**2.6. Collector**

For melt electrospinning, because of the dielectric properties and high viscosity of the polymer melt, the applied voltage is more than 2 times that used in solution electrospinning. Therefore, 20–100 kV is needed to polarize the polymer melt, and induce the generation of polymer jets [26], while usually 5–20 kV is loaded on the end of the syringe needle in solution electrospin‐ ning. Increasing the voltage is a common measure used to obtain finer fiber in melt electro‐ spinning, but it can cause corona or breakdown if the voltage is too high. Ratthapol [27] proposed a vacuum melt electrospinning method, improving the threshold voltage, in which the loading voltage can reach 1–30 kV/cm without breakdown, however, this method may

High conductivity of processed material means a greater number of net charges on the jet when high voltage is loaded, therefore, a smaller fiber diameter can be attained by elevating the conductivity. Higher conductivity also may cause a drastic whipping of the electrospun jet, especially for polymer solutions, however, this may lead to a wide diameter distribution of the electrospun, non-woven fabrics. A widely used method to improve conductivity is by adding salts [28-29], pyridine [30], or carbon nano tube(CNT) [31] in polymer solution or polymer melts. However, this may change the original fiber properties. Some researchers have

Spinning distance was defined as the distance between the spinning tip and the collector. This distance is exactly the route that the electrospun jet experiences. Changing the spinning distance may cause a change in solvent evaporating velocity, the electrical field intensity, and the solidifying state, and thus affect the fiber properties indirectly. When the spinning distance is too short, the fiber will not be thinned enough because of a lack of the whipping process and inadequate solvent evaporation, as a result, the beads may accrue and even prepared fabrics may dissolve back into concentrated solution at this stage [33]. On the contrary, if there is an increase in the spinning distance, and a fixed electric field intensity, smaller fiber can be produced, and naturally, a larger area of deposited non-woven fabrics is prepared [34]. The

It should be noticed that near-field electrospinning has been developed for a patterned deposition of nanofiber, in which the spinning distance was set smaller than 1 mm and jet

Solvent properties including the surface tension [36] and conductivity [37], determine the final solution properties, and effect fiber properties indirectly. Solvent with low surface tension is a good candidate for better electrospinning solution preparation, thus the electrospinning process can be easily carried out by loading a relatively low voltage [36]. Volatility should be another concern when choosing the right solvent. If the volatility is too high, a blockage at the

prove costly if used in large-scale production.

investigated additives that evaporate when jetting [32].

spinning distance in most cases was set at 7-15 cm.

whipping was almost eliminated [35].

**2.5. Solvent properties**

**2.3. Conductivity**

38 Non-woven Fabrics

**2.4. Spinning distance**

Non-woven fabrics are usually defined as random deposited fibers. However, sometimes controlled deposition of fibers, at least partially oriented fibers or patterned fabrics are needed in areas like cell scaffolds, sensors, and tailored filters. Therefore, different collectors or collectors with certain movement were utilized to realize specially controlled fabrics in electrospinning. Li, Wang, and Xia [41] have demonstrated that the nanofibers can be uniax‐ ially aligned by introducing an insulating gap into the conductive collector. Other interesting methods including the use of collector-like knife-edged blades [42], rotating wire drums [43], rings placed in parallel [44], etc., have also been proposed and tested.
