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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]

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 self-healing application in structural composites aims to recover component properties, control damage propagation, and increase component life. In this way, this study proposes to characterize and predict the inter-laminar shear behavior of polymer composites (5HS carbon/epoxy) with different fractions of self-healing agent. In addition, this work aims to measure the influence of self-healing content on the mechanical response. The ANOVA evidenced that the healing agent fraction influences on mechanical properties more than the internal dispersion for the same laminate before the healing cycle. Weibull distribution evidenced a linear decrease in shear stresses for higher EMAA (poly(ethylene-co-methacrylic acid)) content, regarding stiffness decrease as a response to ductile thermoplastic behavior. Ineffective healing effects were observed for the translaminar and intra-laminar damage, once most particles were concentrated in inter-laminar sections. However, the healing efficiency reached an average of 62% for shear stress and 106% for toughness behavior, provided by the closing shear cracks, i.e., up to 57% of reduced area related to the initial crack size. The predictive approach before and after healing action in the mechanical behavior provides the appropriate self-healing level to meet the specific project requirements, thus saving time and cost. [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]

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]

The concern in reducing the environmental impacts caused by human interference is increasing. Thus, the objective of this study was to generate a sustainable solution for sorption of vegetable oil. It was developed and characterized biocomposites obtained from polyurethane derived from castor oil reinforced with fibers from the crown of pineapple for sorption of vegetable oil. The biocomposites were obtained by mass mixing the polyol with the prepolymer (1:1) and reinforced with 5 to 20 % (wt/wt) pineapple crown fiber in 18 and 35 mesh granulometry. The biocomposites and pure polyurethane were characterized by scanning electron microscopy (SEM), optical microscopy (OM), X-ray Diffraction (XRD), porosimetry, contact angle, and density. Sorption tests were carried out on the biocomposites and pure polyurethane (PU). The sorption capacity of the biocomposites was evaluated as a function of the fiber content inserted in the matrix. Results of the sorption tests showed that the biocomposites reinforced with fibers of 18 mesh (20 % wt) presented approximately twice the sorption capacity when compared to pure PU and others biocomposites results, due to high porosity combined with high surface area, which influenced directly in the oil sorption. Response surface methodology (RSM) tecnique confirmed the influence fibers granulometry and content on oil sorption. [ABSTRACT FROM AUTHOR]