Spray coating as a novel, versatile tool to prepare membranes via IP

Polyamide (PA) thin-film composite (TFC) membranes, synthesized by interfacial polymerization (IP), are commonly applied in NF and RO. However, they have a high tendency to foul due to the rough ridge and valley surface. IP requires utilization of toxic solvents and hydrolysis of acyl chlorides can occur as undesired side reaction due to the presence of water. Therefore, a new approach to synthesize TFC membranes is now introduced: spray-based interfacial polymerization prior to solidification (s-IPS). IP is performed on a still liquid polymer film containing a first (amine) monomer while the second monomer (acyl chloride) is sprayed on top. The susceptibility of the liquid cast film to defects due to the impact of spraying, is minimized by the increased viscosity resulting from charge-transfer complex formation between the amine monomer (MPD) and the polymer (PI). This new s-IPS process is more time-efficient, uses less chemicals and produces less waste than the conventional IP. Additionally, problems in conventional IP associated with non-wetted support pores and bad adhesion of the IP layer to the support are eliminated and water-free IP is enabled, limiting hydrolysis of TMC. Properties such as high viscosity and interfacial stability lead to controllable IP and smooth PA top-layer surfaces. [Display omitted] •Spray-based IP prior to solidification is introduced as a new approach to synthesize TFC membranes.•IP is successfully performed on a liquid polymer film containing the amine monomer using spray-coating.•Defects are minimized by increasing the viscosity by formation of CTCs between MPD and PI.•Properties like high viscosity and interfacial stability lead to a controllable IP and smooth top-layer.•PA TFC membranes were synthesized with 98% RB retention and water permeances up to 3 L m-2 h-1 bar-1.