PAN基碳纤维形成过程中热氧稳定化气氛对纤维径向结构演变的关联性研究

EFFECT OF OXIDATIVE STABILIZATION ATMOSPHERE ON THE RADIAL STRUCTURE OF POLYACRYLONITRILE FIBERS DURING THEIR CONVERTION TO CARBON FIBERS

采用红外光谱、X射线能谱、激光显微共焦拉曼光谱、X射线衍射光谱和电子自旋共振等多种表征手段,定量探讨了热氧稳定化气氛中氧气浓度与聚丙烯腈纤维的径向结构转变以及与碳纤维结构和性能的关联.结果表明,随着氧气浓度的增大,氧气自皮层逐渐扩散到纤维内部,热氧稳定化纤维的径向结构趋于均质化.当热氧稳定化过程氧体积浓度(Vo)由20.38%增加到21.15%时,热氧稳定化纤维的皮芯结构逐渐减小,环化程度增幅显著,该过程对碳纤维皮部类石墨结构的形成具有促进作用,所得碳纤维的孔隙率减小,拉伸强度增大.当Vo大于21.34%时,热氧稳定化纤维的皮芯结构基本消失,但氧化程度过高且环化程度增幅缓慢,抑制了碳纤维皮部类石墨结构的形成,所得碳纤维的孔隙率增大,拉伸强度降低.控制Vo为21.15%～21.34%时,热氧稳定化纤维的环化和径向化学结构的均质化程度均得以提高,所得碳纤维在保持皮部较高石墨程度的同时促进了芯部类石墨结构的形成,此时拉伸强度最高,比在常规空气气氛条件下制备的碳纤维提高了12.22%.

The effect of the oxygen concentration of stabilization atmosphere on the radial structure of polyaerylonitrile （PAN） stabilized fibers and the resulting carbon fibers （CFs） was investigated quantitatively by means of X-ray energy dispersive spectrometer, infrared spectrum analysis, microscopic laser Raman spectrometer and electron spin resonance. Results reveal that with the increase of the volume concentration of oxygen（ Vo） ,radial structure of PAN stabilized fibers tends to be more homogeneous as a consequence of the stronger transferring of oxygen into fiber interior. When Vo increases from 20. 38% to 21.15% , an obvious decrease in the radial skin-core structure and a rapid increase in the eyclization degree of PAN stabilized fibers are observed; meanwhile,the porosity of the resulting CFs is decreased and the tensile strength is increased. This condition is demonstrated to be beneficial to form turbostratie graphite structure in the skin region of CFs during the carbonization. In the case of Vo is greater than 21.34% , the radial shin-core structure is almost disappeared in the PAN stabilized fibers, however, the increase of the cyclization degree turns into much slower,which impedes the formation of turbostratic graphite structure in the skin region of the resulting CFs and gives rise to the increase of the porosity and decrease of the tensile strength. When Vo is dominated between 21.15% and 21.34% ,the cyclization and the homogenization of radial structure of PAN stabilized fibers are both facilitated. Meanwhile, the turbostratic graphite structure is increasing in the core and is keeping at a much higher degree in the skin of CFs, enabling a 12.22% increase in tensile strength of the resulting CFs compared to the one obtained from regular air atmosphere.