Electroconductive Polyamide 6/MWNT Nanocomposites: Effect of Nanotube Surface‐Coating by in situ Catalyzed Polymerization

Preparation and analysis of morphologic and electrical properties of high‐performance multiwalled carbon nanotube/polyamide 6 nanocomposites was achieved. The MWNTs were surface‐coated by in situ polymerization of ethylene as catalyzed directly from the nanotube surface previously treated by a highly active metallocene‐based complex. The so‐produced polyethylene‐coated MWNTs were melt‐mixed with the PA6 matrix. Pristine MWNTs were also dispersed in PA6. The in situ ethylene polymerization/coating reaction allowed the destructuring of the native bundle‐like aggregates leading to the preparation of nanocomposites with improved properties even at very low nanofiller content.

     

Miscibility in crystalline polymer blends: Isotactic polypropylene and linear low‐density polyethylene

The phase behavior and the crystallization kinetics of blends composed of isotactic polypropylene (iPP) and linear low‐density polyethylene (LLDPE) were investigated by differential scanning calorimetry. The phase behavior indicates the formation of separate crystals of iPP and LLDPE at each investigated blend composition. The crystallization trace reveals that iPP crystallizes in its normal range of temperatures (i.e., at temperatures higher than that of LLDPE), when its content in the blend is higher than 25% by weight. In the blend whose iPP content is as high as 25%, at least a portion of iPP crystallizes at temperatures lower than that of LLDPE. This behavior has been proposed by Bassett to be attributed to a change in the kind of nucleation from heterogeneous to homogeneous. From the Avrami analysis of the isothermal crystallization of iPP in the presence of molten LLDPE, n values close to 2 are always obtained. According to our previously proposed interpretation of the Avrami coefficient, it can be related to the crystallite fractal dimension, through d = n + 1, which gives values close to 3, according to the spherulitic observed morphology. The kinetics parameter, i.e., the half‐time of crystallization, and the kinetic constant k show that a decrease in the overall rate of crystallization of iPP occurs on blending. Optical microscopy photographs, taken during the cooling of the samples from the melt, confirm the above results and show increasingly less resolved spherulite texture on increasing LLDPE content in the blend. The diffusion parameters evaluated for the neat polymers and for the blends in dichloromethane, which give information on the miscibility in the amorphous state, show that the diffusional behavior of the blends is governed by iPP, suggesting a two‐phase amorphous state. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3338–3346, 2003     

WOx/ZrO2 catalysts: Part 3. Surface coverage as investigated by low temperature CO adsorption: FT-IR and volumetric studies

The adsorption of CO at 77 K on zirconia-supported tungsten oxide (ZW) samples prepared by equilibrium adsorption or by impregnation and with tungsten content up to 12.4 W atoms nm⁻² was studied with the aim of determining the coverage of ZrO₂ surface by the supported tungsten oxospecies. As an essential background for quantitative volumetric measurements, ZW samples were investigated by FT-IR spectroscopy to identify the surface sites responsible for the CO adsorption. FT-IR showed that CO adsorbed selectively and irreversibly on Zr_cus⁴⁺ centers of the support surface, but not on W_cus⁶⁺ sites. By volumetric determinations, the coverage of the zirconia surface by tungsten oxospecies was about 50% at maximum, irrespective of the preparation procedure and of the support crystallographic modification (monoclinic or tetragonal). Zirconia coverage remained significantly unchanged after leaching with a NH₃ solution that removed tungsten oxospecies not directly interacting with the zirconia surface. This finding indicates that ZrO₂ support coverage depends mainly on the tungsten species strongly anchored to the zirconia surface.     

Phenomena – A visual environment for querying heterogenous spatial data

The need to perform complex analysis and decision making tasks has motivated growing interest in Geographic Information Systems (GIS) as a means to compare different scenarios and simulate the evolution of a phenomenon. However, data and function complexity may critically affect human interaction and system performances during planning and prevention activities. This is especially true when the scenarios of interest involve continuous fields, besides discrete objects.In the present paper we describe the visual environment Phenomena, where continuous and discrete data may be handled through a uniform approach. We illustrate how users’ activity is supported by a visual framework where they can interact with, manipulate and query heterogeneous data, with a very small training effort. A preliminary experimental study suggests that when users perform complex tasks, a higher usability degree may be achieved compared to the adoption of a textual spatial SQL.     

Recycling polyethylene from automotive fuel tanks

Polyethylene (PE) from postuse automotive fuel tanks is considered a valuable material for mechanical recycling, and we assessed its properties, paying particular attention to transport properties and processability. The characterization included the study of the sorption–desorption isotherms, the rheological analysis of the molten materials and their processability. In particular, we obtained, sorption‐–desorption isotherms using a model molecule (n‐heptane) to simulate contact with the fuel. The measurements were carried out on films of PE blend for tanks and separately on the components of the blend. Rotational rheometry was carried out on scraps from used tanks and on virgin material for comparison. We performed some extrusion tests to evaluate the possibility of mechanical recycling of the postuse materials. In particular, we examined the melt‐fracture incoming conditions by making use of a twin‐screw extruder with a round die. Stress–strain measurements were carried out on films of virgin and used material, obtained with a press on a laboratory scale to evaluate the change of the mechanical properties of a manufacture obtained by reprocessing a polymer aged in contact with a mixture of liquids. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 347–351, 2002     

Use of a mathematical model in the analysis of survival curves of Daphnia magna exposed to toxicants

Chronic toxicity tests carried out on species of the genus Daphnia (Crustacea: Cladocera) are bioassays commonly used in ecotoxicology. Mortality in the cohorts exposed to toxicants can be examined by the analysis of survival curves. The shape of these curves may be very different because of inter-individual heterogeneity: the less rectangular is the shape the more different is the probability of dying of daphnids in the cohort. Aim of this paper is to analyze the characteristics-in particular the shape-of survival curves of cohorts of Daphnia magna exposed to heavy metals in chronic toxicity tests. Experimental curves were fitted by a mathematical model recently proposed, which puts emphasis just on this heterogeneity, described by the parameter of the model S(0). The information contained in S(0) is very useful for the present purposes: the higher the value of S(0) the less rectangular the shape of the curve and, as a consequence, the higher the age-at-death heterogeneity of the cohort is thought to be. The model contains a second parameter, omega, representing the maximum potential ability of the individuals to survive in a specific environment and is related with the maximal life span. The model fitted well the survival curves in most cases and both S(0) and omega showed statistically different values between treatments, useful for comparisons. It was concluded that S(0) provides a quantitative estimation of curve "rectangularization", useful to check different sensitivities to a specific toxicant concentration among daphnids belonging to the same cohort, while omega provides an estimate of maximal life span.     

Development of a control algorithm for air‐scour reduction in membrane bioreactors for wastewater treatment

BACKGROUND: Membrane bioreactors are used in an increasing number of wastewater treatment facilities because of their compactness and efficiency in solid‐liquid separation, but energy requirements are still higher than other competitive technologies such as conventional activated sludge. RESULTS: In this paper the development of an air‐scour control algorithm based on short‐term and long‐term membrane permeability evolution is presented. An open loop calibration and partial validation was carried out in a semi‐industrial scale pilot plant where manual changes in air‐scour flow had been previously carried out. The control system was successfully tested in closed loop in an industrial scale pilot plant, defining a maximum daily air‐scour decrease or increase of 6% of the air‐scour recommended by membranes suppliers. An average air‐scour saving of 13% and a maximum of 20%, calculated in terms of air flow saved, were achieved during the validation test without any apparent long‐term effect on membrane permeability. CONCLUSION: It was proven that the air‐scour control system is an important tool capable of reducing operational costs in MBR systems. Copyright © 2011 Society of Chemical Industry