An investigation of the pore structure of ultrafiltration cellulose acetate membranes UMA-50 and UAM-100 by spectroscopy and electron microscopy
Abstract
The study presents the results of an investigation into the structure of cellulose acetate membranes UAM-50 and UAM-100 before and after exposure to transmembrane pressure using IR spectroscopy and scanning electron microscopy. In the ranges of stretching vibrations 3000-3700cm-1; 2884.02-2942.35 cm-1 changes in atomic vibrations for working samples of membranes were noted. A decrease in scattering intensity, a change in the shape of absorption bands, and a decrease in their asymmetry index for OH groups to 0.77 for UAM-50 and to 0.79 for UAM-100 were noted. Two "shoulders" appear on the absorption bands. For UAM-50 the first at 3350.2 cm-1, the second at 3412.8 cm-1. For UAM-100 they were at 3248.5 and 3505.9 cm-1. This indicates the destruction of OH groups involved in intermolecular bonds. The study of cellulose acetate membranes by scanning electron microscopy allowed us to establish the thickness of the active layer of the studied samples: for UAM-50 – 28 nm, for UAM-100 – 16 nm. Pores from 2 to 20 nm were observed on the surface of the active layer of the membranes. A decrease in the pore diameter was noted in the working samples of the membranes. This phenomenon is explained by the sorption of the retained substance by the membrane, and the applied pressure compacts the active layer, thereby reducing the pores.
Studies of the surface morphology of ultrafiltration cellulose acetate membranes demonstrated that membranes have an asymmetric pore structure. The finely porous selective layer traps solute molecules, and the coarsely porous layer located under the selective layer removes the solvent, affecting the permeable properties of the membrane.
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