Exploring the Membrane Morphology and Performance Discrepancy of Different Grades of PLA With Different Solvents: Thermodynamics and Kinetic Aspects

Despite the progress in the preparation of bio-based polymeric membranes using traditional solvents, the enhancement of sustainability and minimization of adverse environmental impact through the replacement of greener solvents is imperative. This study investigates the possibility of fabrication and the performance of sustainable membranes prepared by bio-based polymer and green solvent. The primary objective of this study is attributed to the detailed assessment of the membrane formation mechanism, considering thermodynamic and kinetic aspects. In this context, three different types of PLA (two amorphous and one semicrystalline) were utilized to assess the polymer type effect as well as the solvent effect evaluation using DMSO and other conventional solvents (DMF, DMAc, NMP). The detailed examination of the thermodynamic and kinetic aspects was performed by various parameters such as Hansen solubility parameter (HSP), solubility envelope, diffusion coefficient, ternary phase diagram (solvent-nonsolvent-polymer), and solution viscosity. Despite the meaningful impact of these theoretical methodologies, their limitations in the final structure reasoning were also observed. Based on the separation study, various structures of membranes obtained in this examination demonstrate the competition between thermodynamics and kinetics, which makes it difficult to presume the dominance of the factors. While the complexity of the phase separation mechanism has been discussed for decades since its initiation, our study can provide insight into the importance of the solvent/nonsolvent conversion rate, particularly the diffusion coefficient. The overall conclusion of the results obtained by the performance of membranes indicated the possibility of DMSO substitution for PLA-based membrane preparation, especially for textile wastewater treatment.