On the interior morphology of bulk polyethylene

Abstract

The internal crystalline morphology of linear polyethylenes was examined by utilising the P ALMER‐C OBBOLD nitric acid digestion treatment. The basically lamellar morphology reported by P ALMER and C OBBOLD was confirmed in all the cases investigated which includes extreme differences in crystallization condition. The basic lamellae were not only of uniform thickness but also revealed the existence of crystallographic prism faces identified as {110} and {100} – the latter being far the most prominent – by examination of external habit and by diffraction methods. The layer thickness and lateral dimensions depended on the crystallization condition, the basic layer habits, however, were not obviously affected. By diffraction techniques oblique structures were identified with dominant {201} and {101} basal faces for high and low crystallization temperatures respectively. Some subdivision of the lamellae into crystal halves or sectors was indicated but this could not be established conclusively. Multilayer crystals with a regular pile‐up of concentric terraces and others with a variety of splaying layer configurations were observed. All these features have their counterparts amongst solution grown crystals. The thickness of the layers was only about half of that given by X‐rays in the untreated high polymer in cases where such a correlation was possible. In the case of low fractions, layer thickness and X‐ray spacings were both of the same order approximately corresponding to the average extended chain length. Weight losses were also measured but only slight variations were found in the limiting weight loss figures for the different specimens. Twisted airscrew type multilayer objects could be identified in disintegrated samples which showed banded spherulties originally. There was a quantitative agreement between band period and twist. The radial b orientation emerged naturally from the crystal habit. While no definite conclusion is reached as regards the molecular configuration the various factors at play are laid out and discussed. In the cause of this, the importance of the clearly defined crystal textures and particularly the continuity with crystallization from solution as revealed by the morphology is emphasised.