Rubber devulcanization chemical

Ultrasonic devulcanization also alters revulcanization kinetics of rubbers. It was shown (Isayev et al., 1996b) that the revulcanization process of devulcanized SBR was essentially different from those of the virgin SBR. The induction period is shorter or absent for revulcanization of the devulcanized SBR. This is also true for other unfilled and carbon black-filled mbbers such as GRT, SBR, NR, EPDM, and BR cured by sulfur containing curative systems, but not for silicone rubber cured by peroxide. It was suggested that a decrease or disappearance of the induction period in case of the sulfur-cured rubbers is due to an interaction between the rubber molecules chemically modified in the course of devulcanization and unmodified rubber molecules resulting in crosslinking. It was shown that approximately 85% of the accelerator remained in the ultrasonically devulcanized SBR rubber (Levin et al., 1997a). 

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. 

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... 

Rubber Reclaim. For the traditional rubber "reclaim," crumb rubber is mixed with water, oil, and chemicals and heated under pressure, thus rupturing the carbon-sulfur bonds that cross-link the molecular matrix. The resulting partially devulcanized rubber may be formed into slabs or bales and shipped to manufacturers who process and vulcanize it for use as an alternative to virgin rubber to use in tires or to make mats and other rubber products. 

Considerable effort has been directed to solving this problem. Although chemical probes have been developed that selectively cleave carbon-sulfur and sulfur-sulfur bonds but not carbon-carbon bonds, most of the effort on devulcanization processes has been focused on providing a usable form of rubber suitable for use as a reclaimed material in new articles. ... 

A large number of chemical devulcanization agents for natural and synthetic rubbers have been developed. These include phosphines and phosphates, numerous sulfides and mercaptans, metal salts such as methyl iodide, phenyl lithium, lithium aluminum hydride, and phase-transfer catalysts. ... 

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... 

Another chemical method was recently proposed [43]. It is based on the use of 2-butanol solvent as a devulcanizing agent for sulfur-cured rubber under high temperature and pressure. It is claimed that the molecular weight of the rubber is retained, and its microstructure is not significantly altered during the devulcanization process. However, the process is extremely slow and requires separation of the devulcanized rubber from the solvent. 

In addition to the use of organic chemicals, rubbers can be devulcanized by means of inorganic compounds. Discarded tires and tire factory waste were devulcanized by desulfurization of suspended rubber vulcanizate crumb (10 to 30 mesh) in a solvent such as toluene, naphtha, benzene, cyclohexane, etc., in presence of sodium [44]. The alkali metal cleaves mono-, di-, and polysul-fidic crosslinks of the swollen and suspended vulcanized rubber crumb at around 300°C in absence of oxygen. However, this process may not be economical because the process involves swelling of the vulcanized rubber crumb in an organic solvent where the metallic sodium in molten condition should reach the sulfidic crosslink sites in the rubber crumb. Also, the solvent may cause pollution and be hazardous. A technology was also proposed to reclaim... 

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... 

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