Low Oxygen Permeability Research Articles

Microencapsulation of acerola (Malpighia emarginata DC) AND ciriguela (Spondias purpurea L) mixed juice with different wall materials

The effect of five different mixtures containing xanthan gum (XG), maltodextrin (MD) and gum arabic (GA) on microencapsulation by spray drying of mixed acerola and ciriguela juice was investigated in order to preserve its contents of ascorbic acid (AA), total phenolic compounds (PC) and total carotenoids (TC), as well as its antioxidant activity (AO) under different temperatures. All microcapsules produced with the different mixtures showed effective AA retention. Microcapsules produced using the mixtures with the highest and the lowest XG concentrations showed the greatest TC and PC retentions, respectively. As the mixture with MD and the lowest XG concentration ensured the highest AO retention, these microcapsules were stored for 30 days at 5°C, which ensured satisfactory preservation of AA, PC, TC and AO. Examination of their morphology by scanning electron microscopy showed the absence of pores or cracks, which allowed us to infer low oxygen permeability and high oxidative stability.

Ultra-high temperature oxidation resistance of a novel (Mo, Hf, W, Ti)Si2 ceramic coating with Nb interlayer on Ta substrate

In order to solve the challenge of recyclability of tantalum substrates in high temperature oxidation environments, a novel MoSi2-WSi2-HfSi2-TiSi2 composite ceramic coating containing an Nb interlayer was prepared on the surface of tantalum substrate by a three-step method. The mix ceramic silicide coating exhibited superior performance and effective protection for 10.2 h at 1800 °C, possibly due to the formation of an outer SiO2-HfO2-HfSiO4 composite oxide film with low oxygen permeability, moderate viscosity and thermal expansion coefficient, as well as good self-healing ability. Furthermore, the coating successfully passed 537 thermal cycles from room temperature to 1800 °C. The presence of Nb interlayer significantly mitigated the thermal mismatch between the ceramic coating and the tantalum substrate, and the bidirectional diffusion of Nb element during the high temperature oxidation and thermal shock process further reduced the tendency of the coating to crack.

Ablation properties and mechanism of a novel La2Hf2O7 coating

Based on excellent thermal stability and high melting point, La2Hf2O7 coating was prepared on SiC coated C/C composites by SAPS. When exposed to a heat flux of 3.2 MW/m2 for 20 s, the maximum surface temperature reaches 2240 °C, and the linear and mass ablation rates are 0.0030 mm/s and 0.0001 g/s, respectively. The chemical composition of the ablated La2Hf2O7 coating remained unchanged, and the coarsening of La2Hf2O7 grains caused a denser surface morphology with some pinholes and microcracks, which was attributed to thermal accumulation and scouring of heat flux. Owing to the low thermal conductivity, most of the heat was concentrated on the superficial region, promoting the outer La2Hf2O7 coating to evolve into a dense block structure with some defects, and the inner La2Hf2O7 coating maintained the initial structure. Because of the dense structure and low oxygen permeability of LaHf2O7 coating, the inner SiC coating was well protected without oxidation. Moreover, the nano-indentation results show that the hardness of La2Hf2O7 coating increased from 6.39 to 15.67 Gpa, which was ascribed to the intense solid-state sintering of La2Hf2O7 coating.

Renewable Furfural-Based Polyesters Bearing Sulfur-Bridged Difuran Moieties with High Oxygen Barrier Properties

With the goal of achieving high barrier with bio-based materials, for example, for packaging applications, a series of novel furfural-based polyesters bearing sulfide-bridged difuran dicarboxylic acid units with high oxygen barrier properties were synthesized and characterized. For the novel poly(alkylene sulfanediyldifuranoate)s, a 11.2–1.9× higher barrier improvement factor compared to amorphous poly(ethylene terephthalate) was observed which places the novel polyesters in the top class among previously reported 2,5-furandicarboxylic acid (FDCA) and 2,2′-bifuran-based polyesters. Titanium-catalyzed polycondensation reactions between the novel synthesized monomer, dimethyl 5,5′-sulfanediyldi(furan-2-carboxylate), and four different diols, ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol, afforded difuran polyesters with high intrinsic viscosities (0.76–0.90 dL/g). These polyesters had good thermal stability, decomposing at 342–363 and 328–570 °C under nitrogen and air, respectively, which allowed processing them into free-standing films via melt-pressing. In tensile testing of the film specimens, tensile moduli in the range of 0.4–2.6 GPa were recorded, with higher values observed for the polyesters with shorter diol units. Interestingly, besides the low oxygen permeability, the renewable sulfide-bridged furan monomer also endowed the polyesters with slight UV shielding effect, with cutoff wavelengths of ca. 350 nm, in contrast to FDCA-based polyesters, which lack significant UV light absorption at over 300 nm.

Morphology and permeability of bio-based poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate) (PBS) and linear low-density polyethylene (LLDPE) blend films control shelf-life of packaged bread

Poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate) (PBS) and linear low-density polyethylene (LLDPE) were blended to produce bio-based packaging via blown-film extrusion. Blend ratios modified morphology, crystallinity and relaxation temperatures (T α ) of the films. Binary mixtures caused phase separation and non-homogeneous fibrous microstructures of immiscible polymers. Bio-based blend films containing LLDPE (LLDPE/PBAT and LLDPE/PBS) gave less homogeneous structures than PBAT/PBS films. The formation of oriented fibrous networks subsequently controlled mechanical and barrier properties of the blend films. LLDPE blending modified C=O carbonyl groups in PBAT and PBS, forming voids in topographic images indicating incompatibility. PBAT and PBS blends showed good compatibility and adhesion of polymer interface, causing smooth and compact structures with minimal surface roughness. Incorporation of PBAT and PBS sharply reduced crystallinity of LLDPE/PBAT and LLDPE/PBS films. LLDPE/PBAT blends had lower T α than neat PBAT and LLDPE, while T α of PBAT/PBS blends proportionally decreased at increasing PBS which indicated diverse polymer miscibility and molecular mobility. Water vapor permeability (WVP) and oxygen permeability (OP) fitted with polynomial and exponential equations, respectively and depended on blend ratios. Films containing higher PBS had combined higher WVP and lower OP, delaying fungal growth in packaged bread due to dehydration. Ratios of PBAT, PBS and LLDPE blend films clearly affected mold growth and crumb hardness during storage. Regardless of film components, the firmness of bread crumbs increased linearly with package WVP. Conversely, mold growth had insignificant correlation with OP. Moisture loss from bread crumbs due to high WVP showed dominant effects on microbial growth. Blending PBAT and PBS modified the morphology and permeability of bio-based films and increased the shelf-life of packaged bread. • Systematic investigations for packaging properties in bio-based PBAT/PBS/PE blends. • FTIR intensity ratios effectively monitor bonding and morphology modifications. • H 2 O and O 2 permeability in PBAT/PBS/PE blends fitted to cubic and exponential model. • Hardness of packaged bread linearly increased with water vapor permeability. • Water vapor permeability majorly affected mold growth and increasing crumb hardness.

TADF dendronized polymer with vibrationally enhanced direct spin-flip between charge-transfer states for efficient non-doped solution-processed OLEDs

A novel type of thermally activated delayed fluorescence (TADF) dendronized polymer was designed and synthesized. Firstly, one side of the asymmetric TADF unit was encapsulated by 3,6-di-tert-butylcarbazole via a conjugated linkage with strong twisted intramolecular charge transfer (TICT) to minimize the energy gap between 1CT and 3CT, and then the peripheral dicarbazole connects in a non-conjugated way on the other side, showing weak TICT and high-lying 3LE&3CT state; finally, a linear dendronized polymer, PDCDC, was obtained by introducing the alkyl polymer backbone as main chains. As far as we know, this is the first blue or greenish-blue-emitting TADF dendronized polymer. For PDCDC, the spin-forbidden 1CT ↔ 3CT transitions are activated by molecular vibrations, which combine with a small energy gap and reorganization energy to enable 1CT ↔ 3CT spin-flip transition rates reaching 106 s−1 with negligible role of a second triplet state. Films of PDCDC show a double exponential decay (prompt fluorescence and delayed fluorescence) in the presence of oxygen due to a low oxygen permeability ascribed to the entangled polymeric backbone which increases film density. Besides, obvious aggregation-enhanced emission (AEE) property can minimize the exciton quenching in aggregated states. A maximum external quantum efficiency of 9.0% for non-doped PDCDC-based organic light-emitting diodes (OLEDs) can be obtained. To the best of our knowledge, these are the most efficient dendronized polymer devices with blue or greenish-blue emission.

Suppression of Radical Attack in Polymer Electrolyte Membranes Using a Vinyl Polymer Blend Interlayer with Low Oxygen Permeability

Suppression of Radical Attack in Polymer Electrolyte Membranes Using a Vinyl Polymer Blend Interlayer with Low Oxygen Permeability

High temperature oxidation behavior of MoSi2–Al2O3 composite coating on TZM alloy

A novel MoSi2–Al2O3 composite coating was prepared on Mo-based TZM alloy by slurry sintering method. The oxidation behavior of the coating was evaluated at 1600 °C in static air. Microstructure and phase composition of the as-prepared and oxidized coatings were characterized, and the antioxidant mechanism of the coating at high temperature was discussed. A three-layer structure was observed in the as-prepared coating, consisting of a ∼2 μm thick Mo5Si3 diffusion layer, a ∼65 μm thick MoSi2 inner layer and a ∼36 μm thick outer layer of mixture of MoSi2 and Al2O3. After oxidation at 1600 °C for 5 h, all MoSi2 phases were completely converted to intermediate silicide Mo5Si3 by solid-state diffusion, and the formed Mo5Si3 phase would be transformed into Mo3Si phase with further extending the oxidation time. Furthermore, a dense oxide layer of SiO2-mullite was formed on the specimen surface, which can effectively protect the material to further oxidation. The MoSi2–Al2O3 coating could protect the substrate effectively at 1600 °C for 20 h without failure. The enhanced oxidation resistance of MoSi2–Al2O3 coating is due to the formation of multi-layer structure containing a SiO2-mullite composite oxide outer layer with high thermal stability and low oxygen permeability.

Durability of concrete bearing polymer-treated mixed recycled aggregate

The construction industry’s growing interest in the use of recycled aggregate in concrete manufacture is being fuelled by an ongoing demand for more sustainable materials. The main obstacle to implementing that principle is the lower quality of recycled than natural aggregate and consequently of recycled than conventional concrete, especially with regard to durability. A number of techniques have been designed and developed of late to improve the properties of recycled aggregate. This is the first study to assess the effect of incorporating polymer pre-treated mixed recycled aggregate (MRA) on concrete durability. In this way, the properties of the concrete in terms of water transport parameters such as permeability to pressurised water, total water absorption, and capillary absorption; and of chloride penetration, air permeability, microstructure and porosity were studied. In the pre-treatment applied, the MRA was first soaked in a 20% polymeric solution for 60 min and subsequently oven- or air-dried. The results showed similar concrete fresh state density and percentage of entrained air in the mixes studied; as well as no significant effect was found on compressive strength. However, greater durability in air- than oven-dried pre-treated MRA-bearing concrete was obtained, attested to by the 64% lower water permeability, 17% lower sorptivity, 58% lower oxygen permeability, 28% lower chloride penetration and 11 % lower total porosity in the former than observed in a reference concrete prepared with untreated recycled aggregate.

Mechanical, barrier, thermal, and microstructural properties of poly (lactic acid) and gelatin–beeswax emulsion bi‐layer films

In this study, biodegradable bi-layer films from poly (lactic acid) (PLA) and bovine gelatin (BG)–beeswax emulsion were produced. PLA film was used as first layer, while BG containing beeswax at 0, 0.25, 0.50, 0.75, and 1% was the second layer, and optical, mechanical, barrier, thermal, and microstructural properties were characterized. The increasing beeswax concentration significantly increased the color difference (ΔE) and opacity of films, whereas decreased the light transmittance. Although tensile strength (TS) values decreased with the addition of beeswax, elongation at break (EAB) values increased. The highest oxygen permeability was observed from PLA film and production of bi-layer film significantly decreased the oxygen permeability. Microstructural images of bi-layer films containing 0.25 and 0.50% beeswax had good compatibility; however, increasing beeswax concentration to 0.75 and 1% weakened the interfacial adhesion of layers. PLA coated with BG–beeswax emulsions enhances the suitability of PLA films for food packaging applications. Novelty impact statement Poly (lactic acid) film was coated with gelatin–beeswax emulsion films to produce bi-layer films with low oxygen permeability. Gelatin–beeswax emulsion as outer layer improved the oxygen barrier properties of inner PLA layer. The production of PLA–gelatin/beeswax emulsion bi-layer films could be valuable for food packaging applications due to low water vapor and oxygen permeability.

Multilayer Films Based on Poly(lactic acid)/Gelatin Supplemented with Cellulose Nanocrystals and Antioxidant Extract from Almond Shell By-Product and Its Application on Hass Avocado Preservation.

In this work, poly(lactic acid) (PLA)/gelatin/PLA multilayer films supplemented with cellulose nanocrystals and antioxidant extract from almond shell (AS) by-products were developed by solvent casting technique for active food packaging. The almond shell antioxidant extract (ASE) was obtained by microwave-assisted extraction, while cellulose nanocrystals (CNCs) were extracted from AS by a sequential process of alkalization, acetylation and acid hydrolysis. Four formulations were obtained by adding 0 (control), 6 wt.% of ASE (FG/ASE), 4.5 wt.% of CNCs (FG/CNC) and 6 wt.% + 4.5 wt.% of ASE + CNCs, respectively, (FG/ASE + CNC) into fish gelatin (FG). PLA/FG/PLA multilayer films were prepared by stacking two outer PLA layers into a middle FG film. A surface modification of PLA by air atmospheric plasma treatment was optimized before multilayer development to improve PLA adhesion. Complete characterization of the multilayers underlined the FG/ASE + CNC formulation as a promising active reinforced packaging system for food preservation, with low values of transparency, lightness and whiteness index. A good adhesion and homogeneity of the multilayer system was obtained by SEM, and they also demonstrated low oxygen permeability (40.87 ± 5.20 cm3 mm m−2 day) and solubility (39.19 ± 0.16%) values, while mechanical properties were comparable with commercial plastic films. The developed multilayer films were applied to Hass avocado preservation. The initial degradation temperature (Tini), DSC parameters and in vitro antioxidant capacity of the films were in accordance with the low peroxide and anisidine values obtained from avocado pulp after packaging for 14 days at 4 °C. The developed PLA/FG/PLA films supplemented with 6 wt.% ASE+ 4.5 wt.% CNCs may be potential bioactive packaging systems for fat food preservation.

Effects of h-BN/SiC ratios on oxidation mechanism and kinetics of C/C-BN-SiC composites

C/C-BN-SiC composite was prepared by ceramic slurry infiltration combined with resin impregnation and carbonization, and the matrix with continuous distributed self-healing phase was obtained. In this study, the kinetic characteristics and oxidation behavior of the composites with various h-BN/SiC ratios in the temperature range of 600∼1300°C were studied by combining the isothermal oxidation test with the kinetic model. The optimal h-BN/SiC ratio balances the thermal stability and fluidity of the oxidized product, which not only has high thermal stability and low oxygen permeability to acts as an oxygen diffusion barrier but also has a certain fluidity to seal defects.

Increasing efficiency of the homogenization process for production of chitin nanofibers for barrier film applications

Chitin nanofibers (ChNFs) are of interest for barrier materials but are often extracted by high pressure homogenization (HPH) with high energy utilization. We studied the influence of deacetylation (DA) and pressure on HPH of shrimp chitin and the resulting solution cast films. Deacetylation to 72% DA resulted in improved ChNF suspension and film light transmission, strain at break, and tensile strength compared to chitin with DA of 89%. The oxygen permeability (OP) of the films was not affected by the modification and remained at low values of 1.9–2.4 cm3 μm/m2/day/kPa. We also show that deacetylation enables HPH intensity to be reduced during extraction of ChNFs from crab shell chitin (63% lower pressure and 73% reduction in number of passes), while achieving a low OP. Deacetylation pretreatment reduces HPH process intensity required to achieve oxygen barrier properties in ChNF films.

Influence of Ta2O5 on the micromorphology and high-temperature oxidation resistance of MoSi2-based composite coating for protecting niobium

Spent MoSi2-based materials were recycled as coating raw-materials, and MoSi2 and MoSi2-Ta2O5 coatings were fabricated to protect niobium using Spark Plasma Sintering (SPS). The micromorphology and anti-oxidation properties of the coatings at 1773 K were researched. Penetrating cracks were detected in the MoSi2 coating surface while no cracks appeared in MoSi2-Ta2O5 composite coating since the thermal expansion mismatch of the substrate and coating was reduced by adding Ta2O5. (Mo,Nb)5Si3 diffusion layer formed in MoSi2-Ta2O5 composite coatings, showing good metallurgical combination between substrate and coating. After oxidation at 1773 K for 20 h, crack-free Ta-Si-O layer with low oxygen permeability was formed on the composite coating. Compared with the oxidized MoSi2 coating, lower mass gain is gained by MoSi2-Ta2O5 composite coating under same conditions, presenting improved oxygen-barrier properties at high temperature.

Theoretical investigation of formation and diffusion mechanisms for point defects in ytterbium and lutetium silicates

AbstractUnderstanding the mechanism of point defects and the oxygen vacancy diffusion in rare earth (RE) silicates is important to evaluate their performance as environmental barrier coatings. In this work, the defect formation energies are calculated and the similar predominant native point defect type, that is, O Frenkel defect, in RE2SiO5 and RE2Si2O7 (RE = Yb and Lu) is uncovered. Furthermore, the nonstoichiometry related defects and phase composition in RE2SiO5 and RE2Si2O7 is also studied. For RE2SiO5, or is the predominate defect complex accompanied with the RE2Si2O7 separation under SiO2‐rich condition, while or is favorable under RE2O3‐rich condition. In the case of RE2Si2O7, or is the favorable defect complex under SiO2‐rich condition while or dominates the defects, accompanied with the formation of RE2SiO5, under RE2O3‐rich case. Finally, the high oxygen migration barriers are revealed for both RE2SiO5 and RE2Si2O7, indicating the low oxygen permeability in these silicates. These results will not only guide the future performance optimization of RE2SiO5 and RE2Si2O7 through tailoring their composition, but also suggest their potential application as oxidation protective coatings.

Oxidation behavior of Si- rich Mo-Si-B coating doped with La by spark plasma sintering

In this study, Mo-60Si-5B coating doped with 0.5 at% La was deposited on Nb-Si based alloy by spark plasma sintering and the oxidation resistance of the coating at 1300 ℃ was investigated. The results show that the mass gains of 0.5La-Mo-60Si-5B and Mo-60Si-5B coatings are 0.85 mg/cm−2 and 1.02 mg/cm−2 after oxidation at 1300 ℃ for 100 h, respectively. Good oxidation resistance of the coating is attributed to the formation of the glass phases La2SiO5 and SiO2 with low oxygen permeability, as well as the inhibition of oxygen diffusion due to the segregation of La2O3 at the grain boundary.

Addition of Al(OH)3 versus AlO(OH) nanoparticles on the optical, thermo-mechanical and heat/oxygen transmission properties of microfibrillated cellulose films

Differently structured aluminum (tri/mono) hydroxide (Al(OH)3 /AlO(OH)) nanoparticles were prepared and used as thermal-management additives to microfibrillated cellulose (MFC), cast-dried in thin-layer films. Both particles increased the thermal stability of the MFC film, yielding 20–23% residue at 600 °C, and up to 57% lowered enthalpy (to 5.5–7.5 kJ/g) at 0.15 wt% of loading, while transforming to alumina (Al2O3). However, the film containing 40 nm large Al(OH)3 particles decomposed in a one-step process, and released up to 20% more energy between 300 and 400 °C as compared to the films prepared from smaller (21 nm) and meta-stable AlO(OH), which decomposed gradually with an exothermic peak shifted to 480 °C. The latter resulted in a highly flexible, optically transparent (95%), and mechanically stronger (5.7 GPa) film with a much lower specific heat capacity (0.31–0.28 J/gK compared to 0.68–0.89 J/gK for MFC-Al(OH)3 and 0.87–1.26 for MFC films), which rendered it as an effective heat-dissipating material to be used in flexible opto-electronics. Low oxygen permeability (2192.8 cm3/m2day) and a hydrophobic surface (> 60°) also rendered such a film useful in ecologically-benign and thermosensitive packaging.

Towards a Bioactive Food Packaging: Poly(Lactic Acid) Surface Functionalized by Chitosan Coating Embedding Clove and Argan Oils.

Here we introduce a new method aiming the immobilization of bioactive principles onto polymeric substrates, combining a surface activation and emulsion entrapment approach. Natural products with antimicrobial/antioxidant properties (essential oil from Syzygium aromaticum—clove and vegetal oil from Argania spinosa L—argan) were stabilized in emulsions with chitosan, a natural biodegradable polymer that has antimicrobial activity. The emulsions were laid on poly(lactic acid) (PLA), a synthetic biodegradable plastic from renewable resources, which was previously activated by plasma treatment. Bioactive materials were obtained, with low permeability for oxygen, high radical scavenging activity and strong inhibition of growth for Listeria monocytogenes, Salmonella Typhimurium and Escherichia coli bacteria. Clove oil was better dispersed in a more stable emulsion (no separation after six months) compared with argan oil. This leads to a compact and finely structured coating, with better overall properties. While both clove and argan oils are highly hydrophobic, the coatings showed increased hydrophilicity, especially for argan, due to preferential interactions with different functional groups in chitosan. The PLA films coated with oil-loaded chitosan showed promising results in retarding the food spoilage of meat, and especially cheese. Argan, and in particular, clove oil offered good UV protection, suitable for sterilization purposes. Therefore, using the emulsion stabilization of bioactive principles and immobilization onto plasma activated polymeric surfaces we obtained a bioactive material that combines the physical properties and the biodegradability of PLA with the antibacterial activity of chitosan and the antioxidant function of vegetal oils. This prevents microbial growth and food oxidation and could open new perspectives in the field of food packaging materials.

Microwave vs. conventional extraction of pectin from Malus domestica ‘Fălticeni’ pomace and its potential use in hydrocolloid-based films

Conventional extraction (CE) and microwave-assisted extraction (MAE) were compared in terms of efficiency and quality of pectin in two separate processes aimed to extract pectin from Malus domestica ‘Fălticeni’ apple pomace. A similar extraction yield in a shorter extraction time was observed for the microwave-assisted procedure as compared to CE, while the galacturonic acid content and the degree of esterification of pectin were similar for both methods. Apple pectin extracted from this plant source by both methods had high galacturonic acid content, degree of esterification and molecular weight. Considering the high efficiency of microwave-assisted extraction and the composition of the obtained pectin, microwave-assisted apple pectin extracted under optimal conditions was used to produce edible films in combination with hydroxypropyl methylcellulose (HPMC). Films formulated with pectin from microwave extraction had significant lower oxygen permeability as compared to plasticized pure HPMC films, which makes microwave extracted pectin suitable for film-forming applications in which a good barrier to oxygen is required.

Molecular‐Level Contact of Graphene/Silver Nanowires through Simultaneous Dispersion for a Highly Stable Wearable Electrothermal Heater

AbstractSilver nanowires (AgNWs) with low sheet resistances are excellent potential candidates for high‐performance wearable electrothermal heaters operated through Joule heating. However, the thermal oxidation and electrical instability of AgNWs caused by high contact resistance and poor adhesion to different substrates considerably limit their use in devices. Graphene is used in a AgNW/graphene hybrid owing to its low oxygen permeability, lower contact resistance with AgNWs, and good van der Waals interactions. Molecular‐level contacts between AgNWs and graphene must be achieved to maximize the synergy of these properties. In this study, a multifunctional polymer possessing styrene sulfonate‐based copolymer and disulfide groups is designed; these groups allow the simultaneous dispersion of AgNWs and graphene in an aqueous solution through self‐assembly. Since this polymer promotes molecular‐level contact between AgNWs and graphene, the oxidation and Joule‐heating stabilities of the hybrid dramatically increase. In addition, a freestanding AgNW/graphene film is readily prepared, exhibiting good attachable properties on various substrates and superior stability under harsh conditions (85 °C and 85% relative humidity for 7 days). The AgNW/graphene hybrid film displays a low sheet resistance (0.36 ± 0.02 Ω sq−1) with good performance as a high‐performance electrothermal heater (200 °C at 1.5 V).