Abstract:

The hard elastic high density polyethylene(HDPE)cast film was cold-stretched uniaxially with different stretching ratios and rates in a process of preparing HDPE microporous membranes. AFM, FE-SEM and WAXD were used to observe the variations in the lamellar structure during the cold-stretching processes, and the microporous structure of resulting microporous membranes was evaluated with measurements of porosity and permeability. It was found that increasing cold-stretching ratio could promote the separation of row-nucleated lamellar structure in the films, and be beneficial to the increase of porosity and permeability in the microporous membranes. However, over high cold-stretching ratio led to the collapse of the lamellae, destroying the microporous structure. With the increase of stretching rates, the lamellae was separated to a greater extent, resulting in generation of more micropores and more uniform distribution. During the cold-stretching, the broken micro-second crystals at the lamellae edge and the crystallized long tie chains between lamellae converted to bridges connecting separated lamellae.

Key words: microporous membrane, polymer processing, high density polyethylene, casting, cold-stretching, microstructure, morphology

摘要：

以不同拉伸倍率和拉伸速度在室温下对硬弹性HDPE流延基膜施加冷拉作用，通过原子力显微镜、场发射扫描电镜、X射线衍射以及孔隙率和透气率测定来观察冷拉前后薄膜中片晶结构的变化，并且了解这些显微结构变化对微孔膜结构和性能的影响。研究发现，提高冷拉倍率可以增加拉伸膜中片晶分离程度，有利于形成具有较高孔隙率和透气率的微孔膜，但冷拉倍率过高会使片晶弯曲崩溃，部分微孔闭合；随冷拉速度增加，拉伸膜中片晶分离更加彻底，使得微孔膜中微孔数目增多且分布更加均匀；冷拉过程中拉伸应力下结晶的较长连接链和应力作用下破坏的片晶边缘的微次晶共同构成了拉伸膜中分离片晶间的初始桥结构。

关键词: 微孔膜, 聚合物加工, 高密度聚乙烯, 流延, 冷拉, 显微结构, 形态学