Determination of Molecular Orientation of Uniaxially Stretched Polyamide Fibers by Polarized Infrared Spectroscopy: Comparison of X-Ray Diffraction and Birefringence Methods

Abstract

Polarized infrared (IR) spectroscopy has been used to determine the crystalline and amorphous orientation of polyamide fibers. The transition moment angle of the band at 936 cm⁻¹ of PA66 was determined to be 48° using IR spectroscopy and birefringence measurement. The crystalline orientation of PA66 fibers was estimated from the band at 936 cm⁻¹ while the amorphous orientation of PA66 fibers was obtained by an indirect method. The α crystalline orientation of PA6 has been obtained using the band at 930 cm⁻¹ and the amorphous orientation of PA6 has been determined using the band at 1124 cm⁻¹. Crystalline orientation increased rapidly at low draw ratios (DR < 3) and increased slowly at higher draw ratios (DR > 3) for both PA66 and PA6 fibers, while the amorphous orientation increased slowly throughout the whole extension range for PA66 fibers. A good correlation was found between the crystalline orientation values obtained by infrared spectroscopy and other methods such as X-ray diffraction for PA66 and PA6 fibers. On the basis of this observation, it has been concluded that polarized infrared spectroscopy can be used reliably to measure the orientation of polyamide fibers without combining with other techniques.