Comparison of Various Packaging Films for Mango Export

This study compared the effects of the use of various types of packaging films in maintaining quality, preserving bioactive compounds and extending shelf life of the ‘Nam Dok Mai’ mango. The principal techniques for maintaining the quality of mangoes are based on modified atmosphere packaging using highly gas‐permeable films and an ethylene‐removing mechanism. The films studied were non‐perforated highly gas‐permeable film, non‐perforated ethylene‐absorbing highly gas‐permeable film (HNPE), micro‐perforated highly gas‐permeable films (HMP) and common non‐perforated polyethylene film (LNP). These films were compared with non‐packaging treatment, which served as a control (C). Gas composition (O₂, CO₂ and C₂H₄) in the package headspace was monitored during storage at 12°C. The quality of mangoes were assessed by weight loss, colour (L* a* b*), texture, total soluble solids, titratable acidity, total phenolics, total flavonoids, ethanol concentration and sensory quality. Equilibrium‐modified atmospheres of 5 kPaO₂ + 5 kPaCO₂ and 4 kPaO₂ + 5 kPaCO₂ were achieved in the non‐perforated highly gas‐permeable film and HNPE packs, respectively. Carbon dioxide accumulation was observed in the HMP and LNP packs where CO₂ reached 17 and 10 kPa, respectively, after storage for 10 days. The shelf life of mangoes was extended to 40 days with HNPE, 35 days with HNP, and 30 days with HMP, as compared with 20 days with control and 5 days with LNP. HNPE, the film incorporated with fine particles of mordenite framework inverted‐type zeolite with ethylene‐absorbing ability, could further extend the shelf life of mangoes in addition to modified atmosphere packaging alone. Copyright © 2011 John Wiley & Sons, Ltd.     

The effect of zeolite L content on dielectric behavior and thermal stability of polyimide thin films

Zeolite L, with the ratio Si/Al?=?4, was prepared by hydrothermal method and used to obtain composite films based on a polyimide matrix having pendant carboxylic groups. The effect of zeolite L content on dielectric behavior and thermal stability of polyimide thin films was studied. The films were prepared by casting a suspension resulting from direct mixing of a poly(amic acid) (PAA) solution and zeolite L particles onto glass plates, followed by thermal imidization under controlled temperature conditions. The PAA was synthesized by solution polycondensation of a mixture of two diamines, 3,5-diaminobenzoic acid and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (molar ratio 1:3), with 4,4′-oxydiphthalic anhydride, using N-methyl-2-pyrrolidone as solvent. To improve the compatibility between organic and inorganic phases, the surface of zeolite particles was modified by treating with 3-aminopropyltriethoxysilane. The surface morphology of the composite films investigated by scanning electron microscopy showed good compatibility between filler and polymer matrix. The films were flexible, tough, and exhibited high-thermal stability, having the initial decomposition temperature above 450?°C. Dynamic mechanical analysis and dielectric spectroscopy revealed sub-glass transitions, γ and β, and an α relaxation corresponding to the segmental motions above the glass transition temperature. The values of the dielectric constant at 10?kHz and 200?°C were in the range of 3.3–4.2.     

Acidity of modified Y zeolites: Effect of nonskeletal Al,formed by hydrothermal treatment,dealumination with SiCl4, and cationic exchange with Al

The acidity of modified Y zeolites was studied using adsorption and thermal desorption of pyridine (i.r.s. technique). It was found that at least some nonskeletal Al species always take part in the compensation of lattice charge, thus affecting the number of skeletal hydroxyls. Oxidic clusters prevailing on hydrothermally treated zeolites yield a much lower fraction of strong Al electron-accepting sites than of cationic species, which are typical for AIHY and are also formed in a considerable amount in zeolites dealuminated with SiCl₄. Both types of nonskeletal Al species decrease the Brönsted acid strength of the zeolite. The activity of modified zeolites in the oligomerization of ethylene is discussed taking into account the action of Al electron-accepting sites.     

Extruded Blends of Chitosan and Ethylene Copolymers for Antimicrobial Packaging

Chitosan was melt‐processed with an ethylene methyl acrylate copolymer ionomer and with an ethylene vinyl acetate copolymer to create antimicrobial extruded films. The key to obtaining a successful antimicrobial blend was the use of solid chitosonium acetate that remained after evaporation of water from the chitosan solution. When solid free‐flowing powders of chitosonium acetate were formed by spray drying chitosan solutions, blended in an extruder (at 2.5% and 4% chitosan) with Elvax® 3175 ethylene vinyl acetate copolymer, and extruded through a film die onto a chill roll to form films, the films exhibited antimicrobial activity against Escherichia coli 25922, Salmonella enterica serovar Enteritidis Nal^R, and Listeria monocytogenes Scott A. The log₁₀ reductions in CFU/ml after 24 h in a shake‐flask test were near 2 for films containing 4% chitosan. This melt‐blending/extrusion approach is expected to open applications for chitosan‐based antimicrobial packages and articles that were impossible or impractical with chitosan coatings. Copyright © 2011 John Wiley & Sons, Ltd.     

Multistep synthesis of metal sulfide clusters: A novel zeolite modification method

A general approach has been proposed for incorporating high concentrations of modifier metals into high-silica zeolites. MFI zeolites have been modified with mono- and polymetallic sulfide clusters of copper, manganese, zinc, cobalt, and nickel. The metal incorporation sequence and the nature of the anion have been shown to influence both the total content and the ratio of the modifiers in the zeolite. Using multistep syntheses, we have prepared zeolites containing superstoichiometric amounts of modifier metals. Using a variety of physicochemical characterization techniques, the zinc-containing sample has been shown to have a uniform modifier distribution. The Cu-MFI-50 and Mn-MFI-50 zeolites have been characterized by electron paramagnetic resonance and shown to contain isolated Cu²⁺ and Mn²⁺ ions stabilized on the aluminum lattice site.     

Redox modification of high-silica zeolites with chromium via multistep cluster synthesis

This paper examines the modification of zeolites with superstoichiometric amounts of metals using multistep cluster synthesis. Ion-exchange sites in zeolite MFI-50 (SiO₂/Al₂O₃ molar ratio of 50) have been modified with hydrazonium cations. Subsequent redox reaction with chromate anions has yielded a chromium-containing zeolite. The sample prepared by three ion-exchange/redox cycles contains 10 wt % chromium (Cr-MFI-50). EPR results show that most of the chromium in Cr-MFI-50 is in the form of fine Cr₂O₃ particles. In addition, the material contains isolated Cr⁵⁺ ions and, presumably, Cr³⁺ stabilized at aluminum vacancies.     

Efficacy of chitosan‐coated paper incorporated with vanillin and ethylene adsorbents on the control of anthracnose and the quality of Nam Dok Mai mango fruit

Mango fruit is perishable and susceptible to anthracnose. Active‐coated paper is proposed as potential packaging for commercial application in wrapping mango fruit to control anthracnose and delay the ripening process of fruit. The surface of white standard bleached paper was coated using a vanillin‐chitosan coating solution containing varying amounts of zeolite or activated carbon at 0% (vanillin paper), 0.1%, 0.2%, and 0.4%, w/v of ethylene absorbers. The first objective was to study the effect of absorber types and their amounts on ethylene removal. After that, the coating formulation that provided the highest ethylene removal was selected to wrap commercial Nam Dok Mai mango fruit to study the quality changes. The efficacy of active‐coated paper on the severity index of anthracnose disease, change in physicochemical properties, and sensory acceptability during storage (13°C, 90% relative humidity (RH) for 30 days) were investigated. It was found that vanillin‐chitosan coated paper containing 0.2% (w/v) of zeolite (zeolite paper) exhibited the highest capacity of ethylene adsorption. Zeolite paper could delay the disease incidence of wrapped mango fruit and provided the lowest severity index of anthracnose disease throughout storage. Moreover, changes in physicochemical qualities (weight loss, firmness, titratable acidity, total soluble solid, and color) of mango fruits wrapped in zeolite paper was quite low, compared with those wrapped with vanillin and uncoated papers. In addition, mango wrapped by zeolite paper had the highest sensory acceptance score. The results suggest that zeolite paper can efficiently be applied as wrapping to extend the postharvest life of mango fruit.     

Porous Ultrahigh Gas‐Permeable Polypropylene Film and Application in Controlling In‐pack Atmosphere for Asparagus

Porous polypropylene (PP) films with greater gas permeability and lower permeability ratios (β) than existing commercial films were developed for fresh produce packaging. PP containing high content of beta‐form crystal was biaxially stretched under controlled conditions. Resulting porous films with uniquely high oxygen transmission rate (OTR) of 2 659 000 cm³?m^?2?d^?1, water vapor transmission rate of 67 g?m^?2?d^?1, and β value of 0.76 was used as a “breathable window” attached to the less permeable commercial BOPP (biaxially oriented PP) lidding film. Various sizes/areas of the breathable windows were designed and tested on packaging asparagus of 400 g, at 5°C. Results demonstrated that in‐pack O₂ and CO₂ concentrations could be practically controlled and modified by changing areas of the breathable windows. Altered porous high OTR area directly affected total gas permeation of the package. Optimum gas composition of Ο₂ and CΟ₂ within the recommended controlled atmosphere for asparagus, stored at 5°C, was effectively created and maintained in the package containing 25 cm² breathable window (15% of total film lid's area). The shelf life of asparagus under optimum modified atmosphere was extended to 29 days, as compared with <3 days in the normal, low OTR tray sealed with BOPP lidding film. Clearly, these developed porous ultrahigh permeable PP films can be useful materials in designing high OTR package with desirable in‐pack O₂ and CO₂ concentrations. Copyright © 2013 John Wiley & Sons, Ltd.     

Bactericidal effects of different silver-containing materials

The evaluation of the bactericidal effect of different silver-containing materials where silver is available as Ag⁺ (silver nitrate and different silver-exchanged zeolites), as metallic Ag⁰ (commercial silver nanoparticles) or as oxide (silver (I) oxide) was carried out in order to elucidate the importance of the bioavailability of silver (i.e., as free ions, metallic particles, combination of them, clusters, complexes, partially soluble or insoluble salts, etc.) on its bactericidal action.For the different materials tested, their bactericidal effect is ordered in the following sequence: AgNO₃ > Ag-ZSM-5 > Ag₂O > commercial silver-exchanged zeolite (granular) > commercial silver-exchanged zeolite (pellets) > Ag nanoparticles. In general, as the content of bioavailable ionic silver increases, the biocidal effectiveness of the corresponding silver-releasing material increases too.     

PBAT/ZSM-5分子筛共混薄膜的制备与性能

目的 以聚己二酸-对苯二甲酸丁二酯(PBAT)为基材,制备PBAT/ZSM-5分子筛共混薄膜,研究分子筛含量对薄膜性能的影响.方法 通过共混熔融挤出流延法制得含不同质量分数ZSM-5分子筛(0％,1％,3％,5％,7％)的PBAT薄膜,测定分析不同分子筛质量分数对薄膜的颜色、透明性、结构、气体阻隔性、力学性能等性能的影响.结果 随着分子筛质量分数的增加,透明性和断裂伸长率显著降低,抗拉强度先增加后降低,质量分数为1％分子筛的薄膜抗拉强度相对较大,较纯PBAT薄膜增加了12.34％;薄膜氧气透过性能整体上呈上升趋势,二氧化碳透过性和CO2/O2透过比均逐渐增加,水蒸气透过性显著降低,与纯PBAT薄膜相比,质量分数为7％分子筛PBAT薄膜的氧气和二氧化碳透过系数分别增加了18.48％,33.51％,水蒸气透过系数下降了43.28％,CO2/O2透过比由原来的8.84增加到9.96;薄膜表面和横截断面均变得粗糙,局部区域有团聚现象,且随分子筛含量的增加而变得明显.结论 ZSM-5分子筛的少量加入,可以影响PBAT薄膜力学性能,降低其水蒸气透过性,调节薄膜的气体选择透过性,为其应用于生鲜果蔬包装提供基础.     

Coupling Mechanical and Electrical Properties in Spin Crossover Polymer Composites

Spin crossover particles of formula [Fe{(Htrz)₂(trz)}_0.9(NH₂‐trz)_0.3](BF₄)_1.1 and average size of 20 nm ± 8 nm are homogeneously dispersed in poly(vinylidene fluoride‐co‐trifluoro‐ethylene), P(VDF‐TrFE), and poly(vinylidene fluoride) (PVDF) matrices to form macroscopic (cm‐scale), freestanding, and flexible nanocomposite materials. The composites exhibit concomitant thermal expansion and discharge current peaks on cycling around the spin transition temperatures, i.e., new “product properties” resulting from the synergy between the particles and the matrix. Poling the P(VDF‐TrFE) (70–30 mol%) samples loaded with 25 wt% of particles in 18 MV m^?1 electric field results in a piezoelectric coefficient d₃₃ = ?3.3 pC N^?1. The poled samples display substantially amplified discharges and altered spin transition properties. Analysis of mechanical and dielectric properties reveals that both strain (1%) and permittivity (40%) changes in the composite accompany the spin transition in the particles, giving direct evidence for strong electromechanical couplings between the components. These results provide a novel route for the deployment of molecular spin crossover materials as actuators in artificial muscles and generators in thermal energy harvesting devices.     

A Review of Ethylene Permeability of Films

Ethylene plays a major role in regulating fruit ripening and fresh produce senescence during the postharvest period. Accumulated ethylene inside a fresh produce package has the potential to stimulate physiological activity and consequently accelerate deterioration, limiting storage life and leading to product losses. Current scientific effort focuses on the minimization of ethylene effects through ethylene removal or suppression of ethylene response. Other researchers are focussing on the development of sensors for measuring ethylene exposure within supply chain systems in order to be able to use this information to indicate produce quality and predict remaining shelf life. Full and optimal utilization of either ethylene removal or sensing technologies requires knowledge of the rates in which ethylene can flow to or from the package that the product is contained in. This study discusses the need for ethylene permeability data for polymer films and reviews the data available. Ethylene permeability of commercial films was found to range from 57 to 2.7 × 10^?16 mol.m/m².s.Pa at ambient temperatures, with activation energies being in the range of 37 000–48 000 J/mol. Amongst novel films, some containing zeolites could be 10 times more permeable, while permeability of wheat gluten films was highly influenced by relative humidity. However, generally, to date, it would seem that there is a scarcity of information on the transmission of ethylene through commonly used materials, especially at industrially relevant conditions of low temperature and high relative humidity, making prediction of ethylene conditions within a commercial package difficult. Collection of ethylene transmission data for the wide range of available films at industrially relevant conditions is required in order to maximize the utilization of newly developed ethylene removal or sensing technologies and subsequently contribute to the reduction in fresh produce losses within the supply chain. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydrothermal synthesis of zeolites

Recent developments have included the synthesis of new, large pore zeolite structures, zeotypes and metal substituted zeolites, along with the in situ investigation of zeolite synthesis and control of morphologies. In terms of new zeolite structures there is increasing realisation of the aim to specifically design templates to control zeolite structures, and the use of the fluoride ion as a mediating agent has been influential. In terms of zeotypes considerable effort has been directed at transition metal containing systems, particularly those of cobalt, with the potential to generate redox active catalytic centres. Growth of zeolite films on substrates has also been developed and progress is being made in studying directly, using diffraction and NMR techniques, the crystallisation of zeolites.     

Controlling the Pore Size of Mesoporous Carbon Thin Films through Thermal and Solvent Annealing

Herein an approach to controlling the pore size of mesoporous carbon thin films from metal‐free polyacrylonitrile‐containing block copolymers is described. A high‐molecular‐weight poly(acrylonitrile‐block‐methyl methacrylate) (PAN‐b‐PMMA) is synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. The authors systematically investigate the self‐assembly behavior of PAN‐b‐PMMA thin films during thermal and solvent annealing, as well as the pore size of mesoporous carbon thin films after pyrolysis. The as‐spin‐coated PAN‐b‐PMMA is microphase‐separated into uniformly spaced globular nanostructures, and these globular nanostructures evolve into various morphologies after thermal or solvent annealing. Surprisingly, through thermal annealing and subsequent pyrolysis of PAN‐b‐PMMA into mesoporous carbon thin films, the pore size and center‐to‐center spacing increase significantly with thermal annealing temperature, different from most block copolymers. In addition, the choice of solvent in solvent annealing strongly influences the block copolymer nanostructure and the pore size of mesoporous carbon thin films. The discoveries herein provide a simple strategy to control the pore size of mesoporous carbon thin films by tuning thermal or solvent annealing conditions, instead of synthesizing a series of block copolymers of various molecular weights and compositions.     

Effect of mechanical activation on the properties of natural zeolites

We have examined the effect of mechanical activation on the Sr²⁺ and Cu²⁺ ion exchange selectivity of Russian natural zeolites: clinoptilolite-containing tuffs and chabazite concentrates. We have studied their structural changes and thermal properties and determined the specific surface area and porosity of the mechanically activated zeolites. At specific milling energies below 0.5–0.7 kJ/g, the dominant process is disintegration of zeolite particles and changes in their bulk porosity. At higher milling energies, amorphization prevails. Our results demonstrate that, in the initial stage of activation, one can markedly raise the Sr²⁺ selectivity of some zeolites (e.g., by 16 times for Shivyrtuiskoe clinoptilolites and by 300 times for chabazite) and increase the Cu²⁺ selectivity (by 40 to 100 times), which will persist at high specific milling energies.     

Eccentric Loading of Fluorogen with Aggregation‐Induced Emission in PLGA Matrix Increases Nanoparticle Fluorescence Quantum Yield for Targeted Cellular Imaging

A simple strategy is developed to prepare eccentrically or homogeneously loaded nanoparticles (NPs) using poly (DL‐lactide‐co‐glycolide) (PLGA) as the encapsulation matrix in the presence of different amounts of polyvinyl alcohol (PVA) as the emulsifier. Using 2,3‐bis(4‐(phenyl(4‐(1,2,2‐triphenylvinyl)‐phenyl)amino)‐phenyl)‐fumaronitrile (TPETPAFN), a fluorogen with aggregation‐induced emission (AIE) characteristics, as an example, the eccentrically loaded PLGA NPs show increased fluorescence quantum yields (QYs) as compared to the homogeneously loaded ones. Field emission transmission electron microscopy and fluorescence lifetime measurements reveal that the higher QY of the eccentrically loaded NPs is due to the more compact aggregation of AIE fluorogens that restricts intramolecular rotations of phenyl rings, which is able to more effectively block the non‐radiative decay pathways. The eccentrically loaded NPs show far red/near infrared emission with a high fluorescence QY of 34% in aqueous media. In addition, by using poly([lactide‐co‐glycolide]‐b‐folate [ethylene glycol]) (PLGA‐PEG‐folate) as the co‐encapsulation matrix, the obtained NPs are born with surface folic acid groups, which are successfully applied for targeted cellular imaging with good photostability and low cytotoxicity. Moreover, the developed strategy is also demonstrated for inorganic‐component eccentrically or homogeneously loaded PLGA NPs, which facilitates the synthesis of polymer NPs with controlled internal architectures.     

Stimuli‐Responsive,Shape‐Transforming Nanostructured Particles

Development of particles that change shape in response to external stimuli has been a long‐thought goal for producing bioinspired, smart materials. Herein, the temperature‐driven transformation of the shape and morphology of polymer particles composed of polystyrene‐b‐poly(4‐vinylpyridine) (PS‐b‐P4VP) block copolymers (BCPs) and temperature‐responsive poly(N‐isopropylacrylamide) (PNIPAM) surfactants is reported. PNIPAM acts as a temperature‐responsive surfactant with two important roles. First, PNIPAM stabilizes oil‐in‐water droplets as a P4VP‐selective surfactant, creating a nearly neutral interface between the PS and P4VP domains together with cetyltrimethylammonium bromide, a PS‐selective surfactant, to form anisotropic PS‐b‐P4VP particles (i.e., convex lenses and ellipsoids). More importantly, the temperature‐directed positioning of PNIPAM depending on its solubility determines the overall particle shape. Ellipsoidal particles are produced above the critical temperature, whereas convex lens‐shaped particles are obtained below the critical temperature. Interestingly, given that the temperature at which particle shape change occurs depends solely on the lower critical solution temperature (LCST) of the polymer surfactants, facile tuning of the transition temperature is realized by employing other PNIPAM derivatives with different LCSTs. Furthermore, reversible transformations between different shapes of PS‐b‐P4VP particles are successfully demonstrated using a solvent‐adsorption annealing with chloroform, suggesting great promise of these particles for sensing, smart coating, and drug delivery applications.     

The influence of modified zeolites as nucleating agents on crystallization behavior and mechanical properties of polypropylene

Polypropylene (PP) composites with unmodified and modified zeolites were prepared by melt blending in single-screw extruder. The modified zeolites, diethoxy (distearoyl) silane (DDS)–zeolite 13X (DDS-13X) and diethoxy (distearoyl) silane–zeolite 5A (DDS-5A), were obtained by grafting diethoxy (distearoyl) silane onto zeolite 13X and 5A, respectively. The influence of the unmodified and modified zeolites as nucleating agents on properties of polypropylene was investigated with X-ray diffraction (XRD), differential scanning calorimetry (DSC), polarized light microscopy (PLM), Vicat softening temperature (VST) and mechanical properties test. The XRD results revealed that zeolite 13X and DDS-13X had a great influence on nucleation of PP compared to zeolite 5A and DDS-5A. The DSC results showed that the addition of small amount of modified zeolites lead to increase in crystallization temperature (T_c), initial crystallization temperature (T_onset) and crystallinity (X_c) of PP composites compared to unmodified zeolites, especially, DDS-13X was more effective than DDS-5A, and the highest crystallinity X_c (50.48%) was observed in PP/0.3 wt.% DDS-13X, which was responsible to the higher tensile strength and flexural strength of PP/DDS-13X. The PP/DDS-5A, however, exhibited evident increase in flexural strength and a little change in tensile strength compared to pure PP. Moreover, as the addition amount of DDS-5A or DDS-13X up to 1 wt.%, the impact strength of both PP/DDS-5A and PP/DDS-13X reached 43 kJ/m², which was about 2.8 times greater than that of the pure PP (11.3 kJ/m²). These results were in good agreement with the spherulite morphology observed from PLM micrographs.     

Micellar carrier based on methoxy poly(ethylene glycol)-block-poly(<Emphasis Type="Italic">ε</Emphasis>-caprolactone) block copolymers bearing ketone groups on the polyester block for doxorubicin delivery

Block copolymers of Methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) bearing ketone groups (MPEG-b-P(CL-co-OPD)) are synthesized and evaluated for its potential to form micelles containing doxorubicin (DOX), a representative anticancer drug, by using an in vitro method based on membrane dialysis to emulate drug release in vivo. The ¹H NMR spectra of the prepared block copolymers in D₂O solution exhibit peaks due to the P(OPD-co-CL) in decreased intensity, indicates that the polymers form micelle particles containing the hydrophilic segments in their external parts. The CMC of the copolymer decrease with an increase in the content of ketone groups in the hydrophobic chain. Drug-free and drug-loaded solutions of structurally related copolymers indicate the polymeric aggregation into micellar-type constructs. The size of the drug-loaded micelles is found to be larger than corresponding drug-free micelles. The release rate of MPEG-b-PCL micelles is faster than MPEG-b-P(OPD-co-CL) micelles in pH 7.4 buffered solution and they have a similar release rate in pH 5.0 buffered solution. This study, therefore, confirms the potential of a novel functional block copolymers, Methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) bearing ketone Groups, for the formation of polymeric micelles for drug delivery.     

Photoluminescence spectroscopy as a probe of silver doped zeolites as photocatalysts

Nanoclusters of silver ions, dicyanoaurate ions, and dicyanoargentate ions doped in zeolite hosts have been prepared. Luminescence, Raman, and FT-EXAFS spectroscopies along with extended Hückel calculations indicate the formation of silver and [M(CN)₂⁻]_m (M=Au and Ag) oligomers in the zeolite host. The silver and gold nanoclusters in zeolites enhance the photodecomposition rates of NO_x, malathion, and carbaryl when compared to the pollutant's behavior in the absence of silver doped zeolites with the observed rate increase attributed to excimer and exciplex formation.