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

An experimental study of structure development in cast film extrusion and biaxially stretched films of polybutylene terephthalate is present ed. Cast films exhibited only alpha-form crystallites and relatively l ow crystallinities (X-c= 3.5-14%), while biaxially stretched films sho wed a mixed character of both alpha- and beta-form crystallites with c rystallinities of 20-30%. Crystal perfection increases with uniaxial d eformation. Biaxiality causes a decrease both in crystal perfection an d crystallinity of the films. Annealing increases crystallinity. The o rientation of the films has been determined by refractive indices and WAXS pole figures. Polymer chains orient rapidly to the machine direct ion (MD) with uniaxial stretching. Increasing biaxiality causes an inc rease in population of TD-oriented crystals. The planarity of the film increases with simultaneous transverse stretching. The phenyl rings o rient into the plane of the film. Annealing further increased the orie ntation of the films.