The tribological performance and tribochemical analysis of novel borate esters as lubricant additives in rapeseed oil

• The novel borate additives possess high anti-wear and extreme pressure properties.
• The composition and structure of boundary films at the worn surfaces were analyzed.
• The additives form a protective film at the rubbed surfaces based on B2O3 and/or BN.
• B–N synergetic effect was found in the results.

Two novel borate esters, tris (4-dodecylphenyl) borate and 2-(2-(4-dodecylphenoxy)-1, 3, 6, 2-dioxazaborocan-6-yl) ethanol were synthesized and applied as anti-wear and extreme pressure additives in rapeseed oil. The borate esters possess high anti-wear and extreme pressure properties. XANES and XPS were used to analyze the composition and structure of boundary films at the worn surfaces. It is shown that the additives form a protective film at the rubbed surfaces based on B2O3 and/or BN. B–N synergetic effect was found in the results which suggests that tribofilms composed of BN are to be preferred over tribofilms that consists of B2O3.