Synthesis of a new compatibilisant agent PVC‐g‐MA and its use in the PVC/alfa composites

The main objective of this research was to synthesize a new compatibilisant agent (PVC‐g‐MA), which was grafted from the maleic anhydride on the PVC chains. The presence of maleic anhydride grafting on PVC was made evident by infrared analysis. PVC‐g‐MA was used like compatibilisant to solve the problem of the incompatibility between the hydrophobic polymeric matrix (PVC) and hydrophilic fiber (alfa). Composites samples were prepared with different alfa fiber loading (10, 20, and 30 wt %) and incorporating PVC‐g‐MA (1, 3, and 5 wt %) or PP‐g‐MA (3 wt %). The tensile properties, the thermal stability and the morphology of the composites were investigated. The result indicated that the PVC‐g‐MA increased the interfacial adhesion between the fibers and the polymer matrix and this effect was better than that obtained for the maleated‐polypropylene‐coupled composites. Microstructure analysis of the fractured surfaces of MAPP modified composites confirmed improved interfacial bonding. The addition of alfa and PVC‐g‐MA increased the thermal stability of the composites. The temperature of degradation of the polymer matrix increased about 16°C in comparison to the noncoupled composite, indicating that PVC‐g‐MA improved the thermal stability of the polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Numerical simulation of exchange membrane fuel cells in different operating conditions

A two-dimensional, steady state model for proton exchange membrane fuel cell (PEMFC) is presented. The model is used to describe the effect operation conditions (current density, pressure and water content) on the water transport, ohmic resistance and water distribution in the membrane and performance of PEMFC. This model considers the transport of species and water along the porous media: gas diffusion layers (GDL) anode and cathode, and the membrane of PEMFC fuel cell.     

Characterization of cellulose nanowhiskers extracted from alfa fiber and the effect of their dispersion methods on nanocomposite properties

In this study, cellulose nanowhiskers (CNW) were prepared from alfa fiber (Stipa tenacissima) by an alkali treatment at room temperature in association with a bleaching treatment followed by a sulfuric acid hydrolysis. Fourier Transform Infrared (FT-IR) spectroscopy was used to highlight the evolution of chemical composition. Atomic Force Microscopy and Zeta-sizer indicated that the transverse size of the particles varied between 30 nm and 170 nm. Thermal stability was higher for CNW as compared to alfa fiber. FT-IR, X-ray diffraction, and Thermogravimetric analysis studies confirmed the removal of hemicelluloses and lignin during the chemical treatment process. The swelling of CNW in water with Cloisite 30B (CNW/C30B) or with the Polyethylene glycol (CNW/PEG) was carried out. The properties of Polyvinyl Chloride (PVC) nanocomposites reinforced with CNW which was dispersed with two different methods were also compared. The results showed that the morphology of both samples have drastic differences which may explain the fact that the storage modulus prepared with CNW/C30B was higher than those prepared with CNW/PEG. However, PVC/CNW/PEG nanocomposites exhibited more thermal stability. In the end, the obtained CNW may have potential applications in alternative power sources as a reinforcement phase.     

FGF‐23 and cognitive performance in hemodialysis patients

Although cognitive impairment is common in hemodialysis patients, the etiology of and risk factors for its development remain unclear. Fibroblast growth factor 23 (FGF‐23) levels are elevated in hemodialysis patients and are associated with increased mortality and left ventricular hypertrophy. Despite FGF‐23 being found within the brain, there are no prior studies assessing whether FGF‐23 levels are associated with cognitive performance. We measured FGF‐23 in 263 prevalent hemodialysis patients in whom comprehensive neurocognitive testing was also performed. The cross‐sectional association between patient characteristics and FGF‐23 levels was assessed. Principal factor analysis was used to derive two factors from cognitive test scores, representing memory and executive function, which carried a mean of 0 and a standard deviation of 1. Multivariable linear regression adjusting for age, sex, education status, and other relevant covariates was used to explore the relationship between FGF‐23 and each factor. Mean age was 63 years, 46% were women and 22% were African American. The median FGF‐23 level was 3098 RU/mL. Younger age, lower prevalence of diabetes, longer dialysis vintage, and higher calcium and phosphorus were independently associated with higher FGF‐23 levels. Higher FGF‐23 was independently associated with a lower memory score (per doubling of FGF‐23, β = ?0.08 SD [95% confidence interval, CI: ?0.16, ?0.01]) and highest quartile vs. lowest quartile (β = ?0.42 SD [?0.82, ?0.02]). There was no definite association of FGF 23 with executive function when examined as a continuous variable (β = ?0.03 SD [?0.10, 0.04]); however, there was a trend in the quartile analysis (β = ?0.28 SD [?0.63, 0.07], P = 0.13, for 4th quartile vs. 1st quartile). FGF‐23 was associated with worse performance on a composite memory score, including after adjustment for measures of mineral metabolism. High FGF‐23 levels in hemodialysis patients may contribute to cognitive impairment.     

Personal monitor glass badge: theoretical dosemeter response calculated with the Monte Carlo transport code MCNPX

This paper describes the results of the simulation of a radiophotoluminescent (RPL) dosemeter with the Monte Carlo transport code MCNPX. The aim of this study is to calculate the response with MCNPX of the RPL dosemeter in terms of equivalent doses H(p) (0.07) and H(p)(10) using X-ray photon radiation qualities N series, together with S-Cs and S-Co nuclide radiation qualities, specified in ISO 4037-1. After comparison with reference values versus experimental results, the deviation of the theoretical responses of the RPL dosemeter proved to be lower than 5 % for reference values and lower than 10 % for experimental results. This good correlation validates the model over the energy range studied.     

Modeling of the solid–liquid bubble interface in partial nucleate boiling

Several models of heat transfer in partial nucleate boiling are identified in order to determine the relationship between the dominant physical parameters. The correlations are different for different models, so the main goal of this analysis is to determine the validity of each model and to identify the most dominant physical phenomenon in the nucleate boiling heat transfer. This is done by comparing the results of different models with a vast range of reliable experimental data. The comparison shows that the Sakashita and Kumada model gives the best results in the nucleate boiling heat transfer. It is also shown that the most dominating phenomenon in isolated partial bubbles zones is the transient conduction taking place mainly under the bubbles. This is in contradiction with a majority of the models that consider convection as the most important mode in the nucleate boiling heat transfer. The selected model can also be extrapolated and used in the case of fully developed bubbles zones.     

Computation of the relaxation and creep functions of elastomers from harmonic shear modulus

The purpose of this paper is to compute the relaxation and creep functions from the data of shear complex modulus, G ^∗(iν). The experimental data are available in the frequency window ν∈[ν_min,ν_max] in terms of the storage G′(ν) and loss G″(ν) moduli. The loss factor h( n) = \fracG"( n)G￠(n)\eta( \nu) = \frac{G'( \nu )}{G'(\nu )} is asymmetrical function. Therefore, a five-parameter fractional derivative model is used to predict the complex shear modulus, G ^∗(iν). The corresponding relaxation spectrum is evaluated numerically because the analytical solution does not exist. Thereby, the fractional model is approximated by a generalized Maxwell model and its rheological parameters (G _k ,τ _k ,N) are determined leading to the discrete relaxation spectrum G(t) valid in time interval corresponding to the frequency window of the input experimental data. Based on the deterministic approach, the creep compliance J(t) is computed on inversing the relaxation function G(t).     

Thermal and mechanical properties of PA12/C30B nanocomposites in relationship with nanostructure

This work focuses on the effect of nanoclay mass fraction on the properties of polyamide 12 matrix. Relationships between mechanical, thermal, and structural properties of polyamide 12/Cloisite^® 30B nanocomposites were studied. The material structure, previously described from XRD and TEM experiments, was more thoroughly characterized in the present work using SEM and FTIR techniques. The FTIR results clearly showed that clay galleries are intercalated by PA chains, which leads to a partially exfoliated nanostructure, confirming the TEM observations and the XRD analysis. However, a few micrometric aggregates are evidenced by SEM analysis, particularly at high clay fractions. TGA and DTA measurements showed that the thermal stability of PA12 matrix is slightly modified by the Cloisite^® 30B content. Viscoelastic properties of the nanocomposites in solid‐state were analyzed as functions of strain, frequency, and temperature. The extent of the linear response regime of the material is shown to be sensitive to the amount of clay: nonlinearities appear at lower strain values as the clay mass fraction increases. Both relative dynamical moduli also increase with increasing clay mass fraction, with frequency dependence for the viscous modulus and without frequency dependence for the elastic modulus. Finally, similarities have been pointed out between viscoelastic properties of the nanocomposites in solid and melt states. For example, the percolation threshold is highlighted at the same clay mass fraction, ～2%, in both states. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41938.     

Transport phenomena effect on the performance of proton exchange membrane fuel cell (PEMFC)

The aim of this work is to present a two-dimensional transient model, of heat and mass transfer in a proton exchange membrane fuel cell (PEMFC). The model includes various conservation equations such as mass (hydrogen, oxygen, water concentration), Momentum and energy equations this model is combined with the electrochemical model.