Influence of annealing time on the structure and properties of high-density polyethylene microporous membrane

The high-density polyethylene microporous membrane was prepared based on melt-stretching mechanism and the influence of annealing time on the structure and properties of initial annealed film and final microporous membrane was investigated using scanning electron microscopy, differential scanning calorimetry, and capillary flow porometer. It was found that compared with that without annealing, the main melting peak after annealing for 3 h moved to higher temperature. The corresponding lamellar thickness and elastic recovery values were increased by 13.7 and 30.6%, respectively. The porosity and air permeability property of final microporous membrane were increased by 48.0 and 42.9%, respectively. With increasing the annealing time from 3 to 4 h, the lamellar thickness was decreased from 21.0 to 20.6 nm and the corresponding porosity showed a little decrease from 64.1 to 63.6%. With increasing annealing time, more chains in the amorphous regions were induced to crystallize, resulting in higher lamellar thickness and uniform lamellae distribution. The higher the grown crystalline part was, the higher the pores induced during stretching were, resulting in better air permeability property. Therefore, annealing the polyethylene cast film under 125℃ for 3 h is sufficient to obtain final microporous membrane with better properties.