Author Identifier

Aghil Igder

https://orcid.org/0000-0002-8955-9876

Date of Award

2021

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Doctor of Philosophy

School

School of Engineering

First Supervisor

Dr Alireza Keshavarz

Second Supervisor

Professor Colin L. Raston

Abstract

Extensive studies have been performed to improve key properties of filtration membranes via controlling the fabrication process conditions as well as physical and/or chemical modification of the polymers used in membrane fabrication. The Vortex Fluid Device (VFD) is a newly invented platform which has found many applications in materials science and clean technology. The unique features of the VFD originate from a combination of different effects (e.g., micro-mixing, viscous drag, microfluidic flow, enhanced mass transfer) all resulting in faster, greener, and more efficient and better controlled chemical reactions. The main aims of this project are: (i) to investigate the utility of VFD processing in an environmentally friendly process for PSF synthesis, (ii) fine-tuning the process conditions and consequently improving the properties of the polymer, and (iii) the application of the VFD in facilitating a time effective process for PSF ultrafiltration membrane fabrication while investigating the effect of changing the rotational speed of the VFD and Graphene Oxide (GO) incorporation into PSF based membranes along with their filtration performances.

Initially, Polysulfone (PSF) was prepared under high shear in the VFD operating in the confined mode, and its properties compared with that prepared using batch processing. Scanning electron microscopy (SEM) established that the VFD synthesised PSFs are sheet-like, for short reaction times, and fibrous for long reaction times, in contrast to spherical like products from the conventional batch synthesis. The operating parameters of the VFD were systematically varied for establishing their effect on the molecular weight (Mw), glass transition temperature (Tg) and decomposition temperature, featuring gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) respectively. The optimal VFD prepared PSF was obtained at 6000 rpm rotational speed, 45° tilt angle and 160 °C, for 1 h with the material having a Mw ∼10000 g mol−1, Tg ∼158 °C and decomposition temperature ∼530 °C, which is comparable to the conventionally prepared PSF. In the next step, the synthesise process has been systematically varied to improve the main properties of the PSF, including the Mw which is now ∼15500 g mol−1. Morphological study accompanied by BET measurement were conducted to support the results and investigate the effect of the VFD operational parameters on the properties of the new VFD synthesised PSF.

In another aspect of the research, PSF ultrafiltration (UF) membranes were fabricated using a continuous micro-mixing process under high shear in the vortex fluidic device (VFD) followed by phase inversion process of the cast solution. This involved investigating the effect of PSF concentrations (10, 15, and 20%) in 1-methyl-2-pyrrolidone (NMP) as well as the rotational speed of the VFD for a 0.5 mL/min continuously mixing process at 30 °C, on the properties of the membranes. The properties of the VFD mediated membranes were compared with those fabricated using conventional batch mixed polymer solutions (24 h magnet stirring at 60 °C, 3h sonication), with the membranes fully characterized through structural and morphological studies, hydrophilicity, and filtration performance, as well as thermal and mechanical stabilities. Use of the VFD showed a significant impact on essential mixing time by facilitating a very shorter mixing process. SEM established that in the microfluidic mixing, the PSF membranes have more finger-like cross-section, for 10% PSF concentration, and more sponge-like structure for higher concentrations. Moreover, the higher rotational speed in the VFD mediated membranes, the higher their porosity (84.3±2.4) % and permeability (106±4) LMH/bar which were optimal at 7k rpm.

Furthermore, to improve the properties of the membrane, GO was incorporated into the polymer solutions both using VFD and conventional mixing, resulting in GO/PSF composite membranes with enhanced properties. It was also found that compared to pristine PSF membranes, the incorporation of 1 wt.% of GO increased its permeability from (97±3) to (123±4) LMH/bar, salt rejection from (18.5±1.3) to (34.3±1.7) % and bovine serum albumin (BSA) rejection from (53.8±2) to (74.2±2) %, respectively.

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