Durable hydrophilic surface modification for PTFE hollow fiber membranes

A facile one-step process was developed to generate hydrophilic coating on polytetrafluoroethylene (PTFE) hollow fiber membranes based on co-deposition of polymerized dopamine (PDA) and poly (ethyleneimine) (PEI) from aqueous solutions. For comparison, step-by-step coating of PDA and PEI was also applied to modify PTFE membranes. ATR-FTIR, XPS , SEM, AFM and water contact angle measurements were applied to analyze the surface chemistry and morphology evolution of the modified PTFE membranes at varied grafting yields. PDA and PEI were successfully deposited on PTFE membranes while the hydrophilicity and wettability of the modified membrane were greatly improved. The modified PTFE membranes showed high water permeate fluxes, good long-term stability and durability in strong acidic aqueous solution. Although PTFE hollow fiber membranes samples modified by a step-by-step dip-coating process with PDA and PEI tent to lose their hydrophilicity in strong alkaline solutions, the co-deposited PTFE membranes with PDA and PEI were found to have good durability in aqueous solution at pH   13. This work provides a one-step method to improve the hydrophilicity and chemical stability of the PTFE hollow fiber membranes for water treatment applications.