Deformation and annealing behavior. I. Polyethylene terephthalate films

The morphology and deformation behavior of uniaxially and biaxially oriented thin polyethylene terephthalate (PET) films was examined by bright field, diffraction and dark field electron microscopy. A large, 250-500 Å, nodule structure was observed under a variety of conditions, in addition to the smaller 75–100 Å nodules that have been reported previously. Dark field micrographs indicate that oriented PET, heat set at 180° to 240° C, is composed of small (140 Å) isometric crystallites, with a tendency to orient the 100 plane in the plane of the film. It is suggested that the nodular structure and small isometric crystallites may contribute to PET ductility at low temperatures.