聚丙烯中电树枝生长机理研究

摘要

耐电树枝老化特性是表征聚合物绝缘材料介电性能的重要参数之一。聚丙烯(PP)是典型半结晶聚合物，其复杂的非均匀聚集态结构影响电树枝的生长。本文对PP及加入成核剂的PP试样进行了耐电树枝化性能实验，通过偏光显微镜(PLM)及差示扫描量热法(DSC)分析加入成核剂前后PP的结晶形态、结晶度以及结晶结构对电树枝生长特征的影响。以相界面自由能的热驱动作用以及放电雪崩理论为基础，对电树枝生长的热力学和动力学机理进行分析，阐明电场分布对电树枝生长的重要作用。根据半结晶材料的结晶相和非晶相的物理性能，建立材料内部电场分布计算模型，模拟针-板电极条件下聚合物材料内部的局域电场分布情况，分析了电树枝通道的动力学生长特征，探讨了成核剂改变PP的结晶结构抑制电树枝沿电场生长的作用。%Growth property of electrical treeing is an important parameter to evaluate the insulation performance of a polymer. The complex non-uniform state of aggregation structure determines the electrical treeing growth in polypropylene (PP), a typical semi-crystalline polymer. In this paper, the electric treeing resistance property experiments for PP as well as the PP sample with nucleating agents are carried out. Effects of crystal shape, crystallinity, and crystalline structure on the electrical treeing growth characteristics in PP and PP with nucleating agents have been analyzed using polarized light microscopy (PLM) and differential scanning calorimetry (DSC). Thermodynamic and dynamic mechanisms of electrical treeing propagation are represented respectively by the thermodynamically driven action of phase interfacial free energy and the discharge-avalanche theory, demonstrating the essential role of electric field distribution in electrical treeing growth. According to physical properties of crystalline phase and amorphous phase in semi-crystalline materials, a computational model of interior electric field distribution has been established to simulate local electric field distribution in the polymer material under needle-plate electrode configuration, and used to analyze the characteristics of electrical treeing channel growing along the grain boundary in semi-crystalline materials. Inhibition effects of crystalline structure changed due to the nucleating agents on electrical treeing growth along the electric field direction are investigated.