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Continued from page 16


of early bio-lubricants. In the modern lubricants market, OEMs typically recommend saturated esters (HEES), which possess performance benefits, improved oxidative and hydrolytic stability, high biodegradability, and potentially high content of renewables.


Environmental Criteria Environmental criteria are defined as the non-functional requirements outlined by legislators listed technical specifications. However, environmental criteria do not have to necessarily increase the efficiency or durability of hydraulic equipment. Vegetable oils, synthetic esters, polyalkylene glycols (PAGs), bio-olefins, and estolides are the most prevalently used base oils to satisfy environmental criteria.


Eco-toxicological criteria In general terms, lubricants that are biodegradable, minimally toxic to aquatic species, and not bio-accumulative, are considered to be “Environmentally Acceptable Lubricants” (EAL). More specifically, EALs must have an ultimate or ready biodegradation of greater than 60% in 28 days, possess two or three acute aquatic toxicities (fish, algae, and daphnae) of which each is above 100 mg/L or 1,000 mg/L in the case of total loss lubricants, and not be prone to bioaccumulation.


These criteria are in accordance with the U.N. Globally Harmonised System (GHS) adopted by the U.S. in 2012 and Europe (2008/1272/EC) for the hazard statement GHS 09 “Environmental Hazard” [1]. Typically, the primary reason for a substance’s non-degradability is due to the inhibition of bacterial growth.


Bio-based content Certain specifications require a content of renewables, which necessitates the direct usage of vegetable oils or compounds synthesised from renewable or any biogenic resources. Bio-based content requirements are typically present, along with the eco-toxicological criteria for EALs. In 2002, the United States Department of Agriculture (USDA) launched the BioPreferred Program, which was aimed to assist the development and expansion of the market for biobased products. This USDA-led initiative recommended minimum biobased contents starting with 10% for crankcase oils and up to 70% for transformer oils and dielectric fluids [2]. The minimum biobased content for hydraulic oils is situated between this range, at 44%.


18 LUBE MAGAZINE NO.165 OCTOBER 2021


Figure 1: Parameters for the life cycle analysis of hydraulic oils in a medium- sized excavator during 2,000 operating hours (EVONIK) [1].


Shift to synthetics The significantly lower cost of monograde mineral- based hydraulic oils is a major contributor to its dominance in the fuels market, but the greater importance placed on sustainability has incentivised the development of alternative, environmentally friendly options. The higher energy efficiency of multigrade fluids, along with improved eco-toxicity and sustainability will redefine the decision for purchasing. Most hydraulic fluids use hydrocarbons.


Highly functionalised viscosity index (VI) improvers


High viscosity indices offer energy savings over a wide range of working temperatures and can be achieved through polymeric viscosity index improvers. The use of multigrade fluids eliminates the need for oil changes between the summer and winter seasons. Figure 1 compares the amount of saved fuel in a field trial of a conventional single-grade reference hydraulic fluid with a highly shear-stable multigrade hydraulic fluid with a high viscosity index.


Table 1: Viscometrics of base oils with high intrinsic VIs.


Base oils with high intrinsic VIs Inherent multigrade formulations refer to base stocks with high intrinsic viscosity indices. The unique oxygen polarity in the molecular backbones of esters and PAGs increases the viscosity index and favour the lubricity, as Continued on page 20


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