Assessment of the chemical degradation of PFPE lubricants and greases for space applications: implications for long-term on-ground storage

Investigation of long-term storage of space materials for future constellation missions: study of Braycote® 601 EF lubricant

“…Indeed, no new peak was observed after aging suggesting that the grease is not or only slightly oxidized during the aging process. The following peaks were found and interpreted with the references [17,[51][52][53]: 514 cm -1 , 554 cm -1 , 626 cm -1 , 640 cm -1 , 687 cm -1 , 758 cm -1 , 815 cm -1 , 832 cm -1 , 906 cm -1 , 956 cm -1 , 1000 cm -1 , 1072 cm -1 , 1096 cm -1 , 1154 cm -1 , 1206 cm -1 , 1400 cm -1 , 1546 cm -1 , 1578 cm -1 , 1954 cm -1 , 2044 cm -1 , 2372 cm -1 , 2847 cm -1 , 2918 cm -1 and 3621 cm -1 . The large majority of the peaks is attributable to C-F bonds vibrations including, for example, CF stretching, CF2 bending, wagging and rocking, CF3 deformations and CF overtones.…”

“…These observations are coherent with the high stability of the grease. From a thermal point of view and in the absence of catalyst, Z-PFPE thermal degradation has been reported in the range 250 °C to 390 °C with the main decomposition occurring around 370 °C [17][18][19]. The decomposition path is suggested to be driven by successive end group reactions owing to radical formation [19][20][21].…”

“…Al2O3, FeF3), the thermal degradation is hugely accelerated and the decomposition temperature is decreased. [17,22,23]. It is considered to be induced by Lewis acids, causing chain scissions of PFPEs.…”

“…Therefore, in an environment appropriate for a given lubricant, the lubrication failure is often related to its chemical alteration. This alteration is evidenced by grease bleeding, reflow and viscosity changes, oxidation of the lubricant, bond-splitting and reduction of the averaged chain lengths or the molecular weight distribution [17].…”

Synergistic lubrication effect of antioxidant and low content ZDDP on PFPE grease

“…Because of its excellent viscosity-temperature characteristics, wide operating temperature range and chemical inertia, it has been widely used in the field of industrial machinery lubrication. However, under the influence of working temperature and friction heat, PFPE will undergo thermal decomposition and oxidative decomposition, resulting in the loss of the base oil to be lubricated, thus affecting the friction performance and lifespan of grease (Hou et al , 2010; Wolfberger et al , 2021). Therefore, appropriate additives are needed to improve the performance of the grease (Zhang et al , 2017; Shen et al , 2016).…”