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This paper seeks to outline the technical characteristics of certain biodegradable lubricants which can lead to potential energy savings.

Reviews the reasons for introduction of biodegradable lubricants, and describes the outcome of development and establishment of suitable range of lubricants for almost all applications.

Plant‐based lubricants have low toxicity, they are derived from crop resources, they are recognised as safer to use, and are rapidly biodegradable when spilled on to open land or into water. As such they break down to reduce pollution burden and are favoured by the Environment Agency when used near watercourses. Products have been developed now for almost all applications including hydraulics, engines, transmissions, compressors, metalworking, turbines, and for use in all industry sectors. Latest generation biolubricants, however, give additional advantages above and beyond the original concept to reduce pollution: the latest products have high levels of performance in terms of both loading and temperature. In particular, their frictional characteristics have been shown to be considerably more favourable than those for mineral oil, offering energy reduction during use.

The paper is restricted to findings based on ester‐based synthetic lubricants where the esters have been derived principally from renewable resources.

Quite apart from their environmental attributes, reduced energy consumption and therefore lower variable costs are now possible, and the concept of use of these oils to give distinct savings is becoming recognised.

This study emphasises that distinct advantages for synthetic lubricants, particularly for biodegradable synthetic ester lubricants derived from renewable resources, are now being realised.

In order to meet the requests of exploring environmental-friendly and multifunctional lubricant additives, some novel dimercaptothiadiazole derivatives containing hydroxyl are prepared and used as antiwear (AW) and extreme-pressure (EP) additives in biodegradable lithium grease. The paper aims to discuss these issues.

The tribological performances of the grease samples containing these derivatives are evaluated by using a four-ball tester. X-ray absorption near edge structure (XANES) spectroscopy is used to analyze the chemistry of tribofilms under AW/EP regime, and thermal films are also considered for comparison.

The tribological tests show that these derivatives are all effective in reducing wear, especially at lower additive concentrations, but they are basically failed in reducing friction. They are also helpful in improving the EP characteristic of the base grease. The thermal films generated by these derivatives are composed of adsorbed organic sulfide and ferrous sulfate, though for short-chain derivatives, organic sulfide is the only component at 5.0 wt.%. Ferrous sulfide is the main component of the tribofilms formed by these derivatives at various additive concentrations. But for short-chain derivatives, these tribofilms consist of ferrous sulfide and ferrous disulfide at 5.0 wt.%, and the appearance of disulfide suggests that the interfacial temperature between the upper ball and three lower balls under these conditions is considerably low. The EP films generated by short-chain derivatives are all composed of organic sulfide and ferrous sulfide, while for long-chain derivatives, ferrous sulfide is the main component.

These low-toxic and oil-soluble dimercaptothiadiazole derivatives are effective in improving the tribological characteristic of the biodegradable lithium grease, and these heterocyclic derivatives may be good substitutes for some harmful traditional additives.

The purpose of this study was to investigate the biobased (rapeseed) oil with the addition of different amounts of metal-containing additive in a steel–bronze tribological system. The additional purpose was to find the optimal value of the additive.

This paper exposes experimental results of the performance characteristics (coefficient of friction (COF), working temperature and wear) of the biolubricant based on rapeseed oil. The amount of commercial metal-containing additive in formulated lubricant was 1, 1.5, 3 and 5 wt.%. All results were compared with the results obtained for the base rapeseed oil. Two different tribometers were used, with the same tribosystem elements materials (bronze and steel). COF experiments were performed under four different normal loads and fixed sliding speed and time. Temperature and wear were continuously monitored.

Results showed that the metal-containing additive in rapeseed oil reduced all monitored characteristics. It was also found that the dependence of all characteristics on the amount of additive is nonlinear and that there is an optimal value of it.

Owing to growing environmental concerns, vegetable oil-based lubricants and other biodegradable lubricants are expanding their area of application. Currently, one of the most widely used vegetable oil is rapeseed oil. The metal-containing additive used in this study is previously investigated as an addition to mineral- and synthetic-based oils. There are very few studies that investigate its influence on the vegetable oil-based lubricants. In addition, there is no comparative investigation of its influence on several performance characteristics (COF, temperature and wear).

The screening of lube oil performance prior to field trials is the most significant for the formulation of novel lubricants. This paper aims to investigate the efficacy of trimethylolpropane trioleate oil (TMPTO) based lubricants with different additives.

In this endeavor, initially five lubricating blends along-with TMPTO based oil with variable additives were evaluated for their tribological performances using ASTM standards. Out of these, the top three best-performing oils were further investigated for possible physical or chemical synergies among lube oils, additives and ball surface using SEM. The molecule structures of TMPTO based lube oils were confirmed using Fourier transform infrared spectroscopy (FTIR).

The wear preventive and extreme pressure characteristics of different TMPTO based samples were evaluated and compared for compatibility and synergy of additives. Morphological analysis of SEM images was used to understand the wear behavior of the worn surfaces.

Further investigation of TMPTO oil on its oxidation stability at high temperature and pressure to make it technologically competitive and commercially viable metal-working lubricant is suggested.

This paper highlights the tribo-effects of TMPTO to be rendered as a suitable lubricant for metal-cutting operations. The surface morphology of the worn-out surface significantly demonstrates the effect of loading conditions.

Depleting reserves of crude oils and their adverse environmental effects have shifted focus toward environment friendly and biobased lubricant base oils. Natural oils and fats act as good lubricants but they have low oxidation and thermal stability which makes them unsuitable for modern day uses. This paper aims to produce trimethylolpropane ester biolubricant from cottonseed oil and study the effects of its use in spark ignition (SI) engines.

In this work, cottonseed oil is converted to TMP lubricant by a two-step based catalyzed esterification. The lubricants thermophysical properties are then analyzed and a 20% blend with synthetic poly-alpha olefin is used in an spark ignition engine.

The produced lubricant has viscosity @100^oC of 4.91 cSt, a viscosity index of 230 and a flash point of 202^oC. When used as a 20% blend in a petrol engine, the rate of oil deterioration was reduced by 18%, however, the overall wear increased by 6.7%. However, this increase is offset by its improved environmental impacts.

In its current state, such a biolubricant can be used as an additive to most commercially available lubricants to improve oil deterioration characteristics and environmental impact. However, further work on improving biolubricant’s wear characteristics is needed for the complete replacement of mineral oil-based lubricants.

This paper's aim is to present the gear micropitting performance of two industrial gear oils: a standard mineral lubricant (CM) containing a special micropitting additive package and a biodegradable ester with low toxicity additivation.

Gear micropitting tests were performed on the FZG machine, using type C gears made of case carburized steel. Lubricant samples were collected during the tests for analyzing the wear particles generated during operation. Post‐test analysis included the visual inspection of the teeth flanks and the assessment of the micropitting area, the mass loss of the gear, the ferrometric analysis of the lubricant samples and the surface roughness measurement of the teeth flanks, below and above the pitch line.

The micropitting performance of the two lubricants was very similar, confirming the advantage of using the ester lubricant (CE) as an industrial gear oil, now that it is an environmentally friendly product.

The tests were only performed on carburizing steel and refer to the tested lubricants.

The study confirms the appropriateness of biodegradable ester oil to industrial gear applications, allowing the replacement of environmentally harmful gear lubricants. It shows that the micropitting protection conferred is similar to that exhibited by highly additivated CMs.

The paper shows the applicability of biodegradable CEs to gear lubrication, mainly where it concerns micropitting protection, and shows its potential advantages, together with the biodegradability.

The purpose of this paper is to understand the impacts of oleoyl glycine on biodegradation, friction and wear performances of a mineral lubricating oil.

The biodegradabilities of a neat oil and its formulations with oleoyl glycine were evaluated on a biodegradation tester and the microbial characters in the biodegradation sewage observed through a microscope. Also, the friction and wear performances of neat oil and the formulated oil were determined on a four‐ball tribometer. The morphologies and tribochemical features of the worn surfaces were analyzed by scanning electron microscopy and X‐ray photoelectron spectroscopy.

Oleoyl glycine markedly enhanced biodegradation of unreadily biodegradable mineral oil and effectively improved its anti‐wear and friction‐reducing abilities. The enhancement of biodegradability of the mineral oil was preliminarily ascribed to the increment of microbial populations in the biodegradation processes, while the improvement of anti‐wear and friction‐reducing abilities was mainly attributed to the formation of a boundary adsorption film of oleoyl glycine on the friction surfaces.

Oleoyl glycine is a biodegradable and low eco‐toxic compound. The authors' work has shown that oleoyl glycine is effective in improving biodegradability and tribological performances of mineral lubricants. Enhancing biodegradability of petroleum‐based lubricants by additives is a new attempt. The paper has significance for improving ecological and tribological performances of mineral lubricants, even for developing petroleum‐based biodegradable lubricants.

This paper aims to investigate the scuffing load‐carrying capacity of three gear oils: a standard mineral lubricant containing extreme pressure and anti‐wear additives (M0) and two biodegradable saturated esters containing low toxicity additives (E1 and E2).

Four‐ball wear tests were performed, according to standard ASTM D4172. Results from the wear scar diameter and from ferrographic analysis of the test oil samples are presented and related to the lubricant properties. The physical, chemical and biodegradability properties of the lubricants are presented and compared.FZG gear scuffing tests were performed, according to standard DIN 51535, in order to evaluate the scuffing load‐carrying capacity of the two oils. Two reference tests were performed, A20/16.6/90 and A10/16.6/90.

Test results include scuffing load stage, maximum oil bath temperature, pinion weight loss and surface roughness measurement of the teeth flanks.

The paper provides information on the scuffing load‐carrying capacity of three gear oils.