电容膜料聚丙烯热拉伸过程中结构演变研究

Study on hot⁃stretching⁃induced structure evolution of isotactic polypropylene used in capacitance films

通过差示扫描量热仪、X射线衍射、二维小角/广角散射、动态力学分析等手段详细研究了热拉伸引起电容膜料聚丙烯的取向结晶特性,主要关注拉伸应变对有序长周期、取向度、结晶度、熔点、链松弛转变的影响规律。结果表明,拉伸变形造成了取向纤维晶形态,随着应变的增加,取向度和结晶度逐渐提高,即所谓的应变增强结晶现象;而晶片有序堆叠的长周期与拉伸应变无关;热拉伸过程中新生成了厚、薄两种片晶,分别归因于熔融再结晶机理和应变诱导结晶机理;两种新生成片晶的结晶度和熔点受应变影响较小;此外,拉伸取向使得无定形相与结晶相之间电子密度差异减少,不同松弛温度之间相互靠近。

This study mainly focused on the hot-stretching-induced oriented crystallization structure of isotactic polypropyl-ene(iPP)granules specialized for capacitance films(i.e.electrical grade iPP).A series of characterization tools,includ-ing differential scanning calorimetry,wide-angle X-ray diffraction,two-dimensional small-angle/wide-angle X-ray scat-tering,and dynamic mechanical analysis,were employed to determine the long-period spacing,orientation degree,crys-tallinity,melt point and chain relaxation behavior of iPP.The stretching deformation resulted in a highly oriented fibrillar morphology.A strain-induced crystallization enhancement was observed,in which both of the orientation degree and crystallinity increased continuously with an increasing in the strain.Two types of lamellae with thicker or thinner thick-nesses were newly formed during the hot-stretching process.The thicker one can be attributed to the melt-recrystalliza-tion mode,while the thinner one is ascribed to the strain-induced crystallization mechanism.The dependence of strain on their crystallinity and melt point seemed to be weak.Moreover,the electric density difference between the amorphous and crystalline phases decreased with an increase in the strain,and meanwhile the chain relaxation temperatures related to different condensed states became close to each other.