Abstract
Abstract This paper reports a series of studies on the lubricant properties, elastohydrodynamic film thickness, and coefficients of friction of several commercially available ester base stocks, i.e., diisooctyl phthalate (DIOP), diisodecyl phthalate (DIDP), diisotridecyl phthalate (DITDP), diisooctyl sebacate (DOS), diisotridecyl sebacate (DTDS), trihydroxymethylpropyl trioleate (TMPTO), and pentaerythritol tetraoleate (PETO). The results include densities and viscosities from 303 to 398 K, and elastohydrodynamic lubricant film thicknesses and friction in the boundary, mixed and full-film lubrication regimes measured at several temperatures, loads, and speeds. These ester base stocks have different lubrication abilities owing to their chain lengths, geometric configurations, and molecular rigidity. This study provides quantitative insight into the use of ester-based lubricants for low friction through the entire lubrication regime (boundary to full film) by utilization of suitable type and size of the ester base stocks.
Highlights
Synthetic lubricants have received much attention for their beneficial properties, such as good low- and high-temperature viscosity performance at extreme service temperatures, high thermal and oxidative stabilities, and optimal rheological-tribological properties for extensive applications
The ester base stocks studied in the present work are diisooctyl phthalate (DIOP), diisodecyl phthalate (DIDP), diisotridecyl phthalate (DITDP), diisooctyl sebacate (DOS), diisotridecyl sebacate (DTDS), trihydroxymethylpropyl trioleate (TMPTO), and pentaerythritol tetraoleate (PETO) (Fig. 1)
For phthalates (DIOP, DIDP and DITDP), the density decreases and the viscosity increases from DIOP to DIDP to DITDP that have similar molecular structures; but the density decreases with the increase in molecular mass, i.e., the increase in the length of hydrocarbon chain attached to the phenyl ring
Summary
Synthetic lubricants have received much attention for their beneficial properties, such as good low- and high-temperature viscosity performance at extreme service temperatures, high thermal and oxidative stabilities, and optimal rheological-tribological properties for extensive applications. Esters, which include monoesters, diesters, phthalates, and polyol esters, have great biodegradability and benign to the environment and wildlife in case of accidental leakage or spill They are synthesized without waste and sediment. Fernández et al evaluated the influence of load and the type of lubricant on the thickness of the elastohydrodynamic film and the rolling-contact fatigue lives of AISI 52100 steel balls [24]. Lord and Larsson reported the effects of slide-roll ratio and lubricant properties of a synthetic ester VG46 on elastohydrodynamic lubrication film thickness and traction, and suggested that the ester maintained a relatively thicker lubricant film during sliding than did the corresponding polyalphaolefin and mineral oils [27]. There were few reports on how the molecular structures and types of synthetic ester base stocks affect the elastohydrodynamic lubrication properties and friction behaviors. Comparisons of film thicknesses and frictions are conducted to reveal insights into the nature of these lubricants and possibilities to design novel high-performance ester lubricants
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