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.
Chemical Devulcanization of Whole Truck Tire Rubber
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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
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
5. Current scenario
Every year, approximately 800 million scrap tires are disposed off around the globe
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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
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
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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
22. Financial & technical support:
Rubber Maalindustrie Limburg bv (RUMAL), The Netherlands.
Special thanks: Jan van den Brand & Wim Migchels
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ACKNOWLEDGEMENTS
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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