In order to conclude and validate the reaction mechanism of
modification process, the defluorinated PVDF100K membrane
samples obtained at different reaction time (1, 5, 12 and 30 min)
were analyzed by the determination of double bond content,
FTIR and Raman spectra. Before testing, the samples were completely
dried in vacuum at 90 C.
Double bond content determination was as follows. 80 mg
membrane sample was soaked into the solution containing 25 ml
DMF, 10 ml glacial acetic acid and 0.1 mol/L ICl at 25 C for
25 min. Then 20 ml ethanol, 15 ml DI water, 15 ml 0.1 mol/L KI
aqueous solution and a drop of starch aqueous solution were added
to the former solution orderly. Finally, the mixed solution was
titrated by 0.1 mol/L Na2S2O3 standard solution [18]. The blank test
was done to eliminate the effect of extraneous impurity. The total
content of unsaturated double bond is expressed as TCUDB and calculated
in Eq. (1):