24th International Colloquium Tribology - January 2024 247 Moving towards Sustainable Lubrication - Challenges and Findings for Lube Components from Biobased Sources Marcella Frauscher 1 *, Jessica Pichler 1 , Rosa-Maria Nothnagel 1 , Adam Slabon 2 1) AC2T research GmbH, Wiener Neustadt, Austria 2) University of Wuppertal, Wuppertal, Germany Corresponding author: marcella.frauscher@ac2t.at 1. Introduction With the mandatory change towards a sustainable economy, renewable, waste-derived or plant-based materials are investigated as possible replacements for lubricant components with fossil origin. The studied materials include various forms of lignin, food waste such as spent coffee grounds, further valorised after coffee brewing or fish oil waste. One main challenge of bio-based lubricants is the determination and improvement of their stability to fulfil the performance characteristics in industrial applications [1]. For this purpose, a comprehensive approach combining stability assessment, characterization of component degradation and evaluation of triboperformance is necessary [2]. 2. Sustainable sources for lubricant components Within this presentation, three different bio-based materials as potential lubricant components are presented: Lignin, coffee ground oil, and bio-based friction modifiers. 2.1 Green depolymerization of lignin as base for additives Lignin as source for lubricant components is characterized by a strong structural variation depending on the origin. The challenges for lignin-derived components are separation and purification of compounds of interest to create materials and chemicals with added value. A green depolymerization route is presented, resulting in building bricks for synthesis of potential lubricant additives [3]. The effectiveness of the electrochemical setup for cleavage of the main linkage present in the lignin macromolecule and the mechanism and selectivity of lignin depolymerization was evaluated using the cleavage of β-O-4 linkage of 2-phenoxyacetophenone (2-PAP) as a simple model compound [4]. First triboresults for dispersions of nanoscopic flower-like lignin particles (NP) doped with a minimal amount of MoS 2 in polyalphaolefin (PAO) base oil showed significant improvement of the lubricating properties (figure 1) [5]. Figure 1: Tribological properties of lignin/ MoS 2 NPs hybrid additive in mineral oil (0.05 wt.%) [6] 2.2 Spent coffee ground oil as lubricant component source Oil extracted from spent coffee grounds (SCGO) was investigated for friction and wear properties used as both base oil and additive by an oscillating tribometer and rheometer. Furthermore, properties such as viscosity, acid value, water content, thermogravimetric analysis and differential scanning calorimetry were determined. The composition of oils was studied by ATR-FTIR, elemental analysis (CHNSO) and gas chromatography coupled with mass spectrometry (GC-MS). The tribological properties (figure 2) of SCGO were investigated as a base oil (100-%) and as a 5 % additive in polyalphaolefin (PAO 8). Figure 2: Coefficient of friction (COF) of synthetic base oil (PAO 8), spent coffee grounds oil (100-% SCGO), spent coffee grounds oil 5-wt% in PAO 8 (5-% SCGO). Moving towards Sustainable Lubrication - Challenges and Findings for Lube Components from Biobased Sources 248 24th International Colloquium Tribology - January 2024 This revealed that 100 % SCGO as well as 5 % SCGO led to an improvement in the coefficient of friction (COF) compared to neat PAO 8. Microscopically determined wear traces confirmed this improvement (figure 3). Figure 3: Wear scar PAO 8 (A), 100 % SCGO (B), 5 % SCGO (C). 2.3 Friction modifiers from bio-sources Bio-based friction modifiers (FM) were compared with conventional ones by using a developed rheometer method (see figure 4), designed under variation of normal force, temperature, and sliding speed [8]. Bio-based friction modifiers, such as rapeseed and salmon oil, were selected based on a toxicological assessment of literature data. Comparison of performance revealed the advantages and disadvantages of bio-based and conventional friction modifiers, respectively. Measurements of both types of FM in PAO at 80 °C and in distilled water at 30 °C showed that bio-based friction modifiers can perform at least as good as the best performing conventional FM [9]. Figure 4: Test setup - Ball-on-three-plates [8] 3. Conclusion To show the possibilities for sustainable lubricant components and selected results, 3 different materials and approaches were presented. A straightforward approach to produce value-added biobased building blocks from lignin for additives was demonstrated. This was realized by a simple depolymerization process of biomass waste in a biomass-based solvent and a cheap transition metal as electrocatalyst. Spent coffee grounds was used as a valuable waste resource, serving as high-quality feedstock for biodiesel or bio-lubricants. SCGO showed superior friction reduction behavior compared to a synthetic lubricant. Based on a toxicological assessment and the availability on the European market, bio-based FM were selected. Two different applications were considered: bio-based FM mixed in water and FM with petrochemical origin mixed in a conventionally used PAO. The performed tests indicated the advantages and disadvantages of both FM in the respective system. Comparing both it was revealed that bio-based FM could be a promising alternative for conventionally used fossil-based FM in lubricants. Acknowledgements The work presented was funded by the Austrian COMET program (Project InTribology, Nr. 872176) and carried out at the “Excellence Centre of Tribology” (AC2T research GmbH). References [1] A comprehensive review of sustainable approaches for synthetic lubricant components. Pichler J., Eder R.M., Besser C., Pisarova L., Dörr N., Frauscher M., Marchetti-Deschmann M. Green Chemistry Letters and Reviews, Vol 16 No 1 2023 [2] Assessment and design of modern lubricants supported by mass spectrometry. Frauscher M. European Conference on Tribology 2023 Bari (IT) [3] Electrochemical depolymerization of lignin in a biomass based solvent. da Cruz M.G.A., Gueret R., Chen J., Piatek J., Beele B., Sipponen M. H., Frauscher M., Budnyk S., Rodrigues B., Slabon A. ChemSusChem - Chemistry - Sustainability - Energy - Materials, Vol 15 2022 [4] On the product selectivity in the electrochemical reductive cleavage of lignin model compounds. da Cruz M.G.A., Rodrigues B., Ristic A., Budnyk S., Das S., Slabon A. Green Chemistry Letters and Reviews, Vol 15 Is 1 2022 [5] MoS2 nanoflower-decorated lignin nanoparticles for superior lubricant properties. Lindenbeck L.M., Beele B., Morsali M., Budnyk S., Frauscher M., Chen J., Rodrigues B., Sipponen M. H. Nanoscale, Vol 15, 2023 [6] Secret Wood - source of molecules for sustainable lubrication? Frauscher M., Budnyk S., da Cruz M.G.A., Rodrigues B., Slabon A. International Conference on Tribology and Systainable Lubrication 2023 Düsseldorf (DE) [7] Moving towards green lubrication: tribological behaviour and chemical characterization of spent coffee grounds oil. Pichler J., Eder R.M., Widder L., Varga M., Marchetti-Deschmann M., Frauscher M. 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