Effect of Thickener Type on Change the Tribological and Rheological Characteristics of Vegetable Lubricants.

This paper presents the results of a study on the effect of the dispersed phase on the lubricating and rheological properties of selected lubricant compositions. A vegetable oil base (rapeseed oil) was used to prepare vegetable lubricants, which were then thickened with lithium stearate, calcium stearate, aluminum stearate, amorphous silica, and montmorillonite. Based on the results of the tribological tests of selected lubricating compositions, it was found that calcium stearate and montmorillonite have the most beneficial effect on the anti-wear properties of the tested lubricating greases, while silica thickeners (amorphous silica and montmorillonite) provide the effective anti-wear protection in compared to the lubricants produced on lithium and aluminum stearate. The lowest structural viscosity was found for grease thickened with montmorillonite. Much higher values of this parameter were observed for composition, where aluminum stearate was the dispersed phase, while the highest value of structural viscosity was observed for composition, where aerosol-amorphous silica was the thickener. The composition thickened with amorphous silica had the highest yield point value, while the composition in which montmorillonite was the dispersed phase had the lowest value. Dynamic viscosity decreases with temperature, which is characteristic of lubricants. No significant differences in dynamic viscosity were found for the lubricating compositions tested at temperatures above 50 [°C]. The most favorable rheological properties were observed for composition, which was produced using calcium stearate, as it allows the lowest dynamic viscosity at -20 [°C]. Lubricants produced with lithium stearate or aluminum stearate were characterized by higher viscosity at low temperatures. For grease, in which the lithium stearate was used as a thickener, the value of the elasticity index determines the weak viscoelastic properties of tested grease and a greater tendency to change structure under the influence of applied forces. For vegetable grease thickened with aluminum stearate, more than 15 times lower values of the MSD function were observed, and the calculated elasticity index value proves the stronger viscoelastic properties of the aluminum stearate grease in relation to grease thickened with the lithium stearate. The elasticity index value for grease thickened with amorphous silica was lower than for greases thickened with lithium and aluminum stearate, indicating its stronger viscoelastic properties in relation to these two greases. For grease composition prepared on the vegetable oil base and thickened with montmorillonite. The value of the elasticity index was lower than most of the tested grease compositions, without the composition, in which the calcium stearate was used as a thickener. Such results testify to moderately strong viscoelastic properties, which leads to the conclusion that the produced lubricant was a stable substance on changes in chemical structure under the influence of variable conditions prevailing during work in tribological joints.

Lignin-enriched residues from bioethanol production: Chemical characterization, isocyanate functionalization and oil structuring properties.

Lignin-enriched waste products from bioethanol production of agriculture residues were tested as structuring agents in castor oil once functionalized with hexamethylene diisocyanate. Cane bagasse, barley and wheat straw were processed through steam explosion, pre-saccharification and simultaneous saccharification and fermentation (PSSF). Alternatively, cane bagasse was submitted to steam explosion and enzymatic hydrolysis (EH). Several Nuclear Magnetic Resonance techniques were used to characterize both residues and NCO-functionalized counterparts. The ß-O-4'/resinol/phenylcoumaran content and hydroxyphenyl/guaiacyl/syringyl distribution depend on biomass source, pretreatment, and enzymatic hydrolysis. Total hydroxyl content (from 1.23 for cane bagasse to 1.85 for wheat straw residues), aromatic/aliphatic hydroxyl ratio (0.78 for cane bagasse and 0.61 and 0.49 for barley and wheat straw residues, respectively) and S/G ratio (ranging from 0.25 to 0.86) influence the NCO-functionalization and oleogel rheological response. Oleogels obtained with barley straw residues exhibited the highest values of the storage modulus; around 2 × 105 Pa and 104 Pa for 25% and 20% contents, respectively. PSSF process showed weaker modification, leading to softer viscoelastic response compared to EH. These oleogels exhibited rheological properties similar to lubricating greases of different NLGI grades. Therefore, we herein show an integrative protocol for the valorization of lignin-enriched residues from bioethanol production as potential thickeners of lubricating greases.

Cellulose Pulp- and Castor Oil-Based Polyurethanes for Lubricating Applications: Influence of Streptomyces Action on Barley and Wheat Straws.

The replacement of mineral oils and non-renewable gelling agents is an imperative requirement for the lubricant industry in the near future. In this framework, cellulose pulp and castor oil are proposed as sustainable substitutes for these components. Biological treatment has been explored and evaluated to enhance the dispersing and thickening properties of cellulose pulp in oil media. Streptomyces sp. MDG147 and MDG301 strains were employed to modify agricultural wheat and barley straw residues from which cellulose pulp was obtained afterwards. In addition, an environmentally friendly process for the production of cellulose-pulp-/castor-oil-based polyurethanes was applied, in which neither catalysts nor harmful solvents were used, resulting in chemical oleogels. These oleogels were rheologically and tribologically characterized to evaluate their performance as lubricating greases. The enzymatic activity pattern developed was dependent on the raw material, the strain type, and the temperature, influencing the cellulose pulp's composition, polymerization degree, and crystallinity. These modified characteristics tuned the rheological behavior of the different oleogels, providing a beneficial range of viscoelastic responses and viscosity values that were generally favored by the Streptomyces action. Furthermore, the friction coefficient and dimensions of wear scars measured in a tribological contact were comparable to, or even lower than, those found with commercial and other bio-based lubricating greases that have previously been studied.

Experimental study of consistency degradation of different greases in mixed neutron and gamma radiation.

Many of the moving components in accelerator and target environments require lubrication. Lubricants in such environments are exposed to high fluxes of secondary radiation, which originates from beam interactions with the target and from beam losses. The secondary radiation is a mix of components, which can include significant fractions of neutrons. Lubricants are radiation-sensitive polymeric materials. The radiation-induced modifications of their structure reduce their service lifetime and impose additional facility maintenance, which is complicated by the environmental radioactivity. The study of the lubricants radiation resistance is therefore necessary for the construction of new generation accelerators and target systems. Nevertheless, data collected in mixed radiation fields are scarce. Nine commercial greases were irradiated at a TRIGA Mark II Research Reactor to serve for the construction of new accelerator projects like the European Spallation Source (ESS) at Lund (Sweden) and Selective Production of Exotic Species (SPES) at Legnaro, (Italy). Mixed neutron and gamma doses ranging from 0.1 MGy to 9.0 MGy were delivered to the greases. For an experimental quantification of their degradation, consistency was measured. Two of the greases remained stable, while the others became fluid. Post-irradiation examinations evidence the cleavage of the polymeric structure as the dominant radiation effect. Dose and fluence limits for the use of each product are presented. Apart from the scientific significance, the results represent an original and useful reference in selecting radiation resistant greases for accelerator and target applications.

Rheology and thermal degradation of isocyanate-functionalized methyl cellulose-based oleogels.

The -NCO-functionalization of methyl cellulose with HMDI and its application to chemically gel the castor oil is explored in this work by analyzing the influence of functionalization degree on the rheological and thermogravimetric behavior of resulting chemical oleogels. With this aim, different methyl cellulose chemical modifications were achieved by limiting the proportion of HMDI and, subsequently, oleogels were obtained by dispersing these polymers in castor oil and promoting the reaction between those biopolymers and the hydroxyl groups located in the ricinoleic fatty acid chain. -NCO-functionalized methyl cellulose-based oleogels were characterized from themogravimetric and rheological points of view. Suitable thermal resistance and rheological characteristics were found in order to propose these oleogels as promising bio-based alternatives to traditional lubricating greases based on non-renewable resources. In general, -NCO-functionalized methyl cellulose thermally decomposed in three main steps whereas resulting oleogels thermal decomposition takes place in one main single stage which comprises the thermal degradation of both the polymer and the castor oil. Temperature range for thermal degradation is broadened when using highly -NCO-functionalized methyl cellulose. A cross-linked viscoelastic gel was obtained with methyl cellulose functionalized in a relatively low degree (around 6% -NCO molar content). The rheological properties of highly functionalized methyl cellulose-based oleogels evolve during several months of aging, but mainly during the first week, due to the progress of the reaction between -NCO functional groups and castor oil -OH groups. SAOS functions analyzed and oleogel relative elasticity increase with the functionalization degree. Oleogel linear viscoelastic response is also extremely dependent on NCO-functionalized methyl cellulose concentration.