TEM and DOE Optimization Studies of Electrospun Polycarbonate Nanofibers
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TEM and DOE Optimization Studies of Electrospun Polycarbonate Nanofibers
Nirupama Kattamuri and Changmo Sung Center for Advanced Materials, Department of Chemical and Nuclear Engineering, One University Avenue, University of Massachusetts, Lowell, MA 01854, U.S.A. ABSTRACT Electrospinning of polycarbonate with solvent mixtures of THF (Tetrahydrofuran) and DMF (Dimethylformamide) has been performed. The effect of various process parameters like voltage, concentration, flow rate and distance has been investigated to yield uniform polycarbonate nanofibers with minimal bead densities. The temperature and humidity have also been carefully monitored for all the runs. The Design of Experiment (DOE) has been conducted with the help of Minitab software to find the most significant parameter for obtaining uniform beadless nanofibers. These uniform nanofibers can then be used in future work to produce TiO2 nanotubes. INTRODUCTION In contrast to conventional spinning methods like melt spinning, dry spinning etc, electrospinning is an emerging technology which can produce fibers in the sub-micron [3] to nanorange. The high surface area to volume ratio and the high porosity values makes the fibers advantageous in various applications like manufacture of filtration membranes, nanotubes, protective clothing and the like. The process involved in dissolving a suitable polymer in a solvent to form a viscous solution. In our case polycarbonate of Bisphenol A was chosen as it is thermoplastic and can be made flexible at higher temperatures. The dissolved solution was then taken in a syringe and pumped to the tip of the needle with the help of a flow meter. With the application of a critical voltage to the solution the polymer undergoes a whipping process. The surface tension of the solution which puts the solution together is overcome by the electric potential and the polymer starts spinning. During the spinning process the polymer bends and stretches to form fibers. The solvent evaporates during the travel of the fibers towards the grounded target to get a fresh dried mat of electrospun fibers collected on the aluminium foil. EXPERIMENTAL CONDITIONS The polycarbonate of Bisphenol A of MW 27,000 Daltons and the two solvents THF and DMF were purchased from Aldrich Chemical Company Inc. and used without any further processing. The design of experiment was first performed and then electrospinning was done at concentrations ranging from 14 to 18%, voltage 25-30 kV, flow rate 0.01 to 0.5 ml/min and distance 4.5 to 10 inches. A solvent mixture ratio of THF: DMF = 60:40 was used. The temperature and humidity were monitored throughout the experiment. The spun fibers were then imaged with an AMRAY 1400 scanning electron microscope and Philips EM 400 T transmission electron microscope. The image processing to measure the bead density and fiber thickness was done with the help of image processing softwares like GAIA Blue and Scion Imaging.
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IMAGE ANALYSIS Bead density measurement High contrast SEM images were taken and processe
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