Electron microscopy studies of relaxation behavior of polyoxymethylene

The low-strain deformation behavior of polyoxymethylene at various temperatures above liquid nitrogen has been examined by transmission electron microscopy, and the results have been correlated with the mechanical relaxation spectra. Micronecks, their position apparently independent of the local morphology, are seen at all temperatures. Interlamellar slip is observed at and above—80°C and is correlated with molecular motions in the amorphous regions. Orientation of the material in the regions between the dipped lamellae is observed at and above 24°C. This is correlated with large-scale motions in the amorphous regions and, presumably, is indicative of the glass transition of polyoxymethylene. A break-up of the lamellae into mosaic blocks 150–300 Å in size is observed above 120°C and is correlated with the initiation of molecular motions in the crystalline regions.