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using Ti substrates, similar values were also reached at lower temperatures of 800 °C for Polymers 2022, 14, 721 the Cu substrate and even for 500 °C for the Si substrate. Measuring ID/IG after incipient carbonization at 500 °C in an aluminum sandwich resulted in a value of approx. 1.2 [23], i.e., a lower crystallinity than found for the materials used in the recent study. It can be concluded that the metal substrate, possibly through catalytic activity in the pyrolysis re‐ action, has a significant effect on the degree of crystallization of the CNF, which may allo6wof 8 similar results to be obtained at much lower temperature via substrate variation. Figure 4. Raman investigations of the stabilized and carbonized nanofibers: (A) D and G band re‐ gions and (B) corresponding amplitude ratios ID/IG. To investigate the chemical properties, i.e., the gradual removal of oxygen‐functional groups, FTIR spectroscopy was performed. The results are depicted in Figure 5. After sta‐ bilization, the curves measured on different substrates are mostly similar. The well‐ known peaks occur around 800 cm−1 (aromatic C−H ring bending vibrations), 1575 cm−1 (C=N and C=C stretching vibrations), 1370 cm−1 (C–H deformation), and 1240 cm–1 (C–O Figure4.Raamaannininvvesetsitgiagtaiotinosnsofotfhtehsetasbtailbizileidzeadndancdarcbaornbioznediznedannoafinboefirsb:e(rAs:)D(Aa)nDdGanbdanGdbraen‐d vibrations due to oxygen crosslinking between the polymer chains) [9,28]. gions and (B) corresponding amplitude ratios ID/IG. regions and (B) corresponding amplitude ratios ID/IG. To investigate the chemical properties, i.e., the gradual removal of oxygen‐functional groups, FTIR spectroscopy was performed. The results are depicted in Figure 5. After sta‐ bilization, the curves measured on different substrates are mostly similar. The well‐ known peaks occur around 800 cm−1 (aromatic C−H ring bending vibrations), 1575 cm−1 (C=N and C=C stretching vibrations), 1370 cm−1 (C–H deformation), and 1240 cm–1 (C–O vibrations due to oxygen crosslinking between the polymer chains) [9,28]. FFigiguurree55.. FTIIRininvveesstitgigaatitoionnssofofthtehestasbtailbizileizdeadndancdarcbaornbioznedizendannoafinboefirsb:e(rAs:) s(tAab) islitzaabtiloiznaotinondiof‐n ◦ It should be mentioned that besides all aforementioned spinning, stabilization and carbonization parameters, the thickness of the specimen has a significant impact on the carbonization results. It has been observed that a higher sample thickness, i.e., spinning duration (cf. Figure 1B), stabilizes the CNF mats against macroscopic deformation and breaking. In this regard a (3.5 ± 0.8) μm thick nanofiber mat carbonized at 1200 ◦C on Figure 5. FTIR investigations of the stabilized and carbonized nanofibers: (A) stabilization on dif‐ 4. Conclusions PAN nanofiber mats were stabilized and subsequently carbonized at 500 ◦C, 800 ◦C and 1200 ◦C, sandwiched between different metal and metalloid substrates. For higher temperatures, a higher degree of carbonization and crystallinity was found. The highest nanofiber integrity was found for the Si substrate after carbonization at 500 ◦C, which was ferent substrates, (B) carbonization at 500 °C, and (C) carbonized at higher temperatures. different substrates, (B) carbonization at 500 C, and (C) carbonized at higher temperatures. a Ti substrate had mostly maintained its macroscopic appearance (cf. Figure S1A in the ferent substrates, (B) carbonization at 500 °C, and (C) carbonized at higher temperatures. supplementary materials), while a sample with a thickness of (1.1 ± 0.4) μm had shrunk significantly more (cf. Figure S1B in the supplementary materials). An even thinner specimen with (0.2 ± 0.1) μm completely folded in on itself and had no resemblance to the pristine nanofiber mat whatsoever. Apparently, a certain minimum thickness is necessary to maintain useful CNF after carbonization under these conditions.PDF Image | Carbonization of Electrospun PAN Nanofibers
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