The texture of melt crystallised polythene as revealed by selective oxidation

Abstract

It has been discovered that when fuming nitric acid oxidises bulk samples of polythene crystallised from the melt, preferential attack on the links between the lamellar crystals occurs with the consequent release of fragments of these crystals. The reaction is not confined to the surface of samples and lamellar crystals can be separated from relatively massive specimens for further study. Selected area electron diffraction results are presented to show that the molecular chains are oriented approximately prependicular to the plane of the lamellae and that the sheets are substantially single crystals. The results of an examination, by a variety of physical methods, of the lamellar crystals and reaction products from samples with different thermal histories treated for different times are given. Analysis of the results confirms that the attack occurs preferentially at the available amorphous regions, which in the case of the linear polymer are almost exclusively located between the lammellar crystals. In the case of branched materials, some amorphous material probably exists as defects within the lamellae. After treatment sufficient to release the individual lamellae from the bulk the molecular chain length is equal to the lamella thickness and thus at this stage no folds or links remain. At shorter times there is a progressive reduction in molecular weight and increase in crystallinity together with associated changes in other structural parameters. Comparison of the results from quenched samples with those from annealed samples suggests that the reaction may discriminate between intralamellar folds and interlamellar links. Certainly folds are attacked as was demonstrated by an experiment on single crystals grown from solution. Further work is thus being concentrated on the changes occurring at short treatment times.