聚丙烯腈纤维热应力与碳纤维结构及性能的关联性

Relationship between the thermal stress of polyacrylonitrile fibers and the structure and properties of resulting carbon fibers

针对二元共聚聚丙烯腈(PAN)纤维的热应力和聚集态结构特点,借用差示扫描量热(DSC)分析、广角X射线衍射(WAXD)、红外光谱(FTIR)等表征手段研究了预处理阶段(180℃)纤维热应力变化与最终碳纤维结构及性能的关联性。实验结果表明:对于取向度较高,但热应力较大的二元共聚PAN纤维,在180℃进行适当的应力松弛处理有利于最终碳纤维力学性能的提高。进一步的分析表明,随着预处理阶段纤维热应力的降低,PAN纤维内部准晶区的取向度逐渐下降,而纤维的环化反应活化能明显降低,相对环化率逐渐增大,相应碳纤维中类石墨晶体的层间距呈现先减小后增大的趋势,类石墨晶体的堆叠厚度则是先增大后减小;与之对应的碳纤维的拉伸强度以及拉伸模量也呈现出先增大后减小的趋势。综合研究结果表明:对二元共聚PAN纤维进行适当的热应力松弛处理可有效改善最终的碳纤维结构参数,提高其力学性能。

By controlling the on-line thermal stress of Polyacrylonitrile [-P（AN/IA）] at 180 ℃ according to the feature of thermal properties and aggregation structure of PAN binary copolymer [P（AN/IA）], the pre-treated PAN fibers have been continuously stabilized and carbonized to obtain the corresponding stabilized PAN fibers and carbon fibers. The acquired samples were then researched by DSC, FTIR, and WAXD. The analysis results showed that the appropriate thermal stress relaxation treatment of received PAN binary copolymer fibers could improve the tensile strength of resulting carbon fibers. The orientation degree of quasi- crystal areas in PAN fibers has been enhanced with the raise of thermal stress at 180 ℃ ; however, the activation energy of cyclization reaction for pre treatment fibers significantly increased and relative cyclization index for pre-oxidized fibers gradually decreased, the interlayer size of corresponding carbon fibers were initially decreased and then increased, while the crystallite size showed the opposite tendency. The mechanical properties of carbon fibers including tensile strength and tensile modulus showed a strong dependence on the thermal stress relaxation treatment of PAN fibers at 180 ℃. Comprehensive study results show that the binary copolymer [P （AN/IA）] with appropriate thermal stress relaxation treatment could transformed into carbon fibers with superior structure parameters and mechanical properities.