Measurement of Orientation in Polypropylene Film

Abstract

An average fiber axis orientation in polypropylene film was measured quantitatively from x‐ray diffraction determination of orientation of two planes containing this axis. This orientation was expressed as the average square cosine of the angle between the fiber axis and a chosen reference direction in the sample. It was necessary to use an indirect method since there are no crystal planes perpendicular to the fiber axis. The nature of the fiber axis orientation thus determined was found to be consistent with birefringence measurements and qualitative deductions from pole figures. Films produced by flat die extrusion showed a double orientation in which the fiber axis is preferentially oriented in the extrusion direction, and the (010) crystal face is parallel to the film surface. Both components of the orientation tended to be of the same magnitude.