Formation of Non-graphitizing Carbon Fibers Prepared from Poly(p-phenylene terephthalamide) Precursor Fibers


KARACAN I. , ERZURUMLUOGLU L.

FIBERS AND POLYMERS, cilt.16, ss.961-974, 2015 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 16 Konu: 5
  • Basım Tarihi: 2015
  • Doi Numarası: 10.1007/s12221-015-0961-5
  • Dergi Adı: FIBERS AND POLYMERS
  • Sayfa Sayıları: ss.961-974

Özet

The effect of carbonization temperature on the structure and properties of poly(p-phenylene terephthalamide)-based carbon fibers from commercially available Twaror (R) (PPTA) presursor is reported. Turbostratic PPTA-based carbon fibers were produced using a single step procedure in an inert atmosphere at temperatures ranging from 600 to 1100 degrees C. In the present study, fiber diameter, mass yield, density, elemental analysis, X-ray diffraction, Raman spectroscopy, tensile testing and electrical conductivity measurements were performed and evaluated to follow and monitor the properties and structural transformations of carbon fibers with rising temperature. The increase of heat-treatment temperature to 1100 degrees C decreased the interlayer d-spacing (d(002)) and increased the in-plane size (L-a) and thickness (L-c) of the graphene layers. The intensity ratios of D to G bands in the Raman spectra increased with rising temperature, suggesting, in agreement with the X-ray diffraction measurements, that the in-plane size (L-a) of the graphene planes increased with temperature. The density, carbon content, C/H ratio, apparent crystallite size (L-a and L-c), electrical conductivity and tensile properties of the resultant carbon fibers were enhanced with rising temperature. It has been shown that the gage length of the carbon fibers tested has a significant effect on the tensile strength obtained. After taking into account the effects of gage length and porosity dependence, the carbonization of PPTA precursor fibers prepared at 1100 degrees C gave a tensile strength of 191 MPa and a tensile modulus of 83 GPa, respectively.

Carbon fibers with diameters ranging from 8.1 and 12.7 mm were produced using a commercially available meta-aramid precursor after oxidation and carbonization steps. The carbonization process was performed using a single-step procedure between 500 and 1100 °C. The effect of  temperature on the structure and properties of  carbon fibers was investigated in detail. The process of  carbonization was examined using several characterization techniques including fiber diameter, mass yield, density, elemental analysis, mechanical property testing and electrical property measurements. Structural transformations were followed and monitored using X-ray diffraction, IR and Raman spectroscopy techniques. The results suggested that the mass yield  reached a value of 40.4% at a heating temperature of 1100 °C. Density, carbon content, mechanical properties and electrical conductivity values increased and hydrogen and nitrogen contents decreased with an increase in temperature. Analysis of the X-ray diffraction traces of carbon fibers suggested broadening of the (002) and (100) diffraction planes which was attributed to the formation of an amorphous carbon structure. The IR spectra showed, at temperatures of 500 °C and above, initial weakening and eventual disappearance of  the major amide bands (amide I, II, III and IV) due to the loss of hydrogen bonds between the polymer chains indicating the partial removal of nitrogen, hydrogen and oxygen atoms during the carbonization reactions.  The analysis of Raman spectra demonstrated that the positions and the peak widths of the G- and D-bands showed great dependence on treatment temperature. The mechanical properties of the carbon fibers showed strong dependence on heat-treatment temperature, porosity and gage length. Temperature and gage length showed a significant effect on the tensile strength values obtained after each treatment temperature. A marked increase was observed in tensile strength values after extrapolation to 1 mm, which increased from 186 to 589 MPa with carbonization up to 1100 °C.  Tensile modulus values were affected by both temperature and porosity and reached a value of  81 GPa at 1100 °C.  Porosity correction caused an enhancement in tensile modulus values between 21 and 33.5%.  SEM images of carbon fibers demonstrated the presence of structural imperfections confirming the results obtained from the porosity measurements.