2.9. Chemical stability
Five OH form membrane samples were immersed into 2, 4, 6, 8,
10 mol L1 NaOH solutions at 60 C for 120 h, respectively. The sixth
sample was immersed into 1 mol L1 NaOH solution for 120 h as a
comparison. All the membrane samples were thoroughly washed
by deionized water until the free NaOH inside the samples was
completely removed. The ionic conductivities of six samples were
tested at 30 C to investigate the changes