The morphology of fibers from deformed polymer crystals

Electron diffraction and microscopy have been used to investigate the fine structure of fibrils pulled from deformed polyethylene and polyoxymethylene crystals. Since on annealing close to the melting point the striations developed transverse to the fibril axis are thought to be folded chain lamellae, we looked for evidence whereby folds could be detected prior to annealing. In addition to striations observed by allowing iodine vapors to diffuse into polyethylene fibrils, and by dark‐field observation, both reported earlier, we found (1) similar striations in polyoxymethylene by exposure to phosphotungstic acid, and (2) the presence of some monoclinic phase remaining in polyethylene from initial stages of deformation of orthorhombic folded chain crystals. It is suggested that blocks less than 200 A. long of the original crystals break off during deformation. On annealing, tie molecules and some unfolded chains relax and are incorporated into the blocks. The striation periodicity increases with annealing temperature and decreases with molecular weight. Little annealing time dependence is found. The periodicity was independent of draw temperature between 40 and 160°C. in polyoxymethylene indicating that folded chain lamellae could not be formed during deformation.