MPD and TMC supply as parameters to describe synthesis-morphology-performance relationships of polyamide thin film composite membranes

This study assesses the influence during interfacial polymerization on polyamide thin film composite (TFC) morphology and performance of varying monomer concentrations and organic phases with widely varying physico-chemical characteristics (interfacial tensions (IFT) with water, viscosity and monomer equilibrium partitioning). These physico-chemical characteristics were used to introduce two new descriptors of the synthesis-structure-performance relationship of polyamide TFC membranes: ‘MPD supply’ and ‘TMC supply’. Three non-ionic solvents (hexane, isopar G and hexyl acetate (HA)) are studied in parallel with three room temperature ILs (RTILs). It is found that well-performing membranes are prepared until one of the monomers is added in excess. The susceptibility of the system to excess of one of the monomers depends on the interplay of MPD and TMC supply, which determines the system-specific monomer concentration range for high salt rejecting membranes. By combining the results of the current study with literature data, qualitative synthesis-performance relationships are proposed. Overall, the tunability of the synthesis−structure−performance relationship of polyamide TFC membranes is shown by tying the effect of monomer concentration and organic phase on membrane performance and narrowing it down to MPD and TMC supply. The insights provided can assist in reducing the overall carbon footprint of RO membrane synthesis and operation. • New parameters, ‘MPD supply’ and ‘TMC supply’, are introduced. • MPD and TMC supply qualitatively relate RO performance and monomer concentrations. • RO performance shows optimum type behavior as a function of monomer concentrations. • Good RO performance is expected until one of both monomers is added in excess.