Optical anisotropy in polypropylene fibres as a function of the draw ratio

Abstract

In this work optical properties of six samples of polypropylene fibres having different draw ratios are measured interferometrically using multiple-beam Fizeau fringes in transmission. These fibres are found to show considerable optical anisotropy. Three independent techniques have been employed to study the optical anisotropy in these fibres. The first technique determined the geometrical parameters of the fibre from its diffraction pattern using a He-Ne laser beam at 632.8 nm. The second is the application of the Becke-line method to determine the refractive indices and birefringence of the fibre's skin. The third is the application of multiple-beam Fizeau fringes in transmission to determine the mean refractive indices and the mean birefringence of these fibres with different draw ratio. The refractive index of the fibre's core is calculated from the predetermined parameters. Relationships between the mean refractive index and the birefringence of fibres with the draw ratio are given and illustrations with microinterferograms are presented.