低温炭化温度梯度对聚丙烯腈预氧纤维结构演变及碳纤维性能的影响

Effect of low-temperature carbonization temperature gradient on structural evolution of PAN stabilized fiber and properties of carbon fiber

聚丙烯腈(PAN)预氧纤维在低温炭化阶段经热裂解重组而转化为具有乱层石墨结构雏形的低温炭化纤维,此阶段的温度调控对最终碳纤维的结构与性能有着重要影响。采用^(13)C固体核磁共振谱图(^(13)C-NMR)、拉曼光谱(Raman)、X射线衍射(XRD)和力学性能分析等手段,研究预氧纤维在低温炭化阶段的反应进程、温度梯度调控对预氧纤维的结构演变和碳纤维结构及性能的影响。结果表明:PAN预氧纤维在低温炭化过程中,经450℃热处理后碳结构的支链化程度达到最大值0.99,当处理温度达到550℃后,以芳环链段的重组交联为主要反应。低温炭化温度梯度影响预氧纤维的结构演变进程,当采用350—450—650℃的梯度升温模式时,先经450℃处理的低碳纤维中—C—C基团的^(13)C-NMR位移最大,表明纤维内的支化交联反应最多,再经650℃处理的纤维d_(002)以及相应高碳纤维的I_(A)/I_(G)达到最大,说明其无定形碳相对含量最多,因而最终碳纤维的力学性能最差;当采用350—550—650℃的梯度升温模式时,纤维内裂解与重组交联反应有序开展,低碳和高碳纤维的碳结构更优,最终碳纤维的致密性及力学性能得到提升。

In low-temperature carbonization stage,stabilized polyacrylonitrile(PAN)fibers are pyrolyzed and recombined to transform into low-temperature carbonized fiber with rudiment of turbostratic graphite structure.The temperature regulation of low-temperature carbonization has an important influence on the structure and performance of the final carbon fibers.The reaction process of stabilized fiber during low-temperature carbonization stage,the effect of the regulation of low-temperature carbonization temperature gradient on the structural evolution of stabilized fiber and the structure and performance of carbon fiber were studied through ^(13)C-NMR,Raman,XRD and mechanical property analysis.The results indicate that:in the process of low-temperature carbonization heat treatment of stabilized fiber,the carbon structure shows the degree of branched chain reaches a maximum of 0.99,after heat treatment at 450℃.When the heat treatment temperature reaches 550℃,the main reaction is the recombination crosslinking reaction of stabilized fiber’s aromatic chain segments.The low-temperature carbonization temperature gradients affect the structural evolution of stabilized fibers.When the temperature gradient is 350-450-650℃,the ^(13)C-NMR shift of the —C—C group in the low carbon fiber treated at 450℃ is the largest,the branching crosslinking reactions in fiber are the most,causing the d_(002) of the low carbon fiber treated at 650℃ and the I_(A)/I_(G) of the corresponding high-temperature carbon fiber are the largest,the relative content of amorphous carbon is the largest and the mechanical properties of the final carbon fiber are the worst.However,when the temperature gradient is 350-550-650℃,the cracking and recombination crosslinking reaction in fiber are carried out in an orderly manner,resulting in the structure of low-temperature carbonized fiber and carbon fiber more perfect,and the density and mechanical properties of carbon fiber are improved.