Phase separation behaviour modification using co-solvents on PVDF membranes for water filtration

• Main Authors: Wan Ramli, Wan Khairunnisa, Liang, Lew Guo, Othman, Suhaila, Yusri, Nor Aqilah Musfirah, Che Lah, Nuur Fahanis
• Format: Conference Proceeding
• Language: English
• Subjects: Cross flow; Demixing; Ethanol; Filtration; Membranes; Miscibility; Nanofiltration; Phase separation; Rejection; Solvents; Tetrahydrofuran; Ultrafiltration; Wastewater treatment; Water purification
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/5.0113799

Asymmetric PVDF membranes with very thin skin layer are widely used in wastewater treatments, owing to the excellent properties of PVDF. The addition of co-solvents such as tetrahydrofuran (THF) in the dope solution is found imperative in synthesizing additive-free PVDF membranes for nanofiltration. In this present work, the effect of various co-solvents, namely ethanol and THF were evaluated in terms of their phase separation behavior using cloud points measurements. The surface and cross-sectional morphologies of the fabricated membranes were then characterized using SEM. The effects of co-solvents on their performance for water filtration were also evaluated using crossflow ultrafiltration process. PVDF/NMP membrane exhibited the formation of a very thin dense layer with fingerlike porous substructure, attributed to the slowest demixing at 13% polymer concentration. In contrast, membranes with co-solvents formed thicker dense layer due to the immediate liquid-liquid demixing, attributed to the bigger miscibility gap and the delayed demixing in the sublayer due to the increased viscosity. PVDF/ NMP membrane showed significant solute rejection of 80% with 40.83 Lm−2h−1 permeability. The effects of adding co-solvents were significant as PVDF/NMP-EtOH membrane exhibited the highest solute rejection of 94.47% and 43 Lm−2h−1 as compared to PVDF/NMP-THF and those without co-solvent.