Morphological studies of deformed polybutylene terephthalate (PBT)

PBT is a semi-crystalline thermoplastic polymer whose deformation behavior highly depends on processing parameters. This makes it a model polymer for investigating morphological changes caused by deformation on the spherulitic and lamellar level. In the neck region all states of deformation of the spherulites are observed. Even in the fibrillar phase the borders of the spherulites remain visible. The spherulitic structure is not totally destructed in the neck. The lamellar structure of the fibrillar phase significantly differs from that of the spherulitic region. The lamellae are orientated with respect to the direction of deformation and the lamellae heights are reduced distinctly. Scanning electron microscopy of fracture surfaces reveals for some samples a sharp frontier between spherulitic and fibrillar region. This leads to the conclusion that the necking process may be a phase transition between an isotropic and a highly orientated phase, as predicted for a Van der Waals network.