# Electrospinning of High-Performance Nanofibres: State of the Art and Insights into the Path Forward
## 3 Electrospinning of High-Performance Polymers
### Meta-Aramid
Without the SiO\({}_{2}\), the membrane began shrinking at 260 \({}^{\circ}\)C. In addition, the membranes containing SiO\({}_{2}\) showed an increase in tensile strength compared to the pure m-aramid membranes. This is attributed to the van der Waals forces, electrostatic attraction, and polarity of the polymers and SiO\({}_{2}\), which may form a three-dimensional structure allowing for better dispersion of stress in the polymer and nanoparticle network. The pure m-aramid membrane had a tensile strength of 8.75 MPa, whereas the membrane containing 6 wt% SiO\({}_{2}\) had a strength of 18.14 MPa. However, above 6% SiO\({}_{2}\), the membrane strength began to decrease as the nanoparticles agglomerated within the structure. The flame resistance of m-aramid nanofibres has also been investigated, particularly for applications as a flame-retardant coating on other materials. When m-aramid nanofibrous membranes are used to improve the flame resistance of another material, the fibre alignment and the attachment method to the material both impact the flame resistance of the system [9; 43; 44]. Attaching an m-aramid nanofibrous membrane to the surface of wood was found to improve its flame resistance compared to untreated wood [44]. However, it was found that randomly oriented membranes were more effective than aligned nanofibrous membranes at improving flame resistance [43]. During exposure to flame, a buildup of gases between the wood and nanofibrous membrane led to disruptions in the m-aramid layer, exposing the wood to flame. Since the randomly oriented mat had improved mechanical properties in all directions, it was more resistant to failure, thus providing better flame protection to the wood. In contrast, the aligned membrane had poor mechanical strength in the transverse direction, leading to a faster failure time. [PERSON] et al. [9] studied the flame resistance of m-aramid nanofibrous mats bonded to carbon fibre-reinforced composites. The presence of the nanofibrous mats did not improve the flame resistance of the material, but this behaviour was attributed to an outer layer of epoxy present on the samples, which burned before the flame reached the nanofibrous membrane. The only improvement provided by the m-aramid nanofibrous mat was the time to ignition, which increased by 50 s compared to the original carbon fibre-reinforced composite. For liquid filtration applications, the pore size and permeability of the membrane are important in ensuring that the membrane can perform effectively. The nanofibre diameter distribution and membrane thickness are the main factors determining pore size and permeability [8; 10]. In general, m-aramid nanofibrous membranes have a narrow pore size distribution compared to micro-scale fibrous filtration media, with pore sizes between 0 and 2 \(\upmu\)m [8; 10]. Pore size distribution decreases as a smaller distribution of nanofibre diameters is achieved by optimizing the concentration of m-aramid in the spinning solution [8]. Moreover, as membrane thickness increases, average pore size gradually decreases [10]. However, in m-aramid nanofibrous membranes, it was observed that pore size only decreased up to a membrane thickness of 8.95 \(\upmu\)m, after which the pore size plateaued [10]. In general, m-aramid nanofibrous membranes perform well compared to conventional liquid filters. Liquid permeability was found to be improved in m-aramid nanofibrous membranes compared to commercial glass fibre water filters [8]. For applications for air filtration, the water vapour permeability of m-aramid was investigated for a breathable, temperature-resistant membrane [10]. The water vapour permeability was measured to be 7650 g/m\({}^{2}\), nearly twice the minimum value for a breathable membrane (4000 g/m\({}^{2}\)) [52]. However, the addition of PSA used to improve the dimensional stability led to increased pore sizes and decreased mechanical strength in the nanofibrous membranes. M-aramid nanofibrous membranes have also been adapted for specific applications.