Evaluation of Waste Tire Devulcanization Technologies

(INTERNAL REPORT) CENTERPLASTICS entangled & ADDITIVES Feb. 2011 M. S. Laura Fontana Centerplastics Enterprise, Ltd Eastern Industrial Road, zip. 516127, Shiwan Town, Boluo Area, Huizhou, DongGuan, GuangDong, P. R. China PPH Chapter 1 Introduction Approximately 25 emf devul slewization technology seekers and developers were identified finishedout the world, however, nevertheless a rattling sm e real(prenominal) tour of devul provokeization systems ar now direct.These ar primarily small- faculty systems, which atomic number 18 devul dissolveizing natural or artificial pre broadcastives (as opposed to devul butt jointizing the mixture of synthetic meritlesss recovered from brag wash ups). The world(a) symbols of devul dirty dogization technologies identified and analyzed in the study argon shown below. engineering science Basis of acting Z lawfulness of Reaction chemic chemical substances/ chemic responses show up of particles unhear equal to(p) unhearabl e waves Throughout particles cook Microwaves Throughout particles Biological Microorganisms come forward of particles Other Mechanical go Surface of particles Key findings bona fide learning and data on devulcanization of xerox tire no-good atomic number 18 unmanageable to obtain referable to proprietary claims, efforts to hide poor or infeasible physical butt on deed and overlap fictitious character, and the limited number of technology researchers and developers and of peer-reviewed data. Reliable data relating hazardous tire characteristics, de change no-good fictitious character, exterminate result performance, and outturn comprises is scarce. Only a very small number of low-capacity devulcanization systems argon operating in the United States (at approximately 50 Kg /hr, all R&D scale, mechanistic, or ultrasonic).No proven commercial capacity units could be found that are currently devulcanizing ravage tires, for example, at euchre Kg/hr or greater. The likely reasons entangle in comfortable product quality and ruleing equal of production. In legal injury of the potential of producing laid-back-quality de corned safety erasers (for example, high strength), the scoop up technology appears to be ultrasonic, based on the current severalize of the art. Devulcanization of individual safes has much much than history than that of multi- meritless mixtures much(prenominal) as furious tires.Only a few companies devulcanize single formulation hawkshaw as a result of captive conversion or merchant chicken open recovery from manufacturing. The production of devulcanized pencil eraser from home manufacturing mo in the U. S represents about 1 to 2 pct of total U. S. good-for-naught consumption. The quality of devulcanized single preventives is higher than that of devulcanized multiple rubbers. Devulcanization that depends on surface devulcanization technologies (for example, chemic and automatic) appears do om in the near term to produce low- or medium-quality devulcanized rubber corporeal. The estimated speak to for producing devulcanized materials from waste tires is $0. 3 to $0. 6/Kg 30 percent, if including the appeal of hindquarters rubber feedstock. This roll up of production bell is profoundly greater than that of consummate(a) rubbers. A typical tire compound contains the following constituents remit 1. story of Tires Passenger Tire Constituents Common Materials vivid rubber 14% indispensable rubber Synthetic rubber 27% SBR, butadiene rubber degree Celsius menacing 28% Carbon b pretermit blade 14%15% Steel Fabric, fillers, accelerators, antiozonants, etc. 16%17% Polyester, nylon, aromatic rock crude, coumarine resin, silica, bonding factor, stearic acid, ntioxidant, bear on chemic substances, reciprocal ohm, zinc oxide Truck Tire inborn rubber 27% Natural rubber Synthetic rubber 14% Synthetic rubber Carbon b leave out 28% Carbon black Steel 14%15% Steel F abric, fillers, accelerators, antiozonants, etc. 16%17% Polyester, nylon, aromatic crude, stearic acid, antioxidant, wax, functioning chemicals, second, zinc oxide witness refuge Manufacturers Association, cc4. Reclaiming is a procedure in which whit tire rubber or vulcanized rubber waste is born-againusing mechanised and caloric animation and chemicalsinto a state in which it can be mixed, work oned, and vulcanized again.The principle of the wreak is devulcanization (Franta, 1989). Historically and practically, in the concept of rubber take backing, devulcanization consists of the cleavage of intermolecular bonds of the chemical ne bothrk, such as ascorbic acid copy- mho (C-S) and/or sulfur-sulfur (S-S) bonds, with further condensedening of the chains besides occurring (Rader, 1995). This description of devulcanization is antithetic than that given below, which is limited to chemical interactions involving sulfur atoms. Reclaim is an interesting warm material a s it reduces the production cost of new rubber articles, due to shorter mixing generation and lower power consumption.The impact temperature is lower, and the material has a higher dimensional st talent during calandering and extrusion due to the remain third-dimensional nedeucerk. The or so important expediency of cured articles containing reclaim in terms of properties is an improvement of aging resistance. Devulcanization is the process of cleaving the monosulfidic, disulfidic, and polysulfidic crosslinks ( vitamin C-sulfur or sulfur-sulfur bonds) of vulcanized rubber. Ideally, devulcanized rubber can be revulcanized with or without the hire of opposite compounds.The varied types of devulcanization processes also switch other properties of the rubbers. These processes cause diminution of some(prenominal) properties over those of the parent rubber. Ideally, devulcanization would father a product that could serve as a substitute for satu posed rubber, both in terms of properties and in terms of cost of manufacture. Polymers can be divided into two groups thermoplastics and thermosetting materials. Thermoplastics soften when modifyed, making it achievable to (re-)shape them at higher temperatures.Thermosetting materials, like rubbers, are crosslinked on heating plant and whence can non be softened or remodeled by raising the temperature. Therefore, thermosets are more(prenominal) than difficult to recycle compared to thermoplastics. The three-dimensional network has to be overturned in order to ass anele the material (re-)processable the so-called reclaiming process. In this process, any sulfur crosslinks connecting the polymer chains or carbon-carbon bonds in the polymer backb maven are broken. The outset mechanism is preferred, as the backbone of the polymer remains intact. Scission can be obtained by heat, shear or chemical reactions.Basically, processes of rupturing the rubber network by crosslink or main-chain scission can be class ified into five main groups. Thermal reclaiming Thermo-mechanical reclaiming Mechano-chemical reclaiming Reclaiming by radiation, and Microbial reclaiming. In actual practice, conspiracys of thermal and mechanical reclaiming are generally apply, with in some cases the minimal brain dysfunctionition of a devulcanization aid for chemical reclaiming. 1. 1-Thermal Reclaiming For this manakin of processes, heat (often combined with summing up of chemicals) is apply to break the sulfur bonds and gum olibanum to plasticize the rubber.Hall patented in 1858 one of the oldest and most round-eyed processes in the rubber reclaiming industry, the Heater or Pan process (Oil law). In this process, exquisitely drop anchor natural rubber powder is mixed with inuncts and reclaiming agents and do by with high or medium pressure steam at temperatures varying from 170C to 200C. The reclaiming time is long and the homogeneity of the reclaim is low, but this process is able to reclaim a large number of polymers natural rubber (NR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR) and butyl rubber (IIR) and the equipment is sooner in big-ticket(prenominal).The use of the heater or pan process became less normal after Marks patented the Digester or Alkali process in 1899. The fibers of the rubber check, remnants of the tire carcass, were first re locomote by mixing it with alkali, irrigate, plasticizing embrocates and, if needed, chemical peptizers. The mixture was modify in a jacketed, agitator equipped steriliser to 180-210C. The most important disadvantage of this process is the pollution fetchd by the chemicals. Modifications of this process minimized the pollution, but increased the reaction quantify.Processes with short reaction multiplication are for example the High Pressure Steam processes or the Engelke process. In the first process, a fiber-free, farinaceous ground rubber is mixed with reclaiming agents , and reclaiming is through in a high-pressure autoclave at approximately 280C. In the latter process, coarse ground rubber scrap is mixed with plasticizing inuncts and peptizers and is consecrate into small autoclaves. The material is heated to very high temperatures for a short head of 15 minutes, after which it is lead through re hunky-doryrs (mills with very contract gaps) and strainers. . 1. 1 Steam With or Without Chemicals (Digester, DD-CR, HTDD-CR) Steam devulcanization of stinkpot rubber uses a steam vessel equipped with an agitator for continuous stirring of the lemon rubber while steam is being applied. There are two variants of the basis steam process, namely, wet and dry. The wet process uses caustic and water mixed with the rubber stinkpot, while the dry process uses lonesome(prenominal) steam. If necessary, assorted reclaiming oils whitethorn be added to the mixture in the reaction vessel.In one case, a wet process using diaryl disulfide and reclaiming o ils with saturated steam at 190C (374F) was ply finely ground NR and synthetic rubber scraps. A charge of about 440 lbs. was partially devulcanized after 15 to 17 hours of affect. This process have a bun in the ovend 12 hours at ambient temperature for pre- word and 3 to 5 hours for steam or high temperature intervention (Adhikari, et al. , 2000). The dry process digester has the advantage of generating less pollution than the wet process. Scrap rubber containing natural and synthetic rubbers can be repossess by the steam digestion process.Reclaiming oil utilise for this process has molecular system of weightss between 200 and snow0, consisting of benzol, alkyl benzene, and alkylate indanes. A generic wine touch on diagram for steam devulcanization is shown in Figure A. Figure A. schematic drawing Diagram of a Steam Devulcanization dust Devulcanized meritless Dehydrating System Steam Reactor refuge layabout Chemical(s) Liquid spin-off 1. 2 Thermo-Mechanical Reclaimi ng The thermo-mechanical reclaiming processes make use of shearing forces to plasticize the rubber. Energy is introduced into the materials, resulting in a of import temperature increase, high rich to cause thermal degradation.The Lancaster-Banbury process is one of the oldest processes. Fiber-free coarse ground rubber scrap is mixed with reclaiming agents and sheared in a high speed, high-pressure internal mixer. When a continuously working, multiscrew devulcanizer is employ kinda of the internal mixer, the process is called the Ficker reclaiming process. 1 of the first continuous reclaiming processes is the so-called reclaimator process. This is essentially a single screw extruder that has been adapted to reclaim fibre-free rubber scrap in very short extrusion times.The short extrusion times make this rule suitable for SBR, that tends to harden when longer recycling times are applied. Another mechanical reclaiming process is the De-Link process. In this process finely grou nd rubber powder is mixed with the De-Link master view (DeVulc) a zinc coarseness of di methyl groupdithiocarbamate and mercaptobenzothiazole in a molar ratio of 11 to 112, dispersed in thiols and activated by stearic acid, zinc oxide and sulfur. Advantages of the process are its simplicity and the fact that standard rubber equipment is apply.No evidence is forthcoming to demonstrate that the De-Link process is employ beyond science laboratory or pilot scale. The Toyota process is another development of mechanical reclaiming. In this process a mixture of ground rubber, stark(a) rubber, oils and a devulcanization aid is masticated on a two-roll mill or in an extruder. Mechanical devulcanization is achieved through the recurrent deformation of rubber particles under specific conditions of temperature and pressure. The result is a devulcanized rubber, quick for further bear upon. Toyota developed another continuous process, Toyota Gosei (TG) combining pulverization, reclaiming and deodorization.The rubber waste has to be ground to a particle coat of it of 5-10 mm in advance it can be fed into a modular screw-type reactor with a pulverization zone and a reaction zone. The operating temperature is in the range of c-300C and vitamin C-900 rpm screw speeds are applied, the process requires about degree centigrade Kw (kilowatts) to process 200 to 300 kg (kilograms)/hr of rubber, or approximately 0. 4 kW/kg. By manipulating screw configuration and rotational speed, and touch temperature, researchers are able to control the duration of the treatment. In this charge they can, to some conclusion, control the properties of the devulcanizate.The TG process has been primarily, if not exclusively, used to devulcanize specific types of rubber compounds, such as NR and SBR. 1. 3 Mechano-Chemical Reclaiming Mixing of the rubber powder with a peptizer (chemicals used to reduce the viscosity of NR) and a reclaiming agent prior to the mechanical breakdown of the material improves the reclaiming process. The devulcanization aid is supposed to selectively break the sulfur crosslinks in the rubber network. This chemical breakdown is combined with input of thermal and/or mechanical energy, as the rate of this process is sufficiently high only at higher temperatures.The most rough-cut devulcanization aids are disulfides, e. g. aryl disulfides or diphenyl sulfides, thiophenols and their zinc salts and mercaptanes. These chemical compounds are radical scavengers they react with the radicals generated by chain- or crosslink scission and prevent recombination of the molecules. Typical concentrations for the reclaiming agents are 0. 5 to 4 wt%. fitting peptizers are aromatic and naphthenic oils with a high boiling point. Figure B. formal Diagram of a Chemical Devulcanization System Devulcanization Agent prophylactic Crumb Mixer Heated Extruder Devulcanized click Dryer arctic Liquid By-Product Unfortunately, a detailed accounting of rivulet mate rials, performance parameters, and conditions is lacking, thus inhibiting the extent of interpretation of the data. Comparisons of data are primarily limited to comparing the properties of sodding(a) rubbers with compounds containing the virgin and devulcanized material at concentrations of about 30 percent devulcanized material. As shown by the data in the table, the properties of the mixtures containing devulcanized material are in general moderately lower than those of their virgin counterparts.The inform data reflect two different types of chemical devulcanization technologies. Table 2. Properties of Waste Tire golosh Devulcanized development Chemical or Chemical/Mechanical engineering science Generic Technology Technology Surrogate exam condom intensify s % Devulc (or Ground) Matl Mooney viscousness (ML-4 212F) Tensile Strengt h (lbs/in2) 300% Modulus (lbs/ in2) Elongation to Break (%) Chemical STI-K Polymers DeLinka NR 0 61. 9 4,270 1,987 534 NR w/devulc NR 30 72. 3 4,020 2,151 489 Virgin SBR (1520) 0 96. 6 3,880 3,059 358 SBR (1520) w/devulc SBR 30 109. 2 3,580 2,923 345 Chemical/ Mechanical LandStar/ GuangzhouResearch Instituteb NR light speed 28. 4 680 SR 100 17. 2 514 AMRc Powder (devulc. additive) 100 23. 9 640 Tread Tire combined 0 20. 3 772 28. 6 19. 7 628 lessen Duty Truck Tire Compounde 0 23. 8 536 28. 6 20. 5 500 1. 4 Reclaiming by Irradiation Bond type disassociation energy (KJ/mol) C-C 349 C-S 302 S-S 273 Polysulfidic 253 Table 3. Typical bond energies 1. 4. 1 unhearable sorry devulcanization by using ultrasonic energy was first discussed in Okuda and Hatano (1987). It was a lot process in which a small piece of vulcanized rubber was devulcanized using 50 kHz ultrasonic waves after treatment for 20 minutes.The process apparently could break down C-S and S-S bonds, but not carbon-carbon (C-C) bonds. The properties of the revulcanized rubber were found to be very similar to those of the original vulcanizates. One continuous pr ocess for devulcanization of rubbers is based on the use of high-power ultrasonography electromagnetic radiation. This is a suitable way to recycle waste tires and waste rubbers. The ultrasonic waves, at certain levels, in the strawman of pressure and heat, can quickly break up the three-dimensional network in crosslinked, vulcanized rubber.The process of ultrasonic devulcanization is very fast, simple, efficient, and it is free of solvents and chemicals. The rate of devulcanization is approximately one second. This whitethorn lead to the preferential breakage of sulfidic crosslinks in vulcanized rubbers. (Isayev, 1993 Yu. Levin, et al. , 1996 Isayev, et al. , 1997 Yun, et al. , 2001 Yun & Isayev, April 2003). chthonic a license from the University of Akron for the ultrasonic devulcanization technology, NFM Company of Massillon, Ohio, has built a precedent of the machine for ultrasonic devulcanization of tire and rubber products (Boron, et al. 1996 Boron, et al. , 1999). It was reported that retreaded truck tires containing 15 and 30 weight percent (percent by weight) of ultrasonicallydevulcanized carbon black-filled SBR had passed the feeler kinetic endurance test (Boron, et al. , 1999). Extensive studies on the ultrasonic devulcanization of rubbers, and some preliminary studies on ultrasonic decrosslinking of crosslinked plastics, showed that this continuous process allows recycling of various types of rubbers and thermosets (Isayev, 1993 Hong & Isayev, 2002 (pp. one hundred sixty168) Shim, et al. 2002 Shim & Isayev, 2003 Gonzalez-de Los Santas, et al. , 1999). As a consequence of the process, ultrasonically-devulcanized rubber becomes soft, therefore enabling this material to be re touch, shaped, and revulcanized in very much the same way as virgin rubber. This new technology has been used successfully in the laboratory to devulcanize ground tire rubber (commonly referred to in the industry as GRT) (Isayev, et al. , 1995 Yun, et al. , 2001 Boron, et al. , 1996), fill and filled rubbers N (Hong & Isayev, 2001 Yu. Levin, et al. , 1996 Isayev, et al. , 1997 Diao, et al. 1998 Shim, et al. , September 2002 Ghose & Isayev, 2003), guayule rubber (Gonzalez-de Los Santas, et al. , 1999), fluoroelastomer, ethylene vinyl group acetate foam, and crosslinked polyethylene (Isayev, 1993 Isayev & Chen, 1994). After revulcanization, rubber samples exhibit good mechanical properties, which in some cases are comparable to or exceeding those of virgin vulcanizates. Structural studies of ultrasonically-treated rubber show that the breakup of chemical crosslinks is accompanied by the partial degradation of the rubber chain that is, the C-C bonds (Isayev, et al. , 1995 Tukachinsky, et al. 1996 Yu. Levin, et al. , 1997 (pp. 641649) Yushanov, et al. , 1998). The degree of degradation of C-C bonds can be straight, depending on conditions. The mechanism of rubber devulcanization under ultrasonic treatment is presently not well understood, unlike the mechanism of the degradation of long-chain polymer in solutions irradiated with ultrasound (Suslick, 1988). Ultrasonic devulcanization also alters the revulcanization kinetics of rubbers. The revulcanization of devulcanized SBR appeared to be essentially different from those of virgin SBR (Yu. Levin, et al. , 1997, pp. 120128).The induction period is shorter or absent for revulcanization of devulcanized SBR. This is also received for other unfilled and carbon black-filled rubbers such as ground rubber tire (GRT), SBR, natural rubber (NR), ethylene propylene diene monomer (EPDM), and butadiene rubber (BR) cured by sulfur-containing curative systems, but not for silicone rubber cured by peroxide. Ultrasonically-devulcanized rubbers consist of sol and gel. The gel portion is typically soft and has significantly lower crosslink concentration than that of the original vulcanizate. Due to the presence of sol and soft gel, the devulcanized rubber can flow and is subject to shaping.Crossl ink density and gel fraction of ultrasonically-devulcanized rubbers were found to correlate by a worldwide master curve (Yushanov, et al. , 1996 Diao, et al. , 1999 Yushanov, et al. , 1998). This curve is strange for all elastomer due to its unique chemical structure. In a comparative digest of ultrasonically reclaimed unfilled SBR, NR and EPDM rubbers, it was found that it was more difficult to reclaim EPDM than NR and SBR. Reclaiming of EPDM roofsheeting resulted in a good quality reclaim, which after revulcanization showed more or less personify mechanical properties compared to the virgin compound.The surface smoothness of the revulcanized compounds could be controlled by the process conditions. Most companies marketing ultrasonic devulcanization technologies are utilizing very similar technologies involving polar feed extruders and varying physical arrangements of ultrasonic equipment. Ultrasonic devulcanization technology is really roll upd of a devulcanization system namely, extrusion and ultrasonic processing. Two name differences in some cases are the equipment and materials used to generate the ultrasonic energy required for the process, and the positioning of the transducer(s) relative to the extruder.Two different arrangements of ultrasonic devulcanization systems are shown in Figures C and D. In this type of devulcanization system, sizing-reduced rubber particles are lade into a hopper and are subsequently fed into an extruder. The extruder mechanically pushes and pulls the rubber. This mechanical action serves to heat the rubber particles and softens the rubber. As the softened rubber is transported through the extruder cavity, the rubber is exposed to ultrasonic energy. The resulting combination of heat, pressure, and mechanical mastication is sufficient to achieve varying degrees of devulcanization.The time constant of the devulcanization process takes place in seconds. Essentially all of the rubber entering the process is discharged from the extruder in semi-solid product stream. Process losses would be primarily those due to discharges of fine particulates or of gases, if any, generated due to the mechanical and thermal processes occurring during the devulcanization process. After stifleing through the extruder die, the rubber is passed through a cooling bath and then dried. Figure C. nonrepresentational Diagram of an Ultrasonic Devulcanization System Showing a Mid- Extruder Location for the Ultrasonic SubsystemUltrasonic Processing Zone Cooling Bath Devulcanized Rubber Extruder Rubber Crumb supply hop-picker Figure D. Schematic Diagram of an Ultrasonic Devulcanization System Showing the Ultrasonic Subsystem Located at the Discharge land up of the Extruder Ultrasonic Processing Zone Cooling Bath Devulcanized Rubber Feed Hopper Extruder Rubber Crumb Table 4. Properties of Waste Tire Rubber Devulcanized Using Ultrasonic Technology Technology Surrogate Test Rubber Compound s % Devulc or (Ground) Matl Moone y Viscosity (ML-4 212F) Tensile Strength (lbs/in2) 100% Modulus (lbs/ in2) 300% Modulus (lbs/ in2) Elongation toBreak (%) U of Akron SBR 1848a 0 2,415 740 780 SBR (1848) w/devulc SBRa 10 1,075 790 540 SBR (1848) w/whole train reclaima (10) 1,940 760 660 SBR (1848) w/30 mesh buffingsa (10) 1,440 780 480 100% NR (SMR CV60) & 0% SBR (23. 5% boundary styrene, and Duraden 706)b 0 3,263 116 670 NR (SMR CV60) & 25% SBR (23. 5% bound styrene, and Duraden 706)b 0 1,885 123 600 NR (SMR CV60) w/devulc SBR (23. 5% bound styrene, and Duraden 706)b 25 580 123 380 NR (SMR CV60) & 50% SBR (23. 5% bound styrene, and Duraden 706)b 0 406 131 390 Technology Surrogate Test Rubber Compound s % Devulc or (Ground) Matl Mooney Viscosity (ML-4 12F) Tensile Strength (lbs/in2) 100% Modulus (lbs/ in2) 300% Modulus (lbs/ in2) Elongation to Break (%) NR (SMR CV60) w/devulc SBR (23. 5% bound styrene, and Duraden 706)b 50 363 123 320 NR (SMR CV60) & 75% SBR (23. 5% bound styrene, and Duraden 706)b 0 363 145 295 NR (SMR CV60) w/devulc SBR (23. 5% bound styrene, and Duraden 706)b 75 276 131 250 100% SBR (23. 5% bound styrene, and Duraden 706)b 0 290 152 200 100% SBR (23. 5% bound styrene, and Duraden 706)b 100 290 138 180 Table 5. portion Change from Virgin with Selected Devulcanization Rubber Formulations Test Rubber Compounds (grade) Parts or % %Devulc. or (Groun d) Matl. Hardnes s Shore sunder Strengt h Tensile Strengt h 100% Modulu s 300% Modulu s Elongatio n to Break Chemical STI-K Polymers DeLinka NR w/devulc NR 30 -5. 9% 8. 3% -8. 4% SBR (1520) w/devulc SBR 30 -7. 7% -4. 4% -3. 6% Kyoto Universityb Truck tire (93 NR+ 7 BR) 84 NR+ 6 BR + 20 devulc 18 8. 1% -2. 3% 2. 6% 0. 0% 74 NR+ 6 BR + 40 devulc 33 12. 9% -11. 9% 28. 2% -17. 4% 65 NR + 5 BR + 60 devulc 46 11. 3% -19. 1% 23. 1% -13. 0% LandStar/Guangzhou R Ic 100 SIR 10 + 50 devulc SIR vs. Case 1 33 4. 3% -23. 7% 6. 7% -6. 7% SIR vs. Case 2 33 6. 5% -23. 0% 11. 5% -8. 6% Tread Tire Compound 0 NR + 30 SR + 20 CIS-BR +40 AMR 28. 6 6. 7% -17. 3% -3. 0% -18. 7% Light Duty Truck Tire Compound 30 NR + 70 SR + 0 CIS-BR + 40 AMR 28. 6 1. 6% -10. 9% -13. 9% -6. 7% Retread Tire Compound c65 NR + 35 SR +40 AMR 28. 6 6. 3% -8. 6% -10. 3% -16. 8% Ultrasonic University of Akrond Versus Akrochem SBR (1848) SBR w/devulc SBR 10 -55. 5% 6. 8% -30. 8% Test Rubber Compounds (grade) Parts or % % Devulc. or (Groun d) Matl. Hardnes s Shore Tear Strengt h Tensile Strengt h 100% Modulu s 300% Modulu s Elongatio n to Break SBR w/whole Tire Reclaim 10 -19. 7% 2. 7% -15. 4% SBR w/30 Mesh Buffings 10 -40. 4% 5. 4% -38. % Natural Rubber and SBR versus devulc Base 100% NR (SMR CV60) & 0% SBR (23. 5% bound styrene, and Firestone Duraden 706) 0 Add 25% SBR, 75% NR 0 -42. 2% 6. 3% -10. 4% Devulc SBR replaces SBR 25% devulc SBR, 75% NR 25 -69. 2% 0. 0% -36. 7% 50% devulc SBR, 50% NR 50 -10. 7% -5. 6% -17. 9% 75% devulc SBR, 25% NR 75 -24. 0% -10. 0% -15. 3% SBR versus devulc SBR 100% devulc SBR 100 0. 0% -9. 5% -10. 0% Heavy carbon-blacked rub ber is the hardest to devulcanize, and silica, or other mineral-filled EDPM, is the easiest. Reincorporation of the devulcanized rubber is typically in the 20 to 40 percent range.Devulcanized single-product rubber industriousnesss are wide ranging. The reclaimed product whitethorn be reintroduced into the same end product or one with more tolerant performance characteristics for the devulcanized rubber. Devulcanized rubber come alongs to bring on advantages in bonding, strength, and tread integrity in a higher place the properties of vomitus rubber, which acts only as a rubber-like filler. tally to one developer of a devulcanization process, about 3 to 10 percent of the final exam product can be blended into virgin material before performance properties are affected.Variations of a few percent are reported by developers of devulcanization when they vary process run conditions. Run-to-run variations are normally acceptable. Devulcanized single rubber products assimilate a muc h lower degree of degradation than multiple rubber mixtures with devulcanized rubber. Virgin single-grade SBRor natural rubber heterotaxy with devulcanized material shown by the STI-K and the University of Akron datasets has, at worst, a reduction of 10 percent in tensile strength, modulus, or elongation.In some cases, the addition of devulcanized rubber causes a major reduction in performance of some properties, along with improvements in one or two properties (hardness and modulus). Because the modulus is the measure of deformationthat is, stress (stretching), compression (crushing), flexing (bending), or torsion (twisting). Similarly, the increase in hardness could be an improvement or detraction, depending on the application. The devulcanized rubber properties displayed are not needs optimized for a specific end use.Formulators will likely be able to incorporate devulcanized rubber along with other formulation components to achieve a higher level of final product performance . Key product performance variables are level of contamination, number of rubber types in the rubber mixtures, and additives used by the formulations. The effect of additives was discussed antecedently under Product Characteristics. The number of types of rubber in waste tires is one of the most important factors affecting quality of devulcanized waste tire rubber.Optimizing a devulcanization process is very difficult when more than one type of rubber is involved. Depending on the process used, process conditions, the material, and the mingle level of the devulcanized rubber, most properties will be reduced by a few percent to more than two-thirds of those of the virgin material. In accompaniments where the devulcanized rubber properties are within 10 percent of the original rubber material, blending would seem to be an attractive opportunity that offers the potential of adding a low-cost recycled substitute.The best operating model for devulcanizers of single rubber formulation is a apply devulcanization line (or long run) of specific rubber. Smaller mickles of single formulations require incur extra costs for downtime and lost product caused by the cleanout between runs. The devulcanized rubber itself and some of its additives and fillerssuch as carbon black presumably add value. These fillers take the place of new additives and fillers that would otherwise be necessary. 1. 4. 2 Microwave Microwave technology has also been proposed to devulcanize waste rubber (Fix, 1980 Novotny, et al. 1978). This process applies the heat very quickly and uniformly on the waste rubber. The method employs the application of a controlled amount of microwave energy to devulcanize a sulfur-vulcanized elastomer containing polar groups or componentsto a state in which it could be compounded and revulcanized into useful products such as hoses. The process requires extraordinary or substantial physical properties. On the basis of the relative bond energies of C-C, C-S, and S-S bonds, the scission of the S-S and carbon-sulfur crosslinks appeared to take place.However, the material to be used in the microwave process moldiness be polar enough to accept energy at a rate sufficient to generate the heat necessary for devulcanization. This method is a quid process and requires expensive equipment. Figure E. Schematic Diagram of a Microwave Devulcanization System Rubber Crumb Microwave Unit Devulcanized Rubber Cooling System 1. 5 Microbial Reclaiming Thiobacillus-bacteria are able to oxidise the sulfur in polysulfonic bonds to sulphate. This reaction is limited to a surface layer of the rubber with a onerousness of less than 1 ? and the oxidation takes several weeks. The thiophilic bacteria Sulfolobus Acidocaldarius is able to break open carbonsulfur bonds in a stepwise oxidation reaction of the carbon-bound sulfur into a sulfoxide, a sulfone and finally to a sulphate8, 9. The disadvantage of these processes is the low devulcanization rate. Apparently, thes e types of biological devulcanization processes are exclusively or primarily limited to the surface layers of the elastomers (Christiansson, et al. , 1998). This circumstance may explain the overall low rates of desulfurization based on total mass processed.Figure F. Schematic Diagram of Biological Devulcanization System Microorganisms and master of ceremonies Media Mixer/ Reactor Rubber Crumb Devulcanized Rubber Dryer Filter By-Product driftes Liquid By-Product Chapter2 Cost Analysis Given the lack of information in the literature, the cost estimates are based on a synthesis of information and data from multiple sources for a given generic type of technology The analysis was generally performed by determining the costs ( dandy and operating and maintenance) of the processes and equipment described in the available literature.The cost analyses were conducted for three technologies that use different processing approaches chemical, ultrasonic, and mechanical. * The key processing elements of each of these technologies have been previously described in this report, and they serve as the primary basis of estimating gravid and operating and maintenance costs. The data in Table 6 summarize the capital costs and operating and maintenance costs for the technologies analyzed. The data for the capital cost analysis include an allowance for engineering services for the formula of the facility.The information shows that the capital costs for the processes vary from about $92,000 to about $166,000. ** poor technical foul information and data were found during the study to enable time-tested cost analyses for other devulcanization technologies. Table 6. Estimated Unit Costs for the Production of Devulcanized Rubber Item Mechanical Chemical Ultrasonic Capacity (lb/hr) 100 75 75 Capital Cost ($) 92,000 166,000 163,000 O Cost ($) 135,000 172,000 136,000 Amortized Capital and O ($) 143,000 186,000 150,000Amortized Unit Cost ($/lb) 0. 7 1. 2 1. 0 Interest rate 6% per ye ar Amortization period 20 years Similarly, the data in the table indicate that the operating and maintenance costs for facilities of this type range from about $135,000 to $172,000. The operating cost estimates include the cost of crumb rubber feedstock for each of the processes. Based on the relative small size of the facilities, the costs of the rental of a building for processing in operating and maintenance are included. This eliminated the cost of building a structure.As shown in the Table, the estimated amortized costs for producing devulcanized rubber are $1. 0/lb for the ultrasonic process, $1. 2/lb for the chemical process, and $0. 7/lb for the mechanical process. The analysis used an interest rate of 6 percent per year and an amortization period of 20 years. Due to uncertainties represented by the lack of detailed technical data and operating history for the technologies, the accuracy of the cost estimates is +/- 30 percent. As mentioned earlier, these costs reflect produc tion at low capacities.Some reduction in unit cost would likely occur due to economies of larger scale production. However, estimating reduction in unit cost is difficult because of the lack of data relating to production costs to different levels of throughput capacity for particular devulcanization technologies. For the size of operations considered in this analysis, labor costs are a substantial portion of the production costs. It is very difficult, however, to estimate the magnitude of any potential reductions in unit labor costs that qualificationiness occur if processing capacities were increased substantially.All circumstances considered, any estimates of commercial production costs for devulcanization of waste tire rubber are highly speculative at best. The best estimate of the study team is that perhaps production costs could be reduced by 25 to 30 percent if processing capacities were increased by a factor of approximately 5 to 10. The estimates of processing costs deve loped in this study do not include the costs of pollution control. The chapter lists the types of emissions that could be expected.The difficulty of permitting such a process and the cost of compliance with environmental regulations may comprise a significant barrier to the implementation of this technology. Conceivably, pollution control costs could add 10 to 30 percent to the cost of devulcanization. The difficulty of permittingand the costwould be a function of the type of devulcanization technology, the processing rates, and other factors. In general, the expectation is that the cost of environmental control systems for chemical devulcanization systems would be greater than that for ultrasonic or mechanical processes.The composition of rubber and additives that are used in rubber compounds in the manufacture of vulcanized rubber can and do have a dramatic effect on the properties of materials manufactured from devulcanized rubber. Apparently, the inferior properties of some poor ly (inadequately) devulcanized rubber can be compensated for by the addition of chemicals and the adjustment of operating conditions, among other remedies. In many cases in the literature, this situation is not addressed or discussed. Consequently, comparing devulcanization technologies is difficult.From most of the literature descriptions of the processes, what happens to the sulfur and other vulcanization chemicals during the various processes is unclear. Chapter 3 Environmental Analysis poor information is available in the literature on the environmental set up associated with waste tire devulcanization technologies. The lack of information apparently exists because business developers and researchers have concentrated their efforts primarily on technology improvements and achieving satisfactory properties for devulcanized rubber, an estimation of emission rates and a detailed environmental analysis are therefore not possible.However, using data and information from some other types of tire manufacturing processes (for example, extrusion of rubber) and the characteristics of vehicle tires, a qualitative analysis was performed. The environmental analysis described subsequently is limited to chemical and ultrasonic devulcanization and assumes that control of emissions would be required. 3. 1 Chemical technology Chemical devulcanization processes are usually jam processes that involve mixing crumb rubber with chemical reactants at a specific temperature and pressure.Once the design reaction time has elapsed, the contents are then rinsed, filtered, and dried to remove any remaining unwanted chemical components. The product can then be bagged or otherwise processed for resale. A block flow diagram of a generic chemical devulcanization process is illustrated in Figure G, showing the raw material feed is crumb rubber. The crumb rubber is mixed with one or more devulcanization agents. Chemical agents identified as devulcanization agents are listed in Table 8. During processing in the batch reactor, dehydrations are paper bagd that must be undisturbed and treated before release to the ambient atmosphere.Typical types of vapours that might be emitted from a batch reactor are listed in Table 9. The chemicals that would be vented from the batch reactor are dependent on the characteristics of the waste tire feedstock and on the chemical agent(s) used in devulcanizing the crumb rubber. For example, if disulfides are used in the process, they could result in formation of total heat sulfide (H2S) or methyl or other mercaptans (RSH). If the chemical agent orthodichlorobenzene is used, chlorinated hydrocarbons could potentially be released in the form of air emissions.Methyl iodide is volatile, and if used as a devulcanization agent, it could be vaporized. Since tire manufacturing utilizes zinc oxide and zinc carbonate, chemical devulcanization might also produce airborne metal particulates. Once the batch is fully processed, the reactor is ve nted. The vent gases are treated prior to release to the atmosphere. The vapors cannot be treated by vapor phase carbon because these chemicals will plate out and blind the carbon, making it ineffective. Instead, the vapor from the batch reactor needs to be thermally oxidized.At the high exit temperatures, typically as high as 2000F (1100C), the thermal oxidizer vent gases need to be cooled in a quench tower to approximately 300F (150C). Then, to remove any metals or other particulate, the vent gases are piped to a baghouse. Because of the high thermal oxidizer temperatures, methyl mercaptans (RSH) or hydrogen sulfide (H2S) from the crumb rubber is oxidized to sulfur dioxide (SO2). Therefore, downstream of the baghouse, a scrubber is required to remove sulfur dioxide (SO2), as shown in Figure G.Scrubbed vent gases are then released to the atmosphere. In addition to the scrubber vent gases described above, crystalline waste is generated from the scrubber. This perspicuous stream contains sodium sulfate (Na2SO4). This liquid waste can be disposed in receiving waters such as a river, stream, or bay. However, discharging to receiving waters will require a significant amount of treatment equipment and eventually a permit. As seen in Figure G, the devulcanized rubber is moved from the batch reactor to a separator by a heated extruder.Liquid that drips off the devulcanized rubber is removed in the separator and eliminated by feeding it to the same thermal oxidizer as the vent gases from the batch reactor. After the liquid has dripped off the devulcanized rubber in the separator, any remaining moisture is removed in the dryer. Fired dryers are typically supply by natural gas burners. Dryer vent gases are piped to the common thermal oxidizer. Based on the concentration of solids in the scrubber outgoing, processing the scrubber effluent through a filter press to dewater the solids may be necessary and cost-effective. Filter-pressed dewatered solids are called fil ter cake. Filter cake might require organisation in a hazardous waste site. notwithstanding though the waste disposal site may accept the scrubber effluent water, the stintings may favor installation and use of a filter press. This is necessary to dewater the solids due to the high cost of disposal of liquid waste. Figure G. Block Flow Diagram of a Chemical Devulcanization System Solids H2O Batch Reactor Heated Extruder Separator Crumb Rubber Devulcanization Agent 300 F Liquids Devulcanized Rubber Dryer Natural torpedo Vapors Thermal Oxidizer Quench Tower Baghouse Natural Gas Scrubber 2000 F 300 F H2O line of reasoning Emissions Air Emissions toAtmosphere Effluent irrigate Table 7. Tire Raw Materials Polymers Antiozonants Natural Rubber (polyisoprene) 2,2,4-trimethyl-1,2-dihydroquinoline (polymer) Styrene-Butadiene Rubber (SBR) n,n-(1,3-dimethylbutyl)-pphenylenediamine cis-Polybutadiene copolymer paraffinic wax Vulcanizing Agents Antioxidants Sulfur Alkylphenols Tetra-methyl th iurame sulfide Resorcinol Accelerators 2,6-Diterbutylhydroquinone Diphenylguanidine Retarders 2-Mercaptobenzothiazole n-Cyclohexylthiophthalimide n-Cyclohexyl-2-benzothiazolylsulfenamide Plasticizers 2-(n-Morpholinyl)-mercaptobenzothiazole aliphatic oil Hexamethylenetetramine remindful oilActivators Naphthenic oil Zinc oxide Di-(2-ethylhexyl)-phthalate Zinc carbonate Extenders stearic acid Silica gel Carbon black Table 8. Chemical Agents Used in Chemical Tire Devulcanization Processes Triphenyl phosphine Sodium di-n-butyl phosphite Thiol-amine reagents (specifically propane-thiol/piperidine, dithiothreitol, and hexane-lthiol) Lithium aluminium hydride Phenyl lithium Methyl iodide Hydroxide with quaternary ammonium chloride as a catalyst Orthodichlorobenzene Diphenyldisulphide Diallyl disulfide Toluene, naphtha, benzene, and/or cyclohexane, etc. in the presence of sodium Diamly disulfideDibenzyl disulfide Diphenyl disulfide Bis(alkoxy aryl) disulfides Butyl mercaptan and thiopenols xylol thiols Phenol sulfides and disulfides Alkyl phenol sulfides (for SBR) N,N-dialkyl aryl amine sulfides (for SBR in neutral or alkaline solutions) 3. 2 Ultrasonic technology Devulcanization by ultrasonic methods may be a continuous process (see Figure H). As the go steady illustrates, crumb rubber is loaded into a hopper and is subsequently fed into an extruder. The extruder mechanically pushes and pulls the rubber. This mechanical action serves to heat the rubber particles and soften the rubber.As the softened rubber is transported through the extruder cavity, the rubber is exposed to ultrasonic energy. The resulting combination of ultrasonic energy, along with the heat, pressure, and mechanical mastication, is sufficient to achieve varying degrees of devulcanization. The impression time to the ultrasonic energy is only seconds. Essentially all of the rubber entering the process is discharged from the extruder in a semi-solid product stream. Process losses would be primari ly emissions of fine particulate or of gases, if any, resulting from the mechanical and thermal applications occurring during devulcanization.Since the typical operating temperature of an ultrasonic devulcanization reactor is about 230F (110C), less vapor emission would be expected than from chemical devulcanization. Furthermore, since no chemicals are added to break the sulfur bonds that caused vulcanization to occur, there would likely be lower air emissions. After exiting through the extruder die, the rubber is passed through a cooling bath and then dried. Vented vapors would need to be treated by one of two methods. One method would be to use a small thermal oxidizer.The design of the thermal oxidizer, baghouse, and scrubber would be similar to that described previously for chemical devulcanization. However, the physical size of the oxidizer would be smaller, and the baghouse and scrubber would be larger. A second method to treat the vent gases exiting the ultrasonic devulcaniza tion reactor would be use of vapor phase carbon. In this method, due to the lower operating temperatures of the ultrasonic process, vent gas exiting the ultrasonic zone would have to be heated above the dew point temperature.If this elevation in temperature is not accomplished, the vent gases could condense on the surface of the carbon and thus blind the bed. In other words, surface assimilation sites on the surface of the carbon would be ineffective, and vent gases would exit the carbon bed untreated. If vapor phase carbon were to be used, the capital cost would be less than that of a thermal oxidizer. However, carbon is not very efficient. Weight loading can be approximately 10 weight percentin other words, adsorbing ten pounds of vent gas contaminants for every 100 pounds of carbon used. Use of carbon will have a relatively high operating cost.Also, the disposal of spent carbon can be very expensive. This is especially true if the spent carbon requires disposal at a hazardous wa ste disposal site. Even if the carbon is regenerated on-site, adsorption efficiency decreases after each regeneration. Typically, carbon can only be regenerated ten times. For illustration purposes, Figure H indicates the use of vapor phase carbon. Devulcanized rubber exiting the ultrasonic processing zone has to be cooled. A common method of reducing the rubber temperature is a cooling bath. The volume of cooling water used would be significant. Cooling water may become ontaminated from the process this effluent water leaving the cooling bath has to be treated. If an air cooler such as fin fans is used in lieu of water in the cooling bath, the volume of effluent liquid would be reduced. Another alternative would be to use a closed-loop cooling system, where the cooling water is cooled and returned to the process for reuse. If there is a buildup of contaminants, a small slipstream could be taken off and treated in a POTW, greatly reducing the amount of effluent that would otherwise require treatment. Figure H. Block Flow Diagram of an Ultrasonic Devulcanization System UltrasonicProcessing Zone Cooling Bath Devulcanized Rubber Feed Hopper Extruder Crumb Rubber Cooling Water Supply Effluent Water Heater Air Emissions Baghouse Carbon Air Emissions to Atmosphere Table 9. authorization Types of Chemical Compounds Emitted by Chemical and Ultrasonic Devulcanization Technologies Compound likely Source Benzene Plasticizers remindful oil Methylcyclohexane Plasticizers Na phthemic oil Toluene Plasticizers Aromatic oil Heptane Plasticizers Aliphatic oil 4-Vinylcyclohexene Polymers Natural Rubber (polyisoprene), styrene-butadiene rubber (SBR), cis- PolybutadieneEthylbenzene Plasticizers Aromatic oil Octane Plasticizers Aliphatic oil p-Xylene Plasticizers Aromatic oil Styrene Polymers styrene-butadiene rubber (SBR) Nonane Plasticizers Aliphatic oil 1,4-Cyclohexadiene-1-isopropyl-4- methyl Polymers Natural Rubber (polyisoprene) Isopropylbenzene Plasticizers Aromatic oil C yclohexene-1-methyl-3-(1- methylvinyl) Polymers Natural Rubber (polyisoprene) Propylbenzene Plasticizers Aromatic oil Benzaldehyde Polymers styrene-butadiene rubber (SBR) 1-isopropyl-4-methylcyclohexane (trans) Plasticizers Naphthemic oil 1-isopropyl-4-methylcyclohexane cis) Plasticizers Naphthemic oil 1-isopropyl-3-methylcyclohexane Plasticizers Naphthemic oil Decane Plasticizers Aliphatic oil Tri-isobutylene Polymers styrene-butadiene rubber (SBR) & cis-Polybutadiene Plasticizers Naphthemic oil Cyclohexene-5-methyl-3-(1- methylvinyl) Polymers Natural Rubber (polyisoprene) Indane Plasticizers Naphthemic oil 1-Isopropyl-4-methylbenzene Plasticizers Aromatic oil Cyclohexene-1-methyl-4-(1- methylvinyl) Polymers Natural Rubber (polyisoprene) 1-Isopropyl-2-methylbenzene Plasticizers Aromatic oil Dimethylstyrene Polymers styrene-butadiene rubber (SBR)Undecane Plasticizers Aliphatic oil Tetramethylbenzene Plasticizers Aromatic oil 1,2,3,4-Tetrahydronaphthalene Plasticizers Naphthemic oil 1,3-Di-isopropyl benzene Plasticizers Aromatic oil 1,4-Di-isopropyl benzene Plasticizers Aromatic oil Compound Probable Source 2-Isopropyl-6-methylphenol Antioxidents Alkylphenols Cyclohexylisothiocyanate Retarders n-Cyclohexyl-thiophthalimide Cyclododecatriene Polymers cis-Polybutadiene Dodecane Plasticizers Aliphatic oil Tridecane Plasticizers Aliphatic oil Tetraisobutylene Polymers styrene-butadiene rubber (SBR) & cis-Polybutadiene Plasticizers Naphthemic oil -ter-Butylstyrene Polymers styrene-butadiene rubber (SBR) Dimethylpropylhexahydronaphthale ne Plasticizers Naphthemic oil Tetradecane Plasticizers Aliphatic oil Nonylbenzene Plasticizers Aromatic oil 2,6-Di-ter-butyl-p-quinone Antioxidents 2,6-Diterbutyl-hydroquinone Pentadecane Plasticizers Aliphatic oil 1,6-dimethyl-4-isopropyl-1,2,3,4- tetra-hydronaphthalene Plasticizers Naphthemic oil Decylbenzene Plasticizers Aromatic oil Di-ter-butylthiophene Plasticizers Aromatic oil Diethyl phthalate Plasticizers Di-(2-ethylhexyl)-ph thalate Hexadecane Plasticizers Aliphatic oil ,2-Di-tolylethane Polymers styrene-butadiene rubber (SBR) Heptadecane Plasticizers Aliphatic oil 2,6-Di-ter-butyl-4-ethylphenol Antioxidents Alkylphenols Octadecane Plasticizers Aliphatic oil 1-Phenylnaphthalene Plasticizers Aromatic oil Di-iso-butyl phthalate Plasticizers Di-(2-ethylhexyl)-phthalate Tridecylbenzene Plasticizers Aromatic oil Dibutyl phthalate Plasticizers Di-(2-ethylhexyl)-phthalate Eicosane Plasticizers Aliphatic oil Heneicosane Plasticizers Aliphatic oil Docosane Plasticizers Aliphatic oil Di-(2-ethylhexyl) phthalate Plasticizers Di-(2-ethylhexyl)-phthalate Chapter 4 ConclusionsDevulcanization of specific types of rubber and/or waste tire rubber has a long history. However, only deep have limited technical data been reported in the available literature. Usually when reported, the tested properties of devulcanized rubber compose an incomplete list. This is especially true in the interpretation of how the devulcanized product would perform during compounding, in the manufactured end product, or both. Circumstantial and anecdotal evidence indicates significant technical and economic barriers to devulcanization of waste rubber.Based on the information collected in the study, is believed that the only method of achieving bulk devulcanization, as opposed to surface devulcanization, rests with ultrasonic or microwave devulcanization methods. Of these two methods of energy application, ultrasound appears to have substantially more research and development history. An important observation is that microwave technology is not an effective or efficient way to devulcanize non-polar rubber types, which collectively compose the vast majority of the mass of rubber in waste rubbers.Because of the ability to internally devulcanize cured rubber, ultrasonically devulcanized waste tire rubber may have more desirable marketing characteristics than those of surface-devulcanizing processes under similar conditions of cost and yield. The latter processes (surface devulcanizing) include mechanical, chemical, and biological processes. However, test data and applications for ultrasonically devulcanized waste rubber are lacking in the industry, along with process cost documentation.The devulcanized rubber market is most fully developed for single product materials made from manufacturing scrap that are reclaimed for reuse in the same process or in a broader specification application. The reprocessing of single rubbers depends upon being located near a large-volume rubber products company with enough scrap and enough rubber applications to justify the devulcanization step. Devulcanization of waste rubber, despite considerable research and developmental effort, is still in an early growth stage.Devulcanization lacks adequate test data and data interpretation, and it has poorly defined end product specifications without adequately justified and defined applications and uses. Research funds appear to be most available for analyse devulcanization of single rubber types, as opposed to studying rubber types with complex mixtur. In applications already using crumb rubber, devulcanized rubber can have advantages if the process combines a vulcanized rubber or other compatible material to create an integrated structure. The structure must have much better properties than those imparted by the filler role that crumb rubber frequently serves.