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Abstract.Microwave devulcanization is known to be a promising and an efficient rubber recycling method which makes possible for the rubber to regain its fluidity, and makes it capable of being remolded and revulcanized. The focus of this work is to understand the physical and chemical changes that occur in the ground tire rubber after different microwave exposure periods. For this purpose chemical, thermal, rheological and morphological analyses were performed on the tire rubber, which contains natural rubber (NR) and styrene-butadiene rubber (SBR) as polymeric material. The results showed that the microwave treatment promoted the breaking of sulfur cross-links and consequently increased the rubber fluidity. However, long periods of exposure led to degradation and modification of some properties. At nanoscale, the deformation of the devulcanized NR domain under stress was observed, and the morphology obtained appears to be a droplet dispersion morphology. The most exposed samples presented only one glass transition temperature, and from this it was concluded that the treatment may have played an important role in the compatibilization of the elastomeric blend. Based on the results, it is required to control the microwave exposure time and polymeric degradation in order to achieve a regenerated rubber with satisfactory properties.

For a sustainable development, recycling is a very important step, which, beyond saving the use of natural resources, can also be a solution for low-income families, providing them earnings. Recycling is also considered a category of green chemistry and contributes to the reduction of pollution, bringing the improvement to the public health. However, recycling of a material trying to contribute to the environment will not bring positive results if the final properties of the recycled material do not point to an application that is viable. In this sense, the aim of this work is to present a comprehensive study of the revulcanized ground tire rubber samples, previously devulcanized by the action of the microwaves under different exposure times. It is extremely important to know in depth the modifications that occurred in the recycled material during all the stages of the recycling process to which the material was subjected, in order to select the ideal application for the recycled material. The obtained results pointed out to modifications as a result of the revulcanization process, such as in the chemical structure, composition, thermal stability, and morphology.

SbstractThe main objective of this work is the study of the influence of microwaves devulcanization of the elastomeric phase on dynamically revulcanized blends based on Ground Tire Rubber (GTR)/High Density Polyethylene (HDPE). The devulcanization of the GTR was performed in a system comprised of a conventional microwave oven adapted with a motorized stirring at a constant microwaves power and at various exposure times. The influence of the devulcanization process on the final properties of the blends was evaluated in terms of mechanical, viscoelastic, thermal and rheological properties. The morphology was also studied.

The influence of rubber devulcanization by microwaves in the reversion behavior is still modestly explored in the literature. The reversion occurs due to thermal degradation of unstable crosslinkings formed during the vulcanization process. This phenomenon results in poor final mechanical properties of the artifacts. In this work, some formulations based on natural rubber (NR) with the incorporation of NR devulcanized by microwaves at different exposure times to the microwaves were vulcanized by compression molding at the same temperature and time used for the study of their vulcanization characteristics, in order to correlate the properties obtained and understand the influence of the reversion on the mechanical properties. The results showed that levels of devulcanization/degradation of the recycled phase, as well as the additional heating time influenced on the behavior of reversion and, consequently, on the mechanical properties. the influence of density and crosslinking type in the mechanical properties of rubber has been studied by various authors, 4,6,7 since the stress-strain measurement is an indirect method for determining the crosslinking density. 5Currently, a big global problem is related to disposal of solid urban residues, and materials able to make this problem much worse are the vulcanized/cured elastomers. In the same way, the search for processes and/or sustainable materials is of great value, and it is directly related to the solution of this problem, since the use of recycled materials can reduce such problem. In addition, recycling not only protects the environment, but also saves the limited petroleum resources from which the raw material originates, 8 also being a source of income for many families around the world. The recycling method used in this work is the devulcanization by microwaves.Devulcanization is a way of providing energy to destroy, total or partially, the three-dimensional network formed during vulcanization. 9 Devulcanization by microwaves is a well-established recycling technique of vulcanized elastomers. Among its

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Recycling is a process toward sustainable development. However, it does not do any good to recycle a material trying to contribute to the environment, if the final properties of the recycled material do not point to a feasible application. In this sense, the purpose of the present study is to evaluate the kinetics parameters of the revulcanization reaction of ground tire rubber (GTR) devulcanized by microwaves using rheological (ODR) and differential scanning calorimetry (DSC) methods. For ODR, torque versus time curves was obtained at 160, 170, 180, 190, and 200 °C and simulated. In general, occurred a decrease in activation energy values upon microwaves exposure time but all the samples showed an autocatalytic model from simulation curves. For DSC, three different models were used: Kissinger, Ozawa, and Flynn-Wall-Ozawa. All of the methods showed a trend to decrease the activation energy by microwave exposure time as noticed in the rheological curves. Among the reasons, the carbon black and the viscosity of the system are the main contributors; the former by radiation tends to oxidize and facilitates the degradation process, and the latter achieves more facility to chain mobility, reducing the activation energy.

SbstractThe main objective of this work is to study the influence of clay addition on dynamically revulcanized blends of Ground Tire Rubber (GTR)/High Density Polyethylene (HDPE). GTR was previously devulcanized in a system comprised of a conventional microwave oven adapted with a motorized stirring, with a fixed microwave power and at various exposure times. The influence of clay addition on the final properties of the blends was evaluated in terms of mechanical, viscoelastic, thermal and rheological properties, with morphology being also analyzed. The results depict that the clay can modify the rheological behavior of the GTR phase, in addition to the thermal and mechanical properties of some blends.