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RISS 인기검색어
- 검색키워드
- 저자 : Ismail Karacan (검색결과 3 건)
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Karacan Ismail The Korean Fiber Society 2005 Fibers and polymers Vol.6 No.3
A selection of commercially available poly(ethy1ene terephtha1ate) fibers with different degrees of molecular alignment and crystallinity have been investigated utilizing a wide range of techniques including optical microscopy, infrared spectroscopy together with thermal and wide-angle X-ray diffraction techniques. Annealing experiments showed increased molecular alignment and crystallinity as shown by the increased values of birefringence and melting enthalpies. Crystallinity values determined from thermal analysis, density, unpolarized infrared spectroscopy and X-ray diffraction are compared and discussed in terms of the inherent capabilities and limitations of each measurement technique. The birefringence and refractive index values obtained from optical microscopy are found to decrease with increasing wavelength of light used in the experiments. The wide-angle X-ray diffraction analysis shows that the samples with relatively low orientation possess oriented non-crystalline array of chains whereas those with high molecular orientation possess well defined and oriented crystalline array of chains along the fiber axis direction. X-ray analysis showed increasing crystallite size trend with increasing molecular orientation. SEM images showed micro-cracks on low oriented fiber surfaces becoming smooth on highly oriented fiber surfaces. Excellent bending characteristics were observed with knotted fibers implying relatively easy fabric formation.
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Karacan Ismail The Korean Fiber Society 2005 Fibers and polymers Vol.6 No.3
Structural studies of series of 'as spun' and drawn PEEK fibers have been carried out using X-ray diffraction and optical microscopy techniques. The analysis of results suggest that fibers produced at a constant draw ratio with increasing draw temperatures show enhanced orientation and crystalline behaviour. The resolved equatorial and meridional traces provide additional structural parameters in terms of crystallinity, crystallite size, and crystallite thickness. It is concluded that drawing at a temperature below $T_g(i.e.,\;144^{\circ}C)$ results in poorly oriented non-crystalline materials, whereas drawing above $T_g$ results in highly oriented semi crystalline materials. Additional drawing proved to increase the overall orientation with slight improvements in lateral order of the chain molecules. Quantitative analysis revealed that the crystallite size increases with increasing drawing temperature. The results also revealed the increased crystallite size upon additional drawing. Crystalline orientation parameter, $<P_2>_c$, suggests almost perfect orientation. In all cases, the amorphous orientation is found to be lower than the overall orientation parameter obtained from the optical birefringence. As a result of additional drawing, crystalline orientation was found to increase slightly but the increase in the orientation of non-crystalline material was found to be substantial. An average crystalline density was determined from the orthorhombic unit cell dimensions. It was found to vary as a result of processing conditions. It was also found that the value of the maximum birefringence shows heavy dependence on the chain conformation.
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Tuba Demirel,Md. Mahbubor Rahman,Kemal Şahin Tunçel,Ismail Karacan 한국섬유공학회 2022 Fibers and polymers Vol.23 No.11
Thermal-oxidative stabilization of polyacrylonitrile (PAN) fiber pretreated with ammonium bromide (NH4Br) wasperformed in the air atmosphere at temperatures between 200 and 250 °C for periods of 5 to 75 min in a multistep approach. The study demonstrates that the NH4Br incorporation is highly effective in accelerating nitrile group cyclization by reducingthe time required to form a thermally stable structure. After 60 min of the multistep stabilization, NH4Br incorporated andstabilized PAN was entirely thermally stable, infusible, and non-burning. XRD analysis showed the conversion of the pristinePAN molecular structure from a laterally ordered condition to a very disordered amorphous structure by crosslinking andaromatization process. Infrared analysis indicated rapid and concurrent aromatization and dehydrogenation reactions assistedby the formation of oxygen-containing functional groups. With the progression of the stabilization period, TGA thermogramsrevealed a comparative increase in thermal stability, as directed by the continuous rise of carbon yield. By decreasing therequired time for the stabilization process of PAN fiber, the use of NH4Br impregnation is expected to enhance carbon fiberproductivity at a reduced cost considerably.
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