Development of an analytical method to monitor industrial degreasing and rinsing baths

In the metal finishing or aeronautical industries, efficient degreasing of metallic alloy surfaces is an essential step. This step was first performed with halogenated solvents. Legislation has recently required their replacement with green cleaners due to the hazardous effects of the solvents on human health and on the environment. The industrial partners of the study chose to use aqueous cleaners, commonly called detergents, as an alternative. The monitoring of these baths is important to evaluate degreasing power on soiled alloy pieces. This study is focused on the evaluation of typical analytical tools recommended by providers (alkaline titration and electrical conductivity measurements) to perform degreasing bath monitoring. The results demonstrate that these techniques do not provide significant information on the state of the degreasing bath if they are used alone. Indeed, investigations performed on prepared samples simulating a degreasing bath demonstrate that alkaline titration is mainly representative of the oil in solution, whereas electrical conductivity measurements are influenced by oil and surfactants or detergents. Detergents are surfactants that possess adapted characteristics for detergency. From these results, an alternative methodology has been developed to monitor industrial samples, and conductivity measurements were used as age indicators for the rinsing baths.