Chemistry Reference
In-Depth Information
Table 11.4 Results of the PDSC temperature ramp at 10 1Cmin
1
in
air under static 200 psi pressure, and isothermal
experiments at 200 1C (SBO at 170 1C) under 200 psi
pressure with 20 mL min
1
flow of air, for diester SBO
derivatives with additives (4% w/w). (Reproduced from
ref. 47 with kind permission from Springer Science and
Business Media from Springer and the AOCS Press.)
Onset temperature
(T
onset
)/1C
Oxidation induction
time (OIT)/min
Test fluid
25.7
a
SBO
192
Ace-SBO
256
75.3
But-SBO
247
51.0
Isobut-SBO
255
56.2
Hex-SBO
254
55.6
a
Isothermal experiment at 170 1C.
diester samples. The effect of these anti-oxidants was studied using PDSC
temperature ramping and isothermal experiments.
25
The results obtained are
shown in Table 11.4. It was found that the anti-oxidant additive responded very
well to these diester samples and increased their T
onset
by 80-100 1C. The iso-
thermal PDSC experiment was done to determine the oxidation induction time
at 200 1C under 200 psi at a constant flow of 20 mL min
1
of air. These results
also suggested that the anti-oxidant additive could prevent the start of oxidation
for at least 50min at 200 1C. Both the T
onset
and OIT of these diester samples are
higher compared to SBO. Even mineral-oil-based formulations have an OIT of
20 min at 200 1C.
35
This shows that chemical modification of SBOs along with a
suitable anti-oxidant additive can improve their oxidation properties to be
comparable with mineral oils. The effect of chain length on the oxidation sta-
bility of additive-enhanced diester samples is similar to that for non-enhanced
samples, i.e., decreasing oxidation stability was observed with increasing chain
length of the substituents on the CMSBO. Using an optimized set of additives
(2% zinc diamyl dithiocarbamate and 2% antimony dialkyldithiocarbamate),
the oxidation stability can be improved further. With this combination, the
T
onset
for SBO increased to 215 1C, while that for HOSBO increased to 254 1C.
The OIT values also increased to 49min for HOSBO and 1min for SBO at 200 1C.
11.3.4 Low-temperature Properties
Triacylglycerols that are completely hydrogenated for the purpose of elim-
inating sites of unsaturation will tend to harden at room temperature due to
alignment and stacking of adjacent molecules. Therefore, it is important
that there should be at least one site of unsaturation available for derivati-
zation that will yield branching sites. This approach is used here to improve
the low-temperature-flow behavior of SBO by attaching ester branching at
the double-bond sites.
The PP measurements provide a good estimate of the low-temperature
fluidity of the lubricants. PP values for SO, ESO, and CMSBO derivatives are
given in Table 11.3. The PP of SBO is
9 1C, while that of ESO is 0 1C. The
