about 0.2mm/s), used carbon dioxide laser to heat its front end from three direction at the same time, made the polymer rod melt uniformly in part, and applied high voltage to the polymer melt, in the spinning area heating status, manufactured fiber by the electrostatic traction. The laser exposure part is fusiform, generate a fiber from its bottom (Figure 2).
The result of various kinds of polymer fiber trial-manufacture showed that all are forming a fiber from the melt part, the fiber collected by the collector which diameter is less than 1μm. This device’s feature is: because using laser for heating melt, can do local heating in a moment, energy loss is small; because it’s heating indirectly, the requirement of the device is not high; because not using spinneret plate, high melting point slices can also be spun.
6. Concluding Remarks
At present, electrospinning nanofiber technology is in its infancy, but already can see its extensive application prospect, it will produce billions of market value in the future. Researchers will also overcome every technology difficulty of nanofiber application area. Maybe every technology can drive the science and technology progress of the whole spinning industry. Of course, the progress of these technology also need every area of society cooperate closely to complete, such as spinning technology, chemistry technology, biology, polymer science and material science etc.
Source: China Journal Net
Writer: Jiezhuang Guo, Foshan Lepton Precision Measurement And Control Technology Co., Ltd.