聚丙烯腈预氧化纤维碳化中的结构演变与碳纤维微观结构

利用DSC/TG、FT-IR、XRD、元素分析、SEM、TEM和HRTEM系统研究了聚丙烯腈预氧化纤维碳化中的结构演变与碳纤维微观结构。结果表明，中温碳化时，未环化的—C≡N基团继续反应。高温碳化进一步脱H、脱N形成C六元环结构。T-700碳纤维的002衍射峰强度明显高于自制碳纤维，层面间距d₀₀₂小、石墨网堆叠厚度L_c大、结晶度高。碳纤维呈皮芯结构，表皮由片层堆叠而成，结构致密，含大量纳米级微晶的石墨层结构沿纤维轴取向好，而芯部结构疏松。碳纤维皮芯结构的非均质性由原丝和预氧化纤维的结构演变而来。碳纤维分子结构中存在条带结构和球形结构。条带结构的碳层与原丝分子链条带结构状态十分相似。球形结构的碳网面围绕球心排列，与预氧化纤维的球形结构类似，表明原丝至碳纤维的结构转化过程中纤维分子链结构的变化有密切相关性。

Structural evolvement of PAN oxidized fiber during carbonization and microstructure of carbon fiber

The structural evolvement of polyacrylonitrile (PAN) oxidized fiber during the carbonization process and the microstructure of carbon fiber were investigated by the combination of DSC/TG, FT-IR, XRD, elemental analysis, SEM, TEM and HRTEM.The results showed that remnant —C≡N groups continued cyclization reaction in the pre-carbonization process.N hexahydric rings gradually dehydrogenized and denitrogenized.Then they formed C hexahydric rings during the carbonization process.T-700 carbon fiber had high tensile strength due to its smaller d₀₀₂, thicker L_c and higher crystallinity.The microstructure of carbon fiber was composed of 4 parts from skin to core.The high density of sheets packing in the outer skin and the loose structure in the core could be noted.The compact skin of carbon fiber containing lots of nano-crystallites consisted of stacked carbon sheets.The skin-core structure of carbon fiber was evolved from PAN precursor and oxidized fiber.There were strip microstructure and globular microstructure in carbon fiber.The strip microstructure of carbon layers resembled that of PAN molecular chains in precursor fiber.The globular microstructure of carbon layers encircled the center, which was similar to that of the oxidized fiber.It indicated that the microstructure of molecular chains had significant structural interrelationship.