11

CHANCES AND CHALLENGES

OF CLOSING THE MATERIAL CIRCLE FOR

PASSENGER CAR TIRE RUBBER

University Twente

Engineering Technology

Elastomer Technology & Engineering

Sustainable Elastomer Systems

Enschede, the Netherlands

Tomas Bata University Centre of Polymer Systems Zlín, Czech Republic

G. HEIDEMAN

H. VAN HOEK

S. SAIWARI

W. DIERKES

J. NOORDERMEER

A. BLUME

22

CHANCES AND CHALLENGES

OF CLOSING THE MATERIAL CIRCLE FOR

PASSENGER CAR TIRE RUBBER

3

Particulate rubber

Reclaim

Devulca-nizate

Radiation

Biological

Mechanical

Thermo-mechanical

Thermo-mechanical-

spCO2

Thermo-mechanical-

chemical

As such

Compounded

Particulate rubber

Granulate

Powder

ambient

cryogenic

Introduction Types of recycled rubber

4

Particulate rubber

Granulate

Powder

ambient

cryogenic

Introduction Types of recycled rubber

Particulate rubber

Reclaim

Devulca-nizate

Radiation

Biological

Mechanical

Thermo-mechanical

Thermo-mechanical-

spCO2

Thermo-mechanical-

chemical

As such

Compounded

5

Tire parts

Tread

Sidewall

Innerliner

Carcass

Bead

Aged

Post-consumer

Factory

Degree of contamination

High

Low

https://www.futuretire.com/how-are-tires-constructed/

Whole tires

Passenger car

Truck

Off-the-road

Others

Mix

Silica

Carbon black

Introduction Feedstock

6

Tire parts

Tread

Sidewall

Innerliner

Carcass

Bead

Aged

Post-consumer

Factory

Degree of contamination

High

Low

https://www.futuretire.com/how-are-tires-constructed/

Whole tires

Passenger car

Truck

Off-the-road

Others

Mix

Silica

Carbon black

Introduction Feedstock

7

Granulometry

Fine

Coarse

Introduction

Concentration

Devulcanization aid

Processing oil

Stabilizer

Pre-treatment

Swelling time

Swelling temperature

Devulc. process type

Discontinuous

Continuous

Small scale

Larger scale

Process development

8

Granulometry

Fine

Coarse

Introduction Process development

Concentration

Devulcanization aid

Processing oil

Stabilizer

Pre-treatment

Swelling time

Swelling temperature

Devulc. process type

Discontinuous

Continuous

Small scale

Larger scale

9

Experimental Devulcanization

https://media.labcompare.com/m/1/product/13082337-400x300.jpg

Extruder process

Process temperature 220ºC

Residence time 6 min

Atmosphere Inert (N2)

Cooling Calander

Post processing Milling

Particle size feedstock 1-3 mm

Throughput Few kg/h

Internal mixer process

TCU settings 220ºC

Mixing chamber volume 50 ml

Residence time 6 min

Rotor speed 50 rpm

Atmosphere Inert (N2)

Cooling LN2

Particle size feedstock 1-3 mm

Batch size 40 g

Small scale

Larger scale

Type Screw diameter D [mm]

Flight depth[mm]

Length [mm]

Screw type

BerstorffZE 25 A UTXi

25 4.2 42DTwin screw Co-rotating

10

DEVULCANISATION:

REGENERATION:

+sol

gel

sol

Experimental Analytics Horikx-Verbruggen plot

11

Blending of 5% re-plasticized rubber with a bright white compound

Shade of grey from network detached part of the rubber

Particles non-devulcanized cores of the particles or filler clusters

White rubber compound

5% completelyre-plasticized

rubber 10% ground

rubber

Reference samples

Samples with 5% devulcanizate

Experimental Analytics White rubber test

13

Feedstock Particle size

Model compounds Fine: 0,7-2,0 mm

Coarse: 2,0-3,5 mm

Whole passenger car tire rubber

0

100

200

300

400

500

0,0

2,0

4,0

6,0

8,0

10,0

12,0

14,0

16,0

Silica -coarse

Silica -fine

Carbonblack -coarse

Carbonblack -

fine

Elon

gatio

n at

bre

ak [%

]

Tens

ile s

treng

th [M

Pa]

0

100

200

300

400

500

0,0

2,0

4,0

6,0

8,0

10,0

12,0

14,0

16,0

< 3,5 mm 2-3,5 mm 2-0,7 mm < 0,7 mm

Elon

gatio

n at

bre

ak [%

]

Tens

ile s

tren

gth

[MPa

]

14

Feedstock Whole tire - PCT

B

A

A

B

Increasing age

During service life

15

Har

dnes

s [S

hore

A] 60

40

20

0 Increasing age

ML(

1+4)

, MU 100

50

0

ΔTo

rque

[Nm

]

4

3

2

1

0

Additive phr

Devulcanizate 100

Stearic acid 0.5

Zinc oxide 1.5

6PPD 2.0

TMQ 2.0

TBBS 1.5

Sulfur 1.5

AB

Feedstock Whole tire - PCT During service life

16

Tire part - tread Carbon black versus silica

0

100

200

300

400

500

0

5

10

15

20

25

Silica/silane- virgin

Silica/silanede- and

revulcanized

Carbonblack - virgin

Carbonblack de-

andrevulcanized

Elon

gatio

n at

bre

ak [%

]

Tens

ile s

tren

gth

[MPa

]

Additive phr phr

SBR 65 65

BR 35 35

Zinc oxide 3.0 2.5

Stearic acid 2.0 1.0

TDAE 35 32.5

Carbon black N550 80

Silica Zeosil 1165MP 90

TESPT 7.2

6PPD 1.0 2.0

TMQ 2.0 2.0

TBBS 1.5 1.7

DPG 2.0

Sulfur 1.5 1.4

Model compounds (non-aged)

Batch mixer

TDAE: 6.2%

DPDS: 18 mmol

Antioxidant: 1%

Swelling: 30 minutes, 65ºC

Mixer TCU: 220ºC

Devulc, time: 6 minutes

N2 purging

Devulcanization conditions:

Feedstock

17

Silica - silane

0

20

40

60

80

100

0 0,2 0,4 0,6 0,8 1

Sol f

ract

ion

(%)

Decrease in crosslink density

Random main chain scissionCrosslink scissionUntreated TESPTTESPT 220 °CTESPT 250 °C

Additive TESPT TESPD PESPMphr

SSBR 103 103 103BR 25 25 25Zeosil 1165 80 80 80Silane 7.0 6.3 9.0TDAE 5.0 5.0 5.0ZnO 2,5 2,5 2,5Stearic acid 2,5 2,5 2,56PPD 2.0 2.0 2.0TMQ 2.0 2.0 2.0Sulfur 1,4 2.0 2.2TBBS 1,7 1,7 1,7DPG 2.0 2.0 2.0

TESPT

Devulcanization conditions:

Batch mixer

TDAE: 6.2%

DPDS: 15 mmol

Swelling: 30 minutes, 65ºC

Fill factor: 0.7

Rotor speed: 50 rpm

N2 purging

Tire part - tread Feedstock

18

Devulcanization conditions:

Batch mixer

TDAE: 6.2%

DPDS: 15 mmol

Swelling: 30 minutes, 65ºC

Fill factor: 0.7

Rotor speed: 50 rpm

N2 purging 0

20

40

60

80

100

0 0,2 0,4 0,6 0,8 1

Sol f

ract

ion

(%)

Decrease in crosslink density

Random main chain scissionCrosslink scissionUntreated TESPTTESPT 220 °CTESPT 250 °C

0

20

40

60

80

100

0 0,2 0,4 0,6 0,8 1

Sol f

ract

ion

(%)

Decrease in crosslink density

Random main chain scissionCrosslink scissionUntreated TESPDTESPD 220 °CTESPD 250 °C

0

20

40

60

80

100

0 0,2 0,4 0,6 0,8 1

Sol f

ract

ion

(%)

Decrease in crosslink density

Random main chain scissionCrosslink scissionUntreated PESPMPESPM 220 °CPESPM 250 °C

PESPM

TESPD

TESPT

Silica - silaneTire part - tread Feedstock

19

0

100

200

300

400

500

0

5

10

15

20

25

Originaltire tread

TESPT- 220 C

TESPT- 250 C

Elon

gatio

n at

bre

ak [%

]

Tens

ile s

tren

gth

[MPa

]

0

20

40

60

80

100

0

1

2

3

4

5

6

7

Originaltire tread

PESPM -220 C

PESPM -250 C

Har

dnes

s [S

hore

A]

Mod

ulus

100

% [M

Pa]

Silica - silaneTire part - tread Feedstock

20

Process development Oil swelling time

0102030405060708090

100

0 0,2 0,4 0,6 0,8 1

Sol f

ract

ion

(%)

Decrease in crosslink density

Random main chain scissionCrosslink scissionUntreated GTRD-GTRD GTR swollen 30 minsD GTR swollen 60 mins

Process conditions:

Batch mixer

Swelling temp.: 65ºC

TDAE: 5%

DPDS: 15 mmol

Antioxidant: 1%

Fill factor: 0,7

Rotor speed: 50 rpm

Mixer TCU: 220ºC

N2 purging

Screw speed: 50 rpm

Particle size: < 0,42 mm

21

Oil concentration

0102030405060708090

100

0 0,2 0,4 0,6 0,8 1

Sol f

ract

ion

(%)

Decrease in crosslink density

Random main chain scissionCrosslink scissionUntreated GTR5% TDAE15% TDAE30% TDAE50% TDAE

Process conditions:

Batch mixer

DPDS: 15 mmol

Antioxidant: 1%

Swelling: 30 min., 65ºC

Fill factor: 0,7

Mixer TCU: 220ºC

N2 purging

Rotor speed: 50 rpm

Process development

22

Oil / devulcanization aid swelling

Particle size distribution TDAE distributionAdded: 5 w%

Rubber particle

Devulc. aidOil Time

Temperature

Process development

24

Devulcanization - type of process

Process conditions: Swelling: 65ºC, 30 min.TDAE: 5%N2 purging

Batch mixerFill factor: 0,7Rotor speed: 50 rpm Mixer TCU: 220ºCScrew speed: 50 rpm

Extruder process: Screw speed varied to match residence time: 10, 20, 30 rpm

Process development

25

Compound adjustment for silica

Average composition (TGA): Silica: 42 phr

Additional silane(TESPT): 3.2 phr

Silanization: 4 minutes, 145ºCa

After-treatment

26

Summary

Upgrading of the devulcanizate by Silanization and addition of DPG for silica in the devulcanizate Continuous process (extruder) is more efficient

than batch process (internal mixer) Process is sensitive to (pre)treatment of the feedstock No influence of particle size on strength properties

if the devulcanization process is adjusted accordingly

Challenges:

Chances:

For a high quality devulcanizate Single tire parts > whole tire rubber Carbon black filled > silica filled (Type of) silane used in the original silica compound Age of the tire (part) Different devulcanization mechanisms

27

Thank you for your

attention!

Acknowledgements