ABSTRACT: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 distribution function. For most of crystalline polymers with a triclinic unit like PET, there are no crystal planes perpendicular to the a-, b-, and c-axes that can be detected directly by X-Ray diffraction techniques. Accordingly, the functions 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 considerable 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. [DOI 10.1295/polymj.36.394] KEY WORDS The Three Principal Crystallographic Axes / Poly(ethylene terephthalate) / Simultaneous Biaxial Stretching / Orientation Distribution Function of Crystallites / Benzene Rings / The evaluation concerning molecular orientation was first proposed by Herman in terms of the second order orientation factor.1 This factor is a sort of the second moment of the orientation function. After then, the orientation of crystallites was estimated by Roe and Krigbaum 2-4 in terms of the distribution function. The mathematical representation was given by an expansion of the distribution function in a series of generalized spherical harmonics. This method has been very important to obtain the orientation of the three principal crystallographic axes, the a-, b-, and c-axes, in terms of the orientation distribution function. Actually, there are several papers for estimating orientation distribution functions of the three principal crystallographic axes, the a-, b-, and c-axes of polyethylene, 5,6 poly(vinyl alcohol), 7,8 nylon 6 9 and cellulose. 10The first trial for poly(ethylene terephthalate) by Krigbaum and Balta 11 was done by using a simple uniaxially stretched films but their trial was absolutely unsuccessful. However, the recent development of computer program and high power X-Ray source provide easy peak separation of overlapped peaks and the orientation functions for the reciprocal lattice vectors can be obtained for a number of crystal planes with high accuracy. Consequently it becomes possible to calculate the orientation distribution functions of crystallites as well as of the a-, b-, and c-axes from the observed orientation functions of the reciprocal lattice vectors of the crystal planes. In previous paper, 12 the orientation of crystallites with a triclinic unit was evaluated in terms of orientation distribution function for a PBT fi...
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