Influence of UV curing on morphology and performance of polysulfone membranes containing acrylates

UV cross-linked polysulfone (PSU) based membranes containing additives with different number of acrylate groups were prepared via UV curing and nonsolvent induced phase separation (NIPS). The resulting membranes had good solvent resistant nanofiltration (SRNF) performance with superior chemical resistance. The impact of the UV irradiation as well as the presence of the acrylate cross-linkers and the photoinitiator with respect to membrane morphology, chemical stability, and SRNF performance was investigated. Membranes with a cross-linker and a photoinitiator in their matrix had a macrovoid-like morphology. By decreasing the membrane wet thickness from 200 to 50 µm to enhance the depth-curing, a sponge-like structure was achieved. The same macrovoid-free structure was found when 150 and 200 µm thick membranes were treated in the reverse order, i.e. first UV irradiated and then immersed in water (UV/NIPS instead of NIPS/UV). Addition of an acrylate cross-linker decreased the contact angle of the membranes (typically from 76° to 61°). Addition of a penta-acrylate cross-linker to the PSU membrane resulted in a 10-fold higher permeance (3.3 L m−2 h−1 bar−1) in comparison to a reference PSU membrane without acrylate additive with still a 94% retention for Rose Bengal (RB) in IPA. However, after UV curing, the same membrane showed a permeance of only 0.07 L m−2 h−1 bar−1 and a retention of 96%. By reversing the synthesis sequence to UV/NIPS, an increase of permeances up to a value of 1.2 L m−2 h−1 bar−1 and retentions up to 94% were achieved.