Heat relaxation of drawn polyoxymethylene

Abstract

The shrinkage of drawn bulk polyoxymethylene was studied by wide-angle and small-angle X-ray diffraction and electron microscopy as a function of the amount of draw. Upon heating, the drawn material shrinks nearly instantaneously; the rtained strain increases with draw ratio. Small-angle patterns, including circuler, ellipsoidal, four-, six-, and two-point patterns, show various degrees of reversibility which decrease with increasing elongation especially above 100% draw. Wide-angle pole figures indicate changes in chain orientation distribution for samples drawn between 10 and 200% (the maximum examined). Deformation occurs primarily by several micronecking processes as well as lamellar and molecular slip. Morphological changes during shrinkage take place in all of the structural units formed by drawing. In addition to changes in spherulite dimensions, lamellar slip occurs, short fibrils disappear, and large diameter fibrils as well as lamellae normal to the draw direction form.