Spatial localization of membrane degradation by in situ wetting and drying of membranes in the scanning electron microscope

• Investigation of membrane degradation by in situ experiments in the ESEM.
• Identification of the layer which is most affected by chemical membrane treatments.
• IR maps of cross sections of pristine and treated membranes by IR microscopy.
• Measurement of changes at the membrane surfaces by imbibition of water droplets.

Flat sheet microfiltration membranes are often based on PES/PVP (polyethersulfone/polyvinylpyrrolidone), because of their wide range of applications and their excellent resistance to many physical and chemical treatments. Nevertheless, regular cleaning of the membranes is necessary, which often leads to membrane degradation and thus a gradual reduction in performance. This study investigates the impact of three typical cleaning agents (NaClO, NaOH and CA) on multilayered PES/PVP membranes used for water filtration by in situ wetting and drying experiments in an environmental scanning electron microscope (ESEM). It has been proven that this method enables the detection of membrane degradation and is able to identify the layer which is most affected by these chemical treatments. The results were verified by Fourier transform infrared spectroscopy (FT-IR) and a method based on the imbibition of water droplets at the membrane surface. But the ESEM based method is the only method that involves a large sample volume and can thus provide statistically significant results.