Low Oxygen Permeability Research Articles

Development of Nitrogen Gas Bubbling Deaerator Made of Polyvinyliden Fluoride

It is essentially important to remove the dissolved oxygen (DO) in the ultrapure water for the future ultralarge scale integration (ULSI). We have found the existence of the big driving force for the oxygen diffusion through tube materials that increases the DO concentration. The DO concentration through the perfluoro alkoxide (PFA) tube rapidly increased with decreasing the flow rate of the ultrapure water. On the other hand, the DO concentration through the polyvinyliden fluoride (PVDF) tube that is a low oxygen permeability material did not increase with decreasing the flow rate. Based on this finding, we have developed the nitrogen gas bubbling deaerator made of PVDF as a point of use purifier. In this system, the residual DO concentration reached 0.2 ppb at a gas‐liquid ratio of 1.2 m3/m3 at each bubbling tower that is ten times smaller than the previously reported one. Furthermore, other contaminations in the ultrapure water do not increase after this process.

Differences and similarities in the thermooxidative degradation of polyamide 46 and 66

A comparison is made between the thermooxidative degradation of polyamide 46 (PA46) and polyamide 66 (PA66), using oven ageing, oxygen uptake and viscosity measurements on the two polymers. Model experiments were used to determine the degradation mechanism of PA46. Although on a chemical basis it is expected that PA46 would be less stable than PA66, the opposite is found. The time until the tensile strength becomes 50% of its initial value is twice as long for unstabilized PA46 compared with PA66 at 145 °C. It is shown that the degradation of PA46 is a surface phenomenon and thus oxygen diffusion limited. PA46 is more stable than PA66 due to its lower oxygen permeability, probably caused by its higher crystallinity and density of the amorphous phase.

Structure and Properties of Poly (ethylene-<i>ran</i>-vinyl alcohol) Films Crosslinked with Borate Ions

Crosslinks by borate ions were introduced to improve mechanical properties of poly (ethylene-ran-vinyl alcohol) (EVOH), whose films have a very low oxygen permeability. Effects of crosslinks on the mechanical properties and oxygen permeability of the crosslinked films were studied by dynamic viscoelastic, differential scanning calorimetry, wide angle X-ray diffraction, and oxygen permeability measurements, in terms of their structural changes. The mechanical loss tangent due to the glass transition of EVOH at around 70°C was depressed and the decrease in the storage modulus above the transition temperature became less by introducing the borate crosslinks into EVOH. This indicates that the borate crosslinks are effectively formed in amorphous region and restrict the motion of amorphous chains. However, borate crosslinks prevent the crystallization of EVOH and the presence of NaOH, employed to ionize boric acid, leads to an increase in water regain in the film. Because of these effects, the oxygen barrier property became worse than that of non-treated EVOH films. Optimization of these properties is discussed by considering the preparation of gel films.

The synthesis and gas‐transport properties of some hydrosilylation condensation polymers

AbstractHigh‐permeance collection layers are needed in composite membranes but few polymers have the required permeability. Hydrosilylation condensation polymers, because of their high silicon content, were thought to be good candidates to have high permeabilities. Several novel polymers were made and a new and simpler synthesis of ethynylated silanes is reported. One polymer, poly(divinyldimethylsilane‐co‐1,4‐bis [dimethylsilyl] benzene), appears to be of a liquid crystalline nature and has a low oxygen permeability (1.10 barrers). Two others [poly(diethynyldimethylsilane‐co‐1,4‐bis) [dimethylsilyl] benzene and poly(divinyldimethylsilane‐co‐p,p′diethynylbiphenyl‐co‐tetramethyldisiloxane)] were viscous liquids that could be thermally cured to give elastomers with oxygen permeabilities of ˜ 85 barrers. © 1994 John Wiley & Sons, Inc.

Electrochemical study of anticorrosion properties of basalt ? polymer coatings

Investigated was the corrosion properties of the protective coating `ELVI-VKh,` a polymeric composite based on epoxy resin with varying amounts of filler (basalt scale with different degree of dispersion, activated by thermal treatment at 800 C). The results of the corrosion tests showed that the investigated coatings are relatively resistant to the attack of 3% NaCL solution. After exposure to the salt solution, a St3 steel sample with the protective epoxy/basalt coating showed a corrosion depth of only 5.01 x 10{sup -5} to 3.55 x10{sup -4} mm/yr, depending on the degree of dispersion of the basalt scale. The corrosion rate of the uncoated specimen at these conditions was equal to 0.5 to 0.9 mm/yr. The electrochemical investigation showed that coatings with the `ELVI-VKh` polymeric material offered a high anitcorrosion protection. This is assisted by a low porosity of the coating which dictates a low permeability for water, oxygen, and ions, essential for the corrosive electrode reactions to take place.

Photodegradation of blends of poly(vinyl chloride) and polyurethane

Photodegradation of poly(vinyl chloride)/polyurethane (PVC/PU) blends was carried out and the effects of the blend ratio, thickness and irradiation atmosphere were examined by means of ultraviolet-visible and infrared spectrophotometry. Blend films thicker than 10 μm were more stable to photodegradation than either homopolymer, and the two components mutually retarded each other. The results obtained suggested that the retardation phenomena are largely dependent on the physical properties, especially the ultraviolet light absorptivity and the oxygen permeability of the component polymers. Thus, the higher light absorptivity of the PU and the lower oxygen permeability of the PVC are responsible for the photodegradation behavior of the PVC/PU blends.

Effect of dietary vitamin E on pigment and lipid stability of frozen beef: A kinetic analysis

The effect of vitamin E supplementation on pigment and lipid stability was evaluated with beef wrapped in high or low oxygen permeability films and stored in the dark or under constant illumination at −20°C. Dietary vitamin E supplementation improved pigment and lipid stability in both cases. Illumination increased metmyoglobin accumulation but did not affect lipid oxidation rate in both control and supplemented beef. A predisplay dark storage period of 30 days delayed metmyoglobin accumulation during subsequent display. Kinetic analysis showed that vitamin E supplementation stabilized the oxymyoglobin complex by enhancing the deoxymyoglobin oxygenation rate and by decreasing oxymyoglobin autoxidation rate.

Morphology and permeability in extruded polypropylene/ethylene vinyl‐alcohol copolymer blends

AbstractStudies of the morphology of extruded polymer blend systems have shown that it is feasible to produce a laminar structure of an ethylene vinyl‐alcohol copolymer (EVOH) dispersed phase in a polypropylene (PP) matrix phase. The laminar structure forms in the core of the extrudate when a slit die is incorporated into the extrusion process. Morphological studies, including a study of morphology development inside the die and studies of the effect of processing conditions on the morphology of the final product, revealed that the laminar structure is a result of die design. Processing conditions influence mainly the shape and dimensions of the laminar core region of the extrudate. Oxygen permeation tests have shown that the blend exhibits lower oxygen permeability than pure PP, when EVOH is incorporated as a dispersed phase into the system. Oxygen transmission rates obtained with a blend system approach those obtained with a multilayer coextrusion product, although only at high EVOH concentrations. Comparison of experimental data with theoretical permeation predictions shows that, up to 20 wt% EVOH, the reduction in oxygen transmission rate follows the prediction for a homogeneous system. At 25 wt%, a considerable decrease in oxygen transmission rate is noticeable, and the trend for higher EVOH contents is towards the behavior of a multilayer system.

Engineering Aspects of the Plant Design to Separate Volatile Hydrocarbons by Vapor Permeation

Abstract The paper deals with engineering aspects of the design of membrane systems for the separation and recovery of volatile hydrocarbons from off-gases. The membrane which is used for this application is a thin film composite membrane with an elastomeric selective top layer. This membrane has a high permeability for various hydrocarbon vapors and a low permeability for oxygen and nitrogen. The membrane configuration is a flat sheet membrane manufactured to an envelope with a round shape which is installed in the so-called GS module. The energy impact in accordance with the condensation mode and operating pressures is shown. Case studies on the influence of different process parameters, e.g., plant capacity, recovery rate, pressure ratio, stage cut and retentate concentration were carried out on the basis of given feed compressor and vacuum pump capacities. Finally, the investment costs of vapor recovery units in gasoline tank farms are discussed.

Effect of weathering on UV-stabilized low density polyethylene films (LDPE) for a multilayer greenhouse cover

Multilayer films for greenhouses is a current trend in industry. LDPE films for the top layer, stabilized with different concentrations (0·1, 1·0 and 2·5%) of a nickel quencher, were produced in the laboratory by blow extrusion. The effect of natural weathering on the film properties was investigated over a period of 12 months. Significant changes in the mechanical properties were observed in the later stages of degradation. Films stabilized with 0·1% stabilizer crumbled after 12 months of natural weathering whereas films with higher concentrations retained their mechanical properties. We believe that inclusion of the UV stabilizer interferes with the crystallization process and the stabilizer particles accumulate in the amorphous matrix. Degradation of the imperfect crystalline region with its low oxygen permeability, proceeds via cross linking whereas chain scission predominates in the amorphous region with excess of oxygen. Films stabilized with 2·5% nickel quencher form a barrier against the transmission of UV radiation and the bottom layers are least affected by UV radiation. Recycled material can, therefore, be incorporated at high concentrations into these layers.

Modified Atmosphere Packaging of Fresh, “Ready‐to‐use” Grated Carrots in Polymeric Films

ABSTRACT“Ready‐to‐use” grated carrots were packaged in different films (oxygen permeability from 950 to 22,000 cc/m2/day/atm at 25°C) and stored at 2, 6 or 10°C for 10 days. Gaseous atmosphere in packs and the following were monitored: lactic acid bacteria, yeast counts, exudate and potassium ion released, sugars, carotene, ethanol and lactic acid. The respiration rate of the packaged carrots was measured. Films with very low oxygen permeability resulted in anaerobic respiration, high leakage of potassium, and high lactic acid bacteria. With high‐permeability films (between 10,000 and 20,000 cc/m2/day/atm at 25°C), grated carrots showed aerobic respiration and retained good quality. At 10°C, in carrots packed in the most permeable film, sucrose decreased markedly during storage. The gas permeabilities required for packaging grated carrots were evaluated in relation to storage temperature.

Effect of sulphur dioxide on microbial growth in refrigerated pre‐peeled potatoes packaged in plastic films

AbstractMicrobial growth in pre‐peeled potatoes was analysed to determine the simultaneous effect of sodium bisulphite concentration (105–219 mg kg−1), storage temperature (4, 7 and 10°C) and gaseous permeability of the packaging plastic film (polyethylene and EVA—SARAN—EVA used in vacuum) on product storage life.Composition of the microbial flora was determined at the beginning and the end of the storage period, and the principal microorganisms causing spoilage of the product were observed to be Pseudomonas spp and Enterobacteriaceae. Lag phase duration and specific rate constants were determined for these microorganisms in samples stored at each condition.In polyethylene‐packaged samples microbial growth was observed at various temperatures and SO2 concentrations were tested. With vacuum packaging in low oxygen permeability films and residues of 100 mg SO2 kg−1, microbial counts were maintained in the lag phase; larger residues produced microbial inhibition at 4, 7 and 10°C.

Factors influencing frozen display life of lamb chops and steaks: Effect of packaging and temperature

Frozen lamb loin and rib chops and leg steaks were wrapped in film of high oxygen permeability or vacuum packaged in film of low oxygen permeability and stored in the dark at −10, −20 or −35°C for periods from 0–20 weeks. After storage, the wrapped cuts were displayed in an open-top cabinet operating at −20°C under continuous fluorescent lighting (Philips Deluxe 32°). Cuts were evaluated by a trained colour panel to determine acceptable display life, and chop lean colour was evaluated using a Hunter colorimeter. Cuts wrapped in oxygen permeable film had better colour retention during storage and display. Storage of the frozen chops reduced the display life, with the largest effect occurring during the first 4–5 weeks' storage. Cuts stored at −10°C had no display life after 10 weeks' storage, whereas cuts stored at −20 and −35°C had some acceptable display life even after the longest storage period tested. Rib chops in general had better colour stability than loin chops.

Factors affecting the production of hydrogen sulphide by Lactobacillus sake L13 growing on vacuum‐packaged beef

Lactobacillus sake L13 produced hydrogen sulphide during growth at 0°C on vacuum‐packaged beef of normal pH (5·6–5·8) when the packaging films used had oxygen permeabilities as high as 200 ml/m2/24 h/atm (measured at 25°C and 98% relative humidity. No hydrogen sulphide was detected when the film permeability was 300 ml/m2/24 h/atm. Sulphmyoglobin was formed whenever hydrogen sulphide was present except when the film permeability was very low (1 ml of oxygen/m2/24 h/atm). Lactobacillus sake L13 also produced hydrogen sulphide when grown on beef under anaerobic conditions at 5°C. When meat pH was high (6·4–6·6) hydrogen sulphide was first detected after incubation for 9 d. When 250 μg of glucose was added to each g of high pH meat, or when meat pH was normal (5·6–5·8), hydrogen sulphide was first detected after incubation for 18 d. The spoilage of beef by hydrogen sulphide‐producing lactobacilli is more rapid when the pH of the meat is high because high‐pH meat contains less glucose. Sulphmyoglobin formation and greening can be prevented by the use of packaging films of very low oxygen permeability.

Plasma polymerization of ethylene glycol monomethylether and water‐vapor permeability

AbstractPlasma polymerization of ethylene glycol monomethylether (EGMME) was investigated by elemental analysis, infrared spectroscopy, and ESCA. The surface and permeation properties for the formed polymers were discussed. EGMME was plasma‐polymerized to yield films. The films contained a large amount of oxygen‐containing groups such as hydroxy, carbonyl, carboxylate ester, and ether groups. The formation of polymers having hydroxy groups was favorable in plasma polymerization at low W/FM values. Their surface energy was high (63.2–57 dyn/cm) and decreased with increasing the W/FM value. The plasma‐polymers from EGMME had slightly high water‐vapor permeability and low oxygen and nitrogen permeabilities. The plasma‐polymers, conclusively, are characterized to have high selectivity in water‐vapor permeation.

A note on shelf-life extension of British fresh sausage by vacuum packing.

Vacuum packing of British fresh sausage in a low oxygen permeability film (Diolon) extended the product shelf-life at 6 degrees C to more than 20 d compared with 9-14 d in conventional packs. After 10 d storage, counts of key spoilage organisms such as yeasts and Brochothrix thermosphacta were generally 2 log cycles lower in vacuum packs. Vacuum-packed sausages also displayed a slower rate of loss of free sulphite. Variations in pack permeability to SO2 were not responsible for this. Losses of free SO2 in stored sausages are largely due to the production of sulphite-binding agents by yeasts. Selective enumeration of these yeasts showed them to be inhibited by conditions of vacuum packing. The extension of shelf-life observed is ascribed to the reduction in growth rate of the spoilage flora in vacuum packs coupled with the consequent maintenance of inhibitory levels of sulphite for a longer period.

Plastic-bonded electrodes for nickel-cadmium accumulators: VI. Oxygen recombination rate on sealed cell cadmium electrodes

The recombination ( i.e., reduction) of oxygen on pocket-type cadmium electrodes, utilizable in sealed Ni-Cd cells, occurs on areas covered with a thin layer of alkaline electrolyte. Hence, in the presence of a non-woven electrolyte carrier with a low permeability for oxygen, or by blocking the side of the electrode facing the gas space of the cell (which is not in contact with the electrolyte carrier), the recombination of oxygen is reduced to an insignificant level for sealed Ni-Cd cells. A comparison of results obtained with pocket-type and plastic-bonded cadmium electrodes showed that oxygen is reduced on metal parts of the electrode (perforated pocket, current collector, contacting metal screen) which are covered with a thin electrolyte layer, are easily accessible to oxygen, and are short-circuited by the electroactive Cd/Cd 2+ material. The latter has a sufficiently negative potential and electronic conductance to allow the electroreduction of oxygen to take place.

Lactic Acid Concentration and Microbial Spoilage in Anaerobically and Aerobically Stored Ground Beef

Lactic acid concentration of coarsely ground beef, packaged in low oxygen permeability casings, is inversely related to sensory acceptability of the meat following regrinding and aerobic storage for six additional days. Samples, reground and stored aerobically after periods of anaerobic storage, were assayed for total aerobic bacterial counts, percentage of gram‐positive microflora, and pH. Lactic acid concentration ranged from 130 to 1055 mg per 100g ground beef and increased with anaerobic storage. During 6 days of aerobic storage, both increases and decreases in concentration were noted and related to changes in microbial flora. A positive correlation was found between the proportion of gram‐positive bacteria (lactic acid bacteria) and lactic acid and pH.

Modification of in-pack conditions to extend the storage life of vacuum packaged lamb

High pH (>5·9) lamb loins from a research abattoir were subjected to differing packaging treatments to determine whether package modification could reliably extend the storage life of chilled lamb cuts beyond that attained by cuts vacuum-packaged in film of low gas permeability, as in current commercial practice. Treatments applied were carbon dioxide flushing or addition of a citrate buffer (pH 4·8), a 5% lactic acid solution or a Lactobacillus inoculum (plastic packs only) and packaging in a plastic film of moderately low oxygen permeability (140 cc/m 2/24 h at 25°C and 90% relative humidity) or in a foil laminate of immeasurably low oxygen permeability. After 12 weeks' storage at −0.5°C, the cuts packaged in the plastic film were spoiled by off-odours produced by enterobacteria, except for inoculated cuts, which, instead, had developed unacceptable dairy flavours. In contrast, cuts packaged in foil laminate developed floras of lactobacilli that had not caused spoilage after 12 weeks, and meat colour was much improved by the exclusion of oxygen. Loin cuts from a commercial packaging operation were packaged in a shrinkable plastic film of low oxygen permeability (30 to 40 cc/m 2/24 h at 25°C and 90% relative humidity), in foil laminate, or in foil laminate after the addition of 5% lactic acid solution. For the first 6 weeks, cuts were stored in a commercial chiller nominally operating at 0°C; subsequently, they were held in a laboratory chiller at −0.5°C. Some cuts packaged in the shrinkable plastic were spoiled after 9 weeks' storage and all were spoiled at 12 weeks, because of off-flavours produced by enterobacteria. All cuts packaged in the foil laminate were very acceptable at 9 weeks but most were spoiled by off-flavours at 12 weeks. Most cuts treated with lactic acid and packaged in foil laminate were unspoiled after 12 weeks. The packaging requirements indicated to be necessary for reliable extension of the storage life of vacuum packaged lamb are discussed.

Significance of Lactobacilli and Film Permeability in the Spoilage of Vacuum‐Packaged Beef

ABSTRACTThe spoilage of vacuum‐packaged fresh beef during storage at 5°C was studied using analytical taste panels. In the absence of contaminating micro‐organisms, meat spoiled due to the development of an “off” flavor described as “liver‐like.” This occurred even when the meat was packaged in bags made of film of very low oxygen permeability, but the rate of spoilage increased as the film permeability increased. Thus, vacuum‐packaged beef has a limited shelf life even in the absence of a significant population of contaminating microorganisms. Pure cultures of lactic acid bacteria increased the rate of spoilage, which was then due largely to the development of flavor defects described as sour, acid and bitter. Depending upon the strain of bacteria chosen, off flavor became significant 13—28 days after the population reached 108/cm2.