A parametric study on the synergistic impacts of chemical additives on permeation properties of thin film composite polyamide membrane

Thin film composite (TFC) polyamide (PA) membranes are typically prepared via an interfacial polymerization (IP) reaction between polyfunctional amine and polyacyl chloride monomers, dissolved separately in aqueous and organic solutions, at the surface of a porous support. Since the invention of the TFC membranes, various types of chemical additives were utilized in the monomer-containing solutions to control the IP reaction and thus improve the permeation properties of the synthesized membranes. However, the synergistic effects of utilizing different additives and the optimization of their concentration levels for synthesizing high-performance membranes with the minimum sensitivity to the effect of uncontrollable factors (noise) have not been explored so far. In the present work, different concentrations of sodium dodecyl sulfate (SDS) as a surfactant, triethylamine (TEA) as an acid scavenger, dimethyl sulfoxide (DMSO) as a co-solvent, and camphorsulfonic acid (CSA) as a pH regulator were added into the amine solution. An L9 orthogonal array of Taguchi method was used to investigate the simultaneous effect of these additives at three levels. The results showed that increasing the concentration of CSA, DMSO and TEA improved water permeation of the membranes whereas higher concentrations of SDS led to the formation of less permeable membranes with higher salt rejection. The same level setting of additives was also found to make the fabrication process insensitive to the noise factors. Furthermore, based on the analysis of variance, the contribution of the additives to the variation of the water flux was in the order of SDS (40.8%) > DMSO (37%) > CSA (17.78%) > TEA (4.1%). The results of this study are expected to provide useful guidelines for the development of robust TFC membranes by adjusting the additive concentration in amine aqueous solution.