Oxygen permeation resistance of polyethylene,polyethylene/ethylene vinyl alcohol copolymer,polyethylene/modified ethylene vinyl alcohol copolymer,and polyethylene/modified polyamide–ethylene vinyl alcohol copolymer bottles

The oxygen permeation resistance of polyethylene (PE), polyethylene/ethylene vinyl alcohol copolymer (PE/EVOH), polyethylene/modified ethylene vinyl alcohol copolymer (PE/MEVOH), and polyethylene/modified polyamide–ethylene vinyl alcohol copolymer (PE/MPAEVOH) bottles was investigated. The oxygen permeation resistance improved significantly after the blending of ethylene vinyl alcohol copolymer (EVOH) barrier resins in PE matrices during blow molding; less demarcated EVOH laminas were found on the fracture surfaces of the PE/EVOH bottles. Surprisingly, the oxygen permeation resistance of the PE/MEVOH bottles decreased significantly, although more clearly defined modified ethylene vinyl alcohol copolymer (MEVOH) laminas were found for the PE/MEVOH bottles as the compatibilizer precursor contents present in the MEVOH resins increased. In contrast, after the blending of modified polyamide (MPA) in EVOH resins, more demarcated modified polyamide–ethylene vinyl alcohol copolymer (MPAEVOH) laminar structures were observed in the PE/MPAEVOH bottles as the MPA contents present in the MPAEVOH resins increased. In fact, with proper MPAEVOH compositions, the oxygen permeation resistance of the PE/MPAEVOH bottles was even better than that of the PE/EVOH bottles. These interesting oxygen barrier and morphological properties of the PE, PE/EVOH, PE/MEVOH, and PE/MPAEVOH bottles were investigated in terms of the free volumes, barrier properties, and molecular interactions in the amorphous‐phase structures of the barrier resins present in their corresponding bottles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2528–2537, 2004     

High performance structured polymer barrier films obtained from compatibilized polypropylene/ethylene vinyl alcohol blends

The effects of different functionalized polypropylene (PP) and diethyl maleate (DEM) combined with styrene–ethylene–butene–styrene copolymer (SEBS) on various properties of extruded-stretched films of polypropylene/ethylene vinyl alcohol (PP/EVOH) blends were studied. The stretched films of the original PP/EVOH blends and those of the polymer-g-DEM modified blends showed lamellar-type morphology, whereas their maleic anhydride (MAH) functionalized counterparts showed fibrillar morphology. Such peculiar morphology resulted in a dramatic decrease of oxygen permeability as compared with the unmodified or MAH modified PP/EVOH blends. These spectacular improvements in barrier properties were obtained without much altering thermal and mechanical properties of the blend. POLYM. ENG. SCI., 47:1114–1121, 2007. © 2007 Society of Plastics Engineers     

Monitoring of the discoloration on γ‐irradiated PE and EVA films to evaluate antioxidant stability

γ‐Irradiated films could provoke unexpected interaction with proteins for instance just after irradiation and not necessarily after 12 months indicating there is no more reactive species. The optical properties of two multilayer films [polyethylene (PE)/ethylene vinyl alcohol (EVOH)/PE and ethylene vinyl acetate (EVA)/EVOH/EVA] after different γ‐irradiation doses is then studied in this work. The investigation on these films, either non‐irradiated or γ‐irradiated (up to 270 kGy), is performed by colorimetry measurement over time (up to 12 months) to assess the generation of new species inside the materials. The color change is directly correlated with absorbed γ‐doses. Over time, the color decreases and goes back to its initial time level. This discoloration evolution could be therefore used as an indication of the completion of the generated species reactions induced by γ‐irradiation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46114.     

Effects of ionizing radiation in ethylene-vinyl alcohol copolymers and in composites containing microfibrillated cellulose

This study reports on the effect of gamma radiation on morphological, thermal, and water barrier properties of pure ethylene vinyl alcohol copolymers (EVOH29 and EVOH44) and its biocomposites with the nanofiller microfibrillated cellulose (2 wt %). Added microfibrillated cellulose (MFC) preserved the transparency of EVOH films but led to a decrease in water barrier properties. Gamma irradiation at low (30 kGy) and high doses (60 kGy) caused some irreversible changes in the phase morphology of EVOH29 and EVOH44 copolymers that could be associated to crosslinking and other chemical alterations. Additionally, the EVOH copolymers and the EVOH composites reduced the number of hygroscopic hydroxyl functionalities during the irradiation processing and novel carbonyl based chemistry was, in turn, detected. As a result of the above alterations, the water barrier properties of both neat materials and composites irradiated at low doses were notably enhanced, counteracting the detrimental effect on water barrier of adding MFC to the EVOH matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Estimation of phase diagrams for copolymer‐diluent systems in thermally induced phase separation

The binary interaction model was introduced to estimate phase diagrams of copolymer‐diluent systems in thermally induced phase separation. The crystallization curves and cloud points of poly(ethylene‐co‐vinyl alcohol) (EVOH) with 1,4‐butanediol, EVOH/1,3‐propanediol, and EVOH/glycerol were calculated and compared with experimental value or literature data. Fair agreement was obtained. To confirm the importance of incorporating intramolecular interactions, calculations with and without the consideration of intramolecular interactions were performed and compared. It was found that better results can be obtained if intramolecular interaction was introduced. The reason for the small differences between the calculated value and the experimental data of the liquid–liquid phase separation is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

High oxygen barrier multilayer EVOH/LDPE film/foam

High oxygen barrier film/foam system had been developed using multilayer coextrusion technology. The film/foams contained alternating ethylene–vinyl alcohol (EVOH) copolymer film layers and low‐density polyethylene (LDPE) foam layers. To ensure good adhesion and layer integrity, the LDPE was preblended with LDPE grafted maleic anhydride. The layered structure of film/foam was characterized by scanning electron microscopy. The film/foams showed adjustable density, oxygen permeability, and mechanical properties by changing the film and foam composition. Film/foam with 10% EVOH film layer was successfully thermoformed at room temperature. The cells in the foam layer were observed to deform during the mechanical forming process. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46425.     

ESR and FTIR studies on electron beam‐irradiated low‐density polyethylene blends

Low‐density polyethylene (LDPE) composites modified with a resin based on ethylene/methacrylic acid copolymer (surlyn) and/or citric acid were electron beam‐irradiated and investigated by electron spin resonance (ESR) at room temperature. ESR studies were carried out directly after irradiation and after various time intervals up to 72 h postirradiation. The irradiated samples showed the ESR spectrum of seven lines that was assigned to the formation of allyl radical. The nature and yield of the allyl radical of the different LDPE samples were analyzed as a function of time after irradiation. Also, the radical concentration, decay, decay rate, and kinetics of radical decay were evaluated. Fourier transform infrared (FTIR) analysis at a series of different temperatures upon cooling from room temperature to ?175°C and the reverse heating to +125°C was also carried out. The structural changes while cooling and heating of LDPE samples were investigated using FTIR spectrometry. The results showed that cooling of unirradiated LDPE samples to ?175°C results in a decrease of the intensities of IR bands. However, heating the samples from ?175°C up to +125°C led to a consequence increase in the intensities of the IR bands. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3461–3469, 2007     

Improvement of the photostability of isotactic polypropylene by the incorporation of ethylene

The effect of the incorporation of ethylene on the photostability of isotactic poly(propylene) (iPP) was studied with the aim of improving the photostability. iPP was prepared with a random ethylene sequence (ethylene–propylene random copolymer, rPP), and the photooxidative degradation behavior was compared with that of homogeneous iPP. Both samples were thermally post‐treated under vacuum to ensure the same crystallinity. The degradation behavior was studied by infrared spectroscopy (IR), gel permeation chromatography (GPC), and temperature rising elution fractionation (TREF) measurements. The rates of hydroperoxide and carbonyl formation in the irradiated iPP increased with irradiation time for > 192 h, whereas those in the irradiated rPP are almost constant after 96 h. The change in molecular weight with the irradiation time showed similar behavior, suggesting that the degradation reaction in the irradiated rPP was suppressed after 96 h. The degradation behavior of rPP was thought to be due to the dissociation of the methyl group, which leads to the termination of degradation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1863–1867, 2002     

Effect of trimethylolpropane triacrylate (TMPTA) on the properties of irradiated epoxidized natural rubber (ENR‐50), ethylene‐(vinyl acetate) copolymer (EVA), and an ENR‐50/EVA blend

The effect of trimethylolpropane triacrylate (TMPTA) monomer on the tensile properties, dynamic mechanical properties, and morphology of irradiated epoxidized natural rubber (ENR‐50), ethylene‐(vinyl acetate) copolymer (EVA), and an ENR‐50/EVA blend was investigated. The ENR‐50, EVA, and ENR‐50/EVA blend were irradiated by using a 3.0‐MeV electron‐beam apparatus at doses ranging from 20 to 100 kGy. The improvement of tensile properties and morphology with irradiation indicated the advantage of having irradiation‐induced crosslinks in these materials. Observation of the properties studied confirmed that TMPTA was efficient in enhancing the irradiation‐induced crosslinking of ENR‐50, EVA, and the ENR‐50/EVA blend. Addition of TMPTA improved the adhesion between the ENR‐50/EVA blend phases by forcing grafting and crosslinking at a higher irradiation dose (100 kGy). J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers.     

Infrared Spectroscopic Investigation of Hydrogen Bonding in EVOH Containing PVA Fibers

Fibers of poly(vinyl alcohol) (PVA) containing ethylene‐vinyl alcohol copolymer (EVOH) are made by gel spinning. By using IR spectroscopy, the hydrogen bonds of the PVA/EVOH fibers with different EVOH content and different draw ratio are discussed. The peaks in the neighborhood of 3 400 cm^–1 and the peaks near 3 600 cm^–1 are used to analyze the hydroxyl absorption engaged in hydrogen bonds and the free hydroxyl absorption, respectively. As for PVA/EVOH films, with increasing EVOH content the H‐bond is gradually weakened. As for fibers, however, with increasing EVOH content the strength of the H‐bond increases, while the number of H‐bonds is decreased. Similarly, with increasing draw ratio of the PVA/EVOH fibers, the strength of H‐bond increases, while the number of H‐bonds seems decreased. Higher EVOH content in the PVA/EVOH fibers causes a higher maximum draw ratio because of weakening of the H‐bond. However, higher draw ratio does not always cause better mechanical properties of PVA/EVOH fibers.     

Blends of poly(propylene) and polyacetal compatibilized by ethylene vinyl alcohol copolymers

Polymer blends of poly(propylene) (PP) and polyacetal (polyoxymethylene, POM) with ethylene vinyl alcohol (EVOH) copolymers were investigated by differential scanning calorimetry (DSC), rheological, tensile, and impact measurements, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The PP–POM–EVOH blends were extruded with a co‐rotating twin‐screw extruder. The ethylene group in the EVOH is partially miscible with PP, whereas the hydroxyl group in the EVOH can form hydrogen bonding with POM. The EVOH tends to reside along the interface, acting as a surfactant to reduce the interfacial tension and to increase the interfacial adhesion between the blends. Results from SEM and mechanical tests indicate that a small quantity of the EVOH copolymer or a smaller vinyl alcohol content in the EVOH copolymer results in a better compatibilized blend in terms of finer phase domains and better mechanical properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1471–1477, 2003     

Interface modification and characterization in three‐component polymer blends

The effect of interface characteristics on the properties of three‐component polymer blends comprising PP/EVOH/mica and PP/EVOH/glass beads (GB) was investigated (polypropylene‐PP, ethylene‐vinylalcohol‐EVOH). The systems selected are based on the binary PP/EVOH immiscible blend representing a semi‐crystalline apolar polymer (PP) and a semi‐crystalline highly polar copolymer (EVOH), where PP serves as the matrix. A series of the binary and three‐component blends with varying compositions was chosen to study the effect of the molding procedure, i.e. compression versus injection molding. The structures observed by SEM analysis consisted of the filler particles engulfed by the EVOH phase, with some of the minor EVOH component dispersed within the PP matrix. The effects of silane treatment (GB/EVOH interface) and compatibilization, using a maleated‐PP compatibilizer (PP/EVOH interface), were studied in relation to the generated structured and properties. The compatibilizer was added in a unique procedure by which the encapsulated GB/EVOH structures were preserved. The characterization methods used included morphology by Scanning Electron Microscopy, thermal properties and crystallization behavior by Differential Scanning Calorimetry, mechanical properties by tensile testing, and dynamic characteristics by Dynamic Mechanical Thermal Analysis. The work has shown that structure‐performance relationships in the three‐component blends can be varied and controlled.     

Reactive blending of poly(L‐lactic acid) with poly(ethylene‐co‐vinyl alcohol)

Poly(L ‐lactic acid) (PLLA) was blended with poly(ethylene‐co‐vinyl alcohol) (EVOH) in the presence of an esterification catalyst to induce reaction between the hydroxyl groups of EVOH and the terminal carboxylic group of PLLA. Nascent low‐molecular‐weight PLLA, obtained from a direct condensation polymerization of L ‐lactic acid in bulk state, was used for the blending. Domain size of the PLLA phase in the graft copolymer was much smaller than that corresponding to a PLLA/EVOH simple blend. The mechanical properties of the graft copolymer were far superior to those of the simple blend, and the graft copolymer exhibited excellent mechanical properties even though the biodegradable fraction substantially exceeded the percolation level. The grafted PLLA reduced the crystallization rate of the EVOH moiety. Melting peak temperature (T_m) of the PLLA phase was not observed until the content of PLLA in the graft reaction medium went over 60 wt %. The modified Sturm test results demonstrated that biodegradation of EVOH‐g‐PLLA took place more slowly than that of an EVOH/PLLA simple blend, indicating that the chemically bound PLLA moiety was less susceptible to microbial attack than PLLA in the simple blend. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 886–890, 2005     

Thermal and barrier properties of EVOH/EFG nanocomposite films for packaging applications: Effect of the mixing method

Ethylene‐vinyl alcohol copolymer (EVOH)/exfoliated graphite (EFG) nanocomposite films were prepared by precoating EFG on the EVOH surface and conducting a successive melt‐extrusion process. Their physical properties were strongly dependent on the EFG content and the mixing method, which strongly affected the morphology and surface properties of the nanocomposite films. The hydrophobicity and water resistance property of EVOH increased by incorporating hydrophobic EFG and their effects were more pronounced in the precoating method, which is related to good dispersion of EFG in EVOH and an enhanced crystalline structure. The incorporation of EFG into EVOH by the precoating method more effectively diminished the dependence of the relative humidity on the oxygen transmission rate of pure EVOH and increased the oxygen barrier properties of EVOH at a high relative humidity. The incorporation of EFG into EVOH by the precoating method also induced relatively more enhanced thermal stability. These results suggest the feasibility of the application of moisture‐sensitive EVOH resin for food packaging films. POLYM. COMPOS., 37:1744–1753, 2016. © 2014 Society of Plastics Engineers     

Oxygen barrier properties of polyketone/EVOH blend films and their resistance to moisture

Polyketone (PK) has excellent chemical and mechanical properties, but its use in food packaging is limited due to its oxygen barrier properties being insufficient for high-barrier film applications. To improve its oxygen barrier properties, PK has been blended with ethylene vinyl alcohol copolymer (EVOH), which is one of the highest oxygen barrier polymers in use today. The oxygen barrier properties under both dry and humid conditions, as well as the mechanical properties of PK/EVOH blend films were investigated in this study. These novel PK/EVOH blend films exhibited unusually low oxygen permeability values from 0.3 to 0.16 cc 20 μm m⁻² day⁻¹ atm⁻¹ with increasing EVOH content from 30 to 70 wt%, which are even lower than those of the ideal laminar model that expresses the theoretical minimum permeability values attainable for blended barrier films. These high oxygen barrier properties of PK/EVOH blend films can conceivably be attributed to the combination of two dominant effects: a tortuous diffusion path through the EVOH domains in the PK matrix and hydrogen bonding interactions between PK and EVOH. Furthermore, in high-humidity environments with retorting, the PK/EVOH blend films exhibited superior resistance to moisture over EVOH. Immediately after the retorting test, the oxygen permeability of the high-barrier PK/EVOH blend films with an EVOH content of 30–40 wt% increased by less than 3× the pre-retorting value, as opposed to 74× for EVOH. In addition, PK/EVOH blend films displayed superior stretching characteristics, with a breaking strain of over 300%, which are valuable for flexible packaging applications.     

Influence of the ethylene–(methacrylic acid)–Zn2+ ionomer on the thermal and mechanical properties of blends of poly(propylene) (PP)/ethylene–(vinyl alcohol) copolymer (EVOH)

The thermal and mechanical properties and the morphologies of blends of poly(propylene) (PP) and an ethylene–(vinyl alcohol) copolymer (EVOH) and of blends of PP/EVOH/ethylene–(methacrylic acid)–Zn²⁺ ionomer were studied to establish the influence of the ionomer addition on the compatibilization of PP/EVOH blends and on their properties. The oxygen transmission rate (O₂TR) values of the blends were measured as well. PP and EVOH are initially incompatible as was determined by tensile tests and scanning electronic microscopy. Addition of the ionomer Zn²⁺ led to good compatibility and mechanical behaviour was improved in all blends. The mechanical properties on extruded films were studied for 90/10 and 80/20 w/w PP/EVOH blends compatibilized with 10 % of ionomer Zn²⁺. These experiments have shown that the tensile properties are better than in the injection‐moulded samples. The stretching during the extrusion improved the compatibility of the blends, diminishing the size of EVOH domains and enhancing their distribution in the PP matrix. As was to be expected, the EVOH improved the oxygen permeation of the films, even in compatibilized blends. Copyright © 2004 Society of Chemical Industry     

Polyester/lignosulfonate blends, 2. Accelerated aging behavior

The behavior of the poly[(ethylene terephthalate)‐co‐(ethylene isophthalate)] copolymer/epoxy‐modified lignosulfonate (LER) blends has been studied during aging, in the conditions of sewage sludge test. The bulk and surface properties of the aged blends have been followed by electron microscopy, DSC, TG/DTG, IR spectroscopy and contact angle measurements, and compared with undegraded samples. It has been established that the UV‐irradiated blends undergo more important changes in their properties after aging than the unirradiated samples. The physical treatment and increase of LER content in the blend could be a way to obtain materials with a good balance of properties and environmental degradation.     

Structure and properties of isotactic polypropylene functionalized by ultraviolet irradiation

The structural, crystalline, thermal, morphological, and mechanical properties of isotactic polypropylene (iPP) functionalized by lower energy ultraviolet (UV) irradiation are studied by means of infrared spectroscopy (IR), differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), thermogravimetry (TG), thermomechanical analysis (TMA), polariscope, and mechanical measurements. After the UV irradiation in less than a few hours, the oxygen containing polar groups have been introduced onto iPP chains. DSC analysis shows that a new melting peak is observed around 150°C for the UV irradiated iPP, indicating that there is a α‐phase to β‐phase transition during UV irradiation process. Under polariscope, the morphology of the UV irradiated iPP is changed, and the deformed α‐phase morphology can be observed. DSC and WAXD analysis reveal for the crystallinity of the UV‐irradiated iPP increase with UV time, but the relative level and the order of β‐phase increase and then decrease with increasing UV time. Under the controlled UV time, the thermomechanical deformation of iPP decrease, and the initial and final thermal degradation temperature of iPP rises up by 70 to 125°C higher, respectively, indicating that the UV‐irradiated iPP has higher thermal stability than the non‐UV irradiated iPP. The tensile and impact strength, the elongation at break, and the Young's modulus of the UV‐irradiated iPP are enhanced, exhibiting the toughened and strengthened effects. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1456–1466, 2001     

Degradation of poly(D,L‐lactic acid)‐b‐poly(ethylene glycol) copolymer and poly(L‐lactic acid) by electron beam irradiation

This article investigated the effects of electron beam (EB) irradiation on poly(D ,L ‐lactic acid)‐b‐poly(ethylene glycol) copolymer (PLEG) and poly(L ‐lactic acid) (PLLA). The dominant effect of EB irradiation on both PLEG and PLLA was chain scission. With increasing dose, recombination reactions or partial crosslinking of PLEG can occur in addition to chain scission, but there was no obvious crosslinking for PLLA at doses below 200 kGy. The chain scission degree of irradiated PLEG and PLLA was calculated to be 0.213 and 0.403, respectively. The linear relationships were also established between the decrease in molecular weight with increasing dose. Elongation at break of the irradiated PLEG and PLLA decreased significantly, whereas the tensile strength and glass transition temperature of PLLA decreased much more significantly compared with PLEG. The presence of poly(ethylene glycol) (PEG) chain segment in PLEG was the key factor in its greater stability to EB irradiation compared with PLLA. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Viscoelastic response of multilayer polymeric films of linear low‐density polyethylene and ethylene vinyl alcohol copolymer

The viscoelastic response of multilayer polymeric films (sandwiches) of linear low‐density polyethylene (LLDPE) and ethylene vinyl alcohol (EVOH) copolymer has been experimentally analyzed. We propose an equation to predict the mechanical response of the sandwich films from the data experimentally obtained for the monomaterial films. The equation is based on the hypothesis that the layers independently contribute to the final response and that there are no interfacial effects. The predictive character of the equation permits us to conclude that the response of the sandwich does not significantly depend on the individual layer thickness but only on the volume fraction of the EVOH in the system. More important, we find a strong sensitivity of the response to the processing conditions, which we quantitatively describe. POLYM. ENG. SCI., 55:1960–1968, 2015. © 2014 Society of Plastics Engineers