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2 Textile Applications of Nanofibers
Jiadeng Zhu, Yeqian Ge, and Xiangwu Zhang
Wilson College of Textiles, North Carolina State University, Fiber and Science Program, Raleigh, NC, USA
2.1 Introduction of Nanofibers in Textile Applications
Textiles are defined as materials consisting of aggregate structure of natural or artificial fibers (Wong et al. 2007). As a conventional industry, textiles originated from ancient times and the initial purpose was to shield bodies and keep them warm. Whereafter, with the exploration of new fibers and new fabrication techniques, the textile industry started to boom and became mature. However, in order to catch up with the trends of high technology and obtain higher profits and competitiveness, new techniques are extremely in high demand for this traditional industry.
Nanotechnology, currently a quite attractive and promising technology, has become a gold rush in a significant number of textile applications in terms of filtrations, fiber composites, medical textiles, protective clothing, smart garments, etc. (Wong et al. 2007; Feng 2017). It is also practical in functional finishing of fabrics, such as flame‐resistance, anti‐static, antimicrobial properties, and so on, mostly modified by additive nanoparticles (Zhou and Gong 2008; Vitchuli et al. 2010). Additionally, nanotechnology plays a pivotal role in the fabrication of new textile materials to form nonwoven and woven fabrics from nanofibers or nanofiber yarns, in order to obtain some unique functions (e.g. high specific surface area, high porosity).
The diameters of traditional fibers are usually greater than 2 μm. It is important to note that fibers in a smaller size (particular in nanosize, with a diameter less than 500 nm) can bring fantastic features, such as super‐hydrophobicity, excellent flexibility, good electrical property. For instance, Matsumoto et al. found that chitosan/polyethylene oxide nanofiber fabrics provided great electrostatic force, which could contribute to DNA adsorption for biomedical use (Matsumoto et al. 2007). The small size and large porosity of nanofiber nonwoven fabrics were also in favor of capturing PM 2.5 particles (Wang et al. 2016). According to literature, nanofibers can be produced maturely by a variety of techniques such as electrospinning, melt blowing, bicomponent spinning, and flash spinning (Feng 2017; Zhou and Gong 2008). However, it is still in the exploring period to fabricate the nanofiber‐based yarns and fabrics.
This chapter includes the cutting‐edge fabrication methods of nanofibers, nanofiber‐based yarns, and fabrics. Nanosized textile materials are able to provide greater advantages than traditional textile materials, such as smaller pore size and larger surface area. Due to these unique properties, nanofiber‐based woven/nonwoven fabrics have created a variety advanced fields of applications. Here gives an overall vision of their technological processes, mostly in the laboratory stage, to discuss the current research status and bottleneck problems.
2.2 Fabrication of Nanofiber Yarns
In the concept of textiles, a yarn is the assembly of fibers by the force of cohesion, which is continuously long and with suitable strength. It is hard to fabricate extremely fine yarns by the conventional method mainly due to the significantly thinner diameter and lower strength of the individual fibers. At present, efforts have been taken on developing nanofiber yarns by various approaches. Here we mainly introduce techniques of electrospinning, bicomponent spinning, melt blowing, flash spinning, and centrifugal spinning (Feng 2017; Zhou and Gong 2008).
2.2.1 Electrospinning
Electrospinning is a versatile method to fabricate nanofibers from a polymer solution by a high‐voltage electrostatic force. This technique was initially invented by Formhals in 1930s (Anton 1934). It was not until the late twentieth century, electrospinning was being massively investigated for nanofiber fabrication. Electrospinning setup generally consists of a syringe pump, a collector, and a high‐voltage supply. A polymer solution is placed in a syringe, squeezed from the spinneret, meanwhile, stretched by the electrostatic force provided by a high‐voltage power supply, shown in Figure 2.1 (Zhu et al. 2016). At last, nanometer‐scaled fibers are able to be gathered on the collector (Vitchuli et al. 2010).
The electrospinning method is appropriate for a variety of polymers, including nylon (PA), polyurethanes (PU), polybenzimidazole (PBI), polycarbonate (PC), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polylactic acid (PLA), polyethylene‐co‐vinyl acetate, polyethylene oxide (PEO), polyethylene terephthalate (PET), polystyrene (PS), polymethyl methacrylate (PMMA), polyvinyl phenol, polyvinyl chloride (PVC), cellulose acetate, polycaprolactone (PCL), polyacrylamide, poly(vinylidene fluoride) (PVDF), polyether imide, polyethylene glycol, polyvinyl pyrrolidone (PVP), as well as the combination of different polymers with/without inorganic compounds (Vitchuli et al. 2010; Zhu et al. 2016, 2015; Ge et al. 2017). In addition, the structure of resultant nanofibers can be varied according to the spinneret design, such as hollow structure and core–sheath structure (Zhang et al. 2015; Gimenez‐Lopez et al. 2013; Shi et al. 2011; Jiang and Qin 2014).
Figure 2.1 Schematic image of electrospinning setup.
Source: Zhu et al. (2016).
The practical application of electrospinning is limited due to its low production rate. Conventional single‐needle electrospinning brings about low productivity, which cannot meet the high production demand for the industry. Currently, many approaches have been used to improve the production rate by using multiple jets or nozzleless systems, such as bubble solution system (Jiang and Qin 2014; Jiang et al. 2013).
2.2.2 Bicomponent Spinning
Bicomponent spinning is defined as a spinning process using a precursor system containing two different polymers, with the particular shape of spinneret, forming a bicomponent fiber. Usually, these two polymers provide distinct behaviors in thermal properties or solubility in solvents so that one of them can be removed by a thermal or solvent washing process. Using this technique, one can achieve ultrafine fibers via using a particular nozzle, such as the unique shape of islands‐in‐the‐sea or segmented pie, introduced in Figure 2.2 (Chien et al. 2013). The original example of this technique was Japanese industries like Toray and Kanebo, who applied ultrafine fibers in suede leather and clean cloth products. So far, bicomponent spinning is still a promising technique for producing fine filaments.
Figure 2.2 Cross‐section types of bicomponent fibers.
Source: Chien et al. (2013).
Fine fibers made from polymer systems such as PS/PET (Sugawara et al. 2015), PA‐6 and PLA (Fedorova and Pourdeyhimi 2007), hydrophobic polyvinyl acetate (PVAc), and hydrophilic PVP (Rajgarhia et al. 2016) have been used in this process, and the diameters of the obtained fibers can be as small as 300 nm (Zhou and Gong 2008). However, this process is complicated, and the nozzle is difficult to design if a fiber with a small diameter is desired. The sacrificial part of
