Production of Biomass-Derived Chemicals and Energy: Chemocatalytic Conversions of Glycerol

The growing production of biodiesel as a renewable source-based fuel leads to an increased amount of glycerol. Thus, it is a favorable starting material to obtain highly functionalized products. From a variety of catalytic reactions three examples, namely glycerol oxidation, glycerol hydrogenolysis and aqueous-phase reforming, were chosen for detailed studies in our group. The experimental focus for the oxidation of glycerol was set on preparation and detailed examination of supported Pt–Bi catalysts in batch reactions as well as in continuous experiments using a trickle bed reactor. For aqueous-phase reforming of glycerol to hydrogen the addition of tin to supported platinum catalysts was investigated. Ruthenium and copper based catalysts could be successfully applied in the hydrogenolysis of glycerol to 1,2-propanediol.     

A scientific application oriented classification for metal transfer modes in GMA welding

In this work, metal transfer in solid wire GMA welding was studied. Several experiments with different combinations of gas-wire-parameters were carried out to observe metal transfer and to characterize the various transfer modes. A laser shadograph system with synchronized electrical signals and high speed filming were used. New modes were observed and their particular characteristics described for completeness. A classification for metal transfer, oriented to scientific personnel (researchers, scholars and students), is proposed, in which the modes are independent of the type of shielding gas or welding power source.     

Joint strength optimization by the mixed-adhesive technique

An ideal adhesive lap joint is one in which the adhesive flexibility and strength properties vary along the overlap length. Because of greater adhesive shear strains at the edges of the overlap, a ductile and flexible adhesive should be used at the overlap ends, while in the middle a stiff and less-ductile adhesive should be used. This technique has been investigated in the past but only a few studies have reported any experimental evidence. In the present study, single-lap adhesive joints were manufactured and tested maintaining the same brittle adhesive in the middle of the overlap and using three different ductile adhesives of increasing ductility at the ends of the overlap. A simple joint strength prediction is proposed for mixed-adhesive joints. The mixed-adhesive technique gives joint strength improvements in relation to a brittle adhesive alone in all cases. For a mixed adhesive joint to be stronger than the brittle adhesive and the ductile adhesive used individually, the load carried by the brittle adhesive must be higher than that carried by the ductile adhesive.     

Improving the tensile strength of carbon nanotube spun yarns using a modified spinning process

A modified process for the dry spinning of carbon nanotube (CNT) yarn is reported. The approach gives an improved structure of CNT bundles in the web drawn from the CNT forest and in the yarn produced from the twisted web leading to improved mechanical properties of the yarn. The process enables many different mechanical and physical treatments to be applied to the individual stages of the pure CNT spinning system, and may allow potential for the development of complex spinning processes such as polymer-CNT-based composite yarns. The tensile strength and yarn/web structure of yarn spun using this approach have been investigated and evaluated using standard tensile testing methods along with scanning electron microscopy. The experimental results show that the tensile properties were significantly improved. The effect of heat treatments and other yarn constructions on the tensile properties are also reported.     

Poly(vinylidene fluoride) with zinc oxide and carbon nanotubes applied to pressure sheath layers in oil and gas pipelines

In this work, PVDF composites containing 0.2% (m/m) of carbon nanotubes (MWCNTs), PVDF with 5.0% (m/m) of zinc oxide (ZnO), and composites containing both particles in the same contents in the matrix were melt processed in a mini-extruder machine with double screws, using the counter-rotation mode. Composites were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), dynamic-mechanical analysis (DMA), and contact angle tests (CA). The samples presented the predominance of the α phase, with an increased degree of crystallinity as well as an increase in dimensional stability by incorporating both fillers, showing a synergistic effect between these particles, as shown on FTIR, DSC, and XRD results. SEM images showed a good dispersion of high aspect ratio particles. In general, DMA and TGA analysis showed that composites had not decreased their thermal and mechanical performance when compared to neat PVDF. Results of CA analysis showed an increase in the hydrophobicity of the sample containing MWCNTs. Permeability tests were also performed using a differential pressure system, combining high temperature and pressure, obtaining permeability measures and time lag. This work presents an alternative of composite materials, suggesting its application in the internal pressure sheath layers of oil and gas flexible pipes.     

Melt processing of nanocomposites of cellulose nanocrystals with biobased thermoplastic polyurethane

Nanocomposites of thermoplastic polyurethane (TPU) with cellulose nanocrystals (CNC) without and with surface treatment are obtained by melt processing. Nanocomposites are obtained with nanofiller weight content near of the theoretical percolation threshold (3.9 wt%). Visual observation of CNC agglomerates is sufficient to prove the inefficiency of the mixing in systems with untreated CNC. The crystallization kinetics of the TPU changes with the addition of CNC and this is confirmed by differential scanning calorimetry analysis. Thermogravimetric analysis prove that the addition of CNC increases the thermal stability of the TPU. From the rheological analysis it is possible to verify the absence of percolation and an intermediate state of sol–gel transition in the nanocomposites. CNC/TPU nanocomposites with 5 wt% of treated CNC present better mechanical performance than de neat TPU and the other processed nanocomposites and display around 130% increase in Young's modulus while retaining significant values of toughness, tensile strength and elongation at break.     

High-temperature Na2SO4 interaction with air plasma sprayed Yb2Si2O7 + Si EBC system: Topcoat behavior

The high-temperature interaction between ~2.5 mg/cm² of Na₂SO₄ and an atmospheric plasma sprayed (APS) Yb₂Si₂O₇ topcoat–Si bond coat system on SiC CMC substrates was studied for times up to 240 h at 1000°C–1316°C in a 0.1% SO₂–O₂ gaseous environment. Yb₂Si₂O₇ reacted with Na₂SO₄ to form Yb₂SiO₅ and an intergranular amorphous Na-silicate phase. Below 1200°C, the reaction was sluggish, needing days to cause morphological changes to the “splat microstructure” associated with APS coatings. The reaction was rapid at 1200°C and above, needing only a few hours for the entire topcoat to transform into a granulated microstructure consisting of Yb₂SiO₅ and Yb₂Si₂O₇ phases. Na₂SO₄ deposits infiltrated the Yb₂Si₂O₇ topcoat and transformed into an amorphous Na-silicate in less than 1 h at all exposure temperatures. Quantitative assessment of the Yb₂SiO₅ area fraction in the topcoat showed a linear decrease over time at 1316°C, attributed to reaction with the SiO₂ thermally grown oxide (TGO) formed on the Si bond coat and rapid transport through the interpenetrating amorphous Na-silicate grain boundary phase. It was predicted that nearly 2 weeks is needed for complete removal of Yb₂SiO₅ from the topcoat at 1316°C for a single applied loading of Na₂SO₄.     

An investigation of the synergistic effect between magnetite nanoparticles and polypyrrole in nanostructured layer-by-layer films

In this paper, we report the controlled fabrication of layer-by-layer (LbL) films deposited on gold substrates with three different supramolecular architectures using polypyrrole (Ppy) and magnetite nanoparticles (Fe₃O₄-np), besides conventional poly(allylamine hydrochloride) (PAH) e poly(vinyl sulfonic acid) (PVS) polyelectrolytes, demonstrating the synergistic effect between Ppy and Fe₃O₄-np such as a result of their interaction. Modified gold electrodes were analyzed by contact angle (wettability), surface plasmon resonance (SPR), raman spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The (Fe₃O₄-np/Ppy)₃ architecture was also evaluated by scanning electron microscopy. The modified gold electrodes present more homogeneous covering, higher electron transfer and a decrease of resistance with the incorporation of the nanostructured materials such as Ppy and Fe₃O₄-np forming (Fe₃O₄-np/Ppy)₃ LbL film. The results carried out in this study suggest that the (Fe₃O₄-np/Ppy)₃ LbL film can be applied as a possible electrochemical or optical non-enzymatic sensor for analytical detection.     

Increasing the photocatalytic and fungicide activities of Ag3PO4 microcrystals under visible-light irradiation

The present study reports for the first time the performance of silver phosphate (Ag₃PO₄) microcrystals as photocatalyst (degradation of Rodamine B-RhB) and antifungal agent (against Candida albicans–C. albicans) under visible-light irradiation (455 nm). Ag₃PO₄ microcrystals were synthesized by a simple co-precipitation (CP) method at room temperature. The structural and electronic properties of the as-synthetized Ag₃PO₄ have been investigated before and after 4 cycles of RhB degradation under visible light using X-ray diffraction (XRD), micro-Raman spectroscopy, UV–Vis spectrophotometer and field emission scanning electron microscopy (FE-SEM) images. The antifungal activity was analyzed in planktonic cells and 48h-biofilm of C. albicans by colony forming units (CFU) counting, confocal laser and FE-SE microscopies. Statistical analysis was carried out using SPSS software. Morphological and structural modifications of Ag₃PO₄ were observed upon recycling. After 4 recycles, the material maintained its photodegradation property; an eightfold increase in the efficiency of Ag₃PO₄ was observed in planktonic cells and a two fold increase in biofilm when irradiated under visible light. Thus, higher antifungal effectiveness against C. albicans was obtained when associated with visible-light irradiation.