Tribological properties of polyol ester - commercial motorbike engine oil blends

Abstract

This current study investigates the effect of blending bio-lubricant with commercial lubricant on physico-chemical and tribological properties. The synthesis of TMP and PE ester are optimized to obtain 100 % long chain tetra-esters and extreme care was taken during preparation of bio-lubricant to lessen deterioration of physio-chemical properties by blending with commercial oil. SM grade commercial petrol engine oil was blended with Tri-methylolpropane (TMP) ester, Penta-erythritol (PE) ester derived from Calophyllum-inophyllum in 10, 15, 20 and 25 % v/v. The tests for anti-wear, anti-friction and extreme pressure propertiesare conducted on the sample oils on a four-ball wear tester. The friction coefficient and wear of bio-lubricant –commercial oil blends have decreased significantly up to 20 % blending percentage. In the extreme pressure test, there is a substantial improvement in the weld load and marked improvement in the load wear index signifying the better load-bearing capacity of commercial oil – bio-lubricant blends. A synergy between bio-lubricant and additives in the commercial oil was found from a metallographic examination of worn balls after the EP test. The optimum volume percent of blend was found to be 15 % PE blend and 10 % TMP blend for optimum overall performance.

Full text

Journal Pre-proofs
Original article
Tribological properties of polyol ester - commercial motorbike engine oil
blends
V. Srinivas, Kodanda Rama Rao Chebattina, G.V.S Pranay, Babi Lakkoju, V.
Vandana
PII: S1018-3639(20)30280-4
DOI: https://doi.org/10.1016/j.jksues.2020.07.016
Reference: JKSUES 426
To appear in: Journal of King Saud University - Engineering Sci‐
ences
Received Date: 7 September 2019
Accepted Date: 25 July 2020
Please cite this article as: Srinivas, V., Chebattina, K.R.R., Pranay, G.V.S, Lakkoju, B., Vandana, V.,
Tribological properties of polyol ester - commercial motorbike engine oil blends, Journal of King Saud
University - Engineering Sciences (2020), doi: https://doi.org/10.1016/j.jksues.2020.07.016
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover
page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version
will undergo additional copyediting, typesetting and review before it is published in its final form, but we are
providing this version to give early visibility of the article. Please note that, during the production process, errors
may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Production and hosting by Elsevier B.V. on behalf of King Saud University.

Tribological properties of polyol ester - commercial motorbike engine oil
blends
V. Srinivas1* , Kodanda Rama Rao Chebattina2, G.V.S Pranay3, Babi Lakkoju4, V. Vandana5
1, 2 &3 Department of Mechanical Engineering, GITAM (Deemed to be University), India,
4, research scholar, Department of Chemistry, GITAM (Deemed to be University), India
5 Department of Chemistry, GITAM (Deemed to be University), India
* Corresponding author Email: vsvas1973@yahoo.com
Tribological properties of polyol ester - commercial motorbike engine oil blends
Abstract
This current study investigates the effect of blending bio-lubricant with commercial lubricant on
physico-chemical and tribological properties. The synthesis of TMP and PE ester are optimized
to obtain 100 % long chain tetra-esters and extreme care was taken during preparation of bio-
lubricant to lessen deterioration of physio-chemical properties by blending with commercial oil.
SM grade commercial petrol engine oil was blended with Tri-methylolpropane (TMP) ester,
Penta-erythritol (PE) ester derived from Calophyllum-inophyllum in 10, 15, 20 and 25 % v/v.
The tests for anti-wear, anti-friction and extreme pressure propertiesare conducted on the
sample oils on a four-ball wear tester. The friction coefficient and wear of bio-lubricant –
commercial oil blends have decreased significantly up to 20 % blending percentage. In the
extreme pressure test, there is a substantial improvement in the weld load and marked
improvement in the load wear index signifying the better load-bearing capacity of commercial
oil – bio-lubricant blends. A synergy between bio-lubricant and additives in the commercial oil
was found from a metallographic examination of worn balls after the EP test. The optimum
volume percent of blend was found to be 15 % PE blend and 10 % TMP blend for optimum
overall performance.
Keywords: Commercial engine oil, Bio-lubricant, TMP ester, PE ester, Tribological properties,
metallographic studies
Corresponding author: Dr V.Srinivas Email: vsvas1973@yahoo.com
1. INTRODUCTION
Fast utilization of petroleum resources
significantly increased during the past decades
owing to the fast growth in technology. Use of
engine oil is essential to deter the formation of
heat and to prevent corrosion. Several researchers
[1- 19] investigated the use of bio-based oils for
commercial applications. Ting et al. (2011)
established that use of esters extracted from oil
bearing trees is helpful in the development of
novel lubricants, thus decreasing the amount of
toxicity and an eventual improvement of the bio-
degradability of the lubricant. Imran et al. (2013)
and Lathi et al. (2007) established that
biolubricants can be a substitute to petro-based
oils. They are also found possess excellent
tribological properties with high viscosity index
and lubricity. Due to chemical structural
similarities between mineral oils and plant based
oils, the bio lubricants and/or their blends have the
capability to be a substitute to mineral and
synthetic oils. Though numerous efforts were
made to find the relevant substitute to mineral
based oils in IC engines, only a few researchers
(Zulkifli et al. (2015) and Jayadas et al. (2006))
have highlighted the prospects of ester based

biolubricants as a auxiliary to engine oil. Mobarak
et al. (2014) mentioned that apart from
applications in automotive & aviation industry,
petro based oils are also widely used in
manufacturing industries. Yunus et al. (2015)
analyzed that the bio-lubricants when blended
with mineral oil based conventional lubricants can
compete with commercial oils and outperform
them in toxicity, biodegradability and low-cost
reliability. Ponnekanti et al. (2012) postulated that
vegetable oils owing to intense interactions with
the lubricated surfaces can act as anti-wear
additives and friction modifiers. The polar groups
in the long chain fatty acid structure of vegetable
oil make them very effective in boundary as well
as hydrodynamic lubrication conditions.
Notwithstanding the benefits like high stearic and
oleic acid content, and biodegradability, the
incidence of hydrogen atoms on the β-carbon
atom in the esters makes them prone to oxidation,
thus limiting their use to low temperatures.
Furthermore, in the studies carried out by Ting et
al. (2011); Imran et al. (2013); Zulkifli et al.
(2015) and Havet et al. (2001), it was established
that the load-carrying capacity of biolubricants is
less failing them at higher loads thereby rendering
them unsuitable for automotive applications.
Nevertheless, the thermal stability of the bio-
based lubricant can be enhanced by converting
them to per-esters of sugar instead of glycerol
esters. Several studies Imran et al. (2013); Zulkifli
et al. (2015) and Havet et al. (2001) have found
that by changing the glycerol group in the
structure with an alcohol group, oxidation
resistance and thermal stability could be
enhanced. Polyol esters such as tri-
methylolpropane (TMP) ester penta-erythritol(PE)
ester were studied as alternative bio-lubricants
Jayadas et al. (2006); Salih et al. (2011); Masjuki
et al. (2003) and Patel et al. (2017). These studies
indicate that two important parameters namely;
the structure of the polyol ester and the length of
the fatty acid chain influence wear and friction
under boundary lubrication regime. It was also
found that lubricating performance of bio-based
oils is affected by the number of ester groups, the
length of fatty acid chains and linearity of the
polyol.
1.1 Present studies
The current investigations dwell upon
investigating the tribological properties of a blend
of bio-lubricant (esters) derived from
Calophyllum-inophyllum oil with commercial
lubricant. Tri-methylolpropane (TMP ester) and
Penta-erythritol (PE) ester based bio-lubricant are
selected in the current study owing to their typical
four ester groups and longer chain. Previous
studies described the preparation and tribological
performance of Penta-erythritol (PE) ester
containing 50-60 % tetra-ester with tri-ester, di-
ester and mono-ester as balance components. In
the present study, in the synthesis, the reaction is
done till 100 % long chain tetra ester is obtained.
The commercial lubricant selected is formulated
4-stroke motorbike oil containing ZDDP
additives. The Calophyllum-inophyllum oil or
Tamanu seed oil was extracted from their seeds.
The occurrence of sufficient amounts of oleic acid
(>40%), stearic acid (>18%) and good physio-
chemical properties makes it a worthy choice as
bio-lubricant. TMP and PE esters were
synthesized from the seeds of Tamanu tree and the
synergic effect of additives in the commercial oil
and polyol esters in bio-lubricant on the
lubricating properties is investigated. Mixing is
carried out in 10, 15, 20 and 25 % v/v and due to
the additives in the commercial lubricating oil,
higher blending ratios are taken. Importance was
given to find an best blending ratio for greatest
performance.
In this study, all the lubricating properties are
assessed using a four-ball tester. In a four-ball
tester, the three point contact formed by the four
balls under lubricated conditions reflects the
boundary lubrication conditions. The relative
performance of test oils in terms of friction, wear
and extreme pressure properties are assessed using
the method. Materials and methods
2.1 Preparation of bio lubricant samples
The Calophyllum-inophyllum seeds were finely
ground after drying and the oil was extracted in
soxhlet apparatus using a solvent. For separation
of TMP ester- Calophyllum fatty acids (300 g,
1.234 mol), trimethylolpropane (48.62 g, 0.362
mol), p-TSA (3g based on 1% weight of fatty
acid) and 300 ml of toluene were stirred at reflux
temperature. To prepare PE ester, Calophyllum
fatty acid (250 g, 0.885 mol), pentaerythritol
(30.43g, 0.2234 mol), p-TSA (2.5 g based on 1%

weight of fatty acid) and 250ml of toluene were
stirred at reflux temperature.
After reaction, the mix is taken to room
temperature and toluene is removed under
vacuum. The reaction mix is added with aqueous
sodium bicarbonate solution, ethyl acetate and
agitated for half an hour. The organic layer
formed in the reaction was separated, washed two
times with water, dried over anhydrous sodium
sulphate and concentrated under vacuum. The
crude esters were purified by basic alumina
column chromatography using 95% hexane and
ethyl acetate as eluent to obtain TMP and PE
esters. These products are characterized by IR
spectral studies on an FT-IR (Perkin-Elmer)
spectrometer.and investigated for physio-chemical
and basic lubricating properties.
As perceived from Fig. 1, in IR spectrum C=O
widening was witnessed at 1738 cm-1 in PE ester
and 1741 cm-1 in TMP ester. Based on physico-
chemical properties, the synthesis method is
corrected and optimized for best properties.
Similar works were carried out by other authors
[4,8,15] nonetheless the present work involves
synthesis of pure 100 % TMP and PE ester and
mixed with commercial oil to estimate the
tribological performance. The source of bio
lubricant, the percentages of different ester of the
previous works has been provided in Table 1.
Fig. 1 FTIR spectrum of a) PE ester and b) TMP ester
Table1. Studies carried out by previous researchers
on the percentage ester composition
Author
Source of
bio
lubricant
Major findings
Zulkifli
et al. [4]
TMP ester
derived
from Palm
oil base
The triester content in
palm oil based TMP
ester is 95%. The
composition of mono
ester and diester are
5% respectively.
Zulkifli
et al. [8]
Polylol
esters of
TMP and
PE palm oil
methyl
esters.
The percentage fatty
acid content in triester,
diester and monoester
are 82%,9% and 1%
respectively. Whereas,
for PE ester the
composition of
tetraester,triester are
52% and 36%
respectively.

Dalai et
al. [15]
methyl
oleate and
canola bio
diesel based
TMP ester
The highest yield of
TMP tri-ester of 91.2%
was observed at 140°C,
at a molar ratio of 5.
The composition of
diester was found to be
8.8% .
2.2 Preparation of blends of bio lubricant and
commercial lubricant
The commercial base lubricant in the present study
is Racer 4 (SM grade four stroke motor bike engine
oil) containing Zinc and phosphorous based
additives. The elements present in the lubricant
found from ICP analysis is as given in Table 2.
Table 2 elemental analysis of formulated
commercial lubricant
Element
test method
Quantity
Calcium, mg/Kg
ASTM D5185
1862
Zinc , mg/Kg
ASTM D5185
1037
Phosphorous, mg/Kg
ASTM D5185
946
Sulfur ,Wt%
ASTM D4951
0.286
The Trimethylol-propane (TMP) and Penta-
erythritol(PE) ester based biolubricants are mixed
with commercial base lubricant in 10, 15, 20 and
25 % volume percentage. After mixing the mixture
is stirred for 5 minutes in a ultra-sonic bath
sonicator to obtain a uniform dispersion.
2.3 Assessment of tribological properties
In 4 stroke motorbikes, the same lubricating oil acts
as engine oil acts as gear oil and hence the
lubricant is required to lessen friction &wear and
sustain extreme pressures in gears. In the study,
four ball tribometer was used for the assessment of
tribological properties. The wear, friction and
extreme pressure test were performed as per ASTM
standards. In all the tests, three half inch diameter
steel balls are held together and dipped in the
lubricating fluid. A similar fourth ball called “top
ball” is forced against the three clamped balls by a
load, thereby creating a 3 point contact. All the test
conditions during wear, friction and EP tests are
given in the table 3.
For wear test as per ASTM D4172, the top ball is
rotated against the three bottom balls, at a certain
load and a wear scar is formed on the 3 balls due to
rupture. The mean value of the scar diameters on
the 3 balls is taken as wear scar diameter.
Friction test is carried out as per ASTM D 5183
standard, under changing load conditions
simulating an internal combustion engine. Initially
wear-in is performed under the aforesaid (Table 3)
test conditions. After the end of wear-in test for one
hour, the used lubricating oil was removed and
without removing the worn steel balls, the ball pot
was cleaned and 10ml of pristine lubricating
sample is filled again for friction test. During the
friction test, initial load was set at 98.1 N and the
load is increased in increments of 98.1 N every 10
minutes of time interval until sharp increase in the
friction torque is detected which represent the
seizure.
Table 3 test conditions during evaluation of
lubricating properties on four ball tribometer
Wear test as per ASTM D4172
Temperature of
the cabin
75±2 0C
Test duration
1 hour
Speed of the
top ball
1200± 6 RPM
Load applied
40 kgf
Friction test as per ASTM D5183
Temperature of
the cabin
75±2 0C
Duration of
test
1 hour (for wear in)
Followed by friction test up to
seizure load
Speed of the
top ball
600 RPM
40 kgf (During wear in)
Load applied
(In Friction test, starting from
initial load of 10 kgf and
incremented by 10 kgf every
ten minutes till seizure load)
Extreme pressure test as per ASTM D2783
Temperature of
the cabin
Room temperature
Duration
10 tests each of 10s duration
at each load
Speed of the
top ball
1760 RPM
Load applied
32 kgf to weld point

The lubricant’s extreme pressure properties are
evaluated as per ASTM D 2783 for weld load and
load wear index of the oil. A series of ten tests of
10 seconds duration was carried out with load
increased during each tests until a weldment of all
four balls is formed under extreme pressure which
is called the weld load. The series of tests are
conducted starting at an initial load of 32 kgf and
the successive tests were carried out with increased
loads until the four balls weld under extreme
pressure. As per the standard, for loads below 32
kgf, the corrected load is calculated using
compensation scar diameter and the corrected load
is calculated for all ten reading. After each test, the
oil is flushed out and the scar diameter on the balls
is noted down. Likewise all the tests in the ten test
sequence are conducted with fresh oil and fresh
ball set but with varying load. The load-wear index
(LWI) indicate the overall performance of the
engine oil in a range loads between well below
seizure and welding and is calculated from the
formulae given below.
, where L= load applied, kgf,
Corrected load
=
L
D
h
X
X = mean scar diameter on the worn balls,
Hertz scar diameter,
D
H
=
8.73
×
10
―
2
(L)
1
3
and The load wear index, LWI = (A/10), (kgf)
where, A = sum of the corrected loads in all ten
tests.
The details of the loads applied and
compensation scar diameter taken are shown in
Table 4.
Table 4 load conditions during EP test
S.No
Load,
kgf
Compensation/actual
scar diameter, mm
1
16
0.22
2
20
0.237
3
24
0.252
4
32
5
40
6
50
7
60
8
80
9
120
10
140
11
160
12
200
Actual scar diameters
taken for calculations
2.4 Metallographic investigation
The worn balls prior to weld load during EP test
was analyzed using metallurgical microscope to
check the pattern of wear. The worn surfaces were
examined by EDX spectra for deposits on the the
surface to assess the synergic effect of esters in bio-
lubricant and additives in the commercial oil.
3 Results and discussion
3.1 Physico-chemical properties of bio-lubricant
and blends
The physio-chemical properties of bio lubricants
have a significant role in sustaining tribological
properties. Any decline of properties owing to
faulty synthesis of biolubricant would lead to low
performance. The bio-lubricant synthesis is
optimized after assessing the properties using
standard test methods after ascertain they are in the
tolerable range.
It is observed that the acid number of all test oils is
well under 1.5 mg/KOH/g as approved by SAE
standard.
Table 5 Physico-chemical properties of TMP ester bio-lubricants and commercial oil blends
S.No
Properties
Method
TMPester
SM
grade
motor
Oil
SM oil
+10%
TMP
ester
SM oil
+15 %
TMP
ester
SM oil+
20%TMPester
SM
oil+25%
TMP ester
1
Acid number
(mgKOH/g)
ASTM
D664
0.22
1.05
0.99
0.95
0.97
0.93
2
Viscosity at
40oC (cSt)
ASTM
D2245
17.52
137.22
124.33
118.85
112.98
107.11
3
Viscosity at
100oC (cSt)
ASTM
D2245
4.71
15.72
14.42
13.68
12.91
12.24
4
Viscosity
index
ASTM
D2270
207.6
120
116
112
108
104

5
Coppers strip
corrosion
ASTM
D130
1b
1a
1a
1a
1a
1b
Table 6 Physico-chemical properties of PE ester bio-lubricants and commercial oil blends
S.N
o
Properties
Methods
PE
ester
SM grade
motor Oil
SM oil +10
% PE ester
SM oil +15
% PE ester
SM oil+
20% PE
ester
SM oil
+25% PE
ester
1
Acid number
(mgKOH/g)
ASTM
D664
0.28
1.05
0.99
0.95
0.97
0.93
2
Viscosity at
40oC (cSt)
ASTM
D2245
23.85
137.22
124.33
120.21
114.5
108.87
3
Viscosity at
100oC (cSt)
ASTM
D2245
6.68
15.72
14.81
14.36
13.91
13.46
4
Viscosity index
ASTM
D2270
263
120
119
117
116
111
5
Coppers strip
corrosion
ASTM
D130
1b
1a
1a
1a
1a
1b

A minor decline in the viscosity and viscosity index above 20 % blending percentage is observed with the
viscosity index remaining above 90 as required for engine oils. Copper strip corrosion test was performed at
50 oC for 3 hours shown that up to 15 % mixing percentage the corrosion deterrence is found be brilliant and
in line with commercial lubricant. For the blends with 20 and 25 % bio lubricant, the corrosion resistance is
found to be optimal marked by 1b on corrosion standard. The TMP ester based biolubricant mixtures
possess lesser viscosity when matched with PE ester based biolubricant blends. This is owing to longer
chain length of PE ester. The decrease in viscosity and viscosity index of TMP ester based lubricants could
have a bearing on the lubricating properties and engine performance.
3.2 Tribological properties
The tribological tests were performed in ten reproducible experiments and the average values were
taken. Seizure load during friction test plays a vital role in augmenting the efficacy of the lubricant.
From the results, it is established that the PE ester in interaction with the additives of the
commercial oil demonstrating a good enhancement in the tribological properties. The results of
wear test for various test oils at 40 kgf load and 60 kgf load are as given in Fig. 2. From Fig. 2, the
anti-wear performance of test oils at 40 kgf and 60 kgf load can be gauged. PE ester based
lubricants performed better than TMP ester based lubricants. The performance of commercial base
lubricant mixed with PE ester up to 20 % blending ratio is found to be optimum with deterioration
observed past 20 %. In case of TMP ester mixed with commercial lubricant base the optimum
blending ratio is found to be 85:15.
Fig. 2 Wear scars of test oils at 40 and 60 kgf load
From the above findings, it can be predicted that although PE ester offered higher wear scar, blending PE
ester in commercial oil up to 15 % blending volume percentage, due to lower coefficient of friction of ester
there is a significant improvement in the anti-wear properties and anti-friction properties. When the volume
percent is increased beyond 20 %, there is slight decline in the wear resistance with an increase in the wear
scar diameter. Fig. 3 compares the performance of commercial oil and ester of TMP and PE. It can be seen
that although esters could offer low friction coefficient, their performance is limited by low seizure loads.
As can be observed the PE ester gave very low coefficient of friction but possess a low seizure load of 90
kgf which is the main disadvantage of bio-lubricants. TMP ester gave the lowest coefficient of friction
among all but failed at 80 kgf. By mixing PE ester in 10 % and 15 % in commercial base lubricant, there is a
good improvement in both seizure load as well as the friction coefficient.

Fig. 3 Variation of friction torque during the test duration for commercial oil, TMP ester and PE ester
Fig. 4 Variation of friction torque during the test duration with a)PE ester based oils b) TMP based oils
Fig. 4, it can be observed that at lower loads the frictional torque of all lubricants is in the same range.
However, a significant parity can be seen between commercial lubricant and its blends in terms of frictional
toque as the load increases.
From Fig 4a&b for blending percentage of 20 %, it can be observed that the friction torque reduction took
place with an eventual decrease in the seizure load which resulted in early failure of the ester compared to
commercial lubricant. For commercial lubricant blended with 25 %, there is a reduction in friction torque up
to 60 kgf load and beyond that point there is a jump in friction torque indicating beyond 20 % the action of
esters is more prevalent compared to the additives in the lubricant.

In EP test results seen from Fig 5a&b, with blending of PE ester up to 15 % volume and TMP ester up to 10
%, there is an enhancement in the weld load and load wear index with 15 % PE ester blend and 10 % TMP
ester blend giving best results.
Fig. 5 Variation of wear scar diameter with the applied load during the extreme pressure test for a) PE ester based
lubricants, b) TMP ester based lubricants.
As seen from Figs. 5a&b, up to last non seizure load point (C) all blends performed very well indicating
effectiveness at lower loads. In the incipient seizure region (C-D) and immediate seizure region (D-E), the
blends with 20 and 25 % PE ester experienced a sharp increase in the wears scar diameters affecting the load
wear index and the weld load. Due to this, although the weld load weld load remained the same as that of
commercial oil, there is a reduction in the load wear index due to poor anti-wear performance of the blends
after seizure load. Blends with percentage of PE ester below 20 % and TMP ester below 15 % could fare
very well in these regions. This can be ascribed to the synergy between esters and additives in the
commercial oil leading to an enhanced surface lubricity. Poor performance at higher percentages of ester
can be attributed to the thinning of oil which could lead to premature failure.
The following table 7 summarizes the extreme pressure properties of all test oils
Table 7 Results of EP test of test oils
Oil
weld load
load wear
index
Commercial oil (SM Grade)
160
30.07
Commercial oil +10 % PE
ester
200
32.76
Commercial oil +15 % PE
ester
200
34.62
Commercial oil +20 % PE
ester
160
29.7
Commercial oil +25 % PE
140
28.6

ester
Commercial oil +10 % TMP
ester
200
32.61
Commercial oil +15 % TMP
ester
160
30.5
Commercial oil +20 % TMP
ester
140
26.61
3.3 Results of metallographic test
Lubricating oils apart from ZDDP based additives for anti-wear and anti-friction performance,
also comprise of Sulphur as EP additive. Under extreme temperatures produced by extraordinary
operating pressures, the EP additives in the commercial oil react with the metal surfaces creating
new compounds like iron phosphides and iron sulfides on the contact surface. These metal
compounds form a chemical film on the surface which acts as a barrier thereby decreasing friction,
wear and lessen the chance of welding. The worn surfaces of the balls prior to weld load during EP
test were characterized in a metallurgical microscope for the structure. Fig 6&7 depict the images
taken from metallographic microscopes with worn balls of EP test prior to weld load. The images
are taken at 20x resolution on a metallurgical microscope. It can be seen that base oil and base oil
mixed with 10 % and 15 % PE ester as well as TMP have performed very well.
Fig. 6 metallographic images of worn balls in extreme pressure test a) Commercial oil b) Commercial oil +10 % PE
ester c) Commercial oil +15 % PE ester d) Commercial oil +20 % PE ester e) Commercial oil +25 % PE ester

Fig. 7 metallographic images of worn balls in extreme pressure test a) commercial oil b) Commercial oil +10 % TMP
ester c) Commercial oil +15 % TMP ester d) Commercial oil +20 % TMP ester
The wear scar in all cases is less and the esters could prevent abrasive wear during extreme pressure
conditions. In case of pure ester and oils mixed with 20 % and 25 % PE and TMP esters, a severe abrasive
wear could be noted indicating ineffectiveness at higher concentrations. The balls were also tested on
scanning electron microscope equipped with Energy-dispersive X-ray spectroscopy (EDS) for
metallographic depositions on the worn surfaces.
Fig.8a, b & c show the EDS analyses quantifying the elements deposited on the worn surfaces of
the balls tested with commercial oil, commercial oil blended with 15 % PE ester and commercial
oil blended with 10 % TMP ester respectively.
Fig. 8 EDX spectrum of worn balls during EP test a) with commercial oil b) with commercial oil + 15 % PE ester c)
with commercial oil + 10 % TMP ester
From Fig. 8a for worn balls tested with commercial oil have their surfaces covered with some amount of
zinc and phosphorous along Sulphur due to formation of tribo-film consisting of ZDDP (Zinc

dialkyldithiophosphate) which reduce the chances of seizure. Elemental carbon can also be seen in the EDX
spectrum which can be probably due to the combustion products. Fig. 8b&8c, display the EDX spectrum of
the worn ball tested with commercial oil blended with 15 % PE ester and 10 % TMP ester. From the
elements in the spectrum, it can be concluded that the tribo-film on the surface comprises of additives in the
lubricant (Zinc and phosphorous) along with Sulphur, calcium and greater amounts of carbon deposit
compared to EDX spectrum of ball tested with commercial oil. This may be due to combustion products and
also deposition of esters on the mating surface which decreased friction thereby improving seizure load and
weld load.
Conclusions
1. 100 % long chain PE ester and TMP ester when blended with commercial oil in 10 – 15 volume
percentage improved the tribological properties without affecting the physio-chemical properties.
2. A notable decrease in wear and friction coefficient of oils due to mixing with PE and TMP ester.
3. The extreme pressure characteristics have also enhanced with improvement in weld load and load wear
index.
4. For top results, the mixing percentage should be below 20 % for PE ester based lubricant mixtures and
15 % for TMP ester base lubricant blends.
5. An increase in the blending percentage would result in reduction of viscosity and viscosity index
resulting in untimely failure of the engine oil.
6. The metallographic studies suggest synergy between esters and additives in the commercial oil
resulting in superior performance of commercial – biolubricant blends.
Acknowledgements
The authors gratefully acknowledge the support received from Hindustan Petroleum Corporation Ltd., for
conducting the tests. The authors acknowledge the assistance from Andhra University Visakhapatnam in
characterization.
Conflict of interest
The authors declare that they do not have any conflict of interests
References
1. Adhvaryu A, Erhan SZ. Tribological studies of thermally and chemically modified vegetable oils for
use as environmentally friendly lubricants. Wear 2004;257:359–67.
2. Aziz NAM, Robiah Y, Umer R, Nurin W, Zulkifli M. Temperature effect on tribological properties of
polyol ester-based environmentally adapted lubricant. Tribology International 2016:93:43–9.
3. Erhan SZ, Asadauskas S. Lubricant base stocks from vegetable oils. Industrial Crops and Products
2000:11: 277–82.
4. Fox NJ, Stachowiak GW. Vegetable oil-based lubricants—A review of oxidation. Tribology
International 2007: 40: 1035–46.
5. Habibullah M, Masjuki HH, Kalam MA, Ashraful AM, Habib MA, Mobarak HM. Effect of bio-
lubricant on tribological characteristics of steel. Procedia Engineering 2014:90:740 – 45.
6. Hamid H, Yunus T, Rashid U, Choong TSY, Ali S, Syam AM. Synthesis of high oleic palm oil-based
trimethylolpropane esters in a vacuum operated pulsed loop reactor. Fuel 2016:166: 560–66.
7. Havet L, Blouet J , Robbe VF, Brasseur E, Slomka D. Tribological characteristics of some
environmentally friendly lubricants. Wear 2011:248 :140–6.
8. Heikal EK, Elmelawy MS, Salah AK, El-basuny NM. Manufacturing of environment friendly
biolubricants from vegetable oils. Egyptian Journal of Petroleum 2017:26: 53–9.
9. A, Masjuki HH. Kalam MA, Varman M, Hasmelidin M, Al Mahmud KAH, Shahir SA, Habibullah M.
Study of Friction and Wear Characteristic of Jatropha Oil Blended Lube Oil. Procedia Engineering
2013:68: 178 – 85.
10. Jayadas N, Nair K. Coconut oil as base oil for industrial lubricants-evaluation and modification of
thermal, oxidative and low temperature properties. Tribology International 2006:39:873–8.

11. Kamalakar K, Rajak AK, Prasad RBN, Karuna MSL. Rubber seed oil-based biolubricant base stocks: A
potential source for hydraulic oils. Industrial Crops and Products 2013:51 249– 257.
12. Kodali DR. High performance ester lubricants from natural oils. Industrial Lubrication and Tribology.
2002:54(4):165 – 70.
13. Lathi P, Mattiasson M. Green approach for the preparation of biodegradable lubricant base stock from
epoxidized vegetable oil. Applied Catalysis B 2007:9:207–12.
14. Maleque MA, Masjuki HH, Sapuan SM. Vegetable-based biodegradable lubricating oil additives.
Industrial Lubrication and Tribology. 2003:55(3): 137 – 43.
15. Mobarak HM, NizaMohamad E, Masjuki HH, Kalam MA, AlMahmud KAH, Habibullah M, Ashraful
AM. The prospects of biolubricants as alternatives in automotive applications. Renewable and
Sustainable Energy Reviews 2014: 33: 34–43.
16. Panchal TM, Patel A, Chauhan DD, Merlin T, Patel JV. A methodological review on bio-lubricants
from vegetable oil based Resources. Renewable and Sustainable Energy Reviews 2017:70: 65–70.
17. Ponnekanti N, Kaul S. Development of eco-friendly /biodegradable lubricants: An overview.
Renewable and Sustainable Energy Reviews 2012:16: 764– 74.
18. Salih N, Jumat S, Emad Y. The physicochemical and tribological properties of oleic acid based
trimester bio-lubricants. Industrial Crops and Products 2011:34:1089– 96.
19. Laad M and Jatti V.K S. Titanium oxide nanoparticles as additives in engine Oil . Journal of King Saud
University – Engineering Sciences 2018:30 :116-122
Table1. Studies carried out by previous researchers on the percentage ester composition
Author
Source of bio lubricant
Major findings
Author
Source of bio lubricant
Major findings
Zulkifli et al. [4]
TMP ester derived from
Palm oil base
The triester content in palm oil based TMP ester is
95%. The composition of mono ester and diester are
5% respectively.
Zulkifli et al. [8]
Polylol esters of TMP and PE
palm oil methyl esters.
The percentage fatty acid content in triester, diester
and monoester are 82%,9% and 1% respectively.
Whereas, for PE ester the composition of
tetraester,triester are 52% and 36% respectively.
Table 2 elemental analysis of formulated commercial lubricant
Element
test method
Quantity
Element
test method
Quantity
Calcium, mg/Kg
ASTM D5185
1862
Zinc , mg/Kg
ASTM D5185
1037
Phosphorous,
mg/Kg
ASTM D5185
946
Table 3 test conditions during evaluation of tribological properties on four ball tribometer
Wear test as per ASTM D4172
Temperature of the cabin
75±2 0C

Test duration
1 hour
Speed of the top ball
1200± 6 RPM
Load applied
40 kgf
Friction test as per ASTM D5183
Temperature of the cabin
75±2 0C
Duration of test
1 hour (for wear in)
Followed by friction test up to seizure load
Speed of the top ball
600 RPM
40 kgf (During wear in)
Load applied
(In Friction test, starting from initial load of 10 kgf and
incremented by 10 kgf every ten minutes till seizure load)
Extreme pressure test as per ASTM D2783
Temperature of the cabin
Room temperature
Duration
10 tests each of 10s duration at each load
Speed of the top ball
1760 RPM
Load applied
32 kgf to weld point
Table 4 load conditions during EP test
S.No
Load, kgf
Compensation/actual scar diameter, mm
1
16
0.22
2
20
0.237
3
24
0.252
4
32
5
40
6
50
7
60
8
80
9
120
10
140
11
160
12
200
Actual scar diameters taken for
calculations
Table 5 Physico-chemical properties of TMP ester bio-lubricants and commercial oil blends
S.No
Properties
Method
TMPester
SM grade
motor Oil
SM oil
+10% TMP
ester
SM oil
+15 %
TMP ester
SM oil+
20%TMP
ester
SM
oil+25%
TMP
ester
1
Acid number
(mgKOH/g)
ASTM
D664
0.22
1.05
0.99
0.95
0.97
0.93
2
Viscosity at
40oC (cSt)
ASTM
D2245
17.52
137.22
124.33
118.85
112.98
107.11
3
Viscosity at
100oC (cSt)
ASTM
D2245
4.71
15.72
14.42
13.68
12.91
12.24
4
Viscosity
ASTM
207.6
120
116
112
108
104

index
D2270
5
Coppers strip
corrosion
ASTM
D130
1b
1a
1a
1a
1a
1b
Table 6 Physico-chemical properties of PE ester bio-lubricants and commercial oil blends
1
Acid number
(mgKOH/g)
ASTM
D664
0.28
1.05
0.99
0.95
0.97
0.93
2
Viscosity at
40oC (cSt)
ASTM
D2245
23.85
137.22
124.33
120.21
114.5
108.87
3
Viscosity at
100oC (cSt)
ASTM
D2245
6.68
15.72
14.81
14.36
13.91
13.46
4
Viscosity
index
ASTM
D2270
263
120
119
117
116
111
5
Coppers strip
corrosion
ASTM
D130
1b
1a
1a
1a
1a
1b
1
Acid number
(mgKOH/g)
ASTM
D664
0.28
1.05
0.99
0.95
0.97
0.93
Table 7 Results of EP test of test oils
Oil
weld load
load wear index
Commercial oil (SM Grade)
160
30.07
Commercial oil +10 % PE ester
200
32.76
Commercial oil +15 % PE ester
200
34.62
Commercial oil +20 % PE ester
160
29.7
Commercial oil +25 % PE ester
140
28.6
Commercial oil +10 % TMP ester
200
32.61
Commercial oil +15 % TMP ester
160
30.5
Commercial oil +20 % TMP ester
140
26.61