Preparation And Tribological Properties Of Borate Ester Modified Molybdenum Disulfide Based Nanoparticles

As a lubricating additive,nano-sized MoS₂ has been shown to significantly improve the lubrication performance of base oils.However,the high specific surface area of MoS₂ nanoparticles can lead to some shortcomings,such as easy aggregation and poor compatibility with base oils,which can prevent them from being stably dispersed in the oil.Additionally,the chemically inert surface of MoS₂ makes its binding strength with polymer substrates weak,further limiting its application as a lubricating additive.In this paper,triethanolamine borate（TEAB）and polyethylene glycol borate（PEG400-BA）were synthesized through catalytic esterification using the catalytic performance of MoS₂ and its complex C₃N₄/MoS₂.The tribological properties of TEAB-modified MoS₂（MoS₂/TEAB）and PEG400-BA grafted C₃N₄/MoS₂ in polylactic acid（PLA）and polyethylene glycol 600（PEG600）were investigated.（1）Based on the catalytic performance of nano-spherical MoS₂,MoS₂/TEAB was synthesized by catalytic esterification of triethanolamine and boric acid at 145°C.The tribological properties of MoS₂/TEAB with different additives in PLA were tested on a WTM-2E controllable atmosphere micro-friction and wear tester.The results indicated that in a 30-gram PLA substrate,the addition of 0.05,0.25,and 0.5 grams of MoS₂/TEAB could enhance the anti-wear properties of PLA.However,the inclusion of1 gram of MoS₂/TEAB decreased the anti-wear performance of PLA,resulting in an increase in wear width by 9.09%and wear area by 33.89%,respectively.When 0.05 g MoS₂/TEAB was added,the lubrication effect was the most significant,and the average spot diameter and wear rate decreased by～19.10%and～57.21%,respectively,compared with pure PLA.By exploring the influence of different components of MoS₂/TEAB on the lubrication performance,the results showed that MoS₂ and TEAB played a synergistic lubricating role in the friction process,and the anti-wear effect of TEAB was better than MoS₂.The tribological properties of PLA,TEAB+PLA,and MoS₂/TEAB+PLA under different loads were studied.It was found that with the increase of load,MoS₂/TEAB+PLA composite showed less wear than TEAB.The SEM and Raman characterization showed that the matrix of pure PLA showed a large number of peelings during the friction process.Unlike PLA,the wear surface of MoS₂/TEAB+PLA became smooth,and only a few spalling pits and cracked grains of PLA existed,indicating that the addition of MoS₂/TEAB can improve the adhesion wear and fatigue wear of PLA.The improvement was attributed to the formation of MoS₂-containing transfer film.（2）The C₃N₄/MoS₂ composite was prepared by introducing C₃N₄ sheets into the synthesis process of MoS₂,and it was used as the catalyst for the esterification of boric acid and polyethylene glycol 400.Under the bridging action of 3-isocyanatopropyltrimethoxysilane,the C₃N₄/MoS₂@PEG400-BA lubricant additive was synthesized.The results of catalytic esterification experiments showed that the addition of C₃N₄ improved the catalytic efficiency of MoS₂ from 93.8%to 99.1%.The tribological properties of PEG600 with different dosages of C₃N₄/MoS₂@PEG400-BA were tested on a four-ball friction and wear tester.The results showed that 0.75 wt.%,1.5 wt.%,3.00 wt.%,and 6.00 wt.%C₃N₄/MoS₂@PEG400-BA could improve the wear resistance and wear reduction performance of PEG600,and the lubrication effect was the best when 3.00 wt.%C₃N₄/MoS₂@PEG400-BA was added.Compared with pure PEG600,the friction coefficient and average scar diameter of 3.0 wt.%C₃N₄/MoS₂@PEG400-BA decreased by 32.76%and 28.98%,respectively.It is found that C₃N₄/MoS₂ and PEG400-BA play a synergistic role in the friction process of C₃N₄/MoS₂@PEG400-BA.PEG400-BA could effectively improve the dispersion stability of C₃N₄/MoS₂ in PEG600,and no obvious delamination occurred after 28 days of standing.The SEM and XPS characterization of the wear scar showed that the addition of C₃N₄/MoS₂@PEG400-BA improved the abrasive wear and fatigue wear of PEG600 and formed a friction film containing MoO₃,Fe₂O₃,Fe₃O₄,Fe S,Fe SO_4,and B₂O₃ on the surface of the friction pair,results in enhancing the anti-wear and anti-friction performance of PEG600.