Destruction of chlorinated methanes by catalytic hydrolysis

CH₂Cl₂, CHCl₃ and CCl₄ react with water vapour to give CO₂ + HCl over-Al₂O₃, TiO₂ (rutile) and other acidic oxide catalysts; high conversions are obtained between 673 and 773 K. Rates are proportional to concentration of chlorinated methane and are inhibited by high concentrations of water; they are described by a Langmuir-Hinshelwood rate expression.     

Influence of polymerization conditions on the viscosity of polyacrylamide via experimental design

Polyacrylamide was synthesized by a free‐radical inverse emulsion technique and optimized via statistical experimental design, with the objective of developing a polymer with a high viscosity within this synthesis technique. The factors considered to affect the response variable, the viscosity of the polymer, were initiator (K₂S₂O₈) concentration (c), reaction temperature (T), stirring rate (r), and initiator addition method (s, batch or dropwise). An experimental design of the four factors at two levels (2⁴) was carried out to study the effect of these process variables on the viscosity of the polymer. The results show that the main factor having an effect on the viscosity was T, with smaller contributions from r and cs. The optimum combination of values for the factors yielding maximum viscosity was T = 65°C, c = 1 mM, r = 230 rpm, and s = dropwise addition. A close fit was obtained between the experimental and predicted values of the viscosity of the polymer solution. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5719–5724, 2006     

Conformational and packing energy calculations on the two crystalline modifications of poly (trans-1,4-butadiene)

Conformational and packing energy calculations have been performed on the two crystalline modifications of poly(trans-1,4-butadiene), and the results have been compared with experimental data. The conformational energy calculations predict the chain axis and conformation of the modification that is stable below 76°C, without any a priori assumption. Packing energy calculations on this modification show that the best space group is P2₁/a and the position of the chains is in good agreement with X-ray data. Conformational energy calculations on the modification that is stable above 76°C predict that the lowest energy conformation is a statistical sequence with a random distribution of the three minimum torsion angles around the single bonds adjacent to the double bond, with a trans conformation around the other single bond.     

Ascorbic acid consumption and serum levels in smokers and non-smokers adult men in Hermosillo,Sonora, México

Ascorbic acid is one of the important antioxidant nutrients that can aid in the prevention of oxidative cellular damage. Adequate dietary intake is essential as humans can not synthesize this vitamin. It has been reported that smokers require higher dietary intakes to maintain their serum levels. The objective of this study was to determine serum levels of ascorbic acid in young male smokers and non smokers in the city of Hermosillo, Sonora, Mexico. In addition, their dietary intake of ascorbic acid was determined by a 24 h dietary recall. The dietary intake of ascorbic acid in 12 smokers was 64 +/- 11 mg/d and in 13 non smokers it was 70 +/- 12 mg/d. The smokers in this study did not meet the dietary recommendation of 100 mg/d. Serum ascorbic acid values in smokers and non smokers were 24.2 +/- 6.9 mumol/L and 30.9 +/- 3.7 mumol/L respectively. No significant difference was found among the 2 groups. Although the average serum ascorbic acid values fell within the range considered normal, 50% of the smokers had individual values that were below 23 mumol/L, indicating that these subjects have hipovitaminosis. A positive correlation between intake and serum levels was obtained for smokers (r = 0.71; p = 0.03). The results of this study suggest smokers may be at increased risk for chronic diseases due to their low intake and low serum levels of ascorbic acid.     

Grafting of poly(methyl methacrylate) in aqueous slurries of wood pulp

Methods for initiating the free radical graft polymerization of methyl methacrylate onto wood pulp were investigated. Processes considered were all carried out in water slurries of the cellulose, for simplicity and low cost. Of the methods studied only three provided high conversions of monomer to polymer and reasonably good grafting efficiencies. These are ceric ion initiation, a redox reaction with ferrous ion and hydrogen peroxide, and initiation by potassium permanganate/nitric acid mixtures. The ferrous ion/peroxide redox system appears to be the best procedure overall, since it is inexpensive and environmentally innocuous. The best grafting frequency obtained was about one graft per 800 anhydroglucose units in the cellulose. High molecular weight poly(methyl methacrylate) polymers were made, with the grafted species larger than the corresponding homopolymers.     

Mechanical Behavior and Biodegradation of Poly(ε-caprolactone)/Starch Blends with and without Expansor

Summary The use of biodegradable polymers has provided an alternative to the problem of polymer-based products discarded in the environment. Poly(ε-caprolactone) (PCL) is a biodegradable polymer that has been used industrially, but it is very expensive. Starch is a potentially useful material for biodegradable plastics because of its natural abundance and low cost. The aim of this work was to examine the effect of adding azodicarbonomide (ADC) as an expansor to blends of PCL with corn starch. Different proportions, of ADC (0.1%, 0.2% and 0.3%, w/w) were added to pure PCL and to PCL/starch (50/50) blends and their properties were studied. Biodegradable blends of PCL with starch had a higher density than PCL alone and the addition of ADC reduced the density of the materials. The incorporation of starch increased the water absorption and ADC did not significantly alter this property. The incorporation of starch into PCL reduced the tensile strength and the elongation at break; ADC enhanced these reductions and also decreased the Young’s modulus of PCL. SEM showed that blends prepared with starch were immiscible, had a homogeneous dispersion of starch, and poor interfacial adhesion. The addition of ADC resulted in cells in the interior of the polymers. The 50/50 PCL/starch blends biodegraded faster than PCL, and ADC had no significant influence on the biodegradation of the blends but inhibited the biodegradation of PCL.     

Hierarchical multi-label classification using local neural networks

Hierarchical multi-label classification is a complex classification task where the classes involved in the problem are hierarchically structured and each example may simultaneously belong to more than one class in each hierarchical level. In this paper, we extend our previous works, where we investigated a new local-based classification method that incrementally trains a multi-layer perceptron for each level of the classification hierarchy. Predictions made by a neural network in a given level are used as inputs to the neural network responsible for the prediction in the next level. We compare the proposed method with one state-of-the-art decision-tree induction method and two decision-tree induction methods, using several hierarchical multi-label classification datasets. We perform a thorough experimental analysis, showing that our method obtains competitive results to a robust global method regarding both precision and recall evaluation measures.     

Influence of processing conditions on the morphological and mechanical properties of compatibilized PP/LCP blends

The main aim of this work is to study the influence of the application of different processing conditions on the morphological and mechanical properties of thermoplastic/LCP blends, in which the viscosity ratios are inferior to unity and decrease with increasing temperature. The way the microstructure evolves along the extruder determines the final morphology and thus, the mechanical performance of the systems. In the present case, the mechanical properties are related with the degree of fibrillation in the final composites. The best degree of fibrillation was obtained for low screw speeds and temperatures and for intermediate outputs. The use of high screw speeds and processing temperatures results in a decrease of the viscosity ratio, in the former case via an increase in the viscous dissipation, at the regions of higher shear rates (kneading‐elements). The application of a lower processing temperature is advantageous for deformation, break‐up, and fibrillar formation because of the higher viscosity ratios and higher shear stresses involved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Ethanolysis of castor and cottonseed oil: A systematic study using classical catalysts

Several classical catalytic systems for the transesterification reaction have been used to produce FA ethyl esters (FAEE) from castor and cottonseed oils The effects of the amount and nature of the catalyst, and of the reaction temperature, on the yields of FAEE were determined. The most efficient transesterification of castor oil was achieved in the presence of methoxide and acid catalysts, whereas for cottonseed oil, which has a composition that is much more similar to most vegetable oils than is castor oil, the highest yields of FAEE were obtained following base-catalysed ethanolysis.     

Mechanism and kinetics of transesterification in poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalene dicarboxylate) polymer blends

In a previous work [L. Alexandrova, A. Cabrera, M.A. Hernández, M.J. Cruz, M.J.M. Abadie, O. Manero, D. Likhatchev, Polymer 43 (2002) 5397. [1]], a model compounds study on the kinetics of a transesterification reaction in poly(ethylene terphthalate)-poly(ethylene naphthalene 2,6-dicarboxylate), PET-PEN blends, resulting from melt processing, was simulated using model compounds of ethylene dibenzoate (BEB) and ethylene dinaphthoate (NEN). A first-order kinetics was established under pseudo first-order conditions for both reactants, and thus the overall transesterification reaction was second-order reversible. Direct ester-ester exchange was deduced as a prevailing mechanism for the transesterification reaction under the conditions studied.In this work, the actual PET-PEN system was melt processed by mixing the polymers below the critical reaction temperature in a twin-screw extruder. Thereafter, the reaction was induced by temperature in open glass ampoules. A second order reversible kinetics was measured, in agreement with the kinetics established in the previous model compounds study. The equilibrium constant value corresponds to a forward rate constant which is four times larger than the reverse rate constant. The activation thermodynamic parameters confirmed the direct ester-ester exchange mechanism for the reaction.