Structure and properties of heterogeneous and homogeneous ion-exchange membranes subjected to ageing in sodium hypochlorite

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• 作者：W. Garcia-Vasquez ; R. Ghalloussi ; L. Dammak ; C. Larchet ; V. Nikonenko ; D. Gr ; e
• 关键词：Ion-exchange membranes ; Artificial oxidizing ageing ; Cleaning-in-place ; Sodium hypochlorite ; Electrodialysis
• 刊名：Journal of Membrane Science
• 出版年：15 February, 2014
• 年：2014
• 卷：452
• 期：Complete
• 页码：104-116
• 全文大小：3568 K

文摘

The effects of sodium hypochlorite (NaClO) on ion-exchange membranes were carefully investigated and discussed with the aim to assess one of their possible causes of ageing. A thorough comparison was carried out for the degradation of ion-exchange membranes with different structures, i.e. homogeneous and heterogeneous ones, as well as with different functional groups, i.e. anionic (bearing 3CH₂N⁺R₃ groups) and cationic (bearing groups) ones. An artificial ageing protocol was implemented, which consisted in immersing four types of membranes, homogeneous AMX-SB and CMX-SB as well as heterogeneous, MA-41 and MK-40 in aqueous NaClO solutions at constant pH and concentration for different times over a 700 h period. The physico-chemical, structural, and mechanical properties of each sample were investigated, before and after ageing, by means of complementary analytical techniques, namely conductivity, ion-exchange capacity, water uptake, and thickness measurements, as well as SEM, ATR-FTIR, TGA, and tensile strength tests.

The results demonstrated that ageing mechanisms were different for anion-exchange membranes and cation-exchange membranes; however, ageing was similar among homogeneous and heterogeneous membranes of the same type (anionic or cationic). Sodium hypochlorite provoked a degradation of the quaternary ammonium sites of anion-exchange membranes and chain scission of the poly(styrene-co-divinylbenzene) backbone from anion and cation-exchange membranes through chain radical oxidation. No significant degradation was found for the polymer binder of membranes investigated in this paper.