NLG
The Path Leading to a Novel OBCS Grease with Superior
High Temperature Performance for Extended Use
Liwen Wei, Novitas Chem Solutions, LLC, Bellaire, Texas, USA
Content partly presented at NLGI’s 79th Annual Meeting, June, 2012, Pa/rn Beach, florida, USA
Introduction:
Q
form
verbased
or complex
calciumform
sulfonate
through
grease
the inclusion
in its native
of the
soap-based thickener such as 1 2-hydroxy stearate,
hereinafter collectively called OBCS grease, is known
for its water resistance and inherently high load car
rying, anti-rust, and higher temperature performance.
This combination of performance advantages made
OBCS grease ideally suited for severe operations, for
instance, in steel, marine, mining and construction
industries, and for food grade and many others that
want to stay away from the traditional use of EP and
anti-rust agents that contain sulfurs or heavy metals [1].
Since the creation of its native form nearly half a
century ago [2-4], or complex grease more than 20
years ago [5], the art of making OBCS grease is all but
simple [6]. It begins with the conversion of amorphous
calcium carbonate present in the Newtonian overbased
sulfonates solutions into a calcite structure which was
identified as the key factors contributing to the thixo
tropic properties, enhanced yield, and high temperature
properties of the grease [7]. From time to time, how
ever, the calcite conversion process, the so-called “gell
ing process” as known in the trade, does not proceed
as smooth as one would expect. For instance, overbased calcium sulfonate gel from one source but not
so from another source, and even if it does gel, would
result in vastly different grease consistency and texture!
appearance among various sources of overbased cal
cium sulfonate. Such inconsistency may be attributed
to the compositional differences in the makeup of the
overbased sulfonates and its original alkylates and
the sensitivities of the gelling process toward the pro
moter chemistries [5 and 61 that alters the nature and
kinetics in the crystallization process of the colloidal
dispersed calcium carbonates and ultimately impacts
the properties and performance of the resulting grease
composition. Adding to the complexity for the complex
grease is the subsequent use of soap acids such as
1 2-hydroxystearic acid and the use of borates [5] or
phosphates [8] and other components to further forfeit
OBCS ‘s three-dimensional grease microstructures.
For most of the OBCS greases available today the
appearance is characterized as “smooth” or “gel-like”.
Colors range from light tan to dark amber (or dyed
color). These variations in the visual appearance are not
insignificant which are tied closely to the “chemistry” of
overbaseci used and the “state” of the colloidal calcite
aggregates present or the so-called reverse micelle
like thickener involved. In a recent paper [9], the OBCS
grease microstructure was described as consisting of
a fine dispersion of spherical and agglomerate particles
with an average size of 230nm through the use of the
non-disturbed Atomic Force Microscopy. One of the
direct outcome of this unique chemistry and an out
standing property of OBCS grease is the high dropping
Picture 1
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VOLUME 77, NUMBER 4
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Jade Like OBcS Grease
LGI
points (ASTM D2265) that has been claimed to reach
308C and higher, a reflection on the lack of melt
In the wet mechanical stability testing (10,000
strokes in the presence of 30% water added accord
ing to ASTM D7342) this grease hardened dramati
ing point for these calcite aggregates and a sigificant
improvement over the soap thickener based grease.
This high dropping point apparently contributes to its
high temperature performance as confirmed by the
temperature-sweep rheological testing [10] wherein
Sulfonation/Overbasing
AB
OBCS grease outperforms traditional soap based
complex grease. However, at high temperatures of
1 50C and above and after OEM’s extended use OBCS
grease was found in occasions that did not perform as
well, many harden or soften despite their outstanding
dropping points (>308°C) [11]. The aim of this paper is
to uncover a path that leads to the making of a robust
and genuinely high temperature OBCS grease.
)
OB
Gel-formation
OBCS
Complex Grease
Scheme 1
Complaxation
OBCS
Sulfonate Grease
—Synthetic Path to OBCS Grease
100000
The synthetic path leading to the
preparation of novel OBCSC
OBCS-A
Overbased A
10000
Good
HT Grease
1000
Scheme 1 gives one of the typical preparations
Overbased C
of OBCS grease that begins with alkyl benzene
100.0 ~B
alkylates (abbreviated as AB). There are three
general types of alkylates, namely MAB (mono
10.00
alkyl benzenes), HAB (heavy alkyl benzenes
1.000
available as the byproducts from LAB/BAB pro
Overbased B
duction), and PAB (polyalkyl benzene including
0.1000
alkyltoluenes and xylenes). MAB and PAB are
the two types that have well-defined molecular
00.1000
0
10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0
structure, namely mono to poly-substituted
benzene, HAB, however, contain a majority of
Figure 1 Grease Stability Determined by Thermal Ramp Method (12)
PAB but also a significant and varied amount of
co-products such as dialkylt
etralins and diphenylalkanes.
Table 1
Table 1 summarizes results
Effects of Alkylates on OBCS Performance
with each of these three types
OBCS-A
OBCS-B
OBCS-C
of alkylates under the identi
PAB
MAB
HAB
cal run conditions without the
OB/OiI Ratio
complexation step (without
Dropping Point, C
>308
>308
>308
the use of soap acids). It was
~j:~’
CI!Ii
Cliii
Penetration
#
noted that MAB (OBCS-B)
Mechanical Stability
257
228
283
after the gel conversion into
10,000 Stroke, 30% water
Calcite forms gives the high
est oil separation rate (90%),
Penetration # Change
~J.
smallest particle size and rela
Particle Size, nm
129
68
207
tively soft grease composition.
Oil Separation, 3Hr/100C
90%
I~.
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~.:
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NLGI SPOKESMAN, SEPTEMBER/OCTOBER 2013
NLGI
cally. OBCS grease tends to harden in the presence of
water; however, a total collapse of the grease struc
ture is unexpected. Under the Thermal Ramp Method
at 180°C, this grease further breaks down to liquid
while the grease made with PAB (OBCS-A) and HAB
(OBCS-C) are able to withstand the thermal stress
[Figure 1].
white color, or jade like appearance. This visual appeal
clearly stands out from the rest of OBCS greases made
today. The color is a sign of purity and the near trans
parency we believe is a testimony on the complete
inclusion of reverse micelle, or the so-called colloidal
dispersed calcium carbonates present in the OBCSG
grease microstructure.
Given the identical run conditions, it is not unreason
High temperature durability of OBCS grease
able to assume the small particle size of the colloidal
calcite aggregates is due to the smaller molecular
In previous studies in search of high temperature grease,
dimension of MAB (mono-alkyl benzene). This (smaller
a plurality of HAB based commercial OBCSC samples
calcite aggregates) may signal a less robust inorganic
were tested for high temperature durability under the
core that in turn affects the overall integrity of the
accelerated conditions @500°F/266°C in oven (no stir
grease. Alkylates with larger molecular dimension
ring). It was found all of OBCS samples outperformed
(HAB and PAB) appear to be more desirable
in the formatior~ of larger colloidal calcite
8000
aggregates.
7000~
Table 2 continues with the complex
6000
ation runs with overbased made with HAB
5000
and PAB alkylates in various proportions.
4000
PUG (334# (S0220)
OBCSG made with PAB (OBCS-2) give the
3000
best overall performance where it has a much
>
2000
OBCS-5 (376# ISO100)
improved wet mechanical stability test with
1000 ~
improved long term storage and brighter
0
— OBCS-6 (325#; 1S0320)
— CA SOAP (31 7# 1S0320)
appearance than those made with HAB.
0
15
30
45 ~60
75
90
105 120
Picture 1 is an OBCS grease made
Time (mm)
(OBCS-5) with PAB based alkylate and GIl
base oil with near transparency and offFigure 2 Rotational Viscosity @1 50C
.
Table 2
OBCS Complex Grease Examples
OBCS 1
OBCS 2
OBCS 3
HAB
PAB
HAB
08%
Dropping Point, C
Penetration #
Mechanical Stability
10,000 Stroke, 30% water
Penetration # Change
Oil Separation, 3Hr/1 000
6 months Long Term
Storage Stability (Oil Bleed)
Transparencies
OBCS 4
HAB
28%
>308
cP2;
36%
>308
36%
>308
>308
228
298
252
234
LI
~I
FAIL
PASS
FAIL
PASS
POOR
BEST
POOR
FAIR
-28VOLUME 77, NUMBER 4
4..
NLGI
traditional grease; however, either hardening or soft
ening was observed [12]. This method is a quick and
effective test for the thermal stability of grease but is not
ideal as the grease is tested in oven/still mode. A new
method is developed by measuring the rotational
viscosity of the grease at elevated temperature over
an extended period of time, based on a Brookfield
viscometer. This method calls for the use of thermal
seal (a constant temperature bath) under fixed shear
rate / speed / spindle conditions. Four samples
include two OBCS grease samples made with PAB
(OBCS-5) and HAB (OBCS-6) respectively, polyurea
grease and Calcium soap grease were tested.
Table 3 gives the sample characteristics and rota
tional viscosity (represented by By) data and
Figure 2 shows the flow curves of the four samples
at 150°C with a fixed/selected shear rate.
It can readily be seen on Figure 2 that the PUG
grease suffers a 3,500cP drop (and continues to
drop at the end of run) over a two hour period
despite its high dropping point (>>308°C) while
calcium soap grease liquefied in the beginning of
the run. OBCS-5 and OBCS-6 made through the
two hours run with averaged 1 ,300cP and 800cP
respectively. OBCS-5 has the minimum rotational
viscosity change (300cP) as opposed to OBCS-6
(1,500), an indication of its outstanding high tem
perature durability at 150 C. Figure 3a shows the
room temperature run for OBCS-5 and OBCS-6.
Properties
Thickener Type
Penetration, 60S
Base Oil ISO Grade
Dropping Point, C
50,000 Strokes
half P# Change
D1831 (160C/l2Hrs)
Half P# Change
BV @ 150°C, cP (average)
BV Change, cP (2Hr@1 50C)
The wide-swing of the flow curve for OBCS-6 is a sign
of the torque fluctuation likely due to the discontinu
ity generated along the wall of the spindle, a phe
nomenon attributed to the higher consistency of the
5000
3000
OBCS-5 (376# ISO100)
~IL
2000
_____
I~
OBCS-6 (325# 1S0320)
1000
0
0
15
30
75
90
105
120
5000
OBCS-5 (376# ISO1 00)
0
>,
4000
4-
OBCS-6 (325# 1S0320)
3000
RT Viscosity
1 50C Viscosity
Figure 3b — Rotational Viscosity Index
PUG
Diurea
Calcium Soap
320
>308
220
>308
320
Not Tested
9
Not Tested
Not Tested
16.8
Not Tested
800
1,500
2,400
3,500
0
Liquefied
I
28
60
Figure 3a — Rotational Viscosity @RT
Table 3
Rotation Viscosity @1 50C
OBCS-5
OBCS 6
OB-PAB
OB-HAB
100
>308
6
45
1,300
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NLGI SPOKESMAN, SEPTEMBER/OCTOBER 2013
Soap
1:1i
NLGI
grease. Figure 3b plots the average rotational viscosity
versus temperature, at room temperature and 15000
respectively. The higher rotational viscosity (and slightly
higher rotational viscosity index) of OBCS-5 despite its
softer consistency (376#) and lower base oil viscosity
(ISO100) suggest a significantly more robust grease
microstructure than OBCSG-6 (325# and ISO 320).
Higher rotation viscosity (Figure 3b) under shear sug
gests a higher bearing viscosity and likely a higher EHL
film strength. Further study with a range of shear rates
and extended run are clearly warranted.
5) Ron Muir, William Blokhuis, Witco Corporation, “High
Performance Calcium Borate Modified Overbased
Calcium Complex Grease,” U.S. Patent 4560489,
September, 1983
6) Richard Denis, M.S. & Matthew Sivik, Ph.D., “Calcium
Sulfonate Grease-Making Processes,” NLGI 75th
Annual Meeting Paper #0812, June 7, 2008
7) William D. Olson, Ronald J. Muir, Theo I. Eliades,
Witco Corporation, “Sulfonate Grease Improvements,”
U.S. Patent 5338467, August 14, 19
8) John Barnes, NCH Corporation, “Calcium Sulfonate
Grease and Method of Manufacture,” U.S. Patent
5,126,062. June 30, 1992.
Conclusion
This paper presents Jade-like robust and high perfor
mance OBCSG grease that is successfully prepared
with PAB for extended and high temperature applica
tions at 150°C and above. The jade appearance, we
believe, is a testimony to the purity and the complete
inclusion of reverse micelle, or the so-called colloi
dal dispersed calcium carbonates present in OBCS’s
grease microstructure. The high temperature durability
is confirmed with the rotational viscosity study carried
out with the Brookfield viscometer under appropriate
conditions.
9) M. C. Sanchez, J. M. Franco, C. Valencia, C.
Gallegos, F. Urquiola, R. Urchegui, “Atomic Force
Microscopy and Thermo-Rheological Characterisation
of Lubricating Greases,” Tribol Lett. 41:463-470,
2011
10) Matthew Sivik and Stephen J. Nolan, “Studies on
High-Temperature Rheology of Lithium Complex
Grease,” NLGI 74th Annual Meeting Paper #071 0,
June 10, 2007
References:
11) Private communication and unpublished results
1) Wayne Mackwood and Ronald Muir, “Calcium
Sulfonate Greases. One Decade Later,” NLGI
Spokesman, Volume 63, NumberS, pp24-37, 1998.
12) Liwen Wei, David Duckworth, Ping Sui, Halliburton,
“Microscopic Perspectives of Calcium Sulfonate
Grease Exploring its full potentials,” STLE, May
17, 2010
.
.
–
2) Richard L. McMillen, The Lubrizol Corporation,
“Basic Metal-Containing Thickened Oil Compositions,”
U.S. Patent 3,242,079. March 22, 1966.
3) Richard L. McMillen, The Lubrizol Corporation,
“Process For Preparing Lubricating Grease,” U.S.
Patent 3,376,222. April 2, 1966.
ABOUT THE AUTHOR
Dr. Liwen Wei
Novitas
Chemical Solutions
Liwen Wei
(speaker) is the Senior consultant
and President of Novitas Chem
Solutions, LLC. His main focus is
to provide consultant services to
clients in lubricant industries.
—
—
4) Mack W. Hunt, Continental Oil Company, “Method
For Preparing Highly Basic Grease and Rust
Inhibiting Compositions,” U.S. Patent 3,816,310.
June11, 1974.
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VOLUME 77, NUMBER 4