1. Additives in lubricant: Types and chemical composition of lubricant additives
Semira Hajrlahovic Mehic, M.Sc.
Inspector Counsellor
Chemicals Office of the Republic of Slovenia

2. Content Lubricant function Formulation of lubricants
Types of additives
Main reasons to add additives
Typical additives

3. Lubricant function
Modern equipment must be lubricated in order to prolong its lifetime
A lubricant performs a number of critical functions:
lubrication, cooling, cleaning, suspending,
protecting metal surfaces against corrosive damage….

4. Formulation of lubricants
Lubricant comprises a base and an additive package
The primary function of the base fluid:
to lubricate and act as a carrier of additives
The function of additives:
to enhance an already existing property of the base fluid
viscosity, viscosity index, pour point, oxidation resistance
to add a new property
cleaning/suspending ability, antiwear performance, corrosion control

5. Formulation of lubricants
Typically lubricants contain 90% base oil and less than 10% additives
Base :
most often petroleum fractions (called mineral oils)
vegetable oils or synthetic liquids such as hydrogenated polyolefins, esters, silicones, fluorocarbons are sometimes used as base oils

6. Formulation of lubricants
Non-liquid lubricants include grease, powders (dry graphite, molybdenum disulfide, tungsten disulfide)
Dry lubricants such as graphite, molybdenum disulfide and tungsten disulfide offer lubrication at temperatures (up to 350 °C)
The amount of additive used varies from a few hundredths of a percent to 30% or more

7. Lube oil base and additives logic
The lube oil base is the building block
which appropriate additives are selected and properly blended
to achieve a balance in performance characteristics of the finished lubricant
To achieve the highest levels of performance in finished lubricants:
understanding of the interactions of base oil and additives
matching those to requirements of machinery and operating conditions

8. Types of additives
Some additives impart new and useful properties to the lubricant
Some enhance properties already present
Some act to reduce the rate at which undesirable changes take place in the product during its service life

9. Main reasons to add additives
To impart desirable characteristics
Improvements in lubricating oil over the last decades
Are organic compounds like:
chlorine (as in chlorinated esters),
sulphur (as in sulphurized oils)
phosphorus (as in tricresyl phosphate)

10. Main reasons to add additives
To protect the lubricant in service by limiting the chemical change and deterioration
To protect the mechanism from
harmful combustion products
malfunctioning combustion products and
malfunctioning lubricating oil
To improve existing physical properties and to create new beneficial characteristics

11. Typical additives Increase oil and machinery life
effect many oil and surface characteristics
Decrease sludge on surface (metal), varnish the metal parts, clean the surface
Some are multifunctional:
certain viscosity index improvers also have function as pour point depressants
dispersants or anti-wear agents have also function as oxidation inhibitors

12. Typical additives Friction modifiers Anti-wear agents
Extreme-pressure additives
Anti-oxidation additives
Rust and corrosion inhibitors
Foam inhibitors
Oiliness agents
Detergents and dispersants
Alkaline agents
Pour point depressants (PPD)
Viscosity index improvers

13. Friction modifiers
Added to lubricants to reduce the surface friction of the lubricated parts
Mechanism similar to rust and corrosion inhibitors
form durable low resistance lubricant films via adsorption on surfaces and via association with the oil
Polar chemical compounds with high affinity for metal surfaces and possessing long alkyl chains
long-chain fatty acids, their derivatives, and the molybdenum compounds

14. Anti-wear agents
Protect rubbing surfaces operating with film boundary lubrication
Organo-sulfur and organo-phosphorus compounds:
organic polysulfides
phosphates, dithiophosphates
dithiophosphates (ZDDP)
Also antioxidant

15. Extreme-pressure additives
Form extremely durable protective films by thermo-chemically reacting with the metal surfaces
The film can withstand extreme temperatures and mechanical pressures and minimizes direct contact between surfaces
Anti-wear agents have a lower activation temperature than the extreme-pressure

16. Extreme-pressure additives
Chlorinated paraffins
2,3,4,5,6,8-hexachlorodecane (short-chained chlorinated paraffin)
Sulphurized fats
Zinc dialkyldithiophosphate (ZDDP)
Molybdenum disulfide (MoS2)

17. Anti-oxidation additives
One of the most important aspects of lubricating oils
Engine's metal parts (copper and iron) act as effective oxidation catalysts
engine oils are probably more susceptible to oxidation
High temperature, high pressure, high friction, and high metal concentration in motors, lead to oxidation of lubricating oil
Oxidation generally increase oil viscosity and results in formation of resins, lacquers and acidic compounds

18. Anti-oxidation additives
Protect by forming the oxidation of metal component
Sulfur compounds
Phosphorus compounds
Sulfur-phosphorus compounds
Aromatic amine compounds
Hindered phenolic compounds
Organo-zinc compounds (Zn- dithiophosphate ZDDP)
Organo-copper compounds
Organo-molybdenum compounds

19. Rust and corrosion inhibitors
Rust inhibitors: compounds with high polar attraction toward metal surfaces
By physical or chemical interaction at the metal surface, they form a continuous film that prevents water from reaching the metal surface
Amino salts and salts of sulphonic acids (functional group R-SO3−)

20. Rust and corrosion inhibitors
Form a protective film on the bearing surfaces
prevents the corrosive materials from reaching or attacking the metal
The film may be adsorbed on the metal or chemically bonded to it
Inclusion of highly alkaline materials in the oil help to neutralize strong acids, greatly reducing this corrosion

21. Rust and corrosion inhibitors
Alkaline compounds
Organic acids
Esters
Amino-acid derivatives

22. Foam inhibitors Foaming of lubricants is a very undesirable effect
can cause enhanced oxidation by the intensive mixture with air
Dimethylsilicones (dimethylsiloxanes)

23. Oiliness agents Reduce friction seizure point and wear rates
Glycerin monooleate (GMO)
Pentaerythritol Monooleate
(PMO)

24. Detergents Tend to neutralize the deposits
before formation under high temperature and pressure conditions, or
as a result of using a fuel with high sulphur content
The organic portion of the detergent (“soap”), has the ability to
associate with the salts to keep them suspended in the bulk lubricant
to suspend nonacidic oxygenated products, such as alcohols, aldehydes, and resinous oxygenates
To keep surfaces clean

25. Detergents

26. Detergents in lubricants
Phenolates, sulphonates and phosphonates of alkaline and alkaline-earth elements
calcium (Ca), magnesium (Mg), sodium (Na) or Ba (barium) salts
Sodium dodecylbenzenesulfonate

27. Dispersants
Used to disperse or suspend the deposits forming contaminants
More effective than detergents due to higher molecular weight
Molecules have a polar charge at one end which attracts and holds the deposits
Polyesters and benzlamides

28. Dispersants
Long chain hydrocarbons succinimides (such as polyisobutylene succinimides)

29. Detergents and dispersants
Together make about 45–50%, of the total volume of the lubricant additives manufactured
Differences:
Dispersants are metal-free, detergents contain metals (magnesium, calcium)
Dispersants have little or no acid-neutralizing ability, but detergents do
Dispersants are much higher in molecular weight, (approx. 4–15 times higher) than the organic portion (soap) of the detergent

30. Alkaline agents
Alkaline level (total base number=TBN) must  match  the  acidity of the lubricant
Neutralize acids of the oil and include additives such as dispersants and detergents
Acid neutralizing alkalis are present in the detergents
failure to keep an oil alkaline can lead to damage to bearings due to acidic attack as well as increased liner wear

31. Pour point depressants (PPD)
The lowest temperature at which the oil is fluid
Improve low temperature viscosity
Polymethacrylate (PMA)
Styrene Esters
Oils used under low-temperature conditions must have low pour points

32. Pour point depressants (PPD)
Two general types:
Alkylaromatic polymers adsorb on the wax crystals as they form, preventing them from growing and adhering to each other
Polymethacrylates co-crystallize with wax to prevent crystal growth
The additives do not entirely prevent wax crystal growth, but rather lower the temperature at which a rigid structure is formed

33. Viscosity index improvers
Probably the most important single property of a lubricating oil
Viscosity varies with temperature → it is necessary to consider the actual operating temperature of the oil in the machine
Different oils have different rates of change of viscosity with temperature
a distillate oil from a naphthenic base crude shows a greater rate of change of viscosity than a distillate oil from a paraffin crude

34. Viscosity index improvers
Can be blended into oils to increase V.I.
But not always stable in lubricating environments exposed to shear or thermal stressing
Methacrylate polymers and copolymers

35. Viscosity index improvers
Acrylate polymers
Olefin polymers and copolymers
Styrene butadiene copolymers

36. General capabilities expected from an engine lubricant
Dispersivity or capacity to keep the cold parts of an engine clean
Detergency or capacity to keep hot parts of an engine clean
Thermal strength or capacity to withstand temperature changes
Anti-oxidant or capacity to resist the action of oxygen

37. General capabilities expected from an engine lubricant
Anti-wear or capacity to contain wear
Anti-scuffing or capacity to preserve oil film even in the presence of high pressures
Alkalinity reserve/capacity to neutralize acids formed during combustion
Deemulsibility or capacity to separate contaminants

38. General capabilities expected from an engine lubricant
Resistance to hydrolysis or capacity to withstand the action of water which can affect additives
Centrifuge ability and filterability or capacity to separate insoluble elements
Anti-rust, anti-corrosive and anti-foam
just some of the other properties which protect the metalic object from wear down

39. semira.hajrlahovic-mehic @gov.si
Thank you!