Effects of Preparation Conditions on Morphology of Polyacrylonitrile Micro/Ultrafiltration Membrane and Its Application in Protein and Fat Separation from Milk

Polyacrylonitrile (PAN) micro/ultrafiltration membranes were prepared by phase inversion method. The effects of various preparation conditions including polymeric solution concentration، evaporation time، temperature، composition and residence time of the coagulation bath were investigated. Various important membrane characteristics such as pore size، bulk porosity، and mechanical and morphological properties were taken into the consideration. The characterizations were performed by measuring the bubble point، water flux، tensile strength and scanning electron microscopy (SEM) analyses. The results showed that by increasing the polymeric solution concentration from 13 to 17 wt%، the porosity and water flux were decreased. Moreover، the membrane skin layer was considerably thickened with a very significant decrease in its pore sizes which was achieved in ultrafiltration region. By increasing the evaporation time at atmospheric pressure، membrane skin layer was thickened and the pore sizes were decreased. Low coagulation bath temperatures (below 30°C) resulted in lower pore size، water flux، and an increase in membrane mechanical strength. Introduction of isopropanol (IPA) into the water coagulation bath led to lower coagulation rate and consequently، the formation of smaller pores became possible by using pure isopropanol as coagulation bath. Furthermore، by increasing the residence time in coagulation bath، a more porous structure with more uniform pore sizes were formed that showed better mechanical properties. Finally، the so-called ultrafiltration membranes were applied in concentration process of protein and milk fat. A protein rejection more than 93% was attained while a complete removal of milk fat was achieved.