Plastic deformation of polypropylene. VI. mechanism and properties

Abstract

Abstract Small- and wide-angle X-ray investigation of drawing and annealing of polypropylene quenched films in wide ranges of draw ratio (λ = 1-20) and of temperature (20°-150°C) shows the discontinuity of the elementary act of transformation in the microneck of the original lamella of the microspherulitic into the microfibrils of the final fiber structure. The long period, the orientation, and the crystalline disorder change abruptly. The continuity of macroscopical deformation in the neck is a consequence of superposition of the effects of a great many microneck zones which are more or less randomly scattered over the whole neck area. In the first stages of plastic deformation before the appearance of micronecks the lamellae parallel to the draw direction are compressed and those perpendicular to the draw direction become physically separated. This was checked by noting the drastic reduction of scattering after the introduction of dodecane which fills the holes between lamellae created in the initial stage of drawing. The diagonally oriented lamellae retain their thickness. As a consequence of steady rotation of lamellae from the perpendicular to the parallel orientation to the draw and of the destruction of nearly parallelized lamellae the diagonally oriented lamellae retain their numbers and yield a strong diagonal smallangle X-ray scattering maximum, whereas the equatorial and meridional maxima rapidly decrease in intensity. Annealing at a temperature above that of drawing makes the long period increase very nearly linearly with log tA and concurrently the crystals disorient and the sample shrinks. Clamped samples exhibit a slightly slower increase of L and much less disorientation.