Sustainable Water Treatment Membranes Made with Mussel-Sourced Polydopamine Reinforced Polymers: Thermo-Mechanical Characterisation

Dopamine, sourced from mussels, was utilised as a sustainable modifier to enhance the thermo-mechanical and filtration performance of polysulfone (PSf)-based ultrafiltration membranes for water treatment. Membranes, fabricated by phase inversion with dopamine/Tris doping (with or without polyvinylpyrrolidone, (PVP)) and polydopamine (PDA) surface coating, were characterised using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), and Dynamic Mechanical Analysis (DMA). Contact angle, water retention capacity (WRC), and porosity were also measured. Micromechanical modelling (Voigt, Reuss, Hill, Self-Consistent) was used to determine the stiffness of the polymers using membrane data. WRC reached 67.6% for PSf/PVP, decreased to 39.2% for PSf/Dopamine, and was 63–66.6% for PDA-coated membranes. Porosity was 15.9–20.2% for neat PSf and PSf/PVP, reduced to 7.3–8.1% with dopamine/Tris doping, and increased by PDA coating (17.7–20.9%). Contact angles of 54–67° indicated increased hydrophilicity with PDA. DSC revealed glass transition temperatures between 201–223 °C, with PVP reducing Tg in a PS-Dopamine system from ~215 °C to ~203 °C. DMA up to 100 °C showed stable storage modulus and rising loss modulus, with higher stiffness in solution-treated membranes than in coated ones. Modelling predicted elastic moduli of polymers in the 180–260 MPa range. Flux performance was highest for PSf/PVP/Tris/Dopamine (487.6 L·m⁻²·h⁻¹ pure water, 452.5 L·m⁻²·h⁻¹ lake water, 462.4 L·m⁻²·h⁻¹ fouled), while Mn(II) removal reached 62% for PDA-coated PSf/Dopamine. This study presents the first systematic comparison of dopamine/Tris doping and PDA coating, integrating characterisation with modelling and establishes a framework for sustainable membrane design.