Chemistry Reference
In-Depth Information
resultant modified SBO products are characterized by lower PP values, as
demonstrated by the superior PP values for Hex-SBO (
21 1C). The PP values
decreased with increasing chain length of ester branching. This can be ra-
tionalized by the presence of branching groups attached to the sites of un-
saturation, which does not allow individual molecules to come close for easy
stacking, due to steric interactions, and thus inhibits crystallization, re-
sulting in a lower PP. Unmodified vegetable oils have a tendency to form
macrocrystalline structures via a uniform stacking of the 'bent' triacylgly-
cerol backbone at low temperatures. The branching groups of optimum
length at the epoxy carbons, not only serve to eliminate the sites of un-
saturation, but also impose spacing from other triacylglycerol molecules,
thereby interfering with the formation of macrocrystalline structures. The
ester branching groups with chain lengths of at least six carbons, were found
to be the most effective for imposing the desired molecular spacing and thus
imparting the most desirable PP properties.
Further improvement in the low-temperature fluidity of Hex-SBO was at-
tained by using a Pour Point depressant (PPD) additive (L7671-A from
Lubrizol Corporation, Wickliffe, OH). Blending was carried out by stirring
the CMSBO derivatives with an optimized additive dose at room temperature
for 2 h. The purpose of the PPD additives is to sterically hinder crystal-
lization of triacylglycerol molecules at low temperatures by disrupting the
stacking mechanism. In general, PPDs can lower PP by 30 1C in mineral oils
at concentrations of only 0.1-0.4% (w/w), while in vegetable oils, a PP re-
duction of only 9-12 1C can be achieved with a higher treat rate of 1%. Since
the additive response of PPD in vegetable oils is not as good as in mineral oils,
a higher amount of PPD is needed to lower the PP significantly. An optimum
PPD additive concentration of 1% in the Hex-SBO enabled a PP of
30 1C.
Further addition of PPD additives made no significant improvement in the PP.
In order to further improve the low-temperature properties of the formulation,
diluents such as polyalphaolefins, dibutyl adipate and high-oleic vegetable
oils can be used. Here we used a biodegradable synthetic ester, dibutyl adipate
(96% purity), that was uniformly blended into the formulation as a diluent at
several concentrations. The final optimized formulation was Hex-SBO
þ
1%
PPD
þ
diluent (70 : 30 oil-to-diluent ratio) and had a PP of
42 1C.
The results thus showed that use of a suitable anti-oxidant additive can
bring the oxidation performance of CMSBO derivatives on a par with mineral
oils. The fully formulated lubricant using CMSBO as a base fluid, dibutyl
adipate as a diluent, PPD and an anti-oxidant additive has excellent oxi-
dation stability (PDSC T
onset
of 248 1C and an OIT of 28.5 min). This ap-
proach of chemical modification significantly improves the thermo-oxidative
stability of vegetable oils. Their cold-flow properties were also improved
using a combination of PPD and suitable diluents. The basic vegetable oil
structure is retained even after chemical modification of SBO, thus main-
taining excellent biodegradability.
Moringa oil showed a higher PP than SBO and HOSBO despite the fact
that it has more UFAs. This high PP is due to the presence of
23%
SFAs compared to 11.5% for SBO and 9% for HOSBO. It appears that
B
