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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.

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Rheological and morphological studies were performed on polymer blends of ethylene-octene copolymer [polyethylene elastomer (PEE)] and polypropylene (PP). The viscosities of PEE, PP, and PEE/PP blends were analyzed using an Instron capillary rheometer and a Rheometrics Dynamic Stress Rheometer, SR 200. A non-Newtonian flow behavior was observed in all samples in the shear rate range from 27 to 2700 s Ϫ1 , whereas at shear rates in the range from 0.01 to 0.04 s Ϫ1 , a Newtonian flow behavior was verified. The scanning electron micrographs showed that dual-phase continuity may occur between 50 and 60 (wt %) of PEE. This result is consistent with the Sperling's model. The mechanical analysis showed that PEE/PP, with 5 wt % of PEE, presented an increase on the mechanical properties and as the PEE content increased, a negative deviation in relation to an empirical equation was observed. Thermal analysis showed that there were no change in the crystallization behavior of the matrix when different elastomer contents were added. Dynamic mechanical thermal analysis showed that samples with low PEE contents presented only one peak, indicating a certain degree of miscibility between the components of these blends.

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.

Vulcanized rubbers are materials commonly used in various industrial applications. In this study, scraps of ethylene‐propylene‐diene rubber (EPDM‐r) from the automotive industry were submitted to different microwave exposure times (2–5 min). Samples of recycled rubber with (as received) and without (after extraction) paraffinic oil were analyzed. The devulcanized EPDM‐r was characterized by gel content, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The gel content indicated that the presence of paraffin oil in EPDM‐r affects the devulcanization process. The DSC analysis showed significant changes in the glass transition temperature (Tg). The Tg values for EPDM‐r decreased with an increase in the microwave exposure time. Furthermore, the presence of a thermal phenomenon characteristic of uncured material was observed. Sample degradation was studied through TGA, and the values for the activation energy (Ea) of the degradation process were determined using the Flynn‐Wall‐Ozawa method. For conversions up to 0.10, the Ea values of the EPDM‐r samples without oil decreased with an increase in the microwave exposure time. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers

The recycling of waste rubber has considerable significance in terms of environmental protection and energy conservation. Considering that most of the relevant literature is concerned with tire recycling, the objective of this study is to develop and characterize styrene-butadiene rubber composites containing only industrial rubber scraps devulcanized by microwave. The styrene-butadiene rubber extruded profile scraps were collected and ground under ambient conditions. The obtained powder styrene-butadiene rubber-r was physically, thermally, and chemically characterized. From the devulcanized styrene-butadiene rubber-r two composites were prepared, varying the exposure time of the powder in the microwave (3 and 4 min). These composites were compared to a control sample supplied by the industry from which the styrene-butadiene rubber extruded profile scraps were collected. Vulcanization parameters were determined by oscillatory disk rheometry. Vulcanized composites were characterized by crosslink density and physical-mechanical properties (Shore A hardness, tensile and tear strength, and compression set) before and after a postcure process. The mechanical properties of the compositions were ∼25% for tensile strength and 41% for tear strength compared to the control sample. The results for the crosslink density verified those for the mechanical properties of the composites.