الفهرس | Only 14 pages are availabe for public view |
Abstract Electrospinning is a unique process in that it is able to produce polymer fibers having diameters ranging over several orders of magnitude, from the micrometer range typical of conventional fibers down to the nanometer range. Ultrafine fibers were electrospun from polyacrylonitrile (PAN) and /N,N-dimethylformamide (DMF) solution to be used as a precursor for carbon nanofibers. An electrospinning set-up was designed, constructed used to collect fibers with diameter ranging from 104 nm to 434 nm. Morphology of fibers and its distribution were investigated by varying Berry’s number, charge density, spinning angle, spinneret diameter and collector area. A more systematic understanding of process parameters was obtained and a quantitative relationship between electrospinning parameters and average fiber diameter was established by using response surface methodology (RSM). Optimum electrospinning conditions by using RSM have been utilized to produce five MWCNTs/PAN nanofibril composites. The as electrospun fabrics have been heat treated through two steps; stabilization and carbonization assisted by using static pressure. Morphological characterization via SEM showed a reduction in the electrospun nano fibril average diameter due to hot-pressing from 180 nm to 130 nm. TEM analysis showed a formation of 2-D graphitic structure for the hot-pressed samples. Raman spectroscopy analysis showed an increase in the crystallite size from 3.7 to 9.6 nm for the hot-pressed 5wt.% MWCNTs/PAN samples. Electrical conductivity of the fabrics has been investigated by using (H10K13532-50LCR meter). Analytical approach has been applied based on Lichteneker formula to evaluate the electrical properties of MWCNTs, single nanofiber and single nanofibril composite as a function in its fabric measured properties. The conductivity and Dielectric values of hot-pressed fabrics proved the possibility of using it as a good candidate for surface mounted components especially in biomedical applications. Finally, mechanical and tribological characterization of the hot pressed fabrics by adding MWCNTs improved fabrics modulus of the modulus of elasticity, coefficient of friction (from 1.7 to 0.15) and abrasive mass loss (as low as 0.2 mg) have been achieved. The hot-pressed electrospun MWCNTs/carbon nanofibril composite fabrics can be used, by controlling MWCNTs wt%, as a good candidate for both journal bearings (C.O.F. below 0.4 is required) and brake pads (C.O.F. from 0.4 to 0.7 are required) applications. |