**4.1. Productivity improvement**

Different measures have been adopted to improve the productivity of electrospinning for nonwoven fabric production [56], however, limited output still exists compared with traditional processes. Needleless electrospinning has shown great potential having advantages over needle-based lines, but a lot of problems remain to be solved. The electrospinning conditions required restrict control of temperature, humidity, and dust around the spinning pool; the processed polymer should be well dissolved into the solvent and kept for hours or days; and the evaporated solvent should be completely collected and recycled during electrospinning. These requirements change when the material changes. Presently, only a few polymers like PAN, PA6, and PVA can be processed well on a needleless electrospinning line. More polymers and their composites need to be tested to find suitable processing parameters. It should be noticed that it would be difficult to carry out electrospinning without needle-based setups for some materials and morphologies, especially for two component nanofiber and core-shell nanofiber [59]. Therefore, fundamental research should be carried out to optimize on-going production lines to cater for different requirements.
