MARCIO RUBENS XAVIER BARTOLOMEI

MARCIO RUBENS XAVIER BARTOLOMEI

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Use of biodegradable oils as an alternative cooling in quenching treatment
2020 - BARTOLOMEI, S.S.; BARTOLOMEI, M.R.; SILVA, F.A.; OLIVEIRA, A.A.
Ferrous alloys stand out for their use in various branches of the mechanical industry, as they encompass a series of mechanical properties that directly influence their application. For their implementation to be successful, they must have a suitable microstructure, which provides steel with sufficient mechanical characteristics so that it can withstand various types of efforts resulting from its implementation. Heat treatments are responsible for developing this microstructure in a controlled manner, through a set of heating and cooling operations with controlled conditions of temperature, time, atmosphere and cooling speed, in order to change their properties or give them some features. One of the most conventional treatments used worldwide to impart mechanical resistance to steels is the quenching treatment, which consists of heating the metal to austenitization temperature, kept at the same temperature for a certain time and after cooling it rapidly in a liquid medium. great efficiency in the extraction of heat, which can be water, saline solutions, polymeric solutions and oils, in order to form a new microstructure, harder but more fragile than its initial state, called martensite, which after tempering, has its stress-free internal structure, increasing its toughness. The most common cooling medium of the last decades is mineral oil, which due to its viscosity, has excellent capacity to extract heat, but it is a great villain when it comes to environmental issues, an example of this is the increase of water contamination. underground, where mineral oils are the most abundant contaminants present in the analyzed samples of these sources. Due to these and other environmental problems, studies have been developed to obtain an alternative cooling medium as effective as mineral oil, but which has less environmental impact. One solution to this problem is to use compound oils from renewable and biodegradable sources such as vegetable oils. Therefore, this work studies the effects of tempering on SAE 1045 carbon steel and AISI 420 martensitic stainless steel, using biodegradable soy and castor oil as cooling medium. For this, the viscosity of the oils was measured at room temperature and heated to 70 °C, temperatures at which tempering treatments were performed on 10 x 20 x 20mm rectangular section specimens. The specimens were cut, embedded and polished to be characterized by optical micrograph and Vickers microhardness. The results showed that biodegradable oils have excellent stability to bath temperature variation and can be applied over large temperature ranges due to their high flash points. Regarding the hardness and microstructure formed inside the specimen, the vegetable oils were also efficient, presenting values very similar to mineral oil, being soy oil more efficient than castor oil due to its low viscosity influencing hardness of the pieces and also in the formation of martensite. Biodegradable oils have proven to be an alternative.
UV Barrier influence according to the amount of TiO2 in PBAT biodegradable flexible film
2020 - BARTOLOMEI, M.R.; ISHIKAWA, O.; BARTOLOMEI, S.S.; MOURA, E.M.
Manufacturing and consumption of polymeric products and packaging continues to grow despite concerns about environmental contamination due to improper post-consumer disposal, causing polymeric waste to emerge in increasingly remote places, polluting seas and soil, affecting flora, fauna and human health. Among these wastes are flexible food packaging. One of the alternatives to reduce this problem is the use of biodegradable materials, such as poly (butylene adipate-terephthalate) (PBAT), but the properties of this material do not meet all the needs of a food packaging, focus of this work. Additives and / or fillers must be added to improve the properties of this polymer, such as mechanical, thermal and barrier properties. One of the important features of a food packaging is the UV light barrier, as many products have shortened shelf life due to interaction with light. This work studies the effect of the addition of titanium dioxide (TiO2) particles to improve UV light barrier in biodegradable flexible PBAT films, with clay addition to improve mechanical properties. The films were obtained by melt processing so that the application is industrially and economically viable. For this, known amounts of TiO2 (0.1, 0.2 and 0.3 wt%) were added in a poly (vinyl alcohol) (PVA) solution, along with 0.5 wt% organophilized light green clay. This mixture was sonicated, poured onto PBAT pellets and oven dried. Then, the particle coated pellets were processed in a twin screw extruder, cooled and pelleted. Then the flexible film was produced in a flat die single screw extruder, thus producing 4 nanocomposites (PBAT + 0.5wt% Clay; PBAT + 0.5wt% Clay + 0.1wt% TiO2; PBAT + 0.5wt% Clay + 0.2wt% TiO2; PBAT + 0.5wt% Clay + 0.3wt% TiO2). The results of X Rays Diffraction (XRD), Scanning Electron Microscopy (SEM) and tensile test showed that the clay was exfoliated in the polymer matrix, allowing improvements in the mechanical strength and elongation of the films. UV-vis absorption assays showed that the higher the TiO2 concentration the higher the UV barrier.
Effect on flame propagation in recycled expanded polystyrene with flame retardant/white clay/titanium dioxide nanocomposite
2020 - BARTOLOMEI, S.S.; BARTOLOMEI, M.R.; MOURA, E.M.; WIEBECK, H.; OLIVEIRA, R.R.
Polystyrene is widely used in construction due to its properties such as low density, heat resistance, durability and ease of processing and molding. However, it is highly flammable, releases a lot of heat and toxic smoke when exposed to a flame. However, in order for a material to be applied in habitable indoor environments, it must comply with fire safety standards, which predict the behavior of materials during their burning. Halogenated flame retardants have been used to reduce the spread of flame, but they are toxic and polluting, so more environmentally friendly products are being developed. Polymeric nanocomposites, formed by inorganic nanoparticles, have many advantages in flame retardation, such as low heat release rate, low smoke and toxic gas production. Alternatively, the organofilized, exfoliated or polymer-intercalated montmorillonite clay (MMT) can be used to form a nanocomposite with greater flame resistance. However, for the clay to achieve the results required by the standards, it is necessary to add a large amount of particles, which generates agglomerates in the material and losses in the mechanical properties. Therefore, the use of clays to improve flame resistance to the material must be accompanied by the use of other flame retardants. Thus clay will provide reduction in flammability and secondary flame retardant will provide ignition resistance. The addition of other particles, together with clay, can corroborate with the reduction in flame spread of the material, with titanium dioxide being used to increase thermal stability, UV light stability, mechanical properties as well as reduction in flame spread. In this work expanded polystyrene (EPS) from construction waste, with flame retardant in its composition, was recycled and plasticized with glycerol. In this polymeric matrix was added white clay and titanium dioxide in order to maintain the flameproof properties and improve the mechanical and thermal properties of the material. The results showed that it is possible to recycle EPS and maintain flame self-extinguishing through the material even in the presence of glycerol as plasticizer. The addition of white clay improved the mechanical properties of the material and increased thermal stability, but impaired the fire behavior of the material, ceasing to self-extinguish the flame immediately after extinguishing the external flame. Titanium dioxide (TiO2) kept the mechanical and thermal properties unchanged and reduced flame propagation in the specimen when compared to the results of clay nanocomposite.
Graphene oxide nanosheets as fillers for thermoplastic-matrix nanocomposites
2020 - MOURA, E.A.; SANTOS, B.S.; ISHIKAWA, O.; SANTANA, J.G.; BARTOLOMEI, M.R.; OLIVEIRA, R.R.
Recent studies have shown that the synthesis of graphene oxide (GO) by chemical oxidation of graphite followed by its reduction is one's the most promising routes to prepare remarkable polymer/graphene nanocomposite materials with significant improvement of properties compared to the base polymer. The addition of a very small amount of reduced graphene oxide (RGO)in a polymer can enhance its properties, with respect to electrical conductivity, barrier resistance, stiffness, abrasion resistance, mechanical resistance, and fire retardancy. Numerous approaches have been established to prepare RGO from the desoxygenation of GO. This work presents the synthesis of graphene oxide by chemical oxidation of graphite followed by its photoreduction in aqueous dispersion using UV radiation and highlights some examples of RGO/thermoplastic-matrix nanocomposites prepared by melt processing. To evaluate the potential application of thermoplastic composites prepared, the RGO's content on the morphological, mechanical and thermal properties of the as-obtained nanocomposites has been assessed. In addition, GO/RGO nanosheets were characterized by ATR–FTIR, XRD, Raman, and FE-SEM. According to the results, it can be inferred that the addition of RGO leads to a remarkable improvement in the performance of thermoplastic-matrix nanocomposites and offers a competitive solution for various potential applications.
Sonochemical synthesis of reduced graphene oxide
2020 - MOURA, E.A.; ISHIKAWA, O.; MANGIERI, F.; BARTOLOMEI, M.R.; BARTOLOMEI, S.S.; OLIVEIRA, R.R.; FRANCISCO, D.L.; GUIMARÃES, K.
The reduction of graphene oxide (GO) by a safe and eco-friendly route, without the use of harmful chemicals, has drawn much attention as one of the most promising routes to produce graphene nanosheets, a 2D material with excellent electrical and thermal conductivity, optical and mechanical properties. Graphite exfoliation is widely performed by the chemical reduction of GO, which is commonly produced by oxidation of graphite using a strong oxidizing agent by Hummers’ method. This work presents a study of the influence of sonochemical application on synthesis of reduced graphene oxide induced by UV radiation. Commercial graphite powder was used as raw material. Firstly, graphite powder was dispersed into a DMF/deionized water solution and ultrasonicated using a high intensity ultrasonic device for 1 8 hours in other to reduce the particle sizes. After, sonicated graphite samples were frozen for 24 hours and freeze-dried for 24 hours to obtain the powder. Graphite powder obtained with different particle sizes was used to prepared GO through a chemical route. GO prepared was dispersed into a DMF/deionized water solution, ultrasonicated using a high intensity ultrasonic device for 1-2 hours, frozen for 24 hours and freeze-dried for 24 hours. Finally, GO powder samples were dispersed in a mixture of isopropyl alcohol, acetone, and deionized water and irradiated using UV radiation by different irradiation time to obtain reduced GO (RGO). The GO and RGO were characterized by BET, ATR–FTIR, XRD, Raman, TG, and FE-SEM analysis. In addition, graphite samples were characterized by BET, SEM and XRD analysis. The results showed that sonochemical application has a fundamental role in the synthesis of GO nanosheets and RGO. Ultrasonically prepared GO exhibited higher surface area, higher crystallinity and higher oxidation efficiency with many hydrophilic groups. FE-SEM analysis of the GO showed that sonochemical application reduced the aggregated domains and close stacking of sheets on the GO surface and led to obtaining reduced GO with a smooth surface, fewer layers and significant effective surface area.
Investigation on mechanical and thermal behaviours of PBAT/PLA blend reinforced with reduced graphene oxide nanosheets
2020 - BARTOLOMEI, MARCIO R.X.; CARMO, KARINA H.S.; SANTOS, BIANCA S.; BARTOLOMEI, SUELLEN S.; OLIVEIRA, RENE R.; MOURA, ESPERIDIANA A.B.
The aim of this study was to process and investigate the changes in the mechanical and morphological properties of the biodegradable nanocomposites based on polybutylene adipate-co-terephthalate (PBAT)/poly(lactic acid) (PLA) blend (PBAT/PLA blend) due to the incorporation of reduced graphene oxide (RGO) nanosheets. The biodegradable polymeric nanocomposites were prepared by melting extrusion process using a twin-screw extruder machine. The influence of the RGO nanosheets incorporation on mechanical and thermal properties of PBAT/PLA blend was investigated by tensile Thermogravimetric (TG), X-Ray diffraction (XRD), differential scanning calorimetry (DSC), and tensile test analysis. Results showed that incorporation of the small amount ofRGO(0.1wt.%) ofRGOnanosheets in the blend matrix of PBAT/PLA resulted in an important gain of mechanical properties of the blend. This result indicates that a very small amount of RGO nanosheets addition in the PBAT/PLA can lead to obtaining materials with superior properties suitable for several industrial applications.