Polyethylene glycol monomethyl ethers as the main component of brake fluid

Article abstract of DOI:10.1134/S107042720611022X

The main physicochemical properties of polyethylene glycol monomethyl ethers in a wide temperature range were determined. The effect exerted on the main quality indices of brake fluids by the introduction of polyethylene glycol monomethyl ethers borates was studied. The use of these ethers as the main component of DOT-5.1 brake fluids was analyzed.

Full text of DOI:10.1134/S107042720611022X

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 11, pp. 1853 1856. Pleiades Publishing, Inc., 2006.
Original Russian Text R.F. Khamidullin, N.Yu. Bashkirtseva, A.I. Abdullin, I.I. Akhmetov, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79,
No. 11, pp. 1874 1877.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Polyethylene Glycol Monomethyl Ethers
as the Main Component of Brake Fluid
R. F. Khamidullin, N. Yu. Bashkirtseva, A. I. Abdullin, and I. I. Akhmetov
Kazan State Technological University, Kazan, Tatarstan, Russia
Received March 24, 2006
Abstract The main physicochemical properties of polyethylene glycol monomethyl ethers in a wide tem-
perature range were determined. The effect exerted on the main quality indices of brake fluids by the introduc-
tion of polyethylene glycol monomethyl ethers borates was studied. The use of these ethers as the main com-
ponent of DOT-5.1 brake fluids was analyzed.
DOI: 10.1134/S107042720611022X
Brake fluids (BFs) are used to transfer energy to
the actuating mechanism in the hydraulic drive of the
brake assembly of a car and to remove heat from the
brake disks. The modern requirements to BFs are
determined by FMVSS 116 (DOT) American federal
motor vehicle safety standards [1].
The viscosity temperature properties of brake fluids
should provide their efficiency in a wide temperature
range. At low temperatures the fluid should be mov-
able. To ensure reliable operation of a hydraulic drive
of the brakes in summer time or in the South, the
saturated vapor pressure of the fluid should be low
and its boiling point should be sufficiently high [2].
According to this standard, BFs are subdivided into
three classes: DOT-3, DOT-4, and DOT-5.1. The
main requirements to these BFs are high operation
temperatures, good low-temperature and viscosity
temperature properties, physical and chemical stabil-
ity, protection of metals from corrosion, inactivity
with respect to mechanical rubber articles, and lub-
ricating effect. Some requirements of FMVSS 116
Analysis of the available literature [3 5] revealed
growing use of glycols or their derivatives, in particu-
lar, di-, tri-, and tetraethylene glycol monoalkyl ethers
[3 8], in the last decade as the main components of
BFs. To increase the boiling point of both wet and dry
liquid, tris(methyl glycol) borates are introduced in
BF [9, 10]. At the present time, Russian analogs of
DOT-3 and DOT-4 brake fluids are widely used in
Russia. Since the motor vehicle safety standards
become tougher, the requirements to brake fluids
become more stringent. Therefore, preparation of a BF
of DOT-5.1 grade meeting these requirements is an
urgent problem. However, no detailed data are avail-
able in the literature on physicochemical properties of
tris(methyl glycol) borates of both pure polyethylene
(DOT) are summarized in Table 1.
The boiling point is the main parameter determin-
ing the maximal operation temperature of a hydraulic
drive of a brake assembly. Boiling point of most of
brake fluids decreases in the course of their operation
owing to high hygroscopicity of the fluids. In practice,
the advantages of high-boiling BFs are actually useful
when the fluids are frequently replaced.
Table 1. Some requirements of FMVSS 116 (DOT)
Thus, a high boiling point of BF does not ensure
its efficiency under hard operation conditions. Hence,
not only dry equilibrium reflux boiling point
Quality index
DOT-3 DOT-4 DOT-5.1
(
ERBP) of BF but also wet equilibrium reflux boiling
Boiling point, C:
dry fluid
wet fluid
Kinematic viscosity, mm s , 1400
at 40 C no higher than
point (WERBP) of BF containing 3.5% water [1] is
determined. The WERBP corresponds to the tempera-
ture at which the liquid will boil after its operation
in a hydraulic drive of a brake assembly of a vehicle
for 1.5 3 years.
205
140
230
155
1800
260
180
900
2
1
1853

1854
KHAMIDULLIN et al.
Table 2. Main physicochemical properties of the examined ethers
ERBP WERBP Kinematic vis-
Dynamic
viscosity,
mPa s
Ether
cosity at 40 C, T, C
Density, g cm 3
Refractive index
2
1
C
mm s
MeDEG
193.2
235.3
298.0
332.0
134.0
145.1
151.0
203.0
72.6
281
20
1.0211 (1.0211 [11])
1.0059
4.19
2.74
1.86
1.19
1.4261(1.4263 [11])
40
60
80
0.9907
0.9731
MeTEG
20
1.0494 (1.0494 [11])
1.0428
7.44
4.2
2.77
1.89
1.4368(1.4370 [11])
1.4448(1.4452 [11])
1.4434
40
60
80
1.0217
1.0054
MeTetraEG
BMeTEG
20
1.0659
1.0505
1.0326
1.0182
11.39
6.42
3.87
1.61
40
60
80
20
1.0804
1.0653
1.0465
1.0295
19.11
9.52
5.66
4.04
40
60
80
1
glycol monomethyl ethers and their mixtures with
tris(methyl glycol) borates, as well as on the influence
of the degree of boration of the initial compounds on
the boiling point and viscosity of BF.
300 ml min , respectively. The temperature of the
vaporizer and junction chamber of the detector was
170 and 180 C, respectively. The temperature in the
course of the analysis was automatically changed from
10 to 200 C at a rate of 10 deg min . The tempera-
ture was controlled by a BU-125 control unit of the
chromatograph with an accuracy of 0.1 C.
1
1
The aim of this study was to determine how addi-
tions of borates affects the boiling point and low-tem-
perature viscosity of brake fluids.
The density was determined pycnometrically ac-
cording to GOST (State Standard) 3900 85. The ki-
nematic viscosity measured on a VPZh-3 viscometer
EXPERIMENTAL
(
GOST 33 82) was converted into the dynamic vis-
Diethylene glycol monomethyl ether (MeDEG),
triethylene glycol monomethyl ether (MeTEG), and
tetraethylene glycol monomethyl ether (MeTetraEG)
were isolated from polyoxide-101 in accordance with
TU (Technical Specifications) 2422-027-56649936
cosity. The substances were controlled thermostatic-
ally in a UT2/77 thermostat with an accuracy of
0
.05 C. The densities and dynamic viscosities of
the pure ethers are summarized in Table 2.
0
1 and were purified by repeated vacuum distillation
The boiling points were measured in accordance
with the MFVSS 116 standard [1]. The results are
presented in Table 2 and in the figure.
on a bench unit at a residual pressure of 2 5 mm Hg.
The purity (99%) was determined by comparison of
their main physicochemical properties with the pub-
lished data and by chromatographic analysis. The
results are presented in Table 2.
The borates were prepared by conventional esteri-
fication on a vacuum bench unit consisting of a round-
bottom flask used for distillation of the polymeriza-
tion products, adapter with a reflux condenser, and
a receiver for liberating water. The initial compounds
were boric acid (GOST 9656 75) and MeTEG. These
substances taken in a required ratio were placed in
the reaction flask. The flask was evacuated to a resid-
ual pressure of 10 20 mm Hg. The reaction mixture
Chromatographic analysis was performed on a
Tsvet-500 chromatograph. We used a 2-m steel
column 3 mm in diameter packed with PEG-20M on
a Chromaton and a flame ionization detector with
a sensitivity of 1 10 . The flow rate of hydro-
gen, carrier gas (nitrogen), and air was 30, 30, and
7
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POLYETHYLENE GLYCOL MONOMETHYL ETHERS
1855
ing point of a wet fluid [6]. However, since the vis-
cosity of borate esters is high, introduction of large
amounts of these compounds is undesirable. The main
advantage of brake fluids containing borate esters is
insignificant change of their physical properties in
the presence of moisture. Esters of boric acid not only
bind water but also have good lubricating and corro-
sion-preventing properties.
T, C
As noted above, an increase in the fraction of borate
esters of methoxypolyethylene glycols in a brake fluid
increases its boiling point. We studied the influence
of methoxyethylene glycol borates on boiling points
of their mixtures with individual polyethylene glycol
monomethyl ethers. The content of tris(methoxy-
ethoxyethoxyethyl) borate (BEMeTEG) ranged from 0
to 100%.
mm s 1
2
,
As seen from the figure, the kinematic viscosity
of the mixtures monotonically increases with in-
creasing borate content. The maximal permissible
kinematic viscosity in accordance with FMVSS 116
2
1
(
900 mm s ) is reached at the borate content of
c, wt %
Fig. 1. (1) ERBP and (2) WERBP (T, C) and (3) kinematic
viscosity at 40 C as functions of the concentration of
about 60 wt %. The ERBP and WERBP of brake
fluids containing this amount of borate are 260 and
180 C, respectively, which meets the FMVSS 116
tris(methoxyethoxyethoxyethyl)borate in MeTEG c.
(DOT) requirements.
was continuously stirred by a nitrogen flow fed
through a capillary. The flask was gradually (over
a period of 1.5 2.0 h) heated to 120 C, and the
liberated water was distilled off.
CONCLUSIONS
1) A mixture of triethylene glycol monomethyl
(
As seen from Table 2, the temperature dependence
of the density and viscosity of pure ethers mono-
tonically decreases in the series MeDEG MeTEG
MeTetraEG. The density and viscosity increase, prob-
ably due to densification of the structure (an increase
in the degree of association) and increase in the
number of intermolecular hydrogen bonds. The ERBP
of MeTetraEG meets the requirements for DOT-5.1
BF. However, this ether freezes at 40 C. MeTEG,
in turn, has good low-temperature viscosity but un-
satisfactory boiling point. Oxyethylated additives have
a negative effect on the properties of BF: the low-
molecular-weight additives decrease the boiling point
and the additives with higher molecular weight in-
crease the low-temperature viscosity. Thus, MeTEG
has good ERBP and low-temperature properties and
can be used as the main component of BF.
ether with its full borate ester can be used as the main
component of DOT-5.1 brake fluid. The ERBP,
WERBP, and low-temperature viscosity of this BF
meet the FMVSS requirements.
(2) To meet the FMVSS requirements to boiling
points and low-temperature properties, the content of
tris(methoxyethoxyethoxyethyl)borate in its mixture
with triethylene glycol monomethyl ether should be in
the range 55 60 wt %.
REFERENCES
1
. FMVSS (Federal Motor Vehicle Safety Standards)
16: Car Brake Fluids, USA, 1999.
1
2. Manusadzhyants, O.I. and Smal’, F.V., Avtomobil’nye
ekspluatatsionnye materialy (Car Operating Materi-
als), Moscow: Transport, 1981.
To eliminate the negative effect of water and to
increase the boiling point, borate esters of alkylene
glycol monoethers were added to BF [9, 12]. The
borate additive is readily hydrolyzed by water present
in BF, binding this water and thus increasing the boil-
3
4
. US Patent 4371448.
. RF Patent 2174536.
5. RF Patent 2087528.
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1856
KHAMIDULLIN et al.
6
. Brusyantsev, N.V., Ekspluatatsionno-tekhnicheskie 8. RF Patent 2159760.
svoistva i primenenie avtomobil’nykh topliv, smazoch-
nykh materialov i spetszhidkostei (Operation-Tech-
nical Properties and Application of Car Fuels, Lub-
ricants, and Special Fluids), Moscow: Avtotransizdat,
9. US Patent 3925223.
0. US Patent 4116846.
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slovar’ (Chemical Encyclopedia), Moscow: Nauka,
1
1
1
963.
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983, 2nd ed.
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. Danilov, A.V., Vvedenie v khimmotologiyu (Introduc-
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