Low Oxygen Permeability Research Articles

Physical Properties of Whey Protein–Hydroxypropylmethylcellulose Blend Edible Films

The formations of glycerol (Gly)-plasticized whey protein isolate (WPI)-hydroxypropylmethylcellulose (HPMC) films, blended using different combinations and at different conditions, were investigated. The resulting WPI: Gly-HPMC films were analyzed for mechanical properties, oxygen permeability (OP), and water solubility. Differences due to HPMC quantity and blend method were determined via SAS software. While WPI: Gly and HPMC films were transparent, blend films were translucent, indicating some degree of immiscibility and/or WPI-HPMC aggregated domains in the blend films. WPI: Gly-HPMC films were stronger than WPI: Gly films and more flexible and stretchable than HPMC films, with films becoming stiffer, stronger, and less stretchable as the concentration of HPMC increased. However, WPI: Gly-HPMC blended films maintained the same low OP of WPI: Gly films, significantly lower than the OP of HPMC films. Comparison of mechanical properties and OP of films made by heat-denaturing WPI before and after blending with HPMC did not indicate any difference in degree of cross-linking between the methods, while solubility data indicated otherwise. Overall, while adding HPMC to WPI: Gly films had a large effect on the flexibility, strength, stretchability, and water solubility of the film polymeric network, results indicated that HPMC had no effect on OP through the polymer network. WPI-HPMC blend films had a desirable combination of mechanical and oxygen barrier properties, reflecting the combination of hydrogen-bonding, hydrophobic interactions, and disulfide bond cross-linking in the blended polymer network.

Thermal properties of single-phase Y 2SiO 5

Y 2SiO 5 is a promising candidate for oxidation-resistant or environmental/thermal barrier coatings (ETBC) due to its excellent high-temperature stability, low elastic modulus and low oxygen permeability. In this paper, we investigated the thermal properties of Y 2SiO 5 comprehensively, including thermal expansion, thermal diffusivity, heat capacity and thermal conductivity. It is interesting that Y 2SiO 5 has a very low thermal conductivity (∼1.40 W/m K) but a relatively high linear thermal expansion coefficient ((8.36 ± 0.5) × 10 −6 K −1), suggesting compatible thermal and mechanical properties to some non-oxide ceramics and nickel superalloys as ETBC layer. Y 2SiO 5 is also an ideal EBC on YSZ TBC layer due to their close thermal expansion coefficients. As a continuous source of Y 3+, it is predicted that Y 2SiO 5 EBC may prolong the lifetime of zirconia-based TBC by stopping the degradation aroused by the loss of Y stabilizer.

Oxygen permeability of polyethylene-extrusion-coated greaseproof paper

Polyethylene-extrusion-coated greaseproof paper exhibited significantly lower oxygen permeability than predicted from the oxygen permeability of polyethylene and greaseproof paper itself. Two mecha ...

Effects of lotrafilcon A and omafilcon A bandage contact lenses on visual outcomes after photorefractive keratectomy

To evaluate postoperative healing between bandage contact lenses with high and low oxygen permeability in patients having photorefractive keratectomy (PRK). Center for Refractive Surgery, Walter Reed Army Medical Center, Washington, DC, USA. This retrospective study compared patients receiving a high-oxygen-transmission bandage contact lens (Focus Night & Day [N&D], Ciba Vision; n = 92) and those receiving a low-oxygen-transmission lens (Proclear, Cooper Vision; n = 114) after PRK. Visual outcomes, safety, and efficacy were assessed postoperatively at 1, 4, and 7 days and 1, 3, 6, and 12 months. Overall pain scores were higher in the Proclear group at 1 day (P = .000) and 4 days (P = .027). The N&D group had an increase in corneal infiltrates at 4 days (P = .025) and 1 week (P = .017). At 1 month, 40.4% of patients in the Proclear group and 18.6% in the N&D group had a 1 or more line decrease in best spectacle-corrected visual acuity (BSCVA) (P = .002). Although there was a trend toward a higher haze rate in the Proclear group, it was not statistically significant (P = .064). There was no statistically significant difference in uncorrected visual acuity, goal of emmetropia, contrast sensitivity, or reepithelialization. The N&D lens produced less pain and better postoperative results in terms of haze and BSCVA at 1 month. However, it led to a higher incidence of corneal infiltrates. There was no difference between the lenses in the end result at 12 months.

New Oxygen Barrier Stretch Film Enhances Quality of Alfalfa Wrapped Silage

The objectives of this research were to (i) test a new oxygen barrier (OB) stretch film with a 20‐fold lower oxygen permeability than the polyethylene (PE) film commonly used on farms to wrap bales and (ii) determine the effects on microbial status, dry matter (DM) losses, and fermentation of alfalfa (Medicago sativa L.) bale silage. Five field trials were conducted on a farm near Turin, Italy. In Trial 1, the bales were wrapped with two, four, six, or eight layers of either conventional PE or OB film. A further four trials were conducted to compare bales wrapped with four layers of OB with bales wrapped with six layers of PE. In the outer layer of bales, the pH was lower in the OB than the PE silages. There was a significant effect of the film type and number of layers on the percentage of bale surface covered by mold (P < 0.001), with less than 15% in bales wrapped with at least four layers of OB film. Storage DM losses ranged from 50 to 123 g kg−1 DM and were affected by the type of film used (P < 0.001) and by the number of layers applied (P = 0.035), with consistently lower values in OB silages. The new stretch film supports the possibility of conserving high quality alfalfa silage for up to 14 mo, with less film than currently used.

Material Properties of Films from Enzymatically Tailored Arabinoxylans

Rye arabinoxylan, with an initial arabinose to xylose (Ara/Xyl) ratio of 0.50, was enzymatically modified with alpha-L-arabinofuranosidase. Different enzyme dosages were used to prepare arabinoxylan samples with a gradient of arabinose content varying from Ara/Xyl ratio 0.50 to 0.20. The degree of polymerization of the arabinoxylans was not affected by the enzymatic treatment, as detected with SEC-MALLS. Arabinoxylan samples with an Ara/Xyl ratio of 0.30 and below agglomerated in a water solution as seen by changes in light scattering. All samples, however, formed cohesive films upon drying, without addition of external plasticizers. The film from untreated arabinoxylan was completely amorphous; whereas films of the enzyme-treated arabinoxylans were semicrystalline with an increasing degree of crystallinity with decreasing arabinose content as determined by WAXS. Oxygen permeability measurements of the films showed that decreased arabinose content also resulted in lower oxygen permeability of the films. All films were strong and relatively stiff, but showed variations in strain at break. The moderately debranched film with an Ara/Xyl ratio of 0.37 had highest strain at break among all the films tested, yet was stiff and strong. This material also exhibited yielding and had stress/strain behavior similar to synthetic semicrystalline polymers, with a tendency to strain-induced crystallization. Such a combination of mechanical properties combined with oxygen barrier properties is very attractive for packaging applications.

Commercially Available Gas-Permeable Cell Culture Bags May Not Prevent Anoxia in Cultured or Shipped Islets

Prolonged anoxia has deleterious effects on islets. Gas-permeable cell culture devices can be used to minimize anoxia during islet culture and especially during shipment when elimination of gas-liquid interfaces is required to prevent the formation of damaging gas bubbles. Gas-permeable bags may have several drawbacks, such as propensity for puncture and contamination, difficult islet retrieval, and significantly lower oxygen permeability than silicone rubber membranes (SRM). We hypothesized that oxygen permeability of bags may be insufficient for islet oxygenation. We measured oxygen transmission rates through the membrane walls of three different types of commercially available bags and through SRM currently used for islet shipment. We found that the bag membranes have oxygen transmission rates per unit area about 100-fold lower than SRM. We solved the oxygen diffusion-reaction equation for 150-μm diameter islets seeded at 3000 islet equivalents per cm 2, a density adequate to culture and ship an entire human or porcine islet preparation in a single gas-permeable device, predicting that about 40% of the islet volume would be anoxic at 22°C and about 70% would be anoxic at 37°C. Islets of larger size or islets accumulated during shipment would be even more anoxic. The model predicted no anoxia in islets similarly seeded in devices with SRM bottoms. We concluded that commercially available bags may not prevent anoxia during islet culture or shipment; devices with SRM bottoms are more suitable alternatives.

Influence of paper structure on barrier properties of starch-coated greaseproof paper

Greaseproof paper has a dense structure and therefore provides a natural barrier against materials like fat and oils. The barrier is obtained by extensive refining of the pulp. This refining is however a costly operation, not only in terms of direct costs for the refining but also in terms of indirect costs because the energy consumption for the drying of the paper is affected by the refining. A full-scale trial was performed to investigate the role of the pulp with respect to the energy demand and the barrier properties of the final papers. Paper made of 100% sulphite pulp with a low degree of refining exhibited the lowest energy consumption at a given level of air permeance. In addition, the effect of refining on the air permeance was compared with that of calendering. The calendering affected the air permeance less than the refining. The papers produced in the full-scale trial were later used as substrates for coatings and for detailed studies of the paper structure. Coating with chitosan was examined on a bench-scale and on a pilot scale. The studies showed that greaseproof paper can be upgraded with an oxygen barrier, but also that suitable coating techniques are lacking for the application of the coating in a sufficient amount. The influence of the base paper on the barrier properties of chitosan-coated paper was investigated in another study, in which it was found that greaseproof paper possesses a unique coating hold-out which cannot be met by other types of paper with a more open structure. It was also found that the coated paper had a lower oxygen permeability than the chitosan coating itself, and this indicates that the dense surface layer of greaseproof paper contributed to the oxygen permeability of the coated paper. The pore volume fraction of the greaseproof paper was found to be approximately 40% and it is therefore surprising that its air permeance is so low. To bring understanding to this question, the structure of greaseproof paper was studied using several methods. It was found that the structure was dominated by very small pores with a median diameter of <0.3 µm. The fraction of closed pores was also substantial. A porosity gradient was also found, indicating that the papers used in the study had a closed surface. The hypothesis that the surface layer of the paper contributed to the oxygen barrier was tested in an experiment in which greaseproof paper was extrusion-coated with polyethylene. The oxygen permeability was measured at 0%, 50% and 90% relative humidity, and the permeability was found to increase with increasing moisture content. Because only the cellulose layer in the paper and not the polyethylene layer in the coating is affected by moisture, this result supports the hypothesis that the surface layer of the paper contributed to the oxygen barrier properties of the coated paper.

Sulfonated poly(arylene ether sulfone) ionomers containing fluorenyl groups for fuel cell applications

A series of sulfonated poly(arylene ether sulfone)s (SPEs) containing fluorenyl groups as bulky components were synthesized and characterized for fuel cell applications. Introduction of disodium 3,3′-disulfo-4,4′-difluorophenyl sulfone (SFPS) monomer gave ionomers with high acidity and accordingly high proton conductivity as well as high proton diffusion coefficient ( D σ ) at low humidity. The membrane of SPE60 (where the number denotes mole percentage of the component containing sulfonic acid groups; IEC (ion exchange capacity) = 1.68 mequiv./g) exhibited high proton conductivity of 4.6 × 10 −3 S/cm at 40% RH and 80 °C, which is one order of magnitude higher than that (6 × 10 −4 S/cm) of our previous SPE (SPE-1, IEC = 1.58 mequiv./g). D σ of SPE60 membrane was ca. 4 times higher than that of the SPE-1 membrane at low water volume fraction. SPE membranes showed good oxidative and hydrolytic stability as well as favorable thermal and mechanical properties. Small-angle X-ray scattering analyses showed that the phase separation of SPE membranes was much less developed than that of the perfluorinated Nafion membrane which accounts for lower hydrogen and oxygen permeability of the former membranes.

A simple model for the interaction between water vapour and oxygen transmission in multilayer barrier materials intended for food packaging applications

AbstractThe low oxygen permeability of the ethylene‐vinyl alcohol copolymer, EVOH, is outstanding, but is also known to be very sensitive to moisture uptake and cannot be used as a monolayer packaging material. In this paper, theory is presented in order to calculate the average water activity of the EVOH layer at steady state and the corresponding oxygen barrier for different multilayer structures using various polymer types and layer thicknesses. Multilayer materials can be designed for different food packaging applications and storage conditions, in order to keep the relative humidity of the barrier below recommended 75%, by varying the thickness of the outside versus the inside protective layers and/or varying the water vapour transmission rate of the outside versus the inside layer. The conclusion reached is that to retain the optimal barrier properties and thereby the optimal protection of the food, asymmetric multilayer structures are necessary. Copyright ©2007 John Wiley &amp; Sons, Ltd.

Relation between types of packaging, frozen storage and grilling on cholesterol and fatty acids oxidation in Atlantic hake fillets ( Merluccius hubbsi)

Two different commercial samples of frozen and packaged, in low and high-oxygen permeability packaging, Atlantic hake fillets were stored at −18 °C for 4 months and the intensity of lipid oxidation, as well as the formation of cholesterol oxidation products (COP), during storage and subsequent grilling were studied. Raw fillets at the initial time of storage showed low total COP levels, however, after 120 days of storage the concentrations were raised significantly, under both packed conditions. During freezing and subsequent grilling there was a significant decrease ( p < 0.02) in the contents of the cholesterol and polyunsaturated fatty acids in all the hake samples. Correlations were found between the cholesterol and fatty acid parameters and cholesterol oxides formation during storage and heat treatment. The commercial frozen storage with a low-oxygen permeability packaging was more effective in preventing lipid oxidation than high-oxygen permeability packaging, with less accented cholesterol degradation as well as cholesterol oxides formation.

Oxygen‐transport properties of liquid‐crystalline polyesters based on 4,4′‐bibenzoic acid

AbstractThis study examined the oxygen‐transport properties of aromatic liquid‐crystalline (LC) polyesters of 4,4′‐bibenzoic acid (BB) and an aliphatic diol. The effect of the spacer length was probed by the number of methylene groups in the diol being increased from 3 to 6. Parallel studies were performed on polymers in which the LC character was reduced or removed by copolymerization with 30 mol % nonmesogenic isophthalic acid (BB‐30I) or by the replacement of BB with 4,4′‐oxybis(benzoic acid) (OBB). The oxygen‐transport properties were interpreted in terms of the solid‐state structure as revealed by the thermal behavior and wide‐angle X‐ray diffraction. The strong odd–even effect of the spacer length that characterized the thermal transitions of the BB polyesters was weak or absent from the oxygen‐transport properties when the effect of crystallinity was considered. Permeability and diffusivity tended to increase with the spacer length. The lower oxygen permeability of all the BB polyesters compared with that of the BB‐30I copolyesters and the OBB polyesters was due primarily to lower oxygen solubility. The low solubility of the noncrystalline LC phase was ascribed to a smaller free‐volume hole size and possibly to a lower free‐volume hole density in comparison with an amorphous glass. The solubility of oxygen in the noncrystalline regions of the BB‐30I copolyesters and in the amorphous OBB polyesters conformed to the relationship between the solubility and the glass‐transition temperature previously established for amorphous and glassy aromatic polyesters. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 30–37, 2007

Thermal stability of nanoclay polypropylene composites by simultaneous DSC and TGA

The thermooxidative and thermal stability of polypropylene nanocomposite with fully exfoliated MMT was studied by simultaneous measurements by DSC and TGA methods in a wide range of temperature. By comparing both the mass loss from TGA and enthalpy changes from DSC in a temperature range from room temperature to 500 °C it was possible to identify precisely the specific mechanisms of polymer degradation. In oxygen-free atmosphere the thermal degradation of polypropylene in nanocomposites is strongly inhibited up to the temperature of 420 °C in contrast to pristine polypropylene degradation beginning with 300 °C. Simultaneous TGA and DSC made possible to show that exfoliated clay platelets modified with alkylammonium salt exhibit a strong stabilizing effect on polypropylene macromolecules in oxygen-free atmosphere. It was further shown that the lower sensibility to thermal oxidation of nanocomposites was correlated with lower oxygen permeability resulting from an increased diffusion path for oxygen as well as for volatile decomposition products.

Effect of the aspect ratio of silicate platelets on the mechanical and barrier properties of hydrogenated acrylonitrile butadiene rubber (HNBR)/layered silicate nanocomposites

The role of the aspect ratio of the layered silicate platelets on the mechanical and oxygen permeation properties of hydrogenated nitrile rubber (HNBR)/organophilic layered silicate nanocomposites was investigated. Montmorillonite (MMT) and fluorohectorite (FHT) bearing the same type of intercalant (i.e., octadecylamine; ODA), however, showing different aspect ratio was involved in this study. The dispersion of the layered silicates was assessed by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Increasing aspect ratio (MMT < FHT) resulted in higher stiffness under uniaxial tensile loading. The dispersion state (“secondary structure”) of the organophilic layered silicates reduced dramatically the oxygen permeability of the rubber matrix based on the labyrinth principle. The lowest oxygen permeability was measured for the HNBR/FHT–ODA films in which the layered silicates had the highest aspect ratio. By varying the FHT–ODA volume fraction in the latter compound the mechanical and permeation properties were measured and modelled. It was found that the modified Guth’s and Nielsen’s equations predicted accurately the mechanical and permeation responses, respectively.

Transparent anodes for polymer photovoltaics: Oxygen permeability of PEDOT

The oxygen permeability of the transparent organic anode poly(3,4,-ethylene dioxythiophene) with paratoluenesulphonate as the anion (PEDOT:pTS) was determined to be 2.5 ± 0.7 × 10 - 15 cm 3 (STP) cm cm - 2 s - 1 Pa - 1 , and is thus comparable in magnitude to the oxygen permeability of polyethyleneterephthalate (PET). The oxygen diffusion through bilayers of polyethylene (PE) and PEDOT:pTS and bilayers of PET and PEDOT:pTS was established. The bilayer structures were applied as the carrier substrate and the transparent anode in polymer-based photovoltaic devices employing a mixture of poly(1-methoxy-4-(2-ethylhexyloxy)- p-phenylenevinylene) (MEH-PPV) and [6,6]-phenyl- C 61 -butanoicacidmethylester (PCBM) as the active layer and aluminium as the cathode. The oxygen permeability of the layers and the aluminium cathode was correlated with the lifetime of the solar cell devices. It was found that the performance of the devices with PET as the carrier substrate degraded more slowly due to the lower oxygen and water permeability, whereas devices using PE as the carrier substrate gave devices with a very short lifetime. It was found that PEDOT:pTS on its own is a not a significant barrier for oxygen in the context of photovoltaic devices where long lifetimes are anticipated. It is concluded that the large oxygen permeability of the barrier layers contribute to the short device lifetimes while other permeates such as water also contribute to device degradation.

Objective and Subjective Responses in Patients Refitted to Daily-Wear Silicone Hydrogel Contact Lenses

Silicone hydrogel (SiH) lenses offer many physiological advantages for daily wear (DW) in addition to the continuous-wear modality for which they were originally developed. The purpose of this study was to investigate the clinical performance and physiological responses in a group of successful long-term wearers of conventional hydrogel lenses when refitted with DW SiH contact lenses. Eighty-seven successful soft lens wearers (8.4+/-4.7 years of prior lens wear) participated in this study. Bulbar and limbal hyperemia were subjectively graded and digitally photographed for subsequent masked objective evaluation. Subjective symptoms were scored using visual analog scales. In addition, refractive error, corneal curvature, and corneal thickness were measured. All subjects were refitted with Focus Night & Day (lotrafilcon A) SiH lenses; however, to reduce the potential for bias, they were informed that they were being randomly assigned to wear either low oxygen permeability (Dk) lenses or high Dk SiH lenses and were "masked" as to their lens assignment. Subjects returned after 1 week, 1 month, and 2 months of DW, at which time all gradings, photographs, and measurements were repeated. End-of-day subjective symptoms were also graded periodically during the study. Ninety-three percent of subjects were successfully refitted. Both objective and subjective evaluations showed that bulbar and limbal hyperemia decreased significantly in all quadrants during the study (p<0.001), particularly for those subjects with greater baseline hyperemia (p<0.001). Subjects reported a concurrent reduction in end-of-day dryness and improved end-of-day comfort compared with their habitual lenses (p<0.001). No significant changes in refractive error, tarsal papillary response, corneal curvature, or corneal thickness were found during the study. Hyperemia in contact lens wearers may be attributed to a number of factors, including hypoxia. Refitting existing low Dk lens wearers with SiH lenses on a DW basis can result in a decrease in hyperemia, which may be significant for some subjects and also results in improvements in symptoms of dryness and discomfort.

Study of mechanical properties, oxygen permeability and AFM topography of zein films plasticized by polyols

AbstractThe use of plastic for packaging has grown extensively in recent years. In this context, biodegradable films can be a source of energy saving and an important issue for environmental protection. Zein protein (prolamin of corn) is one of the best biopolymers for edible film making and polyols are convenient plasticizers for biopolymers. Polyols (sorbitol, glycerol and mannitol) at three levels (0.5, 0.7 and 1g/g zein) were used as plasticizers and the tensile properties, oxygen permeability (OP) and AFM topography of zein films were studied. Films plasticized by sorbitol had a relatively higher ultimate tensile strength (UTS) than films containing glycerol and mannitol at low levels of plasticizers (0.25, 0.7g/g zein). There was no significant difference between the strain at break values (SB) of films plasticized by sorbitol and glycerol at low levels of plasticizers, while films plasticized by sorbitol had higher SB than the films containing glycerol and mannitol at a high level of plasticizer (1g/g zein). Pure zein films had low oxygen permeability (OP), and increasing the plasticizer level to 0.5g/g zein decreased OP values in films containing sorbitol and glycerol. Films containing sorbitol and mannitol had the lowest and highest OP values, respectively. AFM images were used to evaluate the surface morphology (qualitative parameter) and roughness (quantitative parameter) of zein films. Films plasticized by glycerol had smoother surfaces and a lower roughness parameter (Rq). No relationship between OP values and the roughness of the zein films was observed. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Large area plastic solar cell modules

Preliminary data on the fabrication of 0.1 m 2 polymer solar cells are presented. The process employed screen-printing of an active layer onto an indium-tin-oxide (ITO) electrode pattern (50 Ω square −1) on a 200 μm polyethyleneterphthalate (PET) substrate. After the printing, vacuum coating of an optional layer of C 60 and the final aluminium electrode was employed to complete the device. The active layer consisted of poly-1,4-(2-methoxy-5-ethylhexyloxy)phenylenevinylene (MEH-PPV). Chlorobenzene was used as solvent for the screen-printing process. The design of the solar cell module was chosen to employ both serial and parallel connection of individual solar cells. Thirteen individual solar cells with an active area of 7.2 cm 2 were thus connected in series. The serial connection was chosen to reduce the current density for the large area employed. A step up in voltage is thus preferable to avoid resistive loss. The parallel connection of seven such rows through a screen-printed silver bus gave a solar cell module measuring 40 cm × 25 cm (0.1 m 2). The active area was 65% of the total area. The remaining 35% of the area was used for interconnections between cells and for the separation between rows. The 65% active area was chosen to encompass a good margin for prototyping/research and to keep contact resistances between the cells low. In a fully automated process the active area could perhaps reach 90–99% interval but problems with current extraction and interconnections were found to become very critical. There are obvious shortcomings to this approach but the advantage of low current density is believed to be the biggest problem in efficient energy extraction from the module when no simple method for reducing the sheet resistance is available. In the simple geometry ITO/MEH-PPV/aluminium the module gave an open circuit voltage ( V oc) of 10.5 V, a short circuit current ( I sc) of 5 μA, a fill factor (FF) of 13% and an efficiency ( η) of 0.00001% under AM1.5 illumination with an incident light intensity of 1000 W m −2. A geometry employing a sublimed layer of C 60 (ITO/MEH-PPV/C 60/Al) improved V oc, I sc, FF and η to 3.6 V, 178 μA, 19% and 0.0002%, respectively. The lifetimes ( τ ½) of the devices defined as the time it takes for the module efficiency to attain half of its maximum value were found to improve significantly when a sublimed layer of C 60 was included between the polymer and the aluminium electrode. The modules were laminated with 200 μm polyethyleneterephthalate (PET) foil to mechanically protect the cells. τ ½ values of 150 h were typically obtained. This short lifetime is linked to reaction between the reactive metal electrode (aluminium) and the constituents of the active layer. The modules were tested outdoors in different weather condition (wind, high temperature excursion, rain, snow). Tested during a storm the polymer photovoltaic laminate was subject to vibration stress and deformation and delamination in the organic layer was observed with fast bleaching of the active material. Efficient encapsulation with barriers that has very low oxygen and water permeabilities will be needed before future commercialisation can be anticipated.

A viologen-based UV indicator and dosimeter

A UV indicator/dosimeter based on benzyl viologen (BV2+) encapsulated in polyvinyl alcohol (PVA) is described. Upon exposure to UV light, the BV2+/PVA film turns a striking purple colour due to the formation of the cation radical, BV*+. The usual oxygen sensitivity of BV*+ is significantly reduced due to the very low oxygen permeability of the encapsulating polymer, PVA. Exposure of a typical BV2+/PVA film, for a set amount of time, to UVB light with different UV indices produces different levels of BV*+, as measured by the absorbance of the film at 550 nm. A plot of the change in absorbance at this wavelength, DeltaAbs(550), as a function of UV index, UVI, produces a linear calibration curve which allows the film to be used as a UVB indicator, and a similar procedure could be employed to allow it to be used as a solar UVI indicator. A typical BV2+/PVA film generates a significant, semi-permanent (stable for >24 h) saturated purple colour (absorbance approximately 0.8-0.9) upon exposure to sunlight equivalent to a minimal erythemal dose associated with Caucasian skin, i.e. skin type II. The current drawbacks of the film and the possible future use of the BV2+/PVA film as a personal solar UV dosimeter for all skin types are briefly discussed.

Mechanical and ablation properties of 2D-carbon/carbon composites pre-infiltrated with a SiC filler

In order to improve the mechanical and ablation properties of 2D-carbon/carbon composites, a SiC filler was added to a 2D-preform before isothermal chemical vapor infiltration densification by using a powder infiltration technique. Backscattered electron images showed that the SiC filler was mainly concentrated between the fiber bundles and between the layers. The tensile and flexural strengths of the composites were improved by the addition of the SiC filler because of the increase of interfacial surface areas between the bundles and between the layers, the less residual open porosity, and also the strong bonding between the SiC particles and the pyrocarbon matrix. The composites with filler experienced a 15.2% lower thickness erosion rate and a 51.7% lower mass erosion rate, compared to those C/C without filler. This was attributed to the low oxygen permeability of the SiO 2 shielding the exterior inter-bundle pores as well as to a thermal barrier effect.