Preparation And Characterization Of Quaternized Polyepichlorohydrin Anion Exchange Membranes

Electrodialysis(ED)has played prominent roles in various environment and energy-related fields,which has been successfully used in the waste water treatment,chemical and food industry.More specifically,in water and waste water treatment,ED has attracted growing attention owing to the contribution to water purification,demineralization of drinking water,desalination,and treatment of industrial effluents.As a key component of ED,anion exchange membranes(AEMs)are applied to facilitate the selective permeation of anions.Compared with cation exchange membranes(CEMs),the fabrication of common AEMs mainly consists in two steps: methyation(chloromethylation or bromomethyation)and quaternary amination.Especially for chloromethylation,the commonly used chloromethyl methyl ether(CEM)and bis-chloromethylether(BCME)are highly toxic and carcinogenic,which have been restricted since the 1970 s.Polyepichlorohydrin(PECH)has been extensively studied to fabricate AEMs by different research groups,It is an elastomer having inherent chloromethyl groups that allow the incorporation of quaternary ammonium functions by nucleophilic reaction of substitution.Nevertheless,the quaternized PECH undergoes high degree of swelling and would become brittle in water,which will greatly hinder its further practical application in ED.The works in this report are committed to develop a method which can avoid the chloromethylation reaction.The specific studies are shown as follows:(1)PVDF and PECH were used as starting materials to synthesize anion exchange membrane by forming semi-interpenetrating networks(sIPNs).A cyclic diamine(DABCO)was used as crosslinking agent and for simultaneous improved the ion-exchange capacity by amination.SEM indicated that the composite membranes exhibited dense and homogeneous structure.Successful formation of PECH-DABCO copolymer within the sIPN membranes was also confirmed by Fourier transform infrared(FTIR)and X-ray photo-electron spectroscopy(XPS).The PVDF percentage and inherent properties of membranes such as ion exchange capacity(IEC),water uptake(WR),thermal stability,mechanical property and,area resistance,were investigated to evaluate their applicability in electrodialysis(ED).The experimental results showed that the composite membrane maintained a good perspective for ED application.(2)PECH was crosslinked with polyethyleneimine(PEI)and combined with nylon mesh to form crosslinked PECH/nylon composite anion exchange membrane,the composite membranes showed dense and smooth surface.The membrane exhibited good mechanical properties with 36.5-38.5 MPa of breaking strength and 9.3-15.3% of breaking elongation ratio.Ion exchange capacity(IEC)of CPECH/nylon membrane reached 0.92-0.73 mmol/g,the membrane area resistance was 2.9-6.5Ω at room temperature,indicating good comprehensive performance.