Investigation of the Crystallinity and Water Permeability of Surface Layers of UAM-50 and UAM-100 Ultrafiltration Membranes

Abstract

We perform X-ray diffractometry, electron-microscopic, and kinetic studies of the surface layers of UAM-50 and UAM-100 ultrafiltration membranes. The crystallinity of the membranes is studied by X-Ray diffraction in the region of large angles 2θ from 2° to 40°, using a DRON-3 diffractometer with modern methods of the computer processing of experimental data. Comparative analysis of the X-ray diffraction patterns reveal the coincidence of the diffraction angles for the working and air-dry samples of ultrafiltration membranes, while the membrane samples have three pronounced maxima located approximately in the angular range from 17.50° to 25.60°. The crystallinity for the air-dry samples is 68% for UAM-50 and 74% for UAM-100, and for the working samples, it is 32 and 41% for UAM-50 and UAM-100, respectively. Investigations of the surface of drainage layers of the UAM-50 and UAM-100 ultrafiltration membranes are carried out by scanning electron microscopy. The thickness of the active layer is 27 nm for the UAM-50 membrane and 15 nm for the UAM-100 membrane. Pores of different sizes are visible on the surface of the active layer of the membrane; the pore sizes range from 2.5 to 40 nm for UAM-50 and from 10 to 40 nm for UAM-100. Kinetic studies of the ultrafiltration membranes confirm that they have an asymmetric pore structure. Small pores in the membrane trap contaminant molecules, while large pores allow the permeate to pass quickly to a more open permeate carrier, that is, a purified solution. The water permeability of the working membrane increases with an increase in the transmembrane pressure due to an increase in the driving force of the process and rearrangement of the crystal structure (a decrease in the size of crystals in the working sample of the membrane) and a decrease in the crystallinity of the membranes.