Effects of deformation history on the development of structure and properties in biaxially stretched poly(butylene terephthalate) (PBT) films are described. PBT cast films are stretched at two temperatures: 65°C and 90°C, with varying draw ratios. The refractometer and X-ray scattering techniques characterize the resultant films. As-stretched films have crystals of small sizes, in which the α crystals are appreciably larger and oriented more than the β phase. Films that are stretched at the low temperature, on the other hand, exhibit higher orientations of both the overall and amorphous chains. Annealing of the films under constraint causes the crystalline phase to undergo perfection and transition. A model of crystalline morphology is presented which describes the mechanical anisotropy present in biaxially oriented PBT films.
© 2000, Carl Hanser Verlag, Munich