Effect of PLA crystallization on the structure of biomimetic composites of PLA and clay

Composites of poly(lactic acid) (PLA) and organoclays with clay loadings of up to 80% were prepared as self‐supporting films using a doctor‐blading approach. Depending on the properties of the used organoclay, either intercalated nanocomposites or conventional composites were obtained. The incorporation of such high amounts of clay resulted in up to 10‐fold decrease in the water vapor transmission rate when compared to the pristine polymer. The effect of clay platelets on the crystallization of PLA chains was also studied; it was found that high amounts of clay hinder only the melt crystallization of the polymer, whereas cold crystallization proceeds as usual. On the other hand, the crystallization of PLA also influenced the composite structure by increasing the extent of intercalation of polymer between clay layers. This study thus shows that the change in the extent of clay‐polymer interactions is also an important factor in controlling nanocomposite structure, especially for high loading. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Linear viscoelastic behavior of compatibilized PMMA/PP blends

In this work, the morphology and linear viscoelastic behavior of PMMA/PP blends to which a graft copolymer PP‐g‐PMMA has been added was studied. The copolymer concentration varied from 1 to 10 wt % relative to the dispersed phase concentration. The rheological data were used to infer the interfacial tension between the blended components. It was observed that PP‐g‐PMMA was effective as a compatibilizer for PMMA/PP blends. For PP‐g‐PMMA concentration added below the critical concentration of interface saturation, two rheological behaviors were observed depending on the blend concentration: for 70/30 blend, the storage modulus, at low frequencies, increased as compared to the one of the unmodified blend; for 90/10 blend, it decreased. For 90/10 blend, the relaxation spectrum presented an interfacial relaxation time related to the presence of the compatibilizer (τ_β). For PP‐g‐PMMA concentrations added above the critical concentration of interface saturation, the storage modulus of all blends increased as compared with the one of the unmodified blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

CPFD flow pattern simulation in downer reactors

This study contributes with a computational fluid dynamic simulation based on the numerical solution of continuity and momentum balance equations in a three‐dimensional (3‐D) framework. The proposed down flow gas–solid suspension model includes a unit configuration and C_D drag coefficients recommended for these units. Computational particle fluid dynamics (CPFD) calculations using suitable boundary conditions and a Barracuda (version: 14.5.2) software allow predicting local solid densification and asymmetric “wavy flows.” In addition, this model forecasts for the conditions of this study higher particle velocity than gas velocity, once the flow reaches 1 m from the gas injector. These findings are accompanied with observations about the intrinsic rotational character of the flow. CPFD numerical 3‐D calculations show that both gas and particle velocities involve the following: (a) an axial velocity component, (b) a radial velocity component (about 5% of axial velocity component), and (c) an angular velocity component. The calculated velocity components and the rotational flow pattern are established for a wide range of solid flux/gas flux ratios. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1635–1647, 2013     

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     

Cover Image,Volume 141, Issue 17

The cover image by Lizandra Viana Maurat da Rocha highlights one of our innovative biodegradable films, which incorporated molybdenum trioxide and zinc oxide into the poly(butylene adipate-co-terephthalate) matrix through casting. The photo emphasizes its partial transparency and homogeneity. Some analytical results reported as FTIR, TD-NMR, XRD and TGA validates nanomaterial's exceptional mechanical and chemical properties. Icons below underscore its potential as an eco-friendly food packaging,with bacteriostatic features and no formation of microplastics after disposal. DOI: 10.1002/app.55294

     

Evidences of the Cerium Oxide-Catalysed DPF Regeneration in a Real Diesel Engine Exhaust

The active phase Ce_0.5Pr_0.5O₂ has been loaded on commercial substrates (SiC DPF and cordierite honeycomb monolith) to perform DPF regeneration experiments in the exhaust of a diesel engine. Also, a powder sample has been prepared to carry out soot combustion experiments at laboratory. Experiments performed in the real diesel exhaust demonstrated the catalytic activity of the Ce–Pr mixed oxide for the combustion of soot, lowering the DPF regeneration temperature with regard to a counterpart catalyst-free DPF. The temperature for active regeneration of the Ce_0.5Pr_0.5O₂-containing DPF when the soot content is low is in the range of 500–550 °C. When the Ce_0.5Pr_0.5O₂-containing DPF is saturated with a high amount of soot, pressure drop and soot load at the filter reach equilibrium at around 360 °C under steady state engine operation due to passive regeneration. The uncoated DPF reached this equilibrium at around 440 °C. Comparing results at real exhaust with those at laboratory allow concluding that the Ce_0.5Pr_0.5O₂-catalysed soot combustion in the real exhaust is not based on the NO₂-assisted mechanism but is most likely occurring by the active oxygen-based mechanism.     

Biosynthesis and Site of Production of Sex Pheromone Components of the Cerambycid Beetle, Hedypathes betulinus

We determined the site of pheromone production tissues and a partial route for the biosynthesis of the sex pheromone in Hedypathes betulinus (Coleoptera: Cerambycidae: Lamiinae), Brazil’s main green maté pest. Pheromone was found predominantly in the prothorax of males, suggesting that this is the region of production of pheromones in this insect. Scanning electron microscopy revealed small pores that may be associated with pheromone release in males; these pores also were observed in females. A deuterium-labeled putative precursor (geranyl acetone-D₅) of the sex pheromone of H. betulinus was synthesized. When applied to the prothorax of males, label from the precursor was incorporated into the pheromone components, confirming that pheromone production occurs in the prothorax and that the pheromone components are biosynthesized from geranyl acetone.     

Aggregation Behavior of Perfluorononanoic Acid/Sodium Dodecyl Sulfate Mixtures

The mixed system of an anionic hydrocarbon surfactant, sodium dodecyl sulfate, and a perfluorinated surfactant, perfluorononanoic acid (PFNA), was investigated by a combination of methods. The critical micellar concentrations (CMC) were determined over a wide range of sample compositions by surface tension, conductivity and UV–visible spectrophotometry using N-(4-nitrophenyl)perfluorononanamide as a molecular probe. The values of CMC obtained by different techniques were in good agreement. In addition, the aggregation numbers were determined in the mixtures with a low content of hydrocarbon surfactant, by measuring the fluorescence quenching of pyrene. The hydrodynamic radii of the aggregates were estimated through the diffusion ordered ¹⁹F- and ¹H-NMR spectroscopy. The values obtained are in agreement with those expected according to the measured aggregation numbers. The analysis of the data with different aggregation models suggests the formation of a non-ideal mixed micelle that is enriched in the perfluorinated surfactant when its mole fraction increases, and that is practically formed by PFNA only at mole fractions higher than 0.8.     

Corrosion inhibition of aluminum by organic coatings formulated with calcium exchange silica pigment

One of the first commercial ion-exchange anticorrosive pigments to be developed was Shieldex^® (Si/Ca). Its proposed corrosion protection mechanism, based on the retention of aggressive cations and the subsequent release of calcium cations, has created certain controversy. A number of studies have focused on the anticorrosive behavior of this pigment on carbon steel and galvanized steel to replace chromates (Cr⁶⁺) as inhibitor pigment, but none has considered its performance on aluminum or aluminum alloys. In this research, alkyd coatings have been formulated with Si/Ca pigment at different concentrations and applied on aluminum 1050 (Al 99.5%) specimens. These specimens have then been subjected to accelerated tests (condensing humidity, salt spray, and Kesternich) and natural weathering in atmospheres of different aggressivity. Corrosion performance has been also evaluated in the laboratory by electrochemical impedance spectroscopy. The study has also considered an organic coating with zinc chromate anticorrosive pigment for comparative purposes. The results obtained with organic coatings formulated with Si/Ca pigments confirm that they provide corrosion protection of the underlying aluminum substrate, even improving the behavior of the reference zinc chromate in some environmental conditions.