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SCREENING OF DEVULCANIZATION AIDS FOR

TRUCK TIRE RUBBER

Vignesh Kumar R, Louis Reuvekamp, Jacques

Noordermeer, Wilma Dierkes, Anke Blume

Researcher

University of Twente

Faculty of Engineering Technology

Department of Elastomer Technology

and Engineering

Vulcanization - An industrial revolution

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1839: Charles Goodyear discovered sulfur vulcanization by combining

masticated rubber with sulfur an irreversible process to shape rubber products

Plastic (Virgin Rubber) → Elastic (Vulcanized Rubber)

Increased strength & resistance to changes in temperature

Mark, James E. Science and Technology of Rubber, CA, 1994

End of Life for tires

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Tire production requires a significant

amount of petroleum products & is an

energy intensive process.

Malaysian Rubber Board, NR Statistics 2014

Difficult to dispose in an

environmentally friendly way

Tonnes

Recycled rubber applications

140

Current scenario

Every year, approximately 800 million scrap tires are disposed off around the globe

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Why Devulcanization

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Lansink’s LadderClosing the Tire loop

http://www.recybem.nl/en/raw-materials-future

► The higher the method of processing on

the ladder, the better it is for environment

Devulcanization Vs Reclaiming

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Reclamation/ Reclaiming - uncontrolled breakdown of the network

Devulcanization - process of selective crosslink cleaving

CHEMICAL DEVULCANIZATION

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Function- “Radical scavenger”

- initiate cleavage of sulfur crosslinks

- react with the free radicals generated by C-C, C-S & S-S bond cleavage

and prevent recombination

- gel prevention action by acting as a radical acceptor

Common devulcanization aids

- disulfides, thiophenols and their zinc salts, mercaptans & amines

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Devulcanization process – Devulcanization aid

http://www.levgum.com/index.php/technolog

y

Devulcanization process – Process oil

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Swelling of GTR in a blend of process oil & devulcanization aid

→ increases efficieny of thermo-chemical devulcanization

Functions

raises plasticity of devulcanized rubber

facilitates dispersion of devulcanization aid into the rubber matrix

Prerequisite

high compatibility with rubber & devulcanization aid

high boiling point

Aim :

Development of an “efficient & environmentally sound” devulcanization

process for truck tires

Efficient:

1. easy blendable with virgin compound

2. used in higher quantities than the current recycled rubber products

Environmentally sound:

1. devulcanization aids to be environmentally safe

2. bio-oils to be used as process oils

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Process-design for devulcanization of whole truck tire rubber

Challenge :

eliminate usage of conventional devulcanization aids (DPDS, DADS, & DBDS)

→ expensive & repelling smell

Choice of devulcanization aids

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Different devulcanization aids (radical scavengers) were tested

Rubber

accelerators

Silanes

Antioxidants

Modifier

Conventional

Devulcanization

Aids

DPDS

DADS

DBDS

Devulcanization process flowchart

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Devulcanization

aid TDAE Pre-mix

GTR swollen

with pre-mix

(30mins @

650C)

DEVULCANIZATION

PROCESS

(Internal mixer)

Fill Factor = 0.70

Time = 10 mins

Temperature = 1700C

Rotor = 50 rpm

GTR- Ground Truck tire rubber

0,01 0,1 1 10

0,0

3,0x106

6,0x106

9,0x106

1,2x107

1,5x107

1,8x107

Co

mp

lex

vis

co

sit

y (

Pa

-s)

Frequency (Hz)

DBDS

CA-1

CA-2

A/Ox

Acc-2

Acc-7

Acc-3

Acc-6

Acc-4

CA-3

DPDS

DADS

Modifier

Acc-9

Acc-1

Acc-8

Results - Complex viscosity after devulcanisation

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DPDS & Modifier give the

lowest complex viscosity

after devulcanization RPA:

Freq Sweep= 0.01- 33

Hz

Const. Strain=0.56%

Temp= 1000C

* CA - Coupling agent, A/Ox - Antioxidant, Acc - Accelerator

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Analytics – Horikx plot

REGENERATION:

+sol

gel

Random main chain &

crosslink scission

Results – Horikx plot of the Devulcanizates

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Fine-tuning

* CA - Coupling agent, A/Ox - Antioxidant, Acc - Accelerator

0 10 20 30 40 50 60

1

2

3

4

5

6

7

8

9

To

rqu

e (

dN

.m)

Time (mins)

DBDS

CA-1

CA-2

A/Ox

Acc-2

Acc-7

Acc-3

Acc-6

Acc-4

CA-3

DPDS

DADS

Modifier

Acc-9

Acc-1

Acc-8

Acc-5

Results – Rheo curve after adding curing agents

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Rheo curve of DPDS &

Modifier are comparable

phr

D-GTR 182

ZnO 5

St.acid 3

CBS 1.6

S 1.2

Process:

Fill factor- 0.8

Temp- 400C

Time- 8 mins

* CA - Coupling agent, A/Ox - Antioxidant, Acc - Accelerator

T (dN.m)

DPDS 3.01

Modifier 2.62

Results - Tensile properties (ASTM D 412)

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Conclusion:

Modifier devulcanizate has comparable

properties with DPDS devulcanizate

except Modulus at 100%

* 4 devulcanizates were choosen on the basis of Horikx

plot, complex viscosity, curing behaviour & sheetability

* A/Ox - Antioxidant, Acc - Accelerator

Results – Smell panel

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Strong odour

or smell

Less odour* CA - Coupling agent,

A/Ox - Antioxidant,

Acc - Accelerator

CA-1

CA-2

CA-3

A/Ox

Acc-1

Acc-2

DBDS

Acc-3

Acc-4

DPDS

Acc-5

Acc-6

DADS

Acc-7

Acc-8

Acc-9

Modifier

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CONCLUSIONS

Devulcanisation with DPDS or Modifier are

comparable in terms of:

Complex viscosity

Sol content

Curing activity after addition of curing agents

Mechanical properties

Crosslink densities after devulcanization are lower for modifier devulcanizate

Less smell for modifier devulcanizate

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FUTURE WORK

• Optimize processing conditions for devulcanization with Modifier:

- concentration

- temperature

- time

- addition of stabilizer

• Extrapolate the results to an extruder process suitable for a production

line (Output= 25 Kg/hr)

www.theadvancedteam.com/laser_extruder.php

Financial & technical support:

Rubber Maalindustrie Limburg bv (RUMAL), The Netherlands.

Special thanks: Jan van den Brand & Wim Migchels

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ACKNOWLEDGEMENTS

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Thank you for your kind attention !

Mail ID:

v.k.rajendran@utwente.nl

Compounding considerations

Requires little or no new carbon black, avoiding emissions created in its manufacture

Short scorch & cure time, increased cure rate & lower maximum torque

Much higher hardness & modulus, much lower tensile properties

Increases the tear strength

Decrease in flex resistance & resilience

Increase in compression set

Good aging resistance→ avoid usage of antioxidant

Less tendency to revert

Increased thermal stability

Increased tack & penetration into textile cord

Practical usage limited in tire tread compounds - 5 wt%

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Challenges of the devulcanization proces

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