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Fluid Resistance of TFE-Olefin Fluoroelastomers
9 Fluid Resistance of TFE-Olefin Fluoroelastomers � 9.1 � Introduction TFE-olefin fluoroelastomers (ASTM designation FEPM) are resistant to strong aqueous base and organic amines that attack VDF-based FKM fluoroelastomers (See Ch. 7). The major FEPM is TFE/ propylene copolymer, a nearly alternating polymer with a slight excess of TFE over propylene units. In the Aflas 100 copolymer series made by Asahi Glass, heat treatment is used to generate enough unsaturation to allow peroxide curing. The resulting TFE/P vulcanizates have excellent base resistance and exhibit relatively low swell in polar solvents. However, swell in hydrocarbons, especially aromatics, is high because of the low fluorine content (about 56%). Also, low-temperature flexibility is poor, with vulcanizate TR-10 about 0°C, and the peroxide cure limits continuous service to a maximum temperature of about 220°C. Various terpolymers of TFE/P/VDF have been developed to allow bisphenol curing, with resultant better processing behavior and improved heat resistance. Depending on VDF level, base resistance is somewhat compromised, while hydrocarbon swell is reduced because of higher fluorine content (57%59%). More efficient bisphenol curing has been attained in TFE/P elastomers by the incorporation of small amounts of trifluoropropylene (TFP), CH2=CHCF3. The ratio of TFE to propylene units can also be increased in these terpolymers to get higher fluorine content (58%59%) and reduced swell in hydrocarbons, while retaining excellent base resistance. A specialty FEPM elastomer, ethylene/TFE/ PMVE terpolymer with halogen cure sites for peroxide curing, also has excellent base resistance, since ethylene units flanked by TFE or PMVE units are resistant to dehydrofluorination. Vulcanizates have better low-temperature flexibility than TFE/P, and with the nonpolar nature and higher fluorine content (67%) of the polymer, show low swell in both polar and nonpolar solvents.
9.2 � Fluid Resistance of TFE/ Propylene Elastomers Table 9.1 is a tabulation of chemical resistance data for TFE-propylene copolymer and TFE/P/VDF terpolymer, taken from a previous volume in the PDL Handbook Series.[1] The data were obtained on vulcanizates of heat-treated TFE/P Aflas copolymer made by Asahi Glass and sold in the U.S. by 3M (Dyneon), designated as 3M Aflas (TFP copolymer), or on vulcanizates of TFE/P/VDF terpolymer (probably Aflas 200 made by Asahi Glass) precompounded with bisphenol and accelerator by 3M (Dyneon), designated as 3M Fluorel II FX 11900 (TFP terpolymer). The choice of fluids in Table 9.1 gives a good picture of the suitability of these polymers for service in a wide range of environments. (See Appendix for a description of the PDL Ratings shown in the table.)
9.2.1
TFE/P Dipolymer
From Table 9.1, peroxide-cured vulcanizates of TFE/P dipolymer have excellent resistance to steam, inorganic base, motor oils, lubricants, and oil field mixtures such as sour gas. The vulcanizates have high swell in hydrocarbons and fuels, especially with aromatics present, and relatively high swell in ketones, esters, ethers, and some chlorinated solvents. A typical formulation for medium hardness is:[2] Aflas TFE/P dipolymer MT Black N990
100 30
Peroxide, Vul-Cup 40KE
4
TAIC
4
Sodium stearate
1
The peroxide often used is 2,2´-bis(t-butylperoxy)diisopropylbenzene. For higher hardness and modulus, black level may be increased (furnace black may be added), and also peroxide and/or trap may be increased. Sodium stearate is often used for better release from mill rolls or molds. Dyneon offers five grades of dipolymers differing in molecular weight.[2] In the formulation above, these give typical physical properties as listed in Table 9.2.
228
Table 9.1 Tetrafluoroethylene Propylene Copolymer and Terpolymer[1]
(Contd.)
Table 9.1 (Contd.)
229
(Contd.)
230
Table 9.1 (Contd.)
(Contd.)
Table 9.1 (Contd.)
231
(Contd.)
232
Table 9.1 (Contd.)
9 FLUID RESISTANCE OF TFE-OLEFIN FLUOROELASTOMERS
233
Table 9.2 Properties of TFE/P Dipolymer Compounds[2]
Polymer (Aflas FA):
100H
100S
150P
150E
150L
ML, in-lb
30
24
14
7
3
MH, in-lb
68
70
60
46
43
ts2, minutes
1.3
1.4
1.6
1.7
1.9
tc90, minutes
6.7
7.1
7.7
8.3
8.8
ODR, 177°C, 3° arc
Typical Physical Properties (press cure 10 min/177°C, post cure 16 h/200°C) M100, MPa
3.9
4.6
4.7
4.1
5.5
TB, MPa
15.8
16.8
14.1
12.3
11.7
EB, %
325
285
270
285
220
72
72
72
73
73
50
44
44
48
42
Hardness, Shore A O-Ring compression set, % 70 hours at 200°C
Heat aging in air at 260°C for 70 hours results in significant loss of modulus and tensile strength, as expected for peroxide-cured vulcanizates.
9.2.2
TFE/P/VDF Terpolymers
The limited data shown for TFE/P/VDF terpolymer vulcanizates in Table 9.1 indicate them to be resistant to automotive lubricants for 7 days: gear lube (150°C), motor oil (163°C), and transmission fluids (163°C). These exposures are not long enough to establish long-term usefulness. The base polymer for Fluorel II probably contains 30%35% VDF, enough for significant reduction of resistance to amine components of these automotive fluids. An early version of Fluorel II was described by W. M. Grootaert et al., in an ACS Rubber Division paper[3] and appears to have been described in more detail in a subsequent patent.[4] The base polymer exemplified has approximate composition TFE/P/VDF = 42/28/30 mole % (about 59% fluorine) and is precompounded with a tributyl(2-methoxy)propyl phosphonium Bisphenol AF curative complex along
with tetramethylene sulfone and dimethyl sulfone as additional accelerators and processing aids. The final compounds for curing also contain the usual ingredients 6 phr calcium hydroxide and 3 phr highactivity magnesium oxide along with filler such as 30 phr MT Black N990. Later, bisphenol-curable TFE/P/VDF terpolymers with lower VDF content (10%15%) were developed to get better base resistance. These terpolymer products are marketed as Dyneon Base Resistance Elastomers, with lowVDF terpolymers designated as the BRE 7100 series and high-VDF terpolymers designated as the BRE 7200 series. Both are more resistant to basic fluids than VDF/HFP/TFE FKM fluoroelastomers, but less resistant than TFE/P dipolymers. Significant differences show up in extended exposures to such fluids at elevated temperatures, as shown in a recent paper by J. G. Bauerle and P. L. Tang. [5] Vulcanizates of TFE/P dipolymer and TFE/P/VDF terpolymers with varying VDF content were exposed at 150°C to an aggressive test oil, ASTM Reference Oil 105, and changes in elongation at break were reported for exposures as long as 12 weeks, as shown in Table 9.3.
234
FLUOROELASTOMERS HANDBOOK
Table 9.3 TFE/P Dipolymer and TFE/P/VDF Tripolymer Vulcanizates: Percent Change in EB after Oil Aging at 150°C[5]
% VDF in Polymer
Exposure time, hours 500
1000
2000
0
-10
-13
-22
10
-18
-26
-42
16
-40
-47
-65
30
-48
-65
-82
Thus, TFE/P/VDF terpolymers exhibit intermediate resistance to aqueous base and amine-containing fluids, so the severity of the fluid exposure conditions needs to be evaluated carefully before deciding on suitability for the service. As noted in Sec. 5.4, TFE/P/VDF terpolymers treated with strong base undergo dehydrofluorination at VDF sites. Most of the resulting unsaturated sites are not susceptible to nucleophilic attack (e.g., polyamines in hydrocarbon automotive lubricants), so vulcanizates usually do not fail by surface cracking and embrittlement. However, such sites are subject to hydrolysis and chain scission in aqueous base.
9.2.3
TFE/P/TFP Terpolymers
Elastomeric copolymers of TFE and propylene with small amounts of trifluoropropylene (TFP), CH2=CHCF3, are curable with bisphenol and can be made with relatively high fluorine content.[6] As discussed in Sec. 5.4, W. W. Schmiegel has shown that treatment of these terpolymers with strong base results in dehydrofluorination only at TFP sites.[7] J. G. Bauerle and P. L. Tang[5] show that vulcanizates of TFE/P/TFP terpolymer are less affected by exposure to an aggressive test oil than any of the TFE/P/VDF polymers listed in Table 9.3, including the TFE/P dipolymer. In general, TFE/P/ TFP vulcanizates have fluid resistance similar to that of TFE/P dipolymer, but exhibit lower swell in hydrocarbons because of higher fluorine content. Bisphenol-cured TFE/P/TFP has better heat resistance than peroxide-cured TFE/P dipolymer or TFE/P/VDF terpolymers.
Cure characteristics, physical properties, and resistance to heat and oil are shown in Table 9.4 for compounds with various fillers in Viton® Extreme TBR-605CS, a precompound of TFE/P/TFP that contains a proprietary bisphenol-accelerator combination.[8] For this precompound, high activity magnesium oxide is recommended for reasonable cure rates instead of the usual combination of calcium hydroxide and magnesium oxide. Relatively high levels of low-reinforcing fillers such as thermal black (MT, N990) or blanc fixe (barium sulfate) can be used with little reduction in cure rate to get vulcanizates of reasonable modulus and hardness, and with reduced swell in hydrocarbon fluids. Reinforcing furnace blacks (FEF or SRF) can be used at modest levels to get vulcanizates with higher modulus, but with some reduction in cure rate. These fillers would have similar effects in compounds of other TFE/P elastomers. The good heat stability of bisphenol-cured vulcanizates is shown by the minimal change in properties after heat aging in air at 250°C for a week. Vulcanizates of this TFE/P/TFP elastomer also show very good resistance to an aggressive test oil, with little loss of properties after six weeks exposure at 150°C. Changes in elongation were 15% or less for these vulcanizates, comparable to that observed for peroxide-cured TFE/P dipolymer and less than changes noted for TFE/P/VDF terpolymers (See Table 9.3). In addition, the relatively high fluorine content of the TFE/P/TFP terpolymer leads to lower swell in oil and other hydrocarbon fluids. Good sealing performance at high temperature is indicated by low compression set of o-rings.
9 FLUID RESISTANCE OF TFE-OLEFIN FLUOROELASTOMERS
235
����������Effect of Fillers on TFE/P/TFP Compounds[8]
Compound Viton® Extreme TBR-605CS
100
100
100
100
100
100
MgO (high activity)
8
8
8
8
8
8
MT (N990) Carbon Black
10
30
60
SRF (N774) Carbon Black
25
FEF (N550) Carbon Black
20
Blanc Fixe (BaSO4)
60
MDR 2000 at 177°C, 0.5°C ML, dN·m
1.1
1.4
2.2
1.7
1.9
1.5
MH, dN·m
12.6
18.5
30.1
18.1
17.3
16.4
ts2, minutes
1.6
1.5
1.4
2.1
2.4
1.1
tc50, minutes
2.6
3.1
3.9
4.7
5.5
2.1
tc90, minutes
5.4
6.3
8.6
10.2
12.3
4.7
Physical properties - original, press cure 10 min/177°C, post cure 16 h/200°C M100, MPa
3.1
7.2
12.6
9.5
9.9
4.8
TB, MPa
13.9
15.5
15.9
17.9
20.9
11.0
EB, %
280
240
165
175
210
275
Hardness, Shore A, points
66
77
89
79
77
75
Physical properties - heat aged 168 h/ 250°C in oven M100, MPa
2.8
7.6
14.7
8.9
8.6
5.8
TB, MPa
15.7
17.1
17.3
19.2
19.7
10.7
EB, %
285
205
120
185
180
235
Hardness, Shore A, points
64
75
88
78
75
74
Change in physical properties after heat aging M100 change, %
-10
6
17
-6
-13
21
TB change, %
13
10
9
7
-6
-3
EB change, %
2
-15
-27
6
-14
-15
Hardness change, points
-2
-2
-1
-1
-2
-1 ���������
236
FLUOROELASTOMERS HANDBOOK
Table 9.4�(Contd.)
Physical properties - aged 1008 h/150°C in ASTM 105 Oil (5W/30) M100, MPa
2.9
6.7
11.2
9.2
8.0
4.7
TB, MPa
12.5
13.6
13.6
19.4
20.7
11.1
EB, %
255
205
145
195
230
255
Hardness, Shore A, points
61
74
87
75
75
71
Change in physical properties after oil aging M100 change, %
-6
-7
-11
-3
-19
-2
TB change, %
-10
-12
-14
8
-1
1
EB change, %
-9
-15
-12
11
10
-7
Hardness change, points
-5
-3
-2
-4
-2
-4
Volume swell, %
5.4
4.6
3.7
5.1
5.5
4.4
After 70 h at 150°C
15
14
16
17
17
17
After 70 h at 200°C
27
29
33
31
27
31
Compression set, Method B, o-rings, %
9.2.4
Service Recommendations
TFE/P FEPMs are recommended for service in aqueous base or amine-containing fluids at high temperature, applications where VDF-based FKMs may fail in long-term service. TFE/P elastomers are resistant to automotive lubricants and oil well fluids. Peroxide-cured versions are recommended for service in aqueous base. Generally, these products are not recommended for service in automotive or aircraft fuels or other hydrocarbon fluids containing significant fractions of aromatics. Fluid swell may be relatively high in some solvent mixtures; terpolymers with higher fluorine content may be satisfactory in such environments.
9.3 � Fluid Resistance of Ethylene/TFE/PMVE Elastomer Ethylene/TFE/PMVE elastomer (ETP) is a specialty FEPM product designed to have base resistance comparable to TFE/P copolymer, but better
fluid resistance and low-temperature flexibility.[9] The fluorine content of ETP is comparable to that of Viton GFLT and GF, so ETP exhibits low swell in both polar and nonpolar organic fluids. ETP vulcanizates have higher swell in many fluids than perfluoroelastomers (FFKM), but are often usable and have the advantage of better low-temperature characteristics. Because ETP contains ethylene units, it is not resistant to strong oxidizing agents; FFKM should be used in such service. Composition and compounding of ETP elastomers, together with vulcanizate characteristics and comparison of fluid resistance with other fluoroelastomers, are described in Sec. 5.5. Table 5.11 illustrates the wider range of fluid resistance of ETP compared to TFE/P and high-fluorine VDF-based FKM.[10] The description is for the original versions, Viton® Extreme ETP-500 and ETP-900, with a bromine-containing cure-site monomer incorporated to allow peroxide curing. A better-processing version with iodine cure sites, Viton® Extreme ETP600S, has been introduced recently.[11] Both versions have the same broad range of fluid resistance.
9 FLUID RESISTANCE OF TFE-OLEFIN FLUOROELASTOMERS 9.3.1 �
Fluid Resistance Data
ETP elastomers are resistant to a wide range of fluids.[10] With its high fluorine content, ETP is resistant to: Aliphatic and aromatic hydrocarbons Hydraulic fluids Motor oils Fuels and alcohol ETP has good resistance to base-containing fluids and polar fluids: Strong aqueous base EP gear lubricants Ketones Organic amines Methyl-t-butyl ether (MTBE) Complex solvent mixtures � ETP is not recommended for use in: � CFC fluids, (e.g., CFC113, CClF2CCl2F) Effects of several classes of fluids on ETP and other fluoroelastomers are shown in Table 5.11.
9.3.2 �
Resistance to Oil Field Environments
ETP was originally designed for good resistance to strong base and to mixtures of fluids encountered in oil and gas wells. Extensive testing has been carried out at high temperature in fluid mixtures simulating conditions in deep oil wells. Typical results are shown in Table 9.5.[12] The last two fluids simulate oil field environments: an aqueous brine containing hydrogen sulfide and a water-soluble amine to behave like a high concentration of corrosion inhibitor; and a wet, sour oil containing an oil-soluble amine. VDF-containing fluoroelastomers are essentially destroyed and retain no usable properties under these conditions. TFE/ P dipolymer vulcanizates are also resistant to these base-containing fluids, but would swell more in oil than ETP.
9.3.3 �
Cure System Effects
The original ETP polymers with a bromine-containing cure-site monomer are made in a continuous
237 emulsion polymerization process. ETP-500 and ETP900 are cured with peroxide using triallyl isocyanurate (TAIC) or trimethallyl isocyanurate (TMAIC) as radical trap. TMAIC gives somewhat better compression set resistance, but slower cure. A new version, ETP-600S, contains iodine cure sites and is made with a semibatch process designed to give high molecular weight polymer with narrow molecular weight distribution. ETP-600S has better processing characteristics,[11] including better mold flow and extrusion characteristics, better demolding, higher modulus and tensile strength at elevated temperatures, and better compression set resistance. TMAIC is not recommended for curing of ETP-600S. The two versions are compared[11] in the same compound: Polymer 100, MT (N990) Black 30, zinc oxide 3, TAIC 3, and peroxide 3 [45% active 2,5-dimethyl2,5-bis(t-butyl peroxy)hexane on an inert filler]. Results are shown in Table 9.6.
9.3.4 �
Service Recommendations
ETP fluoroelastomer is recommended for service in environments where lower-cost conventional VDF-based FKMs or TFE/P FEPMs are not satisfactory. This may include severe service in automotive, aeronautical, chemical processing, or oil field industries. ETP can also give satisfactory service in many environments for which FFKM perfluoroelastomers are used. However, FFKM may be necessary in applications where swell in fluids must be minimized, and in special uses such as semiconductor manufacturing operations which require both high environmental resistance and no significant contamination from elastomer parts.
Table 9.5 ETP-500 Fluoroelastomer: Exposure to Severe Environments (3 days at 150°C)[12]
Fluid
% Volume Swell
30% KOH
12
Sour brine (10% H2S, 5% amine)
17
Wet sour oil (10% H2S, 5% amine)
12
238
FLUOROELASTOMERS HANDBOOK
Table 9.6 Comparison of ETP Elastomers[11]
Viton Extreme
ETP-900
ETP-600S
ML, dN·m
2.5
1.7
MH, dN·m
14.4
25.4
ts2, minutes
0.5
0.4
tc50, minutes
0.9
0.7
tc90, minutes
3.3
1.6
MDR, 177°C, 0.5° arc
Physical properties - original, cured 7 min/177°C, post cure 16 h/232°C M100, MPa
8.9
9.1
TB, MPa
18.3
19.0
EB, %
201
191
Hardness, Shore A
76
80
Compression set, Method B, O-Rings, % After 70 hours at 200°C
49
43
TR-10, °C
-6
-7
Gehman, T10, °C
-11
-11
TB, % change
-9
-14
EB, % change
12
38
Methyl ethyl ketone (MEK), 23°C
21
18
Toluene, 40ºC
9
9
50/50 MEK/Toluene blend, 40°C
17
16
Methyl t-butyl ether (MTBE)
30
28
Water, 100°C
8
5
30% Potassium hydroxide, 100°C
1
4
ASTM service fluid 105, 150°C
2
2
Wheel bearing lubricant, 150°C
3
3
Shell EP gear lube, 150°C
4
3
Low temperature properties
Physical properties - after heat aging 168 h at 250°C
Volume change, % - after aging 168 h in various fluids
9 FLUID RESISTANCE OF TFE-OLEFIN FLUOROELASTOMERS
239
REFERENCES 1. � Chemical Resistance Volume 2: Elastomers, Thermosets and Rubbers, PDL Handbook Series, Chemical Resistance Tetrafluoroethylene Propylene Copolymer and Terpolymer, Second Edition, pp. 280-284, William Andrew Inc., Norwich, NY (1994) 2. � Chemical Resistance - Aflas TFE Elastomers, Dyneon Technical Information bulletin 98-0504-11515 (January 2001) 3. � W. M. Grootaert, R. E. Kolb, and A. T. Worm, A Novel Fluorocarbon Elastomer for High-Temperature Sealing Applications in Aggressive Motor Oil Environments, paper presented at ACS Rubber Division meeting, Detroit, Michigan (October 17-20, 1989) 4. � W. M. A. Grootaert and R. E. Kolb, U.S. Patent 4,912,171, assigned to Minnesota Mining and Manufacturing Company (March 27, 1990) 5. � J. G. Bauerle and P. L. Tang, A New Development in Base-Resistant Fluoroelastomers, Paper Number 02M-137, SAE World Congress, Detroit, Michigan (March 2002) 6. � J. G. Bauerle and W. W. Schmiegel, U.S. Patent Application Publication No. U.S. 2003/0065132 (April 3, 2003) 7. � W. W. Schmiegel, A Review of Recent Progress in the Design and Reactions of Base-Resistant Fluoroelastomers, paper presented at International Rubber Conference, Nurenberg, Germany (June 30 July 3, 2003) 8. � Viton® Extreme TBR-605CS: A New, Bisphenol-Cure, Base-Resistant Polymer, DuPont Dow Elastomers Technical Information Bulletin VTE-A10197-00-A1003 (October 2003) 9. � A. L. Moore, U.S. Patent 4,694,045, assigned to DuPont Company (September 15, 1987) 10. � R. D. Stevens and A. L. Moore, A New, Unique Viton® Fluoroelastomer With Expanded Fluids Resistance, paper presented at ACS Rubber Division Meeting, Cleveland, Ohio (October 21-27, 1997) 11. � T. M. Dobel and R. D. Stevens, A New Broadly Fluid Resistant Fluoroelastomer Based on APA Technology, Viton® Extreme ETP-S, paper presented at ACS Rubber Division Meeting, Cleveland, Ohio (October 14-17, 2003) 12. � A. L. Moore, Base-Resistant Fluoroelastomers Developed For Severe Environments, Elastomerics, pp. 14-17 (September, 1986)
9.2 � Fluid Resistance of TFE/ Propylene Elastomers Table 9.1 is a tabulation of chemical resistance data for TFE-propylene copolymer and TFE/P/VDF terpolymer, taken from a previous volume in the PDL Handbook Series.[1] The data were obtained on vulcanizates of heat-treated TFE/P Aflas copolymer made by Asahi Glass and sold in the U.S. by 3M (Dyneon), designated as 3M Aflas (TFP copolymer), or on vulcanizates of TFE/P/VDF terpolymer (probably Aflas 200 made by Asahi Glass) precompounded with bisphenol and accelerator by 3M (Dyneon), designated as 3M Fluorel II FX 11900 (TFP terpolymer). The choice of fluids in Table 9.1 gives a good picture of the suitability of these polymers for service in a wide range of environments. (See Appendix for a description of the PDL Ratings shown in the table.)
9.2.1
TFE/P Dipolymer
From Table 9.1, peroxide-cured vulcanizates of TFE/P dipolymer have excellent resistance to steam, inorganic base, motor oils, lubricants, and oil field mixtures such as sour gas. The vulcanizates have high swell in hydrocarbons and fuels, especially with aromatics present, and relatively high swell in ketones, esters, ethers, and some chlorinated solvents. A typical formulation for medium hardness is:[2] Aflas TFE/P dipolymer MT Black N990
100 30
Peroxide, Vul-Cup 40KE
4
TAIC
4
Sodium stearate
1
The peroxide often used is 2,2´-bis(t-butylperoxy)diisopropylbenzene. For higher hardness and modulus, black level may be increased (furnace black may be added), and also peroxide and/or trap may be increased. Sodium stearate is often used for better release from mill rolls or molds. Dyneon offers five grades of dipolymers differing in molecular weight.[2] In the formulation above, these give typical physical properties as listed in Table 9.2.
228
Table 9.1 Tetrafluoroethylene Propylene Copolymer and Terpolymer[1]
(Contd.)
Table 9.1 (Contd.)
229
(Contd.)
230
Table 9.1 (Contd.)
(Contd.)
Table 9.1 (Contd.)
231
(Contd.)
232
Table 9.1 (Contd.)
9 FLUID RESISTANCE OF TFE-OLEFIN FLUOROELASTOMERS
233
Table 9.2 Properties of TFE/P Dipolymer Compounds[2]
Polymer (Aflas FA):
100H
100S
150P
150E
150L
ML, in-lb
30
24
14
7
3
MH, in-lb
68
70
60
46
43
ts2, minutes
1.3
1.4
1.6
1.7
1.9
tc90, minutes
6.7
7.1
7.7
8.3
8.8
ODR, 177°C, 3° arc
Typical Physical Properties (press cure 10 min/177°C, post cure 16 h/200°C) M100, MPa
3.9
4.6
4.7
4.1
5.5
TB, MPa
15.8
16.8
14.1
12.3
11.7
EB, %
325
285
270
285
220
72
72
72
73
73
50
44
44
48
42
Hardness, Shore A O-Ring compression set, % 70 hours at 200°C
Heat aging in air at 260°C for 70 hours results in significant loss of modulus and tensile strength, as expected for peroxide-cured vulcanizates.
9.2.2
TFE/P/VDF Terpolymers
The limited data shown for TFE/P/VDF terpolymer vulcanizates in Table 9.1 indicate them to be resistant to automotive lubricants for 7 days: gear lube (150°C), motor oil (163°C), and transmission fluids (163°C). These exposures are not long enough to establish long-term usefulness. The base polymer for Fluorel II probably contains 30%35% VDF, enough for significant reduction of resistance to amine components of these automotive fluids. An early version of Fluorel II was described by W. M. Grootaert et al., in an ACS Rubber Division paper[3] and appears to have been described in more detail in a subsequent patent.[4] The base polymer exemplified has approximate composition TFE/P/VDF = 42/28/30 mole % (about 59% fluorine) and is precompounded with a tributyl(2-methoxy)propyl phosphonium Bisphenol AF curative complex along
with tetramethylene sulfone and dimethyl sulfone as additional accelerators and processing aids. The final compounds for curing also contain the usual ingredients 6 phr calcium hydroxide and 3 phr highactivity magnesium oxide along with filler such as 30 phr MT Black N990. Later, bisphenol-curable TFE/P/VDF terpolymers with lower VDF content (10%15%) were developed to get better base resistance. These terpolymer products are marketed as Dyneon Base Resistance Elastomers, with lowVDF terpolymers designated as the BRE 7100 series and high-VDF terpolymers designated as the BRE 7200 series. Both are more resistant to basic fluids than VDF/HFP/TFE FKM fluoroelastomers, but less resistant than TFE/P dipolymers. Significant differences show up in extended exposures to such fluids at elevated temperatures, as shown in a recent paper by J. G. Bauerle and P. L. Tang. [5] Vulcanizates of TFE/P dipolymer and TFE/P/VDF terpolymers with varying VDF content were exposed at 150°C to an aggressive test oil, ASTM Reference Oil 105, and changes in elongation at break were reported for exposures as long as 12 weeks, as shown in Table 9.3.
234
FLUOROELASTOMERS HANDBOOK
Table 9.3 TFE/P Dipolymer and TFE/P/VDF Tripolymer Vulcanizates: Percent Change in EB after Oil Aging at 150°C[5]
% VDF in Polymer
Exposure time, hours 500
1000
2000
0
-10
-13
-22
10
-18
-26
-42
16
-40
-47
-65
30
-48
-65
-82
Thus, TFE/P/VDF terpolymers exhibit intermediate resistance to aqueous base and amine-containing fluids, so the severity of the fluid exposure conditions needs to be evaluated carefully before deciding on suitability for the service. As noted in Sec. 5.4, TFE/P/VDF terpolymers treated with strong base undergo dehydrofluorination at VDF sites. Most of the resulting unsaturated sites are not susceptible to nucleophilic attack (e.g., polyamines in hydrocarbon automotive lubricants), so vulcanizates usually do not fail by surface cracking and embrittlement. However, such sites are subject to hydrolysis and chain scission in aqueous base.
9.2.3
TFE/P/TFP Terpolymers
Elastomeric copolymers of TFE and propylene with small amounts of trifluoropropylene (TFP), CH2=CHCF3, are curable with bisphenol and can be made with relatively high fluorine content.[6] As discussed in Sec. 5.4, W. W. Schmiegel has shown that treatment of these terpolymers with strong base results in dehydrofluorination only at TFP sites.[7] J. G. Bauerle and P. L. Tang[5] show that vulcanizates of TFE/P/TFP terpolymer are less affected by exposure to an aggressive test oil than any of the TFE/P/VDF polymers listed in Table 9.3, including the TFE/P dipolymer. In general, TFE/P/ TFP vulcanizates have fluid resistance similar to that of TFE/P dipolymer, but exhibit lower swell in hydrocarbons because of higher fluorine content. Bisphenol-cured TFE/P/TFP has better heat resistance than peroxide-cured TFE/P dipolymer or TFE/P/VDF terpolymers.
Cure characteristics, physical properties, and resistance to heat and oil are shown in Table 9.4 for compounds with various fillers in Viton® Extreme TBR-605CS, a precompound of TFE/P/TFP that contains a proprietary bisphenol-accelerator combination.[8] For this precompound, high activity magnesium oxide is recommended for reasonable cure rates instead of the usual combination of calcium hydroxide and magnesium oxide. Relatively high levels of low-reinforcing fillers such as thermal black (MT, N990) or blanc fixe (barium sulfate) can be used with little reduction in cure rate to get vulcanizates of reasonable modulus and hardness, and with reduced swell in hydrocarbon fluids. Reinforcing furnace blacks (FEF or SRF) can be used at modest levels to get vulcanizates with higher modulus, but with some reduction in cure rate. These fillers would have similar effects in compounds of other TFE/P elastomers. The good heat stability of bisphenol-cured vulcanizates is shown by the minimal change in properties after heat aging in air at 250°C for a week. Vulcanizates of this TFE/P/TFP elastomer also show very good resistance to an aggressive test oil, with little loss of properties after six weeks exposure at 150°C. Changes in elongation were 15% or less for these vulcanizates, comparable to that observed for peroxide-cured TFE/P dipolymer and less than changes noted for TFE/P/VDF terpolymers (See Table 9.3). In addition, the relatively high fluorine content of the TFE/P/TFP terpolymer leads to lower swell in oil and other hydrocarbon fluids. Good sealing performance at high temperature is indicated by low compression set of o-rings.
9 FLUID RESISTANCE OF TFE-OLEFIN FLUOROELASTOMERS
235
����������Effect of Fillers on TFE/P/TFP Compounds[8]
Compound Viton® Extreme TBR-605CS
100
100
100
100
100
100
MgO (high activity)
8
8
8
8
8
8
MT (N990) Carbon Black
10
30
60
SRF (N774) Carbon Black
25
FEF (N550) Carbon Black
20
Blanc Fixe (BaSO4)
60
MDR 2000 at 177°C, 0.5°C ML, dN·m
1.1
1.4
2.2
1.7
1.9
1.5
MH, dN·m
12.6
18.5
30.1
18.1
17.3
16.4
ts2, minutes
1.6
1.5
1.4
2.1
2.4
1.1
tc50, minutes
2.6
3.1
3.9
4.7
5.5
2.1
tc90, minutes
5.4
6.3
8.6
10.2
12.3
4.7
Physical properties - original, press cure 10 min/177°C, post cure 16 h/200°C M100, MPa
3.1
7.2
12.6
9.5
9.9
4.8
TB, MPa
13.9
15.5
15.9
17.9
20.9
11.0
EB, %
280
240
165
175
210
275
Hardness, Shore A, points
66
77
89
79
77
75
Physical properties - heat aged 168 h/ 250°C in oven M100, MPa
2.8
7.6
14.7
8.9
8.6
5.8
TB, MPa
15.7
17.1
17.3
19.2
19.7
10.7
EB, %
285
205
120
185
180
235
Hardness, Shore A, points
64
75
88
78
75
74
Change in physical properties after heat aging M100 change, %
-10
6
17
-6
-13
21
TB change, %
13
10
9
7
-6
-3
EB change, %
2
-15
-27
6
-14
-15
Hardness change, points
-2
-2
-1
-1
-2
-1 ���������
236
FLUOROELASTOMERS HANDBOOK
Table 9.4�(Contd.)
Physical properties - aged 1008 h/150°C in ASTM 105 Oil (5W/30) M100, MPa
2.9
6.7
11.2
9.2
8.0
4.7
TB, MPa
12.5
13.6
13.6
19.4
20.7
11.1
EB, %
255
205
145
195
230
255
Hardness, Shore A, points
61
74
87
75
75
71
Change in physical properties after oil aging M100 change, %
-6
-7
-11
-3
-19
-2
TB change, %
-10
-12
-14
8
-1
1
EB change, %
-9
-15
-12
11
10
-7
Hardness change, points
-5
-3
-2
-4
-2
-4
Volume swell, %
5.4
4.6
3.7
5.1
5.5
4.4
After 70 h at 150°C
15
14
16
17
17
17
After 70 h at 200°C
27
29
33
31
27
31
Compression set, Method B, o-rings, %
9.2.4
Service Recommendations
TFE/P FEPMs are recommended for service in aqueous base or amine-containing fluids at high temperature, applications where VDF-based FKMs may fail in long-term service. TFE/P elastomers are resistant to automotive lubricants and oil well fluids. Peroxide-cured versions are recommended for service in aqueous base. Generally, these products are not recommended for service in automotive or aircraft fuels or other hydrocarbon fluids containing significant fractions of aromatics. Fluid swell may be relatively high in some solvent mixtures; terpolymers with higher fluorine content may be satisfactory in such environments.
9.3 � Fluid Resistance of Ethylene/TFE/PMVE Elastomer Ethylene/TFE/PMVE elastomer (ETP) is a specialty FEPM product designed to have base resistance comparable to TFE/P copolymer, but better
fluid resistance and low-temperature flexibility.[9] The fluorine content of ETP is comparable to that of Viton GFLT and GF, so ETP exhibits low swell in both polar and nonpolar organic fluids. ETP vulcanizates have higher swell in many fluids than perfluoroelastomers (FFKM), but are often usable and have the advantage of better low-temperature characteristics. Because ETP contains ethylene units, it is not resistant to strong oxidizing agents; FFKM should be used in such service. Composition and compounding of ETP elastomers, together with vulcanizate characteristics and comparison of fluid resistance with other fluoroelastomers, are described in Sec. 5.5. Table 5.11 illustrates the wider range of fluid resistance of ETP compared to TFE/P and high-fluorine VDF-based FKM.[10] The description is for the original versions, Viton® Extreme ETP-500 and ETP-900, with a bromine-containing cure-site monomer incorporated to allow peroxide curing. A better-processing version with iodine cure sites, Viton® Extreme ETP600S, has been introduced recently.[11] Both versions have the same broad range of fluid resistance.
9 FLUID RESISTANCE OF TFE-OLEFIN FLUOROELASTOMERS 9.3.1 �
Fluid Resistance Data
ETP elastomers are resistant to a wide range of fluids.[10] With its high fluorine content, ETP is resistant to: Aliphatic and aromatic hydrocarbons Hydraulic fluids Motor oils Fuels and alcohol ETP has good resistance to base-containing fluids and polar fluids: Strong aqueous base EP gear lubricants Ketones Organic amines Methyl-t-butyl ether (MTBE) Complex solvent mixtures � ETP is not recommended for use in: � CFC fluids, (e.g., CFC113, CClF2CCl2F) Effects of several classes of fluids on ETP and other fluoroelastomers are shown in Table 5.11.
9.3.2 �
Resistance to Oil Field Environments
ETP was originally designed for good resistance to strong base and to mixtures of fluids encountered in oil and gas wells. Extensive testing has been carried out at high temperature in fluid mixtures simulating conditions in deep oil wells. Typical results are shown in Table 9.5.[12] The last two fluids simulate oil field environments: an aqueous brine containing hydrogen sulfide and a water-soluble amine to behave like a high concentration of corrosion inhibitor; and a wet, sour oil containing an oil-soluble amine. VDF-containing fluoroelastomers are essentially destroyed and retain no usable properties under these conditions. TFE/ P dipolymer vulcanizates are also resistant to these base-containing fluids, but would swell more in oil than ETP.
9.3.3 �
Cure System Effects
The original ETP polymers with a bromine-containing cure-site monomer are made in a continuous
237 emulsion polymerization process. ETP-500 and ETP900 are cured with peroxide using triallyl isocyanurate (TAIC) or trimethallyl isocyanurate (TMAIC) as radical trap. TMAIC gives somewhat better compression set resistance, but slower cure. A new version, ETP-600S, contains iodine cure sites and is made with a semibatch process designed to give high molecular weight polymer with narrow molecular weight distribution. ETP-600S has better processing characteristics,[11] including better mold flow and extrusion characteristics, better demolding, higher modulus and tensile strength at elevated temperatures, and better compression set resistance. TMAIC is not recommended for curing of ETP-600S. The two versions are compared[11] in the same compound: Polymer 100, MT (N990) Black 30, zinc oxide 3, TAIC 3, and peroxide 3 [45% active 2,5-dimethyl2,5-bis(t-butyl peroxy)hexane on an inert filler]. Results are shown in Table 9.6.
9.3.4 �
Service Recommendations
ETP fluoroelastomer is recommended for service in environments where lower-cost conventional VDF-based FKMs or TFE/P FEPMs are not satisfactory. This may include severe service in automotive, aeronautical, chemical processing, or oil field industries. ETP can also give satisfactory service in many environments for which FFKM perfluoroelastomers are used. However, FFKM may be necessary in applications where swell in fluids must be minimized, and in special uses such as semiconductor manufacturing operations which require both high environmental resistance and no significant contamination from elastomer parts.
Table 9.5 ETP-500 Fluoroelastomer: Exposure to Severe Environments (3 days at 150°C)[12]
Fluid
% Volume Swell
30% KOH
12
Sour brine (10% H2S, 5% amine)
17
Wet sour oil (10% H2S, 5% amine)
12
238
FLUOROELASTOMERS HANDBOOK
Table 9.6 Comparison of ETP Elastomers[11]
Viton Extreme
ETP-900
ETP-600S
ML, dN·m
2.5
1.7
MH, dN·m
14.4
25.4
ts2, minutes
0.5
0.4
tc50, minutes
0.9
0.7
tc90, minutes
3.3
1.6
MDR, 177°C, 0.5° arc
Physical properties - original, cured 7 min/177°C, post cure 16 h/232°C M100, MPa
8.9
9.1
TB, MPa
18.3
19.0
EB, %
201
191
Hardness, Shore A
76
80
Compression set, Method B, O-Rings, % After 70 hours at 200°C
49
43
TR-10, °C
-6
-7
Gehman, T10, °C
-11
-11
TB, % change
-9
-14
EB, % change
12
38
Methyl ethyl ketone (MEK), 23°C
21
18
Toluene, 40ºC
9
9
50/50 MEK/Toluene blend, 40°C
17
16
Methyl t-butyl ether (MTBE)
30
28
Water, 100°C
8
5
30% Potassium hydroxide, 100°C
1
4
ASTM service fluid 105, 150°C
2
2
Wheel bearing lubricant, 150°C
3
3
Shell EP gear lube, 150°C
4
3
Low temperature properties
Physical properties - after heat aging 168 h at 250°C
Volume change, % - after aging 168 h in various fluids
9 FLUID RESISTANCE OF TFE-OLEFIN FLUOROELASTOMERS
239
REFERENCES 1. � Chemical Resistance Volume 2: Elastomers, Thermosets and Rubbers, PDL Handbook Series, Chemical Resistance Tetrafluoroethylene Propylene Copolymer and Terpolymer, Second Edition, pp. 280-284, William Andrew Inc., Norwich, NY (1994) 2. � Chemical Resistance - Aflas TFE Elastomers, Dyneon Technical Information bulletin 98-0504-11515 (January 2001) 3. � W. M. Grootaert, R. E. Kolb, and A. T. Worm, A Novel Fluorocarbon Elastomer for High-Temperature Sealing Applications in Aggressive Motor Oil Environments, paper presented at ACS Rubber Division meeting, Detroit, Michigan (October 17-20, 1989) 4. � W. M. A. Grootaert and R. E. Kolb, U.S. Patent 4,912,171, assigned to Minnesota Mining and Manufacturing Company (March 27, 1990) 5. � J. G. Bauerle and P. L. Tang, A New Development in Base-Resistant Fluoroelastomers, Paper Number 02M-137, SAE World Congress, Detroit, Michigan (March 2002) 6. � J. G. Bauerle and W. W. Schmiegel, U.S. Patent Application Publication No. U.S. 2003/0065132 (April 3, 2003) 7. � W. W. Schmiegel, A Review of Recent Progress in the Design and Reactions of Base-Resistant Fluoroelastomers, paper presented at International Rubber Conference, Nurenberg, Germany (June 30 July 3, 2003) 8. � Viton® Extreme TBR-605CS: A New, Bisphenol-Cure, Base-Resistant Polymer, DuPont Dow Elastomers Technical Information Bulletin VTE-A10197-00-A1003 (October 2003) 9. � A. L. Moore, U.S. Patent 4,694,045, assigned to DuPont Company (September 15, 1987) 10. � R. D. Stevens and A. L. Moore, A New, Unique Viton® Fluoroelastomer With Expanded Fluids Resistance, paper presented at ACS Rubber Division Meeting, Cleveland, Ohio (October 21-27, 1997) 11. � T. M. Dobel and R. D. Stevens, A New Broadly Fluid Resistant Fluoroelastomer Based on APA Technology, Viton® Extreme ETP-S, paper presented at ACS Rubber Division Meeting, Cleveland, Ohio (October 14-17, 2003) 12. � A. L. Moore, Base-Resistant Fluoroelastomers Developed For Severe Environments, Elastomerics, pp. 14-17 (September, 1986)