Modeling the rheology of SR1500 and LY556 epoxies under manufacturer's recommended cure cycles after viscosimetry and rheometry characterization

The evolution of the viscosity of two commercial epoxy resin systems subjected to manufacturer's recommended cure cycles was studied in detail. The two systems were characterized through rotational viscosimetry and oscillatory rheometry. It was observed that the different size of the samples in the two setups influenced the kinetics and, thus, the evolution of the cure and viscosity. The differences resided in the effective temperature experienced by the resin at each moment. Original rheological constitutive relations are proposed for each resin system and mass quantity, aiming to capture the “real” processing conditions. All the experimental and modeling procedures are described in detail and the new rheological constitutive relations are presented. POLYM. ENG. SCI., 54:831–839, 2014. © 2013 Society of Plastics Engineers     

Photocatalytic degradation of malic acid using a thin coated TiO2‐film: Insights on the mechanism of photocatalysis

Decontamination of opaque fluids using photocatalysts and near Ultraviolet (UV) irradiation involves major technical challenges. This study considers a thin TiO₂ layer placed in a new Chemical Reactor Engineering Centre (CREC)‐photoreactor cell. This new photoreactor cell is used for the photocatalytic degradation of malic and malonic acids, typical apple juice components. Conversion of organic species can only proceed through the “dark side” of the TiO₂ layer, which is in direct contact with the fluid. Under the selected operating conditions both external mass‐transfer limitations and photolysis are found to be negligible. Macroscopic radiation balance shows that 92% of near UV radiation is absorbed by the ‘back side” of the TiO₂‐film. Photocatalytic degradation experiments with 10, 20, 30, and 40 ppm malic acid initial concentrations, show that malonic acid is a main intermediate. Complete malic acid conversion occurs after 5–8 h of irradiation. Kinetic modeling of malic and malonic acid photodegradation with kinetic parameter estimation is performed using both an “in series” and an “in series‐parallel” reaction networks. The “in series‐parallel” reaction network displays better ability for predicting CO₂ formation, showing maximum quantum yields of 14.2%. Given that in the CREC‐photoreactor cell with a thin TiO₂‐film, photocatalysis can only proceed via the transfer of mobile “h⁺” sites from the irradiated side to the “dark side', this study demonstrates the significance of this step on the overall photocatalysis mechanism. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3286–3299, 2014     

Polymer networks based in (4‐vinylbenzyl)‐N‐methyl‐D‐glucamine supported on microporous polypropylene layers with retention boron capacity

New cellulose porous layers, with capacity to transport and retain boron from aqueous solution, were developed via interpenetrating polymer network (IPNs). These polymer systems were made to assemble mimetic systems of plant root tissue for the study of available boron transport. For that cellulose porous layers supported on polypropylene matrix were used as primary network for the formation of IPN. A vinyl monomer, (4‐vinylbenzyl)‐N‐methyl‐d ‐glucamine (VbNMDG), was synthesized at three concentration levels and cellulose ultrafiltration membranes were modified by in situ polymerization in the inside of the pores. Change of hydrophilicity, percent of secondary network, permeability and retention properties were studied. The formation of IPNs in the inside of the pores decreased the permeabilities of polymer layers. In addition, a decrease of hydrophilicity was seen. A linear increase of boron retention in function of VbNMDG concentrations was observed for the different boron concentrations and a negative effect on retention capability was evidenced for several charge and discharge cycles. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40653.     

The corrosion-inhibiting effect of polypyrrole films doped with p-toluene-sulfonate,benzene-sulfonate or dodecyl-sulfate anions,as coating on stainless steel in NaCl aqueous solutions

This article presents a study of the conditions for electro-synthesis of polypyrrole (PPy) films on stainless steel, in the presence of the anions p-toluene-sulfonate (pTS), benzene-sulfonate (BS) or dodecyl-sulfate (DS). Cyclic voltammetry (CV) was used in the synthesis of the polypyrrole films on the stainless steel (SS). These polymeric films were characterized by IR and UV–vis spectroscopy and their morphology and thickness were analyzed by scanning electron microscopy (SEM). Their performance as protective films against corrosive processes presented by the SS/PPy-pTS, SS/PPy-BS or SS/PPy-DS systems was evaluated in 0.1 M NaCl aqueous solution. The study of the corrosion processes of the stainless steel/polymer systems was conducted through measurements of open circuit potential (E_OCP), polarization curves (PC) and electrochemical impedance spectroscopy (EIS). The results showed that the protective capacity of these polymeric systems on stainless steel, mainly with regard to pitting, depends on the nature of the anion dopant used during electro-synthesis of the PPy film. The best performance was seen with the dopants pTS and BS.     

Zapallar II住宅

此度假屋的地面长且陡峭,自北向南落下,高处连接一条通往海边的高速路,低处连接去本地Zapallar街的道路。从高处到低处可以在这里看到度假村和海湾壮丽优美的景色。     

Effect of the vinyl concentration on the structural and rheological characteristics of peroxide‐modified high‐density polyethylenes

The effect of the hydrogenation of the terminal vinyl groups on the peroxide modification and rheological properties of high‐density polyethylene (HDPE) was investigated. The aim of the study was to determine exclusively the effect of the terminal vinyl groups on the peroxide crosslinking and rheological properties of HDPE with one polymer type. This was achieved by hydrogenation of the terminal vinyl groups of a commercial HDPE to obtain an identical material from a structural point of view, which differed only in the nature of the terminal unsaturations, and the comparison of its level of peroxide crosslinking with that of the original polymer. Hydrogenated and unhydrogenated polymer samples were modified at 170°C with different amounts of organic peroxide ranging from 125 to 5000 ppm. Changes in the molecular structure were determined by Fourier transform infrared spectroscopy, size exclusion chromatography, and rheological measurements. Hydrogenation of the terminal groups of the original polymer significantly reduced the rate of modification or crosslinking. The dynamic viscosity and elasticity increased with the level of peroxide modification. Unhydrogenated samples exhibited rapid increases in viscosity and elastic modulus, whereas their hydrogenated counterparts required about 500% of the amount of peroxide needed for the unhydrogenated sample to attain similar structural changes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Comparative study of the effect of sulfur on the morphology and rheological properties of SB‐ and SBS‐modified asphalt

The modification of asphalt with styrene‐ butadiene block copolymers and sulfur was studied to elucidate the effect of the molecular characteristics of the polymer, polymer content, and sulfur/polymer ratio on the physical properties of modified asphalts. Two types of styrene‐butadiene copolymers were used (SB and SBS), which differed considerably in terms of their chain architecture, average molecular weights, and size and distribution of their polybutadiene and polystyrene blocks, as shown by gel permeation chromatography, infrared spectroscopy, nuclear magnetic resonance, and differential scanning calorimetry. Sulfur/polymer/asphalt blends were prepared by a hot mixing process and characterized by conventional tests, fluorescence microscopy, and rheology. The results revealed that the morphology of the blends is strongly dependent on polymer concentration and sulfur/polymer ratio. In‐depth rheological characterization showed that the thermomechanical properties changed considerably upon addition of small amounts of sulfur. Collectively, these results suggest that sulfur increases the compatibility between polymer and asphalt by crosslinking polymer chains. Interestingly, the rheological behavior of blends prepared with a combination of SB and sulfur was similar to that exhibited by blends prepared with SBS either in the presence or absence of sulfur. This is explained by assuming that the addition of small amounts of sulfur to SB‐modified asphalt facilitates the formation of an elastomeric network that resembles the one found in SBS‐modified asphalt, effectively contributing to asphalt reinforcement. Nonetheless, the exact dosage of sulfur must be carefully controlled to prevent gel formation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of Structured Phosphatidylcholine Containing n-3 PUFA Residues via Acidolysis Mediated by Immobilized Phospholipase A<Subscript>1</Subscript>

Structured phosphatidylcholine (PC) was successfully synthesized by acidolysis of PC derived from soybean with n-3 polyunsaturated fatty acids (PUFA) obtained from fish oil using an immobilized phospholipase-A₁ from Thermomyces lanuginosus/Fusarium oxysporum as the biocatalyst. The effect of water activity in the range from 0.43 to 0.93 on n-3 PUFA residue content was investigated. The immobilized phospholipase was more active at water activities greater than 0.53. The yield of PC decreased as the water activity increased from 0.43 to 0.93. The yield of lysophosphatidylcholine (LPC) increased significantly during the first 4 h of reaction as a consequence of hydrolysis of the PC. As the enzyme loading increased, the proportion of n-3 PUFA residues in the PC and LPC present at various times in the mixture of these species increased to as much as 15% of the total weight of substrate. For all enzyme loadings tested, both the proportion of n-3 PUFA residues in the total PC (unreacted and modified) and the production of LPC increased significantly when the reaction time was increased, although differences in n-3 PUFA content were observed. When both the n-3 PUFA content of the PC and the total yield of PC are considered, the optimum water activity and enzyme loading for production of structured PC and LPC are 0.65 and 15%, respectively.     

Uncertainty determination methodology, sampling maps generation and trend studies with biomass thermogravimetric analysis

This paper investigates a method for the determination of the maximum sampling error and confidence intervals of thermal properties obtained from thermogravimetric analysis (TG analysis) for several lignocellulosic materials (ground olive stone, almond shell, pine pellets and oak pellets), completing previous work of the same authors. A comparison has been made between results of TG analysis and prompt analysis. Levels of uncertainty and errors were obtained, demonstrating that properties evaluated by TG analysis were representative of the overall fuel composition, and no correlation between prompt and TG analysis exists. Additionally, a study of trends and time correlations is indicated. These results are particularly interesting for biomass energy applications.     

32 bin near-infrared time-multiplexing detector with attojoule single-shot energy resolution

We present two implementations of photon counting time-multiplexing detectors for near-infrared wavelengths, based on Peltier cooled InGaAs/InP avalanche photodiodes. A first implementation is motivated by practical considerations using only commercially available components. It features 16 bins, pulse repetition rates of up to 22 kHz, and a large range of applicable pulse widths of up to 100 ns. A second implementation is based on rapid gating detectors, permitting dead times below 10 ns. This allows one to realize a high dynamic-range 32 bin detector, able to process pulse repetition rates of up to 6 MHz for pulse widths of up to 200 ps. Analysis of the detector response at 16.5% detection efficiency reveals a single-shot energy resolution on the attojoule level.