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Fluoropolymers
9 Fluoropolymers Traditionally, a fluoropolymer or fluoroplastic is defined as a polymer consisting of carbon (C) and fluorine (F). Sometimes these are referred to as perfluoropolymers to distinguish them from partially fluorinated polymers, fluoroelastomers, and other polymers that contain fluorine in their chemical structure. For example, fluorosilicone and fluoroacrylate polymers are not referred to as fluoropolymers. The monomers used to make the various fluoropolymers are shown in Figure 9.1. Details of each of the fluoropolymers are in the following sections. The melting points are all compared in Table 9.1.
9.1 Polytetrafluoroethylene Polytetrafluoroethylene (PTFE) polymer is an example of a linear fluoropolymer. Its structure in simplistic form is shown in Figure 9.2. The CAS number for PTFE is 9002-84-0. Formed by the polymerization of tetrafluoroethylene (TFE), the (aCF2aCF2a) groups repeat many thousands of times. The fundamental properties of fluoropolymers evolve from the atomic structure of fluorine and carbon and their covalent bonding in specific chemical structures. The backbone is formed of carbon carbon bonds and the pendant groups are carbon fluorine bonds. Both are extremely strong bonds. The basic properties of PTFE stem from these two very strong chemical bonds. The size of the fluorine atom allows the formation of a uniform and continuous fluorine covering around the carbon carbon bonds and protects them from chemical attack, thus imparting chemical resistance and stability to the molecule. PTFE is rated for use up to 260°C. PTFE does not dissolve in any known solvent. The fluorine sheath is also responsible for the low surface energy (18 dynes/ cm) and low coefficient of friction (0.05 0.8, static) of PTFE. Another attribute of the uniform fluorine sheath is the electrical inertness (or nonpolarity) of the PTFE molecule. Electrical fields
impart only slight polarization in this molecule, so volume and surface resistivity are high. The PTFE molecule is simple and is quite ordered. This is shown in the three-dimensional models in Figures 9.3 and 9.4. PTFE can align itself with other molecules or other portions of the same molecule. Disordered regions are called amorphous regions. This is important because polymers with high crystallinity require more energy to melt. In other words, they have higher melting points. When highly ordered it forms what is called a crystalline region. Crystalline polymers have a substantial fraction of their mass in the form of parallel, closely packed molecules. High-molecular-weight PTFE resins have high crystallinity and therefore high melting points, typically as high as 320 342°C (608 648°F). The crystallinity of as-polymerized PTFE is typically 92 98%. Further, the viscosity in the molten state (called melt creep viscosity) is so high that high-molecular-weight PTFE particles do not flow even at temperatures above its melting point. They sinter much like powdered metals; they stick to each other at the contact points and combine into larger particles. PTFE is called a homopolymer, a polymer made from a single monomer. Recently many PTFE manufacturers have added minute amounts of other monomers to their PTFE polymerizations to produce alternate grades of PTFE designed for specific applications. Fluoropolymer manufacturers continue to call these grades modified homopolymer at below 1% by weight of comonomer. DuPont grades of this type are called Teflon® NXT Resins. Dyneont TFMt modified PTFE incorporates less than 1% of a comonomer perfluoropropyl vinyl ether (PPVE). Daikin’s modified grade is Polyflont M-111. These modified granular PTFE materials retain the exceptional chemical, thermal, anti-stick, and low-friction properties of conventional PTFE resin, but offer some improvements:
• Weldability • Improved permeation resistance
The Effect of Long Term Thermal Exposure on Plastics and Elastomers. DOI: http://dx.doi.org/10.1016/B978-0-323-22108-5.00009-6 © 2014 Elsevier Inc. All rights reserved.
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• Less creep • Smoother, less porous surfaces • Better high-voltage insulation.
Tetrafluoroethylene (TFE)
Ethylene
Hexafluoropropylene (HFP)
Perfluoromethyl vinyl ether (MVE)
Perfluoroethyl vinyl ether (EVE)
Perfluoropropyl vinyl ether (PVE)
ON
PLASTICS
AND
ELASTOMERS
The copolymers described in the next sections contain significantly more of the non-TFE monomers. Manufacturers and trade names: DuPontt Teflon® PTFE, Dyneon PTFE, Daikin Polyflont, many others
Figure 9.2 Chemical structure of PTFE.
Figure 9.3 Three-dimensional representation of PTFE. Chlorotrifluoroethylene
Vinyl fluoride (VF)
Vinylidene fluoride (VF2)
2,2-Bistrifluoromethyl4,5-difluoro-1,3-dioxole
Figure 9.1 Structures of many monomers used to make fluoropolymers.
Figure 9.4 Ball and stick three-dimensional representation of PTFE.
Table 9.1 Melting Point Ranges of Various Fluoroplastics Fluoroplastic
Melting Point (°C)
Polytetrafluoroethylene (PTFE)
320 340
Polyethylene chlorotrifluoroethylene (ECTFE)
240
Polyethylene tetrafluoroethylene (ETFE)
255 280
Fluorinated ethylene propylene (FEP)
260 270
Perfluoroalkoxy (PFA)
302 310
Perfluoroalkoxy (MFA)
280 290
Polychlorotrifluoroethylene (PCTFE)
210 212
Polyvinylidene fluoride (PVDF)
155 170
9: FLUOROPOLYMERS
185
Applications and uses: Pipe liners, fittings, valves, pumps, and other components used for transferring aggressive, ultrapure fluids. Data for PTFE plastics are contained in Tables 9.2 9.4 and Figures 9.5 9.10.
Table 9.2 Degradation (TGA) Rates of PTFE Fluoroplastics in Air as a Function of Time and Temperature [1] Temperature (°C)
% Weight Loss/h TE to 15 min
TE 1 60 min
Fine Powder
9.2 Fluorinated Ethylene Propylene (FEP) If one of the fluorine atoms on TFE is replaced with a trifluoromethyl group (aCF3), then the new monomer is called hexafluoropropylene (HFP). Polymerization of monomers HFP and TFE yield a fluoropolymer, fluorinated ethylene propylene, called FEP. The number of HFP groups is typically 13% by weight or less and its structure is shown in Figure 9.11. The CAS number for FEP is 25067-11-2. The effect of using HFP is to put a “bump” along the polymer chain as shown in the threedimensional models in Figures 9.12 and 9.13. This bump disrupts the crystallization of the FEP, which has a typical as-polymerized crystallinity of 70% versus 92 98% for PTFE. It also lowers its melting point. The reduction of the melting point depends on the amount of trifluoromethyl groups added and
400
2 0.06
425
0.15
425
0.04a 255c
525
95.0
Granular 350
0.02
350
0.005b
400
0.03
400
0.006b
425
0.06
425
0.06a
a
Hourly rate from 8 to 11.8 h after beginning run. Hourly rate from 3.3 to 6.6 h after beginning run. c Gross decomposition in 1 h. Initial rate 255% per hour. TE 5 thermal equilibrium. b
Table 9.3 Tape Length Required to Abrade Through Wire Coatinga Heat Aging Resin
None
96 h at 150°C
500 h at 150°C
96 h at 200°C
PTFE
191.5
196.6
247
211.7
a
Armstrong Abrasion Test (MIL-T-5438): This test measures abrasion resistance of wire coating by drawing, under load, a clean abrasive cloth tape of continuous length across the test wire until the coating is worn through. A 0.45 load on No. 400 grit tape was used on a coating thickness of 0.038 cm. (Average Tape Length in Centimeters) [2]
Table 9.4 Effects of Oven Aging at 300°C on the Electrical Properties of PTFE Resins [3] Exposure Time at 300°C
Dissipation Factor
Dielectric Constant
Dielectric Strength, kV/mm (ASTM-D-149)
As received
0.0001
2.1
117.1
1 month
0.0001
2.1
3 months
0.0001
2.1
6 months
0.0001
2.1
9 months Note: 125 µm extruded PTFE film.
115.6 118
186
THE EFFECT
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LONG TERM THERMAL EXPOSURE
ON
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AND
ELASTOMERS
Figure 9.5 Thermogravimetric analysis (TGA) of Diakin PTFE [4].
Figure 9.6 Tensile strength versus aging time at 250°C of PTFE Insulated Wire made from Daikin Polyflont PTFE fine powder [5].
secondarily on the molecular weight. Most FEP resins melt around 274°C (525°F), although lower melting points are possible. Even high-molecular-
weight FEP will melt and flow. The high chemical resistance, low surface energy, and good electrical insulation properties of PTFE are retained.
9: FLUOROPOLYMERS
187
Figure 9.7 Elongation versus aging time at 250°C of PTFE Insulated Wire made from Daikin Polyflont PTFE fine powder [5].
Figure 9.8 Specific gravity versus aging time at 380°C of Daikin Polyflont PTFE fine powder [5].
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THE EFFECT
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LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.9 Elongation versus aging time at 380°C of Daikin Polyflont PTFE fine powder [5].
Figure 9.10 Tensile strength versus aging time at 380°C of Daikin Polyflont PTFE fine powder [5].
Figure 9.11 Chemical structure of FEP.
Figure 9.12 Three-dimensional representation of FEP.
9: FLUOROPOLYMERS
189
Data for FEP plastics are contained in Table 9.5 and Figures 9.14 9.16.
9.3 Perfluoroalkoxy (PFA) Figure 9.13 Ball and stick three-dimensional representation of FEP.
Manufacturers and trade names: DuPontt Teflon® FEP, Dyneont THV FEP, Daikin Neoflont. Applications and uses: Applications requiring excellent chemical resistance, superior electrical properties, and high service temperatures. Release films, tubing, cable insulation and jacketing.
Making a more dramatic change in the side group than that done in making FEP, chemists put a perfluoroalkoxy (PFA) group on the polymer chain. This group is signified as OaRf, where Rf can be any number of totally fluorinated carbons. The most common comonomer is perfluoropropyl (aOaCF2aCF2aCF3). However, other comonomers are given in Table 9.6. The polymers based on perfluoropropyl vinyl ether (PVE) are called PFA and the perfluoroalkylvinylether group is typically added at 3.5% or less.
Table 9.5 Degradation (TGA) Rates of FEP Fluoroplastics in Air as a Function of Time and Temperature [1] Temp. (°C)
% Weight Loss/h TE to 15 min
15 65 min
, 0.05
205 300 350
TE 1 60 min
0.45
B0.03
, 0.05
0.13
0.18
375
0.67
400
3.2
TE 5 thermal equilibrium.
Figure 9.14 Tensile strength versus aging time at 200°C of Diakin Neoflon FEP NP-20 [4].
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THE EFFECT
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LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.15 Elongation versus aging time at 200°C of Diakin Neoflont FEP NP-20 [4].
Figure 9.16 TGA of Diakin Neoflont FEP [4].
Table 9.6 PFA Comonomers Comonomer
Structure
Perfluoromethyl vinyl ether (MVE)
CF2QCFaOaCF3
Perfluoroethyl vinyl ether (EVE)
CF2QCFaOaCF2aCF3
Perfluoropropyl vinyl ether (PVE)
CF2QCFaOaCF2aCF2aCF3
9: FLUOROPOLYMERS
191
When the comonomer is Perfluoromethyl vinyl ether (MVE) the polymer is called MFA. A structure of PFA is shown in Figure 9.17. The CAS number of PFA using PVE as comonomer is 26655-00-5. The large side group as shown in Figures 9.18 and 9.19 reduces the crystallinity drastically. The melting point is generally between 305°C and 310° C (581 590°F) depending on the molecular weight. The melt viscosity is also dramatically dependent on the molecular weight. Since PFA is
still perfluorinated as with FEP the high chemical resistance, low surface energy, and good electrical insulation properties are retained. Solvay Solexis Hyflon® MFA and PFA are semicrystalline fully-fluorinated melt-processible fluoropolymers. Hyflon® PFA belongs to the class of PFA having a lower melting point than standard PFA grades. Manufacturers and trade names: DuPontt Teflon®; Solvay Solexis Hyflon®; Dyneont (a 3M Company); Daikin. Applications and uses: Lined and coated processing equipment, vessels and housings, high purity chemical storage. Data for PFA plastics are contained in Table 9.7 and Figures 9.20 9.25.
9.4 Polyvinyl Fluoride Figure 9.17 Chemical structure of PFA.
Polyvinyl fluoride (PVF) is a homopolymer of vinyl fluoride. The molecular structure of PVF is shown in Figure 9.26.
Figure 9.18 Three-dimensional representation of PFA.
Figure 9.19 Ball and stick three-dimensional representation of PFA.
Table 9.7 Degradation (TGA) Rates of Fluoroplastics in Air as a Function of Time and Temperature [1] Resins
Temperature (°C)
% Weight Loss/h TE to 15 min
PFA-1
PFA-2
300
0.18
15 65 min 0.05
TE 1 60 min 0.07
350
0.22
400
0.58
300 350 400
0.12
, 0.05
, 0.05
B0.03
0.05 0.26
192
THE EFFECT
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LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.20 Thermogravimetric analysis (TGA) of Daikin Neoflont PFA [6].
Figure 9.21 Change in tensile strength of PFA wire coating due to thermal exposure in air [7].
DuPontt is the only known manufacturer of this polymer they call Tedlar®. The structure above shows a head-to-tail configuration of the vinyl fluoride (VF) monomer; there are no fluorines on adjacent carbons. But in reality vinyl fluoride polymerizes in both head-to-head and head-to-tail configurations. DuPont’s commercial PVF contains 10 12% of
head-to-head and tail-to-tail units, also called inversions [9]. Its CAS number is 24981-14-4. PVF has excellent resistance to weathering, staining, and chemical attack (except ketones and esters). It exhibits very slow burning and low permeability to vapor. Its most visible use in on the interiors of the passenger compartments of commercial aircraft.
9: FLUOROPOLYMERS
193
Figure 9.22 Change in break elongation of PFA wire coating due to thermal exposure in air [7].
Figure 9.23 Change in melt flow rate of PFA wire coating due to thermal exposure in air [7].
General description: PVF is available only commercially in film form. DuPontt Tedlar® films are available in clear, translucent, or opaque white film and in several surface finishes. Applications and uses: Aircraft interiors, architectural fabrics, curtain walls, roofing, pipe, vessel jacketing, release films, solar panels, wind turbines.
Data for PVF Figures 9.27 9.30.
plastics
are
shown
in
9.5 Polychlorotrifluoroethylene Polychlorotrifluoroethylene (PCTFE) is a homopolymer of chlorotrifluoroethylene, characterized
194
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.24 Strength at break retained of Solvay Solexis Hyflon® MFA F1540 due to thermal aging in air at various temperatures [8].
Figure 9.25 Elongation at break retained of Solvay Solexis Hyflon® MFA F1450 due to thermal aging in air at various temperatures [8].
by the structure shown in Figure 9.31. The CAS number is 9002-83-9. The addition of the one chlorine atom contributes to lowering the melt viscosity to permit extrusion and injection molding. It also contributes to the transparency, the exceptional flow, and the
rigidity characteristics of the polymer. Fluorine is responsible for its chemical inertness and zero moisture absorption. Therefore, PCTFE has unique properties. Its resistance to cold flow, dimensional stability, rigidity, low gas permeability, and low moisture absorption is superior to any other
9: FLUOROPOLYMERS
Figure 9.26 Structure of PVF.
195
fluoropolymer. It can be used at low temperatures. Some products contain a small amount of a comonomer. Manufacturers and trade names: Honeywell Aclar®, Arkema VOLTALEF®, Daikin Industries Neoflon® CTFE.
Figure 9.27 Tensile strength versus hours of aging at 149°C of DuPont Tedlar® PVF films [10].
Figure 9.28 Elongation versus hours of aging at 149°C of DuPont Tedlar® PVF films [10].
196
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.29 Impact strength versus hours of aging at 149°C of DuPont Tedlar® PVF films [10].
Figure 9.30 Flex life versus hours of aging at 149°C of DuPont Tedlar® PVF films [10].
Figure 9.31 Chemical structure of PCTFE.
Applications and uses: Pharmaceutical blister packaging, electroluminescent lamps, liquid crystal display (LCD) panels. Data for PCTFE plastics are contained in Table 9.8 and Figures 9.32 and 9.33.
9: FLUOROPOLYMERS
197
Table 9.8 Rates of Degradation of PCTFE [11] Temperature (°C)
Test Duration (min)
Total Volatilized (%)
Initial Volatilization Rate (%/min)
365
400
78.1
0.20
370
300
82.9
0.28
375
200
75.0
0.42
380
160
82.3
0.58
385
130
83.2
0.84
Figure 9.32 Thermogravimetric analysis (TGA) of Arkema Voltalef® PCTFE [12].
Figure 9.33 Thermal degradation of PCTFE; percentage of sample volatilized versus time [11].
198
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
9.6 Polyvinylidene Fluoride
Key attributes of PVDF include the following:
The polymers made from 1,1-di-fluoro-ethene (or vinylidene fluoride) are known as polyvinylidene fluoride (PVDF). They are resistant to oils and fats, water and steam, and gas and odors, making them of particular value for the food industry. PVDF is known for its exceptional chemical stability and excellent resistance to ultraviolet radiation. It is used chiefly in the production and coating of equipment used in aggressive environments, and where high levels of mechanical and thermal resistance are required. It has also been used in architectural applications as a coating on metal siding where it provides exceptional resistance to environmental exposure. The chemical structure of PVDF is shown in Figure 9.34. Its CAS number is 2493779-9. Some products are copolymers. The alternating aCH2aand aCF2agroups along the polymer chain provide a unique polarity that influences its solubility and electric properties. At elevated temperatures PVDF can be dissolved in polar solvents such as organic esters and amines. This selective solubility offers a way to prepare corrosion-resistant coatings for chemical process equipment and long-life architectural finishes on building panels.
• • • • • • • • • • • •
Mechanical strength and toughness High abrasion resistance High thermal stability High dielectric strength High purity Readily melt processible Resistant to most chemicals and solvents Resistant to ultraviolet and nuclear radiation Resistant to weathering Resistant to fungi Low permeability to most gases and liquids Low flame and smoke characteristics.
Manufacturers and trade names: Arkema Kynar®, Solvay Solexis Solef® and Hylar®. Applications and uses: Electrical wires, tactile sensor arrays, strain gauges, audio transducers, piezoelectric panels, lithium ion batteries, monofilament fishing line, membranes. Data for PVDF plastics are contained in Tables 9.9 and 9.10 and Figures 9.35 9.37.
9.7 Ethylene Tetrafluoroethylene Copolymer Ethylene tetrafluoroethylene (ETFE) is a copolymer of ethylene and TFE. The basic molecular structure of ETFE is shown in Figure 9.38.
Figure 9.34 Chemical structure of PVDF.
Table 9.9 Thermal Aging Tests at Various Temperatures of Solvay Solexis Solef® PVDF 1008 [13] Aging Period (Days)
Tensile Yield Strength (MPa)
Secant Modulus at 1% Deformation (MPa)
Elongation at Break (%)
20°C
120°C
150°C
20°C
120°C
150°C
20°C
120°C
1
50
53
51
1900
1700
1600
9.5
10.5
11.8
11
49
54
51
2000
1900
1800
8.5
10.0
13.0
160
53
54
51
2300
2100
1800
7.0
9.0
11.5
358
54
55
53
2300
2300
2200
7.0
10.0
.11.0
730
52
54
2300
1800
6.6
10.4
RAPRA 5 injection molded specimens.
150°C
Table 9.10 Thermal Aging Tests at 150°C of Solvay Solexis Solef® 11010 PVDF [11] Aging period (h)
0
8
100
1000
Tensile properties Yield stress (MPa)
28
28
29
28
Strength at break (MPa)
41
34
34
40
Elongation at break (%)
.500
.480
.480
.500
Modulus (MPa)
1020
1070
1020
870
113
122
132
149
Thermal properties HDT under 0.46 MPa, °C
Note: Compression molded plates, thickness 2 mm. Rate of pulling: 10 mm/min (modulus: 1 mm/min).
Figure 9.35 Mechanical properties of cables jacketed with Solvay Solexis Solef® 31508/0003 copolymer versus aging at 158°C [11].
Figure 9.36 Change in tensile strength and break elongation of PVDF due to thermal exposure in air at 165°C [14].
200
THE EFFECT
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LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.37 Thermogravimetric analysis (TGA) of Solvay Solexis Solef® PVDF [15].
• Mechanical strength ETFE is good with excellent tensile strength and elongation and has superior physical properties compared to most fluoropolymers.
• With low smoke and flame characteristics, Figure 9.38 Chemical structure of polyethylene tetrafluoroethylene.
It is sometimes called polyethylene tetrafluoroethylene. The depicted structure in Figure 9.38 shows alternating units of TFE and ethylene. While this can be readily made, many grades of ETFE vary the ratio of the two monomers slightly to optimize properties for specific end uses. Its CAS number is 25038-71-5. ETFE is a fluoroplastic with excellent electrical and chemical properties. It also has excellent mechanical properties. ETFE is especially suited for uses requiring high mechanical strength, chemical, thermal, and/or electrical properties. The mechanical properties of ETFE are superior to those of PTFE and FEP. ETFE has the following:
• Excellent resistance to extremes of temperature, ETFE has a working temperature range of 2200°C to 150°C.
• Excellent chemical resistance.
ETFE is rated 94V-0 by the Underwriters Laboratories Inc. It is odorless and non-toxic.
• Outstanding resistance to weather and aging. • Excellent dielectric properties. • Non-stick characteristics. Manufacturers and trade names: DuPontt Tefzel®, Asahi Glass Fluon®, 3M Dyneont. Applications and uses: Electrical and fiber optic wiring, stadium roofing, liner in pipes, tanks, and vessels. Data for ETFE plastics are contained in Tables 9.11 9.16 and Figures 9.39 9.46.
9.8 Ethylene Chlorotrifluoroethylene Copolymer Ethylene chlorotrifluoroethylene copolymer, also called polyethylene chlorotrifluoroethylene or ECTFE, is a copolymer of ethylene and chlorotrifluoroethylene. Its CAS number is 25101-45-5.
9: FLUOROPOLYMERS
201
Table 9.11 Estimated Upper Service Temperatures (°C), No Load Thermal Aging End-of-Life Criterion Based on Elongation for DuPont Tefzel® ETFE [16] End-of-Life Criterion
Exposure Time (h)
Actual Elongation (%)
Elongation Retained (%)
1000
3000
10 k
20 ka
50 ka
100 ka
135
50
210
195
172
159
143
132
18
b
211
188
175
158
147
9
b
b
196
182
165
153
50 25 a
These estimates were extrapolated from 10,000 hour aging results. Estimates are not available for these exposure regions.
b
Table 9.12 Estimated Upper Service Temperatures (°C), No Load Thermal Aging End-of-Life Criterion Based on Tensile Strength for DuPont Tefzel® ETFE [15] End-of-Life Criterion
Exposure Time (h)
Actual Tensile Strength (psi)
Tensile Strength Retained (%)
10 k
20 ka
50 ka
100 ka
3750
50
190
176
159
147
2000
27
204
190
172
158
a
These estimates were extrapolated from 10,000 h aging results.
Table 9.13 Effect of Temperature Aging on Izod Impact Strength, DuPontt Tefzel® HT-2004 [15] Temperature Izod °C
°F
23
73
23 23
Aging
Izod Impact Strength J/m
ft lb/in.
As molded
491
9.1
73
168 h at 150°C (302°F)
491
9.1
73
168 h at 180°C (356°F)
416
7.7
Table 9.14 Initial Weight Loss of DuPontt Tefzel® 200 Resin Above 300°C (572°F) [15] °C
°F
300
572
0.05
330
626
0.26
350
662
0.86
370
698
1.60
% Weight Loss/h
202
THE EFFECT
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AND
ELASTOMERS
Table 9.15 Degradation (TGA) Rates of ETFE in Air as a Function of Time and Temperature [1] Temperature (°C)
% Weight Loss/h TE to 15 min
15 65 min
TE 1 60 min , 0.05
150 260
0.31
0.06
0.11
300
0.42
0.09
0.14
325
0.67 B2
350
6.8
TE 5 thermal equilibrium.
Table 9.16 Grades of Fluon® ETFE for Figure 9.45 [17] Grade
Melt Flow Rate
Melt Index
Characteristic
Application
Molding Method
C-55AP
3.9 6.5
1 2
Standard
General
Extrusion molding
C-88AP
9.0 12.0
3 4
Standard
General
Extrusion molding, injection molding
C-55AP
3.9 6.5
1 2
Stress crack resistant
Wire cover
Extrusion molding
C-88AP
9.0 12.0
3 4
Stress crack resistant
Wire cover
Extrusion molding
Figure 9.39 Retention at various levels of room temperature tensile elongation after heat aging of DuPontt Tefzel® 200 [15].
9: FLUOROPOLYMERS
Figure 9.40 Retention at various levels of room temperature tensile strength after heat aging of DuPontt Tefzel® 200 [15].
Figure 9.41 Effect of heat aging on the tensile strength at 23°C of DuPontt Tefzel® HT-2004 [15]. Note: All values of elongation between 5% and 10% regardless of test temperature; no load during aging.
203
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THE EFFECT
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ON
PLASTICS
AND
ELASTOMERS
Figure 9.42 Effect of heat aging on the tensile strength at 150°C of DuPontt Tefzel® HT-2004 [15]. Note: All values of elongation between 5% and 10% regardless of test temperature; no load during aging.
Figure 9.43 Tensile strength after exposure at 200°C of Diakin Neoflont ETFE [18].
9: FLUOROPOLYMERS
205
Figure 9.44 Elongation after exposure at 200°C of Diakin Neoflont ETFE [16].
Figure 9.45 Half-life of elongation versus temperature for various AGC chemical Fluon® ETFE resins [18].
Figure 9.47 shows the molecular structure of ECTFE. This simplified structure shows the ratio of the monomers being 1:1 and strictly alternating, which is the desirable proportion. Commonly known by the trade name, Halar®, ECTFE is an expensive, melt-processable, semicrystalline, whitish semiopaque thermoplastic with good chemical resistance
and barrier properties. It also has good tensile and creep properties and good high frequency electrical characteristics. Processing methods include extrusion, compression molding, rotomolding, blow molding, and liquid and powder coating. Manufacturers and trade names: Solvay Solexis Halar®.
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THE EFFECT
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Figure 9.46 Thermogravimetric analysis (TGA) of ETFE resin [4].
Figure 9.47 Chemical structure of polyethylene chlorotrifluoroethylene.
Figure 9.48 Effect of time on the yellowness index of Solvay Solexis Halar® ECTFE film upon thermooxidative aging at various temperatures [19].
9: FLUOROPOLYMERS
Applications and uses: Chemically resistant linings and coatings, valve and pump components, hoods, tank and filter house linings, nonwoven filtration fibers, barrier films, and release/vacuum bagging films. It is used in food processing particularly involving acidic food and fruit juice processing. Data for ECTFE plastics are shown in Figure 9.48.
References [1] Baker BB, Kasprzak DJ. Thermal degradation of commercial fluoropolymer in air. Polym Degrad Stab 1994;42:181 8. [2] Teflon® PTFE Fluoropolymer Resin, Properties Handbook, DuPont Co., July, 1996. [3] The Journal of Teflon®, Reprint No. 25, April 10, 1965. [4] Product Information Neoflont ETFE, Diakin Industries LTD., 2007. [5] Polyflont PTFE Fine Powder, Product information, Daikin Industries Ltd., 2001. [6] Product Information, Neoflont PFA, Daikin, 2002. [7] Teflon® PFA Fuoropolymer Resin, Properties Handbook, DuPont Co., Publication No. E96679-4, May 1997. [8] Hyflon® MFA Design and Processing Guide, Solvay Solexis, 2008.
207
[9] Lin FMC. Chain microstructure studies of poly(vinyl fluoride) by high resolution NMR spectroscopy, Ph.D. dissertation, University of Akron; 1981. [10] Technical Information, Tedlar® Polyvinyl Fluoride Film, Dupont, 1995. [11] Madorsky SL, Straus S. Thermal degradation of polychlorotrifluoroethylene, poly-alpha, beta, beta-trifluorostyrene, and poly-p-xylylene in a vacuum. J Res Nat Bur Stand 1955;55(4). [12] Voltalef® PCTFE Technical Brochure, Arkema, 2004. [13] Solef® & Hylar® PVDF Polyvinylidene Fluoride—Design and Processing Guide, Solvay Solexis, 2006. [14] Solef® PVDF Engineering Polymer, Solvay Polyvinylidene Fluoride, Solvay & Cie Corp., Publication No. Br 1292c-B-5-0485, Belgium. [15] Solef® PVDF Design and Processing Guide, Solef® PVDF, Solvay, 2012. [16] DuPontt Tefzel® Properties Handbook, DuPont, 2003. [17] Technical Data Ethylene Tetrafluoroethylene Copolymer, AGC Chemicals, 2007. [18] Neoflont ETFE EP-521, EP-541, Daikin Industries, 2007. [19] Khanna Y, Turi E, Sibilia J. High temperature aging of halar film. I. Study of physicochemical changes. J Appl Polym Sci 1984;29: 3607 20.
9.1 Polytetrafluoroethylene Polytetrafluoroethylene (PTFE) polymer is an example of a linear fluoropolymer. Its structure in simplistic form is shown in Figure 9.2. The CAS number for PTFE is 9002-84-0. Formed by the polymerization of tetrafluoroethylene (TFE), the (aCF2aCF2a) groups repeat many thousands of times. The fundamental properties of fluoropolymers evolve from the atomic structure of fluorine and carbon and their covalent bonding in specific chemical structures. The backbone is formed of carbon carbon bonds and the pendant groups are carbon fluorine bonds. Both are extremely strong bonds. The basic properties of PTFE stem from these two very strong chemical bonds. The size of the fluorine atom allows the formation of a uniform and continuous fluorine covering around the carbon carbon bonds and protects them from chemical attack, thus imparting chemical resistance and stability to the molecule. PTFE is rated for use up to 260°C. PTFE does not dissolve in any known solvent. The fluorine sheath is also responsible for the low surface energy (18 dynes/ cm) and low coefficient of friction (0.05 0.8, static) of PTFE. Another attribute of the uniform fluorine sheath is the electrical inertness (or nonpolarity) of the PTFE molecule. Electrical fields
impart only slight polarization in this molecule, so volume and surface resistivity are high. The PTFE molecule is simple and is quite ordered. This is shown in the three-dimensional models in Figures 9.3 and 9.4. PTFE can align itself with other molecules or other portions of the same molecule. Disordered regions are called amorphous regions. This is important because polymers with high crystallinity require more energy to melt. In other words, they have higher melting points. When highly ordered it forms what is called a crystalline region. Crystalline polymers have a substantial fraction of their mass in the form of parallel, closely packed molecules. High-molecular-weight PTFE resins have high crystallinity and therefore high melting points, typically as high as 320 342°C (608 648°F). The crystallinity of as-polymerized PTFE is typically 92 98%. Further, the viscosity in the molten state (called melt creep viscosity) is so high that high-molecular-weight PTFE particles do not flow even at temperatures above its melting point. They sinter much like powdered metals; they stick to each other at the contact points and combine into larger particles. PTFE is called a homopolymer, a polymer made from a single monomer. Recently many PTFE manufacturers have added minute amounts of other monomers to their PTFE polymerizations to produce alternate grades of PTFE designed for specific applications. Fluoropolymer manufacturers continue to call these grades modified homopolymer at below 1% by weight of comonomer. DuPont grades of this type are called Teflon® NXT Resins. Dyneont TFMt modified PTFE incorporates less than 1% of a comonomer perfluoropropyl vinyl ether (PPVE). Daikin’s modified grade is Polyflont M-111. These modified granular PTFE materials retain the exceptional chemical, thermal, anti-stick, and low-friction properties of conventional PTFE resin, but offer some improvements:
• Weldability • Improved permeation resistance
The Effect of Long Term Thermal Exposure on Plastics and Elastomers. DOI: http://dx.doi.org/10.1016/B978-0-323-22108-5.00009-6 © 2014 Elsevier Inc. All rights reserved.
183
184
THE EFFECT
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• Less creep • Smoother, less porous surfaces • Better high-voltage insulation.
Tetrafluoroethylene (TFE)
Ethylene
Hexafluoropropylene (HFP)
Perfluoromethyl vinyl ether (MVE)
Perfluoroethyl vinyl ether (EVE)
Perfluoropropyl vinyl ether (PVE)
ON
PLASTICS
AND
ELASTOMERS
The copolymers described in the next sections contain significantly more of the non-TFE monomers. Manufacturers and trade names: DuPontt Teflon® PTFE, Dyneon PTFE, Daikin Polyflont, many others
Figure 9.2 Chemical structure of PTFE.
Figure 9.3 Three-dimensional representation of PTFE. Chlorotrifluoroethylene
Vinyl fluoride (VF)
Vinylidene fluoride (VF2)
2,2-Bistrifluoromethyl4,5-difluoro-1,3-dioxole
Figure 9.1 Structures of many monomers used to make fluoropolymers.
Figure 9.4 Ball and stick three-dimensional representation of PTFE.
Table 9.1 Melting Point Ranges of Various Fluoroplastics Fluoroplastic
Melting Point (°C)
Polytetrafluoroethylene (PTFE)
320 340
Polyethylene chlorotrifluoroethylene (ECTFE)
240
Polyethylene tetrafluoroethylene (ETFE)
255 280
Fluorinated ethylene propylene (FEP)
260 270
Perfluoroalkoxy (PFA)
302 310
Perfluoroalkoxy (MFA)
280 290
Polychlorotrifluoroethylene (PCTFE)
210 212
Polyvinylidene fluoride (PVDF)
155 170
9: FLUOROPOLYMERS
185
Applications and uses: Pipe liners, fittings, valves, pumps, and other components used for transferring aggressive, ultrapure fluids. Data for PTFE plastics are contained in Tables 9.2 9.4 and Figures 9.5 9.10.
Table 9.2 Degradation (TGA) Rates of PTFE Fluoroplastics in Air as a Function of Time and Temperature [1] Temperature (°C)
% Weight Loss/h TE to 15 min
TE 1 60 min
Fine Powder
9.2 Fluorinated Ethylene Propylene (FEP) If one of the fluorine atoms on TFE is replaced with a trifluoromethyl group (aCF3), then the new monomer is called hexafluoropropylene (HFP). Polymerization of monomers HFP and TFE yield a fluoropolymer, fluorinated ethylene propylene, called FEP. The number of HFP groups is typically 13% by weight or less and its structure is shown in Figure 9.11. The CAS number for FEP is 25067-11-2. The effect of using HFP is to put a “bump” along the polymer chain as shown in the threedimensional models in Figures 9.12 and 9.13. This bump disrupts the crystallization of the FEP, which has a typical as-polymerized crystallinity of 70% versus 92 98% for PTFE. It also lowers its melting point. The reduction of the melting point depends on the amount of trifluoromethyl groups added and
400
2 0.06
425
0.15
425
0.04a 255c
525
95.0
Granular 350
0.02
350
0.005b
400
0.03
400
0.006b
425
0.06
425
0.06a
a
Hourly rate from 8 to 11.8 h after beginning run. Hourly rate from 3.3 to 6.6 h after beginning run. c Gross decomposition in 1 h. Initial rate 255% per hour. TE 5 thermal equilibrium. b
Table 9.3 Tape Length Required to Abrade Through Wire Coatinga Heat Aging Resin
None
96 h at 150°C
500 h at 150°C
96 h at 200°C
PTFE
191.5
196.6
247
211.7
a
Armstrong Abrasion Test (MIL-T-5438): This test measures abrasion resistance of wire coating by drawing, under load, a clean abrasive cloth tape of continuous length across the test wire until the coating is worn through. A 0.45 load on No. 400 grit tape was used on a coating thickness of 0.038 cm. (Average Tape Length in Centimeters) [2]
Table 9.4 Effects of Oven Aging at 300°C on the Electrical Properties of PTFE Resins [3] Exposure Time at 300°C
Dissipation Factor
Dielectric Constant
Dielectric Strength, kV/mm (ASTM-D-149)
As received
0.0001
2.1
117.1
1 month
0.0001
2.1
3 months
0.0001
2.1
6 months
0.0001
2.1
9 months Note: 125 µm extruded PTFE film.
115.6 118
186
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.5 Thermogravimetric analysis (TGA) of Diakin PTFE [4].
Figure 9.6 Tensile strength versus aging time at 250°C of PTFE Insulated Wire made from Daikin Polyflont PTFE fine powder [5].
secondarily on the molecular weight. Most FEP resins melt around 274°C (525°F), although lower melting points are possible. Even high-molecular-
weight FEP will melt and flow. The high chemical resistance, low surface energy, and good electrical insulation properties of PTFE are retained.
9: FLUOROPOLYMERS
187
Figure 9.7 Elongation versus aging time at 250°C of PTFE Insulated Wire made from Daikin Polyflont PTFE fine powder [5].
Figure 9.8 Specific gravity versus aging time at 380°C of Daikin Polyflont PTFE fine powder [5].
188
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.9 Elongation versus aging time at 380°C of Daikin Polyflont PTFE fine powder [5].
Figure 9.10 Tensile strength versus aging time at 380°C of Daikin Polyflont PTFE fine powder [5].
Figure 9.11 Chemical structure of FEP.
Figure 9.12 Three-dimensional representation of FEP.
9: FLUOROPOLYMERS
189
Data for FEP plastics are contained in Table 9.5 and Figures 9.14 9.16.
9.3 Perfluoroalkoxy (PFA) Figure 9.13 Ball and stick three-dimensional representation of FEP.
Manufacturers and trade names: DuPontt Teflon® FEP, Dyneont THV FEP, Daikin Neoflont. Applications and uses: Applications requiring excellent chemical resistance, superior electrical properties, and high service temperatures. Release films, tubing, cable insulation and jacketing.
Making a more dramatic change in the side group than that done in making FEP, chemists put a perfluoroalkoxy (PFA) group on the polymer chain. This group is signified as OaRf, where Rf can be any number of totally fluorinated carbons. The most common comonomer is perfluoropropyl (aOaCF2aCF2aCF3). However, other comonomers are given in Table 9.6. The polymers based on perfluoropropyl vinyl ether (PVE) are called PFA and the perfluoroalkylvinylether group is typically added at 3.5% or less.
Table 9.5 Degradation (TGA) Rates of FEP Fluoroplastics in Air as a Function of Time and Temperature [1] Temp. (°C)
% Weight Loss/h TE to 15 min
15 65 min
, 0.05
205 300 350
TE 1 60 min
0.45
B0.03
, 0.05
0.13
0.18
375
0.67
400
3.2
TE 5 thermal equilibrium.
Figure 9.14 Tensile strength versus aging time at 200°C of Diakin Neoflon FEP NP-20 [4].
190
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.15 Elongation versus aging time at 200°C of Diakin Neoflont FEP NP-20 [4].
Figure 9.16 TGA of Diakin Neoflont FEP [4].
Table 9.6 PFA Comonomers Comonomer
Structure
Perfluoromethyl vinyl ether (MVE)
CF2QCFaOaCF3
Perfluoroethyl vinyl ether (EVE)
CF2QCFaOaCF2aCF3
Perfluoropropyl vinyl ether (PVE)
CF2QCFaOaCF2aCF2aCF3
9: FLUOROPOLYMERS
191
When the comonomer is Perfluoromethyl vinyl ether (MVE) the polymer is called MFA. A structure of PFA is shown in Figure 9.17. The CAS number of PFA using PVE as comonomer is 26655-00-5. The large side group as shown in Figures 9.18 and 9.19 reduces the crystallinity drastically. The melting point is generally between 305°C and 310° C (581 590°F) depending on the molecular weight. The melt viscosity is also dramatically dependent on the molecular weight. Since PFA is
still perfluorinated as with FEP the high chemical resistance, low surface energy, and good electrical insulation properties are retained. Solvay Solexis Hyflon® MFA and PFA are semicrystalline fully-fluorinated melt-processible fluoropolymers. Hyflon® PFA belongs to the class of PFA having a lower melting point than standard PFA grades. Manufacturers and trade names: DuPontt Teflon®; Solvay Solexis Hyflon®; Dyneont (a 3M Company); Daikin. Applications and uses: Lined and coated processing equipment, vessels and housings, high purity chemical storage. Data for PFA plastics are contained in Table 9.7 and Figures 9.20 9.25.
9.4 Polyvinyl Fluoride Figure 9.17 Chemical structure of PFA.
Polyvinyl fluoride (PVF) is a homopolymer of vinyl fluoride. The molecular structure of PVF is shown in Figure 9.26.
Figure 9.18 Three-dimensional representation of PFA.
Figure 9.19 Ball and stick three-dimensional representation of PFA.
Table 9.7 Degradation (TGA) Rates of Fluoroplastics in Air as a Function of Time and Temperature [1] Resins
Temperature (°C)
% Weight Loss/h TE to 15 min
PFA-1
PFA-2
300
0.18
15 65 min 0.05
TE 1 60 min 0.07
350
0.22
400
0.58
300 350 400
0.12
, 0.05
, 0.05
B0.03
0.05 0.26
192
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.20 Thermogravimetric analysis (TGA) of Daikin Neoflont PFA [6].
Figure 9.21 Change in tensile strength of PFA wire coating due to thermal exposure in air [7].
DuPontt is the only known manufacturer of this polymer they call Tedlar®. The structure above shows a head-to-tail configuration of the vinyl fluoride (VF) monomer; there are no fluorines on adjacent carbons. But in reality vinyl fluoride polymerizes in both head-to-head and head-to-tail configurations. DuPont’s commercial PVF contains 10 12% of
head-to-head and tail-to-tail units, also called inversions [9]. Its CAS number is 24981-14-4. PVF has excellent resistance to weathering, staining, and chemical attack (except ketones and esters). It exhibits very slow burning and low permeability to vapor. Its most visible use in on the interiors of the passenger compartments of commercial aircraft.
9: FLUOROPOLYMERS
193
Figure 9.22 Change in break elongation of PFA wire coating due to thermal exposure in air [7].
Figure 9.23 Change in melt flow rate of PFA wire coating due to thermal exposure in air [7].
General description: PVF is available only commercially in film form. DuPontt Tedlar® films are available in clear, translucent, or opaque white film and in several surface finishes. Applications and uses: Aircraft interiors, architectural fabrics, curtain walls, roofing, pipe, vessel jacketing, release films, solar panels, wind turbines.
Data for PVF Figures 9.27 9.30.
plastics
are
shown
in
9.5 Polychlorotrifluoroethylene Polychlorotrifluoroethylene (PCTFE) is a homopolymer of chlorotrifluoroethylene, characterized
194
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.24 Strength at break retained of Solvay Solexis Hyflon® MFA F1540 due to thermal aging in air at various temperatures [8].
Figure 9.25 Elongation at break retained of Solvay Solexis Hyflon® MFA F1450 due to thermal aging in air at various temperatures [8].
by the structure shown in Figure 9.31. The CAS number is 9002-83-9. The addition of the one chlorine atom contributes to lowering the melt viscosity to permit extrusion and injection molding. It also contributes to the transparency, the exceptional flow, and the
rigidity characteristics of the polymer. Fluorine is responsible for its chemical inertness and zero moisture absorption. Therefore, PCTFE has unique properties. Its resistance to cold flow, dimensional stability, rigidity, low gas permeability, and low moisture absorption is superior to any other
9: FLUOROPOLYMERS
Figure 9.26 Structure of PVF.
195
fluoropolymer. It can be used at low temperatures. Some products contain a small amount of a comonomer. Manufacturers and trade names: Honeywell Aclar®, Arkema VOLTALEF®, Daikin Industries Neoflon® CTFE.
Figure 9.27 Tensile strength versus hours of aging at 149°C of DuPont Tedlar® PVF films [10].
Figure 9.28 Elongation versus hours of aging at 149°C of DuPont Tedlar® PVF films [10].
196
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.29 Impact strength versus hours of aging at 149°C of DuPont Tedlar® PVF films [10].
Figure 9.30 Flex life versus hours of aging at 149°C of DuPont Tedlar® PVF films [10].
Figure 9.31 Chemical structure of PCTFE.
Applications and uses: Pharmaceutical blister packaging, electroluminescent lamps, liquid crystal display (LCD) panels. Data for PCTFE plastics are contained in Table 9.8 and Figures 9.32 and 9.33.
9: FLUOROPOLYMERS
197
Table 9.8 Rates of Degradation of PCTFE [11] Temperature (°C)
Test Duration (min)
Total Volatilized (%)
Initial Volatilization Rate (%/min)
365
400
78.1
0.20
370
300
82.9
0.28
375
200
75.0
0.42
380
160
82.3
0.58
385
130
83.2
0.84
Figure 9.32 Thermogravimetric analysis (TGA) of Arkema Voltalef® PCTFE [12].
Figure 9.33 Thermal degradation of PCTFE; percentage of sample volatilized versus time [11].
198
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
9.6 Polyvinylidene Fluoride
Key attributes of PVDF include the following:
The polymers made from 1,1-di-fluoro-ethene (or vinylidene fluoride) are known as polyvinylidene fluoride (PVDF). They are resistant to oils and fats, water and steam, and gas and odors, making them of particular value for the food industry. PVDF is known for its exceptional chemical stability and excellent resistance to ultraviolet radiation. It is used chiefly in the production and coating of equipment used in aggressive environments, and where high levels of mechanical and thermal resistance are required. It has also been used in architectural applications as a coating on metal siding where it provides exceptional resistance to environmental exposure. The chemical structure of PVDF is shown in Figure 9.34. Its CAS number is 2493779-9. Some products are copolymers. The alternating aCH2aand aCF2agroups along the polymer chain provide a unique polarity that influences its solubility and electric properties. At elevated temperatures PVDF can be dissolved in polar solvents such as organic esters and amines. This selective solubility offers a way to prepare corrosion-resistant coatings for chemical process equipment and long-life architectural finishes on building panels.
• • • • • • • • • • • •
Mechanical strength and toughness High abrasion resistance High thermal stability High dielectric strength High purity Readily melt processible Resistant to most chemicals and solvents Resistant to ultraviolet and nuclear radiation Resistant to weathering Resistant to fungi Low permeability to most gases and liquids Low flame and smoke characteristics.
Manufacturers and trade names: Arkema Kynar®, Solvay Solexis Solef® and Hylar®. Applications and uses: Electrical wires, tactile sensor arrays, strain gauges, audio transducers, piezoelectric panels, lithium ion batteries, monofilament fishing line, membranes. Data for PVDF plastics are contained in Tables 9.9 and 9.10 and Figures 9.35 9.37.
9.7 Ethylene Tetrafluoroethylene Copolymer Ethylene tetrafluoroethylene (ETFE) is a copolymer of ethylene and TFE. The basic molecular structure of ETFE is shown in Figure 9.38.
Figure 9.34 Chemical structure of PVDF.
Table 9.9 Thermal Aging Tests at Various Temperatures of Solvay Solexis Solef® PVDF 1008 [13] Aging Period (Days)
Tensile Yield Strength (MPa)
Secant Modulus at 1% Deformation (MPa)
Elongation at Break (%)
20°C
120°C
150°C
20°C
120°C
150°C
20°C
120°C
1
50
53
51
1900
1700
1600
9.5
10.5
11.8
11
49
54
51
2000
1900
1800
8.5
10.0
13.0
160
53
54
51
2300
2100
1800
7.0
9.0
11.5
358
54
55
53
2300
2300
2200
7.0
10.0
.11.0
730
52
54
2300
1800
6.6
10.4
RAPRA 5 injection molded specimens.
150°C
Table 9.10 Thermal Aging Tests at 150°C of Solvay Solexis Solef® 11010 PVDF [11] Aging period (h)
0
8
100
1000
Tensile properties Yield stress (MPa)
28
28
29
28
Strength at break (MPa)
41
34
34
40
Elongation at break (%)
.500
.480
.480
.500
Modulus (MPa)
1020
1070
1020
870
113
122
132
149
Thermal properties HDT under 0.46 MPa, °C
Note: Compression molded plates, thickness 2 mm. Rate of pulling: 10 mm/min (modulus: 1 mm/min).
Figure 9.35 Mechanical properties of cables jacketed with Solvay Solexis Solef® 31508/0003 copolymer versus aging at 158°C [11].
Figure 9.36 Change in tensile strength and break elongation of PVDF due to thermal exposure in air at 165°C [14].
200
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.37 Thermogravimetric analysis (TGA) of Solvay Solexis Solef® PVDF [15].
• Mechanical strength ETFE is good with excellent tensile strength and elongation and has superior physical properties compared to most fluoropolymers.
• With low smoke and flame characteristics, Figure 9.38 Chemical structure of polyethylene tetrafluoroethylene.
It is sometimes called polyethylene tetrafluoroethylene. The depicted structure in Figure 9.38 shows alternating units of TFE and ethylene. While this can be readily made, many grades of ETFE vary the ratio of the two monomers slightly to optimize properties for specific end uses. Its CAS number is 25038-71-5. ETFE is a fluoroplastic with excellent electrical and chemical properties. It also has excellent mechanical properties. ETFE is especially suited for uses requiring high mechanical strength, chemical, thermal, and/or electrical properties. The mechanical properties of ETFE are superior to those of PTFE and FEP. ETFE has the following:
• Excellent resistance to extremes of temperature, ETFE has a working temperature range of 2200°C to 150°C.
• Excellent chemical resistance.
ETFE is rated 94V-0 by the Underwriters Laboratories Inc. It is odorless and non-toxic.
• Outstanding resistance to weather and aging. • Excellent dielectric properties. • Non-stick characteristics. Manufacturers and trade names: DuPontt Tefzel®, Asahi Glass Fluon®, 3M Dyneont. Applications and uses: Electrical and fiber optic wiring, stadium roofing, liner in pipes, tanks, and vessels. Data for ETFE plastics are contained in Tables 9.11 9.16 and Figures 9.39 9.46.
9.8 Ethylene Chlorotrifluoroethylene Copolymer Ethylene chlorotrifluoroethylene copolymer, also called polyethylene chlorotrifluoroethylene or ECTFE, is a copolymer of ethylene and chlorotrifluoroethylene. Its CAS number is 25101-45-5.
9: FLUOROPOLYMERS
201
Table 9.11 Estimated Upper Service Temperatures (°C), No Load Thermal Aging End-of-Life Criterion Based on Elongation for DuPont Tefzel® ETFE [16] End-of-Life Criterion
Exposure Time (h)
Actual Elongation (%)
Elongation Retained (%)
1000
3000
10 k
20 ka
50 ka
100 ka
135
50
210
195
172
159
143
132
18
b
211
188
175
158
147
9
b
b
196
182
165
153
50 25 a
These estimates were extrapolated from 10,000 hour aging results. Estimates are not available for these exposure regions.
b
Table 9.12 Estimated Upper Service Temperatures (°C), No Load Thermal Aging End-of-Life Criterion Based on Tensile Strength for DuPont Tefzel® ETFE [15] End-of-Life Criterion
Exposure Time (h)
Actual Tensile Strength (psi)
Tensile Strength Retained (%)
10 k
20 ka
50 ka
100 ka
3750
50
190
176
159
147
2000
27
204
190
172
158
a
These estimates were extrapolated from 10,000 h aging results.
Table 9.13 Effect of Temperature Aging on Izod Impact Strength, DuPontt Tefzel® HT-2004 [15] Temperature Izod °C
°F
23
73
23 23
Aging
Izod Impact Strength J/m
ft lb/in.
As molded
491
9.1
73
168 h at 150°C (302°F)
491
9.1
73
168 h at 180°C (356°F)
416
7.7
Table 9.14 Initial Weight Loss of DuPontt Tefzel® 200 Resin Above 300°C (572°F) [15] °C
°F
300
572
0.05
330
626
0.26
350
662
0.86
370
698
1.60
% Weight Loss/h
202
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Table 9.15 Degradation (TGA) Rates of ETFE in Air as a Function of Time and Temperature [1] Temperature (°C)
% Weight Loss/h TE to 15 min
15 65 min
TE 1 60 min , 0.05
150 260
0.31
0.06
0.11
300
0.42
0.09
0.14
325
0.67 B2
350
6.8
TE 5 thermal equilibrium.
Table 9.16 Grades of Fluon® ETFE for Figure 9.45 [17] Grade
Melt Flow Rate
Melt Index
Characteristic
Application
Molding Method
C-55AP
3.9 6.5
1 2
Standard
General
Extrusion molding
C-88AP
9.0 12.0
3 4
Standard
General
Extrusion molding, injection molding
C-55AP
3.9 6.5
1 2
Stress crack resistant
Wire cover
Extrusion molding
C-88AP
9.0 12.0
3 4
Stress crack resistant
Wire cover
Extrusion molding
Figure 9.39 Retention at various levels of room temperature tensile elongation after heat aging of DuPontt Tefzel® 200 [15].
9: FLUOROPOLYMERS
Figure 9.40 Retention at various levels of room temperature tensile strength after heat aging of DuPontt Tefzel® 200 [15].
Figure 9.41 Effect of heat aging on the tensile strength at 23°C of DuPontt Tefzel® HT-2004 [15]. Note: All values of elongation between 5% and 10% regardless of test temperature; no load during aging.
203
204
THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.42 Effect of heat aging on the tensile strength at 150°C of DuPontt Tefzel® HT-2004 [15]. Note: All values of elongation between 5% and 10% regardless of test temperature; no load during aging.
Figure 9.43 Tensile strength after exposure at 200°C of Diakin Neoflont ETFE [18].
9: FLUOROPOLYMERS
205
Figure 9.44 Elongation after exposure at 200°C of Diakin Neoflont ETFE [16].
Figure 9.45 Half-life of elongation versus temperature for various AGC chemical Fluon® ETFE resins [18].
Figure 9.47 shows the molecular structure of ECTFE. This simplified structure shows the ratio of the monomers being 1:1 and strictly alternating, which is the desirable proportion. Commonly known by the trade name, Halar®, ECTFE is an expensive, melt-processable, semicrystalline, whitish semiopaque thermoplastic with good chemical resistance
and barrier properties. It also has good tensile and creep properties and good high frequency electrical characteristics. Processing methods include extrusion, compression molding, rotomolding, blow molding, and liquid and powder coating. Manufacturers and trade names: Solvay Solexis Halar®.
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THE EFFECT
OF
LONG TERM THERMAL EXPOSURE
ON
PLASTICS
AND
ELASTOMERS
Figure 9.46 Thermogravimetric analysis (TGA) of ETFE resin [4].
Figure 9.47 Chemical structure of polyethylene chlorotrifluoroethylene.
Figure 9.48 Effect of time on the yellowness index of Solvay Solexis Halar® ECTFE film upon thermooxidative aging at various temperatures [19].
9: FLUOROPOLYMERS
Applications and uses: Chemically resistant linings and coatings, valve and pump components, hoods, tank and filter house linings, nonwoven filtration fibers, barrier films, and release/vacuum bagging films. It is used in food processing particularly involving acidic food and fruit juice processing. Data for ECTFE plastics are shown in Figure 9.48.
References [1] Baker BB, Kasprzak DJ. Thermal degradation of commercial fluoropolymer in air. Polym Degrad Stab 1994;42:181 8. [2] Teflon® PTFE Fluoropolymer Resin, Properties Handbook, DuPont Co., July, 1996. [3] The Journal of Teflon®, Reprint No. 25, April 10, 1965. [4] Product Information Neoflont ETFE, Diakin Industries LTD., 2007. [5] Polyflont PTFE Fine Powder, Product information, Daikin Industries Ltd., 2001. [6] Product Information, Neoflont PFA, Daikin, 2002. [7] Teflon® PFA Fuoropolymer Resin, Properties Handbook, DuPont Co., Publication No. E96679-4, May 1997. [8] Hyflon® MFA Design and Processing Guide, Solvay Solexis, 2008.
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[9] Lin FMC. Chain microstructure studies of poly(vinyl fluoride) by high resolution NMR spectroscopy, Ph.D. dissertation, University of Akron; 1981. [10] Technical Information, Tedlar® Polyvinyl Fluoride Film, Dupont, 1995. [11] Madorsky SL, Straus S. Thermal degradation of polychlorotrifluoroethylene, poly-alpha, beta, beta-trifluorostyrene, and poly-p-xylylene in a vacuum. J Res Nat Bur Stand 1955;55(4). [12] Voltalef® PCTFE Technical Brochure, Arkema, 2004. [13] Solef® & Hylar® PVDF Polyvinylidene Fluoride—Design and Processing Guide, Solvay Solexis, 2006. [14] Solef® PVDF Engineering Polymer, Solvay Polyvinylidene Fluoride, Solvay & Cie Corp., Publication No. Br 1292c-B-5-0485, Belgium. [15] Solef® PVDF Design and Processing Guide, Solef® PVDF, Solvay, 2012. [16] DuPontt Tefzel® Properties Handbook, DuPont, 2003. [17] Technical Data Ethylene Tetrafluoroethylene Copolymer, AGC Chemicals, 2007. [18] Neoflont ETFE EP-521, EP-541, Daikin Industries, 2007. [19] Khanna Y, Turi E, Sibilia J. High temperature aging of halar film. I. Study of physicochemical changes. J Appl Polym Sci 1984;29: 3607 20.