Strain‐induced crystallization I. Limiting extents of strain‐induced nuclei

Abstract

AbstractThis paper points out that interpretations from stress changes alone during oriented crystallization have led to widely different proposed chain conformations and consequently very different crystallization mechanisms for strain‐induced crystallization (SIC). Many of the proposals, including the one by Keller and Machin which takes into account some electron microscopy and X‐ray observations, show varying degrees of incompatibility with existing stress relaxation, kinetic or morphological data on SIC. Another problem lies in the difficulty with proper interpretation of observed morphology on samples which have been Subjected to additional thermally‐induced crystallization (TIC) after SIC, especially, in the absence of prior characterization of SIC crystallites, the finding of a fibrillar‐to‐lamellar transformation in stretched polymers upon additional TIC (Part H) also indicates that the generally‐observed oriented lamellar morphology has a much more subtle origin than‐that depicted by most crystallization models. Part I discusses our previously published morphological data on the characteristics of SIC crystallites from the melt, which includes: (a) their melting point elevation, (Tm » T°m), (b) their nearly perfect crystalline orientation function (fc ∼ 1), (c) their fast rates of crystallization (t1/2 < 1 sec), and (d) their fibrillar morphology and limited dimensions along the fibrillar stretch axis (∼100Å). Examples of morphology of SIC from the glass and from stirred solution are also included to show the overall similarity of fibrillar morphology brought about by stretching.