Devulcanization of rubbers

Devulcanization of Rubber Peelings. Rubber peelings (10 g)(8) were charged into a 3-neck, 250 mL flask fitted with a water-cooled condenser and paddle stirrer. A solution of catalyst in 50 mL of... 

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... 

D. S. Novotny et al. Microwave devulcanization of rubber. US4104205. Proprietor Goodyear Tire Rubber Company, 1978. 

Extensive studies on the ultrasonic devulcanization of rubbers and some preliminary studies on ultrasonic decrosslinking of crosslinked plastics were... 

FIGURE 15.3 Schematic diagram of coaxial reactor (a), barrel reactor (b), and grooved barrel reactor (c) built for devulcanization of rubbers. 

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. 

Recently, a novel continuous process has been developed for devulcanization of rubbers as a suitable way to recycle used tires and waste rubbers [83-119]. This technology is based on the use of high-power ultrasounds. The ultrasonic waves of certain levels, in the presence of pressure and heat, can quickly break up the three-dimensional network in crosslinked rubber. The process of ultrasonic devulcanization is very fast, simple, efficient, and solvent and chemical free. Devulcanization occurs at the order of a second and may... 

Extensive studies on the ultrasonic devulcanization of rubbers and some preliminary studies on ultrasonic decrosslinking of crosslinked plastics were carried out [83-122]. It was shown that this continuous process allows one to recycle various types of rubbers and thermosets. As a most desirable consequence, ultrasonically devulcanized rubber becomes soft, therefore making it possible for this material to be reprocessed, shaped, and revulcanized in very much the same way as the virgin rubber. This new technology has been used successfully in the laboratory to devulcanize a ground tire rubber (GRT)... 

FIGURE 3 Schematic diagram of (a) coaxial reactor, (b) barrel reactor, and (c) grooved barrel reactor built for devulcanization of rubbers. 

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... 

Somewhat similar is the devulcanization of rubber, in which a sulfur cross-linked network is converted to a system of more-or-less thermoplastic components. Rubber reclaiming has fallen on hard times for various reasons, including the difficulty of making an environmentally attractive process. 

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