抄録
Crystalline and noncrystalline orientations of poly (ethylene terephthalate) were evaluated by means of simultaneous measurements of X-ray diffraction and birefringence. The test specimens were prepared by uniaxial or orthogonal-biaxial stretching of a quenched film with various %-elongations at 90°C and then annealing of the stretched films with fixed length at 200°C for 2 hr.
For the uniaxially stretched films, some positive orientation of reciprocal lattice vector of the (100) crystal plane, the crystal a*-axis, and slightly negative orientation of the crystal c-axis were found at relatively low %-elongations less than ca. 90%-elongation, and these anomalies turned out to highly positive orientation of the c-axis and equally negative orientations of reciprocal lattice vectors of the paratropic crystal planes, such as the (100), (010) and (110) planes, at relatively high %-elongations.
For the orthogonal-biaxially stretched films, uni-planar orientation of the (100) crystal plane and planar orientation of the crystal c-axis, both parallel to the film surface, were found in an extent depending on the degree of stretching and the mode of biaxial stretching, such as simultaneous, alternate, and strip-biaxial stretching. Assuming the optical anisotropy of PET crystal to be orthogonal-biaxial symmetry with respect to the crystal c-, a*-, and b′-axes having refractive indicies of nc: 1.806, na*: 1.398 and nb′: 1.733, the noncrystalline birefringence was evaluated to draw a conclusion that the noncrystalline chain segments orient in some extent in a manner of uniplanar orientation of their phenyl rings parallel to the film surface.
