Resumo em Inglês:

This research aims at studying the photodegradation of a polypropylene formulation filled with lanthanide complexes. These complexes can be used as tracers for the identification of polymer materials in order to facilitate an high speed automatic sorting of plastic wastes for an economically efficient recycling. By paying attention to the evolution of carbonyl absorption bands in FTIR spectra, it is observed that the addition of lanthanide complexes into our formulation improves UV stability of polypropylene by reducing the extent of photo-degradation. Furthermore, TG analyses show that the traced blends can maintain better thermal properties, after irradiation. A significant increase of the crystallinity degree and a decrease of the melting temperature are more pronounced for the unfilled UV–irradiated PP. This might result from chemi-crystallization that can occur when chain entanglements are broken as a result of chain scissions. From SEM analyses, it is observed that the severity of surface cracks induced by photo degradation is reduced for filled PP. The mechanical tests are in agreement with this result and show a fundamental change in the behavior of the as-exposed blends from a ductile to a brittle material.

Resumo em Inglês:

A low cost and environmental friendly extrusion process of the Polyacrylonitrile (PAN) polymer was viabilized by using the 1,2,3-propanetriol (glycerol) as a plasticizer. The characterization of the fibers obtained by this process was the object of study in the present work. The PAN fibers were heat treated in the range of 200 °C to 300 °C, which is the temperature range related to the stabilization/oxidation step. This is a limiting phase during the carbon fiber processing. The characterization of the fibers was made using infrared spectroscopy, thermal analysis and microscopy. TGA revealed that the degradation of the extruded PAN co-VA fibers between 250 °C and 350 °C, corresponded to a 9% weight loss to samples analyzed under oxidizing atmosphere and 18% when the samples were analyzed under inert atmosphere. DSC showed that the exothermic reactions on the extruded PAN co-VA fibers under oxidizing synthetic air was broader and the cyclization started at a lower temperature compared under inert atmosphere. Furthermore, FT-IR analysis correlated with thermal anlysis showed that the stabilization/oxidation process of the extruded PAN fiber were coherent with other works that used PAN fibers obtained by other spinning processes.

Resumo em Inglês:

Two polyethylene-based on single-site metallocene catalyst (mLLDPE) were selected to characterize the effect of long chain branching (LCB) on blown film processability, optical and mechanical properties. 13C NMR and parallel plate rheology were used to identify LCB presence on LLDPEs. Blown films were produced from 100% LLDPEs using three different machine direction (MD) stretch ratios. When the same processing conditions for the two LLDPEs grades were used, better processability was observed for LLDPE with LCB. In relation to mechanical and physical properties, Elmendorf tear and optical properties were highly influenced by the presence of LCB. Tear resistance is affected by film orientation and is inversely proportional to the level of LCB in the polymer. It was observed a reduction of 50% in the MD tear strength when comparing with the polymer without LCB. However, haze decreases significantly with the presence of LCB, about 40%.

Resumo em Inglês:

Fly ash, an inorganic alumino silicate has been used as filler in epoxy matrix, but it reduces the mechanical properties due to its poor dispersion and interfacial bonding with the epoxy matrix. To improve its interfacial bonding with epoxy matrix, surface treatment of fly ash was done using surfactant sodium lauryl sulfate and silane coupling agent glycidoxy propyl trimethoxy silane. An attempt is also made to reduce the particle size of fly ash using high pressure pulverizer. To improve fly ash dispersion in epoxy matrix, the epoxy was modified by mixing with amine containing liquid silicone rubber (ACS). The effect of surface treated fly ash with varying filler loadings from 10 to 40% weight on the mechanical, morphological and thermal properties of modified epoxy composites was investigated. The surface treated fly ash was characterized by particle size analyzer and FTIR spectra. Morphological studies of surface treated fly ash filled modified epoxy composites indicate good dispersion of fillers in the modified epoxy matrix and improves its mechanical properties. Impact strength of the surface treated fly ash filled modified epoxy composites show more improvement than unmodified composites.

Resumo em Inglês:

Acrylamide/2-hydroxyethyl methacrylate hydrogels were prepared by simultaneous radiation-induced cross-linking copolymerization of acrylamide (AAm), 2-hydroxyethyl methacrylate (HEMA) and water mixtures at a radiation dose of 10 kGy. Hydrogels were characterized by infrared spectroscopy. Dynamic and equilibrium swelling of hydrogels in water and in buffer solutions were investigated. They were sensitive to pH and temperature. Swelling was non-Fickean and increased with increasing the acrylamide content. Temperature dependence of the equilibrium water uptake of copolymers exhibited a discontinuity around 35 °C resulting from the weakening of the hydrogen bonds between the hydroxyl groups of HEMA and the amide groups of AAm. The thermodynamic and network parameters derived from swelling and mechanical measurements are compared and discussed. They exhibit a strong dependence on the AAm content in the hydrogel. These hydrogels can be considered for applications in fields requiring environmentally responsive hydrogels such as medicine, pharmacy and bioengeneering.

Resumo em Inglês:

The morphological and mechanical properties of Ziegler–Natta catalyzed isotactic polypropylenes as influenced by the molecular weight and tacticity was investigated. Polypropylene samples were injection moulded into standard disks with a HAAKE MiniJet II injection moulder at 190 °C and 200 bar for morphological and mechanical tests. The morphological and mechanical properties of specimens were investigated by means of optical microscope (OM), scanning electron microscopy (SEM), microhardness (MH) and dynamic mechanical analysis (DMA). The samples exhibited a typical α-modification spherulite structure of isotactic polypropylenes crystallized from the melt. It was found that the most important factor affecting the structure and properties of these polymers is the isotacticity content. A clear molecular weight effect was also found for samples with low molecular weights. The microhardness and storage modulus values increased as crystallinity did. Accordingly, isotacticity degree is considered as the main parameter affecting the crystallinity of samples.

Resumo em Inglês:

The cooling channels of a mold for plastic injection have to be as close as possible to the part geometry in order to ensure fast and homogeneous cooling. However, conventional methods to manufacture cooling channels (drilling) can only produce linear holes. Selective laser melting (SLM) is an additive manufacturing technique capable to manufacture complex cooling channels (known as conformal cooling). Nevertheless, because of the high costs of SLM the benefits of conformal collings are still not clear. The current work investigates two designs of conformal coolings: i) parallel circuit; ii) serial circuit. Both coolings are evaluated against to traditional cooling circuits (linear channels) by CAE simulation to produce parts of polypropylene. The results show that if the conformal cooling is not properly designed it cannot provide reasonable results. The deformation of the product can be reduced significantly after injection but the cycle time reduced not more than 6%.

Resumo em Inglês:

Polymeric hindered amine light stabilizers (polymeric HALS) have been extensively studied because they combine a high ability to protect the polymers against harmful effects of weathering with minimum physical loss. In this study a new polymeric N-methylated HALS was synthesized by the radical copolymerization of a cyclic tertiary amine with vinyl acetate (VAc). 4-Acryloyloxy-1,2,2,6,6-pentamethylpiperidine (APP), the cyclic tertiary amine, was prepared by the initial conversion of 2,2,6,6-tetramethyl-4-piperidinol derivatives via two different routes. The APP/VAc copolymer synthesized was characterized by size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR) and carbon-13 nuclear magnetic resonance (13C NMR). The photostabilizing performance, particularly the induction period of polypropylene (PP) films containing different concentrations of APP/VAc copolymer, when exposed to accelerated aging, was comparable to that of PP films compounded with commercial polymeric HALS.

Resumo em Inglês:

Polylactic acid (PLA) is an attractive candidate for replacing petrochemical polymers because it is from renewable resources. In this study, a specific PLA 2002D was melt-mixed with two plasticizers: triethyl citrate (TEC) and acetyl tributyl citrate (ATBC). The plasticized PLA with various concentrations were analyzed by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), melt flow index (MFI), thermogravimetric analysis (TGA), X-ray diffraction (XRD), UV-Visible spectroscopy and plasticizer migration test. Differential scanning calorimetry demonstrated that the addition of TEC and ATBC resulted in a decrease in glass transition temperature (Tg), and the reduction was the largest with the plasticizer having the lowest molecular weight (TEC). Plasticizing effect was also shown by decrease in the dynamic storage modulus and viscosity of plasticized mixtures compared to the treated PLA. The TGA results indicated that ATBC and TEC promoted a decrease in thermal stability of the PLA. The X-ray diffraction showed that the PLA have not polymorphic crystalline transition. Analysis by UV-Visible spectroscopy showed that the two plasticizers: ATBC and TEC have no effect on the color change of the films. The weight loss plasticizer with heating time and at 100°C is lesser than at 135 °C. Migration of TEC and ATBC results in cracks and changed color of material. We have concluded that the higher molecular weight of citrate in the studied exhibited a greater plasticizing effect to the PLA.

Resumo em Inglês:

Kaolin clay/poly (butylene terephthalate) (clay/PBT) composites films were prepared by solution casting technique. The scanning electron microscope (SEM) study showed that clay particles were well dispersed and embedded within the PBT matrix. The TGA thermograms showed that the thermal stability of PBT matrix was slightly improved by the incorporation of clay into the polymer matrix. The polarized optical microscopy (POM) study presented that the size of spherulites of PBT was decreased by the incorporation of clay into matrix, which might be due to nucleation effect of kaolin clay. The tensile strength and modulii of PBT polymer matrix were also significantly improved by the addition of clay polymer matrix. The solvent uptake study showed that the uptake of various solvents by clay/PBT nanocomposite were lower than neat PBT.

Resumo em Português:

Polímeros Molecularmente Impressos (MIPs) são polímeros sintéticos que apresentam alta seletividade a uma molécula de interesse. O objetivo deste trabalho foi a síntese e caracterização de MIPs para aplicação na extração em fase sólida (SPE), visando a determinação de fenilalanina. Os MIPs foram sintetizados a partir do MAA, fenilalanina, EGDMA, AIBN, em clorofórmio. Também foi sintetizado o polímero não-impresso (NIP), para controle da seletividade dos MIPs. A dessorção da fenilalanina foi realizada em extrator Soxhlet. Os MIPs e NIP foram caracterizados pelas técnicas de análise: FTIR, UV-Vis, MEV, DSC e TG. O MIP apresentou maior capacidade adsortiva à fenilalanina do que o NIP, com uma taxa média de adsorção de 55% comparada a 11% para o NIP. Por MEV o MIP apresentou superfície mais porosa, importante característica para aplicação em SPE. Os estudos realizados mostraram que o MIP sintetizado apresentou grande potencial para aplicação em técnica de SPE.

Resumo em Inglês:

Abstract Molecularly imprinted polymers (MIPs) are synthetic polymers that have high selectivity to a molecule of interest. The objective of this work was the synthesis and characterization of MIPs for use in solid phase extraction (SPE), in order to determine Phenylalanine. The MIPs were synthesized from the MAA, Phenylalanine, EGDMA AIBN, in chloroform. Non imprinted polymer (NIP) was synthesized to control the selectivity of MIPs. The desorption of Phenylalanine was carried out in Soxhlet extractor. The MIPs and NIP were characterized by the following analytical techniques: FTIR, UV-Vis, SEM, DSC and TG. MIP showed higher adsorption capacity to Phenylalanine than the NIP with an average rate of adsorption of 55% compared to 11% for NIP. SEM MIP showed more porous surface, an important feature for use in SPE. The synthesized MIP in the present study showed great potential for use in SPE technique.

Resumo em Português:

Neste trabalho foram incorporadas duas fontes de nitrogênio (ureia e caulinita intercalada com ureia) em matriz polimérica de álcool polivinílico e alginato de sódio na proporção de 3:1, utilizando a metodologia de gotejamento em solução de CaCl2. As partículas foram submetidas ao congelamento e posterior descongelamento com o intuito de melhorar a estrutura e resistência térmica da matriz polimérica. As partículas foram caracterizadas através de Análise Elementar, FTIR, DRX e Análise Térmica. As partículas que apresentaram as melhores formulações foram as de álcool polivinílico+alginato de sódio+ureia, pois apresentaram eficiência de incorporação próximas as das partículas de álcool polivinílico+alginato de sódio+caulinita intercalada, mas com maior estabilidade térmica, cerca de 200 °C.

Resumo em Inglês:

Abstract In this work two nitrogen sources (urea and urea intercalated kaolinite) were incorporated in the polymer matrix polyvinyl alcohol and sodium alginate in the ratio of 3: 1, using the methodology drip in CaCl2. The particles were subjected to freezing and subsequent thawing in order to improve the structure and thermal resistance of the polymer matrix. The particles were characterized by elemental analysis, FTIR, XRD, and thermal analysis. The particles that showed the best formulations were those of polyvinyl alcohol+sodium alginate+urea, because they showed the efficiency of incorporation nearby particles polyvinyl alcohol+sodium alginate+urea intercalated kaolinite, but with greater thermal stability, about 200 °C.