Oxygen Vapor Research Articles

Quantification of dominant diffusion processes through plasma enhanced chemical vapor deposition-coated plastics by combining two complementary methods for porosity analysis

Thin plasma polymerized gas barrier coatings were applied on PET films using low-pressure microwave excited hexamethyldisiloxane plasma. Oxygen and water vapor transmission rates were determined for the same barrier coating of varying thickness and correlated with the coating porosity. The porosity was quantified on different scales with two complementary methods. A plasma etching process with subsequent high-resolution SEM imaging and an automated defect detection as well as an overall porosity measurement by means of cyclic voltammetry. This method combination can be used to assign and classify Knudsen diffusion and Knudsen diffusion for different coatings and defect distributions applied. Film growing process could be observed with correlating defect distributions and it could be determined that almost no macro defects with a radius rd > 150 nm are present while growing process. With visually closed coatings, the entire oxygen and water vapor permeation could be attributed to Knudsen and solid body diffusion, although it is difficult to divide the proportions of these two processes.

Influence of BCl3/NH3 flow ratio on growth and microstructure of CVI-processed boron nitride interfacial coatings

Chemical vapor infiltration (CVI) is usually utilized to deposit hexagonal boron nitride (h-BN) interfacial coatings with layered microstructure. The deposition rate of BN coating increased with the increase of ammonia flow, indicating that the nucleation occurs on the surface of fibers rather than the gaseous phase. However, when ammonia flow is increased from 3.0 L min−1 to 7.5 L min−1, the deposition rate exhibits an increase of only 30%, which implies that the deposition of BN coatings is controlled by the boron deposition. Furthermore, the coating samples, prepared with ammonia flow of 3.0–4.2 L min−1, exhibits a relatively smooth surface, whereas the flow rates of 5.4 and 7.5 L min−1 result in strumae with a diameter of >4 μm. The smooth coatings demonstrate a near-stoichiometric ratio of boron and nitrogen, and render excellent thermal stability from room temperature to 1300 °C in argon and air. Moreover, the chemical composition of strumae-containing coatings is far from the desired stoichiometry and both coatings contain a lower amount of hexagonal phase, which can be ascribed to the lower thermal stability in the presence of oxygen and water vapors. The present study provides useful insights into the influence of CVI process parameters on the quality of BN coatings.

In vacuo atomic layer deposition and electron tunneling characterization of ultrathin dielectric films for metal/insulator/metal tunnel junctions

Metal-insulator-metal tunnel junctions (MIMTJs) are an enabling technology for future electronics including advanced computing, data storage, sensors, etc. MIMTJs are formed by inserting an ultrathin insulating layer, known as the tunnel barrier (TB), between metal electrodes. Devices based on MIMTJs have advantages of enhanced quantum coherent transport, fast speed, small size, and energy efficiency. The performance of MIMTJs depends critically on the thickness and quality of the tunnel barrier. Specifically, the tunneling current, for example, the superconducting critical current in superconductor-insulator-superconductor Josephson junctions (JJs) or the spin tunneling current in ferromagnetic-insulator-ferromagnetic magnetic tunnel junctions (MTJs), decreases exponentially with the TB thickness. This means thinner TBs would enable stronger coherent tunneling in MIMTJs. In addition, the defects in the TBs can degrade the quantum coherence of electrons (spins) of JJs and MTJs, respectively, resulting in decoherence and degraded performance of the MIMTJs. This justifies the urgent need in research and development of ultrathin (subnanometers to 1 nm) pinhole-free and defect-free TBs beyond the current state-of-the-art TBs of larger thickness (>1–2 nm) and high defect concentration made using thermal diffusion of oxygen or physical vapor deposition (PVD) including magnetron sputtering and molecular beam epitaxy. Atomic layer deposition (ALD) can provide a unique resolution to achieving ultrathin and defect-free dielectric TBs for high-performance MIMTJs for future electronics. In this article, a review on their recent effort in the development of in vacuo ALD for the fabrication of ultrathin TBs for JJs and MTJs is presented. A custom-designed system that integrates high-vacuum/ultrahigh-vacuum PVD, ALD, and scanning probe microscopy was established for in vacuo fabrication of MIMTJs and characterization of the electronic properties of ALD TBs including Al2O3, MgO, and Al2MgO4 on both superconductor metals (Al) and ferromagnetic metals (Fe and FeCoB). Capacitors with ALD dielectric of thickness in the range of 1–5 nm were also constructed for the characterization of the dielectric properties of the ALD TBs. The authors have found that the metal-insulator interface plays a critical role in controlling the quality of the ALD TBs including the tunnel barrier height, dielectric constant, electric breakdown, and uniformity. They have shown that JJs and MTJs with 0.1–1.0 nm thick ALD Al2O3 TBs can be obtained with highly promising performance. The result obtained suggests that the in vacuo ALD may provide a unique approach toward MIMTJs with an atomic-scale control of the device structure required for high-performance future electronics.

Functionality of ultra-high barrier metal oxide-coated polymer films for in-package, thermally sterilized food products

Abstract Defects in metal oxide (MO)-coated polymer films increase their oxygen and water vapor transmission rates (OTRs, WVTRs), lowering the shelf-life of packaged food. In this study, we investigated the effects of thermal processing on six multilayered MO-coated films: MO-A (MO-coated PET(12 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (50 μm)), MO-B (SiOx-coated PET(12 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (60 μm)), MO-C (Overlayer/AlOx-organic-coated PET(13 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (50 μm)), MO-D (Overlayer/SiOx-coated PET(12 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (60 μm)), MO-E (AlOx-coated PET(12 μm)//AlOx-coated PET(12 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (70 μm)) and MO-F (AlOx-coated PET(12 μm)//AlOx-coated PET(12 μm)//AlOx-coated PET(12 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (70 μm)). Water filled film pouches were processed with a pilot-scale retort (30 and 40 min at 121 °C; F0 = 6–9 min) and microwave-assisted thermal sterilization unit (25-kW, single-mode, 915 MHz MATS system; F0 = 10.9 min). Subsequently, the pouches were emptied, filled with a color-changing oxygen sensor and stored at 23 ± 2 °C for 180-days. MO-F with three AlOx-coated PET layers, showed no oxygen permeation before and after retort and MATS processes. Compared to other films, MO-F exhibited low WVTRs after processing. Oxygen sensor in MO-F changed color at limited locations, indicating fewer defects. Confocal laser scanning microscope and scanning electron microscope images also showed less deterioration in MO-F. The dielectric loss factor (er) for MO-F was significantly less than other films (P

Measurements of Density and Sound Speed in Mixtures Relevant to Supercritical CO2 Cycles

Abstract The objective of this research is to validate properties of mixtures relevant to supercritical carbon dioxide (sCO2) power cycles. Direct-fired sCO2 cycles are a promising technology for the future power generation systems. The working fluid of sCO2 cycles will be near and above critical point of CO2. One of the challenges is that the simulation of mixtures should consider real gas behavior. Expected operating conditions of Allam cycles reach up to 300 bar and 1000 °C. Characterizing the mixtures at the extreme conditions is an important issue in current researches and industrial applications. Thermophysical properties of mixtures may be beyond the valid range of the widely used database such as NIST REFPROP. Experimental data of mixture properties in the literature are limited which is necessary to develop high-fidelity design tools for sCO2 power cycles. We measured the density and sound speed of several multi-component mixtures. A temperature-controlled high-pressure test cell was used for the density measurements. Sound speed was measured by resonant frequency detection using an external speaker and a piezoelectric pressure sensor. Mixtures studied in this work include carbon dioxide, methane, oxygen, and water vapor. Properties of pure CO2 were measured to show the validity of our technique. Compositions were selected to be close to frozen mixtures at the inlet, mid-progress, and exhaust conditions of a model sCO2 combustor in the previous numerical simulation work. Corresponding reaction progress variables (RPV) were RPV = 0, 0.5, and 1. Temperature and pressure conditions of experiments are 310–450 K and 0–150 bar. In our study, density and sound speed from the NIST REFPROP database agree with experimental measurements within the range of our measurement uncertainties.

Reactive extrusion of sustainable PHBV/PBAT-based nanocomposite films with organically modified nanoclay for packaging applications: Compression moulding vs. cast film extrusion

The mechanical, thermal and barrier properties of a sustainable PHBV/PBAT blend was investigated under the influence of organically modified nanoclay (0.6, 1.2 and 1.8 wt%) after processing by two different techniques i.e. compression moulding and cast film extrusion. Firstly, a pelletized nanoclay masterbatch was fabricated by blending PBAT with 20% nanoclay using melt extrusion. The masterbatch was used as a reinforcement phase for the PHBV/PBAT blend matrix to fabricate nanocomposite pellets using a melt extrusion process. The prepared PHBV/PBAT/Nanoclay nanocomposite pellets were used to fabricate films using compression moulding and cast film extrusion. The cast extruded PHBV/PBAT nanocomposite films showed improved barrier properties (oxygen and water vapour) as compared to compression moulded films because of the chain orientation during the high-speed stretching. The barrier properties results showed significant improvement of ~79 and ~70% in oxygen and water vapour permeability respectively in cast PHBV/PBAT composite films after adding 1.2 wt% nanoclay, which indicates a good dispersion of nanoclay and strong interfacial adhesion between the matrix and filler. The intercalation/exfoliation of nanoclay in PHBV, as well as at the interface of the PHBV and PBAT blend matrix, was confirmed by transmission electron microscopy (TEM). The % elongation at break (567.6 ± 0.1) of the cast PHBV/PBAT/Nanoclay(1.2%) nanocomposite film was highly improved as compared to that of the PHBV/PBAT blend due to better stress transfer ability as compared to the compression moulded film. The rheological properties also support better dispersion of nanoclay and interaction between the matrix and filler. Hence, the cast extruded nanocomposite film with 1.2% nanoclay is a potential candidate to be used in flexible packaging.

Infusing High-density Polyethylene with Graphene-Zinc Oxide to Produce Antibacterial Nanocomposites with Improved Properties

Nanocomposites of high-density polyethylene (HDPE) modified with 0.2 phr graphene-zinc oxide (GN-ZnO) exhibited optimal mechanical properties and thermal stability. Two other nano-materials—GN and nano-ZnO—were also used to compare them with GN-ZnO. Increasing the content of GN-ZnO gradually enhanced the antibacterial and barrier properties, but the addition of 0.3 phr GN-ZnO led to agglomeration that caused defects in the nanocomposites. Herein, we investigated the antibacterial and barrier properties of HDPE nanocomposites infused with different nanoparticles (GN, ZnO, GN-ZnO) of varying concentrations. HDPE and the nanoparticles were melt-blended together in a Haake-Buchler Rheomixer to produce a new environment-friendly nano-material with improved physical and chemical properties. The following characterizations were conducted: tensile test, thermogravimetric analysis, morphology, differential scanning calorimetry, X-ray diffraction, antibacterial test, and oxygen and water vapor permeation test. The results showed that the crystallinity of HDPE was affected with the addition of GN-ZnO, and the nanocomposites had effective antibacterial capacity, strong mechanical properties, high thermal stability, and excellent barrier performance. This type of HDPE nanocomposites reinforced with GN-ZnO would be attractive for packaging industries.

Improved Process to Obtain Nanofibrillated Cellulose (CNF) Reinforced Starch Films with Upgraded Mechanical Properties and Barrier Character.

Nowadays, the interest on nanofibrillated cellulose (CNF) has increased owing to its sustainability and its capacity to improve mechanical and barrier properties of polymeric films. Moreover, this filler shows some drawbacks related with its high capacity to form aggregates, hindering its dispersion in the matrix. In this work, an improved procedure to optimize the dispersability of CNF in a thermoplastic starch was put forward. On the one hand, CNF needs a hydrophilic dispersant to be included in the matrix, and on the other, starch needs a hydrophilic plasticizer to obtain a thermoformable material. Glycerol was used to fulfil both targets at once. CNF was predispersed in the plasticizer before nanofibrillation and later on was included into starch, obtaining thin films. The tensile strength of these CNF–starch composite films was 60% higher than the plain thermoplastic starch at a very low 0.36% w/w percentage of CNF. The films showed a noticeable correlation between water uptake, and temperature and humidity. Regarding permeability, a ca. 55% oxygen and water vapor permeability drop was found by nanofiller loading. The hydrolytic susceptibility of the composite was confirmed, being similar to that of the thermoplastic starch.

Characterization and antioxidant activity of trilayer gelatin/dextran-propyl gallate/gelatin films: Electrospinning versus solvent casting

In this study, trilayer films were prepared with an electrospun dextran interlayer, and gelatin outlayers fabricated by solvent casting and electrospinning, respectively. The trilayer film either with casted or electrospun outlayers showed an enhanced thermal stability, and acceptable color and opacity properties. Compared to the electrospun outlayers, the casted outlayers endowed the trilayer film with improved oxygen and water vapor barrier properties, and significantly enhanced the elastic modulus and tensile strength, indicating a greater resistance to deformation. The DPPH radical-scavenging activity assay indicated that the applied electrospun or casted outlayers effectively prolonged the release time of propyl gallate from the interlayer by 2-fold or more, with a sustained antioxidant activity. These results suggest the promising applications of multilayer films as active packaging materials with prolonged release of antioxidants to retard oil oxidation in the food industry.

NO Detection By Cyclic Voltammetry with Platinum Electrodes on YSZ

Introduction Solid electrolyte sensors (SES) based on yttria stabilized zirconia (YSZ) can be used to detect traces of other components in inert gases such as Ar or N2. The O2--conducting solid electrolyte YSZ is thermodynamically highly stable and can be operated at high temperatures with stationary (potentiometry, amperometry) or dynamic methods (pulse polarization [1], cyclovoltammetry (CV) [2]). In the stationary mode, the selectivity of such sensors is limited to an extend that it is usually not possible to distinguish between individual gas components. In contrast to that, dynamic methods allow a significantly increased selectivity by using different rates of electrode reactions of the individual components in order to detect them independently in a gas mixture [2]. Dynamic electrochemical methods have been successfully used in liquids for many decades, and preliminary investigations on solid electrolyte gas sensors also show that such methods can be used to measure the concentrations of several redox-active gases, for example, oxygen and carbon monoxide [3]. The commercial solid electrolyte sensor used in this work was previously successfully tested to measure selectively different gases such as hydrogen, oxygen and water vapor [4] in nitrogen by using CV. In this work, these studies will be continued to investigate the ability of CV for selective detection of nitrogen oxides (NOx) and to elucidate the mechanisms of signal formation. Experimental setup The experimental setup shown in Fig. 1 and described in detail in [2] was used to adjust the O2 concentration (SES 1) and the measurement of the concentrations of O2 and NO in nitrogen (SES 2). Both SES of the type "Test gas, Pt|YSZ|Pt, air" contain a YSZ-tube equipped with two cylindrical platinum mesh electrodes at the inner and outer surface. The area of the inner measuring electrode was estimated by SEM to be about 3.5 cm2. A porous YSZ sintered layer was applied to join electrolyte and electrodes. Covering large parts of the reference and measuring electrode this porous layer offers an extended three-phase boundary for the oxygen transfer.SES 1 was continuously polarized during each experiment providing a constant O2 concentration in the purified carrier gas N2. At SES 2, the CVs were obtained at polarization voltages between -0.1 and -0.9 V against the Pt air reference electrode and scan rates in the range 100 ... 5000 mV/s. In each experiment, the second cycle was evaluated to obtain reproducible results. Between two consecutive cyclovoltammograms (CVM), the open circuit potential (OCP) was measured to monitor depolarization of the measuring electrode. Results and discussion The CVMs shown in Fig. 2 exhibit NO-related peaks developing in the cathodic scan direction between -0.2 and -0.7 V at scan rates between 100 and 2000 mV/s. The peak maximum shifts in the cathodic direction with increasing scan rate. The highest sensitivity was achieved at 2000 mV/s for 650 °C. At higher scan rates it decreases again. This is apparently caused by the shift of the oxygen reduction peaks from range -0.1 ... -0.3 V at lower scan rates to the cathodic direction at higher scan rates and leads to their superposition with the NO peaks. The curve shifts to higher electrolysis currents with increasing NO-concentration in the cathodic region, visible for every scan rate at U < -0.7 V correspond to the Faraday currents calculable for the NO reduction. The different peak potentials for O2 and NO enable a highly selective determination NO in O2 containing gases at scan rates between 200 – 2000 mV/s at concentrations c(NO) ≥ 10 vol.-ppm.The height of the NO peak as a suitable NO-related signal was calculated and plotted in Fig. 3 for different scan rates. This peak height rises almost linearly with the NO concentration and the curve slopes increase with the scan rate up to 2000 mV/s. Further investigations revealed that this scan rate-induced slope increase depends also on flow rate.OCP measurements at different NO concentrations and sensor temperatures (Fig. 4) indicate the known tendency of NO to decompose at hot and catalytically active platinum electrodes into N2 and O2. Therefore, in the investigated temperature range, the absolute value of the OCP decreases with increasing NO concentration, coming with rising oxygen partial pressure according to NO decomposition. Another process guiding the OCP in the NO-free carrier gas is the electronic conductivity of the solid electrolyte that increases exponentially with temperature [5].

Effectiveness of PECVD deposited nano-silicon oxide protective layer for polylactic acid film: Barrier and surface properties

Abstract This study evaluated the effectiveness of a silicon oxide (SiOx) layer of approximately 100 nm thickness manufactured by plasma enhanced chemical vapor deposition (PECVD) as a protective coating for PLA-based films to reduce the corrosion and contaminant migration caused by food contact. The migration kinetics of plasticizer diethylene glycol dibenzoate (DEDB) in the films and the barrier and surface properties of films were studied. Results indicated that compared to PLA-based films, the final DEDB migration amount of SiOx/PLA-coated films was reduced by 23.75-36.90% in food simulants A, B, C and D1, while the time to reach migration equilibrium was prolonged. SiOx layer increased the static water contact angle of the PLA film from 85.5 ± 0.4° to 101.8 ± 1.2° and decreased the oxygen and water vapor transmission rates by 48.45% and 28.53%, respectively. The nanostructured SiOx barrier layer was effective in protecting the shape and transparency of the coated films.

Influence of hydrogen, oxygen, nitrogen, and water vapor on the formation of pores at welding of copper using laser light at 515 nm wavelength

Due to increased absorptivity of laser light at 515 nm wavelength in copper materials, welds with low formation of spatters and homogeneous weld depths can be performed.1 However, depending on the used process parameters, a process regime with strong formation of pores is observed. These pores are not resulting from instabilities of the capillary (process pores), but they are observed to result from the interaction of ambient gas with the melted material in the welding zone. Different gaseous elements such as nitrogen, hydrogen, oxygen, and water vapor, therefore, were applied to the welding process to investigate their influence on the resulting weld seam porosity. For this purpose, all welds were performed in a welding chamber. It is found that the reaction of ambient nitrogen with ambient oxygen during the welding process has a strong influence on the resulting weld seam porosity. Furthermore, pores are observed in the weld seam when the raw copper material contains an increased amount of oxygen. Depending on which copper material is used, strategies are derived to perform welds with low or no formation of pores.

Investigation on the Corrosion Behavior of Nickel‐Base Alloys in Molten Chlorides for Sensible Heat Energy Applications

Nine selected alloys are exposed in molten KCl–LiCl (eutectic composition) at 1073 K for 167 h under argon atmosphere to predict the long‐term corrosion behavior of these structural materials. The corrosive attack of each alloy is assessed with gravimetric methods, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy measurements. The corrosion rate of each alloy is calculated in accordance with ASTM G1‐03. Low chromium containing alloys as HAYNES 242, Hastelloy B‐3, and Hastelloy N revealed minor or no significant corrosive attack after molten chloride exposure. Alloy 600, Alloy 617, HAYNES 625, Hastelloy X, HAYNES 230, and HAYNES 188 with a chromium content wCr &gt; 8% show severe corrosive attack with complete chromium depletion along the near‐surface layer and partially along grain boundaries. The results show that chromium forms chromium oxide with impurities of oxygen and water vapor at low oxygen partial pressures. This initiates an accelerated corrosion of the alloying elements in the matrix of Ni, Cr, Mo, Fe, and Co, due to chlorine formation. The influence of the composition of nickel‐base alloys on the corrosion resistance is discussed based on the comparison of the gravimetric measurements and thermodynamic calculations.

Nano-patching defects of reduced graphene oxide by cellulose nanocrystals in scalable polymer nanocomposites

Reduced graphene oxide (rGO) has been widely produced by exfoliation of pristine graphite followed by oxidation and reduction. However, a number of defects can be generated during the synthesis of rGO, restricting the ability to scale-up in industrial production of defect-free rGO. The defects in rGO have limited its capacity for utilization of the full potential of the physical properties of polymer nanocomposites, such as gas and water barrier performances. Hence, this study analyzes the nano-patching of rGO defects through hydrophilic interactions of oxygen functional groups in rGO with cellulose nanocrystals (CNCs) in polyvinylidene chloride (PVDC) nanocomposites. For scalable production of defect-engineered PVDC nanocomposite barrier films, the surface energies of rGO and CNC dual nanofiller systems were regulated to prevent phase-separation of nanofillers in the PVDC matrices. The barrier properties of the PVDC/nano-patched filler composites showed drastic reduction of oxygen and water vapor transmission rates corresponding to 0.45 cm3 m−2 day−1 and 0.52 cm3 m−2 day−1, respectively, that decreased by 94.2% and 87.9% compared to that of the neat PVDC host. The nano-patching strategy provides novel and effective defect engineering of graphene for polymer nanocomposites.

Development and evaluation of soy protein isolate-based antibacterial nanocomposite films containing cellulose nanocrystals and zinc oxide nanoparticles

This study aimed to develop soy protein isolate (SPI)-based active nanocomposite films reinforced with cellulose nanocrystals (CNC), zinc oxide nanoparticles (ZnONP), CNC/ZnONP mixture (physical mixing), or CNC@ZnONP nanohybrids (in situ growth). The tensile strength, oxygen and water vapor barrier properties, water resistance ability, and thermal stability were substantially improved by the incorporation of nano reinforcements, particularly the CNC-containing agents. However, the nanocomposite films displayed a lower elongation at break, surface hydrophobicity, and transmittance compared with the pure SPI-based film. The filling effect of reinforcements and their hydrogen bonds with the film matrix contributed to the formation of a compact and homogeneous film structure. The ZnO-containing films obviously inhibited the growth of foodborne pathogens (Escherichia coli and Staphylococcus aureus) and also reduced the total viable counts and the total volatile basic nitrogen values in a pork sample. Furthermore, the CNC@ZnONP film prevented the migration of zinc from the film into the food system. Therefore, the obtained nanocomposite films have broad application prospects in the field of active food packaging.

Evaluation of the Suitability of Poly(Lactide)/Poly(Butylene-Adipate-co-Terephthalate) Blown Films for Chilled and Frozen Food Packaging Applications.

The use of biopolymers can reduce the environmental impact generated by plastic materials. Among biopolymers, blends made of poly(lactide) (PLA) and poly(butylene-adipate-co-terephthalate) (PBAT) prove to have adequate performances for food packaging applications. Therefore, the present work deals with the production and the characterization of blown films based on PLA and PBAT blends in a wide range of compositions, in order to evaluate their suitability as chilled and frozen food packaging materials, thus extending their range of applications. The blends were fully characterized: they showed the typical two-phase structure, with a morphology varying from fibrillar to globular in accordance with their viscosity ratio. The increase of PBAT content in the blends led to a decrease of the barrier properties to oxygen and water vapor, and to an increase of the toughness of the films. The mechanical properties of the most ductile blends were also evaluated at 4 °C and −25 °C. The decrease in temperature caused an increase of the stiffness and a decrease of the ductility of the films to a different extent, depending upon the blend composition. The blend with 40% of PLA revealed to be a good candidate for chilled food packaging applications, while the blend with a PLA content of 20% revealed to be the best composition as frozen food packaging material.

Preparation and characterization of environmentally safe and highly biodegradable microbial polyhydroxybutyrate (PHB) based graphene nanocomposites for potential food packaging applications

Polyhydroxybutyrate (PHB) is a natural polyester of microbial origin and is an excellent substitute for petroleum-based food packaging materials. However, moderate mechanical, thermal and barrier properties limit utilization of PHB for commercial food packaging applications. In order to overcome these drawbacks, the present study evaluated the solution casting method for the preparation of PHB nanocomposite by incorporating various concentration (0–1.3 wt%) of graphene nanoplatelets (Gr-NPs). The prepared nanocomposites were tested for their morphology, mechanical, thermal, barrier, cytotoxicity and biodegradable properties. A Gr-NPs concentration of 0.7 wt% was found to be optimum without any agglomeration. In comparison with pristine PHB, the PHB/Gr-NPs nanocomposite showed a higher melting point (by 10 °C), thermal stability (by 10 °C), tensile strength (by 2 times) along with 3 and 2 times reduction in oxygen and water vapour permeability, respectively. The penetration of UV and visible light was greatly reduced with the addition of Gr-NPs. Furthermore, cytotoxic effect of the prepared nanocomposite was found to be statistically insignificant in comparison with the pristine PHB. A four-fold increase in the shelf life was demonstrated by a simulation study conducted using moisture and oxygen-sensitive food items (potato chips and milk product).

High pressure-assisted thermal sterilization of low-acid fruit and vegetable purees: Microbial safety, nutrient, quality, and packaging evaluation

The objective of this study was to assess the influence of pressure-assisted thermal sterilization (PATS) on nutrients and quality of pumpkin, butternut squash, pea, beetroot, and purple potato purees. PATS processing parameters included preheating of purees at 98 °C for 5 min and pressurizing at 600 MPa in a vessel set at 90 °C for 5 min. Colorimetric temperature sensors, two types of Bacillus amyloliquefaciens spores, total aerobic and anaerobic plate count, HPLC, as well as spectrometer and spectrophotometer were utilized. The colorimetric temperature sensor based on its color value when extrapolated suggested the purees' temperature reached 122 °C. Thus, at least 9-log10 reduction of B. amyloliquefaciens spores was achieved in a purple potato puree, and no detectable aerobic and anaerobic microorganisms were found after PATS in all purees. Vitamin C showed 3–14% reduction after PATS. Total chlorophyll and β-carotene did not vary significantly (p > 0.05) after PATS, while betalains and anthocyanin were sensitive and decreased significantly. Interestingly, total color change (ΔE) of pumpkin, butternut squash, and beetroot purees ranged between 2.5 and 3.4 below the threshold (ΔE = 6) value that can be observed by the naked eyes. EVOH-based packages did not show any visual deformation, but their oxygen and water vapor transmission rates increased significantly (p < 0.05) after PATS. The present research suggests that PATS can be used to produce safe and high-quality shelf-stable fruit and vegetable products.

654 Investigation of Germ Patency of a Polylactic Acid-based Membrane for the Treatment of Burns

Abstract Introduction Infections are a very serious complication during the treatment of burns. To avoid such infections, burn care dressings and skin substitutes should be impermeable to germs. Polylactic membranes (PLM) are based on polylactic acid (PLA) and as an elastic membrane it mimics the natural skin. They are indicated for superficial (2a°) and deep dermal/partial thickness (2b°) skin loss diseases like burns. While being permeable to oxygen and water vapor, they provide a physical barrier for microorganisms. The infection rate of the PLM in burns was about 2,9% on average and was published in 11 studies. The effectiveness of the physical barrier for microorganism was tested in an in-vitro model. Methods The sterile PLM samples were aseptically transferred into sterile petri dishes and inoculated with 100 µl each of a bacterial suspension. The test strains Staphylococcus aureus (ATCC 6538) with approximately 730 colony forming units (cfu) and Pseudomonas aeruginosa (ATCC 10145) with approximately 350 CFU / sample were used. The bacterial suspension was spread over the surface and dried. PLM were transferred to Tryptic Soy Agar (TSA) plates. The incubation was carried out in each case with 3 batches per test strain after 1 day and 3 days at 37°C. After incubation, the PLM samples were visually examined for microbial growth under the samples and photographically documented. A control group with inoculation of culture medium and covered with PLM was also tested. Results There was no growth of bacteria detectable after 1 day and after 3 days under the PLM indicating that the PLM is not permeable to germs. The control group resulted in growth of bacteria and colony forming units and thus confirms that test method works well. Conclusions PLM is an effective physical barrier for microorganisms as germs do not pass the PLM. Applicability of Research to Practice immediately.

Amperometric H2S sensor based on a Pt-Ni alloy electrode and a proton conducting membrane

In this work, carbon fiber carrying platinum-nickel alloy is used as a sensing electrode material to develop a H2S gas sensor based on Nafion proton membrane. Characterizations of the material by X-ray diffraction (XRD), scanning electron microscope (SEM) and Energy Dispersive Spectrometer (EDS) reveal that the structure and morphology of the particles change with the ratio of the alloy. The electrochemical specific area (ECSA) of the material is calculated by cyclic voltammetry, which further proves the influence of alloy formation on the catalytic performance of the materials. When the ratio of platinum to nickel is 1:1, the material is uniformly loaded and its catalytic performance is optimal. Thus, the device made with it has the highest sensitivity. The sensor's low detection limit is 0.2 ppm. For the incorporation of nickel, the sensitivity is increased to -0.306 μA/ppm, which is 18 % higher than before. Not only does the sensor have good repeatability and short response recovery time, the presence of oxygen and water vapor does not have much effect on the sensor. Therefore, it has a great application potential in the field of gas detection at room temperature.