Effect of Additives on Performance of Polyamide 66 Ultrafiltration Membrane Prepared for Milk Concentration.

Polyamide (PA 66) membranes were prepared with immersion precipitation via phase inversion from mixtures of polyvinylpirrolidone (PVP) and ammonium oxalate (OX) as constant additives and acetic acid, acetone, formamide, and water as variable additives. The formic acid and pure water were employed as solvent and nonsolvent, respectively. The influences of additives on structure and permeation properties of the membranes were analyzed by scanning electron microscopy (SEM) technique and separation expriments using milk as the feed. In general the addition of water and formamide in the casting solution slightly improves the flux without a pronounced effect on the retention of protein. This behaviour is due to instantaneous demixing (for water) and swelling mechanism (for formamide). When acetone was added to the casting solution, flux was lower and rejection was higher in comparison with the addition of water and formamide. This is due to the establishment of hydrogen bonding between acetone and polyamide. The addition of acetic acid results in lower flux and higher retention due to delay demixing.