An FT-IR Study of the Water Absorbed in Kevlar-49® Fibers

Abstract

Diffuse reflectance Fourier transform infrared spectroscopy has been used in order to detect absorbed water hydrogen-bonded to Kevlar-49® fibers. Varying amounts of KBr overlayers were used on the top of each sample in order to increase the surface selectivity of the technique. Three different O-H stretching vibrations of absorbed water were detected in the fibers exposed to saturated water-vapor atmosphere. Two peaks at 3640 and 3560 cm−1 are attributed to absorbed water that is weakly hydrogen-bonded to amide groups of the polymer. A broad absorption around 3450 cm−1 is characteristic of liquid-like water clustered in microvoids and other sites inside the fibers. The spectra of dried Kevlar-49® fibers show an unbonded amide N-H stretching peak at 3431 cm−1, indicative of regions with less perfect chain packing. At least part of these groups hydrogen-bond with absorbed water, depending on their availability.