The role of oligomeric poly(-caprolactone)-diol and Laponite addition on biodegradability, anti-fouling, mechanical properties, organic dye, and heavy metal ion adsorption of PCL porous membrane

Biodegradable polymeric membranes for water treatment and desalination could help mitigate the environmental impact of polymeric waste from discarded membranes. In this context, poly(ε-caprolactone) (PCL) is a promising choice, but its hydrophobicity limits salt and water contaminant adsorption. To address these issues, PCL was blended with oligomeric PCL-diol (PCL-D) in ratios of 90:10, 80:20, and 70:30, and further 12 wt% Laponite (Lap), an anionic synthetic hectorite clay, was incorporated to the above blends to impart functionality and mechanical stiffness. The addition of PCL-D improved the porosity, hydrophilicity, and antifouling properties, while Lap enhanced mechanical properties and functionality vis-à-vis the above properties. Notably, the pure water flux (PWF) increased from ~188 Lm⁻²h⁻¹ for neat PCL to 1124 Lm⁻²h⁻¹ for the 70:30 PCL:PCL-D blend with 12 wt% Lap (P7D3-L12), and the water contact angle (WCA) decreased from ~96° to ~49°. The membranes showed excellent desalination and adsorption of heavy metal ions and organic dyes. The P7D3-L12 membrane had an adsorption capacity of ~45 mg/g for MB, ~57 mg/g for NR dye, ~84.9 mg/g for Pb²⁺, and ~90.6 mg/g for Cd²⁺. It also achieved 35.6% and 39.8% salt retention for NaCl and Na₂SO₄ after 4 cycles. The fouling recovery rate (FRR) for the P7D3-L12 membrane was ~93% after the 1st cycle and ~82% after the 5th cycle. The P7D3-L12 membrane showed 78% weight loss in compost over 54 days, highlighting its improved biodegradability. Thus, these modified membranes offer a promising biodegradable solution for water treatment and desalination.