Scrap rubber devulcanization

Scission of Polysulfide Crosslinks in Scrap Rubber Particles. Throughout this study, we used a single lot of scrap rubber peelings having the average composition described in the Experimental Section. We began our studies with Aliquat 336 as the phase transfer catalyst because of its proven effectiveness in simple systems and its commercial availability. When devulcanization is performed in a refluxing benzene/aqueous NaOH mixture, the chemical crosslink density (M... 

A biotechnological process was developed by Straube et al. for the devulcanization of scrap rubber by holding the comminuted scrap rubber in a bacterial suspension of chemolithotropic microorganisms with a supply of air until elemental sulfur or sulfuric acid is separated. This seems to be an interesting process, which obtains reclaim rubber and sulfur in a simplified manner. 

Butyl and NR tubes and other fiber-free scrap rubbers are reclaimed by means of the heater or pan process. Brass tube fittings and other metal are removed from the scrap. The scrap is mechanically ground, mixed with reclaiming agents, loaded into pans or devulcanizing boats, and autoclaved at steam pressures of 10-14 atm (1.03-1.40 MPa) for 3-8 h. The reclaim is finally processed much the same way as... 

There are certain technical limitations in the devulcanization of rubbers, and vulcanization is, in fact, not truly reversible (Pryweller, 1999). The partial devulcanization of scrap rubber will result in a degradation of physical properties. In many cases, this may limit the amount of substitution levels in high-tech applications such as passenger tires. But it can provide the compounder of less stringent products with an excellent low-cost rubber that can be used as the prime rubber or at very high substitution levels. According to Franta (1989), reclaim cannot be used for tread compounds in tires because every addition may decrease their resistance to wear. However, this statement has not been checked in case rubber devulcanized without an addition of chemicals. Considerable amounts of reclaim are consumed for carcasses of bias ply tires for cars if the compounds are of NR for carcasses of radial tires no reclaim is added. On the other hand, reclaim is added to compounds for bead wires and it may also be added to sidewalls. Within the framework of direct recycling options a number of applications for GRT outside the rubber industry have been proposed. Such applications include the use as a tiller in asphalt for the surface treatment of roads and as a rubberized surface for sport facilities. 

There are certain technical limitations in the devulcanization of rubbers, and vulcanization is, in fact, not truly reversible [11]. The partial devulcaniza-tion of scrap rubber will result in a degradation of physical properties. In many cases, this may limit the amount of substitution levels in high-tech applications such as passenger tires. But it can provide the compounder of less stringent products with an excellent low-cost rubber that can be used as the prime rubber or at very high substitution levels. According to Franta [12], reclaim... 

As an example of modification of substances may be cited the devulcanization of rubber scrap (patented by Gross, Ref 2, and the further development by H.F. Palmer). The method consisted essentially in subjecting rubber scrap ro high pressure steam for a period of time sufficient to soften and impregnate the mass, and then the pressure was abruptly released. The resulting product consisted of plastic, devulcanized particles, directly suitable for further milling and compounding... 

Vehicle tire scrap containing polyisoprene rubber, SBR, and butadiene rubber was devulcanized by low-temperature phase-transfer catalyst. Both the devulcanizing agent composition and the process were patented. The novelty of this process lies in the use of low-temperature phase-transfer catalyst and a process temperature lower than 150" C. The devulcanized rubber of this invention is distinguishable from conventional reclaimed rubber in that the devulcanized rubber is substantially free from polysulfide crosslinks, which are selectively broken during the process with negligible main chain scission. 

The reclaimator process is more attractive than the above processes. The reclaimator is essentially a high-pressure extruder that devulcanizes fiber-free rubber continuously. Ground scrap is mechanically treated in hammer mills to remove the textile material, mixed with reclaiming oils and other materials, and then fed into the reclaimator. High pressure and shear between the rubber mixture and the extruder barrel walls effectively reclaim the rubber mixture. Devulcanization occurs at 175-205°C in a few minutes and turns the rubber into reclaim that issues from the machine continuously. The whole regeneration, which is a dry process, may be completed in about 30 min. 

Reclaiming is a procedure in which the scrap tire rubber or vulcanized rubber waste is converted, using mechanical and thermal energy and chemicals, into a state in which it can be mixed, processed, and vulcanized again. The principle of the process is devulcanization. In devulcanization, it is assumed that the cleavage of intermolecular bonds of the chemical network, such as carbon-sulfur and/or... 

The tire is a complicated composite product consisting of tread, undertread, carcass, innerliner, bead, and sidewall. Many different types of rubber and carbon black reinforcement are used in manufacturing tires. Therefore, GRT is a blend of various rubbers and carbon blacks. Accordingly, in using GRT powder and devulcanized GRT in new tire manufacturing, many factors should be considered. Evidently, scrap tire powder can be used as a filler for virgin rubbers and devulcanized GRT can be used in blends with virgin rubbers. This market consumed approximately 1.354 x 10 tons of scrap tire rabber in 2009 (US Scrap Tire Markets, 2009). 

Until recently, it was generally understood that only a few percent of ground rubber can be used in new tires. Scrap Tire Management Council reports that 5% of recycled tire rubber is used in an original equipment tire for the Ford Windstar. Although no other information on the amount of devulcanized rubber used in new tires is available in open literature, a possibility exists for the use up to 10 wt.% of recycled tire rubber in new tire compounds (Myhre and MacKillop, 2002). It was reported that actual road tests of buck tire containing 10 wt.% of the devulcanized rubber in the tread exhibited tread wear behavior almost equal to that for standard type with the new rubber compound (Fukumori et al., 2002). The increase in the amount of recycled mbber in tires is growing but it is likely that results will not be available for a number of years. 

Many different reclaiming processes [8, 13, 15-17, 19-22] have been applied through the years in an attempt to solve the problem of rubber recycling. Generally, ground rubber scrap is, in most cases, the feedstock for the devulcanization step. Warner [13] and recently Adhikari et al. [23] and Isayev [24] presented reviews of the existing literature that is relevant to various methods of devulcanization. 

Styrene butadiene rubber (SBR) composites filled with SBR industrial scraps (SBR-r) were devulcanized by microwave. For further application in automotive profiles, the set of results indicated that the best performance was achieved by the composite containing SBR-r devulcanized for 2 min in a microwave [130]. 

---