Impact of the ethylene content on poly (ethylene-co-vinyl alcohol) membrane morphology and performance via immersion precipitation for lithium extraction
2019
Huang, Tao | Song, Jianfeng | Xing, Lixin | Li, Xuemei | He, Tao
Poly (ethylene-co-vinyl alcohol, EVAL) polymers were reported as one of the best candidates for solvent resistance membrane because of a block copolymer nature. In this paper, we aim to explore the contribution of the hydrophobic/hydrophilic block to the membrane morphology, mechanical strength, crystallinity, and ion permeance via immersion precipitation phase separation. The membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), wettability, water uptake, tensile strength, and ion permeance. Increase in the ethylene content led to smaller pore size, increased crystallinity temperature and improved mechanical strength, however reduced water flux and ion permeability. A decrease in crystallinity of EVAL polymer followed an increase in the ethylene content, but increased crystallinity for membrane was observed; this was ascribed to the competition between the solid-liquid demixing and liquid-liquid demixing that allowed more time for chain rearrangement and ordering. High crystallinity of EVAL-44 membrane contributed to reduction of 50% in the lithium permeance comparing to EVAL-27 membrane. This work provided a theoretical methodology for controlling the membrane morphology and performance from a semicrystalline polymer and benefit for improvement of the EVAL membrane performance in lithium membrane extraction.
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