**3. Scaling-up the technology of electrospinning**

A basic electrospinning setup includes a chamber of polymer melt or solution, a spinning head, a high-voltage supplier, and a collector. Most electrospinning setups have their spinning heads connected to a positive high-voltage output end while the collectors are earthed or connected to a relatively low negative voltage. The electrospinning process requires a very small flow rate supply, so a microfluidic pump or fluid distributor is usually used to control the flow.

However, output of most solution-based, single-jet electrospinning setups is only 0.01-0.1g per hour, which is much smaller than that of traditional melt-blowing processes [48]. A lot of researchers have made great effort to improve the efficiency of the electrospinning process in different ways. The methods used can be grouped into two types. One method works by multiplying the output by establishing matrices of commonly used orifices (Figure 5a) [49]. The other uses a fluid-free surface or creates some protuberances on a fluid-free surface to motivate multiple jets by loading extremely high voltages (Figure 5b) [50].

**Figure 5.** Pictures of (a) multineedle electrospinning and (b) needleless electrospinning setups [49, 50].

The spinneret matrices for scaling-up electrospinning as figure 5(a) shows is an on-brain method by simplly copying single spinnerets. Its most impressive advantage is that there is no risk in carrying out any scaling-up processes of materials that are realized in a single needle setup. However, if the neighboring spinning heads are too close, the jets' distribution on the deposited fabrics will not be even because of the electrical field interference between the needles [49]. In order to deal with this problem, it has been suggested that the array parameters, of the spinning heads, be improved [49]. It has also been demonstrated that the interference of the electrical field can be minimized by adding a hat to the spinning head [51].

The latter method, needleless electrospinning [50] or so-called free-surface electrospinning [52] or the nozzleless electrospinning method [53], is much simpler than the method mentioned above. This was first published by A.L. Yarin and E. Zussman [54] in 2003. They used magnetic fl003 prepared by mixing magnetic powder in kerosene with oleic acid as a stabilizer to initiate multiple jetting from the free surface under the action of the normal magnetic and electric fipre, which yields about 26 jets/cm2 , while the former method with nine orifices yields only 2.25 jets/cm2 [49]. Subsequently, many kinds of varieties of method emerged by improving the spinning heads (as shown in Table 1). Outputs have been listed below, from which we can find that most of them have yield close to 10g/h.


**Table 1.** Comparison of different nozzles [55].

**2.7. Ambient temperature and humidity**

**3. Scaling-up the technology of electrospinning**

humidities change [45].

40 Non-woven Fabrics

High temperature and low humidity in the spinning area benefit the evaporation of solvent, and this is helpful to obtain smaller fiber diameters [45]. When the temperature is too high in solution electrospinning, the spinneret may easily be blocked because of fast evaporation. In melt electrospinning, the high ambient temperature can keep the spinning jet in melt state for a long time, which increases the thinning time of the jet and is beneficial to smaller fiber production [46]. The electrospinning process can rarely be carried out when the humidity surpasses some value since a corona or breakdown may happen [47]. Obvious changes on the surface of the solution electrospun fiber have been observed when spinning temperatures and

A basic electrospinning setup includes a chamber of polymer melt or solution, a spinning head, a high-voltage supplier, and a collector. Most electrospinning setups have their spinning heads connected to a positive high-voltage output end while the collectors are earthed or connected to a relatively low negative voltage. The electrospinning process requires a very small flow rate supply, so a microfluidic pump or fluid distributor is usually used to control the flow.

However, output of most solution-based, single-jet electrospinning setups is only 0.01-0.1g per hour, which is much smaller than that of traditional melt-blowing processes [48]. A lot of researchers have made great effort to improve the efficiency of the electrospinning process in different ways. The methods used can be grouped into two types. One method works by multiplying the output by establishing matrices of commonly used orifices (Figure 5a) [49]. The other uses a fluid-free surface or creates some protuberances on a fluid-free surface to

motivate multiple jets by loading extremely high voltages (Figure 5b) [50].

**Figure 5.** Pictures of (a) multineedle electrospinning and (b) needleless electrospinning setups [49, 50].

The spinneret matrices for scaling-up electrospinning as figure 5(a) shows is an on-brain method by simplly copying single spinnerets. Its most impressive advantage is that there is no risk in carrying out any scaling-up processes of materials that are realized in a single needle setup. However, if the neighboring spinning heads are too close, the jets' distribution on the It is hard to evaluate and compare which method is the best when considering jet number per unit area. However, the most popularly used systems in industry may reflect such an evalu‐ ation. Table 2 lists some pioneering companies which have used electrospinning machines for scaling-up production, among which, Elmarco is the most popular company supplying complete equipment [56]. Their technology has evolved from drum type to wire type, which can produce 80,000,000m2 /year using an NS 8S1600U machine. For melt electrospinning, thick fiber and high voltage security have always represented an obstacle until Yang's team developed a new method called melt differential electrospinning [57]. In this method more than 60 simultaneous electrified jets are attained using umbellate systems with a flow rate of about 12 g/h [57–58]. The authors also indicated that a scaling-up machine has been established for non-woven fabric production with a 1-m width [58].


**Table 2.** Companies supplying mass production machines
