Biodegradable lubricants: definition, properties and benefits
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(by Dimitris Katsieris, Technical Manager, Castrol Marine)

Mr. Katsieris is pretty familiar with the events of our Society. On November 2007, he held an interesting and updating conference about the "TRAINING FOR MERCHANT MARINE GRADUATING ENGINEERS ON THE LUBRICATION OF TWO & FOUR STROKE ENGINES AND SUITABLE LUBRICANTS FOR LOW SULPHUR MARINE FUELS" at the Seamen's House of Camogli.
That important meeting, was aimed to familiarize the Merchant Marine Academy cadets and the Nautical School students with the incoming matters and requirements of the IMO Annex VI about the gas emissions of ships. Here, he explains, very clearly, what is the impact of biodegradable lubricating oils in the environment and in the industry.


A significant amount of lubricating oils and greases can enter the environment, producing contamination of both soil and water.Never has the marine industry been under greater social, moral and legislative pressure to minimize the impact of its activities on its environment: the seas and oceans of the world. MARPOL 73/78 (International Convention for the Prevention of Pollution from Ships) sets the standard in marine environmental legislation around the world. Now, more & more regional, national and port regulations are also coming into effect – such as reduced port fees for “green ships”.
As a result of normal ship operations it is inevitable that significant volumes of oil lubricants find their way into the marine environment. Although much of this comes from machinery spaces, a significant proportion comes from stern tube leakages and deck machinery as well.

It is estimated that over 30 million gallons of oil is leaked from ships during normal operations in ports and harbours every year – more than three times the Exxon Valdez oil spill (estimate from 2007 GESAMP report on Estimates of Oil Entering the Marine Environment from Sea Based Activities - based on data from 1988-97).
A number of countries now restrict their own use of mineral based lubricants, particularly in environmentally sensitive areas.

How oil pollution affect the environment and the business

Oil has the ability to form a film on the surface of seas, which can drastically reduce the level of oxygen in the water, making the fish difficult to feed and breathe. Oil has the potential to coat micro-organisms, plants and animals with which it comes into contact. But the business impact of an oil leakage is also important. Authorities now impose heavy fines for such pollution offences, which, when added to the costs of cleaning up the pollution, the suspension of operations and the subsequent bad publicity, can cost companies harmful relationships with their customers and for sure thousand of dollars.
Responsible ship operators, port authorities and regulators are embracing more environmentally friendly lubricants to mitigate the environmental impact of leakage. These alternatives are much less polluting if accidentally spilled. They are known by a variety of names, such as biolubes, environmentally friendly oils, green oils, etc.

In order to enhance their competitive position, oil companies, vehicle manufacturers and cruise tour operators are just some of the many customers of the marine industry who are demanding higher levels of environmental responsibility from their carries above and beyond that required by legislation. The use of environmentally friendly lubricants can be a valuable asset in enhancing and promoting companies` green credentials to their customers.

Figure 1: Why to introduce “Green” Products, a business prospective

Green lubricants are biodegradable and non-toxic lubes that are environmentally friendlier alternatives to traditional mineral oil lubricants. They fulfill the same function as mineral oils, while reducing the environmental effects associated with spillage and leakage. 

The language of green

Biodegradation is the process of chemical breakdown or transformation of a material caused by organisms or their enzymes. Figure 2 defines it:

Figure 2: Aerobic Biodegradation Process

Readily biodegradable concepts

- a substance that rapidly breaks down in the marine environment through the action of micro-organisms;
- the oil must biodegrade within a certain period of time;
- the standard test method for Biodegradability:
...... a) Seawater OECD 306 – If more than 60% of lubricant has been broken down by biological action with 28 days is defined as being ‘ultimate biodegradable' in sea water;
...... b) Fresh water OECD 301B.
Toxicity, the ability of a substance to cause harmful effect across the marine food chain including the below organisms:
- algae – microscopic organisms living on or near the water surface which are the start of the aquatic food chain , Standard test – OECD 201;
- daphnia- living in the water phase, Standard test – OECD 202;
- fish - both bottom feeding and free swimming, Standard test – OECD 203.

Figure 3: Marine Toxicity, Organisms affected

Bioaccumulation is an increase in the concentration of a chemical in a biological organism over time, compared to the chemicals concentration in the environment. Compounds accumulate in living things when they are taken up and stored faster than they are broken down or excreted. Standard test – OECD 117 – measures the build up of organic chemicals in fatty issues.

Environmentally Acceptable Lubricants

Much has been said and written about biodegradable lubricants for the past several years. In order to understand their applications and requirements, it is necessary to review the various types of biodegradable lubricants to point out their advantages and disadvantages.
An environmentally acceptable lubricant includes base fluids (97-98%) and additives like anti-oxidants (1-1,5%), anti-wear (0.4-0.5%), antifoam (0.2-0.5%). The performance of the lubricant is mainly ruled by choice and quality of base fluid.
These fluids can be:

- Vegetable oils , like corn, soybean, rapeseed (canola), sunflower, peanut, olive oil and others. In their natural form, these oils consist primarily of triglyceride molecular structures and as such they have performance limitations, most notably, poor thermal, hydrolytic and oxidation stability. For example, most natural vegetable oils cannot withstand reservoir temperatures greater than 80ºC. In addition, water, even in small amounts of a few hundred parts per million, is the natural enemy of vegetable oils and can cause serious foaming and degradation problems. In general, these oils also exhibit low cold-flow abilities. On the other hand, most of these natural oils have good lubricating qualities due to their polar nature. This provides good metal-wetting attraction and also makes them good solvents for helping keep dirt and debris off metal surfaces;
- Synthetic Esters , based on natural and renewable resources or fully synthetic esters based on petrochemical raw materials. These products have good antioxidation characteristics and seal swell properties;
- Synthetic Polyalphaolefines (PAO) with excellent low-temperature properties, but tend to shrink rubber seal materials;
- Synthetic Polyglycols (PAGs), can be both water soluble (ethylene-oxide) and water insoluble (propylene-oxide). Water soluble PAGs are ideally suited for fire-resistant lubricants. One disadvantage of PAGs is their tendency to emulsify water in certain equipment, such as gear boxes, which will cause foaming, sludge and corrosion. Also, a major disadvantage of both PAOs and PAGs is their poor solubility with regard to additives.

Most of the manufacturers depending on the application and the environmental performance are using mixtures of the above base fluids as their chemical structures determine their properties and the function of the fluid in the system. To determine the lubricating capability or property of a lubricant, various “mechanical” testing methods are traditionally used.
Esters are predominantly used as base fluids in the formulation of the environmentally acceptable lubricants and can be considered to fall into one of the 3 categories:
- Natural oils and fats:
........Plant and animal derived;
- Oleochemical derived esters:
........Fatty unsaturated esters (e.g. oleates, dimerates);
........Fatty saturated esters (e.g. stearates, isostearates);
- Petrochemical esters:
........Diesters such as adipates.

The following table summarizes the advantages and disadvantages of above fluids:

(Source: Castrol Marine)
Natural Esters
Quality can vary from year to year
High Biodegradability
Very Poor Oxidation Stability for rape seed
Good Lubricity and high Load Carrying Capacity
Moderate to very poor low temp. asphaltenes
Oleochemical Esters
Broad Viscosity Range
Medium oxidation stability for unsaturated esters

Good to Very Good Biodegradability

Medium Biodegradability for dicarboxylic acid esters
Not classified as dangerous and harmful for the environment and the aquatic organisms
Medium Lubricity for dicarboxylic acid esters
Excellent Shear stability
Excellent Oxidation Stability
Medium to very good Low temp. features
Petrochemical Esters
Broad Viscosity range
Useful only as co-base fluids
Good to Very Good Biodegradability
Excellent Shear stability
Good to Excellent Oxidation Stability
Very good Low temp. characteristics

Marine Applications

In Marine Industry the demand for Biolubes, is mainly in Stern Tube and Deck Machinery applications, where bio-based synthetic esters performed excellent at a lower cost compared to synthetic esters. This is possible due to recent advancements in biotechnology of vegetable oils and the chemical modifications that could be applied to convert these natural esters into high performance lubricants.
Particularly, these advantages are mainly due to polar ester structure and higher molecular weight in comparison to all non-polar petroleum derived hydrocarbons.
Also, types of ester synthetic derived from renewable resources such as rapeseed and sunflower oil are ideal, and even give additional performance benefits. From the above it is obvious that many factors should be considered when choosing a biodegradable fluid. The key considerations to be evaluated prior to selecting any fluid include: temperature, pressure, seals and elastomers, water intervention, fluid life, spill potential.

The environmental performance that includes readily biodegradability, low toxicity and low bioaccumulation are common for all biodegrade oils that should be used in Marine Industry.
But there are also additional requirements depending on the application: a stern tube biodegradable oil should:
- be extremely versatile providing high level of protection to heavily loaded bearings;
- have high water tolerance providing far greater protection than mineral oils (Figure 4);
- be energy efficient due to low friction coefficient;
- be miscible and compatible with other oils, seals , paints and filters.

Figure 4: Water Tolerance ( Source: Castrol Marine)

A hydraulic biodegradable oil should:
- be miscible and compatible with other oils, seals , paints and filters;
- have specific benefits above and beyond mineral oils;
- have Lower coefficient of Friction and superior density pressure characteristics – more energy efficient and more effective as hydraulic fluid (Figure 7);
- have excellent wear and corrosion protection, and oxidation stability providing long term machinery protection and extended oil life (Figure 7);
- have high viscosity index and lower pour point compared to mineral oil equivalents allowing start-ups at low temperatures and providing a thicker lubricating film at high temperatures for additional anti-wear protection.

Figure 6: Oxidation Stability
Figure 7: Coefficient of Friction (Source: Castrol Marine)

Gear biodegradable oils should:
- have specific benefits above and beyond mineral oils;
- have exception gear oil performance, provide high level of gear protection to maximise reliability and minimise maintenance costs (Figure 8);
- have approvals from key OEMs for clutch compatibility – common on some deck machinery;
- have excellent wear, corrosion protection, and oxidation stability providing long term machinery protection and extended oil life.
- High viscosity index and lower pour point allows start-ups at low temperatures and provides for a thicker lubricating film at high temperatures for additional anti-wear protection be miscible and compatible with other oils, seals , paints and filters

Figure 8: Average Coefficient of Friction (Source: Castrol Marine)

Biodegradable greases should have:
- Specific benefits above and beyond mineral oil-based Greases;
- Good resistance against water spray off reducing the need for frequent application (Figure 9);
- Good pumpability at low temperatures providing excellent lubrication over wide range of climatic conditions;
- Good Load carrying capacity and anticorrosion properties protecting equipment and reducing costs;
- Fully compatible with normal sealing materials, as well as mineral oil based greases.

Figure 9: Water Spray-off Resistance (Source: Castrol Marine)


In summary, biodegradable lubricants offer the best way to minimize pollution due to their performance in terms of readily biodegradability, low toxicity and low bioaccumulation. In Marine Industry, the operation of equipment using high-performance lubricants based on esters from natural or renewal resources offers outstanding technical properties.
Ester-based products also have economic advantages in terms of energy saving due to low friction coefficient compared to mineral oils or conventional synthetic grades.

Dimitris Katsieris - 3/2008

- Bartz W.J, “Lubricants and the Environment”, Tribology International Vol. 31, Nos 1-3, pp. 35-47, 1998;
- Lea C, “Energy savings through the use of advanced biodegradable lubricants”, Industrial Lubrication and Tribology, 59/3 , 132-136, 2007;
- Mortier R.M. & Orszulik S.T., “Chemistry & Technology of Lubricants” 2 nd edition, 1997;
- Feldmann D.G., & Kessler M., “Fluid qualification tests – evaluation of the lubricating properties of biodegradable fluids”, Industrial Lubrication and Tribology, Vol.54 – Number 3, pp.117-129, 2002;Kodali D., “High performance ester lubricants from natural oils”, Industrial Lubrication and Tribology, Vol.54, No 4, pp. 165-70, 2002.