posted on 2022-11-11, 21:33authored byZhiwen Zheng, Xiaolong Liu, Hongxiang Yu, Dapeng Feng, Dan Qiao
Using natural products as raw materials to prepare lubricating
additives that can enhance both the tribological performance and biodegradability
of base oils has huge application potential. Here, two natural cholesterol-derived
ionic liquids (ILs) with long-chain alkyl amines or alkyl betaines
as cations were successfully synthesized. The tribological properties
of the two ILs as lubricating oil additives in white oil and castor
oil were tested on the steel interface at room temperature and high
temperature. The biodegradability of the ILs was evaluated according
to the CECL-33-A-9 test method. The results showed that both ILs have
an excellent ability to enhance the antiwear properties and to accelerate
the biodegradation of base oils. Therein, the wear volume of white
oil with 1.5 wt % alkyl amine IL decreases by 80%, the biodegradability
at 21 days increases to 75%, the wear volume of castor oil with 1.5
wt % alkyl betaine IL decreases by 42%, and the biodegradability at
21 days increases to 85%. The improvement of the antiwear ability
of base oils by the ILs was mainly ascribed to the formation of a
more efficient boundary lubrication film due to the adsorption and
tribochemical reactions of the ILs on the contact interfaces. The
promotion of biodegradation is attributed to the nutrients needed
for the early reproduction of microorganisms provided by cholesterol-based
ILs and the increase in oil–water interfacial area owing to
the surface activity of cations, thus causing microorganisms to better
metabolize lubricants. Hence, it is feasible for some natural compounds
to contribute to the development of green and sustainable products
and processes.