冷拉程度对聚丙烯微孔膜结构和性能的影响

Effect of Cold-Drawing Ratio on Structure and Properties of Polypropylene Microporous Membranes

采用熔融拉伸法制备聚丙烯微孔膜,研究了不同冷拉程度对微孔膜微观结构和性能的影响。采用差示扫描量热仪、扫描电镜、毛细管流动分析仪测试后发现,随着冷拉拉伸比的增大,微孔膜拉伸曲线塑性平台减弱,对应差示扫描量热曲线中由于热定型过程结晶带来的吸热平台减弱。冷拉拉伸比为15%时,微孔膜具有较好的微观结构和透气性,冷拉拉伸比达到60%时,微孔分布和排列变差,孔径变小,孔隙率降低,透气性变差。热处理过程中由于Tie链结晶形成的不稳定结构在冷拉后转变为连接分离片晶的架桥,随着冷拉拉伸比的增大,这部分转变越彻底,但同时也带来片晶结构崩溃,导致孔径减小,性能变差。

Polypropylene microporous membrane was prepared by melt-stretching method. The influence of cold- stretching ratio on the microstructure and properties was investigated by differential scanning calorimetry, scanning electron microscopy and capillary flow porometer. The results show that with the increase of cold-stretching ratios, the plastic plateau in the stress-strain curves and the endotherm plateau in the DSC curves of microporous membrane decrease. The membrane shows better air permeation ability and microstructure when the cold-stretching ratio is 15 %. The cold-stretching ratio up to 60 % results in the decrease of pore size and worse air permeability. During cold stretching, the metastable crystalline phase formed by annealing converts to the initial bridges connecting separated lamellae. With the increase of stretching ratios, the lamellae is separated completely, but at the same time the separated lamellae is collapsed, resulting in the decrease of pore size and worse air permeability.