The structure evolution and deformation behavior of tenter-frame biaxially oriented polyethylene (TF-BOPE) films were investigated in this study. For sequential biaxial stretching, the original spherulites were broken into small pieces, and the fibrillar structure simultaneously formed during the machine direction (MD) stretching. Subsequently, the single fibrils were pulled away, and some fine fibrils developed via partial melting–recrystallization or lamellar rearrangement during the transverse direction (TD) stretching, which leads to the formation of the vein structure and nanosized fiber-like network. For simultaneous biaxial stretching, the fractured lamellae and the newly formed crystals were evenly distributed in the MD-TD plane like an isotropous fibrillar network. Moreover, compared with the unstretched sample, both films could achieve up to about 2 times the tensile modulus and 4.5 times the tensile strength and also exhibited the superior optical property.
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