Yazar "Hariri, Hiba" seçeneğine göre listele

Listeleniyor 1 - 2 / 2
  • [ X ]
    Öğe
    Multi-step heating strategy during thermal stabilization of polyacrylonitrile multi-filament bundle before carbonization
    (Wiley, 2024) Hariri, Hiba; Tuncel, Kemal Sahin; Karacan, Ismail
    A polyacrylonitrile (PAN) multi-filament bundle underwent a multi-step heat treatment following impregnation with a solution of ammonium bromide, phosphoric acid and urea (A-P-U). The multi-step thermal stabilization process was conducted in an air atmosphere at temperatures ranging from 200 to 245 degrees C for various stabilization times spanning from 10 to 70 min. Comprehensive analysis of physical and mechanical properties, infrared (IR) spectroscopy, X-ray diffraction (XRD) and thermal analysis (DSC and TGA) revealed the significant influence of stabilization time on the structure and properties of thermally stabilized PAN multi-filament bundle. The fiber thickness and linear density of the stabilized fibers decreased by approximately 29.5% and 10.6%, respectively, after 70 min of heat treatment. However, the fiber density value increased from 1.18 to 1.38 g cm(-3) during the same stabilization time. Additionally, the carbon yield value obtained using TGA increased from 31% to 73% at 850 degrees C. The presence of A-P-U markedly reduced the time needed for the conversion of the PAN polymer into a cyclized structure through its nitrile groups, thereby accelerating the stabilization reactions. Furthermore, the IR spectra exhibited the appearance of C=C bonds, signaling the creation of a crosslinked ladder-like structure. The XRD traces confirmed the decrease in crystallinity with increasing stabilization time, consistent with the findings from IR spectra. The findings showed that the A-P-U integrated system is notably successful and proficient in promoting the cyclization of nitrile groups, thereby decreasing the time needed to establish a thermally stable structure capable of withstanding elevated carbonization temperatures. (c) 2024 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
  • [ X ]
    Öğe
    Structure and Properties of Thermally Stabilized and Ecologically Friendly Organic Cotton Fibers as a New Activated Carbon Fiber Precursor
    (Korean Fiber Soc, 2024) Hariri, Hiba; Tuncel, Kemal Sahin; Karacan, Ismail
    Organic cotton precursor yarn was impregnated in an aqueous solution consisting of diammonium hydrogen phosphate (DAP), boric acid (BA), and urea (U) mixtures before the thermal stabilization stage and then subjected to heat treatments in an air environment at 245 degrees C. The effect of chemical pretreatment on organic cotton yarn was examined using methods such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and infrared (IR) spectroscopy. The XRD analysis revealed a gradual decrease in the crystalline structure, attributed to the disruption of intermolecular hydrogen bonds. DSC and TGA measurements showed an improved thermal stability due to the formation of pre-graphitic structures with aromatic entities at higher temperatures. For samples chemically impregnated and then stabilized, the char yield values increased from 25% to 68% at 500 degrees C and 23% to 53% at 1000 degrees C. Analysis of IR spectra indicated a gradual reduction in both intermolecular and intramolecular hydrogen bonds associated with dehydration and dehydrogenation reactions. The IR spectra also confirmed a decrease in crystallinity with increasing oxidation time, which is consistent with the findings from X-ray diffraction. In addition, the IR spectra showed the presence of C = C bonds, indicating the formation of a crosslinked ladder-like structure. The results showed that DAP-BA-U integration increased the thermal stability of organic cotton fibers and the obtained samples were ready for the next stage, carbonization.