On the dynamic mechanical behavior of poly(methyl methacrylate) reinforced with Kevlar fibers

The dynamic mechanical relaxation behavior of poly(methyl methacrylate) reinforced by continuous parallel Kevlar-49 fibers is investigated here on samples with several fiber volume fractions. The shifts in the temperature of the main relaxation of the matrix are interpreted according to free volume considerations and with the help of a thermomechanical block model. The dependence of the storage and loss moduli both on temperature and fiber content found experimentally can be reproduced by the model. It is not necessary to rely on the existence of an interphase to account for the modifications evidenced by the spectrum of the matrix, which can be explained on the basis of the two phase model.     

Combining multiway principal component analysis (MPCA) and clustering for efficient data mining of historical data sets of SBR processes.

A methodology based on Principal Component Analysis (PCA) and clustering is evaluated for process monitoring and process analysis of a pilot-scale SBR removing nitrogen and phosphorus. The first step of this method is to build a multi-way PCA (MPCA) model using the historical process data. In the second step, the principal scores and the Q-statistics resulting from the MPCA model are fed to the LAMDA clustering algorithm. This procedure is iterated twice. The first iteration provides an efficient and effective discrimination between normal and abnormal operational conditions. The second iteration of the procedure allowed a clear-cut discrimination of applied operational changes in the SBR history. Important to add is that this procedure helped identifying some changes in the process behaviour, which would not have been possible, had we only relied on visually inspecting this online data set of the SBR (which is traditionally the case in practice). Hence the PCA based clustering methodology is a promising tool to efficiently interpret and analyse the SBR process behaviour using large historical online data sets.     

The effect of the molecular weight on the glass transition temperature in amorphous poly(ethylene terephthalate)

Summary The glass transition temperature of amorphous and fractionated poly(ethylene terephthalate) has been measured by differential scanning calorimetry. The application of the Fox-Flory equation for the range of molecular weights between 37100 and 4500 gives the values of Tg=342.4 K and Kg=51200. The low value of Kg is interpreted by the free volume theory. The flex energy of the chain is evaluated by the Gibbs-Di Marzio theory with a value of 1483 cal/mol. These results are compared with those obtained by other authors for the poly(ethylene adipate) and the poly(diethylene terephthalate).     

Behaviour of amorphous poly(ethylene terephthalate) annealed at T<T g by thermally stimulated currents

Thermally stimulated current (TSC) discharges in open circuit of amorphous poly(ethylene terephthalate) (PET) corona-charged electrets show a heteropolar relaxation at 87 °C, ₁ between and peaks. This relaxation tends to become homopolar when the sample is annealed at temperatures below the glass transition temperature. This is due to the formation of a trapped charge density on the surface of the material that originates, during the TSC discharge, a current that counteracts the one that results in ₁ This trapping effect, which initially is null, increases with annealing due to the rise in resistivity. On the other hand, TSC discharges in short-circuited annealed samples result in a heteropolar peak, ^*, that corresponds to ₁ The area of ^* increases with the annealing time in a bounded way. This peak is related to the formation of thermal nuclei (embryos) in the bulk of the material that act as heterogeneities. This suggests that ₁ is associated with a barrier-type polarization. If the annealed sample is heated to temperatures above the glass transition temperature, the tendency to the inversion of ₁ vanishes and ^* disappears, whereas and are modified. This suggests that relaxation is related to a Maxwell-Wagner-Sillars effect.     

Effect of Sr2+ doping on sintering behavior,microstructural development and electrical properties of LaPO4·nH2O nanorods prepared by dry mechanical milling

The effect of Sr²⁺ doping on the presence of second phases, sintering behavior, microstructural development, and electrical properties of LaPO₄·nH₂O nanorods (La_1?xSr_xPO_4?x/2 where x = 0.025 and 0.05) obtained by a dry mechanochemical milling process was investigated. When Sr²⁺ is present monazite-type La_1?xSr_xPO₄ nanopowders were obtained instead of rhabdophane-type LaPO₄·nH₂O. In addition, Sr²⁺ doping implies a larger P/La ratio and it enhances the formation of lanthanum tryoxophosphate (La(PO₃)₃), a thermodinamically stable phase, in doped samples. Dilatometric studies reveal a shift of the maximum shrinkage rate at lower temperatures for doped samples, with larger shifts with higher Sr²⁺ contents. This shift is related to the presence of oxygen vacancies but also to a higher content of La(PO₃)₃. Furthermore, the derivative of the linear shrinkage curves for all the samples showed peaks at temperatures higher than 1300 °C that are associated to the volatilization of P₄O₁₀ gas and to the recrystallization of monazite from the incongruent melting of La(PO₃)₃. After the dilatometric tests at 1500 °C the samples showed polygonal grains with a bimodal size distribution. For the doped samples the smaller grains do not present Sr²⁺ in their composition and it is related to those grains form from the recrystallization of monazite-LaPO₄ formed in turn from La(PO₃)₃. The total conductivity of the studied samples (x = 0.05) is higher for the samples sintered at 1000 °C for 1 h than for those sintered at 1500 °C without any dwell time. It can be due in part to the fact that the smaller grains of the samples sintered at 1500 °C do not contain Sr²⁺ and it can hinder the charge transport.     

Environmental risk index: A tool to assess the safety of dams for leachate

Dams for leachate store very toxic substances that contain a large amount of organic material and, probably, heavy metals; they therefore constitute an important threat to the environment. Existing models of environmental risk assessment for landfills do not take into consideration the specific risk that leachate dams may represent for the environment. In this paper a methodology to improve the environmental safety is presented according to the parameters used in their construction and management. In order to do that, the following characteristics of the dam must be known: (1) geotechnical stability, (2) erosion of downstream slope, (3) type of sealing of the dam, (4) overtopping probability, (5) volume of leachate stored inside the dam and (6) pollution load of leachate. Once these parameters have been calculated, they are transformed by means of rating curves into homogeneous units, so as to make it possible to operate between them. From the study and analysis of these parameters an environmental risk index for a dam for leachate can be calculated. If the environmental risk index exceeds an established value then it involves a dam for leachate with high environmental risk, therefore preventive measures in its design, construction and management would be necessary.     

Squamous cell carcinoma and infection in a solitary hepatic cyst

A case of mediastinal cavernous hemangioma was reported. An abnormal shadow on the chest X-ray film was pointed out in a 55-year-old male. CT scan and MRI revealed a right posterior mediastinal tumor but did not aid in the final diagnosis. We underwent extirpation of the tumor through thoracoscope and confirmed to be a cavernous hemangioma histologically. No major vascular connections between the tumor and major vessels were found. It was useful of thoracoscopic surgery in this case.     

Multifunctional hybrid materials composed of [60]fullerene-based functionalized-single-walled carbon nanotubes

We report the synthesis and characterization of several hybrid [60]fullerene-SWCNT materials that combine [60]fullerenes with appended photoactive ferrocenyl or porphyrinyl functionalities and SWCNTs into a single multifunctional structure, where the dyads are covalently attached to the exo-surface of SWCNTs. The structural properties of all hybrids have been characterized using a large variety of spectroscopic and HR-TEM techniques. Raman spectra showed how all SWCNTs were functionalized and the presence of functional groups in the nanotube derivatives. Furthermore, these spectra reveal a new electronic activity of the compounds due to the interaction of the functional groups with the SWCNT frameworks. XPS investigations have documented the presence of [60]fullerene derivatives around the exo-surface of the oxidized SWCNT walls, exhibiting a characteristic photoelectron N 1s emission peak at 400.3 eV. Very importantly, by means of HR-TEM investigations we have also observed the presence of the [60]fullerene functions on the SWCNT outer surface by imaging spherical structures. The presence of the porphyrinyl and ferrocenyl fragments, which can act as effective chromophores and electroactive species, makes this class of materials very interesting for applications in optoelectronics and photovoltaics, and bio-applications, for example in the field of diagnosis and treatment.