# Electrospinning of High-Performance Nanofibres: State of the Art and Insights into the Path Forward
## 3 Electrospinning of High-Performance Polymers
### Meta-Aramid
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Reference** & \begin{tabular}{c} **Solution** \\ **Concentration** \\ \end{tabular} & **Voltage** & **Distance** & **Flow Rate** & \
\begin{tabular}{c} **Collector and** \\ **Substrate** \\ \end{tabular} &
\begin{tabular}{c} **Temperature and** \\ **Relative Humidity** \\ \end{tabular} \\ \hline
[49] & \
\begin{tabular}{c} 14 wt\% m-aramid \\ in DMAc \\ \end{tabular} & 15 kV & 10 cm & 0.05 \(\mu\)L/min &
\begin{tabular}{c} Rotating drum \\ (300 rpm) \\ \end{tabular} & Not reported \\ \hline
[8] & \
\begin{tabular}{c} 15 wt\% m-aramid \\ and 10 wt\% \\ CaCl\({}_{2}\) in DMAc \\ \end{tabular} & 20 kV & 20 cm & 1.5 mL/h &
\begin{tabular}{c} Rotating drum \\ with aluminum \\ foil \\ \end{tabular} & Not reported \\ \hline
[10] & \
\begin{tabular}{c} 9–18 wt\% \\ m-aramid in DMAc \\ \end{tabular} & 15–25 kV & 10–20 cm & 0.5-1.5 mL/h &
\begin{tabular}{c} Rotating drum \\ with stainless \\ steel sheet \\ \end{tabular} & 25 \({}^{\circ}\)C + 40\% \\ \hline
[11] & \
\begin{tabular}{c} 8–14 wt\% \\ m-aramid and \\ m-aramid and 1–8 wt\% LiCl in \\ DMAc \\ \end{tabular} & 25 kV & 15 cm & 0.5 mL/h &
\begin{tabular}{c} Stationary \\ collector with \\ aluminum foil \\ \end{tabular} & Not reported. \\ \hline
[44] & \
\begin{tabular}{c} 14 wt\% m-aramid \\ and 4 wt\% LiCl in \\ DMAc \\ \end{tabular} & 20–25 kV & 15 cm & 0.10 mL/h &
\begin{tabular}{c} Rotating drum, \\ PE paper (60 rpm) \\ \end{tabular} & 20–25 \({}^{\circ}\)C + 25\% \\ \hline
[45] & \
\begin{tabular}{c} 12, 14, 16 wt\% \\ m-aramid and 5:2 \\ ratio of \\ m-aramid:LiCl in \\ DMAc \\ \end{tabular} & 15 to 20 kV & 15 cm & 0.2 mL/h &
\begin{tabular}{c} Rotating drum \\ covered in \\ aluminum foil \\ \end{tabular} & 20–25 \({}^{\circ}\)C + 40–50\% \\ \hline
[12] &
\begin{tabular}{c} 14 wt\% m-aramid \\ and 7.5 wt\% \\ CaCl\({}_{2}\) in DMAc \\ \end{tabular} & 12 to 15 kV & 15 cm & 10 \(\mu\)L/min & Not reported & 23 \({}^{\circ}\)C + 25\% \\ \hline
[48] &
\begin{tabular}{c} 8 to 16 wt\% \\ Nomex in DMAc \\ \end{tabular} & 10–25 kV & 15 cm & Not reported & Not reported & Not reported \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Electrospinning conditions of m-aramid nanofibres found in the literature. Compared to conventional m-aramid fibres, initial investigations of the mechanical strength of as-spun m-aramid nanofibres found that nanofibrous membranes displayed reduced elastic modulus and strength [45]. This was attributed to a more segmented crystalline structure of the spun polymer. This lower mechanical performance limits the practical usage of electrospun m-aramid nanofibres, particularly in applications where high strength is required. One of the reasons identified for the reduced crystallinity of the as-spun nanofibrous mats is that the salts added into the polymer solution to assist with dissolution remain in the nanofibrous mats at high concentrations [45]. For example, the addition of 2 to 3.5 wt% LiCl in a solution of 14 wt% m-aramid produced a nanofibrous membrane with between 12.5 and 20 wt% LiCl [9]. The presence of this salt disrupts the formation of crystalline regions within nanofibres [9; 45]. The hygroscopic nature of LiCl also leads to higher water adsorption, which can cause fibre disentanglement when the material is under tensile deformation [9]. Depending on the amount of salt, it may also increase the diameter of the nanofibres. As a result, post-treatments of m-aramid nanofibrous membranes are being investigated to increase the crystallinity of the nanofibers and improve the mechanical properties of m-aramid nanofibrous mats. One study used a washing treatment to remove excess salt from the nanofibrous mats and improve the mechanical properties [9].