A facile strategy to fabricate skin-free porous polymer membranes based on sandwich structure

The skin layer, i.e. the surface dense layer with relatively lower porosity, may significantly impede the permeability of porous polymer membranes. In this work, with the combination of experiment and finite element simulation, a facile strategy based on sandwich structure is proposed to eliminate the skin layer. The simulation results indicate that removing skin layers can increase the water flux of porous membranes by more than 4 times. In experiment, first the formation mechanism of skin layer is studied for the porous membranes fabricated from poly(ether-ether-ketone)/poly(ether-imide) (PEEK/PEI) blend based on crystallization template. It is found that the stronger interaction between PEI and the polyimide releasing film during hot-pressing is the cause of the PEEK skin layers of the obtained membranes. According to this mechanism, a skin-free PEEK membrane is prepared from the PEI/(PEEK/PEI blend)/PEI sandwich structure. The separation test indicates that the PEEK membrane fabricated following the new strategy has remained rejection ratio and enhanced flux by 3–5 times as the simulation result predicts. Furthermore, the universality of developed sandwich strategy has been validated in polyformaldehyde/poly(L-lactic acid) (POM/PLLA) blend (crystalline/crystalline system). Our results provide a novel solution to regulate the skin layer of porous membranes.