Chemistry Reference
In-Depth Information
10.3.3 Oxidative Stability
The oxidative stability (OS) data for MWO and its derivatives, which were
obtained using the RPVOT method, are summarized in Table 10.6. Oxidation
stability evaluations were conducted on samples with (3.5 wt%) and without
blended commercial anti-oxidant additives. For comparison, similar litera-
ture data for CANO and SBOs are included in Table 10.6. As can be seen,
MWO derivatives (PHMWO, etc.) without anti-oxidant additives displayed
slight improvements in OS compared to unmodified SB or CAN oils. On the
other hand, samples containing the commercial anti-oxidant additives dis-
played significant improvements in OS. However, the improvements due to
added anti-oxidant varied and were dependent on the nature of the oil being
tested. For PHMWO, the oxidation stability improved by a third (from 15 to
20 min). For the polyesters (AMWO, BMWO and VMWO), however, the
changes were more significant - up to a four-fold increase in RPVOT was
observed. A closer examination of the OS data indicated that, for the MWO
polyesters, the oxidative stability decreases with increasing substituent chain
length.
10.3.4 EHD Film Thickness
Film thickness was investigated using an optical interferometry method.
Film thickness was measured as a function of lubricant entrainment speed,
temperature and applied load. In these studies, only acetylated (AMWO) and
valerylated (VMWO) milkweed esters were investigated. These two oils were
chosen because they had the highest and lowest viscosities, respectively,
among the three milkweed esters investigated in this work (Tables 10.3 and
10.4). Also, PHMWO was not investigated because it was too viscous for the
measurement system. A typical data set from film thickness measurements
by optical interferometry is illustrated in Figure 10.11. The data in
Figure 10.11 is for VMWO, but similar data were also obtained for AMWO.
AMWO and VMWO oils displayed the familiar entrainment speed vs. film
thickness profiles displayed by lubricating oils. The film thickness increased
Table 10.6 RPVOT oxidative stability (min) results for soybean
(SB) and milkweed (MW) derivatives, with and
without a blended commercial anti-oxidant.
No
anti-oxidant
3.5 wt%
anti-oxidant
a
Oil
Ref.
SBO
13
28
22
CANO
10
43
22
b
HMWO
15
20
b
AMWO
—
74
b
BMWO
16
67
b
VMWO
—
52
a
LZ 7652 from Lubrizol Corporation.
b
This work.
