Investigation of polarclean and gamma-valerolactone as solvents for polysulfone membrane fabrication

Petroleum-derived solvents used for membrane fabrication through the nonsolvent induced phase separation (NIPS) process are known for their toxicity. Therefore, bio-derived and low-toxicity solvents are starting to be investigated. Examples of bio-derived, low-toxicity solvents include methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (PolarClean) and gamma-valerolactone (GVL). PolarClean has been previously used to fabricate polysulfone (PSf) membranes but with mixed results, such as having similar flux and rejection as traditional membranes, but having membrane pores collapse during membrane cleaning. To address this issue, GVL was investigated as a sole solvent and a co-solvent with PolarClean to fabricate PSf membranes. Membranes prepared using GVL as a sole solvent were observed to be gelatinous, hence not ideal for filtration. On the other hand, when GVL and PolarClean were used as co-solvents, viable membranes were cast with surface charge and hydrophicility not being significantly different from membranes made using PolarClean alone. Furthermore, the average pore size of membranes decreased as the weight percent of GVL in dope solutions increased. Therefore, the use of PolarClean/GVL as co-solvents shows promise for the fabrication of PSf membranes.