Elektro-üretim yöntemi ile poliakrilonitril nano liflerden iplik üretilmesi

Nanotechnology is an interdisciplinary technology that finds more application areas to itself over time. Nanoscale materials exhibit different optical, thermal and magnetic properties compared to their bulk forms, and they promise a great opportunity and possibility in technologies including medicine, information technologies, energy and environment. Nano structures are defined as materials with at least one dimension is below 100 nm. However, nanofibers are defined as fibers with diameters less than 1 µm as the current production techniques cannot produce fibers under 100 nm. There are many methods to produce nanofibers. Electrospinning is accepted as the most effective and versatile technology among those methods. Electrospinning process relies on applying electrostatic forces to produce nanofibers from various polymer solutions or melts. Basic set-up consists of three main units; feeding unit (spinneret), collector and high voltage power supply. Voltage is applied to the droplet, which is held at tip of the spinneret`s needle under influence of surface tension. When the electrostatic forces overcome the surface tension, jets eject from the droplet towards to the collector. Jets undergo stretching, elongation, solidification during their travel and nanofibers are collected on the collector. However, they are generally in randomly oriented nonwoven mat form, which limits the utilization areas. In this study it is aimed to modify the needle electrospinning technique in order to obtain three dimensional yarns from nanofibers and expand the usage areas. Polyacrylonitrile (PAN) is a polymer used in many studies due to its suitability for versatile investigations and being precursor of carbon fibers. In this study, PAN is used as the polymer and dimethylformamide (DMF) is used as solvent. Polymer solutions were prepared in three different concentrations. In the first part of the study, experiments and device modifications made based on needle electrospinning technique are explained. In the first studies, three spinnerets, which are connected to positive high voltage power supply, a grounded vertically rotating collector and yarn winding unit was used. It was observed that, although it was possible to obtain staple yarn continuously with that apparatus, all the nanofibers cannot be drawn as yarn due to tendency of the same loaded nanofibers to repel each other. Some of the nanofibers were accumulated on the collector`s walls, which would cause the yarn to break after a while. At this stage the feeding unit has been modified to use two spinnerets connected to positive and negative high voltage power supplies separately, taking advantage of the tendency of oppositely charged nanofibers to hold together. The modified apparatus was finalized using a vertically rotating unearthed collector and yarn winding unit. Ejected nanofibers were deposited towards the collector and formed a nanofibrous web by covering mouth of the collector. A conventional guide yarn, of which one end was attached to collector and the other end to the winding system, was used to pull fibrous web from the center. A cone shape was formed due to pulling of the fibrous web. Vertically rotating collector was used to give twist to the yarn at the apex of the cone. Experiments were done with different polymer concentrations, applied voltage values, polymer feed rates, spinning distances, spinnerets angles, collector types and the speeds of the collector and the winding systems. It was tried to obtain twisted PAN staple yarn, composed of nanofibers, continuously by optimizing all process parameters. It is important to ensure dried nanofibers to join yarn structure as wet nanofibers cause yarn structure to be defected. For this reason, optimization of process parameters has been studied to obtain enough stretching, elongation and solvent evaporation of nanofibers during their travel between the spinneret and the collector. The characterization of the yarns was done visually with scanning electron microscope (SEM). The effects of varying process parameters on nanofiber diameter, yarn smoothness and continuity of the process have been investigated. In the last part of the study, the experimental work held with other spinnable polymers was explained. It was observed that the developed apparatus can be used to obtain yarns from all spinnable polymers.