DOT HS 811 270 February 2010

Dynamic Mechanical Properties Of Passenger and Light Truck Tire Treads

DISCLAIMER

This publication is distributed by the U.S. Department of Transportation, National Highway Traffic Safety Administration, in the interest of information exchange. The opinions, findings, and conclusions expressed in this publication are those of the authors and not necessarily those of the Department of Transportation or the National Highway Traffic Safety Administration. The United States Government assumes no liability for its contents or use thereof. If trade names, manufacturers’ names, or specific products are mentioned, it is because they are considered essential to the object of the publication and should not be construed as an endorsement. The United States Government does not endorse products or manufacturers.

TECHNICAL REPORT DOCUMENTATION PAGE

Report No.

DOT HS 811 270 cal analysis , rolling reRecipient's Catalog No.

Recipient's Catalog No.

Title and Subtitle

Dynamic Mechanical Properties of Passenger and Light Truck Tire Treads Report Date

February 2010 Performing Organization Code

Author(s)

Edward R. Terrill, Ph.D.1, Mark Centea1, Larry R. Evans2, James D. MacIsaac Jr.3 1Akron Rubber Development Laboratory, Inc., 2Transportation Research Center Inc., 3National Highway Traffic Safety Administration

Performing Organization Report No.

Performing Organization Name and Address

Akron Rubber Development Laboratory, Inc. 2887 Gilchrist Rd. Akron, Ohio 44305

. Work Unit No. (TRAIS)

. Contract or Grant No.

DTNH22-03-R-08660, DTNH22-07-D-00060

. Sponsoring Agency Name and Address

National Highway Traffic Safety Administration 1200 New Jersey Avenue SE. Washington, DC 20590

. Type of Report and Period Covered

Final . Sponsoring Agency Code

NHTSA/NVS-312 . Supplementary Notes

Project support, testing, and analysis services provided by the Akron Rubber Development Laboratory, Inc. and Transportation Research Center, Inc.

. Abstract

As part of the Energy Independence and Security Act of 2007, the USDOT/NHTSA is establishing a national tire fuel efficiency consumer information program for replacement tires to educate consumers about the effect of tires on automobile fuel efficiency, safety, and durability. As part of the mandate, the agency is examining possible tradeoffs between improved tire rolling resistance and tire safety. It is well reported in scientific literature that tire wet traction capability (an important tire safety parameter) is the primary tradeoff to achieve lower tire rolling resistance if the tread compound is not reformulated to use advanced, and often more costly, constituents. To validate this hypothesis, the tread compounds of forty-eight commercially available passenger and light truck tire were examined by Thermo-Gravimetric Analysis (TGA) and Dynamic Mechanical Analysis (DMA). TGA identifies the chemical composition of the tread rubber, such as filler level, filler type, and polymer mix, all of which affect the rubber’s physical properties. The DMA test evaluates the resulting physical properties of the rubber, and is often used to predict both rolling resistance and wet traction properties. This short report documents the results of those tests, as well as analyzes the predicted rolling resistance and wet traction properties in relation to tread compound formulation. The main study’s Phase 2 report compares these predicted properties to actual rolling resistance and wet traction data for the same tires. Literature on DMA testing has shown that increasing the “tan δ at 0°C” measure of the tread compound correlates to improved wet traction. Conversely, lowering “tan δ at 60°C” correlates to improved rolling resistance. Generally, conventional tread rubber compounds that optimize tan δ at one temperature negatively impact tan δ at the other temperature. These results were evident in the predictions of tread properties by DMA. While the compounding of each tire tread appeared to be tailored to its intended application (high performance, snow, etc.), most treads fit a linear tradeoff between better predicted wet traction (higher tan δ at 0°C) and better predicted rolling resistance (lower tan δ at 60°C). For the tires not predicted to exhibit this tradeoff, an analysis of tread materials indicated that manufacturers employed a variety of compounding techniques including varying filler level, polymer type and/or use of precipitated silica, which may have increased the tire’s manufacturing costs. Additional techniques such as infrared analysis and mass spectrometry would be necessary to identify or quantify the specific polymer blends, and were beyond the scope of this program.

. Key Words

Tire, thermo-gravimetric analysis, dynamic mechanical analysis , rolling resistance prediction, wet traction prediction

. Distribution Statement

Document is available to the public from the National Technical Information Service www.ntis.gov

.

Security Classif. (of this report)

Unclassified . Security Classif. (of this page)

Unclassified . No. of Pages

28 . Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorize

i

TABLE OF CONTENTS BACKGROUND ............................................................................................................................ 1 EXPERIMENTAL TECHNIQUES ................................................................................................ 2 

Test Tires .................................................................................................................................... 2 Dynamic Mechanical Analysis (Temperature Sweeps) .............................................................. 4 Thermal Gravimetric Analysis .................................................................................................... 4 

RESULTS ....................................................................................................................................... 5 TGA Analysis ............................................................................................................................. 5 DMA Analysis ............................................................................................................................ 8 

OVERALL SUMMARY .............................................................................................................. 19 BIBLIOGRAPHY ......................................................................................................................... 20 

ii

LIST OF FIGURES Figure 1. TGA Weight Loss Curve (Tire 3154) ............................................................................. 7 Figure 2. TGA Derivative Weight Loss Curve (Tire 3154) ............................................................ 7 Figure 3. Tan δ as a Function of Temperature from the Tension Test (Tire 3154) ........................ 8 Figure 4. Tan δ as a Function of Temperature from the Shear Test (Tire 3154) ............................ 8 Figure 5. Correlation Between Tan δ at 0°C from the Shear Test and Tan δ at 0°C from the

Tension Test .......................................................................................................................... 11 Figure 6. Correlation Between Tan δ at 60°C from the Shear Test and Tan δ at 60°C from the

Tension Test .......................................................................................................................... 11 Figure 7. Rolling Resistance Indicator Versus phr Filler Level in Compound ............................ 14 Figure 8. Light Truck Tire Tan δ at 0°C (Tension) by Tire Type ................................................ 15 Figure 9. Light Truck Tan δ at 60°C (Tension) by Tire Type ...................................................... 16 Figure 10. Light Truck, Ratio of (Tan δ at 0°C) to (Tan δ at 60°C) by Tire Type ....................... 16 Figure 11. Passenger Tire Tan δ at 0°C (Tension) by Tire Type .................................................. 17 Figure 12. Passenger Tire Tan δ at 60°C (Tension) by Tire Type ................................................ 17 Figure 13. Passenger, Ratio of (Tan δ at 0°C) to (Tan δ at 60°C) by Tire Type .......................... 18 Figure 14. Tan δ at 0°C vs. Tan δ at 60°C (Tension), Tires with Silica and without Silica ......... 18 

iii

LIST OF TABLES Table 1. Test Tires .......................................................................................................................... 2 Table 2. Tire Tread TGA Analysis ................................................................................................. 5 Table 3. Tire Tread DMA Analysis ................................................................................................ 9 Table 4. Tire Tread Categories ..................................................................................................... 12 

iv

EXECUTIVE SUMMARY As part of the Energy Independence and Security Act of 2007, the USDOT/NHTSA is establish-ing a national tire fuel efficiency consumer information program for replacement tires to educate consumers about the effect of tires on automobile fuel efficiency, safety, and durability. As part of the mandate, the agency is examining possible tradeoffs between improved tire rolling resis-tance and tire safety. It is well reported in scientific literature that tire wet traction capability (an important tire safety parameter) is the primary tradeoff to achieve lower tire rolling resistance if the tread compound is not reformulated to use advanced, and often more costly, constituents. To validate this hypothesis, the tread compounds of forty-eight commercially available passenger (P-metric and hard metric) and light truck tire were examined by Thermo-Gravimetric Analysis (TGA) and Dynamic Mechanical Analysis (DMA). TGA identifies the chemical composition of the tread rubber, such as filler level, filler type, and polymer mix, all of which affect the rubber’s physical properties. The DMA test evaluates the resulting physical properties of the rubber, and is often used to predict both rolling resistance and wet traction properties. This short report will document the results of those tests, as well as analyze the predicted rolling resistance and wet traction properties in relation to tread compound formulation. The main study’s Phase 2 report1 compares the predicted properties to actual rolling resistance and wet traction data for the same tires. Scientific literature on the results of DMA testing has shown that increasing the “tan δ at 0°C” measure of the tread compound correlates to improved wet traction. Conversely, lowering “tan δ at 60°C” correlates to improved rolling resistance. Generally, conventional tread rubber com-pounds that optimize tan δ at one temperature negatively impact tan δ at the other temperature, and therefore one component of tread performance is traded for another. Vehicle manufacturers will often specify levels of both wet traction and rolling resistance when sourcing original equipment light vehicle tires. Similarly, consumers looking to purchase replacement tires are provided information on most passenger tires’ wet traction capabilities through the NHTSA’s Uniform Tire Quality Grading Standards (UTQGS). However, the UTQGS system does not pro-vide information on a tire’s rolling resistance. While the compounding of each tire tread appeared to be tailored to its intended application (high performance, snow, etc.), most treads fit a linear tradeoff between better predicted wet trac-tion (higher tan δ at 0°C) and better predicted rolling resistance (lower tan δ at 60°C). For the tires not predicted to exhibit this tradeoff, an analysis of tread materials indicated that manufac-turers employed a variety of compounding techniques including varying filler level, polymer type and/or use of precipitated silica, which may have increased the tire’s manufacturing costs. Use of additional techniques such as infrared analysis and mass spectrometry would be necessary to identify or quantify the specific polymer blends, and were beyond the scope of this program.

v

1

BACKGROUND

Vehicle manufacturers will often specify levels of wet traction, tread life, and rolling resistance (properties which can be traded-off for each of the others) when sourcing original equipment light vehicle tires. Similarly, consumers looking to purchase replacement tires are provided in-formation on most passenger (P-metric and hard metric) tires’ wet traction capabilities through the NHTSA’s Uniform Tire Quality Grading Standards (UTQGS). According to agency data, 3% of tires in the system are rated with the highest (wet) traction grade of “AA”, 75% are rated “A”, 22% are rated “B”, only 1 line of tires rated “C”. (1) UTQGS also provides a rating for treadwear that indicates a tire's wear rate relative to a control tire. The control tire is assigned a grade of 100, and the higher the assigned grade the longer the projected tread life. According to agency data, 15% of tires in the system are rated below 200, 25% are rated 201 - 300, 32% are rated 301 - 400, 20% are rated 401 - 500, 6% are rated 501 - 600, and 2% are rated above 600.2 However, the UTQGS system does not provide information on a tire’s rolling resistance. Therefore it is logical to predict that tire manufacturers may reduce the cost of replacement market tires by sa-crificing rolling resistance, which is unreported to consumers, and optimizing wet traction and tread life. Understanding tire tread viscoelastic (dynamic mechanical) properties in relation to its com-pound composition was the focus of this report. The tire’s tread compound has been shown to be a major contributor to both a tire’s rolling resistance3,4 and to its wet traction. As has been re-ported,5,6 there are often tradeoffs between tire rolling resistance and tire wet traction. The tan-gent delta (δ) at 60°C has been shown to be a predictor of a compound’s rolling resistance, while tangent delta (δ) at 0°C of the tread compound has been shown to be a predictor of wet traction.6-

10 The use of low temperature allows evaluation of dynamic mechanical properties of the tread compound for excitation frequencies not achievable in conventional laboratories. For that reason, the tangent delta (δ) at both 60°C and 0°C was studied. Thermo-Gravimetric Analysis (TGA) is a useful tool for characterizing polymer blends.11-16 The tire tread compound compositions were determined by TGA. This method provides general le-vels of rubber chemicals, polymer, carbon black, and ash. High levels of ash were taken as an indication of silica filler (greater than approximately 3 percent by weight, which is a typical level for zinc oxide curative plus minor impurities). Radial tire treads usually include a blend of polymer types to provide balanced properties. His-torically, emulsion styrene butadiene rubber (E-SBR) provides good wet traction, while natural rubber (NR) has less hysteresis and is thereby better for rolling resistance.17 Recent advances in tread technology have improved the ability of the tire manufacturers to produce tires with both good wet grip and low rolling resistance. Solution styrene butadiene rubber (S-SBR) has been used for years to reduce rolling resistance and improve traction.18,19 The rolling resistance is bet-ter because the S-SBR has fewer chain ends.20 S-SBR offers a higher glass transition temperature (Tg) polymer through the modification of microstructure (medium vinyl polybutadiene).21,22 The use of silica filler plus coupling agent has been shown to improve both rolling resistance and wet traction, particularly when used in conjunction with S-SBR. The effect of a high Tg for an elas-tomer has been found to be improved traction (i.e., a high tangent δ at 0°C). One example of a

high Tg elastomer is 3,4 polyisoprene. High vinyl cis-polybutadiene (PBD) is often used to im-prove treadlife, since tire wear is often a major tradeoff with either rolling resistance and/or wet traction. There are a myriad of additional compounding ingredients and techniques to change traction, wear, and rolling resistance properties. For instance, tires with high levels of reinforcing carbon black provide better treadlife and traction, but have poorer rolling resistance.

EXPERIMENTAL TECHNIQUES

Test Tires The tires in Table 1 were dissected to remove a slice of tread compound for DMA and TGA analysis. The tires in this study covered a broad range of brands, types, sizes, and applications. The reader may notice several small-volume tire sizes, such as a 155R12 or 325/35R28 mixed in with a conventional list of tire sizes like P225/60R16. These small-volume tires were purchased for evaluation of new bead unseat test shoesi and represent the dimensional extremes that were available in the market at that time. The tire tread from these tires had no testing or wear when dissected for DMA or TGA.

2

Table 1. Test Tires

Tire Type

Barcode TIN (DOT Number)

Tire Brand Name

Tire Model Tire Size Sample #

A1 3002 UT7VACM2404 Avon Tech ST 245/45R20 110S ertnb3-72-1

B10 3104 ELA60DD3005 Bridgestone Blizzak RE-VO 1

225/60R16 89Q ertnb3-72-20

B11 3129 7XX0C6A2506 Bridgestone Potenza RE92A

P225/60R16 97H ertnb3-72-21

B12 3154 ELA6CNH1206 Bridgestone Potenza RE750

P225/60R16 98W ertnb3-72-22

B13 3179 EJA6JLC1906 Bridgestone Turanza LS-T P225/60R16 97T ertnb3-72-23

B14 3204 ELA6DCJ0806 Bridgestone Turanza LS-V P225/60R16 97V ertnb3-72-24

B15 3337 VNK3W632006 Dayton Winterforce 225/60R16 98S ertnb3-72-29

B8 2286 0BURB411606 Bridgestone B450 P205/65R15 92S ertnb3-72-45

C1 3049 P5E42V53005 General Ameri G4S 155/80R13 79S ertnb3-72-17

C6 3012 CUDLN2H82604 Continental Cross Con-tact HP

P305/40R23 115W ertnb3-72-4

C8 2567 P5UR4421806 General Ameri G4S P205/65R15 92T ertnb3-72-46

C9 3387 P5111NJ2506 General AmeriTrac TR LT245/75R16 120Q ertnb3-72-31

D1 3034 Y1C8CJLR4204 Arizonian (Dis-count Tire)

Premium Me-tric

155R12 76S ertnb3-72-12

i New bead unseat shoes had to be evaluated to allow tires up to 28-inches in diameter to be tested under the current tests in Federal Motor Vehicle Safety Standards.

Tire Type

Barcode TIN (DOT Number)

Tire Brand Name

Tire Model Tire Size Sample #

D10 3313 U9X3C982305 Cooper Lifeliner Tour-ing SLE H

225/60R16 98H ertnb3-72-28

D7 3229 UP0RC7M3806 Cooper Discoverer ST-C

LT235/85R16 120N ertnb3-72-25

D8 3258 UP11C7M3606 Cooper Discoverer ST-C

LT245/75R16 120N ertnb3-72-26

D9 3287 UPW8C7N3606 Cooper Discoverer ST-C

LT265/75R16 123N ertnb3-72-27

G10 3466 MDUL1MHR3006 Goodyear Integrity P205/75R15 97S ertnb3-72-34

G11 3491 M679B3DR2806 Goodyear Integrity P225/60R17 98S ertnb3-72-35

G5 3016 MK0TBPEV4604 Goodyear Wrangler AT/S

LT275/65R20 126S ertnb3-72-6

G7 3064 M6XEDBDR0906 Goodyear Eagle F1 EMT

P325/30ZR19 94Y ertnb3-72-18

G8 3412 M6X3C9DR3106 Goodyear Integrity 225/60R16 98S ertnb3-72-32

G9 3441 MDKC1MHR3106 Goodyear Integrity P205/75R14 95S ertnb3-72-33

K1 3019 H2WDYCBA5202* Kumho ECSTA STX P305/40R23 115V ertnb3-72-7

K2 3074 H23UYC3A0906 Kumho ECSTA STX 325/35R28 120V ertnb3-72-19

K4 3520 4T11YD1P1206 Kumho Road HT

Venture LT245/75R16 120Q ertnb3-72-36

M10 3545 B72K2EHX1106 Michelin LTX A/S LT245/75R16 120R ertnb3-72-37

M11 3570 B32KB3RX3006 Michelin LTX M/S LT245/75R16 120R ertnb3-72-38

M12 3595 M32KEHFX2906 Michelin X RADIAL LT LT245/75R16 120R ertnb3-72-39

M13 3620 B93VMMRX3505 Michelin Pilot HX MXM4

225/60R16 98H ertnb3-72-40

M14 3720 ANX0EVUU0906 Uniroyal Tiger Paw ASTM 16" SRTT

225/60R16 97S ertnb3-72-44

M2 3038 BAKRFEXX2905 Michelin Pilot Sport Cup

345/30R18 104Y ertnb3-72-13

M5 3047 BE1HUF113404 B F Goodrich All Terrain T/A KO

35x12.50R20LT 120S

ertnb3-72-16

M6 3005 BALAYK115004 B F Goodrich gForce T/A Drag Radial

P345/30R18 LL ertnb3-72-2

M7 3044 BE1AKE113404 B F Goodrich MUD Terrain T/A KM

35x12.50R18LT 118Q

ertnb3-72-15

M8 3008 4M6MLT111905 B F Goodrich gForce T/A 2 305/35R24 112W ertnb3-72-3

M9 3026 K4E4PAUU1306 Uniroyal Tiger Paw AWP

P155/80R13 79S ertnb3-72-9

P3 2056 UTHLPAN2806 Futura [Pep Boys]

Scrambler A/P (P-XL)

P235/75R15XL 108S ertnb3-72-47

P4 3645 UP11PAL2906 Pep Boys Scrambler A/P

LT245/75R16 120N ertnb3-72-41

3

Tire Type

Barcode TIN (DOT Number)

Tire Brand Name

Tire Model Tire Size Sample #

P5 3670 UPX0XB32406 Pep Boys Touring HR P225/60R16 97H ertnb3-72-42

R1 3032 N95CF7731305 Pirelli Scorpion ATR LT325/45R24 120S ertnb3-72-11

R4 3695 XT9HB0612406 Pirelli P6 Four Sea-sons

225/60R16 98H ertnb3-72-43

T1 3023 3D22MBD0705 Mickey Thomp-son

Baja Radial MTZ Tire

LT375/50R18 124 ertnb3-72-8

U1 3014 EUCD4MDR4904 Dunlop SP Sport 5000

P205/60R15 90V ertnb3-72-5

U2 2081 EUFC3TMR4705 Dunlop SP Sport 4000 DSST (Run Flat)

P225/60R17 98T ertnb3-72-48

U3 3362 EUFC3T6R2406 Dunlop SP 4000T DSST

P225/60R17 98T ertnb3-72-30

Y1 3028 FDANNVM0505 Yokohama ADVAN ST 305/35R24 112W ertnb3-72-10

Z1 3041 EJ7BCMJ3704 Fuzion Zri P275/45R20 106V ertnb3-72-14

*Note: The tire from model K1 was made in the 52nd week of 2002 and was few years older than the rest of the tire models (manufactured 2004-2006). This tire may have experienced more evolution of tread properties during the longer period of storage.

4

Dynamic Mechanical Analysis (Temperature Sweeps) A Metravib DMA+150 Dynamic Mechanical Analyzer was used to complete temperature sweeps using two geometries, shear, and tension. The temperature sweep in shear was performed with 2°C/minute heating rate from -60°C to 80°C at 2 Hz, with 0.0025 dynamic strain. The tem-perature sweep in tension was performed with 1°C/minute heating rate from -120°C to 60°C at 2 Hz, with 0.0033 dynamic strain and 0.015 static strain. Thermal Gravimetric Analysis TGA is a useful tool for characterizing polymers. TGA has been utilized to characterize the po-lymer type in blends. The weight loss as a function of temperature has been used to determine polymer loading, rubber chemical loading, carbon black loading, and ash levels. For polymers with very different thermal stabilities the TGA curves can be used to determine the amount of each polymer present. Thermogravimetric analysis (TGA) was performed using about 10 mg of sample. The purge (He) gas flow rate to the TGA was set at 10ml/min during weight loss mea-surements. The heating rate was 10°C/min to improve the resolution of small variations in the decomposition curves. At 600°C, the purge gas was switched over to air for carbon black com-bustion. These average values represent the average of three measurements. Figure 1 shows a representative weight loss curve with the regions that represent each component identified. The derivative curve, shown in Figure 2, provides insight into the transition from each component and also provides some information about polymer blends.

RESULTS

TGA Analysis The tire treads TGA composition analysis averages (rubber chemicals, polymer, carbon black, and ash) are shown in Table 2. High levels of ash were taken as an indication of silica filler (greater than 3 percent by weight). The non-polymer ingredients are estimated as parts-per-hundred-rubber (phr), which is the normal way that rubber formulations are expressed. The re-sults shown are averages of triplicate analyses with good reproducibility. However the phr esti-mates are at best ± 5 phr due to unknown compounding techniques and varying levels of impuri-ties in the individual formulations. For instance part of a high molecular weight resin may par-tially decompose as a “volatile” and the remainder as a “polymer.” Inorganic ash above 5 phr was assigned to “silica,” but could have been any inorganic component.

5

Table 2. Tire Tread TGA Analysis

Tire # Polymer,% (325-550°C)

Volatiles, phr (25-325°C)

Black, phr (550-

850°C) Ash, phr (Residue)

Total Filler, phr

Silica, phr

Total For-mulation,

phr 2056 46.6 32 76 6 76 0 208 2081 51 19 35 42 71 36 190 2286 56.2 19 33 26 53 20 172 2567 55.1 18 60 3 60 0 176 3002 47 31 77 5 77 0 207 3005 51 32 61 4 61 0 190 3008 49.9 24 57 19 70 13 194 3012 49.7 26 72 3 72 0 195 3014 51.7 21 68 4 68 0 188 3016 54.2 18 59 7 59 0 178 3019 50 26 71 3 71 0 194 3023 51.1 26 67 3 67 0 190 3026 52.2 20 68 3 68 0 186 3028 51.1 21 43 31 69 25 190 3032 51.4 21 60 14 67 8 188 3034 53.9 19 63 3 63 0 180 3038 47.8 26 63 20 77 14 203 3041 53.2 22 62 4 62 0 182 3044 55.9 19 57 3 57 0 173 3047 54.5 20 59 4 59 0 178 3049 51.9 21 69 3 69 0 187 3064 47.1 33 53 27 73 21 206 3074 49.1 27 73 3 73 0 198 3104 57 18 32 25 51 19 169 3129 56.8 18 31 27 52 21 170 3154 49 25 54 25 73 19 198 3179 51.3 22 44 29 67 23 189

Tire # Polymer,% (325-550°C)

Volatiles, phr (25-325°C)

Black, phr (550-

850°C) Ash, phr (Residue)

Total Filler, phr

Silica, phr

Total For-mulation,

phr 3204 52 25 13 54 62 48 186 3229 55.9 19 52 8 52 0 173 3258 55.8 20 51 8 51 0 173 3287 56 19 51 8 51 0 173 3313 46.9 33 77 3 77 0 207 3337 54.3 19 63 3 63 0 178 3362 52.4 18 33 40 67 34 185 3387 53.7 18 67 2 67 0 180 3412 60.4 15 38 12 45 6 159 3441 52.9 23 60 6 60 0 183 3466 58.3 22 45 4 45 0 165 3491 63.3 15 33 11 37 5 152 3520 56.4 21 53 4 53 0 171 3545 63.6 10 43 2 43 0 150 3570 63.3 11 45 2 45 0 152 3595 65.2 11 41 1 41 0 148 3620 54.3 19 10 55 59 49 178 3645 55.3 24 55 1 55 0 175 3670 47.1 29 79 4 79 0 206 3695 48.3 30 42 35 71 29 201 3720 55 19 30 32 57 26 176

6

Figure 1. TGA Weight Loss Curve (Tire 3154)

Figure 2. TGA Derivative Weight Loss Curve (Tire 3154)

1

Der

ivat

ive

of W

eigh

t Los

s

0

-1

-2

-3

-4

-5

-60 100 200 300 400 500 600 700 800 900

Temperature (deg C)

120

100

W

eigh

t Ret

aine

d (%

)

80

60

40

20

00 200 400 600 800 1000

Temperature (deg C)

Volatile Components

Polymer

Carbon Black

Ash (Zinc Oxide, Silica, …

7

8

DMA Analysis Typical examples of temperature sweep data by the tension method (Figure 3) and the shear me-thod (Figure 4) are shown below. Because the temperature sweep in tension started at -120°C, the tread composition of elastomer blends can be observed along with their effect on tangent del-ta at 0°C and 60°C. Qualitative information about polymer types can also be obtained using the tangent delta temperature sweep data. These results may be combined with the TGA derivative curves to provide some estimate of the probable polymers. Additional techniques such as infra-red analysis and mass spectrometry would be necessary to identify or quantify polymer blends, and were beyond the scope of this program.

Figure 3. Tan δ as a Function of Temperature from the Tension Test (Tire 3154)

Figure 4. Tan δ as a Function of Temperature from the Shear Test (Tire 3154)

0.6

0.5

Tang

ent D

elta 0.4

0.3

0.2

0.1

0-100 -50 0 50 100-0.1

Temperature (deg C)

0.8

Tang

ent D

elta

0.70.60.50.40.30.20.10.0

-150 -100 -50 0 50 100Temperature (deg C)

Understanding tire tread viscoelastic (dynamic mechanical) properties is a main focus of the work (Table 3). Tangent δ at 60°C was used as a predictor of the tread compound’s contribution to tire rolling resistance. Tangent δ at 0°C was used as a predictor of tread compound wet trac-tion. Also shown is the ratio of the (Tangent δ at 0°C) / (Tangent δ at 60°C). This ratio and the absolute level of the values are often related to the design parameters of the tire. For instance, tire 2286, which is an OE-type passenger all-season tire, would be expected to have a reasonable level of wet traction, and very good rolling resistance, while tire 3038, an ultra high-performance summer tire, would be expected to have very high wet traction, but poor rolling resistance. A low Tangent δ at 60°C also relates to minimizing the heat build-up of the tire tread, a concern for deep lug tires.

9

Table 3. Tire Tread DMA Analysis Tension Shear

Tire # Tan δ at

0°C Tan δ at

60°C Ratio 0/60

Tan δ at 0°C

Tan δ at 60°C

Ratio 0/60

2056 0.239 0.162 1.48 0.17 0.125 1.36 2081 0.287 0.214 1.34 0.183 0.158 1.16 2286 0.207 0.0959 2.16 0.199 0.0911 2.18 2567 0.253 0.184 1.38 0.186 0.144 1.29 3002 0.256 0.197 1.30 0.177 0.151 1.17 3005 0.432 0.256 1.69 0.351 0.207 1.70 3008 0.31 0.226 1.37 0.214 0.177 1.21 3012 0.347 0.171 2.03 0.271 0.144 1.88 3014 0.318 0.235 1.35 0.207 0.165 1.25 3016 0.2 0.176 1.14 0.148 0.148 1.00 3019 0.287 0.207 1.39 0.208 0.16 1.30 3023 0.233 0.161 1.45 0.171 0.125 1.37 3026 0.253 0.2 1.27 0.181 0.154 1.18 3028 0.406 0.21 1.93 0.297 0.164 1.81 3032 0.268 0.215 1.25 0.204 0.172 1.19 3034 0.226 0.178 1.27 0.171 0.156 1.10 3038 0.557 0.272 2.05 0.437 0.202 2.16 3041 0.268 0.194 1.38 0.198 0.149 1.33 3044 0.233 0.174 1.34 0.165 0.143 1.15 3047 0.224 0.162 1.38 0.163 0.128 1.27 3049 0.255 0.191 1.34 0.19 0.157 1.21 3064 0.499 0.216 2.31 0.434 0.167 2.60 3074 0.282 0.203 1.39 0.204 0.154 1.32 3104 0.2 0.155 1.29 0.16 0.133 1.20 3129 0.194 0.0771 2.52 0.174 0.067 2.60 3154 0.387 0.193 2.01 0.28 0.146 1.92 3179 0.265 0.168 1.58 0.19 0.138 1.38 3204 0.313 0.145 2.16 0.233 0.132 1.77 3229 0.184 0.119 1.55 0.147 0.0878 1.67

Tire # 3258 3287 3313 3337 3362 3387 3412 3441 3466 3491 3520 3545 3570 3595 3620 3645 3670 3695 3720

Tension Tan δ at Tan δ at

0°C 60°C 0.193 0.135 0.174 0.108 0.26 0.192

0.208 0.15 0.256 0.173 0.269 0.214 0.169 0.0762 0.245 0.1880.242 0.181 0.174 0.086 0.238 0.181 0.192 0.1540.198 0.157 0.206 0.158 0.254 0.147 0.247 0.181 0.271 0.207 0.296 0.201 0.289 0.195

Ratio 0/60 1.43 1.61 1.351.39 1.48 1.26 2.22

1.30 1.34 2.02 1.31

1.25 1.26 1.30 1.73 1.36 1.31 1.47 1.48

Shear Tan δ at Tan δ at

0°C 60°C 0.139 0.08550.136 0.0867

0.183 0.16 0.158 0.1230.202 0.147 0.191 0.171 0.164 0.0689 0.18 0.152

0.184 0.151 0.177 0.07540.176 0.138 0.16 0.136

0.161 0.133 0.157 0.132 0.168 0.117 0.183 0.142 0.161 0.156 0.211 0.159 0.202 0.146

Ratio 0/60

1.63 1.57

1.14 1.28

1.37 1.12 2.38

1.18 1.22

2.35 1.28

1.18 1.21 1.19 1.44 1.29 1.03 1.33 1.38

10

The correlation between tangent δ at 0°C data from the tension and shear experiments were high-ly correlated with an r-squared of 0.91 (Figure 5). The correlation between tangent δ at 60°C data from the tension and shear experiments were highly correlated with an r-squared of 0.94 (Figure 6). Therefore, the ratios of the tangent δ’s at 0°C and 60°C are independent of the measurement technique used.

Figure 5. Correlation Between Tan δ at 0°C from the Shear Test and Tan δ at 0°C from the

Tension Test

Figure 6. Correlation Between Tan δ at 60°C from the Shear Test and Tan δ at 60°C from

the Tension Test

0.50

est

t y = 0.7619x - 0.0025

ear 0.40

R2 = 0.9062 s

hmor 0.30f

Ceg

lta a

t 0d 0.20

e 0.10d naT

0.000.0 0.1 0.2 0.3 0.4 0.5 0.6

Tan delta at 0degC from tension test

0.25

test

y = 0.704x + 0.016

ear

0.20 R2 = 0.936

sh

mo 0.15

frC

eg 6

0d 0.10

at

atle 0.05

dnaT 0.000.00 0.05 0.10 0.15 0.20 0.25 0.30

Tan delta at 60degC from tension test

11

Table 4 lists the general tire types along with the filler level and tangent δ values for the tires. The tires in this study covered a broad range of brands, types, sizes, and applications. Therefore it is not surprising that the tread data indicate that a broad range of compounding strategies was used in these tires. In general the highway all-season light truck tires seem to be similar, with the traction and on/off or off road tires having more variety among the tires. Passenger tires appear to be compounded for more specialized applications, even within tire types. In general, the all-season tire types trend toward lower predicted rolling resistance while the high-performance tires trend toward higher predicted wet traction. The level of filler is also important. Figure 7 illu-strates the tendency of the rolling resistance of the compound to increase as the total phr of filler in the tread compound increases.

12

Table 4. Tire Tread Categories

Barcode Tire Category Tire Class Filler,

phr Silica,

phr

Tension Method

Shear Method

Tan δ at 0°C

Tan δ at

60°C

Tan δ at 0°C

Tan δ at 60°C

2056 Passenger All-season 76 0 0.239 0.162 0.170 0.125 2081 Passenger Touring All-season Run Flat 71 36 0.287 0.214 0.183 0.158 2286 Passenger All-season 53 20 0.207 0.0959 0.199 0.09112567 Passenger All-season 60 0 0.253 0.184 0.186 0.144 3002 Light Truck Street/Sport Truck

All-season 77 0 0.256 0.197 0.177 0.1513005 Passenger Street-Legal Drag Racing 61 0 0.432 0.256 0.351 0.207 3008 Passenger High-Performance Summer 70 13 0.310 0.226 0.214 0.177 3012 Light Truck Street/Sport Truck

All-season 72 0 0.347 0.171 0.271 0.1443014 Passenger High-Performance

All-season 68 0 0.318 0.235 0.207 0.1653016 Light Truck Light Truck Traction 59 0 0.200 0.176 0.148 0.148 3019 Light Truck Street/Sport Truck

All-season 71 0 0.287 0.207 0.208 0.1603023 Light Truck Off-Road Maximum

Traction 67 0 0.233 0.161 0.171 0.1253026 Passenger All-season 68 0 0.253 0.200 0.181 0.154 3028 Light Truck Street/Sport Truck Summer 69 25 0.406 0.210 0.297 0.164 3032 Light Truck Light Truck Traction 67 8 0.268 0.215 0.204 0.172 3034 Passenger All-season 63 0 0.226 0.178 0.171 0.156 3038 Passenger High-Performance Summer 77 14 0.557 0.272 0.437 0.202 3041 Passenger High-Performance Summer 62 0 0.268 0.194 0.198 0.149 3044 Light Truck Off-Road Maximum

Traction 57 0 0.233 0.174 0.165 0.1433047 Light Truck Light Truck Traction 59 0 0.224 0.162 0.163 0.128

Barcode Tire Category Tire Class Filler,

phr Silica,

phr

Tension Method

Shear Method

Tan δ at 0°C

Tan δ at

60°C

Tan δ at 0°C

Tan δ at 60°C

3049 Passenger All-season 69 0 0.255 0.191 0.190 0.157 3064 Passenger High-Performance Run Flat 73 21 0.499 0.216 0.434 0.167 3074 Light Truck Street/Sport Truck

All-season 73 0 0.282 0.203 0.204 0.154 3104 Passenger Winter 51 19 0.200 0.155 0.160 0.133 3129 Passenger High-Performance

All-season 52 21 0.194 0.0771 0.174 0.06703154 Passenger High-Performance Summer 73 19 0.387 0.193 0.280 0.146 3179 Passenger Touring All-season 67 23 0.265 0.168 0.190 0.138 3204 Passenger Touring All-season 62 48 0.313 0.145 0.233 0.132 3229 Light Truck Light Truck Traction 52 0 0.184 0.119 0.147 0.08783258 Light Truck Light Truck Traction 51 0 0.193 0.135 0.139 0.08553287 Light Truck Light Truck Traction 51 0 0.174 0.108 0.136 0.08673313 Passenger Touring All-season 77 0 0.260 0.192 0.183 0.160 3337 Passenger Winter 63 0 0.208 0.150 0.158 0.123 3362 Passenger Touring All-season 67 34 0.256 0.173 0.202 0.147 3387 Light Truck Light Truck Traction 67 0 0.269 0.214 0.191 0.171 3412 Passenger All-season 45 6 0.169 0.0762 0.164 0.06893441 Passenger All-season 60 0 0.245 0.188 0.180 0.152 3466 Passenger All-season 45 0 0.242 0.181 0.184 0.151 3491 Passenger All-season 37 5 0.174 0.0860 0.177 0.07543520 Light Truck Highway All-season 53 0 0.238 0.181 0.176 0.138 3545 Light Truck Highway All-season 43 0 0.192 0.154 0.160 0.136 3570 Light Truck Highway All-season 45 0 0.198 0.157 0.161 0.133 3595 Light Truck Highway All-season 41 0 0.206 0.158 0.157 0.132 3620 Passenger Touring All-season 59 49 0.254 0.147 0.168 0.117 3645 Light Truck Highway All-season 55 0 0.247 0.181 0.183 0.142 3670 Passenger All-season 79 0 0.271 0.207 0.161 0.156 3695 Passenger High-Performance

All-season 71 29 0.296 0.201 0.211 0.159 3720 Passenger Touring All-season 57 26 0.289 0.195 0.202 0.146

13

Figure 7. Rolling Resistance Indicator Versus phr Filler Level in Compound

Tan delta at 60C

0.070.080.090.100.110.120.130.140.150.160.170.180.190.200.210.220.230.240.250.260.270.28

Total Filler Level30 40 50 60 70 80

14

Figures 8-10 show the range of tangent δ values for light truck tires. The mean and 95% confi-dence intervals are shown for each category. A bar indicates that only a single value for that cat-egory was available. For the light truck tires, the wet traction, predicted by tangent δ values at 0°C, are similar across categories, with sport models and a summer tire being somewhat higher. Parallel trends were seen for the rolling resistance, predicted by tangent δ values at 60°C. The average ratio of tangent δ values at 0°C to 60°C ranged from 1.3 to 1.5 with the exception of the highway summer tire at 1.9. Figures 11-13 show the range of tangent δ values for passenger tires, with the mean and 95% confidence intervals for each category. All-season tires had similar mean values for wet traction (tangent δ values at 0°C), but they cover a considerable range of values. High-performance and specialty tires had higher levels of predicted wet traction and cover a very large range. For pas-senger tires the average predicted rolling resistance (tangent δ values at 60°C) was lower for all-season tires than for high-performance and specialty tires. Again, all types covered a wide range of values. The ratio of tangent δ values at 0°C to tangent δ values at 60°C varied from 1.5 to 1.8 for most of the passenger tires, with a very wide range of values among the tires. Figure 14 shows the tangent δ values at 0°C versus the tangent δ values at 60°C for the 30 tires that contained no silica versus the 18 tires that contained silica in the tread compound. The re-duction in wet traction (lower tangent δ values at 0°C) as the rolling resistance of the tire im-

proves (lower tangent δ values at 60°C) is evident, especially for the tires that do not contain sili-ca. The two tires that do not fit the linear relationship are a drag-racing tire and a high-performance sport light truck tire that apparently use other compounding techniques, such as specialized polymers, to achieve a higher ratio of tangent δ values. As has been extensively pub-lished, many tires that contain silica tend to have better wet traction at the same rolling resistance value, however the overall trade-off between rolling resistance and wet traction is still evident. It should be noted that the use of silica to improve rolling resistance while maintaining wet traction requires complementary compounding ingredients and techniques. Silica is also added to tradi-tional tread formulations for a variety of reasons, such as improving tear strength and lowering heat build-up, especially for deep-lug and winter tires. It also was used in two of the high-performance summer tire treads, presumably to improve wet traction without attempting to main-tain low rolling resistance.

15

Figure 8. Light Truck Tire Tan δ at 0°C (Tension) by Tire Type

Tangent delta 0oC (Tension), Light Truck Tires

0.45

0.4

0.35

Tang

ent d

elta 0.3

0.25

0.2

0.15

0.1

0.05

0Highway All Traction Off Road Sport All Season Highway

Season Summer

Light Truck Tire Category

Figure 9. Light Truck Tan δ at 60°C (Tension) by Tire Type

Figure 10. Light Truck, Ratio of (Tan δ at 0°C) to (Tan δ at 60°C) by Tire Type

Tangent delta 60oC (Tension), Light Truck Tires

0.3

0.25

a 0.2

t d

elt

en 0.15

gTa

n

0.1

0.05

0Highway All Traction Off Road Sport All Season Highway

Season Summer

Light Truck Tire Category

Ratio of Tangent delta 0oC to 60oC (Tension), Light Truck Tires

2.5

60C 2

0C /

Rat

io, T

ange

nt d

elta

1.5

1

0.5

0Highway All Traction Off Road Sport All Season Highway

Season SummerLight Truck Tire Category

16

Figure 11. Passenger Tire Tan δ at 0°C (Tension) by Tire Type

Figure 12. Passenger Tire Tan δ at 60°C (Tension) by Tire Type

Tangent delta 0oC (Tension), Passenger Tires

0.8

0.7

0.6

Tang

ent d

elta 0.5

0.4

0.3

0.2

0.1

0

All Season High High High Drag Racing Touring All Touring All WinterPerformance Performance Performance Season Season RunAll Season Run Flat Summer Flat

Passenger Tire Category

Tangent delta 60oC (Tension), Passenger Tires0.45

0.4

0.35

0.3atlen

t de 0.25

Tang 0.2

0.15

0.1

0.05

0All Season High High High Drag Racing Touring All Touring All Winter

Performance Performance Performance Season Season RunAll Season Run Flat Summer Flat

Passenger Tire Category

17

Figure 13. Passenger, Ratio of (Tan δ at 0°C) to (Tan δ at 60°C) by Tire Type

Figure 14. Tan δ at 0°C vs. Tan δ at 60°C (Tension), Tires with Silica and without Silica

Ratio of Tangent delta 0oC to 60oC (Tension), Passenger Tires

4

3.5

/ 60

C

3

a 0C 2.5

tlen

t de

2

Tang 1.5

o tia 1

R

0.5

0All Season High High High Drag Racing Touring All Touring All Winter

Performance Performance Performance Season Season RunAll Season Run Flat Summer Flat

Passenger Tire Category

Tan delta at 0°C Versus Tan delta at 60°C

0.6High-Performance Summer Passenger

0.55

0.5

at 0

°C

Drag Racing Tire0.45 Compounds

Containing Silica

Tang

ent d

elta

0.4Sport Light Truck Tire

0.35 Compounds with 0 phr Silica

0.3

0.25

0.2

0.15

0.10.06 0.11 0.16 0.21 0.26 0.31

Tangent delta at 60°C

18

OVERALL SUMMARY

Forty-eight commercial tire treads were examined by TGA for compositional analysis and DMA for prediction of rolling resistance and wet traction. These results are compared to actual rolling resistance and wet traction data in the main study’s Phase 2 report.1 Each tire appeared to have been compounded to maximize specific performance properties in its intended application. All-season light truck tires appear to have relatively uniform properties of wet traction and rolling resistance, while sport and traction light truck tires have a wide range of traction properties. For passenger tires, the high-performance tires generally appear to have been compounded to max-imize traction while the all-season tires appear to have more tires that emphasize rolling resis-tance. Overall (i.e., for any tire type), the wide range of properties found is consistent with the variety of the manufacturers, types, sizes and market segments for the tires studied. Most tire treads fit a linear tradeoff between better predicted wet traction (higher tan δ at 0°C) and better predicted rolling resistance (lower tan δ at 60°C). When examined by TGA, tires pre-dicted to have improved rolling resistance without reductions in wet traction appeared to use a variety of compounding techniques including varying filler level, polymer type, and/or use of precipitated silica to achieve these values. Use of additional techniques such as infrared analysis and mass spectrometry would be necessary to identify or quantify the specific polymer blends, and were beyond the scope of this program.

19

20

BIBLIOGRAPHY

1. Evans, L. R.; MacIsaac, J. D.; Harris, J. R.; Yates, K.; Dudek, W.; Holmes, J.; Popio, J.; Rice, D.; Salaani, M. K. NHTSA Tire Fuel Efficiency Consumer Information Program Development: Phase 2 — Effects of Tire Rolling Resistance Levels on Traction,Treadwear, and Vehicle Fuel Economy; U.S. Department of Transportation, National Highway Traffic Safety Adminstration: Washington, DC, 2009.

2. U.S. Department of Transportation, National Highway Traffic Safety Adminstration. Tire Ratings-UTQGS. www.Safercar.gov .

3. Chang, L. Y.; Shackleton, J. S. An Overview of Rolling Resistance. Elastomerics 1983, 115(3), 18-26.

4. Hall, D. E.; Moreland, J. C. Rubber Chem. Technol. 2001, 74 (3), 525. 5. Saito, Y. Kautsch. Gummi Kunstst. 1986, No. 39, 30. 6. Nordsiek, K. H. Kautsch. Gummi Kunstst. 1985, No. 38, 178. 7. Patkar, S. D.; Bice, J.-A. E.; Okel, T. A. Effect of Silica on the Viscoelastic Properties of a

Model Tread Compound. Rubber World 1998, 218, 21. 8. Wolff, S.; Gorl, U.; Wang, M. J.; Wolff, W. Silica-based tread compounds: Background and

performance. TyreTech '93, Basel, Switzerland, October 1993. 9. Saito, Y. Kautsch. Gummi Kunstst. 1986, No. 39, 30.

10. Scriver, R. M. Tire with Tread of Selective Rubber Blend. U.S. Patent 4,894,420, January 16, 1990.

11. Shield, S. R.; Ghebremeskel, G. N.; Hendrix, C. Rubber Chem. Technol. 2001, 74 (5), 803. 12. Sichima, W. J. American Laboratory 1993, 25 (7), 45. 13. Laird, J. L. Rubber World 1990, 201 (4), 13. 14. Zeyen, R. L. TA: Practical applications for chemical reconstruction of rubber compounds.

Rubber World 1989, 199 (4), 14. 15. Schwartz, N. V. Gummi Fasern Kunststoffe 1984, 37 (6), 274. 16. Azumi, T.; Takashima, S. Kogyo Kagaku Zasshi 1966, 69 (9), 1823. 17. Bond, R.; Williams, A. R. Pneumatic Tires. U.S. Patent 4,280,543, July 28, 1981. 18. Nordsiek, K. H.; Kiepert, K. M. Kautsch. Gummi Kunstst. 1980, 33 (4), 251. 19. Nordsiek, K. H.; Kiepert, K. M. New Structures of Butadiene-Styrene Copolymers.

International Rubber Conference, Venice, Italy, October 3-6, 1979. 20. Sommer, N. Kautsch. Gummi Kunstst. 1975, 28 (3), 131. 21. Nordsiek, K. H. Kautsch. Gummi Kunstst. 1972, 25 (3), 87. 22. Nordsiek, K. H.; Kiepert, K. M. The Characteristic features of vinylbutadienes. International

Rubber Conference, Harrogate, England, June 8-12, 1982.

DOT HS 811 270February 2010