2025 Volume 74 Issue 1 Pages 9-15
Hot-drawing of polystyrene (PS) films improved the fracture nature from brittle to ductile due to the chain orientation. However, the brittle-to-ductile transition mechanism has not been clearly understood. This study investigated the ductile deformation mechanism of the oriented PS films by using birefringence and polarized FT-IR measurements during tensile tests. Comparison of tensile properties for the oriented PS films with various drawing conditions revealed that the brittle-to-ductile transition occurred at around 0.05 of the degree of chain orientation. The birefringence data, which were analyzed with a modified stress-optical rule (MSOR), suggested the chain orientation beyond the yield point during the ductile deformation. The polarized FT-IR data represented that, before yield point, the main chain of PS became oriented to the tensile direction, and, after the yield point, a phenyl ring as a side-group of PS aligned. The difference in the orientation behaviors of main-chain and side-group dissipated the stress concentration in the oriented PS films, and generated the shear-yielding deformation, resulting in the ductile deformation.
