M C. Paina et al. / Carbon 41(2003)1399-1409 1407 (a) (b) Fig 9. SEM micrographs of carbonized fibers obtained from(a)M, and(b)VTa tensile strength results primarily from the critical flaws eems reasonable to anticipate better mechanical properties present in these fiber samples prepared by a batch pre or the v fibers if the molecular weight and orientation In contrast, the flaw-insensitive property, tensile mod can be improved, and the polymer and fibers are produced is not very different for the two types of fibers that have by a continuous process undergone stabilization. It is noted that fibers that were only UV-treated did not depicts the importance of the survive the carbonization step. However, fibers that re- properties of the fibers as related to those of the ceived thermal oxidation treatment after uv irradiation final fibers. The could be successfully carbonized, i., thermal oxidation is orientation in M fibers that went through a post-drawing necessary for fiber stabilization, Table 3 summarizes the step(whereas the VT fibers did not) result in better tensile properties of the M fibers that were stabilized using properties for M fibers. Also, as illustrated in micrographs the dual Uv-thermal treatment and subsequently carbon- of Fig. 9, the larger number and size of flaws in the Vt ized (M. to M,). The results indicate that the introduction fibers manifested into low strength and strain-to-failure. It of a UV irradiation step does not decrease the final Tensile properties of the M fibers Uv irradiated, heat oxidized and carbonized at 1500C No. tests Strain-to-failure (MPa 9.2±0.3 188±26 10±0.4 MMMMMvM 8.8±0.3 674±250 6±17 10±0.3 8.5±0.3 143+28 1.1±0.3 8.6±0.2 020±320 06±30 1.1±0.2 7.1±0.3 15.7+0.7 34+73 0.6±0.1 4410-4900 235-295 1.5-2.0 Range of values from the technical data sheet of Mitsubishi rayon, for a standard PAN-based carbon fiber.M.C. Paiva et al. / Carbon 41 (2003) 1399–1409 1407 Fig. 9. SEM micrographs of carbonized fibers obtained from (a) M and (b) VT . 2 4 tensile strength results primarily from the critical flaws seems reasonable to anticipate better mechanical properties present in these fiber samples prepared by a batch process. for the VT fibers if the molecular weight and orientation In contrast, the flaw-insensitive property, tensile modulus, can be improved, and the polymer and fibers are produced is not very different for the two types of fibers that have by a continuous process. undergone stabilization. It is noted that fibers that were only UV-treated did not Fig. 10a also clearly depicts the importance of the survive the carbonization step. However, fibers that re￾properties of the as-spun fibers as related to those of the ceived thermal oxidation treatment after UV irradiation final fibers. The higher molecular weight and degree of could be successfully carbonized, i.e., thermal oxidation is orientation in M fibers that went through a post-drawing necessary for fiber stabilization. Table 3 summarizes the step (whereas the VT fibers did not) result in better tensile properties of the M fibers that were stabilized using properties for M fibers. Also, as illustrated in micrographs the dual UV-thermal treatment and subsequently carbon￾of Fig. 9, the larger number and size of flaws in the VT ized (M to M ). The results indicate that the introduction a d fibers manifested into low strength and strain-to-failure. It of a UV irradiation step does not decrease the final T able 3 Tensile properties of the M fibers UV irradiated, heat oxidized and carbonized at 1500 8C Sample No. tests Diameter Max. strength Modulus Strain-to-failure (mm) (MPa) (GPa) (%) M 10 9.2 a 60.3 10306260 188626 1.060.4 M 9 8.8 b 60.3 6746250 136617 1.060.3 M 16 8.5 c 60.3 6906230 143628 1.160.3 M 18 8.6 d 60.2 10206320 206630 1.160.2 M 22 7.1 2 60.3 12636309 181620 0.760.2 VT 18 15.7 4 60.7 334673 5866 0.660.1 M – 7 4410–4900 235–295 1.5–2.0 *commercial * Range of values from the technical data sheet of Mitsubishi Rayon, for a standard PAN-based carbon fiber