shown in Figure 2.18. After assembly, the optical and electrical analysis demonstrated that the devices were bendable and gave out lights of white, yellow, and red color. Gheibi et al. produced a one‐step nanogenerator by using piezoelectric electrospun PVDF nanofibers incorporating the electrodes within the structure of the device for use as self‐powering wearable electronics (Gheibi et al. 2014). The effect of deformation on the output voltage of the device was measured on the Keithley instrument by tapping, and a maximum peak of voltage output reached 1 V.
Figure 2.18 (a–f) Schematic illustration of assembling flexible PLEDs by using a sandwiched structure of keratin/PVA nanofiber nonwoven fabric/polymer light‐emitting diodes (s)/keratin/PVA nanofiber nonwoven fabric.
Source: Reproduced with permission from Park et al. (2016). Copyright 2016, Elsevier.
2.5.4 Functional Fabrics
In the industry of textiles, the finishing process is one of the most important steps to enable fabric functionalities, including hydrophobic and hydrophilic finishing, flame‐proof finishing, etc. Some of the work is based on nanofiber structure carried with functional nanoparticles.
Zohoori et al. introduced a durable photoactive nylon fabric by electrospinning polyamide‐6,6 nanofibers containing nanophotocatalysts onto a nylon fabric (Zohoori et al. 2014). The resultant fabric displayed excellent photoactivity toward dye degradation even after repeated washing because of the firm bonding of nanophotocatalyst and PA‐66 nanofibers. Wijesena et al. grafted nanofibers onto cotton fabric to improve the ability of moisture transport from the inner side to outer side of the fabric (Wijesena et al. 2014). This controllable moisture transport capability was realized by electrospinning high‐water absorbent chitin nanofibers onto one side of the cotton fabric, which formed wicking power.
2.5.5 Biomedical Textiles
By using biomaterials, nanofiber nonwoven fabrics can be made to be suitable for biomedical applications, including tissue scaffolds, drug release control, catalysts, and enzyme carriers (Feng 2017). Zhang et al. produced PLA/ poly(N‐isopropylacrylamide) (PNIPAM) core–shell nanofiber nonwovens to control thermosensitive drug distribution (Zhang et al. 2015). PLA loaded with additives and drugs was electrospun as the core fiber, and the PNIPAM fiber shell was undertaken by UV initiation. The morphology showed nanosized pores on the surface of the fibers, which could improve the loading of the drug. The prepared nanofiber fabric was thermosensitive and had potential in the biomedical fields involving drug delivery and tissue engineering.
Besides, the nanofiber woven fabrics are also a good candidate for biomedical applications, owing to higher mechanical properties, dimensional stability. Shao et al. fabricated a multilayer nanofiber woven fabric for use as medical scaffolds, which made from PLA/TSF nanofibers (Shao et al. 2016). In that work, mechanical property, wettability, protein adsorptivity, hemocompatibility, and other medical properties were investigated. The fabric obtained a tensile strength of 180.36 MPa, Young's modulus of 417.65 MPa and great strain of 20.4%, which were higher than those of the nonwoven structure with the same material. Besides, this multilayer nanofiber woven fabric was hydrophilic with a water contact angle of 71.3° and excellent hemocompatibility.
2.6 Summary and Future Trends
Nanosized textile materials, such as nanofiber‐based yarns and woven/nonwoven fabrics, are able to provide greater advantages than traditional textile materials, such as smaller pore size and larger surface area. The structure of those nanofiber‐based textile materials mainly depends on their fabrication approaches and processes. Due to the unique properties of nanofibers, the applications of these nanostructured textile materials in protective clothing, filtrations, and biomedical textiles, etc., have been explored. Although some products (e.g. nanofiber facial masks) made from nanofiber‐based fabrics have been commercialized, most other applications are still in early development stage. Hence, more efforts are needed for the research and development of nanofiber‐based textiles and their practical applications. The following are the future development trends of nanofiber‐based textile materials.
1 In order to achieve mass production and high product quality, the appropriate design of nanofiber‐based textile materials is extremely important. For example, by optimizing the approach of fiber spinning, collecting, and winding, together with a quality control system, highly aligned, and continuous nanofiber bundles can be obtained with enhanced mechanical properties.
2 Introducing polymers with various functionalities to prepare multifunctional nanofibers can potentially provide improved physical or chemical properties, including high electrical conductivity, excellent chemical resistance, etc. This will enable the use of nanofiber textile materials in various practical applications.
3 From another perspective, smart textiles (e.g. wearable devices) based on nanofibers are promising and their robust growth is expected in sports and fitness fields. Nanofiber‐based woven/nonwoven fabrics with enhanced wearing comfort, durability, water vapor permeability, etc., are needed for smart textiles.
In brief, nanofiber‐based textile materials are becoming a tremendous opportunity for both academic researchers and industry developers, and numerous progresses have been made on the fabrication and application of these novel materials. It is believed that nanofiber‐based textiles will definitely play an essential role in the future textile market.
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