Approche Multi-Echelle de la dégradation en conditions d’USagE de membranes polymères de filtration – MéDUSE

Ultrafiltration with polymeric membranes is highly established in the production of drinking water as well as in dairy industry. In use conditions in industrial plants, membranes have to be frequently cleaned by physical and chemical treatments. These treatments avoid the bacterial development in the installations and eliminate the fouling which directly rises from filtration. The cleaning/disinfection solutions employed are selected on the basis of their oxidizing, acido-basic or bactericide properties. This is the case for sodium hypochlorite largely employed in water and dairy industries. The impact of chemical cleanings on the properties of the membranes is poorly documented but it seems that treatments are likely to undergo ageing of the polymer, which can lead to a drastic break of one or several membranes in a module. As the mechanisms leading to the degradation of membranes integrity are not elucidated, one cannot anticipate these phenomena. This aim of the project is to identify the mechanisms responsible for the membrane degradation at the molecular scale. This will bring the necessary knowledge on the degradation of the membranes in use conditions. It will be then possible to propose methodologies and tools allowing the study of the degradation of polymeric membranes in conditions of accelerated ageing representative of use conditions. The ageing of membrane is complex due to the simultaneous contribution of many factors. In this project, we propose then to focus on the ageing resulting only from chemical treatments. A multi-scale fundamental approach (processes, materials, interfaces) will be developed, which aims are : 1) to understand the mechanism of degradation of the membranes in conditions of use, 2) to define relevant protocols of accelerated ageing reproducing the damage caused at the molecular level due to cleaning/disinfection solutions on plant, 3) to identify the most relevant macroscopic parameters to follow and reveal this degradation, 4) to propose a strategy in order to increase the lifetime of the membranes. The architecture of the project makes it possible to simultaneously consider the two applications concerned: production of drinking water and filtration of skimmed milk. This is made possible by the fact that membranes used in both fields of application are based on the same polymer, which is polyethersulfone. The procedures of cleaning/disinfection are obviously specific to each application, but the variables are the concentration in oxidizing agent, the frequency of the cycles of cleaning and the temperature, parameters which could be modulated since the relevant protocols of ageing will have been identified. The knowledge of the relations between properties at the molecular level and macroscopic characteristics of material and their respective evolution in use conditions will constitute the first stage in the development of a tool for prediction of membranes lifetime.