# Electrospinning of High-Performance Nanofibres: State of the Art and Insights into the Path Forward
## 3 Electrospinning of High-Performance Polymers
### Polyamide-Imide
For example, a mat with randomly aligned nanofibres annealed at 400 \({}^{\circ}\)C had a strength of 120 \(\pm\) 10 MPa, several times lower than the oriented nanofibrous mat. The high strength of PAI's nanofibres also makes them an excellent candidate for reinforcement with other nanofibrous materials. PAI nanofibres have been used as a re  
Figure 3: Biomimetic PAI nanofibres produced using a multi-solvent system. The image displays (**a**) the mason pine needles the researchers were trying to mimic, (**b**) the grooved surface of the needles under SEM, and (**c**) the grooved surface of a PAI nanofibre produced using the multi-solvent system. The schematic for producing the grooved nanofibres is shown in (**d**). Reprinted with permission from Ref. [19]. 2019, Elsevier. infercement in an electrospun polytetrafluoroethylene (PTFE) membrane, where it was found to significantly increase the strength of the nanofibrous membrane at a 3% concentration [17]. The PAI precursor was blended with PTFE and electrospun at a voltage of 12 kV onto a stationary collector. The membrane was then heat-treated at 380 \({}^{\circ}\)C for 10 min to obtain a PTFE/PAI composite. The addition of PAI was found to increase the thermal stability and strength of the nanofibrous membranes. At 20 wt% PAI, the randomly oriented membrane had a strength of 19 MPa, which was a 31% increase compared to the 100% PTFE membrane. However, the PAI led to significant changes in morphology. Where pure PTFE nanofibres showed even diameters, increasing amounts of PAI produced thinner fibres with a wider diameter distribution. The feasibility of industrial scale-up for PAI fibres has also been examined by electrospinning PAI nanofibres on a wire-based electrospinninging setup [20]. A solution of PAI was electrospun on an Elmarco Nanospider(tm) to determine the viability of the industrial scale-up of aramid nanofibres. While needle-based electrospinningning is suitable for preliminary studies on nanofibre production, the throughput is extremely small and thus unsuitable for industrial applications. Needleless electrospinninging allows for the free formation of jets across the surface of a polymer solution [55]. This allows jets to be configured optimally, leading to the most efficient spacing of jets for multi-jet electrospinningning. Wire-based electrospinninging is a technique patented by Elmarco; it involves a stationary wire electrode that is coated in polymer solution via a moving carriage [56]. Jets form across the surface of the wire and are distributed on a collector, which is positioned above the wire. [PERSON] et al. [20] used the enhanced productivity of the wire-based electrospinninging setup to determine the feasibility of electrospinninging PAI nanofibres at an industrial scale. A solution of PAI in 1,3-dimethyl-2-imidazolione is prepared with a viscosity of 60 Pa.s. Voltage, airflow, distance, relative humidity, and temperature were manipulated in order to determine the best processing parameters for PAI. It was found that relative humidity, voltage, and distance had the greatest effect on the mean fibre diameter. Relative humidity and distance were observed to have a positive effect on the mean fibre diameter. In contrast, an increase in voltage was found to slightly decrease the mean fibre diameter. Within the set parameters, increasing airflow and temperature showed no effect on the mean fibre diameter. Finally, post-treatment of PAI has been used to increase the hydrophilicity of PAI nanofibrous mats [21]. PAI nanofibres were electrospun from a solution of PAI and DMF using a needle-based electrospinninging setup. Nanofibrous membranes then underwent atmospheric-pressure plasma treatment at various times (60, 120, 180, and 240 s). Longer atmospheric-pressure plasma treatments were found to alter the chemical structure of the fibres, as well as the surface morphology. From these observations, it was found that a treatment time of 120 s was optimal to improve hydrophilicity whilst minimizing etching and oxidative reactions.