等规和嵌段聚丙烯的结构和性能

Structure and Properties of Isotactic Polypropylene and Ethylene-propylene Copolymer

聚丙烯(PP)不仅具有良好的电气性能和耐热性能,而且在寿命终止后可循环利用,有可能替代交联聚乙烯(XLPE)作为电缆绝缘材料。因而通过研究乙烯–丙烯嵌段共聚聚丙烯(EPC)和等规均聚聚丙烯(iPP)的微观结构、力学冲击强度和电学性能,探讨了EPC作为高压直流电缆绝缘材料的潜力。结果表明:iPP和EPC中只有α球晶,EPC中的α球晶较iPP中的小而密集,球晶之间没有明显的界面,球晶生长速度慢,但总结晶速度快。在不同温度下的非等温结晶过程中,EPC的结晶度低,熔点高。同时EPC中嵌段共聚的乙烯分子链片段形成橡胶态结构,显著提高了其抗冲击强度,低温脆化温度可达–57.3℃,远低于iPP的–5℃。EPC的常温体积电阻率和直流击穿场强低于iPP,但随温度升高其体积电阻率和击穿场强的稳定性高于iPP。在90℃,iPP和EPC的直流击穿场强分别下降了27%和21%,体积电阻率分别下降了128.8×10^(15)?·cm和52.5×10^(15)?·cm。在40 kV/mm下,iPP积聚的空间电荷密度约为EPC的3倍,因而EPC更适用于挤出型高压直流电缆绝缘料。EPC性能的改善均与其相态结构和微观晶体结构有关。

Polypropylene （PP） is well-known for its excellent electrical and thermal properties, as well as good recycling performance, so it has the potential to replace the cross-linked polyethylene （XLPE） as the cable insulation material in the future. Two kinds of PP such as isotactic homo-propylene （iPP） and ethylene-propylene copolymer （EPC） are selected to study the microstructure, impact strength, and electrical properties. The results show that, there is only ct spherulite in iPP and EPC, the spherulites of EPC are smaller and denser than iPP and spherutites of EPC have no distinct interface. The growth rate of the spherulites in EPC is slower than that of iPP, but the crystallization rate is faster. In the different crys- tallization process, the degree of crystallinity of EPC is lower but the melting point of EPC is higher than that of iPP. The ethylene copolymer molecular chain fragment of EPC can be formed into rubber （EPR） structure, which enhances the EPC impact strength, and temperature of the low temperature brittleness of EPC is -57.3 ℃, which is much lower than iPP -5 ℃. It is found that, at room temperature, the DC breakdown and volume resistivity ofiPP are higher than those of EPC. However, with the increasing temperature, the breakdown strength and vohmae resistivity of EPC become more sta- ble. At 90 ℃, the DC breakdown strengths ofiPP and EPC drop by 27% and 21%, and the volume resistivities ofiPP and EPC drop by 128.8× 1015 Ω cm and 52.5× 1015 Ω cm, respectively. The space charge density of iPP is about three times of EPC, so EPC is more suitable for extrusion insulation material of HVDC cables. The improvements of EPC properties are influenced by the phase structure and spherulite structure.