Parameter Screening of PVDF/PVP Multi-Channel Capillary Membranes

Abstract

The increasing research in the field of polymeric multi-channel membranes has shown that their mechanical stability is beneficial for a wide range of applications. The more complex interplay of formation process parameters compared to a single-channel geometry makes an investigation using Design of Experiments (DoE) appealing. In this study, seven-channel capillary membranes were fabricated in a steam–dry–wet spinning process, while varying the composition of the polymer solution and the process temperatures in a three-level fractional factorial linear screening design. The polymers polyvinylidene flouride (PVDF) was the chemically resistant main polymer and polyvinylpyrrolidone (PVP) was added as hydrophilic co-polymer. Scanning electron microscopy and atomic force microscopy were applied to study the membrane morphology. Fabrication process conditions were established to yield PVDF/PVP multi-channel membranes, which reached from high flux (permeability P = 321.4 L / m 2 / h /bar, dextran 500 kDa retention R = 18.3%) to high retention (P = 66.8 L / m 2 / h /bar, R = 80.0%). The concentration of the main polymer PVDF and the molecular weight of the co-polymer PVP showed linear relations with both P and R. The permeability could be increased using sodium hypochlorite post-treatment, although retention was slightly compromised. The obtained membranes may be suitable for micro- or ultra-filtration and, at the same time, demonstrate the merits and limitations of DoE for multi-channel membrane screening.

Statistical Analysis of Synthesis Parameters to Fabricate PVDF/PVP/TiO2 Membranes via Phase-Inversion with Enhanced Filtration Performance and Photocatalytic Properties

“…These parameters are consistent with most of the papers published on this topic. [ 22 , 24 , 37 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 ]. After that, the membrane was washed with ultrapure water and kept for 48 h in an ultrapure water bath at room temperature prior to the experiments.…”

“…To evaluate how the fabrication conditions influence the membrane performance, four different variables with low (−1) and high (+1) levels were analyzed by CCD ( Table 1 ). The chosen values are within the interval that is most commonly applied for the preparation of membranes [ 37 , 38 , 40 ]. It is important to highlight that using values beyond these limits could result in membranes with too high or too low viscosities that could not be cast properly.…”

“…Many studies have investigated different conditions separately, varying one factor while keeping the others fixed [ 32 , 33 , 34 , 35 ]. Recently, a few researchers have started to evaluate the variable conditions simultaneously, for which statistical analysis is required [ 36 , 37 , 38 , 39 , 40 , 41 ]. As a result, the statistical approach for membrane fabrication using the response surface methodology became an important step.…”

“…Zhao et al [ 39 ] performed a statistical analysis to evaluate the performance of membranes for filtering yeast dispersions in a series of experiments where they used three different solvents and different PVDF, PVP, and graphene-oxide contents. Back et al [ 37 ] studied how the molecular weight of polymers (PVDF and PVP) affects the dextran removal efficiency of membranes using various polymer concentrations, bath and dope solution temperatures. Ahmad et al [ 36 ] investigated how the bovine serum albumin protein (BSA) binds to the membrane surface when altering the PVDF concentration, dope solution temperature, and casting thickness.…”

How does porosity heterogeneity affect the transport properties of multibore filtration membranes?

“…While pore size distribution and porosity are regarded as homogeneous over the membrane cross-section in ceramic membranes [6][7][8][9], polymeric membranes often possess porosity gradients inside the porous structure. Especially in polymeric multibore membranes, these heterogeneities are more predominant than in tubular or fiber membranes because micro-and macro-voids form during fabrication in the precipitation step [10][11][12][13]. At the heart of the inhomogeneous porosity is the polymer coagulation process which is highly non-linear in phase separation and solidification and accompanies considerable shrinkage [14].…”