Key Laboratory of Engineering Dielectrics and Its Application, Ministry of Education, School of Electrical and Electronic Engineering, Harbin University of Science and Technology, Harbin 150080, China.
Molecules. 2020 Aug 12;25(16):3669. doi: 10.3390/molecules25163669.
Water-tree resistances of styrene block copolymer/polypropylene (SEBS/PP) composites are investigated by characterizing crystallization structures in correlation with the dynamic mechanical properties to elucidate the micro-structure mechanism of improving insulation performances, in which the accelerated aging experiments of water trees are performed with water-knife electrodes. The water-tree morphology in spherulites, melt-crystallization characteristics and lamella structures of the composite materials are observed and analyzed by polarizing microscopy (PLM), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively. Dynamic relaxation and stress-strain characteristics are specifically studied by means of a dynamic thermomechanical analyzer (DMA) and electronic tension machine, respectively. No water-tree aging occurs in both the highly crystalline PP and the noncrystalline SEBS elastomer, while the water trees arising in SEBS/PP composites still has a significantly lower size than that in low-density polyethylene (LDPE). Compared with LDPE, the PP matrix of the SEBS/PP composite represent a higher crystallinity with a larger crystallization size in consistence with its higher mechanical strength and lower dynamic relaxation loss. SEBS molecules agglomerate as a "island" phase, and PP molecules crystallize into thin and short lamellae in composites, leading to the blurred spherulite boundary and the appreciable slips between lamellae under external force. The high crystallinity of the PP matrix and the strong resistance to slips between lamellae in the SEBS/PP composite essentially account for the remarkable inhibition on water-tree growth.
苯乙烯嵌段共聚物/聚丙烯（SEBS/PP）复合材料的耐水树性能通过与动态力学性能相关联的结晶结构来表征，以阐明改善绝缘性能的微观结构机理，其中采用水刀电极进行了水树的加速老化实验。通过偏光显微镜（PLM）、差示扫描量热法（DSC）和扫描电子显微镜（SEM）分别观察和分析了复合材料中的球晶中的水树形态、熔融结晶特性和片层结构。通过动态热机械分析仪（DMA）和电子拉力机分别专门研究了动态松弛和应力-应变特性。高结晶度的 PP 和非晶态 SEBS 弹性体均未发生水树老化，而 SEBS/PP 复合材料中的水树仍然明显小于低密度聚乙烯（LDPE）中的水树。与 LDPE 相比，SEBS/PP 复合材料中的 PP 基体具有更高的结晶度，结晶尺寸更大，这与其更高的机械强度和更低的动态松弛损耗一致。SEBS 分子聚集为“岛”相，PP 分子在复合材料中结晶成薄而短的片层，导致在外力作用下球晶边界模糊，片层之间明显滑动。PP 基体的高结晶度和 SEBS/PP 复合材料中片层之间滑动的强烈阻力，从根本上解释了对水树生长的显著抑制作用。
