# Electrospinning of High-Performance Nanofibres: State of the Art and Insights into the Path Forward
## 4 Discussion
### Challenges, Limitations, and Avenues of Solutions
#### 4.2.1 Standardized Characterization Methods  
In general, a major challenge with the study of nanofibres has been the lack of standardized test methods for assessing the performance of the membranes. Since electrospinninging is a highly variable process, different research studies have used a wide range of parameters to produce similar nanofibres. This makes a comparison of the outcomes of the electrospinninging process between studies very difficult. In addition, the characterization methods of nanofibres are not standardized and the literature varies widely in terms of which characterization methods are used. Visual fibre and web morphologies are generally the easiest to compare within the literature, as most research uses scanning electron microscopy (SEM) and similar image analysis software to determine average fibre diameters and the distributions of fibre diameters and quantify non-fibrous areas. In other instances, the characterization that was performed may not always describe a property in a comprehensive manner. For example, some studies of m-aramid looked at the pore size distribution [10; 47]. However, this value is dependent on the thickness of the membrane, which was not always reported. Likewise, studies of chemical changes to the polymer to improve molecular weight or solubility were often reported without the assessment of the effect on mechanical properties [3]. This makes a comparison of different electrospinninging and post-treatment methods very difficult. However, such a comparison is necessary to move forward productively in the field. As research on nanofibres continues to grow and standards are published, creating a framework of test methods for characterizing nanofibre performance will be an important tool to increase accuracy and comparability between studies. The standardized assessment of the mechanical properties of nanofibres continues to be a challenge for nanofibrous membranes due to difficulties in handling the membrane and the extraction of a single nanofibre from the mat without damaging it and the use of load cells outside of their useful range, among others [42]. Table 2 describes test methods typically used to determine the mechanical strengths of high-performance nanofibres. In general, likely due to both the difficulty of extracting a single nanofibre from the membrane and the interest in the overall mechanical properties of the membrane, the entire membrane strength tends to be measured instead of a single fibre. However, the preparation of samples for tensile testing is highly variable between studies. When the membrane is being tested, specimens are typically cut into a rectangular shape or dog-bone shape (Table 2). Some authors also report the use of a paper frame or additional support for the membrane to discourage clamp breakage or damage while mounting the specimen [15; 33]. Clamp breakage is a major issue with low-strength material; thus, sample preparation and the use of the correct clamp type are critical to obtain accurate results. The sample preparation procedures used for measuring the strength of high-performance nanofibers have sometimes been adapted from mechanical characterization standards developed for micro-scale materials, for instance, ASTM D638 and ASTM D882. Both methods are intended to assess the mechanical properties of thin plastic sheeting. However, the highly porous structure of nanofibrous membranes compared to plastic sheeting presents some challenges in the applicability of the method, particularly in assessing the overall strength of the membrane [9]. [PERSON] et al. [43] suggest measuring tensile stress by considering the membrane density in order to account for the high volume of air present in nanofibrousmaterials. As the nanofibre alignment and the presence of other additives such as salts can have major impacts on the strength of a nanofibrous membrane, these factors should also be considered when interpreting the results [9].