OPTOTHERMAL PROPERTIES OF FIBERS - 3-EFFECT OF ANISOTROPIC OPTICAL-PARAMETERS IN POLYPROPYLENE FIBERS AS A FUNCTION OF ANNEALING PROCESS

This study deals with the changes in the optical properties of polypro pylene fibres (4:1 draw radio 515 tex polypropylene, Bolton, UK) due T o the effect of thermal annealing on its structural characteristics. C hanges in the structure of annealed polypropylene fibres at a constant time of 2 h and different temperatures (60-140 degrees C) were studie d interferometrically. The diffraction of a He-Ne laser beam was used to measure the dimensional parameters transverse sectional shape and t he area of the polypropylene fibres sections. An optical microscope wa s used to confirm the geometrical parameters of the cross-sections. Th e diffraction technique was utilized to study the effect of annealing on swelling factors of these fibres for some different liquids at room temperature 19 +/- 1 degrees C. Two methods were applied for the meas urement of the refractive indices and birefringence of the polypropyle ne annealed and unannealed fibres. The first was concerned with the ap plication of the Becke-line method for determining the refractive indi ces and the birefringence of the skin layer. The second method used mu ltiple-beam Fizeau fringes in transmission to observe the changes in t he values of the refractive indices due to the annealing process in th e skin and core layers. Also, the mean refractive indices and their pr ofiles were determined taking the refraction and different temperature s into consideration. The resulting data were used to calculate the po larizabilities per unit volume and the isotropic refractive index. (C) 1996 Elsevier Science Ltd.