Ambient oxygen ingress rate method—an alternative method to Ox‐Tran for measuring oxygen transmission rate of whole packages

The ambient oxygen ingress rate method (AOIR) is an alternative method to Ox‐Tran for measuring the oxygen transmission rates (OTR) of whole packages. The objective of the present work was (a) to compare OTR values obtained by the two methods, and (b) to evaluate the use of the AOIR method for measuring OTR at realistic food storage temperatures and humidity levels. The AOIR method gave equal OTR values compared to the Ox‐Tran method for the five different types of whole packages used in the experiment, with OTR values in the range 0.06–1.48 ml O₂/day. The repeatability of the AOIR method measured on an HDPE bottle was ±2.6% of the measured value in this experiment. This is slightly higher than the general specifications of the Ox‐Tran method (1% of reading for packages). However, the AOIR method can be considered to be a reliable, precise and cheap alternative method to the Ox‐Tran method for measuring OTR of whole packages. The capacity of the method is also high. The AOIR method showed satisfactory results when comparing OTR for packages tested under realistic food storage conditions covering 23°C/50% relative humidity (RH) and at 4°C/60% RH on the outside, combined with water (100% RH) or dry air inside the packages. Copyright © 2000 John Wiley & Sons, Ltd.     

Predicting changes in oxygen concentration in the headspace of nitrogen flushed packages by the ambient oxygen ingress rate method

The ambient oxygen ingress rate (AOIR) method is an alternative/supplementary method to Ox‐Tran for measuring the oxygen transmission rates of packages. The AOIR method facilitates high‐capacity testing of packages under realistic food storage conditions, on the one hand, and on the other hand provides the possibility to predict the oxygen concentration over time in packages flushed with nitrogen at the time of packaging. The predicted oxygen concentration values showed good agreement with experimental values for flexible packages stored over a period of 91 days at 23°C and 38°C. The prediction of the oxygen concentration in­nitrogen‐flushed packages may be a useful tool, e.g. in shelf life studies, in the selection of the optimal food package as regards to oxygen protection and within quality control purposes. Copyright © 2002 John Wiley & Sons, Ltd.     

Oxygen barrier properties of thermoformed trays manufactured with different drawing methods and drawing depths

A comparison was made of oxygen barrier properties and wall thickness distribution of different thermoformed trays. The thermoformed trays were manufactured with three drawing depths and two different thermoforming methods; with and without plug‐assist. Four different polymer combinations were evaluated. The oxygen transmission rate (OTR) [cm³/(package/day)] was measured at three conditions (23°C/50% relative humidity (RH) with 0% RH inside, 6°C/80% RH with 0% RH inside, and 6°C/80% RH with 100% RH inside. Wall thickness was measured at five different positions in the trays. In general, temperature had more influence on the oxygen transmission rate (OTR) than the humidity. The OTR in the packages increased with increasing drawing depth, but the increase was not linear. Other effects besides thinning, such as orientation, may have influenced the OTR, since the relationship between OTR, given as cm³/(m²/day), and the drawing depth was not linear. Plug‐assisted thermoforming only had an effect on the OTR in trays with 70 mm drawing depth made of 600 µm thick laminate of PP/PE, which was probably due to exceeding the maximum drawing depth of this material. There was no correlation between the OTR value in the packages and the wall thickness in either of the positions, but a quite high correlation between the drawing depth and the relative wall thickness in all measured positions was observed. Copyright © 2004 John Wiley & Sons, Ltd.     

Oxygen‐ and light‐barrier properties of thermoformed packaging materials used for modified atmosphere packaging. evaluation of performance under realistic storage conditions

The oxygen transmission rate (OTR) of packaging materials used for modified atmosphere packaging (MAP) of chilled products varies extensively with temperature, relative humidity (RH) and material thickness after the thermoforming of packages. Two different polymer combinations were studied: APET/PE (tray) and PA/PE (lid). A temperature reduction of 8°C (in the interval 7–23°C) caused an OTR reduction of 26–48% depending on material type, degree of thermoforming and RH. A 2–3‐fold increase in OTR was observed for PA/PE film when measured at 100/100% RH compared to 0/100% RH, whereas the APET/PE trays were not affected by RH. Increased OTR was observed as a result of material thinning; however, the increase was not always directly proportional to the degree of material thinning. Even very small amounts of oxygen have, in combination with light exposure, significant effects on oxidative quality deterioration of many products. Consequently, the changes in OTR observed in this study emphasize the necessity of evaluating the performance of packaging materials under realistic storage conditions, in order to estimate the real oxygen content of a chosen package solution. The light transmission through the packaging material was found to be reduced to 0–30% (300–800 nm) by dyeing of the lid and/or addition of labels. Thus, it is easy to protect the products from light, at least partly. Copyright © 2005 John Wiley & Sons, Ltd.     

A comparative study of oxygen transmission rates through polymer films based on fluorescence quenching

Information on oxygen permeability through polymer films is essential for some applications, especially in food packaging where the control of oxygen levels can be critical in avoiding food spoilage. A permeability testing device using fluorescence‐based optical oxygen sensing was developed as a potential new instrument for measuring the oxygen permeability of packaging films. The fluorescence‐based permeability tester was validated against two existing commercial oxygen permeability measuring devices, the Mocon Ox‐Tran 2/20 and PBI‐Dansensor OPT‐5000. Oxygen transmission rates (OTR) of polylactide (PLA) and nanoclay‐reinforced PLA films, as well as polyethylene/poly(ethylene terephthalate) (PE/PET) and polypropylene/poly(ethylene terephthalate) (PP/PET) laminated films were determined at 23°C and 50% relative humidity using each of these instruments. No significant differences were observed between mean OTR values obtained by the fluorescence method and the corresponding values obtained using the OPT‐5000 but significantly lower values were measured when using the Mocon Ox‐Tran 2/20. In general, oxygen permeability data for the tested films were within the range of values found in the literature; however, in terms of further development, the fluorescence‐based technique gave OTR with relatively high standard deviation compared to the commercial methods and equipment modifications to address this issue are considered desirable. Copyright © 2010 John Wiley & Sons, Ltd.     

Liquid crystalline polymer pouches for local ­anaesthetic emulsion

In order to enhance the long‐term properties of a high‐pH local anaesthetic drug, emulsion tests were conducted where the emulsion was stored in pouches made of a compression moulded high‐barrier liquid‐crystalline polymer, Vectra A950. The oxygen permeability of the pouch material was too low to be detected at 23°C and 0% relative humidity with the instrument used. The water vapour transmission rate was 0.135 (g.mm/m².day) at 38°C and 100% relative humidity. The emulsion, containing prilocain and lidocain as active substances, was stored in pouches which were sealed by the thermal impulse technique at 260°C for 1.08 s. It was possible to obtain good quality films and good quality seals by optimization of the compression moulding and sealing operations. The concentrations of prilocain and lidocain in the emulsion were studied for 14 weeks at two different temperatures, 40°C and 60°C, and at 100% relative humidity. The decrease in concentration was higher for prilocain (5.4–8.3%) than for lidocain (3.4–3.6%). The loss of the substances from the emulsion was due mainly to adsorption onto the polar surface of the liquid crystalline polymer. Copyright © 2001 John Wiley & Sons, Ltd.     

Influence of sorbed vegetable oil and relative humidity on the oxygen transmission rate through various polymer packaging films

In this study, the effect of a vegetable oil on the oxygen barrier properties of different polymer packaging materials [i.e. amorphous polyethylene terephtalate (APET), polypropylene (PP) and high density polyethylene (HDPE)] was investigated. The influence of both relative humidity and the combination of relative humidity and sorbed oil on the oxygen transmission rate (OTR) was studied. Regardless of the relative humidity, the APET film remained an excellent oxygen barrier even after storage in rapeseed oil for 40 days. An increased OTR was observed in both the PP and HDPE films stored for 40 days in rapeseed oil. The OTR of the HDPE films was altered to a much greater extent than the OTR of the PP film. The OTR of the HDPE film was also significantly increased for films stored for 20 days in rapeseed oil. The increase in OTR of an HDPE film stored for 40 days in rapeseed oil was between 36 and 44%, depending on the relative humidity, compared to the OTR through the virginal polymer. The amount of oil sorbed by the polymer films used decreased in the following order: HDPE ? APET > PP.     

Prediction of oxygen transmission rate for thermoformed trays

There is a desire in the food industry to be able to estimate the oxygen transmission rate (OTR) of packages by knowing the permeability data of unconverted sheet/film, instead of measuring the OTR of packages. Due to thermoforming, the permeability of a material changes and therefore it is difficult to estimate the permeability (OTR) of converted trays from the OTR values of unconverted material. This paper evaluates the possibilities and limitations of predicting the OTR of thermoformed trays. Different methods for the calculation of OTR due to thickness measurements were compared. The use of theoretical thickness was satisfactory in the calculation of OTR of trays based on the OTR of unconverted sheet, area and thickness. Both linear and quadratic regression models were evaluated. Validation of the regression models was made by comparing the measured and calculated OTR of trays made of PS/EVOH/PE, A‐PET/PE, PS/PE and PP/PE. These trays were manufactured on different thermoforming machines, different processing parameters and different sizes of mould. None of the models (linear and quadratic) were suitable for the calculation of OTR of trays made of PS/PE and PP/PE. Both linear and quadratic models gave satisfactory agreement with measured values for trays made of both PS/EVOH/PE and A‐PET/PE. This case study indicates that a general equation for the calculation of OTR for different polymer combinations was not possible to generate. The equations presented in this paper are strictly applicable only for the polymer combinations used in this experiment, and can not be considered as general equations. Copyright © 2004 John Wiley & Sons, Ltd.     

The Effect of Pressure on Moisture Diffusion in Polymer Matrix Composites

Temperature and humidity play a significant role in the mechanical behavior and long-term durability of polymer matrix composites (PMCs). Several standard test methods including some accelerated test methods involving higher temperatures and pressures are available for environmental qualification of these PMCs. While the effect of temperature on humidity diffusion has been studied extensively, the effect of pressure has received less attention. This study seeks to interrogate the effect of pressure on diffusion. This effect was observed by building test chambers designed to maintain a constant relative humidity of 80 % at 60 °C at three different pressures (0.1014 MPa, 0.5171 MPa, and 1.0342 MPa). A liquid water immersion test chamber at 60 °C was also considered. It was observed that the time to saturation and the saturation moisture content increased with increasing chamber pressure. Immersion in liquid water provided the upper bound for the maximum moisture saturation and a lower bound for the time to saturation.     

相变材料用于可拆卸护臂热防护服的实验研究

针对传统降温服降温效果差、续航时间低、能耗高、噪声大等问题,本文通过应用相变恒温材料Na2SO4·10H2O在高温时发生相变吸收热量的特性,设计了一种应用于夏季高温环境的人体作业可拆卸护臂的热防护服,并在此基础上进行了热水模拟热源实验和真人实验。结果表明：在热水模拟实验中,防护服在30、41、45 ℃的工况下,前胸、侧腹、后背、腹部4测点温度在60 min升至最高,4测点平均温度最终能降至约26 ℃,其中在30 ℃工况下防护服降温性能较好,在45 ℃工况下降温性能较差。在真人实验中,防护服在37.1、39、41 ℃工况下,3 h内4测点平均温度最终能降至约26 ℃;在60 ℃高温极限工况下,3 h内4测点平均温度最终能降至约31 ℃,防护服护臂内外侧平均温度最终均能降至约32 ℃,低于人体的灼痛临界温度45 ℃。因此该防护服有良好的降温效果,能满足夏季户外工作者的热舒适性要求。     

Effect of packaging materials and storage conditions on bacterial growth,off‐odour,pH and colour in chicken breast fillets

A comparison was made of the effect of different packaging materials on bacterial growth, off‐odour, pH and colour of chicken breast fillets stored at 4°C. For one of the packaging materials, the effects of temperature (4°C and 8°C) and initial oxygen present (0%, 2% and 4%) on bacterial growth, off‐odour, pH and colour in chicken breast fillets were also evaluated. Chicken breast fillets stored in the packaging material with the highest oxygen transmission rate (OTR) measured at actual storage conditions had the highest bacterial growth and the highest degree of off‐odour. Chicken breast fillets stored in packaging material mainly consisting of expanded PET had similar bacterial growth and off‐odour as in the barrier display film (BDF) packages, despite a smaller headspace volume and lower initial concentration of CO₂. No differences in discoloration and pH of the chicken breast fillets, due to storage temperature and amount of initial oxygen present, were found when one of the packaging materials was studied. In the early phase of the storage period, Pseudomonas spp. constituted the majority of the total viable counts, while after about 12 days, lactic acid bacteria dominated. At the end of the storage period, both Pseudomonas spp. and Enterobacteriaceae were present in high numbers. Significant differences in counts of Brochothrix thermosphacta were only obtained with initial presence of oxygen. The storage temperature had greater impact on microbial growth and off‐odour than the initial presence of oxygen in the packages. Copyright © 2004 John Wiley & Sons, Ltd.     

Effects of Liquid Contaminants on Heat Seal Strength of low‐density polyethylene Film

Heat sealing is commonly applied for making form‐fill‐seal packages fabricated from thermoplastic films. One of the challenges frequently faced by the industry is inadvertent contamination of film–film interface by the product during filling, which can compromise package seal strength. In this study, the effects of dwell time (0.5–1.5 s), jaw pressure (28–1860 kPa), jaw configuration (narrow versus wide contact area) and jaw temperature (150°C–180°C) on the interface temperature and seal strength of a linear low‐density polyethylene (LLDPE) film were investigated. Three different film–film interface conditions were studied: (1) no contaminant; (2) with water contaminant; and (3) with vegetable oil contaminant. In the presence of liquid contaminant, jaw pressure played an important role in displacing the liquid from the seal area to form intact seals. Short dwell time (0.3 s) and low jaw temperature (150°C) was not favourable for forming intact seals in both water‐contaminated and vegetable oil‐contaminated films. The optimum jaw temperature and dwell time required to produce intact seals for oil contaminated films was 180°C and 0.3 s, respectively, whereas a combination of 165°C jaw temperature and 1 s dwell time was required to form intact seals for water‐contaminated films. Within the experimental conditions investigated, interface temperatures of 130°C–140°C resulted in the most optimum seal strength for both water‐contaminated and clean film specimens. Above 140°C, a weakening of seal strength was observed, presumably because of the change in melt flow characteristics and possible initiation of thermal degradation of the polymer. Copyright © 2011 John Wiley & Sons, Ltd.     

On the preparation of PLZT thin films grown by pulsed laser deposition

Polycrystalline PLZT thin films have been grown onto glass slides substrate, from a sintered stoichiometric 9/65/35 commercial target, by using a Nd:YAG laser (1064 nm, 7 ns, 10 Hz). The substrate temperature and oxygen pressure were varied during the deposition, as was the post-deposition annealing temperature in order to achieve stoichiometric films with a perovskite structure and with a composition near the ratio 9/65/35. Perovskite PLZT is formed around the substrate temperature of 500°C and oxygen pressure of ∼0.5 mbar after annealing at 580°C during 90 min. The pyrochlore structure, on the other hand, is always formed in the films during the deposition. However, this structure disappear for annealing temperatures above 550°C, for the films grown at oxygen pressure in the range 0.5–1 mbar and temperature deposition above 450°C. The degree of crystallinity and the structure present in the films is correlated with the deposition conditions. The influence of post-deposition annealing conditions on the formation of perovskite PLZT structure and optical transparency of the films is also discussed.     

Comparison of New Dynamic Accumulation Method for Measuring Oxygen Transmission Rate of Packaging against the Steady‐State Method Described by ASTM D3985

A new dynamic accumulation method for measuring the oxygen transmission rate (OTR) of packages and packaging films using robust and inexpensive fluorescence oxygen sensing technology has been developed. The method allows for oxygen to transfer through a given area of packaging or sample film and accumulate over time. The test volume incorporates a fluorescence‐based oxygen sensor that does not consume oxygen and therefore does not interfere with the real‐time measurement of oxygen concentration. The new method was tested against a widely used, commercially available instrument (Mocon Oxtran 2/20; Mocon, Inc., Minneapolis, MN, USA) designed around the steady‐state gas permeation measurement approach described by ASTM D3985. Sample films were chosen to provide comparison over several orders of magnitude of OTR. Specifically, sample films with OTR values in the range of 10¹, 10³ and 10⁴ ml O₂/m²/day were measured, and results using the two methods were compared. Results showed that the new dynamic accumulation method provides comparable results with the steady‐state method (ASTM D3985). Copyright © 2012 John Wiley & Sons, Ltd.     

High-pressure synthesis of diamond from phenolic resin

Two kinds of phenolic resin, novolak and resols, have been studied with an addition of cobalt at pressures between 2 and 4 GPa and at temperatures from 1300 to 1900 °C, all under thermodynamically graphite-stable conditions. Diamond was synthesized from these resins which had been pre-fired at 500–1000 °C. From such resins, carbon precursors carrying a great number of radicals, being nearly free of hydrogen and oxygen, and turbostratic in structure, can be constructed. The pressure–temperature conditions suitable for the diamond synthesis were dependent on the pre-firing temperatures. The cobalt served as a catalyst–solvent, similar to the case of conventional diamond synthesis from graphite under diamond-stable conditions. Well-defined single crystals cubo-octahedral in shape, measuring 0.3–0.7 mm across and classified as type Ib were obtained. This revised version was published online in November 2006 with corrections to the Cover Date.     

Rapid Assessment Testing of Polymer Aluminum Electrolytic Capacitors in Elevated Temperature–Humidity Environments

Aluminum electrolytic capacitors with polymer electrolytes were developed to obtain lower equivalent series resistance (ESR) than that is achievable with liquid electrolytes. Replacement of the liquid electrolyte with a solid conductive polymer also overcomes the propensity of the liquid to evaporate over time, which leads to a reduction in capacitance and an increase in ESR values. However, capacitor manufacturers acknowledge that humidity can degrade the polymer, thereby having an adverse effect on the reliability of polymer aluminum (PA) capacitors. In the current study, surface mount and thru-hole PA capacitors from two different manufacturers were subjected to highly accelerated stress testing (110 °C, 85% RH) and elevated temperature–humidity (85 °C, 85% RH) conditions for rapid assessment. The polymer electrolyte in the capacitors was poly(3,4-ethylenedioxythiophene). Failure analysis was performed to determine the observed failure modes and the underlying failure mechanisms. The dominant failure modes observed were an increase in leakage current and an increase in ESR.     

Effects of curing time and temperature on strength development of inorganic polymeric binder based on natural pozzolan

This paper reports the results of a study on the influence of curing conditions on compressive strength development in inorganic polymeric binder prepared from natural pozzolan. Three mixes with different chemical formulations were prepared and cured hydrothermally at different temperatures and times. In particular, the effect of a precuring at an atmosphere of more than 95% relative humidity at room temperature on compressive strength development before the application of heat was studied. Different curing regimes including hydrothermal treatment in steam-saturated atmosphere at different temperatures of 45, 65, 85 °C and for different time periods of 5, 10, 15, and 20 h after 1 and 7 days of precuring were applied. The mix exhibiting the maximum compressive strength after hydrothermal treatment was selected and cured in autoclave at temperatures of 125, 150, 180, and 210 °C for different time periods of 20, 30, 40, and 50 h for investigating the effects of higher times and temperatures of curing on strength development and also to determine the maximum achievable compressive strength. Results show that relatively long precuring in humid atmosphere is very beneficial for compressive strength development. The highest compressive strength achieved for three different regimes of curing including 28 days at an atmosphere of more than 95% relative humidity at 25 °C, 20 h hydrothermal treatment at 85 °C after 1 day precuring, and 20 h hydrothermal treatment at 85 °C after 7 days precuring were 37.5, 37.5, and 57.5 MPa, respectively. The maximum achievable compressive strength under autoclave curing at 210 °C for 30 h after 7 days of precuring was 108.7 MPa.     

Determination of oxygen and water vapour in modified atmosphere packages for meat sausages with and without an oxygen absorber

A gas chromatographic method has been developed that measures both the residual oxygen concentration and the level of relative humidity during the same run in modified atmosphere packages (N₂/CO₂) with and without an oxygen absorber. A processed meat product with a high content of water served as the foodstuff in those packages. The chromatographic system consists mainly of a loop-injector connected to capillary columns coupled in series and a thermocouple detector. The introduction of an oxygen absorber seems to be attractive, since the concentrations obtained for the residual amount of oxygen in the packages with an oxygen absorber varied between 0.0043 and 0.029%. For packages without an absorber, the oxygen concentrations were much higher and fluctuated between 0.26 and 0.56%. The whole measuring period lasted for 27 days. The relative humidity, also a factor that can cause food deterioration, was 100%. © 1997 John Wiley & Sons, Ltd.     

Effect of electrolyte temperature on the polarization characteristics of an Al-Li-Cu-Mg alloy in NaOH

The effect of electrolyte temperature on the polarization characteristics of an Al-Li alloy of composition Al-1·90 Li-1·80 Cu-1·00Mg-0·09Zr in 0·1 M NaOH solution was studied by the potentiodynamic polarization method. The electrolyte temperature was the equilibrium temperature established due to the prevailing weather conditions at different times in the year. The alloys exhibited active-passive behaviour at all the temperatures. It was found that the temperature of electrolyte affected the polarization behaviour of the alloys. The zero current potential and the open circuit potential were nobler with decreasing temperature. The corrosion current density, critical current density and passive current density increased with temperature, indicating the activated nature of the electrochemical process. The passive range was higher at 35°C compared to other temperatures. The temperature effect on polarization behaviour has also been explained by considering the dissolved oxygen concentration in the electrolyte at different temperatures. The ennoblement of Cu on the Al-Li alloy surface has also been addressed.     

Tribologisches Verhalten von Kunststoffen bei tiefen Temperaturen

Tribological Behaviour of Thermoplastics at low Temperatures The lubrication of sliding bearings for application to low temperatures is difficult, caused by the special failure after long standing of the most lubricants. An alternative is given by so-called „self-lubricated”︁ thermoplastic materials. Thermoplastic based composites with different filler materials have a good mechanical and thermal load capacity up to temperatures T = 200°C. The addition of sliding modifiers gives low friction coefficient and wear. Unknown is the behaviour of these materials at low temperatures. The aim of this work is to develope a test facility to estimation the tribological behaviour of materials at temperatures up to T = – 196°C and to investigate the application of different thermoplastic materials in friction with a steel of typ 100Cr6 as the counterbody under dry wear condition. Advanced thermoplastics, e.g. PPS, PAEK, PES or PI and PTFE with different fillers using for the investigations at temperatures T = − 40°C, room temperature and T = 160°C. The typical failure mechanism depending on the proof temperature are discussed.