Recycling of rubber is the need of the hour considering the rapid depletion of resources. Used tires are one waste stream worth to consider for recycling. Possibilities for re-use of tire materials are granulate, reclaim or devulcanizate. Devulcanization is a chemical process; however, the most efficient devulcanization aids are generally disulfides or mercaptans, which are expensive and have a repellant smell, thus difficult to use on an industrial scale. In order to develop an environmentally-sound and efficient devulcanization process, different rubber chemicals are compared concerning their devulcanization efficiency as well as the smell of the devulcanizate.

1. 18/02/2016 137
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

2. 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

3. 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

4. Recycled rubber applications
140

5. Current scenario
 Every year, approximately 800 million scrap tires are disposed off around the globe
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https://www.reddit.com/r/woahdude/comments/26i61g
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6. Why Devulcanization
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Lansink’s Ladder
Closing 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

7. Devulcanization Vs Reclaiming
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Reclamation/ Reclaiming - uncontrolled breakdown of the network
Devulcanization - process of selective crosslink cleaving

8. CHEMICAL DEVULCANIZATION
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9.  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

10. 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

11. 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

12. 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

13. 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

14. 0,01 0,1 1 10
0,0
3,0x106
6,0x106
9,0x106
1,2x107
1,5x107
1,8x107
Complexviscosity(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

15. 151
Analytics – Horikx plot
REGENERATION:
+
sol
gel
Random main chain &
crosslink scission

16. Results – Horikx plot of the Devulcanizates
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Fine-tuning
* CA - Coupling agent, A/Ox - Antioxidant, Acc - Accelerator

17. 0 10 20 30 40 50 60
1
2
3
4
5
6
7
8
9
Torque(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

18. 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

19. 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

21. 04-03-2014 157
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

22. 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

24. 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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25. Challenges of the devulcanization proces
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