Optical Properties and Geometrical Parameters of Poly(p-phenylene Terephthalamide) Fibers

Abstract

Forward scattering of a He-Ne laser beam was used to measure the dimensional parameters, transverse-sectional shape, and area for two different samples of poly( p- phenylene terephthalamide) (PPT) fibers, PRD 49 and Kevlar 49. A double-beam interferometric technique was applied to determine the mean refractive indices for plane polarized light vibrating parallel and perpendicular to the fiber axis, and the mean birefringence was also determined for the two samples of PPT fibers. The area enclosed under the interference fringe shift, when crossing the fiber, represents the path difference integrated across the fiber. The mean values of the transverse-sectional area of fibers measured from the forward scattering of the laser beam were used to calculate the refractive indices and the birefringence of the fibers. Multiple-beam Fizeau fringes in transmission were used to determine the perpendicular refractive indices for each of the two samples of PPT fibers, using the value of the fiber thickness measured by the diffraction method. The obtained values for refractive indices, the birefringence, and diameter of PRD 49 and Kevlar 49 fibers measured by this technique are in a good agreement with previously published values.