A sustainable protection of water-containing technical fluids like cooling lubricants against microbial attack using renewable resources

Abstract There is a need to develop new chemical protection concepts for water-based cooling lubricants (CL) against microbial infestation. To this end, research was carried out into potential active substances that can be obtained or produced from renewable raw materials. In this project, seven substance groups with more than 70 compounds were identified and subjected to a literature-based suitability assessment. The substances with good expected suitability could be assigned to two groups according to their antimicrobial effect: minimum inhibitory concentration (MIC) 0.25–1% (e.g. terpenes, coumarins) and MIC 5–30% (e.g. divalent and trivalent alcohols). The former should be incorporated into the CL as additives, the latter should rather be classified as base fluid components. Chemical-physical, tribological and biological tests were carried out in the laboratory. Interestingly, in the microbiological tests with a test duration of 20 d, a complete biostatic but no biocidal inhibitory effect was found for all the active ingredients considered. In a CL reference formulation, glycerol was replaced by the newly identified active ingredient 1,6-hexanediol as an example. This formulation was successfully tested in an industrial machine for cylindrical grinding of steel, demonstrating the immediate applicability for machining. Thus, a comprehensive research and development strategy for novel CL additives is presented which can be used for all identified antimicrobial compounds. Furthermore, it is certainly applicable to novel additives with other performance spectra, as well.