copolymerizing two or more monomers, using either block or graft ..... grade, with antioxidants. Specialty: 3078âvery low modulus extrusion/molding grade, with ...
10 Thermoplastic Elastomers Thermoplastic elastomers (TPEs) have two big advantages over the conventional thermoset (vulcanized) elastomers. Those are ease and speed of processing. Other advantages of TPEs are recyclablity of scrap, lower energy costs for processing, and the availability of standard, uniform grades (not generally available in thermosets). TPEs are molded or extruded on standard plasticsprocessing equipment in considerably shorter cycle times than those required for compression or transfer molding of conventional rubbers. They are made by copolymerizing two or more monomers, using either block or graft polymerization techniques. One of the monomers provides the hard, or crystalline, polymer segment that functions as a thermally stable component; the other monomer develops the soft or amorphous segment, which contributes the elastomeric or rubbery characteristic. Physical and chemical properties can be controlled by varying the ratio of the monomers and the length of the hard and soft segments. Block techniques create long-chain molecules that have various or alternating hard and soft segments. Graft polymerization methods involve attaching one polymer chain to another as a branch. The properties that are affected by each phase can be generalized as follows: 1. “hard phase”—plastic properties: a. processing temperatures b. continuous use temperature c. tensile strength d. tear strength e. chemical and fluid resistance
f. adhesion to inks, adhesives, and overmolding substrates 2. “soft phase”—elastomeric properties: a. lower service temperature limits b. hardness c. flexibility d. compression set and tensile set Three high-performance types of TPEs make up this chapter.
10.1 Thermoplastic Polyurethane Elastomers Urethanes are a reaction product of a diisocyanate and long- and short-chain polyether, polyester, or caprolactone glycols [1]. The polyols and the shortchain diols react with the diisocyanates to form linear polyurethane molecules. This combination of diisocyanate and short-chain diol produces the rigid or hard segment. The polyols form the flexible or soft segment of the final molecule. Fig. 10.1 shows the molecular structure in schematic form. There are three main chemical classes of thermoplastic polyurethane (TPU): polyester, polyether, and a smaller class known as polycaprolactone [2]. • Polyester TPUs are compatible with polyvinyl chloride (PVC) and other polar plastics. Offering value in the form of enhanced properties, they are unaffected by oils and chemicals, provide excellent abrasion resistance, offer a good
Figure 10.1 Molecular structure of a thermoplastic polyurethane elastomer.
Fatigue and Tribological Properties of Plastics and Elastomers. http://dx.doi.org/10.1016/B978-0-323-44201-5.00010-1 Copyright © 2016 Elsevier Inc. All rights reserved.
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Fatigue and Tribological Properties of Plastics and Elastomers
balance of physical properties, and are perfect for use in polyblends. • Polyether TPUs are slightly lower in specific gravity than polyester and polycaprolactone grades. They offer low-temperature flexibility and good abrasion and tear resilience. They are also durable against microbial attack and provide excellent hydrolysis resistance— making them suitable for applications where water is a consideration. • Polycaprolactone TPUs have the inherent toughness and resistance of polyester-based TPUs combined with low-temperature performance and a relatively high resistance to hydrolysis. They are an ideal raw material for hydraulic and pneumatic seals. TPUs can also be subdivided into aromatic and aliphatic varieties: • Aromatic TPUs based on isocyanates such as 4,49-methylenediphenyl diisocyanate (MDI) are workhorse products and can be used in applications that require flexibility, strength, and toughness. • Aliphatic TPUs based on isocyanates such as methyldicyclohexyl-diisocyanate (H12 MDI), 1,6-hexamethylene-diisocyanate (HDI), and isophorone diisocyanate (IPDI) are light stable and offer excellent optical clarity. They are commonly employed in automotive interior and exterior applications and as laminating films to bond glass and polycarbonate together in the glazing industry. They are also used in projects where attributes such as optical clarity, adhesion, and surface protection are required. The properties of the resin depend on the nature of the raw materials, the reaction conditions, and the ratio of the starting raw materials. The polyols used have a significant influence on certain properties of the TPU. Both polyether and polyester polyols are used to produce many products. The polyester-based TPUs have the following characteristic features: • • • • •
good oil/solvent resistance good UV resistance abrasion resistance good heat resistance mechanical properties
The polyether-based TPUs have the following characteristic features: • • • •
fungus resistance low-temperature flexibility excellent hydrolytic stability acid/base resistance
In addition to the basic components described earlier, most resin formulations contain additives to facilitate production and processability. Other additives can also be included such as: • • • •
demolding agents flame retardants heat/UV stabilizers plasticizers
The polyether types are slightly more expensive and have better hydrolytic stability and lowtemperature flexibility than the polyester types. Manufacturers and trade names include the following: Lubrizol Advanced Materials Estane® TPU, Covestro Texin® and Desmopan®, BASF Elastollan®, Huntsman IROGRAN®, AVALON®, KRYSTALGRAN®, and IROSTIC®. Applications and end uses include the following: medical thin-walled, flexible tubing, catheters, connectors, luers, and stopcocks, films and fabric coatings, component housings, soft touch grips, dental parts, automotive battery cables, ski goggles, ski boot shells, snowboard surfaces, and sports shoe soles.
10.1.1 Tribology Data Tribology data for TPU elastomers are found in Tables 10.1–10.8.
10.2 Thermoplastic Copolyester Elastomers Thermoplastic copolyester elastomers (TPE-E or COPE) are block copolymers. The chemical structure of one such elastomer is shown in Fig. 10.2. These TPEs are generally tougher over a broader temperature range than the urethanes described in Section 10.1.1. Also, they are easier and more forgiving in processing: • excellent abrasion resistance • high tensile, compressive, and tear strength
10: Thermoplastic Elastomers
281
Table 10.1 Abrasion Loss (Per DIN 53516 and ISO 4649) of BASF Elastollan® 1100 Grades PolyetherPolyurethane Thermoplastic Elastomers (Shore A or D Hardness) [3] Elastollan® Grade
Abrasion Loss (mm3)
Table 10.2 Abrasion Loss (Per DIN 53516 and ISO 4649) of BASF Elastollan® C Grades PolyetherPolyurethane Thermoplastic Elastomers [3] Elastollan® Grade
Abrasion Loss (mm3)
C 65 A HPM—65 Shore A, hard phase modified
40
C 70 A HPM—70 Shore A, hard phase modified
35
C 75 A HPM—75 Shore A, hard phase modified
35
C 85 A HPM—85 Shore A, hard phase modified
40
C 78 A—78 Shore A
30
C 80 A—80 Shore A
30
C 85 A—85 Shore A
30
25
C 88 A—88 Shore A
30
1195 A—95 Shore A
25
C 90 A—90 Shore A
25
1198 A—98 Shore A
25
C 95 A—95 Shore A
25
1154 D—54 Shore D
20
C 98 A—98 Shore A
30
1154 D FHF—54 Shore D, halogen-free flame retardant
30
C 59 D—59 Shore D
20
C 60 D—60 Shore D
20
1160 D—60 Shore D
20
C 64 D—64 Shore D
20
1164 D—64 Shore D
20
C 74 D—74 Shore D
20
1174 D—74 Shore D
20
1175 A W—75 Shore A, plasticized
45
1180 A—80 Shore A
30
1185 A W—85 Shore A, plasticized
40
1185 A—75 Shore A
25
1185 A M—85 Shore A, matt surface
60
1185 A WM—85 Shore A, matt surface, plasticized
38
1185 A FHF—85 Shore A, halogen-free flame retardant
35
1190 A—90 Shore A
• good flexibility over a wide range of temperatures • good hydrolytic stability • resistance to solvents and fungus attack • selection of a wide range of hardness In these polyester TPEs, the hard polyester segments can crystallize, giving the polymer some of the attributes of semicrystalline thermoplastics, most particularly better solvent resistance than ordinary rubbers, but also better heat resistance. Above the melting temperature of the crystalline regions, these TPEs can have low viscosity and can be molded easily in thin sections and complex structures. Properties of thermoplastic polyester elastomers can be fine-tuned over a range by altering the ratio of hard to soft segments. In DuPont Hytrel® polyester TPEs, the resin is a block copolymer. The hard phase is polybutylene terephthalate (PBT). The soft segments are longchain polyether glycols.
Table 10.3 Abrasion Loss (Per DIN 53516 and ISO 4649) of BASF Elastollan® B Grades PolyetherPolyurethane Thermoplastic Elastomers [3] Elastollan® Grade
Abrasion Loss (mm3)
B 60 A ESD—60 Shore A, electronic sensitive devices
120
B 80 A—80 Shore A
35
B 85 A—85 Shore A
35
B 90 A—90 Shore A
30
B 95 A—95 Shore A
30
B 98 A—98 Shore A
25
B 60 D—60 Shore D
25
B 64 D—64 Shore D
25
Manufacturers and trade names include the following: Ticona Riteflex®, DuPont™ Hytrel®, Eastman Ecdel®, and DSM Engineering Plastics Arnitel®.
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Fatigue and Tribological Properties of Plastics and Elastomers
Table 10.4 Abrasion Loss (Per DIN 53516 and ISO 4649) of BASF Elastollan® 600 Grades PolyetherPolyurethane Transparent Thermoplastic Elastomers [3]
Table 10.6 Abrasion Loss (Per DIN 53516 and ISO 4649) of BASF Elastollan® 500 Grades PolyetherPolyurethane Thermoplastic Elastomers [3]
Abrasion Loss (mm3)
Elastollan® Grade
Abrasion Loss (mm3)
598 A—98 Shore A
30
670 AWHU—70 Shore A, antistatic, plasticized, UV stabilized
40
560 D—60 Shore D
30
564 D—64 Shore D
30
685 AU—85 Shore A, antistatic, UV stabilized
40
690 AU—90 Shore A, antistatic, UV stabilized
40
695 AU—95 Shore A, antistatic, UV stabilized
40
660 DU—60 Shore D, antistatic, UV stabilized
40
Elastollan®/Elastoblend® Grade
664 DU—60 Shore D, antistatic, UV stabilized
40
LP 9192 polyether based for matt surfaces
100
1085 A alternative polyether basis
70
SP 806 polyether based for opaque films
30
SP 883 polyester based for opaque films
40
880 AN polyester based for transparent films
45
Abrasion Loss (mm3)
890 AN polyester based for transparent films
45
S 50 A SPF—50 Shore A, soft plasticizer free
35
2180 A polyester/polyether based for fibers/films
45
S 60 A SPF—60 Shore A, soft plasticizer free
30
SP 9213 polyether based for easy flow
70
S 70 A SPF—70 Shore A, soft plasticizer free
30
SP 852 polyester based for easy flow
30
S 60 AWH—60 Shore A, antistatic, plasticized
50
1154 D KFFC polyether based for flexible flat cables
30
S 70 AWH—70 Shore A, antistatic, plasticized
65
S 80 A—80 Shore A, antistatic
40
S 85 A—85 Shore A, antistatic
35
S 90 —90 Shore A, antistatic
30
S 95 A—95 Shore A, antistatic
30
S 98 A—98 Shore A, antistatic
25
S 60 D—60 Shore D
25
S 64 D—64 Shore D
25
S 74 D—74 Shore D
25
Elastollan® Grade
Table 10.5 Abrasion Loss (Per DIN 53516 and ISO 4649) of BASF Elastollan® 600 Grades PolyetherPolyurethane Transparent Thermoplastic Elastomers [3] Elastollan® Grade
Table 10.7 Abrasion Loss (Per DIN 53516 and ISO 4649) of BASF Elastollan and Elastoblend Special Grades Polyether-Polyurethane Thermoplastic Elastomers [3] Abrasion Loss (mm3)
Applications and end uses include the following: seals, belts, bushings, pump diaphragms, gears, protective boots, hose and tubing, springs, impactabsorbing devices, sporting goods, footwear, and wire and cable. Various DuPont Hytrel® TPE-E or COPE are discussed in the subsequent figures and tables. General purpose: G3548L—low modulus grade, with antioxidants
extrusion/molding
10: Thermoplastic Elastomers
283
Table 10.8 Tribology Properties of Covestro Texin® and Desmopan® TPU Thermoplastic Elastomers [4] Texin® 285 Resin
Texin® 390 Resin
Desmopan® 453 Resin
5000
6000
5000
Property
Test
Units
Ultimate tensile strength
ASTM D 412
Pounds per square inch
Abrasion resistance
ASTM D 3849 Taber (d)
Milligram loss
15
40
50
Abrasion resistance
ASTM D 1630 NBS
Percent of standard
190
4600
1975
Dynamic coefficient of friction versus steel
ASTM D 1894
0.53
0.38
0.31
Dynamic coefficient of friction versus aluminum
ASTM D 1894
0.61
0.55
0.40
Dynamic coefficient of friction versus brass
ASTM D 1894
0.70
0.64
0.46
Figure 10.2 Molecular structure of Ticona Riteflex® thermoplastic copolyester elastomers.
G4074—low modulus extrusion/molding grade, with antioxidants G4078W—low modulus extrusion/molding grade, with antioxidants G4774—low–medium modulus extrusion/ molding grade, with antioxidants G4778—low–medium modulus extrusion/ molding grade, with antioxidants G5544—medium modulus extrusion/molding grade, with antioxidants High performance: 4056—low modulus extrusion grade, with antioxidants 4068—low modulus extrusion grade, with antioxidants, hardness 40D 4069—low modulus extrusion grade, with antioxidants 4556—medium–low modulus extrusion grade, with antioxidants 5526—medium modulus extrusion grade, with antioxidants 5556—medium modulus extrusion grade, with antioxidants
6356—medium–high modulus extrusion/ molding grade, with antioxidants 7246—high modulus extrusion/molding grade, with antioxidants 8238—highest modulus extrusion/molding grade, with antioxidants Specialty: 3078—very low modulus extrusion/molding grade, with antioxidants HTR4275 BK—pigmented black 5555HS—medium modulus extrusion grade, heat stabilized with antioxidant HTR5612 BK—pigmented black HTR6108—medium–low modulus, with antioxidants HTR8068—medium–low modulus, with flame-retardant compound HTR8139 LV—medium modulus, high viscosity, black pigmented HTR8171 HTR8206
284
Fatigue and Tribological Properties of Plastics and Elastomers
Table 10.9 Goodrich Flexometer of Various DuPont Hytrel Thermoplastic Copolyester Elastomers ASTM D 636 Type of Hytrel
®
Sample Temperature After 20 min (°C)
4056
48
5556
66
2.54 mm stroke, 1.0 MPa static load, 23°C [5].
Type of Hytrel®
Fatigue Limit (MPa)
23°C
G3548 L
>1 × 106
G4074, G4078 W
>1 × 106
G4774, G4778
>1 × 106
G5544
Table 10.10 Flex Fatigue of Various DuPont Hytrel® Thermoplastic Copolyester Elastomers Per ASTM D 671 Type of Hytrel®
Table 10.11 Resistance to Flex Cut Growth, by Ross Flexing Apparatus of Various DuPont Hytrel Thermoplastic Copolyester Elastomers
8 × 105
3078
>1 × 106
4056
>1 × 106
4068
>1 × 106
4556
>1 × 106
4056
5.2
5526, 5556
5 × 105
5556
6.9
6356
5 × 105
6356
6.9
7246
3 × 104
7246
11.0
HTR4275 BK
5 × 104
5555HS
1 × 105
HTR5612 BK
6 × 105
HTR6108
6 × 105
Samples tested to 2.5 million cycles without failure [5].
10.2.1 Fatigue Data Fatigue data for TPE-E or COPE are found in Tables 10.9–10.12.
10.2.2 Tribology Data Tribology data for TPE-E or COPE are found in Tables 10.13–10.15.
10.3 Thermoplastic Polyether Block Amide Elastomers Polyether block amides (PEBA) are plasticizerfree TPEs. The soft segment is the polyether and the hard segment is the polyamide (nylon). For example, Arkema Pebax® 33 series products are based on Nylon 12 (see Section 8.3) and polytetramethylene glycol (PTMG) segments. These are easy to process by injection molding and profile or film extrusion. Often they can be easily melt-blended with other polymers, and many compounders will provide custom products by doing this. Their chemistry allows them to achieve a wide range of physical and mechanical properties by varying the monomeric block types and ratios: • light weight • great flexibility (extensive range)
HTR8139 LV
>1 × 106
HTR8171
>1 × 106
Pierced, ASTM D 1052, cycles to five times cut growth [5].
Table 10.12 DeMattia Flex Life (Pierced) of Various DuPont Hytrel® Thermoplastic Copolyester Elastomers (Per ASTM D 813) [5] Type of Hytrel®
Cycles to Failure at 23°C
G3548 L
3.6 × 104
G4074, G4078 W
3.6 × 104
G4774, G4778
1.6 × 105
G5544
7 × 103
4056
>1 × 106
4068
1.7 × 105
4556
3.6 × 103
5526, 5556
>1 × 106
HTR4275 BK
5.4 × 104
HTR5612 BK
1.1 × 105
HTR6108
5.4 × 103
10: Thermoplastic Elastomers
285
Table 10.13 Coefficient of Friction of DuPont Hytrel® Thermoplastic Copolyester Elastomers [5] Type of Hytrel
®
Hytrel on Steel, Moving Sled—ASTM D 1894 ®
Hytrel® on Steel, Thrust Washer—ASTM D 3702
Static
Dynamic
Dynamic
4056
0.32
0.29
0.88
5526/5556
0.30
0.18
0.94
6356
0.30
0.21
0.90
7246
0.23
0.16
0.90
Table 10.14 Coefficient of Friction of DuPont Hytrel® Thermoplastic Copolyester Elastomers [5,6] Taber Abrasion, CS-17 Wheel (mg/1000 Revolutions)
Taber Abrasion, H-18 Wheel (mg/1000 Revolutions)
G3548L
30
310
G4074
10
223
G4078W
20
260
G4774
13
168
G4778
12
162
G5544
9
116
4056
8
109
4069
15
80
4556
3
72
5526
7
70
5556
6
97
6356
15
109
7246
15
75
8238
9
20
3078
2
90
HTR4275BK
20
227
5555HS
—
112
HTR5612BK
38
186
HTR6108
9
116
HTR8068
25
—
HTR8139LV
4
65
Type of Hytrel® General purpose
High performance
Specialty
• resiliency • very good dynamic properties • high strength
• outstanding impact resistance properties at low temperature • easy processing • good resistance to most chemicals
286
Fatigue and Tribological Properties of Plastics and Elastomers
Table 10.15 Taber Abrasion of Various Riteflex® Thermoplastic Polyester Elastomers (H-18 Wheel, 1000 g ASTM D1044) [7] Riteflex Product
Shore Hardness, D Scale
Melting Point (°C)
Weight Loss (mg/1000 Cycles)
635
35
163
121
640
40
171
90
647
47
187
67
655
55
200
65
663
63
210
62
672
72
214
30
677
77
217
30
Figure 10.3 DeMattia flexural fatigue at −20°C of Arkema Pebax® polyether block amide elastomers [8].
Manufacturers and trade names include the following: Arkema Pebax® and Evonik Vestamid® E. Applications and end uses include the following: noiseless gears and functional elements of sports shoes, as well as for high-performance extrusion components such as paint spray hoses, and vacuum brake booster lines.
10.3.1 Fatigue Data Fatigue data for thermoplastic PEBA elastomers are found in Fig. 10.3.
10.3.2 Tribology Data Tribology data for thermoplastic PEBA elastomers are found in Tables 10.16 and 10.17.
Table 10.16 Taber Abrasion of Arkema Pebax® Polyether Block Amide Elastomers (ASTM D1044, H18 Wheel, 1 kg Load) Pebax® Product Code
mg/1000 Cycles
7233
29
7033
57
6333
84
5533
93
4033
94
3533
104
2533
161
10: Thermoplastic Elastomers
287
Table 10.17 Abrasive Behavior of Evonik Industries Vestamid® E Polyether Block Amide Elastomers [9]
Shore Hardness D
Test Procedure According to DIN 53754 (mg/100 Revolutions)
Test Procedure According to DIN 53516 (mm/40 m Rubbing Distance)
E40-S3
40
20
105
E47-S3
47
—
63
E55-S3
55
8–9
50
E62-S3
62
9–10
47
Vestamid®
Table 10.18 Tribological Properties of RTP Company RTP 2800-40D (40-D Durometer) Versus 1018 C Steel Load (N)
Speed (m/s)
Wear Factor × 10−8 [mm3/(N m)]
Dynamic Coefficient of Friction
35
0.90
0.25
129
0.46
70
1.80
0.25
90
0.69
PV (kPa m/s)
Data obtained per ASTM 3702 [11].
Table 10.19 Tribological Properties of RTP Company RTP 2800-40D TFE 20 (40-D Durometer With 20% PTFE) Versus 1018 C Steel Load (N)
Speed (m/s)
Wear Factor × 10−8 [mm3/(N m)]
35
0.90
0.25
46
0.63
87.5
2.25
0.25
586
0.78
PV (kPa m/s)
Dynamic Coefficient of Friction
Data obtained per ASTM 3702 [11].
10.4 Olefinic Thermoplastic Elastomer Olefinic thermoplastic elastomer (TPO) materials are defined as compounds (mixtures) of various polyolefin polymers, semicrystalline thermoplastics, and amorphous elastomers. Most TPOs are composed of polypropylene and a copolymer of ethylene and propylene called ethylene–propylene rubber (EPR) [10]. A common rubber of this type is called ethylene–propylene diene monomer (EPDM) rubber, which has a small amount of a third monomer, a diene (two carbon–carbon double bonds in it). The diene monomer leaves a small amount of unsaturation in the polymer chain that can be used for sulfur cross-linking. Like most TPEs, TPO products are composed of hard and soft segments. TPO compounds include fillers, reinforcements,
lubricants, heat stabilizers, antioxidants, UV stabilizers, colorants, and processing aids. They are characterized by high impact strength, low density, and good chemical resistance; they are used when durability and reliability are primary concerns. Manufacturers and trade names include the following: ExxonMobil Santoprene® and LyondellBasell Advanced Polyolefins Dexflex®. Applications and uses include the following: roofing and automotive exterior parts; capping distilled water, dairy products, fruit juices, sports drinks, beer, wine, and food; and cosmetics, toiletries, and pharmaceutical packaging—sterilized closures, seals, and liners.
10.4.1 Tribology Data Tribology data for TPO are found in Tables 10.18– 10.24.
288
Fatigue and Tribological Properties of Plastics and Elastomers
Table 10.20 Tribological Properties of RTP Company RTP 2800-60A (60-A Durometer) Versus 1018 C Steel Load (N)
Speed (m/s)
Wear Factor × 10−8 [mm3/(N m)]
17.5
0.45
0.25
52
2.29
35
0.90
0.25
11398
1.63
PV (kPa m/s)
Dynamic Coefficient of Friction
Data obtained per ASTM 3702 [11].
Table 10.21 Tribological Properties of RTP Company RTP 2800-60A TFE 20 (60-A Durometer With 20% PTFE) Versus 1018 C Steel Load (N)
Speed (m/s)
Wear Factor × 10−8 [mm3/(N m)]
17.5
0.45
0.25
647
2.41
35
0.90
0.25
277
2.09
PV (kPa m/s)
Dynamic Coefficient of Friction
Data obtained per ASTM 3702 [11].
Table 10.22 Tribological Properties of RTP Company RTP 2800-35A (35-A Durometer) Versus 1018 C Steel Load (N)
Speed (m/s)
Wear Factor × 10−8 [mm3/(N m)]
8.75
0.22
0.25
103
2.91
17.5
0.45
0.25
23777
1.51
PV (kPa m/s)
Dynamic Coefficient of Friction
Data obtained per ASTM 3702 [11].
Table 10.23 Tribological Properties of RTP Company RTP 2800-35A TFE 20 (35-A Durometer With 20% PTFE) Versus 1018 C Steel Load (N)
Speed (m/s)
Wear Factor × 10−8 [mm3/(N m)]
8.75
0.22
0.25
27231
1.63
17.5
0.45
0.25
35665
1.23
PV (kPa m/s)
Dynamic Coefficient of Friction
Data obtained per ASTM 3702 [11].
Table 10.24 Tribological Properties of RTP Company RTP 2800-35A SI 2 (35-A Durometer With 2% Silicone) Versus 1018 C Steel Load (N)
Speed (m/s)
Wear Factor × 10−8 [mm3/(N m)]
8.75
0.22
0.25
2,343
2.14
17.5
0.45
0.25
62,152
1.42
PV (kPa m/s)
Data obtained per ASTM 3702 [11].
Dynamic Coefficient of Friction
10: Thermoplastic Elastomers
10.5 Other Elastomers There are many other thermoplastic and thermosetting elastomers available. Fatigue and tribological data are scarce for these but two are discussed in this section.
10.5.1 Styrenic Block Copolymer Thermoplastic Elastomers Styrenic block copolymer (SBS) TPEs are multiphase compositions in which the phases are chemically bonded by block copolymerization (see chapter: Introduction to Plastics and Polymers). At least one of the phases is a hard styrenic polymer. This styrenic phase may become fluid when the TPE composition is heated. Another phase is a softer elastomeric material that is rubber-like at room temperature. The polystyrene blocks act as cross-links, tying the elastomeric chains together in a three-dimensional network. SBS TPEs have no commercial applications when the product is just a pure polymer. They must be compounded with other polymers, oils, fillers, and additives to have any commercial value.
10.5.2 Elastomeric AlloyThermoplastic Vulcanizate Vulcanized elastomeric alloys (EA) are TPEs composed of mixtures of two or more polymers that have received a proprietary treatment. Elastomeric alloy-thermoplastic vulcanizates (EA-TPVs) are a category of TPEs made of a rubber and plastic polymer mixture in which the rubber phase is highly vulcanized. The plastic phase of an EA-TPV is a polypropylene, and the rubber phase is an ethylene– propylene elastomer. The vulcanization of the rubber phase of an EA-TPV results in various property improvements
289
such as being insoluble in rubber solvents and reduced swelling in some solvents. The vulcanization offers other property improvements such as: • • • •
increase in tensile strength and modulus decrease in compression set decrease in swelling caused by oils improved retention of properties at temperatures below 200°F (93°C) • improved fatigue resistance
References [1] Drobny JG. Handbook of thermoplastic elastomers. New York: William Andrew; 2007. p. 215–34. [2] A guide to thermoplastic polyurethanes (TPU). Huntsman Chemical; 2010. [3] Thermoplastic polyurethane elastomers (TPU) Elastollan®—product range. BASF; 2009. [4] Texin and Desmopan thermoplastic polyurethane elastomers, a guide to engineering properties. Bayer MaterialScience; 2004. [5] Hytrel® thermoplastic polyester elastomer, technical information. DuPont; 2012. [6] Hytrel® thermoplastic polyester elastomer, module V. DuPont; 2000. [7] Hytrel® thermoplastic polyester elastomer, product-information Europe. Ticona; 2009. [8] Despotopoulou M, O’Brien G. The superior dynamic properties of Pebax® resins. Philadelphia, PA: Arkema; 2004. [9] VESTAMID® E polyamide 12 elastomers. Evonik Industries; 2012. [10] Drobny JG. Handbook of thermoplastic elastomers. New York: William Andrew; 2007. p. 191–9. [11] ; 2008, webpages no longer available.