Lube-Tech
poor pour point and gumming effects restrict their direct use as biolubricants (base oil/additive). These limitations can be mitigated by different chemical treatments and/or blending with suitable additives. The use of additives in a base fluid is crucial to improve the overall performance of lubricating oils thereby increasing the lifespan of engines. The additives generally improve thermo-oxidative stability, pour point, antiwear performance, and viscosity index of the lubricating oils. They may be synthetic, semi-synthetic, and/or biobased. The commercially used additives are generally petro-based synthetic (e.g., acrylate-based polymers, polycaprolactones, polyesteramides, aliphatic copolyester). They exhibit satisfactory performances but are non-biodegradable and slightly toxic to the biosphere. Organic additives like zinc dithiophosphate (ZDDP), a well known class of organophosphate additive, molybdenum di-thiocarbamate (Mo-DTC), are widely used as efficient antifriction additives in turbine oil lubricants but produce harmful emissions. According to the Environmental Protection Agency, within lubricant additives, the following are considered harmful priority chemicals: acenaphthene, acenaphthylene, benzo(ghi)perylene, fluorene, phenanthrene, and pyrene.
The synthesis of bioadditives is an emerging area of research in the lubricant sector considering several environmental hazards associated with commercial petroleum-based additives, the performance of lubricants, and the lifetime of engines. Currently, the advantages of renewable resources will provide satisfactory lubrication to applications in the machinery industry without compromising the effects of lubricant performance. The suitability of vegetable oils and other natural resources as lubricant base oils or additives is constantly being evaluated in the field of tribology. Within the next decade, advancements in the application of biobased additives in the formulation of biodegradable lubricants will become more significant as legislatures have become more
26 LUBE MAGAZINE NO.172 DECEMBER 2022
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.143 page 2
proactive for ecosystem protection. In addition to pure VO, waste cooking oils and other bio-resources like microalgae oil, plant-based materials like cellulose, lignin, chitosan, and bio-based ionic liquids are also being investigated as starting materials to prepare efficient bio-additives. There are many reports of chemically modified VO or other bio-based materials being used as additives in the formulation of environmentally acceptable lubricants.
The application of soybean oil, sunflower oil, castor oil, rice bran oil, palm oil, olive oil, and jojoba oil-based additives for lubricants have been reported. Recently palmitoylated lignin was reported to be used as an antioxidant additive in castor oil and showed better performance compared to butylated hydroxytoluene, a commonly used petroleum-based antioxidant. In another work, the advantages of vegetable oil-based antioxidant additives like tocopherols, propyl gallate, and ascorbyl palmitate were disclosed over synthetic additive (4, 4’-methylenebis(2,6-di-tert-butylphenol). The experimental results reveal that the antioxidants, even at low concentrations, defer the onset of oxidation or slow the oxidation rate, thus improving the thermal stability of the vegetable oils studied. Oils from microalgae after chemical treatment have been recently reported to be used in the formulation of biolubricants. In this context the synthesis and utilisation of new bio-based multifunctional additives towards the formulation of biolubricants is explored.
Synthesis of bio-based additives from VO/waste cooking oils and other natural resources: Many green additives have been synthesised from VOs, like soybean oil, palm oil, and sunflower oil due to their high availability. However, non-edible vegetable oils with lower degrees of unsaturation such as neem, castor, mahua, karanja, jatropha, and linseed have an advantage in producing additives for biofuel/biolubricants. Recently additives were synthesised from less expensive sources such as waste
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