热处理对紫外辐照聚丙烯腈纤维环化交联结构的影响

Effect of heat treatment on cyclization crosslinking structure of ultraviolet irradiated polyacrylonitrile fiber

为探究预氧化阶段紫外(UV)辐照聚丙烯腈(PAN)纤维诱导环化交联反应的机理,对紫外辐照后的PAN纤维(UVRPAN)在不同气氛下进行热处理,分析温度对纤维内交联结构、环化结构和热性能的影响。结果表明:随着热处理温度增加,UVRPAN纤维中的交联结构与环化结构增加,环化结构长度增加,交联度由34.4%逐渐上升至44.9%,氰基转化率由33.5%升高至58.4%;O2促进了纤维内环化结构的产生,并延长了环化结构长度;热处理后,UVRPAN内自由基的种类未发生改变,自由基浓度随热处理温度升高而降低;随热处理温度升高,空气条件下环化放热焓值由550.9J/g降低至431.9J/g,氮气条件下由423.1J/g降低至372.6J/g,证实热处理可缓解预氧化过程中的集中放热。

In order to explore the mechanism of cyclization crosslinking reaction induced by ultraviolet(UV)irradiation of polyacrylonitrile(PAN)fibers in the pre-oxidation stage,the UV irradiated PAN fibers(UVRPAN)were heat treated in different atmospheres and the effects of temperature on the crosslinking structure,cyclization structure and thermal properties of the fibers were analyzed.The results showed that with the increase of heat treatment temperature,the crosslinking structure,cyclization structure of UVRPAN fibers increased,and the length of cyclization structure extended.The crosslinking degree increased from 34.4%to 44.9%,and the conversion of cyano group increased from 33.5%to 58.4%.The O2 promoted the generation of cyclization structure in the fiber and prolonged the length of the cyclization structure.The types of free radicals in the UVRPAN fibers remained the same as those before the heat treatment and the concentration of free radicals decreased with the increase of heat treatment temperature.With the increase of heat treatment temperature,the exothermic enthalpy of cyclization decreased from 550.9 J/g to 431.9 J/g in air,and the exothermic enthalpy of cyclization decreased from 423.1 J/g to 372.6 J/g in N2,which proved that heat treatment could alleviate the concentrated heat release in the process of pre-oxidation.