Development of an alternative analytical methodology to monitor industrial degreasing baths by dynamic light scattering

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 involved since 1999 their replacement with green cleaners due to the hazardous effects of solvents on human health and on environment. Aqueous cleaners, commonly called detergents, are widely used as an alternative. The monitoring of such degreasing baths is usually realized by alkaline titration or conductimetry. However these techniques do not provide significant information on the state of degreasing baths. In this study a new method is proposed using dynamic light scattering (DLS). This technique can evaluate the size of the micelles formed in the degreasing bath. The free and “full of oil” micelles can be identified and quantified due to their different sizes. The contamination rate and the loss of detergent all along the use of the bath can be determined with these new indicators. After a validation step with prepared degreasing solutions, this method has allowed monitoring precisely industrial degreasing baths, reducing the frequency of the baths replacement, the volume of aqueous effluents and optimizing baths management.