Membrane-based water treatment systems are often prone to fouling, necessitating periodic cleaning using agents such as sodium hypochlorite (NaClO). However, exposure to NaClO can compromise membrane integrity, structure, and performance leading to degradation. This study investigates the chlorine tolerance of three types of upcycled polyvinyl chloride (PVC) membranes—Rigid-PVC (R-PVC), Flexible-PVC (F-PVC), and Research Grade-PVC (RG-PVC)—fabricated via non-solvent-induced phase separation (NIPS). Their performance was benchmarked against a commercial polyethersulfone (PES) membrane. The membranes were subjected to a 5000 ppm NaClO solution at pH 11 and 50 psi for one hour. Characterization before and after exposure included analysis of surface and cross-sectional morphology, surface charge, hydrophilicity (contact angle), and functional group composition. Among the tested membranes, the PES membrane exhibited the most severe degradation. The molecular weight cutoff (MWCO) increased from 1,500 Da to 12,000 Da, surface charge shifted from –15 mV to –35 mV (at pH 7), and the water contact angle decreased from 64° to 41°, indicating increased hydrophilicity. This degradation was attributed to polymer chain scission of the PES backbone, particularly cleavage of the C–S bond, leading to the formation of sulfonic acid and phenyl chloride groups. In contrast, the F-PVC membrane exhibited moderate degradation. The MWCO increased from 1,700 Da to 8,000 Da, surface charge changed from –24 mV to –34 mV (at pH 7), and the contact angle decreased from 125° to 82°. This behavior was associated with the breakdown and leaching of dioctyl phthalate (DOP), the primary plasticizer in F-PVC, into 2-ethylhexanol and phthalic acid derivatives upon exposure to NaClO. The R-PVC and RG-PVC membranes demonstrated significantly higher chlorine tolerance. For R-PVC, the MWCO increased from 1,850 Da to 4,000 Da, surface charge shifted from –26 mV to –32 mV, and the contact angle decreased from 70° to 60°. RG-PVC showed a minimal MWCO increase from 1,600 Da to 1,900 Da, a surface charge change from –11 mV to –14 mV, and a contact angle reduction from 66° to 63°. The improved resistance of R-PVC is attributed to the presence of calcium carbonate, the main additive in R-PVC, which is chemically stable in the presence of NaClO. The minor observed changes may result from the ring opening of epoxide structures, leading to the formation of diols and chlorohydrins. RG-PVC, which contains no additives, benefits from its stable C–C, C–H, and C–Cl bonds, which possess high bond dissociation energies and are resistant to oxidation by NaClO. Additionally, the chlorine atoms within the PVC backbone offer a degree of shielding against further chlorination. Water permeability and humic acid rejection were evaluated at 100 psi before and after NaClO exposure. The PES membrane exhibited the largest increase in permeability, from 22 to 53 LMH/bar, followed by F-PVC (30 to 51 LMH/bar), R-PVC (32 to 43 LMH/bar), and RG-PVC (26 to 29 LMH/bar). After exposure, humic acid rejection was lowest for the PES membrane (72 %), while the upcycled PVC membranes demonstrated higher rejection rates: 79 % for F-PVC, 84 % for R-PVC, and 81 % for RG-PVC. These results underscore the superior chlorine resistance of upcycled PVC membranes—particularly R-PVC and RG-PVC—relative to commercial PES membranes. Consequently, these upcycled PVC membranes represent promising and durable alternatives for water treatment applications involving exposure to oxidizing cleaning agents such as NaClO.
