Search

Biochar (BC) is a by-product rich in carbon, from the pyrolysis of biomass, and therefore, it has great appeal to be used in several applications. In the present work, the use of biochar from poultry litter waste (PLW) as a filler for composites with epoxy resin is evaluated regarding its performance in the thermal, mechanical and dynamic mechanical properties. The BC was produced from the pyrolysis of the PLW, and the composites were produced from concentrations of 2.5, 5.0 and 10.0 wt% of BC, in relation to the epoxy resin mass. The composites were characterized in terms of micrography (MEV), infrared spectroscopy with Fourier transform (FTIR), thermogravimetric analysis (TGA), mechanical properties (tension and impact) and dynamic mechanical analysis (DMA). From the dynamic mechanical point of view, there was a considerable increase in parameters such as storage modulus at both glassy (≈ 23%) and rubbery regions (≈ 43%) and loss modulus (≈ 32%). However, a decrease at the glass transition temperature, in loss modulus, (≈ 19 °C) was reported, comparing the neat epoxy with those composites with 10 wt% of BC. This behavior was mainly related to the poor dispersion of BC into the composites, especially those with 10 wt% of reinforcement. [ABSTRACT FROM AUTHOR]

High-performance composites are subjected to different mechanical forces and stresses during their lifetime. Hence, knowledge of the time-dependent deformation at different temperatures is crucial for engineering applications. In this context, a polyetherimide/carbon fiber composite was analyzed via creep behavior from the glassy to the elastomeric state (30–250 °C). Creep tests were carried out under low-stress loads. An artificial neural network (ANN) was used to fit the curves for all tested temperatures. The ANN allowed excellent fit for all conditions independently of the curve shape, mainly for the glassy region, in which most of the analytical models did not fit well. This study is a growing and promising field in the materials science field due to the fact that it uses ANN as an alternative to fit creep behavior not fitted by usual analytical equations, which utilize closed-form solutions. Furthermore, it is expected that this study will allow the formulation of new equations and methods to determine the creep behavior at high stresses, for example. [ABSTRACT FROM AUTHOR]

In this study, thermogravimetric (TG) curves of a synthetized renewable polyurethane–urea were modelled in intermediate heating rates from those experimentally tested. The response surface methodology (RSM) was used to optimize the tests by creating new TG curves. Flynn–Wall–Ozawa kinetic model was applied in the theoretical curves and re-applied in the new theoretical ones. The predicted curves showed similar curve format, but different kinetic results compared to the experimental ones (Ea = 170.56 kJ mol−1 and A = 4.11E10 s−1 for the experimental curves, and Ea = 84.71 kJ mol−1 and A = 0.02 s−1 for the predicted ones). Also, Pearson correlation coefficient was plotted in function of the heating rate, mass loss at 5%, the three peak temperatures and mass residue, showing that the mass loss has no significant influence on the other parameters tested. Considering the heating rates and the peak temperatures, the p values were 0.11, 0.078, and 0.056 for the Tp1, Tp2, and Tp3, respectively. This means that there are 89%, 92.2%, and 94.4% of chance that the results are not due to random chance. As main conclusion, the poorer correlation among the variables of the predicted curves using the Pearson correlation reflected in distinct Flynn–Wall–Ozawa parameters. [ABSTRACT FROM AUTHOR]

This paper focuses on the re-use of original data of an available study about PLA bio-composites. New focus, regarding the discussion of the viscoelastic curves, in terms of structure vs. property relationships, followed by a correlation on the mechanical, structural and morphological characteristics were made. Response surface methodology (RSM) was carried out to describe the interaction between the storage and loss moduli as a function of bio-composite exposure conditions and thermal cycles. It was proved, using some considerations, that the effective restriction in the molecular motion of the amorphous polymer chains, imposed by the natural fibers, is given mainly at the elastomeric region. Furthermore, the microcavities at the interface minimize the fiber–matrix stress transfer, while the higher chains proximity promotes lower free volume and a higher molecular restriction. The width of relaxation curves seems to be higher for the aged bio-composites, indicating that a more heterogeneous relaxation process occurs in a broader temperature range. Storage modulus curves were predicted by RSM and it enabled the generation of a single prediction equation with high reliability. On the other hand, due to the greater complexity of the loss modulus, the curves were divided into two parts, aiming to ensure reliability and linearity coefficient. [ABSTRACT FROM AUTHOR]

Vegetal fibers can be applied in several areas, from the medical field to the development of new advanced materials. They have a complex chemical structure including cellulose, hemicellulose, and lignin. Each component plays a different role in the thermal degradation. Apart from it, this study aims to simulate and predict different ratios of cellulose/hemicellulose/lignin in the thermal degradation behavior of a vegetal fiber. This study was divided into two distinct parts: (i) firstly, the thermogravimetric curves (TG) were simulated based on their chemical composition to verify the influence of each component ratio in the degradation behavior. Briefly, 100% hemicellulose sample showed the lowest Tonset, 100% lignin sample showed the highest residue, and 100% cellulose sample showed the lowest residue at 600 °C among all samples studied. (ii) Secondly, a prediction of the thermal behavior for any combination of cellulose, hemicellulose, and lignin was performed by using an artificial neural network (ANN) combined with a surface response methodology (SRM). The prediction curves presented high reliability with the experimental fit, which allowed the thermal degradation behavior prediction of a vegetal fiber with any cellulose, hemicellulose, and lignin ratio. [ABSTRACT FROM AUTHOR]

The ability to undergo from a deformed shape to its original shape when induced by an external stimulus brought many benefits in the polymer field. Despite the shape recovery, the structure vs property relationship has to be profoundly understood aiming to highlight the most important factors regarding the shape-memory polyurethanes (SMPUs). Based on a previous study, we show herein a complete description of the dynamic mechanical analysis for twelve different SMPUs. Also, it is presented an artificial neural network approach followed by a response surface methodology that allows modeling the dynamic mechanical curves with high reliability and low error. This principle expands the design versatility for SMP, which has broad implications in many other areas including soft robotics, flexible electronics, and medical devices. [ABSTRACT FROM AUTHOR]

The study of silane-functionalized microcrystalline cellulose as reinforcement in polymeric composite materials have been increasing. Since polymer composites are constantly subjected to stress and deformation over time an in-depth understanding of the creep and stress relaxation behavior and mechanisms can be determinative to its final application. This work aims to show a comprehensive study regarding the influence of MCC silane-functionalized (MCC-Si) on the creep and stress relaxation behavior of MCC-epoxy composites. Two distinct composites with 5% of microcrystalline cellulose with and without functionalization (MCC 5% and MCC 5%-Si) were compared with the neat epoxy resin. The dispersion of the microcrystalline cellulose through the matrix was observed by X-ray microtomography. Creep behavior was investigated and discussed using Findley and Weibull models while stress relaxation by the Eyring model. In addition to the classic analytic methods, the artificial neural network approach was applied (ANN) to the curves. The MCC-Si had shown only a small trend to agglomerate due to good chemical compatibility due to the functionalization. The microcrystalline cellulose prevented the rapid creep strain as observed in the neat epoxy resin while the MCC-Si demonstrated small deformation among the samples in the vitreous region. However, in the elastomeric region the same behavior for all samples was observed. A better fit was obtained using the ANN approach than the classic analytical methods due to the higher capacity to model non-linear and complex behavior. In summary, MCC-Si enhanced the creep and stress relaxation resistance at glassy region by effectively improving the interfacial adhesion. At higher temperatures, this effect was not observed. [ABSTRACT FROM AUTHOR]

Micro crystalline cellulose is mostly used to improve thermo-mechanical properties of composites. This study aims to evaluate the creep behaviour of micro-cellulose epoxy-based composites, and the effect of silanization treatment on the reinforcements. A new viscoelastic model, based on the generalized logistic function was successfully tested. The results were directly associated with the material's structure–property relationships. Rigid particles restricted the molecular chain's motion, mainly on the amorphous segments. This difference achieved the needing of more energy, to achieve creep deformation. Then, MCC improved the structural integrity, when incorporated into an epoxy matrix. On one hand, the incorporation of silanized-MCC increased the mechanical behavior of the composite, due to the stiffer structure. Furthermore, the chemical modification provided an increment in the glassy plateau, associated with higher thermal energy required to initiate strain of the amorphous polymeric chains. This behaviour resulted in an abrupt decrease of load-bearing capability for the composites. Finally, the proposed model is suitable to be employed in creep curves, aiming to easily interpret the structure–property relationships of this test. [ABSTRACT FROM AUTHOR]

Toughening of epoxy resins is a trend emerging field in high-performance polymers due to the outstanding properties of the final material. When fully cured, epoxy has a tridimensional crosslinked structure that makes it inherently brittle. The incorporation of liquid rubber (LR) is a possible strategy to minimize this drawback, considerably increasing the fracture toughness of cured epoxies. It is also possible to add a rigid particle to the epoxy/liquid rubber systems, seeking to recover some original properties. This systematic review addresses the toughening of epoxy resin using liquid rubber (binary composites) and hybrid liquid epoxy/liquid rubber/particle composites focusing on the last ten years. The systematic review was performed according to PRISMA protocol, which delivers a rationale, meticulous and planned method of all available primary research in response to an investigation. After the primary search, forty-three studies were deeply analyzed and discussed, concentrating on the types of constituents and their effect on the mechanical (tensile, impact and fracture toughness) and morphological characteristics of the composites, as well as on the methodologies employed to produce them. Finally, the identified trends and future perspectives are given for easier identification of main gaps and opportunities in the field. [ABSTRACT FROM AUTHOR]

Cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs) were incorporated into polystyrene (PS), and thermal stability and lifetime prediction of the nanocomposites were investigated for variable filler content (0.25, 0.50 and 1% w/w). Thermogravimetric analysis (TG) was carried out at four different heating rates (5, 10, 20 and 40 °C min−1) in a non-isothermal condition, and the degradation kinetics was studied based on Friedman and Flynn–Wall–Ozawa (FWO) methods. The same thermal degradation behavior was observed for all samples in the studied range of reinforcement content. For both reinforcements (CNFs and CNCs), Friedman and FWO results showed no dependence of the activation energy on conversion degree. A single-step degradation mechanism was observed for all samples (A → B degradation model), and the kinetic studies indicated an autocatalytic reaction model with a good fitting of the curves. Lifetime prediction based on kinetic analysis was successfully applied. Lastly, nanocellulose morphology influenced nanocomposite lifetime prediction, which became more stable over time, maintaining almost 100% of the mass for 10 years exposed at 30–120 °C. [ABSTRACT FROM AUTHOR]

Supercritical carbon dioxide (scCO2) has been used as a physical blowing agent to produce polymer expanded materials. Firstly, a statistic study was performed to determine the neat polystyrene (PS) expansion parameters, using the ANOVA and response desirability approach. The results suggested that the optimal parameters are 120 °C (temperature), 2500 psi/17.23 MPa (pressure), and 2 h (residence time). Secondly, defibrillated curauá fibers (CF) were used as reinforcement in the PS matrix, in three different proportions (1.0, 2.5, and 5.0% (w/w)), to produced expanded composites. The results showed that CF acted as a nucleating agent, facilitating scCO2 to sip into the composite due to the reinforcement/matrix interface. The expanded composites were characterized by SEM, apparent density, cell population density, void volume fraction, and mechanical properties by the compression test, water uptake, dye absorption and, water contact angle (WCA). CF incorporation in the composite increased the compressive strength value and modified the expanded composite final morphology, decreasing the cell size and increasing void content and density. The PS/CF 5.0% sample showed higher water and organic dye absorption and the addition of CF on the expanded composite slightly decrease WCA. [ABSTRACT FROM AUTHOR]

Vegetal fibers are prominent reinforcements for polymer composite materials, considering their properties and application possibilities. In particular, thermal degradation behavior is crucial for determining an application subjected to a temperature range. Methods to predict properties are a trend in materials science and have the main advantage of saving cost and time. For this reason, in the present study, an artificial neural network (ANN) approach was used to predict the thermal degradation curves. The heating rate of 10 °C·min− 1 was carried out to train the network with 12 hidden layers and optimal training dataset of 60. Other heating rates were simulated and showed an excellent agreement with the experimental data. The coefficient of determination was R2 > 0.99 for all sources of biomass, exhibiting appropriate predictive fit with error following the sequence: ramie (1.15 %) < kenaf (1.33 %) < curaua (1.83 %) < jute (1.97 %). In conclusion, ANNs can learn from their data and optimize processing, formulations, predict properties, and other input data combinations. The predictive curves present high reliability with the experimental fit allowing the prediction of the mass loss for different temperatures versus the heating rate set. [ABSTRACT FROM AUTHOR]

Expanded nanocomposite production is an evolutionary and emerging technology in the field of porous materials, because it's characterized by combining the structural characteristics of the nanocomposites with the lightness of the polymeric foams. Three different processes were used in the present study: (1) extraction of two types of nanocellulose: cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs), both from curaua fibers. CNFs were obtained by mechanical defibrillation method and CNCs by 2,2,6,6-tetramethylpiperidine-1-oxyl (T.E.M.P.O.)-mediated oxidation method. (2) incorporation of reinforcement in a polystyrene matrix, producing nanocomposites in the following concentrations: 0.25%, 0.50% and 1.00% (w/w). (3) nanocomposite expansion with supercritical carbon dioxide fluid (scCO2), a new expander agent trend. The nanocomposites all had increased storage and loss moduli in relation to neat PS. In the expanded nanocomposites, the incorporation of CNFs promoted an increase in the compressive strength and a decrease in the cell size in comparison to the samples reinforced with CNCs and polystyrene foam. In the nanocomposites produced with CNCs, no significant variations were observed when compared to pure polystyrene foam. [ABSTRACT FROM AUTHOR]

A case of mycetoma caused by the black fungus Madurella grisea in northern Brazil is reported. The lesion was located on the patient’s right foot without bone involvement. Clinical samples were collected by opening the fistules with a scalp and the grains removed for microbiological and histopathological analyses. Although mycetoma caused by M. grisea has been previously reported in Brazil, this is the first time that of this fungus has been identify in this particular region of the country. [ABSTRACT FROM AUTHOR]