RESUMO
The present study introduces the analysis of single-lap co-cured joints of thermoplastic self-reinforced composites made with reprocessed low-density polyethylene (LDPE) and reinforced by ultra-high-molecular-weight polyethylene (UHMWPE) fibers, along with a micromechanical analysis of its constituents. A set of optimal processing conditions for manufacturing these joints by hot-press is proposed through a design of experiment using the response surface method to maximize their in-plane shear strength by carrying tensile tests on co-cured tapes. Optimal processing conditions were found at 1 bar, 115 °C, and 300 s, yielding joints with 6.88 MPa of shear strength. The shear failure is generally preceded by multiple debonding-induced longitudinal cracks both inside and outside the joint due to accumulated transversal stress. This composite demonstrated to be an interesting structural material to be more widely applied in industry, possessing extremely elevated specific mechanical properties, progressive damage of co-cured joints (thus avoiding unannounced catastrophic failures) and ultimate recyclability.
RESUMO
Currently, CO2 emission is the main cause of climate change and its various related environmental impacts. Therefore, we have as a prime the development of clean sources of energy. The hydrogen economy is very attractive in this regard, however, when generated from the methane reform, there are also large-scale CO2 emissions. Thus, this research aims to develop and characterize bismuth and iron niobate-based photoanodes for hydrogen production via water photoelectrolysis. Bi2FexNbO7 films were synthesized by the sol-gel method and deposited on FTO coated glass plates by dip-coating technique. The influence of heat treatment (400, 500 and 600°C) and amount of iron on the structure (Bi2FexNbO7, x = 0, 0.8, 1, 1.2) were evaluated. Optical, structural and morphological properties were performed, as well as photoanode efficiency in photocurrent assays. The results indicate that the increase of temperature as well as the amount of iron leads to a higher absorption capacity and hence to lower band gap values. Regarding the structural properties, it was possible to observe the BFNO phase in the samples treated at 500 and 600°C. The films heat-treated at 400°C had a heterogeneous texture and a good covering. At 600°C there were some cracks in films surface. Therefore, samples with more iron and treated at 400°C showed better responses in photocurrent assays. It can be concluded that bismuth-iron niobate has a great potential to be applied in photoelectrolysis hydrogen production.
Assuntos
Luz , Nióbio , Bismuto , Hidrogênio , ÁguaRESUMO
OBJECTIVES: The aim of this study was to evaluate the influence of nanostructured zirconium dioxide incorporation in an experimental adhesive resin. METHODS: ZrO2 particles were characterized by X-ray diffraction (XRD), micro-Raman spectroscopy and Brunauer-Emmett-Teller (B.E.T). Experimental adhesive resins were formulated with 0, 0.5, 1, 4.8, and 9.1% ZrO2 in weight. The adhesives were evaluated based on degree of conversion (DC), radiopacity, softening in solvent and microtensile bond strength (µTBS) 24 h and after 1 year of aging. Mineral deposition at the hybrid layer was assessed with micro-Raman spectroscopy at the baseline and after 14 days. RESULTS: XRD showed monoclinic and tetragonal phases of ZrO2.particles. B.E.T data revealed a surface area of 37.41 m2/g, and typical chemical groups were shown on the Raman spectra. The addition of ZrO2 did not influence the radiopacity. The addition of 4.8% and 9.1 wt.% ZrO2 showed higher initial hardness with increased softening in solvent (P < 0.05) and promoted mineral deposition at the dentin interface. DC was significantly increased in the group with 1% ZrO2 (P < 0.05). The µTBS test showed difference on the group with 9.1 wt.% of ZrO2, with a significant reduction after aging. CONCLUSION: The incorporation of ZrO2 promoted mineral deposition on the adhesive interface and the addition of 1 wt.% caused a significant increase on the DC without compromising the other physicochemical characteristics, which may prove promising for the development of new dental adhesive systems. CLINICAL RELEVANCE: The mineral deposition on the hybrid layer can result in a longer stability of the adhesive, thus delaying the hydrolytic degradation.