Low Oxygen Permeability Research Articles

Yttrium silicate coating system for oxidation protection of C/C–Si–SiC composites: Electrophoretic deposition and oxygen self-diffusion measurements

Yttrium silicate (YSI) coatings are promising complements to SiC coatings for protecting C/C–Si–SiC composites against oxidation owing to the pronounced chemical and mechanical properties of this material (low Young's modulus, low thermal expansion coefficient, low evaporation rate and oxygen permeability, good erosion resistance). Under control of deposition voltage and duration, yttrium silicate coatings of various thicknesses were electrophoretically deposited from powder suspensions. The protectiveness of these coatings was tested by means of thermogravimetric analysis in air. Diffusion data for oxygen in yttrium silicate needed to correlate the experimentally obtained oxidation rates in a phenomenological model were obtained by the IEDP (isotope exchange depth profiling) method from tracer diffusion measurements in single crystalline yttrium silicate and compared to diffusion data in mullite.

Novel Hydrothermal Electrodeposition Technology For Preparation Of Yttrium Silicates Coating On Carbon/Carbon Composites

Carbon/carbon (C/C) composites exhibit excellent mechanical properties such as high strength-to-weight ratio and the retention of strength at high temperature. The most important factor which currently precludes the use of C/C composites at high temperature applications is their oxidation in an oxygen containing atmosphere [I]. The deposition of an oxidation resistant coating on the C/C surface is one of the reasonable choices to solve this problem. Yttrium silicates have been shown to possess the required properties for use in oxidation resistant coatings. These can be summarized as low Young's modulus ... low thermal expansion coefficient, low oxygen permeabIlity and good erosion resistance [2]. The preparation technology is considered to be extremely important to attainina .. . 0 an antIcIpatIve yttrium silicate coating. Yttrium silicates coatings have been prepared by plasma spray and slip dipping method [3-5]. These preparation processes, however, must be carried out at hi~h temperature which will result in bad bonding between the coating and carbon substrate. The purpose of this work is to design a novel low temperature preparation technology to deposit yttrium silicate coating on C/C composites. Electrodeposition technology has been used to produce various coatings because of its numerous advantages such as the low cost, high efficiency and simple operation and, in particular, homogeneous coating on substrates with complex structures can be easily achieved. Moreover, the special physical and chemical conditions provided by a hydrothermal environment could effecti vely accelerate the speed of mass transfer and reduce the crystallization point without subsequent high temperature heat treatment as in conventional technology. In other words. hydrothermal technology makes it possible to acquire highl; crystallized coatings at low temperature with fewer t1aws. Therefore, the combination of electrodeposition and hydrothermal technologies is a promising way to deposit ceramic coatings such as yttrium silicates on constructed substrates.

Shelf‐life of a dragee product based on sunflower kernel depending on packaging materials used

SummaryIn this study, we investigated the quality and shelf‐life of a dragee product obtained by coating a confectionery sunflower kernel with sugar syrup. The product was packed in oriented polypropylene/oriented polypropylene, oriented polypropylene/metallised oriented polypropylene, polyester/polyethylene and kept at room temperature in daylight for 5 months. At the beginning of the experiment, the dragee product was in the category of excellent sensory quality (total score of sensory evaluation is between 18.0 and 20.0) in terms of its colour, smell, taste, mastication and structure. During the storage, these properties changed and the product lost its stability. Peroxide value in the dragee product increased from 0.5 to 9.0 mmol O/kg during the 5 months of storage. The free fatty acid content also increased from 1.3% in fresh dragee product to 2.5% after 5 months of storage. The packaging material metallised polyester/polyethylene, labelled metPET/PE, has the lowest oxygen permeability (8.0 mL m−2/dan Δp 1 bar) and because of this it had the strongest influence in the prevention of hydrolytic and oxidative changes in the final product.

Preparation and Properties of Biodegradable Multilayer Films Based on Soy Protein Isolate and Poly(lactide)

Multilayer film composed of a soy protein isolate (SPI) inner layer and poly(lactide) (PLA) outer layers were prepared by a simple solvent casting method in order to exploit the advantageous properties of both film materials. Tensile strength and elongation at break of the multilayer film were 17.0 ± 0.3 MPa and 176.9 ± 27.9%, respectively. Especially the tensile strength of the multilayer film increased more than 5-fold compared with that of the SPI film. The mechanical properties of the multilayer film were comparable to those of low-density polyethylene (LDPE) or high-density polyethylene (HDPE) films. The lamination of PLA layers on SPI film also resulted in desirable gas barrier properties of the film with both low water vapor permeability (WVP) of PLA and low oxygen permeability (OP) of SPI. The WVP of the multilayer film [(6.66 ± 0.27) × 10-14 kg·m/m2·s·Pa] decreased 40-fold compared with that of the SPI film, and the OP of the multilayer film [(2.40 ± 0.24) × 10-18 m3·m/m2·s·Pa] decreased more tha...

Edible films made from membrane processed soy protein concentrates

Edible films were prepared from membrane processed soy protein concentrate (MSC) at various film forming solution pHs, and their mechanical, barrier, and physical properties were compared with soy protein isolate (SPI) films. As the film solution pH increased from 7 to 10, the resulted MSC films were more transparent, yellowish, and had lower oxygen permeabilities. However, tensile strength (TS), modulus of elasticity (ME) and water vapor permeabilities of MSC films were not affected by film solution pHs. The values of MSC films prepared at pH 7 were not significantly ( P > 0.05 ) different from those of SPI films prepared at alkaline solutions (pH 8–10). The uniform TS and ME values of MSC film over the wide film solution pH ranges were attributed to the higher solubility of MSC at pH 7. For the films formed at neutral film solutions (pH 7.0), MSC films showed significantly ( P < 0.05 ) higher elongation value, film solubility, and transparency compared to SPI films.

Staphylococcus aureus Ulcer Associated With Continuous Wear of Silicone Hydrogel Contact Lenses

To report a case of culture-positive Staphylococcus aureus keratitis associated with continuous wear of lotrafilcon A lenses. The case report of a patient who developed microbial keratitis while wearing lotrafilcon A contact lenses is presented. A 41-year-old white man had worn polymacon contact lenses successfully for at least 10 years. He habitually replaced the lenses every 1 to 2 years and frequently wore them continuously for up to 3 months. He was refitted with silicone hydrogel lenses and was advised to remove and replace the lenses monthly. Approximately 18 months later, he developed a midperipheral, culture-positive S. aureus ulcer in his right eye. He was treated with fortified cefazolin and gentamicin for 2 weeks, followed by ciprofloxacin for 2 weeks. The ulcer resolved completely. The patient's final visual acuity was 20/20 in the affected eye. The increased oxygen permeability of silicone hydrogel contact lens materials may reduce the risk of hypoxic complications of continuous contact lens wear. As this case shows, however, even patients who have continuously worn lenses with very low oxygen permeability without incident can develop microbial keratitis when wearing silicone hydrogel lenses. Contact lens practitioners should inform patients of the potential risks of continuous wear and of factors that may increase those risks.

Solid state structure and oxygen transport properties of copolyesters based on smectic poly(hexamethylene 4,4′-bibenzoate)

This study examined the solid state structure and oxygen barrier properties of copolyesters based on smectic poly(hexamethylene 4,4′-bibenzoate) (PHBB) and non-liquid crystalline poly(hexamethylene isophthalate) (PHI). The isophthalate content was varied from 10 to 75mol%. Differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), dynamic mechanical thermal analysis (DMTA), and atomic force microscopy (AFM) were employed to characterize the polymers. The strong ordering tendency of 4,4′-bibenzoate was demonstrated by the persistence of ordered PHBB structures in copolymers with large amounts of the kinked isophthalate comonomer. Copolymers with up to 50mol% isophthalate gave evidence of liquid crystalline (LC) character in the precursor melt. Copolymers with up to 75mol% isophthalate crystallized in the PHBB α-crystal form with only small perturbations of the unit cell. The copolymers provided insight into the low gas permeability of LC polymers. Changes in both solubility and diffusivity contributed to the lower oxygen permeability of the smectic glass compared to the amorphous glass. Smaller free volume hole size of the smectic glass gave rise to lower oxygen solubility and contributed to lower diffusivity. The extended chain conformation in the smectic glass, which reduced the fraction of glycol units in gauche conformations, was a second factor that contributed to lower diffusivity.

Oxygen permeation in bismuth-based materials. Part I: Sintering and oxygen permeation fluxes

Oxygen permeation measurements were performed on two layered bismuth based oxide ceramics: a rhombohedral phase belonging to the Bi 2O 3–CaO system, (Bi 2O 3) 0.73–(CaO) 0.27 (BICAO) and a BICOVOX phase. Oxygen permeability for these systems was compared to permeability of the cubic fluorite type structure with composition (Bi 2O 3) 0.75(Er 2O 3) 0.25 (BE25). Low oxygen permeability was observed for the pure ceramic. As for BE25, permeability was considerably increased if 40 vol.% of silver was added to BICAO. In contrast, permeability was not improved by addition of gold to BICOVOX. For this latter phase, the oxygen molecular exchange at the surface is clearly the limiting step in the oxygen transfer.

Refractive behavior changes with six months daily wear of high and low oxygen permeability hydrogel contact lenses

Introduction: The investigation of myopia and soft contact lenses is not new. Many reports show that the wearing of silicone hydrogel lenses as opposed to conventional disposable hydrogel lenses results in little progression of myopia in the eyes wearing silicone hydrogels. Method: Six subjects wore a silicone hydro-gel lens on one eye while the other eye wore a habitual disposable hydrogel lens for six months of daily wear. Fifty measurements of refractive state in each eye were taken prior to the subjects wearing a silicone lens in one eye and a conven-tional hydrogel lens in the other eye. After six months of daily wear another fifty measurements of refractive state were taken for each subject. Results: Although there is no statisti-cal support for the findings of this study, comet stereo-pairs are used to show the chang-es in refractive state for each subject. Four of the six subjects showed an increase in myopia in the eye wearing the silicone lens. Discussion: The increase in myopia in eyes wearing a silicone hydrogel lens is contrary to the findings of other studies.

The fundamental radiation properties of normoxic polymer gel dosimeters: a comparison between a methacrylic acid based gel and acrylamide based gels

Polymer gel dosimeters offer a wide range of applications in the three-dimensional verification of complex dose distributions such as in intensity-modulated radiotherapy. One of the major difficulties with polymer gel dosimeters is their sensitivity to oxygen, as oxygen inhibits the radiation-induced polymerization reaction. For several years, oxygen was removed from the gels by bubbling the sol with inert gases for several hours during the gel fabrication. Also, the gel had to be poured in containers with low oxygen permeability and solubility. Recently, it was found that these technical difficulties can easily be solved by adding an antioxidant to the gel. These gels are called ‘normoxic’ gels as they can be produced under normal atmospheric conditions. In this study several properties of polymer gel dosimeters have been investigated: the dose sensitivity, the temporal and spatial stability of the gel, the sensitivity of the dose response to temperature during irradiation and during MR imaging, the energy dependence and the dose-rate dependence. This study reveals that the normoxic polymer gel dosimeter based on methacrylic acid (nMAG) studied in this work has inferior radiation properties as compared to the polyacrylamide gelatine (PAG) gel dosimeters. It is shown that from the three different gel dosimeters investigated in this study, the nPAG gel dosimeter results in a less sensitive gel dosimeter but with superior radiation properties as compared to the nMAG gel dosimeter. The importance of investigating relevant radiation properties of gel dosimeters apart from the radiation sensitivity—prior to their use for dosimetric validation experiments—is illustrated and emphasized throughout this study. Other combinations of monomer and gelling agent may result in more reliable normoxic polymer gel dosimeters.

Synthesis and Electrophoretic Deposition of an Yttrium Silicate Coating System for Oxidation Protection of C/C-Si-SiC Composites

Due to favorable chemical and mechanical properties of yttrium silicate coatings (low Young’s modulus, low thermal expansion coefficient, low evaporation rate and oxygen permeability, good erosion resistance), this material is a promising complement to SiC coatings for protecting C/C-Si-SiC composites. For the preparation of silicate powders, the Pechini method was used. As a coating method, electrophoretic deposition from stable suspensions based on isopropanol was chosen. Under controlled deposition voltage and duration, coatings of various thicknesses were deposited. The deposited layers were characterized by SEM and EDX analysis. The protectiveness of these coatings was tested by isothermal thermogravimetry.

Improving oxygen barrier properties of poly(ethylene terephthalate) by incorporating isophthalate. I. Effect of orientation

AbstractThe present study examined poly(ethylene terephthalate) (PET) and a series of statistical and blocky copolymers in which up to 30% of the terephthalate was replaced with isophthalate by copolymerization and melt blending, respectively. Some level of transesterification during processing of melt blends resulted in blocky copolymers, as confirmed by NMR. Random and blocky copolymers exhibited similar properties in the glassy state, including a single glass transition, due to miscibility of the blocks. However, random copolymerization effectively retarded cold‐crystallization from the glass whereas blocky copolymers readily cold‐crystallized to a crystallinity level close to that of PET. The polymers were oriented at four temperatures in the vicinity of the Tg and characterized by oxygen transport, wide‐angle X‐ray diffraction, positron annihilation lifetime spectroscopy, and infrared spectroscopy. Orientation of all the copolymers resulted in property changes consistent with strain‐induced crystallization. However, blocky copolymers oriented more easily than random copolymers of the same composition and after orientation exhibited slightly lower oxygen permeability, higher density, and higher fraction trans conformers. Analysis of oxygen solubility based on free volume concepts led to a two‐phase model from which the amount of crystallinity and the amorphous phase density were extracted. Dedensification of the amorphous phase correlated with the draw temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1615–1628, 2005

The Effects of High-Dk Rigid Contact Lens Center Thickness, Material Permeability, and Blinking on the Oxygen Uptake of the Human Cornea

The human corneal oxygen uptake responses associated with the static (nonblinking) and dynamic (blinking) wear of five rigid gas-permeable materials with high oxygen permeabilities were determined for three different center thicknesses and compared with the responses for the normal open eye and severe hypoxic stress (static wear of polymethylmethacrylate). Corneal oxygen uptake rates were measured with a Clark-type polarographic electrode during two sessions with each of 10 human subjects. Measurements were made on the right eye for the normal open eye (air) and after 5 minutes of static and dynamic wear of polymethylmethacrylate and five rigid gas-permeable contact lens materials: Fluoroperm 92 (paflufocon A, Dk = 92), Fluoroperm 151 (paflufocon D, Dk = 151), 1992 Menicon SF-P (melafocon A, Dk = 102), 1995 Menicon SF-P (melafocon A, Dk = 159), and Menicon Z (tisilfocon A, Dk = 163-250). Lenses were manufactured in three different center thicknesses (0.12, 0.16, and 0.20 mm), with all other parameters remaining constant. Repeated-measures analysis of variance was used and included lens material (five levels), blinking condition (two levels), and lens thickness (three levels) as within-subject effects. Significant differences were found in corneal oxygen responses to lens material (p < 0.001) and lens thickness (p < 0.001), with lenses of lower oxygen permeability and thicker lenses being associated with higher oxygen uptake. No statistically significant differences were noted between static or dynamic wear of the lens materials (p = 0.59). For those very high Dk rigid lens materials studied here, moderate changes in lens thickness or material permeability may result in modest differences in corneal hypoxic relief, whereas blinking results in no significant improvement to corneal oxygenation.

白色フィラー配合ゴムの性質と高性能化 ５．白色フィラーと環境劣化，熱可塑性エラストマーへの配合効果と白色フィラーの今後

This paper referred to the effects of inorganic fillers on photo and heat aging of vulcanizates and the mechanical properties of thermoplastic elastomers. The photo aging resistance of vulcanizates filled with a plate-like filler such as kaolin clay was superior to that of vulcanizates filled with a granular-like filler such as silica and calcium carbonate. It was due to low permeability for both light and oxygen of vulcanizates filled with a plate-like filler. On the other hand, in the case of heat aging, vulcanizates filled with silica showed better resistance than those filled with carbon black in the presence of antioxidants. It seemed that an acidic filler such as silica activated antioxidants by acid-base interaction between a hydroxyl group on filler surface and an antioxidant. Some references of the effect of inorganic fillers on the physical properties of thermoplastic elastomers were reviewed. Several topics of inorganic fillers in the future were also referred.

Oxygen potential distribution during disappearance of the internal oxidation zone formed in the steam oxidation of Fe–9Cr–0.26Si ferritic steel at 973 K

For discussing quantitatively the disappearance of the internal oxidation zone (IOZ), which was observed in the high temperature steam oxidation of the commercial Fe–9Cr–0.26Si ferritic steel (ASME T91), the oxygen potential distribution in the IOZ was calculated as a function of the normalized thickness of the IOZ. The distribution of the internal oxides was predicted with the calculated oxygen potential distribution and thermodynamic data. The predicted distribution of the internal oxides was in good agreement with the TEM observation at the internal oxidation front. When a sheet of amorphous SiO2 formed at the internal oxidation front, the oxygen potential at IOZ/SiO2 interface was calculated to be almost as same as that at the inner scale/IOZ interface because of the low oxygen permeability in the sheet of the SiO2. The increase in the oxygen potential oxidizes the matrix of iron in the IOZ and converts the IOZ to the inner scale.

A novel process to form a silica-like thin layer on polyethylene terephthalate film and its application for gas barrier

A novel process for polyethylene terephthalate (PET) surface modification with a silica-like thin layer is proposed. 3-Aminopropyltrimethoxysilane was employed to react with acetone to form dimethyliminopropyltrimethoxysilane (DIPTMS) after aging for 10 days at room temperature. After hydrolysis of alkoxy groups in DIPTMS, dimethylimine-modified silica clusters occurred resulting in an increase of the solution viscosity. Consequently, a dense and homogeneous thin layer was easily dip-coated onto a PET film. After heat treatment at 150 °C, a smooth, flexible and transparent silica-like film (about 70 nm thick) was formed via dehydration and condensation. The surface of the PET dramatically changed from hydrophobic (water contact angle: 70±2°) to hydrophilic (45±3°). As an attempt for application, a dense film of lithium metasilicate (Li 2O·2SiO 2· nH 2O) was successfully prepared by dip coating on the modified PET film, which appeared very low oxygen permeability of about 0.17 cm 3/m 2 day atm at 23 °C and 85% humidity.

In vivo confocal microscopy: increased conjunctival or episcleral leukocyte adhesion in patients who wear contact lenses with lower oxygen permeability (Dk) values.

Contact lens wear is known to threaten the health of the ocular surface. In vivo confocal microscopy (IVCM) to visualize leukocyte rolling and extravasation in inflammation was recently described. We tested the hypothesis that contact lens wear is associated with measurable inflammation in superficial vessels. Leukocyte rolling and sticking (hallmarks of the inflammatory process) were recorded by IVCM. IVCM was performed on conjunctival or episcleral blood vessels bilaterally on 55 contact lens wearers (15 male, 40 female) and 22 non-contact lens wearers (8 male, 14 female). Data were analyzed in 2 ways. Considering each vessel as an independent variable resulted in 132 analyzable vessel segments (13 daily disposable contact lenses, 67 traditional contact lenses, 14 rigid gas-permeable lenses, and 38 controls). Considering each subject as an independent variable resulted in analyzable data for 47 subjects (5 daily disposable contact lens wearers, 22 traditional contact lens wearers, 5 rigid contact lens wearers, and 15 control patients). Free-flowing, sticking, and rolling cells were counted in the vessels. Multiple parameters including mean flow velocity, shear rate, rolling cells/mm/min, and sticking cells/mm were calculated. We found no significant difference in leukocyte adhesion between control patients and patients wearing daily disposable, traditional disposable, or rigid gas-permeable lenses in both types of statistical analyses. However, the data regarding vessel segments as an independent variable show that there were more rolling cells in patients who wore contact lenses with oxygen permeability values (Dk) less than 10 as compared to those who wore contact lenses with oxygen permeability values greater than 16 (P < 0.01) or compared to controls (P < 0.01). IVCM is a novel, powerful technique to recognize a critical but subclinical component of inflammation. Although our data indicate that contact lens wear does not markedly increase rolling and sticking of leukocytes in conjunctival or episcleral vessels, there may be subclinical inflammation in association with lenses with the lowest oxygen permeability.

Flavor Characteristics of Irradiated Apple Cider During Storage: Effect of Packaging Materials and Sorbate Addition

ABSTRACT: Apple cider, with (0.1%) and without potassium sorbate, was packaged in 3 different materials to evaluate the effects of irradiation (2 kGy) and storage on flavor. Irradiated apple cider samples were compared with unirradiated samples stored in glass jars. Volatile flavor compounds, soluble solids, and titratable acidity were determined weekly throughout 3 wk of refrigerated storage. Oxygen permeability of the packaging materials was important in the retention of flavor during storage. Cider irradiated and stored in polystyrene containers or nylon‐6 packaging materials (low oxygen permeability) had lower rates of loss of characteristic flavor compounds compared with unirradiated apple cider and cider irradiated and stored in low‐density polyethylene (high oxygen permeability). The presence of sorbate, functioning as a yeast and mold inhibitor, reduced the rates of loss of the characteristic flavor compounds and the fermentation of sugars to acids. Principal component analysis resulted in several esters characteristic of apple flavor, soluble solids, and titratable acidity loading onto the 1st principal component (PC‐1). Packaging material and sorbate treatment had the greatest effect on the compounds that loaded onto PC‐1.

Material properties of plasticized hardwood xylans for potential application as oxygen barrier films.

Free films based on glucuronoxylan isolated from aspen wood were prepared by casting from aqueous solutions and drying in a controlled environment. Addition of xylitol or sorbitol facilitated film formation and thus examination of the material properties of these films. The mechanical properties of the films were evaluated using tensile testing and dynamic mechanical analysis in a controlled ambient relative humidity. The strain at break increased, and the stress at break and Young's modulus of the films decreased with increasing amounts of xylitol and sorbitol due to plasticization. At high amount of plasticizer, it was found that films with xylitol gave lower extensibility. Wide-angle X-ray scattering analysis showed that xylitol crystallized in a distinct phase, which we believe contributes to the more brittle behavior of these films. The effect of the plasticizers on the glass transition temperature was determined using dynamic mechanical analysis and differential scanning calorimetry. An increased amount of plasticizer shifted the glass transition to lower temperatures. The effect of moisture on the properties of plasticized films was investigated using water vapor sorption isotherms and by humidity scans in dynamic mechanical analysis. Sorption isotherms showed a transition from type II to type III when adding plasticizer. The films showed low oxygen permeability and thus have a potential application in food packaging.

Nafion-Teflon- Zr ( HPO 4 ) 2 Composite Membranes for High-Temperature PEMFCs

Nafion membranes suffer high resistance due to dehydration when they are used at elevated temperatures and atmospheric pressures (Nafion at and 31% relative humidity). Thinner composite membranes containing Nafion and zirconium hydrogen phosphate, were prepared and showed lower resistance at these conditions. Thermogravimetric analysis showed that the composite membrane was stable below 200°C in oxygen. Hydrogen crossover of a 18 μm thick composite membrane was only at When the temperature of a cell using this membrane was raised from 80°C (100% relative humidity) to 120°C (31% relative humidity), the main performance loss at the elevated temperature was from low protonic conductivity and low oxygen permeability in the cathode catalyst layer and dehydration of the membrane. © 2004 The Electrochemical Society. All rights reserved.