In drinking water production plants, the use of oxidants such as sodium hypochlorite during in place cleanings may impair the membrane integrity and radically impact the ultrafiltration process efficiency, leading to potential contamination of the permeate water with pathogens. This study investigates the effects of hypochlorite exposure on the properties of a commercially available UP hollow fiber. Mechanical performances and water permeability appeared to be greatly affected by the contact with hypochlorite. Monitoring the molecular changes by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance infrared spectroscopy (ATR-IR), size exclusion chromatography (SEC) and VITA mode atomic force microscopy (VITA-AFM) revealed high stability of the main polymer constituting the membrane (i.e. polyethersulfone (PES)) and very high reactivity of the additive (i.e poly(N-vinyl pyrrolidone) (PVP)) towards immersion in aqueous sodium hypochlorite solution with maximal reaction rate for neutral to slightly basic pH. Correlation of those results unexpectedly leads to the conclusion that the overall membrane properties changes are governed by the additive fate. (c) 2013 Elsevier B.V. All tights reserved