The Use of Biochar as Filler in Polyurea Lubricants

Gorbacheva S.N., Yarmush Y.M., Ilyin S.O.

Due to the instability of the dispersions of cellulose particles in non-polar esters, they cannot be considered for use as lubricants or for other purposes. However, such dispersions can be made stable by addition a third component that can create a structural network to prevent aggregation and sedimentation of the cellulose particles. A series of di(2-ethylhexyl) sebacate greases have been obtained using microcrystalline cellulose as a thickener and organomodified montmorillonite as a stabilizer. The characteristics of physicochemical properties of greases have been obtained: yield stress, elastic modulus, friction and wear coefficients, and wear scar diameter under heavy loads were measured. The effect of component concentration and mixing conditions on the rheological and tribological parameters was shown.

Adolfsson K.H., Yadav N., Hakkarainen M.

Hydrothermally carbonized cellulose and its further modifications are intriguing materials for a wide range of potential applications. Hydrothermal carbonization is a sustainable process for conver ...

Tonkonogov B.P., Kilyakova A.Y., Stenina N.D., Popova O.V., Safieva R.Z., Vinokurov V.A., Gorbacheva S.N., Il’in S.O.

Polyurea lubricant composition with conditionally two and four urea units per polyurea thickener molecule in the presence of a second biodegradable thickener (nanocellulose, cetearyl alcohol) were synthesized. The drop point, penetration, and oil separation and rheological, tribological, and antiwear properties were evaluated. The lubricant composition properties changed depending on the number of urea units per polyurea molecule and content of second biodegradable thickener. Tetraurea-based greases had lower viscosity and better tribological and antiwear properties regardless of the nanocellulose content, confirming that the urea-thickener structure had a decisive influence on the lubricant-composition properties.

Maksimova Y.M., Shakhmatova A.S., Ilyin S.O., Pakhmanova O.A., Lyadov A.S., Antonov S.V., Parenago O.P.

Lubricating greases based on pentaerythritol and trimethylolpropane esters and dioctyl sebacate have been synthesized using diureas as a thickener prepared by reactions of toluene diisocyanate, aniline, and primary aliphatic amines of various structures. The physicochemical properties of the greases, such as ultimate strength, yield stress, modulus of elasticity, dropping point, and colloid stability, have been characterized, and data on their antiwear activity have been obtained. The relationship between the structure of grease components, its rheology, and antiwear properties has been revealed.

Lyadov A.S., Maksimova Y.M., Ilyin S.O., Gorbacheva S.N., Parenago O.P., Antonov S.V.

Greases based on poly-α-olefin oils of various viscosities, thickened with diureas of various structures, were studied systematically. The influence of the base oil viscosity and/or thickener structure on the physicochemical properties of lubricants was demonstrated. Diurea thickeners differing in the length of the hydrocarbon substituent influence the properties of lubricants prepared with base oils of similar chemical nature but different viscosity in different fashion. The revealed trends were confirmed by rheological studies in a wide range of shear rates. Tribological measurements at loads in the interval 20–80 kgf demonstrated significant dependence of the antiwear properties of ureate lubricants based on low-viscosity poly-α-olefin oils on the thickener structure. This dependence becomes less pronounced in going to higher-molecular-mass oils.

Ilyin S.O., Arinina M.P., Malkin A.Y., Kulichikhin V.G.

Possible variants of the rheological behavior of silica model dispersions have been analyzed. Different types of interaction between the particles and a dispersion medium make it possible to obtain different systems from low-viscosity sols to gels. Proton-donor (water) and aprotic (dimethyl sulfoxide) media have been used for comparison. Dispersions in the aprotic medium behave as non-Newtonian viscous fluids exhibiting shear thinning or shear thickening depending on deformation rate. Aqueous dispersions are viscoelastic and viscoplastic objects that exhibit the shear thickening at stresses higher than the yield stress. The introduction of small amounts of poly(ethylene oxide) into the organic dispersion medium initiates gelation. An increase in the polymer content in the dispersion medium above the concentration corresponding to the formation of a macromolecular network promotes an increase in stiffness and strength of the gels. The rheological behavior of gels is influenced by the polymer molecular mass and its affinity for a solvent.

Ilyin S.O., Malkin A.Y., Kulichikhin V.G.

The rheological properties of concentrated suspensions of metal oxides dispersed in transformer oil, which are used as electrorheological fluids, are systematically studied. Colloidal particles have intermediate sizes between nano- and microsized scales. Low-amplitude dynamic measurements show that the storage moduli of the examined suspensions are independent of frequency and these materials should be considered as solidlike elastic media. The storage modulus is proportional to the five-powdered particle volume concentration. At the same time, a transition through an apparent yield stress with a reduction in the viscosity by approximately six orders of magnitude is distinctly seen upon shear deformation. The character of the rheological behavior depends on the regime of suspension deformation. At very low shear rates, a steady flow is possible; however, upon an increase in the rate, an unsteady regime is realized with development of self-oscillations. When constant shear stresses are preset, in some range of stresses, thickening of the medium takes place, which can also be accompanied by self-oscillations. In order to gain insight into the nature of this effect, measurements are performed for samples with different volume/surface ratios, which show that, in some deformation regimes, suspension is separated into layers and slipping occurs along a low-viscosity layer with a thickness of several dozen microns. Direct observations show a distinct structural inhomogeneity of the flow. The separation and motion of layers with different compositions explain the transition to the flow with the lowest apparent Newtonian viscosity. Thus, the deformation of concentrated suspensions is associated with self-oscillations of stresses and slipping along a low-viscosity interlayer.

Kozdrach R., Radulski P.

Effect of modifying a vegetable grease with different amounts of chokeberry biocarbon on its tribological and rheological properties. The aim of the research was to investigate the effect of the incorporation of biochar derived from the pyrolysis of chokeberry biomass at 500 and 700 °C respectively, in lubricants formulated with vegetable oil, on their functional characteristics in terms of tribology and rheology. Fumed silicon dioxide was utilized as a thickening agent, ensuring the production of lubricants with a consistency class of II. The biochar was introduced into the lubricating formulations in concentrations of 1, 3, and 5%. A rapeseed-based grease with commercial activated carbon served as the reference sample. The research focused on assessing how this innovative additive influenced both the tribological and rheological behaviors of the resulting lubricants. The study evaluated the effects of chokeberry-derived biochar on the wear resistance and scuffing prevention properties of the vegetable-based greases. Additionally, the biochar’s influence on various rheological parameters such as flow curves, viscosity profiles, hysteresis loops, and viscoelastic characteristics was analyzed. Results demonstrated that the biochar additive considerably enhanced the tribological and rheological performance of the tested rapeseed-based grease.

Molza A., Cesaire T., Bercion Y., Thomas P.

In Caribbean islands, the washing ashore of tons of pelagic Sargassum spp., consisting of two species Sargassum fluitans and Sargassum natans, has been regularly occurring since 2011. As green lubrication is a growing trend in the tribology industry, biochar is a promising alternative. Sargassum biochars, produced from Sargassum pelagic algae, are therefore being studied as solid lubricants. This study aims to explore their potential applications. Biochars from brown algae were pyrolyzed at 400 °C and then annealed at different temperatures (from 600 °C to 1500 °C). The Raman spectra collected on the different biochars showed that there was a structural organization of the biochars as the temperature increased. The tribologic properties of the biochars were studied and compared to a solid lubricant reference (exfoliated graphite). Raman spectroscopy analysis revealed a progressive structural reorganization with increasing temperature, leading to a 58% reduction in the coefficient of friction. The morphology and the structure of the tribofilm are investigated by profilometry, scanning electron microscopy, and Raman microspectrometry. Overall, these results can be considered as a first step for utilizing the biochar derived from brown algae Sargassum sp. as an additive in the lubricant industry, for the purpose of emission reduction.

Wang Y., Hou X., Zhang L., Ali M.K., Jiang H., Ma Y.

Nano-materials, given their excellent anti-friction and anti-wear characteristics, have attracted significant attention in tribological applications. However, conventional nano-materials have difficulty meeting the development requirements of the eco-friendly lubricants. In this study, nano biochar derived from sesame stalk was synthesized and used as a lubricant additive in poly-alpha olefin-6 (PAO6). The tribological properties were evaluated by four ball tribological tests with steel and ceramic balls as the friction pair. Following the friction experiment, the worn surface on the steel ball was analyzed by X-ray photoelectron spectrometry. The steel ball friction results showed that the lubricants containing 0.2 wt% nano biochar achieved a maximum wear volume reduction of 46% compared to PAO6, and the friction coefficient decreased by 34.6% for the ceramic balls. Analysis indicated that the enhanced wettability of nano biochar lubricant contributed to improving the anti-wear properties. Characterization of the worn surface revealed that the addition of nano biochar facilitated the formation of strong Fe3O4 tribofilms. This study demonstrated that nano biochar could serve as an environmentally friendly additive in the liquid lubricant industry.