FTIR spectroscopic characterization of structural changes in polyamide-6 fibers during annealing and drawing

Abstract

First, we report the development of Fourier transform infrared (FTIR) spectroscopic methods to determine the α/γ-crystalline phase ratio of polyamide-6 fibers and, in combination with density measurements, the total crystallinity. Using density determinations of the crystallinity of pure α and pure γ samples, we found the absorption coefficient ratio for the 930 (α) and 973 cm−1 (γ) bands to be 4.4, from which we could obtain the α/γ ratio for any polyamide-6 sample. The application of this FTIR method to the quantitative analysis of phase changes during thermal treatment and the drawing of polyamide-6 was then made. We confirmed that crystallization during thermal treatments involved increases in both phases and did not involve crystal-to-crystal transformation, whereas drawing involved both crystallization of the amorphous phase in the α form and γ→α transformation. Finally, we revisited the band assignments for the amorphous phase of polyamide-6 and found that the band at 1170 cm−1 was not an amorphous band but, because its absorbance was independent of crystallinity, could be used as an internal reference band. The band at 1124 cm−1 was reliably attributed to the amorphous phase. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 536–547, 2001