Chemistry Reference
In-Depth Information
cooling, leading to gel-like structures which entrap low-melting-point mol-
ecules, thus resulting in higher PP, CP, WDT and SM values. PUFAs in their
bent configurations prevent the close-packing of triacylglycerol molecules
during cooling more than MUFAs, thus high amounts of PUFAs in oils (such
as in jatropha and sunflower oils) result in lower PP, CP, WDT and SM values.
SM values obtained using Cryo-DSC were found to be a better measure of
PP as shown by a better correlation (R
2
¼
0.90) than WDT (R
2
¼
0.70). Simi-
larly, CP also showed better correlation with SM values (R
2
¼
0.78) than WDT
(R
2
¼
0.64). In all these correlations, the major outlier point was jatropha oil.
On removing this point, the R
2
value for the PP-SM correlation increased to
0.99, for PP-WDT to 0.88, for CP-SMT to 0.92, and for CP-WDT to 0.96.
Testing more oil samples will help to develop better correlations between
these two methods.
11.3.5 Lubricity Data
An important property of lubricants is their ability to maintain a stable lu-
bricating film at the metal contact zone. Triacylglycerols of vegetable oils are
known to provide excellent lubricity due to their ester functionalities. This is
because, the polar head of the triacylglycerol molecule, i.e., the glycerol end,
attaches to the metal surface and allows a monolayer film to form, with the
non-polar end of the FA chains sticking away from the metal surface. This
prevents metal-to-metal direct contact by providing a sliding surface. With-
out a good sliding surface, the two metals at the contact zones of moving
parts come in direct contact with each other, and this results in an increase
in temperature causing adhesion, scung or even welding. The ester
structures in triacylglycerols offer active oxygen sites that trigger binding to
the metal surface forming a protective film. This protective film builds
further with time to reduce friction. During this rubbing process under lu-
bricated conditions, at high load and low speed, bond cleavage of FA mol-
ecules might take place. Under such conditions, the epoxy groups of ESBO
offer active oxygen sites that trigger polymerization on the metal surface
forming a protective film. This protective film builds further with time to
reduce friction. The COF data from the ball-on-disk experiments on vege-
table oils blended into hexadecane at a 0.003 molar concentration are 0.269
for SBO, 0.248 for HOSBO, and 0.232 for ESBO, while at 10 times higher
concentrations (0.03 molar), the COF values are 0.135 for SBO, 0.132 for
HOSBO, and 0.104 for ESBO. Under a high load of 181.44 kg and a low speed
of 6.22 mm s
1
(5 rpm), all of the vegetable oils show an excellent reduction
in COF at low molar concentrations.
The anti-wear and friction-reducing properties of moringa oil and other
vegetable oils were evaluated using a high-frequency reciprocating rig
(HFRR) lubricity tester. The HFRR method determines the lubricity or the
ability of a fluid to affect friction and wear between the surfaces in relative
motion under load. The average ball scar diameter, disk wear scar width and
length on the x-axis, film percentage, and coecient of friction (COF) for
