An overview on waste rubber recycling by microwave devulcanization.

This review deals with waste rubber recycling by devulcanization treatment using microwave method. In fact, vulcanized rubbers have been extensively used in various fields due to their superior performances. Subsequently, the massive use of such materials, especially in the automotive industry, has generated a substantial amount of wastes which are not easily to be degraded due to the three-dimensional network formed by the vulcanization process. One of the optimal solutions for the successful recycling of rubber is devulcanization, i.e., the process in which the sulfur bonds in the vulcanized material are selectively broken. Currently, to achieve rubber devulcanization, the microwave treatment has been proposed as a promising alternative process due to its precise manipulation of process variables. Furthermore, the microwave process is easily to be coupled with effects of other elements such as chemical and swelling agents. In this work, different microwave devulcanization methods are reviewed, the utilization of the corresponding devulcanized materials has also been discussed. The reviewed contents are believed to be of great interest to academics and industries since they represent a great challenge from scientific, economic and environmental points of view.

Devulcanization of natural rubber industry waste in supercritical carbon dioxide combined with diphenyl disulfide.

The elimination of rubber wastes without affecting the environment is one of the most important challenges of the 21st century waste management. Accordingly, the present work is focused on the recycling of natural rubber (NR) industry waste by means of devulcanization in supercritical carbon dioxide (scCO2) atmosphere. With that aim, a novel device allowing to perform rubber devulcanization was developed. It consists of a triaxial compression reactor integrated into a dynamic hydraulic universal testing machine with a heating chamber. NR industry waste was devulcanized in the mentioned device at different temperatures, in scCO2 by using diphenyl disulfide (DD) as devulcanizing reagent. The devulcanization degree and quality of the treated materials were evaluated by the swelling test combined with the Horikx theory. It was appeared that a successful devulcanization, with almost no degradation, was obtained, and the devulcanization degree reached maximum value of ~90%. Thermogravimetric tests and scanning electron microscopy (SEM) images strengthened these results. Finally, it was concluded that the developed device is appropriate to perform rubber recycling, which contributes to the progress in the environmental protection.

Recycling of waste tire rubber: Microwave devulcanization and incorporation in a thermoset resin.

This study focused on the possibility of recycling Waste Tire Rubber (WTR) to be used as polymer modifier. Thus, WTR was grinded into powder, at ambient temperature, with a disc mill PQ500 and microwave electromagnetic energy was used to devulcanize this powder with the final aim of producing a new composite by its incorporation in a thermoset resin. The influence of the treatment microwave energy on the devulcanization ratio was investigated. FTIR analysis revealed that rupture of Sulfur-Sulfur (SS) and Carbon-Sulfur (CS) bonds have occurred during the treatment. Swelling analysis showed that the microwave treatment can lead to a very significant degree of devulcanization. The Ground Tire Rubber (GTR) and the Devulcanized Ground Tire Rubber (DGTR) were then separately used to prepare epoxy based composites. It appeared that epoxy composites filled with DGTR have better mechanical properties than those filled with untreated GTR. This result agrees with scanning electron microscopy observations which highlighted a better interface coherence between DGTR and epoxy. A complementary analysis pointed out a linear relationship between the rubber modulus and the number of crosslink per chain.