Improving Liquid Entry Pressure of Polyvinylidene Fluoride (PVDF) Membranes by Exploiting the Role of Fabrication Parameters in Vapor-Induced Phase Separation VIPS and Non-Solvent-Induced Phase Separation (NIPS) Processes

Abstract

Polyvinylidene fluoride (PVDF) is a popular polymer material for making membranes for several applications, including membrane distillation (MD), via the phase inversion process. Non-solvent-induced phase separation (NIPS) and vapor-induced phase separation (VIPS) are applied to achieve a porous PVDF membrane with low mass-transfer resistance and high contact angle (hydrophobicity). In this work, firstly, the impacts of several preparation parameters on membrane properties using VIPS and NIPS were studied. Then, the performance of the selected membrane was assessed in a lab-scale direct-contact MD (DCMD) unit. The parametric study shows that decreasing PVDF concentration while increasing both relative humidity (RH) and exposure time increased the contact angle and bubble-point pore size (BP). Those trends were investigated further by varying the casting thickness. At higher casting thicknesses and longer exposure time (up to 7.5 min), contact angle (CA) increased but BP significantly decreased. The latter showed a dominant trend leading to liquid entry pressure (LEP) increase with thickness.

The Formation of Polyvinylidene Fluoride Membranes with Tailored Properties via Vapour/Non-Solvent Induced Phase Separation

“…The slow penetration of humid air inside the forming membranes for different time intervals strongly affected membrane permeability to water; that is, PWP increased with an increase in the exposure time. This is in accordance with what was reported in literature [ 12 , 26 , 36 ]. A similar effect was observed by changing the relative humidity in the environment at fixed exposure times [ 49 ].…”

“…The formation of open polymeric surface in which pores are interconnected should represent an important parameter for a potential application of the produced PVDF membranes in MF, especially considering that the bicontinuous morphology is not the simplest to obtain, so that other structures, including cellular- or nodular-like, are more prevalent [ 35 , 36 , 37 ].…”

“…In Table 5 , a comparison between the obtained results and those reported in similar works is presented. Although the operational conditions, such as the RH% and the delayed time during the VIPS step, are not the same in the cited works, Peng et al [ 34 ] and Almarzooqi et al [ 36 ] detected a pore size below or close to 0.1 μm and tested the produced membranes in membrane distillation (MD). Fan et al [ 50 ] described the preparation of PVDF membrane by using a double layer casting process.…”

How Can the Desert Beetle and Biowaste Inspire Hybrid Separation Materials for Water Desalination?

“…LEP for water was established according to the Cantor–Laplace equation ( eq 1 ). 15 , 25 , 26 where γ is the surface tension of testing liquid (0.07199 N m –1 for water at 25 °C), cos(CA) is the cosine of the CA generating by water on the membrane surface, and r max is the maximum pore radius for the membrane (bubble point).…”

Effect of Pore Characteristics in Polyvinylidene Fluoride/Fumed Silica Membranes on Mass Flux in Solar-Assisted Evaporation Applications

“…All of the previous studies were important to highlight pore transport mechanisms and to provide directions for high-performance membrane design. However, although important, very little has been performed in the literature to demonstrate those effects experimentally in a continuous flow system [19][20][21][22]. All of the previously reported solar-assisted evaporation experiments [23][24][25][26][27][28][29][30] involved batch-mode setups.…”