Closing the loop: 1 Rubber Recycling Joint seminar Kumi-instituutti instituutti & MOL
Contents 2 - Introduction - Present: Rubber crumb Surface activated rubber crumb Reclaim / devulcanizate - Future
Introduction Used tires 3 (V.L. Shulman, 2008, ETRA) Landfill 20% Others 3% 2006 Retreading 12% Export 7% 800,000,000 tires/year Increase: 2%/year Material recycling 27 % Energy recovery 31% EU countries: 2000: ca. 2,700,000 tons 2006: ca. 3,200,000 tons
Introduction 4 Legislation ELV: EU legislation End of life vehicles 2015: < 5 % landfill ( End of life vehicles EU legislation, Dir. 2000/53/EC) 2006: Prohibtion of landfill of shredded tires (Dir.1999/31/EC) 2006: < 15% landfill (ELV) 2003: Prohibition of landfill of whole tires (Dir. 1999/31/EC)
Introduction 5 Recycling loops CO 2 + H 2 O + energy C n H m Monomers Polymers Compounds Vulcanized products Energy recovery Increasing Feedstock recovery degree of valorization Material recycling Energy consumption: New rubber: 115 J/kg Rubber granulate: 2 J/kg
Rubber powder 6 Vulcanized Granulate Surface activation Rubber rubber Powder Regeneration product Buffings Rubber granulate, 5 mesh = 4 mm Rubber powder, 16 mesh = 1.19 mm Rubber powder, 30 mesh = 0.595 mm cryogenically ground ambiently ground 10 μm 2 μm
Surface activated rubber powder 7 Vulcanized Granulate Surface activation Rubber rubber Powder Regeneration product Biological treatment Granulate Powder Mechanical treatment Physical treatment Chemical treatment Surface activated powder
Surface activated rubber powder 8 Vulcanized Granulate Surface activation Rubber rubber Powder Regeneration product Biological treatment Granulate Powder Mechanical treatment Physical treatment Chemical treatment Surface activated powder
Surface activated rubber powder Chemical treatment 9 Coating: + Polymer Latex, low-molecular liquid polymer, polymer-oil blends + Curing additives Swelling: + Oligomer, evtl. with functional groups + Oil with (curing) additives Grafting: + Silanes + Ethylacrylate
(Surface activated) rubber powder Influence on compound properties 10 System: latex + curing agents Powder: truck treads (70%NR/30%SBR) NR compound SBR compound Tensile strength [MPa] 30 20 10 Tear strength [N] 100 50 Tensile strength [MPa] 20 10 0 Tear strength [N] 50 25 0 0 10 20 30 40 50 - Concentration rubber crumb [%] 0 0 10 20 30 40 50 Concentration rubber crumb [%] Surface activated rubber crumb Untreated rubber crumb Technical Information Rubber Resources
(Surface activated) rubber powder Influence on compound properties 11 NR compound SBR compound Abrasion [mm 3 ] Abrasion [mm³] 200 150 200 100 100 50 Compression set (70º) [%] 75 50 25 Rebound resilience (70ºC), [%] 60 0 Compression set (70ºC) [%] 100 50 0 Rebound resilience(70º) [%] 50 50 40 40 0 10 20 30 40 50 - Concentration rubber crumb [%] 30 0 10 20 30 40 50 Concentration rubber crumb [%] Surface activated rubber crumb Untreated rubber crumb Technical Information Rubber Resources
Reclaim 12 Vulcanized Granulate Surface activation Rubber rubber Powder Reclaiming product Definition reclaim: A process in which vulcanized rubber is converted into a material which can be blended, processed, and cured again by using mechanical, thermal or chemical processes Devulcanization: Selective scission of sulfur crosslinks Crosslink scission Polymer scission Polymer Crosslinks http://www.coe-nr.org
Reclaim Processes 13 Mechanical reclaiming Granulate Powder Reclaim Thermal reclaiming Chemical devulcanization
Reclaim 14 Thermomechanical breakdown Softeners Polymers mechanical thermal Viscosity decrease 120 C Temperature Thermal: - non-selective in terms of chain length - non-selective for polymer chains and crosslinks - reactive chain ends Molecular weight Initial MWD MWD after thermal breakdown MWD after mechanical breakdown Mechanical: + selective for longer chains - non-selective for polymer chains and crosslinks - reactive chain ends Polymer degradation
Reclaim Processes 15 Mechanical reclaiming Granulate Powder Reclaim Thermal reclaiming Chemical devulcanization
Reclaim Chemical devulcanization aids 16 Radical breakdown - Disulfides Oxidation - Oxygen (air) Nucleophilic breakdown - Mercaptanes - Hydroxydes -Amines Breakdown of C-S bonds - Raney-Nickel - Alkali metals
Reclaim Processes 17 Mechanical reclaiming Granulate Powder Reclaim Thermal reclaiming Chemical devulcanization
Reclaim 18 Effect of temperature, reclaiming aid and concentration EPDM roofing sheet compound, EV cured (short crosslinks) 200 C 225 C ( ): HDA CH 3 (CH 2 ) 15 NH 2 ( ): DPDS 250 C 275 C S S ( ): BAFD S S N H N H CO CO Dijkhuis, K., thesis, 2008, ISBN 978-90-365-2643-2
Reclaim 19 Effect of temperature, reclaiming aid and concentration EPDM roofing sheet compound: conventionally cured (long crosslinks) 225 C 250 C 275 C ( ): HDA ( ): DPDS ( ): BAFD CH 3 (CH 2 ) 15 NH 2 S S S N H CO S N H CO Dijkhuis, K., thesis, 2008, ISBN 978-90-365-2643-2
Reclaim 20 Influence on compound properties (EPDM) EPDM roofing sheet compound Conventionally cured ( ): HDA CH 3 (CH 2 ) 15 NH 2 ( ): DPDS S S ( ): BAFD S S N H N H CO CO EV cured Dijkhuis, K., thesis, 2008, ISBN 978-90-365-2643-2
Reclaim 21 Influence on compound properties (NR/SBR) NR/SBR truck tire tread reclaim in a similar compound Reclaiming aid: Diphenyldisulfide Tensile strength [MPa] Tensile strength [MPa] 28 Tear strength [N] Abrasion [mm³] 24 20 0 10 20 30 40 50 NR/SBR reclaim concentration [phr] Compression set [%] Rebound resilience [%] 0 20 40 60 80 100 % relative to basic compound Basic compound (NR/SBR) 22% NR/SBR Reclaim Technical Information Rubber Resources
Reclaim 22 (Dis)advantages In a blendwithvirginrubber: + Shorter mixing, milling, extrusion cycles + Lower processing temperature, less scorch + Better tack + Improved temperature resistance + Higher green strength + Easier escape of air from the mold + Improved aging resistance - Influence on property profile
Reclaim 23 More efficient devulcanization Influencing factors for reclaiming efficiency: - Temperature - Time - Shearing forces - Devulcanization aid - Restoration of double bonds Shifting to devulcanization: - Low temperatures - Low shearing forces - Appropriate devulcanization aid The right choice of the devulcanization aid is crucial! Dijkhuis, K., thesis, ISBN 978-90-365-2643-2
Rubber Recycling 24 The future 50% of recycled material back into (the original) rubber products Material recycling 50% Landfill 0% Others 3% Retreading 12% Export 7% Energy recovery 28% Shifting the balance between thermomechanical breakdown and chemical devulcanization to devulcanization Emphasis on tire rubbers - SBR (main tire rubber) is the most difficult elastomer to reclaim - Blend of elastomers can give only a best compromise
Closing the loop: 25 Rubber Recycling Thank you for your attention!