Orientation Distribution Functions of the Three Principal Crystallographic Axes as well as Crystallites of Poly(ethylene terephthalate) Films under Biaxially Stretching

The orientation of the three principal crystallographic axes, the a-, b-, and c-axes of crystallites of poly(ethylene terephthalate) (PET) under simultaneous biaxial stretching was estimated in terms of the orientation dis- tribution function. For most of crystalline polymers with a triclinic unit like PET, there are no crystal planes perpen- dicular to the a-, b-, and c-axes that can be detected directly by X-Ray diffraction techniques. Accordingly, the func- tions of the a-, b-, and c-axes must be calculated by the method proposed by Roe and Krigbaum. In doing so, the orientation functions of the reciprocal lattice vectors must be measured for a number of crystal planes. In this paper, as an example, the orientation of crystallites and the orientation of the a-, b-, and c-axes were estimated for a PET film under simultaneous biaxial stretching in terms of the orientation distribution function of crystallites because of consid- erable utilization rate of PET as commercial films. The estimated orientation functions of the b- and c-axes predicted the detailed information concerning uniplanner orientation of benzene rings parallel to the film surface.