Evolution of functional groups during the preparation of cellulose-based carbon fibers characterized by nanoscale infrared spectroscopy
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摘要: 从纤维截面微区化学基团变化的角度，深入地解析了纤维素基炭纤维制备过程中微观结构的演变。首先利用超薄切片技术获得低温热解各阶段（室温~600℃）纤维的横截面，通过纳米红外技术（Nano IR）获得了纤维的形貌、红外光谱图以及截面微区基团分布的mapping图。结果发现-OH、CO基团在纤维截面上分布不均匀，裂解过程中基团变化显著，皮层和芯层反应不同步；拉曼光谱分析了ID/IG的变化，进一步证实了截面微区结构的不均质导致的性能变化。Abstract: The evolution of functional groups during the preparation of cellulose-based carbon fibers (CFs) was investigated by nanoscale infrared spectroscopy (Nano IR) of the fiber cross-section and surface. The cross-sections of cellulose-based fibers at different stages of low-temperature pyrolysis from room temperature to 600℃ were obtained by an ultra-thin sectioning technique. The infrared spectra and maps of the functional groups at different locations on the cross-section and the surface of a fiber were obtained by the Nano IR. Results showed that C-O and CO groups were distributed evenly on the fiber surface, but -OH groups were unevenly distributed. The -OH group concentration was higher near the surface than in the inner area, but CO groups were distributed evenly on the fiber cross-section. The number of both -OH and CO groups started decreasing at 150℃ and levelled off at 300 and 600℃, respectively. Pyrolysis reactions proceeded from the outer to the inner part of the fiber, indicating that the skin and core were not pyrolyzed simultaneously. ID/IG values from Raman spectroscopy also confirmed the structural heterogeneity in the cross-section at the different pyrolysis temperatures examined. This study is useful to effectively optimize the preparation parameters of CFs with improved properties.
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Key words:
- Nanoscale infrared spectroscopy /
- Cellulose fiber /
- Carbon fiber /
- Functional groups /
- Cross section
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