Effect of water on the oxygen barrier properties of poly(ethylene terephthalate) and polylactide films

The aim of this work was to study the variations in the oxygen diffusion, solubility, and permeability coefficients of polylactide (PLA) films at different temperatures (5, 23, and 40°C) and water activities (0–0.9). The results were compared with the oxygen diffusion, solubility, and permeability coefficients obtained for poly(ethylene terephthalate) (PET) films under the same experimental conditions. The water sorption isotherm for PLA films was also determined. Diffusion coefficients were determined with the half‐sorption time method. Also, a consistency test for continuous‐flow permeability experimental data was run to obtain the diffusion coefficient with the lowest experimental error and to confirm that oxygen underwent Fickian diffusion in the PLA films. The permeability coefficients were obtained from steady‐state permeability experiments. The results indicated that the PLA films absorbed very low amounts of water, and no significant variation of the absorbed water with the temperature was found. The oxygen permeability coefficients obtained for PLA films (2–12 × 10^?18 kg m/m² s Pa) were higher than those obtained for PET films (1–6 × 10^?19 kg m/m² s Pa) at different temperatures and water activities. Moreover, the permeability coefficients for PLA and PET films did not change significantly with changes in the water activity at temperatures lower than 23°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1790–1803, 2004     

Determination of hydroperoxides and structures by high-performance liquid chromatography with post-column detection with diphenyl-1-pyrenylphosphine

A high-performance liquid chromatographic method, using post-column detection with diphenyl-1-pyrenyl-phosphine (DPPP), was developed for the quantitative and qualitative determination of isomeric lipid hydroperoxides (OOH). The OOH eluted from a normal-phase column were passed through a photodiode array detector and then mixed with DPPP solution in a reaction coil heated at 80°C. DPPP oxide formed by the reaction with OOH was determined by monitoring the fluorescence intensity at 380 nm and excitation at 352 nm. The conjugated diene OOH (13-cis, trans- and 9-cis, trans-OOH) and nonconjugated OOH (12-cis-trans- and 10-cis, trans-OOH) from photosensitized oxidation of methyl linoleate were determined in a molar ratio of 31∶29∶19∶21, respectively. However, only the two conjugated hydroperoxides were detected by ultraviolet absorption at 234 nm. Further applications were carried out for the determination of OOH of methyl oleate and methyl linolenate. This method proved to be useful for the determination of the OOH containing both conjugated and nonconjugated diene structures.     

Structure–property relationships of poly(urethane urea)s with ultra‐low monol content poly(propylene glycol) soft segments. I. Influence of soft segment molecular weight and hard segment content

Structure–property relationships in poly(urethane urea)s synthesized with ultra‐low monol content poly(propylene glycol) soft segments were investigated as soft segment molecular weight (2000, 4000, and 8000 g/mol) and hard segment content (6.3 and 9.0 wt %) were varied. Morphological features such as interdomain spacing and interphase thickness were quantified and revealed with small‐angle X‐ray scattering (SAXS) and atomic force microscopy (AFM). The thermal and mechanical behavior was assessed with a dynamic mechanical analyzer (DMA) and by differential scanning calorimetry (DSC) and stress‐strain tests. Hard segment content, over the limited range studied, had little effect on the morphology and soft segment thermal and mechanical properties. The molecular weight of the soft segments had considerably more influence on the morphology and mechanical properties. Increasing soft segment molecular weight resulted in greater interdomain spacings, as shown by SAXS, and a noticeable change in the structure, as shown by AFM. Additionally, as soft segment molecular weight decreased the soft segment glass transition broadened and rose to higher temperatures. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 229–243, 2002; DOI 10.1002/app.10168     

SOLUBILITY OF CO2 AND H2S IN A HINDERED AMINE SOLUTION

The solubility of H₂S and CO₂ in aqueous solutions of the sterically hindered amine, 2-amino-2-methyl-1-propanol (AMP), was determined at 40 and 100°C. Partial pressures of C)₂ ranged from approximately 2 to 6000 kPa and of H₂S from 2 to 2200 kPa. The solubility results were compared with previously reported acid gas solubilities in aqueous monoethanolamine (MEA) solutions.     

The Thermodynamic Properties of Silicon Oxynitride

A critical assessment of thermal and equilibrium data for silicon oxynitride (Si₂N₂O) is presented. Selected values for the heat of formation of Si₂N₂O from the elements and the absolute entropy of Si₂N₂O at 298.15 K are ΔH⁰_f,298=−947.7 ± 5.4 kJ/mol and S⁰₂₉₈= 45.35 ± 0.4 J/mol·K, respectively. A table of thermodynamic functions for Si₂N₂Ofrom 298 to 2500 K, which has been calculated from the analysis of the literature data, is also presented.     

Flow Regime Maps for Flow of Liquid Through Downcomer in a Turbulent Bed Contactor

The provision of a downcomer to classical turbulent bed Contactor (TBC) increases the gas treating capacity of the equipment. When the downcomer is provided, it is expected that all the liquid passes through the downcomer only without any liquid flow through the distributor. In the present study, the operational regime for the flow of liquid only through the downcomer is experimentally evaluated for various geometric parameters and particle characteristics. It is observed that the preferred operational regime without dumping and weeping increases with an increase in Archimedes number and downcomer diameter, and decreases with an increase in static bed height and downcomer weir height. Correlations are proposed to satisfactorily predict experimentally observed operational regime.     

Scalable Realistic Rendering with Many‐Light Methods

Recent years have seen increasing attention and significant progress in many‐light rendering, a class of methods for efficient computation of global illumination. The many‐light formulation offers a unified mathematical framework for the problem reducing the full lighting transport simulation to the calculation of the direct illumination from many virtual light sources. These methods are unrivaled in their scalability: they are able to produce plausible images in a fraction of a second but also converge to the full solution over time. In this state‐of‐the‐art report, we give an easy‐to‐follow, introductory tutorial of the many‐light theory; provide a comprehensive, unified survey of the topic with a comparison of the main algorithms; discuss limitations regarding materials and light transport phenomena and present a vision to motivate and guide future research. We will cover both the fundamental concepts as well as improvements, extensions and applications of many‐light rendering.     

Creep and Stress Rupture Behavior of an Advanced Silicon Nitride: Part I, Experimental Observations

Cylindrical buttuohead specimens of an advanced silicon nitride were tested in uniaxial tension at temperatures between 1422 and 1673 K. In the range 1477 to 1673 K, creep deformation was reliably measured using high-temperature contact probe extensometry. Extensive scanning and transmission electron microscopy has revealed the formation of lenticular cavities at two-grain junctions at all temperatures (1422–1673 K) and extensive triple-junction cavitation occurring at the higher temperatures (1644–1673 K). Cavitation is believed to be part of the net creep process. The stress rupture data show stratification of the Monkman–Grant lines with respect to temperature. Failure strain increased with increase in rupture time or temperature, or decrease in stress. Fractography showed that final failure occurred by subcritical crack growth in all specimens.     

Iron(II)‐based catalysts for ethene oligomerization

The synthesis of iron(II) complexes with various tridentate di(imino)pyridine ligands and their potential as ethene oligomerization catalysts are described. The ligands are characterized by ¹H‐ and ¹³C‐NMR spectroscopy and the complexes only by mass spectrometry due to their paramagnetism. After activation either with methylalumoxane (MAO) or with a heterogeneous cocatalyst consisting of partially hydrolyzed trimethylaluminum and silica gel, the prepared complexes proved to be good catalysts for the oligomerization of ethene. 1‐Octene, 1‐hexene, and 1‐decene were the major products, formed in very high isomeric purity (99.9 %). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 476–482, 2003     

Thermal degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

The degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005