Evidencing the chemical degradation of a hydrophilised PES ultrafiltration membrane despite protein fouling

•Evidencing PES/PVP membrane degradation by FTIR despites presence of protein fouling.•Methodology of treatment of FTIR spectra to reveal membrane degradation due to NaOCl.•Application to mapping of PVP degradation due to NaOCl in a spiral membrane.•Application to mapping of PES degradation due to NaOCl in a spiral membrane.