Abstract:

Polymer films often experience complex temperature fields and tensile fields during processing. Stretching affects the aggregated structure by inducing molecular chain orientation, thereby affecting various properties of the film. Compared to other crystal modifications, βcrystal isotactic polypropylene (iPP) has much better mechanical properties. In this work, we used WBG to improve the βcrystal content of iPP and investigated its structural evolution during casting and post-stretching. With the increase of draw ratio and the decrease of temperature, the crystallinity and tensile strength of iPP casting film increase, however, the βcrystal content decreases. During the post stretching process, increasing the stretch temperature and strain accelerates the transition of iPP from βcrystal to αcrystal. Meanwhile, cavitation occurs at the late stage of post-stretching, which provides the foundation of iPP microporous membrane preparation.

Key words: isotactic polypropylene, βnucleating agent, film, polymer processing, crystallization

摘要：

高分子薄膜在加工过程中往往经历复杂的温度场以及拉伸场，拉伸通过诱导分子链取向而影响聚集态结构，进而影响薄膜各项性能。由于β晶聚丙烯（iPP）具有更好的力学性能，通过加入稀土类β成核剂（WBG）提高了iPP中β晶含量，并且利用流延的方法制备了iPP流延膜，研究了流延以及后拉伸条件对iPP结晶结构的影响。研究结果发现，随着牵伸比的增加以及流延温度的降低，iPP的结晶度增大，β晶含量减少，同时流延膜具有更高的拉伸强度。在后拉伸过程中，增加拉伸温度和应变能够促进β晶向α晶的转变，并且流延膜在拉伸后期出现空洞结构，基于此制备了iPP微孔膜。

关键词: 聚丙烯, β成核剂, 膜, 高分子加工, 结晶