Abstract
An experimental study of structure development in cast film, single bubble tubular film extrusion and double bubble tubular film extrusion of polybutylene terephthalate is described. We also study the characteristics of biaxially stretched PBT films. Cast and single bubble film exhibited only α-form crystallite and relatively low crystallinity (Xc = 18-22%), while double bubble and biaxially stretched cast films showed a mixed character of both α-andβ-form crystallites with crystallinity (Xc = 20-30%). WAXS pole figures indicate that polymer chains orient rapidly with uniaxial stretching. Biaxiality of orientation increases with simultaneous transverse stretching. The phenyl rings become aligned parallel to the film plane with biaxial stretching. The level of orientation is substantially higher in both double bubble and biaxially stretched cast films than in single bubble films. Annealing further increases crystallinity and orientation of the films.
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