FORMATION AND CHARACTERIZATION OF CAST, TUBULAR AND BIAXIALLY STRETCHED POLY(BUTYLENE TEREPHTHALATE) FILM

An experimental study of structure development in cast film, single bu bble tubular film extrusion and double bubble tubular film extrusion o f polybutylene terephthalate is described. We also study the character istics of biaxially stretched PBT films. Cast and single bubble film e xhibited only alpha-form crystallite and relatively low crystallinity (X-C = 18-22%), while double bubble and biaxially stretched cast films showed a mixed character of both alpha- and beta-form crystallites wi th crystallinity (X-C = 20-30%). WAXS pole figures indicate that polym er chains orient rapidly with uniaxial stretching. Biaxiality of orien tation increases with simultaneous transverse stretching. The phenyl r ings become aligned parallel to the film plane with biaxial stretching . The level of orientation is substantially higher in both double bubb le and biaxially stretched cast films than in single bubble films. Ann ealing further increases crystallinity and orientation of the films.