Preparation And Performance Of PVBCl Alkaline Anion Exchange Membrane

Anion exchange membrane direct methanol fuel cell (AEM-DMFC) uses anion exchange membrane as polyelectrolyte. In alkaline media, the methanol oxidative rate gets much faster. Moreover, the direction of the carriers OH" anion motion opposes that of the methanol flux through the membrane leading to an intrinsic reduction in methanol permeability. Therefore, AEM-DMFC can greatly overcome the problem of DMFC.The main chain of poly(vinylbenzyl chloride) (PVBCl) is styrene structure with chloromethyl in 3-/4- of benzene ring. Anion exchange membranes can be prepared through PVBCl directly reacting with quaternary aminating agents. In that case, the chloromethylation process can be avoided. In this study, PVBCl anion exchange membranes were prepared. The processing technologies and properties were studied as well.The preparation route of PVBCl anion exchange membranes was designed in this work. Isoamyl acetate was used as solvent to prepare polymer solution with the concentration of 100～200mg/mL. Diamine compounds were used as quaternary aminating agents to introduce the quaternary amine group and crosslinking structure into PVBCl after the crosslinking reaction between PVBCl and diamine. By phase separation, PVBCl anion exchange membranes were prepared through polymer solution extending in the glass plate.Comparison of different amount of the same crosslinking agent, it was shown that with the increasing of the amount, the toughness of membranes got higher, water content decreasd and ion exchange capacity increased. Comparison of crosslinking agents with different length of methylene, it could be seen that under the same amount, with the increasing of the length of methylene, the toughness of membranes got higher, water content increased, and yet ion exchange capacity changed very little.Using real-time FTIR tracking the crosslinking reaction course between PVBCl and TMHDA, the effects of reaction time and temperature on degree of crosslinking were studied. The experimental results demonstrated that the degree of crosslinking increased rapidly at the beginning, and then changed slowly to a constant value with the addition of reaction time. It also showed that higher temperature was conducive to the conduct of the crosslinking reaction which was an endothermic process. In addition, the reaction kinetics was studied through FTIR spectral data treatment. The kinetics results showed that the reaction order (n) equaled to 4, and the reaction activation energy (Ea) was about 97.2KJ·mol-1·K-1.Using TMHDA with the longest length of methylene in the experiment as crosslinking agent, it appeared that membranes cracked with the increasing of the amount of TMHDA. Under the low amount, the ion exchange capacity of membranes was very little. Ion exchange capacity could be improved by using mixed crosslinking agents or adding other quaternary aminating agents such as triethylamine.Due to styrene rigid structure of PVBCl main chain, PVBCl anion exchange membranes appeared obviously brittle. Thus, blending SEBS with chloromethylation as plasticizer into PVBCl was tried to prepare membranes. With the addition of SEBS, the toughness of membranes got much higher. And as the content of SEBS increased, the toughness of blend membranes gradually enhanced. Under the effect of external electric field, it was achieved that OH- transmitted through membranes. Compared with the Nafion membranes, blending membranes have lower methanol permeability.