The purpose of this paper was to examine the film-forming behaviour of simple compositions of polyalphaolefin (PAO) containing an oil-soluble polyalkylene glycol (OSP) alone, a zinc dialkyl dithiophosphate (ZDDP) alone and then combinations of an OSP and ZDDP.
A Mini-Traction Machine with Spacer Layer Imaging technology was used to evaluate friction and film formation under a specific contact pressure, temperature and slide-to-roll ratio. Electrical contact resistance measurements were used to follow surface film formation.
The inclusion of an OSP to a PAO showed evidence of friction-reducing behaviour with low friction values over the rubbing cycle but no significant tribo-film build up. When a ZDDP (1 per cent) is added to the PAO, a thick tribo-film forms of about 100 nm. Addition of an OSP (10 per cent) shows this film still forms despite the OSP being a polar and surface-active additive.
The study was conducted under a narrow range of test conditions (e.g. temperature and contact pressure), and future work will focus on friction and film formation across a broader set of conditions.
Despite OSPs being polar and surface-active, they do not interfere with the ZDDP in forming an anti-wear film in a PAO and, therefore, their inherent properties of good deposit control could enhance the performance of modern lubricants.
OSPs offer promising benefits as friction reducers in PAOs. The research also suggests that OSPs do not negate the formation of ZDDP anti-wear tribo-films when in combination in a PAO.
Greaves, M. and Topolovec Miklozic, K. (2015), "Film forming behaviour of oil soluble polyalkylene glycols", Industrial Lubrication and Tribology, Vol. 67 No. 2, pp. 133-138. https://doi.org/10.1108/ILT-01-2013-0014
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