NLGII
PFPE-TFE Copo~ymer: The New Frontier of F~uor~nated Lubricants
G. Boccaletti, S. Rovinetti, M. Avataneo, F. Di NicolO, Solvay Specialty Polymers Italia Spa., Milan, Italy
Presented at NLGI’s 79th Annual Meeting, June, 2012, Palm Beach, Florida, USA
is the reaction of the peroxidic PFPE (I) with tetrafluo
roethylene, which provides copolymers containing
perfluoropolyether blocks alternated with polytetrafl uo
roethyelene blocks [3].
This new proprietary technology is able to produce
different types of products, like solids, waxes and liq
uids. For example, the liquid copolymer can be used
as lubricant oils, while the solid ones, which are soluble
in perfluoropolyether oils can be used as thickener to
obtain fully fluorinated lubricant gel.
In the present work, we report the synthesis, the
physical-chemical characterization and the tribological
behavior of PFPE-TFE block copolymers obtained by the
reaction of the peroxidic PFPE with tetrafluoroethylene.
INTRODUCTION
p
erfluoropolyethers
are synthetic
fluids
largelyperfor
used
as
high quality lubricants
[1]. Their
superior
mances can be explained on the basis of their unique
properties like chemical and thermal stability, electri
cal resistance, wide operating temperature range, non
flammability, non-toxicity.
Among the several routes reported in literature for
the synthesis of PFPEs, the process developed by
Solvay Specialty Polymers is based on the low temper
ature photo oxy-polymerization of perfluoroolefins [1].
In particular, in the case of tetrafluoroethylene as mono
mer, the product of this reaction is a peroxidic PFPE
with the following structure:
CF3O[(CF2O)p(CF2CF2O)q(O)~,]CF3
(I)
EXPERIMENTAL PART
The peroxidic units (O)~, of the structure (I), randomly
distributed along the chain, can be easily removed by
thermal treatment or under UV exposure, thus obtain
ing a highly stable PFPE [2].
The chemistry of the peroxidic PFPE5 was recently
exploited for the synthesis of a new class of PFPE
block copolymers that can be prepared by decompos
ing the peroxidic units of (I) in the presence of free
radical homopolymerizable fluoroolefins and perfluoro
aromatic compounds [3—5]. A representative example
Materials
Some samples of PFPE-TFE copolymers, solid and
liquid, were investigated. Their main physical proper
ties are reported in section 3.2. Besides, two gels were
obtained by using the solid copolymer a~s thickener
and, respectively, a linear and a branched perfluo
ropolyether as base oils. The characteristics of these
experimental products are reported in the following
paragraphs.
Table 1
Commercial perfluoropolyethers oils characteristics
Sample
PFPE
structure
Numeric
average
molecular
weight (a.m.u)
Kinematic viscosity (cSt)
A~
At
A~
20°C
40°C
100°C
Viscosity
Index
Sample A
Branched
3200
250
80
10
108
Sample B
Linear
9800
280
159
45
338
Sample C
Branched
7250
1850
510
47
135
Sample D
Linear
26000
1300
700
200
375
—31
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NLGL SPOKESMAN, NOVEMBER/DECEMBER 2013
NLGI
To explore the behavior of these new structures a
comparison with commercial perfluoropolyether oils,
the linear and branched ones, and a standard grease
was carried out; their characteristics are reported,
respectively in Table 1 and Table 2 [6]. The structures of
branched and linear perfluoropolyethers are the follow
ing ones:
–
–
Cone penetration of lubricating grease
The sample consistency was evaluated through
ASTM D21 7 method, which is a test for measuring the
consistency of lubricating greases by penetration of
standard cone.
Friction torque at low temperature
Branched PFPE.’
CF3O~[CF2CF(CF3)O1n[CF2O]mCF3 with n/m>40
Linear PFPE:
CF3O~(CF2CF2O)p(CF2O)q_CF3 with n/m
The test method ASTM D 1478 describes the determi
nation of the starting and running torque of a greaselubricated ball bearing. The test method allows to
examine the serviceability of lubrication greases at low
temperatures. The starting and running torque were
measured after a defined cooling period and a holding
time of two hours at the specified test temperature.
1
Characterization methodology
The thermogravimetric (TGA) analysis
Friction torque at room temDerature (RT)
and at high-speed
The thermogravimetric (TGA) analyses were carried out
with a Perkin Elmer PYRIS 1 TGA. The samples were
heated from 3000 to 750°C at 10°C/mm.
Figure 1 shows the machine used to measure under
controlled speed the friction torque generated from a
ball bearing filled
with grease and
accurately sealed.
The load cell had a
calibration spanning
from 0 to 12 kg.
The experimental
setup allows the
determination,
as a function of
time, of the friction
torque produced
from a ball bear
ing under rotation,
until 16000 rpm
Rheological evaluation
The kinematic viscosity (v) at a given temperature was
determined by using capillary viscosimeters of the
Cannon-Fenske type in accordance to the ASTM D445
method. The complex viscosity (11*) was measured
with the dynamic mechanical spectrometer Rheometric
ARES (geometry: Parallel Plates 50 mm and Concentric
Cylinders) with a dynamic frequency sweep test in a dry
nitrogen environment after having identified the linear
viscoelastic domain.
Dropping point
ASTM D2265 method was used to evaluate the drop
ping point, which is the temperature at which the first
drop of material falls from the test cup, where it is con
tained and warmed up.
Oil separation
FTMS 791/321 method was used to determine
the amount of oil segregating from the grease
over a period of 30 hours. Measurements were
made at 120°C.
Figure 1
—
Friction torque machine
Table 2
Pet-fluorinated grease based on perfluoropolyether as base
oil and Polytetrafluoroethyelene powder as thickener
Composition
Sample
Base
Sample F
Sample B
(70% by weig
~
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VOLUME 77, NUMBER 5
~
Thickener
PTFE
(30% by weight)
NLGD
The wear scar diameter on the ball was evaluated after
test by optical microscopy, as far as the coefficient of
friction (f) is registered during the test, and the value at the
end of the test (fend’ t=1 20 minutes) has been reported.
are reached, as well as the local temperature generated
from the friction. The operative conditions were:
–
–
–
Ball bearings: model SKF 6303 filled with 30% by
weight grease and sealed with especially designed
0-rings in FKM elastomers;
RESULTS AND DISCUSSION
Synthesis of PFPE—TFE block copolymers
Bearing rotation: from startup to 16000 rpm,
according to a ramp of eight 2000 rpm steps, each
lasting 1 hour;
PFPE-TFE block copolymers are synthesized by feed
ing TFE in a solution of peroxidic PFPE (I) heated at a
temperature sufficiently high to decompose the perox
idic units. Details of their preparation are reported in the
reference [3]. In fact, in these conditions, the peroxidic
bonds of (I), here indicated as RCF2—O—OCF2R where R
is a PFPE moiety, homolitically decompose and gener
ate two alkoxy radicals [7]:
No additional load applied.
The results are given in terms of the starting and running
friction torque and of the temperature at each step.
Four ba/I wear test
A Four-ball wear machine, by Falex, was adopted to
determine wear scar according to ASTM D2266 standard.
R-CF2O—O–CF2R —*2 R—CF20
(Eq.1)
These alkoxy radicals can then undergo B-scission
reactions followed by the formation of new alkyl radicals
and the evolution of a molecule of carbonyl fluoride:
Operative conditions were:
Temperature: 75°C
Load applied: 40 kgf
Ball rotation: 1200 rpm
Duration: 1 hour
R-CF20
—~
R
+
COF2
(Eq.2)
In absence of TFE, the recombination of these radicals
leads to a highly stable and non-peroxidic PFPE, whose
repeating units are CF2O—, —CF2CF2O—.
Instead, when an olefin like TFE is present in the
reaction medium, the radicals of Eq. 1 and Eq. 2 can
act as initiators for its polymerization, thus leading to
the formation of TFE blocks inside the perfluoropoly
ether chain. The mechanism can be described by using
The wear scar diameter on the balls was evaluated by
optical microscopy.
—
SRV Test
The wear and friction properties of the oils were
evaluated by using the Optimol SRV Ill machine under
oscillatory conditions, with ball on disk configuration
according to the method
Table 3
ASTM D 6425.
Main characteristics of the PFPE-TFE copolymer samples
For all the tests the oper
Numeric
Numeric
Glass
ative conditions were:
Physical
average
average B
Transition
Melting
Sample
State
molecular
block length Temperature
point (°C)
Stroke = 1 mm;
weight
(Nr. C atoms)
(°C)
Frequency = 50 Hz;
(a.m.u)
Load applied = 50 N
Sample 1
Solid
25000
21.3
-116
220-240
for 30 s, then 300N
Sample2
Liquid
30000
8.2
-116
for 120 minutes;
Temperature = 50°C.
Sample 5
Solid
35000
13.4
-113
120-140
.
___________
___________
Sample6
Liquid
–
30000
9.4
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NLGI SPOKESMAN, NOVEMBER/DECEMBER 2013
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–
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the classic kinetic scheme of the radical polymerizations:
Initiation: R + CF2=CF2
—‘
out on copolymers with different structures indicates
that the length of the B block is the parameter that
mostly influences the physical state of the copolymer.
This parameter can be modified by tuning the reaction
conditions [8], In particular, for copolymers with short
B blocks the formation of crystallites is avoided and
the copolymer is totally amorphous and liquid at room
temperature. By increasing the B block length, the perfluorocarbon sequences can crystallize, as evidenced
by the presence of a melting transition, and the PFPE
TFE copolymers become wax-like or solid. Figure 2
exemplifies the variation of the physical state versus the
block B length.
It has to be noted that the viscosity for the liquid
copolymers is also tunable by regulating TFE, their
kinematic viscosity could reach also values more than
50,000 cSt at 20°C.
Table 3 reports the main characteristics for four
samples, which were analyzed for the present work.
The thermal stability for these new structures was
evaluated through thermogravimetric analysis (TGA):
the PFPE-TFE copolymers, independently from their
physical state, showed very high thermal stability. In
fact, the degradation, considering the 10% weight loss
as reference, occurs at temperature higher than 450°C
thus indicating a very high thermal stability for these
R—CF2—CF2 (Eq. 3)
Propagation: R—CF2—CF2 + n CF2=CF2
R—(CF2—CF2)~~ (Eq. 4)
—*
Termination: R—(CF2—CF2)~÷1 + R~(CF2~CF2)m
R~(CF2~CF2)n+rn+i R (Eq. 5)
R—(CF2—CF2)~~1 + R
—~
R—(CF2—CF2)~~1—R (Eq. 6)
R can be indifferently a perfluoroalkyl or perliuoroalk
oxy radical coming from Eq. 1 and Eq. 2. Due to the
high reactivity of TFE, R rapidly reacts with this mono
mer (Eq. 3) and forms a new pertluoroalkyl radical that
grows by addition of other molecules of TFE (Eq. 4).
The kinetic chain terminates by coupling with another
radical of the same type (Eq. 5) or with a primary radi
cal (Eq. 6).
The final structure of the PFPE-TFE block copolymers
so obtained can be depicted by the following formula:
CF3O—(A) [(B) ]t—A–CF3 (II)
where A is a perfluoropolyether block containing —CF2O—
and —CF2CF2O— units, B is a —(CF2CF2)— polytetrafluoro
ethylene block, t is the number of blocks B per chain.
Physical properties of PFPE—
TFE block copolymers
Table 4
Fluorinated gel compositions
PFPE-TFE copolymers can be liq
uid, wax or solid depending on their
composition. An internal study carried
0
2
4
6
8
Sample
Base oil
Thickener
Sample 3
Sample A (80% by weight)
Sample 1 (20% by weight)
Sample 4
Sample B (80% by weight)
Sample 1 (20% by weight)
10
12
14
16
18
20
22
24
26
TEE
block length
(C atoms)
Figure 2 — PFPE-TFE copolymers physical state as a function of the B block length
_________________________
7
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VOLUME 77, NUMBER 5
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features: they substantially do not separate under
storage or usage. Figure 4 exemplifies as gels appear.
Their characterization is reported in the following
paragraphs.
structures. Low weight loss values (1 and 2%) can be
ascribed to the evaporation of low molecular weight
fractions. As example, in figure 3 is reported the TGA
curve for sample 1 obtained under nitrogen flow with a
heating rate about 10°C/minute. No significant differ
ences were observed using air as carrier gas.
100
Preparation of fluorinated
gel lubricant
90
80
The solid PFPE-TFE copolymer
(sample 1) is soluble in both linear
70
and branched perfluoropolyether oils.
60
When it is dissolved in these oils at
concentration generally higher than
50
c~)
10% by weight, a lubricant gel formu
0)
40
lation is obtained. Two gels were pre
pared; their formulations are reported
30
T 1 % = 308°C
in Table 4, while the characteristics of
T 2% = 339°C
20
the base oils are reported in Table 1.
T 10% = 460°C
They were prepared with the following
10
T 50% = 569°C
procedure: a flask having a volume
0
of 250 ml was filled with the base
0
100
200
300
400
500
600
700
PFPE oil and heated at 240°C. After
Temperature (°C)
30 minutes at that temperature,
Figure 3 TGA curve (N2, 1 0°c/minute) for sample 1
the solid copolymer
(sample 1) was added
Table 5
step by step during
Kinematic viscosities and viscosity index of sample 2
1 hour until the
Kinematic viscosity
Viscosity Index
required gel composi
Sample
Mn (amu)
(cSt; ASTM D445)
(ASTM D2270)
tion was reached. The
20°C
40°C
100°C
mixture was stirred
for 4 hours and then
Sample 2
30000
2901
1433
337
380
passed through a triple
roll mill for final refining
Table 6
before usage.
Experimental data for the samples of gels and perfluorinated grease
The gel differs from
Oil
4-Ball
Friction Torque at T= 40°C
both the perfluorinated
oils, that are fluids,
Sample
Dropping
separation
Wear Scar
Starting
Running
Point (°C)
(%wt) at
Diameter
Torque
Torque
and the perfluorinated
1 20°Cx3Oh
(mm)
(g cm)
(g cm)
greases, that are dis
persions of PTFE pow
Sample3
157
0.80
1.30
2632
777
ders in oils. These new
Sample4
179
3.62
1.48
777
186
gel lubricants have
Sample F
161
3.50
1,40
800
300
some very interesting
—
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—
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NLGI SPOKESMAN, NOVEMBER/DECEMBER 2013
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Rheological properties
The kinematic viscosity of the liquid copolymer
(sample 2) was measured at three different tempera
tures and the values are reported in Table 5 together
with the viscosity index. This product was compared
to high viscous branched and linear PFPE oils, respec
tively sample C and D (see Table 1). Due to the pres
ence of the rigid TFE blocks, the viscosity of the liquid
PFPE-TFE copolymer is much higher than that of the
linear PFPE (sample D), even if the numeric average
molecular weight of the two samples is comparable.
Quite surprisingly the viscosity index, a parameter that
indicates the viscostaticity of the oils [9], does not sig
nificantly differ between the linear PFPE and the copoly
mer whereas, as predictable, it is much higher than that
of the branched structure (sample C) due to the effect,
in this sample, of CF3- side groups along the chain.
In the case of the solid copolymer formulated as gel,
a complete rheological characterization was performed.
In figure 5 the complex viscosities [rl*(w)l measured at
different temperatures are depicted. From these flow
curves it can be inferred that in the range 130-190°C
sample 3 passes from a highly pseudoplastic behavior
(“solid-like”) to an almost Newtonian behavior (“fluid-like”).
Friction torque evaluation at room temperature and
at high-speed
o Four ball wear test
o
For sample 2 in comparison with sample C and D:
o
SRV test
The data on the further characterizations are sum
marized respectively, for the gels in Table 6 and in the
graphs in Figure 6 and 7; whereas for the liquid copoly
mer in Table 7 and in Figure 8. The detailed results are
reported in the paragraphs below.
Figure 4 — Picture of the gel (sample 3)
Lubricant properties for the
PFPE-TFE cop&ymers
The lubricant properties for the
PFPE-TFE copolymers, respectively
the fully fluorinated gels (sample
3 and 4) and oil (sample 2), were
evaluated in comparison with
a perfluorinated grease (sample F)
and oils (sample C and D) as
references:
For sample 3 and 4 in comparison
with sample F:
o Dropping point evaluation
o
Oil separation at 120°C for
30 hours
Friction torque evaluation
at -40°C
T~’I C
1.E+05
T = 70°C
T = 100°C
1 E+04
T
T
=
T
=
=
145° 160°C
1.E+03
13
~1.E+02
190°C
1.E+01
1.E+00
i.E-ni
1.E-02
i.E-02
1.E-01
1.E÷00
Frequency (rad/s)
Figure 5 — Flow curves of sample 3 obtained at different temperatures
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VOLUME 77, NUMBER 5
1.E+01
1.E÷02
NLGÜ
torque test at room temperature and at high speed,
using the machine shown in Figure 1.
Any time the speed was increased, according to the
programmed ramp, the starting torque was registered.
The running torque after 1 hour at the programmed
ramp speed, and the temperature of the external ring of
Eva’uation of the perfluorinated ge’s
The gel samples (sample 3 and 4) were evaluated
according to the standard method for the dropping
point measurement (ASTM 2265) in comparison with
the perfluorinated grease (sample E). During this test
the gels showed different values depending from the
base oil: the sample with linear PFPE as base
90
oil has the highest dropping point. It has to be
noted that the dropping point value is in the
80
interval where the gel change its rheological
70
behavior (range of temperature between 130
E
z 60
and 190°C) as evidenced in the precedent
E
paragraph (see Figure 5).
~50
As far as the separation behavior according
~ 40
to FTMS 791/321 method (at 120°C/30h), the
~ 30
sample 3, whose base oil is a branched PFPE,
C
C
~ 20
showed almost no separation, while sample 4
behavior was similar to the pertluorinated grease
10
one, giving an oil segregation about 3.5%wt.
0
The wear properties for the two gels were
0 2000 4000 6000 8000 10000 12000 14000 16000 18000
evaluated according to ASTM D 2266 method.
rpm
The two gels showed different anti-wear per
formances: sample 3 has the lowest wear
Sample 3 —‘-~Sample 4
Sample E
scar [10]. The differences for the gels could be
Figure 6 Running Torque vs. rpm for perfluorinated gels vs perfluorinated grease
ascribed to the different wear properties of the
base oils; in fact, it is known that the branched
structure gives lower wear values under these
200
test conditions [1; 8].
180
Friction torque was evaluated according to
160
ASTM Dl 478 at —40°C. Among the evaluated
140
/r~
samples, the one with linear PFPE as base oil
120
showed the lowest starting torque and running
100
torque. The differences for the gels could be
80
ascribed to the different rheological behavior
60
of the base oils: in fact, linear PFPEs have a
much better viscostaticity at low temperature
40
than branched structures. Besides, the torque
20
is also influenced from the apparent viscosity of
0
the evaluated greases [11]; this could explain
o 2000 4000 6000 8000 1000012000140001600018000
why the sample 4, which is characterized from
rpm
a lower viscosity than the grease thickened with
PTFE, has a lower running torque.
l~5amp1e3 —k~Sample4 —‘-Sample El
Ball bearings filled with 30% by weight of
Figure 7 Temperature vs. rpm for perfluorinated gels vs perfluorinated grease
these greases were submitted to the friction
—
—~
-~—
—
_
I
—
—37 NLGI SPOKESMAN, NOVEMBER/DECEMBER 2013
NLG~
the bearing were also recorded. During the whole test
a maximum starting torque was observed.
In all experiments, the running torque was always
definitely lower than the starting torque. Moreover,
along the programmed speed ramp, we observed a
general trend in each test: the higher the speed the
lower is the running torque. Interestingly, a family of
curves is generated when plotting running torque/tem
perature vs. the rotating speed, each curve being dis
tinctive of a sample type: gels curves are different from
the reference grease, in particular at rotational speed
> 8000 rpm the running
torque are lower than those
for the reference grease
0
(see Figure 6). In all experiOff
ments it was observed that
£
the gels displayed a con
06
sistent reduction of tern
perature compared with
the perfluorinated grease
(see Figure 7).
corresponds to the value in the steady state. All data
are summarized in the Table 7, while Figure 8 shows
the run of the coefficient of friction during the test for all
the samples under scrutiny.
Under these test conditions the liquid copolymer
showed the lowest wear value compared with the two
reference oils, respectively sample C (branched PFPE)
and 0 (linear PFPE). About coefficient of friction, this
property is close to the linear PFPE behavior, while the
highest value is ascribed to the branched structure.
Sample D
sample c
~ sample 2
~
:~
Evaluation of the
liquid copolymer
The tribological characteristics for the liquid copo
lymers (sample 2) were
evaluated with SRV
tribometer according to
the ASTM 6425 test
method. The wear
scar diameter on the
ball after the test was
evaluated by optical
microscopy; as far as
the coefficient of fric
tion is recorded during
the whole test and its
value at the end of
each experiment were
reported. It has to be
noted that the coef
ficient of friction at the
end of the test (fend)
8)
0
c_)
0:110
1203
2406
3606
14812
10615
~ 1210
12421
13624
14827
Time
Figure 8— The run of the coefficient of friction during SRV test
Kinematic Viscosity at 20GC
8000
‘Jvv
6000
5000
4000
•Sample D1
51 Sample B
•~ 3000
>2000
1000
0
0
10
20
30
40
50
60
70
Percentage of liquid copolymer PFPE-TFE sample 6 (w/w%)
Figure 9
—
change of kinematic viscosity of sample
D
—38—
VOLUME 77, NUMBER 5
and
B by
varying sample 6 content
80
90
NLGII
with the following procedure: a flask having a volume of
250 ml was filled with the base oil, which can be PFPE
with linear structure oil or PFPE-TFE copolymer, and
heated at 150°C. Affer 30 minutes at that temperature,
the solid thickener is added step by step during 1 hour
until the required composition was reached. The mix
ture is then stirred for 1 hour and then cooled till room
temperature. The sample consistency was evaluated
PFPE-TFE copolymer as viscosity modifier
The PFPE-TFE copolymer solid and liquid samples are
soluble in perfluoropolyether fluids, so it is possible to
use these products as additive to modify the viscosity
of the fluorinated standard oils.
Adding a sample of liquid copolymer PFPE-TFE
sample 6 to sample B and D, which are linear PFPE
structure chemicals with kinematic viscosity at 20°C of
respectively of about 280 cSt and 1000 cSt,
the kinematic viscosity increases. (Figure 9)
Kinematic viscosity at 20°C
Adding few percentage of the solid copoly
6000
mer sample 5 (melting point 120—140°C) to the
linear PFPE samples B and D, it is possible to
5000
obtain very high viscosity and stable products.
In this case if the amount of the added copoly
p
~ 4000
mer should be lower than 10%, otherwise a gel
ce
St Sample Dl
lubricant was obtained (as explained in a previ
3000
ous paragraph). Using 10% of solid copolymer
>,
as additive, it is possible to increase five times
St
2000
the kinematic viscosity. (Figure 10)
It is possible even to mix the liquid copo
VA
St
1000
lymer PFPE-TFE Sample 6 with the solid
copolymer PFPE-TFE sample 5 increasing its
0
viscosity and obtaining a product with a kine
0
2
4
6
8
10
12
matic viscosity higher than 30,000 cSt at 20°C
Percentage of solid copolymer PFPE-TFE sample 5 (w/w%)
(Figure 11).
Figure 10 change of kinematic viscosity of sample D by varying sample 5 content
Using the liquid and solid copolymer
as additive, it is possible to modify
Kinematic Viscosity at 20°C
the viscosity of the liquid oils and to
fine tuning the viscosity for specific
35000
applications.
—
—
30000
Liquid copolymer PFPE-TFE
as base oil for greases
Usually fully fluorinated greases are
formulated with perfluoropolyether as
base oil and polytetrafluoethylene as
thickener.
Different samples were prepared
starting from PFPE-TFE liquid copo
lymer by using different thickeners in
comparison with formulation coming
from linear PFPE oils sample B (see
Table 1). The samples were prepared
25000
Cl)
~-
>,
20000
e
0
8
0
15000
>
10000
Hq~dPF~E
5000
0
0
Figure 11
—
1
2
3
4
5
Percentage of solid copolymer PFPE-TFE sample 5 (w/w%)
change of kinematic viscosity of sample 6 by varying sample 5 content
—39 NLG~ SPOKESMAN, NOVEMBER/DECEMBER 2013
6
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through ASTM D21 7 method. The results are summa
rized in Table 9.
Surprisingly and unexpectedly when micronized
PTFE is used as thickener the samples based on
PFPE-TFE liquid copolymer differ from the ones based
on PFPE oils: in fact, the formulations based on the
copolymer are still fluid even if the viscosity of the oil
and the filler amount (>40%wt) are higher than for
standard perfluorinated greases. This behavior isn’t
observed if another thickener, for example silica micropowder, is added: in fact, in this case, the consistency
of the final formulation is exactly the same for both
types of base oils.
greases, are transparent or semitransparent and do not
separate under storage or usage. In addition, the gels
showed improved performances in terms of starting/
running torque during the tests performed at different
temperatures and rotational speeds.
Even if these systems are still under evaluation and
optimization, we can conclude that due to their out
standing properties the new PFPE-TFE copolymers
could be used as lubricants in a variety of high-per
formance applications as well as to lubricate precision
mechanical instruments to minimize mechanical wear
and, due to the absence of solid particle, noise.
Besides due to the high compatibility of the PFPE
TFE liquid copolymers with the PTFE powder, this
outstanding behavior can lead to several advantages.
As example it is possible to have a fluid formulation
with less oil amount, with different viscosities and
even improved performances under extreme pressure
CONCLUS~ONS
PFPE-TFE copolymers are new-to-the-world products
obtainable by means of an innovative technological
platform recently developed by Solvay Specialty
Polymers. Being block copolymers, they
Table 7
Experimental
data
for
the
liquid copolymer and PFPE oils
combine the lubricant properties typical of the
perfluoropolyethers with those of the perfluo
Wear Scar
Coefficient of friction at t=1 20
Sample
Diameter (mm)
minutes (f end)
ropolymers, such as an extremely high thermal
and chemical stability. Their physical state can
Sample2
1.13
0.119
be liquid or solid, depending on the length of
SampleC
1.22
0.154
the TFE blocks, always maintaining the solubility
Sample D
1.41
0.118
in fluorinated solvents and oils. This property,
in particular, has been successfully exploited
Table 8
for the preparation, by dissolution of the solid
Kinematic viscosities and viscosity index of sample 6
PFPE-TFE copolymers in PFPE oils, of perfluo
Kinematic visocisty
Viscosity Index
Mn
(cSt; ASTM D445)
(ASTM D2270)
rinated lubricants in the form of gels that have
Sample
(amu)
never been obtained before.
20°C
40°C
100°C
In the present work we have evaluated the
Sample 6
12700
4400
500
300
30000
main tribological and rheological properties of
one liquid PFPE-TFE copolymer and of two
Table 9
Characterization Formulated sample
gel lubricants. They are reported together with
with ASTM D 217 test method
those of commercial perfluoropolyether oils and
Base Oil
Thickener
NLGI Grade
perfluorinated grease as references.
Sample B
PTFE (25% by weight)
1
Among the most relevant properties of the
liquid PFPE-TFE copolymer, we can highlight
Sample B
PTFE (30% by weight)
2
the very good viscostaticity, since the viscosity
Sample 2
PTFE (40% by weight)
0/00
index remain high despite the molecular weight
Sample 2
PTFE (45% by weight)
0
of these copolymers, and the wear values which
Sample B
Silica (2, 5% by weight)
2
are lower than that of linear and branched PFPE
Sample 2
Silica (2, 5% by weight)
2
oils. The lubricant gels, unlike perfluorinated
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VOLUME 77, NUMBER 5
NLG~
conditions and lower evaporation weight loss at high
temperature.
Due to all above features formulations of PFPE-TFE
liquid copolymers and PTFE could be applied to lubri
cate, for example, chain systems under extreme tem
perature conditions where the weight loss performance
is really important.
[3] M. Avataneo, PA. Guarda, G. Marchionni, P.
Maccone, G. Boccaletti US Patent 2010105584
[4] M. Avataneo, W. Navarrini, U. De Patto, C.
Marchionni, J. Fuorine Chern., 130, (2009) 933-937
[5] G. Marchionni, M. Avataneo, P. A. Guarda, Fur. Pat.
AppI. 2100909 (2008);
[6] http ://www.solvayplastics. corn
[7] D. Sianesi, G. Marchionni, R,J. De Pasquale,
in: R.E. Banks, BE. Smart, J.C. Tatlow (Eds.),
Organofluorine Chemistry: Principles and
Commercial Applications, Plenum Press, New York,
1994, pp. 431—461
ACKNOWLEDGEMENT
The authors would like to thank Davide Vicino, Andrea
Pepe Marco Beltramin and Claudia Zani for their sup
port and Solvay Specialty Polymers for the permission
to present this work.
[8] Solvay Specialty Polymers internal data
[9] T. Mang and W. Dresel, Lubricants and Lubrication,
Wiley-VCH Gmbh, Weinheirn, p. 13, 2005
REFERENCES
[1] G. Marchionni, G. Ajroldi, G. Pezzin, in: S.L.
Aggarwal, S. Russo (Eds.), Comprehensive Polymer
Science, Second Supplement, Pergamon, London,
1996, pp. 347—388
[10] P Maccone, G. Boccaletti, Fluorinated Grease
Lubricants, TAE 2006
[11] Thelen, Devine, Stallings The starting Torques
and Rheology of Lubricating greases at low
temperature Journal of American Society of
Lubrication Engineers 1971 pp 305 310
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[2] G. Marchionni, G.T. Viola, U.S. Patent 4 668 357, 1987
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ABOUT THE AUTHORS
Giovanni Boccaletti Solvay Specialty
Polymers Italy Spa. Giovanni obtained
his Ph.D. in Chemistry from the Univer
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sity of Padova (2002). Post doctoral
fellowship at University of Ban work
ing on Platinum Cationic Complexes.
Since 2004, he has worked for Solvay
as a Technical Marketing Engineer and
Researcher in the PFPE’s Application
Development and Lubrification Labs.
Marco Avantaneo Solvay Specialty
Polymers Italy S.p.a. Marco earned
his degree in Industrial Chemistry with
specialization in macromolecular chem
istry from the University of Turin (Italy)
in 1999. From 2001 -2008, he was a
researcher in the field of pertluoropoly
ethers and oxyradicals chemistry. Since
2008, he has been R&D Manager of the
Innovative Fluoromaterials group, whose
research activities are focused on the
development of new fluorinated and perfluorinated materials.
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NLGI SPOKESMAN, NOVEMBER/DECEMBER 2013
Sara Rovinetti
Solvay Specialty
Polymers Italy S.p.a.
Rovinetti
received her Masters degree in Industrial
Chemistry at Bologna University (Italy)
in 2005. She joined Solvay Specialty
Polymers in 2006 as a researcher
in the Perfluoro-polyethers Fluids and
Auxiliaries Application Development labs.
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Emanuele DiNicolo Solvay Specialty
Polymers Italy S.p.a. Mr. DiNicolo grad
uated in Physics from the University of
Bologna in 1997, and earned his Master
of Philosophy degree in Physics from
the University of Southhampton in 2001.
Since 2000, he has been responsible
for the Laboratory of Rheology in the
Material Science Department, and in
2010 assumed the manager position of
the Membrane Lab.
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