Structure Evolution of Polyethylene in Sequential Biaxial Stretching along the First Tensile Direction

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Two linear low-density polyethylene samples (PE-A and PE-B), with similar melt index and molecular weight but different molecular structures, were used to explore the structural evolution during sequential biaxial stretching. Only PE-A could be successfully stretched into a film with the biaxial draw ratio of 6 × 6. The interlamellae crossing adjacent lamellar stacks were observed in PE-A but not in PE-B, which could increase the lateral tie connection. Moreover, the amount of fibril was less in PE-A than that in PE-B and the fibrillar structure lacked tie chains between each other. In addition, the newly formed lamellae in PE-A (derived from fine lamellae) could lock the molecular chains of different crystals, which increased the lateral connection via anchoring the tie chains from adjacent lamellae. Therefore, the above specific structures increased the lateral connection and were beneficial for biaxial stretching. Furthermore, the relationship between molecular structure and condensed structure was als...