(211b) A Comparison of Polarclean, Gamma-Valerolactone and Their Mixture As Bio-Derived 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. One big challenge is that by 2020, some common solvents, N-Methyl-2-Pyrrolidone (NMP) and Dimethylacetamide (DMAc) will be banned by Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) in Europe[1]. Therefore, bio-derived and low-toxicity solvents are a focus of increasing investigations. 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 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[2,3]. Membranes prepared using GVL as a sole solvent were observed to be gelatinous, hence not ideal for filtration[2].

GVL and PolarClean were used as co-solvents, viable membranes were cast with surface charge and hydrophilicity not being significantly different from membranes made using PolarClean alone. Specifically, the solvent mixture produced PSf membranes with zeta potential values of about -20mV and contact angles at around 65°. Furthermore, the average pore size of membranes decreased from 48nm to lower than 1nm as adding GVL in dope solutions. The membranes prepared using solvent mixtures showed pure water flux at 300-500 LMH and over 99% BSA rejection. Therefore, the use of PolarClean/GVL as co-solvents showed promise for the fabrication of PSf membranes.

1. https://chemicalwatch.com/22940/reach-clp-hub-authorisation-vs-restriction
2. Dong, X.; Shannon, H.D.; Escobar, I.C. Investigation of polarclean and gamma-valerolactone as solvents for polysulfone membrane fabrication. In Green polymer chemistry: New products, processes, and applications, American Chemical Society: 2018; Vol. 1310, pp 385-403.
3. Wang, H.H.; Jung, J.T.; Kim, J.F.; Kim, S.; Drioli, E.; Lee, Y.M. A novel green solvent alternative for polymeric membrane preparation via nonsolvent-induced phase separation (nips). J. Membr. Sci. 2019, 574, 44-54.