Comparative life cycle assessment of lubricating greases for nut-runners used in industrial assembly lines

Abstract: Greases are used extensively in almost all areas of life. Considering the fact that they are used in sparing quantities in most applications, the environmental impacts associated with these greases can range from different magnitudes based on the constituents of the grease. As the complexity of greases increases, the tendency to impact the natural ecosystems increases as well, which leads to the question of how sustainable greases can be. Although previous studies illustrate the environmental potency of greases, additives and thickeners that constitute an integral part of the grease have not been analysed adequately. To identify impacts from key constituents of the grease, a life cycle assessment (LCA) approach needs to be applied. While a complete LCA is highly demanding in terms of data, time and expertise, the results allow accurate decision-making based on the different life cycle stages of the product or entity in focus.  Hence the aim of the thesis is to compare two lubricating greases; a mineral oil based lithium complex grease and a synthetic polymer grease, and identify key areas that influence the environmental impacts of these greases through their life cycle by utilising the life cycle assessment approach. The study also tries to understand the significance of these impacts when implementing a ‘systems thinking’ approach to the greases which is performed by introducing the wheel and pinion assembly to the life cycle assessment of the greases. This has been done to understand the interactions between the gear and the grease systems. Pre- existing performance data of the greases including the quantities and life of the gear and the greases were used which were obtained from conducted bench tests. Furthermore, real-time estimates of the used greases in the nut runners were also used. Additional information and data was gathered from scientific literatures for areas where data gaps were identified.  The analysis of the LCA showed that the polymer grease performed better than the lithium complex grease in majority of the selected impact categories. It was also evident that the presence of molybdenum in any form is a major influence on the environmental performance of the greases following which, the production methods of the base oils and the type of energy used further influenced these impacts but to a more reduced level. However, once the systems approach was applied it was noticed that the overall environmental performance of the polymer grease increases with time due to its durability while the lithium complex grease showed a relatively better environmental performance within the first 12 months of its use. Learnings from the study showed that a systems approach in LCA aided decision making while also allowing one to pinpoint areas that have the most impacts.