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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
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
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
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
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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