24th International Colloquium Tribology - January 2024 239 Bio-Lubricants as Metal-Working Fluids: More than an Environmental-Friendly Choice Marco Bellini *1 , Simone Pota 1 1 Bellini SpA, Zanica, Italy * Corresponding author: mbellini@bellini-lubrificanti.it 1. Introduction Metal-Working Fluids (MWFs) are supposed to reduce Coefficient of Friction (CoF) in all lubrication regimes (boundary, mixed and hydrodynamic lubrication). To obtain so, a blend of performance additives has to be added to the base fluid. There are a plenty of additives known to be effective on performance’s enhancement for MWFs and, even if each company uses its technology, they can be grouped into four main clusters: chlorine based, sulphur based, phosphorous based additives and super-lubricity additives. However, increasing quality and quantity of additives in Metal-Working Fluids sometimes does not lead to better results. R&D departments experienced this in the past two decades, when an increase of R&D effort was not paired to better performances. This forced to find alternatives and to consider different base stocks other than the standard ones. Among the others, esters were the perfect candidate due to their chemistry and to their tribological behaviour. Nowadays bio-lubricants are a trend topic in lubricants market. The raising focus on green alternatives and HSE advantages of bio-lubricants in respect of mineral oil are the main drivers of this big change in lubricants market. However, bio-lubricants are more than an environmental-friendly choice: they offer a complete range of advantages. 1.1 Bio-lubricants technology Bio-lubricants have many advantages compared to mineral oil lubricants. From molecular point of view, esters are more polar than mineral oil. Esters create a layer of organized molecules on the workpiece surface due to their polarity. This layer is responsible to CoF drop observed in tribology measurement. Each type of ester, depending on many factors such as carbon chain length and viscosity, has its typical tribological behavior, extensively studied in the first screening. The selection of low CoF ester base stock to be used has been characterized and deeply studied. The main advantages of ester compared to mineral oil are related to its chemistry: biodegradability, lower CoF, vapor tension, higher flash and fire point and so on. How much is biodegradable lubricants technology ready to replace mineral oil technology? Bellini SpA tried to reply to this question by testing extensively biodegradable formulations on the field in the past years in many different applications. Replacement of mineral oil based product with ester based product often leaded to improvement of performances in terms of lubrication, reduction of oil consumption and reduction of tool wear. 1.2 Health, Safety & Environment Some types of esters are biodegradable according to OECD 301 B method and they have a lower carbon footprint compared to mineral oil. Moreover, some classes of synthetic esters come from renewable sources while natural esters has vegetable origin. Bio-lubricants are the right choice even for Health and Safety reasons. It is well known that some mineral oil based products contains polycyclic aromatic hydrocarbon (PAH) compounds and PAH content increases because of cutting fluids use [1]. We tested concentration of PAH in new MWF, and in the same fluid after 3, 6 and 9 months of intensive use. PAH concentration has been studied in new and after 6 months MWF (ester based and mineral oil based both). Analysis in workplace atmosphere and on the clothes and skin of the operators show high concentrations of PAH when mineral oil is used. References [1] Apostoli P. et al, Int Arch Occup Environ Health (1993) 64, 473-477