Evolution of micro-deformation in inner-selective thin film composite hollow fiber membranes and its implications for osmotic power generation

Since thin film composite (TFC) hollow fiber (HF) membranes may experience micro-deformation under high hydraulic pressures in the pressure retarded osmosis (PRO) process due to their polymeric nature and self-supported configuration, this paper aims to elucidate (1) the micro-deformation of polyethersulfone (PES) TFC HF membranes within the pressure range from 0 to 20 bar and (2) its effects on water and salt permeability of the polyamide layer, and structure parameter and tortuosity of the substrate layer for osmotic power generation. It is found that pre-stabilization of the TFC HF membranes at a high pressure close to their burst pressures for a certain period of time is a powerful way to maximize their PRO performance. After stabilization at 20 bar for 30 min, the power density of the PES TFC HF membranes increase from 15.37 to 22.05 W/m² due to the increased membrane surface area, stretched polyamide selective layer (i.e., decreased water transport length and resistance) and decreased membrane structure parameter (i.e., lower tortuosity and internal concentration polarization (ICP)). The intermittent cycle tests have confirmed the sustainability of the enhanced water flux and power density after stabilization of the TFC HF membranes at 20 bar without compromising their selectivity.