Tribological study of borated hydroxyalkyldithiocarbamate as additive for environmentally adapted lubricants

Purpose - The fast growing concern for maintaining integrity of the environment has built up development of environmentally-adapted lubricants. Because of their toxicity most of the traditional lubricating additives cannot be used in this kind of lubricant. The purpose of this paper is to find a borate ester derivative which can be used as a multifunctional additive in rapeseed oils (RSO). Design/methodology/approach - A borated S-2-hydroxypropyl N, N-dibutyl dithiocarbamate (BDTC) was synthesized and characterized. Its tribological properties in rapeseed oil as multifunctional additive were evaluated, using a four-ball tribometer and compared with one kind of commercial MoDTC. In addition, its thermal stability was identified using TGA and antioxidative ability tested by PDSC. The action mechanism of BDTC was studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and atmospheric pressure chemical ionization mass spectrometer (APCl/MS) analysis. Findings - Results show that BDTC exhibits high thermal stability, possesses comprehensive tribological performance in rapeseed oil, and has evident effect in controlling the oxidation of RSO. Analysis of worn surface indicates that BDTC was decomposed and reacted with metal during the friction process. The lubricating film mainly contains inorganic boron compound (B2O3), organic nitrogen derivatives and FeSO4. Originality/value - This paper provides a borate ester derivative which possesses excellent tribological properties and can be used as a multifunctional ashless additive in environmentally-adapted lubricants. Furthermore, an innovative method, APCl/MS, was used to analyze the tribo-fragmentation behavior of BDTC.