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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The full understanding of the mechanisms involved in the development of polymer blend microstructure during its processing has not yet been achieved; the understanding of blends composed by a highly elastic dispersed phase is even more indefinite. The proposal of this work is to analyze the deformation behavior of a new system composed by a partially devulcanized rubber dispersed in polypropylene using 2D and 3D images, both as complementary tools. For this purpose, ground tire rubber (GTR) was partially devulcanized by microwave irradiation for different exposure periods. After this step, each treated rubber was incorporated into recycled PP. The molded blends were analyzed using effective tools as 2D and 3D images and rheological data. In general, the polymer blends exhibited refined microstructure, especially the blend composed of the most devulcanized rubber, even though they had high values of viscosity ratio (≥4). Based on the 3D images, it is clear that breakup mechanisms of the dispersed phase, like parallel breakup, have played an important role in the evolution of the blend's microstructure, mainly in the region of higher shear rate during processing. However, in areas where the rubber is still vulcanized, the breakup may have been caused by erosion of its surface.

Os resíduos sólidos urbanos (RSUs) são atualmente um dos maiores problemas ambientais, por serem gerados em grande quantidade e ocuparem extensos espaços por um longo período, resultando na diminuição do tempo de vida útil dos aterros sanitários. Os polímeros constituem um grande percentual da composição do RSUs, sendo que as embalagens plásticas contribuem com maior volume e massa. Apesar da reciclagem de polímeros estarem se consolidando no Brasil, graças ao seu mercado ascendente e promissor, existem ainda restrições quanto a sua utilização em contato com alimentos devido aos eventuais processos de migração de contaminantes que podem ocorrer da resina reciclada para o alimento. Por outro lado, dados recentes do setor indicam que a maior parte do consumo de resina virgem é destinada, justamente, para o mercado de embalagens alimentícias. Assim, o desenvolvimento e o gerenciamento de tecnologias que possibilitem o retorno destes materiais a sua aplicação original é de grande importância para sociedade contemporânea. Em um panorama geral, este trabalho aborda as exigências e limitações do uso de polímeros reciclados para contato com alimentos.

In this work, flower-like molybdenum disulfide (MoS2) microspheres were produced with polyethylene glycol (PEG) to form MoS2-PEG. Likewise, gold nanoparticles (AuNPs) were added to form MoS2-PEG/Au to investigate its potential application as a theranostic nanomaterial. These nanomaterials were fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), photoelectron X-ray spectroscopy (XPS), Fourier-transformed infrared spectroscopy (FTIR), cyclic voltammetry and impedance spectroscopy. The produced hierarchical MoS2-PEG/Au microstructures showed an average diameter of 400 nm containing distributed gold nanoparticles, with great cellular viability on tumoral and non-tumoral cells. This aspect makes them with multifunctional characteristics with potential application for cancer diagnosis and therapy. Through the complete morphological and physicochemical characterization, it was possible to observe that both MoS2-PEG and MoS2-PEG/Au showed good chemical stability and demonstrated noninterference in the pattern of the cell nucleus, as well. Thus, our results suggest the possible application of these hybrid nanomaterials can be immensely explored for theranostic proposals in biomedicine.

In this work, we designed and studied two synthetic routes, based on modified Hummers method, to obtain graphene oxide (GO), and investigated their influence on the performance of polypropylene (PP)/GO nanocomposites. The two synthetic routes differed in the application condition of the oxidizing agent, potassium permanganate (KMnO4), which was added either as a powder (GO‐P) or as a water solution (GO‐S). This apparently subtle synthetic change yielded GOs with different degrees of oxidation and particle sizes, where GO‐P presented a higher oxidation degree and smaller particles. The different GOs were then melt‐blended with PP and the correlation between their different chemical/morphological structures and the nanocomposites' thermomechanical/rheological properties were evaluated. The milder oxidation process suffered by GO‐S, and consequent less hydrophilic character, yielded a PP/GO‐S nanocomposite with improved performance as the consequence of a better matrix/filler chemical affinity, mainly in compositions with lower GO‐S contents. The thermal stability was increased by more than 10°C when 0.1 wt% GO‐S was inserted into PP. When compared to the composition with 0.1 wt% GO‐P, the increase was 13°C. Reinforcing effects were also observed in that sample (with 0.1 wt% GO‐S), which exhibited the highest storage modulus and complex viscosity. These results suggest that tailoring the GO's oxidation degree and morphology is a key point to obtain an ideal interfacial interaction between phases.

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Many studies have been carried out in order to enable the use of recycled polymers in food packaging. The main problem is the presence of residual contaminants in recycled plastic, because it could pose a risk to public health when in contact with food. Our purpose is to evaluate different types of mechanical recycling in order to decontaminate the polypropylene. Firstly, pellets of polypropylene were contaminated, following the protocol recommended by the FDA. The pellets were subsequently recovered (washed and dried) and the samples were submitted to different extrusion processes. In order to evaluate the decontamination degree of the samples that went through each type of mechanical recycling, extractability tests were performed under different conditions of time, temperature and using different food simulants. The surrogates that migrated (suffered forced migration) were quantified using chromatographic techniques. The results showed that the decontamination degree of the samples changed with the different methods of extrusion applied. They also showed that conditions of time, temperature and different food simulants actually influenced the extraction of the surrogates.