Gas Permeability and Structure of Crazes for Crazed Polymer Films

Abstract

By the unique crazing process with sharp bending and tensile stress, the voids of the crazes were generated in polypropylene (PP) and polystyrene (PS) films. The tensile strength of the crazed PP and PS films was almost unchanged after the crazing processing, while Young's modulus decreased with the crazing tension increasing. The gas permeability of all the PP and PS films increased with the crazing tension because of the increase in void fraction. The crazes of PP and PS films penetrated completely in the direction of film thickness above 4 N/cm and 5 N/cm, respectively, of the crazing tension. Permeation model was proposed on the basis of the relationship between the measured gas permeability and the void fraction in the films. The gas permeability of the crazed films was estimated by the combination of the parallel and the series models which were constituted of the crazed and non-crazed regions in parallel or serial order in the direction of gas permeation.