1. 1
1
PROGRESS AND HURDLES
IN TIRE RECYCLING
Wilma Dierkes
University of Twente
Enschede
the Netherlands
H. van Hoek
S. Saiwari
J. Noordermeer
A. Blume
6. 6
Technology Readiness Levels (TRL):
- Passenger car tire rubber: TRL5-6 (technology demonstration)
- Truck tire rubber: TRL 7-8 (system development)
Concentration of devulcanizate in tire compounds: a multitude of
current concentrations (depending on the compound type)
‘Tires back into tires’:
The only way to considerably broaden the market for recycled rubber
Technology Readiness Levels (TRL):
- No significant development potential of conventional technologies
(batch, long residence time, high temperatures)
- Improvements by after-treatments
- New technologies!
Large-scale application in tires only possible with significant quality
improvements
Pyrolysis
Grinding
Technology available, also for very fine powder
No further quality improvements possible
Very limited application in virgin compounds
Devulcanizate
Introduction
Status of recycling alternatives
9. 9
M. M. Horikx, J. Polym. Sci. 19, 445 (1956)
Analytics – Horikx plot
Hurdles to be taken
The original Horikx calculations
are based on polymer networks
without fillers
Adjustments for the presence
of fillers are necessary
Filler-polymer networks are not
taken into consideration
Changes from polymer to
crosslink scission in Horikx plot
do not necessarily show linear
correlation with distance from
lines
Additional analytical methods are
necessary
10. 10
Analytical methods
White rubber test
Blending of 5% re-plasticized rubber with a bright white compound
Shade of grey devulcanized part of the material
Particles non-devulcanized cores of the particles or filler clusters
White rubber
compound
5% completely
re-plasticized
rubber
10% ground
rubber
Reference samples
Samples with 5% devulcanizate
12. 12
Component Polymers
Tread SBR, BR
Belt NR
Sidewall NR, BR
Carcass SBR, NR, BR
Bead NR
Apex SBR, NR, BR
Cap-ply NR, BR
Inner liner SBR, NR, IIR
Blend of different types and brands of tires
Blend of different polymers and tire parts
Contamination with sand, …
Removal of reinforcing textile fibers
Residual activity of curatives
Reduced reinforcing strength of fillers
With courtesy from Apollo Global R&D
(Passenger car) tire rubber
Hurdles to be taken
13. 13
Component Polymers
Tread SBR, BR
Belt NR
Sidewall NR, BR
Carcass SBR, NR, BR
Bead NR
Apex SBR, NR, BR
Cap-ply NR, BR
Inner liner SBR, NR, IIR
Blend of different polymers and tire parts
With courtesy from Apollo Global R&D
(Passenger car) tire rubber
Hurdles to be taken
14. 14
DE-VULCANIZATION OF TIRE RUBBERS
Thermal treatment in presence of oxygen
recombination
S. Saiwari: Post-consumer tires back into new tires; thesis; University Twente, 2013
SBR: Thermo-mechanical treatment
Hurdles taken
15. 15
DE-VULCANIZATION OF TIRE RUBBERS
Devulcanization aid: DPDS, 15 mmol/100 g
Oil: TDAE, 5%wt
Temperature: 220C
Time: 6 minutes
Atmosphere: N2 purging
Cooling: Liquid nitrogen
Passenger car tire elastomers
Devulcanization mechanisms
SBR
BR
NR
CIIR
16. 16
Low devulcanization efficiency due to stable filler-polymer network (short bonds)
New formation of filler-polymer network required
Blendability with virgin compound
Degree of devulcanization ↔ stress-strain properties?
Passenger car tire elastomers: fillers
Silica-silane filler systems
100% ‘devulcanizate’
17. 17
DE-VULCANIZATION OF TIRE RUBBERS
Stress-strain properties of devulcanizate closer to original material!
Passenger car tire rubber
Selected compounds: tread
18. 18
Material design for
recycling:
New curing systems
A look into the future
Resins
New additives
Crosslink scission ‘on demand’
Reversible covalent filler-
polymer bonds
Low molecular weight rubbers
Modified polymers
Interpenetrating
networks
Trigger:
temperature, radiation,
chemicals …
https://www.google.nl/search?biw=1455&bih=712&tbm=isch&sa=1&ei=I_PiWtnAKpHFwQLTqrXQDQ&q=modified+sbr+silica+&oq=modified+sbr+silica+&gs_l=psy-
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19. 19
Progress
Summary
Passenger car tire rubber
- Devulcanizate is not smooth
breaking filler clusters
devulcanization of silica-polymer network
- Different types of networks
Shifting balance to crosslink scission and away from polymer breakdown
- Different types of compounds
Separation of different parts of tires by e.g. waterjet
- Different types of tires
Preference: Truck tires > passenger car tires, non-silica > passenger
car tires, silica
Hurdles
Whole truck tire rubber: upscaling with special extruder technology (TRL7-8)
Whole passenger car tire material prototype extruder process is operational (5-6)
but….
