not mean the fluid is totally harmless to the environment and/ or living things, only that it is less harmful than something else. Environmentally friendly lubricants should be used and disposed of carefully and responsibly.

Three types of EFLs can be described: • Primary: Contribute to environmental quality directly as a result of their properties, such as biodegradability.

• Secondary: Contribute to environmental quality indirectly by improving an existing benefit or reducing pollution, such as fuel saving.

• Tertiary: Improve the environment by using recycled materials, thereby reducing consumption of raw materials and waste products.

EFLs are becoming increasingly important in Europe and North America, particularly for applications such as: • Agricultural machinery. • Earth moving and construction machinery. • Chain saws. • Motor boats. • Railway switch-gear. • Concrete moulds.

Interest in biodegradable lubricants began in Europe in the mid 1980s. While the strongest environmental pressures and the resulting acceptance of biodegradable lubricants began in Northern Europe, the same pressures have started to appear in other European Countries. The first country in Europe to introduce bio-lubricants was Sweden, in 1988, when rapeseed oil based hydraulic fluids were introduced. Unfortunately, problems with oxidation stability and low temperature properties triggered a backlash which gave bio-lubricants a bad reputation.

Between 1990 and 1992, a number of initiatives to overcome the technical problems associated with vegetable oil based products led to a series of tests performed by the Swedish Machinery Testing Institute, with the co-operation of equipment manufacturers (OEMs), lubricant suppliers and forestry companies. The City of Gothenburg published the first Ren Smörja (“Clean Lubrication”) list in 1995, comprising 14 products from 10 lubricant suppliers. The list was expanded to 24 products from 13 suppliers in 1996 and has been further expanded every year since then.

Swedish standard SS 15 54 34 was revised in 1997 to include the environmental criteria in the Ren Smörja list and the control of data to support environmental compliance claims was transferred to the Swedish National Testing and Research Institute. By 2000, around 25% of all hydraulic fluids sold in Sweden were environmentally friendly, of which around 80% were synthetic esters. Almost all forestry operations now use environmentally friendly lubricants, including gear oils and chain bar oils, because this is now mandated for all forestry operators in Sweden. Significant amounts of biodegradable hydraulic fluids are also used in off-highway and construction equipment.

In 2002, the International Standards Organisation (ISO) issued a new global standard for biodegradable hydraulic fluids, ISO 15380. This standard contains specifications for four new categories of “environmentally acceptable” (HE) hydraulic fluids: • HETG: Triglycerides (Vegetable oils) • HEPG: Polyglycols • HEES: Synthetic esters • HEPR: Polyalphaolefins and related hydrocarbons

(Specifications for mineral oil (classification H) hydraulic fluids are contained in ISO 11158 and specifications for fire-resistant (classification HF) hydraulic fluids are contained in ISO 12922.)

Development of the ISO standard was based on the experiences of suppliers and users of biodegradable hydraulic fluids in a number of European countries, including Sweden, Germany, Austria and Switzerland. In addition to the usual tests for viscosity, pour point, flash point, rust prevention, copper corrosion, oxidation stability, foaming tendency, air release, demulsibility and anti-wear performance, ISO 15380 contains limits for biodegradability, acute fish toxicity, acute daphnia toxicity and bacterial inhibition, using standard ISO test methods.

HETG fluids are water insoluble derived from vegetable or animal oils, with soybean, sunflower and rapeseed being the most common sources. They frequently contain soluble thickeners to increase their natural viscosity. Natural triglycerides have excellent lubricity but poor thermal and hydrolytic stability. They also oxidise rapidly. Additives, chemical modification and even genetic modification of the seeds used to produce the base oil can improve hydrolytic stability and oxidation resistance.

HETG fluids are highly biodegradable, non-toxic, have excellent lubricity and anticorrosion properties, have a high viscosity index and high flash point and are readily available. However, high-temperature operation can cause quick aging, rapid oxidation, extreme thickening and gumming. Also, they are susceptible to water contamination, which causes hydrolysis and increases total acid number (TAN). They tend to thicken and gel at low temperatures, which impacts machine performance. Because they are miscible with mineral oils, this can lower biodegradability in circuits that are not properly flushed. Additionally, they tend to be double the cost of mineral oils.

HEES fluids are water-insoluble synthetic esters derived from either petroleum or vegetable (typically rapeseed) oil feedstocks. Petroleum-sourced HEES fluids combine an organic acid and alcohol, whereas vegetable sourced fluids combine a fatty acid and alcohol. HEES fluids are available as unsaturated, partially saturated or fully saturated products. The fully saturated versions generally offer the best performance and command the highest price.

HEES fluids give long service lifetimes, due to high thermal and oxidative stabilities and good fluidity at low temperatures. They are also available in a wide range of viscosities, generally ISO 32, 46 and 68. They are highly biodegradable. However, they are expensive and, like HETG fluids, require special system-design requirements. They can also hydrolyze in the presence of water, if they have not been manufactured correctly. And, like HETG fluids, because they are miscible with mineral oils, this can impact biodegradability.

HEPG fluids are water-soluble polyalkylene glycols (PAG) polymers made from reacting alkylene-oxide monomers such as ethylene oxide, propylene glycol or propylene oxide with glycol. Those with 50% to l00% ethylene oxide are water soluble, while those with 100% propylene oxide are water insoluble. Both types are inherently fire resistant.

The biodegradability of HEPG fluids depends on the ratio of propylene to ethylene oxides. The higher the molecular weight, the lower the biodegradability of the fluid. HEPG fluids are available in a wide range of viscosities and have an operating temperature range of -20ºC to 80ºC. However, they require special system designs. They are incompatible with polyurethane seals. Pumps and motors may need to be de-rated when used with HEPG fluids.

HEPR fluids are water-insoluble polyalphaolefins (PAOs) and related hydrocarbon-based fluids. These synthetic hydrocarbons are made by polymerising linear alphaolefins (LAOs). Only low viscosity PAOs are considered environmentally friendly.



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