Devulcanization, unfilled

A devulcanization process that utilizes supercritical CO2 as a devulcanization reaction medium in the presence of diphenyl disulfide as a devulcanizing reagent has been reported [45]. The process devulcanizes unfilled NR vulcanizates effectively. Further, a comparison of measured sol/gel components as well as dynamic mechanical properties of the devulcanized rubber products of filled and unfilled NR vulcanizates has indicated that the presence of carbon black in the vulcamizate does not disturb the devulcanization in supercritical CO2. 

Tapale, M. Isayev, A.I. Continuous ultrasonic devulcanization of unfilled NR vulcanizates. J. Appl. Polym. Sci. 1998, 70, 2007. 

It was reported (Isayev et al., 1997) that under some devulcanization conditions the tensile strength of unfilled revulcanized SBR was found to be... 

FIGURE 15.6 The stress-strain curves of unfilled virgin vidcanizates and revulcanized SBR obtained from rubbers devulcanized in coaxial reactor at various values of ultrasonic amplitude. 

FIGURE 15.7 The stress-strain curves for unfilled NR vulcanizates prepared from ultrasonically devulcanized NR in coaxial reactor at various flow rates and amplitudes at a die gap of 2.54 mm and a barrel temperature of 120°C. 

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). 

X. Sun, The devulcanization of unfilled and carbon black filled isoprene rubber vulcanizates by high power ultrasound, PhD dissertation, university of Akron, 2007. 

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