Highly permeable, environmentally-friendly, antifouling polylactic acid-hydroxyapatite/polydopamine (PLA-HAp/PDA) ultrafiltration membranes

Membrane-based technologies are vital in water purification processes such as desalination and wastewater recycling. Polymeric membranes dominate the membrane market; however, they still suffer from issues related to their chemical, mechanical, and thermal stability, and more importantly, membrane fouling. However, these membranes are associated with various environmental problems that occur during their production and disposal. In this work, an eco-friendly and biodegradable membrane composed of polylactic acid (PLA), hydroxyapatite (HAp) as filler, and polydopamine (PDA) as surface coating was proposed. This unique combination and synergic effect of HAp and PDA were found to enhance the PLA membrane's permeation notably. The fabricated PLA/HAp/PDA membrane resulted in an increase in water permeability of the pristine PLA membrane from 359 ± 76 L/m2.h.bar to 788 ± 58 L/m2.h.bar for the membrane coated with 2 wt% HAp/1-h PDA (PLA-H/PDA-1). Similarly, the flux recovery ratio (FRR) increased from 20% for the pristine PLA membrane to 54% for the PLA-H/PDA-1 membrane after 3 cycles. These properties were found to be due to the enhanced membrane characteristics. For instance, the contact angle dropped by 5% (i.e., the membrane became more hydrophilic) and the porosity increased from 55 to 60%. The pore size was also increased from 97 to 133 nm as a result. The modified membranes retained up to 87% of the normal organic matter (NOM), and no deterioration in the thermal properties of the membranes was observed. These membranes open a new route to a circular economy in membrane technology by reducing environmental costs while allowing continuous operation of the membranes.