A Study on the Degree of Amidoximation of Polyacrylonitrile Fibers and Its Effect on Their Capacity to Adsorb Uranyl Ions

Amidoximation of polyacrylonitrile (PAN) fibers was studied by reacting them with hydroxylamine. The chemical structure, mechanical intensity, and morphologies of PAN and amidoximated PAN (AO-PAN) fibers were evaluated by Fourier transform infrared spectroscopy, tensile tests, dynamic mechanical analysis, and scanning electron microscopy, respectively. A higher degree of amidoximation resulted in a higher conversion ratio (CR) of the nitrile group and a higher density of the amidoxime group, while also reducing the mechanical intensity of the fibers. During amidoximation, a hydrogel layer formed on the fiber surface by bonding with H<sub>2</sub>O molecules, increasing the diameter of the AO-PAN fibers. The layer thickness increased as the CR of the AO-PAN fibers’ nitrile group was increased. The hydrogel layer decreased the adsorption capability by hindering the diffusion of uranyl ions to the interior of the AO-PAN fibers. Therefore, a CR of about 10.8% would provide an appropriate balance between the mechanical properties and the adsorption capability.