In the laboratory, under the guidance of Li Liangbin, Dr. Meng Lingpu and Ph.D. student Wan Caixia used a laboratory-made large scientific device, a film biaxial stretching device, to study the structural evolution of polyethylene gel films during biaxial stretching process. The work was published in the journal Polymer (2019, 164: 59-66).

During MD stretching process, the original lamellar stacks are gradually transformed into fibrillar crystals through melting recrystallization. While during TD stretching process, there are three kinds of deformation mechanisms according to different λMD: (1) at small λMD, the lamellar stacks slightly oriented in MD are stretched to melt and recrystallize into fibrillar crystals along TD; (2) under the condition of moderate λMD from 4 to 6, the original crystals are stretched to melt just like the case of small λMD, meanwhile the fibrillar crystals oriented along MD are tilted towards TD together with the formation of fibrillar crystals oriented in TD; (3) in case of large λMD from 7 to 8, the microfibrils are teared into more thinner microfibrils or fibrillar crystals which are stretched aslant subsequently, accompanied with formation of few fibrillar crystals in TD. Finally, the crystal morphology diagram in 2D strain space is summarized, providing the guidance for choosing the optimal manufacture window of PE microporous membranes with desired structure and morphology in industry.

This work was supported by the National Natural Science Foundation of China (No. 51703218 and 51633009), Anhui Provincial Science and Technology Major Projects (No. 16030901044). We also thanks Prof. Zhongming Li from Sichuan University for helping the measurements of SEM.

Related links:https://www.sciencedirect.com/science/article/pii/S0032386119300308