Design and development of nanocomposite fibers

Nanotechnology is science, engineering, and technology performed at the nanoscale to control and restructure the matter at the atomic and molecular levels. It has become very popular due to the rapidly developing techniques to synthesize, manufacture, and characterize materials at the nanoscale and offers substantial improvements in many different fields including environmental protection, medicine, chemistry, electronics, and engineering. Nanocomposites, which are produced by the addition of nanoparticles to improve a particular property of the material, are being widely investigated. Polymer nanocomposites exploit the useful properties of nanomaterials for a variety of applications such as automotives and packaging industries, building and construction, electrical and electronics, and sports and medical devices. Batteries with greater output, faster healing broken bones, structural components with high strength to weight ratio, lightweight sensors, and flexible batteries have been developed with the use of nanocomposites. Textile industry is also experiencing the benefits of nanocomposites in the form of fibers (nano/micro), and coatings. Nanocomposite fibers are the advanced new class of polymer nanocomposite materials with an ultrafine dispersion of nanoparticles in a polymeric matrix and offer properties that are lacking in the commodity synthetic fibers. The wide selection of nanoparticles (nanotubes, metal and metal oxides, nanoclays, etc.) makes it possible to produce a range of functional nanocomposite fibers that can be successfully used in various applications. When compared with neat polymers or conventional composites, nanocomposite fibers show much superior properties such as higher modulus, increased strength, improved thermal stability, flame retardancy, antimicrobial properties, water repellency, dyeability, soil-resistance, antiinfrared, and useful electrical, optical, barrier properties at very low loadings (<5 wt%) of nanofillers. These novel materials are expected to have a major impact in tyre reinforcement, electro-optical devices, filtration, medical textiles, protective clothing and so on. Polyacrylonitrile (PAN) is one of the most important polymers with fiber-forming ability. Because of its form stability, color fastness to washing and sunlight, chemical resistance, moth resistance, similarity to wool in means of texture and look, clothing is one of the important applications for PAN fibers. It also has a wide range of applications other than clothing (outdoor awnings, sails for yachts, hot gas filtration systems, and fiber-reinforced concrete) due to its high durability, friction resistance, abrasion resistance, and biocompatibility. PAN fiber is a good candidate for biomaterials (i.e. artificial muscles) since it has excellent biocompatibility. It is also widely used in nanofiber production. PAN nanowebs can be used in tissue scaffolds, filtration, and protective clothing with higher efficiency. Polyaniline is important among the conductive polymers due to its unique properties such as easy synthesis, low cost of raw material, good compatibility with other polymer supports, tunable electrical and electrochemical properties, etc. It has wide application potential in electrochromic devices, sensors, separation membranes, batteries, and smart fabrics. PANI addition/incorporation into PAN nanofibers/fibers may form a competitive system for the production of fibers with multifunctional properties. Due to their superior thermal, mechanical, and electronic properties, CNTs are widely used in composites for reinforcement and/or functionalization. They have unique properties such as high strength and aspect ratio, good thermal and electrical conductivities, and a low density. On the other hand, nanocomposites acquire catalytic, optical, and especially antibacterial properties with the addition of silver nanoparticles. Nanocomposites with silver nanoparticles may have the potential to be used in wound-healing applications, filtering media, chemical and biological protective materials (biocidal agents against bacteria), air or water filters for purification purposes due to their good electrical conductivity, antimicrobial, reinforcing and catalyst properties. TiO2 nanoparticles have outstanding photocatalytic degradation activity. Their superior performance in photocatalytic degradation makes them preferable in self cleaning, antibacterial agent, environmental purification, water and air purifier, gas sensors applications. Besides, they are also used to impart antibacterial, antistatic, UV protection properties. Nanoclays are reported to improve flame-retardant behavior, thermal stability, mechanical properties, and barrier properties. This PhD investigates the feasibility of developing multifunctional PAN nanofibers/fibers by adding polyaniline and different nanoparticles to the fiber structure. Polyaniline (PANI), carbon nanotubes (CNTs), silver nanoparticles (AgNPs), titanium dioxide nanoparticles (TiO2 NPs), and nanoclays are used as additives. They are added either alone or in different combinations into the nanofiber/fiber structure in order to obtain nanofibers/fibers with new functions and/or multifunctions. Electrospinning is used to produce nanocomposite PAN nanofibers, while wet spinning is used to produce nanocomposite PAN filaments. The strategy for combining different materials into fibers is expected to offer a key to develop new fibers with improved functionalities. In Chapter 1, after a brief introduction, the purpose of thesis is presented together with the objectives and outline of the thesis. Chapter 2 provides general information about the materials and methods used in this study and presents literature survey, which covers the studies about composite PAN nanofibers produced with the addition of PANI, CNTs, AgNPs; composite fibers produced with the addition of PANI, CNTs, AgNPs; nanofibers and coaxial nanofibers produced with the addition of TiO2; and nanofibers/fibers produced with the addition of nanoclays. Chapter 3 is reserved for experimental work. Nanocomposite nanofibers and fibers are produced with the addition of polyaniline and different nanoparticles (CNTs, TiO2, AgNPs, nanoclays) with the aim of developing multifunctional nanofibers and fibers, and the results obtained are explained with the help of relevant tables and figures within this chapter. It includes 6 subsections. In part 3.1, nanofibers of PAN/PANI, PAN/CNT/AgNP and PAN/PANI/CNT/AgNP are produced and investigated in terms of structural and functional properties. Effects of different solvent and dopant types, PANI loadings, application of different homogenization and mixing methods during soluiton preparation, and redoping on PAN/PANI nanofiber properties have been investigated. The effects of the simultaneous addition of different additives and the application of chemical reduction process have been investigated for PAN/CNT/AgNP and PAN/PANI/CNT/AgNP nanofibers. Part 3.2 consists of studies about production and characterization of PAN/AgNP, PAN/PANI/AgNP, PAN/PANI/CNT, and PAN/CNT/AgNP filaments. While part 3.3 includes experimental work performed for the production of PAN/TiO2/AgNP nanofibers displaying photocatalytic degradation ability, antibacterial and antistatic properties, part 3.4 includes studies about the production of PAN/TiO2/AgNP filaments. In part 3.5, nanoclays is added to PAN nanofiber structure and the nanocomposite PAN/nanoclays nanofiber is characterized in terms of burning behavior. In part 3.6, coaxial PA 6 nanofibers are produced. TiO2 is added to the shell part of the coaxial nanofibers in order to improve nanofibers with photocatalytic degradation ability. Additionally, coaxial nanofibers with PA6/AgNP core and PA6/TiO2 shell are produced with the aim of producing nanofibers showing both antibacterial properties and photocatalytic degradation ability. Coaxial nanofibers are characterized in terms of structural and functional properties. Chapter 4 presents the main conclusions reached and some suggestions about the possible future work. This PhD showed the possibility of producing multifunctional nanofibers/fibers by adding different types of additives to the nanofiber/fiber structure. The nanocomposite nanofibers/fibers with improved properties and/or functions are expected to be ideal candidates for applications such as antibacterial textiles, protective clothing, filtration media, biomedical textiles, antistatic textiles, electrostatic discharge applications, charge storage devices, sensors and actuators, electromagnetic shielding, and so on.