Effect of Hot Stretching on the Structure of Polypropylene Microporous Membranes with in situ Small Angle X-Ray Scattering

With in situ small angle X-ray scattering and scanning electron microscopy measurements, effects of hot stretching temperatures and draw ratios on the lamellae and pore structure of the polypropylene microporous membrane were studied. The results show that the lamellar clusters are separated during the cold stretching and heat setting process, while the internal structures do not undergo separation during the hot stretching process. With the increase of the hot stretching ratio, the bridge length of microporous membrane after hot stretching process increases substantially. Also, it has better periodicity along the equatorial direction compared with the cold-stretching and heat-setting samples. The results of different stretching temperatures show that the length of the bridge increases with the increase of the stretching temperature. When the temperature is too high, the bridge will partially melt. This work can provide guidance for the structural control during preparation of polypropylene microporous membranes.