The Lubrication Properties of Microbial Cells and their Biopolymers

Abstract

Many machining operations e.g. turning, milling or grinding are dependent on the application of water-based metalworking fluids (MWF) which contribute significantly to their high level of performance. MWF in-use are exposed to a microbial contamination, which leads to a deterioration of water-based MWF components and can cause a premature failure of the whole coolant system. Expensive monitoring and the addition of biocides are needed to maintain the MWF quality and to reduce the microbial load, regardless of the potential risk for health and environment. To overcome these limitations, the paradigm shift of using microorganisms as a replacement for conventional MWF is investigated in this paper. Microbial cell components and some microbial inclusions are comparable to conventional MWF components like e.g. fatty acids or sulfur compounds. Due to this fact, it is possible to create a regenerative system on a microbiological basis for the substitution of conventional MWF components. In preliminary tribological investigations the basic lubrication properties of microorganisms and their potential as a replacement for conventional MWF were shown. The presented approach intends to investigate the influence of microbial cell counts, cells size and extracellular polymeric substances (EPS) on the lubrication behavior respectively. The results of the tribological tests show that especially microorganisms with a big cell volume or a high EPS productivity exhibit superior Brugger-values (up to 174%) compared to a highly concentrated conventional MWF (emulsion 10%) and indicate the great potential of microorganisms as a replacement for conventional MWF.