Ethylene-vinyl Alcohol Copolymer Films Research Articles

Structure-Property Relationship of Cellulose Nanocrystal-Polyvinyl Alcohol Thin Films for High Barrier Coating Applications.

CO2 and O2 gas permeability are paramount concerns in food packaging. Here, the permeability of cellulose nanocrystals (CNCs) and polyvinyl alcohol (PVA) coatings was explored as it relates to varied CNC content. Specifically, this work focuses on the role of PVA in rheology and barrier performance of the CNC films. Results show that shear-casted CNC films are transparent and have a high-order parameter, which is attributed to the shear-thinning behavior of the CNCs. The barrier performance of the CNC films improved because of the synergistic effect of having both alignment of CNCs and a lower free volume. The CNC-PVA films exhibited excellent barrier performance as compared to traditional engineered polymers, even much higher than high barrier ethylene-vinyl alcohol copolymer films. Furthermore, the moisture sensitivity of the films was greatly diminished with the addition of PVA. Overall, the results show applicability of CNC-PVA coating formulations for high barrier packaging applications.

Machine learning approach for predicting Fusarium culmorum and F. proliferatum growth and mycotoxin production in treatments with ethylene-vinyl alcohol copolymer films containing pure components of essential oils

Fusarium culmorum and F. proliferatum can grow and produce, respectively, zearalenone (ZEA) and fumonisins (FUM) in different points of the food chain. Application of antifungal chemicals to control these fungi and mycotoxins increases the risk of toxic residues in foods and feeds, and induces fungal resistances. In this study, a new and multidisciplinary approach based on the use of bioactive ethylene-vinyl alcohol copolymer (EVOH) films containing pure components of essential oils (EOCs) and machine learning (ML) methods is evaluated. Bioactive EVOH-EOC films were made incorporating cinnamaldehyde (CINHO), citral (CIT), isoeugenol (IEG) or linalool (LIN). Several ML methods (neural networks, random forests and extreme gradient boosted trees) and multiple linear regression (MLR) were applied and compared for modeling fungal growth and toxin production under different water activity (aw) (0.96 and 0.99) and temperature (20 and 28 °C) regimes. The effective doses to reduce fungal growth rate (GR) by 50, 90 and 100% (ED50, ED90, and ED100) of EOCs in EVOH films were in the ranges 200 to >3330, 450 to >3330, and 660 to >3330 μg/fungal culture (25 g of partly milled maize kernels in Petri dish), respectively, depending on the EOC, aw and temperature. The type of EVOH-EOC film and EOC doses significantly affected GR in both species and ZEA and FUM production. Temperature also affected GR and aw only affected GR and FUM production of F. proliferatum. EVOH-CIT was the most effective film against both species and ZEA and FUM production. Usually, when the EOC levels increased, GR and mycotoxin levels in the medium decreased although some treatments in combination with certain aw and temperature values induced ZEA production. Random forest models predicted the GR of F. culmorum and F. proliferatum and ZEA and FUM production better than neural networks or extreme gradient boosted trees. The MLR mode provided the worst performance. This is the first approach on the ML potential in the study of the impact that bioactive EVOH films containing EOCs and environmental conditions have on F. culmorum and F. proliferatum growth and on ZEA and FUM production. The results suggest that these innovative packaging systems in combination with ML methods can be promising tools in the prediction and control of the risks associated with these toxigenic fungi and mycotoxins in food.

Comparative characteristics of TEMPO-oxidized cellulose nanofibers and resulting nanopapers from bamboo, softwood, and hardwood pulps

Bamboo, softwood, and hardwood pulp fibers were used as starting materials to prepare TEMPO-oxidized nanofibrillated cellulose (TO-NFC) dispersions. The resulting TO-NFC dispersions were then used to fabricate cellulose nanopapers and to coat poly(lactic acid) (PLA) films. The chemical and morphological characteristics of the dispersions together with the physical properties of the resultant nanopaper and PLA films were systematically compared. The maximum degree of oxidation was achieved for the bamboo pulp fiber. Transmission electron microscopy micrographs revealed that the oxidized pulp fibers were successfully disintegrated into cellulose nanofibrils with an average width of 5–6 nm. However, bamboo-derived TO-NFC was more densely entangled and crimped, with a heterogeneous distribution in width. It was further revealed that morphologies of the obtained TO-NFC may arise from the organizational structure of microfibrils in the cellulose fibers rather than the presence of hemicelluloses or the pulping process. The PLA films coated with a thin layer of TO-NFC from the bamboo pulp exhibited the highest oxygen-barrier property, which was even slightly higher than commercial ethylene–vinyl alcohol copolymer film, known for its high oxygen-barrier functionality.

Effects of Sorbic Acid-Chitosan Microcapsules as Antimicrobial Agent on the Properties of Ethylene Vinyl Alcohol Copolymer Film for Food Packaging.

This paper discusses the possibility of using sorbic acid-chitosan microcapsules (S-MPs) as an antibacterial component of active ethylene vinyl alcohol copolymer (EVOH) film. S-MPs with a diameter of approximately 1 to 4 μm showed a sorbic acid loading capacity of 46.5%. Addition of S-MPs (3%, w/w) increased the tensile strength, haze, oxygen, and water vapor barrier properties, as well as reduced the elongations at break and transmittance of S-MPs-EVOH (S-MP-EVOH) film. Antibacterial tests showed that the inhibitory capacity of S-MP-EVOH film against Salmonella Enteritidis and Escherichia coli was higher than that against Listeria monocytogenes. Moreover, the antibacterial effect of sorbic acid-EVOH (S-EVOH) film was stronger than that of S-MP-EVOH film. However, S-MP-EVOH film demonstrated a longer effective time than S-EVOH film. Using the total viable counts and total volatile base nitrogen as the judgment standard, S-MP-EVOH/polyethylene terephthalate (PET) composite film could extend the shelf life of fish fillets by 4 d at 4 °C, compared with EVOH/PET film. For this reason, S-MP could be a potential antibacterial component of active films.

Antioxidant and antimicrobial properties of ethylene vinyl alcohol copolymer films based on the release of oregano essential oil and green tea extract components

Polymer films with antioxidant and antimicrobial properties were manufactured for the active packaging of food products. Green tea extract (GTE) and oregano essential oil (OEO) were incorporated in an ethylene–vinyl alcohol copolymer (EVOH). Release studies of the main active components of the films into three food simulants, 3% acetic acid, 10% ethanol and 50% ethanol, were conducted at 4°C and 23°C. The total antioxidant activity at equilibrium was measured in the food simulants and the antimicrobial capacity of the films was tested in vitro against Listeria monocytogenes, Escherichia coli and Penicillium expansum. The results suggest that the release kinetics depend on the affinity between the active agents and the food simulants. In general, the fastest diffusion was obtained when films were exposed to 50% ethanol and that effect was concurrent with greater antioxidant efficiencies. The films also showed microbial growth inhibition in liquid media and in vapour phases, demonstrating that the developed films show strong potential for development as active food packaging films.

Reducing Oxidation of Foods Through Antioxidant Active Packaging Based on Ethyl Vinyl Alcohol and Natural Flavonoids

The development of antioxidant active packaging systems is attracting considerable attention as one of the preferred emerging technologies for reducing the incidence of lipid peroxidation. This work presents the use of ethylene vinyl alcohol copolymer films containing two natural flavonoids, catechin and quercetin, to reduce the oxidation of food. In a series of experiments, these materials showed their ability to reduce the presence of hydroxyl radicals in the package headspace. Packaging fried peanuts in bags manufactured with these active films resulted in a large reduction in the presence of hexanal, a compound produced during peroxidation of the unsaturated fat in peanuts. The results indicated that the materials actively reduced the presence of radical oxidative species although the antioxidants are not released into the food. On exposing sunflower oil to the films, the peroxide values obtained showed that the films actively protected the oil; because of the higher solubility of quercetin in this food product as well as the higher antioxidant capacity, the samples containing this flavonoid were more efficient.Industrial relevance: Active packaging is receiving considerable attention as an emerging technology that can be used to improve the quality and the stability of food, reducing the direct addition of chemicals and the need for changes in formulation. The results of this study show that it is possible to reduce food oxidation without adding antioxidants to the food. The films obtained can be used to protect any type of food, including dry or fatty products. Copyright © 2012 John Wiley & Sons, Ltd.

Preliminary in vivo study of apatite and laminin‐apatite composite layers on polymeric percutaneous implants

A polymeric material coated with a hydroxyapatite (HA) layer would be useful as a flexible percutaneous device with good biocompatibility and resistance to bacterial infection. We have recently developed a simple, safe, and mild coating process to form an HA layer on the surfaces of polymeric materials. In this study, our coating process was applied to an ethylene-vinyl alcohol copolymer film. The resulting HA-coated film was percutaneously implanted in the scalp of a rat to examine the stability and biocompatibility of the HA layer. From the results of histological analysis, the HA layer remained undissolved on the film surface under the skin tissue even 3 days after implantation. Owing to the good biocompatibility of HA, the HA-coated film suppressed a host's foreign-body response and integrated with the surrounding skin tissue for as long as 14 days, in a similar fashion to a conventional percutaneous device composed of ceramic HA. Immobilization of a cell adhesion protein, laminin, into the HA layer was found to improve the adhesion strength between the film and the surrounding skin tissue without compromising good biocompatibility of HA. Our coating process to form HA and laminin-HA composite layers would be useful in fabricating polymeric percutaneous devices with a reduced risk of bacterial infection, although further in vivo studies are required.

Oxygen permeability and free volume hole size in ethylene–vinyl alcohol copolymer film: temperature and humidity dependence

Relationship between oxygen permeability and free volume hole size evaluated from ortho-positronium lifetime in ethylene–vinyl alcohol copolymer (EVOH) was studied as functions of temperature and relative humidity. As the relative humidity rises at room temperature, the permeability first decreases and then increases. This behavior is attributed to the effects of pore filling and plasticization by water molecules. Linear correlations are obtained on the plots of logarithmic permeability versus reciprocal free volume hole size for EVOH at different temperatures and humidities as well as for different polymers including EVOH at room temperature, suggesting that the free volume hole size plays a crucial role in the oxygen permeation in EVOH and other polymers.

Sorption Behavior of Flavors with Water Sensitive Ethylene-Vinyl Alcohol Copolymer Film in Aqueous Solution.

Water sorption into ethylene-vinyl alcohol copolymer (EVOH) film largely affected the sorption behavior of flavors in aqueous solution. For EVOH-F (vinyl alcohol content; 68 mol%), the sorptions of flavors increased with temperature up to 20°C (10°C for EVOH-E; vinyl alcohol content; 56 mol%), and afterwards decreased. On the basis of the behavior of the water sorption and the corresponding glass transition temperature (Tg) changes in EVOH films, the signbell-type sorption behavior was considered to result from the flexibility change due to water sorption. Namely, the increase in sorption up to 20°C-storage for EVOH-F (10°C for EVOH-E) would be caused by the increasing free volume in EVOH films with decreasing Tg due to water sorption. On the other hand, at >20°C (EVOH-F)- and 10°C (EVOH-E)-storage, because the EVOH would behave as a rubbery polymer and have a roughly constant Tg, the sorption decreased with temperature.

Photografting of acrylamide on ethylene–vinyl alcohol copolymer film

AbstractPhotografting (λ > 300nm) of acrylamide on ethylene‐vinyl alcohol copolymer film (vinyl alcohol unit = 56 mol%, film thickness = 20μm) was investigated at 60°C in water medium, where photoinitiators were coated on the film earlier. The percent grafting decreased in the order of xanthone ≈ benzophenone > anthraquinone > benzoyl peroxide. The graft efficiencies in each sensitized system were less than 30%, showing a predominant formation of homopolymer. Grafting of acrylamide on the film was also initiated in systems with and without photoirradiation when ceric salt was used as an initiator. Based on electron probe microanalysis of the grafted films, the grafted chains of the sample prepared by photografting were distributed inside the film, while those of the sample prepared by ceric salt‐initiated grafting without photoirradiation were located mainly on the film surface. The grafted films prepared by the former system exhibited a higher moisture permeability than those prepared by the latter system.

Temperature‐responsive characteristics of N‐isopropylacrylamide‐grafted polymer films prepared by photografting

AbstractPhotografting of N‐isopropylacrylamide (NIPAAm) on ethylene–vinyl alcohol copolymer films (thickness = 15,20, and 25 μm) and low‐and high‐density polyethylene films (thickness = 30 μm) was carried out at 60°C in a water medium. Xanthone was used as a photoinitiator by coating it on the film samples. The resultant NIPAAm‐grafted films exhibited a temperature‐responsive character, which was evaluated by measuring a dimensional change of the grafted films. The grafted films swelled and shrank in water at temperatures lower and higher than around 30°C, respectively. The character was found to be reversible between 0 and 50°C. It was observed that the extent of the character is largely influenced by film thickness, location of NIPAAm‐grafted chains, and crystallinity of film substrate. © 1994 John Wiley & Sons, Inc.

Sorption of Volatile Compounds in Aqueous Solution by Ethylene‐Vinyl Alcohol Copolymer Films

ABSTRACTSorption of volatile compounds by ethylene‐vinyl alcohol copolymer (EVOH) films from an aqueous solution was investigated to evaluate the merit of their use for food packaging. With regard to EVOH, equilibrium swelling values gave rise to a bimodal solubility parameter distribution with maxima at δ values of 8.5 assigned to ethylene units and 14.5 to vinyl alcohol units. Comparing distribution ratios of EVOH with those of middle‐density polyethylene (MDPE), the ratios were 1:100 for terpene hydrocarbons, 1:10 for esters, 1:2 for alcohols, and almost 1:1 for aldehydes. By biaxial orientation of EVOH film, the sorption could be depressed below 60%. These results suggested EVOH films are more appropriate than MDPE for food container lining.

Textures and Barrier Properties of Ethylene-Vinylalcohol Copolymer Films

The effect of textures produced by various types of deformation processing on gas barrier property of copolymer film has been studied in the case of ethylene-vinylalcohol (EVOH) resin which is known as a semicrystalline polymer with low gas permeability.The heavily cold rolling and cold stretching give rise to highly oriented molecular structures and strong crystallographic textures, which reduce gas permeability of the film at high humidity. It was found, in particular, that the increased tri-axial orientation type texture and resulting molecular structure changes due to the plane strain compression type deformation, such as rolling, improved greatly the barrier property of the EVOH film.

Synthesis and Biomedical Properties of Poly-[(Ethylene-Vinylalcohol)-g-Acrylamide

Abstract This paper deals with the graft copolymerization of acrylamide (AM) onto ethylene-vinyl alcohol copolymer (EVAL) film initiated by cerium(IV) ion. It was found that both the chemical and diffusion factors had influences on the graft reaction. The reaction was initiated on the surface and then penetrated inward as the grafting percentage was increased. The permeability of urea through the grafted EVAL film was improved compared to that of the original film as was the blood compatibility.

Kinetics and equilibria associated with the absorption and desorption of water and lithium chloride in an ethylene—vinyl alcohol copolymer

Sorption and desorption equilibria and kinetics for LiCl and H 2O in an ethylene—vinyl alcohol copolymer film containing 70 mole percent vinyl alcohol were investigated at 25°C. The swelling behavior of water in the polymer was characterized by vapor and liquid sorption experiments over a range of water activities. p]The effects of LiCl content on the water sorption kinetics and equilibria in the films are presented and discussed. The kinetics and mechanism of LiCl sorption have also been studied. The amount of salt sorbed into the polymeric films increases linearly with the salt concentration in the external aqueous solutions. Both the rate and the amount of sorbed water increase significantly as the LiCl content increases. p]The desorption of LiCl, previously sorbed into the polymer, was characterized for different salt loadings. The rate of fractional salt release is independent of LiCl concentration in the film. Initially, the salt release is controlled by the nearly constant-rate absorption of water. The salt release, at long times, lags behind the swelling-controlled water uptake, indicating that the salt release is not completely controlled by the water sorption and that diffusion in the swollen polymer matrix contributes significantly to the long term elution of LiCl. Independent thermal analysis experiments suggest the formation of a metal salt—poly(ethylene—vinyl alcohol) complex.