Enhancing The Sustainability of Thermally Induced Phase Separation and Non-Solvent Induced Phase Separation Techniques for Membrane Fabrication

Abstract

Membranes are widely used in industrial applications to provide an alternative separation technique to thermally driven separations. Ultrafiltration membranes, in particular, are typically made using phase separation techniques, such as thermally induced phase separation (TIPS) and non-solvent-induced phase separation (NIPS). However, these membrane fabrication strategies pose significant environmental challenges due to the use of hazardous solvents and high energy consumption. This dissertation aims to enhance the sustainability of membrane fabrication by utilizing eco-friendly solvents as such as terpineol, non-toxic plant-based solvent, commonly found in perfumes and cosmetics, and Rhodiasolv® PolarClean, a byproduct of Nylon-66 production that also has a low-hazard profile. Additionally, this research explores the use of recycled plastics. The first study of this dissertation successfully investigated the impact of the small molecules as additives on the polystyrene terpineol system exhibiting an upper critical solution temperature (UCST). This research highlights a new path to reduce the phase transition temperature for TIPS by managing hydrogen bonding interactions and polymer solubility by decreasing the transition from 65 °C to room temperature. This approach allows membrane formation at room temperature, resulting in lower energy consumption. The fabricated membranes were characterized by analyzing their pore size, morphology, and filtration performance, showing comparable or improved properties over conventionally fabricated membranes. The second study investigated the fabrication of poly(acrylonitrile-co-butadiene co-styrene) (ABS) membrane using green solvent and the effect of the diluents on the ABS membrane. Rhodiasolv® PolarClean was used as the primary solvent, and ethanol and acetone were used as additives to study the fabrication of ABS membrane using the NIPS. Using PolarClean as the primary solvent and varying the additive ratios allowed for the control of the membrane morphology and performance. Whereas, using only PolarClean for fabrication ABS resulting fingerlike pore morphology and relatively low bovine serum albumin (BSA) rejection. The additive addition impacts the volatility and stability of the system therefore impacting the kinetic phase inversion, and membrane morphology. In the third study, recycled polymers from LEGO® blocks, including high impact polystyrene (HIPS), ABS, and poly(methyl methacrylate-co-acrylonitrile-co-butadiene-co styrene) (MABS), were employed to fabricate membrane via NIPS . There are limited studies of the impact of different polarity segments in HIPS, ABS, and MABS on phase separation of recycled polymer membranes. Membranes were fabricated from recycled LEGO blocks using NIPS with Rhodiasolv® PolarClean and acetone. Blending MABS and ABS allowed to control the ratio of acrylonitrile and methyl methacrylate in the sample. The increase in the ratio of MABS in the blended samples altered the membrane structure from sponge-like to finger-like, likely due to the increased hydrophilicity attributed to the polar block, which allowed water to penetrate as a nonsolvent and caused growth in the lean polymeric phase, resulting in a stretched finger-like sublayer. Blended membranes exhibited only modest changes in their thermal stability and tensile strength, likely due to the similar chemical structures of some segments. Overall, this dissertation establishes that the sustainability of the membrane fabrication can be improved using small molecular weight additives, green solvent, and recycled polymers resulting in more environmentally friendly polymeric membranes with comparable performance to conventionally synthesized structures.