Resumo em Inglês:

New Fe3O4/polyvinyl alcohol (PVA)/sodium alginate (C6H7O6Na)n nanohybrid ferrogels for antibacterial applications were fabricated. The crystal and molecular structures along with optical and magnetic properties of the prepared samples were characterized. The antibacterial activity of the ferrogels against Bacillus subtilis and Escherichia coli was investigated using the agar dilution method. X-ray diffraction analysis showed that the Fe3O4/PVA comprised a PVA amorphous phase and a spinel-structured Fe3O4 crystalline phase. The Fe3O4/PVA crystallite size was 7.5–9.9 nm and the scanning electron micrographs showed that the Fe3O4/PVA agglomerated. The ferrogels were superparamagnetic with saturation magnetizations from 14.8 × 10−3 to 82.1 × 10−3 emu/g. The absorption of the ferrogels showed a bathochromic effect, accompanied by an increase in the bandgap from 2.09 to 2.18 eV with increasing Fe3O4 content in the ferrogels. The ferrogels demonstrated new potency as antibacterial agents against B. subtilis and E. coli, where their antibacterial performance increased with increasing Fe3O4 content.

Resumo em Inglês:

The use of nanocomposite coatings on carbon steel has been very promising. In this paper, the formation mechanism of multilayer of Ni-Co/SiC nanocomposite coating electrodeposited in API 5L X80 steel was investigated. The coatings were obtained by galvanostatic deposition technique using a single bath and a single cathodic current density value. The results showed a variation in morphology and chemical composition of the coatings both on the surface and along the cross-section at all time conditions tested, confirming the functional gradient of the coating. The formation of the Ni-Co/SiC nanocomposite coating occurred through the multilayer deposition mechanism, with compositions mostly alternated between Ni and Co. The preferred orientation of the plane (220) and phase structure FCC remained constant on the surface of all the obtained samples. It was observed that the coating became more compact in the region located closer to the substrate, where an increase in micro-hardness was observed.

Resumo em Inglês:

Abstract Refractory ceramics were produced from clays and alumina waste. Specimens were shaped by uniaxial pressing, subjected to thermal analysis by dilatometry and heat-treated in a conventional furnace at 1300 and 1400ºC, applying a heating rate of 5ºC/min and a dwell time of 2 and 3 hours at the maximum temperature. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and physicomechanical properties. The dilatometric analysis before heat treatment indicated that the formulation containing the largest amount of fluxing oxides presented the highest linear shrinkage. The XRD analysis revealed that mullite was the major phase and needle shaped crystals typical of mullite obtained from clay minerals were observed by SEM. The increase in firing temperature and dwell time at the maximum temperature improved the physicomechanical properties of the specimens. The thermal expansion coefficient (TEC) in the range of 25 to 1000ºC varied from 6.2 to 6.9 x 10-6°C-1.

Resumo em Inglês:

Abstract This study aims at presenting a new analysis method for adhesive (interfacial) and cohesive (bulk) failures in aluminum (Al) and high-density polyethylene (HDPE) sandwich composites. The samples were submitted to tensile strength tests, according to ASTM C297 so as to obtain the pull-off stresses. The delaminated aluminum surfaces were analyzed with SEM/EDS (Scanning Electronic Microscopy with Energy Dispersive Scanning). The images were calculated using a genetic algorithm (GA), where the areas with cohesive and adhesive failures were identified by the presence or absence of organic compounds. The proposed method also uses the data from the pull-off tests to determine the stress values of adhesion and cohesion separately. Applying the new method, the mean stress of cohesion was 4.17 MPa, and for adhesion it was 0.57 MPa. Thus, it was possible to distinguish and calculate the failure stresses applied to metal/polymer composites.

Resumo em Inglês:

Abstract Herein, the structural, morphological, compositional, optical, electrical and dielectric properties of Bi1.5Zn0.92Nb1.5-6x/5WxO6.92 (BZN) solid solutions are reported. Tungsten substituted BZN ceramics which are fabricated by the solid state reaction technique exhibited solubility limits at substitution level below x=0.18. Remarkable engineering in the structural, optical, electrical and dielectric properties of the pyrochlore ceramics is achieved via W substitution. Namely, shrinkage in both of the lattice parameters and in the energy band gap accompanied with decrease in the microstrain, in the dielectric constant and in the electrical resistivity is observed upon increasing the W content below the solubility limit. The increase in the W content in the BZN ceramics enhances the densification of the pyrochlore and leads to higher light absorbability and larger crystallites growth. The temperature dependent electrical resistivity measurements has also shown that the pyrochlore exhibit thermal stability below 380 K.

Resumo em Inglês:

Abstract Polymer processing parameters may considerably affect final product characteristic as, if properly chosen, these parameters may lead to products with optimal properties. The aim of this work is to evaluate the rheological characteristics of poly(ethylene terephthalate) (PET) by torque rheometry, as well as to estimate its incipient degradation rate during processing in an internal laboratory mixer. In order to estimate the temperature coefficient of the viscosity (β), and the pseudoplasticity index (n) of PET, two sets of experiments need to be performed. In the first one, the polymer is processed at three different temperatures at a single rotor speed for 10 min, getting temperature coefficient of the viscosity equal to β = 0.053 °C-1. In the second set of experiments, the resin (PET) is processed at a single temperature at six different rotor speeds for the same time interval and the pseudoplasticity index was determined, n = 0.78. From the results obtained, it is possible to indicate the internal mixer as an equipment not only for mixing polymers or composites, but as a tool for determining important rheological variables for predicting degradative processes.

Resumo em Inglês:

Abstract This research work investigates the two body wear behavior of natural fiber reinforced composites using a pin on disc test set-up. Natural fibers such as Polyalthia Longifolia, Mangifera Indica and Jute were used as reinforcements with epoxy matrix. Four types of composites with 30% fiber weight fraction were fabricated using hand layup and compression molding technique. Taguchi experimental design with L16 orthogonal array was considered. Four factors viz. fiber type, normal load, sliding speed and sliding distance at four levels were analyzed for obtaining minimum specific wear rate. Normal load was the most significant factor influencing the response with percentage contribution of 56.21% while the least contribution was the factor sliding speed (2.30%). Based on the optimum combination, confirmation experiments were conducted, the results of which were obtained with a minimal error of 4.64%. Micrographs revealed different wear mechanisms like fiber-matrix de-bonding, fiber pull-out, matrix cracking, furrows and crater formation.

Resumo em Inglês:

Abstract Al-Si-Zn-Mg quaternary alloys represent a potential range of feedstock's for semisolid processing (SSM) that combine the advantages of the thixoforming process with the possibility of heat treatment to improve mechanical performance. In this work, the suitability of the Al-5wt%Si-5wt%Zn-0.5wt%Mg alloy for use in thixoforming was assessed by thermodynamic characterization and by an analysis of its microstructural evolution and rheological behavior. Thermodynamic analysis was performed by numerical simulation and by application of the differentiation method to Differential Scanning Calorimetry (DSC) curves for heating cycles up to 700 °C at 5 and 25 °C/min. Microstructural evolution during partial melting at 594 °C for 0, 30, 60 and 90 s and the corresponding rheological behavior were analyzed. The findings indicate good agreement between the thermodynamic behavior predicted by DSC and Calculation of Phase Diagrams (CALPHAD) and the data obtained from semisolid forging. Although the alloy has a coarse microstructure (GSmax = 200 μm), its rheological behavior is appropriate for thixoforming (σmax = 1.06 MPa and μmax = 1.79x104 Pa.s), indicating that the microstructure only plays a secondary role in determining viscosity when enough liquid (fl = 0.63) is present in the slurry to enhance the flow. The alloy is suitable for use as raw material for semisolid processing.

Resumo em Inglês:

Abstract The effects of heat treatment on the microstructural evolution and mechanical behavior of Al-Si-Cu alloy were investigated. Solution heat treatment was performed at 500oC/6h and 540oC/6h, followed by quenching in warm water at 60ºC. Lastly, artificial ageing treatment was performed at 160ºC/6h, 190ºC/4h and 210ºC/2h. The microstructural evolution of the samples before and after heat treatments was analyzed by optical microscopy, scanning electronic microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Analyses revealed the presence Al5FeSi, Al15(FeMn)3Si2, Al2Cu and Si particles. The morphologies of the present phases were dependent on the heat treatment. Solution treatment at 540ºC/6h resulted in significant softening of the alloy compared with the treated samples at 500ºC/6h. Vickers hardness analysis indicated that the hardness peak of the alloy after heat treatment was about 125 HV. Mechanical properties of different phases have been investigated by nanoindentation technique, which indicated that the highest hardness and modulus of elasticity were found for the Si particle, especially those distributed in the microstructures of the samples submitted to higher solution and ageing temperatures.

Resumo em Inglês:

Abstract Friction and wear are influenced by the surface conditions of the material, since there is deformation, segregation, generation of oxide films, among others. Roughness is an important characteristic in tribological studies, where the parameters of skewness and kurtosis have greater influence than the conventional parameters Ra and Rq. This study is aimed to investigate the influence of the parameters of skewness Rsk and Rku kurtosis on the surface of the USI AR 360 steel machining by the milling and turning processes in the pin-on-disc sliding wear test. Results showed that surfaces with the same Ra and Rq could be distinguished by the skewness parameter. Different behaviors were observed in the analysis of friction curves, where the skewness effect showed a tendency to reduce the friction coefficient. It was also observed that the feed marks orientation in relation to the sliding direction can influence the tribological behavior of the surfaces.

Resumo em Inglês:

Abstract The kinetics of phase transformations in isothermal processes is well described by the classic JMAK model. However, it is known that most industrial facilities employ continuous cooling processes and, for this condition, the JMAK model is adapted but, sometimes, without success. Considering the importance to predict critical temperatures, the present work proposes an alternative empirical functional equation to describe the kinetics of steel phase transformation under continuous cooling, being useful when the JMAK use is not successful. In this study, the continuous cooling austenite to ferrite transformation was experimentally characterized by dilatometry for an IF-Ti-stabilized steel. The proposed equation was compared with the classic adapted JMAK model regarding to evaluate its efficacy to fit the dilatometric experimental data. Using the constants obtained by the both model fittings as input parameters, a computational simulation was performed to determine the CCT diagram of the IF-Ti steel. The proposed functional equation was efficient to predict the critical temperatures, the kinetics of austenite decomposition and the CCT diagram of the studied steel. The results predicted by the proposed model greatly met the experimental data measured by dilatometry.

Resumo em Inglês:

Abstract Composites based on recycled high-density polyethylene (rHDPE) and muscovite mica, with different rHDE/mica ratios (100/0, 95/5, 90/10, 85/15 and 80/20, weight percentage) were prepared in an internal mixer with roller-type rotors at temperature of 170 ºC for 10 minutes. The materials obtained were characterized by tests of density, Shore hardness D and melt-flow index, along with infrared spectroscopy, thermogravimetry, differential scanning calorimetry and scanning electron microscopy. The hardness analysis confirmed the action of mica as a reinforcing load in the matrix, but this effect stabilized at around 15%. The TG analysis showed that the 85/15 composite presented slightly better performance than the 80/20, indicating that mica, up to 15%, caused disorganization of the polymer structure instead of reinforcing it. The DSC results revealed that the composites had slightly lower melting temperatures than the matrix. The FTIR spectrum indicated there was no chemical interaction between the rHDPE and mica.

Resumo em Inglês:

Abstract High Strength Low Alloy steels (HSLA) for oil and gas pipelines should display high mechanical strength, toughness, ductility and weldability. In this work we studied the influence of quenching and tempering temperature on the yield strength, ultimate tensile strength, percent elongation and hardness of API 5L steel pipes in order to optimize heat treatments to be performed after hot induction bending of the material. The thermal cycles involved soaking temperatures of 880, 920 and 960 °C, cooling water at 15, 23 and 31 °C and tempering at 530, 600 and 670 °C. From this, experimental design techniques were used to reduce the number of experiments. The results from contour maps suggest that soaking temperatures of 910 and 950 °C and tempering between 540 and 610 °C were the most suitable for treatment, regarding mechanical strength. The variation of the water temperature was not significant for the assumed cooling conditions. The prediction regression models of the mechanical properties from the variables involved in the heat treatments showed a good fit between the experimental and predicted results, with correlation coefficient between 0.89 and 0.94.

Resumo em Inglês:

Abstract In this research, syntactic foams including Al-7075 matrix and 2-4 mm low-cost pumice particles were manufactured via a novel casting method called as sandwich infiltration. According to physical evaluations, thanks to extremely porous structure of pumice, density values of the fabricated foams varied between 1.42 and 1.61 g/cm3. Porosity values were between 40.62% and 47.39%. Microstructural observations showed that there was a perfect infiltration between Al matrix and pumice particles because of correct process optimization (process pressure of 0.1 MPa, matrix melting temperature of 720°C and filler pre-temperature of 500°C). Furthermore, T6 treatment was applied to samples to comprehend effect of the aging on mechanical properties. The results indicated that there was an affirmative relation between the heat treatment and quasi-static compressive properties of the fabricated foams. The highest compressive strength, plateau stress and energy absorption values were measured as 64.4 MPa, 74.3 MPa and 34 MJ/m3 for heat treated samples. It was also observed that although the highest energy efficiency of 0.89 was calculated for heat treated sample, there was no relation between the heat treatment and efficiency. As for failure modes, as-cast samples exhibited ductile barreling characteristic whereas T6 treated foams indicated brittle v-shape fracture.

Resumo em Inglês:

Abstract Associated with the use of removable prostheses, the development of candidiasis, called prosthetic stomatitis, is frequently observed. In view of the application of silver nanoparticles (AgNP) in dentistry that may offer antimicrobial effect, the aim of this study was to evaluate the effect of adding AgNP with different concentrations during thermopolymerization or immersion of acrylic in this substance in the properties antifungal, mechanical and cytotoxic. The groups were divided: addition of 1% silver nanoparticle solution (G1), addition of 2.5% silver nanoparticle solution (G2), addition of 5% silver nanoparticle solution (G3), immersed for 10 min in aqueous silver nanoparticle solution (G4), immersed for 24 hours in aqueous silver nanoparticle solution (G5). In the cytotoxicity assay, at all evaluation times, all groups showed cytotoxic effect (p <0.05) when compared to the control group (CG). For the microbiological assay, C. albicans reduction was observed only for G4 and G5 when compared to CG (p <0.05). The lowest resistance values were observed in the group with 5% silver nanoparticle (G3) incorporation (p <0.05). It was concluded that the thermopolymerized acrylic resin immersed in AgNP, G4 and G5 promoted microbiological reduction, cytotoxicity increase and flexural strength decrease at 5% concentration.

Resumo em Inglês:

Abstract Commercially free, C10300 Copper was submitted to cold rolling to 80% thickness reduction using three different rolling schedules. Rolling was conducted in 5, 8 and 11 rolling passes. Samples were then submitted to EBSD analysis at the surface and X-Ray Diffraction at the surface and mid-thickness to evaluate the deformation texture. EBSD analysis showed an increase in the intensity of the Copper component at the surface as the number of rolling passes decreased, and a very strong Goss component in all samples analyzed. X-ray diffraction analysis confirmed the strong copper component, but the Goss texture was much weaker when analyzed by X-ray diffraction, ultimately being nearly inexistent at mid thickness. The Brass component was very weak in EBSD analyses, but was found with higher intensity when texture was calculated using x-ray diffraction. The appearance of Goss component in surface grains can be explained by friction and shearing conditions in the roll-metal contact.

Resumo em Inglês:

In order to investigate the hot deformation behaviors of Invar36 alloy, isothermal compressive tests were conducted on a Gleeble 1500 thermo-mechanical simulator at the temperatures of 873, 948, 1023, 1098 and 1173 K and the strain rates of 0.01, 0.1, 1 and 10 s−1. The effects of strain, temperature and strain rate on flow stress were analyzed, and a dynamic recrystallization type softening characteristic with unimodal flow behavior is determined. An artificial neural network based on back-propagation algorithm was proposed to handle the complex deformation behavior characteristics. The ANN model was evaluated in terms of correlation coefficient and average absolute relative error. A comparative study was performed on ANN model and constitutive equation by regression method for Invar36 alloy. Finally, the ANN model was applied to the finite element simulation, and an experimental study on trial hot forming of a V-shaped part was conducted to demonstrate the precision of the finite element simulation based on predicted flow stress data by ANN model. The results have sufficiently showed that the well-trained ANN model with BP algorithm is able to deal with the complex flow behaviors of Invar36 alloy and has great application potentiality in hot deformation.

Resumo em Inglês:

The pure magnesium was fabricated by directional solidification, and the effect of the distribution characteristics of magnesium oxide (MgO) on the mechanical properties of pure magnesium was investigated. The statistical results showed that the area fraction, number and size of MgO were decreased gradually from the top region ingot to the bottom region ingot, and these reflected the advantages of directional solidification technology in the controllability of MgO distribution characteristics. The top parts of magnesium ingots have the highest tensile strength (44 MPa), which is mainly due to the presence of a large amount of the coarse MgO. Though the coarse MgO increases the strength obviously, it has harm for the ductility of magnesium. The top parts of magnesium ingots have higher ultimate tensile strength, but lower failure strain (13% and -21% respectively) than the ingot at the center. These results indicate that if the suitable size and amount of MgO existed in magnesium matrix, it could avoid the disadvantages of MgO and provide positive effect for both the strength and ductility of magnesium alloys.

Resumo em Inglês:

The influence of Fe2O3 additions on the microstructure, mechanical properties and translucence of zirconia with 3 mol-% or 5 mol-% Y2O3 was evaluated. Samples were pressed with different thickness and sintered at 1475, 1500, 1550 and 1600°C for 2 h. Density, phases, microstructure, roughness, strength and translucency were analyzed. All samples showed densification greater than 99%. After sintering at 1600°C, the phase analysis revealed only tetragonal ZrO2 in samples with 3% Y2O3, while in samples with 5% Y2O3 the cubic ZrO2 phase was identified. Significant increase in the grain size was noted, when increasing the Y2O3 content from 3% to 5% from 0.8 µm to 2.3 µm for sintered samples at 1600°C. The strength was affected with Y2O3 content and no relevant influence of the Fe2O3 on density, microstructure or mechanical properties. Visible reflectance spectroscopy analyses, related to the CIELab scale, indicate variation in the contrast ratio as function of thickness of samples and coloring agent Fe2O3 content.

Resumo em Inglês:

Recently, a model was proposed to predict cv as a function of temperature from the absolute zero to the melting temperature applied. This solution was based on critical grain nucleation to determine the volume, which contains the total number of modes for a particular equilibrium and non-equilibrium state to calculate the density of state (DoS), which is strongly dependent on the nucleus radius for both pure element and compound. Electronic and rotational energies were regarded for both elements and compounds in this formulation. The anomalies associated with cv can be easily considered in terms of their entropies, independent of their nature, as a local change in the DoS. Comparisons of cv for elements and compounds are performed against Thermodynamics software simulations and experimental data.

Resumo em Inglês:

Abstract Nowadays, the concept of high entropy alloys (HEAs) has expanded the limits of metallurgy and high-quality metallurgical HEAs ingots have already been successfully obtained on an industrial scale. High Chromium Cast Irons (HCCI) and Multi-Component Cast Irons (MCCI) are known to be a useful material for applications when abrasion resistance is required. Inspired by the concepts of high-entropy alloys, a base HCCI was modified, by adding other carbide-forming elements, at concentrations higher than what is currently used, in order to develop a new class of white cast iron, High Entropy White Cast Iron (HEWCI). The characterization of carbides precipitated during the HEWCI solidification was performed by scanning electron microscopy, energy dispersive spectroscopy, electron backscattered diffraction (SEM/EDS/EBSD) and X-ray diffraction (XRD). With the characterization techniques employed, the as-cast microstructure obtained of HEWCI is composed of approximately 50% of austenite matrix and 50% of different types of carbides, MC, M7C3 and M2C carbides.

Resumo em Inglês:

Abstract Thermo-mechanical treatments using continuous cooling after forging are an established method for producing bainitic steels, mainly because of the elimination of energy intensive additional heat treatment processes. The cooling is usually employed in an uncontrolled manner in the industrial sector, which can be detrimental to the resulting microstructural morphology and, consequently, to the final product properties. In this study, a new controlled two-step cooling route based on the principles of bainitic displacive growth was designed and applied in a 0.18C (wt-%) steel. Inverse finite element method was used on the cooling data to obtain the evolution of temperatures for the samples during cooling, allowing to assess point to point cooling rates. Investigations via X-ray diffraction, optical microscopy analysis and hardness testing revealed a variation of bainitic morphology, namely, the transition from granular bainite to lath-like bainite with relatively high hardness and constituents/phase boundaries than the pre-treated microstructure.

Resumo em Inglês:

AZ31B magnesium alloy/AA6061 aluminium alloy welded structures have been widely used in the lightweight design of automobile bodies. To improve the joint strength, the ultrasonic spot welding (USW) solid state connection method is used in this paper. The results show that at a welding energy of 1540 J, there is evidence of melting in the weld joint. As the welding energy increases, the intermetallic compounds (IMCs) grow rapidly and form a reaction layer approximately 17 μm thick. The IMCs are mainly composed of the γ-Mg17Al12+β-Mg2Al3 phase, where the β-Mg2Al3 phase hardness is as high as 6.5 GPa and shows a typical pop-in phenomenon and the average hardness of the γ-Mg17Al12 cubic structure phase is 3.4 GPa. When the welding energy reaches 1540 J, the β phase rapidly grows, and the joint performance decreases rapidly. The fracture morphology indicates a cleavage fracture and is accompanied by a large number of secondary cracks.

Resumo em Inglês:

Commercial archwires NiTiCu (Ormco) and NiTi (Morelli) and samples of the corresponding raw materials were tested to assess the influence of Cu addition and sterilization on the corrosion resistance and biocompatibility. Raw materials samples and commercial archwires exhibited similar corrosion resistance when compared. The addition of Cu decreased the corrosion resistance of NiTi alloy, whiling the sterilization process had no influence. The biocompatibility tests were carried out in different extracts of the alloys and no cytotoxicity effects were observed for the ionic concentrations used. SEM and Confocal laser analysis permitted to observe the localized corrosion morphology obtained after anodic polarization tests. Although Cu addition on NiTi can be introduced to better adjust the mechanical resistance, this third element induced detrimental effect on the corrosion resistance of raw materials and commercial archwires.

Resumo em Inglês:

We demonstrate here for the first time an original and facile approach to preparing titanium oxide (TiO2) tubes using hydrogen peroxide (H2O2) and titanyl (IV) oxysulfate (TiOSO4) as sacrificial templates. The method involves dissolving TiOSO4 powder in H2O2 solution and subsequently applying thermal treatment on the resulting amorphous precipitate. Prepared samples were characterized by X-ray diffraction, scanning electron microscopy (SEM) images, thermogravimetric (TG) analysis, and UV-vis analysis. Experimental results indicated that the samples exhibit tube-like structures with lengths of approximately 1.9 mm in diameter and 11.5 mm in length. Anatase and rutile phases were formed after annealing at different temperatures in air. The crystallite size estimated by Rietveld refinement showed an increase from 34.69 to 354.28 nm with an increase in the annealing temperature from 600 to 1000 °C. At the same time, the band gap values decreased from 3.14 to 2.97 eV. The electron density maps were calculated, and the electronic density was observed to increase from 497.56 e- Å-2 (600 °C) to 533.10e- Å-2 (740 °C) and decrease with the annealing temperature of samples. A possible mechanism for the formation of TiO2 tubes was proposed.

Resumo em Inglês:

Abstract Nickel-aluminum bronze (NAB) alloys are suitable, in cast condition, to be used in marine propellers due to its excellent behavior avoiding erosion and cavitation as well as corrosion. A complex microstructure, intrinsic to this copper base system, is the result of a well-controlled chemical composition. There are few works related to the effect of adding small quantities of specific chemical elements on NAB alloys properties. The aim of this paper is to study the effect of Ti on the microstructure, mechanical properties, and corrosion behavior of a particular NAB alloy, CuAl10Fe5Ni5 (C95500), and the comparison to the Ti-free NAB alloy. Although the as- cast microstructure is very similar for both materials, the addition of only 120 ppm Ti leads to a significant grain refinement that plays a key role on the mechanical properties. It has been observed an increase in both microhardness and nanohardness as well as in the resultant Young moduli values, meanwhile no significant impact on the corrosion susceptibility has been observed.

Resumo em Inglês:

Abstract Biocomposite films were prepared using normal maize starch plasticized with glycerol and water and sodium montmorillonite clay particles employing the solution mixing procedure. Scanning electron microscopy (SEM), X-ray diffraction (XRD), three-dimensional profilometry and tensile along with nanoindentation tests assisted with a Finite Element Analysis (FEA) were used for the assessment of starch-based films with various percentages of nanoclay particles. XRD analysis revealed intercalation of the test specimens while their morphology was ascertained using SEM/EDX. The FEA results were compared with the experimental measurements from nanoindentation and tensile tests. A satisfactory correlation was obtained between the experimental measurements and the computational models, demonstrating FEA-assisted nanoindentation as a useful technique for assessment, showing the effect of the different nanoclay concentrations on the mechanical properties.

Resumo em Inglês:

Abstract In this work, NRL films were enriched with red propolis and silver nanoparticles with the aim of obtaining dressings with bactericide properties. To improve the properties of these materials, plasma treatment was also applied to the films. Cytotoxic effects were evaluated by MTT and agar diffusion assays on secondary and stem cells. Determination of cell behavior on the films were assessed by EDS and FEG-SEM. In general, the plasma modified NRL films presented hydrophilic character, favorable condition for biomedical applications. RBS results showed that silver is probably in nanoparticulate form. MTT assays revealed that non-cytotoxic effects were observed for all the samples extracts. Either the plasma treatment or silver deposition were effective in sterilizing the samples and modifying their surfaces. It was demonstrated in this in vitro study that ADSCs associated with NRL films enriched with propolis should be considered promising for application in the healing of occlusive wounds.

Resumo em Inglês:

Abstract Vat photopolymerization (VP) stands out among ceramic additive manufacturing processes for its ability to print sub-100 micrometer complex features. One of the main challenges of this process is the preparation of a homogeneous and stable ceramic slurry with a high solid load and low viscosity. In this work, different dispersants and resins were tested, aiming to provide a solvent-free slurry suitable for DLP additive manufacturing. Disperbyk-111 and PEGDA 250 stood out in the tests, providing a 40 vol% ceramic slurry with no noticeable sedimentation and viscosity of 2.3 Pa.s at 30 s-1 despite the relatively high specific surface area (15 m2/g) of the 3Y-TZP powder used compared to powders usually used for VP slurries. The adsorption of Disperbyk-111 on ceramic particles surface was investigated by FTIR. Finally, ceramic bodies were 3D printed, debound and sintered at 1500 ºC for 2 h, confirming the ability to manufacture detailed dense ceramic parts.