Plastic deformation of highly drawn polypropylene monofilaments

The tensile properties of highly oriented polypropylene (PP) filaments are markedly dependent on their fabrication drawn history. Highly oriented filaments prepared by drawing at <100°C were capable of appreciable plastic deformation after passing through a marked yield point. This deformation process was very rate dependent, transforming to essentially brittle behavior at deformation rates >500%/min. Filaments produced by drawing at a higher temperature, or by annealing above 100°C of those produced at 100°C, had a slightly lower modulus, greatly reduced residual elongation to break, and showed no yield point. A model for the plastic deformation is proposed involving localized fibrillation to produce craze‐like structures. This model is consistent with the observed filament susceptibility to chromic acid etching. Electron micrographs of highly drawn then etched samples show that just prior to fracture only small plastes of the acid resistant (presumably original, unvoided) structure remain.