INCORPORATION OF DEVULCANIZED RUBBER IN A TIRE ...

INCORPORATION OF DEVULCANIZED RUBBER IN A TIRE RUBBER COMPOUNDIN A TIRE RUBBER COMPOUND

M. Meysami, S. Zhu, and C. Tzoganakis

Department of Chemical EngineeringUniversity of Waterloo

W t l O t i C dWaterloo, Ontario, CanadaIP

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Outline

I t d ti• IntroductionRecycled Tires/ Rubber Crumb/

Vulcanization & DevulcanizationVulcanization & Devulcanization

Background and Objectives

• Experimental• ExperimentalProcess/ Materials/Characterization

• Results and Discussion• Results and Discussion• Concluding Remarks• Current Efforts

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Introduction

• Annual generation

of Scrap tires :

World :1.6 billions

USA: 299 millionsUSA: 299 millions

Canada: 30 millions

References:

• “Scrap Tire Market in The United States” , Rubber Manufacturer Association, Nov 2006 ,page 15

•Sangari, S.S.; Kao, N.; Bhattacharya, S.N.; Pavel, D and Silva, K. Mechanochemical Devulcanisation of Elastomers, Rubber Div. ACS, Oct., 2001

•Schnekenburger, Michael, Tire Recycling in Canada‐1999, Rubber Division, ACS, Paper No.166, Set.21‐24, 1999

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Introduction

Tire RecyclingTire Recycling• Statistics in 2005 for the USA show that nearly 87% of scrap tires in the U.S. were

used in end use market.

S i i h h h i i h f ld i i f i f• Statistics show that there is an eight‐fold increase in percentage of consuming of scrap tires by end use market annually since 1990.

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Introduction

( i d i d f l) li i d b 2 % f l i i S• TDF (tire derived fuel) application consumed about 52 % of total scrap tire in U.S

• Civil engineering market is another big consumer of scrap tires in U.S (16%)

• 12 % is consumed by ground rubber products

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Introduction

Ground Rubber : Production Methods

• Ambient grinding process

• Cryogenic grinding process• Cryogenic grinding process

• Wet grinding process

• Extrusion IPR 20

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Introduction

• Rubber Crumb ApplicationsRubber Crumb Applications

• Sport Surfaces

• Geotechnical/ Asphalt Applications

• Rubber and Plastic Products

• Automotive Industry

• Adhesives and Sealants

• Construction

• Shock Absorption and Safety ProductsIP

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Introduction

Rubber Vulcanization

• Raw rubber is soft and sticky material with a

l t il t th d l ti itlow tensile strength and elasticity

• Atomic bridges composed of sulphur or carbon‐

carbon bonds link the polymer chains together

• First discovered by Charles Goodyear in 1839• First discovered by Charles Goodyear in 1839

• The vulcanized rubber is a thermoset material

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Introduction

Rubber Devulcanization

• Devulcanization refers to a process in which the crosslink bonds in the vulcanized rubber cleave totally or partiallyrubber cleave totally or partially.

• The devulcanized rubber is able to be re‐vulcanized and utilized again like a virgin bbrubber

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Introduction

Ad t f b ki th 3D t kAdvantages of breaking the 3D network :

(Devulcanized Rubber)(Devulcanized Rubber)

•Re ‐ CompoundableRe Compoundable

•Re – Processable

•Re ‐ VulcanizeableIP

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Introduction

D l i ti M th dDevulcanization Methods

•MechanicalMechanical

•Ultrasonic

•Chemical

•Microwaves

•MicroorganismsIP

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IntroductionThermo‐Mechanical Devulcanization Process

with Supercritical CO2

• A continuous devulcanization process which is carried out in a twin screw extruder

• No chemical agents

CO t l ti i d f ilit t th• scCO2 acts as a plastisizer and facilitates the process

• US patent 7,189,762

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IntroductionDevulcanization Mechanism

V l i d bb Crosslink

SY

Vulcanized rubber Crosslink

SY

CO2

• ScCO2 diffuses and swells the rubber network

• Elastic constant (k) for S S bonds is about 1/30 that for C C bonds• Elastic constant (k) for S‐S bonds is about 1/30 that for C‐C bonds

• Selective cleavage of S‐S bonds occursIP

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Experimentalp

Valve ValveControl Panel

Feeder

COSyringe Pump

CO2Cylinder

Thermocouples

50 rpm200 C

Gearboxbox

Extruder Pressure TransducersIP

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Experimentalp

50 mm twin screw extruder (American Leistritz, NJ)

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Experimentalp

Screw configuration

• In the first zone the crumb rubber is heated to the devulcanization temperaturep

• Kneading elements after injection of CO2 give the CO2 and rubber crumb a good

mixing and enough shearing and stretching

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Experimentalp

• Rubber Crumb (Edge Rubber co.)Rubber Crumb (Edge Rubber co.)

P ti l iParticle size :

60 mesh

• scCO2 (Praxair)

Sc Co2 injection system

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Experimentalp

Typical devulcanized samples :

a) Samples of devulcanized rubber in strand shape

b) Devulcanized rubber ribbons exiting the die;

c) Samples of devulcanized rubber in ribbon shape

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Intruduction : Tire tread

Tire Tread :• Tread is the wear resistance component of the tire in contact with

the road It must provide traction wet skid and also minimum noise• It must provide traction, wet skid, and also minimum noise generation and low heat buildup

• A blend of natural rubber, polybutadiene (BR),and styrene–butadiene rubber (SBR), compounded with carbon black, silica, oils, and vulcanizing chemicals

Why devulcanized rubber incorporation ?• Lowering the cost of raw material• Recycling of scrap tires

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Intruduction : Tire tread

C i f hi h f iCross‐section of a high‐performance passenger tire

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Experimental

Compounding recipe for samples

p

p g p f p

Ingredients Control 10% 20% 30%

Tread MB 194 phr 174 phr 155 phr 135 phrp p p p

Devulcanized rubber ‐ 20 phr 39 phr 59 phr

OBTS 1.25 phr 1.25 phr 1.25 phr 1.25 phr

PVI 0 3 h 0 3 h 0 3 h 0 3 hPVI 0.3 phr 0.3 phr 0.3 phr 0.3 phr

Sulfur 1.95 phr 1.95 phr 1.95 phr 1.95 phr

•Tire tread MB is a compound of NR and BR plus carbon black, oil, anti ozonant, and etc., ,

•Tire tread MB was replaced by Devulcanized rubber in order to lower the cost of compound

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Experimental

Sample preparation

p

Sample preparation

• The virgin tire compound and devulcanized rubber were first mixed in a• The virgin tire compound and devulcanized rubber were first mixed in a Banbury mixer

• Then curing chemicals were added during milling the compound on a two roll mill

• Appropriate curing time was determined using the MDR test data

• Samples were pressed and cured into standard testing specimens using a hot press

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Experimental Characterization

p

•Mooney viscosity

i i ( )•Curing Properties ( MH, Ts2, T90)

•Tensile properties ( Tensile strength, Elongation at break, Modulus)Modulus)

•Tear strength

•Hardness (shore A)Hardness (shore A)

•Heat aging ( 72 hr @ 70 °C)•Hysteresis (heat build up)y ( p)

•Cut and chip (% of mass loss)IP

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Results & Discussion

Mooney Viscosityy y

40

45

50

(1+4

))

25

30

35

40

visc

osity

(ML(

10

15

20

Moo

ney

• A slight increase for Mooney viscosity can be observed when the percent of

0 10 20 30 40

Devulcanized rubber content in virgin tire compound (%)

g f y y p fdevulcanized rubber in virgin rubber compound increases

• Presence of remained cross‐link bonds could be the reason for the Mooney viscosity increasingy g

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Curing characteristics (Ts2 & Tc90)g ( )

1

1.2

1.4

0.4

0.6

0.8

Tim

e (M

in)

Ts2

Tc90

0

0.2

0.4

0 10 20 30 40

• Scorch time (Ts2) and optimum cure time (Tc90) do not change by incorporation of


( ) p ( ) g y p fdevulcanized rubber into a tire tread compound up to 30 %.

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Curing characteristics (MH)g ( )

9

9.5

10

7.5

8

8.5

MH

(lb-

in)

6

6.5

7

0 10 20 30 40

• A very slight increase at the beginning can be observed for the MH value and then it

0 10 20 30 40


y g g g f Hstarts to decrease

• The difference is very low so one can say the M value remains almost constant• The difference is very low so one can say the MH value remains almost constant.

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Tensile strengthg100 96

87 83100

120

engt

h (%

)

40

60

80

of T

ensi

le s

tre

0

20

40

0 10 20 30 40

Ret

entio

n

• Tensile strength decreases as devulcanized rubber content increases

0 10 20 30 40


g

• Sample with 30 % devulcanized rubber shows an 83% retention of tensile strengthIP

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Elongation at breakg

10094.7

85.580.4

100

120br

eak

(%)

80.4

40

60

80

Elon

gatio

n at

0

20

40

Ret

entio

n of

• Elongation at break decreases as devulcanized rubber content increases

0 10 20 30 40


g

• Sample with 30 % devulcanized rubber shows an 80.4% retention of elongation at breakbreak

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Tensile Modulus

130

140

Modulus 100% Modulus 200% Modulus 300%

90

100

110

120

ntio

n (%

)

60

70

80

90

Ret

en

500 10 20 30 40


• Modulus increases as the content of devulcanized rubber increases in the tire tread compound

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Tear strengthg

100

110

120gt

h (%

)

70

80

90

n of

Tea

r str

en

40

50

60

Ret

entio

n

• Tear strength increases by 7% at the beginning (when 10 % devulcanized rubber is

0 10 20 30 40


g y g g (added) and then starts to decrease

• Compound containing 30% devulcanized rubber shows around 95 % retention of• Compound containing 30% devulcanized rubber shows around 95 % retention of tear strength

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Hardness

62 63 63 62

60

65

70)

45

50

55

60

ness

(sho

re A

)

30

35

40

45

Har

d

300 10 20 30


• Addition of devulcanized rubber does not change the hardness of tire tread compound

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Results & DiscussionHeat aging (72 hr @ 70 °C)

5

0

15

20

Tensile Elongation

10

-8

16 16

-10

-5

10

15

Elon

gatio

n (%

)

∆Te

nsile

(%)

3 3 3.4

-16 -16-18

-20

-15

0

5

0 10 20 30

∆E∆

• Tensile strength increases around 10% after aging for the control compound, this


value for the compounds having devulcanized rubber is around 3 %

• Elongation at break decreases by 8 % for control compound while for samples 10 & 20 this value is 16%. For sample having 30 % devulcanized rubber elongation decreases by 18% after aging process

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Results & DiscussionDamping and Hysteresis

0 4

0.45

0.5

25

30

Hysteresis Tan delta

0.25

0.3

0.35

0.4

10

15

20

Tan δ

yste

resi

s (°

C)

0.1

0.15

0.2

0

5

10

0 10 20 30

Hy

• Specimens were subjected to a dynamic load for 25 min at 148 °C using a flexometer

0 10 20 30


flexometer

• Hysteresis (heat build up under dynamic stress) decreases as content of devulcanized rubber increases in tire tread compound

• Tan δ (damping) does not show a distinguishable trend and fluctuates from 0.332 to 0.408

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Mass loss in cut & chip testp

1314.216

18

20

1111.7

13

8

10

12

14

ass

Loss

(%)

2

4

6

Ma

00 10 20 30 40


• This test shows the service performance of tire treads

• Percent of mass loss in a cut and chip test increases as the percent of devulcanizedrubber increases in a tire tread compoundrubber increases in a tire tread compound

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Concluding remarksg

• Devulcanization of ground tire rubber crumbs under stress in the twin screwextruder with supercritical CO2 is a continuous, cost‐effective, and environmentallyfriendly process

• A reasonably high throughput of devulcanized rubber has been obtained in thedevulcanization process in a twin screw extruder, which is stable

• Devulcanized rubber obtained from our devulcanization process was incorporated• Devulcanized rubber obtained from our devulcanization process was incorporated in a virgin tire compound and the results show that by addition up to 30 % of devulcanized rubber the Mooney viscosity, Hardness, tear strength and curing properties does not change significantly. Tensile strength and elongation at breakproperties does not change significantly. Tensile strength and elongation at break decrease up to 15 % and 20%, and heat build up improves.

• These results show that devulcanized rubber can be incorporated in a tire compound in order to lower the price without significant deterioration ofcompound in order to lower the price without significant deterioration of compound properties. However, additional experiments are required to further optimize the tire compound properties.

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Current Efforts

•Optimization the properties of the tire tread and•Optimization the properties of the tire tread and devulcanized rubber compound

• Incorporation of devulcanized rubber in a conveyor belt compound

•Devulcanization of EPDM scrap rubber

•Preparation of TPV material by using the d l i d bbdevulcanized rubber

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Acknowledgements

/

g

• Financial support from NSERC and C4/Ontario Ministry of Research and Innovation's Ontario Research Commercialization Program is gratefully acknowledgedCommercialization Program is gratefully acknowledged

• Airboss rubber compounding assocciation for using their• Airboss rubber compounding assocciation for using their facilities is greatly appreciated

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