Effect of processing procedures and conditions on structural,morphological, and rheological properties of polyethylene/polyamide/nanoclay blends

The article deals with the effect of processing procedures and conditions on structural, morphological, and rheological properties of ternary blends composed of polyethylene (PE), polyamide (PA)‐12, and organically modified montmorillonite nanoclay with selective affinity. Samples were prepared from PE/PA and PA/PE blends, either by simultaneous mixing or from a polymer/clay masterbatch, using two processing conditions. The results have shown the existence of a weight fraction threshold, above which no significant processing effect was observed. Below this weight fraction threshold, the results tend to underline the significant role of two parameters that depend on processing procedures and/or conditions: the contact time between PE and PA phases and the contact time between clay and PA. Clay structure, blend morphology, and rheological properties were all shown to depend on these two parameters, and also on the nature of the matrix (PE or PA), because of the selective affinity of clay toward polymer phases. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Processing and properties of transparent hydroxyapatite and β tricalcium phosphate obtained by HIP process

Stoichiometric β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA) powders were synthesized by chemical precipitation of aqueous solutions of diammonium phosphate and calcium nitrate. After a calcination treatment and a milling step, the powders were shaped by slip casting. The sintering temperature effect on the relative density and the average grain size was investigated. By natural sintering at 1200 and 1120 °C, densities of 98% and 99% were obtained for HA and TCP, respectively. After determination of minimum temperatures to obtain only closed porosity and a pre-sintering at these temperatures, hot isostatic pressing (HIP) treatment was carried out. Transparent or translucent samples were obtained, indicating a relative density very close to the theoretical value (>99.9%). Mechanical properties (three-point bending strength, fracture toughness, Young's modulus and Vickers hardness) were measured on both materials with similar grain size (～ 1 μm). Bending strengths of 181 and 105 MPa were measured for TCP and HA, respectively.     

Simulation of Superheated Steam Drying from Coupling Models

Modeling of the transfer between a porous medium and its surroundings is commonly made using transfer coefficients that are theoretically well known only under boundary layer hypothesis. The resolution of Navier–Stokes equations in the surroundings of the product in order to get information about the boundary conditions avoids the classical use of these transfer coefficients. In this article, a modeling and a simulation of superheated steam drying of a rectangular piece of porous medium is proposed using a coupling method between a porous medium code and a CFD software. In some cases of superheated steam drying, even if a thermal boundary layer exists, a mass boundary layer cannot be defined. Moreover, boiling occurs during the process. An analysis of the interfacial transfer coupled with the analysis of the temperature, moisture content, and pressure profiles inside the porous medium is proposed.     

From Drying to Thermo-Hydro-Rheology—A Thirty-Year-Long Unfinished Maze

By 1976, chemical and mechanical engineering had produced a tremendous effort to understand drying in physical terms, mainly for consolidated bodies. In spite of an obvious interest aroused by the food processing industry, very little had been done on saturated deformable media. This article relates how a succession of nineteen Ph.D. students tried to enforce into practical and fundamental drying the relatively few laws we have at our disposal in continuum mechanics. Practical problems suggested by industry alternated with more theoretical work in an unplanned manner: it was my duty and my pleasure to ensure that all treatments echoed correctly with a certain harmony.     

Preparation of chitosan‐based adhesives and assessment of their mechanical properties

The aim of this study is to develop chitosan‐based adhesives and to characterize their shear strength. The desirable features of such adhesives are biodegradability, biocompatibility, non‐toxicity, and anti‐microbial properties. Various eco‐friendly polyanionic polysaccharides, acids, and plasticizers, in single or multiple formulations, were associated with chitosan. The resulting crosslinked polymers were glued on some chemically treated aluminum adherends. The shear strength of these formulations was measured with the “double lap‐joint” bonding method, as it features a low‐peeling effect. The shear strength of 40.8 MPa obtained for formulations containing chitosan and glycerol plasticizer was the most significant finding in this study. This value is equivalent to that obtained with a synthetic adhesive used in industry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Solid Phase Enhanced Direct Spectrofluorometric Determination of Polychlorinated Biphenyls (PCBs) in Natural Waters

A method of detection of PCBs in water, based on extraction/concentration with chips cut from an SPE disk-shaped C18 inverse phase coupled with a fluorescence detection and quantification directly on the phase has been evaluated. Experiments were performed with PCBs congeners IUPAC N° 3, 35, 67 and 169. Within the experimental conditions used : Hitachi F-4500 fluorometer, band-paths: 2.5 nm and extraction time: 60 min. the limits of detection were estimated to be respectively : 0.07, 0.4, 0.3 and 0.2 ppb. These values are within the range of PCB concentrations found in highly polluted waters and thus confer some interest to the method. However its sensitivity is not sufficient for application to moderately polluted natural water and the method needs some further improvements. Moreover, fluorescence quenching by humic substances was shown to substantially affect PCB's fluorescence intensity and must be taken into consideration for quantitative analysis.     

The structure of a linear chip firing game and related models

In this paper, we study the dynamics of sand grains falling in sand piles. Usually sand piles are characterized by a decreasing integer partition and grain moves are described in terms of transitions between such partitions. We study here four main transition rules. The worst classical one, introduced by Brylawski (Discrete Math. 6 (1973) 201) induces a lattice structure L_B(n) (called dominance ordering) between decreasing partitions of a given integer n. We prove that a more restrictive transition rule, called SPM rule, induces a natural partition of L_B(n) in suborders, each one is associated to a fixed point for the SPM rule. In the second part, we extend the SPM rule in a natural way and obtain a model called Linear Chip Firing Game (Theoret. Comput. Sci. 115 (1993) 321). We prove that this new model has interesting properties: the induced order is a lattice, a natural greedoid can be associated to the model and it also defines a strongly convergent game. In the last section, we generalize the SPM rule in another way and obtain other lattice structure parametrized by some θ, denoted by L(n,θ), which form a decreasing sequence of lattices when θ varies in [−n+2,n]. For each θ, we characterize the fixed point of L(n,θ) and give the value of its maximal sized chain's length. We also note that L(n,−n+2) is the lattice of all compositions of n.     

Influence of Rh nanoparticle size and composition on the photocatalytic water splitting performance of Rh/graphitic carbon nitride

The effect of Rh co-catalyst nanoparticle size for photocatalytic water splitting using graphitic carbon nitride (g-C₃N₄) as light absorber was investigated. Rh nanoparticles with sizes in the 4–9 nm range were synthesized and deposited on g-C₃N₄. The light-absorption properties of the g-C₃N₄ and the particle size of Rh supported on g-C₃N₄ were also not influenced by the catalyst synthesis procedures. Rh/C₃N₄ is active in the photocatalytic splitting of water using visible light. The activity for H₂ generation does not depend on Rh particle size. The results obtained point to two important design criteria for a successful photocatalyst: firstly, the surface of the semiconductor should support a sufficient number of Rh nanoparticles to remove the photogenerated electrons before their recombination with holes; secondly, the nanoparticles should be metallic in nature to catalyze the proton-electron transfer reaction to generate adsorbed H atoms. Surface oxidation of the Rh nanoparticles substantially lowers their photocatalytic activity.     

Effect of extraction conditions on the yield and purity of ulvan extracted from Ulva lactuca

A study of the influence of extraction conditions (pH: 1.5 and 2; temperature: 80 °C and 90 °C; extraction time: 1–3 h), on the yield, chemical composition and purity of the sulphated cell wall polysaccharides ulvan, extracted from the green seaweed Ulva lactuca and precipitated by alcohol is carried out. The alcohol precipitate yields varied from 21.68% to 32.67% (%dw/dw) depending on the pH. At pH 2, the alcohol precipitate yields and the uronic acid recovery from extract juice are higher than those obtained at pH 1.5. Other compounds than ulvan such as cellulose, hemicellulose, proteins and ash are solubilized from the cell walls of Ulva lactuca at both pH, and they are precipitated with alcohol. The alcohol precipitate obtained from different extraction conditions has high uronic acid (20.37%–23.60%) and neutral sugar content (20.09%–29.12%), especially when the conditions (pH, temperature) are drastic. It contains rhamnose (13.35%–15.59%), glucose (2.90%–10.97%), and xylose (2.36%–2.73%). A decrease in the molecular weight of ulvan was observed at acid pH, and for long extraction times. The presence of proteins (1.94%–2.32%) and inorganic material (33.36%–47.15%) in alcohol precipitate prove the lower purity of ulvan extracted and shows that ulvan precipitation with ethanol is not specific.