Preparation And Characterization Of Proton Exchange Membranes Based On Chitosan

As a natural basic polymer, chitosan has attracted many attentions to develop proton exchange membranes (PEM). The pristine chitosan has a very low electrical conductivity. For protonation of chitosan, the proton acids and ion liquids were used as additives to prepare anhydrous proton conducting membranes based on chitosan in this study.Studies on casting chitosan membranes with a good mechanical strength were made. The acids including sulfonic acid, phosphoric acid, oxalic acid, and amino trimethylene phosphonic acid (ATMP) were employed to prepare composite membranes of chitosan. Doping of proton acids in chitosan improved the conductivity of the membrane, however, decreased the mechanical strength. A highest conductivity was achieved by a composite membrane of ATMP-chitosan. The conductivity of 34.78%(wt) ATMP-chitosan membrane under anhydrous conditions was 3.08×10-5 S·cm-1 at 30℃, and 1.55×10-3 S·cm-1 at 140℃, respectively.Three types of ion liquids including 1-buty-3-methylimidazolium hexafluoroph-osphate (BMIMPF6), chlorinous 1-buty-3-methyl-imidazolium (BMIMCl) and triflu-oroacetic propylamine (TFAPA) were prepared and used to prepare composite membranes with chitosan. The introduction of ion liquids in the membranes improved the conductivity, but deteriorated the mechanical properties of the membranes. Doping of BMIMC in the chitosan membrane (molar ratio 1:1) increased its conductivity most. At 50℃, its conductivity was 1.05×10-4S·cm-1 with a dry membrane. When the temperature increased to 240℃, a conductivity as high as 1.19×10-2S·cm-1 was reached.For composite membranes of sulfonic acid, oxalic acid, ATMP, BMIMCl and TFAPA characterization by means of infrared spectra (IR), thermogravimetric analysis (TGA) and mechanical strength were made.