高分子量级分含量对熔体挤出拉伸法制备聚丙烯微孔膜的影响

通过熔体挤出拉伸法以两种聚丙烯为原料制备微孔膜.通过考察原料分子量数据发现高分子量聚丙烯(PPH)在高分子量级分(重均分子量>106)含量上大于低分子量聚丙烯(F401).PPH的弛豫时间在相同条件下也远大于F401.红外二向光法结果表明,PPH在相同熔体牵伸比下片晶取向度较F401高.相同加工条件下PPH微孔膜片较F401成孔分布更均匀,孔径尺寸也更均匀.2种微孔膜孔隙率都随熔体牵伸比的增加而提高,微孔分布随着熔体牵伸比的提高和片晶取向度的增加而趋于均匀,孔尺寸也随之区域均匀.研究表明,聚合物树脂中高分子量级分含量是影响预制膜中片晶取向度、冷热拉伸成孔分布和尺寸均匀度的重要影响因素.

EFFECT OF THE CONTENT OF HIGH MOLECULAR WEIGHT COMPONENT ON PP MICROPOROUS MEMBRANES OBTAINED BY MELT-EXTRUSION-STRETCHING METHOD

Two types of resins(F401 and PPH) were selected to develop microporous membranes using cast film extrusion followed by stretching.The roles of the molecular weight and molecular weight distribution on the row-nucleated lamellar crystallization and micropore formation were investigated.The relaxation spectra of the resins were examined by dynamic rheology.The content of high molecular weight component(Mw>106) for PPH was 1.5 times larger than that of that for F401.Under the same temperature,the relaxation time of PPH was much longer than of F401.The crystalline orientation was measured by Fourier transform infrared spectroscopy(FTIR).At the same draw ratio(DR),the crystalline orientation of the precursor film for PPH was higher than that of F401.Scanning electron microscopy(SEM) images of the membrane surface showed the high molecular weight component or long chains played a remarkable role in the formation of mircopores and were included in the part of ’bridging structure’ as tie chains.Under the same processing condition,the pore structure of microporous membrane for PPH was more regular and uniform.The porosities of the microsporous membranes were tested by the liquid absorption method.For both resins,the porosities of the microporous membranes increased with DR.The content of high molecular weight component of the resins primarily influenced the pore structure of the microporous membranes.