Nonisothermal thermophysical evaluation of a polypropylene + ethylene propylene diene (EPDM) blend

Recent theoretical evidence indicates that the rate effects of quenching seen in the isothermal crystallization kinetics can be eliminated through use of a nonisothermal method based on constant rate heating and cooling through inclusion of an activation energy. To investigate the potential of this method for polymers, we apply it to semicrystalline polymers: polypropylene (PP), a binary blend PP + ethylene propylene diene rubber (EPDM) and a ternary system PP + EPDM + high-density polyethylene (PE). As opposed to traditional rubber-modified systems such as high-impact polystyrene (HIPS) wherein an amorphous component is blended with a rubbery one, the PP + EPDM system has a semicrystalline component. From the perspective of crystal lamellae growth or stress induced slip, the thermophysical properties are also a concern. Therefore, we use differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The results indicate that differences between isothermal and nonisothermal conditions must be taken into account since the latter conditions prevail in extrusion, injection molding, and in hot coating-slow cooling processes. Our nonisothermal analysis of crystallization should assist in the optimization of cooling of semicrystalline polymers.     

Epoxy and glass composites in water studied with 2H-NMR

The amount, behavior, and localization of water in epoxy resin composites largely influence the mechanical properties and aging. Gravimetric analysis combined with ²H-NMR of heavy water in epoxy resin glass fabric composites provides direct information about types of water, which can be distinguished by their mobility. Three different epoxy composites were analyzed with this technique. The results are correlated with mechanical properties.     

Phase stability of rare earth sesquioxides with grain size controlled in the nanoscale

Rare earth oxides are important materials due to their chemical and physical properties. The rare earth sesquioxides (RESOXs) possess a cubic, monoclinic, or hexagonal structure, depending on pressure, temperature and ionic radius. When RESOXs take the form of single crystalline grains with diameter in the nanoscale range (nanocrystals), it is suspected that the grain size determines the phase stability as well. RESOXs with medium ionic radius such as Gd₂O₃, Eu₂O₃ and Sm₂O₃ in the low temperature range up to 900°C may take the monoclinic structure or the cubic structure, depending on the synthesis process. The structure determining factor can be, besides temperature, also the grain size. In order to determine the stable structure taking into account grain size as a parameter, we produced Gd₂O₃ and Sm₂O₃ nanocrystals embedded in a neutral MgO matrix. This way, we prevented grain growth during annealing. For comparison, we annealed pure Gd₂O₃ and Sm₂O₃ nanocrystals in which temperature increase caused grain growth, as in traditional experiments for phase stability determination. We have shown that for coarse grained materials at low temperature monoclinic is the stable structure. For nano-sized crystallites, cubic is the stable structure. This explains the controversial results as far as which phase is the stable one below 900°C and permits to program the needed structure by controlling crystallization kinetics and grain growth.     

CO2 Methanation in the Presence of Ce-Promoted Alumina Supported Nickel Catalysts: H2S Deactivation Studies

Topics in Catalysis - The performance of alumina supported unpromoted and cerium promoted nickel catalysts in CO2 methanation reaction was investigated. It was found that the activity of catalysts...     

Wear resistance and wear mechanisms in polymer + metal composites

We have investigated composites containing metallic micro-size and nano-sized particles as the 10 wt% dispersed phase. Branched low density polyethylene (LDPE) was the matrix. Microsized metals were Al, Ag and Ni; nanosized metals were Al and Ag. Several mechanisms of wear are observed in function of the kind and size of metal used: deformation, delamination, abrasion, adhesion and rolls formation. The presence of Ag particles increases the wear rate as compared to neat LDPE. The presence of Al particles lowers the wear of LDPE significantly; nanoparticles are more effective than microparticles.     

Scratch resistance of polycarbonate containing ZnO nanoparticles: effects of sliding direction

Abrasive wear resistance of injection molded polycarbonate (PC) and polycarbonate + zinc oxide nanocomposites containing 0.5 wt% ZnO nanoparticles was determined as a function of the sliding direction with respect to injection flow. First we have performed single scratch testing under progressively increasing the load applied. Then sliding wear testing consisting of 15 successive scratches along the same groove was performed. Neat PC shows anisotropic behavior, with instantaneous penetration depth more than 50% higher in the direction parallel to the melt injection flow than in the transverse direction. Viscoelastic recovery after scratching of neat PC is also higher in the longitudinal than in the transverse direction, hence final residual depth values are similar in both directions. The addition of ZnO nanoparticles reduces the instantaneous penetration depth in the longitudinal direction but lowers viscoelastic recovery so that the residual depth is large. In the transverse direction, the scratch resistance is similar for neat PC and the nanocomposite. Dynamic mechanical analysis, SEM/FIB results and wear mechanisms from SEM observations of wear scars are discussed. Below the glass transition region the nanocomposite has distinctly higher storage modulus E' than PC--a clear reinforcement effect. However, the addition of ZnO nanoparticles to the polymer increases the material brittleness at room temperature by a factor of 2.72.     

Vortex‐induced vibrations on a modern wind turbine blade

This article investigates the aero‐elastic response of the DTU 10‐MW RWT blade in deep stall conditions with angles of attack in the vicinity of 90 degrees. The simulations were conducted with the high‐fidelity fluid–structure interaction simulation tool HAWC2CFD employing the multi‐body‐based structural model of HAWC2 and the incompressible computational fluid dynamics solver EllipSys3D. The study utilizes detached eddy simulation computations and considers the three‐dimensional blade geometry including blade twist and taper. A preliminary frequency analysis of the load variations on a stiff blade showed that an inclined inflow with a velocity component along the blade axis can trigger a spanwise correlated vortex shedding over large parts of the blade. Moderate wind speeds were sufficient to generate vortex shedding with frequencies close to the first edgewise eigenfrequency of the blade. Aero‐elastic computations of the elastic blade confirmed the findings of the frequency analysis. Inflow conditions with inclination angles between Ψ = 20° and Ψ = 55° and relatively low to moderate wind speeds between V = 16 and V = 26ms^?1 were sufficient to trigger severe edgewise blade vibrations with blade tip amplitudes of several metres. The investigated inflow conditions are considered realistic and might occur when the wind turbine is idling or standing still and the yaw system is unable to align the wind turbine with the incoming wind. Copyright © 2016 John Wiley & Sons, Ltd.     

The effect of pulsed electric field on drying kinetics,color, and microstructure of carrot

The aim of the study was to investigate the impact of pulsed electric field (PEF) treatment on the convective drying kinetics of a carrot and color and microstructure changes of the dried product. Samples were treated by PEF with the specific energy input equal to 5.63, 8 and 80 kJ · kg^?1. After PEF treatment, thermal conductivity and electrical conductivity were measured. Drying time of the PEF-treated samples was reduced up to 8.2% (W_s = 8 kJ · kg^?1, 5 kV · cm^?1; 10 pulses) in comparison to intact tissue. Statistical analysis showed that Midilli et al.’s model was considered to describe the kinetics of the process the most precisely. Pulsed electric field treatment increased the effective water diffusion coefficient up to 16.7%. Moreover, PEF treatment and drying caused the alteration of the sample color. After drying, the lightness and chroma were higher or unchanged in comparison to the intact tissue. The dried PEF-treated samples exhibited significantly higher redness (higher value of a^* parameter) in comparison to the untreated dried samples. Moreover, the visual inspection of scanning electron microscope images revealed that PEF pretreatment performed at high electric field intensity (5 kV · cm^?1, regardless of pulse number) provoked the material to form greater cavities during drying in comparison to the untreated material.     

Chitosan-Human Bone Composite Granulates for Guided Bone Regeneration

The search for the perfect bone graft material is an important topic in material science and medicine. Despite human bone being the ideal material, due to its composition, morphology, and familiarity with cells, autografts are widely considered demanding and cause additional stress to the patient because of bone harvesting. However, human bone from tissue banks can be used to prepare materials in eligible form for transplantation. Without proteins and fats, the bone becomes a non-immunogenic matrix for human cells to repopulate in the place of implantation. To repair bone losses, the granulate form of the material is easy to apply and forms an interconnected porous structure. A granulate composed of β-tricalcium phosphate, pulverized human bone, and chitosan—a potent biopolymer applied in tissue engineering, regenerative medicine, and biotechnology—has been developed. A commercial encapsulator was used to obtain granulate, using chitosan gelation upon pH increase. The granulate has been proven in vitro to be non-cytotoxic, suitable for MG63 cell growth on its surface, and increasing alkaline phosphatase activity, an important biological marker of bone tissue growth. Moreover, the granulate is suitable for thermal sterilization without losing its form—increasing its convenience for application in surgery for guided bone regeneration in case of minor or non-load bearing voids in bone tissue.