碳化过程中改性聚丙烯腈预氧化纤维的高温热应力应变研究

采用对比方法研究了高锰酸钾改性与未改性聚丙烯腈(PAN)预氧化纤维在碳化过程中的高温热应力应变行为。表征了过程纤维的基本物化性质,并用SEM,WAXD,EA等对其结构进行了研究。研究结果表明,改性纤维的热应力应变变化可分为370,500,900℃前后4个区域。与未改性纤维相比,改性纤维的应力在370℃以下增长较快;370~500℃快速下降;500~900℃则迅速增高,同时比未改性PAN纤维应力增加20%以上;900℃以上应力基本保持稳定。大负荷下改性纤维易伸长,小负荷下易收缩,与未改性纤维的差别随负荷减少而减小,500℃以上,两种纤维应变速率变化趋势相近。热应力和热应变是纤维在碳化过程中聚集态结构、化学组成、热化学反应能力的综合体现。与热应变相比,热应力的变化趋势更显著,因而可采用控制碳化过程中纤维热应力的变化控制连续制备中纤维结构的变化。经KMnO4改性PAN纤维制取碳纤维的抗张强度比未改性纤维增加了约20%。

High-temperature Thermal Stress and Strain of Modified Polyacrylonitrile Oxidized Fiber During Carbonization Process

Polyacrylonitrile (PAN) precursors were post spinning modified by the use of KMnO_4, which was aimed to result in certain improvements in the quality of carbon fibers. Comparative studies on the thermal stress and strain of modified and unmodified stabilization fiber during carbonization process were performed. Some conventional characterization methods, such as density, mechanical properties, orientation index, etc and SEM, WAXD and EA were employed to characterize the effects of modification on the structure and properties of all fibers. The result indicated that the thermal stress and strain of modified fiber was compartmentalized into 4 temperature regions by the points of 370, 500 and 900. It's stress increased rapidly under 370, decreased swiftly in 370~500, raised remarkably in 500900, kept almost invariable above 900. At the same time, modified fiber elongated easily in heavy pre-load and shrunk easily in light pre-load. The difference between thermal strain of modified fiber and that of unmodified fiber became unremarkable along with the decrescence of pre-load. The trend of speed of the two fibers' strain was close above 500. Because the thermal stress and strain of modified fiber were well related to its structure, chemical component and thermal reaction ability, and the variation of stress vs. temperature was remarkable, it was a good choice to use the stress to control the changes of structure of fibers during continuous carbonization process. The tensile strength of carbon fiber which made by modified fiber was 20% greater than that of unmodified.