Structure and self-reinforcing mechanism of biaxially oriented polyethylene pipes produced by solid phase die drawing

摘要

Biaxially oriented polyethylene (PE) pipes were prepared through solid phase die drawing technology. Drawing speed presented a prominent effect on the hoop draw ratio (DRhoop) and axial draw ratio (DRaxial) of the pipes. For pipe with DRhoop/DRaxial of 2.465/1.182, the tensile strength was improved significantly along hoop direction as well as axial direction, reaching respectively 1.75 and 1.3 times of the isotropic sample. Through die drawing, more uniform and dense oriented lamellar structure formed, resulting in the decrease of long period (L-ac) and lateral size of the lamellae (L-lateral). With increasing DRaxial, in hoop-radial plane, the orientation degree increased first and then decreased, and lamellar twisting became more and more prominent. At low DRaxial, lamellae were arranged mainly perpendicular to hoop direction. However, at high DRaxial, the normal of lamellae deviated from hoop direction to axis, and biaxial orientation structure formed, resulting in biaxial self-reinforcement for PE pipes.