The effect of orientation on the morphology and kinetics of solvent crazing in polystyrene



Unoriented, uniaxially oriented, and biaxially oriented polystyrene films were crazed by immersing samples in liquid n-hexane at 45°C. The craze morphology and crazing kinetics were studied as a function of the preorientation and thermal histories of the polymer films. The shape of the micropores was related to the degree of orientation of the film. Ellipsoidal microvoids were formed on the surfaces of uniaxially oriented films containing a residual glassy core. Unoriented samples displayed spherical microvoids 0.1 to 3 μ in diameter. The major-to-minor axis ratio of the micropores increased monotonically from 1/1 to 10/1 as the sample orientation was increased from 0% to 200%. The kinetics of the crazing process similarly increased with uniaxial orientation. Surfaces of unannealed films which crazed mainly during the sorption of liquid n-hexane displayed numerous micropores when examined by the SEM. Conversely, films which were extensively annealed crazed mainly during desorption regardless of subsequent orientation. These extensively annealed films exhibited surfaces with many fine cracks and few, if any, micropores.