Novel sodium alginate-poly(N-isopropylacrylamide) semi-interpenetrating polymer network membranes for pervaporation separation of water + ethanol mixtures

Novel semi-interpenetrating polymer network (semi-IPN) membranes of sodium alginate (NaAlg) and thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) were prepared by free radical polymerization using potassium persulfate as an initiator. Membranes were crosslinked with glutaraldehyde and used in pervaporation (PV) separation of water–ethanol mixtures at varying feed compositions and temperatures. Membranes were characterized by Fourier transform infrared spectroscopy (FTIR) to assess intermolecular interactions. Thermogravimetry (TGA) was used to study their thermal stability. PV separation characteristics of the membranes showed a dependence on thermosensitive nature of NIPAAm. Increasing the NIPAAm content of the semi-IPN network resulted in an increased selectivity with a decreased permeation flux. The membrane containing 30 wt.% NIPAAm showed the highest selectivity of 18,881 with a flux of 0.137 kg/m2 h at 40 °C, i.e., the above lower critical solution temperature (LCST) of NIPAAm, but below its LCST, i.e., at 25 °C, it exhibited considerably a lower selectivity of 92 with a flux of 0.185 kg/m2 h for 15 wt.% water containing feed. Selectivity decreased with decreasing temperature at 15 wt.% water in the feed mixture below the LCST region, i.e., at 30 °C due to increase in the membrane pore size, thereby affecting the membrane selectivity with a considerable increase in flux of up to 0.225 kg/m2 h. The reported membranes are of the first kind in the membrane literature, wherein a thermoresponsive NIPAAm polymer is used with a hydrophilic NaAlg polymer to form the semi-IPN membrane for PV dehydration of ethanol.