Membrane and Water Treatment

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Preparation and characterization of PVDF Flat sheet membrane for VMD: Effect of different non-solvent additives and solvents in dope solution

  • Meenakshi Yadav (Department of Chemical Engineering, Malaviya National Institute of Technology Jaipur) ;
  • Sushant Upadhyaya (Department of Chemical Engineering, Malaviya National Institute of Technology Jaipur) ;
  • Kailash Singh (Department of Chemical Engineering, Malaviya National Institute of Technology Jaipur)
  • Received : 2024.07.03
  • Accepted : 2024.09.05
  • Published : 2024.10.25
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Abstract

Asymmetric flat sheet poly(vinylidene fluoride) (PVDF) membranes were fabricated using the phase inversion technique, employing four distinct solvents with varying solubility power: N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), Dimethyl sulfoxide (DMSO), and N-Methyl-2-pyrrolidone (NMP). The influence of these solvents on the crystalline properties of the polymers was investigated using X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) to elucidate their role in PVDF polymorphism during membrane formation. Our findings revealed significant variations in membrane crystalline phase due to the dissolution of PVDF in different solvents, with α-polymerization predominant in membranes cast with NMP and DMSO, while DMF and DMAc solvents favored β-type polymerization. Further, various additives including PEG-400, TiO2, LiCl, LiBr, acetone, ethanol, propanol, and water were employed to evaluate their impact on membrane morphology and properties. Scanning electron microscopy (SEM) and Ultimate testing machine (UTM) were utilized to analyze membrane morphology, while the tensile strength, contact angle, pore size, and porosity were estimated using the sessile drop method, imageJ, and gravimetric method, respectively. Our results demonstrated that all additives exerted influence on membrane morphology and properties depending on their characteristics and interactions with solvents and polymers. Notably, acetone, being volatile, facilitated the formation of a thin PVDF layer on the membrane surface, resulting in a reduced average pore size (0.18㎛). Conversely, LiCl and LiBr acted as pore-forming additives, yielding membranes with distinct pore characteristics and porosity. Moreover, water as a non-solvent additive induced pregelation during the nonsolvent-induced phase separation (NIPS) process, thereby promoting pore formation (53% porosity) and enhancing membrane hydrophobicity (104° contact angle). To evaluate the quality of synthesized membranes, permeate flux ranging from 16.2 L/m2.hr to 27.9 L/m2.hr with a salt rejection rate of 98 %, was evaluated using Vacuum Membrane Distillation (VMD).

Keywords

Acknowledgement

The authors are also extremely grateful to the Material research center (MRC) at MNIT for for all the facilities to determine SEM micrographs, Tensile strength determination.

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