Structure development in biaxially stretched polystyrene film: Part I. Property-orientation correlation

A study of orientation development in polystyrene film by biaxial stretching is described. Stretch ratios up to 7.2 × 7.2 were used. Mechanical properties of polystyrene films were correlated with the level of molecular orientation developed by uniaxial or biaxial stretching. Sensitivity of the mechanical properties to change due to development of orientation varied as follows: Yield strength < Young's modulus < Tensile strength < Elongation to break. Brittle to ductile transition phenomena were observed at certain orientation values in the orientation triangle diagram. The transition occurs when f × f ～ 0.0025 for biaxially oriented and f ～ 0.015 in the machine direction for uniaxially oriented films. SEM photomicrographs show that the fracture surfaces of ductile failures exhibit many fibrils while brittle failures exhibit no fibrils.