Effect of non-solvent additives on the morphology, pore structure, and direct contact membrane distillation performance of PVDF-CTFE hydrophobic membranes

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• 作者：Libing Zheng¹ ; ² ; ^{zhenglibing12@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Zhenjun Wu³ ; Yong Zhang¹ ; ² ; Yuansong Wei¹ ; ² ; Jun Wang¹ ; ² ; ^{junwang@rcees.ac.cn" class="auth_mail" title="E-mail the corresponding author}
• 关键词：PVDF-CTFE ; Additives ; Phase inversion ; Membrane distillation ; Pre-gelation
• 刊名：Journal of Environmental Sciences
• 出版年：2016
• 出版时间：July 2016
• 年：2016
• 卷：45
• 期：Complete
• 页码：28-39
• 全文大小：2693 K

文摘

Four common types of additives for polymer membrane preparation including organic macromolecule and micromolecule additives, inorganic salts and acids, and the strong non-solvent H₂O were used to prepare poly (vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) hydrophobic flat-sheet membranes. Membrane properties including morphology, porosity, hydrophobicity, pore size and pore distribution were investigated, and the permeability was evaluated via direct contact membrane distillation (DCMD) of 3.5 g/L NaCl solution in a DCMD configuration. Both inorganic and organic micromolecule additives were found to slightly influence membrane hydrophobicity. Polyethylene glycol (PEG), organic acids, LiCl, MgCl₂, and LiCl/H₂O mixtures were proved to be effective additives to PVDF-CTFE membranes due to their pore-controlling effects and the capacity to improve the properties and performance of the resultant membranes. The occurrence of a pre-gelation process showed that when organic and inorganic micromolecules were added to PVDF-CTFE solution, the resultant membranes presented a high interconnectivity structure. The membrane prepared with dibutyl phthalate (DBP) showed a nonporous surface and symmetrical cross-section. When H₂O and LiCl/H₂O mixtures were also used as additives, they were beneficial for solid–liquid demixing, especially when LiCl/H₂O mixed additives were used. The membrane prepared with 5% LiCl + 2% H₂O achieved a flux of 24.53 kg/(m²·hr) with 99.98% salt rejection. This study is expected to offer a reference not only for PVDF-CTFE membrane preparation but also for other polymer membranes.