Effect of the presence of partially sulfonated polyaniline on the proton and methanol transport behavior of partially sulfonated PVdF membrane

Abstract

Poly(vinylidene fluoride) (PVdF) and polyaniline (PAni) were partially sulfonated using chlorosulfonic acid (CSA) as the sulfonating agent. Partially sulfonated PVdF (SPVdF) having a degree of sulfonation (DS) of ~22% and partially sulfonated PAni (SPAni) having a DS of ~29% were blended at constituent wt% ratios of SPVdF:SPAni=95:5, 90:10, 85:15 and 80:20 to fabricate different blend membranes. These blend membranes exhibited extremely low methanol uptake and methanol permeability, as well as high membrane selectivity ratios (especially at high methanol concentrations). The blend membranes also exhibited superior water uptake capacity, water swellability, ion-exchange capacity (IEC) and proton conductivity compared with pristine PVdF and SPVdF membranes. The SPVdF:SPAni (80:20) blend membrane was found to produce the lowest methanol permeability values of 1.50 × 10−9 cm2 s−1 (at 2 m methanol) and 6.30 × 10−9 cm2 s−1 (at 8 m methanol) and the highest membrane selectivity values of 3.27 × 106 Ss cm−3 (at 2 m methanol) and 7.78 × 105 Ss cm−3 (at 8 m methanol). However, the introduction of Nafion to the SPVdF/SPAni blend membrane to form a ternary blend membrane (that is, SPVdF:Nafion:SPAni=50:30:20) resulted in much improved IEC and proton conductivity. The incorporation of SPAni within SPVdF, to form SPVdF/SPAni blend membranes, increased the %WU, the %SR, the IEC, the proton conductivity and the membrane selectivity of the base SPVdF membrane, whereas substantially decreased the %MUs and the methanol permeability values. The SPVdF/SPAni (80/20) blend membrane was found to produce the lowest methanol permeability values of 1.50 × 10−9 cm2 s−1 (at 2 m methanol) and 6.30 × 10−9 cm2 s−1 (at 8 m methanol) and the highest membrane selectivity values of 3.27 × 106 Ss cm−3 (at 2 m methanol) and 7.78 × 105 Ss cm−3 (at 8 m methanol).