Rheological and crystallization enhancement in polyphenylenesulfide and polyetheretherketone POSS nanocomposites

Polyhedral oligomeric silsesquioxane (POSS) additives have been shown to increase melt‐flow and crystallization in thermoplastics. In this study, the effect of incorporation of trisilanolphenyl‐POSS molecules in polyphenylenesulfide (PPS) and polyetheretherketone (PEEK) on rheology, crystallization kinetics, and thermal and mechanical properties was evaluated. Parallel plate rheometry revealed a reduction in the viscosity of PPS and PEEK with the addition of POSS. The magnitude and concentration dependence of rheological modification were shown to depend on the polymer structure and POSS solubility. Isothermal crystallization kinetics were analyzed using the Avrami model and it was found that the addition of POSS accelerated the crystallization rate of PPS blends with no significant effect on PEEK blends. Interestingly, no statistical difference in degradation temperature, tensile modulus, or tensile strength of PPS or PEEK blends was observed. The findings indicate the potential for improvements in melt viscosity and crystallization of high temperature thermoplastics with tailored POSS/polymer interactions. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44462.     

Biodegradable baked foam made with chayotextle starch mixed with plantain flour and wood fiber

New renewable materials are needed to reduce petroleum‐based plastic packaging. The effect of plantain flour (PF) and wood fiber (WF) on the properties of starch‐based foams (SBFs) were investigated. The SBFs were characterized using physical, thermal, and mechanical methods to better understand the relationship between PF and WF concentration. Contact angle values showed that the addition of WF or PF increased the hydrophobic character of the SBFs. Also, the addition of PF increased the heat transfer resistance and density of the foams, while their solubility decreased. The values of tensile strength and Young's modulus increased with increasing concentrations of PF in the SBFs. However, the addition of PF and WF promoted a decrease on the elongation at break of the SBFs. An increase in concentration of PF also showed a decrease in water vapor permeability, and an increase in the thickness of the cell wall layer of the SBFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45565.     

Corrosion of Borosilicate Sealing Glasses for Molten Carbonate Fuel Cells

The development of a new sealant for molten carbonate fuel cells (MCFC) requires a study of the attack of molten carbonates on selected materials. Silica and Pyrex® glasses have better corrosion resistance against molten carbonates than other glasses, but they have unsuitable thermal expansion coefficients. Comparisons have also been made between borosilicate glasses of suitable thermal expansion for sealants for MCFC and silica and Pyrex® glasses. The corrosion kinetics in molten carbonates follows two limiting relations and involves two corrosion mechanisms. The weight loss varied linearly with time, indicating a dissolution of the glass network at short times. Longer times show corrosion, depending on the square root of time, typical of a diffusion mechanism and indicating formation of a protective layer on the surface of the glass. The main crystalline corrosion product is lithium methasilicate. The glass-corrosion rate follows the well-known Arrhenius law. These studies used scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and chemical analysis. A general corrosion mechanism of borosilicate glasses in molten carbonates is proposed.     

Micro-genetic algorithms for detecting and classifying electric power disturbances

The power quality analysis represents an important aspect in the overall society welfare. The analysis of power disturbances in electrical systems is typically performed in two steps: disturbance detection and disturbance classification. Disturbance detection is usually made through space transform techniques, and their classification is usually performed through artificial intelligence methods. The problem with those approaches is the adequate selection of parameters for these techniques. Due to the advantages of a variant scheme known as the micro-genetic algorithms, in this investigation, a new methodology to directly detect and classify electrical disturbances in one step is developed. The proposed approach is validated through synthetic signals and experimental test on real data, and the obtained results are compared with the particle swarm optimization method in order to show the effectiveness of this methodology.

     

Supply chain management: a modular Fuzzy Inference System approach in supplier selection for new product development

The critical objectives of purchasing departments include obtaining the product requested, at the right cost, in the right quantity, with the best quality, at the right time, from the right supplier. These goals require effective decisions concerning supplier selection at the early stage of product development. This work provides an application of fuzzy set theory in supply chain management, specifically in supplier selection for new product development. Here, a Fuzzy Inference System is proposed as an alternative approach to handle effectively the impreciseness and uncertainty that are normally found in supplier selection processes. This paper also shows that the proposed decision-making model is applicable to any supply chain system.     

High pressure responsive luminescence of flexible Eu~(3+) doped PVDF fibrous mats

Exploring lanthanide doped materials and their high-pressure optical properties is important from the perspective of designing pressure sensors, piezoelectric materials, scintillators, and optoelectronic devices, just to mention a few. Understanding the high-pressure optical properties of polymeric fibrous mats provides significant advantages in terms of flexibility, tunability, facile processability, and malleability. In this work, we have developed flexible polyvinylidene difluoride(PVDF) fibrous mats doped with an Eu³⁺ source of Eu(NO₃)₃·5H₂O(EN-PF) or Eu₂(SO₄)₃(ES-PF) by a Forcespinning■ method. Microstructural analysis of these two systems indicates that Eu(NO₃)₃·5H₂O and Eu₂(SO₄)₃ are homogeneously distributed and dispersed into the PVDF matrix. Fiber formation promotes a β-phase PVDF. Eu³⁺ doping increases the β-phase. Its fraction is larger for the ES-PF mats. To understand their high-pressure optical properties, their photoluminescence spectra have been taken at various pressures up to 58 GPa in a diamond anvil cell. High-pressure luminescence illustrates a clear change in asymmetry ratio, peak intensity, peak breadth, color coordinate, and color temperature of Eu³⁺ ions from both EN-PF and ES-PF with a different extent of changes. Specifically, Eu³⁺ ions in the ES-PF mats switch from asymmetric to symmetric environment as pressure increases. Those in the EN-PF mats present symmetric environment for all tested pressures. Both of the Eu³⁺ doped PVDF systems present irreversible changes. Therefore,the EN-PF fibrous mats present an opportunity to make pressure induced red-orange-yellow tunable phosphors for multifunctional applications.     

Pre‐service teachers’ understanding and teaching of nature of science: An intervention study

Abstract:

This study is the third in a line of investigations that examines pre‐service teachers’ conceptions of nature of science (NOS) and the translation of those conceptions into classroom practice. The purpose of the present study was to delineate the effectiveness of an intervention designed to facilitate pre‐service teachers’ inclusion of NOS in their classroom teaching. Four factors were identified as most influential in participants’ teaching efforts: (1) knowledge of NOS, (2) knowledge of subject matter, (3) pedagogical knowledge, and (4) intentions towards teaching NOS. Intentions were the most critical factor. Participants, regardless of NOS views or science background, did not teach in accordance with their NOS views if they had not internalized the importance of teaching NOS. Those with strong intentions to address NOS explicitly were more successful. Those participants with strong intentions, well‐developed NOS views, and extensive knowledge of science content were most successful in their instruction. Implications for the development of pedagogical content knowledge for NOS are discussed.     

Molecular mobility in polycyanurate networks investigated by viscoelastic measurements and molecular simulations

The dynamic mechanical behavior of a series of polycyanurate networks has been studied in the glassy state as a function of cyanate conversion. Two relaxations, β and γ, were defined and the Arrhenius dependence and Starkweather treatments were applied. To understand the origin of these sub-T_g relaxations, molecular modeling (both mechanics and dynamics) was used on model molecules representative of the network structure. Two types of molecular motion were examined: rotation of the phenylene ring and crankshaft of the chain segment between crosslinks (i.e., triazine rings).