MEASUREMENTS OF THREE PRINCIPAL BIREFRINGENCES OF POLYMER FILMS BY INCLINATION METHOD

Abstract

The Relation between three principal refractive indices (orthogonal refractive indices nx, ny and nz, where nz is the refractive index perpendicular to the film plane) and birefringences of inclined polymer film was studied basing on the idea of index-ellipsoid. Experiments were carried out by using a new apparatus together with the polarizing microscope, and the birefringences of polypropylene films were measured. Following results were obtained; (1) A cubic equation was derived from the three birefringences which were measured at angels 0°, 30° and 45° from the horizontal plane respectively. In principle, by solving the equation, the three principal refractive indices were to be obtained, but acutuary it can be carried out only when the birefringences are large enough to be measured accurately. (2) The sequence of the order of magnitudes of the three principal refractive indices could be obtained by plotting a few values of birefringences and angles of inclination only, (3) By the alternative method to Stein's one, the three main birefringences were approximately calculated by using two values of the birefringence that were measured at horizontal position and at inclined position of the film. This method is more or less complicated as compared with Stein's method, but were obtainable. (4) When polypropylene films were stretched uniaxially and biaxially by using the new extentional and inclinational apparatus, the relation between the birefringence and the uniaxial draw ratio at 90°C was similar to that reported in Okazima and Kurihara's study. However, in the case of biaxial drawing at 90°C, it was found that the birefringence of the drawing film is influenced by the initial orientation of the film.