However, the fact that there is no universal industry definition of environmentally-acceptable lubricants can cause confusion. Products that are less harmful to the environment is a strong umbrella description, but this can be tied in to the bio-lubricant market which can mean something very different and tends to consider the renewable or bio-based content of the fluid.

In terms of measurement, biodegradability leads the pack, but without consensus, this causes difficulties in developing products which fit all requirements.

The Organisation for Economic Co-operation and Development (OECD) Environment Committee has established a series of tests in its 301 guideline, based on which compounds can then be classified as: readily biodegradable, inherently biodegradable, or non-biodegradable.

A product’s classification will come down to how swiftly it degrades. For example, as per OECD 301B, which is probably the most commonly used test method, readily biodegradable product will show degradation of over 60 per cent in 28 days of exposure to naturally occurring micro-organisms and in an aerobic aqueous medium, which means the chemical will undergo rapid and ultimate biodegradation in the environment. Inherently biodegradable product will result in more than 20 per cent but less than 60 per cent degradation. A product is deemed to be non-biodegradable if after 28 days it exhibits less than 20 per cent breakdown.

Mineral oil based solutions Due to the emerging importance of renewability requirements, mineral oil-based fluids have been somewhat overlooked in the bio-lubricants space, when in fact, they can offer an environmentally responsible solution. Advances in refining technology, and the use of high-quality and severely hydrotreated base oils with specific additives have led to the production and availability of ‘readily biodegradable’ mineral oil-based lubricants.

This demonstrates two things: first, that lubricant manufacturers are increasing their technical capabilities, and second, that operators need to carefully cross reference their needs with potential products. Taking one factor in isolation could be misleading.

So, mineral oil-based hydraulic fluids can be environmentally-friendly, but should you be using them? The answer is, yes. Where renewability is not a requirement there are several additional benefits that mineral oil-based hydraulic fluids offer when contrasted with the common solutions such as vegetable oil, saturated or un-saturated ester-based fluids.

Exploring the options While vegetable oil-based products are on face-value a clean choice, their toxicity means that when the product has come to the end of its life, it has to be incinerated or sent to landfill, which not only costs money, but also energy.

In contrast, mineral oil-based fluids can be recycled, reclaimed and re-additised, and their high viscosity index eliminates the need for seasonal change out and therefore reduces time, waste, and cost. In addition, extended product life calls for a lower energy consumption making the mineral product the more sustainable choice.

Other short comings of vegetable oils are their tendency to both solidify at low temperatures and oxidise more readily at high temperatures, making them unsuitable for operators in extreme conditions, such as forestry. They are prone to being swiftly affected by external interference, for example by changing colour when they absorb light, risking a degradation of the lubricant and compromised performance. This makes them unsuitable for dusty, heavy-duty environments such as mining or agriculture.

Unsaturated ester-based products have similar limitations. Their low cost may on face-value be appealing, but it is matched by their low oxidative stability and consequent low performance and limited lifespan. They will breakdown in the presence of water and often have seal compatibility problems. Most tellingly, they are not approved for use by some equipment manufacturers.

So, if these limitations are too much, what options are operators left with?

Products based on saturated esters satisfy many requirements for operators working in highly regulated geographies. They are environmentally

Continued on page 16 LUBE MAGAZINE NO.160 DECEMBER 2020 15

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