Influence of cocrystallization behavior on structure and properties of HDPE/LLDPE microporous membrane

The microporous membranes of high-density polyethylene (HDPE) and linear-lower-density polyethylene (LLDPE) blend were prepared based on melt-stretching mechanism and the influence of cocrystallization behavior on the structure and properties of stretched microporous membranes was investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS) and capillary flow porometer. It was found that compared with that without LLDPE, the main melting peak and the maximum crystallization temperature of HDPE/LLDPE blend precursor film with LLDPE content up to 12 wt.% were moved to lower temperature. The crystallinity of HDPE/LLDPE blend with LLDPE content of 5 wt.% was increased from 65.8 to 73.0 % due to the existence of cocrystallization behavior. The porosity and air permeability property of corresponding stretched microporous membrane were decreased by 7.1 and 44.4 %, respectively, whereas the puncture resistance was increased by 111.4 %. But further increase of LLDPE content to 12 wt.% lead to the decrease of cocrystallization ability and puncture resistance. To obtain final microporous membrane with better puncture resistance, adding 5 wt.% LLDPE to HDPE is appropriate. At the same time, although the air permeability is decreased, the value is still acceptable for the application of this kind of microporous membrane in the field of Li-ion battery as a separator.