Abstract
15th Academic Sessions, University of Ruhuna
Investigating the Lubricating Properties of Palm Oil and White
Coconut Oil
Bio-lubricants are prospective substitute for the conventional mineral oils based lubricant production because they
provide good lubricating properties as mineral oils with the characteristics of being renewable, biodegradable, and
non-toxic and are associated with fewer environmental problems. Reports indicate that global bio-lubricants market
nearly value USD 2.01 billion in 2016 and is expected to reach USD 2.64 billion by 2021, with a compound annual
growth rate of 5.6%. Altering regulations of lubricant industry towards the bio lubricants makes it an industry with
high future growth prospects. Generally, bio lubricants are made from vegetable oils. Triglycerides are the major
component in the vegetable oils, which are glycerol molecules with three long-chain fatty acids attached at the
hydroxyl group via ester linkages. Triglyceride structure gives good qualities for boundary lubrication. Their long
polar fatty acid chains interact strongly to metallic surfaces providing high strength lubricant films. The long
hydrocarbon chain is oriented away from the metal surface to form a monomolecular layer reducing both friction
and wear. This paper discusses the evaluation of lubricating properties of RBD (Refined, Bleached and Deodorized)
Palm Oil (PO) and White Coconut Oil (WCO) with three commercial lubricating oils (SAE40, SAE30,
Hydraulic68). Kinematic Viscosity, viscosity index, flash point, pour point, Total Acid Number, Copper corrosion
and demulsibility of the samples were measured. Both PO and WCO showed comparable Viscosity Index, Flash
point, Acidity, Corrosion stability, Demulsibility with mineral oils. But the pour point of both the oil specially the
pour point of WCO is considerably higher than mineral oil thus should be adjusted using a suitable additive. PO
showed better performance than WCO as a lubricating oil which is a worthy substitute for mineral oils.
Keywords: Bio-lubricant, Lubricating properties,Mineral oil,Palm oil,White Coconut oil
Extended Abstract
15th Academic Sessions, University of Ruhuna
Investigating the Lubricating Properties of Palm Oil and White Coconut
Oil
1. Introduction and research problem/issue
Due to depletion of the world’s crude oil reserve, rise in crude oil prices, and issues related to environment there is a
renewed concern about the use of bio-based lubricants. Generally, bio lubricants are lubricants made from vegetable
oil. Vegetable oils are potential substitutes for petroleum-based oils; not only they are environmentally friendly,
renewable and less toxic, but also they have excellent lubricating properties such as high viscosity index, high
lubricity and low volatility. In general, vegetable oils consist of triglycerides, which are glycerol molecules with
three long-chain fatty acids attached at the hydroxyl group via ester linkages. The long-chain carbon is generally
held together with one, two, or three double bonds: oleic, linoleic, and linoleic fatty acid components, respectively.
Most plant-based oils contain at least four, and sometimes as many as twelve different fatty acids. Triglyceride
structure gives good qualities for boundary lubrication. The long chain fatty acid chains in in these triglycerides
interact strongly to metallic surfaces providing high strength lubricant films. The long hydrocarbon chain is oriented
away from the metal surface to form a monomolecular layer reducing both friction and wear.
Palm oil (Elaeis guineensis) is a primordial tropical plant from the West African tropical rainforest region which is
cultivated across the tropics. Cocos nucifera or Coconuts is another chief crop grown in tropical countries.
Philippines, Indonesia, china, India and Sri Lanka are some of leading coconut oil manufactures across the world.
This study is carried out to investigate the lubricating properties of refined palm oil and white coconut oil available
in Sri Lanka and compare their results with standard lubricating oils.
2. Materials and Methods
Fresh samples of Refined Palm oil, White Coconut oil and mineral oils (SAE 30, SAE 40, and Hydraulic 68) were
collected from market.
Kinematic Viscosity was measured using a capillary tube viscometer according to ASTM D445 at 400C and 1000C
temperatures. Viscosity Index is calculated using Kinematic viscosities at 40 oC and 100oC according to ASTM
D2270. Flash point was measured using Cleveland Open Cup Tester according to ASTM D92 while Demulsibility,
total Acid Number and Copper corrosion were measured according to ASTM D1401, ASTM D 974, and ASTM
D130 respectively. Chemical composition of PO and WCO is analysed using Gas chromatography. Knowing the
exact chemical composition of the oil will help to understand the behavioural changes of the oils.
3. Results and Discussion
According to the chemical composition analysis PO is composed of about 50% saturated fatty acids (SFAs), 40%
mono-unsaturated fatty acids (MUFAs) and 10% poly-unsaturated fatty acids (PUFAs) while palmtic, oleic and
linoleic is being the main contributor for each category. WCO is made up of about 90% saturated fats, 9%
unsaturated fats and 1% poly-unsaturated. The main saturated fat constituents are lauric and myristic acids while
oleic acid is key unsaturated constituent. Viscosity of PO (38.83 cSst, 9.99 cSt) is higher than WCO (28.27 cSt, 6.75
cSt) at both 40oC and 100oC (Table1). PO consists of long-chain length fatty acids while WCO consists of
equivalent amount of medium-chain length fatty acids and long-chain length fatty acids (LCFA). As the chain
lengths of the fatty acid increases, the degree of random intermolecular interactions and consequently the viscosity
increases. The effect becomes more evident at lower temperatures. where the molecular movements are even more
restricted. Mono-unsaturation gives rise to stronger intermolecular interactions between the p electrons of the double
bonds thus increase in viscosity. But poly-unsaturation led to a configuration like a coil, hindering the approach of
the sp2 atoms from the double bonds of neighboring molecules resulting reduction in viscosity. So presence of
higher amount of LCFAs and MUFAs in PO results higher viscosity. Both PO and WCO possess relatively higher
viscosity indices (Table1) thus protecting better in operations with temperature variations due to their long chains
resistant to changes in temperature. Plant oils have an affinity to form macro-crystalline structures at low
temperature. Such macro-crystals restrict the easy flow of the system. So both PO (PP＝9℃) and WCO (PP＝24℃)
have low pour points compare to mineral oils (Table1). This implies that the both PO and WCO could be used
mostly in tropical counties otherwise pour point should be reduced using a suitable additive. Unsaturated fatty acids
disrupt this macro-crystalline stacking because of the bends and kinks introduced by the carbon–carbon double
bonds. Thus rather unsaturated PO has better low-temperature properties than WCO. Flash points of PO and WCO
are 3050C and 2790C respectively (Table1). High molecular weight of the triacylglycerol molecules in vegetable oils
affords a low volatility thus higher flash point which ensures to safety. There is a slight increase in flash points of
PO than WCO as PO molecular weight is higher than WCO. The ability of a hydraulic fluid to separate rapidly from
moisture and successfully resist emulsification is known as “demulsibility.” If oil emulsifies with water, the
emulsion promotes the destruction of lubricating and sealant properties. Both PO and WCO possess better
demulsibility characteristics as mineral oils (Table1). The presence of free fatty acids in the oil can be characterized
by the acid number. Acid number indicates the quantity of potassium hydroxide, which is necessary for the
neutralization of the free fatty acids occurring in 1 g sample. The ISO specification for hydraulic fluid acid is 1.5
mgKOH/g (max) of which PO and WCO are below the specified value (Table1). As depicted in Table1, PO, WCO
and Hydraulic68 show slightly corrosion (1a) on Cu strip whereas other mineral oils have marked corrosion (1b)
effect on Cu strip.
4. Conclusions
Both PO and WCO oil show good possibility as improved as lubricating oil while PO show better qualities than
WCO to improve as a lubricating oil as it has high kinematic viscosity (PO; @40oC=38.88cSt, @100oC=9.99cSt,
WCO; @40oC=28.27cSt, @100oC=6.7cSt), high viscosity index (PO=259, WCO=181), high Flash point
(PO=305oC, WCO=279oC), low pour point (PO=6oC, WCO=21oC) and low Acid number (PO=0.67 mgKOH/g oil,
WCO=1.08 mgKOH/g oil) than WCO.
As the both PO and WCO has low kinematic viscosity than mineral oil suitable modification should be
accomplished to improve their kinematic viscosity.
Since Pour point of PO(6oC) and WCO (24oC) is considerably higher than mineral oil. So both the oils should be
used in temperate regions of the world or should be adjusted using suitable additive specially pour point of WCO.
References (Selected)
[1] Yalcin, H., Toker, O. S., & Dogan, M. (2012). Effect of Oil Type and Fatty Acid Composition on Dynamic and
Steady Shear Rheology of Vegetable Oils. Journal of Oleo Science, 61(4), 181–187.
https://doi.org/10.5650/jos.61.181
[2] Covitch, M. J., & Trickett, K. J. (2015). How Polymers Behave as Viscosity Index Improvers in Lubricating
Oils. Advances in Chemical Engineering and Science, 5(April), 134–151. https://doi.org/10.4236/aces.2015.52015
[3] Quinchia, L. A., Delgado, M. A., Franco, J. M., Spikes, H. A., & Gallegos, C. (2012). Low-temperature flow
behaviour of vegetable oil-based lubricants. Industrial Crops and Products, 37(1), 383–388.
https://doi.org/10.1016/j.indcrop.2011.12.021
[4] Marotrao, T. K. (n.d.). PHYSIOCHEMICAL PROPERTIES OF OIL BLEND AND THEIR EFFECTS ON
LUBRICATION PROPERTIES. International Journal of Advanced Engineering Research, 35–38.
[5] Erhan, S. Z., Sharma, B. K., & Perez, J. M. (2006). Oxidation and low temperature stability of vegetable oilbased lubricants. Industrial Crops and Products, 24(3), 292–299. https://doi.org/10.1016/j.indcrop.2006.06.008
Annex
Table1: Performance data for selected vegetable oils and mineral oils
Performance Data
Palm oil
White
Coconut oil
SAE40
SAE30
Hydraulic68
Kinematic Viscosity at 40 oC / cSt
38.88
28.27
135.74
92.73
69.3
Kinematic Viscosity at 100 oC / cSt
9.99
6.75
15.9
13.31
10.67
Viscosity Index
259
181
123
143
173
Flash Point / oC
305
279
277
266
260
Pour point /oC
6
24
-21
-21
-22
Total Acid Number / mg KOH/g oil
0.67
1.08
2.8
2.8
0.44
Copper Corrosion, Strip 3hr @ 100o C
1a
1a
1b
1b
1a
Demulsibility/ ml Oil/Water/Emulsion
40/40/0
(3min)
40/40/0
(1 min)
40/40/0
(5 min)
40/40/0
(6 min)
40/40/0
(6 min)