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

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

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….

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

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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−)

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

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

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

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

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

Detergents

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

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

Dispersants Long chain hydrocarbons succinimides (such as polyisobutylene succinimides)

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

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

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

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

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

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

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

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

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

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

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